material from the ,google ,print        
project47                 ,,chambers',s 
,,elementary ,,science ,,manuals4       
,,geology       ,,by       ,,james      
,,geikie1 ,,ll4,d41 ,f4,r4,s4      ,,of 
,h4,m4 ,,geological ,,survey2 ,,author  
,,of     ',,the ,,great ,,ice ,,age4'   
,logo      ,w4  ,r4 ,,chambers          
,,london ,,and ,,edinburgh     #ahhc    
,edinburgh3     ,printed by ,w4 and ,r4 
,chambers4     ,,preface4   ,the vital  
importance of diffusing some knowledge  
of the leading principles of ,science   
among all classes of society1 is        
becoming daily more widely and deeply   
felt2 and to meet and promote this      
important movement1 ,w4  ,r4 ,,chambers 
have resolved on issuing the present    
,series of ,,elementary ,,science       
,,manuals4 ,the ,editors believe that   
they enjoy special facilities for the   
successful execution of such an         
undertaking1 owing to their long        
experience--now extending over a period 
of forty years--in the work of popular  

education1 as well as to their having   
the co-operation of writers specially   
qualified to treat the several subjects4
 ,in particular1 they are happy in      
having the editorial assistance of      
,,andrew ,,findlater1 ,,ll4,d41 to whose
 labours they were so much indebted in  
the work of editing and preparing       
,chamber's ,encyclopaedia4  ,the        
,manuals of this series are intended to 
serve two somewhat different purposes3  
#a4 ,they are designed1 in the first    
place1 for ,,self-,,instruction1 and    
will present1 in a form suitable for    
private study1 the main subjects        
entering into an enlightened education2 
so that young persons in earnest about  
self-culture may be able to master them 
for themselves4  #b4 ,the other purpose 
of the ,manuals is1 to serve as         
,,text-,,books ,,in ,,schools4 ,the mode
 of treatment naturally adopted in what 
is to be studied without a teacher1 so  
far from being a drawback in a          
school-manual1 will1 it is believed1 be 

a positive advantage4 ,instead of a     
number of abrupt statements being       
presented1 to be taken on trust and     
learned1 as has been the usual method in
 school-teaching2 the subject is made1  
as far as possible1 to unfold itself    
gradually1 as if the pupil were         
discovering the principles himself1 the 
chief function of the book being1 to    
bring the materials before him1 and to  
guide him by the shortest road to the   
discovery4 ,this is now acknowledged to 
be the only profitable method of        
acquiring knowledge1 whether as regards 
self-instruction or learning at school4 
,for simplification in teaching1 the    
subject has been divided into           
sub-sections or articles1 which are     
numbered continuously2 and a series of  
,questions1 in corresponding divisions1 
has been appended4 ,these ,questions1   
while they will enable the private      
student to test for himself how far he  
has mastered the several parts of the   
subject as he proceeds1 will serve the  

teacher of a class as specimens of the  
more detailed and varied examination to 
which he should subject his pupils4     
,,note ,,by ,,the ,,author4  ,in the    
present ,manual of ,,geology it has been
 the aim of the author rather to        
indicate the methods of geological      
inquiry and reasoning1 than to present  
the learner with a tedious summary of   
results4 ,attention has therefore been  
directed chiefly to the physical        
branches of the science--,palaeontology 
and ,historical ,geology1 which are very
 large subjects of themselves1 having   
been only lightly touched upon4 ,the    
student who has attained to a fair      
knowledge of the scope and bearing of   
,physical ,geology1 should have little  
difficulty in subsequently tackling     
those manuals in which the results      
obtained by geological investigation are
 specially treated of4     ,,contents4  
,,page   ,,introductory                 
#g    ,,classification ,,of ,,rocks     
#h    ,,mineralogy                      

#ab       ,,rock-,,forming ,,minerals   
#ad    ,,petrology--                    
,,mechanically ,,formed ,,rocks         
#ag       ,,chemically ,,formed ,,rocks 
#ai       ,,organically ,,derived       
,,rocks                                 
#bj       ,,metamorphic ,,rocks         
#ba       ,,igneous ,,rocks             
#bc       ,,structure ,,and             
,,arrangement ,,of ,,rock-,,masses--    
,stratification1 c42 ,mud-cracks and    
,rain-prints2           ,succession of  
,strata2 ,extent of ,beds2 ,sequence of 
,beds--,joints2 ,cleavage2 ,foliation2  
,concretions2           ,inclination of 
,strata2 ,contemporaneous ,erosion2     
,unconformability2 ,overlap2 ,faults2   
,mode of           ,occurrence of       
,metamorphic and ,igneous ,rocks2       
,mineral ,veins                         
#bf-df    ,,dynamical ,,geology--       
,,the ,,atmosphere ,,as ,a ,,geological 
,,agent ,,of ,,change                #df
       ,,water ,,as ,a ,,geological     
,,agent ,,of ,,change                   

#dh       ,,geological ,,action ,,of    
,,plants ,,and ,,animals                
#fj       ,,subterranean ,,forces       
#fd       ,,metamorphism                
#gb    ,,physiography                   
#gd    ,,palaeontology                  
#gg    ,,historical ,,geology           
#hd    ,,questions                      
#hi       ,illustration3 ,,geology      
,,introductory4   #a4                   
,definition4--,geology is the science of
 the origin and development of the      
structure of the earth4 ,it treats of   
the nature and mode of formation of the 
various materials of which the earth's  
crust is composed2 it seeks to discover 
what mutations of land and water1 and   
what changes of climate1 have supervened
 during the past2 it endeavours to trace
 the history of the multitudinous tribes
 of plants and animals which have       
successively tenanted our globe4 ,in a  
word1 ,geology is the ,physical         
,geography of past ages4  #b4           
,rocks4--,every one knows that the crust

 of the earth is composed of very       
various substances1 some of which are   
hard and crystalline in texture1 like   
granite2 others less indurated and      
non-crystalline1 such as sandstone1     
chalk1 shale1 c42 while yet others are  
more or less soft and incoherent masses1
 as gravel1 sand1 clay1 peat1 c4 ,now1  
all these heterogeneous materials1      
whether they be hard or soft1 compact or
 loose1 granular or crystalline1 are    
termed rocks4 ,blowing sand-dunes1      
alluvial silt and sand1 and even peat1  
are1 geologically speaking1 rocks1 just 
as much as basalt or any indurated      
building-stone4 ,the variety of rocks is
 very great1 but we do not study these  
long before we become aware that many   
kinds which present numerous contrasts  
in detail1 yet possess certain          
characters in common4 ,and this not only
 groups these diverse species together1 
but serves also to distinguish them from
 other species of rock1 which in like   
manner are characterised by the presence

 of some prevalent generic feature or   
features4  ,classification of           
,rocks4--,all the rocks that we know of 
are thus capable of being arranged under
 five classes1 as follows3      ,i4     
,,mechanically ,,formed4    ,,ii4       
,,chemically ,,formed4   ,,iii4         
,,organically ,,derived4    ,,iv4       
,,metamorphic4     ,v4 ,,igneous4  #c4  
,the ,,mechanically ,,formed class      
comprises a considerable variety of     
rocks1 all of which1 however1 come under
 only two subdivisions--namely1         
,sedimentary1 and ,eolian or ,aerial1   
the former being by far the more        
important4 ,of the ,sedimentary group1  
there are three rocks which may be taken
 as typical and representative--namely1 
conglomerate or puddingstone1 sandstone1
 and shale4 ,a short examination of the 
nature of these will sufficiently       
explain why they come to be grouped     
together under one head4 ,conglomerate  
consists of a mass of various-sized     
rounded stones cemented together2 each  

stone has been well rubbed1 and rolled1 
and rounded4 ,it is quite obvious that  
the now solid rock must at one time have
 existed in a loose and unconsolidated  
state1 like gravel and shingle4 ,nor can
 we resist the conclusion that the      
stones were at one time rolled about by 
the action of water--that being the only
 mode in which gravel-stones are shaped4
 ,again1 when we have an opportunity of 
examining any considerable vertical     
thickness of conglomerate1 we shall     
frequently observe that the stones are  
arranged more or less definitely along  
certain lines4 ,these1 there can be no  
question1 are lines of deposition--the  
rounded stones have evidently not been  
formed and accumulated all at once1 but 
piled up gradually1 layer upon layer4   
,and since there is no force in nature1 
that we know of1 save water in motion1  
that could so round and smooth stones1  
and spread them out in successive layers
 or beds1 we may now amplify our        
definition of conglomerate1 and describe

 it as a compacted mass of stones which 
have been more or less rounded1 and     
arranged in more or less distinct layers
 or beds1 by the action of water4  #d4  
,sandstone may at the outset be         
described as a granular non-crystalline 
rock4 ,this rock shews every degree of  
coarseness1 from a mass in which the    
constituent grains are nearly as large  
as turnip-seed1 down to a stone so fine 
in the grain that we need a lens to     
discover what the particles are of which
 it is composed4 ,when these latter are 
examined1 they are found to exhibit     
marks of attrition1 just like the stones
 of a conglomerate4 ,sharp edges have   
been worn off1 and the grains rounded   
and rubbed2 and whereas lines of        
deposition are often obscure1 and of    
infrequent occurrence in                
conglomerate--in sandstone1 on the      
contrary1 they are usually well marked  
and often abundant4 ,we can hardly      
doubt1 therefore1 that sandstone has    
also had an aqueous origin1 or in other 

words1 that it has been formed and      
accumulated by the force of water in    
motion4 ,in short1 sandstone is merely  
compacted sand4  #e4 ,if it be easy to  
read the origin of conglomerate and sand
 in the external character of their     
ingredients1 and the mode in which these
 have been arranged1 we shall find it   
not less easy to discover the origin of 
shale4 ,shale is1 like sandstone1 a     
granular non-crystalline rock4 ,the     
particles of which it is built up are   
usually too small to be distinguished   
without the aid of a lens1 but when put 
under a sufficient magnifying power1    
they exhibit evident marks of attrition4
 ,in structure it differs widely from   
sandstone4 ,in the latter rock the      
layers of deposition1 though frequently 
numerous1 are yet separated from each   
other by some considerable distance1 it 
may be by a few inches or by many yards4
 ,but in shale the layers are so thin   
that we may split the rock into laminae 
or plates4 ,now we know that many       

sedimentary materials of recent origin1 
such as the silt of lakes1 rivers1 and  
estuaries1 although when newly dug into 
they appear to be more or less          
homogeneous1 and shew but few lines of  
deposition1 yet when exposed to the     
action of the atmosphere and dried1 they
 very often split up into layers        
exhibiting division planes as minute as 
any observable in shale4 ,there is no   
reason to doubt1 therefore1 that shale  
is merely compacted silt and mud--the   
sediment deposited by water4 ,it becomes
 evident1 therefore1 that conglomerate1 
sandstone1 and shale are terms of one   
series4 ,they are all equally           
sedimentary deposits1 and thus1 if we   
slightly modify our definition of       
conglomerate1 we shall have a definition
 which will include the three rocks we  
have been considering4 ,for they may all
 be described as granular               
non-crystalline rocks1 the constituent  
ingredients of which have been more or  
less rounded1 and arranged in more or   

less distinct layers1 by the action of  
water4  #f4 ,the ,eolian or ,aerial     
group of rocks embraces all natural     
accumulations of organic or inorganic   
materials1 which have been formed upon  
the land4 ,the group is typically       
represented by debris1 such as gathers  
on hill-slopes and at the base of       
cliffs1 by the sand-hills of deserts and
 maritime districts1 and by soil4 ,all  
these accumulations owe their origin to 
atmospheric agencies1 as will be more   
particularly described in the sequel4   
,as the ,sedimentary and ,eolian rocks  
are the results of the mechanical action
 of water and the atmosphere1 they are  
fitly arranged under one great          
class--the ,,mechanically ,,formed      
,,rocks4  #g4 ,,chemically ,,formed     
,,rocks constitute another well-marked  
class1 of which we may take rock-salt as
 a typical example4 ,this rock has      
evidently been deposited in water1 but  
not in the manner of a sedimentary bed4 
,it is not built up of water-worn       

particles which have been rolled about  
and accumulated layer upon layer1 but   
has been slowly precipitated during the 
gradual evaporation of water in which it
 was previously held in solution4 ,its  
formation is therefore a chemical       
process4 ,various other rocks come under
 the same category1 as we shall         
afterwards point out4  #h4 ,the         
,,organically ,,derived class comprises 
a number of the most important and      
useful rock-masses4 ,chalk may be       
selected as a typical example4 ,even a  
slight examination shews that this rock 
differs widely from any of those        
mentioned above4 ,conglomerate1         
sandstone1 shale1 c4 are built up of    
pebbles1 particles1 grains1 c4 of       
various inorganic materials4 ,but chalk1
 when looked at under the microscope1   
betrays an organic origin4 ,it consists1
 chiefly1 of the hard calcareous parts  
of animal organisms1 and is more or less
 abundantly stocked with the remains of 
corals1 shells1 crustaceans1 c4 in every

 degree of preservation2 indeed1 so     
abundant are these relics1 that they go 
to form a great proportion of the rock4 
,coal is another familiar example of an 
organically derived rock1 since it      
consists entirely of vegetable remains4 
#i4 ,the ,,metamorphic class1 as the    
name implies1 embraces all those rocks  
which have undergone some decided change
 since the time of their formation4     
,this change generally consists in a    
re-arrangement of their constituent     
elements1 and has frequently resulted in
 giving a crystalline texture to the    
rocks affected4 ,hence certain          
sedimentary deposits like sandstone and 
shale have been changed from granular   
into crystalline rocks1 and the like has
 happened to beds of limestone and      
chalk4 ,mica-schist1 gneiss1 and        
saccharoid marble are typical of this   
class4  #aj4 ,the ,,igneous rocks are   
those which owe their origin to the     
action of the internal forces of the    
earth's crust4 ,most of them have been  

in a state of fusion1 and betray their  
origin by their crystalline and         
sometimes glassy texture1 and also1 as  
we shall see in another section1 by the 
mode of their occurrence4 ,lava1 basalt1
 and obsidian are characteristic types  
of this group of igneous rocks4 ,another
 group embraces a large variety of      
igneous rocks which are non-crystalline1
 and vary in texture from fine-grained1 
almost compact1 bedded masses1 like     
certain varieties of tuff1 up to coarse1
 irregular accumulations of angular     
stones imbedded in a fine-grained or    
gritty matrix1 like volcanic breccia and
 volcanic agglomerate4     ,,mineralogy4
   #aa4 ,having learned that all the    
rocks met with at the surface of the    
earth's crust are capable of being      
arranged under a few classes1 we have   
now to investigate the matter more in   
detail4 ,it will be observed that the   
classification adopted above is based   
chiefly upon the external characters of 
the constituent ingredients of the      

rocks1 and the mode in which these      
particles have been collected4 ,in some 
rocks the component materials are       
crystalline1 in others they are rounded 
and worn2 in one case they have been    
brought together by precipitation from  
an aqueous solution1 or they have       
crystallised out from a mass of once    
molten matter2 in another case their    
collection and intimate association is  
due to the mechanical action of the     
atmosphere or of water1 or to the agency
 of the organic forces4 ,we have next to
 inquire what is the nature of those    
crystals and particles which are the    
ingredients of the rocks8 ,the answer to
 this question properly belongs to the  
science of mineralogy1 with which1      
however1 the geologist must necessarily 
make some acquaintance4  #ab4           
,granite--its composition4--,it will    
tend to simplify matters if we begin our
 inquiry by selecting for examination   
some familiar rock1 such as granite4    
,this rock1 as one sees at a glance1 is 

crystalline1 nor is it difficult to     
perceive that three separate kinds of   
ingredients go to compose it4 ,one of   
these we shall observe is a gray1 or it 
may be1 clear glassy-looking substance1 
which is hard1 and will not scratch with
 a knife2 another is of a pink1 red1    
gray1 or sometimes even pale green      
colour1 and scratches with difficulty2  
while the third shews a glistering      
metallic lustre1 and is generally of a  
brownish or black colour4 ,it scratches 
easily with the knife1 and can be split 
up into flakes of extreme thinness4 ,if 
the granite be one of the coarse-grained
 varieties1 we shall notice that these  
three ingredients have each more or less
 definite crystalline forms2 so that    
they are not distinguished by colour and
 hardness alone4 ,the metallic-looking  
substance is mica2 the hard gray1 or    
glassy and unscratchable ingredient is  
quartz2 and the remaining material is   
felspar4 ,the mineralogist's analysis of
 granite ends here4 ,but there is still 

much to be learned about quartz1        
felspar1 and mica2 for1 as the chemist  
will tell us1 these are not 'elementary 
substances4' ,quartz is a compound1     
consisting of two elements1 one of which
 is a non-metallic body 7silicon71 and  
the other an invisible gas 7oxygen74    
,felspar,a is a still more complex      
compound1 being made up of two metals   
7potassium1 aluminium7 and one          
non-metallic body 7silicon71 each of    
which is united to an invisible gas     
7oxygen74 ,mica1 again1 contains no     
fewer than four metals 7potassium1      
magnesium1 iron1 calcium7 and one       
non-metallic body 7silicon71 each of    
which is in like manner chemically      
united to its share of oxygen4 ,thus the
 rock-forming substances1 quartz1       
felspar1 and mica1 have each a definite 
chemical composition4  #ac4             
,minerals4--,now1 any inorganic         
substance which has a definite chemical 
composition1 and crystallises in a      
definite crystalline or geometric form1 

is termed a mineral4 ,having once       
discovered that quartz is composed of   
silicon and oxygen--that is1 silica--and
 that the faces of its crystals are     
arranged in a certain definite order1 we
 may be quite sure that any mineral     
which has not this composition and form 
cannot be quartz4 ,and so on with mica  
and felspar1 and every other mineral4   
,the study of the geometric forms       
assumed by minerals 7crystallography7   
forms a department of the science of    
mineralogy4 ,but1 in the great majority 
of cases1 the mineral ingredients of the
 rocks are either so small individually1
 or so broken1 and rounded1 and altered1
 that crystallography gives             
comparatively little aid to the         
practical geologist in the field4 ,he   
has1 therefore1 recourse to other tests 
for the determination of the mineral    
constituents of rocks4 ,many of these   
tests1 however1 can only be applied by  
those who have had long experience4 ,the
 simplest and easiest way for the       

student to begin is to examine the forms
 and appearance of the more common      
minerals in some collection1 and        
thereafter to accustom his eye to the   
aspect presented by the same minerals   
when they are associated together in    
rocks1 of which illustrative specimens  
are now to be met with in most museums4 
,the microscope is largely employed by  
geologists for determining the          
mineralogical composition of certain    
rocks2 and1 indeed1 many rocks can      
hardly be said to be thoroughly known   
until they have been sliced and examined
 under the microscope1 and analysed by  
the chemist4 ,but with a vast number    
such minute examination is not required1
 the eye after some practice being able 
to detect all that is needful to be     
known4     ,a ,there are various kinds  
of felspar2 the one referred to above is
        orthoclase1 or potash-felspar4  
,,rock-,,forming ,,minerals4  #ad4      
,nearly all the minerals we know of     
contain oxygen as a necessary           

ingredient1 there being only a very few 
minerals in which that gas does not     
occur in chemical union with other      
elements4 ,three of these minerals1     
sulphur1 the diamond1 and graphite1     
consist of simple substances1 and are of
 great commercial importance1 but none  
of them is of so frequent occurrence1 as
 a rock constituent1 as the minerals    
presently to be described4 ,sulphur     
occurs sometimes in thin beds1 but more 
frequently in small nests and nodules1  
c4 in other rocks1 or in joints1 and    
fissures1 and veins4 ,it is frequently  
found in volcanic districts4 ,the       
diamond1 which consists of pure carbon1 
is generally met with in alluvial       
deposits1 but sometimes1 also1 in a     
curious flexible sandstone1 called      
itacolumite4 ,graphite is another form  
of carbon4 ,it occurs both in a         
crystalline and amorphous form1 the     
latter1 or non-crystalline kind1 being  
extensively used for lead-pencils4      
,rock-salt is a chloride of sodium1 and 

appears sometimes in masses of a hundred
 feet and more in thickness4 ,another   
mineral which contains no oxygen is the 
well-known fluor-spar4 ,it occurs       
chiefly in veins1 and is often          
associated with ores4 ,with these1 and a
 few other exceptions1 all the minerals 
hitherto discovered contain oxygen as an
 essential element2 and so large is the 
proportion of this gas which enters into
 union with other elements to constitute
 the various minerals of which the rocks
 are composed1 that it forms at least   
one-half of all the ponderable matter   
near the earth's surface4 ,when the     
student learns that there are probably  
no fewer than six or seven hundred      
different minerals1 he will understand  
how impossible it is to do more in a    
short geological treatise than point out
 a few of the most commonly occurring   
ones4 ,and1 indeed1 a knowledge of the  
chief rock-forming minerals1 which are  
few in number1 is all that is absolutely
 requisite for geological purposes4     

,some of these we accordingly proceed to
 name4,b     ,b ,it is needless to      
describe the minerals minutely here4    
,the        student can only learn to   
distinguish the different species       
by carefully examining actual specimens4
  #ae4 ,quartz4--,this mineral has      
already been partially described4 ,it is
 the most abundant of all the           
rock-forming minerals1 and occurs in    
three forms3 7#a7 crystallised quartz or
 rock crystal2 7#b7 chalcedony1 both of 
which are composed of silica--that is1  
silicon and oxygen2 and 7#c7 hydrated   
quartz--that is1 silica with the        
addition of water4  ,hematite4--,this is
 an oxide of iron4 ,it occurs in        
mammillary rounded masses1 with a       
fibrous structure1 and a dull metallic  
lustre4 ,magnetite or magnetic iron ore1
 specular iron1 and limonite are also   
oxides of iron4 ,hematite shews a red   
streak when scratched with a knife1     
which distinguishes it from magnetite4  
,iron pyrites4--,this is a sulphide of  

iron of very common occurrence4 ,its    
crystalline form is cubical4 ,when      
broken1 it emits a sulphurous smell4    
,the brass-yellow coloured cubes so     
often seen in roofing-slates are        
familiar examples of the mode of its    
occurrence4 ,but it is also frequently  
found in masses having a crystalline    
surface4  #af4 ,,sulphates4--,only two  
sulphates may be noticed--namely1       
gypsum1 which is a sulphate of lime1    
with its varieties1 selenite1           
satin-spar1 and alabaster2 and barytes1 
a sulphate of baryta4 ,barytes scratches
 easily with the knife1 and from its    
great specific gravity is often called  
heavy-spar4 ,gypsum is softer than      
barytes4  ,,carbonates4--,two of these  
only need be mentioned3 calcite or      
calc-spar1 a carbonate of lime1 which   
scratches with the knife1 and           
effervesces readily with dilute         
hydrochloric acid2 and arragonite1 also 
a carbonate of lime1 but denser than    
calcite4  ,,silicates4--,these are by   

far the most abundantly occurring       
minerals4 ,the species are also         
exceedingly numerous1 but we may note   
here only a few of the more important4  
,they are composed of silica and various
 bases1 such as lime1 potash1 magnesia1 
soda1 alumina1 c4 ,augite or pyroxene is
 a black or greenish-black mineral1     
found1 either as crystals1 which are    
generally small1 or as rounded grains   
and angular fragments1 in basaltic and  
volcanic rocks4 ,it never occurs in     
granite rocks4 ,it is brittle1 and has a
 vitreous or resinous lustre4 ,there are
 a number of varieties or sub-species of
 augite4 ,hornblende1 like augite1 also 
includes a great many minerals4 ,when   
the crystals are small1 it is often     
difficult to distinguish hornblende from
 augite4 ,common hornblende occurs      
crystallised or massive1 and is dark    
green or black1 with a vitreous lustre4 
,it is generally sub-translucent4 ,it   
usually crystallises in igneous rocks   
which contain much quartz or silica2    

while augite1 on the other hand1        
crystallises in igneous rocks which are 
of a more basic character--that is to   
say1 rocks in which silica is not so    
abundantly present4 ,felspar is a       
generic term which embraces a number of 
species1 such as orthoclase or          
potash-felspar1 albite or soda-felspar1 
and anorthite or lime-felspar4          
,orthoclase is white1 red or pink1 and  
gray4 ,it is one of the ordinary        
constituents of granite1 and enters into
 the composition of many rocks4 ,albite 
is usually white4 ,it often occurs as a 
constituent of granite1 not unfrequently
 being associated in the same rock with 
pink felspar or orthoclase4 ,in syenite 
and greenstone it occurs more commonly  
than orthoclase4 ,anorthite occurs in   
white translucent or transparent        
crystals4 ,it is not so common a        
constituent of rocks as either of the   
other felspars just referred to4 ,mica3 
this term includes several minerals1    
which all agree in being highly         

cleavable into thin elastic flakes or   
laminae1 which have a glistening        
metallic lustre4 ,mica is one of the    
common constituents of granite4 ,talc is
 a silvery white1 grayish1 pale or      
dark-green coloured mineral1 with a     
pearly lustre4 ,it splits readily into  
thin flakes1 which are flexible1 but not
 elastic1 and may be readily scratched  
with the nail4 ,it is unctuous and      
greasy to the touch4 ,it occurs in beds 
7talc-slate71 and is often met with in  
districts occupied by metamorphic       
crystalline rocks4 ,serpentine is       
generally of a green colour1 but brown1 
red1 and variously mottled varieties    
occur4 ,it has a dull lustre1 and is    
soft1 and easily cut2 it is tough1      
however1 and takes on a good polish4 ,it
 forms rock-masses in some places4 ,the 
finer varieties are called noble        
serpentine4 ,chlorite is another soft1  
easily scratched mineral1 generally of a
 dark-green colour4 ,it has a pearly    
lustre4 ,sometimes it occurs in beds    

7chlorite-slate71 and is often found    
coating the walls of fissures in certain
 rocks4 ,it has a somewhat greasy feel4 
,the three last-mentioned               
minerals--talc1 serpentine1 and         
chlorite--are all silicates of magnesia4
 ,zeolites is a term which comprises a  
number of minerals of varying chemical  
composition1 all of which tend to form a
 jelly when treated with acids4 ,when   
heated by the blow-pipe they bubble up1 
owing to the escape of water2 hence     
their name zeolites1 from zeo1 ,i boil1 
and lithos1 a stone4 ,the zeolites occur
 very commonly in cavities in igneous   
rocks1 and also in mineral veins4       
,having now mentioned the chief         
rock-forming minerals1 we proceed to a  
brief description of some of the more   
typical representatives of the five     
great classes of rocks referred to at   
page #h4     ,,petrology4,c     ,c      
,petros1 a rock1 and logos1 a discourse4
 ,some geologists        restrict this  
term to the study of the structure and  

arrangement of rock-masses1 and apply   
the term lithology        7lithos1 a    
stone1 and logos1 a discourse7 to the   
study of        the mineralogical       
composition of rocks4   ,,mechanically  
,,formed ,,rocks4  #ag4 7,a47           
,,sedimentary ,,class4--,three of the   
most commonly occurring rocks of this   
class have already been described1 but a
 few details are added here4            
,conglomerate4--,this is a consolidated 
mass of more or less water-worn and     
rounded stones4 ,these stones may be of 
any size4 ,when they are very large1 the
 rock is called a coarse conglomerate2  
the finer varieties1 in which the stones
 are small1 are known as pebbly         
conglomerates4 ,the ingredients of a    
conglomerate may consist of any kind of 
rock1 or of a mixture of many different 
kinds4 ,when they consist entirely of   
quartz1 the rock becomes quartzose4 ,the
 finer-grained conglomerates usually    
shew lines of deposition or bedding1 but
 in some of the coarser sorts it is     

often difficult to detect any kind of   
arrangement4 ,the stones are usually    
imbedded in a matrix of quartzose grit  
and sand1 but sometimes this is very    
scanty4 ,when the nature of the material
 which binds the stones together is very
 well marked1 the rock becomes          
ferruginous1 calcareous1 arenaceous1 or 
argillaceous1 according as the binding  
or cementing material is iron1 lime1    
sand1 or clay4 ,breccia is a rock in    
which the included fragments are        
angular4  #ah4 ,sandstone is1 as already
 remarked1 merely consolidated sand4    
,the coarser varieties1 in which the    
grains are as large and larger than     
turnip-seeds1 are termed grit4 ,from    
these coarse varieties the rock passes  
insensibly1 in one direction1 into a    
fine or pebbly conglomerate1 and in     
another into a rock1 so fine-grained    
that a lens is needed to distinguish the
 component particles4 ,quartz is the    
prevailing ingredient--sometimes clear1 
at other times white4 ,frequently1      

however1 the grains are coated with an  
oxide of iron1 which gives the resulting
 rock a red colour4 ,the other colours  
assumed by sandstone--such as yellow1   
brown1 green1 c4--are also in like      
manner due to the presence of some      
compound of iron4 ,when mica or felspar 
occurs plentifully1 we have1 in the one 
case1 micaceous sandstone1 and in the   
other felspathic sandstone4 ,a sandstone
 in which the grains are cemented by    
carbonate of lime is said to be         
calcareous4 ,freestone is a sandstone   
which can be worked freely in any       
direction4 ,in most sandstones1 the     
lines of bedding are distinct2 when they
 are so numerous as to render the rock  
fissile1 the sandstone is said to be    
shaly4  ,shale is a more or less        
indurated fissile or laminated clay4    
,when the rock becomes coarse by the    
admixture of sand1 it gradually passes  
into a shaly sandstone4 ,there are many 
other varieties of clay-rocks--such as  
fire-clay1 pipe-clay1 marl1 loam1       

c4--which are sufficiently familiar4    
#ai4 7,b47 ,,eolian or ,,aerial         
,,class4--,blown-sand is found at many  
places on sea-coasts4 ,it generally     
forms smooth rounded hummocks1 which are
 sometimes arranged in long lines       
parallel to the trend of the coast1 as1 
for example1 in the ,tents ,moor1 near  
,st ,andrews4 ,the sand-hills of deserts
 also belong to this class4  ,debris is 
the loose angular rubbish which collects
 at the base of cliffs1 on hill-tops1   
and hill-slopes4 ,immense accumulations 
of it occur in lofty mountainous        
districts and in arctic regions4 ,in    
,nova ,zembla1 for example1 the solid   
rock of the country is almost concealed 
beneath a thick covering of debris4 ,but
 the various kinds of debris will be    
more particularly described further on4 
,soil4--,an account of this can hardly  
be given without entering into the      
theory of its origin1 and therefore we  
reserve its consideration for the       
present4   ,,chemically ,,formed        

,,rocks4  #bj4 ,stalactites and         
stalagmites are carbonates of lime4     
,they vary in colour1 being white1 or   
yellow1 or brown4 ,stalactites are      
usually found adhering to the roofs of  
limestone caverns1 c41 or depending from
 limestone rocks2 stalagmites1 on the   
other hand1 commonly occur on the floors
 of limestone caverns1 where they often 
attain a thickness of many feet4        
,siliceous sinter is silica with the    
addition of water--in other words1 a    
hydrated quartz4 ,it is not a very      
abundant rock1 and is found chiefly in  
volcanic countries4  ,rock-salt has     
already been described4 ,it occurs      
either as thin beds1 or in the form of  
thick cake-like masses1 often reaching  
ninety or one hundred feet in thickness4
 ,it is rudely crystalline in texture1  
and is usually discoloured brown and red
 with various impurities4               
,,organically ,,derived ,,rocks4  #ba4  
,limestone consists of carbonate of     
lime1 but usually contains some         

impurities4 ,the varieties of this rock 
are numerous2 some of them are as       
follows3 ,chalk2 oolite1 a rock built up
 of little spheroidal concretions1      
whence its name1 egg or roe stone 7the  
coarser oolites are called pisolite1 or 
pea-stone72 lacustrine limestone1 c4    
,when much silica is diffused through   
the rock1 we have a siliceous limestone2
 the presence of clay and of            
carbonaceous matter gives us            
argillaceous and carbonaceous           
limestones4 ,cornstone is a limestone   
containing a large quantity of          
arenaceous matter or sand4 ,many        
limestones are distinguished by the     
different kinds of organic remains which
 they yield4 ,thus1 we have muschelkalk 
or shell-limestone1 nummulitic1         
crinoidal1 c4 limestone4 ,the           
crystalline limestones1 such as statuary
 marble1 are metamorphosed limestones4  
,not a few limestones are chemically    
formed rocks1 and many1 also1 are partly
 of chemical and partly of organic      

origin1 so that no hard and fast line   
can be drawn between these two classes  
of rock4  ,dolomite1 or magnesian       
limestone4--,this is a compound of      
carbonate of lime and carbonate of      
magnesia4 ,its colour is usually yellow1
 or yellowish brown1 but gray and black 
varieties are sometimes met with4 ,it is
 generally fine-grained1 with a         
crystalline texture1 and pearly lustre4 
,it effervesces less freely with acids  
than pure limestone4 ,in many cases     
dolomite is merely a metamorphosed      
limestone4  #bb4 ,coal is composed of   
vegetable matter1 but usually contains a
 greater or less percentage of          
impurities4 ,the varieties of this      
substance are very numerous1 and differ 
from each other principally in regard to
 their bituminous or non-bituminous     
character4 ,coal is bituminous or       
non-bituminous according as it is less  
or more highly mineralised4 ,bitumen    
results from the decomposition of       
vegetable matter2 but1 when the         

mineralising process 7to which the      
formation of coal is due7 has proceeded 
far enough1 the vegetable matter        
gradually loses its bituminous          
character1 and the result is a          
non-bituminous coal4 ,varieties of coal 
are the following3 ,lignite or brown    
coal2 caking coal2 cannel1 parrot1 or   
gas coal2 splint coal2 cherry or soft   
coal2 anthracite or blind coal1 so      
called because it burns with no flame4  
,peat may be mentioned as another       
natural fuel4 ,it is composed of        
vegetable matter4 ,in some kinds it is  
so far decomposed1 or mineralised1 that 
the eye does not detect vegetable       
fibres2 when thoroughly dried1 such peat
 breaks like a good lignite1 and forms  
an excellent fuel4   ,,metamorphic      
,,rocks4  #bc4 ,quartz-rock1 or         
quartzite1 is an altered quartzose      
sandstone or grit2 it is generally a    
white or grayish-yellow rock1 very hard 
and compact4 ,the original gritty       
character of the rock is distinct1 but  

the granules appear as if they had been 
fused so far as to become mutually      
adherent4 ,when the altered sandstone   
has been composed of grains of quartz1  
felspar1 or mica1 set in a siliceous1   
felspathic1 or argillaceous base1 we get
 a rock called greywacke1 which is      
usually gray or grayish blue in colour4 
#bd4 ,clay-slate is a grayish blue1 or  
green1 fine-grained hard rock1 which    
splits into numerous more or less thin  
laminae1 which may or may not coincide  
with the original bedding4 ,most usually
 the 'cleavage1' as this fissile        
structure is termed1 crosses the bedding
 at all angles4  #be4 ,crystalline      
limestone is an altered condition of    
common limestone4 ,saccharoid marble is 
one of the fine varieties3 it frequently
 contains flakes of mica4 ,dolomite1 or 
magnesian limestone1 already described1 
is probably in many cases an altered    
limestone2 the carbonate of lime having 
been partially dissolved out and        
replaced by carbonate of magnesia4      

,serpentine is also believed by some    
geologists to be a highly metamorphosed 
magnesian limestone4  #bf4              
,schists4--,under this term comes a     
great variety of crystalline rocks which
 all agree in having a foliated         
texture--that is to say1 the constituent
 minerals are arranged in layers which  
usually1 but not invariably1 coincide   
with the original bedding4 ,amongst the 
schists come mica-schist 7quartz and    
mica in alternate layers72              
chlorite-schist 7chlorite with a little 
quartz1 and sometimes with felspar or   
mica72 talc-schist 7talc with quartz or 
felspar72 hornblende schist 7hornblende 
with a variable quantity of felspar1 and
 sometimes a little quartz72 gneiss     
7quartz1 felspar1 and mica74  #bg4      
,general ,character of ,metamorphic     
,rocks4--,all these rocks betray their  
aqueous origin by the presence of more  
or less distinct lines of bedding4 ,they
 consist of various kinds of arenaceous 
and argillaceous deposits1 which1 under 

the influence of certain metamorphic    
actions1 to be described in the sequel1 
have lost their original granular       
texture1 and become more or less        
distinctly crystallised4 ,and not only  
so1 but their chemical ingredients have 
in many cases entered into new          
relations1 so as to give rise to        
minerals which existed either sparingly 
or not at all in the original rocks4    
,frequently1 it is quite impossible to  
say what was the original condition of  
some metamorphic rocks2 often1 however1 
this is sufficiently obvious4 ,thus1    
highly micaceous sandstones1 as they are
 traced into a metamorphic region1 are  
seen to pass gradually into mica-schist4
 ,when the bedding of gneiss becomes    
entirely obliterated1 it is often       
difficult to distinguish that rock from 
granite1 and in many cases it appears to
 pass into a true granite4  #bh4        
,granite is a crystalline compound of   
quartz1 felspar 7usually                
potash-felspar71 and mica4 ,some        

geologists consider it to be invariably 
an igneous rock2 but1 as just stated1 it
 sometimes passes into gneiss in such a 
way as to lead us to infer its          
metamorphic origin4 ,there are certain  
areas of sandstone in the south of      
,scotland which are partially           
metamorphosed1 and in these we may trace
 a gradual passage from highly baked    
felspathic sandstones with a            
sub-crystalline texture into a more     
crystalline rock which in places        
graduates into true granite4 ,granite1  
however1 also occurs as an igneous rock4
  #bi4 ,syenite is a crystalline        
compound of a potash-felspar and        
hornblende1 and quartz is frequently    
present4 ,diorite is a crystalline      
aggregate of a soda-felspar and         
hornblende4 ,both syenite and diorite   
also occur as igneous rocks4  ,there are
 a number of other metamorphic rocks1   
but those mentioned are the most        
commonly occurring species4   ,,igneous 
,,rocks4  #cj4 ,subdivisions4--,in their

 chemical and mineralogical composition1
 igneous rocks offer great variety2 but 
they all agree in having felspar for    
their base4 ,they may be roughly divided
 into two classes1 distinguished by the 
relative quantity of silica which they  
contain4 ,those in which the silica     
ranges from about #ej to #gj or #hj per 
cent4 form what is termed the acidic    
group2 while those in which the         
percentage of silica is less constitute 
the basic group of igneous rocks1 so    
called because they contain a large     
proportion of the heavier bases1 such as
 magnesia1 lime1 oxides of iron and     
manganese1 c4 ,igneous rocks vary in    
texture from homogeneous1 compact1 and  
finely crystalline masses up to coarsely
 crystalline aggregates1 in which the   
crystals may be more than an inch in    
diameter4 ,sometimes they are dull and  
earthy in texture1 at other times       
vesicular4 ,when the vesicles are filled
 up with some mineral1 the rock is said 
to be amygdaloidal1 from the almond     

shape assumed by the kernels filling the
 cavities4 ,when single crystals of any 
mineral are scattered through a rock1 so
 as to be readily distinguished from the
 compact or crystalline base1 the rock  
becomes porphyritic4   ,,acidic ,,or    
,,felspathic ,,group4  #ca4 ,trachyte   
7trachys1 rough7 is a pale or dark-gray 
rock1 harsh and rough to the touch1 in  
which felspar is the predominant        
mineral4 ,it is a common product of     
eruption in modern volcanoes4           
,clinkstone or phonolite is a           
greenish-gray1 compact1 felspathic rock1
 somewhat slaty or schistose1 and       
weathers with a white crust4 ,it gives a
 clear metallic sound under the hammer4 
,it is a rock not met with among the    
older formations of the earth's crust1  
being confined to ,tertiary 7see table1 
p4 #he7 or still more recent times4     
,obsidian or volcanic glass is usually  
black1 brown1 or green1 and usually     
resembles a coarse bottle-glass4 ,when  
it becomes vesicular1 it passes         

gradually into the highly porous rock   
called pumice4 ,it is eminently a       
geologically modern volcanic rock4      
,felstone is a reddish-gray1 bluish1    
greenish1 or yellowish1 hard1 compact1  
flinty-looking rock1 composed of        
potash-felspar and silica4 ,it is       
generally splintery under the hammer4   
,some varieties are slaty1 and are      
frequently mistaken for clinkstone1     
which they closely resemble4 ,when the  
quartz in felstone is distinctly visible
 either as grains or crystals1 the rock 
passes into a quartz-porphyry4  ,granite
 is recognised as an igneous as well as 
a metamorphic rock4 ,sometimes the veins
 and dykes which proceed from or occur  
near a mass of granite contain no       
mica--this kind of rock is called elvan 
or elvanite4  ,porphyrite or felspathite
 includes a number of rocks which have a
 felspathic base1 through which felspar 
crystals are scattered more or less     
abundantly4 ,sometimes hornblende1 or   
augite1 or mica is present4 ,the colour 

is usually dark--some shade of blue1    
green1 red1 puce1 purple1 or brown--and 
the texture varies from compact and     
finely crystalline up to coarsely       
crystalline4 ,porphyrites are usually   
porphyritic1 and frequently             
amygdaloidal4   ,,augitic ,,and         
,,hornblendic ,,or ,,basic ,,group4     
#cb4 ,basalt is a dark or almost black  
compact homogeneous rock1 composed of   
felspar and augite with magnetic iron4  
,an olive-green mineral called olivine  
is very frequently present4 ,the        
coarser-grained basalts are called      
dolerite4 ,the columnar structure is not
 peculiarly characteristic of basalt4   
,many basalts are not columnar1 and not 
a few columnar rocks are not basalts4   
,greenstone or diorite is usually a dull
 greenish rock1 sometimes gray1 however1
 speckled with green4 ,it is composed of
 soda-felspar and hornblende4 ,the      
fine-grained compact greenstones are    
called aphanite4  ,syenite1 like        
granite1 is recognised as an igneous as 

well as a metamorphic rock4 ,there are  
several other rocks which come into the 
basic group1 but those mentioned are the
 more common and typical species4  #cc4 
,fragmental ,igneous ,rocks4--,all the  
igneous rocks briefly described above   
are more or less distinctly crystalline 
in texture4 ,there is a class of igneous
 rocks1 however1 which do not present   
this character1 but when fine-grained   
are dull and earthy in texture1 and     
frequently consist merely of a rude     
agglomeration of rough angular fragments
 of various rocks4 ,these form the      
,,fragmental group of igneous rocks4    
,the ejectamenta of loose materials     
which are thrown out during a volcanic  
eruption1 consist in chief measure of   
fragments of lava1 c4 of all sizes1 from
 mere dust1 sand1 and grit1 up to blocks
 of more than a ton in weight4 ,these   
materials1 as we shall afterwards see1  
are scattered round the orifice of      
eruption in more or less irregular beds4
 ,the terms applied to the varieties of 

ejectamenta found among modern volcanic 
accumulations1 will be given and        
explained when we come to consider the  
nature of geological agencies4 ,in the  
,british ,islands1 and many other       
non-volcanic regions1 we find besides   
crystalline igneous rocks1 abundant     
traces of loose ejectamenta1 which      
clearly prove the former presence of    
volcanoes4 ,these materials are         
sometimes quite amorphous--that is to   
say1 they shew no trace of water        
action--they have not been spread out in
 layers1 but consist of rude tumultuous 
accumulations of angular and subangular 
fragments of igneous rocks4 ,such masses
 are termed trappean agglomerate and    
trappean breccia4 ,at other times1      
however1 the ejectamenta give evidence  
of having been arranged by the action of
 water1 the materials having been sifted
 and spread out in more or less regular 
layers4 ,what were formerly rude        
breccias and agglomerates of angular    
stones now become trappean              

conglomerates--the stones having been   
rounded and water-worn--while the fine  
ingredients1 the grit1 and sand1 and    
mud1 form the rock called trap tuff4    
,fragmental rocks are often quite       
indurated--the matrix being as hard as  
the included stones4 ,but as a rule they
 are less hard than crystalline igneous 
rocks1 and in many cases are loose and  
crumbling4 ,when a fragmental rock is   
composed chiefly of rocks belonging to  
the acidic group1 we say it is          
felspathic4 ,when augitic and           
hornblendic materials predominate1 then 
other terms are used2 as1 for example1  
dolerite tuff1 greenstone tuff4         
,,structure ,,and ,,arrangement ,,of    
,,rock-,,masses4  #cd4 ,the student can 
hardly learn much about the             
mineralogical composition of rocks1     
without at the same time acquiring some 
knowledge of the manner of their        
occurrence in nature4 ,we have already  
briefly described certain sedimentary   
rocks1 such as conglomerate1 sandstone1 

and shale1 and have in some measure     
touched upon their structure as         
rock-masses4 ,these rocks1 as we have   
seen1 are arranged in more or less thick
 layers or beds1 which are piled one on 
the top of the other4 ,rocks which are  
so arranged are said to be stratified1  
and are termed strata4 ,we may also use 
the word stratum as an occasional       
substitute for bed4 ,the planes of      
bedding or stratification are sometimes 
very close together1 in other cases they
 are wide apart4 ,when the separate beds
 are very thin1 as in the case of shale1
 it is most usual to term them laminae1 
and to speak of the lamination of a     
shale1 as distinguished from the bedding
 of a sandstone4 ,planes of bedding are 
generally more strongly marked than     
planes of lamination4 ,the laminae      
frequently cohere1 while beds seldom do4
 ,in the above figure1 which represents 
a vertical cutting or section through   
horizontal strata1 the planes of        
lamination are shewn at l1 l1 l1 and    

those of stratification at s1 s1 s4     
,there are hardly any limits to the     
thickness of a bed--it may range from an
 inch up to many feet or yards1 while   
laminae vary in thickness from an inch  
downwards4     ,illustration3 ,fig4     
#a4--st1 sandstone1 and sh1 shale3 s1   
lines or planes of bedding2 l1 lines or 
planes of    lamination4  #ce4 ,hitherto
 we have been considering the laminae   
and strata as lying in an approximately 
horizontal plane4 ,sometimes1 however1  
the layers of deposition in a single    
stratum are inclined at various angles  
to themselves1 as in the following      
figure4 ,this structure is called false 
bedding2 the layers or laminae not      
coinciding with the planes of           
stratification4 ,it owes its origin to  
shifting currents1 such as the ebb and  
flow of the tide1 and very often        
characterises deposits which have been  
formed in shallow water4 7,hillocks of  
drifting sand frequently shew a similar 
structure1 but their false bedding is1  

as a rule1 much more pronounced47       
,illustration3 ,fig4 #b4--;,false       
,bedding4  #cf4 ,mud-cracks and         
,rain-prints4--,the surfaces of some    
beds occasionally exhibit markings      
closely resembling those seen upon a    
flat sandy beach after the retreat of   
the tide--hence they are called         
ripple-marks or current-marks4 ,they    
are1 of course1 due to the gentle       
current action which pushes along the   
grains of sand1 and hence1 such marks   
may be formed wherever a current sweeps 
over the bottom of the sea with energy  
just sufficient for the purpose4 ,but   
since the necessary conditions for the  
formation of ripple-mark occur most     
abundantly in shallow water1 its        
frequent appearance in a series of      
strata may often be taken as evidence1  
so far1 for the shallow-water origin of 
the beds4 ,besides ripple-marks we may  
also detect occasionally on the surfaces
 of certain strata mud-cracks and       
rain-prints4 ,these occur most commonly 

in fine-grained beds1 as in flagstones1 
argillaceous sandstones1 shales1 c4 ,the
 mud-cracks resemble those upon a       
mud-flat which are caused by the        
desiccation and consequent shrinkage of 
the mud when exposed to the sun4 ,the   
old cracks have been subsequently filled
 up again by a deposition of mud or     
sand1 usually of harder consistency than
 the rock traversed by the cracks4      
,hence1 when the bed that overlies the  
mud-cracks is removed1 we find a cast of
 these projecting from its under        
surface1 or frequently the cast remains 
in its mould1 and forms a series of     
curious ridges ramifying over the whole 
surface of the old mud-flat4            
,rain-prints are the small pits caused  
by the impact of large drops4 ,they are 
usually deeper at one side than the     
other1 from which we can infer the      
direction of the wind at the time the   
rain-drops fell4 ,like the mud-cracks1  
they are most commonly met with in      
fine-grained beds1 and have been        

preserved in a similar manner4 ,some    
geologists have also been able to detect
 wave-marks1 'faint outlinings of curved
 form on a sandstone layer1 like the    
outline left by a wave along the limit  
where it dies out upon a beach4'  #cg4  
,succession of ,strata4--,the succession
 of strata is often very diversified4   
,thus1 we may observe in one and the    
same section numberless alternating beds
 of sandstone and shale from an inch or 
so up to several feet each in thickness1
 with seams of coal1 fireclay1          
ironstone1 and limestone interstratified
 among them4 ,in other cases1 again1 the
 succession is simpler1 and some deep   
quarries shew only one bed1 as is the   
case with certain limestones1           
fine-grained sandstones 7liver-rock71   
and many volcanic rocks4 ,some          
limestones1 indeed1 shew small trace of 
bedding throughout a vertical thickness 
of hundreds of feet4  #ch4 ,beds1 their 
,extent1 c4--,beds of rock are not only 
of very different thicknesses1 but they 

are also of very variable extent4 ,some 
may thin gradually away1 or 'die out'   
suddenly1 in a few feet or yards1 while 
others may extend over many square      
miles4 ,beds of limestone1 for example1 
can often be traced for leagues in      
several directions2 and if this be the  
case with certain single beds1 it is    
still more true of groups of strata4    
,thus the coal-bearing strata belonging 
to what is called the ,carboniferous    
period cover large areas in ,wales1     
,england1 ,scotland1 and ,ireland1 not  
less1 probably1 than #fjjj square miles2
 and strata belonging to the same great 
period spread over considerable tracts  
on the ,continent1 and a very extensive 
area in ,north ,america4 ,it holds      
generally true that beds of fine-grained
 materials are not only of more equal   
thickness throughout1 but have also a   
wider extension than coarser-grained    
rocks4 ,fine sandstones1 for example1   
extend over a wider area1 and preserve a
 more equable thickness throughout than 

conglomerates1 while limestones and     
coals are more continuous than either4  
#ci4 ,when a bed is followed for any    
distance it is frequently found to thin 
away1 and give place to another         
occupying the same plane or horizon4    
,thus a shale will be replaced by a     
sandstone1 a sandstone by a             
conglomerate1 and vice versa4 ,sometimes
 also we may find a shale1 as we trace  
it in some particular direction1        
gradually becoming charged with         
calcareous matter1 so as by and by to   
pass1 as it were1 into limestone4 ,every
 bed must1 of course1 end somewhere1    
either by thus gradually passing into   
another1 or by thinning out so as to    
allow beds which immediately overlie and
 underlie it to come together4 ,not     
unfrequently1 however1 a bed will stop  
abruptly1 as in fig4 #c4                
,illustration3 ,fig4 #c4--,sudden ending
 of ,bed at x4  #dj4 ,sequence of       
,beds4--,it requires little reflection  
to see that the division plane between  

two beds may represent a very long      
period of time4 ,let the following      
diagram represent a section of strata1 s
 being beds of grit1 and a1 b1 c1 beds  
of sandstone and shale4 ,it is evident  
that the beds s must have been formed   
before the strata b were deposited above
 them4 ,at x1 the beds a and b come     
together1 and were attention to be      
confined to that part of the section1   
the observer might be led to infer that 
no great space of time elapsed between  
the deposition of these two beds4 ,yet  
we see that an interval sufficient to   
allow of the formation of the beds s    
must really have intervened4 ,it is now 
well known that in many cases planes of 
bedding represent 'breaks in the        
succession' of strata--'breaks' which   
are often the equivalents of            
considerable thicknesses of strata4 ,in 
one place1 for example1 we may have an  
apparently complete sequence of beds1 as
 a1 b1 c1 which a more extended         
knowledge of the same beds1 as these are

 developed in some other locality1      
enables us to supplement1 as a1 s1 b1 c4
     ,illustration3 ,fig4 #d4--,sequence
 of ,beds4  #da4 ,joints4--,besides     
planes or lines of bedding1 there are   
certain other division planes or joints 
by which rocks are intersected4 ,the    
former1 as we have seen1 are congenital2
 the latter are subsequent4 ,joints cut 
right across the bedding1 and are often 
variously combined1 one set of joint    
planes traversing the rock in one       
direction1 and another set or sets      
intersecting these at various angles4   
,thus1 in many cases the rocks are so   
divided as easily to separate into more 
or less irregular fragments of various  
sizes4 ,besides these confused joints   
there are usually other more regular    
division planes1 which intersect the    
strata in some definite directions1 and 
run parallel to each other1 often over a
 wide area3 these are called            
master-joints4 ,two sets of             
master-joints may intersect the same    

strata1 and when such is the case1 the  
rock may be quarried in cuboidal blocks1
 the size of which will vary1 of course1
 according as the two sets of joints are
 near or wide apart4 ,joints may either 
gape or be quite close2 so close1       
indeed1 as in many cases to be invisible
 to the naked eye4 ,certain igneous     
rocks frequently shew division planes   
which meet each other in such a way as  
to form a series of polygonal prisms4   
,the basalt of ,staffa and ,giants'     
,causeway are familiar examples of this 
structure4 ,jointing is due to the      
gradual consolidation of the strata1 and
 hence1 in a series of strata1 we may   
find the separate beds1 according to    
their composition1 very variously       
affected1 some being much more          
abundantly jointed than others4         
,master-joints which traverse a wide    
district in some definite direction     
probably owe their origin to tension1   
the strata having been subjected to some
 strain by the underground forces4      

,illustration3 ,fig4 #e4--;,beds of     
,limestone 7a71 ,sandstone    7b71 and  
,shale 7c71 divided into cuboidal masses
 by    master-joints4     ,illustration3
 ,fig4 #f4--;,columnar ,structure4      
,illustration3 ,fig4 #g4--;,bedding1    
,joints1 and ,cleavage 7after           
,murchison74  #db4                      
,cleavage4--,fine-grained rocks1 more   
especially those which are argillaceous1
 occasionally shew another kind of      
structure1 which is called cleavage4    
,common clay-slate is a type of the     
structure4 ,this rock splits up into    
innumerable thin laminae or plates1 the 
surface of which may either be somewhat 
rough1 or as smooth nearly as glass4    
,the cleavage planes1 however1 need not 
be parallel with the planes of bedding2 
in most cases1 indeed1 they cut right   
across these1 and continue parallel to  
each other often over a very wide       
region4 ,the original bedding is        
sometimes entirely obliterated1 and in  
most cases of well-defined cleavage is  

always more or less obscure4  ,in the   
preceding diagram1 the general phenomena
 of bedding1 jointing1 and cleavage are 
represented4 ,the lines of bedding are  
shewn at ,s1 ,s2 another set of         
division-planes 7joints7 is observed at 
,j1 ,j1 intersecting the former at right
 angles--,a1 ,b1 ,c being the exposed   
faces of joints4 ,the lines of cleavage 
are seen at ,d1 ,d1 cutting across the  
planes of bedding and jointing4  #dc4   
,foliation is another kind of           
superinduced structure4 ,in a foliated  
rock the mineral ingredients have been  
crystallised and arranged in layers     
along either the planes of original     
bedding or those of cleavage4           
,mica-schist and gneiss are typical     
examples4  #dd4 ,concretions4--,in many 
rocks a concretionary structure may be  
observed4 ,some sandstones and shales   
appear as if made up of spheroidal      
masses1 the mineral composition of the  
spheroids not differing apparently from 
that of the unchanged rock4 ,so in some 

kinds of limestone1 as in dolomite1 the 
concretionary structure is often highly 
developed1 the rock resembling now      
irregular heaps of turnips with         
finger-and-toe disease1 again1 piles of 
cannon-balls1 or bunches of grapes1 and 
agglomerations of musket-shot4 ,a       
spheroidal structure is occasionally met
 with amongst some igneous rocks4 ,this 
is well seen in the case of rocks having
 the basaltic structure1 in which the   
pillars1 being jointed transversely1    
decompose along their division planes1  
so as to form irregular globular masses4
 ,in many cases1 certain mineral matter 
which was originally diffused through a 
rock has segregated so as to form       
nodules and irregular layers4 ,examples 
of this are chert nodules in limestone2 
flint nodules in chalk2 clay-ironstone  
balls in shale1 c4     ,illustration3   
,fig4 #h4--;,dip and ,strike of ,strata4
  #de4 ,inclination of ,strata4--,beds  
of aqueous strata must have been        
deposited in horizontal or approximately

 horizontal planes2 but we now find them
 most frequently inclined at various    
angles to the horizon1 and often even   
standing on end4 ,they sometimes1       
however1 retain a horizontal position   
over a large tract of country4 ,the     
angle which the inclined strata make    
with the horizon is called the dip1 the 
degree of inclination being the amount  
of the dip2 and a line drawn at right   
angles to the dip is called the strike  
of the beds4 ,thus1 a bed dipping       
south-west will have a north-west and   
south-east strike4 ,the crop or outcrop 
7sometimes also1 but rarely1 called the 
basset edge7 of a bed is the place where
 the edge of the stratum comes to view  
at the surface4 ,we may look upon       
inclined beds as being merely parts of  
more or less extensive undulations of   
strata1 the tops of the undulations     
having been removed so as to expose the 
truncated edges of the beds4 ,in the    
following diagram1 for example1 the     
outcrops of limestone seen at l1 l1 are 

evidently portions of one and the same  
stratum1 the dotted lines indicating its
 former extent4 ,the trough-shaped      
arrangement of the beds at s is called a
 synclinal curve1 or simply a syncline2 
the arched strata at a forming1 on the  
contrary1 an anticlinal curve or        
anticline4     ,illustration3 ,fig4     
#i4--;,anticlines and ,synclines4       
,illustration3 ,fig4 #aj4--;,contorted  
,strata4  ,when strata shew many and    
rapid curves1 they are said to be       
contorted4 ,the diagram section 7fig4   
#aj7 will best explain what is meant by 
this kind of structure4  #df4 ,in       
certain regions1 the strata often dip in
 one and the same direction for many    
miles1 at an angle approaching          
verticality1 as in the following        
section4 ,it might be inferred1         
therefore1 that from ,a to ,b we had a  
gradually ascending series--that as we  
paced over the outcrop we were stepping 
constantly from a lower to a higher     
geological horizon4 ,but1 in such cases1

 the dip is deceptive1 the same beds    
being repeated again and again in a     
series of great foldings of the strata4 
,such is the case over wide areas in the
 upland districts of the south of       
,scotland4 ,the section 7fig4 #aa7 shews
 that the beds are actually inverted1   
the strata at x x being bent back upon  
strata which really overlie them4       
,illustration3 ,fig4 #aa4--;,inversion  
of ,strata4     ,illustration3 ,fig4    
#ab4--;,contemporaneous ,erosion4  #dg4 
,contemporaneous                        
,erosion4--,occasionally a group of     
strata gives proof that pauses in the   
deposition of sediment took place1      
during which running water scooped out  
of the sediment channels of greater or  
less width1 which subsequently became   
filled up with similar or dissimilar    
materials4 ,the diagram 7fig4 #ab7 will 
render this plain4 ,at a we have beds of
 sandstone1 which it is evident were at 
one time throughout as thick as they    
still are at x x4 ,having been worn away

 to the extent indicated1 a deposition  
of clay 7b7 succeeded2 and this1 in     
turn1 became eroded at c1 c1 the hollows
 being filled up again with coarse sand 
and gravel4 ,in former paragraphs1 we   
found reason to believe that lines of   
bedding indicated certain pauses in the 
deposition of strata4 ,here1 in the     
present case1 we have more ample proof  
in the same direction4                  
,illustration3 ,fig4                    
#ac4--,unconformability4  #dh4          
,unconformability4--,but the most       
striking evidence of such pauses in the 
deposition of strata is afforded by the 
phenomenon called unconformability4     
,when one set of rocks is found resting 
on the upturned edges of a lower set1   
the former are said to be unconformable 
to the latter4 ,in the above section    
7fig4 #ac71 a1 a1 are beds of sandstone 
resting on the upturned edges of beds of
 limestone1 shale1 and sandstone1 l1 s4 
,figs4 #ad and #ae give other examples  
of the same appearance4 ,it is evident  

that1 in the case of fig4 #ad1 the      
discordant bedding chronicles the lapse 
of a very long period4 ,we have to      
conceive first of the deposition of the 
underlying strata in horizontal or      
approximately horizontal layers2 then we
 have to think of the time when they    
were crumpled up into great             
convolutions1 and the tops of the       
convolutions 7the anticlines7 were      
planed away3 all these changes          
intervened1 of course1 after the lower  
set was deposited1 and before the upper 
series was laid down4 ,in the case      
represented in fig4 #ae1 we have a      
double unconformability1 implying a     
still more elaborate series of changes1 
and probably1 therefore1 a still longer 
lapse of time4     ,illustration3 ,fig4 
#ad4--,violent ,unconformability4       
,illustration3 ,fig4 #ae4--;,double     
,unconformability4  #di4                
,overlap4--,when the upper beds of a    
conformable group of strata spread over 
a wider area than the lower members of  

the same series1 they are said to       
overlap4 ,the accompanying diagram shews
 this appearance4 ,an overlap proves    
that a gradual submergence of the land  
was going on at the time the strata were
 being accumulated4 ,as the land        
disappeared below the water1 the        
sediment gradually spread over a wider  
area1 the more recently deposited       
sediment being laid down in places which
 existed as dry land at the time when   
the earliest accumulations were formed4 
,thus1 in the accompanying illustration 
7fig4 #af71 the stratum marked #a1      
resting unconformably upon older strata1
 is overlapped by #b1 as that is by #c1 
and so on--all the beds in succession   
coming to repose upon the older strata  
at higher and higher levels1 as the old 
land subsided4     ,illustration3 ,fig4 
#af4--,overlap4     ,illustration3 ,fig4
 #ag4--;,fault4  #ej4 ,dislocations or  
,faults4--,when strata1 once continuous1
 have been broken across1 and displaced 
or shifted along the line of breakage1  

they are said to be faulted1 the fissure
 along which the displacement occurs    
being termed a fault or dislocation4    
,the simplest form of a fault is that   
shewn in the following diagram1 where   
strata of sandstone and shale1 with a   
coal-seam1 ,s1 have been shifted along  
the line f4 ,the direction in which the 
fault is inclined,d is its hade1 and the
 degree of vertical displacement of the 
beds is the amount of the dislocation4  
,generally1 the beds seem to be pulled  
down in the direction of the downthrow1 
and drawn up on the opposite side of the
 fault1 as shewn in the diagram4        
,sometimes the rocks on each side of a  
fault are smoothed and polished1 and    
covered with long scratches1 as if the  
two sides of the fissure had been rubbed
 together4 ,this is the appearance      
called slickensides4 ,slickensides1     
however1 may occur on the walls of a    
fissure which is not a displacement1 but
 a mere joint or crack4 ,a dislocation  
is spoken of as a downthrow or an       

upcast1 according to the direction in   
which it is approached4 ,thus1 a miner  
working along the coal-seam ,s1 from a  
to b1 would describe the fault1 f1 as an
 upcast1 since he would have to mine to 
a higher level to catch his coal again4 
,but1 had he approached the fault from c
 to d1 he would then have termed it a   
downthrow1 because he would see from the
 hade of the fault that his coal-seam   
must be sought for at a lower level4    
,faults are of all sizes1 from a foot or
 two up to vertical displacements of    
thousands of feet4 ,powerful            
dislocations can often be followed for  
many miles across a country1 running in 
a more or less linear direction4 ,thus1 
one large fault has been traced across  
the breadth of ,scotland1 from near ,st 
,abb's ,head1 in the east1 to the coast 
of ,wigtown1 in the west4 ,every large  
throw is accompanied by a number of     
smaller ones--some of which run parallel
 to the main fault1 while many others   
seem to run out from this at various    

angles4 ,faults are of all geological   
ages4 ,some date back to a most remote  
antiquity1 others are of quite recent   
origin2 and no doubt faults are         
occurring even now4 ,in the following   
diagram1 the strata1 a1 a1 have been    
faulted and planed away before the      
strata1 b1 were deposited4 ,hence1 in   
this case1 it is evident that if we know
 the geological age of the beds1 a and  
b1 we can have an approximation to the  
age of the fault4 ,if the beds1 a1 be   
,carboniferous1 and those at b ,permian1
 then we should say the fault was       
post-,carboniferous or pre-,permian4    
,d ,the degree of inclination is very   
variable4 ,it may occur at        almost
 any angle up to vertical4 ,but1 as a   
rule1 the hade of the        more       
powerful faults is steeper than that of 
minor displacements4     ,illustration3 
,fig4 #ah4--;,ground-plan of ,large     
,main ,fault and    ,minor ,displacement
 ,fissures4     ,illustration3 ,fig4    
#ai4--;,faulted ,strata covered by      

undisturbed    ,strata4  #ea4           
,metamorphic and ,igneous ,rocks--mode  
of their occurrence4--,in the foregoing 
remarks on the structure and arrangement
 of rocks we have had reference chiefly 
to the aqueous strata--that is to say1  
the mechanically1 chemically1 and       
organically formed rocks4 ,we were      
necessarily compelled1 however1 to make 
some reference to1 and to give some     
description of1 certain structures and  
arrangements which are not peculiar to  
aqueous strata1 but characterise many   
metamorphic and igneous rocks as well4  
,to avoid repetition it was also        
necessary1 while treating of joints1 c41
 to give some account of certain        
structures which are the result of      
metamorphic action4 ,but1 for sake of   
clearness1 we have reserved special     
account of the structure and mode of    
occurrence of metamorphic and igneous   
rocks to this place4 ,after what has    
been said as to the structure and       
arrangement of aqueous strata1 it is    

hardly needful to say much about the    
crystalline schists4 ,these the student 
will understand to be merely highly     
altered aqueous rocks1,e in which the   
marks of their origin are still more or 
less distinctly traceable4 ,as a rule1  
metamorphic strata are contorted1       
twisted1 and crumpled1 although here and
 there comparatively horizontal         
stretches of altered rocks may be       
observed4 ,the regions in which they    
occur are often hilly and mountainous1  
but this is by no means invariably the  
case4 ,the greater part of the          
mountainous regions of the ,british     
,islands is occupied by rocks which are 
more or less altered2 the more          
crystalline rocks1 such as mica-schist1 
gneiss1 c41 being abundantly developed  
in the ,scottish ,highlands1 and in the 
north and west of ,ireland2 while those 
which are less altered cover large areas
 in the south of ,scotland1 and in      
,wales and the north-west of ,england4  
,throughout these wide areas the rocks  

generally dip at high angles1 and       
contortion and crumpling are of common  
occurrence4 ,the finer-grained          
clay-rocks also exhibit fine cleavage   
planes1 and are in some places quarried 
for roofing-slates--the ,welsh quarries 
being the most famous4 ,here and there1 
bedding is entirely effaced1 and the    
resulting rock is quite amorphous1 and1 
becoming gradually more and more        
crystalline1 passes at last into a rock 
which in many cases is true granite4    
,the original strata have disappeared1  
and granite occupies their place1 in    
such a way as to lead to the inference  
that the granite is merely the aqueous  
strata which have been fused up1 as it  
were1 in situ4 ,at other times the      
granite would appear to have been       
erupted amongst the aqueous strata1 for 
these are highly confused1 and baked1 as
 it were1 at their junction with the    
granite1 from which1 also1 long veins   
are seen protruding into the surrounding
 beds4 ,metamorphic granite1 then1      

graduates1 as a rule1 almost            
imperceptibly into rocks which are      
clearly of aqueous origin2 while on the 
contrary the junction-line between      
igneous granite and the surrounding     
rocks is always well marked4 ,the origin
 of granite1 however1 is a difficult    
question1 and one which has given rise  
to much discussion4 ,some further       
remarks upon the subject will be found  
in the sequel under the heading of      
,metamorphism4     ,e ,igneous rocks    
have also in some cases undergone       
considerable        alteration2         
fine-grained tuffs1 for example1        
occasionally        assume a crystalline
 texture4  #eb4 ,true igneous rocks     
occur either in beds or as irregular    
amorphous masses4 ,when they occur as   
beds interstratified with aqueous       
strata1 they are said to be             
contemporaneous1 because they have      
evidently been erupted at the time the  
series of strata among which they appear
 was being amassed4 ,when1 on the other 

hand1 they cut across the bedding1 they 
are said to be subsequent or intrusive1 
because in this case they have been     
formed at a period subsequent to the    
strata among which they have been       
intruded4 ,the bed upon which a         
contemporaneous igneous rock reclines1  
often affords marks of having been      
subjected to the action of heat2        
sandstones being hardened1 and          
frequently much jointed and cracked1    
owing to the shrinking induced by the   
heat of the once molten rock above1 and 
clay-rocks often assuming a baked       
appearance4 ,there is generally1 also1  
some discoloration both in the pavement 
of rock upon which the igneous mass     
lies1 and in the under portions of the  
latter itself4 ,the beds overlying a    
contemporaneous igneous rock1 however1  
do not exhibit any marks of the action  
of heat2 the old lava-stream having     
cooled before the sediment1 now forming 
the overlying strata1 was accumulated   
over its surface4 ,one may often notice 

how the sand and mud have quietly       
settled down into the irregular hollows 
and crevices of the old lava1 as in the 
following section1 where i represents   
the igneous rock2 a being the baked     
pavement of sandstone1 c42 and b the    
overlying sedimentary deposits4 ,when   
the igneous rock itself is examined1 its
 upper portions are often observed to be
 scoriaceous or cinder-like1 and the    
under portions likewise frequently      
exhibit a similar appearance4 ,it is    
generally most solid towards the centre 
of the bed4 ,the vesicles1 or pores1 in 
the upper and lower portions are often  
flattened1 and are frequently filled    
with mineral matter4 ,sometimes these   
cavities may have been filled at the    
time the rock was being erupted1 but in 
most cases the mineral matter would     
appear to have been introduced          
subsequently by the action of water     
percolating through the rock4           
,occasionally we meet with igneous rocks
 which are more or less vesicular and   

amygdaloidal throughout their entire    
mass4 ,others1 again1 often shew no     
vesicular structure1 but are homogeneous
 from top to bottom4 ,the texture is    
also very variable1 and this even in the
 same rock-mass2 some portions being    
compact or fine-grained1 and others     
coarsely crystalline4 ,as a rule the    
rock is most crystalline towards the    
centre1 and gets finer-grained as the   
top and bottom of the bed are           
approached4 ,not unfrequently1 however1 
an igneous rock will preserve the same  
texture throughout4 ,the jointing is    
also highly irregular as a rule4 ,but in
 many cases1 especially when the rock is
 fine-grained1 the jointing is very     
regular4 ,the basaltic columns of the   
,giants' ,causeway and the ,isle of     
,staffa are well-known examples of such 
regularly jointed masses4 ,igneous rocks
 frequently decompose into a loose      
earthy mass 7wacke71 and this is most   
markedly the case with those belonging  
to the basic group4     ,illustration3  

,fig4 #bj4--;,contemporaneous ,igneous  
,rock4  #ec4 ,contemporaneous igneous   
rocks are frequently associated with    
more or less regular beds of breccia1   
conglomerate1 ash1 tuff1 c4 ,these are  
evidently the loose volcanic ejectamenta
 which accompanied former eruptions of  
lava1 and have been arranged by the     
action of water4 ,beds of such          
materials1 however1 frequently occur    
without any accompanying lava-form      
rocks4 ,nor are they always arranged in 
bedded masses4 ,they sometimes appear   
filling vertical pipes which seem to    
have been the funnels of old volcanoes4 
,the following section exhibits the     
general appearance of one of these      
volcanic necks4 ,they are very common in
 some parts of ,scotland1 as in         
,ayrshire1 and are frequently ranged    
along the line of a fault in the strata4
 ,fig4 #ba shews such a neck of         
ejectamenta1 made up of fragments of    
various kinds of rock1 such as          
sandstone1 shale1 limestone1 coal1 c41  

sometimes without any admixture of      
igneous rocks4 ,the strata through which
 the pipe has been pierced usually dip  
in towards the latter1 and at their     
junction with the coarse agglomerate    
often shew marks of the action of heat1 
coal-seams having sometimes been        
'burned' useless for a number of yards  
away from the 'neck4'     ,illustration3
 ,fig4 #ba4--,neck filled with ,volcanic
 ,agglomerate4  #ed4 ,intrusive igneous 
rocks occur as sheets1 dykes1 and necks4
 ,the sheets frequently conform for long
 distances to the bedding of the strata 
among which they occur1 and are thus    
liable to be mistaken for               
contemporaneous rocks4 ,but when they   
are closely examined1 it will be seen   
that they not only bake or alter the    
beds above and below them1 but seldom   
keep precisely to one horizon or        
level--occasionally rising to a higher1 
or sinking to a lower position in the   
strata1 as shewn in the following       
diagram-section4 ,dykes are wall-like   

masses of igneous strata which cut      
across the strata1 generally at a high  
angle 7see d1 d1 fig4 #bb74 ,in the     
neighbourhood of a recent volcanic      
orifice1 numerous dykes are seen        
ramifying in all directions4 ,in the    
,british ,islands some dykes have been  
followed in a linear direction for very 
long distances4 ,sometimes these occupy 
the sites of large dislocations1 at     
other times they have cut through the   
strata without displacing them4         
,occasionally they appear to have been  
the feeders of the great sheets of      
igneous rock which here and there occur 
in their vicinity4 ,the phenomena       
presented by the necks of intrusive rock
 do not differ from those characteristic
 of agglomerate or tuff necks4 ,the     
strata are bent down towards the central
 plug of igneous rock1 and are generally
 more or less altered at the line of    
junction4     ,illustration3 ,fig4      
#bb4--;,intrusive ,sheet and ,dykes3 i1 
igneous    intrusive sheet2 d1 d1 dykes2

 s1 s1 sedimentary strata4  #ee4        
,intrusive rocks offer1 as a rule1 some 
contrasts in texture to contemporaneous 
masses4 ,they are seldom amygdaloidal1  
but when they are so it is generally    
towards the centre of the mass4 ,the    
kernels are usually minute and more or  
less spherical4     ,illustration3 ,fig4
 #bc4--;,contemporaneous and ,intrusive 
,igneous    ,rocks3 c1 c1               
contemporaneous trap-rocks#a2 t1 t1     
contemporaneous fragmental igneous      
rocks2 i1 p1 n1 d1    intrusive igneous 
rocks4  ,the diagram 7fig4 #bc7 shews   
the general mode of occurrence of       
igneous rocks on the large scale4 ,the  
stratified aqueous deposits are         
indicated at a1 a4 ,these are overlaid  
by a series of alternating beds of      
crystalline 7c7 and fragmental 7t7      
igneous rocks4 ,an irregular intrusive  
sheet at i cuts across the beds a1 a4   
,at p1 another intrusive mass is seen   
rising in a pipe1 as it were1 and       
overflowing the beds a1 a1 so as to form

 a cap4 ,a volcanic neck filled with    
angular stones intersects the strata at 
n1 and two dykes1 approaching the       
vertical1 traverse the bedded rocks at  
d1 d4 ,it will be noticed that the      
contemporaneous igneous rocks form a    
series of escarpments rising one above  
the other4  ,the alteration effected by 
igneous rocks is generally greatest in  
the case of intrusive masses4 ,this is  
well seen in some of our coal-fields1   
where the coal has frequently been      
destroyed over large areas by the       
proximity of masses of what was once    
melted rock4 ,it is curious to notice   
how the intrusive sheets in a great     
series of strata have forced their way  
along the lines of least resistance4    
,thus1 in the ,scottish coal-fields1 we 
find again and again that intrusive     
sheets have been squirted along the     
planes occupied by coal-seams1 these    
having been more easily attacked than   
beds of sandstone or shale4 ,the coal in
 such cases is either entirely 'eaten   

up1' as it were1 or converted into a    
black soot4 ,at other times1 however1 it
 is changed into a kind of coke1 while  
other seams at a greater distance from  
the intrusive mass have been altered    
into a kind of 'blind coal' or          
anthracite4  ,these remarks on the mode 
of occurrence of igneous rocks are meant
 to refer chiefly to those masses which 
occur in regions where volcanic action  
has long been extinct1 as1 for instance1
 in the ,british ,islands4 ,in the      
sequel1 some account will be given of   
the appearances presented by modern     
volcanoes and volcanic rocks4     #a ,it
 has been usual to apply the term trap  
or trappean rock        to all the old  
igneous rocks which could neither be    
classed        with the granites and    
syenites1 nor yet with the recent lavas1
        c41 which are connected with a  
more or less well-marked        volcanic
 vent4 ,the term trap 7,swedish trappa1 
a flight of        steps7 was suggested 
by the terraced or step-like appearance 

presented by hills which are built up of
 successive beds of        igneous rock4
 ,but the passage from the granitic into
 the        so-called trap rocks1 and   
from these into the distinctly          
volcanic1 is so very gradual1 that it is
 impossible to say        where the one 
class ends and the other begins4 ,the   
term trap1        therefore1 has no     
scientific precision1 although it is    
sometimes very convenient as a kind of  
broad generic term to        include a  
large number of rocks4   ,,mineral      
,,veins4  #ef4 ,the cracks and crevices 
and joint planes which intersect all    
rocks in a greater or less degree1 are  
not unfrequently filled with            
subsequently introduced mineral matter1 
forming what are termed veins4 ,this    
introduced matter may either be harder  
or less durable than the rock itself2 in
 the former case1 the veins will project
 from the surface of the stone1 where   
that has been subjected to the          
weathering action of the atmosphere2 in 

the latter case1 the veins1 under like  
circumstances1 are often partially      
emptied of their mineral matter4 ,not   
unfrequently1 however1 the more or less 
irregularly ramifying1 non-metalliferous
 veins appear as if they had segregated 
from the body of the rock in which they 
occur1 as in the case of the quartz     
veins in granite4 ,besides these        
irregular veins1 the rocks of certain   
districts are traversed in one or more  
determinate directions by fissures1     
extending from the surface down to      
unknown depths4 ,these great fissures   
are often in like manner filled with    
mineral matter4 ,the minerals are       
usually arranged in bands or layers     
which run parallel to the walls of the  
vein4 ,quartz1 fluor-spar1 barytes1     
calcite1 c4 are among the commonest     
vein-minerals1 and with these are       
frequently associated ores of various   
metals4 ,a vein may vary in width from  
less than an inch up to many yards1 and 
the arrangement of its contents is also 

subject to much variation4 ,instead of  
parallel layers of spars and ores1      
frequently a confused mass of clay and  
broken rocks1 which are often cemented  
together with sparry matter1 chokes up  
the vein4 ,the ore in a vein may occur  
in one or more ribs1 which often vary in
 thickness from a mere line up to masses
 several yards in width4 ,sometimes the 
rocks are dislocated along the line of  
fissure occupied by a great vein2 at    
other times no dislocation can be       
observed4 ,mineral veins1 however1 do   
not necessarily occupy dislocation      
fissures4 ,they often occur in cavities 
which have been formed by the erosive   
action of acidulated water1 in the way  
described in pars4 #ei1 #fj1 and #fa4   
,this is frequently the case in         
calcareous strata4 ,such veins usually  
coincide more or less with the bedding  
of the rocks1 but in the case of thick  
limestones they not unfrequently cut    
across the bedding in a vertical or     
nearly vertical direction1 forming what 

are termed pipe-veins4     ,,dynamical  
,,geology4   #eg4 ,having considered the
 composition1 structure1 and arrangement
 of the rock-masses which form the solid
 crust of our globe1 we have next to    
inquire into the nature of those        
physical agencies by the action of which
 the rocks1 as we now see them1 have    
been produced4 ,the work performed by   
the various forces employed in modifying
 the earth's crust is at one and the    
same time destructive and               
reconstructive4 ,rocks are being        
continually demolished1 and out of their
 ruins new rocks are being built4 ,in   
other words1 matter is constantly       
entering into new relations--now        
existing as solid rock1 or in solution  
in water1 or carried as the lightest    
dust on the wings of the wind2 now being
 swept down by rivers into the sea1 or  
brought under the influence of          
subterranean heat--but always changing1 
sooner or later1 slowly or rapidly1 from
 one form to another4 ,the great        

geological agents of change are these3  
#a4 ,,the ,,atmosphere2 #b4 ,,water2 #c4
 ,,plants ,,and ,,animals2 #d4          
,,subterranean ,,forces4 ,we shall      
consider these in succession4   ,,the   
,,atmosphere4  #eh4 ,all rocks have a   
tendency to waste away under the        
influence of the atmosphere4 ,this is   
termed weathering4 ,under the influence 
of the sun's heat1 the external portions
 of a rock expand1 and again contract   
when they cool at night4 ,the effect of 
this alternate expansion and contraction
 is often strikingly manifest in        
tropical countries3 some rocks being    
gradually disintegrated1 and crumbling  
into grit and sand2 others becoming     
cracked1 and either exfoliating or      
breaking up all over their surface into 
small angular fragments4 ,again1 in     
countries subject to alternations of    
extreme heat and cold1 similar          
weathering action takes place4 ,the     
chemical action of the atmosphere is    
most observable in the case of          

calcareous rocks4 ,the carbonic acid    
almost invariably present acts as a     
solvent1 so that dew and rain1 which    
otherwise would in many cases have but  
feeble disintegrating power1 are enabled
 to eat into such rocks as chalk and    
limestone1 calcareous sandstones1 c4    
,the oxygen of the atmosphere also      
unites with certain minerals1 such as   
the proto-salts of iron1 and converts   
them into peroxides4 ,it is this action 
which produces the red and yellow       
ferruginous discolorations in sandstone4
 ,chemical changes also take place in   
the case of many igneous rocks1 the     
result being that a weathered 'crust'   
forms wherever such rocks are exposed to
 the action of the atmosphere4 ,of      
course1 the rate at which a rock        
weathers depends upon its mineralogical 
and chemical composition4 ,limestones   
weather much more rapidly than          
clay-rocks2 and augitic igneous rocks1  
as a rule1 disintegrate more readily    
than the more highly silicated species4 

,the weathering action of the atmosphere
 is also greatly aided by frost1 as we  
shall see presently4 ,the result of all 
this weathering is the formation of     
soil--soil being only the fine-grained  
debris of the weathered rocks4 ,the     
angular debris found at the base of all 
cliffs in temperate and arctic regions1 
and on every hill and mountain which is 
subjected to alternations of extreme    
heat and cold1 is also the effect of    
weathering4 ,but these and other effects
 of frost will be treated of under the  
head of ,frozen ,water4 ,the hillocks   
and ridges of loose sand 7sand dunes7   
found in many places along the          
sea-margin1 and even in the interior of 
some continents1 as in ,africa and      
,asia1 are due to the action of the     
wind1 which drives the loose grains     
before it1 and piles them up4 ,sometimes
 also the wind carries in suspension the
 finest dust1 which may be transported  
for vast distances before it falls to   
the ground4 ,thus1 fine dust shot into  

the air by the volcanoes of ,iceland has
 been blown as far as the ,shetland     
,islands2 and in tropical countries the 
dust of the dried-up and parched beds of
 lakes and rivers is often swept away   
during hurricanes1 and carried in thick 
clouds for leagues4 ,rain falling       
through this dust soaks it up1 and comes
 down highly discoloured1 brown and red4
 ,this is the so-called blood-rain4     
,minute microscopic animal and vegetable
 organisms are often commingled with    
this dust1 and falling into streams1    
lakes1 or the sea1 may thus become      
eventually buried in sediments very far 
removed from the place that gave them   
birth4   ,,water4  #ei4 ,the geological 
action of water in modifying the crust  
of the earth is twofold--namely1        
chemical and mechanical4  ,underground  
,water4--,all the moisture which we see 
falling as rain or snow does not flow   
immediately away by brooks and rivers to
 the sea4 ,some portion of it soaks into
 the ground1 and finds a passage for    

itself by cracks and fissures in the    
rocks below1 from which it emerges at   
last as springs1 either at the surface  
of the earth1 or at the bottom of the   
sea4 ,such are the more obvious courses 
pursued by the water--it flows off      
either by sub-aerial or subterranean    
channels4 ,but a not inconsiderable     
portion soaks into the solid rocks      
themselves1 which are all more or less  
porous and pervious4 ,water thus slowly 
soaking often effects very considerable 
chemical changes4 ,sometimes the binding
 matter which held the separate         
particles of the rock together is       
dissolved out1 and the rock is thus     
rendered soft and crumbling2 at other   
times1 the reverse takes place1 and the 
water deposits1 in the minute           
interstitial pores1 some binding matter 
by which the partially or wholly        
incoherent grains are agglutinated into 
a solid mass4 ,thus what were originally
 hard and tough rocks become            
disintegrated to such a degree1 that    

they crumble to powder soon after they  
are exposed to the air2 while some again
 are converted into a clay1 and may be  
dug readily with a spade4 ,and1 on the  
other hand1 loose sand is glued into a  
hard building-stone4 ,there are many    
other changes effected upon rocks by    
water1 in virtue of the chemical agents 
which it holds in solution4 ,indeed1 it 
may be said that there are very few1 if 
any1 rocks in which the chemical action 
of interstitial water has not formerly  
been1 or is not at present being1       
carried on4 ,besides that which soaks   
through the rocks themselves1 there is  
always a large proportion of underground
 water1 which1 as we have said above1   
finds a circuitous route for itself by  
joints1 cracks1 and crevices4 ,after    
coursing for1 it may be1 miles          
underground1 such water eventually      
emerges as springs1 which contain in    
solution the various ingredients which  
the water has chemically extracted from 
the rocks4 ,these ingredients are then  

deposited in proportion as the mineral  
water suffers from evaporation4 ,water  
impregnated with carbonate of lime1 for 
example1 deposits that compound as soon 
as evaporation has carried off a certain
 percentage of the water itself1 and the
 carbonic acid gas which it held4 ,this 
is the origin of the mineral called     
travertine or calcareous tufa1 which is 
so commonly met with on the margins of  
springs1 rivers1 and waterfalls4  #fj4  
,stalactites and stalagmites have been  
formed in a similar way4 ,water slowly  
oozing from the roof of a limestone     
cavern partially evaporates there1 and a
 thin pellicle of carbonate of lime is  
formed2 while that portion of the water 
which falls to the ground1 and is there 
evaporated1 likewise gives rise to the  
formation of carbonate of lime4 ,by such
 constant dropping and evaporating1 long
 tongue-and icicle-like pendants        
7stalactites7 grow downwards from the   
roof2 while at the same time domes and  
bosses 7stalagmites7 grow upwards from  

the floor1 so as sometimes to meet the  
former and give rise to continuous      
pillars and columns4 ,the great solvent 
power of carbonated water is shewn first
 by the chemical analysis of springs1   
and1 secondly1 by the great wasting     
effects which the long-continued action 
of these has brought about4 ,thus1 it   
has been estimated that the fifty       
springs near ,carlsbad1 which yield     
eight hundred thousand cubic feet of    
water in twenty-four hours1 contain in  
solution as much lime as would go to    
form a mass of stone weighing two       
hundred thousand pounds4 ,warm1 or1 as  
they are termed1 thermal springs1       
frequently carry away with them1 out of 
the bowels of the earth1 vast quantities
 of mineral matter in solution4 ,the    
waters at ,bath1 for instance1 are      
estimated to bring to the surface an    
annual amount of various salts1 the mass
 of which is not less than #eed cubic   
yards4 ,one of the springs of ,loueche1 
,france1 however1 carries out with it no

 less than #h1hbb1djj pounds of gypsum  
annually1 which is equal to about #babb 
cubic yards4  #fa4 ,it is easy to       
conceive1 therefore1 that in the course 
of ages great alterations must be caused
 by springs4 ,caves and winding         
galleries1 and irregular channels1 will 
be worn out of the rocks which are thus 
being dissolved4 ,especially will this  
be the case in countries where          
calcareous rocks abound4 ,it is in such 
regions1 accordingly1 where we meet with
 the most striking examples of caves and
 underground river-channels4 ,the       
largest cave at present known is the    
,mammoth ,cave1 in ,kentucky4 ,this     
remarkable hollow consists of numerous  
winding galleries and passages that     
cross and recross1 and the united length
 of which is said to be #bag miles4 ,in 
calcareous countries1 rivers1 after     
flowing for1 it may be1 miles at the    
surface1 suddenly disappear into the    
ground1 and flow often for long         
distances before they reappear in the   

light of day4 ,in some regions1 indeed1 
nearly all the drainage is subterranean4
 ,the surface of the ground1 in         
calcareous countries1 frequently shews  
circular depressions1 caused by the     
falling in of the roofs of caverns4     
,sometimes1 also1 great masses of rock1 
often miles in extent1 get loosened by  
the dissolving action of subterranean   
water1 and crash downwards into the     
valleys4 ,such landslips1 as they are   
called1 are not1 however1 confined to   
calcareous regions4 ,in #ahjf1 a large  
section of the ,rossberg1 a mountain    
lying to the north of the ,righi1       
consisting of conglomerate overlying    
beds of clay1 rushed down into the      
plains of ,goldau1 overwhelming four    
villages and nearly a thousand          
inhabitants4 ,the cause of this         
catastrophe was undoubtedly the         
softening into mud of the clay-beds on  
which the conglomerate rested1 for the  
season which had just terminated when   
the slip took place had been very wet4  

,the mass of material that slid down was
 estimated to contain upwards of        
fifty-four millions of cubic yards2 it  
reached not less than two and a half    
miles in length1 by some three hundred  
and fifty yards wide1 and thirty-five   
yards thick4  #fb4                      
,surface-water--,rain4--,having now     
learned something as to the             
modifications produced by underground   
water1 we turn next to consider the     
action of surface-water1 and the results
 arising from that action4 ,rain1 when  
it falls to the ground1 carries with it 
some carbonic acid gas which it has     
absorbed from the atmosphere4 ,armed    
with this solvent1 it attacks certain   
rocks1 more especially limestones and   
chalk1 a certain proportion of which it 
licks up and delivers over to brooks and
 streams4 ,under its influence1 also1   
the finer particles of the soil are ever
 slowly making their way from higher to 
lower levels4 ,rocks which are being    
gradually disintegrated by weathering   

have their finer grains and particles1  
thus loosened1 carried away by rain4    
,nor is this rain-action so             
inconsiderable as might be supposed4 ,in
 the gentler hollows of an undulating   
country1 we frequently find             
accumulations of clay1 loam1 and        
brick-earth1 which often reach many feet
 in thickness1 and which are undoubtedly
 the results of rain washing down the   
particles of soil1 c4 from the adjacent 
slopes4  #fc4 ,river-action4--,the water
 of streams and rivers almost invariably
 contains in solution one or more       
chemical compounds1 and in this respect 
does not differ from the water of       
springs4 ,of course1 this mineral matter
 is derived in considerable measure from
 springs1 but is also no doubt to a     
large extent taken up by the rivers     
themselves1 as they wash the rocks and  
soils on their journey to the sea4 ,the 
amount of mineral matter thus           
transported must be something enormous1 
as is shewn by the chemical analyses of 

river-water4 ,bischof calculated that   
the ,rhine carries in solution as much  
carbonate of lime as would suffice for  
the yearly formation of three hundred   
and thirty-two thousand millions of     
oyster-shells of the usual size--a      
quantity equal to a cube five hundred   
and sixty feet in the side1 or a square 
bed a foot thick1 and upwards of two    
miles in the side4 ,but the mechanical  
erosion effected by running water is    
what impresses us most with the         
importance of rivers as geological      
agencies4 ,this erosive action is due to
 the gravel1 sand1 and mud carried along
 by the water4 ,these ingredients act as
 files in the hand of a workman1 and    
grind1 polish1 and reduce the rocks     
against which they are borne4 ,the beds 
of some streams that flow over solid    
rock are often pitted with circular     
holes1 at the bottom of which one       
invariably finds a few rounded stones4  
,these stones1 kept in constant motion  
by the water1 are the means by which the

 pot-holes1 as they are called1 have    
been excavated4 ,when pot-holes are     
numerous1 they often unite so as to form
 curious smooth-sided trenches and      
gullies4 ,the same filing action goes on
 all over the bed of the stream wherever
 the solid rock is exposed4 ,and while  
the latter is being gradually reduced1  
the stones and grit which act as the    
files are themselves worn and reduced2  
so that stones diminish in size1 and    
grit passes into fine sand and mud1 as  
they move from higher to lower levels4  
,no doubt the erosive action of running 
water appears to have but small effect  
in a short time1 and we are apt1        
therefore1 to underestimate its power4  
,but when our observations extend1 we   
see it is quite otherwise1 and that1 so 
far from being unimportant1 running     
water is really one of the most powerful
 of all the geological agencies that are
 employed in modifying the earth's      
crust4 ,even within a comparatively     
short time1 it is able to effect very   

considerable changes4 ,thus1 the river  
,simeto1 in ,sicily1 having become      
dammed by a stream of lava flowing from 
,etna1 succeeded1 in two hundred and    
fifty years1 in cutting through hard    
solid basalt a new channel for itself1  
which measured from twenty to fifty     
metres in depth1 and from twelve to     
eighteen in breadth4 ,when1 also1 we    
remember the fact1 that no river is     
absolutely free from mineral matter held
 in suspension1 but that1 on the        
contrary1 all running water is more or  
less discoloured with sediment1 which is
 merely the material derived from the   
disintegration of rocks1 it will appear 
to us difficult to overestimate the     
power of watery erosion4 ,to the mineral
 matter held in suspension1 we have to  
add the coarser detritus1 gravel and    
sand1 which is being gradually pushed   
along the beds of rivers1 and which1 in 
the case of the ,mississippi1 has been  
estimated to equal a mass of seven      
hundred and fifty million cubic feet1   

discharged annually into the ,gulf of   
,mexico4 ,by careful measurements1 it   
has also been ascertained that the same 
river carries down annually into the sea
 a weight of mud held in suspension     
which reaches the vast sum of           
#hab1ejj1jjj1jjj pounds4 ,the total     
annual amount of mineral matter1 whether
 held in suspension or pushed along the 
bottom of this great river1 has been    
estimated to equal a mass #bfh feet in  
height1 with an area of one square mile4
  #fd4 ,alluvium4--,the sediment carried
 along and deposited by a river is      
called alluvium4 ,sometimes this        
alluvium covers wide areas1 forming     
broad flats on one or both sides of a   
river1 and in such cases it is due to   
the action of the floodwaters of the    
stream4 ,every time the river overflows 
the low grounds through which it passes1
 a layer of sediment is laid down1 which
 has the effect of gradually raising the
 level of the alluvial tract4 ,by and by
 a time comes when the river1 which has 

all the while been slowly deepening its 
channel1 is unable to flood the flats1  
and thereupon it begins to cut into     
these1 and to form new flats at a       
somewhat lower level4 ,in this way we   
often observe a series of alluvial      
terraces1 consisting of gravel1 sand1   
and silt1 rising one above another along
 a river valley4 ,such are the terraces 
of the ,thames and other rivers in      
,england1 and of the ,tweed1 ,clyde1    
,tay1 c4 in ,scotland4 ,the great plains
 through which the ,rhine flows between 
,basel and ,bingen1 are also well-marked
 examples of alluvial accumulations4    
,there are very few streams1 indeed1    
which have not formed such deposits     
along some portion of their course4     
#fe4 ,when a river enters a lake1 the   
motion of the water is of course        
checked1 and hence the heavier detritus1
 such as gravel and coarse sand1 moves  
more slowly forward1 and at last comes  
to rest on the bed of the lake1 at no   
great distance from the mouth of the    

river4 ,finer sand and mud are carried  
out for some distance further1 but      
eventually they also cease to move1 and 
sink to the bottom4 ,when the lake is   
sufficiently large1 it catches all or   
nearly all the matter brought down by   
the river1 which1 as it issues from the 
lower end of the lake1 is bright and    
clear4 ,a well-known example of this    
phenomenon is that of the ,rhone1 which 
enters the ,lake of ,geneva turbid and  
muddy1 but rushes out quite clear at the
 lower end of the lake4 ,lakes1         
therefore1 are all being slowly or more 
rapidly silted up1 and this1 of course1 
is most conspicuous at the points where 
they are entered by rivers4 ,thus1 at   
the head of the ,lake of ,geneva1 it is 
manifest that the wide flat through     
which the river flows before it pours   
into the lake1 has been conquered by the
 ,rhone from the latter4 ,in the times  
of the ,romans1 the lake1 as we know1   
extended for more than one mile and a   
half further up the valley4  #ff4       

,deltas4--,when there are no lakes to   
intercept fluviatile sediment1 this     
latter is borne down to the sea1 where  
it is deposited in precisely the same   
way as in a lake3 the heavier detritus  
comes to rest first1 the finer sediment 
being swept out for some distance       
further4 ,so that1 in passing from the  
river-mouth outwards1 we have at first  
gravel1 which gradually gets finer and  
finer until it is replaced by sand1     
while this in turn is succeeded by mud  
and silt4 ,there is this difference1    
however1 between lacustrine and         
fluvio-marine deposits1 that while the  
former accumulate in water which is     
comparatively still1 the latter are     
often brought under the influence of    
waves and currents1 and become shifted  
and sifted to such a degree that fine   
and coarse detritus are frequently      
commingled2 and there is1 therefore1 not
 the same orderly succession of coarse  
and fine materials which characterises  
lacustrine deposits4 ,often1 indeed1 the

 currents opposite the mouth of a river 
are so strong1 that little or no        
sediment is permitted to gather there4  
,usually1 however1 we find that rivers  
have succeeded in reclaiming more or    
less wide tracts from the dominion of   
the waves1 or at all events have        
cumbered the bed of the sea with banks  
and bars of detritus4 ,the broad plains 
formed at the mouth of a river are      
called deltas1 from their resemblance to
 the ,greek letter ,delta4 ,the deltas  
of the ,nile1 ,ganges1 and ,mississippi 
are among the most noted4 ,the term     
delta1 however1 is not exclusively      
applied to fluvio-marine deposits2      
rivers also form deltas in fresh-water  
lakes4 ,it is usual1 however1 to        
restrict the term to extensive alluvial 
plains which are intersected by many    
winding channels1 due to the rapid      
bifurcation of the river1 which begins  
to take place at the very head of the   
great flat--that is to say1 at the point
 where the river originally entered the 

sea 7or lake74  #fg4 ,frozen            
,water4--,we have now seen what can be  
done by the mechanical action of running
 water4 ,we have next to consider what  
modifications are effected by freezing  
and frozen water4 ,water1 as every one  
knows1 expands in the act of freezing1  
and in doing so exerts great force4 ,let
 the reader bear in mind what has been  
said as to the passage of water through 
the minute and often invisible pores of 
rocks1 and to its presence in cracks and
 crevices after every shower of rain1   
and he will readily see how excessive   
must be the waste caused by the action  
of frost4 ,the water1 to as great a     
depth as the frost extends1 passes into 
the solid state1 and in doing so pushes 
the grains of the rocks asunder1 or     
wedges out large masses4 ,no sooner does
 thaw ensue than the water1 becoming    
melted1 allows the grains of the rock to
 fall asunder2 the outer skin of the    
rock1 as it were1 is disintegrated1 and 
crumbles away1 while fragments and      

masses lose their balance in many cases1
 and topple down4 ,hence it is1 that in 
all regions where frost acts1 the       
hill-tops and slopes are covered with   
angular fragments and debris1 and a soil
 is readily formed by the disintegration
 of the rocks4  ,river-ice is often a   
potent agent of geological change4      
,stones get frozen in along the margins 
of a river1 and often debris falls down 
from cliff and scaur upon the surface of
 the ice2 when thaw sets in1 and the ice
 breaks up1 stones and rubbish are      
frequently floated for long distances1  
and may even be carried out to sea      
before their support fails them1 and    
they sink to the bottom4 ,in some cases1
 when the ice is very thick1 it may run 
aground in a river1 and confuse and     
tumble up the deposits gathering at the 
bottom4 ,ice sometimes forms upon stones
 at the bottom of a river1 and floats   
these off2 and this curious action may  
take place even although no ice be      
forming at the time on the surface of   

the water4  #fh4 ,glaciers1 ,icebergs1  
and ,ice-foot4--,in certain mountainous 
districts1 and in arctic and antarctic  
regions1 snow accumulates to such an    
extent that its own weight suffices to  
press the lower portions into ice4      
,alternate thawing and freezing also aid
 in the formation of the ice1 which soon
 begins to creep down the               
mountain-slopes into the valleys1 where 
it constitutes what are called glaciers 
or ice-rivers4 ,these great masses of   
ice attain often a great thickness1 and 
frequently extend for many miles along  
the course of a valley4 ,in the ,alps   
they occasionally reach as much as five 
hundred or six hundred feet in depth4   
,in ,greenland1 however1 there are      
glaciers probably not less than five    
thousand feet thick2 and the glacier ice
 of the antarctic continent has been    
estimated even to reach twelve miles in 
thickness4 ,glaciers flow slowly down   
their valleys1 at a rate which varies   
with the slope of their beds and the    

mass of the ice4 ,some move only a few  
inches1 others two or three feet1 in a  
day4 ,their forward motion is arrested  
at a point where the ice is melted just 
as fast as it comes on4 ,a glacier is   
always more or less seamed with yawning 
cracks1 which are called crevasses4     
,these owe their origin to the unequal  
rate at which the different parts of the
 ice flow2 this differential motion     
causing strains1 to which the ice yields
 by snapping asunder4 ,the flanks of a  
glacier are usually fringed with heaps  
of angular blocks and debris which fall 
from the adjacent rocky slopes1 and some
 of this rubbish tumbling into the      
gaping crevasses must occasionally reach
 to the bottom of the ice4 ,the rubbish 
heaps 7superficial moraines7 travel     
slowly down the valley on the surface of
 the ice1 and are eventually toppled    
over the end of the glacier1 where they 
form great banks and mounds4 ,these are 
called terminal moraines4 ,the rocky bed
 of a glacier is invariably smoothed and

 polished1 and streaked with coarse and 
fine striae1 or scratches1 which run    
parallel to the direction of the        
ice-flow4 ,these are due to the         
presence1 at the bottom of the ice1 of  
such angular fragments as become        
detached from the underlying rocks1 or  
of boulders and rubbish which have been 
introduced from above4 ,the stones are  
ground by the ice along the surface of  
its bed1 causing ruts and scratches1    
while the finer material resulting from 
the grinding action forms a kind of     
polisher4 ,the stones acting as gravers 
are themselves covered with striae1 and 
their sharp edges get smoothed away4 ,in
 alpine districts there is always a good
 deal of water circulating underneath a 
glacier1 and this washes out the sand   
and fine clay4 ,thus it is that rivers  
issuing from glaciers are always more or
 less discoloured brown1 yellow1 green1 
gray1 or blue1 according to the nature  
of the rocks which the ice has pounded  
down into mud4 ,in ,greenland many of   

the large glaciers go right out to sea1 
and owing to their great thickness are  
able to dispossess the sea sometimes for
 miles4 ,but erelong the greater        
specific gravity of the sea-water forces
 off large segments from the terminal   
front of the ice1 which float away as   
icebergs4 ,large masses are also always 
falling down from the ice-front4        
,occasionally1 big blocks and debris are
 floated away on the icebergs1 but this 
does not appear to be common4 ,in       
,greenland there is very little         
rock-surface exposed1 from which blocks 
can be showered down upon the glaciers1 
and the surface of the latter is        
therefore generally free from           
superficial moraines4 ,a kind of        
submarine terminal moraine1 however1    
gathers in front of some glaciers1 made 
up chiefly of the stones and rubbish    
that are dragged along underneath the   
ice1 and exposed by the breaking-off of 
icebergs1 but partly composed also of   
the sand and mud washed out by          

sub-glacial waters4 ,a narrow belt of   
ice forms along the sea-coast in arctic 
regions1 which often attains a thickness
 of thirty or forty feet4 ,this is      
called the ice-foot4 ,it becomes loaded 
with debris and blocks1 which fall upon 
it from the cliffs above2 and1 as large 
portions are frequently detached from   
the cliffs in summer-time1 they sail off
 with their cargoes of debris1 and drop 
these over the sea-bottom as they       
gradually melt away4 ,the ice-foot is   
the great distributor of erratics or    
wandered blocks1 the part taken in this 
action by the huge icebergs which are   
discharged by the glaciers being1       
comparatively speaking1 insignificant4  
,but when these latter run aground1 they
 must often cause great confusion among 
the beds of fine material accumulating  
upon the floor of the sea4  #fi4 ,the   
,sea4--,sea-water owes its saltness to  
the presence of various more or less    
soluble substances1 such as common salt1
 gypsum1 ,epsom salts1 chloride of      

magnesium1 c4 ,besides these1 there are 
other ingredients held in solution1     
which1 although they can be detected in 
only minute quantities in sea-water1 are
 yet of the very utmost importance to   
marine creatures4 ,this is the case with
 carbonate of lime1 vast quantities of  
which are carried down by many rivers to
 the sea4 ,but it must be nearly all    
used up in the formation of hard shells 
and skeletons by molluscs1 crustaceans1 
corals1 c41 for very little can be      
traced in the water itself4 ,silica is  
also met with sparingly1 and is         
abstracted by some creatures to form    
their hard coverings4  #gj4             
,breaker-action--,currents4--,the most  
conspicuous action of the sea1 as a     
geological agent1 takes place along its 
margin1 where the breakers are hurled   
against the land4 ,stones and gravel are
 borne with more or less intense force  
against the rocks1 and by their constant
 battering succeed eventually in        
undermining the cliffs1 which by and by 

become top-heavy1 and large masses fall 
down and get broken up and pounded into 
gravel and sand4 ,the new wall of rock  
thus exposed becomes in turn assaulted1 
and in course of time is undermined in  
like manner4 ,the waste of the cliffs is
 greatly aided by the action of frost1  
which loosens the jointed rocks1 and    
renders them an easier prey to the force
 of the waves4 ,of course1 the rapidity 
with which a coast-line is eaten into   
depends very much upon the nature of the
 rocks4 ,where these are formed of loose
 materials like sand1 gravel1 or clay1  
considerable inroads are effected by the
 sea in a comparatively short time4     
,thus1 along some parts of the ,english 
coast1 as between ,flamborough ,head and
 the mouth of the ,humber1 and between  
the ,wash and the ,thames1 it is        
estimated that the land is wasted away  
at the rate of a yard per annum4 ,where 
hard rocks form the coast-line the rate 
of waste is often exceedingly slow1 and 
centuries may elapse without any        

apparent change being effected4 ,when   
the rocks are of unequal hardness the   
coast-line becomes very irregular1 the  
sea carving out bays and gullies in the 
softer portions1 while the more durable 
masses stand out as capes and bold      
headlands4 ,not unfrequently1 such      
headlands are converted into sea-stacks 
and rocky islets1 as one may observe    
along the rockier parts of our          
shore-lines4 ,close inshore1 the bulkier
 debris derived from the waste of the   
land often accumulates1 forming beds and
 banks of shingle and gravel4 ,the finer
 materials are carried farther out to   
sea1 and distributed over the sea-floor 
by the action of the tide and currents4 
,tidal and other currents may also have 
some denuding effect upon the           
sea-bottom1 but this can only be in     
comparatively shallow water4 ,the great 
bulk of the material derived from the   
waste of the coasts by the mechanical   
action of the breakers1 travels for no  
great distance4 ,but the fine mud       

brought down by rivers is frequently    
transported for vast distances before it
 settles4 ,so fine1 indeed1 is some of  
this sedimentary material1 that it may  
be carried in suspension by sea-currents
 for thousands of miles before it sinks 
to the bottom4  #ga4 ,from this short   
outline it becomes evident1 therefore1  
that the coarser-grained the deposit1   
the smaller will be the area it covers2 
while conversely1 the finer the         
accumulation1 the more widely will it be
 distributed4 ,a partial exception to   
this rule is that of the debris         
scattered over the bottom of the ocean  
by icebergs and detached portions of    
ice-foot4 ,these are often floated for  
vast distances by currents before they  
finally melt away1 and hence the coarse 
debris transported by them must be very 
widely distributed over that part of the
 sea-bottom which is traversed by       
currents flowing out of the ,arctic and 
,antarctic ,oceans4 ,although the deeper
 recesses of the ocean appear to be     

covered only with ooze and fine mud1 yet
 in some instances coarse sand1 and even
 small stones1 have been brought up from
 depths of a hundred fathoms1 so that   
currents may occasionally carry coarser 
materials for great distances from the  
shore4 ,the shifting action of tidal    
currents succeeds in giving rise to very
 irregular deposits in shallow seas4    
,the soundings often shew sudden changes
 from gravel to sand and mud1 nor can   
there be any doubt that1 could we lay   
bare the sea-bottom1 we should often    
observe gravel shading off into sand1   
and sand into mud1 and vice versa4 ,but 
as we receded from the shore1 and       
approached areas which were once deeply 
submerged1 we should find that the      
change of material was generally from   
coarse to fine4   ,,geological ,,action 
,,of ,,plants ,,and ,,animals4  #gb4    
,plants4--,the disintegration of rocks  
is often aided by the action of plants1 
which force their roots into joints and 
crevices1 and thus loosen blocks and    

fragments4 ,carbonic acid1 derived from 
the decay of plants1 being absorbed by  
rain-water1 acts chemically upon many   
rocks1 as in the case of limestone 7see 
#ei1 #fj1 #fa74 ,in temperate regions1  
vegetation frequently accumulates1 under
 certain conditions1 to form very       
considerable masses4 ,of such a nature  
is peat1 which1 as is well known1 covers
 many thousands of acres in the ,british
 ,islands4 ,this substance is composed  
fundamentally of the bog-moss 7,sphagnum
 palustre71 with which1 however1 are    
usually associated many other           
marsh-loving plants4 ,the lower parts of
 bog-moss die and decay while its upper 
portions continue to flourish1 and thus1
 in process of time1 a thickness of peat
 is accumulated to the extent of six1   
twelve1 twenty-four1 or even forty feet4
 ,many of the hill-tops and hill-slopes 
in ,scotland and ,ireland are covered   
with a few feet of peat1 but it is only 
in valleys and hollows where the        
peat-bogs attain their greatest depth4  

,in not a few cases1 the bogs seem to   
occupy the sites of ancient lakes1      
shell-marl often occurring at the bottom
 of these4 ,the trunks and roots of     
trees are also commonly met with        
underneath peat1 and occasionally the   
remains of land animals4 ,frequently1   
indeed1 it would seem as if the         
overthrow of the trees1 by obstructing  
the drainage of the country1 had given  
rise to a marsh1 and the consequent     
formation of peat4 ,some of the most    
valuable peat closely resembles lignite1
 and makes a good fuel4 ,in tropical    
countries1 the rapidity with which      
vegetation decays prevents1 as a rule1  
any great accumulation taking place2 but
 the mangrove swamps are exceptions4    
#gc4 ,animals4--,the action of animal   
life is for the most part conservative  
and reconstructive4 ,considerable       
accumulations of shell-marl take place  
in fresh-water lakes1 and the flat      
bottoms which mark the sites of lakes   
which have been drained are frequently  

dug to obtain this material4 ,but by far
 the most conspicuous formations due to 
the action of animal life accumulate in 
the sea4 ,molluscs1 crustaceans1 corals1
 and the like1 secrete from the ocean   
the carbonate of lime of which their    
hard shells and skeletons are composed1 
and these hard parts go to the formation
 of limestone4 ,the most remarkable     
masses of modern limestone occur within 
intertropical regions4 ,these are the   
coral reefs of the ,pacific and ,indian 
,oceans4     ,illustration3 ,fig4       
#bd4--;,formation of ,coral ,reefs4     
#gd4 ,coral is the calcareous skeleton  
of certain small soft-bodied gelatinous 
animals called actinozoa4 ,these        
zoophytes flourish only in clear water1 
the temperature of which is not below   
#ff deg4 ,f41 and they cannot live at   
greater depths than one hundred feet4   
,there are three kinds of coral         
reef--namely1 fringing reefs1 barrier   
reefs1 and atolls4 ,fringing reefs      
occur1 as a rule1 near to the shore2 but

 if this latter be gently sloping1 they 
may extend for one or even two miles out
 to sea2 as far1 indeed1 as the depth of
 water is not too great for the         
actinozoa4 ,barrier reefs are met with  
at greater distances from the land1 and 
often rise from profound depths4 ,the   
barrier reef which extends along the    
north-east coast of ,australia1 often at
 a distance from the land of fifty or   
sixty miles1 stretches1 with            
interruptions1 for about #abej miles1   
with a breadth varying from ten to      
ninety miles4 ,in some places1 the depth
 of the sea immediately outside of this 
reef exceeds #ahjj feet4 ,sometimes     
barrier reefs completely encircle an    
island or islands1 which are usually    
mountainous1 as in the case of          
,pouynipete1 an island in the ,caroline 
,archipelago1 and the ,gambier ,islands 
in the ,low ,archipelago4 ,atolls are   
more or less irregular ring-shaped reefs
 inclosing a lagoon of quiet water4     
,they usually rise from profound depths2

 ,keeling ,atoll1 in the ,indian ,ocean1
 is a good example4 ,the upper surface  
of atolls and barrier reefs often peers 
at separate points above the level of   
the sea1 so as to form low-lying islets4
 ,in some cases1 the land thus formed is
 almost co-extensive with the reef1 and 
being clothed with palms and tropical   
verdure1 resembles a beautiful chaplet  
floating1 as it were1 in mid-ocean4 ,the
 rock of a coral reef is a solid white  
limestone1 similar in composition to    
that of the limestones occurring in this
 country4 ,in some places1 it is quite  
compact1 shewing few or no inclosed     
shells or other animal remains2 in other
 places1 it is made up of broken and    
comminuted corals cemented together1 or 
of masses of coral standing as they     
slowly grew1 with the spaces between the
 separate clumps filled up with coral   
sand and triturated fragments and grit  
of coral and shell4 ,the thickness of   
the reefs is often very great1 reaching 
in many cases to thousands of feet4 ,at 

the ,fijis1 the reef can hardly be less 
than #bjjj or #cjjj feet thick4 ,below a
 depth of one hundred feet1 all the     
coral rock is dead1 and since the coral 
zoophytes do not live at greater depths 
than this1 it follows that the bed of   
the sea in which coral reefs occur must 
have slowly subsided during a long      
course of ages4 ,mr ,darwin was the     
first to give a reasonable explanation  
of the origin of coral reefs4 ,briefly  
stated1 his explanation is as follows3  
,the corals began to grow first in water
 not exceeding one hundred feet in      
depth1 and built up to the surface of   
the sea1 thus forming a fringing reef at
 no great distance from the land4 ,this 
initial step is shewn at ,a1 ,b1 in the 
accompanying section across a coral     
island4 ,a1 ,a1 are the outer edges of  
the fringing reef2 ,b1 ,b1 the shores of
 the island2 and ,s#a the level of the  
sea4 ,subsidence ensuing1 the island and
 the sea-bottom sink slowly down1 while 
the coral animals continue to grow to   

the surface--the building of the reef   
keeping pace with the subsidence4 ,by   
and by the island sinks to the level    
,s#b1 when ,b'1 ,b'1 represent the      
shores of the now diminished island1 and
 ,a'1 ,a'1 the outer edges of the reef1 
which has become a barrier reef2 ,c1 ,c1
 being the lagoon between the reef and  
the central island4 ,we have now only to
 suppose a continuance of the           
submergence to the level ,s#c1 when the 
island disappears1 its site being       
occupied by a lagoon1 ,c'--the reef1    
which has at the same time become an    
atoll1 being shewn at ,a''1 ,a''4  #ge4 
,in extra-tropical latitudes1 great     
accumulations of carbonate of lime are  
also taking place4 ,the bottom of the   
,atlantic has been found to be covered1 
over vast areas1 by a fine calcareous   
sticky deposit called ooze1 which would 
appear to consist for the most part of  
the skeletons of minute animal          
organisms1 called ,foraminifera4 ,this  
accumulation1 when dried1 closely       

resembled chalk1 and there can be no    
doubt that in the deep recesses of the  
,atlantic we have thus a gradually      
increasing deposit of carbonate of lime1
 which rivals1 if it does not exceed1 in
 extent the most widely spread          
calcareous rocks with which we are      
acquainted4 ,a small percentage of      
siliceous materials occurs in the ooze1 
made up partly of granules of quartz1   
and partly of the skeletons and         
coverings of minute animal and vegetable
 organisms4 ,when in process of time the
 chemical forces begin to act upon the  
siliceous matter diffused through the   
,atlantic ooze1 segregation1 or the     
gathering together of the particles1 may
 take place1 and nodules of flint will  
be the result1 similar to the flint     
nodules which occur in chalk1 and the   
cherty concretions in limestones4       
,animalcules with siliceous envelopes   
and skeletons are by no means so        
abundant as those that secrete carbonate
 of lime1 but they are very widely      

diffused through the oceans1 and in     
favourable places are so abundant that  
they may well give rise eventually to   
extensive beds of flint4 ,ehrenberg     
calculated that #ag1idf cubic feet of   
these organisms were formed annually in 
the muddy bottom of the harbour at      
,wismar1 in the ,baltic4  ,it would     
appear from recent observations         
7,challenger expedition7 that the       
calcareous ooze at the bottom of the    
,atlantic and ,southern ,oceans1 which  
occurs at a mean depth of #bbej fathoms1
 passes gradually as the ocean deepens  
into a gray ooze1 which is less         
calcareous1 and which occurs at a mean  
depth of #bdjj fathoms4 ,at still       
greater depths this gray ooze also      
disappears1 and is replaced by red clay 
at a mean depth of #bgjj fathoms4 ,the  
minute creatures 7foraminifera and      
pelagic mollusca chiefly7 whose shells  
go to form the calcareous ooze1 live for
 the most part on the surface1 and swarm
 all over the areas in which ooze and   

red clay occur at the bottom4 ,hence it 
seems probable that the clay is merely  
the insoluble residue or ash1 as it     
were1 of the organisms--the delicate    
shells1 as they slowly sink to the more 
profound depths1 being dissolved by the 
free carbonic acid1 which1 as           
observations would seem to shew1 occurs 
rather in excess at great depths4 ,thus 
we see how the organic forces may give  
rise to extensive accumulations of      
inorganic matter1 closely resembling the
 finest silt or mud which is carried    
down to the sea by rivers1 and          
distributed far and wide by ocean       
currents4   ,,subterranean ,,forces4    
#gf4 ,there have been many speculations 
as to the condition of the interior of  
the earth4 ,some have inferred that the 
external crust of the globe incloses a  
fluid or molten mass2 others think it   
more probable that the interior is      
solid1 but contains scattered throughout
 its bulk1 especially towards the       
surface of the earth1 irregular seas of 

molten matter1 occupying large vesicles 
or tunnels in the solid honey-combed    
mass4 ,at present1 the facts known would
 appear to be best explained by the     
latter hypothesis4 ,all that we know    
from observation is1 that the           
temperature increases as we descend from
 the surface4 ,the rate of increase is  
very variable4 ,thus1 in the ,artesian  
well at ,neuffen1 in ,wuertemberg1 it   
was as much as #a deg4 ,f4 for every #ai
 feet4 ,in the mines of ,central        
,germany1 however1 the increase is only 
#a deg4 ,f4 for every #gf feet2 while in
 the ,dukinfield coal-pit1 near         
,manchester1 the increase was still     
less1 being only #a deg4 ,f4 in #hi     
feet4 ,taking the average of many       
observations1 it may be held as pretty  
well proved that the temperature of the 
earth's crust increases #a deg4 for     
every #ej or #fj feet of descent after  
the first hundred4  #gg4 ,the crust of  
the earth is subject to certain         
movements1 which are either sudden and  

paroxysmal1 or protracted and tranquil4 
,the former are known as earthquakes1   
which may or may not result in a        
permanent alteration of the relative    
level of land and sea2 the latter always
 effect some permanent change1 either of
 upheaval or depression4  #gh4          
,earthquakes have been variously        
accounted for4 ,those who uphold the    
hypothesis of a fluid interior think the
 undulatory motion experienced at the   
surface is caused by movements in the   
underlying molten mass--an earthquake   
being thus 'the reaction of the liquid  
nucleus against the outer crust4' ,by   
others1 again1 earthquakes are supposed 
to be caused by the fall of large       
rock-masses from the roofs of           
subterranean cavities1 or by any sudden 
impulse or blow1 such as might be       
produced by the cracking of rocks in a  
state of tension1 by a sudden volcanic  
outburst1 or sudden generation or       
condensation of steam4 ,in support of   
this latter hypothesis1 many facts may  

be adduced4 ,the undulatory motion      
communicated to the ground during       
gunpowder explosions1 or by the fall of 
rocks from a mountain1 is often         
propagated to great distances from the  
scene of these catastrophes1 and the    
phenomena closely resemble those which  
accompany a true earthquake4 ,when the  
level of a district has been permanently
 affected by an earthquake1 the movement
 has generally resulted in a lowering of
 the surface4 ,thus1 in #ahai1 the      
,great ,runn of ,cutch1 in ,hindustan1  
was depressed over an area of several   
thousand square miles1 so as during the 
monsoons to become a salt lagoon4       
,occasionally1 however1 we find that    
elevation of the land has taken place   
during an earthquake4 ,this was the case
 in ,new ,zealand in #ahee1 when the    
ground on which the town of ,wellington 
stands rose about two feet1 and a cape  
in the neighbourhood nearly ten feet4   
,sometimes the ground so elevated is1   
after a shorter or longer period1 again 

depressed to its former level4 ,a good  
example of this occurred in ,south      
,america in #ahce4 ,the shore at        
,concepcion was raised a yard and a     
half2 and the ,isle ,santa ,maria was   
pushed up two and a half yards at one   
end1 and three and a half yards at the  
other4 ,but only a few months afterwards
 the ground sank again1 and everything  
returned to its old position4 ,the      
heaving and undulatory motion of an     
earthquake produces frequently          
considerable changes at the surface of  
the ground1 besides an alteration of    
level4 ,rocks are loosened1 and         
sometimes hurled down from cliff and    
mountain-side1 and streams are          
occasionally dammed with the soil and   
rubbish pitched into them4 ,sometimes   
also the ground opens1 and swallows     
whatever chances to come in the way4 ,if
 these chasms close again permanently1  
no change in the physiography of the    
land may take place1 but sometimes they 
remain open1 and affect the drainage of 

the country4  #gi4 ,movements of        
,upheaval and ,depression4--,besides the
 permanent alteration of level which is 
sometimes the result of a great         
earthquake1 it is now well known that   
the crust of the earth is subject to    
long-continued and tranquil movements of
 elevation and depression4 ,the cause of
 these movements is at present merely   
matter for speculation1 some being of   
opinion that they may be caused by the  
gradual contraction of the slowly       
cooling nucleus of the earth1 which     
would necessarily give rise to          
depression1 while this movement1 again1 
would be accompanied by some degree of  
elevation--the result of the lateral    
push or thrust effected by the          
descending rock-masses4 ,it is doubtful1
 however1 if this hypothesis will       
explain all the appearances4 ,the       
,scandinavian peninsula affords a fine  
example of the movements in question4   
,at the extremity of the peninsula      
7,scania71 the land is slowly sinking1  

while to the north of that district     
gradual elevation is taking place at a  
very variable rate1 which in some places
 reaches as much as two or three feet in
 a century4 ,movements of elevation are 
also affecting ,spitzbergen1 ,northern  
,siberia1 ,north ,greenland1 the whole  
western borders of ,south ,america1     
,japan1 the ,kurile ,islands1 ,asia     
,minor1 and many other districts in the 
,mediterranean area1 besides various    
islets in the great ,pacific ,ocean4    
,the proofs of a slow movement of       
elevation are found in old sea-beaches  
and sea-caves1 which now stand above the
 level of the sea4 ,in the case of      
,scandinavia1 it has been noticed that  
the pine-woods which clothe the         
mountains are being slowly elevated to  
ungenial heights1 and are therefore     
gradually dying out along their upper   
limits4 ,the proofs of depression of the
 land are seen in submerged forests and 
peat1 which occur frequently around our 
own shores1 and there is also strong    

human testimony to such downward        
movements of the surface4 ,the case of  
,scania has already been referred to4   
,several streets in some of its coast   
towns have sunk below the sea1 and it is
 calculated that the ,scanian coast has 
lost to the extent of thirty-two yards  
in breadth within the past hundred and  
thirty years4 ,the coral reefs of       
southern oceans also afford striking    
evidence of a great movement of         
depression4  ,not long ago a theory was 
started by a ,french savant1 ,m4        
,adhemar1 to account for changes in the 
sea-level1 without having recourse to   
subterranean agency4 ,he pointed out    
that a vast ice-cap1 covering the       
northern regions of our hemisphere1 as  
was certainly the case during what is   
termed the glacial epoch1 would cause a 
rise of the sea by displacing the       
earth's centre of gravity4 ,mr ,james   
,croll has recently strongly supported  
this opinion2 and there can be no doubt 
that we have here a vera causa of       

considerable mutations of level4 ,it is 
unquestionably true1 however1 that great
 oscillatory movements1 such as         
described above1 and which can only be  
attributed to subterranean agencies1    
have frequently taken and are still     
taking place4  #hj4 ,such movements of  
the earth's crust cannot take place     
without effecting some change upon the  
strata of which that crust is composed4 
,during depression of the curved surface
 of the earth1 the under strata must    
necessarily be subjected to intense     
lateral pressure1 since they are        
compelled to occupy less space1 and     
contortion and plication will be the    
result4 ,it is evident also that        
contortion will diminish from below     
upwards1 so that we can conceive that   
excessive contortion may be even now    
taking place at a great depth from the  
surface in ,greenland4 ,during a        
movement of elevation1 on the other     
hand1 the strata are subjected to       
excessive tension1 and must be seamed   

with great rents3 when the elevating    
force is removed1 the disrupted rocks   
will settle down unequally--in other    
words1 they will be faulted1 and their  
continuity will be broken4 ,but both    
contortion and faulting may be due1 on a
 small scale1 to local causes1 such as  
the intrusion of igneous rocks1 the     
consolidation of strata1 the falling in 
of old water-courses1 c4 ,cleavage is   
believed to have been caused by         
compression1 such as the rocks might    
well be subjected to during great       
movements of the earth's crust4 ,the    
particles of which the rock is composed 
are compressed in one direction1 and of 
course are at the same time drawn out at
 right angles to the pressure4 ,this is 
observed not only as regards the        
particles of the rock themselves1 but   
imbedded fossils also are distorted and 
flattened in precisely the same way4    
#ha4 ,volcanoes4--,besides movements of 
elevation and depression1 there are     
certain other phenomena due to the      

action of the subterranean forces4 ,such
 are the ejection from the interior of  
the earth of heated matters1 and their  
accumulation upon the surface4 ,the     
erupted materials consist of molten     
matter 7lava71 stones and dust1 gases   
and steam--the lava1 ashes1 and stones  
gradually accumulating round the focus  
of ejection1 and thus tending to form a 
conical hill or mountain4 ,could we     
obtain a complete section of such a     
volcanic cone1 we should find it built  
up of successive irregular beds of lava1
 and layers of stones and ashes1 dipping
 outwards and away from the source of   
eruption1 but having round the walls of 
the crater 7that is1 the cavity at the  
summit of the truncated cone7 a more or 
less perceptible dip inwards4 ,fig4 #be 
gives a condensed view of the general   
phenomena accompanying an eruption4 ,in 
this ideal section1 a is the funnel or  
neck of the volcano filled with lava2 b1
 b1 the crater4 ,the molten lava is     
highly charged with elastic fluids1     

which continually escape from its       
surface with violent explosions1 and    
rise in globular clouds1 d1 d1 to a     
certain height1 after which they dilate 
into a dark cloud1 c4 ,from this cloud  
showers of rain1 e1 are frequently      
discharged4 ,large and small portions of
 the incandescent lava are shot upwards 
as the imprisoned vapour of water       
explodes and makes its escape1 and1     
along with these1 fragments of the rocks
 forming the walls of the crater and the
 funnel are also violently discharged2  
the cooled bombs1 angular stones1 and   
lapilli1 as the smaller stones are      
called1 falling in showers1 f1 upon the 
exterior parts of the cone or into the  
crater1 from which they are again and   
again ejected4 ,most frequently the     
great weight of the lava inside the     
crater suffices to break down the side  
of the cone1 and the molten rock escapes
 through the breach4 ,sometimes1        
however1 it issues from beneath the base
 of the cone4 ,at other times1 finding  

for itself some weak place in the cone1 
it may flow out by a lateral fissure1 g4
 ,in the diagram1 i1 i represents the   
lava streaming down the outward slopes1 
jets of steam and fumaroles escaping    
from almost every part of its surface4  
,forked lightning often accompanies an  
eruption1 and is supposed to be         
generated by the intense mutual friction
 in the air of the ejected stones4 ,the 
trituration to which these are subjected
 reduces them1 first1 to a kind of      
coarse gravel 7lapillo72 then to sand   
7puzzolana72 and lastly1 to fine dust or
 ashes 7ceneri74     ,illustration3     
,fig4 #be4--;,diagrammatic ,section of  
,volcano4  #hb4 ,lava4--,any rock which 
has been erupted from a volcano in a    
molten state is called lava4 ,some      
modern lava-streams cover a great extent
 of surface4 ,one of two streams which  
issued from the volcano of ,skaptur     
,jokul 7,iceland7 in #aghc overflowed an
 area fifty miles in length1 with a     
breadth in places of fifteen2 the other 

was not much less extensive1 being forty
 miles in length1 with an occasional    
breadth of seven4 ,in some places the   
lava exceeded #ejj feet in thickness4   
,again1 in #ahee1 an eruption in the    
island of ,hawaii sent forth a stream of
 lava sixty-five miles long1 and from   
one to ten miles wide4 ,the surface of a
 stream quickly cools and consolidates1 
and in doing so shrinks1 so as to become
 seamed with cracks1 through which the  
incandescent matter underneath can be   
seen4 ,as the current flows on1 the     
upper crust separates into rough ragged 
scoriform blocks1 which are rolled over 
each other and jammed into confused     
masses4 ,the slags that cake upon the   
face or front of the stream roll down   
before it1 and thus a kind of rude      
pavement is formed1 upon which the lava 
advances and is eventually consolidated4
 ,thus1 in most cases1 a bed of lava is 
scoriaceous as well below as above4     
,other kinds of lava are much more      
ductile and viscous1 and coagulate      

superficially in glossy or wrinkled     
crusts4 ,when lava has inclosed         
fragments of aqueous rocks1 such as     
limestone1 clay1 or sandstone1 these are
 observed to have undergone some        
alteration4 ,the sandstone is often much
 hardened1 the clay is porcelainised1   
and the limestone1 still retaining its  
carbonic acid1 assumes a crystalline    
texture4 ,but the aqueous rock upon     
which lava has cooled does not usually  
exhibit much change1 nor does the       
alteration1 as a rule1 extend more than 
a few feet 7often only a few inches7    
into the rock4 ,a lava-current which    
entered a lake or the sea1 however1 has 
sometimes caught up much of the sediment
 gathering there1 and become so         
commingled with it1 that in some parts  
it is hard to say whether the resulting 
rock is more igneous or aqueous4 ,lava  
which has been squirted up from below   
into cracks and crevices1 and there     
consolidated so as to form dykes1       
sometimes1 but not often1 produces      

considerable alteration upon the rocks  
which it intersects4 ,the basaltic      
structure is believed to be due to the  
contraction of lava consequent upon its 
cooling4 ,the axes of the prisms are    
always perpendicular to the cooling     
surface or surfaces1 and in some cases  
the columns are wonderfully regular4    
,there are numerous varieties of lava1  
such as basalt1 obsidian1 pitchstone1   
pearlstone1 trachyte1 c42 some are heavy
 compact rocks1 others are light and    
porous4 ,many are finely or coarsely    
crystalline2 others have a glassy and   
resinous or waxy texture4 ,some shew a  
flaky or laminated structure2 others are
 concretionary4 ,most of the lava rocks1
 however1 are granularly crystalline4   
,in many1 a vesicular character is      
observed4 ,these vesicles1 being due to 
the bubbles of vapour that gathered in  
the molten rock1 usually occur in       
greatest abundance towards the upper    
surface of a bed of lava4 ,they are also
 more or less well developed near the   

bottom of a bed1 which1 as already      
explained1 is frequently scoriaceous4   
,occasionally the vesicles are          
disseminated throughout the entire rock4
 ,as a rule1 those lavas which are of   
inferior specific gravity are much more 
vesicular than the denser and heavier   
varieties4 ,the vesicles are usually    
more or less flattened1 having been     
drawn out in the direction in which the 
lava-current flowed4 ,sometimes they are
 filled1 or partially filled1 with      
mineral matter introduced at the time of
 eruption1 or subsequently brought in a 
state of solution and deposited there by
 water filtering through the rock3 this 
forms what is called amygdaloidal lava4 
,in volcanic districts1 the rocks are   
often traversed by more or less vertical
 dykes or veins of igneous matter4      
,these dykes appear in some cases to    
have been formed by the filling up of   
crevices from above--the liquid lava    
having filtered downwards from an       
overflowing mass4 ,in most cases1       

however1 the lava has been injected from
 below1 and not unfrequently the 'dykes'
 seem to have been the feeders from     
which lava-streams have been            
supplied--the feeders having now become 
exposed to the light of day either by   
some violent eruption which has torn the
 rocks asunder1 or else by the gradual  
wearing away of the latter by           
atmospheric and aqueous agencies4       
,,metamorphism4  #hc4 ,mention has      
already been made of the fact1 that the 
heated matters ejected from volcanoes1  
or forcibly intruded into cracks1       
crevices1 c41 occasionally alter the    
rocks with which they come in contact4  
,when this alteration has proceeded so  
far as to induce a crystalline or       
semi-crystalline character1 the rock so 
altered is said to be metamorphosed4    
,metamorphism has likewise been produced
 by the chemical action of percolating  
water1 which frequently dissolves out   
certain minerals1 and replaces these    
with others having often a very         

different chemical composition4 ,but    
metamorphism on the large scale--that is
 to say1 metamorphism which has affected
 wide areas1 such as the northern       
,highlands of ,scotland and wide regions
 in ,scandinavia1 or the still vaster   
areas in ,north ,america--has most      
probably been effected both by the      
agency of heat and chemical action1 at  
considerable depths1 and under great    
pressure4 ,when we observe what effect  
can be produced by heat upon rocks1     
under little or no pressure1 and how    
water percolating from above gradually  
changes the composition of some         
rock-masses1 we may readily believe that
 at great depths1 where the heat is     
excessive1 such metamorphic action must 
often be intensified4 ,thus1 for        
example1 limestone heated in the usual  
way gives off its carbonic acid gas1 and
 is reduced to quicklime2 but1 under    
sufficient pressure1 this gas is not    
evolved1 the limestone becoming         
converted into a crystalline marble4    

,some crystalline limestones1 indeed1   
have all the appearance of having at one
 time been actually melted and squirted 
under great pressure into seams and     
cracks of the surrounding strata4       
,heated water would appear to have been 
the agent to which much of the          
metamorphism which affects the rocky    
strata must be attributed4 ,but the mode
 or modes in which it has acted are     
still somewhat obscure2 as may be       
readily understood when it is remembered
 how difficult1 and often how impossible
 it is to realise or reproduce in our   
laboratories the conditions under which 
deep-seated metamorphic action must     
frequently have taken place4 ,in        
foliated rocks1 the minerals are chiefly
 quartz1 felspar1 and mica1 talc1 or    
chlorite4 ,the ingredients of these     
minerals undoubtedly existed in a       
diffused state in the original rocks1   
and heated water charged with alkaline  
carbonates1 as it percolated through the
 strata1 either along the layers of     

bedding or lines of cleavage1 slowly    
acted upon these1 dissolving and        
redepositing them1 and thus inducing    
segregation4 ,there is every kind of    
gradation in metamorphism4 ,thus1 we    
find certain rocks which are but        
slightly altered--their original        
character being still quite apparent2   
while1 in other cases1 the original     
character is so entirely effaced that we
 can only conjecture what that may have 
been4 ,when we have a considerable      
thickness of metamorphic rocks which    
still exhibit more or less distinct     
traces of bedding1 like the successive  
beds of gneiss1 mica-schist1 and quartz 
rock of the ,scottish ,highlands1 we can
 hardly doubt that the now crystalline  
masses are merely highly altered aqueous
 strata4 ,but there are cases where even
 the bedding becomes obliterated1 and it
 is then much more difficult to         
determine the origin of the rocks4      
,thus1 we find bedded gneiss passes     
often1 by insensible gradations1 into   

true amorphous granite4 ,there has been 
much difference of opinion as to the    
origin of granite--some holding it to be
 an igneous rock1 others maintaining its
 metamorphic origin4 ,it is probably    
both igneous and metamorphic1 however4  
,if we conceive of certain aqueous rocks
 becoming metamorphosed into gneiss1 we 
may surely conceive of the metamorphism 
being still further continued until the 
mass is reduced to a semi-fluid or pasty
 condition1 when all trace of foliation 
and bedding might readily disappear1 and
 the weight of the superincumbent strata
 would be sufficient to force portions  
of the softened mass into cracks and    
crevices of the still solid rocks above 
and around it4 ,hence we might expect to
 find the same mass of granite passing  
gradually in some places into gneiss1   
and in other places protruding as veins 
and dykes into the surrounding rocks2   
and this is precisely what occurs in    
nature4  #hd4 ,mineral veins have1 as a 
rule1 been formed by water depositing   

along the walls of fissures the various 
matters which they held in solution1 but
 certain kinds of veins 7such as quartz 
veins in granite7 probably owe their    
origin to chemical action which has     
induced the quartz to segregate from the
 rock mass4 ,some have maintained that  
the metallic substances met with in many
 veins owe their deposition to the      
action of currents of voltaic           
electricity2 while others have          
attributed their presence to sublimation
 from below1 the metals having been     
deposited in the fissures very much as  
lead is deposited in the chimney of a   
leadmill4 ,but in many cases there seems
 little reason to doubt that the ores   
have merely been extracted from the     
rocks1 and re-deposited in fissures1 by 
water1 in the same way as the other     
minerals with which they are associated4
   ,,physiography4  #he4                
,denudation4--,by the combined action of
 all the geological agencies which have 
been described in the preceding         

sections1 the earth has acquired its    
present diversified surface4 ,valleys1  
lacustrine hollows1 table-lands1 and    
mountains have all been more or less    
slowly formed by the forces which we see
 even now at work in the world around   
us4 ,when we reflect upon the fact that 
all the inclined strata which crop out  
at the surface of the ground are but the
 truncated portions of beds that were   
once continuous1 and formed complete    
anticlinal arches or curves1 we must be 
impressed with the degree of denudation1
 or wearing-away1 which the solid strata
 have experienced4 ,if we protract in   
imagination the outcrop of a given set  
of strata1 we shall find them curving   
upwards into the air to a height of1 it 
may be1 hundreds or even thousands of   
feet1 before they roll over to come down
 and fit on to the truncated ends of the
 beds on the further side of the        
anticline 7see figs4 #i and #aa1 pages  
#cc1 #cd74 ,dislocations or faults      
afford further striking evidence in the 

same direction4 ,sometimes these have   
displaced the strata for hundreds and   
even thousands of feet--that is to say1 
that a bed occurring at1 for example1 a 
few feet from the surface upon one side 
of a fault1 has sunk hundreds or        
thousands of feet on the other side4    
,yet it often happens that there is no  
irregularity at the surface to betray   
the existence of a dislocation4 ,the    
ground may be flat as a bowling-green1  
and yet1 owing to some great fault1 the 
rocks underneath one end of the flat may
 be geologically many hundred feet1 or  
even yards1 higher or lower than the    
strata underneath the other end of the  
same level space4 ,what has become of   
the missing strata8 ,they have been     
carried away grain by grain by the      
denuding forces--by weathering1 rain1   
frost1 and fluviatile and marine action4
 ,the whole surface of a country is     
exposed to the abrading action of the   
subaerial forces1 and has been carved by
 them into hills and valleys1 the       

position of which depends partly upon   
the geological structure of the country1
 and partly upon the texture and        
composition of the rocks4 ,the original 
slope of the surface1 when it was first 
elevated out of the sea1 would be       
determined by the action of the         
subterraneous forces--the dominant      
parts1 whether table-lands or undulating
 ridges1 forming the centres from which 
the waters would begin to flow4 ,after  
the land had been subjected for many    
long ages to the wearing action of the  
denuding agents1 it is evident that the 
softer rocks--those which were least    
capable of withstanding weathering and  
erosion--would be more worn away than   
the less easily decomposed masses4 ,the 
latter would1 therefore1 tend to form   
elevations1 and the former hollows4     
,this is precisely what we find in      
nature4 ,the great majority of isolated 
hills and hilly tracts owe their        
existence as such merely to the fact    
that they are formed of more durable    

materials than the rock-masses by which 
they are surrounded4 ,when a line of    
dislocation is visible at the surface1  
it is simply because rocks of unequal   
durability have been brought into       
juxtaposition4 ,the more easily denuded 
strata have wasted away to a greater    
extent than the tougher masses on the   
other side of the dislocation4 ,nearly  
all elevations1 therefore1 may be looked
 upon as monuments of the denudation of 
the land2 they form hills for the simple
 reason that they have been better able 
to withstand the attacks of the denuding
 agents than the rocks out of which the 
hollows have been eroded4  #hf4 ,to this
 general rule there are exceptions1 the 
most obvious being hills and mountains  
of volcanic origin1 such as ,hecla1     
,etna1 ,vesuvius1 c41 and1 on a larger  
scale1 the rocky ridge of the ,andes4   
,again1 it is evident that the great    
mountain-chains of the world are due in 
the first place to upheaval2 but these  
mountains1 as we now see them--peaks1   

cliffs1 precipices1 gorges1             
ravines--have been carved out of the    
solid block1 as it were1 by the         
ceaseless action of the subaerial       
forces4 ,the direction of river-valleys 
has in like manner been determined in   
the first place by the original slope of
 the land2 but the deep dells1 the broad
 valleys and straths1 have all been     
scooped out by running water4 ,the      
northern ,highlands of ,scotland1 for   
example1 evidently formed at one time a 
broad table-land1 elevated above the    
level of the sea by the subterranean    
forces4 ,out of this old table-land the 
denuding agents1 acting through untold  
ages1 have carved out all the numerous  
ravines1 glens1 and valleys1 the        
intervening ridges left behind now      
forming the mountains4 ,it is true that 
now and again streams are found flowing 
in the direction of a fault1 but that is
 simply because the dislocation is a    
line of weakness1 along which it is     
easier for the denuding forces to act4  

,for one fault that we find running     
parallel to the course of a river1 we   
may observe hundreds cutting across its 
course at all angles4 ,the great rocky  
basins occupied by lakes1 which are so  
abundant in the mountainous districts of
 temperate regions and in northern      
latitudes1 are believed to have been    
excavated by the erosive power of       
glacier-ice2 and they point1 therefore1 
to a time when our hemisphere must have 
been subjected to a climate severe      
enough to nourish massive glaciers in   
the ,british ,islands and similar       
latitudes4 ,it may be concluded that the
 present physiography of the land is    
proximately due solely to the action of 
the denuding agents--rain1 frost1       
rivers1 and the sea4 ,but the lines     
along which these agents act with       
greatest intensity have been determined 
in the first place by the subterranean  
forces which upheaved the solid crust   
into great table-lands or mountain      
undulations4 ,both the remote and the   

proximate causes of the earth's         
surface-features1 however1 have acted in
 concert and contemporaneously1 for no  
sooner would new land emerge above the  
sea-level than the breakers would assail
 it1 and all the forces of the          
atmosphere would be brought to bear upon
 it--rain1 frost1 and rivers--so that   
the beginning of the sculpturing of hill
 and valley dates back to the period    
when the present lands were slowly      
emerging from the ocean4 ,so great is   
the denudation of the land1 that in     
process of time the whole would be      
planed down to the level of the sea1 if 
it were not for the subterranean forces1
 which from time to time depress and    
elevate different portions of the       
earth's crust4 ,it can be proved that   
strata miles in thickness have been     
removed bodily from the surface of our  
own country by the seemingly feeble     
agents of denudation4 ,all the denuded  
material--mud1 sand1 and gravel--carried
 down into the sea has been re-arranged 

into new beds1 and these have ever and  
anon been pushed up to the light of day1
 and scarped and channelled by the      
denuding forces1 the resulting detritus 
being swept down as before into the sea1
 to form fresh deposits1 and so on4 ,it 
follows1 therefore1 that the present    
arrangement of land and sea has not     
always existed4 ,there was a time before
 the present distribution of land       
obtained1 and a time will yet arrive    
when1 after infinite modifications of   
surface and level1 the continents and   
islands may be entirely re-arranged1 the
 sea replacing the land1 and vice versa4
 ,to trace the history of such changes  
in the past is one of the great aims of 
the scientific geologist4               
,,palaeontology4,f     ,f ,palaios1     
ancient1 onta1 beings1 and logos1 a     
discourse4   #hg4 ,fossils4--,in our    
description of rock-masses1 and again in
 our account of geological agencies1 we 
referred to the fact that certain rocks 
are composed in large measure1 or       

exclusively1 of animal or vegetable     
organisms1 or of both together2 and we  
saw that analogous organic formations   
were being accumulated at the present   
time4 ,but we have deferred to this     
place any special account of the organic
 remains which are entombed in rocks4   
,fossils1 as these are called1 consist  
generally of the harder and more durable
 parts of animals and plants1 such as   
bones1 shells1 teeth1 seeds1 bark1 and  
ligneous tissues1 c4 ,but it is usual to
 extend the term fossil to even the     
casts or impressions of such remains1   
and to foot-marks and tracks1 whether of
 vertebrates1 molluscs1 crustaceans1 or 
annelids4 ,the organic remains met with 
in the rocks have usually undergone some
 chemical change4 ,they have become     
petrified wholly or in part4 ,the       
gelatine which originally gave          
flexibility to some of them has         
disappeared1 and even the carbonate and 
phosphate of lime of the harder parts   
have frequently been replaced by other  

mineral matter1 by flint1 pyrites1 or   
the like4 ,so perfect is the            
petrifaction in many cases1 that the    
most minute structures have been        
entirely preserved--the original matter 
having been replaced atom by atom4 ,as a
 rule1 fossils occur most abundantly and
 in the best state in clay-rocks1 like  
shale2 while in porous rocks1 like      
sandstone1 they are generally poorly    
preserved1 and not of so frequent       
occurrence4 ,one reason for this is1    
that clay-rocks are much less pervious  
than sandstone1 and their imbedded      
fossils have consequently escaped in    
greater measure the solvent powers of   
percolating water4 ,but there are other 
reasons for the comparative paucity of  
fossils in arenaceous strata1 as we     
shall see presently4  #hh4 ,proofs of   
varied ,physical ,conditions4--,organic 
remains are either of terrestrial1      
fresh-water1 or marine origin1 and they 
are therefore of the utmost value to the
 geologist in deciphering the history of

 those great changes which have         
culminated in the present4 ,but we can  
go a step further than this4 ,we know   
that at the present day the distribution
 of animal and vegetable life is due to 
a variety of causes--to climatic and    
physical conditions4 ,the creatures     
inhabiting arctic and temperate regions 
contrast strongly with those that tenant
 the tropics4 ,so also we observe a     
change in animal and vegetable forms as 
we ascend from the low grounds of a     
country to its mountain heights4        
,similar changes take place in the sea4 
,the animals and plants of littoral     
regions differ from those whose habitat 
is in deeper water4 ,now1 the           
fossiliferous strata of our globe afford
 similar proofs of varying climatic and 
physical conditions4 ,there are littoral
 deposits and deep-sea accumulations3   
the former are generally coarse-grained 
7conglomerates1 grit1 and sandstone72   
the latter are for the most part        
finer-grained 7clay1 shale1 limestone1  

chalk1 c472 and both inshore and        
deep-water formations have each their   
peculiar organic remains4 ,again1 we    
know that some parts of the sea-bottom  
are not so prolific in life as          
others--where1 for example1 any         
considerable deposit of sand is taking  
place1 or where sediment is being       
constantly washed to and fro upon the   
bottom1 shells and other creatures do   
not appear in such numbers as where     
there is less commotion1 and a finer and
 more equable deposit is taking place4  
,it is partly for the same reason that  
certain rocks are more barren of organic
 remains than others4  #hi4 ,fossil     
,genera and ,species frequently         
extinct4--,it might perhaps at first be 
supposed that similar rocks would       
contain similar fossils4 ,for example1  
we might expect that formations         
resembling in their origin those which  
are now forming in our coral seas would 
also1 like the latter1 contain corals in
 abundance1 with some commingling of    

shells1 crustaceans1 fish1 c41 such as  
are peculiar to the warm seas in which  
corals flourish4 ,and this in some      
measure holds good4 ,but when we        
examined carefully the fossils in       
certain of the limestones of our own    
country1 we should find that while the  
same great orders and classes were      
actually present1 yet the genera and    
species were frequently entirely        
different2 and not only so1 but that    
often none of these were now living on  
the earth4 ,moreover1 if we extended our
 research1 we should soon discover that 
similar wide differences actually       
obtained between many of the limestones 
themselves and other fossiliferous      
strata of our country4  #ij4            
,fossiliferous ,strata of ,different    
,ages4--,another fact would also        
gradually dawn upon us--this1 namely1   
that in certain rocks the fossils depart
 much more widely from analogous living 
forms1 than the organic remains in      
certain other rocks do4 ,the cause of   

this lies in the fact that the          
fossiliferous strata are of different   
ages2 they have not all been formed at  
approximately the same time4 ,on the    
contrary1 they have been slowly amassed1
 as we have seen1 during a long         
succession of eras4 ,while they have    
been accumulating1 great vicissitudes in
 the distribution of land and sea have  
taken place1 climates have frequently   
altered1 and the whole organic life of  
the globe has slowly changed again and  
again--successive races of plants and   
animals flourishing each for its        
allotted period1 and then becoming      
extinct for ever4,g ,thus1 strata formed
 at approximately the same time contain 
generally the same fossils2 while1 on   
the other hand1 sedimentary deposits    
accumulated at different periods are    
charged with different fossils4 ,fossils
 in this way become invaluable to the   
geologist4 ,they enable him to identify 
formations in separate districts1 and to
 assign to them their relative          

antiquity4,h ,if1 for example1 we have a
 series of formations1 ,a1 ,b1 ,c1 piled
 one on the top of the other1 ,a being  
the lowest1 and ,c the highest1 and each
 charged with its own peculiar fossils1 
we may compare the fossils met with in  
other sets of strata with the organic   
remains found in ,a1 ,b1 ,c4 ,should the
 former be found to correspond with the 
fossil contents of ,b1 we conclude that 
the rocks in which they occur are       
approximately of contemporaneous origin 
with ,b1 even although the equivalents  
of the formations ,a and ,c should be   
entirely wanting4 ,further1 we soon     
learn that the order of the series ,a1  
,b1 ,c1 is never inverted4 ,if ,a be the
 lowest1 and ,c the highest stratum in  
one place1 it is quite certain that the 
same order of succession will obtain    
wherever the equivalents of these strata
 happen to occur together4 ,but the     
succession of strata is not invariably  
the same all the world over2 in some    
countries1 we may have dozens of        

separate formations piled one on the top
 of the other2 in other countries1 many 
members of the series are absent2 in    
brief1 blanks in the succession are of  
constant occurrence4 ,but by            
dovetailing1 as it were1 all the        
formations known to us1 we are enabled  
to form a more or less complete series  
of rocks arranged in the order of their 
age4 ,a little reflection will serve to 
shew that the partial mode in which the 
strata are distributed over the globe   
arises chiefly from two causes4 ,we have
 to remember1 first1 that the deposits  
themselves were laid down only here and 
there in irregular spreads and          
patches--opposite the mouths of rivers1 
at various points along the ancient     
coast-lines1 and over certain areas in  
the deeper abysses of the ocean--the    
coarser accumulations being of much less
 extent than those formed of finer      
materials4 ,and1 second1 we must not    
forget the intense denudation which they
 have experienced1 so that miles and    

miles of strata which once existed have 
been swept away1 and their materials    
built up into new formations4     ,g ,to
 this there are some exceptions4        
,certain small foraminifers1        for 
example1 met with in some of the oldest 
formations1 do not        seem to differ
 from species which are still living4   
,the genus        ,lingula 7,mollusca7  
has also come down from remotest ages1  
having outlived all its earlier         
associates4     ,h ,this holds strictly 
true1 however1 only in regard to        
comparatively        limited areas4 ,the
 student must remember that strata      
occurring        in widely separate     
regions of the earth1 even although they
        contain very much the same      
assemblage of fossils1 are not          
necessarily contemporaneous1 in the     
strict meaning of the word2        for  
the fauna and flora 7the animal and     
plant life7 may have        died out1   
and become replaced by new forms more   
rapidly in one        place than        

another4 ,the term 'contemporaneous1'   
therefore1 is a        very lax one1 and
 may sometimes group together deposits  
which1        for aught that we can     
tell1 may really have been accumulated  
at        widely separated times4  #ia4 
,gradual ,extinction of ,species4--,when
 a sufficient number of fossils has been
 diligently compared1 we discover that  
those in the younger strata approach    
most nearly to the present living forms1
 and that the older the strata are1 the 
more widely do their organic remains    
depart from existing types of animals   
and plants4 ,we may notice also1 that   
when a series of beds graduate up into  
each other1 so that no strongly marked  
line separates the overlying from the   
underlying strata1 there is also a      
similar gradation amongst the fossils4  
,the fossils in the highest beds may    
differ entirely from those in the       
lowest2 but in the middle beds there is 
an intermingling of forms4 ,in short1 it
 is evident that the creatures gradually

 became extinct1 and were just as       
gradually replaced by new forms1 until a
 time came when all the species that    
were living while the lowest beds were  
being amassed1 at last died out1 and a  
complete change was effected4  #ib4     
,proofs of ,cosmical ,changes of        
,climate4--,from the preceding remarks  
it will be also apparent that fossils   
teach us much regarding the climatology 
of past ages4 ,they tell us how the area
 of the ,british ,islands has           
experienced many vicissitudes of        
climate1 sometimes rejoicing in a warm  
or almost tropical temperature1 at other
 times visited with a climate as severe 
as is now experienced in arctic and     
antarctic regions4 ,not only so1 but we 
learn from fossils that ,greenland once 
supported myrtles and other plants which
 are now only found growing under mild  
and genial climatic conditions2 while1  
on the other hand1 remains of arctic    
mammals are met with in the south of    
,france4 ,such great changes of climate 

are due1 according to ,mr ,croll1 to    
variations in the eccentricity of the   
earth's orbit combined with the         
precession of the equinox4 ,it is well  
known that the orbit of our earth       
becomes much more elliptical at certain 
irregularly recurring periods than it is
 at present4 ,during a period of extreme
 ellipticity1 the earth is1 of course1  
much further away from the sun in       
aphelion,i than it is at a time of      
moderate ellipticity1 while1 in         
perihelion1,j it is considerably nearer4
 ,now1 let us suppose that1 at a time   
when the ellipticity is great1 the      
movement known as the precession of the 
equinox has changed the incidence of our
 seasons1 so that our summer happens in 
perihelion and not in aphelion1 while   
that of the southern hemisphere occurs  
in aphelion1 and not1 as at present1 in 
perihelion4 ,under such conditions1 the 
climate of the globe would experience a 
complete change4 ,in the northern       
hemisphere1 so long and intensely cold  

would the winter be1 that all the       
moisture that fell would fall as rain1  
and although the summer would be very   
warm1 it would nevertheless be very     
short1 and the heat then received would 
be insufficient to melt the snow and ice
 which had accumulated during the       
winter4 ,thus gradually snow and ice    
would cover all the lands down to       
temperate latitudes4 ,in the southern   
hemisphere1 the reverse of all this     
would obtain4 ,the winter there would be
 short and mild1 and the summer1        
although cool1 would be very long4 ,but 
such changes would bring into action a  
whole series of physical agencies1 every
 one of which would tend still further  
to increase the difference between the  
climates of the two hemispheres4 ,owing 
to the vast accumulation of snow and ice
 in the northern hemisphere1 the        
difference of temperature between       
equatorial and temperate and polar      
regions would be greater in that        
hemisphere than in the southern4 ,hence 

the winds blowing from the north would  
be more powerful than those coming from 
the southern and warmer hemisphere1 and 
consequently the warm water of the      
tropics would necessarily be impelled   
into the southern ocean4 ,this would    
tend still further to lower the         
temperature of our hemisphere1 while1 at
 the same time1 it would raise          
correspondingly the temperature at our  
antipodes4 ,the general result would be1
 that in our hemisphere ice and snow    
would cover the ground down to low      
temperate latitudes--the ,british       
,islands being completely smothered     
under a great sea of confluent glaciers4
 ,in the southern hemisphere1 on the    
contrary1 a kind of perennial summer    
would reign even up to the pole4 ,such  
conditions would last for some ten or   
twelve thousand years1 and then1 owing  
to the precession of the equinox1 a     
complete change would come about--the   
ice-cap would disappear from the north1 
and be replaced by continuous summer1   

while at the same time an excessively   
severe or glacial climate would         
characterise the south2 and such great  
changes would occur several times during
 each prolonged epoch of great          
eccentricity4 ,this1 in few words1 is an
 outline of ,mr ,croll's theory4 ,that  
theory is at present sub judice1 but    
there can be no doubt that it gives a   
reasonable explanation of many          
geological facts which have hitherto    
been inexplicable4 ,of course1 it is not
 maintained that all changes of climate 
are due directly or indirectly to       
astronomical causes4 ,local changes of  
climate--changes affecting limited      
regions--may be induced by mutations of 
land and sea1 resulting in the partial  
deflection of ocean currents1 which are 
the chief secondary means employed by   
nature for the distribution of heat over
 the globe's surface4     ,i ,apo1 away 
from2 helios1 the sun4     ,j ,peri1    
round about or near by2 helios1 the sun4
  ,from what has been stated in the     

foregoing paragraphs1 it is clear that  
in our endeavours to decipher the       
geological history of our planet1       
palaeontological must go hand in hand   
with stratigraphical evidence4 ,we may  
indeed learn much from the mode of      
arrangement of the rocks themselves4    
,but the test of superposition does not 
always avail us4 ,it is often hard1 and 
sometimes quite impossible1 to tell from
 stratigraphical evidence which are the 
older rocks of a district4 ,in the      
absence of fossils we must frequently be
 in doubt4 ,but physical evidence alone 
will often afford us much and varied    
information4 ,it will shew us what was  
land and what sea at some former period2
 it will indicate to us the sites of    
ancient igneous action2 it will tell us 
of rivers1 and lakes1 and seas which    
have long since passed away4 ,nay1 in   
some cases1 it will even convince us    
that certain great climatic changes have
 taken place1 by pointing out to us the 
markings1 and debris1 and wandered      

blocks which are the sure traces of ice 
action1 whether of glaciers or icebergs4
 ,the results obtained by combining     
physical and palaeontological evidence  
form what is termed ,historical         
,geology4     ,,historical ,,geology4   
#ic4 ,the fossiliferous strata1 as they 
are generally termed1 have been         
chronologically arranged in a series of 
formations1 each of which is            
characterised by its own peculiar suites
 of fossils4 ,their relative age has    
been determined1 as we have indicated   
above1 by their fossils1 and also by    
certain physical tests1 the chief of    
these being superposition4 ,it holds    
invariably true that a formation1 ,a1   
found resting upon another series of    
strata1 ,b1 will always occur in        
precisely the same position1 wherever   
these two deposits occur together4 ,if  
,b should appear in some place as       
resting upon ,a1 we may be sure that the
 beds have been inverted during the     
contortion of the strata consequent upon

 subterranean action 7see fig4 #aa1 page
 #cd74 ,again1 another useful test of   
the relative age of strata lies in the  
circumstance that one is often made up  
or contains fragments of the other4 ,in 
this case1 then1 it is quite clear which
 is the more recent accumulation4 ,these
 tests have now been applied to the     
strata in many parts of the world1 and  
the result is that geologists have been 
able to arrive at a chronological       
arrangement or classification1 and so to
 construct a table shewing the relative 
position which would be occupied by all 
the different formations1 if these      
occurred together in one place4 ,in the 
,british ,islands the long series of    
strata is well developed1 but many of   
the formations are much more meagrely   
represented than their equivalents in   
other countries4 ,but even when we      
attempt to fill up the blanks in our own
 series by dovetailing with them the    
strata of foreign countries1 there yet  
remain numerous breaks in the           

succession1 pointing to the fact that   
the stony record is a very fragmentary  
one at the best4 ,no doubt there are    
many large tracts of the earth's surface
 which have not yet been investigated1  
and when these are known we may hope to 
have our knowledge greatly increased4   
,but no one who reflects upon the mode  
of origin of the fossiliferous strata1  
and the wonderful mutations which the   
earth has undergone1 can reasonably     
anticipate that a perfect and complete  
record of the geological history of our 
planet shall ever be compiled from the  
broken and fragmentary testimony of the 
rocks4  #id4 ,the following table gives 
the names of the different formations   
arranged in the order of their          
superposition1 the youngest being at the
 top1 and the oldest known at the       
bottom3    ,,iv4 ,,post-,,tertiary ,,or 
,,quaternary--         ,historical or   
,recent4         ,pleistocene4    ,,iii4
 ,,tertiary ,,or ,,cainozoic--          
,pliocene4         ,miocene4            

,eocene4    ,,ii4 ,,secondary ,,or      
,,mesozoic--         ,cretaceous4       
,jurassic4         ,triassic4    ,i4    
,,primary ,,or ,,palaeozoic--           
,permian4         ,carboniferous4       
,devonian and ,old ,red ,sandstone4     
,silurian4         ,cambrian4           
,laurentian or ,pre-,cambrian4  #ie4    
,the ,,primary formations are so called 
because they are the oldest known to us3
 they are not necessarily the           
first-formed aqueous deposits4 ,dr      
,hutton said truly3 ,there is no trace  
of a beginning1 and no signs of an end4 
,in the ,,primary or ,,palaeozoic       
7ancient-life7 formations are found the 
earliest traces of life4 ,the forms as a
 rule depart very widely from those with
 which we are acquainted now4 ,the      
,laurentian rocks have yielded only one 
fossil--a large foraminifer named       
,eozoon ,canadense4 ,the ,cambrian      
formation contains but few              
fossils--crustaceans1 molluscs1         
zoophytes1 and worm-tracks4 ,the        

,silurian strata are often abundantly   
fossiliferous4 ,all the great classes of
 invertebrates are represented1 and fish
 remains also occur4 ,the ,devonian and 
,old ,red ,sandstone are also           
characterised by the presence of an     
abundant fauna4 ,in the ,old ,red       
,sandstone are numerous fish remains2 it
 appears to have been an estuarine or   
lacustrine deposit2 the ,devonian1 on   
the other hand1 was marine1 like the    
,silurian and ,cambrian4 ,the           
,carboniferous formation is the chief   
repository of coal in ,britain4 ,it     
consists of terrestrial1 fresh or       
brackish water1 and marine deposits4    
,the fauna and flora of the ,permian1   
which is partly a marine and partly a   
fresh-water formation1 are allied1 upon 
the whole1 to those of the              
,carboniferous1 but offer at the same   
time many contrasts4  #if4 ,the         
,,secondary ,,or ,,mesozoic             
7middle-life7 formations contain        
assemblages of fossils which do not     

depart so widely from analogous living  
forms as those belonging to ,palaeozoic 
times4 ,the ,triassic strata yield      
abundance of rock-salt4 ,in ,britain    
they contain very few fossils1 but these
 are more abundant in the ,triassic     
deposits of foreign countries4 ,the     
oldest known mammals first appear in    
this formation4 ,the ,jurassic formation
 is very highly fossiliferous4 ,it is   
distinguished by the occurrence of      
numerous reptilian remains4 ,nearly all 
the beds of this formation are marine1  
but there are associated with these the 
remains of a forest or old land surface1
 and a considerable accumulation of     
estuarine or fresh-water deposits2      
impure coals also occur in this         
formation4 ,the ,cretaceous strata are  
almost wholly marine1 and chiefly of    
deep-water origin4 ,but some land-plants
 are found1 chiefly ferns1 conifers1 and
 cycads4 ,near the base of the formation
 occurs a great river deposit 7,weald   
clay7 with numerous remains of reptiles4

  #ig4 ,among the oldest strata of the  
,,tertiary or ,,cainozoic 7recent-life7 
division we meet with the dawn of the   
existing state of the testaceous        
fauna--the ,eocene 7eos1 dawn1 and      
kainos1 recent7 containing three and a  
half per cent4 of recent species among  
its shells4 ,the proportion of recent   
species increases in the ,miocene       
7meion1 less1 and kainos1 recent71      
although the majority of the molluscs   
entombed in that formation belong to    
extinct species4 ,in the ,pliocene      
7pleion1 more1 and kainos1 recent71     
however1 the extinct species are in a   
minority4  ,the ,,post-,,tertiary or    
,,quaternary division comprises the     
concluding chapters of geological       
history4 ,the ,pleistocene 7pleistos1   
most1 and kainos1 recent7 contains no   
extinct species of shells1 but a number 
of extinct mammalia4 ,in the ,recent    
deposits all the species of animals and 
plants are living4 ,the ,tertiary and   
,quaternary formations are partly of    

marine and partly of terrestrial and    
fresh-water origin4 ,at the close of the
 ,tertiary period the 'glacial epoch' of
 ,pleistocene times began1 and the      
,british ,islands and a large part of   
northern ,europe and ,north ,america    
were then cased in snow and ice4 ,traces
 of glacial conditions have also been   
met with in the ,eocene and ,miocene4   
,the evidence furnished by ,palaeozoic  
and ,mesozoic formations points chiefly 
to mild1 genial1 and sometimes tropical 
conditions4 ,but traces of ice action   
are occasionally noted 7namely1 in the  
,silurian1 ,old ,red ,sandstone1        
,carboniferous1 ,permian1 and           
,cretaceous formations71 pointing1      
perhaps1 in some of the cases1 to former
 alternations of cold and warm periods4 
,indeed1 the belief is now gaining      
ground1 that the so-called glacial epoch
 of ,pleistocene times was not one long 
continuous age of ice1 but rather       
consisted of an alternation of warm and 
cold periods4 ,and it is not improbable1

 but highly likely1 that similar        
alternations of climate have happened   
during every period of great            
eccentricity of the earth's orbit4      
,,questions4   ,section #a4 ,what is    
,geology8  #b4 ,define the term rock4   
,how many classes of rock are there8    
#c1 #d1 #e4 ,into what groups are the   
mechanically formed rocks divided8      
,define the terms conglomerate1         
sandstone1 and shale4  #f4 ,what is the 
nature of the rocks belonging to the    
,aerial or ,eolian group8  #g4 ,give an 
example of a chemically formed rock4    
#h4 ,give examples of organically       
derived rocks4  #i4 ,what kinds of rocks
 are embraced by the ,metamorphic class8
  #aj4 ,what are igneous rocks8  #ab4   
,what is the mineralogical composition  
of granite8  #ac4 ,what is meant by a   
mineral8  #ad4 ,name five minerals which
 do not contain oxygen4 ,where does     
fluor-spar occur8 ,what is the element  
that enters most largely into the       
composition of the earth's crust8  #ae4 

,name the forms under which the mineral 
quartz occurs4 ,name some of the oxides 
of iron4 ,what is iron pyrites8  #af4   
,name two sulphates4 ,name two          
carbonates4 ,name some of the silicates4
 ,in what kinds of rock is augite found8
 ,where does it never occur8 ,in what   
kinds of rock does hornblende usually   
occur8 ,mention three species of        
felspar4 ,what is one of the most       
distinguishing characteristics of mica8 
,name three silicates of magnesia4      
,mention some of their distinguishing   
peculiarities4 ,where do zeolites       
commonly occur8  #ag4 ,what is a        
quartzose conglomerate8 ,what is a      
calcareous conglomerate8  #ah4 ,what is 
grit8 ,what is freestone8 ,to what are  
the various colours of sandstone due8   
,what is shale8  #ai4 ,name some typical
 ,eolian rocks1 and tell where they     
occur4  #bj4 ,how do stalactites and    
stalagmites occur8 ,what is siliceous   
sinter1 and how does it occur8 ,how does
 rock-salt occur8  #ba4 ,mention some of

 the varieties of limestone4 ,what is   
cornstone8 ,what is the composition of  
dolomite8  #bb4 ,name some of the       
varieties of coal4  #bc4 ,what is       
quartzite8  #bd4 ,describe clay-slate4  
#be4 ,mention some altered limestones4  
#bf4 ,what are schists8 ,name and give  
the mineralogical composition of three  
schists4  #bg4 ,what is the general     
character of metamorphic rocks8  #bh4   
,how would you classify granite8  #bi4  
,what is the mineralogical composition  
of syenite and diorite8  #cj4 ,how do we
 distinguish the two groups into which  
igneous rocks are subdivided8 ,what is  
meant by the terms amygdaloidal and     
porphyritic8  #ca4 ,name some rocks that
 belong to the acidic group4 ,what is   
quartz-porphyry8  #cb4 ,give examples of
 augitic igneous rocks4 ,name a         
hornblendic igneous rock4  #cc4 ,what   
are fragmental igneous rocks8 ,what is  
the difference between trappean breccia 
and trappean conglomerate8  #cd4 ,what  
is meant by the terms stratum1 strata1  

and stratified8 ,what is the difference 
between lamination and bedding8 ,what is
 a section8  #ce4 ,what is false        
bedding8  #cf4 ,briefly describe the    
general appearance of mud-cracks and    
rain-prints1 and say how these have been
 formed4  #cg4 ,what is meant by a      
succession of strata8  #ch4 ,which kinds
 of stratified rocks generally have the 
greatest extension8  #ci4 ,how do beds  
terminate8  #dj4 ,how may planes of     
bedding sometimes indicate a break in   
the succession of strata8  #da4 ,what is
 the nature of joints8 ,what are        
master-joints1 and what is their        
probable cause8  #db4 ,what is cleavage1
 and what is its effect upon the bedding
 of rocks8  #dc4 ,what is foliation8    
#dd4 ,give examples of concretionary    
rocks4 ,what is the nature of chert and 
flint nodules8  #de4 ,define the terms  
dip and strike4 ,what is the crop of a  
bed8 ,what are anticlines and synclines8
  #df4 ,what is meant by an inversion of
 strata8  #dg4 ,how does contemporaneous

 erosion indicate a pause in the        
deposition of a series of strata8  #dh4 
,what is meant by unconformability8 ,how
 does unconformability prove a lapse of 
time between the accumulation of the    
underlying and overlying strata8  #di4  
,what is overlap8  #ej4 ,what is a      
fault8 ,what is hade8 ,how are the      
strata affected on either side of a     
fault8 ,what is the appearance called   
slickensides8 ,under what circumstances 
should we term a fault a downthrow8 and 
when should we term it an upcast8 ,how  
is the approximate age of a fault       
sometimes shewn8  #ea4 ,what are        
metamorphic rocks1 and what is their    
general appearance8 ,in what districts  
of the ,british ,islands are they most  
abundantly developed8 ,what are some of 
the appearances relied upon for         
distinguishing metamorphic from igneous 
granite8  #eb4 ,how do igneous rocks    
occur8 ,define what is meant by         
contemporaneous and subsequent or       
intrusive igneous rocks4 ,how does a    

contemporaneous igneous rock affect the 
beds upon which it rests8 ,what is the  
character of the bed overlying a        
contemporaneous rock8 ,what is the      
general structure of a contemporaneous  
igneous rock8 ,what is meant by         
vesicular structure8 ,what is the       
general texture of a contemporaneous    
igneous rock8 ,what is the nature of the
 jointing in igneous rocks8 ,what is    
wacke8  #ec4 ,what is the nature of the 
beds of breccia1 conglomerate1 ash1 and 
tuff1 with which contemporaneous igneous
 rocks are often associated8 ,what is a 
neck of volcanic agglomerate8 ,how are  
the strata affected at their junction   
with a 'neck'8  #ed4 ,how do intrusive  
igneous rocks occur8 ,how do intrusive  
sheets occur8 ,what effect have they    
produced upon the strata above and below
 them8 ,what is a dyke8 ,what relation  
do they occasionally bear to sheets of  
igneous rock8 ,what is a neck of        
intrusive igneous rock1 and how have the
 strata surrounding it been affected8   

#ee4 ,mention some of the contrasts     
between intrusive and contemporaneous   
igneous rocks4 ,what alteration is      
produced upon coal with which an        
intrusive sheet has come in contact8    
#ef4 ,what are mineral veins8 ,what is  
the nature of the quartz veins in       
granite8 ,how are the minerals usually  
arranged in the great metalliferous     
veins8 ,what is a pipe-vein8  #eg4 ,what
 are the great geological agents of     
change8  #eh4 ,what is meant by         
weathering8 ,how are rocks affected at  
the surface in tropical countries8 ,what
 chemical effect has the atmosphere on  
calcareous rocks8 ,how is soil formed8  
,how are sand dunes formed8 ,mention    
some effects of the transporting power  
of the atmosphere4  #ei4 ,mention some  
of the chemical effects of interstitial 
water4 ,what is the origin of travertine
 or calcareous tufa8  #fj4 ,how have    
stalactites and stalagmites been formed8
 ,give some instances of the solvent    
power of springs4  #fa4 ,how are caves  

in limestone formed8 ,describe some of  
the appearances of a country composed of
 calcareous rocks4 ,describe briefly how
 a river erodes its channel4  #fb4      
,describe the geological action of rain4
  #fc4 ,what do chemical analyses of    
river-water prove8 ,give an example4    
,what are pot-holes8 ,give an example of
 the erosive power of running water4    
,what amount of mud is carried in       
suspension by the ,mississippi1 and     
discharged annually into the sea8 ,what 
estimate has been formed of the total   
amount of mineral matter annually       
transported by that river8  #fd4 ,what  
is alluvium8 ,how is it formed8 and     
mention some examples of its occurrence4
  #fe4 ,how is sediment deposited by a  
river in a lake8  #ff4 ,what is the     
difference between lacustrine and       
fluvio-marine deposits8 ,what is a      
delta8  #fg4 ,describe the geological   
action of frost4 ,describe the          
geological action of river-ice4  #fh4   
,what are glaciers8 ,what thickness do  

they attain in the ,alps8 ,what is their
 rate of motion8 ,what are crevasses1   
and how do they originate8 ,what are    
superficial moraines8 ,what are terminal
 moraines8 ,what changes does a glacier 
effect upon its bed1 and how are these  
modifications produced8 ,what is the    
character of a glacial river8 ,what is  
the origin of icebergs8 ,how is the     
general absence of blocks and stones in 
,greenland icebergs to be explained8    
,what is the nature of a submarine      
terminal moraine8 ,what is the ice-foot8
 ,what is the chief agent in            
distributing erratic stones and blocks  
over the sea-bottom8 ,what effect upon  
the sea-bed must stranding icebergs     
produce8  #fi4 ,what are some of the    
chemical compounds held in solution in  
sea-water8 ,which of these go to form   
the shells and skeletons of marine      
animals8  #gj4 ,describe the action of  
breakers on a sea-coast4 ,how does frost
 aid the wasting action of breakers8    
,what effect has the nature of the rocks

 in the production of inequalities in a 
coast-line8 ,upon what part of the      
sea-bottom does the material derived by 
the action of the breakers chiefly      
accumulate8 ,what effect have the tides 
and ocean currents in the distribution  
of sediment8  #ga4 ,what is the general 
rule as regards fine-grained and        
coarse-grained deposits8 ,mention a     
partial exception to this rule4 ,what   
effect have tidal currents in shallow   
seas8  #gb4 ,how are rocks disintegrated
 through the action of plants8 ,what is 
peat8 ,what may be inferred from the    
occurrence of shell-marl underneath     
peat8 ,what does the appearance of roots
 and trunks of trees1 and of remains of 
land animals under peat1 indicate8  #gc4
 ,what1 generally1 is the geological    
action of animal life8  #gd4 ,what is   
coral8 ,what is a fringing reef8 ,what  
is the general character of a barrier   
reef8 ,give an example of one4 ,what is 
an atoll8 ,what is the nature of coral  
rock8 ,what is ,mr ,darwin's theory of  

the formation of coral reefs8  #ge4     
,what is the nature of the ,atlantic    
ooze8 ,in what respects may it          
eventually come to resemble chalk and   
limestone8 ,mention an instance of the  
abundant occurrence in the sea of       
animalcules with siliceous coverings and
 skeletons4 ,what is the nature of the  
red clay found at great depths in the   
,atlantic and ,southern ,oceans8  #gf4  
,what are some of the notions held in   
regard to the internal condition of the 
earth8 ,at what 7average7 rate does the 
temperature of the earth's crust        
increase as we descend from the surface8
  #gg4 ,what is the nature of the       
movements to which the earth's crust is 
subjected8  #gh4 ,describe the          
hypotheses advanced to account for      
earthquakes4 ,mention some of the       
effects of earthquakes--#ast1 as regards
 alterations of level2 and #b;d1 as     
regards modifications of the surface4   
#gi4 ,mention a good example of tranquil
 elevation and depression of the earth's

 crust4 ,mention some of the proofs of  
an elevatory movement4 ,give proofs that
 shew depression of the land4 ,how may  
certain former changes of sea-level be  
accounted for without inferring any     
movement of the land8  #hj4 ,what effect
 must depression have upon the strata   
forming the earth's crust8 ,what is the 
result of a movement of elevation8 ,what
 is the cause of cleavage8  #ha4 ,what  
is the nature of the materials thrown   
out during volcanic eruptions8 ,what is 
the general structure of a volcanic     
cone8 ,how does molten rock make its    
escape from the orifice of eruption8    
,what is the meaning of the terms       
lapillo1 puzzolana1 and ceneri8  #hb4   
,what is lava8 ,describe the general    
appearance and mode of progression of a 
stream of lava4 ,what effect is produced
 upon fragments of rock caught up and   
inclosed in lava2 and what changes are  
caused in the pavement upon which it    
cools8 ,how does a lava stream entering 
a lake or the sea behave in regard to   

the sediment gathering therein8 ,to what
 is the basaltic structure due8 ,how are
 the axes of the prisms in a columnar   
igneous rock arranged8 ,name some of the
 varieties of lava4 ,what is the origin 
of the vesicular structure in igneous   
rocks8 ,what portions of a bed of lava  
are most frequently scoriaceous8 ,in    
what kinds of lava is the vesicular     
structure most abundantly met with8 ,how
 have the vesicles become flattened8 ,in
 what manner have they been filled with 
mineral matter8 ,what is the origin of  
the dykes of modern volcanic districts8 
#hc4 ,how is metamorphism on the large  
scale supposed to have been induced8    
,how may granite be at one and the same 
time a metamorphic and igneous rock8    
#hd4 ,mention some of the views held    
with regard to the origin of mineral    
veins4  #he4 ,what is denudation8 ,how  
do inclined strata prove that the strata
 have been denuded8 ,how do faults      
afford proof of denudation8 ,what have  
been the general effects produced by    

denudation on the face of the land8     
#hf4 ,what part have the subterranean   
forces acted in the formation of        
mountains8 ,to what geological action is
 the present aspect of these mountains  
due8 ,what has determined the direction 
of river valleys8 ,how have the valleys1
 dells1 c4 been formed8 ,what effect    
have faults had in determining the      
direction of river valleys8 ,what is    
supposed to be the origin of the deep   
rock-basins occupied by many fresh-water
 lakes8 ,how is the waste of land by    
denudation compensated8  #hg4 ,what are 
fossils8 ,what is meant by petrifaction8
 ,in what kind of rocks do fossils occur
 most abundantly1 and in the best state 
of preservation8 and what reason can be 
given for this8  #hh4 ,how do fossils   
afford proof of varied physical         
conditions8 ,give a reason for some     
rocks being more barren of fossils than 
others4  #hi4 ,state some of the        
characters which distinguish broadly the
 older fossiliferous strata from those  

similar accumulations which are being   
formed in our own day4  #ij4 ,how may we
 identify formations in separate        
districts8 ,how is the interrupted and  
partial distribution of strata to be    
accounted for8  #ia4 ,in what respect do
 the fossils in younger strata differ   
from those in older strata8 ,what       
general proof can be adduced to shew    
that species have become gradually      
extinct8  #ib4 ,give an instance how    
fossils prove changes of climate in the 
past4 ,what is supposed to be the cause 
of great cosmical changes of climate8   
,describe ,mr ,croll's theory of        
cosmical changes of climate4  #ic4 ,what
 is the test of superposition8 ,mention 
another test of the relative age of     
strata4 #id4 ,name the four great       
divisions under which the fossiliferous 
rocks are arranged4  #ie4 ,name the     
,primary or ,palaeozoic formations4     
,what are the principal kinds of fossils
 found in the ,old ,red ,sandstone8     
,which formation is the chief repository

 of coal in ,britain8  #if4 ,in what    
other formations do coals occur8 ,in    
which formation do the oldest known     
mammals occur8 ,name the ,secondary     
formations4  #ig4 ,name the ,tertiary   
formations4 ,what kind of climate       
characterised the northern hemisphere at
 the beginning of ,pleistocene times8   
,what kinds of climate would appear from
 the evidence to have chiefly prevailed 
in ,primary1 ,secondary1 and ,tertiary  
ages8 ,have we any trace of frigid      
conditions during these ages8 ,what is  
the growing opinion with regard to the  
climatic conditions during the glacial  
period of ,pleistocene times8           
,,the ,,end4         ,edinburgh3        
,printed by ,w4  ,r4 ,chambers4         
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99   ,transcriber's ,notes    ,the only 
minor correction that was noted in      
converting this document   from a       
printed version into an electronic      
version was an unpaired   parenthesis on
 the first line of the ,title ,page4    

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