,,american ,,science                    
,,series--,,advanced ,,course           
,,geology                               
,,by                ,,thomas ,c4        
,,chamberlin ,,and ,,rollin ,d4         
,,salisbury    ,heads of the            
,departments of ,geology and ,geography1
 ,university of ,chicago                
,members of the ,united ,states         
,geological ,survey                     
,editors of the ,journal of ,geology    
,,in ,,three ,,volumes                  
,,vol4 ,i4--,,geologic ,,processes ,,and
 ,,their ,,results                      
,,second ,,edition1 ,,revised           
,illustration                           
,,new ,,york                            
,,henry ,,holt ,,and ,,company          
#aiji                                   
,copyright1 #aijd1                      
,,by                           ,,henry  
,,holt ,,and ,,company                  
,,printed ,,in ,,the ,u4 ,s4 ,a4        
,,preface4      ,in the preparation of  
this work it has been the purpose of the

 authors  to present an outline of the  
salient features of geology1 as now     
developed1 encumbered as little as      
possible by technicalities and  details 
whose bearings on the general theme are 
unimportant4 ,in common  with most      
writers of text-books on geology1 the   
authors believe that  the subject is    
best approached by a study of the forces
 and processes  now in operation1 and of
 the results which these forces and     
processes  are now bringing about4 ,such
 study necessarily involves a           
consideration  of the principles which  
govern the activities of geologic       
agencies4  ,these topics are presented  
in ,volume ,i1 and prepare the way for  
the  study of the history of past ages1 
which is outlined in ,volume ,,ii4      
,the general plan of the work has been  
determined by the experience of  the    
authors as instructors4 ,little emphasis
 is laid on the commonly  recognized    
subdivisions of the science1 such as    
dynamic geology1  stratigraphic geology1

 physiographic geology1 etc4 ,the       
treatment  proceeds rather from the     
point of view that the science is a     
unit1 that  its one theme is the history
 of the earth1 and that the discussions 
of dynamic geology1 physiographic       
geology1 etc41 apart from their         
historical bearing1 lose much of their  
significance and interest4  ,the effort 
has1 therefore1 been to emphasize the   
historical element1  even in the        
discussion of special themes1 such as   
the work of rivers1  the work of snow   
and ice1 and the origin and descent of  
rocks4 ,this  does not mean that phases 
of geology other than historical have   
been neglected1 but it means that an    
effort has been made to give a          
historical cast to all phases of the    
subject1 so far as the topics  permit4  
,throughout the work the central purpose
 has been not merely to set  forth the  
present status of knowledge1 but to     
present it in such a way  that the      
student will be introduced to the       

methods and spirit of the  science1 led 
to a sympathetic interest in its        
progress1 and prepared to  receive      
intelligently1 and to welcome cordially1
 its future advances4  ,where           
practicable1 the text has been so shaped
 that the student may  follow the steps 
which have led to present conclusions4  
,to this end  the working methods of the
 practical geologist have been implied  
as  frequently as practicable4 ,to this 
end also there has been frankness of    
statement relative to the limitations of
 knowledge and the uncertainty  of many 
tentative conclusions4 ,in these and in 
other respects1 the  purpose has been to
 take the student into the fraternity of
 geologists1  and to reveal to him the  
true state of the development of the    
science1  giving an accurate and        
proportionate view of the positive      
knowledge  attained1 of the problems yet
 unsolved1 or but partially solved1 and 
of  solutions still to be attained4     
,the theoretical and interpretative     

elements which enter into the  general  
conceptions of geology have been freely 
used1 because they  are regarded as an  
essential part of the evolution of the  
science1  because they often help to    
clear and complete conceptions1 and     
because they stimulate thought4 ,the aim
 has been1 however1 to  characterize    
hypothetical elements as such1 and to   
avoid confusing the  interpretations    
based on hypothesis1 with the statements
 of fact and  established doctrines4    
,especial care has been taken to        
recognize the  uncertain nature of      
prevalent interpretations when they are 
dependent  on unverified hypotheses1    
especially if this dependence is likely 
to be  overlooked4 ,if this shall seem  
to give prominence to the hypothetical  
element1 it should also be regarded as  
giving so much the more emphasis  to    
that which is really trustworthy1 in    
that it sets forth more frankly  that   
which is doubtful4 ,hypothetical and    
unsolved problems have been  treated1 so

 far as practicable1 on the multiple    
basis2 that is1  alternative hypotheses 
and alternative interpretations are     
frequently  presented where knowledge   
does not warrant positive conclusions4  
,in many cases the topics discussed will
 be found to be presented in  ways      
differing widely from those which have  
become familiar4 ,in some  cases1       
fundamentally new conceptions of        
familiar subjects are involved2  in     
others1 topics not usually discussed in 
text-books are stated with  some        
fullness2 and in still others1 the      
emphasis is laid on points  which have  
not commonly been brought into          
prominence4 ,whether the  authors have  
been wise in departing to this extent   
from beaten paths1  the users of the    
volumes must decide4    ,the work is    
intended primarily for mature students1 
and is designed to  furnish the basis   
for a year's work in the later part of  
the college  course4 ,by judicious      
selection of material to be presented   

and omitted1  the volumes will be found 
useful for briefer courses1 and by the  
use of  the numerous references to the  
fuller discussions of special treatises1
  they may be made the basis for more   
extended courses than are commonly      
given in undergraduate work4 ,the       
attempt has also been made to make the  
volumes readable1 in the belief that    
many persons not in colleges or         
universities will be interested in      
following a connected account of the    
earth's history1 and of the means by    
which that history is recorded and      
read4 ,antecedent elementary courses in 
geology will not be necessary to  the   
use of these volumes1 though such       
courses may be helpful4    ,the         
arrangement of themes adopted is such as
 to bring to the fore  processes with   
which all students are immediately in   
contact1 and  which are available for   
study at all seats of learning4 ,the    
commoner  geologic agents1 such as the  
atmosphere and running water1 have been 

elaborated somewhat more fully than is  
customary1 and the common  rather than  
the exceptional phases of the work of   
these agents have  been emphasized1 both
 because of their greater importance and
 their  universal availability4 ,the    
text has been so shaped as to suggest   
field  work in connection with these    
topics especially1 since work of this   
sort is everywhere possible4    ,after  
the preliminary outline1 which is       
intended to give some idea of  the scope
 of the science1 and of its salient     
features1 and to show the  relations of 
the special subjects which follow1 the  
order of treatment  is such as to pass  
from the commoner and more readily      
apprehended  portions of the subject to 
those which are less readily accessible 
and  more obscure4 ,following the same  
general conception1 the treatment of    
the topics is somewhat graded1 the      
earlier chapters being developed  with  
greater simplicity and fullness1 while  
the later are somewhat more  condensed4 

,many acknowledgments are made in the   
text and foot-notes1 but it  is         
impossible to adequately acknowledge all
 the sources which have  been drawn     
upon1 since the whole body of literature
 has been laid  under contribution4 ,the
 authors especially acknowledge the     
generous  assistance of ,professor ,j4  
,p4 ,iddings in connection with the     
chapter on  ,the ,origin and ,descent of
 ,rocks2 of ,dr4 ,f4 ,r4 ,moulton1      
,professor ,c4 ,s4  ,slichter1          
,professor ,l4 ,m4 ,hoskins1 ,mr4 ,a4   
,c4 ,lunn1 and ,mr4 ,w4 ,h4 ,emmons  in 
connection with mathematical problems2  
of ,professor ,c4 ,r4 ,barnes in        
connection with the geologic functions  
of life2 and of ,professor ,julius      
,stieglitz in connection with chemical  
subjects4    ,the illustrations have    
been selected from numerous sources1    
which are  usually acknowledged in the  
text4 ,especial acknowledgment is due to
 the  ,u4 ,s4 ,geological ,survey for   
the use of numerous photographs and     

maps1  and to ,mr4 ,g4 ,a4 ,johnson1 who
 has made many of the drawings          
reproduced  in ,volume ,i4 ,the authors 
are under even larger obligations for   
assistance in the preparation of ,volume
 ,,ii1 for which acknowledgment  will be
 made in the proper place4              
,university of ,chicago1 ,january1      
#aijd4                                  
,,contents4                             
,,volume ,i4                            
,,chapter ,i4                           
,,preliminary ,,outline4                
,subdivisions1 #a4 ,dominant processes1 
#b4                                     
,,page    ,astronomic ,geology          
#b    ,the earth as a planet1 #b4 ,its  
satellite1 #c4 ,dependence on the sun1  
#d4 ,meteorites1 #d4    ,geognosy       
#e      ,i4 ,the ,atmosphere            
#e          ,mass and extent1 #f4       
,geologic activity1 #f4 ,a thermal      
blanket1        #g4     ,,ii4 ,the      
,hydrosphere                            
#g        ,oceanic dimensions1 #h4      

,geologic activity1 #h4 ,chief          
horizons of activity1 #i4    ,,iii4 ,the
 ,lithosphere                           
#i          ,irregularities1 #aj4       
,epicontinental seas1 #aa4 ,diversities 
of        surface1 #ab4 ,the surface    
mantle of the lithosphere1 #ab4 ,the    
crust of the lithosphere1 #ac4 ,the     
interior1 #ad4 ,varieties        of rock
 in crust1 #ad4 ,stratified rocks1 #ad4 
,conformability1        #ae4 ,relative  
ages1 #ae4 ,the crystalline rocks1 #af4 
,four great        sedimentary eras1    
#ag4 ,the ,archean complex1 #ah4        
,general ,table of ,geologic ,divisions 
#ai                                     
,,chapter ,,ii4                         
,,the ,,atmosphere ,,as ,a ,,geological 
,,agent4    ,the ,atmosphere as a       
,direct ,agency                         
#ba      ,i4 ,mechanical ,work          
#ba        ,transportation and          
deposition of dust1 #bb4 ,transportation
        and deposition of sand1 #be4    
,formation of dunes1 #bf4 ,shapes       

of dunes1 #bf4 ,the topographic map1    
#cj4 ,topography of dune        areas1  
#cb4 ,migration of dunes1 #cc4          
,distribution of dunes1 #ce4            
,wind ripples1 #cg4 ,abrasion by the    
wind1 #ch4 ,effects of wind        on   
plants1 #dj4 ,indirect effects of the   
wind1 #da4     ,,ii4 ,chemical ,work    
#da        ,precipitation from solution1
 #da4 ,oxidation1 #db4 ,carbonation1    
#dc4 ,other chemical changes1 #dc4      
,conditions favorable for               
chemical changes1 #dc4    ,the          
,atmosphere as a ,conditioning ,agency  
#dc      ,i4 ,temperature ,effects      
#dd     ,,ii4 ,evaporation and          
,precipitation                          
#ej    ,,iii4 ,effects of ,electricity4 
#eb    ,summary                         
#ed                                     
,,chapter ,,iii4                        
,,the ,,work ,,of ,,running ,,water4    
,rain and ,river ,erosion               
#eg    ,subarial ,erosion without       
,valleys                                

#eh    ,the ,development of ,valleys    
#fc        ,by the growth of gullies1   
#fc4 ,limits of growth1 #fg4 ,the       
permanent stream1 #gj4 ,other modes of  
valley development1        #gc4         
,structural valleys1 #gg4 ,the courses  
of valleys1 #gg4 ,the        development
 of tributaries1 #gh4    ,a ,cycle of   
,erosion4 ,its ,stages                  
#hj    ,general ,characteristics of     
,topography ,developed by ,river        
,erosion    #ib    ,special ,features   
,resulting from ,special ,conditions of 
,erosion       #ib        ,bad-land     
topography1 #ic4 ,special forms of      
valleys2 canyons1        #id4    ,the   
,struggle for ,existence ,among ,valleys
 and ,streams               #ajj        
,piracy1 #ajc4    ,rate of ,degradation 
#aje        ,material in solution in    
river water1 #ajg4    ,economic         
,considerations                         
#ajh    ,analysis of ,erosion           
#aaj    ,weathering4                    
#aaj    ,transportation                 

#aae        ,transporting power and     
velocity1 #aae4 ,how sediment is        
carried1 #aaf4    ,corrasion            
#aai        ,abrasion1 #aai4 ,solution1 
#abb4    ,conditions ,affecting the     
,rate of ,erosion                       
#abc    ,the ,influence of ,declivity   
#abc    ,the ,influence of ,rock        
#abd        ,physical constitution1     
#abd4 ,chemical composition1 #abd4      
,structure1 #abe4    ,the ,influence of 
,climate                                
#abg    ,effects of ,unequal ,hardness  
#acb        ,rapids and falls1 #acb4    
,rock terraces1 #adj4 ,narrows1 #ada4   
,other effects on topography1 #adb4     
,adjustment of streams to        rock   
structures1 #adf4    ,influence of      
,joints and ,folds                      
#aej        ,joints1 #aej4 ,folds1 #aed4
    ,effect of ,changes of ,level       
#afa        ,rise1 #afa4 ,sinking1 #agj4
 ,differential movement1 warping1       
#aga4    ,the ,aggradational ,work of   
,running ,water                         

#agg        ,principles involved1 #agg4 
,the ,deposits                          
#aha        ,types1 #aha4 ,alluvial fans
 and cones1 #aha4 ,ill-defined          
alluvium1 #ahc4 ,alluvial plains1 #ahd4 
,flood-plains due to        alluviation1
 #ahf4 ,flood-plains due to             
obstructions1 #ahh4        ,levees1     
#ahh4 ,flood-plain meanders1            
cut-and-fill1 #aij4                     
,scour-and-fill1 #aid4 ,materials of the
 flood-plain1 #aif4        ,topography  
of the flood-plain1 #aif4 ,topographic  
adjustment of        tributaries1 #aig4 
,river-lakes1 #aih4 ,deltas1 #aih4      
,delta lakes1        #bjd4    ,stream   
,terraces                               
#bjd        ,due to inequalities of     
hardness1 #bjd4 ,normal flood-plain     
terraces1 #bje4 ,flood-plain terraces   
due to other causes1 #bjh4              
,discontinuity of terraces1 #bji4       
,termini of terraces1 #baj4             
,,chapter ,,iv4                    ,,the
 ,,work ,,of ,,ground 7,,underground7   

,,water4          ,conditions           
influencing descent of rain-water1 #bac4
 ,supply        of ground-water not     
altogether dependent on local rainfall1 
#bae4 ,ground-water surface--water      
table1 #bae4 ,depth to which            
ground-water sinks1 #baf4 ,movement of  
ground-water1 #bbj4        ,amount of   
ground-water1 #bba4 ,fate of            
ground-water1 #bba4    ,the ,work of    
,ground-water                           
#bbb    ,chemical ,work                 
#bbb          ,quantitative importance  
of solution1 #bbc4 ,deposition of       
mineral matter from solution1 #bbe4     
,mechanical ,work                       
#bbf    ,results of the ,work of        
,ground-water                           
#bbf        ,weathering1 #bbf4 ,caverns1
 #bbg4 ,creep1 slumps1 and landslides1  
#bca4    ,summary                       
#bcb    ,springs and ,flowing ,wells    
#bcd        ,mineral matter in solution1
 #bce4 ,geysers1 #bcf4 ,artesian        
wells1 #bdb4                            

,,chapter ,v4                           
,,the ,,work ,,of ,,snow ,,and ,,ice4   
,snow- and ,ice-fields                  
#bdd        ,the passage of snow into nv
 and ice1 #bdf4 ,structure of the       
ice1 #bdg4 ,texture1 #bdg4 ,inauguration
 of movement1 #bdh4    ,types of        
,glaciers                               
#bea    ,the ,general ,phenomena of     
,glaciers                               
#bef        ,dimensions1 #bef4 ,limits1 
#beh4 ,movement1 #bei4 ,conditions      
affecting rate of movement1 #bfa4       
,likenesses and unlikenesses        of  
glaciers and rivers1 #bfb4    ,surface  
,features                               
#bff        ,topography1 #bff4 ,surface 
moraines1 #bff4 ,relief due to surface  
dbris1 #bfh4 ,dust-wells1 #bfi4 ,dbris  
below the surface1 #bgb4                
,temperature1 ,waste1 and ,drainage     
#bgc        ,the winter wave1 #bgd4 ,the
 summer wave1 #bgf4 ,the temperature    
of the bottom1 #bgf4 ,temperature of the
 interior of the        ice1 #bgg4      

,compression and friction as causes of  
heat1        #bgh4 ,summary1 #bgi4      
,movement under low temperature1 #bgi4  
,evaporation1 #bgi4 ,drainage1 #bhj4    
,the ,work of ,glaciers                 
#bha    ,erosion and ,transportation    
#bha        ,getting load1 #bhb4        
,conditions influencing rate of erosion1
        #bhc4 ,summary1 #bhf4 ,varied   
nature of glacial dbris1 #bhf4 ,the     
topographic effects of glacial erosion1 
#bhg4 ,fiords1 #bij4 ,the               
positions in which dbris is carried1    
#bij4 ,transfers of load1        #bib4  
,wear of drift in transit1 #bih4        
,deposition of the ,drift               
#bih        ,beneath the body of the    
ice1 #bih4 ,at ends and edges of        
glaciers1 #bii4    ,types of ,moraines  
#cja          ,the terminal moraine1    
#cja4 ,the ground moraine1 #cja4 ,the   
lateral moraines1 #cjb4 ,distinctive    
nature of glacial        deposits1 #cjd4
 ,glaciated rock surfaces1 #cjd4        
,glacio-,fluvial ,work                  

#cje    ,icebergs                       
#cjg    ,the ,intimate ,structure and   
the ,movement of ,glaciers              
#cjh        ,the growth and constitution
 of a glacier1 #cjh4 ,the               
arrangement of the crystal axes1 #cab4  
,the ,probable ,fundamental ,element in 
,glacial ,motion               #cac     
,melting and freezing1 #cac4            
,accumulated motion in the terminal     
part of a glacier1 #caf4    ,auxiliary  
,elements                               
#cag        ,shearing1 #cag4 ,high      
temperature and water1 #cah4            
,applications1        #cai4             
,corroborative ,phenomena               
#cbj    ,other ,views of ,glacier       
,motion                                 
#cba                                    
,,chapter ,,vi4                         
,,the ,,work ,,of ,,the ,,ocean4        
,volume and composition1 #cbd4          
,topography of bed1 #cbf4               
,distribution of marine life1 #cbh4     
,processes in ,operation in the ,sea    

#cbi        ,diastrophism1 #cbi4        
,vulcanism1 #ccb4 ,gradation1 #ccc4     
,movements of the ,sea-water            
#ccd        ,differences in density and 
their results1 #cce4 ,differences in    
level and their results4 #cce4          
,movements generated by winds1          
#ccf4 ,movements generated by           
attraction1 #cbb4 ,aperiodic            
movements1 #cch4 ,summary1 #cci4        
,waves                                  
#cci        ,wave-motion1 #cci4    ,work
 of the ,waves                          
#cdb    ,erosion                        
#cdb        ,by waves and undertow1     
#cdb4    ,topographic ,features         
,developed by ,wave ,erosion            
#cdi        ,the sea-cliff1 #cdi4       
,chimney rocks1 etc41 #cej4 ,sea caves1 
#cej4 ,the wave-cut terrace1 #cea4 ,wave
 erosion and horizontal                 
configuration1 #cec4    ,transportation 
by ,waves                               
#ced    ,deposition by ,waves1          
,undertow1 and ,shore ,currents         

#cee        ,the beach1 #cee4 ,the      
barrier1 #cef4 ,the spit1 the bar1 and  
the        loop1 #ceg4 ,wave-built      
terraces1 #cfc4    ,effect of ,shore    
,deposition on ,coastal ,configuration  
#cfc    ,summary of ,coastal            
,irregularities                         
#cfd    ,the ,work of ,ocean-currents   
#cff    ,deposits of the ,ocean-bed     
#cfh    ,shallow-water ,deposits        
#cfi        ,littoral deposits1 #cfi4   
,non-littoral1 mechanical deposits      
in shallow water1 #cfi4 ,characteristics
 of shallow-water        deposits1 #cgc4
 ,topography of shallow-water deposits1 
#cgd4        ,chemical and organic      
deposits1 #cge4 ,limestone1 #cgh4       
,deep-sea ,deposits                     
#cgh        ,contrasted with            
shallow-water deposits1 #cgh4 ,sources1 
#chj4        ,mechanical inorganic      
deposits1 #chj4 ,organic constituents of
        pelagic deposits1 #chb4         
,chemical deposits1 #chc4    ,lakes #chf
          ,changes taking place in      

lakes1 #chg4 ,lacustrine deposits1      
#chh4 ,extinct lakes1 #chh4 ,lake ice1  
#chi4 ,saline lakes1 #cia4              
,indirect effects of lakes1 #cib4       
,composition of lake waters1            
#cib4                                   
,,chapter ,,vii4                        
,,the ,,origin ,,and ,,descent ,,of     
,,rocks4    ,composition of ,igneous    
,rocks                                  
#cie        ,leading elements1 #cif4    
,union of elements1 #cig4 ,formation    
of minerals1 #cig4 ,sources of          
complexity1 #cih4 ,the leading          
minerals of igneous rocks1 #cii4 ,the   
feldspathic minerals1        #djj4 ,the 
ferromagnesian minerals1 #djj4 ,summary 
of salient        facts1 #dja4    ,the  
,nature of ,molten ,magmas              
#dja        ,time required in           
crystallization1 #djb4 ,successive      
stages of        crystallization1 #djc4 
,the ,fragmental ,products of ,sudden   
,cooling                          #djd  
,pyroclastic rocks1 #djd4    ,the       

,glassy ,rocks                          
#djf        ,the solid glasses4 #djf4   
,the first stages of crystallization1   
#djg4 ,the obsidians1 #djg4    ,special 
,structures                             
#daj        ,flow structure1 #daj4      
,amygdaloids1 #daa4    ,the ,porphyritic
 ,rocks                                 
#daa    ,the ,phanerocrystalline ,rocks 
#dab        ,the phanerites1 #dab4 ,the 
granites1 #dac4 ,the syenites1          
#dae4 ,the diorites1 #daf4 ,the gabbros1
 #daf4 ,the peridotites1        #daf4   
,the basalts1 #dag4 ,the dolerites1     
#dag4 ,general        names1 #dah4      
,derivation of ,secondary ,rocks        
#dbj        ,regolith1 #dbb4 ,disrupted 
products3 arkose and wacke1 #dbb4       
,disintegrated products1 #dbb4          
,classes of ,sedimentary ,rocks         
#dbb        ,shales1 sandstones1 and    
conglomerates1 #dbb4 ,limestones and    
dolomites1 #dbd4 ,precipitates1 #dbd4   
,iron-ore beds1 #dbe4        ,silicious 
deposits1 #dbe4 ,organic rocks1 #dbf4   

,internal ,alterations of ,rocks        
#dbf        ,oxidation and deoxidation1 
#dbg4 ,solution and deposition1         
#dbg4 ,hydration and dehydration1 #dbh4 
,carbonation and        decarbonation1  
#dbi4 ,molecular rearrangements1 #dca4  
,the ,salient ,features of ,rock        
,descent                                
#dca    ,the ,reascensional ,process    
#dcb        ,induration under ordinary  
pressures and temperatures1 #dcb4       
,cavity filling1 #dcf4 ,fissure filling2
 veins1 #dcg4 ,solution as        well  
as deposition1 #dcg4 ,concretions1 #dch4
 ,replacements and        pseudomorphs1 
#dci4 ,incipient crystallization1 #dci4 
,reconstruction under ,exceptional      
,conditions                        #ddj 
,slaty structure1 #dda4 ,foliation1     
schistosity1 #ddc4        ,metamorphism 
by heat1 #ddf4 ,metamorphism by heat and
 lateral        pressure1 #ddh4         
,deep-seated metamorphism1 #ddi4        
,completion of        the rock cycle1   
#ddi4    ,various ,classifications and  

,nomenclatures                          
#ddi    ,new ,system of ,classification 
and ,nomenclature                       
#dea    ,the ,proposed ,field ,system   
#dea        ,the phanerites1 #dea4 ,the 
aphanites1 #deb4    ,the ,proposed      
,quantitative ,system                   
#ded    ,reference ,list of the ,more   
,common ,minerals                       
#dfj    ,reference ,list of the ,more   
,common ,rocks                          
#dfg    ,ore ,deposits                  
#dgd        ,concentration1 #dgd4       
,exceptional and doubtful cases1 #dgd4  
,original distribution1 #dge4 ,magmatic 
segregation1 #dge4 ,marine              
segregation and dispersion1 #dgf4       
,origin of ore regions1        #dgg4    
,surface residual concentration1 #dgh4  
,purification        and concentration1 
#dgh4 ,concentration by solution and    
reprecipitation1 #dgi4 ,location of     
greatest solvent action1        #dhj4   
,short-course action1 #dha4 ,long-course
 action1 #dha4        ,summary1 #dhc4   

,the influence of contacts1 #dhd4 ,the  
effect of        igneous intrusions1    
#dhd4 ,the influence of rock walls1     
#dhd4                                   
,,chapter ,,viii4                       
,,structural 7,,geotectonic7 ,,geology4 
,the structural phases which rocks      
assume1 #dhf4    ,structural ,features  
of ,sedimentary ,rocks                  
#dhf        ,stratification1 #dhf4      
,lateral graduation1 #dhh4 ,special     
markings1 #dhi4 ,concretionary          
structure1 #dij4 ,secretions1 #dig4     
,structural ,features of ,igneous ,rocks
                               #dih     
,structural ,features ,arising ,from    
,disturbance                       #ejj 
,inclination and folding of strata1     
#ejj4 ,joints1 #eaj4        ,sandstone  
dikes1 #ead4 ,faults1 #ead4 ,the        
significance of        faults1 #eba4    
,effect of faulting on outcrops1 #ebb4  
,,chapter ,,ix4              ,,the      
,,movements ,,and ,,deformations ,,of   
,,the ,,earth',s ,,body                 

7,,diastrophism74    ,minute and ,rapid 
,movements                              
#ebf    ,earthquakes                    
#ebg        ,points of origin1 foci1    
#ebg4 ,the amplitude of the vibrations1 
#ebi4 ,destructive effects1 #ecj4       
,direction of throw1 #eca4 ,rate        
of propagation1 #ecb4 ,sequences of     
vibrations1 #ecc4 ,gaseous              
emanations1 #ecc4 ,distribution of      
earthquakes1 #ecc4    ,the ,geologic    
,effects of ,earthquakes                
#ecd        ,fracturing of rock1 #ecd4  
,changes of surface1 #ecd4 ,effects on  
drainage1 #ece4 ,effects on standing    
water1 #ece4 ,changes of        level1  
#ecf4    ,slow ,massive ,movements      
#ecg        ,present movements1 #ech4   
,fundamental conceptions1 #eci4         
,nearly ,constant ,small ,movements     
#edj        ,reciprocal features1 #eda4 
,the ,great ,periodic ,movements        
#edb        ,mountain-forming movements1
 #edb4 ,distribution of        folded   
ranges1 #edc4 ,plateau-forming          

movements1 #edc4                        
,continent-forming movements1 #edd4     
,relations of these        movements in 
time1 #ede4 ,relations of vertical to   
horizontal        movements1 #ede4 ,the 
squeezed segments1 #edf4 ,the depressed 
or master segments1 #edf4 ,the          
differential extent of crustal          
movements1 #edh4    ,the ,causes of     
,movement                               
#eea    ,general ,considerations        
#eea      #a4 ,the centripetal agencies 
#eeb        ,gravity1 #eeb4 ,molecular  
and sub-molecular attractions1 #eed4    
,cohesion and crystallization1 #eed4    
,diffusion1 #eee4 ,chemical             
combination1 #eef4 ,sub-atomic forces   
#eef4      #b4 ,the resisting agencies  
#eeg        ,heat1 #eeg4 ,all resistance
 perhaps due to motion1 #eeh4           
,alternative ,views of ,original ,heat  
,distribution                    #eei   
,thermal distribution on the convection 
hypothesis1 #eei4 ,level        of no   
stress1 #efa4 ,thermal distribution on  

the hypothesis of        central        
solidification1 #efb4 ,thermal          
distribution under the        accretion 
hypothesis1 #efd4 ,computed ,pressures1 
,densities1        and ,temperatures    
within the ,earth ,based on ,laplace's  
,law #efd        ,recombination of      
material1 #efh4 ,comparison of the      
hypotheses1        #efh4    ,observed   
,temperatures in ,excavations           
#efi        ,explanations of varying    
increment1 #egj4 ,the permeation and    
circulation of water1 #egj4 ,chemical   
action1 #egj4 ,differences        in the
 conductivity of rock1 #ega4            
,compression1 #ega4 ,gradients          
projected1 #ega4 ,the amount of loss of 
heat1 #egb4 ,the amount        of       
shrinkage from loss of heat1 #egb4      
,other ,sources of ,deformation         
#egd        ,transfer of internal heat1 
#egd4 ,denser aggregation of            
matter1 #egd4 ,extravasation of lavas1  
#egd4 ,change in the        rate of     
rotation1 #ege4 ,distribution of        

rigidity1 #egh4      ,sphericity as a   
,factor in ,deformation                 
#ehj        ,the influence of the domed 
form of the surface1 #eha4              
,theoretical strength of domes of       
earth-dimensions1 #eha4                 
,stress-accumulation independent of     
sphericity1 #ehc4 ,the        actual    
configuration of the surface1 #ehd4     
,concave tracts1        #ehd4 ,general  
conclusion1 #ehh4                       
,,chapter ,x4                           
,,the ,,extrusive ,,processes4          
,outward movements1 #eij4    ,vulcanism 
#eij        ,phases of vulcanism1 #eia4 
#a4 ,intrusions                         
#eia        ,the heating action1 #eib4  
#b4 ,extrusions                         
#eib        ,fissure eruptions1 #eic4   
,volcanic eruptions1 #eid4 ,intermediate
        phenomena1 #eif4 ,lunar craters1
 #eih4    ,volcanoes                    
#eii        ,number of1 #eii4           
,distribution of ,volcanoes             
#eii        ,in time1 #eii4 ,relative to

 land and sea1 #eii4 ,relative to       
crustal deformations1 #fja4 ,in         
latitude1 #fjc4 ,in curved lines1       
#fjc4    ,relations of ,volcanoes       
#fjd        ,relations to rising and    
sinking surfaces1 #fjd4 ,relations to   
one another1 #fje4 ,unimportant         
coincidences1 #fjf4 ,periodicity1       
#fjg4    ,formation of ,cones           
#fjh        ,lava-cones1 #fjh4          
,cinder-cones1 #fjh4 ,subordinate cones1
 #faj4        ,composite cones1 #faj4   
,extra-cone distribution1 #faj4         
,lavas                                  
#fab        ,their nature1 #fab4        
,consanguinity and succession of lavas1 
#fad4 ,temperature of lavas1 #fae4      
,depth of source1 #faf4    ,volcanic    
,gases                                  
#fag        ,differences in gas action1 
#fag4 ,spasmodic action1 #fah4 ,kinds   
of gases1 #fah4 ,residual gases in      
volcanic rock1 #fai4 ,the        source 
of the gases1 #fba4    ,the ,cause of   
,vulcanism                              

#fbc      ,i4 ,on the ,assumption that  
the ,lavas are ,original                
#fbc        ,lava outflows from a molten
 interior1 #fbd4 ,lavas assigned to     
molten reservoirs1 #fbd4       ,,ii4 ,on
 the ,assumption that the ,lavas are    
,secondary              #fbe            
,lavas assigned to the reaction of water
 and air penetrating        to hot      
rocks1 #fbe4 ,lavas assigned to relief  
of pressure1 #fbg4        ,lavas        
assigned to melting by crushing1 #fbh4  
,lavas assigned to        melting by    
depression1 #fbi4 ,vulcanism assigned to
 the outflow        of deep-seated heat1
 #fbi4    ,modes of ,reaching the       
,surface                                
#fca    ,additional ,considerations     
,relative to the ,gases                 
#fcc    ,thermal ,considerations        
#fce                                    
,,chapter ,,xi4                         
,,the ,,geologic ,,functions ,,of       
,,life4    ,i4 ,the ,distinctive        
,features of ,organic ,processes        

#fch    ,the ,chemical ,work of ,life   
#fch        ,life material chiefly      
atmospheric1 #fch4 ,the non-atmospheric 
factors1 #fci4      7#a7 ,changes in the
 composition of the atmosphere          
#fci        ,the consumption and        
restoration of carbon dioxide1 #fdj4    
,the freezing and consumption of oxygen1
 #fdj4 ,the organic        residue1     
#fdj4 ,the meaning of the organic       
residue1 #fda4 ,the        more inert   
factor1 #fdb4 ,probable fluctuations of 
atmospheric        composition1 #fdb4   
,the climatic effects of organic action1
 #fdc4      7#b7 ,aid and hindrance to  
inorganic action                        
#fdd        ,the promotion of           
disintegration1 #fdd4 ,protection       
against        erosion1 #fdd4 ,the      
influence of land vegetation on the     
character of the sediments1 #fde4       
7#c7 ,distinctive deposits              
#fdf        ,organic rocks1 #fdf4       
,inorganic rocks due to life1 #fdf4     
,fossils                                

#fdf        ,the general order of life  
succession determined by                
stratigraphy1 #fdg4 ,fossils as means of
 correlation1 #fdg4    ,special ,modes  
of ,aggregation and of ,movement        
#fdh    ,the ,mental ,element           
#fdi        7#a7 ,the material effects  
of the mental element1 #fdi4 ,human     
modification of the animal and vegetal  
kingdoms1 #fej4 7#b7 ,the               
psychological factors as such1 #fea4    
,,ii4 ,special ,contributions of the    
,organic ,kingdoms                  #feb
    ,contributions of the ,plant        
,kingdom                                
#feb        ,reference table of the     
principal groups of plants1 #fec4 ,the  
contribution of the ,thallophytes1 #fec4
 ,the contribution of        the        
,bryophytes1 #fef4 ,the contribution of 
the ,pteridophytes1        #feg4 ,the   
contribution of the ,spermatophytes1    
#feg4 ,plant life        terrestrial    
rather than marine1 #feh4               
,contributions of the ,animal ,kingdom  

#feh        ,reference table of the     
principal groups of animals1 #fei4 ,the 
contribution of the ,protozoa1 #ffj4    
,the contribution of the                
,clenterata1 #ffa4 ,the contribution of 
the ,echinodermata1 #ffa4        ,the   
contribution of the ,vermes1 #ffb4 ,the 
contribution of the                     
,molluscoidea1 #ffb4 ,the contribution  
of the ,mollusca1 #ffb4 ,the            
contribution of the ,arthropoda1 #ffb4  
,the contribution of the                
,vertebrata1 #ffc4    ,,iii4 ,the       
,associations and ,ecological ,relations
 of ,life             #ffc    ,the      
,basis of ,floras and ,faunas           
#ffc    ,assemblages ,influenced by the 
,mutual ,relations of ,organisms        
#ffd        ,food relations1 #ffd4      
,adaptive relations1 #ffe4 ,competitive 
relations1 #ffe4 ,offensive and         
defensive relations1 #ffe4              
,implied forms of life1 #fff4           
,assemblages ,influenced by ,environment
                            #fff        

,plant societies1 #ffg4    ,the         
,influence of ,geographic ,conditions on
 the ,evolution of      ,floras and     
,faunas                                 
#ffh        ,the development of         
provincial and cosmopolitan faunas1     
#ffh4        ,restrictive and           
expansional evolution1 #fgb4            
,,plates4      plate                    
face page        ,i4 ,bathymetrical     
,chart of the ,oceans                   
#aj       ,,ii4 ,fig4 #a4 ,new ,jersey4 
,fig4 #b4 ,kansas4 ,fig4 #c4 ,indiana4  
,fig4 #d4           ,nebraska           
#ci      ,,iii4 ,fig4 #a4 ,kansas4 ,fig4
 #b4 ,nevada                            
#gb       ,,iv4 ,fig4 #a4 ,illinois4    
,fig4 #b4 ,north ,dakota                
#gc        ,v4 ,fig4 #a4 ,kentucky4     
,fig4 #b4 ,virginia                     
#he       ,,vi4 ,parts of ,los ,angeles 
and ,san ,bernardino ,counties1         
,california4  #hg      ,,vii4 ,kansas   
#ij     ,,viii4 ,about #af ,miles       
,southwest of ,st4 ,louis1 ,mo4         

#ia       ,,ix4 ,niagara ,falls         
#ajj        ,x4 ,fig4 #a4 ,yellowstone  
,park4 ,fig4 #b4 ,arizona               
#aja       ,,xi4 ,part of the           
,catskills1 ,n4 ,y4                     
#ajf      ,,xii4 ,fig4 #a4 ,new ,mexico4
  ,fig4 #b4 ,virginia1 ,west ,virginia1 
and           ,maryland                 
#ajg     ,,xiii4 ,fig4 #a4 ,colorado4   
,fig4 #b4 ,kansas                       
#afb      ,,xiv4 ,fig4 #a4              
,pennsylvania4 ,fig4 #b4 ,california    
#afc       ,,xv4 ,near ,hahnville1      
,louisiana                              
#ahh      ,,xvi4 ,missouri              
#ahi     ,,xvii4 ,fig4 #a4 ,hunterdon   
,county1 ,n4 ,j4 ,fig4 #b4 ,near        
,pikeville1 ,tenn4 #bcb    ,,xviii4     
,fig4 #a4 ,washington4 ,fig4 #b4        
,california                        #bcc 
,,xix4 ,part of the ,big ,horn ,range1  
,wyoming                           #bhf 
,,xx4 ,section of the ,california ,coast
 near ,san ,mateo1 ,cal4          #bhg  
,,xxi4 ,new ,jersey                     

#cef     ,,xxii4 ,fig4 #a4 ,portion of  
,south ,coast of ,martha's ,vineyard1   
,mass4           ,fig4 #b4 ,portion of  
the ,california ,coast near ,tamalpais  
#ceg    ,,xxiii4 ,fig4 #a4              
,massachusetts4 ,fig4 #b4 ,maine        
#cfd     ,,xxiv4 ,portion of the ,coast 
of ,maine                               
#cfe                                    
,,tables4      ,analyses of ,american   
,river-waters                           
#ajf    ,analyses of ,american          
,spring-waters                          
#bcf    ,analyses of the ,waters of     
,inclosed ,lakes                        
#cib                                    
,,geology                               
,,chapter ,i4                           
,,preliminary ,,outline4    ,geology    
treats of the structure of the earth1 of
 the various stages  through which it   
has passed1 and of the living beings    
that have dwelt  upon it1 together with 
the agencies and processes involved in  
the  changes it has undergone4 ,geology 

is essentially a history of the  earth  
and its inhabitants4 ,it is one of the  
broadest of the sciences1  and brings   
under consideration certain phases of   
nearly all the  other sciences1         
particularly those of astronomy1        
physics1 chemistry1  zoology1 and       
botany4 ,it also embraces the earlier   
expressions of mental  development and  
of life-relationships1 chiefly as found 
in the lower  animals4                  
,subdivisions4--,naturally so broad a   
science has many special aspects  which 
constitute subdivisions1 in a sense1    
though they are rather  dominant phases 
than independent sections4 ,that phase  
which treats  of the outer relations of 
the earth is ,cosmic or ,astronomic     
geology2 that which treats of the       
constituent parts of the earth  and its 
material is ,geognosy1 of which the most
 important branch  is ,petrology1 the   
science of rocks4 ,that branch which    
investigates  the structural arrangement
 of the material1 or 8the architecture  

of  the earth10 is ,geotectonic1 or     
,structural geology2 while that  which  
deals with the surface changes and      
topographic forms1 that is1  with the   
face of the earth1 is ,physiographic    
geology4 ,the study of  the fossils that
 have been preserved in the rocks1 and  
of the faunas  and floras that these    
imply1 constitutes ,paleontologic       
geology1  or ,paleontology4 ,the        
treatment of the succession of events   
forms  ,historical geology4 ,this is    
chiefly worked out by the succession  of
 beds laid down in the progress of the  
ages1 which constitutes  ,stratigraphic 
geology4 ,the treatment of causes1      
agencies1 and  processes is the function
 of ,dynamic or ,philosophic geology4   
,besides these there are special        
applications which give occasion  for   
other terms1 as ,economic geology1 which
 is concerned with the  industrial      
applications of geologic knowledge2     
,mining geology1 which  is a sub-section
 of economic geology1 relating to the   

application  of geologic facts and      
principles to mining operations2        
,atmospheric  geology1 ,glacial geology1
 and others that define themselves1 and 
are  for the greater part but limited   
aspects of the broad science4           
,dominant processes4--,three sets of    
processes1 now in operation  on the     
surface of the lithosphere1 have given  
rise to most of the  details of its     
configuration1 and even many of its     
larger features4  ,these processes have 
been designated diastrophism1 vulcanism1
 and  gradation4 ,diastrophism includes 
all crustal movements1 whether  slow or 
rapid1 gentle or violent1 slight or     
extensive4 ,many parts of  the land1    
especially along coasts1 are known to be
 slowly sinking  relative to the        
sea-level1 while other parts are known  
to be rising4  ,the fact that rocks     
originally formed beneath the sea now   
exist at  great elevations1 and the     
further fact that areas which were once 
land  are now beneath the sea1 are      

sufficient evidence that similar changes
  have taken place in the past4         
,vulcanism includes all processes       
connected with the extrusion of lava and
 other volcanic products1  and with the 
rise of lava from lower to higher       
levels1 even if not  extruded4          
,vulcanism and diastrophism may be      
closely associated1 for  local movements
 at least are often associated with     
volcanic eruptions1  and more           
considerable movements may be connected 
with the movements  of subsurface lavas1
 even when the connection is not        
demonstrable4  ,gradation includes all  
those processes which tend to bring the 
surface of the lithosphere to a common  
level4 ,gradational processes  belong to
 two categories--those which level down1
 degradation1 and  those which level up1
 aggradation4 ,the transportation of    
material  from the land1 whether by     
rain1 rivers1 glaciers1 waves1 or winds1
  is degradation and the deposition of  
material1 whether on the land  or in the

 sea1 is aggradation4 ,degradation      
affects primarily the  protuberances of 
the lithosphere1 while aggradation      
affects primarily  its depressions4     
,astronomic ,geology4    ,the earth as a
 planet4--,though supremely important to
 us1 the earth is  but one of the minor 
planets attendant upon the sun1 and is  
in no very  special way distinguished as
 a planetary body4 ,of the eight        
planets1  four1 ,jupiter1 ,saturn1      
,uranus1 and ,neptune1 are much larger  
than the  earth1 while three1 ,mars1    
,venus1 and ,mercury1 are smaller4      
,there are a  host of asteroids1 but all
 together they do not equal the mass of 
the  smallest planet4 ,the average mass 
of the eight planets is more than  fifty
 times that of the earth1 while the     
largest1 ,jupiter1 is more than  three  
hundred times as massive as the earth4  
,the earth's position in  the group is  
in no sense distinguished4 ,it is       
neither the outer nor the  inner1 nor   
even the middle planet4 ,even in the    

minor group to which it  belongs1 it is 
neither the outermost nor the innermost 
member1 though  in this group it is the 
largest4 ,its average distance from the 
sun is  about #ib4i million miles1 and  
this fixes its revolution at #cfe days1 
for its period of revolution is directly
 dependent on its distance from  the    
sun1 and is necessarily longer than the 
revolutions of the inner  planets and   
shorter than those of the outer planets4
 ,its rotation in  twenty-four hours is 
not far different from that of its      
neighbor ,mars1  but is much slower than
 the more distant and larger planets1   
,jupiter  and ,saturn1 which rotate in  
about ten hours4 ,comparison cannot be  
made  with the innermost and outermost  
planets1 because their rotations are    
not yet satisfactorily determined4 ,the 
plane of the earth's revolution  lies   
near the common plane of the whole      
system1 but this is not  peculiar1 as   
all of the planets revolve in nearly the
 same plane4  ,only a few of the small  

asteroids depart notably from this      
common  plane4 ,this has an important   
bearing on theories of the origin of    
the system1 since this close coincidence
 of the planes of the orbits  is not    
consistent with any haphazard           
aggregation of the material4 ,of        
similar importance is the fact that all 
of the planets revolve in  the same     
direction and in ellipses that do not   
depart widely from  circles4 ,the       
eccentricity of the earth's orbit is    
only about 4 ,this  eccentricity varies 
somewhat1 due to the disturbing         
influences of the  other planets1 and   
this variation has been regarded by some
 geologists  as an influential cause of 
climatic changes1 but its adequacy to   
produce great effects has been doubted  
by others4 ,the inclination of  the     
earth's axis1 now about #bc1 holds an   
intermediate position1 some  of the     
planets having axes more inclined1 as   
,saturn1 #bf1 and others  less inclined1
 as ,jupiter1 #c4 ,the inclination of   

the axis is subject  to trivial         
variations at present1 and in the long  
periods of the past  has possibly       
changed more notably4 ,this possible    
change has also been  thought to be a   
cause of climatic variation1 but its    
efficiency has not  been demonstrated4  
,its satellite4--,the earth is peculiar 
in having one unusually large           
satellite1 which has a mass  of its own4
 ,the great planets have  several       
satellites whose combined mass exceeds  
that of the moon1 and  perhaps in some  
few cases the individual satellites may 
be larger than  the moon1 but they do   
not sustain so large a ratio to their   
planets1  for ,titan1 probably the      
largest1 is only  of the mass of        
,saturn4  ,there is little doubt that   
the moon has played an important part in
  the history of the earth4 ,it is the  
chief agency in developing oceanic      
tides1 and it possibly also develops a  
body tide in the earth itself4  ,these  
tides act as a brake on the rotation of 

the earth and tend to  reduce its rate1 
and thereby to lengthen the day4 ,while 
this may have  been counteracted in some
 measure by the shrinkage of the earth1 
which  tends to increase its rate of    
rotation1 it has been held by eminent   
physicists and geologists that the      
rotation of the earth has been  greatly 
lessened during its history1 and that a 
long train of important  consequences   
has resulted4 ,if the contraction of the
 earth has been  sufficient to offset   
this lessening1 the tidal brake must be 
credited  with the prevention of the    
excessive speed of rotation which would 
otherwise have been developed4 ,the     
tides are efficient agencies in the     
shore wear of the oceans1 and in the    
distribution of marine sediments1  and  
these1 it will be seen later1 are       
important elements in the  formation of 
strata4    ,dependence on the sun4--,by 
far the most important external relation
  of the earth1 however1 is its         
dependence on the sun4 ,the earth is a  

mere satellite of the sun1 less than  of
 its mass1 and hence  under its full    
gravitative control4 ,the earth is      
dependent on the sun  for nearly all its
 heat and light1 and1 through these1 for
 nearly all  of the activities that have
 given character to its history4 ,it is 
too much to say that all activities on  
the surface of the earth are  solely    
dependent on those of the sun1 for a    
certain measure of heat and  light and  
other energy is derived from other      
bodies1 and a certain not               
inconsiderable source of energy is found
 in the interior of the earth  itself2  
yet all of these are so far subordinate 
to that great flood of  energy which    
comes from the sun that they are quite  
inconsequential4  ,the history of the   
earth in the past has been intimately   
dependent upon  that of the sun1 and its
 future is locked up with the destiny of
 that  great luminary4 ,geology in its  
broadest phases can therefore scarcely  
be separated from the study of the sun1 

but this falls within the  function of  
the astronomer rather than the          
geologist4    ,meteorites4--,there are a
 multitude of small bodies passing      
through  space in varying directions and
 with varying velocities and            
occasionally encountering the earth1 to 
which they add their substance4  ,some  
of these meteorites revolve about the   
sun much as if they were  minute        
planets1 but some of them come from such
 directions and with  such velocities as
 to show that they do not belong to the 
solar family4  ,some consist almost     
wholly of metal1 chiefly iron alloyed   
with a  small percent4 of nickel        
7holosiderites72 some consist of metal  
and  rock intimately mixed 7syssiderites
 and sporadosiderites72 and some        
consist wholly of rock 7asiderites74    
,the rock is usually composed of  the   
heavier basic minerals1 though some     
meteorites consist largely  of          
carbonaceous material4 ,besides         
meteorites1 there is little doubt  that 

wandering gaseous particles strike the  
earth1 but this is beyond  the reach of 
present demonstration4 ,the amount of   
substance added to  the earth by these  
meteorites and gases in recent times is 
relatively  slight compared with the    
whole body of the earth4 ,what          
contribution may  have come to the earth
 in earlier times from such sources is a
 matter  of hypothesis which will be    
discussed later4                        
,geognosy4    ,the constitution of the  
earth4--,turning from its external      
relations to  the earth itself1 a       
natural threefold division is presented3
 7#a7 the  atmosphere1 7#b7 the         
hydrosphere1 and 7#c7 the lithosphere4  
,i4 ,the ,atmosphere4    ,the atmosphere
 is an intimate mixture of 7#a7 all     
those substances  that cannot take a    
liquid or solid state at the            
temperatures and  pressures which       
prevail at the earth's surface1 together
 with 7#b7 such  transient vapors as the
 various substances of the earth throw  

off4 ,the  first class form the         
permanent gases of the atmosphere1 and  
consist  of nitrogen about #gi parts1   
oxygen about #ba parts1 carbon dioxide  
about 4#jc part1 together with small    
quantities of argon1 neon1 xenon1       
krypton1 helium1 and other rare         
constituents4 ,the second class are  the
 transient and fluctuating constituents 
of the atmosphere1 chief  among which is
 aqueous vapor1 which varies greatly in 
amount according  to temperature1       
pressure1 and other conditions4 ,to this
 are to be  added volcanic emanations   
and a great variety of volatile organic 
substances4 ,theoretically1 every       
substance1 however solid1 discharges    
particles which may transiently become  
constituents of the atmosphere4         
,practically1 only a few of these exist 
in such quantity as to be  appreciable4 
,dust and other suspended matter are    
usually regarded as  impurities rather  
than constituents of the atmosphere1 but
 they play a  not unimportant part by   

affecting its temperature and           
luminosity1 and  by facilitating the    
condensation of moisture4    ,mass and  
extent4--,the total mass of the         
atmosphere is estimated at  five        
quadrillion tons1 or  of the mass of the
 earth4 ,it is  relatively dense at the 
surface of the earth and decreases in   
density  outwards in a manner difficult 
of absolute determination1 so that the  
actual height of the appreciable        
atmosphere is not positively known4     
,the true conception of the atmosphere  
is perhaps that of a tenuous  envelope  
exerting a pressure of about fifteen    
pounds per square inch  at the          
sea-level1 and thinning gradually       
upwards until it reaches a  tenuity     
which is inappreciable1 but perhaps not 
ceasing absolutely  until the sphere of 
gravitative control of the earth is     
passed1 about  #fbj1jjj miles from the  
lithosphere4 ,in the lower portion1     
according to  the kinetic theory of     
gases1 the molecules fly to and fro1    

colliding  with each other with almost  
inconceivable frequency1 and with very  
short paths between successive          
collisions1 but in the upper rare       
portion some of the molecules bound     
outwards1 and do not strike other       
molecules1 and hence pursue long        
elliptical paths until the gravity of   
the earth overcomes their momentum1 when
 they return1 perhaps to bound  off     
again or to force other molecules to do 
so4 ,this fountain-like  nature of the  
outer part of the atmosphere makes any  
sharp definition  of its limit          
impracticable4 ,some molecules are      
believed to be shot away  at such speed 
that they do not return4 ,beyond about  
#fbj1jjj miles from  the surface of the 
lithosphere1 the differential attraction
 of the sun  is greater than that of the
 earth1 and if the attraction of the    
earth  does not turn the molecules back 
before reaching this distance1 they  are
 almost certain to be lost to the earth4
    ,the measurement of heights by the  

aneroid barometer1 which is much used   
in practical geology1 is dependent on   
the lessening of pressure as the        
instrument is carried upward4           
,geologic activity4--,the atmosphere is 
the most mobile and active  of the three
 great subdivisions of the earth1 and   
when its indirect  effects through the  
agency of water1 as well as its direct  
effects1  are considered1 it is to be   
regarded as one of the most effective   
agencies of change4 ,it acts chemically 
upon the rock substance of the  earth1  
causing induration in some instances1   
but more often inducing  disintegration 
and change of composition by means of   
which rock is  reduced to soil1 or      
soil-like material1 and rendered        
susceptible of  easy removal by winds   
and waters4 ,when in motion the         
atmosphere acts  mechanically on the    
surface of the earth1 transporting dust 
and sand1  and by the friction of these 
it abrades the surface4 ,it is chiefly  
effective1 however1 in furnishing the   

conditions for water action4  ,partly by
 its mechanical aid1 but chiefly by     
securing the right  temperature1 it is a
 necessary factor in the action of      
rains1 streams1  glaciers1 and the      
various forms of moving water upon land4
 ,so also1  on the ocean1 wave action is
 essentially dependent on the winds4 ,in
  the absence of atmospheric propulsion1
 wave action would be chiefly  confined 
to the tides and to occasional          
earthquake impulses1 and would  lose    
nearly all its efficiency4 ,stream      
action and wave action1 which  are the  
most declared of the geological         
agencies1 are therefore to be  credited 
as much to the atmosphere as to the     
hydrosphere1 since the  action is a     
joint one to which both envelopes are   
essential4    ,a thermal blanket4--,a   
function of the atmosphere of supreme   
importance  is the thermal blanketing of
 the earth4 ,in its absence the heat of 
the sun would reach the surface with    
full intensity1 and would be  radiated  

back from the surface almost as rapidly 
as received1 and only  a transient      
heating would result4 ,during the night 
an intensity of cold  would intervene   
scarcely less severe than the           
temperature of space4 ,in  penetrating  
the atmosphere certain portions of the  
radiant energy of  the sun are absorbed4
 ,of the remainder which reaches the    
surface of the  earth1 a part is        
transformed into vibrations of lower    
intensity1 which  are then more         
effectively retained by the atmosphere4 
,the air thus  distributes and equalizes
 the temperature4 ,the two constituents 
of the  atmosphere which are most       
efficient in this work are aqueous vapor
 and  carbon dioxide1 and the climate of
 the earth is believed to have been     
very greatly affected by the varying    
amounts of these constituents in  the   
atmosphere1 as well as by the total mass
 of the atmosphere4    ,the function of 
the atmosphere in sustaining life and   
promoting all  that depends on life is  

too obvious to need comment4    ,the    
special geological action of the        
atmosphere will be discussed in  the    
next chapter4                           
,,ii4 ,the ,hydrosphere4    ,about #acjj
 quadrillion tons of water lie upon the 
surface of the solid  earth4 ,this      
equals about  part of the earth's mass4 
,were the  surface of the solid earth   
perfectly spheroidal1 this would        
constitute  a universal ocean somewhat  
less than two miles deep4 ,owing to the 
inequalities of the rock surface1 the   
water is chiefly gathered into a  series
 of great basins or troughs occupying   
about three-fourths 7#gb7  of the       
earth's surface4 ,these basins are all  
connected with each other  and act as a 
unit1 so that anything which changes the
 level of the  water in one changes the 
level of all4 ,this helps to make a     
common  record of all great movements of
 the earth's body1 for the level of  the
 ocean determines where the detritus    
from the land shall lodge1 and  hence   

where the edge of the marine beds shall 
be formed4 ,this will  appear more      
clearly when the formation of marine    
strata is discussed4    ,oceanic        
dimensions4--,the surface area of the   
ocean is estimated  by ,murray at       
#adc1bei1cjj square miles4 ,of this1    
somewhat more than  #aj1jjj1jjj square  
miles lie on the continental shelf1     
i4e41 lap up on  the borders of the     
continental platforms4 ,this shows that 
the great  basins are somewhat more than
 full4 ,if about #fjj feet of the upper 
part of the ocean were removed1 the true
 ocean basins would be just  full1 and  
the surfaces of the true continental    
platforms would be dry  land4 ,the area 
of the true oceanic basins is about     
#acc1jjj1jjj square  miles1 and that of 
the true continental platforms about    
#fd1jjj1jjj  square miles4 ,under about 
#bj of the ocean area1 the bottom sinks 
to  depths between #fjjj and #ab1jjj    
feet2 under about #ec it sinks to depths
  between #ab1jjj and #ah1jjj feet2 and 

under the remaining #d it ranges  from  
#ah1jjj feet down to about #cj1jjj4 ,the
 last includes those singular  sunken   
areas known as 8deeps10 and sometimes   
called anti-plateaus1 as  they extend   
downward from the general ocean bottom  
much as the plateaus  protrude upwards  
from the general land surface4          
,besides the ocean1 the hydrosphere     
includes all the water which            
constitutes the surface streams and     
lakes1 together with that which         
permeates the pores and fissures of the 
outer part of the solid earth2  but     
altogether these are small in amount    
compared with the great ocean  mass4    
,geologic activity4--,of all geological 
agencies water is the most  obvious and 
apparently the greatest1 though its     
efficiency is  conditioned upon the     
presence of the atmosphere1 upon the    
relief of  the land1 and upon the       
radiant energy of the sun4 ,through the 
agency  of rainfall1 of surface streams1
 of underground waters1 and of wave     

action1 the hydrosphere is constantly   
modifying the surface of the            
lithosphere1 while at the same time it  
is bearing into the various  basins the 
wash of the land and depositing it in   
stratified beds4 ,it  thereby becomes   
the great agency for the degradation of 
the land and  the building up of the    
basin bottoms4 ,it works upon the land  
partly  by dissolving soluble portions  
of the rock substance1 and partly by    
mechanical action4 ,the solution of the 
soluble part usually loosens  the       
insoluble1 and renders it an easy prey  
of the surface waters4  ,these transport
 the loosened material to the valleys   
and at length to  the great basins1     
meanwhile rolling and grinding it and   
thus reducing  it to rounder forms and a
 finer state1 until at length it reaches
 the  still waters or the low gradients 
of the basins and comes to rest4  ,the  
hydrosphere is therefore both           
destructive and constructive in its     
action4 ,as the beds of sediment which  

it lays down follow one another  in     
orderly succession1 each later one lying
 above each earlier one1  they form a   
time record4 ,and as relics of the life 
of each age become  more or less        
imbedded in these sediments1 they       
furnish the means of  following the     
history of life from age to age4 ,the   
historical record  of geology is        
therefore very largely dependent upon   
the fact that the  waters have thus     
buried in systematic order the          
successive life of the  ages4 ,aside    
from this1 the means of determining the 
order of events of  the earth's history 
are limited and more or less uncertain4 
,the special processes of the           
hydrosphere in its various phases will  
be the subject of discussion hereafter  
7,chaps4 ,,iii1 ,,iv1 ,,vi74 ,suffice   
it here to recognize its great function 
in the constant degradation  of the     
land1 and in the deposition of the      
derived material in orderly  succession 
in the basins4    ,chief horizons of    

activity4--,the great horizons of       
geological activity  are 7#a7 the       
contact zone between the atmosphere and 
the hydrosphere1  chiefly the surface of
 the ocean1 7#b7 the contact zone       
between the  hydrosphere and the        
lithosphere1 chiefly the shore belts1   
and 7#c7 the  contact zone of the       
atmosphere and surface waters1 with the 
face of the  continents4 ,it is in these
 three zones that the greatest external 
work  is being done and has been done in
 all the known ages4                    
,,iii4 ,the ,lithosphere4    ,the       
atmosphere and hydrosphere are rather   
envelopes or shells than true  spheres1 
though in some degree both penetrate the
 lithosphere4 ,the  lithosphere1 on the 
other hand1 is a nearly perfect oblate  
spheroid  with a polar diameter of      
#ghii4g miles1 and an equatorial        
diameter of  about #bf4h miles more4    
,its equatorial circumference is #bd1ijb
 miles1  its meridional circumference   
#bd1hfj miles1 its surface area         

#aif1idj1gjj  square miles1 its volume  
#bfj1jjj1jjj1jjj cubic miles1 and its   
average  specific gravity about #e4eg4  
,the oblateness of the spheroid is an   
accommodation to the rotation of the    
earth1 the centrifugal force  at the    
equator being sufficient to cause the   
specified amount of  bulging there4     
,computations seem to indicate that the 
accommodation  is very nearly what would
 take place if the earth were in a      
liquid  condition1 from which the       
inference has been drawn that it must   
have  been in that condition when it    
assumed this form1 and must have        
continued essentially liquid until it   
attained its present rate of  rotation1 
since1 if the earth once rotated at a   
much higher speed1 the  flattening at   
the poles and the bulging at the equator
 must have been  correspondingly        
greater4 ,it is thought by others1      
however1 that the  plasticity of the    
earth is such that it would at all times
 assume a  close degree of approximation

 to the demands of rotation1 even if the
  interior were in a solid condition4   
,by still others it is thought that  the
 contraction of the earth has tended to 
accelerate the rotation  about as much  
as the tides have tended to retard it1  
and that it has  undergone little change
 of form4    ,irregularities4--,it is   
only in a general view1 however1 that   
there is  a close approximation to a    
perfect spheroidal surface4 ,in detail  
there  are very notable variations from 
it4 ,geodetic surveys seem to have      
shown that the equatorial diameters are 
not all equal1 even when the            
measurements are reduced to sea-level1  
but research along this line has  not   
reached a sufficient stage of           
completeness to permit satisfactory     
discussion4 ,it is1 however1 highly     
probable that the ocean surface  as well
 as the average land surface is warped  
out of the perfect  spheroidal form to  
some notable degree4 ,this is very      
likely due to  inequalities in the      

density of the earth's interior4 ,the   
fact that the  larger portion of the    
water is gathered on one side of the    
globe1 while  the land chiefly protrudes
 on the opposite side1 is very possibly 
due  to unequal specific gravity in the 
interior of the earth4    ,the most     
obvious departure from a spheroidal form
 is found in the  protrusion of the     
continents and in the sinking away of   
the earth  surface under the oceans4 ,as
 these inequalities present themselves  
to-day1 they are known as continental   
platforms and ocean basins4 ,these  do  
not correspond accurately with the      
present land and water surfaces4  ,about
 the continental lands there is a       
submerged border extending some         
distance out from the shore1 and        
constituting a sea-shelf beyond which   
the surface descends rapidly to the     
great depths of the ocean4 ,this        
slightly submerged portion1 known as the
 continental shelf1 belongs  as properly
 to the continent as the adjacent low   

lands which are not  submerged4 ,the    
submergence of the edge of this shelf at
 present is  usually about #ajj fathoms1
 so that if the upper #fjj feet of the  
ocean were removed1 the outlines of the 
land would correspond quite  closely    
with the border of the true continental 
platform4    ,illustration3             
,,bathymetrical ,,chart ,,of ,,the      
,,oceans      ,,showing ,,the 8,,deeps0 
,,according ,,to ,,sir ,,john ,,murray  
,it is customary to look upon the       
protrusions of the continents as the    
great features of the earth's surface1  
but in reality the oceanic  depressions 
are the master phenomena4 ,in breadth1  
depth1 and capacity  they much exceed   
the continental protrusions1 and if the 
earth be  regarded as a shrunken body1  
the settling of the ocean bottoms has   
doubtless constituted its greatest      
surface movement4 ,from the estimates   
of ,murray1 ,gilbert has derived the    
following tables1 showing the  relative 
areas of the lithosphere above1 below1  

and between certain  levels4#a    ,from 
these estimates it appears that if the  
surface were graded to a  common level  
by cutting away the continental         
platforms and dumping the  matter in the
 abysmal basins1 the average plane would
 lie somewhere  near #ijjj feet below   
the sea-level4 ,the continental platform
 may  be conceived as rising from this  
common plane rather than from the       
sea-level4                              
----------------------------------------
---------------------------             
,percent4 of     ,percent4 of           
,contours4               ,surface       
,surface                                
above4          below4                  
----------------------------------------
---------------------------    ,contour 
#bd1jjj feet above sea-level      #j4jjd
           #ii4iif           #ah1jjj    
#j4ji            #ii4ia                 
#ab1jjj                        #j4g     
#ii4c            #f1jjj                 
#b4c             #ig4g    ,sea level    

#bg4g             #gb4c    ,contour     
#f1jjj feet below sea-level     #db4e   
#eg4e           #ab1jjj                 
#eg4c             #db4g                 
#ah1jjj                       #if4h     
#c4b           #bd1jjj                  
#ii4ic             #j4jg                
----------------------------------------
---------------------------             
,percent4        ,more than #fjjj feet  
above sea-level                         
#b4c        ,between sea-level and #fjjj
 feet above                   #be4e     
,between sea-level and #fjjj feet below 
#ad4h        ,between #fjjj and #ab1jjj 
feet below sea-level            #ad4h   
,between #ab1jjj and #ah1jjj feet below 
sea-level          #ci4d        ,between
 #ah1jjj feet and #bd1jjj feet          
#c4a    ,epicontinental seas4--,those   
shallow portions of the sea which lie   
upon the continental shelf1 and those   
portions which extend into the  interior
 of the continent with like shallow     
depths1 such as the ,baltic  ,sea and   

the ,hudson ,bay1 may be called         
epicontinental seas1 for they  really   
lie upon the continent1 or at least upon
 the continental  platform2 while those 
other detached bodies of water which    
occupy deep  depressions in the surface 
are to be regarded as true abysmal seas1
  as1 for example1 the ,mediterranean   
and ,caribbean seas and the ,gulf of    
,mexico1 whose bottoms are as profound  
as many parts of the true ocean  basin  
itself4    ,diversities of              
surface4--,the bottoms of the oceanic   
basins are  diversified by broad        
undulations which range through many    
thousands  of feet1 but they are not    
carved into the diversified forms that  
give  variety to land surfaces4 ,the    
ocean bottoms are also diversified by   
volcanic peaks1 many of which rise to   
the surface and constitute  isolated    
islands4 ,some of them have notable     
platforms at or near the  surface1 cut  
by the waves or built up by the         
accumulation of sediment  and of        

coralline and other growths about them4 
,aside from these  encircling platforms1
 the solid surface usually shelves      
rapidly down to  abysmal depths1 so that
 the islands constitute peaks whose     
heights and  slopes would seem          
extraordinary if the ocean were removed4
    ,the surface of the land is         
diversified in a similar way by broad   
undulations and volcanic peaks1 and also
 by narrower wrinklings and  foldings of
 the crust2 but all of these            
irregularities have been carved  into   
diversified and picturesque forms by    
subarial erosion4 ,in this  respect the 
surface of the land differs radically   
from the bed of the  sea4 ,the agencies 
which have produced the continental     
platforms and  abysmal basins1 and the  
great undulations and foldings1 as well 
as the  volcanic extrusions that mark   
them1 are yet subjects of debate4 ,here 
lie some of the most difficult problems 
of geology1 but these cannot be  stated 
with sufficient brevity to find a place 

here4    ,the surface mantle of the     
lithosphere4--,the surface of the       
lithosphere  is very generally mantled  
by a layer of loose material composed of
  soil1 clay1 sand1 gravel1 and broken  
rock4 ,this loose material is  sometimes
 known as mantle rock1 and sometimes as 
rock waste4 ,on  the land1 mantle rock  
is often composed of the disintegrated  
products  of underlying rock formations4
 ,it represents the results of the      
recent  action of the atmosphere1 of    
water1 of changes of temperature1 and of
  other physical agencies acting on the 
outer part of the rock sphere4  ,the    
surface of this mantle is being         
constantly removed by wind and  water1  
but as constantly renewed by continued  
decomposition of the rock  below4 ,in   
some areas1 especially in the northern  
part of ,north ,america  and the        
northwestern part of ,europe1 the soil  
graduates down into an  irregular sheet 
of mixed clay1 sand1 gravel1 and        
bowlders1 known as  drift4 ,from this   

and other evidence it is inferred that  
at a time  not greatly antedating our   
own1 ice1 chiefly in the form of        
glaciers1  spread extensively over the  
high latitudes of the northern          
hemisphere4  ,in some parts of the earth
 the surface is still covered by fields 
of  snow and ice1 comparable to those   
which formed the drift4 ,in still  other
 places1 especially along the flood     
plains of streams1 the mantle  rock     
consists of deposits made by streams    
which were unable to carry  their loads 
of sediment to the sea4    ,the crust of
 the lithosphere4--,much of the detritus
 washed down  from the land finds its   
way to bodies of standing water1 and    
beneath  lakes and seas the mantle of   
loose material is made up largely of the
  gravel1 sand1 and mud derived from the
 land4 ,before deposition these         
materials are more or less assorted and 
arranged in layers by waves  and        
currents4 ,when consolidated they       
constitute rock4 ,the weathering  of the

 rocks of the land1 the wearing away of 
the resulting detritus1  and its        
deposition beneath standing water1 are  
among the most important  processes of  
geologic change4    ,on the land1 the   
mantle of loose material is sometimes   
absent1 and  in such places the surface 
of solid rock of the crust appears4     
,bare  surfaces of rock are most        
commonly seen where the topography is   
rough1  especially on the slopes of     
steep-sided valleys and mountains1 and  
on  the slopes of cliffs which face seas
 or lakes4 ,solid rock1 without         
covering of soil or loose material of   
any sort1 is also frequently seen  in   
the channels of streams1 especially     
where there are falls or rapids4    ,we 
have but to note the effects of a       
vigorous shower on a steep slope1  or of
 a swift stream on its channel1 or of   
waves on the cliffs which  face lakes   
and seas1 to understand at least one of 
the reasons why  loose materials are    
frequently absent from steep slopes4    

,the very  general exposure of solid    
rock where conditions favor surface     
erosion  suggests that rock is          
everywhere present beneath the soil or  
subsoil4  ,fortunately there is an easy 
way of testing the universality of the  
crust beneath the mantle4 ,in all lands 
inhabited by civilized peoples  there   
are numerous wells and other excavations
 ranging from a few feet  to several    
hundred feet in depth1 and occasional   
wells and mine-shafts  reach depths of  
several thousand feet4 ,even in shallow 
excavations  rock is often encountered1 
and in most regions excavations as much 
as  two or three hundred feet deep      
usually reach rock1 and no really deep  
boring has ever failed to find it4 ,it  
may1 therefore1 be accepted as a  fact  
that the upper surface of the solid rock
 is nowhere far below the  surface4     
,concerning the thickness of the crust1 
if there be any true crust  at all1     
little is known by direct observation4  
,the deepest valleys1  such as the      

canyon of the ,colorado1 and the shafts 
and borings of  the deepest mines and   
wells1 give knowledge of nothing but    
rock4 ,the  deepest excavations extend  
rarely more than a mile below the       
surface4  ,it is certain that rock of   
known kinds extends to far greater      
depths4    ,the interior4--,concerning  
the great interior of the earth1 little 
is known except by inference4 ,from the 
weight of the earth1#b it is  inferred  
that its interior is much more dense    
than its surface4 ,from  its behavior   
under the attraction of other bodies1 it
 is believed to  be at least as rigid as
 steel1 and its interior cannot1        
therefore1  be liquid1 in the usual     
sense of that term4 ,from the phenomena 
of  volcanoes1 and from observations on 
temperature in deep borings1 it is      
inferred that its interior is very hot4 
,further inferences concerning  its     
character are less simply stated1 and   
will be referred to later4    ,the solid
 part of the earth is therefore composed

 of 7#a7 a thin layer  of unconsolidated
 or earthy material1 a few feet to a few
 hundred feet  in thickness1 covering   
7#b7 a layer or zone many thousands of  
feet1 and  probably many miles1 thick1  
composed of solid rock comparable to    
that  exposed at numerous points on the 
surface1 and 7#c7 a central mass1 to    
which the preceding layers are but a    
shell1 composed of hot1 dense1 and      
rigid rock1 the real nature of which is 
not known by observation4    ,varieties 
of rock in crust4--,if the mantle of    
soil1 subsoil1 and  glacial rubbish were
 stripped from the land1 the surface    
beneath would  be found to be made up of
 a great variety of rocks1 all of which 
may be  grouped into two great classes4 
,about four-fifths of the land surface  
would be of rock arranged in layers1 and
 the other fifth would be of            
crystalline rock1 generally without     
distinct stratification1 and often      
bearing evidence of the effects of high 
temperature4    ,stratified rocks4--,the

 composition of most stratified rocks   
corresponds somewhat closely with the   
composition of sediments now  being     
carried from the land and being         
deposited in the sea4 ,their            
arrangement in layers is the same1 and  
the markings on the surfaces  of the    
layers1 such as ripple-marks1           
rill-marks1 wave-marks1 etc41  are      
identical4 ,furthermore1 the stratified 
rocks of the land1 like  the recent     
sediments of the sea1 frequently contain
 the shells and  skeletons of animals1  
and sometimes the impressions of plants4
 ,most of  the relics of life found in  
the stratified rocks belonged to animals
  or plants which lived in salt water4  
,because of their structure1 their      
composition1 their distinctive markings1
 and the remains of life which  they    
contain1 it is confidently inferred that
 most of the stratified  rocks which lie
 beneath the mantle rock of the land    
were originally  laid down in beds      
beneath the sea1 and that the familiar  

processes of  the present time furnish  
the key to their history4               
,illustration3 ,fig4 #a4--;,beds of     
7,cambrian7 sandstone1 a1 are           
conformable with one another1 but       
unconformable on beds of 7,huronian7    
quartzite1 b1 ,near ,ableman1 ,wis4     
,conformability4--,when the stratified  
rocks exposed by the removal of  the    
mantle rock are examined1 the successive
 beds are sometimes found  to lie on one
 another in regular succession1 showing 
that they were  laid down one after     
another1 without change in the attitude 
of the  surface on which they were      
deposited4 ,such rocks are conformable  
7the beds of series a1 ,fig4 #a74 ,in   
other cases it would be seen that       
certain beds overlie the worn surfaces  
of lower beds1 the layers of  which may 
have a different angle of inclination   
7series a1 ,fig4 #a1  is unconformable  
on series b74 ,such relations show that 
the lower  series of beds was disturbed 
and eroded before the overlying beds    

were  deposited on them4 ,such series of
 rocks are unconformable4    ,relative  
ages4--,the structure and relations of  
rocks lead to  inferences as to their   
relative ages4 ,in the case of          
stratified  rocks it is obvious that    
overlying beds were deposited later than
  those below1 and where there is       
unconformity it is evident that an      
interval of time elapsed between the    
deposition of the unconformable  series4
 ,another and in some respects more     
important means of telling  their order 
of formation is found in the remains of 
life entrapped  in the water-laid       
sediments4 ,whatever life existed in the
 waters  in which the sediments were    
deposited was liable to burial1 and if  
it was possessed of hard parts1 such as 
bones1 teeth1 shells1 hard  integuments1
 etc41 these parts1 or at least their   
impressions1 were  likely to be         
preserved in the sediments4 ,even tracks
 and imprints of  perishable parts are  
sometimes preserved4 ,all these relics1 

which we  call fossils1 give indications
 of the kinds of life which existed     
when the beds were formed4 ,the fossils 
of the youngest beds show that  the life
 which existed when they were deposited 
was quite like that  of the present     
time4 ,the fossils of the next older and
 lower beds  show greater departure from
 present types4 ,this series of changes 
continues downward as lower and lower   
beds are studied1 until beds at         
considerable depths contain no relics of
 existing species but1 in lieu  thereof1
 forms of more primitive types4 ,some of
 these earlier types are  clearly the   
ancestors of more modern forms1 while   
others seem to have  no living          
descendants4 ,going still deeper1 the   
fossils indicate life of  more and more 
primitive types1 until they depart very 
widely from the  living forms1 and seem 
to be but remotely ancestral4 ,so the   
beds may be  followed downward until the
 lowest1 which contain distinct         
evidences of  life1 are reached4    ,it 

should be understood that it is not     
possible to proceed directly  downward  
through the whole succession of bedded  
rocks1 but that the  edges of the       
various beds may be found here and there
 where they have  been brought to the   
surface by warpings or tiltings1 or     
exposed by  the wearing away of the beds
 which once overlay them4 ,the full     
series  of strata is made out only by   
putting together the data gathered      
throughout all lands1 and even when this
 is done an absolutely complete  series 
cannot yet be made out or1 at least1 has
 not been4    ,the crystalline          
rocks4--,the crystalline rocks which    
would appear  if the mantle rock were   
removed are of two types1 igneous and   
metamorphic4 ,igneous rocks may be      
loosely defined as hardened lavas4      
,metamorphic rocks are those which are  
greatly changed from their  original    
condition4 ,either stratified or igneous
 rocks may become  metamorphic4         
,igneous rocks sustain various relations

 to the stratified rocks1 as            
illustrated by ,fig4 #b4 ,from these    
relations it is possible to tell        
something of the order of their         
formation4 ,where the stratified rocks  
are broken through by lavas1 it is      
obvious that the stratified rocks  were 
formed first1 and the lavas intruded    
later4 ,lava sheets intruded  between   
beds of stratified rock can be told from
 those which flowed out  on the surface 
and were subsequently buried1 for in the
 former case the  sedimentary rocks1    
both above and below the igneous rock1  
were affected  by the heat1 while in the
 latter case only those below were so   
affected4    ,illustration3 ,fig4       
#b4--;,diagrammatic representation of   
the relations    of igneous rock to     
stratified rock4 ,the igneous rocks1    
represented in    black1 have been      
forced up from beneath4    ,more        
commonly than otherwise the metamorphic 
rocks 7,fig4 #c7 lie beneath  the       
sedimentary beds and are often broken   

through by the igneous rocks4  ,from    
their position in many places their     
great age may be inferred1 but  locally1
 especially where dynamic action has    
been severe1 relatively  young rocks are
 metamorphic4    ,illustration3 ,fig4   
#c4 ,the figure represents a section of 
the    earth about #ajjj miles long4    
,the unequally thick black line at the  
top represents on something like its    
proper scale the depth of the           
stratified rock4 ,the area below        
represents crystalline rock1 largely    
metamorphic4    ,four great sedimentary 
eras4--,the water-laid series represents
 four  great eras in the history of the 
earth1 as shown by the relics of life   
imbedded in them4 ,beginning with the   
latest1 these are the ,cenozoic  7recent
 life71 during which the life took on   
its modern aspect2 the  ,mesozoic       
7middle life71 during which the life    
bore a medival aspect2  the ,paleozoic  
7ancient life71 during which the life   
belonged to  older types2 and the       

,proterozoic 7earlier life71 during     
which it is  inferred that much life    
prevailed1 though its record is very    
imperfect4  ,it may safely be assumed to
 have been more primitive than that of  
the  ,paleozoic1 as it was earlier4     
,each of these great divisions embraced 
several lesser periods or epochs1 and   
these again are subdivided more  and    
more closely according to the degrees of
 refinement to which  studies are       
carried4 ,the chief of these            
subdivisions are given in the  table on 
page #ai1 and others will come under    
consideration in the  historical        
chapters4    ,in these four great series
 of sedimentary rocks there are1 here   
and  there1 intrusions of igneous rocks1
 and in some places the sedimentary     
beds have been metamorphosed into       
crystalline rocks by heat and  pressure4
 ,this is particularly true in the      
lowest of these series1 the             
,proterozoic1 where a large part of the 
sediment is metamorphosed1 and  where   

there is much igneous rock1 but it is   
still clear that the main  portion of   
this series was originally water-laid   
sediment1 and so it  belongs to the     
sedimentary series rather than the      
,archean1 in which the  sediments are   
the minor rather than the main factor4  
,it has1 however1  usually been classed 
with the ,archean1 and it is certainly  
not always  easy to draw the dividing   
line4 ,in a sense it may be regarded as 
a  transition series4    ,the ,archean  
complex4--,beneath the dominantly       
sedimentary but partly  metamorphic and 
igneous series there is a very complex  
group of rocks  largely of metamorphosed
 igneous origin1 though containing some 
metamorphosed sediments4 ,these extend  
downwards to unknown depths4  ,while all
 the great formations are occasionally  
bent and broken1 these  lowest ones are 
almost everywhere warped1 folded1 and   
contorted1 often  in the most intricate 
way4 ,they have been very generally     
mashed and  sheared by enormous         

pressure1 so that they have become      
foliated1 and  their original character 
is much masked4 ,they therefore form a  
series  of great obscurity and          
complexity4 ,as they are at the bottom  
of the  known series1 they have been    
called the 8,fundamental gneiss0 and the
  8,basement complex10 but as the part  
which we see is not the true base  nor  
the true foundation1 it is safer to call
 them simply the ,archean  7very        
ancient7 complex4 ,as life appears to   
have been present during  a part at     
least of the period of its formation is 
referred to the  ,archeozoic era4       
,illustration3 ,fig4 #d4--;,diagram to  
illustrate the relations of the    five 
great groups of formations4 ,,ar        
,archean1 ,pr  ,proterozoic1    ,p      
,paleozoic1 ,m  ,mesozoic1 ,c           
,cenozoic4    ,beyond and below this    
series1 the structure of the earth is a 
matter  of inference4 ,vast as are the  
preceding series1 they together form    
relatively but a thin shell on the outer

 surface of the globe4    ,the foregoing
 series are diagrammatically expressed  
in ,fig4 #d1 and  systematically        
presented to the eye in the following   
table4                       ,,general  
,,table ,,of ,,geologic ,,divisions4    
,present4                               
,pleistocene4                           
,pliocene4    ,cenozoic       ,miocene4 
,oligocene4                     ,eocene4
                    3 ,transition       
7,arapahoe  and ,denver74               
,upper ,cretaceous4    ,mesozoic        
,lower ,cretaceous 7,comanche or        
,shastan74                              
,jurassic4                              
,triassic4                              
,permian4                     ,coal     
,measures or ,pennsylvanian4            
,subcarboniferous1 or ,mississippian4   
,paleozoic      ,devonian4              
,silurian4                              
,ordovician4                            
,cambrian4                        ,great
 interval4                              

,keweenawan4                            
,interval4    ,proterozoic    ,animikean
 or ,penokean4                          
7,upper ,huronian of some authors74     
,interval4                              
,huronian4                        ,great
 interval4                              
,great ,granitoid ,series4              
7,intrusive in the main1                
,laurentian47    ,archeozoic            
,archean ,complex4  ,great ,schist      
,series4                                
7,mona1 ,kitchi1 ,lower                 
,keewatin1 ,coutchiching1               
,lower ,huronian of some                
authors47    ,the purpose of this       
general survey is to bring the salient  
features  of the earth's structure into 
view preparatory to entering in more    
detail into the study of particular     
processes and special formations  and to
 lay a foundation for the fuller        
apprehension of the successive  stages  
of the history of the earth1 which      
constitutes the chief purpose  of       

geological study4 ,it is now advisable  
to turn to the detailed  consideration  
of individual processes and specific    
structures4 ,the  complexity of the     
actions involved in the history of the  
earth is so  great that such separate   
consideration at the outset is helpful4 
,,chapter ,,ii4                         
,,the ,,atmosphere ,,as ,a ,,geological 
,,agent4      ,while it is convenient to
 regard the lithosphere as the earth    
proper1  and the atmosphere as its      
envelope1 the latter is as truly a part 
of  the planet as the former1 and its   
activities and its history are as  truly
 subjects of geological study as the    
formation of the rocks4 ,this  view is  
in no way vitiated by the fact that the 
special study of the  atmosphere is set 
apart under the name ,meteorology1 for  
in the same  way the special study of   
rocks is set apart under the name       
,petrology1  that of ancient life under 
the name ,paleontology1 and that of     
other  phases of the subject under other

 names4 ,the atmosphere is one of the   
three great formations of the earth1 and
 as a geological factor takes  its place
 beside the hydrosphere and the         
lithosphere4 ,it has played  a part in  
the history of the earth comparable to  
that of the water1  though its mass is  
less and its record more elusive4       
,unsubstantial as  the atmosphere seems 
when contrasted with the liquid and     
solid portions  of the earth1 its       
extreme mobility and its chemical       
activity compensate  for its lightness  
and tenuity1 and give it a function of  
the first  order of importance4    ,the 
atmosphere plays a direct part as 7#a7 a
 mechanical and 7#b7 a  chemical agent1 
and at the same time serves an indirect 
function  in furnishing favorable       
conditions under which 7#c7 solar       
radiation  produces temperature effects1
 and 7#d7 evaporation gives origin  to  
precipitation and stream effects1 and   
furnishes the necessary  conditions for 
land plants and animals1 and the        

important influences  that spring from  
them4    ,this chapter is devoted to the
 work of the atmosphere in these and    
some  less notable phases4 ,the         
consideration of the origin and history 
of the  atmosphere will receive         
attention later4                        
,a4 ,,the ,,atmosphere ,,as ,a ,,direct 
,,agency4                               
,i4 ,mechanical ,work4    ,the          
mechanical work of the atmosphere is    
accomplished chiefly through  its       
movement4 ,a feeble breeze is competent 
to move particles of dust1  and winds of
 moderate velocity to shift sand4       
,exceptionally strong  winds sometimes  
move small pebbles1 but winds of        
sufficient force to  move larger pieces 
of rock are rare4 ,it follows1          
therefore1 that the  impact of the wind 
has little direct effect except on      
surfaces covered  with dust and dry     
sand4    ,the transportation of material
 by the wind is limited by the size  of 
the particles to which it has access4   

,dust particles expose more  surface to 
the wind relative to their mass than    
sand grains4 ,winds  which are unable to
 carry sand may still carry dust1 and   
winds which  are able to shift sand no  
more than a trivial distance may blow   
dust  great distances4    ,the common   
conception of wind as a horizontal      
movement of some part  of the atmosphere
 is not altogether accurate4 ,every     
obstacle against  which wind blows      
causes deflections of its currents1 and 
some of these  deflections are upward4  
,furthermore1 there are exceptional     
winds1  in which the vertical element   
predominates4 ,particles of dust are    
often involved in these upward currents1
 and by them carried to great  heights1 
and in the upper air are transported    
great distances4    ,transportation and 
deposition of dust4#c--,the universality
 of the  transportation of dust by the  
wind is well known4 ,no house1 no room1 
and scarcely a drawer can be so tightly 
closed but that dust enters it1  and the

 movements of dust in the open must be  
much more considerable4  ,the visible   
dustiness of the atmosphere in dry      
regions during  wind-storms is adequate 
and familiar proof of the efficiency of 
the  wind as a transporter of dust4     
,under special circumstances1           
opportunity is afforded for rough       
determinations of the distance and      
height to which wind-blown dust is      
transported4 ,snow taken from           
snow-fields in high mountain regions is 
found to contain a small amount of      
earthy matter4 ,its particles are  often
 found to be in part volcanic1 even when
 the place whence the snow  was taken is
 scores or even hundreds of miles from  
the nearest volcano4  ,there is probably
 no snow-field so high1 or so far from  
volcanoes1 but  that volcanic dust      
reaches it4 ,if this be true of all     
snow-fields1  it is probably true of all
 land surfaces4 ,in the great           
,krakatoa#d  eruptions of #ahhc large   
quantities of volcanic ash 7pulverized  

lava7  were projected to great heights  
into the atmosphere4 ,the coarser       
particles soon settled2 but1 caught by  
the currents of the upper  atmosphere1  
many of the finer particles were        
transported incredible  distances4      
,through all their long journey1 the    
particles of dust were  gradually       
settling from the atmosphere1 but not   
until the dust had  traveled repeatedly 
round the earth did its amount become so
 small as  to cease to make its         
influence felt in the historic red      
sunsets which  it occasioned4#e ,some of
 this dust completed the circuit of the 
earth  in #ae days4    ,in various parts
 of ,kansas and ,nebraska#f there are   
very considerable  beds of volcanic     
dust1 locally as much as #cj feet thick1
 which must  have been transported from 
volcanic vents by the wind1 though there
  are no known centers of volcanic      
action1 past or present1 within some    
hundreds of miles of some of the        
localities where the dust occurs4       

,these beds of volcanic dust1 so far    
from its source1 may serve as an        
illustration of the importance of       
atmospheric movements as a geological   
force4    ,volcanic dust is shot into   
the atmosphere rather than picked up by 
it4 ,dust picked up by the wind is      
perhaps transported not less widely     
than volcanic dust1 but1 after settling1
 its point of origin is less  readily   
determined4 ,it would perhaps be an     
exaggeration to say that  every square  
mile of land surface contains particles 
of dust brought to  it by the wind from 
every other square mile1 but such a     
statement would  probably involve much  
less exaggeration than might at first be
 supposed4    ,examples of extensive    
deposits of dust other than volcanic are
 also  known4 ,in ,china there is an    
extensive earthy formation1 the loess1  
sometimes reaching #a1jjj feet in       
thickness1 which von ,richtofen         
believes to have been deposited by the  
wind4#g ,this conclusion has1  however1 

not passed unchallenged4#h ,the loess of
 some other regions  has been referred  
to the same origin1 and some of it is   
quite certainly  eolian4#i    ,the      
transportation of dust is important     
wherever strong winds blow over  dry    
surfaces1 free or nearly free of        
vegetation1 and composed of earthy      
matter4 ,its effects may be seen in such
 regions as the sage-brush  plains of   
western ,north ,america4 ,the roots of  
the sage-brush hold the  soil           
immediately about them1 but between the 
clumps of brush1 where  there is little 
other vegetation1 the wind has often    
blown away the  soil to such an extent  
that each clump of brush stands up      
several  inches1 or even a foot or two1 
above its surroundings 7,fig4 #e74 ,such
  mounds are often partly due to the    
lodgment of dust about the bushes4      
,illustration3 ,fig4 #e4--,this figure  
shows the effect of sage-brush or       
other similar vegetation in holding sand
 or earth1 or in causing its            

lodgment1 in dry regions4    ,where the 
earthy matter is moist1 the cohesion of 
the particles is  great1 and the wind   
cannot pick them up4 ,furthermore1 if   
the surface  is generally moist1 it is  
likely to be covered with vegetation    
which  protects it against the wind4    
,but even where vegetation is prevalent 
the wind finds many a vulnerable point4 
,thus on the edges of plains  or        
plateaus facing abrupt valleys1 the wind
 attacks the soil from  the side1 and in
 such situations all earthy matter may  
be stripped  from the underlying rock   
for considerable distances from the edge
 of  the cliff 7,fig4 #f74 ,this may be 
seen at numerous points on the lava     
plateaus of ,washington4                
,illustration3 ,fig4 #f4--;,diagram to  
illustrate the way in which    the wind 
sometimes strips the soil from the edge 
of a bluff4 ,this    phenomenon is not  
rare in the basin of the ,columbia      
,river in    ,washington4    ,the       
presence of dust in the upper atmosphere

 during a rain-storm is  sometimes the  
occasion of phenomena which are often   
misinterpreted4 ,if  there be abundant  
dust in the atmosphere through which    
rain-drops or  snowflakes fall1 much of 
it is gathered up by them1 and the water
 is  thereby rendered turbid and the    
snow discolored4 ,here is to be found   
the explanation of 8mud-rain10          
8blood-rain0 7red dust71 etc4    ,since 
dust is carried to a considerable extent
 in the upper atmosphere1  its movements
 and its deposition are little affected 
by obstacles on  the surface of the     
land4 ,a building or a hedge can only   
affect the  lodgment of that part of the
 atmospheric dust which comes in contact
  with it or is swept into its lee4     
,since most obstacles on the surface  of
 the solid part of the earth reach up   
but slight distances into the           
atmosphere1 the dust of the greater part
 of the air settles without  especial   
reference to them1 and is spread more or
 less uniformly over  the surface on    

which it falls4    ,illustration3 ,fig4 
#g4--;,diagram to illustrate the effect 
of an    obstacle on the transportation 
and deposition of sand4 ,the direction  
of    the wind is indicated by the upper
 arrow4 ,the lower arrows represent     
the direction of eddies in the air      
occasioned by the obstacle4 ,if the     
surface in which the obstacle was set   
was originally flat 7dotted    line71   
the sand would tend to be piled up on   
either side at a little    distance from
 the obstacle1 but more to leeward4 ,at 
the same time1    depressions would be  
hollowed out near the obstacle itself   
7see full    line74 7,after ,cornish47  
,much of the dust transported by the    
wind is carried out over seas or  lakes 
and falls into them4 ,by this means1    
sedimentation is doubtless  going on at 
the bottom of the whole ocean1 and at   
the bottoms of all  lakes4 ,while means 
of determining the amount of dust blown 
into the  sea are not at hand1 it is    
safe to say that1 were such             

determinations  possible1 the result1 if
 stated in terms of weight1 would be    
surprising4    ,transportation and      
deposition of sand4--,in its            
transportation by  the wind1 sand is not
 commonly lifted far above the surface  
of the  land1 and its movement is       
therefore more generally interfered with
 by  surface obstacles than is the      
movement of dust4 ,a shrub1 a tree1 a   
fence1 a building1 or even a stone may  
occasion the lodgment of sand  in       
considerable quantity1 though it has    
little effect on the lodgment  of dust4 
,the effect of obstacles is illustrated 
by ,fig4 #g 7see also  ,fig4 #e74 ,if   
the obstacle which occasions the        
lodgment of sand presents  a surface    
which the wind cannot penetrate1 such as
 a wall1 sand is  dropped abundantly on 
its windward side as well as on the     
leeward2  but if it be penetrable1 like 
an open fence1 the lodgment takes place 
chiefly on its leeward side4 ,in        
cultivated regions cases are known      

where1 in a few weeks of dry weather1   
sand has been drifted into lanes  in the
 lee of hedges to the depth of two or   
three feet1 making them  nearly         
impassable to vehicles4    ,formation of
 dunes4--,in contrast with dust         
deposited from the  atmosphere1         
wind-blown sand is commonly aggregated  
into mounds and  ridges in the process  
of lodgment4 ,these mounds and ridges   
are dunes4  ,once a dune is started1 it 
occasions the further lodgment of sand1 
and  is a cause of its own growth4      
,dunes sometimes reach heights of #bjj  
or  #cjj feet1 but they are much more   
commonly no more than #aj or #bj feet in
  height4 ,on plane surfaces1 there is a
 limit in height above which they  do   
not rise1 though the limit is different 
under different conditions4  ,the       
velocity of wind at the bottom of the   
air is not so great as that  higher up1 
and as a dune is built up1 a level is   
presently reached  where the stronger   
upper winds sweep away as much sand as  

is brought to  the top4 ,the very even  
crests of many dune ridges are probably 
to be  accounted for in this way4       
,wind-blown or eolian sand1 not piled up
 in  heaps or ridges1 is somewhat       
widespread1 but does not constitute     
dunes4    ,shapes of dunes4#aj--;,dunes 
may assume the form of ridges or of     
hillocks4 ,the ridges may be transverse 
to the direction of the  prevailing wind
 or parallel with it4 ,where dunes      
assume the form of  hillocks rather than
 ridges1 a group of them may be elongate
 in a  direction parallel to the        
dominant wind1 or at right angles       
thereto4  ,the shape assumed by a dune  
or a group of dunes depends on the      
abundance of the sand1 the strength and 
direction of the wind1 and the  shape of
 the obstacle which occasions the       
lodgment4    ,illustration3 ,fig4       
#h4--;,dune ridges parallel to the      
direction of    the wind4 ,southwest    
part of ,india4 ,scale about #c miles to
 the inch4    7,cornish47               

,illustration3 ,fig4 #i4--;,dune ridges 
transverse to the direction of the      
wind4 ,scale about #c miles to the inch4
 7,cornish47    ,the incipient stages of
 dune formation are readily seen in many
 dry1  sandy regions4 ,the dune is      
likely to start in the lee of some      
obstacle1  and to be elongate in the    
direction of the wind1 especially if the
 wind  be strong relative to the supply 
of sand4 ,this shape is permanently     
preserved if the proper relations       
between the supply of sand and  strength
 and direction of wind are preserved4   
,in the dune region of the  ,indian     
desert#aa the prevailing winds are      
alternately the southwest  and northeast
 monsoons1 the former being the         
stronger4 ,the supply  of sand comes    
from the southwest4 ,near the southwest 
coast the dune  ridges are parallel to  
the direction of the wind 7,fig4 #h72 in
 the  interior1 where the winds are less
 strong1 the dunes are transverse to  it
 7,fig4 #i72 while between the districts

 where these two types prevail          
intermediate forms occur4 ,the          
transverse dune ridges 7,fig4 #i7 are   
said  to be the result of the lateral   
growth and erosion of longitudinal      
dunes4#ab ,in regions of changeable     
winds the shape of the dunes  is subject
 to great variation4 ,dunes are         
sometimes crescentic1 the  convexity    
facing the wind 7,fig4 #aj74            
,illustration3 ,fig4 #aj4--;,crescentic 
dunes in ground-plan1 the    convexities
 facing the wind4 7,bokhara47           
7,walther47    ,along coasts1 dune      
ridges are often transverse to the wind1
 and groups  of dune hillocks are       
frequently elongate in the same         
direction4 ,here  the source of supply  
of the sand is itself an elongate belt1 
often  transverse to the dominant wind1 
and the resulting dunes often have      
great length transverse to the wind4    
,where the wind has strong mastery  over
 the sand1 the longitudinal tendency is 
seen1 even along coasts4#ac             

,illustration3 ,fig4 #aa4--,section of a
 dune showing1 by the dotted    line1   
the steep leeward 7bc7 and gentler      
windward 7ab7 slope4 ,by    reversal of 
the wind the cross-section may be       
altered to the form shown    by the line
 adc4 7,cornish47    ,illustration3     
,fig4 #ab4--;,cross-section of a dune   
showing the profiles    developed by    
scour of the wind on both flanks4       
7,cornish47    ,the shapes of dunes in  
section1 like the shapes in ground-plan1
 depend  on the relative strength and   
constancy of the winds and the supply of
  sand4 ,with constant winds and        
abundant drifting sand1 dunes are steep 
on the lee side 7bc1 ,fig4 #aa71 where  
the angle of slope is the angle  of rest
 for the sand4 ,it rarely exceeds #bc or
 #bd4ad ,under the same  conditions the 
windward slope is relatively gentle 7ab1
 ,fig4 #aa74  ,if the winds be variable 
so that the windward slope of one period
  becomes the leeward slope of another1 
and vice versa1 this form is not        

preserved4 ,thus1 by reversal of the    
wind1 the section abc1 ,fig4 #aa1  may  
be changed to adc4 ,if the winds and the
 supply of sand be equal1  on the       
average1 from opposite directions1 the  
slopes should1 on the  average1 be      
equal1 though perhaps unequal after any 
particular storm4  ,the steep slopes of 
new-made dunes are lost after the sand  
has ceased  to be blown4 ,at some points
 where the winds erode 7scour7 more than
  they deposit1 new profiles are        
developed 7,figs4 #ab and #ac74 ,the    
erosion  profiles may be very irregular 
if the dunes are partially covered with 
vegetation4 ,the effect of vegetation in
 restraining wind erosion is  shown in  
,fig4 #ad1 where plants have preserved a
 remnant of a dune4      ,the           
topographic map4--,since dunes as well  
as other topographic    features are    
conveniently represented on contour     
maps1 and since    such maps will be    
used frequently in the following pages1 
a general    explanation of them is here

 introduced4      8,the features        
represented on the topographic map are  
of three    distinct kinds3 7#a7        
inequalities of surface1 called relief1 
as    plains1 plateaus1 valleys1 hills1 
and mountains2 7#b7 distribution    of  
water1 called drainage1 as streams1     
lakes1 and swamps2 7#c7 the    works of 
man1 called culture1 as roads1          
railroads1 boundaries1    villages1 and 
cities4      ,illustration3 ,fig4       
#ac4--;,diagram showing the outline of  
dunes in      process of destruction4   
,seven ,mile ,beach1 ,n4 ,j4 7,n4 ,j4   
,geol4      ,surv47      ,illustration3 
,fig4 #ad4--;,illustrates the protective
 effect of      vegetation against wind 
erosion4 ,dune ,park1 ,ind4 7,cowles7   
,relief4--,all elevations are measured  
from mean sea-level4 ,the    heights of 
many points are accurately determined1  
and those    which are most important   
are given on the map in figures4 ,it is 
desirable1 however1 to give the         
elevation of all parts of the area      

mapped1 to delineate the horizontal     
outline1 or contour1 of all    slopes1  
and to indicate their grade or degree of
 steepness4 ,this    is done by lines   
connecting points of equal elevation    
above mean    sea-level1 the lines being
 drawn at regular vertical intervals4   
,these lines are called contours1 and   
the uniform vertical space    between   
each two contours is called the contour 
interval4 ,on    the maps of the ,united
 ,states ,geological ,survey the        
contours and    elevations are printed  
in brown 7see ,plate ,,ii74             
,illustration3 ,fig4 #ae4--,sketch and  
map of the same area to      illustrate 
the representation of topography by     
means of contour      lines 7,u4 ,s4    
,geol4 ,surv47      ,the manner in which
 contours express elevation1 form1 and  
grade is    shown in the following      
sketch and corresponding contour map1   
,fig4    #ae4      ,the sketch          
represents a river valley between two   
hills4 ,in the    foreground is the sea1

 with a bay which is partly closed by a 
hooked sand bar4 ,on each side of the   
valley is a terrace4 ,from    the       
terrace on the right a hill rises       
gradually1 while from that    on the    
left the ground ascends steeply in a    
precipice4 ,contrasted    with this     
precipice is the gentle descent of the  
slope at the left4    ,in the map each  
of these features is indicated1 directly
 beneath    its position in the sketch1 
by contours4 ,the following explanation 
may make clearer the manner in which    
contours delineate elevation1    form1  
and grade3      #a4 ,a contour indicates
 approximately a certain height above   
sea-level4 ,in this illustration the    
contour interval is #ej feet2           
therefore the contours are drawn at #ej1
 #ajj1 #aej1 #bjj feet1 and    so on1   
above sea-level4 ,along the contour at  
#bej feet lie all    points of the      
surface #bej feet above sea2 and        
similarly with any    other contour4 ,in
 the space between any two contours are 

found    all elevations above the lower 
and below the higher contour4 ,thus     
the contour at #aej feet falls just     
below the edge of the terrace1    while 
that at #bjj feet lies above the        
terrace2 therefore all points    on the 
terrace are shown to be more than #aej  
but less than #bjj    feet above sea4   
,the summit of the higher hill is stated
 to be #fgj    feet above sea2          
accordingly the contour at #fej feet    
surrounds it4    ,in this illustration  
nearly all the contours are numbered4   
,where    this is not possible1 certain 
contours--say every fifth one--are      
accentuated and numbered2 the heights of
 others may then be    ascertained by   
counting up or down from a numbered     
contour4      #b4 ,contours define the  
forms of slopes4 ,since contours are    
continuous horizontal lines conforming  
to the surface of the    ground1 they   
wind smoothly about smooth surfaces1    
recede into    all rentrant angles of   
ravines1 and project in passing about   

prominences4 ,the relations of contour  
curves and angles to forms of    the    
landscape can be traced in the map and  
sketch4      #c4 ,contours show the     
approximate grade of any slope4 ,the    
vertical    space between two contours  
is the same1 whether they lie along a   
cliff or on a gentle slope2 but to rise 
a given height on a gentle    slope one 
must go farther than on a steep slope1  
and therefore    contours are far apart 
on gentle slopes and near together on   
steep    ones4      ,for a flat or      
gently undulating country a small       
contour interval    is used2 for a steep
 or mountainous country a large interval
 is    necessary4 ,the smallest interval
 used on the atlas sheets of the        
,geological ,survey is #e feet4 ,this is
 used for regions like the              
,mississippi delta and the ,dismal      
,swamp4 ,in mapping great mountain      
masses1 like those in ,colorado1 the    
interval may be #bej feet4 ,for         
intermediate relief contour intervals of

 #aj1 #bj1 #be1 #ej1 and #ajj    feet   
are used4      ,drainage4--,watercourses
 are indicated by blue lines4 ,if the   
streams flow the year round the line is 
drawn unbroken1 but if the    channel is
 dry a part of the year the line is     
broken or dotted4    ,where a stream    
sinks and reappears at the surface1 the 
supposed    underground course is shown 
by a broken blue line4 ,lakes1 marshes1 
and other bodies of water are also shown
 in blue1 by appropriate    conventional
 signs4      ,culture4--,the works of   
man1 such as road1 railroads1 and towns1
    together with boundaries of         
townships1 counties and states1 and     
artificial details1 are printed in      
black40#ae    ,topography of dune       
areas4--,from what has been said1 it is 
clear that  the topography of dune      
regions may vary widely1 but it is      
always  distinctive4 ,where the dunes   
take the form of ridges 7,fig4 #a1 ,pl4 
,,ii71 the ridges are often of          
essentially uniform height and width for

  considerable distances4 ,if there are 
parallel ridges1 they are often         
separated by trough-like depressions4   
,where dunes assume the form of         
hillocks 7,figs4 #b and #c1 ,pl4 ,,ii71 
rather than ridges1 the topography  is  
even more distinctive4 ,in some regions1
 depressions 7basins7 are  associated   
with the dune hillocks4 ,occasionally   
they are hardly less  notable than the  
dunes themselves4 ,a somewhat similar   
association of  hillocks and basins is  
locally developed by other means1 but   
dunes are  made up of sand and usually  
of sand only1 while the composition of  
similarly shaped hillocks and           
depressions shaped by other agencies is 
notably different4      ,in ,fig4 #a1   
,plate ,,ii 7,five ,mile ,beach1 #h     
miles northeast of ,cape    ,may1 ,n4   
,j471 the contour interval is #aj feet4 
,there is here but one    contour line  
7the #aj-;foot contour71 though this    
appears in several    places4 ,since    
this line connects places #aj feet above

 sea-level1    all places between it and
 the sea 7or marsh7 are less than #aj   
feet above the water1 while all places  
within the lines have an    elevation of
 more than #aj feet4 ,none of them      
reaches an elevation    of #bj feet1    
since a #bj-;foot contour does not      
appear4 ,it will be    seen that some of
 the elevations in ,fig4 #a are         
elongate1 while    others have the form 
of mounds4      ,fig4 #b 7,pl4 ,,ii7    
shows dune topography along the         
,arkansas ,river in    ,kansas 7near    
,larned72 ,fig4 #d1 dune topography in  
,nebraska 7,lat4    #db1 ,long4 #ajc71  
not in immediate association with a     
valley or    shore2 and ,fig4 #c shows  
irregular ridge-like dunes at the head  
of    ,lake ,michigan4 ,in ,fig4 #b the 
contour interval is #bj feet4 ,all the  
small hillocks southeast of the river   
are dunes4 ,some of them are            
represented by one contour and some by  
two4 ,the altitude of the    region is  
considerable1 the heavy contour         

representing an elevation    of #bajj   
feet2 but the dunes themselves are      
rarely more than #bj feet    above their
 surroundings4 ,in ,fig4 #d1 where the  
contour interval is    also #bj feet1   
there are1 besides the numerous         
hillocks1 several    depressions        
7basins74 ,these are represented by     
hachures inside the    contour lines4   
,in some cases there are intermittent   
lakes 7blue7 in    the depressions4 ,the
 heavy contour at ,spring ,lakes in this
 figure    is the contour of #dcjj feet4
 ,there are two depression contours     
7#dbhj and #dbfj7 below it4 ,the bottom 
of the depression is therefore    lower 
than #dbfj1 but not so low as #dbdj4 ,in
 ,fig4 #c the contour    interval is #aj
 feet1 and the dune ridges north of     
,miller are more    than #ej feet high4 
,the dune ridges here have helped to    
determine    the position of this branch
 of the ,calumet ,river1 and have       
blocked    its former outlet4 ,the      
present drainage is to the westward4    

,migration of dunes4--,by the continual 
transfer of sand from its  windward to  
its leeward side1 a dune may be moved   
from one place to  another1 though      
continuing to be made up1 in large part1
 of the same  sand4 ,in their migration 
dunes sometimes invade fertile lands1   
causing  so great loss that means are   
devised for stopping them4 ,the simplest
  method 7employed in ,france and       
,holland7 is to help vegetation to get  
a foothold in the sand4 ,the effect of  
the vegetation is to pin the  sand down4
 ,as a dune ridge along a coast travels 
inland1 another may be  formed behind   
it4 ,successions of dune ridges are thus
 sometimes formed4    ,illustration3    
,fig4 #af4--;,diagram illustrating the  
migration of dunes    on the ,kurische  
,nehrung4 7,credner47    ,a remarkable  
instance of the migration of a sand dune
 is recorded  on the ,kurische ,nehrung 
on the north coast of ,germany4 ,the    
,nehrung  consists of a long narrow neck
 of land composed of sand1 lying  off   

the main coast4 ,at the beginning of    
this century there was a  notable dune  
ridge on one side4 ,since that time it  
has migrated a  considerable distance1  
and in its migration it has been brought
 into  the relationships illustrated in 
the accompanying diagrams 7,fig4 #af74  
,in #ahjj the dune ridge was on one side
 of a church1 which was then in  use4   
,in #ahci the ridge had been so far     
shifted to the leeward as to  completely
 bury the church1 and in #ahfi1 its     
migration had progressed  so far as to  
again discover the building4#af         
,illustration3 ,fig4 #ag4--,migration of
 dunes into a timbered region4    ,dune 
,park1 ,ind4 ,head of ,lake ,michigan4  
7,meyers47    ,when dunes migrate into a
 timbered region they bury and kill the 
trees  7,fig4 #ag74 ,in one instance on 
the coast of ,prussia a tall pine       
forest1  covering hundreds of acres1 was
 destroyed during the brief period      
between #ahjd and #ahbg4ag ,at some     
points in ,new ,jersey orchards have    

been so far buried within the lifetime  
of their owners that only the  tops of  
the highest trees are exposed4 ,trees   
and other objects once  buried may be   
again discovered by farther migration of
 the sand 7,figs4  #ah and #ai74ah      
,illustration3 ,fig4 #ah4--;,a          
resurrected forest4 ,the dune sand after
    burying and killing the timber has  
been shifted beyond it4 ,dune ,park4    
,ind4 7,meyers47    ,eolian sand1 not   
aggregated into distinct dunes1 is often
 destructive4  ,even valleys and cities 
are sometimes buried by it4 ,drifting   
sands had  so completely buried ,nineveh
 two centuries after its destruction    
that  its site was unknown4             
,distribution of dunes4--,dunes are     
likely to be developed wherever dry     
sand is exposed to the wind4 ,their     
favorite situations are the dry and     
sandy shores of lakes and seas1 sandy   
valleys1 and arid sandy plains4         
,along coasts1 dunes are likely to be   
extensively developed only where  the   

prevailing winds are on shore4 ,thus    
about ,lake ,michigan1 where the        
prevailing winds are from the west1     
dunes are abundant and large on the     
east shore1 and but few and small on the
 west4 ,in shallow water1 shore         
currents and storm waves often build up 
a reef of sand a little above  the      
normal level of the water4 ,when the    
waves subside1 the sand dries  and the  
wind heaps it up into dunes4 ,this      
sequence of events is in  progress at   
many points on the ,atlantic ,coast4    
,sandy ,hook1 ,new ,jersey1  and the    
8beaches0 farther south started as      
barrier ridges4 ,when the  waves had    
built them above normal water-level1 the
 wind re-worked the  sand1 piling it up 
into mounds and hillocks 7,fig4 #a1 ,pl4
 ,,ii74 ,such dune  belts a little off  
shore are sometimes turned to good      
account4 ,they are  usually separated   
from the mainland by a shallow lagoon4  
,where land  is valuable1 the lagoon is 
sometimes filled in1 making new land1   

thus  anticipating the result which     
nature would achieve more slowly4 ,this 
has been done at some points on the     
western coast of ,europe4               
,illustration3 ,fig4 #ai4--,migration of
 dune sand exposing bones in a          
cemetery4 ,hatteras ,island1 ,n4 ,c4    
7,collier ,cobb47    ,dunes are likely  
to occur along stream valleys 7,fig4 #b1
 ,pl4 ,,ii71 if  their bottoms or slopes
 are of sand1 and not covered by        
vegetation4  ,dunes along valleys are   
usually on the side toward which the    
prevailing winds blow4 ,thus they are   
more common on the east side of  the    
,mississippi than on the west4 ,dunes   
may be formed in the valley  bottoms1   
but the sand is often blown up out of   
the valley and lodged on  the bluffs    
above4    ,apart from these special     
classes of situations1 any sandy region 
the  surface of which is dry is likely  
to have its surface material shifted  by
 the wind and piled up into dune ridges 
or hillocks 7,fig4 #d1 ,pl4  ,,ii74     

,dunes probably reach their greatest    
development in the ,sahara1  where some 
of them take the form of hillocks1 and  
some the form of  ridges4 ,travelers in 
that region report that dune ridges are 
sometimes  encountered the faces of     
which are so high and steep as to be    
difficult  of ascent1 and that parties  
have been obliged to travel miles along 
their bases before finding a break where
 crossing was practicable4              
,illustration3 ,fig4                    
#bj4--,wind-ripples4 7,cross1 ,u4 ,s4   
,geol4 ,surv47    ,wind-ripples4--,the  
surface of the dry sand over which the  
wind has  blown for a few hours is      
likely to be marked with ripples 7,fig4 
#bj7 similar to those made on a sandy   
bottom beneath shallow water1  under the
 influence of waves4 ,like ripple marks 
made by the water1  wind-ripples have   
one side 7the lee7 steeper than the     
other4 ,while the  ripples are1 as a    
rule1 but a fraction of an inch high1   
they throw  much light on the origin of 

the great dune ridges4 ,if the ripples  
be watched closely during the progress  
of a wind-storm1 they are  found        
gradually to shift their position4 ,sand
 is blown up the gentler  windward slope
 to the crest of the ridge and falls    
down on the other  side4 ,the moment it 
falls below the crest of the ridge to   
leeward1 it  is protected against the   
wind1 and is likely to lodge4 ,wear on  
the  windward side is about equal to    
deposition on the leeward1 and the      
result is the orderly progression of the
 ripples in the direction in  which the 
wind is blowing1 just as in the case of 
dune ridges4    ,abrasion by the        
wind4--,while the effect of the wind on 
sandy and dusty  surfaces may be        
considerable1 its effect on solid rock  
is relatively  slight and accomplished1 
not by its own impact1 but by that of   
the  material it carries4 ,the effect of
 blown sand on rock surfaces over and   
against which it is driven is perhaps   
best understood by recalling the        

effects of artificial sand-blasts1 by   
means of which glass is etched4  ,in a  
region where sand is blowing1 exposed   
surfaces of rock suffer  from a         
multitude of blows struck by the sand   
grains in transit4 ,the  result is that 
such rock surfaces are worn1 and worn in
 a way peculiar  to the agency          
accomplishing the work4 ,if the rock be 
made up of lamin  which are of unequal  
hardness1 the blown sand digs out the   
softer ones1  leaving the harder        
projecting as ridges between them4      
,adjacent masses  of harder and softer  
rock of whatever thickness are similarly
 affected4  ,the sculpturing thus       
effected on projecting masses of rock is
 often  picturesque and striking 7,figs4
 #ba and #bb71 and is most common in    
arid  regions4 ,details of wind-carving 
are shown in ,fig4 #bc4                 
,illustration3 ,fig4 #ba4--,wind-carved 
rock4 7,green47      ,illustration3     
,,plate ,,ii4      ,fig4 #a4 ,,new      
,,jersey4      ,u4 ,s4 ,geol4 ,surv4    

,fig4 #b4 ,,kansas4      ,u4 ,s4 ,geol4 
,surv4      ,fig4 #c4 ,,indiana4        
,u4 ,s4 ,geol4 ,surv4      ,fig4 #d4    
,,nebraska4      ,u4 ,s4 ,geol4 ,surv4  
,sand drifted over loose stones lying on
 the surface often develops  flat or    
flattish faces or facets on them4 ,these
 facets are likely to  be three in      
number1 and the exposed portion of the  
stone is likely to  develop a sort of   
pyramidal shape1 the three flattish     
surfaces being  mutually limited by     
tolerably well-defined lines 7,fig4     
#bd74 ,thus arise  the three-faceted    
stones 7,dreikanter of the ,germans7    
commonly seen  where sands have been    
long in movement4    ,illustration3     
,fig4 #bb4--,wind-carved hillock of     
cross-bedded    sandstone4 ,missouri    
,river1 ,montana4 7,calhoun1 ,u4 ,s4 ,g4
 ,s47    ,not only does the drifting    
sand wear the surface over which it     
passes  and against which it strikes1   
but the grains themselves are worn in   
the  process4 ,they are liable to be    

broken as they strike rock surfaces1 and
  they are likely to strike one another 
in the atmosphere4 ,in both cases  they 
are subject to wear1 and so to reduction
 to a finer and finer  state4    ,the   
erosion accomplished by the wind is     
therefore of various sorts4 ,the  impact
 of the wind itself picks up the fine   
materials which are already  loosened1  
thus wearing down the surface from which
 they are removed2  the materials picked
 up wear the rock surfaces against which
 they are  blown1 and the transported   
materials themselves suffer reduction in
  transit4    ,effects of wind on       
plants4--,another effect of wind work is
 seen in the  uprooting of trees 7,fig4 
#be74 ,the uprooting disturbs the       
surface in  such a way as to make loose 
earth more readily accessible to wind   
and  water4 ,the uprooting of trees on  
steep slopes often causes the descent   
of considerable quantities of loose rock
 and soil4 ,again1 organisms  of various
 sorts 7certain types of seeds1 germs1  

etc471 as well as  dust and sand1 are   
extensively transported by the wind4    
,while this is  important biologically  
its geological effects are remote4      
,illustration3 ,fig4 #bc4--;,figure     
showing details of wind-carving on      
rock surface 7rhyolite74 ,mono ,valley1 
,california4    ,illustration3 ,fig4    
#bd4--,wind-worn stones 7,dreikanter74  
,illustration3 ,fig4 #be4--,shows the   
disturbance of surface earth and        
rocks by upturning of trees4 7,darton1  
,u4 ,s4 ,geol4 ,surv47    ,indirect     
effects of the wind4--,other dynamic    
processes are called into  being or     
stimulated by the atmosphere4 ,winds    
generate both waves and  currents1 and  
both are effective agents in geological 
work4 ,the results  of their activities 
are discussed elsewhere4                
,,ii4 ,the ,chemical ,work of the       
,atmosphere4    ,the chemical work of   
the atmosphere 7including solution and  
precipitation from solution7 is         
principally accomplished in connection  

with water1 a dry atmosphere having     
relatively little direct chemical       
effect on rock or soils4                
,precipitation from solution4--,the     
water in the soil is constantly         
evaporating4 ,such substances as it     
contains in solution are deposited      
where the water evaporates1 and where   
evaporation is long continued  without  
re-solution of the substances deposited1
 the surface becomes  coated with an    
efflorescence of mineral matter4        
,conspicuous examples  are found in the 
alkali plains of certain areas in the   
western part of  the ,united ,states4   
,since the alkaline efflorescence is the
 result of  evaporation it is connected 
with the atmosphere1 but the material of
  the efflorescence was brought to its  
present position by water4 ,the         
principle involved is illustrated by the
 white efflorescence which  frequently  
appears on brick walls during the dry   
days which follow a  drenching rain4    
,the water penetrates the brick and     

mortar and dissolves  something of their
 substance1 and when it is evaporated   
from the  surface the material in       
solution is left behind4    ,in arid    
regions the deposition of substances    
other than alkali is  common4 ,the      
percolating waters dissolve whatever is 
soluble1 and when  they evaporate their 
mineral content is left4 ,the pebbles   
and stones of  the arid plains have in  
many places become heavily coated with  
mineral  matter deposited in this way1  
and not infrequently cemented into      
conglomerate4 ,one of the commonest     
mineral substances found in such        
situations is lime carbonate4 ,in some  
cases it was doubtless derived  by      
solution from limestone beds beneath the
 surface1 but this is not  always the   
case4 ,it often encrusts the bits of    
lava on lava plains  where it can hardly
 have been derived from limestone4 ,the 
faces of  cliffs of granite or gneiss1  
hundreds and even thousands of feet     
above  all other sorts of rock1#ai are  

sometimes spotted with patches of lime  
carbonate4 ,in the first case the lime  
carbonate was derived by chemical       
change from the lava1 and in the second1
 from the granite or gneiss  7see       
,carbonation below71 but its present    
position is the result of  evaporation4 
,oxidation4--,in the presence of        
moisture the oxygen of the air enters   
into combination with various elements  
of the soil and rocks4 ,this is         
oxidation4 ,no other common mineral     
substance shows the results of          
oxidation so quickly and so distinctly  
as iron4 ,the oxidized portion  is loose
 and friable1 and a mass of iron exposed
 to a moist atmosphere  will ultimately 
crumble away4 ,this change is comparable
 to other less  obvious changes taking  
place in many minerals at and below the 
surface4  ,oxidation generally involves 
the disintegration of the rock          
concerned4  ,its effects in this        
direction will be referred to in other  
connections4    ,carbonation4--,the     

production of lime carbonate from rock  
containing  calcium compounds1 but not  
in the form of carbonates1 is known as  
carbonation1 and is one of the important
 chemical changes effected  by the      
carbon dioxide of the atmosphere in     
coperation with water4 ,in  the process 
of carbonation the original minerals of 
complex composition  are decomposed and 
simpler ones usually formed4 ,volumetric
 changes are  involved1 which often lead
 to the disruption of the rock 7see     
,ground  water74 ,furthermore1          
carbonates are among the more soluble   
minerals1  and their production         
therefore brings some of the rock       
materials into  a soluble condition1 and
 their extraction through solution tends
 still  further to disintegrate the     
rock4 ,the carbonation of crystalline   
rocks  is therefore a disintegrating    
process1 and will be considered further 
in its many concrete applications4      
,other chemical changes4--,a third      
chemical process which often            

accompanies oxidation and carbonation is
 hydration4 ,this is effected  by water 
rather than by air1 and will be         
considered in that connection4  ,in     
general it leads to the disintegration  
of the minerals and rocks  affected4    
,the chemical effects of nitric acid1   
etc41 developed through  the agency of  
atmospheric electricity1 and the        
corresponding effects  of the gases and 
vapors which issue from volcanoes1 many 
of them  chemically active1 are to be   
mentioned in this connection4           
,conditions favorable for chemical      
changes4--,conditions are not           
everywhere equally favorable for the    
chemical work of the atmosphere4  ,in   
general1 high temperatures facilitate   
chemical action1 and1 other  things     
being equal1 rocks are more readily     
decomposed by atmospheric  action in    
warm than in cold regions4 ,chemical    
activity is probably  greater where the 
climate is continuously warm than where 
there are  great changes of temperature4

 ,changes of temperature1 on the other  
hand1 tend to disrupt rock1 and thus    
increase the amount of surface  exposed 
to chemical change4 ,since nearly all   
the chemical changes  worked by the     
atmosphere on the rocks are increased by
 the presence of  moisture1 the chemical
 activity of the atmosphere is greater  
in moist  than in dry regions4          
,b4 ,,the ,,atmosphere ,,as ,a          
,,conditioning ,,agency4    ,the most   
obvious mechanical work of the          
atmosphere is effected by the  wind1 but
 mechanical results of great importance1
 conditioned by the  atmosphere1 are    
also effected when the air is still4    
,i4 ,temperature ,effects4    ,when the 
sun shines on bare rock its surface is  
heated and expanded1  and the expanded  
particles crowd one another with great  
force4 ,since  rock is a poor conductor 
of heat its surface is heated and       
expanded  notably more than parts       
beneath the surface4 ,it follows that   
strains  are set up between the expanded

 outer portion and the cooler and less  
expanded parts within4 ,in the cooling  
of the same rock mass it is the         
outermost portion which cools first and 
fastest1 and1 contracting as  it cools1 
strains are again set up between the    
outer part1 which is  cooled more1 and  
the inner part1 which is cooled less4   
,the result may  be illustrated by the  
effect of cold water on hot glass1 or of
 hot  water on cold glass4 ,in either   
case the fracture is the result of the  
sudden and considerable differential    
expansion or contraction4 ,since  the   
heating and cooling of rock are much    
slower than the heating and  cooling of 
glass under the conditions mentioned1   
the rupturing effects  are less         
conspicuous1 but none the less real4    
,the actual effects  of temperature     
changes are illustrated by familiar     
phenomena4 ,the  surface portions of    
bowlders exposed to the sun are         
frequently seen  to be shelling off     
7,fig4 #bf74 ,the loosened concentric   

shells may be a  fraction of an inch1 or
 sometimes even several inches in       
thickness4  ,this process of exfoliation
 affects not only bowlders1 but bare    
rock surfaces wherever exposed to the   
sun 7,figs4 #bg1 #bh74 ,it is often     
conspicuous on the faces of cliffs4     
,illustration3 ,fig4                    
#bf4--;,exfoliation4 ,a bowlder of      
weathering1 the    rock being granite4  
,wichita ,mountains1 ,oklahoma4         
,illustration3 ,fig4 #bg4--;,a weathered
 summit of granite in the ,wichita      
,mountains4 ,oklahoma4 7,willis1 ,u4 ,s4
 ,geol4 ,surv47    ,several conditions1 
some of which are connected with the    
atmosphere and  some with the rock1     
determine the efficiency of this        
process4 ,since  the breaking of the    
rock results from the expansion and     
contraction  due to its changes of      
temperature1 it follows that1 other     
things being  equal1 the greater the    
change1 the greater the breaking2 but   
the  suddenness of the temperature      

change is even more important than its  
amount4 ,it follows that great daily1   
rather than great annual1 changes  of   
temperature#bj favor rock-breaking1     
though with changes of a given          
frequency their effectiveness is greater
 the greater their range4 ,a  partial   
exception to this generalization should 
be noted4 ,if abundant  moisture is     
present in the pores and cracks of the  
rock a change of  temperature from #de  
to #ce 7,fahr47 might be far less       
effective in  breaking the rock than a  
change from #ce to #be in the same time1
 for  in the latter case the sudden and 
very considerable expansion 7about      
one-tenth7 which water undergoes on     
freezing is brought into play4 ,this    
may be called the wedge-work of ice4    
,the daily range of temperature  is     
influenced especially by latitude1      
altitude1 and humidity4 ,other  things  
being equal1 the greatest daily ranges  
of temperature occur  in high-temperate 
latitudes1 though to this general       

statement there  are local exceptions1  
depending on other conditions4 ,high    
altitudes  favor great daily ranges of  
temperature1 so far as the rock surface 
is concerned 7see ,figs4 #bi1 #cj71 for 
though the rock becomes heated  during  
the sunny day1 the thinness and dryness 
of the atmosphere allow  its heat to    
radiate rapidly at night4 ,here1 too1   
the daily range of  temperature is      
likely to bring the wedge-work of ice   
into play4 ,since  the south side of a  
mountain 7in the northern hemisphere7 is
 heated  more than the north1 it is     
subject to the greater daily range of   
temperature1 and the rock on this side  
suffers the greater disruption4         
,similarly1 rock surfaces on which the  
sun shines daily are subject to  greater
 disruption than those much shielded by 
clouds4 ,isolated peaks1  because of    
their greater exposure1 are subject to  
rather greater daily  ranges of         
temperature than plateaus of the same   
elevation4    ,illustration3 ,fig4      

#bh4--;,exfoliation on a mountain slope4
 ,mt4    ,starr-,king 7,cal47 from the  
north4    ,the daily range of           
temperature is also influenced by       
humidity4 ,because  of the effect of    
water vapor in the atmosphere on        
insolation and  radiation1 a rock       
surface becomes hotter in the day and   
cooler at night  beneath a dry          
atmosphere than beneath a moist one4    
,aridity therefore  favors the          
disruption of rock by changing          
temperatures4    ,turning from the      
conditions of the atmosphere which      
affect the  disruption of rock to the   
conditions of the rock which influence  
the  same process1 several points are to
 be noted4 ,in the first place1 the     
disrupting effects of changes of        
temperature are slight or nil where  the
 solid rock is protected by soil1 clay1 
sand1 gravel1 snow1 or other  incoherent
 material4 ,if the constituent parts of 
the loose material are  coarse1 like    
bowlders1 their surfaces are affected   

like those of larger  bodies of rock4   
,the color of rock1 its texture and its 
composition1  also influence its range  
of daily temperature by influencing     
absorption  and conduction4             
,dark-colored rocks absorb more heat    
than light-colored  ones1 and compact   
rocks are better conductors than porous 
ones4 ,great  absorption and slow       
conduction favor disruption4 ,a given   
range of  temperature is unequally      
effective on rocks of different mineral 
composition4 ,in general crystalline    
rocks 7igneous and metamorphic7 are     
more subject to disruption by this means
 than sedimentary rocks1 partly  because
 they are more compact1 but especially  
because they are made up  of aggregates 
of crystals of different minerals which1
 under changes of  temperature1 expand  
and contract at different rates1 while  
the common  sedimentary rocks are made  
up largely of numerous particles of one 
mineral4    ,illustration3 ,fig4        
#bi4--,top of ,notch ,peak1 ,bighorn    

,mountains1 ,wyo4    ,shows the         
thoroughly broken character of the rock 
on the summit1 the    absence of soil1  
vegetation1 etc4 7,kmmel47              
,illustration3 ,fig4 #cj4--;,a detail   
from ,fig4 #bi showing the size of the  
rock blocks4 7,kmmel47    ,illustration3
 ,fig4 #ca4--,peak north of ,kearsarge  
,pass1 the ,sierras4    ,shows the way  
in which serrate peaks break up into    
angular blocks4    ,the freezing of     
water in the pores of rock is effective 
in disrupting  them only when the pores 
are essentially full at the time of     
freezing4  ,otherwise there is room for 
the expansion attending the freezing4   
,if  the pores of the rock are large1   
the expansion on freezing may force  out
 sufficient water to balance the        
increase of volume1 even though the     
rock was completely saturated4 ,if the  
pores be very small the water  passes   
out less readily1 and if the rock is    
saturated1 freezing is more  likely to  
be attended with disruption4#ba    ,in  

view of these considerations the        
breaking of rock by changes  of         
temperature should be greatest on the   
bare slopes of isolated  elevations of  
crystalline rock1 where the temperature 
conditions of  temperate latitudes      
prevail1 and where the atmosphere is    
relatively  free from moisture4 ,all    
these conditions are not often found in 
one  place1 but the disrupting effects  
of changing temperatures are best  seen 
where several of them are associated    
7,figs4 #bi1 #cj1 and #ca74    ,the     
importance of this method of            
rock-breaking has rarely been           
appreciated except by those who have    
worked in high and dry regions4         
,climbers of high mountains know that   
almost every high peak is covered  with 
broken rock to such an extent as to make
 its ascent dangerous to  the           
uninitiated4 ,high serrate peaks1       
especially of crystalline rock1  are1 as
 a rule1 literally crumbling to pieces  
7,fig4 #ca74 ,the piles  of talus which 

lie at the bases of steep mountain      
slopes are often  hundreds of feet in   
height1 and their materials are often in
 large part  the result of the process  
here under discussion4 ,in mountain     
regions  where atmospheric conditions   
favor sudden changes of temperature1 the
  sharp reports of the disruption of    
rock masses are often heard4 ,masses  of
 rock1 scores and even hundreds of      
pounds in weight1 are frequently  thus  
detached and started on their downward  
course4#bb ,small pieces  of rock are of
 course much more commonly broken off   
than large ones4  ,the disruption of    
rock by changes of temperature is not   
usually the  result of a single change  
of temperature1 but rather of many      
successive  expansions and contractions4
    ,the sharp needle-like peaks which  
mark the summits of most high  mountain 
ranges 7,fig4 #cb7 are largely developed
 by the process here  outlined4 ,the    
altitude at which the serrate topography
 appears varies  with the latitude1     

being1 as a rule1 higher in low         
latitudes and lower  in high4 ,but even 
in the same latitude it varies notably  
with the  isolation of the mountains and
 with the aridity of the climate4 ,thus 
within the ,united ,states the sharply  
serrate summits appear in some  places1 
as in ,washington and ,oregon1 at       
altitudes of #fjjj to #aj1jjj  feet1    
while in the isolated ,wichita range of 
,oklahoma1 much farther  south1 but in a
 much drier climate1 the same sort of   
topography is  developed at altitudes of
 #bejj to #cjjj feet4    ,even in low   
latitudes and moist climates the effects
 of temperature  changes are often seen4
 ,thin beds of limestone at the bottom  
of  quarries are sometimes so expanded  
by the heat of the sun as to arch up    
and break4#bc ,in desert and arid       
regions1#bd whatever the altitude1  the 
effects of temperature changes are often
 striking4    ,illustration3 ,fig4      
#cb4--,serrate peaks of granitic rock in
 ,black    ,hills4 7,darton1 ,u4 ,s4    

,geol4 ,surv47    ,the disruption of    
rock by changes of temperature is one   
phase of  weathering4 ,it tends to the  
formation of a mantle of rock waste1    
which1  were it not removed1 would soon 
completely cover the solid rock beneath 
and protect it from further disruption  
by heating and cooling2 but the  loose  
material thus produced becomes an easy  
prey to running water1  so that the work
 of the atmosphere prepares the way for 
that of other  eroding agencies4        
,,ii4 ,evaporation and ,precipitation4  
,perhaps the most important work of the 
atmosphere as a dynamic  agent lies in  
its function as the medium for the      
circulation and  distribution of water4 
,atmospheric temperature is the primary 
factor governing evaporation1 an        
important factor in the circulation  of 
the vapor after it is formed1 and       
controls its condensation and           
precipitation4    ,the average amount of
 annual precipitation on the land is    
variously  estimated at from forty to   

sixty inches1 the lesser figure being   
probably more nearly correct4 ,since    
much of this water falls at high        
altitudes1 the work which it            
accomplishes in getting back to the sea 
is great4 ,the water which falls on the 
land1 if withdrawn wholly from  the     
ocean1 would exhaust that body of water 
in #aj1jjj to #ae1jjj years  if none of 
it returned4 ,the work of evaporation is
 of course not done  by the atmosphere1 
though the atmosphere determines the    
effect of the  solar energy which does  
the work4#be    ,the precipitation is   
distributed with great inequality1 and  
this  inequality affects both the rain  
and the snow4 ,some regions have heavy  
precipitation and some light2 some      
regions have much rain and little  snow2
 others have much snow and little rain2 
others have rain and no  snow1 and still
 others have snow and little or no rain4
 ,the amount and  distribution of rain  
and snow determine the size and         
distribution of  streams and glaciers1  

and streams and glaciers are the most   
important  agencies modifying the       
surface of the land4    ,it is          
impossible to separate sharply the      
geologic work of the water of  the      
atmosphere from that of other waters2   
but so long as moisture is in  the      
atmosphere 7including the time of its   
precipitation7 its effects  are best    
considered in connection with the       
atmosphere4    ,the mechanical work of  
the rain4--,in falling the rain washes  
the  atmosphere1 taking from it much of 
the dust1 spores1 etc41 which the  winds
 have lifted from the surface of the dry
 land4 ,not only this1  but in passing  
through the atmosphere the water        
dissolves some of its  gases1 and       
perhaps particles of soluble solid      
matter4 ,when therefore  the falling    
water reaches the surface of the land it
 is no longer pure1  and some of the    
gases it has taken up in its descent    
enable it to  dissolve various mineral  
matters on which pure water has little  

effect4    ,as it falls on the surface  
of the land the rain produces various   
effects of a mechanical nature4 ,in the 
first place1 it leaves on the  surface  
the solid matter taken from the air4    
,the amount of material1  thus added to 
any given region in any particular      
shower is trivial1  but in the course of
 long periods of time the total amount  
of material  washed out of the air must 
be very great4    ,every rain-drop      
strikes a blow4 ,if the drops fall on   
vegetation1  they have little effect1   
but if they fall on sand or unprotected 
earthy matter they cause movements of   
the particles on one another1  and this 
movement involves friction and wear4    
,while the results thus  effected are   
inconsiderable in any brief period of   
time1 they are not  so insignificant    
when the long periods of the earth's    
history are  considered4    ,clayey     
soils contract and often crack on       
drying4 ,falling on such a soil  when it
 is dry the rain causes it to expand1   

and the cracks are healed  by lateral   
swelling4 ,the same soils are baked     
under the influence of  the sun1 and    
when in this condition are softened and 
made more mobile  by the falling of     
rain4 ,under the influence of the       
expansion and  contraction occasioned by
 wetting and drying1 the soils and      
earths on  slopes creep slowly downward4
 ,when rain falls on dry sand or dust   
the  cohesion is at once increased1 and 
shifting by the wind is temporarily     
stopped4    ,after the water has fallen 
on the land its further work cannot be  
looked upon as a part of the work of the
 atmosphere2 but any conception  of the 
geological work of the atmosphere which 
did not recognize the  fact that the    
waters of the land have come through the
 atmosphere would  be inadequate4 ,the  
work of the water after it has been     
precipitated  from the atmosphere must  
be considered in another chapter4       
,,iii4 ,effects of ,electricity4        
,another dynamic effect conditioned by  

the atmosphere is that produced  by     
lightning4 ,in the aggregate this result
 is inconsequential2 yet  instances are 
known where large bodies of rock have   
been fractured by  a stroke of          
lightning1 and masses many tons in      
weight have sometimes  been moved       
appreciable distances4 ,incipient fusion
 in very limited  spots is also known to
 have been induced by lightning4 ,where 
it strikes  sand it often fuses the sand
 for a short distance1 and1 on cooling1 
the partially fused material is         
consolidated1 forming a little tube or  
irregular rod 7a fulgurite7 of partially
 glassy matter4 ,fulgurites  are usually
 only a few inches in length1 and more  
commonly than  otherwise a fraction of  
an inch in diameter4 ,strictly speaking 
these  results are the effect of the    
electricity of the atmosphere rather    
than of the atmosphere itself1 but they 
are best mentioned in this  connection4 
,allusion has already been made to the  
chemical changes in the  atmosphere     

occasioned by electric discharges4      
,illustration3 ,fig4 #cc4--,stratified  
jointed rock in process of              
weathering4 7,cross1 ,u4 ,s4 ,geol4     
,surv47    ,illustration3 ,fig4         
#cd4--,represents a later stage of the  
processes    illustrated by ,fig4 #cc4  
7,darton1 ,u4 ,s4 ,geol4 ,surv47        
,,summary4    ,weathering4--,the result 
of all atmospheric processes1 whether   
physical  or chemical1 by which surface 
rock is disrupted1 decomposed or in any 
way loosened1 is weathering4 ,this      
convenient term also includes  similar  
results effected by ground water1       
plants1 etc4 ,the tendency  of          
weathering is to produce a mantle of    
residuary earth over solid  rock4       
,weathering by mechanical means tends to
 produce material which1  though in a   
finer state of division1 is still like  
the original rock  in chemical          
composition4 ,weathering by chemical    
means tends to produce  a mantle made up
 chiefly of the less soluble parts of   

the rock from  which it was derived4    
,all processes of weathering prepare    
material for  transportation by wind and
 water4    ,illustration3 ,fig          
#ce4--;,details of a weathered rock     
surface1 due    partly to wind work and 
partly to solution4 ,the particular     
phase    of weathering illustrated by   
this figure is known as 8honeycomb0     
weathering4 7,gilbert1 ,u4 ,s4 ,geol4   
,surv47    ,many considerations         
determine the thickness which the mantle
 of  weathered rock 7mantle rock7       
attains4 ,some of these considerations  
have  to do with the atmosphere1 and    
some with drainage4 ,since the latter   
are1 on the whole1 more important1 this 
matter will be discussed in  connection 
with the work of water 7,chapters ,,iii 
and ,,iv74                              
,,chapter ,,iii4                        
,,the ,,work ,,of ,,running ,,water4    
,familiar phenomena1 both of land and   
sea1 reveal the constant activity  and  
importance of water as a geologic agent4

 ,even when there is no  precipitation  
the moisture in the air influences its  
activity in  certain ways4 ,just as iron
 8rusts0 more readily in moist air than 
in dry1 so changes in other mineral     
substances are influenced by            
atmospheric humidity4 ,where            
precipitation takes place the results   
are  more obvious4 ,the passing shower  
works changes in the surface of the     
land1 striking in proportion to the rate
 and amount of precipitation4  ,the     
rains feed the streams1 and every stream
 is modifying its bed1 and  with        
increasing rapidity as its current is   
swollen4 ,even the moisture  which is   
precipitated as snow works its          
appropriate results4 ,before it  melts  
it protects the surface against other   
agents of change2 but if  it accumulates
 in sufficient quantity in appropriate  
situations1 it  may give rise to        
avalanches and glaciers1 which1 like    
running water1  degrade the surface over
 which they pass4    ,a part of the     

water which falls as rain1 and a part of
 that which  results from the melting of
 snow and ice1 sinks into the soil and  
into  the rock below1 becoming ground   
water4 ,it is this ground water which   
especially justifies the name           
hydrosphere1 often applied to the       
waters of the earth1 for it literally   
forms a spherical layer in the  outer   
portion of the solid part of the earth4 
,during the stay of the  water beneath  
the surface it effects changes in the   
rocks through which  it passes1         
dissolving mineral matter here and      
depositing it there1  substituting one  
substance for another in this place1 and
 effecting new  chemical combinations in
 that4 ,slow as these processes are1    
they have  worked wondrous changes in   
the course of the earth's history4      
,when the waters are gathered together  
in ponds1 lakes1 and oceans1 they  are  
still active1 and the results of their  
activity are seen along the  shores1    
where winds and waves produce their     

chiefest effects4 ,even the  ocean      
currents1 far from land1 and the        
processes of the deep sea1 are  not     
without their effect on the course of   
geological history4    ,the work of the 
surface waters1 ground 7underground7    
waters1  standing waters1 and ice will  
be considered in order4                 
,,rain ,,and ,,river ,,erosion4    ,rain
 and river erosion began when the first 
rains fell on land  surfaces4 ,neither  
the location nor the nature of the first
 land surface  is known4 ,there is      
little reason to believe that the ocean 
was ever  universal1 but there is reason
 to believe that most land areas have at
  some time or other been covered by the
 sea4 ,the prevalent conception  that   
land areas which were once submerged    
came into existence by being  elevated  
above sea-level1 should be supplemented 
by the alternative  conception that     
submerged areas may have become land by 
the depression  of the ocean basins1    
thus drawing off the water from the     

areas where it  was shallow4 ,thus in   
,fig4 #cf the sinking of the sea-bottom 
from a to  b would lower the surface of 
the water from cc1 to dd1 and draw  off 
the water from the surfaces cd and cd4  
,illustration3 ,fig4 #cf4--;,diagram to 
illustrate the origin of lands by    the
 lowering of the sea-level due to       
depression of the sea bottom4 ,if    the
 bottom is depressed from a to b the    
surface will be drawn    down from cc to
 dd1 and the surfaces cd and cd will    
become    land4    ,without attempting  
to picture the character of the original
 land our  study of subarial erosion may
 begin with an area which has just been 
changed from sea bottom to land4 ,what  
is the nature of such a land  surface8  
,of what material is it composed1 and   
what is the character of  its           
topography8 ,concerning its constitution
 something may be inferred  from the    
nature of the deposits now found at the 
bottom of the sea4  ,near the shore and 
in shallow water they often consist of  

gravel and  sand1 though other materials
 are not wanting4 ,far from shore and in
  deep water they consist for the most  
part of fine sediments1 some of  which  
were washed or blown from the land1 some
 of which came from the  shells and     
other secretions of marine animals1 some
 from volcanoes1 and  some from various 
other sources4 ,the topography of the   
newly emerged  land may have had some   
likeness to the topography of the sea   
bottom4  ,the numerous soundings which  
have been made over large areas of the  
sea have shown that its bottom is1 as a 
rule1 free from the numerous  small     
irregularities which affect the surface 
of the land4 ,they seem  to show that a 
large part of the ocean bottom is so    
nearly flat that1  if the water were    
removed1 the eye would hardly detect    
irregularities  in the surface4 ,this   
statement does not lose sight of the    
fact that  the ocean bottom is1 in      
certain places1 markedly irregular4     
,volcanic  peaks and striking           

irregularities of other sorts abound in 
some places4  ,nevertheless if the      
bottom of the sea could be seen as the  
land is1 its  most striking feature1    
taken as a whole1 would be its apparent 
flatness4    ,with the topography of the
 sea bottom the topography of the land  
is1  in its details1 in sharp contrast4 
,in order to get at the history of  the 
latter1 we may study the sequence of    
events which would follow the  emergence
 of a portion of the former4            
,subarial ,erosion without ,valleys4    
,for the sake of emphasizing the        
fundamental principles involved in  the 
work of running water1 a hypothetical   
case will first be studied  in some     
detail1 even at the risk of elaborating 
processes already  understood4 ,the     
principles themselves will find         
application later in  relations which   
are much less simple4    ,let it be     
assumed that the area of newly emerged  
land is a circular  dome-shaped island4 
,the simplest possible condition is     

represented by  assuming its slope to be
 the same in all directions from the    
center1  and its materials to be        
absolutely homogeneous4 ,such an island 
would  be subject to all the forces     
ordinarily operating on land surfaces4  
,the chief agency tending to modify land
 surfaces is atmospheric  precipitation4
 ,it will be assumed that the rain falls
 on the surface  of the island with     
absolute equality at all points1 and    
that all other  forces which affect it  
operate equally everywhere4    ,the rain
 falling on a land area disappears in   
various ways2 part of it  evaporates1   
part of it sinks1 and part of it runs   
off over the surface4  ,if the island be
 composed of fine and unconsolidated    
materials1 such  as clay1 the water     
which runs off over the surface will    
carry sediment  down to the sea4 ,if the
 island be composed of solid rock       
instead1  exposure to the air will cause
 it to decay1 and the products of decay1
  such as sand and mud1 will suffer a   

like fate4    ,for the sake of a clear  
understanding of the processes involved1
 two  cases may be postulated2 one in   
which the waters of the sea remove the  
sediment washed down from the           
hypothetical island as fast as it       
reaches  the shore1 and one in which    
they allow it to accumulate without let 
or  hindrance4 ,in both cases the wear  
of the waves will be neglected4    #a4  
,in the first case the water flowing off
 over the surface 7the  run-off7 will   
descend equally in all directions4 ,it  
will constitute a  continuous sheet of  
surface-water1 and both its volume and  
its velocity  will be the same at all   
points equally distant from the summit4 
,erosion  accomplished by sheets of     
running water1 as distinct from streams1
 is  sheet 7or sheet-flood7 erosion4#bf 
,since the material of the  surface is  
homogeneous1 the wear effected by the   
water will be equal  at all points where
 its velocity and volume are equal4 ,for
 obvious  reasons the depth of the      

run-off will increase from summit to    
base4  ,the gradient 7slope7 also       
increases in the same direction1 and the
  increase of volume and of gradient    
conspire to augment the velocity  of the
 water1 and therefore of the wear       
effected by it4 ,if the thin  sheet of  
water starting from the top of the      
island with relatively  low velocity be 
able to wash off even a little fine     
material from the  surface1 the thicker 
sheet farther down the slope1 moving    
with greater  velocity1 will be able to 
carry away more of the same sort of     
material1  and the increase will be     
progressive from summit to base4 ,it    
follows1  therefore1 that the surface   
will be worn equally at points equally  
distant from the summit1 but unequally  
at points unequally distant  from it4   
,the first shower which falls on the    
island may be conceived  to wash off    
from its surface a very thin sheet of   
material1 but a  sheet which increases  
in thickness from top to bottom4 ,the   

run-off  will not be stopped immediately
 on reaching the sea1 but will displace 
the sea-water to some slight depth1 and 
wear the surface some trivial  distance 
below the normal level of the sea4 ,the 
result of successive  showers working in
 the same way through a long period of  
time will  be to diminish the area of   
the island and to steepen its slopes4   
,the  results of a considerable period  
of erosion under these conditions  are  
shown diagrammatically in ,fig4 #cg1    
which illustrates both the  diminution  
in area which the island has suffered1  
and the increase in  the angle of its   
slopes4 ,immediately about it1 at the   
stage represented  by aa1 ,fig4 #cg1    
there is a narrow marginal platform1 or 
submerged  terrace1 in place of the land
 area which has been worn away at or    
just  below the level of the sea4 ,long 
successions of rains working in the     
same way will give the island steeper   
slopes1 a smaller area1 and a  wider    
marginal terrace4 ,successive stages are

 shown by the lines bb  and cc1 ,fig4   
#cg4    ,illustration3 ,fig4            
#cg4--;,diagram to illustrate the effect
 of rain    erosion on an island where  
there is no deposition or wave erosion  
about its borders4 ,the uppermost curve 
represents the original    surface1     
while aa1 bb1 and cc represent          
successive surfaces    developed by     
sheet erosion1 on the supposition that  
no material is    deposited along the   
shores4    ,if rain falls on such an    
island until it completes the work which
  it is possible for running water to   
do1 the island will be reduced          
essentially to the level of the sea1 and
 in its place there will be a  plain1   
the area of which will be equal to that 
of the original island4  ,its central   
point will be at the level of the sea1  
and its borders a  trifling distance    
below it 7,fig4 #ch74 ,the island is    
gone1 and in its  place there is a plain
 as low as running water can wear it4   
,other  agencies might come in to defeat

 the result just outlined1 but if the   
island did not rise or sink after its   
formation1 rain falling upon  it would1 
under the conditions specified1 finally 
bring about the  result which has been  
sketched4 ,the plain 7,fig4 #ch7 which  
succeeds the  island is a base-level of 
erosion1 though this term is also used  
in  other ways4 ,under these conditions 
the slope of the land would remain      
convex at all stages1 but the convex    
erosion profile of the land  would meet 
a nearly straight line just below       
sea-level4 ,the relative  lengths of    
these two elements of the profile1 the  
curve above and the  straight line      
below1 vary as erosion progresses1 the  
convex portion  becoming shorter and the
 other longer1 ,the two parts of the    
profile  taken together are concave     
upward at the lower end all the time1   
and  for a greater distance from its    
lower end in all the advanced stages of 
erosion 7,fig4 #cg74    ,illustration3  
,fig4 #ch4--;,diagram to illustrate the 

final effect of    rain erosion under   
the conditions specified in the text4   
,the diagram    expresses the final     
result of the processes suggested by    
,fig4 #cg4    ,in the destruction of the
 land under these conditions neither    
valleys  nor hills would be developed1  
nor would the topography of the land be 
fashioned to correspond with the        
surfaces with which we are familiar4    
,it is to be distinctly borne in mind   
that the foregoing is a  hypothetical   
case2 it is not probable that such an   
island ever existed1  or ever will2 but 
that does not diminish the value of the 
illustration1  since the principles     
involved are operating on every land    
mass1 though  in less simple relations4 
#b4 ,the second case differs from the   
first in that the sediment washed  down 
from the land is deposited about its    
borders4 ,this results in  the building 
up of a marginal platform1 as shown in  
,figs4 #ci-da4 ,as  erosion goes on more
 sediment is washed down and deposited1 

partly on  the narrow marginal shelf    
which has already been developed1 and   
partly  on its outer slope1 as shown in 
the figures4 ,the marginal flat is thus 
extended beyond the original shores of  
the island on the one hand1 and  toward 
its center on the other4 ,as it         
develops1 its inner portion1  and indeed
 all except its outer edge 7ab1 ,figs4  
#dj and #da71 will be  gradually built  
up above the level of the water4 ,this  
marginal lowland  is developed at a     
level as low as running water1 under the
 conditions  then and there present1 can
 reduce the land4 ,such a surface may be
  said to be at grade1 since running    
water neither wears it down nor  builds 
it up4 ,its angle of slope is a function
 of 7#a7 the volume of the  water       
running over it1 and 7#b7 of the load   
which the water carries4                
,illustration3 ,figs4                   
#ci-da4--;,diagrams to illustrate the   
effect of    rain erosion on an island  
when all the eroded material is         

deposited    about the shore4 ,the black
 portions represent deposition4 ,the    
dotted    lines represent the original  
surface4 ,the several diagrams represent
    successive stages in the process4   
,since the marginal plain of the above  
illustration extends beyond the         
original shore of the island1 the area  
of land is increased1 though  both its  
average elevation and its mass 7above   
water7 are reduced4 ,in  case           
destructive processes did not operate on
 the marginal graded  plain the         
spreading and lowering suggested by     
,figs4 #ci and #dj would go  on until   
the central mass of the island was      
brought down to a gradient  in harmony  
with that of the gently sloping border1 
as shown in ,fig4  #da4 ,when this had  
been accomplished there would be a      
relatively large  land area with low    
slopes 7,fig4 #da7 in place of the      
smaller area with  steeper ones 7compare
 ,figs4 #ci and #dj74 ,the basal part of
 the larger  island from the center to  

the original margin would be made up of 
the  original material in its original  
position 7unshaded part of ,fig4 #da74  
,its surface would be covered1 least    
deeply near its center and most  deeply 
near the original margin1 with dbris    
gradually shifted from  higher levels1  
as shown in ,fig4 #da4    ,were such an 
island as that shown in ,fig4 #da once  
formed1 the rain  falling on it1 and    
flowing off over its surface1 would     
carry off its  surface soil and spread  
it about the shores4 ,though the surface
 of the  marginal flat of ,fig4 #dj was 
as low as running water could bring it  
at  the time it was developed1 the      
conditions of erosion have changed by   
the time the land reaches the conditions
 shown in ,fig4 #da1 and the same       
amount of rainfall may now be effective 
in erosion4 ,in the first case  7,fig4  
#dj7 the water descending from the      
higher part of the land brought  down   
sediment and started across the flat    
with a load4 ,its energy was  consumed  

in transporting what it had1 not in     
getting new material4 ,in  the second   
case 7,fig4 #da7 the water flowing over 
the gently sloping  surface has no      
initial load1 and its energy is         
therefore available for  erosion4 ,under
 continued rainfall1 the area of the    
land shown in ,fig4  #da would be       
increased as before by successive       
marginal deposits 7see  ,fig4 #db71 and 
at the same time its average height     
would be reduced4 ,the  lowering and    
enlarging of the island would continue  
until the whole  surface was brought so 
nearly to the level of the sea that     
water would  cease to run over it with  
sufficient velocity to carry away even  
the  fine material of its surface4 ,such
 a surface1 brought down as low as      
running water can degrade it1 is also   
7see p4 #eg7 a base-level4 ,it  will be 
seen from the foregoing illustrations   
that a graded surface  may pass into a  
base-level1 with no sharper line of     
demarkation than  that which separates a

 mature man from an old one4 ,in this   
case1 as in  the preceding1 the island  
has been base-leveled1 but still without
 the  formation of valleys or hills4    
,illustration3 ,fig4 #db4--;,diagram to 
illustrate the result of the            
continuation of the processes shown in  
,figs4 #ci-da4    ,both the preceding   
hypothetical cases make it clear that1  
from the  point of view of erosion1     
every drop of water which runs off over 
the surface of the land has for its     
mission the getting of the land  into   
the sea4 ,under ordinary conditions     
surface drainage must fail to  bring a  
land area altogether to sea-level1 the  
absolute base-level of  subarial forces2
 but it is not simply the water which   
runs off over  the surface which        
degrades the land4 ,that which sinks    
beneath the  surface contributes to the 
same end by slowly dissolving mineral   
matter  below the surface1 and finally  
carrying it to the sea4 ,in this way the
  reduction of land areas to sea-level  

may be completed4    ,the rain-water    
which evaporates from the surface       
without sinking  beneath it does not    
effect much wear2 but the water thus    
evaporated is  subject to               
reprecipitation1 so that1 in the long   
run1 it may assist  in the work which   
has been sketched4 ,thus it is not      
simply the waters  which run off over   
the surface of the land1 but all which  
fall upon it1  which unite to compass   
its destruction4                        
,the ,development of ,valleys4    ,by   
the growth of gullies4--,had the slopes 
of the hypothetical island  not been    
absolutely uniform the processes of     
erosion would have been  different4 ,let
 the departure from uniformity be       
supposed to consist  of a single slight 
meridional depression near the base of  
the island  7,fig4 #dc74 ,as the rain   
falls it will no longer run off equally 
in all  directions4 ,a greater volume   
will flow through the depression than   
over  other parts of the surface having 

the same altitude1 and the greater      
volume of water along this line will    
give greater velocity1 greater  velocity
 will occasion greater erosion1 and     
greater erosion will deepen  the        
depression4 ,the immediate result is a  
gully or wash 7,fig4 #dd74  ,so soon as 
the gully is started it tends still     
further to concentrate  drainage in     
itself1 and is thereby enlarged4 ,the   
water which enters it  from the sides   
widens it2 that which enters at its head
 lengthens it  by causing its upper end 
to recede2 and all which flows through  
it1 so  long as its bottom is above     
base-level1 deepens it4 ,the enlarged   
gully  will gather more water to itself1
 and1 as before1 increased volume  means
 increased velocity1 and increased      
velocity increased erosion4 ,as  the    
gully grows1 therefore1 its increased   
size becomes the occasion of  still     
further enlargement4    ,illustration3  
,fig #dc4--;,diagram showing a slight   
meridional depression    in the surface 

of an otherwise even-sloped island4     
,continued growth transforms the gully  
into a ravine1 though between a  gully  
and a ravine there is no distinct line  
of demarkation4 ,but growth  does not   
stop with ravine-hood4 ,water from every
 shower gathers in  the ravine1 and1    
flowing through it1 increases its       
length1 width1 and  depth1 until it     
reaches such proportions that the term  
ravine is laid  aside1 as childhood     
names are1 and the depression becomes a 
valley4    ,illustration3 ,fig4         
#dd4--;,diagram illustrating the        
development of a    gully1 starting from
 the condition shown in ,fig4 #dc4      
,it was assumed in the preceding        
paragraphs that the single depression   
in the slope was meridional and low on  
the slope1 but almost any sort  of      
depression in almost any position would 
bring about a similar  result1 since it 
would lead to concentration of the      
run-off4 ,had the  original surface been
 interrupted by ridges instead of       

depressions1  the effect on valley      
development would have been much the    
same1 for  a ridge1 like a depression1  
would1 in almost any position1 occasion 
the concentration of the run-off1 and so
 the development of valleys4  ,under the
 conditions represented in ,fig4 #dd the
 lengthening of the  drainage depression
 is effected chiefly at its upper end1  
the head of  the valley working its way 
farther and farther back into the land4 
,this  method of elongation is known as 
head erosion4 ,but the lengthening  of  
the valley is not always wholly by head 
erosion4 ,the gully normally  begins    
where concentration of run-off begins1  
and if this were not at  sea-level1 the 
gully might be lengthening at both ends 
at the same  time4 ,this would have been
 the case1 for example1 had the original
  depression of ,fig4 #dc been half-way 
up the slope of the island4    ,if while
 the slopes of the island were          
absolutely uniform its surface  material
 failed of homogeneity1 the result would

 be much the same as  if the slopes were
 unequal4 ,if the material lying along a
 certain  meridian of the island be     
slightly softer than that over the rest 
of  the surface1 the run-off1 which     
would at the outset be equal on all     
sides1 would effect more erosion along  
the line of the less resistant  material
 than elsewhere4 ,the result would be a 
depression along this  line1 and1 once  
started1 the depression would be a cause
 of its own  growth4 ,if the soft       
material were disposed in any way other 
than  that indicated1 the final result  
would be much the same1 for it  would   
quickly give origin to a depression     
which would lead to the  concentration  
of the surface-waters1 and this is the  
condition for the  development of a     
gully1 a ravine1 and finally a valley4  
,illustration3 ,fig4 #de4--;,diagram to 
illustrate the effect of sheet and      
stream erosion on the outline of an     
island when no deposition takes    place
 about its borders4 ,the dotted line    

represents the original    outline of   
the island1 the full line its border at 
a later time4 ,the    stream develops a 
rentrant 7bay7 in the outline4    ,in   
the presence of sufficient rainfall1    
either heterogeneity of slope  or of    
material will therefore occasion the    
development of valleys4 ,if  the lack of
 uniformity appears at but a single     
point there will be but  a single       
valley4 ,if it appears at many points   
the number of valleys  will be large4   
,since it is incredible that a land mass
 of perfectly  homogeneous material and 
of absolutely uniform slopes ever       
existed1  it is believed that every land
 mass1 affected for any considerable    
length of time by rain1 has had valleys 
developed in it4 ,the degree of         
heterogeneity of material and slope is  
usually so great as to lead to  the     
development of many valleys1 even on    
areas which are not large2  but for the 
sake of emphasizing the simpler elements
 of the complex  processes of stream    

work1 the hypothetical case of an island
 with but  a single valley1 and that    
without tributaries1 may first be       
studied4  ,under these conditions two   
cases may be considered1 the one where  
there  is no deposition about the       
island1 and the other where deposition  
takes  place4    #a4 ,if all the        
material eroded from the surface of such
 an island1 both  in and out of the     
valley1 were carried well beyond the    
borders of the  land before being       
deposited1 the edge of the island would 
recede from  its original position      
toward the center1 as illustrated by    
,figs4 #cg and  #de2 but the recession  
would be most rapid where the valley    
joins the  sea 7,fig4 #de74 ,at this    
point therefore a rentrant would be     
developed  7a1 ,fig4 #de71 and the      
island would lose its circular outline4 
,continued erosion would cause the      
shore-line to retreat on all sides1  but
 fastest at the lower end of the valley1
 and the final result would  be a       

base-level differing from that developed
 under the conditions  specified on p4  
#fj1 in that the last part to be brought
 low would not  be the center of the    
original island4    ,under the foregoing
 conditions the profile of that part of 
the valley  which is above sea-level    
7cb7 would be convex1 following the     
analogy  of sheet erosion on a          
hypothetical island of uniform slopes   
and  homogeneous material with no       
marginal deposition4 ,its side slopes1  
likewise developed under the influence  
of running water augmented in  volume   
from top to bottom1 would also be       
convex4    ,illustration3 ,fig4         
#df4--;,diagram showing the outline of  
an island    as modified by sheet and   
stream erosion where eroded material is 
deposited at the shore4 ,the dotted line
 represents the original    outline2 the
 full line1 a later one4 ,the excess of 
deposition at the    end of the valley  
causes a projection of land into the    
sea4    #b4 ,if the sediment washed down

 from the land is deposited about its   
borders1 both the outline of the island 
and the profile of the valley  will be  
altered4 ,deposition at the debouchure  
of the valley follows  the same         
principles as deposition elsewhere2 but 
if all the sediment  brought to the sea 
be deposited at the shore1 the seaward  
extension of  the land by deposition    
would be more rapid opposite the valley 
than  elsewhere1 and the island would   
lose its circular outline1 and develop  
some such form as is shown in ,fig4 #df4
 ,in this case the profile of the  upper
 end of the valley1 and the upper parts 
of its side slopes1 as  well as the     
upper parts of the extra-valley slopes  
of the island1 are  convex 7compare     
,figs4 #ci and #dj72 but the convexity  
above is exchanged  for concavity below1
 the change beginning at the point where
 downward  erosion of the descending    
waters is checked4 ,as a valley         
lengthens1 the  larger part of its      
profile becomes concave 7compare the    

profiles of  ,figs4 #ci to #da71 but the
 extreme upper end still remains convex4
 ,since  the side slopes of a valley are
 much shorter than its lengthwise slope1
  a larger proportion remains convex4   
,under the conditions here discussed    
the change from convexity above to      
concavity below would begin at about    
the point where deposition begins4#bg   
,illustration3 ,fig4 #dg4--;,diagram    
representing several meridional         
valleys developing in a circular island4
 ,the valleys are all young    and      
narrow4 ,all are making deposits at     
their debouchures4    ,the deposition at
 the debouchure of the valley1 and later
 above the  debouchure1 will follow the 
same course as about the island under   
the  conditions already discussed 7pp4  
#fa1 #fb74    ,limits of growth4--,in   
all cases there are limits in depth1    
length1  and width1 beyond which a      
valley may not grow4 ,in depth it may   
reach  base-level4 ,at the coast1       
base-level is sea-level1#bh but inland  

it  rises by a gentle gradient4 ,in     
length1 the valley will grow as long as 
its head continues to work inland4 ,in  
the case represented by ,figs4  #de and 
#df the head of the valley would not    
cease to advance when the  center of the
 island was reached1 though beyond that 
point head erosion  would not be more   
rapid than lateral erosion on either    
side4 ,if but  a single valley affected 
a land area the limit toward which it   
would  tend1 and beyond which it could  
never pass1 would be the length of the  
land area in the direction of the       
valley's axis4 ,in width1 a valley is   
increased by the side cutting of the    
stream1 by the wash of the rain  which  
falls on its slopes1 and by the action  
of gravity which tends to  carry down to
 the bottom of the slope the material   
which is loosened  above by any process 
whatsoever4 ,if there be but one valley 
in a land  area its limiting width is   
scarcely less than the width of the land
  itself4    ,illustration3 ,fig4       

#dh4--,same as ,fig4 #dg1 with the      
valleys more    developed4 ,the dotted  
line represents the original outline of 
the    island4 ,its area is being       
extended by deposition everywhere1 but  
most    at the debouchures of the       
streams4    ,illustration3 ,fig4        
#di4--;,a later stage of the island     
shown in ,fig4 #dh4    ,illustration3   
,fig4 #ej4--;,diagram to illustrate the 
lowering of a    divide without shifting
 it4 ,the crest of the divide is at a1  
b1    and c successively4 ,if erosion   
were unequal on the two sides1 the      
divide would be shifted4    ,had there  
been several initial meridional         
depressions instead of one  in the      
island1 or had there been several       
meridional belts where the  material of 
the surface was less resistant than     
elsewhere1 several  valleys would have  
been developed1 converging toward the   
center 7,fig4  #dg74 ,if the conditions 
were such as to allow of the equal      
development  of valleys on all sides of 

the island1 each would be lengthened by 
head  erosion until it reached the      
center of the island1 where the         
permanent  divide between their heads   
would be established4 ,each would be    
widened  by all the processes which     
widen valleys1 and their widening would 
narrow the intervening areas 7,figs4 #dh
 and #di74 ,under conditions of  equal  
erosion the limits of width for each    
valley would be the centers  of the     
ridges on either side1 and here the     
divides between them would  be          
permanently established4 ,though erosion
 would continue even after  the crest of
 the ridge had been narrowed to a line1 
the permanence of  the divide would     
follow from the fact that erosion would 
be equal on  both sides of this line1   
and its effect would be to lower the    
divide1  but not to shift it            
horizontally 7,fig4 #ej74 ,the limits in
 length and  width are therefore not the
 same where there are several valleys as
  where there is but one4 ,the limit in 

depth1 however1 remains the same1  and  
the final result of erosion1 proceeding 
along these lines1 would  be the        
base-leveling of the land1 leaving a    
plain but slightly above  sea-level4    
,the plain would not be absolutely flat1
 though its relief  would be very       
slight1 and the higher parts would be   
along the lines of  the divides between 
the streams 7,fig4 #ea4 ,compare also   
,fig4 #db74 ,many  valleys would        
occasion more rapid degradation than    
few1 and the period  of base-leveling   
would be correspondingly shortened4     
,had the initial depressions which gave 
origin to the valleys had  positions    
other than meridional1 the valleys would
 have had other  and less regularly     
radial courses1 but the final result of 
their  development would have been the  
same4    ,it is not to be inferred that 
the method of valley development which  
has been sketched is the only one4 ,the 
processes of valley development  are    
complex1 and the history of some valleys

 has run a different  course2 yet the   
processes outlined above are in         
operation in all cases1  and they were  
probably the most important ones in the 
development of  the first drainage      
system on any land surface4 ,as will be 
seen in the  sequel the history of      
valleys is subject to serious accidents1
 and they  are often of such a nature as
 to mask the simplicity of the more     
normal  processes4    ,illustration3    
,fig4 #ea4--;,diagram illustrating the  
further development    of ,fig4 #di4    
,the land here has been reduced greatly1
 though not yet to    base-level4       
,the permanent stream4--,from the       
foregoing discussion1 it is seen that  a
 valley may be developed by the run-off 
of successive showers4 ,if  supplied    
only from this source surface streams   
would cease to flow soon  after the rain
 ceased to fall1 and a valley might     
attain considerable  size without       
possessing a permanent stream4 ,how does
 the valley  developed by the run-off of

 successive showers come to have a      
permanent  stream8 ,the answer to this  
question involves a brief consideration 
of  that part of the rainfall which     
sinks beneath the surface4    ,if wells 
be sunk in a flat region of uniform     
structure and composition  the water in 
them is generally found to stand at a   
nearly common level4  ,the meaning of   
this fact is not far to seek4 ,if a hole
 #fj feet deep  fills with water up to a
 point #bj feet from the surface1 it is 
because  the material in which the well 
is sunk is full of water up to that     
level4 ,when the well is dug the water  
leaks into it1 filling the hole  up to  
the level to which the rock 7or subsoil7
 is itself full4 ,this  level1 below    
which the rock and subsoil 7down to     
unknown depths7 are  full of water1 is  
known as the ground-water level1        
ground-water  surface1 or water-table4  
,the ground-water level fluctuates4 ,in 
a wet season it rises1 because  more    
water has fallen and sunk beneath the   

soil2 but several processes  at once    
conspire to bring it down again4 ,where 
there is growing  vegetation its roots  
draw up water from beneath1 and         
evaporation also  goes on independently 
of vegetation4 ,the water is drawn out  
through  wells and runs out through     
openings4 ,it may also flow underground 
from  one region to another where the   
ground-water surface is lower4 ,all     
these processes depress the ground-water
 surface4    ,illustration3 ,fig4       
#eb4--;,diagram illustrating the        
fluctuation of a    ground-water        
surface4 a  wet-weather ground-water    
level2 b     ground-water level during  
drought4 ,well ,no4 #a will contain     
water    during the wet season1 but will
 go dry in times of drought4 ,well ,no4 
#b will be permanent4    ,a well sunk to
 such a level as to be supplied with    
abundant water  in a wet season may go  
dry during a period of drought because  
the  ground-water level is depressed    
below its bottom4 ,thus either well     

shown in ,fig4 #eb will have water      
during a wet season when the            
water-level is at a2 but well ,no4 #a   
will go dry when the water  surface is  
depressed to b4    ,the principles      
applicable to wells are applicable to   
valleys4 ,when  a valley has been       
deepened until its bottom reaches below 
the  ground-water level1 water seeps or 
flows into it from the sides4 ,the      
valley is then no longer dependent on   
the run-off of showers for a  stream4   
,it will be readily seen that at some   
stage in its development1  the bottom of
 a valley may be below the ground-water 
level of a  wet season without being    
below that of a dry one4 ,thus the      
valley  represented in cross-section by 
the line #b-b1 in ,fig4 #ec1 will have a
  stream when the ground-water level is 
at aa1 but none when this level  is     
depressed to bb4 ,if the rainfall of the
 year were concentrated in  a single wet
 season1 the intermittent stream would  
flow not only during  that season1 but  

for so long a time afterward as the     
ground-water  level remained well above 
the valley bottom4 ,in regions subject  
to  frequent and short periods of heavy 
precipitation1 alternating with         
droughts1 the periods of intermittent   
flow may be many and short4  ,since the 
precipitation of many regions varies    
greatly from year to  year1 it follows  
that a stream may flow continuously one 
year and be  intermittent the next4     
,many valleys in various parts of the   
earth are  now in the stage of          
development where their streams are     
intermittent4    ,as a valley containing
 an intermittent stream becomes deeper1 
the  periods when it is dry become      
shorter1 and when it has been sunk below
  the lowest ground-water level1 it will
 have a permanent stream 7#c1 ,fig4     
#ec74 ,since a valley normally develops 
headward1 its lower and older  portion  
is likely to acquire a permanent stream1
 while its upper and  younger part has  
only an intermittent one 7,fig4 #dg and 

,fig4 #a1 ,pl4 ,,iii1  near ,anthony1   
,kan4 ,the intermittent part of the     
stream is indicated  by the dotted blue 
line74 ,for the same reason the head of 
a stream is  likely to be farther up the
 valley in wet weather than in dry4 ,so 
soon  as a valley gets a permanent      
stream1 the process of enlargement goes 
on without the interruption to which it 
was subject when the supply of  water   
was intermittent4    ,illustration3     
,fig4 #ec4--;,diagram to illustrate the 
intermittency of    streams due to      
fluctuations of the ground-water level4 
,the water    level aa would be         
depressed next the valley #b-b by the   
flow of the    water into the valley4   
,the profile of the ground-water surface
 would    therefore be aca rather than  
aa4    ,in general a permanent stream at
 one point in a valley means a          
continuous stream from that point to the
 sea or lake which the valley  joins2   
but to this rule there are many         
exceptions4 ,they are likely to  arise  

where a stream heads in a region of     
abundant precipitation1 and  flows      
thence through an arid tract where the  
ground-water level is low1  and         
evaporation great4 ,in such cases1      
evaporation and absorption may          
dissipate the water gathered above1 and 
the stream disappears 7,fig4 #b1  ,pl4  
,,iii1 near ,paradise1 ,nev474          
,illustration3 ,,plate ,,iii4      ,fig4
 #a4 ,,kansas4    ,u4 ,s4 ,geol4 ,surv4 
,fig4 #b4 ,,nevada4    ,u4 ,s4 ,geol4   
,surv4    ,illustration3 ,,plate ,,iv4  
,fig4 #a4 ,,illinois4    ,u4 ,s4 ,geol4 
,surv4      ,fig4 #b4 ,,north ,,dakota4 
,u4 ,s4 ,geol4 ,surv4    ,other modes of
 valley development4--,if as a new area 
of land emerges  from the sea its       
surface has a depression without an     
outlet1 and  such an assumption is by no
 means improbable1 the depression would 
be filled with sea-water4 ,the inflowing
 water from the surrounding  land might 
fill the basin to overflowing1 and the  
outflow1 finding  exit at the lowest    

point in the rim of the basin1 would    
flow thence  toward the sea4 ,such a    
stream would develop a valley1 the      
history of  which would be somewhat     
different from that which has been      
sketched4  ,instead of developing       
headward from the sea1 the valley would 
be in  process of excavation all the way
 from the initial basin to the sea at   
the same time 7,fig4 #ed74 ,the upper   
end of the valley might ultimately  be  
cut to the level of the bottom of the   
basin1 when the lake would  disappear4  
,the head of the valley might then work 
back across the  former site of the lake
 into the territory beyond4 ,valleys    
might have  developed above the lake    
before it was drained1 and after this   
event1  such valleys would make         
connections with the valley below 7,fig4
 #ee74 ,a  valley developed in this     
manner is not simply a gully grown big  
by head  erosion1 and the valley would  
not precede the stream4                 
,illustration3 ,fig4 #ed4--;,diagram to 

show how a valley may be    developing  
all the way from a water-filled basin   
7lake7 to the sea at    the same time4  
,small valleys leading to the lake are  
also developing4    ,the black area  the
 sea4    ,illustration3 ,fig4 #ee4--,the
 stream leading out from the lake 7,fig4
    #ed7 has drained the lake1 and the  
valleys above and below the site of     
the former lake have united4    ,if a   
surface of land were notably irregular  
before valleys were  developed in it1   
there might be many lakes1 and the flow 
from a higher  lake might pass to a     
lower4 ,if the lakes were ultimately    
drained1 the  several sections of the   
valley would be joined to one another   
without  intervening basins4 ,in certain
 regions1 especially those which have   
been affected by continental ice-sheets1
 this has been a common method  of      
valley development in post-glacial time4
 ,in this case also the  stream precedes
 its valley1 and not the valley its     
stream4 ,many  post-glacial valleys1 on 

the other hand1 antedated their         
permanent  streams1 as in the cases     
first described4    ,if the gradient of 
a slope on which valleys are to develop 
is notably  unequal1 though without     
basins1 the development of valleys may  
follow  somewhat different lines4 ,if on
 emergence the seaward part of a new    
land area assumes the form of a plain1  
bordered landward by a steeper  slope   
7,fig4 #ef71 the most notable early     
growth of the valleys would be  on the  
latter4 ,the run-off would develop      
gullies on the steep slope1  but on     
reaching the plain below the velocity of
 the water would be  checked1 and it    
would drop much of the detritus washed  
down from above4  ,this deposition would
 build up 7aggrade7 the surface1 and    
much or  even all the water might sink  
into and seep through the dbris thus    
deposited1 and disappear altogether from
 the surface1 as at b1 ,fig4  #ef4 ,this
 would be most likely to occur where the
 dbris is abundant and  coarse1 and the 

precipitation slight4 ,if the water     
disappears at the  base of the mountain 
7see ,fig4 #b1 ,pl4 ,,iii71 the early   
growth of the  valley may be confined to
 the steep slope remote from the sea    
7ab1  ,fig4 #ef72 but on the slope where
 the valley is growing there will be    
headward lengthening1 as in the general 
case already considered4 ,if the        
surface drainage does not disappear at  
the base of the steep slope1 the        
run-off will find its way over the plain
 along the lowest accessible  route to  
the sea 7de1 ,fig4 #ef74 ,in this case  
the valley may be  growing throughout   
its length at the same time4            
,illustration3 ,fig4 #ef4--;,diagram    
showing the phases of valley            
development described in the text4      
,illustration3 ,fig4 #eg4--;,diagram    
representing the further development    
of the valleys fg and hi in ,fig4 #ef4  
,the head of the latter 7,fig4    #ef7  
has worked back until it has reached the
 lower end of the former4    ,the       

conditions represented by ab1 ,fig4 #ef1
 may be no more than  temporary4 ,sooner
 or later a valley developing headward  
across the  plain 7hi1 ,fig4 #ef7 may   
provide a channel for the water         
descending  from the higher land beyond4
 ,in this case the valley develops in   
sections1 the one on the slope above1   
the other on the plain below1 and  their
 union 7compare fghi1 ,fig4 #ef1 with   
,fig4 #eg7 results from their  growth4  
,the principles here sketched have been 
in operation wherever land  areas were  
so elevated as to give rise to unequal  
slopes1 and this has  perhaps been the  
rule rather than the exception4 ,the    
results effected  by the operation of   
these principles would of course be     
dependent on  the varieties of slope1 on
 the abruptness with which a slope of   
one  gradient gave place to another1 on 
the texture of the rock1 the amount  and
 distribution of precipitation1 etc41   
etc4    ,in the preceding paragraphs the
 lengthening of a valley at its upper   

end by head erosion has been repeatedly 
referred to4 ,if all valleys  began     
their development at the sea and        
lengthened headward1 it might  seem that
 their seaward ends should be their     
oldest parts2 but since  the development
 of valleys is begun somewhat promptly  
after the land  appears above the sea1  
and since the emergence is generally    
gradual1  that part of a valley which is
 at the seashore at one time may be far 
inland a little later1 because the land 
has been extended seaward4  ,on an      
emerging land area therefore the normal 
growth of a valley  involves its        
lengthening at its lower end as well as 
at its upper4 ,the  lengthening of a    
valley1 or at least the lengthening of a
 stream1 also  takes place at its lower 
end if the land in which it lies is     
being  extended seaward by deposition4  
,structural valleys4--,in mountain      
regions valleys are sometimes formed  by
 the uplift of parallel mountain folds1 
leaving a depression between  7,fig4    

#eh74 ,drainage will appropriate such a 
valley so that it becomes  in some sense
 a river valley4 ,but it is not a river 
valley in the sense  in which the term  
has been used in the preceding pages4   
,it is rather  a structural valley4 ,in 
its bottom a river valley may be        
developed  7a1 ,fig4 #eh74              
,illustration3 ,fig4 #eh4--,structural  
valley with a river valley    developing
 its bottom4    ,the foregoing          
illustrations by no means exhaust the   
list of conditions  under which valleys 
develop1 but they suffice for the       
present4    ,illustration3 ,fig4 #ei4   
,fig4 #fj4      ,figures to show why the
 head of a gully 7and therefore a       
valley7    departs from a direct course4
    ,the courses of valleys4--,river    
valleys are rarely straight4 ,to        
understand why they are crooked it is   
only necessary to understand the        
methods by which they grow4 ,in so far  
as a river valley is a gully  grown big1
 that is1 in so far as its length is the

 result of head  erosion1 its course was
 determined by the course of the        
antecedent  gully4 ,if in the case shown
 in ,fig4 #ei the slope of the surface  
above  the head of the gully is uniform1
 its material homogeneous1 and the      
rainfall everywhere equal1 more water   
will come into the gully from  the      
direction a than from any other4 ,in    
this case there would be  more wear in  
the direct line of its extension than   
elsewhere1 and the  head would advance  
in a straight line4 ,but if there be    
inequalities of  slope about the head of
 a gully at any stage of its development
 more  water may come in from some      
direction other than that in the direct 
line of its extension4 ,in ,fig4 #ei1   
for example1 more water may enter  from 
the direction of b than from that of a4 
,since most wear is  likely to be       
affected along the line of greatest     
inflow1 the head of  the gully will be  
turned in that direction 7,fig4 #fj74   
,started in this  course it will        

continue in the new direction so long as
 erosion in this  line is greater than  
that elsewhere2 but whenever the        
configuration  of the surface causes    
more water to enter the head of the     
gully from  some direction other than   
that in which it is headed1 the line of 
axial growth is again changed1 as toward
 c1 ,fig4 #fj4 ,since new land  surfaces
 are probably more or less undulatory1  
crookedness should be  the rule among   
valleys developed from gullies by head  
erosion4 ,streams  and valleys the      
courses of which are determined by the  
original slope  of the land are said to 
be consequent4    ,illustration3 ,fig4  
#fa4--;,diagram illustrating the        
development of two    equal gullies from
 the head of one4    ,inequalities of   
material1 leading to unequal rates of   
erosion1 effect  the same result1 in the
 absence of inequalities of slope4 ,if  
at any  stage of a valley's development 
erosion were equal in two directions  at
 its head1 and at the same time greater 

than at points between1 two  gullies    
would result 7,fig4 #fa7 diverging from 
the point in question4    ,in the case  
of a valley developed by overflow from a
 lake its course is  determined by the  
lowest line of flow to which the water  
has access4 ,if  this line be straight  
the valley will be straight2 if it is   
crooked1 as  it generally is1 the valley
 is crooked also4    ,the development of
 tributaries4--,thus far valleys leading
  immediately to the sea have been      
considered1 and no account taken  of    
tributaries4 ,as a matter of fact most  
considerable valleys have  numerous     
tributaries4 ,it is now in order to     
inquire into their mode of  development4
    ,so soon as a gully is started1 the 
water flowing into it from either  side 
wears back the slopes4 ,the least       
inequality of slope1 or the least       
variation in the character of the       
material1 is sufficient to make the     
lateral erosion unequal at different    
points1 and unequal erosion in  the     

slopes results in the development of    
tributary gullies4 ,the oldest          
tributaries may be nearly as old as the 
main which they join1 and from  which   
they developed1 for the possibilities of
 unequal side erosion  exist as soon as 
a gully is opened4 ,while the main gully
 is developing  into a ravine1 and the  
ravine into a valley1 the tributary     
gullies  are likewise developing into   
maturer stages4 ,tributary to a young   
valley1 therefore1 there may be gullies 
near its head1 ravines in its  middle   
course1 and small valleys along its     
oldest portion4 ,it is not  to be       
understood1 however1 that the oldest    
tributaries are necessarily  the        
largest1 for because of more favorable  
conditions for growth the  younger      
tributaries often outstrip the older4   
,illustration3 ,fig4 #fb4--;,diagram to 
illustrate the oblique position    of a 
tributary gully at its inception1 and   
its later normal change of    direction4
    ,the position of tributaries with   

reference to their mains is worthy  of  
note4 ,the water flowing down a slope   
follows the line of steepest  descent4  
,a gully is usually wider at its lower  
end1 and narrower at its  upper4        
,wherever this is true the line of      
steepest descent down its side  is not a
 line perpendicular to its axis1 but a  
line slightly oblique  to it 7ef1 ,fig4 
#fb71 and oblique in such a direction   
that it meets  the axis with an obtuse  
angle below and an acute angle above4   
,it is in  the direction corresponding  
to this line that tributary gullies tend
  to develop4 ,thus at the inception of 
its history a tributary gully is  likely
 to join its main with an angle slightly
 acute on the up-stream  side4 ,if the  
tributary did not begin until after its 
main was farther  advanced this tendency
 would be less and less pronounced4     
,inequalities  of material or slope     
would often counteract this tendency1   
which1 at  best1 would cause the courses
 of tributaries to depart but little    

from  perpendicularity to their mains4  
,after the head of a tributary has      
worked back from the immediate slope  of
 its main every condition which         
determines the course of a gully  is    
likely to affect it1 and it is by no    
means certain that it will  continue to 
lengthen in the direction in which it   
started4 ,since the  general slope of   
the surface into which the tributary    
works is likely  to be seaward1 more    
water is likely to enter from the       
landward than  from the seaward side of 
its head1 so that1 except where there   
are  notable irregularities of slope1   
its tendency will be to turn more and   
more toward the direction of its main   
7efg1 ,fig4 #fb74    ,in depth the      
tributary is always limited by its main4
 ,the principles  which determine the   
length and width of a main valley       
determine also  the length and width of 
a tributary 7see p4 #fg et seq474       
,a ,,cycle ,,of ,,erosion4 ,,its        
,,stages4    ,from what has preceded it 

is clear that the topography of a region
  undergoing erosion will change greatly
 from time to time4 ,the first  effect  
of erosion is to roughen the surface by 
cutting out valleys1  leaving ridges and
 hills4 ,the final effect is to make it 
smooth again  by cutting the ridges and 
hills down to the level of the valleys4 
,the base-level of erosion has already  
been defined2 but the mode of  its      
development may now be illustrated in   
the light of the preceding  discussion4 
,suppose a land surface affected by a   
series of parallel  young valleys       
without tributaries 7,fig4 #fc74        
,between them there is  a series of     
upland plateaus4 ,the profile of the    
surface between two  adjacent valleys is
 represented in section by the uppermost
 line in  ,fig4 #fd4 ,as the valleys are
 widened from #a-a and #a1-a1 to #b-b   
and  #b-b1 the intervening plateau is   
correspondingly narrowed4 ,when  the    
valleys have attained the form          
represented by #c-c and #c-c1  the      

intervening upland has been narrowed to 
a ridge1 a1 and the  valley flats have  
become wide4 ,with continued erosion the
 ridge  will be lowered 7to b and       
below71 and in time the surface will    
approach a plain4 ,in this condition it 
is known as a peneplain 7an             
8almost-plain074 ,finally1 when running 
water has done its utmost1  the ridges  
will be essentially obliterated and a   
base-leveled plain  7e1 e1 e7 results4  
,the figure expresses the fact that the 
base-level develops laterally from the  
axis of the valley4 ,it also  develops  
headward from the seaward end of the    
valley4 ,similarly1 taking  into account
 all the valleys which affect it1 the   
seaward margin of a  base-leveled plain 
is developed first1 and thence it       
extends itself  inland4                 
,illustration3 ,fig4 #fc4--;,diagram    
showing three parallel valleys in a     
land surface4    ,illustration3 ,fig4   
#fd4--;,diagram to illustrate the       
lowering of the    surface by valley    

erosion4 ,the successive cross profiles 
of the    valleys are represented by the
 lines #a-a1 #a-a1 #b-b1 #b-b1 etc4     
,tributaries are tolerably sure to      
develop along each main valley4 ,the    
heads of the tributaries work back      
across the uplands between the main     
valleys1 dissecting them into secondary 
ridges 7,fig4 #fe74 ,tributaries  will  
develop on the tributaries1 and these   
tertiary valleys dissect  the secondary 
ridges into those of a lower order4     
,this process of  tributary development 
goes on until drainage lines of the     
fourth1  fifth1 sixth1 and higher orders
 are formed 7,fig4 #ff74 ,since the     
process  of valley development under    
such circumstances is also the process  
of ridge dissection1 a stage is         
presently reached where the ridges  are 
cut into such short sections that they  
cease to be ridges1 and  become hills   
instead4 ,even then the processes of    
erosion do not stop1  for the rain-water
 falling on the hills washes the loose  

material  from their surfaces1 and      
starts it on its seaward journey4 ,thus 
the  8everlasting hills0 themselves are 
lowered1 and1 given time enough1  will  
be carried to the sea4 ,under these     
conditions1 as under those  already     
discussed1 the final result of stream   
erosion is the reduction  of the land to
 base-level4 ,the base-leveled surface1 
as before1 would  not be absolutely     
flat4 ,the area reduced by each stream  
will have a  slight gradient            
down-stream1 and from each lateral      
divide toward the  axis of the valley4  
,the crests of the scarcely perceptible 
elevations  which remain will be in the 
position of the former divides1 and     
these  will be highest where most       
distant from the sea by the course which
  this part of the drainage took4 ,even 
the insensible divides between  streams 
flowing in a common direction may       
disappear1 for when valleys  have       
reached their limits in depth1 their    
streams do not cease to cut  laterally4 

,meandering in their flat-bottomed      
valleys1 they often reach  and undercut 
the divides 7,pl4 ,,vii71 whether they  
be high or low4 ,by  lateral planation1 
therefore1 the divides between streams  
may be  entirely eaten away4            
,illustration3 ,fig4 #fe4--;,diagram    
showing the dissection of the upland    
shown in ,fig4 #fd by tributary valleys4
    ,illustration3 ,fig4 #ff4--;,diagram
 showing tributaries of several orders  
developed from the conditions sketched  
in the text4    ,it has now been seen   
that by whatever method erosion by      
running water  proceeds1 whether there  
be many valleys1 or few or none1 the    
final  result of subarial erosion must  
be the production of a base-level4 ,it  
has also been seen that the base-level  
is first developed at the lower  ends of
 the main streams1 and that it extends  
itself systematically  up the main      
valleys and up all tributaries4 ,the    
time involved in the  reduction of a    
land area to base-level is a cycle of   

erosion4    ,it will have been evident  
from the preceding pages that the terms 
8grade10 8graded plain10 and            
8base-level0 and 8base-leveled plain10  
are somewhat variously1 and therefore   
somewhat confusingly1 used4  8,grade is 
a condition of essential balance between
 corrasion and  deposition40#bi ,a      
graded valley is one in which deposition
 and  corrasion are1 in the vertical    
sense1 balanced4 ,its angle of slope is 
most variable1 and is dependent on the  
capacity of the stream for work1  and on
 the work it has to do4 ,a weak river   
must have a higher gradient  than a     
strong one2 a stream with much sediment 
must have a higher  gradient than one   
with little1 and a stream with a load of
 coarse  material must have a higher    
gradient than one with a load of fine4  
,thus the graded valley of the lower    
,mississippi has an inappreciable  angle
 of slope1 but the graded valleys of    
many of its tributaries have  slopes of 
hundreds of feet per mile4 ,since both  

the size of the stream  and the amount  
and coarseness of its load at a given   
place vary from  time to time1 it is    
clear that the inclination of a graded  
valley  must vary also1 and further1    
that it must be in process of continual 
readjustment4 ,with the changing        
conditions of advancing years the slope 
of a graded valley normally decreases4  
,the same principles apply to  graded   
surfaces outside of valleys4    ,in the 
continual readjustment of grades        
incident to a river's normal  history   
the land is brought nearer and nearer to
 sea-level without  ceasing to be at    
grade4 ,when the inclination of a graded
 surface  becomes so low that it is     
sensibly flat1 the surface may be said  
to be  at base-level1 although this does
 not mean that the surface can never  be
 degraded further4 ,if the term be used 
in this way1 it is clear that  there is 
no sharp line of distinction between a  
graded surface and a  base-leveled      
surface1 and as the terms are now       

commonly applied no such  distinction   
exists4    ,if the term base-level were 
made synonymous with sea-level1 as has  
been proposed1#cj the term might as well
 be discarded1 for sea-level  could     
always be used in its stead4            
,furthermore1 streams often erode  below
 sea-level4 ,the bottom of the channel  
of the ,mississippi is below  sea-level 
for some #djj miles above its           
debouchure1 and locally 7,fort          
,jackson7 it is nearly #bej feet below4 
,this deep channel is the result  of the
 erosive activity of the stream1 not of 
subsidence4 ,again1 the  sea-level is   
itself inconstant4 ,the extent of its   
changes cannot now be  measured1 but    
they have probably been more            
considerable in the course  of          
geological history than has been        
commonly recognized4 ,it is true  that  
they take place slowly1 as far as known1
 but it is also true that  the duration 
of an erosion cycle is sufficiently long
 for even very  slow changes to reach   

great magnitude4 ,the sea-level1        
therefore1 can  hardly be accepted as   
the absolute base-level1 unless 7#a7 the
 absolute  base-level is a variable1 and
 unless 7#b7 the absolute base-level be 
a  surface below which rivers may cut to
 the extent of at least #bej feet4      
,the ocean may be looked upon as a      
barrier which in a general way limits   
the down-cutting of running water2 for  
only very large streams cut much  below 
its level4 ,other barriers1 such as     
lakes1 and the outcrops of  hard rock in
 a stream's bed1 have a comparable1     
though more temporary1  effect on the   
development of valley plains above4     
,plains thus developed  have been called
 temporary base-levels4 ,they differ    
from other graded  plains in being      
controlled primarily by a barrier below1
 rather than by  conditions which exist 
above4    ,since river valleys have a   
beginning and pass through various      
stages  of development before the       
country they drain is base-leveled1 it  

is important to recognize their various 
stages of advancement4 ,nor  is this    
difficult4 ,an old valley and a young   
one have different  characteristics1 and
 the one would no more be mistaken for  
the other by  those who have learned to 
interpret them1 than the face of an aged
 man  would be mistaken for that of a   
child4    ,illustration3 ,fig4 #fg4--;,a
 gully developed by a single shower4    
7,blackwelder47    ,the cycle begins    
with the beginning of valley            
development1 and at that  stage drainage
 is in its infancy4 ,the type of the    
infant valley is  the gully or ravine   
7,figs4 #fg and #fh74 ,it has steep     
slopes and a  narrow bottom4 ,fig4 #a of
 ,plate ,,iv represents similar1 or     
rather older1  ravines in contour 7shore
 of ,lake ,michigan1 just north of      
,chicago74  ,with age1 the valley       
widens1 lengthens1 and deepens1 and     
passes from  infancy to youth4 ,in this 
stage also the valleys are relatively   
narrow1 and the divides between them    

broad4 ,they may be deep or  shallow1   
according to the height of the land in  
which they are cut1 and  the fall of the
 water flowing through them2 but in any 
case the streams  flowing through them  
have done but a small part of the work  
they are  to do before the country they 
drain is base-leveled4 ,figs4 #fi and   
#gj1  respectively1 represent youthful  
valleys in regions of moderate and      
great relief4 ,fig4 #b1 ,plate ,,iv1    
shows a youthful valley in a region of  
slight relief 7near ,casselton1 ,n4 ,d41
 lat4 #df #dj1 long4 #ig #be74 ,the     
uppermost line in ,fig4 #fd likewise    
represents topographic youth1 as  shown 
in cross-profile4    ,illustration3     
,fig4 #fh4--;,a gully somewhat older    
than that shown in    ,fig4 #fg4        
7,alden47    ,illustration3 ,fig4       
#fi4--;,a young valley in a region of   
slight relief4    ,not only are narrow  
valleys said to be young1 but the       
territory  affected by them is said to  
be in its topographic youth1 since but  

a small part of the time necessary to   
reduce it to base-level has  elapsed4   
,an area is in its topographic youth    
when considerable portions  of it are   
still unaffected by valleys4 ,thus the  
areas 7as a whole71 as  well as the     
valleys1 represented on ,plate ,,iv1 are
 in their topographic  youth4 ,it is    
often convenient to recognize various   
sub-stages1 such  as early1 middle1 and 
late1 within the youthful stage of      
valleys or  topographies4 ,the different
 parts of the areas shown on ,plate     
,,iv1 for  example1 represent different 
stages of youth4    ,youthful streams1  
as well as youthful topographies1 have  
their  distinctive characteristics4     
,they are usually swift2 their cutting  
is  mainly at the bottom rather than at 
the sides1 and their courses are  often 
marked by rapids and falls4    ,as      
valleys approach base-level they develop
 flats4 ,as the valleys and  their flats
 widen1 and as their tributaries        
increase in numbers and  size1 a stage  

of erosion is presently reached where   
but little of the  original upland      
surface remains4 ,the country is largely
 reduced to  slopes4 ,in this condition 
the drainage and the topography which it
  has determined are said to be mature4 
,mature topography is shown in  contours
 in the figures of ,plate ,v1 and in the
 northern part of ,plate  ,,vi1 where   
slopes1 rather than upland or valley    
flats1 predominate4  ,fig4 #a of ,plate 
,v represents an area in southeastern   
,kentucky 7lat4  #cg #ab1 long4 #hc     
#aj72 ,fig4 #b1 an area in western      
,virginia4 ,plate  ,,vi represents an   
area in southern ,california1 somewhat  
west of ,san  ,bernardino4 ,the three   
areas are alike in representing mature  
drainage1  though not of equal stages of
 advancement4 ,the striking differences 
of topography of the three areas are the
 result of differences in  rock         
structure and altitude1 and will be     
considered later4 ,mature  topography is
 also shown in ,fig4 #ga1 where the     

relief is moderate1  and in ,figs4 #gb  
and #gc1 where it is great4 ,figs4 #gb  
and #gc illustrate  clearly the         
universal tendency of rivers in regions 
of notable relief  to develop new flats 
well below the old surface of the       
region4 ,at the  same time that these   
low-lying flats are developing1         
tributary drainage  is dissecting and   
roughening the upper surfaces4 ,this    
process is well  shown in ,fig4 #gc4 ,in
 both ,figs4 #gb and #gc the summits of 
the mountains  on either side of the    
valleys appear to have had about the    
same  elevation4 ,the new flat is       
therefore developed at the expense of   
the  old flat4 ,as will be seen in the  
sequel1 the first flat which a stream   
develops along its course is usually    
somewhat above base-level4 ,it is a     
graded flat4    ,illustration3 ,,plate  
,v4      ,fig4 #a4 ,,kentucky4    ,u4   
,s4 ,geol4 ,surv4      ,fig4 #b4        
,,virginia4    ,u4 ,s4 ,geol4 ,surv4    
,illustration3 ,,plate ,,vi4            

,,parts ,,of ,,los ,,angeles ,,and ,,san
 ,,bernardino ,,counties1 ,,california4 
,u4 ,s4 ,geol4 ,surv4    ,illustration3 
,fig4 #gj4--,the valley 7canyon7 of the 
,yellowstone4 ,a    young valley in an  
elevated region4    ,illustration3 ,fig4
 #ga4--,mature erosion topography in a  
region of    slight relief1 ,iowa4      
7,calvin47    ,illustration3 ,fig4      
#gb4--,mature erosion in a mountain     
region4 ,from    mouth of ,gray ,copper 
,gulch1 ,silverton1 ,colo41 quadrangle4 
7,cross1    ,u4 ,s4 ,geol4 ,surv47      
,the same processes which have made     
young valleys mature will in time  work 
further changes4 ,when the gradients of 
the valleys have become low  and their  
bottoms wide1 and when the intervening  
ridges and hills have  become narrow and
 small1 the drainage and the drainage   
topography have  reached old age1 and   
the streams are in a condition of       
senility4 ,this  is illustrated by ,fig4
 #a1 ,plate ,,vii 7central ,kansas71 and
 in section  by the third and lower     

lines in ,fig4 #fd4 ,topographic old age
 sometimes  has a different expression2 
this is shown in ,fig4 #gd1 where most  
of  the surface has been brought low4   
,the elevations which rise above the    
general plain are small in area1 but    
have abrupt slopes4 ,this phase  of     
old-age topography is usually the result
 of the unequal resistance  of the rock 
degraded4 ,the effects of unequal       
rock-resistance will be  considered     
later4    ,illustration3 ,fig4          
#gc4--,mature erosion in a mountain     
region4    ,silverton1 ,colo4 7,cross1  
,u4 ,s4 ,geol4 ,surv47    ,the marks of 
old streams are as characteristic as    
those of young  ones4 ,they have low    
gradients and are sluggish4 ,instead of 
lowering  their channels steadily they  
cut them down in flood1 and fill them up
  when their currents are not swollen4  
,they meander widely in their           
flat-bottomed valleys 7,fig4 #a1 ,pl4   
,,vii1 ,central ,kansas7 and their      
erosion1 except in time of flood1 is    

largely lateral4    ,if the processes of
 degradation were to continue until the 
land  surface was brought to sea-level1 
and this might be done by solution      
though not by mechanical erosion of     
running water1 the rivers would no      
longer flow1 and the drainage system    
would have reached the end of its       
history--death4    ,not only do valleys 
normally pass from birth to youth1 from 
youth to  maturity1 and from maturity to
 old age1 but a single river system  may
 show these various stages of           
development in its various parts4  ,thus
 in the area shown in ,fig4 #b1 ,plate  
,,vii 7north central ,kansas71  there is
 a tract 7extreme southwest7 where the  
erosion history is  scarcely begun4 ,the
 zone of land a little farther          
northeast1 and just  reached by the     
heads of the valleys 7same figure71 is  
in its youth4  ,the well-drained and    
uneven tract southwest of the flat of   
the ,solomon  ,river is in maturity1    
while the flat of the main valley has   

the general  characteristics of old age4
    ,illustration3 ,fig4 #gd4--;,a      
peneplained surface where the elevations
    are small but steep-sided4 ,near    
,camp ,douglas1 ,wis4 7,atwood47    ,the
 age of valleys in terms of erosion is  
also expressed more or  less perfectly  
by their cross-sections4 ,the line #a-a 
7and #a-a7 of  ,fig4 #fd represents in  
cross-section a narrow ,v-shaped valley4
 ,such a  section is always indicative  
of youth4 ,the stream which developed it
  cut chiefly at its bottom1 not at its 
sides4 ,it was therefore rapid1  and    
rapid streams are young4 ,the line #b-b1
 7#b-b7 7,fig4 #fd7 shows  the same     
valley at a later and maturer stage when
 downward cutting  has nearly ceased4   
,the widening of the valley by slope    
wash has  become relatively more        
important than before1 and the stream   
has so far  lost velocity as the result 
of diminished gradient as to be unable  
to  carry away all the detritus washed  
down from the sides4 ,as a result of    

deposition at the bases of the side     
slopes1 a concave curve has been        
developed4 ,up the valley from the point
 where such a section as is  represented
 by #b-b occurs1 the valley may still   
have a section similar  to that         
represented by #a-a4    ,illustration3  
,,plate ,,vii4      ,fig4 #a4 ,,kansas4 
,u4 ,s4 ,geol4 ,surv4      ,fig4 #b4    
,,kansas4    ,u4 ,s4 ,geol4 ,surv4      
,illustration3 ,,plate ,,viii4          
,,about #ae ,,miles ,,southwest ,,of    
,,st4 ,,louis1 ,,missouri4    ,u4 ,s4   
,geol4 ,surv4    ,still later stages of 
development are represented by the      
cross-sections  #c-c and #d-d4 ,not only
 has the valley become larger1 but the  
stream  has deposited detritus 7not     
shown in the figure7 in the bottom of   
its  valley1 developing an alluvial     
flat4 ,on this flat the stream meanders1
  and the valley may be widened by the  
undercutting of the bluffs  wherever the
 stream in its wanderings reaches them  
7,pl4 ,,viii1 near  ,st4 ,louis74 ,a    

valley might possess the characteristics
 shown by the  cross-sections #c-c1     
#b-b1 and #a-a1 ,fig4 #fd1 in its lower1
 middle1 and  upper courses1            
respectively4    ,the preceding         
discussion1 and the illustrations which 
accompany it1  give some idea of the    
topography which characterizes an area  
in various  stages of its erosion       
history4 ,whether the valleys are deep  
or shallow1  and the intervening ridges 
high or low1 depends on the original    
height  of the land and its distance    
from the sea4 ,the higher the land1 and 
the  nearer it is to the sea1 the       
greater the relief developed by erosion4
 ,a  plateau near the sea may become    
mountainous in the mature stage of its  
erosion history1 while a plain in the   
same situation would only become  hilly4
 ,a plateau in the heart of a continent 
would have less relief  in its maturity 
than one of equal elevation near the    
sea1 since the  grade-plain in the      
former position is higher than in the   

latter4 ,plates  ,,iv and ,,ix show     
youthful topography where the relief is 
relatively  slight1 and ,plate ,x shows 
youthful topography where the relief is 
great4 ,similarly1 ,plates ,v and ,,vi  
show mature topography where the  relief
 is great1 and ,fig4 #a1 ,plate ,,iii1  
shows mature topography where  the      
relief is relatively slight4            
,topographic youth1 topographic         
maturity1 and topographic old age  are  
also indicated in other ways1 and       
especially by the presence of  features 
which rivers tend to destroy4 ,if1 for  
example1 the surface  of the land1 well 
above the valley bottoms1 is marked by  
numerous  ponds and marshes1 it is clear
 that drainage has not yet progressed   
beyond its early stages1 for1 unless the
 lakes be very deep1 valleys  working   
back into the land will find and drain  
them before topographic  maturity has   
been reached4 ,their presence is        
evidence that the region  where they    
occur has not yet been thoroughly       

dissected by erosion  lines1 and        
therefore has not reached maturity4     
,still other marks of  topographic      
youth1 such as rapids1 falls1 etc41 as  
well as marks of  topographic maturity  
and old age1 will be mentioned in the   
following  pages4        ,,general      
,,characteristics ,,of ,,topographies   
,,developed ,,by ,,river ,,erosion4     
,with the characteristics of river      
valleys and the methods by which  they  
grow clearly in mind it is easy to say  
whether rivers have been  the chief     
agents in the development of a given    
topography4 ,river  valleys are         
distinguished from other depressions on 
land surfaces by  their linear form and1
 leaving out of consideration the       
relatively  insignificant inequalities  
in a stream's channel1 by the fact that 
any  point in the bottom of a river     
valley is lower than any other point    
farther up the stream in the same       
valley1 and higher than any point       
farther down the stream4 ,the second    

point might be otherwise stated  by     
saying that every valley excavated by   
erosion leads to a lower  valley1 or to 
the sea1 or an inland basin4 ,streams   
which dry up1 or  otherwise disappear as
 they flow1 constitute partial          
exceptions4 ,if1  therefore1 the        
depressions on a land surface are       
linear1 lead to other  and deeper       
valleys1 and finally to an inland basin1
 or the sea1 and  if the elevations     
between these valleys are such as might 
have been  left by the excavation of the
 valleys1 it is generally clear that    
rain and rivers have been the chief     
factors in the development of  the      
topography4 ,if1 on the other hand1 a   
surface is characterized by  topographic
 features which streams cannot develop1 
such as enclosed  depressions1 or hills 
and ridges whose arrangement is         
independent of  drainage lines1 other   
agents besides rain and surface streams 
have been  concerned in its development4
          ,,special ,,features          

,,resulting ,,from ,,special            
,,conditions ,,of ,,erosion4    ,many   
striking topographic and scenic features
 result from rain and  river erosion4   
,some of them depend primarily on the   
conditions of  erosion1 such as climate1
 altitude1 etc41 while others depend    
largely  on the structure and resistance
 of the rock4 ,between these two classes
  there is no sharp line of demarkation4
 ,illustrations of two types1  dependent
 largely but by no means wholly on      
conditions independent of  the rock1 are
 cited at this point4 ,others will be   
mentioned in other  connections4        
,bad-land topography4--,to a type of    
topography developed in early  maturity 
in certain high regions where the rock  
is but slightly1 though  unequally1     
resistant1 a special name is sometimes  
given4 ,such regions  are termed bad    
lands4 ,some idea of bad-land topography
 is gained from  ,figs4 #ge to #gh4     
,bad-land topography is found in various
 localities  in the ,west1 but          

especially in western ,nebraska and     
,wyoming1 and the  western parts of the 
,dakotas4 ,the formations here are often
 beds of  sandstone or shale1           
alternating with unindurated beds of    
clay4 ,climatic  factors are also       
concerned in the development of bad-land
 topography4 ,a  semi-arid climate1     
where the precipitation is much         
concentrated1 seems  to be most         
favorable for its development4 ,the     
bad-land topography is  most striking in
 early maturity4    ,illustration3 ,fig4
 #ge4--;,bad-land topography4 ,north of 
,scott's ,bluff1    ,neb4 7,darton1 ,u4 
,s4 ,geol4 ,surv47    ,illustration3    
,fig4 #gf4--,toadstool ,park1 ,sioux    
,co41 ,neb4 ,the peculiar    topography 
is the result of erosion working on     
jointed rocks of    unequal hardness in 
an arid region of considerable elevation
 where    rainfall is unequally         
distributed4 7,darton1 ,u4 ,s4 ,geol4   
,surv47    ,special forms of valleys2   
canyons4--,various conditions influence 

the  size and shape of valleys1         
especially in the early stage of their  
development4 ,if the altitude of the    
land be great1 the gradient of  the     
streams at this stage will be high4 ,a  
high gradient means a  swift stream1 and
 a swift stream erodes chiefly at its   
bottom4 ,high  altitudes therefore favor
 the development of deep valleys4 ,such 
valleys  will be narrow if the          
conditions which determine widening are 
absent  or unfavorable4 ,since slope    
wash is one of the main factors in the  
widening of valleys1 an arid climate    
favors the development of narrow        
valleys1 if there be sufficient water to
 maintain a vigorous stream4            
,narrowness and steepness of slopes will
 also be favored if the valley  is cut  
in rock which is capable of standing    
with steep faces4 ,thus  a stream may   
develop a narrow valley in indurated    
rock where it  would not do so in loose 
gravel1 and1 other things being equal1  
it  will develop a narrower valley in   

rock which is horizontally bedded  than 
in rock the beds of which are inclined4 
,aridity1 high altitude1  and the proper
 sort of rock structure therefore favor 
the development  of canyons1 and many of
 the young valleys in the western part  
of the  ,united ,states where these     
conditions prevail1 belong to this      
class4    ,illustration3 ,fig4          
#gg4--;,detail of bad-land topography4  
,head of ,indian    ,draw1 ,washington  
,co41 ,s4 ,d4 ,protoceras sandstone on  
,oreodon clay4    7,darton1 ,u4 ,s4     
,geol4 ,surv47    ,illustration3 ,fig4  
#gh4--;,detail of bad-land topography4  
,southwest foot    of ,mesa ,verde1     
,colo4 7,matthes1 ,u4 ,s4 ,geol4 ,surv47
    ,illustration3 ,fig4 #gi4--;,grand  
,canyon of the ,colorado4 7,peabody47   
,illustration3 ,fig4 #hj4--;,grand      
,canyon of the ,colorado4 7,peabody47   
,illustration3 ,fig4 #ha4--;,diagram    
showing the relations of depth and      
width of a valley1 the width of which is
 eight times the depth4    ,while all   

canyons are valleys1 most valleys are   
not canyons4 ,the  distinction between a
 canyon and a valley which is not a     
canyon is not  sharp4 ,the canyon       
depends for its distinctive character on
 the relation  of depth1 width1 and     
angle of slope to one another2 but any  
definition  of the depth1 width1 and    
angle of slope necessary to constitute a
  valley a canyon is arbitrary4#ca ,in  
popular usage the rule seems to  be that
 if a valley is sufficiently deep1      
narrow1 and steep-sided to  be          
distinctly striking1 it is called a     
canyon in regions where that  term is in
 use4 ,whether a valley is deep1 narrow1
 and steep-sided  enough to be striking 
clearly depends on the observer4 ,the   
,colorado  ,canyon 7,figs4 #gi and #hj7 
is the greatest canyon known1 but it is 
rarely  more than a mile deep1 and where
 its depth approaches this figure it  is
 often eight1 ten1 or even twelve miles 
wide from rim to rim4 ,its  width at    
bottom is little more than the width of 

the stream2 that is1  a few hundred     
feet4 ,its cross-profile throughout much
 of its course  is therefore not in     
keeping with the conventional idea of a 
canyon4  ,with a depth of one mile and a
 width of eight1 the slope1 if uniform1 
would have an angle of less than #ae4   
,such a valley is represented in  ,fig4 
#ha4 ,as a matter of fact the slopes of 
a canyon are not commonly  uniform4 ,the
 slopes represented in ,fig4 #hb        
correspond more nearly than  those of   
,fig4 #ha1 to the actual slopes of the  
,colorado ,canyon4 ,the  inequalities of
 slope are occasioned by the            
inequalities of hardness4  ,it is       
perhaps needless to say that to an      
observer on the rim of the  canyon the  
slopes seem several times as steep as   
those shown in the  diagrams4    ,like  
all valleys which are narrow relative to
 their depth1 the ,colorado  ,canyon1   
great as it is1 is a young valley2 for  
it represents but a  small part of the  
work which the stream must do to bring  

its drainage  basin to base-level4      
,while aridity and altitude are         
conditions which favor the development  
of canyons1 as shown by the fact that   
most canyons are high and dry  regions1 
they are not indispensable4 ,niagara    
,river has a canyon below  its falls    
7,pl4 ,,ix71 and the surrounding region 
is neither high nor  arid4 ,the narrow  
part of the valley has been developed by
 the recession  of the falls1 and is so 
young that side erosion has not yet     
widened the  valley or lowered its angle
 of slope to such an extent as to       
destroy  its canyon character4 ,this    
canyon is often called a gorge1 a term  
frequently applied to small valleys of  
the canyon type4    ,illustration3 ,fig4
 #hb4--;,cross-section of the ,colorado 
,canyon4 7,after    ,gilbert and        
,brigham47    ,illustration3 ,fig4      
#hc4--;,detail of erosion in the ,grand 
,canyon4    ,the inequalities of slope  
are the result of unequal hardness4 ,the
    vertical planes which give the      

architectural effect are the result of  
joints4 7,holmes47    ,plate ,x shows   
portions of the canyons of the          
,yellowstone and the  ,colorado rivers  
respectively4 ,in the first the contour 
interval is #ajj  feet1 and in the      
second1 #bej feet4 ,the horizontal scale
 is   7about #b miles to the inch7 in   
the first1 and  in the second4  ,these  
scales should be borne in mind in       
interpreting the map4    ,falls1 rapids1
 narrows1 and other peculiar features1  
due primarily to  inequalities in the   
hardness of the rock affected by        
erosion1 will be  considered later4     
,illustration3 ,fig4 #hd4--;,a surface  
illustrating the struggle for           
existence among gullies4 ,most of the   
smaller gullies shown on the    slope   
can have but little growth before being 
absorbed by their    larger neighbors4  
,a type of erosion surface common in the
 ,bad ,lands4    ,scott's ,bluff1 ,neb4 
7,darton1 ,u4 ,s4 ,geol4 ,surv47        
,,the ,,struggle ,,for ,,existence      

,,among ,,valleys ,,and ,,streams4      
,it is not to be inferred that every    
gully becomes a valley1 nor that  every 
small valley becomes a large one4 ,among
 valleys1 as among living  things1 there
 is a struggle for existence1 and       
fitness determines  growth and survival4
 ,at an early stage of its erosion      
history the  number of small valleys in 
a given area is often great1 while at a 
later stage the number is less and the  
size of the survivors greater4          
,illustration3 ,,plate ,,ix4            
,,niagara ,,falls4    ,u4 ,s4 ,geol4    
,surv4    ,illustration3 ,,plate ,x4    
,fig4 #a4 ,,yellowstone ,,park4    ,u4  
,s4 ,geol4 ,surv4      ,fig4 #b4        
,,arizona4    ,u4 ,s4 ,geol4 ,surv4     
,illustration3 ,fig4 #he4--;,diagram    
illustrating the absorption of one      
gully by another by lateral erosion4    
,the successive lines represent         
successive cross-sections4    ,one phase
 of the struggle for existence is often 
well illustrated  on a freshly exposed  

slope of clay4 ,the number of miniature 
gullies  which develop on such a slope1 
even in a single shower1 may be very    
large 7,fig4 #hd72 but the history of   
many of them is ephemeral4 ,if two      
adjacent ones are of unequal depth the  
widening of the deeper narrows  and     
finally eliminates the divide between   
them1 and the two become one  7,fig4    
#he74    ,another phase of the struggle 
for existence is shown in other         
situations4 ,examination of a good map  
of the north shore of ,lake  ,superior  
or the west shore of ,lake ,michigan    
shows a large number of  small streams  
and gullies 7,fig4 #a1 ,pl4 ,,iv74 ,the 
valleys are short and  narrow1 and      
between and beyond them are considerable
 areas untouched by  erosion4 ,the      
drainage near the lake is therefore     
young1 and each of the  small valleys is
 growing4 ,this condition of things is  
perhaps typical  of that which has been1
 is1 or will be along the average coast 
at a  certain stage in its erosion      

history4 ,no equal stretch of coast-line
  where erosion is far advanced can     
boast of a number of large rivers       
comparable to that of the many small    
ones along the coasts mentioned4  ,it   
therefore seems evident that of these   
many small streams a few only  will     
attain considerable size4    ,some of   
the methods by which the growth of the  
many is arrested  are easily understood4
 ,some of the young valleys on a given  
coast  will work their heads back into  
the land faster than others because  of 
inequalities of slope and material4     
,this will be true of the  tributaries  
no less than of their mains4 ,if valleys
 develop in ways  other than by head    
erosion 7see p4 #gc7 the chances are    
also against  their equality of growth4 
,if two streams1 such as a and c1 ,fig4 
#hf1 develop faster than the            
intermediate stream b1 it is clear that 
their tributaries may work back into the
 territory which at the outset  drained 
into b1 so as to cut off the supply of  

water from the latter  stream 7compare  
abc1 ,fig4 #hg74 ,as a result1 the      
growth of b  will be checked1 and       
ultimately stopped4 ,similarly other    
valleys1  such as f1 will get the better
 of their neighbors1 and many of the    
competitors1 as b1 d1 e1 and g will soon
 drop out of the  race4 ,between the    
stronger streams competition still goes 
on4 ,if a  and f develop faster than c  
its prospective drainage territory  will
 be prempted by its rivals 7compare     
,figs4 #hg and #hh74 ,thus as  the      
result of the unequal rate at which     
valleys are lengthened1 the  larger     
number of those which come into         
existence are arrested in their         
development4 ,as a result of growth in  
the manner indicated1 the basins  of    
even the large streams remain narrow at 
their lower ends while  they expand     
above4 ,this is the usual form of a     
drainage basin the  development of which
 has been normal4    ,illustration3     
,figs4 #hf-hh4--;,diagrams to illustrate

 successive stages    in the struggle   
for existence and dominion among        
streams4    ,did valleys grow in length 
only1 competition would not destroy the 
small ones2 it would simply limit them4 
,but valleys widen as well as  lengthen1
 and by widening1 adjacent valleys may  
eliminate the divide  between them and  
become one4 ,the elimination of the     
intervening ridge  may be by lateral    
planation 7p4 #hb71 or1 if the valleys  
be of unequal  depth1 by slope wash 7see
 ,fig4 #he74 ,by these and other        
processes many  young valleys are       
dwarfed1 and many others are destroyed4 
,piracy4--,streams do not always hold   
the courses which they establish  for   
themselves at the outset4 ,if the valley
 occupied by the stream a1  ,fig4 #hi1  
is deepened more rapidly than the valley
 occupied by b1 a  tributary from the   
former1 c1 may work back across the     
inter-stream  area to e and steal the   
head waters of that stream 7,fig4 #ij74 
,the  tributary which does the stealing 

is known as a pirate4 ,stream f  7,fig4 
#ij7 is said to be beheaded1 and its    
upper portion1 de1  diverted4 ,the      
beheaded stream is diminished in volume2
 or if its total  supply of water came  
in above the point of tapping it would  
disappear  altogether4    ,illustration3
 ,figs4 #hi and #ij4--;,diagrams to     
illustrate piracy4    ,the process may  
not end even here4 ,if after the        
diversion of de the  point in the       
channel to the left is lowered faster   
than the channel of  the beheaded stream
 f1 the divide between dg and the head  
of f  7,fig4 #ij7 will be shifted down  
the valley of the latter1 as shown in   
,fig4 #ia4 ,the shifting will go on     
until the divide reaches a position of  
stability1 that is1 until erosion on its
 opposite sides is equal4    ,the       
foregoing case may be called foreign    
piracy because the valleys  of different
 systems are concerned4 ,domestic piracy
 may also take  place1 as illustrated in
 the accompanying diagrams 7,figs4 #ib  

and #ic74  ,here a tributary to a       
crooked river may develop1 working back 
until  it taps the main at a higher     
point1 thus straightening the course of 
the stream4 ,the change takes place only
 when the highest point in the          
tributary valley is brought below the   
surface of the water in the main  stream
 at the point where the tapping takes   
place4 ,this would be likely  to occur  
only after the main stream had attained 
a low gradient1 for so  long as it is   
deepening its channel notably1 the small
 amount of water  flowing through the   
tributary valley would not be likely to 
bring it  down to the level of the main4
 ,in any case the flow of water from the
  main stream through the new valley    
would be likely to be started during    
flood1 and at such time the erosion in  
the new channel would be great4  ,the   
complete and final diversion of the     
stream through the new channel  might be
 a slow process4    ,illustration3 ,fig4
 #ia4--;,diagram showing the shifting of

 a divide    after piracy4              
,illustration3 ,figs4 #ib and           
#ic4--;,domestic piracy4 ,the tributary1
 a    of ,fig4 #ib1 develops headward   
until it taps the main stream at b1     
giving the result shown in ,fig4 #ic4   
,piracy may occur where the material in 
which the valleys are cut is            
homogeneous2 but1 as will be seen later1
 heterogeneity of material1  by         
determining unequal rates of erosion1   
stimulates the piratical  proclivities  
of streams4    ,an actual case of piracy
 is shown on ,plate ,,xi4 ,north and    
,south ,lakes  formerly drained westward
 to the ,schoharie ,creek1 the present  
head  of which is in the extreme        
northwest corner of the map4 ,the head  
of  ,kaaterskill ,creek1 which had a    
much higher gradient1 worked back  and  
captured the head of the                
westward-flowing stream1 diverting the  
drainage from ,north and ,south ,lakes  
to itself4 ,schoharie ,creek was thus   
beheaded4    ,plaatekill ,creek1 near   

the south limit of the map1 appears to  
have  beheaded the creek flowing west   
and northwest1 similarly diverting its  
head waters4 ,the ,dells1 ,wis41        
quadrangle 7,u4 ,s4 ,geol4 ,surv47      
affords an  illustration of domestic    
piracy4                                 
,,rate ,,of ,,degradation4    ,the      
amount of mechanical sediment which the 
,mississippi ,river carries  to the     
,gulf of ,mexico is estimated to        
represent a rate of degradation  for the
 ,mississippi basin of about one foot in
 #ejjj years4 ,but the  mechanical      
sediment carried to the ,gulf does not  
really represent the  total degradation 
of the basin1 for the water which sinks 
beneath the  surface is dissolving more 
or less rock substance1 especially lime 
carbonate4 ,this material is carried to 
the sea in solution1 and does  not      
appear in the sediment on which the     
above estimate is based4 ,taking  into  
account the matter dissolved by the     
water and carried to the sea  in        

solution1 the average rate of           
degradation for the ,mississippi basin  
is estimated at one foot in #cjjj to    
#djjj years4    ,it is not to be        
inferred that this rate is uniform1 or  
even that  erosion at any rate          
whatsoever is taking place in all parts 
of the  basin4 ,such is not the fact4   
,on the whole the rate of erosion is    
doubtless greatest toward the margins of
 the basins where the land  is in its   
topographic youth or early maturity4 ,it
 is notably less in  the middle courses 
of the valleys1 and erosion is locally  
exceeded by  deposition along the lower 
courses of the ,mississippi and some of 
its  main tributaries4    ,the average  
elevation of ,north ,america is not     
accurately known1 but it  is probably   
not far from #bjjj feet4 ,if the present
 rate of degradation1  say one foot in  
#cejj years1 were to continue1 it would 
take something  like #g1jjj1jjj years to
 bring the continent to sea-level4 ,but 
this rate  of degradation could not     

continue to the end1 for as the         
continent  became lower streams would   
become sluggish and erosion less rapid4 
,long before the continent reached      
base-level the rate of degradation1  so 
far as dependent on mechanical erosion1 
would become so slow that  the time     
necessary to bring the continent to     
sea-level would be almost  inconceivably
 prolonged4 ,furthermore1 it is quite   
possible that  the land is suffering1 or
 is liable to suffer1 uplift1 relative  
or  absolute4 ,if the rate of rise were 
equal to the rate of degradation the    
average height of the continent would of
 course not be affected4      ,the      
amount of sediment carried by streams in
 suspension varies    notably according 
to the stage of the water4 ,during a    
year when    the stream was under       
careful study the ,mississippi at       
,carrollton    7,miss47 was found to    
carry  of its weight of sediment during 
the high-water stage of ,june1 and      
during the low-water of    ,october1 the

 average for the year being 4 ,the      
average of a    greater number of       
records gives about  as the average     
ratio    between the weight of the      
sediment and the weight of the water4   
,this corresponds to about  by volume1  
the average specific    gravity being   
about #a4i4 ,the amount of material     
carried in the    upper part of the     
water was notably less than that carried
 at    greater depths1 but that carried 
midway between top and bottom was       
about the same as that carried at the   
bottom4#cb      ,the discharge of the   
,mississippi ,river is about            
#ai1ejj1jjj1jjj1jjj    cubic feet of    
water per year1 and the sediment it     
carries in    suspension is estimated to
 weigh about #hab1ejj1jjj1jjj pounds4   
,this    is equivalent to about         
#f1gad1fid1djj cubic feet4 ,it is       
estimated    that about #gej1jjj1jjj    
cubic feet of sediment is rolled along  
the    bottom1 giving a total of        
#g1dfh1fid1djj cubic feet as the        

aggregate    annual load carried to the 
,gulf by the river4 ,this would be      
adequate to cover an area one square    
mile in extent to the depth of    #bfh  
feet per year4    ,illustration3 ,,plate
 ,,xi4      ,,part ,,of ,,the           
,,catskills1 ,,new ,,york4    ,u4 ,s4   
,geol4 ,surv4    ,illustration3 ,,plate 
,,xii4      ,fig4 #a4 ,,new ,,mexico4   
,u4 ,s4 ,geol4 ,surv4      ,fig4 #b4    
,,virginia1 ,,west ,,virginia ,,and     
,,maryland4    ,u4 ,s4 ,geol4 ,surv4    
,,analyses ,,of ,,american              
,,river-,,waters4#cc            ,reduced
 to ,parts per #ajjj by ,dr4 ,h4 ,j4    
,van ,hoesen4                           
----------------------------------------
----------------------------    ,name of
 river                            ,bear 
,croton                                 
,collected at                           
,evanston1 ,wy4    ,reservoir1 ,new     
,york ,city                             
,date                                   
,dec41 #ahgc          #ahha             

,analyst                                
,f4 ,w4 ,clarke      ,e4 ,waller        
,reference                              
,bulletin ,no4 #i1 ,u4 ,water supply of 
,s4 ,geol4 ,surv41    ,new ,york ,city1 
p4 #cj             #ahha                
----------------------------------------
----------------------------    ,sodium1
 ,na                            4#jjhb  
#b4jjbih                                
,potassium1 ,k                          
444444             4#jjaed              
,calcium1 ,ca                           
4#jdcb             4#jjije              
,magnesium1 ,mg                         
4#jabe             4#jjccf              
,chlorine1 ,cl                          
4#jjdi             4#jjbac              
,carbonic acid1 ,,co1                   
#c4jihb         #cd4jbbdh               
,sulphuric acid1 ,,so                   
4#jaje             4#jjdda              
,phosphoric acid1 ,h,,po                
,nitric acid1 ,,hno                     
444444             444444               

,silica1 ,si,o                          
4#jjgj             4#jccfj              
,alumina1 ,al,o                         
,sesquioxide of iron1 ,fe,o             
444444                                  
,sesquioxides of iron and alumina1      
,fe,o and ,al,o                         
4#jjjgh                                 
iron and manganese1                     
,fe,o and ,mn,o                         
,carbonates of iron and manganese1      
,fe,c,o and ,mn,c,o                     
,oxide of iron1 ,fe,o                   
manganese1 ,mn,o                        
,hydrogen in bicarbonates1 ,h           
,chloride and sulphate of sodium1       
,na,cl1 and ,na,,so                     
,ammonia1 ,,nh                          
444444                                  
,organic matter                         
4#jjdjj                                 
,carbonates and sulphates of            
,na1 ,k1 and ,mg                        
444444           444444                 
----------------------------------      

4#ahde            4#jhdcc               
----------------------------------------
----------------------------            
----------------------------------------
----------------------------------------
------     ,cumberland     ,delaware    
,hudson1 ,n4 ,y4     ,james        ,los 
,angeles   ,maumee1 ,o4                 
,reservoir at  ,reservoir at            
,richmond ,water  ,hydrant at           
,nashville1     ,trenton1               
,works1 ,va4    ,los ,angeles1          
,tenn4         ,n4 ,j4                  
,cal4                                   
----------------------------------------
----------------------------------------
------                                  
,oct4 #bd4 #ahgf1 ,sept4 #h1 #ahgh      
after light rain                        
,n4 ,t4 ,lupton   ,h4 ,wurtz     ,c4 ,f4
 ,chandler  ,w4 ,h4 ,taylor   ,w4 ,j4   
,jones ,c4 ,f4 ,chandler                
,am4 ,chemist1 ,geol4 of ,n4,j41 ,public
 ,health    ,ann4 ,rept4     ,rept4     
,cal4   ,report of       ,july #af1     

#ahgf1 #ahfh1 p4 #gjb ,papers1 ,vol4    
,i1,board of ,health1 ,state ,board     
,toledo ,water         p4 #af           
,am4 ,pub4    ,richmond1 ,va41   of     
,health1  ,works1 #ahha                 
,health ,ass4  #ahgf                    
#ahgh                                   
----------------------------------------
----------------------------------------
------                                  
4#jajcb       4#jjjgb         4#jjbdd   
4#jjbcd        4#jbifh        4#jjafb   
4#jjjej       4#jjagh         4#jjjeh   
4#jjbea        444444        4#jjcji    
4#jbihg       4#jaajd         4#jbbbj   
4#jabhd        4#jagej        4#jbfde   
4#jjbhj       4#jjdce         4#jjdfe   
4#jjcgg        4#jbjig        4#jjddc   
4#jjbii       4#jjaba         4#jjeha   
4#jjaje        4#jajdd        4#jjbej   
4#jegbg       4#jbeeb         4#jgbgh   
4#jbied        4#jefce        4#jddch   
4#jjefc       4#jjage         4#jabeg   
4#jjcfc        4#jegbd        4#jadja   
444444       4#jjagb                    

,trace        4#jbfch                   
4#jjeaa       444444         444444     
4#jjbca        444444        444444     
,trace       4#jjheb         4#jjfih    
4#jajbd        4#jbjje        4#jjgbd   
4#jjjda        4#jjaga        444444    
4#jjjdg                                 
444444                    444444        
4#jjajj                                 
4#jjfga                      4#jjabj    
444444                                  
4#jjjgb        444444                   
444444                                  
4#jjddc                                 
,trace         444444                   
4#jjaba                                 
444444                                  
444444                    444444        
4#jjjja                      444444     
4#jajhg                                 
4#jafff                    4#jaaig      
4#jjbii                      4#jjdii    
444444       444444         444444      
444444        444444        444444      
----------------------------------------

----------------------------------------
------        4#acghf4      4#jfgie     
4#adbch          4#jgbdf        4#bddge 
4#ajiga                                 
----------------------------------------
----------------------------------------
------                                  
----------------------------------------
----------------------------------------
-------      ,mississippi    ,ottawa    
,passaic       ,rio ,grande             
,sacramento  ,st4 ,lawrence             
del ,norte                              
,hydrant1 ,city   ,st4 ,ann's ,lock1 #d 
miles above   ,fort ,craig1   ,hydrant1 
,south side        ,water ,works1       
,montreal1 ,can4  ,newark1 ,n4 ,j4      
,new ,mexico   ,sacramento1   ,point des
      ,new ,orleans1 ,la4               
,cal4       ,cascades                   
,mar4 #i1 #ahed       #ahea             
#ahgc     ,sept41 #ahgh  ,mar4 #cj1     
#ahfc                                   
,w4 ,j4 ,jones      ,t4 ,s4 ,hunt   ,e4 
,n4 ,horsford    ,o4 ,loew     ,w4 ,j4  

,jones  ,t4 ,s4 ,hunt                   
,rept4 ,la4 ,state ,geol4 of            
,canada1,geol4 of ,n4 ,j41 ,u4 ,s4      
,geog4   ,rept4 ,cal4    ,geol4 of      
,board of ,health1  #ahfc1 p4 #efg      
#ahfh1 p4 #gjh ,surv4 west of ,state    
,board    ,canada1        #ahhb1 p4 #cgj
                                        
#ajjth ,m41 ,vol4 of ,health1  #ahfc1 p4
 #efg                                   
,,iii4 p4 #egf    #ahgh                 
----------------------------------------
----------------------------------------
-------        4#jcaj           4#jjbci 
4#jbceg         4#jcbbj        4#jjbjj  
4#jjeac                                 
444444           4#jjaci         4#jjafc
         4#jjjfc        444444          
4#jjaae                                 
4#jcgb           4#jjiib         4#jadei
         4#jafcc       4#jabgi          
4#jcbcc                                 
444444           4#jjafa         4#jjdjd
         4#jjabc       4#jjaba          
4#jjehe                                 

4#jdhj           4#jjjgf         4#jcaib
         4#jcfjd       4#jjbdb          
4#jchc           4#jbbee         4#jbfcd
         4#jajbe       4#jjhhg          
4#jfhcf                                 
4#jjaid         4#jagaf         4#jdgjj 
4#jjcig       4#jjhca                   
,trace                        ,faint    
trace   4#jagid        ,trace           
444444         ,trace                   
4#jbjfj                      ,trace     
4#jcafg       4#jcgjj                   
,trace         4#jacdb        ,trace    
4#jjabj       ,trace                    
444444                                  
444444                        444444    
4#jajhh        444444                   
,trace                         ,trace   
,trace                                  
,trace                                  
,trace                                  
444444                                  
4#jbdca                                 
,trace                                  
444444                                  

4#jacib                                 
4#jaed           444444         444444  
444444       444444       444444        
----------------------------------------
----------------------------------------
-------        4#afii           4#jfaaf 
4#acbfg         4#aegfj       4#aadhd   
4#afjee                                 
----------------------------------------
----------------------------------------
-------                                 
----------------------------------------
----------------------------------------
--------------------         ,humboldt  
,truckee            ,walker             
,jordan         ,mohawk        ,genesee 
,battle ,mt41 ,nev4  ,lake ,tahoe1 ,nev4
    ,mason ,valley1     ,utah ,lake     
,utica1 ,n4 ,y4 ,rochester1 ,n4 ,y4     
,nev4                                   
,dec41 #ahgb       ,oct41 #ahgb         
,oct41 #ahgb       ,nov41 #ahgc         
,t4 ,m4 ,chatard      ,f4 ,w4 ,clarke   
,f4 ,w4 ,clarke     ,f4 ,w4 ,clarke     
,c4 ,f4 ,chandler ,c4 ,f4 ,chandler     

,u4 ,s4 ,geol4 ,surv41,u4 ,s4 ,geol4    
,surv41,u4 ,s4 ,geol4 ,surv41 ,bulletin 
,no4 #i1   ,johnson's      ,johnson's   
,monograph ,,xi1      ,monograph ,,xi1  
,monograph ,,xi1      ,u4 ,s4 ,geol4    
,cyclopedia1     ,cyclopedia1           
p4 #da             p4 #db             p4
 #dj          ,surv41 p4 #bi     ,vol4  
,,iv        ,vol4 ,,iv                  
----------------------------------------
----------------------------------------
--------------------                    
4#jdfg            4#jjgc                
4#jcah            4#jagh          4#jjcf
          4#jjdd                        
4#jajj            4#jjcc                
,trace           444444          4#jjji 
4#jjbc                                  
4#jdhi            4#jjic                
4#jbbh            4#jeeh          4#jcah
          4#jdag                        
4#jabd            4#jjcj                
4#jjch            4#jahf          4#jjfi
          4#jjhif                       
4#jjge            4#jjbc                

4#jaca            4#jabd          4#jjbc
          4#jjbd                        
#c4aedd         #c4jbhg                 
#ce4jegf            4#jfjh              
4#jefi          4#jfdf                  
4#jdgg            4#jjed                
4#jbhd            4#acjf          4#jahg
          4#jdca                        
444444                                  
444444                                  
444444           444444         444444  
444444                                  
4#jcbf            4#jacg                
4#jbbe            4#jajj          4#jjfg
          4#jjad                        
4#jjac                                  
444444         444444                   
4#jjac          4#jjad                  
444444                                  
444444        444444         444444     
444444        444444         444444     
444444        444444         444444     
444444            444444         4#jbcd 
4#jbej                                  
444444           444444                 

444444            444444        444444  
444444                                  
----------------------------------------
----------------------------------------
--------------------          4#cfae    
4#jgcj              4#ahjj              
4#cjfj         4#aebe          4#aiebf  
----------------------------------------
----------------------------------------
--------------------    ,the following  
table#cf gives the percentage of        
material carried in  suspension by      
various rivers3                         
,height      ,thickness                 
,mean                            in     
,feet     of ,sediment                  
,annual                           of    
,column   in ,inches                    
,drainage  ,discharge                   
,ratio of   of ,sediment if ,spread     
,areas in  7in ,cubic                   
,sediment to with a ,base   over        
,square   ,feet47 per ,total ,tons      
,water by    of ,one     ,drainage      
,river4    ,miles4    ,second4          

,annually4     ,weight4   ,square ,mile4
  ,area4                                
----------------------------------------
-------------------------------------   
,potomac        #aa1jdc    #bj1afj      
#e1eeg1bej  #a 3  #c1ege      #d4j      
4#jjdcc  ,mississippi #a1bdd1jjj        
#faj1jjj  #djf1bej1jjj  #a 3  #a1ejj    
#bda4d     4#jjbbc  ,rio ,grande        
#cj1jjj     #a1gjj    #c1hcj1jjj  #a 3  
#bia      #b4h     4#jjaaf  ,uruguay    
#aej1jjj   #aej1jjj   #ad1ghb1ejj  #a 3 
#aj1jjj     #aj4f     4#jjjhe  ,rhone   
#cd1hjj    #fe1hej   #cf1jjj1jjj  #a 3  
#a1gge     #ca4a     4#jajge  ,po       
#bg1ajj    #fb1bjj   #fg1jjj1jjj  #a 3  
#ijj     #ei4j     4#jaaci  ,danube     
#cbj1cjj   #cae1bjj  #ajh1jjj1jjj  #a 3 
#b1hhj     #ic4b     4#jjced  ,nile     
#a1ajj1jjj   #aac1jjj   #ed1jjj1jjj  #a 
3  #b1jej     #ch4h     4#jjjdb         
,irrawaddy     #abe1jjj   #dge1jjj      
#bia1dcj1jjj  #a 3  #a1faj    #bji4j    
4#jbjje  ,mean          #ccd1fic        
#bja1dfh  #aji1fdi1igb  #a 3  #b1gca    

#gf4fe    4#jjfad                       
----------------------------------------
-------------------------------------   
,the composition of rain-water falling  
near ,london1 as determined by          
analysis1 was as follows3#cg            
,organic carbon                         
4#ii part in #a1jjj1jjj of water4       
,organic nitrogen                       
4#bb                        ,ammonia    
4#ej                        ,nitrogen as
 nitrates and nitrites    4#jg          
,chlorine                               
#f4cj parts in                 ,total   
solids                       #ci4ej     
,a comparison of the composition of     
rain-water with that of springs    and  
rivers gives some idea of the solvent   
work of water4 ,from a    study of the  
water of nineteen of the principal      
rivers of the world    ,murray has      
compiled the following table#ch showing 
the amount of    mineral matter in      
average river water3     ,,material ,,in
 ,,solution ,,in ,,one ,,cubic ,,mile   

,,of ,,average ,,river ,,water4#ci      
,constituents4                   ,tons  
in a ,cubic ,mile4    ,calcium carbonate
 7,ca,c,o7                 #cbf1gaj     
,magnesium carbonate 7,mg,c,o7          
#aab1hgj    ,calcium phosphate 7,ca,p,o7
                 #b1iac    ,calcium     
sulphate 7,ca,s,o7                      
#cd1cfa    ,sodium sulphate 7,na,,so7   
#ca1hje    ,potassium sulphate 7,k,,so7 
#bj1ceh    ,sodium nitrate 7,na,n,o7    
#bf1hjj    ,sodium chloride 7,na,cl7    
#af1feg    ,lithium chloride 7,li,cl7   
#b1dfb    ,ammonium chloride 7,,nh,cl7  
#a1jcj    ,silica 7,si,o7               
#gd1egg    ,ferric oxide 7,fe,o7        
#ac1jjf    ,alumina 7,al,o7             
#ad1cae    ,manganese oxide 7,mn,o7     
#e1gjc    ,organic matter               
#gi1jbj                                 
-------        ,total dissolved matter  
#gfb1ehg      ,murray also estimates    
that the aggregate amount of water      
flowing    into the sea annually is     
about #febh cubic miles1 which1 on the  

above basis1 would carry about          
#d1ige1jjj1jjj tons of mineral matter   
in solution4      ,a large number of    
analyses of waters of rivers from the   
,united    ,states and ,canada give an  
average of about 4#ae1jdd part in a     
thousand of mineral matter in solution1 
more than one-third being    ,ca,c,o4   
,the average amount of mineral matter in
 solution in #dh    ,european streams   
cited by ,bischoff#dj is 4#babg part in 
a thousand1    of which ,ca,c,o is      
rather more than half4 ,the average     
mineral matter    in solution in #cf    
rivers cited by ,roth#da 7including some
 of those    tabulated by ,bischoff7 is 
4#bjcc part in a thousand1 of which     
,ca,c,o    is slightly less than        
one-half4      ,an average for ,american
 and ,european rivers1 so far as        
determinable    from data at hand1 is   
about 4#ahhh part in a thousand in      
solution1    of which ,ca,c,o is        
slightly less than one-half4 ,these last
 figures    are probably not very far   

from an average for river water in      
general4      ,the following table shows
 the total amount of solids carried in  
solution by the rivers indicated3#db    
,rhine           #e1haf1hje tons per    
year4    ,rhone           #h1bij1dfd    
,danube         #bb1eba1dcd             
,thames            #fac1icj             
,nile           #af1iej1jjj             
,croton             #ff1gie             
,hudson            #dch1jjj             
,mississippi   #aab1hcb1aga             
,,economic ,,considerations4    ,certain
 considerations of human interest in    
connection with river  erosion are      
worthy of note4 ,when a drainage system 
has reached its  mature stage its basin 
has the roughest topography which it    
will have  at any time during that cycle
 of erosion4 ,at that stage1 therefore1 
road construction is relatively         
difficult4 ,if the relief be great1     
roads must follow the valleys1 or the   
crests of the ridges between  them1 if  
they would avoid heavy grades4 ,in such 

regions roads are  usually few and      
crooked4    ,the stage of development of
 valleys has an influence on the        
navigability of their streams4 ,streams 
well advanced in life are much  more    
readily navigable than young ones1      
because their grades are lower  and     
their volumes of water greater4 ,old    
streams1 on the other hand1 are         
sometimes depositing sand or silt along 
their lower courses to such an  extent  
as to interfere with navigation4    ,at 
certain stages of their development the 
power of streams is more  easily        
utilized than at others4 ,young streams1
 depending as they do for  their supply 
on the rainfall of a limited area1 are  
likely to be fitful  in their flow1 and 
therefore unreliable as a source of     
power4 ,this is  especially true where  
the precipitation is unequally          
distributed1 and  where the slopes are  
steep and free from forests4 ,because of
 their  great volume1 old and large     
streams1 though sluggish1 have great    

power1  but it is less easily           
controlled4 ,where streams are large    
enough to be  navigable industrial      
considerations often prevent the        
utilization of  their power1 the streams
 being more serviceable as highways than
 as  sources of power4 ,other things    
being equal1 it follows that streams are
  most available for water-power when   
they are large enough to have a         
moderately steady flow1 and not so large
 as to be beyond ready control1  or to  
be valuable for purposes of navigation4 
,streams are subject to more disastrous 
floods in some stages of their          
development than in others4 ,floods     
resulting from heavy rains are  likely  
to be greatest where the slopes above   
the drainage lines are on  the whole    
greatest1 for this is the condition     
under which the water is  most quickly  
gathered into the drainage channels4    
,the most disastrous  floods1 humanly   
speaking1 are those which affect        
wide-bottomed valleys1  where the flats 

are settled4 ,in such cases a relatively
 slight rise  may flood very extensive  
areas4 ,in such valleys the most        
disastrous  floods are generally in the 
spring1 when the waters from the melting
  snows of the preceding winter are     
being discharged4#dc ,many other        
considerations enter into the problem of
 floods4 ,the presence of  forests and  
other forms of vegetation on the slopes 
retards the flow of  water into the     
valleys1 and so tends to prevent floods1
 or at any rate  to make them less      
severe4 ,porous soil and subsoil1 or in 
their absence  porous rock1 absorb the  
rainfall1 and prevent its prompt descent
 into  the valleys and so tends to      
prevent or diminish floods4    ,the     
acreage of arable land within a given   
area stands in some relation  to its    
drainage development4 ,at an early stage
 in its erosion history1  before an     
upland has been dissected by valleys1   
nearly all of it may  be arable4 ,later1
 when drainage is at its maturity1 and  

when hillsides  and ridge slopes        
constitute a large part of the area1    
there is probably  the least acreage of 
arable land4 ,this is especially true if
 the slopes  are so steep as to allow   
the soil to be readily washed away4 ,at 
a still  later stage1 when the valley   
bottoms have become wide and the slopes 
of the ridges and hills so reduced as to
 be available1 the area of  cultivable  
land is again increased4    ,marshes1   
ponds1 and lakes have some bearing on   
the resources and  industries of a      
region1 and they stand in a more or less
 definite  relation to the stage of     
erosion in which a region finds itself4 
,in its  youth ponds and lakes may      
occupy much of the surface2 in its      
maturity  they will have been largely   
drained4    ,these suggestions are      
sufficient to show that the topography  
of a  region1 even in so far as shaped  
by erosion1 touches human interests at  
many points4                            
,,analysis ,,of ,,erosion4#dd           

,erosion is the term applied to all the 
processes by which earthy matter  or    
rock is loosened and removed from one   
place to another4 ,it consists  of three
 sub-processes1 namely1 weathering1     
transportation1 and  corrasion4         
,weathering4    ,the term weathering is 
applied to nearly all those natural     
processes  which tend to loosen or      
change the exposed surfaces of rock4    
,the  lettering of inscriptions on      
exposed marble becomes fainter and      
fainter  as time goes by1 and finally   
disappears1 because the rock in which   
the letters were cut has weathered away4
 ,some of it has crumbled off  as the   
result of the expansion and contraction 
induced by changes of  temperature1 and 
some of it has been dissolved by the    
rain which has  fallen upon it4 ,in this
 case the weathering is effected partly 
by the  atmosphere and partly by water4 
,these are the chief1 but not the only  
agents concerned in the general         
processes of weathering4 ,those phases  

of weathering which are the result of   
the activities of the atmosphere1       
whether physical or chemical1 have been 
discussed in connection with  the       
atmosphere 7pp4 #db and #ed74    ,the   
rain which falls upon the surface of    
exposed rock1 and that which  sinks     
through the soil to the solid rock      
below1 dissolves1 even if  slowly1 some 
of the rock constituents4 ,each         
constituent of a rock  composed of      
several minerals may be looked upon as a
 binding material  for the others4 ,when
 one is dissolved the rock crumbles1    
much as mortar  does when the lime which
 cements the sand is dissolved4    ,the 
solution of mineral matter by ground    
water1 as well as the  other chemical   
changes it effects1 is greatly augmented
 by the  impurities1 especially carbonic
 and other organic gases1 dissolved by  
the water from the atmosphere and the   
soil4 ,the commonest chemical  changes  
effected by the joint action of water   
and air1 oxidation  and carbonation1    

have been referred to in ,chapter ,,ii4 
,hydration is  more exclusively the work
 of water1 and is one of the commonest  
processes of rock change1 and often of  
rock disintegration4 ,numerous  other   
less simple chemical changes resulting  
from the activities  of ground water are
 constantly in progress1 and in so far  
as they  lead to the disintegration of  
rock are processes of weathering4 ,many 
chemical changes involve notable changes
 in volume of the mineral  matter       
concerned4 ,merrill has calculated that 
in the conversion of  the granitic rock 
of the vicinity of ,washington1 ,d4 ,c41
 into soil1  its volume has been        
increased #hh percent41 largely as the  
result  of hydration4#de ,even when the 
chemical changes do not themselves      
directly involve the disintegration of  
the rock1 the accompanying  increase of 
volume is sometimes sufficient to cause 
its physical  disruption4 ,this also may
 be regarded as a phase of weathering4  
,the weathering accomplished by water1  

or under its influence1 proceeds  at    
rates which vary with the composition of
 the rock1 the amount and  composition  
of the water1 the temperature1 and      
certain other factors  less susceptible 
of brief statement4 ,the weathering     
effected by ground  water has a wider   
range both in area and depth than that  
due to  changes of temperature1 for     
while the latter is effective only where
  temperature changes are considerable1 
and where coherent material lies  at the
 surface 7p4 #de71 the former is        
operative to all depths to which  water 
sinks4    ,illustration3 ,fig4          
#id4--,talus accumulation at the base of
 a steep    bluff4 ,weber ,canyon1      
,uinta ,mountains1 ,utah4 ,the talus has
 accumulated    since the last          
glaciation of the valley and is         
therefore of very    recent origin4     
7,church47    ,there are other processes
 of weathering not due directly either  
to  the atmosphere or to water4 ,the    
roots of trees and smaller plants       

frequently grow into cracks of rocks1   
and1 increasing in size1 act much  like 
freezing water 7p4 #de7 in similar      
situations4 ,this wedge-work of  roots  
is a phase of weathering4    ,from the  
faces of steep cliffs masses of rock    
frequently fall4 ,however  dislodged1   
their descent is effected by gravity4   
,the quantities of  dbris at the bases  
of many cliffs1 forming slopes of talus 
7,fig4  #id71 testify to the importance 
of the action of gravity in getting     
material from higher to lower levels4   
,another phase of gravity-work is  shown
 in ,fig4 #ie4 ,here1 under the         
influence of gravity and expansion  and 
contraction1 due to freezing and thawing
 and wetting and drying1  the surface   
material is creeping down slope4 ,in the
 process the rock  is being broken4 ,the
 process illustrated by the figure      
involves  weathering as well as other   
factors4    ,the foregoing are among the
 commoner processes of weathering1      
although  they do not exhaust the list4 

,the more active and tangible processes 
by which surface rocks are broken up1   
such as wave wear1 river wear  and      
glacier wear1 are processes of          
corrasion4 ,the mechanical wear         
effected by wind-driven sand might be   
considered either as corrasion  or as   
weathering4 ,it is more likely to be    
regarded as corrasion if the  amount of 
wear is considerable enough to be       
obvious4 ,rock is sometimes  decomposed 
by the chemical action of hot vapors1   
gases1 and waters  rising to the surface
 from considerable depths4 ,this is     
often seen in  volcanic regions4 ,a     
conspicuous illustration is seen in the 
canyon of  the ,yellowstone in the      
,national ,park4 ,decay of this sort is 
perhaps not  properly weathering1 but is
 not always readily distinguished from  
it4    ,illustration3 ,fig4 #ie4--,shows
 the downward creep of soil and slaty   
rock under the influence of gravity4    
,the importance of weathering in the    
general processes of erosion is  shown  

in many ways4 ,in regions where the     
mantle rock is the product  of the decay
 of the solid rock beneath1 and such    
regions constitute a  large portion of  
the earth's surface1 the soil and       
subsoil represent  the excess of        
weathering over transportation4 ,since  
most of the earth's  surface is covered 
with soil to a greater or less depth1 it
 is clear  that1 on the whole1          
weathering keeps ahead of               
transportation4 ,again1  it is clear    
that the loosening of rock by weathering
 greatly increases  the erosion which a 
given amount of moving water can        
accomplish4  ,not only this1 but        
weathering plays a much more important  
rle in  the development of valleys than 
is commonly realized4 ,this is best     
illustrated by the valleys of young     
swift streams4 ,the valley which  is not
 at its top ten times as wide as its    
stream is rare4 ,the stream  which has  
such a canyon has been cutting chiefly  
at its bottom4  ,ignoring its lateral   

corrasion1 which is slight1 the valley  
which it  would cut would have a width  
equal to its own4 ,this is illustrated  
by  ,fig4 #if4 ,weathering in its       
broadest sense is largely responsible   
for  the width of such a valley1 in so  
far as it exceeds the width of the      
stream4 ,the work of weathering1 slope  
wash1 etc41 has been to get the         
material which originally lay between a1
 b1 and c down to the  stream4 ,the     
stream has then carried it away4 ,the   
above illustration  would not apply to  
old and sluggish streams1 for they1 by  
their  meandering1 widen their valleys  
independently of weathering4            
,illustration3 ,fig4 #if4--;,diagram of 
a valley the top of which is ten        
times the width of the stream4          
,weathering is a part of erosion1 but   
only a part4 ,in so far as it is        
effected by solution the process        
involves the transportation of that     
which is dissolved to some other point4 
,transportation is also involved  to    

some extent in the other processes of   
weathering1 but the central  idea of the
 processes embraced under this term is  
the loosening and  disrupting of rock by
 which it is prepared for               
transportation4                         
,transportation4    ,the second element 
of erosion is transportation4 ,the      
transportation  of mechanical sediment  
is to be distinguished from the         
transportation  of materials in         
solution4 ,in so far as mineral matter  
is dissolved  it becomes1 so far as     
flowage is concerned1 a part of the     
stream4 ,if  the quantity dissolved were
 large it might influence the mobility  
of  the water1 but the amount is usually
 too slight to influence the flow       
sensibly4    ,the sediment transported  
by a stream is either rolled along its  
bottom  or carried in suspension at some
 higher level4 ,the coarser materials   
7gravel and sand7 are carried chiefly in
 the former position1 and the  finer    
7silt and mud7 largely in the latter4   

,transporting power and velocity4--,the 
transporting power of running  water    
depends on its velocity4 ,the formula   
expressing the relations  between them  
is as follows3 ,transporting power1 t1  
varies as the  sixth power of velocity1 
v1 7tv72 that is1 doubling the velocity 
of the stream increases its transporting
 power #fd-;fold4 ,strictly  speaking1  
this means that if a stream of given    
velocity is just able  to move a stone  
of a given size1 a stream with double   
that velocity  will be just able to move
 a stone of the same shape #fd times as 
large  as the first4 ,this may be       
graphically illustrated as follows3 ,let
 a  current be supposed just able to    
move the cube a 7,fig4 #ig74 ,if the    
current be doubled1 twice as much water 
will strike the same surface  with twice
 the force in the same time2 that is1   
the force exerted on  the cube a will be
 quadrupled4 ,it will1 therefore1 be    
able not only  to move the one cube1 but
 it will be able to move three other    

cubes  7b1 c1 and d7 besides 7,fig4     
#ih74 ,the same current against any     
other equal surface would also be able  
to move four small cubes1 and  there are
 sixteen such surfaces on the face of   
the large cube 7,fig4  #ii74 ,it follows
 that the dimension of the cube which   
the stream with  the doubled velocity   
can move is four times as great as that 
of the  cube which the original current 
could move1 and the cubical contents  of
 such a cube is #fd times as great as   
that of the first 7#fd  #b7  7,fig4     
#ii74 ,swift streams1 therefore1 have   
enormously greater power of             
transportation than sluggish ones4 ,it  
does not necessarily follow that        
transportation keeps pace with          
transporting power2 that depends on the 
accessibility of materials suitable for 
transportation4 ,a stream of  great     
transporting power1 like the ,niagara at
 its rapids1 may carry  little sediment1
 because there is little to be had4     
,the velocity of a stream depends       

chiefly on three elements--its          
gradient1 its volume1 and its load1     
7i4e41 the sediment it is moving74  ,the
 higher the gradient the greater the    
volume1 and the less the load  the      
greater the velocity4 ,the relation     
between gradient and velocity  is       
evident2 that between volume and        
velocity is illustrated by every  stream
 in time of flood1 when its rate of flow
 is greatly increased4  ,the relation   
between velocity and load is less       
obvious1 but none the  less definite4   
,every particle of sediment carried by a
 stream makes  a draught on its energy1 
and energy expended in this way reduces 
the  velocity4 ,the draught on a        
stream's energy of a particle carried in
  suspension is measured by its mass    
into the distance it would fall in a    
unit of time in still water4 ,it follows
 that a large particle makes a  stronger
 draught on a stream's energy than the  
same amount of material  in smaller     
pieces4 ,it follows also that the       

comminution of sediment  facilitates    
transportation in much more than a      
simple ratio1 for not  only can a given 
amount of energy carry more fine        
material than coarse1  but a larger     
proportion of a stream's energy can be  
utilized in the  transportation of the  
fine4    ,illustration3 ,figs4          
#ig-ii4--;,diagrammatic representation  
of the effect    of increased velocity  
on transporting power4    ,how sediment 
is carried4--,coarse materials1 such as 
gravel stones1  are rolled along the    
bottoms of the swift streams which carry
 them4  ,their movement is effected by  
the impact of water4 ,the same is true  
to  a large extent of sand grains1      
especially if they be coarse4 ,so far as
  concerns the material rolled along the
 bottom it is to be noted that a        
stream's transporting power is dependent
 on the velocity of the water  at its   
bottom4 ,this is much less than the     
surface1 or even the average  velocity4 
,the particles of fine sediments1 such  

as silt and mud1 are  frequently carried
 by streams quite above their bottoms1  
as shown by  the roiliness of many      
streams4 ,a particle of mud is usually a
 small  bit of mineral matter1 the      
specific gravity of which is two or     
three  times that of water4 ,why does it
 not sink through the water and come  to
 rest at the bottom of the stream1 or   
suffer transportation as the  gravel    
does8    ,illustration3 ,fig4           
#ajj4--;,diagram to illustrate the      
relative strength    of the two forces  
acting on a particle in suspension4 ,the
 arrows    represent the relative       
strength of the two forces when the     
stream's    velocity is #e miles per    
hour4 ,no account is taken in the       
diagram of    the viscosity of the      
water1 or of the acceleration of        
velocity of    fall4    ,a particle of  
sediment in running water is obviously  
subject to two  forces1 that of the     
current which tends to move it nearly   
horizontally  down-stream1 and that of  

gravity which tends to carry it to the  
bed of the stream4 ,in ,fig4 #ajj1 the  
arrows ab and ac represent  respectively
 the relative force of gravity and a    
current of #e miles  per hour4 ,as a    
result of these two forces the particle 
would tend to  descend in the general   
direction of ad1 a line which represents
  the resultant of these forces1 though 
not the exact path which a  particle    
acted on by them would take in water4   
,if a river were the  simple            
straightforward current which it is     
popularly thought to be1  a particle in 
suspension would reach its bottom in the
 time it would  take to sink through an 
equal depth of still water1 for the     
descent  would be none the less certain 
and none the less prompt because of the 
forward movement of the water4 ,the     
current would simply be a factor in     
determining the position of the particle
 when it reached the bottom1  not the   
time of reaching it4 ,very fine         
particles1 like those of clay1  though  

having the same specific gravity as     
grains of sand1 would sink  less readily
 than coarser ones1 because they expose 
larger surfaces1  relative to their     
mass1 to the water through which they   
sink4 ,but even  such particles1 unless 
of extraordinary fineness1 would        
presently reach  the bottom if acted on 
only by a horizontal current and        
gravity4 ,since  even sediment which is 
not of exceeding fineness is kept in    
suspension  it is clear that some other 
factor is involved4 ,this is found1 in  
part  at least1 in the subordinate      
upward currents in a stream4    ,where a
 bowlder occurs in the bed of a stream  
7,fig4 #aja7 the water  which strikes it
 is in part forced up over it4 ,if there
 be many  bowlders the process is       
frequently repeated1 and the number of  
upward  currents is great4 ,any         
roughness will serve the same purpose1  
and  every stream's bed is rough to a   
greater or less extent4 ,where there    
are roughnesses at the sides of a       

channel1 currents are started which     
flow from them toward the center4 ,the  
varying velocities of the  different    
parts of a stream serve a similar       
purpose4 ,the curves in a  river tend to
 give the water a rotatory movement4 ,a 
river is therefore  to be looked upon   
not as a single straightforward current1
 but as a  multitude of currents1 some  
rising from the bottom toward the top1  
some  descending from top to bottom1    
some diverging from the center toward   
the sides1 and some converging from the 
sides toward the center4 ,the  existence
 of these subordinate currents is often 
evident from the  boiling and eddying   
readily seen in many streams4 ,it is1 of
 course1  true that the sum of the      
upward currents is always less than the 
sum of  the downward1 so that the       
aggregate motion of the water is down   
slope2  but it is also true that minor  
upward currents are common4 ,sediment   
in suspension is held up chiefly by such
 currents1 which1 locally  and          

temporarily1 overcome the effect of     
gravity4 ,the particles in  suspension  
are constantly tending to fall1 and     
frequently falling2 but  before they    
reach the bottom many of them are seized
 and carried upward  by the subordinate 
currents1 only to sink and be carried up
 again4 ,even  if they reach the bottom1
 as they frequently do1 they may be     
picked  up again4 ,it is probable that  
every particle of sediment of such size 
that it would sink readily in still     
water is dropped and picked up many     
times in the course of any long river   
journey1 and its periods of rest  often 
exceed its periods of movement4         
,illustration3 ,fig4 #aja4--;,diagram to
 illustrate the effect of    bowlders1 a
 and b1 in a stream's bed on the        
currents of water    impinging against  
them4    ,independently of the          
subordinate currents1 the different     
velocities of  the different parts of a 
stream tend to keep materials in        
suspension  by exerting different       

pressures on the different sides of     
suspended  particles4#df    ,river ice  
sometimes facilitates the transportation
 of dbris which the  water alone could  
not carry4 ,the ice freezes to bowlders 
in the banks  of the streams1 to those  
which are partially submerged1 and      
sometimes  to those altogether submerged
 beneath slight depths of water4 ,when  
the  ice breaks up in the spring such   
bowlders1 buoyed up by the ice1 may be  
floated far down the stream4 ,the       
influence of ice in this connection  is 
most considerable in high latitudes1 but
 it is of consequence as  far south as  
,virginia1 where the river deposits     
sometimes contain  bowlders which the   
unaided streams could not have carried4 
,ground ice  sometimes forms about      
bowlders in the bottoms of streams1     
especially  in the quiet pools of       
turbulent rivers1 and floats them to the
 surface  before the surface itself is  
frozen4#dg ,in the floods of spring     
rivers  often spread their ice widely   

over their flood-plains4 ,it is         
sometimes  massed in constricted        
portions of valleys so as to form great 
dams1 the  breaking of which is attended
 with great destruction4                
,corrasion4    ,abrasion4--,the wear    
effected by running water is corrasion4 
,so  long as the materials to be carried
 away are incoherent it is easy  to see 
how running water picks them up and     
carries them forward4 ,the  water which 
gathers in the depressions on the slope 
of a cultivated  field gathers earthy   
matter from the surface over which it   
passes1  even before it is concentrated 
into rills1 and the rills continue the  
process4 ,thus the loose materials of   
the surface are gathered at the  very   
sources of the streams1 and the amount  
of sediment in the water  after a heavy 
shower1 even at the head of the stream1 
may be great4  ,the run-off from the    
slopes of any valley in any part of its 
course  likewise brings sediment to the 
stream1 which gathers more from its bed 

whereever it flows with sufficient      
velocity over incoherent material4      
,streams also undercut their banks1 and 
receive new load from the fall  of the  
overhanging material4    ,by far the    
larger part of the sediment acquired by 
a normal stream is  made up of material 
loosened in advance by the processes of 
weathering4  ,the stream1 or the waters 
which get together to make the stream1  
find them ready-made2 but rivers        
frequently wear rock which is not       
weathered1 for the principal valleys of 
the earth's surface are cut in  solid   
rock1 and many of them in rock of       
exceeding hardness4 ,how does  the      
stream wear the solid rock8    ,when a  
stream flows over a rock bed1 the wear  
which it accomplishes  depends chiefly  
on the character of the rock1 the       
velocity of the  stream1 and the load it
 carries4 ,if the rock be stratified and
 in thin  layers1 and if these thin     
layers be broken by numerous joints at  
high  angles to the stratification      

planes1 the impact of the water of a    
clear  stream of even moderate strength 
may be effective in dislodging bits of  
the rock4 ,this condition of things is  
often seen where streams run on  beds of
 shale or slate4 ,if the rock be hard   
and without bedding-planes  and joints1 
or if its layers be thick and its joints
 few1 clear water  will be much less    
effective4 ,if the surface of the rock  
be rough1 the  mechanical action of a   
swift stream of clear water might still 
produce  some effect on it2 but if      
massive hard rock presents a smooth     
surface  to a clear stream1 the         
mechanical effect of even a swift       
current is  slight4    ,this general    
principle is illustrated by the ,niagara
 ,river4 ,just above  the falls the     
current is swift4 ,when the river is    
essentially free from  sediment1 the    
surface of the limestone near the bank  
beneath it is  sometimes distinctly     
green from the presence of the          
one-celled plants  7fresh-water alg7    

which grow upon it4 ,the whole force of 
the mighty  torrent is not able to sweep
 them from their moorings4 ,were the    
stream  supplied with a tithe of the    
sand which it is capable of carrying1 it
  would not take many hours1 and perhaps
 not many minutes1 to remove the  last  
trace of vegetation4 ,this illustration 
furnishes a clue to the  method by which
 the erosion of solid rock in a stream's
 bed is effected4    ,it has been seen  
that the ingathering waters which make a
 stream often  have abundant sediment   
before they reach well-defined stream   
channels1  and that the streams continue
 to gather sediment whereever their beds
  are composed of material which is     
readily detached4 ,the sediments which  
the stream carries are the tools with   
which it works4 ,without them  it is    
relatively impotent1 so far as the      
abrasion of solid rock is  concerned2   
with them1 it may wear any rock over    
which it passes 7,fig4  #ajb74    ,we   
have next to inquire the methods by     

which running water uses its  tools in  
the excavation of valleys4 ,when gravel 
is rolled along in  the channel of a    
stream there is friction between it and 
the bed over  which it moves4 ,if the   
pebbles be as hard as the bed over which
 they  are rolled their movement must   
result in its wear1 and even if they be 
softer more or less wear takes place4   
,as the moving stones wear the  rock of 
the stream's bed they are themselves    
worn by impact with it and  with one    
another4 ,in all cases the softer       
material suffers the more  rapid wear4  
,the first effect of wear on materials  
in transportation is  the reduction of  
their rugosities of surface4 ,the       
projecting points  and sharp angles are 
worn off1 and the stones are reduced to 
rounded  water-worn forms4 ,the         
particles broken off make grains of     
sand1 or1  if very fine1 particles of   
silt or mud4 ,even after a stone has    
been  rounded it is subject to further  
wear and reduction1 and in the course   

of time may be literally worn out4      
,the sediment carried in suspension1 as 
well as that rolled along  the bottom1  
may wear the rock bed of a stream4 ,when
 a grain of sand  in suspension escapes 
from an upward moving current it may not
 sink  quietly4 ,if it be caught by a   
downward current it may be made to      
strike  a blow on the bed of the stream1
 and the effect of the blow is to wear  
the surface which receives it4 ,the     
larger the grain and the stronger  the  
current the greater the wear4           
,illustration3 ,fig4 #ajb4--,some of the
 tools with which a stream works4       
,the cobbles and bowlders have been     
shifted by the stream in its flow4      
,other stones and bowlders now in       
transit cause the ripples in the        
stream4 ,the ,chelan ,river1 ,wash41    
just above its junction with the        
,columbia4 7,willis1 ,u4 ,s4 ,geol4     
,surv47    ,the ceaseless repetition of 
the blows struck by the material in     
suspension1 or rolled on its bottom1    

hour after hour1 day after day1  and    
year after year1 will accomplish        
sensible results4 ,in the long  course  
of the ages this process has excavated  
deep valleys4 ,concomitant  processes   
are largely concerned in making valleys 
wide1 but the depth  of valleys cut in  
solid rock is chiefly the result of the 
impact and  friction of the sediment in 
transportation4    ,the wear effected in
 this way is not proportional to the    
number of  blows struck4 ,since every   
pebble and every grain of sand carried  
diminishes the velocity of a stream1 and
 since with diminished velocity  the    
force of the blows struck is diminished1
 it follows that the blows  may become  
so weak1 as the result of their         
multiplication1 as to be  ineffective4  
,the larger the load1 therefore1 which  
the stream carries1  the more the tools 
with which it has to work1 but the less 
effectively  can it use them2 and the   
load may be so far increased as to      
destroy its  corrasive power altogether4

 ,on the other hand1 the smaller the    
load  of the stream the greater its     
velocity and the more effectively will  
its tools be used2 but their number may 
be so far reduced that their  aggregate 
effect is slight4 ,to accomplish the    
greatest results on a bed  of solid rock
 a stream must have tools to work with1 
but must not be so  heavily burdened as 
to interfere with its effective use of  
them4    ,whatever the cause of their   
unequal velocities swift and slow       
streams  corrade their valleys          
differently4 ,the erosion of a swift    
stream is  chiefly at the bottom of its 
channel4 ,the sluggish stream lowers    
its channel less rapidly1 while lateral 
erosion is relatively more  important4  
,the result is that slow streams        
increase the width of their  valleys    
more than the depth1 while swift streams
 increase the depth  more than the      
width4 ,it follows that slow streams    
develop flats1 while  swift ones do not4
 ,not only is a slow stream more likely 

to have a  flat1 and therefore a better 
chance to meander1 but it is more likely
  to take advantage of opportunities in 
this line1 for a slow stream gets  out  
of the way for such obstacles as it may 
encounter1 while a swift  stream is much
 more likely to get obstacles out of its
 way4    ,special phases of corrasion   
are introduced where waterfalls and     
other  peculiarities dependent on       
inequalities of rock resistance occur4  
,solution4--,in most cases the solution 
effected by a stream is  much less      
important than its mechanical work4     
,only when conditions  are unfavorable  
to the latter1 is solution the chief    
factor in the  excavation of a valley4  
,this may be the case where a stream's  
bed is  over soluble rock1 such as      
limestone1 and where the stream is      
clear1  or its gradient so low that its 
current is sluggish4 ,the solvent power 
of water is not influenced by the       
presence of sediment1 though the        
presence of sediment offers the water a 

greater surface on which to  work4      
,,conditions ,,affecting ,,the ,,rate   
,,of ,,erosion4    ,in considering the  
rate of erosion1 both the work of the   
stream in  its valley and that of the   
general run-off are to be considered4   
,the  conditions which favor the most   
rapid erosion in a stream's channel are 
not necessarily those which determine   
most rapid degradation in the  basin    
outside of the valley4                  
,the ,influence of ,declivity4    ,in   
general the greater the declivity the   
more rapid the rate of  erosion1 whether
 in the stream's channel or on the      
slopes above it4 ,the  truth of this    
conclusion is illustrated by the great  
erosive power of  swift streams as      
compared with slow ones4    ,it does not
 follow1 however1 that high declivity   
favors each element  of erosion4 ,the   
effect of declivity on weathering is far
 from simple4  ,for example1 great      
declivity1 by allowing more of the      
rainfall to flow  off over the surface1 

and by causing it to flow off more      
promptly1  restricts the work of        
solution1 and therefore of              
decomposition1 both  at the surface and 
beneath it4 ,high declivity is also     
unfavorable to  the growth of           
vegetation1 and so to the wedge-work of 
roots4 ,on the  other hand1 a given     
amount of wedge-work of roots and ice is
 more  effective where the slope is     
steep than where it is gentle1 for such 
materials as are loosened descend the   
slopes more readily4 ,the prompt        
removal of weathered materials1 by      
exposing fresh surfaces of rock1        
accelerates weathering4 ,the total      
amount of weathering may therefore  not 
be diminished by the increase of slope1 
even though certain of its  processes   
are hindered4    ,the effect of high    
declivity on transportation1 the second 
element of  erosion1 is too patent to   
need explanation4    ,corrasion likewise
 is favored by high declivity1 for the  
abrasive power  of a stream increases as

 the square of its velocity4 ,with      
corrasive  power increased1 corrasion   
will also be increased if the water has 
tools to work with4 ,since high         
declivity greatly increases both the    
transporting and the corrasive power of 
running water1 and favors  certain      
elements of weathering1 it is clear that
 the aggregate effect  of high declivity
 is to favor erosion1 whether in the    
channel of the  stream or on the general
 surface of its drainage basin4         
,the ,influence of ,rock4    ,the       
physical constitution1 the chemical     
composition1 and the  stratigraphy of a 
rock formation1 influence the rate at   
which it may  be broken up and carried  
away4 ,clastic or fragmental rocks are  
usually  stratified and made up of      
cemented pebbles 7conglomerate71 sand   
grains  7sandstone71 or particles of mud
 7shale74 ,igneous rocks1 such as       
granite1 are massive instead of         
stratified1 and are usually made up of  
great numbers of interlocking crystals  

which bind one another together4  ,some 
crystalline rocks1 such as schists1     
though not stratified1 possess          
cleavage1 which has much the effect of  
stratification1 so far as  erosion is   
concerned4 ,all rocks are affected by   
systems of more or less  nearly vertical
 cracks called joints4 ,all these       
structures have their  influence upon   
the rate of degradation4    ,physical   
constitution4--,clastic rocks may be    
firmly cemented1 or their  constituents 
may be loosely bound together4 ,the less
 the coherence the  more ready the      
disintegration1 and the finer the       
particles the more  easily are they     
carried away4 ,when the particles in    
transportation  are angular they effect 
more wear on the bed over which they    
move1  and on one another1 than when    
they are round4 ,the difference is great
  where the particles are large1 and    
little where they are very small4  ,if  
the materials carried be harder than the
 bed over which they pass1  corrasion of

 the latter is favored4    ,chemical    
composition4--,something also depends on
 the chemical  composition of the rock1 
since this affects its solubility1 and  
therefore its rate of decomposition4    
,the more soluble the rock the  larger  
the proportion of it which will be taken
 away in solution2 but  it does not     
follow that the most soluble rock will  
be most rapidly  eroded1 since the rate 
of erosion depends on abrasion as well  
as  solution1 and a rock which is       
readily soluble1 as rocks go1 may be    
less  easily abraded than a rock which  
is made of discrete and insoluble       
particles bound together by a soluble   
cement4 ,in such rocks1 for  example a  
sandstone in which the grains are       
cemented together by  lime carbonate1   
the solution of the cement sets free a  
considerable  quantity of sand1 so that 
a small amount of solution prepares a   
large  amount of sediment for removal4  
,a stream might cut its valley much     
more rapidly in such a sandstone than in

 a compact limestone1 though  the latter
 is1 as a whole1 the more soluble4 ,the 
constituent minerals  of crystalline    
rocks resist solution and decay         
unequally1 and when any  one is         
dissolved or decomposed the rock        
crumbles and the less soluble           
constituents are ready for removal by   
mechanical means4 ,so long as the       
material loosened by disintegration is  
removed1 chemical heterogeneity  favors 
erosion2 but if the loosened dbris is   
not removed erosion is  not favored by  
chemical heterogeneity4 ,in such a case 
erosion would be  most rapid where the  
rock was most soluble4                  
,structure4--,the structure of the rock 
has much to do with the rate of  its    
erosion4 ,other things being equal1     
stratified rock is more readily  eroded 
than massive rock1 since                
stratification-planes are planes of     
cleavage1 and therefore of weakness4    
,taking advantage of these planes  the  
water has less breaking to perform to   

reduce the material to a  transportable 
condition4 ,for the same reason a       
thin-bedded formation is  more easily   
eroded than a thick-bedded one4         
,illustration3 ,figs4 #ajc and          
#ajd4--;,diagrams to illustrate the fact
    that a stream crosses many more     
cleavage-planes when the beds of rock   
are inclined than when they are         
horizontal4    ,the beds of stratified  
rock may be horizontal1 vertical1 or    
inclined1  and inclined strata may stand
 at any angle between horizontality and 
verticality4 ,in indurated formations   
the rate of erosion is influenced  both 
by the position of the strata and by the
 relation of the direction  of the      
flowing water to their dip and strike4  
,on the whole the strata  which are     
horizontal1 or but slightly inclined1   
are probably less  favorable for rapid  
erosion than those which are vertical or
 inclined  at considerable angles4 ,this
 is at least true where the layers are  
of  uniform hardness and the joints     

infrequent4    ,horizontal strata expose
 fewer cleavage planes to the water     
flowing  over them than strata in any   
other position4 ,in ,fig4 #ajc the      
stream  which has the profile ad crosses
 bedding-planes at b and c4 ,in  ,fig4  
#ajd1 where the beds dip up-stream1 many
 more division-planes  are crossed in   
the same distance4 ,since bedding-planes
 are planes of  weakness1 it follows    
that horizontal and nearly horizontal   
strata are  not1 under ordinary         
conditions of erosion1 in a position    
favorable for  most rapid wear4 ,when   
strata are horizontal1 it makes no      
difference  which way the stream runs1  
for the current sustains the same       
relation  to the cleavage-planes        
whatever its course4    ,in the case of 
incoherent material the position of the 
beds1 or even  their existence1 has     
little influence on the rate of erosion4
 ,such  formations are weak in all      
directions1 not simply along            
bedding-planes4    ,illustration3 ,fig4 

#aje4--;,diagram to illustrate the      
various relations    a stream may       
sustain to the outcrop of vertical      
layers of rock4    ,illustration3 ,fig4 
#ajf4--;,diagram to illustrate the      
various relations    a stream may       
sustain to the outcrops of inclined     
layers of rock4    ,when the strata are 
vertical1 three distinct cases may arise
 7,fig4  #aje74 ,the stream may flow    
7#a7 with the strike 7aa72 7#b7 at right
  angles to the strike 7bb72 or 7#c7    
oblique to it 7cc7 at any angle         
whatsoever4 ,it is perhaps not possible 
to say which of these positions  is most
 favorable for erosion1 for the         
character of the rock1 the  thickness of
 its layers1 its ability to stand with  
steep slopes1 and  the strength of the  
currents concerned1 would influence the 
result4 ,a  stream which flows at right 
angles to the strike 7bb1 ,fig4 #aje7   
would  cross more cleavage-planes in a  
given distance than a stream flowing in 
any other direction1 and would strike   

the outcropping edges of layers  at the 
angle of greatest advantage4 ,a stream  
flowing along the strike  7aa71 on the  
other hand1 has better opportunity to   
sink its channel  on cleavage-planes1   
and the current oblique to the strike   
7cc71 has  some of the advantages of    
each of the others4    ,when the strata 
are inclined five cases may arise4 7#a7 
,the stream  may be parallel to the     
strike 7aa1 ,fig4 #ajf71 when it makes  
no  difference which way the current    
flows2 it may be at right angles to  the
 strike 7bb71 and 7#b7 flowing with the 
dip 7toward b71 or  7#c7 against it     
7toward b72 it may be oblique to the    
strike1 and  flowing 7#d7 in the general
 direction of dip 7toward c72 or 7#e7 in
  the opposite direction 7toward c74 ,as
 before1 the stream flowing at  right   
angles to the strike would cross the    
largest number of layers  in a given    
distance1 and so have an opportunity to 
take advantage of  more cleavage-planes 
than a stream in any other position4    

,but in the  case of inclined strata a  
new element enters into the problem4    
,when the  stream flows parallel to the 
strike1 the valley which is in process  
of  deepening is not sunk vertically1   
but is shifted more or less in the      
direction of the dip 7,fig4 #ajg74 ,this
 is called monoclinal shifting4  ,the   
result is that there is a constant      
tendency to undermine 7sap7 the  valley 
bluff on the down-dip side1 and this    
process of sapping will1  according to  
its rate1 accelerate the growth of the  
valley1 especially  in width4           
,monoclinal shifting is favored by the  
presence of a hard  layer 7,h71 as shown
 in ,fig4 #ajg1 if this stratum is the  
bed of the  stream4    ,illustration3   
,fig4 #ajg4--;,diagram to illustrate    
monoclinal shifting4 ,the    valley abc1
 as seen in cross-section1 becomes deb1 
as the stream    lowers its channel4    
,in the second and third cases mentioned
 above1 the only difference is  in the  
angle at which the current strikes the  

outcropping edges of  layers and lamin4 
,the mechanical advantage is with the   
stream which  flows with the dip4 ,in   
the fourth and fifth cases something    
will  depend on the angle which the     
stream's course makes with the strike4  
,in all these cases1 as in those where  
the strata are vertical1 much  will     
depend on the thickness and resistance  
of the layers and on the  strength of   
the currents concerned4                 
,the ,influence of ,climate4    ,climate
 has both a direct and an indirect      
effect on erosion4 ,its  direct         
influence is through precipitation1     
evaporation1 changes of  temperature1   
and wind2 its indirect1 through         
vegetation4 ,like declivity  and rock   
structure1 climate does not affect all  
elements of erosion  equally4    ,the   
chief elements of climate are           
temperature1 moisture1 and  atmospheric 
movements2 the principal factors which  
influence it are  latitude1 altitude1   
distance from the sea1 direction of     

prevailing  winds1 and topographic      
relations4    ,the effects of variations
 in temperature on rock weathering have 
already been discussed 7p4 #dc74 ,they  
are chiefly mechanical1 and are  seen at
 their best where the daily range is    
great4    ,high temperature favors      
chemical action1 and the weathering of  
rock  by decomposition is at its best in
 the presence of abundant moisture  in  
regions where the temperature is        
uniformly high4 ,furthermore1 a  warm   
moist climate favors the growth of      
vegetation1 the decay of which  supplies
 the water with organic acids which     
greatly increase its  solvent power4    
,the climatic conditions favoring       
mechanical weathering  are therefore    
different from those favoring chemical  
weathering4 ,high  temperature and      
abundant moisture and vegetation are    
found in many  tropical regions1 and    
here the rock is often decomposed to    
greater  depths1 on the whole1 than in  
high latitudes4 ,how far this is the    

result of rapid weathering1 and how far 
of slow removal1 due in part  to the    
protective influence of the plants1     
cannot be affirmed4 ,if the  weathered  
material is not removed1 it will        
presently become a mantle  thick enough 
to retard the processes which brought it
 into existence4    ,so long as the     
water of the surface and that in the    
soil remains  unfrozen1 temperature     
affects neither corrasion nor           
transportation4  ,but in middle and high
 latitudes the surface is frozen for    
some part  of each year4 ,during this   
time corrasion is at a minimum1 for     
although  the streams continue to flow  
there is relatively little water running
  over the surface outside the drainage 
channels1 and that little is  relatively
 ineffective4 ,under some conditions1   
therefore1 temperature  affects both    
corrasion and transportation4    ,the   
humidity of the atmosphere has an       
influence even more important  than that
 of temperature on the rate of erosion1 

and its influence  is exerted on each of
 the elements of that complex process4  
,a moist  atmosphere favors oxidation1  
carbonation1 hydration1 and the growth  
of  vegetation1 all of which promote    
certain phases of rock weathering4  ,on 
the other hand1 humidity tends to       
prevent sudden and considerable         
variations in temperature1 thus checking
 the weathering effected  by this means4
 ,precipitation1 the most important     
single factor in  determining the rate  
of erosion1 is dependent on atmospheric 
humidity4  ,its amount1 its kind 7rain  
or snow71 and its distribution in time1 
are  the elements which determine its   
effectiveness in any given place4       
,other things being equal the greater   
the amount of precipitation  the more   
rapid the corrasion and transportation4 
,much1 however1  depends on its         
distribution in time4 ,a given amount of
 rainfall may  be distributed equally   
through the year1 or it may fall during 
a  wet season only4 ,the maximum        

inequality of distribution would occur  
if all the rainfall of a given period   
were concentrated in a single  shower4  
,with such concentration the volume of  
water flowing off over  the surface     
immediately after the down-pour would be
 greater than  under any other          
conditions of precipitation1 and since  
velocity is  increased with volume1 and 
erosive power with velocity1 it follows 
that the erosive power of a given amount
 of water would be greater  under these 
circumstances than under any other4     
,furthermore1 a larger  proportion of   
the precipitation would run off over the
 surface under  these circumstances than
 under any other1 for less of it would  
sink  beneath the surface and less would
 be evaporated4 ,if erosive power  and  
rate of erosion were equal terms1 this  
would therefore be the  condition for   
greatest erosion2 but erosive power and 
rate of erosion  do not always          
correspond4 ,if the water falling in    
this way could  get hold of all the     

material it could carry1 extreme        
concentration  of precipitation would be
 the condition favorable for most rapid 
erosion4 ,but if the amount of available
 material for transportation  is slight1
 a large part of the force of the water 
could not be  utilized in erosion4 ,it  
follows that if there were a large      
amount of  disintegrated material on the
 surface1 erosion would be greater the  
greater the concentration of            
precipitation4 ,if1 on the other hand1  
there were but little disintegrated     
material on the surface1 frequent       
showers1 with intervening periods when  
conditions were favorable for           
weathering1 that is1 for preparing      
material for transportation1 might  be  
more favorable for rapid erosion4 ,while
 the total energy of running  water     
available for erosion under these       
conditions would be less than  before1  
there might in the long run be more     
material for transport2  for weathering 
in the presence of moisture1 and all    

that goes with  it1 might be more       
effective in preparing material for     
transportation1  than weathering during 
the long periods of drought which would 
occur  if the precipitation were        
concentrated to its maximum4            
,temperature  favoring1 the uniform     
distribution of moisture through the    
year would  allow the growth of         
vegetation1 which1 although favoring    
some processes  of weathering1 retards  
erosion in general4 ,while therefore it 
is not  possible to say what            
distribution of rainfall favors most    
rapid erosion  without knowing the      
nature of the surface on which it is to 
fall1  enough has been said to show that
 the problem is by no means a simple    
one4 ,some of the most striking phases  
of topography developed by  erosion1    
such as those of the ,bad ,lands 7,figs4
 #ge to #gh1 and #ajh71 are  developed  
where the rainfall is unequally         
distributed in time1 and too  slight or 
too infrequent to support abundant      

vegetation4    ,illustration3 ,fig4     
#ajh4--;,bad-land topography developed  
under    conditions of aridity and      
unequal distribution of rainfall4 ,slope
 of    ,pinal ,mountains1 ,ariz4        
7,ransome1 ,u4 ,s4 ,geol4 ,surv47       
,during its fall1 and immediately after1
 rain is more effective than  an equal  
amount of snow2 but the snow may be     
accumulated through  a considerable     
period of the year1 and then melted     
rapidly1 when  it has an effect         
comparable to that which would be       
produced by the  concentration of the   
rainfall into a limited period of the   
year4 ,if  the ground beneath be frozen 
when the snow melts 7and this is often  
the case7 the erosion accomplished by   
the resulting water will be  diminished4
    ,except in dry regions1 where       
wind-work sometimes exceeds water-work1 
the movements of the atmosphere are of  
less importance directly  than          
precipitation in determining the rate of
 erosion4 ,but even in  regions which   

are not arid the winds have much to do  
with the rate of  evaporation and the   
distribution of rainfall1 so that their 
indirect  effect is great4 ,even their  
direct effects in moist climates are not
 to  be lost sight of1 for even here the
 surface is sometimes dry enough to     
yield dust and sand1 and the uprooting  
of trees so disturbs the surface  as to 
make earthy dbris more accessible to    
wind and water4 ,where trees  gain      
precarious footholds on steep slopes1 as
 they often do1 they are  likely to be  
overturned as soon as they are large    
enough to offer  considerable resistance
 to the wind1 and in the overturning1   
large  quantities of rock are sometimes 
loosened and carried down the slope  by 
gravity4 ,this phase of destructive work
 is seen at its best on the  walls of   
gorges1 where trees often flourish until
 their tops project  above the rim of   
the valley4    ,through vegetation1     
climate influences erosion in ways which
 are  easily defined qualitatively1 but 

not quantitatively4 ,both by its  growth
 7wedge-work of roots7 and by its decay 
7supplying ,,co1 etc41  to descending   
waters7 it favors certain phases of     
weathering2 but1 on  the other hand1 it 
retards corrasion and transportation    
both by wind  and water4 ,this is well  
shown along the banks of streams and on 
the  faces of cliffs1 in clay1 sand1    
etc4 ,its aggregate effect is probably  
unfavorable to erosion by mechanical    
means1 and favorable to that by         
chemical processes4    ,illustration3   
,fig4 #aji4--;,characteristic cliffs of 
high arid regions4    ,right wall of    
,snake ,river canyon1 nearly opposite   
the mouth of ,salmon    ,river1 ,id4    
,two spring-formed coves1 with 8,castle 
,rock0 between4    7,russell1 ,u4 ,s4   
,geol4 ,surv47    ,erosion in high arid 
regions differs from that in regions of 
abundant  rainfall in several ways4 ,it 
is obvious that the valleys will develop
  more slowly in the former1 that they  
will remain young longer1 that the      

period necessary for the dissection of  
the surface is greater1 that  the       
watercourses will be less numerous1 and 
that fewer of them will  have permanent 
streams4 ,there are certain other       
differences which are  less obvious4 ,if
 the arid region be high and composed of
 heterogeneous  strata1 the topography  
which erosion develops is more angular  
7,fig4  #hc7 than that of the humid     
region4 ,this is because there is less  
rock decay1 and less vegetation to hold 
the products of decay4 ,the  more       
resistant beds of rock therefore come   
into greater prominence1  especially on 
slopes1 where they develop cliffs       
7,figs4 #aji and #aaj74  ,these general 
principles find abundant illustration in
 the plateaus of  the western part of   
the ,united ,states1#dh where the cliffs
 are by no  means confined to the       
immediate valleys of the streams 7,fig4 
#a1 ,pl4  ,,xii74    ,illustration3     
,fig4 #aaj4--;,a ,butte4 ,a             
characteristic feature of the    arid   

plateau region of the ,west4 7,dutton1  
,mono4 ,,ii1 ,u4 ,s4 ,geol4    ,surv47  
,,effects ,,of ,,unequal ,,hardness4    
,in the preceding pages incidental      
reference has been made to the  results 
of inequalities of rock resistance4     
,this topic will now be  considered more
 fully4    ,rapids and                  
falls4--,returning for a moment to the  
hypothetical island  with which our     
study of erosion began1 let a horizontal
 layer of hard  rock be assumed to run  
through it 7,h1 ,fig4 #aaa74 ,as the    
rain falls  on the land and runs off    
over it1 wear will be less rapid where  
the  hard layer comes to the surface    
than at the higher or lower levels4 ,as 
a result1 the slope will become steeper 
at and below the outcrop of  the hard   
layer1 and less steep immediately above 
it1 as shown by ab  in ,fig4 #aaa4      
,under these conditions the water       
passing over the hard  ledge constitutes
 rapids4 ,the increased erosion which   
accompanies  the increased velocity     

makes the rapids more rapid4 ,the       
process may  continue until the water   
falls1 rather than flows over the hard  
layer 7cd1 ,fig4 #aaa74 ,with continued 
rainfall the edges of the hard  layer1  
together with the slopes above and      
below1 would continue to  recede toward 
the center of the island4 ,under        
conditions of absolute  homogeneity of  
material1 save for the hard layer       
specified1 no valley  would be          
developed1 and therefore no stream4     
,if the surface was so changed as to    
allow of the development of a  valley   
7p4 #fc7 the same principles would be   
applicable4 ,as an active  stream passes
 from a hard layer to one less          
resistant1 the greater  wear on the     
latter gives origin to rapids4 ,at first
 the rapids would  be slight 7a1 ,fig4  
#aab71 but would become more            
considerable 7b7 as  time and erosion go
 on4 ,when the bed of the rapids becomes
 sufficiently  steep1 the rapids become 
falls#di 7cd74 ,when the water falls    

rather than flows over the rock surface 
below the hard layer1 erosion  assumes a
 new phase4 ,the hard layer is then     
undermined1 and the  undermining causes 
the falls to recede4 ,this phase of     
erosion is  sometimes called sapping4   
,illustration3 ,fig4 #aaa4--;,diagram   
representing a horizontal layer of      
hard rock in an island1 and its effects 
on erosion4    ,illustration3 ,fig4     
#aab4--;,diagram illustrating the       
development of a    fall where the hard 
layer dips gently up-stream4            
,illustration3 ,fig4 #aac4--;,diagram   
illustrating the conditions which       
exist at ,niagara ,falls4 7,gilbert47   
,if the hard layer which occasions a    
fall dips up-stream 7,fig4 #aab71 its   
outcrop in the stream's bed becomes     
lower as the fall recedes 7e74  ,when it
 has become so low that the water       
passing over it no longer  reacts       
effectively against the less resistant  
material beneath 7f71  sapping ceases1  
and the point of greatest erosion may be

 shifted from  the soft material beneath
 the fall to the hard layer itself4 ,the
 actual  rate of erosion at this point  
may be no greater than before1 though   
the relative rate is4 ,under these      
circumstances the vertical edge of  the 
hard layer will presently be converted  
into an incline 7f71 and  as this takes 
place the fall becomes rapids4 ,the     
conversion of the  falls into the rapids
 begins about the time the lower edge of
 the hard  stratum in the channel       
reaches grade4 ,by continuation of the  
process  which transformed the falls    
into rapids1 the rapids become less     
rapid1  and when the upper edge of the  
hard layer has been brought to grade1   
the rapids disappear 7h1 ,fig4 #aab74   
,the history of rapids which  succeed   
falls is the reverse of that which      
preceded4 ,the later rapids  are        
steepest at the beginning of their      
history1 the earlier at their  end4     
,stated in other terms1 rapids are      
steepest when nearest falls  in time4   

,slight differences in hardness in      
successive layers often  occasion       
successive falls or rapids 7,fig4 #aad74
    ,if the hard layer which occasions  
the falls be horizontal1 instead of     
dipping up-stream1 the general result   
would be the same2 but1 other  things   
being equal1 the duration of the falls  
developed under these  conditions would 
be greater1 since they must recede      
farther before  becoming rapids4    ,if 
the layers of unequal hardness in a     
stream's bed be vertical and the  course
 of the stream at right angles to the   
strike1 rapids1 and perhaps  falls1 will
 develop 7,fig4 #aae74 ,the chances for 
falls are greater1  the greater the     
difference in hardness4 ,falls developed
 under these  conditions1 as well as the
 rapids preceding and following1 would  
remain  constant in position until the  
resistant layer was brought to grade1   
but they would ultimately disappear as  
in the preceding cases4 ,falls  are not 
likely to develop where the strata of   

the stream's bed dip  down-stream1      
though they may develop even under these
 conditions if the  gradient of the     
stream is greater than the dip of the   
strata 7,fig4 #aaf74    ,illustration3  
,fig4 #aad4--;,falls in ,utica shale1   
,canajoharie1 ,n4 ,y4    7,darton1 ,u4  
,s4 ,geol4 ,surv47    ,the inequality of
 resistance in the rock which occasions 
a fall may  be original or secondary4   
,in the case of ,niagara ,falls#ej      
7,fig4  #aac7 relatively resistant      
limestone overlies relatively weak      
shale4  ,at the ,falls of ,st4 ,anthony 
7,minneapolis7 limestone overlies       
friable  sandstone4 ,the falls of the   
,yellowstone and the ,shoshone ,falls of
  the ,snake ,river 7,idaho71 are in    
igneous rock4 ,in the former case the   
unequal resistance is occasioned by     
unequal decay of the rock1 due  perhaps 
to the rise of hot vapors which have    
decomposed the rock along  the lines of 
their ascent2 in the latter1 a more     
resistant sort of  igneous rock overlies

 a less resistant4    ,structural       
features1 such as jointing1 sometimes   
give rise to falls1  or determine their 
distinctive features 7,fig4 #aag71 even 
where the  formations involved are of   
uniform hardness4 ,a joint plane has the
  effect of a weak vertical or highly   
inclined bed4 ,if an open joint  is     
discovered in a stream's bed1 the water 
enters it4 ,if it finds an  outlet      
below1 a channel is worn along the new  
line of flow1 with rapids  or falls     
where the water descends4 ,rock         
originally homogeneous may be  much     
fractured in some parts1 while it       
remains unbroken in others4  ,where a   
stream passes from the solid to the     
broken portion rapids1 or  even falls1  
may develop4    ,illustration3 ,fig4    
#aae4--;,diagram illustrating the       
development of    falls over a vertical 
hard layer4    ,illustration3 ,fig4     
#aaf4--;,diagram illustrating the       
possibility of    falls where the beds  
dip down-stream4    ,falls may originate

 in still other ways4 ,if for any reason
 a stream is  forced out of its valley1 
it may in its flow find entrance to     
another  valley1 or to another part of  
its own valley1 over a steep slope4 ,if 
the structure of the slope favors1 a    
fall may speedily develop4 ,the  ,falls 
of ,st4 ,anthony are an example1 the    
,mississippi having been turned  out of 
its earlier course by deposits of       
glacial drift4 ,again1 if an            
obstruction of any sort1 such as a flow 
of lava1 dams a stream1 rapids  or falls
 are developed where the water overflows
 the dam4 ,when a main  valley is       
notably deepened by glaciation the      
drainage from tributary  valleys may    
fall into it1 if the tributaries were   
not equally deepened4  ,falls which     
originated in this way are common in the
 western mountains  of the ,united      
,states1 as well as in most mountain    
regions recently  affected by local     
glaciers 7,fig4 #aah74    ,one waterfall
 often breeds others4 ,thus where a fall

 recedes beyond  the mouth of a         
tributary stream1 the tributary falls4  
,the ,falls of  ,minnehaha1 on a small  
tributary to the ,mississippi1 near     
,minneapolis1  may serve as an          
illustration4 ,in such cases the falls  
may not develop  from rapids4 ,once in  
existence1 the fall of a tributary      
follows the  same history as that of a  
main stream4    ,illustration3 ,fig4    
#aag4--,kepler's ,cascade1 in the       
,yellowstone ,park4    ,the jointed and 
fractured character of the igneous rocks
 occasions a    series of falls and     
rapids4 7,iddings1 ,u4 ,s4 ,geol4       
,surv47    ,streams which have falls are
 relatively clear4#ea ,if a stream      
favorably situated for the development  
of a fall carried a heavy  load1        
deposition would take place below the   
rapids1 and the tendency  would be to   
aggrade the channel at that point and so
 to prevent  the development of the     
fall4 ,falls occur only on streams which
 have  relatively high gradients4 ,this 

means that the streams which have falls 
are well above base-level1 and streams  
well above base-level are young4  ,falls
 therefore are a mark of topographic    
youth4    ,illustration3 ,fig4          
#aah4--,the ,upper ,yosemite ,falls4    
,the fall of the ,niagara#eb 7,pl4 ,,ix7
 is one of the most remarkable  known1  
both because of its large volume of     
water and its great descent1  between   
#afj and #agj feet4 ,the rate at which  
the fall is receding is a  matter of    
interest not only in itself1 but        
because1 once determined1  it may be    
made to serve as a unit of measurement  
for certain important  events in        
geological history4 ,it was formerly    
conjectured that this  fall was receding
 at the rate of one to three feet per   
century1 but  it was not until recent   
years that its actual rate of recession 
was  approximately fixed4 ,by surveys   
executed in #ahdb and #ahij it has been 
determined that its average rate of     
recession between those dates was       

something like #d feet per year1 or     
about #aej times as great as the        
highest estimate stated above4 ,it is to
 be noted that this is the  average rate
 of recession1 for all parts of the     
ledge over which  the water falls are   
not receding at the same rate4 ,the     
point of the  8,horseshoe0 has1 during  
the same time1 gone back at more than   
twice  this rate4#ec    ,illustration3  
,fig4 #aai4--;,a group of pot-holes4    
7,turner1 ,u4 ,s4 ,geol4    ,surv47     
,rapids and falls sometimes occasion the
 development of pot-holes  7,fig4 #aai71
 a peculiar rather than important       
erosion feature4 ,the holes  are        
excavated in part by the falling and    
eddying of silt-charged water1  but     
chiefly by stones which the eddies move4
 ,pot-holes which are not  now in       
immediate association with rapids or    
falls often point to the  former        
existence of rapids or falls4    ,rock  
terraces4--,the tendency to sapping     
shown in many waterfalls is  also shown 

in the weathering and erosion of the    
sides of a valley where  a hard layer   
outcrops above the bottom1 and the      
profile of the side  slopes of the      
valley simulates that of the stream2    
that is1 the slope  becomes gentle just 
above the hard layer1 and steep1 or even
 vertical1  at and below its outcrop4   
,this is illustrated by ,fig4 #abj1     
where the  hard layer through which the 
stream has sunk its valley stands out as
  a rock terrace on either side of the  
valley4 ,such terraces are not  rare and
 are popularly believed to be old       
8water-lines02 that is1  to represent   
the height at which the water once      
stood4 ,in one sense  this              
interpretation is correct1 since a river
 has stood at all levels  between that  
of the surface in which its valley      
started1 and its  present channel1 but  
the shelf of hard rock does not mean    
that the  river1 after attaining its    
present channel1 was ever so large as to
  fill the valley to the level of the   

terrace4 ,rock terraces may also  result
 from changes of level4                 
,illustration3 ,fig4 #abj4--;,diagram to
 illustrate the development of    rock  
terraces4    ,narrows4--,inequalities in
 hardness occasion another peculiarity  
common  to valleys4 ,if a stream crosses
 vertical or highly inclined strata of  
unequal hardness1 its valley is usually 
constricted at the crossing  of the     
harder layers4 ,if such a constriction  
be notable it is called  a narrows1 or  
sometimes a water-gap 7,figs4 #aba1     
#aei1 and ,fig4 #b1  ,pl4 ,,xii74 ,the  
,appalachian ,mountains afford numerous 
examples4 ,the  constriction arises     
because the processes which widen the   
valley are  less effective on the hard  
layer than on the less resistant ones on
  either hand4 ,though most narrows are 
due to the superior resistance  of the  
rock where they occur1 they are         
sometimes the result of other  causes4  
,illustration3 ,fig4 #aba4--,lower      
narrows of the ,baraboo ,river1 ,wis4   

,the    even-crested ridge is ,huronian 
quartzite4 ,the surroundings are of     
,cambrian sandstone4 7,atwood47         
,illustration3 ,fig4 #abb4--;,a         
hog-back1 ,jura-,trias4 ,colorado ,city1
 ,colo4    7,russell1 ,u4 ,s4 ,geol4    
,surv47    ,narrows are much more       
conspicuous in certain stages of erosion
 than  in others4 ,while a valley is    
still so young as to be narrow at all   
points1 no narrows will be conspicuous2 
but at a later stage in  its history1   
when the valley is otherwise wide1      
narrows are more  pronounced4 ,at a     
still later stage1 when the hard strata 
themselves  approach base-level1 the    
narrows again become inconspicuous4     
,from what has preceded it is clear that
 rapids or falls are likely to  occur at
 narrows1 especially in the early part  
of their history4    ,other effects on  
topography4--,inequalities in the       
hardness of rock  develop certain       
peculiarities of topography other than  
those of  valleys4 ,the less resistant  

portions of a land area more or less    
distant from streams are worn down more 
readily than those which are  more      
resistant4 ,if great areas of high land 
be capped with hard rock  they are      
likely to remain as plateaus after      
surrounding areas of  less resistance   
are brought low4 ,if the hard capping   
affects a small  area instead of a large
 one1 the elevation is a butte1 a hill1 
or a  mountain1 instead of a plateau    
7,fig4 #aaj74 ,many buttes and small    
mesas  are but remnants of former       
plateaus 7,mesa ,lauriano1 ,n4 ,m41     
,fig4 #a1 ,pl4  ,,xii74 ,a feature of   
buttes and mesas capped by hard rock is 
the steep  slope or cliff corresponding 
to the edge of the hard bed 7,figs4 #gh 
and  #aji74    ,illustration3 ,fig4     
#abc4--;,a ridge due to the outcropping 
edge of hard    ,jurassic rock4         
,wyoming4    ,if the rock of a region be
 stratified and the layers tilted1 the  
removal of the softer beds leaves the   
harder ones projecting above  the       

general level in the form of ridges or  
8hog-backs0 7,figs4 #abb  and #abc74    
,dikes of igneous rock1 harder than the 
beds which they  intersect1 likewise    
become ridges after the degradation of  
their  surroundings4 ,the plugs of old  
volcanic vents and other igneous        
intrusions of limited area often        
constitute conspicuous hills or         
mountains after erosion has removed     
their less resistant surroundings       
7,fig4 #abd74 ,inequalities of hardness 
are therefore responsible for many      
hills and ridges4 ,in the isolation of  
the hills and ridges picturesque  coves 
are developed1 where the attitude and   
distribution of the weak  and strong    
rocks are propitious4 ,the bottoms of   
the coves are located  on the weak      
rocks1 and above them rise the          
precipitous slopes of  the resistant    
ones4 ,round valley 7,fig4 #a1 ,pl4     
,,xvii1 ,high ,bridge1 ,n4  ,j41        
quadrangle1 ,u4 ,s4 ,geol4 ,surv47 and  
the coves about the head of  ,hiawassee 

,river 7,dahlonega1 ,ga41 quadrangle7   
are examples4    ,illustration3 ,fig4   
#abd4--,matteo tepee1 ,wyo4 ,mass of    
igneous rock    exposed by erosion1 and 
preserved because of its superior       
resistance4    7,detroit ,photo4 ,co47  
,ridges and hills resulting from the    
unequal degradation of unequally        
resistant terranes are not equally      
prominent at all stages in an  erosion  
cycle4 ,in early youth the material     
surrounding the hard bodies  of rock has
 not been removed2 in early maturity    
considerable portions  of their         
surroundings still remain about them2   
but in late maturity  or early old age  
the outcropping masses of hard rock have
 been more  perfectly isolated and are  
most conspicuous4 ,most of the          
even-crested  ridges of the ,appalachian
 system1 as well as many others which   
might be  mentioned1 became ridges in   
this way4 ,in the final stages of an    
erosion  cycle the ridges of hard rock  
are themselves brought low4 ,isolated   

remnants of hard rock which remain      
distinctly above their surroundings  in 
the late stages of an erosion cycle     
7,fig4 #abd7 are known as  ,monadnocks1 
the name being derived from ,mount      
,monadnock1 ,n4 ,h41 an  elevation of   
this sort developed in a cycle          
antedating the present4                 
,illustration3 ,figs4                   
#abe-bg4--;,diagrams illustrating       
piracy1 where the    stream which does  
not flow over rock of superior hardness 
captures    those which do4 ,fig4 #abf  
represents a further development of the 
drainage shown in ,fig4 #abe1 and ,fig4 
#abg represents a still later    stage4 
,illustration3 ,figs4                   
#abh-cj4--;,diagrams to illustrate      
piracy1 where    the competing streams  
all cross a hard layer4 ,the diagrams   
represent    successive stages of       
development4    ,adjustment of streams  
to rock structures4--,valleys 7gullies7 
locate  themselves at the outset without
 immediate regard to the hardness and   

softness of their beds4 ,it is primarily
 the slope about the head of a  gully   
which determines its line of growth1    
though relative hardness  often         
determines the details of slope1 even in
 the early stages of an  erosion cycle4 
,once established1 streams tend to hold 
their courses1  even if this involves   
the crossing of resistant layers4       
,while a region where more and less     
resistant layers of rock come to the    
surface is in a youthful stage of       
erosion1 some of the valleys 7and       
therefore the streams7 are likely to be 
located on the less resistant  rock1    
some on the more resistant1 and some    
partly on the one and partly  on the    
other4 ,the streams on the weaker rock  
will deepen their valleys  more rapidly 
than the others1 and those which flow   
across stronger  and weaker rocks       
alternately will deepen their valleys   
more rapidly  than those which run on   
hard rock all the time4 ,the former     
conclusion  is self-evident4 ,the latter

 appears from the fact that rapids will 
be  likely to develop at the crossing of
 each hard layer1 thus accelerating     
erosion at those points4 ,such a stream 
therefore not only has less hard  rock  
to erode than one which flows on        
resistant rock all the time1 but  it    
erodes that which it does cross much    
faster4    ,illustration3 ,figs4 #aca1  
#acb4--,the capture of the head of      
,beaverdam    ,creek by the ,shenandoah 
,va4-,w4 ,va4 7,after ,willis47         
,streams which do not cross hard layers 
therefore have an advantage  over those 
which do1 and the tributaries to such   
streams1 since they  join deeper mains1 
have an advantage over the tributaries  
to the  others4 ,the valleys of the     
former may lengthen until their heads   
reach  the latter1 and capture their    
streams4 ,this sequence of events is    
illustrated in the accompanying diagrams
 7,figs4 #abe-bg74 ,even where  several 
streams cross the same resistant bed1   
piracy is likely to take  place among   

them1 for some are sure to deepen their 
valleys faster than  others1 because of 
inequalities of volume1 load1 or        
hardness4 ,this is  illustrated by      
,figs4 #abh-cj4 ,an actual case is shown
 in ,figs4 #aca1  #acb4 ,though piracy  
may take place when streams do not flow 
over rock  of unequal hardness 7p4      
#ajc71 it is much more common where     
unequal  resistance of the rock puts one
 stream at a disadvantage as compared   
with another4    ,the changes in the    
courses of streams1 by means of which   
they come to  sustain definite and      
stable relations to the rock structure  
beneath1  are known as processes of     
adjustment4#ed ,since streams and       
valleys  adjust themselves to other     
conditions as well1 this phase of       
adjustment  may be called structural    
adjustment4 ,structural adjustment is   
not  uncommon among rivers flowing over 
strata which are vertical or highly     
inclined1 since in these positions the  
hard and soft strata are most  likely to

 come to the surface in frequent        
alternation4 ,the smaller  streams      
suffer capture and adjustment first1    
since1 as a rule1 they  have shallower  
valleys4 ,it often happens that main    
streams1 because of  their deeper       
valleys1 hold courses not in adjustment 
with structure  7the ,delaware1 the     
,susquehanna1 etc471 while tributary    
streams are  captured1 diverted1 and    
adjusted4 ,the capture of a tributary1  
however1  leads both to the diminution  
of its main and to the increase of its  
captor1 and the weakened stream may     
ultimately fall a prey to the one  which
 is strengthened4    ,the processes of  
adjustment go on until the streams flow 
as much as  possible on the weaker beds1
 and as little as possible on the       
stronger1  when adjustment is complete4 
,this amounts to the same thing as      
saying  that the outcrops of the hard   
layers tend to become divides4 ,in many 
cases an area is so situated that there 
is no escape for its drainage  except   

across resistant rock4 ,in this case its
 drainage is completely  adjusted when  
as few streams as possible cross the    
resistant rock1 and  these by the       
shortest routes4    ,adjustment has been
 carried to a high degree of perfection 
in most  parts of the ,appalachian      
system4 ,here1 as in all other mountains
 of  similar structure1 strata of       
unequal hardness were folded into       
ridges4  ,in this case1 the folds have  
been truncated by erosion1 exposing  the
 more and the less resistant beds 7,h   
and ,s respectively7 in  alternate belts
 along the flanks of the truncated folds
 7ab and  cd1 ,fig4 #acc74 ,the streams1
 especially the lesser ones1 now flow   
along the strike of the softer beds much
 more commonly than elsewhere1  and     
where they cross the hard layers it is  
usually at right angles to  the strike4 
,this is shown in ,fig4 #acd1 where the 
arrows indicate the  direction of       
strike4 ,in the history of these rivers1
 however1 a factor  is involved which   

has not yet been considered1 and these  
streams will  be referred to later4     
,illustration3 ,fig4 #acc4--;,diagram   
showing the outcrops of hard layers     
on the flanks of a truncated fold4 cd   
represents the present    surface2      
dotted lines above1 earlier surfaces4   
,illustration3 ,fig4 #acd4--;,example of
 adjusted drainage in a region of       
folded rocks1 ,va4-,w4 ,va4             
,illustration3 ,fig4 #ace4--;,diagram to
 illustrate readjustment of    drainage1
 as base-level is approached4           
,illustration3 ,fig4 #acf4--;,diagram to
 illustrate superimposition4 ,the       
consequent stream on the upper formation
 is superimposed on the    underlying   
structures when the upper bed has been  
cut through4    ,as base-level is       
approached1 the outcrops of hard rock   
are brought  low4 ,when they have been  
reduced to the level of their           
surroundings1  the streams may flow     
without regard to the resistance of the 
rock  beneath1 for downward cutting has 

ceased4 ,as this stage of erosion is    
approached1 a readjustment of the       
drainage may take place1 and the  waters
 which had taken long and circuitous    
courses to avoid hard rock1  may change 
their courses to more direct ones       
7compare ,figs4 #acj and  #ace74        
,adjustment is1 therefore1 a relative   
term1 and streams which  are adjusted at
 one stage of erosion1 are not          
necessarily adjusted at  another4    ,it
 sometimes happens that rocks of unequal
 resistance are covered  by beds of     
uniform hardness4 ,a consequent stream  
developed on the  latter may find itself
 out of structural adjustment when it   
has cut  its channel down to the level  
of the heterogeneous beds below4 ,such  
a stream is said to be superimposed     
7,fig4 #acf7 on the underlying          
structure4 ,structural adjustment is    
likely to follow4                       
,,influence ,,of ,,joints ,,and ,,folds4
    ,joints4--,various structural       
features of rock other than hardness    

influence its erosion4 ,apart from the  
stratification planes1 most rock        
formations are affected by joints or    
fissures4 ,the joints are often1  but   
not always1 nearly vertical4 ,two sets  
are generally present1 and  sometimes   
more4 ,if but two1 they usually meet at 
a large angle2 if more  than two1 two   
are likely to be nearly perpendicular to
 each other1  while the third and fourth
 sets have such directions as to cut the
  others at large angles4 ,these joints 
allow the ingress of water1 roots1      
etc41 which help to weather and disrupt 
rocks4 ,occasionally there is  notable  
sag of the beds of rock along joint     
planes1 but this effect  is usually     
superficial only 7,fig4 #acg74 ,where   
the jointage planes are  frequent and   
open1 the columns bounded by them       
sometimes topple over on  cliff faces1  
either by undercutting1 or by the       
wedge-work of roots or  ice4    ,the    
effect of joints on erosion may often be
 seen along a stream  which flows in a  

rock gorge4 ,in such situations1 the    
outlines of the  banks are sometimes    
angular1 and sometimes crenate 7,fig4   
#ach71 the  rentrants being located at  
the joints4 ,by working into and        
widening  joints1 running water         
sometimes isolates masses of rock as    
islands  7,fig4 #aci74 ,in a region free
 from mantle rock1 or where the mantle  
rock  is meagre1 joints often determine 
the courses of valleys by directing  the
 course of surface drainage4 ,this is   
shown in many parts of the  arid west4  
,in regions where the rocks are notably 
faulted1 the courses  of the streams are
 sometimes controlled by the courses of 
the fault  planes4 ,this is the case1   
for example1 in central ,washington4#ee 
,illustration3 ,fig4 #acg4--,shows the  
sagging of beds along joints4 ,the      
disturbance does not extend far below   
the surface4 ,cook's quarry    7,niagara
 limestone7 near ,la ,salle1 ,niagara   
,co41 ,n4 ,y4 7,gilbert1 ,u4 ,s4        
,geol4 ,surv47    ,the jointing of rocks

 often shows itself distinctly in the   
weathered  faces of cliffs 7,figs4 #adj 
and #ada71 especially in arid and       
semi-arid  regions1 or where the slope  
is too steep for the accumulation of    
soil  and rock-waste on its surface4    
,if a stream flowing over jointed rock  
has falls1 the conditions are  sometimes
 afforded for the development of an     
exceptional and striking  scenic        
feature4 ,if above ,niagara ,falls1 for 
example1 there were an  open joint in   
the bed of the stream 7as at b1 ,fig4   
#adb71 some portion  of the water would 
descend through it4 ,after reaching a   
lower level  it might find or make a    
passage through the rock to the river   
below  the falls4 ,if even a little     
water took such a course1 the flow would
  enlarge its channel1 making a         
passageway between the joint through    
which the water descended and the valley
 below the falls 7bcde1 ,fig4  #adb74   
,this passageway might become large     
enough to accommodate all the  water of 

the river4 ,in this case1 the entire    
fall would be transferred  from the     
position which it previously occupied   
7f7 to the position of  the enlarged    
joint 7b74 ,the fall would then recede4 
,the underground  channel between the   
old falls and the new would be bridged  
by rock  7bf and f1 ,fig4 #adc71 making 
a natural bridge4 ,the natural  bridge  
near ,lexington1 ,va4 7,fig4 #add71     
almost #bjj feet above the stream  which
 flows beneath it1 is believed to have  
been developed in this  way4 ,a similar 
bridge is now in process of development 
in ,two ,medicine  ,river in            
northwestern ,montana 7,fig4 #ade74     
,once in existence1 a natural  bridge   
will slowly weather away4               
,illustration3 ,fig4 #ach4--;,figure    
showing crenate river bank1 the         
rentrants being determined by joints4   
,dells of the ,wisconsin ,river1    near
 ,kilbourn1 ,wis4 7,atwood47            
,illustration3 ,fig4 #aci4--,lone ,rock4
 ,an island isolated by the notable     

widening of a series of joints4 ,the    
joints in the rock of the island    have
 themselves been so widened that a      
rowboat may be taken through    it in   
two directions4 ,lower ,dells of the    
,wisconsin4 7,meyers47    ,illustration3
 ,fig4 #adj4--;,effect of columnar      
structure on weathering4    ,material   
unconsolidated4 ,spur of south end of   
,sheep ,mountain4    7,lippincott1 ,u4  
,s4 ,geol4 ,surv47    ,it is not to be  
understood that all natural bridges have
 had this  history4 ,they are sometimes 
developed from underground caves when   
parts  of their roofs are destroyed1 as 
well as in various other ways4          
,illustration3 ,fig4 #ada4--;,effect of 
columnar structure on weathering4       
,big ,bad ,lands1 ,s4 ,d4 7,darton1 ,u4 
,s4 ,geol4 ,surv47    ,folds4--,the     
erosion of folded strata 7anticlines and
 synclines7 leads  to the development of
 distinctive topographic features4 ,so  
soon as a  fold begins to be lifted1 it 
is1 by reason of its position1 subject  

to more rapid erosion than its          
surroundings4 ,for the same reason the  
crest of the fold is likely to be       
degraded more rapidly than its lower    
slopes1 and must suffer more degradation
 before it is brought to  base-level4   
,folds are usually composed of beds of  
unequal resistance1  and as the         
degradation of a fold proceeds1         
successive layers are worn  from the    
top1 and the alternating hard and soft  
layers composing it are  exposed4 ,so   
soon as this is accomplished1 adjustment
 of the streams  is likely to begin1 and
 the watercourses1 and later the valley 
plains1  come to be located on the      
outcrops of the less resistant layers1  
while  the outcrops of the harder beds  
become ridges4    ,if the axis of an    
eroded anticline were horizontal1 a     
given hard layer1  the arch of which has
 been cut off1 would1 after erosion1    
outcrop on  both sides of the axis4     
,when the topography was mature these   
outcrops  would constitute parallel     

ridges1 or parallel lines of hills2 when
 the  region had been base-leveled1 the 
outcrops would be in parallel belts1    
though no longer ridges or hills4 ,the  
lower the plane of truncation1  the     
farther apart would the outcrops be in  
the anticline1 and the  nearer together 
in the syncline 7compare ab and cd1     
,fig4 #acc74    ,illustration3 ,fig4    
#adb4--;,a natural bridge in process of 
development2    longitudinal section at 
the left2 transverse section1 looking   
toward    e1 at the right4    ,if1 on   
the other hand1 the axis of the         
anticline or syncline to be  eroded was 
not horizontal1 that is1 if it plunged1 
the topographic  result would be        
somewhat different4 ,suppose a plunging 
anticline to  be truncated at           
base-level4 ,if either end of the fold  
plunged below  the plane of truncation1 
the outcrops of a given layer on        
opposite  sides of the axis would       
converge in the direction of plunge1 and
 come  together at the end4 ,at a stage 

of erosion antedating planation 7say    
late maturity7 there would have been a  
ridge1 or a succession of hills1  in the
 position corresponding to the outcrop  
of a hard layer1 with a  canoe-shaped   
valley within4 ,if two hard layers were 
involved1 instead  of one1 there would  
be two encircling ridges1 with a curved 
valley  between them1 and a canoe-shaped
 valley within the innermost 7,fig4     
#adf74 ,if the anticline plunged both   
ways1 the valley enclosed by  the       
hard-layer ridge would be canoe-shaped  
at both ends 7,fig4 #adg74  ,in such a  
case there would be likely to be a low  
gap 7water-gap7 in  the rim of the      
valley through which the drainage which 
degraded the  surface escaped1 but there
 would be likely to be but one1 for if  
two or more streams had drained the area
 of the valley at an early  stage of    
erosion1 one would be likely to have    
captured the others  7see p4 #ach7      
before late maturity4 ,a succession of  
doubly-plunging  anticlines and         

synclines might give rise to a very     
complex series of  ridges and valleys4  
,illustrations of the above phenomena   
are found at  various points in the     
,appalachian ,mountains1 especially in  
eastern  ,pennsylvania4#ef              
,illustration3 ,fig4 #adc4--,the same as
 ,fig4 #adb at a later stage of         
development4    ,illustration3 ,fig4    
#add4--,the ,natural ,bridge of         
,virginia1 from the    southeast        
7,walcott1 ,u4 ,s4 ,geol4 ,surv47       
,illustration3 ,fig4 #ade4--;,a natural 
bridge in development4 ,two    ,medicine
 ,river1 ,mont4 ,corresponds to the     
stage represented by ,fig4    #adb1 and 
the view corresponds to that shown      
diagrammatically at the    right-hand   
end of the figure4 7,whitney47    ,in   
the structural adjustment which goes    
with the erosion of  folds1 it often    
happens that the valleys come to be     
located on the  anticlines1 while the   
outcrops of the hard layers on the      
flanks of the  anticlines1 or even in   

the original synclines1 become the      
mountains4  ,the adjustments by which   
valleys come to be located on anticlines
  are somewhat as follows3#eg ,fig4 #adh
 represents two doubly-plunging         
anticlines with a syncline between1 the 
relative elevations being shown  by     
contour lines4 ,at the outset1 the      
drainage of such a region must  have    
followed the structural valley1 and its 
initial course1 consequent  on the      
slope1 must have been down the axial    
trough4 ,drainage from the  anticlines  
into the synclines would have promptly  
developed valleys1  and the valleys     
would soon have acquired streams4       
,illustration3 ,fig4 #adf4--;,a         
canoe-shaped valley bordered by a ridge 
formed by the outcrop of a hard layer in
 a plunging syncline4 ,the    ridge     
bounding the canoe-valley is separated  
from an outer ridge by a    curved      
valley underlain by relatively weak     
rock4 7,after ,willis47                 
,illustration3 ,fig4 #adg4--;,a diagram 

to illustrate the effects of    erosion 
on a doubly-plunging anticline made up  
of beds of unequal    hardness4         
,illustration3 ,figs4                   
#adh-ea4--;,diagrams to illustrate the  
shifting of    rivers from a synclinal  
to an anticlinal position4 7,after      
,davis47    ,the anticlines and         
synclines under consideration are       
assumed to have a  thick hard layer at  
the surface1 and softer beds below4     
,this is shown  in the cross-section    
introduced in the figure1 the upper hard
 stratum  7m7 being indicated by the    
dots1 while the softer one 7n7 is white4
  ,the line oo represents base-level1   
which is below the hard layer both  in  
the syncline and anticline1 but much    
farther below in the latter  position   
than in the former4 ,because of their   
higher gradients1 and  because of the   
greater fracturing to which the region  
they drain was  presumably subject at   
the time of folding1 the tributary      
streams might  cut through the hard     

layer sooner than the main stream which 
they join4  ,this done1 they would      
enlarge their valleys rapidly in the    
softer rock  beneath1 and secondary     
tributaries would be developed 7,fig4   
#adi74 ,when  the condition of things   
represented in ,fig4 #adi is reached1   
the streams  c and d1 tributary to the  
synclinal stream1 come into competition4
  ,the former has the advantage over the
 latter1 because it joins the  main     
stream at a lower level4 ,stream c will 
therefore be likely to  capture d4 ,the 
incipient stages of the capture are     
stealthy1 and the  later bold4 ,at first
 the divide between their head waters is
 shifted  northward inch by inch1       
because the gradient toward g is higher 
than  that toward e4 ,the capture of the
 head waters of e is as slow as  the    
migration of the divide1 until the      
divide reaches the point where  e joins 
f4 ,the stream f is then diverted       
promptly into the valley  of g1 and is  
at once led away to c 7see ,fig4 #aej74 

,strengthened  by its increased volume1 
the stream c 7,fig4 #aej7 lowers its    
valley  across the hard layer more      
rapidly than before1 and so holds the   
advantage it has gained4 ,not only this1
 but the beheaded stream d  7,fig4      
#aej71 because of its diminished volume1
 sinks its valley into the  hard layer  
less rapidly than before1 and its       
decrease in power also  works to the    
advantage of the stream leading to c4   
,the result is that  the divide between 
fg and d does not remain constant1 but  
is driven  back step by step toward a4  
,similarly a tributary to the main      
stream at b 7,fig4 #aej71 may by  means 
of its tributary h1 capture the waters  
of fg1 and lead them  to the synclinal  
valley at b 7compare ,figs4 #aej and    
#aea74 ,deprived  of its main source of 
supply 7at c7 the synclinal stream is   
greatly  diminished above b1 and cuts   
more and more slowly1 while the stream  
fgh 7,fig4 #aea71 having greater volume 
and working mainly in softer  rock1     

sinks its channel faster than the stream
 in the synclinal axis4  ,under these   
circumstances1 the stream at f may cut  
its valley below  the valley in the     
synclinal axis a 7,fig4 #aej74 ,in this 
event1 the  divide between f and a      
7,fig4 #aej7 may be pushed back until   
the  synclinal stream is beheaded at a  
and carried out of the syncline and     
over into the anticlinal valley 7,fig4  
#aea74 ,thus1 the old anticlinal  axis  
comes to be the course of the main      
stream4 ,similarly the stream  entering 
the syncline at b 7,fig4 #aea7 might    
later be captured by i1  thus           
lengthening its anticlinal course4      
,it is not to be understood that this   
sequence of events will take  place in  
the degradation of every anticline1 but 
the principles here  set forth will     
always be operative4 ,the result        
specified will be  accomplished wherever
 hard and soft layers have the relations
 indicated  in the diagrams2 that is1   
where the stream in the syncline finds  

itself  on a resistant layer as it      
approaches base-level1 while at the same
  time the 7original7 tributary streams 
are working in softer beds4 ,it is  not 
to be understood1 therefore1 that       
streams migrate from synclines to       
anticlines for the sake of getting out  
of the former positions into the        
latter4 ,if they shift their courses it 
is to find easier ones4    ,that these  
changes are not fanciful is shown by the
 fact that the  adjustment described    
corresponds with that shown in many     
parts of the  ,appalachian ,mountains1  
and in other mountains of similar       
structure4    ,if in a later stage of   
its history1 the new main stream1 fh1   
were  to cut its bed down to a lower    
hard layer1 while the original stream1  
ab1 reached a softer bed beneath the    
hard one above1 the latter would  again 
have an advantage1 and a new series of  
adjustments would be  inaugurated which 
might result in re-establishing the main
 stream in  its original synclinal      

position4                               
,,effect ,,of ,,changes ,,of ,,level4   
,rise4--,if after being base-leveled1 or
 notably reduced by erosion1 a  region  
is uplifted so as to increase the       
gradients and therefore the  velocities 
of the streams which drain it1 the      
streams are said to be  rejuvenated1 and
 a new cycle of erosion is begun4 ,if   
the rise of the  area were equal        
everywhere1 while the coast line        
remained constant  in position1 there   
would be an immediate increase in       
velocity only  at the debouchures of the
 streams flowing directly into the sea4 
,at the debouchures of such streams     
there would be rapids or falls4  ,each  
rapids or falls would promptly recede1  
and with the recession1  the            
acceleration of velocity resulting from 
the uplift would be felt  farther and   
farther up-stream1 and ultimately to its
 source4 ,the  rejuvenated streams would
 cut new valleys in the bottoms of their
  old ones 7,figs4 #aeb and #aec74 ,the 

new valleys would begin where the       
increase in velocity was first felt1 and
 they would be lengthened by  head      
erosion just as valleys of the first    
cycle were lengthened4    ,illustration3
 ,fig4 #aeb4--;,cross-section of a wide 
valley1 ab1 in the    bottom of which a 
younger valley1 cd1 has been excavated  
as the    result of uplift4             
,illustration3 ,fig4 #aec4--;,diagram to
 illustrate in ground plan an    ideal  
case of rejuvenation as the result of   
uplift4    ,when the head of the new    
part of a valley of a rejuvenated stream
  recedes past the mouth of a tributary 
adjusted#eh to the gradient of  the main
 stream before rejuvenation1 the        
velocity of the tributary  is           
accelerated at its debouchure1 and it   
begins to excavate a new  valley in the 
bottom of its old one4 ,the new valley  
commences at the  lower end of the old  
one1 and develops headward 7a and b1    
,fig4  #aec74 ,good illustrations are   
furnished by the streams in the west    

central part of ,new ,jersey4 ,the      
,delaware has here a sharply defined    
valley1 and its tributaries are         
essentially as deep as their main at    
the point of junction4 ,above this point
 they have high gradients for a  short  
distance 7three to six miles71 beyond   
which they wind sluggishly  in wide     
valleys with low gradients across a     
relatively high plateau4  ,their        
profiles are illustrated by ,fig4 #aed4 
,the flat1 though high1  surface in     
which their upper courses lie1 appears  
to have been nearly  base-leveled in an 
earlier cycle1 and then to have been    
elevated4  ,the date of the elevation is
 fixed1 in terms of erosion1 by the time
  necessary for the excavation of the   
,delaware gorge1 and the narrow  gorges 
along the lower courses of its          
tributaries4 ,it was so recent  that the
 effects of rejuvenation1 proceeding    
from the debouchures of  the tributaries
 toward their heads1 have not yet       
advanced far from the  ,delaware4       

,similar relations are found elsewhere  
7,fig4 #a1 ,pl4 ,,xiii1  s4 c4 ,col474  
,another peculiarity of rejuvenated     
drainage is shown in  ,fig4 #b1 ,plate  
,,xiii 7s4 ,kan474 ,here ,elm ,creek    
flows at a level #bjj feet  below that  
of ,sand ,creek1 #d miles distant4 ,the 
valley of the former  appears to have   
entered upon a new cycle as the result  
of uplift1  while that of the latter1 in
 the area shown on the map1 is still    
unrejuvenated4 ,farther down-stream1 the
 valley of ,sand ,creek shows  signs of 
rejuvenation4 ,it may be noted that a   
tributary of ,amber ,creek  has good    
opportunity to capture ,sand ,creek1 for
 the latter flows about  #be miles      
before reaching the level of ,amber     
,creek at its junction with  ,elm       
,creek4    ,illustration3 ,,plate       
,,xiii4      ,fig4 #a4 ,,colorado4      
,u4 ,s4 ,geol4 ,surv4      ,fig4 #b4    
,,kansas4    ,u4 ,s4 ,geol4 ,surv4      
,illustration3 ,,plate ,,xiv4      ,fig4
 #a4 ,,pennsylvania4    ,u4 ,s4 ,geol4  

,surv4      ,fig4 #b4 ,,california4     
,u4 ,s4 ,geol4 ,surv4    ,illustration3 
,fig4 #aed4--,profile of a rejuvenated  
stream4 ,the    ,lockatong ,river 7,n4  
,j47 to the head of ,mud ,run4          
,should the lower end of a tributary    
valley fail to be degraded as fast  as  
the valley of the main at the point of  
junction1 the tributary is  out of      
topographic adjustment with its main4   
,falls or rapids may  result4 ,when the 
lower end of a tributary valley is      
distinctly above  the level of its main1
 the former is called a hanging valley4 
,hanging  valleys developed by stream   
erosion alone are not common except just
  after the recession of a falls past   
the mouth of a tributary4 ,hanging      
valleys1 as well as the characters and  
relations illustrated by ,figs4         
#aeb-aed are criteria of rejuvenation1  
but they must be applied with           
discretion4 ,such profiles1 for example1
 as that shown in ,fig4 #aed may  be    
developed when the rock of a stream's   

bed is unequally resistant1  and hanging
 valleys are generally a result of      
glaciation 7see ,chapter  ,v74          
,rejuvenated streams sometimes inherit  
certain peculiarities from their  aged  
ancestors4 ,thus a rejuvenated stream   
may intrench the meanders  possessed by 
the old stream which preceded 7see ,fig4
 #a1 ,pl4 ,,xiv1 near  ,harrisburg1     
,pa471 and intrenched meanders are one  
of the marks of  rejuvenated streams4   
,they are not uncommon in the           
,appalachian ,mountain  regions1 and are
 known in other parts of the world4 ,the
 ,seine and the  ,moselle furnish       
further illustrations4#ei    ,the       
history of the new cycle of erosion     
inaugurated by the uplift would  differ 
from that of the preceding cycle in that
 the new one would begin  with a        
drainage system already developed4      
,other things being equal1  therefore1  
the reduction of the land would proceed 
more rapidly in a  subsequent cycle than
 in the first4    ,the recognition of   

different cycles of erosion1 separated  
by uplifts1  is often easy4 ,the        
principles involved are illustrated by  
,fig4 #aee  which represents an ideal   
profile of considerable length 7say #ej 
miles74 ,the points a1 a1 and a reach a 
common level4 ,below  them there are    
areas b1 b1 and b which have a nearly   
common  elevation1 below which are the  
sharp valleys d1 d1 and d4 ,the  points 
a1 a1 and a represent the cross-sections
 of ridges  formed by the outcrops of   
layers of hard rock4 ,if the crests of  
the  ridges are level1 the points a1 a1 
and a must represent  remnants of an old
 base-level1 since at no time after a   
ridge of hard  rock becomes deeply      
notched does it acquire an even crest1  
until it is  base-leveled4#fj ,at all   
earlier stages its crest is uneven4     
,after the  cycle represented by the    
remnants a1 a1 and a was completed1  the
 region suffered uplift4 ,a new cycle   
represented by the plain b1  b1 and b   
was well advanced1 though not completed1

 when the region  was again elevated1   
and the rejuvenated streams began to cut
 their  valleys d1 d1 and d in the plain
 of the previous incomplete  cycle4 ,the
 elevations1 c and c 7intermediate in   
elevation between  a1 a1 and a1 and b1  
b1 and b7 may represent either  remnants
 of the first base-level plain which    
were lowered1 but not  obliterated1     
while the plane b1 b1 b was developing2 
or they may  represent a cycle          
intermediate between that during which  
a1 a1 a  and b1 b1 b were developed4 ,if
 the intermediate elevations 7c1  c7    
have a common height and level crests1  
the presumption would be in  favor of   
the latter interpretation4 ,if they be  
numerous and of varying  heights1 as is 
possible1 they may in the field obscure 
the planes 7a1  a1 a and b1 b1 b7       
developed in the different cycles1      
which1 in  the figure1 are distinct4    
,illustration3 ,fig4 #aee4--;,diagram to
 illustrate cycles of erosion    where  
the beds are tilted4    ,if the strata  

involved be horizontal the determination
 of cycles is  sometimes less easy4     
,thus in ,fig4 #aef1 it is not possible 
to say  whether a and a represent       
remnants of an old base-level1 or       
whether they represent the original     
surface from which degradation  started4
 ,so1 too1 the various benches below a1 
such as b1 b1 and  b may readily be the 
result of the superior hardness of the  
beds at  this level4 ,for the           
determination of successive uplifts in  
the field it  is necessary to consider  
areas of considerable size1 and to      
eliminate  the topographic effects of   
inequalities of hardness1 and of certain
  other factors to be mentioned         
presently4    ,illustration3 ,fig4      
#aef4--;,diagram to illustrate cycles of
 erosion    where the beds are          
horizontal4    ,the inequalities in the 
depths of the young valleys in ,figs4   
#aee and  #aef may be explained on the  
supposition that the deeper ones belong 
to  main streams1 and the shallower ones

 to tributaries4 ,such a valley as  that
 shown at e1 ,fig4 #aee1 suggests       
rejuvenation at this point2 but  farther
 up the stream which occupies this      
valley1 rejuvenation might  not be      
apparent4 ,in this case1 the main       
streams might be flowing in new         
valleys1 d1 d1 etc41 while the heads of 
their tributaries are still  flowing in 
the older valleys of the preceding cycle
 7compare ,fig4 #aed  and ,fig4 #a1 ,pl4
 ,,xiii74    ,it is by the application  
of the preceding principles that it is  
known  that the ,appalachian ,mountains1
 after being folded1 were reduced to  a 
peneplain 7p4 #gf71 throughout their    
whole extent from the ,hudson  ,river to
 ,alabama4 ,the peneplain level is      
indicated by the level  crests of the   
,appalachian ridges1 shown in cross     
profile by the high  points of ,fig4    
#aeg4 ,the system was then uplifted1 and
 in the cycle  of erosion which         
followed1 broad plains were developed at
 a new and  lower level1 corresponding  

in a general way to the plains b1 b1    
and b of ,fig4 #aee4 ,the plains were   
located1 for the most part1  where the  
less resistant strata come to the       
surface4 ,above them rose  even-crested 
ridges1 the outcrops of the resistant   
layers1 which  had been isolated by the 
degradation of the softer beds between4 
,they constitute the present mountain   
ridges 7the high points of ,fig4  #aeg74
 ,the evenness of their crests1         
testifying to the completeness  of the  
first peneplanation1 is shown in ,fig4  
#aeh1 which represents1                 
diagrammatically1 a longitudinal profile
 of an ,appalachian ,mountain  ridge4   
,the evenness of the crest is           
interrupted by 7#a7 notches 7b1  c1     
etc41 ,fig4 #aeh7 cut by the streams in 
later cycles1 and 7#b7 by  occasional   
elevations above the common level       
7monadnocks1 a1 a1 ,fig4  #aeh74 ,the   
monadnocks are generally rather         
inconspicuous1 but there is a  notable  
group of them in ,north ,carolina and   

,tennessee4 ,mount ,mitchell  and ,roane
 ,mountain are examples4 ,when long     
distances are considered1  the ridge    
crests depart somewhat from             
horizontality4 ,this is believed  to be 
due1 in part at least1 to deformations  
of the old peneplain  during the uplift 
which inaugurated the second cycle of   
erosion4    ,illustration3 ,fig4        
#aeg4--;,cross-section of a portion of  
the    ,appalachian ,mountains to       
illustrate the phenomena of erosion     
cycles4    7,after ,rogers47            
,illustration3 ,fig4 #aeh4--;,a         
diagrammatic longitudinal profile of an 
,appalachian ,mountain ridge4    ,the   
extent to which the second cycle of     
erosion recorded in the  present        
topography had proceeded before its     
interruption by uplift1  is indicated by
 the extent of the valley plains 7,fig4 
#aeg7 below the  mountain ridges4 ,while
 these plains were being developed on   
the weak  rocks1 narrow valleys only    
7,fig4 #aeh7 were cut in the resistant  

rocks  which now stood out as ridges4   
,in ,fig4 #aeh some of these valleys are
  shallow 7c1 c1 c1 etc471 and but one  
of them deep4 ,the former may  be either
 7#a7 the valleys of streams which      
crossed the hard layer  at the beginning
 of the cycle1 and which were diverted  
before their  valleys became deep2 or   
7#b7 they may represent the heads of    
valleys  now working back into the      
ridges4 ,the deep valley 7b7 represents 
the  work of a stream which has held its
 course across the hard layer while  the
 latter was being isolated as a mountain
 ridge 7compare ,figs4 #aca  and #acb74 
,deep narrows of this sort are often    
called water-gaps4  ,similar valleys1   
whether shallow or deep1 from which     
drainage has  been diverted1 are        
sometimes called wind-gaps4 ,the second 
cycle of  erosion1 while still far from 
complete1 was interrupted by uplift     
7relative or absolute71 and a new cycle 
inaugurated4 ,this event was so  recent 
that the new 7third7 cycle has not yet  

advanced far4    ,illustration3 ,fig4   
#aei4--,the ,kittatinny ,mountains and  
,delaware    ,water-,gap from ,manunka  
,chunk4 7,n4 ,j4 ,geol4 ,surv47         
,recently it has been urged that another
 cycle1 intermediate between the  first 
and second1 is to be recognized4#fa     
,some of the features just described are
 illustrated by ,fig4 #aei4 ,the  even  
mountain crest in the background is the 
,kittatinny ,mountain of  ,new ,jersey  
and its continuation in ,pennsylvania4  
,in common with other  corresponding    
crests it represents the oldest recorded
 base-level 7or  peneplain7 of the      
region4 ,the great gap in the mountain  
is the ,delaware  ,water-,gap4 ,below   
the mountain crest there is another     
plain1 developed  in a subsequent cycle 
of erosion1 while the valley plain in   
the  foreground represents the work of a
 still later cycle4    ,illustration3   
,fig4 #afj4--,showing certain           
peculiarities of ,appalachian           
drainage4 #a  the ,susquehanna2 #b  the 

,potomac2 #c  the ,james2 #d     the    
,roanoke2 #e the ,coosa2 #f  the        
,tennessee2 #g  the ,kanawha2 #h        
head of ,new ,river2 #i  head of the    
,french ,broad4    ,the oldest erosion  
plain of the ,appalachian ,mountains1   
the results of  which are seen in the   
even-crested ridges so characteristic of
 the  system1 is sometimes called the   
,kittatinny base-level4#a ,it was       
completed early in the ,cretaceous      
period1 and hence is sometimes known  as
 the ,cretaceous base-level4 ,the next  
lower plain1 imperfectly  developed1 has
 been called the ,shenandoah ,plain1#fb 
from the  ,shenandoah ,valley where it  
is well seen 7,fig4 #acb and ,fig4 #b1  
,pl4 ,,xii74  ,it is to be noted that   
the terms base-level and peneplain have 
both been used in connection with these 
old plains4 ,graded plain is  equally   
applicable4 ,the truth is that the      
topographic types represented  by these 
three terms grade into one another4 ,it 
may be questioned  whether definitions  

should be insisted on which             
differentiate these  types more sharply 
than ,nature has4    ,many of the       
peculiarities of the drainage of the    
,appalachian ,mountain  system are      
intimately connected with the history   
just outlined4 ,thus  three great       
rivers1 the ,delaware1 the ,susquehanna1
 and the ,potomac1  have their sources  
west of the ,appalachians proper1 cross 
the system  in apparent disregard of the
 structure1 and flow into the ,atlantic4
  ,the ,james and ,roanoke head far to  
the west1 although not beyond the       
mountain system1 and flow eastward1     
while the ,new ,river 7leading to  the  
,kanawha7 farther south1 heads east of  
the mountain-folds1 and  flows          
northwestward across the alternating    
hard and soft beds of the  whole        
,appalachian system1 to the ,ohio 7,fig4
 #afj74 ,the ,french ,broad1  a         
tributary to the ,tennessee1 has a      
similar course4 ,such streams are       
clearly not in structural adjustment1   

and afford good opportunities  for      
piracy4 ,their courses were apparently  
assumed during the time of  the         
,kittatinny base-level1 when the streams
 had so low a gradient as  not to be    
affected by the structure 7p4 #aej74    
,elevation rejuvenated  them1 and they  
have held their courses in succeeding   
cycles across beds  of unequal          
resistance1 though smaller streams have 
become somewhat  thoroughly adjusted4   
,crustal deformations have also helped  
them to hold  their courses1 for the    
,cretaceous peneplain seems to have been
 tilted  to the southeast at its        
northern end1 and to the southwest at   
its  southern1 when the succeeding cycle
 began4    ,streams which hold their    
early courses in spite of changes which 
have taken place since their courses    
were assumed are said to  be antecedent4
 ,they antedate the crustal movements   
which1 but  for pre-existent streams1   
would have given origin to a different  
arrangement of river courses4 ,as a     

result of crustal movements1  therefore1
 a consequent stream may become         
antecedent4 ,master streams  are more   
likely to hold their courses1 and       
therefore to become  antecedent1 than   
subordinate ones4    ,the uplift of     
base-leveled beds1 especially if the    
beds are tilted so  as to bring layers  
of unequal resistance to the surface at 
frequent  intervals1 affords conditions 
favorable for extensive adjustment4 ,the
  numerous wind-gaps in the mountain    
ridges1 representing the abandoned      
courses of minor streams1 and the less  
numerous water-gaps1 which  indicate the
 resistance of large streams to         
structural adjustment1 are  instructive 
witnesses of the extent to which        
adjustment has gone4 ,so  extensive has 
been the adjustment among the streams of
 the ,appalachian  ,mountains that there
 is probably no considerable stream in  
the whole  system which has not gained  
or lost through its own or its          
neighbors'  piracy4 ,the history of the 

rivers of the ,appalachian ,mountains   
has been  further complicated by a      
considerable amount of warping during   
the  periods of uplift4#fc              
,illustration3 ,figs4 #afa1             
#afb4--;,diagrams to illustrate the     
effect of    crustal warping on stream  
erosion4 ,the dotted lines represent the
    profiles of the streams before      
deformation2 the full lines1 after4     
,erosion will be stimulated between a   
and b in each case1 and    between c and
 d in ,fig4 #afb4 ,below b1 ,fig4 #afa1 
the stream    will be drowned1 and      
erosion therefore stopped4 ,erosion will
 also be    stopped or retarded above a1
 between b and c1 and below d in        
,fig4 #afb4    ,sinking4--,the land on  
which a river system is developed may be
  depressed relative to sea-level4 ,in  
this case the sea would occupy  the     
lower ends of valleys1 converting them  
into bays and estuaries4 ,a  stream in  
this condition is said to be drowned4   
,of drowned rivers  there are many      

examples along the ,atlantic coast4     
,thus the ,st4  ,lawrence ,river is     
drowned up to ,montreal1 and the ,hudson
 up to ,albany4  ,if the drowned portion
 of the latter valley were not so       
narrow1 it  would be a bay4 ,delaware   
and ,chesapeake ,bays1 as well as many  
smaller  ones1 both north and south1 are
 likewise the drowned ends of river     
valleys 7see figures1 ,chapter ,,vi74   
,if all parts of a drainage basin  sank 
equally1 the velocities of the streams  
above the limit of drowning  would not  
be changed1 for the gradients would     
remain the same as  before4 ,the fact   
that a river's channel is below         
sea-level is not to  be taken as proof  
that the valley is drowned4 ,thus the   
bottom of the  channel of the           
,mississippi is as much as #ajj feet    
below the level of  the ,gulf1 some #bj 
miles above ,new ,orleans4#fd           
,differential movement4                 
,warping4--,where a land surface on     
which a river  system is established    

suffers warping1 some parts going up and
 others  down1 the opposite movements   
being either absolute or relative1      
various  phenomena would result4 ,this  
may be illustrated by the accompanying  
diagrams 7,figs4 #afa and #afb71 where  
the profiles of the streams are         
represented as warped from the positions
 represented by the dotted  lines1 to   
the positions shown by the full lines4  
,the velocity will be  accelerated below
 the points of differential elevation   
7between a and  b1 ,fig4 #afa1 and      
between a and b1 and c and d1 ,fig4     
#afb71 but  checked above 7above a1 and 
between b and c1 ,fig4 #afb74 ,above an 
elevation which notably checks its flow1
 a stream is ponded4 ,if the  ponding is
 slight1 a marsh may develop above the  
obstruction2 if more  considerable1 a   
lake is formed4 ,lakes of this class are
 likely to be  short-lived1 since the   
ponded waters are likely to soon        
overflow and  lower their outlet so as  
to drain the lake4 ,the elevation which 

ponds  the stream may be great enough   
and rapid enough so that the resulting  
lake finds an outlet by some course     
other than that originally followed  by 
the stream4 ,where a stream holds its   
course across an uplift athwart  its    
valley1 either with or without ponding1 
it becomes an antecedent  stream 7see p4
 #afi71 since it has a course assumed   
before the latest  deformation of the   
crust and in apparent disregard of      
present surface  configuration4 ,thus   
the ,columbia ,river holds its          
antecedent course  across areas which   
have been uplifted 7differentially7     
hundreds and  even thousands of feet4#fe
 ,some of the striking scenic features  
of  this noble valley are the result of 
these changes in the country  through   
which it flows4 ,a lesser stream would  
have been diverted1 as  many of its     
tributaries have been4 ,even its course 
across the ,cascade  ranges is believed 
to be antecedent4#ff    ,illustration3  
,figs4 #afc1 #afd4--,piracy stimulated  

by warping4 ,uplift    along axis #a-b4 
,another peculiarity of valleys and     
streams resulting from changes of  level
 is illustrated in ,fig4 #b1 ,pl4 ,,xiv 
7southern ,california74 ,the  main      
valleys of this part of the coast were  
developed when the land  stood          
considerably higher than now4 ,later the
 subsidence of the coast  converted the 
lower ends of the valleys into bays or  
fiords4 ,the bays  were then transformed
 into lagoons by deposition4 ,subsequent
 rise of  the land or depression of the 
sea allowed the drainage from the old   
lagoons to cut across the deposits which
 had converted the bays into  lagoons4  
,the result is an old1 wide valley      
above1 suggested by a young  one below4 
,if the warpings were considerable1 much
 more decisive changes in  drainage     
would result4 ,suppose the drainage of a
 given region to be  represented by the 
streams in ,fig4 #afc4 ,if there is     
uplift along the  axis #a-b1 that part  
of ac above the axis of uplift would be 

ponded1  or at least have its velocity  
checked1 while the flow of some of the  
tributaries of d would be accelerated1  
and might work back and  capture the    
other stream 7,fig4 #afd74    ,crustal  
warping was one of the conditions under 
which the ,tennessee  achieved its      
present anomalous course1 and its       
history#fg is  illustrative of the      
complex changes which drainage suffers  
when warping  affects the area where the
 rock structures are of unequal         
resistance4  ,at the close of the       
,cretaceous cycle of erosion1 when the  
,appalachian  ,mountains had been       
reduced to a peneplain1 the waters      
falling in  the area now drained by the 
upper course of the ,tennessee flowed   
south-south-west to the ,gulf in a      
stream 7the ,appalachian ,river1 a1     
,fig4 #afe7 the lower part of which had 
the general position of the ,coosa  and 
the ,alabama4    ,to the west of the    
,appalachian ,river1 shorter streams    
flowed west  and southwest into the     

,mississippi embayment 7,fig4 #afe7 by  
courses  which are not now definitely   
known4 ,the succeeding cycle of erosion 
was inaugurated by uplift and           
deformation of the peneplain4 ,the axis 
of greatest elevation 7,,ab1 ,fig4 #aff7
 was nearly parallel to the             
,appalachian ,river1 and the effect of  
the differential uplift was to  impose a
 greater task on this river 7a1 ,fig4   
#aff71 which flowed  along the axis of  
uplift1 than upon the rivers which      
flowed westward  and southwestward to   
the ,mississippi embayment4 ,the result 
was that  the strongest of the          
southwesterly flowing streams worked its
 head  back into the drainage basin of  
the ,appalachian ,river1 and captured1  
one by one1 the head-waters of its      
westerly tributaries1 establishing  some
 such drainage relations as are shown in
 ,fig4 #aff4 ,still later1  after the   
land area of the region had been        
considerably extended by  the withdrawal
 of the sea1 the ,appalachian ,river    

itself was reached by  the invading     
stream1 and its waters carried away to  
the ,mississippi ,bay  by a course the  
lower part of which is thought to have  
corresponded  approximately with the    
course of the present ,black ,river 7b1 
,fig4  #afg74    ,illustration3 ,fig4   
#afe4--,shows the general position of   
the main    drainage lines in the       
southern ,appalachians at the close of  
the    ,cretaceous cycle of erosion4    
,the lower part of stream b is made to  
follow the course of a portion of the   
present ,tennessee4    ,illustration3   
,fig4 #aff4--,shows the general position
 of the main    drainage lines in the   
southern ,appalachians1 after the       
capture of the    westerly tributaries  
of the ,appalachian ,river by stream b4 
,compare    ,fig4 #afe4                 
,illustration3 ,fig4 #afg4--;,a stage   
later than that shown in ,fig4 #aff4    
,the sea is represented as having       
withdrawn from a considerable area      
which was submerged at earlier stages   

7,figs4 #afe1 #aff74    ,illustration3  
,fig4 #afh4--,shows the final change    
which resulted in the    present course 
of the ,tennessee4 ,the land is         
represented as somewhat    higher than  
now4#fh    ,still later there was       
further deformation which caused        
additional  changes in the drainage4    
,the whole region was uplifted1         
relatively if  not absolutely1 but the  
uplift was differential1 being greatest 
along  the axis represented by ,,ab1    
,fig4 #afg4 ,the effect of the          
deformation  was to stimulate the       
tributaries of the ,ohio flowing north  
from this  axis4 ,their growth was      
further accelerated by the weakness of  
the  strata over which they ran4 ,at the
 same time1 the uplift to the south  led
 the southwesterly flowing stream 7b1   
,fig4 #afg7 to discover  relatively hard
 beds of rock in its lower course1 and  
these beds  retarded its down-cutting4  
,the result was that a tributary of the 
,ohio  7a1 ,fig4 #afg7 finally tapped   

the main stream flowing to the southwest
  7b1 ,fig4 #afg7 and carried its upper 
part over to the ,ohio 7,fig4 #afh74    
,this was the beginning of the present  
,tennessee4                     ,,the   
,,aggradational ,,work ,,of ,,running   
,,water4    ,principles                 
involved4--,since deposition results    
from the failure  of transportation1 the
 factors which control transportation   
also  influence deposition4             
,transportation by streams is determined
 largely  by velocity1 and the most     
important factors influencing velocity  
are  slope1 volume1 and load 7p4 #aae74 
,of these the first two are usually of  
greater importance than the third4    ,a
 stream is said to be loaded when it has
 all the sediment it can  carry2 it is  
loaded with fine material when it has   
all the fine  material it can carry1 and
 with coarse material when it has all   
the  coarse it can transport4 ,a stream 
loaded with coarse material flows  more 
swiftly than one loaded with fine1 for a

 larger percentage of a  stream's energy
 can be utilized in carrying fine       
material than coarse1  and hence a      
larger percentage of the energy of a    
stream which carries a  load of the     
latter will express itself in velocity4 
,deposition takes place whenever a      
stream finds itself with more load  than
 it can carry1 and is an expression of  
the stream's refusal to  remain         
overloaded4 ,a stream may become        
overloaded in various ways4  ,it might  
at first seem unnecessary to inquire    
whether a stream may  be overloaded at  
its source1 but the question is not     
necessarily to  be answered in the      
negative4 ,the source of a stream is not
 always a  definite point4 ,in a general
 way it may be said that the source of  
the  normal stream is at that point in  
its valley where the bottom is as low   
as the ground-water level of the region4
 ,but since the ground-water  level is  
not constant 7p4 #ga7 the source of a   
stream is likely to be  farther up its  

valley in a wet season than in a dry one
 7p4 #gb74 ,after  a heavy shower1 the  
run-off descends to the axis of the     
valley from the  slopes on all sides1   
and temporarily the stream begins above 
the point  which marks even its         
wet-season source4 ,if under such       
circumstances  the slopes about the head
 of the valley are notably steeper than 
the  slope of the valley itself1 as they
 frequently are1 the water flowing  down
 them may gather an amount of material  
which it cannot carry after  it reaches 
the bottom of the valley4 ,this may be  
the case at1 or even  above1 the point  
which marks the source of the permanent 
stream4 ,it is1  therefore1 possible for
 a stream to be overloaded at its       
source1 if we  take the source to be the
 point whence the water permanently     
flows4  ,deposition may1 therefore1 be  
taking place in a valley at the head of 
its permanent stream1 or temporarily    
even in the valley above it4    ,streams
 issuing from glaciers sometimes have   

more load than they can  carry after    
they escape from the ice4 ,if the stream
 be regarded as  beginning at the point 
where it issues from beneath the ice it 
may be  overloaded at its source4#fi    
,under certain circumstances1 a stream  
may overload itself4 ,thus if a  stream 
loaded with coarse detritus reaches a   
portion of its valley  where fine       
material is accessible in abundance1    
some of the velocity  which is helping  
to carry the coarse may be used in      
picking up and  carrying the fine4 ,this
 reduces the velocity1 and since the    
stream  already had all the coarse      
material it could carry1 reduction of   
velocity must result in deposition4 ,it 
follows that when a stream fully  loaded
 with coarse material picks up fine1 it 
becomes overloaded1 so  far as the      
coarse material is concerned4    ,again1
 tributaries may overload their mains4  
,while tributaries  are usually smaller 
than their mains1 they frequently have  
higher  gradients1 and the smaller      

stream of higher gradient may bring to  
the  larger stream of lower gradient    
more material than the latter can  carry
 away4 ,thus deposition may take place  
at the point of junction of  tributaries
 with their mains4 ,this may go so far  
as to pond the latter  enough to cause  
its expansion into a river-lake4 ,lake  
,pepin1 in the  ,mississippi ,river at  
the mouth of the ,chippewa 7in ,wis471  
is an example4    ,streams may become   
overloaded by losing velocity or volume1
 or both4  ,decrease in velocity is     
brought about either by decrease in     
declivity  or in volume4 ,in general1   
streams have lower gradients and greater
  volumes in their lower courses than in
 their upper1 and these two  elements   
affect velocity in different ways4 ,if  
the increase in volume  be not enough to
 counterbalance the decrease in         
declivity1 as is often  the case1 a     
stream which is loaded in its upper     
course will deposit  in its lower4 ,the 
decrease of velocity at the debouchure  

of a stream  almost always leads to     
deposition4    ,decrease in velocity as 
the result of decrease in volume is less
  common4 ,when decrease in volume      
occurs1 it may be the result of 7#a7    
evaporation1 7#b7 the absorption of     
water into the bed of the stream1  or   
7#c7 branching--the giving off of       
distributaries4 ,while evaporation  is  
going on everywhere1 the diminution of a
 stream by this means is  usually more  
than balanced by the increase from      
tributaries1 rainfall1  and springs2 but
 in arid regions a very different       
condition of things  sometimes exists4  
,if mountains in an arid region be      
capped with  snow1 its melting supplies 
the streams during the melting season4  
,as  the streams flow out from the      
mountains through dry regions1 they     
receive little or no increment from     
rainfall1 tributaries1 or springs1  and 
evaporation reduces the volume of water1
 or even dissipates it  altogether4     
,absorption of water into the bed of the

 stream often  accompanies evaporation4 
,reduction of volume by evaporation and 
by  absorption is especially common in  
arid regions4 ,wherever loaded  streams 
are reduced in volume1 whether by       
evaporation or absorption1  deposition  
takes place4    ,the third way by which 
velocity is decreased as the result of  
decreasing volume is illustrated at the 
debouchures of many streams4  ,near the 
,gulf1 for example1 the ,mississippi    
branches repeatedly 7see  ,fig4 #aij74  
,the same phenomena are often seen where
 one stream joins  another 7,fig4 #afi74
 ,individually the distributaries are   
much smaller  than the main stream      
before they separated from it1 and      
because they  are smaller their combined
 surfaces are greater1 and the amount of
  energy consumed in the friction of    
flow is increased4 ,the velocity of  the
 water and its carrying power are1      
therefore1 reduced4 ,thus the  branching
 of streams gives rise to deposition1   
and where deposition  takes place the   

gradient of the stream is reduced1 and  
this occasions  still further           
deposition4 ,the sediment which fills up
 the channel and  checks the flow       
finally compels the stream1 or some part
 of it1 to  transgress its banks4       
,deposition1 therefore1 favors the      
development of  distributaries1 and the 
development of distributaries in turn   
favors  deposition4    ,illustration3   
,fig4 #afi4--;,delta of the ,chelan     
,river at its junction  with the        
,columbia4 ,shows the tendency of       
streams to distribute where  active     
deposition is in progress4 7,willis1 ,u4
 ,s4 ,geol4 ,surv47    ,the foregoing   
statements make it clear that a stream  
may be eroding  in one part of its      
valley while it is depositing in        
another1 and that  erosion may alternate
 with deposition in the same place1 on  
account of  fluctuations in volume1 and1
 therefore1 in velocity of the stream4  
,it  will be seen in the sequel that    
erosion and deposition may be taking    

place at the same time in the same part 
of the valley4 ,the activities  of a    
river are so nicely balanced that slight
 disturbance at one point  causes       
disturbance at all points below4        
,the deposits4    ,types4--,turning from
 the principles which underlie river    
deposition to  the deposits themselves1 
they are found to occur in various      
situations4  ,running water usually     
descends from steeper slopes above to   
gentler  slopes below1 and ends at the  
sea1 or in a lake or inland basin4      
,wherever there is a sudden decrease in 
its gradient1 as at the base of  a hill1
 ridge1 or mountain1 running water is   
likely to leave a large  part of its    
load1 building an alluvial fan or cone  
7,figs4 #fg1 #fh1  and ,pl4 ,,vi74 ,even
 where there is no sudden decrease in   
the gradient  of a stream1 there is     
likely to be a gradual one1 and in spite
 of the  fact that the increased volume 
of a stream in its lower course tends to
  overcome the effect of diminished     

gradient on velocity1 deposition is     
likely to take place as the gradient is 
reduced4 ,deposits occasioned by  the   
gradual reduction of a stream's velocity
 often have great extent  in the        
direction of a stream's flow4 ,they     
cover the flood plains of  streams1     
making them alluvial plains 7,fig4 #gc74
 ,when a stream reaches  the sea or a   
lake its current is destroyed and its   
load dropped1 unless  taken in charge by
 the waves and currents of the standing 
water4  ,sediment accumulated in        
quantity at the debouchures of streams  
gives  rise to deltas 7,figs4 #afi1     
#ahg74 ,alluvial cones and fans1        
alluvial  plains1 and deltas1 are the   
principal types of river deposits4      
,apart  from these well-defined types   
there are bars in the channels of       
depositing streams1 and much ill-defined
 alluvium which does not allow  of ready
 classification4    ,alluvial fans and  
cones4--,the only distinction between   
the alluvial  fan and the alluvial cone 

is one of slope1 the cones 7they are but
  half-cones at best7 being steeper than
 the fans4 ,alluvial fans and  cones    
have their most striking development    
where temporary torrents1  occasioned by
 showers or the rapid melting of snow1  
issue from mountain  ravines4 ,such     
streams usually carry heavy loads of    
detritus1 the  coarser part of which is 
likely to be deposited at the base of   
the  mountain slope4 ,cones and fans    
built by such streams have a periodic   
rather than a steady growth4    ,at the 
beginning of its development the        
material of the alluvial cone  is       
deposited much as in a talus cone       
7compare ,fig4 #agj with ,figs4 #fg  and
 #fh74 ,its deposition chokes the       
channel of the stream1 and some of  the 
water then seeks new courses to right   
and left of the apex of the  deposit4   
,this expands the area of deposition to 
right and left1 while  the water which  
flows over it lengthens it in the       
direction of flow4    ,the course and   

behavior of the water after reaching an 
alluvial cone is  instructive4 ,as its  
velocity is checked1 deposition often   
takes place  in the channel1 diminishing
 its capacity4 ,as the channel is filled
 up1  the water tends to overflow on    
either side4 ,the overflowing water1    
being shallow1 has so little velocity   
that much of its load is dropped  on    
either margin of the channel1 building  
up levees4 ,the water ever and  anon    
breaks through the levees1 giving rise  
to distributary streams1  each of which 
aggrades its channel and builds its own 
miniature  levees 7,fig4 #aga74 ,not    
rarely this process of channel-filling  
and  levee-building goes on until the   
channels of the little rivulets are     
above the general level of the cone on  
which they rest4 ,the rivulet  then runs
 in a groove on the crest of a little   
ridge4 ,the channels on  the surfaces of
 fans and cones are fewest and deepest  
at their heads1  and more numerous and  
shallower below4 ,in some cases the     

surface-water  disappears altogether    
before the outer border of the fan is   
reached1 by  sinking into the dbris4    
,illustration3 ,fig4 #agj4--;,a talus   
cone4 ,north ,greenland ,coast4 ,the    
talus cone reaches the sea-level4 ,drawn
 from photograph4    ,alluvial fans and 
cones have various forms1 and often     
attain  considerable dimensions4 ,their 
angles of slope depend on the amount  of
 reduction of velocity which the        
depositing water suffers1 and the       
amount and kind of load which it        
carries4 ,the maximum slope of the  cone
 is the angle at which the loose        
material involved will lie4 ,the        
minimum slope of the fan1 on the other  
hand1 approaches horizontality4  ,if    
many alluvial fans develop in proximity 
to one another1 as at the  base of a    
mountain range1 they may expand         
laterally until they merge4  ,a long    
succession of them may thus give rise to
 an extensive alluvial  piedmont plain1 
or a compound alluvial fan4 ,the lower  

edge of such a  fan is often somewhat   
lobate4 ,such plains exist along the    
bases of many  mountain ranges 7,pl4    
,,vi71 and may be seen in miniature even
 along low  ridges4    ,illustration3   
,fig4 #aga4--,miniature levees on an    
alluvial cone4 ,slope    of ,gray ,peak1
 ,colo4 7,r4 ,t4 ,chamberlin47    ,a    
permanent stream1 as well as a temporary
 one1 may develop an alluvial  fan at   
the base of a mountain slope2 but since 
the mountain course of  the former is   
likely to be less steep than that of the
 latter1 its  waters suffer a           
correspondingly less reduction of       
velocity at any  one point4 ,the fan of 
the permanent stream is therefore likely
 to be  relatively flat1 and to stretch 
far down the valley4 ,such fans grade   
into valley plains4 ,from the general   
principles already discussed1 it  is    
clear that well-developed fans go with  
relatively youthful stages of  erosion1 
and belong normally to the upper parts  
of drainage lines4    ,ill-defined      

alluvium4--,there is a widespread mantle
 of alluvial  material deposited by     
running water which was not organized   
into  distinct streams4 ,the water which
 runs down smooth slopes in sheets      
during showers carries fine earthy      
matter1 as well as some that  is        
coarser4 ,these materials are largely   
deposited at the bases of  the slopes1  
forming basal accumulations of greater  
or less extent1  comparable in origin to
 alluvial fans4 ,a relatively small     
amount of the  slope wash is carried far
 out from the base of the declivities4  
,it is  not easy to realize the extent  
to which this process is taking place4  
,there is hardly a slope without loose  
material1 and there is hardly an  acre  
of low land below a slope on which      
running water has not deposited         
sediment washed down from above4 ,when  
it is remembered that this is  as true  
of gentle slopes and their surroundings 
as of steep slopes1  though perhaps not 
to the same extent1 and that a very     

large part of  the earth's surface is   
made up of sensible slopes1 or of flats 
at their  bases1 some idea of the       
aggregate effect may be gained4         
,there is another way of looking at the 
same question4 ,earthy matter  is being 
continually transferred from land to    
sea1 and chiefly from  high land4       
,rarely does it start from any point    
distant from the shore  and move        
uninterruptedly to it4 ,it is           
transported a short distance and        
lodged1 to be again picked up1 carried  
forward another step in its  journey1   
and lodged again4 ,for a very large part
 of the earth's surface  it would be    
true to say that its mantle rock is     
material in transit  from higher land to
 the sea4    ,alluvial plains4--,most   
streams1 whether heading in mountains or
 not1  have gentler gradients in their  
lower courses than in their upper1 and  
in spite of increasing volume are       
usually unable to carry to their        
debouchures all the material gathered   

above4 ,the excess of load is  dropped  
chiefly on the flood-plains of the      
streams and constitutes them  alluvial  
plains4    ,the making of an alluvial   
plain usually involves both erosion and 
deposition4 ,when a stream has cut its  
channel to grade1 downward  erosion     
ceases1 or more exactly1 downward       
cutting is1 on the average1             
counterbalanced by deposition4 ,so long 
as a stream is cutting downward         
rapidly1 it carries away whatever dbris 
descends the side slopes4  ,when it     
approaches grade1 the dbris which       
descends the side slopes  tends to      
accumulate at their bases1 and the      
,v-shaped cross-section of  the valley  
becomes ,u-shaped 7see ,fig4 #agb74 ,at 
about the same time the  stream begins  
to meander1 for1 having lost something  
of its former  velocity1 it is more     
easily turned from side to side4 ,as it 
begins to  meander1 it widens the bottom
 of its valley4 ,this is the initial    
stage  in the development of the valley 

flat 7#b and #c1 ,fig4 #agb74 ,in its   
meandering the stream encroaches on the 
talus accumulations at the  bases of its
 valley's slopes4 ,the side-cutting may 
remove all the loose  dbris and even    
undercut the bluff as at a1 ,fig4 #agc4 
,the stream's  meanders shift their     
positions from time to time so that the 
valley  flat is successively widened at 
different points4 ,by lateral planation1
  therefore1 a stream tends to develop a
 flat as soon as it reaches  grade4     
,this is the initial part of erosion in 
the making of a river  flat1 but a flat 
developed by erosion alone is not an    
alluvial plain4    ,so soon as the flat 
developed by a stream exceeds the width 
of its  channel1 the water 7except in   
times of flood7 does not cover it all at
  the same time4 ,on any part which it  
temporarily abandons1 some dbris        
7alluvium7 is likely to be left4 ,this  
deposit of alluvium constitutes  the    
valley flat an alluvial plain 7,fig4    
#agd74 ,it will be seen that the  valley

 flat is commonly an alluvial plain from
 the beginning4    ,illustration3 ,fig4 
#agb4--;,diagram illustrating the       
transformation of a    ,v-shaped valley 
into a ,u-shaped valley4                
,illustration3 ,fig4 #agc4--;,diagram to
 illustrate the widening of a    valley 
flat by erosion4 ,compare #c1 ,fig4     
#agb4    ,once the valley flat and      
alluvial plain are begun1 their further 
development is easily followed4 ,the    
stream in flood overflows the banks  of 
its channel4 ,the velocity of the       
overflowing water is reduced1  and if it
 has much load a part of it will be     
dropped and the plain  aggraded4        
,meantime meandering and lateral        
planation continue4 ,thus the           
flood-plain is widened by erosion1 and  
aggraded by alluviation1 the two        
processes going on simultaneously4      
,illustration3 ,fig4 #agd4--;,an        
alluvial plain4 ,the diagram suggests   
the relative importance of lateral      
planation and alluviation in the        

development of the flat4                
,flood-plains1 chiefly the result of    
planation1 but partly of  aggradation1  
are a normal feature of river valleys1  
after a certain  stage of development   
has been reached4 ,this stage is that at
 which  downward erosion becomes slight 
in comparison with lateral erosion4 ,it 
follows that an alluvial plain normally 
begins its development where  the valley
 is first brought to grade1 that is1 in 
its lower course4  ,as the development  
of the valley goes on1 the head of the  
flood-plain  advances up-stream1 and at 
the same time its older parts become    
wider4    ,illustration3 ,fig4          
#age4--;,diagrammatic representation of 
a flood plain    developed by           
alluviation only4    ,flood-plains due  
to alluviation only4--,exceptionally1 an
 alluvial  plain is developed by        
deposition only4 ,thus if a stream      
becomes  overloaded while its valley is 
still narrow1 as sometimes happens1     
deposition follows1 and1 as aggradation 

proceeds1 the narrow valley  acquires a 
progressively wider bottom 7,fig4 #age74
 ,wide valley plains  are sometimes     
developed in this way4 ,flood plains    
developed wholly by  alluviation are    
sometimes formed under conditions which 
are independent  of the stage of a      
valley's development4 ,thus if a stream 
suddenly  acquires an exceptional supply
 of detritus in its upper course1 the   
development of an alluvial plain begins 
immediately below the point of          
overloading4    ,the overload might be  
acquired in various ways4 7#a7 ,if a    
stream taps  another 7piracy7 which     
carries a large quantity of sediment1   
carrying  off both water and sediment to
 a channel with a lower gradient1       
deposition may take place where1 under  
the earlier conditions1 there  was none4
 7#b7 ,again1 when a stream cuts through
 a barrier near its  head waters1 its   
velocity1 and1 therefore1 its eroding   
power1 may be  so increased in its upper
 course that sediment enough is acquired

  to occasion deposition below1 where   
none took place before4 7#c7 ,in        
working back through formations of      
varying degrees of resistance1 a        
stream's head may presently reach a     
formation or a region which yields      
abundant sediment1 even though there was
 no especial barrier below4  7#d7 ,if an
 advancing glacier should reach the head
 waters of a stream1  its discharge to  
the stream would greatly increase the   
load of the  latter1 and1 although its  
volume would be augmented at the same   
time1  deposition might result4 ,as a   
matter of fact1 streams carrying glacial
  drainage are usually aggrading        
streams4 ,in general1 anything which    
greatly increases the load of a stream  
near its head is likely to cause        
deposition1 and so the development of a 
flood plain1 at some point  farther down
 the valley4    ,illustration3 ,fig4    
#agf4--;,anastomosing of a depositing   
stream4 ,yahtse    ,river1 ,alaska4     
7,russell1 ,u4 ,s4 ,geol4 ,surv47       

,streams which are actively aggrading   
their valleys are likely to  anastomose 
7,figs4 #agf1 #agg74 ,this results from 
the filling of the  channels until they 
are too small to accommodate all the    
water4 ,the  latter then breaks out of  
the channel at few or many points4 ,the 
new  channels thus established suffer   
the same fate4    ,illustration3 ,fig4  
#agg4--;,anastomosing of the ,platte    
,river1 ,dawson    ,co41 ,neb4 7,u4 ,s4 
,geol4 ,surv47    ,flood-plains due to  
obstructions4--,again1 any obstacle in a
 stream's  course is likely to cause    
deposition above4 ,thus dams built      
across  rivers entail the deposition of 
sediment above4 ,where a stream flows   
over the outcropping edges of strata of 
different strength1 the more  resistant 
serve1 in some sense1 as dams4 ,above   
them the stream cuts its  bed to a low  
gradient1 and1 becoming sluggish1 drops 
more or less of  the detritus brought   
down from above4 ,obstacles of any sort 
across a  stream's channel1 therefore1  

favor the development of alluvial       
plains4    ,illustration3 ,fig4         
#agh4--,the levees of the ,mississippi  
in    cross-section1 #d miles north of  
,donaldsonville1 ,la4 ,vertical scale   
#ej4 ,the horizontal line in the diagram
 represents sea-level4 ,the    bottom of
 the channel at this point is far below 
sea-level4    ,levees4--,as the stream  
in flood escapes its channel and        
overspreads  its plain1 its immediate   
banks are the site of active deposition1
 for  it is here that the velocity of   
the overflowing water is first notably  
checked4 ,on the banks of the channel1  
therefore1 low alluvial ridges1  called 
natural levees1 are built up 7,fig4     
#agh1 and ,pl4 ,,xv74 ,they may  be     
narrow1 or hundreds of feet in width1   
and are often several feet  above the   
plains behind them1 giving the latter a 
slope away from the  channel of the     
stream4 ,they are sometimes high enough 
to control the  courses of tributary    
streams1 as shown by numerous           

tributaries to the  ,mississippi below  
the ,ohio4 ,the ,yazoo1 for example1    
flows some #bjj  miles on the           
flood-plain of the ,mississippi before  
it joins that river  near ,vicksburg4   
,the levees even become divides1        
directing drainage away  from the       
streams they guard 7,pl4 ,,xv74 ,streams
 sometimes build levees  faster than    
their tributaries aggrade their         
channels4 ,the latter are  then ponded1 
giving rise to lakes4 ,the lakes on the 
lower courses of  the tributaries to the
 ,red ,river of ,louisiana are          
examples4#gj ,they  are sometimes built 
up above their natural level and kept in
 repair by  human agency so as to       
confine the streams in time of flood4   
,this is a  source of danger unless they
 be steadily maintained1 for the        
breaking  of such levees often occasions
 great destruction4 ,a case in point is 
the breaking of the levees of the       
,mississippi near ,new ,orleans in      
#ahij4  ,the water broke through the    

levees at the ,nita and ,martinez       
crevasses  7,fig4 #ahg7 and flowed      
eastward 7from the former7 with a       
current of #ae  miles per hour1         
spreading destruction in its path4 ,the 
water flowed  eastward through ,lakes   
,pontchartrain and ,borgne1 and entered 
,mobile ,bay  with such volume1         
velocity1 and load of mud1 as to destroy
 for a time  the oyster and fish        
industries of that locality4#ga         
,illustration3 ,,plate ,,xv4      ,,near
 ,,hahnville1 ,,louisiana4    ,u4 ,s4   
,geol4 ,surv4    ,illustration3 ,,plate 
,,xvi4      ,fig4 #a4 ,,missouri4    ,u4
 ,s4 ,geol4 ,surv4      ,fig4 #b4       
,,missouri4    ,u4 ,s4 ,geol4 ,surv4    
,fig4 #c4 ,,missouri4    ,u4 ,s4 ,geol4 
,surv4    ,illustration3 ,fig4          
#agi4--;,flood-plain of the ,mississippi
 ,river south    of the mouth of the    
,ohio4 7,from charts of the ,miss4 ,riv4
    ,commission47    ,illustration3     
,fig4 #ahj4--;,diagram illustrating an  
early stage in the    development of    

meanders4 ,the shaded part represents   
the area over    which the stream has   
worked4    ,flood-plain meanders4       
,cut-and-fill4--,a stream with an       
alluvial plain  is likely to meander    
widely 7,pl4 ,,xvi74 ,in general terms  
this may be  said to be the result of   
low velocity1 which allows it to be     
easily  turned aside4 ,were the course  
of such a stream made straight1 it would
  soon become crooked again4 ,the manner
 of change is illustrated by ,figs4     
#ahj and #aha4 ,if the banks be less    
resistant at some points than at        
others1 as is always the case1 the      
stream will cut in at those points4  ,if
 the configuration of the channel is    
such as to direct a current  against a  
given point1 a 7,fig4 #ahj71 the result 
is the same1 even  without inequality of
 material4 ,once a curve in the bank is 
started1  it is increased by the current
 which is directed into it4             
,furthermore1  as the current issues    
from the curve1 it impinges against the 

opposite  bank and develops a curve at  
that point4 ,the water issuing from this
  curve develops another1 and so on4    
,once started1 the curves or meanders   
tend to become more and more  pronounced
 7compare ,figs4 #ahj and #aha74 ,in the
 case represented by ,fig4  #a1 ,plate  
,,xvi 7,missouri ,river near ,brunswick1
 ,mo47 the narrow neck of  land between 
curves is almost cut through4 ,when this
 is accomplished1  the stream will      
abandon its wide curve4 ,a later stage  
in the process is  shown in ,fig4 #b1   
,plate ,,xvi 7the ,osage ,river near    
,schell1 ,mo474    ,the straightening of
 the channel is often accomplished in   
another way4  ,even before the meanders 
reach the stage represented by ,fig4 #a1
 ,plate  ,,xvi1 the position of the     
channel becomes unstable4 ,in time of   
flood1  the whole flat is covered with  
flowing water4 ,the greater depth of    
water in the channel tends to give it a 
velocity greater than that of  the water
 on the flat outside4 ,but the distance 

from a to c via b  7,fig4 #aha7 is much 
greater than that in a direct line4 ,it 
follows that  the slope from a to c     
direct is greater than that by way of b4
 ,if  the current between a and c in    
time of flood be strong enough to       
erode1 it may deepen its bed1 and       
thereby increase the volume of water    
following this course4 ,the increased   
volume gives increased velocity1  and   
the result may be the opening of a      
channel between a and c  direct4 ,the   
channel may be worn so deep that when   
the flood subsides1  the stream will    
follow it4 ,so long as the abandoned    
channel-curve  remains unfilled with    
sediment1 it is often called a cut-off4 
,if  it contains standing water and has 
the proper form1 it is called an  ox-bow
 lake 7,fig4 #ahb71 or sometimes a      
bayou4 ,the water-filled  portions are  
not always bows 7,fig4 #ahc1 ,osage     
,river1 near ,butler1 ,mo474  ,cut-offs1
 with or without standing water1 are of 
common occurrence  along most rivers    

with wide plains4 ,meandering is not    
confined to  streams which are near     
sea-level4 ,even small creeks at high   
altitudes  may meander1 if so situated  
as to have slight velocity4 ,trout      
,creek in  the ,yellowstone ,park 7,fig4
 #ahd7 is an example4    ,illustration3 
,fig4 #aha4--;,diagram illustrating     
later stages in the    development of   
meanders4    ,illustration3 ,fig4       
#ahb4--,meanders and cut-offs 7ox-bow   
lakes7 in    the ,mississippi ,valley a 
little below ,vicksburg4 ,the figure    
also    shows the migration of meanders 
down-stream1 and their tendency to      
increase themselves4 7,from charts ,nos4
 #ah and #ai1 ,mississippi ,river       
,commission47    ,illustration3 ,fig4   
#ahc4--;,bayou ,lakes1 ,osage ,river1   
near ,butler1 ,mo4    ,there seems to be
 some relation between the width of the 
belt within  which a stream meanders1   
and the width of the stream itself4     
,recently  it has been estimated that   
the ratio between them is #ah 3 #a4gb   

,during the development of the meanders 
it is to be noted that lateral          
planation on the one side of a stream is
 accompanied by deposition on  the      
other4 ,this is cut-and-fill4 ,the      
sediment eroded from the curve  which is
 concave toward the stream is shifted   
down-stream1 while that  deposited in   
the curve which is convex toward the    
stream is brought  down from above4     
,thus even in the development of        
meanders1 the material  which is        
dislodged is shifted down-stream4 ,since
 the current directed  against the      
down-stream side of a growing meander is
 on the average  stronger than that     
directed against the opposite side1 the 
meander  itself has a tendency to       
migrate down-stream 7,fig4 #ahb74    ,in
 their evolution1 the curves of a       
stream's channel often reach and        
undermine the valley bluff 7,pl4 ,,vii74
 ,since the meanders are1 on the        
average1 shifted down-stream            
individually1 and since meanders are    

frequently developed in new places1 it  
follows that a meandering stream  tends 
to widen its valley throughout4         
,widening is also effected in  other    
ways1 for a stream with a flood-plain   
sometimes abandons its  channel         
altogether for miles at a stretch1 and  
the new course chosen  may be against   
one of the bluffs of the valley4 ,such  
changes are most  likely to take place  
where deposition along channel and      
levees has  brought the part of the     
flood-plain 7though not necessarily the 
bottom  of the channel7 adjacent to the 
stream above the level of that farther  
from it 7,fig4 #agh74 ,the change is    
likely to be effected in time of  flood4
    ,flood-plains often attain great    
size4 ,that of the ,mississippi below   
the  ,ohio 7,fig4 #agi7 has a width     
ranging from rather more than #bj miles 
at  ,helena 7,ark471 to something like  
#hj miles in the latitude of ,greenville
  7,miss474#gc ,below the ,ohio its area
 is something like #cj1jjj square       

miles1 and its entire area has been     
estimated at about #ej1jjj square       
miles4#gd    ,theoretically1 the        
rotation of the earth should affect the 
erosion  of streams1 increasing it on   
the one bank 7the right in the northern 
hemisphere and the left in the southern7
 and decreasing it on the  other4#ge    
,the streams doubtless accommodate      
themselves to the rotation  of the earth
 in the original development of their   
gradation-plains  and flood-plains1 and 
the later effects of rotation are       
usually  inconspicuous4                 
,illustration3 ,fig4 #ahd4--,meanders of
 ,trout ,creek1 ,yellowstone ,park4     
7,walcott1 ,u4 ,s4 ,geol4 ,surv47       
,scour-and-fill4--,it has already been  
shown that aggrading streams cut        
laterally at the same time that they    
build up their plains4 ,it is now  to be
 added that they periodically deepen    
their channels to a notable  extent1 and
 that the deepening of the channel takes
 place at the very  time when the       

flood-plain is being aggraded4 ,in other
 words1 the stream  in flood aggrades   
its plain1 and degrades its channel4    
,this follows  from the fact that the   
current is sluggish in the former       
position1  where the water is shallow1  
and rapid in the latter1 where it is    
deep4  ,when the flood subsides1 the    
channel1 deepened while the current was 
torrential1 is filled again by the      
feebler current which follows4 ,this    
alternate deepening and filling is known
 as scour-and-fill4 ,it is well         
illustrated by the ,missouri ,river4 ,at
 ,nebraska ,city1 scour is believed  to 
occasionally reach depths of #gj to #ij 
feet4#gf ,at ,blair1 about #be  miles   
above ,omaha1 the same river is believed
 to cut to bed-rock 7about  #dj feet    
below the bottom of the channel in low  
water7 twice a year1  that is1 during   
floods4#gg ,fig4 #ahe shows the changes 
recorded in the  channel of the river at
 this point during the year #ahhc4 ,it  
shows that  the scour-and-fill during   

this year amounted to almost #dj feet4  
,all  streams similarly situated do a   
like work4 ,the material thus eroded  is
 shifted down-stream1 some of it for    
short distances only1 and some  of it to
 the sea4 ,even an aggrading stream     
therefore is not without  erosive       
activity2 it is a stream whose fill     
exceeds its scour1 not one  which has   
ceased to erode4    ,illustration3 ,fig4
 #ahe4--;,diagram illustrating scour and
 fill in the    ,missouri ,river4 ,a    
record of soundings at ,blair ,bridge   
7near ,omaha71    #ahhc4 ,shows also the
 cross-sections of the river at various 
rates4    7,todd1 ,bull4 #aeh1 ,u4 ,s4  
,geol4 ,surv47    ,materials of the     
flood-plain4--,as a result of its       
varying velocities  in flood and low    
water1 a stream may deposit coarse      
material at one  time and fine at       
another4 ,a similar sequence of deposits
 takes place  in the flood-plain of a   
meandering stream1 irrespective of      
floods4  ,flood-plain deposits are often

 therefore very heterogeneous1 as shown 
in ,fig4 #ahf1 which represents the     
constitution of the alluvium of the     
,missouri ,river at ,omaha4 ,the        
deposits of the streams range from the  
finest clay1 through sand to gravel1 and
 even bowlders4 ,in general they  become
 finer down-stream4 ,in a given plain1  
they are usually coarser  below and     
finer above4    ,illustration3 ,fig4    
#ahf4--;,diagram to show the            
heterogeneous character    of alluvial  
deposits4 7,todd1 ,bull4 #aeh1 ,u4 ,s4  
,geol4 ,surv47    ,topography of the    
flood-plain4--,the flood-plain is       
nearly1 but not  altogether1 flat4 ,it  
has a gentle slope down-stream1 and     
often for a  distance from the sides    
toward the center 7,fig4 #agd74 ,this   
latter slope  is the result of          
deposition by waters descending to the  
plain from the  sides4 ,it is destroyed 
wherever a meandering stream reaches its
 bluffs4  ,when levees are well         
developed1 there is a slope from them   

toward the  sides of the valley 7,fig4  
#agh71 but it rarely continues to the   
limiting  bluffs4 ,since a stream with a
 well-developed flat frequently shifts  
its course1 old levees and abandoned    
channels lend variety to the  topography
 of the flood-plain4    ,the topographic
 adjustment of tributaries4#gh--,the    
meandering and  shifting of a main      
stream affects its tributaries4 ,if a   
main stream  swings against the bluff   
through which a tributary enters1 the   
latter  brings its channel into         
topographic adjustment by lowering its  
end to  the level of the main4 ,if now  
the main stream opposite the tributary  
swings to the other side of its valley1 
the tributary must make its  way across 
the flat with a very low gradient4 ,not 
only this1 but the  flat of the main    
valley through which the tributary must 
flow is likely  to be aggraded by the   
main in time of flood4 ,the result is   
that the  tributary stream becomes an   
aggrading stream at its debouchure1 and 

topographic adjustment is not           
established until it has filled up the  
lower end of its valley to some notable 
extent4 ,the filling of the  lower end  
of the tributary likewise affects the   
lower ends of its lower  tributaries4   
,illustration3 ,fig4 #ahg4--;,a general 
view of the ,mississippi delta4    ,if  
the main stream again swings over to the
 point where the tributary  issues from 
its valley1 the tributary stream and all
 its affected  tributaries again become 
eroding streams4 ,thus scour-and-fill   
are not  confined to the valley of the  
main stream4    ,river-lakes4--,while   
rivers are in general hostile to lakes1 
they  sometimes give origin to them4    
,oxbow lakes 7,fig4 #ahb and ,pl4       
,,xvi71  due to the cut-offs of         
meandering streams1 have already been   
referred  to4 ,lakes formed in the same 
way have other forms 7,pl4 ,,xvi and    
,fig4  #ahc74 ,rivers also give rise to 
lakes through the deposits they make4   
,if a main stream obstructs its         

tributaries by deposition at their      
debouchures1 their lower courses are    
ponded and converted into lakes4  ,the  
lakes along the tributaries to the ,red 
,river of ,louisiana have  already been 
cited as examples4 ,if a tributary      
brings more load to its  main than the  
latter can carry away1 the detritus     
constitutes a partial  dam1 ponding the 
river and causing it to expand into a   
lake above4 ,such  is the origin of     
,lake ,pepin already referred to4 ,in   
mountain regions1  the alluvial cones of
 tributary valleys sometimes pond their 
mains4    ,illustration3 ,fig4          
#ahh4--,longitudinal section of an      
incipient delta    made of coarse       
material4    ,rivers may be dammed in   
other ways1 as by lava flows1 by        
landslides1 by  glacial drift1 etc4 ,in 
all such cases1 lakes may come into     
existence1  but they are not due        
primarily to the activity of the river  
itself4    ,deltas4#gi--,where a stream 
enters standing water1 or a slower      

stream1  a special form of plain1 the   
delta1 is sometimes built up 7,figs4    
#afi1  #ahg1 and #ahh74 ,deltas and     
alluvial fans have much in common1 and  
their  only notable differences are     
those imposed by the differences in the 
conditions of deposition4 ,the current  
of the stream is checked1 but not       
altogether stopped1 at its immediate    
debouchure4 ,if it carries abundant     
sediment1 much of it will be promptly   
dropped where the decrease in  velocity 
is first felt4 ,such flow as there is   
beyond the debouchure is  not confined  
to a definite channel1 and the deposits 
made are therefore  spread more or less 
on either side of the line which        
represents the  continuation of the     
stream's course4    ,as the depth of the
 water into which the stream flows      
increases1 the  current diminishes4 ,out
 to the point where the depth of the    
standing  water is less than the depth  
of the current1 the latter affects the  
bottom1 and the surface of the deposits 

made slopes gently seaward2 but  where  
the depth of the standing water is such 
that the projected stream  current is   
ineffective at the bottom1 all the load 
rolled along the  bottom is dropped1 and
 a depositional slope is established    
7,fig4 #ahh71  its upper edge being     
below sea-level by an amount            
corresponding roughly  to the depth of  
the current which brings the detritus4  
,the outer slope  is relatively steep   
and well-defined where the detritus is  
coarse1 and  relatively gentle and      
ill-defined where it is fine4 ,thus the 
stream  tends to construct a sort of    
platform in the water just beyond its   
debouchure4 ,the successive deposits on 
the outer abrupt slope will dip         
conformably with its surface 7,fig4     
#ahi74 ,the finest sediment will be     
carried beyond the steep slope1 and     
conform to the topography of the  bottom
 beyond 7c1 ,fig4 #ahi74    ,at the     
beginning1 the top of the delta platform
 is at the level of the  bottom of the  

stream's channel at the point of        
debouchure1 but it is  gradually        
aggraded as water continues to flow over
 it4 ,its landward  margin is presently 
built up to sea-level and then above it1
 and as the  delta grows the delta-land 
is extended seaward 7compare ,figs4 #ahh
 and  #ahi74 ,at the same time the      
channel of the stream above the original
  head of the delta is aggraded1 for the
 current there is checked by the        
aggradation of the delta4 ,thus alluvial
 deposits continuous with the  delta are
 extended landward4    ,illustration3   
,fig4 #ahi4--,longitudinal section of   
the delta at a later    stage of        
development4    ,the projection of the  
direction of the lower end of the stream
 may be  said to be the axis of the     
extra-debouchure current4 ,from this    
axis1  where the flow is strongest1 the 
movement diverges more or less to  right
 and left4 ,since the velocity of the   
diverging water is reduced  more rapidly
 than that of the water which follows   

the axis of flow1  deposition is likely 
to take place faster on either side of  
the axis  than along the axis itself4   
,the result is that the extra-debouchure
  current tends to build up levee-like  
ridges on either side1 making a  sort of
 sluice-way for itself4 ,this sluice-way
 is gradually extended  seaward1 and at 
the same time gradually filled4 ,as its 
capacity is  reduced1 more and more of  
the water flows over its sides4         
,presently  the escape of the water over
 the little side-levees will develop a  
break at some point1 and a line of      
distinct flow then diverges from the    
main current4 ,this distributary repeats
 the history of its main4 ,thus  the    
processes of levee-building1            
channel-filling1 and levee-breaking     
follow one another1 until some such     
system of currents as shown in  ,fig4   
#aij is developed4 ,the result is that a
 delta's growth is not  simply in the   
line of extension of the main stream1   
but in a more or  less semicircular     

area1 the center of the circle being a  
point slightly  below the position of   
the debouchure of the stream when the   
delta  began4 ,at any stage in its      
development the margin of the delta is  
more  or less crenate 7,fig4 #aia71 or  
characterized by delta fingers 7,fig4   
#aij71 the projections corresponding to 
the positions of the debouchures  of the
 latest streams flowing across it4 ,the 
extreme ends of the  delta lobes 7,fig4 
#aij71 and of groups of the delta       
fingers1 often  have something of the   
shape of the ,greek letter from which   
the name  originated1 but the           
resemblance in form between a           
well-developed delta  and the ,greek    
letter is not striking4 ,deltas are     
sometimes built in  bays1 and in such   
cases their forms are predetermined on  
all sides but  one4 ,the head of a delta
 is sometimes arbitrarily located at the
 point  where the first distributaries  
are given off4 ,since this point shifts 
widely with time1 the definition can    

hardly be accepted4 ,on this basis  the 
head of the ,mississippi delta is about 
#bjj miles above its lower  end4 ,in    
reality it is much farther north4       
,illustration3 ,fig4 #aij4--,the        
terminus of the delta of the            
,mississippi4 7,c4 and ,g4 ,survey47    
,illustration3 ,fig4 #aia4--;,a         
miniature delta4    ,the structure of a 
delta1 shown in ,fig4 #ahi1 shows its   
history4 ,at any  stage in its growth   
the river discharges its sediment across
 that part  of the platform already     
built4 ,the sediment rolled at the      
bottom of  the current is dumped on     
reaching the steep slope1 and           
constitutes  the inclined fore-set beds 
shown in ,fig4 #ahi4 ,the material in   
suspension is carried farther1 settles  
more gradually1 and constitutes  the    
bottom-set beds 7c1 ,fig4 #ahi74 ,in    
time the bottom-set beds1  originally   
deposited some distance beyond the      
debouchure1 may come to  be overlain by 
the fore-set beds1 deposited at a later 

time4 ,while the  fore-set beds are     
being deposited on the steep slopes of  
the delta1 and  the bottom-set beds     
beyond1 deposition is also taking place 
on the top  of the delta4 ,these top-set
 beds are laid down in a nearly         
horizontal  position1 and their seaward 
margin is gradually extended4 ,thus the 
delta comes to have the threefold       
structure shown in ,fig4 #ahi4    ,that 
part of the delta which is above the    
abrupt slope of its front  corresponds  
in all essentials to an alluvial fan2   
but the delta as a  whole differs from  
the fan in its abrupt and crenate or    
digitate margin4    ,it is to be noted  
that the delta is not wholly the product
 of a  stream's activity4 ,the stream   
supplies the material1 but the lake  or 
sea renders at least passive assistance 
in its disposition4 ,not  all rivers    
opening into the sea build deltas1 and  
their failure is  often the result of   
waves or shore currents which carry off 
the river  sediment4 ,deltas are1       

however1 sometimes formed in tidal seas1
 as at  the debouchures of the ,yukon2  
the ,mackenzie1 where the tidal range is
  three feet2 the ,niger1 where the     
range is four feet2 the ,hoang-,ho1     
where the range is eight feet2 and the  
,brahmaputra and ,ganges1 where  the    
range is sixteen feet4#hj ,since lakes1 
bays1 gulfs1 and inland  seas have      
weaker waves and currents than the open 
sea1 they are more  favorable than the  
latter for the growth of deltas4 ,hence 
occur such  deltas as those of the      
,mississippi1 the ,nile1 the ,po1 and   
the ,danube4    ,deltas are likely to be
 absent1 or confined to the heads of    
bays1 on  coasts which have recently    
sunk4 ,their general absence on the     
,atlantic  coast of the ,united ,states 
is a case in point4    ,the following   
figures give some idea of the extent of 
deltas1 and of  their importance in land
 building4 ,the ,mississippi delta is   
advancing  into the ,gulf at the rate of
 about #ajj yards per year1 or a mile in

  #af or #ag years4 ,its length is more 
than #bjj miles1 its area more than     
#ab1jjj square miles1 and its depth at  
,new ,orleans has been estimated  at    
#gjjha to #ajjjhb feet4 ,this great     
depth is believed to be the  result of  
subsidence1 and so of the superposition 
of one delta on  another4#hc ,the delta 
of the ,yukon has a sea margin of #gj   
miles1 and  extends more than #ajj miles
 inland4 ,the delta of the ,rhne has    
also  had a remarkable growth1          
considering the size and the history of 
the  stream4 ,arles1 near the debouchure
 of the stream1 was #ad to #af miles    
inland in the fourth century ,b4,c41 and
 is now #cj miles inland4#hd  ,the ,rhne
 has also built a great delta in ,lake  
,geneva1 and its lower  delta is built  
of sediment gathered below the lake4    
,the ,po has built  a delta #ad miles   
beyond ,adria1 the port which gave its  
name to the  ,adriatic ,sea4 ,the       
extension of this delta has been at the 
average rate  of about #ej feet per     

year1 but recently1 on account of       
artificial  embankments1 the rate has   
been much more rapid4#he ,the ,ganges   
and  ,brahmaputra together have made a  
delta of great size4 ,its area is       
sometimes estimated to be as high as    
#ej1jjj or #fj1jjj square miles1  and   
its head is more than #bjj miles from   
the sea4#hf ,the head of the  ,nile     
delta is #ij miles from the sea1 and it 
has a coastal border of  #ahj miles4    
,the head of the delta of the ,hoang-,ho
 is about #cjj miles  from the coast1   
and its seaward border has a length of  
about #djj miles1  though with some     
highland interruptions4#hg    ,after a  
delta has been built into a lake1 the   
lake may disappear1  leaving the delta  
out of water4 ,such 8fossil0 deltas1 if 
so recently  exposed that erosion has   
not destroyed their distinctive         
features1  are readily recognized by    
their flat tops1 their abrupt and lobate
  fronts1 and their characteristic      
structure4 ,they are often a means  of  

determining the former existence of     
extinct lakes1#hh or the  former higher 
levels of lakes which still exist4#hi   
,elevated deltas  on seashores show     
either a rise of the land or a          
depression of the  sea-level4    ,the   
material which is carried along the     
coasts or shores from the  mouths of    
rivers may take on various and peculiar 
forms1 according  to the strength1      
direction1 and relations of waves and   
currents4 ,the  consideration of these  
forms belongs more properly to the work 
of the  sea than to that of rivers1     
since rivers are not concerned in their 
construction except in supplying        
material4    ,delta                     
lakes4--,delta-building streams         
sometimes help to form lakes by         
throwing their deposits around an area  
which fails to be aggraded to           
sea-level4 ,lake ,pontchartrain1 and    
other lakes in the delta of the         
,mississippi are examples 7,fig4 #ahg74 
,illustration3 ,fig4 #aib4--,terraces of

 the ,frazier ,river at ,lillooet1      
,b4 ,c4 7,calvin47                      
,,stream ,,terraces4    ,stream         
terraces#ij are bench-like flats or     
narrow plains along the  sides of       
valleys 7,fig4 #aib74 ,they are usually 
narrow1 but sometimes  have great length
 in the direction of the axis of the    
valley4 ,they  originate in various     
ways4    ,due to inequalities of        
hardness4--,reference has already been  
made  7p4 #adj7 to the effect of hard   
horizontal layers in the development  of
 terraces and terraciform projections on
 the sides of valleys 7,fig4  #abj74    
,such terraces are the result of        
differential degradation1 and  the upper
 surface of the hard layer marks the    
lower limit of the  terrace1 which      
commonly has a distinct slope toward the
 stream4 ,except  where interrupted by  
tributary valleys1 such terraces are    
likely to  be continuous in a valley so 
long as the structure remains the same  
and the stream sustains the same        

relation to it4 ,such terraces would    
first show themselves in the older part 
of the valley4 ,the effect of           
inclination of the hard stratum on the  
development of such terraces  will be   
readily inferred4 ,terraces and benches 
of this sort are not  equally distinct  
at all stages of a valley's history4    
,for great  distinctness1 the hard layer
 should have been exposed long enough to
  allow the general processes of erosion
 to have effected considerable          
differential wear1 but not long enough  
to allow the topographic effects  of    
unequal resistance to be obliterated4   
,illustration3 ,fig4 #aic4--;,diagram   
illustrating a distinct terrace and    a
 8second bottom 7b710 which may be      
regarded as a low terrace4    ,normal   
flood-plain terraces4--,it has been seen
 that deposition in  a river valley     
stands in more or less definite         
relationship to the  stage of its       
development1 and that the deposition    
which leads to  the development of an   

alluvial plain is likely to take place  
where  the higher gradient of the upper 
course gives place to the gentler       
gradient of the lower4 ,it has also been
 seen that as a stream's history        
advances1 the stretch where the gradient
 is high recedes up-stream1  and that   
the point which marks the head of active
 deposition follows4  ,it follows that a
 river flat or flood-plain normally     
begins in the  lower part of a valley1  
and works progressively headward1 its   
upper end  following1 at some           
considerable distance1 the head of the  
valley itself4    ,the commoner river   
terraces are remnants of former         
flood-plains1  below which the streams  
which made them have cut their channels4
 ,it  has already been pointed out 7p4  
#ahd7 that processes of erosion and     
deposition work together in the         
development of flood-plains1 and that   
some flood-plains have but little       
alluvium 7,fig4 #agd71 while others  owe
 their origin wholly to stream deposits 

7,fig4 #age74 ,it follows that  terraces
 developed from flood-plains may be of  
rock1 of alluvium1 or of  rock covered  
with alluvium4    ,the amount which a   
river channel must be deepened in order 
to change  the remnants of its          
flood-plain to terraces cannot be       
definitely  stated4 ,when a channel is  
so deep that the remnants of a former   
flood-plain are no longer flooded1 they 
would be called terraces1  especially if
 a lower flood-plain has been developed4
 ,even though not  above the reach of   
floods1 they are often called terraces  
if they are  notably above the channel  
and separated from it by a lower plain4 
,thus  the flat at b1 ,fig4 #aic1 would 
be called a terrace1 even though        
covered by water in exceptional floods2 
but the flat at c1 but  slightly above  
the channel1 would hardly be called a   
terrace4    ,illustration3 ,fig4        
#aid4--;,diagram illustrating the       
beginning of the    development of a    
terrace from a flood-plain4    ,the     

question now arises why a stream1 having
 once developed a  flood-plain1 should  
sink its channel to a lower level1      
leaving parts  of the old flood-plain as
 terraces4 ,this may be brought about by
 the  operation of various causes4      
7#a7 ,in the first place1 the head of   
the valley-plain where the first        
notable deposition takes place normally 
advances up-stream4 ,after the  advance 
has been considerable1 the descending   
stream may1 on reaching  the head of its
 valley-plain1 lose so much of its load 
as to be able  to sink its channel into 
the flood-plain farther down the valley 
7,fig4  #aid74    7#b7 ,ordinarily a    
stream does not drop all its load at the
 head of its  plain1 but only its       
excess2 but it will always drop coarse  
sediment  to take fine1 if fine be      
available4 ,for a relatively small      
amount of  coarse material dropped1 a   
relatively large amount of fine may be  
taken up 7p4 #agi74 ,other things being 
equal1 it follows that when a  stream   

drops coarse material to take fine1 its 
channel is degraded  unless there is at 
the same time a great reduction in the  
stream's  energy4 ,such reduction is    
likely to go with the decreasing        
declivity  down-stream2 but this is     
partly1 or sometimes wholly1            
counterbalanced  by the increasing      
volume of water4 ,by the exchange of    
load1 therefore1  a stream may          
ultimately sink its channel below the   
flood-plain which  the earlier and      
perhaps smaller stream had developed4   
,illustration3 ,fig4 #aie4--;,diagram to
 illustrate the development of    river 
terraces by the widening of a channel or
 meander belt4 ,the    valley flat above
 might not be called a terrace2 but the 
same plain    below1 where the meander  
belt has some width1 would be called a  
terrace4    7#c7 ,again1 so long as a   
stream is actively eroding at its head1 
there  is likely to be some aggradation 
below4 ,at a later stage in the         
stream's history1 when active erosion at

 the head has ceased because  of the    
reduction of the surface1 less material 
will be carried from  the upper part of 
the valley1 and the stream on the       
flood-plain below1  formerly loaded with
 material from up the valley1 is now    
free to take  up and carry away material
 temporarily left on the flood-plain4   
,the  result is a deepening of the      
channel4    7#d7 ,any stream which has  
reached the flood-plain stage is likely 
to  meander4 ,after the flood-plain has 
become wide1 the width of the belt      
within which the stream meanders is less
 than the width of its plain4  ,in the  
,lower ,mississippi1 for example1 the   
meander belt is often no  more than a   
third to a tenth of the width of the    
flood-plain4 ,it has  already been      
pointed out that the meanders migrate   
down the valley4 ,in  so doing they     
depress the meander belt1 the tendency  
being to reduce  it to the level of the 
channel1 and1 therefore1 below the level
 of  the flood-plain4 ,as the meander   

belt widens1 the depression which it    
develops becomes more and more          
capacious4 ,presently it may attain such
  dimensions as to hold the water of    
ordinary floods4 ,at this stage1  or    
even before1 such parts of the earlier  
flood-plain as remain1 are  terraces4   
,these several tendencies conspire to   
partially destroy river  flood-plains1  
and to transform such parts as remain   
into terraces in  the normal course of a
 river's history4 ,they appear first in 
the  lower part of the valley1 and      
migrate headward1 following the course  
of nearly every other phase of activity 
in a stream's history4 ,the  heads of   
the terraces follow1 at a respectful    
distance1 the head of the  flood-plain1 
just as the head of the flood-plain     
follows at a distance  the head of the  
valley4 ,the second and subsequent      
flood-plains and the  terraces to which 
they give origin follow the same course4
    ,terraces developed by the normal   
activities of a stream are always low1  

and it is improbable that they would    
ordinarily be conspicuous4 ,the         
vertical distance between the first     
7highest7 and second is greater  than   
that between the second and third4 ,the 
principles developed on  page #fe et    
seq41 in connection with the erosion of 
the hypothetical  island1 are applicable
 here4    ,flood-plain terraces due to  
other causes4--,certain other causes1   
accidental rather than normal to a      
stream1 result in the development of    
terraces from flood-plains4 7#a7 ,if    
there be uplift in a region where  the  
rivers have flats1 the streams are      
rejuvenated1 and the remnants  of their 
former flood-plains become terraces4    
7#b7 ,if an alluvial  flood-plain has   
been built as the result of an excessive
 supply of  sediment 7p4 #ahf71 the     
exhaustion or withdrawal of the         
excessive supply  would leave the stream
 again relatively clear1 and free to    
erode where  it had been depositing4 ,it
 would forthwith set to work to carry   

away  the material which it had         
temporarily unloaded on the plain4 ,the 
plains  built up in many valleys in the 
northern part of our continent during   
the glacial period1 when the drainage   
from the ice coursed through  them1 have
 subsequently been partially destroyed  
by erosion1 and their  remnants have    
become terraces4 ,a notable reduction in
 the amount of  available sediment1 even
 when the earlier supply was not        
excessive1  produces a similar result4  
7#c7 ,a notable increase in the volume  
of a  stream1 without corresponding     
increase in load1 as when one stream    
captures another1 may occasion the      
development of terraces by allowing  the
 stream to deepen its channel4 7#d7     
,above any barrier which dams a  stream1
 a flood-plain is likely to be          
developed4 ,when the barrier is  removed
 the stream will cut more or less deeply
 into the plain above1  leaving         
terraces4 7#e7 ,the recession of a falls
 through a flood-plain  converts such   

parts of it as remain1 into terraces4   
,in conclusion1 it may be stated that   
many river terraces1 mostly  very low1  
are normal features of valley           
development1 coming into  existence at  
definite stages in a valley's history4  
,they are generally  composed1 in large 
part1 of river alluvium4 ,others result 
from more  or less accidental causes1   
working singly or in conjunction1 and to
  this class belong all of the more     
conspicuous terraces developed from     
flood-plains4 ,the structure of a       
terrace often affords some clue to its  
origin 7,fig4 #aif74    ,illustration3  
,fig4 #aif4--,terraces partly of rock   
and partly of    alluvium4 ,such        
terraces indicate successive uplifts1 or
 some other    change which had a       
similar effect on the stream which made 
the    valley4    ,discontinuity of     
terraces4--,when a stream sinks its     
channel into  its flood-plain1 it does  
not follow that a terrace remains on    
each  side4 ,where the stream's deepened

 channel is in the middle of its        
flood-plain1 there is1 temporarily1 a   
terrace on either side2 but  wherever   
the deepened channel is at one margin of
 its flood-plain1  a terrace remains on 
the other side only4 ,even where        
continuous at  the outset1 terraces soon
 become discontinuous1 for all processes
 of  subarial erosion conspire to       
destroy them4 ,a stream is likely to    
meander on its second and later         
flood-plains1 as on its first and       
highest one4 ,wherever the meanders on  
its second flood-plain reach the        
borders of the first flood-plain1 the   
terrace at that point disappears1  and  
since the meanders are continually      
migrating1 terraces are  continually    
disappearing4 ,the same would be true of
 the second terrace1  if a second were  
developed4 ,the removal of portions of a
 terrace by  the sweep of meanders is   
likely to leave the remnants cuspate    
toward  the stream4#ia ,again1 tributary
 streams1 in bringing their channels    

into topographic adjustment with their  
mains1 cut through the terraces  of the 
latter4 ,new gullies develop on the     
faces of the terraces and  their heads  
work back across them1 dissecting them  
still further4 ,at  the same time1 sheet
 erosion and other phases of slope wash 
tend to  drive the scarps of the        
terraces back toward the bluff beyond4  
,by the  time a second series of        
terraces is well developed1 no more than
 meagre  remnants of the first may      
remain4    ,from the foregoing          
considerations it is clear that the     
extent to which  river terraces once    
developed1 now remain1 is dependent in  
part on the  length of time which has   
elapsed since the river sank its channel
 below  them4 ,other things being equal1
 the greater their age the more meagre  
their remnants4    ,terraces developed  
from river plains formed chiefly by     
alluviation  stand a better chance of   
long life than most other alluvial      
terraces4  ,this is because of the      

configuration of the original valley1   
the  aggradation of which gave origin to
 the plain4 ,the principle involved  is 
illustrated by ,fig4 #aig4 ,in          
developing the second flood-plain the   
river encounters the rock wall of the   
valley4 ,this greatly retards  lateral  
erosion1 and the terrace above1         
defended#ib by the rock1 is  likely to  
be long-lived4    ,illustration3 ,fig4  
#aig4--;,diagram to show why certain    
terraces are    longer lived than       
others4    ,alluvial terraces1 like rock
 shelves1 are popularly thought to mark 
8old levels of the river40 ,in one sense
 this is true1 but not in the  sense in 
which the expression is commonly used4  
,every level1 from the  crest of the    
bounding bluffs to the bottom of a      
valley1 is a level at  which water ran  
for a longer or shorter time2 but the   
terrace does not  mean that the river   
was once so much larger than now as to  
fill the  valley from its present       
channel to the level of the terraces4   

,termini of terraces4--,from the mode of
 development of terraces it will  be    
seen that1 traced up-stream1 each       
terrace should theoretically grade  into
 a flood-plain at its upper end 7,fig4  
#aid71 and that the upper end  of the   
second 7from the top7 terrace1 where    
there are two1 would not  be so far     
up-stream as the upper end of the first 
7highest74 ,this is  represented        
diagrammatically in ,fig4 #aih4    ,the 
down-stream termini of terraces are     
rarely distinct4 ,this is partly        
because the notable meandering of the   
streams in their lower courses  is      
antagonistic to the preservation of     
terraces4 ,if all terraces  once        
developed remained1 and if              
delta-building proceeded without        
interruption from waves1 the relations  
should be somewhat as follows3  ,traced 
down-stream1 the cliff between the      
oldest 7highest7 terrace and  the next  
younger becomes gradually lower until it
 finally disappears1  and the           

continuation of the two is found in a   
common plain4 ,the cliff  between the   
second and third terraces should        
disappear in the same way1  and below   
its disappearance the plain representing
 their continuation  is continuous with 
that representing the continuation of   
the first and  second4 ,the cliff       
between the second and third terraces   
may or may not  continue farther        
down-stream than that between the first 
and second4  ,the plains below the      
terraces finally become continuous with 
the lowest  flood-plain and with the    
delta4 ,these relations can rarely be   
seen  because of the destruction of the 
older terraces1 and because of the      
erosion by waves along shore4           
,illustration3 ,fig4 #aih4--;,diagram   
looking up the valley1 showing two      
terraces below1 one in the middle1 and  
none above4 ,the relations are    purely
 diagrammatic4    ,the topography of    
terraces is similar to that of          
flood-plains1 except  in so far as      

modified by erosion4 ,while flat in     
general1 the terrace  may slope either  
toward or from the valley bluff1 and its
 surface  may be marked by all the minor
 irregularities which characterize a    
flood-plain4                            
,,chapter ,,iv4                   ,,the 
,,work ,,of ,,ground- 7,,underground7   
,,water4      ,many familiar facts      
demonstrate the general presence of     
abundant water  beneath the surface of  
the land4 ,the thousands of wells in    
regions  peopled by civilized races1 and
 the countless springs which issue from 
the sides of mountains and valleys are a
 sufficient proof both of the  wide     
distribution of ground-water and of its 
great abundance4    ,certain well-known 
facts make it clear that ground-water is
 intimately  connected with rainfall4   
,in a dry season the level of the water 
in  wells commonly sinks1 and after a   
heavy rain it rises 7p4 #ga72 and  the  
amount of sinking is greater when the   
drought is long1 and the  rise is most  

notable when the rainfall is heavy4     
,many springs which  discharge large    
quantities of water during a wet season 
flow with  reduced volume1 or cease to  
flow altogether in periods of drought4  
,furthermore1 the water of springs and  
wells has the properties which          
rain-water would possess after sinking  
beneath the surface and  dissolving     
mineral substances4 ,rain-water is seen 
to sink beneath the  surface with every 
shower1 and since this source seems     
altogether  adequate for ground-water1  
and since no other source is known      
whence  any considerable amount of      
ground-water might come1 it is concluded
  that atmospheric precipitation is its 
chief source4    ,water gets beneath the
 surface by processes which are readily 
seen4  ,wherever the soil is porous some
 of the rain which falls upon it is     
absorbed4 ,sinking through the soil to  
the solid rock it finds cracks  and     
pores through which it descends to great
 depths4 ,nowhere are the  rocks beneath

 the mantle rock so compact and so free 
from cracks1 when  any considerable area
 is considered1 as to prevent the       
percolation of  water through them4     
,conditions influencing descent of      
rain-water4--,there are several         
conditions which influence not only the 
amount of water which sinks  beneath the
 surface in a given area1 but the       
proportion of the  precipitation which  
follows this course4 ,these are as      
follows3 7#a7  ,amount of               
precipitation4--,in a general way it is 
true that the  greater the amount of    
precipitation the greater the amount of 
water  which will sink beneath the      
surface4 ,other things being equal1 a   
region  of heavy precipitation is a     
region where wells are easily obtained  
and springs common4 7#b7 ,rate of       
precipitation4--,a given amount of      
precipitation may be concentrated in a  
short interval1 or distributed  through 
a considerable period of time4 ,in the  
latter case more of the  water sinks    

beneath the surface2 in the former1 a   
larger proportion  runs off over the    
surface4 ,the reason is readily seen4   
,water passes  through small spaces1    
such as those of soil1 slowly1 and its  
rate of  passage decreases rapidly with 
decreasing size of the passageways4     
,when rain falls rapidly on a surface of
 even moderately close texture1  the    
uppermost layer of soil is promptly     
filled with water1 and since  the water 
passes downward slowly1 the uppermost   
saturated part of the  soil becomes     
virtually impervious4 ,while in this    
condition1 the water  which falls on it 
will run off if there be slope1 and     
stand if there be  none4 ,in the latter 
case it will sink slowly as the water in
 the soil  passes down to lower levels4 
,if precipitation takes place no faster 
than the water can sink through the     
soil1 all the water may become          
ground-water4 7#c7 ,the topography of   
the surface has much to do with         
determining the proportion of rainfall  

which becomes ground-water4 ,if  the    
surface be flat1 more will sink in2 if  
it be sloping1 more of it  will run off 
before it has time to sink4 ,other      
things being equal1 the  steeper the    
slope the larger the proportion of the  
rainfall which will  run off over it4   
7#d7 ,the texture of the soil1 or other 
material on  which the rain falls1 helps
 to determine what proportion of it     
sinks  beneath the surface4 ,if the     
surface materials be porous1 the water  
sinks readily2 if of close texture1 it  
finds less ready ingress4 ,other  things
 being equal1 the closer the texture of 
the soil the less the  proportion of the
 rainfall which will enter it4 7#e7 ,the
 texture and  structure of the rock     
beneath the surface have some influence 
on the  amount of ground-water4 ,the    
rock may be stratified or massive2 it   
may  be abundantly or sparsely jointed2 
it may be porous or compact4 ,on the    
whole1 stratified rock is more favorable
 for the entrance of water  than        

unstratified1 partly because of its     
greater average porosity1  and partly   
because the planes of division between  
beds often allow  the passage of water4 
,if the beds of stratified rock are     
vertical or  inclined1 water finds its  
way into them more readily than if they 
are  horizontal1 in so far as it        
descends along stratification planes4   
,horizontally bedded rock1 or rock which
 is not bedded at all1 may be so  much  
jointed1 and the joints so open1 as to  
allow the water to enter  readily4      
,the conditions favorable to the sinking
 of abundant water below the  surface   
are therefore heavy precipitation1      
falling slowly on a surface  with little
 relief1 a soil of open texture         
underlain by rock which is  porous1 or  
affected by vertical or highly inclined 
planes of cleavage4  ,the annual        
discharge of water by rivers is         
estimated to be about #bb  percent4 of  
the rainfall on the land4#ic    ,supply 
of ground-water not altogether dependent

 on local  rainfall4--,the amount of    
ground-water in a given region is not   
always  entirely dependent on the local 
rainfall4 ,ground-water is in constant  
movement1 and entering the soil or rock 
at one point it may1 after  a long      
subterranean journey1 reach a point far 
from that at which  it entered4 ,thus   
beneath the ,great ,plains of the ,west 
there is much  subterranean water which 
fell on the eastern slopes of the       
mountains to  the west4 ,it has flowed  
beneath the surface to the ,plains1     
where some  of it is now withdrawn for  
the purposes of irrigation in regions   
where  rainfall is deficient4 ,the      
accompanying diagram 7,fig4 #aii7       
illustrates  the flow here described4   
,illustration3 ,fig4 #aii4--;,diagram   
illustrating the general point that     
ground-water is not dependent entirely  
upon local supply4    ,illustration3    
,fig4 #bjj4--;,diagram illustrating the 
position of the    ground-water surface 
7the dotted line7 in a region of        

undulatory    topography4    ,the       
ground-water surface4 ,water            
table4--,the water table has already    
been defined 7p4 #ga7 as the upper      
surface of the ground-water4 ,in  a flat
 region of uniform structure the        
ground-water surface is  essentially    
level1 but rises and falls with the     
rainfall4 ,where the  topography of a   
region is not flat1 the ground-water    
surface is not  level4 ,as a rule it is 
higher1 though farther below the        
surface1 under  an elevation than under 
surrounding lowlands1 as illustrated by 
,fig4  #bjj4 ,the explanation is not far
 to seek4 ,if a hill of sand be exposed 
to rainfall1 most of the water falling  
on its porous surface will sink  into   
it4 ,if the precipitation continues long
 enough1 as in a protracted  rain1 the  
hill of sand will be filled with water1 
the water occupying  the interstices    
between the grains4 ,if the sand of the 
hill could be  removed1 leaving the     
water which it contains on the same     

area1 it would  constitute a mound      
perhaps a third or a fourth as high as  
the hill  itself4 ,if unsupported1 this 
mound of water would spread promptly in 
all directions until its surface was    
level4 ,while the sand remains1  the    
water in it constitutes a mound1 and has
 a tendency to spread4 ,it  does in fact
 spread1 but since the process involves 
great friction the  spreading is slow4  
,with the spreading the surface of the  
water in the  sand sinks1 and sinks     
fastest at the center where it is       
highest 7b1  ,fig4 #bja74 ,if the       
process were not interrupted the surface
 of the  water in the hill would1 in    
time1 sink approximately to the level of
  the water in the surrounding land 7d1 
,fig4 #bja72 but at every stage         
preceding the last1 the surface of the  
water would be higher beneath  the      
summit of the hill than elsewhere1      
though farther from the surface4  ,in   
regions of even moderate precipitation  
the water surface beneath  the hills    

rarely sinks to the level of that in the
 lowlands adjacent1  before being raised
 by further rains4    ,illustration3    
,fig4 #bja4--;,diagram to illustrate the
 relations of    ground-water to the    
surface4    ,the water-level beneath the
 lowlands also sinks4 ,some of it finds 
its  way into valleys1 some of it sinks 
to greater depths1 and some of it       
evaporates2 but since the water surface 
beneath the elevation sinks  more       
rapidly than that beneath the lowland1  
the two approach a common  level4 ,their
 difference will be least at the end of 
a drought1 and  greatest just after     
heavy rains4    ,depth to which         
ground-water sinks4--,the depth to which
 ground-water  penetrates has not been  
determined empirically4 ,no borings or  
excavations of any sort have been made  
to such depths as to indicate  that its 
limit was being approached1 though some 
of them are a mile  or more deep4 ,there
 is a popular belief that water sinks   
until it  reaches a temperature         

sufficient to convert it into steam1 but
 except  for special localities where   
hot lava lies near the surface1 this    
belief is not well founded4 ,in the     
first place1 it is not known at what    
temperature water below the surface     
would be converted into steam4  ,while  
water boils at sea-level at a           
temperature of #bab 7,fahr47 a  higher  
temperature would be necessary below    
that level4    ,assuming the temperature
 of water sinking beneath the surface to
  be #ej ,fahr41 its temperature must be
 raised #afb to bring it to  the        
temperature at which it would boil at   
sea-level4 ,on the above  assumption of 
initial temperature1 the following table
 shows the depths  at which water would 
reach a temperature of #bab ,fahr4 under
 various  assumptions as to the rate of 
increase of temperature4 ,it shows also 
the pressure in atmospheres which would 
exist at these several depths  if the   
overlying rock were full of water4      
,depth at which      ,equivalent        

,rate of ,increase  ,temperature of #bab
   ,pressure in     of ,temperature4    
would be reached4    ,atmospheres4      
#a for #ej feet        #h1ajj feet      
#bch 7approximately7    #a for #fj      
#i1gbj             #bhe           #a for
 #gj           #aa1cdj             #ccc 
,with an initial temperature of #hj1    
corresponding to that of the warmer     
parts of the earth's surface1 instead of
 #ej1 the table would be as  follows3   
#a for #ej feet        #f1fjj feet      
#aid 7approximately7    #a for #fj      
#g1ibj             #bad           #a for
 #gj            #i1bdj             #bgb 
,the temperature at which water boils   
increases with the pressure4 ,a         
pressure of about #bjj atmospheres is   
the critical pressure for water2  that  
is1 the pressure which1 if increased1   
will prevent boiling  altogether4 ,the  
depth at which a pressure of #bjj       
atmospheres would  be reached1 supposing
 the upper rock to be full of water1 is 
about  #fhjj feet4 ,the temperature of  

the water at this depth1 under various  
assumptions as to initial temperature   
and rate of increase of heat1 is  shown 
in the following table3                 
,rate of ,increase    ,temperature at a 
,initial ,temperature4  of ,temperature4
   ,depth of #f1hjj ,feet4           #ej
             #a for #ej feet      #ahf  
,fahr4           #ej             #a for 
#fj          #afc             #ej       
#a for #gj          #adg             #hj
             #a for #ej          #baf   
#hj             #a for #fj          #aic
             #hj             #a for #gj 
#agg      ,only one of these            
temperatures reaches the boiling-point  
of water at  sea-level4 ,it is therefore
 clear that at this depth water has not 
even closely approached the boiling     
temperature for this depth1 and  since  
this is the depth of the critical       
pressure1 it is clear that it  cannot   
boil at any greater depth4 ,the descent 
of water is therefore  not stopped1     
under normal conditions of crustal      

temperature1 because  it reaches its    
boiling-point4 ,locally1 as in the      
vicinity of active or  recently extinct 
volcanoes1 the case may be different4   
,it is conceivable that water may       
descend until it reaches its critical   
temperature 7somewhere between #faj and 
#fce ,fahr474 ,the depth at which  the  
critical temperature would be reached1  
under various assumptions1  is shown in 
the following table3                    
,rate of ,increase   ,depth of ,critical
    ,initial ,temperature4   of         
,temperature4      ,temperature4        
#ej              #a for #ej feet        
#bh1jjj to #bi1bej feet           #ej   
#a for #fj        #cc1fjj to #ce1ajj    
#ej              #a for #gj             
#ci1bjj to #dj1iej             #hj      
#a for #ej        #bf1ejj to #bg1gej    
#hj              #a for #fj             
#ca1hjj to #cc1cjj             #hj      
#a for #gj        #cg1ajj to #ch1hej    
,there is good reason1 in the increasing
 density beneath the surface1  for      

believing that the rate of increase of  
temperature decreases with  depth1 and  
therefore that the rate of #a for #ej   
feet for the depths  concerned is too   
high4 ,the greater depths of the table  
above are  therefore believed to more   
nearly represent the truth than the     
lesser  ones4 7,see discussion of       
underground temperature in ,chapter     
,,xi47    ,if descending water attained 
its critical temperature1 the extent to 
which the resulting water-gas might be  
absorbed is not known4 ,so far  as      
limited by temperature1 therefore1 it is
 not possible to assign  a limit to the 
descent of water under average          
conditions of crustal  temperature4     
,other considerations seem to place a   
limit to the descent of water4  ,rock1  
solid and unyielding as it seems1 is yet
 plastic when under  sufficiently great 
pressure4 ,the cracks and cavities      
affecting it  are believed to descend a 
distance which is but slight in         
comparison  with the radius of the      

earth4 ,even if openings were once      
formed at  greater depths1 they could   
not persist1 for the adjacent rock1     
under  the pressure which there exists1 
would 8flow0 in1 in effect 7though      
perhaps not in principle7 much as stiff 
liquid might1 and close them4  ,the     
outer zone of the earth where cavities  
may exist is known as the  zone of      
fracture4#id ,the depth of the zone of  
fracture differs for  different rocks1  
but is not believed to extend below some
 such depth as  five or six miles1 even 
for the most resistant4#ie ,it is to be 
noted  that these depths are less than  
those at which the critical temperature 
of water would be reached under most of 
the conditions1 including all  the more 
probable ones1 specified in the above   
table4    ,let it be assumed that water 
descends through openings in the rock   
to a depth of six miles4 ,at this depth 
it would1 under the various  assumptions
 specified in the first and second      
columns of the following  table1 have   

the temperature indicated in the third  
column3        ,initial       ,rate of  
,increase     ,temperature at           
,temperature4      of ,temperature4     
,depth of ,six ,miles4        #ej       
#a for #ej feet       #fhc ,fahr4       
#ej           #a for #fj           #egh 
#ej           #a for #gj           #ejb 
#hj           #a for #ej           #gac 
#hj           #a for #fj           #fjh 
#hj           #a for #gj           #ecb 
,in two of these cases1 namely1 those in
 which the assumed rate of  increase of 
temperature is highest1 the temperature 
of the water at  the assumed lower limit
 of the zone of fracture is above the   
critical  temperature of water4 ,if the 
assumptions involved in these two cases 
be  correct1 water might descend to the 
point where it would be converted  into 
water-gas1 and in this condition it     
might be occluded by the hot  rock4 ,in 
the other cases1 involving the more     
probable assumptions1 the  critical     
temperature is not reached at a depth of

 six miles4 ,if pores  and cracks do not
 extend to greater depths1 liquid water 
could not2 and  since the water at this 
depth has probably not reached its      
critical  temperature1 it cannot exist  
as water-gas4 ,if it does not exist in  
the  form of water-gas1 its occlusion by
 the hot rock substance would not  be   
probable4 ,it would seem1 therefore1    
that the descent of water under         
ordinary conditions is much more likely 
to be limited by the zone of  fracture1 
than by temperature4    ,movement of    
ground-water4#if--;,ground-water is in  
more or less  continual movement4 ,if   
all the water be pumped out of a well it
 soon  fills up again to its normal     
level by inflow from all sides4 ,springs
  and flowing wells also demonstrate the
 movement of ground-water4 ,near  the   
surface the movement of ground-water is 
primarily downward if the  medium       
through which it passes is equally      
permeable in all directions2  but so    
soon as the descending water reaches the

 water surface1 its  descent is checked 
and its movement is partly lateral4     
,the commonest sort of movement of      
ground-water is that exemplified  as the
 water sinks beneath the surface1       
namely1 slow percolation  through the   
pores and cracks of the soil and rock4  
,ground-water is  not generally         
organized into definite streams1 though 
underground  streams1 mostly small1 are 
sometimes seen in caves and crevices1   
and  sometimes issue as springs4 ,most  
underground streams which issue as      
springs probably have definite channels 
for short distances only  before they   
issue4 ,it is probable that ground-water
 frequently flows  in considerable      
quantity along somewhat definite planes1
 without  having open channels4 ,thus   
every porous bed of rock is likely to   
serve as the pathway along which        
subterranean drainage passes4 ,this  is 
especially true where the porous bed is 
underlain by an impervious  one4 ,the   
8reservoirs0 from which artesian wells  

draw their supply are  not usually      
streams or lakes1 but porous beds of    
rock through which  abundant water      
passes4 ,as the supply is drawn off at  
one point1 it is  renewed by water      
entering elsewhere4 ,since the freedom  
of movement of  ground-water is notably 
influenced by the porosity of the rock1 
and  since the rock is1 on the average1 
most porous and the pores largest  near 
the surface1 the movement of            
ground-water is1 on the average1        
greatest near the surface1 and least at 
its lower limit4 ,in general the        
decrease of movement is much more rapid 
than the decrease in the size  of the   
pores4 ,it follows that while the upper 
part of the ground-water1  especially   
that above ground-water level1 moves    
somewhat freely1 the  lower part moves  
much more slowly4 ,it is probable1      
indeed1 that the  movement in the lower 
part of the subterranean hydrosphere is 
extremely  slight4    ,the amount of    
ground-water4--,the porosity of surface 

rocks varies  widely1 and the porosity  
of but few has been determined4#ig ,such
  determinations as have been made are  
chiefly on building stones1 in  which   
the range of porosity varies from a     
fraction of one percent41  in the case  
of granite1 to nearly #cj percent4 in   
the case of some  sandstones4 ,building 
stone is perhaps more dense than the    
average  surface rock4 ,furthermore1    
such tests as have been made do not take
  account of the larger cracks and      
openings of rock1 for these would  not  
appear in the specimens tested2 nor of  
the mantle rock1 which  generally       
contains a large amount of water4 ,from 
such determinations  as have been made  
it is estimated that the average        
porosity of the  outer part of the      
lithosphere is somewhere between #e and 
#aj percent4  ,if the porosity          
diminishes regularly to a depth of six  
miles1 where  it becomes zero1 the      
average porosity to this depth would be 
half  the surface porosity4#ih ,an      

average porosity of two and one-half    
percent4 would mean that the rock       
contains enough water to form a  layer  
nearly #hjj feet deep4 ,with an average 
porosity of #e percent41  this figure   
would be doubled4#ii ,while these       
figures are not to be  regarded as      
measurements1 they perhaps give some    
idea of the amount of  ground-water4 ,it
 is this sphere of ground-water which   
justifies the  term hydrosphere1 as     
applied to the waters of the earth4     
,fate of ground-water4--,most of the    
water which sinks into the earth        
reaches the surface again after a longer
 or shorter journey4 ,some of  it is    
evaporated from the surface directly2   
some of it is taken up by  plants and is
 passed by them into the atmosphere2    
some of it issues  in the form of       
springs2 some of it seeps out2 some of  
it is drawn out  through wells2 and much
 of the remainder finds its way         
underground  to the sea or to lakes1    
issuing as springs beneath them4 ,a     

small  portion of the descending waters 
enters into permanent combination  with 
mineral matter4 ,many minerals are known
 to take up water1 being  changed       
thereby from an anhydrous to a hydrous  
condition4 ,it does not  necessarily    
follow1 however1 that the total supply  
of water is thereby  decreasing4        
,minerals once hydrated may be          
dehydrated subsequently1  the water     
being set free4 ,furthermore1           
considerable quantities of  water in the
 form of vapor issue from volcanoes1 and
 volcanic vents  often continue to steam
 long after volcanic action proper has  
ceased4  ,it is probable that some1 and 
perhaps much of the water issuing from  
these vents has never been at the       
surface before1 and it is not now       
possible to affirm that the supply from 
this source does not offset1 or  even   
surpass1 the depletion of the           
hydrosphere resulting from mineral      
hydration4                              
,,the ,,work ,,of ,,ground-,,water4     

,ground-water effects very considerable 
results in the course of its  history4  
,these results are partly chemical and  
partly mechanical1 the  former being far
 more important than the latter4        
,chemical ,work4    ,the results of the 
chemical and chemico-physical action of 
water may be  grouped in several more or
 less distinct categories4    #a4 ,the  
simplest effect is the subtraction of   
soluble mineral  matter4 ,pure water is 
in itself a solvent of certain minerals2
 but  the carbonic-acid gas extracted   
from the atmosphere1 and the products   
of organic decay extracted from the soil
 make ground-water a much  more         
efficient solvent4 ,something of the    
results which it achieves  is shown by  
its composition4 ,all ground-water1     
whether issuing as  springs or drawn out
 through wells1 contains much more      
mineral matter  than the water which    
falls as rain1 and the excess is        
acquired in its  underground course4    
,the subtraction of soluble matter from 

rock renders it porous4 ,the  amount of 
material dissolved from a given place   
may be trivial or  considerable1        
according to the character of the rock1 
the readiness  with which water has     
access to it1 and the character of the  
water4  ,locally1 the subtraction of    
mineral matter may be the chief1 or even
  the only appreciable1 effect of the   
ground-water4    #b4 ,it sometimes      
happens that ground-water with certain  
mineral  substances in solution         
exchanges them for other substances     
extracted  from the rock4 ,thus the     
process of substitution is effected4 ,by
 this  process the lime carbonate of a  
shell imbedded in rock may be removed1  
molecule by molecule1 and some other    
substance1 such as silica1 left  in its 
place4 ,when the process is complete1   
the substance of the shell  has been    
completely removed1 though its form and 
structure are still  preserved in the   
new material which has taken the place  
of the old4  ,buried logs are sometimes 

converted into stone by the substitution
  of mineral matter for the vegetable   
tissue4 ,this is petrification4         
,petrification is altogether distinct   
from incrustation1 which simply  means  
the coating of an object with mineral   
matter4 ,a bird's nest may  be incrusted
 with lime carbonate1 but it is not     
thereby petrified4  ,solution is a      
necessary antecedent of substitution4   
#c4 ,the materials which are subtracted 
from the rock at one point may be  added
 to other rock elsewhere4 ,thus a third 
type of change1 addition1  is effected4 
,rock may at one time and place be      
rendered porous by the  subtraction of  
some of its substance1 and the openings 
thus formed may  subsequently become the
 receptacles of deposits from solution4 
,this is  exemplified in the stalactitic
 deposits of many caves4 ,not uncommonly
  cracks and fissures are filled with   
mineral matter deposited by the  waters 
which pass through them4 ,thus arise    
veins which1 for the most  part1 are    

nothing more than cracks and crevices   
filled by mineral  matter brought to    
them in solution1 and precipitated on   
their walls4  ,most veins of metallic   
ores have originated in this way4    #d4
 ,a further series of changes is        
effected by ground-water when it1  or   
the mineral matter it contains1 enters  
into combination with the  mineral      
matter through which it passes4 ,one of 
the commonest processes  of this sort1  
hydration1 has already been referred to 
7pp4 #dc and #dbh72  but in the         
development of many of the commoner     
hydrous minerals changes  other than    
hydration are involved4 ,these changes  
result in new mineral  combinations1 the
 new minerals being developed out of the
 old1 usually  with some additions or   
subtractions4 ,in the long course of    
time changes  of this sort may be very  
great1 so great indeed that large bodies
 of  rock are radically changed1 both   
chemically and physically4 ,much of the 
old substance may remain1 but it has    

entered into new and more stable        
combinations with the materials which   
the water has brought to it4            
,quantitative importance of             
solution4--,in general1 solution is     
probably  most effective at a relatively
 slight distance below the surface4  ,in
 the outermost zone of mantle rock the  
materials are usually less  soluble than
 below1 for they often represent the    
residuum after  the soluble parts of the
 formation from which they originated   
were  dissolved out4 ,below this zone   
the rock contains more soluble matter1  
and the water1 charged with organic     
matter in its descent through the  soil1
 is in condition to dissolve it4 ,at    
greater depths the water has  become    
saturated to some extent1 and1 so far   
forth1 less active4 ,here1  too1 the    
movement is less free4 ,the increased   
pressure at considerable  depths1 on the
 other hand1 facilitates solution1 which
 must be  understood to take place under
 proper circumstances in any zone       

reached  by the water4    ,calculations 
have been made which illustrate the     
quantitative  importance of the solution
 effected by ground-water4 ,the springs 
of  ,leuk 7,switzerland7 bring to the   
surface annually more than #bjjj tons of
  calcium sulphate 7gypsum7 in solution1
 and in the same time the springs  of   
,bath 7,england7 bring up an amount of  
mineral matter in solution  sufficient  
to make a column #i feet in diameter1   
and #adj feet high4#ajj    ,the amount  
of mineral matter in solution in streams
 is also  significant1 for while        
stream-water is not all derived from    
ground-water1 much of it had such an    
origin4 ,in the case of several         
streams1 among them the ,thames and the 
,elbe1 careful estimates of the  amount 
of dissolved mineral matter have been   
made4 ,though the ,thames  drains an    
area only about one-tenth as large as   
the ,state of ,new ,york1  it is        
estimated to carry about #aejj tons of  
mineral matter in solution  to the sea  

daily4#aja    ,from the uppermost       
#bj1jjj square miles of its drainage    
basin the ,elbe  is estimated to carry  
yearly about #a1cgj1jjj tons of mineral 
matter in  solution4 ,estimates of the  
amounts of material carried to the sea  
in  solution by several rivers are given
 on pp4 #ajb and #ajc4 ,much of this    
matter was brought to the rivers by     
waters which had been underground       
before reaching the streams4    ,from   
these figures it is clear that we have  
to reckon here with a very  considerable
 factor in the lowering of land         
surfaces4 ,from the amount  of lime     
carbonate carried by the ,thames it has 
been estimated that  the average amount 
of this material dissolved from the     
limestone area  drained by this stream  
is #adcajb tons per square mile per     
year4 ,it is  estimated that1 on the    
average1 something like one-third as    
much matter  is carried to the sea in   
solution as in the form of sediment1 and
 that  by this process alone land areas 

would be lowered something like one     
foot in #ac1jjj years4#ajc              
,deposition of mineral matter from      
solution4--,the deposition of  material 
from solution is effected in several    
ways4 7#a7 ,it is sometimes  deposited  
by evaporation4 ,this is well shown     
where water seeps out on  arid lands4   
,the same process is illustrated when   
water is boiled4 7#b7  ,reduction of    
temperature often occasions deposition4 
,in general1 hot  water is a better     
solvent of mineral matter than cold1#ajd
 and if it  issues with abundant mineral
 matter in solution the precipitation of
  some of it is likely to take place4   
7#c7 ,plants sometimes cause the        
precipitation of mineral matter from    
solution4 ,about some hot springs1  even
 where the temperature of the water is  
very high small plants of  low type     
7alg7 grow in profusion4 ,in ways which 
are not perfectly  understood these alg 
extract the mineral matter from the hot 
water4  ,they are now thought to be a   

chief factor in the deposits about the  
hot springs of the ,yellowstone         
,park4#aje ,the influence of organisms  
on precipitation from solution is not   
confined to the waters of hot  springs4 
7#d7 ,a fourth factor involved in the   
deposition of mineral  matter from      
solution is pressure4 ,pressure         
increases the solvent power  of water   
with respect to minerals directly2 it   
produces the same effect  indirectly by 
its effect on the solution of gases4 ,as
 water charged  with gas comes to the   
surface1 the pressure is relieved and   
some of the  gas escapes4 ,such mineral 
matter as was held in solution by the   
help  of the gas which escapes is then  
precipitated4 7#e7 ,precipitation is    
also sometimes effected by the mingling 
of waters containing different  mineral 
substances in solution4 ,such mingling  
of solutions would be  most common along
 lines of ready subterranean flow1 and  
while each  portion of the water        
entering a crevice or porous bed may be 

able to  keep its own mineral matter in 
solution1 their mingling may involve    
chemical changes resulting in the       
formation of insoluble compounds1  and  
therefore in deposition4 ,this principle
 has probably been involved  in the     
filling of many fissures and crevices1  
converting them into  veins4 7#f7 ,the  
escape of gases from water1 whether from
 increase of  temperature or by the     
disturbance of water1 sometimes causes  
the  deposition of mineral matter held  
in solution4    ,the deposition of      
material held in solution is most       
notable at two  zones1 one below that of
 most active solution1 and the other at 
the  surface1 where evaporation is      
active4 ,under proper conditions1       
however1  deposition may take place at  
any level reached by water4             
,mechanical ,work4    ,the mechanical   
work of ground-water is relatively      
unimportant4 ,wherever  it is organized 
into definite streams1 the channels     
through which it  flows are likely to be

 increased by mechanical erosion as well
 as by  solution4 ,either beneath the   
surface1 or after the streams issue1 the
  mechanical sediment carried will be   
deposited4    ,illustration3 ,fig4      
#bjb4--;,diagram to illustrate the      
general form    and relations of caves  
developed by solution4 ,the black       
portions    represent the cavern spaces4
 ,some limestone sinks are represented  
on    the surface above4                
,,results ,,of ,,the ,,work ,,of        
,,ground-,,water4    ,illustration3     
,fig4 #bjc4--;,ground-plan of ,wyandotte
 ,cave4 ,the unshaded    areas represent
 the passageways4 7#bast ,ann4 ,rept41  
,ind4 ,geol4 ,surv47                    
,weathering4--,where the solution       
effected by ground-water in any         
locality is slight and equally          
distributed1 the result is to make  the 
rock porous4 ,if1 for example1 some of  
the cement of sandstone is  dissolved1  
the texture of the rock becomes more    
open2 but if all the  cement be removed 

the rock is changed from sandstone to   
sand4 ,if a  complex crystalline rock   
contains among its many minerals some   
one  which is more soluble than the     
others1 that one may be dissolved4 ,this
  has the effect of breaking up the     
rock1 since each mineral acts as a      
binder for the rest4 ,it might happen   
that no one of the minerals is          
dissolved completely1 but that some one 
of them is decomposed by water1  and    
certain of its constituents removed4    
,such change would be likely  to cause  
the mineral so affected to crumble1 and 
with its crumbling1  if it be an        
important constituent of the rock1 the  
integrity of the  rock is destroyed4    
,where considerable chemical changes1   
especially  subtractions1 are going on1 
the rock is likely to crumble4 ,the     
increase  in volume attendant on        
hydration1 etc41 sometimes leads to the 
disruption of rock4 ,these are phases of
 weathering4 7,for other phases  of     
weathering see pp4 #ed and #aaj47       

,caverns4#ajf--,where local solution is 
very great results of another  sort may 
be effected4 ,in formations like        
limestone1 which are  relatively        
soluble1 considerable quantities of     
material are frequently  dissolved from 
a given place4 ,instead of making the   
rock porous1 in  the usual sense of the 
term1 large caverns may be developed    
7,fig4  #bjb74 ,in their production1    
solution may be abetted by the          
mechanical  action of the water passing 
through the openings which solution has 
developed4 ,considerable caves are found
 chiefly in limestone4 ,they were       
probably developed when the surface     
relief was slight1 and surface  drainage
 therefore poor4 ,regions where caves   
were developed under these  conditions  
may subsequently acquire relief1 so that
 caves are not now  confined to flat    
regions4    ,one of the best known      
regions of caves is in the basin of the 
,ohio in  ,kentucky and southern        
,indiana1 where the number of caves is  

large1  and the size of some of them1   
such as ,mammoth and ,wyandotte1 very   
great4 ,a ground-plan of ,wyandotte     
7,ind47 ,cave is shown in ,fig4 #bjc4   
,the  aggregate length of the           
passageways is about #bc miles4         
,illustration3 ,fig4 #bjd4--;,deposits  
in ,wyandotte 7,ind47 ,cave4 7,hains47  
,illustration3 ,fig4 #bje4--;,deposits  
in ,wyandotte ,cave4 7,hains47          
,deposition often takes place in caves  
after they are formed 7,figs4 #bjd  and 
#bje74 ,it may even go on at the same   
time that the cave is being  excavated4 
,here are formed the well-known         
stalactites and stalagmites4  ,a        
stalactite may start from a drop of     
water leaking through the roof  of the  
cave4 ,evaporation1 or the escape of    
some of the carbonic gas in  solution1  
results in the deposition of some of the
 lime carbonate about  the margin of the
 drop1 in the form of a ring4           
,successive drops make  successive      
deposits on the lower edge of the ring1 

which grows downward  into a hollow tube
 through which descending water passes1 
making its  chief deposits at the end4  
,deposition in the tube may ultimately  
close  it1 while deposition on the      
outside1 due to water trickling down in 
that position1 may greatly enlarge it4  
,illustration3 ,fig4 #bjf4--;,a         
limestone sink-hole1 east-northeast of  
,cambria1 ,wyo41 exceptional for its    
steep sides4 ,minnekahta limestone4     
7,darton1 ,u4 ,s4 ,geol4 ,surv47        
,underground caves sometimes give rise  
to topographic features which  are of   
local importance4 ,when the solution of 
material in a cavern  has gone so far   
that its roof becomes thin and weak1 it 
may collapse1  giving rise to a sink or 
depression in the surface over the site 
of  the original cave4 ,this is so      
common that regions of limestone caves  
are often affected by frequent sinks    
formed in this way4 ,they are a         
conspicuous feature of the landscape in 
the cave region of ,kentucky1  and are  

well known in many other limestone      
districts4 ,they are known as  limestone
 sinks4 7,fig4 #bjf and ,fig4 #b1 ,pl4  
,,xvii47    ,illustration3 ,fig4        
#bjg4--;,a fresh landslide near         
,medicine ,lake1 ,mont4    ,the bare    
space shows the position from which the 
slide started4    7,whitney47           
,illustration3 ,fig4 #bjh4--,landslide  
topography4 ,the protruding mass on     
the right has slumped down from the     
mountain to the left4 ,south face    of 
,landslip ,mountain1 ,colo41 seen from  
the west2 ,rico quadrangle4    7,cross1 
,u4 ,s4 ,geol4 ,surv47    ,under certain
 circumstances caves may give rise to   
striking features  of another sort4 ,if 
for any reason the roof is destroyed at 
the two  ends of a cave1 remaining      
intact over the middle1 the latter part 
constitutes a natural bridge4 ,natural  
bridges also originate in other  ways   
7pp4 #aea1 #aec74    ,illustration3     
,fig4 #bji4--,landslide topography on   
,badger ,mountain1    ,washington4 ,the 

slumping material in this case is       
basalt4    ,creep1 slumps1 and          
landslides4--,when the soil and subsoil 
on a slope  become charged with water   
they tend to move downward4 ,when the   
movement  is too slow to be sensible it 
is called creep4 ,the common downward   
inclination of trees growing in such    
situations1 the result of the more      
rapid creep of the surface as compared  
with the deeper part of the  soil1 is   
both an expression of the movement and  
of its slowness4 ,other  factors besides
 ground-water are involved in creep 7see
 p4 #aab74    ,when the movement is     
rapid enough to be sensible the material
 is  said to slump or slide4 ,this may  
happen when the slope on which          
water-charged mantle rock lies is steep 
7,fig4 #bjg74 ,great landslides of  this
 sort have been recorded1 and some of   
them have done great damage4  ,where a  
stream's banks are high1 and of         
unindurated material1 such as  clay1    
considerable masses sometimes slump from

 the bank or bluff into  the river1 or  
settle away slowly from their former    
positions4 ,this is  a common phenomenon
 along streams which have cut valleys in
 drift1  and along shores on which waves
 are encroaching4 ,the same phenomenon  
is common on a larger scale on the      
slopes of steep mountains4#ajg          
,considerable terraces are sometimes    
developed on their slopes in this  way1 
but they are usually irregular and      
discontinuous 7,figs4 #bjh1 and  #bji74 
,the loose dbris on steep slopes        
sometimes assumes a sort of  flowing    
motion and descends the slope with some 
such form and at some  such rate as a   
glacier4 ,such bodies of dbris are      
sometimes called  8talus glaciers0      
7,fig4 #baj74 ,in many such cases1 snow 
and ice have had  some part in their    
development4    ,in creep and in        
landslides gravity is the force         
involved1 and the  ground-water only a  
condition which makes gravity effective4
 ,gravity  alone accomplishes similar   

results1 as illustrated by ,fig4 #baa4  
,summary4    ,all in all1 ground-water  
is to be looked upon as a most important
  geological agent4 ,when it is         
remembered that a very large part of all
  the water which falls on the surface  
of the earth1 either in the form  of    
rain or snow1 sinks beneath the surface2
 that much of it sinks to  a great      
depth2 that much of it has a long       
underground course before  it reappears 
at the surface2 that it is everywhere   
and always active1  either in           
subtracting from the rock through which 
it passes1 in adding  to it1 in         
effecting the substitution of one       
mineral substance for  another1 or in   
bringing about new chemical             
combinations2 and when it  is remembered
 that this process has been going on for
 untold millions  of years1 it will be  
seen that the total result accomplished 
must be  stupendous4 ,the rock          
formations of the earth to the depths to
 which  ground-water penetrates are to  

be looked upon as a sort of chemical    
laboratory through which waters are     
circulating in all directions1  charged 
with all sorts of mineral substances4   
,some of the substances  in solution are
 deposited beneath the surface1 and some
 are brought to  the surface where the  
waters issue4 ,much of the material     
brought to  the surface in solution is  
carried to the sea and utilized by      
marine  organisms in the making of      
shells4 ,without the mineral matter     
brought  to the sea by springs and      
rivers1 many shell-bearing animals of   
great  importance1 geologically1 would  
perish4 ,biologically1 therefore1 as    
well as geologically1 ground-water is of
 great importance4    ,illustration3    
,,plate ,,xvii4      ,fig4 #a4          
,,hunterdon ,,county1 ,,new ,,jersey4   
,u4 ,s4 ,geol4 ,surv4      ,fig4 #b4    
,,near ,,pikeville1 ,,tennessee4    ,u4 
,s4 ,geol4 ,surv4    ,illustration3     
,,plate ,,xviii4      ,fig4 #a4         
,,washington4    ,u4 ,s4 ,geol4 ,surv4  

,fig4 #b4 ,,california4    ,u4 ,s4      
,geol4 ,surv4    ,illustration3 ,fig4   
#baj4--;,a 8talus glacier10 in ,silver  
,basin1 near    ,silverton1 ,colo4      
7,cross1 ,u4 ,s4 ,geol4 ,surv47         
,illustration3 ,fig4 #baa4--;,a huge    
mass of rock settling into the ,canyon  
of the ,colorado4 ,a result of gravity  
action4 7,atwood47                      
,,springs ,,and ,,flowing ,,wells4      
,the term spring is applied to any water
 which issues from beneath  the surface 
with sufficient volume to cause a       
distinct current4 ,if the  water issues 
so slowly as to merely keep the surface 
moist1 it is not  called a spring1 but  
seepage4 ,the spring from which water   
issues with a  strong current1          
especially if it be upward1 is          
comparable to a flowing  well1 while the
 spring from which water issues with    
little force1 and  without upward       
movement1 is comparable to the flow of  
water into a  common well4    ,springs  
often issue from the sides of valleys   

7,fig4 #bab71 the bottoms  of which are 
below ground-water level4 ,they are     
especially likely to  issue at the      
surface of relatively impervious layers1
 and where the  valley slopes cut       
joints1 porous beds1 or other structures
 which allow  free flow of ground-water4
    ,illustration3 ,fig4                
#bab4--;,diagram illustrating positions1
 a and b1    favorable for springs4     
,springs are classified in various ways1
 and these several  classifications     
suggest characteristics worthy of note4 
,they are  sometimes said to be deep and
 shallow4 ,the 8deep0 spring1 as the    
term is ordinarily used1 is one which   
issues with great force1 and  with      
something of upward movement1 and the   
8shallow0 spring1 one which  issues with
 little force1 and without upward       
movement2 but the spring  which issues  
with force is not necessarily deep1 nor 
is the one which  issues with little    
force necessarily shallow4 ,the idea    
involved in  this grouping would be     

better expressed by strong and feeble4  
,springs are also classified as cold and
 thermal1 the latter term  meaning      
simply that the temperature is such as  
to make the springs  seem warm or hot4  
,the temperature of thermal springs     
ranges up to the  boiling-point of      
water4 ,between deep springs and shallow
 ones1 and  between cold springs and    
thermal1 respectively1 there is no sharp
 line  of demarkation4 ,again1 some     
springs are continuous in their flow1   
while  others are intermittent4 ,most   
intermittent springs flow after periods 
of precipitation1 but dry up during     
droughts 7see p4 #bjb74 ,springs are    
also classified as mineral and common4  
,mineral springs1 in the  popular sense 
of the term1 are of two types3 7#a7     
,those which contain  an unusual amount 
of mineral matter1 and 7#b7 those which 
contain some  unusual mineral4 ,springs 
are especially likely to be called      
mineral  if the substances which they   
contain1 have1 or are supposed to have1 

some medicinal property4 ,all springs   
which are not 8mineral0 are  8common40  
,this classification is not altogether  
rational1 for all  springs contain more 
or less mineral matter1 and many springs
 which  are 8common10 contain more      
mineral matter than some springs that   
are  8mineral40 ,mineral springs are    
themselves classified according to the  
kind and amount of mineral matter they  
contain4 ,thus saline springs  contain  
salt2 sulphur springs contain compounds 
7especially gaseous7  of sulphur2       
chalybeate springs contain iron         
compounds1 especially  the sulphate2    
calcareous springs contain abundant lime
 carbonate1  etc4 ,these various mineral
 substances are extracted from the rock1
  sometimes by simple solution1 and     
sometimes by solution resulting from    
other chemical change4 ,the salt of     
saline springs is usually extracted     
from beds of salt beneath the surface4  
,lime carbonate1 one of the  commonest  
substances in solution in ground-water1 

is dissolved from  limestone1 or derived
 by chemical change from rocks          
containing other  calcium compounds4    
,thus lime feldspars1 by carbonation1   
give rise to  lime carbonate4 ,the      
chalybeate waters often arise from the  
oxidation  of iron sulphide1 a mineral  
which is common in many sedimentary     
rocks4  ,the iron sulphate is itself    
subject to change in the presence of the
  ubiquitous lime carbonate4 ,from this 
change iron carbonate results1 and  this
 is usually quickly altered to iron     
oxide1 which1 being relatively          
insoluble1 is precipitated4 ,about      
chalybeate springs1 therefore1 iron     
oxide is frequently being deposited4    
,medicinal springs are those  which     
contain some substance or substances    
which have1 or are supposed  to have1   
curative properties4    ,mineral matter 
in solution4--,the number and variety of
 mineral  substances in spring water is 
very great1 and the amount of solid     
matter in solution varies widely4 ,some 

of the hot springs of the  ,yellowstone 
,park contain nearly three grams        
7#b4hgcc7 of mineral matter  per        
kilogram4#ajh    ,the composition of    
various spring and well waters is shown 
in the  accompanying table1 which gives 
some idea of the range of mineral       
substances commonly in solution in      
ground-water4    ,geysers4--,geysers are
 intermittently eruptive hot springs4   
,they occur  only in volcanic regions   
7past or present7 and in but few of     
them4  ,active geysers are virtually    
confined to the ,yellowstone ,park and  
,iceland1 though they formerly existed  
at other places4 ,those of ,new         
,zealand have but recently become       
extinct4 ,the great geyser region of    
the world is the ,yellowstone ,park1    
where there are said to be more than    
sixty active geysers4    ,the cause of  
the eruption is steam4 ,the             
surface-water sinks down until1  at some
 unknown depth1 it comes into contact   
with rock sufficiently hot  to boil it4 

,the source of the heat is not open to  
inspection1 but it is  believed to be   
the uncooled part of an extrusive lava  
flow1 or of an  intrusive lava mass4    
,from what was said on pp4 #baf and #bag
 it is clear  that geysers do not have  
their origin in water which sinks down  
to the  zone of great heat1 where the   
increment of heat is normal4    ,the    
water of a geyser issues through a tube 
of unknown length4 ,whether  the tube is
 open down to the source of the heat is 
not determinable1  but water from such a
 source finds its way to the tube4      
,water may enter  the tube from all     
sides and at various levels from top to 
bottom4 ,the  heating may precede or    
follow its entrance into the tube1 or   
both4 ,so  far as the water is heated   
after it enters the tube1 the point of  
most  rapid heating may be at the bottom
 of the tube or at some point above4    
,if the temperature of the source of    
heat were high enough to convert  the   
descending water into steam as fast as  

it enters the tube1 the  steam would    
escape continuously1 though there would 
be no geyser2 but  if the rock is only  
hot enough to bring the water to the    
boiling-point  after some lapse of time1
 and after some water has accumulated1  
an  eruption is possible4               
,,analyses ,,of ,,american              
,,spring-,,waters4#aji                  
,reduced to ,parts per #ajjj by ,dr ,h4 
,j4 ,van ,hoesen4                       
----------------------------------------
----------------------------------------
----------------------------------------
----------------------------------------
----------------------------------------
-----------------------     ,waters     
,artesian well       ,artesian well     
,artesian well#aaj    ,manitou ,spring  
,opal ,spring         ,sulphur ,spring  
,hot ,spring        ,hot ,spring        
,boiling ,spring       ,warm ,spring    
8,glacier ,spouting                     
,spring0                                
,location                               

,lexington1 ,ky4      ,saratoga1 ,n4 ,y4
    ,sheboygan1 ,wis4     ,manitou1     
,col4     ,yellowstone           ,los   
,angeles1 ,cal4   ,hot ,sp4 ,station1   
,ward's ,ranch1     ,shaffer's ,ranch1  
,warm ,spring ,sta4                     
,national ,park                         
,c4 ,p4 ,r4 ,r4       base of ,granite  
,honey ,lake        ,b4  ,b4 ,r4        
,mts41 ,nev4        ,valley1 ,cal4      
,mono ,basin            ,date           
#ahgb               ,feb4 #ahgf         
,analyst                       ,r4      
,peters           ,f4 ,a4 ,cairns and   
,c4 ,f4 ,chandler      ,oscar ,loew     
,h4 ,leffman            ,oscar ,loew    
,t4 ,m4 ,chatard     ,t4 ,m4 ,chatard   
,t4 ,m4 ,chatard     ,t4 ,m4 ,chatard   
,c4 ,f4 ,chandler                       
,references                    ,ky4     
,geol4 ,surv41   ,am4 ,chemist1 ,nov4   
,am4 ,chemist1 #ahgf1  ,u4 ,s4 ,g4 ,s4  
,w41   ,u4,s4 ,geol4  ,geog4    ,an4    
,rep4 ,u4 ,s4 ,g4   ,ante1 p4 #di       
,ante1 p4 #ec     ,ante1 p4 #ea         

,bulletin ,no4 #i1 ,u4                  
,n4 ,s41 ,vol4 ,v1 p4   #ahgb1 p4 #afd  
p4 #cgj              #ajjth ,m44 ,vol4  
,surv4 ,id41 ,wyo4     ,s4 ,w41 #ajjth  
,m41                                    
,s4 ,geol4 ,survey1                     
#ahi                                    
,,iii1 p4 #fah        ,ter41 #ahgh1 p4  
#cic  #ahgf1 p4 #aie                    
p4 #bg                                  
----------------------------------------
----------------------------------------
----------------------------------------
----------------------------------------
----------------------------------------
-----------------------     ,sodium1 ,na
                          4#jibbg       
#d4gbfdj             #b4jcih            
4#deafd             4#dfae              
4#ajdbd              4#ggdc             
4#ceed             4#cjdj               
4#faaf                                  
,potassium1 ,k                          
4#jjiai              4#cehjf            
4#abhe              4#jeihj             

444444               ,trace             
4#jffi            4#jaia                
4#jjid              4#jfcj              
,calcium1 ,ca                           
4#jbacf              4#idjej            
#a4jgci              4#dddjj            
4#jcdd                                  
4#jcje            4#jcfg                
4#jaba              4#jehi              
4#ejfjjaaa                              
,magnesium1 ,mg                         
4#jahje              4#ecdgj            
4#bceb              4#jehfj             
444444                                  
4#jjaj            4#jjcd                
4#jjjd              4#jfjd              
,barium1 ,ba                            
444444              4#jahdh             
,trace                                  
,strontium1 ,sr                         
,trace#aab           4#jjjeg            
,lithium1 ,li                           
,trace               4#jajgh            
4#jjjc              4#jjjci             
444444               ,trace             

,iron1 ,fe                              
,trace#aac           4#jjcda            
4#jjbg              ,trace#aad          
444444               ,trace             
,manganese1 ,mn                         
444444              444444              
4#jjji              444444              
444444               ,trace             
,chlorine1 ,cl                          
4#jgdfe             #g4dgdjj            
#d4bgcj              4#bdhej            
4#gdif                ,trace#aae        
4#ifig            4#bcif                
4#bjgj              4#bbgb              
,bromine1 ,br                           
4#jdffa              4#jjbe             
,iodine1 ,i                             
4#jjjfj               ,trace            
,fluorine1 ,fl                          
444444              ,trace#aaf          
,carbonic acid1 ,,co                    
4#abafj             #e4hbfjc            
4#agib             #a4aajja             
444444              4#jceaf             
444444           ,trace                 

444444             4#eghg               
,sulphuric acid1 ,h,,so                 
4#jcbah              4#jjbcd            
#b4jcah              4#bjfif            
4#jcbe               4#afadj            
4#ceee            4#cija                
4#cdib              4#caca              
,phosphoric acid1 ,h,,po                
,trace              4#jjjje             
4#jjjd              444444              
444444              ,trace              
,boracic acid1 ,h,,bo                   
,trace              ,trace              
,alumina1 ,al,o                         
444444              4#jjggj             
4#jjbb              444444              
444444              ,trace              
4#jjaj            444444                
444444             4#jjah               
,silica1 ,si,o                          
4#jjidj              4#jaagd            
4#jjhj              4#jbjaj             
4#gfhj               ,trace             
4#bghh            4#aacf                
4#acaj              4#abbj              

,hydrogen in bicarbonates1 ,h           
444444              4#jigac             
4#jjcj                                  
,organic substances                     
,trace               ,trace             
,trace              444444              
444444             ,trace               
,oxygen1 ,o                             
444444              444444              
444444             444444               
444444             444444               
4#jaidaag         4#jbeeaag             
4#jjhjaag           4#jcbeaag           
----------------------------------------
----------------------------------------
----------------------------------------
----------------------------------------
---------------------------------       
4#cghgj            #bj4jeiaj            
#i4ihad             #b4fjjjj            
#b4jdfj              4#hjfhj            
#b4diec           #a4ahcd               
#a4jbaa             #b4jfib             
,carbonic acid1 ,,co                    
444444             #b4jaeaah            

444444             444444               
444444            ,in excess            
,trace                                  
,sulphuretted hydrogen1 ,h,s            
444444              444444              
444444             444444               
444444            #j4ejjj               
----------------------------------------
----------------------------------------
----------------------------------------
----------------------------------------
----------------------------------------
-----------------------                 
,illustration3 ,fig4 #bac4--8,old       
,faithful0 in eruption4    ,the exact   
sequence of events which leads up to an 
eruption is not  known1 but a definite  
conception of the principles involved   
may  perhaps be secured by a definite   
case4 ,suppose a geyser-tube filled     
with water1 and heated at its lower end4
 ,as the water is heated below1         
convection tends to distribute the heat 
throughout the column of  water above4  
,if convection were free1 and the tube  

short1 the result  would be a boiling   
spring2 but if the tube is long1 and    
especially  if convection is impeded1   
the water at some level below the       
surface  may be brought to the          
boiling-point earlier than that at the  
top4  ,under these circumstances if even
 a little water in the lower part of    
the tube is converted into steam1 the   
steam will raise the column of  water   
above1 and it will overflow4 ,the       
overflow relieves the pressure  on all  
parts of the column of water below the  
surface4 ,if before the  overflow there 
was any considerable volume of water    
essentially ready  to boil1 the relief  
of pressure following the overflow might
 allow it  to be converted into steam   
suddenly1 and the sudden conversion of  
any  considerable quantity of water into
 steam would cause the eruption of  all 
the water above it 7,figs4 #bac and     
#bad74 ,the height to which the  water  
would be thrown would depend upon the   
amount of steam1 the size  and          

straightness of the tube1 etc4    ,it is
 clear that everything which impedes    
convection in the geyser  tube will     
hasten the period of eruption1 since    
impeded circulation  will have the      
effect of holding the heat down1 and so 
of bringing the  water at some level    
below the top more quickly to the       
boiling-point4  ,it follows that        
anything which chokes up the tube1 or   
which increases  the viscosity of the   
water1 or its surface tension1 would    
hasten an  eruption4#aai    ,geysers    
often build up crater-like basins or    
cones 7,figs4 #bad to #bag7  about      
themselves1 the cone being of material  
deposited from solution4  ,in the       
,yellowstone ,park the precipitation of 
the matter in solution  7chiefly silica7
 is partly due to cooling and partly to 
the alg which  abound even in the       
boiling water1 and the brilliant colors 
of the  deposits about the springs are  
attributable to these plants4 ,when the 
water from any geyser or hot spring     

ceases to flow the plants die and  the  
colors disappear4 ,the details of the   
surface of the deposits about  geysers  
and hot springs are often complicated1  
and frequently very  beautiful 7,fig4   
#bah74    ,illustration3 ,fig4          
#bad4--8;,giant0 ,geyser1 ,yellowstone  
,park1 in    eruption4 ,shows also the  
cone4 7,wineman47    ,illustration3     
,fig4 #bae4--;,cone 7or crater7 of      
,castle ,geyser1    ,yellowstone ,park4 
7,detroit ,photo4 ,co47                 
,illustration3 ,fig4 #baf4--;,cone 7or  
crater7 of ,grotto ,geyser1             
,yellowstone ,park4 7,detroit ,photo4   
,co47    ,illustration3 ,fig4           
#bag4--;,cone of ,giant ,geyser1        
,yellowstone ,park4    7,wineman47      
,the heating of geyser and hot-spring   
water must cool the lava or  other      
source of heat below4 ,as this takes    
place1 the time between  eruptions      
becomes longer and longer4 ,in the      
course of time1 therefore1  the geyser  
must cease to be eruptive1 and when this

 change is brought  about the geyser    
becomes a hot spring4 ,within historic  
times several  geysers have ceased to   
erupt and new ones have been developed4 
,in the  ,yellowstone ,park1 where there
 are said to be something like #cjjj    
vents  of all sorts1 hot springs which  
are not eruptive greatly outnumber the  
geysers4 ,from many of the vents but    
little steam issues1 and from some1     
little else4    ,illustration3 ,fig4    
#bah4--;,hot springs deposits4 ,terraces
 of ,mammoth    ,hot ,springs1          
,yellowstone ,park4    ,a few geysers   
have somewhat definite periods of       
eruption4 ,of such 8,old  ,faithful0 is 
the type2 but even this geyser1 which   
formerly erupted at  regular intervals  
of about an hour1 is losing the         
reputation on which  its name is based4 
,not only is its period of eruption     
lengthening1  but it is becoming        
irregular1 and the irregularity appears 
to be  increasing4 ,in the short time   
during which this geyser has been under 

observation its period has changed from 
a regular one of sixty minutes1  or a   
little less1 to an irregular one of     
seventy to ninety minutes4  ,in the case
 of some geysers years elapse between   
eruptions1 and in  some the date of the 
last eruption is so distant that it is  
uncertain  whether the vent should be   
looked upon as a geyser or merely a hot 
spring4    ,in the ,yellowstone         
,park#abj the geysers are mainly in the 
bottoms  of valleys 7,fig4 #bai71 but   
the deposits characteristic of geysers  
are found in not a few places well above
 the present bottoms4 ,these  deposits  
record the fact that in earlier times   
the geysers were at  higher levels than 
now4 ,it is probable that they have     
been1 at all  stages in their history1  
near the bottoms of the valleys1 and    
that1 as  the valleys have been deepened
 the ground-water has found lower and   
lower points of issue4 ,in this respect 
the geysers have probably had  the same 
history as other springs4               

,illustration3 ,fig4 #bai4--;,hot       
springs and geysers4 ,norris ,geyser    
basin1 ,yellowstone ,park4    ,unless   
new intrusions of lava occur1 or unless 
heat is otherwise  renewed at the proper
 points1 it is probable that all        
existing geysers  will become extinct   
within a time which is1 geologically1   
short4 ,new  geyser regions may1        
however1 develop as old ones disappear4 
,artesian wells4--,originally the terms 
artesian wells and flowing  wells were  
synonymous2 but at the present time any 
notably deep well  is called artesian1  
especially if it descends to            
considerable depths  below the mantle   
rock4 ,the artesian well which does not 
flow1 does not  differ from common wells
 in principle2 but being deeper1 the    
water  which it affords is often more   
thoroughly filtered and frequently more 
highly mineralized than that of other   
wells4 ,the flowing well is really  a   
gushing spring1 the opening of which was
 made by man4    ,flowing wells#aba     

depend upon certain relations of rock   
structure1  water supply1 and elevation4
 ,generally speaking a flowing well is  
possible in any place underlain by any  
considerable bed of porous rock1  if    
such rock outcrops at a sufficiently    
higher level in a region of  adequate   
rainfall1 and is covered by a layer or  
bed of impervious1 or  relatively       
impervious rock4 ,this statement        
involves four conditions1  all of which 
are illustrated by ,fig4 #aii1 where a  
is the bed  of porous rock4 ,it is not  
necessary that the beds of rock form a  
structural basin1 nor is it usually     
necessary to take account of the        
character of the rock beneath the porous
 bed which contains the water4    ,the  
bed of porous rock is the 8reservoir0 of
 the flowing well4  ,formations of sand 
or sandstone1 and of gravel or          
conglomerate1 most  commonly serve as   
the reservoirs4 ,in order that it may   
contain abundant  water it must have    
some thickness1 and its outcropping edge

 must be so  situated that the water may
 enter freely and be replenished1       
chiefly by  rain1 as the water flows out
 at the well4    ,a relatively          
impervious layer of rock above the      
reservoir 7b1 ,fig4  #aii7 is most      
important2 otherwise the water in the   
reservoir will  leak out1 and there will
 be little or no 8head0 at the well     
site4  ,thus if the rock overlying      
stratum a 7,fig4 #aii7 were badly       
broken1  the fractures extending up to  
the surface1 the conditions would be    
unfavorable for flowing wells4 ,under   
such conditions1 wells in the  positions
 of those shown in ,fig4 #aii might get 
abundant water1 but they  would not be  
likely to flow4 ,if the stratum next    
below the reservoir  is not impervious1 
some lower one probably is4 ,no layer of
 rock is more  impervious than one which
 is full of water1 and the substructure 
of any  bed which might serve as a      
reservoir is usually full of water1 even
 if  the rock be porous4    ,if the     

outcrop of the reservoir be notably     
above the site of the well1  and if it  
be kept full by frequent rains1 the     
8head0 will be strong1  though the water
 at the well will not rise to the level 
of the outcrop  of the reservoir4       
,experience has shown that an allowance 
of about one  foot per mile of          
subterranean flow should be made4 ,thus 
if the site of  the well be #ajj miles  
from the outcrop of the water-bearing   
stratum1  and #bjj feet below it1 the   
water will rise something like #ajj feet
  above the surface at the well4 ,this  
rule is1 however1 not applicable        
everywhere4 ,the failure of the water to
 rise to the level of its head  is due  
to the adhesion and the friction of flow
 through the rock4 ,the  more porous the
 rock the less the reduction of head by 
friction4 ,the  height of the flow is   
also influenced by the number of wells  
drawing on  the same reservoir1 on the  
degree of imperviousness of the         
confining  bed above1 etc4    ,flowing  

wells1 often relatively shallow1 are    
frequently obtained from  unconsolidated
 drift4 ,some such relations as         
suggested by ,fig4 #bbj  would afford   
the conditions for flowing wells in such
 a formation4    ,illustration3 ,fig4   
#bbj4--;,figure illustrating the        
principle of    artesian wells in drift4
                                        
,,chapter ,v4                           
,,the ,,work ,,of ,,snow ,,and ,,ice4   
,a part of the atmospheric precipitation
 falls as snow1 and this1 like  the     
rain1 does its appropriate work in      
degrading the land4 ,over the  larger   
part of the land surface the snow of the
 winter does not endure  through the    
succeeding summer1 and when it melts it 
follows the same  course as the         
precipitation which falls as rain2 but  
in cold regions  where the fall of snow 
is heavy some of it remains unmelted and
  constitutes perennial snow-fields4    
,,snow- ,,and ,,ice-,,fields4           
,snow-fields4--,mountain heights and    

polar lands are the most common         
habitats of snow-fields1 though they are
 not confined to these  situations4 ,in 
,north ,america there are numerous small
 snow-fields in  the western mountains1 
from ,mexico on the south to ,alaska on 
the north1  their number and size       
increasing in the latter direction4 ,in 
the ,united  ,states there are few      
snow-fields south of the parallel of #cf
 #cj1 and  most of the many hundreds    
north of that latitude 7excluding       
,alaska7 are  small 7,pl4 ,,xviii1 ,fig4
 #a1 ,washington1 lat4 #dh #e1 long4    
#aba #e2 ,fig4  #b1 lat4 #da #be1 long4 
#abb #ab4 ,from ,glacier ,peak and      
,shasta ,special  ,quadrangles1 ,u4 ,s4 
,geol4 ,surv474 ,farther north1         
especially in ,alaska1  the snow-fields 
of the western mountains attain much    
greater size4 ,in  ,europe snow-fields  
comparable to those of the northwestern 
part of  the ,united ,states and        
,british ,columbia occur in the ,alps   
7,fig4 #bba71  the ,pyrenees1 the       

,caucasus1 and the ,scandinavian        
mountains4 ,in ,asia  snow-fields occur 
in the ,himalayas and in many of the    
high mountains  farther north1 from     
,turkestan on the southwest nearly to   
the coast on  the northeast4 ,in ,south 
,america there are snow-fields of small 
size  even in equatorial latitudes1 and 
farther south in the ,chilean ,andes    
there are some of considerable size4    
,small snow-fields occur on the  highest
 peaks of tropical ,africa1 and in the  
mountains of ,new ,zealand4  ,for       
reasons which will appear later1 much of
 every considerable  snow-field is      
really ice4    ,in addition to these    
limited fields of snow in mountain      
regions1 there  are fields of much      
greater extent covering wide expanses of
 plain  and plateau in the polar        
regions4 ,the greater part of the island
 of  ,greenland is covered with a single
 field of ice and snow1 the size of     
which is variously estimated at #cjj1jjj
 to #djj1jjj square miles 7,fig4        

#bbb7--;an area #djj to #fjj times as   
large as the snow-and-ice-covered  area 
of ,switzerland4 ,numerous islands to   
the west of ,north ,greenland  are also 
partly covered with snow1 the areas of  
the snow-fields far  exceeding those of 
most mountain regions4 ,in ,antarctica  
there is  believed to be a still larger 
field1 the largest of the earth4 ,its   
area  is not even approximately known1  
but such data as are at hand indicate   
that it may have an extent of #c1jjj1jjj
 or #d1jjj1jjj square miles4            
,illustration3 ,fig4 #bba4--;,an alpine 
snow-field4    ,illustration3 ,fig4     
#bbb4--,map of ,greenland4 ,the borders 
only are free    from ice4 7,stieler47  
,the only condition necessary for a     
snow-field is an excess of snowfall     
over snow waste4 ,the lower edge of a   
snow-field1 the snow-line1 is  dependent
 chiefly on temperature and snowfall4   
,in general it does not  depart much    
from the summer isotherm of #cb1 though 
it may be well  above this isotherm     

where the snowfall is light4 ,that the  
snow-line  is not a function of         
temperature only is shown by its        
position in  various places4 ,in the    
equatorial portion of the ,andes1 for   
example1  the snow-line has an altitude 
of about #af1jjj feet on the east side  
of  the mountains1 where the            
precipitation is heavier1 and of about  
#ah1ejj  feet on the west side1 where it
 is lighter4 ,for the same reason the   
snow-line in the ,himalayas is #cjjj or 
#djjj feet lower on the south  side than
 on the north4    ,while in equatorial  
regions the snow-line has an altitude of
 #ae1jjj to  #ah1jjj feet1 it approaches
 or even reaches sea-level in the       
latitude  of ,antarctica and ,north     
,greenland4 ,in intermediate latitudes  
it has an  intermediate position4       
,while temperature and snowfall are the 
most important factors  controlling the 
position of the snow-line1 both humidity
 and the  movements of the air are of   
some importance1 since both affect the  

rate  of evaporation of snow and ice4   
,the passage of snow into nv and        
ice4--,the snow does not lie on the     
surface long before it undergoes obvious
 change4 ,the light flakes  soon begin  
to be transformed into granules1 and the
 snow becomes  8coarse-grained40 ,the   
granular character1 so pronounced in the
 snow of  the last banks which remain in
 the spring in temperate latitudes1 is  
even more distinct in perennial         
snow-fields1 either at the surface or   
just beneath it4 ,this granular snow is 
called nv1 or firn4 ,still  deeper      
beneath the surface1 where the thickness
 of the snow is great1  the nv becomes  
more compact and finally coherent1 and  
grades into  porous ice4 ,this gradation
 is accomplished at no great depth1     
though  the thicknesses of snow and nv  
are by no means constant4    ,structure 
of the ice4--,ice formed beneath a      
snow-field is in some  sense stratified4
 ,it is made up of successive falls of  
snow which  tend to retain the form of  

layers4 ,this follows from two or three 
conditions4 ,the snow of one season1 or 
of one period of precipitation1  may    
have been considerably changed before   
the succeeding fall of snow4  ,so also  
the surface of the snow-field at the end
 of the melting season  is often covered
 with a visible amount of earthy matter1
 some of which  was blown up and dropped
 on the surface during the melting      
season1 and  some of which was          
concentrated in that position by the    
melting of the  snow in which it was    
originally imbedded4 ,the amount of     
earthy matter  is often sufficient to   
define snows of successive years1 or    
perhaps of  minor periods of            
precipitation1 and makes distinct the   
stratification  which would otherwise   
remain obscure4 ,the snowfall of        
successive years  has been estimated by 
this means#abb where the snow is exposed
 in  crevices in the snow-field4    ,in 
addition to its rude stratification1 the
 ice of the deeper portions  often      

acquires a stratiform structure which   
may perhaps best be called  foliation to
 distinguish it from the stratification 
which arises  from deposition4 ,the     
foliation appears to result mainly from 
the  shearing of one part over another  
in the course of the movements to  which
 the ice is subjected1 as will be       
illustrated presently4                  
,texture4--,the ice derived from the    
snow is formed of interlocking          
crystalline grains4 ,the crystalline    
character is present from the           
beginning1 for it is assumed by the     
snowflakes when they form1 and  the     
subsequent changes seem only to modify  
the original crystals  by building up   
some and destroying others4 ,by the time
 the snow is  converted into nv1 the    
granules have become coarse1 and        
wherever the  ice derived from the nv   
has been examined1 the granular         
crystalline  texture is present4 ,the   
individual crystals in the ice are      
usually  larger than those of the nv1   

and more closely grown together4 ,in the
  fresh unexposed ice the crystals are  
so intimately interlocked that  they are
 not readily seen except under a        
polarizing microscope1 but  when the ice
 has been honeycombed by partial        
melting1 the granules  become partially 
separated and may be easily seen4 ,fig4 
#bbc shows  quantities of them which    
have been washed down from the surface1 
and disposed as cones at its base4      
,while a given mass of snow in a  great 
snow- and ice-field cannot be followed  
consecutively through  its whole        
history1 yet since 7#a7 the granular    
texture is pronounced  in the nv stage  
where the granules show evidences of    
growth1 and  since 7#b7 the same texture
 is also pronounced in the last stages  
of  the ice when it is undergoing       
dissolution1 as well as at all observed 
intermediate stages1 and since 7#c7 the 
crystals are1 on the average1  larger in
 proportion to the lateness of the stage
 of their history1  while 7#d7          

experiment has shown that granules grow 
under the conditions  which exist in    
snow-fields1 and 7#e7 that they persist 
under very  considerable pressure1 it is
 legitimate to assume that a granular   
crystalline condition persists          
throughout all stages1 and is a feature 
of progressive growth4    ,illustration3
 ,fig4 #bbc4--;,figure showing cones of 
granules of ice    which have been      
washed down the front of the glacier by 
streamlets1    and accumulated after the
 manner of talus or alluvial cones4     
,north    ,greenland4    ,inauguration  
of movement4--,eventually the increase  
in depth of  snow and ice in a          
snow-field gives rise to motion4 ,the   
exact nature  of the motion has not yet 
been demonstrated to the satisfaction of
  all investigators4 ,brittle and       
resistant as ice seems1 it exhibits1    
under proper conditions1 some of the    
outward characteristics of a  plastic   
substance4 ,thus it may be made to      
change its form1 and may  even be       

moulded into almost any desired shape if
 carefully subjected  to sufficient     
pressure1 steadily applied through long 
intervals  of time4#abc ,these changes  
may be brought about without visible    
fracture1 and have been thought to point
 to a viscous condition of the  ice4    
,there is much reason1 however1 as will 
be seen later1 to question  this        
interpretation of the ultimate nature of
 the movement4 ,whatever  this may be1  
the mass result of the movement in a    
field of ice is  comparable1 in a       
superficial way at least1 to that which 
would be  brought about if the ice were 
capable of moving like a viscous liquid1
  the motion taking place with extreme  
slowness4 ,this slow motion of ice  in  
an ice-field is glacier motion1 and ice 
thus moving is glacier  ice4            
,illustration3 ,fig4 #bbd4--;,ice-caps  
of small size4 ,the figure also    shows
 some valley glaciers extending out from
 the main ice-sheet and    from the     
local ice-caps4 ,a portion of the ,north

 ,greenland coast1    north of          
,inglefield ,gulf4 ,lat4 about #gh4     
7,peary47    ,illustration3 ,fig4       
#bbe4--,small ice-caps in the           
northwestern part of    ,iceland4       
7,thoraddsen's geological map of        
,iceland47    ,illustration3 ,fig4      
#bbf4--;,a glacial lobe1 midway between 
an ice-cap    and a valley glacier4 ,a  
protrusion from a local ice-cap east of 
,cape    ,york1 ,greenland4    ,if both 
the surface on which the ice-sheet      
develops and its  surroundings be       
essentially plane1 as may happen in high
 latitudes1  and if the snow- and       
ice-field be symmetrical in shape1 the  
outward  movement will be approximately 
equal in all directions1 and the area   
covered by the spreading ice-field will 
remain more or less circular4  ,if the  
ice-field rests on a steeply inclined   
surface1 like a mountain  slope1 the    
movement becomes one-sided in conformity
 to the slope4 ,if  the surface1        
otherwise plane1 be affected by valleys 

parallel to the  direction of movement1 
the ice in the valleys will be deeper   
than  that on the divides between them1 
and its movement stronger4 ,in the      
valleys1 therefore1 the ice will advance
 farther than elsewhere before  being   
melted1 and the outline of the ice will 
become lobate1 the lobes  occupying the 
depressions4 ,these general relations   
are shown in ,figs4  #bbd and #bbe4 ,if 
the depressions be wide and shallow1 the
 lobes will be  broad and short 7,fig4  
#bbf72 if the depressions be narrow and 
deep1 the  lobes will be relatively     
narrow and long4 ,if the snow and ice   
rest on  a surface consisting chiefly of
 steep valleys and sharp ridges1 as is  
common on mountain slopes1 the snow and 
ice are chiefly gathered in the         
valleys1 and take a linear form4        
,,types ,,of ,,glaciers4    ,these      
different forms give rise to different  
terms4 ,the ice which  spreads with some
 approach to equality in all directions 
from a center  is a glacier1 is indeed  

the type of the greatest glaciers1 but  
is  commonly called an ice-cap4 ,the    
same name is applied to any glacier  in 
which there is movement in all          
directions from the center1 even  though
 its shape departs widely from a circle4
 ,the glacier covering  the larger part 
of ,greenland 7,fig4 #bbb7 is a good    
example of a large  ice-cap1 and the    
glaciers on some of the flat-topped     
peninsular  promontories of the same    
island are good examples of small ones  
7,fig4  #bbd74 ,if ice-caps cover a     
large part of a continent1 as some of   
those  of the past have done1 they are  
often called continental glaciers4      
,illustration3 ,fig4                    
#bbg4--;,characteristic end of a ,north 
,greenland    7,bryant7 glacier4        
,illustration3 ,fig4 #bbh4--,the ,rhne  
glacier4 7,reid47    ,illustration3     
,fig4 #bbi4--;,characteristic end of a  
,north ,greenland    glacier4 ,north    
side of ,herbert ,island1 ,inglefield   
,gulf4    ,illustration3 ,fig4          

#bcj4--,the end of an alpine 7,forno1   
,switzerland7    glacier4 7,reid47      
,illustration3 ,fig4 #bca4--;,deploying 
end of a ,north ,greenland glacier4     
,where ice-caps are developed on        
plateaus whose borders are trenched  by 
valleys1 ice-tongues from the edge of   
the ice-cap often extend  down into the 
valleys and give rise to one type of    
valley glacier  7,figs4 #bbd and #bbg74 
,a second and more familiar type of     
valley glacier  occupies mountain       
valleys1 and is the offspring of        
mountain snow-fields  7,fig4 #bbh74 ,the
 former are confined chiefly to high    
latitudes1 and are  distinguished as    
polar or high-latitude glaciers 7,figs4 
#bbg and  #bbi72 the latter are known as
 alpine glaciers 7,figs4 #bbh and #bcj74
  ,the end and side slopes of polar     
glaciers are1 as a rule1 much steeper   
than those of alpine glaciers4 ,when a  
valley glacier descends through  its    
valley to the plain beyond1 its end     
deploys1 forming a fan 7,fig4  #bca74   

,the deploying ends of adjacent glaciers
 sometimes merge1 and the  resulting    
body of ice constitutes a piedmont      
glacier 7,fig4 #bcb74 ,at  the present  
time1 piedmont glaciers are confined to 
high latitudes4 ,in  some cases the     
snow-field that gives rise to a glacier 
is restricted  to a relatively small    
depression in the side of a mountain1 or
 in the  escarpment of a plateau4 ,in   
such cases the snow-field and glacier   
are  hardly distinguishable1 and the    
latter descends but little below  the   
snow-line4 ,in many cases it does not   
even enter the narrow valley  which     
leads out from the depression occupied  
by the snow-field4 ,such  a glacier is  
nestled in the face of a cliff1 and may 
therefore be  called a cliff glacier#abd
 7,figs4 #bcc and #bcd74 ,the snow-field
 of a  cliff glacier is sometimes no    
more than a great snowdrift1 accumulated
  through successive years4 ,cliff      
glaciers are often as wide as long1  and
 are always small1 and between them and 

valley glaciers there are  all          
gradations 7,fig4 #bce74 ,occasionally  
the end of a valley glacier1  or the    
edge of an ice-sheet reaches a          
precipitous cliff1 and the end  or edge 
of the ice breaks off and accumulates   
like talus below4 ,the  ice fragments   
may then again become a coherent mass by
 regelation1 and  the whole may resume  
motion4 ,such a glacier is called a     
reconstructed  glacier4 ,the precipitous
 cliffs of the ,greenland coast furnish 
illustrations4    ,illustration3 ,fig4  
#bcb4--,the ,malaspina glacier1 ,alaska2
 the best    known example of a piedmont
 glacier4 7,russell47    ,illustration3 
,fig4 #bcc4--;,a cliff glacier4 ,north  
,greenland type4 ,north    side of      
,herbert ,island1 ,inglefield ,gulf4    
,the lower half of the white    area is 
snow1 and snow talus4 ,so also are the  
white patches to the    right4 ,the     
height of the cliff is perhaps #bjjj    
feet4 ,the water in the    foreground is
 the sea4    ,illustration3 ,fig4       

#bcd4--;,chancy glacier2 a cliff glacier
 of the    ,montana type4 7,shepard47   
,of the foregoing types of glaciers1 the
 ice-caps far exceed all others  both in
 size and importance1 while the valley  
glaciers out-rank1 in the  same         
respects1 the other types2 but since the
 valley glaciers are the  most familiar 
type1 the general phenomena of glaciers 
will be discussed  with primary         
reference to them4                      
,,the ,,general ,,phenomena ,,of        
,,glaciers4#abe                         
,dimensions4--,glaciers which occupy    
valleys leading down from  snow-fields  
sometimes reach the upper parts of the  
valleys only1  sometimes extend through 
them1 and sometimes push out on the     
plain  beyond4 ,in length they range    
from a fraction of a mile to many       
miles1 and though their width is usually
 much less than their length1  the      
reverse is sometimes the case 7,figs4   
#bcc1 #bcd1 and #bce74 ,their  thickness
 is usually measured by hundreds of feet

 rather than by  denominations of other 
orders1 but the variation is great1 and 
exact  measurements are almost wholly   
wanting4 ,the minimum thickness is that 
necessary to cause movement1 and this   
varies with the slope1 the  temperature1
 and other conditions4 ,there is also   
much variation in the  thickness in     
different parts of a glacier4 ,as a     
rule1 it is thinnest in  its terminal   
portion1 and thickest at some point     
intermediate between  this and its      
source1 but nearer the latter than the  
former4 ,cliff and  reconstructed       
glaciers are comparable in size to the  
smaller valley  glaciers4 ,piedmont     
glaciers may attain greater size4       
,illustration3 ,fig4 #bce4--;,a glacier 
in the ,cascades near ,cascade ,pass1   
,wash4 ,a glacier intermediate between a
 cliff glacier and a valley    glacier4 
7,willis1 ,u4 ,s4 ,geol4 ,surv47    ,an 
ice-cap is theoretically thickest at its
 center and thins away to  its borders1 
but its actual dimensions are influenced

 by the topography  on which it is      
developed4 ,the ,greenland ice-cap is   
known to rise about  #ijjj feet above   
the sea1 and it probably reaches        
considerably higher  than this in the   
unexplored center of its broad dome4    
,the height of the  land surface beneath
 is unknown1 but it is unlikely that it 
averages  half this amount1 and hence   
the ice is probably #ejjj feet or more  
thick  in the center4 ,there is reason  
to think that it is much thicker in     
,antarctica4    ,limits4--,the ice of a 
glacier is always moving forward        
7neglecting  temporary halts71 but the  
end of a glacier may be retreating1     
advancing or remaining stationary1      
according as the rate of wastage is     
greater1 less1 or just equal to the     
forward movement of the ice4 ,the       
position of the lower end of the glacier
 is therefore determined by the  ratio  
of movement to wastage4 ,its upper end  
is generally ill-defined4  ,in a        
superficial sense1 it is the point where

 the ice emerges from the  snow-field2  
but the lower limit of the snow-field is
 often ill-defined1  and in any case is 
not the true upper limit of the glacier1
 since there  must be movement from the 
granular mass of ice beneath the snow to
  make up for the waste below1 and the  
moving ice beneath the snow-field  which
 feeds the tongue of ice in the valley  
is just as really a part  of the glacier
 as the more consolidated portion in the
 valley below4  ,if a definite upper    
limit for an alpine glacier is to be    
named1 it  should probably be the       
,bergschrund1 a gaping crevasse1 or     
series of  crevasses which sometimes    
open near the precipitous slope of the  
peak  or cliff where the snow-field     
lies4 ,the ,bergschrund is formed by the
  moving of the lower part of the       
snow-field away from the portion above4 
,the lower end of a glacier is usually  
free from snow and nv in  summer1 but1  
traced toward its source1 it first      
becomes covered with  nv1 then with     

snow1 and finally merges into the       
snow-field without  having ceased to be 
a glacier4 ,the term glacier is1        
however1 commonly  used to mean merely  
the more solid portion outside 7below7  
the nv4    ,movement4--,the fact of     
glacier movement is established in      
various  ways1 the most obvious being by
 the advance of its lower end4 ,such    
advance is too slow to be seen from day 
to day1 and is only detected  when the  
lower end of the glacier overrides or   
overturns objects in  front of it1 or   
moves out over ground previously        
unoccupied4 ,but even  when the end of a
 glacier is not advancing1 the movement 
of the ice may  be established by means 
of stakes or other marks set on the     
surface4  ,if the positions of these    
marks relative to fixed points on the   
sides  of the valley be determined1 they
 are found after a time to have moved   
down the valley4 ,rows of stakes or     
lines of stones set across a glacier  in
 the upper1 middle and lower portions   

have revealed many facts  concerning the
 movement of the ice4    ,generally     
speaking1 the middle of a valley glacier
 moves more rapidly  than its sides     
7,fig4 #bcf71 but in some cases1        
especially in large  glaciers1 there are
 found to be two or more main lines of  
movement1  with belts of lesser movement
 between4 ,the top of a glacier moves1  
on  the whole1 more rapidly than the    
bottom1 though the observations made  do
 not show that the rate of movement     
diminishes regularly downward1  and it  
probably does not so diminish in many   
cases4 ,in ,switzerland1  where the     
glaciers have been studied more         
carefully than elsewhere1  the          
determined rates of movement range from 
one or two inches to four  feet or more 
per day4 ,some of the larger glaciers in
 other regions  move more rapidly1 but  
it does not follow that large glaciers  
always  move faster than small ones4    
,the ,muir glacier of ,alaska has been  
found  to move seven feet or more per   

day1#abf and some of the glaciers of    
,greenland have been found to move1 in  
the summer time1 #ej1 #fj1 or even  more
 feet per day4 ,a single estimate as    
high as #ajj feet per day has  been     
made2 but these high rates have been    
observed only where the ice  of a large 
inland area crowds down into a          
comparatively narrow fjord1  and        
debouches into the sea1 and then only in
 the summer4 ,in the case of  the       
glacier with the highest recorded rate  
of summer movement1 #ajj feet  per day1 
the advance was only #cd feet at about  
the same place in ,april4               
,illustration3 ,fig4 #bcf4--;,diagram to
 show the rate of movement of the       
,rhone ,glacier at various points in its
 course at centre and sides4 ,it  also  
shows the fluctuations in the positions 
of the end of the glacier  between #ahgd
 and #ahhb1 and the profile of the ice4 
7,heim47    ,the average movement of the
 border of the inland ice of ,greenland 
is  very small4 ,rink says that 8between

 #fb and #fh #cj1 the edge of the       
inland ice is almost stationary for a   
remarkably long distance40#abg  ,the    
observations of the authors between #gg 
and #gh were of like  import4 ,probably 
the average movement of the border of   
the ,greenland  ice-cap is less than one
 foot a week4    ,conditions affecting  
rate of movement4--,the rate of glacier 
movement  appears to depend on 7#a7 the 
depth of the moving ice2 7#b7 the slope 
of  the surface over which it moves2    
7#c7 the slope of the upper surface  of 
the ice2 7#d7 the topography of the bed 
over which it passes2 7#e7  the         
temperature2 and 7#f7 the amount of     
water which falls upon it or  is carried
 to it by the drainage of its           
surroundings1 in addition to  that      
produced by the melting of the glacier  
itself4 ,great thickness1  a steep      
slope1 much water1 smoothness of bed1   
and a high 7for ice7  temperature favor 
rapid movement4 ,since some of these    
conditions1  notably temperature and    

amount of water1 vary with the season1  
the rate  of movement for any given     
glacier is not constant throughout the  
year4  ,other conditions1 especially the
 first of those mentioned above1 vary   
through longer periods of time1 and     
occasion periodic variations in the     
rate of movement4    ,since the volume  
of ice concerned influences the rate of 
movement1  anything which changes the   
volume affects the rate4 ,an excess of  
snowfall with favorable conditions for  
its preservation for a period  of years1
 increases the volume of ice1 and tends 
to accelerate its  movement4 ,a         
deficiency in snowfall1 or in its       
preservation1 as from  high average     
temperature or from aridity1 diminishes 
the quantity of  ice1 and so retards the
 movement4 ,an acceleration of velocity 
causes  the ice to move down the valley 
farther before being melted1 that  is1  
causes the end of the glacier to        
advance1 while a decrease of  velocity  
produces the opposite effect4 ,as a     

matter of fact1 the lower  ends of      
glaciers advance for a period of years  
and then retreat1 to  advance again at a
 later time4#abh ,observation has shown 
that the  periods of advance follow a   
succession of years when the snowfall   
has been heavy and the temperature low1 
while the periods of retreat  follow a  
succession of years when the snowfall   
has been light and the  temperature     
above the average4 ,the periods of      
advance and retreat lag  behind the     
periods of heavy and light snowfall     
respectively1 by some  years1 and a long
 glacier responds less promptly than a  
short one4  ,present knowledge seems to 
point to a period of #ce to #dj years as
 the  time within which a cycle of      
fluctuation1 that is1 an advance and a  
retreat1 takes place4    ,a declining   
upper surface is essential to glacier   
motion4 ,there are  short stretches     
where this is not the case1 and indeed  
there are  particular places where the  
upper surface slopes backward4#abi ,this

  may occur where the ice is pushed up  
over a swell in its bed1 or is  crowded 
up against any considerable obstacle2   
but such cases are no  more than local  
exceptions1 and do not militate against 
the truth of  the general statement that
 the upper surface of a glacier declines
 in  the direction of motion4 ,a        
declining lower surface is less         
necessary4  ,in the case of valley      
glaciers1 the bed does1 as a rule1      
decline in  the direction of motion1 but
 that there are local exceptions is     
shown  by the deep basins in rock which 
such glaciers often leave behind them   
when they retreat4 ,in the great        
continental glaciers of recent geologic 
times1 the ice frequently moved up      
slopes for scores1 and even hundreds  of
 miles2 but in all such cases1 the upper
 surface must have declined  in the     
direction of movement4 ,with a given    
thickness of ice1 the  greater the      
decline of its lower surface in the     
direction of motion1  the more rapid its

 progress4 ,a rough bed1 or a crooked   
course retards  the motion of a glacier1
 while a smooth bottom and a straight   
course  facilitate it4    ,slope1       
roughness of bed1 and volume affect the 
movement of glaciers  somewhat as they  
affect the movement of rivers4 ,the     
temperature of  the water1 on the other 
hand1 has little effect on the flow of a
  river so long as it remains unfrozen2 
but the effect of temperature  on the   
motion of ice is most important4 ,in    
many cases1 indeed1 the  temperature1   
together with the water that is         
incidental to it1 seems  to be the chief
 factor in determining the rate of      
movement4 ,the way in  which its effects
 are felt will be discussed later4      
,likenesses and unlikenesses of glaciers
 and rivers4--,many of the              
characteristics of a valley glacier may 
be understood from the study of  the    
accompanying figure 7,fig4 #bcg7 of the 
,white 7,alaska7 glacier4 ,from  this   
figure it will be seen that the glacier 

is an elongate river-like  body1        
following the curves of the valley in   
stream-like fashion4 ,it  has its origin
 in the snows collected on the mountain 
heights seen  in the distance1 and it   
works its way down the valley in a      
manner  which1 in the aggregate1 is     
similar to the movement of a stiff      
liquid4  ,the likeness to a river       
extends to many details4 ,not only does 
the  center move faster than the sides1 
and the upper part faster than the      
bottom1 as in the case of streams1 but  
the movement is more rapid in           
constricted portions of the valley and  
slower in the broader parts4  ,these and
 other likenesses1 some of which are    
apparent rather than  real1 have given  
origin to the view that glacier ice     
moves like a stiff  viscous liquid4     
,illustration3 ,fig4 #bcg4--,white      
glacier 7central background7 joining a  
larger glacier 7foreground71 ,alaska4   
7,reid47    ,but while the points of    
likeness between glaciers and rivers are

  several1 their differences are at     
least equally numerous and  significant4
 ,the trains of dbris on the surface    
7the dark bands in the  illustration71  
like the central currents of streams1   
pass nearer the  projecting points of   
the valley walls and farther from the   
receding  bends2 but beyond this point  
the analogy fails1 for the trains of    
dbris on the ice do not conform in      
detail to the courses of the  currents  
of a winding stream1 nor is there       
evidence of the rotatory  motion that   
characterizes river water4 ,furthermore1
 the glacier is  readily fractured1 as  
the numerous gaping crevices on many    
glaciers  show4 ,the crevasses are      
sometimes longitudinal1 sometimes       
transverse1  and sometimes oblique4 ,in 
the case of ,arctic glaciers1           
longitudinal  crevassing is especially  
conspicuous4    ,illustration3 ,fig4    
#bch4--;,cracking of glacier due to     
change in grade    of bed4 ,a ,north    
,greenland glacier overriding a mound of

    moraine-stuff4    ,crevasses appear 
to be developed wherever there is       
appreciable  tension1 and the causes of 
this tension are many4 ,an obvious cause
 is  an abrupt increase of gradient in  
the bed 7,fig4 #bch74 ,if the change  of
 gradient be considerable1 an ice-fall  
or cascade results1 and the  ice may be 
greatly riven 7,fig4 #bbh74 ,below the  
cascade1 the surface  may bristle with  
wedges and pinnacles of ice 7sracs1     
,fig4 #bci74  ,transverse crevices at   
the margin sometimes appear to be the   
result  of the tension developed on a   
curve4 ,oblique crevices on the surface 
near the sides are commonly ascribed to 
the tension between the  faster-moving  
center and the slower-moving margins1   
and in like manner  crevasses that rise 
obliquely from the bottoms are          
attributed to the  tension between the  
faster-moving portions above and the    
slower-moving  portions below4 ,all     
these crevasses indicate strains to     
which a liquid1  whose pressures are    

equal in all directions1 does not offer 
a close  analogy4 ,longitudinal         
crevasses may affect both the river-like
 part  of a glacier and its deploying   
end1 and are the result of tension      
developed by movement within the ice    
itself1 to which1 again1 rivers  offer  
no analogy4 ,somewhat similar cracks    
develop in the outer crust  of asphalt1 
when a mass of it is allowed to stand   
and spread2 but in  this case there is  
evaporation of the volatile ingredients1
 giving to  the outer part relative     
rigidity and brittleness1 while the     
inner part  remains more fluent4 ,the   
analogy is therefore not perfect and    
probably  not really illustrative4 ,the 
crevices may be narrow or wide1 and both
  narrow and wide may be found in the   
same glacier4 ,the narrow crevices  that
 never open much are the most           
significant1 as they show that very     
little stretching is needed to satisfy  
the tension4 ,the opening of a  gaping  
crevice is sometimes the work of weeks1 

and1 in the slow-moving  glaciers of    
high latitudes1 sometimes the work of   
successive seasons4  ,all this shows    
that the glacier is a very brittle body1
 incapable of  resisting even very      
moderate strains brought to bear upon it
 very  slowly4 ,had the ice even        
moderate ductility1 it would adapt      
itself to  tension brought to bear upon 
it so slowly as are many of the tensions
  which produce crevassing4 ,in its     
behavior under tension therefore a      
glacier is notably unlike a river4      
,illustration3 ,fig4 #bci4--,sracs of   
glacier4 7,reid47                       
,,surface ,,features4                   
,topography4--,many of the minor        
irregularities of the surface of a      
glacier are the result of crevassing4   
,after the ice is crevassed1  the sun's 
rays and the air which has been warmed  
by them penetrate  the openings and melt
 the ice4 ,the melting is most rapid at 
the  top1 and decreases downward4 ,the  
result is that the sections of ice      

between adjacent crevasses are narrowed 
into wedges4 ,if there be               
cross-crevassing1 as is common1 points  
instead of wedges result4 ,as the  sort 
of surface shown in ,fig4 #bci develops1
 any dbris which was on the  ice slides 
into the crevices1 and the upper surface
 becomes clean4    ,where ice is        
crevassed transversely1 and where       
melting is not rapid1  the crevasses may
 close as the ice moves forward1 and the
 regelation  of adjoining faces heals   
the rents in the surface4 ,even in this 
case1  however1 the surface is likely to
 be more or less undulating because of  
the waste on the sides of the crevices  
before they are closed4 ,after          
regelation1 surface ablation tends to   
obliterate the protuberances4    ,the   
topography of the surface of the ice is 
affected by other  conditions4 ,all     
parts of the surface of the ice are not 
equally  compact1 and the least compact 
portions melt most rapidly1 giving rise 
to depressions1 while the more solid    

parts occasion protuberances4  ,both    
depressions and protuberances may be    
regular or irregular in form  7,figs4   
#bdj and #bda74 ,undulations of the bed 
often show themselves  in the surface of
 the ice as suggested by ,fig4 #bdb4 ,in
 such cases1  ponds or lakelets         
sometimes accumulate on the surface of  
the ice4 ,the  topography of the ice in 
such cases seems to show that the ice is
  forced up slope4    ,surface          
moraines4--,the surface of a glacier is 
often affected by  dbris of one sort or 
another1 and this also influences its   
topography4  ,the dbris is sometimes    
disposed in the form of belts or        
moraines  7,figs4 #bcg1 #bdc74 ,the     
surface moraines may be lateral1 medial1
  or terminal4 ,a lateral moraine is any
 considerable accumulation  of dbris in 
a belt on the side of a glacier4 ,a     
medial moraine is  a similar            
accumulation at some distance from the  
margins1 but not  necessarily in or near
 the middle4 ,there may be several      

medial  moraines on one glacier1 in     
which case some of them may be far from 
the center4 ,in alpine glaciers1 the    
surface terminal moraine is less        
well-defined2 in polar glaciers it often
 connects two lateral moraines1  making 
a loop roughly concentric with the      
terminus of the glacier4                
,illustration3 ,fig4 #bdj4--;,end of    
,mount ,dana glacier1 ,cal4 ,shows      
irregularities of surface due to        
crevassing farther up the glacier1      
and to unequal melting4                 
,illustration3 ,fig4 #bda4--,shows      
irregularities due to unequal melting   
of veined ice4 ,end of small glacier    
south of ,forno hut1 ,engadine1         
,switzerland4 7,reid47    ,besides the  
surface moraines1 which represent belted
 aggregations of  dbris1 there may be   
scattered bowlders and bits of rock of  
various  sizes on the ice1 and1 in      
addition to the coarse material1 there  
is  often some dust which has been blown
 upon the ice4    ,relief due to surface

 dbris4--,the dbris on the ice affects  
its  topography by influencing the      
melting of the subjacent and adjacent   
ice4 ,the rock dbris absorbs heat more  
readily than the ice4 ,a small  and thin
 piece of stone lying on the ice is     
warmed through by the  sun's rays1 and1 
melting the ice beneath1 sinks1 just as 
a piece of  black cloth on snow will    
sink because of the increased melting   
beneath  it4 ,though a good absorber of 
heat1 rock is a poor conductor1 and so  
the lower surface of a large mass of    
stone is not notably warmed4 ,the  ice  
beneath it is protected from the direct 
rays of the sun1 and is  therefore      
melted more slowly than that around it4 
,the result is that  the bowlder        
presently stands on a protuberance of   
ice 7,fig4 #bdd74 ,when  its pedestal   
becomes high1 the oblique rays of the   
sun and the warm air  surrounding it    
cause it to waste away1 and the capping 
bowlder falls4  ,in high latitudes1 the 
great obliquity of the rays sometimes   

allows  them to strike under isolated   
bowlders4 ,in this case1 they are warmed
  from below1 and thus aid rather than  
hinder the melting of the ice4          
,illustration3 ,fig4 #bdb4--;,irregular 
surface due to uneven bottom4  ,bowdoin 
glacier1 ,inglefield ,gulf1 ,north      
,greenland4 ,the dark patches  near the 
left margin of the glacier are lakelets 
in basins produced by  the upward       
bending of the ice as it overrides an   
elevation in its bed4  ,the figure also 
shows a depressed medial moraine4       
,the same principles apply to the       
moraines4 ,a thin bowlder moraine in    
high latitudes is sometimes sunk below  
the surface 7,fig4 #bdb74 ,usually1     
however1 a medial moraine protects the  
ice beneath from melting1 and  occasions
 the development of a ridge of ice      
beneath itself4 ,as the ice  on either  
side is then lowered by ablation1 the   
moraine matter of the  medial belt tends
 to slide down on either hand4 ,the same
 is true of the  lateral moraines4 ,so  

far does this spreading go1 that in some
 cases the  lower end of a glacier is   
completely covered with the dbris which 
has  spread from the medial and lateral 
moraines4 ,examples of this may be  seen
 in almost any region of abundant1 long1
 alpine glaciers4    ,illustration3     
,fig4 #bdc4--;,a ,swiss glacier1 showing
 surface moraines1    characteristic    
profile1 etc4    ,dust-wells4--,the     
wind-blown dust sometimes gives rise to 
peculiar  topographic features of small 
size4 ,the dust is not distributed by   
the  wind with absolute equality1 and   
the surface drainage of the ice tends   
to aggregate it4 ,every dust particle   
acts like a small stone1 and where      
aggregations of dust occur1 they melt   
their way down into the ice1  developing
 holes or 8dust-wells0 7,fig4 #bde74    
,these wells rarely reach a  depth of   
more than a few inches1 but they may be 
so numerous that the  pedestrian is     
obliged to watch his steps4 ,this is    
especially true near  the edge of the   

large ice-caps4 ,it is evident that the 
depth of these  dust wells must be      
slight1 for so soon as they are deep    
enough to cut  off the sun's rays from  
the dust at the bottom1 the deepening   
ceases4  ,other things being equal1 they
 are deeper in low latitudes than in    
high4    ,illustration3 ,fig4           
#bdd4--;,bowlder on ice pinnacle4 ,forno
 glacier1    ,switzerland4 7,reid47     
,illustration3 ,fig4                    
#bde4--;,dust-wells4 ,igloodahomyne     
glacier1 ,north    ,greenland4          
,illustration3 ,fig4                    
#bdf4--;,disposition of dbris in ice4   
,north    ,greenland glacier4 7,libbey47
    ,illustration3 ,fig4 #bdg4--,profile
 of the lower part of the lateral       
margin of a glacier4 ,southeast side of 
,mc,cormick ,bay1 ,north    ,greenland4 
,dbris below the surface4--,the lower   
part of a glacier1 as well as  the      
upper1 carries rock dbris4 ,this dbris  
is sometimes so abundant1  especially   
near the ends and edges of the ice1 that

 it is difficult to  locate the bottom  
of the glacier2 for between the moving  
ice which is  full of dbris1 and the    
stationary dbris which is full of ice1  
there  seems to be a nearly complete    
gradation4 ,the dbris in the lower part 
of arctic glaciers1 and to some extent  
of others1 is often disposed in  thin   
sheets sandwiched in between layers of  
clean ice4 ,these dbris  sheets are     
often numerous and usually              
discontinuous1 though groups  of such   
sheets often persist for considerable   
distances4 ,dbris also  occurs to some  
extent in the ice well above its base4  
,it is sometimes  in belts1 as seen in  
section1 and sometimes in bunches4      
,these various  relations are           
illustrated by ,figs4 #bbg1 #bbi1 and   
#bdf-bdi4    ,another characteristic of 
the basal dbris-laden part of some      
glaciers  is the foliation of the ice   
7,figs4 #bdh1 #bdi1 etc474 ,this is     
especially well shown in the arctic     
glaciers1 the ends and sides of  which  

have steep or vertical faces4 ,the      
foliation is best developed  in the     
dbris zone1 though often shown above4   
,the foliation is  sometimes minute1    
consisting of layers of clean ice1 an   
inch or less  in thickness1 separated by
 mere films of earthy matter4 ,in       
extreme  cases there are a score or more
 of lamin within a foot4 ,locally1 and  
especially where dbris is abundant1 the 
lamin are much contorted4  ,this is seen
 both in section 7,figs4 #bdh and #bdi7 
and on the surface  7,fig4 #bej74       
,,temperature1 ,,waste1 ,,and           
,,drainage4    ,the temperature of      
glacier ice may range downward from the 
freezing  point of water much as other  
solid portions of the earth's surface1  
but it has a fixed upper limit at #cb   
,fahr4 7#j ,c47 because all the  heat it
 receives tending to raise its          
temperature above that point1 is        
converted into the latent form by the   
melting of the ice4 ,the range of       
temperature is greatest at the surface1 

where it varies from #cb in the  summer1
 to the coldest temperature of the      
region where the ice occurs4  ,beneath  
the surface the range of temperature is 
more restricted1 and  increasingly so   
with increasing depth4    ,illustration3
 ,fig4 #bdh4--,side view of end of      
glacier4 ,southeast side    of          
,mc,cormick ,bay1 ,north ,greenland4    
,shows structure of ice as well as      
position of dbris4    ,the variation of 
temperature at the surface is due       
primarily to the  varying temperature of
 the air4 ,during the cold season1 a    
wave of low  temperature 7the winter    
wave71 starting at the surface1         
penetrates  the ice1 and during the warm
 season a wave of higher temperature    
7the  summer wave7 takes the same       
course4 ,the day and night waves and    
other  minor variables are1 for present 
purposes1 negligible4    ,illustration3 
,fig4 #bdi4--,side view of a ,north     
,greenland glacier 7,east    glacier71  
showing position of dbris and structure 

of the ice4    ,the winter wave4--,there
 are but few observations on the        
internal  temperatures of glaciers      
during the winter season1 but it seems  
certain  that the winter wave diminishes
 rapidly downward and dies out below1   
much as does the winter wave which      
affects land surfaces not covered  with 
ice4 ,conduction alone considered1 the  
temperature of the ice where  the cold  
wave dies out1 should correspond1       
approximately1 to the mean  annual      
temperature of the region1 provided that
 temperature is below  the melting point
 of ice4    ,assuming that in the high  
altitudes and high latitudes where      
glaciers  abound1 the temperature of the
 surface may average about -#ab ,fahr4  
7about -#be ,c47 for the winter half of 
the year1 which is about the  case for  
north ,greenland1 ,spitzbergen1 and     
,franz ,josef ,land1 and that  the      
conductivity of the ice in the ,c4 ,g4  
,s4#acj system is 4#jje1  the           
temperature would be lowered appreciably

 only about #dj feet  below the surface 
at the close of the winter period1      
conduction only  being considered4 ,how 
far the internal temperature may be     
influenced  by air forced through the   
ice by winds and by variations of the   
barometer is not known and cannot well  
be estimated4 ,the wave of low          
temperature descending from the surface 
in winter would probably become         
inappreciable before reaching a depth of
 #fj feet4 ,at this depth the           
temperature should be about #ae         
,fahr4--the mean annual temperature of  
the region4    ,illustration3 ,fig4     
#bej4--;,contorted lamination shown at  
the surface4 ,a    small glacier south  
of ,forno hut1 ,engadine1 ,switzerland4 
7,reid47    ,the summer wave4--,the warm
 wave follows the analogy of the summer 
wave  of ice-free land surfaces much    
less closely4 ,this is because of the   
low melting temperature of ice as       
compared with other forms of solid      
earth-matter4 ,on this account the      

summer wave is bi-fold4 ,the one part   
travels downward by conduction1 the     
other by the descent of water2 the  one 
has to do primarily with the temperature
 before the melting-point  of ice is    
reached2 the other1 with the temperature
 after that point  is reached2 the first
 conforms measurably to the warm wave   
affecting  other solid earth-matter1    
while the second is governed by special 
laws4 ,after the surface portion of the 
ice is brought to the melting           
temperature1 the additional heat which  
it receives melts the ice and  is       
transformed from sensible into potential
 heat4 ,ice charged with  water is      
potentially1 but not sensibly1 warmer   
than ice which has  just reached the    
melting temperature4    ,the warm wave  
of conduction dies out below like the   
cold wave4 ,the  warm wave descending by
 the flow of water stops where the      
freezing  temperature of water is       
reached4 ,in regions where the average  
temperature is below freezing1 the      

water-wave does not descend so far  as  
the wave of conduction1 since the latter
 descends below the zone  where the     
melting temperature is found4    ,the   
foregoing considerations warrant the    
generalization that glaciers  normally  
consist of two zones 7#a7 an outer or   
upper zone of fluctuating  temperature1 
and 7#b7 an under zone of nearly        
constant temperature4 ,the  under zone  
obviously does not exist where the      
thickness of the ice is  less than the  
thickness of the zone of fluctuating    
temperature4 ,this  may be the case in  
very thin glaciers in very cold regions1
 and in the  thin ends and edges of all 
glaciers4    ,the temperature of the    
bottom4--,the internal heat of the earth
 is  slowly conducted to the base of a  
glacier where it melts the ice at  the  
estimated average rate of about         
one-fourth of an inch per year4  ,the   
temperature of melting is a little below
 #cb ,fahr4 since pressure  lowers the  
melting-point at the rate of 4#jacc     

,fahr4 74#jjge ,c47 for  one atmosphere 
of pressure4 ,at the bottom of a mile of
 ice therefore  the melting temperature 
is about #cj4b ,fahr4 7-#a ,c47 ,it is  
probable  that in all thick glaciers the
 temperature of the bottom is constantly
  maintained at the melting-point4 ,this
 may be indicated by the streams  which 
issue from beneath glaciers during the  
winter1 though this  criterion is hardly
 decisive since the issuing waters may  
be derived  partly or wholly from the   
rock beneath4 ,in glaciers or in parts  
of  glaciers so thin as to lie wholly   
within the zone of fluctuating          
temperature1 the temperature of the     
bottom is obviously not constant4       
,temperature of the interior of the     
ice4--,the variation of temperature  of 
the surface of a glacier has already    
been shown to lie between a  maximum of 
#cb ,fahr4 and the minimum temperature  
of the region where  the glacier occurs4
 ,lower1 in the zone of fluctuating     
temperature1 the  variation is less1 and

 where the zone of fluctuating          
temperature passes  into the zone of    
constant temperature1 variation ceases4 
,the thickness  of the zone of          
fluctuating temperature varies with the 
temperature of  the region where the    
glacier occurs1 being greatest where the
 winters  are coldest4 ,in the case of  
all glaciers except thin ones in very   
cold  regions1 the temperatures within  
the zone of constant temperature range  
from the mean annual temperature of the 
region at the top of the zone  7provided
 this is not above the melting-point of 
ice at this depth7 to  the melting      
temperature of the ice at the bottom4   
,within these limits  the range may be  
great or slight4    ,if we consider only
 the effects of the external seasonal   
temperatures  and the internal heat of  
the earth1 it appears that all the ice  
in  the zone of constant temperature in 
the lower end of a typical alpine       
glacier should have a constant melting  
temperature1 for the average            

temperature of regions where the ends of
 such glaciers occur is usually  above  
#cb ,fahr41 and this determines a       
temperature of #cb ,fahr4 7or a  little 
less7 at the top of the zone1 while a   
melting temperature is  maintained at   
the bottom by the earth's interior heat4
 ,in thin glaciers  of very cold        
regions1 where the zone of constant     
temperature has  relatively slight      
thickness1 the low temperature          
descending from the  surface may so far 
overcome the effect of internal heat as 
to keep the  bottom of the ice at a     
freezing temperature4 ,in all other     
cases1 the  ice at the bottom of the    
under zone has a melting temperature1   
while  that above is probably colder4   
,in the higher altitudes and in the     
polar latitudes where glaciers  are     
chiefly generated1 the mean annual      
temperature of the surface is  usually  
below the melting-point of ice4 ,here   
the temperature of the  ice between the 
top and bottom of the zone of constant  

temperature  must1 on the average1 be   
below the melting-point1 unless heat    
enough  is generated in the interior of 
the ice to offset the effect of the     
temperature above4 ,for example1 where  
the mean annual temperature is  #bj     
,fahr4 or lower1 as in middle           
,greenland1 ,spitzbergen1 and ,franz    
,josef ,land1 and at certain high       
altitudes in more southerly latitudes1  
the mean temperature in the zone of     
constant temperature should range  from 
#bj ,fahr4 at the top to #cb ,fahr4 7or 
a little less7 below2  i4e41 it should  
average about #f below the              
melting-point4 ,under these  conditions1
 all the ice in the zone of constant    
temperature1 except  that at its bottom1
 must be permanently below the          
melting-point1 but it  is perhaps worthy
 of especial note that much of it is but
 little below4  ,in alpine glaciers the 
part of the ice affected by this        
constant low  temperature 7below        
freezing7 is presumed to be chiefly that

 which lies  beneath the snow-fields4   
,in polar glaciers the low temperature  
probably  prevails beneath the surface1 
not only throughout the great ice-caps1 
but also in the marginal glaciers which 
descend from them4    ,from these       
theoretical considerations we may deduce
 the generalization  that in the zone of
 constant temperature within the area of
 glacial  growth1 the temperature of the
 ice is generally below the             
melting-point1 while within the area of 
wastage1 the temperature of  the        
corresponding zone is generally at the  
melting-point4    ,compression and      
friction as causes of heat4--,the       
foregoing conclusions  are somewhat     
modified by dynamic sources of heat4    
,the compression  arising from gravity1 
and the friction developed where there  
is motion1  are causes of heat4 ,since  
friction occurs only when motion takes  
place1  the heat which it generates is  
secondary and may1 for present purposes1
  be neglected4 ,compression not only   

lowers the melting-point slightly1  but 
it produces heat at the point of        
compression4 ,where the ice is          
granular1 the compression1 due to       
weight1 takes place at the contacts  of 
the grains4 ,at intermediate points the 
pressure tends to cause  them to bulge1 
and this has the effect of lowering the 
temperature  of the bulging points4 ,if 
therefore the compression be            
considerable1  the granules may be      
warmed to the melting-point where they  
press each  other1 while at other points
 their temperature may be lower4 ,in    
this  case melting will take place at   
the points of compression1 and the      
moisture so produced will be transferred
 to the adjacent parts of the  granule  
and immediately refrozen4 ,melting at   
the points of compression  would result 
in some yielding of the mass1 and in    
some shifting of  the pressure to new   
points where compression and melting    
would again  take place4 ,thus the      
melting1 the refreezing1 and the        

attendant  movement might go on until   
the limits of the power of gravity in   
this  direction were reached4 ,from     
considerations already adduced1 it      
appears  that the temperature in some   
parts of every considerable body of ice 
must be such as to permit these changes4
 ,the heat due to depression  and       
friction may modify the theoretical     
deductions drawn above from  atmospheric
 and internal influences4               
,summary4--,if the foregoing            
generalizations be correct1 7#a7 the    
surface of a glacier is likely to be    
melted during the summer1 7#b7 its      
immediate bottom is slowly melting all  
the time 7unless the thickness  of the  
ice be less than the thickness of the   
zone of annual variation  or of         
permanent freezing temperature72 7#c7   
its subsurface portion in  the zone of  
waste is generally melting1 owing to    
descending water1  compression1 and     
friction2 while 7#d7 its subsurface     
portion in the  zone of growth is       

probably below the melting-point except 
as locally  brought to that temperature 
by compression1 friction1 and descending
  water1 and at the bottom by conduction
 from the rock beneath4    ,movement    
under low temperature4--,glacier motion 
will not be discussed  at this point1   
but one of the bearings of the preceding
 conclusions  on glacier motion may be  
pointed out4 ,since there must be motion
  in the area of growth to supply the   
loss in the area of waste1 the          
fundamental cause of motion must be     
operative in bodies of ice the  mean    
temperature of which is below the       
melting-point1 unless the  dynamic      
sources of heat are considerable4 ,this 
fundamental cause does  not exclude the 
coperation of causes that work only 7#a7
 at the  melting temperature1 or 7#b7   
where the ice is bathed with water1 or  
7#c7  in the plane of contact between   
wet ice above and dry ice below4 ,these 
may be auxiliary causes which abet the  
fundamental one in producing  the more  

rapid movement of warm seasons1 or in   
bringing about the  especially rapid    
movement in situations where there is   
abundant water1  or in inducing the     
shearing which is such a remarkable     
feature of  arctic glaciers4            
,evaporation4--,the ice wastes by       
evaporation as well as by melting1 and  
while the former process is far less    
important than the latter1 its  results 
are probably larger than is commonly    
apprehended4 ,one of the  most          
remarkable features of some of the      
deposits of ancient glaciers is  the    
slight evidence they afford of escaping 
waters4 ,the most plausible  explanation
 seems to lie in the supposition that   
the ice was largely  wasted by          
evaporation4 ,this conclusion finds     
support in many places  in the presence 
of a mantle of fine silt over the drift1
 the silt  being apparently composed of 
dust blown upon the ice4 ,it is supposed
  to imply aridity in the region about  
the ice4 ,if a sufficient mantle  of    

dust were spread over the border zone of
 the ice1 and if the air  were very dry1
 nearly all the water melted on the     
surface of the ice  might be held back  
by the dust-wells until the water was   
evaporated or  absorbed4                
,illustration3 ,fig4 #bea4--,spouting   
stream4 ,glacier south side of          
,olriks ,bay1 ,north ,greenland4        
,drainage4--,some of the water produced 
by surface melting forms little  streams
 on the ice4 ,sooner or later they      
plunge into crevasses or over  the sides
 and ends of the glacier4 ,in the former
 case1 they may melt  or wear out       
well-like passages 7moulins7 in the ice1
 and even in the  rock beneath4 ,much of
 the surface water sinks into the ice4  
,its ready  penetration is aided by the 
8dust-wells0 which mark the surface of  
many glaciers4 ,in north ,greenland     
wells which contain six or eight  inches
 of water at the end of a warm day are  
often dry in the morning4  ,the water   
has leaked out and passed to lower      

levels4 ,from these and  other          
harmonious observations it is inferred  
that the superficial  part of a glacier 
at least is readily penetrated by water4
 ,the depth  to which surface water     
penetrates is undetermined1 but it      
doubtless  varies greatly1 not only in  
different glaciers1 but in different    
parts  of the same glacier1 and in the  
same part at different times4 ,above    
the line of perennial snow there is     
little water either from melting  or    
from rain1 and hence relatively slight  
penetration4 ,below the line  of        
perennial snow there is much melting and
 much rain1 and here it is  probable    
that the water sometimes1 perhaps       
usually1 penetrates to the  bottom of   
the ice during the melting season1 even 
independently of  crevasses4    ,once   
within the glacier1 the course of the   
water is variable4  ,exceptionally it   
follows definite englacial channels1 as 
shown by  springs or streams issuing    
from the ice at some point above its    

bottom  7,fig4 #bea74 ,oftener it       
descends or moves forward through the   
irregular  openings which the accidents 
of motion have developed4 ,if it reaches
 a  level where the temperature is below
 its freezing-point1 it congeals4       
,otherwise it remains in cavities or    
descends to the bottom4 ,the water      
produced by melting within the glacier  
probably follows a similar  course4 ,so 
far as these waters descend to the      
bottom1 they join those  produced by    
basal melting and issue from the glacier
 with them4 ,in  alpine glaciers the    
waters beneath the ice often unite in a 
common  stream in the axis of the       
valley1 and hollow out a tunnel4 ,thus  
the  ,rhone is already a considerable   
stream where it issues from beneath the 
,rhone glacier4 ,in the glaciers of high
 latitudes1 subglacial tunnels  are less
 common and the drainage is in streams  
along the sides of the  glaciers or     
through the dbris beneath and about     
them4    ,at the end of the glacier1 all

 waters1 whether they have been         
superglacial1 englacial or subglacial1  
unite to bear away the silt1  sand1     
gravel1 and even small bowlders set free
 from the ice1 and  to spread them in   
belts along the border of the ice or in 
trains  stretching down the valleys     
below4 ,these are the most common of the
  glacio-fluvial deposits4              
,,the ,,work ,,of ,,glaciers4           
,erosion and transportation4    ,the    
work accomplished by glaciers is        
distinctive1 for while like  rivers1    
they abrade the valleys through which   
they pass1 carry forward  the material  
which they remove from the surface1 and 
wear1 grind1 and  ultimately deposit it1
 and while their work therefore includes
 erosion1  transportation1 and          
deposition1 their method is peculiar4   
,getting load4--,if the surface on which
 the snow-field which is to  become a   
glacier accumulates be rough and covered
 with abundant rock  dbris1 as such     
surfaces usually are1 the glacier       

already has a basal  load when its      
movement begins1 for the snow covers1   
surrounds1 and  includes such loose     
blocks of rock as project above the     
general surface  and envelops all       
projecting points of rock within its    
field4 ,when the  snow becomes ice and  
the ice begins to move1 it carries      
forward the  loose rock already imbedded
 in it1 and tears off the weak points of
  the enveloped rock-projections4 ,it   
may perhaps also move some of the  soil 
and mantle rock of the original surface 
to which it is frozen4 ,in  addition to 
the subglacial load which the glacier   
thus has at the  outset1 there may be a 
surface load which has fallen on the    
snow or ice  from cliffs above4 ,this is
 especially true of mountain-valley     
glaciers4  ,if this has been buried by  
snow and ice it is englacial2 if it lies
  on the surface it is superglacial4    
,once in movement1 the ice carries away 
the dbris to which it was  originally   
attached1 and at the same time gathers  

new load from the  same area4 ,the new  
load is acquired partly by the rasping  
effect of the  rock-shod ice on its bed1
 and partly by its rending power which1 
under  favorable circumstances1 may     
quarry out considerable blocks of rock4 
,this 8plucking0 process is at its best 
where the ice passes over cliffs  of    
jointed rock or steep-sloped hills4     
,as the ice advances into new territory 
it acquires additional basal  load1     
partly by rasping1 partly by plucking1  
partly by freezing to  it1 and partly in
 other ways4 ,one of these ways may be  
illustrated by  the sequence of events  
when the end of a glacier advances on a 
very  large bowlder4 ,as the ice        
approaches it1 the reflection of heat   
from  it melts the adjacent edge of the 
ice1 making a slight rentrant4 ,with    
farther advance1 the ice closes in      
against and around the bowlder1 and     
finally carries it along in the bottom  
of the moving mass4 ,in some  cases1    
especially when its advance is rapid1   

the ice may push dbris in  front of     
itself4 ,even where this is the case1   
the amount of material  pushed forward  
is generally slight1 partly because the 
extreme edge of  the ice often fails to 
rest on the land in summer1 when the    
movement  is greatest1 being melted from
 below by the heat of the surface over  
which it is spreading 7see ,fig4 #beb71 
and partly because the earth in  front  
of the glacier is frozen during a large 
part of the year4 ,in this  condition1  
the earthy matter has greater resistance
 than the ice1  and the latter rides    
over it4 ,superglacial material may be  
acquired  during movement by the fall of
 dbris from cliffs1 or by the descent of
  avalanches4    ,illustration3 ,fig4   
#beb4--;,diagram showing lack of contact
 of the edge    of the ice with its bed4
    ,conditions influencing rate of     
erosion4--,an obstructive attitude  of  
the surface toward the movement of the  
ice is as necessary for  effective      
erosion as the movement of the ice      

itself4 ,advancing over a  flat surface1
 ice ordinarily inflicts but little     
wear1 since there is  little for it to  
get hold of4 ,so slight is the abrasive 
power of ice  under these conditions    
that it frequently overrides and buries 
the soil  with more or less of its      
herbaceous vegetation4 ,but while a     
certain  measure of roughness of surface
 is favorable for glacial erosion1 the  
topography may be so uneven as to       
seriously impede the ice4 ,erosion  is  
probably at its maximum1 so far as      
influenced by topography1 when  the     
roughness of the surface is such as to  
offer notable catchment for  the basal  
ice1 but not such as to impede its      
motion very seriously4  ,the amount of  
relief favorable for the greatest       
erosion increases with  increasing      
thickness of the ice4    ,other         
conditions which influence erosion by   
ice are 7#a7 the amount of  loose or    
slightly attached dbris on the surface1 
7#b7 the resistance of  the rock1 7#c7  

the slope of the surface1 7#d7 the      
thickness of the ice1  7#e7 the rate of 
movement1 and 7#f7 the abundance and    
character of the  dbris which the ice   
has to work with4 ,the effect of the    
first five of  these conditions is      
evident4 ,the effect of the last is less
 simple4  ,clean ice passing over a     
smooth surface of solid rock has little 
effect  upon it2 but a rock-shod glacier
 will abrade the same surface notably4  
,the effect of this abrasion is shown in
 the grooves and scratches  7stri7 which
 the stones in the bottom of the ice    
inflict on the  surface of the rock over
 which they pass 7,figs4 #bec1 #bee1 and
 #bef74  ,at the same time the stones in
 the ice are themselves worn both by    
abrasion with the bottom1 and with one  
another 7,fig4 #bed74 ,it does not      
follow1 however1 that the more material 
in the bottom of the ice the  greater   
the erosion it effects2 for with        
increase of dbris there may  be decrease
 of motion#aca and1 beyond a certain    

point1 the decrease  of motion seriously
 interferes with the efficiency of      
erosion4 ,when any  considerable        
thickness of ice at the bottom of the   
glacier is full of  dbris1 this loaded  
basal portion may approach stagnancy1   
and the lower  limit of considerable    
movement may lie between the loaded ice 
below  and the relatively clean ice     
above4 ,a moderate1 but not an excessive
  load of dbris is1 therefore1 favorable
 for great erosion4 ,something  depends1
 too1 on the character of the load4     
,coarse1 hard1 and angular  dbris is a  
more effective instrument of erosion    
than fine1 soft1 or  rounded material4  
,the adverse influence of the           
overloading of the ice  on its motion   
has been likened to the stiffening of a 
viscous liquid by  the addition of      
foreign matter1 but it may better       
perhaps be referred  to the destruction 
of the granular-crystalline continuity  
on which  glacier motion probably       
depends4    ,illustration3 ,fig4        

#bec4--;,glacial stri and bruises4 ,the 
block to the    right shows two sets of 
stri3 that to the left shows the        
peculiar    curved fractures known as   
,chatter ,marks4    ,illustration3 ,fig4
 #bed4--;,bowlders showing glacial      
striation4 7,drawn    by ,miss ,matz47  
,illustration3 ,fig4 #bee4--,stri on bed
 rock1 ,kingston1 ,des ,moines ,co41    
,ia4 7,iowa ,geol4 ,surv47    ,from the 
preceding statement1 it is evident that 
erosion is not equally  effective at all
 points beneath a glacier4 ,so far as   
concerns the ice  itself1 erosion is not
 most effective at the end of a valley  
glacier1  or at the edge of an ice      
sheet1 for here the strength of movement
 is  too slight and the load too great2 
nor is the most effective erosion  at   
the source or near it1 for though the   
ice may here be thick1 the  movement is 
slow and the load likely to be slight4  
,ice conditions only  being considered1 
erosion is most effective somewhere     
between the  source and the terminus1   

and probably much nearer the latter than
 the  former4 ,the conditions of the    
surface over which the ice passes may   
be such as to vary the place of greatest
 erosion widely4 ,thus in an  ,alpine   
glacier1 erosion may be most effective  
at the ,bergschrund  because the slope  
here favors 8plucking40 ,here1 notable  
amphitheatres  7cirques7 are sometimes  
excavated4 ,after the glacier           
disappears1  the bottom of the cirque is
 often seen to contain rock basins      
7,fig4  #beg74 ,glacial cirques abound  
in mountains where glaciers once        
existed1  but from which they have now  
disappeared4 ,the cirques of the        
,bighorn  mountains of ,wyoming 7,pl4   
,,xix7 are examples4    ,illustration3  
,fig4 #bef4--,stri1 grooves1 etc41 in a 
canyon tributary    to ,big ,cottonwood 
,canyon1 ,wasatch ,mountains4 7,church47
    ,summary4--,in summary it may be    
said that rapidly moving ice of         
sufficient thickness to be working under
 goodly pressure1 shod with  a          

sufficient but not excessive quantity of
 hard-rock material1  passing over      
incoherent or soft formations possessing
 a topography  of sufficient relief to  
offer some resistance1 and yet too      
little to  retard seriously the progress
 of the ice1 will erode most            
effectively4    ,varied nature of       
glacial dbris4--,from its mode of       
erosion it will  readily be seen that   
the bottom of a glacier may be charged  
with  various sorts of material4 ,there 
may be 7#a7 bowlders which the ice has  
picked up from the surface1 or which it 
has broken off from projecting  points  
of rock over which it has passed2 7#b7  
smaller pieces of rock  of the size of  
cobbles1 pebbles1 etc41 either picked up
 by the ice  from its bed or broken off 
from larger masses2 7#c7 the fine       
products  7rock-flour7 produced by the  
grinding of the dbris in the ice on the 
rock-bed over which it passes1 and      
similar products resulting from the     
rubbing of stones in the ice against one

 another2 and 7#d7 sand1 clay1  soil1   
vegetation1 etc41 derived from the      
surface overridden4 ,thus  the materials
 which the ice carries 7drift7 are of   
all grades of  coarseness and fineness1 
from large bowlders to fine clay4 ,the  
coarser  material may be angular or     
round at the outset1 and its form may be
  changed and its surface striated as it
 is moved forward4 ,whether one  sort of
 material or another predominates1      
depends primarily on the  nature of the 
surface overridden4    ,illustration3   
,,plate ,,xix4      ,,part ,,of ,,the   
,,bighorn ,,mountain ,,range1 ,,wyoming4
    ,u4 ,s4 ,geol4 ,surv4               
,illustration3 ,,plate ,,xx4      ,a    
,,section ,,of ,,the ,,california       
,,coast ,,near ,,san ,,mateo1           
,,california4    ,u4 ,s4 ,geol4 ,surv4  
,illustration3 ,fig4 #beg4--;,a glacial 
cirque4 ,the lake occupies a rock       
basin1 produced by glacier erosion4     
,head of ,little ,timber ,creek1        
,montana4    ,the topographic effects of

 glacial erosion4--,in passing through  
its  valley1 an alpine glacier deepens  
and widens its bottom and smooths  its  
slopes up to the upper limit of the ice4
 ,it tends to change a  ,v-shaped valley
 7,fig4 #beh7 into a ,u-shaped one      
7,fig4 #bei74 ,the change  in topography
 at the upper limit of glaciation is    
often marked 7,figs4  #bfj and #bfa74   
,illustration3 ,fig4 #beh4--,the ,valley
 of the ,american ,fork4 ,a ,v-shaped   
non-glaciated valley in the ,wasatch    
,mountains of ,utah4 ,compare ,fig4     
#bei4 7,church47    ,illustration3 ,fig4
 #bei4--,u-shaped valley resulting from 
glaciation4    ,little ,cottonwood      
,canyon1 ,wasatch ,mountains4 7,church47
    ,illustration3 ,fig4                
#bfj4--;,contrast between glaciated     
topography below    and non-glaciated   
topography above4 ,the minarets in the  
,sierras1 ,cal4    ,illustration3 ,fig4 
#bfa4--;,contrast between glaciated     
topography below1    and non-glaciated  
topography above4 ,needles ,mountains1  

from slope    west of ,hidden ,lake4    
7,cross1 ,u4 ,s4 ,geol4 ,surv47    ,the 
deepening of a valley by glacial erosion
 may throw its tributaries  out of      
topographic adjustment4 ,thus if a main 
valley is lowered #ajj  feet by glacial 
erosion while its tributary is not      
deepened1 the  lower end of the latter  
will be #ajj feet above the former when 
the  ice disappears4 ,such a valley is  
called a hanging valley 7,figs4 #bfb    
and #bfc74 ,such valleys are of common  
occurrence in regions recently          
glaciated1 but now ice-free4 ,examples  
are common in the western  mountains of 
,north ,america and elsewhere4          
,ice-caps which overspread the surface  
irrespective of valleys and  hills1 tend
 to reduce the angularities of the      
surface4 ,hills and ridges  are cut down
 and smoothed 7,figs4 #bfd and #bfe72   
but since valleys  parallel to the      
direction of movement are deepened at   
the same time1  it is doubtful if the   
relief of the surface is commonly       

reduced by the  erosion of an ice-cap4  
,illustration3 ,fig4 #bfb4--;,a hanging 
valley4 ,east side of ,lake             
,kootenai1 ,b4 ,c4 ,all except the      
highest summits glaciated4 7,atwood47   
,fiords4--,a glacier descending into the
 head of a narrow bay may gouge  out the
 bay to a very considerable depth1      
causing its head to recede4  ,when the  
ice finally melts1 the bay may be a     
fiord4 ,thus have arisen  the glacial   
features of many of the fiords of       
high-latitude coasts1 and  many of the  
glaciers of those coasts are now making 
fiords 7,fig4 #bff74  ,fiords also arise
 in other ways4 ,coasts indented by     
fiords are likely  to be bordered by    
islands4    ,the positions in which     
dbris is carried4--,as a result of the  
methods  by which a glacier becomes     
loaded1 there are three positions in    
which  the dbris is carried3 7#a7 the   
basal or subglacial1 7#b7 the englacial1
  and 7#c7 the superglacial4 ,the       
material picked up or rubbed off from   

the surface over which the ice moves is 
normally carried forward in  the base of
 the ice2 while that which falls on the 
surface is usually  carried in the form 
of surface moraines4 ,in the former     
position the  drift is basal2 in the    
latter1 superglacial4 ,it is doubtful if
 much  dbris is moved along beneath     
7that is1 strictly below the bottom of7 
the ice1 though the movement of the     
latter would have a tendency to  drag or
 urge along with it the loose material  
of its bed4 ,if drift were  carried     
forward in such positions1 it would be  
strictly subglacial4    ,illustration3  
,fig4 #bfc4--;,a hanging valley4 ,the   
water falls 7,bridal    ,veil7 from a   
hanging valley4 7,wineman47    ,the     
basal load of a glacier is constantly   
being mixed with new  accessions derived
 from ground over which the ice is      
passing1 and  this admixture tells the  
story of the work done by the bottom of 
the  ice4 ,the englacial and            
superglacial material1 on the other     

hand1 is  normally borne from the place 
of origin to the place of deposition    
without such intermixture4 ,it is a case
 of 8local0 versus 8through0            
transportation4    ,transfers of        
load4--,while the origin of the load    
usually determines  its position1       
exceptions and complications arise from 
the transfer  of load from one position 
to another1 and from the gradation of   
one  horizon into another4              
,illustration3 ,fig4 #bfd4--;,a         
non-glaciated hill4 ,dalrymple ,island4 
,north ,greenland4    ,illustration3    
,fig4 #bfe4--;,a glaciated hill4        
,southeastern ,carey ,island4    ,about 
#cj miles west-northwest of ,dalrymple  
,island4    ,most of the dbris gathered 
by ice is acquired at its bottom4 ,while
  such material is basal at the outset1 
some of it may find itself  above the   
bottom a little later4 ,thus when ice   
passes over a hill 7,fig4  #bfg7 the    
bottom of the ice rends dbris from the  
top of the hill4 ,when  it descends from

 one level to another there is a similar
 result 7,fig4  #bfh74 ,to the lee of   
the hill the ice from either side may   
close in  under that which came over the
 top1 in which case the dbris derived   
from the top of the hill by the bottom  
of the overriding ice will be  well up  
in the ice4 ,it has passed from an      
initial basal to a subsequent  englacial
 position4 ,the change does not usually 
involve an actual rise  of the material1
 but rather a decline4 ,if carried      
upward at all1 the  upward movement is  
temporary only1 and incident to the     
passage of the  ice over the hill1 or to
 other local causes4 ,the englacial     
dbris may  be little or much above the  
basal zone according to the height of   
the  elevation overridden4              
,illustration3 ,fig4 #bff4--;,alaskan   
fiords4 ,the shaded areas represent     
land4 7,from charts of the ,c4  ,g4     
,surv47    ,illustration3 ,fig4         
#bfg4--;,diagram to illustrate the      
taking of dbris    from a hill-top4 ,it 

also illustrates how englacial dbris may
 become    superglacial as the result of
 surface ablation4    ,illustration3    
,fig4 #bfh4--,taking dbris from a       
protuberance of the    bed4             
,superglacial dbris may obviously become
 englacial by falling into  crevasses or
 by being carried down by descending    
waters4 ,either  superglacial or        
englacial dbris may become basal by the 
same means4    ,from their form and     
position1 there is less ice-free land in
 immediate  association with ice-caps   
than with valley glaciers4 ,furthermore1
 the  ice-free land about the borders of
 an ice-cap is less likely to be in  the
 form of cliffs above it4 ,as a result1 
the surfaces of ice-caps are            
comparatively clean1 except at their    
edges where the ice is thin4            
,illustration3 ,fig4 #bfi4--,side view  
of end of a glacier on the south    side
 of ,olriks ,bay1 ,north ,greenland4    
,illustration3 ,fig4 #bgj4--;,closer    
view of a part of the ice shown in      

,fig4 #bfi4    ,englacial material may  
become superglacial by surface ablation4
 ,in this  case the drift does not rise1
 but melting brings the surface of the  
ice  down to its level4 ,this occurs    
chiefly at the end or edge of the ice1  
where the surface melting is greatest4  
,englacial dbris1 especially  that near 
the bottom1 may also become basal by the
 melting of the  bottom of the ice4     
,englacial material plucked or rasped   
from an elevation over which the  ice   
has passed is liable to be disposed in a
 longitudinal belt in  the ice in the   
lee of the elevation itself4 ,by surface
 ablation this  material may reach the  
surface at some point below its source1 
and  be disposed as a medial moraine4   
,such a moraine has an origin very      
different from that of a medial moraine 
formed by the junction of two  lateral  
moraines of superglacial origin4        
,much less in the natural order of      
things is the transfer of material  from
 a basal to an englacial and from an    

englacial to a superglacial  position by
 upward movement of the dbris itself4   
,such transfer is  remarkable because   
the specific gravity of rock is from two
 and a half  to three times as great as 
that of ice1 so that its normal tendency
 is  to sink4    ,illustration3 ,fig4   
#bga4--,surface terminal moraines due to
 upturning4    ,edge of the ice-sheet1  
,north ,greenland4    ,in arctic        
glaciers1 and probably in others1 some  
material which has  been basal becomes  
englacial by being sheared forward over 
ice in front  of it4 ,so far as observed
 this takes place chiefly where the ice 
in  front of the plane of shearing lies 
at a lower level than that behind1  as  
where the surface of an upland falls off
 into a valley1 or where  a boss of rock
 shelters the ice in its lee from the   
thrust of the  overriding ice 7,fig4    
#bfh74    ,illustration3 ,fig4          
#bgb4--;,diagram illustrating the       
upturning of the  layers of ice at the  
end of an arctic glacier as seen in     

end-section4  ,the bottom line          
represents sea level4    ,at the borders
 of arctic glaciers the lower layers are
 not infrequently  upturned1 as shown in
 ,figs4 #bfi to #bgb4 ,where the layers 
turn up at  the end of a glacier 7,figs4
 #bfi and #bgj71 basal and englacial    
dbris  is carried to the surface by     
actual upward movement1 and a terminal  
moraine or a series of terminal moraines
 sometimes aggregated where  the        
upturned layers of ice outcrop at the   
surface 7,fig4 #bga74 ,that  the        
material of these moraines was          
originally basal is abundantly          
demonstrated by the bruised and         
scratched condition of the bowlders  and
 pebbles1 and sometimes by the nature of
 the material itself4 ,for  example1 in 
two cases in ,north ,greenland where    
glaciers descend into  the heads of     
shallow bays and move forward on their  
bottoms1 moraines  formed by the        
upturning of the layers were seen to    
contain abundant  molluscan shells      

derived from the bottom of the bay4 ,the
 upturning  sometimes affects the       
side-edges of ice-tongues 7,fig4 #bgb7  
as well as  their ends1 and the material
 thus brought to the surface gives      
origin  to lateral moraines altogether  
different in origin from the lateral    
moraines formed by the falling of dbris 
upon the glaciers4 ,sometimes  also     
there is an upturning of the ice along a
 longitudinal zone well  back from the  
lateral margins 7,fig4 #bgc71 and the   
material so borne  to the surface in    
such a zone gives rise to a moraine     
resembling the  medial moraine formed by
 the union of lateral moraines1 but of  
wholly  different origin4               
,illustration3 ,fig4 #bgc4--;,diagram   
illustrating the same point as #bgb1    
where the structure is more complex4    
,the bottom line of the figure          
represents sea level4    ,the phenomenon
 of upturning here referred to has been 
observed only at  or near the terminus  
of the ice1 and is perhaps due in most  

part to the  resistance of frozen       
morainic or other material beneath and  
in front of  the edge4 ,to this should  
probably be added the effect of the     
increased  rigidity of the ice at its   
borders1 due to the low external        
temperature  during the larger part of  
the year1 while the interior1 with its  
higher temperature1 remains more fluent4
 ,but even this probably leaves  the    
explanation inadequate4 ,in not a few   
instances the upturning is  associated  
with a notable thickening of the layers 
toward their  edges 7,fig4 #bgd74 ,this 
suggests that perhaps there is an       
exceptional  growth of the granular     
crystals of the ice near the edge of the
  layers1 owing to the penetration of   
the surface-waters which are much  more 
abundant at the borders than elsewhere1 
and which in the arctic  glaciers       
probably do not penetrate deeply before 
they reach a freezing  temperature4     
,wear of drift in transit4--,drift      
carried at the bottom of the ice is     

subject to notable wear4 ,the materials 
in transportation abrade one  another   
and are abraded by the bed over which   
they pass4 ,englacial  drift is subject 
to less wear because it is commonly more
 scattered4  ,superglacial drift is worn
 little or none while it lies on the    
surface  of the ice2 but in so far as   
superglacial or englacial drift is      
derived  from the basal load1 it may    
show the same evidences of wear as the  
basal drift itself4 ,superglacial drift 
often reveals its history in  this way4 
,illustration3 ,fig4 #bgd4--,thickening 
of the upturned layers of ice4          
,deposition of the ,drift4    #a4       
,beneath the body of the ice4--,during  
the advance of a glacier1  deposition   
may take place both beneath the body of 
the ice and beneath  its end and edges4 
,deposition beneath the body of the ice 
is liable to  take place wherever the   
topography favors lodgment1 or wherever 
the ice  is overloaded4 ,the topography 
favoring deposition is much the same as 

that favoring erosion1 but the two      
processes are not favored at the  same  
point4 ,erosion is greatest on the      
8stoss0 side of an obstruction  7the    
side against which the ice advances71   
and deposition on the lee  side4 ,the   
ice is likely to be overloaded 7#a7 just
 beyond a place where  conditions have  
favored the gathering of a heavy load1  
and 7#b7 where  the ice is rapidly      
thinning4 ,on the whole1 however1 the   
deposition of  material beneath the main
 body of a glacier is much more than    
balanced  by erosion in the same        
position4    ,illustration3 ,fig4       
#bge4--;,glacier building an embankment4
 ,southeast    side of ,mc,cormick ,bay1
 ,north ,greenland4    #b4 ,at ends and 
edges of glaciers4--,at and near the end
 of a glacier  the conditions of        
deposition are somewhat different4 ,here
 deposition  beneath the ice goes on    
faster than elsewhere1 chiefly because  
of the  more rapid melting and the more 
rapid thinning and weakening of the     

ice4 ,if the end of the glacier be      
stationary in position1 drift is  being 
continually brought to it and left      
there1 for though the end is            
stationary1 the ice continues to move4  
,if the glacier moves forward  #ejj feet
 per year1 and if its end is melted at  
the same rate1 all the  dbris in the    
#ejj feet of ice which has been melted  
has been deposited1  and all except that
 which has been washed away has been    
deposited  at and beneath the end of the
 glacier4 ,if the end of the glacier  is
 retreating1 the retreat means that the 
waste at the end exceeds  the forward   
movement4 ,if the ice advances #cjj feet
 per year1 and is  melted back #ejj feet
 in the same time1 all the dbris carried
 by the  #ejj feet which has been melted
 has been deposited1 and largely in the 
narrow zone 7#bjj feet7 from which the  
ice has receded4 ,even in this  case1   
therefore1 there is a notable tendency  
to marginal accumulation4  ,if the end  
of the glacier is advancing #ejj feet   

per year while it is  being melted but  
#cjj feet1 all the drift in the #cjj    
feet melted has  been deposited1 and    
chiefly at or beneath the immediate     
margin of the  ice4 ,to the marginal and
 sub-marginal accumulations made in this
 way1  the material carried on the ice  
is added whenever the ice is melted     
from beneath it4 ,this addition is      
sometimes considerable and sometimes    
meagre4 ,if the edge of the ice is      
without much fluctuation in position1   
the material dumped over its end may    
take the form of a narrow ridge or      
bowlder-wall 7,geschiebe-wall74 ,if a   
glacier pushes material in front  of it1
 this1 too1 becomes a part of the       
general terminal aggregation of  drift4 
,illustration3 ,fig4 #bgf4--;,embankment
 completed4 ,near the last4             
,,types ,,of ,,moraines4    ,the        
terminal moraine4--,the thick           
accumulation of drift made at the  end  
of a glacier or at the edge of an ice   
sheet1 especially where its  end or edge

 is stationary1 or nearly stationary1   
for a considerable  time1 is the        
terminal moraine4 ,that part of the     
aggregation deposited  beneath the ice  
is sometimes called the lodge moraine   
7,figs4 #bge and  #bgf2 see also ,fig4  
#bce72 that carried on the ice and      
dropped at its  edge1 the dump moraine2 
and that pushed before the ice1 the push
  moraine4 ,many moraines marginal to   
the ice appear to be push moraines1     
when they are really lodge moraines from
 which the ice has withdrawn  7,fig4    
#bgg74 ,the push moraine can rarely be  
distinguished1 and the dump  moraine by 
no means always1 after the disappearance
 of the ice4    ,illustration3 ,fig4    
#bgg4--;,end of a glacier a few miles   
west of  ,kaslo on ,lake ,kootenai1 ,b4 
,c4 ,a lodge moraine from which the ice 
has  withdrawn1 giving it the appearance
 of a push moraine4 ,it is possible     
that the lodge moraine material has been
 pushed up a little by  re-advance of   
the ice4 7,atwood47    ,the ground      

moraine4--,when a glacier disappears by 
melting1 all its  dbris is deposited4   
,all the drift deposited beneath the    
advancing  ice and all deposited from   
the base of the ice during its          
dissolution  constitutes the ground     
moraine4 ,the thickness of the ground   
moraine  is notably unequal4 ,in        
general1 it is thicker toward the       
terminus of  the glacier and thinner    
toward its source1 but considerable     
portions of  a glacier's bed are often  
left without dbris when the ice melts4  
,in  general1 the terminal moraine is   
not only thicker1 but more irregularly  
disposed than the ground moraine4       
,the lateral moraines4--,the surface    
lateral moraines of valley glaciers  are
 let down on the surface beneath when   
the ice melts out from under  them2 but 
the lateral moraines in a valley from   
which the ice has  melted are not merely
 the lateral moraines which were on the 
glacier  at a given time4 ,they are     
often far more massive than any which   

ever  existed on the ice itself at any  
one time 7,fig4 #bgh74 ,as a glacier    
retreats1 its lateral moraine material  
is more or less bunched4 ,thus if  the  
ice advances #bjj feet while its end is 
being melted back #cjj feet1  the       
lateral moraines on the #cjj feet melted
 are concentrated into #ajj  feet1 as   
they are delivered on to the land by the
 melting of the ice  from beneath4 ,if  
the retreat of the end of a glacier be  
very slow1 the  bunching may be great4  
,but even this cannot explain the       
massiveness of  some lateral moraines4  
,furthermore1 the materials of which    
many lateral  moraines are composed are 
nearly as well worn as those of the     
ground  moraine4 ,the massive lateral   
moraines of which this is true are often
  made up chiefly of the drift          
accumulated beneath the lateral margins 
of the glaciers4 ,this accumulation is  
the result of the lateral motion  of the
 ice from center to side4 ,such         
sublateral accumulations are akin  to   

terminal moraines4 ,some of the lateral 
moraines of ancient valley  glaciers1   
such as those of the ,uinta1 ,wasatch1  
and ,bighorn mountains  are several     
hundred feet high1 and in one case about
 #ajjj feet4 ,in  northern ,italy       
lateral moraines are said to be #aejj to
 #bjjj feet  high4#acb    ,illustration3
 ,fig4 #bgh4--;,a lateral moraine from  
which the ice has    retreated4 ,bighorn
 ,mountains1 ,wyo4 7,blackwelder47      
,illustration3 ,fig4 #bgi4--;,glacial   
drift1 coarse and fine together4        
7,geol4 ,surv4 of ,n4 ,j47    ,most of  
the material which was englacial during 
the transportation  becomes either      
subglacial or superglacial before       
deposition1 for it  ordinarily reaches  
the bottom or the top of the ice before 
being  deposited4 ,where the ends or    
edges of a glacier are vertical or      
nearly  so1 as in the high arctic       
regions1 deposition may take place from 
the  englacial position directly4       
,distinctive nature of glacial          

deposits4--,the deposits made by        
glaciers are distinctive4 ,in the first 
place the ice does not assort  its      
material1 and bowlders1 cobbles1        
pebbles1 sand1 and clay are  confusedly 
commingled 7,fig4 #bgi74 ,in this       
respect1 the deposits of ice  differ    
notably from those of water4            
,furthermore1 many stones of the  drift 
show the peculiar type of wear which    
glaciers inflict4 ,they are  not rounded
 as the stones carried by rivers1 though
 they are notably  worn4 ,many of them  
have subangular forms with planed and   
beveled  faces1 the planes being        
striated and bruised 7,fig4 #bed74 ,the 
absence  of stratification1 the physical
 heterogeneity1 and the striation  of at
 least a part of the stones are among   
the most distinctive  characteristics of
 glacial drift4 ,a not less real though 
less obvious  characteristic is the     
constitution of the fine material1 for  
it is in  general not the product of    
rock decay1 but of rock grinding4 ,the  

fine  material handled by streams       
7except glacial streams7 on the other   
hand1  is usually the product of rock   
decay4    ,illustration3 ,fig4          
#bhj4--,roche moutonne1 ,victoria       
,harbor1 ,b4 ,c4    ,glaciated rock     
surfaces4--,another distinctive mark    
which a glacier  leaves behind it is the
 character of the surface of the rock on
 which  the drift rests4 ,this is       
generally smoothed by the severe        
abrasion to  which it has been          
subjected1 and the smoothed surfaces are
 marked by  grooves and stri1 similar to
 those on the stones of the drift       
7,figs4  #bee and #bef74 ,other         
distinctive features of a glaciated area
 are the  rounded bosses of rock 7roches
 moutonnes1 ,fig4 #bhj2 see also surface
  about the lakes1 ,fig4 #bfa71 the rock
 basins1 the lakes 7,fig4 #bfa71  ponds1
 and marshes1 and the peculiar          
topographies resulting from the  unequal
 erosion1 and the still more unequal    
deposition of the drift4  ,surface      

bowlders1 often unlike the underlying   
formations of rock1 and  sometimes in   
peculiar and apparently unstable        
positions1 are still  another mark of a 
glaciated area4                         
,,glacio-,,fluvial ,,work4    ,the      
constant but unequal waste of glaciers  
has already been referred  to4 ,the     
streams to which this gives rise are    
usually laden with  gravel1 sand and    
silt derived from the ice4 ,since the   
mud is often  light-colored1 the streams
 are sometimes described as 8milky40    
,where  the amount of material carried  
is great1 much of it is dropped at  a   
slight distance from the ice1 the       
coarsest being dropped first4  ,glacial 
streams are1 as a rule1 aggrading       
streams1 and therefore  develop alluvial
 plains1 called valley trains 7,fig4    
#bha and #bhb71  or where they enter    
lakes 7,fig4 #bhc71 bays1 or other      
streams1 deltas4  ,in its               
transportation1 the river-borne drift is
 assorted2 after its  deposition1 it is 

stratified4 ,true glacial deposits in   
the upper  part of a mountain valley    
are1 therefore1 often continued below by
  glacio-fluvial deposits derived from  
the same source4    ,illustration3 ,fig4
 #bha4--;,alluviation by glacial stream3
 ,nicolai    ,creek1 ,alaska4           
7,schrader1 ,u4 ,s4 ,geol4 ,surv47      
,the most common form of such deposit is
 a valley train 7,fig4 #bha7 of  glacial
 wash stretching indefinitely down the  
valley4 ,the silt1 sand1  and gravel of 
such trains can usually be distinguished
 from valley  deposits of non-glacial   
origin by the character of the material1
 as  much of it is the product of       
grinding1 crushing1 and fracture1 rather
  than of ordinary surface decay4 ,its  
materials are1 therefore1 fresh  and    
often include rock material which1 if   
long exposed at the surface1  would be  
decomposed or dissolved4                
,illustration3 ,fig4                    
#bhb4--;,alluviation by glacial stream  
below ,hidden    glacier1 ,alaska4      

7,gilbert1 ,u4 ,s4 ,geol4 ,surv47       
,where an ice sheet ends in a broad     
face1 as did the ancient continental    
glaciers1 numerous streams flow from it 
and spread their dbris in  front of the 
terminal moraine1 forming a broad       
fringing sheet or  8apron0 7outwash     
plain7 along it4 ,where streams of      
considerable size  form tunnels under or
 in the ice1 these may become more or   
less filled  with wash1 and when the ice
 melts the aggraded channels appear as  
long  ridges of gravel and sand known as
 eskers 7osars and serpentine  kames and
 kames of authors4 ,see chapter on      
glacial period74 ,it has  been thought  
that similar ridges are sometimes formed
 in valleys cut  in the ice from top to 
bottom1 and even that they arise from   
gravel  and sand lodged in superglacial 
channels4 ,the latter at least is       
probably rare1 as the surface streams   
usually have high gradients1  swift     
currents1 and smooth bottoms1 and hence 
give little opportunity  for lodgment4  

,in the case of ice-sheets1 too1 in     
connection with which  eskers are       
chiefly developed1 there is usually no  
surface material  except at the         
immediate edge1 where the ice is thin   
and its layers  upturned4    ,at the    
mouths of ice-tunnels or ice-channels1  
especially where they  end against      
terminal moraines1 sands and gravels are
 liable to be  bunched in quantity1     
giving rise1 after the adjacent ice has 
melted1  to peculiar hills and hollows  
of the knob-and-basin type4 ,the hills  
and short ridges are known as kames 7see
 glacial period74 ,subglacial  streams  
may leave washed and assorted material  
in their tracks under  the ice1 and this
 is sometimes buried under deposits made
 by the ice  itself1 so that            
glacio-fluvial and glacial deposits are 
interbedded4    ,illustration3 ,fig4    
#bhc4--;,delta at ,isola1 ,lake of      
,sils1 ,engadine1    ,switzerland4      
7,reid47                                
,,icebergs4    ,when glaciers advance   

into water1 the depth of which          
approaches their  thickness1 their ends 
are broken off 7,fig4 #bhd71 and the    
detached  masses float away as icebergs 
7,fig4 #bhe74 ,many of the bergs are    
overturned1 or at least tilted1 as they 
set sail4 ,if this does not  happen at  
the outset1 it is likely to occur later 
as the result of the  melting and       
wave-cutting which disturb their        
equilibrium4 ,the great  majority of    
bergs do not travel far before losing   
all trace of stony  and earthy dbris1   
but the finding of glacial material in  
dredgings far  south of all glaciers    
shows that they occasionally carry      
stones far  from land4    ,illustration3
 ,fig4 #bhd4--;,end of ,muir glacier1   
,alaska4 7,reid47               ,,the   
,,intimate ,,structure ,,and ,,the      
,,movement ,,of ,,glaciers4    ,with the
 preceding account of glaciers in mind1 
we may return to a  closer study of     
their origin1 their intimate structure1 
and their mode  of motion4 ,the key to  

this study is the thesis that a glacier 
is a mass  of crystalline rock--the     
purest and simplest type of crystalline 
rock  known--since it is made up of a   
single mineral of simple composition    
and rare purity1 which never appears in 
a solid state except in the  crystalline
 form4    ,the growth and constitution  
of a glacier4--,the origin and history  
of a glacier is little more than the    
origin and aggregate history of  the    
crystals that compose it4 ,the          
fundamental conception of a glacier  is 
therefore best obtained by tracing the  
growth of its constituent  crystals4 ,a 
basal fact ever to be kept in mind is   
that water in  the solid form is always 
controlled by crystalline forces4 ,when 
it  solidifies from the vapor of the    
atmosphere it takes the form of         
separate crystals 7,figs4 #bhf-bia74    
,perfect forms are developed only  when 
the flakes fall quietly through a       
saturated atmosphere which  allows them 
to grow as they descend4 ,under other   

conditions1 the  crystals are imperfect 
in growth and are mutilated by impact4  
,but  however modified1 they are always 
crystals4 ,the molecules are arranged   
on the hexagonal plan1 and1 as the      
expansive power of freezing water       
shows1 the arrangement is controlled by 
a strong force4 ,once the  definite     
crystalline arrangement is established1 
the molecules can be  displaced only by 
relatively great force4                 
,illustration3 ,fig4 #bhe4--;,an        
iceberg1 west coast of ,greenland4      
,snow crystals often continue to grow so
 long as they are in the  atmosphere2   
but if they pass through an             
under-saturated stratum of  air or a    
stratum whose temperature is above #cb  
,fahr41 they suffer  from evaporation or
 melting4 ,when they reach the ground1  
the processes  of growth and decadence  
continue1 and the crystals grow or      
diminish  according to circumstances4   
,a glacier is a colossal aggregation of 
crystals grown from snowflakes  to      

granules of much greater sizes4 ,the    
microscopic study of new-fallen  snow   
reveals the mode of change from flakes  
to granules4 ,the slender  points and   
angles of the former yield to melting   
and evaporation more  than the more     
massive central portions1 and this      
change probably  illustrates a law of   
vital importance4 ,it may often be seen 
that the  water melted from the         
periphery of a flake gathers about its  
center1  and if the temperature be      
right1 it freezes there4 ,this is a     
first  step toward the pronounced       
granulation of snow which has lain for  
some  time on the ground4 ,if measured  
systematically from day to day1 the     
larger granules taken from beneath the  
surface of this coarse-grained  snow are
 found to be growing4 ,in a series of   
experiments#acc to  determine the law of
 growth it was found that when the      
temperature of  the atmosphere was above
 the melting-point the growth was       
appreciably  more rapid than when the   

air was colder1 but there was1 on the   
average1  an increase under all         
conditions of temperature4 ,a portion of
 this  average increase of the larger   
granules appears to come from the       
diminution and destruction of the       
smaller ones1 for the total number  of  
granules steadily diminishes4 ,a portion
 of the growth doubtless  comes from the
 moisture of the atmosphere which       
penetrates the snow  and another portion
 from the moisture derived from surface 
melting2  but beneath the surface of a  
large body of snow the growth of the    
large granules is probably chiefly at   
the expense of the small ones4  ,to     
follow the process it should be noted   
that the free surface of  every granule 
is constantly throwing off particles of 
water-vapor  7evaporation72 that the    
rate at which the particles are thrown  
off is  dependent1 among other things1  
on the curvature of the surface1 being  
greater the sharper the curve2 that the 
surfaces of the granules are  at the    

same time liable to receive and retain  
molecules thrown from  other granules1  
and that1 other things being equal1 the 
retention  of particles also depends on 
the curvature of the surface1 the less  
curved surface retaining more than the  
sharply curved one4 ,under these  laws1 
it is obvious that the larger granules  
of smaller curvature will  lose less and
 gain more1 on the average1 than the    
smaller granules of  greater curvature4 
,it follows that the larger granules    
will grow at the  expense of the        
smaller4 ,it is also to be noted that1  
other things being  equal1 small        
granules melt more readily than large   
ones1 and that where  the temperature is
 nicely adjusted between melting and    
freezing1 the  smaller may lose while   
the larger gain4    ,illustration3      
,figs4 #bhf-ia4--,snowflakes4           
7,photographed by ,w4 ,a4    ,bentley47 
,another factor that enters into the    
process is that of pressure and         
tension4 ,the granules are compressed at

 the points of contact and put  under   
tension at points not in contact1 and   
the pressure and tension  are1 on the   
average1 likely to be relatively        
greatest for the smallest  granules4    
,tension increases the tendency to      
evaporation and adds its  effects to    
curvature1 and the capillary spaces     
adjoining the points  of contact        
probably favor condensation4 ,ice       
expands in crystallizing  and pressure  
reduces the melting-point1 while tension
 raises it4 ,the  effect of this is     
slight 7p4 #bgf71 and it probably plays 
little part in  glacial action1 but it  
is to be correlated with the much more  
important  fact that compression        
produces heat which may raise the       
temperature  of the ice to the          
melting-point1 while tension may reduce 
the  temperature to or below freezing4  
,there is therefore a tendency for the  
ice to melt at the points of contact and
 compression1 and for the water  so     
produced to refreeze at adjacent points 

where the surface is under  tension4    
,this process becomes effective beneath 
a considerable body of  snow1 and here  
the granules gradually lose the         
spheroidal form assumed  in the early   
stages of granulation and become        
irregular polyhedrons  interlocked into 
a more or less solid mass4    ,a third  
factor is also to be recognized1 though 
its effectiveness is  unknown4 ,under   
severe wind pressure1 air penetrates    
porous bodies  with appreciable         
facility4 ,the 8breathing0 of soils and 
the curious  phenomena of               
8blowing-wells0 and 8blowing-caves0     
teach us of the  effective penetration  
and extrusion of the air under          
variations of  barometric pressure4 ,in 
the snow-fields1 and in the more        
granular  portions of glaciers near     
their heads1 the porosity is doubtless  
sufficient to allow of the appreciable  
penetration of the atmosphere4  ,during 
a part of the time1 the probable effect 
is the condensation  within the ice of  

moisture from the air1 and during       
another part1  evaporation from the ice4
 ,these alternating processes are       
attended by  oscillations of            
temperature4 ,while the balance between 
loss and gain  of substance may be      
immaterial1 the oscillating nature of   
the process  and the fluctuations of    
temperature are probably favorable to   
granular  change4    ,whether these     
processes furnish an adequate           
explanation of the changes  or not1 the 
observed fact is that there are all     
gradations from  snowflakes and pellets 
into granular nv1 and thence into       
glacier  granules 7,gletscherkrner71    
varying in size up to that of filberts  
and walnuts1 and even beyond4 ,in       
coherence1 these aggregations may  vary 
from the early slightly coherent        
granular stage1 where the grains  are   
small and spheroidal1 to the ice stage1 
where the cohesion has  become strong   
through the interlocking growths of the 
large granules4  ,even when the mass has

 become seemingly solid ice1 sufficient 
space is  usually left between the      
granules to give the dispersive         
reflection to  light which imparts to   
glacier ice its distinctive whitish     
color4    ,the arrangement of the       
crystal axes4--,the most radical        
difference  between glacier ice and ice 
formed directly from water is in the    
arrangement 7orientation7 of the        
crystals4 ,in the ice formed on         
undisturbed water1 the bases of the     
crystals are at the surface and  their  
principal axes are vertical1 as shown by
 ,mgge4#acd ,as they  grow1 the crystal 
prisms extend downwards4 ,this gives a  
columnar or  prismatic structure to the 
ice1 well seen when it is 8honeycombed0 
by partial melting4 ,in the glacier1 on 
the other hand1 the crystals1  starting 
from snowflakes1 have their axes turned 
in various directions  according to the 
accidents of their fall2 and as the snow
 develops  into ice1 the principal axes 
of the crystals continue to lie in all  

directions4 ,hence glacier ice1 unlike  
pond ice1 cannot usually be split  along
 definite planes1 except where cleavage 
planes are subsequently  developed by   
extraneous agencies4    ,illustration3  
,fig4 #bia;a4 ,fig4 #bia;b4 ,fig4       
#bia;c4      ,figures to illustrate the 
method of deformation of ice crystals4  
,while the crystals of a glacier usually
 have their principal axes in  various  
directions1 there appears to be a       
tendency for them to approach           
parallelism in certain positions1       
especially in the basal parts of a      
glacier near its terminus4 ,observations
 on this point are not so full  and     
critical as could be desired1 but it is 
probable that the parallel  orientation 
is partly general1 and due to the       
vertical pressure of the  ice1 and      
partly special and local1 and connected 
with the shearing  planes and foliation4
    ,the bearing of this partial        
parallelism of the crystals on shearing 
and  foliation is supposed to reside in 

the fact that a crystal of ice is  made 
up of a series of plates arranged at    
right angles to the principal  axis of  
the crystal4 ,these plates may be       
likened to a pile of cards1  the        
principal axis being represented by a   
line vertical to them4 ,if  a cube be   
cut from a large crystal of ice1 it will
 behave much like  a cube cut from the  
pile of cards4 ,if the cube be so placed
 that its  plates are horizontal 7,fig4 
#bia;a71 and if it be rested on supports
 at  two edges and heavily weighted in  
the middle1 it will sag1 the plates     
sliding slightly over one another so as 
to give oblique ends1 but in  this case 
the cube offers considerable resistance 
to deformation4 ,if  the cube be so     
placed that the plates stand on edge1   
each reaching from  support to support  
7,fig4 #bia;b71 it will offer very great
 resistance  to deformation2 but if the 
plates be vertical and transverse to the
  line joining the supports1 as in ,fig4
 #bia;c1 the middle portion will  sag   

under very moderate weighting by the    
sliding of the plates on one  another1  
and in a comparatively short time the   
middle portion may be  pushed entirely  
out1 dividing the cube4 ,these          
properties have been  demonstrated by   
,mc,connel#ace and ,mgge1 and they      
appear to throw light  on certain phases
 of the action of glaciers that are most
 pronounced in  their basal parts1 and  
are best illustrated in arctic glaciers4
               ,the ,probable           
,fundamental ,element in ,glacial       
,motion4    ,melting and freezing4--,it 
has already been shown 7p4 #bgi7 that   
the  initial or fundamental cause of    
glacial motion must be operative at the 
heads of glaciers where the temperature 
is lowest and the material  most loosely
 granular4 ,in this condition1 there is 
reason to believe  that motion takes    
place between the grains1 rather than by
 their  distortion through the          
displacement of their lamin4 ,the fact  
that the  granular structure is not     

destroyed1 as it would be by the        
indefinite  sliding of the crystal      
plates over each other1 sustains this   
view4 ,the  inference is that the       
gliding planes play a notable rle in    
glacial  movement only in the basal     
parts of the lower ends of glaciers1    
where  the greatest thrusts are         
developed1 and where the granules have  
become  largest and most completely     
interlocked4 ,at the heads of glaciers1 
where motion is initiated1 there may be 
great downward pressure1 but  not       
vigorous thrusts from behind1 and       
probably only moderate thrusts          
developed within the body itself4 ,there
 seems therefore no escape from  the    
conclusion that the primal cause of     
glacial motion is one which  may operate
 even under the relatively low          
temperatures1 the relatively  dry       
conditions1 and the relatively granular 
textures which affect the  heads of     
glaciers4 ,these considerations lead to 
the view that movement  takes place by  

the minute individual movements of the  
grains upon one  another4 ,while they   
are in the spheroidal form1 as in the   
nv1 this  would not seem to be at all   
difficult4 ,they may rotate and slide   
over  each other as the weight of the   
snow increases2 but as they become      
interlocked by growth1 both rotation and
 sliding must apparently  encounter more
 resistance4 ,the amount of rotary      
motion required of an  individual       
granule is1 however1 surprisingly small1
 and the meltings  and refreezings      
incident to shifting pressures and      
tensions1 and to  the growth of the     
granules1 seem adequate to meet the     
requirements4  ,in order to account for 
a movement of three feet per day in a   
glacier  six miles long1 the mean motion
 of the average granule relative to its 
neighbor would be1 roundly1  of its own 
diameter per day1 or one  diameter in   
#aj1jjj days2 in other words1 it would  
change its relations  to its neighbors  
to the extent of its diameter in about  

thirty  years4 ,a change of so great    
slowness under the conditions of        
granular  alteration can scarcely be    
thought incredible1 or even improbable1 
in  spite of the interlocking which the 
granules may develop4 ,the movement  is 
supposed to be permitted chiefly by the 
temporary passage of minute  portions of
 the granules into the fluid form at the
 points of greatest  compression1 the   
transfer of the moisture to adjoining   
points1 and its  resolidification4 ,the 
points of greatest compression are      
obviously  just those whose yielding    
most promotes motion1 and a successive  
yielding of the points that come in     
succession to oppose motion most  7and  
thus to receive the greatest stresses7  
permits continuous motion4  ,it is      
merely necessary to assume that the     
gravity of the accumulated  mass is     
sufficient to produce the minute        
temporary liquefaction at the  points of
 greatest stress1 the result being      
accomplished not so much  by the        

lowering of the melting-point as by the 
development of heat by  pressure4       
,illustration3 ,fig4 #bib4--,portion of 
the east face of ,bowdoin glacier1      
,north ,greenland1 showing oblique      
upward thrust1 with shear4    ,this     
conception of glacial 8flowage0 involves
 only the momentary  liquefaction of    
minute portions of the mass1 while the  
ice as a whole  remains rigid1 as its   
crystalline nature requires4 ,instead of
 assigning  a slow viscous fluidity like
 that of asphalt to the whole mass1     
which  seems inconsistent with its      
crystalline character1 it assigns a free
  fluidity to a succession of particles 
that form only a minute fraction  of the
 whole at any instant4    ,this         
conception is consistent with the       
retention of the granular  condition of 
the ice1 with the heterogeneous 7in the 
main7 orientation  of the crystals1 with
 the rigidity and brittleness of the    
ice1 and with  its strictly crystalline 
character1 a character which a viscous  

liquid  does not possess however much   
its high viscosity may make it resemble 
a  rigid body4    ,accumulated motion in
 the terminal part of a                 
glacier4--,however slight  the relative 
motion of one granule on its neighbor1  
the granules in any  part of a glacier  
partake in the accumulated motion of all
 parts nearer  the source1 and hence all
 are thrust forward4 ,herein appears to 
lie the  distinctive nature of glacial  
movement4 ,each part of a stream of     
water  feels the hydrostatic pressure of
 neighboring parts 7theoretically  equal
 in all directions7 and the momentum of 
motion1 but not the  rigid thrust of the
 mass behind4 ,lava streams are good    
types of viscous  fluids flowing in     
masses comparable to those of glaciers  
and on similar  slopes1 and1 in their   
last stages1 at similar rates1 but their
 special  modes of flow and their       
effects on the sides and bottoms of     
their paths  are radically different    
from those of glaciers4 ,forceful       

abrasion1 and  particularly the rigid   
holding of imbedded stones while they   
score and  groove the rock beneath1 is  
unknown in lava streams and is scarcely 
conceivable4 ,there is1 so far as we    
know1 no experimental or natural        
evidence that any typical viscous body  
in flowing over a rugose bottom         
detaches and picks up fragments and     
holds them as graving tools in its  base
 so fixedly as to cut deep1 long1       
straight grooves in the hard  bottom    
over which it flows4 ,it would seem that
 competency to do this  peculiar class  
of work1 which is distinctive of        
glaciers1 should be  demonstrated before
 the viscous theory of glacial movement 
is accepted  as even a good working     
hypothesis4 ,somewhat in contrast with  
viscous  movement1 it is conceived that 
a glacier is thrust forward rigidly by  
internal elongation1 shears forcibly    
over its sides and bottoms1 and  leaves 
its distinctive marks upon them4        
,illustration3 ,fig4 #bic4--,shearing   

plane well defined4 ,a ,spitsbergen     
glacier4 7,hamberg47                    
,auxiliary ,elements4    ,shearing4--,in
 the lower portion of a glacier where   
normally the  thrusts are greatest1 the 
granules fewest1 and their interlocking 
most intimate1 shearing takes place     
within the ice itself4 ,this is         
illustrated by the accompanying ,figs41 
#bib-bie4 ,the shearing results  in the 
foliation of the ice and in the forcing 
of dbris between the  sheared layers4   
,thus the ice becomes loaded in a       
special englacial or  baso-englacial    
fashion1 as previously mentioned and    
illustrated in ,fig4  #bfh4    ,within  
the zone of shearing1 it is probable    
that the gliding planes  of the crystals
 come into effective function4 ,it is   
thought that the  combined effect of the
 vertical pressure1 the forward thrust1 
and the  basal drag of the ice1 may be  
to increase the number of granules whose
  gliding planes are parallel to the    
glacier's bottom4 ,at any rate1         

,drygalski reports#acf that there is a  
tendency to such an arrangement  in the 
basal portion of the ,greenland glaciers
 at their borders4 ,it  is conceived    
that where strong thrusts are brought to
 bear upon such  a mass of granules1    
those whose gliding planes are parallel 
to the  direction of thrust are strained
 with sufficient intensity to cause the 
plates to slide over each other1 while  
those which are not parallel  to the    
direction of thrust are either rotated  
into parallelism--when  they also       
yield--or are pressed aside out of the  
plane of shear4 ,as  previously noted1  
shearing is observed to occur chiefly   
where the ice  below the plane of       
shearing is protected more or less from 
the force  of the thrust4 ,it perhaps   
also occurs where the basal ice becomes 
so  overloaded with dbris that it is    
incapable of ready movement4            
,illustration3 ,fig4 #bid4--,portion of 
the lateral margin of a ,north          
,greenland glacier4 ,shows upturning of 

the layers at the base1 the    cleanness
 of the ice above the bottom1 and1      
possibly1 shearing4    ,it is also      
probable that sharp differential strain 
and shearing are  developed at the level
 where the surface-water of the warm    
season1  descending into the ice1       
reaches the zone of freezing4 ,the      
expanding of  the freezing water at the 
upper limit of the cold zone may cause  
the  layer expanded by it to shear over 
that below4 ,as the level of freezing   
is lowered with the advance of the warm 
season1 the zone of shearing  also      
sinks4 ,this may be regarded as an      
auxiliary agency of shearing1 of        
application to a special horizon4       
,high temperature and water4--,in the   
zone of waste1 a higher  temperature and
 more water lend their aid to the       
fundamental  agencies of movement1 and  
there is need for these aids to promote 
a  proportionate movement1 for here the 
granules are more intimately            
interlocked and the ice more compact and

 inherently more solid and  rigid4 ,the 
average temperature is1 however1 near   
the melting-point 7p4  #bgf71 and during
 the warm season the ice is bathed in   
water so that  the necessary changes in 
the crystals are facilitated1 and       
movement  apparently takes place even   
more readily than in the more open      
granular  portion of lower temperature  
and dryer state4 ,the extraordinary     
movements of certain tongues of ice in  
some of the great fiords of  ,greenland 
are probably due to the convergence of  
very thick slow-moving  ice from the    
interior into basins leading down to the
 fiords4 ,into the  same basins a large 
amount of surface-water is concentrated 
at the same  time1 with the result that 
the thick ice1 bathed with water and    
having  a high gradient1 develops       
unusual velocity during the warm season4
    ,illustration3 ,fig4 #bie4--,lateral
 margin of a ,north ,greenland glacier1 
,inglefield ,gulf region4 ,the          
overhanging edges of the successive     

layers are not altogether the result of 
shear4 ,they are due in part    at least
 to differential melting along the lines
 where dbris comes    to the surface4   
,the dbris planes may be shear planes4  
,applications4--,by a studious          
consideration of the coperation of the  
auxiliary agencies with the fundamental 
ones1 the peculiarities of  glacial     
movement may apparently be explained4   
,in regions of intense  cold1 where a   
dry state and low temperature prevail1  
as in the heart  of ,greenland1 the     
snow-ice mass may accumulate to         
extraordinary  thicknesses1 for the     
burden of movement seems to be thrown   
almost  wholly upon compression1 with   
the slight aid of molecular changes due 
to internal evaporation and allied      
inefficient processes4 ,since the       
temperature in the upper part of the ice
 is very adverse 7see p4 #bgg71  the    
compression must be great before it     
becomes effective in melting  the ice1  
and hence the great thickness of the    

mass antecedent to much  motion4        
,similar conditions more or less affect 
the heads of alpine  glaciers1 though   
here the high gradients favor motion    
with lesser  thicknesses of ice2 but in 
the lower reaches of alpine glaciers1   
where  the temperatures are near the    
melting-point1 and the ice is bathed in 
water1 movement may take place in ice   
which is thin and compact4    ,if the   
views here presented are correct1 there 
is also1 near the end  or edge of a     
glacier1 the coperation of rigid thrust 
from behind with  the tendency of the   
mass to move on its own account4 ,the   
latter is  controlled by gravity1 and   
conforms in its results to laws of      
liquid  flow4 ,the former is a derived  
factor1 and is a mechanical thrust4     
,this  thrust is different from the     
pressure of the upper part of a liquid  
stream on the lower part1 because it is 
transmitted through a body  whose       
rigidity is effective1 while the latter 
is transmitted on the  hydrostatic      

principle of equal pressure in all      
directions4                             
,corroborative ,phenomena4    ,the      
conception of the glacier and its       
movement here presented explains  some  
of the anomalies that otherwise seem    
paradoxical4 ,while a glacier  in a     
sense flows over a surface1 it often    
cuts long1 deep furrows in  firm rock4  
,it is difficult to explain this if the 
ice be so yielding  as to flow under its
 own weight on a surface which is almost
 flat4 ,if  the mass is really viscous1 
its hold on its imbedded dbris should   
also be viscous1 and a bowlder in the   
bottom should be rotated in the         
yielding mass when its lower point      
catches on the rock beneath1 instead  of
 being firmly held while a deep groove  
is cut4 ,this is more to the  point     
since viscous fluids flow by a partially
 rotary movement4 ,if1  on the other    
hand1 the ice is always a rigid body    
which yields only  as its interlocking  
granules change their form by loss and  

gain1 a  rigid hold on the imbedded rock
 at some times1 and a yielding hold at  
others1 is intelligible1 for on this    
view the nature of its hold is          
dependent on the temperature and dryness
 of the ice4 ,stones in the base  of a  
glacier may be held with very great     
rigidity when the ice is dry1  scoring  
the bottom with much force1 while they  
may be rotated with  relative ease when 
the ice is wet4 ,in short1 the relation 
of the ice to  the bowlders in its      
bottom varies radically according to its
 dryness  and temperature4 ,a dry       
glacier is a rigid glacier4 ,a dry      
glacier is  necessarily cold1 and a cold
 glacier is necessarily dry4    ,on the 
view here presented1 a glacier should be
 more rigid in winter  than in summer1  
and the whole thickness of the glacier  
should  experience this rigidity chiefly
 at the ends and edges1 where the       
relative thinness of the ice permits the
 low temperature to reach its  bottom4  
,the motion in these parts during the   

winter is1 therefore1 very  small4      
,in this view may also be found an      
explanation of the movement of  glaciers
 for considerable distances on upward   
slopes1 even when the  surface as well  
as the base is inclined backwards4 ,so  
far does  this go that superglacial     
streams sometimes run for some distance 
backwards1 i4e4 toward the heads of the 
glaciers1 while in other  places        
surface-waters are collected into ponds 
and lakelets4 ,such a  slope of the     
surface of ice is not difficult to      
understand if the  movement be due to   
thrust from behind1 or if it be         
occasioned by  internal crystalline     
changes acting upon a rigid body2 but it
 must be  regarded as very remarkable if
 the movement be that of a fluid body1  
no matter how viscous1 for the length of
 the acclivity is sometimes  several    
times the thickness of the ice4         
,crevassing and other evidences  of     
brittleness and rigidity find a ready   
elucidation under the view  that the ice

 is a really solid body at all times1   
and that its apparent  fluency is due to
 the momentary fluidity of small        
portions of the mass  assumed in        
succession as compression demands4      
,in addition to the considerations      
already adduced1 it may be urged that  a
 glacier does not flow as a stiff liquid
 because its granules are not           
habitually drawn out into elongated     
forms1 as are cavities in lavas and     
plastic lumps in viscous bodies4        
,flowage lines comparable to those in   
lavas are unknown in glaciers4    ,all  
this is strictly consistent with our    
primary thesis1 that a glacier  is a    
crystalline rock of the purest and      
simplest type1 and that it  never has   
other than the crystalline state4 ,this 
strictly crystalline  character is      
incompatible with viscous liquidity4    
,other ,views of ,glacier ,motion4#acg  
,while these views of glacial motion    
seem to us to best accord with the      
known facts1 they are not to be regarded

 as established in scientific  opinion1 
or as the views most commonly held4 ,the
 mode of glacial  motion has long been a
 mooted question1 and is still so       
regarded4 ,the  main alternative        
interpretations that have been          
entertained are the  following3    7#a7 
,in the early days of glacial studies   
,de ,saussure thought that  glaciers    
slid bodily on their beds2    7#b7      
,charpentier and ,agassiz referred the  
movement to the expansion of  descending
 water freezing within the glacier2     
7#c7 ,rendu and ,forbes1 followed by    
many1 perhaps most1 modern writers1     
believed ice to be viscous1 and that in 
sufficiently large masses it  flows     
under the influence of its own weight1  
like pitch or asphalt2    7#d7 ,others1 
realizing the fundamental difference    
between crystalline  ice and a true     
viscous body1 have fallen back on a     
vague notion of  plasticity which       
scarcely amounts to a definite          
hypothesis at all2    7#e7 ,tyndall     

urged that the movement was accomplished
 by minute repeated  fracturing and     
regelation1 appealing to the fact that  
broken pieces of  ice slightly pressed  
together at melting temperatures freeze 
together1  but neglecting the fact that 
this would destroy the integrity of the 
crystals2    7#f7 ,moseley assigned the 
movement to a bodily expansion and      
contraction of the glacier1 analogous to
 the creeping of a mass of  lead on a   
roof2    7#g7 ,james ,thompson          
demonstrated that pressure lowers the   
melting-point1  and while this effect is
 so small as probably to be ineffectual1
 it  is correlated with the very        
important fact that compression may     
cause  melting1 which is not the case in
 most other rocks4 ,he recognized that  
under pressure partial liquefaction took
 place1 that the water so  liberated    
might be refrozen as it escaped from    
pressure1 and appears to  have regarded 
this as a vital factor2    7#h7 ,croll  
held that the movement was due to a     

consecutive series of  molecular changes
 somewhat like the chain of chemical    
combinations in  electrolysis2    7#i7  
,hugi1 ,eli de ,beaumont1 ,bertin1      
,forel1 and others thought that the     
growth of the granules was the leading  
factor in the ice movement2    7#aj7    
,mc,connel and ,mgge have made the      
gliding planes of the ice  crystals     
serve an important function in glacial  
movement4    ,it will be seen that the  
principle of partial liquefaction for   
which  ,thompson laid the basis1 the    
crystallization of descending water1    
urged  by ,charpentier and ,agassiz1 and
 the granular growth on which ,hugi1    
,beaumont1 ,forel1 and others founded   
their hypotheses1 are incorporated  in  
the view already presented4 ,probably   
the agencies on which some of  the other
 views are based may also be            
participants in producing glacial       
motion1 sometimes as incidental factors1
 and sometimes perhaps as  important    
ones1 for under different conditions1   

different agencies may  play rles of    
varying importance4 ,for example1 in    
going over the brinks  of precipices of 
sufficient height1 glaciers break into  
fragments  which are re-cemented below1 
and the 8reconstructed0 glacier moves on
  as before4 ,here fracture and         
regelation are evident4 ,the movement of
  the gliding planes of the ice crystals
 over each other1 which has been  looked
 upon as a special kind of viscoid      
movement1 probably plays a  large part  
in the shearing movements in certain    
cases4 ,but neither of  these is        
probably a large factor in ordinary     
glacial movement1 and it  seems highly  
improbable that any of them are         
essential factors in the  primary       
movements in the snow-fields where      
glacial action begins4                  
,,chapter ,,vi4                         
,,the ,,work ,,of ,,the ,,ocean4        
,the general facts concerning the depth 
of the ocean and the  distribution of   
its water have been given on a preceding

 page 7p4 #h71  and the origin of the   
ocean and the ocean basins is discussed 
in the  second volume4 ,this chapter has
 to do primarily with the processes  now
 going on in the sea and its borders1 in
 so far as they are of  importance in   
the interpretation of geologic history4 
,the study of  these processes is       
prefaced by a few words concerning the  
amount and  composition of the          
sea-water1 the life of the ocean1 and   
the topography  of its bed4#ach         
,volume and composition4--,every #ajjj  
parts of sea-water contain about  #cd4dj
 parts by weight of mineral matter in   
solution4 ,the principal  solids1 acids1
 and bases1 combined according to the   
principles laid  down by ,dittmar1 are  
shown in the following table3#b         
,chloride of sodium                     
#gg4geh    ,chloride of magnesium       
#aj4hgh    ,sulphate of magnesium       
#d4gcg    ,sulphate of calcium          
#c4fjj    ,sulphate of potassium        
#b4dfe    ,bromide of magnesium         

#j4bag    ,carbonate of calcium         
#j4cde                                  
-------         ,total salts            
#ajj4jjj    ,expressed in terms of tons 
per cubic mile of sea-water1 the        
composition  is as follows3#aci         
,tons per ,cubic ,mile4    ,chloride of 
sodium 7,na,cl7                         
#aag1dcd1jjj    ,chloride of magnesium  
7,mg,cl7                     #af1dbh1jjj
    ,sulphate of magnesium 7,mg,s,o7    
#g1aed1jjj    ,sulphate of calcium      
7,ca,s,o7                               
#e1dcg1jjj    ,sulphate of potassium    
7,k,,so7                      #c1gbc1jjj
    ,bromide of magnesium 7,mg,br7      
#cbh1jjj    ,carbonate of calcium       
7,ca,c,o7                               
#eba1jjj                                
-----------         ,for sea-water1     
total dissolved matter                  
#aea1jbe1jjj    ,aside from the         
ingredients shown in the above tables1  
the presence of  the following has been 
proved3 iodine1 fluorine1 phosphorus1   

silicon1  boron1 silver1 lead1 copper1  
zinc1 cobalt1 nickel1 iron1 manganese1  
aluminum1 barium1 strontium1 arsenic1   
lithium1 csium1 rubidium1 and  gold4    
,oxygen1 nitrogen1 and carbonic acid gas
 are also present in  quantity4 ,the    
amount of carbonic acid is estimated to 
be #ah times as  great as in the        
atmosphere4#adj    ,the amount of       
sea-water is estimated by ,murray at    
#cbc1gbb1aej cubic  miles1#ada or about 
#ae times the volume of the land above  
sea-level4  ,the volume and composition 
of the sea-water being known1 the amount
 of  mineral matter which it contains   
may be readily calculated4 ,assuming    
the average specific gravity of the     
mineral matter in solution to be  #b4e1 
the #c4e by weight becomes #a4d by      
volume1 and #a4d of #cbc1gbb1aej  cubic 
miles is #d1ecb1aaj cubic miles4 ,this  
then represents the  aggregate volume of
 mineral matter in the sea if it were   
precipitated  and compacted so as to    
have an average specific gravity of     

#b4e4  ,assuming the average depth of   
the sea to be #bjgf fathoms 7#ab1def    
feet71  as given by ,murray1 the mineral
 matter in solution1 if precipitated1   
would cover the ocean bottom to a depth 
of about #age feet4 ,assuming the  area 
of the land to be to that of the sea as 
#bh to #gb1 this amount of  mineral     
matter would make a layer about #dej    
feet deep over the land4  ,its amount is
 equal to about #bj of that of all lands
 above sea-level1  and it falls but     
little short of that in all lands below 
#fjj feet in  altitude4 ,if it were     
precipitated and concentrated in the    
shallow  waters about the borders of the
 lands1 it would fill the sea out to    
the depth of about #djjj feet1 and would
 diminish its area by some  #ai1jjj1jjj 
to #bj1jjj1jjj square miles1 an area    
which is more than   of the present land
 surface4 ,in other words1 if the       
mineral matter in  the sea-water were   
precipitated and concentrated in the    
shallow waters  about the lands1 it     

would restore the continental shelves to
 the land  areas1 and add an almost     
equal area beyond4    ,these comparisons
 may perhaps help to give some idea of  
the amount of  mineral matter in        
solution in the sea1 but they give no   
more than a  hint of the importance of  
the solvent power of water in the       
general  processes of rock decay1 for   
most of the substances carried to the   
sea  in solution by rivers are extracted
 from the water about as rapidly  as    
they are supplied4 ,thus calcium        
carbonate is about twenty times as      
abundant as sodium chloride in          
river-water1#adb but is only  as        
abundant in sea-water4    ,the total    
river discharge into the sea is         
estimated at #febd cubic miles  of water
 per year4#adc ,this water is estimated 
to carry to the sea  annually about half
 a cubic mile of mineral matter in      
solution4 ,at this  rate it would take  
about #i1jjj1jjj years for the streams  
to bring to  the sea an amount of       

mineral matter equal to that it now     
contains1 but  the proportions of the   
ingredients would be very different4    
,the sodium chloride makes up about #b4d
 of the mineral matter in  river-water  
and nearly #gh of the mineral matter of 
the sea4 ,at this  rate it would take   
nearly #cjj1jjj1jjj years for the salt  
of the sea  to have been contributed by 
the rivers4 ,it is not to be understood1
  however1 that this figure indicates   
the age of the ocean4 ,the salt is  not 
all brought in by the rivers2 the rivers
 have probably not always  contributed  
at the present rate2 and much salt once 
in the sea has been  precipitated4      
,nevertheless the above figure gives    
some suggestion as to  the order of     
magnitude of the figures which represent
 the age of the  ocean4    ,in contrast 
with the salt1 the amount of calcium    
carbonate in the sea  is so small that  
at their present rate of contribution1  
it would be  brought to the sea by      
rivers in about #fb1jjj years4          

,topography of bed4--,the general       
relations of ocean basins to  continents
 are suggested by ,fig4 #bif4 ,the      
borders of the continental  platforms   
are covered by the epicontinental sea1  
while the abysmal  sea occupies the     
ocean basins proper4 ,from the figure it
 is seen that  an ocean basin is        
pronouncedly convex upward1 and so      
departs as widely  as may be from the   
current notion of the homely utensil    
from which  it is named4 ,only when it  
is remembered that a level surface 7on  
the  earth7 is one which has the mean   
curvature of the earth1 and that the    
deeper parts of the ocean basin are well
 below the mean sphere level1  does the 
current name seem justified4#add ,the   
figure also shows that  the depth of an 
ocean basin is slight compared with the 
radius of the  earth4    ,the bed of the
 ocean1 like the face of the land1 is   
affected by  elevations and depressions1
 and its deepest points are about as far
  below its surface as the highest      

mountains are above it4 ,there are      
areas of the sea bottom which1 as a     
whole1 may be compared to the  plains of
 the land1 and others which may be      
likened to plateaus1 and  the lines of  
gradation between them are as indistinct
 as they often  are on the land4 ,there 
are mountain peaks1 chiefly of volcanic 
origin1  and depressions comparable to  
the great basins on the land4 ,but apart
  from these general features1 there is 
little in common between the  topography
 of the sea bottom and that of the land4
 ,mountain systems  are1 for the most   
part1 absent1 though certain islands1   
like ,cuba and  some of its associates1 
may be regarded as the crests of systems
 which  are chiefly submerged4 ,if the  
water were drawn off from the ocean's   
bed so that it could be seen as the land
 is1 its most impressive  feature would 
be its monotony4 ,the familiar hills and
 valleys which1  in all their           
multitudinous forms1 give the land      
surface its most  characteristic        

features are essentially absent4 ,a     
large part of its  surface would be     
found to be so nearly flat that the eye 
would not  detect its departure from    
planeness4    ,illustration3 ,fig4      
#bif4--;,general relations of ocean     
basins to the    lithosphere4 ,lat4 #bj 
,s4 ,depth of the water 7black7 and     
height of    land exaggerated ten times4
 7,data from ,murray1 ,scot4 ,geogr4    
,mag41    ,vol4 ,,xv1 #ahii47    ,the   
reason for this profound difference is  
readily found4 ,on the land1  the       
dominant processes which shape the      
details of the surface are              
degradational1 and though the final     
result of degradation is flatness       
7base-level71 the immediate result is   
relief1 and1 most commonly1  relief of  
the hill-and-valley type4 ,in the sea1  
the dominant processes  are             
aggradational1 and tend to monotonous   
planeness4    ,distribution of marine   
life4--,marine life has been of such    
importance  in the history of the earth 

that the elementary facts concerning its
  distribution and the principles which 
control it are here recalled4  ,the     
distribution of marine life is          
influenced by many factors1 chief  among
 which are temperature and depth of     
water4 ,not only is life  more abundant 
in the warmer parts of the ocean than in
 the colder1 but  the species inhabiting
 cold waters are different from those in
 warm1  and few species range through   
great variations4 ,many forms of life   
are restricted to shallow water4 ,many  
more1 especially those which do  not    
live on the bottom1 swim about freely   
without reference to the  depth of the  
water beneath them1 while relatively few
 are restricted  to great depths4 ,many 
species are also influenced by the      
salinity of  the water1 which varies    
notably along coasts where the fresh    
waters  from the land are discharged2 by
 the character of the sediment at the   
bottom1 some species preferring mud1    
others sand1 and others gravel2  by the 

movement of the waters1 some species    
preferring still waters  and others     
rough2 and some species by the abundance
 and nature of the  food-supply1 and by 
rival and hostile species4    ,subject  
to the exceptions determined by         
temperature1 etc41 plant life  abounds  
in shallow water out to depths of #ajj  
fathoms or so1 and is  found in         
abundance at the surface where the depth
 is much greater4  ,animal life abounds 
in shallow water1 both at the bottom and
 above it1  out to depths of #bjj or    
#cjj fathoms1 and occurs in great       
profusion in  the surface-waters of     
temperate and tropical regions without  
regard to  the depth4 ,the great body of
 the ocean water lying below a depth of 
some few hundred fathoms is nearly      
tenantless1 though life reappears       
sparingly at the bottom1 even where the 
depth is great4 ,for further  discussion
 of this topic1 see ,chapter ,,xi4      
,,processes ,,in ,,operation ,,in ,,the 
,,sea4    ,within the area of the sea1  

as on the area of the land1 three sets  
of  processes are at work--diastrophism1
 vulcanism1 and gradation4              
,diastrophism 7p4 #b7 affects the       
sea-bottom as the land1 but the  results
 are notably different in certain       
respects4 ,so far as the  lithosphere is
 concerned1 the sea-level may be said to
 be the critical  level4 ,at and above  
it1 many processes are in operation     
which do not  appear below1 and below   
it1 many which do not take place above4 
,changes  of level which do not involve 
the submergence of areas which were     
land1 or the emergence of areas which   
were under water1 are relatively        
unimportant1 compared with those which  
effect such changes4 ,the rise  of the  
bottom of the sea from a depth of #ejj  
fathoms to a depth of #bjj  fathoms     
would not lead to important             
consequences1 so far as the area  itself
 is concerned1 while an equal rise of   
the bottom beneath #bjj  fathoms of     
water1 or an equal subsidence of land   

#ejj feet high1 would  be attended by   
more striking consequences4 ,it follows 
that the changes  effected by           
diastrophism are much more obvious along
 coasts than in the  deep seas4         
,emergence or submergence shifts the    
zones of aggradation  and degradation1  
shifts the zone of contact of ocean and 
land1 and  changes the region concerned 
from one appropriate for sea life to one
  appropriate for terrestrial forms1 or 
vice versa4    ,over the continental    
shelves the water is shallow and the    
bottom  relatively smooth4 ,if a coastal
 region be elevated evenly1 or if the   
sea-level be drawn down1 the new        
shore-line on the smooth surface of  the
 former submerged shelf will be         
relatively regular1 even though the     
coast was notably irregular before the  
change4 ,thus in ,fig4 #big the         
coast-line is notably irregular4 ,a     
sea-withdrawal or a land-uplift of  #abj
 feet would change the coast-line to the
 position of the #bj-;fathom  line1 when

 it would be notably less irregular than
 now4 ,if it were  shifted to the       
#ajj-;fathom line1 few irregularities   
would remain4 ,in so  far as new        
coast-lines formed by the lowering of   
the sea 7or rise of  the crust7 depart  
from straightness1 it is usually by     
broad1 smooth  curves4 ,local uplifts of
 coastal lands1 and especially uplifts  
along  axes normal to the trend of the  
coast1 would give rise to projections   
of land1 and so to coastal              
irregularities2 but such uplifts are    
rarely  so localized as to give origin  
to minor projections4 ,it follows that  
rising coasts1 and those which have     
recently risen1 or more likely1  coasts 
along which the sea-level is sinking or 
has recently sunk1  are likely to be    
regular so far as details of outline are
 concerned4  ,subsidence of a coast-line
 7or rise of the sea-level7 tends to the
  opposite results1 for in this case the
 sea advances on a surface which  has   
more or less relief1 and the water takes

 possession of every  depression brought
 to its level4 ,the lower parts of the  
valleys are  converted into bays1 the   
length and width of which depend on the 
slope  and width of the valleys drowned4
 ,the numerous bays at the debouchures  
of the streams along the ,atlantic coast
 of the ,united ,states1 from ,long     
,island ,sound to ,carolina1 such as the
 ,delaware1 ,chesapeake1 7,fig4 #big7   
and numerous smaller bays1 are the      
results of recent sinking1 which  has   
allowed the sea to invade the lower ends
 of river valleys4 ,the  ragged coast of
 ,maine is another example1 though      
glaciation as well as  subsidence has   
been operative here4 ,from the present  
configuration of  coast-lines1 it has   
been inferred that the present is1 on   
the whole1 an  era of continental       
depression4#ade ,river valleys1 the     
lower ends of  which are embayed1 are   
sometimes found to be continuous with   
submerged  valleys beyond the coast-line
 7,fig4 #bih74 ,submerged river valleys 

show  that the surface in which they lie
 was once land4    ,illustration3 ,fig4 
#big4--,sketch of the eastern coast of  
the ,united    ,states from ,cape ,may  
to ,cape ,henry1 showing coastal        
irregularities4    ,the figures         
represent the depths of water in        
fathoms4 7,from charts of    ,c4 and ,g4
 ,surv47    ,illustration3 ,fig4        
#bih4--,sketch of ,carmel ,bay1 ,cal4   
,the contours    below sea-level show a 
deep submerged channel4 7,from charts of
 ,c4 and    ,g4 ,surv47    ,bays may be 
developed by local subsidence as well as
 by the submerging  of valleys1 though  
decisive examples are not readily cited4
 ,bays may  also be produced by uplift  
of the surface on either side of an area
  which does not change its level4 ,for 
example1 uplift on either side of  the  
,gulf of ,california has probably been  
one element1 though probably  not the   
only one1 in the development of this    
indentation4 ,the general  outline of a 
great bay produced by coastal warping   

might be regular1  though it would be   
likely to be marked by small            
irregularities where  the streams enter4
 ,it is not to be understood that all1  
or even most1  bays are due to local    
diastrophism4    ,diastrophism1 then1 as
 it affects the ocean-bottoms and the   
ocean-borders1 may make the water of any
 ocean shallower or deeper2 it  may     
cause the emergence or submergence of   
land2 it may make coast-lines  regular  
or irregular2 it may shift the habitat  
of life1 and through  these changes may 
greatly influence the processes of      
gradation1 which  are especially active 
along the contact of sea and land4      
,vulcanism affects the sea-bottom much  
as it affects the land4 ,at the         
volcanic centers1 where the great body  
of extruded matter accumulates1  mounds 
and mountains are built up4 ,most of the
 mountain peaks of the  sea-bottom1     
whether their crests are islands1 or    
whether they are  wholly submerged1 have
 had a volcanic origin4 ,the rock       

material ejected  from submarine vents  
is probably less widely distributed than
 that  from vents on land1 and so far   
forth1 the volcanic cones in the oceans 
are steeper than those on land4 ,where  
volcanic cones are built up near  the   
surface of the sea1 they often furnish a
 home for shallow-water  life1 such as  
polyps4 ,wherever built up so as to be  
within the reach of  waves1 gradational 
processes are stimulated4    ,the       
processes of vulcanism do not commonly  
influence coasts of  continents         
directly1 for few volcanoes lie         
immediately on coasts4  ,in places1     
however1 as at various points in and    
about ,italy1 the  configuration of the 
coast is influenced by the building of  
volcanoes4  ,indirectly1 vulcanism      
influences the shape of coast-lines1 for
 the  resistance of igneous rock is     
often different from that of the rock   
with which it is associated1 and under  
the influences of the forces of         
gradation it may come to form projecting

 points or rentrants1 as the  case may  
be4    ,the number of active volcanoes  
on islands is about #bjj1 or about      
two-thirds of all now known4 ,since the 
area of the sea is about three  times   
that of the land1 the known active      
volcanoes in the sea are  rather less   
numerous per unit area than those on the
 land4 ,the number  of active vents     
beneath the sea is altogether unknown4  
,a few submarine  eruptions have been   
observed1 and those observed are        
probably but a  small percentage of     
those which have taken place in historic
 time4  ,slight eruptions in deep water 
might not manifest themselves at the    
surface in an unequivocal way1 even were
 observers stationed near them4         
,volcanic cones which fail to reach the 
surface are known1 and the forms  of    
many sea-bottom mountain peaks are such 
as to make it probable that  they are   
volcanic4 ,these phenomena1 as well as  
the numerous volcanic  islands1 give    
some indication of the importance of    

submarine eruptions  in past time4      
,ocean volcanoes1 and especially        
submarine volcanoes1 affect both the    
temperature and the composition of the  
sea-water4 ,both the increase of        
temperature and the solution of volcanic
 gases increase the capacity of  the    
water for mineral matter1 and both the  
change in temperature and  composition  
affect the life of the adjacent waters4 
,the destruction  of life during        
eruptions occasions the generation of   
the products of  organic decomposition1 
and these stimulate further chemical    
changes4  ,the diffusion of affected    
waters occasions chemical changes       
wherever  they go4 ,the effects of      
oceanic volcanoes on the sea-water are1 
therefore1 appreciable1 when long       
periods of time are considered4 ,the    
deposition of the finer parts of        
volcanic discharges will be considered  
in connection with the deposits of the  
deep sea4    ,gradation4--,the          
gradational processes of the land and   

the sea are  in striking contrast4 ,on  
the land1 degradation predominates1 and 
aggradation is subordinate4 ,in the sea1
 aggradation predominates1 and          
degradation is subordinate4 ,on the     
land1 degradation is1 on the whole1     
greatest where the land is highest1     
while aggradation is of consequence     
only where the land is low1 or where    
steep slopes give place to gentle  ones4
 ,in the sea1 degradation is virtually  
confined to shallow water1  or to what  
might be called the highlands of the    
sea1 while aggradation  is nearly       
universal1 but most considerable in     
shallow water1 or  where shallow water  
gives place to deep4 ,both the          
degradational and  aggradational work of
 the sea are greatest near its shores4  
,opposed as  the gradational work of the
 land and sea are1 they yet tend to a   
common  end--the leveling of the surface
 of the lithosphere4    ,the gradational
 processes which affect the sea-bottom  
may be divided  into three categories3  

7#a7 ,those effected by mechanical      
means1 7#b7  those effected by chemical 
means1 and 7#c7 those effected by       
organic  agencies4    ,the mechanical   
work of gradation in the sea is effected
 chiefly by the  movements of the water1
 and1 very subordinately1 by the        
movements of  the ice which the water   
carries4 ,the results of these movements
 may be  degradational wherever the     
water is sufficiently shallow for the   
motion  to affect the bottom4 ,elsewhere
 it is aggradational4    ,the direct    
gradational work effected by chemical   
means is likewise  partly degradational 
and partly aggradational4 ,if at any    
time or  place the water becomes        
supersaturated with any mineral         
substance1  precipitation takes place1  
and the precipitate accumulates as      
sediment  on the bottom4 ,this sometimes
 happens in lagoons and other small     
inclosures1 and perhaps in open water4  
,on the other hand1 wherever  solution  
is effected1 degradation is the result4 

,solution is most  important where the  
bottom consists of relatively soluble   
rock1 such as  lime carbonate4          
,organic agencies are1 on the whole1    
aggradational4 ,accumulations of  coral1
 coral dbris1 shells1 etc41 help to     
build up the sea-bottom1  and most      
rapidly in shallow water where the      
proper forms of life are  most abundant4
 ,here also should be mentioned the     
accumulations of  carbonaceous matter1  
especially in the form of plant bodies4 
,in the  aggradation effected directly  
by organic agencies1 the sea is passive4
  ,its only part is to support the life 
which gives rise to the solid  matter1  
and incidentally to float a part of it  
in its currents4                        
,,movements ,,of ,,the ,,sea-,,water4   
,the movements of the sea-water fall    
into several categories4 ,there is  7#a7
 a general circulation of sea-water1    
determined chiefly by three  factors3   
differences in density in the sea-water1
 differences of level1  and the general 

movements of the atmosphere2 7#b7       
periodic movements  which are not       
primarily circulatory1 brought about by 
the attraction  of the sun and moon2 and
 7#c7 aperiodic movements1 due to       
occasional  causes1 such as earthquakes1
 volcanic explosions1 landslides1 etc41 
which determine local and temporary     
movements1 often of exceptional         
strength4    ,differences in density and
 their results4--,differences in density
  result from differences in temperature
 and salinity4 ,temperature alone       
considered1 water would be densest where
 it is coldest1 namely in  the polar    
regions4 ,differences in salinity result
 from differences  in evaporation and   
from inequalities in the supply of fresh
 water4  ,evaporation alone considered1 
the sea-water should be densest where   
evaporation is greatest2 but the        
equatorial region1 where evaporation  is
 greatest1 is also a region where       
precipitation is heavy1 and             
precipitation1 by freshening the water1 

opposes the effect of great             
evaporation4 ,the greatest differences  
in density due to the unequal  supply of
 fresh water are to be found near the   
borders of continents1  where the       
precipitation on the land is discharged 
into the sea4 ,in  the polar regions1   
the great supply of fresh water1        
especially during  the season when the  
ice is melting1 opposes the effect of   
the low  temperature1 so far as the     
density of the water is concerned4 ,the 
result of the operation of these factors
 affecting the density of the  sea-water
 is to insure a general circulation1    
directed to the end  of equalizing the  
densities2 and since the disturbing     
factors are  constantly in operation1   
equilibrium is never established1 and   
the  movements of the water are         
perpetual4    ,the pressure gradients   
resulting from differences of density   
are so  slight that the resulting       
movements are scarcely more than a creep
 of  the waters4 ,in general they are   

far too slow to be of importance in     
gradational work2 but the earth's       
rotation deflects the creeping waters   
and tends to concentrate the            
equator-ward movement into currents on  
the east sides of the continents1 and   
the pole-ward movement on the  west     
sides4 ,in favorable situations these   
currents may be competent to  produce   
sensible mechanical results4 ,even where
 this is not the case  the circulation  
helps to equalize the temperatures of   
the sea1 and so  of the air above and of
 the land about4 ,indirectly1 therefore1
 the  circulation of the ocean-waters   
affects every geological process which  
is sensitive to climate4    ,differences
 in level and their results4--,while the
 surface of the  ocean is the common    
datum plane to which elevations and     
depressions  are referred1 it is to be  
remembered that the sea has 8a very     
complicated undulating surface in       
consequence of the attraction which  the
 heterogeneous and elevated portions of 

the lithosphere exercise on  the liquid 
hydrosphere4 ,in the opinion of         
geodesists1 the geoid may in  some      
places depart from the figure of the    
spheroid by #ajjj feet40#adf  ,these    
variations in level would1 however1 not 
occasion circulation4 ,the  differences 
in level which determine circulation are
 much more trivial4  ,every stream which
 pours fresh water into the sea tends to
 raise the  level of the water where it 
enters4 ,the waters brought to the ocean
 by  the ,amazon1 the ,mississippi1 and 
other great rivers would appreciably    
change the level of the sea at their    
debouchures1 if the excess did  not     
promptly flow away4 ,the ready mobility 
of the water1 however1  prevents its    
accumulation1 and the discharge of every
 stream generates  widespread movement4 
,this movement is strongest at the      
debouchure1 and  weakens with increasing
 distance from it1 though in the case of
 great  streams1 such as the ,amazon1   
the movement is traceable1 by means of  

the  sediment which the water carries1  
hundreds of miles out to sea4           
,changes of level are also brought about
 by the winds1 which pile up  water     
along the shore against which they blow4
 ,the level of the water  is said to    
have risen #bd feet at ,calcutta on     
,october #e1 #ahfd1 as the  result of a 
severe storm4 ,while this is            
exceptional1 a rise of #b  feet is not  
rare4 ,this piling up of the waters     
along shore insures a  compensating     
movement 7undertow1 littoral currents1  
etc47 in some other  direction4 ,unequal
 evaporation and precipitation likewise 
disturb the  level of the sea and       
occasion movement4 ,in the open sea the 
movements  generated by differences of  
level1 like those generated by          
differences  of density1 are chiefly    
slow1 creeping movements1 but movements 
which  never cease4 ,in bays and gulfs1 
on the other hand1 the surface of the   
water may be so raised1 either as the   
result of wind1 river discharge1  or    

heavy precipitation1 as to give rise to 
strong outward currents4  ,there is     
little doubt at the present time that   
the ,gulf ,stream owes its  origin      
primarily to the difference of level    
between the ,gulf of ,mexico  and the   
,atlantic4#adg    ,movements generated  
by winds4--,the circulation resulting   
from the  tendency of the winds to      
change the level of the sea-water has   
already  been mentioned1 but the wind   
also works in other ways4 ,where the    
winds  have a somewhat constant         
direction and are at the same time      
strong1  they determine a general       
movement of the surface-waters in their 
own  direction1 the surface-water being 
dragged along at a rate somewhat  less  
than that of the wind itself4 ,the      
constant trades appear to be  the chief 
generators of the equatorial            
ocean-currents4 ,once generated1  these 
currents may be concentrated and their  
courses modified4 ,the  currents        
generated by trades are turned north and

 south when directed  against a         
continent2 they are modified by the     
configuration of the  bottom if the     
water be shallow1 and always and        
everywhere1 except1 at  the equator1    
they are deflected by the rotation of   
the earth1 in the  northern hemisphere  
to the right1 and in the southern to the
 left4 ,the  pole-ward currents         
generated in the equatorial region by   
the trades1  and directed by the winds1 
the lands1 the configuration of the     
bottom1  and the rotation of the earth1 
determine compensating currents from    
high latitudes to low1 and the same     
influences which control the course  of 
the former direct the latter as well4   
,since the atmospheric movements are so 
far constant that there is a  prevailing
 direction of winds in all latitudes1   
the winds1 as well  as differences of   
density and differences of level1 insure
 a general  and continual circulation of
 sea-water4 ,the geological effects of  
this circulation are direct and         

indirect2 direct1 by gradation of the   
bottom over which they flow1 and        
indirect1 by the modifications of       
climate they produce4 ,since rotation   
deflects the pole-ward currents  to the 
east sides of the oceans 7west sides of 
the continents7 and the  equator-ward   
movements to the west sides of the      
oceans 7east sides of  the continents71 
the east shores of the oceans are warmer
 than the west  in corresponding        
latitudes1 and the west sides of the    
continents are  both warmer and         
moister#adh than the east sides4    ,the
 most obvious disturbance of sea-water  
resulting from the winds is  the        
generation of waves4 ,waves are not     
primarily parts of the general  oceanic 
circulation4 ,since they are generated  
in other ways than by  winds1 and since 
the gradational effects of waves are    
independent  of their origin1 the       
effects of wind-waves will not be       
considered  separately4    ,movements   
generated by attraction4--,one of the   

movements of the  sea-water which is not
 primarily circulatory results from the 
attraction of the moon and sun4 ,the    
tide is really the result of the        
inequalities of the attraction of these 
bodies on different parts  of the earth4
 ,the lunar tide is more important than 
the solar1 not  because the attraction  
of the moon is greater1 for it is not1  
but  because its differential           
attraction1 the result of its lesser    
distance1  is greater4    ,the distance 
of the moon from the earth is about     
#bdj1jjj miles4 ,if  this be taken as   
the distance from the center of the moon
 to the  center of the earth1 #bcf1jjj  
and #bdd1jjj miles respectively are the 
distances from the center of the moon to
 the nearest and most distant  points on
 the earth4 ,the distance of the sun    
from the earth is about  #ic1jjj1jjj    
miles4 ,if this be taken as the distance
 between the centers  of these bodies1  
then the distances from the center of   
the sun to the  nearest and most distant

 points on the earth's surface are      
#ib1iif1jjj  and #ic1jjd1jjj miles      
respectively4 ,the ratio of #djjj to    
#bcf1jjj or to  #bdd1jjj is much greater
 than the ratio of #djjj to #ib1iif1jjj 
or to  #ic1jjd1jjj4 ,hence the          
tide-producing force of the moon is     
greater than  that of the sun4    ,the  
tides show themselves along shores in   
the form of waves which1 in  shallow    
water1 become translatory4 ,they differ 
from the wind-waves in  their           
periodicity1 and locally in their       
greater height4 ,the effects of  the    
tidal waves on the shores of the sea1   
and on the bottom in shallow  water1 are
 the same as the effect of wind-waves of
 equal strength1 and  need not be       
separately considered in connection with
 the gradation of  the sea-bottom4 ,in  
passing through narrow straits or narrow
 passes of  any sort1 the tidal movement
 becomes a current which1 under         
favorable  conditions1 abrades or       
8scours0 the bottom effectively4 ,the   

tidal  currents in the narrow passes    
about ,new ,york harbor may serve as an 
illustration4    ,aperiodic             
movements4--,in addition to the         
wind-waves which are  essentially       
constant and universal1 and to the tidal
 waves1 which are  periodic1 there are  
accidental waves which are locally and  
temporarily  of importance4 ,such are   
earthquake-waves1 which are sometimes   
extremely  destructive4 ,thus an        
earthquake-wave on the coast of ,peru in
 #agdf swept  a frigate several miles   
inland and deluged ,lima1 seven miles   
from the  shore4 ,the havoc of most     
earthquakes affecting coasts1 such as   
that  of ,lisbon in #agee1 is greatly   
aggravated by accompanying sea-waves4   
,earthquake-waves differ from ordinary  
waves in being translatory1 and  so in  
being more effective on the bottom in   
deep water4 ,their greatest  force1     
however1 is felt in shallow water and on
 shores4 ,volcanic  eruptions likewise  
give rise to exceptional aperiodic      

waves4 ,the same  is true of landslides 
where they affect the coast or any part 
of the  sea-bottom4 ,the fall of glacier
 ends and the capsizing of icebergs     
likewise generate strong waves4 ,to the 
category of exceptional waves  also     
belong those generated by the winds of  
exceptional storms1 such as  that which 
devastated ,galveston in #aijj4adi      
,summary4--,from the point of view of   
their direct geological results  in     
shallow water1 all movements of the     
sea-water may be grouped into  two main 
classes--7#a7 waves1 with the undertow  
and the littoral currents  they         
generate1 and 7#b7 ocean-currents4#aej  
,,waves4    ,wave-motion4#aea--,the most
 common waves1 and from the present     
point  of view the most important1 are  
those generated by winds4 ,during the   
passage of a wave1 each particle        
affected by it rises and falls1 and     
moves forward and backward describing an
 orbit in a vertical plane4 ,if  the    
passing wave is a swell1 the orbit of   

the particle is closed and is  either a 
circle or an ellipse2 but in the case of
 a wind-wave the orbit  is not closed4  
,in such a wave two things move forward1
 the undulation  and the water4 ,the    
velocity of the undulation is relatively
 rapid2  that of the water1 slow and    
rhythmic4 ,on the crest of the wind-wave
  each particle of water moves forward1 
and in the trough it moves less  rapidly
 backward1 and the excess of the forward
 movement over the  backward gives it a 
slight residual advance4 ,this residual 
advance is  the initiatory element of   
current4 ,by virtue of it1 the upper    
layer  of water is carried forward with 
reference to the layer below1 in the    
direction toward which the wind blows4  
,the waves of any considerable or       
long-continued wind1 therefore1 generate
 a current tending in the same          
direction as the wind4    ,the agitation
 of which waves are the superficial     
manifestation  is not restricted to the 
surface1 but is propagated indefinitely 

downward4 ,near the surface the amount  
of motion diminishes rapidly  with      
increasing depth 7,fig4 #bii71 but the  
rate of diminution itself  diminishes1  
and there seems no theoretic reason for 
assigning any  definite limit to the    
downward propagation of the oscillation4
    ,illustration3 ,fig4 #bii4--;,figure
 illustrating the decrease in the       
amount of wave-movement with increase of
 depth4 7,fenneman47    ,at the surface1
 the radius of the circular orbit which 
a particle of  water in a wave tends to 
describe is half the height of the wave4
 ,at a  depth equal to one wave-length1 
the radius of the circle described by  a
 particle is  as great as at the        
surface1 and at a depth equal  to two   
wave-lengths1 4 ,if the height of a wave
 be #dc feet1 the  radius of the circle 
described by a surface particle is #ba  
feet4 ,if  the length of the wave be    
#cjj feet1 the radius of a particle at a
 depth  of #cjj feet is only about  of  
an inch1 and at #fjj feet  of an        

inch4#aeb ,these figures make it clear  
that effective agitation of the  water  
does not extend to great depths4    ,so 
long as the velocity of the wind remains
 constant1 the velocity  of the current 
which the wind-waves generate is less   
than that of  the wind1 and there is    
always a differential movement of the   
water1  each layer moving faster than   
the one beneath4 ,the friction is thus  
distributed through the whole vertical  
column of the water in movement1  and is
 even borne in part by the sea-bottom if
 the movement extends  so far down4 ,the
 greater the depth1 the smaller the     
share of the  friction each layer of    
water is called upon to bear1 and the   
greater  the velocity of the current    
generated by a given wind4 ,but while   
the  wave-motion extends indefinitely   
downward1 the lower limit of agitation  
effective in erosion is soon reached4   
,engineering operations have shown  that
 submarine structures are little        
disturbed at depths of five  meters in  

the ,mediterranean and eight meters in  
the ,atlantic4#aec ,on  the other hand1 
dbris as coarse as gravel1 which is     
transported by  rolling on the bottom1  
is not infrequently carried out to      
depths of  #ej feet1 and sometimes even 
to #aej feet4 ,fine sediment1 like silt1
 is  disturbed at still greater depths1 
for ripple-marks1 which indicate        
agitation of the water1 are said to have
 been found at depths of #ajj           
fathoms4#aed    ,when a wave approaches 
a shelving shore1 its habit is changed4 
,the  velocity of the undulation is     
diminished1 while the velocity of the   
advancing particle of water in the crest
 is increased2 the wave-length1         
measured from trough to trough1 is      
diminished1 and the wave-height is      
increased2 the crest becomes acute1 with
 the front steeper than the  back1 and  
these changes culminate in the breaking 
of the crest1 when  the undulation      
proper ceases4 ,waves of a given height 
break in about  the same depth of water1

 and the line along which incoming waves
 break  is the line of breakers4 ,the   
line of breakers is in deeper water and 
farther from shore when the waves are   
strong than when they are weak4  ,waves 
are reported to have broken in #ajj     
fathoms of water1#aee but  this must be 
regarded as very exceptional4 ,the      
return of the water  thrown forward in  
the crests of waves is accomplished by a
 current  along the bottom called the   
undertow4 ,the undertow is sensibly     
normal  to the coast when uninfluenced  
by oblique waves1 and is efficient in   
removing the products of erosion4       
,since the incoming wave affects water  
which is at the same time under  the    
influence of the undertow1 it gives to  
that current a pulsating  character1 for
 the wave-motion sometimes supports and 
sometimes  opposes the undertow1 and    
thus endows it with a higher            
transporting  power than belongs to its 
mean velocity4 ,near the breaker-line1  
the  oscillations communicated by the   

wave may momentarily overcome and  even 
reverse the movement of the undertow4   
,inside the breaker-line1  irregular    
oscillation only is communicated4 ,the  
broken wave-crest1  dashing forward1    
overcomes the undertow and throws it    
back1 and the  water returns as a simple
 current descending a slope4 ,the power 
of the  undertow diminishes rapidly from
 the breaker-line outward as the depth  
of the water increases4                 
,illustration3 ,fig4 #cjj4--;,diagram   
showing relative directions of wave1    
undertow1 and shore-current4    ,when   
waves advance on the shore obliquely1 a 
shore-current is developed  as          
illustrated by ,fig4 #cjj1 where ab     
represents the direction of the         
incoming wave1 bc the direction of the  
littoral current1 and bd the  direction 
of the undertow4 ,where they strike the 
borders of land1 the  wind-waves1       
therefore1 generate two other movements1
 the undertow and  the littoral current4
 ,any particle of water near shore may  

be affected  by any two or by all three 
of these movements at the same moment4  
,the  effect of littoral current and    
undertow is to give a particle of water 
on which both are working a direction   
between the two1 as be4 ,the  effect of 
other combinations can be readily       
inferred4 ,these various  combinations  
are of consequence in the transportation
 of dbris4                              
,,work ,,of ,,the ,,waves4              
,erosion4    ,the general effects of the
 waves and the other movements to which 
they give rise along shores are 7#a7 the
 wear of the shores2 7#b7 the           
transportation for greater or less      
distances of the products of wear2  and 
7#c7 the deposition of the transported  
materials4    ,by waves and             
undertow4--,in the dash of the waves    
against the shore1  the chief wear is   
effected by the impact of the water and 
of the dbris  which the water carries4  
,lesser results are accomplished in     
other ways4    ,when the land at the    

margin of the water consists of         
unconsolidated  material1 or of         
fragmental material but slightly        
cemented1 the impact  of the water is   
sufficient to displace or erode it4 ,if 
weak rock be  associated with resistant 
rock within the zone of wave-work1 the  
removal of the former may lead to the   
disruption and fall of the  latter1     
especially when weak rock is washed out 
from beneath the  strong4 ,the impact of
 the water is competent also to break up
 and  remove rock which was once        
resistant1 but which has been           
superficially  weakened by changes of   
temperature4 ,rock affected by numerous 
open  joints is likewise attacked with  
success1 for by the dash of the waves   
the blocks between the joints may be    
loosened and literally quarried  out4   
,it may1 however1 be doubted whether the
 dash of waves of clear  water1 even    
when their force is many tons to the    
square foot1 has any  appreciable power 
to wear rock which is thoroughly solid4 

,illustration3 ,fig4 #cja4--;,angular   
blocks of rock which have fallen    from
 the cliff above1 as a result of        
undercutting by the waves4    ,grand    
,island1 ,lake ,champlain4 ,the rock is 
,black ,river limestone4    ,although   
from the shore of a lake instead of the 
sea1 the principles    illustrated are  
the same4 7,perry47    ,the impact of   
the waves is generally reinforced and   
made effective  by the impact of the    
detritus they carry4 ,the sand1 the     
pebbles1 and  such stones as the waves  
can move are used as weapons of attack1 
being  turned against one another and   
against the shore4 ,masses of rock too  
large for the waves to move 7,fig4 #cja7
 are worn by the detritus    driven back
 and forth over them1 and in time       
reduced to movable  dimensions 7,fig4   
#cjb74 ,they then become the tools of   
the waves1 and in  use1 are reduced to  
smaller and smaller size4 ,thus bowlders
 are reduced  to cobbles1 cobbles to    
pebbles1 pebbles to sand1 and sand to   

silt4  ,the silt is readily held in     
suspension in agitated water1 and thus  
is  carried out beyond the range of     
breakers1 and settles in water so deep  
as not to be effectively agitated to its
 bottom4 ,thus one generation  of       
bowlders after another is worn out1 and 
the comminuted products are  carried out
 from the immediate shore and deposited 
in deeper water4    ,the effectiveness  
of waves1 whether they work by impact of
 water alone1  or by impact of water and
 detritus1 is dependent on their        
strength  and on the concentration of   
their blows4#aef ,the strength of waves 
is dependent on the strength of the     
winds 7or other generating cause7  and  
the depth and expanse of the water1 and 
the concentration of  their blows is    
conditioned by the slope against which  
they break4 ,on  exposed ocean-coasts   
the fetch of the waves is always great4 
,the winds  are variable4 ,for a given  
coast they have an average strength1 but
  the effectiveness of wave-erosion is  

determined less by the average  strength
 of waves than by the strength of the   
storm-waves4 ,this is  often very great4
 ,on the ,atlantic and ,north ,sea      
coasts of ,britain1  winter breakers    
which exert a pressure of three tons per
 square  foot are not infrequent4#aeg   
,so great is the force of exceptional   
storm-waves that blocks of rock         
exceeding #ajj tons in weight are  known
 to have been moved by them4            
,ground-swells1 8even when no wind  is  
blowing1 often cover the cliffs of north
 ,scotland with sheets of  water and    
foam up to heights of #ajj or even      
nearly #bjj feet4 ,during  northeasterly
 gales the windows of the ,dunnet ,head 
lighthouse1 at  a height of upwards of  
#cjj feet above high-water mark1 are    
said  to be sometimes broken by stones  
swept up the cliffs by sheets of        
sea-water40#aeh ,the average force of   
waves on the ,atlantic coast of         
,britain has been found to be #faa lbs4 
per square foot in summer1 and  #bjhf   

lbs4 in winter4#aei    ,where deep water
 extends up to the shore1 the force of  
the wave is  almost wholly expended near
 the water line2 where shallow water    
borders  the land1 the force of the     
waves is expended over a greater area4  
,waves are1 therefore1 most efficient on
 bold coasts bordered by broad  expanses
 of deep water4    ,the less familiar   
phases of wave-work are accomplished by 
hydraulic  pressure1 compressed air1 the
 use of ice1 etc4 ,when the water of a  
wave is driven into an open joint or a  
cave1 the hydraulic pressure  is great1 
and if the structure be weak1 the rock  
may be broken4 ,when  water is driven   
with force into a cave1 the compression 
of the air  may be great if the wave be 
high enough to close the entrance4 ,when
  the water runs out of a cave1 the air 
within may be greatly rarefied1  while  
that above exerts its normal pressure4  
,in either case the roof  of the cave1  
if it be weak1 may be broken4 ,at       
certain seasons of the  year1 especially

 during the spring1 waves make          
destructive use of the  ice which is    
then breaking up1 but it is only in high
 latitudes that  sea-ice is of          
consequence in this way4 ,in general1   
the effect of its  presence in keeping  
down waves overbalances its effect as an
 agent of  erosion4    ,illustration3   
,fig4 #cjb4--,showing blocks similar to 
those of ,fig4 #cjf1    reduced and     
rounded by wave-action4 ,shore of ,lake 
,champlain4 ,the rock    is ,utica      
shale4 7,perry47    ,the direct effect  
of wave-erosion is restricted to a zone 
which is  narrow both horizontally and  
vertically4 ,there is no impact of      
breakers  at levels lower than the      
troughs of the waves1 though erosion may
  extend down to the limit of effective 
agitation 7p4 #cda74 ,the efficient     
impact of waves is limited upward by the
 level of the wave-crests1  although the
 dash of the water produces feebler     
blows at higher levels4  ,the rise and  
fall of the water during the flow and   

ebb of the tides  gives the waves a     
greater vertical range than wind-waves  
alone would  have4 ,the vertical zone of
 direct wave-work is therefore limited  
above  by the level of wave-crests1 and 
below by the depth of wave-troughs      
7nearly74 ,the indirect work of waves is
 limited only by the height  of the     
shore1 for as the zone of excavation is 
carried landward1  masses higher up the 
slope are undermined and fall4 ,the     
fallen rock  temporarily protects the   
shore against the waves1 but are        
themselves  eventually broken up4       
,illustration3 ,fig4 #cjc4--;,diagram   
illustrating high sea-cliffs4 ,it       
also shows a submerged terrace1 due     
partly to wave-cutting 7wave-cut        
terrace71 and partly to building        
7wave-built terrace74 7,gilbert47       
,illustration3 ,fig4 #cjd4--;,diagram   
showing a low sea-cliff4 7,gilbert47    
,the pulsating current of the undertow  
7p4 #cda7 has both an erosive and  a    
transporting function4 ,it carries the  

detritus of the shore to and  fro1 and  
dragging it over the bottom1 continues  
downward the erosion  initiated by the  
breakers4 ,this downward erosion is the 
necessary  concomitant of the shoreward 
progress of wave-erosion2 for1 if the   
land were merely planed away to the     
level of the wave-troughs1 the  incoming
 waves would break where shoal water was
 first reached1 and  become ineffective 
at the water margin4 ,the rate of       
erosion by the  undertow becomes less   
and less as the surface it affects is   
lowered4  ,littoral currents do little  
erosive work beyond that inflicted on   
the  material which they transport4     
,the general result of wave-erosion is  
the advance of the sea on the  land1 the
 rate of advance being determined       
chiefly by the nature of the  material  
attacked and the strength of the waves4 
,numerous as examples  are of the       
retreat of coast-lines before the       
advance of the sea1 it  is not to be    
understood that the advance of the sea  

on the land is  universal or            
uninterrupted4 ,numerous instances may  
be cited of the  encroachment of the    
land on the sea4 ,at ,long ,branch the  
advance of the  sea1 in spite of        
elaborate breakwaters1 has been so rapid
 in recent  years as to menace important
 buildings1 while a few miles to the    
north  and south1 the land is advancing 
in the face of the waves4 ,the low      
coast of the ,middle ,netherlands has   
retreated two miles or more in  historic
 times1#afj but the opposite tendency is
 shown at other points  in the same     
region4 ,on the coast of ,england the   
sites of villages have  disappeared by  
the advance of the sea within historic  
times1#afa but  the coast of the same   
island affords illustrations of land    
advance4 ,on  the south side of         
,nantucket island1 the sea-cliff has    
been known to  retreat before the waves 
as much as six feet in a single         
year4#afb  ,almost every considerable   
stretch of coast affords illustrations  

both  of the advance of the sea on the  
land and of land on the sea2 but in  the
 long run1 the former must exceed the   
latter1 diastrophic movements  aside4   
,illustration3 ,fig4 #cje4--,steep cliff
 developed by waves4 ,allen ,point1     
,grand ,island1 ,lake ,champlain4       
7,perry47    ,illustration3 ,fig4       
#cjf4--;,cliff in unconsolidated        
material 7bowlder    clay71 with        
lake-beach in foreground4 ,south        
,manitou ,island1 ,lake    ,michigan4   
7,russell1 ,u4 ,s4 ,geol4 ,surv47       
,illustration3 ,fig4 #cjg4--,steep cliff
 in unconsolidated material1 the        
result of rapid cutting4 ,southeast     
extremity of ,grove ,point1 ,md4        
,topographic ,features ,developed by    
,wave-erosion4    ,illustration3 ,fig4  
#cjh4--,standing ,rock4 ,a wave-erosion 
monument4 ,west    shore of ,random     
,sound1 south of ,clarenville1 ,n4 ,f4  
7,walcott1 ,u4 ,s4    ,geol4 ,surv47    
,the sea-cliff4--,the action of the     
waves1 cutting as they do along  a      

definite horizontal zone1 has been      
compared to the action of a  horizontal 
saw4 ,as the waves cut into the shore at
 and near the  water-level1 the material
 above1 being unsupported1 falls1       
leaving a  steep face above the line of 
cutting4 ,this steep face is known as   
the  sea-cliff 7,figs4 #cja to #cjf74   
,the same term is sometimes applied to  
the cliffs of lakes4 ,the principles    
involved in the development of the      
sea-cliff are applicable to any broad   
stretch of water4    ,the height of the 
cliff depends on the height of the land 
on which  the sea is advancing4 ,its    
slope may be steep or gentle 7compare   
,figs4  #cjc to #cjf71 according to the 
nature of the material of which it is   
composed and the rapidity of the        
cutting4 ,rapid cutting tends to        
produce steep cliffs and slow cutting   
gentle ones1 for in the latter  case    
weathering is more important relative to
 the cutting1 and at  sea-level 7low    
altitudes7 weathering generally tends to

 reduce the  angle of slope4 ,in        
general1 the more resistant the material
 the steeper  the slope of the cliff4   
,incoherent materials1 such as sand and 
clay1  are not likely to form steep     
cliffs2 but if the cutting be very      
rapid1  bold faces may be developed even
 in such materials 7,fig4 #cjg74 ,if    
beds  of slight resistance at sea-level 
underlie beds of greater resistance1    
the development of steep cliffs is      
favored4 ,the structure of the          
cliff-rock also has an influence on the 
slope4 ,the rock may be massive  or     
bedded4 ,if bedded1 the beds may be     
horizontal1 or they may dip at  any     
angle1 in any direction4 ,the rock1     
whether stratified or not1 may  be      
abundantly or sparsely jointed4 ,all    
these structures influence the  slope   
and configuration of the sea-cliff 7see 
,figs4 #cje to #cjh74    ,illustration3 
,fig4 #cji4--8,old ,man of ,hoy40       
7,geikie47    ,chimney-rocks1 etc4--,by 
working in along the joints of the rock1

  widening them and quarrying out the   
intervening blocks1 pillars of  rock    
78chimney-rocks10 8pulpit-rocks07 or    
even considerable islets are  sometimes 
isolated by the waves4 ,this is most    
readily accomplished  where the joints  
converge back from the shore4 ,a        
well-known example  of this sort is the 
8,old ,man of ,hoy0 7,fig4 #cji7 on the 
coast of the  ,orkneys4 ,a pulpit-rock  
or other island1 or any jutting point of
  rock may be pierced1 giving an arch or
 bridge4 ,la ,roche ,perce1 a           
steep-faced isle near ,gasp ,harbor1 is 
an example4    ,sea-caves4--,waves      
sometimes excavate caves at the bases of
 cliffs4  ,this is especially likely to 
occur where the rock is much jointed and
  where the joints are not continued to 
the surface in a single plane4  ,the    
bottom and roof of a sea-cave usually   
have a pronounced inclination  landward4
 ,if the cliff be low1 the cave may be  
extended landward until  its roof is    
pierced4 ,through such an opening in the

 top of the cliff  the water of the     
incoming waves may be forced in the form
 of spray4  ,on the ,new ,england coast 
such holes are sometimes known as       
8spouting  horns40 ,similar openings may
 be made1 as already pointed out1 by the
  compression or rarefaction of the air 
in the cave as the wave enters or       
retreats4 ,if the roof of the cave be   
partially destroyed1 the portion  which 
remains may form an arch or bridge4     
,such a bridge occurs on  ,santa ,cruz  
,island1 ,california 7,fig4 #caj74      
,illustration3 ,fig4 #caj4--;,an arch   
developed by waves4 ,santa ,cruz        
,island1 ,cal4 7,law47    ,the cave1 the
 8spouting horn10 the 8bridge10 the     
8pulpit-rock10 and  other isolated      
islets1 are all closely associated with 
the sea-cliff in  origin4    ,the       
wave-cut terrace4--,the bottom of the   
sea-cliff is bordered by a  submerged   
platform over which the water is        
shallow4 ,this platform1  or at any rate
 its landward portion1 represents the   

area over which  the water has advanced 
as the result of wave-cutting1 and is1  
therefore1 known as the wave-cut        
terrace4 ,from the method of cliff      
development it will be seen that the    
wave-cut terrace is its necessary       
accompaniment4 ,such a terrace has a    
gentle slope to seaward1 for its  outer 
and older edge has been degraded longer 
and more4 ,its slope is  influenced by  
the strength of the waves1 being greater
 where they are  stronger4 ,the outer   
edge of the wave-cut terrace is often   
marked by  an abrupt descent4 ,fig4 #cjc
 represents the wave-cut terrace in its 
relation to the sea-cliff above4        
,illustration3 ,fig4 #caa4--;,an        
elevated cliff above ,great ,salt ,lake4
    ,in this case the water-level has   
been lowered4 7,gilbert1 ,u4 ,s4 ,geol4 
,surv47    ,so long as wave-cut terraces
 are submerged1 they do not appear on   
topographic maps of the land1 though    
they appear on the charts of the        
coasts2 but if a coastal tract with     

wave-cut terraces be elevated1 or  if   
the sea-level be drawn down1 the        
terraces become land4 ,elevated         
sea-cliffs and wave-cut terraces are    
among the best evidences of change  of  
relative level between water and land   
7,fig4 #caa74    ,wave-erosion and      
horizontal configuration4--,the         
structure of the rock  along shore has  
as much to do with the horizontal       
configuration of  the wave-shaped coast1
 as with its relief4 ,in general1 waves 
develop  rentrants in the less resistant
 portions of the shore1 leaving the     
more resistant parts as headlands 7,san 
,pedro ,point and ,devil's ,slide1  ,pl4
 ,,xx1 ,coast of ,california74 ,it is to
 be noted that the resistance  of rock  
to wave-erosion is not determined by its
 hardness alone4  ,every division plane1
 whether due to bedding1 to jointing1 or
 to  irregular fracture1 is a source of 
weakness to the rock1 and rock  of great
 hardness may be so broken as to offer  
relatively little  resistance4          

,inequalities of resistance1 whatever   
their cause1 give  origin to            
inequalities of coastal configuration   
where wave-erosion is  in progress4     
,given a coast of marked regularity and 
equal exposure1  but composed of        
unequally resistant material1 the waves 
will make it  irregular by cutting most 
where the material is least resistant4  
,a  regular coast of uniform material1  
but unequal exposure1 will be made      
irregular by the greater cutting at the 
points of greater exposure4 ,a  coast of
 marked irregularity and homogeneous    
material will be made more  regular by  
the cutting off of the projecting       
points1 because they are  most exposed4 
,with a given set of conditions1 waves  
tend to develop  a certain sort of      
shore-line which1 so far as its         
horizontal form is  concerned1 is       
relatively stable4 ,such a shore-line   
may be said to be  mature#afc so far as 
wave-erosion is concerned4 ,since       
coastal lands  are1 in general1 both    

heterogeneous and unequally exposed1 a  
mature  coast-line is somewhat          
irregular4 ,its maturity is attained    
when the  lesser exposure in the        
rentrants developed in the less         
resistant  parts1 balances the superior 
exposure of the projections of the more 
resistant portions4    ,since the       
conditions of erosion along coasts are  
constantly1 even if  slowly1 changing1  
maturity is constantly being approached1
 but rarely  reached4 ,other forces and 
processes1 such as those of aggradation1
  vulcanism1 and diastrophism1 are in   
operation along coasts1 and  their      
results are sometimes antagonistic to   
those of the waves4 ,the  horizontal    
configuration of coasts is1 therefore1  
the result of many  coperating forces1  
of which waves are but one4 ,it is1     
nevertheless1  important to note the    
goal to which the waves are working1    
even though  they are continually       
defeated in their attempt to reach it4  
,their  immediate goal is an equilibrium

 of erosion-rate and maturity of        
configuration2 their final goal is the  
destruction of the land and the         
deposition of its substance in the sea1 
that is1 in a position nearer  the      
center of gravity of the earth4         
,transportation by ,waves4    ,the      
material eroded from the shore by the   
waves in the shaping of the  cliff and  
terrace is carried away by the joint    
action of the waves1  undertow1 and     
shore-currents4    ,the in-coming wave  
begins to shift material where it begins
 to drag  bottom1 that is1 a little     
outside the line of breakers4 ,from the 
line  where transportation begins1 to   
the line of breakers1 bottom detritus   
is shifted shoreward by the waves1 while
 the undertow tends to carry it  back   
again4 ,between the breakers and the    
shore there is also a tendency  for the 
on-shore movement to carry dbris to the 
water's edge1 and for  the ebbing wave  
to carry it back again4 ,the result of  
these opposed  tendencies is to keep    

sediment in transit between the shore   
and the  line of breakers4 ,if the      
in-coming waves have a direction normal 
to the  shore1 the advance and recoil of
 the water move particles toward and    
from the shore1 but effect no transfer  
along the shore2 but the results  which 
waves normal to the shore would achieve 
are always modified by  other waves and 
by littoral currents4    ,if the        
in-coming wave is oblique to the shore1 
it shifts material in  its own          
direction4 ,the transfer by undertow1   
taken alone1 would be  sensibly normal  
to the shore1 but the effect of the     
oblique waves is  to slightly modify    
this direction4 ,there is thus a slow   
transportation  along shore1 even in the
 absence of steady currents4 ,a great   
amount  of transportation would be      
effected in this way1 though it would   
be carried on at a slow rate4 ,oblique  
waves also tend to develop a  definite  
shore-current 7p4 #cdb7 which affects   
both the amount and  direction of the   

transportation4 ,any particle in        
suspension1 or in  motion on the bottom 
as the result of the wave or undertow1  
is shifted  along shore by the littoral 
current1 which affects the same water   
7,fig4 #cjj74 ,by the coperation of     
wave- and shore-current1 more and       
heavier material can be moved than by   
either alone1 and the direction  of     
movement is more nearly parallel to the 
shore than that of the  wave4           
,similarly1 by the coperation of        
undertow and shore-current1  more and   
heavier material can be moved than by   
either alone4 ,the  direction of        
movement is readily inferred from ,fig4 
#cjj4 ,the direction  in which dbris is 
shifted by wave- and shore-current is   
modified by  the undertow1 and the      
direction which would result from       
undertow and  current is modified by the
 wave4 ,it is often the waves of storms1
  rather than those of the prevailing   
winds1 which determine the  direction of
 greatest shore transportation4    ,the 

waves1 the undertow1 and the littoral   
currents work together in  assorting the
 detritus of the shore4 ,the coarsest   
parts may be beyond  the power of all   
but the strongest waves4 ,they          
accumulate where  agitation is great4   
,less coarse parts are shifted farther  
from the site  of greatest agitation1   
but no materials which are classed as   
coarse  are carried beyond the depth of 
sensible movement4 ,the coarse material 
which covers the bottom where the       
agitation of the water at the bottom  is
 effective1 constitutes shore drift4    
,shore drift is not all derived from the
 shore by the cutting of the  waves4 ,a 
part of it is brought to the sea by     
streams and mingled with  that eroded   
from the cliffs4 ,the material which is 
fine enough to be  held in suspension is
 measurably independent of depth4 ,this 
is shown  during storms when the water  
becomes turbid far beyond the line of   
breakers1 and clears only after the     
waves have died away4    ,this sorting  

of shore drift1 effected while it is in 
transportation1 is  often very perfect4 
,the conditions favoring assortment are 
7#a7 vigorous  wave-action1 7#b7        
prolonged transportation1 and 7#c7 a    
moderate volume of  sediment4#afd ,the  
effect of these several conditions will 
be readily  understood4    ,extensive   
transportation of shore drift of a given
 degree of coarseness  is favored by    
7#a7 strong waves and undertow1 7#b7    
continuous currents1  and 7#c7 shallow  
water1 deepening but gradually off      
shore4             ,deposition by       
,waves1 ,undertow1 and                  
,shore-currents4#afe    ,illustration3  
,fig4 #cab4--;,cross-section of the     
beach4 7,gilbert47    ,the beach4--,the 
zone occupied by the shore drift in     
transit is the  beach4 ,the lower margin
 is beneath the water1 a little beyond  
the  line where the great storm-waves   
break4 ,its upper margin is at the      
level reached by storm-waves1 and is    
usually a few feet above the level  of  

still water4 ,to the beach1 material is 
brought from seaward by the  in-coming  
waves1 and from it detritus is carried  
out by the undertow4  ,the cross-section
 of a beach is shown in ,fig4 #cab4 ,in 
horizontal  position the beach follows  
the general boundary between water and  
land1  though it does not conform to its
 minor irregularities 7,fig4 #cac74 ,the
  beach or barrier ridge often causes   
the deflection of the lower courses  of 
streams descending to it 7,pl4 ,,xxi74  
,illustration3 ,fig4 #cac4--;,a         
lake-beach 7barrier72 ,griffin's ,bay1  
,lake  ,ontario4    ,illustration3      
,,plate ,,xxi4      ,,new ,,jersey      
,u4 ,s4 ,geol4 ,surv4    ,illustration3 
,,plate ,,xxii4      ,fig4 #a4 ,,portion
 ,,of ,,south ,,coast ,,of ,,marthas    
,,vineyard1 ,,massachusetts4    ,u4 ,s4 
,geol4 ,surv4      ,fig4 #b4 ,,portion  
,,of ,,the ,,california ,,coast ,,near  
,,tamalpais4    ,u ,s4 ,geol4 ,surv4    
,illustration3 ,fig4 #cad4--,section of 
a barrier4 7,gilbert47    ,the          

barrier4--,when the agitation of the    
water along shore becomes  insufficient 
to carry the material1 it is dropped4   
,in its deposition it  assumes various  
forms4 ,where the bottom of the lake or 
sea near shore  has a very gentle       
inclination1 the in-coming waves break  
some distance  from the shore-line1 and 
it is here that the most violent        
agitation  occurs when the waves are    
strong4 ,to this line of breakers1      
material  is shifted from both          
directions3 from shore by undertow1 and 
from  seaward by the waves4             
,accumulating here1 it builds up a low  
ridge4  ,this is a barrier 7,fig4 #cad74
 ,if it is built up above the surface of
  the water by storm-waves1 it may shut 
in a lagoon behind it1 and this  may    
ultimately be filled by sediment washed 
down from the land4 ,at one  stage in   
the filling1 the lagoon becomes a       
marsh4#aff ,in the part  which the      
barrier plays in the history of a coast1
 it is identical with  the beach4       

,illustration3 ,fig4 #cae4--;,a recurved
 spit4 ,dutch ,point1 ,grand ,traverse  
,bay1 ,lake ,michigan4    ,illustration3
 ,fig4 #caf4--;,cross-section of a bar4 
7,gilbert47    ,the spit1 the bar1 and  
the loop4--,the disposition of          
shore-deposits  depends largely on the  
currents at and near shore4 ,if the     
coast-line  is deeply indented1 the     
littoral current usually fails to follow
 the  rentrants4 ,in holding its course 
across the mouth of a small bay1  a     
shore-current usually passes into deeper
 water4 ,here its velocity  is checked  
because its motion is communicated to   
the water beneath  it1 and a larger     
amount of water being involved in the   
motion1 the  motion of each part is     
diminished4 ,if sediment was being moved
 along  its bottom before the current   
was checked1 some part of it is dropped 
when and where the current is slackened4
 ,it follows that deposition  commonly  
takes place beneath a littoral current  
as it crosses the  mouth of a bay4 ,the 

belt of deposition is often narrow1 and 
the result  is the construction of a    
ridge beneath the water in the direction
 of  the current4 ,the current would    
never build the embankment up to the    
water-level1 but when its surface       
approaches the level of effective       
agitation1 the waves may begin to work  
on it1 as on a barrier1 and  may build  
it up to1 and even above1 the surface of
 the water4 ,so long  as the end of such
 an embankment is free1 it is a spit    
7,fig4 #cae  and ,pl4 ,,xxi74 ,if the   
spit be lengthened until it crosses1 or 
nearly  crosses1 the bay1 shutting it   
off from the open water1 it becomes a   
bar4 ,bars have shut in lakes 7ponds7 on
 the coast of ,martha's ,vineyard1      
,mass4 7,fig4 #a1 ,pl4 ,,xxii71 and     
lakes and lagoons at numerous points    
both on the ,atlantic and the ,pacific  
coasts 7,fig4 #b1 ,pl4 ,,xxii1 ,rodeo   
lagoon74 ,the same phenomena are to be  
seen along many lake shores4  ,bars     
sometimes tie islands to the mainland   

7,pl4 ,,xxiii1 ,fig4 #a1 ,nahant1       
,mass42 ,fig4 #b1 near ,biddeford1      
,me474 ,the structure of a bar as seen  
in  cross-section is shown in ,fig4     
#caf4    ,the construction of a spit has
 been aptly compared to the construction
  of a railway embankment across a      
depression4 ,the material is first      
carried out from the bordering upland   
7shallow water7 and dumped where  the   
slope to the depression 7deep water7    
begins4 ,the embankment thus  begun is  
extended by the carrying out of new     
material1 which is left at  the end of  
the dump already made4    ,if the bay   
across which the bar is built receives  
abundant drainage  from the land1 the   
outflow from the bay may be sufficient  
to prevent  the completion of the bar   
7,fig4 #b1 ,pl4 ,,xxii71 for when the   
growth of  the spit has sufficiently    
narrowed the outlet of the bay1 the     
sediment  brought to the end of the spit
 by the littoral current will be swept  
out beyond the spit by the current      

setting out from the bay4    ,the       
completion of a bar may be interfered   
with by tidal currents1 even  without   
land-drainage4 ,currents generated by   
the tides may sweep in  or out of the   
bay with increased force as the entrance
 is narrowed1  carrying in or out the   
sediment which the littoral current     
would have  left at the end of the spit4
 ,the scour of the tides often insures  
deep entrances 7inlets7 to bays1 and    
maintains definite channels or          
8thorofares0 in the lagoon marshes      
behind barriers and spits4 ,the         
sediment brought down from the land1 as 
well as that washed in by tidal         
currents and waves1 tends to fill up the
 lagoon behind a barrier1 a  spit1 or a 
bar1 converting it into land 7,fig4     
#cag74    ,illustration3 ,fig4          
#cag4--,sketch of a portion of the ,new 
,jersey coast4    ,the dotted belt next 
the sea is the barrier1 modified by the 
wind4    ,the area marked by the        
diagonal lines is the mainland4 ,in the 

marshy    area between1 there are       
numerous channels or 8thorofares0 kept  
open    by the currents4 ,the figures   
show the depths of water in feet4 ,scale
    about  inch  #a mile4    ,since     
spits and bars are built only where     
there is shore-drift in  transit1 they  
are always built out from a beach or    
barrier4 ,the distal  end of the bar may
 also join a beach or barrier4 ,traced  
back to  its source1 the beach from     
which a spit leads out is often found to
  terminate in the cliff from which the 
material of the beach and the  spit were
 derived 7,pl4 ,,xx and ,fig4 #b1 ,pl4  
,,xxii74 ,in such cases the  sediment of
 the beach has been shifted but a short 
distance2 but in  other cases it has    
traveled far4    ,illustration3 ,fig4   
#cah4--,map of shore-terraces1 largely  
wave-built4    ,lake ,bonneville4       
7,gilbert47    ,illustration3 ,fig4     
#cai4--;,a portion of the ,texas coast  
showing the    tendency of              
shore-deposition to simplify the        

coast-line4 ,the deposits    7the narrow
 necks of land parallel to the coast7   
shut in the bays4    7,from chart of ,c4
 and ,g4 ,surv47    ,illustration3 ,fig4
 #cbj4--,map showing that in the early  
stages of the    simplification of a    
shore-line the irregularities are       
increased4 ,the    numbers indicate the 
depth of water in fathoms4 7,from chart 
of ,c4 and    ,g4 ,surv47    ,the spit  
is usually either straight or in        
conformity with the general  course of  
the shore-current1 but since the        
littoral current itself is  subject to  
alteration as the result of shifting    
winds1 the spit may  depart from        
straightness4 ,winds which simply       
reverse the direction of  the littoral  
current retard its construction1 but may
 not otherwise  affect it2 but if a     
strong current be made to flow past the 
end of a  spit1 it may cut away its     
extremity and rebuild the materials into
 a  smaller spit1 joining the main one  
at an angle4 ,this gives rise to a  hook

 7,fig4 #cae74 ,successive storms may   
develop successive hooks along  the side
 of a growing spit4 ,the end of a hook  
may be so extended as to  join the      
mainland1 when it becomes a loop4       
,wave-built terraces4--,under the       
influence of off-shore currents1        
littoral currents may be drawn from the 
coast-line4 ,if such a current          
continues as a well-defined             
surface-current1 it builds a spit1 but  
if it spreads1 it tends to build a      
terrace4 ,the accumulation then  is not 
at the end of a beach1 as in the case of
 a spit1 but on its  side1 and the      
result of the deposition is to carry the
 beach seaward4  ,the undertow abets the
 process4 ,the widened beach is a       
wave-built  terrace4 ,the wave-built    
terrace often borders the wave-cut      
terrace  along its seaward margin       
7,figs4 #cjc and #cah74 ,with the help  
of waves1  the surface of the terrace   
may be built up into land by the        
expansion  of the crest of the beach4   

,terrace-cutting and terrace-building   
are  both involved in the development of
 the continental shelves4    ,beach     
ridges1 spits1 bars1 etc41 like         
sea-cliffs and wave-cut terraces1  are  
often preserved after the relative level
 of sea and land has  changed4 ,if the  
shore has risen1 relatively or          
absolutely1 these  features are relied  
on as evidences of the change4 ,if shore
 features  be submerged instead of      
elevated1 they furnish less accessible1 
though  not less real1 evidence of the  
change of level4 ,similar features      
about lakes have a like significance1   
but in this case it is often            
demonstrable that it is the water rather
 than the land which has  changed its   
level4              ,effect of          
,shore-deposition on ,coastal           
,configuration4    ,the tendency of     
shore-deposition is to cut off bays and 
to straighten  and simplify the         
shore-lines4 ,this is abundantly        
illustrated along  the ,atlantic and    

,gulf coasts of the ,united ,states 7see
 ,fig4 #cai and  ,pl4 ,,xxii74 ,it is to
 be noted1 however1 that in the         
simplification of  the shore-line       
through deposition1 the initial stages  
often result  in great irregularity     
7,fig4 #cbj and ,pl4 ,,xxiii74 ,in some 
cases1 the  irregularities are not      
temporary4 ,thus deltas 7p4 #aih71      
though  not wholly the work of sea- 7or 
lake-7 water1 often constitute          
irregularities of a more or less        
permanent nature4 ,this is the case     
where they project beyond the general   
trend of the coast-line4 ,where1  on the
 other hand1 they are built at the heads
 of bays1 they tend to  simplify the    
coast-line by obliterating the          
indentation4 ,the delta at  the head of 
the ,gulf of ,california is an example4 
,so too is the delta  of the            
,mississippi1 the real head of which is 
far above the present  debouchure of the
 stream4 ,the form of the delta in      
ground-plan depends  on the horizontal  

configuration of the coast where it is  
developed1 on  the strength of the waves
 and shore-currents1 and on their       
relation  to the amount of detritus     
contributed by the stream concerned4    
,good  illustrations are furnished by   
the ,gulf of ,mexico where the deltas of
  the ,mississippi and ,rio ,grande are 
in contrast4    ,so far as concerns the 
vertical configuration of coasts1       
erosion and  deposition are in contrast1
 for while the former tends to develop  
steep1 irregular1 and often high slopes 
7p4 #cdi7 from the land to  the sea1 the
 latter tends to develop gentle1        
regular1 and low ones4  ,a partial      
exception to the latter part of this    
general statement  comes about through  
the building of dunes1 the material for 
which is  furnished by the waves4       
,,summary ,,of ,,coastal                
,,irregularities4    ,the horizontal    
irregularities of coasts are both large 
and small4  ,some of them1 like         
,florida1 ,sandy ,hook1 etc41 consist   

primarily of  projections of land into  
the sea2 others1 like ,chesapeake ,bay1 
the ,gulf  of ,mexico1 and ,puget       
,sound1 are projections of the sea into 
the land2  while still others1 like the 
,gulf of ,california and its associated 
peninsula1 cannot readily be put in     
either of the foregoing classes4  ,some 
of the irregularities of the land       
border1 such as ,yucatan1 are  more or  
less nearly normal to the general trend 
of the coast which they  affect1 while  
others1 such as the 8beaches0 along the 
,atlantic and  ,gulf coasts of the      
,united ,states 7,figs4 #cai and #cbj71 
are more or less  nearly parallel with  
it4 ,some of the irregularities1        
especially some of  the small ones1 are 
more or less angular in their outline   
7,pl4 ,,xx and  parts of ,fig4 #b1 ,pl4 
,,xxii71 while others are bounded by    
curves instead4    ,in many cases more  
than one factor has been involved in the
 development  of irregularities4 ,in the
 case of great irregularities1          

diastrophism  has generally been the    
dominant factor4 ,the ,gulf of ,mexico  
and the  ,mediterranean ,sea perhaps    
represent differential subsidence1 while
  ,florida and the ,iberian peninsula   
represent differential uplift           
7relative1 though perhaps not absolute74
 ,the narrow bays which indent  many    
coasts generally represent the          
subsidence of a region previously       
affected by valleys 7,fig4 #big74 ,many 
of them1 such as ,narragansett1         
,delaware1 and ,chesapeake ,bays1 are   
primarily the drowned ends of  river    
valleys1 while others1 such as ,puget   
,sound1#afg are primarily  structural   
valleys 7synclines74 ,many of the long  
and narrow bays or  fiords common in the
 high latitudes of ,north ,america and  
,europe 7,fig4  #bff1 p4 #bic7 appear to
 be the drowned ends of valleys         
previously  deepened by glaciers4 ,the  
drowned ends of river canyons1 and the  
submerged parts of valleys excavated    
7not sunk7 beneath the sea by  glaciers1

 would also be fiords4    ,illustration3
 ,,plate ,,xxiii4      ,fig4 #a4        
,,massachusetts4    ,u4 ,s4 ,geol4      
,surv4      ,fig4 #b4 ,,maine4    ,u4   
,s4 ,geol4 ,surv4    ,illustration3     
,,plate ,,xxiv4      ,,portion ,,of     
,,the ,,coast ,,of ,,maine4    ,u4 ,s4  
,geol4 ,surv4    ,the processes which   
develop coastal indentations1 together  
with the  antecedent subarial and the   
subsequent wave gradation1 account for  
most of the islands which affect        
indented coasts4 ,some of them are  high
 and some low for reasons which will be 
readily understood4 ,the  long narrow   
belts of land constituting              
irregularities parallel to the  general 
trend of the coast 7,figs4 #cai and     
#cbj7 are usually the result  of        
deposition in shallow water4 ,they are  
usually sand or coral reefs1  built up  
above water-level by waves4 ,the        
deposits at the debouchures  of streams 
give rise to projecting deltas4 ,most   
small irregularities  of angular form1  

especially if high 7,pl4 ,,xx71 indicate
 wave-erosion1  and their details of    
form are determined by the structure of 
the rock  along shore1 while most       
irregularities of curved outline involve
  something of shore-deposition1 if not 
due wholly to it4 ,glaciation1 or       
glaciation and subsidence1 may also give
 rise to peninsulas1 capes1 and  islands
 of curved outlines 7,pl4 ,,xxiv1 coast 
of ,maine74 ,curving outlines  may1     
however1 be developed by erosion alone  
in weak rock structures4  ,this is      
illustrated by the weak rock structures 
7clay1 sand1 etc47 of  most of the      
,atlantic coastal plain4 ,thus          
inspection of the horizontal            
configuration of coasts will often      
indicate the processes which  have been 
dominant there in recent times4 ,on the 
other hand1 the  interpretations of many
 coastal irregularities1 such as ,hudson
 ,bay1  ,puget ,sound1 the ,gulf of     
,california1 the ,baltic ,sea1 etc41 are
 not to  be read from the map4 ,in such 

cases1 diastrophism and gradation have  
usually coperated1 but the relative     
importance of the two processes  can    
only be determined by detailed study in 
the field4 ,when it is  remembered that 
the tendency of shore-erosion is to     
reduce great  irregularities of         
horizontal configuration1 though not to 
obliterate  small ones if the coast be  
heterogeneous in composition 7p4 #cec71 
and  that the tendency of               
shore-deposition is also to regularity1 
it is  clear that the great             
irregularities of coast-lines are due   
neither to  shore-erosion nor to        
shore-deposition1 though minor ones may 
be due to  either4                      
,,the ,,work ,,of ,,ocean-,,currents4   
,as agents of erosion1 ocean-currents   
are not1 in general1 of great           
importance4 ,currents which reach the   
bottom are comparable1 in  their        
effects1 to rivers of the same velocity 
and volume2 but most  ocean-currents do 
not touch bottom1 and1 therefore1 do not

 erode it4  ,where the current agitates 
the bottom sensibly1 as it often does in
  shallow water1 the bottom is abraded1 
and in the lee of such places  it is    
doubtless aggraded4 ,since              
ocean-currents do not1 for the most     
part1 flow in shallow water1 their      
erosive work is1 on the whole1          
relatively slight2 but where they are   
forced through narrow and shallow       
passageways1 their abrasive work may be 
considerable4 ,thus the ,gulf  ,stream1 
where it issues from the ,gulf1 has a   
velocity of four or five  miles per     
hour1 and its shallow and narrow channel
 is current-swept4    ,a rough test of  
the abrasive work of an ocean-current is
 found in the  nature of the bottom     
beneath it4 ,if this be hard1 it        
indicates that the  loose sediment on   
the floor of the ocean has been swept   
away1 while the  presence of fine       
detritus indicates that the current is  
not wearing4  ,thus the abrasive power  
of the ,gulf ,stream is known to        

continue  somewhat beyond its narrow    
channel1 for on the ,blake plateau      
7between  the ,bahamas and ,cape        
,hatteras71 where the water is #fjj     
fathoms and less  in depth1 8the bottom 
of the ,gulf ,stream 444 is swept clean 
of lime and  ooze and is nearly barren  
of animal life40#afh ,other             
illustrations  of the erosive power of  
currents have been noted near ,gibraltar
 in  water #ejj fathoms deep1 and       
between the ,canary ,islands at depths  
of  #ajjj fathoms4#afi ,in spite of     
these examples1 and of many others      
which probably exist in similar         
situations1 it yet remains true that    
ocean-currents are on the whole but     
feeble agents of erosion4    ,as agents 
of transportation1 ocean-currents are   
scarcely more important  than as agents 
of corrasion1 for they transport only   
what they erode1  if the life which     
inhabits them be left out of            
consideration4 ,this  phase of their    
work has probably been exaggerated      

through a confusion  of transporting    
energy and actual transportation4       
,ocean-currents which  do not touch     
bottom roll no sediment and carry only  
what may be held  in suspension4 ,a     
river's power of transporting sediment  
in suspension  is due largely to the    
cross-currents occasioned by the        
unevenness of  its resistant bottom 7p4 
#aag74 ,if a particle of mud in         
suspension in  a river drops to the     
bottom1 as it frequently does1 it may be
 picked  up again and carried forward4  
,if1 on the other hand1 a particle in   
suspension in an ocean-current once     
escapes the moving water by  settling   
through it1 the current which does not  
drag bottom has no  chance to pick it up
 again4 ,very fine sediment may be      
carried by an  ocean-current far beyond 
the point where it was acquired1 but    
currents  which do not touch bottom are 
rarely strong enough to hold any but the
  finest material for any considerable  
length of time4 ,as transporters  of    

sediment1 therefore1 ocean-currents are 
at a great disadvantage as  compared    
with rivers4    ,how readily particles  
of extreme fineness may be kept in      
suspension1  and how little agitation is
 necessary to keep them from sinking1 is
  shown by the experiments of ,sorby1   
who showed that while a sand grain   of 
an inch in diameter will settle one foot
 per second in still  water1 fine       
particles of clay require days to sink  
through the same  distance4 ,the        
,challenger found fine sediment derived 
from the land #djj  miles from the coast
 of ,africa1 and that not opposite the  
debouchure of  any large river4         
,sediment settles more readily in salt  
water than in  fresh1 despite the fact  
that the former is heavier4 ,this is    
presumably  because the salt diminishes 
the cohesion of the water4              
,deposition by ocean-currents is limited
 by their transportation4 ,only  where  
they erode their bottoms do they gather 
coarse materials1 and  only in the lee  

of such places are their deposits       
coarse4 ,since the  material which they 
carry is generally fine1 it is widely   
distributed  before deposition4         
,ocean-currents have little influence on
 the configuration of  coast-lines4     
,,deposits ,,on ,,the ,,ocean-,,bed4    
,something has already been said        
concerning the sediments which          
accumulate in the shallow waters along  
shores2 but the area of marine          
sedimentation is as extensive as the    
ocean itself1 and the deposits  must now
 be reviewed from another point of view4
    ,oceanic deposits may be            
conveniently divided into two chief     
groups1  dependent on the depth of the  
water in which they are made4#agj ,these
  groups are 7#a7 shallow-water         
deposits1 made in water less than some  
such depth as #ajj fathoms1 and 7#b7    
deep-sea deposits1 laid down in  water  
of greater depth4 ,the selection of the 
#ajj-;fathom line as the  dividing depth
 is less arbitrary than it seems1 for   

passing outward  from the shore1 it is  
at about this depth that the bottom     
ceases to be  commonly disturbed by the 
action of currents and waves2 that      
sunlight  and vegetable life cease to be
 important at the bottom2 and that the  
coarser sediments which predominate     
along shore give place1 as a rule1  to  
muds and oozes4 ,furthermore1 the       
#ajj-;fathom line 7or some line very    
near it7 is an important one in the     
physical relief of the globe1 for  it   
appears to mark1 approximately1 the     
junction of continental plateaus  and   
ocean-basins4 ,only because the latter  
are a little over-full does  the water  
run over their rims1 covering about     
#aj1jjj1jjj square miles  of the borders
 of the continents1 converting them from
 land into  epicontinental seas4        
,aside from the deposits made by        
organisms1 shallow-water deposits are   
divisible into two groups--7a7 those    
immediately along the shore1 the        
littoral deposits1 and 7b7 those made   

between the littoral zone  and the      
#ajj-;fathom line4 ,both are            
terrigenous4 ,the deep-sea deposits     
likewise are divisible into two groups1 
7a7 terrigenous deposits  formed close  
to land1 and made up chiefly of         
materials derived  immediately from the 
disintegration of land formations2 and  
7b7 the  pelagic deposits1 made up      
chiefly of the remains of pelagic       
organisms  and the ultimate products    
arising from the decomposition of rocks 
and  minerals4 ,the former predominate  
in the less deep waters relatively  near
 shore2 the latter in the deeper water  
far from land4 ,the shallow-  and       
deep-water deposits grade into each     
other in a belt along the  #ajj-;fathom 
line4                                   
,shallow-water ,deposits4    ,littoral  
deposits4--,the littoral zone is the    
zone between high- and  low-water marks4
 ,it is the zone in which bowlders1     
gravels1 sands1 and  all coarser        
materials accumulate1 though muds are   

occasionally met  with in sheltered     
estuaries4 ,generally speaking1 the     
nature of these  deposits is determined 
by the character of the adjoining lands 
and the  nature of the local organisms4 
8,the heavier materials brought by      
rivers  from high terrestrial regions1  
or thrown up by the tides and waves  of 
the sea1 are here arranged with great   
diversity of stratification  through the
 alternate play of the winds and waves4 
,twice in the  twenty-four hours the    
littoral zone is covered by water and   
exposed  to the direct rays of the sun  
or the cooling effects of the night4    
,there is a great range of temperature2 
mechanical agencies produce  their      
maximum effects10#aga and physical      
conditions in general are  most varied4 
,still greater diversity is introduced  
by the fact that  the zone is inhabited 
by both marine and terrestrial          
organisms1 while  the evaporation of the
 sea-water which flows over tidal       
marshes and  lagoons leads to the       

formation of saline deposits4 ,if the   
length of  the coast-lines of the world 
be taken at #abe1jjj miles 7about       
#bjj1jjj  kilometers71 and the average  
width of this zone at half a mile1 these
  deposits are now forming over an area 
of #fb1ejj square miles 7about  #afj1jjj
 square kilometers7 of the earth's      
surface4    ,non-littoral1 mechanical   
deposits in shallow water4--,these      
deposits  are laid down in the zone of  
the ocean between low-water mark and the
  #ajj-;fathom line4 ,they cover about  
#aj1jjj1jjj square miles4#agb ,their    
composition is much the same as that of 
the littoral deposits1 with  which they 
are continuous1 though on the whole they
 are finer4 ,at  their lower limit they 
pass insensibly into the fine deposits  
of the  deep sea4 ,coarse material1 such
 as gravel and sand1 prevails1 though   
in special situations1 such as          
depressions and inclosed basins1 muddy  
deposits are found4 ,while some of the  
deposits are wholly composed  of        

inorganic dbris1 organic remains are    
freely mingled with others4  ,the       
mechanical effects of tides1 currents1  
and waves are everywhere  present1 but  
become less and less well marked as the 
#ajj-;fathom line  is approached4 ,the  
forms of vegetable and animal life are  
numerous1  though the former decrease as
 depths which exclude the sunlight are  
approached4    ,both littoral deposits  
and deposits in shallow water outside   
the  littoral zone have already been    
referred to in connection with the work 
of waves and currents 7pp4 #cee-ff74 ,a 
few additional points only need  here be
 added4    ,illustration3 ,figs4 #cba   
and #cbb4--;,diagrams showing how       
shallow-water    deposits may attain    
considerable depth by the shifting of   
the zone of    deposition seaward4      
,illustration3 ,fig4 #cbc4--;,diagram   
showing the interwedging of gravel-1    
sand-1 and mud-beds4    ,in general the 
coarser sediments are lodged near shore 
and those  farther from the land become 

progressively finer4 ,even the coarser  
part of the material carried in         
suspension by the undertow is partly    
left in the shallow water4 ,on the other
 hand1 waves of exceptional  strength   
may carry coarse material into water of 
some depth4 ,thus  coarse shingle       
7gravel7 and even bowlders have been    
found at depths of  #aj fathoms4#agc    
,coarse deposits may extend far out from
 land if the  waves are strong1 and     
especially if the water is shallow1 and 
since  the zone of shallow water may be 
extended seaward by the aggradation  of 
the bottom1 shallow-water deposits may  
cover extensive areas4 ,they  may become
 deep at the same time1 for as the outer
 border of the  shallow-water zone is   
shifted seaward by aggradation1 the     
vertical  space to be filled becomes    
greater 7compare ,figs4 #cba and #cbb74 
,again1 if the coast be sinking1 new    
deposits of coarse material may  be made
 on older ones4 ,in this way also great 
thicknesses of sediment  may be         

accumulated1 all parts of which were    
deposited in shallow water4  ,the great 
thickness of some of the conglomerate   
beds of the past shows  how far this    
process may go4    ,illustration3 ,fig4 
#cbd4--,ripple-marks4    ,illustration3 
,fig4 #cbe4--,rill-marks resembling     
impressions of    seaweeds4 ,beach at   
,noyes ,point1 ,r4 ,i4 7,walcott1 ,u4   
,s4 ,geol4 ,surv47    ,illustration3    
,fig4 #cbf4--,rill-marks4 ,same locality
 as #cbe4 7,walcott47    ,as a rule1 no 
definite line marks the seaward terminus
 of the coarse  detritus1 since coarse  
material is carried farther out when the
 waves  run high 7and the undertow is   
strong7 than when they are feeble4 ,in  
calm weather1 therefore1 fine sediment  
may be deposited where coarse  had been 
laid down in the preceding storm1 only  
to be covered in turn  by other deposits
 of a different character4 ,thus gravel 
grades off into  sand1 with more or less
 overlapping or interwedging1 and sand  
grades  off into silt in the same way4  

,this is diagrammatically illustrated by
  ,fig4 #cbc4    ,characteristics of    
shallow-water deposits4--,clastic       
sediments laid  down in shallow water   
have several distinctive                
characteristics4 ,while  they are1 in   
the aggregate1 coarse1 they are         
characterized by frequent  variations in
 coarseness4 ,the surfaces of successive
 beds are likely  to be ripple- and     
rill-marked 7,figs4 #cbd1 #cbe1 #cbf71  
and cross-bedding  7,fig4 #cbg7 is of   
common occurrence4 ,clayey sediments    
accumulated  between high and low water 
are often sun-cracked 7,fig4 #cbh71 and 
the  tracks of land animals are         
sometimes preserved on their surfaces4  
,shallow-water deposits often contain   
fossils of organisms which live  in     
waters of slight depth4 ,these          
characteristics are sufficient to       
differentiate sedimentary formations    
made in shallow water from those  made  
in deep water1 even after they have been
 converted into solid  rock and after   

the rock has emerged from the sea4 ,many
 of these  characteristics are1 however1
 shared by deposits made by streams on  
the  land4 ,subarial and lacustrine     
sediments are usually distinguishable   
from those made in the sea by their     
fossils1 and sometimes by their         
distribution4    ,illustration3 ,fig4   
#cbg4--;,cross-bedding4 7,gilbert47     
,illustration3 ,fig4 #cbh4--,sun-cracks4
 ,these cracks were on the    mud-flats 
of the ,missouri a few miles above      
,kansas ,city1 but    the sun-cracks on 
shore-deposits are not essentially      
different4    7,calvin47    ,topography 
of shallow-water deposits4--,the        
shallow-water deposits  have1 on the    
whole1 a rather plane surface1 though   
there are some  notable departures from 
flatness4 ,the steep slopes of the delta
 fronts  and of wave-built terraces have
 already been spoken of4 ,barriers often
  shut in depressions1 and the          
disposition of the material deposited is
  sometimes uneven1 owing to shore and  

tidal currents4 ,the result is that  the
 surface of the shallow-water deposits  
is often affected by low  elevations and
 by shallow depressions4 ,the elevations
 and depressions  may be elongate1      
circular1 or irregular in form4 ,these  
general facts  are shown in ,figs4 #cai1
 #cbj1 and #cbi4 ,this topography is    
sometimes  preserved on newly emerged   
lands1 as at various points on the      
,coastal  ,plain of the ,united ,states4
    ,illustration3 ,fig4                
#cbi4--;,irregularities of topography of
    shallow-water deposits4 ,the depths 
of the water are shown in fathoms4      
7,chart of ,c4 and ,g4 ,surv47          
,chemical and organic deposits4--,there 
is no sharp line of distinction  between
 the deposits usually classed as        
chemical and those regarded as  organic4
 ,the latter are chemical in the broader
 sense of the term1 but  as they are    
immediately associated with life and are
 dependent upon it1  it is a matter of  
practical convenience to separate them4 

,aside from  the organic deposits1 the  
chemical deposits made in shallow       
sea-water  embrace 7#a7 those due to    
reactions between constituents so       
brought  together that new and insoluble
 compounds are formed and precipitated1 
and 7#b7 those due to evaporation4 ,the 
points of saturation for the  various   
substances dissolved in sea-water are   
reached at different  stages1 and hence 
they are deposited more or less in      
succession4    ,the chemical deposits   
made in the shallow water of the sea1 or
 in  shallow bodies of water isolated   
from the sea1 are chiefly simple        
precipitates resulting from evaporation2
 but new combinations are  sometimes    
made in the process of concentration and
 precipitation4  ,all substances in     
solution are necessarily precipitated on
 complete  evaporation1 but since the   
sea-water is in general far from        
saturation1  so far as all its leading  
salts are concerned1 only a few are     
thrown down in quantity sufficient to   

have geological importance  where       
evaporation is incomplete4 ,the leading 
deposits are lime  carbonate 7,ca,c,o71 
lime sulphate 7gypsum1 ,ca,s,o1#b;,h,o71
 common salt  7rock-salt1 ,na,cl71 and  
the magnesium salts1 usually the        
chlorides and  sulphates1 which are     
later changed to carbonates4 ,in        
investigations  on ,mediterranean       
water#agd which had an initial density  
of #a4jb1 no  deposit took place until  
concentration by evaporation had brought
 the  water to a specific gravity of    
#a4je4 ,between this density and that   
of #a4ac1 lime carbonate and some iron  
oxide were deposited4 ,between  #a4ac   
and #a4bb1 lime sulphate was the most   
abundant precipitate1 while  between    
#a4bb and #a4ca1 #ie of the deposit was 
common salt4 ,with still  further       
concentration1 the remaining substances 
in solution1 especially  the magnesium  
salts1 were thrown down4    ,while there
 is somewhat more than ten times as much
 lime sulphate as  lime carbonate in the

 ocean 7p4 #cbd71 the deposits of the   
carbonate  7including the organic7 have 
been very much greater than those of the
  sulphate4 ,this is due partly to the  
fact that the sulphate is much more     
soluble in natural waters than the      
carbonate4 ,rivers bring much more      
carbonate than sulphate to the sea1 so  
that the point of saturation for  the   
sulphate would normally be reached much 
later than that of the  carbonate4 ,the 
more important fact1 however1 is that   
marine plants and  animals use lime     
carbonate freely for skeletal and       
housing purposes4  ,it is held by some  
that they get their lime from the       
sulphate1 but if  so they convert it    
into carbonate before it takes the form 
of shells1  coral1 etc41 the sulphuric  
acid set free in the process            
reproducing1  directly or indirectly1   
more sulphate4 ,the secretion of lime   
carbonate  by organisms is not dependent
 on the saturation of the water1 but may
  be carried on when the amount in      

solution is very small4    ,there can be
 little doubt that the chief deposits of
 lime carbonate  have been and are being
 made through the agency of plants and  
animals  in the form of shells1 coral1  
bones1 teeth1 and other devices for     
supporting1 stiffening1 housing1        
protecting1 and arming themselves2  but 
while it is agreed that the larger part 
of the lime carbonate  deposited in the 
open sea is of organic origin1 it is    
equally clear  that in closed seas      
subject to concentration from           
evaporation1 simple  precipitation takes
 place freely4 ,there is some difference
 of opinion  as to the importance of    
these two classes of deposits1 past and 
present4 ,the debated point is whether  
simple precipitation takes place  in any
 appreciable degree under the usual     
oceanic conditions4 ,there is  much more
 evidence of solution by sea-water than 
of precipitation from  it4 ,the ocean   
appears to be under-saturated with lime 
carbonate on the  whole1 though it is   

still possible that deposition may take 
place in  favorable situations1 as1 for 
example1 where the very calcareous      
waters  of rivers are spread out in thin
 sheets on the surface of the heavier   
salt water1 and thus exposed to         
exceptional evaporation1 or where there 
is very exceptional agitation and       
aration4#age    ,gypsum appears to be   
deposited in quantity only in the closed
 basins of  arid regions where          
concentration reaches an advanced state4
    ,since normal sea-water is far from 
saturation with common salt1  the latter
 is precipitated only in lagoons1 closed
 seas1 or other  situations favorable to
 great concentration4 ,this is usually  
achieved  only in notably arid regions1 
and in basins that receive little or no 
drainage from the land4    ,deposits of 
salt usually1 therefore1 signify highly 
arid conditions1  and where they occur  
over wide ranges in latitude and        
longitude1 as  in certain periods of the
 past1 unusual aridity is inferred4     

,where  confined to limited areas1 their
 climatic significance is less1 for     
topographic conditions may determine    
local aridity4 ,the total area  where   
salt is now being precipitated is small1
 though on the whole  the present is    
probably to be regarded as a rather arid
 period of the  earth's history4 ,on the
 other hand1 ancient deposits of salt   
preserved  in the sedimentary strata    
show that the area of salt deposition   
has  been much more considerable than   
now at one time and another in the      
earth's history4 ,the salt and gypsum   
deposits of the past seem1  therefore1  
to tell an interesting tale of the      
climates of the past4    ,the magnesium 
salts are among the last to be thrown   
down as the  sea-water is evaporated1   
and they most commonly take the form of 
sulphates and chlorides4 ,they often    
form double salts with potassium1  a    
relatively small and soluble constituent
 of sea-water4 ,in the  artificial      
evaporation of salt water to obtain     

common salt1 the process  is usually    
stopped before the saturation-point for 
the magnesium salts  is reached1 and the
 residue1 the 8mother-liquor10 or       
8bittern10 is  drawn off to prevent     
these 8bitter0 salts from mixing with   
the common  salt4 ,the magnesium salts  
are among the last to be precipitated1  
not  only because they are readily      
soluble1 but because their quantity is  
small2 yet in the original rock from    
which all the sea-salts came1  there is 
at least as much magnesium as sodium1   
while in the sea there  is about five   
times as much sodium as magnesium4 ,just
 what becomes of  the remaining         
magnesium is not yet well understood4   
,it has a notable  disposition to form  
double salts with some other            
constituent1 as noted  above4 ,in the   
earlier marine strata1 dolomite1 that   
is1 limestone  composed partly or wholly
 of the double carbonate of lime and    
magnesia1  7,ca,mg7,,co1 abounds4 ,this 
appears to have been formed by a gradual

  substitution of molecules of magnesium
 for those of calcium1 but  just how and
 when and why it was done has not been  
fully worked out4  ,it appears to be a  
case where the saline matter of the sea 
made its  contribution to the           
sedimentary deposits by chemical        
reaction upon  them1 rather than by     
precipitation because of saturation4    
,the relatively small amount of potash  
in the sea-water is probably due  to its
 disposition to remain united with the  
clays and earths of the  mantle rock and
 of the shaley deposits4    ,to some    
extent the salts in solution act        
directly on the earthy matter  brought  
down into the sea by rivers1 but where  
sedimentation is rapid1  as it often is 
in shallow water1 this action is limited
 and obscure4  ,in the main1 the        
ocean-waters protect the sediments from 
weathering  and similar changes1 except 
as organic matter buried with them      
induces  change4    ,while the lime     
deposits are by far the greatest of the 

chemical and  organic deposits of the   
sea1 plants and animals also secrete    
notable  quantities of silica4 ,silica  
deposits of organic origin are          
relatively  much more important in the  
deep sea than in shallow water1 and will
 be  mentioned in that connection4      
,limestone4--,something concerning the  
origin of limestone has already  been   
given in the preceding paragraphs1 but  
because of the importance  of this      
formation1 it may be added by way of    
summary that shallow seas  free1 or     
nearly free1 from terrigenous sediment1 
and abounding in  lime-secreting life1  
furnish the conditions for nearly pure  
deposits  of limestone1 and that most of
 the limestone within the areas of the  
present continents appears to have      
originated under such conditions4  ,the 
common notion that limestone is normally
 a deep-water formation is  a serious   
error4 ,although limestones are formed  
in deep as well as in  shallow waters1  
by far the more important classes of    

lime-secreting  organisms are           
photobathic1 i4e4 are limited to the    
depths to which  light penetrates4 ,in  
the shallow waters1 these plants and    
animals are  in part free and in part   
attached4 ,within the areas of deep     
water they  are free and at the surface1
 and their remains drop to the bottom1  
if not sooner dissolved4 ,but few forms 
live on the deep1 dark1 cold  bottoms of
 abysmal depths4 ,clear waters1 free    
from abundant terrigenous  sediments and
 abounding in lime-secreting life1      
rather than deep  waters1 are1          
therefore1 the most favorable conditions
 for the origin of  limestone4    ,the  
purely chemical deposits of limestone   
are probably all of  shallow-water      
origin4 ,once made1 they are subject to 
solution1  redeposition1 and other      
mutations like other deposits4 ,as a    
result1  they often lose many of their  
original characteristics1 but enough    
usually remain to tell the story of     
their origin4                           

,deep-sea ,deposits4    ,contrasted with
 shallow-water deposits4--,the deep-sea 
deposits cover  the ocean-bottom below  
the #ajj-;fathom line4 ,their area is   
considerably  more than half the earth's
 surface4 ,the characteristic deposits  
are  muds1 organic oozes1 and clays1    
which in their physical characteristics 
are remarkably uniform4 ,in regions of  
floating ice1 greater diversity  is     
introduced from the varied nature of the
 materials which the ice  transports1   
but gravels and sands1 comparable to    
those of shallow  water1 are rarely     
found4 8,tides1 currents1 and waves     
produce some  mechanical effects at the 
upper limits of the deep-sea region1 but
  on the whole there is an absence of   
the phenomena of erosion1 and           
mechanical action would appear to be    
absent except in the case of  submarine 
eruptions4 ,the depth is too great for  
sunlight to penetrate1  and vegetable   
life is limited to the upper zone4      
,animal life is present  in the same    

zone and on the bottom1 but absent or   
nearly so in the  middle depths4 ,the   
temperature 7at the bottom7 is below #dj
 ,fahr4  throughout the larger part of  
the area1 and if subject to variation   
with latitude or change of season1 these
 changes affect only the depths         
immediately beyond the #ajj-;fathom     
line4 ,throughout the whole region      
there is a very uniform set of          
conditions4 ,in the shallow-water and   
littoral zones1 owing to the rapid      
accumulation and the mechanical  effects
 of transportation and erosion1 the     
effects of chemical  modification are   
not very apparent in the deposits2 but  
in deep-sea  deposits1 in consequence of
 the less rapid rate of accumulation1   
absence of transport1 the nature and    
small size of the particles1 many       
evident chemical reactions have taken   
place1 resulting in the formation  in   
situ of glauconite1 phosphatic and      
manganese nodules1 zeolites1  and other 
secondary products40#a ,with increasing 

depth and distance  from the shore1 the 
character of the deposits undergoes a   
change4 ,there  is less and less        
material derived directly from the land1
 and more  8amorphous matter arising    
from the ultimate decomposition of      
minerals  and rocks1 and accompanied1 in
 all moderate depths1 by an increase    
relative of the remains of pelagic      
organisms4 ,we thus pass insensibly     
from those deep-sea deposits of a       
terrestrial origin1 which we call       
#8terrigenous1' to those deep-sea       
deposits denominated #8pelagic1' in     
which the remains of calcareous and     
siliceous organisms1 clays and  other   
substances of secondary origin play the 
principal rle40#agf    ,the following   
table#agg shows the relations of the    
various groups of  marine deposits4     
#a4 ,deep-sea deposits beyond   ,red    
clay          ,i4 ,pelagic deposits     
#ajj fathoms                ,radiolarian
 ooze     formed in deep                
,diatom ooze          water removed     

,globigerina ooze     from land4        
,pteropod ooze                          
,blue mud                               
,red mud                                
,green mud                              
,volcanic mud      ,,ii4 ,terrigenous   
,coral mud             deposits formed  
in deep and    #b4 ,shallow-water       
deposits     ,sands1 gravels1           
shallow water1       between low-water  
mark       muds1 etc4          mostly   
close       and #ajj fathoms            
to land4                                
#c4 ,littoral deposits between  ,sands1 
gravels1         high- and low-water    
marks    muds1 etc4                     
,sources4--,the pelagic deposits are    
made up in part of materials of  organic
 origin1 and in part of materials of    
inorganic origin4 ,the  inorganic       
materials may be of mechanical or       
chemical origin4 ,mechanical  pelagic   
deposits originate in various ways4     
,they may come 7#a7 from  the land by   
the ordinary processes of gradation1    

7#b7 from volcanic  vents1 or 7#c7 from 
extra-terrestrial sources4 ,chemical    
deposits may  be formed 7#a7 in situ by 
the chemical interaction of substances  
in  the sea-water on materials of       
organic and inorganic origin1 and 7#b7  
by  direct precipitation from the       
sea-water4    ,mechanical inorganic     
deposits4--,the terrigenous materials   
which reach  the deep sea are1 as a     
rule1 only the finest products of land  
decay1  and are carried out by movements
 of water or by the winds4 ,they are    
not commonly recognized in the dredgings
 more than #bjj miles from  the shore1  
but opposite the mouths of great rivers 
they extend much  farther1--#ajjj miles 
in the case of the ,amazon4 ,they are   
especially  abundant on the slopes of   
the continental shelves4 ,here occur the
  blue1 green1 and red muds1 with which 
are associated volcanic  and coral muds4
 ,the color of these various muds is    
dependent in part  on the changes which 
they have undergone since their         

deposition4  ,the green muds usually    
contain enough glauconite to give them  
their  color1 and are most commonly     
found off bold coasts where             
sedimentation  is not rapid4 ,the blue  
muds indicate lack of oxidation1 or     
perhaps  deoxidation4 ,red muds are not 
common1 though they have been found in  
some situations4 ,in general1 these     
deposits are analogous to certain       
shales1 marls1 etc41 found within the   
continents4    ,though coarse materials 
derived from the land are occasionally  
found in  the deep-sea deposits1 their  
presence must be looked upon as in some 
sense accidental4 ,occasional pebbles1  
or even bowlders1 are carried out  into 
the ocean entangled in the roots of     
floating trees4 ,within limits1  too1   
icebergs have carried out land dbris1   
though it is probable that              
transportation by this means has been   
exaggerated4 ,the amount which  icebergs
 might carry1 if fully loaded1 is far   
greater than the amount  which they do  

carry4    ,of the identifiable inorganic
 materials in the deep sea1 the most    
abundant are of volcanic origin1 and    
among these the most common is  pumice1 
which is frequently so light that it    
floats readily until it  becomes        
water-logged4 ,pieces of pumice brought 
up by the ,challenger and  thoroughly   
dried were found to float for months in 
sea-water before  settling even through 
the depth of water contained in the     
vessel  in which the experiment was     
performed4#agh ,the next most abundant  
substance of volcanic origin in pelagic 
deposits is volcanic glass4  ,this      
ranges from pieces of the size of a     
walnut down to the smallest  fragments1 
which often serve as centers for        
concretions4 ,lapilli  7cinders7 and    
volcanic ash also are abundant in parts 
of the deep  sea4 ,the distribution of  
these volcanic products is essentially  
universal1 though by no means uniform4  
,some of them are probably from         
submarine volcanoes4    ,the study of   

the deep sea deposits has revealed the  
presence of many  nodules and grains    
which are believed to be of             
extra-terrestrial  origin4 ,many of them
 are magnetic4#agi ,the dust of         
countless meteors  which enter the      
atmosphere daily settles on land and sea
 alike1 and  enters into the sediment of
 the bottom of the latter4 ,it is       
probably  no more abundant in deep water
 than in shallow1 but it is relatively  
more important1 since other             
sedimentation is more meager4 ,the      
number of  meteorites which enter the   
atmosphere daily has been estimated at  
from  #ae1jjj1jjj to #bj1jjj1jjj4ahj ,if
 on the average the meteorites weigh    
ten grains each1 probably a rather high 
estimate1 the total amount of           
extra-terrestrial matter reaching the   
earth yearly would be #e1jjj to  #g1jjj 
tons1 and something like three-fourths  
of this must1 on the  average1 fall into
 the sea4 ,but even at this rate it     
would take some  fifty billion years to 

cover the sea-bottom with a layer one   
foot in  thickness4    ,organic         
constituents of pelagic deposits4--,with
 increasing distance  from shores1 and  
especially with increasing depth of     
water1 terrigenous  deposits become less
 and less abundant1 and sediments       
derived from  pelagic life increase in  
relative importance4 ,beyond the upper  
part of  the outer slopes of the        
continental shelves1 the pelagic        
deposits are  largely made up of shells 
and skeletons of marine organisms which 
live  in the surface-waters4 ,pelagic   
molluscs1 foraminifera1 and alg secrete 
shells of lime carbonate1 while diatoms 
and radiolarians secrete shells  of     
silica4 ,when the organisms die1 they   
sink to the bottom with their  shells1  
and these mineral matters of organic    
origin are mingled with  the volcanic   
products which are universal over the   
sea-floor4 ,pelagic  deposits of organic
 origin are named according to their    
characteristic  constituents4 ,thus     

there are pteropod oozes1 globigerina   
oozes1 diatom  oozes1 radiolarian oozes1
 etc4#aha ,it is not to be understood   
that  these oozes are made up           
exclusively of the shells which give    
them their  names4 ,diatom ooze is an   
ooze in which diatom shells are         
abundant1 not  an ooze made up wholly of
 diatom shells2 and globigerina ooze is 
an  ooze in which globigerina shells are
 abundant1 though in many cases  they do
 not make up even the bulk of the       
matter4 ,while samples of these  various
 oozes might be selected which are      
thoroughly distinct from one  another1  
there are all gradations between them1  
since pelagic life does  not recognize  
boundary-lines4    ,it is a significant 
fact that with increasing depth the     
proportion  of lime carbonate in the    
ooze decreases4 ,thus in tropical       
regions  remote from land where the     
depths are less than #fjj fathoms1 the  
carbonate of lime of the shells of      
pelagic organisms may constitute  #hj or

 #ij of the deposit4 ,with the same     
surface conditions1 but with  increasing
 depth1 the percentage of lime carbonate
 decreases1 until at  #bjjj fathoms it  
is less than #fj2 at #bdjj fathoms1 #cj1
 and at #bfjj  fathoms1 #aj4 ,beyond    
this depth there are usually no more    
than traces  of carbonate of lime4 ,the 
data at hand show that the percentage of
 lime  carbonate falls off below #bbjj  
fathoms more rapidly than at lesser     
depths4    ,when the percentage of lime 
carbonate becomes very low1 the         
calcareous  oozes grade off into the red
 clay with which the sea-floor below    
#bdjj  to #bfjj fathoms is covered4     
,chemical deposits4--,the chemical      
deposits of the deep sea are chiefly    
the alteration products of sediments    
which reach the sea-bottom  by          
mechanical means4 ,all sediment         
deposited in the sea undergoes  more or 
less chemical change1 but it is only    
when the change is  very considerable   
that the product is referred to this    

class4 ,where  sedimentation is rapid   
and the sediment coarse1 the chemical   
change is  relatively slight2 but where 
the sedimentation is slow and the       
sediment  fine1 the chemical change is  
relatively great2 for the longer        
exposure  to the sea-water and the      
greater proportion of surface exposed to
  attack1 both favor change4 ,both the  
area and the mass of sea-bottom         
sediment radically changed in this way  
are large1 but most of the  deposit does
 not correspond to any formation known  
on the land4    ,the red clay already   
referred to belongs to this class of    
deposits4  ,its origin has been the     
subject of much discussion4 ,it contains
 much  volcanic dbris1 various          
concretions1 bones of mammals1 zeolitic 
crystals1 and extra-terrestrial         
spherules1 and doubtless the insoluble  
products of the shells of pelagic life2 
but it is still a mooted  question how  
far the clay itself is the product of   
decomposed shells1  and how far the     

altered product of pulverized pumice1   
volcanic ash1  dust1 etc4 ,pelagic life 
does not seem to be less abundant at the
  surface where the water is deep than  
where it is shallow1 and it would       
appear that the shells must sink in such
 situations as elsewhere4 ,if  the lime 
carbonate of globigerina ooze be removed
 by dilute acid1 the  inorganic residue 
is similar to the red clay in the       
ocean-bottom4 ,this  suggests that owing
 to the more complete solution in the   
very deep  water1 the lime carbonate of 
the shells has been dissolved1 leaving  
the red clay as a residuum4 ,the more   
complete solution at the bottom  might  
be the result either of the greater     
pressure1 or of a greater  percentage of
 ,,co in the water due to emanations    
from the sea-floor1 or  to both2 but the
 suddenness of the transition from oozes
 to red clay1  with increasing depth1   
does not seem to be fully explained by  
these  assumptions4 ,the study of the   
dredgings has inclined the students of  

these materials to the conclusion that  
volcanic materials1 rather than  shells1
 are the principal source of the red    
clay4#ahb ,the volcanic  materials are  
thought to have accumulated slowly and  
to have been long  exposed to the action
 of sea-water4 ,the various nodules and 
crystals in  the clay are believed to be
 secondary products1 the materials for  
which  were derived from the            
decomposition of the same materials4    
,eolian dust  may be a notable          
constituent of the red clay4    ,various
 specific products of chemical change   
may be briefly referred  to4 ,the       
decomposition of certain mineral        
particles1 such as feldspar1  gives rise
 to kaolin1 and kaolin is a very        
considerable constituent  of most of the
 clayey deposits of the ocean-bottom4   
,the kaolinization  of feldspar may take
 place both on land and in the sea4     
,manganiferous  deposits are widespread 
in the ocean-bottom1 occurring both as  
coatings  on grains of mechanical       

sediments1 shells1 etc41 and as         
concretions  ranging in sizes from      
minute particles to nodules an inch or  
more in  diameter4 ,the concretions are 
sometimes approximately spheroidal1 but 
often botryoidal4 ,these manganiferous  
nodules are believed to have  arisen    
from the decay of fragments of volcanic 
rocks4 ,in their decay1  the manganese  
and iron are believed to have been first
 changed to  carbonates1 and            
subsequently to oxides4 ,after manganese
 oxide1 iron  oxide and silica are by   
far the most abundant constituents1 but 
many  other substances enter into their 
composition in minor quantities4        
,another substance somewhat widely      
distributed in the sea-bed1 though  by  
no means universal1 is glauconite1 a    
complex silicate of alumina1  iron1     
potassium1 etc4 ,glauconite is1 on the  
whole1 most abundant  along the edges of
 the continental shelves1 though it is  
by no means  universal in this position4
 ,it is not commonly found in deep      

water1  nor very near the shore1 but    
approximately at the 8mud-line40 ,the   
glauconite grains begin to form1 as a   
rule1 in tiny shells1 chiefly  the      
shells of foraminifera4 ,after filling  
the shell1 the shell itself  may        
disappear1 while the glauconite goes on 
accumulating around the  core already   
formed1 until the grain attains         
considerable size4  ,glauconite is      
believed to be an alteration product of 
certain sorts  of mechanical sediment1  
the change being effected under the     
influence  of the decaying organic      
matter in the shells4#ahc ,it does not  
occur  where sedimentation is rapid1 and
 its formation appears to be favored  by
 considerable changes of temperature4   
,glauconite deposits occur on  the land 
and are commonly known as green sand    
marl4 ,glauconite also  occurs sparingly
 in many other sedimentary rocks4       
,illustration3 ,fig4                    
#ccj4--;,distribution of various sorts  
of deep-sea    deposits4 7,murray4      

,challenger ,reports47    ,another      
substance which is somewhat widespread  
in the ocean-bottom is  phosphate of    
lime1 which occurs in various sorts of  
oozes1 in the  manganiferous nodules1 in
 glauconite1 and in independent nodules4
 ,like  the grains of glauconite1 the   
grains of phosphate of lime appear to   
have started as concretions in shells1  
and to be the result of the  reaction of
 organic matter on the contents of      
sea-water4 ,the immediate  source of the
 lime phosphate in the water appears to 
have been the  shells or bones of the   
numerous animals living in the sea4     
,secondary minerals made from the       
constituents of volcanic matter which   
has been decomposed occur not uncommonly
 in the bottom of the sea4  ,these      
minerals belong to the general class of 
zeolites1 phillipsite  being the most   
abundant4 ,their distribution is        
somewhat wide1 but their  quantity is   
slight4    ,unfortunately1 knowledge of 
the deep-sea deposits is limited to     

their  superficial layers4 ,soundings do
 not usually penetrate more than a few  
inches1 or at most a foot or two4       
,unlike shallow-water deposits1 those of
 the really deep sea seem to  find no   
correlatives in the known rock          
formations of the land4                 
,,lakes4    ,most of the phenomena of   
the ocean are repeated on a smaller     
scale in  lakes4 ,the waves of lakes and
 their attendant undertows and littoral 
currents are governed by the same laws  
and do the same sort of work  as the    
corresponding movements of the ocean4   
,tides are absent1 or  insignificant1   
but slight changes of level1 known as   
seiches1#ahd  have been observed in many
 lakes4 ,they are probably caused by    
sudden  changes in atmospheric pressure4
 ,while they are generally very slight1 
they frequently amount to as much as a  
foot1 and occasionally to  several feet4
 ,the seiches are oscillatory movements1
 and their period  is influenced by the 
length and depth of the lake4 ,they have

 been  studied most carefully in        
,switzerland4 ,currents corresponding to
 those  of the ocean are slight or      
wanting in lakes1 but since most lakes  
have  inlets and outlets1 their waters  
are in constant movement toward the     
latter4 ,in most cases this movement is 
too slow to be readily noted1 or  to do 
effective work either in corrasion or   
transportation4 ,the work of  the ice1  
on the other hand1 is relatively more   
important in lakes than  in the sea4    
,changes taking place in lakes4--,the   
processes in operation in lakes  are    
easily observed and readily understood4 
7#a7 ,the waves wear the  shores1 and   
the material thus derived is            
transported1 assorted1 and  deposited as
 in the sea1 and all the topographic    
forms resulting from  erosion or        
deposition along the seacoast are       
reproduced on their  appropriate scale  
in lakes4 7#b7 ,streams bear their      
burden of gravel1  sand1 and mud into   
lakes and leave it there4 7#c7 ,the     

winds blow dust  and sand into the      
lakes1 and in some places pile the sand 
up into dunes  along the shores4 7#d7   
,animals of various sorts live in the   
lakes1 and  their shells and bones give 
rise to deposits comparable to the      
animal  deposits in the sea4 7#e7       
,abundant plants grow in the shallow    
water  about the borders of many ponds  
and lakes1 and as they die1 their       
substance accumulates on the bottom4    
7#f7 ,at the outlet the water is        
constantly lowering its channel4 ,the   
lowering of the outlet is often  slow1  
especially if the rock be coherent1 for 
the outflowing water  is usually clear1 
and therefore inefficient in corrasive  
work4 ,these  six processes are         
essentially universal1 and all conspire 
against the  perpetuity of the lakes4   
7#g7 ,in lakes where the temperature is 
low  enough for ice to be formed1 it    
crowds on the shores and develops       
phenomena peculiar to itself4 ,the ice  
of the sea may work in similar  ways1   

but its work is restricted to high      
latitudes4 7#h7 ,in lakes in  arid      
regions1 deposits are often made by     
precipitation from solution4  ,the first
 five and the last of these processes   
are filling the basins  of the lakes4   
,as the sediment is deposited1 a        
corresponding volume  of water is       
displaced1 and1 if there be outlets1    
forced out of the  basins2 the sixth    
process is equally antagonistic to the  
lakes1 while  the seventh has little    
influence on their permanence4 ,given   
time  enough1 these processes must bring
 the history of any lake to an end4     
,the lowering of the outlet will alone  
accomplish this result if the  bottom of
 the basin is above base-level4 ,many   
lakes have already become  extinct1     
either through the filling or draining  
of their basins1 or  through both       
combined4 ,the antagonism of rivers and 
lakes long ago  led to the epigram      
8,rivers are the mortal enemies of      
lakes40 ,true as  this statement is1 it 

does not follow that lakes will ever    
cease to  exist1 for the causes which   
produce new lakes may be in operation   
contemporaneously with those which bring
 lakes now in existence to an  end4     
,lacustrine deposits4--,the beds of     
sediment deposited in lakes are  similar
 in kind1 in structure1 and in          
disposition to beds of sediment  laid   
down in the sea1 but river-borne        
sediment is more commonly  concentrated 
into deltas1 since waves and            
shore-currents are less  effective4     
,even the limestone of the sea has its  
correlative in some  lakes4 ,some of it 
was made of the shells of fresh-water   
animals which  throve where the inwash  
of terrigenous sediment was slight1 some
 of  it from the calcareous secretions  
of plants1#ahe and some of it was       
precipitated from solution4#ahf ,salt   
and iron-ore#ahg deposits are  also     
sometimes made in lakes4    ,extinct    
lakes4--,the former existence of lakes  
where none now exist  may be known in   

various ways4 ,if the lake basin was    
filled1 its former  area is a flat1 the 
beds of which bear evidence1 in their   
composition1  their structure1 and often
 in their fossil contents1 of their     
origin  in standing water4 ,such a flat 
is commonly so situated topographically 
that the basin would be reproduced if   
the lacustrine deposits were  removed4  
,to this general rule there might be    
exceptions1 as where a  glacier formed  
one side of the basin when it was       
filled4 ,if the lake  was destroyed by  
the reduction of its outlet1 or by the  
removal of some  other barrier1 such as 
glacier ice1 or by desiccation1 shore   
phenomena1  such as beaches1 spits1     
etc41 may be found4 ,in time such       
evidences are  destroyed by subarial    
erosion1 so that they are most distinct 
soon  after the lake becomes extinct4   
,many lakes1 some of them large#ahh and 
many of them small1 are known  to have  
become extinct1 while many others are   
now in their last stages1  namely1      

marshes4 ,many others have been greatly 
reduced in size4 ,such  reductions are  
often obvious where deltas are built    
into lakes4 ,thus  the delta built by   
the ,rhone into ,lake ,geneva is several
 miles in  length1 and has been         
lengthened nearly two miles since the   
time of  the ,roman occupation4 ,the end
 of ,seneca 7,n4 ,y47 lake has been     
crowded  northward some two miles by    
deposition at its head4 ,similar changes
  have taken place and are now in       
progress in many other lakes4    ,lake  
ice4#ahi--,since fresh water is densest 
at #ci ,fahr41 ice does  not commonly   
form on the surface until the           
temperature from top to  bottom is      
reduced to this point4 ,cooled below    
this temperature1 the  surface-water    
fails to sink1 and with sufficient      
reduction freezes4 ,if  the lake be     
small1 and especially if it be shallow1 
it is likely to  freeze over completely 
in any region where the temperature is  
notably  below the freezing-point for   

fresh water for any considerable period 
of time4 ,it is under these             
circumstances that the ice becomes most 
effective4    ,illustration3 ,fig4      
#cca4--;,ice crowding upon low shore4   
,clear ,lake1 ,ia4    7,calvin47        
,suppose a lake in temperate latitudes1 
where the range of temperature  is      
considerable1 to be frozen over when the
 temperature is #bj ,fahr4  ,if now the 
temperature be suddenly lowered to -#aj1
 and such change of  temperature is not 
uncommon in the northern part of the    
,united ,states1  the ice contracts     
notably4 ,in contracting1 it either     
pulls away from  the shores or cracks4  
,if the former1 the water from which the
 ice is  withdrawn quickly freezes2 if  
the latter1 water rises in the cracks   
and freezes there4 ,in either case1 the 
ice-cover of the lake is again          
complete4 ,if the temperature now rises 
to #bj the ice expands4 ,the  cover is  
now too large for the lake1 and it must 
either crowd up on the  shores 7,fig4   

#cca7 or arch up 7wrinkle7 elsewhere4   
,it follows the one  course or the      
other1 or both1 according to the        
resistance offered by  the shore4    ,if
 the water near the shore is very       
shallow1 the ice freezes to the  sand1  
gravel1 and bowlders at the bottom4 ,if 
the adjacent land is low1  the ice in   
expanding may shove up over it1 carrying
 the dbris frozen  in its bottom4 ,it   
may even push up loose gravel and sand  
in front of  its edge if they be present
 on the shore4 ,where bowlders are      
frozen  to the bottom of the ice1 the   
shoreward thrust in expanding has the   
effect of shifting them in the same     
direction1 and even of lifting  them a  
little above the normal water-level4    
,this constant process of  concentrating
 bowlders at the shore-line gives rise  
to the 8walled0  lakes1 which are not   
uncommon in the northern part of the    
,united  ,states4 ,the 8wall0 does not  
commonly extend entirely around a lake1 
though it exists at various points on   

the shores of many lakes4 ,in  making   
the walls1 the ice shoved up by winds1  
especially in the spring  when the ice  
is breaking up1 coperates4              
,illustration3 ,fig4 #ccc4--;,calcareous
 tufa domes4 ,pyramid ,lake1 ,nev4      
7,russell47    ,if the lake be bordered 
by a low marsh1 the ice and frozen earth
 of the  latter are really continuous   
with the ice of the lake1 and the push  
of  the latter sometimes arches up the  
former into distinct anticlines1  the   
frozen part only being involved in the  
deformation4 ,a succession  of colder   
and less cold periods may give rise to a
 succession of such  anticlines4#aij ,if
 the shore be steep and of non-resistant
 material1  the crowding of the ice     
produces different but not less striking
  results4 ,where the thrust of the ice 
is against a low cliff of yielding      
material1 such as clay1 it disturbs all 
above the shore-line4 ,where the  cliff 
is sufficiently resistant1 it withstands
 the push of the ice1 and  the ice      

itself is warped and broken4    ,saline 
lakes4--,a few lakes1 especially in arid
 or semi-arid regions1  are salt1 and   
others are 8bitter40 ,beside sodium     
chloride1 salt  lakes usually contain   
magnesium chloride1 and magnesium and   
calcium  sulphates4 8,bitter0 lakes     
usually contain much sodium carbonate1  
as  well as some sodium chloride and    
sulphate1 and sometimes borax4 ,the     
degrees of saltness and bitterness vary 
from freshness on the one  hand to      
saturation on the other4 ,the water of  
the ,caspian ,sea 7lake7  contains1 on  
the average1 less salt than that of the 
sea2 that of ,great  ,salt ,lake        
contains about #ah2 that of the ,dead   
,sea1 about #bd2 and that  of ,lake ,van
 7eastern ,turkestan71 the densest body 
of water known1 about  #cc4 ,see        
accompanying table4    ,many salt lakes1
 such as the ,dead ,sea and ,great ,salt
 ,lake1 are  descended from fresh-water 
ancestors1 while others1 like the       
,caspian  and ,aral ,seas1 are probably 

isolated portions of the ocean4 ,lakes  
of  the former class have usually become
 salt through a decrease in the         
humidity of the region where they occur4
 ,the water begins to be salt  when the 
aridity is such that evaporation from   
the lake exceeds its  inflow4 ,in this  
case the inflowing waters bring in small
 amounts of  saline and alkaline matter1
 which is concentrated as evaporation   
takes  place4 ,the concentration may go 
on until the point of saturation is     
reached1 or until chemical reactions    
cause precipitation4 ,in general  the   
least soluble minerals are precipitated 
first4 ,thus gypsum begins  to be       
deposited from sea-water when #cg of it 
has been evaporated2 but  the           
saturation-point for salt is not reached
 until #ic of the water has  been       
evaporated 7see p4 #cge74 ,the relations
 in lakes are similar1 and  gypsum      
deposits often underlie those of salt4  
,deposits of salt and  other mineral    
matters once in solution are making in  

some salt lakes  at the present time1   
and considerable formations of the same 
sort have  been so made in the past4    
,buried beneath sediments of other      
sorts1 beds  of common salt or of other 
precipitates are preserved for ages4    
,lime  carbonate has been precipitated  
in quantity from some extinct lakes     
7,fig4 #ccc74    ,the lakes which       
originate by the isolation of portions  
of the sea  are salt at the outset4 ,if 
inflow exceeds evaporation1 they become 
fresher and may ultimately become fresh2
 otherwise they remain salt4  ,if       
evaporation exceeds inflow they diminish
 in size and their waters  become more  
and more salt or bitter4    ,indirect   
effects of lakes4--,lakes tend to modify
 the climate of  the region where they  
occur1 both by increasing its humidity  
and  by decreasing its range of         
temperature4 ,they act as reservoirs    
for surface-waters1 and so tend to      
restrain floods and to promote          
regularity of stream flow4 ,they purify 

the waters which enter them by  allowing
 their sediments to settle1 and so      
influence the work and the  life of the 
waters below4    ,composition of        
lake-waters4--,the accompanying         
table#aia shows the  composition of     
various inclosed lake-waters1 and gives 
some idea of  the wide range1 both in   
kind and quantity1 of the mineral matter
  held in solution by them4 ,it is to be
 noted that the table shows the         
composition of the waters of            
exceptional1 rather than common1 lakes4 
,the waters of fresh lakes do not depart
 widely from those of rivers 7p4  #ajg74
                ,,table--,,analyses ,,of
 ,,the ,,waters ,,of ,,inclosed ,,lakes4
          ,reduced to ,parts per #ajjj  
by ,dr4 ,h4 ,j4 ,van ,housen4           
----------------------------------------
--------------------------------------  
,locality           ,abert ,lake1       
,bogdo ,lake    ,caspian ,sea4          
#b;,caspian ,sea1                       
,oregon                        ,w4 ,s4  

,w4 of    near mouth                    
,pischina1 at   of the ,volga           
#ae feet                                
depth1 wind1                            
,w4 ,s4 ,w4                             
,specific gravity    #ajbc4ag           
,date               ,may #c1 #ahhc      
,analyst           ,f4 ,w4 ,taylor      
,gobel           ,gobel        ,h4 ,rose
                                        
,reference       ,fourth ,ann4          
,rep4,lariet ,geological,bischof's      
,bischof's                           ,u4
 ,s4 ,geol4     ,exploration of         
,chemical      ,chemical                
,survey1 p4 #ded  ,dead ,sea1 p4        
,geology1 ,vol4 ,geology1               
#bhd              ,i1 p4 #hi      ,vol4 
,i1 p4 #hi                              
----------------------------------------
--------------------------------------  
,sodium1 ,na            #b4hch          
#gd4gjj          #a4dddj          4#cjha
                                        
,potassium1 ,k         #aj4hhj          

#a4jda           4#jcih                 
,rubidium1 ,rb                          
444444          444444         444444   
,calcium1 ,ca          444444           
#c4fdg           4#ahed          4#abch 
,magnesium1 ,mg          4#jjb          
#ac4ggg           4#djie          4#jgbh
                                        
,lithium1 ,li                           
,iron1 ,fe             444444           
444444          444444         444444   
,chlorine1 ,cl          #h4daj          
#afc4cdd          #b4gcgf               
4#degf                                  
,bromine1 ,br          444444           
4#jdc           ,trace         444444   
,carbonic acid                          
gas1 ,,co            #d4fec             
444444           4#achb          4#cgdf 
,sulphuric acid1                        
,h,,so                4#eji             
4#aih          #a4ccgb          4#caji  
,phosphoric acid1                       
,,hpo                                   
,nitric acid1                           

,,no                                    
,boracic acid1                          
,h,,bo              444444              
,silica1 ,si,o           4#jfd          
,alumina1                               
,al,o              444444               
444444         444444                   
,hydrogen in                            
bicarbonates1 ,h                        
4#jjbc          4#jjfb                  
,ammonium1 ,,nh                         
444444                                  
,organic matter       444444            
444444          444444         444444   
----------------------------------------
----------------------                  
#bg4ceg         #bef4gej                
#f4bidj         #a4fedj                 
----------------------------------------
--------------------------------------  
----------------------------------------
----------------------------------------
----------------        ,dead ,sea1     
,dead ,sea1 near  ,dead ,sea1 at #cic   
,dead ,sea1 at       ,elton ,lake       

,elton ,lake      ,ras ,dale1 surface   
the ,island1    ft41 between ,ras #fef  
ft41 between                            
surface        ,feschkak  and    ,ras   
,feschkak                               
,ras ,zerka       and ,ras ,zerka       
#a4jbaf           #a4afdg               
#a4bbbe           #a4bcjj               
,mar4 #bj1 #ahfd    ,apr4 #g1 #ahfd     
,mar4 #ae1 #ahjd    ,mar4 #ae1 #ahfd    
,april        ,august                   
,terreil          ,terreil              
,terreil           ,terreil             
,gobel        ,erdman                   
,lartet ,geological,lartet              
,geological,lartet ,geological,lartet   
,geological,bischof's     ,bischof's    
,exploration of   ,exploration of       
,exploration of   ,exploration of       
,chemical      ,chemical          ,dead 
,sea1 p4 #bgh ,dead ,sea1 p4 #bgh ,dead 
,sea1 p4 #bgh ,dead ,sea1 p4 #bgh       
,geology4 ,vol4 ,geology1 ,vol4         
,i1 p4 #djc-dje ,i1 p4 #djc-dje         
----------------------------------------

----------------------------------------
----------------           4#hhe        
#bb4djj           #be4jga               
#be4ajg          #ea4eij        #bi4cjj 
4#dgd            #c4edg                 
#c4iij            #d4ejc                
#a4afb                                  
444444           444444           444444
           444444                       
444444                                  
#b4aej            #i4jid                
#c4gjd            #d4bah          444444
          4#ajf                         
#d4aig           #be4ebi                
#da4cjf           #db4jjf               
#bi4iga        #de4eih                  
444444           444444           444444
           444444                       
,trace            ,trace                
,trace            ,trace          444444
        444444                          
#ag4fbh          #abf4eba               
#aff4cdj          #agj4dbe              
#aei4dih       #aff4hij                 
4#afg            #d4efh                 

#d4hgj            #d4che                
4#jei        444444                     
,trace            ,trace                
,trace            ,trace          444444
          4#bgb                         
4#bjb             4#did                 
4#dea             4#dei          #ac4cbj
        #ag4gcd                         
444444           444444           444444
           444444                       
4#jjf            ,trace                 
,trace            ,trace                
,trace            ,trace                
,trace            ,trace                
444444           444444           444444
           444444                       
,truce            ,trace                
,trace            ,trace          444444
        444444                          
,trace            ,trace                
,trace            ,trace          ,trace
          #e4jhj                        
----------------------------------------
----------------------------------------
----------------         #be4gji        

#aib4aec          #bde4gcb              
#bea4ajc         #bee4fjj      #bfd4ihj 
----------------------------------------
----------------------------------------
----------------                        
----------------------------------------
----------------------------------------
-------------------       ,elton ,lake  
,great ,salt ,lake  ,great ,salt ,lake  
,great ,salt ,lake  ,humboldt#aib ,lake 
,indevak ,lake                          
#a4bgbhh           #a4agj               
#b4d             #a4ajb                 
#a4jjg          444444                  
,october           #ahej                
#ahfi          ,aug41 #ahgc             
444444         4444444                  
,h4 ,rose        ,l4 ,d4 ,gale       ,o4
 ,d4 ,allen       ,h4 ,bassett      ,o4 
,d4 ,allen       ,gobel                 
,bischof's        ,stambury's       ,u4 
,s4 ,geological  ,amer4  ,chemist1 ,u4  
,s4 ,geol4 ,expl4,lartet ,geol4         
,chemical         ,expedition to        
,expl4 #djth par4  #ahgd1 p4 #cie       

#djth par4 #ahgg1   ,expl4 of           
,geology4 ,vol4    ,great ,salt         
#ahgg1 ,vol4 ,,ii1                      
,vol4 ,i1 p4 #ebh    ,dead ,sea1        
,i1 p4 #djc-dje    ,lake1 p4 #daj     p4
 #dce                                   
p4 #bhd                                 
----------------------------------------
----------------------------------------
-------------------         #ae4jfj     
#he4ccj           #di4fij               
#ch4c           4#bghdb                 
#id4jej                                 
#a4bjd                                  
#b4djg              #i4i                
4#jfjhc             4#ebi               
444444           444444           444444
           444444           444444      
444444            ,trace#aif            
4#bee               4#f                 
4#jabeg             4#abc               
#fj4edj             4#fcf               
#c4ghj              #c4j                
4#jafdh            #e4jgf               
,trace            ,trace                

444444           444444           444444
           444444           444444      
444444                                  
#aga4icf          #abd4ded              
#hc4idf             #gc4f               
4#biede          #aeh4fhg               
,trace                            444444
                                        
444444           444444           444444
            444444          4#bjabf     
444444                                  
#db4efj           #ab4djj               
#i4heh               #h4h               
4#jcjdj            #c4jfe               
4#jjjfi                                 
444444                            444444
                                        
,trace                                  
,trace                                  
444444                                  
4#jcbej                                 
444444                                  
,trace           444444           444444
           444444           444444      
44444                                   

----------------------------------------
----------------------------------------
-------------------        #bia4cjj     
#bbb4hbj          #adi4icf              
#acd4b           4#ibhjj                
#bfa4ecj                                
----------------------------------------
----------------------------------------
-------------------                     
----------------------------------------
----------------------------------------
------     ,soda ,lake1 near  ,soda     
,lake1 near  ,mono ,lake1 ,cal41        
,urmiah ,lake   ,owen's ,lake1 ,cal4    
,ragtown1 ,nev41    ,ragtown1 ,nev41    
at #a foot below                        
at #a foot below at #ajj feet below     
surface                                 
surface          surface                
#a4aja           #a4aja           #a4jdh
              #a4aee           #a4jea   
444444          444444        ,july #af1
 #ahhc        444444           444444   
,t4 ,m4 ,chatard    ,t4 ,m4 ,chatard    
,t4 ,m4 ,chatard       ,hitchcock       

,o4 ,loew                               
,ante1 p4 #gj      ,ante1 p4 #gj        
,bulletin ,no4 #i4  ,lartet ,geological 
,appendix ,,jj ,ann4                    
,u4,s4 ,geol4 ,survey1 ,exploration of  
,rep4 ,chief                            
p4 #bf       ,dead ,sea1 p4 #bhd        
,engineers1 #ahgf                       
p4 #aij                                 
----------------------------------------
----------------------------------------
------          #da4fcb          #dj4bjf
           #ah4ajj            #gd4hij   
#ba4fej                                 
#b4bij           #b4dbe                 
#a4aaa                                  
#b4gea                                  
444444            444444                
444444                                  
444444           444444            4#bgh
              4#ebi            ,trace   
4#bde             4#bde            4#abe
             #b4iad            ,trace   
444444                                  
,trace                                  

444444           444444          444444 
444444           444444                 
#da4dif           #dj4bjf               
#aa4faj           #aai4dif              
#ac4ddj                                 
444444           444444          444444 
444444                                  
#ae4fejg        #ah4jehg       #ad4dfeg 
444444           #ac4adj                
#aa4gga           #aa4idc               
#f4ebj             #g4fga               
#i4cfb                                  
444444                                  
,trace                                  
444444           444444          444444 
,trace                                  
4#bhe             4#bhg            4#aec
                              ,trace    
4#bge             4#bha            4#bfh
                               4#afd    
444444                                  
,trace                                  
444444                                  
444444                                  
444444           444444          444444 

444444            ,trace                
----------------------------------------
----------------------------------------
------         #aac4fdd                 
#aac4fea          #di4fcj               
#bje4ejj           #fj4ejg              
----------------------------------------
----------------------------------------
------                                  
----------------------------------------
----------------------------------------
----------------------                  
,pyramid ,lake1#aic  ,sevier ,lake1     
,walker ,lake1#aid    ,winnemucca       
,van ,lake          ,aral ,sea          
,nev4            ,utah             ,nev4
          ,lake1 ,nev4                  
444444          444444            #a4jjc
            #a4jja                      
,aug4 #ahhb          #ahgb              
,sept41 #ahhb      ,aug41 #ahhb         
,f4 ,w4 ,clarke      ,o4 ,loew          
,f4 ,w4 ,clarke     ,f4 ,w4 ,clarke     
,chancourtois                           
,ante1 pp4 #eg ,u4 ,s4 ,survey1 ,w4     

,ante1 p4 #gj   ,ante1 p4 #fc           
,bischof's ,chemical  ,roth ,chemical   
and #eh    #ajj ,m41 ,vol4 ,,iii1       
,geology1 ,vol4 ,i1  ,geology1 p4 #dfe  
p4 #add                                 
p4 #id                                  
----------------------------------------
----------------------------------------
----------------------         #a4agif  
#bh4hdj          4#heece                
#a4bigj            #h4ejbd              
#b4deab                                 
4#jgcc                           ,trace 
4#jfhf             4#bdf                
4#jehd                                  
444444          444444          444444  
444444                                  
4#jjbb                                  
4#jjhi            4#aah          4#jbbae
            4#jaif           444444     
4#deha                                  
4#jgig           #b4jjj          4#jchcj
            4#jagc             4#aegd   
4#eife                                  
444444             44444                

444444          444444          444444  
44444            ,trace#aig             
4#jjjh                                  
#a4dcjj          #de4ejj                
4#ehcge           #a4ficd               
#e4fic           #c4hchf                
444444                          444444  
444444            444444                
4#jjbi                                  
4#dijjg       444444          4#dgddeg  
4#cdehaih          #e4bfgaie            
4#jiah                                  
4#ahbb           #i4cde          4#ebjjj
            4#accc             #b4eee   
#c4ccfh                                 
444444                                  
4#jjaa                                  
,trace                                  
444444                          444444  
444444           444444                 
4#jccd                          4#jjgej 
4#jbge              4#ahj               
4#jjcb                                  
4444444            444444               
444444                                  

444444                                  
,trace                                  
,trace                                  
----------------------------------------
----------------------------------------
----------------------         #c4dhfa  
#hf4djc         #b4ejaej                
#c4fjbe            #bb4fjj              
#aj4hdaf                                
----------------------------------------
----------------------------------------
----------------------                  
,,chapter ,,vii4                        
,,the ,,origin ,,and ,,descent ,,of     
,,rocks4      ,it has been the current  
opinion that the earth was once in a    
molten  state1 and thence cooled to a   
solid condition1 and hence that all the 
primitive rocks were igneous4 ,even     
those who think that the earth may      
never have passed through a molten state
 agree that the oldest known  rocks are 
either true igneous rocks1 or rocks of  
very similar nature4 ,a  molten magma   
may1 therefore1 be taken as the mother  

state of the rocks4  ,starting with this
 conception1 the natural order of events
 suggests the  inquiries 7#a7 how rocks 
are formed from molten magmas1 7#b7 what
 natures  they assume1 7#c7 how other   
rocks are derived from them1 7#d7 how   
still  other rocks are derived from     
these derivatives1 and so on4 ,to answer
  these inquiries is to trace out the   
generations of rocks and learn the      
general history of rock-formation4      
7#a7 ,the process by which igneous rocks
 are formed from lavas is  actually     
taking place in existing volcanoes4 ,as 
these are widely  scattered over the    
face of the earth1 the material poured  
out by  them represents different parts 
of the interior and varies in nature    
accordingly4 ,this affords the means of 
studying the differences that  arise    
from differences of material4 ,this is a
 radical consideration1  for variations 
in composition give rise to the most    
fundamental  distinctions between rocks1
 though by no means the only ones4      

,rocks  which have the same composition 
often differ greatly in texture or      
structure1 owing to the varying         
conditions under which they were        
formed4 ,in the solidification of rocks 
from the molten state1 the  rate of     
cooling causes many differences4 ,a     
means of studying this is  afforded by  
the various lava flows that are now     
being poured out on  the surface under  
different conditions2 but a more        
important means is  afforded by extinct 
volcanoes1 especially by those which    
have been  deeply cut open by erosion4  
,in certain very ancient volcanoes1 not 
only have the solidified lava streams of
 the surface been cut across  by        
erosion1 but the lava that remained in  
the crater1 or in the neck  that led up 
from below1 is laid bare for inspection4
 ,exposures of even  more profound      
nature have been made by the great      
disruptions which  the outer part of the
 crust has suffered4 ,in certain tracts 
there have  been profound fractures1 and

 the formations on one side of these    
have  settled down and on the other side
 have been pushed up 7faulted71 so as   
to expose parts that were once much     
below the surface4 ,sometimes also  the 
crust has been folded and crumpled1 and 
the wrinkles thus formed  have          
afterwards been worn away or cut open by
 deep valleys1 and rocks  that were once
 deeply buried have been laid bare4 ,by 
the revelations  made in these and other
 ways1 it has been learned that at      
various times  in the history of the    
earth molten matter has been thrust into
 fissures  or intruded between layers of
 the crust and cooled there1 without    
coming to the surface4 ,sometimes the   
lava appears to have forced its  way    
into the rocks1 and sometimes to have   
lifted the upper beds and  formed great 
subterranean layers or tumor-like       
aggregates1 called  bathyliths and      
laccoliths 7,fig4 #ccd74 ,such intruded 
bodies of molten  rock1 solidifying     
under the varying conditions of such    

subterranean  situations1 are a fruitful
 source of instruction respecting the   
influence of varying rates and modes of 
cooling1 as well as of other  attendant 
conditions4    ,illustration3 ,fig4     
#ccd4--;,diagram of a laccolith4        
7,gilbert47    ,it will thus be readily 
seen that the rate of cooling of the    
various  molten rocks must have differed
 very greatly4 ,in the portions  poured 
out upon the surface there were         
sometimes narrow streams and  thin      
sheets1 giving large exposure in        
proportion to the mass 7,fig4  #cce71   
and sometimes thick flows and deep      
pondings in basins and  choked valleys1 
giving massive bodies with relatively   
small surface  exposure4 ,there were    
explosions of the lava into minute      
particles  with almost instantaneous    
cooling1 and there were eruptions       
beneath  the sea the peculiar effects of
 which are rather matters of inference  
than of positive knowledge4 ,in the     
portions underground there were         

insinuations into thin fissures1 on the 
one hand1 and in-thrustings of  thick   
bodies1 on the other4 ,some intrusions  
entered the upper part of  the crust    
where the rocks were cold and wet1 and  
some were thrust into  the deeper       
portions where the rocks were warmer and
 less penetrated  by water4 ,sometimes  
the lava rose rapidly and was little    
cooled in  passage1 sometimes slowly    
with more cooling en route1 and         
sometimes  there were long halts between
 eruptions1 with much opportunity to    
cool4  ,an almost infinite variety of   
conditions is thus presented1 and with  
it  a rich field for the study of the   
modes of solidification4                
,illustration3 ,fig4 #cce4--;,fresh lava
 flow1 with large surface    exposure4  
,holemaumau1 ,hawaii4 7,libbey47    ,in 
the underground intrusions the          
additional factor of high pressure  was 
also present1 and this is the third     
important condition in  determining the 
nature of igneous rocks4    ,the three  

factors1 composition1 rate of cooling1  
and degree of  pressure1 require special
 consideration4                         
,composition of ,igneous ,rocks4    ,all
 or nearly all the chemical elements    
known on the earth are found  in greater
 or less amounts in igneous rocks1 and  
in a broad sense are  constituents of   
them4 ,if there are any exceptions1 they
 are most likely  to be found in the    
rarer elements in the atmosphere4       
,oxygen1 nitrogen1  hydrogen1 aqueous   
vapor1 and carbonic acid1 which make up 
the mass of  the present atmosphere1 are
 all found in lavas and in their cooled 
products4 ,probably all the rarer       
elements also occur in igneous rocks4   
,helium is known to be given forth by   
springs4    ,leading elements4--,but    
although nearly or quite all the known  
chemical  elements enter into the       
igneous rocks1 only a few of them are   
abundant4  ,these are regarded as normal
 or essential constituents1 while the   
rarer  substances are regarded as       

incidental4 ,by combining a large number
 of  the most trustworthy analyses of   
rocks of all sorts1 ,f4 ,w4 ,clarke#aii 
has estimated the relative amounts of   
the more abundant elements in the  crust
 of the earth with the following result3
                               ,percent4
 in    ,element4     ,symbol4   the     
,solid ,crust4    ,oxygen        7,o7   
#dg4jb    ,silicon       7,si7          
#bh4jf    ,aluminum      7,al7          
#h4af    ,iron          7,fe7           
#d4fd    ,calcium       7,ca7           
#c4ej    ,magnesium     7,mg7           
#b4fb    ,sodium        7,na7           
#b4fc    ,potassium     7,k7            
#b4cb    ,titanium      7,ti7           
4#da    ,hydrogen      7,h7             
4#ag    ,carbon        7,c7             
4#ab    ,phosphorus    7,p7             
4#ji    ,manganese     7,mn7            
4#jg    ,sulphur       7,s7             
4#jg    ,barium        7,ba7            
4#je    ,strontium     7,sr7            
4#jb    ,chromium      7,cr7            

4#ja    ,nickel        7,ni7            
4#ja    ,lithium       7,li7            
4#ja    ,chlorine      7,cl7            
4#ja    ,fluorine      7,fl7            
4#ja                              ------
                              #ajj4jj   
,it will be seen that only eight of the 
elements hold a high rank  in quantity4 
,many that are of the utmost importance 
in the history  of the earth and the    
affairs of men are low in the list1 or  
do not  even appear in it at all1       
because their quantity is too small to  
be  estimated in percentages4 ,the      
precious metals1 and even some of the   
more common metals1 as lead1 zinc1 and  
copper1 are too scarce to form  an      
appreciable percentage4    ,union of    
elements4--,in a general study of the   
igneous rocks we may  for the present   
neglect all but the first eight of these
 elements4  ,out of these elements      
spring various chemical combinations1   
and out  of these combinations spring   
the various minerals1 and out of the    

combinations of minerals come the       
various rocks4 ,the union of oxygen     
with the other seven elements may be    
taken as a fundamental step in  this    
series of combinations4 ,the result is  
the following oxides3 ,silica  7,si,o71 
alumina 7,al,o71 ferrous1 ferric1 and   
magnetic oxide 7,fe,o1  ,fe,o1 and      
,fe,o71 magnesia 7,mg,o71 calcium oxide 
or lime 7,ca,o71 soda  7,na,o71 and     
potash 7,k,o74 ,the oxygen sometimes    
unites in proportions  different from   
those here given1 but such exceptions   
may be neglected  in a general study4   
,we thus have nine leading oxides4 ,of  
these1 silica  acts as an acid1 or more 
strictly according to the newer chemical
 view1  as an acid anhydride4 ,all the  
rest1 except the magnetic oxide of iron1
  and sometimes the oxide of aluminum1  
act as basic oxides4    ,in the older   
chemical philosophy these oxides were   
supposed to combine  by the simple union
 of an acid oxide with a basic oxide1   
and to remain  as oxide joined to oxide2

 thus silica 7,si,o7 and lime 7,ca,o7   
formed  silicate of lime 7,ca,o1,si74   
,the symbols express the idea better    
than  the words4 ,this method is used in
 the older geological works and in  some
 of the later4 ,but in the newer        
chemical doctrine1 the oxides are  not  
believed to remain so distinct after    
their union1 and the symbols  are       
written ,ca,si,o1 and the compound is   
named calcium silicate4  ,according to  
the modern doctrine of solution1 some of
 the calcium1  silicon1 and oxygen may  
exist as free ions in molten rock4 ,the 
precise  way in which the elements are  
related to each other in these compounds
  can scarcely be said to be known4 ,for
 the general purposes of geology  it is 
most convenient to think of these oxides
 as uniting in the  simple fashion first
 named1 and this involves no apparent   
geological  error in general studies1   
since they are oxides when they enter   
the  compound1 and if the compound is   
decomposed they usually come forth      

again as oxides2 but in closer studies  
more complex unions1 attended by        
dissociations 7ionization71 must be     
recognized4    ,formation of            
minerals4--,as but one of the leading   
oxides that abound  in an average magma 
plays the part of an acid1 the silica1 a
 very  simple conception of the general 
nature of igneous rocks may be  reached 
by noting that they are mostly silicates
 of the seven leading  basic            
oxides--alumina1 potash1 soda1 lime1    
magnesia1 and the iron  oxides4 ,this   
general idea is a very useful one and   
represents a most  important truth2 but 
in its use we must not forget that there
 are many  exceptions4 ,sulphur1        
phosphorus1 chlorine1 and other elements
 unite  with the bases to form          
sulphates1 sulphides1 phosphates1       
phosphides1  chlorides1 etc4 ,so also   
there are many minor bases that form    
silicates2  and these minor bases unite 
with the minor acids to form many more  
or  less rare minerals4 ,again1 there   

are native metals in some igneous       
rocks4 ,but altogether these hardly     
reach more than one or two percent4  of 
the whole4    ,there are1 however1 two  
exceptions of more importance4 ,in the  
molten  magma the acid and basic        
elements are not always evenly matched4 
,when  there is an excess of silica1 a  
portion remains free and takes the  form
 of quartz 7,si,o74 ,if there is an     
excess of the basic oxides1 the  weakest
 one is usually left out of the         
combination4 ,this is commonly  the iron
 oxide1 which then usually takes the    
form of magnetite 7,fe,o74  ,it is a    
singular fact that quartz often forms   
when there is no excess  of silica1 and 
magnetite when there is no excess of    
base4 ,quartz  7free acid anhydride7 and
 magnetite 7free basic oxide7 sometimes 
occur in the same rock4 ,the explanation
 for this is yet to be found4  ,these   
form rather important exceptions to the 
generalization that the  igneous rocks  
are mostly made up of silicates1 but1   

thus qualified1  it expresses the       
essential truth1 and has the merit of   
embodying the  central chemical fact    
relative to these rocks4    ,sources of 
complexity4--,but here simplicity ends4 
,as we pass on to  the specific         
silicates that are formed1 we encounter 
several sources  of complexity4 ,in the 
first place1 the silica unites with the 
bases in  different ratios and thus     
gives rise to unisilicates or           
orthosilicates  7ratio of oxygen of     
bases to oxygen of silica1 #a3a71       
subsilicates  7ratio more than #a71     
bisilicates 7ratio #a3b71 trisilicates  
or  polysilicates 7ratio #a3c or        
higher71 and combinations of these4 ,all
 the  bases are not known to combine in 
all these ways1 but many do in more     
than one of them4 ,still1 if the silica 
were content to unite with each  of the 
bases by itself alone1 the results would
 remain comparatively  simple2 but      
instead of this it unites with two or   
more at the same  time2 and1 more than  

that1 it unites with them in varying    
amounts4 ,the  case would still remain  
measurably simple if these chemical     
compounds  always crystallized out by   
themselves1 each compound forming one   
mineral1 and but one2 but the different 
silicates have the confusing  habit of  
crystallizing together in the same      
mineral4 ,a crystal  may thus sometimes 
be seen1 under the microscope1 to be    
made up of  alternating layers of       
different silicates2 e4g41 a microscopic
 layer  of an aluminum-calcium silicate 
may be overlain by a microscopic layer  
of an aluminum-sodium silicate1 and the 
alternation may be repeated  throughout 
the crystal1 giving it a banded         
structure4 ,there is reason  to believe 
that this is true in many cases where   
the microscope fails  to detect it1 and 
that less symmetrical comminglings of   
silicates may  take place4 ,as such     
alternations or mixtures are not        
governed by any  known mathematical law1
 as is the case in chemical compounds1  

there is  no determinate limit to the   
number of combinations that may arise4  
,as  a matter of fact1 new ones are     
still being discovered in the progress  
of research1 and the total number that  
may ultimately be found can  scarcely be
 prophesied4    ,as a result of all this
 fertility of combination1 the total    
number of  silicious minerals in igneous
 rocks is large4 ,it is the function of 
the  mineralogist to treat of these     
minerals as such4 ,the geologist deals  
with them as constituents of the earth  
and as factors in its history4  ,only a 
few of them are so abundant as to       
require special individual  notice in a 
general study of the earth4 ,it may be  
remarked also that  only a few of them  
can be identified by simple inspection  
as they  occur in the rocks1 partly     
because of the delicacy of the          
distinctions  between many of them1 and 
partly because of their minuteness and  
intricate intermixture4 ,the resources  
of the polarizing microscope  are       

necessary for safe determination in most
 cases4 ,the student need  not feel     
embarrassment or discouragement if he is
 often unable to  recognize the         
constituents of the intimately          
crystalline rocks4 ,their  determination
 has grown to be a profession by itself4
    ,the leading minerals of igneous    
rocks4--,fortunately for the simplicity 
of geological study1 a few minerals make
 up the great mass of the  igneous      
rocks4 ,these few are quartz1 the       
feldspathic minerals1  the              
ferromagnesian minerals1 and the iron   
oxides4 ,quartz 7silica1  ,si,o7 is the 
free acid already mentioned4 ,the       
feldspathic and  ferromagnesian minerals
 are the leading silicates of the       
earth's crust1  and vastly surpass all  
others in abundance4 ,the feldspathic   
group  embraces minerals formed by      
silica in union with alumina1 together  
with either potash1 soda1 or lime1 or   
two or more of these together4  ,the    
ferromagnesian group embraces minerals  

formed by the union of  silica with     
iron1 magnesia1 and lime1 together with 
more or less of the  other basic oxides4
 ,these statements are only true in a   
very general  sense4 ,admixtures1       
replacements1 and impurities are so     
frequent as to  break down all sharp1   
simple definitions4 ,the feldspathic    
minerals  are normally light in color1  
ranging from white to red or gray4 ,the 
ferromagnesian minerals are normally    
dark 7commonly greenish7 from the       
presence of iron1 the great coloring    
element of rocks4 ,but these color      
distinctions do not hold good in detail 
and cannot be much trusted as a  means  
of identification4    ,the feldspathic  
minerals 7p4 #dfb7 embrace the potash   
feldspars1  orthoclase and microcline2  
the soda feldspar1 albite2 the lime     
feldspar1 anorthite2 and the mixed      
feldspars intermediate between  albite  
and anorthite1 viz41 the soda-lime      
feldspar1 oligoclase1 the  lime-soda    
feldspar1 andesine1 in which lime and   

soda are nearly  equal1 and the         
lime-soda feldspar1 labradorite1 in     
which the lime  predominates2 together  
with leucite1 a potash silicate higher  
in  alkali than orthoclase1 and         
nephelite1 a soda silicate higher in    
soda than albite4 ,leucite and nephelite
 are usually classified as              
feldspathoids1 not as feldspars4 ,it is 
to be understood that alumina  is       
normally present in all these4          
,additional details respecting these    
minerals may be found in the reference  
list1 p4 #dfj4    ,among the            
ferromagnesian minerals the most        
important are the  pyroxenes1 the       
amphiboles1 and the biotite type of     
mica4 ,olivine is  of subordinate       
importance4 ,the pyroxenes 7p4 #dfe7 and
 amphiboles  7p4 #dfj7 have nearly the  
same chemical composition1 but differ in
  crystallization and physical          
properties4 ,hornblende 7an amphibole7  
has been melted1 and on cooling under   
proper conditions found to take  on the 

form of augite 7a pyroxene74 ,pyroxene  
is sometimes altered  into uralite1 one 
of the amphiboles4 ,the pyroxenes and   
amphiboles  are the most abundant of the
 dark minerals in crystalline rocks4    
,the leading members of the pyroxene    
group are augite1 diallage1             
hypersthene1 enstatite1 and soda        
pyroxene4 ,the chief members of  the    
amphibole group are hornblende and the  
soda amphiboles4 ,all are  essentially  
silicates of magnesia and iron oxide1   
with or without the  addition of lime1  
soda1 and alumina4 ,details respecting  
these may be  found in the reference    
list4    ,the two leading micas are the 
iron-magnesia mica1 biotite1 and the    
potash mica1 muscovite1 the familiar    
8isinglass0 of the stove-door4          
,chemically1 muscovite should go with   
the potash feldspars1 but it  is        
distinguished from them by its          
crystalline habit and physical          
properties4 ,the biotite should go      
chemically with the pyroxenes and       

amphiboles1 which it closely resembles  
except in its crystalline  properties4  
,details respecting the micas may be    
found in the reference  list1 p4 #dfd4  
,two iron oxides1 magnetite 7,fe,o7 and 
hematite 7,fe,o7 are widely             
disseminated in igneous rocks4 ,they    
constitute the free bases already       
mentioned4    ,summary of salient       
facts4--,the salient facts are1         
therefore1 7#a7 that  out of the        
seventy-odd chemical elements in the    
earth1 eight form the  chief part of it2
 7#b7 that one of these elements uniting
 with the rest  forms nine leading      
oxides2 7#c7 that one of these oxides   
acts as an  acid and the rest as bases2 
7#d7 that by their combination they form
 a  series of silicates of which a few  
are easily chief2 7#e7 that these       
silicates crystallize into a multitude  
of minerals of which again a few  are   
chief2 and 7#f7 that these minerals are 
aggregated in various ways  to form     
rocks4 ,possessed of these leading      

ideas1 we are prepared to  turn to the  
consideration of some of the conditions 
under which these  combinations take    
place in the formation of rocks from    
molten magmas4                          
,,the ,,nature ,,of ,,molten ,,magmas4  
,we easily fall into the habit of       
thinking of molten rock as we think  of 
a molten metal1 merely as a substance   
which has passed from the  solid to the 
liquid condition because of high        
temperature4 ,with the  return of low   
temperature a molten metal returns to   
the solid state  usually in the same    
molecular condition which it possessed  
before4  ,the point of fusion and the   
point of solidification are the same and
  are rigidly fixed4 ,if this were true 
of the constituents of a rock1  a       
definite order for the solidification of
 the several minerals  might be         
anticipated4 ,as a matter of fact1 the  
order is not the  same under all        
conditions1 and1 what is especially     
significant1 the  order is far from     

being that in which the constituents    
would fuse  or would solidify           
separately4 ,for instance1 in a granite 
composed  chiefly of quartz1 feldspar1  
and mica1 the quartz is often the last  
to take form1 although it is more       
infusible than the feldspar or the      
mica4 ,this and other phenomena show    
that a molten magma is not to be  viewed
 simply as a fused substance1 but rather
 as a solution of  one silicate in      
another1 or as a solution of several    
silicates in  one another mutually4 ,the
 high temperature is to be regarded     
merely  as a condition prerequisite to  
solution1 or as the condition of  fusion
 of some one constituent which then     
dissolves the others4 ,if  crystals of  
snow1 sugar1 and salt be mixed at a low 
temperature and  compacted1 the mass may
 be regarded as an artificial rock4 ,on 
raising  the temperature1 all will pass 
into solution while the temperature is  
still somewhat below the melting-point  
of the snow1 the most fusible1  and     

while it is much below that of either   
the sugar or the salt4 ,this  particular
 case is instructive because the ice is 
not simply fused by  temperature2 the   
affinity of the salt plays a part4 ,if  
the temperature  were again lowered1 the
 sugar and salt would not crystallize   
out at  their fusing-points1 but would  
remain in solution down to and even     
below the normal freezing-point of      
water2 in other words1 they would       
remain in solution until the water      
crystallized out and forced them  to    
take the solid state4 ,this holds good  
when the amounts of the  sugar and salt 
are small relative to the water4 ,if1 on
 the contrary1  their quantity is large 
relatively1 crystallization will take   
place  at higher temperatures and before
 the water crystallizes to ice4 ,from   
this it appears that the salt and sugar 
might crystallize either before  the    
water or after it1 according to the     
degree of concentration4 ,the  behavior 
of mixtures of minerals in passing into 

and out of the molten  condition appears
 to be quite analogous to this1 and     
hence a great  variety of results attend
 the process1 dependent upon the number1
 the  nature1 and the relative          
quantities of the ingredients4 ,the     
approved  conception of the genesis of a
 rock from a molten magma 7when ample   
time is given7 is that one compound     
after another crystallizes out  as the  
temperature falls and its point of      
saturation for each is  reached1 until  
the whole has been solidified4 ,the     
modes of combination  of the elements in
 the molten magma are not necessarily   
the same as  those in the derivative    
crystals2 indeed1 the combinations      
doubtless  change as the process        
proceeds2 certain constituents being    
taken out1  the remaining ones probably 
rearrange themselves4    ,time required 
in crystallization4--,the liquid magma  
of igneous rocks  is essentially a fluid
 glass or slag4 ,it is analogous to     
common glass1  which is a silicate of   

potash1 soda1 or other base1 except that
  usually common glass is relatively    
free from iron and other coloring       
substances1 while these abound in the   
natural magmas and render them  dark and
 more or less opaque2 but the           
fundamental nature is the  same1 except 
that the natural lavas are usually      
mixtures of several  silicates1 while   
the artificial glasses consist of only  
one1 or at most  a few4 ,furnace slag is
 essentially an artificial lava4        
,when a lava is cooled quickly1 the     
commingled silicates solidify in the    
diffused condition essentially as they  
were in the liquid2 for there  is no    
time for the silicate molecules of a    
like kind to come together1  particle by
 particle1 in regular systematic order1 
as required in  crystallization4 ,the   
essential feature of crystallization is 
this  systematic arrangement of the     
molecules according to a definite plan1 
giving a specific crystal form1 as a    
cube1 a hexagonal prism1 etc4    ,there 

are six 7sometimes made seven7          
fundamental systems of  crystallization1
 and a multitude of variations of       
special form in each  system4 ,the      
treatment of these forms belongs to     
mineralogy4    ,in a thick viscid       
liquid1 this systematic arrangement of  
molecules  into definite crystal forms  
takes place slowly1 for the crystalline 
force in the silicates is far less      
energetic than that in water1  which    
crystallizes into ice with much rapidity
 and with great force4  ,because of this
 slowness1 the solidification of the    
lava may catch  the process of          
crystallization at any stage4 ,if the   
lava is cooled  quickly1 the result is a
 glass2 if less quickly1 part glass and 
part  crystals2 if slowly enough1 all   
becomes crystalline4 ,in general the    
slower the growth the larger the        
crystals4 ,the solidification product   
may1 therefore1 range from a glass to a 
mass of crystals2 i4e41 it may  be 7#a7 
wholly glass1 7#b7 a glassy matrix with 

a few small crystals  scattered through 
it1 7#c7 a less abundant glassy matrix  
with more and  larger crystals1 7#d7 a  
mere remnant of glass in a mass of      
crystals1 or  7#e7 a mass of crystals   
with no glass4    ,successive stages of 
crystallization4--,since eruptions take 
place  intermittently1 it is obvious    
that cooling of the lava may be in      
progress in its hidden reservoir during 
the quiescent intervals between         
eruptions4 ,after a certain stage of    
partial crystallization has been        
reached during such time of quiet1 a    
renewal of eruption may take place  and 
the whole mass of lava be shifted into  
quite new conditions1 and  a second     
phase of solidification may be          
superposed on the one already  started4 
,the rock will then show two phases of  
crystallization3 7#a7  large crystals of
 the kind or kinds most prone to develop
 in the given  lava may have grown      
during the first long stage of slow     
subterranean  cooling1 while the greater

 part of the lava still remained liquid2
 and  7#b7 small crystals or glass may  
have developed when the more rapid      
cooling under the new conditions took   
place4 ,the result would be large       
crystals set in a matrix of small       
crystals or of glass1 a combination     
styled porphyritic4 ,in such cases the  
lava1 in its later stages1  carries the 
large crystals floating throughout its  
mass1 and is not a  simple liquid4      
,,the ,,fragmental ,,products ,,of      
,,sudden ,,cooling4    ,pyroclastic     
rocks4--,the extreme example of sudden  
cooling is presented  when lavas are    
violently exploded into the air and     
solidify almost  instantly4 ,the        
resulting glassy particles or filaments1
 if small1  constitute volcanic ash4    
,the explosion appears to be due to     
steam and  other gases which are held in
 the deeper lava under great pressure1  
but  which1 as they rise toward the     
surface of the lava where the pressure  
is relieved1 expand with explosive      

violence4 ,it is probably also due in   
part to progressive crystallization1    
which forces the gases out from  the    
part that crystallizes and overcharges  
the rest4 ,sometimes the  projected     
particles draw after themselves long    
filaments like the  threads of spun     
glass1 and sometimes while in the air   
they divide and  draw apart1 spinning a 
filament of viscid lava between them4 ,a
 variety  of this kind at the volcano of
 ,kilauea in ,hawaii is known as        
8,pele's  hair40 ,these light filaments 
drift with the wind and lodge on the lee
  side of the volcano1 covering the     
surface 8like mown grass0 7,dana74      
,illustration3 ,fig4 #ccf4--,volcanic   
bomb4 ,about half natural size4         
7,photo4 by ,church47    ,when the      
exploded fragments are coarser they fall
 about the volcanic  vent and form the  
tuffs 7tufa7 of which most steep        
volcanic cones  are chiefly built4 ,in  
these larger fragments1 crystals are not
  infrequently found1 and the same is   

even true of the volcanic ash4  ,these  
crystals are undoubtedly such as had    
already been formed in the  lava before 
it exploded1 and their formation1 as    
suggested above1 may  have contributed  
to the explosion4    ,fragments too     
large to be borne far away by the air1  
but still small1  are known as lapilli1 
especially if they are somewhat rounded 
and  gravel-like4 ,a finer variety1 of  
the nature of sand1 much used in  making
 ,portland cement1 is locally known as  
puzzolana4    ,illustration3 ,fig4      
#ccg4--,volcanic bomb of unusual form1  
#ac foot long4    ,cinder ,buttes1      
,idaho4 7,russell1 ,u4 ,s4 ,geol4       
,surv47    ,the rougher1 irregular      
fragments of a clinker-like nature      
ejected by  volcanoes are known as scori
 or cinders4 ,they are more or less     
distended by gas-bubbles and are hence  
light and pumiceous4    ,the larger     
masses of lava ejected into the air are 
often caused to  rotate by the unequal  
force of the projection1 or by the      

unequal  friction of the air1 and to    
assume spheroidal forms1 the internal   
gases  at the same time often expanding 
and rendering the mass vesicular4       
,these rounded projectiles are known as 
volcanic bombs 7,figs4 #ccf and  #ccg74 
,balls of lava that have originated in  
rolling movements of the  seething mass1
 or in other ways1 are also styled      
bombs4 ,usage is not  altogether        
harmonious or consistent in the         
application of the term4    ,the larger 
masses that are projected into the air  
are more or less  vesicular from the    
expansion of included gases1 as already 
noted1 and  so the fragmental products  
of volcanic action grade into the       
vesicular4  ,the type of this class is  
pumice1 in which the gas cavities make  
up  by far the larger part of the volume
 of the whole mass1 and the whole  is   
reduced to the condition of a solidified
 froth or foam4 ,so thin are  the       
dividing films of glassy material in    
some cases that the whole is  pure      

white1 though the same material in solid
 mass would be dark4 ,this  solidified  
glassy froth is often lighter than water
 and floats freely  on the sea until it 
becomes 8water-logged0 and sinks4       
,dredgings of  the deep sea show that   
much pumice has accumulated there1 and  
being  far from the land has escaped    
burial by the sediments borne in by the 
rivers4    ,all of these fragmental     
rocks produced by volcanic action are   
known  as pyroclastic 7fire-fragmented7 
rocks1 a general term of much           
convenience in distinguishing them from 
lava-flows1 on the one hand1  and from  
the fragmental rocks produced by air and
 water 7ordinary  clastics71 on the     
other4                                  
,,the ,,glassy ,,rocks4    ,the solid   
glasses4--,the quick cooling of         
lava-flows into solid glasses  is       
chiefly dependent on their exposure at  
the surface4 ,hence it is  often the    
case that the exterior of a lava-flow is
 glassy in greater  or lesser degree1   

while the interior is more or less      
crystalline4  ,quick cooling is         
sometimes also due to the intrusion of  
the lava in  thin sheets into fissures  
in cold rocks4 ,when massive bodies of  
lavas  penetrate solid rocks1 the lava  
does not usually cool so fast as to     
prevent some degree of crystallization1 
and the crystallization may  even become
 complete2 but if the intruded lava     
sheet be very thin1  the lava is liable 
to be cooled to a nearly perfect glass4 
,the glassy  condition is1 therefore1   
subject to indefinite gradations4 ,as a 
rule1  the acid lavas are stiffer at the
 same temperature than the basic ones1  
and crystallize more slowly1 so that    
acid glasses are more common than  basic
 ones4 ,the basic rocks usually         
crystallize pretty thoroughly1  except  
on the immediate surface of the flows4  
,the first stages of                    
crystallization4--,the microscopic study
 of the  volcanic glasses reveals great 
numbers of minute forms known as        

crystallites1 microlites1 globulites1   
etc41 that appear to  be first steps in 
crystallization1 though many of them do 
not take  definite geometrical shapes   
and some do not show the optical        
characters  of crystals4 ,there are     
minute globules 7globulites71 needles1  
and  hair-like bodies 7trichites7 of    
more or less indeterminate nature1      
together with other forms that can be   
seen to be certainly the initial  forms 
of well-known minerals4                 
,illustration3 ,fig4 #cch4--;,flow      
structure in rhyolite4 ,nearly natural  
size4 7,photo4 by ,church47    ,the     
obsidians4--,of the compact glassy      
rocks1 obsidian is the best  type4 ,it  
is essentially a natural glass1 formed  
usually of acid  silicates4 ,it has the 
close texture1 conchoidal fracture1 and 
other  qualities of glass4 ,it is       
usually black1 but sometimes red1 brown1
  purple1 bluish1 or gray4 ,while       
chiefly of glass1 it usually contains   
more or less of the incipient crystals  

above described1 showing  that even here
 the first step in the gradation to the 
next or the  crystalline stage has been 
taken4 ,these incipient crystals        
sometimes  become so abundant as to     
change the texture from the vitreous to 
the  stony order4 ,in some cases1 the   
stony texture seems to have been        
developed in the obsidian after it was  
formed1 the change being a part  of a   
subsequent process of devitrification1  
but in other cases the  crystals seem to
 be original4 ,besides these1 there are 
often small  globular bodies known as   
spherulites4    ,varieties of glassy    
rock in which the embryo crystals are   
more numerous  and the glassy texture   
less perfect1 are known as pitchstones4 
,the  fresh surfaces of these have      
rather the aspect of pitch or resin     
than that of true glass2 hence their    
name4 ,like the obsidians1 they  are    
usually dark1 but they take on greenish1
 brownish1 yellowish1  and light-colored
 hues as well4 ,sometimes glassy rock   

fractures in  small spheroidal forms    
like pearls1 and is known as perlite4   
,basic  glasses are relatively rare1 and
 while usually included under the term  
obsidian1 are sometimes given special   
names4    ,illustration3 ,fig4          
#cci4--;,flow structure in volcanic     
glass4 ,about half    natural size4     
7,photo4 by ,church47    ,illustration3 
,fig4 #cdj4--;,flow structure in        
porphyry1 shown by the    position of   
the large crystals4 ,about two-thirds   
natural size4    7,photo4 by ,church47  
,illustration3 ,fig4 #cda4--,scoriaceous
 texture4 ,about four-fifths    natural 
size4 7,photo4 by ,church47             
,,special ,,structures4    ,flow        
structure4--,lavas that cool into glassy
 rocks frequently contain  gas cavities1
 colored spots and variations of texture
 which1 together  with the hair-like    
embryo crystals1 are drawn out into     
lines1 streaks1  and parallel belts by  
the flow of the viscous mass1 giving    
rise to  rhyolitic or flow structure    

7,figs4 #cch and #cci74 ,rocks in which 
this  is the most pronounced feature    
were formerly known as rhyolites1 though
  the term has drifted away from this   
original meaning and has been  applied  
to a class of acidic rocks4 ,the        
obsidians and pitchstones may  be more  
or less rhyolitic under the microscope1 
though to the naked  eye they may appear
 only as a glassy or resinous mass4 ,the
 rhyolites  generally have but an       
imperfect glassy texture1 since the     
crystals  and the cavities sometimes    
make up a notable part of the mass1 the 
glassy portion being scarcely more than 
a matrix in which the crystals1         
spherulites1 and cavities are carried4  
,by an increase of the crystals  in     
number and size1 the rock passes by     
gradations into porphyry or  phanerite4 
,illustration3 ,fig4 #cdb4--,porphyritic
 texture4 ,two-thirds natural    size4  
7,photo4 by ,church47                   
,amygdaloids4--,in lava-flows the       
included steam often collects in        

bubbles near the surface as the lava    
cools and forms a vesicular  portion    
with a scoriaceous texture 7,fig4 #cda74
 ,in its upper part1  the vapor bubbles 
may be numerous1 while below they become
 more and  more scattered until they    
disappear4 ,similar bubbles are also    
often  found near the bottom of a sheet 
of lava4 ,this is perhaps due to the    
rolling under of the frontal surface of 
the lava-stream as it flows4  ,later1   
these cavities often become filled with 
minerals deposited from  solution and   
the rock then becomes an amygdaloid1 but
 this filling is a  secondary action4   
,illustration3 ,fig4 #cdc4--,porphyritic
 texture4 ,natural size4 7,photo4    by 
,church47                               
,,the ,,porphyritic ,,rocks4    ,when   
the conditions are such that after a    
part of the magma has formed  distinct  
crystals floating in the remaining      
liquid lava1 there is  a change which   
causes the rest to solidify as a glass  
or as a mass  of small crystals1 the    

structure is known as porphyritic1 and  
the  rocks possessing it are called     
porphyries4 ,this differentiation into  
distinct crystals set in a ground-mass  
of minute crystals or of glass  often   
gives a mottled or variegated aspect to 
the rock1 especially  if the matrix of  
glass or minute crystals differs in     
color from the  distinct crystals4 ,this
 structure is much oftener developed in 
acidic  rocks than in basic ones1       
because the latter crystallize more     
readily4  ,the most common porphyritic  
crystals are feldspar and quartz1 though
  they are by no means the only ones4   
,the matrix is also usually felsitic  or
 quartzose1 but not necessarily so4 ,the
 character is a structural  one1 and is 
not dependent upon any special chemical 
or mineralogical  constitution4 ,the    
distinct crystals are known as          
phenocrysts1 and the  varieties of      
porphyries are named from the           
characteristic phenocryst1  e4g41       
quartzophyre 7quartz-porphyry7 if the   

conspicuous crystals  are quartz1       
orthophyre if orthoclase1 augitophyre if
 augite1 etc4 ,a  convenient            
classification has recently been        
proposed#bjj into 7#a7  leucophyre      
7white porphyries71 which have a        
light-colored ground-mass  set with     
phenocrysts of any kind1 and 7#b7       
melaphyres 7black  porphyries71 which   
have a dark-colored ground-mass1 with   
phenocrysts  of any kind4 ,while it is  
to be hoped this usage will prevail1 it 
is to  be noted that these terms1       
especially the latter1 have been used in
 a  different sense4 7,see reference    
list of rocks1 p4 #dde47    ,in many    
cases the ground-mass itself becomes    
minutely crystalline  and the           
porphyritic aspect is due simply to     
large distinct crystals  set in a mass  
of minute obscure ones4 ,the rock is    
then really  holocrystalline1 but the   
term porphyry is applied to it4 ,in     
other  rocks the crystals of the        
ground-mass become more and more        

distinct1  the porphyritic aspect       
gradually disappears1 and there is a    
graduation  into the next class4        
,,the ,,phanerocrystalline ,,rocks4     
,the phanerites4--,when time enough is  
given for the cooling process the       
molten magma becomes completely         
crystalline4 ,the holocrystalline rocks 
hence include a large series1 ranging   
from the most acid to the most  basic4  
,in this class the differentiation of   
the rock material and the  formation of 
distinct minerals reach a high stage1   
and as a natural  result the varieties  
of rock are numerous4 ,taken as a group 
they are  phanerites4 ,if they are to be
 more particularly characterized1 it is 
usually done on the basis of the        
minerals of which they are composed4    
,the following are the leading types1   
beginning with those which are  rich in 
silica and poor in basic oxides1 and    
ending with those which  are rich in    
basic oxides and poor in silica4        
,illustration3 ,fig4 #cdd4--;,granitic  

texture4 ,about half natural size4      
7,photo4 by ,church47    ,the           
granites4--,the term granite was        
originally used to designate  a         
granular1 i4e41 a distinctly            
crystalline1 rock1 and it is still      
popularly and properly so used4 ,in     
scientific treatises it has usually     
been confined to a special aggregate of 
crystals of quartz1 feldspar1  and mica4
 ,it has recently been proposed to give 
it again a more general  application1   
though not quite its original one1 by   
including under it  all holocrystalline 
rocks composed of dominant quartz and   
feldspar  of any kind1 with mica1       
hornblende1 or other minerals in        
subordinate  amount4 ,in scientific     
literature as it now stands1 granite    
consists of  quartz1 feldspar1 and mica1
 the feldspar being of the alkali-potash
  or soda variety 7orthoclase1          
microcline1 or albite71 and the mica1   
either muscovite or biotite4 ,in the    
type form the crystals are distinct  and

 sometimes large 7,fig4 #cdd74 ,they are
 intimately mingled with one  another1  
and in growing1 interfered more or less 
with each other and  so became          
interlocked4 ,the granites are among the
 most common and  easily recognized of  
the holocrystalline rocks4 ,their color 
is mainly  dependent upon the feldspar1 
the red and pink varieties of the       
mineral  giving rise to red granite1 and
 the white varieties to gray granite4   
,illustration3 ,fig4 #cde4--;,graphic   
granitic 7or pegmatitic7 texture4       
,nearly natural size4 7,photo4 by       
,church47    ,very few granites conform 
strictly to the type4 ,they vary by the 
addition and substitution of other      
minerals1 and these sometimes  become as
 prominent as the type minerals4 ,the   
soda-lime feldspars  sometimes take the 
place of the orthoclase1 or accompany   
it2 hornblende  and other minerals take 
the place of the biotite1 or occur with 
it2  and so on4 ,whenever one of these  
replacing or accessory minerals is      

notable in quantity1 its name is often  
prefixed1 as hornblende-granite1        
oligoclase-granite1 zircon-granite1 etc4
 ,in this way the rock grades  almost   
insensibly into the syenites1 diorites1 
etc4 ,variations also  arise from the   
absence of one of the three leading     
minerals4 ,if mica  is absent1 the rock 
is termed an aplite 7quartz and         
feldspar74 ,if  the feldspar is absent1 
it is called a greisen 7quartz and      
mica74  ,if quartz is absent1 it is     
termed a minette 7feldspar and mica74   
,these varietal terms are neither       
universally nor always consistently     
used1 and it is to be hoped they will be
 replaced by the systematic             
nomenclature recently proposed and      
outlined later 7p4 #dea74    ,the       
granites were formed from a magma rich  
in silica1 alumina1 potash1  and soda1  
but generally poor in lime1 iron1 and   
magnesia4 ,incidentally  other          
substances were present4 ,the alumina1  
potash1 and other bases  united with so 

much of the silica as was required to   
form the feldspars  and micas1 and the  
remaining silica crystallized into      
quartz4    ,granite is normally a       
massive rock without foliation or       
banding4 ,if  it takes on these         
characters1 it becomes a gneiss1 and    
passes into  the foliated or schistose  
class of rocks1 to be discussed later4  
,the  texture of graphic granite 7see   
pegmatite7 is notably peculiar1 due to  
the simultaneous crystallization of the 
quartz and feldspar 7,fig4 #cde74       
,the syenites4--,when the mica of a     
granite is replaced by hornblende1  the 
rock is now commonly known as a         
hornblende-granite1 but it was  formerly
 called syenite1 because found at ,syene
 on the ,nile4 ,the term  syenite is now
 applied to a rock consisting           
essentially of feldspar  and hornblende 
or mica1 but there is a complete        
gradation from the  granites to the     
syenites4 ,the magma of the syenites was
 richer in  iron and magnesium than the 

typical granitic magma4 ,the syenites   
also  grade into other classes1 as do   
the granites1 and are named by similar  
prefixes1 as augite-syenite1 etc41 and  
some of these varieties have  special   
names4 ,the syenites are red or gray1   
according to the color of  the feldspar1
 and are usually darker than the        
granites4 ,the texture of  syenite is   
like that of granite4 ,in the scheme of 
field names recently  proposed1 syenite 
is made to include all holocrystalline  
rocks composed  mainly of feldspar of   
any kind1 with subordinate amounts of   
mica1  hornblende1 pyroxene1 and other  
minerals1 but without a noticeable      
amount of quartz4    ,the               
diorites4--,these embrace rocks which   
were crystallized from a  magma still   
poorer in silica and the alkalies1 and  
richer in the earthy  bases4 ,in        
composition they closely approach the   
ideal average rock1  but usually fall a 
little below it in silica and the       
alkalies1 and  rise a little above it in

 the earthy bases4 ,in current usage1   
diorite  is defined as an intimate      
mixture of crystals of hornblende and a 
plagioclase feldspar4 ,it differs from  
the syenite in having plagioclase       
feldspar instead of orthoclase4 ,by     
substitutions and the addition of       
accessory minerals1 the diorites        
graduate toward the granites and        
syenites on the one hand1 as already    
noted1 and into gabbros on the  other4  
,in the scheme recently proposed1 all   
holocrystalline rocks in which          
hornblende is dominant and feldspar     
subordinate are classed as diorites4    
,the gabbros4--,the name gabbro was     
formerly applied to a coarse-grained    
basic rock consisting of labradorite and
 diallage1 but the name has  been       
gradually extended until it embraces a  
large group of rocks that  have         
essentially the same composition as the 
dolerites mentioned below1  but are     
coarser in crystallization1 and the     
crystals do not embrace one  another    

7i4e41 are not ophitic74 ,the principal 
minerals are plagioclase  7normally     
labradorite7 and pyroxene 7normally     
diallage7 with magnetite  or ilmenite4  
,they are usually dark1 heavy rocks4    
,the pearly luster of  the cleavage     
faces of the diallage1 when present1    
gives a peculiar  sheen to a fresh      
surface of the rock4 ,in the recently   
proposed field  names1 gabbro is made to
 include all phanerocrystalline rocks in
 which  pyroxene predominates1 attended 
by feldspar of any kind in subordinate  
quantity1 with or without hornblende or 
mica4    ,the peridotites4--,these stand
 at the basic end of the series1 having 
been formed from a magma in which the   
silica was low 7#ci-de per cent471  as  
were also the alumina1 lime1 and        
alkalies1 but in which the magnesia  was
 relatively very high1 ranging from #ce 
to #dh per cent4 ,the rock  consists    
very largely of olivine associated with 
pyroxene1 magnetite1  and other very    
basic minerals4 ,little or no feldspar  

is present4 ,the  peridotites are much  
less abundant than the preceding classes
 and  represent a very distinctive phase
 of the magma in which the magnesia  was
 greatly concentrated4    ,closely      
allied to the peridotites are rocks     
which are made up largely  of a single  
basic mineral1 as augitite1 pyroxenite1 
hornblendite1  rocks essentially formed 
of the minerals augite1 pyroxene1 and   
hornblende respectively4 ,it will be    
noted that in these rocks the magma     
became quite simple in nature1 just as  
at the acid end of the series  certain  
rocks become comparatively simple from  
the concentration of the  acid element1 
as in certain acidic granites1 felsites1
 etc4 7,see pp4  #ebc-ebd47    ,the     
basalts4--,the term basalt is used in a 
somewhat comprehensive  way to embrace  
dark1 compact1 igneous rocks that appear
 to be nearly  homogeneous1 owing to the
 minuteness of the crystals1 which are  
usually so small as to be identifiable  
only under the microscope4  ,in some    

cases the crystals are scattered        
throughout a ground-mass  after the     
porphyritic fashion4 ,in some of these  
cases there is a true  glassy base1 and 
in such cases the rock does not strictly
 belong in  the holocrystalline group4  
,in the more typical cases the          
constituent  minerals are very minutely 
crystallized and intimately intermixed4 
,the  leading minerals are plagioclase  
7usually labradorite or anorthite7  and 
pyroxene 7usually augite71 with olivine 
and magnetite or ilmenite  usually      
present4 ,there is a considerable range 
in chemical nature1  but the basalts are
 relatively poor in silica1 usually also
 low in  potash and soda1 but rich in   
lime1 magnesia1 and the iron oxides4    
,they  are classed as basic and are     
sometimes highly so4 ,the magmas of the 
basalts are especially fluid1 and when  
poured forth upon the surface  easily   
spread out in thin sheets4 ,in cooling  
they are prone to take on  a columnar or
 basaltic structure1 the columns        

standing at right angles  to the        
surfaces exposed to cooling4 ,the       
columns are sometimes curved1  owing to 
the peculiar attitude of the cooling    
surface4 ,the columns of  ,giant's      
,causeway and ,fingal's ,cave are       
familiar examples4    ,the              
dolerites4--,the basalts graduate       
insensibly into the dolerites2  indeed  
the dolerites may be regarded simply as 
basalts of coarser  crystallization4    
,the minerals are evident to the eye and
 range up  to medium size4 ,the more    
abundant minerals are plagioclase       
feldspar  7labradorite or anorthite71   
with one or more of the ferromagnesian  
minerals 7augite1 olivine1 or biotite71 
and magnetite or ilmenite4 ,in  the     
growth of the minerals one crystal      
frequently embraces others1  giving an  
ophitic structure4 ,the dolerites have  
many varieties1 due  either to accessory
 minerals or to the development of some 
of the  constituents more amply than the
 rest4 ,the type may be said to consist 

of plagioclase and augite1 the other    
minerals being regarded as  accessories4
 ,magnetite or ilmenite is almost       
universally present4 ,the  varieties are
 usually designated by prefixes1 as     
olivine-dolerite1  enstatite-dolerite1  
etc41 but special names are also used   
for some of  these4    ,illustration3   
,fig4 #cdf4--;,conglomerate1            
,carboniferous series4 ,bancroft        
,place1 ,newport1 ,r4 ,i4 7,walcott1 ,u4
 ,s4 ,geol4 ,surv47    ,the ancient     
dolerites have usually undergone        
internal changes and  such rocks are    
often called diabases4 ,while the use of
 the term has  not been uniform1 it     
accords with the better practice to     
regard the  diabases simply as partially
 altered dolerites and basalts4 ,in     
general1  therefore1 the diabases are   
but ancient dolerites4                  
,general names4    ,the difficulty of   
distinguishing many of the foregoing    
rocks from each  other by any means     
available in the field1 owing to the    

minuteness  of the crystals1 and to the 
gradation of one type of rock into      
another1 makes it desirable to employ   
certain general names which will        
correctly express the leading character 
of the rock without implying a          
knowledge of the precise mineral        
composition4 ,a convenient term of this 
kind is greenstone1 which merely        
indicates that the ferromagnesian       
minerals are prominent and usually give 
a greenish or dark cast to the  rock4   
,the greenstones embrace the diorites1  
dolerites1 some of the  gabbros and the 
basalts1 and may even extend to the     
peridotites and  some of the more       
hornblendic of the granitoid rocks4     
,another convenient  name is trap1 which
 may be used for any dark1 heavy igneous
 rock4 ,the  name 7from trappe1 stairs7 
refers to the step-like arrangement     
which  the edges of the superimposed    
sheets of lava often take1 especially   
when the lava is of the free-flowing1   
basaltic kind4    ,illustration3 ,fig4  

#cdg4--;,brecciated limestone1          
,calciferous formation4    ,one mile    
south of ,highgate ,falls1 ,vt4    ,the 
term basalt is sometimes used to embrace
 any of the very  fine-grained dark     
igneous rocks4 ,in such cases1 it covers
 the very  fine-grained dolerites1      
diorites1 peridotites1 etc4 ,the term   
granite  was used originally for any    
coarse-grained crystalline rock1 and    
there  is a tendency to revive this     
early use4 ,in general descriptions1    
some  of our best petrographers call any
 coarsely crystalline rock 7e4g41       
coarse-grained syenites1 diorites1      
gabbros1 etc47 granite4 ,the term       
granitoids may be used with strict      
propriety to cover all rocks of  this   
class4                                  
,,derivation ,,of ,,secondary ,,rocks4  
,rocks1 though commonly made the symbol 
of the abiding1 are subject  to constant
 slow changes4 ,through these changes   
newer rocks have  been derived from     
older ones1 and still others in turn    

from these  derivatives1 and so on in an
 endless chain4 ,all derived rocks are  
conveniently termed secondary1 though   
they may be several generations  removed
 from the primitive rocks1 and even the 
primitive rocks1 as we  now understand  
them1 may be themselves derived4 ,the   
ordinary changes  of rock are most      
active at or near the surface1 and the  
processes  of such change have already  
been discussed in part under the titles 
8,weathering0 7pp4 #ed and #aaj71       
8,erosion0 7pp4 #aai-abc and #cdb-cdi71 
8,transportation0 7pp4 #aae-aai and     
#ced-cee71 and 8,deposition0 7pp4       
#agg-bjd and #cee-cfc74                 
,illustration3 ,fig4 #cdh4--,quartzitic 
breccia4 ,about one-third natural       
size4 7,photo4 by ,church47             
,illustration3 ,fig4 #cdi4--,section of 
limestone showing abundant    fossils   
imbedded in a matrix made up of         
comminuted shell matter4    ,about      
two-thirds natural size4 7,photo4 by    
,church47    ,illustration3 ,fig4       

#cej4--,limestone composed chiefly of   
shells4 ,about    three-fourths natural 
size4 7,photo4 by ,church47             
,regolith4--,the first great product of 
the surface changes is  mantle-rock     
7regolith71 which comprehends all the   
loose matter  that springs from rock    
decay1 wear1 fracture1 and other forms  
of  disintegration4 ,it lies in an      
unconsolidated sheet on the face of the 
land1 whether as soil1 sand1 clay1      
earth1 gravel1 or loose rock4           
,disrupted products3 arkose and         
wacke4--,in dry regions1 in cold        
regions1 on mountain heights and        
precipitous slopes1 and under other     
conditions where sudden changes of      
temperature and frost action work       
efficiently1 rocks are broken down into 
fine fragments without much  chemical   
decomposition4 ,such disaggregated      
rather than decomposed  matter1 if      
derived from granitic and similar       
crystalline rocks1 is  termed arkose1 or
 arkose sand1 and consists of fragments 

of quartz1  feldspar1 mica1 etc4 ,common
 sand consists essentially of quartz    
grains4  ,if the fine fragments are     
derived from the darker igneous rocks1  
and  consist mainly of grains of        
plagioclase feldspar1 and ferromagnesian
  minerals1 it is sometimes called      
wacke4 ,this term is not widely used  in
 just this sense1 but there seems to be 
an important place for it1  and it will 
be so employed in this work4 ,these     
disaggregated sands are  but special    
phases of the mantle-rock4              
,disintegrated products4--,when the     
surface-rock is chemically  decomposed1 
the residual material is confined mainly
 to the insoluble  portions1 i4e41 the  
silicious and clayey parts2 while the   
lime1  magnesia1 soda1 potash1 and      
similar substances are largely dissolved
  and borne to the ocean4 ,the potash is
 somewhat more disposed to remain  with 
the clays than the soda1 lime1 or       
magnesia2 but residues of all  are      
usually present4                        

,classes of ,sedimentary ,rocks4        
,shales1 sandstones1 and                
conglomerates4--,as already shown in the
  discussion of the atmosphere and      
surface-waters1 the mantle-rock is      
constantly being borne away and         
redeposited in lodgment spots on the    
land or in the basins of the sea1 while 
it is constantly being renewed  below4  
,it is an evanescent but ever-renewed   
derivative mantle4 ,in this  process of 
renewal1 removal1 and redeposition1 the 
mantle material is  usually assorted    
into mud1 sand1 and gravel2 and these   
several classes  of material are laid   
down more or less separately1 and       
usually take  the stratified form1      
because their deposition depends on     
different  degrees of motion of the     
transporting waters or wind4 ,when these
  several classes of material become    
cemented or otherwise hardened1  they   
give rise to shales 7cemented muds71    
sandstones 7cemented  sands71 and       
conglomerates 7or pudding-stones1       

cemented gravel1 ,fig4  #cdf74 ,if the  
coarse material remains angular1 they   
form breccia  instead of conglomerates  
7,figs4 #cdg and #cdh74 ,for the most   
part1 the  deposits of mud1 sand1 and   
gravel are made under the sea or in     
lakes  and estuaries1 but they are also 
formed on the land in lodgment basins1  
in low-gradient valleys1 and on         
base-plains4 ,the deposits of sediment  
on land have received less recognition  
than they deserve4 ,when formed  under  
the sea or in other life-sustaining     
waters1 shells and other  organic       
material are liable to be entrapped and 
to form a part of the  rock4 ,these     
organic remains1 or fossils1 greatly aid
 in interpreting  the deposits in which 
they occur4 ,fossils are less liable to 
be  preserved in sedimentary deposits   
formed on land4 ,there is1 therefore1   
some ground to suspect that great series
 of sandstones and shales which  do not 
contain marine or fresh-water fossils   
were formed in lodgment  basins on land1

 though the absence of fossils cannot be
 regarded as  proof of such origin4     
,illustration3 ,fig4                    
#cea4--;,globigerina ooze4 ,magnified   
#bj times4    7,murray and ,renard47    
,illustration3 ,fig4 #ceb4--,pteropod   
ooze4 ,magnified #d times4 7,murray     
and ,renard47    ,limestones and        
dolomites4--,of the lime1 magnesia1     
soda1 and potash  leached out of the    
surface-rocks and carried to the ocean  
in solution1  the lime is largely       
extracted to form the shells1 skeletons1
 teeth1  armor1 and other hard parts of 
sea-animals and sea-plants4 ,these limy 
parts are at length left on the floor of
 the ocean and become more or  less     
disintegrated and help to form beds of  
lime-mud and lime-sand  which in time   
are cemented into limestone 7,figs4     
#cdi1 #cej1 #cea1 and  #ceb74 ,a larger 
proportion of the magnesia remains in   
solution in the  sea-water1 but in ways 
not yet well understood1 the magnesia   
sometimes  unites with the lime to form 

dolomite1 a double carbonate of lime    
and magnesia 7,ca1,mg7,,co4 ,this change
 is sometimes local1 and sometimes      
affects great series of beds1 more      
commonly the ancient ones than the      
modern4 ,sometimes the dolomization     
appears to have taken place long  after 
the original limestone was formed and   
probably sometimes after  it was lifted 
out of the sea1 while in other cases it 
seems to have  taken place while the    
sediment was accumulating1 or at least  
before the  next overlying beds were    
laid down4 ,the potash in solution is to
 some  large extent taken up by the     
land- and sea-plants or is retained in  
the  clays1 and through them becomes    
again incorporated in the sediments4    
,the soda largely remains in solution in
 the sea-water4    ,precipitates4--,when
 a portion of the ocean-water is        
isolated in a  region where evaporation 
from the surface of the water is greater
 than  the rainfall on it1 and the      
inflow from the tributary basin1 the    

lime1  magnesia1 soda1 potash1 and other
 dissolved substances 7solutes7 are     
concentrated until the water becomes    
saturated4 ,the solutes are then        
precipitated in the order in which they 
reach the point of saturation4  ,this   
order1 when taken in strict and full    
detail1 gives a very complex  series1   
but the leading deposits are calcium    
carbonate 7limestone71  calcium sulphate
 7gypsum71 and sodium chloride 7halite  
or rock  salt7 7see p4 #cge74 ,isolated 
lakes in arid regions may give rise  to 
similar deposits4 ,it has sometimes been
 thought that the ancient  limestones   
were produced largely by precipitation  
from concentrated  sea-water4 ,while    
this is probably the case in some       
instances and to  some degree1 it has   
not been demonstrated that the great    
limestone  formations were made to any  
large extent in this way4 ,the more     
accepted  view is that the limestones in
 the main were made from organic        
remains4  ,the lime in solution in the  

ocean is chiefly in the form of the     
sulphate4    ,illustration3 ,fig4       
#cec4--;,diatom ooze4 ,magnified #aej   
times4 7,murray47    ,iron              
,ore-beds4--,in a somewhat different way
 iron ore-deposits are  formed by the   
precipitation of iron oxide or iron     
carbonate from  solutions of ferrous    
compounds4 ,the ferrous compounds in    
solution  were leached from iron-bearing
 rocks by percolating waters4 ,the most 
familiar case is that of iron-bearing   
springs4 ,on exposure to the air1  the  
iron compounds in solution undergo      
change1 and ferric oxide is  thrown     
down1 usually forming limonite          
7,fe,o1#c;,h,o71 but sometimes  hematite
 7,fe,o74 ,this change is common in     
marshes and gives origin  to 8bog-ore40 
,similar deposits take place in certain 
shallow lakes1 and  hence are known as  
8lake ore40 ,iron ore sometimes also    
forms at the  bottom of a peaty bed or  
in muddy soil4 ,in connection with the  
great  coal formations1 beds of iron    

carbonate 7siderite7 occur4 ,organic    
matter seems to play a great part both  
in the original solution and  the later 
deposition of these ores4 ,from certain 
soils and clay-beds  on which the       
ancient coal-producing forests grew1 the
 iron has been  almost completely       
removed1 either by the action of the    
roots1 or  more probably by organic     
acids arising from their decay and from 
the  decaying vegetation on the surface4
 ,on flowing into shallow bodies  of    
water or into marshes1 the waters       
containing such dissolved iron          
compounds usually throw down their iron 
content either as a carbonate           
7siderite71 or as a hydrous ferric oxide
 7limonite74 ,the siderite is  formed   
where decaying vegetation is present to 
furnish abundant carbon  dioxide and to 
partially protect the iron solution from
 oxidation1 and  the limonite where free
 oxidation takes place4 ,sand1 silt1    
clay1 or  calcium carbonate often       
accumulates with the iron precipitate1  

and the  result is an impure deposit    
which becomes an ironstone4 ,such       
deposits  often become segregated into  
nodules1 as will be explained later4 ,it
  is thought that diatoms sometimes aid 
in the deposit of iron ore in  shallow  
waters4    ,silicious deposits4--,in the
 decomposition of igneous rocks1 a      
certain  portion of the silica1 as well 
as of the bases1 is dissolved and       
carried away in solution4 ,certain      
organisms extract this from solution    
for their skeletons1 just as others     
extract calcium carbonate4 ,the         
accumulation of these silicious         
skeletons often forms silicious  rocks4 
,the diatom1 radiolarian1 and other     
oozes 7,fig4 #cec7 of  the deep sea are 
the great examples4 ,sometimes layers of
 infusorial  earth1 tripolite1 arise    
from the shells of diatoms and other    
aquatic  organisms secreting silica4    
,the waters in which such earths        
accumulate  are rather shallow1 and     
either fresh or salt4 ,the most familiar

  examples of indurated rocks formed in 
this general method are the  flints and 
cherts 7impure flints7 that occur in    
limestone and  chalk1 chiefly as        
nodules1 but sometimes in distinct beds4
    ,organic rocks4--,while most        
limestones1 chalks1 flints1 cherts1 and 
the silicious and calcareous oozes are  
formed through the agency of  organisms1
 they are not themselves strictly       
organic4 ,there is1 however1  a small   
but important group of rocks formed     
directly from organic  matter4 ,in      
favorable situations the woody parts of 
plants1 falling  into water1 are so far 
preserved from decay that they          
accumulate in  beds1 and by slow changes
 pass into peat1 lignite1 bituminous    
coal1 anthracite1 and graphite4 ,the    
first of these is composed  essentially 
of carbohydrates and hydrocarbons much  
as plants are1 while  the last two are  
mainly carbon1 and the intermediate     
members represent  stages of passage    
from the first to the last4 ,they are   

all derived from  the strictly organic  
part of the plants1 and spring          
essentially from  the atmosphere and    
hydrosphere4 ,they are only indirectly  
associated  with the evolutions of the  
inorganic series4                       
,,internal ,,alterations ,,of ,,rocks4  
,besides the extreme alterations of     
rocks at the surface of the earth  by   
which they pass into solution and into  
residual mantle-rock1 and  at length by 
transportation and re-sedimentation     
become stratified  rocks1 as just       
described1 those rocks which are not at 
the surface are  subject to changes that
 give rise to several varieties of      
altered  rocks4 ,these changes are      
taking place constantly under ordinary  
conditions1 though usually very slowly4 
,under great pressure and heat  the     
changes are relatively rapid and        
intense1 and lead to results  not       
reached under other conditions4 ,these  
more profound changes are  termed       
metamorphism1 and will be considered    

later4 ,it is1 however1  important to   
recognize the great fact that the outer 
part of the earth1  for perhaps #bj1jjj 
or #cj1jjj feet1 is more or less        
fractured and  permeated by water       
containing in solution various          
substances dissolved  from the          
atmosphere1 the soil1 and the rocks     
through which it has  already passed1   
and that this permeating and circulating
 water is  now1 and for long ages has   
been1 working changes in the rocks1     
partly  by dissolving matter out of     
them1 partly by depositing matter in    
them1  and partly by furnishing a medium
 through which new combinations of      
their constituents may take place4 ,this
 outer fractured portion of the         
lithosphere has been called the zone of 
fracture4#bja    ,oxidation and         
deoxidation4--,at and above the surface 
of the  underground water1 where the    
rocks are easily reached by atmospheric 
waters carrying much free oxygen1 and by
 the air itself1 oxidation  prevails4   

,through oxidation the ferrous oxides   
are changed to ferric  oxides1 a change 
which is usually manifested by a        
transition from a  gray1 green1 or blue 
color1 to buff1 brown1 yellow1 or red4  
,the partial  progress of such oxidation
 is often shown in a fractured block or 
bowlder whose exterior shows the latter 
colors1 while the interior  shows the   
former4 ,the sulphides1 of which common 
pyrites 7,fe,s7 is the  most familiar1  
are oxidized into sulphates1 and then   
sometimes pass  on into the higher      
oxides and other compounds4 ,thus       
copperas 7,fe,s,o7  arises from pyrites 
7,fe,s7 by direct oxidation of both ,fe 
and ,s4 ,the  sulphuric acid of this    
compound1 uniting with some base        
stronger than  the ferrous oxide1 gives 
rise to further oxidation and results in
  hematite 7,fe,o7 and limonite         
7,fe,o1#c;,h,o74 ,in general1 the       
mineral  constituents of the rocks in   
this upper zone take on their maximum   
states of oxidation4 ,this oxidation    

affects more or less profoundly the     
character of the rock as a whole4       
,deeper in the earth oxidation is less  
prevalent1 and the action is sometimes  
reversed and deoxidation takes  place4  
,so also wherever organic matter is     
undergoing decomposition  deoxidation is
 likely to occur4    ,solution and      
deposition4--,solution preponderates in 
the upper part  of the zone of fracture1
 but deposition is prevalent in its     
deeper  parts4 ,the calcium carbonate   
and silica dissolved near the surface   
are  often deposited below as calcite   
and quartz4 ,the sulphates and other    
sulphur compounds that are formed and   
dissolved near the surface are  apt to  
be changed into sulphides lower down by 
deoxidation4 ,the soluble  oxides and   
other compounds formed near the surface 
are often likewise  precipitated below4 
,this is particularly true where the    
descending  waters encounter decomposing
 organic matter1 and where they mingle  
with waters that have followed other    

routes and have become charged  with    
different solutes4 ,on coming together1 
reaction between the  constituents takes
 place1 resulting sometimes in new      
solutions and  sometimes in             
precipitation4    ,if these lower       
deposits of calcite1 quartz1 sulphides1 
etc41 are made  in the pores of the     
rock1 they change its texture and       
composition4 ,if  they are made in      
fissures they constitute veins1 and if a
 sufficient  percentage of the vein     
matter consists of valuable metallic    
compounds1  they constitute ores4    ,as
 the waters descend they suffer greater 
and greater pressure and some  increase 
of temperature1 and these changes modify
 their power to hold  substances in     
solution4 ,in general1 the waters       
increase in solvent  power1 but the     
effect is different for different       
mineral substances1  and hence as a rule
 the waters are taking up some          
substances and  laying down others as   
they proceed4 ,after penetrating to     

greater or  less depths1 the waters may 
come again to the surface1 either       
because  they are pushed up by the      
higher head of the waters behind1 or    
because  they become warmer and thus    
lighter1 and are forced up by the       
heavier  cold waters above1 or else they
 pass up by diffusion through the       
descending waters4 ,in any case1 the    
deep1 warm waters1 usually rather       
highly charged with material dissolved  
in their previous courses1 are  apt to  
deposit some of their burden as they    
ascend to horizons of  lower pressures  
and temperatures4 ,they are particularly
 liable to make  deposits where they    
commingle with other waters differently 
charged  with solutes4 ,thus internal   
changes in the body of the rocks are1   
and  for ages have been1 taking place4  
,in the upper part of the depositing    
zone1 calcite is the dominant mineral   
deposited1 while in the lower1  quartz  
is more common2 but much depends on     
local conditions and other  influences1 

and no rigid rule holds good4           
,hydration and dehydration4--,water     
sometimes unites directly with some  of 
the constituents of a rock and produces 
hydrated minerals1 i4e41  minerals that 
have water as an element of their       
constitution1 not  simply water absorbed
 into their pores4 ,a large class of    
minerals known  as zeolites1 because    
they swell up and undergo life-like     
contortions  when their basic water is  
driven off by heat1 are examples of     
hydrous  products4 ,a more familiar     
example is limonite 7,fe,o1#c;,h,o71 of 
which  yellow ocher is a variety1 which 
on heating sufficiently gives off its   
water and becomes hematite 7,fe,o7 or   
red ocher4 ,the turning of yellow  clay 
to red brick on burning is a familiar   
example of dehydration4  ,the general   
tendency in the upper zones penetrated  
by water is toward  hydration4 ,in the  
lower zones1 where the pressure is      
great1 ,van ,hise  holds that there is a
 tendency toward dehydration1 if the    

rocks have  been previously hydrated4   
,this may be the case if rocks have once
  been near the surface and later deeply
 buried by the accumulation of          
sediments on them4 ,if the principle    
holds1 rocks subjected to intense       
lateral pressure may be dehydrated4     
,carbonation and decarbonation4--,the   
igneous rocks are largely  silicates4   
,the carbonic acid of the surface-waters
 and of the air  acting upon them1      
converts them1 in part1 into carbonates4
 ,in this  way has arisen most of the   
original supply of calcium and magnesium
  carbonates4 ,original carbonates      
formed in this way are precipitated and 
redissolved again and again4 ,the       
carbonates in river-waters are much     
more largely solutions of previously    
solid carbonates than original          
carbonates formed from the silicates4   
,the potassium and sodium of the        
silicates also form carbonates1 but by  
preference they unite with the  sulphur 
and chlorine1 and hence appear more     

largely as sulphates and  chlorides4    
,carbonation is usually accompanied by  
oxidation and hydration4 ,these  several
 processes break up the complex and     
relatively unstable  silicates into     
simpler and more stable silicates1      
carbonates1 and  oxides4 ,this is       
illustrated by the following formulas   
illustrative  of the changes undergone  
by augite and labradorite1 two common   
rock-forming minerals4    ,the          
composition of augite may be represented
 by the formula                         
,ca,o47,mg1,fe7,o4#b,si,o               
7,mg1,fe7,o47,al1,fe7,o4,si,o4          
,assuming ,mg and ,fe to be equal in    
amount in the first half of the above   
formula1 and ,mg and ,fe to be equal in 
the first part of the second  half1 and 
,al and ,fe to be equal in the last part
 of the second half1  doubling the whole
 and allowing it to be acted on by ,,co 
and ,h,o1 we  have                      
#b;,ca,o4#b,mg,o4#b;,fe,o4,al,o4,fe,o4#f
,si,o  #f;,,co  #b;,h,o                 

#b;,ca,c,o  #b,mg,c,o                   
#b;,h,o4,al,o4#b,si,o  #b;,fe,c,o  ,fe,o
  #d,si,o4    ,the hydrous silicate of  
the last part of the equation is kaolin4
    ,the composition of labradorite is  
represented by the formula              
,ca,o4,al,o4#b,si,o                     
,na,o4,al,o4#f,si,o4    ,assuming the   
two molecules represented by this       
formula to be equally  abundant1 and    
allowing the whole to be acted on by    
,h,o and ,,co1 we have                  
,ca,o4,na,o4#b;,al,o4#h,si,o  #d;,h,o   
#b;,,co                       ,ca,c,o   
,na,,co  #b7b;,h,o4,al,o4#b,si,o7       
#d,si,o4    ,when waters charged with   
carbonates descend into the earth they  
are  likely to precipitate a portion of 
their burden1 forming calcite and  other
 crystalline carbonates1 and hence these
 are among the most  common minerals    
found in veins and rock cavities4       
,carbonates are  also deposited when    
carbonate-charged waters come to the    
surface and  evaporate or lose a part of

 their carbon dioxide4    ,decarbonation
 also takes place1 but it is1 at least  
at the surface1 a  much less common     
process1 and its conditions are less    
well understood4  ,sufficiently high    
heat will drive off the carbon dioxide1 
as in the  artificial process of burning
 lime1 but this is rarely observed in   
nature4 ,even lava intrusions do not    
usually reduce limestone to  caustic    
lime at any appreciable distance from   
the contact4 ,it is  believed1 however1 
that in the deeper zones1 where high    
pressure and  heat prevail1 carbonates  
are changed into silicates1 thus in a   
way  reversing the process that prevails
 at the surface1 and setting free  again
 a portion of the carbon dioxide that   
had become locked up in the  formation  
of the carbonates4 ,to this action some 
of the carbon dioxide  of deep-seated   
thermal springs is assigned4    ,the    
carbonation of the silicates takes place
 at the expense of  the carbon dioxide  
of the atmosphere and hydrosphere1 and  

hence  in proportion as the igneous     
rocks are changed into carbonates1  the 
atmosphere and hydrosphere are depleted 
of carbon dioxide1 new  supplies being  
neglected4 ,as plants are dependent on  
carbon dioxide  for their principal     
food1 and as animals are dependent on   
plants for  their food1 directly or     
indirectly1 the process of carbonation  
has  a profound bearing on the          
life-history of the earth1 and will     
often  invite attention in the          
historical chapters4 ,it is sufficient  
here to  note that carbonation is one of
 the chief processes in the alteration  
of igneous rocks and furnishes1 directly
 and indirectly1 a larger  percentage of
 the mineral substances dissolved in the
 waters that flow  from the land1 than  
any other single process4    ,molecular 
rearrangements4--,besides these and     
similar changes that  involve additions 
and subtractions through the agency of  
percolating  water1 the molecules of    
some of the rock constituents rearrange 

themselves1 or the elements enter into  
new chemical relations2 thus1  pyroxene 
may pass into hornblende by a change of 
the crystalline  arrangement of the     
molecules4 ,the change may sometimes be 
caught in  progress1 the outer part of  
the crystal being hornblende 7which when
  thus formed is called uralite71 while 
the heart of the crystal  remains       
pyroxene4 ,so aragonite may pass into   
calcite4    ,by changes of the foregoing
 kinds1 many crystalline rocks are much 
altered4 ,some become chloritic from the
 development of the soft1  green        
hydrated mineral1 chlorite1 derived from
 the pyroxene1 amphibole1  biotite1 and 
perhaps other silicates of the original 
rock4 ,others  become talcose from the  
development of talc1 a very soft1       
unctuous1  hydrous magnesian silicate   
developed from the magnesian minerals   
of the original rock4 ,soapstone or     
steatite is a rock composed  essentially
 of such secondary material4 ,serpentine
 is a rock made  up of a similar        

secondary mineral 7serpentine7          
apparently derived  from chrysolite     
7olivine7 and other magnesian minerals4 
,epidote1 a  complex lime-iron-alumina  
silicate1 often recognizable by its     
peculiar  pistachio-green color1 is     
derived from other silicates1 and is    
rather  common in many varieties of     
crystalline rocks4 ,melaphyre is a name 
applied rather loosely and variously to 
certain altered basic rocks of  the     
basalt family4 ,diabase is essentially  
an altered dolerite4 ,nearly  all the   
very ancient basaltic rocks show notable
 degrees of alteration1  even though    
they appear to have escaped unusual     
dynamic conditions  since their original
 formation1 and hence their alteration  
seems to  have resulted chiefly from the
 operation of unobtrusive agencies1     
chief  among which is the circulation of
 water4                      ,the       
,salient ,features of ,rock ,descent4   
,the foregoing processes by which       
primitive or igneous rocks are          

disintegrated and their constituents    
converted into fragmental material  may 
be said to constitute the descent of    
rocks in its fuller  sense4 ,viewed     
chemically1 the great features of the   
process are 7#a7  the breaking down of  
the complex silicates1 and 7#b7 the     
gathering  of the resultant simpler     
silicates 7mainly aluminum silicates7   
into  the silt and clay beds1 7#c7 the  
assembling of a large part of the  free 
acidic element 7the quartz7 into the    
sand and gravel beds1 and  7#d7 the     
concentration of a large part of the    
earthy basic element  7the calcium1     
magnesium1 and iron oxides7 into the    
calcareous1  magnesian1 and iron        
deposits1 while 7#e7 a large part of the
 alkaline  basic remainder 7the sodium1 
and potassium oxides7 is dissolved and  
held in the sea-water4 ,physically1 the 
great features are 7#a7 the             
disaggregation of the antecedent rock1  
and 7#b7 the separation from  one       
another of products which are physically

 unlike1 that is1 the  coarser from the 
finer1 and the heavier from the lighter1
 and 7#c7 the  aggregation of these     
diverse materials in more or less       
distinct beds4  ,it is to be noted that 
while the rearrangement of the sediments
 is  made on the basis of their physical
 characters1 it results in chemical     
differentiation as well1 for the        
products of rock decay1 which are       
physically diverse1 are often chemically
 diverse as well4 ,the physical         
assortment and the stratification are to
 be looked upon as a step in  the       
direction of a simpler grouping of the  
material4 ,on the whole1 the  process is
 descensional in character4             
,,the ,,reascensional ,,process4        
,running hand in hand with this         
descensional process1 there has  always 
been a reascensional process by which   
the coherence1 the  crystallization1 and
 in some measure the complex composition
 of the  rocks are restored4 ,this is   
partially due to external mechanical    

agencies1 but chiefly to internal       
chemical and molecular forces4    ,two  
general phases of this reconstructional 
work are recognized4 ,the  first1       
simplest and most universal1 is that by 
which the incoherent  materials produced
 by the descensional processes1 i4e41   
the muds1  sands1 and clastic materials 
generally1 are hardened into firm1      
coherent shales1 sandstones1 and        
limestones1 and incidentally more or    
less changed in composition and         
molecular arrangement4 ,the second is   
that by which more profound changes of  
induration and of composition  are      
wrought1 bringing the rock back to a    
state resembling its original           
crystalline character4 ,this is known as
 metamorphism4 ,often1 however1  it is  
but an extension and intensification of 
the more common processes  of the first 
class4 ,metamorphism is essentially     
reconstruction4    ,induration under    
ordinary pressures and                  
temperatures4--,all kinds  of loose     

fragmental material1 whether soils1     
earths1 clays1 sands1  gravels1 volcanic
 ashes1 cinders1 or other forms of      
clastic or  pyroclastic material1 may   
become hardened into firm rock either by
  pressure1 or by cementation1 or by    
both4 ,pressure and cementation         
commonly act together and aid each      
other4 ,the ordinary pressures  arise   
from the weight of the overlying        
material1 and these of course  increase 
with depth4 ,extraordinary pressures    
arise from the shrinkage  of the earth  
and perhaps from other sources4 ,the    
fragments of the  clastic material1 on  
being pressed together for long periods1
 weld  more or less at the points of    
contact4 ,if they are irregular1        
angular1  or elongate1 they come to     
interlock more or less like the         
fragments  of macadam1 and this         
coperates with the welding4 ,the process
 is  greatly aided by water-bearing     
solutions of lime1 silica1 etc4 which   
are deposited at the points where the   

fragments press upon each other4  ,it is
 here that the capillary spaces are most
 minute and deposition  is most liable  
to take place4 ,sometimes a film of     
mineral matter is  laid down over the   
surfaces of the fragments and serves to 
bind them  together4 ,this process goes 
on wherever the ground-waters are in a  
depositing condition1 just as the       
opposite process of disintegration      
takes place wherever the waters are in a
 solvent state4 ,at and near the        
surface of the land1 the waters are     
usually in the latter condition and     
disintegration is in progress1 as       
already noted1 but this is not always   
so4 ,at times and places1 the water from
 within the rock-mass may come  to the  
surface and evaporate1 and in so doing  
leave all its dissolved  material on the
 surface1 or within the outer pores of  
the mass1 as  cementing material4 ,the  
exterior thus becomes firmly bound      
together1  8case-hardened10 as it is    
termed4 ,this may be seen in the drying 

of  a lump of mud1 the exterior of which
 often becomes quite firm4 ,it is  seen 
in quarry-rock1 especially sandstone1   
which is sometimes soft and  easily     
worked when taken wet from the earth1   
but which hardens as the  water--the    
8sap0 of the quarrymen--dries out and   
deposits its solutes in  the capillary  
spaces of the grains of the surface4 ,it
 is obvious that  it is the very last of
 the 8sap0 which contains the most      
concentrated  solutes1 and that this    
last remnant is held in the minute      
capillary  spaces where the grains touch
 each other1 and hence the last stage of
  drying leaves the cement at the points
 where it is most effective4 ,in        
natural exposures of sandstone1 the     
pores of the outer shell sometimes      
become almost completely filled in this 
way with silicious deposits1  and the   
sandstone is changed into a quartzite4  
,in the sea1 and in the deep water      
underground1 the common habit of  the   
water is to deposit more than to        

dissolve1 though it is doing  more or   
less of both4 ,as a rule1 therefore1    
loose material in these  situations     
becomes bound more or less firmly into  
rock1 and hence what  were originally   
loose sand beds become sandstones2 what 
were soft  muds become shales or        
limestone1 according to composition2    
what was  gravel becomes conglomerate2  
what was chipstone becomes breccia2     
what were volcanic ashes1 cinders1 and  
lapilli become tuffs2 and  what were    
masses of volcanic blocks and coarse    
fragments become  agglomerates4         
,illustration3      ,fig4 #ced4--,quartz
 crystal enlarged by secondary growth4  
,the shaded    outline represents the   
outline of the sand grain2 the solid    
lines1    the outline after secondary   
growth4 ,magnified #fg diameters4 7,van 
,hise47      ,fig4 #cee4--,sandstone and
 quartzite texture4 ,the shaded outlines
    represent the surfaces of the sand  
grains before growth1 the    intervening
 white portions1 the added quartz1 and  

the black portions1    unfilled spaces4 
,open spaces characterize sandstone4    
,when the spaces    are filled with     
quartz1 the rock becomes quartzite4     
,magnified #ce    diameters4 7,van      
,hise47    ,the cementing process works 
at times in specially interesting ways4 
,in  quartz sandstones1 the grains are  
worn fragments of quartz crystals1      
formed originally in quartz-bearing     
rock4 ,the crystalline force in  these  
remnants controls the arrangement of the
 new molecules of silica  deposited     
about them4 ,the result is that the new 
deposits tend to  build up the original 
forms of the crystals from which the    
sand grains  were derived 7,fig4 #ced74 
,sometimes a film of iron oxide has     
formed  about the grain of sand before  
the addition of the new silica4 ,this1  
or  some difference of color1 may       
clearly distinguish the original grain  
from subsequent additions4 ,sometimes   
the adjacent grains of sandstone  are   
rebuilt in this way until the           

interstices are completely filled4      
,when this has been accomplished1 the   
sandstone becomes a quartzite  7,fig4   
#cee74 ,most quartzites indeed appear to
 have been formed in this  way1 but     
mainly under special conditions that    
promote the deposition  of silica4      
,grains of other minerals1 such as      
feldspar1 are subject to  similar       
secondary enlargement 7,fig4 #cef74     
,illustration3 ,fig4 #cef4--;,feldspar  
crystals enlarged by secondary          
growth4 ,magnified #ej diameters4 ,,aa  
original grains2 ,,bb     enlargements2 
,d  unfilled spaces4 7,van ,hise47      
,sometimes the new material is deposited
 in the form of concentric  shells about
 the particles of sediment1 building    
them up into little  spheres4 ,rock     
formed of such spherules is known as    
oolite1 from the  resemblance of the    
grains to the roe of fish 7,fig4 #ceg74 
,sometimes the  nuclei of the           
concretions are grains of quartz sand1  
and the added  concentric layers are of 

calcium carbonate4 ,in this case the    
structure  is quite obvious2 but perhaps
 more frequently the nuclei are minute  
and difficult to identify1 and the      
concentric shells make up the main  mass
 of the grains4 ,certain formations1 as 
the oolitic limestone of  ,indiana and  
elsewhere1 and the ,upper and ,lower    
,oolites of ,england1  are characterized
 by this structure4 ,in most cases these
 accretions  probably grew in depositing
 waters that gently rolled the grains   
while  layers were being added4 ,they   
thus do not fall under the head of      
cementation after the beds were formed2 
but concentric additions to the  grains 
appear sometimes to have taken place    
after they were formed into  beds4      
,cavity filling4--,when cavities of some
 size occur in rocks and the            
percolating waters are in a depositing  
state1 the interiors of the  cavities   
are sometimes lined with concentric     
layers of deposit4 ,here1  instead of   
building out from a nucleus1 the waters 

build in from  the walls of the cavity4 
,the agate structure 7,fig4 #ceh7 is a  
case of  this kind1 in which the        
successive layers are commonly silica in
 the  form of chalcedony and differ from
 each other in color and texture4       
,often before the cavity is entirely    
filled1 the deposit changes from        
chalcedony1 to crystals of quartz1 which
 grow with their bases on the  walls and
 their pyramidal points toward the      
center of the cavity4  ,geodes are      
examples of a similar process in which  
the cavity is  but partially filled with
 crystals which have their bases set on 
the  walls of the cavity and their      
points directed inwards 7,fig4 #cei74   
,the  crystals of geodes are most       
commonly quartz or calcite1 but they may
  be any other mineral that the waters  
are capable of depositing4 ,very  large 
cavities lined in this way are known to 
miners as vuggs1 and  these grade on    
into caves lined with crystals and with 
stalactite  and stalagmite4 ,these are  

the largest expression of the           
solidifying  process by means of        
internal deposition4    ,illustration3  
,fig4 #ceg4--,oolitic texture4 ,about   
natural size4 7,photo4    by ,church47  
,illustration3 ,fig4 #ceh4--;,agate     
structure4 ,the cavity was first coated 
with mineral matter deposited from      
solution4 ,the contracted cavity    was 
then nearly filled with the same sort of
 material deposited in    layers1       
apparently over the bottom1 until the   
cavity was nearly    obliterated4       
,fissure-filling2 veins4--,cracks1      
crevices1 and fissures filled by        
deposition in a similar way give rise to
 veins 7,fig4 #cfj74 ,here  the filling 
grows from the walls toward the center1 
and hence often  has a banded           
appearance4 ,by this filling of cracks  
and crevices1  the circulating water    
heals the breaks in the rocks4          
,frequently a  crushed zone is thus     
restored to a solid state4 ,when the    
fissures  are deep and wide and traverse

 different formations1 conditions are   
afforded for very complex deposits1 and 
for the concentration of  rare and      
valuable material originally dispersed  
through a great mass  of rock4 ,ore     
deposition in such veins is usually     
treated as a theme  by itself1 but it is
 really but a declared expression of the
 work  which the percolating waters are 
doing throughout all the rocks which    
they penetrate4 ,most of the fine       
crystals that grace mineralogical       
collections were formed in cavities and 
fissures by deposition from  circulating
 mineralized waters4    ,illustration3  
,fig4 #cei4--;,a geode4 ,about half     
natural size4 7,photo4 by    ,church47  
,solution as well as deposition4--,a    
further phase of the process needs      
attention4 ,the percolating waters are  
constantly taking up matter as  well as 
throwing it down1 and so1 while they are
 cementing fragments  together and      
healing fractures1 they are also        
removing material1 and  a rock may be   

growing porous and cavernous at the same
 time that its  fragments are being     
united4 ,cavities may be formed at one  
stage and  filled at another2 matter may
 be taken up at one point and put down  
at  another1 and so an internal         
reconstruction is in slow progress4     
,illustration3 ,fig4 #cfj4--,veins of   
calcite in limestone4 ,calciferous      
formation near ,highgate ,springs1 ,vt4 
7,walcott1 ,u4 ,s4 ,geol4 ,surv47       
,concretions4--,a notable phase of this 
internal reconstruction is the          
assembling together of like kinds of    
matter4 ,for instance1 silica that  was 
probably deposited in the form of the   
silicious shells and spicules  of plants
 and animals1 and was disseminated      
through the sediments as  originally    
formed1 is aggregated into nodules of   
chert or flint 7,fig4  #cfa72 similarly1
 concretions of ferrous carbonate or    
calcium carbonate  grow in sands1 silts1
 or muds2 clusters of crystals of pyrite
 7,fe,s71  of sphalerite 7,zn,s71 and   

galenite 7,pb,s7 are formed in clayey   
layers1  pressing the clay back as they 
grow2 and in many other cases1 kind     
comes to kind4 ,some concretions        
probably form during the accumulation   
of the beds in which they lie4          
,replacements and pseudomorphs4--,so    
also there are replacements1  sometimes 
resulting in imitative or false forms4  
,frequently the calcium  carbonate of   
corals1 molluscan shells1 etc41 is      
replaced by silica1 and  this           
substitution is brought about so        
gradually1 particle by particle1  that  
the minutest details of structure are   
sometimes fully preserved4  ,this is    
often of great service in their study1  
since the limestone  in which they are  
imbedded may often be dissolved away1   
while the  silicified fossil is         
unaffected4 ,so woody matter is         
sometimes replaced  by silica1 forming  
silicified wood4 ,similarly1 the        
molecules of one  crystal are sometimes 
replaced by different material1 as the  

molecules  of calcite by zinc carbonate1
 giving a pseudomorph of zinc carbonate 
after calcite4    ,illustration3 ,fig4  
#cfa4--,nodule of chert4 ,about half    
natural size4  7,photo4 by ,church47    
,incipient crystallization4--,a more    
general change is incipient             
crystallization4 ,some common limestones
 and dolomites are now largely  made up 
of small crystals1 though the mass was  
originally a calcareous  mud or ooze4   
,incipient crystals are formed in shales
 and other  sediments4 ,this process1   
like the preceding1 is a kind of        
incipient  metamorphism or              
reconstruction1 but it is a pervasive   
process1 taking  place under ordinary   
conditions of heat and pressure1 and    
through the  agency of circulating      
ground-waters4    ,by these and similar 
processes the fragmental deposits are   
solidified  into firm rock and undergo  
internal changes which more or less     
reorganize the matter of which they are 
composed4 ,the process is a very  slow  

one usually4 ,some of the sands and muds
 of very early geologic  ages are yet   
imperfectly solidified2 e4g41 much of   
the ,st4 ,peter's  sandstone1 a very    
ancient formation1 is yet so incoherent 
as to break  down into sand in being dug
 out1 and is used for mortar sand much  
more  than for building stone4 ,some of 
the ,hudson ,river shales of scarcely   
less age are more nearly clay than hard 
rock4 ,but these are examples of        
excessive slowness and slightness of    
change4 ,in general1 all but the  most  
recent deposits show notable progress in
 reconstruction4    ,illustration3 ,fig4
 #cfb4--;,figure showing the elongation 
of pebbles    resulting from pressure4  
,carboniferous formation1 ,bancroft     
,place1    ,newport1 ,r4 ,i4 7,walcott1 
,u4 ,s4 ,geol4 ,surv47                  
,reconstruction under ,exceptional      
,conditions4    ,two special conditions 
greatly influence changes in rocks1     
viz41  pressure and heat4 ,their action 
gives rise to three general cases1  but 

these blend indefinitely3 7#a7          
exceptional pressure without great      
heat1 7#b7 great heat without           
exceptional pressure1 and 7#c7 great    
heat  and great pressure conjoined4     
,exceptional pressure may arise from the
  weight of overlying rocks1 or from    
lateral thrust due to the shrinkage  of 
the globe1 and occasionally from other  
causes4 ,exceptional heat may  arise    
from pressure1 from the intrusion of hot
 lavas1 and occasionally  from other    
sources4 ,in the case of intruded lavas 
there may or may not  be exceptional    
pressure4 ,thrust usually gives heat as 
well as pressure1  but if lateral thrust
 acts on rocks near the surface1 they   
may be  mashed into new forms without   
becoming very exceptionally heated1     
though some rise of temperature is      
inevitable4    ,illustration3 ,fig4     
#cfc4--,pre-,cambrian fossiliferous     
slate4 ,deep ,creek    ,canyon1 #af     
miles southeast of ,townsend1 ,mont4    
7,walcott1 ,u4 ,s4 ,geol4    ,surv47    

7#a7 ,slaty structure4--,when rocks made
 up of clastic particles are  compressed
 in a given direction and are relatively
 free to expand at  right angles to the 
direction of pressure1 the particles    
that are  already elongated tend to take
 positions with their longer axes at    
right angles to the direction of        
pressure1 and all particles1 whether    
elongate or not1 are more or less       
flattened in a plane transverse  to the 
direction of pressure4 ,this may be     
readily seen where the  particles are   
large 7,fig4 #cfb74 ,as a result of the 
orientation and  flattening of their    
particles1 rocks so affected split more 
readily  between the elongate and       
flattened particles than across them4   
,in  other words1 the rocks cleave along
 planes normal to the direction of      
compression1 and break with difficulty  
and with rough fracture across  the     
planes of cleavage4 ,the condition thus 
induced is known as slaty  structure    
7,fig4 #cfc71 and is best illustrated by

 roofing-slate1 which  was originally a 
mud1 later a shale1 and finally assumed 
the slaty  condition under strong       
compression4 ,sometimes the original    
bedding  may still be seen running      
across the induced cleavage planes      
7,fig4  #cfd74 ,as the original mud beds
 were horizontal or nearly so1 and as   
the thrust is usually horizontal or     
nearly so1 the induced cleavage         
commonly crosses the bedding planes at a
 high angle 7,fig4 #cfd72 but  after the
 beds are tilted or bent1 the lines of  
pressure take new  directions relative  
to the bedding planes1 and the angles   
between the  original bedding and the   
slaty cleavages usually become smaller1 
and  may even disappear in exceptional  
cases4 ,limestones1 sandstones1 and     
conglomerates are not so easily         
compressed as mudstones1 and they       
usually take on only an imperfect       
cleavage normal to the direction of     
pressure4 ,often they merely show some  
little compacting1 while the  shaly     

strata between them are converted into  
slate4 ,obviously the  direction of     
slaty cleavage may be used to determine 
the direction of  the compressing force1
 and is thus serviceable in dynamic     
studies4    ,illustration3 ,fig4        
#cfd4--,slaty structure and its relation
 to bedding    planes4 ,two miles south 
of ,walland1 ,tenn4 7,keith1 ,u4 ,s4    
,geol4 ,surv47    ,illustration3 ,fig4  
#cfe4--;,foliated rock4 7,ells1 ,can4   
,geol4 ,surv47    ,foliation1           
schistosity4--,a more intense           
application of pressure in  a given     
direction is capable of breaking down   
and deforming the most  resistant rock4 
,this must necessarily be attended with 
the evolution  of much heat1 and thermal
 effects are mingled with pressure      
effects1  but the thermal effects may be
 neglected for the moment4 ,the first   
stage of the mechanical effect of the   
compression may be to crush the  rock   
more or less4 ,it thus becomes granular 
or fragmental1 and is  really a peculiar

 species of clastic rock 7autoclastic74 
,at a further  stage1 the fragmented    
material may be pressed into layers or  
leaves1  much as in the development of  
slaty cleavage1 but as a result of the  
nature of the material1 the cleavage is 
less perfect4 ,this is often  attended  
by more or less shearing of the material
 upon itself1 and thus  a rude fissility
 and foliation is developed4 ,the       
result1 including the  attendant        
metamorphism about to be described1 is a
 foliated or  schistose structure       
7,figs4 #cfe and #cff74 ,even the most  
massive rocks  may be reduced to the    
foliated form by this process2 thus1 a  
granite  may be mashed into a           
gneiss--which is a granite in           
composition1 but  has a foliated        
structure--or a basalt may be converted 
into a schist1  a common term for       
foliated crystalline rocks4 ,porphyritic
 rock rendered  schistose by pressure is
 shown in ,fig4 #cff4 ,when massive     
rocks like  granite or basalt are thus  

crushed down into the foliated form1 the
  process is in a sense degradational4  
,it is a kind of katamorphism  or       
downward change4 ,it is often difficult 
to differentiate the  schists thus      
derived by degrading massive rocks1 from
 those developed  by ascensional        
processes from clastic formations       
7anamorphism74  ,the action of heat is  
important in the evolution of schists of
 both  classes1 but the effects of heat 
may best be taken up where it acts      
measurably alone4    ,illustration3     
,fig4 #cff4--,porphyry rendered         
schistose by pressure4    ,near ,green  
,park1 ,caldwell ,co41 ,n4 ,c4 7,keith1 
,u4 ,s4 ,geol4 ,surv47    ,illustration3
 ,fig4 #cfg4--,schistose structure      
developed by pressure    shown in the   
left half of the figure1 while it is    
wanting in the    right half4 ,the      
vertical line is a bedding plane4 ,the  
layer to    the left was of sufficiently
 different composition or subject to    
sufficiently different movement to      

develop schistosity1 while that    to   
the right was broken 7brecciated7       
instead4 ,the rock at the left    would 
be called quartz schist1 while that at  
the right is quartzite4    ,huronian    
formation near ,ableman1 ,wis4          
7,atwood47    ,metamorphism by          
heat4--,when a mass of lava is poured   
out upon the  surface1 it bakes the     
mantle-rock which it overruns1 in       
greater or less  degree1 depending on   
the mass and temperature4 ,the nature of
 the effect  is much the same as in the 
process of brick-making1 a dehydration  
of  the material1 a hardening of the    
loose matter by the partial welding of  
the particles1 and sometimes the partial
 fusion of the surface and the          
development of new compounds1 usually   
glassy1 but sometimes partially         
crystalline4 ,in both the natural and   
the artificial process1 the time        
element is short1 the pressure trivial1 
and the water action limited4  ,if the  
heat were to become sufficiently        

intense1 the result would be  fusion1   
i4e41 a lava which would solidify into a
 glass4 ,in such a case1  the rock cycle
 would be carried back to the initial   
molten state and a  new cycle           
instituted1 but this does not usually   
take place when lava  merely overflows  
the surface4    ,if lavas1 instead of   
rising to the surface1 wedge in between 
layers of  rock and form sills1 or      
interstratified sheets1 the surface     
above  as well as that below is baked1  
and as the excess of heat of the  lava  
can only escape through the neighboring 
rock1 the effects for  a given mass of  
lava are more considerable1 and as the  
time element  and the water action 7and 
sometimes the pressure7 are usually     
greater  than in the case of extruded   
lavas1 the effects tend rather toward   
chemical and crystalline change than to 
simple baking4 ,this tendency  increases
 with increase in the mass of the lava  
and in its temperature4  ,sometimes     
enormous masses of very hot lava are    

thrust in between or  among the strata  
that lie beneath the surface1 and bring 
to bear upon  them intense heat for a   
long period4 ,so also1 when a vent or   
fissure  is the passageway for lavas    
that continue to come to the surface for
  long periods1 as in the case of       
persistent volcanoes1 the rocks which   
form the walls of the vent or fissure   
are heated for a long time1 and  this   
gives rise to metamorphism through heat1
 without very unusual  pressure1 but    
usually with the free aid of water4 ,in 
these cases the  chief effect is        
chemical recombination and              
crystallization4 ,in the  limestones and
 sandstones it is simple2 in the shales 
more complex4 ,in  pure limestones and  
dolomites little chemical change takes  
place1 but  the molecules are rearranged
 into larger and more perfect crystals1 
and  marble is the result4 ,the         
coarseness of the crystals is1 in a     
general  way1 a measure of the length of
 time during which the heat acts1 and   

of its intensity1 but much depends on   
the freedom of the attendant  water     
circulation4 ,crystals an inch or two   
across are sometimes formed  in the     
contact zone1 where the attendant water 
action is important4  ,if impurities1 as
 silica1 alumina1 iron1 etc41 are       
present1 various  minerals1 such as     
tremolite and actinolite1 may be formed 
in the  marble4 ,in pure quartzose      
sandstones1 the effect is to cause the  
building up of the quartz grains until  
the interspaces are essentially  filled 
and the whole becomes a massive         
quartzite4 ,here1 as in the  marbles1   
impurities form adventitious crystals1 a
 very common one being  hematite1 formed
 from the segregation of the ferric     
oxide of the  sandstone4    ,in the     
shales1 the material to be acted upon is
 more complex1 for1  while the main mass
 is an aluminum silicate1 there is      
usually much  free quartz1 not a little 
potash and iron1 and more or less of    
lime1  magnesia1 soda1 and other        

ingredients1 for the muds from which the
  shales arose contained not only the   
fully decomposed matter of the  original
 crystalline rocks1 but the fine matter 
worn from them by  wind and water       
without decomposition4 ,when this mixed 
matter is acted  upon by high heat and  
moisture1 it tends to return to its     
original  crystalline state1 so far as  
its changed constitution permits4 ,the  
potash chiefly unites with alumina and  
silica1 and forms potash  feldspar      
7orthoclase chiefly7 and potash mica    
7muscovite74 ,the iron  often unites    
with magnesia1 alumina1 and silica to   
form biotite or one  of the             
ferromagnesian minerals1 chiefly an     
amphibole4 ,the lime usually  aids in   
the formation of other silicates of     
either the feldspar or  the             
ferromagnesian group1 while the surplus 
silica crystallizes into  quartz4 ,there
 is usually a predisposition to form    
mica in preference  to other silicates  
if the proper constituents are present1 

and the  result is that mica schists and
 gneisses1 in which mica abounds1  are  
common products of the metamorphism of  
shales by contact with  bodies of lava4 
,mica schists and micaceous gneisses are
 also formed  in other ways1 and other  
schists1 dependent on the composition of
  the shales1 are formed about          
intrusions of igneous rock4 ,in all such
  cases pressure probably attends the   
heat and is a factor in the  development
 of the schists4 ,when the change       
induced by the heat is less             
considerable1 the shale is baked1 with  
incipient recrystallization1 and  often 
takes the form of argillite1 a compact1 
massive sort of shale4    ,beds of      
hydrous iron oxide 7limonite7 or of iron
 carbonate 7siderite7  are usually      
converted by heat into hematite or      
magnetite4 ,beds of peat1  lignite1 and 
bituminous coal are converted into      
anthracite by the  driving off of the   
volatile hydrocarbons4 ,if the process  
goes to the  extreme1 graphite is the   

result4    ,metamorphism by heat and    
lateral pressure4--,as already          
indicated1  the more common intense     
pressures experienced by rocks at and   
near  the surface are those that come   
from lateral thrusts arising from the   
shrinkage of the earth4 ,these affect   
one dimension of the rock-mass1  while  
they permit it to expand in one or both 
of the other dimensions4  ,this produces
 a strain in all the constituent        
particles of the rock1  and under such  
strain they pass more readily into      
solution than when  free from strain1   
and more readily rearrange their        
molecules internally  into positions of 
less strain4 ,the crystals grow most    
freely along the  planes of least       
stress1 i4e41 at right angles to the    
pressure4#bjb ,as  a consequence1 where 
unidimensional pressure and high heat   
resulting  from the compression unite   
their influence1 the metamorphic changes
  are not only facilitated1 but the     
rearrangement is controlled by the      

pressure and results in a parallel      
arrangement of the constituent          
crystals1 giving a foliated or schistose
 character to the new rock4  ,the       
changes themselves are much the same as 
those produced by heat  and water       
without exceptional pressure1 though    
some distinctions may  be noted4 ,it is 
to be observed1 however1 that two kinds 
of work are  embraced here3 the         
metamorphism of clastic rocks into      
crystalline  schists1 which may be      
regarded as an upbuilding process1      
anamorphism1  and the mashing down of   
massive crystalline rocks into schists1 
which  may be regarded as a             
degradational process1 katamorphism4 ,in
 both  cases1 however1 there is solution
 and rearrangement of the molecules4    
,the katamorphism of basalts and other  
basic rocks gives basic schists2  that  
of granitic and similar rocks gives     
gneisses4 ,the anamorphism of  basic    
pyroclastic tuffs and wackes gives basic
 schists1 while that  of acid           

pyroclastics and most shales gives      
gneisses1 mica schists1  or similar     
acidic schists4 ,it is obvious that     
ordinary shales cannot  usually become  
basic schists1 because in producing the 
original  muds1 the bases were generally
 removed2 but when shales are highly    
calcareous and magnesian1 as when they  
grade toward the limestones and         
dolomites1 they may become basic schists
 by metamorphism1 e4g41 certain         
hornblendic schists4 ,it is even more   
obvious that the limestone and          
sandstone formations must largely retain
 their distinct composition4 ,it  is    
thus seen that1 in general1 a           
sedimentary series anamorphosed must    
differ from a crystalline series        
katamorphosed1 though both give rise  to
 foliated or schistose rocks4           
,deep-seated metamorphism4--,when the   
exceptional pressure arises from  the   
weight of rocks felt at great depth1 it 
is practically equal in  all directions 
and the crystallization probably        

develops normally and  is not forced    
into the parallel or foliated form4     
,rocks metamorphosed  under these       
conditions probably tend to take the    
massive form rather  than the schistose 
form1 but this conclusion is theoretical
 rather than  observational1 for little 
or nothing is known of the history of   
such  rocks4    ,completion of the rock 
cycle4--,the crystallizing processes of 
metamorphism are fundamentally similar  
to the processes by which rocks         
crystallize out of magmas1 only in the  
first case the work is done  chiefly by 
the aid of an aqueous solution1 while in
 the second it is  done through a mutual
 solution of the constituents in        
themselves1  where water was but an     
incident4 ,if the heat factor in        
metamorphism  be sufficiently increased1
 aqueous solution may actually grade    
into  magmatic solution through various 
degrees of softening and melting1 and   
the cycle of changes be closed in upon  
itself4                    ,,various    

,,classifications ,,and ,,nomenclatures4
    ,from the foregoing sketch of the   
processes of rock-making it may easily  
be inferred that the varieties of rocks 
may be almost unlimited1 and  that they 
may be defined1 named1 and classified on
 many different  bases2 for example4    
7#a7 ,if the mode of origin is chiefly  
in mind1 rocks may be classed  as       
igneous 7lavas1 tuffs1 etc472           
metamorphic 7schists1 gneisses1         
anthracite1 magnetite1 etc472 aqueous   
7water-laid sediments1  stalactites1    
travertine1 etc472 eolian 7dunes1 loess 
in part72  glacial 7till1 moraines72    
clastic 7mantle-rock1 sandstone1        
conglomerate1 etc472 organic 7peat1     
lignite1 coal1 etc41 and  indirectly1   
limestone1 chalk1 infusorial earth1     
etc472 and so on4    7#b7 ,if the       
textural or structural characters are in
 mind1 rocks are  designated vesicular  
7pumice1 scoria1 etc472 rhyolitic       
7flow-structure  rocks72 glassy         
7obsidian1 tachylite72 porphyritic      

7distinct crystals  in obscure matrix72 
granitic 7well-grained72 compact1       
porous1 earthy1  arenaceous 7sandy71    
schistose1 etc4    7#c7 ,if the chemical
 composition is chiefly regarded1 they  
may be  classed as silicious1           
calcareous1 carbonaceous1 ferruginous1  
etc42 or1  if the chemical nature is    
considered1 they are grouped as acidic1 
basic1 or neutral4    7#d7 ,if the      
crystalline character is made the basis1
 they  are designated phanerocrystalline
 7distinctly crystallized71             
microcrystalline 7minutely              
crystallized71 cryptocrystalline        
7hiddenly  crystallized71 and amorphous 
7non-crystalline74    7#e7 ,if attention
 is fastened on certain ingredients1    
rocks  are characterized as quartzose1  
micaceous1 chloritic1 talcose1          
pyritiferous1 garnetiferous1 etc4       
7#f7 ,when rocks are regarded as mineral
 aggregates1 if 7a7 the  aggregates are 
simple1 they are named from the dominant
 minerals1  as dolomite1 hornblendite1  

garnetite1 anorthite1 etc42 and if 7b7  
the aggregates are complex they take    
special names1 as syenite  7orthoclase  
and hornblende71 gabbro 7plagioclase    
feldspar and  pyroxene71 etc4    7#g7   
,when the point of view is structure of 
the mass1 they are classed  as massive1 
stratified1 shaly1 laminated1 slaty1    
foliated1 schistose1  etc4    7#h7 ,when
 physical state or genesis is           
considered1 they are grouped  as        
clastic1 fragmental1 or detrital        
7conglomeratic1 brecciated1  arenaceous1
 argillaceous1 etc472 or pyroclastic    
7tufaceous1  scoriaceous1 agglomeratic72
 or massive1 in a sense slightly        
different  from that above 7#g74    ,as 
sometimes one of these characteristics  
and sometimes another is most  important
 in a given rock1 or in a given study1  
no one classification  is satisfactory  
in all cases1 yet each has its          
advantages in particular  cases4        
,new ,system of ,classification and     
,nomenclature4    ,the present systems  

of classifying and naming rocks have    
grown up  gradually out of earlier and  
cruder methods1 many of which were      
inherited from popular usage4 ,most of  
the names and definitions came  into use
 before microscopical and other modern  
means of study were  adopted4 ,these    
systems1 therefore1 retain many         
inherited crudities  and                
inconsistencies1 and lack adaptation to 
present needs4 ,they are  too complex   
and difficult for field use and for     
general discussions1  while not         
sufficiently exact and systematic for   
the more rigorous  petrological         
discussions4 ,a more adaptive and       
consistent practice  has been earnestly 
sought by petrologists1 and a new system
 of  classification of igneous rocks has
 been offered by a group of leading     
,american petrologists1 an outline of   
which is here given4#bjc ,to  some      
extent this may be extended to the      
metamorphic crystalline  rocks with     
necessary modifications and additions4  

,the classification  and nomenclature of
 the secondary rocks must probably      
always remain  variable and plastic to  
express the various points of view which
 it  is desirable to take4 ,during the  
transition to this or some other new    
system1 which seems inevitable1 the     
appended alphabetical reference  lists  
of the most common minerals and rocks1  
with brief definitions in  accordance   
with current usage1 will be found       
serviceable4 ,the proposed  system      
includes two parts1 a field system and a
 quantitative  system1 the one          
applicable to rocks on casual           
inspection1 and the  other1 only after  
detailed study4                         
,the proposed field system4    ,the     
proposed field names are based largely  
on texture and color4  ,the mineral     
constituents are used for subdivisions  
when they can be  determined2 otherwise 
they are neglected4    ,classifying     
chiefly on the basis of texture and     
crystalline state1  there are three     

groups3 ,phanerites1 in which all the   
leading mineral  constituents can be    
seen megascopically2 aphanites1 in which
 all1 or  at least an appreciable part1 
of the constituent minerals cannot be   
distinguished megascopically2 and       
glasses1 in which the material is       
wholly or largely vitreous4    ,i4 ,the 
,phanerites may be further classified by
 their chief mineral  constituents as   
follows3    #a4 ,granites 7f4n471#bjd   
consisting largely of quartz and        
feldspar of any kind1 with or without   
mica1 hornblende1 pyroxene1  or other   
minerals4 ,this differs from the present
 common use in not  regarding mica as an
 essential constituent1 and in not      
distinguishing  between alkali feldspars
 and calcic feldspars1 thus broadening  
the  class4    #b4 ,syenites 7f4n471    
consisting predominantly of feldspar of 
any  kind1 with subordinate amounts of  
hornblende1 mica1 or pyroxene1 but  with
 little or no quartz4 ,this differs from
 the common use in giving  hornblende a 

subordinate place1 and in embracing     
rocks with calcic  feldspars1 thus      
broadening the class4    #c4 ,diorites  
7f4n471 consisting predominantly of     
hornblende and  subordinately of        
feldspar of any kind1 with which there  
may be mica1  pyroxene1 or other        
minerals4 ,this is nearly the present   
use except that  any kind of feldspar   
may form the subordinate element4    #d4
 ,gabbros 7f4n471 consisting            
predominantly of pyroxene and           
subordinately of feldspar of any kind1  
with or without other  minerals4 ,this  
nearly coincides with one of the various
 present uses of  the term except that  
the range of the feldspar is increased4 
#e4 ,dolerites#bje 7f4n471 consisting   
predominantly of any  ferromagnesian    
mineral not distinguishable as          
hornblende or pyroxene1  with           
subordinate elements of feldspar of any 
kind1 and with or  without other        
accessory minerals4 ,a name to be used  
when the dominant  mineral is clearly   

ferromagnesian1 but cannot be           
satisfactorily  identified as either    
hornblende or pyroxene1 although it may 
probably  be one of these4 ,in other    
words1 the dolerites 7deceptive7 embrace
 the  whole diorite-gabbro group when   
too obscure for separation4    #f4      
,peridotites1 consisting predominantly  
of olivine and  ferromagnesian minerals1
 without feldspar1 or with very little4 
#g4 ,pyroxenite1 consisting essentially 
of pyroxene without feldspar or         
olivine4    #h4 ,hornblendite1          
consisting essentially of hornblende    
without  feldspar or olivine4    ,,ii4  
,the ,aphanites may be non-porphyritic  
or porphyritic4    7a7 ,non-porphyritic 
aphanites when light-colored may be     
classed as  felsites2 when dark-colored1
 as basalts4    7b7 ,the porphyritic    
aphanites or porphyries1 when           
light-colored1  are leucophyres2 when   
dark-colored1 are melaphyres 7f4n474    
,they may  be classified further1       
according to the kind of phenocryst     

imbedded in  the aphanitic ground-mass1 
as      ,quartz-porphyries1 or          
quartzophyres2    ,feldspar-porphyries1 
or feldspaphyres 7not felsophyres72     
,hornblende-porphyries1 or              
hornblendophyres2 and so on4    ,these  
may be subclassed by color1 as          
,quartz-leucophyres1 light-colored      
quartz-porphyries2                      
,quartz-melaphyres1 dark-colored        
quartz-porphyries2                      
,feldspar-leucophyres2                  
,feldspar-melaphyres2 and so on4        
,,iii4 ,the glasses are classified1     
according to color and luster1 into     
obsidians or pitchstones when dark and  
lustrous2 perlites1 when a  spheroidal  
fracture gives them a pearly appearance2
 and pumice when  greatly inflated by   
included gases4    ,in general          
discussions1 it is regarded as          
serviceable to use the term  granitoids 
in a broad generic sense1 to include all
 crystalline  rocks of the general      
granitoid type1 including the granites1 

syenites1  gneisses1 etc4 ,in a similar 
broad way1 the term gabbroids may be    
used to include the dark crystalline    
rocks in which the ferromagnesian       
minerals predominate1 as the diorites1  
gabbros1 dolerites1 peridotites1  etc4  
,in this convenient and comprehensive   
way1 two contrasted groups of  igneous  
rocks may be designated4 ,as the        
granitoids are usually acidic  and the  
gabbroids usually basic1 the grouping   
represents a broad fact  of importance4 
,,the ,,proposed ,,quantitative         
,,system4    ,the distinguishing        
characteristic of the more rigorous     
system designed  to meet the needs of   
scientific petrology is its quantitative
 chemical  character4 ,all igneous rocks
 are classified primarily according to  
their chemical composition and only     
secondarily according to their  mineral 
constituents1 texture1 and other        
characters4 ,the rigorous  application  
of the system requires chemical analyses
 of the rocks1 but  as these are not    

available in many cases1 the authors of 
the system  have devised a method of    
optical mineral analysis by which the   
nearly  exact proportions of all the    
constituent minerals can be determined1 
and by knowledge of their chemical      
nature the results may be converted1  by
 computation1 into chemical terms4 ,this
 can only be done for  holocrystalline  
rocks whose crystals are large enough to
 be measured  under the microscope1 but 
aphanitic rocks may often be            
approximately  classified by comparison 
with similar rocks already accurately   
determined4 ,to facilitate this method  
of chemical analysis by measuring  the  
minerals1 the chemical composition of   
certain common rock-making  minerals is 
expressed in proportional parts and     
tabulated1 and is used  somewhat as     
molecular weight is in ordinary chemical
 analysis4 ,certain  of these are       
selected as standard minerals1 the      
selection being such  that the standard 
minerals embrace all the essential      

elements that  enter into the           
composition of rocks4 ,all other        
minerals are converted  into their      
chemical equivalents in terms of these  
standard minerals by  the use of the    
tables4 ,all the mineral constituents   
being thus reduced  to standard         
minerals1 the classification is built up
 systematically on  these standard 7or  
standardized7 minerals4    ,a new system
 of names is required1 and these have   
been very skillfully  formed by         
selecting significant letters from the  
names of the leading  minerals or from  
words signifying their preponderance1 so
 that short  terms which carry their    
meaning in their forms1 are secured1 and
  this has been done so that these are  
usually euphonious1 however  strange    
they may seem to our preoccupied senses4
 ,for example1 minerals  composed       
chiefly of silica and alumina are called
 salic2  those of ferromagnesian        
minerals1 femic2 those of aluminous     
ferromagnesian minerals1 alferric1 etc4 

,when in a combination of  salic and    
femic minerals1 the salic are extremely 
abundant1 the rock is  persalic2 if     
notably dominant1 dosalic2 if the salic 
and femic  minerals are nearly equal1   
salfemic2 if the femic are dominant1    
dofemic2 if extremely abundant1         
perfemic1 and so on1 the system  being  
mnemonic4 ,this method of deriving names
 is applicable only to a  portion of the
 necessary divisions4 ,for the rest1 a  
series of roots  derived from geographic
 names1 with a system of terminations1  
has been  employed4    ,all standard    
minerals are divided into two groups of 
primary  importance3 one of minerals    
characterized by alumina1 as the        
feldspars1--orthoclase1 albite1         
anorthite1--leucite1 nephelite1         
sodalite1  noselite1 and corundum1 to   
which are added the closely associated  
minerals1 quartz and zircon4 ,this is   
called the salic group4 ,the  second    
group contains minerals characterized by
 iron and magnesia with  no alumina1 as 

hypersthene 7enstatite71 acmite1        
olivine1 magnetite1  hematite1 and      
ilmenite1 to which are added the closely
 associated  minerals1 titanite1        
perofskite1 rutile1 apatite1 and all    
other  rock-making minerals except those
 containing alumina together with  iron 
and magnesia4 ,the second group is      
called femic4    ,aluminous             
ferromagnesian minerals1 such as        
hornblende1 augite1 mica1  etc42 are    
called alferric1 and are not classed as 
standard minerals1  because their       
complexity of composition makes it      
better to treat them  as though made up 
of the simpler minerals of the standard 
list4    ,the composition of all igneous
 rocks can be expressed in terms of the 
relative proportions of the two groups  
of the standard minerals1 salic  and    
femic4 ,by subdividing these groups     
successively on a mineral and  chemical 
basis1 a series of classificatory       
divisions of greater and  greater       
precision has been formed4 ,in each     

stage of the series1 two  factors only  
are compared1 and a simple set of ratios
 has been selected  to limit the        
divisions4 ,assuming the possibility of 
a continuous range  of variable mixtures
 of the two factors 7,a and ,b7 from an 
extreme  composed wholly of one 7,a71   
and an extreme composed wholly of the   
other 7,b71 five ideal cases have been  
chosen as types or centerpoints  about  
which variation in mixture may take     
place4 ,these are3        ,a  #a   ,a   
#c   ,a  #a   ,a  #a   ,a  #j    ------ 
--1  ------   --1  ------   --1  ------ 
--1  ------   --4    ,b  #j   ,b  #a    
,b  #a   ,b  #c   ,b  #a    ,division   
lines half-way between these points     
occur as the following  ratios3         
,a   #g      ,a   #g  #e      ,a   #e   
#c      ,a   #c   #a      ,a   #a  7#a7 
------  --1 7#b7 ------  --  --1 7#c7   
------  --  --1 7#d7 ------  --  --1    
7#e7 ------  --4      ,b  #a      ,b  #a
  #c      ,b   #c   #e      ,b   #e   #g
      ,b   #g    ,these ratios are used 

throughout the system4 ,in 7#a7 ,a is   
extreme2  in 7#e7 ,b is extreme2 in 7#b7
 ,a dominates over ,b2 in 7#d7 ,b       
dominates over ,a2 in 7#c7 ,a and ,b are
 equal or nearly equal4    ,all igneous 
rocks are grouped in five 7#e7 primary  
divisions called  ,classes on a basis of
 the proportions of the salic and femic 
minerals1 thus3    ,class  ,i4 ,sal   #g
            ------  --1 extremely rich  
in salic minerals1 called persalane4    
,fem   #g          ,,ii4 ,sal   #g   #e 
------  --  --1 with dominant salic     
minerals1 called dosalane4              
,fem   #a   #c         ,,iii4 ,sal   #e 
#c            ------  --  --1 salic and 
femic minerals1 equal or nearly equal1  
,fem   #c   #e              called      
salfemane4          ,,iv4 ,sal   #c   #a
            ------  --  --1 with        
dominant femic minerals1 called         
dofemane4            ,fem   #e   #g     
,v4 ,sal   #a            ------  --1    
extremely rich in femic minerals1 called
 perfemane4            ,fem   #g        

,each of these classes is divided into  
two subclasses according to  the        
proportions of two subgroups of the     
preponderant group of standard          
minerals4 ,of salic minerals one        
subgroup includes quartz1 feldspars1    
and the feldspathoids2 the other        
includes corundum and zircon4 ,of femic 
minerals one subgroup includes the      
silicates with magnetite1 ilmenite1     
hematite1 and rutile2 the other contains
 apatite and the remaining  minerals of 
this group4 ,most known igneous rocks   
fall into the first  subclass of each   
class4    ,the classes are further      
divided into orders according to the    
proportions of certain minerals in the  
preponderant subgroups4 ,thus  ,classes 
,i1 ,,ii1 and ,,iii are each divided    
into nine orders on a basis of  the     
proportions of quartz and the feldspars1
 and of the feldspars and  the          
feldspathoids1 quartz and feldspathoids 
not occurring together4 ,the  orders may
 be described in the same terms for each

 of the first three  classes as follows3
    ,order ,i4 ,q   #g           --  --1
 extremely rich in quartz1 perquaric4   
,f   #a         ,,ii4 ,q   #g   #e      
--  --  --1 quartz dominant over        
feldspar1 doquaric4           ,f   #a   
#c        ,,iii4 ,q   #e   #c           
--  --  --1 quartz and feldspar equal or
 nearly equal1 quarfelic4           ,f  
#c   #e         ,,iv4 ,q   #c   #a      
--  --  --1 feldspar dominant over      
quartz1 quardofelic4           ,f   #e  
#g          ,v4 ,q or ,l   #a           
------------  --1 extremely rich in     
feldspar1 perfelic4             ,f      
#g         ,,vi4 ,l   #c   #a           
--  --  --1 feldspar dominant over      
feldspathoids 7lenads71 lendofelic4     
,f   #e   #g        ,,vii4 ,l   #e   #c 
--  --  --1 feldspar and lenads equal or
 nearly equal1 lenfelic4           ,f   
#c   #e       ,,viii4 ,l   #g   #e      
--  --  --1 lenads dominant over        
feldspars1 dolenic4           ,f   #a   
#c         ,,ix4 ,l   #g           --   

--1 extremely rich in lenads1 perlenic4 
,f   #a    ,in classes ,,iv and ,v the  
preponderant minerals are femic1 and in 
subclass #a they are silicates1         
titanates1 and ferrates1 with hematite  
and rutile4 ,these are subdivided as    
follows3    ,silicates--pyroxenes and   
olivine with akermanite in one subgroup2
 the  other minerals1 magnetite1        
hematite1 ilmenite1 titanite1           
perofskite1  rutile1 in the second      
subgroup4 ,this first group is called   
polic1  mnemonic of pyroxene and        
olivine2 the second group is called     
mitic1  mnemonic of magnetite1 ilmenite1
 titanite4    ,there are five orders in 
each of these classes1 as follows3      
,order ,i4 ,,po   #g           ----  --1
 extremely rich in pyroxene or olivine1 
perpolic4           ,m    #a            
,,ii4 ,,po   #g   #e           ----  -- 
--1 dominant pyroxene or olivine1       
dopolic4           ,m    #a   #c        
,,iii4 ,,po   #e   #c           ----  --
  --1 pyroxene or olivine1 equal or     

nearly equal to the mitic           ,m  
#c   #e              minerals1 polmitic4
         ,,iv4 ,,po   #c   #a           
----  --  --1 dominant mitic minerals1  
domitic4           ,m    #e   #g        
,v4 ,,po   #a           ----  --1       
extremely rich in mitic minerals1       
permitic4           ,m    #g    ,in the 
first three orders a distinction between
 pyroxene and olivine is  recognized by 
sections1 five in number3    ,section   
#a4 ,p   #g             --  --1         
extremely rich in pyroxene1 perpyric4   
,o   #a            #b4 ,p   #g   #e     
--  --  --1 dominant pyroxene1 dopyric4 
,o   #a   #c            #c4 ,p   #e   #c
             --  --  --1 pyroxene and   
olivine1 equal or nearly equal1 pyrolic4
             ,o   #c   #e            #d4
 ,p   #c   #a             --  --  --1   
dominant olivine1 domolic4              
,o   #e   #g            #e4 ,p   #a     
--  --1 extremely rich in olivine1      
perolic4             ,o   #g    ,in the 
last two orders a distinction between   

the preponderant mitic  minerals is     
recognized by suborders1 five in number4
 ,the minerals  containing ,fe,o are    
compared with those containing ,ti,o4   
,the former1  magnetite and hematite1   
are called hemic1 mnemonic of hematite2 
the  latter subgroup1 titanite1         
ilmenite1 perofskite1 rutile1 are called
  tilic1 mnemonic of titanite and       
ilmenite4 ,of orders #d and #e1 there   
are    ,suborder #a4 ,h   #g            
--  --1 hemic minerals extreme1         
perhemic4              ,t   #a          
#b4 ,h   #g   #e              --  --    
--1 dominant hemic minerals1 dohemic4   
,t   #a   #c             #c4 ,h   #e    
#c              --  --  --1 hemic and   
tilic minerals equal or nearly equal1   
,t   #c   #e               tilhemic4    
#d4 ,h   #c   #a              --  --    
--1 dominant tilic minerals1 dotilic4   
,t   #e   #g             #e4 ,h   #a    
--  --1 tilic minerals extreme1         
pertilic4              ,t   #g          
,further subdivision1 producing rangs   

and subrangs1 is made on the  character 
of the chemical bases in the standard   
minerals used in  forming orders and is 
expressed in terms of the molecular     
proportions  of certain oxides4 ,for the
 salic minerals1 forming orders in the  
first  three classes1 the bases are     
alkalies--,k,o and ,na,o--and lime1     
,ca,o4 ,for  the femic minerals1 forming
 orders in the last two classes1 the    
bases  are ,mg,o1 ,fe,o1 ,ca,o and      
alkalies1 ,k,o1 ,na,o4 ,in classes ,i1  
,,ii1 and ,,iii  rangs are formed by    
comparing salic alkalies1 ,k,o  ,na,o1  
with salic  lime1 ,ca,o2 and subrangs   
are formed by comparing ,k,o with ,na,o4
    ,rang #a4 ,k,o  ,na,o    #g         
----------------------  --1 alkalies    
extreme1 peralkalic4             ,ca,o  
#a         #b4               #g   #e    
--  --1 alkalies dominant1 domalkalic4  
#a   #c         #c4               #e    
#c                      --  --1 alkalies
 and lime equal or nearly so1           
#c   #e              alkalicalcic4      

#d4               #c   #a               
--  --1 lime dominant1 docalcic4        
#e   #g         #e4               #a    
--1 lime extreme1 percalcic4            
#g    ,subrang #a4 ,k,o    #g           
--------  --1 potash extreme1           
perpotassic4             ,na,o   #a     
#b4        #g   #e                  --  
--1 potash dominant1 dopotassic4        
#a   #c            #c4        #e   #c   
--  --1 potash and soda equal1          
sodipotassic4                    #c   #e
            #d4        #c   #a          
--  --1 soda dominant1 dosodic4         
#e   #g            #e4        #a        
--1 soda extreme1 persodic4             
#g    ,in classes ,,iv and ,v rangs are 
formed by comparing femic ,mg,o  ,fe,o  
,ca,o with femic alkalies ,k,o  ,na,o4  
,minerals containing magnesia1 iron1 and
 lime are called mirlic4    ,rang #a4   
,mg,o  ,fe,o  ,ca,o   #g                
--------------------------------  --1   
extremely mirlic1 permirlic4            
,k,o  ,na,o      #a         #b4         

#g   #e                    --  --1      
dominantly mirlic1 domirlic4            
#a   #c         #c4             #e   #c 
--  --1 equally mirlic and alkalic1     
alkalimirlic4                      #c   
#e         #d4             #c   #a      
--  --1 dominantly alkalic1 domalkalic4 
#e   #g         #e4             #a      
--1 extremely alkalic1 peralkalic4      
#g    ,sections of rangs distinguish    
between ,mg,o  ,fe,o and ,ca,o4         
,minerals with  ,mg,o  ,fe,o are called 
miric4    ,section #a4 ,mg,o  ,fe,o   #g
             ------------------  --1    
extremely miric1 permiric4              
,ca,o     #a            #b4             
#g   #e                      --  --1    
dominantly miric1 domiric4              
#a   #c            #c4            #e    
#c                      --  --1 equally 
miric and calcic1 calcimiric4           
#c   #e            #d4            #c    
#a                      --  --1         
dominantly calcic1 docalcic4            
#e   #g            #e4            #a    

--1 extremely calcic1 percalcic4        
#g    ,subrangs distinguish between     
,mg,o and ,fe,o1 thus3    ,subrang #a4  
,mg,o   #g             ------  --1      
extremely magnesic1 permagnesic4        
,fe,o   #a            #b4       #g   #e 
--  --1 dominantly magnesic1 domagnesic4
                   #a   #c              
#c4       #e   #c                 --    
--1 equally magnesic and ferrous1       
magnesiferrous4                   #c    
#e            #d4       #c   #a         
--  --1 dominantly ferrous1 doferrous4  
#e   #g            #e4       #a         
--1 extremely ferrous1 perferrous4      
#g    ,finally a recognition of the     
character of the subordinate standard   
minerals leads to further subdivisions  
known as grads and subgrads4  ,they only
 occur in classes ,,ii1 ,,iii1 and ,,iv1
 because these are the only  ones in    
which the subordinate minerals are in   
notable amounts4 ,grads  are formed in a
 manner similar to that employed to     
produce orders4 ,thus  grads in classes 

,,ii and ,,iii correspond to orders in  
class ,,iv and the  reverse4 ,subgrads  
are the same in form as rangs when the  
difference in  the treatment of salic   
and femic minerals is borne in mind4    
,the names  given to these divisions1   
which in fact recognize only the        
character of  the magma1 are derived    
from geographical localities and embrace
 many of  those already in use1 except  
that the names of orders are taken from 
countries or nations4 ,specific         
terminations indicate the place in the  
series of divisions3      ane for class1
 one for subclass4    are for order1 ore
 for suborder4    ase for rang1 ose for 
subrang4    ate for grad1 ote for       
subgrad4    ,this may be illustrated as 
follows3    ,class ,i4 persalane1 all   
rocks extremely salic4    ,order #d4    
britannare1 feldspar dominant over      
quartz1 quardofelic4 ,many  rocks of    
granitic composition whether crystalline
 or glassy4    ,rang #a4 liparase1      
peralkalic1 rocks in which the potential

 feldspars  are extremely alkalic1      
orthoclase1 or albite4    ,subrang #b4  
,omeose1 dopotassic1 rocks in which the 
extremely alkali  feldspars are         
dominantly potassic1 orthoclase1 with   
subordinate albite4  ,examples of omeose
 are3 granite from ,omeo1 ,victoria1    
,australia1 and  rhyolite from ,silver  
,cliff1 ,colorado4    ,the presence of  
distinctive minerals not indicated in   
the standard  mineral composition of    
norm is expressed by qualifying the     
magmatic  name by the name of the       
distinctive mineral2 as1 a              
hornblende-monzonose4    ,the precise   
texture of the rock is expressed by     
qualifying the magmatic  name by a      
textural adjective2 as1 a               
grano-monzonose1 a vitro-monzonose1  a  
phyro-monzonose1 etc4                   
,,reference ,,list ,,of ,,the ,,more    
,,common ,,minerals4    ,actinolite--a  
magnesium-calcium-iron amphibole 7q4v472
 commonly bright  green to grayish      
green2 crystals usually slender or      

fibrous4    ,agate--a banded or         
variegated chalcedony 7quartz1 q4v474   
,alabaster--a fine-grained variety of   
gypsum 7q4v471 either white or          
delicately colored4    ,albite--a soda  
feldspar 7q4v471 an aluminum-sodium     
silicate2 ,h4 #e-f2  cleavage perfect in
 two planes2 luster vitreous or pearly  
white2  occasionally bluish gray1       
reddish1 greenish2 sometimes opalescent4
    ,amethyst--a variety of quartz of   
purple or bluish-violet color1 due      
probably to manganese4                  
,amphibole--the type of an important    
group of rock-forming minerals  known as
 the amphibole or hornblende group2 a   
ferromagnesian silicate1  monoclinic1   
,h4 #e-f2 luster vitreous to pearly2    
fibrous varieties  often silky2 black1  
ranging through various shades of green 
to  light colors2 embraces the          
magnesium-calcium varieties1 tremolite  
and nephrite2 the magnesium-calcium-iron
 variety actinolite2 the                
aluminous-magnesium-iron-calcium variety

 hornblende1 and others4                
,analcite--analcine1 one of the         
zeolites2 a hydrous aluminum-sodium     
silicate2 luster vitreous1 colorless1   
white2 occasionally grayish1  greenish1 
yellowish1 reddish1 transparent to      
opaque4    ,andesine--a plagioclase     
feldspar 7q4v472 a                      
sodium-calcium-aluminum  silicate1      
intermediate in composition between     
albite and anorthite2 ,h4  #e-f2 white1 
gray1 grayish1 yellowish1 flesh red2    
luster subvitreous1  inclining to       
pearly4    ,andalusite--an aluminum     
silicate2 luster vitreous2 whitish1 rose
 red1  flesh red1 variety pearly gray1  
reddish brown1 olive-green2 ,h4 #g4e1   
infusible2 impurities sometimes so      
arranged in the interior as to  exhibit 
a colored1 crossed1 or tesselated       
appearance in cross-section             
7chiastolite74    ,anhydrite--a calcium 
sulphate2 ,h4 #c-c4e2 luster pearly to  
vitreous2  white1 sometimes bluish or   
reddish2 differs from gypsum in absence 

of  water and in its greater hardness4  
,anorthite--a plagioclase feldspar      
7q4v472 a calcium-aluminum silicate2    
varies much by impurities and           
admixtures2 ,h4 #f-f4e2 pearly or       
vitreous  luster2 white1 grayish1       
reddish4    ,anthracite--hard coal2     
hydrocarbon with impurities2 supposed to
 be  derived from bituminous coal by    
metamorphism4    ,antimony--a native    
metal1 tin-white1 brittle2 rather rare  
in native  form4                        
,apatite--essentially calcium phosphate 
with chlorine or fluorine2  hexagonal2  
,h4 #e2 luster vitreous or subresinous2 
colors usually  greenish to bluish1     
characterized by a hexagonal form4      
,aragonite--a calcium carbonate2 differs
 from calcite in cleavage1  and in being
 orthorhombic2 ,h4 #c4e-d2 luster       
vitreous or resinous2  white1 also gray1
 yellow1 green1 and violet4             
,asphaltum--asphalt2 mineral pitch1     
bitumen2 a natural mixture of  different
 hydrocarbons2 odor bituminous2 melts at

 #ij to #ajj degrees  ,c42 burns with a 
bright flame2 graduates into mineral    
tars and through  these into petroleum2 
probably the residue of the latter4     
,augite--one of the pyroxenes 7q4v472 an
  aluminum-calcium-magnesium-iron       
silicate2 ,h4 #e-f2 monoclinic1 crystals
  usually thick and stout2 sometimes    
lamellar2 also granular2 black1         
greenish black1 deep green2 an important
 rock-forming mineral4                  
,beauxite--essentially hydrated alumina2
 occurs in concretionary grains  of     
clay-like form1 whitish to brown2       
valuable as a source of aluminum4       
,beryl--a beryllium-aluminum silicate2  
hexagonal2 prismatic2 ,h4 #h2  luster   
vitreous or resinous2 marl-green1 pale  
passing into whitish2  closely resembles
 apatite1 but distinguished by superior 
hardness and  in composition4           
,barite--barites1 heavy-spar1 barium    
sulphate2 orthorhombic1 ,h4 #c-c4e2     
luster vitreous to resinous1 sometimes  
pearly2 white1 inclining to  yellow1    

gray1 blue1 red1 or brown2 very heavy1  
sp4 gr4 #d4c-d4g4    ,biotite--black    
mica1 a potash-aluminum-magnesium-iron  
silicate2  monoclinic2 easy basal       
cleavage into thin lamin2 sometimes     
occurs as  a massive aggregation of     
cleavable scales2 ,h4 #b4e-c2 luster    
splendent  on cleavage surface2 black to
 dark green2 cleavage surfaces smooth   
and  shining2 a very common constituent 
of crystalline rocks4    ,bitumen--the  
same as asphaltum 7q4v474    ,bismuth--a
 metal of whitish color and rather      
brittle nature2 occurring  occasionally 
native1 usually as an ore4              
,bronzite--a variety of enstatite       
7q4v472 grayish green to olive-green    
and brown with luster on cleavage       
surface often adamantine1 pearly or     
bronze-like and submetallic4            
,calcite--calcspar2 calcium carbonate2  
rhombohedral1 perfect  rhombohedral     
cleavage2 often taking the forms known  
as dogtooth spar1  nail-head spar2      
frequently stalactitic and stalagmitic2 

,h4 #b4e-c4e2  luster vitreous2 white1  
occasionally pale shades of gray1 red1  
green1  blue1 violet1 yellow1 brown2    
strong double refraction2 embraces      
variety  called ,iceland spar2 a very   
common mineral2 the essential basis of  
limestone4    ,cassiterite--tin stone2  
an oxide of tin2 tetragonal2 luster     
adamantine1 usually splendent2 brown or 
black1 sometimes red1 gray1  white1 or  
yellow2 an important source of tin4     
,catlinite--essentially a hardened red  
clay1 rather a rock than a  mineral2    
much prized by ,indians for pipes4      
,chalcedony--a cryptocrystalline variety
 of quartz having a wax-like  luster1   
either transparent or translucent2      
white1 grayish1 pale brown  to dark     
brown1 black1 sometimes delicate blue1  
occasionally other  shades2 frequently  
occurs as the lining or filling of      
cavities1 taking  on a botryoidal or    
mamillary form4                         
,chiastolite--andalusite 7q4v474        
,chlorite--the type of an important     

group of secondary minerals usually     
characterized by a green color1 softness
 and smoothness or unctuousness  of     
feeling2 they are usually               
aluminum-magnesium-iron silicates1 with 
chemically combined water2 derived from 
several other species1 as  pyroxene1    
amphibole1 biotite1 garnet1 etc42       
embraces a number of  species1 among    
which are clinochlore1 penninite1       
prochlorite1 and  delessite4            
,chromite--chromic iron2 essentially an 
iron chromate2 isometric2  luster       
submetallic2 iron black to brownish     
black2 opaque2 sometimes  magnetic2     
resembles magnetite4                    
,chrysolite--olivine2 essentially a     
magnesium-iron silicate2  orthorhombic2 
,h4 #f-g2 luster vitreous2 green1       
commonly olive-green1  sometimes yellow1
 brownish1 grayish green2 highly        
infusible2 a common  constituent of     
certain basic igneous rocks2 the name   
olivine is more  commonly used by       
geologists4    ,chrysotile--a delicately

 fibrous variety of serpentine 7q4v474  
,corundum--alumina2 an oxide of         
aluminum2 ,h4 #i2 rhombohedral2 large   
crystals usually rough2 luster vitreous2
 color blue1 red1 yellow1 gray1  and    
nearly white2 purer forms of fine colors
 are sapphires2 the red  variety is     
ruby1 the yellow1 oriental topaz1 the   
green1 emerald1  and the purple1        
amethyst2 dark colors1 with iron oxide1 
emery4    ,delessite--a ferruginous     
chlorite1 usually olive-green or        
blackish  green2 occurring commonly in  
the cavities of amygdaloids4            
,diallage--a variety of pyroxene 7q4v472
 ,h4 #d2 characterized by thin  foli2   
usually grayish green to grass-green1 or
 deep green2 luster on  cleavage surface
 pearly1 sometimes metalloid or brassy2 
an essential  mineral in the gabbros1 as
 sometimes defined4    ,elolite--a      
variety of nephelite 7q4v472 occurring  
in large coarse  crystals or massive1   
with greasy luster1 from which the name 
is  derived2 a characteristic           

constituent of elolite syenite4         
,enstatite--one of the pyroxenes2       
essentially a magnesium silicate2       
orthorhombic2 ,h4 #e4e2 luster a little 
pearly on cleavage surface2  metalloidal
 in the bronze variety 7bronzite72      
grayish white1 yellowish  white1        
greenish white to olive-green and brown2
 very infusible2 a  common mineral in   
certain basic crystalline rocks4        
,epidote--a complex                     
aluminum-calcium-iron silicate of       
varying  composition2 monoclinic2 ,h4   
#f-g2 luster vitreous1 pearly1 or       
resinous2  color usually                
pistachio-green1 or yellowish green to  
brownish green2  can usually be detected
 by its peculiar pistachio hue1 which is
 seldom  found in other minerals2 common
 in many crystalline rocks1 usually as a
  secondary product4    ,feldspar--a    
group of minerals of the first          
importance in rock  formation1 embracing
 orthoclase1 microcline1 albite1        
oligoclase1  andesine1 labradorite1     

anorthite1 and numerous variations2     
aluminum  silicates1 with either        
potassium1 sodium1 or calcium or two or 
more  of these2 crystallizes in both the
 monoclinic and triclinic systems2      
possesses very distinct cleavage in two 
directions2 ,h4 #f-f4e2 range in  color 
from white through pale yellow1 red1 or 
green1 and occasionally  dark2 triclinic
 feldspars frequently called plagioclase
 7see individual  feldspars74           
,fluorite--fluorspar2 calcium fluoride2 
isometric1 usually cubic2  ,h4 #d2      
luster vitreous1 sometimes splendent2   
white1 yellow1 green1  rose1 crimson    
red1 violet1 sky-blue1 and brown2       
yellow1 greenish1 and  violet most      
common2 occurs usually in veins or      
cavities in beautiful  crystalline form4
    ,galenite--galena2 lead sulphide2   
isometric1 usually cubic2 perfect  cubic
 cleavage2 luster metallic2 lead-gray2 a
 common ore of lead2  occurs in veins   
and layers1 also as linings of cavities4
    ,garnet--a complex silicate of      

varying composition1 embracing aluminum1
  calcium1 magnesium1 chromium1 iron1   
and manganese1 but usually only  two or 
three of these are present in abundance1
 and the varieties  are characterized by
 the leading constituent2 isometric1    
usually  in dodecahedrons or            
trapezohedrons2 ,h4 #f4e-g4e2 luster    
vitreous to  resinous2 commonly red or  
brown1 sometimes yellow1 white to blue1 
green  or black2 common in mica schist1 
gneiss1 hornblende schist2 also in      
granite1 syenite1 and metamorphosed     
limestone4    ,geyserite--a             
concretionary deposit of silica in the  
opal condition2  formed about geysers2  
white or grayish4                       
,glauconite--green-sand1 a hydrous      
potassium-iron silicate usually  impure1
 amorphous1 or earthy2 dull olive-green 
or blackish1 yellowish1  or grayish     
green2 opaque1 commonly occurs as grains
 or small  aggregations4                
,graphite--plumbago1 black lead2 a form 
of carbon1 usually impure2              

rhombohedral1 but rarely appearing as a 
crystal2 more often as thin  lamin of   
greasy feel2 yields a black adhesive    
powder2 hence its  common use for lead  
pencils2 occurs in granite1 gneiss1 mica
 schist1  crystalline limestone2        
sometimes results from alteration of    
coal by  heat2 occasionally occurs in   
basaltic rocks and meteorites4          
,gypsum--a hydrous calcium sulphate2    
monoclinic2 perfect cleavage into       
smooth polished plates2 occurs in a     
variety of forms1 including fibrous  and
 granular2 ,h4 #a4e-b2 luster pearly and
 shiny2 white1 sometimes gray1          
flesh-red1 yellowish1 and blue2 impure  
varieties dark2 crystallized  varieties 
include selenite1 satinspar1 alabaster1 
etc42 easily  recognized by its softness
 and want of effervescence with acids2  
occurs  in beds2 calcined and ground    
constitutes plaster of ,paris4          
,haynite--a complex sodium-aluminum     
silicate and calcium sulphate2  crystals
 dodecahedrons2 luster vitreous or      

somewhat greasy2 bright  blue1 sky-blue1
 or greenish blue1 or green2 occurs in  
certain igneous  rocks1 commonly        
associated with nephelite and leucite4  
,hematite--ferric oxide1 ,fe,o1         
iron-sesquioxide2 rhombohedral1 more    
commonly columnar1 granular1 botryoidal1
 or stalactitic2 luster  metallic1      
sometimes earthy2 iron-black1 dark      
steel-gray1 red when  earthy2 gives red 
streak or powder2 a leading iron ore1   
#gj percent4  metallic iron when pure2  
the chief source of the red color of    
soils and  rocks generally4             
,hornblende--an amphibole2 name         
sometimes used as a synonym for         
amphibole2 sometimes to designate a     
variety under amphibole 7q4v474         
,hyalite--a variety of silica in the    
opal condition2 clear and  colorless    
like glass1 consisting of globular      
concretions or crusts4                  
,hypersthene--one of the pyroxenes2 a   
ferromagnesian silicate2  orthorhombic2 
,h4 #e-f2 luster somewhat pearly on     

cleavage2 surface often  iridescent2    
dark brownish green1 grayish1 or        
greenish black and brown2  a frequent   
constituent of crystalline rocks4       
,iceland spar--a form of transparent    
calcite 7q4v474                         
,ilmenite--menaccanite2 a titanium iron 
oxide2 rhombohedral2 resembles          
hematite2 luster submetallic2           
iron-black2 powder black or brownish    
red2  occurs frequently in crystalline  
rocks associated with magnetite4        
,iron pyrites--pyrite 7q4v474           
,kaolin--kaolinite2 essentially a       
hydrous aluminum silicate2 usually  in  
clay-like or earthy form2 white or      
grayish white2 often tinged with        
impurities2 commonly arises from        
decomposition of aluminous silicates1   
especially the feldspars2 basis of      
pottery and china4    ,labradorite--a   
plagioclase feldspar2 essentially an    
aluminum-calcium-sodium silicate2       
composition intermediate between that   
of albite and anorthite2 triclinic2 ,h4 

#f2 luster pearly or vitreous1  gray1   
brown1 or greenish2 sometimes colorless 
or white2 frequently  shows play of     
colors2 important constituent of various
 crystalline  rocks1 especially of the  
basic class2 usually associated with a  
pyroxene or amphibole4                  
,lepidolite--lithia mica2 essentially   
like muscovite 7q4v47 except that       
potash is replaced by lithia4           
,leucite--essentially an                
aluminum-potassium silicate1 allied to  
the  feldspars2 ,h4 #e-f2 luster        
vitreous1 white1 ash-gray1 or           
smoke-gray2  occurs in certain volcanic 
rocks1 particularly lavas of ,vesuvius4 
,limonite--brown hematite1 ocher2--a    
hydrous iron oxide2 commonly  earthy2   
also concretionary1 stalactitic1        
botryoidal1 and mamillary1  with fibrous
 structure2 ,h4 #e-e4e2 luster silky1   
sometimes submetallic1  but commonly    
dull and earthy2 brown1 ocherous yellow2
 streak and powder  yellowish brown2    
constitutes ocher1 bog-ore1 ironstone1  

etc42 is the  chief source of the yellow
 color of soils and rocks2 arises from  
the  alteration of other iron ores4     
,magnesite--magnesium carbonate2        
rhombohedral2 white1 yellowish1  grayish
 white to brown2 fibrous1 earthy1 or    
massive2 found in altered  magnesium    
rocks4    ,magnetite--magnetic iron ore2
 iron oxide1 ,fe,o2 octahedral or       
dodecahedral2 strongly magnetic2 ,h4    
#e4e-f4e2 abounds in igneous and        
metamorphic rocks4    ,marcasite--white 
iron pyrites2 iron sulphide2 same       
composition as  pyrite1 which it closely
 resembles2 ,h4 #f-f4e2 luster metallic1
 pale  gray1 bronze1 or yellow2 prone to
 decomposition2 disseminated through    
various rocks1 particularly plastic     
clays containing organic matter4        
,martite--iron sesquioxide2 originally  
magnetite1 which by oxidation  has      
assumed the composition of hematite4    
,mica--the type of an important group of
 rock-forming minerals well  known for  
their perfect cleavage into thin elastic

 lamin2 among the  leading varieties are
 the common potassium mica 7muscovite71 
the sodium  mica 7paragonite71 the      
lithium mica 7lepidolite71 the          
magnesium-iron  mica 7biotite71 the     
magnesium mica 7phlogopite71 and the    
iron-potash  mica 7lepidomelane74       
,menaccanite--ilmenite2 titanium iron   
ore 7q4v474    ,microcline--a triclinic 
feldspar1 closely resembling orthoclase 
in  appearance and having the same      
composition4    ,muscovite--common or   
potash mica2 essentially an             
aluminum-potassium  silicate2 ,h4       
#b-b4e2 monoclinic2 remarkable for its  
basal cleavage2  splits easily into     
exceedingly thin1 flexible1 elastic     
lamin2 luster  vitreous1 more or less   
pearly or silky2 colorless or variously 
tinged  brown1 green1 or violet2 a      
common mineral in crystalline rocks1    
particularly in the granites or         
gneisses4    ,nephelite--nepheline2     
essentially an aluminum-sodium silicate 
with  potash2 allied to the             

soda-feldspars2 hexagonal2 usually in   
thick  prisms2 ,h4 #e4e-f2 luster       
vitreous to greasy1 white or yellowish1 
varying to greenish1 bluish1 and red2   
occurs in volcanic rocks2 the  variety  
elolite characterizes the elolite       
syenite4    ,nosite--nosean2 a complex  
sodium-aluminum silicate and sulphate1  
like  haynite1 but with little calcium2 
common in phonolites4    ,oligoclase--a 
plagioclase feldspar2 essentially an    
aluminum-calcium-sodium silicate which  
may be regarded as a mixture of  albite 
and a small amount of anorthite2        
triclinic2 luster vitreous1  pearly1 or 
waxy2 whitish grading into greenish and 
reddish2 ,h4 #f-g2  common in           
crystalline rocks4    ,orthoclase--a    
potash feldspar2 essentially a          
potassium-aluminum  silicate2 varying by
 the replacement of the potassium by    
sodium and  less frequently by other    
substitutions2 monoclinic2 occurring in 
distinct crystals and also in           
cryptocrystalline forms2 cleavage planes

  perfect with pearly luster on cleavage
 surface2 white1 gray1 and  flesh-red1  
occasionally varying to greenish white  
and bright green2  ,h4 #f-f4e2          
difficultly fusible2 sanidine a glassy  
variety2 felsite  a cryptocrystalline   
form2 a very common mineral1 especially 
in the  granites and gneisses4          
,olivine--chrysolite 7q4v474            
,omphacite--a variety of pyroxene of    
grass-green color and silky to  fibrous 
luster2 allied to diallage4             
,opal--silica with a varying amount of  
water2 differs from quartz in  a lack of
 crystallization and in lower degree of 
hardness2 amorphous1  massive2 sometimes
 reniform1 stalactitic1 or tuberous2    
also earthy2 ,h4  #e4e-f4e2 luster      
vitreous1 inclining to resinous2 white1 
yellow1 red1  brown1 green1 gray1 blue1 
generally pale2 colors arise from       
admixtures2  sometimes play of colors as
 in precious opal4    ,ozocerite--a     
native paraffine1 mineral wax4          
,petroleum--naphtha2 a native mineral   

oil2 a hydrocarbon1 commonly  believed  
to arise from organic matter1 both      
animal and vegetable1 but  held by some 
to be due to deep-seated chemical and   
thermal action4    ,pictotite--a variety
 of spinel1 containing chromium4        
,pisolite--a concretionary variety of   
calcite4    ,picrolite--a variety of    
serpentine4    ,piedmontite--a manganese
 epidote4    ,plagioclase--a general    
term embracing the triclinic feldspars  
whose  two cleavages are oblique to each
 other2 embracing albite1 oligoclase1   
andesine1 labradorite1 and anorthite    
7q4v474    ,plumbago--graphite 7q4v474  
,psilomelane--essentially a hydrous     
manganese oxide occurring  in massive1  
botryoidal1 reniform1 and stalactitic   
forms2 luster  submetallic2 iron-black1 
passing into dark steel-gray2 ,h4 #e-f2 
the  common ore of manganese4           
,pseudomorph--a false form1 i4e41 having
 the form of one mineral and  the       
composition of another2 usually arises  
from the replacement of a  mineral1     

particle by particle1 by a solution of  
another substance1  leaving the original
 form unchanged4    ,pyrite--iron       
pyrites1 fool's gold1 iron sulphide2    
isometric2 commonly  in cubes2 ,h4      
#f-f4e2 luster metallic1 splendent1 or  
glistening2 pale  brass-yellow2 occurs  
widely disseminated throughout a large  
class of  rocks2 usually harder and     
lighter in color than copper pyrites1   
and  deeper in color than marcasite1    
which has the same composition4         
,pyroxene--the type of a large and      
important group of rock-forming         
ferromagnesian minerals2 varies in      
composition and embraces a large  number
 of varieties2 usually a                
magnesium-iron-calcium silicate2        
crystals usually thick and stout1 but   
varying greatly2 sometimes  lamellar and
 fibrous2 ,h4 #e-f2 luster vitreous     
inclining to resinous2  green of various
 shades verging towards light colors1   
occasionally  more often to browns and  
blacks2 among the minerals belonging to 

the  pyroxene group are augite1         
bronzite1 diallage1 diopside1 enstatite1
  hypersthene1 and others4              
,quartz--crystallized silica2           
rhombohedral2 crystals commonly         
six-sided  prisms capped by six-sided   
pyramids2 without cleavage2 ,h4 #g2     
scratches  glass2 usually transparent1  
glassy1 colorless when pure1 shaded by  
impurities to yellow1 red1 brown1 green1
 blue1 and black2 varieties1  amethyst1 
purple1 or violet2 false topaz1 yellow1 
rose-quartz1 smoky1  milky1 cat's eye1  
opalescent2 aventurine1 spangled with   
scales of mica2  chalcedony is a        
cryptocrystalline variety2 carnelian1 a 
red chalcedony2  chrysoprase1 an        
apple-green chalcedony2 prase1 a        
leek-green variety2  agate1 a variegated
 or banded chalcedony2 moss-agate1 a    
chalcedony  containing moss-like or     
dendritic crystallizations of iron or   
manganese  oxide2 onyx1 a chalcedony in 
layers2 sardonyx1 like onyx in          
structure1  but includes layers of sard 

7carnelian72 jasper1 an opaque-colored  
quartz1 usually red or brown2 flint1 an 
opaque impure chalcedony2  chert1 an    
ill-defined term applied to an impure   
flinty rock2 hornstone1  a translucent1 
brittle1 flinty rock4                   
,rutile--titanium oxide2 tetragonal1    
crystals commonly in prisms2 ,h4        
#f-f4e2 luster metallic1 adamantine2    
reddish brown1 passing to red2          
sometimes yellowish1 bluish1 violet1 and
 black2 occurs in crystalline  rocks and
 is a common secondary product in the   
form of microlites4    ,sanidine--a     
glassy variety of orthoclase feldspar4  
,satinspar--a variety of selenite or    
gypsum4    ,selenite--a distinctly      
crystallized transparent form of gypsum4
    ,serpentine--a hydrous magnesium    
silicate2 usually in pseudomorph  forms2
 also fibrous1 granular1                
cryptocrystalline1 and amorphous2 ,h4   
#b4e-d2 luster subresinous to greasy1   
pearly or earthy1 resinous or  wax-like2
 feel1 smooth and somewhat greasy2      

leek-green to blackish  green and siskin
 green verging into brownish and other  
colors2  apparently derived most        
commonly from chrysolite or olivine and 
also  from other magnesian minerals2    
sometimes constitutes the bulk of rock  
masses4    ,siderite--iron carbonate2   
rhombohedral2 ,h4 #c4e-d4e2 luster      
vitreous1  more or less pearly1         
ash-gray1 yellowish or greenish1 also   
brownish2  occurs as extensive iron     
deposits and in crystalline rocks4      
,smaragdite--a form of amphibole or     
hornblende 7q4v474    ,spherosiderite--a
 globular form of siderite4             
,spinel--a magnesium-aluminum oxide2    
crystals1 octahedrons2 red of  various  
shades1 passing into other colors2      
spinel-ruby is a variety4               
,staurolite--a complex hydrous          
iron-magnesium-aluminum silicate2       
orthorhombic2 disposed to cruciform     
shapes2 occurs in schists and  gneisses4
    ,steatite--soapstone1 a variety of  
talc 7q4v472 a hydrous magnesium        

silicate4    ,sulphur--a well-known     
element occurring native in volcanic    
regions2  also formed by the            
decomposition of sulphides1 particularly
 pyrites4    ,talc--a hydrous magnesium 
silicate2 usually in foli2 granular or  
fibrous forms2 also compact2 easy       
cleavage into thin flexible lamina1  but
 not elastic2 feel greasy2 luster pearly
 on cleavage surface2  apple-green to   
silvery white2 ,h4 #a-b2 a secondary    
product from the  alteration of         
magnesian minerals2 distinguished by its
 soft1 soapy  feel1 soapstone being one 
variety2 whitish form is known as       
,french  chalk4                         
,titanite--calcium-titano-silicate2     
monoclinic2 luster adamantine to        
resinous2 brown1 gray1 yellow1 green1   
and black2 ,h4 #e-e4e2 occurs in        
various crystalline rocks4    ,topaz--an
 aluminum silicate1 with part of the    
oxygen replaced by  fluorine2           
orthorhombic2 ,h4 #h2 luster vitreous2  
colorless1 straw-yellow  verging to     

various pale shades1 grayish1 greenish1 
bluish1 and reddish2  distinguished by  
its hardness and infusibility2 occurs in
 crystalline  rock4    ,tremolite--a    
calcium-magnesium amphibole2 a common   
constituent of  certain crystalline     
rocks4    ,viridite--a general term used
 for green products of rock alteration1 
usually hydrous silicates of iron and   
magnesia2 mainly chlorite4    ,wad--bog 
manganese2 a variety of psilomelane     
7q4v474    ,zeolite--a group of minerals
 derived from the alteration of various 
aluminous silicates4                    
,zircon--zirconium silicate2 ,h4 #g4e2  
luster adamantine2 pale yellowish1      
grayish1 yellowish green1 brownish      
yellow1 and reddish brown2  infusible2  
occurs characteristically in square     
prismatic forms2 found  in crystalline  
rocks and granular limestone4           
,,reference ,,list ,,of ,,the ,,more    
,,common ,,rocks4#bjf    ,adobe--a fine 
silty or loamy deposit formed by gentle 
wash from  slopes and subsequent        

lodgment on flats2 especially applied to
 silty  accumulations in the basins and 
on the plains of the western dry region4
    ,agglomerate--an aggregate of       
irregular1 angular1 or subangular blocks
  of varying sizes1 usually of volcanic 
origin1 distinguished from  conglomerate
 in which the constituents are rounded4 
,alluvium--sediment deposited by        
streams4    ,amygdaloid--a vesicular    
igneous rock whose cavities have become 
filled  with minerals2 the fillings are 
called amygdules1 because sometimes     
almond-like in form4    ,andesite--an   
aphanitic igneous rock consisting       
essentially of the  plagioclase feldspar
 andesine 7sometimes oligoclase7 and    
pyroxene 7or  some related              
ferromagnesian mineral72 sometimes      
cellular1 porphyritic1  or even glassy2 
usually rich in feldspar microlites4    
,anorthosite--a rock consisting mainly  
of the feldspar labradorite4            
,aphanite--a rock whose constituents are
 so minute as to be  indistinguishable  

to the naked eye2 rather a condition of 
various rocks  than of any specific     
rock4    ,aqueous rocks--a general term 
applied to rocks deposited through the  
agency of water4    ,arenaceous         
rocks--either those which are mainly    
sand or those in  which sand is a       
notable accessory4    ,argillite--a     
clayey rock2 usually applied to hard    
varieties only4    ,arkose--a sand or   
sandstone formed of disaggregated       
granite or similar  rock in which a     
notable part of the grains are feldspar 
or other  silicate2 sand when undefined1
 is understood to be quartzose4         
,augitite--a rock mainly made up of     
augite4    ,basalt--a dark1 compact     
basic igneous rock consisting of a mass 
of minute crystals sometimes with more  
or less glassy base1 often  containing  
also visible crystals2 composed of      
plagioclase and pyroxene1  with olivine1
 magnetite1 or titaniferous iron as     
common accessories2  a basic lava in    
which the crystallization has taken     

place rapidly2  usually rich in         
crystallites or microlites2 graduates   
into dolerite and  basic andesite4      
,bituminous coal--common soft coal1     
intermediate between lignite and        
anthracite2 contains much bituminous    
matter1 i4e41 hydrocarbons4             
,bowlders--rounded masses of rock1      
particularly those that have been       
shaped by glaciers4    ,breccia--a rock 
composed of angular fragments1          
contrasted with  pudding-stone or       
conglomerate1 in which the fragments are
 rounded4    ,buhrstone--a compact1     
flint-like silicious rock full of small 
cavities1 so named from use as          
millstones4    ,calc-sinter 7calcareous 
tufa7--a loose cellular deposit of      
calcium  carbonate made by springs2     
travertine is the better term1 as tufa  
should be left for volcanic elastics4   
,cannel coal--a very fine-grained       
homogeneous bituminous coal1 giving  off
 much gas and burning with a candle-like
 flame4    ,chalk--a fine-grained soft  

rock composed essentially of calcium    
carbonate derived from minute marine    
organisms4    ,chlorite schist--a       
schistose rock in which chlorite is a   
predominant  mineral2 usually greenish1 
whence the name4    ,clastic            
rock--formed from the dbris of          
broken-down rocks2 the same as          
fragmental or detrital rock4    ,clay--a
 term commonly applied to any soft1     
unctuous1 adhesive deposit1  but in     
strict use confined to material composed
 of aluminum silicate2  many so-called  
clays are chiefly silicious silts or    
loams4    ,clay ironstone--a clayey rock
 heavily charged with iron oxide1       
usually  limonite2 commonly in          
concretionary form4    ,clinkstone--a   
name applied to phonolite because of its
 metallic  clinking sound when struck2  
composed of orthoclase1 with nephelite  
and  one or more of the ferromagnesian  
minerals as accessories4    ,chert--an  
impure flint1 usually of light color1   
occurring abundantly  in concretionary  

form as nodules in certain limestones4  
,coal--a carbonaceous deposit formed    
from the remains of plants by  partial  
decomposition4                          
,concretions--aggregates of rounded     
outlines formed about a nucleus2  the   
material is various3 clay1 iron ore1    
calcite1 silica1 etc4    ,conglomerate  
7pudding-stone7--a rock formed from     
rounded pebbles1  consolidated gravel4  
,coquina--a rock formed almost wholly of
 small and broken shells2  especially   
applied to a shell limestone of         
,florida4    ,dacite                    
7quartz-andesite7--an andesite 7q4v47   
with quartz4    ,diabase--a dolerite    
7q4v47 which has undergone alteration2  
consists  essentially of plagioclase    
feldspar and augite1 with magnetite or  
titaniferous iron as a common accessory2
 one of the greenstones4    ,diatom     
ooze--a soft silicious deposit found on 
the bottom of the deep  sea1 made       
largely or partly of the shells of      
diatoms2 similar deposits  are formed   

from the shells of radiolaria4          
,diorite--an igneous rock usually of    
dark-greenish color1 consisting  of     
plagioclase feldspar and hornblende2    
often speckled from the  commingling of 
light feldspar and dark hornblende4     
,dolerite--a fine-grained igneous rock  
composed of plagioclase feldspar        
7labradorite or anorthite7 and augite   
7or related ferromagnesian  mineral1 as 
enstatite1 olivine1 or biotite71 with   
magnetic or  titaniferous iron as common
 accessories2 crystals usually of medium
  size1 assuming the ophitic structure2 
embraces many of the greenstones2       
graduates into basalt on the one hand   
and gabbro on the other4    ,dolomite--a
 magnesian limestone4    ,drift--in     
common ,american usage1 a mixture of    
clay1 sand1 gravel1 and  bowlders formed
 by glacial agencies4    ,eolian        
rocks--deposits formed by wind1         
embracing especially dunes and  one     
variety of loess4    ,felsite           
7felstone7--a light-colored aphanitic   

rock composed of  feldspar often with   
quartz1 in which the crystallization is 
very  imperfect or obscure1 giving a    
close-grained texture with conchoidal   
fracture and flinty aspect2 certain     
varieties are called petrosilex and     
hlleflinta4    ,flint--a compact dark   
chalcedonic or lithoid form of quartz4  
,freestone--a sandstone of uniform grain
 without special tendency to  split in  
any direction4    ,fulgurites--glassy   
tubes1 produced through fusion by       
lightning in  penetrating sand1 earth1  
or rock4    ,gabbro 7euphotide7--a      
crystalline rock composed of the        
plagioclase  feldspar1 labradorite 7or  
anorthite71 and diallage 7or a related  
ferromagnesian mineral71 with magnetite 
or titaniferous iron as a  common       
accessory4    ,gangue--a term applied to
 the crystalline material in which ores 
are  imbedded4                          
,gannister--essentially a quartz silt or
 pulverized quartz used for  lining iron
 furnaces4    ,garnetite--a rock        

composed largely of garnets4            
,geest--residual earth or clay left by  
the decomposition of rocks1  especially 
limestones4    ,geyserite--the silicious
 sinter deposited about hot springs4    
,globulites--minute spherical bodies    
embraced in volcanic glass4             
,gneiss--a foliated granite1 consisting 
typically of quartz1 feldspar1  and     
mica2 the feldspar typically orthoclase4
    ,granite--a granular crystalline    
aggregate of quartz1 feldspar1 and      
mica2 the feldspar typically orthoclase2
 popularly and properly used  for any   
distinctly granular crystalline rock4   
,granitell--a name used to designate a  
quartz-feldspar rock4    ,granitite--a  
biotite granite with quartz4            
,granulite--a fine-grained granite with 
little or no mica4    ,greensand--a sand
 or sandstone containing a notable      
percentage of  grains of glauconite4    
,greenstone--a comprehensive term used  
to designate igneous and  metamorphic   
crystalline rocks of greenish hue and of

 intricate and  often minute            
crystallization2 they are mostly        
dolerites1 diabases1 and  diorites2 a   
convenient term for field use where the 
constituents cannot  be determined1 and 
for general use when the variety is     
unimportant4    ,greisen--an aggregate  
of quartz and mica1 i4e41 a granite     
without  feldspar4    ,greywacke--a sand
 rock in which the grains are basic     
silicates instead  of quartz4           
,hlleflinta--a compact flint-like       
felsitic rock4    ,hornblendite--a rock 
essentially composed of hornblende4     
,hornstone--a very compact1 silicious   
rock of horn-like texture1 allied  to   
flint2 term also applied to flinty forms
 of felsite4    ,hypogene rocks--those  
formed deep within the earth under the  
influence  of heat and pressure4        
,ironstone--a rock composed largely of  
iron1 usually applied to clayey  rocks  
having a large iron content4            
,infusorial earth 7tripolite7--an earthy
 or silt deposit consisting  chiefly of 

the silicious shells of diatoms4        
,itacolumite--a flexible sandstone whose
 pliability is due to an open           
arrangement of sand grains which are    
held together by scales of mica4        
,jasper--a reddish variety of           
chalcedonic quartz4    ,keratophyre--a  
felsite with a large percentage of soda4
    ,kersantite--a mica dolerite        
consisting chiefly of plagioclase1      
augite1  and biotite4    ,lapilli--small
 fragments of lava ejected from         
volcanoes2 volcanic  cinders4           
,laterite--a red1 porous1 ferruginous   
residual earth of ,india and other      
tropical countries4    ,lava--a molten  
rock1 especially applied to flows upon  
the surface1  whether from vents or from
 fissures2 also applied to the          
solidified  product4    ,lignite 7brown 
coal7--a soft1 brown1 impure coal4      
,limburgite--a compact basic igneous    
rock of the basaltic class1  composed   
essentially of augite and olivine1 with 
magnetite iron and  apatite as common   

accessories4    ,limestone--a rock      
composed primarily of calcium carbonate1
 though  magnesium sometimes replaces a 
part of the calcium4 7,see dolomite and 
marble47    ,liparite 7rhyolite7--an    
acidic igneous rock of aphanitic or     
glassy  texture1 characterized by       
flowage lines and various microscopic   
crystals2 rhyolite is the more common   
,american name4    ,loess--a very fine  
porous silicious silt containing some   
calcareous  material which often        
collects in nodules 7,lss ,kindchen7 or 
in  vertical tubules2 characterized by a
 peculiar competency to stand in        
vertical walls2 held by some to be      
eolian1 by others to be fluvial or      
lacustrine1 and by still others to be   
partly eolian and partly aqueous4       
,marble--typically a granular           
crystalline limestone or dolomite       
produced by metamorphic action2 but the 
term is variously applied to  calcareous
 and even to other rocks that are       
colored ornamentally and  susceptible of

 polish4    ,marl--an earth formed      
largely of calcium carbonate1 usually   
derived  from the disintegration of     
shells2 or the calcareous accretions  of
 plants1 notably the stoneworts2 term   
also sometimes applied to  glauconitic  
and other fertilizing earths4           
,melaphyre--a term of varying usage2    
most commonly applied perhaps to  an    
altered basalt 7q4v471 especially an    
olivine-bearing variety4                
,meta-diabase--a term sometimes used for
 a metamorphic diabase2 in like  manner 
meta is prefixed to dolerite1 syenite1  
etc42 not in general  use4              
,meta-igneous rock--a metamorphosed     
igneous rock4    ,metamorphic rock--a   
rock which has been altered1            
particularly one  which has been        
rendered crystalline1 or recrystallized 
by heat and  pressure4                  
,meta-sedimentary rock--a metamorphosed 
sedimentary rock4    ,microgranite--a   
very fine-grained granite4              
,microlites--incipient crystals found in

 glassy lavas2 usually  needle-shaped1  
or rod-like2 occurring singly and in    
aggregates4    ,millstone--see          
buhrstone4    ,minette 7mica-syenite7--a
 rock consisting essentially of         
orthoclase  and mica1 or a syenite in   
which mica replaces hornblende or       
predominates over it4    ,monzonite--a  
granitic rock composed of orthoclase and
 plagioclase  in nearly equal           
proportions1 with ferromagnesian        
minerals2 a rock  intermediate between  
syenite and diorite4                    
,mudstone--solidified mud or silt1      
shale4    ,nephelinite--a rock composed 
essentially of nepheline and augite1    
with  magnetite and other accessories4  
,nevadite--a variety of rhyolite of     
granitoid aspect due to an  abundance of
 porphyritic crystals4                  
,nodules--concretionary aggregations of 
rounded form4    ,norite--a fine-grained
 rock consisting of plagioclase and     
hypersthene4    ,novaculite 7honestone1 
oilstone7--a very fine-grained1 hard    

sandstone  or silt-stone1 used for      
whetstones4    ,obsidian--a typical form
 of volcanic glass usually of the acidic
 class4    ,onyx--a variety of          
chalcedonic quartz having colored bands 
alternating  with white2 the 8,mexican  
onyx0 is a crystalline calcium          
carbonate1  variegated with delicate    
colors due to iron and manganese4       
,oolite--a limestone or dolomite        
composed of small concretions           
resembling the roe of fish4    ,ooze--an
 exceedingly soft watery deposit of the 
deep sea2  characterized usually by     
microscopic shells from which it is     
mainly  derived1 as diatom ooze1        
globigerina ooze1 etc4    ,orthophyre   
7orthoclase porphyry7--a rock consisting
 of crystals of  orthoclase in an       
aphanitic base4    ,peastone            
7pisolite7--a very coarse variety of    
oolite4    ,peat--the dark brown or     
black residuum arising from the partial 
decomposition of mosses and vegetable   
tissue in marshes and wet places4       

,pegmatite--a term of ill-defined usage 
applied to rocks whose grain  varies    
from coarser to finer1 and often takes  
on peculiar aspects due  to the         
simultaneous crystallization and mutual 
intergrowths of the  crystals2 graphic  
granite is a distinct type of pegmatite 
in which  quartz and orthoclase crystals
 grew together along parallel axes so   
that cross-sections give figures        
resembling certain ,semitic letters     
7,fig4 #cde74    ,peridotite--a very    
basic igneous rock composed chiefly of  
olivine with  augite or related         
ferromagnesian minerals1 with magnetite 
and chromite  as accessories4           
,pelites--a general term embracing clay 
rocks4    ,perlite 7pearlstone7--a form 
of glassy lava made up in part of small 
spheroids formed of concentric layers   
which have a lustrous appearance  like  
pearls4    ,petrosilex--an old name for 
felsite or hlleflinta4    ,phonolite    
7nephelite-trachyte1 clinkstone7--a     
compact resonant igneous  rock formed of

 sanidine and nephelite with            
accessories4    ,phyllite 7argillite7--a
 variety of indurated1 partly           
metamorphosed1  clay silt in which      
finely disseminated micaceous scales are
 abundant  and lustrous2 intermediate   
between typical clay slate and          
mica-schist4    ,pitchstone--a dark     
vitreous1 acid1 igneous rock of less    
perfect glassy  texture than obsidian   
and more resinous and pitch-like4       
,plutonic rocks--igneous rocks formed   
deep within the earth under the         
influence of high heat and pressure2    
hypogene rocks2 distinguished from      
eruptive rocks formed at the surface4   
,porphyrite--a term sometimes used for  
an altered form of andesite1  usually   
porphyritic in structure4               
,porphyry--a rock consisting of distinct
 crystals embedded in an  aphanitic     
ground-mass4    ,propylite--an altered  
form of andesite and similar igneous    
rocks4    ,protogine--a hydrated        
micaceous or chloritic variety of       

granite or  gneiss4    ,pumice--a glassy
 form of lava rendered very vesicular   
through  inflation by steam4            
,pyroclastic rocks--fragmental or       
clastic rocks produced through  igneous 
agencies1 embracing volcanic ashes1     
tuffs1 agglomerates1 etc4               
,pyroxenite--an igneous rock consisting 
essentially of pyroxene4                
,quartzite--a rock consisting           
essentially of quartz1 usually formed   
from quartzose sandstone by cementation 
or metamorphic action4    ,regolith--a  
name recently suggested by ,merrill to  
embrace the  earthy mantle that covers  
indurated rocks1 chiefly residuary      
earths2  mantle-rock4    ,rhyolite--an  
aphanitic or glassy igneous rock showing
 flowage lines1  usually applied only to
 the acidic varieties4                  
,sandstone--indurated sand usually      
composed of grains of quartz1 but  not  
necessarily so2 sometimes formed of     
calcareous grains or of grains  of the  
various silicates4    ,schist--a        

crystalline rock having a foliated or   
parallel structure1  splitting easily   
into slabs or flakes1 less uniform than 
slate2 they  are mainly composed of the 
silicate minerals4    ,scori--light1    
cellular fragments of volcanic rock1    
coarser than  pumice2 cinders4          
,septaria--concretions the interior of  
which have parted1 and the  gaping      
cracks become filled with calcite or    
other mineral deposited  from solution  
7,figs4 #cge-gg74    ,serpentine--a rock
 consisting largely of serpentine2      
derived in most  cases by alteration    
from magnesian silicate rocks4          
,shale--a more or less laminated rock1  
consisting of indurated muds1  silts1 or
 clays4    ,slate--an argillaceous rock 
which is finely laminated and fissile1  
either due to very uniform sedimentation
 or 7more properly7 to  compression at  
right angles to the cleavage planes2    
e4g41 common  roofing-slate 7,fig4      
#cfb74    ,soapstone 7steatite7--a soft 
unctuous rock1 composed mainly of talc4 

,stalactites--pendant icicle-like forms 
of calcium carbonate deposited  from    
dripping water4    ,stalagmite--the     
complement of stalactites formed by     
calcareous waters  dripping upon the    
floors of caverns4    ,steatite--see    
soapstone4    ,syenite--a granitoid rock
 composed of orthoclase and hornblende1 
or other ferromagnesian mineral2 the    
name was formerly applied to a          
granitoid aggregate of quartz1 feldspar1
 and hornblende4    ,tachylite          
7hyalomelane1 basaltic glass7--a black  
glass of basaltic  nature corresponding 
to the acidic glasses1 obsidian and     
pitchstone4    ,till 7bowlder clay7--a  
stony or bowldery clay or rock rubbish  
formed  by glaciers4    ,trachyte--a    
name formerly applied to a rock         
possessing a peculiar  roughness due to 
its cellular structure2 but at present  
mainly confined  to a compact1 usually  
porphyritic igneous rock1 consisting    
mainly of  sanidine associated with     
varying amounts of triclinic feldspar1  

augite1  hornblende1 and biotite4       
,trap--a general term for igneous rocks 
of the darker basaltic types4           
,travertine--a limestone deposited from 
calcareous waters1 chiefly  springs2    
usually soft and cellular1 and hence    
also called calcareous  tufa1 calc      
sinter4    ,tuff 7tufa7--a term         
including certain porous granular or    
cellular  rocks of diverse origins2 the 
volcanic tuffs embrace the finer kinds  
of pyroclastic detritus1 as ashes1      
cinders1 etc42 the calcareous tufa      
embrace the granular and cellular       
deposits of springs2 the better usage   
limits the term to volcanic clastics4   
,water-lime--an impure argillaceous     
limestone possessing hydraulic          
properties4    ,wacke--a dark earthy or 
granular deposit formed from basic tuffs
 or  from the disaggregation of basaltic
 and similar rocks2 a term which may    
well come into more general use to      
distinguish the silicate sands that     
arise from the disaggregation1 but only 

partial decomposition1 of basic  rocks1 
as arkose does1 the like products of the
 acidic or granitoid  rocks1 and as     
sandstone does1 the granular products of
 complete  chemical decomposition4      
,,ore-,,deposits4#bjg    ,ore-deposits  
are but a special phase of the          
rock-forming processes  already         
discussed4 ,they have peculiar interest 
because of their  industrial value4 ,an 
ore is simply a rock that contains a    
metal that  can be profitably extracted1
 though for convenience the term is used
  more broadly to include unworkable    
lean ores and ore material4 ,the  metal 
need not preponderate or form any fixed 
percentage of the whole1  for the       
criterion is solely economic and not    
petrologic4 ,a gold ore  rarely contains
 more than a very small fraction of one 
percent4 of the  precious metal1 while  
high-grade iron ore yields sixty-odd    
percent4  of the metal4 ,in iron ore1   
the metallic oxide or carbonate makes up
  nearly the whole rock2 in gold ore1   

the metal is the merest incidental      
constituent1 from the petrologic point  
of view4    ,concentration4--,the       
essential fact in the formation of ores 
is the  unusual concentration of the    
metal4 ,there are vast quantities of    
all the metals disseminated through the 
rock substance of the earth  and even   
throughout the hydrosphere1 but they do 
not constitute  ores because they have  
no economic value4 ,they become ores    
when  concentrated in accessible places 
to a workable richness4 ,the degree  of 
concentration required is measured by   
the value of the metal4 ,the  essential 
elements for consideration are1         
therefore1 7#a7 the original            
distribution of the metallic materials  
through the rocks1 7#b7 their  solution 
by circulating waters 7or1 rarely1 by   
other means71 7#c7  their transportation
 in solution to the place of deposit1   
7#d7 their  precipitation in            
concentrated form1 and 7#e7 perhaps     
their further  concentration and        

purification by subsequent processes4   
,exceptional and doubtful cases4--,there
 are a few cases where  ore-deposits are
 made by volcanic fumes or vapors1 but  
these may  be neglected here4 ,formerly1
 ores were often attributed to vapors   
supposed to arise from the hot interior1
 but this mode of origin seems          
incompatible with physical conditions4  
,ores have been attributed to  water    
originally contained as steam in lavas1 
and to waters escaping  from the        
interior of the earth1 these waters     
being supposed to be  especially        
mineralized4 ,direct evidence on this   
point is obviously  beyond reach4       
,segregation in the molten state is     
recognized as a source  of ores1 but its
 function is probably confined chiefly  
to partial  enrichment as stated below4 
,there are other occasional methods1 but
 the  chief process of concentration1   
immeasurably surpassing all others1     
consists in the leaching out of ore     
materials disseminated through the      

country rock and their redeposition in  
segregated forms1 as an incident  of the
 recognized system of water circulation4
    ,original distribution4--,the       
original distribution of ore material   
through the primitive rocks is beyond   
the ken of present science1  for even   
the nature of the true primitive rocks  
is unknown4 ,for  present purposes it is
 sufficient to regard all rocks         
concerned in  ore-deposition as either  
igneous or sedimentary1 and to inquire1 
as  a first step1 how far ordinary      
igneous and sedimentary processes       
contribute to the segregation of ore    
material1 leaving for a second  stage of
 inquiry the subsequent processes of    
concentration4    ,magmatic             
segregation4--,in a few instances       
workable masses of ore seem  to have    
arisen from lavas by direct segregation 
in the molten state1  without the aid of
 subsequent concentration by water      
action1 on which  most ores are         
dependent4 ,it is not improbable that   

the segregation  of metallic iron and   
nickel1 and perhaps other metals1 in the
 deeper  parts of the earth may be a    
prevalent process1 giving rise to masses
  like the native iron found in basalt  
in ,greenland4 ,this iron closely       
resembles the nickel-irons of           
meteorites1 which may be illustrations  
of similar action in small planetary    
bodies that have been disrupted4        
,metallic masses so segregated          
presumably gravitate toward the         
planetary  center and hence1 whatever   
their inherent interest1 have little    
relation to a subject whose basal       
criterion is economic4 ,it is not at    
all improbable1 however1 that in the    
magmatic differentiation of the  lavas  
that come to the surface1 there is some 
metallic segregation that  may make the 
enriched parts effective ground for the 
concentrating  processes of water       
circulation1 and so determine the       
location of  ore-deposits4 ,igneous     
rocks are not equally the seats of      

ore-deposits1  even when the circulatory
 conditions seem to be equally          
favorable4  ,these conditions may not   
really be equally favorable1 but there  
is  good ground to believe that some    
igneous masses constitute a richer      
field for concentration than others4 ,no
 definite rule1 however1  for           
distinguishing rich varieties of rock   
from lean ones has been  determined4    
,the basic igneous rocks are1 on the    
whole1 perhaps somewhat  richer in ores 
than the acidic class1 but there is no  
established law4  ,many acidic rocks    
bear more and richer ores than many     
basic ones4 ,the  view here entertained 
is that both classes are subject to     
regional  enrichment through conditions 
connected with their origin1 as yet     
little known4    ,marine segregation and
 dispersion4--,in the formation of the  
sedimentary rocks from the primitive and
 igneous rocks there was  notable       
metallic concentration in some cases1   
and even more notable  depletion in     

others4 ,the ground-waters of the land1 
after their  subterranean circuits1     
carried into the water-basins various   
metallic  substances in solution4 ,these
 were either precipitated early in the  
marine or lacustrine drift of the       
waters1 or became diffused throughout   
the oceanic body4 ,in the main they     
appear to have been widely diffused1    
and either to have remained long in     
solution1 or to have been very  sparsely
 deposited through the marine or        
lacustrine sediments4 ,as a  rule1 these
 sediments seem to contain less of      
valuable ore material  than igneous     
rocks1 and this is rational1 for1 as we 
shall see1 the  ground-water circulation
 of the land tends to concentrate and   
hold back  a part of the metallic       
content of the land rocks so that only a
 residue  reaches the sea4 ,but there   
are important exceptions to this general
  rule of sedimentary leanness4    ,the 
iron-ore beds of ,clinton age ranging   
from ,new ,york to ,alabama1 and        

appearing also in ,wisconsin and ,nova  
,scotia1 form a stratum in the  midst of
 the ordinary sediments1 and contain    
marine fossils4 ,the great  ore beds of 
,lake ,superior were originally of      
similar type1 and so are  most other    
important iron deposits4 ,it cannot be  
said1 in most cases1  that these iron   
deposits are marine as distinguished    
from lacustrine or  lodgment deposits1  
but they are at least sedimentary4 ,the 
ferruginous  material was originally    
disseminated widely through antecedent  
land  rocks1 but was concentrated in the
 course of the sedimentary processes4   
,limestone appears to have been         
sometimes enriched locally in lead and  
zinc1 and more rarely in copper1 in the 
course of its sedimentation4  ,the lead 
and zinc regions of the ,mississippi    
basin have been regarded  as dependent  
on such regional enrichment as a primary
 condition4 ,this  localized enrichment 
has been attributed to solutions brought
 into the  sea from neighboring         

metal-bearing lands and precipitated by 
organic  action in the sea-water1#bjh   
this organic action being more effective
  in some areas than in others because  
of the unequal distribution of  life and
 the concentration of its decaying      
products4 ,it is assumed  that such     
precipitates were at first too diffuse  
to be of value1 and  further            
concentration was required to bring them
 together into workable  deposits2 but  
the further processes appear to have    
been effective only  where the          
preliminary enrichment had taken place4 
,at any rate1 the  workable deposits are
 singularly localized1 while the        
concentrative  processes are very       
general4    ,metallic material is       
sometimes partially concentrated in     
sandstones  and shales in the process of
 sedimentation1 though more rarely4 ,the
  copper-bearing shale 7,kupferschiefer7
 of the ,zechstein group in  ,germany1  
so extensively worked along the flanks  
of the ,harz ,mountains1  is a striking 

example4    ,it is in every way         
reasonable to suppose that land-waters1 
on reaching  the margins of the         
water-basins1 must occasionally find    
conditions  favorable for the           
precipitation of their metallic         
contents1 and that  the ratio of these  
precipitates to other material might be 
relatively  high in the more favorable  
situations1 and that this enrichment of 
the  country rock may be a condition    
precedent to a sufficient subsequent    
concentration to yield workable         
accumulations4    ,it is1 therefore1    
inferred that while the processes of    
sedimentation  tended on the whole to   
leanness1 they gave rise to 7#a7 some   
very  important ore-deposits1 notably   
the chief iron ores1 the greatest of    
all ores in quantity and in real        
industrial value1 and 7#b7 a diffuse    
enrichment of certain other areas which 
made them productive under  subsequent  
concentrative processes1 while the      
sedimentary formations in  general were 

left barren4    ,origin of ore          
regions4--,from these considerations it 
appears that for  the fundamental       
explanation of 8mining regions0 we must 
look mainly 7#a7  to magmatic           
differentiation1 so far as the country  
rock is igneous1 and  7#b7 to           
sedimentary enrichment1 so far as the   
rock is secondary4 ,the  determining    
conditions in both cases are obscure and
 unpredictable1 but  the recognition of 
such regions1 and of the function of    
preliminary  diffuse regional           
enrichment1 contributes to a            
comprehensive view of  the complex      
processes of ore concentration4 ,the    
subsequent processes  consist in the    
further concentration of the ore        
material into sheets1  lodes1 veins1 and
 similar aggregations by ground-water   
circulation1  or else in the            
purification of the ores by the removal 
of useless or  deleterious material1 or 
in both combined4    ,surface residual  
concentration4--,the simplest of all    

modes of  concentration takes place in  
the formation of mantle-rock4 ,an       
insoluble  or slightly soluble metallic 
substance sparsely distributed through a
  rock may be concentrated to working   
value by the decay and removal of  the  
main rock material1 leaving the metallic
 material in the residuary  mantle4 ,the
 tin ores of the ,malay peninsula#bji   
are especially good  examples4 ,the     
crystals of tin oxide were originally   
scattered sparsely  through granite and 
limestone1 but by their decay and       
partial removal  it has accumulated in  
workable quantities4 ,certain gold      
fields and  certain iron ores have      
acquired higher values in the same way4 
,such  residuary material may be further
 concentrated by wash into gulches  or  
alluvial flats1 in the course of which  
the lighter parts of the  mantle-rock   
are largely carried away1 and the       
heavier1 including the  metal or its    
compounds1 are mainly left behind4 ,gold
 placers are the  best example4 ,the    

mining of placers by hydraulic processes
 is but a  further extension of the     
natural process of concentration4       
,such concentrates in past ages have in 
some cases been buried by later         
deposits1 and hence certain ancient     
sandstones1 conglomerates1 and          
mantle-rocks have become ore-bearing    
horizons4 ,the ,rand of ,south ,africa  
appears to be of this type4             
,purification and concentration4--,a    
somewhat different mode of              
concentration and purification has      
affected certain of the great iron      
deposits4 ,as already explained1 the    
iron compounds were originally          
dissolved from the iron-bearing         
constituents of the primitive or of     
igneous rocks1 or their derivatives1 and
 were deposited in beds as  chemical    
stratiform deposits4 ,in some cases they
 were sufficiently  pure1 as first      
precipitated1 to be worked profitably1  
but in most cases  they were seriously  
affected by undesirable mineral         

associates4 ,when1  however1 such impure
 deposits are subjected for long periods
 to the  percolation of waters from the 
surface under favorable conditions1  the
 impurities are often dissolved and the 
ores concentrated4 ,the  great ,bessemer
 ore-deposits of ,lake ,superior are    
examples4 ,originally  impure carbonates
 or silicates1 they have been converted 
into rich and  phenomenally pure ferric 
oxides along certain lines of           
ground-water  circulation1 and in       
certain areas of free leaching4 ,van    
,hise has shown  the definite relation  
between the water circulation and the   
production  of the high-grade ores4#baj 
,vast quantities of unconcentrated lean 
ores lie in the tracts not thus purified
 and enriched by circulating  waters4   
,this does not appear to be simply      
residual concentration4 ,the  waters    
seem to have added ferric oxide brought 
from above1 while they  carried away the
 8impurities10 silica1 carbon dioxide1  
etc4 ,perhaps  this is an instance of   

mass action in which the ore present    
aided in  causing additions to itself4  
,concentration by solution and          
reprecipitation4--,by a process almost  
the opposite of residual concentration1 
ore material is often  leached out of   
the surface-rock by water circulating   
slowly through  its pores1 cleavage     
planes1 and minute crevices1 and is     
carried on  with the circulation until  
it reaches some substance which causes a
  reaction that precipitates the ore    
material4 ,this substance may be a      
constituent of some rock which the      
circulating water encounters1 such  as  
organic matter4 ,more commonly1 the     
precipitation seems to be due  to the   
mingling of waters charged with         
different mineral substances1  the      
mingling inducing reaction and the      
precipitation of the ore4               
,precipitation1 however1 does not       
necessarily follow such commingling4    
,the junctions of underground waterways 
are sometimes characterized by          

barrenness instead of richness4 ,in the 
expressive phraseology of the  miners1 a
 tributary current sometimes 8makes0 and
 sometimes 8cuts out40  ,in chemical    
phrase1 when the mingling waters reduce 
the solubility  of the appropriate      
substance sufficiently1 an ore-deposit  
is formed2  when they increase its      
solubility1 they promote barrenness4    
,changes of  pressure and temperature   
may enter into the process1 and mass    
action  may lend its aid when once a    
deposit is started4    ,more concretely 
stated1 the general process of          
underground ore  formation appears to be
 this3 the permeating waters dissolve   
the ore  material disseminated through  
the rock and carry it thence into the   
main channels of circulation1 usually   
the fissures1 broken tracts1  porous    
belts1 or cavernous spaces4 ,if         
precipitating conditions are  found     
there1 deposition takes place4 ,the     
precipitating conditions  may be merely 
changes of physical state1 such as      

cooling or relief  of pressure1 but     
probably much more generally they       
consist in the  commingling and mutual  
reaction of waters that have pursued    
different  courses and become           
differently mineralized1 as implied     
above4 ,in these  cases the             
metal-bearing current may be scarcely   
more important than the  precipitating  
current4    ,since the solvent action is
 a condition precedent to deposition1   
the  location of the greatest solvent   
action first invites attention4 ,at     
present it must be treated in general   
terms1 for it is not known what         
solutions must be formed beyond the fact
 that they must include the  ore        
material4 ,probably they must include   
much besides4 ,furthermore1  it is not  
known that deep-seated rocks carry more 
ore material than  similar rocks at or  
near the surface or at any other        
horizon4 ,fantastic  conceptions of     
deep-seated metallic richness are to be 
shunned as quite  beyond practical      

consideration4 ,the water circulation is
 probably very  slight below a depth of 
two or three miles at most1 and above   
that  depth there is little ground to   
suppose that the rocks of one horizon   
are inherently more metalliferous than  
others of their kind4 ,there is  no     
assignable reason why the igneous rocks 
at the surface are not as  rich in ore  
material as the igneous rocks two or    
three miles below1  since all are       
probably eruptive and of much the same  
nature on the  whole1 being in many     
cases parts of the same eruptions4      
,location of greatest solvent           
action4--,solvent action is probably    
most  intense where the temperature and 
pressure are highest1 that is1 in  the  
deeper reaches of water circulation2 but
 the amount of water  passing in and out
 of the deeper zone is but a small      
fraction of that  which courses through 
the upper horizons1 and the total       
solvent action  is quite certainly much 
greater in the upper zone than in the   

lower4 ,at  the same time the solutions 
in the upper zone are quite certainly   
more  dilute than those below4 ,the     
horizon of greatest solution lies       
between  the surface and a level        
slightly below the ground-water surface1
 or1 in  other words1 in the zone where 
atmosphere and hydrosphere coperate4    
,surface-waters are charged with        
atmospheric and organic acids and  other
 solvents1 and their general effect upon
 the rocks is markedly  solvent down to 
or often below the permanent            
water-level4 ,in this zone              
concentration by residual accumulation  
may take place1 as already  noted1 if   
the metallic compounds resist solution2 
otherwise this zone  is depleted of its 
ore material by solution1 and           
preparation is made  for deposition     
elsewhere4    ,solution also continues  
to take place varyingly as the water    
descends  below this zone of dominant   
solution1 and extends probably to the   
full  depth of water circulation1 but in

 the deeper circuit1 precipitation  also
 takes place and the action becomes     
complex4 ,with the waters  taking up and
 throwing down material at the same     
time1 it is difficult  to estimate the  
balance of results4    ,when waters that
 have been mineralized near the surface 
descend1 they  often take on a          
precipitating phase at no great depth   
below the upper  level of the           
ground-water2 thus sulphides that were  
oxidized and  dissolved near the surface
 are reprecipitated1 often at horizons  
not  greatly below the permanent        
water-level4 ,waters that dissolve      
metallic  substances in the upper levels
 often become charged with sulphuretted 
hydrogen and other precipitants within a
 few scores or a few hundreds  of feet  
of the surface1 as deep wells abundantly
 prove4 ,the freshness  of surface which
 metallic sulphides often exhibit at    
these levels is  fair ground for        
inferring recency of deposition and     
absence of solvent  action4 ,actual     

demonstrations of depositions in        
progress are not  wanting4              
,short-course action4--,the             
concentration which thus takes place by 
solution in the upper zone1 followed    
closely by reprecipitation within  a few
 score or a few hundred feet1 may well  
be termed the short-course  mode of ore 
concentration4 ,it finds its most       
important illustration in  what is      
commonly known as the 8secondary        
enrichment0 of ore-deposits4  ,the ores 
in the outcropping edge of the vein or  
lode are dissolved  by the              
surface-waters1 carried a short distance
 down the ore tract  and redeposited1   
causing enrichment at that point4 ,this 
is only a  special case of what takes   
place generally at this horizon4 ,it is 
effective in this case because it has a 
previous partial concentration  to work 
upon4 ,secondary enrichments of this    
kind often contain most  or all the     
workable values of the ore tract4 ,if   
instead of a previous  concentration in 

a vein1 lode1 or similar ore tract1     
there had been  partial concentration in
 the country rock by sedimentation1 as  
in the  case of iron-ore beds and       
perhaps lead-1 zinc-1 and               
copper-impregnated  sediments1 the      
short-course method may give working    
values not before  possessed4 ,in some  
of the more obscure cases of previous   
partial  concentration in the           
crystalline and other rocks1 it is      
probably this  short-course action that 
brings the concentration up to working  
value4  ,it is probably effective also  
in concentrating the metallic contents  
of certain igneous rocks that were rich 
in metallic material when  extruded4    
,how far this is true has been1 and     
still remains1 a mooted  question4      
,long-course action4--,after the        
surface-waters have once passed through 
a cycle of dissolving and precipitating 
action1 as they are apt to  do within   
the first few hundred feet of their     
courses below the  water-level1 they are

 liable to pass through a succession of 
dissolving  and depositing stages1 each 
reaction resulting in a state that makes
  a new reaction possible4 ,this is     
especially true if the waters pursue    
deep courses4 ,strictly speaking1 the   
precipitations usually concern  only a  
part of the substances dissolved4 ,new  
substances are often  taken up in the   
very act of throwing down those already 
held1 and the  way thus prepared for    
further changes4 ,if the water pursues a
 deep  and devious course1 it may       
receive additions by solution and suffer
  losses by precipitation at many points
 in its course1 both descending  and    
ascending4 ,the changes are very        
complex1 and in the case of a deep  or  
long circuit where various rocks1       
pressures1 and temperatures are         
encountered1 the history becomes one    
long succession of complexities1  the   
full nature of which is not yet         
revealed4    ,in the deeper circuits1   
each individual current usually takes on

 a  descending1 a lateral1 and ascending
 phase1 the three being necessary  to   
complete a circuit4 ,the chemical       
conditions of the waters in the  three  
phases are probably not sharply         
distinguished from one another1  and    
hence there seems to be no defined      
horizon of concentration  comparable to 
that near the water-level already       
described4 ,the chief  distinctions in  
the deeper regions relate to pressure1  
temperature1  length or depth of        
penetration1 and duration of contact4   
,it seems safe  to assume1 as a general 
truth1 that1 other things being equal1  
the  solutions become more complex and  
more nearly reach general saturation    
the farther and the deeper the waters   
penetrate4    ,it has long been a mooted
 question whether ore-deposits are due  
chiefly  to descending1 to lateral1 or  
to ascending currents4 ,the question in 
its usual form is too undiscriminating  
for advantageous discussion1 but  if the
 ore-deposits due to surface or         

short-course concentrations and         
reconcentrations be set aside1 as in    
some sense a separate class1 the        
relative functions of the descending1   
the lateral1 and the ascending  portions
 of the deeper circulations become a    
measurably definite  question4 ,two     
great working factors enter into the    
comparison3 7#a7 much  greater          
circulation in the upper zone1 where    
lateral movement most  prevails2 7#b7   
much greater heat and pressure in the   
lower zone1 where  the circulation must 
be chiefly vertical4    ,heat and       
pressure in general favor solution1 and 
hence so far as this  factor goes1      
descending water is likely to be        
increasing its mineral  content1 rather 
than diminishing it by deposition4 ,but 
this is  only general2 particular       
elements of the solution may be         
deposited4  ,in ascending1 as the same  
water must later1 it is predisposed to  
deposition from loss of solvent power   
through reduction of pressure  and      

temperature4 ,the theoretical balance is
 here clearly in favor  of preponderant 
deposition by the ascending portion of  
the current4  ,so far as precipitation  
is dependent on the mingling of         
differently  mineralized waters1        
descending and ascending currents seem  
to be  situated much alike1 in general1 
for both are subject to accessions and  
mutual unions4    ,the amount of water  
that circulates in the deeper horizons  
is much less  than that nearer the      
surface4 ,allowing a few hundred1 or at 
most one  or two thousand feet for the  
special short-circuit zone next below   
the  water-level 7it is known to reach  
#ajjj to #aejj feet in some cases71  the
 water circulating through the next     
#ajjj or #bjjj feet is probably  several
 times greater than all that circulates 
at greater depths1 and  this greater    
circulation above doubtless offsets1 in 
greater or less  measure1 the           
intensified action of the deeper        
circulation4 ,much of the  upper and    

more rapid circulation is lateral1 being
 actuated by the  sloping surface of the
 ground-water1 which in turn is         
determined by  topography1              
precipitation1 and other surface        
conditions4 ,theoretical                
considerations1 therefore1 favor the    
view that lateral flow is  an important 
factor in the concentration of ore      
material4 ,but as  descending and       
lateral currents almost inevitably meet 
and mingle  with ascending currents1 it 
is difficult to distinguish1 in the     
ore-deposits1 the special functions of  
each phase of action4 ,it is even  more 
difficult to determine whether the      
different phases are not alike          
essential to the mutual reactions on    
which the deposition depends4  ,it may  
be as necessary to have a precipitant as
 to have a metallic  constituent in     
solution to be precipitated1 and what is
 more1 this  precipitating agency may be
 a substance of no economic value in    
itself  and of no obvious relations to  

the substances that form the ores4 ,if  
the deposition is due solely to a       
physical state1 as relief of pressure   
or lowering of temperature1 these       
considerations do not hold4             
,summary4--,the general results are     
probably these3 ,in the deeper          
circuits1 more ore material is brought  
upward and deposited than is  carried   
downward and deposited1 so that metallic
 values are shifted  toward accessible  
horizons4 ,in the lateral currents1 more
 metallic  values are shifted toward the
 trunk-lines of circulation--the great  
crevices and other waterways--than are  
carried from these into the rock  and   
distributed1 and lateral segregation    
results4 ,at the same time  the         
atmospheric waters acting at or near the
 surface concentrate ore  values        
downwards4 ,the sum total of these      
processes is to promote the  development
 of the higher ore values in accessible 
horizons1 and along  the main lines of  
circulation4    ,the influence of       

contacts4--,as ore-deposits depend on a 
dissolving  state followed by a         
depositing state of the waters1 and     
perhaps on a  complex succession of     
these alterations1 it is obvious that   
conditions  which favor changes of state
 and the commingling of different kinds 
of water are apt to be favorable to ore 
production4 ,at any rate it is  observed
 that many important ore-deposits occur 
at the contact between  formations of   
different character4 ,the contact of    
igneous rock with  limestone is a rather
 notable instance4 ,it is not to be     
inferred that  such contacts are        
generally accompanied by workable       
ore-deposits1 but  merely that a notable
 proportion of workable ore-deposits    
occur at such  junctions4 ,it is        
rational to suppose that where the      
chemical nature of  the two formations  
is in contrast1 the waters that         
percolate through  the one are likely to
 be mineralized very differently from   
those that  course through the other1   

and hence that on mingling at the       
contact1  reactions are specially liable
 to take place1 and that when a valuable
  metallic substance is present it is   
liable to be involved and by chance  to 
suffer precipitation4 ,reactions are the
 more probable because the  contact is  
likely to be a plane of crustal         
movement1 and hence more or  less open  
and accompanied by fractures1 zones of  
crushed rock and other  conditions that 
facilitate circulation and offer        
suitable places for  ore formation4     
,the effect of igneous intrusions4--,a  
special case of much importance  arises 
when lavas are intruded into sediments  
that have previously been  partially    
enriched in the ways above described4   
,the igneous intrusion  not only        
introduces new contact zones1 and more  
or less fracturing1  but it brings into 
play hot waters with their intensified  
solvent  work1 their more active        
circulation1 and the reaction between   
waters  of different temperatures4 ,the 

special efficiency of these agencies is 
believed to be the determining factor in
 many cases4    ,the influence of rock  
walls4--,the rock walls themselves are  
thought  sometimes to be a factor in    
ore-precipitating reactions4 ,by mass   
action1 they may withdraw a constituent 
of the solution and destroy  its        
equilibrium in such a way as to cause   
the precipitation of the  metallic      
constituent4 ,once deposited on the     
walls ores aid1 by mass  action1 the    
further accretion of ores4    ,the      
special forms which ores assume in      
deposition1 as beds1 veins1  lodes1     
stockworks1 disseminations1             
segregations1 etc41 are chiefly         
incidental to the local situation in    
which the essential chemical or         
physical change takes place4            
,,chapter ,,viii4                       
,,structural 7,,geotectonic7 ,,geology4 
,the structural phases which rocks      
assume4--,in the previous chapters1  the
 general method by which rocks are      

formed has been set forth1 and  many of 
their structural features have been     
touched upon incidentally4  ,it remains 
to assemble the structural features     
already mentioned1 and  to consider     
certain additional structural phases    
which rocks assume4                     
,,structural ,,features ,,of            
,,sedimentary ,,rocks4    ,in the       
deposition of sediments in the sea1 or  
in other bodies of  standing water1 the 
coarser portion of the material is      
usually  deposited in the shallow water 
near the shore where the wave-action  is
 strongest1 and the less coarse of      
various grades is deposited at  greater 
and greater distances from the land1    
while only extremely  fine silt is      
usually carried out to abysmal depths   
7see p4 #chj74 ,to  this general law of 
distribution there are important        
exceptions4 ,fine  sediments are        
sometimes deposited near the shore1 and 
where currents1  tidal agitation1 or    
floating ice are effective1 coarse      

deposits are  occasionally carried far  
out from the shore4                     
,stratification4--,sedimentary rocks are
 usually arranged in more  or less      
distinct layers2 that is1 they are      
stratified4 ,the  stratification        
consists primarily in the superposition 
of layers of  different constitution or 
different compactness on one another4   
,layers  of like constitution or        
compactness are often separated by films
 of  different material which cause the 
partings between them4 ,the bedded      
arrangement of stratified rocks is due  
to various causes1 but primarily  to the
 varying agitation of the waters in     
which the sediment was laid  down4      
,where the depositing waters are        
agitated to the bottom1 coarse  sediment
 is likely to be deposited4 ,where the  
waters are quiet at the  bottom1 fine   
sediment is the rule4 ,since the        
agitation of the waters is  subject to  
frequent change1 it follows that coarser
 material succeeds  finer1 and finer    

coarser1 in the same place4 ,hence arise
 beds1  layers1 and lamin4 ,the terms   
layer and bed are generally used  as    
synonyms1 while lamin are thinner       
divisions of the same sort4  ,the term  
stratum is sometimes applied to one     
layer and sometimes to  all the         
consecutive layers of the same sort of  
rock4 ,for the latter  meaning the term 
formation is often used4 ,sometimes     
bedding seems  to have been determined  
by strong currents which temporarily not
 only  prevented deposition over a given
 area1 but even cut away the loose      
surface of deposits already made1 giving
 a firm surface from which  succeeding  
deposits are distinct4 ,this sequence of
 events is sometimes  shown by the      
truncation of lamin1 and by other signs 
of erosion4 ,the  commoner sorts of     
bedded rock are limestones1 shales1     
sandstones1 and  conglomerates4    ,the 
bedding of limestones is often caused by
 the introduction of thin  films of     
clayey material which interrupt the     

continuity of the lime  accumulation and
 cause natural partings4 ,sometimes1    
however1 bedding  arises from variations
 in the physical condition of the lime  
sediment  itself4 ,lamination is not    
usually conspicuous in pure limestone1  
though  it may be well developed in the 
shaly phases of this rock4 ,shales are  
normally laminated as well as bedded1   
and the lamination is often more        
notable than the thicker bedding4       
,bedding in shale may arise from the    
introduction of sandy lamin1 or by      
notable changes in the texture of  the  
shale material4 ,similarly1 sandstones  
are sometimes divided into  beds by     
shaly 7clayey7 partings1 but more often 
by variations in the  coarseness of the 
sand itself1 or by the presence of lamin
 that are  less coherent than those     
above and below4 ,sometimes the layers  
appear  to be determined by the         
compacting of the surface of sand       
already  accumulated before it was      
buried by later deposits4 ,sandstones   

may  be thick- or thin-bedded1 and their
 bedding passes insensibly into         
lamination4    ,sand deposits usually   
take place in relatively shallow water1 
and  the sand is subjected to much      
shifting before it finds a permanent    
lodgment4 ,in the course of this        
shifting1 bars are formed which usually 
have a rather steep face in the         
direction in which they are being       
shifted4 ,the sand carried over the top 
of the bar finds lodgment on  the       
sloping terrace face4 ,the inclined     
lamin thus formed constitute  a kind of 
bedding1 but since its planes do not    
conform to the general  horizontal      
attitude of the formation as a whole1 it
 is called false-  or cross-bedding or1 
more accurately1 cross-lamination 7see  
,fig4  #cfh74 ,the same structure is    
developed on delta fronts and generally 
in  water shallow enough to be subject  
to frequent agitation at the bottom4    
,sandstone is cross-bedded more commonly
 than other sorts of sedimentary  rock4 

,the bedding of conglomerate is due     
chiefly to variations in  coarseness4   
,lamin or thicker layers of sand are    
frequently found  between layers of     
coarser material4 ,conglomerate is      
likely to be  thick-bedded1 and         
cross-bedding is common4    ,lateral    
gradation4--,when the varying nature of 
the agitation of  the sea at different  
depths and along the different parts of 
the  coast-border1 and during different 
phases of the sea-currents1 is          
considered1 it will be readily          
understood that sedimentary beds are    
affected by many irregularities1 and    
that deposits of one kind grade  into   
others horizontally with great freedom4 
,thus a bed of conglomerate  7gravel7   
may grade laterally into sandstone1 and 
this into shale or  limestone4 ,it is   
indeed rather more remarkable that the  
sedimentary  strata should be as regular
 and persistent as they are1 than that  
they  sometimes grade into one another4 
,illustration3 ,fig4                    

#cfh4--;,cross-bedding in sandstone4    
,dells of the    ,wisconsin near        
,kilbourn1 ,wis4 7,bennett47    ,special
 markings4--,the rhythmical action of   
waves gives rise to  undulatory         
lodgment1 known as ripple-marks 7,fig4  
#cbd74 ,they are  usually not the direct
 product of the surface-waves1 since    
they are  much too small4 ,they are     
produced mainly by the vibratory        
movement of  the undertow1 but they     
apparently result from various other    
phases of  vibratory agitation of the   
bottom waters4 ,they are sometimes made 
by  streams and stream-like currents4   
,ripple-marks are apparently preserved  
indefinitely under proper circumstances4
 ,they are sometimes found1 for         
example1 on very ancient quartzites4    
,ripples are also made by wind  7p4     
#cg74 ,ripple-marks are usually only an 
inch or two from crest to  crest1 but in
 rare instances they attain much greater
 size4 ,examples  of ripple-marks #cj   
feet across are known4#baa ,occasional  

ridges  and depressions of much greater 
dimensions are produced which are       
attributable to the formation of        
successive bars1 or to the building  of 
wave-cusps4#bab ,rill-marks are not     
infrequently produced by the  undertow  
and other currents passing over pebbles1
 shells1 etc4 7,figs4  #cbe and #cbf74  
,illustration3 ,fig4 #cfi4--,mud-cracks 
in ,brunswick ,shale1 ,n4 ,j4           
7,kmmel47    ,sediments are sometimes   
exposed between tides1 or under other   
circumstances1 for periods long enough  
to permit drying and cracking at  the   
surface4 ,on the return of the waters1  
the cracks may be filled and            
permanently preserved4 ,these are known 
as sun-cracks or mud-cracks  7,figs4    
#cbh and #cfi74 ,they chiefly affect    
shales1 but are occasionally  seen in   
limestones and fine-grained sandstones4 
,during the exposure of  the sediments a
 shower may pass and rain-drop          
impressions 7,fig4 #cgj7  be made which 
are subsequently filled by fine sediment

 and preserved4  ,the size and depth of 
rain-drop impressions give some hint as 
to the  meteorological conditions of    
far-off ages4 ,wave-marks1 which consist
  of the faint line-ridges developed on 
a sandy beach at the limit of the       
incoming wave1 are sometimes preserved  
and may be seen occasionally on  layers 
of rock deposited millions of years ago4
    ,illustration3 ,fig4                
#cgj4--,rain-drop impressions4          
7,brigham47    ,concretionary           
structure4--,various sedimentary        
formations contain  nodules or          
irregularly shaped masses of mineral    
matter unlike the  rock in which they   
occur4 ,when these nodules consist of   
matter  aggregated about some center1   
they are called concretions4 ,they  are 
common in sedimentary rocks1 and here it
 may sometimes be  seen that the        
aggregation has taken place about a     
shell1 a leaf1  or some other organic   
relic4 ,the nuclei are1 however1 not    
always  organic4 ,the material of the   

concretion may have come from the       
immediately surrounding rock1 having    
been first dissolved by water  and then 
deposited about the nucleus1 or it may  
have been introduced  from without1     
likewise by the agency of water4 ,in the
 first case1  the mineral matter of the 
concretion is usually one of the minor  
constituents of the rock4 ,thus the     
commonest concretions in limestone  are 
composed of impure silica 7chert1 ,fig4 
#cfa72 in shale1 of lime  carbonate or  
iron sulphide2 in sandstone1 of iron    
oxide4 ,the concretion  may be made up  
almost wholly of concentrated matter1 in
 which case  the matter originally in   
the place of the concretion has been    
crowded  aside2 or it may involve much  
of the material of the imbedding rock4  
,thus the concretion of lime carbonate  
in shale may be nearly pure1  or it may 
involve much of the earthy matter of the
 shale1 while the  concretion of iron   
oxide in sandstone commonly includes    
much sand4 ,in  extreme cases1 indeed1  

the concentrated matter of the          
concretion merely  cements the material 
involved into distinct nodules4         
,occasionally the  rock substance itself
 takes on a concretionary form1 all or  
most of its  material being involved4   
,illustration3 ,fig4 #cga4--;,discoid   
calcareous concretions from             
post-glacial clays4 ,ryegate1 ,vt4      
7,photo4 by ,church47    ,illustration3 
,fig4 #cgb4--;,irregular calcareous     
concretions4 ,ryegate1   ,vt4 7,photo4  
by ,church47    ,illustration3 ,fig4    
#cgc4--;,calcareous concretions1 some of
 them showing   bilateral symmetry4     
,ryegate1 ,vt4 7,photo4 by ,church47    
,illustration3 ,fig4 #cgd4--;,irregular 
tubular silicious concretions    in     
,arikaree clays4 ,northwest of ,wildcat 
,mountain1 ,banner ,co41 ,neb4          
7,darton1 ,u4 ,s4 ,geol4 ,surv47    ,in 
size1 concretions may vary from         
microscopic dimensions to huge  masses1 
#h1 #aj1 or even more feet in diameter4 
,the variations in shape  are also      

great4 ,they may be spherical1          
elliptical1 discoid1 or they  may assume
 more irregular and complex forms       
7,figs4 #cga and #cgb74 ,the  conditions
 of growth have much to do with the     
form4 ,thus a concretion  which starts  
as a sphere may find growth easier in   
one plane than  another1 when it becomes
 discoid4 ,two or more concretions      
sometimes  grow together1 giving rise to
 complicated forms4 ,some of the most   
complex and fantastic forms are perhaps 
to be explained in this way4            
,concretions sometimes take the form of 
tubes4 ,some minute tubular  concretions
 were formed about rootlets1 but the    
larger ones appear to  owe their form to
 other influences 7,fig4 #cgd74         
,illustration3 ,fig4 #cge4--,section of 
a concretion 7septarium7 the    cracks  
of which have been filled by matter     
deposited from solution4    ,about half 
natural size4 7,photo4 by ,church47     
,illustration3 ,fig4 #cgf4--,section of 
a concretion1 the cracks in which       

have been filled by deposition from     
solution4 ,the filling appears to       
have wedged the parts of the original   
concretion apart4 ,the fillings    are  
veins4 ,some of them show that the      
vein-material was deposited on    both  
walls4 ,about half natural size4        
7,photo4 by ,church47    ,one of the    
most extraordinary features of some     
concretions of    complex form is their 
symmetry4 ,this may be of various       
phases2 in    exceptional cases there is
 a bilateral symmetry almost as perfect 
as    in the higher types of animals4   
,this is especially true of certain     
calcareous concretions developed in     
plastic clays 7,fig4 #cgc74             
,illustration3 ,fig4 #cgg4--,septarium  
from ,cretaceous clays near the    east 
base of the ,rocky ,mountains in        
,montana4 7,photo4 by ,church47         
,concretions sometimes develop cracks   
within themselves1 and these may  then  
be filled with mineral matter differing 
in composition or color  from that of   

the original concretions 7,figs4 #cge   
and #cgf74 ,concretions  the cracks of  
which have been filled by deposition    
from solution1  are called septaria4    
,they are especially abundant in some of
 the  ,cretaceous shales and clays4 ,in 
not a few cases the filling of the      
cracks appears to have wedged segments  
of the original concretion  farther and 
farther apart1 until the outer surface  
of the septarium is  made up more       
largely of vein-matter than of the      
original concretion  7,fig4 #cgg74 ,such
 concretions are often popularly known  
as 8petrified  turtles40    ,concretions
 of the sort indicated above often      
develop after the  enclosing sedimentary
 rock was deposited4 ,this is shown1    
among other  things1 by the fact that   
numerous planes of lamination may       
sometimes be  traced through the        
concretions4    ,concretions also form  
in water during the deposition of       
sedimentary  rock4 ,exceptionally1      
sedimentary rock is made up chiefly of  

concretions4 ,the chemical precipitates 
from the concentrated waters  of certain
 enclosed lakes sometimes take the form 
of minute spherules  which resemble the 
roe of fish4 ,from this resemblance the 
resulting  rock is called oolite 7,fig4 
#ceg74 ,oolite is now forming about some
  coral reefs1 presumably from the      
precipitation of the lime carbonate     
which was temporarily in solution4      
,considerable beds of limestone  are    
sometimes oolitic4 ,the calcium         
carbonate of such rock may be           
subsequently replaced by silica1 so that
 the oolitic structure is  sometimes    
found in silicious rock4 ,if the        
concretions become larger1  say as large
 as peas1 the rock is called pisolite   
instead of oolite  7,fig4 #cgh74        
,illustration3 ,fig4 #cgh4--,pisolite4  
,half natural size4 7,photo4 by         
,church47    ,illustration3 ,fig4       
#cgi4--;,columnar structure1 8,devil's  
,post ,pile40    ,upper ,san ,joaquin   
,canyon1 ,sierra ,nevada ,mountains4    

,beds of iron ore are likewise sometimes
 concretionary4 ,thus in the  ,clinton  
formation there are widespread beds of  
8flaxseed0 ore made up  of concretions  
of iron oxide which1 individually1      
resemble the seed  which has given the  
ore its name4 ,the nucleus in this case 
is usually  too small for               
identification4    ,secretions4--,when  
cavities in rock are filled by material 
deposited  from solution1 the result is 
sometimes called a secretion4           
,secretions  therefore grow from without
 toward a center1 while concretions     
follow  the opposite order4             
,crystal-lined cavities 7geodes1 ,fig4  
#cei7 and  agates 7,fig4 #ceh7 are      
examples of secretions4 ,crystal-lined  
cavities  and veins are the same in     
principle4                              
,,structural ,,features ,,of ,,igneous  
,,rocks4    ,certain structural features
 of igneous rocks have been mentioned in
  treating of their origin in the       
previous chapter4 ,when a great flow  of

 lava spreads out upon the surface1     
there is no internal lamination  or     
stratification1 and the resulting rock  
is usually classified as  massive rather
 than stratified2 but when a succession 
of flows occur1  each individual flow   
forms a layer1 and the series as a whole
 becomes  stratiform4 ,the successive   
flows are not usually coextensive4 ,if  
the  later flows of the closing stages  
of a period of vulcanism fail to  reach 
as far as the earlier ones1 a terraced  
or step-like aspect is  given to the    
region1 whence the name trap-rock       
7trappe1 steps7  is derived4 ,such lava 
sheets1 especially if of basalt1 often  
assume  a columnar structure in cooling1
 the columns being rude six-sided       
prisms standing at right angles to the  
cooling surfaces 7,figs4 #cgi  and      
#chj74 ,this phenomenon is usually best 
developed where the sheet  is intruded  
between layers of preexisting rock in   
the form of sills4  ,the formation of   
the columns is sometimes regarded as a  

variety of  concretionary action1 but   
more commonly as a result of            
contraction4 ,the  former is suggested  
by the ball-and-socket ends of the      
sections of some  columns 7,fig4 #chb74 
,the development of the columns by      
contraction may  be explained as        
follows3 ,the surface of the homogeneous
 lava contracts  about equally in all   
directions on cooling4 ,the contractile 
force may  be thought of as centering   
about equidistant points4 ,about a given
  point1 the least number of cracks     
which will relieve the tension in all   
directions is three 7,fig4 #chc74 ,if   
these radiate symmetrically from the    
point1 the angle between any two is     
#abj1 the angle of the hexagonal  prism4
 ,similar radiating cracks from other   
centers complete the columns  7,fig4    
#chd74 ,a five-sided column would arise 
from the failure of the  cracks to      
develop about some one of the points    
7,fig4 #che74    ,illustration3 ,fig4   
#chj4--;,columnar structure1 obsidian   

cliff1    ,yellowstone ,park4 7,iddings1
 ,u4 ,s4 ,geol4 ,surv47    ,when lava is
 forced into crevices or rises to the   
surface through  fissures1 and the      
residual portion solidifies in them1 it 
gives rise  to dikes1 as illustrated in 
,figs4 #b and #dag 7not a true dike74   
,dikes  are sometimes affected by       
columnar structure4 ,in this case1 as in
 all  others1 the columns are likely to 
be at right angles to the cooling       
surface4 ,lava solidifying in the       
passageway leading from the interior  of
 a volcano gives rise to a neck or plug4
 ,if the lava is forced  between beds of
 rock in the form of a sheet1 and       
solidifies there1 it  is called a sill4 
,if1 after rising to a certain point in 
the strata1  the lava arches the beds   
above into a dome1 and forms a great    
lens-like  or cistern-like mass1 it     
constitutes a laccolith 7,fig4 #ccd74   
,if an  intrusion of the laccolithic    
type faults the overlying beds instead  
of arching them1 and especially if the  

vertical dimension of the  intruded mass
 be great in comparison with its lateral
 dimensions1 its  shape is more like    
that of a plug or core4 ,such an        
intruded core is a  bysmalith#bac 7,fig4
 #abd74 ,between the bysmalith and the  
laccolith  there are various gradations1
 just as between the laccolith and the  
sill4 ,when lava forces aside the rocks 
at considerable depths or  absorbs them 
by solution or by 8stoping10 and then   
solidifies in great  masses of irregular
 or undetermined forms1 these masses are
 called  batholiths4    ,illustration3  
,fig4 #cha4--,sections of columns from  
,giant's ,causeway1    coast of         
,ireland4    ,illustration3 ,fig4       
#chb4--;,ball-and-socket joints in      
columns of basalt4    7,scrope47        
,illustration3 ,fig4 #chc4--;,diagram to
 illustrate the first stages in    the  
formation of hexagonal columns by       
contraction4    ,illustration3 ,fig4    
#chd4--,the completion of the hexagonal 
columns4    ,illustration3 ,fig4        

#che4--;,diagram to illustrate the      
development of    five-sided columns4   
,volcanic cones are familiar structures 
built up about the vents of    active   
volcanoes1 and will be discussed under  
vulcanism4                              
,,structural ,,features ,,arising ,,from
 ,,disturbance4    ,inclination and     
folding of strata4--,the original       
attitude of beds1  whether formed by    
water or by lava-flows1 is normally     
horizontal1 or  nearly so4 ,both kinds  
of deposits1 however1 occasionally take 
place  on considerable slopes4          
,modifications of the original attitude 
result  from earth movements1 and the   
measurement of these modifications is   
an important feature of field study4 ,it
 is recorded in terms of dip  and       
strike4 ,the dip is the inclination of  
the beds referred to a  horizontal      
plane1 as illustrated in ,fig4 #chf1 and
 is usually measured  by a clinometer1  
the principle of which is shown in ,fig4
 #chg4 ,in  measuring the dip1 the      

maximum angle is always taken4 ,in ,fig4
 #chf1 for  example1 the angle would be 
less if the direction were either to the
  right or left of that indicated by the
 arrow4 ,the direction as well as  the  
amount of the dip is always to be noted4
 ,this must be determined  by the       
compass1 to which the clinometer may be 
conveniently attached4  ,dip #dj1 ,s4   
#bj ,w4 gives the full record of the    
position of the bed of  rock under      
consideration4 ,the strike is the       
direction of the horizontal  edge of    
dipping beds1 or more generally1 the    
direction of a horizontal  line on the  
surface of the beds4 ,this is           
illustrated in ,fig4 #chf4 ,since  the  
strike is always at right angles to the 
dip1 the strike need not be  recorded if
 the direction of the dip is4 ,thus dip 
#dj1 ,s4 #bj ,w4 is the  same as dip    
#dj1 strike ,n4 #gj ,w4                 
,illustration3 ,fig4 #chf4--;,diagram   
illustrating dip and strike4            
7,geikie47    ,illustration3 ,fig4      

#chg4--,the clinometer4                 
,illustration3 ,fig4 #chh4--,open       
anticline1 near ,hancock1 ,md4          
7,russell1    ,u4 ,s4 ,geol4 ,surv47    
,illustration3 ,fig4 #chi4--;,closed    
anticline1 near ,levis ,station1        
,quebec4 7,walcott1 ,u4 ,s4 ,geol4      
,surv47    ,illustration3 ,fig4         
#cij4--;,inclined anticline4 7,van      
,hise1 ,u4 ,s4 ,geol4    ,surv47        
,illustration3 ,fig4 #cia4--,recumbent  
anticline4 7,van ,hise1 ,u4 ,s4 ,geol4  
,surv47    ,illustration3 ,fig4         
#cib4--,syncline1 ,c4  ,o4 canal1 #c    
miles west    of ,hancock1 ,md4 ,the    
beds are shale and sandstone near base  
of the    ,silurian4 7,walcott1 ,u4 ,s4 
,geol4 ,surv47    ,when the beds incline
 in a single direction1 they form a     
monocline4  ,when beds are arched so as 
to incline away from one another1 they  
form an up-fold or anticline 7,figs4    
#chh to #cia74 ,the anticline may       
depart from its simple form1 as shown in
 ,figs4 #cij and #cia4 ,when beds  are  

curved downward so as to incline towards
 one another1 they form  a syncline     
7,fig4 #cib74 ,when beds assume the     
position shown in ,fig4  #cic1 the folds
 are said to be isoclinal4 ,when they   
are arched so as  to form a cone or     
dome1 and incline in all directions from
 a central  point1 they are said to have
 a quaquaversal dip4 ,when considerable 
tracts are bent so as to form great     
arches or great troughs with many  minor
 undulations on the flanks of the       
larger1 they are designated  as         
geanticlines1 or anticlinoria 7,figs4   
#cid and #cie71 and  geosynclines or    
synclinoria 7,figs4 #cif and #cig74     
,folding is often  accompanied by the   
development of slaty cleavage 7p4 #ddj74
    ,illustration3 ,fig4                
#cic4--;,isocline4 7,van ,hise1 ,u4 ,s4 
,geol4 ,surv47    ,illustration3 ,fig4  
#cid4--;,anticlinorium3 diagrammatic4   
7,van ,hise1 ,u4    ,s4 ,geol4 ,surv47  
,illustration3 ,fig4                    
#cie4--;,anticlinorium4 ,general section

 in the    central massif of the ,alps4 
7,heim47    ,illustration3 ,fig4        
#cif4--,synclinorium3 diagrammatic4     
7,van ,hise1 ,u4 ,s4    ,geol4 ,surv47  
,illustration3 ,fig4                    
#cig4--,synclinorium1 ,mt4 ,greylock1   
,mass4 7,dale1 ,u4    ,s4 ,geol4 ,surv47
    ,illustration3 ,fig4 #cih4--;,a     
series of diagrams illustrating actual  
field relations in regions of folded    
strata4 ,westchester ,co41 ,n4 ,y4      
7,dana47    ,illustration3 ,fig4        
#cii4--;,diagram to show how dip and    
strike are    recorded4                 
,illustration3 ,fig4 #djj4--,map record 
of dip and strike1 showing    synclinal 
structure4    ,illustration3 ,fig4      
#dja4--,map record of dip and strike    
showing    anticlinal structure4        
,illustration3 ,fig4 #djb4--,the        
structure of the area shown in ,fig4    
#dja1    in cross-section4              
,illustration3 ,fig4 #djc4--,map record 
of dip and strike showing    plunging   
7dipping down at ends7 anticline4    ,as

 found in the field1 folds are usually  
much eroded1 and often  completely      
truncated 7,fig4 #cih74 ,the            
determination of anticlinal or          
synclinal structure is then not based on
 topography1 or even on such  sections  
as shown in ,figs4 #cid to #cig1 for    
such sections are relatively  rare4 ,the
 structure is determined by a careful   
record of dips and  strikes4 ,on the    
field map1 the record may be made as    
shown in ,figs4  #cii to #dja1 where the
 free ends of the lines with but one    
free end  point in the direction of dip1
 while the other lines represent the    
directions of strike4 ,applying this    
method1 the structure shown in  ,fig4   
#djj represents a syncline1 and that in 
,fig4 #dja an anticline4 ,in            
cross-section1 the structure presented  
by ,fig4 #dja would appear as  in ,fig4 
#djb4 ,fig4 #djc shows a doubly plunging
 anticline2 that is1 an  anticline the  
axis of which dips down at either end4  
,fig4 #djd shows a  combination of      

synclines and anticlines1 and ,fig4 #dje
 a cross-section  along the line ab of  
,fig4 #djd4 ,the outcrops of rock where 
the dip and  strike may be determined   
may be few and far between1 but when    
they  are sufficiently near one another1
 the structure of the rock1 as shown  in
 ,fig4 #dje1 may be worked out1 even    
though the surface be flat4             
,illustration3 ,fig4 #djd4--,map record 
of dip and strike showing complex       
structure4    ,illustration3 ,fig4      
#dje4--;,cross-section of ,fig4 #djd    
along the line    ab4    ,illustration3 
,fig4 #djf4--;,complex folding4 ,section
 across the ,alps    from the           
neighborhood of ,zrich toward ,como3    
about #aaj miles4 7,heim    and         
,prestwich47    ,illustration3 ,fig4    
#djg4--;,generalized fan fold of the    
central massif    of the ,alps4 7,heim47
    ,illustration3 ,fig4                
#djh4--;,intimate crumpling of beds near
 head of    ,sperry glacier1 ,mont4     
7,meyers47    ,illustration3 ,fig4      

#dji4--;,intimate crumpling in detail1  
accompanied by    faulting4 ,jasper     
,hill1 ,ishpeming1 ,mich4 7,meyers47    
,much the larger portion of the earth's 
surface is occupied by beds that  retain
 nearly their original horizontal       
attitude2 but in mountainous  regions   
the beds have usually suffered bending1 
folding1 crumpling1 and  crushing1 in   
various degrees1 in the course of the   
deformations that  gave rise to the     
mountains4 ,distortion is on the whole  
most intense  and characteristic in the 
most ancient rocks known1 the ,archean1 
in  which a distorted condition is      
nearly universal1 so far as observation 
goes4 ,distortion is assigned chiefly to
 lateral thrust arising from  the       
shrinkage of the earth1 as explained in 
the chapter on ,earth  ,movements4 ,the 
simpler1 and some rather complex forms  
of deformation1  are shown in the       
preceding figures1 but the folding is   
sometimes much  more complex 7,fig4     
#djf71 the folds sometimes 8fan0 7,fig4 

#djg71 and the  beds of which they are  
composed are sometimes intricately      
crumpled  7,figs4 #djh to #daj74 ,among 
these various phases of deformation     
there are  all gradations and           
combinations4 ,overturned folds reverse 
the order of  the strata in the under   
limb of the fold4 ,after such folds have
 been  greatly eroded1 so that their    
outer form is lost and their relations  
have become obscure1 the reversed beds  
are likely to be interpreted as  though 
they lay in natural order4 ,in such a   
case as that represented in  ,fig4 #daa1
 a complex structure may be interpreted 
as a simple one4 ,thus  the strata of   
,fig4 #daa may have the structure shown 
in ,fig4 #dab1 #dac1  or #dad1 so far as
 dip and strike show4    ,illustration3 
,fig4 #daj4--,plicated layers of        
thin-bedded chert in    limestone1      
etched by erosion4 ,lower ,cambrian 7871
 two miles southwest    of ,big ,pine1  
,inyo ,co41 ,cal4 7,walcott1 ,u4 ,s4    
,geol4 ,surv47    ,joints4--,the surface

 rocks of the earth are almost          
universally  traversed by deep cracks   
called joints 7,figs4 #dae1 #ach and    
#adj74 ,in  most regions there are at   
least two systems of joints1 the        
crevices of  each system being roughly  
parallel to one another1 while those of 
the  two systems1 where there are two1  
are approximately at right angles4  ,in 
regions of great disturbance1 the number
 of sets of joints is often  three1     
four1 or even more4 ,the joints of each 
set may be many yards  apart1 or in     
exceptional cases1 but a few inches1 or 
even a fraction of  an inch4            
,generally speaking1 there are more     
systems of joints1 and more  frequent   
joints in each system1 where the rocks  
are much deformed than  where they have 
been but little disturbed4 ,in          
undisturbed rocks the  joints approach  
verticality1 but in regions where the   
rocks have been  notably deformed1 the  
joint planes may have any position4 ,not
 rarely  they simulate bedding planes1  

especially in igneous and metamorphic   
rocks 7,fig4 #daf74 ,in the latter case 
especially1 the cleavage due to         
jointing is often mistaken for bedding4 
,they do not ordinarily show  themselves
 at the surface in regions where there  
is much mantle rock1  but they are      
readily seen in the faces of cliffs1 in 
quarries1 and1  in general1 wherever    
rock is exposed 7,figs4 #ach and #adj74 
,though some  of them extend to greater 
depths than rock has ever been          
penetrated1  joints are1 after all1     
superficial phenomena4 ,they must be    
limited to  the zone of fracture1 and   
most of them are probably much more     
narrowly  limited4 ,joints frequently   
end at the plane of contact of two sorts
  of rock4 ,thus a joint extending down 
through limestone may end where  shale  
is reached4 ,joints are frequently      
offset at the contact of  layers or     
formations1 and a single joint sometimes
 gives place to many  smaller ones4 ,all
 these phenomena are to be explained on 

the basis of  the different constitution
 and elasticity of various sorts of     
rock4  ,generally speaking1 rigid rock  
is more readily jointed than that which 
is more yielding4    ,joints may remain 
closed1 or they may gap4 ,in the latter 
case1 they may  be widened by solution1 
weathering1 etc41 but they are quite as 
likely  to be filled by detritus from   
above1 or by material deposited from    
solution 7veins74 ,it is along          
joint-planes that many rich ore-veins   
are  developed 7pp4 #dgh-dhd74          
,illustration3 ,fig4 #daa4--,this       
diagram might represent either          
isoclinal or monoclinal structure4 ,in  
the former case the strata might  have  
the structure shown in any one of the   
following ,figures1 #dab to  #dad1 so   
far as dip and strike show4 7,dana47    
,illustration3 ,fig4 #dab4--;,a possible
 interpretation of ,fig4 #daa4          
7,dana47    ,illustration3 ,fig4        
#dac4--;,a possible interpretation of   
,fig4 #daa4    7,dana47                 

,illustration3 ,fig4 #dad4--;,a possible
 interpretation of ,fig4 #daa4          
7,dana47    ,illustration3 ,fig4        
#dae4--;,jointed rocks4 ,cayuga ,lake1  
,n4 ,y4 7,hall47    ,joints have been   
referred to various causes1 among which 
tension1  torsion1#bad earthquakes1#bae 
and shearing#baf are the most           
important4 ,most of them may probably be
 referred to the tension or  compression
 developed during crustal movements4#bag
 ,in the formation  of a simple fold1   
for example1 tension-joints parallel    
with the fold  will be developed1 if    
tension goes beyond the limit of        
elasticity  of the rock involved4 ,if   
the axis of a fold is not horizontal1   
that  is1 if it 8plunges10 as it        
commonly does1 a second set of joints   
roughly perpendicular to the first will 
be developed4 ,if the uplift be         
dome-shaped and sufficient to develop   
joints1 they will radiate from  the     
center4 ,it is true that joints affect  
regions where the rocks have  not been  

folded1 and where they have been        
deformed but little1 but  deformation to
 some extent is well-nigh universal4    
,illustration3 ,fig4 #daf4--;,jointing  
in granite4 ,the surface of the rock    
is a joint plane4 ,northwest boundary of
 the ,united ,states4 ,the edges    of  
other joint planes normal to the surface
 are also shown4 7,ransome1    ,u4 ,s4  
,geol4 ,surv47    ,illustration3 ,fig4  
#dag4--,sandstone dike4 ,northern       
,california4    7,diller1 ,u4 ,s4 ,geol4
 ,surv47    ,a minor cause of           
tension-jointing is shrinkage1 due 7#a7 
to cooling1 as  in the development of   
the columnar structure of certain lavas1
 and 7#b7  to dessication1 as shown by  
the cracks developed in mud when it     
dries4  ,these causes1 however1 are not 
believed to affect rock structures to   
any considerable depth4 ,torsional      
joints and joints due to earthquake     
vibrations appear to be special phases  
of tension-joints4    ,two or more sets 
of joints may also be produced by       

compression1  the number being dependent
 on the complexity of the folding4 ,many
  compression-joints correspond in      
direction with planes of shearing4      
,they are often associated with minor   
faulting and with slaty cleavage4       
,tension-joints appear to be much more  
widely distributed than                 
compression-joints4    ,sandstone       
dikes4--,exceptionally1 open joints are 
filled by the  intrusion of sedimentary 
material from beneath4 ,thus have arisen
 the  remarkable sandstone dikes#bah of 
the ,west1 especially of ,california    
7,fig4 #dag74 ,such dikes are sometimes 
several miles 7nine at least7 in        
length4 ,the sand of these dikes was    
forced up from beneath either by        
earthquake movements or by hydrostatic  
pressure4    ,illustration3 ,fig4       
#dah4--;,diagram of a normal fault4     
,faults4--,the beds on one side of a    
joint-plane or fissure are  sometimes   
elevated or depressed relative to those 
on the opposite side1  and the          

displacement is known as a fault 7,figs4
 #dah and #dai74 ,the  joint-planes may 
have any position1 and hence            
fault-planes may vary  from verticality 
to approximate horizontality4 ,the angle
 by which the  fault-plane departs from 
a vertical position is known as the hade
  7bac1 ,fig4 #dah74 ,the vertical      
displacement 7ac7 is the throw and  the 
horizontal displacement 7bc7 the heave4 
,the heave and the throw  are to be     
distinguished from the displacement1    
which is the amount of  movement along  
the fault-plane 7ab1 ,fig4 #dah74       
,the cliff above the edge of the        
downthrow side is a fault-scarp4 ,in    
many1 probably in most cases1 the scarp 
has been destroyed1 or at any  rate     
greatly obscured by erosion2 but        
occasionally fault-scarps of            
mountainous heights1 as along the east  
face of the ,sierras and along  many of 
the basin ranges of ,utah1 ,nevada1     
etc41 are found though much  modified by
 erosion 7,fig4 #dai74    ,faults       

sometimes arise from over-intense       
folding 7,fig4 #dbj74 ,a  deformation   
which at one point results merely in a  
bending of the beds1  may occasion a    
fault at another4 ,faults may pass into 
folds either  vertically 7,figs1 #dba   
and #dbb7 or horizontally 7,fig4 #dbc74 
,in such  cases1 thickening and         
thinning1 and stretching and shortening 
of the  beds is often involved 7see     
,figs4 #dba and #dbb74 ,faults are often
 due to  the greater settling of the    
beds on one side of a fissure than on   
the  other1 without special disposition 
to fold4    ,illustration3 ,fig4        
#dai4--;,a fault-scarp2 the triangular  
faces rising    abruptly above the plain
 at the ends of the spurs4 7,davis47    
,illustration3 ,fig4 #dbj4--;,diagrams  
showing relations of faults and         
folds4    ,illustration3 ,fig4          
#dba4--,the fault above grades into a   
fold below4    ,thickening and thinning 
of layers next the fault-plane evident4 
,based    on experimental results of    

,willis 7#acth ,ann4 ,rept41 ,u4 ,s4    
,geol4    ,surv47    ,illustration3     
,fig4 #dbb4--;,fault below grading into 
fold above4    ,stretching and thinning1
 and shortening and thickening of beds  
under    pressure is involved4 ,based on
 experimental results of ,willis4       
,illustration3 ,fig4 #dbc4--;,diagram   
showing a fault grading into a          
monocline horizontally4                 
,illustration3 ,fig4 #dbd4--,slickenside
 surface4 7,prestwich47    ,the rock on 
either side of a fault-plane is often   
smoothed as the  result of the friction 
of movement4 ,such surfaces are         
slickensides  7,fig4 #dbd74 ,a          
slickenside surface has some resemblance
 to a glaciated  surface1 but generally 
gives evidence of greater rigidity      
between the  moving surfaces4    ,faults
 are of two general classes1 normal and 
reversed4 ,in the  normal fault 7,fig4  
#dah7 the overhanging side is the       
downthrow side1  i4e41 the downthrow is 
on the side towards which the           

fault-plane  inclines1 as though the    
overhanging beds had slidden down the   
slope4  ,normal faults1 as a rule1      
indicate an extension of strata1 this   
being  necessary to permit the          
dissevered blocks to settle downwards4  
,in  the reversed fault1 the overhanging
 beds appear to have moved up  the slope
 of the fault-plane1 as though the      
displacement took place  under lateral  
pressure4 ,this is clearly shown to be  
the case where an  overfold passes into 
a reversed fault 7,fig4 #dbj74 ,reversed
 faults are  further illustrated by     
,figs4 #dbe1 #dbf1 and #dbg4 ,where the 
plane of the  reversed fault approaches 
horizontality1 the fault is often called
 a  thrust-fault1 or an overthrust4 ,in 
such cases the throw is to  be          
distinguished from the stratigraphic    
throw 7see ,fig4 #dbf74 ,in             
thrust-faults1 the heave is often great4
 ,the eastern face of the ,rocky        
,mountains near the boundary-line       
between the ,united ,states and ,canada 

has been pushed over the strata of the  
bordering plains to a distance  of at   
least eight miles4#bai ,overthrusts of  
like gigantic displacement  have been   
detected in ,british ,columbia1#bbj     
,scotland1#bba and  elsewhere4          
,illustration3 ,fig4 #dbe4--,perspective
 view and vertical section of a         
thrust-fault4 7,willis1 ,u4 ,s4 ,geol4  
,surv47    ,illustration3 ,fig4         
#dbf4--;,diagram of a thrust-fault      
illustrating the    several terms used  
in describing faults4 ,the distinctions 
between    heave and displacement1 and  
between throw and stratigraphic throw1  
are to be especially noted4 7,willis1   
,u4 ,s4 ,geol4 ,surv47    ,illustration3
 ,fig4 #dbg4 --,step-fold showing 7in   
#a7 break in the    massive limestone   
bed which determines the plane of the   
break-thrust    along which the         
displacement shown in #b takes place4   
7,willis1 ,u4 ,s4    ,geol4 ,surv47     
,sometimes a fault branches 7,fig4 #dbh7
 and sometimes the faulting is          

distributed among a series of parallel  
planes at short distances from  one     
another1#bbb instead of being           
concentrated along a single plane1  thus
 giving rise to a distributive fault    
7,fig4 #dbi74 ,this is perhaps  more    
common in normal than in reversed       
faulting4    ,illustration3 ,fig4       
#dbh4--;,branching-fault4 7,powell47    
,illustration3 ,fig4 #dbi4--;,diagram   
showing a series of small               
faults--distributive faulting4          
,illustration3 ,fig4 #dcj4--;,fault in  
,gering series4 ,near ,rutland ,siding1 
near ,crawford1 ,neb4 7,darton1 ,u4 ,s4 
,geol4 ,surv47    ,the amount of throw  
occasionally reaches several thousand   
feet4  ,occasionally faults of          
incredible dimensions are reported1 but 
these are perhaps misinterpretations4   
,faults are observed to die  out        
gradually when traced horizontally1     
sometimes by passing into  monoclinal   
folds1 and sometimes without connection 
with folding4 ,in  depth they probably  

die out in similar ways in most cases4  
,where the  throw is great1 they        
probably give place to folds below      
7,fig4 #dba74  ,other phenomena of      
faulting are illustrated by ,figs4      
#dcj-dce4 ,a fault  of thousands1 or    
even hundreds of feet is probably the   
sum of numerous  smaller slippings      
distributed through long intervals of   
time4 ,faulting  is probably one of the 
common causes of earthquakes4           
,illustration3 ,fig4 #dca4--;,contorted 
and faulted laminated rock4 ,cook       
,inlet4 7,gilbert1 ,u4 ,s4 ,geol4       
,surv47    ,illustration3 ,fig4         
#dcb4--;,faulting shown in a            
cobblestone4 ,the    fault-planes have  
become veins by deposition from         
solution4 ,the    figure shows how the  
relative ages of crossing-faults may be 
determined4 7,schrader1 ,u4 ,s4 ,geol4  
,surv47    ,illustration3 ,fig4         
#dcc4--;,figure showing minute faulting4
 ,the length    of the specimen is #h   
inches4 ,the number of faults is nearly 

#ajj4    7,photo4 by ,church47          
,illustration3 ,fig4 #dcd4--;,diagram   
illustrating common phenomena of a      
faulted region4 7,dana47                
,illustration3 ,fig4 #dce4--;,diagram   
showing a fault1 the plane of which     
forms an open fissure and has been      
filled with dbris from above4           
7,powell47    ,the significance of      
faults4#bbc--;,faults afford a valuable 
indication  of the conditions of stress 
to which a region has been subjected1   
but  some caution must be exercised in  
their interpretation4 ,normal faults    
usually indicate an extension of the    
surface sufficient to permit the        
fault-blocks to settle down unequally4  
,reversed faults usually signify  a     
compression of the surface which        
requires the blocks to overlap  one     
another more than they did before the   
faulting4 ,in other words1  normal      
faulting usually implies tensional      
stress1 and reversed faulting           
compressional stress4 ,it is not        

difficult to see1 however1 that in an   
intensely compressed and folded region  
there might be cases of normal  faulting
 on the crests of folds where local     
stretching took place1 and  that        
reversed faults might occur even in     
regions of tension4 ,but such  cases    
must usually be local1 and capable of   
detection and elimination  by a study of
 the phenomena of the surrounding       
region4 ,these  exceptional cases aside1
 the general inference from prevailing  
normal  faults is that the regions where
 they occur have undergone stretching1  
while the inference from the less widely
 distributed reversed faults is  that   
the surface where they occur has        
undergone compression4    ,in view of   
the current opinion that the crust of   
the earth has been  subjected to great  
lateral thrust as a result of cooling1  
it is  well to make especial note of the
 fact that the faults which imply       
stretching are called normal because    
they are the more abundant2  and that   

the faults which imply thrust are less  
common1 and are styled  reversed4 ,the  
numerical ratio of normal to reversed   
faults has never  been closely          
determined1 but normal faults very      
greatly preponderate1  and are estimated
 by some writers to embrace #ij-odd per 
cent4 of the  whole4 ,the testimony of  
normal faults is supported by the       
prevalence  of gaping crevices1 and of  
veins which are but crevices that stood 
open until they were filled by          
deposition4 ,all these phenomena seem to
  testify to a stretched condition of   
the larger part of the surface of  the  
continents4 ,this will again claim      
attention in the study of ,earth        
,movements4    ,illustration3 ,fig4     
#dcf4--;,diagram showing an area of rock
 with    monoclinal structure4 ,one     
layer notably unlike the others4        
,effect of faulting on                  
outcrops4--,faulting may bring about    
numerous  complications in the outcrop  
of rock formations4 ,in a series of     

formations having a monoclinal structure
 7,fig4 #dcf71 many changes may  be     
introduced4 ,let it be supposed in the  
following cases that1 after  faulting1  
the surface has been reduced to         
planeness by erosion4 ,if  the          
fault-plane be parallel to the strike of
 the beds 7ab1 ,fig4  #dcf71 and hence a
 strike fault1 the outcrop of a given   
layer may be  duplicated 7,h1 ,fig4     
#dcg71 or it may be eliminated          
altogether 7,fig4  #dch74 ,if the       
fault-plane be parallel to the direction
 of dip 7cd1  ,fig4 #dcf71 a dip fault1 
the layer ,h will outcrop1 as in ,fig4  
#dci1 if the downthrow was on the far   
side1 or as in ,fig4 #ddj if the        
downthrow was on the opposite side4 ,in 
both cases the outcrop ,h is  offset1   
the amount of the offset decreasing with
 increasing angle of  dip and increasing
 with increasing throw of the fault4 ,if
 the fault  be oblique to the direction 
of dip and strike 7ef1 ,fig4 #dcf71 an  
oblique fault1 the outcrop of such a    

layer as ,h will have the  relations    
shown in ,fig4 #dda if the downthrow was
 to the left1 and that  shown in ,fig4  
#ddb if the downthrow was to the right4 
,in the former  case1 it is said that   
there is offset with overlap2 in the    
latter1  offset with gap4 ,the amount of
 the overlap and gap1 respectively1     
increases with the increase of throw and
 hade1 and decreases with  increase of  
dip4 ,in all cases the outcrop 7after   
the degradation of the  upthrow side7 is
 shifted down dip4    ,illustration3    
,fig4 #dcg4--,same as ,fig4 #dcf1 after 
7#a7 displacement by    a strike fault  
and 7#b7 base-leveling4 ,the outcrops of
 certain beds    are repeated4          
,illustration3 ,fig4 #dch4--;,diagram   
illustrating how a strike fault in      
such a structure as that shown in ,fig4 
#dcf may cause the outcrop of    certain
 beds to disappear4    ,illustration3   
,fig4 #dci4--;,diagram illustrating how 
a dip fault in the    structure shown in
 ,fig4 #dcf affects the outcrop when the

 downthrow    was on the farther side of
 the fault-plane4    ,illustration3     
,fig4 #ddj4--,same as ,fig4 #dci1 except
 that the downthrow    was on the       
opposite side4    ,illustration3 ,fig4  
#dda4--,oblique fault in the structure  
shown in ,fig4    #dcf4 ,the downthrow  
was on the left side4 ,the outcrop of   
layer ,h is    offset with overlap4     
,illustration3 ,fig4 #ddb4--,same as    
,fig4 #dda1 except that the downthrow   
was on the right side1 and the offset is
 with a gap instead of an    overlap4   
,illustration3 ,fig4 #ddc4--;,diagram   
showing effect of faulting on the       
outcrops of synclinal beds4             
,illustration3 ,fig4 #ddd4--;,diagram   
showing effect of faulting on           
outcrops of anticlinal beds4            
,illustration3 ,fig4 #dde4--;,diagram   
illustrating the effect of              
diminishing throw on outcrops in regions
 of folded rocks4    ,if a fault crosses
 folds at right angles to their axes1   
the effect is  to change the distance   

between the outcrops of a given bed on  
opposite  sides of the fault1 after the 
truncation of the folded beds4 ,the     
distance is decreased on the upthrow    
side of a syncline 7,fig4 #ddc7 and     
increased on the upthrow side of an     
anticline 7,fig4 #ddd74 ,if the throw   
of a fault in tilted beds diminishes in 
one direction1 it may cause  beds to    
outcrop1 as shown in ,fig4 #dde4        
,various other complications  arise     
under other circumstances4 ,since faults
 rarely show themselves in  the         
topography of the surface1 except under 
special circumstances 7see  p4 #aea71   
their detection and measurement is      
usually based on the study  of the      
relations of the beds involved1 as      
illustrated by ,figs4 #dcf-dde4         
,,chapter ,,ix4              ,,the      
,,movements ,,and ,,deformations ,,of   
,,the ,,earth',s ,,body                 
7,,diastrophism74      ,the body of the 
earth is subject to an infinite variety 
of movements1  ranging from the almost  

inconceivably rapid to the almost       
imperceptibly  slow1 and from the almost
 immeasurably minute to the enormously  
massive2 but1 for practical treatment1  
they fall mainly into two  couplets3    
7#a7 the minute and rapid1 and 7#b7 the 
slow and massive4  ,sudden movements of 
local masses1 giving rise to intense    
vibrations1  are put in the first class4
 ,there are innumerable minute and slow 
movements1 but unless they rise to      
appreciable magnitude by long           
continuance1 they are neglected4        
,,minute ,,and ,,rapid ,,movements4     
,the crust of the earth is in a state of
 perpetual tremor4 ,for the  most part1 
these tremors are too minute to be      
sensible1 but are  revealed by delicate 
instrumental devices4 ,some of them are 
but the  declining stages of sensible   
vibrations1 but others are minute from  
their inception4 ,many of them spring   
from the ordinary incidents of  the     
surface1 and claim attention chiefly as 
obstacles to the study of  more         

significant oscillations4 ,winds1 waves1
 waterfalls1 the tread of  animals1 the 
rumble of traffic1 the blasts of mines1 
the changes of  temperature1 the        
variations in atmospheric pressure1 the 
weighting of  rainfall and the          
lightening of evaporation1 the rupture  
of rock or ice  or frozen earth1 and    
many other processes1 make their        
contributions  to local and minute      
movements4 ,for the greater part1 these 
vibrations  are superficial in origin1  
and are soon damped beyond recognition  
by  dispersal and by the inelastic and  
discontinuous nature of the looser      
material of the surface4 ,when a        
temporary rigid crust is formed by      
freezing1 as in winter1 these surface   
vibrations are transmitted with  much   
less loss1 and the distances at which   
the rumble of winter traffic  is heard1 
is a good illustration of the function  
of continuity and  solidity in the      
conveyance of vibrations4               
,earthquakes4    ,when the tremors      

spring from sources within the earth    
itself and are of  appreciable violence1
 they are recognized as earthquakes4    
,the sources  of earthquake tremors are 
various4 ,the most prevalent is probably
 the  fracture of rocks and the slipping
 of strata on each other in the  process
 of faulting4 ,the interpretation of    
movements of this class  has now been so
 far perfected that the length and depth
 of the fault1  the amount of the slip1 
and the direction of the hade are       
capable of  approximate estimation4#bbd 
,to the same class belong the movements 
due to slumping4 ,they are illustrated  
by the sliding and arrest of  great     
masses of sediment along the steep      
fronts of deltas1 and of  the           
accumulations of deep-sea oozes on steep
 submarine slopes4 ,such  slumping is1  
in reality1 superficial faulting4       
,seismic tremors often  attend volcanic 
eruptions1 and are then probably        
attributable to the  sudden fracture and
 displacement of rock by the penetration

 of lava1  or by rapid and unequal      
heating4 ,they are perhaps also due     
sometimes  to the sudden generation or  
cooling of steam in underground         
conduits1  crevices1 and caverns1 the   
action possibly being in some cases of  
the  8water-hammer0 type4 ,in rare      
instances1 probably1 the bursting of    
beds  overlying pent-up non-volcanic    
gases may give origin to earthquakes4 ,a
  more superficial source of earthquake 
vibrations is the collapse of the  roofs
 of subterranean caverns4    ,seismic   
vibrations seem to be in part           
compressional1 in part  distortional1 in
 part 7on the surface7 undulatory1 and  
in part  irregular4 ,the distortional   
are especially significant1 as they seem
 to  imply a solid medium of            
transmission4    ,points of origin1     
foci4--,it is probable that nearly or   
quite all  earthquake movements start   
within the upper ten miles of the crust1
  and most of them within the upper     
five4 ,some of the earlier estimates    

indeed placed the points of origin as   
deep as #bj or #cj miles1 but in  these 
cases the necessary corrections1        
discussed below1 were neglected4  ,most 
of the recent and more accurate         
estimates fall within the limits  given4
    ,the method of estimating the depth 
of the centers of disturbance  consists 
in observing the directions of throw or 
thrust of bodies  at the surface1 and in
 regarding these as representing the    
lines  of emergence of the              
earthquake-waves4 ,by plotting these    
lines of  emergence1 and projecting them
 backwards to their underground         
crossings1 a first approximation to the 
location of the focus is  reached 7the  
lines ,,ef1 ,fig4 #ddf74 ,from the      
nature of the case1 the  observations of
 the angles of emergence cannot be very 
accurate1 but an  effort is made to     
limit the error by making the number of 
observations  great4    ,two systematic 
corrections are to be applied to all    
such estimates1  the one for varying    

elasticity and density1 and the other   
for  varying continuity4 ,both reduce   
the estimated depth4 ,in making the     
correction for varying elasticity1 it   
must be noted that the velocity  of     
vibrations varies directly as the square
 root of the elasticity1  and inversely 
as the square root of the density4 ,the 
velocity is also  accelerated by        
increase of temperature4 ,the           
elasticity1 temperature1  and density   
all increase with depth4 ,theoretically1
 the increase of  velocity due to the   
increasing elasticity and temperature of
 increasing  depths1 overbalances the   
retardation due to increasing density1  
and  recent observations on the         
transmission of seismic waves through   
deep  chords of the earth have confirmed
 this conclusion4 ,the path of the      
vibration will1 therefore1 be curved    
toward the surface1 as pointed out  by  
,schmidt and illustrated in ,fig4 #ddf1 
taken from his discussion4#bbe  ,from   
this it is clear that the focus is not  

so deep as implied by the  simple       
backward projection of the lines of     
emergence4    ,illustration3 ,fig4      
#ddf4--;,diagram illustrating by closed 
curves the    different rates of        
propagation of seismic tremors from a   
focus ,f1    and1 by lines normal to    
these1 the changing directions of       
propagation    of the wave-front4 ,it   
will be seen that the paths of          
propagation    curve upwards in         
approaching the surface4 ,if the lines  
of emergence1    as at ,e and ,e1 be    
projected backwards1 as to ,f1 the      
points of    crossing will be below the 
true focus4    ,a second correction must
 be made for the differences of         
continuity  of the upper rock in the    
vertical and horizontal directions4 ,in 
the  outer part of the earth1 the       
continuity in horizontal directions is  
interrupted by vertical fissures4 ,were 
these not usually filled with  water1   
they would soon kill the horizontal     
component of the seismic  wave1 and the 

residual portion would be directed      
almost vertically to  the surface1 for  
the width of the fissures is almost     
always greater  than the amplitude of   
the seismic vibrations4 ,the water      
restores the  continuity1 in a measure1 
but not perfectly1 for the elasticity of
  water is much less than that of rock4 
,it is clear that in horizontal         
movement there must be a constant       
transfer from rock to water and from    
water to rock1 and this must retard1 as 
well as partially destroy1 the          
vibrations4 ,in a vertical direction1   
however1 the rocks rest firmly  upon one
 another1 and this gives measurable     
continuity1 the only change  being from 
one layer or kind of rock to another4   
,it seems certain1  therefore1 that the 
vertical component of the seismic wave  
will be less  damped and less retarded  
in transmission than the horizontal4 ,it
 will1  therefore1 reach the surface    
sooner and will have the greater effect 
on  bodies at the surface1 not only for 

the reasons given1 but also because  it 
emerges more nearly in the line of least
 resistance and of freest  projection4  
,on this account1 a second correction   
must be added to the  correction for    
elasticity1 and this must further reduce
 appreciably the  first estimate of the 
depth of the focus4    ,observation     
shows that in some way a seismic wave   
becomes separated in  transmission into 
portions of different natures and       
speeds1 but their  interpretation is yet
 uncertain4 ,these separated portions   
probably  consist of the compressional1 
the distortional1 and the undulatory    
waves1 and perhaps of refractions and   
reflections of these 7see ,fig4  #ddh74 
,a most important recent achievement is 
the detection and investigation  of     
seismic tremors that appear to have come
 through the earth4 ,the  transmission  
of such waves promises to reveal much   
relative to the  nature of the deep     
interior1 when enough data are gathered 
to warrant  conclusions4 ,the rate of   

propagation in the central parts is     
found to  be greater than in the outer  
parts1 implying high elasticity within4 
,the amplitude of the vibrations4--,from
 the very disastrous effects  of severe 
earthquakes1 it is natural to infer that
 the distinctive  oscillations must have
 large amplitude1 but in fact it is the 
suddenness of the vibration1 rather than
 its length1 that is  effective4        
,instrumental investigations indicate   
that the oscillations1  after they have 
left their points of origin1 are usually
 only a  fraction of a millimeter in    
amplitude2 at most they seldom exceed a 
few  millimeters4 ,a sudden shock with  
an amplitude of #e or #f millimeters is 
sufficient to shatter a chimney4 ,it is 
true that estimates assigning           
amplitudes of a foot or more have been  
made1 but their correctness is  open to 
serious doubt4 ,it should be understood 
that it is the length  of oscillation of
 the particles of the subsurface rock   
transmitting  the vibrations that is    

referred to1 not the movement of the    
free  surface1 or of objects on the     
surface4 ,the throw at and on the       
surface  is much greater4 ,just as a    
slight1 quick tap of a hammer on a floor
  is sufficient to make a marble lying  
on it bound several inches1 so  a       
sufficiently sudden rise of the surface 
of the earth1 though but a  fraction of 
an inch1 may project loose bodies many  
feet4    ,illustration3 ,fig4           
#ddg4--;,illustration of the destructive
 effects of    the ,charleston          
earthquake1 showing definite direction  
of throw4 7,w4    ,j4 ,mc,gee47         
,destructive effects4--,the             
interpretation of the disastrous results
  of earthquake shocks has1 therefore1  
its key in the suddenness and  strength 
of rather minute vibrations of the      
earth-matter1 but it is  also dependent 
on the freedom of motion of the bodies  
affected4 ,the  rocks of the deeper     
zones1 where the matter is sensibly     
continuous1  transmit the seismic       

vibrations without appreciable          
disruptive effect1  so far as known1    
though the origin of crevices has been  
assigned to  this cause2 but bodies at  
the surface are fractured1 overturned1  
and  hurled from their places4 ,the     
reason is doubtless this3 ,within a     
great  mass firmly held in place by     
cohesion and pressure on all sides1 the 
forward motion of a particle develops an
 equal elastic resistance1  and it is   
quickly thrown back again and the wave  
passes on4 ,at the  surface1 where      
bodies are freer to move1 the stroke of 
the vibration  projects the body1 and   
so1 instead of vibratory resilience1 the
 chief  energy is converted into        
mass-motion4 ,the tap of a hammer sends 
an  almost imperceptible vibration along
 the floor1 but this vibration may      
throw a glass ball1 beneath which it    
runs1 into the air4 ,so the minute      
vibrations of earth-matter may travel   
miles from their origin through         
continuous substance with little result1

 and then so suddenly thrust a  loose   
body on the surface1 or the base of a   
column1 or the foundation  of a house1  
as to rack it with differential strains1
 or even to hurl  it to destruction4    
,so1 too1 earth-waves striking the      
sea-border may  thrust the waters off   
shore by their sudden impact1 and the   
reaction  may develop a wave which      
overwhelms the coast4 ,such waves may   
doubtless  arise from a sudden stroke of
 seismic vibrations on the sea-bottom4  
,the great gaping fissures that         
sometimes open during earthquakes occur 
oftenest where the surface on one side  
is less well supported than on  the     
other1 as on a slope1 or near a         
bluff-face or a river-channel4 ,when  in
 such situations the earth is once      
suddenly forced in the direction  of    
least resistance1 it is not always met  
by sufficient elastic  resistance to    
throw it back4 ,sometimes1 however1     
there is an elastic  return1 and the    
fissure closes forcibly an instant after

 it is opened4    ,direction of         
throw4--,immediately above the point of 
origin1  technically the epicentrum or  
epi-focal point1 bodies are projected   
upwards4 ,when crushing takes place in  
such a case1 it is due to the  upthrust 
or to the return downfall4 ,at one side 
of the epicentrum the  thrust is oblique
 in various degrees1 and is usually more
 destructive1  if not too far from the  
epicentrum4 ,the destructiveness        
commonly  increases for a certain       
distance from the epi-focal point1 and  
then  diminishes4 ,under ideal          
conditions1 the greatest effects are    
found  where the vibration emerges at an
 angle of about #de1 but various        
influences modify this result4 ,lines   
drawn through points of equal  effect   
7isoseismals7 are not usually regular   
circles or ellipses about  the          
epicentrum1 as they would be under ideal
 conditions4 ,the various  divergencies 
represent differences of effective      
elasticity1 of surface1  and of other   

influences4 ,as most earthquakes        
originate from lines1  planes1 or       
masses1 rather than points1 there are   
doubtless differences  of intensity of  
vibration at different points on the    
lines1 planes1  or areas of origin1 and 
these differences introduce inequalities
 in  propagation and in surface effects4
    ,illustration3 ,fig4                
#ddh4--;,illustrations of the records   
made by    earthquake tremors after     
distant transmission through the earth4 
,the    four diagrams represent the same
 set of tremors as received at ,shide1  
,kew1 ,bidston1 and ,edinburgh in ,great
 ,britain4 ,the movement was from       
left to right4 7,milne47    ,rate of    
propagation4--,the progress of a seismic
 wave varies very  greatly4 ,both       
experimental tests and natural          
observations give very  discordant      
results4 ,at present1 they justify only 
the broad statement  that the velocity  
of propagation varies from several      
hundreds to  several thousands of feet  

per second at the surface4 ,the rate    
seems to  be greater for strong         
vibrations than for weak ones1 and hence
 it is  faster near the origin than     
farther away4 ,the strength of a        
vibration  dies away1 theoretically1    
according to the inverse square of the  
distance from the point of origin4      
,practically there is to be added to    
this the partial destruction of the     
vibrations by conversion into other     
forms of motion4    ,sequences of       
vibrations4--,near the source1 the main 
shocks are apt to  come suddenly and to 
be followed by minor tremors4 ,at a     
distance there  are usually             
8preliminary0 vibrations followed by the
 main tremors1  and these by others of  
gradually diminishing value4 ,this      
development  is assigned to different   
rates of propagation1 and to refractions
 and  reflections not unlike the        
prolongation of thunder 7see ,fig4      
#ddh74  ,this deployment of the         
vibrations is notably developed in the  

shocks  that pass long distances through
 the earth4 ,the vibrations of the      
first phase are regarded as             
compressional1 those of the second as   
distortional1 while the largest         
oscillations which arise still later    
perhaps come around the surface1 and may
 be undulatory1 though their  nature is 
not yet determined4    ,there is often1 
however1 a true succession of original  
shocks caused by  a succession of slips 
or ruptures at the source4 ,sometimes   
these are  exceedingly persistent1      
running through days1 weeks1 or even    
months4 ,in  such cases a slow faulting 
is probably in progress1 and little     
slips  and stops follow in close        
succession4 ,in one instance as many as 
#fjj  shocks in ten days have been      
reported4#bbf    ,gaseous               
emanations4--,vapors and gas frequently 
issue from earthquake  rents1 and are   
popularly made to serve as causes1 but  
they are usually  merely the earth gases
 that are permitted to escape by the    

rending  of the ground1 or are forced   
out by readjustment of the shaken beds4 
,like other subterranean gases1 they are
 often sulphurous1 and they are         
sometimes hot1 especially in volcanic   
regions4 ,where the shocks are          
connected with eruptions1 the gases may 
be truly volcanic4    ,distribution of  
earthquakes4--,over large portions of   
the globe1  severe earthquakes are      
exceedingly rare1 but in certain regions
 they  are unfortunately frequent4 ,for 
the most part1 these are volcanic       
districts1 but this is by no means a    
universal relation4 ,earthquakes  and   
volcanoes are only in part associates4  
,in general1 it may be said  that       
earthquakes are frequent where geologic 
changes are in rapid  progress1 as along
 belts of young mountains1 where the    
stresses are  not yet adjusted1 or at   
the mouths of great streams1 where      
deltas are  accumulating1 or about      
volcanoes1 where temperatures and       
strains are  changing1 or on the great  

slopes1 particularly the submarine      
slopes1  where readjustments in response
 to inequalities of surface stress are  
in progress4 ,not a few1 however1 occur 
where the special occasion is  not at   
all obvious4                      ,the  
,geologic ,effects of ,earthquakes4     
,earthquakes are of much less           
importance1 geologically1 than many     
gentler movements and activities4       
,disastrous as they sometimes are to    
human affairs1 they leave few distinct  
and readily identifiable marks  which   
are more than temporary4    ,fracturing 
of rock4--,during the passage of notable
 earthquake waves1  the solid rock is   
probably often fractured 7see p4 #eji71 
though where  it is covered by deep soil
 the fractures are rarely observable at 
the  surface4 ,elsewhere the crevices   
are readily seen1 especially if they    
gape4 ,in a few instances surface-rock  
has been seen to be thoroughly          
shattered after the passage of an       
earthquake1 as in the ,concepcion       

earthquake of #ahce4bbg ,joints which   
were before closed are often  opened    
during an earthquake4 ,thus in northern 
,arizona1 not far from  ,canyon ,diablo1
 there is a crevice traceable for a     
considerable  distance1 which is said to
 have been opened during an earthquake4 
,locally1 it gaps several feet4 ,other  
notable earthquake fissures  have been  
recorded in ,india1#bbh ,japan1 and ,new
 ,zealand4 ,during an  earthquake which 
shook the ,south ,island of ,new        
,zealand in #ahdh1 8a  fissure was      
formed averaging #ah inches in width1   
and traceable for a  distance of #fj    
miles1 parallel to the axis of the      
adjacent mountain  chain40#bbi ,the     
development of fractures or the opening 
of joints is  sometimes accompanied by  
faulting4 ,this was the case in ,japan  
during  the earthquake of ,october #bh1 
#ahia1 when the surface on one side of a
  fissure1 which could be traced for #dj
 miles1 sank #b to #bj feet4 ,in this   
case there was also notable horizontal  

displacement1 the east wall of  the     
fissure being thrust locally as much as 
#ac feet to the north4#bcj    ,changes  
of surface4--,circular surface openings 
or basins are sometimes  developed      
during earthquakes4 ,this was the case  
during the ,charleston  earthquake of   
#ahhf1bca and similar effects have been 
noted elsewhere4  ,these openings often 
serve as avenues of escape for          
ground-water1  gases1 and vapor4 ,they  
are commonly supposed to be the result  
of the  collapse of caverns1 or other   
subterranean openings1 the collapse     
often  causing the forcible ejection of 
water4 ,such openings are likely to be  
formed only where the surface material  
is incoherent4 ,sandstone dikes  7p4    
#ead7 may perhaps be associated in      
origin with earthquakes4    ,earthquakes
 are likely to dislodge masses of rock  
in unstable  positions1 as on slopes or 
cliffs4 ,they may also occasion slumps  
and  landslides4#bcb    ,effects on     
drainage4--,the fracturing of the rock  

may interfere with  the movement of     
ground-water4 ,after new cracks are     
developed1 or old  ones opened or       
closed1 the movement of ground-water    
adapts itself  to the new conditions4   
,it follows that springs sometimes cease
 to  flow after an earthquake1 while new
 ones break out where there had  been   
none before4 ,the character of the water
 of springs is sometimes  changed1      
presumably because it comes from        
different sources after the  earthquake4
 ,joints may be so widened as to        
intercept rivulets1 and  the waters thus
 intercepted may cause the further      
enlargement of the  opening4            
,illustrations of this sort are         
furnished by the earthquakes  of the    
,mississippi valley 7,lat4 #cf to #ch7  
in #ahaa-ab4 ,where faults  accompany   
earthquakes1 they occasion ponds or     
falls where they cross  streams4        
,illustrations of both were furnished by
 the ,chedrang ,river of  ,india after  
the earthquake of #ahig4bcc    ,effects 

on standing water4--,some of the most   
destructive effects of  earthquakes are 
felt along the borders of the sea4 ,thus
 the great  sea-wave of the ,lisbon     
earthquake 7#agee7 and that of the      
earthquake  which affected the coasts of
 ,ecuador and ,peru in #ahfh are        
examples4  ,such waves have been known  
to advance on the land as walls of water
 #fj  feet in height4 ,they are most    
destructive along low coasts1 for here  
the water may sweep much more           
extensively over the land4 ,the great   
loss of life during an earthquake has   
usually been the direct result  of the  
great waves4 ,lakes are also affected by
 earthquakes1 their  waters sometimes   
rising and falling for several hours    
after the initial  disturbance1 but     
lake-waves are much feebler than those  
of the sea1 and  are not often          
destructive4    ,earthquake shocks are  
sometimes remarkably destructive to the 
life  of lakes and seas4 ,thus during   
the ,indian earthquake of #ahig1 8fishes

  were killed in myriads as by the      
explosion of a dynamite cartridge 444   
and for days after the earthquake1 the  
river 7,sumesari7 was choked  with      
thousands of dead fish 444 and two      
floating carcasses of ,gangetic         
dolphins were seen which had been killed
 by the shock40#bcd ,this  wholesale    
destruction of life is of interest1     
since the surfaces of  layers of rock1  
often of great age1 are sometimes       
covered with fossils  of fish or other  
animal forms1 so numerous and so        
preserved as to  indicate that the      
animals were killed suddenly and in     
great numbers1  and their bodies quickly
 buried4 ,it has been suggested that    
such rock  surfaces may be memorials of 
ancient earthquake shocks4#bce          
,changes of level4--,permanent changes  
of level sometimes accompany an         
earthquake4 ,thus after the earthquake  
of #ahbb 8the coast of ,chili for a     
long distance was said to have risen #c 
or #d feet40#bcf ,similar results  have 

occurred on the same coast at other     
times1 and on other coasts at  various  
times4 ,depression of the surface is    
perhaps even more common  than          
elevation4 ,thus on the coast of ,india 
all except the higher parts  of an area 
#fj square miles in extent were sunk    
below the sea during  an earthquake in  
#agfb4 ,widespread depression in the    
vicinity of the  ,mississippi in        
,missouri1 ,arkansas1 ,kentucky1 and    
,tennessee accompanied  the earthquakes 
of #ahaa and #ahab4 ,some of the        
depressed areas were  converted into    
marshes1 while others became the sites  
of permanent  lakes4 ,reelfoot ,lake1   
mainly in ,tennessee1 is an example4    
,change of  level is involved wherever  
there is faulting1 and faulting is      
probably  rather common in connection   
with earthquakes4    ,changes of level  
are not confined to the land4 ,where    
earthquake  disturbances affect the     
sea-bottom in regions of telegraph      
cables1 the  cables are often broken4   

,in such cases notable changes have     
sometimes  been discovered and recorded 
when the cables were repaired4 ,striking
  examples are furnished by the region  
about ,greece4#bcg ,in one instance     
7#ahgc7 the repairing vessel found about
 #bjjj feet of water where about  #adjj 
feet existed when the cable was laid4   
,in another instance 7#ahgh7  the bottom
 was 8so irregular and uneven for a     
distance of about two  miles1 that a    
detour was made and the cable lengthened
 by five or  six miles40 ,in still      
another case 7#ahhe7 the repairing      
vessel found a  8difference of #aejj    
feet between the bow and stern          
soundings40 ,these  records point to    
sea-bottom faulting on a large scale4   
,it is probably no nearer the truth to  
say that changes of level result  from  
earthquakes than to say that earthquakes
 result from changes of  level4 ,the two
 classes of phenomena are probably to be
 referred to a  common cause4#bch       
,,slow ,,massive ,,movements4    ,it is 

a far cry from the intense and          
inconceivably rapid oscillations  of the
 earthquake1 to the excessively slow    
subsidences of continents1  or even the 
slow wrinkling of mountain folds4 ,not  
infrequently rivers  wear down their    
channels across a mountain range as fast
 as it rises  athwart them4 ,the        
movements of continents are even more   
deliberate4  ,but1 far apart as these   
contrasted movements are1 in rate and   
method1  they are associated in ultimate
 causation1 and the earthquake shock is 
often merely an incident in the         
formation of a mountain range or in the 
subsidence of a continent4    ,the great
 movements are usually classed 7#a7 as  
continent-making  7epeirogenic7 and 7#b7
 mountain-making 7orogenic74 ,they may  
also be  classed as 7#a7 vertical       
movements and 7#b7 horizontal movements1
 and  dynamically1 as 7#a7 thrust       
movements and 7#b7 stretching movements4
  ,it is to be understood that these    
distinctions are little more than       

analytical conveniences1 for continental
 movements are often at the  same time  
mountain-making movements2 vertical     
movements are usually  involved in      
horizontal movements1 and stretching    
usually takes part in  the processes in 
which thrust predominates1 and vice     
versa4 ,but where  one phase greatly    
preponderates1 it may conveniently give 
name to the  whole4    ,present         
movements4--,critical observations on   
seacoasts show that  some shores are    
slowly rising and some slowly sinking   
relative to  the ocean-level4 ,we do not
 certainly know what their movements are
  relative to the center of the earth2  
very possibly all may be sinking1  one  
set faster than the other1 the          
ocean-surface also going down at an     
intermediate rate4 ,theoretically1 all  
might possibly be rising1 one  set      
faster than the other1 the ocean also   
rising at an intermediate  rate1 though 
this is extremely improbable4 ,one set  
may be actually  rising relative to the 

center of the earth1 and the other      
sinking1  while the ocean-level is      
stationary1 or nearly so4 ,this is the  
way in  which we are accustomed to      
interpret them4 ,a general shrinkage of 
the  earth1 however1 is probably going  
on1 carrying down land-surface and      
sea-surface4 ,it has been urged by      
,suess#bci that the general shrinkage   
is so great that the local upward       
warpings and foldings never equal  it1  
and that the real movements are all     
downward1 though in different  degrees4 
,this is probably the general fact at   
least4 ,over against this  is the       
popular disposition to regard earth     
movements generally as  8upheavals40    
,there is also a predilection for       
regarding the rigid land  as moving and 
the mobile sea-level as fixed4 ,in      
reality1 the sea is an  extremely       
adaptive body that settles into the     
irregular hollows of the  lithosphere1  
and is shifted about with every warping 
of the latter4  ,whatever change affects

 the capacity of its depressions affects
 also  the sea-level4 ,if they are      
increased1 the sea settles more deeply  
into  them2 if they are decreased1 the  
sea spreads out more widely on the      
borders of the land4 ,the one thing that
 gives a measure of stability  to the   
sea-level is the fact that all the great
 basins are connected1  and so an       
average is maintained4 ,a warping down  
in one part of the  sea-bottom may be   
offset by an upward warping somewhere   
else in the  #gb of the earth's surface 
covered by the ocean1 and so it is only 
the  sum total of all changes in the    
sea-bottoms and borders that effects    
the common level4 ,thus it happens that1
 notwithstanding its instability  and   
its complete subordination to the       
lithosphere1 the sea-level is  the most 
convenient basis of reference1 and has  
become the accepted  datum-plane4 ,if   
there were some available mode of       
measuring the  distance of points from  
the center of the earth1 it would give  

absolute  data and absolute terms1 and  
would reveal much that is now uncertain 
respecting the real movements of the    
surface4 ,for convenience1 however1     
since absolute terms are impracticable1 
the ordinary language of  geology1 which
 represents movements as upward and     
downward1 according  to their relations 
to the sea-level or to the average      
surface1 will be  employed4             
,notwithstanding this concession to     
convenience in the use  of terms1 it is 
of the greatest importance to form1 and 
to constantly  retain1 true fundamental 
views4    ,fundamental                  
conceptions4--,the existence of any land
 at all is  dependent on the            
inequalities of the surface and of the  
density of the  lithosphere1 for if it  
were perfectly spheroidal and equidense1
 the  hydrosphere would cover it        
completely to a depth of about two      
miles4  ,not only are inequalities      
necessary to the existence of land1 but 
these  inequalities must be renewed from

 time to time1 or the land area  would  
soon1 geologically speaking1 be covered 
by the sea4 ,the renewal  has been made 
again and again in geological history by
 movements that  have increased the     
inequalities in the surface of the      
lithosphere4  ,with each such movement1 
apparently1 the oceans have withdrawn   
more  completely within the basins1 and 
the continents have stood forth more    
broadly and relatively higher1 until    
again worn down4 ,this renewal of       
inequalities appears to have been1 in   
its great features1 a periodic          
movement1 recurring at long intervals4  
,in the intervening times1  the sea has 
crept out over the lower parts of the   
continents1 moving  on steadily and     
slowly toward their complete submersion1
 which would  inevitably have been      
attained if no interruption had checked 
and  reversed the process4 ,these are   
the great movements of the earth1 and   
in them lies1 we believe1 the soul of   
geologic history and the basis  for its 

grand divisions4 ,the reasons for this  
will appear as the  history is followed1
 and its most potential agencies are    
seen unfolding  themselves4 ,at the same
 time1 there have been numerous minor   
surface  movements in almost constant   
progress4 ,while these two classes of   
movements have been associated1 and are 
perhaps due in the main to the  same    
causes1 they are sufficiently different 
in some of their dynamic  aspects to be 
separated in treatment4                 
,nearly ,constant ,small ,movements4    
,innumerable gentle warpings have       
affected nearly every portion of the    
surface of the globe at nearly all      
stages of its history4 ,not only  during
 the periods of great movements were    
there countless minor and  gentler      
movements1 but at times of relative     
quiescence there were  slow swellings   
and saggings of the surface of the      
lithosphere4 ,they  sometimes affected  
small areas and sometimes large ones1   
and they  were sometimes of upward phase

 and sometimes of downward4 ,they were  
the immediate agencies in locating and  
controlling the deposition  of          
stratified rocks1 though they rest back 
on the great movements  for their       
working conditions4 ,very slow sinkings 
of sea-borders have  permitted          
deposition to go on in shallow water for
 long periods  without being interrupted
 by the local filling of the sea4 ,very 
slow  swellings of land tracts1 relative
 or absolute1 have permitted erosion  to
 supply material for such sedimentation 
for long periods without  exhausting the
 sources4 ,very slow upward warpings in 
one region and  downward warpings in    
another have shifted the borders of the 
land  and sea1 and with them the areas  
of erosion and deposition4 ,thus  have  
arisen overlaps and unconformities of   
strata and diversities  in their        
distribution from stage to stage4 ,such 
movements may have  amounted to a few   
inches1 or a few feet1 or a few fathoms 
per century4  ,downward movements have  

sometimes affected a considerable       
section of a  continent1 letting in a   
shallow epicontinental sea upon it1     
such1 for  example1 as the ,north ,sea  
upon the northwestern border of the     
continent  of ,europe1 and ,hudson ,bay 
upon the northeastern part of ,north    
,america4  ,similar movements seem to   
have extended the seas even more widely 
upon the surface of the land in times   
past1 as attested by the great          
transgressions of the ocean-borders and 
the great epicontinental spread  of     
strata4 ,notwithstanding their great    
breadths1 the epicontinental  seas were 
generally shallow4 ,similar gentle      
warpings of upward phase  rescued the   
bottoms of shallow seas from submersion1
 and inaugurated  erosion2 or they bowed
 base-leveled lands upward1 and         
rejuvenated  their streams and          
inaugurated a new cycle of denudation4  
,often they  connected continents       
previously separated by shallow straits1
 and thus  inaugurated inter-continental

 migrations of land life1 while they    
stopped inter-oceanic migration4    ,the
 gentleness and frequency of these      
movements is attested by the  character 
of the sediments and by their relations 
to one another1 as  will be seen in the 
study of the sedimentary series4        
,reciprocal features4--,these minor     
warpings show a notable tendency  to be 
reciprocal4 ,if one area is bowed up1   
another near by is bowed  down4 ,if the 
continents settle1 the oceans rise on   
their borders4 ,if  the land is cut     
down1 the sea is filled up4 ,there is an
 important  phase of this deserving     
especial note4 ,certain tracts have been
 slowly  bowed upwards into long land   
swells1 the streams being rejuvenated   
and  degradation hastened4 ,adjacent    
tracts have been slowly bowed downwards 
into long parallel troughs which        
received the wash from the adjacent     
swells1 and thus became tracts of       
exceptional sedimentation4 ,such a      
tract of parallel swell and sag1 if our 

interpretation be correct1  developed   
along the ,atlantic border of ,north    
,america in the ,paleozoic  era4 ,by the
 slow upward warping of the swells1 the 
feeding-grounds of  the streams were    
maintained1 and the sags were filled    
about as fast  as they sank4 ,thus a    
great depth of sediment was laid down in
 the  course of an era measured by      
millions of years4 ,so in other regions1
  especially near the borders of the    
continents1 there have been similar     
reciprocal movements1 giving at once    
feeding-grounds for the streams  and    
lodgment-grounds for the sediments1 side
 by side in parallel  belts4 ,it is a   
common view that these belts of deep    
sedimentation were  the forerunners of  
mountain formation1 and that they       
determined the  formation of the        
mountains4 ,in view of the grounds for  
doubting the  efficiency of so          
superficial an agency in mountain       
formation1 which  will appear as we go  
on1 it may be well to hold this view in 

abeyance1  and to dwell on the          
reciprocal nature of the action1 in     
which the  upward bowing that gave the  
feeding-grounds is as vital a factor as 
the sagging that accommodated the       
sedimentation4 ,it is important to      
recognize that in so far as the crust   
was weak enough to yield to  these      
gentler forces1 it was not strong enough
 to accumulate the great  stresses      
necessary to form mountain ranges1 and  
further1 that in so far  as the stresses
 were eased by the gentle warping1 they 
could not be  accumulated for the later 
work of mountain-folding4 ,it is        
nevertheless  probable that the         
conditions which located the gentle     
swelling and  sagging also located the  
mountain-folding4                       
,the ,great ,periodic ,movements4       
,mountain-forming movements4--,along    
certain tracts1 usually near the        
borders of the continents1 and at       
certain times1 usually separated by     
long intervals1 the crust was folded    

into gigantic wrinkles1 and these       
constitute the chief type of mountains1 
though not the only type4 ,the          
characteristic force in this folding was
 lateral thrust4 ,the strata  were not  
only arched1 but often closely folded1  
and sometimes intensely  crumpled4 ,in  
extreme cases1 like the ,alps1 the folds
 flared out above1  giving overturn dips
 and reversed strata1 as illustrated in 
the chapter  on ,structural ,geology1   
pp4 #eja-eaa4 ,in these cases there was 
an upward  as well as a horizontal      
movement1 for the folds themselves were 
lifted2 but the horizontal thrust so    
much preponderated1 and was so  much the
 more remarkable1 that the upward       
movement was overshadowed4  ,it is well 
to note1 however1 that these mountain   
ranges are crumpled  outward and not    
inward1 as might be expected if they    
resulted  simply from the shrinkage of  
the under side of a thin shell4 ,the    
folds  are sometimes nearly upright and 
symmetrical1 and sometimes inclined  and

 asymmetrical1 as illustrated in the    
chapter referred to4 ,where the  folds  
lean1 the inference has been drawn that 
the active thrust came  from the side of
 the gentler slope1 the folds being     
pushed over toward  the resisting side1 
and this seems to be commonly true4 ,the
 original  attitude of the beds1        
however1 has much to do with the        
character of  the folds4#bdj ,by a      
slight change in the mode of thrust1    
sheets of  paper may be so pushed as to 
lean forward or backward at pleasure4   
,the leaning of the folds seems1        
therefore1 a doubtful criterion for     
determining the direction of the active 
movement4 ,mountains of the  thrust type
 usually consist of a series of folds   
nearly parallel to  each other1 the     
whole forming an anticlinorium4         
,illustration3 ,fig4 #ddi4--,the great  
,eurasian mountain tract4 ,jones        
,relief ,globe4 7,photo4 by ,r4 ,t4     
,chamberlin47    ,distribution of folded
 ranges4--,the prevailing location of   

this  class of mountains is so generally
 near the borders of the continents     
that the relation is probably           
significant4 ,dana#bda long ago called  
attention to the fact that the greatest 
mountain ranges stand opposite  the     
greatest ocean-basins1 and he connected 
the elevation of the one  with the      
depression of the other4 ,one of the    
most notable exceptions  to this        
relation is the complex system of       
southern ,europe1 from the  ,pyrenees to
 the ,caucasus1 and another is the      
,altai and connected ranges  7,fig4     
#ddi74 ,the ,urals and not a few minor  
ranges are also exceptions4  ,it is     
probably better to regard the crumpled  
tracts as lying on the  borders of great
 segments of the earth that acted       
essentially as units1  and to regard the
 relationship to the sea as a           
coincidence that is only  in part       
causal4#bdb    ,plateau-forming         
movements4--,another leading phase of   
crustal movement  is the settling or    

rising of great blocks of the crust1 as 
though by  vertical rather than         
horizontal force4 ,the western plateau  
of ,north  ,america and the great       
plateau of ,thibet are gigantic         
examples4 ,the  ,american plateau       
embraces numerous blocks which1 while   
they have been  elevated together1 are  
individually tilted in their own        
fashion4 ,at  the surface1 they are     
separated by fault-planes1 but below1   
some of  them1 and perhaps most of them1
 pass into flexures4 ,most of these     
flexures are of the monoclinal type 7p4 
#eaf71 which dynamically means  much the
 same as a fault2 but some of them may  
be of the compressive  type1 without    
inconsistency with vertical fault-relief
 above4 ,research  has not yet covered  
thoroughly any great plateau1 and       
knowledge of  this class of movements is
 less complete than that of folding by  
lateral thrust1 and it has a less ample 
place in the literature of the  subject4
 ,the plateau-forming movements are1    

however1 much more massive  than the    
mountain-folding movements1 and stand   
next in magnitude to  the               
continent-forming movements4 ,plateaus  
may be regarded as smaller  platforms   
superposed on the continental platforms4
    ,in the ocean-basins1 there appear  
to be raised platforms of the  plateau  
type1 and there are remarkable 8deeps0  
that have the aspect of  anti-plateaus4 
,continent-forming movements4--,true    
continent-forming movements  appear to  
have antedated the earliest known       
sediments4 ,as far back  as we can read 
the sedimentary record1 the continents  
seem to have  been well established1 and
 there is little evidence that they have
  since been fundamentally changed4 ,it 
is true that some very eminent          
geologists have rather freely connected 
formations on one continent  with       
formations having similar faunas on an  
opposite continent1 by a  hypothetical  
conversion of the intervening           
ocean-bottoms into land  or shallow     

water2 but most such faunal relations   
can be explained  almost equally well by
 migration around the coasts1 or at most
 by  mere ridge-connections4 ,the       
paucity1 if not total absence1 of       
abysmal  deposits in the strata of the  
continents1 taken with the persistence  
of terrestrial and coastal faunas1      
leaves little room for assigning  an    
interchange of position between abysmal 
depths and continental  elevations1 and 
vice versa4 ,dynamic considerations also
 offer grave  difficulties4 ,the        
doctrine of the persistence of          
continents probably  ought not to be    
pushed so far as to exclude shallow     
water1 or even  land1 connections       
between ,south ,america1 ,antarctica1   
,australia1  ,india1 and ,south ,africa1
 directly or indirectly1 at certain     
stages  of geological history4 ,without 
forming final conclusions as to the     
measure of the change which the         
continents have suffered during known   
geological history1 it is safe to       

conclude that the continents and        
ocean-basins were in the main formed    
very early in the earth's history1  and 
that subsequent changes have consisted  
chiefly in the further  sinking of the  
basins and the further protrusion of the
 land1 save as  the latter has been cut 
down by erosion4 ,incidentally1 the     
ocean-basins  have probably been        
extended and the continents restricted4 
,on the other  hand1 the continents have
 been built out on their borders by wash
  from the land1 and the waters of the  
ocean have been somewhat lifted  by the 
deposition of sediment in their basins4 
,it is estimated that  the cutting away 
of the present continents1 and the      
deposition of the  material in the      
ocean-basins1 would raise the sea-level 
about #fej feet4  7,r4 ,d4 ,george47    
,relations of these movements in        
time4--,the folding movements seem  to  
have had extraordinary prevalence in the
 earliest ages1 for the  ,archean rocks 
are almost universally crumpled1 and    

often in the most  intricate fashion4   
,there is no sign that the folding was  
then limited  to the borders of the     
continents2 it seems rather to have     
affected  the whole continental surface4
 ,after the beginning of the well-known 
sedimentary series1 crumpling appears to
 have taken place chiefly at  long      
intervals1 thus marking off great       
time-divisions1 and to have been        
confined at any given stage to certain  
tracts1 chiefly on the borders  of great
 segments of the earth's crust4         
,concerning the plateau-forming         
movements in the past1 knowledge is very
  meager1 as the detection of plateaus  
of ancient times is more difficult  than
 the detection of folds4 ,gentle        
warpings have apparently been in        
progress at all times4    ,relations of 
vertical to horizontal movements4--,the 
downward movements  are unquestionably  
the primary ones1 and the horizontal    
ones are  secondary and incidental4 ,the
 fundamental feature is doubtless       

central  condensation actuated by       
gravity1 and the master movements are   
the  sinkings of the ocean-basins4 ,the 
great periodic movements that made      
mountains and plateaus1 and changed the 
capacity of the ocean-basins1  probably 
started with the sinking of part or all 
of the ocean-bottoms4  ,in the greater  
periodic movements1 probably all the    
basins participated  more or less1 but  
some seem to have been more active than 
others4 ,for  example1 in the last great
 mountain-making period1 the ,pacific   
basin  seems to have been more active   
than the ,atlantic1 while in the similar
  great event at the close of the       
,paleozoic1 the opposite seems to have  
been true4 ,the squeezing up of the     
continents doubtless took place         
simultaneously with the settling of the 
basins4 ,the true conception is  perhaps
 that the ocean-basins and continental  
platforms are but the  surface forms of 
great segments of the lithosphere1 all  
of which crowd  toward the center1 the  

stronger and heavier segments taking    
precedence  and squeezing the weaker and
 lighter ones between them4 ,the area of
 the  more depressed or master segments 
is almost exactly twice that of the     
protruding or squeezed ones4 ,this      
estimate includes in the latter about   
#aj1jjj1jjj square miles now covered    
with shallow water4 ,the volume  of the 
hydrosphere is a little too great for   
the true basins1 and it  runs over1     
covering the borders of the continents4 
,the amount of the  overflow fluctuates 
from time to time1 and may be neglected 
in a study  of the movements and        
deformations of the lithosphere4    ,the
 squeezed segments4--,the great         
protruding segments show a tendency     
toward rude triangularity4 ,they are    
7#a7 the ,eurasian1 now strongly  ridged
 on the south and east1 and relatively  
flat on the northwest2  7#b7 the        
,african1 rather strongly ridged on the 
east1 but less abruptly  elevated on the
 west and north2 7#c7 the ,north        

,american1 now strongly  ridged on the  
west1 more gently on the east1 and      
relatively flat at the  north and in the
 interior2 7#d7 the ,south ,american1   
strongly ridged on  the west and        
somewhat on the northeast and southeast4
    ,the foregoing form the major group4
 ,the minor group embraces 7#e7 the     
,antarctic segment1 not as yet          
sufficiently known to be well defined1  
and 7#f7 the ,australian1 broadly       
reniform rather than triangular4 ,to    
these are perhaps to be added 7#g7 the  
largely submerged platform that         
stretches from ,sumatra and ,java on the
 southwest to the ,philippines  on the  
northeast1 and is attached to ,india on 
the northwest2 and 7#h7  ,greenland1    
which1 though closely associated with   
,north ,america1 is  partially separated
 by a rather deep depression4    ,the   
depressed or master segments4--,the     
great sunken segments show  a tendency  
to assume roughly polygonal1 rather than
 triangular1  forms4 ,this accords with 

the primary place assigned them1 since1 
in a  spherical surface divided into    
larger and smaller segments1 the major  
parts should be polygonal while the     
minor residual segments are more  likely
 to be triangular4 ,the major segments  
are 7#a7 the ,pacific1 7#b7  the        
,indian1 7#c7 the ,north ,atlantic1 and 
7#d7 the ,south ,atlantic4 ,these  form 
the principal group1 while 7#e7 the     
,arctic deeps 7not including  the       
shallow epicontinental portions71 7#f7  
the ,mediterranean1 7#g7 the            
,caribbean1 and 7#h7 the chain of deep  
pits between the ,philippine ridge  and 
the ,bornean platform1 constitute a     
subordinate group4    ,each member of   
the minor group is an irregular chain of
 depressed pits  rather than a single   
continuous deep1 unless the ,arctic     
depression1 of  which little is now     
known1 proves an exception4 ,they lie   
between the  greater segments at what   
may be conceived to be points of        
critical  working relations1 and are    

accompanied by small elevated blocks4   
,the  ,caribbean1 the ,mediterranean1   
and the ,bornean regions are the seats  
of  the greatest present volcanic and   
related activities4    ,in a general    
view1 there are then four great sunken  
quadrilaterals and  four great elevated 
triangles1 with minor attendants in each
 class4  ,lest fondness for simplicity  
and symmetry lead too far1 we must      
hasten  to observe that the dimensions  
are not alike in either class4 ,the     
,pacific segment is more than twice the 
size of any other basin segment1  and   
four times that of the ,north ,atlantic4
 ,the ,eurasian triangle is  more than  
twice the average size of the other land
 segments1 and  nearly three times that 
of the ,south ,american4 ,nor is there  
any large  common divisor of approximate
 accuracy4 ,this is not at all strange  
if  the earth be regarded as a body of  
somewhat heterogeneous composition      
which naturally shrank in rather        
irregular segments4 ,on the other hand1 

this irregularity is somewhat strange if
 the earth has evolved from a  very     
homogeneous and symmetrical1 primitive1 
fluid state4 ,it is also a  serious     
consideration in any theory that appeals
 to crystalline form1  or analogy1 as in
 the doctrine of a tetrahedral earth4   
,roughly approximated in millions of    
square miles1 the major depressed       
segments are as follows3 the ,pacific1  
#fj1 the ,indian1 #bg1 the ,south       
,atlantic1 #bd1 and the ,north          
,atlantic1 #ad1 leaving #h for minor    
depressions4 ,the elevated segments are 
,eurasian1 #bd1 ,african1 #ab1 ,north   
,american1 #aj1 and ,south ,american1   
#i1 leaving #aj for the minor blocks4   
,if these segments be regarded as the   
great integers of body-movement1        
two-thirds of them taking precedence in 
sinking and the other third  in         
suffering distortion1 it is easy to pass
 to the conception of  sub-segments1    
moving somewhat differently from the    
main segments1  so as to aid in their   

adjustment to one another1 and thus to  
the  conception of plateaus and deeps4  
,it is easy also to pass to the         
conception of mutual crowding and       
crumpling at the edges of these         
segments1 accompanied by fracture and   
slipping4 ,these conceptions  perhaps   
represent the true relations between the
 massive movements  of the abysmal and  
continental segments1 as well as the    
less massive  plateau-forming movements 
and the mountain-forming distortions4   
,the  mountains and plateaus are        
probably the incidental results of the  
great abysmal and continental           
readjustments4    ,the great movements  
are probably to be attributed to        
stresses that  gradually accumulated    
until they overcame the rigidity of the 
thick  massive segments involved1 and   
forced a readjustment4 ,in accumulating 
these stresses1 some local yielding on  
weak lines and at special  points was an
 inevitable incident in distributing    
more equably the  accumulating stresses4

 ,so1 also1 the first great             
readjustments probably  left many local 
strains and unequal stresses which      
gradually eased  themselves by warpings1
 minor faultings1 etc41 so that some    
minor  movements were a natural sequence
 of the great movements4 ,but there     
were doubtless many local and           
superficial causes1 such as irregular   
gains and losses of heat1 regional      
loading and unloading1 solution1        
hydration1 etc41 that have caused local 
or regional movement1 and which  have   
little to do with the great deformations
 of the earth's body4 ,as  implied      
above1 the gentle1 nearly constant      
movements probably fall  mainly into a  
different category from the great       
periodic movements4  ,both will be      
considered further4    ,the differential
 extent of the movements4--,between the 
highest  elevation of the land and the  
lowest depth of the ocean1 there is a   
vertical range of nearly twelve miles4  
,there may have been higher  elevations1

 relatively1 in past times1 but probably
 not deeper  depressions2 and so1 if we 
assume that the surface was once        
perfectly  spheroidal1 this may be taken
 as a maximum expression of differential
  movement1 not absolute vertical       
movement4 ,from the ,thibetan plateau1  
where a considerable area exceeds three 
miles in height1 to the  ,tuscarora     
deep1 where a notable tract exceeds five
 miles in depth1 the  range is eight    
miles1 which may fairly represent the   
vertical range of  rather massive       
differential movement4 ,from the average
 height of the  continents to the       
average abysmal bottoms of the oceans   
the range is  nearly three miles1 which 
may be taken as the differential        
movement of  the great segments4 ,under 
certain hypotheses of the origin and    
early  history of the earth1 to be      
sketched later1 the surface is not      
assumed  to have been perfectly         
spheroidal originally1 and hence the    
present  irregularities do not          

necessarily imply so great differential 
movement4    ,if the protruding portions
 of the lithosphere were graded down and
 the  basins graded up to a common      
level1 this level would lie about #ijjj 
feet below the ocean-surface4 ,this     
equated level is the best basis  of     
reference for relative segmental        
movements4 ,referred to this datum      
plane1 the continents1 having an area   
about half as great as that of  the     
ocean depths1 have been squeezed up     
relatively about two miles1  and the    
basins have sunk about one mile from the
 ideal common plane4  ,the total        
downward movement1 representing the     
total shrinkage of the  earth1 is quite 
unknown from observation4 ,it is        
probably very much  greater than the    
differential movement1 as will appear   
from theoretical  considerations as we  
go on4    ,the extent of the lateral    
movements has a peculiar interest1 for  
it bears theoretically on the shrinkage 
of the earth4 ,every mile of  descent of

 the crust represents #f miles 7#f4bh7  
shortening of the  circumference4 ,if   
the vertical movements were limited to  
the relative  ones just named1 the mile 
of basin descent would give but little  
more  than #f miles of surplus          
circumference for lateral thrust and    
crumpling4  ,how far does this go in    
explaining the known facts8 ,by         
measuring the  folds of the ,alps1 ,heim
 has estimated the shortening           
represented by  them to be #gd          
miles4#bdc ,claypole estimated the      
shortening for the  ,appalachians in    
,pennsylvania1 not including the        
crystalline belt on  the east1 at #df   
miles2#bdd ,mc,connel placed that of the
 ,laramide range  in ,british ,america  
at #be miles1#bde and ,le,conte that of 
the ,coast  range in ,california at #i  
to #ab miles4#bdf ,these estimates must 
be  corrected for the thickening and    
thinning of the beds in the process  of 
folding1 for the composite character of 
the folds1 and for the  effects of      

shearing and faulting4 ,these will in   
part tend to increase  and in part to   
decrease the estimates4 ,the first      
effect of horizontal  thrust is to close
 up all crevices and compact the beds as
 much as they  will stand without       
bending4 ,a part of the unusual         
thickness which the  beds of folded     
regions commonly show is probably due to
 this edgewise  compression4 ,in        
experiments on artificial strata made to
 illustrate  foldings 7,fig4 #ddi;a71   
the thickening of the layers is a very  
appreciable part of the process1 though 
probably natural beds do not  thicken in
 equal proportion4 ,after the beds have 
been closely folded  and the thrust is  
athwart them1 they are thinned and      
stretched on the  limbs of the fold4    
,how far this and other causes of       
extension offset  initial compression is
 undetermined1 and is differently       
estimated4 ,it  seems highly probable   
from the nature of the case that the    
edgewise  compression which resulted    

from sustaining the full stress before  
the  beds bent1 was much greater than   
the crosswise compression on the limbs  
of the folds1 which came into action    
only after the stress had been  largely 
satisfied by folding4    ,illustration3 
,fig4 #ddi;a4--,illustrations of        
,willis' experiments in    the          
artificial representation of mountain   
folding4 ,the sections were    formed of
 layers of wax of different colors1 and 
were mechanically    compressed from the
 right4 ,the upper section shows the    
original    state1 and the offsets of   
the succeeding sections at the right    
indicate the amount of shortening4      
7,thirteenth ,ann4 ,rep4 ,u4 ,s4 ,geol4 
,surv47    ,whatever the correction1 and
 whatever the probable errors of the    
above  estimates1 the amount of         
shortening involved in folding is large4
 ,the  estimates given are merely those 
for certain periods of folding1 and     
represent only that portion of the      
compression of the circumference  which 

was concentrated in a given mountain    
range4 ,the whole shortening  of a      
circumference is to be found by adding  
together all the transverse  foldings on
 a given great circle1 following it     
about the globe at  right angles to a   
given folded tract4 ,in so doing1 it    
will be seen that  the belt does not    
usually cross more than one or two      
strongly folded  tracts of the same age1
 from which it is inferred that the     
shortening  on each great circle was    
largely concentrated in a few tracts    
running  at large angles to each other1 
to accommodate the shrinkage of the     
globe in all directions4 ,if the folding
 in a main range crossing  any great    
circle is doubled1 it will probably     
represent roughly the  shortening for   
that entire circle for that age4 ,if one
 is disposed  to minimize the amount of 
folding1 the estimate may perhaps be put
  roundly at #ej miles1 on an entire    
circumference1 for each of the great    
mountain-making periods4 ,if1 on the    

other hand1 one is disposed to  give the
 estimates a generous figure so as to   
put explanations to the  severest test1 
he may perhaps fairly place the         
shortening at #ajj miles1  or even more4
 ,for the whole shortening since        
,cambrian times1 perhaps  twice these   
amounts might suffice1 for while there  
have been several  mountain-making      
periods1 only three are perhaps entitled
 to be put  in the first order1 that at 
the close of the ,paleozoic1 that at the
  close of the ,mesozoic1 and that in   
the late ,tertiary4 ,the shortening  in 
the ,proterozoic period was             
considerable1 but is imperfectly known4 
,the ,archean rocks suffered great      
compression in their own times1 and     
probably shared in that of all later    
periods1 and if their shortening  could 
be estimated closely1 it might be taken 
as covering the whole4  ,assuming the   
circumferential shortening to have been 
#ej miles during a  given great         
mountain-folding period1 the appropriate

 radial shrinkage  is #h miles4 ,for the
 more generous estimate of #ajj miles1  
it is #af  miles4 ,if these estimates be
 doubled for the whole of the ,paleozoic
 and  later eras1 the radial shortening 
becomes #af and #cb miles1 respectively4
                              ,,the     
,,causes ,,of ,,movement4               
,general ,considerations4    ,the volume
 of the earth is at all times dependent 
on two sets of  antagonistic forces1    
7#a7 the attractive or centripetal1     
consisting of  gravity and the molecular
 and sub-molecular attractions1 and 7#b7
 the  resistant forces--which are not   
necessarily centrifugal--consisting of  
heat and the resistant molecular and    
sub-molecular forces4                   
#a4 ,the centripetal agencies4          
,gravity4--,the most obvious of the     
concentrating forces is gravity1  and in
 most questions relating to great       
segmental movements1 it has  been       
thought sufficient to consider gravity  
alone1 but it is by no  means certain   

that this does not lead to serious      
error4 ,in studying  the causes and     
effects of earth movements1 it is       
necessary to consider  both             
gravitational energy and gravitational  
force4 ,gravitational  energy is        
greatest when the mass is most widely   
dispersed1 and least  when most         
concentrated4 ,gravitational force is   
greatest when the mass  is most         
concentrated1 and least when most       
dispersed4 ,the gravitational  energy of
 the earth matter was at its maximum    
when it was most widely  diffused in the
 supposed nebulous condition4 ,it will  
perhaps reach  its minimum at some      
future period when the shrinkage shall  
reach its  limit4 ,in passing from an   
expanded condition to a more            
concentrated  condition1 potential      
energy1 or energy of position1 is       
transformed  into other forms of energy1
 chiefly heat4 ,the heat thus developed 
is an important factor in the earth's   
dynamics4 ,the total amount of          

gravitational energy involved in the    
earth's evolution is unknown1 for       
neither the maximum dispersion of the   
earliest state1 nor the ultimate        
condensation1 is known4 ,it is not      
difficult1 however1 to compute the      
amount of transformation of             
gravitational energy into heat1 or other
  forms of energy1 during a given degree
 of condensation4 ,if a mass  equal to  
that of the earth were originally       
infinitely scattered1 the  gravitational
 energy given up by it in condensing    
into a homogeneous  sphere of the       
earth's present size would1 if all      
transformed into heat1  suffice to raise
 the temperature of an equal mass of    
water #hijj ,c4  7,hoskins71 or an equal
 mass of rock 7specific heat of 4#b71   
#dd1ejj ,c4  ,if the mass were more     
condensed toward the center1 as is the  
actual  case1 the heat would be         
considerably greater4 ,if the           
condensation  toward the center followed
 the ,laplacian law 7p4 #efd71 the heat 

would  be sufficient to raise the earth 
mass #dh1ijj ,c41 assuming its specific 
heat to be 4#b1 which is about the      
average specific heat of rock at  the   
surface 7,lunn74 ,a further shrinkage of
 one mile would transform  an additional
 amount of gravitational energy into    
heat about equal in  amount to ,tait's  
estimate of the loss of heat from the   
surface of the  earth in #ajj1jjj1jjj   
years 7see p4 #egb74 ,if the radial     
shrinkage has  been #cb miles1 or even  
#af miles1 the amount of heat generated 
is very  much greater than the estimated
 loss from the surface4    ,how much    
gravitational energy can possibly be    
transformed into heat and  other forms  
of energy in the future1 can only be    
computed by making  assumptions as to   
the possible extent of further          
contraction1 and that  involves         
hypotheses as to the atomic and         
sub-atomic constitution of the  earth's 
matter1 and its behavior under the      
prodigious pressures of the  earth's    

interior4 ,all shrinkage develops added 
gravitational force and  further        
tendency to shrinkage1 which follows    
when the heat generated by  the         
shrinkage is lost2 and where the process
 may end1 in a body of the  dimensions  
of the earth1 is beyond present         
determination4 ,if there were  no limit 
to the density that might be attained1  
it would be impossible  to assign any   
limit to the energy that might be       
transformed4 ,it has  usually been      
assumed that contraction could not go on
 indefinitely  because the atoms would  
come into actual contact1 and prevent   
further  increase of density4 ,this     
conception rests on the recently        
prevalent  hypothesis of the atomic     
constitution of matter2 but the more    
recent  hypotheses that substitute      
multitudes of revolving corpuscles or   
electrons for irreducible atoms1 do not 
carry the same presumption of a         
rigorous limit to condensation4 ,it is  
not therefore prudent to try to  set    

such a limit1 or to make it a feature in
 the dynamical doctrines  of the earth4 
,it is even less prudent to try to      
measure the limit of  future conversion 
of the gravitational energy of the sun  
into heat1 and  so to set a limit to the
 habitability of the earth4    ,the     
force of gravity may be defined as the  
effort of gravitational  energy to      
change into other forms of energy4 ,it  
is most familiarly  expressed in terms  
of weight1 which is the resultant of the
  gravitational force of the whole earth
 upon a given portion4 ,weight is       
determined by the distances and         
directions of the given portion from    
all parts of the attracting mass1 the   
amount of the attraction being  directly
 as the mass and inversely as the square
 of the distance1  modified by the      
direction4 ,it is greatest about #faj   
miles below the  surface1 where it is   
#a4jcib times that at the surface4      
,below this point  it declines1 and at  
the center it is zero4 ,the sum total of

 the earth's  gravitative force at the  
present time is equivalent to about #f  
#aj  tons4 ,this gives rise to a        
pressure of about #c1jjj1jjj atmospheres
 at  the center of the earth4           
,gravitational force is also expressed  
in terms of the earth's ability  to     
accelerate the velocity of falling      
bodies at its surface1 which is  now    
approximately #cb feet per second4 ,for 
certain purposes1 the force  of gravity 
may be better pictured by means of the  
velocity required  to overbalance it1   
which is #f4i miles per second2 e4g4 a  
body shot  away from the surface at a   
speed exceeding #f4i miles per second1  
would  escape from the control of the   
earth if the influence of the atmosphere
  and other bodies is neglected2 while a
 body shot away at less than this  speed
 would return to the earth4             
,molecular and sub-molecular            
attractions4--,in addition to gravity1  
there are at least three additional     
classes of attractive agencies  whose   

laws appear to differ from those of     
gravity1 viz4 cohesion1  chemical       
affinity1 and sub-atomic attraction1    
using these terms in  their             
comprehensive generic senses4 ,the      
thought has been entertained  that these
 might be reducible to forms of gravity 
in ulterior analysis1  but it does not  
appear from existing evidence that the  
laws of their  attractions are          
conformable to the ,newtonian law of the
 inverse  square of the distance1 to    
which gravity conforms4 ,apparently the 
forces of the molecular1 atomic1 and    
sub-atomic attractions increase  at     
higher rates1 and have individual       
peculiarities of action quite  different
 from gravity4 ,it would be of the      
utmost service to geological  philosophy
 if these laws of molecular and         
sub-molecular attractions  were firmly  
established1 and could be applied to the
 conditions of  heat and pressure under 
which the matter of the interior of the 
earth  exists4 ,in the absence of such  

determinations1 we can do little more   
than recognize that the matter of the   
interior of the earth tends to  condense
 itself by the aid of molecular and     
sub-molecular attractions1  supplemental
 to the attraction of gravity4          
,cohesion and crystallization4--,the    
force of gravity between small  bodies  
is exceedingly feeble1 but it is        
cumulative1 every particle in a  mass   
attracting every other particle1 so that
 in great masses the force  becomes     
enormous4 ,in cohesion1 and probably in 
the other molecular and  sub-molecular  
attractions1 the particles attract very 
strongly the  particles with which they 
are in close relations1 but beyond      
minute  distances their effects are     
insensible4 ,the force of               
crystallization  is felt for a very     
short distance from the crystal1 and    
8mass action0  is probably dependent on 
a function of similar kind1 acting at a 
very  small distance1 but the range of  
these forces is very limited in         

comparison with that of gravity4        
,rock matter1 as a rule1 tends to become
 crystalline by the assembling  of like 
molecules in systematic order4 ,the     
general effect is  condensation1 though 
this is not universally the case1 for in
 some  instances the crystalline        
arrangement results in expansion4 ,the  
crystallizing force may be regarded as a
 specialized variety of  cohesion which 
usually coperates with gravity to       
produce increased  density4 ,in cases of
 expansion it seems clear that the      
organizing force  does not act according
 to the law of gravity4 ,the intensity  
of the  force exhibited in the formation
 of ice illustrates the superiority of  
the molecular force over the gravitative
 force in small masses2 but in  a planet
 of ice of very moderate dimensions1 the
 internal pressure of  gravity would    
overcome the crystalline force1 which   
illustrates the  superiority of gravity 
in large masses4    ,while the          
crystalline force may thus in           

exceptional cases operate  against      
gravity1 it is known that in most cases 
it not only operates  with it1 but is   
controlled by it1 in this sense--that   
where a substance  has two forms of     
crystallization1 it will take the denser
 one when the  pressure is great4 ,the  
inference is that if the less dense form
 of  crystallization takes place under  
slight pressure1 and subsequently  the  
pressure is greatly increased1 the form 
of crystallization will  change from the
 less to the more dense4#bdg ,it is     
probable that in  general those forms of
 molecular arrangement will be assumed  
in the  deep zones which give the       
greatest density1 and this probably     
includes  concretionary1 colloidal1 and 
other forms of aggregation1 as well as  
crystallization4    ,diffusion4--,the   
same law probably holds relative to     
diffusion1 though  in a molecular sense 
diffusion is the opposite of            
crystallization1  for in                
crystallization1 like comes to like1    

while in diffusion the  molecules       
distribute themselves among those of    
unlike nature4 ,diffusive  action1 quite
 familiar in gases and liquids1 takes   
place to some extent  in solids4 ,the   
molecules of plates of gold and lead    
brought into  intimate contact under    
pressure mutually diffuse among one     
another4  ,so gases seem to be very     
generally diffused or 8occluded0 in     
rocks1  though the nature of this       
relation is imperfectly determined4 ,it 
is known that pressure upon gases       
promotes their diffusion through        
liquids and solids4 ,it is inferred that
 pressure upon a solid tends  to the    
diffusion of the entrapped gases within 
it1 but it is not to  be inferred from  
this that pressure upon rock promotes   
the absorption  of gases into it1 but   
rather the opposite4 ,it is probable    
that great  pressure with high heat     
promotes the diffusion of entrapped     
gases or  other diffusible substances   
through the rock-mass1 and at the same  

time  tends to their extrusion along    
lines of least resistance2 but this is  
an inference rather than a              
demonstration4    ,chemical             
combination4--,the general effect of    
chemical combination  under pressure is 
greater density4 ,in reversible         
reactions capable of  conditions of     
chemical or physical equilibrium1       
pressure invariably  favors the         
formation of the denser of any possible 
products4    ,sub-atomic                
forces4--,recent investigation has made 
it probable  that atoms are composite1  
embracing many exceedingly minute       
bodies--corpuscles or electrons--in a   
state of extremely high activity  and   
possessed of marvelous energy           
notwithstanding their minuteness4  ,this
 discovery possesses deep interest to   
the geologist because it  seems to      
reveal sources of energy of almost      
incalculable potency1 some  portions of 
which at least are being constantly     
freed and added to  the previously      

recognized supplies of energy4 ,attempts
 have been made  during the past few    
decades to limit the habitable age of   
the earth1  both retrospectively and    
prospectively1 by the smallness of the  
sum  total of energy derivable from     
gravity4 ,in these estimates slight     
recognition has been given to the       
resources of molecular and atomic       
energy1 and none at all to the          
possibilities of sub-atomic energy4 ,it 
would be going quite too far to assume  
that these sub-atomic energies  are all 
available for the perpetuation of       
habitable conditions on  the earth or in
 the solar system1 but we are doubtless 
justified in  appealing to them as an   
offset to all dicta restricting the     
period  of the earth's habitability by  
supposed insufficiencies of energy      
deduced merely from the estimated       
resources of gravity4 ,the banishment   
of the idea of the atom as a minute1    
incompressible1 undecomposable  sphere  
takes away the theoretical limit of     

compressibility1 and by  so doing cuts  
away the groundwork for assigning       
definite limits even  to the resources  
of gravity1 since1 as already indicated1
 unlimited  condensation gives          
theoretically unlimited transformation  
of the  potential energy of gravity4    
,while we must await with such patience 
as we can command the  development of   
fuller knowledge concerning the nature  
and laws of the  molecular1 atomic1 and 
sub-atomic energies1 and their          
applicability to  the activities        
resident in the interior of the earth1  
it is permissible  even now to assume   
that1 besides the simple compressive    
action of  gravity1 there are at work   
varied forms of molecular aggregation1  
of  atomic combination1 and perhaps of  
sub-atomic change1 tending toward       
increased density1 and that the ulterior
 limit of these processes is  quite     
undetermined4 ,the condensational forces
 are now restrained at  certain         
temporary limits by the antagonistic    

resistant forces1 some of  which1 such  
as heat1 are the products of the        
condensational forces1 and  are         
gradually being dissipated1 permitting  
further condensation4 ,where  the       
process may ultimately end1 we dare not 
attempt to say4 ,on the  other hand1 we 
are not compelled to accept assigned    
limits that seem to  be inconsistent    
with the phenomena which the earth      
actually presents4                      
#b4 ,the resisting agencies4            
,heat4--,the most familiar of the active
 agencies that resist  condensation is  
heat4 ,upon this the existing volume of 
the earth is  immediately dependent1 in 
some large part at least4 ,as this heat 
is  dissipated1 the earth shrinks4 ,this
 shrinkage increases the force of       
gravity1 and hence the internal pressure
 increases1 and1 if further  compression
 takes place as the result of this      
increased pressure1  additional heat is 
developed1 which checks further         
condensation until  it is dissipated4   

,it is this kind of creative and        
self-checking action  that determines   
the volume of great gaseous bodies like 
the sun4 ,though  their matter is far   
from its ultimate density1 and their    
self-gravity  is enormous1 they condense
 slowly1 because1 with every stage of   
condensation1 heat is generated which   
antagonizes gravity and checks          
condensation1 until at least a part of  
the heat is radiated away4  ,as the     
force of gravity increases with every   
stage of condensation1  the heat        
developed to hold it in check must      
increase1 and hence the  famous law of  
,lane1 that a gaseous body like the sun 
grows hotter as  it condenses4 ,this law
 holds good while the body remains in a 
gaseous  state in which the maintenance 
of the volume is essentially dependent  
on heat4 ,when a body becomes liquid or 
solid1 its volume is dependent  in part 
on forms of resistance other than heat1 
and the force of the  law is abated1    
though the principle still holds good4  

,in small solids1  the principle has    
little application1 since the force of  
self-gravity  is slight compared to the 
resisting forces1 and very little new   
heat  is generated as the body loses    
that which it has2 but in large bodies1 
like the earth1 where the condensational
 forces are enormous and the  internal  
temperature is very high1 it is not     
improbable that the heat  generated at  
every stage of condensation is          
relatively large4 ,it has  been inferred
 by some students of the phenomena that 
the conditions  in the interior of the  
earth are essentially those of gaseous  
matter1  so far as molecular relations  
are concerned1 because the temperatures 
are thought to be above the critical    
temperatures of the substances          
composing it4 ,if this be true1 the new 
heat generated with each stage  of      
condensation is large4 ,however this may
 be1 it seems safe to infer  that in so 
far as the volume of the interior mass  
is dependent on heat  resistance1 the   

loss of existing heat leads to the      
generation of  new heat4 ,the amount of 
this new heat must be enough1 together  
with  the residual heat and the other   
forces of resistance1 to match the  new 
condensational forces4 ,the molecular   
and sub-molecular forces of  resistance 
other than heat1 are probably           
responsible for some large  part of the 
resistance to the increased             
condensational force1 but how  much is  
not determined4    ,all resistance      
perhaps due to motion4--,as now         
interpreted1 the force  of resistance of
 heat is due to the impact of the flying
 particles  of the heated matter4 ,the  
other forms of resistance to compression
  have not usually been interpreted in  
this way1 but the tendency of  recent   
investigation is to place them in the   
same dynamic class4  ,a cold solid body 
offers resistance to compression that is
 in no  obvious way dependent on heat   
motion4 ,in small bodies this resistance
  is immeasurably greater than the      

self-gravity of the body4 ,it is so     
great that it can only be partially     
overcome by any force which human       
ingenuity can bring to bear upon it4    
,this form of resistance has thus1  not 
unnaturally1 come to be regarded as     
approximately immeasurable1 and  perhaps
 as grading into actual immeasurability1
 and as resting back  upon the actual   
contact of irreducible atoms4 ,but the  
recent researches  which have developed 
grounds for the conception that even the
 atoms  are composite1 lead to the      
further conception that their resistance
  to compression is dependent on the    
movement of their constituent           
corpuscles or electrons4 ,this          
encourages the broad conception that the
  whole of the resistance to compression
 arises from molecular1 atomic1  and    
sub-atomic motions1 of which heat is    
merely one form4    ,while all this is  
yet on the frontier of physical         
progress1 these  conceptions may well be
 recognized in framing interpretations  

of the  agencies which determine the    
volume of the earth1 and which control  
the changes that take place in it from  
age to age4 ,the result of their        
combined action at any stage is a state 
of temporary equilibrium  between       
gravity1 aided by the molecular1 atomic1
 and sub-atomic  attractions1 on the one
 hand1 and heat1 aided by the molecular1
  atomic1 and sub-atomic resistances1 on
 the other4 ,the vital problem  is to   
ascertain the original condition of     
balance between these  antagonistic     
forces1 and the changes which have      
affected that balance  since4 ,the      
original state of balance is necessarily
 a matter of  hypothesis1 and the best  
that can be done at present is to       
picture  as clearly as possible the     
different hypotheses that have been     
entertained1 and the different          
consequences that logically flow from   
them4 ,the most important factor in the 
case is the original amount and         
distribution of internal heat4          

,,alternative ,,views ,,of ,,original   
,,heat ,,distribution4    ,the          
hypothetical modes of origin of the     
earth will be treated in the  historical
 section4 ,suffice it here to say that  
one view is that the  earth was once    
gaseous1 passed thence into a liquid1   
and later into  a solid state4 ,under   
this view1 there are two hypotheses as  
to the  original distribution of        
internal heat1 dependent on the mode of 
solidification4 ,according to the one1  
solidification began at the  surface    
after convection had brought the        
temperature of the whole  mass down     
nearly to the point of congelation2     
according to the other1  solidification 
began at the center at a high           
temperature1 because of  pressure1 and  
proceeded thence outwards4 ,the former  
only has been much  developed in the    
literature of the subject1 though the   
latter is now  generally regarded as the
 more probable4    ,another view of the 
globe's origin is that the earth was    

built up  gradually by the infall of    
matter1 bit by bit1 at such a rate that 
though each little mass became hot as a 
result of its fall1 it cooled  off      
before others fell on the same spot1 the
 rain of matter not being  fast enough  
to heat up the whole mass to the        
melting-point4 ,under this  view1 the   
internal heat arose chiefly from        
compression due to the  earth's gravity4
    ,a clear conception of the three    
hypotheses of thermal distribution      
which rest on these two views of the    
origin of the earth is important  to the
 further discussion4    #a4 ,thermal    
distribution on the convection          
hypothesis4--,it was  formerly the      
prevailing opinion that the molten      
condition of the  earth persisted in the
 interior until after the crust had     
formed1  and that solidification        
proceeded from the surface downwards4   
,it was  a natural corollary of this    
view that1 previous to the beginning of 
solidification1 convection stirred the  

liquid mass from center to              
circumference and equalized the         
temperature so that the whole mass      
cooled down equably until it approached 
the point of solidification  and became 
too viscous for ready convection4 ,the  
temperature should1  therefore1 have    
been nearly the same from center to     
surface at the  stage just preceding    
incipient solidification4 ,this         
conception forms  the basis of most     
discussions involving internal          
temperatures4#bdh  ,the famous studies  
of ,lord ,kelvin are based on the       
assumption of a  uniform initial        
temperature of #gjjj ,fahr4#bdi ,other  
temperatures  have been assumed in      
similar studies by others1 but the      
results do not  differ materially4 ,on  
this hypothesis there would be no       
deep-seated  change of temperature until
 a temperature-gradient1 extending to   
the  deeper horizons1 had been developed
 by surface cooling4 ,in the earliest   
eras1 the loss of heat would be felt    

solely in the outer zone4 ,by  surface  
cooling1 a temperature gradient would be
 slowly developed1 and  gradually       
changed from age to age1 as shown by the
 curved lines in  ,fig4 #dej1 each of   
which shows the temperature at the      
successive stages  stated in the legend4
 ,the computations for these curves were
 based  on the methods and assumptions  
of ,lord ,kelvin4 ,the two lower curves 
represent greater periods than those    
usually assigned by geologists to  the  
whole history of the earth4 ,it will be 
seen that the modification  of the      
original temperature line extends only  
about #afj miles below the  surface for 
the #ajj1jjj1jjj-year period1 only about
 #bdj miles for the  #bcg1jjj1jjj-year  
period1 and only about #cbj miles for   
the excessive  period of #fjj1jjj1jjj   
years4 ,the superficial nature of the   
whole  thermal problem under this       
hypothesis is thus made clear and       
impressive4    ,illustration3 ,fig4     
#dej4--;,diagram showing the original   

distribution    of heat assumed by the  
convection hypothesis and the           
modifications    of this distribution   
near the surface in successive long     
periods4    ,the base-line of the figure
 represents divisions of the            
earth-radius    with center at the left 
and surface at the right4 ,the vertical 
lines represent temperatures ranging    
from #j ,c4 to #ejjj ,c4 ,the    assumed
 initial temperature #cijj ,c4 7#gjjj   
,f47 is represented by    the horizontal
 line ,,tc1 full at the left and dotted 
at the right to    indicate the original
 extension of the initial temperature to
 the    surface4 ,the upper curve at the
 right shows how much the temperature   
will have been modified at the end of   
#ajj1jjj1jjj years1 computed            
according to the method of ,lord        
,kelvin4 ,the middle curve shows the    
change at the end of #bcg1jjj1jjj years1
 and the lower curve the    change at   
the end of #fjj1jjj1jjj years4 ,similar 
curves may be found    in an article by 

,clarence ,king1 ,am4 ,jour4 of ,sci41  
,,xlv1 #ahic1 p4 #af4    ,after the     
outer shell had cooled so as to be in   
approximate equilibrium  with the       
environment of the earth1 it suffered   
practically no  contraction4    ,so also
 it appears from the diagram that there 
was practically no  contraction below   
#afj miles up to the end of the         
#ajj1jjj1jjj-year  period1 because      
cooling had not yet reached that depth4 
,between these  two non-contracting     
horizons the greatest rate of           
contraction at the  close of the        
#ajj1jjj1jjj-year period lay about #fj  
miles below the  surface4 ,the          
contraction of this middle zone1 while  
the outermost shell  and the interior   
body remained constant1 is held to have 
developed a  state of horizontal thrust 
in the outer shell1 because this shell1 
being too large for the shrinking       
subcrust1 tended to settle1 and  to     
crowd upon itself horizontally4 ,the    
wrinkling and other modes of            

deformation of the outer part of the    
earth are referred1 under this  view1 to
 the thrust so developed4 ,this is the  
view which has been most  generally     
accepted4    ,level of no stress4--,as  
the outer shell is thus held to be in a 
state  of thrust while the zone below is
 in a state of shrinkage1 there must    
be1 between these two zones1 a level of 
no stress1 where there is  neither      
compression nor stretching4 ,above this 
level1 the thrust  increases to the     
surface1 and below it1 the stretching   
increases to the  depth of most rapid   
change of temperature1 below which it   
decreases  and finally vanishes at the  
lower limit of temperature change4 ,in  
the  earliest stages of cooling1 the    
level of no stress must have been  near 
the surface1 and must have descended    
gradually as the cooling  proceeded4    
,the depth of this level has been       
repeatedly computed on  the basis of    
assumed times and rates of cooling4     
,fisher1 assuming  the temperature of   

solidification to have been #djjj ,fahr4
 and the  period of cooling #cc1jjj1jjj 
years1 computed its depth at only   of a
 mile below the surface4#bej ,t4        
,mellard ,reade1 with somewhat          
different assumptions1 placed it at #b  
miles after #ajj1jjj1jjj years  of      
cooling4#bea ,davison 7#ahig7 placed it 
at #b4ag miles1#beb and ,g4 ,h4  ,darwin
 at #b miles after the same period4#beb 
,in a later computation1  based on the  
assumption that the coefficient of      
dilatation increases  with the          
temperature1 ,davison placed the level  
of no stress at #g4gi  miles1 and stated
 that if the coefficient of conductivity
 and the  initial heat also increased   
down wards1 the zone would lie still    
deeper4 ,to suppose the initial heat to 
increase downwards1 however1 is  to     
abandon the hypothesis we are now       
considering4 ,these computations  seem  
to show that1 at the very utmost1 the   
level of no stress1 under  this         
hypothesis1 lies at a very slight depth1

 and that the thrust zone  above is1    
therefore1 very shallow4 ,this should be
 kept constantly in  mind in all        
deductions drawn from this hypothesis4  
,if the thickness  of the thrust zone be
 taken at #h or #aj miles1 it will      
apparently be  conceding to the view all
 that can legitimately be claimed for   
it4    ,illustration3 ,fig4             
#dea4--;,diagram illustrating the       
internal    temperatures of the earth   
when it first became solid1 under the   
hypothesis that it solidified from the  
center outward1 and assuming    that the
 fusing-point rose directly as the      
pressure1 in accordance    with ,barus' 
experiments with diabase4 ,the divisions
 of the base-line    represent fractions
 of the earth's radius4 ,the divisions  
of the    vertical lines represent      
pressures in atmospheres at the left1   
and temperatures in degrees ,c4 at the  
right4 ,the lower curve1 ,,pc1          
represents the interior pressures1      
ranging from one atmosphere at    the   

surface to #c1jjj1jjj atmospheres at the
 center1 derived from    ,laplace's law 
of density4 ,the upper curve1 ,,fc1     
represents the    fusion-points of      
diabase at the various depths and       
pressures1 and    hence the temperatures
 at which the interior would become     
solid at    the various depths1 or1 in  
other words1 the initial temperatures of
    the solid earth4 ,the lower curve is
 derived from ,slichter2 the upper    is
 formed by directly plotting the        
temperatures given by ,barus 7,am4      
,jour4 ,sci41 #ahic1 p4 #g74    #b4     
,thermal distribution on the hypothesis 
of central  solidification4--,when the  
previous conception was first formed1   
the  effect of pressure on the          
melting-points of lavas was neglected1  
as  little or nothing was known on the  
subject4 ,experiment1 however1 has      
shown that pressure1 as a rule1 raises  
the melting-points of lavas1 and  out of
 this has grown the doctrine that the   
earth solidified first at  the center1  

where the pressure was greatest1 and    
gradually congealed  outwards4 ,barus   
has shown that the melting-point of     
diabase1#bec  selected as a             
representative rock1 rises directly with
 the pressure4  ,if this rate holds good
 to the center of the earth1 the melting
  temperature of diabase there would be 
#gf1jjj ,c4 7#acf1hjj;,f474 ,the  range 
of the experiment is1 however1 very     
small compared with the range  of the   
application1 and little confidence can  
be felt in the special  numerical result
 reached4 ,the rate of rise of the      
fusion-point may  be much changed as the
 extraordinary conditions of the deep   
interior  are invaded4 ,still there is  
good ground for the hypothesis that     
solidification took place at some very  
high temperature at the center1  because
 of the very great pressure there4 ,the 
inference then is that  when the        
temperature of the center of the        
supposed molten globe reached  the      
appropriate point1 solidification began 

there1 and that it took  place at lesser
 depths in succession as the appropriate
 temperatures  were reached4 ,this view 
excludes convection in the successive   
zones from the center outward after the 
time when their temperatures  of        
solidification were reached1 or after   
these were approached  sufficiently near
 to develop prohibitive viscosity4 ,some
 loss of heat  from these horizons would
 be suffered while the outer parts were 
solidifying1 but on account of the      
exceedingly slow conductivity of  rock1 
it is improbable that the amount of loss
 would be sufficient  to change the     
general character of the internal       
distribution of heat  previous to       
solidification at the surface1 the time 
when the existing  phase of the earth's 
history by hypothesis began4 ,fig4 #dea 
shows the  theoretical distribution of  
heat under this view4 ,the consequences 
of  this assumption are very important  
to geological theory and1 carried  out  
to their logical consequences1 lead to  

the conclusion that cooling  and        
shrinkage affected the deep interior of 
the earth1 for the  high central heat   
must have been constantly passing out   
toward the  surface4 ,instead1          
therefore1 of the contraction being     
concentrated  in and limited to the     
outer #bjj miles or so1 as under the    
preceding  hypothesis1 it was deeply    
distributed4 ,the contraction within the
 outer  zone would be less than under   
the preceding view1 because the flow  of
 heat from within would partially offset
 the flow outwards1 and a  corresponding
 part of the contraction would be       
distributed below4          ,,computed  
,,pressures1 ,,densities1 ,,and         
,,temperatures ,,within ,,the           
,,earth ,,based ,,on ,,laplace's ,,law4 
----------------------------------------
---------     ,distance      ,pressure  
from center  in megadynes               
,temperature     in terms of    per sq4 
,density4      in            radius4    
cm4#bed              degrees ,c4        

----------------------------------------
---------       #a4jj               #j  
#b4hj           #j            4#ie      
#ig1jjj      #c4cg         #cbj         
4#ij         #bae1jjj      #c4ie        
#a1aaj            4#he         #cec1jjj 
#d4ed       #b1aij            4#hj      
#eaj1jjj      #e4ac       #c1dgj        
4#ge         #fhd1jjj      #e4ga        
#d1hhj            4#gj         #hgd1jjj 
#f4bh       #f1cej            4#fe      
#a1jgg1jjj      #f4hd       #g1hfj      
4#fj       #a1bhi1jjj      #g4ch        
#i1cfj            4#ee       #a1ejg1jjj 
#g4ij      #aj1hcj            4#ej      
#a1gbg1jjj      #h4ci      #ab1bej      
4#de       #a1idd1jjj      #h4hd        
#ac1eij            4#dj       #b1aed1jjj
      #i4bf      #ad1hdj            4#ce
       #b1cec1jjj      #i4fd            
#ae1ihj            4#cj       #b1ece1jjj
      #i4ih      #ag1jjj            4#be
       #b1fih1jjj     #aj4bg            
#ag1hhj            4#bj       #b1hcf1jjj
     #aj4ea      #ah1faj            4#ae

       #b1idg1jjj     #aj4gj            
#ai1aij            4#aj       #c1jbi1jjj
     #aj4hd      #ai1faj            4#je
       #c1jgh1jjj     #aj4ib            
#ai1hgj            4#jj       #c1jie1jjj
     #aj4ie      #ai1iej                
----------------------------------------
---------    #c4 ,thermal distribution  
under the accretion hypothesis4--,the   
accretion  hypothesis assumes that the  
internal heat was gradually developed   
from  the center outwards as the earth  
grew and the internal compression  was  
progressively developed4 ,the heat1     
therefore1 continued to rise  at the    
center as long as compression continued1
 or at least as long  as the compression
 was sufficient to generate heat faster 
than it  was conducted outwards4 ,as the
 conduction of heat through rock is     
exceedingly slow1 the central heat may  
be assumed to have continued to  rise so
 long as the infall of matter caused    
appreciable compression4  ,in the same  
way1 heat was generated progressively in

 the less central  parts1 and these     
parts also received the heat that passed
 out from  beneath4 ,it is assumed under
 this hypothesis that the degree of     
interior compression stands in close    
relation to interior density1  for while
 there would probably be some           
segregation of heavier matter  toward   
the center and of lighter toward the    
surface by means of  volcanic action and
 internal rearrangement under stress    
differences1  the interior density is   
regarded as due mainly to compression4  
,the  distribution of internal pressure 
and density generally accepted is  that 
of ,laplace1 who assumed that the       
increase of the density varies  as the  
square root of the increase of the      
pressure4 ,this law gives a             
distribution of density that accords    
fairly well with the phenomena of       
precession of the equinoxes1 which      
require that the higher densities  of   
the interior shall be distributed in    
certain proportions between  the center 

and the equatorial protuberance whose   
attraction by the sun  and moon causes  
precession4 ,the increases in pressure1 
density1 and  temperature have been     
computed as follows by ,mr4 ,a4 ,c4     
,lunn1#bee the  average specific gravity
 of the earth being taken at #e4f1 the  
surface  specific gravity at #b4h1 and  
the specific heat at 4#b4    ,the       
temperatures are shown graphically in   
,fig4 #deb1 in which the  curves of     
pressure and density are also given4    
,the nature of the curve  of temperature
 is such that1 if the thermometric      
conductivity of the  material is uniform
 at all depths1 the temperature will    
fall in the  deeper portions and rise in
 the outer ones1 excluding the surface  
portions subject to outside cooling4    
,the curve indicates that the  rising   
temperature would affect somewhat more  
than #hjj miles of the  outer part of   
the spheroid1 or about half its volume1 
i4e4 the inner  half during the initial 
period had a falling temperature and the

  outer half1 except the immediate      
surface1 a rising temperature4 ,this    
introduces a very singular feature into 
the problem1 for the outer  zone must   
shrink to fit the inner portion that is 
losing heat1 while  its own material is 
expanding because of its increase of    
temperature4  ,a double distortional    
effect must result4#bef ,if the         
conductivity of  the dense interior is  
greater than that of the outer parts1   
the effect  is intensified4 ,the        
redistribution of heat resulting from   
this unequal  flowage would in time     
change the curve so that more nearly    
equal  flowage would result4 ,it would  
probably take a very long period for    
this to be effected1 on account of the  
very slow conductivity of rock4    ,the 
accretion hypothesis assumes that1      
during the growth of the  earth1 large  
amounts of heat were carried by volcanic
 action from  deeper horizons to higher 
ones and to the surface1 and that this  
still continues at a diminished rate4   

,it assumes that whenever the  interior 
heat raised any constituent of the      
interior matter above  its fusing-point 
under the local pressure1 it passed into
 the liquid  state1 and was forced      
outwards by the stress differences to   
which  it was subjected1 unless its     
specific gravity was sufficiently  high 
to counterbalance them4 ,it is conceived
 that the more fusible  portions were   
liquefied first1 and that in so doing   
they absorbed the  necessary heat of    
liquefaction and began to work their way
 outward1  carrying their heat into     
higher horizons and temporarily checking
 the  development of more intense       
stresses in the lower horizons4 ,they   
thus  served to keep the temperature    
there below the fusion-point of the     
remaining more refractory substances4   
,meanwhile the extruded portions  were  
raising the temperatures of the higher  
horizons into which  they were intruded 
or through which they were forced to    
pass4 ,there  was thus1 it is thought1  

an automatic action that tended to      
reduce  the heat-curve to the           
fusion-curve4 ,the actual curve of      
internal  temperature may1 therefore1 be
 practically the fusion-curve4 ,this  is
 identical with the curve supposed to   
arise from solidification by  pressure  
from the center outward under the molten
 hypothesis1 except  so far as the two  
would vary as the result of variations  
in the  distribution of matter1 which   
would not be quite the same under the   
two  hypotheses4 ,the curve of fusion   
deduced by an extension of the results  
of ,barus' experiment has been given4   
,it is necessary to recognize  that the 
rate of rise of the fusion-point may1   
and very likely  does1 change in the    
deep interior4 ,the curve given         
represents much  higher temperatures in 
the central parts than those given by   
,lunn's  computations from compression1 
which seem inherently more probable than
  the higher ones4    ,illustration3    
,fig4 #deb4--;,diagram illustrating the 

distribution of    temperature under the
 accretion hypothesis 7neglecting the   
heat from    infall and other external  
sources74 ,the divisions of the         
base-line    represent fractions of the 
earth's radius4 ,the vertical divisions 
represent both pressure in megadynes per
 sq4 cm41 nearly the same as            
atmospheres per sq4 in41 at the left1   
and temperatures in degrees ,c4    at   
the right4 ,it is to be noted that the  
temperature scale is #bjjj    ,c4 per   
division1 while that of ,fig4 #dea is   
#ejjj ,c4 per division4    ,the upper   
curve at the left1 ,,pc1 is the pressure
 curve4 ,the middle    curve1 ,,dc1 is  
the density curve1 beginning at #b4h at 
the surface    and reaching nearly #aa  
at the center4 ,the lower curve1 ,,tc1  
is the    temperature curve1 rising from
 the surface temperature1 #j ,c41 at    
the right1 to #bj1jjj ,c4 at the center4
 ,it is to be noted that the    portion 
of this curve at the left representing  
the deeper part of    the earth is      

convex upwards1 while the portion at the
 right is    concave4 ,it will be seen  
that the gradient increases from the    
center    to a point between 4#f and 4#g
 radius1 and then decreases1 and that   
between 4#h radius and the surface1 a   
distance of about #hjj miles1 the       
decrease is notable4 ,this means that   
with an equal coefficient of            
conductivity the flow from the center   
outward to 4#f or 4#g radius will    be 
faster than the flow from 4#h radius to 
the surface1 neglecting    the immediate
 surface effects of external cooling4   
,these curves were    worked out by ,mr4
 ,lunn4    ,as astronomical and seismic 
evidences strongly favor the view that  
the earth is rigid throughout1 they lend
 support to the view that  the interior 
retains its rigidity by the extrusion of
 liquid matter  practically as fast as  
it is formed1 and that this progressive 
extrusion adjusts the temperature to    
that which is consistent with  solidity4
    ,the bearing of this conception     

becomes evident on consideration4 ,the  
shrinkage of the earth from loss of heat
 by conduction and by the  extrusion of 
molten rock1 affects the deep interior  
as well as the  more superficial zones4 
,it is even possible that the shrinkage 
may  originate chiefly in the deeper    
zones4 ,the postulated transfer of      
fluid rock from the deeper parts to the 
more superficial ones lessens  the heat 
in the former1 and adds to that in the  
latter4 ,the postulated  greater flow of
 heat from the deeper half to the outer 
half1 than from  the latter outward1    
gives a concordant result4 ,if the      
conductivity  of the deeper and denser  
material is appreciably greater than    
that  of the more superficial and less  
dense material1 as seems probable1  this
 effect is intensified4 ,the            
distribution of compressibility at  the 
existing state of condensation may      
possibly be such that more  new heat is 
generated by shrinkage in the outer     
parts than in the  inner4 ,neither of   

these conceptions can be affirmed as    
actually taking  place4 ,they merely lie
 within the range of reasonable         
hypothesis in  the present state of     
experimental data4 ,what the real truth 
is must be  left to further research4   
,present effort may be regarded as      
temporarily  successful if it forms     
consistent conceptions of the applicable
  hypotheses1 and of their consequences4
    ,recombination of material4--,one   
other peculiarity of the accretion      
hypothesis must be recalled here4 ,the  
incoming bodies must probably be        
assumed to have fallen in promiscuous   
order1 and hence to have been           
indiscriminately mingled in the growing 
earth4 ,as they became buried  deeper   
and deeper and their temperatures and   
pressures were raised1  much            
recombination1 chemical and physical1   
may be presumed to have  followed4 ,as  
already noted1 these changes would      
probably give increased  density in the 
main4 ,the material being1 however1 in a

 solid state1 the  rearrangement would  
be slow and its persistence in time     
indeterminate1  and it may yet be far   
from complete4 ,it is not improbable1   
therefore1  under this hypothesis1 that 
some notable part of the recent         
shrinkage  of the earth has been due to 
the continued rearrangement of its      
heterogeneous internal matter4 ,this    
would not be equally so in an  earth    
derived from a molten mass1 for the     
required adjustments of  the material   
should have taken place while in the    
fluid state before  solidification4     
,comparison of the hypotheses4--,by     
comparing the three hypotheses of  the  
early states of the earth's temperature1
 it will be seen that  there is a       
radical difference1 thermally1 between  
the first and  the last two4 ,the first 
assumes a nearly uniform distribution of
  internal temperature1 and hence1 owing
 to the exceedingly slow rate  of       
conduction1 limits the movements and    
deformations of the crust1 so  far as   

dependent on heat1 to very superficial  
horizons4 ,the second  and third views  
agree in postulating changes of         
temperature in the  deep portions1 as   
well as in the superficial1 and hence   
involve the  central portion of the     
earth in the great movements and        
deformations4  ,it is not to be supposed
 that this of itself necessarily        
increases the  sum-total of the effects 
of contraction1 for1 given a certain    
loss of  heat from the surface1 it may  
be relatively immaterial whether this   
loss arose from a large reduction of    
temperature in a shallow zone1 or  a    
small reduction of temperature in a deep
 zone1 for1 except as the  coefficient  
of expansion varies1 the total shrinkage
 would be the same4  ,but the difference
 in distribution makes a radical        
difference in the  resulting movements1 
for1 in the first case1 the movements   
are in a  weak superficial shell that   
cannot accumulate great stresses1 and   
hence  must yield practically as fast as

 the stresses arise1 while1 in the      
second case1 the stress-accumulating    
power of the thick segments may be      
great1 and the stresses may gather for  
long periods and give rise to  great    
cumulative results at long intervals4   
,in this respect the last  two views    
have much in common1 though they differ 
in other important  particulars4        
,with this general background of        
hypothesis1 we may now turn to the      
direct evidences of the distribution of 
internal temperature which  observations
 near the surface afford4 ,unfortunately
 they are limited to  a mere film1 as it
 were1 little more than  of the radius  
of the  earth4                          
,,observed ,,temperatures ,,in          
,,excavations4    ,as the earth is      
penetrated below the zone of seasonal   
changes by wells1  mines1 tunnels1 and  
other excavations1 the temperature is   
almost  invariably found to rise4 ,the  
rate of rise1 however1 is far from      
uniform4 ,if we set aside as exceptional

 the unusually rapid rise near          
volcanoes and in other localities of    
obvious igneous influence1 the  highest 
rates are still six times the lowest4 ,a
 large number of records  have been     
collated by the ,committee on           
,underground ,temperatures1 of the      
,british ,association for the           
,advancement of ,science4 ,these range  
from  #a ,f4 in less than #bj feet to #a
 ,f4 in #acj feet1 with an average of #a
  ,f4 in #ej to #fj feet1 which has     
usually been taken as representative4   
,the more recent deep borings that have 
been carefully measured with due  regard
 to sources of error indicate a slower  
rate of rise4 ,some of the  more notable
 records are as follows3#a              
,depth4    ,rate of rise4    ,sperenberg
 bore 7,germany7                  #cdib 
feet4 #a ,f4 in  #ea4e feet4            
,schladeback bore 7,germany7            
#efcj      #a ,f4 in  #fg4a             
,cremorne bore 7,n4 ,s4 ,wales7         
#bibi      #a ,f4 in  #hj               

,paruschowitz bore 7,upper ,silesia7    
#fdjh      #a ,f4 in  #fb4b             
,wheeling well 7,w4 ,va47               
#ddfb      #a ,f4 in  #gd4a      ,st4   
,gothard tunnel 7,italy-,switzerland7   
#eegh      #a ,f4 in  #hb        ,mt4   
,cenis tunnel 7,france-,italy7          
#ebhj      #a ,f4 in  #gi               
,tamarack mine 7,n4 ,mich47             
#ddej      #a ,f4 in #ajj    #beg       
,calumet and ,hecla mine 7,n4 ,mich47   
#dici      #a ,f4 in #ajc    #beg       
,ditto1 between #ccbd feet and #dhcg    
feet            #a ,f4 in  #ic4d        
,it is to be noted that even these      
selected records vary a hundred per     
cent4 ,very notable variations are found
 in the same mine or well1 and  often   
much difference is found in adjacent    
records1 especially those of  artesian  
wells4 ,some of these are explainable1  
but the full meaning of  other          
variations is yet to be found4          
,explanations of varying                
increment4--,certain apparent variations

 are  merely due to inequalities of     
topography4 ,the isogeotherms1 or planes
  of equal underground temperature1 do  
not normally rise and fall with  every  
local irregularity of the surface1 but  
more nearly strike an  average4 ,a well 
on a bluff #ejj feet high would probably
 reach nearly  the same temperature at  
#ajjj feet1 as a well #ejj feet deep in 
the  adjacent valley1 giving a gradient 
twice as great in the one case as in    
the other4    ,in interpreting the      
temperatures of artesian flows1 regard  
must be  had to the depths of rock under
 which the waters have passed1 as  well 
as the depths at the location of the    
wells4 ,darton has found#beh  unusually 
high and varying temperatures in the    
artesian wells of the  ,dakotas1 some   
part of which may be due to this cause1 
though a full  explanation of their     
singular variations is not yet reached4 
,the permeation and circulation of water
 affect the temperature in two          
important ways3 7#a7 wet rocks are      

better conductors than dry ones1 and    
7#b7 the convective movement of water is
 a means of conveying heat from  lower  
to higher horizons4 ,as the circulation 
of underground water is  very unequal1  
much irregularity of thermal            
distribution in the upper  zones        
probably arises from this source4 ,the  
general effect of water  circulation is 
to reduce the thermal gradient where the
 circulation  is relatively rapid1 as it
 is near the surface and in the main    
thoroughfares of circulation1 and hence 
to cause a relatively rapid  rise in the
 gradient just below the zone of        
effective water influence4  ,some       
records conform to this theoretical     
deduction1 but in general it  is masked 
by other influences4    ,chemical       
action1 especially oxidation1           
carbonation1 hydration1  solution1 and  
precipitation1 modify the normal        
temperature gradient1  but how          
effectively is not well determined4     
,with little doubt the  first three     

mentioned above raise the temperature1  
while solution  and precipitation in    
some large measure offset each          
other4#bei ,the  sum-total is probably  
an appreciable rise in temperature4 ,it 
has even  been conjectured that the heat
 of volcanic action is due to chemical  
combination in the lower reaches of     
water circulation1 but this is          
obviously an over-estimate4             
,differences in the conductivity of rock
 are an obvious source of  varying      
underground temperature gradients4 ,if  
an outer formation  conducts heat more  
freely than those below1 it tends to    
lower the  gradient within itself and to
 cause a relative rise in the gradient  
just below4 ,if a lower formation is    
more conductive than that above1 it     
tends to lower the gradient within      
itself1 and to raise it in the one      
above1 because it carries heat to the   
outer one faster than the latter        
carries it away4    ,the compression to 
which rocks have been subjected affects 

their  temperature4 ,at the surface the 
variation from this source is chiefly   
dependent on the lateral thrust         
suffered4    ,when allowances are made  
for all these and other known causes of 
local  variation of temperature1 it is  
still not clear that a uniform average  
gradient remains as the true conception4
 ,if the earth were once a  molten      
spheroid1 there would be a strong       
presumption that1 aside from  local     
variations1 there would be a normal     
curve applicable to all  regions4 ,on   
the other hand1 if the internal heat has
 arisen chiefly  from compression1 and  
if the compression has varied in        
different  regions1 as the inequalities 
of the surface render probable1 there   
would be no such definite normal curve  
in the accessible zone of the  earth1   
but rather a varying rate in different  
regions4 ,in either case1  the later    
movements1 compressions and strains of  
the crust1 must modify  the original    
thermal gradients4    ,gradients        

projected4--,it is not probable that    
these gradients1 even  when corrected   
for local variations1 continue          
unmodified to the  center of the earth4 
,if they did1 #a ,f4 in #fj feet        
continued to the  earth's center would  
give #cdh1jjj ,f41 and #a ,f4 in #ajj   
feet would  give #bji1jjj ,f4 ,it is    
much more probable that the rates of    
rise fall  away below the superficial   
zone4 ,if water circulation in the      
fracture  zone is the most efficient    
agency cooperating with conductivity in 
the  outward conveyance of heat1 as     
seems probable1 the gradient in that    
zone should rise at an abnormal rate1   
and hence the average gradient  in the  
deeper portions not affected by this    
circulation should be  lower4 ,it will  
be recalled that the central temperature
 deduced from  an extension of ,barus'  
fusion curve is #acf1hjj ,f4 7#gf1jjj   
,c471  which1 high as it is1 gives a    
lower average gradient than the surface 
observations4 ,the computations from    

compression by ,lunn1 giving a  central 
temperature of #cf1jjj ,f4 7#bj1jjj     
,c471 imply a still lower  average rate1
 while the convection hypothesis        
postulates no sensible  increase at all 
below #bjj or #cjj miles4               
----------------------------------------
---------------------------------       
,average material                       
,mineral                         of     
crust      ,norm minerals     equivalent
        ,linear    ,volume              
7,clarke's     calculated from          
7,c4,i4,p4,w4  ,axis4                   
expansion4expansion4   tables74#bfj     
,clarke's average4    system74          
----------------------------------------
---------------------------------  ,si,o
      #eh4ei ,quartz        #aa4d,quartz
            4#jjjjabjf 4#jjjjcfah  ,al,o
     #ae4jd ,orthoclase    #ag4b        
a 4#jjjjaijf   ,fe,o      #c4id ,albite 
#bg4c;,anorthite     b -4#jjjjjbjce     
,fe,o        #c4dh ,anorthite     #ag4h 
c -4#jjjjjadie4jjjjaeec  ,ca,o          

#e4bi ,diopside       #f4h              
a 4#jjjjjhabe  ,mg,o        #d4di       
,hypersthene   #aj4b;,diopside      b   
4#jjjjafifc4jjjjbcd  ,k,o        #b4ij  
,magnetite and                   c      
-4#jjjjjagjg  ,na,o       #c4bj         
,ilmenite      #f4h;,augite        a    
4#jjjjachef  ,ti,o        4#ee ,minor   
7used for                               
constituents      hypersthene7          
,minor            omitted       #b4e    
constituents              ------------  
b 4#jjjjjbgb 4#jjjjbde    omitted  #b4eb
             #ajj4jj,magnetite     c    
4#jjjjjgia            ------------      
4#jjjjjiedj4jjjjbhfb           #ajj4jj  
----------------------------------------
---------------------------------       
,the amount of loss of heat4--,the      
amount of loss of interior heat  which  
the earth suffers may be estimated by   
that which is observed to  be passing   
outward through the rock1 or by         
computing the amount which  should be   
conveyed outwards with the estimated    

gradients and with the  conductivity of 
rock as determined by experiment4 ,the  
latter method  is usually employed in   
general problems4 ,taking the mean      
thermometric  conductivity of rock as   
#j4jjde1 the gradient as #a ,c4 in #cj  
meters1  the average specific heat of   
rock as #j4e small calories per cubic   
centimeter1 it is computed that in      
#ajj1jjj1jjj years the loss of heat     
would amount to #de ,c4 7#ha ,f47 for   
the whole body of the earth4#bfa  ,tait 
makes the more conservative estimate of 
#aj ,c4 7#ah ,f47 in the  same          
period4#bfb ,this is an exceedingly     
small result1 and emphasizes  the low   
conductivity of rock4    ,the amount of 
shrinkage from loss of heat4--,to       
compute the amount of  shrinkage for a  
given amount of cooling1 the average    
coefficient of  expansion of rock is    
required4 ,this has been experimentally 
determined  by several investigators4   
,by combining the determinations of     
others  with his own1 ,t4 ,mellard      

,reade found the linear coefficient to  
be  4#jjjjjebeg per #a ,f41 equivalent  
to 4#jjjjbhch per #a ,c4 per volume4    
,in this the proportions of the         
different rocks in the crust were       
roughly estimated4 ,to secure an        
independent result from the best        
available estimate of what constitutes  
the average rock1 ,w4 ,h4 ,emmons  has  
reduced ,clarke's average of the        
chemical constituents of the  crust to  
the norm minerals under the new system  
of ,cross1 ,iddings1  ,pirsson1 and     
,washington 7see p4 #ded7 and made a    
weighted average of the  conductivities 
of these1 as shown in the following     
table3                                  
----------------------------------------
-------------------                     
,volume      ,volume                    
,percentages ,sp4 ,gr4 proportions      
proportions                   of norm   
of norm   of norm     of temp4          
minerals4 minerals4 minerals4  #a ,c4   
higher4                                 

----------------------------------------
-------------------    ,quartz          
#aa4d      #b4ff      #d4bh             
#d4bhjaedhejd    ,feldspars#bfc    #fb4c
      #b4g      #bc4jg   #bc4jgjcehbgga 
,diopside           #f4h      #c4c      
#b4jf    #b4jfjjdhbjdj    ,hypersthene  
#aj4b      #c4de      #b4ie             
#b4iejjgbbgej    ,magnetite             
#f4h      #e4ag      #a4c               
#a4cjjjcgbjfj                           
--------               ----------       
-------------        ,total             
#ig4e               #cc4ff              
#cc4ffjfgjhabe                          
----------------------------------------
-------------------    ,subtracting the 
stated volume from the volume at a      
temperature of #a  ,c4 higher1 the      
difference is found to be 4#jjjfgjhabe1 
which divided by  the volume gives      
4#jjjjaii1 which is the coefficient of  
expansion of the  theoretical1 average1 
surface rock of the earth4    ,with this
 coefficient1 the radial shrinkage      

resulting from an average  loss of #aj  
,c4 7#ah ,f471 7,tait's estimate71 is a 
little over a quarter  of a mile        
74#begb72 and for a loss of #de ,c4 7#ha
 ,f471 7estimate of  ,daniell's         
,physics71 a little over a mile         
7#a4aegd74 ,the shortening of  the      
circumference for #aj ,c4 loss is #a4f  
miles1 and for #de ,c41 #g4bg  miles4   
,computations based on the coefficient  
of expansion adopted by  ,reade give    
#b4ce miles circumferential shortening  
for a loss of #aj ,c4  and #aj4e miles  
for a loss of #de ,c4 ,in both these    
cases1 the whole  contraction is assumed
 to take a vertical direction1 and hence
 these  are maximum results4 ,they are  
exceedingly small4    ,unless there is a
 very serious error in the estimated    
rate of thermal  loss1 or in the        
coefficients of expansion1 cooling would
 seem to be a  very inadequate cause for
 the shrinkage which the mountain       
foldings1  overthrust faults1 and other 
deformations imply4 ,this inadequacy has

  been strongly urged by ,fisher#bfd and
 by ,dutton4#bfe ,in view of the        
apparent incompetency of external loss  
of heat1 the possibilities of           
distortion from other causes invite     
consideration4                          
,,other ,,sources ,,of ,,deformation4   
,transfer of internal heat4--,it is     
theoretically possible that  deformation
 of the subcrust may result from the    
internal transfer of  heat without      
regard to external loss4 ,it has already
 been shown 7p4  #eci7 that under       
certain possible conditions more heat   
would flow from  the inner parts to     
higher horizons than would be conveyed  
through  these latter to the surface and
 there lost1 and that1 as a result1  the
 temperatures of the inner parts might  
be falling1 while those of  the outer   
parts 7except the surface7 might be     
rising4 ,with the more  conservative    
coefficient of expansion previously     
given1 a lowering of  the average       
temperature of the inner half of the    

earth #ejj ,c4 and the  raising1 by     
transfer1 of the outer half to an equal 
amount would give a  lateral thrust of  
about #hc miles1 which is about the     
order of magnitude  thought to be       
needed4 ,it is not affirmed that this   
takes place1 but  some transfer of this 
kind is among the theoretical           
possibilities under  the accretion      
hypothesis4 ,the process could not      
continue indefinitely2  but1 for aught  
that can now be affirmed1 it may still  
be in progress4    ,denser aggregation  
of matter4--,as already noted1 matter   
under intense  pressure tends to        
aggregate itself in the forms that give 
the greatest  density4 ,if the earth    
were built up of heterogeneous matter   
arranged at  haphazard1 the material    
would probably readjust itself more or  
less1  as time went on1 into            
combinations of greater and greater     
density4  ,this process may be one of   
the important sources of shrinkage1 for 
an  average change of density of #a     

percent41 affecting the matter of the   
whole globe1 would probably meet all the
 demands of deformation since  the      
beginning of the ,paleozoic period4     
,extravasation of lavas4--,it is obvious
 that if lavas are forced out  from     
beneath the crust and spread upon it1 a 
compensating sinking of  the crust will 
follow4 ,this1 however1 is rather a mode
 than an ulterior  cause1 for a cause   
must be found for the extrusion of the  
lavas1 and  this cause may be one of the
 other agencies recognized1 such as a   
transfer of heat1 a reorganization of   
matter1 or a change of pressure4  ,the  
more practical question1 however1       
relates to its competency4 ,can  the    
amount of lava that has been extruded   
have had any very appreciable  effect on
 the descent of the crust8 ,the great   
,deccan flow is credited  with an area  
of #bjj1jjj square miles1 and a         
thickness of #djjj to #fjjj  feet4 ,vast
 as this is for a lava-flow1 it would   
form a layer only  about #e feet thick  

when spread over the whole surface of   
the globe1  and hence the sinking to    
replace it would cause a lateral thrust1
 on  any great circle1 of about #ca feet
 only4 ,it requires a very generous     
estimate of the lavas poured out between
 any two great mountain-making  periods 
since the beginning of the well-known   
stratigraphic series to  cause a        
horizontal thrust of any appreciable    
part of that involved  in               
mountain-making4 ,the case is different1
 however1 if we go back to  the ,archean
 era1 in which the proportion of        
extrusive and intrusive  rocks is very  
high4 ,very notable distortion may then 
be assigned to  the extravasation of    
lavas4 ,the outward movement of lava    
must also be  credited with some        
transfer of heat from lower to higher   
horizons1 and  this is probably one of  
the agencies that have produced the     
relatively  high underground            
temperatures in the outer part of the   
earth4    ,if lavas are thrust into     

crevices of the crust they contribute to
 its  extension1 but causes for the     
crevices and for the intrusion must be  
found1 and these are probably only      
expressions of one or another of the    
more general agencies4    ,change in the
 rate of rotation4--,as previously      
noted1 the tide acts  as a brake on the 
rotation of the earth4 ,the oblateness  
of the present  earth is accommodated to
 its present rate of rotation4 ,it is   
assumed  that such accommodation has    
always obtained1 and that if the        
rotation  has changed1 the form of the  
earth has changed also4 ,now1 the more  
oblate the spheroid1 the larger its     
surface shell and the less the  total   
force of gravity4 ,hence if the earth's 
rotation has diminished1  its crust must
 have shrunk1 because the form of the   
spheroid has  become more compact1 and  
the increase of gravity has increased   
its  density4 ,there is at present a    
water-tide chiefly generated in the     
southern ocean1 and irregularly         

distributed to more northerly waters4   
,this irregularity interferes with its  
systematic action as a brake1  and its  
average effects are difficult of        
estimation4 ,the water-tides  of past   
ages are still more uncertain1 as they  
must have depended on  the configuration
 and continuity of the oceans4 ,there   
are geological  grounds for the belief  
that the southern ocean was interrupted 
by land  during portions of the past at 
least1 and it is unknown whether there  
were elsewhere ocean-belts well suited  
to the generation of large  tides4 ,the 
ocean-tide1 therefore1 furnishes a very 
uncertain basis  for estimating the     
retardation of rotation4#bff ,the       
theoretical case  rests largely on the  
assumption of an effective body-tide4   
,the earth  doubtless has some          
body-tide1 but whether it is            
sufficiently great to  be effective1 and
 whether its position1 which depends on 
its promptness  in yielding and in      
resilience1 is favorable to the         

retardation of  rotation1 are yet open  
questions4 ,the existence of an         
appreciable  body-tide has not yet been 
proved by observation4    ,g4 ,h4       
,darwin1 assuming that the earth is     
viscous enough to give a  body-tide of  
appreciable value and of effective      
position1 has deduced  a series of      
former rates of rotation of the earth   
and has computed the  corresponding     
distances of the moon4#bfg ,c4 ,s4      
,slichter has shown that  the lessening 
of the area of the surface and the      
increase of the force  of gravity       
corresponding to these assigned changes 
of rotation are  large1 and that if the 
changes were actually experienced they  
must have  involved much distortion of  
the crust4#bfh ,these distortions would1
  however1 be of a peculiar nature1 and 
should thereby be detectible1 if  they  
were realized2 for in passing from a    
more oblate to a less oblate  spheroid1 
the equatorial belt shrinks1 and the    
polar tracts rise and  become more      

convex4 ,wrinkles should1 therefore1    
mark the equatorial  belts1 and tension 
the high latitudes4 ,slichter has       
computed that in  a change from a       
rotation period of #c4hb hours to the   
present one1 the  equatorial belt must  
shorten #aaca miles and the meridional  
circles  lengthen #die miles4 ,if we    
take ,heim's estimate of the            
crust-shortening  involved in forming   
the ,alps--#gd miles--as a standard1 the
 #aaca miles  of equatorial shortening  
would be sufficient for the formation of
 #ae  mountain ranges of ,alpine        
magnitude4 ,if1 as some geologists urge1
 the  estimate of mountain folding is   
too great1 the quotient would be still  
larger4 ,these ranges should run across 
the equator and be limited to  about #cc
 ,n4 and ,s4 latitude4 ,the             
high-latitude tension would be          
sufficient to cause the earth to gape   
more than two hundred miles at  the     
poles1 if there were simple ideal       
shrinkage4 ,the amounts and the         

distribution of thrust and shrinkage are
 shown in ,fig4 #dec4 ,if the  change of
 rotation were no more than from #ad    
hours to the present rate1  there would 
still be #eb miles of thrust in the     
equatorial belt1 and  #dj miles of      
shortage in the meridional circles4     
,there are no clear  signs of such a    
remarkable distribution of thrust and   
tension as this  hypothesis requires4   
,mountains are about as abundant and as 
strong  north of #cc1 the neutral line1 
as south of it1 and they extend to  high
 latitudes4 ,the ,archean rocks1 in     
which this agency should have  been most
 effective because of their early       
formation1 are crumpled  and crushed in 
the high latitudes much the same as in  
low latitudes4  ,furthermore1 if there  
had been appreciable change in the form 
of the  earth to accommodate itself to a
 slower rotation1 the water on the      
surface1 being the most mobile element1 
should have gathered toward  the poles1 
and the less mobile solid earth should  

have protruded about  the equator1 but  
the distribution of land and water1     
present and past1  gives no clear       
evidence of this4 ,the equatorial belt  
contains a less  percentage of land than
 the area north of it and more than that
 south  of it4 ,it varies but slightly  
from the average for the whole globe4   
,illustration3 ,fig4 #dec4--,polar      
projection of the earth's hemisphere    
showing the theoretical high-latitude   
tension and low-latitude    compression 
involved in a change of rotation from   
#c4hb hours to    the present rate4 ,the
 figure is drawn to true scale as seen  
from    a point above the pole1 and in  
consequence the equatorial tract    is  
foreshortened4 ,the black triangles show
 compression reduced in    length by    
foreshortening2 the white show tension  
in essentially true    proportions to   
the high-latitude areas4 ,the neutral   
line between the    areas of compression
 and of stretching lies at #cc #bj      
latitude4    ,while the doctrine of     

tidal retardation is theoretically      
sound1 and  while the relations of the  
moon to the earth have probably been    
appreciably affected by tidal action1   
geological evidence indicates  that it  
has not been sufficiently effective in  
producing crustal  deformations to be   
clearly detected by its own distinctive 
results4  ,this may be due 7#a7 to the  
fact that there are compensating        
agencies  that tend to acceleration of  
rotation1 and 7#b7 to the probable fact 
that the central rigidity of the earth  
is too high to give a very  effective   
body-tide4 ,hence the process of        
retardation may have been too  slow to  
have been geologically appreciable in   
the known period4 ,the  recent estimates
 of the effective rigidity of the earth 
are greater  than former ones1 and they 
may need to be modified yet further in  
the  same direction4    ,distribution of
 rigidity4--,an important consideration 
in this  connection is the distribution 
of interior rigidity4 ,it is certain    

that the rigidity of the outermost part1
 taken as a mass1 is somewhat  less than
 that of rock of an average surface     
type1 for it is fissured1  and there is 
no reason to suppose that the rigidity  
of the rock next  below the fissure zone
 rises at once to the rigidity of steel1
 and  hence if the average rigidity of  
the whole earth is equal to that of     
steel1 a portion of the interior must   
have a rigidity much higher than  steel4
 ,there is probably some law of increase
 from surface to center1  and there are 
theoretical grounds for thinking that it
 is in some way  connected with the laws
 of pressure1 density1 compressibility1 
and  temperature4 ,all of these factors 
probably affect rigidity1 but in        
different ways4 ,the modulus of rigidity
 of steel is about #ggj  #aj  grms4 per 
sq4 cm4 ,milne and ,gray#bfi found that 
of granite to be #abh   #aj4 ,the ratio 
of the rigidity of steel to that of rock
 is1 therefore1  about #f 3 #a4 ,if it  
be assumed that the rigidity increases  

in depth  directly as the density1 the  
rigidity will nowhere reach that of     
steel1  being only about two-thirds as  
much at the center4 ,if it be assumed   
that the rigidity increases as the      
squares of the density ratios1 the      
following values are obtained3          
----------------------------------------
----------------------    ,distances    
from                           ,density 
center in terms ,densities under        
,density   ratios    ,deduced     of    
radius4      ,laplace's law4 ratios4    
squared4  rigidities4                   
----------------------------------------
----------------------         #a4jj    
#b4h           #a        #a      #j4af  
,steel          4#ge            #e4g    
#b        #d      #j4f              4#ej
            #h4ci          #c        #i 
#a4e              4#be           #aj4bg 
#c4g     #ac4g    #b4c              4#jj
           #aj4ie          #c4i         
#ae4b    #b4e        ,these values seem 
fairly consistent with the apparent     

requirements of  the case4    ,if the   
distribution of rigidity were of this   
nature1 the average  rigidity would be  
much less than that of steel1 for more  
than half  the volume lies in the outer 
division1 between #a4jj and 4#ge radius1
  and yet the effective resistance to   
tidal deformation would be high1  for1  
according to ,g4 ,h4 ,darwin1#bgj the   
tidal stress-differences are  eight     
times as great in the center as at the  
surface4 ,the rigidity  would1          
therefore1 be distributed so as to be   
much more effective  in resistance than 
if it were uniform4 ,the suggestion     
arises here  that the tidal stresses and
 other analogous stresses arising from  
astronomical sources may be in          
themselves the causes of some such      
distribution of rigidity as this4 ,the  
tidal stresses are rhythmical  and give 
rise to a kind of kneading of the body  
of the earth1 small in  measure to be   
sure1 but persistent and rapidly        
recurrent4 ,since these                 

stress-differences at the center are    
eight times those at the surface1  and  
since also the gravitative stress at the
 center is #c1jjj1jjj times  that at the
 surface1 there is a series of          
persistently recurring                  
stress-differences1 greatest at the     
center and declining outwards1          
superposed on enormous static stresses1 
also intensest at the center  and       
declining outwards4 ,now1 if the earth  
material were once made up  of a mixture
 of minerals of different fusibility1   
some of which became  more mobile       
7whether fluid or viscous7 than others  
under the rising  temperature of the    
interior1 it seems that the more mobile 
portion must  have tended to move from  
the regions of greater                  
stress-differences to  those of lesser  
stress-differences4 ,the persistence and
 the rhythmical  nature of the tidal    
stress-differences seem well suited to  
aid the  mobile parts in gradually      
working their way outwards4 ,at the same

 time  the more solid and resistant     
portions should remain behind1 and thus 
come to constitute the dominant material
 of the central regions where           
stress-differences were greatest1 and   
so1 as it were1 concentrate  rigidity   
there4 ,the process may still be in     
action4    ,if it be assumed that the   
rhythmical stresses have thus developed 
a  resistance to deformation            
proportional to their intensity1 we may 
combine this with density to form the   
basis of another hypothetical           
distribution of rigidity1 as follows3   
----------------------------------------
-----------------------    ,distances   
from  ,densities  ,density  ,ratios     
adjusted    center in terms   under     
ratios4     to stress     ,deduced      
of radius4     ,laplaces                
differences4  rigidities4               
,law4                  7#a3h7           
----------------------------------------
-----------------------         #a4jj   
#b4h        #a           #a             

#j4af ,steel          4#ge          #e4g
        #b           #c4e        #j4eh  
4#ej          #h4ci       #c            
#e4d        #j4ij             4#be      
#aj4bg      #c4g         #g             
#a4af             4#jj          #aj4ie  
#c4i         #h          #a4cc          
,the average rigidity is here also much 
less than that of steel1 but its        
distribution is such as to render it    
ideally fitted to resist tidal          
distortion4    ,these hypothetical      
distributions of rigidity have no claims
 to special  value in themselves1 for   
the grounds on which they are based are 
quite  inadequate1 but they are not     
without importance in giving tangible   
form  to considerations that bear       
vitally not only on tidal problems1 but 
on  many others connected with the      
internal constitution and dynamics of   
the earth4                              
,sphericity as a factor in deformation4 
,it is obvious that if the earth        
shrinks1 its crust must become too      

large for the reduced spheroid1 and must
 be compressed or distorted  to fit the 
new form4 ,the amount of distortion     
required for any given  shrinkage is    
easily computed from the ratio of the   
radius to the  circumference of a       
sphere1 which is approximately #a 3     
#f4bh4 ,if1 for  example1 the radius    
shortens #e miles1 each great circle    
must on the  average be compressed1     
wrinkled1 or otherwise distorted to the 
extent  of about #ca miles1 or1 in      
reversed application1 if the mountain   
foldings on any great circle together   
show a shortening of #ajj miles1  the   
appropriate radial shortening is #af    
miles4 ,the ratio of #a 3 #f  furnishes 
a convenient check on hypotheses that   
assign specific thrusts  to specific    
sinkings of adjacent segments4 ,a       
segment #cjjj miles across1  for        
example1 such as the bottom of the      
,north ,atlantic basin1 sinking  three  
miles1 about the full depth of the      
basin1 would give a lateral  thrust of  

about #b4b miles1 a little over a mile  
on each side1 a  trivial amount compared
 with the foldings on the adjacent      
continental  borders4    ,the influence 
of the domed form of the                
surface4--,because of the  spheroidal   
form of the earth1 each portion of the  
crust is ideally an  arch or dome4 ,when
 broad areas like the continents are    
considered1 it  is the dome rather than 
the arch that is involved1 and in this  
the  thrust is ideally toward all parts 
of the periphery4 ,it is probably for   
this reason that mountain ranges so     
often follow curved or angulated  lines1
 or outline rude triangles or polygons4 
,the sigmoidal courses  of the ranges of
 southern ,europe1 the looped chains of 
the eastern  border of ,asia1 and the   
curved ranges of the ,antillean region1 
are  notable examples4 ,the border      
ranges of the ,americas1 of the         
,thibetan  plateau1 and of other great  
segments1 illustrate the polygonal      
tendency4 ,the general distribution of  

the great ranges is such that a  nearly 
equal portion of crustal crumpling is   
thrown across each great  circle1 as    
theory demands4 ,the common             
generalization that mountain  ranges run
 chiefly in oblique directions1 as      
northeast-southwest1                    
northwest-southeast1 is but a partial   
view of the more general fact  that the 
lines of distortion must lie in all     
directions to accommodate  the old crust
 to the new geoid1 if there be equable  
contraction in all  parts4              
,theoretical strength of domes of       
earth-dimensions4--,as the domed form   
of the crust has played an important    
part in theories of deformation1  it is 
important to form quantitative          
conceptions of the strength of  ideal   
domes having the figure and dimensions  
of segments of the earth's  crust4      
,according to ,hoskins1#bga a dome      
corresponding perfectly to the          
sphericity of the earth1 formed of firm 
crystalline rock of the high  crushing  

strength of #be1jjj pounds to the square
 inch1 and having a  weight of #ahj     
pounds to the cubic foot1 would1 if     
unsupported below1  sustain only  of its
 own weight4#bgb ,this result is        
essentially  independent of the extent  
of the dome1 and also of its thickness1 
provided the former is continental and  
the latter does not exceed a  small     
fraction of the earth's radius4 ,if this
 ideal case be modified  by supposing   
the central part of the spherical dome  
to rise above the  average surface1 the 
supporting power will not be materially 
changed  unless the central elevation is
 a considerable fraction of the radius  
of the dome4 ,assuming a central        
elevation of two miles--to represent    
the protrusion of the continental       
segments--the results for domes of      
different horizontal extent are as      
follows3#bgc          ,,theoretical     
,,strength ,,of ,,ideal ,,domes ,,arched
 ,,two ,,miles ,,above                  
,,the ,,average ,,surface ,,of ,,the    

,,sphere4                               
----------------------------------------
-----------------     ,diameter of      
,multiplier of    ,proportion of its own
     given dome    i4e4 the supporting  
weight sustained by     arched #b miles 
proportion of a      given dome arched  
above sphere4   spherical dome4    #b   
miles above sphere4                     
----------------------------------------
-----------------     #c1jjj miles      
#a4jjf                 #a_/ebb          
#djj   0           #a4cif               
#a_/cgf                #bdj   0         
#b4aa                  #a_/bdi          
#afj   0           #c4di                
#a_/aej                 #hj   0         
#aj4ig                  #a_/dh          
----------------------------------------
-----------------    ,from this table it
 will be seen that for domes of         
continental  dimensions the supporting  
strength equals only a very small       
fraction  of the dome's own weight4     
,increasing the thickness of the shell  

increases its actual supporting power1  
but the proportion is somewhat  less    
when the whole sphere is concerned4 ,the
 problem has not been  worked out for   
domes of limited extent4 ,for rough     
estimates1 where  the dimensions of the 
dome are of continental magnitude1 each 
mile of  thickness may be taken as      
supporting a layer of about #aj feet of 
its  own material4 ,if the hypothetical 
level of no stress be placed at #h      
miles depth1 the shell above this1 by   
reason of its domed shape1 could        
relieve its own pressure on that below  
to an amount equal only to the  weight  
of about #hj feet of rock over its      
surface1 even if its form and  structure
 were ideal4 ,if the shell were thick   
enough 7#hag miles7 to  embrace one-half
 the volume of the earth1 its supporting
 power would  be a little more than the 
weight of one and one-half miles of     
rock4 ,as  the radius of the earth is   
less than #djjj miles1 the extreme      
supporting  power reckoned on this basis

 would be only about #h miles of        
rock-depth4  ,it is interesting1 if not 
significant1 to observe that this depth 
barely reaches the minimum shrinkage    
that will serve1 according to  current  
estimates1 to account for the crustal   
shortening of the great  mountain-making
 periods4 ,it is as if the shrinkage    
stresses accumulated  to the full extent
 of the stress-resisting power of the   
whole sphere1  and then collapsed4 ,it  
is not safe1 however1 to give much      
weight to  this coincidence1 for higher 
densities and probably higher           
resistances  to distortion come into    
play in the deeper horizons4 ,if these  
resistances are proportional to the     
higher densities of the interior1  the  
deductions would remain the same4 ,if   
the effective rigidity of the  earth as 
a whole is that of steel1 as deduced by 
,kelvin and ,darwin  from tidal and     
other observations1 or twice that of    
steel1 as inferred  by ,milne from the  
transmission of seismic vibrations1 the 

supporting  power of the body of the    
earth dependent on its sphericity would 
be  appreciably higher4    ,it would    
seem clear from the foregoing           
considerations that something  more than
 the mere crust of the earth has been   
involved in the great  deformations4    
,indeed it is not clear that the fullest
 resources of  stress-accumulation which
 the spheroidal form of the earth       
affords are  sufficient to meet the     
demands of the problem1 unless the      
rigidity of  the earth be taken at a    
much higher value than that of          
surface-rock1  and this is perhaps an   
additional argument for the high        
rigidities  inferred from tides and     
seismic waves4    ,in view of the       
doubtful competency of even the thickest
 segments to  accumulate the requisite  
stresses1 there is need to consider     
modes  of differential                  
stress-accumulation other than those    
dependent on  sphericity4               
,stress-accumulation independent of     

sphericity4--,the principle of the  dome
 is brought into play whenever an       
interior shell shrinks away1 or  tends  
to shrink away1 from an outer one which 
does not shrink4 ,in this  case1 there  
is a free outer surface and a more or   
less unsupported  under surface toward  
which motion is possible4 ,the dome may1
 therefore1  yield by crushing or by    
contortion4 ,the computations given     
above are  for cases of this kind4 ,but 
where the thickness becomes great and   
the dome involves a large part or even  
all of a sector of the earth1  freedom  
of motion beneath is small1 and to      
readjust the matter to a new  form1     
strains must be developed widely        
throughout the sector1 and must  involve
 regions where the pressure is extremely
 great on all sides1  and crushing in   
the usual sense impossible4 ,assuming   
the correctness  of the modern doctrine 
that such pressure increases rigidity1  
instead  of the older doctrine that it  
gives plasticity1 it becomes reasonable 

to assume that stress-differences would 
be distributed throughout the  mass1 and
 bring into play a large portion of its 
stress-accumulating  competency4 ,when  
the mass yielded1 it would not be by    
crushing1 but by  8flowage10 which would
 be more or less general throughout the 
mass4  ,it might1 however1 be partially 
concentrated1 as1 for example1 on the   
borders of sectors of different specific
 gravity4    ,stress-differences may    
arise from physical changes within the  
rock  itself4 ,whenever there is a      
re-aggregation of matter1 or a change   
of any kind which involves change of    
volume1 a change of stress  is liable to
 be involved4 ,it may be of the nature  
of relief or of  intensification4 ,in an
 earth built up by the haphazard infall 
of  matter1 a very heterogeneous mass   
must result1 and the subsequent  changes
 may be supposed to be intimately       
distributed through the  mass1 being    
slight at any point1 but present at     
innumerable points4  ,an immeasurable   

number of small stress-differences may1 
therefore1 be  developed throughout the 
mass4 ,until these overmatch the        
effective  strength of the mass1 they   
may continue to accumulate4 ,these are  
not  necessarily connected with stresses
 that arise from sphericity1 and may    
work more or less independently of them4
 ,it is not improbable that the  great  
stress-accumulating power of the globe  
finds an essential part of  its         
explanation in supplemental             
considerations of this kind1 and not    
wholly in its spheroidal form4    ,the  
actual configuration of the             
surface4--,the foregoing computations   
relative to the power of shells of the  
earth to sustain pressures  are based on
 ideal forms and structures that are not
 realized in  fact4 ,how far the earth  
fails to conform to these conditions    
must  now be considered4 ,when compared 
with the earth as a whole1 the          
inequalities of its surface are trivial4
 ,if the great dynamic forces  acted    

through the whole or the larger part of 
the body of the earth1  the             
configuration of the surface can be     
supposed to have done little  more than 
influence the location of the surface   
deformations and their  special phases4 
,but if the forces were limited to a    
crust of moderate  thickness1 the       
configuration of the surface is a matter
 of radical  importance4    ,concave    
tracts4--,there is need1 therefore1 to  
inquire if any  considerable breadth of 
the crust is outwardly plane or concave1
 for  the principle of the dome is      
obviously not applicable to a plane or  
concave surface4 ,to be a source of     
fatal weakness1 the concavity must  be  
broad enough to cause the planes of     
equal cooling1 the isogeotherms1  to be 
concave to considerable depths4 ,for    
example1 if the hypothetical  level of  
no stress is eight miles below the      
surface1 as computed on  certain        
assumptions1 the concave portion must be
 so broad that the  isogeotherms will   

also be concave outward at something    
near that  depth2 in other words1 the   
main part of the zone of thrust must be 
concave4 ,a narrow concavity at the     
surface1 such as an ordinary valley  in 
a portion of the crust that has the     
average convexity1 would not  seriously 
depress the isogeotherms1 or affect the 
zone of thrust1 but  a valley several   
times eight miles 7level of no stress7  
in breadth  would4 ,for inspecting the  
surface of the earth in this regard1 it 
is  convenient to know what amounts of  
fall below the level surface give  a    
true plane for given distances4 ,these  
are shown in the following  table3#bgd  
----------------------------------------
-----------             ,length of      
normal to chord  ,average fall of       
,length     at middle point in      true
 plane from     of arc                  
-------------------------- level plane  
per       in                            
mile1 in feet4     miles4     ,feet4    
,fathoms4      ,greater fall            

gives concavity4                        
----------------------------------------
-----------       #be        #ajj4c     
#af4g            #h4             #ej    
#dcb4         #gb4             #ag4c    
#ge        #iac4d       #aeb4b          
#bd4c          #ajj       #a1fhd4       
#bhj4g            #cc4g          #aej   
#c1gdh4h      #fbd4h            #di4i   
#bjj       #f1fgd4      #a1aab4c        
#ff4g          #bej      #aj1cfi4i      
#a1gbh4c           #hb4i          #cjj  
#ad1idb4      #b1dij4c           #ii4f  
#djj      #bf1ffd4      #d1ddd4         
#acc4c          #ejj      #da1fei4      
#f1idc4           #aff4f                
----------------------------------------
-----------    ,applying these criteria 
to the surface of the lithosphere1 it is
 found  that concave tracts from #ajj to
 #cjj miles in breadth are not uncommon4
  ,the more notable of these are shown  
in black on the accompanying map1  ,fig4
 #ded1 and two typical ones are shown in
 cross-section in ,figs4  #dee and #def4

 ,it is to be observed that concave     
tracts border the  continents very      
generally4 ,they are connected with the 
descent from  the continental shelf to  
the abysmal basins1 and are             
unsymmetrical4  ,notable concavities are
 found in some of the great valleys on  
the  continental platforms4 ,the basins 
of ,lake ,superior1 ,michigan1 ,huron1  
and ,ontario are in part concave2 so are
 ,puget ,sound1 the ,adriatic1  and the 
,dead ,sea2 so also are the valleys of  
,california1 of the ,po1  and of the    
,ganges1 when the adjacent mountains are
 included4 ,some of  the 8deeps0 of the 
bottom of the ocean are notably concave4
 ,fig4  #dee1 a cross-section of the    
,challenger ,deep1 drawn to true scale  
and  convexity1 shows the nature of the 
phenomenon4 ,the breadth is here  #cjj  
miles1 and the depression below a true  
plane is #aa1djj feet4 ,the  lower line 
of the figure shows the approximate     
position and form of the  normal        
isogeotherm about ten miles below the   

surface4 ,assuming equal  conductivity  
in all parts1 it is clear that the      
isogeotherms must be  concave upwards   
for a considerable distance below ten   
miles4 ,unless  the shell of thrust is  
much more than ten miles thick1 these   
concave  portions should yield as fast  
as cooling below them permits1 and no   
stresses arising from convexity could be
 accumulated4    ,illustration3 ,fig4   
#ded4--,map of the world1 showing in    
black the chief    submarine concavities
 of the lithosphere4 7,prepared by ,w4  
,h4 ,emmons47    ,illustration3 ,fig4   
#dee4--,section of the ,challenger ,deep
 from an    island on the ,caroline     
plateau1 a1 to an island on the ,ladrone
    plateau1 b1 drawn to a true scale1  
showing the real concavity    of the    
surface of the lithosphere for a breadth
 of #cjj miles4 ,the    upper line      
represents the sea surface1 a natural   
level4 ,the next    line below          
represents a true plane1 eliminating the
 curvature of the    sea surface4 ,the  

third line represents the bottom of the 
deep4 ,by    comparison with the line   
above1 its true concavity may be seen4  
,the    lowest line represents an       
isogeotherm at about #aj miles below the
    surface2 i4e4 appreciably below 8the
 level of no stress10 as usually        
computed1 showing that the whole thrust 
zone is concave outwards1 if    it is   
limited to surface cooling as usually   
computed4 7,prepared by ,w4    ,h4      
,emmons47    ,illustration3 ,fig4       
#def4--,section through the ,atlantic   
coastal plain1    the continental shelf1
 and a portion of the abysmal bottom1   
drawn    to a true scale1 showing that  
the surface of the lithosphere    drops 
below a true plane tangent to the       
continental shelf and the               
ocean-bottom4 ,the upper line represents
 the surface of the coastal    plain at 
the left and of the ocean at the right4 
,the lower line    represents the       
sea-bottom1 and the middle line a true  
plane tangent    to the shelf and the   

sea-bottom4 ,the breadth of the concave 
tract    varies from #ajj to #aej miles4
 7,prepared by ,w4 ,h4 ,emmons47        
,these concavities of surface are so    
extensive and so widely distributed     
over the globe that no part of the outer
 shell can be supposed to  be capable of
 accumulating notable stresses unless   
rigidly attached  to the earth-body     
below4 ,in other words1 so far as       
sphericity is  concerned1 the crust must
 ease all its stresses nearly as fast as
 they  accumulate1 if1 as usually       
assumed1 it rests on a contracting or   
mobile  substratum4    ,surface cooling 
under these conditions should give only 
feeble thrusts1  developed and eased    
nearly constantly4 ,such movements      
should be  admirably adapted to give    
those gentle1 nearly constant           
subsidences  that furnish the nice      
adjustments of water-depth required for 
the  accumulation of thick strata in    
shallow water1 and those slow upward    
warpings that renew the feeding-grounds 

of erosion1 the necessary  complement of
 the deposition4 ,these gentle1 nearly  
constant movements  mark every stage of 
geological history1 and constitute one  
of its  greatest though least obtrusive 
features4 ,but if superficial stresses  
arising in this way are eased in        
producing these effects1 they cannot    
accumulate to cause the great periodic  
movements4    ,even where the crust is  
not concave1 it is so warped and so     
traversed  by folds and fault-planes    
that its resistance to thrust is        
relatively  low1 and it should1         
therefore1 warp easily and at many      
points1 if the  thrust be confined to a 
superficial crust4    ,general          
conclusion4--,when to the weakness of   
the crust1 as computed  under ideal     
conditions1 there is added the weakness 
inherent in these  concave and warped   
tracts1 the conclusion seems imperative 
that while  the crust is the pliant     
subject of minor and nearly constant    
warpings1  such as are everywhere       

implied in the stratigraphic series1 it 
is  wholly incompetent to be the medium 
of those great deformations  which occur
 at long intervals and mark off the     
great eras of geologic  history4 ,these 
great deformations apparently involve   
the whole1 or a  large part1 of the body
 of the earth1 and seem to require a    
very high  state of effective rigidity4 
,general references on crustal          
movements4--,babbage1 ,jour4 ,geol4     
,soc41 ,vol4 ,,iii 7#ahcd71 p4 #bjf2    
,lyell1 ,principles of ,geology1 ,vol4  
,,ii1 p4 #bce2 ,mallet1 ,phil4 ,trans4  
7#ahgc71 p4 #bje2 ,reade1 ,origin of    
,mountain ,ranges1 and ,evolution of    
,earth ,structure2 ,fisher1 ,physics    
of the ,earth's ,crust2 ,dutton1        
,greater ,problems of ,physical         
,geology1    ,bull4 ,phil4 ,soc4 of     
,washington1 ,vol4 ,,xi1 p4 #eb1 also   
,amer4 ,jour4 of    ,sci41 ,vol4 ,,viii 
7#ahgd71 p4 #aba1 and ,geology of the   
,high ,plateaus    of ,utah 7#ahhj72    
,jamieson1 ,quar4 ,jour4 ,geol4 ,soc4   

7#ahhb71 and ,geol4    ,mag4 7#ahhb71   
pp4 #djj and #ebf2 ,heim1 ,mechanismus  
der ,gebirgsbildung2    ,marjerie and   
,heim1 ,les ,dislocations de l'corce    
terrestre 7#ahhh72    ,shaler1 ,proc4   
,boston ,soc4 ,nat4 ,hist41 ,vol4       
,,xvii1 p4 #bhh2 ,dana1    ,manual of   
,geol41 #dth ed41 p4 #cde et seq42      
,woodward1 ,mathematical    ,theories of
 the ,earth1 ,smithsonian ,rept4 for    
#ahij1 p4 #aif2 ,willis1    ,the        
,mechanics of the ,appalachian          
,structures1 #acth ,ann4 ,rept4 ,u4     
,s4 ,geol4 ,surv41 ,pt4 ,,ii 7#ahic71   
pp4 #baa-bhb2 ,le,conte1 ,theories of   
,mountain ,origin1 ,jour4 ,geol4 ,vol4  
,i 7#ahic71 p4 #edb2 ,gilbert1 ,jour4   
,geol41 ,vol4 ,,iii 7#ahie71 p4 #ccc1   
and ,bull4 ,phil4 ,soc4 of ,washington1 
,vol4 ,,xiii 7#ahie71 p4 #ca2 ,van      
,hise1 ,earth ,movements1 ,trans4 ,wis4 
,acad4 ,sci41 ,arts and ,let41 ,vol4    
,,ii 7#ahih71 pp4 #eab-ead2 ,estimates  
and ,causes of ,crustal ,shortening1    
,jour4 ,geol41 ,vol4 ,,vi 7#ahih71 pp4  

#bi-ca2 ,relations of ,rock ,flowage to 
,mountain ,making1 ,mon4 ,,xlvii1    ,u4
 ,s4 ,geol4 ,surv4 7#aijd71 pp4         
#ibd-ica2 ,a4 ,geikie1 ,text-book of    
,geology1 #dth ed41 pp4 #fgb-gjb4       
,,chapter ,x4                           
,,the ,,extrusive ,,processes4          
,outward movements4--,in the preceding  
chapters movements toward the  center   
have been considered4 ,the complementary
 processes of outward  movement now     
invite attention4 ,without doubt these  
are mainly but a  resultant of the      
centripetal actions4 ,for each pound of 
material moved  outwards an equivalent  
is quite surely moved inwards4          
,notwithstanding  this1 the outward     
movements have a peculiar nature of     
their own1 and  serve a function of     
radical importance in the economy of the
 globe4  ,some minor phases have been   
incidentally considered1 such as the    
upward  flow of springs and deep-seated 
waters1 but here the descending and     
ascending factors are alike1 and are    

closely and obviously connected4        
,,vulcanism4    ,the great example of   
ascensive action is the movement of     
fluid rock  from the interior outwards4 
,the term vulcanism will be used to     
embrace  not only volcanic phenomena in 
the narrower sense1 but all outward     
forcing of molten material1 whether     
strictly extrusive or merely  ascensive4
    ,the philosophy of this ascensive   
action1 taken as a whole1 is simple4    
,in the effort at concentration under   
the powerful action of the  earth's     
gravity1 the material of high specific  
gravity is urged more  strongly toward  
the center1 volume for volume1 than that
 of less  specific gravity1 and as      
gravity is perpetually active1 it       
follows that  whenever any movement1    
molecular or molar1 takes place which   
permits a  readjustment of the positions
 of the two kinds of matter1 the heavier
  sinks toward the center and the       
lighter rises1 or at least tends to  do 
so4 ,so also where there are            

stress-differences1 the mobile matter   
tends to flow from the regions of       
greater stress toward those of lesser   
stress4 ,in so far as any portion of the
 interior becomes liquid1 it  is free to
 move up or down according to the       
balance of stress brought  to bear upon 
it1 and adapts itself to any line of    
least resistance  available to it4 ,as a
 natural result1 therefore1 the portion 
of the  interior which becomes fluid    
most largely participates in the outward
  movement4 ,in so far as molecular     
action permits a readjustment of        
material1 there is a tendency1 even in  
the solid state1 for the lighter        
material to move upwards and the heavier
 downwards1 and for the more  stressed  
portions to move toward points of less  
stress2 but this takes  place with      
extreme slowness4 ,in so far as the     
materials of the interior  diffuse      
themselves through each other1 the same 
laws hold good1 but  they are modified  
by the special principles that control  

diffusion4  ,the outward diffusion of   
interior gases may be a factor of       
appreciable  importance1 but this cannot
 be affirmed at present4    ,phases of  
vulcanism4--,the forcing of fluid rock  
outward assumes two  general phases1    
which1 however1 merge into each other2  
and these  main phases take on various  
sub-phases4 ,the first phase embraces   
those outward movements of fluid rock   
which do not reach the surface4  ,the   
lavas1 after ascending to the vicinity  
of the surface1 intrude  themselves into
 the outer formations of the earth and  
congeal  underground 7plutonic74 ,the   
second phase embraces those outward     
movements in which the fluid rock       
reaches the surface and gives rise  to  
eruptive phenomena 7volcanic74 ,the     
first is intrusive1 the  second         
extrusive2 the first constitutes        
irruptions1 the second  eruptions4#bge  
,the fundamental nature of the two is   
the same1 but  the extrusions usually   
take on special phases because of the   

relief  of pressure at the surface of   
the earth1 and because of the action of 
surface-waters in contact with the      
heated lavas4 ,just where the lavas     
come from1 and how they find their way  
through the deep-lying compact  zone    
below the zone of fracture1 may better  
be considered later4 ,when  they reach  
the zone of fracture1 they usually      
either take advantage  of fissures      
already formed1 or force passageways for
 themselves by  fracture4 ,there is     
little evidence that they bore their way
 through  the rocks by melting1 though  
they appear to round out their channels 
in some way into pipes1 ducts1 and other
 tubular forms when they flow  through  
them for long periods of time4          
#a4 ,intrusions4    ,fluid rock forced  
into fissures and solidified there forms
 dikes2  forced into chimney-like       
passages1 it forms pipes or plugs2      
insinuated between beds1 it forms sills2
 bunched under strata  so as to arch    
them upwards1 it forms laccoliths2      

massed in great  aggregations           
underground1 it constitutes batholiths1 
as already  described 7pp4 #cid and     
#ejj74 ,lavas sometimes crowd aside the 
adjacent  rocks so far as to cause them 
to take a concentric form about the     
intruded mass4 ,this is not uncommon in 
the oldest formations1 and is  probably 
not infrequent in the deeper horizons   
where the pressures  are very great4    
,some part of this may1 however1 be due 
to later  deformations4 ,nearer the     
surface1 usually1 the beds are merely   
lifted  as in forming the sills1 or are 
bowed upwards1 as in the laccoliths1 or 
faulted as in bysmaliths 7p4 #ejj74     
,the heating action on the adjacent rock
 varies greatly with the  mass and      
temperature of the intruded lava4 ,thin 
dikes and sills  often produce little   
effect1 while greater and hotter masses 
notably  metamorphose the adjacent rock4
 ,in some cases marked effects are due  
to a thin stream of lava flowing through
 a fissure for a long period1  and so   

maintaining a high temperature4 ,in the 
least effective cases1  the adjacent    
rock usually shows some signs of baking4
 ,in the marked  cases1 there is more or
 less new crystallization4 ,the         
surrounding rock  commonly shows some   
evidence of material derived from the   
lavas2 less  often the lava shows some  
evidence of having received material    
from  the adjacent rock4 ,but since the 
lavas do not usually bore their way     
through the strata in the zone of       
fracture1 nor melt the adjacent rock1   
the constitution of the lavas is not    
appreciably changed by the kinds  of    
rock which they penetrate4 ,on the other
 hand1 the intrusions often  show the   
effects of rather rapid cooling by      
contact with the adjacent  rock1 7a7 by 
a less coarse crystallization near the  
rock-walls1 and  sometimes 7b7 in a     
segregation of the material4            
#b4 ,extrusions4    ,when molten rock is
 forced to the surface it gives rise to 
the most  intense and impressive of all 

geological phenomena4 ,the energies     
acquired in the interior under great    
compression here find sudden  relief4   
,occluded gases often expand with       
extreme violence1 hurling  portions of  
the lavas to great heights and          
shattering them into  fragments         
constituting 8smoke10 ash1 cinders1     
bombs1 and other  pyroclastic material4 
,much of the explosive violence of      
volcanoes  has been attributed to the   
contact of surface-waters with the hot  
rising lava1 but the function of this   
kind of action has probably been        
exaggerated4    ,there are two phases of
 extrusion often quite strongly         
contrasted4  ,the one is explosive      
ejection1 often attended with great     
violence2  the other1 a quiet           
out-welling of the lava1 with little    
more than  ebullition4 ,more or less    
closely related to these differences are
 two  classes of conduits1 7a7 the one1 
great fissures1 out of which the  lava  
pours in great volume and spreads forth 

over wide tracts1 often in  broad thin  
sheets2 7b7 the other1 restricted       
openings1 often pipes1  ducts1 or       
limited fissures1 from which the        
extrusion is usually much  less         
abundant1 and hence it more largely     
congeals near the orifice1  forming     
cones4 ,flows from the former constitute
 massive eruptions2  those from the     
latter1 the more familiar volcanic      
eruptions4 ,there is  no radical        
difference between them1 and the two    
classes blend4 ,the  extent of the      
spreading of lava into thin sheets is   
due more to the  mass and the fluidity  
than to the form of the outlet4 ,the    
stupendous  outflows of certain geologic
 periods appear to have issued mainly   
from  extended fissures1 doubtless      
because these better accommodated the   
outbursting floods4    a4 ,fissure      
eruptions4--,the chief known fissure    
eruptions of recent  times are the vast 
basaltic floods of ,iceland4 ,most of   
the eruptions  of historic times are of 

the volcanic type2 but at certain times 
in  the past there were prodigious      
outpourings1 flow following flow until  
layers thousands of feet thick covering 
thousands of square miles were  built   
up4 ,one of these occurred in ,tertiary 
times in ,idaho1 ,oregon1 and           
,washington1 where some #bjj1jjj square 
miles were covered with sheets  of lava1
 aggregating in places #bjjj feet or    
more in thickness4 ,earlier  than this1 
in ,cretaceous times1 there were        
enormous flows on the ,deccan  plateau  
of ,india1 covering a like area to a    
depth of #djjj to #fjjj feet4  ,still   
earlier than this1 in ,keweenawan times1
 an even more prolonged  succession of  
lava-flows covered nearly all the area  
of the ,lake  ,superior basin1 and      
extended beyond it1 and built up a      
series of almost  incredible thickness1 
the estimates reaching #ae1jjj to       
#be1jjj feet4  ,in these cases there is 
little evidence of explosive or other   
violent  action4 ,there are few beds of 

ash1 cinders1 and similar pyroclastic   
material4 ,the inference is1 therefore1 
that the lavas welled out rather        
quietly and spread themselves rather    
fluently over the surrounding  country4 
,for the most part these wide-spreading 
flows are composed of  basic material1  
which is more easily fusible and more   
highly fluent at  a given temperature   
than the acidic lavas4 ,the latter are  
more disposed  to form thick embossments
 near the point of extrusion4           
,massive outflows of this class         
constitute by far the greatest phenomena
  of the extrusive type1 though they are
 not now the dominant type4  ,it has    
been sometimes thought that the more    
local volcanic type of  extrusion       
followed the more massive fissure type  
as a phase of decline2  but this has not
 been substantiated4    ,illustration3  
,fig4 #deg4--,lava-flow near the ,jordan
 craters1 ,malheur    ,co41 ,oregon4    
,though not of the gigantic order1 it   
illustrates the    general aspect of    

massive lava-flows4 7,russell1 ,u4 ,s4  
,geol4 ,surv47    b4 ,volcanic          
eruptions4--,in the types of eruption   
prevailing at  the present time1 the    
lavas are forced out through ducts or   
perhaps  short fissures or sections of  
fissures1 and build up cones about the  
vents1 the eruptive action maintaining  
craters in the centers of the  cones4   
,the essential feature of a volcano is  
the issuance of hot rock  and gas from a
 local vent4 ,a mountain is the usual   
result1 but the  mountain is secondary  
and not usually present in the first    
stages2 the  localized eruption is the  
primary and necessary factor4 ,the      
amount of  rock matter ejected is not   
necessarily great4 ,compared to the     
massive  extrusions of fissure          
eruptions1 it is usually rather trivial2
 but the  volcano makes up in           
demonstrativeness what it lacks in      
massiveness of  product4                
,illustration3 ,fig4 #deh4--,the volcano
 ,colima1 ,mexico1 in eruption4         

,march #bd1 #aijc4 7,jos ,maria         
,arreola1 per ,frederick ,starr47    c4 
,intermediate phenomena4--,on the       
border-line between the intrusive  and  
the extrusive phenomena there are       
special cases of interest4 ,there       
appear to be certain instances in which 
the intrusion comes so near  the surface
 as to develop explosive phenomena      
without the extrusion  of lava4 ,from   
the nature of the case this is an       
interpretation rather  than a           
demonstration4 ,it is certain1 however1 
that occasional violent  explosions take
 place where no lava comes in sight4    
,this sometimes  occurs in old volcanic 
formations1 and sometimes in regions of 
undisturbed horizontal strata4 ,in the  
former case the phenomena may be  due to
 the intrusion of a fresh tongue of lava
 below1 or it may be due  to the        
penetration of surface-waters to hot    
rocks that have remained  uncooled from 
previous volcanic action1 and the       
development1 by such  contact1 of a     

volume of confined steam sufficient to  
produce the  explosion4 ,a case of this 
doubtful kind occurred at ,bandai-,san  
in ,japan  in #ahhh1 where there was a  
sudden and violent explosion which blew 
away  a considerable part of the side of
 a volcanic mountain which had not  been
 in eruption for at least a thousand    
years4 ,the mass and violence  of the   
exploded material was such as to fill   
the air with ashes and  dbris in a      
fashion altogether similar to a typical 
volcanic eruption4  ,a large tract of   
adjacent country was devastated1 and    
many lives lost4  ,the whole action1    
however1 was concentrated in the initial
 explosion1  and within a few hours the 
cloud of ashes had disappeared and the  
phenomenon was ended4 ,an examination of
 the disrupted area revealed no  signs  
of liquid lava4    ,an example of the   
latter class is ,coon ,butte in         
,arizona4#bgf ,this  consists of a rim  
of fragmental material encircling a     
crater-like pit  from which the         

fragments were obviously forced by      
violent explosion4  ,the pit is in      
ordinary sedimentary strata1 and the    
material of the rim  is composed of the 
disrupted fragments of the sedimentary  
rock ejected  from the pit4 ,there are  
no signs of igneous material1 but there 
was  igneous action in the vicinity4    
,fragments of a meteorite were found  on
 the rim and in the vicinity1 but this  
association appears to be  accidental4  
,computation shows that the volume of   
the material of the  rim closely matches
 the size of the pit4 ,the source of the
 explosion  is not demonstrable1 and it 
may be an error to connect it with an   
intrusion of lava below2 but since      
intrusions rise to various degrees  of  
nearness to the surface1 and in         
innumerable cases reach the surface1    
there is every reason to entertain the  
conception of a class of  intrusions    
which develop explosive phenomena by    
close approach to the  surface1 without 
actually reaching it4    ,illustration3 

,fig4 #dei4--,photograph of a portion of
 the moon taken at    ,lick             
,observatory4    ,lunar craters4--,there
 are grounds for thinking that the      
remarkable  craters of the moon1        
assuming that they are truly            
volcanic1#bgg may  belong to this class1
 for they are very similar to the ,coon 
,butte  pit4 ,the capacities of the     
lunar craters1 so far as they can be    
estimated1 seem to equal1 if they do not
 in many cases exceed1 the  volume of   
matter in their rims4 ,they do not      
appear usually to be  great cones of    
accumulated material with relatively    
small craters1  like the typical        
products of terrestrial volcanoes4      
,besides1 there  are no clear evidences 
of lava-streams4 ,the radiating tracts  
once  interpreted as such have been     
shown by increased telescopic power  and
 the resources of photography to be at  
least something other than              
lava-streams4 ,they are vaguely defined 
tracts which run over heights  and      

depths indifferently1 and are plausibly 
interpreted as lines of  dbris projected
 to extraordinary distances because of  
the absence of a  lunar atmosphere1 and 
because of the low force of the moon's  
gravity4  ,since the moon now has no    
appreciable atmosphere or               
surface-waters1 and  since it is        
doubtful whether it ever possessed      
either on account of its  probable      
inability to hold atmospheric gases or  
the vapor of water in  the form of an   
envelope about it1 owing to its low     
gravity1 there is  reason to suppose    
that the external matter of the moon    
derived from the  explosions of the     
multitude of lunar volcanoes would      
remain in a loose1  incoherent          
condition1 from the absence of          
dissolving and cementing  agencies4 ,it 
is reasonable to suppose that           
lava-tongues arising from  the deeper   
interior would have a higher specific   
gravity1 even in their  heated          
condition1 than this porous covering of 

the moon1 and that  therefore they would
 almost universally become intrusions   
rather than  extrusions1 or at most they
 would not rise beyond the bottom of the
  craters they had produced by          
explosion4 ,this seems to furnish at    
least  a plausible explanation of the   
prevailing differences between the large
  lunar craters encircled by mere rims  
and the much smaller terrestrial        
craters seated in relatively large      
cones4                                  
,,volcanoes4    ,number of              
volcanoes4--,it is impracticable to     
state exactly the  number of volcanoes  
that are active at the present time1    
because most  volcanoes are periodic1   
and become active at more or less       
distant  periods1 and it is impossible  
to say whether a given volcano that may 
be now quiescent has really become      
extinct or is only enjoying its         
customary period of rest4 ,it is quite  
safe to include at least #cjj in  the   
active list1 and the number may reach   

#cej or more4 ,the numbers that  have   
been active so recently that their cones
 have not been entirely  worn away is   
several times as great4                 
,distribution of ,volcanoes4    #a4 ,in 
time4--,in the earliest known ages      
igneous action appears to  have been    
very general1 if not practically        
universal4 ,no area of the  earliest    
7,archean7 rocks is now known which is  
not formed chiefly of  rocks that appear
 to have been either intruded or        
extruded4 ,rocks which  can reasonably  
be assigned to the hypothetical molten  
globe1 if there  be such1 are not here  
included4 ,it is probable that the      
surface of the  early earth was as      
thickly occupied with points of         
extrusion as the  surface of the moon   
appears to be4 ,in the ages between the 
,archean and  the present1 the          
distribution of volcanic action over the
 surface seems  to have been in a       
general way much what it is to-day2 that
 is1 certain  areas were volcanically   

active at times1 while other and larger 
areas  were measurably free from any    
outward expressions of igneous action4  
,this is not equally true of all ages1  
as will be seen in the historical       
studies that follow4 ,there were periods
 when volcanic activity seems  to have  
been widespread and energetic1 and      
others when it was limited  both in     
amount and distribution4 ,the known     
facts do not indicate a  steady decline 
in volcanic activity1 but rather a      
periodicity2 at  least this is so for   
the portion of the globe that is now    
well enough  known geologically to      
warrant conclusions4 ,one of the        
greatest of the  volcanic periods falls 
within the ,cenozoic era1 just preceding
 the  present geological period1 and the
 volcanic activity of the present is    
perhaps but a declining phase of that   
time4    #b4 ,relative to land and      
sea4--,at present the active volcanoes  
are  chiefly distributed about the      
borders of the continents1 and1 less    

notably1 within the great oceanic       
basins4 ,on this account the sea has    
often been supposed to have some        
connection with volcanic action1 and    
the presence of chlorine in the volcanic
 emanations has been cited  in support  
of this position4 ,when critically      
examined1 however1 the  argument from   
distribution is not very strong2 for the
 volcanoes are  not distributed equally 
or proportionately about the several    
oceans1  as if dependent on them4       
,volcanoes are especially numerous      
around and  within the ,pacific1 the    
greatest of the oceans1 and this might  
seem a  favorable instance1 but they are
 also numerous around and within the    
,mediterranean1 a relatively small body 
of water4 ,volcanoes are not  especially
 abundant in or about the margins of the
 ,atlantic4    ,illustration3 ,fig4     
#dfj4--,volcanoes in the ,pacific4      
,jones ,relief    ,globe4 7,photo4 by   
,r4 ,t4 ,chamberlin47    ,if volcanoes  
were dependent upon proximity to the    

sea1 the relation  should be close in   
the past as well as in the present1 but 
this does  not seem to be true4 ,there  
has recently been much volcanic activity
  in the plateau region of western      
,america at long distances from the     
,pacific basin4 ,even on the plains east
 of the ,rocky ,mountains notable       
volcanic action took place4 ,there were 
also volcanoes in the interior  of ,asia
 and of ,africa4    #c4 ,relative to    
crustal deformations4--,the distribution
 of present  and recent volcanoes is    
much more suggestively associated with  
those  portions of the crust that have  
undergone notable changes in position   
in comparatively recent times4 ,the     
great 8world-ridge0 stretching from     
,cape ,horn to ,alaska and thence       
onwards along the east coast of ,asia   
is a striking instance1 for it is dotted
 throughout with active and  recently   
extinct volcanoes4 ,the tortuous zone of
 mountainous wrinkles  that borders the 
,mediterranean and stretches thence     

eastward to the  ,polynesian ,islands is
 another notable volcanic tract4 ,these 
two belts  include the greater number of
 existing and recent volcanoes on the   
land1 while the great basins associated 
with them embrace the chief  oceanic    
volcanoes4    ,illustration3 ,fig4      
#dfa4--;,active volcanic area at the    
junction of the    continental segments 
of ,north and ,south ,america1 and of   
the abysmal    segments of the ,atlantic
 and ,pacific4 ,jones ,relief ,globe4   
7,photo4 by    ,r4 ,t4 ,chamberlin47    
,there is perhaps some significance in  
the fact that the most active  regions  
of vulcanism to-day lie at the angular  
junctions of the great  earth-segments4 
,the ,antillean and ,central ,american  
volcanic region1  that has recently been
 so demonstrative1 lies where the       
southern angle  of the ,north ,american 
continental block joins the northern    
angle of  the ,south ,american          
continental block1 and where the western
 angle  of the ,north ,atlantic abysmal 

segment closely approaches one of the   
eastern angles of the great ,pacific    
abysmal segment4 ,the complex and  very 
active ,java-,philippine volcanic region
 lies where the southeastern  angle of  
the great ,asian segment projects toward
 the ,australian block1  and where the  
western angle of the ,pacific block     
approaches the  northeastern angle of   
the ,indian oceanic segment4 ,the active
 ,alaskan  volcanic area lies at the    
angles of the ,north ,american1 ,asian1 
,pacific1  and ,arctic segments4 ,the   
,mediterranean volcanic area falls less 
notably  under this generalization1 but 
it lies where the continental blocks of 
,europe and ,africa come into peculiar  
relations to each other on either  side 
of the remarkable ,mediterranean trough4
 ,the eastern angle of the  ,north      
,atlantic segment is near by1 but not in
 very close relations4  ,the ,icelandic 
region1 small but vigorous1 lies near   
the junction of  the ,north ,american1  
,european1 ,north ,atlantic1 and ,arctic

 segments1  and the ,new ,zealand       
volcanic region is somewhat less closely
 related  to the approach of the        
,australian1 ,antarctic1 ,pacific1 and  
,southern  oceanic segments4 ,nearly all
 of these angular conjunctions involve  
two depressed segments joining two      
relatively elevated segments4 ,this     
relationship suggests a causal          
connection between the intensified      
movements at these angular conjunctions 
and the intensified volcanic  action of 
these regions4 ,there are enough        
volcanoes1 however1 that do  not fall   
into these groups1 or apparently into   
any other grouping1 to  suggest that the
 development of volcanoes is not wholly 
dependent on  any surface relationship1 
but that it is connected with           
deep-seated  causes that are indeed     
modified1 but not wholly controlled1 by 
surface  conditions1 or even by the     
movements of the master segments of the 
earth's crust4    ,illustration3 ,fig4  
#dfb4--;,active volcanic area at the    

junction of the    continental segments 
of ,asia and ,australia1 and the abysmal
 segments    of the ,pacific and ,indian
 oceans4 ,jones ,relief ,globe4 7,photo4
 by ,r4    ,t4 ,chamberlin47    #d4 ,in 
latitude4--,the distribution of         
volcanoes appears to have no  specific  
relation to latitude4 ,mounts ,erebus   
and ,terror1 amid the  ice-mantle of    
,antarctica1 and ,mount ,hecla in       
,iceland1 as well as  the numerous      
volcanoes of the ,aleutian chain1 give  
no ground for  supposing that volcanoes 
shun the frigid zones4 ,on the other    
hand1  the numerous volcanoes of the    
equatorial zone do not imply that they  
avoid the torrid belt4 ,their           
distribution appears to be independent  
of  latitude4 ,this is not cited because
 of any supposed effects of external    
temperature1 for that must be trivial1  
but because it bears on the  question   
whether strains are now arising from the
 supposed slackening  of the earth's    
rotation1 which have any connection with

 volcanic  action4 ,if the oblateness of
 the earth is decreasing1 the equatorial
  belt must be sinking and growing      
shorter1 and hence must be under        
lateral pressure1 while the polar caps  
must be rising1 and increasing  their   
curvatures1 and should be under tension4
 ,these conditions1 if  real1 might be  
supposed to have something to do with   
the extrusion of  lava4 ,nothing in the 
present or the past distribution of     
igneous action  seems to afford much    
support to this hypothetical inference4 
#e4 ,in curved lines4--,in the          
,antilles1 the ,aleutian ,islands1 the  
,kurile ,islands1 and in other          
instances1 there is a notable linear    
arrangement of volcanoes with           
appreciable curvature4 ,it has been     
noted  that the convexity of the curves 
is turned toward the adjacent ocean4    
,in some cases1 however1 there is a     
notable linear arrangement without      
appreciable curvature1 as in the        
,hawaiian range1 in the recently        

extinct line of cones of the ,cascade   
,range1 and in others4 ,less often1     
volcanoes are bunched irregularly1 as in
 some of the groups of volcanic  islands
 of the ,pacific 7,fig4 #dfj74          
,relations of ,volcanoes4    #a4        
,relations to rising and sinking        
surfaces4--,so far as observations      
cover this point1 the area immediately  
adjacent to active volcanoes  is rising 
7,dutton74 ,this is shown by raised     
beaches1 terraces1 coral  deposits1 etc4
 ,whether this is wholly due to the     
expansional effect  of the heating of   
the subterrane by the rising lava1 or   
whether it  has a wider significance1 is
 not known4 ,if a broader view is taken1
  it does not appear that there are     
sufficient data to connect volcanic     
action exclusively with either the      
rising or the sinking of the general    
surface4 ,it is certain that the great  
mountain ranges and plateaus in  which  
so much of the more recent volcanic     
action has taken place have  been       

recently elevated relatively1 but they  
have also undergone more or  less of    
oscillation1 involving some relative    
depression4 ,the question  whether the  
,pacific basin as a whole has been      
relatively elevated or  depressed in    
modern times is a mooted one4           
,darwin#bgh and ,dana1#bgi  as the      
result of their early studies on its    
coral deposits and on other  phenomena1 
concluded that the ,pacific was a       
sinking area1 but this view  has been   
recently challenged by ,murray#bhj and  
,agassiz#bha with at  least some measure
 of success4 ,from the fiords on the    
borders of the  ,pacific and other      
physical phenomena1 the inference has   
been drawn that  relative sinking of the
 land has recently taken place4 ,raised 
beaches  on the coasts are interpreted  
as indicating a relative rise of the    
land  or a sinking of some ocean basin1 
for the withdrawal of the waters can    
only be the result of increasing the    
capacity of the oceanic basin as  a     

whole4 ,the most probable view is that  
the general areas of present  and recent
 volcanic action are partly rising areas
 and partly sinking  areas1 and that    
movement of either kind may be connected
 with the  extrusion of the lavas4 ,the 
rising and sinking are but complementary
  phases of a deformation of the earth's
 body1 and involve a readjustment  of   
stresses within the body of the earth4  
,these stresses are possibly  an        
essential factor in eruptions4    #b4   
,relations to one another4--,a most     
significant feature of volcanic  action 
is the degree of concurrence or of      
independence of action in  adjacent     
volcanoes4 ,in some instances they act  
as though in sympathy1  as in the recent
 outburst in ,martinique and ,saint     
,vincent1 and the  concurrent symptoms  
of activity in other places4 ,on the    
other hand1  the independence of        
neighboring vents is sometimes          
extraordinary4 ,the  group of volcanoes 
near the center of the ,mediterranean1  

of which  ,vesuvius and ,etna are the   
most conspicuous examples1 usually act  
with  measurable independence of one    
another1 an eruption in the one not     
being habitually coincident with an     
eruption in the others4 ,but the  most  
conspicuous instance of independence is 
found in the great craters  of ,mauna   
,loa and ,kilauea in ,hawaii4 ,they are 
only about twenty miles  apart1 the one 
on the top and the other on the side of 
the same great  mountain mass4 ,the     
crater of ,mauna ,loa is about #aj1jjj  
feet higher  than the crater of         
,kilauea1 and yet1 while the latter has 
been in  constant activity as far back  
as its history is known1 the former is  
periodic4 ,the case is the more         
remarkable because of the greatness of  
the ejections4 ,the outflow of ,mauna   
,loa in #ahhe formed a stream from      
three to ten miles in width1 and        
forty-five miles in length1 with a      
probable average thickness of #ajj feet1
 and some of its other outflows  were of

 nearly equal greatness2 indeed its     
outflows are among the  most massive    
that have issued from volcanoes in      
recent times4 ,besides  this massiveness
 there have been extraordinary movements
 of the lava  within the crater1 if the 
testimony of witnesses may be trusted4  
,but  throughout these great movements  
in the higher crater1 the lava-column   
of ,kilauea1 #aj1jjj feet lower1        
continued its quiet action without      
sensible effects from its boisterous    
neighbor4 ,the bearing of such          
extraordinary independence upon the     
sources of volcanic action is very      
cogent1 for the lavas are of the same   
type1 both being basalts1 that of       
,mauna ,loa being notably basic and     
probably as high in specific gravity  as
 that in ,kilauea4 ,no difference in    
specific gravity that could at  all     
account for a difference in height of   
#aj1jjj feet can be presumed1  unless   
their ducts remain separate to          
extraordinary depths4 ,nor does  it     

appear possible that a superior amount  
of gas within the column of  ,mauna ,loa
 could account for such an extraordinary
 difference in height1  for the         
hydrostatic pressure of such a column is
 not far from #aj1jjj  pounds to the    
square inch4 ,even if the difference in 
the heights of  the columns could be    
explained by differences in specific    
gravity1  the agitation of the one      
should be communicated to the other1 and
 an  outflow of the one1 particularly an
 outflow by a breakage through  its     
walls sufficient to lower its surface   
hundreds of feet1 as has  repeatedly    
occurred in ,kilauea1 should change the 
surface of the other  proportionately1  
if they were in hydrostatic equilibrium4
 ,it seems  a necessary inference1      
therefore1 that the two lava-columns    
have no  connection with each other or  
with a common reservoir4 ,the tops of   
some  lava-columns stand about #bj1jjj  
feet above the sea1 while others emerge 
on the sea-bottom far below sea-level4  

,the total vertical range is1           
therefore1 probably between #cj1jjj and 
#dj1jjj feet1 a difference which  tells 
its own story as to their relative      
independence4    ,illustration3 ,fig4   
#dfc4--,surface of lava-flow of #ahha1  
from ,mauna    ,loa1 as seen back of    
,hilo1 ,hawaii4 7,photo4 by ,calvin47   
#c4 ,unimportant                        
coincidences4--,eruptions seem to be    
somewhat more  liable to occur at times 
of high atmospheric pressure than at    
low1  doubtless because the increased   
atmospheric weight on a large area of   
the adjacent crust aids in forcing out  
the lava or the volcanic gases4  ,this  
can only be effective when other forces 
have almost accomplished  the result1   
and would doubtless have completed it a 
little later had  not the atmospheric   
wave supplied the little remaining      
pressure needed4  ,eruption seems also  
to be more common when the tidal strains
 favor it1  for like reasons4 ,in the   
same class are probably to be put the   

effects  of heavy rains1 whether they   
act by gravity or by giving rise to     
steam4  ,such agencies are to be        
regarded as mere incidents of no moment 
in  the real causation of vulcanism1 but
 of some value in determining the       
precise moment of action4 ,this is not  
to be understood as inconsistent  with  
the view that the periodic stresses of  
the body-tides of the  earth are        
important factors in vulcanism1 as      
elsewhere explained1 but  merely that   
the special time of surface-eruption is 
only incidentally  connected with the   
water-tides4    ,illustration3 ,fig4    
#dfd4--;,crater of ,kilauea4            
,periodicity4--,most volcanoes are      
periodic in their stages of action4     
,long dormant periods intervene between 
eruptive periods4 ,volcanoes  supposed  
to be extinct occasionally awaken with  
terrific violence4  ,sometimes also they
 awaken quietly4 ,this larger           
periodicity yet awaits  an explanation1 
but it very likely means a temporary    

exhaustion of the  supply of gas or of  
lava1 or of both1 to which the active   
stage is due4                           
,formation of ,cones4                   
,lava-cones4--,the lava usually flows   
away from the vent in short  streams    
which solidify before running far4 ,as  
the lava-streams flow in  different     
directions at different times1 the total
 effect is a low cone  formed of        
radiating tongues surrounding the point 
of exit4 ,occasionally  the streams run 
a dozen or a score of miles1 but such   
cases1 except in  the gigantic volcanoes
 of ,hawaii and a few others1 are rare4 
,often the  streams congeal before they 
reach much beyond the base of the cone1 
and  quite often while they are yet on  
its slope4 ,so far1 therefore1 as the   
volcanic cone is formed of lava1 it has 
a radiate structure made up of  a       
succession of congealed lava-streams4   
,in these cases the slopes are  low1    
because the fluidity of the lava        
prevents the development of high        

gradients4 ,it is1 however1 rather the  
exception than the rule1 that  the cone 
is made up mainly of lava-streams1      
though the great ,hawaiian  volcanoes   
are of this class4    ,illustration3    
,fig4 #dfe4--,typical cinder-cone1      
,clayton valley1 ,cal4    7,turner1 ,u4 
,s4 ,geol4 ,surv47                      
,cinder-cones4--,the larger portion of  
the lava blown into the air by  the     
expanding gas-bubbles falls back in the 
immediate vicinity of the  vent and     
builds up a cinder-cone4 ,from the      
nature of the case1 this  often takes on
 a beautiful symmetry and assumes a     
steep slope 7,fig4  #dfe74 ,the ragged  
cinders lend themselves readily to the  
formation of  an acute cone1 quite      
different from the flatter cone formed  
by lavas4  ,sometimes the cinders are   
still plastic when they fall1 and weld  
themselves together and hold their      
places even on very steep slopes1  but  
usually they have already hardened      
before they reach the surface4          

,illustration3 ,fig4                    
#dff4--,spatter-cone and cavern4        
,kilauea1 ,hawaii4    7,photo4 by       
,libbey47    ,illustration3 ,fig4       
#dfg4--;,hollow spatter-cone4 ,oregon4  
7,russell1 ,u4 ,s4    ,geol4 ,surv47    
,subordinate cones4--,small or temporary
 vents formed as offshoots from  the    
main vents often give rise to secondary 
or 8parasitic0 cones4  ,these are       
sometimes numerous1 as in the case of   
,etna1 and they may be  so important    
that the mountain becomes a compound    
cone4 ,a still more  subordinate variety
 consists of 8spatter-cones0 formed by  
small mildly  explosive vents that      
spatter forth little dabs of lava which 
form  chimneys1 or cones1 and sometimes 
completely curved domes over vents      
7,figs4 #dff and #dfg74 ,spatter-cones  
often arise from the lava-flows         
themselves4    ,composite cones4--,from 
most existing volcanoes there issue both
  lava-flows and fragmental ejecta1 and 
the resulting cones are composite  in   

material4 ,the lava more frequently     
breaks through the side of the  cone    
than overflows its summit1 and this     
gives rise to irregularities  of form   
and structure4 ,the cones are also      
subject to partial  destruction both by 
the outbursts of lava and by the        
explosions1 and  perhaps also by        
migration of the vents4 ,as a result1   
many volcanic  regions show old1        
partially destroyed craters1 together   
with new and  more perfect ones1 and the
 history of volcanic action in a region 
may  often be read in the succession of 
cone formations4    ,the form of the    
cone1 when composed chiefly of lava1 is 
also affected  by the mass of the       
outflow and by its fluidity4 ,the larger
 the outflow  at a given time1 other    
things being equal1 the wider it        
distributes  itself and the flatter is  
the cone4 ,as a rule1 the basic lavas   
are more  fluid than the acidic1 and the
 cones of basic lavas are flatter than  
the cones of acidic lavas4              

,extra-cone distribution4--,in violent  
eruptions1 the steam1 accompanied  with 
much ash1 is shot up to great heights1  
often rolling outwards  in cumulus or   
cauliflower-like forms 7,fig4 #deh74 ,in
 the more violent  explosions these     
columns are projected several miles4 ,in
 the phenomenal  case of ,krakatoa the  
projection was estimated at seventeen   
miles4 ,the  steam1 by reason of its    
great expansion and its contact with the
 colder  regions of the upper air1 is   
quickly condensed1 and prodigious floods
  of rain frequently accompany the      
eruption4 ,this rain1 carrying down a   
portion of the ash and gathering up much
 that had previously fallen1  gives rise
 to mud-flows1 which in some cases      
constitute a large  part of the final   
deposit4 ,these mud-flows chiefly lodge 
on the lower  slopes of the volcano or  
adjacent to its base1 and give rise to  
rather  flat cones1 sometimes designated
 as tufa-cones to distinguish them  from
 cinder-cones formed by the direct fall 

of fragmental material4  ,mud-flows     
appear also to be formed by the ejection
 of mud and water  that had gathered in 
quiescent craters during intervals      
between stages  of eruption4    ,a      
portion of the finer exploded material  
floats away in the air to  greater or   
less distances1 and forms widespread    
tufa-deposits4 ,in4  some cases beds of 
volcanic ash of appreciable thickness   
7as those  of ,nebraska7#bhb are found  
far from any known volcanic center4 ,the
  extremely fine ash from the great     
explosion of ,krakatoa floated several  
times around the earth in the equatorial
 belt and spread northward into  the    
temperate zones4    ,illustration3 ,fig4
 #dfh4--,mt4 ,shasta1 a typical extinct 
cone1 furrowed    by erosion1 but       
retaining its general form4 7,diller1   
,u4 ,s4 ,geol4    ,surv47               
,,lavas4    ,their nature4--,in the     
chapter on the ,origin and ,descent of  
,rocks1 the  nature of lavas and of the 
rocks derived from them has been        

discussed  7,chapter ,,vii74 ,in view of
 prevalent misconceptions1 it may be    
repeated1  for the sake of emphasis1    
that lavas are mutual solutions of      
mineral  matter in mineral matter1      
rather than simply melted rock4 ,into   
this  mutual solution there enter not   
only rock materials1 but gases4 ,the    
distinction between mutual solutions and
 simple molten rock cannot be           
rigorously made1 but it is at least     
essential to know that the minerals  do 
not necessarily crystallize from lavas  
in the order of their melting           
temperatures1 or in any uniform order1  
but rather in the order in  which       
saturation of the several mineral       
constituents happens to be  reached in  
the given mutual solution4 ,thus quartz1
 which has a very  high melting-point1  
is often one of the last minerals to    
crystallize4  ,the mutual solutions are 
exceedingly complex1 embracing a wide   
range  of chemical substances1 but the  
chief of them1 as already stated1 are   

silicates of aluminum1 potassium1       
sodium1 calcium1 magnesium1 and iron1   
with minor ingredients of nearly all    
known substances1 in greater or  less   
proportion4 ,the old idea of lavas as   
simply melted rock is not1  however1    
wholly to be abandoned4 ,the mode of    
solidifying is often  simply that of    
molten matter freezing4 ,if lava be     
suddenly cooled1 the  congelation is    
essentially the solidification of a     
melted substance4  ,the result is a     
glassy body1 every part of which has    
essentially the  same composition that  
the liquid had4 ,usually1 however1 even 
in this  case1 the gases escape in part4
 ,if the cooling is slower1 the various 
substances in the mixture crystallize   
out into minerals in the order in  which
 they severally reach saturation4 ,this 
involves the principle that  solubility 
is dependent on temperature1 and that as
 the temperature  sinks the degree of   
solubility declines1 and the            
saturation-point for  some constituents 

of the solution is reached earlier than 
for others4  ,with sufficiently slow    
cooling1 all the material will pass into
 the  solid state by the crystallizing  
of the several minerals in succession4  
,this does not mean that two or more    
minerals may not be forming at the  same
 time1 for crystals often interfere with
 each other's growth4 ,it  does1        
however1 involve the doctrine that some 
substances may complete  their          
crystallization while the surrounding   
material is yet in the  fluid condition4
 ,in most igneous rocks nearly perfect  
crystals of  certain minerals are       
common1 while other minerals1           
crystallizing later1  are compelled to  
adapt themselves to the space left4     
,this conception is  supported by the   
fact that lavas1 while still in the     
fluid condition1  often contain         
well-formed crystals1 and these crystals
 sometimes make  up a considerable      
percent4 of the flowing mass1 just as   
water in  certain conditions may be     

filled with crystals of ice4 ,so also   
crystals  after having been formed may  
be redissolved in part1 doubtless       
because  of changes in the nature of the
 magma due to undetermined conditions   
which may arise in the process of       
crystallization1 or from the  accession 
of gas1 or from new material dissolved  
from the walls of the  passageway4      
,illustration3 ,fig4 #dfi4--,lobular    
form of lava-flow1 8,pahoehoe40         
7,dutton1 ,u4 ,s4 ,geol4 ,surv47        
,illustration3 ,fig4 #dgj4--,terminal   
portion of a rough lava-flow1    8aa40  
,cinder ,buttes1 ,idaho4 7,russell1 ,u4 
,s4 ,geol4 ,surv47    ,illustration3    
,fig4 #dga4--,lava flowing over a       
precipice near ,hilo1    ,hawaiian      
,islands4    ,consanguinity and         
succession of lavas4--,the lavas that   
are poured  forth at different stages in
 the succession of eruptions of a given 
region are usually not the same1 as     
might naturally be expected1 but  form a
 curious series the members of which are

 related to one another4  ,iddings has  
called this relation consanguinity4#bhc 
,no universal  law of succession has yet
 been established1 and perhaps none     
exists2  but ,richthofen#bhd many years 
ago announced a definite order for the  
,tertiary flows of western ,america     
which seems to hold fairly well  in its 
general aspects1 though not everywhere  
completely realized1  so far as surface 
observation goes4 ,richthofen's order   
is3 7#a7 lavas  of neutral types1 7#b7  
lavas of acid types1 7#c7 lavas of basic
 types1  7#d7 lavas of more acid types1 
and 7#e7 lavas of more basic types4 ,the
  special varieties of rock vary1 and   
even the general order is often         
apparently defective4 ,the defects are  
sometimes assigned to the  concealment  
of some of the outflows4 ,while this may
 be true in some  cases1 it is not      
unlikely that in others there is a real 
failure of the  sequence4 ,at any rate1 
the sequence can only be regarded as a  
rough  generalization4 ,it is supposed  

to be due to magmatic differentiation   
caused by the differences of temperature
 to which the different parts  are      
subjected underground1 by differences of
 specific gravity and  fluidity which   
result from changes of temperature1 and 
probably by  other causes4              
,temperatures of lavas4--,accurate      
determinations of the temperatures  in  
the center of the lava-columns1 where   
they have been least reduced  by contact
 with the rock-walls1 have not yet been 
made1 but it is  clear from the         
whiteness of the lavas that their       
temperatures are  often appreciably     
above the melting-point4 ,this is also a
 necessary  inference from the length of
 time they remain fluid1 notwithstanding
  the great surface contact of the      
column in its miles of ascent1 the      
conversion of contact water into steam1 
and the expansion and escape  of the    
gases4 ,in cases where determination has
 been practicable 7and  they certainly  
do not represent the maximum            

temperatures7 it has been  found that   
the melting-points of silver1 about #ifj
 ,c41 and of copper1  about #ajfj ,c41  
are reached4 ,in connection with        
overflows1 it has  been found that brass
 is decomposed into its component       
metals1 the  copper actually            
crystallizing4 ,silver has been         
sublimed1 and made to  redeposit itself 
in crystalline form4 ,this implies much 
more than the  bare melting             
temperatures4 ,even the fine edges of   
flints have been  fused4 ,it is1        
therefore1 probably safe to assume that 
the original  temperatures of the lavas 
as they rise to the surface sometimes   
reach  considerably beyond #bjjj ,fahr4 
7#ajic ,c471 and may perhaps even attain
  #cjjj ,fahr4 or more4 ,even these     
temperatures must be somewhat below  the
 original subterranean temperatures of  
the lavas1 because some heat  must      
necessarily be lost in rising1 partly by
 contact with the walls  of the colder  
rocks through which they pass1 probably 

for as much as a  score of miles at     
least1 and partly from the expansion of 
the gases  within them4 ,if any         
considerable part of these gases is     
derived from  waters which joined the   
lava in its upward course in the        
fracture zone1  the energy consumed in  
raising the water to the high           
temperatures  of the lavas must be      
subtracted from the original heat1 and  
must be  a further source of reduction  
of temperature4 ,it is important to     
emphasize this point in view of its     
bearing upon the origin of the  lavas4  
,it has been suggested that lavas may be
 due to an aqueo-igneous  fusion1 a kind
 of fusion which may take place at      
comparatively moderate  temperatures4   
,it seems obvious1 however1 from the    
phenomena themselves1  that temperatures
 as high as ordinary dry fusion1 and    
perhaps even  higher1 are attained4 ,it 
is clear also that the maintenance of   
the  liquid condition in a constant     
state of ebullition for a long period   

of time implies a large surplus of heat 
above that necessary for  liquefaction  
simply4 ,this is especially true if the 
ebullition comes  from surface-waters   
penetrating to and becoming absorbed in 
the  lava-column below4 ,this process   
must tend rapidly to exhaust the heat   
in the column of lava4 ,if1 on the other
 hand1 the gases are derived  from the  
deep interior1 and the ebullition at the
 surface is due to  their escape1 they  
may bring up new supplies of heat to    
counteract the  cooling effects of their
 expansion4    ,depth of                
source4--,attempts have been made to    
ascertain the depth from  which lavas   
rise1 by means of the earthquake tremors
 that accompany  eruptions4 ,the        
estimates have ranged from seven or     
eight to thirty  miles4 ,the mode of    
estimate is that discussed under        
earthquakes1 and is  subject to the     
corrections there indicated4 ,if these  
could be perfectly  applied1 the        
estimates might probably all fall within

 ten miles1 and  not improbably all     
within six miles of the surface4 ,but in
 any case the  method really tells very 
little as to the true point of origin of
 the  lava4 ,at most it probably only   
tells where the ascending lava begins   
to rupture the rock through which it    
passes1 and rupture may not be  possible
 below the zone of fracture1 which is   
probably not more than  six miles deep4 
,in the zone of flowage below1 where the
 pressure is too  great to permit       
fracture1 the lava not improbably makes 
its way by some  boring or fluxing      
process1 which might not1 because of its
 nature1 be  capable of giving rise to  
seismic tremors4 ,the behavior of the   
tremors  perhaps forces us to locate the
 origin of lava movement at least as    
low as the bottom of the fracture zone1 
but it probably offers no  sufficient   
ground for limiting the lava's origin to
 this or any other  specific depth4     
,,volcanic ,,gases4    ,the most        
distinctive feature of volcanoes is the 

explosive action  arising from the gases
 and vapors pent up in the lava4 ,there 
is not a  little explosive action of a  
secondary character arising from the    
mere  outer contact of surface-waters   
with lavas or with the hot rocks of the 
crater walls1 or with the hot ashes and 
rocks thrown out2 but these are         
incidental1 not essential1 features4    
,the precise nature of the occlusion or 
absorption of gases and vapors  has not 
yet been determined4 ,it is thought that
 lava spontaneously  absorbs such gases 
when at high temperatures1 and          
especially when the  gases are under    
great pressure1 and that as the pressure
 is relieved  and the lava is cooled and
 solidified1 the larger part of the     
gases  escapes4 ,in those cases in which
 the eruption is quiet1 the escape  of  
the gases is but partial while the lava 
is in the crater1 and  much gas remains 
to be given out from the molten material
 after it  has been extruded and is     
about to congeal4 ,the gases are then   

given  off with relative slowness and   
quietness4 ,if1 however1 the lavas are  
surcharged with gases1 and if these are 
restrained from free escape  by the     
viscosity of the lavas1 the gases gather
 in large vesicles in  the lava in the  
throat of the volcano1 and on coming to 
the surface  explode1 hurling the       
enveloping lava upwards and outwards1   
often to  great distances4 ,the violence
 of projection reduces a portion of the 
lava to a finely divided state          
constituting the 8ash0 and 8smoke0 of   
the volcano4 ,other portions less       
divided are inflated by the gases       
disseminated through them1 and form     
8pumice0 and 8scoria10 according  to the
 degree of inflation1 while masses of   
lava that have already  solidified into 
more or less rounded masses in the      
crater are hurled  forth as 8bombs02 not
 infrequently portions of the walls of  
the crater  or of the duct below are    
also disrupted and shot forth4          
,differences in gas action4--,the causes

 of the differences of gas  action in   
different volcanoes are undetermined1   
but the following  suggestions may point
 to a part of the truth3 7#a7 ,doubtless
 some lavas  contain more gases than    
others1 and hence are predisposed to be 
more  explosive2 7#b7 some are more     
viscous than others and hence hold the  
gases more tenaciously until they       
accumulate and acquire explosive  force1
 while the more liquid lavas allow their
 gases to escape more  freely and       
easily2 7#c7 some are hotter than       
others1 and hence hold  their gases     
until after they have escaped from the  
crater1 when they  give them off from   
their expanded surfaces in the open air1
 where there  is no restraint to develop
 explosiveness2 7#d7 some flows are so  
massive  that they cool to the chief    
gas-discharging point only after they   
are  spread out on the surface1 when    
quiet escape is possible2 7#e7 probably 
a main occasion of the very violent     
explosions lies in the fact that  the   

lavas have begun to crystallize while   
yet in the duct of the  volcano4 ,the   
crystals1 in forming in the magma1      
exclude the gases from  themselves1 and 
this excluded portion overcharges the   
remaining portion  of the lava4 ,this   
process continues as the lava rises and 
grows cooler  until the gases acquire   
great volume and explosive force4 ,this 
view is  sustained by the fact that the 
pumice and ash of such extraordinarily  
explosive eruptions as those of         
,krakatoa and ,pele contain many small  
crystals which had certainly formed     
before the explosive inflation took     
place4 ,incipient crystallization does  
not1 however1 appear to be a  universal 
accompaniment of explosive action4      
,spasmodic action4--,the discharge of   
the gases is spasmodic1 and  usually    
consists of a succession of distinct    
explosions4 ,sometimes  these succeed   
one another at rather constant and      
frequent intervals1  as in ,stromboli1  
where the explosions follow one another 

at intervals  of three to ten or more   
minutes4 ,in many others the outbursts  
are  rhythmic1 while in others the      
spasms are distant and irregular4       
,kinds of gases4--,steam is the chief   
volcanic gas4 ,its constituents1        
hydrogen and oxygen1 are also present in
 the free state1 and are  perhaps the   
result of the dissociation of the steam 
at the very  high temperatures of the   
lavas4 ,carbon dioxide is probably next 
in  abundance4 ,no positive statement as
 to the relative amounts of the         
subordinate gases can be made because of
 the obvious difficulties  of obtaining 
anything like a representative analysis 
of the gases  concerned in the great    
volcanic eruptions4 ,the materials for  
the  analyses which have been made were 
derived chiefly from little  secondary  
or 8parasitic0 vents1 or from side-wall 
crevices1 through  which the volcanic   
gases rise4 ,such vents probably derive 
their gases  from the very border of the
 main mass1 where it is most subject to 

the influence of waters and gases from  
the adjacent walls1 and it is  uncertain
 how far they are truly representative  
of the gases in the  interior of the    
lava itself4 ,the data now at command   
seem to indicate  that carbon dioxide   
increases greatly in relative abundance 
as volcanic  action dies away4 ,great   
quantities of this gas are often given  
forth  long after all signs of active   
vulcanism have disappeared4 ,such gases 
have been attributed to the action of   
the lavas on buried beds of  limestone  
or other carbonates1 but in many cases  
the geology of the  region offers no    
special support to this hypothesis4 ,it 
does not seem  inherently probable that 
the heat of the lava would be sufficient
 to  decompose limestone at a period    
very long after the active eruption4 ,an
  alternative suggestion is that the    
stronger volcanic acids mentioned  below
 are gradually conveyed into the        
adjacent rocks and there act on         
limestones or on partially carbonated   

crystalline rocks1 setting free  carbon 
dioxide4 ,whatever may be true with     
regard to secondary gases of  this kind1
 it is quite certain that the lavas     
themselves contain large  quantities of 
carbon dioxide1 and also of carbon      
monoxide1 doubtless  reduced from the   
dioxide4 ,sulphur gases are very common 
accompaniments  of volcanic eruptions4  
,they take the forms of sulphuretted    
hydrogen  and sulphurous acid and       
perhaps of sublimated sulphur1 all of   
which  are liable to pass by oxidation  
and hydration into sulphuric acid4      
,chlorine and hydrochloric gases are    
also common1 particularly at high       
temperatures4 ,fluorine and other gases 
are occasionally present4  ,certain     
gases1 such as hydrogen and chlorine1   
are especially associated  with high    
temperatures and energetic action1 and  
are probably dependent  on them4        
,hydrochloric acid and the sulphurous   
gases are also mainly  associated with  
high temperatures1 while sulphuretted   

hydrogen is  commoner at lower          
temperatures4 ,oxygen1 nitrogen1 and    
probably  carbon dioxide or carbon      
monoxide are present throughout all     
ranges  of temperature4 ,nitrogen is a  
rather frequent but not very abundant   
constituent of the volcanic gases4 ,how 
far it results from admixture  of the   
atmosphere and how far it is original1  
is not determined4 ,it  is1 however1 one
 of the gases found in volcanic rocks   
after they have  cooled1 and is         
presumably original in part4 ,a large   
series of secondary  vapors naturally   
arise from the volatilization of        
substances contained  in the lavas1 such
 as the oxides1 chlorides1 and sulphides
 of the  metals1 etc4    ,residual gases
 in volcanic rocks4--,some light upon   
the vital question  of the original1 as 
distinguished from the secondary gases  
of lavas may  be found in the analyses  
of the gases that remain in the lavas   
after  they are solidified4 ,when the   
lavas lodged underground without free   

communication with the surface1 there is
 reason to think that they  retained a  
larger percentage of their original     
gases in solidification  than in cases  
of free exposure at the surface2 at any 
rate1 such  rocks contain notable       
quantities of gases occluded in some way
 within  themselves4 ,recent            
surface-lavas also contain gases of     
similar kinds1  but not in equal degree1
 so far as available analyses show4 ,the
 gases  are in part held in numerous    
small cavities within the constituent   
minerals1 especially in the quartz4     
,this is perhaps due to the fact  that  
quartz usually crystallizes late in the 
process of solidification1  and its     
mother-material becomes crowded with    
gases excluded by the  previous         
crystallization of other minerals4      
,analyses of twenty-five  crystalline   
rocks of various kinds from many typical
 localities by  ,tilden1#bhe gave an    
average volume of gas1 under ordinary   
atmospheric  pressure1 four and a half  

times that of the containing rock4 ,this
 shows  the condensed condition in which
 the gases are held4 ,of these gases1   
the chief is hydrogen1 which much       
exceeds all the rest4 ,next in order  of
 abundance is carbon dioxide1 followed  
by carbon monoxide1 marsh  gas 7,,ch71  
and nitrogen4 ,water is frequently      
present and free oxygen  almost         
universally absent4 ,the average ratio  
of hydrogen to carbon  dioxide by volume
 in these analyses is about #gj 3 #cj4  
,five complete  analyses gave the       
following averages3 ,h1 #eb4acd2 ,,co1  
#cd4ajd2 ,,co1  #h4dbb2 ,,ch1 #c4bbd2   
,n1 #b4jgb4 ,it will be seen that the   
gases contained  in these rocks are in  
proportions radically different from    
those of  the atmosphere1 and it is     
doubtful whether they can be reasonably 
assigned to any other source than the   
lavas from which the rocks  were formed4
 ,it is to be noted1 however1 that some 
sedimentary and  meta-sedimentary rocks1
 such as quartzite and quartz-schist1   

contain  similar gases1 but this may be 
because the granules of the original    
rock retain them1 notwithstanding the   
secondary processes through  which they 
have passed4 ,analyses of meteorites    
show essentially the  same gases in much
 the same proportions4 ,if evidence of  
this kind can  be trusted1 the standard 
original gases of lavas are the elements
 or  compounds of hydrogen1 carbon1 and 
nitrogen1 in the order named1 while  the
 chlorine and sulphur gases are to be   
regarded as accessory4 ,because  of     
their intensely energetic and noxious   
character1 these latter  gases make     
themselves disproportionately manifest  
in the vicinity  of active volcanoes4   
,that they are really not preponderant  
seems to  be implied by the fact that   
the volcanic rains1 which are extremely 
copious1 are usually fresh1 and only in 
rare cases is the presence of  the      
hydrochloric or sulphurous elements     
sufficient to produce noxious  effects4 
,volcanic and meteoric data seem to     

indicate that steam is held  less       
tenaciously than the other gases in the 
magmas as they solidify  into rocks4    
,the source of the gases4--,as already  
noted1 it is one of the  outstanding    
problems of geology to determine 7a7 how
 far the gases of  lavas were possessed 
by them from their origin1 whatever that
 may be1  and 7b7 how far they have been
 acquired in the lava's ascent to the   
surface4 ,it is recognized that lavas   
have the power of absorbing gases1  and 
one of the views entertained is that    
surface-waters1 percolating  through the
 rocks and coming in contact with the   
ascending column of  lava1 are converted
 into steam1 which is absorbed into the 
lava and  rises with it to the surface4 
,there are two phases of this view4 7#a7
  ,the more conservative one supposes   
that the water merely penetrates  the   
fracture zone of the surface of the     
earth through the ordinary  means of    
passage of underground-waters1 and so   
makes a comparatively  short circuit4   

,under this view1 the steam and other   
gases given forth  are not a            
contribution to the atmosphere and      
hydrosphere1 but merely  a restoration  
to them of water and dissolved gases    
previously carried  down from the       
surface4 ,an even narrower view is      
sometimes entertained  which supposes   
that the larger part of the water       
descends through the  volcanic cone     
itself1 or immediately about its base4  
,the presence of  chlorine gases in the 
volcanic emanations and the nearness of 
most  existing volcanoes to the sea have
 been the basis for the idea that       
sea-water1 penetrating to the lava1 is a
 chief source of the volcanic  gases4   
7#b7 ,the broader phase of the view     
assumes that the waters  penetrate not  
only the outer fracture zone of the     
earth1 which is  probably limited to    
five or six miles in depth1 but that    
they diffuse  themselves through the    
continuous unfractured zone down to     
depths  where temperatures of fusion    

prevail1 and that they there enter into 
combination with the lavas or with hot  
rock to form lavas4 ,it is well  known  
that aqueous vapor facilitates the      
fusion1 or more accurately1  the mutual 
solution of the minerals4 ,this view is 
a part of one of the  hypotheses        
concerning the origin of the lavas      
themselves4    ,the opposing view       
supposes that the gases were in the main
 original4  ,of this view there are two 
phases3 7#a7 ,one supposes that the     
lavas  are remnants of an original      
molten globe which absorbed gases from  
the primitive atmosphere and retained   
them till the time of their  eruption4  
,the possible absorption of steam and   
air into the supposed  molten globe has 
been much neglected in current          
conceptions of  early conditions4 ,if   
the lavas of the supposed molten globe  
absorbed  proportionately as much       
water-vapor as the volcanic lavas often 
contain1 it would probably take forty or
 fifty times the present ocean  and     

atmosphere to supply them4 ,any remnants
 of these original lavas  might well be 
supposed to hold gases4 ,even rocks     
derived from them by  deep-seated       
solidification might retain much gas4   
7#b7 ,the other phase  of the view      
assumes that the gases were entrapped   
when the globe was  built up of         
meteoroidal or planetesimal matter1 as  
assumed in the  accretion hypothesis4   
,under either of the last two views the 
gases may be said to be primary1  and   
genetically connected with the origin of
 the lavas themselves4 ,such  gases     
would be a contribution to the          
atmosphere and the hydrosphere4  ,this  
view does not exclude the idea that as  
the lava rises through the              
surface-rocks1 other gases are formed by
 contact1 and that they may be  absorbed
 into the rising column4 ,on the        
contrary1 the view recognizes  the      
possibility that a tongue of lava rising
 into the upper formations  may         
encounter bodies of water1 or masses of 

thoroughly water-soaked  rock1 from     
which great quantities of steam may be  
generated1 and that  this accessory     
steam may be a large factor in the      
initial explosion  which often          
accompanies the development of a new    
volcano1 or the new  eruption of an old 
one after a long period of quiescence4  
,a decision on the vital question       
whether the volcanic gases are largely  
primary1 or are essentially secondary1  
has not yet been reached2  but it will  
doubtless be reached when a sufficient  
number of really  representative        
analyses of volcanic gases have been    
made1 and when the  phenomena of the    
gases occluded in igneous rocks have    
been thoroughly  investigated4    ,the  
peculiar proportions of the rock-gases1 
in which hydrogen and  carbon dioxide so
 greatly preponderate1 seem to imply    
that they are  not derived from the     
atmosphere2 at least if they were so    
derived1  there must have been a        
selective absorption of a most          

remarkable kind1  because hydrogen is   
present in the atmosphere in exceedingly
 small  quantities1 while carbon dioxide
 is a very minor constituent4 ,at the   
same time1 as already remarked1 no free 
oxygen is usually found in  these       
absorbed gases4    ,the question as to  
whether the larger part of the volcanic 
gases is  original or is merely a       
special form of convective circulation1 
has an  important bearing on the supply 
of the atmosphere1 which is constantly  
being depleted by the oxidation of the  
rocks and by the formation of           
carbonates and carbonaceous deposits4   
,this vital phase of the subject  will  
receive further consideration4 ,while   
recognizing the lack of  decisive proof1
 it would seem that the preponderance of
 evidence lies  in favor of the view    
that a notable portion1 at least1 of    
gaseous  volcanic emanations is derived 
from the interior of the earth1 and  is 
really a contribution to the atmosphere 
and the hydrosphere4 ,the  hydrogen1 on 

coming in contact with the atmosphere1  
ignites and adds  itself to the         
hydrosphere4 ,the carbon dioxide is in  
part decomposed by  plants1 and adds to 
the supply of atmospheric oxygen4 ,the  
nitrogen1  being comparatively inert1   
doubtless gradually accumulates in the  
air  and has thus come to be its        
preponderant constituent4               
,,the ,,cause ,,of ,,vulcanism4    ,the 
extraordinary facts involved in volcanic
 phenomena cannot well be  discussed    
fully until the origin of the earth is  
considered1 and the  great agencies1 as 
well as the peculiar conditions1 which  
the earth  inherited from its birth1 are
 duly weighed1 for these were1 with     
little  doubt1 the true causal          
antecedents of vulcanism4 ,we shall     
return to  the subject after a sketch of
 the early conditions of the earth1 but 
the views that have been entertained may
 be reviewed here while the  phenomena  
are fresh in mind4    ,the explanation  
of vulcanism involves two essential     

elements4 ,these  are 7#a7 the origin of
 the lavas1 which involves a            
consideration of the  necessary         
temperatures1 pressures1 and other      
conditions1 and 7#b7 the  forces by     
which the lavas are expelled4    ,nearly
 all current explanations of vulcanism  
are founded upon  conditions supposed to
 be derived from a molten globe1 and    
fall under  two general classes3 7,i7   
those which assume that the lavas are   
residual  portions of the original      
molten mass1 and 7,,ii7 those which     
assign the  lavas to the local melting  
of rock4                ,i4 ,on the     
,assumption that the ,lavas are         
,original4    ,in this case it is not   
necessary to assume any special         
accession of  heat1 but merely to       
account for extrusion4 ,there are two   
phases of  this view1 7#a7 the one      
postulating a general molten interior1  
7#b7 the  other limiting the molten     
matter to local reservoirs4             
,hypothesis ,i4 ,lava outflows from a   

molten interior4--,in the early  days of
 geology1 when the earth was supposed to
 have a thin crust and  a molten        
interior1 it was very naturally assumed 
that volcanoes were  but pipes leading  
down to the molten mass within4 ,this   
view has been  essentially abandoned4   
,the independence of adjacent vents is  
in itself  almost a fatal objection1    
when it is recalled that the height of  
recent  volcanic craters ranges from    
nearly #bj1jjj feet above the sea1 to   
#aj1jjj to #bj1jjj feet below4 ,the view
 would involve the conception of        
lava-columns connected with a common    
reservoir varying possibly #cj1jjj  to  
#dj1jjj feet in altitude1 and certainly 
more than half that much1               
simultaneously4 ,the lower outlets      
should as certainly be selected for  the
 outflow of the great interior sea of   
fluid rock1 as the lowest  sag in the   
rim of a lake for its outflow1 for no   
great differences in  specific gravity  
are presumable under this hypothesis4   

,an equally grave  objection arises from
 tidal strain4 ,if the earth were liquid
 within and  merely crusted over by a   
shell of rock of moderate thickness1 it 
would  yield appreciably to tidal       
stresses1 and this yielding would change
 the  capacity of the interior so that  
with every distortion of the spheroid  a
 portion of its fluid interior would be 
forced to the outside1 and  with every  
return to the more spheroidal form there
 would either be  a re-flow to the      
interior or a shrinking of the crust4   
,in any case a  very demonstrative      
response to tidal influence would tell  
the story of  interior fluidity4 ,no    
such effects are observed4 ,the tidal   
strains may  perhaps have a slight      
effect in hastening a given eruption    
when the  forces are approaching a      
delicate balance and an eruption is     
imminent1  but the very triviality of   
this influence implies not only the     
absence  of a general liquid interior1  
but also of extensive reservoirs4       

,hypothesis #b4 ,lavas assigned to      
molten reservoirs4--,a modification of  
the preceding view has been made to     
escape the difficulties involved  in the
 hypothesis as stated above4 ,it is     
supposed that while nearly  all the     
subcrust solidified1 numerous liquid    
spots were left scattered  through it4  
,this honeycombed substratum is supposed
 to connect the  continuous outer crust 
with a central solid body1 solidified   
because  of pressure in spite of its    
high temperature4 ,this hypothesis      
escapes  only a portion of the          
objections4 ,for instance1 the lavas in 
,mauna ,loa  and ,kilauea in ,hawaii    
differ nearly #aj1jjj feet in height1   
and hence  cannot well be supposed to   
connect with the same reservoir1 but    
they  are both on the same vast cone1   
which implies at least an equally large 
molten reservoir as its source4 ,if     
there were two distinct reservoirs  of  
the required magnitude1 they must be    
singularly placed to supply  vents so   

near and yet so independent4 ,the       
difficulty grows greater when  the whole
 ,hawaiian chain is considered1 for the 
points of eruption seem  to have        
migrated from the northwesterly islands1
 where the volcanoes  are old1 to the   
southeastern end1 where volcanic        
activity is now in  progress4    ,it    
would be natural under this view to     
suppose that these residuary  lakelets  
of liquid rock should be gradually      
exhausted as time goes  on1 and that    
vulcanism should be a declining         
phenomenon4 ,it is not  clear that this 
is the case4 ,the great number of       
existing volcanoes in  regions where    
great extrusions took place in earlier  
ages does not seem  to be in harmony    
with the hypothesis4               ,,ii4
 ,on the ,assumption that the ,lavas are
 ,secondary4    ,the serious            
difficulties that arise in interpreting 
volcanic lavas  as remnants of an       
original molten mass1 and the strong    
arguments of  recent years for a very   

solid earth1 have turned inquiry chiefly
  toward the second class of hypotheses1
 which refer the origin of  lavas to the
 local melting of deep-seated rock4     
,these differ widely  among themselves4 
,one group seeks for a cause of the     
melting in  the penetration of surface  
air and water2 another1 in the relief   
of pressure2 a third1 in crushing and   
shearing2 a fourth1 in the  depression  
of sediments into the heated interior   
zone2 and a fifth1 in  the outward flow 
of deep-seated heat4    ,hypothesis #c4 
,lavas assigned to the reaction of water
 and air  penetrating to hot rocks4--,as
 steam is one of the great factors in   
the  explosions of volcanoes1 and as    
water reduces the melting-point of      
rocks1 it is a natural and simple view  
that water penetrating through  the     
fissures and pores of the outer crust   
and coming into contact with  the heated
 rocks below1 is absorbed into them and 
renders them liquid1  and that then1    
being rendered swollen and lighter by   

the process1 they  ascend and discharge 
quietly or explosively according to the 
special  conditions of the case4        
,naturally the suggestion arises that   
the waters  would be converted into     
steam long before they could reach rock 
hot  enough to be melted1 and that this 
steam would be forced back along  its   
own track1 as the line of least         
resistance1 rather than force  itself   
into the rock material and rise in the  
lava-column2 but to  this it is answered
 that an experiment of ,daubree's has   
shown that  water will penetrate the    
capillaries of sandstone against high   
steam  pressure and add itself to the   
steam within4 ,the fact is also cited   
that certain substances1 when highly    
heated1 absorb gases which they  give   
out when they cool4 ,the absorption of  
hydrogen by platinum1 and  of oxygen by 
molten silver1 are illustrations4 ,it is
 certain that the  lavas do contain     
large quantities of absorbed gases1 and 
that these  are partly1 and in most     

cases largely1 given out in cooling1    
when the  cooling takes place at the    
surface4 ,the presumption is that the   
lavas  would take the gases up again on 
remelting under similar conditions4  ,if
 the lavas of actual volcanoes had the  
temperatures of aqueo-igneous  fusion   
7#gjj-ajjj ,fahr47 only1 it would       
strengthen this view2 but as            
temperatures of lavas often exceed #bjjj
 ,fahr41 and probably sometimes  reach  
#bejj ,fahr41 and perhaps #cjjj ,fahr41 
it is not easy to account  for such     
temperatures under this hypothesis1     
because they would only  be reached at  
levels far below those at which         
aqueo-igneous fusion  might be presumed 
to take place4 ,perhaps this could be   
met by invoking  pressure which might   
prevent even aqueo-igneous fusion from  
taking  place until these temperatures  
were reached1 but pressure brings in a  
grave difficulty in another line1 as we 
shall presently see4    ,there is a     
phase of the water-penetration          

hypothesis which seeks to  account for  
an accession of heat4 ,it is affirmed   
that the outer rocks  are oxidized1     
while the inner ones were not           
originally1 or at least  not completely 
oxidized1 and that air and water from   
the surface1  reaching the unoxidized   
zone1 enter into combination and        
generate the  necessary heat4 ,this view
 was pardonable before the development  
of  modern thermo-chemistry1 but is now 
quite untenable1 as may be shown by     
working out the reactions thermally4    
,all views which assign the penetration 
of surface air or water as  a cause meet
 with a grave1 if not insuperable1      
difficulty in the  condition of the     
lower part of the earth's crust 7see p4 
#bah74 ,the  fractured condition of the 
crust1 which permits a ready penetration
 of  water1 is a very superficial       
phenomenon4 ,below the first few        
thousand  feet the crevices and         
porosities of the rock are rapidly      
closed by the  pressure of overlying    

rock1 and all appreciable crevices and  
pores  probably disappear at a depth of 
five or six miles4 ,the effective       
function of fissures is1 therefore1     
limited to the upper few miles of  the  
crust1 and even here to certain portions
 only4 ,the great pressures  in gas- and
 oil-wells show that in many quite      
superficial beds1 even  when arched1    
there are no fissures or pores capable  
of letting even  gas escape effectively4
 ,the depths at which the temperatures  
of lavas  are reached are usually       
estimated1 from the downward increase of
  temperature1 at #bj to #cj miles4     
,this leaves from #ad to #bd miles of   
the  compressed zone between the lowest 
assignable limit of the fissured  zone1 
and the highest assignable zone for the 
origin of lavas4 ,this  thick zone of   
dense rock must be reckoned with in all 
hypotheses that  involve the penetration
 of air and water from without1 and1 as 
well1  the extrusion of lavas from      
within4 ,in addition to the difficulties

  of the penetration of ground-water1   
the limitations of its heat1 at         
penetrable depths1 also bear adversely  
7see p4 #bai71 on the descent of  air   
and water4    ,hypothesis #d4 ,lavas    
assigned to relief of pressure4--,it    
seems to  be demonstrated that pressure 
raises the melting-point of average     
rock1 and hence at twenty or thirty     
miles' depth there may be rocks  hot    
enough to melt at the surface1 but still
 solid because of high  pressure4 ,if   
this pressure were in some way relieved 
they would become  liquid4 ,pressure may
 be locally relieved somewhat 7#a7 by   
denudation1  7#b7 by certain phases of  
faulting1 7#c7 by anticlinal arches1 and
 7#d7 by  continental deformation4      
7#a7 ,in most cases of denudation1      
cooling below probably keeps pace  with 
loss above4 ,at any rate1 many volcanoes
 rise from the bottoms  of the oceans   
where no denudation takes place1 and    
this phase of the  hypothesis is not    
workable there4    7#b7 ,the theory of  

relief by faulting finds encouragement  
in the fact  that many volcanoes occur  
on fault-lines4 ,there is no evidence1  
however1 that this is a universal or    
necessary relation4 ,computation as  to 
the amount of lowering of the           
melting-point that might arise from  the
 faulting associated with volcanoes     
indicates that it is necessary  to      
suppose that the rocks were already very
 close to the melting-point  when the   
faulting took place1 to make the        
doctrine applicable4 ,it is  to be      
observed that in faulting the relief of 
pressure on one side  of the fault-line 
is likely to be balanced by increased   
pressure on  the other side1 and that   
this difference in pressure may be lost 
by  distribution at a depth of #bj or   
#cj miles1 where1 at the nearest1 this  
delicate relation between solidity and  
liquidity1 on which the theory  is      
dependent1 may perhaps be reached4      
7#c7 ,immediately under an anticlinal   
arch there may doubtless be some  relief

 of pressure within the limits of       
strength of the arch1 which is  not     
great 7p4 #ehb74 ,the pressure under the
 arch as a whole is greater  than before
 it was bowed up by lateral thrust1 and 
in depth this excess  becomes           
distributed so as to obliterate the     
local relief under the  center of the   
arch1 and so adds the effects of folding
 to the average  pressure of the crust4 
,besides1 as a matter of fact1 volcanoes
 do not  appear to be especially        
associated with mountain folds where    
arching  reaches its best expression4   
7#d7 ,the same general considerations   
bear on the assignment of  liquefaction 
to relief of pressure in connection with
 the more general  deformation of the   
earth's body4 ,besides1 while relief of 
pressure  might account for             
liquefaction1 it leaves the extrusion   
without an  obvious cause2 indeed1 it   
would seem to furnish a condition       
opposed to  extrusion1 and if pressure  
were subsequently added to force the    

liquid  out1 it would tend to restore   
the solid condition4    ,hypothesis #e4 
,lavas assigned to melting by           
crushing4--,mallet#bhf  and others have 
attributed melting to the crushing of   
rock4 ,crushing1  in the ordinary sense 
of the term1 can only take place in the 
zone of  fracture1 and that is          
apparently too shallow to meet the      
requirements  of the case4 ,below this  
zone1 the pressure on all sides is too  
great to  permit any separation of      
fragments1 and a solid mass can only    
change  its form by what is called      
8solid flowage40 ,the rock under these  
conditions may be compressed1 and this  
compression must give rise to  heat1 but
 at the same time the melting-point is  
raised1 according to  all experiments4  
,it seems improbable that melting can be
 produced in  this way4 ,if great       
pressure could be brought to bear upon a
 tract of  rock so as to heat it by     
compression1 and if then the pressure   
were  relaxed before the heat generated 

could be distributed by conduction1  and
 if re-expansion did not follow1        
possibly melting could be effected1  but
 this makes the process complicated and 
apparently inapplicable4 ,it  is        
scarcely possible that such a sequence  
of events can have affected  all the    
tracts that are now volcanic1 much less 
all those that have  been such          
throughout geologic history4 ,as noted  
in the preceding  case1 relaxation would
 seem to be unfavorable to expulsion4   
,besides1  volcanoes do not seem to be  
confined to tracts that show signs of   
great  crumpling and crushing1 as the   
,alps1 the ,appalachians1 and the       
closely  folded ranges generally4       
,extrusions seem rather more common with
  faulted ranges where crushing is less 
notable and where surface tension       
replaces compression4    ,hypothesis #f4
 ,lavas assigned to melting by          
depression4--,it is observed  that in   
certain regions great thicknesses of    
sediments have accumulated  by the slow 

settling of the crust below1 and as     
these sediments  obstruct the outward   
flow of heat while the lower beds settle
 nearer  to the interior source of heat1
 it is conceived that they become       
heated below and1 being saturated with  
water1 take on aqueo-igneous  fusion and
 rise as lavas1 well supplied with      
internal gas and steam  from the water  
and volatile constituents that were     
entrapped and  carried down with them4  
,the question obviously arises whether  
such  depression is sufficient to give  
the temperatures the lavas show1  and   
whether volcanic action is confined to  
such areas of depression  and deep      
sedimentation4 ,at the highest credible 
estimates--which are  none the less to  
be taken with reserve--the post-,archean
 sediments  rarely reach five or six    
miles in thickness at any given point1  
and  probably never exceed ten or       
twelve1 while twenty or thirty miles is 
the computed depth required for the     
acquisition of the temperatures  the    

lavas actually possess4 ,if the ,archean
 terranes be included among  the        
sedimentaries1 the thickness may be     
adequate1 but what then of the  ,archean
 vulcanism1 which much surpasses that of
 later times1 and the  other early      
extrusions before the sediments were    
thick2 and what of the  moon1 where     
there are probably no sediments at all8 
,besides1 it is not at all clear that   
the distribution of vulcanism is        
specially related to that of thick      
sediments1 as it should be if this      
hypothesis were the true one4 ,there are
 many volcanoes in the heart of  the    
great oceans where sedimentation is now 
inappreciable1 and probably  has been in
 all past periods4    ,hypothesis #g4   
,vulcanism assigned to the outflow of   
deep-seated  heat4--,if the earth grew  
up by slow accessions of meteoroidal or 
planetesimal matter1 in a manner to be  
more fully set forth in the  discussion 
of the origin of the earth1 and if its  
interior heat be due  chiefly to        

compression by its own gravity1 the     
internal temperature  would be          
originally distributed according to the 
degree of compression1  and this would  
depend on the intensity of the internal 
pressure4 ,this  can be approximately   
computed1 and is shown in the diagram on
 page #efc1  where this subject has been
 treated4 ,on not improbable assumptions
  regarding the thermometric            
conductivity1 the flow of heat from the 
deep interior to the middle zone would  
be greater than the loss of  this zone  
to the superficial zone4 ,this middle   
zone should1 under  this view1          
experience a rising temperature4 ,by    
hypothesis1 this zone  is composed of   
various kinds of matter mixed as they   
happened to fall  in4 ,hence as the     
temperature rises1 the fusion-points of 
some of these  constituents will be     
reached before those of others4 ,more   
strictly1  the temperatures at which    
some of these constituents will mutually
  dissolve one another will be reached1 

while other constituents remain         
undissolved1 and thus a partial and     
distributed liquefaction will  arise4   
,the gases and volatile constituents in 
the mixed material would  naturally     
enter largely into the liquefied        
portion4 ,it is assumed  that with a    
continued rise of temperature1 the      
partial liquefactions  would increase   
until the liquefied parts found means of
 uniting1 and  the lighter portions1    
embracing the gaseous contingent1 were  
able to  work their way toward the      
surface4 ,as they rose by fusing or     
fluxing  their way1 the pressure upon   
them became less and less1 and hence the
  temperature necessary for liquefaction
 gradually fell1 leaving them a         
constantly renewed margin of temperature
 available for melting their  way       
through the upper horizons4 ,thus it is 
conceived that these fusible  and       
fluxing selections from the middle zone 
might thread their ways up  to the zone 
of fracture and thence1 taking advantage

 of fissures and  fractures1 reach the  
surface4 ,it is conceived that such     
liquefaction  and extrusion would carry 
out from the middle zone the excess of  
temperature received from the deeper    
interior1 and thus regulate its         
temperature and forestall general       
liquefaction1 the zone as a whole       
remaining always solid4 ,the            
independence of volcanoes is assigned   
to the independence of the liquid       
threads that worked their way to  the   
surface4 ,nothing like a reservoir or   
molten lake enters into the  conception4
 ,the prolonged action of volcanoes is  
attributed to the  slow feeding of the  
liquid threads from the locally fused   
middle zone4  ,the frequent pauses in   
action are assigned to temporary        
deficiencies  of supply2 the renewals to
 the gathering of new supplies after a  
sufficient period of accumulation4 ,the 
distribution of volcanoes in            
essentially all latitudes and longitudes
 is assigned to the general  nature of  

the cause4 ,the special surface         
distributions are assumed to  be        
influenced1 though not altogether       
controlled1 by the favorable or         
unfavorable conditions for escape       
presented by the crustal segments of    
the earth4 ,the persistence of volcanic 
action in time is attributed  to the    
magnitude of the interior source1 to its
 deep-seated location1  and to the      
slowness of conduction of heat in the   
earth's interior4 ,the  force of        
expulsion is found in the               
stress-differences in the interior1     
particularly the periodic tidal and     
other astronomic stresses 7see p4       
#ehj71 and in the slow pressure brought 
to bear on the slender threads  of      
liquid by the creep of the adjacent     
rock4 ,the violent expulsions are  due  
to the included gases1 of which steam is
 chief4 ,little efficiency  is assigned 
to surface-waters1 and that little is   
regarded as wholly  secondary and       
incidental4 ,the true volcanic gases are

 regarded as  coming from the deep      
interior and as being true accessions to
 the  atmosphere and hydrosphere4 ,the  
standing of the lavas in volcanic ducts 
for hundreds and even thousands of years
 with only small outflows1  as in some  
of the best-known volcanoes1 is regarded
 as an exhibition  of an approximate    
equilibrium between the hydrostatic     
pressure of  the deep-penetrating column
 of lava1 and the flowage-tendency of   
the  rock-walls1 the outflow being1 of  
course1 also conditioned on the  slow   
rate of supply below1 and the periodic  
stress-differences of the  interior4    
,for the present these hypotheses must  
be left to work out their own  destiny1 
serving in the mean time as stimulants  
of research4 ,all but  the last have    
been for some time under the            
consideration of geologists1  and are   
set forth in the literature of the      
subject 7p4 #fcf74    ,a few special    
phases of the problem need further      
discussion1 though  they have been      

incidentally touched upon4              
,modes of ,reaching the ,surface4       
,all of the views that locate the origin
 of the lavas deep in the earth  must   
face the difficulties of the passage    
through the dense portion of  the sphere
 below the fracture zone4 ,near the     
surface1 the lavas usually  take        
advantage of fissures or bedding-planes 
already existing or made  by themselves4
 ,there is little evidence that they    
bore their way by  melting1 though they 
round out their ducts into pipes as they
 use them1  much as streamlets on       
glaciers falling into crevices round out
 moulins4  ,but this use of fissures and
 bedding-planes for passage is probably 
merely a matter of least resistance     
where the lavas are relatively  cool1   
and their capacity for melting is low or
 perhaps even gone4  ,daly has recently 
urged that lavas work out reservoirs and
 enlarge  passageways for themselves by 
detaching masses of rock from the roofs 
and sides of the spaces already occupied

 by them1 these masses either  melting  
and mingling with the lava1 or else     
sinking to lower positions  in the      
column4 ,this process he designates     
stoping4#bhg    ,in the denser and      
warmer zone below1 the alternatives seem
 to be 7#a7  melting or fluxing1 or 7#b7
 mechanical penetration without         
fracture4 ,as  rocks 8flow0 in this zone
 by differential pressure without       
rupture1  an included liquid mass may be
 forced to flow through the zone by     
sufficient differential pressure4 ,if   
local differential pressures at  the    
surface be neglected as probably        
incompetent1 there only remain the      
stress-differences of the interior and  
the differences of hydrostatic  pressure
 between the lava-column and the        
surrounding solid columns4  ,the latter 
would not be great until a column of    
liquid of much depth  was formed1 and   
the former would probably not be        
concentrated on the  liquid in such a   
way as to force it bodily through the   

solid rock4  ,probably fusing or fluxing
 its way with the aid of                
stress-differences  is the chief        
resource of the lava in the initial     
stages4 ,in this it  may be supposed to 
be assisted by its gases1 by its        
selective fusible  and fluxing nature1  
by its very high temperature if it comes
 from  very great depths1 as held in the
 seventh hypothesis1 and by the         
stress-differences which prevail in the 
deep interior1 as shown in the  last    
chapter4 ,in ascending from lower to    
higher horizons1 the lava  would be     
constantly invading regions of lower    
melting-point because of  less pressure4
 ,it would thus always have an excess of
 heat above the  local melting          
temperature until it invaded the        
external1 cool zone1  where the regional
 temperature is below the melting-point 
of surface  pressure4 ,from that point  
on it must constantly lose portions of  
its  excess of temperature by contact   
with cooler rocks1 and probably in  the 

process of fluxing its way in the       
compact zone4 ,if this excess is        
insufficient to enable it to reach the  
zone of fracture1 the ascending  column 
is arrested and becomes merely a        
plutonic pipe or mass4 ,if  it suffices 
to reach the zone of fracture1 advantage
 may be taken  thereafter of fissures   
and of rupturing1 and the problem of    
further  ascent probably becomes chiefly
 one of hydrostatic pressure1 in which  
the ascent of the lava-column is favored
 by its high temperature  and its       
included gases4 ,the hydrostatic contest
 is here between  the lava-column1      
measured to its extreme base1 and the   
adjacent  rock-columns1 measured to the 
same extreme depth4 ,the result is1     
therefore1 not necessarily dependent on 
the flowage of the outer  rocks1 but may
 be essentially or wholly dependent on  
the deep-seated  flowage of the rock of 
the lower horizons4 ,the ascending      
column may  reach hydrostatic           
equilibrium before it reaches the       

surface1 and may  then form underground 
intrusions of various sorts without     
superficial  eruption1 or it may only   
find equilibrium by coming to the       
surface and  pouring out a portion of   
its substance and discharging its gases4
                ,additional             
,considerations ,relative to the ,gases4
    ,the question whether the volcanic  
gases are a contribution to the         
atmosphere and hydrosphere is so        
important in its bearings on the whole  
history of the atmosphere as to merit   
additional consideration here4 ,as      
already noted1 if the volcanic gases    
arise from water and absorbed air  that 
have previously passed down through the 
strata1 there is no real  contribution  
to the hydrosphere and atmosphere1 but  
merely circulation4  ,if the gases are  
chiefly derived from the deep interior1 
they are an  important accession to the 
atmosphere and hydrosphere4    ,most    
views are more or less intermediate1    
assigning a part of the  gases to the   

interior and a part to the exterior4 ,no
 one will question  that some part at   
least of the steam is due to the contact
 between the  ground-waters and the hot 
lava1 and probably no one will question 
that  some gas comes from the interior  
if the lavas originate there4 ,the      
vital question is1 whence comes the     
major portion8 ,are the constant        
ebullitions of some volcanoes and the   
terrific explosions of others due       
mainly to surface-waters1 or to interior
 gases8    ,it seems to be certain that 
in most cases the gases are diffused    
through the substance of the lava1 and  
are not simply in contact with  the     
walls of the column or with its summit4 
,without doubt steam is  generated      
around the lava-column by external      
contact1 and perhaps some  explosions   
are due to the entrance of the rising   
lava upon a crevice  or cavern filled   
with water1 or to the invasion of a lake
 gathered in  an old crater2 but it     
still remains a question whether the    

importance  of such explosions has not  
been exaggerated4 ,such action does not 
seem competent to produce inflated      
lavas1 but merely shattered  ones4      
,water thus 8suddenly flashed into      
steam0 could scarcely diffuse  itself   
intimately through the lava1 for the    
process of diffusion is  exceedingly    
slow4 ,but inflated lavas1 pumice1      
scori1 and cinders are  the typical     
products of explosive vulcanism4 ,not   
only in the ordinary  ,vesuvian type1   
but in the extraordinary ,krakatoan     
type1 inflated lavas  are the dominant  
product4 ,prodigious quantities of this 
covered  the sea about ,krakatoa after  
its tremendous explosion in #ahhc4 ,judd
  estimates that the volume of included 
steam involved in the inflation  of the 
pumice examined by him1 was from three  
to five times that of the  rock1 and    
that the amount involved in exploding   
the lava into the fine  dust that       
floated in the upper atmosphere for     
months1 was presumably  much greater4   

,if the sudden flashing into steam of   
bodies of water in external  contact    
with hot lava be rejected as only an    
incidental source of  explosion1 it     
remains to be considered whether waters 
permeating the  rock and becoming       
converted into steam may not be absorbed
 into the  rising lava1 become diffused 
through it1 and ascending with it1      
explode  at the surface4 ,so far as     
access through fissures and cavities    
large  enough to be entered by lava are 
concerned1 it may safely be concluded   
that since the hydrostatic pressure of  
the lava must be greater than  that of  
the water in the fissures1 or else it   
could not rise1 the lava  will enter    
them1 forcing back the water or the     
steam generated from  it1 and1 having   
penetrated as far as accessible1 will   
solidify as a  dike1 and plug up the    
avenue of contact between the           
ground-water and  the portion of the    
lava still remaining molten4 ,the       
numerous dikes  that attend volcanic    

necks testify to the prevalence of this 
action4  ,the capillary pores of the    
wall-rock1 which cannot be thus bodily  
occupied by the lava1 must doubtless    
become filled with steam1 and  this1    
following the principles of ,daubree's  
experiment1 will force  itself into     
contact with the lava and be absorbed by
 it1 but whether  this will be in       
sufficient quantity1 and will become    
sufficiently  diffused through the body 
of the lava-column to produce the       
observed  effects1 is an open question4 
,the increasing testimony of deep mining
  is that relatively little water flows 
through the deeper horizons4 ,it  is    
urged that the water remaining in       
solidified lavas is very unequal  in    
distribution1 as though due to unequal  
access and partial diffusion4  ,the     
argument seems strong1 but to make it   
thoroughly good1 it must be  shown that 
this inequality is not due to           
irregularity of discharge  of the gases 
during and after eruption1 rather than  

to irregularity of  original accession4 
,there is1 perhaps1 as much ground for  
assigning  differences in the degree of 
parting with the included gases1 as in  
acquiring them4 ,doubtless those lavas  
that boiled and seethed for a  long     
period in the caldron were more fully   
deprived of their gases than  those that
 were more promptly disgorged and cooled
 with less convection  and surface      
exposure4    ,thermal                   
considerations4--,probably the most     
important consideration  relates to the 
heat effects4 ,if underground-waters    
enter the  lava-column and come forth as
 steam1 great quantities of heat are    
consumed in the process4 ,has the lava a
 sufficient excess of heat to  stand    
this8 ,can ebullition be maintained for 
the observed periods if  the steam comes
 from ground-waters8    ,many lavas     
probably do not carry a very large      
excess of heat above  that necessary for
 liquefaction1 for not a few of them    
contain  crystals already forming1 which

 shows that they are within the range   
of the temperatures of solidification of
 their constituents4 ,the same          
conclusion is indicated by the limited  
fusing effects shown by the  walls of   
dikes and sills4 ,on the other hand1 as 
already remarked1  dikes and sills often
 show the effects of a rather rapid     
cooling from  the walls4 ,the method of 
flow often implies the same condition   
for  the acidic lavas1 since they       
usually behave as stiff1 pasty masses   
of limited liquidity4 ,on the other     
hand1 the basic lavas1 whose            
fusion-point is much lower1 often flow  
freely and reach great distances  before
 solidifying4 ,the facts taken          
altogether imply that the average       
temperature of the lavas is not much    
above the fusing-point of the  acidic   
lavas1 while it may probably be very    
considerably above the  fusing-point of 
basalt4 ,for a rough estimate1 with no  
pretensions to  accuracy1 it may be     
assumed that in an average case there   

are #ejj  ,fahr4 excess1 but probably   
not #ajjj ,fahr4 ,a computation based on
 even  so rough an estimate as this may1
 by showing the order of magnitude  of  
the thermal considerations1 indicate    
their radical bearing4 ,the  average    
temperature of the ground-water of the  
upper two or three miles  of the        
crust--the only portion through which   
water probably penetrates  with         
sufficient freedom to be effective in   
this case--is probably less  than #bjj  
,fahr4 ,the specific heat of rock       
appears to average somewhat  less than  
#j4b4 ,the temperature of the lava may  
be taken at #cjjj ,fahr4  as a          
sufficiently high average4 ,from these  
data it follows that if  an amount of   
ground-water equal to five percent4 of  
the volume of  the lava entered the lava
 and was brought up to its temperature  
and  then discharged1 the temperature of
 the whole mass would be lowered  #eej  
,fahr4 ,it is therefore evident that    
only a small percentage of              

surface-water can pass through the lava 
consistently with its continued         
fluidity4    ,m4 ,fouqu estimated that  
the discharge of steam from a merely    
parasitic cone of ,etna during #ajj days
 was equal to #b1ajj1jjj cubic  meters  
of water4 ,if this were ground-water1   
and the lava from which  it issued had  
an excess of #ejj ,fahr4 above the      
fusion-point1 the  formation of this    
steam would congeal a column #djj feet  
in diameter  and #cjjj feet deep in the 
time given4 ,if this case is typical1   
and  if ,fouqu's estimate is not greatly
 exaggerated or very exceptional1  the  
view that any large portion of the steam
 from volcanoes comes  from             
surface-waters seems to be incompatible 
with the persistence of  ebullition and 
explosion which many of them exhibit4   
,stromboli has been  in constant        
eruption as far back as the history of  
the region runs4 ,it  is now exploding  
every three to ten minutes1 and yet the 
mass of lava  seems to be small and its 

outflow inconsiderable4 ,is it possible 
that  a current of steam1 given out with
 this activity for so long a period1    
was derived from adjacent ground-waters1
 and has not yet solidified the  lava8  
,the problem takes on a very different  
aspect if the steam1 or at least  some  
large part of it1 rises from great      
depths and brings thence an  excess of  
heat4 ,it then becomes an agency for the
 maintenance of  the liquidity of the   
lava1 for giving it convective motion1  
and for  promoting explosive action1 so 
long as it continues to rise4    ,for   
these and other reasons the balance of  
present evidence seems to us  to favor  
the view that most of the steam and     
other gases come with the  lava from its
 original source deep in the earth4     
,references on vulcanism4--,g4 ,p4      
,scrope1 ,volcanoes1 ,london1    #ahgb4 
,r4 ,mallet1 on ,volcanic ,energy1      
,phil4 ,trans41 #ahgc4 ,c4    ,darwin1  
,geological ,observations on ,volcanic  
,islands1 ,london1    #ahgf4 ,e4 ,reyer1

 ,beitrag zur ,physik der ,eruptionen1  
,vienna1 #ahgg2    ,theoretische        
,geologie1 #ahhh4 ,fouqu1 ,santorin et  
ses ruptions1    ,paris1 #ahgi1         
,sartoris von ,waltershausen and ,a4 von
 ,lasaulx1 ,der    ,aetna1 ,leipzig1    
#ahhj4 ,c4 ,e4 ,dutton1 ,geology of the 
,high ,plateaus of    ,utah1 ,u4 ,s4    
,geog4 and ,geol4 ,surv41 #ahhj2 ,the   
,hawaiian ,volcanoes1    ,fourth ,ann4  
,rept4 ,u4 ,s4 ,geol4 ,surv41 #ahhc4    
,judd1 ,volcanoes1 #ahha2    ,the       
,eruption of ,krakatoa 7,com4 of the    
,roy4 ,soc471 #ahhh4 ,j4 ,d4    ,dana1  
,characteristics of ,volcanoes1 #ahij4  
,h4 ,j4 ,johnston-,lavis1    ,the ,south
 ,italian ,volcanoes1 ,naples1 #ahia4   
,e4 ,hull1 ,volcanoes1    ,past and     
,present1 #ahib4 ,milne and ,burton1    
,the ,volcanoes of ,japan1    #ahib4 ,j4
 ,p4 ,iddings1 ,the ,origin of ,igneous 
,rocks1 ,bull4 ,phil4 ,soc41            
,washington1 ,vol4 ,,xii1 #ahib4 ,a4 ,c4
 ,lane1 ,geologic ,activity of the      
,earth's ,originally ,absorbed ,gases1  

,bull4 ,geol4 ,soc4 ,am41 ,vol4 ,v1     
#ahid4 ,a4 ,geikie1 ,ancient ,volcanoes 
of ,great ,britain1 ,london1 #ahig4     
,i4 ,c4 ,russell1 ,volcanoes of ,north  
,america1 #ahig4 ,t4 ,g4 ,bonney1       
,volcanoes1 ,their ,structure and       
,significance1 ,new ,york 7and ,london71
    #ahii4 ,f4 ,miron1 tude des         
,phnomnes ,volcaniques1 ,paris1 #aijc4  
,g4 ,c4 ,curtis1 ,secondary ,phenomena  
of the ,west ,indian ,volcanic          
,eruptions of #aijb1 ,jour4 ,geol41     
,vol4 ,,xi1 ,no4 #b1 #aijc4 ,a4         
,heilprin1    ,mont ,pele and the       
,tragedy of ,martinique1 ,philadelphia  
7and    ,london71 #aijc4 ,robert ,t4    
,hill1 ,report on the ,volcanic         
,disturbances    in the ,west ,indies1  
,nat'l ,geog4 ,mag41 ,vol4 ,,xiii1 ,no4 
#g1 #aijb4 ,i4    ,c4 ,russell1 ,the    
,recent ,volcanic ,eruptions in the     
,west ,indies1    ,nat'l ,geog4 ,mag41  
,vol4 ,,xiii1 ,no4 #g1 #aijb2 ,volcanic 
,eruptions on    ,martinique and ,st4   
,vincent1 ,nat'l ,geog4 ,mag41 ,vol4    

,,xiii1 ,no4 #ab1    #aijb4 ,j4 ,s4     
,diller1 ,volcanic ,rocks of ,martinique
 and ,st4 ,vincent1    ,nat'l ,geog4    
,mag41 ,vol4 ,,xiii1 ,no4 #g1 #aijb4 ,w4
 ,f4 ,hillebrand1    ,chemical          
,discussion of ,analyses of ,volcanic   
,ejecta from ,martinique    and ,st4    
,vincent1 ,nat'l ,geog4 ,mag41 ,vol4    
,,xiii1 ,no4 #g1 #aijb4 ,e4 ,o4         
,hovey1 ,the ,eruptions of ,la          
,soufrire1 ,st4 ,vincent1 in ,may1      
#aijb1    ,nat'l ,geog4 ,mag41 ,vol4    
,,xiii1 ,no4 #ab1 #aijb4                
,,chapter ,,xi4                         
,,the ,,geologic ,,functions ,,of       
,,life4                 ,i4 ,,the       
,,distinctive ,,features ,,of ,,organic 
,,processes4    ,there is no reason to  
suppose that life processes1 as we know 
them1  were in operation in the earliest
 stages of the earth's history4 ,they   
were introduced and developed gradually 
during its progress4 ,with  life there  
came into the processes of the earth's  
development three  distinctive factors3 

,a4 ,certain chemical actions giving    
rise to compounds that are not known  to
 occur independently of life4    ,b4    
,certain modes of aggregation of        
material1 and certain kinds of  bodily  
movements1 not known except in          
association with life4    ,c4 ,the      
mental element1 under the direction of  
which certain new  processes were       
inaugurated1 and certain previous       
processes were  modified and controlled4
                          ,a4 ,the      
,chemical ,work of ,life4    ,the       
peculiar chemical phenomena connected   
with life chiefly concern  the carbon   
compounds4 ,in the inorganic world the  
carbon compounds are  few and simple4   
,in the organic world they become       
extremely numerous  and complicated4    
,these compounds are very unstable1 for 
the greater  part1 and their partial    
decomposition gives rise to many        
additional  compounds4 ,some of the true
 organic compounds and some of their    
decomposition products have the power of

 combining with inorganic  substances1  
and so produce an additional series of  
semi-organic  combinations4 ,the total  
number of the compounds thus directly   
and  indirectly connected with life     
greatly exceeds that of all inorganic   
compounds4 ,their mass1 however1 is very
 greatly inferior4    ,life material    
chiefly atmospheric4--,in the building  
up of the organic  compounds1 a         
necessary step is the decomposition of  
certain inorganic  compounds4 ,the chief
 of these is the carbon dioxide of the  
atmosphere  and hydrosphere1 the        
decomposition of which furnishes the    
carbon  needed for the organic          
compounds4 ,on this account carbon      
dioxide may  be regarded as in some     
sense the basal material or the         
fundamental  food of the organic        
kingdom1 and hence it plays a radical   
rle in the  life-history of the earth4  
,water1 and the constituents of water1  
oxygen and hydrogen1 play a  larger part
 quantitatively1 but a less distinctive 

part4    ,nitrogen is also an essential 
element1 and usually stands next to     
carbon1 oxygen1 and hydrogen in         
quantity4    ,these1 it will be noted1  
are all atmospheric constituents1 and   
the  material of life is1 therefore1    
dominantly atmospheric4 ,this is  even  
true of aquatic life1 for it lives      
largely on the atmospheric  constituents
 dissolved in the water4 ,the function  
of life1 considered  from the material  
point of view1 is not only fundamentally
 concerned  with the atmosphere1 and    
intimately dependent on its conditions1 
but  its most important material effects
 appear to lie in its modification  of  
the constitution of the atmosphere4     
,the non-atmospheric factors4--,the     
atmospheric constituents are not1       
however1 the only elements intimately   
connected with the life function4       
,compounds of sulphur1 phosphorus1      
potassium1 sodium1 chlorine1 iron1      
calcium1 magnesium1 silicon1 and other  
elements are more or less  essential to 

the life of many organisms1 or are      
employed by them for  their skeletons1  
coverings1 etc4 ,incidentally1 nearly   
all the common  elements become         
intimately related to living organisms  
either in the  relations of active      
elements in their physiological         
functions1 or of  passive elements in   
their structure or in their auxiliary   
parts4                            ,three
 ,classes of ,effects4    ,out of life  
processes grow three rather distinct    
classes of results3  7#a7 changes in the
 amounts and proportions of the         
constituents of  the atmosphere and1 to 
some slight extent1 of the hydrosphere  
and  lithosphere2 7#b7 aid or hindrance 
to inorganic processes1 such as         
disintegration1 erosion1 and deposition2
 and 7#c7 distinctive products1  either 
7a7 of organic matter that would not    
have come into the  existing combination
 but for life1 such as peat1 lignite1   
amber1 etc41  or 7b7 of special forms of
 inorganic matter that would not have   

arisen but for life1 such as coral      
deposits1 shell-marl1 diatom ooze1  etc4
                7#a7 ,changes in the    
composition of the atmosphere4    ,the  
succession of modifications which the   
atmosphere has undergone  from time to  
time through the action of life will be 
discussed as the  earth's history is    
followed in the second volume4 ,it may  
suffice here  to note briefly the chief 
ways in which the atmosphere has        
probably  been modified by the agency of
 life1 not only as regards its quantity 
but also as regards the proportions of  
its constituents4    ,the consumption   
and restoration of carbon dioxide4--,as 
the fundamental  food of the organic    
world1 carbon dioxide has suffered      
enormous  consumption in the course of  
the geological ages1 and is now reduced 
to the very small proportion of 4#jjjd  
or 4#jjjc of the whole4 ,at the  outset 
it was probably one of the most abundant
 constituents2 possibly  even the chief 
one4 ,it has been partially restored1   

concurrently with  its consumption1 by  
animal respiration1 by certain classes  
of plant  action1 and by combustion and 
other forms of inorganic combination4   
,this restorative action has been       
incomplete at all known stages of  the  
earth's history1 and hence there has    
been constant loss of carbon  dioxide4  
,the inorganic processes which have also
 profoundly affected  both the          
consumption and restoration of carbon   
dioxide are here  neglected and         
discussed elsewhere4    ,the freeing and
 consumption of oxygen4--,the oxygen of 
the atmosphere  is actively consumed by 
animals and by plants1 but on the other 
hand1  it is set free abundantly by     
green plants1 and hence its amount has  
probably fluctuated from time to time   
according to the state of  balance      
between the organic processes of its    
production1 and those of  its           
consumption4 ,the consumption of oxygen 
by organic processes is1  however1      
little more than a reversal of the      

previous process by which  it was set   
free2 for instance1 green plants in     
forming their food set  free the oxygen 
of the carbon dioxide used for the      
purpose4 ,when the  organic substance so
 formed is ultimately consumed through  
plant or  animal action or by inorganic 
means1 an equivalent amount of oxygen   
reunites with the carbon to again form  
carbon dioxide4 ,and so if the  whole of
 the organic matter is returned to the  
inorganic state1 no more  oxygen is     
consumed than had been before set free  
in the process of  forming the organic  
matter4 ,but1 as a matter of fact1 a    
large amount  of organic matter has not 
gone back completely to the inorganic   
state1  and this residue constitutes a  
factor of no small importance in the    
geological record4    ,the organic      
residue4--,there is a certain portion of
 vegetation that  is not consumed by    
animals or by other plants1 and that    
escapes  combustion and all kinds of    
ordinary decay1 and this constitutes a  

part of the organic residue4 ,animals   
never completely oxidize all  the       
organic matter they take into their     
systems2 their bodies never  entirely   
consume themselves4 ,a like statement   
may be made respecting  those plants    
that feed on organic matter4 ,that which
 animals and plants  leave unoxidized is
 indeed more or less preyed upon by     
other animals  and plants1 and          
relatively little escapes final         
reoxidation1 but there  is a remnant1   
and this constitutes another part of the
 organic residue4  ,the more conspicuous
 forms of the organic residue are found 
in the  mucks1 peats1 lignites1 coals1  
organic oils1 and gases1 but in addition
  there is not a little disseminated    
organic matter in nearly all the        
sedimentary rocks2 in the aggregate1    
this probably amounts to more than  the 
distinct organic deposits4    ,the      
meaning of the organic residue4--,all   
the unoxidized1 or  incompletely        
oxidized1 carbon in the organic residue 

implies that  oxygen has previously been
 separated from this residual carbon by 
plants and given to the atmosphere1 and 
hence has been a source of  atmospheric 
enrichment in oxygen4 ,the amount thus  
contributed is  equal to that which is  
required to restore the residual carbon 
to its  original state of oxidation4    
,so1 in a similar way1 the unoxidized   
hydrogen in the organic hydrocarbons and
 like compounds implies that  oxygen has
 been separated from the hydrogen of    
water and given to the  atmosphere1 and 
hence this also is a source of          
atmospheric enrichment  in oxygen4 ,it  
seems safe1 therefore1 to conclude that 
the action of  life1 taken as a whole1  
has increased the free oxygen of the    
atmosphere4    ,while not here under    
consideration1 it is not to be forgotten
 that  inorganic processes involving the
 same atmospheric constituents have     
been in operation concurrently with the 
organic processes1 and that  they have  
also affected the amounts and           

proportions of the atmospheric          
constituents4 ,rocks have been oxidized 
in greater or less measure  at the      
expense of the atmospheric oxygen1 and  
hence when the total  atmospheric       
problem is considered1 there arises the 
question whether  the amount of oxygen  
in the atmosphere has been increased or 
diminished  during geological history1  
when the balance is struck between the  
inorganic and the organic actions4 ,the 
probabilities seem to us to  strongly   
favor the view that organic action has  
preponderated1 and that  the oxygen has 
been increased beyond its primitive     
amount1 but that it  has fluctuated     
during known geological history4 ,the   
reasons for this  view will appear in   
the historical chapters4    ,the        
disintegration of the crystalline rocks 
and the solution of  limestone have     
consumed much carbon dioxide1 and this  
is to be added to  the loss through     
organic action4 ,on the other hand1     
there are inorganic  processes that     

supply carbon dioxide1 and hence when   
the larger problem  of the atmosphere is
 raised1 the factors become so          
complicated that  their consideration is
 best deferred to the historical        
chapters4 ,this  passing reference may  
stand us in good part lest we forget1   
for the  moment1 the inorganic factors  
in the atmospheric problem4    ,the more
 inert factor4--,nitrogen in the free   
state is relatively inert  chemically1  
and it does not appear that it can be   
used directly by the  higher plants and 
animals in appreciable amounts4 ,certain
 bacteria1  and perhaps certain alg#bhh 
and other low forms of plants1 have the 
power of using free nitrogen1 and this  
is a principal way in which it  is put  
within the reach of higher plants4      
,nitrogen is also combined  in small    
quantity in the atmosphere by electric  
action1 and thus made  available for    
plants4 ,on account of the inertness of 
nitrogen and  of the relatively limited 
amount required for organic purposes1   

the  nitrogen of the atmosphere has been
 less consumed than the carbon  dioxide4
 ,besides this1 the nitrogen compounds  
are very decomposable1  and are very    
generally and completely returned to    
their original state4  ,deposits of     
nitrates or other nitrogenous compounds 
are relatively rare4    ,it is obvious  
that if there is any considerable source
 of supply  concurrent with this slight 
loss1 the amount of nitrogen in the     
atmosphere must have been increasing4   
,we have seen that volcanoes  give forth
 considerable quantities of nitrogen1   
and that this may  be a real addition to
 the atmosphere1 and not merely a return
 of  the atmospheric nitrogen that had  
been carried down previously by         
underground-water4 ,it has also been    
noted that crystalline rocks  contain   
occluded nitrogen1 which is doubtless   
freed by their  disintegration4 ,it is1 
therefore1 not improbable that the      
nitrogen of  the atmosphere has been    
increasing1 both actually and           

relatively4    ,probable fluctuations of
 atmospheric composition4--,with this   
general  sketch of the interplay of the 
atmospheric elements under organic      
influence1 we are prepared for the      
further conception that if one  or      
another of these actions was relatively 
more vigorous than usual  for a period1 
it would bring about a variation in the 
proportions of  the atmospheric         
constituents4 ,if1 for example1         
vegetation flourished  luxuriantly for a
 long period1 but was measurably        
protected from the  organisms that      
preyed upon it and from inorganic       
decomposition1 as by  falling into water
 or by prompt burial under sediment1 the
 atmosphere  might be growing richer in 
oxygen4 ,if1 on the other hand1         
vegetation  were being relatively       
reduced1 as perhaps it is being reduced 
now  by man1 and if previous organic    
products were being reoxidized at an    
unusual rate1 as they are now in the    
burning of timber1 coal1 natural  oil   

and gas1 the carbon dioxide of the      
atmosphere might be relatively          
increasing1 while the oxygen might be   
relatively diminishing4 ,the  possible  
fluctuations of the atmosphere as the   
result of organic action  are1          
therefore1 matters of vital importance1 
and invite attention in  the historical 
study of the earth and in the outlook   
into its future4    ,the climatic       
effects of organic action4--,interest   
does not1 however1  rest at this point4 
,the researches of physicists have made 
it probable1  if they have not          
altogether demonstrated1 that the       
composition of  the atmosphere has much 
to do with the climatic conditions at   
the  surface of the earth4 ,the         
atmosphere blankets the earth and       
equalizes  its temperature4 ,acting as a
 screen1 it subdues in some measure the 
intensity of the sun's rays by day1     
while it retards the radiation  of the  
earth's acquired heat at night4 ,this is
 in some measure the  function of all   

the constituents of the atmosphere1 but 
by no means  of all equally4 ,the oxygen
 and nitrogen are relatively            
diathermous1  letting the sun's rays    
pass in freely1 and the earth's rays    
pass  out freely2 but carbon dioxide and
 the vapor of water are much less       
diathermous1 particularly to rays of low
 intensity1 such as are thrown  out by  
non-luminous bodies like the earth4 ,it 
follows that while the  solar rays come 
in rather freely and heat the surface of
 the earth1  the dark rays which the    
earth radiates back are measurably      
arrested by  the carbon dioxide and     
vapor of water1 and serve to keep the   
air warm4  ,the influence of the vapor  
of water is vividly shown in the        
different  degrees to which cooling     
takes place at night in a dry and in a  
moist  atmosphere1 respectively1 where  
other conditions are the same4 ,ice is  
said to form at night in desert regions 
where the air is extremely dry1  even   
within the tropics1 while in humid      

regions of the same latitude  and       
altitude oppressively hot nights are    
common4 ,the influence of the  carbon   
dioxide is not thus familiarly          
demonstrated1 since its amount  varies  
but slightly in different localities1   
but physical experiment  indicates that 
it has a similar function4    ,if the   
amount of carbon dioxide in the         
atmosphere varies from age to  age1 the 
climate of the earth must apparently    
vary accordingly1 and on  this is built 
one of the hypotheses of climatic       
variation subsequently  to be           
considered4 ,we shall find that there   
have been great changes in  the climate 
of the earth during its history4 ,there 
is good evidence  of former glaciation1 
not only in the northern ,united ,states
 and in  ,england1 ,germany1 and central
 ,russia1 but in ,india1 ,australia1 and
  ,south ,africa4 ,at other times1 figs 
and magnolias grew in ,greenland  and   
,spitzbergen1 and corals flourished in  
the ,arctic seas4 ,there is  good       

evidence of arid periods where humidity 
now prevails1 and of  humid periods     
where aridity now prevails4 ,it is not  
assumed that the  influence of organic  
action on the atmosphere has been the   
sole1 or  perhaps even the main1 cause  
of these great climatic changes1 but it 
is  believed that it has been an        
important contributing factor4 ,it is   
even  possible that the climate of the  
future is much dependent on the agency  
of man1 as implied above1 however little
 ground there may be to suppose  that he
 will1 with altruistic purpose1 control 
his action with a view  to its bearing  
on the generations that may live tens of
 thousands of  years hence4             
7#b7 ,aid and hindrance to inorganic    
action4    ,the promotion of            
disintegration4--,while the influence of
 organic  action on the lithosphere is  
quite superficial1 and far less radical 
than that on the atmosphere1 it is still
 important4 ,plants promote  both       
disintegration and disaggregation under 

certain conditions1  and hinder them    
under others1 as already set forth4     
,chemical action  of a decomposing and  
solvent nature takes place in connection
 with  the roots of plants1 while their 
growth sometimes rends rocks into  whose
 crevices they have insinuated          
themselves4 ,the acids and other        
products of organic growth and of       
organic decomposition attack some  of   
the constituents of the rocks and       
contribute to their solution and        
disintegration4 ,on the other hand1     
organic matter entrapped in the         
sediments1 and so introduced into the   
strata at various depths1 often  acts as
 a reducing agency1 causing the deposit 
of substances carried in  solution in   
the underground-waters4 ,ores are       
sometimes thus formed1 as  explained in 
the discussion of ore-deposits 7p4      
#dgf74 ,organic action  on the whole    
promotes solution and disintegration at 
the surface1 and  prepares the way for  
deposition below4    ,protection against

 erosion4--,another important function  
of vegetation  is the protection of the 
land surface against erosion1 as already
 noted  in the discussion of erosion4 ,a
 mantle of grass1 especially if it forms
  a turf1 or a carpet of leaves         
protected by bush and forest1 greatly   
retards surface wash4 ,it does this not 
only because it directly covers  the    
soil1 but because it holds back the     
run-off and tends to prevent  those     
violent floods which give to erosion its
 greatest intensity4  ,there is a marked
 difference between the erosive work    
which a given  amount of water will do  
if1 in the one case1 it runs off        
gradually1 and  in the other1           
precipitately4 ,by way of offset1 it is 
to be noted that  the disintegrating    
action of vegetation prepares the rock  
material for  easy erosion1 and to this 
extent helps in its removal by the      
drainage2  but on the average this is   
greatly overbalanced by the protection  
afforded by the vegetal covering1 though

 this is not true in every  instance4   
,the influence of land vegetation on the
 character of the  sediments4--,the     
presence or absence of a vegetal        
covering influences  the kind of deposit
 which is derived from the land1        
particularly  if the surface be occupied
 by crystalline rocks4 ,if the surface  
be  well clothed with vegetation1 the   
crystals of the complex silicates1  such
 as the feldspars1 micas1 and           
ferromagnesian minerals1 are  usually   
disintegrated into clayey products      
before they are removed1  so that1 when 
borne away and deposited1 the result is 
common shale4  ,concurrently1 the       
relatively undecomposable quartz-grains 
are rounded  into sand1 and deposited as
 common quartzose sandstone1 while the  
calcareous material is borne away in    
solution and deposited as  limestone4   
,but if the surface be bare of          
vegetation1 the crystalline  rocks are  
usually disaggregated before they are   
decomposed1 for  destructive action     

works best at the junctions of crystals1
 and along  cleavage lines1 and hence   
the crystals are usually separated from 
one  another before they are fully      
decomposed4 ,in the absence of a        
covering  to hold them in place until   
they are decomposed1 they are apt to be 
washed away1 and the resulting deposit  
consists in considerable part  of grains
 of feldspar1 mica1 hornblende1 and     
other minerals1 which  do not usually   
occur in well-decomposed sediments4 ,the
 deposits are1  therefore1 of the nature
 of arkose1 if the original rocks are   
granitic1  or of the nature of wacke1 as
 the term is used in this book1 if they 
are of the basic type4 ,on this is based
 the inference that a vegetal  covering 
of the land extended as far back in the 
history of the  earth as clay shales1   
quartzose sandstones1 and limestones    
form the  prevailing sediments4         
7#c7 ,distinctive deposits4    ,organic 
rocks4--,in the chapter on the origin   
and descent of rocks1  a group of rocks 

formed directly from organic matter is  
recognized  and described4 ,the chief of
 these are peat1 lignite1 bituminous    
coal1 anthracite1 and graphite4 ,it is  
the belief of many geologists  that     
natural gases1 oils1 and asphalts are   
also mainly derived  from animal and    
vegetal remains4 ,an alternative view1  
advocated by  ,mendelejeff and ,moissan1
 assigns the oils1 gases1 etc41 in part 
at  least1 to deep-seated carbides to   
which water has gained access and       
developed hydrocarbons1 after the       
analogy of acetylene4#bhi ,whatever  may
 be the truth relative to inorganic     
action1 it is clear from  geological    
conditions that some of the natural     
gases and oils are  organic products4   
,besides the more common organic        
deposits1 there  is a long list of minor
 products1 among which are amber1       
copalite1  paraffine1 ozocerite1        
camphene1 etc4 ,guano and coprolites    
represent the  excrementitious class4   
,inorganic rocks due to life4--,besides 

these deposits of organic  matter1 or of
 its decomposition products1 there is a 
large class formed  from the inorganic  
matter that served auxiliary functions  
in the  economy of life1 such as shells1
 skeletons1 etc4 ,for the greater part  
these are composed of calcium carbonate1
 and give rise to limestones1  marls1   
chalk1 etc4 ,not a few1 however1 are    
silicious1 and give rise  to flints1    
cherts1 and silicious earths4 ,some are 
formed of calcium  phosphate1 and a few 
of other inorganic material4 ,the       
deposits formed  in these ways have been
 defined in the chapter on rocks4       
,fossils4    ,the term fossil is used so
 comprehensively as to include not only 
the remains of plants and animals       
themselves1 but their tracks1           
impressions1 casts1 replacements1 and   
all other distinct traces4  ,it also    
embraces nests1 borings1 implements1 and
 other distinctive  products4 ,these    
enter into the formation of the two     
classes of rocks  just considered1 but  

they have an independent function4 ,they
 constitute  the specific record of     
life1 and their study not only reveals  
much of  the past history of plants and 
animals1 but furnishes one of the most  
important means by which the ages of    
formations are determined4 ,in the      
early development of the science it was 
found that the uppermost and  hence the 
latest beds of rock contain fossil forms
 either identical  with those now       
living1 or closely similar to them2 that
 beds below  these bear life relics that
 depart somewhat more from the living   
forms1  and are somewhat less highly    
developed2 that beds still lower bear   
fossils that depart still more from the 
living types1 and are more  primitive in
 general1 and so on down as far as      
fossils are found4    ,the general order
 of life succession determined by       
stratigraphy4--,thus  it appeared from  
the evidence of the strata that there   
was a general  order of life succession4
 ,it was also found that this was1 in   

its  main features1 the same for all the
 continents4 ,by continued and  close   
studies1 the particulars of the         
succession were worked out more  and    
more fully1 and the work is still being 
pushed forward to greater  and greater  
degrees of refinement4 ,at the same     
time1 it was found  that there were     
different faunas and floras in different
 parts of the  world in past times1 much
 as there are now2 that there were      
shiftings  and migrations as now2 that  
given species were increasing in some   
regions and dying out in others1 and    
that innumerable variations and         
complications entered into the evolution
 and distribution of the life  forms4   
,but under and through all these there  
run a sufficient number  of common      
features to show beyond reasonable      
question the order of  succession of    
life4    ,throughout all this study1 the
 chief guide was the actual order in    
which the fossils were found in the     
succession of strata1 because  there is 

no evidence so conclusive of the order  
of events as the  superposition of the  
sedimentary beds when they are normal   
and  undisturbed4 ,by the study of the  
fossils in the successive beds1 it was  
found that there was a more or less     
progressive evolution of plants and     
animals brought about by modifications  
of their forms1 and that these          
modifications assisted in determining   
the order of succession when  the       
evidence of the strata was defective2   
and so the biological and               
stratigraphical factors reacted         
helpfully on each other4    ,fossils as 
means of correlation4--,while           
stratigraphy was thus1 in  the earliest 
stages1 the main reliance in determining
 the order of  events1 and biology was  
the chief gainer1 in the end            
stratigraphy  received ample            
compensation1 if indeed it did not      
become the greater  beneficiary2 for at 
no known and accessible place is there a
 complete  succession of sedimentary    

beds4 ,there are great series here and  
there1  but their connections with one  
another are more or less concealed  by  
surface formations or water-bodies4 ,so 
also at many places the  stratified     
series has been broken up by            
deformation1 or cut away by  erosion4   
,hence there was need for some reliable 
means of matching the  beds of separated
 series1 and of making up a complete    
ideal series4  ,this means is found in  
the fossils they contain4 ,while the    
variations  of the faunas and floras in 
different regions1 and their migrations1
  introduce some minor difficulties1 the
 relations of the fossiliferous  beds of
 one region to those of another can be  
determined with great  satisfaction1 and
 often with great precision4 ,this is   
particularly so  when abundant floating 
or free-swimming species lived in the   
seas and  were freely fossilized1 for   
they were deposited on the coasts of all
  the continents at practically the same
 time1 and no uncertainties from        

migration or local differences in rate  
of evolution intervened to throw  doubt 
upon the correlation4 ,without the aid  
of fossils1 the correlation  of the     
deposits on the separate continents     
would be attended with  grave obstacles 
and much uncertainty1 if not with quite 
prohibitive  difficulties4              
,b4 ,special ,modes of ,aggregation and 
of ,movement4    ,inorganic solid matter
 is chiefly crystalloidal2 organic      
matter is  chiefly colloidal2 but there 
are colloidal states of inorganic matter
  and there are crystalloids among the  
organic products4 ,in the inorganic     
world1 solids very generally tend to    
organize in the form of crystals2  in   
the organic world1 they as generally    
tend to organize in the form of  cells4 
,neither tendency is complete or        
exclusive1 but each is dominant  in its 
own sphere4    ,still more distinctive  
than the formation of cells is the      
growth of  complex organized bodies1 the
 differentiated members of which perform

  special functions for one another1 and
 are mutually dependent on one  another4
 ,this is a profound departure from the 
habitual modes of the  inorganic world4 
,still more so is the power of voluntary
 motion in more or less  disregard of   
outside physical influences4 ,through   
this power1  distribution may take place
 contrary to current and wind1 and  to  
gravitation itself4 ,from the view-point
 of past geologic  transportation1 this 
is perhaps more singular than important1
 for no  great mass of matter has been  
transported contrary to the influences  
of gravity1 wind1 and current1 by the   
exercise of this peculiar  power of     
animals1 but it is not without geologic 
importance in the  migrations and in the
 redistributions of organic influences  
that arise  from migrations4 ,when the  
influence of man is included1 the       
geologic  effects require consideration1
 but here the third distinctive factor1 
the mental element1 comes into effective
 play1 and we pass to its               

consideration4                          
,c4 ,the ,mental ,element4    ,current  
opinion does not recognize a mental     
element as residing in the  plant world1
 and it is divided as to the degree of  
its development in  the lower animal    
kingdom1 but its influential presence in
 the higher  animal orders and in man is
 beyond legitimate question4 ,two phases
  are to be recognized3 7#a7 the        
material work done under the stimulus   
and direction of mental impulses1 as1   
for example1 excavations1               
transportations1 changes of drainage1   
removal of forests1 cultivation  of     
soil1 etc41 and 7#b7 the intellectual   
work of the faculties  themselves       
irrespective of material changes4 ,in   
one view1 geology  is a purely material 
science concerned solely with the       
formation of  the earth and with the    
physical development and relations of   
its  inhabitants4 ,in another1 geology  
is a comprehensive historical science   
concerned with every phase of the       

world's history1 and certainly  not     
least with the higher forms of life     
development1 with their  psychological1 
sociological1 and other phases of mental
 attainments1  since these are the      
highest output of the earth's evolution4
 ,the latter  seems to us the more      
comprehensive view4    7#a7 ,the        
material effects of the mental          
element4--,lyell long since  urged that 
the direct work of man in changing the  
face of the earth was  slight compared  
with that of the contemporaneous        
inorganic agencies4  ,he called         
attention to the relative insignificance
 of the quarries1  pits1 cellars1 and   
other excavations of man1 compared with 
the work  of streams1 waves1 and other  
inorganic agencies4 ,there is justness  
in  this view1 but it needs             
qualification4 ,it is to be observed    
that the  mental era has but just begun1
 and that its effects are increasing    
with a rapidity quite phenomenal when   
measured by the slow pace of  most      

geologic events4 ,the excavations and   
transportations of material  to-day show
 an enormous advance on those of        
,lyell's day1 which was1  geologically  
speaking1 but a moment ago4 ,the        
mile-tons of industrial  freightage in  
the ,mississippi basin are to-day not   
wholly incomparable  with the drainage  
transportation of the same area a       
century ago4 ,a  century ago is named1  
because the surface was then covered    
with natural  vegetation1 and the normal
 effect of surface erosion1 independent 
of  man1 was then experienced4 ,at      
present the indirect effects of man's   
action are mingled with those of natural
 processes1 and these indirect  effects 
are probably much more important than   
the direct ones4 ,the  removal of the   
native vegetation and the cultivation of
 the soil  expose the surface to wash to
 a degree far beyond that prevalent when
  the surface was prairie sod1 or       
leaf-carpeted forest1 and denudation    
and transportation have been greatly    

multiplied in consequence4 ,not  only   
has this cultivation increased the      
exposure to erosion1 but1 by  increasing
 the rate of run-off1 it has added to   
the erosive power  of the streams4 ,the 
ditching of swamps and other tracts of  
retarded  drainage has contributed to   
this acceleration4 ,the naked1 soil-less
  uplands of some of the once populous  
kingdoms of the ,orient1 notably        
portions of ,syria and ,greece1 are sad 
witnesses of the accelerated  erosion   
that attends cultivation4 ,the erosion  
of certain southern  fields of the      
,united ,states in the last forty years 
is another striking  illustration4 ,it  
is doubtful whether some parts of this  
region suffered  as much erosion in the 
preceding five centuries as they have   
during  the last one4 ,on the other     
hand1 some compensation is found in the 
reservoirs established for water-power1 
and in artificial devices for  retarding
 and steadying stream flow4    ,in the  
light of considerations such as these1  

man may well be regarded  not only as a 
potent geological agent1 but as         
dangerously so to  himself4 ,the hope is
 that the intelligence that has wrought 
a change  of surface conditions         
serviceable for the present1 but        
dangerous to  the future1 will be so    
enlarged as to inspire a still more     
intelligent  control of surface         
conditions which shall compass the      
future welfare as  well as transient    
benefit4    ,human modification of the  
animal and vegetal kingdoms4--,man's    
agency  is also coming to be felt       
powerfully in the modification of the   
plant  and animal life of the land and  
even to some extent of the sea4 ,the    
larger animals that are not propagated  
by man are fast approaching  extinction4
 ,at the present rate of extension of   
man's dominion1 a  century or so will   
see the disappearance of nearly every   
large mammal  and reptile that he does  
not choose to protect or propagate4 ,by 
way  of compensation1 certain selected  

animals are increasing and will         
doubtless continue to increase4 ,the    
result is1 therefore1 likely to  be a   
peculiar assemblage of animal life      
dependent strictly on the  choice of a  
dominant type1 a state of things that   
has apparently never  occurred in an    
equal degree in the past history of the 
earth4 ,how far  the minor forms of     
life1 especially the insect life1 and   
the denizens  of the sea1 may be brought
 under this monopolistic control may not
 be  predicted so easily4    ,a similar 
profound transition in vegetation is    
being forced by man4 ,the  native       
vegetation is rapidly being replaced by 
selected varieties1 and  by varieties   
that take advantage of conditions       
furnished by man4 ,as the  agricultural 
control of the earth becomes more       
complete and effective1  a result toward
 which very rapid progress is being     
made1 a new flora  of man's selection   
will very generally prevail over the    
whole land  surface of the globe4 ,it is

 doubtful whether at any time in the    
history  of the earth changes of flora  
and of fauna1 and of surface1 have been 
more rapid than those that are now      
taking place under the accelerating     
influence of man's action1 and this     
accelerating influence springs  not     
mainly from automatic or instinctive    
reaction1 but from conscious  impulse   
and intelligent direction4    7#b7 ,the 
psychological factors as such4--,are the
 introduction and  the evolution of the 
psychological factors themselves to be  
regarded  as subjects of geological     
study8 ,we shall find that1 at the      
outset1  the geologic record is a       
complete blank so far as clear evidence 
of  terrestrial organisms actuated by   
their own intelligence is concerned2    
that later1 organisms with some apparent
 consciousness and intelligence         
appeared1 and that the mental element   
increased apace unto its present        
attainment4 ,we know that relationships 
of a sociological nature arose  in      

apparent feebleness1 and gradually      
evolved into more definite1  higher1 and
 more complex forms4 ,by sociological   
factors we mean merely  those conscious 
relations which one organism bears to   
another1 of  which the parental and the 
gregarious impulses are two fundamental 
expressions4 ,for manifest reasons1 the 
introduction and evolution of  the      
psychological and sociological factors  
themselves have received  little direct 
recognition as a portion of geological  
studies4 ,the  record of such factors in
 the fossils of past ages is necessarily
  obscure and imperfect1 and the        
interpretation of what there is lacks   
certainty and precision4 ,none the less1
 this psychological record1  with all   
its imperfections1 is beyond valuation1 
and must1 we think1  come to be an      
indispensable factor in the study of    
psychological and  sociological         
evolution1 for it shows1 what nothing   
else can show  equally well1 the        
extremely prolonged history of that     

evolution1 and  it gives hints of modes 
and means which no study of existing    
stages  can equally reveal4 ,the        
organization of the ,cambrian           
trilobites1  for example1 implies no    
small development of the senses and of  
the  coordinating faculties even at that
 early stage1 and a study of the        
relations of these to their fellow      
creatures opens up the first  known     
chapter in the sociological record of   
the earth's inhabitants4  ,from this    
stage onward the progress in the        
development of the higher  faculties1   
and of the sociological relations of the
 leading forms1 is  one of the most     
instructive phases of the great history4
 ,such a study  reveals the fact that   
many questions1 narrowly supposed to be 
purely  human1 have had their prototypes
 in the earlier experiences of the      
animal kingdom4 ,some of these questions
 have found solutions1 temporary  or    
permanent1 which passed under the test  
of ages to whose length human           

experience affords no parallel1 and have
 received the sanction or  disapproval  
of such tests according as they were    
well or ill adapted to  the actual      
conditions involved4 ,if one seeks the  
lessons of history in  the largest      
sense1 he cannot wisely neglect the     
prolonged record of the  great          
biological family4                ,,ii4 
,,special ,,contributions ,,of ,,the    
,,organic ,,kingdoms4    ,an essential  
part of the historical chapters of the  
second volume will  consist of the      
description and illustration of the life
 progress of the  successive periods4   
,it will suffice here to give a         
preliminary synopsis  of the kinds of   
record made by the several groups of    
plants and animals4                     
,a4 ,contributions of the ,plant        
,kingdom4#bij    ,the record of plants  
in the early geological ages is         
extremely  imperfect4 ,in the very      
earliest times the conditions seem to   
have been  wholly unsuited to the       

preservation of any relics of life2 but 
even  after animal remains were         
abundantly preserved in the sea         
sediments1  the plant record was still  
very meager for a long period4 ,this was
  probably due in the main to two chief 
causes3 7#a7 the probable  softness and 
perishability of the early types of     
vegetation1 and 7#b7  the fact that     
vegetation is preponderantly            
terrestrial4 ,at no time  has marine    
vegetation reached a high development4  
,land conditions  favor decomposition1  
transportation1 and erosion1 and through
 these1  destruction2 and only under    
rather occasional and exceptional       
conditions did the old lands leave a    
good record of their life4              
,nevertheless all the great groups of   
plants1 viz4 the ,thallophytes  7alg1   
fungi71 the ,bryophytes 7mosses1        
liverworts71 the ,pteridophytes  7ferns1
 horsetails1 lycopods71 and the         
,spermatophytes 7gymnosperms1           
angiosperms7 have left some record4     

,,reference ,,table ,,of ,,the          
,,principal ,,groups ,,of ,,plants4     
,cyanophyce1 blue-green alg4            
,chlorophyce1 green alg4                
,rhodophyce1 red alg4                   
,alg and          ,phophyce1 brown alg4 
algoid forms    ,diatomace1 diatoms4    
,coccospheres                           
,rhabdospheres  ,pelagic alg7874        
,thallophytes                           
,charophyta1 stoneworts4    7,thallus   
plants7                                 
,phycomycetes1 alg-fungi1 water-molds4  
,ascomycetes1 ascus-fungi1 mildews4     
,fungi and         ,basidiomycetes1     
basidium-fungi1 mushrooms4              
fungoid         cidiomycetes1           
cidium-fungi1 8rusts40                  
forms           ,schizomycetes1         
8fission-fungi10 bacteria4              
,myxomycetes1 8animal fungi10           
slime-molds4                            
,lichens            ,symbiont alg and   
fungi4    ,bryophytes     ,hepatic1     
liverworts4    7,moss plants7  ,musci1  

mosses4                    ,filicales   
,filices1 true ferns4                   
,cycadofilices1 cycad-ferns4            
,equisetales        ,equiset1           
scouring-rushes1 horsetails4            
,pteridophytes                          
,calamites4    7,fern plants7           
,sphenophyllales4                       
,lycopodiace1 club-mosses4              
,lycopodiales       ,lepidodendra4      
,sigillaria and stigmaria4              
,cordaite1 cordaites4                   
,cycadales   ,bennettite4               
,gymnosperm         7cycads7  ,cycadace4
                     7,naked seed7      
,conifer1 evergreens4  ,spermatophytes  
,ginkgoace1 ginkgo4    7,seed plants7   
,angiosperm       ,monocotyledone1      
cereals1 grasses1 etc4                  
7,covered ,seed7    7one-leafed seed74  
7,flowering      ,dicotyledone1 oaks1   
poplars1 peas1 etc4                     
plants7         7two-leafed seed74      
,the contribution of the ,thallophytes  
7alg1 fungi1 bacteria74--,the           

,thallophytes embrace the simplest types
 of plants1 and are probably the        
nearest present representatives of the  
ancestral forms4 ,some of them  are     
minute one-celled organisms1 as simple  
as an organism can well be  conceived to
 be4 ,the simple blue-green alg of our  
fresh waters well  represent this class4
 ,the most are1 however1 multicellular1 
and some  7as the great seaweeds7 rise  
to a degree of complexity and of a      
bodily  segmentation resembling that of 
the higher plants4 ,the various species 
are adapted to an extremely wide range  
of conditions2 some live in hot  springs
 at #agj ,fahr41 and some in ,arctic    
seas at the freezing-point2  some       
flourish in fresh water1 some in        
brackish1 some in salt water1 and  some 
even out of the water4 ,this wide       
adaptation implies an ancient  and      
plastic type4 ,the fact that they       
flourish in waters so hot and  sometimes
 also so sulphurous as to be fatal to   
most plants1 suggests  the possibility  

of their introduction during the very   
early volcanic  stages of the earth1    
while conditions were yet uncongenial   
for other  plants4    ,the geologic work
 of the thermal alg is well shown in the
 beautiful  travertine and sinter       
deposits of the ,yellowstone ,park      
7,figs4 #bae and  #bah74 ,at the        
,mammoth ,hot ,springs the deposits are 
calcareous1 while  at most of the other 
hot springs silicious deposits are      
formed1 in  both cases partly1 but not  
wholly1 by the aid of alg4 ,the         
beautiful  yellows1 reds1 browns1 and   
greens of these springs are not mineral 
coloring1 but living plants4#bia ,in the
 calcareous waters1 the alg  are        
believed to cause the deposition of     
calcium carbonate from calcium          
bicarbonate by consuming the second     
equivalent of carbon dioxide  that      
rendered the carbonate soluble4#bib ,in 
the silicious waters1  the process of   
deposition is not understood4 ,similar  
deposits by the  aid of alg take place  

in the geyser regions of ,iceland and of
 ,new  ,zealand1 in the hot springs of  
,carlsbad1 where they have been well    
studied by ,cohn1#bib and in most other 
hot springs4 ,the same1 or very         
similar1 forms of alg abound in nearly  
all waters1 fresh and salt1  but the    
question whether they make calcareous   
and silicious deposits  in notable      
quantity appears not to have received as
 yet the critical  investigation its    
importance deserves1 except in a few    
special cases4  ,it is clear1 however1  
that in the cool waters such deposits do
 not  reach the conspicuous amounts that
 they attain in the thermal springs4    
,in the shallow waters of the ocean1    
especially in the warmer regions1       
lime-secreting alg are abundant and make
 large contributions to the  lime       
deposits4    ,among the higher alg are  
the lime-secreting corallines or        
nullipores  7,rhodophyce1 red alg71 once
 regarded as animals1 which contribute  
a notable part of the calcareous        

substance of coral reefs4 ,they are     
important geologic agents in the        
temperate and tropical seas1 and have   
been traced as far back in time as the  
early ,paleozoic era4    ,the           
,challenger reports#bic describe two    
forms of minute calcareous  spherical   
organisms1 ,rhabdospheres and           
,coccospheres1 as very  abundant in the 
surface-waters of the temperate and     
tropical seas1  and as important in     
contributing to the calcareous deposits 
of the  sea-bottoms4 ,the affinities of 
these bodies are in doubt1 but they are 
regarded by ,murray as probably pelagic 
alg4    ,the stoneworts 7,charace71 an  
aberrant group of alg inhabiting fresh  
and brackish water1 secrete notable     
quantities of calcium carbonate  in and 
around their tissues1 and the           
accumulation of these gives rise  to    
marl or limestone4 ,it has recently been
 urged that our so-called  shell-marls  
are mainly due to ,char1#bid the        
molluscan shells being  incidental      

rather than essential constituents4     
,in very ancient and also in some of the
 later strata1 there are  limestones    
that do not carry any visible fossils1  
and their origin is1  therefore1        
debatable4 ,there are also not a few    
limestones that are made  up of a       
fine-grained base through which are     
scattered molluscan shells1  corals1    
etc41 in a fine state of preservation4  
,the condition of these  fossils bears  
rather adversely on the view that       
shells1 etc41 have been  powdered in    
sufficient numbers and to a sufficient  
degree to form the  compact base4 ,in   
all these cases the usual explanations  
leave something  to be desired4 ,it is  
worth considering whether low forms of  
plants may  not be among the            
undemonstrated agents in forming these  
apparently  unfossiliferous limestones  
or parts of limestones4 ,the calcium    
carbonate deposited by the alg is in    
minute and delicate form1 and is        
usually crystalline while yet in the    

living tissues4 ,it is1 therefore1      
easily subject to comminution and to    
such further crystallization as  would  
obscure the minute features that        
constitute the evidences of  algal      
origin4    ,the more complex and        
conspicuous alg1 the seaweeds1 have left
  impressions of their stems and fronds 
on the marine beds of most of the       
periods1 but they are usually obscure4  
,seaweeds are perhaps the source  of the
 vegetal matter in certain carbonaceous 
shales and limestones4 ,as  seaweeds    
extract bromine and iodine and certain  
metallic ingredients  from the          
sea-water1 some of the iodine and       
bromine springs issuing from  ancient   
marine deposits1 and certain ores1 may  
owe their origin to  ancient seaweeds4  
,diatoms1 minute plants of the          
,thallophyte group1 secrete a delicate  
framework of silica which becomes a     
contribution to the silicious  deposits4
 ,diatoms have sometimes contributed the
 material for very  considerable beds1  

such as those of the ooze-bogs now      
forming in the  marshes of the geyser   
basins of the ,yellowstone ,park1#bie   
and the  diatom oozes of the deep sea   
7,fig4 #cec1 p4 #dbe74    ,fungi1 for   
obvious reasons1 have left but scant    
traces of themselves4    ,bacteria are  
believed to be recognizable as far back 
as the ,paleozoic  era4 ,they are now   
the chief agents in the decomposition of
 organic  matter1 and may be regarded as
 the prime enemies of the fossil record4
  ,it is probable that similar          
decomposition took place actively in the
  earliest ages1 for otherwise the      
remains of the ancient organisms  should
 be more abundant4 ,there is hence a    
theoretical probability that  bacteria  
flourished as far back as the           
stratigraphic record goes4  ,not        
unlikely they were originally simple alg
 that turned from the  primitive habit  
of making their own food1 to living on  
other organisms  or their remains1 and  
in so doing lost their power of         

manufacturing  chlorophyll and of using 
inorganic carbon compounds4 ,their      
remarkable  adaptation to the most      
varied conditions1 and their            
extraordinary  ability to endure the    
greatest vicissitudes of environment1   
support the  view that they are a very  
ancient and plastic form4    ,at present
 certain bacteria are important to      
higher vegetation because  of their     
ability to use the free nitrogen of the 
atmosphere and to  combine it into forms
 available for the higher plants4 ,it is
 not  improbable that they have         
subserved this important function       
through  all the known ages4 ,some      
experiments seem to show that certain of
 the  existing alg have this power1 and 
possibly the ancestral forms of  plants 
possessed it4 ,the bacteria1 being a    
derived and not an original  form1 could
 not have performed the function for the
 first plants4 ,it is  possible1 of     
course1 that the inorganic supply of    
nitrogen compounds  was sufficient for  

plant life at the outset4    ,the       
contribution of the ,bryophytes         
7liverworts1 mosses74--,the mosses  and 
liverworts have left no certain record  
of their work in the  earlier and middle
 geologic eras1 and1 if they existed at 
all1 their  contributions were          
unimportant4 ,although low forms of     
plant life1  they are not primitive     
ones1 as they are characterized by a    
definite  alternation of generations    
implying a considerable time antecedent 
to  the attainment of their present     
forms2 hence there are no very cogent   
theoretical reasons for assigning them a
 place in early geologic  history1      
though their absence cannot be affirmed4
 ,some botanists think  the             
,pteridophytes were derived from some   
ancestral form of liverwort1  which1 if 
true1 would require the presence of the 
latter in an early  geologic period2 but
 the negative geological evidence       
relative to  their presence favors the  
alternative view that the ,pteridophytes

 were  derived from some form of the    
,thallophytes by an independent line4   
,in  recent times1 certain of the       
mosses1 especially the sphagnum mosses1 
have played a notable part in the       
formation of peat accumulations4 ,for   
this1 their habit of growing in bogs1   
and of dying below while they  continue 
to grow above admirably fits them4      
,the contribution of the ,pteridophytes 
7ferns1 horsetails1 lycopods1           
,sphenophyllum74--,the ,pteridophytes   
include the most important fossil       
plants of the earlier and middle        
geologic eras4 ,to them we owe chiefly  
the great carbonaceous deposits of the  
,coal ,measures and probably  most of   
the disseminated carbons of the early   
and middle eras2  perhaps also much of  
the natural oil and gas4 ,their special 
work is  so conspicuous that it will be 
noted at length in the chapters on  the 
,devonian and ,carboniferous periods1   
and hence may be passed here  with      
brevity4 ,the ferns1 now known more for 

their beauty than their  importance1 are
 the representative type of the group1  
and are really  a wonderful family1     
having preserved their characteristic   
leaf-forms  with a persistence attained 
by no other group of plants4 ,the       
,paleozoic  ferns are recognizable as   
such by every one1 irrespective of      
botanical  knowledge2 indeed it is the  
detection of the differences1 rather    
than  the resemblances1 between the     
ancient and modern forms1 that requires 
expert knowledge4 ,this continuity shows
 that since their introduction  the     
changes of climate have never been so   
great as to prevent their  propagation1 
without radical modification1 in some   
part of the globe1  and this fact rather
 narrowly limits the range of surface   
temperatures1  and of other climatic    
vicissitudes4 ,the persistence of the   
,equiset  7horsetails1 scouring-rushes7 
and the lycopods 7club-mosses7 bears    
like testimony1 as does the persistence 
of life in general2 but the  rather     

delicate ferns are perhaps more         
obviously significant than most         
organisms4    ,the contribution of the  
,spermatophytes 7seed plants1 including 
gymnosperms or 8evergreens0 and         
angiosperms or 8flowering               
plants074--,the angiosperms1 the        
dominant group to-day1 make their       
appearance in the record in the latter  
part of the ,mesozoic era1 and  their   
contribution is1 therefore1 relatively  
modern4 ,they contributed  to the coals1
 lignites1 oils1 and organic gases of   
the late geological  periods1 as did the
 ,pteridophytes in the earlier periods1 
the  latter participating1 however1 in  
the late deposits4 ,perhaps the  most   
important function of the               
,spermatophytes lay in their superior   
serviceability as food for the higher   
land animals1 by virtue of their  seeds1
 fruits1 and foliage4 ,neither the      
,thallophytes1 ,bryophytes1 nor         
,pteridophytes1 nor all combined1       
approach the ,spermatophytes in food    

value for the higher types of animal    
life1 and it is doubtful whether  the   
higher evolution of the land animals    
could have taken place without  the     
previous introduction of the seed       
plants4 ,it will be noted in the        
historical narrative that the great     
placental group of mammals came in  and 
deployed with marvelous rapidity1 as    
geological progress goes1 soon  after   
the ,spermatophytes became the dominant 
form of vegetation4    ,plant life      
terrestrial rather than marine4--,it is 
to be noticed that  the chief           
development of all the great groups of  
plants took place  on the land1 or in   
the land-waters1 rather than in the sea4
 ,this is  preeminently true of the     
higher types1 and appears also to be    
true of  even the ,thallophytes1        
although the number of individual alg   
and their  total mass is very much      
greater in the sea than on the land and 
in the  land-waters4 ,but the           
fresh-water alg appear to possess in a  

higher  degree than the marine forms    
those plastic and germinal characters   
from which new forms spring1 and are    
probably to be regarded as the  parental
 type4 ,these are facts to be pondered  
on1 since it has been  the current      
opinion of geologists that life arose in
 the sea and was  propagated thence to  
the land4 ,the alternative view that    
life developed  primarily on the land   
and in the land-waters and migrated to  
the sea is  not1 however1 without its   
support in the plant world1 as we thus  
see1  and the plant world was the       
primitive one2 the dependent animal     
world  necessarily followed its         
development4 ,the hypothesis of a       
terrestrial  origin of life throws a    
very suggestive cross-light on many     
geological  problems1 as will be seen   
later1 and it may well be entertained as
 an  alternative working hypothesis     
until the facts are more fully          
developed4                  ,b4         
,contributions of the ,animal           

,kingdom4#bif    ,as already noted1     
animal life is dependent on the         
decomposition of  matter organized by   
green plants1 and the conversion of its 
potential  energy into active forms4    
,animals are1 therefore1 dynamic rather 
than  constructive agencies4            
,nevertheless they transform organic    
vegetal  matter into organic animal     
matter1 and this is sometimes really an 
advance in organization4 ,the organized 
animal matter is subject to             
preservation in some small degree1      
though it usually perishes4 ,some       
contribution is1 therefore1 made to the 
organic deposits1 chiefly in  the form  
of hydrocarbons4 ,it is the view of some
 geologists that the  natural oils and  
gases have an animal origin in the main4
             ,,reference ,,table ,,of   
,,the ,,principal ,,groups ,,of         
,,animals4#big    ,protozoa             
,rhizopoda   ,foraminifera4    7,the    
simplest                                
,radiolaria4      animals7              

,flagellata                             
,infusoria   ,unknown in fossil state4  
,gregarina      ,clenterata    ,porifera
    ,spongi     ,calcareous sponges4    
7,sponges1                              
,silicious sponges4     corals1         
,cnidaria    ,anthozoa1 coral polyps4   
jellyfishes7              ,hydrozoa1    
hydroids and medus4    ,echinodermata   
,pelmatozoa  ,cystoidea1 cystids4       
7,crinoids1                 ,crinoidea1 
stone lilies4     starfishes1           
,blastoidea1 blastids4     sea-urchins7 
,asterozoa   ,ophiuroidea1 brittle-stars
                                        
,asteroidea1 starfishes4                
,echinozoa   ,echinoidea1 sea-urchins4  
,holothuroidea1 sea-cucumbers4          
,vermes                                 
,platyhelminthes     7,worms7           
,rotifera                               
,nemathelminthes  ,rare as fossils4     
,gephyrea                               
,annelida1 sea-worms4    ,molluscoidea  
,bryozoa1 sea-mosses4    7,mollusc-like 

forms7        ,brachiopoda1 lamp-shells4
    ,mollusca                           
,pelecypoda1 lamellibranchs1 bivalves4  
7,molluscs7                             
,scaphopoda1 tusk-shells4               
,amphineura1 chiton4                    
,gastropoda1 univalves1 snails1 etc4    
,cephalopoda1 nautilus1 cuttlefish4     
,arthropoda     ,branchiata  ,crustacea4
    7,the                               
,trilobita1 trilobites4     articulates7
                ,gigantostraca1         
horse-shoe crabs4                       
,entomostraca1 ostracoids1 barnacles4   
,malacostraca1 lobsters1 crabs4         
,tracheata   ,myriapoda1 centipedes4    
,arachnoidea1 spiders1 scorpions4       
,insecta1 insects4                      
,cyclostomata1 lampreys4                
,pisces      ,selachii1 sharks4         
7fishes7  ,holocephali1 spook-fishes4   
,dipnoi1 lung-fishes4                   
,teleostomi1 ganoids and teleosus4      
7common fishes74  ,vertebrata           
,amphibia1 amphibians1 batrachians4     

,reptilia1 reptiles4                    
,aves1 birds4                           
,mammalia    ,prototheria1 monotremes4  
7mammals7 ,metatheria1 marsupials4      
,eutheria1 placentals4    ,as dynamic   
organisms animals have need for         
supporting- and  working-frames1 for    
protective covering or housing1 and for 
offensive  and defensive weapons1 and   
these have been constructed chiefly out 
of  inorganic matter1 and subordinately 
of indurated organic matter4 ,it is     
through these that animals have made    
their chief contribution to the         
material of the geologic record4        
,skeletons and other hard parts to give 
internal stiffness or firmness2 shells1 
plates1 indurated integuments1  and     
various other forms of external         
protection2 teeth1 spines1 horns1  and  
other means of gathering and masticating
 food1 and of attack and  defense1      
contribute material to the deposits1 and
 form a record of the  life activities  
and of the physiographic environment4   

,all of the eight  groups of animals1   
viz4 ,protozoa1 ,clenterata1            
,echinodermata1 ,vermes1  ,molluscoidea1
 ,mollusca1 ,arthropoda1 and            
,vertebrata1 have left some  record1 but
 it is in all cases a very imperfect    
one4    ,the contribution of the        
,protozoa4--,the ,protozoa are related  
to the  animal kingdom much as the      
,thallophytes are to the vegetable1 and 
the two bear a close structural         
resemblance to one another4 ,so near1   
indeed1 do the ,protozoa and the        
,thallophytes approach one another in   
their minuteness and simplicity1 that   
the place of not a few organisms  is in 
doubt1 and the two kingdoms1 in general 
so different1 seem here  to blend in the
 group ,flagellata4 ,the ,protozoa are  
usually very minute  one-celled         
organisms with very little              
differentiation of tissue or  organs4   
,of the four classes of ,protozoa1 only 
one1 the ,rhizopoda1 is  found in the   
fossil state4 ,the rhizopods secrete    

silicious skeletons1  and calcareous1   
silicious1 and chitinous tests of a     
great variety of  forms1 and this gives 
them geologic importance4 ,the deep-sea 
oozes and  the chalk deposits are their 
best-known contributions at present4    
,they  have probably played a more      
important rle in the formation of       
ordinary  limestones and silicious silts
 than can be demonstrated1 because of   
the  delicacy of their relics and the   
ease with which these are pulverized  by
 wave-action in the shallow seas1 or    
changed by recrystallization  or by     
concretionary aggregation4 ,the         
globigerina oozes are formed  largely   
from the calcareous shells of           
,foraminifera 7,fig4 #cea71 one  of the 
orders of rhizopods1 among which the    
genus ,globigerina is a  leading form4  
,those forms which make the deep-sea    
oozes live1 not on  the bottom1 but near
 the surface of the open sea1 and on the
 death of  the organisms1 the shells1   
tests1 and skeletons sink to the bottom4

  ,chalk is formed in a similar way from
 calcareous ,foraminifera1 but not      
necessarily in very deep water4         
,foraminifera live in shallow water as  
well as in the open sea1 and in this    
case they sometimes creep on the  bottom
 or are attached to alg1 but their      
deposits in shallow water are  usually  
much obscured by other kinds of         
deposition and by destructive  action4  
,some of the foraminiferal shells are   
divided into chambers and  assume       
various spiral forms1 of which the      
,nummulites1 named from  their          
resemblance to coins1 are notable       
examples4 ,these formed an  important   
part of the nummulitic limestone of the 
,eocene period4    ,the radiolarian ooze
 is characterized by the silicious tests
 of various  members of the             
silica-bearing order1 ,radiolaria4 ,the 
8,barbadoes earth0  and 8,tripoli0 are  
notable deposits of fossil radiolarians4
    ,the contribution of the            
,clenterata4--,the ,clenterata embrace  

the  sponges1 the coral polyps          
7,anthozoa71 and the hydroids and medus 
7,hydrozoa74 ,the contribution of coral 
polyps to the formation of  limestone is
 most important1 and is too familiar to 
require elaboration  here4 ,the corals  
range throughout nearly the whole       
fossiliferous  series1 and their        
development will be followed and        
illustrated in the  historical chapters4
    ,the sponges are widely represented 
by their spicules1 and not  uncommonly  
their aggregate form is preserved even  
in very ancient  strata4 ,their         
contribution is largely silicious1 but  
is partly  calcareous4 ,the hydroids and
 medus have left little trace of        
themselves in the rocks1 although       
impressions supposed to represent  medus
 are found in strata as early as the    
,cambrian4 ,certain coral-like  forms1  
as the ,millepores1 ,tubularia1 and     
,stromatopora1 are classed as           
,hydrozoa4 ,the graptolites1 delicate   
leaf-like floating forms1 very          

serviceable in marking exact horizons on
 different continents because  of their 
free distribution1 are also classed     
here4    ,the contribution of the       
,echinodermata4--,under the echinoderms 
are  grouped the crinoids 7sea-lilies71 
cystoids1 blastoids1 ophiuroids         
7brittle stars71 asteroids 7starfishes71
 echinoids 7sea-urchins71  and          
holothuroids 7sea-cucumbers74 ,this is  
one of the marked groups  of ancient as 
well as modern life1 and its beautiful  
fossils grace  every period in which    
life relics are well preserved4 ,the    
cystoids and  crinoids1 and later the   
blastoids1 were prominent in the        
,paleozoic  ages1 while the remaining   
forms were more conspicuous later1      
though  early introduced4 ,all          
divisions1 except the holothuroids1     
whose  softness prevented1 have left a  
good record1 as fossil records go4      
,their relics are chiefly calcareous1   
and they most abound in the  limestones1
 some of which are largely made up of   

their remains1 as the  encrinital       
limestone 7,fig4 #cdi74 ,they will be   
subjects of frequent  comment and       
illustration in the historical chapters4
    ,the contribution of the            
,vermes4--,most of the worms are ill    
adapted to  fossilization and are not   
known in the fossil form4 ,the segmental
 worms  of the sea1 the annelids1       
however1 left some traces of themselves 
in  tubes and borings and in tracks and 
sometimes by fossil jaws and teeth4     
,they range from the earliest           
fossil-marked horizons onward1 but seem 
to  have always been an inferior group4 
,the contribution of the                
,molluscoidea4--,this group includes the
  bryozoans1 whose fossil products      
closely resemble the minute-celled      
corals1 and the brachiopods1 whose      
shells closely resemble those of  the   
molluscs4 ,both are calcareous and make 
important contributions  to the         
formation of limestone 7,fig4 #cej74 ,a 
few brachiopods secrete  calcium        

phosphate instead of calcium carbonate4 
,both classes have a  great geologic    
range and their fossils are valuable    
aids in identifying  and correlating    
formations4 ,probably the brachiopods   
are more utilized  for this purpose than
 any other single class4 ,they are the  
symbol of  conservatism and persistence1
 ranging from the ,cambrian to the      
present  time1 and embracing some forms 
that have scarcely changed to the extent
  of generic difference in that time4   
,the contribution of the                
,mollusca4--,the molluscs have also     
ranged from  the earliest well-recorded 
times1 and some divisions1 as the       
pelecypods  7lamellibranchs1 embracing  
clams1 oysters1 etc47 and gastropods    
7snails1 etc471 have undergone no very  
marked change beyond a rather  ample and
 progressive development2 but others1 as
 the cephalopods  7nautilus1 squids1    
cuttlefish1 etc471 mark out the progress
 of the ages  by distinct and striking  
changes of form4 ,their shells are      

chiefly  calcareous and they have       
contributed materially to the formation 
of  limestone4 ,muddy and sandy bottoms 
are1 however1 more congenial to the     
pelecypods and gastropods than to the   
corals1 crinoids1 and many other        
limestone-forming types1 and hence      
fossils of these molluscs frequently    
abound in shales and sandstones and give
 them a calcareous element4 ,in         
sandstones1 however1 the calcareous     
matter is often dissolved out and  only 
the casts of the shells remain4 ,the    
molluscs will be much cited  and        
illustrated in the historical chapters4 
,the contribution of the                
,arthropoda4--,this group embraces the  
crustaceans1 myriopods1 spiders1 and    
insects4 ,the hard parts of their       
bodies are mainly horny or chitinous    
forms of organic matter1 and hence      
their relics differ notably from the    
inorganic calcareous and silicious      
remains of most of the preceding forms4 
,the ,arthropoda did not at  any time   

form a notable stratum of rock4 ,their  
geologic value lies  chiefly in what    
they teach of the progress of life and  
its relations1  and the aid they render 
in correlation and identification4 ,in  
these  respects the group is a notable  
one4 ,it was represented in the early   
fossiliferous strata by the trilobites1 
one of the most interesting of  all     
types of fossils4 ,these were probably  
the most highly developed  organisms of 
their times and give the clearest hints 
of the stage of  psychological and      
sociological development that had been  
reached when  first the record of life  
is opened to us4 ,the record of the     
myriopods1  spiders1 and insects dates  
from the middle ,paleozoic1 and gives   
the  first clear hints of animal life on
 the land4    ,the contribution of the  
,vertebrata4--,in the vertebrates the   
dynamic or  working organism may be said
 to reach its highest expression1 unless
  it be in the flying insects1 and their
 inorganic residue becomes  relatively  

unimportant in rock formation4 ,although
 the greatest of all  animal types in   
most respects1 it has never formed more 
than trivial  beds of rocks4 ,there are 
occasional 8bone beds10 but they are    
thin and  limited in extent1 and only   
partially formed of vertebrate matter4  
,the  geological importance of the      
vertebrates lies in the higher field of 
life evolution and in its mental        
accompaniment4 ,fishes excepted1 the    
vertebrates are mainly land types1 and  
have for their chief colleagues  plants 
and insects4 ,the other groups of       
animals are mainly1 though not  wholly1 
marine4 ,the vertebrates have little    
place in the ,paleozoic  record1 except 
near its close1 but they dominate the   
,mesozoic and  ,cenozoic eras1 and are  
conspicuously the master type to day4   
,,iii4 ,,the ,,associations ,,and       
,,ecological ,,relations ,,of ,,life4   
,a4 ,the ,basis of ,floras and ,faunas4 
,geologic interest is not confined to   
the kinds of plants and animals  that   

have lived and the contributions they   
have made to the deposits1  but embraces
 also their assemblage into floras and  
faunas1 and the  relations of these     
assemblages to the prevailing           
physiographic  features4 ,these         
assemblages and relationships are among 
the most  suggestive factors of the     
earth's evolution1 and are the most     
instructive for purposes of comparison  
with human history1 and for  forecasting
 the future of man and of the whole     
biological kingdom4  ,moreover1 floras  
and faunas1 as such1 are used in the    
correlation  of formations1 and in this 
application they give surer results than
  correlations by individual species4 ,a
 particular species may live  far beyond
 the usual period of a species1 and if  
fossilized in one  region in its early  
history and in another in its late      
history1 the  two formations might be   
referred erroneously to the same stage4 
,this  is far less likely to happen with
 a whole assemblage of forms4 ,there  is

 a similar liability to error in        
interpreting migrations on the  basis of
 a single or a few species1 for a single
 species or a few  species may be       
transported by unusual or accidental    
means1 so to speak1  when there is no   
normal pathway for general migration1   
and when no  systematic migration takes 
place4 ,in most of the great questions  
that  arise concerning the connections  
and disseverances of the continents1    
and concerning the unions and           
separations of the oceans1 which are the
  fundamental causes of the migrations  
and of the isolations of plants  and    
animals1 typical floras and faunas are  
to be studied1 rather than  isolated    
species or sporadic forms4 ,a brief     
sketch of the leading  causes and       
consequences of these special           
assemblages of plants and  animals may  
aid in appreciating the underlying      
significance of floras  and faunas1 and 
in interpreting their meaning as they   
are met in the  study of the strata4 ,a 

part of these grow out of the relations 
of  the organisms to one another1 and a 
part out of the relations of the        
organisms to their environment4         
7#a7 ,assemblages ,influenced by the    
,mutual ,relations of ,organisms4    7a7
 ,food relations4--,the relations of    
food-supply are among the most  obvious 
reasons for assemblages4 ,as animals are
 dependent directly  or indirectly on   
plants for their food1 they must gather 
where the  plants grow1 or in the       
currents in which the plant products are
 borne4  ,whatever determines an        
assemblage of plants also causes1 or at 
least  invites1 an assemblage of        
animals4 ,whatever causes an assemblage 
of  particular plants1 invites an       
assemblage of the particular animals    
that use these plants4 ,animals that    
feed on plants are in turn preyed  upon 
by other animals1 and these in turn by  
others4 ,a whole train of  organisms    
may1 therefore1 be gathered into a      
region by the conditions  that foster a 

certain kind of vegetation there4 ,in   
interpreting the  physical significance 
of such a train1 it is obvious that the 
head of  the train carries the          
fundamental meaning4 ,the dependent     
creatures  that follow the primary forms
 may be only incidentally1 and perhaps  
very slightly1 adapted to the physical  
environment4    7b7 ,adaptive           
relations4--,organisms depending on     
other organisms  for food or other      
necessary conditions of life1 present   
many forms  of adaptation the better to 
secure their food and to use it4 ,these 
adaptations are the consequences and the
 signs of the assemblage1 and  are of   
the greatest service in interpreting the
 place and significance  of the         
organisms in the assemblage4 ,teeth     
usually reveal the food  of their       
possessors1 and hence teeth are among   
the most significant  of fossils4       
,fortunately their functions require    
them to be hard and  durable1 and hence 
well suited to fossilization4 ,the      

growth of low  plants into trees forced 
a notable series of adaptations in the  
animals  that fed upon them in the      
matter of height1 of reaching members1  
of  climbing1 and probably at length of 
parachuting and flying4 ,in these  and  
similar ways the floras and faunas took 
on special phases because  of the mutual
 relations of their members4    7c7     
,competitive relations4--,the assembling
 of plants and animals1  with their     
prodigious possibilities of             
multiplication1 brought  competition1   
and with it a struggle for food which   
often became a  struggle for existence1 
and out of this grew innumerable        
modifications  of form and habit4 ,these
 have become so familiar since the great
  awakening caused by the doctrines of  
,darwin and ,wallace that they need  no 
elaboration here4    7d7 ,offensive and 
defensive relations4--,within limits1   
plants are  benefited by the feeding of 
animals and respond by developing seeds 
and  fruits that especially invite such 

action1 their compensation being  found 
in planting and distribution4 ,it is    
obvious that1 on the whole1  the        
continued growth of plants is largely   
dependent on the renewal of a  supply of
 carbon dioxide through the agency of   
animals and some plants1  bacteria in   
particular4 ,otherwise the supply would 
become so reduced as  to greatly limit  
plant life4 ,it has been estimated#bih  
that the whole  of the present supply of
 carbon dioxide would be consumed by    
plants in  one hundred years if the     
consumption continued at the present    
rate and  no carbon dioxide was         
returned4 ,it is now well known that the
 so-called  decay by which carbon       
dioxide is freed is due more to         
microscopic  organisms than to inorganic
 processes4 ,it seems clear1 therefore1 
that  the continued activity of plants  
is largely due to their consumption  by 
animals and other plants4 ,but still1   
though the larger good of  plants is    
conserved by the predaceous action of   

animals1 and of certain  parasitic and  
saprophytic plants1 their individual    
preservation  is often conserved by     
defensive devices1 such as thorns1      
poisons1  bitter compounds1 etc4 ,this  
is notably true in desert regions where 
the conditions are hard and the total   
extinction of plants would be           
threatened if animals were permitted to 
feed freely upon them4 ,within  the     
animal world1 the preying of one form   
upon another is the main  source of that
 great struggle for existence which has 
characterized  the whole known history  
of life1 and has been one of the        
influential  factors in shaping the     
evolution of life and in modifying the  
special  aspects assumed by the floras  
and faunas of each period4    ,implied  
forms of life4--,the full meaning of the
 fossils of any period  can only be     
gathered by duly considering these      
relationships in their  interpretation4 
,the existence of animals implies the   
existence of  plants in supporting      

abundance1 whether the record contains  
their  relics or not2 an animal with a  
protective covering implies an enemy2  a
 tooth of a specific kind implies the   
appropriate class of food1  etc4 ,while 
inferences of this kind are subject to  
error1 they are at  present the only    
means by which the faunas and floras of 
most ages  can be rounded out into a    
rational assemblage of organisms1 that  
is1  an assemblage that affords the     
necessary food for its members and  an  
adequate function for the offensive and 
defensive devices which  its members    
present4 ,only a small part of the life 
that lived was  fossilized1 and only a  
small part of the fossils actually      
carried  in the strata have been        
collected1 because only a small part of 
the  strata are exposed at the surface4 
,the direct record now accessible  is1  
therefore1 very incomplete and hence the
 need--and in the need the  excuse--for 
adding the forms that are implied by the
 character of the  known fossils4       

7#b7 ,assemblages ,influenced by        
,environment4    ,it has been noted that
 some animals depend for existence on   
other  animals2 that ultimately all     
animals depend on plants1 and that green
  plants alone can make food directly   
from inorganic material4 ,green  plants1
 therefore1 head the train of           
dependencies1 and their relations  to   
the physical conditions that surround   
them are the primal relations4    ,plant
 societies4#bii--,the control of        
physical conditions has been  sufficient
 to develop special associations or     
societies of plants by  fostering those 
adapted to these conditions and         
eliminating those  that are not4 ,among 
these are 7#a7 the hydrophytes 78water  
plants071  embracing those that grow in 
water or in very wet situations2 7#b7   
xerophytes 78drought plants071 embracing
 the opposite class1 which are  adapted 
to very dry situations2 7#c7 mesophytes1
 including those suited  to conditions  
lying between these extremes1 the great 

middle class to  which the prevailing   
upland vegetation belongs2 and 7#d7 the 
halophytes  78salt plants071 which are  
dependent on the presence of certain    
salts1  and embrace such plants as are  
found on the seacoast1 around salt      
springs1 on alkaline flats1 etc4 ,the   
characters which distinguish the        
xerophytes from the hydrophytes and     
mesophytes have special geological      
interest1 as they aid in determining the
 climatic conditions1 a feature  whose  
interest increases as the variability of
 the ancient climates is  more fully    
recognized4    ,within these greater    
groups there are special minor          
associations  determined by soil1       
temperature1 topography1 subjacent      
strata1 and  by the relations of the    
plants to one another4#cjj ,these       
natural  groups are valuable indications
 of the agricultural capabilities of    
the districts occupied by them4 ,they   
may be regarded as the outcome of       
,nature's experiments in crop-raising1  

running consecutively through  thousands
 of years4 ,they are natural            
correlations of compatible members  into
 communities of plants4 ,some members of
 the society are obviously  dependent on
 others1 as certain forms of undergrowth
 on the shadowing  of the upper growth1 
as of vines upon supporting-trees1 etc4 
,there is  probably a more occult       
relation in some cases1 the effects of  
certain  plants on the soil being       
sometimes advantageous to other plants1 
and  sometimes harmful1 as illustrated  
in the conditions that require a        
rotation of crops4    ,the chief point  
of geologic interest lies in the fact   
that floras  are not mere miscellaneous 
mixtures of plants that happen to live  
in a given area at a given period1 but  
are organized communities1  in a more or
 less definite sense4 ,they therefore   
imply more or less  definitely the      
physical conditions which are congenial 
to them1 and  thus furnish the basis for
 interpreting such conditions in the    

past1 so  far as the floras are well    
preserved4 ,the faunas1 especially the  
land  faunas1 being primarily dependent 
on the floras1 furnish a basis for      
interpretations of like import4         
,b4 ,the ,influence of ,geographic      
,conditions on the ,evolution of        
,floras and ,faunas4    ,the geographic 
features of the earth impose on         
organisms a complex  series of          
influences which modify the evolution of
 life and produce  faunal and floral    
variation on a large scale4 ,the larger 
assemblages of  life1 which inhabit a   
continent or dwell in a great sea1 are  
designated  faunas and floras1 as well  
as the smaller assemblages just         
discussed1  but obviously in a broader  
and in a different sense4 ,the          
disseverance  of the land by the sea1 or
 of the sea by the land1 isolates the   
life  and forces independent            
development4 ,the introduction of cold  
zones1  desert tracts1 or other potent  
climatic belts has somewhat the same    

effect4 ,so1 measurably1 does the       
raising of a mountain range or a        
plateau1 or the sinking of critical     
portions of the sea-bottom4    ,the     
development of provincial and           
cosmopolitan faunas4#cja--;,if a  region
 is isolated from other regions by the  
cutting off of all ready  means of      
intermigration1 as by the formation of  
an island from what  had been a         
peninsula1 or of an inland sea from what
 had been a bay1  the flora and fauna   
are developed by themselves without much
 influx of  other forms1 and hence      
become local or provincial4 ,this is    
usually more  marked in the case of the 
fauna than of the flora1 because the    
latter  has more ample means of         
dispersion1 on the whole1 and so the    
fauna may  for convenience be taken as  
the type4 ,a good illustration is the   
native  fauna of ,australia which was   
once connected with ,asia1 but has long 
been separated from it4 ,previous to    
importations by man1 this continent  had

 a very peculiar and distinct fauna1    
descended from its ,mesozoic            
inhabitants4 ,most of the isolated      
islands have peculiar faunas1 but in    
many cases they were isolated from the  
beginning1 having been built up  by     
volcanic action from the bottom of the  
sea1 and their faunas are  due to the   
accidents of transportation and to the  
development of these  sporadic forms in 
isolation4#cjb    ,it is evident that   
whenever any geographic change          
introduces a  barrier to migration1 the 
faunas of the dissevered portions will1 
in  all probability1 develop along      
different lines1 and will diverge into  
provincial faunas4 ,on the other hand1  
any geographic change that unites  areas
 and leads to intermigration1 tends to a
 community of fauna or to               
cosmopolitanism4 ,these tendencies have 
been markedly felt all through  the     
geologic ages1 and constitute one of the
 most vital features of  their history4 
,when continents are connected1 their   

faunas intermingle  and the exchange    
gives rise to common forms4 ,they tend  
to blend into  one great fauna except so
 far as the local differences develop   
those  minor assemblages previously     
discussed4 ,when continents are         
separated1  they tend to develop        
peculiar faunas1 as do islands1 but on a
 larger  scale4 ,this is very obvious in
 the case of the land life1 but needs   
more special statement for the oceans4  
,the oceans constitute a single body of 
water with ample connections and        
stirred by a system of constant         
circulation4 ,probably this has been    
true for most of known geologic time4 ,a
 single cosmopolitan fauna of  the      
largest type might be expected4 ,this is
 in a measure realized in  the pelagic  
fauna of the open ocean1 though this is 
somewhat modified  by the climatic      
zones4 ,but the marine faunas that are  
fossilized in  the known strata1 and    
have most geologic interest1 are1 with  
rare  exceptions1 not those of the open 

ocean1 but those of the shore zones  and
 of the shallow seas4 ,now1 although    
these shore belts and shallow  seas are 
broadly connected with the great ocean  
body1 and are usually  regarded as a    
part of it1 they are singularly         
separated from it1  or rather they are  
singularly separated by it1 so far as   
the life  dependent on shallow-water    
conditions is concerned4 ,to this life1 
the  deep sea is a barrier not quite as 
effective as the land1 but still a      
barrier4 ,the key to this important fact
 may be found in a consideration  of the
 vertical distribution of life4    ,the 
great horizon of life is at or near the 
contact zone of the  atmosphere with the
 hydrosphere and lithosphere4 ,life     
declines with  increasing altitude1     
partly because of the lowering          
temperature1  and partly because of the 
increasing tenuity of the atmosphere4   
,the successive changes of plant and    
animal life with the ascent of          
mountains and plateaus is familiar4     

,life declines in descent into the  sea 
chiefly from lack of light1 and         
secondarily from the lowering of        
temperature4 ,light is essential to the 
formation of chlorophyll and1  through  
it1 of all other organic compounds4 ,the
 chlorophyll-forming  plants are1       
therefore1 limited to such depths as are
 penetrated by the  rays necessary for  
the photosynthesis of organic matter4   
,vision is cut  off within #bjj to #cjj 
feet1 and most plant growth takes place 
above  that depth4 ,photographic effects
 become feeble or inappreciable at #ajjj
  to #abjj feet4#cjc ,the photosynthesis
 of plants is chiefly aided by the      
lower and middle part of the spectrum1  
while the ordinary photographic  work is
 chiefly done by the upper end1 so that 
the photographic limit  is below the    
photosynthetic limit4 ,microscopic      
plants are sometimes  found lower than  
these limits1 but they may have been    
carried below  their working limits by  
currents or other incidental agencies4  

,for  all general purposes1 the limiting
 depth of living carbon-compounding     
plants may be set at #ajj fathoms1 as a 
generous figure--about the  average     
depth of the border of the continental  
shelf--while the vast  majority flourish
 only in the upper third of this depth4 
,life does not cease here1 for the      
products of this surface-life sink  to  
greater depths and are fed upon by forms
 of sea animals that have  become       
adapted to the dark and cold abyss of   
the ocean4 ,obviously1  these deep-sea  
forms are a very distinct type of life1 
and constitute a  fauna of the most     
pronounced kind1 the abysmal fauna4     
,another distinct  fauna occupies the   
open-ocean surface1 the pelagic fauna4  
,still a  third fauna occupies the      
shallow-water tract1 whose bottom lies  
within  the light zone--the photobathic 
zone--and embraces the animals that  are
 dependent on the plants of this zone1  
or on its light and warmth1  and that   
are more or less fixed to the bottom or 

confined to the zone  because their food
 is there4    ,the physical plane of    
demarkation between the surface or      
pelagic fauna  and the abysmal fauna is 
much more distinct and more fundamental 
than  any that is found in ascending    
above the surface of the sea4 ,the      
habitat of the shallow-water fauna is   
limited below by the darkness1  limited 
above by the water-surface1 limited at  
one side by the land1  and limited on   
the other side by the deep sea4 ,it is  
hemmed in  vertically between two planes
 only a few hundred feet apart4         
,laterally1  it is confined to a narrow 
belt about the borders of the continents
 and  to the more or less land-girt     
epicontinental seas4 ,its vertical      
limits  are fixed1 but its lateral      
extent varies with the relations of the 
sea  to the surface of the continental  
platforms4    ,this variation profoundly
 affects the development of the fauna4  
,when a  major deformation of the earth 
takes place which increases the capacity

  of the oceanic basins1 the water is   
drawn down into them more fully1  and   
correspondingly retreats from the       
continental shelf4 ,the shore is  thus  
carried out toward or to the border of  
the shelf1 or even perhaps  down to some
 line on the abysmal slope4 ,in either  
case1 the zone of  shallow water suited 
to the photobathic life is narrowed1 and
 at points  it may be practically cut in
 two4 ,there are1 however1 shelves and  
tracts that were below the light zone   
before1 which now are brought  within it
 by the lowering of the sea-level4 ,into
 these1 as into harbors  of refuge1 the 
life migrates so far as it may4 ,but    
these tracts are  less prevalent and    
continuous than the typical continental 
shelf1 and  under the conditions        
supposed they would be but imperfectly  
connected  with each other by available 
shallow-water tracts4 7,the steep       
shelving  shore tracts1 although        
furnishing a shallow-water connection   
possibly  available for some species1   

would be unsuited to others and1 under  
certain conditions of the sea-currents1 
would be an effective barrier47  ,to    
these limited tracts1 therefore1 the    
life of the photobathic type  is        
restricted and measurably isolated1 and 
develops into local and  provincial     
faunas4    ,after a deforming movement  
has ceased1 the seashore habitually     
advances1 developing a new continental  
shelf1 and in time new  epicontinental  
gulfs and seas4 ,in this it is assisted 
by the erosion  of the continent and the
 filling of the sea1 and probably by the
 slow  settling of the continents4 ,as  
the sea-shelf broadens1 the isolated    
tracts1 the harbors of refuge1 become   
connected1 and migration is             
facilitated4 ,when the connection       
becomes general and broad1 and when     
epicontinental seas have formed         
available tracts across the face of the 
continents1 a general commingling of    
faunas follows1 and a cosmopolitan      
fauna results4    ,in the same way1 but 

more obviously1 when the land is        
extended and  connection between the    
continents becomes general1 there is    
migration  and commingling of the land  
faunas and floras1 and cosmopolitan     
communities are the result4    ,it is   
obvious that the development on the land
 is the reciprocal of  that in the sea4 
,when the seas are extended and their   
life is tending  toward cosmopolitanism1
 the lands are dissevered1 and their    
life is  tending toward provincialism1  
and vice versa4 ,when1 however1 the land
  is greatly extended1 it is usually    
accentuated by mountain ranges1  and    
other products of the deformation which 
extended it1 and these  form barriers4  
,desert wastes and other inhospitable   
tracts1 and even  glaciation1 are liable
 to develop as secondary consequences1  
and to  interpose barriers1 and hence   
the cosmopolitanism of the land-life is 
liable to be less complete than that of 
the sea-life4    ,restrictive and       
expansional evolution4--,it is obvious  

from the last  discussion that if the   
picture of the earth's movement above   
drawn  be true1 the areas available for 
particular classes of life may vary     
greatly from age to age4 ,at times the  
shallow-water sea-life may be  forced to
 retreat into a very narrow tract on the
 border of the land1  and into chance   
expansions here and there4 ,in being    
crowded into this  limited tract1       
perhaps also less adapted for a habitat 
on account of  the change1 the life is  
subjected to severe competition and to  
hard  conditions1 and must experience in
 an intensified degree the effects  of  
the struggle for existence4 ,whatever of
 evolutionary potency there  may be in  
such a struggle under such restrictive  
conditions should be  revealed in the   
modifications of the fauna that ensued4 
,on the other hand1 when the shallow    
seas are generally extending  themselves
 upon the land and the land is being    
base-leveled1 and  thus adapted to      
shallow submergence1 the shallow-water  

life enjoys  an enlarging realm1 and    
should reveal the effects of evolution  
under  expansional conditions4 ,in      
affording a comparison between these    
opposite and alternating phases of      
restrictional and expansional           
evolution1 geology makes one of its     
great contributions to the external     
causes and conditions of organic        
evolution4 ,these will come under       
repeated consideration in the historical
 chapters4                              
,,index4                                
,,volume ,i4        ,abbot1 ,m4 ,l4 7and
 ,humphreys1 ,a4 ,a471 #ajf1 #bjb       
,abrasion1      by ice1 #bha      by    
streams1 #aai      by waves1 #cdb       
by wind1 #ch      ,abysmal fauna1 #fga  
,abysmal sea1 #cbf      ,accretion      
hypothesis1      internal temperature   
on1 #efd1 #efg      recombination of    
material on1 #efh      ,actinolite1     
#ddg1 #dfj      ,adams1 ,f4 ,d41 #dgd   
,adjustment of streams1      structural1
 #adf1 #aej      topographic1 #afb1     

#afc1 #aig      ,adobe1 #dfg            
,agassiz1 #cff1 #fjd      ,agassiz1 ,l41
 #cba1 #cbb1 #cbc1 #cff      ,agate1    
#dfj      ,agate structure1 #dcf        
,agglomerate1 #dcd1 #dfg                
,aggradation1      by ice1 #bih      by 
streams1 #b1 #agg      by wind1 #be     
in sea1 #ccc1 #cee      ,aggrading      
streams1 characteristics1 #agi1 #ahg    
,airy1 ,sir ,g41 #cda      ,alabaster1  
#dfj      ,albite1 #djj1 #dfj           
,alferric rocks1 #ded      ,alg1        
geologic contribution of1 #fec          
influence on precipitation1 #bbe        
,alkalicalcic rocks1 #deh      ,alluvial
 cone1 #aha-c      growth1 #aha         
levees1 #ahb      ,alluvial deposits1   
#agg-if      ,alluvial fans1 #aha-c     
,alluvial plains1 #aha1 #ahd-if         
material of1 #aif      origin of1 #ahd1 
#ahe      piedmont1 #ahc      topography
 of1 #aif      ,alluviation1 #aha1 #aif1
 #dfg      ill-defined1 #ahc            
,alpine glaciers1 #bea      ,alps1      
crustal shortening involved in formation

 of1 #edi1 #egf      structure1 #ejd1   
#ejg      ,amber1 #fdf      ,amethyst1  
#dfj      ,amphibole1 #dfj              
,amphiboles1 #djj      ,amygdaloid1     
#daa1 #dfg      ,analcite1 #dfj         
,analyses1      ,american river-waters1 
#ajg      ,american spring-waters1 #bce 
rain-waters1 #ajg      river-waters1    
#ajf1 #ajg1 #ajh      sea-water1 #cbd   
waters of enclosed lakes1 #cib          
,anamorphism1 #ddf      ,andalusite1    
#dfj      ,andes1 snow-line in1 #bdf    
,andesine1 #djj1 #dfj      ,andesite1   
#dfg      ,angiosperms1 #feg            
,anhydrite1 #dfj      ,animal kingdom1  
geologic contribution of1 #feh-fc       
synopsis of1 #fei      ,anorthite1 #dfj 
,anorthosite1 #dfg      ,antarctica1    
snow-line in1 #bdf      ,antecedent     
streams1 #afi1 #agc      ,anthracite1   
#dbf1 #dfj      ,anticlinal valleys1    
#aei      ,anticline1 #ejd              
plunging1 #aee1 #aeg1 #ejf              
,anticlinoria1 #ejd      ,antimony1 #dfj
      ,apatite1 #dfj      ,aphanite1    

#dea1 #deb1 #dfg      ,aplite1 #dae     
,appalachian ,riser1 #agc               
,appalachians1      crustal shortening  
due to folding1 #edi      extent of     
piracy in1 #afi      peculiarities of   
drainage1 #afi      rejuvenation of     
streams in1 #afe      stream adjustment 
in1 #adg      ,aqueous rocks1 #dfg      
,aragonite1 #dfj      ,archean complex1 
#ah      ,arch of earth's crust1        
strength of1 #ehb      ,archeozoic era1 
#ai      ,arenaceous rocks1 #dfh        
,arid regions1 erosion in1 #aca         
,argillite1 #ddh1 #dfh      ,arkose1    
#dbb1 #dfh1 #fde      ,artesian wells1  
#bdb      ,arthropoda1 geologic         
contribution of1 #ffb      ,asiderites1 
#e      ,asphaltum1 #dfj                
,asteroids1 #ffa      ,astronomic       
geology1 #a1 #b      ,atlantic coastal  
plain1 #ehg      ,atmosphere1 #e        
affected by life1 #fci1 #fdj            
carbonation by1 #dc      chemical work  
of1 #da-dc      evaporation and         
precipitation1 #ej      fluctuations in 

composition1 #fci-dd      geologic      
activity of1 #f1 #ba-dc      mass and   
extent1 #f      mechanical work of1     
#ba-da      oxidation by1 #db           
thermal effects of1 #g      ,atmospheric
 electricity1 #dc1 #eb      ,atmospheric
 precipitation1 amount of1 #ea          
,augite1 #djj1 #dbi1 #dfa               
,augitite1 #dfh      ,autoclastic rock1 
#ddd      ,australia1 fauna of1 #ffh    
,babb1 ,c4 ,c41 #ajg      ,bad-lands1   
#ic1 #acj      ,badger ,mountain1 #bca  
,bain1 ,h4 ,f41 #fg1 #dgd               
,barbadoes earth1 #ffa      ,barite1    
#dfa      ,barrier1 the1 #cef           
,bars1 #aha1 #ceg      ,barus1 ,carl1   
#efb1 #efc      ,basalt1 #dag1 #deb1    
#dfh      ,basaltic columns1 #dag       
,base-level1 #fj1 #fb1 #hb1 #afh        
,cretaceous1 #afi      ,kiltatinny1 #afh
      temporary1 #hd      ,basement     
complex1 #ah      ,batholiths1 #ejj1    
#eib      ,bayou1 #aib      ,bayou      
lakes1 #aic      ,bays1 origin of1 #cca1
 #ccb      ,beach1 the1 #cee            

,beauxite1 #dfa      ,beck1 ,r41 #dgd   
,becker1 ,g4 ,f41 #dgd                  
,bergschrund1 #beh      ,bertin1 #cbc   
,beryl1 #dfa      ,bighorn ,mountains1  
lateral moraines in1 #cjb      ,biotite1
 #djj1 #dfa      ,bischoff1 ,gustav1    
#ajh      ,bismuth1 #dfa                
8,bittern10 #cgg      ,bitumen1 #dfa    
,bituminous coal1 #dbf1 #dfh            
,blake1 ,w4 ,p41 #dgd      ,blanford1   
,w4 ,t41 #bh1 #bjc      ,blood rain1 #be
      ,blue mud1 #chj      ,bone beds1  
#ffc      ,bonneville lake1 #cfj        
,bonneville shore1 #ceb      ,bottom-set
 beds1 #bjb      ,bowlders1 #dfh        
,brachiopods1 geologic contributions of1
 #ffb      ,brahmaputra delta1 #bjc     
,branner1 ,j4 ,c41 #dhi      ,breakers1 
#cda      force of1 #cdd      ,breccia1 
#dbc1 #dcd1 #dfh      ,britannare1 #dei 
,bronzite1 #dfa      ,bryozoans1        
geologic contributions of1 #ffb         
,buckley1 ,e4 ,r41 #dh1 #ej1 #bba       
,buhrstone1 #dfh      ,burton 7and      
,milne1 ,j471 #fcf      ,buttes1 #adb   

,bysmaliths1 #ejj1 #eib                 
,calcareous springs1 #bce               
,calcareous tufa1 #cij      ,calcimiric 
rocks1 #deh      ,calcite1 #dfa         
,calc-sinter1 #dfh      ,calumet and    
,hecla mine1 temperature in1 #efi       
,calvin1 ,s41 #hh1 #bjd1 #cgc1 #chi     
,campbell1 ,m4 ,r41 #afg1 #aga1 #agc    
,camphene1 #fdf      ,cannel coal1 #dfh 
,canoe-shaped valleys1 #aee             
,canyons1 #id-ajj      ,colorado1 #ih1  
#bcc      ,niagara1 #ii                 
,yellowstone1 #ajj      ,carbonation1   
#dc1 #dbi      ,carbon dioxide1         
amount in air1 #e1 #fdj      and        
plant-life1 #ffe      climatic effects  
of1 #fdc      loss of1 #fdj      supply 
of1 #fah1 #fdj      ,cascade1 #bfd      
,cassiterite1 #dfa      ,catlinite1 #dfa
      ,causes of crustal movement1      
#eea-eeg      ,caverns 7see ,caves7     
,caves1 #adc1 #bbg-bca      deposits in1
 #bbh      ,mammoth1 #bbg      sea1 #cej
      ,wyandotte1 #bbg      ,cazin1 ,f4 
,m4 ,f41 #dgd      ,cementation1        

effected through chemical precipitation1
 #bbb1 #bbe1 #bbf      effected through 
evaporation1 #db      ,cephalopods1     
geologic contributions of1 #ffb         
,chalcedony1 #dfa      ,chalk1 #dfh1    
#ffj      ,challenger deep1 #ehg1 #ehh  
,chalybeate springs1 #bce               
,chamberlin1 ,t4 ,c41 #bc1 #bdb1 #bef1  
#cbb1 #dgg1 #efe1 #ffh      ,changes of 
level1 #ecg-eea      caused by          
earthquakes1 #ecf      causes of1       
#eea-eeg      effect on drainage1 #afa  
sea versus land1 #ech      ,changes of  
temperature1      conditions affecting1 
#de      effect on rocks1 #dd1 #di      
internal 7see ,internal temperatures7   
,charleston earthquake1 #ecj            
,chatter marks1 #bhd      ,chemical     
combination1 cause of crustal movement1 
#eef      ,chemical deposits1 #bbb-bf   
in deep sea1 #chc      in lakes1 #cia   
in shallow sea1 #cgd-cgh      ,chemical 
work of atmosphere1 #da-dc              
,chemical work of life1 #fch-df         
,chert1 #dbf1 #dfh      ,chiastolite1   

#dfa      ,chimney rocks1 #cej          
,chlorite1 #dfa      ,chlorite schist1  
#dfh      ,chloritic rock1 #dca         
,chromite1 #dfa      ,chrysolite1 #dfb  
,chrysotile1 #dfb      ,cinder-cones1   
#fjh      ,cinders1 #dje      ,cirques1 
#bhf      ,clarke1 ,f4 ,w41 #cif1 #egc  
,classification of rocks1 #ddi      new 
system of1 #dea      ,clastic rock1 #dfh
      ,clay1 #dfh      ,clay ironstone1 
#dfh      ,claypole1 ,e4 ,w41 #edi      
,cleavage planes and erosion1 #abe      
development of 7see ,slate and ,schist7 
,cliff glacier1 #bef      ,climate1     
influence on erosion1 #abg-acb          
,climatic effects of carbon dioxide1    
#fdc      ,climatic effects of life1    
#fdc      ,climatic effects of water    
vapor1 #fdc      ,clinkstone1 #dfh      
,clinometer1 #eja      ,coal1 #dfh      
,coast-lines #cec1 #cfc-f      effect of
 gradation on1 #ccc1 #cfc      effect of
 subsidence on1 #cbi1 #ccb      effect  
of vulcanism on1 #ccb-cc        forms   
of1 #cbi1 #ccc1 #cfc1 #cfd      ,coast  

ranges1 crustal1 shortening due to      
folding of1 #edi      ,coasts1 natural  
bridges on1 #cea      ,cobb1 ,c41 #cf   
,clenterata1 geologic contribution of1  
#ffa      ,collins1 ,a4 ,l41 #dgd       
,colorado1 ,canyon of1 #ih1 #bcc        
,columbia ,river1 #aga      ,columnar   
structure1 #dih-ejj      effect on      
weathering1 #aec1 #aed      ,common     
springs1 #bce      ,compression joints1 
#ead      ,concave tracts of crust1     
#ehe1 #ehf      ,concretions1 #dch1     
#dfh1 #dij      ,cones1      cinder1    
#fjh      composite1 #faj      formation
 of1 #fjh      geyser1 #bcg      lava1  
#fjh      spatter1 #faj      tufa1 #faa 
,configuration of coasts1 #cbi1 #ccj1   
#cca1 #ccb1 #ccc1 #cec1 #cfc-f          
,conformability1 #ae      ,conglomerate1
 #dbc1 #dcd1 #dfh1 #dhg                 
,continental glaziers1 #bea             
,continental platforms1 #aa      relief 
of1 #aa      ,continental segments1 size
 of1 #edg      ,continental shelf1 #aa  
,continent-forming movements1 #edd      

,contour interval1 #ca      ,contour    
lines1 #ca      ,convection hypothesis1 
internal heat on1 #eei      thermal     
distribution on1 #eei      ,cooley1 ,e4 
,g41 #aie      ,coon ,butte1 #eif       
,copalite1 #fdf      ,coprolites1 #fdf  
,coquina1 #dfi      ,coral mud1 #chj    
,cornish1 ,v41 #bf1 #bh1 #bi            
,corrasion1 #aaj1 #aac      by glaciers1
 #bha-hf      by streams1 #aai      by  
waves1 #cdb-di      by wind1 #ch        
effect of sediment on1 #abj             
,corthell1 ,e4 ,l41 #bjb                
,cosmopolitan faunas1 #ffh              
,coulter1 ,j4 ,m41 #ffg      ,coves1    
#adc      ,cowles1 ,h4 ,c41 #ce1 #ffg   
,credner1 ,h41 #ce1 #ech      ,creep1   
#bca      ,cretaceous base-level1 #afi  
,crevasses1 #bfd      ,crinoids1 #ffa   
,croll1 ,james1 #cbb1 #cbc1 #cci        
,crosby1 ,w4 ,o41 #eac                  
,cross-bedding1 #cgc1 #dhg              
,cross-currents1 in streams1 #aag       
,cross1 ,whitman1 #dab1 #dea1 #ece1 #egc
      ,croton ,river1 material in       

solution in1 #ajh      ,crustal         
movements1 #ebf-ehi      causes of1     
#eea-eg      differential extent of1    
#edh      due to chemical changes1 #eef 
due to cohesion and crystallization1    
#eed      due to diffusion1 #eee        
earthquake1 #ebg-cc      minute and     
rapid1 #ebf      periodicity of1 #eag1  
#eci      resistance to1 #eeg      slow 
and massive1 #ecg-ei      ,crustal      
shortening1 #edh-ea      ,crust of      
earth1 #ac      depth of1 #ad           
varieties of rock in1 #ad               
,crystalline rocks1 types of1 #af       
,crystallites1 #djg                     
,crystallization of lava1 #dja-b        
stages of1 #djc      ,crystals1         
enlargement of1 #dce      ,cut-and-fill1
 #aij1 #aic      ,cut-off1 #aia         
,cycle of erosion1      its stages1 #hj 
definition of1 #hb      recognition of1 
#afd      ,cystoids1 #ffa               
,dacite1 #dfi      ,dale1 ,t4 ,n41 #eje 
,daly1 ,r4 ,a41 #fca      ,dana1 ,j4    
,d41 #bjc1 #cdj1 #cdi1 #eaa1 #edc1 #fjd1

 #fcf      ,daniell1 ,a41 #egb1 #egc    
,danube ,river1      delta of1 #bjb     
material in solution in1 #ajh           
sediment carried by1 #ajg      ,darton1 
,n4 ,h41 #da1 #ej1 #ec1 #id1 #ace1 #aed1
 #did1 #egj      ,darwin1 ,c41 #fjd1    
#fcf1 #ffe      ,darwin1 ,g4 ,h41 #ecd1 
#efa1 #egf1 #egi1 #ehc1 #fjd            
,daubree1 ,g4 ,a41 #fbf      ,davis1 ,b4
 ,m41 #bbe      ,davis1 ,w4 ,m41 #hc1   
#aei1 #afd1 #agj1 #ahh1 #bjb1 #bjd #baj 
#cdi1      and ,shaler1 ,n4 ,s41 #bef   
,davis1 ,c4 ,a41 #fee      ,davison1    
,c41 #ebg1 #ech1 #efa      ,de,beaumont1
 ,eli1 #cbc      ,decarbonation1 #dbi1  
#dcj      ,de,charpentier1 ,j41 #cba1   
#cbb1 #cbc      ,deeley1 ,r4 ,m41 #cbb  
,deep-sea deposits1 #cfh1 #cgh-hf       
chemical1 #chc-hf                       
extra-terrestrial1 #cha      inorganic1 
#chj      manganiferous1 #chd           
organic1 #chb      ,deep-sea fauna1 #fgj
      ,deposition1      by glaciers1    
#bih-cje      by streams1 #agg-bjd      
by shore currents1 #cee      by         

undertow1 #cee      by waves1 #cee-fc   
by wind1 #be-cg      ,deformation of    
earth's crust1 #ebf-hi      causes of1  
#eea-eg1 #egd-hi      relation to       
distribution of volcanoes1 #fja1 #fjd1  
#fbg1 #fbi      ,deformation of ice1    
#cab      ,degradation1 #b      by      
water1 #eh-agg      rate of1 #aje       
,de ,launay1 ,l4 ,c41 #dgd              
,delesse1 ,a41 #bba1 #cda               
,delessite1 #dfb      ,dells of the     
,wisconsin1 #aeb      ,delta lakes1 #bjd
      ,deltas1 #aha1 #aih-bjd           
bottom set beds1 #bjb      development1 
#aii      fore-set beds1 #bjb           
fossil1 #bjc      in tidal seas1 #bjb   
of the ,ganges and ,brahmaputra1 #bjb   
of the ,hoang-,ho1 #bjb1 #bjc      of   
the ,mackenzie1 #bjb      of the        
,mississippi1 #aig1 #bjb      of the    
,nile1 #bjb      of the ,po1 #bjb       
of the ,rhone1 #bjc      of the ,yukon1 
#bjb      rate of growth1 #bjb          
shape1 #bja      structure1 #aih1 #aii  
top-set beds1 #bjb      ,densities      

within the earth1 on ,laplace's law1    
#efd      ,denudation and volcanic      
action1 #fbg      ,deoxidation1 #dbg    
,deposition of mineral matter from      
solution1 #ej1 #bbe1 #dbh      at       
surface1 #ej1 #bbd      by ground-water1
 #bbd1 #dbh      in lakes1 #chg      in 
sea1 #cge1 #chc      ,deposition of     
sediment1 #ff      by rivers1 #agg-bjd  
by wind1 #be-ch      in ocean1 #cee-fc1 
#cfh-hf      ,deposition of drift1 at   
edge of glaciers1 #bii      at end      
glaciers #bii      beneath ice1 #bih    
,deposits1      deep-sea1 #cfh1 #cgh-hf 
hot springs1 #bcg1 #bda      lacustrine1
 #chg      littoral1 #cfi      made by  
animals1 #feh-fc      made by           
,arthropoda1 #ffb      made by          
,bryophytes1 #fef      made by          
,echinodermata1 #ffa      made by ice1  
#bih-cje      made by ,mollusca1 #ffb   
made by ,molluscoidea1 #ffb      made by
 ,protozoa1 #ffj      made by           
,pteridophytes1 #feg      made by plant 
kingdom1 #feb-eh      made by rivers1   

#agg-bjd      made by ,spermatophytes1  
#feg      made by ,thallophytes1 #fec   
made by ,vermes1 #ffb      made by      
,vertebrata1 #ffc      made by wind1    
#be-ch      shallow-water1 #cfi-gh      
silicious1 #bcg1 #bda1 #dbe      tufa1  
#bcg1 #bda1 #dgc1 #faa1 #fec            
,depression and volcanic action1 #fbi   
,depth of the ocean1 #g      greatest1  
#h1 #edh      ,diabases1 #dah1 #dca1    
#dfi      ,diallage1 #djj1 #dfb         
,diastrophism1 #b1 #cbi1 #ebf           
effect on coast lines1 #cbi      ,diatom
 ooze1 #chj1 #chb1 #dbe1 #dfi           
,diffusion1      in earth's interior1   
#eee      cause of crustal movement1    
#eee      ,dikes1 #eia      effect on   
topography1 #adc      sandstone1 #ead   
,diller1 ,j4 ,s41 #bi1 #ead             
,diorites1 #daf1 #deb1 #dfi      ,dip1  
#eja      quaquaversal1 #ejd            
,dip-fault1 #ebb      ,di,rossi1 ,m4    
,s41 #ecg      ,displacement of fault1  
#ead      ,disruption of rock1 due to   
changes of temperature1 #dd1 #di      by

 carbonation1 #dc      by hydration1    
#aaa      ,distributive fault1 #eai     
,divides1 permanence of1 #fi            
,docalcic rocks1 #deh      ,dodge1 ,r4  
,e41 #bjd      ,dofemane1 #dee          
,dofemic rocks1 #ded      ,doferrous    
rocks1 #dei      ,dohemic rocks1 #deg   
,dolenic rocks1 #def      ,dolerites1   
#dag1 #deb1 #dfi      ,dolomites1 #dbd1 
#dfi      ,domagnesic rocks1 #dei       
,domalkalic rocks1 #deh      ,domes of  
crust1 strength of1 #eha1 #ehb          
,domilic rocks1 #ehb      ,domiric      
rocks1 #deh      ,domirlic rocks1 #deh  
,domitic rocks1 #deg      ,dopolic      
rocks1 #def      ,dopotassic rocks1 #deh
      ,dopyric rocks1 #deg              
,doquaric rocks1 #def      ,dosalic     
rocks1 #ded      ,dosodic rocks1 #deh   
,dotilic rocks1 #deg      ,drainage1    
effect of change of level on1 #afa      
mature1 #hf      of glaciers1 #bgc      
old age1 #hi      youthful1 #hf         
,dreikanter1 #dj      ,drift1 #bhg1 #dfi
      composition of1 #cjd              

deposition of1 #bih-cje      wear of1 in
 transit1 #bih      ,drygalski1 ,e4 von1
 #cbb      ,dump moraine1 #cja          
,dune areas1 topography of1 #cb         
,dunes1 #bd-cg      distribution of1 #ce
      effect of vegetation on1 #bi      
formation of1 #bf      migration of1 #cc
      shapes of1 #bf      slopes of1 #bi
      ,dust1      volcanic1 #bb1 #bc    
wind-blown1 #bb      ,dust-wells1 #bfi1 
#bhj      ,dutton1 ,c4 ,e41 #acb1 #ecd1 
#egd1 #fcf      ,dynamic geology1 #a    
,earth1 the1      as a planet1 #b       
constitution1 #e      crust1 #ac        
deformation of1 #ebf      dependence on 
sun1 #d      distance from sun1 #c      
inclination of axis1 #c      interior   
of1 #ad1 #eei      internal heat1       
#eei-gd      motions1 #c      orbit1 #c 
tremors of surface1 #ebf      warpings  
of crust1 #ebf-hi      ,earthquakes1    
#ebg-ecg      causes of1 #ebg           
destruction of life by1 #ecf            
distribution of1 #ecc      destructive  
effects of1 #ecj      epicentra of1 #eca

      foci of1 #ebg      gaseous        
emanations during1 #ecc      geologic   
effects of1 #ecd-ecg      ,earthquake   
vibrations1 #ebf      amplitude of1 #ebi
      ,charleston1 #ecd      ,lisbon1   
#ece      sequences of1 #ecc            
,earth's crust1      composition of1    
#ad1 #cif      warpings of1 #ech-eea    
,eastman1 ,c4 ,r41 #feh                 
,echinodermata1 geologic contributions  
of1 #ffa      ,echinoids1 geologic      
contributions of1 #ffa      ,economic   
geology1 #a      ,efflorescence1 #db    
,elolite1 #dfb      ,electricity1       
atmospheric1 #dc      chemical effects  
of1 #dc      geological effects of1 #dc1
 #eb      ,ells1 ,r41 #ddc      ,emmons1
 ,s4 ,f41 #dgd      ,emmons1 ,w4 ,h41   
#dgd1 #egc1 #ehe      ,englacial drift1 
#bhb      ,enlargement of crystals1 by  
secondary growth1 #dce      ,enstatite1 
#djj1 #dfb      ,eolian rocks1 #dfi     
,epeirogenic movements1 #ecg            
,epicontinental seas1 #aa1 #cbf         
,epidote1 #dca1 #dfb      ,equiset1     

geologic contribution of1 #feg          
,eras1 #ag-ai      ,erosion1            
affected by rotation1 #aid      analysis
 of1 #aaj      base-level of1 #fj       
by glaciers1 #bha-bhf      by rain1 #eg 
by rivers1 #ef-agg      by undertow1    
#cdb1 #cdf      by waves1 #cdb-cdi      
by wind1 #ch      conditions affecting  
rate of1 by glaciers1 #bhc              
conditions affecting rate of1 by running
 water1 #abc      cycle of1 #hj1 #hb1   
#afd      in arid regions1 #aca         
influenced by climate1 #abg1 #abh1 #abi 
influenced by composition of rock1 #abd 
influenced by declivity1 #abc           
influenced by structure1 #abd1 #abf     
influenced by vegetation1 #abi1 #fdd    
sheet1 #ei      subarial1 #eh           
,erosion and cleavage planes1 #abe      
,erosion and joints1 #abe      ,erosion 
by streams 7see ,erosion by running     
water7      ,eruptions1 #eia            
fissure1 #eic      volcanic1 #eid       
,eskers1 #cjf      ,etna1 #fje1 #faj    
discharge of stream from1 #fcf          

,evaporation1 #ej      ,everett1 #egh   
,evolution restrictive and expansional1 
#fgb      ,exfoliation1 #dd             
,expansional evolution1 #fgb            
,expansion and contraction1      due to 
temperature1 #dd      due to wetting and
 drying1 #eb      ,extinct lakes1 #chh  
,extrusive processes1 #eij-fcg          
,falb1 ,r41 #ecg      ,false bedding1   
#dhg      ,faulting and vulcanism1 #fbg 
,faults1      conditions of1 #eba       
dip1 #ebb      displacement1 #ead       
distributive1 #eai      effect on       
outcrops1 #ebb      hade1 #ead          
heave of1 #ead      normal1 #eag        
oblique1 #ebe      relation to folds1   
#eae      reversed1 #eag1 #eba          
stratigraphic throw1 #eah               
significance of1 #eba      strike1 #ebb 
thrust1 #eag1 #eah      ,fault scarp1   
#ead      ,faunas1      abysmal1 #fgj   
,australian1 #ffh      cosmopolitan1    
#ffh      deep-sea1 #fgj      pelagic1  
#fgj      photobathic1 #fgj      ,faunas
 and floras1      basis of1 #ffc        

effect of geographic conditions on      
evolution of1 #ffh      ,feldspar1 #dfb 
,feldspar-leucophyres1 #dec             
,feldspar-melaphyres1 #dec              
,feldspathic minerals1 #djj             
,feldspathoids1 #djj      ,felsites1    
#deb1 #dfi      ,fenneman1 ,n4 ,m41 #cci
      ,ferguson1 ,a4 ,m41 #bjc          
,ferns1 geologic contribution of1 #feg  
,fiords1 #bij      ,fisher1 ,o41 #efa1  
#efe1 #egd1 #eha      ,fissure          
eruptions1 #eic      ,fletcher1 ,g4 7and
 ,deeley1 ,r4 ,m471 #cbb      ,flints1  
#dbf1 #dfi      ,floods1 #aji      of   
the ,mississippi1 #ahh      ,flood-plain
 meanders1 #aij      ,flood-plains1     
#ahd-ih      development of1 #afe       
materials of1 #aif      ,mississippi1   
#aid      relation to terraces1 #bje    
topography1 #aif      ,floras and       
faunas1      basis of1 #ffc      effect 
of geographic conditions on1 #ffh       
,flowering plants1 geologic             
contributions of1 #feg      ,flowing    
wells1 #bcd1 #bdb      ,flow structure  

of lavas1 #daj      ,fluorite1 #dfb     
,fluvio-glacial work1 #cje-g            
,folded ranges1 distribution of1 #edc   
,folding and vulcanism1 #fbh            
,folds1      anticlinal1 #ejd1 #eje     
effect on valleys1 #aed      isoclinal1 
#ejd      synclinal1 #ejd      ,folds   
and faults1 #eae      ,foliation of ice1
 #bgb      ,foliation of rocks1 #ddc    
,foraminifera1 geologic contribution of1
 #ffj      ,forbes1 ,j4 ,d41 #bef1 #cbb 
,forel1 ,f4 ,a41 #cbc1 #chf             
,fore-set beds1 #bjb      ,formation1   
#dhg      ,forster1 ,w4 ,g41 #ecf       
8,fossil0 deltas1 #bjc      ,fossils1   
#af1 #fdf      a means of correlation1  
#fdg      ,fossils and stratigraphy1    
#fdg      ,fouqu1 ,f41 #fce1 #fcf       
,fracture1 zone of1 #bai      ,frank1   
,a4 ,b41 #fdb      ,freestone1 #dfi     
,french ,broad ,river1 the1 #afh        
,fulgurites1 #eb1 #dfi      ,fungi1     
geologic contribution of1 #fec          
,gabbroids1 #dec      ,gabbros1 #daf1   
#deb1 #dfi      ,galenite1 #dda         

,ganges ,river1 delta of1 #bjc          
,gangue1 #dfi      ,gannister1 #dfi     
,garnet1 #dfb      ,garnetite1 #dfi     
,gaseous emanations1      during        
earthquakes1 #ecc      from volcanoes1  
#fag      ,gases in volcanic rocks1 #fai
      ,gases1 volcanic1 #fag-fbc        
amount of1 #fbj      kinds of1 #fah1    
#fai      proportions of1 #fbj1 #fbb    
sources of1 #fba      ,gastropods1      
geologic contributions of1 #ffb         
,geantcline1 #eje      ,geest1 #dfi     
,geikie1 ,a41 #bjc1 #bbd1 #cdd1         
#ecd-ecf1 #fcf      ,geodes1 #dcf1 #dig 
,geognosy1 #a1 #e1 #cic-dhe             
,geologic effects of earthquakes1 #ecd  
,geologic functions of life1 #fch       
,geologic processes1 man's influence on1
 #fdi      ,geologic time divisions1 #ai
      ,geology1      astronomic1 #a1 #b 
atmospheric1 #b      cosmic1 #a         
dominant processes of1 #b      dynamic1 
#a      economic1 #a      geotectonic1  
#a1 #dhf      glacial1 #b               
historical1 #a      mining1 #a          

paleontologic1 #a      philosophic1 #a  
physiographic1 #a      scope of1 #a     
structural1 #a1 #dhf      subdivisions  
of1 #a      ,george1 ,r4 ,d41 #ede      
,geosyncline1 #eje      ,geotectonic    
geology1 #a1 #dhf-ebe      ,gerber1 ,e41
 #aie      ,gerland1 #ech               
,geschiebe wall1 #cjj      ,geyserite1  
#dfc1 #dfi      ,geysers1 #bcf          
deposits of1 #bcg      of ,yellowstone  
,park1 #bci      period of eruption1    
#bdj      positions of1 #bda            
,gilbert1 ,g4 ,k41 #aa1 #aaj1 #adj1     
#aid1 #aih1 #bjc1 #cci1 #cee1 #chh1     
#dhi1 #eif      ,glacial dbris1      how
 carried1 #bij      nature of1 #bhf     
shifting position in transit1 #bib1     
#bic1 #bid1 #bif1 #big      ,glacial    
deposits1 nature of1 #cjd      ,glacial 
erosion1      conditions influencing1   
#bhc      topographic effects of1 #bhg  
,glacial motion1 #cac-cba      auxiliary
 elements of1 #cag      fundamental     
element of1 #cac      ,glacial plucking1
 #bhb      ,glaciated rock surfaces1    

#cjd      ,glacier ice1      beginning  
of movement1 #bdh      definition of1   
#bej      granular texture of1 #bdg     
shearing of1 #cag      ,glacier         
movement1 #bei1 #cac-cbc      at low    
temperature1 #bgi      effect of water  
on1 #cah      rates1 #bfj1 #bfa         
views of1 #cba      ,glaciers1          
alpine1 #bed      cliff1 #bef           
compared with rivers1 #bfb              
conditions influencing movement1 #bfa   
constitution1 #cjh      continental1    
#bea      crevasses1 #bfd               
deformation1 #cab      drainage of1     
#bgc1 #bhj      foliation1 #bdg1 #bgb   
evaporation1 #bgi      general          
phenomena1 #bef      getting load1 #bhb 
growth of1 #cjh      growth of granules1
 #caj1 #caa      high-latitude1 #bed    
limits of1 #beh      motion in terminal 
part1 #caf      movements of1 #bei1     
#bgi1 #cac-cbc      piedmont1 #bed      
polar1 #bed      rate of movement of1   
#bfj1 #bfa      reconstructed1 #bef     
stratification of1 #bdg      structure  

of1 #cjh      surface features of1 #bff 
temperature of1 #bgc-bgi      thickening
 of layers at end1 #big      topography 
of1 #bff      types of1 #bea            
upturning of ice at ends and edges1     
#bif1 #big1 #bih      valley1 #bed      
waste of1 #bgc      work of1 #bdd1 #bha 
,glacio-fluvial work1 #cje-cjh          
,glass1 volcanic1 #dea      ,glassy     
rocks1 #djf      ,glauconite1 #chd1     
#chf1 #dfc      ,globigerina ooze1 #chj1
 #chb1 #ffj      ,globulites1 #djg1 #dfi
      ,gneiss1 #dae1 #ddf1 #ddh1 #dfi   
,gooch1 ,f4 ,a4 7and ,whitfield1 ,j4    
,e471 #bcf      ,gorge1 #ajj      ,grad1
 ,ch41 #cbb      ,gradation1 #b      by 
running water1 #ef-bab      effect on   
coast-lines1 #ccd      in ocean1 #ccd   
,grade1 #fa      ,graded plain1 #hb1    
#afi      ,graded valley1 #hc           
,granitell1 #dgj      ,granites1 #dac1  
#deb1 #dfi      ,granitite1 #dgj        
,granitoids1 #dbj1 #dec      ,granulite1
 #dgj      ,graphite1 #dbf1 #dfc        
,gravitational energy1 #eeb             

,gravitational force1 #eeb1 #eec        
,gravity1      a cause of crustal       
movements1 #eeb      effect on erosion1 
#aac      ,gray1 ,t4 7and ,milne1 ,j471 
#egh      ,greenland1      glaciers of1 
#bdf      snow-fields of1 #bde          
snow-line in1 #bdf      ,green mud1 #chj
      ,greensand1 #dgj      ,greensand  
marl1 #chf      ,greenstone1 #dai1 #dgj 
,greisen1 #dae1 #dgj      ,greywacke1   
#dgj      ,ground ice1 #aai      ,ground
 moraine1 #cja      ,ground-water1      
#bac-bdc      affects internal heat1    
#egj      amount of1 #bba      descent  
of1 #bac      fate of1 #bba      lower  
limit of1 #baf      movement of1 #bbj   
results of1 #bbf      solution by1 #bbb1
 #bbc      work of1 #bbb                
,ground-water and vulcanism1 #fce       
,ground-water level1 #ga1 #bae          
,ground-water surface1 #ga1 #bae        
,guano1 #fdf      ,gulf stream1 #cff    
,gullies1 growth of1 #fc                
,gymnosperms1 geologic contributions of1
 #feg      ,gypsum1 deposition of1 #cgf1

 #cgg        ,hade of faults1 #ead      
,hall1 ,jas41 #eaa      ,halleflinta1   
#dgj      ,halophytes1 geologic         
contributions of1 #ffg      ,hanging    
valley1 #afd1 #bij      ,haynite1 #dfc  
,hayes1 ,w41 #agc      ,hayes1 ,w4 7and 
,campbell1 ,m4 ,r471 #aga      ,head    
erosion1 #fd      ,heat1 by compression 
of ice1 #caa      causes crustal        
movement1 #eeg      causes of1 in ice1  
#bgh1 #bgi      distribution of1 within 
earth1 #eei      distribution1 original1
 #eei      internal1 of earth1 #eei-egj 
metamorphism by1 #ddf1 #ddh             
original distribution of1 #eei          
,heave of faults1 #ead      ,heilprin1  
,a41 #fcf      ,heim1 ,a41 #bef1 #cbb1  
#edi1 #egf      ,hematite1 #dbe1 #ddg1  
#dfc      ,high-latitude glaciers1 #bed 
,himalayas1 snow-line in1 #bdf          
,historical geology1 #a      ,hoang-,ho 
delta1 #bjb1 #bjc      ,hog-backs1 #adb 
,holden1 ,e4 ,s41 #ech      ,holmes1 ,w4
 ,h41 #ii      ,holocrystalline rock1   
#dab      ,holosiderites1 #e      ,hook 

7along shore71 #cfc      ,hopkins1 ,w41 
#cbb      ,horizontal configuration of  
coasts1 due to deposition1 #cfc1 #cfd   
due to wave erosion1 #cec               
,hornblende1 #djj1 #dfc                 
,hornblende-granite1 #dae               
,hornblendite1 #dag1 #deb1 #dgj         
,hornstone1 #dgj      ,horsetails 7see  
,equiset7      ,hoskins1 ,l4 ,m41 #bai1 
#eeb1 #eha      ,hot springs1 deposits  
of1 #bbe      ,howell1 ,capt41 #aga     
,hudson ,river1 material in solution in1
 #ajh      ,hugi1 ,f4 ,j41 #cba         
,hull1 ,e41 #fcf      ,humphreys1 ,a4   
,a4 7and ,abbot1 ,m4 ,l471 #ajf1 #bjb   
,huxley1 ,t4 ,h41 #cbb      ,hyalite1   
#dfc      ,hydration1 #dc1 #bbb         
disruption of rock by1 #aaa             
,hydrophytes1 geologic contributions of1
 #ffg      ,hydrosphere1 the1 #g 7see   
also ,ground-water and ,ocean7          
geologic activity of1 #h      horizons  
of activity1 #i      ,hypersthene1 #djj1
 #dfc      ,hypogene rocks1 #dgj        
,ice1 glacial 7see ,glaciers7           

ground1 #aai      of lakes1 #chi      of
 rivers1 #aah      ,icebergs1 #cjg      
,ice-caps1 #bdi1 #bej      ,ice         
crystals1 arrangement in glacier ice1   
#caa      ,ice-fall1 #bfd      ,iceland 
spar1 #dfc      ,iddings1 ,j4 ,p41 #dab1
 #dea1 #egc1 #fad1 #fcf      ,igneous   
rocks1 #af      composition of1 #cie    
leading minerals of1 #cii      origin   
of1 #cic      relations to stratified   
rocks1 #af      structural features of1 
#dih      ,ilmenite1 #dfc               
,incrustation1 #bbc      ,infusorial    
earth1 #dgj      ,inorganic deposits1 in
 deep sea1 #chj      ,interior of earth1
 #ad 7see ,vulcanism7      densities1   
based on ,laplace's law1 #efd      heat 
of1 #efb1 #efd      pressures1 #efd     
,intermittent springs1 #bce             
,internal heat 7see ,internal           
temperature7      ,internal temperature1
 #efb      affected by ground-water1    
#egj      at centre of earth1 #ega      
on accretion hypothesis1 #efd1 #efg     
on convection hypothesis1 #eei      on  

,laplacian hypothesis1 #eei             
,intrusions1 #eia      ,iron-ore beds1  
origin1 #dbe      ,iron oxide1 #djj     
,iron pyrites1 #dfc      ,ironstone1    
#dbe1 #dgj      ,irruptions1 #eia       
,isoclinal folds1 #ejd                  
,isoseismals1 #ecb      ,itacolumite1   
#dgj      ,italy1 lateral moraines in1  
#cjc        ,jasper1 #dgj               
,jefferson1 ,m4 ,w41 #aic      ,johnson1
 ,s4 ,w41 #aji1 #aij1 #ffe              
,johnston-,lavis1 ,h4 ,j41 #fcf         
,joints1 #eaj      causes of1 #eaa1 #eca
      compression1 #ead      effect on  
valleys1 #aej      ,joints1 tension1    
#ead      ,joints and erosion1 #abe     
,judd1 ,j4 ,w41 #fcf        ,kaaterskill
 ,creek1 piracy of1 #aje      ,kames1   
#cjg      serpentine1 #cjf      ,kansas1
 volcanic dust in1 #bc      ,kanawha    
,river1 #afh      ,kaolin1 #dfc         
,katamorphism1 #ddf      ,keith1 ,a41   
#ddb1 #ddd      ,kelvin1 ,lord1 #efj1   
#ehc      ,keratophyre1 #dgj            
,kersantite1 #dgj      ,keyes1 ,c4 ,r41 

#dgd      ,kidd1 ,d4 ,a41 #cac          
,kilauea1 #fje      ,king1 ,c41 #efj    
,king1 ,f4 ,h41 #bbj      ,kittatinny   
base-level1 #afh      ,kot1 ,dr41 #ecd  
,krakatoa1 #bb1 #faj1 #faa1 #fah        
,kmmel1 ,h4 ,b41 #bjc                   
,labradorite1 #djj1 #dbi1 #dfd          
,laccolith1 #ejj1 #eib      ,lacustrine 
deposits1 #chh      ,lake ice1 #chi     
,lake ,pepin1 #agi      ,lakes1 #chf-cib
      bayou1 #aib1 #aic      changes    
taking place in1 #chg      delta1 #bjd  
deposits in1 #chg      extinct1 #chh    
formed by rivers1 #aia1 #aib1 #aih      
ice of1 #chi      ox-bow1 #aib1 #aih    
,landslide1 #bca      topography of1    
#bcj      ,landslip mountain1 #bcj      
,lane1 ,a4 ,c41 #eeg1 #fcf              
,lapilli1 #dgj      in sea1 #cha1 #dje  
,laplace1 ,marquis de1 #efd             
,laramide range1 crustal shortening due 
to folding1 #edi      ,lateral moraines1
 #bff1 #cjb      in ,bighorn ,mountains1
 #cjc      in ,italy1 #cjc      in      
,uinta ,mountains1 #cjc      in ,wasatch

 ,mountains1 #cjc      ,lateral         
pressure1 metamorphism by1 #ddh         
,laterite1 #dgj      ,lava cones1 #fjh  
,lavas1 #fab-faf      and ground-water1 
#faf      consanguinity and succession  
of1 #fad      crystallization of1 #djb1 
#djc      depth of source of1 #faf      
modes of reaching surface1 #fca         
origin of1 #fbc-fca      rhyolitic      
7flow7 structure of1 #daj               
solidification of1 #cic                 
temperatures of1 #fae1 #fbf      ,lavas 
and underground water1 #fbg             
,le,conte1 ,j41 #dgd1 #edi              
,lendofelic1 #def      ,lenfelic1 #def  
,lepidolite1 #dfd      ,leucite1 #dfd   
,leucophyre1 #dab1 #dec      ,levees1   
breaking of1 #ahh      miniature1 #ahb  
natural1 #ahh      on alluvial cones1   
#ahb      ,level of no stress1 #efa     
,life1 #fch-fgb      atmospheric effects
 of1 #fch-fdd      chemical work of1    
#fch-fdf      climatic effects of1 #fdc 
effect on rock decomposition1 #acj1 #fdd
      geologic effects of1 #fci         

inorganic rocks due to1 #fdf            
influenced by environment1 #fff         
man's influence on1 #fej      protection
 against erosion1 #acj1 #fdd      ,life 
and carbon dioxide1 #fdj1 #fdb1 #fdc    
,lightning1 effects of1 #eb             
,lignite1 #dbf1 #dgj      ,limburgite1  
#dgj      ,lime carbonate1 deposition   
of1 #cge1 #cgf      ,limonite1 #dbe     
,limestone1 #cgh1 #dbd1 #dcd      origin
 of1 #cgh1 #fed1 #fee                   
stratification of1 #dhg                 
,limestone-forming animals1 #ffj-ffb    
plants1 #fed1 #fee      ,limestone      
sinks1 #bbg1 #bca      ,lindgren1 ,w41  
#dgd      ,liparase1 #dei               
,liparite1 #dgj      ,lisbon earthquake1
 #ece      ,lithosphere1 #i-ai          
crust of1 #ac      irregularities of1   
#aj      relief of1 #aa      size and   
shape of1 #i      surface mantle of1 #ab
      ,littoral currents1 #cdb          
,littoral deposits1 #cfh1 #cfi1 #cgi    
,littoral zone1 #cfi      ,liverworts1  
geologic contribution of1 #fef          

,livingstone1 ,d41 #di      ,load 7of   
streams71 #agg-agi      ,loess1 #bc1    
#dgj      ,lodge moraine1 #cja          
,loop 7along shore71 #ceg1 #cfc         
,lunar craters1 #eih      ,lunn1 ,a4    
,c41 #eeb1 #efe1 #eff1 #efg1 #egb       
,lycopods1 geologic work of1 #feg       
,lydekker1 ,r4 7and ,nicholson1 ,a471   
#feh      ,lyell1 ,sir ,charles1 #fdi   
,mackenzie ,river1 delta1 #bjb          
,magma1 nature of1 #dja      ,magnesite1
 #dfd      ,magnesium salts in sea1 #cgg
      ,magnetic nodules in sea1 #cha    
,magnetite1 #dfd      ,malay peninsula1 
tin ores of1 #dgh      ,malaspina       
glacier1 #bed      ,mallet1 ,r41 #cbb1  
#ecg1 #ech1 #fbh1 #fcf      ,mammoth    
,cave1 #bbg      ,mammoth hot springs1  
#fed      ,manganiferous deposits1 #chd 
,mantle rock1 #ab1 #dbb      ,marble1   
#ddg1 #dga      ,marcasite1 #dfd        
,marine deposits1 #cee-cfc1 #cgj-chf    
chemical1 #cfg1 #cge1 #chc              
deep-sea1 #cfh1 #cgh-chf                
extra-terrestrial1 #cha      littoral1  

#cfh1 #cfi      mechanical1 #cfi1 #chj  
organic1 #cge      shallow-water1       
#cfi-cgh      table of1 #chj            
,marine life1 distribution of1 #cbh     
,marl1 #dga 7see also ,greensand marl   
and ,shell marl7      formed by plants1 
#fee      green-sand 7see ,greensand    
marl7      ,martinique1 #fje            
,martite1 #dfd      ,mason1 ,w4 ,p41    
#ajg      ,mass action1 #dgh1 #dhd1 #eed
      ,mature drainage1 #hf      ,mature
 streams1 characteristics of1 #hf       
,mauna ,loa1 #fje1 #fjf1 #fbd           
,mc,connell1 ,j4 ,c41 #cac1 #cbb1 #cbc1 
#edi      ,mc,gee1 ,w4 ,j41 #ei1 #ebd   
,meander belt1 relation to width of     
stream1 #aic      ,meanders1            
flood-plain1 #aij      intrenched1 #afd 
of the ,meuse1 #afd      of the         
,moselle1 #afd      of the ,seine1 #afd 
,mean sphere level1 #edh      ,medial   
moraine1 #bff1 #big      ,medlicott1 ,h4
 ,b41 #bjc      ,medicinal springs1 #bce
      ,melaphyres1 #dab1 #dca1 #dec1    
#dga      ,menaccanite1 #dfd            

,mendelejeff1 ,d4 7and ,moissan1 ,h471  
#fdf      ,mental element1 material     
effects of1 #fdi      ,merrill1 ,g4 ,p41
 #ce1 #aaa1 #bba      ,mesas1 #adb      
,mesophytes1 #ffg      ,meta-diabase1   
#dga      ,meta-igneous rock1 #dga      
,metamorphic rocks1 #ag                 
,metamorphism1 #dbg1 #dcc1 #ddj1 #ddi   
by heat1 #ddf      by lateral pressure1 
#ddh      deep-seated1 #ddi             
,meteorites1 #d      number of1 #cha    
,meuse1 meanders of1 #afd      ,mica1   
#djj1 #dfd      ,mica schists1 #ddh     
,microcline1 #djj1 #dfd                 
,microlites1 #djg1 #dga                 
,microgranite1 #dga      ,migration of  
dunes1 #cc      ,millstone1 #dga        
,milne1 ,j41 #ecc1 #ecg1 #ech1 #ehc     
7and ,gray1 ,t471 #egh      7and        
,burton71 #fcf      ,mineral matter in  
sea1 #cbd-cbf      amount of1 #cbe      
,minerals1 felspathic1 #djj1 #dfb       
ferromagnesian1 #djj1 #dfj              
formation of1 #cig1 #fab      of igneous
 rocks1 #cii      list of1 #dfj-dfg     

,mineral springs1 #bce      ,minette1   
#dae1 #dga      ,mining geology1 #a     
,minnehaha ,falls1 #acg      ,mirlic    
rocks1 #deh      ,mississippi ,river1   
delta1 #aig1 #bjb      depth of channel1
 #aga      flood-plain1 #aid      floods
 of1 #ahh      levees of1 #ahh          
material in solution in1 #ajh           
sediment carried by1 #ajf               
,mississippi flood-plain1 #aid          
lakes of1 #aib      ,missouri ,river1   
scour-and-fill of1 #aie      ,mitic     
rocks1 #def      ,moissan1 ,h41 #fdf    
,mollusca1 geologic contribution of1    
#ffb      ,molluscoidea1 geologic       
contribution of1 #ffb      ,molten      
interior1 lava from1 #fbd      ,molten  
magmas1 nature of1 #dja      ,molten    
reservoirs1 lavas from1 #fbd            
,monadnocks1 #ade      ,monoclinal      
shifting1 #abg      ,monocline1 #ejd    
,monzonite1 #dga      ,moon1 #c1 #eih   
,moraines1 dump1 #cja      ground1 #cjb 
lateral1 #bff1 #cjb      lodge1 #cja    
medial1 #bff1 #big      molluscan shells

 in1 #big      push1 #cja      surface1 
#bff      terminal1 #bff1 #cja          
types1 #cja      ,moselle ,river1       
intrenchment meanders1 #afd             
,moseley1 ,h41 #cbb      ,mosses1       
geologic contributions of1 #fef         
,moulton1 ,f4 ,r41 #efe                 
,mountain-forming movements1 #edb       
,mountains1 serration of1 #dh1 #ej      
,mount ,erebus1 #fjc      ,mount ,hecla1
 #fjc      ,mount ,shasta1 #faa         
,mount ,terror1 #fjc      ,movements of 
glaciers1 #bei1 #bfa1 #bgi1 #cac-cbc    
,movements of sea-water1 #ccd-cdb       
causes of1 #ccd-cci      ,movements of  
the earth's body1 #ebf-ehi      causes  
of1 #eea-eeg      continent-forming1    
#edd      distribution in time1 #ede    
epeirogenic1 #ecg      folding          
movements1 #ede      minute and rapid1  
#ebf      mountain-forming1 #edb        
orogenic1 #ecg      periodic1 #edb      
plateau-forming1 #edc      relation of  
vertical and horizontal1 #ede      slow 
and massive1 #ecg      ,mud-cracks1 #dhi

      ,mud-flows1 volcanic1 #faj        
,mud-rain1 #be      ,mudstone1 #dga     
,mgge1 ,o41 #cac1 #cbb1 #cbc      ,muir 
glacier1 #bei      ,murray1 ,sir ,john1 
#aa1 #bae1 #cbe1 #cbf1 #cfi1 #fjd1 #fee 
,muscovite1 #djj1 #dfd        ,narrows1 
#ada      ,natural bridges1 #aec1 #bca  
of ,virginia1 #aef      on coasts1 #cea 
,natural gases1 #fdf      ,natural      
levees 7see ,levees7      ,natural oils1
 #fdf      ,nebraska1 volcanic dust in1 
#bc      ,nephelinite1 #dga             
,nephelite1 #djj1 #dfd      ,nevadite1  
#dga      ,nv1 #bdf      ,new ,river1   
#afh      ,newsom1 ,j4 ,f41 #ead        
,niagara ,falls1 #aci      recession of1
 #aci      ,niagara ,river1 #abj        
,nicholson1 ,a4 7and ,lydekker1 ,r471   
#feh      ,nile ,river1 delta of1 #bjb  
material in solution in1 #ajh           
sediment carried by1 #ajg      ,nitrogen
 and life1 #fdb      ,nodules1 #dga     
,nomenclature of rocks1 #ddi      new   
system of1 #dea      ,norite1 #dga      
,normal faults1 #eag      ,north        

,america1 average elevation of1 #ajf    
,nosite1 #dfe      ,novaculite1 #dga    
,nummulites1 #ffa        ,oblique fault1
 #ebe      ,obsidian1 #djg1 #dec1 #dga  
,ocean basins1 #aa      areas of1 #g    
connection of1 #h      deposits on1     
#cfh-chf      relief of bottom1 #aa     
topography of1 #cbf      ,ocean basin   
segments1 size of1 #edg      ,oceanic   
deposits1 chemical1 #cge      deep-sea1 
#cfh1 #cgh-chf      organic1 #cge1 #chb 
shallow water1 #cfi-cgh      ,ocean1    
the1 #g1 #cbd-cib      changes in1 #cbi 
composition of1 #cbd      diastrophism  
in1 #cbi      gradation in1 #ccc        
salts of1 #cbd      volume of1 #h       
vulcanism in1 #ccb      work of1        
#cbd-cib      ,offset with gap1 #ebe    
,offset with overlap1 #ebe      ,oldham1
 ,r4 ,d41 #ecd1 #ece      ,oligoclase1  
#djj1 #dfe      ,olivine1 #djj1 #dfe    
,omeose1 #dei      ,omphacite1 #dfe     
,onyx1 #dga      ,oolite1 #dce1 #dga1   
#dif      ,ooze1 #dga      ,opal1 #dfe  
,ore deposits 7see ,ores7               

,o',reilly1 ,j4 ,p41 #ech      ,ore     
regions1 origin of1 #dgg      ,ores1    
#dbh1 #dgd-dhe      concentration by    
reprecipitation1 #dgi      concentration
 by solution1 #dgi      concentration by
 surface leaching1 #dgh      8flaxseed10
 #dig      influence of rock walls on   
deposition1 #dhd      magmatic          
segregation1 #dge      marine           
segregation1 #dgf      original         
distribution1 #dge      purification by 
leaching1 #dgh      residual            
concentration1 #dgh      ,organic       
processes1 #fch      ,organic residue1  
#fdj1 #fda      ,organic rocks1 #ddi1   
#fdf      ,original heat distribution1  
#eei-efh      ,origin and descent of    
rocks1 #cic-dhd      ,orogenic          
movements1 #ecg      ,orthoclase1 #djj1 
#dfe      ,orthophyre1 #dga      ,osars1
 #cjf      ,outcrops1 effects of faults 
on1 #ebb      ,outwash plain1 #cjf      
,overloading of streams1 #agg1 #agh1    
#ahf      ,overthrust1 #eah      ,oxbow 
lakes1 #aib1 #aih      ,oxidation1 #db1 

#dbg      ,ozocerite1 #dfe1 #fdf        
,paleontologic geology1 #a              
,paleontology1 #a      ,paraffine1 #fdf 
,peastone1 #dgb      ,peat1 #djf1 #dgb  
,pegmatite1 #dgb      ,pelagic deposits1
 #cgi-chf      organic constituents of1 
#chb      ,pelagic fauna1 #fgj          
,pelecypods1 shells of1 #ffb            
,pele's1 #fah      8,pele's hair10 #djd 
,pelites1 #dgb      ,peneplain1 #ha1    
#afi      ,penrose1 ,r4 ,a4 ,f41 ,jr41  
#dgh      ,peralkalic rocks1 #deh       
,percaleic rocks1 #deh1 #dei            
,perfemane1 #dee      ,perfemic rocks1  
#ded      ,perfelic rocks1 #def         
,perferrous rocks1 #dei                 
,peridotites1 #daf1 #dec      ,perlenic 
rocks1 #def      ,perlite1 #djh1 #dec1  
#dgb      ,permiric rocks1 #deh         
,permirlic rocks1 #deh      ,permitic   
rocks1 #deg      ,perolic rocks1 #deg   
,perpolic rocks1 #def      ,perpotassic 
rocks1 #deh      ,perpyric rocks1 #deg  
,perquaric rocks1 #def      ,perrey1    
,a41 #ecg      ,perrine1 #ech           

,persalane1 #dee1 #dei      ,persalic   
rocks1 #ded      ,persodic rocks1 #deh  
,pertilic rocks1 #deg                   
,petrifaction1 #bbc      8,petrified    
turtles10 #dif      ,petroleum1 #dfe    
,petrology1 #a1 #cic-dhe                
,petrosilex1 #dgb      ,pfaff1 ,f41 #ecg
      ,phanerites1 #dea                 
,phanerocrystalline rocks1 #dab         
,phenocrysts1 #dab      ,philosophic    
geology1 #a      ,phonolite1 #dgb       
,photobathic fauna1 #fgj                
,photobathic zone1 #fgj      ,phyllite1 
#dgb      ,physiographic geology1 #a    
,picrolite1 #dfe      ,pictotite1 #dfe  
,piedmontite1 #dfe      ,piedmont       
glacier1 #bed      ,piedmont plain1     
alluvial1 #ahc      ,piracy1 #afj       
domestic1 #ajd      extent of1 in       
,appalachians1 #agj      foreign1 #ajd  
of ,kaaterskill ,creek1 #aje      of    
,plaaterskill ,creek1 #aje              
,pirsson1 ,louis ,v41 #dab #dea1 #egc   
,pisolite1 #dfe1 #dif      ,pitchstones1
 #djh1 #dec1 #dgb      ,plagioclase1    

#dfe      ,plain1 alluvial1 #aha1 #ahd  
graded1 #afi      outwash1 #cjf         
,planation1 #hb      ,plant kingdom1    
geologic contributions of1 #feb-feh     
,plant life and carbon dioxide1 #ffe    
,plant societies1 #ffg      ,plants1    
contributions to deposits1 #feb-feh     
contribution to limestone1 #fed         
effect on erosion1 #aca1 #fdd           
reference table of1 #fec      weathering
 influenced by1 #aab      ,platte       
,river1 #ahg      ,plaaterskill ,creek1 
piracy of1 #aje      ,plugs1 volcanic1  
#eia      ,plumbago1 #dfe      ,plunging
 anticline1 #aee      ,plutonic rocks1  
#dgb      ,polar glaciers1 #bed         
,poincar1 ,h41 #egf      ,polic rocks1  
#def      ,polmitic rocks1 #deg         
,ponding of streams1 #aga      ,po      
,river1 delta of1 #bjb      sediment    
carried by1 #ajg      ,porphyries1 #dec 
,porphyrite1 #dgb      ,porphyritic     
rocks1 #daa      ,porphyry1 #dgb        
,posepny1 ,f41 #dgd      ,potash1 in    
sea-water1 #cgg      ,pot holes1 #adj   

,potomac ,river1 #afh      sediment     
carried by1 #ajg      ,potoni1 ,h41 #feb
      ,powell1 ,j4 ,w41 #eai1 #eba      
,precipitation1 #ej      from           
atmosphere1 #ea      from solution1 #da1
 #bbe1 #bci1 #cge-cgi                   
,precipitation from solution1 conditions
 influencing1 #bbe      influenced by   
alg1 #bbe      ,pressures within earth1 
based on ,laplace's law1 #efd           
,prestwich1 ,j41 #bjc1 #bbe             
,propylite1 #dgb      ,protogine1 #dgb  
,protozoa1 geologic contribution of1    
#ffj      ,provincial faunas1 #ffh      
,pseudomorphs1 #dfe      ,psilomelane1  
#dfe      ,psychological factors #fea   
,pteridophytes1 geologic contribution   
of1 #feg      ,pteropod ooze1 #chj1 #chb
      8,pulpit rocks10 #cej             
,pumice1 #djf1 #dec1 #dgb      ,push    
moraine1 #cja      ,puzzalana1 #dje     
,pyrite1 #dfe      ,pyroclastic rocks1  
#djd1 #djf1 #dgb      ,pyrolic rocks1   
#deg      ,pyroxene1 #djj1 #dfe         
,pyroxenite1 #dag1 #deb1 #dgb           

,quaquaversal dip1 #ejd                 
,quardofelic rocks1 #def      ,quarfelic
 rocks1 #def      ,quartz1 #dff         
,quartzite1 #ddg1 #dgb                  
,quartz-leucophyres1 #dec               
,quartzophyres1 #dec                    
,quartz-porphyries1 #dec                
,radiolarian ooze1 #chj1 #chb1 #dbe1    
#ffa      ,rain1 amount of1 #ea         
erosion by1 #eg      mechanical work of1
 #ea      ,rain-drop impressions1 #dij  
,rainfall1 effect on erosion1 #abh      
,ransome1 ,f4 ,l41 #acj1 #eac           
,rapids1 development of1 #acc1 #adf     
,rate of erosion1 conditions affecting1 
#abc      ,ravine1 #fd      ,raymond1   
,r4 ,w41 #dgd      ,reade1 ,t4 ,m41     
#bbe1 #cff1 #efa1 #egb                  
,reconstructed glacier1 #bef      ,red  
clay1 #chj1 #chc1 #chd      ,red mud1   
#chj      ,red ,river of ,louisiana1    
#ahh      ,reid1 ,h4 ,f41 #bef1 #bei1   
#bfa      ,regolith1 #djj1 #dgb         
,rejuvenation of streams1 #afb-afc      
criteria of1 #afd1 #afe1 #aff           

,relief1 of lithosphere1 #aa      of    
ocean basins1 #aa      representation on
 maps1 #cj      ,relief of pressure1 a  
cause of volcanic action1 #fbg          
,rendu1 ,l4 ,c41 #cba1 #cbb             
,restrictive evolution1 #fgb            
,reversed fault1 #eag1 #eba      ,reyer1
 ,e41 #fcf      ,rhine ,river1 material 
in solution in1 #ajh      ,rhizopoda1   
geologic contributions of1 #ffj         
,rhone ,river1 delta of1 #bjc           
material in solution in1 #ajh           
sediment carried by1 #ajg               
,rhyolite1 #dgb      ,rhyolitic         
structure1 of lavas1 #da      ,ricard1  
,t4 ,a41 #dgd      ,richthofen1 ,baron  
von1 #bc1 #fjd1 #fad1 #fae              
,rigidity1 distribution of1 #egh        
,rill-marks1 #cgb1 #dhi      ,rink1 ,h41
 #bdh      ,ripple-marks1 #cga1 #dhi    
due to wind1 #cg      ,rio ,grande      
,river1 sediment of1 #ajg      ,river   
lakes1 #aih      ,river erosion 7see    
,stream erosion7      ,roanoke ,river1  
#afh      ,roches ,moutonnes1 #cjd      

,rock breaking1 by changes of           
temperature1 #dd1 #di      ,rocks1      
alferric1 #ded      alkalicalcic1 #deh  
alkalimirlic1 #deh      alterations of1 
#dbf      aqueous1 #dfg      arenaceous1
 #dfh      autoclastic1 #ddd            
calcimiric1 #deh      8chimney10 #cej   
chloritic1 #dca      classification and 
nomenclature1 #ddi      clastic1 #dfh   
crystalline1 #af      determination of  
age1 #ae      disruption by hydration1  
#aaa      docalcic1 #deh      dofemic1  
#ded      doferrous1 #dei      dohemic1 
#deg      dolenic1 #def      domagnesic1
 #dei      domalkalic1 #deh             
domilic1 #deg      domiric1 #deh        
domirlic1 #deh      domitic1 #deg       
dopolic1 #def      dopotassic1 #deh     
dopyric1 #deg      doquaric1 #def       
dosalic1 #ded      dosodic1 #deh        
dotilic1 #deg      eolian1 #dfi         
femic1 #ded      glassy1 #djf           
holocrystalline1 #dab      hypogene1    
#dgj      igneous1 #af1 #cic1 #dih      
leading elements of1 #cif               

lendofelic1 #def      lenfelic1 #def    
magnesiferrous1 #dei      meta-igneous1 
#dga      metamorphic1 #af      mirlic1 
#deh      mitic1 #def      organic1 #fdf
      origin and descent of1 #cic-dhe   
peralkalic1 #deh      percalcic1 #deh1  
#dei      perfelic1 #def      perfemic1 
#ded      perferrous1 #dei      perhemic
 #deg      perlenic1 #def               
permagnesic1 #dei      permiric1 #deh   
permerlic1 #deh      permitic1 #deg     
perolic1 #deg      perpolic1 #def       
perpotassic1 #deh      perquaric1 #def  
persalic1 #ded      persodic1 #deh      
pertilic1 #deg      perpyric1 #deg      
phanerocrystalline1 #dab      plutonic1 
#dgb      polic1 #def      polmitic1    
#deg      porphyritic1 #daa             
precipitate1 #dbg      8pulpit10 #cej   
pyroclastic1 #djd1 #djf1 #dgb           
quardofelic1 #def      quarfelic1 #def  
salfemic1 #ded      salic1 #ded         
secondary1 #dbj      sedimentary1 #dbb1 
#dhf      sodipotassic1 #deh            
solution of1 #dbg      specific heat of1

 #eeb      stratified1 #ad      talcose1
 #dca      tilhemic1 #deg      ,rock    
terraces1 #adj1 #bjd      ,rock waste1  
#ab      ,roots1 wedge-work of1 #aab1   
#aca1 #aej      ,rotation of earth1     
change in rate of1 #ege      effect on  
stream erosion1 #aid      ,rotation and 
vulcanism1 #fjd      ,roth1 ,j41 #ajh   
,running water 7see ,streams7           
,run-off1 #ei      ,russell1 ,i4 ,c41   
#ajh1 #aah1 #aea1 #agb1 #aid1 #bjc1     
#bcb1 #bef1 #bhc1 #chh1 #cib1 #fcf      
,rutile1 #dff        ,saint ,vincent1   
#fje      ,salfemane1 #dee              
,salfemic rocks1 #ded      ,saline lakes
 7see ,salt lakes7      ,saline springs1
 #bce      ,salisbury1 ,r4 ,d41 #bjc1   
#bef      ,salt lakes1 #cia             
composition of1 #cgb      deposits in1  
#chh      ,salts1 deposition of1        
#cge-cgh      in sea-water1 #cbd-cbf    
,sand1 eolian1 #bf-cg      ,sandstone1  
#dbb1 #dcd1 #dgb      stratification of1
 #dhg      ,sandstone dikes1 #ead       
,sanidine1 #dff      ,sapping1 #abg1    

#acc      ,satinspar1 #dff      ,schist1
 #ddf1 #dgb      ,schistosity1 #ddc     
,schmidt1 ,j4 ,f4 ,j41 #ecg             
,schoharie ,creek1 beheaded1 #aje       
,scori1 #dje1 #dgc      ,scour-and-fill1
 #aid      of ,missouri ,river1 #aie    
,scrope1 ,g4 ,p41 #fcf      ,sea-caves1 
#cej      ,sea-cliffs1 #cdi      ,sea1  
the 7see ,ocean7      ,sea-water1       
aperiodic movements of1 #cch            
movements generated by attraction1 #ccg 
movements of1 #ccd-cdb      salts in1   
#cgf1 #cgg1 #cgh      ,sea-waves1 caused
 by earthquake1 #ece      ,secondary    
rocks1 derivation of1 #dbj      8,second
 bottoms10 #bje      ,secretions1 #dig  
,sediment1 carried by ,danube1 #ajg     
carried by ,irrawaddy1 #ajg      carried
 by ,mississippi1 #ajg      carried by  
,nile1 #ajg      carried by ,po1 #ajg   
carried by ,potomac1 #ajg      carried  
by ,rhone1 #ajg      carried by ,rio    
,grande1 #ajg      carried by ,uruguay1 
#ajg      character of1 influenced by   
land vegetation1 #fde      deposited by 

rivers1 #fe1 #agg-bjd      deposited in 
lakes1 #chg      deposited in sea1      
#cfh-chf      effect on corrasion1 #abj 
effect on falls1 #acg      how carried  
by streams1 #aaf      ,sedimentary      
rocks1 classes of1 #dbb      structural 
features of1 #dhf      ,sedimentation   
and vulcanism1 #fbi      ,seed-plants1  
#feg      ,segregation of ores1 #dge    
,seiches1 #chf      ,seine ,river1      
intrenched meanders of1 #afd            
,selenite1 #dff      ,septaria1 #dgc1   
#die      ,serpentine1 #dca1 #dff1 #dgc 
,serpentine kames1 #cjf      ,seward1   
,a4 ,c41 #feb      ,shale1 #dbb1 #dcd1  
#dgc      stratification of1 #dhg       
,shaler1 ,n4 ,s41 #bbg1 #cdi1 #ceg 7and 
,davis1 ,w4 ,m471 #bef                  
,shallow-water deposits1 #cfh1 #cfi1    
#cgi      characteristics of1 #cgc      
topography of1 #cgd      ,shearing of   
glacier ice1 #cag      ,sheet erosion1  
#ei      ,shell marl1 #fee      ,shore  
currents1 #cdb      deposition by1 #cee 
,shore deposition and coastal           

configuration1 #cfc      ,shore drift1  
#cee      ,shore ice1 #chi              
,shoshone ,falls1 #ace      ,siderite1  
#dbe1 #dff      ,silicified wood1 #dci  
,silicious deposits1 #dbe      ,sills1  
#ddf1 #eib      ,sketcherly1 ,s4 ,b41   
#bc      ,slate1 #dgc      ,slaty       
structure1 #dda      ,slichter1 ,c4 ,s41
 #bba1 #efc1 #egf      ,slumps1 #bca    
,smaragdite1 #dff      ,smith1 ,e4 ,a41 
#edc      ,snow-fields1 #bdd            
distribution of1 #bdd      ,snowflakes1 
forms of1 #caj      ,snow-line1 #bde    
in ,andes1 #bdf      in ,antarctica1    
#bdf      in ,greenland1 #bdf      in   
,himalayas1 #bdf      ,snow1 work of1   
#bdd      ,soapstone1 #dca1 #dgc        
,sodipotassic rocks1 #deh               
,solms-,laubach1 #feb      ,solution1 by
 ground-water1 #bbb      by rivers1     
#ajh1 #abb      ,solution of rocks1 #dbg
      ,solvent action1 location of1 #dhj
      ,sorby1 ,h4 ,c41 #cfg      ,source
 of streams1 #agh      ,spatter cones1  
#fji1 #faj      ,specific heat of rock1 

#eeb      ,spermatophytes1 geologic     
contribution of1 #feg                   
,sphenophyllum1 #feg      ,sphericity1 a
 factor in deformation1 #ehj            
,spherosiderite1 #dff      ,spinel1 #dff
      ,spit1 the1 #ceg      ,sponges1   
secretions of1 #ffa                     
,sporadosiderites1 #e      8,spouting   
horn10 #cea      ,springs1 calcareous1  
#bce      chalybeate1 #bce      cold1   
#bcd      common1 #bce      deep1 #bcd  
intermittent1 #bce      medicinal1 #bce 
mineral1 #bce      saline1 #bce         
shallow1 #bcd      sulphur1 #bce        
,stalactite1 #dcg1 #dgc      formation  
of1 #bbg      ,stalagmite #dcg1 #dgc    
,st4 ,anthony ,falls1 #acf      ,stapff1
 ,f4 ,m4 #chh      ,staurolite1 #dff    
,steam discharge from volcanoes1 #fce   
,steatite1 #dca1 #dff1 #dgc             
,stevenson1 ,d41 #cda1 #cdd1 #cgj       
,stoping1 #fcb      ,stoss side1 #bii   
,strachey1 ,r41 #ea                     
,stratification1 #dhf      ,stratified  
rocks1 #ad      ,stratigraphic geology1 

#a      ,stratigraphy and fossils1 #fdg 
,stratigraphy and paleontology1 #fdg    
,stream erosion1 #ef-agg      economic  
effects of1 #ajh      influenced by     
rock1 #abd      influenced by declivity1
 #abc      influenced by structure1     
#abe1 #abg      topography developed by1
 #ib      ,streams1 abrasion by1 #aai   
adjustment in ,appalachians1 #adh       
adjustment of1 #adf1 #adg      affected 
by rotation of earth1 #aid              
aggradational work of1 #agg-bjd         
antecedent1 #afi1 #aga                  
characteristics of aggrading1 #agi1 #ahg
      compared with glaciers1 #bfb      
consequent1 #gh      corrasion by1 #aai 
cross-currents in1 #aag      decrease in
 size of1 #agi1 #ahj      deposition by1
 #agg      drowning of1 #agj      effect
 of change of level on1 #afa1 #aga      
erosion by1 #eg-agg      floods of1 #aji
      ice of1 #aah      intermittent1   
#ga1 #gb      mature1 #hf               
mechanical work of1 #bbf      migration 
from synclines to anticlines1 #aei      

mineral matter in solution in1 #bbe     
old age of1 #hi      overloading of1    
#agh1 #agi1 #ahf      permanent1 #gj    
piracy of1 #ajc      ponding of1 #aga   
relation of width to meander belt1 #aic 
solution by1 #ajh1 #abb      sources of1
 #agh      struggle for existence among1
 #ajj      superimposed1 #aej           
topographic adjustment of1 #afb1 #afc1  
#aig      transportation by1 #aae1 #aaf 
velocity of1 #aae      young1 #he       
,stream-terraces1 #bjd-bab      ,stream 
velocity1 effect on transportation1 #aae
      ,stream work1 #eg-bab             
,stress-accumulation1 #ehc1 #ehh        
,stri1 #bhc      ,strike1 #eja          
,strike fault1 #ebb      ,stromboli1    
#fcf      ,structural adjustment of     
valleys1 #adg      ,structural features 
of rocks1 #dhf-ebe      arising from    
disturbance1 #ejj      of igneous rocks1
 #dih      of sedimentary rock1 #dhf    
,structural geology1 #a1 #dhf           
,structural valleys1 #gg      ,structure
 of glacier ice1 #cjh      ,structure of

 rock1 influence on erosion1 #abe       
,struggle for existence among valleys1  
#ajj      ,subarial erosion1 #eh        
,sub-atomic forces1 causes of crustal   
movement1 #eef      ,subdivisions of    
geology1 #a      ,subglacial load1 #bhb 
,subsidence1 effect on coast-lines1 #cca
      ,suess1 ,edw41 #ech      ,sulphur1
 #dff      ,sulphur springs1 #bce       
,sun-cracks1 #cgc1 #dij                 
,superglacial load1 #bhb                
,superimposed streams1 #aej             
,surface moraines1 #bff                 
,susquehanna ,river1 #afh               
,switzerland1 snow-fields of1 #bde      
,syenites1 #dae1 #deb1 #dgc             
,syncline1 #aeg1 #ejd      ,synclinoria1
 #ejd      ,syssiderites1 #e            
,tachylite1 #dgc      ,tait1 ,p4 ,g41   
#eeb1 #egb1 #egc 7and ,thompson1 ,j471  
#efj1 #egi      ,talc1 #dff             
,talcose rock1 #dca      ,talus1 #aab   
,talus cone1 #ahb      ,talus glacier1  
#bcc1 #bcb      ,tarr1 ,r4 ,s41 #afe    
,temperature1 at centre of earth1 #ega  

atmospheric1 #dc1 #df1 #di      based on
 ,laplace's law1 #efd      effect on    
erosion1 #abi      effects of changes on
 rocks1 #dd      expansion and          
contraction due to changes of1 #dd      
in excavations1 #efi      of interior of
 earth1 #eei-egj      of lavas1 #fae1   
#fbg      ,tennessee ,river1 history of1
 #afh-afi      ,tension joints1 #ead    
,terminal moraine1 #bff1 #cja           
,terraces1 stream1 #bjd-bab             
flood-plain1 #bje      rock1 #adj1 #bjd 
termini of1 #baj      wave-built1 #cfc  
wave-cut1 #cea1 #cec      ,terrigenous  
deposits1 in sea1 #cgi                  
,thallophytes1 geologic contribution of1
 #fec      ,thames ,river1 #bbd         
material in solution in1 #ajh           
,thibetan plateau1 #edh      ,thompson1 
,james1 #cbb1 #efj1 #egi      ,thompson1
 ,w4 ,g41 #aai      8,thorofares10 #ceh 
,thrust-fault1 #eag1 #eah      ,tides1  
#d1 #cch      effect on rotation1 #d    
,tilden1 ,w4 ,a41 #fbj      ,tilhemic   
rocks1 #deg      ,till1 #dgc            

,titanite1 #dfg      ,todd1 ,j4 ,e41    
#aie      ,topaz1 #dfg      ,topographic
 adjustment of streams1 #afb1 #afc1 #aig
      ,topographic effects of glacial   
erosion1 #bhg      ,topographic effects 
of ground-water1 #bca      ,topographic 
map1 explanation of1 #cj                
,topographic maturity1 #hf              
,topographic old age1 #hi               
,topographic youth1 #hf                 
,topography1 developed by river erosion1
 #ib      dune1 #cb      landslide1 #bca
      mature1 #hf      of alluvial      
deposits1 #aif      of glaciers1 #bff   
of ocean bottom1 #cbf      of           
shallow-water deposits1 #cgd            
youthful #hf      ,top-set beds1 #bjb   
,trachyte1 #dgc      ,transportation1   
#aaj      by glaciers1 #bha      by     
ocean currents1 #cfg      by streams1   
#aae1 #aai      by waves1 #ced      by  
wind1 #bb1 #be      ,trap1 #dai1 #dgc   
,travertine1 #dgc      ,trees1 uprooting
 of1 #dj      ,tremolite1 #ddg1 #dfg    
,tributaries1 development of1 #gh       

position of1 #gi      topographic       
adjustment of1 #aig      ,tripoli1 #ffa 
,tripolite1 #dbf      ,trout creek1 #aic
      ,tschermak1 ,g41 #ech      ,tufa  
7see ,tuffs7      ,tufa cones1 #faa     
,tufa deposits1 #faa      ,tuffs1 #djd1 
#dcd1 #dgc      ,tuscarora deep1 #edh   
,two ,medicine ,river1 #aed1 #aeg       
,tyndall1 ,j41 and ,huxley1 ,t4 ,h41    
#cbb        ,udden1 ,j4 ,a41 #bb        
,uinta ,mountains1 lateral moraines of1 
#cjc      ,underground water 7see       
,ground-water7      ,undertow1 #cda     
deposition by1 #cee      erosion by1    
#cdb1 #cdg      ,united ,states         
,geological ,survey1 ,,vi41 #cb         
,upham1 ,w41 #chh      ,uprooting of    
trees1 #dj      ,uralite1 #dca          
,uruguay ,river1 sediment carried by1   
#ajg      ,usiglio1 #cge                
,valleys1      affected by folds1 #aed  
antecedent 7see ,streams1 antecedent7   
canoe-shaped1 #aee      consequent1 #gh 
courses of1 #gg      development of1    
#fc1 #gj1 #gc1 #hj      hanging1 #afd1  

#bij      limits of growth1 #fg         
oldest parts1 #gf      profiles of1 #ff 
relations to lakes1 #gd      slopes of1 
#id      special forms of1 #id          
structural1 #gg      struggle for       
existence among1 #ajj      ,van ,hise1  
,c4 ,r41 #bai1 #dcd1 #ddh1 #dgd1 #dgi1  
#ejd1 #edc1 #eee1 #egj      ,vegetation1
      effect on dunes1 #bi      effect  
on erosion1 #aca1 #fdd      effect on   
sediments1 #fde      effect on          
weathering1 #aca      ,veins1 #bbc1     
#dbh1 #eaa      ,vermes1 geologic       
contribution of1 #ffb      ,vermeule1   
,c4 ,c41 #aji      ,vertebrata1 geologic
 contribution of1 #ffc      ,vesuvius1  
#fje      ,virginia1 natural bridge of1 
#aef      ,viridite1 #dfg      ,volcanic
 action1 causes of1 #fbc-fcc            
activity1 periodicity of1 #fjg      ash1
 #bc1 #djd1 #eib1 #fag      bombs1 #djf1
 #eib1 #fag      cinders1 #eib          
cones1 #ejj      dbris in sea1 #cha     
dust 7see ,volcanic ash7      eruptions1
 #eid        and atmospheric pressure1  

#fjf        and tidal strain1 #fjg      
types of1 #eic      gases1 #fag-fbc     
action of1 #fag        kinds of1 #fah   
proportions of1 #fbj1 #fbb              
sources of1 #fai1 #fbj1 #fba1 #fcc      
glass 7see ,obsidian7        in sea1    
#cha      mud1 #chj        flows of1    
#faj      neck1 #ejj      plug1 #ejj    
rocks1 #cie-dah        residual gases   
in1 #fai      smoke1 #eib1 #fag         
,volcanoes1 #eii-faa      coincidence in
 eruption of1 #fjf      cones of1 #fjh  
distribution of1 in curved lines1 #fjc  
distribution of1 in latitude1 #fjc      
distribution of1 in relation to crustal 
movements1 #fja1 #fjd1 #fbh             
distribution of1 in relation to land and
 sea1 #eii      distribution of1 in     
time1 #eii      independence of1 #fje1  
#fbc      periodicity of1 #fjg          
relations of1 #fjd-fjg      relations to
 one another1 #fje      ,volume of      
ocean1 #cbe      ,vuggs1 #dcg           
,vulcanism1 #b1 #eij-fcg      causes of1
 #fbc-fcc      effects on coast-lines1  

#ccb      in ocean1 #ccb      ,vulcanism
 and deep sedimentation1 #fbi           
ground-water1 #fce      rotation1 #fjc  
,wacke1 #dbb1 #dgc1 #fde      ,wad1 #dfg
      ,walcott1 ,c4 ,d41 #aid1 #bdf1    
#cga1 #dch1 #ddj1 #dda1 #ejb1 #ejc1 #eji
      ,wallace1 ,a4 ,r41 #ffe1 #ffh     
,walther1 ,j41 #ej1 #fgj      ,warming1 
,e41 #ffg      ,warping1 effect of1 on  
streams1 #aga      of earth's crust1    
#ebf1 #eda1 #edb      ,wasatch          
,mountains1 lateral moraines of1 #cjc   
,washington1 ,h4 ,s41 #dab1 #dea1 #egc  
,waste of glaciers1 #bgc      ,water    
7see ,streams1 ,ground-water1 ,ocean1   
etc47      amount of1 #g      geologic  
activity of1 #h      ,water-gaps1 #ada1 
#afg      ,waterfalls1 #acb             
development of1 #acc      ,minnehaha1   
#acg      ,niagara1 #aci      ,shoshone1
 #ace      ,st4 ,anthony1 #ace          
,upper ,yosemite1 #ach                  
,yellowstone1 #ace      ,waterfalls and 
sediment1 #acg      ,water-lime1 #dgc   
,water-table1 #ga1 #bae                 

,water-vapor1 climatic effects of1 #fdc 
,wave-built terraces1 #cfc              
,wave-cut terraces1 #cea1 #ceb          
,wave erosion1 #cdb-ced      range of1  
#cdf      topographic features developed
 by1 #cdi      ,wave erosion and        
horizontal configuration1 #cec1 #cfc1   
#cfd      ,wave-marks1 #dij             
,wave-motion1 #cci      ,waves1 #cci    
deposition by1 #cee      erosion by1    
#cdb-ced      force of1 #cdd            
transportation by1 #ced      work of1   
#cdb-cff      ,weathering1 #ed1 #aaj1   
#bbf      affected by life1 #fdd        
aided by plants1 #aab      aided by hot 
vapors1 #aac      effect of gravity1    
#aab      effect of joints1 #aea1 #aec  
importance of1 in valley growth1 #aad   
,wedgework of ice1 #de1 #dh1 #aej       
of roots1 #aab1 #aca1 #aej      ,weed1  
,w4 ,h41 #bbe1 #bcg1 #dgd1 #fef         
,wells1      artesian1 #bdb             
flowing1 #bcd1 #bdb1 #bdc      ,wheeling
 well1 temperature of1 #efi      ,white 
glacier1 #bfc      ,whitfield1 ,j4 ,e4  

7and ,gooch1 ,f4 ,a471 #bcf             
,williams1 ,h4 ,s41 #feh      ,willis1  
,b41 #aeg1 #afh1 #afi1 #beg1 #cdd1 #cee1
 #cfe1 #eaf1 #edc1 #eej      ,winchell1 
,h4 ,v41 #dgd      ,wind1 abrasion by1  
#ch      effects on plants1 #dj         
movements of sea1 generated by1 #ccf    
transports organisms1 #da      work of1 
#ba-da      ,wind-blown dust1 #bb       
,wind-blown sands1 #be                  
,wind-ripples1 #cg      ,winslow1 ,a41  
#dgd      ,wisconsin ,river1 dells of1  
#aeb      ,woodward1 ,r4 ,s41 #efj1 #eha
      ,work of glaciers1 #bha           
,wyandotte ,cave1 #bbg1 #bbh            
,yazoo ,river1 #ahh      ,yellowstone   
,park1      geysers of1 #bch      hot   
springs of1 #bbe      ,yellowstone      
,river1      canyon of1 #ajj      falls 
of1 #ace      ,yukon ,river1 delta of1  
#bjb        ,zeiller1 #feb              
,zeolites1 #dbh1 #dfg      ,zircon1 #dfg
      ,zittel1 ,k4 von1 #feh1 #fei      
,zone of fracture1 #bai1 #dbg           
,,footnotes3    #a ,the ,earth4         

,johnson's ,encyclopdia4 ,see also      
statement of ,murray in    ,smithsonian 
,an4 ,rept41 #ahii1 p4 #cab4 ,reprint   
from ,brit4 ,a4 ,a4 ,s41    ,dover      
meeting1 #ahii1 and ,scot4 ,geog4 ,mag41
 ,vol4 ,,xv1 #ahii1 p4 #eaa4    #b ,its 
specific gravity as a whole is about    
#e4eg1 and the specific    gravity of   
its outer portion is about #b4g4    #c  
,for an excellent study of the erosion1 
transportation1 and    sedimentation    
performed by the atmosphere1 see ,udden1
 ,jour4 of ,geol41    ,vol4 ,,ii1 pp4   
#cah-cca4 ,see also ,pop4 ,sci4 ,mo41   
,september1 #ahif4    #d ,the ,eruption 
of ,krakatoa4 ,committee of the ,royal  
,society1 #ahhh4    #e ,a brief account 
of the influence of the dust on sunsets 
is found in    ,davis's ,elementary     
,meteorology1 pp4 #he and #aai4    #f   
,science1 ,new ,ser41 ,vol4 ,,iv1 p4    
#haf1 #ahif4    #g ,von ,richtofen4     
8,china40    #h ,sketcherley and        
,kingsmill4 ,quar4 ,jour4 ,geol4 ,soc41 
,vol4 ,,li1 #ahie1    pp4 #bch-bed4     

#i ,chamberlin4 ,jour4 of ,geol41 ,vol4 
,v1 p4 #gie4    #aj ,a thoroughgoing    
study of the ,formation of ,sand ,dunes 
7by ,v4    ,cornish7 is to be found in  
the ,geog4 ,jour41 ,vol4 ,,ix1 #ahig1   
pp4    #bgh-cji4    #aa ,blanford4      
,geology of ,india1 #b;d ed41 p4 #dee et
 seq4    #ab ,cornish1 loc4 cit4    #ac 
,cornish1 loc4 cit41 p4 #bid4    #ad    
,diller states 7#agth ,ann4 ,rept41 ,u4 
,s4 ,geol4 ,surv41 ,pt4 ,i1 p4 #dej7    
that on the coast of ,oregon the slope  
of dunes is sometimes #dj4    #ae ,from 
folio preface1 ,u4 ,s4 ,geol4 ,surv4    
#af ,credner4 ,elemente der ,geologie1  
#fth ed41 p4 #bga4    #ag ,merrill4     
,rocks1 ,rock ,weathering1 and ,soils1  
p4 #bie4    #ah ,cowles4 ,the           
,ecological ,relations of the           
,vegetation of the ,sand    ,dunes of   
,lake ,michigan4 ,botanical ,gazette1   
,vol4 ,,xxvii1 #ahii4 ,an    excellent  
study of the relations of sand dunes and
 vegetation4    #ai ,for example1 in the
 ,big ,horn ,mountains of ,wyoming4     

#bj ,it should be noted that it is the  
change of temperature of the    rock    
surface1 not the change of temperature  
of the air above it1    which is to be  
considered4 ,many data concerning       
temperature changes    are to be found  
in ,bartholomew's ,atlas of             
,meteorology4    #ba ,buckley4          
,wisconsin ,survey1 ,bull4 ,,iv1 #ahii1 
pp4 #ha-c4    #bb ,livingstone has      
reported that the temperature of rock   
surfaces    in ,africa sometimes reaches
 #acg ,fahr4 during the day1 and cools  
sufficiently at night to split off      
blocks of #bjj lbs4 weight4    #bc      
,buckley4 ,surv4 of ,wis41 ,bull4 ,,iv1 
pp4 #ai1 #bj4    #bd ,for an excellent  
discussion of erosion in dry regions see
    ,walther's ,die ,denudation in der  
,wste4    #be ,on the assumption that   
condensation takes place at an average  
elevation of #cjjj feet1 it has been    
estimated that the force    necessary to
 evaporate and diffuse the moisture     
which falls as    rain and snow would be

 equivalent to #cjj1jjj1jjj1jjj         
horse-power    constantly in operation4 
7,strachey1 ,lectures on ,geography1 p4 
#ade47    #bf ,mc,gee4 ,bull4 ,geol4    
,soc4 ,am41 ,vol4 ,,viii1 pp4 #hg-aab4  
#bg ,for a discussion of convex and     
concave erosion slopes see ,bain1       
,geol4 ,surv4 of ,ia41 ,vol4 ,,vi1 p4   
#ddi4    #bh ,great rivers1 like the    
,mississippi1 cut their channels        
somewhat    below sea-level1 but        
probably not by an amount exceeding the 
depth of    the stream itself 7see p4   
#gi74    #bi ,davis4 ,jour4 of ,geol41  
,vol4 ,x1 p4 #hg4    #cj ,ibid41 p4 #gg 
et seq4    #ca ,in regions where canyons
 are common1 the term is often applied  
to    all valleys4    #cb ,humphreys and
 ,abbot4 ,physics and ,hydraulics of the
 ,mississippi    ,river4    #cc ,from   
,russell's ,rivers of ,north ,america1  
p4 #gh4    #cd ,alkaline carbonates     
considered as sodium carbonates4    #ce 
,carbonic acid by difference4    #cf    
,babb4 ,science1 ,vol4 ,,xxi1 p4 #cdc4  

#ahic4    #cg ,quoted by ,mason4        
,water-supply1 p4 #bjd4    #ch ,sot4    
,geog4 ,mag41 ,vol4 ,,iii1 p4 #gf4      
#ahhg4    #ci ,acids and bases combined 
according to the principles indicated by
    ,bunsen4    #dj ,chemical ,geology1 
,vol4 ,i1 pp4 #gf1 #gg1 ,english ed41   
#ahed4    #da ,allgemeine und chemische 
,geologie1 ,vol4 ,i1 pp4 #def1 #deg4    
#ahgi4    #db ,russell4 ,rivers of      
,north ,america1 p4 #gi4    #dc ,for    
disastrous floods of the lower          
,mississippi1 see ,johnson1 ,bull4      
,geol4 ,soc4 ,am41 ,vol4 ,,ii1 pp4      
#bj-be4 ,for effect of precipitation    
and forests on floods1 see ,russell's   
,meteorology1 pp4 #aih-bag1 and         
,vermeule1 ,report on ,water ,supply1   
,geol4 ,surv4 of ,n4 ,j4    #dd ,an     
excellent discussion of this subject is 
given by ,gilbert in ,the    ,henry     
,mountains1 pp4 #ii et seq41 and more   
briefly in the ,am4 ,jour4    ,sci41    
,vol4 ,,xii1 p4 #he et seq4 #ahgf4      
#de ,jour4 of ,geol41 ,vol4 ,,iv1 p4    

#gah4 ,an excellent summary of the      
principles of ,rock ,weathering4    #df 
,russell4 ,rivers of ,north ,america1 p4
 #ag4    #dg ,w4 ,g4 ,thompson4 ,nature1
 ,vol4 ,i1 p4 #eee1 #ahgj4 ,the         
,matapediac    ,river1 ,n4 ,b4 ,cited by
 ,russell in ,rivers of ,north ,america1
 p4 #be4    #dh ,dutton4 ,tertiary      
,history of the ,grand ,canyon          
,district1 ,mono4 ,,ii1    ,u4 ,s4      
,geological ,survey4    #di ,the terms  
rapids1 falls1 and cataracts are rather 
loosely used4    ,many moderate rapids  
are incorrectly called falls4 ,the      
8,falls of the    ,ohio0 is an example4 
,the term cataract is often applied to  
very steep    rapids or falls4    #ej   
,gilbert1 article on ,niagara ,falls1 in
 ,physiography of the ,united           
,states4    #ea ,gilbert4 ,am4 ,jour4   
,sci41 ,vol4 ,,xii4 p4 #ii1 #ahgf4      
#eb ,for a brief account of this fall   
see ,gilbert in ,physiography of    the 
,united ,states4    #ec ,gilbert4       
,science1 ,vol4 ,,viii1 p4 #bje1 #ahhf4 

#ed ,see ,campbell1 ,jour4 ,geol41 ,vol4
 ,,iv1 pp4 #efg1 #feg4    #ee ,russell4 
,rivers of ,north ,america1 p4 #bhj4    
,the influence of joints    on drainage 
is further discussed by ,hobbs1 ,jour4  
,geol41 ,vol4 ,,ix1 p4    #dfi4    #ef  
,see ,willis4 ,the ,northern            
,appalachians1 in ,physiography of the  
,united ,states4    #eg ,this process of
 adjustment has been well described by  
,davis in ,the    ,rivers and ,valleys  
of ,pennsylvania1 ,natl4 ,geog4 ,mag41  
,vol4 ,i1 p4 #baa    et seq4    #eh     
,this sort of adjustment may be called  
topographic adjustment4    ,a tributary 
is in topographic adjustment when its   
gradient is    harmonious with that of  
its main4    #ei ,davis4 ,the ,seine1   
the ,meuse and the ,moselle4 ,nat'l     
,geog4 ,mag41    ,vol4 ,,vii1 pp4       
#aha-bjb1 and #bbh-bch4 ,an article     
which throws much    light on the       
behavior of rivers4    #fj ,another view
 has been advocated by ,tarr1 ,am4      
,geol4 ,vol4 ,,xxi1 pp4    #cea-cgj4    

#fa ,campbell4 ,bull4 ,geol4 ,soc4 of   
,am41 ,vol4 ,,xiv1 p4 #bgg4    #fb      
,willis4 ,physiography of the ,united   
,states4 ,the ,northern                 
,appalachians4    #fc ,for excellent    
accounts of the rivers of the           
,appalachian ,mountains    see ,davis1  
,rivers of ,northern ,new ,jersey1      
,nat'l ,geog4 ,mag41 ,vol4    ,,ii1 pp4 
#ha-aaj2 and ,rivers of ,pennsylvania1  
op4 cit41 pp4 #ahc-bec2    ,willis1 ,the
 ,northern ,appalachians1 ,physiography 
of the ,united ,states1    pp4 #afi-bjb2
 ,hayes1 the ,southern ,appalachians1   
op4 cit41 pp4 #cje-ccf2    ,hayes and   
,campbell1 ,the ,geomorphology of the   
,southern ,appalachians1    ,nat'l      
,geog4 ,mag41 ,vol4 ,,vi1 pp4 #fc-abf1  
and ,hayes1 ,physiography of the        
,chattanooga ,district1 #aith ,ann4     
,rep4 ,u4 ,s4 ,geol4 ,surv41 ,pt4 ,,ii1 
pp4    #a-eh4    #fd ,this is the case  
at ,davis and ,lone ,star4 ,capt        
,howell1 ,miss4 ,riv4    ,commission4   
#fe ,russell4 ,rivers of ,north         

,america1 p4 #bgi4    #ff ,russell4     
,rivers of ,north ,america1 p4 #bgi4    
#fg ,hayes4 ,physiography of the        
,chattanooga ,district1 #aith ,ann4     
,rep41    ,u4 ,s4 ,geol4 ,surv41 ,pt4   
,,ii1 pp4 #i-eh4 ,see1 also1 ,hayes and 
,campbell1    ,geomorphology of the     
,southern ,appalachians1 ,nat'l ,geog4  
,mag41 ,vol4    ,,vi1 pp4 #fc-abf4      
#fh ,figs4 #afe-afh are based on reports
 of ,hayes1 and ,hayes and    ,campbell1
 already referred to4 ,drawn by ,e4 ,s4 
,bastin4    #fi ,a question might be    
raised in this case as to what should be
    called the source4 ,a spring issues 
from beneath the surface and flows      
away in a stream4 ,the stream is said to
 begin where the water appears    at the
 surface1 though in some cases the water
 of the spring was a    subsurface      
stream before it reached the surface4   
,water escaping from    beneath a       
glacier as a stream may likewise be     
considered a spring at    the point of  
its issue4    #gj ,davis4 ,science1     

,vol4 ,x1 p4 #adb1 #ahhg4    #ga ,l4 ,c4
 ,johnson4 ,bull4 ,geol4 ,soc4 ,am41    
,vol4 ,,ii1 pp4 #bj-be1 #ahia4    #gb   
,jefferson4 ,nat'l ,geog4 ,mag41 ,vol4  
,,xiii1 pp4 #cgc-hd4    #gc ,according  
to map published by the ,mississippi    
,river ,commission in    #ahhg4    #gd  
,russell4 ,rivers of ,north ,america1 p4
 #aad4    #ge ,gilbert4 ,am4 ,jour4     
,sci41 ,vol4 ,,xxvii1 #ahhd1 pp4        
#dbg-cd4    #gf ,cooley4 ,rept4 ,u4 ,s4 
,engineers for #ahgi-hj1 ,pt4 ,,ii1 pp4 
#ajfj and    #ajga4    #gg ,gerber4     
,cited by ,todd4 ,bull4 #aeh1 ,u4 ,s4   
,geol4 ,surv41 pp4 #aej1 #aea4    #gh   
,chamberlin4 ,jour4 of ,geol41 ,vol4 ,x1
 pp4 #gdg-ged4    #gi ,for an excellent 
discussion of deltas1 see ,gilbert1     
,fifth ,ann4    ,rept4 ,u4 ,s4 ,geol4   
,surv41 pp #ajd-h4 ,also ,lake          
,bonneville1 ,monograph ,i1    ,u4 ,s4  
,geol4 ,surv4 7same article74    #hj    
,davis4 ,physical ,geography1 p4 #bid4  
#ha ,humphreys and ,abbot4 ,physics and 
,hydraulics of the ,mississippi         

,river4    #hb ,corthell4 ,nat'l ,geog4 
,mag41 ,vol4 ,,viii1 p4 #cea1 #ahig4    
#hc ,russell4 ,rivers of ,north         
,america1 p4 #acb4    #hd ,prestwich4   
,chemical and ,physical ,geology1 ,vol4 
,i1 p4 #he4    #he ,geike4 ,text-book of
 ,geology1 #c;d ed41 p4 #djb4    #hf    
,medlicott and ,blanford1 ,geology of   
,india4 ,chap4 ,,xvii2 ,medlicott1      
,records of the ,geological ,survey of  
,india1 #ahha2 ,oldham1 ,geology of     
,india1 #b;d ed41 ,chap4 ,,xvii2 and    
,ferguson1 ,q4 ,j4 ,g4 ,s41 ,vol4 ,,xix1
 pp4    #cba-ed4 ,the extent of this and
 other deltas is variously stated1      
probably because it is difficult to     
determine the exact position of    its  
head and borders4    #hg ,dana4 ,manual 
of ,geology1 #dth ed41 p4 #aih4    #hh  
,salisbury and ,kmmel4 ,lake ,passaic4  
,ann4 ,rept4 of the ,state    ,geologist
 of ,new ,jersey1 #ahic1 and ,jour4 of  
,geol41 ,vol4 ,,iii4 p4 #ecc4    #hi    
,gilbert4 ,lake ,bonneville1 ,mono4 ,i1 
,u4 ,s4 ,geol4 ,surv4    #ij ,for       

discussions of terraces see ,gilbert's  
,henry ,mountains1 p4 #abf2    ,davis'  
,river ,terraces in ,new ,england1      
,bull4 of the ,mus4 of ,comp4    ,zool41
 ,geol4 ,series1 ,vol4 ,v1 pp4 #bhb-cdf2
 and ,dodge1 ,proc4 ,boston    ,soc4 of 
,nat4 ,hist41 ,vol4 ,,xxvi1 pp4 #beg-gc4
    #ia ,davis1 ,bull4 ,mus4 ,comp4     
,zool41 ,geol4 ,ser41 ,vol4 ,v4    #ib  
,this point has recently been emphasized
 by ,davis1 loc4 cit41 pp4    #bhb-cdf4 
#ic ,murray4 ,scot4 ,geog4 ,mag41 ,vol4 
,,iii1 p4 #gj1 #ahhg4    #id ,hoskins4  
#afth ,ann4 ,rept41 ,u4 ,s4 ,geol4      
,surv41 p4 #hec4    #ie ,van ,hise4     
,principles of ,north ,american         
,pre-,cambrian ,geology1 #afth    ,ann4 
,rept41 ,u4 ,s4 ,geol4 ,surv4    #if    
,for a full discussion of this subject  
see ,king1 #aith ,ann4 ,rept41    ,u4   
,s4 ,geol4 ,surv41 ,pt4 ,,ii1 and       
,slichter1 ,water ,supply and           
,irrigation1    ,paper ,no4 #fg1 ,u4 ,s4
 ,geol4 ,surv4    #ig ,for tables see   
,buckley1 ,building and ,ornamental     

,stones1 ,bull4 ,,iv1    ,wis4 ,surv41  
and ,merrill1 ,stones for ,building and 
,decoration1 and    various ,survey     
,reports4    #ih ,it is probable that   
the porosity decreases in more than an  
arithmetic ratio1 both because the      
deeper rocks are not of porous    kinds1
 and because of the pressure which tends
 to close openings4    #ii ,slichter    
7op4 cit41 p4 #ae7 estimates that the   
ground-water is    sufficient in amount 
to cover the earth's surface to a depth 
of    #cjjj to #cejj feet4 ,earlier     
estimates gave still higher figures 7see
    ,delesse1 ,bull4 ,soc4 ,geol41      
,france1 ,second ,series1 ,vol4 ,,xix1  
#ahfa-fb1    p4 #fd74    #ajj ,geikie4  
,text-book of ,geology1 #c;d ed41 p4    
#cfg4    #aja ,ibid41 p4 #cgh4    #ajb  
,prestwich1 ,q4 ,j4 ,geol4 ,soc41 ,vol4 
,,xxviii1 p4 lxvii4    #ajc ,reade4     
,liverpool ,geol4 ,soc41 #ahgf and      
#ahhd4    #ajd ,this is not true in the 
case of minerals1 such as lime          
carbonate1    dissolved under the       

influence of gases in solution in the   
water4    #aje ,weed4 ,the ,formation of
 ,hot ,springs ,deposits4 ,excursion to 
the    ,rocky ,mountains4 ,compte       
,rendu4 ,fifth ,session of the          
,international    ,geological ,congress1
 p4 #cfj1 and ,ninth ,ann4 ,rept4 ,u4   
,s4 ,geol4 ,surv41    pp4 #fac-gf4 ,also
 ,b4 ,m4 ,davis1 ,science1 ,vol4 ,,vi1  
pp4 #ade-eg1 #ahig4    #ajf ,for a racy 
and interesting account of caverns see  
,shaler's    ,aspects of the ,earth4    
#ajg ,russell has emphasized this point 
in #bjth ,ann4 ,u4 ,s4 ,geol4 ,surv41   
,pt4 ,,ii1 pp4 #aic-bjb1 and ,cross1    
#bast ,ann4 ,u4 ,s4 ,geol4 ,surv41 ,part
 ,,ii1    pp4 #abi-aej4    #ajh ,gooch  
and ,whitfield4 ,bull4 #dg1 ,u4 ,s4     
,geol4 ,surv4    #aji ,copied from      
,russell1 ,mono41 ,,xi4 ,u4 ,s4 ,geol4  
,surv41 p4 #agf4    #aaj ,correction for
 specific gravity only approximate1 as  
specific    gravity was not given in    
original analyses4    #aaa ,as          
carbonates4    #aab ,as carbonate4      

#aac ,as oxide4    #aad ,as carbonate4  
#aae ,as sodium chloride4    #aaf ,as   
fluoride of calcium4    #aag ,oxygen    
added to ,si,o to form ,si,o of         
,na,si,o4    #aah ,liters of gas thrown 
off per liter of water4    #aai ,weed4  
,ninth ,ann4 ,rept4 ,u4 ,s4 ,geol4      
,surv41 pp4 #fac-gf1 and ,am4    ,jour4 
,sci41 ,vol4 ,,xxxvii1 #ahhi1 pp4       
#cea-ei4    #abj ,geikie4 ,geological   
,sketches1 pp4 #bjf-ch4 ,hayden4 ,amer4 
,jour4    ,sci41 ,vol4 ,,iii1 #ahgb1 pp4
 #aje-ae and #afa-gf4    #aba           
,chamberlin4 ,geol4 of ,wis41 ,vol4 ,i1 
pp4 #fhi-ig1 and ,fifth ,ann4    ,rept41
 ,u4 ,s4 ,geol4 ,surv41 pp4 #aca-gc4    
,the former a brief1 and the    latter  
an elaborate1 exposition of the         
principles involved4    #abb ,russell4  
,nat'l ,geog4 ,mag41 ,vol4 ,,iii1 pp4   
#abg and #aha4    #abc ,for an account  
of experiments illustrating the mobility
 of ice    see ,aitkin1 ,am4 ,jour4     
,sci41 ,vols4 ,v1 p4 #cjc1 and ,,xxxiv1 
p4 #adi1 and    ,nature1 ,vol4 ,,xxxix1 

p4 #bjc4    #abd ,jour4 of ,geol41 ,vol4
 ,,iii1 p4 #hhh4    #abe ,the following 
list includes many of the more available
 articles    and treatises on existing  
glaciers2 others are referred to in the 
following pages4      ,alaskan glaciers3
 ,reid1 7#a7 ,nat4 ,geog4 ,mag41 ,vol4  
,,iv1 pp4 #ai-ee2    7#b7 ,sixteenth    
,ann4 ,rept41 ,u4 ,s4 ,geol4 ,surv41    
,part ,i1 pp4 #dba-dfa4    ,russell1    
7#a7 ,nat4 ,geog4 ,mag41 ,vol4 ,,iii1   
pp4 #agf-ahh2 7#b7 ,jour4 of    ,geol41 
,vol4 ,i1 pp4 #bai-bde4      ,glaciers  
in the ,united ,states3 ,russell1 7#a7  
,fifth ,ann4 ,rept41 ,u4    ,s4 ,geol4  
,surv41 pp4 #cji-cee2 7#b7 ,eighteenth  
,ann4 ,rept41 ,u4 ,s4 ,geol4    ,surv41 
,part ,,ii1 pp4 #cgi-dji2 7#c7 ,glaciers
 of ,north ,america4      ,greenland    
glaciers3 ,chamberlin1 ,jour4 of ,geol41
 ,vol4 ,,ii1 pp4    #gfh-ghh2 ,vol4     
,,iii1 pp4 #fa-fi1 #aih-bah1 #dfi-dhj1  
#efe-ehb1 #ffh-fha1    and #hcc-hdc2    
,vol4 ,,iv1 pp4 #ehb-eib4 ,salisbury1   
,jour4 of ,geol41 ,vol4    ,,iii1 pp4   

#hge-ijb1 and ,vol4 ,,iv1 pp4 #gfi-haj4 
,glaciers in general3 ,shaler and       
,davis1 ,illustrations of the           
,earth's ,surface2 ,forbes1 ,norway and 
its ,glaciers1 and ,theory of           
,glaciers2 ,heim1 ,handbuch der         
,gletscherkunde4    #abf ,reid4 ,natl4  
,geog4 ,mag41 ,vol4 ,,iv1 p4 #dd4       
#abg ,rink's ,greenland4    #abh ,reid4 
,variations of ,glaciers4 ,jour4 of     
,geol41 ,vols4 ,,iii1 p4 #bgh2    ,v1 p4
 #cgh2 ,,vi1 p4 #dgc2 ,,vii1 p4 #bag2   
,,viii1 p4 #aed2 ,,ix1 p4 #bej1 and ,x1 
p4 #cac4    #abi ,for example1 in the   
,middle ,blase ,dale glacier1 ,island of
 ,disco1    ,jour4 of ,geol41 ,vol4     
,,ii1 p4 #ghd1 and in the ,bowdoin      
glacier 7,fig4    #bdb74    #acj        
,centimeter-gramme-second system4 ,the  
rate of conductivity has not    been    
very accurately determined4    #aca     
,russell4 ,jour4 of ,geol41 ,vol4 ,,iii1
 p4 #hbc4    #acb ,geikie4 ,the ,great  
,ice ,age1 #c;d ed41 p4 #ebi4    #acc   
,carried out by ,c4 ,e4 ,peet and ,e4   

,c4 ,perisho under the direction    of  
one of the authors4    #acd ,ueber die  
,plasticitt der ,eiskrystalle4 ,neues   
,jahrbuch fr    ,mineralogie1 etc41     
#ahie1 ,bd4 ,,ii1 p4 #baa4    #ace ,on  
the ,plasticity of ,glaciers and other  
,ice4 ,proc4 ,roy4 ,soc41    ,vol4      
,,xliv1 #ahhh1 pp4 #cca-fg 7with ,d4 ,a4
 ,kidd72 ,vol4 ,,xlviii1 #ahij1 pp4     
#bei1 #bfj2 ,vol4 ,,xlix1 #ahia1 pp4    
#cbc-dc4    #acf ,grnland-,expedition   
der ,gesellschaft fr ,erdkunde zu       
,berlin1    #ahia-ic1 ,bd4 ,i1 p4 #dia  
et seq4    #acg ,references on glacier  
structure and motion4--,l4 ,agassiz1    
tudes    sur les ,glaciers1 ,neuchtel1  
#ahdj4 ,rendu1 ,thorie des ,glaciers de 
la    ,savoie1 ,soc4 ,roy4 ,acad41      
,savoie1 ,mm4 #ahdj 7in ,english1 ed4 by
 ,geo4    ,forbes1 ,london1 #ahgd74 ,j4 
de ,charpentier1 ,essai sur les         
,glaciers    et le terrain erratique du 
,basin du ,rhone1 ,lausanne1 #ahda4 ,f4 
,j4    ,hugi1 ,ueber das ,wesen der     
,gletscher und ,wintereise in dem       

,eismeer1    ,stuttgart1 #ahdb4 ,r4     
,mallet1 ,the ,mechanism of ,glaciers1  
,jour4 ,geol4    ,soc4 ,dublin1 ,vol4   
,i1 p4 #cag2 ,on the ,plasticity of     
,glacier ,ice1    ,jour4 ,geol4 ,soc4   
,dublin1 #ahde1 ,vol4 ,,iii1 p4 #abb2   
,on the ,brittleness    and             
,non-plasticity of ,glacier ,ice1 ,phil4
 ,mag41 ,,xxvi1 p4 #ehf4 ,james         
,thompson1 ,on the ,plasticity of ,ice  
as ,manifested in ,glaciers1 ,roy4      
,soc4 ,proc41 ,vol4 #h1 #aheg1 pp4      
#dee-eh4 ,j4 ,tyndall and ,t4 ,h4       
,huxley1    ,on the ,structure and      
,motion of ,glaciers1 ,phil4 ,trans41   
#aheg1 ,vol4    ,,cxlvii1 p4 #cbg4 ,j4  
,d4 ,forbes1 ,occasional ,papers on the 
,theory of    ,glaciers1 ,edinburgh1    
#ahei4 ,w4 ,hopkins1 ,on the ,theory of 
the ,motion    of ,glaciers1 ,phil4     
,trans41 #ahfb1 p4 #fgg2 ,phil4 ,mag41  
#ahfc1 ,vol4 ,,xxv1    p4 #bbd4 ,j4     
,tyndall1 ,forms of ,water1 ,new ,york1 
#ahgb2 ,the ,glaciers of    the ,alps1  
,london1 #ahfa4 ,james ,croll1 ,on the  

,physical ,cause of the    ,motion of   
,glaciers1 ,phil4 ,mag41 #ahfi1 ,vol4   
#ch1 pp4 #bja-f4 ,a4 ,heim1    ,on      
,glaciers1 ,phil4 ,mag41 #ahga1 ,vol4   
#da1 pp4 #dhe-ejh2 ,handbuch der        
,gletscherkunde1 #ahhe4 ,h4 ,moseley1   
,on the ,cause of the ,descent of       
,glaciers1 ,br4 ,assoc4 ,rept41 #ahfj1  
,pt4 #b1 p4 #dh2 also ,phil4 ,mag41     
#ahfi1 ,vol4 #cg1 pp4 #bbi1 #cfc2 ,vol4 
#ci1 p4 #bda2 ,vol4 #db1 p4 #ach2 ,vol4 
#dc1 p4 #ch4 ,ch4 ,grad1 ,la            
,constitution et le movement des        
,glaciers1    ,revue ,sci41 #ahgb4 ,h4  
,j4 ,rink1 ,danish ,greenland1 #ahgg4   
,r4 ,m4 ,deeley1    ,a ,theory of       
,glacial ,motion1 ,phil4 ,mag41 #ahhh1  
,vol4 #be1 pp4 #acf-fd4    ,j4 ,c4      
,mc,connel1 ,on the ,plasticity of an   
,ice ,crystal1 ,proc4 ,roy4    ,soc4    
,london1 ,vol4 #dh1 #ahij1 pp4 #bef-fj2 
ibid41 ,vol4 #di1 #ahia1 pp4    #cbc-dc4
 ,o4 ,mgge1 ber die ,plasticitt der     
,eiskrystalle1 ,nachr4 k4    ,ges4 d4   
,wiss41 ,gttingen1 #ahie1 pp4 #a-d4 ,r4 

,m4 ,deeley and ,george    ,fletcher1   
,the ,structure of ,glacier ,ice and its
 ,bearings on ,glacier    ,motion1      
,geol4 ,mag4 7,london71 ,decade #d1     
,vol4 #b1 #ahie1 pp4 #aeb-fb4 ,t4    ,c4
 ,chamberlin1 ,presidential address     
before the ,geol4 ,soc4 ,am41 ,bull4    
,geol4 ,soc4 ,am41 ,vol4 ,,vi1 ,february
 #ahie1 pp4 #aii-bbj4 ,reid1 ,mechanics 
of ,glaciers1 ,jour4 ,geol41 ,vol4 ,,iv1
 #ahif1 p4 #iab4 ,erich von ,drygalski1 
,grnland-,expedition der ,gesellschaft  
fr ,erdkunde zu ,berlin1 #ahia-ic1      
,vol4 ,i1 #ahig4    #ach ,much          
information on these and other points is
 to be found in    the following books3 
,wild's ,thalassa2 ,thompson's ,depths  
of the ,sea2    ,barker's ,deep ,sea    
,soundings1 and ,maury's ,physical      
,geography2 ,agassiz'    ,the ,three    
,cruises of the ,blake1 and the         
,challenger ,reports give much    more  
detailed information concerning these   
and other matters4    #aci ,dittmar1    
,challenger ,reports1 ,physics and      

,chemistry1 ,vol4 ,i1 p4    #bjd4       
#adj ,for a discussion of the way in    
which this gas is held in    solution1  
see ,tolman1 ,jour4 of ,geol41 ,vol4    
,,vii1 pp4 #eih-fah4    #ada ,murray1   
,scot4 ,geogr4 ,mag41 ,vol4 ,,iv1 p4    
#ci4    #adb ,murray1 ,scot4 ,geogr4    
,mag41 ,vol4 ,,iii1 p4 #gf4    #adc     
,ibid41 p4 #gj4    #add ,limited areas  
of the ocean bottom are actually concave
 upward2    that is1 they are basins in 
the more commonly accepted sense of the 
term 7see ,chapter ,,ix74    #ade ,j4   
,geikie4 ,earth ,sculpture1 p4 #cbi4    
#adf ,murray4 ,scottish ,geographical   
,magazine1 ,vol4 ,,xv1 p4 #ejg4    #adg 
,lindenkohl4 ,science1 ,vol4 ,x1 #ahii1 
p4 #hjg4    #adh ,this does not hold for
 tropical latitudes4    #adi ,national  
,geographic ,magazine1 ,vol4 ,,xi1 pp4  
#cgg-cib4    #aej ,for causes of        
ocean-currents1 see ,croll's ,climate   
and ,time2 ,proc4    ,roy4 ,soc41       
#ahfi-gc1 and ,jour4 ,roy4 ,geog4 ,soc41
 #ahga-gg4    #aea ,in the following    

pages concerning the waves and their    
work    ,gilbert's classic discussion of
 shore features1 in the ,fifth ,annual  
,report of the ,u4 ,s4 ,geol4 ,survey1  
pp4 #hj-ajj1 is freely drawn on4        
,another incisive discussion of certain 
shore phenomena is that of    ,fenneman1
 ,jour4 of ,geol41 ,vol4 ,x1 pp4 #a-cb4 
#aeb ,dana4 ,manual of ,geology1 #dth   
ed41 p4 #bac4    #aec ,delesse4         
,lithologie des ,mers de ,france4 ,cited
 by ,geikie1    ,text-book of ,geology1 
#c;d ed41 p4 #dch4    #aed ,sir ,g4     
,airy4 ,encyclopedia ,metropolitana1    
,art4 ,waves4 ,cited by    ,geikie1 loc4
 cit41 p4 #dch4    #aee ,stevenson4     
,treatise on ,harbors4    #aef ,willis4 
,jour4 of ,geol41 ,vol4 ,i1 p4 #dha4    
#aeg ,stevenson4 ,trans4 ,roy4 ,soc4    
,edin41 ,vol4 ,,xvi1 p4 #be4 ,treatise  
on    ,harbors1 p4 #db4 ,quoted by      
,geikie1 ,text-book of ,geology1 p4     
#dcg4    #aeh ,geikie4 ,text-book of    
,geology1 #c;d ed41 p4 #dcg4    #aei    
,brit4 ,assoc4 ,rept41 #ahej1 p4 #bf4   

#afj ,davis4 ,physical ,geography1 p4   
#ced4    #afa ,dana4 ,manual of         
,geology1 #dth ed41 p4 #bai4    #afb    
,shaler4 ,sea and ,land1 p4 #bi4    #afc
 ,gulliver1 ,shore ,line ,topography3   
,proc4 ,am4 ,acad4 ,arts and ,sci41     
,vol4 ,,xxxiv1 #ahii1 pp4 #aea-beh4 ,a  
valuable study of shore-line            
topography4    #afd ,willis4 ,jour4 of  
,geol41 ,vol4 ,i1 p4 #dha4    #afe ,see 
,gilbert4 ,topographic ,features of     
,lake ,shores1 #eth ,ann4 ,rept4    ,u4 
,s4 ,geol4 ,surv4    #aff ,shaler1 ,sea 
,coast ,swamps of the ,u4 ,s41 #fth     
,ann4 ,rept4 ,u4 ,s4 ,geol4    ,surv42  
and ,merrill1 ,pop4 ,sci4 ,mo41 ,oct41  
#ahij4    #afg ,willis4 ,bull4 ,geol4   
,soc4 ,amer41 ,vol4 ,,ix1 p4 #aac1 and  
,tacoma1    ,wash41 ,folio1 ,u4 ,s4     
,geol4 ,surv4    #afh ,agassiz4 ,three  
,cruises of the ,blake1 ,vol4 ,i1 p4    
#bei4 ,agassiz    would ascribe the     
,blake plateau itself to the ,gulf      
,stream1 p4 #ach4    ,see also ,am4     
,jour4 ,sci41 ,vol ,,xxxv1 #ahhh1 p4    

#dih4    #afi ,reade4 ,phil4 ,mag41     
,vol4 ,,xxv 7#ahhh71 p4 #cdb4    #agj   
,murray4 ,challenger ,report1 ,deep ,sea
 ,deposits1 pp4 #ahd1 #ahe4    #aga     
,murray1 loc4 cit41 pp4 #ahg1 #ahh4     
#agb ,ibid4    #agc ,stevenson4         
,harbors1 #b;d ed41 p4 #ae4    #agd     
,usiglio4 ,encyclopdia ,britannica4     
,article on ,salt4    #age ,willis4     
,jour4 of ,geol41 ,vol4 ,i1 p4 #ejj1    
where the evidences for    deposition   
are fully set forth4    #agf ,murray1   
loc4 cit4    #agg ,ibid41 p4 #ahf4      
#agh ,murray1 loc4 cit41 p4 #bie4       
#agi ,challenger ,report1 ,deep ,sea    
,deposits1 p4 #cbg4    #ahj ,young's    
,astronomy1 p4 #dgb4    #aha ,murray4   
,scottish ,geog4 ,mag41 ,vol4 ,,xv1 p4  
#eaa4 ,an excellent    summary of       
deep-sea deposits4    #ahb ,murray1     
,challenger ,report on ,deep ,sea       
,deposits1 p4 #ccg et seq41    and      
,buchanan1 ,proc4 ,roy4 ,soc4 ,edin41   
,vol4 ,,xviii1 #ahib1 pp4 #ag-ci4       
#ahc ,challenger ,report on ,deep ,sea  

,deposits1 pp4 #che-cia4 ,see also      
,jour4 of ,geol41 ,vol4 ,,ii1 pp4       
#afg-agb4    #ahd ,forel1 ,compte       
,rendu1 #ahge1 #ahgf1 #ahgh1 #ahgi1 and 
,p4 ,du ,bois1    #ahia4 ,also ,forel's 
,lac ,leman4    #ahe ,c4 ,a4 ,davis1    
,journ4 of ,geol41 ,vol4 ,,viii1 pp4    
#dhe-ig1 and #dih-ejc1    and ,vol4     
,,ix1 pp4 #dia-ejf4    #ahf ,russell1   
,lake ,lahontan1 ,mono4 ,,xi1 ,u4 ,s4   
,geol4 ,surv41 ,chap4 ,v2    also ,third
 ,ann4 ,rept41 pp4 #baa-bba4 ,gilbert1  
,lake ,bonneville1 ,mono4    ,i1 ,u4 ,s4
 ,geol4 ,surv41 p4 #afg4    #ahg        
,stapff1 ,zeit4 deut4 geol4 ,gesell41   
,vol4 ,,xviii1 pp4 #hf-agc4    #ahh     
,upham1 ,lake ,agassiz1 ,mono4 ,,xxv1   
,u4 ,s4 ,geol4 ,surv42 ,salisbury and   
,kmmel1 ,lake ,passaic1 ,rept4 of the   
,state ,geologist of ,n4 ,j41 #ahic1    
and ,jour4 of ,geol41 ,vol4 ,,iii1 pp4  
#ecc-efj2 ,gilbert1 ,lake ,bonneville1  
,mono4 ,i1 ,u4 ,s4 ,geol4 ,surv42       
,russell1 ,lake ,lahontan1 ,mono4 ,,xi1 
,u4 ,s4    ,geol4 ,surv42 and ,mono     

,lake1 ,eighth ,ann4 ,rept41 ,u4 ,s4    
,geol4 ,surv41 ,pt4    ,i4    #ahi      
,gilbert1 ,lake ,bonneville1 ,mono4 ,i1 
,u4 ,s4 ,geol4 ,surv41 p4 #ga1 and      
,topographic ,features of ,lake ,shores1
 ,fifth ,ann4 ,rept4 ,u4 ,s4 ,geol4     
,surv41 p4 #aji4    #aij ,buckley4 ,wis4
 ,acad4 of ,sci41 ,vol4 ,,xiii1 ,pt4 ,i1
 #aijj4 ,a study    of ice ramparts     
formed about the shores of ,lake        
,mendota1 ,wis41 in    #ahih-ii4    #aia
 ,copied from ,russell's ,lake          
,lahontan1 ,mono4 ,,xi1 ,u4 ,s4 ,geol4  
,surv4    #aib ,less 4#jdbed carbonic   
acid added to amount found4 ,average of 
two    analyses4    #aic ,average from  
four analyses4    #aid ,average of two  
analyses4    #aie ,as sesquicarbonates4 
#aif ,as chloride4    #aig ,as peroxide4
    #aih ,carbonic acid by difference4  
#aii ,analyses of ,rocks1 ,bull4 #afh1  
,u4 ,s4 ,geol4 ,surv41 #aijj1 p4 #ae4   
#bjj ,quantitative ,classification of   
,igneous ,rocks1 by ,whitman ,cross1    
,joseph ,p4 ,iddings1 ,louis ,v4        

,pirsson1 and ,henry ,s4 ,washington4   
#aijc4    #bja ,van ,hise4 #afth ,ann4  
,u4 ,s4 ,geol4 ,surv41 ,pt4 ,i1 pp4     
#ehi-id4    #bjb ,the application of    
these principles we owe chiefly to ,van 
,hise3    ,metamorphism of ,rocks and   
,rock ,flowage1 ,bull4 ,geol4 ,soc4     
,am41 ,vol4 #i1    pp4 #bfi-cbh4    #bjc
 ,cross1 ,iddings1 ,pirsson1 and        
,washington4 ,quantitative              
,classification of ,igneous ,rocks4     
#bjd ,the initials f4n4 7field names7   
are introduced to show that the    term 
is used in the broad field sense        
proposed4    #bje ,added by the authors 
of this work4    #bjf ,the following    
definitions are given1 as nearly as     
practicable1 in    accordance with      
present common usage1 which is1 however1
 more or less    varying and            
inconsistent4    #bjg ,a comprehensive  
discussion of the 8,genesis of ,ore     
,deposits0 may    be found in ,vols4    
,,xxiii and ,,xxiv of the ,trans4 of the
 ,am4 ,inst4 of    ,min4 ,eng4 7also    

printed with additions in book form by  
the ,institute1    #aijb71 in which     
,posepny1 ,emmons1 ,van ,hise1          
,le,conte1 ,blake1 ,becker1    ,ricard1 
,raymond1 ,lindgren1 ,weed1 ,vogt1      
,winslow1 ,winchell 7,h4 ,v471          
,church1 ,cazin1 ,adams1 ,keyes1 ,bain1 
,collins1 ,beck1 and ,de,launay         
participated4 ,various phases of the    
leading modern views are set    forth4  
#bjh ,chamberlin4 ,geol4 of ,wis41 ,vol4
 ,,iv1 p4 #eii et seq41 #ahhb4    #bji  
,penrose4 ,jour4 of ,geol41 ,vol4 ,,xi1 
pp4 #ace-aee1 #aijc4    #baj ,van ,hise1
 ,mono4 ,,xix1 ,u4 ,s4 ,geol4 ,surv41   
pp4 #bfh-bie1 #ahib4    #baa ,gilbert4  
,bull4 ,geol4 ,soc4 ,am41 ,vol4 ,x1 pp4 
#ace-adj1 #ahih4    #bab ,branner4      
,jour4 of ,geol41 ,vol4 ,,viii1 pp4     
#dha-dhd1 #aijj4    #bac ,iddings4      
,jour4 of ,geol41 ,vol4 ,,vi1 pp4       
#gjd-gaj4    #bad ,daubre4 ,gologie     
d',exprimentale1 pp4 #cjf-cgb4    #bae  
,crosby4 ,american ,geologist1 ,vol4    
,,xii1 #ahic1 pp4 #cfh-cge4    #baf     

,becker4 ,bull4 ,u4 ,s4 ,geol4 ,surv41  
,vol4 ,x1 pp4 #da-ge4    #bag ,van      
,hise4 ,principles of ,north ,american  
,pre-,cambrian ,geology4 #afth    ,ann4 
,rept4 ,u4 ,s4 ,geol4 ,surv41 ,pt4 ,i1  
pp4 #ffh-fgb4    #bah ,diller4 ,bull4   
,geol4 ,soc4 ,am41 ,vol4 ,i1 pp4        
#dda-ddb4 ,ibid4 ,hay1    ,vol4 ,,iii1  
pp4 #ej-ee2 and ,newsom1 ibid4 ,vol4    
,,xiv1 pp4 #bbg-bfh4    #bai ,willis4   
,bull4 ,geol4 ,soc4 of ,am41 ,vol4      
,,xiii1 pp4 #cca-ccf4    #bbj           
,mc,connell4 ,canada ,geol4 and ,nat4   
,hist4 ,surv41 #ahhf1 ,pt4 ,,ii4    #bba
 ,geikie4 ,text-book of ,geology4       
#bbb ,becker4 ,geology of the ,comstock 
,lode1 ,mono4 ,,iii1 ,u4 ,s4 ,geol4     
,surv41 ,chapter ,,iv4    #bbc          
,reference1 ,van ,hise4 ,sixteenth ,ann4
 ,rept4 ,u4 ,s4 ,geol4 ,surv41 ,pt4     
,i1 pp4 #fgb-fgh4    #bbd ,davison4     
,jour4 of ,geol41 ,vol4 ,,viii1 p4 #cja4
    #bbe ,nature1 ,october #bd1 #ahie4  
#bbf ,milne4 ,the ,geog4 ,jour41 ,vol4  
,,xxi1 p4 #a4 ,see also ,seismology1 a  

more technical work than the same       
author's ,earthquakes4    #bbg ,darwin4 
,journal of ,researches1 #ahde1 p4 #cjc4
    #bbh ,oldham4 ,quar4 ,jour4 ,geol4  
,soc41 ,vol4 ,,xxviii1 p4 #beg4    #bbi 
,geikie4 ,text-book of ,geology1 #dth   
ed41 p4 #cgb4    #bcj ,kot4 ,jour4      
,coll4 ,sci41 ,japan1 ,vol4 ,v1 ,pt4    
,,iv 7#ahic71 pp4 #cbi1    #cci4 ,cited 
by ,geikie1 loc4 cit41 p4 #cgc4    #bca 
,an elaborate account of this earthquake
 is given by ,dutton1 ,ninth    ,ann4   
,rept41 ,u4 ,s4 ,geol4 ,surv41 pp4      
#bji-ebh4    #bcb ,cross4 ,twenty-first 
,ann4 ,rept41 ,u4 ,s4 ,geol4 ,surv41    
,pt4 ,,ii1 ,chap4    ,v4    #bcc        
,oldham4 ,report on the ,indian         
,earthquake of ,june #ab1 #ahig1 p4     
#ach4    ,mem4 ,geol4 ,surv4 of ,india4 
,cited by ,geikie1 loc4 cit41 p4 #cgd4  
#bcd ,oldham1 loc4 cit41 p4 #hj4    #bce
 ,geikie4 ,text-book of ,geology1 #dth  
ed41 p4 #cge4    #bcf ,ibid41 p4 #cgf4  
#bcg ,forster1 ,seismology1 #ahgg4      
,summarized in the ,am4 ,geol41 ,vol4   

,,iii1    #ahhi1 p4 #ahb4    #bch ,the  
literature of seismology is very        
extensive4 ,some of the    more general 
treatises are the following3 ,mallet1   
,brit4 ,assoc41    #ahdg1 ,part ,,ii1 p4
 #cj2 #ahej1 p4 #a2 #ahea1 p4 #bgb2     
#aheb1 p4 #a2 #aheh1    p4 #a2 #ahfa1 p4
 #bja2 and ,the ,great ,neapolitan      
,earthquake of #aheg1    #b ,vols41     
#ahfb2 ,a4 ,perrey1 ,mm4 ,couronn4      
,bruxelles1 ,,xviii 7#ahdd71    ,comptes
 ,rendus1 ,,lii1 p4 #adf2 ,r4 ,falb1    
,grundzge einer ,theorie der            
,erdbeben und ,vulkanenausbrche1 ,graz1 
#ahga1 and ,gedanken und ,studien    ber
 den ,vulkanismus1 etc41 #ahgd2 ,pfaff1 
,allgemeine ,geologie als    exacte     
,wissenschaft1 ,leipzig1 #ahgc1 p4 #bbd2
 ,schmidt1 ,studien ber    ,erdbeben1   
#b;d ed41 #ahgi1 and ,studien ber       
,vulkane und ,erdbeben1    #ahha2       
,dieffenbach1 ,neues ,jahrb41 #ahgb1 p4 
#aee2 ,m4 ,s4 di ,rossi1 ,la            
,meteorologia ,endogena1 #b ,vols41     
#ahgi and #ahhb2 ,j4 ,milne1            

,earthquakes    and other               
,earth-movements 7contains a            
bibliography71 #dth ed41 #ahih2         
,seismology1 ibid41 #ahih2 ,dutton1     
,earthquakes1 #aijd4      ,records of   
earthquakes have been preserved more or 
less fully in    several countries1     
especially in recent years4 ,a few of   
the more    accessible publications     
where these records are found are cited 
below3 ,california earthquakes1         
,perrine1 ,bull4 #adg1 ,u4 ,s4 ,geol4   
,surv42 ,earthquakes of the ,pacific    
,coast1 ,holden1 ,smithson4 ,misc4      
,coll41 ,no4 #ajhg1 #ahih2 ,records of  
recent earthquake movements in    ,great
 ,britain since #ahij are published by  
,davison in ,quar4 ,jour4    ,geol4     
,soc41 ,geol4 ,mag41 and ,nature2       
,records of earlier earthquakes    are  
found in the reports of the ,brit4      
,assoc4 7,mallet71 in the    ,edinburgh 
,new ,philos4 ,jour41 ,vols4            
,,xxxi-,,xxxvi 7,milne71 and in         
,trans4 of the ,roy4 ,irish ,acad41     

#ahhd and #ahhf 7,o',reilly72 ,the      
,earthquakes of ,scandinavia have been  
recorded in volumes of the    ,geol4    
,fren1 ,frhandl42 ,records of other     
continental ,european    earthquakes are
 found in ,gerland's ,beitrge zur       
,geophysik1 #ahie1    #aijj1 and #aija2 
,neues ,jahrb41 #ahfe-ga2 ,zeitschr4    
,naturwissen4    7#ahhd71 7,credner72   
,bericht4 k4 ,sachs4 ,geol4 ,wissen41   
#ahhi and #aijj    7,credner72 ,jahrb4  
,geol4 ,reichsanst41 #ahie and #ahig2   
,tschermak's    ,min4 ,mitth41 #ahgc1   
and later2 ,transactions of the         
,seismological    ,soc4 of ,japan4 ,an  
index to these ,transactions is given at
 the end    of ,milne's ,seismology4    
#bci ,antlitz der ,erde4 ,vol4 #a1 p4   
#acf4    #bdj ,eugene ,a4 ,smith4       
,underthrust ,folds and ,faults1 ,am4   
,jour4 ,sci41    ,vol4 ,,xlv1 #ahic1 pp4
 #cje-f4    #bda ,manual of ,geology1   
#c;d ed41 p4 #bc4    #bdb ,for          
discussions of folds1 see ,van ,hise1   
,sixteenth ,ann4 ,rept4    ,u4 ,s4      

,geol4 ,surv41 ,pt4 ,i1 pp4 #fjc-fcb2   
and ,willis1 ,thirteenth ,ann4          
,rept41 ,pt4 ,,ii1 pp4 #bag-bif4    #bdc
 ,mechanismus der ,gebirgsbildung1 p4   
#bac4    #bdd ,am4 ,nat41 ,vol4 ,,xix1  
p4 #beg1 #ahhe4    #bde ,geol4 ,surv4 of
 ,canada1 p4 #cc ,d1 #ahhf4    #bdf     
,elements of ,geology1 #eth ed41 p4     
#bff4    #bdg ,van ,hise4 ,bull4 ,geol4 
,soc4 of ,am41 #ahig1 ,vol4 ,,ix1 p4    
#bia4    #bdh ,see ,woodward's address1 
,mathematical ,theories of the ,earth1  
,proc4    ,am4 ,assc4 for ,adv4 ,sci41  
#ahhi1 pp4 #ei-fc4    #bdi ,nat4 ,phil4 
,thompson and ,tait1 ,pt4 ,,ii1 p4 #dgg4
 ,see also ,popular    ,lectures and    
,addresses1 #ahid1 ,,ii1 p4 #cac4       
#bej ,physics of the ,earth's ,crust1   
,fisher1 p4 #ie4    #bea ,origin of     
,mountain ,ranges1 ,t4 ,mellard ,reade1 
p4 #abe4    #beb ,phil4 ,trans4 ,roy4   
,soc41 ,vol4 #agh1 pp4 #bca-di4    #bec 
,amer4 ,jour4 ,sci41 #ahic1 #c;d series1
 ,vol4 #de1 p4 #g4    #bed ,essentially 
the same as atmospheres4    #bee ,the   

pressures and densities here given are  
essentially the same    as those        
previously worked out by others and     
already published4 ,the    temperatures 
are the results of recent preliminary   
computations made    under the auspices 
of the ,carnegie ,institution1 and are  
subject    to change on further study4  
,they are based on the assumption that  
the increase in density is due to       
compression4 ,they are in general       
accord with the results previously      
reached by ,dr4 ,f4 ,r4 ,moulton    7see
 8,a ,group of ,hypotheses ,bearing on  
,climatic ,changes10 by ,t4 ,c4         
,chamberlin1 ,jour4 of ,geol41 #ahig1 p4
 #fgd74 ,the ,rev4 ,o4 ,fisher1 in the  
,am4 ,jour4 of ,sci41 #aija1 p4 #dbj1   
gives much higher results4    #bef      
,attention was called to this feature by
 ,chamberlin in a paper    before the   
,geol4 ,soc4 of ,am4 at ,rochester1     
,december1 #aija4    #beg ,these are    
reckoned by assuming that the           
temperature of no    variation at #ej   

feet below the surface is #dj ,f4       
#beh ,am4 ,jour4 of ,sci41 ,vol4 ,v1    
#ahih1 p4 #afa4    #bei ,van ,hise4     
,personal communication4    #bfj ,bull4 
#afh ,u4 ,s4 ,geol4 ,surv41 p4 #ad4     
#bfa ,daniell's ,physics1 p4 #djg4      
#bfb ,heat4 ,tait1 p4 #bbe4    #bfc ,all
 the feldspars are calculated as        
anorthite4 ,augite is used for          
hypersthene1 ilmenite is included with  
magnetite1 and all minerals    are      
calculated as if of the isometric       
system4    #bfd ,physics of the ,earth's
 ,crust1 ,chap4 ,,viii4    #bfe ,penn   
,monthly1 ,philadelphia1 ,may1 #ahgf4   
#bff ,the following conclusion by an    
eminent authority has come to our       
notice since this was written3          
,l'influence des mares ocanienes sur la 
dure du jour est donc    tout  fait     
minime et n'est nullement comparable    
l'effet des    mares dues  la viscosit  
et  l'elasticit de la partie solide     
du globe1 effet sur lequel ,m4 ,darwin  
insist dans une series    de ,mmoires du

 plus haut intrt4 ,par ,h4 ,poincar1    
,bulletin    ,astronomique1 tome ,,xx   
7,june1 #aijc71 p4 #bbc4    #bfg ,on the
 ,secular ,changes in the ,elements of  
the ,orbit of a    ,satellite revolving 
about a ,tidally-distorted ,planet4     
,phil4 ,trans41    ,roy4 ,soc41 ,pt4    
,,ii1 #ahhj4    #bfh ,jour4 ,geol41     
,vol4 ,,vi1 #ahih1 p4 #fe4    #bfi      
,quar4 ,jour4 ,geol4 ,soc41 ,vol4 #ci1  
#ahhc1 p4 #adj4 ,everett 7,units and    
,physical ,constants7 gives #hcg  #aj   
for steel1 but as the modulus    for    
granite seems low1 we have taken the    
lower estimate for steel to    avoid    
exaggerating the ratio between them4    
#bgj ,nat4 ,phil4 ,thompson  ,tait1     
,vol4 ,,ii1 p4 #dbd1 #ahij4    #bga     
,computations made at the request of the
 authors4 ,see also ,fisher1    ,physics
 of the ,earth's ,crust1 p4 #cf4    #bgb
 ,of like import is the statement of    
,woodward--8,if the crust of the        
earth were self-supporting1 its crushing
 strength would have to be    about     

thirty times that of the best cast      
steel1 or five hundred to    one        
thousand times that of granite40        
,mathematical ,theories of the          
,earth1 ,proc4 ,am4 ,assoc4 for ,adv4   
,sci41 #ahhi1 p4 #di4    #bgc ,it is    
assumed that the direction of the       
supporting thrust at the    periphery of
 the dome is at every point parallel to 
the tangent to    the domed surface4    
,this is justified by symmetry in the   
case of a    shell conforming to the    
sphericity of the earth1 and in the     
other    cases it would seem to be as   
favorable an assumption in the direction
    of high supporting capacity as can  
reasonably be made4    #bgd ,prepared at
 the authors' request by ,w4 ,h4        
,emmons4    #bge ,the terms are here    
used in their narrow technical sense4   
,extrusion is also used in a broad      
generic sense to indicate the whole     
process of outward movement4    #bgf    
,gilbert4 #adth ,ann4 ,rept4 ,u4 ,s4    
,geol4 ,surv41 ,pt4 ,i1 p4 #ahg4    #bgg

 ,gilbert1 after a careful study of the 
moon's topography1 has    suggested that
 the lunar pits may be indentations     
produced by    infalling meteorites or  
planetoids1 and has shown by experiment 
that    pits of a similar type1 with    
similar central cones1 can be produced  
by impact4 ,the ,moon's ,face3 ,a ,study
 of the ,origin of its ,features4       
,presidential address1 ,phil4 ,soc4 of  
,washington1 #ahib1 ,bull4 ,vol4 ,,xii1 
pp4 #bda-bib4    #bgh ,structure and    
,distribution of ,coral ,islands4       
#bgi ,corals and ,coral ,islands4       
#bhj ,proc4 ,roy4 ,soc4 ,edin41 ,vol4   
,x1 pp4 #eje-ah1 and ,vol4 ,,xvii1 pp4  
#gi-aji2 ,nature1 ,vol4 ,,xxxii1 p4     
#fac2 ,narrative ,chal4 ,exp41 ,vol4 ,i1
 pp4    #gha-b4    #bha ,bull4 ,mus4    
,comp4 ,zool41 ,vol4 ,,xvii1 #ahhi4     
#bhb ,ante1 p4 #bb4    #bhc ,origin of  
,igneous ,rocks4 ,phil4 ,soc4 of ,wash41
 ,vol4 ,,xii1 pp4    #hi-bad4    #bhd   
,the ,natural ,system of ,volcanic      
,rocks4 ,cal4 ,acad4 of ,sci41 #ahfh4   

#bhe ,chemical ,news1 ,april #i1 #ahig4 
#bhf ,phil4 ,trans41 #ahgc4    #bhg     
,mechanics of ,igneous ,intrusion1 ,am4 
,jour4 ,sci41 ,apr41 p4 #bfi1 and       
,aug41 p4 #ajg1 #aijc4    #bhh ,frank4  
,lehrbuch der ,botanik1 ,i1 p4 #egf1    
#ahib4    #bhi ,science1 ,vol4 ,,vi1 p4 
#hch1 #ahig4 ,zeitschrift fr            
,anorganische    ,chemie1 #ahig4    #bij
 ,reference works3 ,scott1 ,studies in  
,fossil ,plants1 #aijj2    ,zeiller1    
lments de ,palobotanique1 #aijj2        
,potoni1 ,lehrbuch    der               
,pflanzenpaleontologie1 #ahii2 ,seward1 
,fossil ,plants1 #ahih2                 
,solms-,laubach1 ,fossil ,botany1 #ahhg4
    #bia ,weed4 ,ninth ,ann4 ,rept4 ,u4 
,s4 ,geol4 ,surv41 #ahhg-hh1 pp4        
#fac-gf2    also ,bradley ,m4 ,davis4   
,science1 ,vol4 ,,vi1 #ahig1 pp4        
#ade-eg4    #bib ,cohn4 ,abhandl4       
,schles4 ,gesell4 ,naturwiss41 ,heft    
,,ii1 #ahfb4    #bic ,deep ,sea         
,deposits1 p4 #beg4    #bid ,c4 ,a4     
,davis4 ,jour4 of ,geol41 ,vol4 ,,ix1   

#aija1 p4 #dia4    #bie ,weed4 ,ninth   
,ann4 ,rept4 ,u4 ,s4 ,geol4 ,surv41     
#ahhg-h4    #bif ,reference books3      
,zittel's ,text-book on ,paleontology1  
translated    and edited by ,eastman2   
,williams' ,geological ,biology2        
,nicholson's    ,manual of              
,paleontology4    #big ,after ,zittel in
 the main4    #bih ,s4 ,w4 ,johnson1    
,how ,crops ,feed1 p4 #dg4    #bii      
,reference works3 ,plant ,relations1    
,coulter1 #aijj1--;a convenient         
elementary work2 ,schimper1             
,pflanzengeographie1 #ahih2 ,warming1   
,lehrbuch der oekologischen             
,pflanzengeographie1 #ahif2 ,cowles1    
,botanical ,gazette1 ,vol4 ,,xxvii1     
#ahih4    #cjj ,one of the earliest     
attempts to map these and develop their 
significance and value is found in ,vol4
 ,,ii1 ,geol4 of ,wis41 #ahgc-gg1       
,native ,vegetation1 pp4 #agf-hg4       
#cja ,chamberlin4 ,a ,systematic ,source
 of ,evolution of ,provincial           
,faunas1 ,jour4 of ,geol41 ,vol4 ,,vi1  

#ahih1 pp4 #eig-fji4    #cjb ,wallace4  
,island ,life4    #cjc ,for data1 see   
,walther's ,einleitung in die ,geologie1
 pp4 #ce-de4          ,transcriber's    
,notes3     - ,text enclosed by         
underscores is in italics 7italics74   -
 ,text enclosed by equals is in antiqua 
font 7antiqua74   - ,text enclosed by   
pluses is in small caps 7,small ,caps74 
- ,blank pages have been removed4   -   
,obvious typographical errors have been 
silently corrected4