includes the more than #ejj original illustrations4 ,see #ejfga-;h4htm or #ejfga-;h4zip3 7https3_/_/www4gutenberg4org_/cache_/epu b_/#ejfga_/pg#ejfga-;images4html7 or 7https3_/_/www4gutenberg4org_/files_/#ej fga_/ejfga-;h4zip7 ,images of the original pages are available through ,internet ,archive4 ,see https3_/_/archive4org_/details_/cu#caibd jjdigegfc ,transcriber's note3 ,text enclosed by underscores is in italics 7italics74 ,text enclosed by equal signs is in bold face 7bold74 ,a carat character is used to denote superscription4 ,a single character following the carat is superscripted 7example3 b#a74 ,multiple superscripted characters are enclosed by curly brackets 7example3 #a-b74 ,subscript numbers in chemical formulas have been rendered as n or n4 ,,earth ,,features ,,and ,,their ,,meaning 99 99 99 99 99 99 ,illustration3 ,,logo ,the ,macmillan ,company ,new ,york ,boston ,chicago ,dallas ,san ,francisco ,macmillan ,co41 ,limited ,london ,bombay ,calcutta ,melbourne ,the ,macmillan ,co4 ,of ,canada1 ,ltd4 ,toronto 99 99 99 99 99 99 ---------------------------------------- --------------------- ,,plate #a4 ,illustration3 ,mount ,balfour and the ,balfour ,glacier in the ,selkirks4 ---------------------------------------- --------------------- ,,earth ,,features ,,and ,,their ,,meaning ,an ,introduction to ,geology for the ,student and the ,general ,reader by ,,william ,,herbert ,,hobbs ,professor of ,geology in the ,university of ,michigan ,author of 8,earthquakes4 an ,introduction to ,seismic ,geology02 8,characteristics of ,existing ,glaciers02 etc4 ,new ,york ,the ,macmillan ,company #aiba ,all rights reserved ,copyright1 #aiab1 ,by ,the ,macmillan ,company4 ,norwood ,press ,j4 ,s4 ,cushing ,co4--,berwick ,smith ,co4 ,norwood1 ,mass41 ,u4,s4,a4 ,,to ,,the ,,memory ,,of ,,george ,,huntington ,,williams ,,preface ,,the series of readings contained in the present volume give in somewhat expanded form the substance of a course of illustrated lectures which has now for several years been delivered each semester at the ,university of ,michigan4 ,the keynote of the course may be found in the dominant characteristics of the different earth features and the geological processes which have been betrayed in the shaping of them4 ,such a geological examination of landscape is replete with fascinating revelations1 and it lends to the study of ,nature a deep meaning which cannot but enhance the enjoyment of her varied aspects4 ,that there is a real place for such a cultural study of geology within the ,university is believed to be shown by the increasing number of students who have elected the work4 ,even more than in former years the ,american travels afar by car or steamship1 and the earth's surface features in all their manifold diversity are thus one after the other unrolled before him4 ,the thousands who each year cross the ,atlantic to roam over ,european countries may by historical1 literary1 or artistic studies prepare themselves to derive an exquisite pleasure as they visit places identified with past achievement of one form or another4 ,yet the ,channel coast1 the gorge of the ,rhine1 the glaciers of ,switzerland1 and the wild scenery of ,norway or ,scotland have each their fascinating story to tell of a history far more remote and varied4 ,to read this history1 the runic characters in which it is written must first of all be mastered2 for in every landscape there are strong individual lines of character such as the pen artist would skillfully extract for an outline sketch4 ,such character profiles are often many times repeated in each landscape1 and in them we have a key to the historical record4 ,an object of the present readings has thus been to enable the student to himself pick out in each landscape these more significant lines and so read directly from ,nature4 ,in the landscapes which have been represented1 the aim has been to draw as far as possible upon localities well known to travelers and likely to be visited1 either because of their historical interest or their purely scenic attractions4 ,it should thus be possible for a tourist in ,america or ,europe to pursue his landscape studies whenever he sets out upon his travels4 ,the better to aid him in this endeavor1 some suggestions concerning the itinerary of journeys have been supplied in an appendix4 ,regarded as a textbook of geology1 the present work offers some departures from existing examples4 ,though it has been customary to combine in a single text historical with dynamical and structural geology1 a tendency has already become apparent to treat the historical division apart from the others4 ,again1 a desire to treat the science of geology comprehensively has led some authors into including so many subjects as to render their texts unnecessarily encyclopedic and correspondingly uninteresting to the general reader4 ,it is the author's belief that there is a real need for a book which may be read intelligently by the general public1 and it must be recognized that the beginner in the subject cannot cover the entire field by a single course of readings4 ,the present work has1 therefore1 been prepared with a view to selecting for study those dominant geological processes which are best illustrated by features in northern ,north ,america and ,europe4 ,it is this desire to illustrate the readings by travels afield1 which accounts for the prominence given to the subject of glaciation2 for the larger number of colleges and universities in both ,america and ,europe are surrounded by the heavy accumulations that have resulted from former glaciations4 ,emphasis has also been placed upon the dependence of the dominant geological processes of any region upon existing climatic conditions1 a fact to which too little attention has generally been given4 ,this explains the rather full treatment of desert regions1 of which1 in our own country particularly1 much may be illustrated upon the transcontinental railway journeys4 ,more than in most texts the attempt has here been made to teach directly through the eye with the efficient aid of apt illustrations intimately interwoven with the text4 ,for such success as has been reached in this endeavor1 the author is greatly indebted to two students of the ,university of ,michigan1--,mr4 ,james ,h4 ,meier1 who has prepared the line drawings of landscapes1 and ,mr4 ,hugh ,m4 ,pierce1 who has draughted the diagrams4 ,though credit has in most cases been given where illustrations have been made from another's photographs1 yet especial mention should here be made of the debt to ,dr4 ,h4 ,w4 ,fairbanks of ,berkeley1 ,california1 whose beautiful and instructive photographs are reproduced upon many a page4 ,as given at the ,university of ,michigan1 the lectures reflected in the present volume are supplemented by excursions and by so much laboratory practice as is necessary to become familiar with the more common minerals and rocks1 and to read intelligently the usual topographical and geological maps4 ,in the appendices the means for carrying out such studies1 in part with newly devised apparatus1 have been indicated4 ,the scope of the book precludes the possibility of furnishing the reader with the sources for the body of fact and theory which is presented1 although much may be inferred from the names which appear beneath the illustrations1 and more definite knowledge will be found in the references to literature supplied at the ends of chapters4 ,a large amount of original and unpublished material is for a similar reason unlabeled1 and it has been left for the professional geologist to detect these new strands which have been drawn into the web4 ,,william ,,herbert ,,hobbs4 ,,ann ,,arbor1 ,,michigan1 ,october #be1 #aiaa4 ,,contents ,,chapter ,i ,,the ,,compilation ,,of ,,earth ,,history ,,page ,the sources of the history--,subdivisions of geology--,the study of earth features and their significance--,tabular recapitulation--,geological processes not universal--,change1 and not stability1 the order of nature--,observational geology versus speculative philosophy--,the scientific attitude and temper--,the value of the hypothesis--,heading references #a ,,chapter ,,ii ,,the ,,figure ,,of ,,the ,,earth ,the lithosphere and its envelopes--,the evolution of ideas concerning the earth's figure--,the oblateness of the earth--,the arrangement of oceans and continents--,the figure toward which the earth is tending--,astronomical versus geodetic observations--,changes of figure during contraction of a spherical body--,the earlier figures of the earth--,the continents and oceans at the close of the ,paleozoic era--,the flooded portions of the present continents--,the floors of the hydrosphere and atmosphere--,reading references #h ,,chapter ,,iii ,,the ,,nature ,,of ,,the ,,materials ,,in ,,the ,,lithosphere ,the rigid quality of our planet--,probable composition of the earth's core--,the earth a magnet--,the chemical constitution of the earth's surface shell--,the essential nature of crystals--,the lithosphere a complex of interlocking crystals--,some properties of natural crystals1 minerals--,the alterations of minerals--,reading references #bj ,,chapter ,,iv ,,the ,,rocks ,,of ,,the ,,earth',s ,,surface ,,shell ,the processes by which rocks are formed--,the marks of origin--,the metamorphic rocks--,characteristic textures of the igneous rocks--,the classification of rocks--,subdivisions of the sedimentary rocks--,the different deposits of ocean1 lake1 and river--,special marks of littoral deposits--,the order of deposition during a transgression of the sea--,the basins of deposition of earlier ages--,the deposits of the deep sea--,reading references #cj ,,chapter ,v ,,contortions ,,of ,,the ,,strata ,,within ,,the ,,zone ,,of ,,flow ,the zones of fracture and flow--,experiments which illustrate the fracture and flow of solid bodies--,the arches and troughs of the folded strata--,the elements of folds--,the shapes of rock folds--,the overthrust fold--,restoration of mutilated folds--,the geological map and section--,measurement of the thickness of formations--,the detection of plunging folds--,the meaning of an unconformity--,reading references #dj ,,chapter ,,vi ,,the ,,architecture ,,of ,,the ,,fractured ,,superstructure ,the system of the fractures--,the space intervals of joints--,the displacements upon joints3 faults--,methods of detecting faults--,the base of the geological map--,the field map and the areal geological map--,laboratory models for study of geological maps--,the method of preparing the map--,fold vs4 fault topography--,reading references #ee ,,chapter ,,vii ,,the ,,interrupted ,,character ,,of ,,earth ,,movements3 ,,earthquakes ,,and ,,seaquakes ,nature of earthquake shocks--,seaquakes and seismic sea waves--,the grander and the lesser earth movements--,changes in the earth's surface during earthquakes3 faults and fissures--,the measure of displacement--,contraction of the earth's surface during earthquakes--,the plan of an earthquake fault--,the block movements of the disturbed district--,the earth blocks adjusted during the ,alaskan earthquake of #ahii #fg ,,chapter ,,viii ,,the ,,interrupted ,,character ,,of ,,earth ,,movements3 ,,earthquakes ,,and ,,seaquakes 7concluded7 ,experimental demonstration of earth movements--,derangement of water flow by earth movement--,sand or mud cones and craterlets--,the earth's zones of heavy earthquake--,the special lines of heavy shock--,seismotectonic lines--,the heavy shocks above loose foundations--,construction in earthquake regions--,reading references #ha ,,chapter ,,ix ,,the ,,rise ,,of ,,molten ,,rock ,,to ,,the ,,earth',s ,,surface2 ,,volcanic ,,mountains ,,of ,,exudation ,prevalent misconceptions about volcanoes--,early views concerning volcanic mountains--,the birth of volcanoes--,active and extinct volcanoes--,the earth's volcano belts--,arrangement of volcanic vents along fissures1 and especially at their intersections--,the so-called fissure eruptions--,the composition and the properties of lava--,the three main types of volcanic mountain--,the lava dome--,the basaltic lava domes of ,hawaii--,lava movements within the caldron of ,kilauea--,the draining of the lava caldrons--,the outflow of the lava floods #id ,,chapter ,x ,,the ,,rise ,,of ,,molten ,,rock ,,to ,,the ,,earth',s ,,surface2 ,,volcanic ,,mountains ,,of ,,ejected ,,materials ,the mechanics of crater explosions--,grander volcanic eruptions of cinder cones--,the eruption of ,volcano in #ahhh--,the eruption of ,taal volcano on ,january #cj1 #aiaa--,the materials and the structure of cinder cones--,the profile lines of cinder cones--,the composite cone--,the caldera of composite cones--,the eruption of ,vesuvius in #aijf--,the sequence of events within the chimney--,the spine of ,pel--,the aftermath of mud flows--,the dissection of volcanoes--,the formation of lava reservoirs--,character profiles--,reading references #aae ,,chapter ,,xi ,,the ,,attack ,,of ,,the ,,weather ,the two contrasted processes of weathering--,the rle of the percolating water--,mechanical results of decomposition3 spheroidal weathering--,exfoliation or scaling--,dome structure in granite masses--,the prying work of frost--,talus--,soil flow in the continued presence of thaw water--,the splitting wedges of roots and trees--,the rock mantle and its shield in the mat of vegetation--,reading references #adi ,,chapter ,,xii ,,the ,,life ,,histories ,,of ,,rivers ,the intricate pattern of river etchings--,the motive power of rivers--,old land and new land--,the earlier aspects of rivers--,the meshes of the river network--,the upper and lower reaches of a river contrasted--,the balance between degradation and aggradation--,the accordance of tributary valleys--,the grading of the flood plain--,the cycles of stream meanders--,the cut-off of the meander--,meander scars--,river terraces--,the delta of the river--,the levee--,the sections of delta deposits #aeh ,,chapter ,,xiii ,,earth ,,features ,,shaped ,,by ,,running ,,water ,the newly incised upland and its sharp salients--,the stage of adolescence--,the maturely dissected upland--,the ,hogarthian line of beauty--,the final product of river sculpture3 the peneplain--,the river cross sections of successive stages--,the entrenchment of meanders with renewed uplift--,the valley of the rejuvenated river--,the arrest of stream erosion by the more resistant rocks--,the capture of one river by another--,water and wind gaps--,character profiles--,reading references #afi ,,chapter ,,xiv ,,the ,,travels ,,of ,,the ,,underground ,,water ,the descent within the unsaturated zone--,the trunk channels of descending water--,the caverns of limestones--,swallow holes and limestone sinks--,the sinter deposits--,the growth of stalactites--,formation of stalagmites--,the ,karst and its features--,a desert from the destruction of forests--,the ponore and the polje--,the return of the water to the surface--,artesian wells--,hot springs and geysers--,the deposition of siliceous sinter by plant growth--,reading references #ahj ,,chapter ,,xv ,,sun ,,and ,,wind ,,in ,,the ,,lands ,,of ,,infrequent ,,rains ,the law of the desert--,the self-registering gauge of past climates--,some characteristics of the desert waste--,dry weathering3 the red and brown desert varnish--,the mechanical breakdown of the desert rocks--,the natural sand blast--,the dust carried out of the desert #aig ,,chapter ,,xvi ,,the ,,features ,,in ,,desert ,,landscapes ,the wandering dunes--,the forms of dunes--,the cloudburst in the desert--,the zone of the dwindling river--,erosion in and about the desert--,characteristic features of the arid lands--,the war of dune and oasis--,the origin of the high plains which front the ,rocky ,mountains--,character profiles--,reading references #bji ,,chapter ,,xvii ,,repeating ,,patterns ,,in ,,the ,,earth ,,relief ,the weathering processes under control of the fracture system--,the fracture control of the drainage lines--,the repeating pattern in drainage networks--,the dividing lines of the relief patterns3 lineaments--,the composite repeating patterns of the higher orders--,reading references #bbc ,,chapter ,,xviii ,,the ,,forms ,,carved ,,and ,,molded ,,by ,,waves ,the motion of a water wave--,free waves and breakers--,effect of the breaking wave upon a steep1 rocky shore3 the notched cliff--,coves1 sea arches1 and stacks--,the cut rock terrace--,the cut and built terrace on a steep shore of loose materials--,the work of the shore current--,the sand beach--,the shingle beach--,bar1 spit1 and barrier--,the land-tied island--,a barrier series--,character profiles--,reading references #bca ,,chapter ,,xix ,,coast ,,records ,,of ,,the ,,rise ,,or ,,fall ,,of ,,the ,,land ,the characters in which the record has been preserved--,even coast line the mark of uplift--,a ragged coast line the mark of subsidence--,slow uplift of the coasts2 the coastal plain and cuesta--,the sudden uplifts of the coast--,the upraised cliff--,the uplifted barrier beach--,coast terraces--,the sunk or embayed coast--,submerged river channels--,records of an oscillation of movement--,simultaneous contrary movements upon a coast--,the contrasted islands of ,san ,clemente and ,santa ,catalina--,the ,blue ,grotto of ,capri--,character profiles--,reading references #bde ,,chapter ,,xx ,,the ,,glaciers ,,of ,,mountain ,,and ,,continent ,conditions essential to glaciation--,the snow-line--,importance of mountain barriers in initiating glaciers--,sensitiveness of glaciers to temperature changes--,the cycle of glaciation--,the advancing hemicycle--,continental and mountain glaciers contrasted--,the nourishment of glaciers--,the upper and lower cloud zones of the atmosphere #bfa ,,chapter ,,xxi ,,the ,,continental ,,glaciers ,,of ,,polar ,,regions ,the inland ice of ,greenland--,the mountain rampart and its portals--,the marginal rock islands--,rock fragments which travel with the ice--,the grinding mill beneath the ice--,the lifting of the grinding tools and their incorporation within the ice--,melting upon the glacier margins in ,greenland--,the marginal moraines--,the outwash plain or apron--,the continental glacier of ,antarctica--,nourishment of continental glaciers--,the glacier broom--,field and pack ice--,the drift of the pack--,the ,antarctic shelf ice--,icebergs and snowbergs and the manner of their birth--,reading references #bga ,,chapter ,,xxii ,,the ,,continental ,,glaciers ,,of ,,the 8,,ice ,,age0 ,earlier cycles of glaciation--,contrast of the glaciated and nonglaciated regions--,the 8driftless area0--,characteristics of the glaciated regions--,the glacier gravings--,younger records over older3 the glacier palimpsest--,the dispersion of the drift--,the diamonds of the drift--,tabulated comparison of the glaciated and nonglaciated regions--,unassorted and assorted drift--,features into which the drift is molded--,marginal or 8kettle0 moraines--,outwash plains--,pitted plains and interlobate moraines--,eskers--,drumlins--,the shelf ice of the ice age--,character profiles #big ,,chapter ,,xxiii ,,glacial ,,lakes ,,which ,,marked ,,the ,,decline ,,of ,,the ,,last ,,ice ,,age ,interference of glaciers with drainage--,temporary lakes due to ice blocking--,the 8parallel roads0 of the ,scottish glens--,the glacial ,lake ,agassiz--,episodes of the glacial lake history within the ,st4 ,lawrence ,valley--,the crescentic lakes of the earlier stages--,the early ,lake ,maumee--,the later ,lake ,maumee--,lakes ,arkona and ,whittlesey--,lake ,warren--,lakes ,iroquois and ,algonquin--,the ,nipissing ,great ,lakes--,summary of lake stages--,permanent changes of drainage effected by the glacier--,glacial ,lake ,ojibway in the ,hudson's ,bay drainage basin--,reading references #cbj ,,chapter ,,xxiv ,,the ,,uptilt ,,of ,,the ,,land ,,at ,,the ,,close ,,of ,,the ,,ice ,,age ,the response of the earth's shell to its ice mantle--,the abandoned strands as they appear to-day--,the records of uplift about ,mackinac ,island--,the present inclinations of the uplifted strands--,the hinge lines of uptilt--,future consequences of the continued uptilt within the lake region--,gilbert's prophecy of a future outlet of the ,great ,lakes to the ,mississippi--,geological evidences of continued uplift--,drowning of southwestern shores of ,lakes ,superior and ,erie--,reading references #cdj ,,chapter ,,xxv ,,niagara ,,falls ,a ,,clock ,,of ,,recent ,,geological ,,time ,features in and about the ,niagara gorge--,the drilling of the gorge--,the present rate of recession--,future extinction of the ,american ,fall--,the captured ,canadian ,fall at ,wintergreen ,flats--,the ,whirlpool ,basin excavated from the ,st4 ,david's gorge--,the shaping of the ,lewiston ,escarpment--,episodes of ,niagara's history and their correlation with those of the glacial lakes--,time measures of the ,niagara clock--,the horologe of late glacial time in ,scandinavia--,reading references #ceb ,,chapter ,,xxvi ,,land ,,sculpture ,,by ,,mountain ,,glaciers ,contrasted sculpturing of continental and mountain glaciers--,wind distribution of the snow which falls in mountains--,the niches which form on snowdrift sites--,the augmented snowdrift moves down the valley3 birth of the glacier--,the excavation of the glacial amphitheater or cirque--,life history of the cirque--,grooved and fretted uplands--,the features carved above the glacier--,the features shaped beneath the glacier--,the cascade stairway in glacier-carved valleys--,the character profiles which result from sculpture by mountain glaciers--,the sculpture accomplished by ice caps--,the ,norwegian tind or beehive mountain--,reading references #cfg ,,chapter ,,xxvii ,,successive ,,glacier ,,types ,,of ,a ,,waning ,,glaciation ,transition from the ice cap to the mountain glacier--,the piedmont glacier--,the expanded-foot glacier--,the dendritic glacier--,the radiating glacier--,the horseshoe glacier--,the inherited-basin glacier--,summary of types of mountain glacier--,reading references #chc ,,chapter ,,xxviii ,,the ,,glacier',s ,,surface ,,features ,,and ,,the ,,deposits ,,upon ,,its ,,bed ,the glacier flow--,crevasses and sracs--,bodies given up by the ,glacier des ,bossons--,the moraines--,selective melting upon the glacier surface--,glacier drainage--,deposits within the vacated valley--,marks of the earlier occupation of mountains by glaciers--,reading references #cij ,,chapter ,,xxix ,a ,,study ,,of ,,lake ,,basins ,fresh water and saline lakes--,newland lakes--,basin-range lakes--,rift-valley lakes--,earthquake lakes--,crater lakes--,coule lakes--,morainal lakes--,pit lakes--,glint or colk lakes--,ice-dam lakes--,glacier-lobe lakes--,rock-basin lakes--,valley moraine lakes--,landslide lakes--,border lakes--,ox-bow lakes--,saucer lakes--,crescentic levee lakes--,raft lakes--,side-delta lakes--,delta lakes--,barrier lakes--,dune lakes--,sink lakes--,karst lakes3 poljen--,playa lakes--,salines--,alluvial-dam lakes--,rsum--,reading references #dja ,,chapter ,,xxx ,,the ,,ephemeral ,,existence ,,of ,,lakes ,lakes as settling basins--,drawing off of water by erosion of outlet--,the pulling in of headlands and the cutting off of bays--,lake extinction by peat growth--,extinction of lakes in desert regions--,the rle of lakes in the economy of nature--,ice ramparts on lake shores--,reading references #dbf ,,chapter ,,xxxi ,,the ,,origin ,,and ,,the ,,forms ,,of ,,mountains ,a mountain defined--,the festoons of mountain arcs--,theories of origin of the mountain arcs--,the ,atlantic and ,pacific coasts contrasted--,the block type of mountain--,mountains of outflow or upheap--,domed mountains of uplift2 laccolites--,mountains carved from plateaus--,the climatic conditions of the mountain sculpture--,the effect of the resistant stratum--,the mark of the rift in the eroded mountains--,reading references #dce ,,appendices ,a4 ,the quick determination of the common minerals #ddi ,b4 ,short descriptions of some common rocks #dfb ,c4 ,the preparation of topographical maps #dfg ,d4 ,laboratory models for study in the interpretation of geological maps #dgb ,e4 ,suggested itineraries for pilgrimages to study earth features #dge ,,index #dhi ,,list ,,of ,,plates ,,plate #a4 ,mount ,balfour and the ,balfour ,glacier in the ,selkirks ,frontispiece ,,facing ,,page #b4 ,a4 ,layers compressed in experiments and showing the effect of a competent layer in the process of folding #dd ,b4 ,experimental production of a series of parallel thrusts within closely folded strata #dd ,c4 ,apparatus to illustrate shearing action within the overturned limb of a fold #dd #c4 ,a4 ,an earthquake fault opened in ,formosa in #aijf with vertical and lateral displacements combined #gb ,b4 ,earthquake faults opened in ,alaska in #ahhi on which vertical slices of the earth's shell have undergone individual adjustments #gb #d4 ,a4 ,experimental tank to illustrate the earth movements which are manifested in earthquakes4 ,the sections of the earth's shell are here represented before adjustment has taken place #hb ,b4 ,the same apparatus after a sudden adjustment #hb ,c4 ,model to illustrate a block displacement in rocks which are intersected by master joints #hb #e4 ,a4 ,once wooded region in ,china now reduced to desert through deforestation #aef ,b4 8,bad ,lands0 in the ,colorado ,desert #aef #f4 ,a4 ,barren ,karst landscape near the famous ,adelsberg grottoes #ahh ,b4 ,surface of a limestone ledge where joints have been widened through solution #ahh #g4 ,a4 ,ranges of dunes upon the margin of the ,colorado ,desert #baj ,b4 ,sand dunes encroaching upon the oasis of ,oued ,souf1 ,algeria #baj #h4 ,a4 ,the granite needles of ,harney ,peak in the ,black ,hills of ,south ,dakota #baf ,b4 ,castellated erosion chimneys in ,el ,cobra ,caon1 ,new ,mexico #baf #i4 ,map of the ,high ,plains at the eastern front of the ,rocky ,mountains #bbj #aj4 ,a4 ,view in ,spitzbergen to illustrate the disintegration of rock under the control of joints #bbh ,b4 ,composite pattern of the joint structures within recent alluvial deposits of the ,syrian ,desert #bbh #aa4 ,a4 ,ripple markings within an ancient sandstone #bcb ,b4 ,wave breaking as it approaches the shore #bcb #ab4 ,a4 ,v-shaped caon cut in an upland recently elevated from the sea1 ,san ,clemente ,island1 ,california #bef ,b4 ,a 8hogback0 at the base of the ,bighorn ,mountains1 ,wyoming #bef #ac4 ,a4 ,precipitous front of the ,bryant ,glacier outlet of the ,greenland inland ice #bgb ,b4 ,lateral stream beside the ,benedict ,glacier outlet1 ,greenland #bgb #ad4 ,view of the margin of the ,antarctic continental glacier in ,kaiser ,wilhelm ,land #bhb #ae4 ,a4 ,an ,antarctic ice foot with boat party landing #bij ,b4 ,a near view of the front of the ,great ,ross ,barrier1 ,antarctica #bij #af4 ,a4 ,incised topography within the 8driftless area0 #cjj ,b4 ,built-up topography within the glaciated region #cjj #ag4 ,a4 ,soled glacial bowlders which show differently directed stri upon the same facet #cjf ,b4 ,perched bowlder upon a striated ledge of different rock type1 ,bronx ,park1 ,new ,york #cjf ,c4 ,characteristic knob and basin surface of a moraine #cjf #ah4 ,a4 ,fretted upland of the ,alps seen from the summit of ,mount ,blanc #cgb ,b4 ,model of the ,malaspina ,glacier and the fretted upland above it #cgb #ai4 ,a4 ,contour map of a grooved upland1 ,bighorn ,mountains1 ,wyoming #cgb ,b4 ,contour map of a fretted upland1 ,philipsburg ,quadrangle1 ,montana #cgb #bj4 ,map of the surface modeled by mountain glaciers in the ,sierra ,nevadas of ,california #cgf #ba4 ,a4 ,view of the ,harvard ,glacier1 ,alaska1 showing the characteristic terraces #cid ,b4 ,the terminal moraine at the foot of a mountain glacier #cid #bb4 ,a4 ,model of the vicinity of ,chicago1 showing the position of the outlet of the former ,lake ,chicago #djj ,b4 ,map of ,yosemite ,falls and its earlier site near ,eagle ,peak #djj #bc4 ,a4 ,view of the ,american ,fall at ,niagara1 showing the accumulation of blocks beneath #dad ,b4 ,crystal ,lake1 a landslide lake in ,colorado #dad #bd4 ,a4 ,apparatus for exercise in the preparation of topographic maps #dfh ,b4 ,the same apparatus in use for testing the contours of a map #dfh ,c4 ,modeling apparatus in use #dfh ,,illustrations ,,in ,,the ,,text ,,fig4 ,,page #a4 ,diagram to show the measure of the earth's surface irregularities #aa #b4 ,map to show the reciprocal relation of areas of land and sea #aa #c4 ,the tetrahedral form toward which the earth is tending #ab #d4 ,a truncated tetrahedron to show the reciprocal relation of projection and depression upon the surface #ac #e4 ,approximations to earlier and present figures of the earth #ae #f4 ,diagrams for comparison of coasts upon an upright and upon an inverted tetrahedron #ag #g4 ,the continents1 including submerged portions #ah #h4 ,diagram to indicate the altitude of different parts of the lithosphere surface #ah #i4 ,diagram to show how the terrestrial rocks grade into the meteorites #bb #aj4 ,comparison of a crystalline with an amorphous substance #bd #aa4 8,light figure0 seen upon etched surface of calcite #be #ab4 ,battered sand grains which have developed crystal faces #bf #ac4 ,unassimilated grains of quartz within a garnet crystal #bh #ad4 ,new minerals developed about the core of an augite crystal #bh #ae4 ,a common rim of new mineral developed by reaction where earlier minerals come into contact #bh #af4 ,laminated structure of a sedimentary rock #cj #ag4 ,characteristic textures of igneous rocks #cc #ah4 ,diagram to show the order of sediments laid down during a transgression of the sea #cg #ai4 ,fractures produced by compression of a block of molder's wax #da #bj4 ,apparatus to illustrate the folding of strata #da #ba4 ,diagrams of fold types #db #bb4 ,diagrams to illustrate crustal shortening #db #bc4 ,anticlinal and synclinal folds #dc #bd4 ,diagrams to illustrate the shapes of rock folds #dd #be4 ,secondary and tertiary flexures superimposed upon the primary ones #dd #bf4 ,a bent stratum to illustrate tension and compression upon opposite sides #de #bg4 ,a geological section with truncated arches restored #dg #bh4 ,diagram to illustrate the nature of strike and dip #dg #bi4 ,diagram to show the use of ,t symbols for strike and dip observation #dh #cj4 ,diagram to show how the thickness of a formation is determined #di #ca4 ,a plunging anticline #ej #cb4 ,a plunging syncline #ej #cc4 ,an unconformity upon the coast of ,california #ea #cd4 ,series of diagrams to illustrate the episodes involved in the production of an angular unconformity #eb #ce4 ,types of deceptive or erosional unconformities #ec #cf4 ,a set of master joints in shale #ee #cg4 ,diagram to show the manner of replacement of one set of joints by another #ef #ch4 ,diagram to show the different combinations of joint series #ef #ci4 ,view of the shore in ,west ,greenland #eg #dj4 ,view in ,iceland which shows joint intervals of more than one order #eg #da4 ,faulted blocks of basalt near ,woodbury1 ,connecticut #eh #db4 ,a fault in previously disturbed strata #ei #dc4 ,diagram to show the effect of erosion upon a fault #fj #dd4 ,a fault plane exhibiting drag #fj #de4 ,map to show how a fault may be indicated by abrupt changes in strike and dip #fa #df4 ,a series of parallel faults revealed by offsets #fa #dg4 ,field map prepared from the laboratory table #fd #dh4 ,areal geological map based upon the field map #fd #di4 ,a portion of the ruins of ,messina #fg #ej4 ,ruins of the ,carnegie ,palace of ,peace at ,cartaga1 ,costa ,rica #fh #ea4 ,overturned bowlders from ,assam earthquake of #ahig #fi #eb4 ,post sunk into ground during ,charleston earthquake #fi #ec4 ,map showing localities where shocks have been reported at sea off ,cape ,mendocino1 ,california #gj #ed4 ,effect of seismic water wave in ,japan #gj #ee4 ,a fault of vertical displacement #ga #ef4 ,escarpment produced by an earthquake fault in ,india #gb #eg4 ,a fault of lateral displacement #gb #eh4 ,fence parted and displaced by lateral displacement on fault during ,california earthquake #gb #ei4 ,fault with vertical and lateral displacements combined #gb #fj4 ,diagram to show how small faults may be masked at the earth's surface #gc #fa4 8,mole hill0 effect above buried earthquake fault #gc #fb4 ,post-glacial earthquake faults #gd #fc4 ,earthquake cracks in ,colorado desert #gd #fd4 ,railway tracks broken or buckled at time of earthquake #ge #fe4 ,railroad bridge in ,japan damaged by earthquake #ge #ff4 ,diagrams to show contraction of earth's crust during an earthquake #gf #fg4 ,map of the ,chedrang fault of ,india #gf #fh4 ,displacements along earthquake fault in ,alaska #gg #fi4 ,abrupt change in direction of throw upon an earthquake fault #gg #gj4 ,map of faults in the ,owens ,valley1 ,california1 formed during earthquake of #ahgb #gh #ga4 ,marquetry of the rock floor in the ,tonopah district1 ,nevada #gi #gb4 ,map of ,alaskan coast to show adjustments of level during an earthquake #gi #gc4 ,an ,alaskan shore elevated seventeen feet during the earthquake of #ahii #hj #gd4 ,partially submerged forest from depression of shore in ,alaska during earthquake #hj #ge4 ,effect of settlement of the shore at ,port ,royal during earthquake of #aijg #hj #gf4 ,diagrams to illustrate the draining of lakes during earthquakes #hc #gg4 ,diagram to illustrate the derangements of water flow during an earthquake #hd #gh4 ,mud cones aligned upon an earthquake fissure in ,servia #hd #gi4 ,craterlet formed near ,charleston1 ,south ,carolina1 during the earthquake of #ahhf #he #hj4 ,cross section of a craterlet #he #ha4 ,map of the island of ,ischia to show the concentration of earthquake shocks #hg #hb4 ,a line of earth fracture revealed in the plan of the relief #hg #hc4 ,seismotectonic lines of the ,west ,indies #hh #hd4 ,device to illustrate the different effects of earthquakes in firm rock and in loose materials #hh #he4 ,house wrecked in ,san ,francisco earthquake #ij #hf4 ,building wrecked in ,california earthquake by roof and upper floor battering down the upper walls #ia #hg4 ,breached volcanic cone in ,new ,zealand showing the bending down of the strata near the vent #if #hh4 ,view of the new ,camiguin volcano formed in #ahga in the ,philippines #ig #hi4 ,map to show the belts of active volcanoes #ih #ij4 ,a portion of the 8fire girdle0 of the ,pacific #ih #ia4 ,volcanic cones formed in #aghc above the ,skaptr fissure in ,iceland #ii #ib4 ,diagrams to illustrate the location of volcanic vents upon fissure lines #ajj #ic4 ,outline map showing the arrangement of volcanic vents upon the island of ,java #ajj #id4 ,map showing the migration of volcanoes along a fissure #aja #ie4 ,basaltic plateau of the northwestern ,united ,states due to fissure eruptions of lava #ajb #if4 ,lava plains about the ,snake ,river in ,idaho #ajb #ig4 ,characteristic profiles of lava volcanoes #ajc #ih4 ,a driblet cone #ajd #ii4 ,leffingwell ,crater1 a cinder cone in the ,owens ,valley1 ,california #ajd #ajj4 ,map of ,hawaii and its lava volcanoes #ajf #aja4 ,section through ,mauna ,loa and ,kilauea #ajf #ajb4 ,schematic diagram to illustrate the moving platform in the crater of ,kilauea #ajg #ajc4 ,view of the open lava lake of ,halemaumau #ajh #ajd4 ,map to show the manner of outflow of the lava from ,kilauea in the eruption of #ahdj #aji #aje4 ,lava of ,matavanu flowing down to the sea during the eruption of #aijf #aaj #ajf4 ,lava stream discharging into the sea from a lava tunnel #aaa #ajg4 ,diagrammatic representation of the structure of lava volcanoes as a result of the draining of frozen lava streams #aab #ajh4 ,diagram to show the formation of mesas by outflow of lava in valleys and subsequent erosion #aab #aji4 ,surface of lava of the ,pahoehoe type #aac #aaj4 ,three successive views to show the growth of the island of ,savaii1 from lava outflow in #aijf #aac #aaa4 ,view of the volcano of ,stromboli showing the excentric position of the crater #aaf #aab4 ,diagrams to illustrate the eruptions within the crater of ,stromboli #aag #aac4 ,map of ,volcano in the olian ,islands #aah #aad4 8,bread-crust0 lava projectile from the eruption of ,volcano in #ahhh #aai #aae4 8,cauliflower cloud0 of steam and ash rising above the cinder cone of ,volcano #abj #aaf4 ,eruption of ,taal volcano in #aiaa seen from a distance of six miles #abj #aag4 ,the thick mud veneer upon the island of ,taal 7after a photograph by ,deniston7 #aba #aah4 ,a pear-shaped lava projectile #aba #aai4 ,artificial production of a cinder cone #abb #abj4 ,diagram to show the contrast between a lava dome and a cinder cone #abc #aba4 ,mayon volcano on the island of ,luzon1 ,philippine ,islands #abc #abb4 ,a series of breached cinder cones due to migration of the eruption along a fissure #abd #abc4 ,the mouth upon the inner cone of ,mount ,vesuvius from which flowed the lava of #ahgb #abd #abd4 ,a row of parasitic cones raised above a fissure opened on the flanks of ,etna in #ahib #abe #abe4 ,view of ,etna1 showing the parasitic cones upon its flanks #abe #abf4 ,sketch map of ,etna to show the areas covered by lava and tuff respectively #abf #abg4 ,panum crater showing the caldera #abf #abh4 ,view of ,mount ,vesuvius before the eruption of #aijf #abg #abi4 ,sketches of the summit of the ,vesuvian cone to bring out the changes in its outline #abh #acj4 ,night view of ,vesuvius from ,naples before the outbreak of #aijf1 showing a small lava stream descending the central cone #abi #aca4 ,scoriaceous lava encroaching upon the tracks of the ,vesuvian railway #acj #acb4 ,map of ,vesuvius1 showing the position of the lava mouths opened upon its flanks during the eruption of #aijf #aca #acc4 ,the ash curtain over ,vesuvius lifting and disclosing the outlines of the mountain #acb #acd4 ,the central cone of ,vesuvius as it appeared after the eruption of #aijf #acb #ace4 ,a sunken road upon ,vesuvius filled with indrifted ash #acc #acf4 ,view of ,vesuvius from the southwest during the waning stages of the eruption #acc #acg4 ,the main lava stream advancing upon ,boscotrecase #acc #ach4 ,a pine snapped off by the lava and carried forward upon its surface #acc #aci4 ,lava front pushing over and running around a wall in its path #acd #adj4 ,one of the ruined villas in ,boscotrecase #acd #ada4 ,three diagrams to illustrate the sequence of events during the cone-building and crater-producing periods #ace #adb4 ,the spine of ,pel rising above the chimney of the volcano after the eruption of #aijb #acf #adc4 ,successive outlines of the ,pel spine #acg #add4 ,corrugated surface of the ,vesuvian cone due to the mud flows which followed the eruption of #aijf #ach #ade4 ,view of the ,kammerbhl near ,eger in ,bohemia #aci #adf4 ,volcanic plug exposed by natural dissection of a volcanic cone in ,colorado #adj #adg4 ,a dike cutting beds of tuff in a partly dissected volcano of southwestern ,colorado #adj #adh4 ,map and general view of ,st4 ,paul's rocks1 a volcanic cone dissected by waves #ada #adi4 ,dissection by explosion of ,little ,bandai-san in #ahhh #ada #aej4 ,the half-submerged volcano of ,krakatoa before and after the eruption of #ahhc #adb #aea4 ,the cicatrice of the ,banat #adb #aeb4 ,diagram to illustrate a probable cause of formation of lava reservoirs and the connection with volcanoes upon the surface #adc #aec4 ,effect of relief of load upon rocks by arching of a competent formation #add #aed4 ,character profiles connected with volcanoes #adf #aee4 ,diagrams to show the effect of decomposition in producing spheroidal bowlders #aej #aef4 ,spheroidal weathering of an igneous rock #aea #aeg4 ,dome structure in granite mass #aeb #aeh4 ,talus slope beneath a cliff #aec #aei4 ,striped ground from soil flow #aed #afj4 ,pavement of horizontal surface due to soil flow #aed #afa4 ,tree roots prying rock apart on fissure #aed #afb4 ,bowlder split by a growing tree #aee #afc4 ,rock mantle beneath soil and vegetable mat #aee #afd4 ,diagram to show the varying thickness of mantle rock upon the different portions of a hill surface #aef #afe4 ,gullies from earliest stage of a river's life #afj #aff4 ,partially dissected upland #afj #afg4 ,longitudinal sections of upper portion of a river valley #afa #afh4 ,map and sections of a stream meander #afc #afi4 ,tree undermined on the outer bank of a meander #afd #agj4 ,diagrams to show the successive positions of stream meanders #afd #aga4 ,an ox-bow lake in the flood plain of a river #afe #agb4 ,schematic representation of a series of river terraces #afe #agc4 8,bird-foot0 delta of the ,mississippi ,river #afg #agd4 ,diagrams to show the nature of delta deposits as exhibited in sections #afh #age4 ,gorge of the ,river ,rhine near ,st4 ,goars #afi #agf4 ,valley with rounded shoulders characteristic of the stage of adolescence #agj #agg4 ,view of a maturely dissected upland #agj #agh4 ,hogarth's line of beauty #aga #agi4 ,view of the oldland of ,new ,england1 with ,mount ,monadnock rising in the distance #aga #ahj4 ,comparison of the cross sections of river valleys of different stages #agb #aha4 ,the ,beavertail ,bend of the ,yakima ,river #agc #ahb4 ,a rejuvenated river valley #agd #ahc4 ,plan of a river narrows #agd #ahd4 ,successive diagrams to illustrate the origin of 8trellis drainage0 #age #ahe4 ,sketch maps to show the earlier and present drainage near ,harper's ,ferry #agf #ahf4 ,section to illustrate the history of ,snickers ,gap #agg #ahg4 ,character profiles of landscapes shaped by stream erosion in humid climates #agg #ahh4 ,diagram to show the seasonal range in the position of the water table #ahj #ahi4 ,diagram to show the effect of an impervious layer upon the descending water #aha #aij4 ,sketch map to illustrate corrosion of limestone along two series of vertical joints #aha #aia4 ,diagram to show the relation of limestone caverns to the river system of the district #ahb #aib4 ,plan of a portion of ,mammoth ,cave1 ,kentucky #ahc #aic4 ,trees and shrubs growing upon the bottoms of limestone sinks #ahc #aid4 ,diagrams to show the manner of formation of stalactites and stalagmites #ahe #aie4 ,sinter formations in the ,luray caverns #ahf #aif4 ,map of the dolines of the ,karst region #ahg #aig4 ,cross section of a doline formed by inbreak #ahg #aih4 ,sharp ,karren of the ,ifenplatte #ahh #aii4 ,the ,zirknitz seasonal lake #ahi #bjj4 ,fissure springs arranged at intersections of rock fractures #aij #bja4 ,schematic diagrams to illustrate the different types of artesian wells #aia #bjb4 ,cross section of ,geysir1 ,iceland #aib #bjc4 ,apparatus for simulating geyser action #aic #bjd4 ,cone of siliceous sinter about the ,lone ,star ,geyser #aid #bje4 ,former shore lines in the ,great ,basin #aih #bjf4 ,map of the former ,lake ,bonneville #aii #bjg4 ,borax deposits in ,death ,valley1 ,california #bja #bjh4 ,hollowed forms of weathered granite in a desert of ,central ,asia #bja #bji4 ,hollow hewn blocks in a wall in the ,wadi ,guerraui #bjb #baj4 ,smooth granite domes shaped by exfoliation #bjc #baa4 ,granite blocks rent by diffission #bjd #bab4 8,mushroom ,rock0 from a desert in ,wyoming #bje #bac4 ,windkanten shaped by sand blast in the desert #bje #bad4 ,the 8stone lattice0 of the desert #bjf #bae4 ,shadow erosion in the desert #bjf #baf4 ,cliffs in loess with characteristic vertical jointing #bjg #bag4 ,a caon in loess worn by traffic and wind #bjg #bah4 ,diagrams to illustrate the effects of obstructions in arresting wind-driven sand #bji #bai4 ,sand accumulating on either side of a firm and impenetrable obstruction #baj #bbj4 ,successive diagrams to illustrate the history of the town of ,kunzen upon the ,kurische ,nehrung #baj #bba4 ,view of desert barchans #baa #bbb4 ,diagrams to show the relationships of dunes to sand supply and wind direction #baa #bbc4 ,ideal section showing the rising mountain wall about a desert and the neighboring slope #bab #bbd4 ,dry delta at the foot of a range upon the borders of a desert #bac #bbe4 ,map of distributaries of streams which issue at the western base of the ,sierra ,nevadas #bac #bbf4 ,a group of 8demoiselles0 in the 8bad lands0 #bad #bbg4 ,amphitheater at the head of the ,wadi ,beni ,sur #bae #bbh4 ,mesa and outlier in the ,leucite ,hills of ,wyoming #baf #bbi4 ,flat-bottomed basin separating dunes #baf #bcj4 ,billowy surface of the salt crust on the central sink of the desert of ,lop #bag #bca4 ,schematic diagram to show the zones of deposition in their order from the margin to the center of a desert #bag #bcb4 ,mounds upon the site of the buried city of ,nippur #bah #bcc4 ,exhumed structures in the buried city of ,nippur #bah #bcd4 ,section across the ,high ,plains #bai #bce4 ,section across the lenticular threads of alluvial deposits of the ,high ,plains #bbj #bcf4 ,distributaries of the foot hills superimposed upon an earlier series #bbj #bcg4 ,character profiles in the landscapes of arid lands #bbj #bch4 ,rain sculpturing under control by joints #bbd #bci4 ,sagging of limestone above joints #bbd #bdj4 ,map of the joint-controlled ,abisko ,caon in ,northern ,lapland #bbe #bda4 ,map of the gorge of the ,zambesi ,river below ,victoria ,falls #bbe #bdb4 ,controlled drainage network of the ,shepaug ,river in ,connecticut #bbf #bdc4 ,a river network of repeating rectangular pattern #bbf #bdd4 ,squared mountain masses which reveal a distribution of joints in block patterns of different orders #bbh #bde4 ,island groups of the ,lofoten ,archipelago #bbi #bdf4 ,diagrams to illustrate the composite profiles of the islands on the ,norwegian coast #bbi #bdg4 ,diagram to show the nature of the motions within a free water wave #bca #bdh4 ,diagram to illustrate the transformation of a free wave into a breaker #bcb #bdi4 ,notched rock cliff and fallen blocks #bcc #bej4 ,a wave-cut chasm under control by joints #bcc #bea4 ,grand ,arch upon one of the ,apostle ,islands in ,lake ,superior #bcd #beb4 ,stack near the shore of ,lake ,superior #bcd #bec4 ,the ,marble ,islands1 stacks in a lake of the southern ,andes #bce #bed4 ,squared stacks revealing the position of the joint planes on which they were carved #bce #bee4 ,ideal section cut by waves upon a steep rocky shore #bcf #bef4 ,map showing the outlines of the island of ,heligoland at different stages in its history #bcf #beg4 ,ideal section carved by waves upon a steep shore of loose materials #bcg #beh4 ,sloping cliff and boulder pavement at ,scituate1 ,massachusetts #bcg #bei4 ,map to show the nature of the shore current and the forms which are molded by it #bch #bfj4 ,crescent-shaped beach in the lee of a headland #bci #bfa4 ,cross section of a beach pebble #bci #bfb4 ,a storm beach on the northeast shore of ,green ,bay #bdj #bfc4 ,spit of shingle on ,au ,train ,island1 ,lake ,superior #bdj #bfd4 ,barrier beach in front of a lagoon #bda #bfe4 ,cross section of a barrier beach with lagoon in its rear #bdb #bff4 ,cross section of a series of barriers and an outer bar #bdb #bfg4 ,a barrier series and an outer bar on ,lake ,mendota at ,madison1 ,wisconsin #bdb #bfh4 ,series of barriers at the western end of ,lake ,superior #bdc #bfi4 ,character profiles resulting from wave action upon shores #bdc #bgj4 ,the even shore line of a raised coast #bdf #bga4 ,the ragged coast line produced by subsidence #bdf #bgb4 ,portion of the ,atlantic coastal plain at the base of the oldland #bdf #bgc4 ,ideal form of cuestas and intermediate lowlands carved from a coastal plain #bdg #bgd4 ,uplifted sea cave on the coast of ,california #bdh #bge4 ,double-notched cliff near ,cape ,tiro1 ,celebes #bdh #bgf4 ,uplifted stacks on the coast of ,california #bdi #bgg4 ,uplifted shingle beach across the entrance to a former bay upon the coast of ,california #bej #bgh4 ,raised beach terraces near ,elie1 ,fife1 ,scotland #bej #bgi4 ,uplifted sea cliffs and terraces on the ,alaskan coast #bej #bhj4 ,diagrams to show how excessive sinking upon the sea floor will cause the shore to migrate landward #bea #bha4 ,a drowned river mouth or estuary upon a coastal plain #bea #bhb4 ,archipelago of steep rocky islets due to submergence #beb #bhc4 ,the submerged ,hudsonian channel which continues the ,hudson ,river across the continental shelf #beb #bhd4 ,marine clay deposits near the mouths of the ,maine rivers which preserve a record of earlier subsidence and later elevation #bec #bhe4 ,view of the three standing columns of the ,temple of ,jupiter ,serapis1 at ,pozzuoli #bed #bhf4 ,three successive views to set forth the recent oscillations of level on the northern shore of the ,bay of ,naples #bee #bhg4 ,relief map of ,san ,clemente ,island1 ,california #bef #bhh4 ,relief map of ,santa ,catalina ,island1 ,california #beg #bhi4 ,cross section of the ,blue ,grotto1 on the island of ,capri #beh #bij4 ,character profiles of coast elevation and subsidence #bei #bia4 ,map showing the distribution of existing glaciers and the two important wind poles of the earth #bfc #bib4 ,an ,alaskan glacier spreading out at the foot of the range which nourishes it #bfd #bic4 ,surface of a glacier whose upper layers spread with but slight restraint from retaining walls #bfe #bid4 ,section through a mountain glacier #bfg #bie4 ,profile across the largest of the ,icelandic ice caps #bfg #bif4 ,ideal section across a continental glacier #bfg #big4 ,view of the ,eyriks ,jkull1 an ice cap of ,iceland #bfh #bih4 ,the zones of the lower atmosphere as revealed by recent kite and balloon exploration #bfi #bii4 ,map of ,greenland1 showing the area of inland ice and the routes of explorers #bga #cjj4 ,profile in natural proportions across the southern end of the continental glacier of ,greenland #bgb #cja4 ,map of a glacier tongue with dimple above #bgc #cjb4 ,edge of the ,greenland inland ice1 showing the nunataks diminishing in size toward the interior #bgd #cjc4 ,moat surrounding a nunatak in ,victoria ,land #bgd #cjd4 ,a glacier pavement of ,permo-,carboniferous age in ,south ,africa #bgf #cje4 ,diagrams to illustrate the manner of formation of scape colks #bgg #cjf4 ,marginal moraine now forming at the edge of the continental glacier of ,greenland #bgi #cjg4 ,small lake between the ice front and a moraine which it has recently built #bgi #cjh4 ,view of a drained lake bottom between the ice front and an abandoned moraine #bhj #cji4 ,diagrams to show the manner of formation and the structure of an outwash plain and fosse #bhj #caj4 ,map of the ice masses of ,victoria ,land1 ,antarctica #bhb #caa4 ,sections across the inland ice and the shelf ice of ,antarctica #bhc #cab4 ,diagram to show the nature of the fixed glacial anticyclone above continental glaciers #bhd #cac4 ,snow deltas about the margins of a glacier tongue in ,greenland #bhe #cad4 ,view of the sea ice of the ,arctic region #bhf #cae4 ,map of the north polar regions1 showing the area of drift ice and the tracks of the ,jeannette and the ,fram #bhh #caf4 ,the shelf ice of ,coats ,land with surrounding pack ice #bij #cag4 ,tidewater cliff on a glacier tongue from which icebergs are born #bij #cah4 ,a ,greenlandic iceberg after a long journey in warm latitudes #bia #cai4 ,diagram showing one way in which northern icebergs are born from the glacier tongue #bia #cbj4 ,a northern iceberg surrounded by sea ice #bib #cba4 ,tabular ,antarctic iceberg separating from the shelf ice #bic #cbb4 ,map of the globe1 showing the areas covered by continental glaciers during the 8ice age0 #big #cbc4 ,glaciated granite bowlder weathered out of a moraine of ,permo-,carboniferous age1 ,south ,australia #bih #cbd4 ,map to show the glaciated and nonglaciated regions of ,north ,america #bih #cbe4 ,map of the glaciated and nonglaciated areas of northern ,europe #bii #cbf4 ,an unstable erosion remnant characteristic of the 8driftless area0 #cjj #cbg4 ,diagram showing the manner in which a continental glacier obliterates existing valleys #cja #cbh4 ,lake and marsh district in northern ,wisconsin #cjb #cbi4 ,cross section in natural proportion of the latest ,north ,american continental glacier #cjc #ccj4 ,diagram showing the earlier and the later glacier records together upon the same limestone surface #cjd #cca4 ,map to show the outcroppings of peculiar rock types in the region of the ,great ,lakes1 and some localities where 8drift copper0 has been collected #cje #ccb4 ,map of the 8bowlder train0 from ,iron ,hill1 ,rhode ,island #cjf #ccc4 ,shapes and approximate natural sizes of some of the diamonds from the ,great ,lakes region #cjg #ccd4 ,glacial map of a portion of the ,great ,lakes region #cjh #cce4 ,section in coarse till #caj #ccf4 ,sketch map of portions of ,michigan1 ,ohio1 and ,indiana1 showing the distribution of moraines #cab #ccg4 ,map of the vicinity of ,devil's ,lake1 ,wisconsin1 partly covered by the continental glacier #cac #cch4 ,moraine with outwash apron in front #cac #cci4 ,fosse between an outwash plain and a moraine #cad #cdj4 ,view along an esker in southern ,maine #cae #cda4 ,outline map of moraines and eskers in ,finland #cae #cdb4 ,sketch maps showing the relationships of drumlins and eskers #caf #cdc4 ,view of a drumlin1 showing an opening in the till #cag #cdd4 ,outline map of the front of the ,green ,bay lobe to show the relationships of drumlins1 moraines1 outwash plains1 and ground moraine #cag #cde4 ,character profiles referable to continental glacier #cah #cdf4 ,view of the flood plain of the ancient ,illinois ,river near ,peoria #cbj #cdg4 ,broadly terraced valleys which mark the floods that once issued from the continental glacier of ,north ,america #cba #cdh4 ,border drainage about the retreating ice front south of ,lake ,erie #cba #cdi4 ,the 8parallel roads0 of ,glen ,roy in the ,scottish ,highlands #cbb #cej4 ,map of ,glen ,roy and neighboring valleys of the ,scottish ,highlands #cbb #cea4 ,three successive diagrams to set forth the late glacial lake history of the ,scottish glens #cbd #ceb4 ,harvesting time on the fertile floor of the glacial ,lake ,agassiz #cbe #cec4 ,map of ,lake ,agassiz #cbe #ced4 ,map showing some of the beaches of ,lake ,agassiz and its outlet #cbf #cee4 ,narrows of the ,warren ,river where it passed between jaws of granite and gneiss #cbg #cef4 ,map of the valley of the ,warren ,river near ,minneapolis #cbg #ceg4 ,portion of the ,herman beach on the shore of the former ,lake ,agassiz #cbh #ceh4 ,map of the continental glacier of ,north ,america when it covered the entire ,st4 ,lawrence basin #cbi #cei4 ,outline map of the early ,lake ,maumee #ccj #cfj4 ,map to show the first stages of the ice-dammed lakes within the ,st4 ,lawrence basin #ccj #cfa4 ,outline map of the later ,lake ,maumee and its outlet #ccb #cfb4 ,outline map of lakes ,whittlesey and ,saginaw #ccc #cfc4 ,map of the glacial ,lake ,warren #ccc #cfd4 ,map of the glacial ,lake ,algonquin #ccd #cfe4 ,outline map of the ,nipissing ,great ,lakes #cce #cff4 ,probable preglacial drainage of the upper ,ohio region #ccg #cfg4 ,diagrams to illustrate the episodes in the recent history of a ,connecticut river #cch #cfh4 ,the notched rock headland of ,boyer ,bluff on ,lake ,michigan #cda #cfi4 ,view of ,mackinac ,island from the direction of ,st4 ,ignace #cdb #cgj4 ,the 8,sugar ,loaf01 a stack of ,lake ,algonquin upon ,mackinac ,island #cdb #cga4 ,beach ridges in series on ,mackinac ,island #cdc #cgb4 ,notched stack of the ,nipissing ,great ,lakes at ,st4 ,ignace #cdc #cgc4 ,series of diagrams to illustrate the evolution of ideas concerning the uplift of the lake region since the ,ice ,age #cdd #cgd4 ,map of the ,great ,lakes region to show the isobases and hinge lines of uptilt #cde #cge4 ,series of diagrams to indicate the nature of the recovery of the crust by uplift when unloaded of an ice mantle #cdf #cgf4 ,portion of the ,inner ,sandusky ,bay1 for comparison of the shore line of #ahbj with that of to-day #cej #cgg4 ,ideal cross section of the ,niagara ,gorge to show the marginal terrace #cec #cgh4 ,view of the bed of the ,niagara ,river above the cataract where water has been drained off #cec #cgi4 ,view of the ,falls of ,st4 ,anthony in #ahea #ced #chj4 ,ideal section to show the nature of the drilling process beneath the cataract #cee #cha4 ,plan and section of the gorge1 showing how the depth is proportional to the width #cee #chb4 ,comparative views of the ,canadian ,falls in #ahbg and #ahie #cef #chc4 ,map to show the recession of the ,canadian ,fall #ceg #chd4 ,comparison of the present with the future falls #ceh #che4 ,bird's-eye view of the captured ,canadian ,fall at ,wintergreen ,flats #ceh #chf4 ,map of the ,whirlpool ,basin #cfj #chg4 ,map of the cuestas which have played so important a part in fixing the boundaries of the lake basins #cfa #chh4 ,bird's-eye view of the cuestas south of ,lakes ,ontario and ,erie #cfb #chi4 ,sketch map of the greater portion of the ,niagara ,gorge to illustrate ,niagara history #cfc #cij4 ,snowdrift hollowing its bed by nivation #cfh #cia4 ,amphitheater formed upon a drift site in northern ,lapland #cfi #cib4 ,the marginal crevasse on the highest margin of a glacier #cgj #cic4 ,niches and cirques in the ,bighorn ,mountains of ,wyoming #cga #cid4 ,subordinate cirques in the amphitheater on the west face of the ,wannehorn #cga #cie4 8,biscuit cutting0 effect of glacial sculpture in the ,uinta ,mountains of ,wyoming #cgb #cif4 ,diagram to show the cause of the hyperbolic curve of cols #cgb #cig4 ,a col in the ,selkirks #cgc #cih4 ,diagrams to illustrate the formation of comb ridges1 cols1 and horns #cgd #cii4 ,the ,u-shaped ,kern ,valley in the ,sierra ,nevadas of ,california #cge #djj4 ,glaciated valley wall1 showing the sharp line which separates the abraded from the undermined rock surface #cge #dja4 ,view of the ,vale of ,chamonix from the sracs of the ,glacier des ,bossons #cgf #djb4 ,map of an area near the continental divide in ,colorado #cgg #djc4 ,gorge of the ,albula ,river in the ,engadine cut through a rock bar #cgh #djd4 ,idealistic sketch1 showing glaciated and nonglaciated side valleys #cgh #dje4 ,character profiles sculptured by mountain glaciers #cgi #djf4 ,flat dome shaped under the margin of a ,norwegian ice cap #cgi #djg4 ,two views which illustrate successive stages in the shaping of tinds #chj #djh4 ,schematic diagram to bring out the relationships of the various types of mountain glaciers #chc #dji4 ,map of the ,malaspina ,glacier of ,alaska #chd #daj4 ,map of the ,baltoro ,glacier of the ,himalayas #che #daa4 ,view of the ,triest ,glacier1 a hanging glacieret #che #dab4 ,map of the ,harriman ,fjord ,glacier of ,alaska #chf #dac4 ,map of the ,rotmoos ,glacier1 a radiating glacier of ,switzerland #chf #dad4 ,outline map of the ,asulkan ,glacier in the ,selkirks1 a horseshoe glacier #chg #dae4 ,outline map of the ,illecillewaet ,glacier of the ,selkirks1 an inherited-basin glacier #chh #daf4 ,diagram to illustrate the surface flow of glaciers #cij #dag4 ,diagram to show the transformation of crevasses into sracs #cia #dah4 ,view of the ,glacier des ,bossons1 showing the position of accidents to ,alpinists #cib #dai4 ,lines of flow upon the surface of the ,hintereisferner ,glacier in the ,alps #cic #dbj4 ,lateral and medial moraines of the ,mer de ,glace and its tributaries #cic #dba4 ,ideal cross section of a mountain glacier #cid #dbb4 ,diagrams to illustrate the melting effects upon glacier ice of rock fragments of different sizes #cid #dbc4 ,small glacier table upon the ,great ,aletsch ,glacier #cie #dbd4 ,effects of differential melting and subsequent refreezing upon a glacier surface #cif #dbe4 ,dirt cone with its casing in part removed #cif #dbf4 ,schematic diagram to show the manner of formation of glacier cornices #cig #dbg4 ,superglacial stream upon the ,great ,aletsch ,glacier #cih #dbh4 ,ideal form of the surface left on the site of a piedmont glacier apron #cii #dbi4 ,map of the site of the earlier piedmont glacier of the ,upper ,rhine #cii #dcj4 ,diagram and map to bring out the characteristics of newland lakes #djb #dca4 ,view of the ,warner ,lakes1 ,oregon #djb #dcb4 ,schematic diagram to illustrate the characteristics of basin-range lakes #djc #dcc4 ,schematic diagram of rift-valley lakes and the valley of the ,jordan #djc #dcd4 ,map of the rift-valley lakes of ,east ,central ,africa #djd #dce4 ,earthquake lakes formed in #ahaa in the flood plain of the ,lower ,mississippi #djd #dcf4 ,view of a crater lake in ,costa ,rica #dje #dcg4 ,diagrams to illustrate the characteristics of crater lakes #djf #dch4 ,view of ,snag ,lake1 a coule lake in ,california #djf #dci4 ,diagrams to illustrate the characteristics of morainal lakes #djg #ddj4 ,diagram to show the manner of formation of pit lakes #djh #dda4 ,diagrams to illustrate the characteristics of pit lakes #djh #ddb4 ,diagram to show the manner of formation of glint lakes #dji #ddc4 ,map of a series of glint lakes on the boundary of ,sweden and ,norway #dji #ddd4 ,map of ice-dam lakes near the ,norwegian boundary of ,sweden #daj #dde4 ,wave-cut terrace of a former ice-dam lake in ,sweden #daj #ddf4 ,view of the ,mrjelen ,lake from the summit of the ,eggishorn #daa #ddg4 ,diagrams to illustrate the arrangement and the characters of rock-basin lakes #dab #ddh4 ,convict ,lake1 a valley-moraine lake of ,california #dac #ddi4 ,lake basins produced by successive slides from the steep walls of a glaciated mountain valley #dad #dej4 ,lake ,garda1 a border lake upon the site of a piedmont apron #dad #dea4 ,diagrams to bring out the characteristics of ox-bow lakes #dae #deb4 ,diagrammatic section to illustrate the formation of saucer-like basins between the levees of streams on a flood plain #dae #dec4 ,saucer lakes upon the bed of the former river ,warren #daf #ded4 ,levee lakes developed in series within meanders in a delta plain #dag #dee4 ,raft lakes along the banks of the ,red ,river in ,arkansas and ,louisiana #dah #def4 ,map of the ,swiss lakes ,thun and ,brienz #dai #deg4 ,delta lakes formed at the mouth of the ,mississippi #dai #deh4 ,delta lakes at the margin of the ,nile delta #dbj #dei4 ,diagrams to illustrate the characteristics of barrier lakes #dbj #dfj4 ,dune lakes on the coast of ,france #dba #dfa4 ,sink lakes in ,florida1 with a schematic diagram to illustrate the manner of their formation #dba #dfb4 ,map of the ,arve and the ,upper ,rhone #dbf #dfc4 ,view of the ,arve and the ,rhone at their junction #dbg #dfd4 ,a village in ,switzerland built upon a strath at the head of ,lake ,poschiavo #dbh #dfe4 ,view of the floating bog and surrounding zones of vegetation in a small glacial lake #dbi #dff4 ,diagram to show how small lakes are transformed into peat bogs #dcj #dfg4 ,map to show the anomalous position of the delta in ,lake ,st4 ,clair #dca #dfh4 ,a bowlder wall upon the shore of a small lake #dcb #dfi4 ,diagrams to show the effect of ice shove in producing ice ramparts upon the shores of lakes #dcc #dgj4 ,various forms of ice ramparts #dcc #dga4 ,map of ,lake ,mendota1 showing the position of the ridge which forms from ice expansion and the ice ramparts upon the shores #dcd #dgb4 ,the great multiple mountain arc of ,sewestan1 ,british ,india #dcf #dgc4 ,diagrams to illustrate the theories of origin of mountain arcs #dcg #dgd4 ,festoons of mountain arcs about the borders of the ,pacific ,ocean #dch #dge4 ,the interrupted ,armorican ,mountains common to western ,europe and eastern ,north ,america #dch #dgf4 ,a zone of diverse displacement in the western ,united ,states #dci #dgg4 ,section of an ,east ,african block mountain #dci #dgh4 ,tilted crust blocks in the ,queantoweap valley #ddj #dgi4 ,view of the laccolite of the ,carriso ,mountain #dda #dhj4 ,map of laccolitic mountains #dda #dha4 ,ideal sections of laccolite and bysmalite #ddb #dhb4 ,the gabled faade largely developed in desert landscapes #ddc #dhc4 ,balloon view of the ,mythen in ,switzerland #ddd #dhd4 ,the battlement type of erosion mountain #dde #dhe4 ,symmetrically formed low islands repeated in ranks upon ,temagami ,lake1 ,ontario #dde #dhf4 ,forms of crystals of a number of minerals #ded #dhg4 ,forms of crystals of a number of minerals #deg #dhh4 ,a student's contour map #dfi #dhi4 ,models to represent outcrops of rock #dgb #dij4 ,special laboratory table set with a problem in geological mapping which is solved in ,figs4 #dg and #dh #dgb #dia4 ,three field maps to be used as suggestions in arranging laboratory table for problems in the preparation of areal geological maps #dgc #dib4 ,sketch map of ,western ,scotland and the ,inner ,hebrides to show location of some points of special geological interest #dha #dic4 ,outline map of a geological pilgrimage across the continent of ,europe #dhc ,,explanatory ,,list ,,of ,,abbreviations ,,for ,,journal ,,names ,,in ,,reading ,,references ,am4 ,geol43 ,american ,geologist4 ,am4 ,jour4 ,sci43 ,american ,journal of ,science1 ,new ,haven4 ,ann4 de ,gogr43 ,annales de ,gographie1 ,paris4 ,ann4 ,rept4 ,geol4 and ,geogr4 ,surv4 ,ter43 ,annual ,report of the ,geological and ,geographical ,survey of the ,territories 7,hayden71 ,washington4 ,ann4 ,rept4 ,geol4 and ,nat4 ,hist4 ,surv4 ,minn43 ,annual ,report of the ,geological and ,natural ,history ,survey of ,minnesota1 ,minneapolis4 ,ann4 ,rept4 ,mich4 ,geol4 ,surv43 ,annual ,report of the ,michigan ,geological ,survey1 ,lansing4 ,ann4 ,rept4 ,u4 ,s4 ,geol4 ,surv43 ,annual ,report of the ,united ,states ,geological ,survey1 ,washington4 ,bull4 ,am4 ,geogr4 ,soc43 ,bulletin of the ,american ,geographical ,society1 ,new ,york4 ,bull4 ,earthq4 ,inv4 ,com4 ,japan3 ,bulletin of the ,earthquake ,investigation ,committee of ,japan1 ,tokyo4 ,bull4 ,geogr4 ,soc4 ,philadelphia3 ,bulletin of the ,geographical ,society of ,philadelphia4 ,bull4 ,geol4 ,soc4 ,am43 ,bulletin of the ,geological ,society of ,america4 ,bull4 ,mus4 ,comp4 ,zol43 ,bulletin of the ,museum of ,comparative ,zology1 ,harvard ,college1 ,cambridge4 ,bull4 ,n4 ,y4 ,state ,mus43 ,bulletin of the ,new ,york ,state ,museum1 ,albany4 ,bull4 ,soc4 ,belge d',astronomie3 ,bulletin de la ,socit ,belge d',astronomie1 ,brussels4 ,bull4 ,soc4 ,belge ,gol43 ,bulletin de la ,socit ,belge de ,gologie1 ,brussels4 ,bull4 ,soc4 ,sc4 ,nat4 ,neuchtel3 ,bulletin de la ,socit des ,sciences ,naturelles de ,neuchtel4 ,bull4 ,univ4 ,calif4 ,dept4 ,geol43 ,bulletin of the ,university of ,california1 ,department of ,geology1 ,berkeley4 ,bull4 ,u4 ,s4 ,geol4 ,surv43 ,bulletin of the ,united ,states ,geological ,survey1 ,washington4 ,bull4 ,wis4 ,geol4 and ,nat4 ,hist4 ,surv43 ,bulletin of the ,wisconsin ,geological and ,natural ,history ,survey1 ,madison4 ,c4 ,r4 ,cong4 ,gol4 ,intern43 ,comptes ,rendus de la ,congrs ,gologique ,internationale4 ,dept4 of ,mines1 ,geol4 ,surv4 ,branch1 ,canada3 ,department of ,mines1 ,geological ,survey ,branch1 ,canada4 ,geogr4 ,abh43 ,geographische ,abhandlungen4 ,geogr4 ,jour43 ,geographical ,journal1 ,london4 ,geol4 ,folio ,u4 ,s4 ,geol4 ,surv43 ,geological ,folio of the ,united ,states ,geological ,survey4 ,geol4 ,mag43 ,geological ,magazine1 ,london 7sections designated by decades74 ,jour4 ,am4 ,geogr4 ,soc43 ,journal of the ,american ,geographical ,society1 ,new ,york4 ,jour4 ,coll4 ,sci4 ,imp4 ,univ4 ,tokyo3 ,journal of the ,college of ,science of the ,imperial ,university1 ,tokyo1 ,japan4 ,jour4 ,geol43 ,journal of ,geology1 ,chicago4 ,jour4 ,sch4 ,geogr43 ,journal of ,school ,geography4 ,livret ,guide ,cong4 ,gol4 ,intern43 ,livret ,guide ,congrs ,gologique ,internationale4 ,mem4 ,geol4 ,surv4 ,india3 ,memoirs of the ,geological ,survey of ,india1 ,calcutta4 ,mitt4 ,geogr4 ,ges4 ,hamb43 ,mitteilungen der ,geographische ,gesellschaft1 ,hamburg4 ,mon4 ,u4 ,s4 ,geol4 ,surv43 ,monograph of the ,united ,states ,geological ,survey1 ,washington4 ,nat4 ,geogr4 ,mag43 ,national ,geographic ,magazine1 ,washington4 ,nat4 ,geogr4 ,mon43 ,national ,geographic ,monographs1 ,american ,book ,company1 ,new ,york4 ,naturw4 ,wochenschr43 ,naturwissenschaftliche ,wochenschrift4 ,pet4 ,mitt43 ,petermanns ,mittheilungen aus ,justus ,perthes' ,geographischer ,anstalt1 ,gotha4 ,pet4 ,mitt41 ,ergnzungsh4 or ,erg43 ,petermanns ,mittheilungen1 ,gotha 7,ergnzungsheft or ,supplementary ,paper74 ,phil4 ,jour4 ,sci43 ,philippine ,journal of ,science1 ,manila4 ,phil4 ,trans43 ,philosophical ,transactions of the ,royal ,society1 ,london4 ,proc4 ,am4 ,acad4 ,arts and ,sci43 ,proceedings of the ,american ,academy of ,arts and ,sciences4 ,proc4 ,am4 ,assoc4 ,adv4 ,sci43 ,proceedings of the ,american ,association for the ,advancement of ,science4 ,proc4 ,am4 ,phil4 ,soc43 ,proceedings of the ,american ,philosophical ,society1 ,philadelphia4 ,proc4 ,bost4 ,soc4 ,nat4 ,hist43 ,proceedings of the ,boston ,society of ,natural ,history1 ,boston4 ,proc4 ,ind4 ,acad4 ,sci43 ,proceedings of the ,indiana ,academy of ,science4 ,proc4 ,linn4 ,soc4 ,new ,south ,wales3 ,proceedings of the ,linnean ,society of ,new ,south ,wales4 ,proc4 ,ohio ,state ,acad4 ,sci43 ,proceedings of the ,ohio ,state ,academy of ,science4 ,prof4 ,pap4 ,u4 ,s4 ,geol4 ,surv43 ,professional ,paper of the ,united ,states ,geological ,survey1 ,washington4 ,pub4 ,carneg4 ,inst43 ,publication of the ,carnegie ,institution of ,washington4 ,pub4 ,mich4 ,geol4 and ,biol4 ,surv43 ,publication of the ,michigan ,geological and ,biological ,survey1 ,lansing4 ,quart4 ,jour4 ,geol4 ,soc4 ,lond43 ,quarterly ,journal of the ,geological ,society1 ,london4 ,rept4 ,brit4 ,assoc4 ,adv4 ,sci43 ,report of the ,british ,association for the ,advancement of ,science4 ,rept4 ,geol4 ,surv4 ,mich43 ,report of the ,geological ,survey of ,michigan1 ,lansing4 ,rept4 ,mich4 ,acad4 ,sci43 ,report of the ,michigan ,academy of ,science1 ,lansing4 ,rept4 ,nat4 ,conserv4 ,com43 ,report of the ,national ,conservation ,commission1 ,washington4 ,rept4 ,smithson4 ,inst43 ,report of the ,smithsonian ,institution1 ,washington4 ,sci4 ,bull4 ,brooklyn ,inst4 ,arts and ,sci43 ,science ,bulletin of the ,brooklyn ,institute of ,arts and ,sciences4 ,scot4 ,geogr4 ,mag43 ,scottish ,geographic ,magazine1 ,edinburgh4 ,smith4 ,cont4 to ,knowl43 ,smithsonian ,contributions to ,knowledge1 ,washington4 ,tech4 ,quart43 ,technology ,quarterly of the ,massachusetts ,institute of ,technology1 ,boston4 ,trans4 ,am4 ,inst4 ,min4 ,eng43 ,transactions of the ,american ,institute of ,mining ,engineers1 ,new ,york4 ,trans4 ,roy4 ,dublin ,soc43 ,transactions of the ,royal ,dublin ,society4 ,trans4 ,seis4 ,soc4 ,japan3 ,transactions of the ,seismological ,society of ,japan1 ,tokyo4 ,trans4 ,wis4 ,acad4 ,sci43 ,transactions of the ,wisconsin ,academy of ,sciences1 ,arts1 and ,letters1 ,madison4 ,u4 ,s4 ,geogr4 and ,geol4 ,surv4 ,rocky ,mt4 ,region3 ,united ,states ,geographical and ,geological ,survey of the ,rocky ,mountain ,region 7,powell71 ,washington4 ,zeit4 d4 ,gesell4 f4 ,erdk4 z4 ,berlin3 ,zeitschrift der ,gesellschaft fr ,erdkunde zu ,berlin4 ,zeit4 f4 ,gletscherk3 ,zeitschrift fr ,gletscherkunde1 ,berlin4 ,,earth ,,features ,,and ,,their ,,meaning ,,chapter ,i ,,the ,,compilation ,,of ,,earth ,,history ,the sources of the history4--,the science which deals with the chapters of earth history that antedate the earliest human writings is geology4 ,the pages of the record are the layers of rock which make up the outer shell of our world4 ,here as in old manuscripts pages are sometimes found to be missing1 and on others the writing is largely effaced so as to be indistinct or even illegible4 ,an intelligent interpretation of this record requires a knowledge of the materials and the structure of the earth1 as well as a proper conception of the agencies which have caused change and so developed the history4 ,these agencies in operation are physical and chemical processes1 and so the sciences of physics and chemistry are fundamental in any extended study of geology4 ,not only is geology1 so to speak1 founded upon chemistry and physics1 but its field overlaps that of many other important sciences4 ,the earliest earth history has to do with the form1 size1 and physical condition of a minor planet in the solar system4 ,the earliest portion of the story belongs therefore to astronomy1 and no sharp line can be drawn to separate this chapter from those later ones which are more clearly within the domain of geology4 ,subdivisions of geology4--,the terms 8cosmic geology0 and 8astronomic geology0 have sometimes been used to cover the astronomy of the earth planet4 ,the later earth history develops1 among other things1 the varied forms of animal and vegetable life which have had a definite order of appearance4 ,their study is to a large extent zology and botany1 though here considered from an essentially different viewpoint4 ,this subdivision of our science is called paleontological geology or paleontology1 which in common usage includes the plant as well as the animal world1 or what is sometimes called paleobotany4 ,in order to fix the order of events in geological history1 these biological studies are necessary1 for the pages of the record have many of them been misplaced as a result of the vicissitudes of earth history1 and the remains of life in the rock layers supply a pagination from which it is possible to correctly rearrange the misplaced pages4 ,as compiled into a consecutive history of the earth since life appeared upon it1 we have the division of historical geology2 though this differs but little from stratigraphical geology1 the emphasis in the case of the former being placed on the history itself and in the latter upon the arrangement of events--the pagination of the record4 ,so far as they are known to us1 the materials of which the earth is composed are minerals grouped into various characteristic aggregates known as rocks4 ,here the science is founded upon mineralogy as well as chemistry1 and a study of the rock materials of the earth is designated petrographical geology or petrography4 ,the various rocks which enter into the composition of the earth's outer shell--the only portion known to us from direct observation--are built into it in an architecture which1 when carefully studied1 discloses important events in the earth's history4 ,the division of the science which is concerned with earth architecture is geotectonic or structural geology4 ,the study of earth features and their significance4--,the features upon the surface of the earth have all their deep significance1 and if properly understood1 a flood of light is thrown1 not only upon present conditions1 but upon many chapters of the earth's earlier history4 ,here the relation of our study to topography and geography is very close1 so that the lines of separation are but ill defined4 ,the terms 8physiographical geology01 8physiography01 and 8geomorphology0 are concerned with the configuration of the earth's surface--its physiognomy--and with the genesis of its individual surface features4 ,it is this genetical side of physiography which separates it from topography and lends it an absorbing interest1 though it causes it to largely overlap the division of dynamical geology or the study of geological processes4 ,in fact1 the difference between dynamical geology and physiography is largely one of emphasis1 the stress being laid upon the processes in the former and upon the resultant features in the latter4 ,under dynamical geology are included important subdivisions1 such as seismic geology1 or the study of earthquakes1 and vulcanology1 or the study of volcanoes4 ,another large subject1 glacial geology1 belongs within the broad frontier common to both dynamical geology and physiography4 ,a relatively new subdivision of geological science is orientational geology1 which is concerned with the trend of earth features1 and is closely related both to physiography and to dynamical and structural geology4 ,tabular recapitulation4--,in a slightly different arrangement from the above order of mention1 the subdivisions of geology are as follows3-- ,subdivisions of ,geology ,petrographical ,geology4 ,materials of the earth4 ,geotectonic ,geology4 ,architecture of the earth's outer shell4 ,dynamical ,geology4 ,earth processes4 ,seismic ,geology--earthquakes4 ,vulcanology--volcanoes4 ,glacial ,geology--glaciers1 etc4 ,physiographical ,geology4 ,earth physiognomy and its genesis4 ,orientational ,geology4 ,the arrangement and the trend of earth features4 ,in one way or another all of the above subdivisions of geology are in some way concerned in the genesis of earth physiognomy1 and they must therefore be given consideration in a work which is devoted to a study of the meaning of earth features4 ,the compiled record of the rocks is1 however1 something quite apart and without pertinence to the present work4 ,as already indicated its subdivisions are3-- ,astronomic ,geology4 ,planetary history of the earth4 ,statigraphic ,geology4 ,the pagination of earth records4 ,historical ,geology4 ,the compiled record and its interpretation4 ,paleontological ,geology4 ,the evolution of life upon the earth4 ,in every attempt at systematic arrangement difficulties are encountered1 usually because no one consideration can be used throughout as the basis of classification4 ,such terms as 8economic geology0 and 8mining geology0 have either a pedagogical or a commercial significance1 and so would hardly fit into the system which we have outlined4 ,geological processes not universal4--,it is inevitable that the geology of regions which are easily accessible for study should have absorbed the larger measure of attention2 but it should not be forgotten that geology is concerned with the history of the entire world1 and that perspective will be lost and erroneous conclusions drawn if local conditions are kept too often before the eyes4 ,to illustrate by a single instance1 the best studied regions of the globe are those in which fairly abundant precipitation in the form of rain has fitted the land for easy conditions of life1 and has thus permitted the development of a high civilization4 ,in degree1 and to some extent also in kind1 geologic processes are markedly different within those widely extended regions which1 because either arid or cold1 have been but ill fitted for human habitation4 ,yet in the historical development of the earth1 those geologic processes which obtain in desert or polar regions are none the less important because less often and less carefully observed4 ,change1 and not stability1 the order of nature4--,man is ever prone to emphasize the importance of apparent facts to the disadvantage of those less clearly revealed though equally potent4 ,the ancient notion of the terra firma1 the safe and solid ground1 arose because of its contrast with the far more mobile bodies of water2 but this illusion is quickly dispelled with the sudden quaking of the ground4 ,experience has clearly shown that1 both upon and beneath the earth's surface1 chemical and physical changes are going on1 subject to but little interruption4 8,the hills rock-ribbed and ancient as the sun0 is a poetical metaphor2 for the ,himalayas1 the loftiest mountains upon the globe1 were1 to speak in geological terms1 raised from the sea but yesterday4 ,even to-day they are pushing up their heads1 only to be relentlessly planed down through the action of the atmosphere1 of ice1 and of running water4 ,even more than has generally been supposed1 the earth suffers change4 ,often within the space of a few seconds1 to the accompaniment of a heavy earthquake1 many square miles of territory are bodily uplifted1 while neighboring areas may be relatively depressed4 ,thus change1 and not stability1 is the order of nature4 ,observational geology versus speculative philosophy4--,there appears to be a more or less prevalent notion that the views which are held by scientists in one generation are abandoned by those of the next2 and this is apt to lead to the belief that little is really known and that much is largely guessed4 ,some ground there undoubtedly is for such skepticism1 though much of it may be accounted for by a general failure among scientists1 as well as others1 to clearly differentiate that which is essentially speculative from what is based broadly upon observed facts4 ,even with extended observation1 the possibility of explaining the facts in more than one way is not excluded2 but the line is nevertheless a broad one which separates this entire field of observation from what is essentially speculative philosophy4 ,to illustrate3 the mechanics of the action which goes on within volcanic craters is now fairly well understood as a result of many and extended observations1 and it is little likely that future generations of geologists will discredit the main conclusions which have been reached4 ,the cause of the rise of the lava to the earth's surface is1 on the other hand1 much less clearly demonstrated1 and the views which are held express rather the differing opinions than any clear deductions from observation4 ,again1 and similarly1 the physical history of the great continental glaciers of the so-called 8ice age0 is far more thoroughly known than that of any existing glacier of the same type2 but the cause of the climatic changes which brought on the glaciation is still largely a matter for speculation4 ,in the present work1 the attempt will be1 so far as possible1 to give an exposition of geologic processes and the earth features which result from them1 with hints only at those ultimate causes which lie hidden in the background4 ,the scientific attitude and temper4--,the student of science should make it his aim1 not only clearly to separate in his studies the proximate from the ultimate causes of observed phenomena1 but he should keep his mind always open for reaching individual conclusions4 ,no doctrines should be accepted finally upon faith merely1 but subject rather to his own reasoning processes4 ,this should not be interpreted to mean that concerning matters of which he knows little or nothing he should not pay respect to the recognized authorities2 but his acceptance of any theory should be subject to review so soon as his own horizon has been sufficiently enlarged4 ,false theories could hardly have endured so long in the past1 had not too great respect been given to authorities1 and individual reasoning processes been held too long in subjection4 ,the value of the hypothesis4--,because all the facts necessary for a full interpretation of observed phenomena are not at one's hand1 this should not be made to stand in the way of provisional explanations4 ,if science is to advance1 the use of hypothesis is absolutely essential2 but the particular hypothesis adopted should be regarded as temporary and as indicating a line of observation or of experimentation which is to be followed in testing it4 ,thus regarded with an open mind1 inadequate hypotheses are eventually found to be untenable1 whereas correct explanations of the facts by the same process are confirmed4 ,most hypotheses of science are but partially correct1 for we now 8see through a glass darkly02 but even so1 if properly tested1 the false elements in the hypothesis are one after the other eliminated as the embodied truth is confirmed and enlarged4 ,thus 8working hypothesis0 passes into theory and becomes an integral part of science4 ,,reading ,,references ,,for ,,chapter ,i ,the most comprehensive of general geological texts written in ,english is ,chamberlin and ,salisbury's 8,geology0 in three volumes 7,henry ,holt1 #aijd-aijf71 the first volume of which is devoted exclusively to geological processes and their results4 ,an abridged one-volume edition of the work intended for use as a college text was issued in #aijf 7,college ,geology1 ,henry ,holt74 ,other standard texts are3-- ,,sir ,,archibald ,,geikie4 ,text-book of ,geology1 #dth ed4 #b vols4 ,london1 #aijb1 pp4 #adgb4 ,w4 ,b4 ,,scott4 ,an ,introduction to ,geology4 #b;d ed4 ,macmillan1 #aijg1 pp4 #haf4 ,j4 ,d4 ,,dana4 ,manual of ,geology4 ,new edition4 ,american ,book ,company1 #ahie1 pp4 #ajhg4 ,,joseph ,,leconte4 ,elements of ,geology4 7,revised by ,fairchild47 ,appleton1 #aije1 pp4 #ffg4 ,a very valuable guide to the recent literature of dynamical and structural geology is ,branner's 8,syllabus of a ,course of ,lectures on ,elementary ,geology0 7,stanford ,university1 #aijh74 ,on the relation of geology to landscape1 a number of interesting books have been written3-- ,,james ,,geikie4 ,earth ,sculpture or the ,origin of ,land-,forms4 ,new ,york and ,london1 #ahif1 pp4 #cig4 ,,john ,e4 ,,marr4 ,the ,scientific ,study of ,scenery4 ,methuen1 ,london1 #aijj1 pp4 #cfh4 ,,sir ,a4 ,,geikie4 ,the ,scenery of ,scotland4 #c;d ed4 ,macmillan1 ,london1 #aija1 pp4 #edj4 ,,sir ,,john ,,lubbock4 ,the ,scenery of ,switzerland and the ,causes to which it is ,due4 ,macmillan1 ,london1 #ahif1 pp4 #dhj4 ,,lord ,,avebury4 ,the ,scenery of ,england4 ,macmillan1 ,london1 #aijb1 pp4 #ecd4 ,,sir ,a4 ,,geikie4 ,landscape in ,history1 and ,other ,essays4 ,macmillan1 ,london1 #aije1 pp4 #ceb4 ,n4 ,s4 ,,shaler4 ,aspects of the ,earth4 ,scribners1 ,new ,york1 #ahhi1 pp4 #cdd4 ,g4 ,,de ,,la ,,noe ,,et ,,emm4 ,,de ,,margerie4 ,les ,formes du ,terrain1 ,service ,gographique de l',arme4 ,paris1 #ahhh1 pp4 #bje1 pls4 #dh4 ,w4 ,m4 ,,davis4 ,practical ,exercises in ,physical ,geography1 with ,accompanying ,atlas4 ,ginn and ,co41 ,boston1 #aijh1 pp4 #adh1 pls4 #de4 ,,john ,,muir4 ,the ,mountains of ,california4 ,unwin1 ,london1 #ahid1 pp4 #cha4 ,upon the use and interpretation of topographic maps in illustration of characteristic earth features1 the following are recommended3-- ,r4 ,d4 ,,salisbury and ,w4 ,w4 ,,atwood4 ,the ,interpretation of ,topographic ,maps1 ,prof4 ,pap41 #fj ,u4,s4 ,geol4 ,surv41 pp4 #hd1 pls4 #agj4 ,d4 ,w4 ,,johnson and ,f4 ,e4 ,,matthes4 ,the ,relation of ,geology to ,topography1 in ,breed and ,hosmer's ,principles and ,practice of ,surveying1 vol4 #b4 ,wiley1 ,new ,york1 #aijh4 ,g,n,,ral ,,berthaut4 ,topologie1 tude du ,terrain1 ,service ,gographique de l',arme4 ,paris1 #aiji1 #b vols41 pp4 #ccj and #fgd1 pls4 #bfe4 ,the ,united ,states ,geological ,survey issues free of charge a list of #ajj topographic atlas sheets which illustrate the more important physiographic types4 ,in his 8,trait de ,gographie ,physique01 ,professor ,e4 de ,martonne has given at the end of each chapter the important foreign maps which illustrate the physiographic types there described4 8,the ,principles of ,geology01 by ,sir ,charles ,lyell1 published first in three volumes1 appeared in the years #ahcj-ahcc1 and may be said to mark the beginning of modern geology4 ,later reduced to two volumes1 an eleventh edition of the work was issued in #ahgb 7,appleton7 and may be profitably read and studied to-day by all students of geology4 ,those familiar with the ,german language will derive both pleasure and profit from a perusal of ,neumayr's 8,erdgeschichte0 7#b;d ed4 revised by ,uhlig4 ,leipzig and ,vienna1 #b vols41 #ahie-ahig71 and especially the first volume1 8,allgemeine ,geologie40 ,a recent ,french work to be recommended is ,haug's 8,trait de ,gologie0 7,paris1 #aijg74 ,some texts of physical geography may well be consulted1 especially ,emm4 de ,martonne's 8,trait de ,gographie ,physique40 ,colin1 ,paris1 #aiji1 pp4 #iaj1 pls4 #dh1 and figs4 #cif4 99 99 99 99 99 ,,note4 ,an explanatory list of abbreviations used in the reading references follows the ,list of ,illustrations4 ,,chapter ,,ii ,,the ,,figure ,,of ,,the ,,earth ,the lithosphere and its envelopes4--,the stony part of the earth is known as the lithosphere1 of which only a thin surface shell is known to us from direct observation4 ,the relatively unknown central portion1 or 8core01 is sometimes referred to as the centrosphere4 ,inclosing the lithosphere is a water envelope1 the hydrosphere1 which comprises the oceans and inland bodies of water1 and has a mass #a_/dedj that of the lithosphere4 ,if uniformly distributed1 the hydrosphere would cover the lithosphere to the depth of about two miles1 instead of being collected in basins as it now is4 ,though apparently not continuous1 if we take into account the zone of underground water upon the continents1 the hydrosphere may properly be considered as a continuous film about the lithosphere4 ,it is a fact of much significance that all the ocean basins are connected1 so that the levels are adjusted to furnish a common record of deposits over the entire surface that is sea-covered4 ,enveloping the hydrosphere is the gaseous envelope1 the atmosphere1 with a mass #a_/abjjjjj that of the lithosphere4 ,the atmosphere is a mixture of the gases oxygen and nitrogen in parts by volume of one of the former to four of the latter1 with a relatively small percentage of carbon dioxide4 ,locally1 and at special seasons1 the atmosphere may be charged with relatively large percentages of water vapor2 and we shall see that both the carbon dioxide and the vapor contents are of the utmost importance in geological processes and in the influence upon climate4 ,unlike the water which composes the hydrosphere1 the gases of the atmosphere are compressible4 ,forced down by the weight of superincumbent gas1 the layers of the atmosphere at the level of the sea sustain a pressure of about fifteen pounds to the square inch2 but this pressure steadily decreases in ascending to higher levels4 ,from direct instrumental observation1 the air has now been investigated to a height of more than twelve miles from the earth's surface4 ,the evolution of ideas concerning the earth's figure4--,the ideas which in all ages have been promulgated concerning the figure of the earth have been many and varied4 ,though among them are not wanting the purely speculative and fantastic1 it will be interesting to pass in review such theories as have grown directly out of observation4 ,the ancient ,hebrews and the ,babylonians were dwellers of the desert1 and in the mountains which bounded their horizon they saw the confines of the earth4 ,pushing at last westward beyond the mountains1 they found the ,mediterranean1 and thus arrived at the view that the earth was a disk with a rim of mountains which was floated upon water4 ,the rare but violent rainfalls to which they were accustomed--the desert cloudburst--further led them to the belief that the mountain rim was continued upward in a dome or firmament of transparent crystal upon which the heavenly bodies were hung and from which out of 8windows of heaven0 the water 8which is above the earth0 was poured out upon the earth's surface4 ,fantastic as this theory may seem to-day1 it was founded upon observation1 and it well illustrates the dangers of reasoning from observation within too limited a field4 ,as soon as men began to sail the sea1 it was noticed that the water surface is convex1 for the masts of ships were found to remain visible long after their hulls had disappeared below the horizon4 ,it is difficult to say how soon the idea of the earth's rotundity was acquired1 but it is certainly of great antiquity4 ,the ,dominican monk ,vincentius of ,beauvais1 in a work completed in #abdd1 declared that the surfaces of the earth and the sea were both spherical4 ,the poet ,dante made it clear that these surfaces were one1 and in his famous address upon 8,the ,water and the ,land01 which was delivered in ,verona on the #bjth of ,january1 #acbj1 he added a statement that the continents rise higher than the ocean4 ,his explanation of this was that the continents are pulled up by the attraction of the fixed stars after the manner of attraction of magnets1 thus giving an early hint of the force of gravitation4 ,the earth's rotundity may be said to have been first proven when ,magellan's ships in #aeba had accomplished the circumnavigation of the globe4 ,circumnavigation1 soon after again carried out by ,sir ,francis ,drake1 proved that the earth is a closed body bounded by curving surfaces in part enveloped by the oceans and everywhere by the atmosphere4 ,the great discovery of ,copernicus in #aecj that the earth1 like ,venus1 ,mars1 and the other planets1 revolves about the sun as a part of a system1 left little room for doubt that the figure of the earth was essentially that of a sphere4 ,the oblateness of the earth4--,every schoolboy is to-day familiar with the fact that the earth departs from a perfect spherical figure by being flattened at the ends of its axis of rotation4 ,the polar diameter is usually given as #a_/bii shorter than the equatorial one4 ,this oblateness of the spheroid was proven by geodesists when they came to compare the lengths of measured degrees of arc upon meridians in high and in low latitudes4 ,illustration3 ,,fig4 #a4--;,diagrams to afford a correct impression of the measure of the inequalities upon the earth's surface compared to the earth's radius4 ,the shell represented in b is #a_/ajj of the earth's radius1 and in a this zone is magnified for comparison with surface inequalities4 ,the oblateness of the geoid is well understood from accepted hypotheses to be the result of the once more rapid rotation of the planet when its materials were more plastic1 and hence more responsive to deformation4 ,an elastic hoop rotating rapidly about an axis in its plane appears to the eye as a solid1 and becomes flattened at the ends of its axis in proportion as the velocity of rotation is increased4 ,like the earth1 the other planets in the solar system are similarly oblate and by amounts dependent on the relative velocities of rotation4 ,the departure of the geoid from the spherical surface1 owing to its oblateness1 is so small that in the figures which we shall use for illustration it would be less than the thickness of a line4 ,since it is well recognized and not important in our present consideration1 we shall for the time being speak of the figure of the earth in terms of departures from a standard spherical surface4 ,the arrangement of oceans and continents4--,there are other departures from a spherical surface than the oblateness just referred to1 and these departures1 while not large1 are believed to be full of significance4 ,lest the reader should gain a wrong impression of their magnitude1 it may be well to introduce a diagram drawn to scale and representing prominent elevations and depressions of the earth 7,fig4 #a74 ,wrong impressions concerning the figure of the lithosphere are sometimes gained because its depressions are obliterated by the oceans4 ,the oceans are1 indeed1 useful to us in showing where the depressions are located1 but the figure of the earth which we are considering is the naked surface of the rock4 ,in a broad way1 the earth's shape will be given by the arrangement of the oceans and the continents4 ,as soon as we take up the study of this arrangement1 we find that quite significant facts of distribution are disclosed4 ,illustration3 ,,fig4 #b4--,map on ,mercator's projection to show the reciprocal relation of the land and sea areas 7after ,gregory and ,arldt74 ,one of the most significant facts involved in the distribution of land and sea1 is a concentration of the land areas within the northern and the seas within the southern hemisphere4 ,the noteworthy exception is the occurrence of the great and high ,antarctic continent centered near the earth's south pole2 and there are extensions of the northern continent as narrowing land masses to the southward of the equator4 ,hardly less significant than the existence of land and water hemispheres is the reciprocal or antipodal distribution of land and sea 7,fig4 #b74 ,a third fact of significance is a dovetailing together of sea and land along an east-and-west direction4 ,while the seas are generally ,a-shaped and narrow northward1 the land masses are ,v-shaped and narrow southward1 but this occurs mainly in the southern hemisphere4 ,lastly1 there is some indication of a belt of sea dividing the land masses into northern and southern portions along the course of a great circle which makes a small angle with the earth's equator4 ,thus the western continent is nearly divided by a mediterranean sea1--the ,caribbean1--and the eastern is in part so divided by the separation of ,europe from ,africa4 ,illustration3 ,,fig4 #c4--,the form toward which the figure of the earth is tending1 a tetrahedron with symmetrically truncated angles4 ,the figure toward which the earth is tending4--,thus far in our discussion of the earth's figure we have been guided entirely by the present distribution of land and water4 ,there are1 however1 depressions upon the surface of the land1 in some cases extending below the level of the sea1 which are not to-day occupied by water4 ,by far the most notable of these is the great ,caspian ,depression1 which with its extension divides central and eastern ,asia upon the east from ,africa and ,europe upon the west4 ,this depression was quite recently occupied by the sea1 and when added to the present ocean basins to indicate depressions of the lithosphere1 it shows that the earth's figure departs from the standard spheroid in the direction of the form represented in ,fig4 #c4 ,this form approximates to a tetrahedron1 a figure bounded by four equal triangular faces1 here with symmetrically truncated angles4 ,of all regular figures with plane surfaces the tetrahedron has the smallest volume for a given surface1 and it presents moreover a reciprocal relation of projection to depression4 ,every line passing through its center thus finds the surface nearer than the average distance upon one side and correspondingly farther upon the other 7,fig4 #d74 ,astronomical versus geodetic observations4--,confirmation of the conclusions arrived at from the arrangement of oceans and continents has been secured in other fields4 ,it was pointed out that the earth's oblateness was proven by comparison of the measured degrees of latitude upon the earth's surface in lower and higher latitudes1 the degree being found longer as the pole is approached4 ,any variation from the spherical surface must obviously increase the size of the measured degree of latitude in proportion to the departure from the standard form1 and so the tetrahedral figure with one of its angles at the south pole will require that the degrees of latitude be longer in the southern than they are in the northern hemisphere4 ,this has been found by measurement to be the case1 and the result is further confirmed by pendulum studies upon the distribution of the earth's attraction or gravity4 ,if less of the mass of the earth is concentrated in the southern hemisphere1 its attraction as measured in vibrations of the pendulum should be correspondingly smaller4 ,illustration3 ,,fig4 #d4--;,a truncated tetrahedron1 showing how the depression upon one side of the center is balanced by the opposite projection4 ,other confirmations of the tetrahedral figure of the earth have been derived from a comparison of astronomical data1 which assume the earth to be a perfect spheroid1 with geodetic measurements1 which are based upon direct measurements4 ,thus the arc measured in an east-and-west direction across ,europe revealed a different curvature near the angle of the tetrahedral figure from what was found farther to the eastward4 ,changes of figure during contraction of a spherical body4--,if we inquire why the earth in cooling should tend to approach the tetrahedral figure1 an answer is easily found4 ,when formed1 the earth appears to have been a but slightly oblate spheroid1 or practically a sphere--the shape which of all incloses the most space for a given surface4 ,cooled and solidified at the surface to the temperature of the surrounding air1 and the core still hot and continuing to lose heat1 the core must continue to contract though the outer shell is no longer able to do so4 ,the superficial area being thus maintained constant while the volume continues to diminish1 the figure must change from the initial one of greatest bulk to others of smaller volume1 and ultimately1 if the process should continue indefinitely1 to the tetrahedron1 which of all regular figures has the minimum volume for a given surface4 ,that a contracting sphere does indeed pass through such a series of changes has been shown by the behavior of contracting soap bubbles and of rubber balloons1 as well as by experiments upon the exhaustion of air contained in hollow metal spheres of only moderate strength4 ,in all these instances1 the ultimate form produced indicates an indenting of four sides of the sphere which have the positions of the faces of a tetrahedron4 ,the late ,professor ,prinz of ,brussels secured some extremely interesting results in which he obtained intermediate forms with six angles1 but unfortunately these studies were not prepared for publication at the time of his death4 ,the earth's departure from the spheroid in the direction of the modified tetrahedron is1 as we have seen1 no hypothesis1 but observed fact revealed in 7#a7 the concentration of the land about a central ocean in the northern hemisphere2 in 7#b7 the antipodal relation of the land to the water areas1 and in 7#c7 the threefold subdivision of the surface into north and south belts by the two greater oceans and the ,caspian ,depression4 ,the earlier figures of the earth4--,the manner in which continent and ocean are dovetailed into each other in an east-and-west direction has been generally adduced as additional evidence for the tetrahedral figure as above described4 ,closer examination shows that instead of being in harmony with this figure1 it indicates a departure from it1 and1 as we shall see1 a significant departure which undoubtedly has its origin in the earlier history of the planet4 ,the mediterranean seas of both the eastern and the western hemispheres likewise interfere with the perfection of the tetrahedral figure and require an explanation4 ,let us then examine in outline the past history of the world with reference especially to the evolution of the continents and to the times and the manners of surface change4 ,it is now well known that there have been three major periods of great deformation of the earth's shell4 ,the first of these of which we have record came at the end of the first great era of geologic history1 the so-called ,eozoic era2 a second great transformation came at the close of the second or ,paleozoic era2 and a third began at the end of the next or ,mesozoic era1 an adjustment which is apparently continuing to-day4 ,each of these great surface deformations was accompanied by great volcanic eruptions of which we have the evidence in the lavas remaining for our inspection1 and each was followed by the formation of great glaciers which spread over large areas of the existing continents4 ,before the earliest of these great changes1 the earth appears to have approximated in its figure somewhat closely to the ideal spheroid1 for it was everywhere enveloped in the hydrosphere as a universal ocean4 ,toward the close of this period came the adjustments which brought the lithosphere to protrude through the hydrosphere in shield-like continents whose distribution1 as shown by the rocks of this period1 is of great significance4 ,within the northern hemisphere rose three land shields spaced at nearly equal intervals and at nearly equal distances from the northern pole4 ,one of these was centered where now is ,hudson ,bay1 another about the present ,baltic ,sea1 and the relics of the third are found in northeastern ,siberia4 ,these earliest continents have been referred to as the ,laurentian1 ,baltic1 and ,angara shields4 ,within the southern hemisphere shields appear to have developed in somewhat similar grouping1 namely1 in ,south ,america1 in ,south ,africa1 and in ,australia 7,figs4 #c and #e74 ,illustration3 ,,fig4 #e4--;,approximations to earlier and present figures of the earth4 ,these coigns or angles of a form into which the earlier spheroid of the earth was being transformed have persisted through the greater part of subsequent geologic time1 and have been enlarged by the growth of sediments about them as well as by the later elevation and wrinkling of these deposits into marginal mountain ranges4 ,the continents and oceans which arose at the close of the ,paleozoic era4--,at the close of the second great era in the recorded history of the earth1 the now somewhat enlarged continents were profoundly altered during a series of convulsive movements within the surface shell of the lithosphere4 ,when these convulsions were over1 there was a new disposition of land and sea1 but one quite different from the present arrangement4 ,instead of being extended in north-south belts1 as they are at present1 the continents stretched out in broad east-west zones1 one in the northern and the other in the southern hemisphere4 ,to the broad southern continent of which so little now remains1 the name 8,gondwana ,land0 has been given1 and to the sea which divided the northern from the southern continent the name 8,ocean of ,tethys40 ,the northern continent stretched across the site of the present ,atlantic ,ocean as the 8,north ,atlantis01 its northern shore to the westward being somewhat farther south than the present northern coast of ,north ,america1 since life forms migrated in the northern ocean from the site of ,behring ,sea to that of the present ,north ,atlantic4 ,this arrangement of land and water during the middle period of the earth's recorded history1 when considered with reference both to its earlier and to its later evolution1 may perhaps be best accounted for by the assumption that the lithosphere was then shaped like ,fig4 #e 7middle74 ,in this figure two truncated tetrahedrons are joined in a common plane of contact which may be described as the twin plane4 ,this medial depression upon the lithosphere was occupied by the intercontinental sea1 the ,ocean of ,tethys4 ,near the close of this second great era of the earth's continental history1 crustal convulsions1 which were perhaps the most remarkable in the entire record1 resulted in the almost complete disappearance of the southern continent and a concentration of the land within the northern hemisphere as a somewhat interrupted belt surrounding a central polar ocean 7,figs4 #c and #e74 ,upon the assumption of twin tetrahedrons in the intermediate era of continental evolution1 both the ,ocean of ,tethys of that time and its present remnants1 the ,caribbean and ,mediterranean seas1 are accounted for4 ,the ,v-shaped continent extensions and the ,a-shaped oceans of the southern hemisphere 7,fig4 #b7 may likewise be considered as relics of the now largely submerged tetrahedron of the southern hemisphere1 since this had its apex to the northward 7,fig4 #f74 ,illustration3 ,,fig4 #f4--;,diagrams for comparison of shore lines upon tetrahedrons which have an angle1 the first at the south and the second at the north4 ,thus we see that the lithosphere can scarcely be regarded as a perfect spheroid1 since in the course of geologic ages it has undergone successive departures from this original form4 ,in its present state it has been described as tetrahedral1 though we must keep in mind that the sharp angles of that figure are deeply truncated4 ,the soundings first by ,nansen and more recently by ,peary in the ,arctic basin1 far to the north of the continental border1 showed that this depression is characterized by profound depths1 and so have afforded confirmation of the tetrahedral figure4 ,to match this depression at the northern extremity of the earth's axis1 a high continent reaching to elevations in excess of #aj1jjj feet has been penetrated by ,sir ,ernest ,shackleton at the opposite extremity of this polar diameter4 ,considering its size and its elevation1 the ,antarctic continent with its glacier mantle is the largest protuberance upon the surface of the lithosphere4 ,in our study of the departures of the earth from the standard spheroidal surface1 we might even go a step farther and show how the tetrahedron1 which best represents the symmetry of the present figure1 is somewhat deformed by a flattening perpendicular to the ,pacific ,ocean4 ,to draw attention to this flattening of the earth1 it has sometimes been described as 8potato-shaped01 since the outline perpendicular to this face is imperfectly heart-shaped or like a flattened 8peg top40 ,illustration3 ,,fig4 #g4--,the continents with submerged portions added 7after ,gilbert74 ,the flooded portions of the present continents4--,we are accustomed to think of the continents as ending at the shores of the oceans4 ,if1 however1 we are to regard them as platforms which rise from the ocean depressions1 their margins should be considerably extended1 for a submerged shelf now practically surrounds all the continents to a nearly uniform depth of #ajj fathoms or #fjj feet4 ,the oceans thus more than fill their basins and may be thought of as spilling over upon the continents4 ,in ,fig4 #g1 the submerged portions of the continents have been joined to those usually represented1 thus adding about #aj1jjj1jjj square miles to their area1 and giving them one third1 instead of one fourth1 of the lithosphere surface4 ,illustration3 ,,fig4 #h4--;,diagram to indicate the altitude of different parts of the lithosphere surface4 ,the floors of the hydrosphere and atmosphere4--,the highest altitudes upon the continents and the profoundest deeps of the ocean are each removed about #cj1jjj feet1 or nearly #f miles1 from the level of the sea4 ,in comparison with the entire surface of the lithosphere1 these extremes of elevation represent such small areas as to be almost inappreciable4 ,only about #a_/hj of the lithosphere surface rises more than #fjjj feet above sea level1 and about the same proportion lies deeper than #ah1jjj feet below the same datum plane 7,fig4 #h74 ,almost the entire area of the lithosphere is included either in the so-called continental plateau or platform1 in the oceanic platform1 or in the slope which separates the two4 ,the continental platform includes the continental shelf above referred to1 and represents about one third of the entire area of the planet4 ,this platform has a range of elevation from #fjjj feet above to #fjj feet below sea level and has an average altitude of about #bcjj feet4 ,the oceanic platform slopes more steeply1 ranges in depth from #ab1jjj to #ah1jjj feet below sea level1 and comprises about one half the lithosphere surface4 ,the remaining portion of the surface1 something less than one eighth of all1 is included in the steep slopes between the two platforms1 between #fjj and #ab1jjj feet below sea4 ,the two platforms and the slope between them must not1 however1 be thought of as continuous features upon the surface1 but merely as representing the average elevations of portions of the lithosphere4 ,,reading ,,references ,,for ,,chapter ,,ii ,on the evolution of ideas concerning the earth's figure3-- ,,suess4 ,the ,face of the ,earth 7,clarendon ,press1 #aijf71 vol4 #b1 ,chapter #a4 ,v4 ,,zittel4 ,history of ,geology and ,paleontology 7,walter ,scott1 ,london1 #aija71 ,chapters #a-b4 ,the departure of the spheroid toward the tetrahedron3-- ,w4 ,,lowthian ,,green4 ,vestiges of the ,molten ,globe1 ,part #a4 ,london1 #ahge4 7,now a rare work1 but it contains the original statement of the idea47 ,j4 ,w4 ,,gregory4 ,the ,plan of the ,earth and ,its ,causes1 ,geogr4 ,jour41 vol4 #ac1 #ahii1 pp4 #bbe-bea 7the best general statement of the arguments for a tetrahedral form74 ,w4 ,,prinz4 ,l'chelle reduite des expriences gologiques1 ,bull4 ,soc4 ,belge d',astronomie1 #ahii4 ,b4 ,k4 ,,emerson4 ,the ,tetrahedral ,earth and ,zone of the ,intercontinental ,seas1 ,bull4 ,geol4 ,soc4 ,am41 vol4 #aa1 #aiaa1 pp4 #fa-ajf1 pls4 #i-ad4 ,m4 ,p4 ,,rudski4 ,physik der ,erde 7,tauchnitz1 ,leipzig1 #aiaa71 ,chapters #a-c 7the best discussion of the geoid from the purely mathematical standpoint1 so far as the spheroid is concerned74 ,the earlier figures of the earth3-- ,,th4 ,,arldt4 ,die ,entwicklung der ,kontinente und ihrer ,lebewelt4 ,engelmann1 ,leipzig1 #aijg4 7,contains a valuable series of map plates1 showing the probable boundaries of the continents in the different geological periods74 ,,chapter ,,iii ,,the ,,nature ,,of ,,the ,,materials ,,in ,,the ,,lithosphere ,the rigid quality of our planet4--,for a long time it was supposed that the solid earth constituted a crust only which was floated upon a liquid interior4 ,this notion was clearly an outgrowth of the then generally accepted ,laplacian hypothesis of the origin of the universe1 which assumed fluid interiors for the planets1 the crust being suggested by the winter crust of frozen water upon the surface of our inland lakes4 ,to-day the nebular hypothesis in the ,laplacian form is fast giving place to quite different conceptions1 in which solid particles1 and not gaseous ones1 are conceived to have built up the lithosphere4 ,the analogy with frozen water has likewise been abandoned with the discovery that frozen rock1 instead of floating1 sinks in its molten equivalent4 ,yet even more cogent arguments have been brought forward to show that whatever may be the state of aggregation within the earth's core--and it may be different from any now known to us--it nevertheless has many of the properties recognized as belonging to solid and rigid bodies4 ,provisionally1 therefore1 we may regard the earth's core as rigid and essentially solid4 ,it was long ago pointed out by the late ,lord ,kelvin that if our lithosphere were not more rigid than a ball of glass of the same size1 it would be constantly passing through periodic six-hourly distortions of great amplitude in response to the varying attractions of the moon4 ,an equally striking argument emanating from the same high authority is furnished by the well-known egg-spinning demonstration4 ,for illustration1 ,kelvin was accustomed to take two eggs1 one boiled and the other raw1 and attempt to spin them upon their ends4 ,for the boiled1 and essentially solid1 egg this is easily accomplished1 but internal friction of the liquid contents of the raw egg quickly stops any rotary motion which is imparted to it4 ,upon the same grounds it is argued that had the earth's interior possessed the properties of a liquid1 rotation must long since have ceased4 ,a stronger proof of earth rigidity than either of these has been lately furnished by the instrumental study of earthquakes4 ,with the delicate apparatus which is now installed for the purpose1 heavy earthquakes may be sensed which have occurred anywhere upon the earth's surface1 the earth movement sending its own message by the shortest route through the core of the earth to the observing station4 ,a heavy shock which occurs in ,new ,zealand is recorded in ,england1 almost diametrically opposite1 in about twenty-one minutes after its occurrence4 ,the laws of wave propagation and their relation to the properties of the transmitting medium are well known1 and in order to explain such extraordinary velocity it is necessary to assume that for such impulses the earth's interior is much more rigid than the finest tool steel4 ,probable composition of the earth's core4--,in deriving views concerning the nature of the earth's interior we are greatly aided by astronomical studies4 ,the common origin long ago indicated for the planets of the solar system and the sun has been confirmed by the analysis of light with the aid of the spectroscope4 ,it has thus been found that the same chemical elements which we find in the earth are present also in the sun and in the other stellar bodies4 ,again1 the group of planets of the solar system which are nearest to the sun--,mercury1 ,venus1 the ,earth1 and ,mars--have each a high density1 all except ,mars1 the most distant1 having specific gravities very closely #e1 that of ,mars being about #d4 ,this average specific gravity is also that of the solid bodies1 the so-called meteorites1 which reach the surface of our planet from the surrounding space4 ,yet though the earth as a whole is thus found to have a specific gravity five and a half times that of water1 its surface shell has an average density of less than half this value1 or #b4g4 ,the study of meteorites has given us a possible clew to the nature of the earth's interior2 for when both terrestrial and celestial rock types are classified and placed in orderly arrangement1 it is found that the chemical elements which compose the two groups are identical1 and that these are united according to the same physical and chemical laws4 ,no new element has been discovered in the one group that has not been found in the other1 and though some compounds of these elements1 the minerals1 occur in the earth's crust that have not been found in meteorites1 and though some occur in meteorites which are not known from the earth1 yet of those which are common to both bodies there is agreement1 even to the minor details 7,fig4 #i74 ,it is found1 however1 that the commonest of the minerals in the earth's shell are absent from meteorites1 as the commoner constituents of meteorites are wanting in the earth's crust4 ,this observation would go far to show that we may in the two cases be examining different portions of quite similar bodies2 and this view is strikingly confirmed when the rocks of the two groups are arranged in the order of their densities 7,fig4 #i74 ,illustration3 ,,fig4 #i4--;,diagram to show how terrestrial rocks grade into those of the meteorites4 #a1 oxygen2 #b1 silicon2 #c1 aluminium2 #d1 alkali metals2 #e1 alkaline earth metals2 #f1 iron1 nickel1 cobalt1 etc42 a1 granites and rhyolites2 b1 syenites and trachytes2 c1 diorites and andesites2 d1 gabbros and basalts2 e1 ultra-basic rocks2 f1 basic inclosures in basalt1 etc42 g1 iron basalts of west ,greenland2 h1 iron masses of ,ovifak1 west ,greenland2 a'-d'1 meteorites in order of density 7after ,judd74 ,in a broad way1 density1 structure1 and chemical composition are all similarly involved in the gradations illustrated by the diagram2 and it is significant that while there are terrestrial rocks not represented by meteorites1 the densest and the most unusual of the terrestrial rocks are chemically almost identical with the less dense of the celestial bodies4 ,the earth a magnet4--,the denser1 and likewise the more common1 of the meteorite rocks--the so-called meteoric irons--are composed almost entirely of the elements iron1 nickel1 and cobalt4 ,such aggregates are not known as yet from terrestrial sources1 although transitional types appear to exist upon the island of ,disco off the west coast of ,greenland4 ,if it were possible to explore the earth's interior1 would such combinations of the iron minerals be encountered8 ,apart from the surprising velocity of transmission of earthquake waves1 the strongest argument for an iron core to the lithosphere is found in the magnetic property of the earth as a whole4 ,the only magnetic elements known to us are those of the heavy meteorites--iron1 nickel1 and cobalt1--and the earth is1 as we know1 a great magnet whose northern pole in ,british ,america and whose southern pole in ,antarctica have at last been visited by ,amundsen and ,david1 respectively4 ,the specific gravity of iron is #g4ae1 and those of nickel and cobalt1 which in the meteorites are present in relatively small amounts1 are #g4h and #g4e1 respectively4 ,considering that the surface shell of the earth has a specific gravity of #b4g1 these values must be regarded as agreeing well with the determined density of the earth 7#e4f7 and the other planets of its group 7,mercury #e4g1 ,venus #e4d1 ,mars #d74 ,the chemical constitution of the earth's surface shell4--,the number of the so-called chemical elements which enter into the earth's composition is more than eighty1 but few of these figure as important constituents of the portion known to us4 ,nearly one half of the mass of this shell is oxygen1 and more than a quarter is silicon4 ,the remaining quarter is largely made up of aluminium1 iron1 calcium1 magnesium1 and the alkalies sodium and potassium1 in the order named4 ,these eight constituent elements are thus the only ones which play any important rle in the composition of the earth's surface shell4 ,they are not found there in the free condition1 but combined in the definite proportions characteristic of chemical compounds1 and as such they are known as minerals4 ,the essential nature of crystals4--,a crystal we are accustomed to think of as something transparent bounded by sharp edges and angles1 our ideas having been obtained largely from the gem minerals4 ,this outward symmetry of form is1 however1 but an expression of a power which resides1 so to speak1 in the heart or soul of the crystal individual--it has its own structural make-up1 its individuality4 ,no more correct estimates of the comparison of crystal individualities would be obtained by the study of outward forms alone of two minerals than would be gained by a judgment of persons from the cut of their clothing4 ,too often this outward dress tells only of the conditions by which both men and crystals have been surrounded1 and but little of the power inherent in the individual4 ,many a battered mineral fragment with little beauty to recommend it1 when placed under suitable conditions for its development1 has grown into a marvel of beauty4 ,few minerals are so mean that they have not within them this inherent power of individuality which lifts them above the world of the amorphous and shapeless4 ,illustration3 ,,fig4 #aj4--;,comparison of a crystalline with an amorphous substance when expanded by heat and when attacked by acid4 ,just as the real nature of a person is first disclosed by his behavior under trying circumstances1 so of a crystal it is its conduct under stress of one sort or another which brings out its real character4 ,by way of illustration let us prepare a sphere from the mineral quartz--it matters not whether we destroy the beautiful outlines of the crystal or employ a battered fragment--and then prepare a sphere of similar size and shape from a noncrystalline or amorphous substance like glass4 ,if now these two spheres be introduced into a bath of oil and raised to a higher temperature1 the glass globe undergoes an enlargement without change of its form2 but the crystal ball reveals its individuality by expanding into a spheroid in which each new dimension is nicely adjusted to this more complex figure 7,fig4 #aj74 ,we may1 instead of submitting the two balls to the 8trial by fire01 allow each to be attacked by the powerful reagent1 hydrofluoric acid4 ,the common glass under the attack of the acid remains as it was before1 a sphere1 but with shrunken dimensions4 ,the crystal1 on the other hand1 is able to control the action of the solvent1 and in so doing its individuality is again revealed in a beautifully etched figure having many curving outlines--it is as though the crystal had possessed a soul which under this trial has been revealed4 ,this glimpse into the nature of the crystal1 so as to reveal its structural beauty1 is still more surprising when the crystal is taken from the acid in the early stages of the action and held close beneath the eye4 ,now the little etchings upon the surface display each the individuality of the substance1 and joining with their neighbors they send out a beautifully symmetrical and entirely characteristic picture 7,fig4 #aa74 ,illustration3 ,,fig4 #aa4--8,light figure0 seen upon an etched surface of a crystal of calcite 7after ,goldschmidt and ,wright74 ,the lithosphere a complex of interlocking crystals4--,to the layman the crystal is something rare and expensive1 to be obtained from a jeweler or to be seen displayed in the show cases of the great museums4 ,yet the one most striking quality of the lithosphere which separates it from the hydrosphere and the atmosphere is its crystalline structure1--a structure belonging also to the meteorite1 and with little doubt to all the planets of the earth group4 ,a snowflake caught during its fall from the sky reveals all the delicate tracery of crystal boundary2 collected from a thick layer lying upon the ground1 it appears as an intricate aggregate of broken fragments more or less firmly cemented together4 ,and so it is of the lithosphere1 for the myriads of individuals are either the ruins of former crystals1 or they are grown together in such a manner that crystal facets had no opportunity to develop4 ,such mineral individuals as once possessed the crystal form may have been broken and their surfaces ground away by mutual attrition under the rhythmic beating of the waves upon a shore or in the continuous rolling of pebbles on a stream bed1 until as battered relics they are piled away together in a bed of sand4 ,yet no amount of such rough handling is sufficient to destroy the crystal individuality1 and if they are now surrounded with conditions which are suitable for their growth1 their individual nature again becomes revealed in new crystal outlines4 ,many of our sandstones when turned in the bright sunlight send out flashes of light to rival a bank of snow in early spring4 ,these bright flashes proceed from the facets of minute crystals formed about each rounded grain of the sand1 and if we examine them under a lens1 we may note the beauty of line formed with such exactness that the most delicate instruments can detect no difference between the similar angles of neighboring crystals 7,fig4 #ab74 ,illustration3 ,,fig4 #ab4--;,battered sand grains which have taken on a new lease of life and have developed a crystal form4 a1 a single grain grown into an individual crystal2 b1 a parallel growth about a single grain2 c1 growth of neighboring grains until they have mutually interfered and so destroyed the crystal facets--the common condition within the mass of a rock 7after ,irving and ,van ,hise74 ,this individual nature of the crystal is believed to reside in a symmetrical grouping of the chemical molecules of the substance into larger and so-called 8crystal molecules40 ,the crystal quality belongs to the chemical elements and to their compounds in the solid condition1 but not to ordinary mixtures of them4 ,some properties of natural crystals1 minerals4--,no two mineral species appear in crystals of the same appearance1 any more than two animal species have been given the same form2 and so minerals may be recognized by the individual peculiarities of their crystals4 ,yet for the reason that crystals have so generally been prevented from developing or retaining their characteristic faces1 in the vast number of instances it is the behavior1 and not the appearance1 of the mineral substance which is made use of for identification4 ,when a mineral is broken under the blow of a hammer1 instead of yielding an irregular fracture1 like that of glass1 it generally tends to part along one or more directions so as to leave plane surfaces4 ,this property of cleavage is strikingly illustrated for a single direction in the mineral mica1 for two directions in feldspar1 and for three directions in calcite or ,iceland spar4 ,other properties of minerals1 such as hardness1 specific gravity1 luster1 color1 fusibility1 etc41 are all made use of in rough determinations of the minerals4 ,far more delicate methods depend upon the behavior of minerals when observed in polarized light1 and such behavior is the basis of those branches of geological science known as optical mineralogy and as microscopical petrography4 ,an outline description of some of the common minerals and the means for identifying them will be found in appendix ,a4 ,the alterations of minerals4--,by far the larger number of minerals have been formed in the cooling and consequent consolidation of molten rock material such as during a volcanic eruption reaches the earth's surface as lava4 ,beginning their growth at many points within the viscous mass1 the individual crystals eventually may grow together and so prevent a development of their crystal faces4 ,another class of minerals are deposited from solution in water within the cavities and fissures of the rocks2 and if this process ceases before the cavities have been completely closed1 the minerals are found projecting from the walls in a beautiful lining of crystal--the ,krystallkeller or 8crystal cellar40 ,it is from such pockets or veins within the rocks that the valuable ores are obtained1 as are the crystals which are displayed in our mineral cabinets4 ,illustration3 ,,fig4 #ac4--;,crystal of garnet developed in a schist with grains of quartz included because not assimilated4 ,there is1 however1 a third process by which minerals are formed1 and minerals of this class are produced within the solid rock as a product of the alteration of prexisting minerals4 ,under the enormous pressures of the rocks deep below the earth's surface1 they are as permeable to the percolating waters as is a sponge at the surface4 ,under these conditions certain minerals are dissolved and their material redeposited after traveling in the solution1 or solution and redeposition of mineral matter may go on together within the mass of the same rock4 ,one new mineral may have been produced from the dissolved materials of a number of earlier species1 or several new minerals may be the result of the alteration of a prexisting mineral with a more complex chemical structure4 ,where the new mineral has been formed 8in place01 it has sometimes been able to utilize the materials of all the minerals which before existed there1 or it may have been obliged to inclose within itself those earlier constituents which it could not assimilate in its own structure 7,fig4 #ac74 ,illustration3 ,,fig4 #ad4--;,a crystal of augite within the mass of a rock altered in part to form a rim of the minerals hornblende and magnetite4 ,note the original outline of the augite crystal4 ,at other times a crystal which is imbedded in rock has been attacked upon its surface by the percolating solutions1 and the dissolved materials have been deposited in place as a crown of new minerals which steadily widens its zone until the center is reached and the original crystal has been entirely transformed 7,fig4 #ad74 ,it is sometimes possible to say that the action by which these changes have been brought about has involved a nice adjustment of supply of the chemical constituents necessary to the formation of the new mineral or minerals4 ,in rocks which are aggregates of several mineral species1 a newly formed mineral may appear only at the common margin of certain of these species1 thus showing that they supply those chemical elements which were necessary to the formation of the new substance 7,fig4 #ae74 ,thus it is seen that below the earth's surface chemical reactions are constantly going on1 and the earlier rocks are thus locally being transformed into others of a different mineral constitution4 ,illustration3 ,,fig4 #ae4--;,a new mineral 7hornblende7 forming as an intermediate 8reaction rim0 between the mineral having irregular fractures 7olivine7 and the dusty white mineral 7lime-soda feldspar74 ,near the earth's surface the carbon dioxide and the moisture which are present in the atmosphere are constantly changing the exposed portions of the lithosphere into carbonates1 hydrates1 and oxides4 ,these compounds are more soluble than are the minerals out of which they were formed1 and they are also more bulky and so tend to crack off from the parent mass on which they were formed4 ,as we are to see1 for both of these reasons the surface rocks of the lithosphere succumb to this attack from the atmosphere4 ,in connection with those wrinklings of the surface shell of the lithosphere from which mountains result1 the underlying rocks are subjected to great strains1 and even where no visible partings are produced1 the rocks are deformed so that individual minerals may be bent into crescent-shaped or ,s-shaped forms1 or they are parted into one or more fragments which remain imbedded within the rock4 ,,reading ,,references ,,for ,,chapter ,,iii ,theories of origin of the earth3-- ,,thomson and ,,tait4 ,natural ,philosophy4 #b;d ed4 ,cambridge1 #ahhc1 pp4 #dbb4 ,t4 ,c4 ,,chamberlin4 ,chamberlin and ,salisbury's ,geology1 vol4 #b1 pp4 #a-ha4 ,rigidity of the earth3-- ,,lord ,,kelvin4 ,the ,internal ,condition of the ,earth as to ,temperature1 ,fluidity1 and ,rigidity1 ,popular ,lectures and ,addresses1 vol4 #b1 pp4 #bii-cah2 ,review of evidence regarding the physical condition of the earth1 ibid41 pp4 #bch-bgb4 ,,hobbs4 ,earthquakes 7,appleton1 ,new ,york1 #aijg71 ,chapters xvi and xvii4 ,composition of the earth's core and shell3-- ,o4 ,c4 ,,farrington4 ,the ,preterrestrial ,history of ,meteorites1 ,jour4 ,geol41 vol4 #i1 #aija1 pp4 #fbc-bcf4 ,e4 ,s4 ,,dana4 ,minerals and ,how to ,study ,them 7a book for beginners in mineralogy74 ,wiley1 ,new ,york1 #ahie4 ,on the nature of crystals3-- ,,victor ,,goldschmidt4 ,ueber das ,wesen der ,krystalle1 ,ostwalds ,annalen der ,naturphilosophie1 vol4 #i1 #aiji-aiaj1 pp4 #abj-aci1 #cfh-dai4 ,,chapter ,,iv ,,the ,,rocks ,,of ,,the ,,earth',s ,,surface ,,shell ,the processes by which rocks are formed4--,rocks may be formed in any one of several ways4 ,when a portion of the molten lithosphere1 so-called magma1 cools and consolidates1 the product is igneous rock4 ,either igneous or other rock may become disintegrated at the earth's surface1 and after more or less extended travel1 either in the air1 in water1 or in ice1 be laid down as a sediment4 ,such sediments1 whether cemented into a coherent mass or not1 are described as sedimentary or clastic rocks4 ,if the fluid from which they were deposited was the atmosphere1 they are known as subarial or eolian sediments2 but if water1 they are known as subaqueous deposits4 ,still another class are ice-deposited and are known as glacial deposits4 ,illustration3 ,,fig4 #af4--,laminated structure of sedimentary rock1 ,western ,kansas 7after a photograph by ,e4 ,s4 ,tucker74 ,but1 as we have learned1 rocks may undergo transformations through mineral alteration1 in which case they are known as metamorphic rocks4 ,when these changes consist chiefly in the production of more soluble minerals at the surface1 accompanied by thorough disintegration1 due to the direct attack of the atmosphere1 the resulting rocks are called residual rocks4 ,the marks of origin4--,each of the three great classes of rocks1 the igneous1 sedimentary1 and metamorphic1 is characterized by both coarser and finer structures1 in the examination of which they may be identified4 ,the igneous rocks having been produced from magmas1 which are essentially homogeneous1 are usually without definite directional structures due to an arrangement of their constituents1 and are said to have a massive structure4 ,sedimentary rocks1 upon the other hand1 have been formed by an assorting process1 the larger and heavier fragments having been laid down when there was high velocity of either wind or water current1 and the smaller and lighter fragments during intermediate periods4 ,they are therefore more or less banded1 and are said to have a bedded or laminated structure 7,fig4 #af74 ,again1 igneous rocks1 being due to a process of crystallization1 are composed of mineral individuals which are bounded either by crystal planes or by irregular surfaces along which neighboring crystals have interfered with each other2 but in either case the grains possess sharply angular boundaries4 ,quite different has been the result of the attrition between grains in the transportation and deposition of sediments1 for it is characteristic of the sedimentary rocks that their constituent grains are well rounded4 ,eolian sediments have usually more perfectly rounded grains than subaqueous deposits4 ,glacial deposits1 if laid down directly by the ice1 are unstratified1 relatively coarse1 and contain pebbles which are both faceted and striated4 ,such deposits are described as till or tillite4 ,if glacier-derived material is taken up by the streams of thaw water and is by them redeposited1 the sediments are assorted or stratified1 and they are described as fluvio-glacial deposits4 ,the metamorphic rocks4--,both the coarser structures and the finer textures of the metamorphic rocks are intermediate between those of the igneous and the sedimentary classes4 ,a metamorphosed sedimentary rock1 in proportion to its alteration1 loses the perfect lamination and the rounded grain which were its distinguishing characters2 while an igneous rock takes on in the process an imperfect banding1 and the sharp angles of its constituent grains become rounded off by a sort of peripheral crushing or granulation4 ,metamorphic rocks are therefore characterized by an imperfectly banded structure described as schistosity or gneiss banding1 and the constituent grains may be either angular or rounded4 ,if the metamorphism has not been too intense or too long continued1 it is generally possible to determine1 particularly with the aid of the polarizing microscope1 whether the original rock from which it was derived was of igneous or of sedimentary origin4 ,there are1 however1 many examples which have defied a reliable verdict concerning their origin4 ,characteristic textures of the igneous rocks4--,in addition to the massiveness of their general aspect and the angular boundaries of their constituents1 there are many additional textures which are characteristic of the igneous rocks4 ,while those that have consolidated below the earth's surface1 the intrusive rocks1 are notably compact1 the magmas which arrive at the surface of the lithosphere before their consolidation reveal special structures dependent either upon the expansion of steam and other gases within them1 or upon the conditions of flow over the earth's surface4 ,magmas which thus reach the surface of the earth are described as lavas1 and the rocks produced by their consolidation are extrusive or volcanic rocks4 ,the steam included in the lava expands into bubbles or vesicles which may be large or small1 few or many4 ,according to the number and the size of these cavities1 the rock is said to have a vesicular1 scoriaceous1 or pumiceous texture4 ,most lavas1 when they arrive at the earth's surface1 contain crystals which are more or less disseminated throughout the molten mass4 ,the tourist who visits ,mount ,vesuvius at the time of a light eruption may thrust his staff into the stream of lava and extract a portion of the viscous substance in which are seen beautiful white crystals of the mineral leucite1 each bounded by twenty-four crystal faces4 ,it is clear that these crystals must have developed by a slow growth within the magma while it was still below the surface1 and when the inclosing lava has consolidated1 these earlier crystals lie scattered within a groundmass of glassy or minutely crystalline material4 ,this scattering of crystals belonging to an earlier generation within a groundmass due to later consolidation is thus an indication of interruption in the process of crystallization1 and the texture which results is described as porphyritic 7,fig4 #ag b74 ,should the lava arrive at the surface before any crystals have been generated and consolidate rapidly as a rock glass1 its texture is described as glassy 7,fig4 #ag c74 ,when the crystals of the earlier generation are numerous and needle-like in form1 as is very often the case1 they arrange themselves 8end on0 during the rock flow1 so that when consolidation has occurred1 the rock has a kind of puckered lamination which is the characteristic of the fluxion or flow texture4 ,this texture has sometimes been confused with the lamination of the sedimentary rocks1 so that wrong conclusions have been reached regarding origin4 ,at other times the same needle-like crystals within the lava have grouped themselves radially to form rounded nodules called spherulites4 ,such nodules give to the rock a spherulitic texture1 which is nowhere better displayed than in the beautiful glassy lavas of ,obsidian ,cliff in the ,yellowstone ,national ,park4 ,illustration3 ,,fig4 #ag4--;,characteristic textures of igneous rocks4 a1 granitic texture characteristic of the deep-seated intrusive rocks2 b1 porphyritic texture characteristic of the extrusive and of the near-surface intrusive rocks2 c1 glassy texture of an extrusive rock4 ,those intrusive rocks which consolidate deep below the earth's surface1 part with their heat but slowly1 and so the process of crystallization is continued without interruption4 ,starting from many centers1 the crystals continue to grow until they mutually intersect in an interlocking complex known as the granitic texture 7,fig4 #ag a74 ,classification of rocks4--,in tabular form rocks may thus be classified as follows3-- ,intrusive4 ,granitic or porphyritic texture4 ,igneous4 ,massive and ,extrusive4 ,glassy or porphyritic with sharply angular texture2 often also with vesicular1 grains4 scoriaceous1 pumiceous1 fluxion1 or spherulitic textures4 ,subarial4 ,sands and loess4 ,subaqueous4 7,see below47 ,sedimentary4 ,laminate ,glacial4 ,coarse1 unstratified and with rounded deposits with faceted pebbles4 ,till grains4 and tillite4 ,fluvio-glacial4 ,stratified sands and gravels with 8worked over0 glacial characters4 ,metamorphic4 ,schistose ,metamorphic proper4 ,due to below and with grains either surface changes4 angular or rounded4 ,residual4 ,disintegrated at or near surface4 ,subdivisions of the sedimentary rocks4--,while the eolian sediments are all the product of a purely mechanical process of lifting1 transportation1 and deposition of rock particles1 this is not always the case with the subaqueous sediments1 since water has the power of dissolving mineral substance1 as it has also of furnishing a home for animal and vegetable life4 ,deposited materials which have been in solution in water are described as chemical deposits1 and those which have played a part in the life process as organic deposits4 ,the organic deposits from vegetable sources are peat and the coals1 while limestones and marls are the chief depositories of the remains of the animal life of the water4 ,the tabular classification of the sediments is as follows3-- ,classification of ,sediments4 ,subaqueous ,conglomerate1 sandstone ,deposited by water4 and shale4 ,subarial or ,eolian ,sandstone and loess4 ,mechanical ,deposited by wind4 ,glacial ,till and tillite4 ,deposited by ice4 ,fluvio-glacial ,sands and gravels4 ,glacier-water deposits4 ,calcareous tufa ,deposited in springs and rivers4 ,chemical ,olitic limestone ,deposited at the mouths of rivers between high and low tide4 ,formed of plant remains4 ,peats and coals4 ,organic ,formed of animal remains4 ,limestones and marls4 ,winds are under favorable conditions capable of transporting both dust and sand1 but not the larger rock fragments4 ,the dust deposits are found accumulating outside the borders of deserts as the so-called loess 7,fig4 #baf71 though the sand is never carried beyond the desert border1 near which it collects in wide belts of ridges described as dunes4 ,when this sand has been cemented into a coherent mass1 it is known as eolian sandstone4 ,a section of the appendix 7,b7 is devoted to an outline description of some of the commoner rock types4 ,the different deposits of ocean1 lake1 and river4--,of the subaqueous sediments1 there are three distinct types resulting3 7#a7 from sedimentation in rivers1 the fluviatile deposits2 7#b7 from sedimentation in lakes1 the lacustrine deposits2 and 7#c7 from sedimentation in the ocean1 marine deposits4 ,again1 the widest range of character is displayed by the deposits which are laid down in the different parts of the course of a stream4 ,near the source of a river1 coarse river gravels may be found2 in the middle course the finer silts2 and in the mouth or delta region1 where the deposits enter the sea or a lake1 there is found an assortment of silts and clays4 ,except within the delta region1 where the area of deposition begins to broaden1 the deposits of rivers are stretched out in long and relatively narrow zones1 and are so distinguished from the far more important lacustrine and marine deposits4 ,lakes and oceans have this in common that both are bodies of standing as contrasted with flowing water2 and both are subject to the periodical rhythmic motions and alongshore currents due to the waves raised by the wind4 ,about their margins1 the deposits of lake and ocean are thus in large part wrested by the waves from the neighboring land4 ,their distribution is always such that the coarsest materials are laid down nearest to the shore1 and the deposits become ever finer in the direction of deeper water4 ,relatively far from shore may be found the finest sands and muds or calcareous deposits1 while near the shore are sands1 and1 finally1 along the beach1 beds of beach pebbles or shingle4 ,when cemented into coherent rocks1 these deposits become shales or limestones1 sandstones1 and conglomerates1 respectively4 ,as regards the limestones1 their origin is involved in considerable uncertainty4 ,some1 like the shell limestone or coquina of the ,florida coast1 are an aggregation of remains of mollusks which live near the border of the sea4 ,other limestones are deposited directly from carbonate of lime in solution in the water4 ,a deposit of this nature is forming in southern ,florida1 both as a flocculent calcareous mud and as crystals of lime carbonate upon a limestone surface4 ,again1 there is the reef limestone which is built up of the stony parts of the coral animal1 and1 lastly1 the calcareous ooze of the deep-sea deposits4 ,the marine sediments which are derived from the continents1 the so-called terrigenous deposits1 are found only upon the continental shelf and upon the continental slope just outside it4 ,of these terrigenous deposits1 it is customary to distinguish3 7#a7 littoral or alongshore deposits1 which are laid down between high and low tide levels2 7#b7 shoal water deposits1 which are found between low-water mark and the edge of the continental shelf2 and 7#c7 aktian or offshore deposits1 which are found upon the continental slope4 ,the littoral and shoal water deposits are mainly gravels and sands1 while the offshore deposits are principally muds or lime deposits4 ,special marks of littoral deposits4--,the marks of ripples are often left in the sand of a beach1 and may be preserved in the sandstone which results from the cementation of such deposits 7pl4 #aa ,a74 ,very similar markings are1 however1 quite characteristic of the surface of wind-blown sand4 ,for the reason that deposits are subject to many vicissitudes in their subsequent history1 so that they sometimes stand at steep angles or are even overturned1 it is important to observe the curves of sand ripples so as to distinguish the upper from the lower surface4 ,in the finer sands and muds of sheltered tidal flats may be preserved the impressions from raindrops or of the feet of animals which have wandered over the flat during an ebb tide4 ,when the tide is at flood1 new material is laid down upon the surface and the impressions are filled1 but though hardened into rock1 these surfaces are those upon which the rock is easily parted1 and so the impressions are preserved4 ,in the sandstones of the ,connecticut valley there has been preserved a quite remarkable record in the footprints of animals belonging to extinct species1 which at the time these deposits were laid down must have been abundant upon the neighboring shores4 ,between the tides muds may dry out and crack in intersecting lines like the walls of a honeycomb1 and when the cracks have been filled at high tide1 a structure is produced which may later be recognized and is usually referred to as 8mud-crack0 structure4 ,this structure is of special service in distinguishing marine deposits from the subarial or continental deposits4 ,a variation in the direction of winds of successive storms may be responsible for the piling up of the beach sand in a peculiar 8plunge and flow0 or 8cross-bedded0 structure1 a structure which is extremely common in littoral deposits1 though simulated in rocks of eolian origin4 ,the order of deposition during a transgression of the sea4--,many shore lines of the continents are almost constantly migrating either landward or seaward4 ,when the shore line advances over the land1 the coast is sinking1 and marine deposits will be formed directly above what was recently the 8dry land40 ,such an invasion of the land by the sea1 due to a subsidence of the coast1 is called a transgression of the sea1 or simply a transgression4 ,though at any moment the littoral1 shoal water1 and offshore deposits are each being laid down in a particular zone1 it is evident that each must advance in turn in the direction of the shore and so be deposited above the zones nearer shore4 ,thus there comes to be a definite series of continuous beds1 one above the other1 provided only that the process is continued 7,fig4 #ah74 ,at the very bottom of this series there will usually be found a thin bed of pebbly beach materials1 which later will harden into the so-called basal conglomerate4 ,if the size of the pebbles is such as to make possible an identification1 it will generally be found that these represent the ruins of the rock over which the sea has advanced upon the land4 ,illustration3 ,,fig4 #ah4--;,diagram to show the order of the sediments laid down during a transgression of the sea4 ,next in order above the basal conglomerate1 will follow the coarser and then the finer sands1 upon which in turn will be laid down the offshore sediments--the muds and the lime deposits4 ,later1 when cemented together1 these become in order1 coarser and finer sandstones1 shales1 and limestones4 ,the order of superposition1 reading from the bottom to the top1 thus gives the order of decreasing age of the formations4 ,a subsequent uplift of the coast will be accompanied by a recession of the sea1 and when later dissected by nature for our inspection1 the order of superposition and the individual character of each of the deposits may be studied at leisure4 ,from such studies it has been found that along with the inorganic deposits there are often found the remains of life in the hard parts of such invertebrate animals as the mollusks and the crustacea4 ,these so-called fossils represent animals which were gradually developed from simpler to more and more complex forms2 and they thus serve the purpose of successive page numbers in arranging the order of disturbed strata1 at the same time that they supply the most secure foundation upon which rests the great doctrine of evolution4 ,the basins of earlier ages4--,it was the great ,viennese geologist1 ,professor ,suess1 who first pointed out that in mountain regions there are found the thickest and the most complete series of the marine deposits2 whereas outside these provinces the formations are separated by wide gaps representing periods when no deposits were laid down because the sea had retired from the region4 ,the completeness of the series of deposits in the mountain districts can only be interpreted to mean that where these but lately formed mountains rise to-day1 were for long preceding ages the basins for deposition of terrigenous sediments4 ,it would seem that the lithosphere in its adjustment had selected these earlier sea basins with their heavy layers of sediment for zones of special uplift4 ,the deposits of the deep sea4--,outside the continental slope1 whose base marks the limit of the terrigenous deposits1 lies the deeper sea1 for the most part a series of broad plains1 but varied by more profound steep-walled basins1 the so-called 8deeps0 of the ocean4 ,as shown by the dredgings of the ,challenger expedition and others of more recent date1 the deposits upon the ocean floor are of a wholly different character from those which are derived from the continents4 ,except in the great deeps1 or between depths of five hundred and fifteen hundred fathoms1 these deposits are the so-called 8ooze01 composed of the calcareous or chitinous parts of alg and of minute animal organisms4 ,the pelagic or surface waters of the ocean are1 as it were1 a great meadow of these plant forms1 upon which the minute crustacea1 such as globigerina1 foraminifera1 and the pteropods1 feed in countless myriads4 ,the hard parts of both plant and animal organisms descend to the bottom and there form the ooze in which are sometimes found the ear bones of whales and the teeth of sharks4 ,in the deeps of the ocean1 none of these vegetable or animal deposits are being laid down1 but only the so-called 8red clay01 which is believed to represent decomposed volcanic material deposited by the winds as fine dust on the surface of the ocean1 or the product of submarine volcanic eruption4 ,from the absence of the ooze in these profound depths1 the conclusion is forced upon us that the hard parts of the minute organisms are dissolved while falling through three or four miles of the ocean water4 ,,reading ,,references ,,for ,,chapter ,,iv ,j4 ,s4 ,,diller4 ,the ,educational ,series of ,rock ,specimens collected and distributed by the ,united ,states ,geological ,survey1 ,bull4 #aej ,u4 ,s4 ,geol4 ,surv41 #ahih1 pp4 #a-djj4 ,l4 ,v4 ,,pirsson4 ,rocks and ,rock ,minerals4 ,wiley1 ,new ,york1 #aijh4 ,,sir ,,john ,,murray4 ,deep-sea ,deposits1 ,reports of the ,challenger expedition1 ,chapter iii4 ,l4 ,w4 ,,collet4 ,les dpts marins4 ,doin1 ,paris1 #aijg 7,encyclopdie ,scientifique74 ,,chapter ,v ,,contortions ,,of ,,the ,,strata ,,within ,,the ,,zone ,,of ,,flow ,the zones of fracture and flow4--,it is easy to think of the atmosphere and the hydrosphere as each sustaining at any point the load of the superincumbent material4 ,at the sea level the weight of air upon each square inch of surface is about fifteen pounds1 whereas upon the floor of the hydrosphere in the more profound deeps the load upon the square inch must be measured in tons4 ,near the lithosphere surface the rocks support by their strength the load of rock above them1 but at greater depths they are unable to do this1 for the load bears upon each portion of the rock with a pressure equivalent to the weight of a rock column which extends upward to the surface4 ,the average specific gravity of rock is #b4g1 and it is thus easy to calculate the length of the inch square column which has a weight equivalent to the crushing strength of any given rock4 ,at the depth represented by the length of such a column1 rocks cannot yield to pressure by fracture1 for the opening of a crack implies that the rock upon either side is strong enough to prevent the walls from closing4 ,at this depth1 rock must therefore yield to pressure not by fracture1 as it would at the surface1 but by flow after the manner of a liquid2 and so the zone below this critical level is referred to as the zone of flow4 ,illustration3 ,,fig4 #ai4--,two intersecting parallel series of fractures produced upon each free surface of a prismatic block of stiff molders' wax when broken by compression from the ends 7after ,daubre and ,tresca74 ,in contrast1 the near-surface zone is called the zone of fracture4 ,but different rocks possess different strengths1 and these are subject to modifications from other conditions1 such1 for example1 as the proximity of an uncooled magma4 ,the zone of flow is therefore joined to the zone of fracture1 not upon a definite surface1 but in an intermediate zone described as the zone of fracture and flow4 ,experiments which illustrate the fracture and flow of solid bodies4--,a prismatic block prepared from stiff molders' wax1 if crushed between the jaws of a testing machine1 yields a system of intersecting fractures which are perpendicular to the free surfaces of the block and take two directions each inclined by half of a right angle to the direction of compression 7,fig4 #ai74 ,this experiment may illustrate the manner in which fractures are produced by the compression within the zone of fracture of the lithosphere1 as its core continues to contract4 ,to reproduce the conditions within the zone of flow1 it will be necessary to load the lateral surfaces of the block instead of leaving them unconstrained as in the above-described experiment4 ,the experiment is best devised as in ,fig4 #bj4 ,here a series of layers having varying degrees of rigidity is prepared from beeswax as a base1 either stiffened by admixture of varying proportions of plaster of ,paris1 or weakened by the use of ,venice turpentine4 ,such a series of layers may represent rocks of as widely different characters as limestone and shale4 ,the load which is to represent superincumbent rock is supplied in the experiment by a deep layer of shot4 ,illustration3 ,,fig4 #bj4--;,apparatus to illustrate the folding of strata within the zone of flow 7after ,willis74 ,when compression is applied to the layers from the ends1 these normally solid materials1 instead of fracturing1 are bent into a series of folds4 ,the stiffer1 or more competent1 layers are found to be less contorted than are the weaker layers1 particularly if the latter have been protected under an arch of the more competent layer 7pl4 #b ,a74 ,the arches and troughs of the folded strata4--,every series of folds is made up of alternating arches and troughs4 ,the arches of the strata the geologist calls anticlines or anticlinal folds1 and the troughs he calls synclines or synclinal folds 7,fig4 #ba74 ,when a stratum is merely dropped in a bend to a lower level without producing a complete arch or a complete trough1 this half fold is termed a monocline4 ,illustration3 ,,fig4 #ba4--;,diagrams representing a1 an anticline2 b1 a syncline2 and c1 a monocline4 ,any flexuring of the strata implies a reduction of their surface area1 or1 considering a single section1 a shortening4 ,if the arches and troughs are low and broad1 the deformation of the strata is slight1 the shortening is comparatively small1 and the folds are described as open 7,fig4 #bb b74 ,if they be relatively both high and narrow1 the deformation is considerable1 a larger amount of crustal shortening has gone on1 and the folds are described as close 7,fig4 #bb c74 ,this closing up of the folds may continue until their sides have practically the same slope1 in which case they are said to be isoclinal 7,fig4 #bb d74 ,illustration3 ,,fig4 #bb4--;,a comparison of folds to express increasing degrees of crustal shortening or progressive deformation within the zone of flow3 a1 stratum before folding2 b1 open folds2 c1 close folds2 d1 isoclinal folds4 ,the elements of folds4--,folds must always be thought of as having extension in each of the three dimensions of space 7,fig4 #bc71 and not as properly included within a single plane like the cross sections which we so often use in illustration4 ,a fold may be conceived of as divided into equal parts by a plane which passes along the middle of either the arch or the trough1 and is called the axial plane4 ,the line in which this plane intersects the arch or the trough is the axis1 which may be called the crestline in an anticline1 and the troughline in a syncline4 ,in the case of many open folds the axis is practically horizontal1 but in more complexly folded regions this is seldom true4 ,the departure of the axis from the horizontal is called the pitch1 and folds of this type are described as pitching folds or plunging folds4 ,the axis is in reality in these cases thrown into a series of undulations or 8longitudinal folds01 and hence pitch will vary along the axis4 ,illustration3 ,,fig4 #bc4--;,anticlinal and synclinal folds in strata 7after ,willis74 ,illustration3 ,,fig4 #bd4--;,diagrams to illustrate the different shapes of rock folds4 ,the shapes of rock folds4--,by the axial plane each fold is divided into two parts which are called its limbs1 which may have either the same or different average inclinations4 ,to describe now the shapes of rock folds and not the degree of compression of the district1 some additional terms are necessary4 ,anticlines or synclines whose limbs have about the same inclinations are known as upright or symmetrical folds4 ,the axial plane of the symmetrical fold is vertical 7,fig4 #bd74 ,if this plane is inclined to the vertical1 the folds are unsymmetrical4 ,so soon as the steeper of the two limbs has passed the vertical position and inclines in the same direction as the flatter limb1 the fold is said to be overturned4 ,the departure from symmetry may go so far that the axial plane of the fold lies at a very flat angle1 and the fold is then said to be recumbent4 ,the observant traveler by train along any of the routes which enter the ,alps may from his car window find illustrations of most of these types of rock folds1 as he may also1 though generally less easily1 in passing through the ,appalachian ,mountains4 ,illustration3 ,,fig4 #be4--,secondary and tertiary flexures superimposed upon the primary ones4 ,in regions which have been closely folded the larger flexures of the strata may be found with folds of a smaller order of magnitude superimposed upon them1 and these in turn may show crumplings of still lower orders4 ,it has been found that the folds of the smaller orders of magnitude possess the shapes of the larger flexures1 and much is therefore to be learned from their careful study 7,fig4 #be74 ,it is also quite generally discovered that parallel planes of ready parting1 which are described as rock cleavage1 take their course parallel to the axial plane within each minor fold4 ,as was long ago shown by the pioneer ,british geologists1 these planes of cleavage are essentially parallel and follow the fold axes throughout large areas4 ,,plate #b4 ,illustration3 ,a4 ,layers compressed in experiments and showing the effect of a competent layer in the process of folding 7after ,willis74 ,illustration3 ,b4 ,experimental production of a series of parallel thrusts within closely folded strata 7after ,willis74 ,illustration3 ,c4 ,apparatus to illustrate shearing action within the overturned limb of a fold4 ,the overthrust fold4--,whenever a stratum is bent1 there is a tendency for its particles to be separated upon the convex side of the bend1 at the same time that those upon the concave side are crowded closer together--there is tension in the former case and compression in the latter 7,fig4 #bf74 ,within an unsymmetrical or an overturned fold1 the peculiar distortions in the different sections of the stratum are less simple and are best illustrated by pl4 #b ,c4 ,this apparatus shows two similar piles of paper sheets1 upon the edges of each of which a series of circles has been drawn4 ,when now one of the piles is bent into an unsymmetrical fold1 it is seen that through an accommodation by the paper sheets sliding each over its neighbor large distortions of the circles have occurred4 ,in that steeper limb which with closer folding will be overturned the circles have been drawn out into long and narrow ellipses1 and this indicates that those rock particles which before the bending were included in the circle have been moved past each other in the manner of the blades of a pair of shears4 ,such extreme 8shearing0 action is thus localized in the underturned limb of the fold1 and a time must come with continuation of the compression when the fold will rupture at this critical place along a plane parallel to the longest axis of the ellipses or nearly parallel to the axial plane of the anticline4 ,such structures probably occur in the zone of combined fracture and flow1 up into which the beds are forced in cases of close compression4 ,relief thus being found upon this plane of fracture1 the upper portion of the fold will now ride over the lower1 and the displacement is described as a thrust or overthrust4 ,illustration3 ,,fig4 #bf4--;,a bent stratum to illustrate tension upon the convex and compression upon the concave side 7after ,van ,hise74 ,in the long series of experiments conducted by ,mr4 ,bailey ,willis of the ,united ,states ,geological ,survey1 all the stages between the overturned fold and the overthrust fold were reproduced4 ,where a series of folds was closely compressed1 a parallel series of thrusts developed 7pl4 #b ,b71 so that a series of slices cutting across neighboring strata was slid in succession1 each over the other1 like the scales upon a fish or the shingles upon a roof4 ,quite remarkable structures of this kind have been discovered in rocks of such closely folded districts as the ,northwest ,highlands of ,scotland1 where the overriding is measured in miles4 ,near the thrust planes the rocks show a crushing of the grains1 and the planes themselves are sometimes corrugated and polished by the movement4 ,restoration of mutilated folds4--,since flexuring of the rocks takes place within the zone of flow at a distance of several miles below the earth's surface1 it is quite obvious that the results of the process can be studied only after some thousands of feet of superincumbent strata have been removed4 ,we are a little later to see by what processes this lowering of the surface is accomplished1 but for the present it may be sufficient to accept the fact1 realizing that before foldings in the strata can reach the surface1 they must have passed through the upper zone of fracture4 ,it might perhaps be supposed that the anticlines would appear as the mountains upon the surface1 and occasionally this is true2 as1 for example1 in the folded ,jura ,mountains of western ,europe4 ,more generally1 the mountains have a synclinal structure and the valleys an anticlinal one2 but as no general rule can be applied1 it is necessary to make a restoration of the truncated folds in each district before their character can be known4 ,the geological map and section4--,the earth's surface is in most regions in large part covered with soil or with other incoherent rock material1 so that over considerable areas the hard rocks are hidden from view4 ,each locality at which the rock is found at the earth's surface 8in place0 is described as an outcropping or exposure4 ,in a study of the region each such exposure must be examined to determine the nature of the rock1 especially for the purpose of correlation with neighboring exposures1 and1 in addition1 both the probable direction in which it is continued along the surface--the strike--and the inclination of its beds--the dip4 ,if the outcroppings are sufficiently numerous1 and rock type1 strike and dip1 may all be determined1 the folds of the district may be restored with almost as much accuracy as though their curves were everywhere exposed to view4 ,a cross section through the surface which represents the observed outcrops with their inclinations and the assumed intermediate strata in their probable attitudes is described as a geological section 7,fig4 #bg74 ,a map upon which the data have been entered in their correct locations1 either with or without assumptions concerning the covered areas1 is known as a geological map4 ,illustration3 ,,fig4 #bg4--;,a geological section based upon observations at outcrops1 but with the truncated arches restored4 ,if the axes of folds are absolutely horizontal1 and the surface of the earth be represented as a plain1 the lines of intersection of the truncated strata with the ground1 or with any horizontal surface1 will give the directions of continuation of the individual strata4 ,this strike direction is usually determined at each exposure by use of a compass provided with a spirit level4 ,when that edge of the leveled compass which is parallel to the north-south line upon the dial is held against the sloping rock stratum1 the angle of strike is measured in degrees by the compass needle4 ,if the cardinal directions have been placed in their correct positions upon the compass dial1 the needle will point to the northwest when the strike is northeast1 and vice versa 7,fig4 #bh a74 ,upon the geologist's compass it is therefore customary to reverse the initials which represent the east and west directions1 in order that the correct strike may be read directly from the dial 7,fig4 #bh b74 ,illustration3 ,,fig4 #bh4--;,diagram to illustrate the manner of determining the strike of rock beds at an outcropping4 a1 a compass which has the cardinal directions in their natural positions2 b1 a compass with the east and west initials reversed upon the dial2 c1 home-made clinometer in position to determine the dip4 ,by the dip is meant the inclination of the stratum at any exposure1 and this must obviously be measured in a vertical plane along the steepest line in the bedding plane4 ,the dip angle is always referred to a horizontal plane1 and hence vertical beds have a dip of #ij4 ,the device for measuring this angle of dip1 the clinometer1 is merely a simple pendulum which serves as an indicator and is centered at the corner of a graduated quadrant4 ,a home-made variety is easily constructed from a square piece of board and an attached paper quadrant 7,fig4 #bh c71 but the geologist's compass is always provided with a clinometer attachment to the dial4 ,illustration3 ,,fig4 #bi4--;,diagram to show the use of ,t symbols to indicate the dip and strike of outcroppings4 ,since the strike is the intersection of the bedding plane with a horizontal surface1 and the dip is the intersection with that particular vertical plane which gives the steepest inclination1 the strike and dip are perpendicular to each other4 ,to represent them upon maps1 it is more or less customary to use the so-called ,t symbols1 the top of the ,t giving the direction of the strike and the shank that of the dip4 ,if meridians are drawn upon the map1 the direction or attitude of the ,t can be found by the use of a simple protractor2 and when entered upon the map1 the exact angle of the strike may be supplied by a figure near the top of the ,t1 and the dip angle by a figure at the end of the shank4 ,it is the custom1 also1 to make the length of the shank inversely proportional to the steepness of the dip1 so that in a broad way the attitudes of the strata may be taken in at a glance 7,fig4 #bi74 ,it is further of advantage to make the top of the ,t a double line1 so that some symbol or color may show the correlations of the different exposures4 ,to illustrate1 in ,fig4 #bi1 the symbol marked a represents an outcrop of limestone1 the strike of which is #ej east of north 7,n4 #ej ,e471 and the dip of which is #de southeast4 ,in the same figure b represents a shale outcrop in horizontal beds1 which have in consequence a universal strike and a dip of #j4 ,an exposure of limestone in vertical beds which strike ,n4 #fj ,e4 is shown at c1 etc4 ,illustration3 ,,fig4 #cj4--;,diagram to show how the thickness of a formation may be obtained from the angle of the dip and the width of the exposures4 ,measurement of the thickness of formations4--,when formations still lie in horizontal beds1 we may sometimes learn their thickness directly either from the depth of borings to the underlying rock1 or by measurements upon steep caon walls4 ,if the beds stand vertically1 the matter is exceedingly simple1 for in this case the thickness is the width of the outcrops of the formation between the beds which bound it upon either side4 ,in the general case1 in which the beds are neither horizontal nor vertical1 the thickness must be obtained indirectly from the width of the exposures and the angle of the dip4 ,the factor by which the exposure width must be multiplied is known as the sine of the dip angle 7,fig4 #cj71 which is given with sufficient accuracy for most purposes in the following table4 ,it is obvious that in order to obtain the full thickness of a formation it is necessary to measure from the contact with the adjacent formation upon the one side to a similar contact with the nearest formation upon the other4 ,natural ,sines #j 4#jj #ce 4#eg #gj 4#id #e 4#ji #dj 4#fd #ge 4#ig #aj 4#ag #de 4#ga #hj 4#ih #ae 4#bf #ej 4#gg #he #a4jj #bj 4#cd #ee 4#hb #ij #a4jj #be 4#db #fj 4#hg #cj 4#ej #fe 4#ia ,illustration3 ,,fig4 #ca4--;,combined surface and sectional views of a plunging anticline 7after ,willis74 ,illustration3 ,,fig4 #cb4--;,combined surface and sectional views of a plunging syncline 7after ,willis74 ,the detection of plunging folds4--,when the axis of a fold is horizontal1 its outcrops upon a plain will continue to have the same strike until the formation comes to an end4 ,upon a generally level surface1 therefore1 any regular progressive variation in the strike direction is an indication that the folds have a plunging or pitching character4 ,many serious mistakes of interpretation have been made because of a failure to recognize this evidence of plunging folds4 ,the way in which the strikes are progressively modified will be made clear by the diagrams of ,figs4 #ca and #cb1 the first representing a pitching anticline and the second a pitching syncline4 ,in both these reciprocal cases the strikes of the beds undergo the same changes1 and the dip directions serve to distinguish which of the two structures is present in a given case4 ,there is1 however1 one further difference in that the hard layers of the plunging anticline1 where they disappear below the surface in the axis1 will present a domed surface sloping forward like the back of a whale as it rises above the surface of the sea4 ,plunging folds in series will thus appear in the topography as a series of sharply zigzagging ranges at those localities where the harder layers intersect the surface4 ,such features are encountered in eastern ,pennsylvania1 where the hard formations of the ,appalachian ,mountain system plunge northeastward under the later formations4 ,the pitch of the larger fold is often disclosed by that of the minor puckerings superimposed upon it4 ,illustration3 ,,fig4 #cc4--,unconformity between a lower and an upper series of beds upon the coast of ,california4 ,note how the hard layer stands in relief upon the connecting surface 7after ,fairbanks74 ,the meaning of an unconformity4--,the rock beds1 which are deposited one above the other during a transgression of the sea1 are usually parallel and thus represent a continuous process of deposition4 ,such beds are said to be conformable4 ,where1 upon the other hand1 two series of deposits which are not parallel to each other are separated by a break1 they are said to form unconformable series1 and the break or surface of junction is an unconformity 7,fig4 #cc74 ,here it is evident that the sediments which compose the lower series of beds have been folded in the zone of flow1 though the upper series has evidently escaped this vicissitude4 ,furthermore1 the surface which delimits the lower series from the upper is somewhat irregular and shows a hard layer standing in relief1 as it would if it had opposed greater resistance to the attacks of the atmosphere upon it4 ,illustration3 ,,fig4 #cd4--,series of diagrams to illustrate in succession the episodes involved in the historical development of an angular unconformity4 ,the vertical arrows indicate direction of movement of the land1 and the horizontal arrows the direction of shore migration4 ,in reality1 an unconformity between formations must be interpreted to mean that the lower series is not only older than the upper1 as shown by the order of superposition1 but that the time of its deposition was separated from that of the upper by a hiatus in which important changes took place in the lower series4 ,the stages or episodes in the history of the beds represented in ,fig4 #cc may be read as follows 7see ,fig4 #cd a-e73-- 7a7 ,deposition of the lower series during a transgression of the sea4 7b7 ,continued subsidence and burial of the lower series beneath overlying sediments1 and flexuring in the zone of flow4 7c7 ,elevation of the combined deposits to and far above sea level and removal by erosion of vast thicknesses of the upper sediments4 7d7 ,a new subsidence of the truncated lower series and deposition of the upper series across its eroded surface4 7e7 ,a new elevation of the double series to its present position above sea level4 ,illustration3 ,,fig4 #ce4--,types of deceptive or erosional unconformities4 ,from this succession of episodes it is seen that a break of this kind between two series of deposits involves a double oscillation of subsidence followed by elevation--a large depression followed by a large elevation1 a smaller subsidence followed by elevation4 ,the time interval which must have been represented by these repeated operations is so vast as at first to stagger the mind in contemplating it4 ,when1 as in this instance1 the dips of the lower series of beds differ from those of the upper1 we have to do with an angular unconformity4 ,it may be1 however1 that the lower series was not so far depressed as to enter the zone of flow1 and that its beds meet those of the upper series with apparent conformity4 ,such an unconformity is often extremely difficult to recognize1 and it is described as a deceptive or erosional unconformity4 ,with a deceptive unconformity the clew to its real nature is usually some fact which indicates that the lower series of sediments had been raised above the level of the sea before the upper series was deposited upon it4 ,this may be apparent either in the irregularity of the surface on which the two series are joined1 in some evidence of the action of waves such as would be furnished by a basal conglomerate in the upper series1 or some indication of different resistance of different rocks of the lower series to attacks of the atmosphere upon them 7,figs4 #cc and #ce a-c74 ,in most cases1 at least1 the lowest member of the upper series will be a different type of rock from the uppermost member of the lower series1 hence the frequent occurrence of the discordant cross bedding in sandstone should not deceive even the novice into the assumption of an unconformity4 ,,reading ,,references ,,to ,,chapter ,v ,the zones of fracture and flow3-- ,c4 ,r4 ,,van ,,hise4 ,principles of ,north ,american ,precambrian ,geology1 #afth ,ann4 ,rept4 ,u4,s4 ,geol4 ,surv41 #ahie1 ,pt4 ,i1 pp4 #eha-fjc4 ,,bailey ,,willis4 ,mechanics of ,appalachian ,structure1 #acth ,ann4 ,rept4 ,u4,s4 ,geol4 ,surv41 #ahic1 ,pt4 ,,ii1 pp4 #bag-bec4 ,a4 ,,daubr,e4 tudes ,synthtiques de ,gologie ,exprimentale4 ,paris1 #ahgi1 pp4 #cjf-cbh1 pl4 ,,ii4 ,w4 ,,prinz4 ,quelques remarques gnrales propos de l'essai de carte tectonique de la belgique1 etc41 ,bull4 ,soc4 ,belge ,geol41 vol4 #ah1 #aijd1 p4 #adc1 pl4 ,v4 ,analysis of folds3-- ,,van ,,hise and ,,willis as above2 ,,de ,,margerie et ,,heim2 ,les dislocations de l'corce terrestre 7in ,french and ,german languages74 ,zurich1 #ahhh4 ,geological maps3-- ,,wm4 ,h4 ,,hobbs4 ,the ,mapping of the ,crystalline ,schists1 ,jour4 ,geol41 vol4 #aj1 #aijb1 pp4 #ghj-gib1 #heh-hij4 ,,chapter ,,vi ,,the ,,architecture ,,of ,,the ,,fractured ,,superstructure ,illustration3 ,,fig4 #cf4--;,a set of master joints developed in shale upon the shores of ,cayuga ,lake near ,ithaca1 ,new ,york 7after ,u4 ,s4 ,g4 ,s474 ,illustration3 ,,fig4 #cg4--;,diagram to show how sets of master joints differing in direction by half a right angle may abruptly replace each other4 ,illustration3 ,,fig4 #ch4--;,diagram to show the different combinations of the series composing two double sets of master joints1 and in a1 a1 a additional disorderly fractures4 ,the system of the fractures4--,in referring to experiments made upon the fracture of solid blocks under compression 7p4 #da71 it was shown that two series of parallel fractures develop perpendicular to each free surface of the block1 and that these series are each of them inclined by half of a right angle to the direction of compression1 and thus perpendicular to each other4 ,the fragments into which a block with one free surface would thus tend to be divided should be square prisms perpendicular to the free surface4 ,it would be interesting1 if it were practicable1 to learn from experiment how these prisms would be further fractured by a continuation of the compression4 ,from mechanical considerations involving the resolution of forces with reference to the ready-formed fractures1 it seems probable that the next series of fractures to form would bisect the angles of the first double series or set4 ,wherever rocks are found exposed in their original attitudes1 they are1 in fact1 seen to be intersected by two parallel series of fractures which are perpendicular to the earth's surface and to each other and are described as joints4 ,in many cases more than two series of such fractures are found1 yet even in these cases two more perfectly developed series are prominent and almost exactly perpendicular to each other as well as to the earth's surface4 ,this omnipresent double series or set of joints is the well-known set of master joints1 and very often it is found developed practically alone 7,fig4 #cf74 ,over large areas1 the direction of the set of master joints may remain practically constant1 or this set may quite suddenly give place to a similar set which is1 however1 turned through half a right angle from the first 7,fig4 #cg74 ,not infrequently two such sets of master joints are found together bisecting each other's angles within the same rocks1 and to them are sometimes added additional though less perfect series of joint planes4 ,studied throughout a considerable district1 the various series which make up these two sets of master joints may be seen locally developed in different combinations as well as in association with additional fissure planes which are not easily reduced to any simple law of arrangement 7,fig4 #ch a1 a1 a74 ,only rarely are regular joint series observed which do not stand perpendicular to the original attitude of the rock beds4 ,in a few localities1 however1 rectangular joint sets have been discovered which divide the rock into prisms parallel to the earth's surface and with the joint series inclined to it each by half a right angle4 ,where the rock beds have been much disturbed1 the complex of joints may be such as to defy all attempts at orderly arrangement4 ,illustration3 ,,fig4 #ci4--,view on the shore at ,holstensborg1 ,west ,greenland1 to show the subequal spacing of the joints 7after ,kornerup74 ,illustration3 ,,fig4 #dj4--,view of an exposed hillside in ,iceland upon which the snow collected in crannies along the joints brings out to advantage both the larger and the smaller intervals of the joint system 7after ,thoroddsen74 ,the space intervals of joints4--,the same kind of subequal spacing which characterizes the fractures near the surface of the block in ,daubre's experiment 7,fig4 #ai1 p4 #da7 is found simulated by the rock joints 7,fig4 #ci74 ,such unit intervals between fractures may be grouped together into larger units which are separated by fractures of unusual perfection4 ,we may think of such larger space units as having the smaller ones superimposed upon them 7,fig4 #dj74 ,the displacements upon joints--faults4--,in the vast majority of cases1 the joint fractures when carefully examined betray no evidence of any appreciable movement of the two walls upon each other4 ,generally the rock layers are seen to cross the joints without apparent displacement4 ,joints are therefore planes of disjunction only1 and not planes of displacement4 ,illustration3 ,,fig4 #da4--;,faulted blocks of basalt divided by joints near ,woodbury1 ,connecticut4 ,to show the structure of the rock1 some of the foliage has been removed in preparing the sketch from a photograph4 ,within many districts1 however1 a displacement may be seen to have occurred upon certain of the joint planes1 and these are then described as faults4 ,such displacements of necessity imply a differential movement of sections or blocks of the earth's crust1 the so-called orographic blocks1 which are bounded by the joint planes and play individual rles in the movement4 ,a simple case of such displacements in rocks intersected by a single set of master joints is represented in the model of plate #d ,c4 ,the most prominent fault represented by this model runs lengthwise through the middle1 and the displacement which is measured upon it not only varies between wide limits1 but is marked by abrupt changes at the margins of the larger blocks4 ,this vertical displacement upon the fault is called its throw4 ,though not illustrated by the model1 horizontal displacements may likewise occur1 and these will be more fully discussed when the subject of earthquakes is considered in the following chapter4 ,an actual example of blocks displaced by vertical adjustment is represented in ,fig4 #da1 a simple type of faulting which has taken place in rocks but slightly disturbed from their original attitude1 but intersected by a relatively simple system of master joints4 ,in those regions where the beds have been folded and perhaps overthrust before their elevation into the zone of fracture1 and which are further intersected by disorderly fissure planes1 the results are far more complex4 ,in such cases the planes of individual displacement may not be vertical1 though they are generally steeper than #de4 ,for their description it is necessary to make use of additional technical terms 7,fig4 #db74 ,the inclination of a sloping fault plane measured against the vertical is called the hade of the fault4 ,the total displacement is measured along the plane of the fault from a point upon one limb to the point from which it was separated in the other4 ,the additional terms are made sufficiently clear by the diagram4 ,illustration3 ,,fig4 #db4--;,a fault in previously disturbed strata4 ,,ab1 displacement2 ,,ac1 throw2 ,,bd1 stratigraphic throw2 ,,bc1 heave2 angle ,,cab1 hade4 ,methods of detecting faults4--,the first effect of a fault is usually to produce a crack at the surface of the earth2 and1 provided there is a vertical displacement or throw1 an escarpment which rises upon the upthrown side of the fault4 ,in general it may be said that escarpments which appear at the earth's surface as plane surfaces probably represent planes of fracture1 though not necessarily planes of faulting4 ,in many cases the actual displacements lie buried under loose rock dbris near to and paralleling the escarpment1 and in some cases as a result of the erosional processes working upon alternately hard and soft layers of rock1 the escarpment may later appear upon the downthrown side or limb of the fault 7,fig4 #dc74 ,as an illustration of a fault escarpment1 the faade of ,el ,capitan and many other rock faces of the ,yosemite valley may be instanced4 ,illustration3 ,,fig4 #dc4--;,diagrams to show how an escarpment originally on the upthrown side of the fault may1 through erosion1 appear upon the downthrown side4 ,illustration3 ,,fig4 #dd4--;,a fault plane exhibiting 8drag40 ,the opening is artificial 7after ,scott74 ,when we have further studied the erosional processes at the earth's surface1 it will be appreciated that faults tend to quickly bury themselves from sight1 whereas fold structures will long remain in evidence4 ,many faults will thus be overlooked1 and too great weight is likely to be ascribed to the folds in accounting for the existing attitudes and positions of the rock masses4 ,faults must therefore be sought out if mistakes of interpretation are to be avoided4 ,the most satisfactory evidence of a fault is the discovery of a rock bed which may be easily identified1 and which is actually seen displaced on a plane of fracture which intersects it 7,fig4 #db1 p4 #ei74 ,when such an easily recognizable layer is not to be found1 the plane of displacement may perhaps be discovered as a narrow zone composed of angular fragments of the rock cemented together by minerals which form out of solution in water4 ,such a fractured rock zone which follows a plane of faulting is a fault breccia4 ,if the fault breccia1 or vein rock1 is much stronger than the rock on either side1 it may eventually stand in relief at the surface like a dike or wall4 ,at other times the displacement produces little fracture of the walls1 but they slide over each other in such a manner as to yield either a smoothly corrugated or an evenly polished surface which is described as 8slickensides40 ,it may be1 however1 that during the movement either one or both of the walls have 8dragged01 and so are curled back in the immediate neighborhood of the fault plane 7,fig4 #dd74 ,when1 as is quite generally the case1 the actual plane of displacement of a fault is not open to inspection1 the movement may be proven by the observation of abrupt1 as contrasted with gradual1 changes in the strikes and dips of neighboring exposures 7,fig4 #de72 or by noting that some easily recognized formation has been sharply offset in its outcrops 7,fig4 #df74 ,illustration3 ,,fig4 #de4--,map to show how a fault may be indicated in abrupt changes of the strike and dip of neighboring exposures4 ,illustration3 ,,fig4 #df4--;,a series of parallel faults indicated by successive offsets in the course of an easily recognizable rock formation4 ,there are in addition many indications rather than proofs of the presence of faults1 which must be taken account of in every general study of the geology of a district4 ,thus the outcrops of all neighboring formations may terminate abruptly upon a straight line which intersects all alike4 ,deep-seated fissure springs may be aligned in a striking manner1 and so indicate the course of a prominent fracture1 though not necessarily of a fault4 ,much the same may be said of the dikes of cooled magma which have been injected along prexisting fractures4 ,the base of the geological map4--,modern topographic maps form an important part of the library of the serious student of physiography2 they are the gazetteer of this branch of science4 ,every civilized nation has to-day either completed a topographic atlas of its territory1 or it is vigorously prosecuting a survey to furnish maps which represent the relief with some detail1 and publishing the results in the form of an atlas of quadrangles4 ,thus a relief map will erelong be obtainable of any part of the civilized world1 and may be purchased in separate sections4 ,nowhere is this work being taken up with greater vigor than in the ,united ,states1 where a vast domain representing every type of topographic peculiarity is being attacked from many centers4 ,here and elsewhere the relief of the land is being expressed by so-called contours or lines of equal altitude upon the earth's surface4 ,it is as though a series of horizontal planes1 separated by uniform intervals of #bj or #dj or #ajj feet1 had been made to intersect the surface1 and the intersection curves1 after consecutive numeration1 had been dropped into a single plane for printing4 ,where the slopes are steep1 the contour lines in the topographic map will appear crowded together and so produce a deep shade upon the map2 whereas with relatively flat surfaces white patches will stand out prominently upon the map4 ,more and more the topographic map is coming into use1 and for the student of nature in particular it is important to acquire facility in interpreting the relief from the topographic map4 ,to further this end1 a special model has been devised1 and its use is described in appendix ,c4 ,usually before any satisfactory geological map can be prepared1 a contoured topographic map of the district to be studied must be available4 ,the field map and the areal geological map4--,as the atlas of topographic maps is the physiographic gazetteer1 so geological maps together constitute the reference dictionary of descriptive geology4 ,not only are topographic maps of many districts now generally available1 but more and more it has become the policy of governments to supply geological maps in the same quadrangle form which is the unit of the topographic map4 ,the geological map is1 however1 a complex of so many conventional symbols1 that without some practical experience in the actual preparation of one1 it is exceedingly difficult for the student to comprehend its significance4 ,a modern geological map is usually a rectangular sheet printed in color1 upon which are many irregular areas of individual hue joined to each other like the parts of a child's picture puzzle4 ,the colored areas upon the geological map are each supposed to indicate where a certain rock type or formation lies immediately below the surface1 and this distribution represents the best judgment of the geologist who1 after a study of the district1 has prepared the map4 ,unfortunately the conventions in use are such that his observation and his theory have been hopelessly intermingled in the finished product4 ,armed with the geological map1 the student who visits the district finds spread out before him1 it may be1 a landscape of hill and valley1 of green forest and brown farming land1 which is as different as may be from the colored puzzle which he holds in his hand4 ,hidden under the farm vegetation or masked by the woods are scattered outcroppings of rock which have been the basis of the geologist's judgment in preparing the map4 ,experience shows that in order to bridge the wide gap between the geology in the landscape and the patches of color upon the map something more than mere examination of the colored sheet is necessary4 ,we shall therefore describe1 with the aid of laboratory models1 the various stages necessary to the preparation of a geological map1 and every student should be advised to follow this by practical study of some small area where rocks are found in outcrop4 ,though the published areal geological map represents both fact and theory1 the map maker retains an unpublished field map or map of observations1 upon which the final map has been based4 ,this field map shows the location of each outcrop that has been studied1 with a record of the kind of rock and of such observations as strike1 dip1 and pitch4 ,our task will therefore be to prepare3 7#a7 a field map2 7#b7 an areal geological map2 and 7#c7 some typical geological sections4 ,laboratory models for the study of geological maps4--,in order to represent in the laboratory the disposition of rock outcrops in the field1 special laboratory tables are prepared with removable covers and with fixed tops1 which are divided into squares numbered like the township sections of the national domain 7,fig4 #dg74 ,to represent the rock outcrops1 blocks are prepared which may be fixed in any desired position by fitting a pin into a small augur hole bored through the table4 ,the outcrop blocks for the sedimentary rock types are so constructed as to show the strike and dip of the beds4 7,see ,appendix ,d47 ,illustration3 ,,fig4 #dg4--;,field map prepared from a laboratory table4 ,the method of preparing the map4--,to prepare the map1 use is made of a geological compass with clinometer attachment1 a protractor1 and a map base divided into sections like the top of the table1 and on the scale of one inch to the foot4 ,each exposure represented upon the table is 8visited0 and then located upon the base map in its proper position and attitude4 ,the result is the field map 7,fig4 #dg71 which thus represents the facts only1 unless there have been uncertainties in the correlation of exposures or in determining the position of the bedding plane4 ,illustration3 ,,fig4 #dh4--;,areal geological map constructed from the field map of ,fig4 #dg1 with two selected geological sections4 ,to prepare the areal geological map from the field map1 it is first necessary to fix the boundaries which separate formations at the surface2 and now perhaps for the first time it is realized how large an element of uncertainty may enter if the exposures were widely separated4 ,it is clear that no two persons will draw these lines in the same positions throughout1 though certain portions of them--where the facts are more nearly adequate--may correspond4 ,in ,fig4 #dh is represented the areal geological map constructed from the field map1 with the doubtful area at one side left blank4 ,some conclusions from this map may now be profitably considered4 ,the complexly folded sandstone formation at the left of the map appears as the oldest member represented1 since its area has been cut through by the intrusive granite which does not intrude other formations1 and is unconformably overlaid by the limestone and its basal layer of conglomerate4 ,the limestone in turn is unconformably overlaid by the merely tilted sandstone beds at the right of the map4 ,these three sedimentary formations clearly represent decreasing amounts of close folding1 from which it is clear that each earlier formation has passed through an episode not shared by that of next younger age4 ,of the other intrusive rocks1 the dike of porphyry is younger than all the other formations1 with the possible exception of the upper sandstone4 ,offsetting of the formations has disclosed the course of a fault1 and from its relations to the dikes we may learn that of these the porphyry is younger and the basalt older than the date of the faulting4 ,the dashed lines upon the map 7,,ab and ,,cd7 have been selected as appropriate lines along which to construct geological sections 7,fig4 #dh1 below map71 and from these sections the exposed thicknesses of the different formations may be calculated4 ,in one instance only1 that of the conglomerate1 can we be sure that this exposed thickness measures the entire formation4 ,fold versus fault topography4--,the more resistant or 8stronger0 rock beds1 as regards attacks of the atmosphere1 in the course of time come to stand in relief1 separated by depressions which overlie the 8weaker0 formations4 ,simple open folds which are not plunging exercise an influence upon topography by producing generally long and straight ridges4 ,more complex flexures1 since they generally plunge1 make themselves apparent by features which in the map are represented by curves4 ,fracture structures1 and especially block displacements1 are differentiated from these curving features by the dominance of straight or nearly rectilinear lines upon the map4 ,the effect of erosion is to reduce the asperity of features and to mold them with flowing curves4 ,the fracture structures are for this reason much more likely to be overlooked1 and if they are not to elude the observer1 they must be sought out with care4 ,fold and fracture structures may both be revealed upon the same map4 ,,reading ,,references ,,to ,,chapter ,,vi ,joint systems3-- ,,john ,,phillips4 ,observations made in the ,neighborhood of ,ferrybridge in the ,years #ahbf-ahbh1 ,phil4 ,mag41 #b;d ser41 vol4 #d1 #ahbh1 pp4 #dja-dji2 ,illustrations of the geology of ,yorkshire1 ,pt4 ,,ii1 ,the ,limestone ,district4 ,london1 #ahcf1 pp4 #ij-ih4 ,,samuel ,,haughton4 ,on the ,physical ,structure of the ,old ,red ,sandstone of the ,county of ,waterford1 considered with reference to cleavage1 joint surfaces1 and faults1 ,trans4 ,roy4 ,soc4 ,london1 vol4 #adh1 #aheh1 pp4 #ccc-cdh4 ,w4 ,c4 ,,br,,gger4 ,spaltenverwerfungen in der ,gegend ,langesund-,skien1 ,nyt ,magazin for ,naturvidernskaberne1 vol4 #bh1 #ahhd1 pp4 #bec-dai4 ,,wm4 ,h4 ,,hobbs4 ,the ,newark ,system of the ,pomperaug ,valley1 ,connecticut1 #bast ,ann4 ,rept4 ,u4 ,s4 ,geol4 ,surv41 ,pt4 ,,iii1 #aija1 pp4 #he-adc4 ,geological map3-- ,,wm4 ,h4 ,,hobbs4 ,the ,interpretation of ,geological ,maps1 ,school ,science and ,mathematics1 vol4 #i1 #aiji1 pp4 #fdd-fec4 ,,chapter ,,vii ,,the ,,interrupted ,,character ,,of ,,earth ,,movements3 ,,earthquakes ,,and ,,seaquakes ,nature of earthquake shocks4--,man's belief in the stability of ,mother ,earth--the terra firma--is so inbred in his nature that even a light shock of earthquake brings a rude awakening4 ,the terror which it inspires is no doubt largely to be explained by this disillusionment from the most fundamental of his beliefs4 ,were he better advised1 the long periods of quiet which separate earthquakes1 and not the lighter shocks which follow all grander disturbances1 would occasion him concern4 ,illustration3 ,,fig4 #di4--,view of a portion of the ruins of ,messina after the earthquake of ,december #bh1 #aijh4 ,earthquakes are the sensible manifestations of changes in level or of lateral adjustments of portions of the continents1 and the seismic disturbances upon the sea--seaquakes and seismic sea waves--relate to similar changes upon the floor of the ocean4 ,during the grander or catastrophic earthquakes1 the changes are indeed terrifying1 and have usually been accompanied by losses to life and property1 which are only to be compared with those of great conflagrations or of inundations on thickly populated plains4 ,the conflagration has all too frequently been an aftermath of the great historic earthquakes4 ,the earthquake of ,december #bh1 #aijh1 in southern ,italy1 destroyed almost the entire population of a great city1 and left of its massive buildings only a confused heap of rubble 7,fig4 #di74 ,two years later a heavy earthquake resulted in great damage to cities in ,costa ,rica 7,fig4 #ej71 while two years earlier our own country was first really awakened to the danger in which it stands from these convulsive earth throes2 though1 as we shall see1 these dangers can be largely met through proper methods of construction4 ,illustration3 ,,fig4 #ej4--,ruins of the ,carnegie ,palace of ,peace at ,cartago1 ,costa ,rica1 destroyed when almost completed by the great earthquake of ,may #d1 #aiaj 7after a photograph by ,rear-,admiral ,singer1 ,u4,s4,n474 ,earthquakes are usually preceded for a brief instant by subterranean rumblings whose intensity appears to bear no relation to the shocks which follow4 ,the ground then rocks in wavelike motions1 which1 if of large amplitude1 may induce nausea1 prevent animals from keeping upon their feet1 and wreck all structures not specially adapted to withstand them4 ,heavy bodies are sometimes thrown up from the ground 7,fig4 #ea71 and at other times similar heavy masses are1 apparently because of their inertia1 more deeply imbedded in the earth4 ,thus gravestones and heavy stone posts are often sunk more deeply in the ground and are surrounded by a hollow and perhaps by small open cracks in the surface 7,fig4 #eb74 ,when bodies are thrown upward1 it would imply that a quick upward movement of the ground had been suddenly arrested1 while the burial of heavy bodies in the earth is probably due to a movement which begins suddenly and is less abruptly terminated4 ,illustration3 ,,fig4 #ea4--;,bowlders thrown into the air and overturned during the ,assam earthquake of #ahig 7after ,r4 ,d4 ,oldham74 ,illustration3 ,,fig4 #eb4--;,heavy post sunk deeper into the ground during the ,charleston earthquake of ,august #ca1 #ahhf 7after ,dutton74 ,seaquakes and seismic sea waves4--,upon the ocean the quakes which emanate from the sea floor are felt on shipboard as sudden joltings which produce the impression that the ship has struck upon a shoal1 though in most instances there is no visible commotion in the water4 ,the distribution of these shocks1 as indicated either by the experiences of neighboring ships at the time of a particular shock1 or by the records of vessels which at different times have sailed over an area of frequent seismic disturbance1 appears to be limited to narrow zones or lines 7,fig4 #ec74 ,the same tendency of under-sea disturbances to be localized upon definite straight lines has been often illustrated by the behavior of deep-sea cables which are laid in proximity to one another and which have been known to part simultaneously at points ranged upon a straight line4 ,illustration3 ,,fig4 #ec4--,map showing the localities at which shocks have been reported at sea off ,cape ,mendocino1 ,california4 ,far grander disturbances upon the floor of the ocean have been revealed by the great sea waves--the so-called 8tidal waves01 properly referred to as tsunamis--which recur in those sea districts which adjoin the special earthquake zones upon the continents 7p4 #hf74 ,the forerunner of such a sea wave approaching the shore is usually a sudden withdrawal of the water so as to lay bare a portion of the bottom1 but this is well-recognized to be the premonition of a gigantic oncoming wave which sweeps all before it and is only halted when it has rolled over all the low-lying country and encountered a mountain wall4 ,such seismic waves have been especially common upon the ,pacific shore of ,south ,america and upon the ,japanese littoral 7,fig4 #ed74 ,these waves proceed from above the great deeps upon the ocean bottom1 and clearly result from the grander earth movements to which these depressions owe their exceptional depth4 ,the withdrawal of the water from neighboring shores may be presumed to be connected with a descent of the floor of the depression and the consequent drawing-in of the ocean surface above4 ,the later high wave would thus represent the dispersion of the mountain of water which is raised by the meeting of the waters from the different sides of the depression4 ,illustration3 ,,fig4 #ed4--;,effect of a seismic water wave at ,kamaishi1 ,japan1 in #ahif 7after ,e4 ,r4 ,scidmore74 ,illustration3 ,,fig4 #ee4--;,a fault of vertical displacement4 ,the grander and the lesser earth movements4--,upon the land the grander and so-called catastrophic earthquakes are usually the accompaniment of important changes in the surface of the ground that will be discussed in later sections4 ,those shocks which do little damage to structures produce no visible changes in the earth's surface1 except1 it may be1 to shake down some water-soaked masses of earth upon the steeper slopes4 ,still other movements1 and these too slight to be felt even in the night when the animal world is at rest1 may yet be distinguished by their sounds1 the unmistakable rumblings which are characteristic alike of the heaviest and the lightest of earthquake shocks4 ,illustration3 ,,fig4 #ef4--;,escarpment produced by an earthquake fault of vertical displacement which cut across the ,chedrang ,river and thus produced a waterfall1 ,assam earthquake of #ahig 7after ,r4 ,d4 ,oldham74 ,changes in the earth's surface during earthquakes--faults and fissures4--,each of the grander among historic earthquakes has been accompanied by noteworthy changes in the configuration of the earth's surface within the district where the shocks were most intense4 ,a section of the ground is usually found to have moved with reference to another upon the other side of a vertical plane which is usually to be seen2 we have here to do with the actual making of a fault or displacement such as we find the fossil examples of within the rocks4 ,the displacement1 or throw1 upon the fault plane may be either upward or downward or laterally in one direction or the other1 or these movements may be combined4 ,a movement of adjacent sections of the ground upward or downward with reference to each other 7,fig4 #ee7 has been often observed1 notably at ,midori after the great ,japanese earthquake of #ahia1 and in the ,chedrang valley of ,assam after the earthquake of #ahig 7,fig4 #ef74 ,illustration3 ,,fig4 #eg4--;,a fault of lateral displacement4 ,illustration3 ,,fig4 #eh4--;,fence parted and displaced fifteen feet by a transverse fault formed during the ,california earthquake of #aijf 7after ,w4 ,b4 ,scott74 ,illustration3 ,,fig4 #ei4--;,fault with vertical and lateral displacements combined4 ,a lateral throw1 unaccompanied by appreciable vertical displacement 7,fig4 #eg71 is especially well illustrated by the fault in ,california which was formed during the earthquake of #aijf 7,fig4 #eh74 ,a combination of the two types of displacement in one 7,fig4 #ei7 is exemplified by the ,baishiko fault of ,formosa at the place shown in plate #c ,a4 ,the measure of displacement4--,to afford some measure of the displacements which have been observed upon earthquake faults1 it may be stated that the maximum vertical throw measured upon the fault in the ,neo valley of ,japan 7#ahia7 was #ah feet1 in the ,chedrang valley of ,assam 7#ahig7 #ce feet1 and of the ,alaskan coast 7#ahii7 #dg feet4 ,large sections of land were bodily uplifted in these cases within the space of a few seconds1 or at most a few minutes1 by the amounts given4 ,the largest recorded lateral displacement measured upon an earthquake fault is about #ba feet upon the ,california rift after the earthquake of #aijf2 though an amount only slightly less than this is indicated in the shifting of roads and arroyas dating from the earthquake of #ahgb in the ,owens valley1 ,california4 ,fault lines once established are planes of special weakness and become later the seat of repeated movements of the same kind4 ,,plate #c4 ,illustration3 ,a4 ,an earthquake fault opened in ,formosa in #aijf1 with vertical and lateral displacements combined 7after ,omori74 ,illustration3 ,b4 ,earthquake faults opened in ,alaska in #ahhi1 on which vertical slices of the earth's shell have undergone individual adjustments 7after ,tarr and ,martin74 ,illustration3 ,,fig4 #fj4--;,diagram to show how small faults in the rock basement may be masked at the surface through adjustments within the loose rock mantle4 ,the greater number of earthquake faults are found in the loose rock cover which so generally mantles the firmer rock basement1 and it is almost certain that the throws within the solid rock are considerably larger than those which are here measured at the surface1 owing to the adjustments which so readily take place in the looser materials4 ,those lighter shocks of earthquake which are accompanied by no visible displacements at the surface do1 however1 in some instances affect in a measure the flow of water upon the surface1 and thus indicate that small changes of surface level have occurred without breaks sufficiently sharp to be perceived 7,fig4 #fj74 ,intermediate between the steep escarpment and the masked displacement just described is the so-called 8mole-hill0 effect1--a rounded and variously cracked slope or ridge above the position of a buried fault 7,fig4 #fa74 ,illustration3 ,,fig4 #fa4--;,diagram to show the appearance of a 8mole hill0 above a buried earthquake fault 7after ,kot74 ,the escarpments due to earthquake faults in loose materials at the earth's surface can obviously retain their steepness for a few years or decades at the most2 for because of their verticality they must gradually disappear in rounded slopes under the action of the elements4 ,smaller displacements within a rock which rapidly disintegrates under the action of frost and sun will likewise before long be effaced4 ,in those exceptional instances where a resistant rock type has had all altered upper layers planed away until a fresh and hard surface is exposed1 and has further been protected from the frost and sun beneath a thin layer of soil1 its original surface may be retained unaltered for many centuries4 ,upon such a surface the lightest of sensible shocks1 or even the smaller earth movements which are not perceived at the time1 may leave an almost indelible record4 ,such records particularly show that the movements which they register occur upon the planes of jointing within the rock1 and that these ready formed cracks have probably been the seats of repeated and cumulative adjustments 7,fig4 #fb74 ,illustration3 ,,fig4 #fb4--,post-glacial earthquake faults of small but cumulative displacement1 eastern ,new ,york 7after ,woodworth74 ,illustration3 ,,fig4 #fc4--;,earthquake cracks in ,colorado desert 7after a photograph by ,sauerven74 ,contraction of the earth's surface during earthquakes4--,the wide variations in the amount of the lateral displacement upon earthquake faults1 like those opened in ,california in #aijf1 show that at the time of a heavy earthquake there must be large local changes in the density of the surface materials4 ,literally1 thousands of fissures may appear in the lowlands1 many of them no doubt a secondary effect of the shaking1 but others1 like the quebradas of the southern ,andes or the 8earthquake cracks0 in the ,colorado desert 7,fig4 #fc71 may have a deeper-seated origin4 ,many facts go to show1 however1 that though local expansion does occur in some localities1 a surface contraction is a far more general consequence of earth movement4 ,in civilized countries of high industrial development1 where lines of metal of one kind or another run for long distances beneath or upon the surface of the ground1 such general contraction of the surface may be easily proven4 ,comparatively seldom are lines of metal pulled apart in such a way as to show an expansion of the surface2 whereas bucklings and kinkings of the lines appear in many places to prove that the area within which they are found has1 as a whole1 been reduced4 ,illustration3 ,,fig4 #fd4--;,diagrams to show how railway tracks are either broken or buckled locally within the district visited by an earthquake4 ,illustration3 ,,fig4 #fe4--,the ,biwajima railroad bridge in ,japan after the earthquake of #ahia 7after ,milne and ,burton74 ,illustration3 ,,fig4 #ff4--;,diagrams to show how the compression of a district and its consequent contraction during an earthquake may close up the joint spaces within the rock basement and concentrate the contraction of the overlying mantle where this is partially cut through and so weakened in the valley sections4 ,water pipes laid in the ground at a depth of some feet may be bowed up into an arch which appears above the surface2 lines of curbing are raised into broken arches1 and the tracks of railways are thrown into local loops and kinks which imply a very considerable local contraction of the surface 7,fig4 #fd74 ,with unvarying regularity railway or other bridges which cross rivers or ravines1 if the structures are seriously damaged1 indicate that the river banks have drawn nearer together at the time of the disturbance4 ,in such cases1 whenever the bridge girder has remained in place upon its abutments1 these have either been broken or back-tilted as a whole in such a manner as to indicate an approach of the foundations which was prevented at the top by the stiffness of the girder 7,fig4 #fe74 ,illustration3 ,,fig4 #fg4--,map of the ,chedrang fault which made its appearance during the ,assam earthquake of #ahig4 ,the figures give the amounts of the local vertical displacement measured in feet 7after ,r4 ,d4 ,oldham74 ,the simplest explanation of such an approach of the banks at the sides of the valleys cut in loose surface material is to be found in a general closing up of the joint spaces within the underlying rock1 and an adjustment of the mantle upon the floor mainly in the valley sections 7,fig4 #ff74 ,illustration3 ,,fig4 #fh4--,map giving the displacements in feet measured along an earthquake fault formed in ,alaska in #ahii 7after ,tarr and ,martin74 ,the plan of an earthquake fault4--,in our consideration of earthquake faults we have thus far given our attention to the displacement as viewed at a single locality only4 ,such displacements are1 however1 continued for many miles1 and sometimes for hundreds of miles2 and when now we examine a map or plan of such a line of faulting1 new facts of large significance make their appearance4 ,this may be well illustrated by a study of the plan of the ,chedrang fault which appeared at the time of the ,assam earthquake of #ahig 7,fig4 #fg74 ,from this map it will be noticed that the upward or downward displacement upon the perpendicular plane of the fault is not uniform1 but is subject to large and sudden changes4 ,thus in order the measurements in feet are #cb1 #j1 #ah1 #ce1 #j1 #h1 #be1 #ab1 #h1 #b1 #j4 ,the fault formed in #ahii upon the shores of ,russell ,fjord in ,alaska 7,fig4 #fh7 reveals similar sudden changes of throw1 only that here the direction of the movement is often reversed2 or1 otherwise expressed1 the upthrow is suddenly transferred from one side of the fault to the other4 ,such abrupt changes in the direction of the displacement have been observed upon many earthquake faults1 and a particularly striking one is represented in ,fig4 #fi4 ,illustration3 ,,fig4 #fi4--;,abrupt change in the direction of throw upon an earthquake fault which was formed in the ,owens valley1 ,california1 in #ahgb4 ,the observer looks directly along the course of the fault from the left foreground to the cliff beyond and to the left of the impounded water 7after a photograph by ,w4 ,d4 ,johnson74 ,the block movements of the disturbed district4--,the displacements upon earthquake faults are thus seen to be subdivided into sections1 each of which differs from its neighbors upon either side and is sharply separated from them1 at least in many instances4 ,these points of abrupt change of displacement are1 in many cases at least1 the intersection points with transverse faults 7,fig4 #fi74 ,such points of abrupt change in the degree or in the direction of the displacement may be1 when looked at from above1 abrupt turning points in the direction of extension of the fault1 whose course upon the map appears as a zigzag line made up of straight sections connected by sharp elbows 7,fig4 #gj74 ,illustration3 ,,fig4 #gj4--,map of the faults within an area of the ,owens valley1 ,california1 formed in part during the earthquake of #ahgb1 and in part due to early disturbances1 ,in the western portions the displacements cut across firm rock and alluvial deposits alike without deviation of direction 7after a map by ,w4 ,d4 ,johnson74 ,such a grouping of surface faults as are represented upon the map is evidence that the area of the earth's shell1 which is included1 has at the time of the earthquake been subject to adjustments as a series of separate units or blocks1 certain of the boundaries of which are the fault lines represented4 ,the changes in displacement measured upon the larger faults make it clear that the observed faults can represent but a fraction of the total number of lines of displacement1 the others being masked by variations in the compactness of the loose mantling deposits4 ,could we but have this mantle removed1 we should doubtless find a rock floor separated into parts like an ancient ,pompeiian pavement1 the individual blocks in which have been thrown1 some upward and some downward1 by varying amounts4 ,less than a hundred miles away to the eastward from the ,owens ,valley1 a portion of this pavement has been uncovered in the extensive operations of the ,tonapah ,mining ,district1 so that there we may study in all its detail the elaborate pattern of earth marquetry 7,fig4 #ga7 which for the floor of the ,owens valley is as yet denied us4 ,illustration3 ,,fig4 #ga4--,marquetry of the rock floor of the ,tonapah ,mining ,district1 ,nevada 7after ,spurr74 ,illustration3 ,,fig4 #gb4--,map of a portion of the ,alaskan coast to show the adjustments in level during the earthquake of #ahii 7after ,tarr and ,martin74 ,the earth blocks adjusted during the ,alaskan earthquake of #ahii4--;,for a study of the adjustments which take place between neighboring earth blocks during a great earthquake1 the recent ,alaskan disturbance has offered the advantage that the most affected district was upon the seacoast1 where changes of level could be referred to the datum of the sea's surface4 ,here a great island and large sections of the neighboring shore underwent movements both as a whole in large blocks and in adjustments of their subordinate parts among themselves 7,fig4 #gb74 ,some sections of the coast were here elevated by as much as #dg feet1 while neighboring sections were uplifted by smaller amounts 7,fig4 #gc71 and certain smaller sections were even dropped below the level of the sea4 ,illustration3 ,,fig4 #gc4--,view on ,haencke ,island1 ,disenchantment ,bay1 ,alaska1 revealing the shore that rose seventeen feet above the sea during the earthquake of #ahii1 and was found with barnacles still clinging to the rock 7after ,tarr and ,martin74 ,the amount of such subsidence is1 however1 difficult to ascertain1 for the reason that the former shore features are now covered with water and thus removed from observation4 ,in favorable localities the minimum amount of submergence may sometimes be measured upon forest trees which are now flooded with sea water4 ,in ,fig4 #gd a portion of the coast is represented where the beach sand is now extended back into the spruce forest1 a distance of a hundred feet or more1 and where sedgy beach grass is growing among trees whose roots are now laved in salt water4 ,at the front of this forest the great storm waves overturn the trees and pile the wreckage in front of those that still remain standing4 ,illustration3 ,,fig4 #gd4--,partially submerged forest upon the shore of ,knight ,island1 ,alaska1 due to the sinking of a section of the coast during the earthquake of #ahii 7after ,tarr and ,martin74 ,illustration3 ,,fig4 #ge4--,settlement of a section of the shore at ,port ,royal1 ,jamaica1 during the earthquake of ,january #ad1 #aijg1 adjacent to a similar but larger settlement of the near shore during the earthquake of #afib 7after a photograph by ,brown74 ,upon the glaciated rock surfaces of the ,alaskan coast1 exceptionally favorable opportunities are found for study of the intricate pattern of the earth mosaic which is under adjustment at the time of an earthquake4 ,upon ,gannett ,nunatak the surface was found divided by parallel faults into distinct slices which individually underwent small changes of level 7plate #c ,b74 ,,chapter ,,viii ,,the ,,interrupted ,,character ,,of ,,earth ,,movements3 ,,earthquakes ,,and ,,seaquakes 7,concluded7 ,experimental demonstration of earth movements4--,the study of the ,alaskan earthquake of #ahii showed that during this adjustment within the earth's shell some of the local blocks moved upward and by larger amounts than their neighbors1 and that still others were actually depressed so that the sea flowed over them4 ,it must be evident that such differential vertical movements of neighboring blocks at the earth's surface can only take place if lateral transfers of material are made beneath it4 ,from under those strips of coast land which were depressed1 material must have been moved so as to fill the void which would otherwise have formed beneath the sections that were uplifted4 ,if we take into consideration much larger fractions upon the surface of our planet1 we are taught by the great seaquakes which are now registered upon earthquake instruments at distant stations that large downward movements are to-day in progress beneath the sea much more than sufficient to compensate all extensions of the earth's surface within those districts where the land is rising in mountains4 ,from under the offshore deeps of the ocean to beneath the growing mountains upon the shore1 a transfer of earth material must be assumed to take place when disturbances are registered4 ,within the time interval that separates the sudden adjustments of the surface which are manifested in earthquakes1 the condition of strain which brings them about is steadily accumulating1 due1 as we generally assume1 to earth contraction through loss of its heat4 ,it seems probable that the resistance to an immediate adjustment is found in the rigidity of the shell because of the compression to which it is subjected4 ,to illustrate3 a row of blocks well fitted to each other may be held firmly as a bridge between the jaws of a vice1 because so soon as each block starts to fall a large resistance from friction upon its surface is called into existence1 a force which increases with the degree of compression4 ,it is thus possible upon this assumption crudely to demonstrate the adjustment of earth blocks by the simple device represented in plate #d ,a4 ,the construction of this experimental tank is so simple that little explanation is necessary4 ,wooden blocks of different heights are supported in water within a tank having a glass front1 and are kept in a strained condition at other than their natural positions of flotation by the compression of a simple vice at the top4 ,held firmly in this position1 they may thus represent the neighboring blocks within the earth's outer shell which are supported upon relatively yielding materials beneath1 and prevented from at once adjusting themselves to their natural positions through the compression to which they are subjected4 ,held as they now are1 the water near the ends of the tank is forced up beneath the blocks to higher than its natural level1 and thus tends to flow from both ends toward the center4 ,such a movement would permit the end blocks to drop and force the middle ones to rise4 ,the end blocks are1 let us say1 the sections of ,alaskan coast line which sunk during the earthquake1 as the center blocks are the sections which rose the full measure of #dg feet4 ,upon a larger scale the end blocks may equally well be considered as the floor of the great deeps off the ,alaskan coast1 whose sinking at the time of the earthquake was the cause of the great sea wave4 ,upon this assumption the center blocks would represent the ,alaskan coast regarded as a whole1 which underwent a general uplift4 ,though we may not1 in our experiment1 vary the tendency to adjustment by any contractional changes in either the water or the blocks1 we may reduce the compression of the vice1 which leads to the same general result4 ,as the compression of the vice is slowly relaxed1 a point is at last reached at which friction upon the block surfaces is no longer sufficient to prevent an adjustment taking place1 and this now suddenly occurs with the result shown in plate #d ,b4 ,in the case of the earth blocks1 this sudden adjustment is accompanied by mass movements of the ground separated by faults1 and these movements produce successional vibrations that are particularly large near the block margins1 and other frictional vibrations of such small measure as to be generally appreciated by sounds only4 ,the jolt of the adjustments has thrown some blocks beyond their natural position of rest1 and these sink and rise subsequently in order to readjust themselves with lighter vibrations1 which may be repeated and continued for some time4 ,in the case of the earth these later adjustments are the so-called aftershocks which usually continue throughout a considerable period following every great earthquake4 ,gradually they fall off in intensity and frequency until they can no longer be felt1 and are thereafter continued for a time as rumblings only4 ,,plate #d4 ,illustration3 ,a4 ,experimental tank to illustrate the earth movements which are manifested in earthquakes4 ,the sections of the earth's shell are here represented before adjustment has taken place4 ,illustration3 ,b4 ,the same apparatus after a sudden adjustment4 ,illustration3 ,c4 ,model to illustrate a block displacement in rocks which are intersected by master joints4 ,derangement of water flow by earth movement4--,the water which supported the blocks in our experiment has represented the more mobile portion of the earth's substance beneath its outer zone of fracture4 ,the surface water layers in the tank may1 however1 be considered in a different way1 since their behavior is remarkably like that of the water within and upon the earth's surface during an earth adjustment4 ,at the instant when adjustment takes place in the tank1 water frequently spurts upward from the cracks between the sinking end blocks2 and if in place of one of the higher center blocks we insert one whose top is below the level of the water in the tank1 a 8lake0 will be formed above it4 ,when the adjustment occurs1 this lake is immediately drained by outflow of the water at its bottom along one of the cracks between the blocks 7,fig4 #gf74 ,illustration3 ,,fig4 #gf4--;,diagrams to illustrate the draining of lakes during earthquakes4 ,such derangements of water flow as have been illustrated by the experiment are among the commonest of the phenomena which accompany earthquakes4 ,lakes and swamp lands have during earthquakes been suddenly drained1 fountains of water have been seen to shoot up from the surface and have played for some minutes or hours before their sudden disappearance in a sucking down of the water with later readjustment4 ,during the great earthquake of the lower ,mississippi valley in #ahaa1 known as the ,new ,madrid earthquake1 the earlier ,lake ,eulalie was completely drained1 and upon the now exposed bed there appeared parallel fissures on which were ranged funnel-like openings down which the water had been sucked4 ,in other sections of the affected region the water shot up in sheets along fissures to the tops of high trees4 ,areas where such spurting up of the water has been observed have in most cases been shown to correspond to areas of depression1 and such areas have sometimes been left flooded with water4 ,during the ,indian earthquake of #ahai an area of some #bjj square miles suddenly sank and was transformed into a lake4 ,illustration3 ,,fig4 #gg4--;,diagram to illustrate-the derangements of flow of water at the time of an earthquake2 water issuing at the surface over downthrown rocks1 and being sucked down in upthrown blocks4 ,illustration3 ,,fig4 #gh4--,mud cones aligned upon a fissure opened at ,moraza1 ,servia1 during the earthquake of ,april #d1 #aijd 7after ,michailovitch74 ,sand or mud cones and craterlets4--,from a very moderate depth below the surface to that of several miles1 all pore spaces and all larger openings within the rock are completely filled with water1 the 8trunk lines0 of whose circulation is by way of the joints or along the bedding planes of the rocks4 ,the principal reservoirs1 so to speak1 of this water inclosed within the rock are the porous sand formations4 ,when1 now1 during an earthquake a block of the earth's shell is suddenly sunk and as suddenly arrested in its downward movement1 the effect is to compress the porous layers and so force the contained water upward along the joints to the surface1 carrying with it large quantities of the sand 7,fig4 #gg74 ,illustration3 ,,fig4 #gi4--,one of the many craterlets formed near ,charleston1 ,south ,carolina1 during the earthquake of ,august #ca1 #ahhf4 ,the opening is twenty feet across1 and the leaves about it are encased in sand as were those upon the branches of the overhanging trees to a height of some twenty feet 7after ,dutton74 ,illustration3 ,,fig4 #hj4--;,cross section of a craterlet to show the trumpet-like form of the sand column4 ,ejected at the surface this water appears in fountains usually arranged in line over joints1 or even in continuous sheets1 and the sand collecting about the jets builds up lines of sand or mud cones sometimes described as 8mud volcanoes0 7,fig4 #gh74 ,the amount of sand thus poured out is sometimes so great that blankets of quicksand are spread over large sections of the country4 ,most frequently1 however1 the sand is not built above the general level of the surface1 but forms a series of craterlets which are largely shaped as the water is sucked down at the time of the readjustment with which the play of such earthquake fountains is terminated 7,fig4 #gi74 ,subsequent excavations made about such craterlets have shown them to have the form of a trumpet1 and that in the sand which so largely fills them there are generally found scales of mica and such light bodies as would be picked out from the heterogeneous materials of the sand layers and carried upward in the rush of water to the surface 7,fig4 #hj74 ,the earth's zones of heavy earthquake4--,since earthquakes give notice of a change of level of the ground1 the special danger zones from this source are the growing mountain systems which are usually found near the borders of the sea4 ,such lines of mountains are to-day rising where for long periods in the past were the basins of deposition of former seas4 ,they thus represent the zones upon the earth's surface which are the most unstable--which in the recent period have undergone the greatest changes of level4 ,illustration3 ,,fig4 #ha4--,map of the island of ,ischia to show how the shocks of recent earthquakes have been concentrated at the crossing point of two fractures 7after ,mercalli and ,johnston-,lavis74 ,by far the most unstable belt upon the earth's surface is the rim surrounding the ,pacific ,ocean1 within which margin it has been estimated that about #ed per cent of the recorded shocks of earthquake have occurred4 ,next in importance for seismic instability is the zone which borders both the ,mediterranean ,sea and the ,caribbean--the ,american ,mediterranean--and is extended across central ,asia through the ,himalayas into ,malaysia4 ,both zones approximate to great circles upon the earth's surface and intersect each other at an angle of about #fg4 ,it has been estimated that about #ie per cent of the recorded continental earthquakes have emanated from these belts4 ,illustration3 ,,fig4 #hb4--;,a line of earth fracture indicated in the plan of the relief1 which may at any time become the seat of movement and resultant shock4 ,the special lines of heavy shock4--,within any earthquake district the shocks are not felt with equal severity at all places1 but there are1 on the contrary1 definite lines which the disturbance seems to search out for special damage4 ,from their relations to the relief of the land these lines would appear to be lines of fracture upon the boundaries of those sections of the crust that play individual rles in the block adjustment which takes place4 ,more or less masked as these lines are beneath the rounded curves of the landscape1 they are given an altogether unenviable prominence with each succeeding earthquake4 ,at such times we may think of the earth's surface as specially sensitized for laying bare its hidden structure1 as is the sensitized plate under the magical influence of the ,x rays4 ,when1 at the time of an earthquake1 blocks are adjusted with reference to their neighbors1 the movements of oscillation are greatest in those marginal portions of direct contact4 ,corners of blocks--the intersecting points of the important faults--should for the same reason be shaken with a double violence1 and this assumption appears to be confirmed by observation4 ,upon the island of ,ischia1 off the ,bay of ,naples1 the shocks from recent earthquakes have been strangely concentrated near the town of ,casamicciola1 which was last destroyed in #ahhc4 ,this unfortunate city lies at the crossing point of important fractures whose course upon the island is marked by numerous springs and suffioni 7,fig4 #ha74 ,seismotectonic lines4--,the lines of important earth fractures1 as will be more clearly shown in the sequel 7p4 #bbg71 are often indicated with some clearness by straight lines in the plan of the surface relief 7,fig4 #hb74 ,lines of this nature are easily made out upon the map of the ,west ,indies1 and if we represent upon it by circles of different diameters the combined intensities of the recorded earthquakes in the various cities1 it appears that the heavily shaken localities are ranged upon lines stamped out in the relief1 with the most severely damaged places at their intersections 7,fig4 #hc74 ,these lines of exceptional instability are known as seismotectonic lines--earthquake structure lines4 ,illustration3 ,,fig4 #hc4--,seismotectonic lines of the ,west ,indies4 ,the heavy shocks above loose foundations4--,it is characteristic of faults that they soon bury themselves from sight under loose materials1 and are thus made difficult of inspection4 ,the escarpment which is the direct consequence of a vertical displacement upon a fault tends to migrate from the place of its formation1 rounding the surface as it does so and burying the fault line beneath its deposits 7,fig4 #dc1 p4 #fj74 ,this is not1 however1 the sole reason why loose foundations should be places of special danger at the time of earth shocks1 for the reason that earthquake waves are sent out in all directions from the surfaces of displacement through the medium of the underlying rock4 ,these waves travel within the firm rock for considerable distances with only a gradual dissipation of their energy1 but with their entry into the loose surface deposits their energy is quickly used up in local vibrations of large amplitude1 and hence destructive to buildings4 ,illustration3 ,,fig4 #hd4--;,device to illustrate the different effects upon the transmission and the character of shocks which are produced by firm rock and by loose materials4 ,the essential difference between firm rock and such loose materials as are found upon a river bottom or in the 8made land0 about our cities may be illustrated by the simple device which is represented in ,fig4 #hd4 ,two similar metal pans are suspended from a firm support by bands of steel and 8elastic0 braid of similar size and shape1 and carry each a small block of wood standing upon its end4 ,similar light blows are now administered directly to the pans with the effect of upsetting that block which is supported by the loose braid because of the large range or amplitude of movement that is imparted to the pan4 ,the 8elastic0 braid1 because of these large vibrations of which it is susceptible1 may represent the loose materials when an earthquake wave passes into them4 ,in the case of the steel support1 the energy of the blow1 instead of being dissipated in local swingings of the pan1 is to a large extent transmitted through the elastic metal to materials beyond4 ,the steel thus resembles in its high elasticity the firmer rock basement1 which receives and transmits the earthquake shocks1 but except when ruptured in a fault is subject to vibrations of small amplitude only4 ,construction in earthquake regions4--,wherever earthquakes have been felt1 they are certain to occur again2 and wherever mountains are growing or changes of level are in progress1 there no record of past earthquakes is required in order to forecast the future seismic history4 ,although the future earthquakes may be predicted1 the time of their coming is1 fortunately or unfortunately1 still hidden from us4 ,if one's lot is to be cast in an earthquake country1 the only sane course to pursue is to build with due regard to future contingencies4 ,the danger1 from destructive fires may to-day be largely met by methods of construction which levy an additional burden of cost4 ,though the danger from seismic disturbances can hardly be met as fully as that from fire1 yet it is true that buildings may be so constructed as to withstand all save those heaviest shocks in the immediate vicinity of the lines of large displacement4 ,here1 also1 a considerable additional expense is involved in the method of construction1 in the case of residences particularly4 ,from what has been said1 it is obvious that much of the danger from earthquakes can be met by a choice of site away from lines of important fracture and from areas of relatively loose foundation4 ,the choice of building materials is next of importance4 ,those buildings which succumb to earthquakes are in most cases racked or shaken apart1 and thus they become a prey to their own inherent properties of inertia4 ,each part of a structure may be regarded as a weight which is balanced upon a stiff rod and pivoted upon the ground4 ,when shocks arrive1 each part tends to be thrown into vibration after the manner of an inverted pendulum4 ,in proportion1 therefore1 as the weights are large and rest upon long supports1 the danger of overthrow and of tearing apart is increased4 ,in general1 structures are best constructed of light materials whose weight is concentrated near the ground4 ,masonry structures1 and especially high ones1 are1 therefore1 the least suited for resisting earthquakes1 of which the late complete destruction of the city of ,messina is a grewsome reminder4 ,despite repeated warnings in the past1 the buildings of that stricken city were generally constructed of heavy rubble1 which in addition had been poorly cemented 7,fig4 #di1 p4 #fg74 ,such structures are usually first ruptured at the edges and corners1 since here the vibrations which tend to tear the building asunder are resisted by no supports and are renforced from neighboring walls4 ,illustration3 ,,fig4 #he4--;,house wrecked in ,san ,francisco earthquake of #aijf because the floors and partitions were not securely fastened to the walls 7after ,r4 ,l4 ,humphrey74 ,an advantage of the first importance is evidently secured if the rods of the pendulum1 of which the building is conceived to be composed1 have sufficient elasticity to be considerably distorted without rupture and to again recover their original position4 ,this is the supreme advantage of structural steel for all large buildings1 which is coupled1 however1 with the disadvantage that the riveted fastenings are apt to be quickly sheered off under the vibrations4 ,large and high buildings1 when sufficiently elastic1 have fortunately the property of destroying the earth waves by interference before they have traveled above the lower stories4 ,for large structures in which wood cannot be used1 strongly renforced concrete is well adapted1 for it has in general the same advantages as steel with somewhat reduced elasticity1 but with a more effective binding together of the parts4 ,this requirement of thorough bracing and tying together of the several parts of a building causes it to vibrate1 not as many pendulums1 but as one body4 ,if met1 it removes largely the danger from racking strains1 and for small structures particularly it is the requirement which is most easily complied with4 ,for such buildings it is therefore necessary that the framework should be built in a close network with every joint firmly braced and with all parts securely tied together4 ,especial attention should be given to the fastenings of floor and partition ends4 ,the house shown in ,fig4 #he could not have been subjected to heavy shocks1 for though the walls are thrown down1 the floors and partitions have been left near their original positions4 ,illustration3 ,,fig4 #hf4--;,building wrecked at ,san ,mateo1 ,california1 during the late earthquake4 ,the heavy roof and upper floor1 acting as a unit1 have battered down the upper walls 7after ,j4 ,c4 ,branner74 ,this tendency of the walls1 floors1 partitions1 and roof to act as individual units in the vibration1 is one that must be reckoned with and be met by specially effective bracing and tying at the junctions4 ,otherwise these larger parts of the structure may act like battering rams to throw over the walls or portions of them 7,fig4 #hf74 ,,reading ,,references ,,for ,,chapters ,,vii ,,and ,,viii ,general works3-- ,,john ,,milne4 ,seismology4 ,london1 #ahih1 pp4 #cbj4 ,c4 ,e4 ,,dutton4 ,earthquakes in the ,light of the ,new ,seismology4 ,putnam1 ,new ,york1 #aijd1 pp4 #cad4 ,a4 ,,sieberg4 ,handbuch der ,erdbebenkunde4 ,braunschweig1 #aijd1 pp4 #cfb4 ,,count ,f4 ,,de ,,montessus ,,de ,,ballore4 ,les ,tremblements de ,terre1 ,gographie ,sismologique4 ,paris1 #aijf1 pp4 #dge2 ,la ,science ,sismologique4 ,paris1 #aijg1 pp4 #egi4 ,,william ,,herbert ,,hobbs4 ,earthquakes1 an ,introduction to ,seismic ,geology4 ,appleton1 ,new ,york1 #aijg1 pp4 #ccf4 ,c4 ,g4 ,,knott4 ,the ,physics of ,earthquake ,phenomena4 ,clarendon ,press1 ,oxford1 #aijh1 pp4 #bhc4 ,e4 ,,rudolph4 ,ueber ,submarine ,erdbeben und ,eruptionen1 ,beitrge zur ,geophysik1 vol4 #a1 #ahhg1 pp4 #acc-cfe2 vol4 #b1 #ahie1 pp4 #ecg-fff2 vol4 #c1 #ahih1 pp4 #bgc-ecf4 ,descriptive reports of some important earthquakes3-- ,c4 ,e4 ,,dutton4 ,the ,charleston ,earthquake of ,august #ca1 #ahhf1 #ith ,ann4 ,rept4 ,u4 ,s4 ,geol4 ,surv41 #ahhi1 pp4 #bjc-ebh4 ,b4 ,,kot4 ,on the ,cause of the ,great ,earthquake in ,central ,japan1 #ahia1 ,jour4 ,coll4 ,sci4 ,imp4 ,univ41 ,tokyo1 ,japan1 vol4 #e1 #ahic1 pp4 #bie-cec1 pls4 #bh-ce4 ,,john ,,milne and ,w4 ,k4 ,,burton4 ,the ,great ,earthquake of ,central ,japan4 #ahia1 pp4 #aj1 pls4 #cj4 ,r4 ,d4 ,,oldham4 ,report on the ,great ,earthquake of #abth ,june1 #ahig1 ,mem4 ,geol4 ,surv4 ,india4 ,vol4 #bi1 #ahii1 pp4 #cgi1 pls4 #db4 ,a4 ,c4 ,,lawson1 and others4 ,the ,california ,earthquake of ,april #ah1 #aijf1 ,report of the ,state ,earthquake ,investigation ,commission1 three quarto vols4 7,carnegie ,institution of ,washington72 many plates and figures4 ,italian ,photographic ,society1 ,messina and ,reggio before and after the ,earthquake of ,december #bh1 #aijh 7an interesting collection of pictures74 ,florence1 #aiji4 ,r4 ,s4 ,,tarr and ,l4 ,,martin4 ,recent ,changes of ,level in the ,yakutat ,bay ,region1 ,alaska1 ,bull4 ,geol4 ,soc4 ,am41 vol4 #ag1 #aijf1 pp4 #bi-fd1 pls4 #ab-bc4 ,,william ,,herbert ,,hobbs4 ,the ,earthquake of #ahgb in the ,owens ,valley1 ,california1 ,beitrge zur ,geophysik1 vol4 #aj1 #aiaj1 pp4 #ceb-che1 pls1 #aj-bc4 ,faults in connection with earthquakes3-- ,,william ,h4 ,,hobbs4 ,on ,some ,principles of ,seismic ,geology1 ,beitrge zur ,geophysik1 vol4 #h1 #aijg1 ,chapters iv-v4 ,expansion or contraction of the earth's surface during earthquakes3-- ,,william ,h4 ,,hobbs4 ,a ,study of the ,damage to ,bridges during ,earthquakes1 ,jour4 ,geol41 vol4 #af1 #aijh1 pp4 #fcf-fec2 ,the ,evolution and the ,outlook of ,seismic ,geology1 ,proc4 ,am4 ,phil4 ,soc41 vol4 #dh1 #aiji1 pp4 #bg-bi4 ,earthquake construction3-- ,,john ,,milne4 ,construction in ,earthquake ,countries1 ,trans4 ,seis4 ,soc41 ,japan1 vol4 #ad1 #ahhi-ahij1 pp4 #a-bdf4 ,f4 ,,de ,,montessus ,,de ,,ballore4 ,l'art de btir dans les pays tremblements de terre 7#cdth ,congress of ,french ,architects71 ,l',architecture1 #aic ,anne1 #aijf1 pp4 #a-ca4 ,,gilbert1 ,,humphrey1 ,,sewell1 and ,,soul4 ,the ,san ,francisco ,earthquake and ,fire of ,april #ah1 #aijf1 and their ,effects on ,structures and ,structural ,materials1 ,bull4 #cbd1 ,u4 ,s4 ,geol4 ,surv41 #aijg1 pp4 #a-agj1 pls4 #a-eg4 ,,william ,h4 ,,hobbs4 ,construction in ,earthquake ,countries1 ,the ,engineering ,magazine1 vol4 #cg1 #aiji1 pp4 #a-ai4 ,,lewis ,,alden ,,estes4 ,earthquake-proof ,construction1 a discussion of the effects of earthquakes on building construction with special reference to structures of renforced concrete1 published by ,trussed ,concrete ,steel ,company4 ,detroit1 #aiaa1 pp4 #df4 ,,chapter ,,ix ,,the ,,rise ,,of ,,molten ,,rock ,,to ,,the ,,earth',s ,,surface ,,volcanic ,,mountains ,,of ,,exudation ,prevalent misconceptions about volcanoes4--,the more or less common impression that a volcano is a 8burning mountain0 or a 8smoking mountain0 has been much fostered by the school texts in physical geography in use during an earlier period4 ,the best introduction to a discussion of volcanoes is1 therefore1 a disillusionment from this notion4 ,far from being burning or smoking1 there is normally no combustion whatever in connection with a volcanic eruption4 ,the unsophisticated tourist who1 looking out from ,naples1 sees the steam cap which overhangs the ,vesuvian crater tinged with brown1 easily receives the impression that the material of the cloud is smoke4 ,even more at night1 when a bright glow is reflected to his eye and soon fades away1 only to again glow brightly after a few moments have passed1 is it difficult to remove the impression that one is watching an intermittent combustion within the crater4 ,the cloud which floats away from the crest of the mountain is in reality composed of steam with which is admixed a larger or smaller proportion of fine rock powder which gives to the cloud its brownish tone4 ,the glow observed at night is only a reflection from molten lava within the crater1 and the variation of its brightness is explained by the alternating rise and fall of the lava surface by a process presently to be explained4 ,not only is there no combustion in connection with volcanic eruptions1 but so far as the volcano is a mountain it is a product of its own action4 ,the grandest of volcanic eruptions have produced no mountains whatever1 but only vast plains or plateaus of consolidated molten rock1 and every volcanic mountain at some time in its history has risen out of a relatively level surface4 ,when the traditional notions about volcanoes grew up1 it was supposed that the solid earth was merely a 8crust0 enveloping still molten material4 ,as has already been pointed out in an earlier chapter1 this view is no longer tenable1 for we now know that the condition of matter within the earth's interior1 while perhaps not directly comparable to any that is known1 yet has properties most resembling known matter in a solid state2 it is much more rigid than the best tool steel4 ,while there must be reservoirs of molten rock beneath active volcanoes1 it is none the less clear that they are small1 local1 and temporary4 ,this is shown by the comparative study of volcanic outlets within any circumscribed district4 ,it is perhaps not easy to frame a definition of a volcano1 but its essential part1 instead of being a mountain1 is rather a vent or channel which opens up connection between a subsurface reservoir of molten rock and the surface of the earth4 ,an eruption occurs whenever there is a rise of this material1 together with more or less steam and admixed gases1 to the surface4 ,such molten rock arriving at the surface is designated lava4 ,the changes in pressure upon this material during its elevation induce secondary phenomena as the surface is approached1 and these manifestations are often most awe inspiring4 ,while often locally destructive1 the geological importance of such phenomena is by reason of their terrifying aspect likely to be greatly exaggerated4 ,early views concerning volcanic mountains4--,as already pointed out1 a volcano at its birth is not a mountain at all1 but only1 so to speak1 a shaft or channel of communication between the surface and a subterranean reservoir of molten rock4 ,by bringing this melted rock to the surface there is built up a local elevation which may be designated a mountain1 except where the volume of the material is so large and is spread to such distances as to produce a plain 7see fissure eruptions below74 ,in the early history of geology it was the view of the great ,german geologist von ,buch and his friend and colleague von ,humboldt1 that a volcanic mountain was produced in much the same manner as is a blister upon the body4 ,the fluids which push up the cuticle in the blister were here replaced by fluid rock which elevated the sedimentary rock layers at the surface into a dome or mound which was open at the top--the so-called crater4 ,this 8elevation-crater0 theory of volcanoes long held the stage in geological science1 although it ignored the very patent fact that the layers on the flanks of volcanic cones are not of sedimentary rock at all1 but1 on the contrary1 of the volcanic materials which are brought up to the surface during the eruption4 ,the observational phase of science was1 however1 dawning1 and the ,english geologists ,scrope and ,lyell were able to show by study of volcanic mountains that the mound about the volcanic vent was due to the accumulation of once molten rock which had been either exuded or ejected4 ,making use of data derived from ,new ,zealand1 ,scrope showed that1 instead of being elevated during the formation of a volcanic mountain1 the sedimentary strata of the vicinity may be depressed near the volcanic vent 7,fig4 #hg74 ,illustration3 ,,fig4 #hg4--;,breached volcanic cone near ,auckland1 ,new ,zealand1 showing the bending down of the sedimentary strata in the neighborhood of the vent 7after ,heaphy and ,scrope74 ,the birth of volcanoes4--,to confirm the impression that the formation of the volcanic mountain is in reality a secondary phenomenon connected with eruptions1 we may cite the observed birth of a number of volcanoes4 ,on the #bjth of ,september1 #aech1 a new volcano1 since known as ,monte ,nuovo 7new mountain71 rose on the border of the ancient ,lake ,lucrinus to the westward of ,naples4 ,this small mountain attained a height of #ddj feet1 and is still to be seen on the shore of the bay of ,naples4 ,from ,mexico have been recorded the births of several new volcanoes3 ,jorullo in #agei1 ,pochutla in #ahgj1 and in #ahha a new volcano in the ,ajusco ,mountains about midway between the ,gulf of ,mexico and the ,pacific ,ocean4 ,the latest of new volcanoes is that raised in ,japan on ,november #i1 #aiaj1 in connection with the eruption of ,usu-san4 ,this 8,new ,mountain0 reached an elevation of #fij feet4 ,illustration3 ,,fig4 #hh4--,view of the new ,camiguin volcano from the sea4 ,it was formed in #ahga over a nearly level plain4 ,the town of ,catarman appears at the right near the shore 7after an unpublished photograph by ,professor ,dean ,c4 ,worcester74 ,as described by von ,humboldt1 ,jorullo rose in the night of the #bhth of ,september1 #agei1 from a fissure which opened in a broad plain at a point #ce miles distant from any then existing volcano4 ,the most remarkable of new volcanoes rose in #ahga on the island of ,camiguin northward from ,mindanao in the ,philippine archipelago4 ,this mountain was visited by the ,challenger expedition in #ahge1 and was first ascended and studied thirty years later by a party under the leadership of ,professor ,dean ,c4 ,worcester1 the ,secretary of the ,interior of the ,philippine ,islands1 to whom the writer is indebted for this description and the accompanying illustration of this largest and most interesting of new-born volcanoes4 ,as in the case of ,jorullo1 the eruption began with the formation of a fissure in a level plain1 some #djj yards distant from the town of ,catarman 7,fig4 #hh74 ,the eruption continued for four years1 at the end of which time the height of the summit was estimated by the ,challenger expedition to be #aijj feet4 ,at the time of the first ascent in #aije1 the height was determined by aneroid as #agej feet1 with sharp rock pinnacles projecting some #ej or #ge feet higher4 ,active and extinct volcanoes4--,the terms 8active0 and 8extinct0 have come into more or less common use to describe respectively those volcanoes which show signs of eruptive activity1 and those which are not at the time active4 ,the term 8dormant0 is applied to volcanoes recently active and supposed to be in a doubtfully extinct condition4 ,from a well-known volcano in the vicinity of ,naples1 volcanoes which no longer erupt lava or cinder1 but show gaseous emanations 7fumeroles7 are said to be in the solfatara condition1 or to show solfataric activity4 ,experience shows that the term 8extinct01 while useful1 must always be interpreted to mean apparently extinct4 ,this may be illustrated by the history of ,mount ,vesuvius1 which before the ,christian era was forested in the crater and showed no signs of activity2 and in fact it is known that for several centuries no eruption of the volcano had taken place4 ,following a premonitory earthquake felt in the year #fc1 the mountain burst out in grand explosive eruption in #gi ,a4,d4 ,this eruption profoundly altered the aspect of the mountain and buried the cities of ,pompeii1 ,stabeii1 and ,herculaneum from sight4 ,once more1 this time during the middle ages1 for nearly five centuries 7#aaci to #afca7 there was complete inactivity1 if we except a light ash eruption in the year #aejj4 ,during this period of rest the crater was again forested1 but the repose was suddenly terminated by one of the grandest eruptions in the mountain's history4 ,illustration3 ,,fig4 #hi4--,map showing the location of the belts of active volcanoes4 ,the earth's volcano belts4--,the distribution of volcanoes is not uniform1 but1 on the contrary1 volcanic vents appear in definite zones or belts1 either upon the margins of the continents or included within the oceanic areas 7,fig4 #hi74 ,the most important of these belts girdles the ,pacific ,ocean1 and is represented either by chains or by more widely spaced volcanic mountains throughout the ,cordilleran ,mountain system of ,south and ,central ,america and ,mexico1 by the volcanoes of the ,coast and ,cascade ranges of ,north ,america1 the festooned volcanic chain of the ,aleutian ,islands1 and the similar island arcs off the eastern coast of the ,eurasian continent4 ,the belt is further continued through the islands of ,malaysia to ,new ,zealand1 and on the ,pacific's southern margin are found the volcanoes of ,victoria ,land1 ,king ,edward ,land1 and ,west ,antarctica4 ,illustration3 ,,fig4 #ij4--;,a portion of the 8fire girdle0 of the ,pacific1 showing the relation of the chains of volcanic mountains to the deeps of the neighboring ocean floor4 ,this volcano girdle is by no means a perfect one1 for in addition to the principal festoons of the western border there are many secondary ones1 and still other arcs are found well toward the center of the oceanic area4 ,another broad belt of volcanoes borders the ,mediterranean ,sea1 and is extended westward into the ,atlantic ,ocean4 ,narrower belts are found in both the northern and southern portions of the ,atlantic ,ocean1 on the margins of the ,caribbean ,sea1 etc4 ,the fact of greatest significance in the distribution seems to be that bands of active volcanoes are to be found wherever mountain ranges are paralleled by deeps on the neighboring ocean floor 7,fig4 #ij74 ,as has been already pointed out in the chapter upon earthquakes1 it is just such places as these which are the seat of earthquakes2 these are zones of the earth's crust which are undergoing the most rapid changes of level at the present time4 ,thus the rise of the land in mountains is proceeding simultaneously with the sinking of the sea floor to form the neighboring deeps4 ,illustration3 ,,fig4 #ia4--,volcanic cones formed in #aghc above the ,skaptr fissure in ,iceland 7after ,helland74 ,illustration3 ,,fig4 #ib4--;,diagrams to illustrate the location of volcanic vents upon fissure lines1 a1 openings caused by lateral movement of fissure walls2 b1 openings formed at fissure intersections4 ,arrangement of volcanic vents along fissures and especially at their intersections4--,within those districts in which volcanoes are widely separated from their neighbors1 the law of their arrangement is difficult to decipher1 but the view that volcanic vents are aligned over fissures is now supported by so much evidence that illustrations may be supplied from many regions4 ,an exceptionally perfect line of small cones is found along the ,skaptr cleft in ,iceland1 upon which stands the large volcano of ,laki4 ,this fissure reopened in #aghc1 and great volumes of lava were exuded4 ,over the cleft there was left a long line of volcanic cones 7,fig4 #ia74 ,there are in ,iceland two dominating series of parallel fissures of the same character which take their directions respectively northeast-southwest and north-south4 ,many such fissures are traceable at the surface as deep and nearly straight clefts or gjs1 usually a few yards in width1 but extending for many miles4 ,the ,eldgj has a length of more than #ah ,english miles and a depth varying from #djj to #fjj feet4 ,on some of these fissures no lava has risen to the surface1 whereas others have at numerous points exuded molten rock4 ,sometimes one end only of a fissure1 the more widely gaping portion1 has supplied the conduits for the molten lava4 ,this is well illustrated by the cratered monticules raised by the common ant over the cracks which separate the blocks of cement sidewalk1 the hillocks being located where the most favorable channel was found for the elevation of the materials4 ,illustration3 ,,fig4 #ic4--,outline map of the eastern portion of the island of ,java1 displaying the arrangement of volcanic vents in alignment upon fissures with the larger mountains at fissure intersections 7after ,verbeek74 ,those places upon fissures which become lava conduits appear to be the ones where the cleft gapes widest so as to furnish the widest channel4 ,wherever a differential lateral movement of the walls has occurred1 openings will be found in the neighborhood of each minor variation from a straight line 7,fig4 #ib;a74 ,wherever there are two or more series of fissures1 and this would appear to be the normal condition1 places favorable for lava conduits occur at fissure intersections4 ,within such veritable volcano gardens as are to be found in ,malaysia1 the law of volcano distribution became apparent so soon as accurate maps had been prepared4 ,thus the outline map of a portion of the island of ,java 7,fig4 #ic7 shows us that while the volcanoes of the island present at first sight a more or less irregular band or zone1 there are a number of fissures intersecting in a network1 and that the volcanoes are aligned upon the fissures with the larger cones located at the intersections4 ,so also in ,iceland1 the great eruption of ,askja in #ahge occurred at the intersection of two lines of fissure4 ,outside these closely packed volcanic regions1 similar though less marked networks are indicated2 as1 for example1 in and near the ,gulf of ,guinea4 ,if now1 instead of reducing the scale of our volcano maps1 we increase it1 the same law of distribution is no less clearly brought out4 ,the monticules or small volcanic cones which form upon the flanks of larger volcanic mountains are likewise built up over fissures which on numerous occasions have been observed to open and the cones to form upon them4 ,illustration3 ,,fig4 #id4--,map of the ,puy ,pariou in the ,auvergne of central ,france4 ,the seat of eruption has migrated along the fissure upon which the earlier cone had been built up 7after ,scrope74 ,still further reducing now the area of our studies and considering for the moment the 8frozen0 surface of the boiling lava within the caldron of ,kilauea1 this when observed at night reveals in great perfection the sudden formation of fissures in the crust with the appearance of miniature volcanoes rising successively at more or less regular intervals along them4 ,it not infrequently happens that after a volcanic vent has become established above some conduit in a fissure1 the conduit migrates along the fissure1 thus establishing a new cone with more or less complete destruction of the old one 7,fig4 #id74 ,the so-called fissure eruptions4--,the grandest of all volcanic eruptions have been those in which the entire length and breadth of the fissures have been the passageway for the upwelling lava4 ,such grander eruptions have been for the most part prehistoric1 and in later geologic history have occurred chiefly in ,india1 in ,abyssinia1 in northwestern ,europe1 and in the northwestern ,united ,states4 ,in western ,india the singularly horizontal plateaus of basaltic lava1 the ,dekkan traps1 cover some #bjj1jjj square miles and are more than a mile in depth4 ,the underlying basement where it appears about the margins of the basalt is in many places intersected by dikes or fissure fillings of the same material4 ,no cones or definite vents have been found4 ,illustration3 ,,fig4 #ie4--;,basaltic plateau of the northwestern ,united ,states due to fissure eruptions of lava4 ,the larger portion of the northwestern ,british ,isles would appear to have been at one time similarly blanketed by nearly horizontal beds of basaltic lava1 which beds extended northwestward across the sea through the ,orkney and ,faroe islands to ,iceland4 ,remnants of this vast plateau are to-day found in all the island groups as well as in large areas of northeastern ,ireland1 and fissure fillings of the same material occur throughout large areas of the ,british ,isles4 ,in many cases these dikes represent once molten rock which may never have communicated with the surface at the time of the lava outpouring1 yet they well illustrate what we might expect to find if the basalt sheets of ,iceland or ,ireland were to be removed4 ,the floods of basaltic lava which in the northwestern ,united ,states have yielded the barren plateau of the ,cascade ,mountains 7,fig4 #ie7 would appear to offer another example of fissure eruption1 though cones appear upon the surface and perhaps indicate the position of lava outlets during the later phases of the eruptive period4 ,the barrenness and desolation of these lava plains is suggested by ,fig4 #if4 ,illustration3 ,,fig4 #if4--,lava plains about the ,snake ,river in ,idaho4 ,though the greater effusions of lava have occurred in prehistoric times1 and the manner of extrusion has necessarily been largely inferred from the immense volume of the exuded materials and the existence of basaltic dikes in neighboring regions1 yet in ,iceland we are able to observe the connection between the dikes and the lava outflows4 ,professor ,thoroddsen has stated that in the great basaltic plateau of ,iceland1 lava has welled out quietly from the whole length of fissures and often on both sides without giving rise to the formation of cones4 ,at three wider portions of the great ,eld cleft1 lava welled out quietly without the formation of cones1 though here in the southern prolongation of the fissure1 where it was narrower1 a row of low slag cones appeared4 ,where the lava outwellings occurred1 an area of #bgj square miles was flooded4 ,illustration3 ,,fig4 #ig4--;,characteristic profiles of lava volcanoes4 #a1 basaltic lava mountain2 #b1 mountain of siliceous lava 7after ,judd74 ,the composition and the properties of lava4--,in our study of igneous rocks 7,chapter ,,iv7 it was learned that they are composed for the most part of silicate minerals1 and that in their chemical composition they represent various proportions of silica1 alumina1 iron1 magnesia1 lime1 potash1 and soda4 ,the more abundant of these constituents is silica1 which varies from #ce to #gj per cent of the whole4 ,whenever the content of silica is relatively low1--basic or basaltic lava1--the cooled rock is dark in color and relatively heavy4 ,it melts at a relatively low temperature1 and is in consequence relatively fluid at the temperatures which lavas usually have on reaching the earth's surface4 ,furthermore1 from being more fluid1 the water which is nearly always present in large quantity within the lava more readily makes its escape upon reaching the surface4 ,eruptions of such lava are for this reason without the violent aspects which belong to extrusions of more siliceous 7more 8acidic07 lavas4 ,for the same reason1 also1 basaltic lava flows more freely and can spread much farther before it has cooled sufficiently to consolidate4 ,this is equivalent to saying that its surface will assume a flatter angle of slope1 which in the case of basaltic lava seldom exceeds ten degrees and may be less than one degree 7,fig4 #ig74 ,illustration3 ,,fig4 #ih4--;,a driblet cone 7after ,j4 ,d4 ,dana74 ,siliceous lavas1 on the other hand1 are1 when consolidated1 relatively light both in color and weight and melt at relatively high temperatures4 ,they are1 therefore1 usually but partly fused and of a viscous consistency when they arrive at the earth's surface4 ,because of this viscosity they offer much resistance to the liberation of the contained water1 which therefore is released only to the accompaniment of more or less violent explosions4 ,the lava is blown into the air and usually falls as consolidated fragments of various degrees of coarseness4 ,illustration3 ,,fig4 #ii4--,view of ,leffingwell crater1 a cinder cone in the ,owens valley1 ,california 7after an unpublished photograph by ,w4 ,d4 ,johnson74 ,it must not1 however1 be assumed that the temperature of lava is always the same when it arrives at the surface1 and hence it may happen that a siliceous lava is exuded at so high a temperature that it behaves like a normal basaltic lava4 ,on the other hand1 basaltic lavas may be extruded at unusually low temperatures1 in which case their behavior may resemble that of the normal siliceous lavas4 ,if1 however1 as is generally the case1 the energy of explosion of a basaltic lava is relatively small1 any ejected portions of the liquid lava travel to a moderate height only in the air1 so that on falling they are still sufficiently pasty to adhere to rock surfaces and thus build up the remarkably steep cones and spines known as 8spatter cones0 or 8driblet cones0 7,fig4 #ih74 ,when1 on the other hand1 the energy of explosion is great1 as is normally the case with siliceous lavas1 the portions of ejected lava have been fully consolidated before their fall to the surface1 so that they build up the same type of accumulation as would sand falling in the same manner4 ,the structures which they form are known as tuff1 cinder1 or ash cones 7,fig4 #ii74 ,whenever the contained water passes off from siliceous lavas without violent explosions1 the lava may flow from the vent1 but in contrast to basaltic lavas it travels a short distance only before consolidating4 ,the resulting mountain is in consequence proportionately high and steep 7,fig4 #ig74 ,eruptions characterized by violent explosions accompanied by a fall of cinder are described as explosive eruptions4 ,those which are relatively quiet1 and in which the chief product is in the form of streams of flowing lava1 are spoken of as convulsive eruptions4 ,the three main types of volcanic mountain4--,if the eruptions at a volcanic vent are exclusively of the explosive type1 the material of the mountain which results is throughout tuff or cinder1 and the volcano is described as a cinder cone4 ,if1 on the other hand1 the vent at every eruption exudes lava1 a mountain of solid rock results which is a lava dome4 ,it is1 however1 the exception for a volcano which has a long history to manifest but a single kind of eruption4 ,at one time exuding lava comparatively quietly1 at another the violence with which the steam is liberated yields only cinder1 and the mountain is a composite of the two materials and is known as a composite volcanic cone4 ,the lava dome4--,when successive lava flows come from a crater1 the structure which results has the form of a more or less perfect dome4 ,if the lava be of the basaltic or fluid type1 the slopes are flat1 seldom making an angle of as much as ten degrees with the horizon and flatter toward the summit 7,fig4 #aja1 p4 #ajf74 ,if of siliceous or viscous lava1 on the other hand1 the slopes are correspondingly steep and in some cases precipitous4 ,to this latter class belong some of the ,kuppen of ,germany1 the puys of central ,france1 and the mamelons of the ,island of ,bourbon4 ,illustration3 ,,fig4 #ajj4--,map of ,hawaii and the lava volcanoes of ,mokuaweoweo 7,mauna ,loa7 and ,kilauea 7after the government map by ,alexander74 ,the basaltic lava domes of ,hawaii4--,at the 8crossroads of the ,pacific0 rises a double line of lava volcanoes which reach from #bj1jjj to #cj1jjj feet above the floor of the ocean1 some of them among the grandest volcanic mountains that are known4 ,more than half the height and a much larger proportion of the bulk of the largest of these are hidden beneath the ocean's surface4 ,the two great active vents are ,mokuaweoweo 7on ,mauna ,loa7 and ,kilauea1 distinct volcanoes notwithstanding the fact that their lava extravasations have been merged in a single mass4 ,the rim of the crater of ,mauna ,loa is at an elevation of #ac1fge feet above the sea1 whereas that of ,kilauea is less than #djjj feet and appears to rest upon the flank of the larger mountain 7,figs4 #ajj and #aja74 ,although one crater is but #bj miles distant from the other and nearly #aj1jjj feet lower1 their eruptions have apparently been unsympathetic4 ,nowhere have still active lava mountains been subjected to such frequent observations extending throughout a long period1 and the dynamics of their eruptions are fairly well understood4 ,to put this before the reader1 it will be best to consider both mountains1 for though they have much in common1 the observations from one are strangely complementary to those of the other4 ,the lower crater being easily accessible1 ,kilauea has been often visited1 and there exists a long series of more or less consecutive observations upon it1 which have been assembled and studied by ,dana and ,hitchcock4 ,the place of outflow of the ,kilauea lavas has not generally been visible1 whereas ,mokuaweoweo has slopes rising nearly #ad1jjj feet above the sea and displays the records of outflow of many eruptions1 some of which were accompanied by the grandest of volcanic phenomena4 ,illustration3 ,,fig4 #aja4--,section through ,mauna ,loa and ,kilauea4 ,lava movements within the caldron of ,kilauea4--,the craters of these mountains are the largest of active ones1 each being in excess of seven miles in circumference4 ,in shape they are irregularly elliptical and consist of a series of steps or terraces descending to a pit at the bottom1 in which are open lakes of boiling lava4 ,enough is known of the history of ,kilauea to state that the steep cliffs bounding the terraces are fault walls produced by inbreak of a frozen lava surface4 ,the cliff below the so-called 8black ledge0 was produced by the falling in of the frozen lava surface at the time of the outflow of #ahdj1 the lava issuing upon the eastern flank of the mountain and pouring into the sea near ,nanawale4 ,since that date the floor of the pit below the level of this ledge has been essentially a movable platform of frozen lava of unknown and doubtless variable thickness which has risen and descended like the floor of an elevator car between its guiding ways 7,fig4 #ajb74 ,the floor has1 however1 never been complete1 for one or more open lakes are always to be seen1 that of ,halemaumau located near the southwestern margin having been much the most persistent4 ,within the open lakes the boiling lava is apparently white hot at the depth of but a few inches below the surface1 and in the overturnings of the mass these hotter portions are brought to the surface and appear as white streaks marking the redder surface portions4 ,from time to time the surface freezes over1 then cracks open and erupt at favored points along the fissures1 sending up jets and fountains of lava1 the material of which falls in pasty fragments that build up driblet cones4 ,small fluid clots are shot out1 carrying a threadlike line of lava glass behind them1 the well-known 8,pel's hair40 ,sometimes the open lakes build up congealed walls1 rising above the general level of the pit1 and from their rim the lava spills over in cascades to spread out upon the frozen floor1 thus increasing its thickness from above 7,fig4 #ajc74 ,at other times a great dome of lava has been pushed up from the pit of ,halemaumau under a frozen shell1 the molten lava shining red through cracks in its surface and exuding so as to heal each widely opened fissure as it forms4 ,illustration3 ,,fig4 #ajb4--,schematic diagram to illustrate the moving platform of frozen lava which rises and falls in the crater of ,kilauea4 ,at intervals of from a few years to nine or ten years the crater has been periodically drained1 at which times the moving platform of frozen lava has sunk more or less rapidly to levels far below the black ledge and from #ijj to #agjj feet below the crater rim4 ,following this descent a slow progressive rise is inaugurated1 which has sometimes gone on at a rate of more than a hundred feet per year1 though it is usually much slower than this4 ,when the platform has reached a height varying from #gjj to #cej feet below the crater rim1 another sudden settlement occurs which again carries the pit floor downward a distance of from #cjj to #gjj feet4 ,illustration3 ,,fig4 #ajc4--,view of the open lava lake of ,halemaumau within the crater of ,kilauea1 the molten lava shown cascading over the raised lava walls on to the floor of the pit 7after ,pavlow74 ,the draining of the lava caldrons4--,the changes which go on within the crater of ,mokuaweoweo1 though less studied than those of ,kilauea1 appear to be in some respects different4 ,here every eruption seems to be preceded by a more or less rapid influx of melted lava to the pit of the crater1 this phenomenon being observed from a distance as a brilliant light above the crater--the reflection of the glow from overhanging vapor clouds4 ,the uprising of the lava has often been accompanied by the formation of high lava fountains upon the surface1 and the molten lava sometimes appears in fissures near the crater rim at levels well above the lava surface within the pit4 ,although in many cases the lava which has thus flooded the crater has suddenly drained away without again becoming visible1 it is probable that in such cases an outlet has been found to some submarine exit1 since under-ocean discharge effects have been observed in connection with eruptions of each of the volcanoes4 ,illustration3 ,,fig4 #ajd4--,map showing the manner of outflow of lava from ,kilauea during the eruption of #ahdj4 ,the outflowing lava made its appearance successively at the points ,a1 ,b1 ,c1 m1 n1 and finally at a point below n1 from whence it issued in volume and flowed down to the sea at ,nanawale 7after ,j4 ,d4 ,dana74 ,inasmuch as no earthquakes are felt in connection with such outflows as have been described1 it is probable that the hot lava fuses a passageway for itself into some open channel underneath the flanks of the mountain4 ,such a course is well illustrated by the outflow of ,kilauea in #ahdj1 when1 it will be remembered1 occurred the great down-plunge of the crater that yielded the pit below the black ledge4 ,at this time the lava first made its appearance upon the flanks of the mountain at the bottom of a small pit or inbreak crater which opened five miles southeast of the main crater of ,kilauea 7,fig4 #ajd74 ,within this new crater the lava rose1 and small ejections soon followed from fissures formed in its neighborhood4 ,some time after1 the lava sank in the first new crater1 only to reappear successively at other small openings 7,fig4 #ajd1 ,b1 ,c1 m1 n7 and finally to issue in volume at a point eleven miles from the shore and flow thereafter upon the surface of the mountain until it had reached the sea4 ,only the slightest earth tremors were felt1 and as no rumblings were heard1 it is evident that the lava fused its way along a buried channel largely open at the time 7see below1 p4 #aab74 ,in a majority of the eruptions of ,mokuaweoweo1 when the outflowing lavas have become visible1 the molten rock has apparently fused its way out to the surface of the mountain at points from #ajjj to #cjjj feet below the bottom of the crater1 and this discharge has corresponded in time to the lowering of the lava surface within the crater4 ,there are1 however1 three instances upon record in which the lava issued from definite rents which were formed upon the mountain flanks at comparatively low levels4 ,in contrast to the formation of fused outlets1 these ruptures of a portion of the mountain's flank were always accompanied by vigorous local earthquakes of short duration4 ,in one instance 7the eruption of #ahea7 such a rent appeared under the same conditions but at an elevation of #ab1ejj feet1 or near the level of the lava in the crater4 ,the outflow of the lava floods4--,in order to properly comprehend these and many otherwise puzzling phenomena connected with volcanoes1 it is necessary to keep ever in mind the quite remarkable heat-insulating property of congealed lava4 ,so soon as a thin crust has formed upon the surface of molten rock1 the heat of the underlying fluid mass is given off with extreme slowness1 so that lava streams no longer connected with their internal lava reservoirs may remain molten for decades4 ,illustration3 ,,fig4 #aje4--,lava of ,matavanu upon the ,island of ,savaii flowing down to the sea during the eruption of #aijf4 ,the course may be followed by the jets of steam escaping from the surface down to the great steam cloud which rises where the fluid lava discharges into the sea 7after ,h4 ,i4 ,jensen74 ,we have seen that for ,mokuaweoweo and ,kilauea1 lava either quietly melts its way to the surface at the time of outflow1 or else produces a rent for its egress to the accompaniment of vigorous local earthquakes4 ,in either case if the lava issues at a point far below the crater1 gigantic lava fountains arise at the point of outflow1 the fluid rock shooting up to heights which range from #bej to #fjj or more feet above the surface4 ,a certain proportion of this fluid lava is sufficiently cooled to consolidate while traveling in the air1 and falling1 it builds up a cinder cone which is left as a location monument for the place of discharge4 ,from this outlet the molten lava begins its journey down the slope of the mountain1 and quickly freezes over to produce a tunnel1 beneath the roof of which the fluid lava flows with comparatively slow further loss of heat4 ,save for occasional steam jets issuing from its surface1 it may give little indication of its presence until it has reached the sea 7,fig4 #aje74 ,illustration3 ,,fig4 #ajf4--,lava stream discharging into the sea from beneath the frozen roof of a lava tunnel4 ,eruption of ,matavanu on ,savaii in #aijf 7after ,sapper74 ,if sufficient in volume and the shore be not too distant1 the stream of lava arrives at the sea1 where1 discharging from the mouth of its tunnel1 it throws up vast volumes of steam and induces ebullition of the water over a wide area 7,fig4 #ajf74 ,professor ,dana1 who visited ,hawaii a few months only after the great outflow of #ahdj1 states that the lava1 upon reaching the ocean1 was shivered like melted glass and thrown up in millions of particles which darkened the sky and fell like hail over the surrounding country4 ,the light was so bright that at a distance of forty miles fine print could be read at midnight4 ,illustration3 ,,fig4 #ajg4--;,diagrammatic representation of the structure of the flanks of lava volcanoes as a result of the draining of frozen lava streams4 ,protected from any extensive consolidation by its congealed cover1 the lava within a stream may all drain away1 leaving behind an empty lava tunnel1 which in the case of the ,hawaiian volcanoes sometimes has its roof hung with beautiful lava stalactites and its floor studded with thin lava spines4 ,later lava outflows over the same or neighboring courses bury such tunnels beneath others of similar nature1 giving to the mountain flanks an elongated cellular structure illustrated schematically in ,fig4 #ajg4 ,these buried channels may in the future be again utilized for outflows similar in character to that of ,kilauea in #ahdj4 ,illustration3 ,,fig4 #ajh4--;,diagram to show the manner of formation of mesas or table mountains by the outflow of lava in valleys and the subsequent more rapid erosion of the intervening ridges4 ,r1 earlier river valley2 ,r',r'1 later valleys4 ,while the formation of lava stalactites of such perfection and beauty is peculiar to the ,hawaiian lava tunnels1 the formation of the tunnel in connection with lava outflow is the rule wherever a dissipation at the end has permitted of drainage4 ,a few hours only after the flow has begun1 the frozen surface has usually a thickness of a few inches1 and this cover may be walked over with the lava still molten below4 ,at first in part supported by the molten lava1 the tunnel roof sometimes caves in so soon as drainage has occurred4 ,illustration3 ,,fig4 #aji4--,surface of lava of the ,pahoehoe type4 ,wherever basaltic lava has spread out in valleys on the surface of more easily eroded material1 either cinder or sedimentary formations1 the softer intervening ridges are first carried away by the eroding agencies1 leaving the lava as cappings upon residual elevations4 ,thus are derived a type of table mountain or mesa of the sort well illustrated upon the western slopes of the ,sierra ,nevadas in ,california 7,fig4 #ajh74 ,illustration3 ,,fig4 #aaj4--,three successive views to illustrate the growth of the ,island of ,savaii from the outflow of lava at ,matavanu in the year #aijf4 a1 near the beginning of the outflow2 b1 some weeks later than a2 c1 some weeks later than b 7after ,h4 ,i4 ,jensen74 ,the surface which flowing lava assumes1 while subject to considerable variation1 may yet be classified into two rather distinct types4 ,on the one hand there is the billowy surface in which ellipsoidal or kidney-shaped masses1 each with dimensions of from one to several feet1 lie merged in one another1 not unlike an irregular collection of sofa pillows4 ,this type of lava has become known as the ,pahoehoe1 from the ,hawaiian occurrence 7,fig4 #aji74 ,a variation from this type is the 8corded0 or 8ropy0 lava1 the surface of which much resembles rope as it is coiled along the deck of a vessel1 the coils being here the lines of scum or scori arranged in this manner by the currents at the surface of the stream 7,fig4 #abc1 p4 #abd74 ,a quite different type is the block lava 7,aa type7 which usually has a ragged scoriaceous surface and consists of more or less separate fragments of cooled lava 7,fig4 #aca1 p4 #acj74 ,wherever lava flows into the sea in quantity1 it extends the margin of the shore1 often by considerable areas4 ,the outflow of ,kilauea in #ahdj extended the shore of ,hawaii outward for the distance of a quarter of a mile1 and a more recent illustration of such extension of land masses is furnished by ,fig4 #aaj4 ,,chapter ,x ,,the ,,rise ,,of ,,molten ,,rock ,,to ,,the ,,earth',s ,,surface ,,volcanic ,,mountains ,,of ,,ejected ,,materials ,the mechanics of crater explosions4--,if we now turn from the lava volcano to the active cinder cone1 we encounter an entire change of scene4 ,in place of the quiet flow and convulsive movements of the molten lava1 we here meet with repeated explosions of greater or less violence4 ,if we are to profitably study the manner of the explosions1 considering the volcanic vent as a great experimental apparatus1 it would be well to select for our purpose a volcano which is in a not too violent mood4 ,the well-known cinder cone of ,stromboli in the ,eolian group of islands north of ,sicily has1 with short and unimportant interruptions1 remained in a state of light explosive activity since the beginning of the ,christian era4 ,rising as it does some three thousand feet directly out of the ,mediterranean1 and displaying by day a white steam cap and an intermittent glow by night1 its summit can be seen for a distance of a hundred miles at sea and it has justly been called the 8,lighthouse of the ,mediterranean40 ,the 8flash0 interval of this beacon may vary from one to twenty minutes1 and it may show1 furthermore1 considerable variation of intensity4 ,for the reason that the crater of the mountain is located at one side and at a considerable distance below the actual summit1 the opportunity here afforded of looking into the crater is most favorable whenever the direction of the wind is such as to push aside the overhanging steam cloud 7,fig4 #aaa74 ,long ago the ,italian vulcanologist ,spallanzani undertook to make observations from above the crater1 and many others since his day have profited by his example4 ,within the crater of the volcano there is seen a lava surface lightly frozen over and traversed by many cracks from which vapor jets are issuing4 ,here1 as in the ,kilauea crater1 there are open pools of boiling lava4 ,from some of these1 lava is seen welling out to overflow the frozen surface2 from others1 steam is ejected in puffs as though from the stack of a locomotive4 ,within others lava is seen heaving up and down in violent ebullition1 and at intervals a great bubble of steam is ejected with explosive violence1 carrying up with it a considerable quantity of the still molten lava1 together with its scumlike surface1 to fall outside the crater and rattle down the mountain's slope into the sea4 ,following this explosion the lava surface in the pool is lowered and the agitation is renewed1 to culminate after the further lapse of a few minutes in a second explosion of the same nature4 ,the rise of the lava which precedes the ejection appears at night as a brighter reflection or glow from the overhanging steam cloud--the flash seen by the mariner from his vessel4 ,illustration3 ,,fig4 #aaa4--,the volcano of ,stromboli1 showing the excentric position of the crater 7after a sketch by ,judd74 ,what is going on within the crater of ,stromboli we may perhaps best illustrate by the boiling of a stiff porridge over a hot fire4 ,any one who has made corn mush over a hot camp fire is fully aware that in proportion as the mush becomes thicker by the addition of the meal1 it is necessary to stir the mass with redoubled vigor if anything is to be retained within the kettle4 ,the thickening of the mush increases its viscosity to such an extent that the steam which is generated within it is unable to make its escape unless aided by openings continually made for it by the stirring spoon4 ,if the stirring motion be stopped for a moment1 the steam expands to form great bubbles which soon eject the pasty mass from the kettle4 ,for the crater of ,stromboli this process is illustrated by the series of diagrams in ,fig4 #aab4 ,as the lava rises toward the surface1 presumably as a result of convectional currents within the chimney of the volcano1 the contained steam is relieved from pressure1 so that at some depth below the surface it begins to separate out in minute vesicles or bubbles1 which1 expanding as they rise1 acquire a rapidly accelerating velocity4 ,soon they flow together with a quite sudden increase of their expansive energy1 and now shooting upward with further accelerated velocity1 a layer of liquid lava with its cover of scum is raised on the surface of a gigantic bubble and thrown high into the air4 ,cooled during their flight1 the quickly congealed lava masses become the tuff or volcanic ash which is the material of the cinder cone4 ,illustration3 ,,fig4 #aab4--;,diagrams to illustrate the nature of eruptions within the crater of ,stromboli4 ,grander volcanic eruptions of cinder cones4--,most cinder and composite cones1 in the intervals between their grander eruptions1 if not entirely quiescent1 lapse into a period1 of light activity during which their crater eruptions appear to be in all essential respects like the habitual explosions within the ,strombolian crater4 ,this phase of activity is1 therefore1 described as ,strombolian4 ,by contrast1 the occasional grander eruptions which have punctuated the history of all larger volcanoes are described in the language of ,mercalli as ,vulcanian eruptions1 from the best studied example4 ,just what it is that at intervals brings on the grander ,vulcanian outburst within a volcano is not known with certainty2 but it is important to note that there is an approach to periodicity in the grander eruptions4 ,it is generally possible to distinguish eruptions of at least two orders of intensity greater than the ,strombolian phase2 a grander one1 the examples of which may be separated by centuries1 and one or more orders of relatively moderate intensity which recur at intervals perhaps of decades1 their time intervals subdividing the larger periods marked off by the eruptions of the first order4 ,illustration3 ,,fig4 #aac4--,map of ,volcano in the ,eolian group of islands4 ,the smaller craters partially dissected by the waves belong to ,vulcanello 7after ,judd74 ,the eruption of ,volcano in #ahhh4--;,in the ,eolian ,islands to the north of ,sicily was located the mythical forge of ,vulcan4 ,from this locality has come our word 8volcano01 and both the island and the mountain bear no other name to-day 7,fig4 #aac74 ,there is in the structure of the island the record of a somewhat complex volcanic history1 but the form of the large central cinder cone was1 according to ,scrope1 acquired during the eruption of #aghf1 at which time the crater is reported to have vomited ash for a period of fifteen days4 ,passing after this eruption into the solfatara condition1 with the exception of a light eruption in #ahgc1 the volcano remained quiet until #ahhf4 ,so active had been the fumeroles within the crater during the latter part of this period that an extensive plant had been established there for the collection especially of boracic acid4 ,in #ahhf occurred a slight eruption1 sufficient to clear out the bottom of the crater1 though not seriously to disturb the ,english planter whose vineyards and fig orchards were in the valley or atrio near the point d upon the map 7,fig4 #aac71 nearly a mile from the crater rim4 ,on the #c;d of ,august1 #ahhh1 came the opening discharge of an eruption1 which1 while not of the first order of magnitude1 was yet the greatest in more than a century of the mountain's history1 and may serve us to illustrate the ,vulcanian phase of activity within a cinder cone4 ,during the day1 to the accompaniment of explosions of considerable violence1 projectiles fell outside the crater rim and rolled down the steep slopes toward the atrio4 ,these explosions were repeated at intervals of from twenty to thirty minutes1 each beginning in a great upward rush of steam and ash1 accompanied by a low rumbling sound4 ,during the following night the eruptions increased in violence1 and the anxious planter remained on watch in his villa a mile from the crater4 ,falling asleep toward morning1 he was rudely awakened by a rain of projectiles falling upon his roof4 ,hastily snatching up his two children he ran toward the door just as a red hot projectile1 some two feet in diameter1 descended through the roof1 ceiling1 and floor of the drawing room1 setting fire to the building4 ,a second projectile similar to the first was smashed into fragments at his feet as he was emerging from the house1 burning one of the children4 ,making his escape to ,vulcanello at the extremity of the island1 the remainder of the night and the following day1 until rescue came from ,lipari1 were spent just beyond the range of the falling masses4 ,illustration3 ,,fig4 #aad4--8;,bread-crust0 lava projectile from the eruption of ,volcano in #ahhh 7after ,mercalli74 ,when the writer visited the island some months later1 the eruption was still so vigorous that the crater could not be reached4 ,the ruined villa1 smashed and charred1 stood with its walls half buried in ash and lapilli1 among which were partly smashed pumiceous lava projectiles4 ,the entire atrio about the mountain lay buried in cinder to the depth of several feet and was strewn with projectiles which varied in size from a man's fist to several feet in diameter 7,fig4 #aad74 ,the larger of these exhibited the peculiar 8bread-crust0 surface and had generally been smashed by the force of their fall after the manner of a pumpkin which has been thrown hard against the ground4 ,one of these projectiles fully three feet in diameter was found at the distance of a mile and a half from the crater4 ,though diminished considerably in intensity1 the rhythmic explosions within the crater still recurred at intervals varying from four minutes to half an hour1 and were accompanied by a dull roar easily heard at ,lipari on a neighboring island six miles away4 ,simultaneously1 a dark cloud of 8smoke01 the peculiar 8cauliflower cloud0 or pino mounted for a couple of miles above the crater 7,fig4 #aae71 and the rise was succeeded by a rain of small lava fragments or lapilli outside the crater rim4 ,illustration3 ,,fig4 #aae4--,peculiar 8cauliflower cloud0 or pino composed of steam and ash1 rising above the cinder cone of ,volcano during the waning phases of the explosive eruption of #ahhh 7after a photograph by ,b4 ,hobson74 ,there seems to be no good reason to doubt that ,vulcanian cinder eruptions of this type differ chiefly in magnitude from the rhythmic explosion within the crater of ,stromboli1 if we except the elevation of a considerable quantity of accessory and older tuff which is derived from the inner walls of the crater and carried upward into the air together with the pasty cakes of fresh lava derived from the chimney4 ,it is this accessory material which gives to the pino its dark or even black appearance4 ,illustration3 ,,fig4 #aaf4--;,double explosive eruption of ,taal volcano on the morning of ,january #cj1 #aiaa4 ,the eruption of ,taal volcano on ,january #cj1 #aiaa4--,the recent eruption of the cinder cone known as ,taal volcano is of interest1 not only because so fresh in mind1 but because two neighboring vents erupted simultaneously with explosions of nearly equal violence 7,fig4 #aaf74 ,this ,philippine volcano lies near the center of a lake some fifteen miles in diameter and about fifty miles south of the city of ,manila4 ,after a period of rest extending over one hundred and fifty years1 the symptoms of the coming eruption developed rapidly1 and on the morning of ,january #cj grand explosions of steam and ash occurred simultaneously in the neighboring craters1 and the condensed moisture brought down the ash in an avalanche of scalding mud which buried the entire island4 ,almost the entire population of the island1 numbering several hundreds1 was literally buried in the blistering mud 7,fig4 #aag72 and the gases from the explosions carried to the distant shores of the lake added to this number many hundred victims4 ,illustration3 ,,fig4 #aag4--,the thick mud veneer upon the island of ,taal 7after a photograph by ,deniston74 ,illustration3 ,,fig4 #aah4--;,a pear-shaped lava projectile4 ,the shocks which accompanied the explosions raised a great wave upon the surface of the lake1 which1 advancing upon the shores1 washed away structures for a distance of nearly a half mile4 ,the materials and the structure of cinder cones4--,obviously the materials which compose cinder cones are the cooled lava fragments of various degrees of coarseness which have been ejected from the crater4 ,if larger than a finger joint1 such fragments are referred to as volcanic projectiles1 or1 incorrectly1 as 8volcanic bombs40 ,of the larger masses it is often true that the force of expulsion has not been applied opposite the center of mass of the body4 ,thus it follows that they undergo complex whirling motions during their flight1 and being still semiliquid1 they develop curious pear-shaped or less regular forms 7,fig4 #aah74 ,when crystals have already separated out in the lava before its rise in the chimney of the volcano1 the surrounding fluid lava may be blown to finely divided volcanic dust which floats away upon the wind1 thus leaving the crystals intact to descend as a crystal rain about the crater4 ,such a shower occurred in connection with the eruption of ,etna in #affi1 and the black augite crystals may to-day be gathered by the handful from the slopes of the ,monti ,rossi 7,fig4 #abe1 p4 #abe74 ,illustration3 ,,fig4 #aai4--;,artificial production of the structure of a cinder cone with use of colored sands carried up in alternation by a current of air 7after ,g4 ,linck74 ,the term lapilli1 or sometimes rapilli1 is applied to the ejected lava fragments when of the average size of a finger joint4 ,this is the material which still partially covers the unexhumed portions of the city of ,pompeii4 ,volcanic sand1 ash1 and dust are terms applied in order to increasingly fine particles of the ejected lava4 ,the finest material1 the volcanic dust1 is often carried for hundreds and sometimes even for thousands of miles from the crater in the high-level currents of the atmosphere4 ,inasmuch as this material is deposited far from the crater and in layers more or less horizontal1 such material plays a small rle in the formation of the cinder cone4 ,the coarser sands and ash1 on the other hand1 are the materials from which the cinder cone is largely constructed4 ,the manner of formation and the structure of cinder cones may be illustrated by use of a simple laboratory apparatus 7,fig4 #aai74 ,through an opening in a board1 first white and then colored sand is sent up in a light current of air or gas supplied from suitable apparatus4 ,the alternating layers of the sand form in the attitudes shown2 that is to say1 dipping inward or toward the chimney of the volcano at all points within the crater rim1 and outward or away from it at all points outside 7,fig4 #aai74 ,if the experiment is carried so far that at its termination sand slides down the crater walls into the chimney below1 the inward dipping layers will be truncated1 or even removed entirely1 as shown in ,fig4 #aai b4 ,illustration3 ,,fig4 #abj4--;,diagram to show the contrast between a lava dome and a cinder cone4 ,,aaa1 cinder cone2 ,bab,c1 lava dome2 ,,de1 line of low cinder cones above a fissure 7after ,thoroddsen74 ,the profile lines of cinder cones4--,the shapes of cinder cones are notably different from those of lava mountains4 ,while the latter are domes1 the mountains constructed of cinder are conical and have curves of profile that are concave upward instead of convex 7,fig4 #abj74 ,in the earlier stages of its growth the cinder cone has a crater which in proportion to the height of the mountain is relatively broad 7,fig4 #ii1 p4 #ajd74 ,illustration3 ,,fig4 #aba4--,mayon volcano on the island of ,luzon1 ,p4,i4 ,a remarkably perfect high cinder cone4 ,speaking broadly1 the diameter of the crater is a measure of the violence of the explosions within the chimney4 ,a single series of short and violent explosive eruptions builds a low and broad cinder cone4 ,a long-continued succession of moderately violent explosions1 on the other hand1 builds a high cone with crater diameter small if compared with the mountain's altitude1 and the profile afforded is a remarkably beautiful sweeping curve 7,fig4 #aba74 ,toward the summit of such a cone the loose materials of which it is composed are at as steep an angle as they can lie1 the so-called angle of repose of the material2 whereas lower down the flatter slopes have been determined by the distribution of the cinder during its fall from the air4 ,when one makes the ascent of such a mountain1 he encounters continually steeper grades1 with the most difficult slope just below the crest4 ,illustration3 ,,fig4 #abb4--;,a series of breached cinder cones where the place of eruption has migrated along the underlying fissure4 ,the ,puys ,noir1 ,solas1 and ,la ,vache in the ,mont ,dore ,province of central ,france 7after ,scrope74 ,the composite cone4--,the life histories of volcanoes are generally so varied that lava domes and the pure types of cinder cones are less common than volcanoes in which paroxysmal eruptions have alternated with explosions1 and where1 therefore1 the structure of the mountain represents a composite of lava and cinder4 ,such composite cones possess a skeleton of solid rock upon which have been built up alternate sloping layers of cinder and lava4 ,in most respects such cones stand in an intermediate position between lava domes and cinder cones4 ,illustration3 ,,fig4 #abc4--,the bocca or mouth upon the inner cone of ,mount ,vesuvius from which flowed the lava stream of #ahgb4 ,this lava stream appears in the foreground with its characteristic 8ropy0 surface4 ,regarded as a retaining wall for the lava which mounts in the chimney1 the cinder cone is obviously the weakest of all4 ,should lava rise in a cinder cone without an explosion occurring1 the cone is at once broken through upon one side by the outwelling of the lava near the base4 ,thus arises the characteristic breached cone of horseshoe form 7,fig4 #abb74 ,illustration3 ,,fig4 #abd4--;,a row of parasitic cones raised above a fissure which was opened upon the flanks of ,mount ,etna during the eruption of #ahib 7after ,de ,lorenzo74 ,quite in contrast with the weak cinder cone is the lava dome with its rock walls and relatively flat slopes4 ,considered as a retaining wall for lava it is much the strongest type of volcanic mountain1 and it is likely that the hydrostatic pressure of the lava within the crater would seldom suffice to rupture the walls1 were it not that the molten rock first fuses its way into old stream tunnels buried under the mountain slopes 7see ante1 p4 #aab74 ,composite cones have a strength as retaining walls for lava which is intermediate between that of the other types4 ,their ,vulcanian eruptions of the convulsive type are initiated by the formation of a rent or fissure upon the mountain flanks at elevations well above the base1 the opening of the fissure being generally accompanied by a local earthquake of greater or less violence4 ,from one or more such fissures the lava issues usually with sufficient violence at the place of outflow to build up over it either an enlarged type of driblet cone1 referred to as a 8mouth01 or bocca#a 7,fig4 #abc71 or one or more cinder cones which from their position upon the flanks of the larger volcano are referred to as parasitic cones 7,fig4 #abd74 ,the lava of ,vesuvius more frequently yields bocchi at the place of outflow1 whereas the flanks of ,etna are pimpled with great numbers of parasitic cinder cones1 each the monument to some earlier eruption 7,fig4 #abe74 ,illustration3 ,,fig4 #abe4--,view looking toward the summit of ,etna from a position upon the southern flank near the village of ,nicolosi4 ,the two breached parasitic cones seen behind this village are the ,monti ,rossi which were thrown up in #affi and from which flowed the lava which overran ,catania 7after a photograph by ,sommer74 ,it is generally the case that a single eruption makes but a relatively small contribution to the bulk of the mountain4 ,from each new cone or bocca there proceeds a stream of lava spread in a relatively narrow stream extending down the slopes 7,fig4 #abf74 ,illustration3 ,,fig4 #abf4--,sketch map of ,etna1 showing the individual surface lava streams 7in black7 and the tuff covered surface 7stippled74 ,the caldera of composite cones4--,because of the varied episodes in the history of composite cones1 they lack the regular lines characteristic of the two simpler types4 ,the larger number of the more important composite cones have been built up within an outer crater of relatively large diameter1 the ,somma cone or caldera1 which surrounds them like a gigantic ruff or collar4 ,this caldera is clearly in most cases at least the relic of an earlier explosive crater1 after which successive eruptions of lesser violence have built a more sharply conical structure4 ,this can only be interpreted to mean that most larger and long-active volcanoes have been born in the grandest throes of their life history1 and that a larger or smaller lateral migration of the vent has been responsible for the partial destruction of the explosion crater4 ,upon ,vesuvius we find the crescent-like rim of ,monte ,somma2 on ,etna it is the ,val del ,bove1 etc4 ,it is this caldera of composite cones which gave rise to the theory of the 8elevation crater0 of von ,buch 7see ante1 p4 #ie1 and ,fig4 #abg74 ,illustration3 ,,fig4 #abg4--,panum crater1 showing the caldera and the later interior cones 7after ,russell74 ,the eruption of ,vesuvius in #aijf4--,the volcano ,vesuvius rises on the shores of the beautiful bay of ,naples only about ten miles distant from the city of ,naples4 ,the mountain consists of the remnant of an earlier broad-mouthed explosion crater1 the ,monte ,somma1 and an inner1 more conical elevation1 the ,monte ,vesuvio4 ,before the eruption of #aijf this central cone was sharply conical and rose to a height of about #dcjj feet above the surface of the bay1 or above the highest point of the ancient caldera4 ,the base of this inner cone is at an elevation of something less than half that of the entire mass1 and is separated from the encircling ring wall of the old crater by the atrio1 to which corresponds in height a perceptible shelf or piano upon the slope toward the bay of ,naples 7,fig4 #abh74 ,illustration3 ,,fig4 #abh4--,view of ,mount ,vesuvius as it appeared from the ,bay of ,naples shortly before the eruption of #aijf4 ,the horn to the left is ,monte ,somma4 ,an active composite cone like that of ,vesuvius is for the greater part of the time in the ,strombolian condition2 that is to say1 light crater explosions continue with varying intensity and interval1 except when the mountain has been excited to the periodic ,vulcanian outbreaks with which its history has been punctuated4 ,the ,strombolian explosions have sufficient violence to eject small fragments of hot lava1 which1 falling about the crater1 slowly built up a rather sharp cone4 ,the period of ,strombolian activity has1 therefore1 been called the cone-producing period4 ,just before each new outbreak of the ,vulcanian type1 the altitude of the mountain has1 therefore1 reached a maximum1 and since the larger explosive eruptions remove portions of this cone at the same time that they increase the dimensions of the crater1 the ,vulcanian stage in contrast to the other has been called the crater-producing period4 ,in this period1 then1 the material ejected during the explosions does not consist solely of fresh lava cakes1 but in part of the older dbris derived from the crater walls1 whence it is avalanched upon the chimney after each larger explosion4 ,the overhanging cloud1 which during the ,strombolian period has consisted largely of steam and is noticeably white1 now assumes a darker tone1 the 8smoke0 which characterizes the ,vulcanian eruption4 ,illustration3 ,,fig4 #abi4--;,a series of consecutive sketches of the summit of the ,vesuvian cone1 showing the modifications in its outline 7after ,sir ,william ,hamilton74 ,on several historical occasions the cone of ,vesuvius has been lowered by several hundred feet1 the greatest of relatively recent truncations having occurred in #ahbb and in #aijf4 ,between ,vulcanian eruptions the ,strombolian activity is by no means uniform1 and so the upward growth of the cone is subject to lesser interruptions and truncations 7,fig4 #abi74 ,the ,vesuvian eruption of #aijf has been selected as a type of the larger ,vulcanian eruption of composite cones1 because it combined the explosive and paroxysmal elements1 and because it has been observed and studied with greater thoroughness than any other4 ,the latest previous eruption of the ,vulcanian order had occurred in #ahgb4 ,some two years later the period of active cone building began and proceeded with such rapidity that by #ahhj the new cone began to appear above the rim of the crater of #ahgb4 ,from this time on occasional light eruptions interrupted the upbuilding process1 and as the repairs were not in all cases completed before a new interruption1 a nest of cones1 each smaller than the last1 arose in series like the outdrawn sections of an old-time spyglass4 ,at one time no less than five concentric craters were to be seen4 ,for a brief period in the fall of #aijd ,vesuvius had been in almost absolute repose1 but soon thereafter the ,strombolian crater explosions were resumed4 ,on ,may #be1 #aije1 a small stream of lava began to issue from a fissure high up upon the central cone1 and from this time on the lava continued to flow down to the valley or atrio1 separating the inner cone from the caldera remnant of ,monte ,somma4 ,seen in the night1 this stream of lava appeared from ,naples like a red hot wire laid against the mountain's side 7,fig4 #acj74 ,with gradual augmentation of ,strombolian explosions and increase in volume of the flowing lava stream1 the same condition continued until the first days of ,april in #aijf4 ,the flowing lava had then overrun the tracks of the mountain railway and accumulated in considerable quantity within the atrio 7,fig4 #aca74 ,illustration3 ,,fig4 #acj4--,night view of ,vesuvius from ,naples before the outbreak of #aijf4 ,a small lava stream is seen descending from a high point upon the central cone 7after ,mercalli74 ,on the morning of ,april #d1 a preliminary stage of the eruption was inaugurated by the opening of a new radial fissure about #ejj feet below the summit of the cone 7,fig4 #acb a71 and by early afternoon the cone-destroying stage began with the rise of a dark 8cauliflower cloud0 or pino to replace the lighter colored steam cloud4 ,the cone was beginning to fall into the crater1 and old lava dbris was mingled in the ejections with the lava clots blown from the still fluid material within the chimney4 ,from now on short and snappy lightning flashes played about the black cloud1 giving out a sharp staccato 8tack-a-tack40 ,the volume and density of the cloud and the intensity of the crater explosions continued to increase until the culmination on ,april #g4 ,on ,april #e at midnight a new lava mouth appeared upon the same fissure which had opened near the summit1 but now some #cjj feet lower 7,fig4 #acb b74 ,the lava now welled out in larger volume corresponding to its greater head1 and the stream which for ten months had been flowing from the highest outlet upon the cone now ceased to flow4 ,the next morning1 ,april #f1 at about #h o'clock1 lava broke out at several points some distance east of the opening b1 and evidently upon another fissure transverse to the first 7,fig4 #acb c74 ,the lava surface within the chimney must still have remained near its old level1--effective draining had not yet begun1--since early upon the following morning a small outflow began nearly at the top of the cone upon the opposite side and at least a thousand feet higher4 ,illustration3 ,,fig4 #aca4--,scoriaceous lava encroaching upon the tracks of the ,vesuvian railway 7after a photograph by ,sommer74 ,illustration3 ,,fig4 #acb4--,map of ,vesuvius1 showing the position and order of formation of the lava mouths upon its flanks during the eruption of #aijf 7after ,johnston-,lavis74 ,the culmination of the eruption came in the evening of ,april #g1 when1 to the accompaniment of light earthquakes felt as far as ,naples1 lava issued for the first time in great volume from a mouth more than halfway down the mountain side 7,fig4 #acb f71 and thus began the drainage of the chimney4 ,at about the same time with loud detonations a huge black cloud rose above the crater in connection with heavy explosions1 and a rain of cinder was general in the region about the mountain but especially within the northeast quadrant4 ,those who were so fortunate as to be in ,pompeii had a clear view of the mountain's summit where red hot masses of lava were thrown far into the air4 ,the direction of these projections was reported to have been not directly upward1 but inclined toward the northeast quadrant of the mountain2 but since with a northeast surface wind the heaviest deposit of ash and dust should have been upon the southwestern quadrant of the mountain1 it is evident that the material was carried upward until it reached the contrary upper currents of the atmosphere1 to be by them distributed4 ,illustration3 ,,fig4 #acc4--,the ash curtain which had overhung ,vesuvius lifting and disclosing the outlines of the mountain on ,april #aj1 #aiaa 7after ,de ,lorenzo74 ,illustration3 ,,fig4 #acd4--,the central cone of ,vesuvius as it appeared after the eruption of #aijf1 but with the earlier profile indicated4 ,the truncation represents a lowering of the summit by some five hundred feet1 with corresponding increase in the diameter of the crater 7after ,johnston-,lavis74 ,when the heavy curtain of ash1 which now for a number of succeeding days overhung all the circum-,vesuvian country1 began to lift 7,fig4 #acc71 it was seen that the summit of the cone had been truncated an average of some #ejj feet 7,fig4 #acd74 ,all the slopes and much of the surrounding country had the aspect of being buried beneath a cocoa-colored snow of a depth to the northeastward of several feet1 where it had drifted into all the hollow ways so as almost to efface them 7,fig4 #ace74 ,more than thrice as heavy as water1 the weak roof timbers of the houses at the base of the mountain gave way beneath the added load upon them1 thus making many victims4 ,inasmuch1 however1 as the ash-fall partakes of the same general characters as in eruptions from cinder cones1 we may here give our attention especially to the streams of lava which issued upon the opposite flank of the mountain 7,fig4 #acf74 ,illustration3 ,,fig4 #ace4--;,a sunken road filled with indrifted cocoa-colored ash from the ,vesuvian eruption of #aijf4 ,illustration3 ,,fig4 #acf4--,view of ,vesuvius taken from the southwest during the waning stages of the eruption of #aijf4 ,in the middle distance may be discerned the several lava mouths aligned upon a fissure1 and the courses of the streams which descend from them4 ,in the foreground is the main lava stream with scoriaceous surface 7after ,w4 ,prinz74 ,the main lava stream descended the first steep slopes with the velocity of a mile in twenty-five minutes1 about the strolling speed of a pedestrian1 but this rate was gradually reduced as the stream advanced farther from the mouth4 ,taking advantage of each depression of the surface1 the black stream advanced slowly but relentlessly toward the cities at the southwest base of the mountain4 ,with a motion not unlike that of a heap of coal falling over itself down a slope1 the block lava advances without burning the objects in its path 7,fig4 #acg74 ,illustration3 ,,fig4 #acg4--,the main lava stream of #aijf advancing upon the village of ,boscotrecase4 ,illustration3 ,,fig4 #ach4--;,an ,italian pine snapped off by the lava and carried forward upon its surface as a passenger 7after ,haug74 ,the beautiful pines are merely charred where snapped off and are carried forward upon the surface of the stream 7,fig4 #ach74 ,when a real obstruction1 such as a bridge or a villa1 is encountered1 the stream is at first halted1 but the rear crowding upon the van1 unless a passage is found at the side1 the lava front rises higher and higher until by its weight the obstruction is forced to give way 7,figs4 #aci and #adj74 ,illustration3 ,,fig4 #aci4--,lava front both pushing over and running around a wall which lies athwart its course 7after ,johnston-,lavis74 ,illustration3 ,,fig4 #adj4--,one of the villas in ,boscotrecase which was ruined by the ,vesuvian lava flow of #aijf4 ,the fragments of masonry from the ruined walls traveled upon the lava current1 where they sometimes became incased in lava4 ,the sequence of events within the chimney4--,the thorough study of this ,vesuvian eruption has placed us in a position to infer with some confidence in our conclusions the sequence of events within the chimney and crater of the volcano1 both before and during the eruption4 ,anticipating some conclusions derived from the observed dissection of volcanoes1 which will be discussed below1 it may be stated that what might be termed the core of the composite cone--the chimney--is a more or less cylindrical plug of cooled lava which during the active period of the vent has an interior bore of probably variable caliber4 ,this plug in its lower section appears in solid black in all the diagrams of ,fig4 #ada4 ,during the cone-building period 7,fig4 #ada a and b7 the plug is obviously built upward along with the cone1 for lava often flows out at a level a few hundred feet only below the crater rim4 ,by what process this chimney building goes on is not well understood1 though some light is thrown upon it by the post-eruption stage of ,mont ,pel in #aijb-aijc 7see below74 ,illustration3 ,,fig4 #ada4--,three diagrams to illustrate the sequence of events within the crater of a composite cone during the cone-building and crater-producing periods4 a and b1 two successive stages of the cone building or ,strombolian period2 c1 enlargement of the crater1 truncation of the cone1 and destruction of the upper chimney during the relatively brief crater-producing or ,vulcanian period4 ,both the older and newer sections of this plug or chimney are furnished some support against the outward pressure of the contained lava by the surrounding wall of tuff2 and they are1 therefore1 in a condition not unlike that of the inner barrel of a great gun over which sleeves of metal have been shrunk so as to give support against bursting pressures4 ,on the other hand1 when not sustaining the hydrostatic pressure of the liquid lava within1 the chimney would tend to be crushed in by the pressure of the surrounding tuff4 ,its strength to withstand bursting pressures is dependent not alone upon the thickness of its rock walls1 but also upon its internal diameter or caliber4 ,a steam cylinder of given thickness of wall1 as is well known1 can resist bursting pressures in proportion as its internal diameter is small4 ,so in the volcanic chimney1 any tendency to remelt from within the chimney walls must weaken them in a twofold ratio4 ,we are yet without accurate temperature observations upon the lava in volcanic chimneys1 but it seems almost certain that these temperatures rise as the ,vulcanian stage is approaching1 and such elevation of temperature must be followed by a greater or less re-fusion of the chimney walls4 ,the sequence of events during the late ,vesuvian eruption is1 then1 naturally explained by progressive re-fusion and consequent weakening of the chimney walls1 thus permitting a radial fissure to open near the top and gradually extend downwards4 ,thus at first small and high outlets were opened insufficient to drain the chimney1 but later1 on ,april #g1 after this fissure had been much extended and a new and larger one had opened at a lower level1 the draining began and the surface of lava commenced rapidly to sink4 ,illustration3 ,,fig4 #adb4--,the spine of ,pel rising above the chimney of the volcano after the eruption of #aijb 7after ,hovey74 ,when the rapid sinking of the lava surface occurred1 the lower lava layers were almost immediately relieved of pressure1 thus causing a sudden expansion of the contained steam and resulting in grand crater explosions4 ,the partially refused and fissured upper chimney1 now unable to withstand the inward pressure of the surrounding tuff walls1 since outward pressures no longer existed1 crushed in and contributed its materials and those of the surrounding tuff to the fragments of fresh lava rising in volume in the grand explosions 7,fig4 #ada c74 ,in outline1 then1 these seem to be the conditions which are indicated by the sequence of observed events in connection with the late ,vesuvian outbreak4 ,illustration3 ,,fig4 #adc4--,outlines of the ,pel spine upon successive dates4 ,the full line represents its outline on ,december #bf1 #aijb2 the dotted-dashed line is a profile of ,january #c1 #aijb2 while the dotted line is that of ,january #i1 #aijc4 ,the dark line is a fissure 7after ,e4 ,o4 ,hovey74 ,the spine of ,pel4--,the disastrous eruption of ,mont ,pel upon ,martinique in the year #aijb is of importance in connection with the interesting problem of the upward growth of volcanic chimneys during the cone-building period of a volcano4 ,after the conclusion of this great ,vulcanian eruption1 a spine of lava grew upward from the chimney of the main crater until it had reached an elevation of more then a thousand feet above its base1 a figure of the same order of magnitude as the probable height of the upper section of the ,vesuvian chimney previous to the eruption of #aijf4 ,the ,pel spine 7,fig4 #adb7 did not grow at a uniform rate1 but was subject to smaller or larger truncations1 but for a period of #ah days the upward growth was at the rate of about #da feet per day4 ,later1 the mass split upon a vertical plane revealing a concave inner surface1 and was somewhat rapidly reduced in altitude to #fjj feet 7,fig4 #adc71 only to rise again to its full height of about #ajjj feet some three months later4 ,while apparently unique as an observed phenomenon1 and not free from uncertainty as to its interpretation1 the growth of this obelisk has at least shown us that a mass of rock can push its way up above the chimney of an active volcano even when there are no walls of tuff about it to sustain its outward pressures4 ,illustration3 ,,fig4 #add4--;,corrugated surface of the ,vesuvian cone after the mud flows which followed the eruption in #aijf 7after ,johnston-,lavis74 ,the aftermath of mud flows4--,when the late ,vulcanian explosions of ,vesuvius had come to an end1 all slopes of the mountain1 but especially the higher ones1 were buried in thick deposits of the cocoa-colored ash1 included in which were larger and smaller projectiles4 ,as this material is extremely porous1 it greedily sucks up the water which falls during the first succeeding rains4 ,when nearly saturated1 it begins to descend the slopes of the mountain and soon develops a velocity quite in contrast with that of the slow-moving lava4 ,the upper slopes are thus denuded1 while the fields and even the houses about the base are invaded by these torrents of mud 7lava d'acqua74 ,inasmuch as these mud flows are the inevitable aftermath of all grander explosive eruptions1 the ,italian government has of late spent large sums of money in the construction of dikes intended to arrest their progress in the future4 ,it was streams of this sort that buried the city of ,herculaneum after the explosive eruption of #gi ,a4,d4 ,after the mud flows have occurred1 the ,vesuvian cone1 like all similar volcanic cones under the same conditions1 is found with deep radial corrugations 7,fig4 #add71 such as were long ago described as 8barrancoes0 and supposed to support the 8elevation crater0 theory of volcano formation4 ,the dissection of volcanoes4--,to the uninitiated it might appear a hopeless undertaking to attempt to learn by observation the internal structure of a volcano1 and especially of a complex volcano of the composite type4 ,the earliest successful attempt appears to have been made by ,count ,caspar von ,sternberg in order to prove the correctness of the theory of his friend1 the poet ,goethe4 ,goethe had claimed that a little hill in the vicinity of ,eger1 on the borders of ,bohemia1 was an extinct volcano1 though the foremost geologist of the time the famous ,werner1 had promulgated the doctrine that this hill1 in common with others of similar aspect1 originated in the combustion of a bed of coal4 ,the elevation in question1 which is known as the ,kammerbhl1 consists mainly of cinder1 and ,goethe had maintained that if a tunnel were to be driven horizontally into the mountain from one of its slopes1 a core or plug of lava would be encountered beneath the summit4 ,the excavations1 which were completed in #ahcg1 fully verified the poet's view1 for a lava plug was found to occupy the center of the mass and to connect with a small lava stream upon the side of the hill 7,fig4 #ade74 ,illustration3 ,,fig4 #ade4--,the ,kammerbhl near ,eger1 showing the tunnel completed in #ahcg which proved the volcanic nature of the mountain 7after ,judd74 ,it is not1 however1 to such expensive projects that reference is here made1 but rather to processes which are continually going on in nature1 and on a far grander scale4 ,the most important dissecting agent for our purpose is running water1 which is continually paring down the earth's surface and disclosing its buried structures4 ,how much more convincing than any results of artificial excavation1 as evidence of the internal structure of a volcano1 is the monument represented in ,fig4 #adf1 since here the lava plug stands in relief like a gigantic thumb still surrounded by a remnant of cinder deposits4 ,such exposed chimneys of former volcanoes are found in many regions1 and have become known as volcanic necks1 pipes1 or plugs4 ,illustration3 ,,fig4 #adf4--,volcanic plug exposed by natural dissection of a volcanic cone in ,colorado 7,u4 ,s4 ,g4 ,s474 ,illustration3 ,,fig4 #adg4--;,a dike cutting beds of tuff in a partly dissected volcano of southwestern ,colorado 7after ,howe1 ,u4 ,s4 ,g4 ,s474 ,not infrequently the beds of tuff composing the flanks of the volcano1 upon dissection by the same process1 bring to light walls of cooled lava standing in relief 7,fig4 #adg7--the filling of the fissure which gave outlet to the flanks of the mountain at the time of the eruption4 ,study of exposed dikes formed in connection with recent eruptions of ,vesuvius has shown that in many instances they are still hollow1 the lava having drained from them before complete consolidation4 ,another agent which is effective in uncovering the buried structures of volcanoes is the action of waves on shores4 ,always a relatively vigorous erosive agency1 the softer structures of volcanic cones are removed with especial facility by this agent4 ,on the shores of the island of ,volcano1 the little cone of ,vulcanello has been nearly half carried away by the waves1 so as to reveal with especial perfection the structure of the cinder beds as well as the internal rock skeleton of the mass4 ,here the characteristic dips of lava streams1 intercalated as they now are between tuff deposits and the lava which consolidated in fissures1 are both revealed4 ,illustration3 ,,fig4 #adh4--,map and general view of ,st4 ,paul's ,rocks1 a volcanic cone dissected by waves4 ,in mid-,atlantic a quite perfect crater1 the ,st4 ,paul's ,rocks1 has been cut nearly in half so as to produce a natural harbor 7,fig4 #adh74 ,in still other instances we may thank the volcano itself for opening up the interior of the mountain for our inspection4 ,the eruption in #ahhh of the ,japanese volcano of ,bandai-san1 by removing a considerable part of the ancient cone1 has afforded us a section completely through the mountain4 ,the summit and one side of the small ,bandai was carried completely away1 and there was substituted a yawning crater eccentric to the former mountain and having its highest wall no less than #aejj feet in height 7,fig4 #adi74 ,in two hours from the first warning of the explosion the catastrophe was complete and the eruption over4 ,illustration3 ,,fig4 #adi4--;,dissection by explosion of ,little ,bandai-san in #ahhh 7after ,sekiya74 ,the eruption of ,krakatoa in #ahhc1 probably the grandest observed volcanic explosion in historic times1 left a volcanic cone divided almost in half and open to inspection 7,fig4 #aej74 ,rakata1 ,danan1 and ,perbuatan had before constituted a line of cones built up round individual craters subsequent to the partial destruction of an earlier caldera1 portions of which were still existent in the islands ,verlaten and ,lang4 ,by the eruption of #ahhc all the exposed parts and considerable submerged portions of the two smaller cones were entirely destroyed1 and the larger one1 known as ,rakata1 was divided just outside the plug so as to leave a precipitous wall rising directly from the sea and showing lava streams in alternation with somewhat thicker tuff layers1 the whole knit together by numerous lava dikes4 ,illustration3 ,,fig4 #aej4--,the half-submerged volcano of ,krakatoa in the ,sunda ,straits before and after the eruption of #ahhc 7after ,verbeek74 ,in order to carry our dissecting process down to levels below the base of the volcanic mountain1 it is usually necessary to inspect the results of erosion by running water4 ,here the plug or chimney1 instead of being surrounded by tuff1 is inclosed by the country rock of the region1 which is commonly a sedimentary formation4 ,such exposed lower sections of volcanic chimneys are numerous along the northwestern shores of the ,british ,isles4 ,where aligned upon a dislocation or noteworthy fissure in the rocks1 the group of plugs has been referred to as a scar or cicatrice 7,fig4 #aea74 ,associated with the plugs of the cicatrice are not infrequently dikes1 or1 it may be1 sheets of lava extended between layers of sediment and known as sills4 ,illustration3 ,,fig4 #aea4--,the cicatrice of the ,banat 7after ,suess74 ,if we are able to continue the dissection process to still greater depths1 we encounter at last igneous rock having a texture known as granitic and indicating that the process of consolidation was not only exceedingly slow but also uninterrupted4 ,this rock is found in masses of larger dimensions1 and though generally of more or less irregular form1 no one dimension is of a different order of magnitude from the others4 ,such masses are commonly described as bosses1 or1 if especially large1 as batholites 7,fig4 #aeb74 ,wherever the rock beds appear as though they had been forced up by the upward pressure of the igneous mass1 the latter takes the form of a mushroom and has been described as a laccolite 7,figs4 #dgi-dha1 pp4 #dda-ddb74 ,evidence seems1 however1 to accumulate that in the greater number of cases the molten rock has fused its way upward1 in part assimilating and in part inclosing the rock which it encountered4 ,this process of upward fusion has been likened to the progress of a red hot iron burning its way through a board4 ,the formation of lava reservoirs4--,the discarding of the earlier notion that the earth has a liquid interior makes it proper in discussing the subject of volcanoes to at least touch upon the origin of the molten rock material4 ,as already pointed out1 such reservoirs as exist must be local and temporary1 or it would be difficult to see how the existing condition of earth rigidity could be maintained4 ,from the rate at which rock temperatures rise1 at increasing depths below the surface1 it is clear that all rocks would be melted at very moderate depths only1 if they were not kept in a solid state by the prodigious loads which they sustain4 ,any relief from this load should at once result in fusion of the rock4 ,illustration3 ,,fig4 #aeb4--;,diagram to illustrate a probable cause of formation of lava reservoirs1 and to show the connection between such reservoirs and the volcanoes at the surface4 ,now the restriction of active volcanoes to those zones of the earth's surface within which mountains are rising1 and where in consequence earthquakes are felt1 has furnished us at least a clew to the origin of the lava4 ,regarded as a structure capable of sustaining a load1 the competency of an arch is something quite remarkable1 so that the arching up of strong rock formations into anticlines within the upper layers of the zone of flow1 or of combined fracture and flow1 would be sufficient to remove the load from relatively weak underlying beds1 which in consequence would be fused and form local reservoirs of lava 7,figs4 #aeb and #aec74 ,it has been further quite generally observed that lines of volcanoes1 in so far as they betray any relation in position to neighboring mountain ranges1 tend to appear upon the rear or flatter limb of unsymmetrical arches1 or where local tension would favor the opening of channels toward the surface4 ,moreover1 wherever recent block movements of surface portions of the earth's shell have been disclosed in the neighborhood of volcanoes1 the latter appear to be connected with downthrown blocks1 as though the lava had1 so to speak1 been squeezed out from beneath the depressed block or blocks4 ,illustration3 ,,fig4 #aec4--,result of experiment with layers of composition to illustrate the effect of relief of load upon rocks by arching of competent formation 7after ,willis74 ,we must not1 however1 forget that the igneous rocks are greatly restricted in the range of their chemical composition4 ,no igneous rock type is known which could be formed by the fusion of any of the carbonate rocks such as limestone or dolomite1 or of the more siliceous rocks1 such as sandstone or quartzite4 ,there remains only the argillaceous class of sediments1 the shales and slates1 and so soon as we examine the composition of these rocks we are struck by the remarkable resemblance to that of the class of igneous rocks4 ,for purposes of comparison there is given below the composite or average constitution of igneous rocks in parallel column1 with the average attained by combining the analyses of #ef slates and shales1 the latter recalculated with water excluded3 ,,average ,,igneous ,,rock ---------------------------------------- -------------------------- ,,average ,,shale 7,clark7 7,washington7 ---------------------------------------- ---------------------------------------- ---------------------------------------- ------ ,si,o#b #fa4be #fa4fi #fc4cd ,al#b,o#c #ae4ha #ae4id #af4ef ,fe#b,o#c #b4gj #f4ca #a4hh #d4ec #d4da #g4hi ,fe,o #c4fa #b4fe #c4dh ,mg,o #d4dg #d4ij #c4ed ,ca,o #e4jc #e4jb #c4cc ,na#b,o #c4fd #d4ji #a4bi ,k#b,o #b4hg #c4ce #c4eb ,ti,o#b 4#fb 4#dh 4#ec ------------ ------------ ------------ #ajj4jj #ajj4jj #ajj4jj ,this close resemblance is probably of deep significance1 for the reason that shales and slates are structurally the weakest of all rocks and for the further reason that they rather generally directly underlie the carbonate rocks1 which are by contrast the strongest 7see ante1 p4 #cg74 ,for these reasons shales and slates are the only rocks which are likely to be fused by relief from load through the formation of anticlinal arches within the earth's zone of flow4 ,if this view is well founded1 lavas and other igneous rocks are in large part fused argillaceous sediments formed in connection with the process of folding1 or are refused rocks of igneous origin and similar composition4 ,character profiles4--,the character profiles of features connected in their origin with volcanoes are particularly easy to recognize1 and in a few cases in which they might be confused with others of a different origin1 an examination of the materials of the features should lead to a definitive judgment4 ,the lava plains which result from massive outflows of basalt might perhaps strictly be regarded as lack of feature1 so great may be their continuous extent4 ,wherever definite vents exist1 a broad flat dome is the usual result of the extravasation of a basaltic lava4 ,the puys of ,france and many of the ,kuppen of ,germany1 being formed from less fluid lava1 have afforded profiles with relatively small radius of curvature4 ,in its youthful stage1 the cinder cone usually presents a broad summit sag and relatively short side slopes1 whereas the cone of later stages is apt to present long sweeping and upwardly concave curves with both the gradient and the radius of curvature increasing rapidly toward the summit4 ,in contrast1 too1 with the earlier stage1 the crest is relatively small4 ,a marked reduction in the high symmetry of such profiles is noted wherever a breaching by lava outflow has occurred 7,fig4 #aed74 ,with the composite cone1 complexity and corresponding lack of symmetry is introduced1 especially in the partially ruined caldera1 and by the more or less accidental distribution of parasitic cones1 as well as by migrations of the central cone4 ,peculiarly similar acuminated profiles result from spatter-cone formation1 from the formation of a superchimney spine1 and by the uncovering of the chimney through denudational processes--the volcanic neck4 ,illustration3 ,,fig4 #aed4--;,character profiles connected with volcanoes4 ,another important feature resulting from denudation is the ,mesa or table mountain with its protecting basalt cap above softer rocks4 ,its profile most resembles that of table mountains due to differential erosion of alternately strong and weak horizontally bedded rocks1 such as compose the upper portion of the section in the ,grand ,caon of the ,colorado4 ,here1 however1 in place of a single unusually strong top layer there are found several strong layers in alternation with weaker ones so as to produce additional steps in the profile4 ,,reading ,,references ,,to ,,chapters ,,ix ,,and ,x ,general works3-- ,,paulett ,,scrope4 ,the ,geology of the ,extinct ,volcanoes of ,central ,france4 ,john ,murray1 ,london1 #aheh1 pp4 #beh4 7,an epoch-making work of early date which1 like the following reference1 may be studied to advantage to-day47 ,,sir ,,charles ,,lyell4 ,principles of ,geology1 vol4 #a1 ,chapters xxiii-xxv4 ,,melchior ,,neumayr4 ,erdgeschichte1 vol4 #a1 ,allgemeine ,geologie1 revised edition by v4 ,uhlig1 #ahig1 pp4 #acc-bgg 7a storehouse of valuable information clearly presented74 ,j4 ,d4 ,,dana4 ,characteristics of ,volcanoes1 with ,contributions of ,facts and ,principles from the ,hawaiian ,islands4 ,dodd1 ,mead1 and ,company1 ,new ,york1 #ahij1 pp4 #cig4 ,,tempest ,,anderson4 ,volcanic ,studies in ,many ,lands1 being reproductions of photographs by the author with explanatory notes4 ,john ,murray1 ,london1 #aijc1 pp4 #bjj1 pls4 #aje4 ,t4 ,g4 ,,bonney4 ,volcanoes1 their ,structure and ,significance4 ,john ,murray1 ,london1 #ahii1 pp4 #cca4 ,i4 ,c4 ,,russell4 ,volcanoes of ,north ,america4 ,macmillan1 ,new ,york1 #ahig1 pp4 #cdf4 ,,elis,e ,r,,clus4 ,les volcans de la terre1 ,belgian ,society of ,astronomy1 ,meteorology1 and ,physics of the ,globe1 #aijf-aiaj 7a valuable descriptive geographical and bibliographical work of reference74 ,g4 ,,mercalli4 ,i vulcani attivi della terre4 ,hoepli1 ,milan1 #aijg1 pp4 #dba4 7,a most valuable work1 beautifully illustrated1 but in the ,italian language47 ,arrangement of volcanic vents3-- ,,th4 ,,thoroddsen4 ,die ,bruchlinien und ihre ,beziehungen zu den ,vulkanen1 ,pet4 ,mitt41 vol4 #ea1 #aije1 pp4 #a-e1 pl4 #e4 ,r4 ,d4 ,m4 ,,verbeek4 ,various volumes and atlases of maps covering the ,dutch ,east ,indies and fully cited in the following reference 7p4 #ba74 ,,william ,h4 ,,hobbs4 ,the ,evolution and the ,outlook of ,seismic ,geology1 ,proc4 ,am4 ,phil4 ,soc41 vol4 #dh1 #aiji1 pp4 #ag-bg4 ,birth of volcanoes3-- ,f4 ,,omori4 ,the ,usu-san ,eruption and ,earthquake and ,elevation ,phenomena1 ,bull4 ,earthq4 ,inv4 ,com41 ,japan1 vol4 #e1 ,no4 #a1 #aiaa1 pp4 #a-cg1 pls4 #a-ac4 ,fissure eruptions3-- ,,th4 ,,thoroddsen4 ,island1 ,,iv1 ,vulkane1 ,pet4 ,mitt41 ,ergnzungsh4 #aec1 #aijf1 pp4 #ajh-aaa4 ,a4 ,,geikie4 ,text-book of ,geology1 #dth ed41 pp4 #cdb-cdf4 ,lava domes of ,hawaii3-- ,j4 ,d4 ,,dana4 ,characteristics of ,volcanoes 7as above74 ,c4 ,h4 ,,hitchcock4 ,hawaii and ,its ,volcanoes4 ,honolulu1 #aiji1 pp4 #cad4 ,eruption of ,matavanu volcano in #aijf3-- ,,karl ,,sapper4 ,der ,matavanu-,ausbruch auf ,savaii1 #aije-aijf1 ,zeit4 d4 ,gesell4 f4 ,erdk4 z4 ,berlin1 vol4 #ai1 #aijf1 pp4 #fhf-gji1 #d pls4 ,h4 ,j4 ,,jensen4 ,the ,geology of ,samoa1 and the ,eruptions in ,savaii1 ,proc4 ,linn4 ,soc41 ,new ,south ,wales1 vol4 #ca1 #aijf1 pp4 #fda-fgb1 pls4 #ed-fd4 ,,tempest ,,anderson4 ,the ,volcano of ,matavanu in ,savaii1 ,quart4 ,jour4 ,geol4 ,soc41 ,london1 vol4 #ff1 #aiaj1 pp4 #fba-fci1 pls4 #de-eb4 ,eruption of ,volcano in #ahhh3-- ,h4 ,j4 ,,johnston-,,lavis4 ,the ,south ,italian ,volcanoes4 ,naples1 #ahia1 pp4 #cdb1 pls4 #af4 ,eruption of ,taal volcano in #aiaa3-- ,w4 ,e4 ,,pratt4 ,the ,eruption of ,taal ,volcano1 ,january #cj1 #aiaa1 ,phil4 ,jour4 ,sci41 vol4 #f1 ,no4 #b1 ,sec4 ,a1 #aiaa1 pp4 #fc-hf1 pls4 #a-ad4 ,f4 ,h4 ,,noble4 ,taal ,volcano1 album of views of #aiaa eruption1 ,manila1 #aiaa1 pp4 #a-dh4 ,the volcano of ,etna3-- ,g4 ,,vom ,,rath4 ,der ,aetna4 ,bonn1 #ahgb1 pp4 #a-cc4 7,a beautiful piece of descriptive writing from both the geological and scenic standpoints47 ,,sartorius ,,von ,,waltershausen4 ,der ,aetna4 ,leipzig1 #ahhj1 #b quarto vols41 pp4 #cga and #edh4 ,the eruption of ,vesuvius in #aijf3-- ,h4 ,j4 ,,johnston-,,lavis4 ,geological ,map of ,monte ,somma and ,vesuvius1 with a short and concise account1 etc4 ,geo4 ,philip ,son1 ,london1 #ahia4 ,h4 ,j4 ,,johnston-,,lavis4 ,the ,eruption of ,vesuvius in ,april1 #aijf1 ,trans4 ,roy4 ,dublin ,soc41 vol4 #i1 #aiji1 ,pt4 ,,viii1 pp4 #aci-bjj1 pls4 #c-bc 7the most authoritative work upon the subject74 ,t4 ,a4 ,,jaggar1 ,,jr4 ,the ,volcano ,vesuvius in #aijf1 ,tech4 ,quart41 vol4 #ai1 #aijf1 pp4 #aje-aae4 ,w4 ,,prinz4 ,l'ruption du ,vesuv d'avril1 #aijf1 ,ciel et ,terre1 #bg;e ,anne1 #aijf1 pp4 #a-di4 ,,frank ,a4 ,,perret4 ,notes on the ,electrical ,phenomena of the ,vesuvian ,eruption1 ,april1 #aijf1 ,sci4 ,bull41 ,brooklyn ,inst4 ,arts and ,sci41 vol4 #a1 ,no4 #aa1 pp4 #cjg-cab2 ,vesuvius1 ,characteristics and ,phenomena of the ,present ,repose ,period1 ,am4 ,jour4 ,sci41 vol4 #bh1 #aiji1 pp4 #dac-dcj4 ,,william ,h4 ,,hobbs4 ,the ,grand ,eruption of ,vesuvius in #aijf1 ,jour4 ,geol41 vol4 #ad1 #aijf1 pp4 #fcf-fee4 ,the spine of ,pele3-- ,e4 ,o4 ,,hovey4 ,the ,new ,cone of ,mont ,pele and the ,gorge of the ,rivire ,blanche1 ,martinique1 ,am4 ,jour4 ,sci41 vol4 #af1 #aijc1 pp4 #bfi-bha1 pls4 #aa-ad4 ,a4 ,,heilprin4 ,the ,tower of ,pele4 ,philadelphia1 #aijd1 pp4 #fb1 pls4 #bb4 ,a4 ,,lacroix4 ,la montagne ,pele et ses ruptions1 ,acad4 des ,sciences1 ,paris1 #aijd1 ,chapter iii4 ,,karl ,,sapper4 ,in den ,vulkangebieten ,mittelamerikas und ,westindiens1 ,stuttgart1 #aije1 pp4 #agb-agh4 ,a4 ,c4 ,,lane4 ,absorbed ,gases of ,vulcanism1 ,science1 ,n4,s41 vol4 #ah1 #aijc1 p4 #gfj4 ,g4 ,k4 ,,gilbert4 ,the ,mechanism of the ,mont ,pele ,spine1 ibid41 vol4 #ai1 #aijd1 pp4 #ibg-ibh4 ,i4 ,c4 ,,russell4 ,pele ,obelisk once ,more1 ibid41 vol4 #ba1 #aije1 pp4 #ibd-ica4 ,the dissection of volcanoes3-- ,j4 ,w4 ,,judd4 ,volcanoes1 ,chapter v4 ,s4 ,,sekya and ,y4 ,,kikuchi4 ,the ,eruption of ,bandai-,san1 ,trans4 ,seis4 ,soc41 ,japan1 vol4 #ac1 ,pt4 #b1 #ahij1 pp4 #adj-bbb1 pls4 #a-i4 ,r4 ,d4 ,m4 ,,verbeek4 ,krakatau4 ,batavia1 #ahhe1 pp4 #eeg1 pls4 #be4 ,,royal ,,society4 ,the ,eruption of ,krakatoa and ,subsequent ,phenomena4 ,london1 #ahhh1 pp4 #did4 ,g4 ,k4 ,,gilbert4 ,report on the ,geology of the ,henry ,mountains1 ,u4,s4 ,geogr4 and ,geol4 ,surv41 ,rocky ,mt4 ,region1 ,washington1 #ahgg1 pp4 #bb-fj4 ,,sir ,a4 ,,geikie4 ,ancient ,volcanoes of ,great ,britain1 vol4 #b especially4 ,d4 ,w4 ,,johnson4 ,volcanic ,necks of the ,mount ,taylor ,region1 ,new ,mexico1 ,bull4 ,geol4 ,soc4 ,am41 vol4 #ah1 #aijg1 pp4 #cjc-cbd1 pls4 #be-cj4 ,,chapter ,,xi ,,the ,,attack ,,of ,,the ,,weather ,the two contrasted processes of weathering4--,it has already been pointed out that change and not stability is the order of nature4 ,within the earth's outer shell and upon it rock alteration goes on continually1 and from some portions of its surface the changed material is as constantly migrating to neighboring or even far distant regions4 ,before such transportation can begin the hard rock must first be broken down and reduced to fragments which the transporting agencies are competent to move4 ,to accomplish this breaking down1 or degeneration1 of the rock masses1 either a wide range in temperature or chemical reaction is essential4 ,in the atmosphere are found such active chemical agents as oxygen and carbon dioxide1 the so-called carbonic acid gas2 and these agents in the presence of water react chemically with the minerals of the rocks and form other minerals such as the hydrates and carbonates1 which are lighter in weight and more soluble4 ,this chemical attack upon the outer shell of the lithosphere is described as decomposition4 ,on the other hand the rock may succumb to changes which are purely mechanical and are due either to the stresses set up by differences between surface and interior temperatures1 or to the prying action of the frost in the crevices4 ,such purely mechanical degeneration of the rocks is in contrast with decomposition and is described as disintegration4 ,the two processes of decomposition and disintegration may1 however1 go on together2 and the changes of volume that are caused by decomposition may result directly in considerable disintegration1 as we are to see4 ,the rle of the percolating water4--,in order to effect chemical change or reaction1 it is essential that the substances which are to react must be brought into such intimate contact with each other as it is seldom possible to attain except by solution4 ,the chemical reactions which go on between the gaseous atmosphere and the solid lithosphere are accomplished through solution of the gases in water4 ,this water1 derived from rain or snow1 percolates into the ground or descends along the crevices in the rocks1 carrying with it a certain measure of dissolved air4 ,this air differs from that of the surrounding atmospheric envelope by containing relatively large amounts of oxygen and of the other active element carbon dioxide4 ,it follows from the important rle thus performed by the percolating water that the process of decomposition will be relatively important in humid regions where the atmospheric precipitation is sufficient for the purpose4 ,illustration3 ,,fig4 #aee4--,successive diagrams to show the effect of decomposition and resulting disintegration upon joint blocks so as to produce spheroidal bowlders by weathering4 ,within hot and dry regions there is a larger measure of rock disintegration1 and distinct chemical changes unlike those of humid regions take place in the higher temperatures and with the more concentrated saline solutions4 ,the discussion of such changes will be deferred until desert conditions are treated in another chapter4 ,mechanical results of decomposition--spheroidal weathering4--,from an earlier chapter it has been learned that the rocks of the earth's outermost shell are generally intersected by a system of vertical fissures which at each locality tend to divide the rock into parallel and upright rectangular prisms4 ,it is these joints which offer relatively easy paths for the descent of the water into the rocks4 ,in rocks of sedimentary origin there are found1 in addition to the vertical joints1 planes of bedding originally horizontal1 and in the intrusive and volcanic rocks a somewhat similar parting1 likewise parallel to the surface of the ground4 ,the combined effect of the joints and the additional parting planes is thus to separate the rock mass into more or less perfect squared blocks 7,fig4 #aee1 upper figure7 which stand in vertical columns4 ,the water which percolates downward upon the joints1 finds its way laterally along the parting planes1 and so subjects the entire surface of each block to simultaneous attack by its reagents4 ,though all parts of the surface of each block are alike subject to attack1 it is the angles and the edges which are most vigorously acted upon4 ,in the narrow crevices the solutions move but sluggishly1 and as they are soon impoverished of their reagents in the attack upon the rock1 fresh solution can reach the middle of the faces from relatively few directions4 ,the edges are at the same time being reached from many more directions1 and the corners from a still larger number4 ,the minerals newly formed by these chemical processes of hydration and carbonization are notably lighter1 and hence more bulky than the minerals from whose constituents they have been largely formed4 ,strains are thus set up which tend to separate the bulkier new material from the core of unaltered rock below4 ,as the process continues1 distinct channels for the moving waters are developed favorable to action at the edges and corners of the blocks4 ,eventually1 the squared block is by this process transformed into a spheroidal core of still unaltered rock wrapped in layers of decomposed material1 like the outer wrappings of an onion4 ,these in turn are usually imbedded in more thoroughly disintegrated material from which the shell structure has disappeared 7,fig4 #aef74 ,illustration3 ,,fig4 #aef4--,spheroidal weathering of an igneous rock4 ,exfoliation or scaling4--,a fact of much importance to geologists1 but one far too often overlooked1 is that rocks are but poor conductors for heat4 ,it results from this that in the bright sun of a summer's day a thin skin1 as it were1 upon the rock surface may be heated to a relatively high temperature1 although the layer immediately below it is practically unaffected4 ,the consequent expansion of the surface layer causes stresses that tend to scale it off from the layer below1 which1 uncovered in its turn1 develops new strains of the same sort4 ,this process of exfoliation acquires exceptional importance in desert regions where the rock surfaces are daily elevated to excessively high temperatures 7see ,chapter ,,xv74 ,illustration3 ,,fig4 #aeg4--;,dome structure in granite mass1 ,yosemite valley1 ,california 7after a photograph by ,sinclair74 ,dome structure in granite masses4--,in large granite masses1 such as are to be found in the ranges of the ,sierra ,nevada of ,california1 a peculiar dome structure is sometimes found developed upon a large scale1 and has had an important influence upon the breaking down of the rock and upon the shaping of the mountain 7,fig4 #aeg74 ,such a structure1 made up as it is of prodigious layers1 can have little in common with the veneers of weathered minerals which are the result of exfoliation1 and it is quite likely that the dome structure is in some way connected with the relief of these massive rocks from their load--the rock which once rested upon them1 but has been carried away by erosion since the uplift of the range4 ,the prying work of frost4--,in all countries where winter temperatures range below the freezing point of water1 a most potent agent of rock disintegration is the frost which pries at every crevice and cranny of the surface rock4 ,important in the temperate zones1 in the polar regions it becomes almost the sole effective agent of rock weathering4 ,there1 as elsewhere1 its efficiency as a disintegrating agent is directly dependent upon the nature of the crevices within the rock1 so that the omnipresent joints are able to exercise a degree of control over the sculpturing of the surface features which is hardly to be looked for elsewhere 7see plate #aj ,a74 ,illustration3 ,,fig4 #aeh4--,talus slope beneath a cliff4 ,talus4--,wherever the earth's surface rises in steep cliffs1 the rock fragments derived from frost action1 or by other processes of disintegration1 as they become detached either fall or slide rapidly downward until arrested upon a flatter slope4 ,upon the earlier accumulations of this kind1 the later ones are deposited1 until their surface slopes up to the cliff face as steeply as the material will lie--the angle of repose4 ,such dbris accumulations at the base of a cliff 7,fig4 #aeh7 are known as talus1 and the slope is described as a talus slope1 or in ,scotland as a 8scree40 ,illustration3 ,,fig4 #aei4--,striped ground from soil flow of chipped rock fragments upon a slope1 ,snow ,hill ,island1 ,west ,antarctica 7after ,otto ,nordenskild74 ,soil flow in the continued presence of thaw water4--,so soon as the rocks are broken down by the weathering processes1 they are easily moved1 usually to lower levels4 ,in part this transportation may be accomplished by gravity slowly acting upon the disintegrated rock and causing it to creep down the slope4 ,yet even in such cases water is usually present in quantity sufficient to fill the spaces between the grains1 and so act as a lubricant to facilitate the migration4 ,upon a large scale rocks which were either originally incoherent or have been made so by weathering1 after they have become saturated with water1 may start into sudden motion as great landslides or avalanches1 which in the space of a few moments materially change the face of the country1 and by burying the bottom lands leave disaster and misery in their wake4 ,illustration3 ,,fig4 #afj4--,pavement of horizontal surface due to soil flow1 ,spitzbergen 7after ,otto ,nordenskild74 ,within the subpolar regions1 where a large part of the surface is for much of the year covered with snow1 the underlying rocks are for long periods saturated with thaw water1 and in alternation are repeatedly frozen and thawed4 ,essentially similar conditions are met with in the high1 snow-capped mountains of temperate or torrid regions4 ,for the subpolar regions particularly it is now generally recognized that somewhat special processes of soil flow1 described under the name solifluction1 are characteristic4 ,the exact nature of these processes is as yet imperfectly understood1 but there can be little doubt concerning the large rle which they have played in the transportation of surface materials4 ,such soil flow is clearly manifested under different aspects1 and it is likely that by this comprehensive term distinct processes have been brought together4 ,illustration3 ,,fig4 #afa4--,tree roots entering fissured rock and prying its sections apart4 ,possibly the most striking aspect of the soil flow in subpolar regions is furnished by the remarkable 8stone rivers0 and 8rock glaciers02 though the more generally characteristic are peculiar stripings or other markings which appear upon the surface of the ground and thus betray the movements of the underlying materials4 ,upon slopes it is not uncommon for the surface to be composed of angular rock fragments riven by the frost and crossed by broad parallel furrows as though a gigantic plow had gone over it 7,fig4 #aei74 ,the direction of the furrows is always up and down the slope1 and the striping is marked in proportion as the slope is steep4 ,where the bottom is reached1 the furrows are replaced by a sort of mosaic pavement of hexagonal repeating figures1 each of which may be an area of the surface six feet or more across 7,fig4 #afj1 and ,fig4 #cij1 p4 #cfh74 ,the depressions which separate the 8blocks0 of the pavement are often filled with clay1 while the inclosed surfaces are made up of coarsely chipped stone4 ,the splitting wedges of roots and trees4--,in the mechanical breakdown of the rocks within humid regions a not unimportant part is sometimes taken by the trees1 which insinuate the tenuous extremities of their rootlets into the smallest cracks and by continued growth slowly wedge even the firmer rocks apart 7,fig4 #afa74 ,in a similar manner the small tree trunk growing within a crevice of the rock may in time split its parts asunder 7,fig4 #afb74 ,illustration3 ,,fig4 #afb4--;,a large glacial bowlder split by a growing tree near ,east ,lansing1 ,michigan 7after a photograph by ,bertha ,thompson74 ,the rock mantle and its shield in the mat of vegetation4--,through the action of weathering1 the rocks1 as we have seen1 lose their integrity within a surface layer1 which1 though it may be as much as a hundred feet or more in thickness1 must still be accounted a mere film above the underlying bed rock4 ,the mechanical agents of the breakdown operate only within a few feet of the surface1 and the agents of rock decomposition1 derived as they are from the atmosphere1 become inert before they have descended to any considerable depth4 ,the surface layer of incoherent rock is usually referred to as the rock mantle 7,fig4 #afc74 ,where the rock mantle is relatively deep1 as it is in the states south of the ,ohio in the eastern ,united ,states1 there is found1 deep below the outer layer of soil1 a partially decomposed and disintegrated rock1 of which the unaltered minerals lie unchanged in position but separated by the new minerals which have resulted from the breakdown of their more susceptible associates4 ,while thus in a certain sense possessing the original structure1 this altered material is essentially incoherent and easily succumbs to attack by the pick and spade1 so that it is only at considerably greater depths that the unaltered rock is encountered4 ,illustration3 ,,fig4 #afc4--,rock mantle consisting of broken rock1 above which is soil and a vegetable mat4 ,coast of ,california 7after a photograph by ,fairbanks74 ,because of the tendency of mantle rock to creep down upon slopes it is generally found thicker upon the crests and at the bases of hills and thinnest upon their slopes 7,fig4 #afd74 ,in the transformation of the upper portion of the mantle rock into soil1 additional chemical processes to those of weathering are carried through by the agency of earthworms1 bacteria1 and other organisms1 and by the action of humus and other acids derived from the decomposition of vegetation4 ,the bacteria particularly play a part in the formation of carbonates1 as they do also in changing the nitrogen of the air into nitrates which become available as plant food4 ,within the humid tropical regions ants and other insects enter as a large factor in rock decomposition1 as they do also in producing not unimportant surface irregularities4 ,illustration3 ,,fig4 #afd4--;,diagram to show the varying thickness of mantle rock upon the different portions of a hill surface 7after ,chamberlin and ,salisbury74 ,how important is the cover of vegetation in retaining the rock mantle and the upper soil layer in their respective positions1 as required for agricultural purposes1 may be best illustrated by the disastrous consequences of allowing it to be destroyed4 ,wherever1 by the destruction of forests1 by the excessive grazing of animals1 or by other causes1 the mat of turf has been destroyed1 the surface is opened in gullies by the first hard rain1 and the fertile layer of soil is carried from the slopes and distributed with the coarser mantle upon the bottom lands4 ,thus the face of the country is completely transformed from fertile hills into the most desolate of deserts where no spear of grass is to be seen and no animal food to be obtained 7plate #e ,a74 ,the soil once washed away is not again renewed1 for the continuation of the gullying process now effectively prevents its accumulation4 ,,plate #e4 ,illustration3 ,a4 ,once wooded region in ,china now reduced to desert through deforestation 7after ,willis74 ,illustration3 ,b4 8,bad ,lands0 in the ,colorado ,desert 7after ,mendenhall74 ,,reading ,,references ,,to ,,chapter ,,xi ,decomposition and disintegration3-- ,,george ,p4 ,,merrill4 ,the ,principles of ,rock ,weathering1 ,jour4 ,geol41 vol4 #d1 #ahif1 pp4 #gjd-gbd1 #hej-hga4 ,rocks1 ,rock ,weathering1 and ,soils4 ,macmillan1 ,new ,york1 #ahig1 ,pt4 iii1 pp4 #agb-daa4 ,,alexis ,a4 ,,julien4 ,on the ,geological ,action of the ,humus ,acids1 ,proc4 ,am4 ,assoc4 ,adv4 ,sci41 vol4 #bh1 #ahgi1 pp4 #caa-daj4 ,corrosion of rocks3-- ,c4 ,w4 ,,hayes4 ,solution of ,silica under ,atmospheric ,conditions1 ,bull4 ,geol4 ,soc4 ,am41 vol4 #h1 #ahig1 pp4 #bac-bbj1 pls4 #ag-ai4 ,m4 ,l4 ,,fuller4 ,etching of ,quartz in the ,interior of ,conglomerates1 ,jour4 ,geol41 vol4 #aj1 #aijb1 pp4 #hae-hba4 ,c4 ,h4 ,,smyth1 ,,jr4 ,replacement of ,quartz by ,pyrites and ,corrosion of ,quartz ,pebbles1 ,am4 ,jour4 ,sci4 7#d71 vol4 #ai1 #aije1 pp4 #bhb-bhe4 ,dome structure of granite masses3-- ,g4 ,k4 ,,gilbert4 ,domes and ,dome ,structure of the ,high ,sierra1 ,bull4 ,geol4 ,soc4 ,am41 vol4 #ae1 #aijd1 pp4 #bi-cf1 pls4 #a-d4 ,,ralph ,,arnold4 ,dome ,structure in ,conglomerate1 ibid41 vol4 #ah1 #aijg1 pp4 #fae-faf4 ,soil flow3-- ,j4 ,,gunnar ,,andersson4 ,solifluction1 a ,component of ,subarial ,denudation1 ,jour4 ,geol41 vol4 #ad1 #aijf1 pp4 #ia-aab4 ,,otto ,,nordenski,,ld4 ,die ,polarwelt und ihre ,nachbarlnder1 ,leipzig1 #aiji1 pp4 #fj-fe4 ,,ernest ,,howe4 ,landslides in the ,san ,juan ,mountains1 ,colorado1 etc41 ,prof4 ,pap41 #fg ,u4 ,s4 ,geol4 ,surv41 #aiji1 pp4 #a-eh1 pls4 #a-bj4 ,g4 ,e4 ,,mitchell4 ,landslides and ,rock ,avalanches1 ,nat4 ,geogr4 ,mag41 vol4 #ba1 #aiaj1 pp4 #bgg-bhg4 ,,william ,h4 ,,hobbs4 ,soil ,stripes in ,cold ,humid ,regions and a ,kindred ,phenomenon1 #abth ,rept4 ,mich4 ,acad4 ,sci41 #aiaj1 pp4 #ea-ec1 pls4 #a-b4 ,relation of deforestation to erosion3-- ,n4 ,s4 ,,shaler4 ,origin and ,nature of ,soils1 #abth ,ann4 ,rept4 ,u4 ,s4 ,geol4 ,surv41 #ahia1 ,pt4 #a1 pp4 #bfh-bhg4 ,w4 ,j4 ,,mcgee4 ,the ,lafayette ,formation1 ibid41 pp4 #dcj-ddh4 ,f4 ,h4 ,,king4 ,soils4 ,macmillan1 ,new ,york1 #aijh1 pp4 #ej-ed4 ,,bailey ,,willis4 ,water ,circulation and ,its ,control1 ,rept4 ,nat4 ,conserv4 ,com41 #aiji1 vol4 #b1 pp4 #fhg-gaj4 ,w4 ,j4 ,,mcgee4 ,soil erosion1 ,bull4 #ga1 ,u4 ,s4 ,bureau of ,soils1 #aiaa1 pp4 #fj1 pls4 #cc4 ,,chapter ,,xii ,,the ,,life ,,histories ,,of ,,rivers ,the intricate pattern of river etchings4--,the attack of the weather upon the solid lithosphere destroys the integrity of its surface layer1 and through reducing it to rock dbris makes it the natural prey of any agent competent to carry it along the surface4 ,we have seen how1 for short distances1 gravity unaided may pile up the dbris in accumulations of talus1 and how1 when assisted by thaw water which has soaked into the material1 it may accomplish a slow migration by a peculiar type of soil flow4 ,yet far more potent transporting agencies are at work1 and of these the one of first importance is running water4 ,only in the hearts of great deserts or in the equally remote white deserts of the polar regions is the sound of its murmurings never heard4 ,every other part of the earth's surface has at some time its running water coursing in valleys which it has itself etched into the surface4 ,it is this etching out of the continents in an intricate pattern of anastomosing valleys which constitutes the chief difference between the land surface and the relatively even floor of the oceans4 ,the motive power of rivers4--,every river is born in throes of ,mother ,earth by which the land is uplifted and left at a higher level than it was before4 ,it is the difference of elevation thus brought about between separated portions of the land areas that makes it possible for the water which falls upon the higher portions to descend by gravity to the lower4 ,this natural 8head0 due to differences of elevation is the motive power of the local streams1 and for each increase in elevation there is an immediate response in renewed vigor of the streams4 ,the elevated area off which the rivers flow is here termed an upland4 ,the velocity of a stream will be dependent not only upon the difference in altitude between its source and its mouth1 but upon the distance which separates them1 since this will determine the grade4 ,the level of the mouth being the lowest which the stream can reach is termed the base level1 and the current is fixed by the slope or declivity4 ,the capacity to lift and transport rock dbris is augmented at a quite surprising rate with every increase in current velocity1 the law being that the weight of the heaviest transportable fragment varies with the sixth power of the velocity of the current4 ,thus if one stream flows twice as rapidly as another1 it can transport fragments which are sixty-four times as heavy4 ,old land and new land4--,the uplifts of the continents may proceed without changes in the position of the shore lines1 in which case areas1 already carved by streams but no longer actively modified by them1 are worked upon by tools freshly sharpened and driven by greater power4 ,the land thus subjected to active stream cutting is described as old land1 and has already had engraved upon it the characteristic pattern of river etchings1 albeit the design has been in part effaced4 ,if1 upon the other hand1 the shore line migrates seaward with the uplift1 a portion of the relatively even sea floor1 or new land1 is elevated and laid under the action of the running water4 ,as we are to see1 stream cutting is to some extent modified when a river pattern is inherited from the uplift4 ,the uplift1 whether of old land only or of both old land and new land1 marks the starting point of a new river history1 usually described as an erosion cycle4 ,illustration3 ,,fig4 #afe4--,two successive forms of gullies from the earliest stage of a river's life 7after ,salisbury and ,atwood74 ,the earlier aspects of rivers4--,though geologists have sometimes regarded the uplift of the continents as a sort of upwarping in a continuous curved surface1 the discussions of river histories and the pictorial illustrations of them have alike clearly assumed that the uplift has been essentially in blocks and that the elevated area meets the lower lying country or the sea in a more or less definite escarpment4 ,the first rivers to develop after the uplift may be described as gullies shaped by the sudden downrush of storm waters and spaced more or less regularly along the margin of the escarpment 7,fig4 #afe74 ,these gullies are relatively short1 straight1 and steep2 they have precipitous walls and few1 if any1 tributaries4 ,illustration3 ,,fig4 #aff4--,partially dissected upland 7after ,salisbury and ,atwood74 ,with time the gully heads advance into the upland as they take on tributaries2 and so at length they in part invest it and dissect it into numerous irregularly bounded and flat-topped tables which are separated by caons 7,fig4 #aff74 ,at the same time the grade of the channel is becoming flatter1 and its precipitous walls are being replaced by curving slopes1 as will be more fully described in the sequel4 ,it is because of this progressive reduction of grades with increasing age that the early stages of a river's life are much the most turbulent of its history4 ,the water then rushes down the steep grades in rapids1 and is often at times opened out in some basin to form a lake where differences of uplift have been characteristic of neighboring sections4 ,for several reasons such basins in the course of a stream are relatively short lived 7,chapter ,,xxx71 and they disappear with the earlier stages of the river history4 ,the meshes of the river network4--,from the continued throwing out of new tributaries by the streams1 the meshes in the river network draw more closely together as the stages of its history advance4 ,the closeness of texture which is at last developed upon the upland is in part determined by the quantity of rainfall1 so that in ,new ,jersey with heavy annual precipitation the meshes in the network are much smaller than they are1 for example1 upon the semiarid or arid plains of the western ,united ,states4 ,its design will1 however1 in either case more or less clearly express the plan of rock architecture which is hidden beneath the surface 7,chapter ,,xvii74 ,the upper and lower reaches of a river contrasted4--,from the fact that the river progressively invades new portions of the upland and lays the acquired sections under more and more thorough investment1 it has near its headwaters for a long time a frontier district which may be regarded as youthful even though the sections near its mouth have reached a somewhat advanced stage4 ,the newly acquired sections of river valley may thus possess the steep grade and precipitous walls which are characteristic of early gullies and caons and are in contrast with the more rounded and flat-bottomed sections below4 ,lateral streams1 from the fact that they are newer than the main or trunk stream to which they are tributary1 likewise descend upon somewhat steeper grades 7,fig4 #afg74 ,illustration3 ,,fig4 #afg4--;,characteristic longitudinal sections of the upper portion of a river valley and its tributaries 7after scaled sections by ,nussbaum74 ,the balance between degradation and aggradation4--,we have seen that the power to transport rock fragments is augmented at a most surprising rate with every increase in the current velocity4 ,while the lighter particles of rock may be carried as high up as the surface of the water1 the heavier ones are moved forward upon the bottom with a combined rolling and hopping motion aided by local eddies4 ,those particles which come in contact with the bottom or sides of the channel abrade its surface so as ever to deepen and widen the valley4 ,this cutting accomplished by partially suspended dbris in rapidly moving currents of water is known as corrasion and the stream is said to be incising its valley4 ,as the current is checked upon the lower and flatter grades1 some of its load of sediment1 and especially the coarser portion1 will be deposited and so partially fill in the channel4 ,a nice balance is thus established between degradation and the contrasted process known as aggradation4 ,the older the river valley the flatter become the grades at any section of its course1 and thus the point which separates the lower zone of aggradation from the upper one of degradation moves steadily upstream with the lapse of time4 ,the accordance of tributary valleys4--,it is a consequence of the great sensitiveness of stream corrasion to current velocity that no side stream may enter the trunk valley at a level above that of the main stream--the tributary streams enter the trunk stream accordantly4 ,each has carved its own valley1 and any abrupt increase in gradient of the side streams near where they enter the main stream would have increased the local corrasion at an accelerated rate and so have cut down the channel to the level of the trunk stream4 ,the grading of the flood plain4--,all rivers are subject to seasonal variations in the volume of their waters4 ,where there are wet and dry seasons these differences are greatest1 and for a large part of the year the valleys in such regions may be empty of water1 and are in fact often utilized for thoroughfares4 ,in the temperate climates of middle latitudes rivers are generally flooded in the spring when the winter snows are melted1 though they may dwindle to comparatively small streams during the late summer4 ,in the upper reaches of the river the current velocities are such that the usual river channel may carry all the water of flood time2 but lower down and in the zone of aggradation1 where the current has been checked1 the level of the water rises in flood above the banks of its usual channel and spreads over the surrounding lowlands4 ,as a deposit of sediment is spread upon the surface1 the succession of the annual deposits from this source raises the general level as a broad floor described as the flood plain of the river4 ,the cycles of stream meanders4--,the annual flooding with water and simultaneous deposition of silt is not1 however1 the only grading process which is in operation upon the flood plain4 ,it is characteristic of swift currents that their course is maintained in relatively straight lines because of the inertia of the rapidly moving water4 ,in proportion as their currents become sluggish1 rivers are turned aside by the smallest of obstructions2 and once diverted from their straight course1 a law of nature becomes operative which increases the curvature of the stream at an accelerated rate up to a critical point1 when by a change1 sudden and catastrophic1 a new and direct course is taken1 to be in its turn carried through a similar cycle of changes4 ,this so-called meandering of a stream is accompanied by a transfer of sediment from one bend or meander of the river to those below and from one bank to the other4 ,inasmuch as the later meanders cross the earlier ones and in time occupy all portions of the plain to the same average extent1 a process of rough grading is accomplished to which the annual overflow deposit is supplementary4 ,illustration3 ,,fig4 #afh4--,map and sections of a stream meander4 ,the course of the main current is indicated by the dashed line4 ,the course of the current in consecutive meanders and the cross sections of the channel which result directly from the meandering process will be made clear from examination of ,fig4 #afh4 ,so soon as diverted from its direct course1 the current1 by its inertia of motion1 is thrown against the outer or convex side so as to scour or corrade that bank4 ,upon the concave or inner side of the curve there is in consequence an area of slack water1 and here the silt scoured from higher meanders is deposited4 ,the scouring of the current upon the outer bank and the filling upon the inner thus gives to the cross section of the stream a generally unsymmetrical character 7,fig4 #afh ab74 ,between meanders near the point of inflection of the curve1 and there only1 the current is centered in the middle of the channel and the cross section is symmetrical 7,fig4 #afh cd74 ,illustration3 ,,fig4 #afi4--,tree in part undermined upon the outer bank of a meander4 ,the scour upon the convex side of a meander causes the river to swing ever farther in that direction1 and through invasion of the silted flood plain to migrate across it4 ,trees which lie in its path are undermined and fall outward in the stream with tops directed with the current 7,fig4 #afi74 ,whenever the flood plain is forested1 the fallen trees may be so numerous as to lie in ranks along the shore1 and at the time of the next flood they are carried downstream to jam in narrow places along the channel and give the erroneous impression that the flood has itself uprooted a section of forest 7see p4 #dah74 ,illustration3 ,,fig4 #agj4--;,diagrams to show the successive positions of stream meanders and the relatively stationary point near the sharpest curvature4 ,the cut-off of the meander4--,as the meander swings toward its extreme position it becomes more and more closely looped4 ,adjacent loops thus approach nearer and nearer to each other1 but in the successive positions a nearly stationary point is established near where the river makes its sharpest turn 7,fig4 #agj1 ,g1 and ,fig4 #ded1 p4 #dag74 ,at length the neck of land which separates meanders is so narrow that in the next freshet a temporary jamming of logs within the channel may direct the waters across the neck1 and once started in the new direction a channel is scoured out in the soft silt4 ,thus by a breaking through of the bank of the stream1 a so-called 8crevasse01 the river suddenly straightens its course1 though up to this time it has steadily become more and more sharply serpentine4 ,after the cut-off has occurred1 the old channel may for a time continue to be used by the stream in common with the new one1 but the advantage in velocity of current being with the cut-off1 the old channel contains slacker water and so begins to fill with silt both at the beginning and the end of the loop4 ,eventually closed up at both ends1 this loop or 8ox-bow0 is entirely separated from the new channel1 and once abandoned of the stream is transformed into an ox-bow lake 7,fig4 #aga and p4 #dae74 ,illustration3 ,,fig4 #aga4--;,an ox-bow lake in the flood plain of a river4 ,meander scars4--,swinging as it occasionally does in its meanderings quite across the flood plain and against the bank of the earlier degrading river in this section1 the meander at times scours the high bank which bounds the flood plain1 and undermining it in the same manner1 it excavates a recess of amphitheatral form which is known as a meander scar 7,fig4 #agb74 ,at length the entire bank is scarred in this manner so as to present to the stream a series of concave scallops separated by sharp intermediate salients of cuspate form4 ,illustration3 ,,fig4 #agb4--,schematic representation of a series of river terraces4 a1 b1 c1 e1 successive terraces in order of age4 d1 d1 d1 d1 terrace slopes formed of meander scars4 ,river terraces4--,whenever the river's history is interrupted by a small uplift1 or the base level is for any reason lowered1 the stream at once begins to sink its channel into the flood plain4 ,once more flowing upon a low grade1 it again meanders1 and so produces new walls at a lower level1 but formed1 like the first1 of intersecting meander scars4 ,thus there is produced a new flood plain with cliff and terrace above1 which is known as a river terrace4 ,a succession of uplifts or of depressions of the base level yields terraces in series1 as they appear schematically represented in ,fig4 #agb4 ,such terraces are to be found well developed upon most of our larger rivers to the northward of the ,ohio and ,missouri4 ,the highest terrace is obviously the remnant of the earliest flood plain1 as the lowest represents the latest4 ,the delta of the river4--,as it approaches its mouth the river moves more and more sluggishly over the flat grades1 and swings in broader meanders as it flows4 ,yet it still carries a quantity of silt which is only laid down after its current has been stopped on meeting the body of standing water into which it discharges4 ,if this be the ocean1 the salinity of the sea water greatly aids in a quick precipitation of the finest material4 ,this clarifying effect upon the water of the dissolved salt may be strikingly illustrated by taking two similar jars1 the one filled with fresh and the other with salt water1 and stirring the same quantity of fine clay into each4 ,the clay in the salt water is deposited and the water cleared long before the murkiness of the other has disappeared4 ,by the laying down of the residue of its burden of sediment where it meets the sea1 the river builds up vast plains of silt and clay which are known as deltas and which often form large local extensions of the continents into the sea4 ,whereas in its upper reaches the river with its tributary streams appears in the plan like a tree and its branches1 in the delta region the stream1 by dividing into diverging channels called distributaries 7,fig4 #deh1 p4 #dbj71 completes the resemblance to the tree by adding the roots4 ,from the divergence of the distributaries upon the delta plain the ,greek capital letter is suggested and has supplied the name for these deposits4 ,of great fertility1 the delta plains of rivers have become the densely populated regions of the globe1 among which it is necessary to mention only the delta of the ,nile in ,egypt1 those of the ,ganges and ,brahmaputra in ,india1 and those of the ,hoang and ,yangtse rivers in ,china4 ,the levee4--,when the snows thaw upon the mountains at the headwaters of large rivers1 freshets result and the delta regions are flooded4 ,at such times heavily charged with sediment1 a thin deposit of fertile soil is left upon the surface of the delta plain1 and in ,egypt particularly this is depended upon for the annual enrichment of the cultivated fields4 ,though at this time the waters spread broadly over the plain1 the current still continues to flow largely within the normal channel1 so that the slack water upon either side becomes the locus for the main deposit of the sediment4 ,there is thus built up on either side of the channel a ridge of silt which is known as a levee1 and this bank is steadily increased in height from year to year 7,fig4 #deb74 ,to prevent the danger of floods upon the inhabited plains1 artificial levees are usually raised upon the natural ones1 and in a country like ,holland1 such levees 7dikes7 involve a large expenditure of money and no small degree of engineering skill and experience to construct4 ,so important to the life of the nation is the proper management of its dikes1 that in the past history of ,china each weak administration has been marked by the development of graft in this important department and by floods which have destroyed the lives of hundreds of thousands of people4 ,illustration3 ,,fig4 #agc4--8;,bird-foot0 delta of the ,mississippi ,river4 ,wherever there has been a markedly rapid sinking upon a delta region1 and depressions are common in delta territory1 no doubt as a result of the loading down of the crust1 the river may present the paradoxical condition of flowing at a higher level than the surrounding country4 ,between the levees of neighboring distributaries there are peculiar saucer-shaped depressions of the country which easily become filled with water4 ,at the extremity of the delta the levee may be the only land which shows above the ocean surface1 and so present the peculiar 8bird-foot0 outline which is characteristic of the extremity of the ,mississippi delta1 though other processes than the mere sinking of the deposits may contribute to this result 7,fig4 #agc74 ,the sections of delta deposits4--,if now we leave the plan of the delta to consider the section of its deposits1 we find them so characteristic as to be easily recognized4 ,considered broadly1 the delta advances seaward after the manner of a railroad embankment which is being carried across a lake4 ,though the greater portion of the deposit is unloaded upon a steep slope at the front1 a smaller amount of material is dropped along the way1 and a layer of extremely fine material settles in advance as the water clears of its finely suspended particles 7,fig4 #agd74 ,simultaneous deposits within a delta thus comprise a nearly horizontal layer of coarser materials1 the so-called top-set bed2 the bulk of the deposit in a forward sloping layer1 the so-called fore-set bed2 and a thin film of clay which is extended far in advance1 the bottom-set bed 7,fig4 #agd1 #b74 ,if at any point a vertical section is made through the deposits1 beds deposited in different periods are encountered2 the oldest at the bottom in a horizontal position1 the next younger above them and with forward dip1 and the youngest and coarsest upon the top in nearly horizontal position 7,fig4 #agd1 #c74 ,illustration3 ,,fig4 #agd4--;,diagrams to show the nature of delta deposits as exhibited in section4 ,it has been estimated that the surface of the ,united ,states is now being pared down by erosion at the average rate of an inch in #gfj years4 ,the derived material is being deposited in the flood plain and delta regions of its principal rivers4 ,some #eac million tons of suspended matter is in the ,united ,states carried to tidewater each year1 and about half as much more goes out to sea as dissolved matter4 ,if this material were removed from the ,panama ,canal cutting1 an #he-;foot sea-level canal would be excavated in about #gc days4 ,the ,mississippi ,river alone carries annually to the sea #cdj million tons of suspended matter1 or two thirds of the entire amount removed from the area of the ,united ,states as a whole4 ,it is thus little wonder that great deltas have extended their boundaries so rapidly and that the crust is so generally sinking beneath the load4 ,,chapter ,,xiii ,,earth ,,features ,,shaped ,,by ,,running ,,water ,the newly incised upland and its sharp salients4--,the successive stages of incising1 sculpturing1 and finally of reducing an uplifted land area1 are each of them possessed of distinctive characters which are all to be read either from the map or in the lines of the landscape4 ,upon the newly uplifted plain the incising by the young rivers is to be found chiefly in the neighborhood of the margins4 ,in this stage the valleys are described as ,v-shaped caons1 for the valley wall meets the upland surface in sharp salients 7plate #ab ,a71 and the lines of the landscape are throughout made up from straight elements4 ,though the landscapes of this stage present the grandest scenery that is known and may be cut out in massive proportions1 often with rushing river or placid lake to enhance the effect of crag and gorge1 they lack the softness and grace of outline which belong only to the maturer erosion stages4 ,the grand caon of the ,colorado presents the features characteristic of this stage in the grandest and most sublime of all examples1 and the castled ,rhine is a gorge of rugged beauty1 carved out from the newly elevated plateau of western ,prussia1 through which the water swirls in eddying rapids 7,fig4 #age74 ,illustration3 ,,fig4 #age4--;,gorge of the ,river ,rhine near ,st4 ,goars1 incised within an uplifted plain which forms the hill tops4 ,the stage of adolescence4--,as the upland becomes more largely invaded as a consequence of the headward advance of the caons and their sending out of tributary side caons1 the sharp angles in which the caon walls intersect the plain become gradually replaced by well-rounded shoulders4 ,thus the lines in the landscape of this stage are a combination of the straight line with a simple curve convex toward the sky 7,fig4 #agf74 ,in this stage large sections of the original plateau remain1 though cut into small areas by the extensions of the tributary valleys4 ,illustration3 ,,fig4 #agf4--,v-shaped valley with well-rounded shoulders characteristic of the stage of adolescence4 ,allegheny plateau in ,west ,virginia4 ,the maturely dissected upland4--,continued ramifications by the rivers eventually divide the entire upland area into separated parts1 and the rounding of the shoulders of valleys proceeds simultaneously until of the original upland no easily recognizable compartments are to be found4 ,where before were flat hilltops are now ridges or watersheds1 the well-known divides4 ,the upland is now said to be completely dissected or to have arrived at maturity4 ,the streams are still vigorous1 for they make the full descent from the upland level to base level1 and yet a critical turning point of their history has been reached1 and from now on they are to show a steady falling off in efficiency as sculpturing agents4 ,illustration3 ,,fig4 #agg4--,view of a maturely dissected upland from one of its hilltops1 ,klamath ,mountains1 ,california 7after a photograph by ,fairbanks74 ,viewed from one of the hilltops1 the landscape of this stage bears a marked resemblance to a sea in which the numberless divides are the crests of billows1 and these1 as distance reduces their importance in the landscape1 fade away into the even line of the horizon 7,fig4 #agg74 ,the ,hogarthian line of beauty4--,since the youthful stage of the upland1 when the lines of its landscape were straight1 its character rugged1 and its rivers wild and turbulent1 there has been effected a complete transformation4 ,the only straight line to be seen is the distant horizon1 for the landscape is now molded in softened outlines1 among which there is a repeated recurrence of the line of beauty made famous by ,hogarth in his 8,analysis of ,beauty40 ,as well known to all art students1 this is a sinuous line of reversed or double curvature--a curve which passes insensibly at a point of inflection from convex to concave 7,fig4 #agh74 ,the curve of beauty is now found in every section of the hills1 and it imparts to the landscape a gracefulness and a measure of restfulness as well1 which are not to be found in the landscapes of earlier stages in the erosion cycle4 ,in the bottoms of the valleys also the initial windings of the rivers within their narrow flood plains add silver beauty lines which stand out prominently from the more somber background of the hills4 ,illustration3 ,,fig4 #agh4--;,hogarth's line of beauty4 ,considered from the commercial viewpoint1 the mature upland is one of the least adaptable as a habitation for highly civilized man4 ,direct lines of communication run up hill and down dale in monotonous alternation1 and almost the only way of carrying a railroad through the region1 without an expenditure for trestles which would be prohibitive1 is to follow the tortuous crest of a main divide or the equally winding bed of one of the larger valleys4 ,illustration3 ,,fig4 #agi4--,view of the old land of ,new ,england1 with ,mount ,monadnock rising in the distance4 ,the final product of river sculpture--the peneplain4--,when maturity has been reached in the history of a river1 its energies are devoted to a paring down of the valley slopes and crests so as to reduce the general level4 ,from this time on hill summits no longer fall into a common level--that of the original upland--for some mount notably higher than others1 and with increasing age such differences become accentuated4 ,there is now also a larger aggradation of the valleys to form the level floors of flood plains1 out of which at length the now slight elevations rise upon such gentle slopes that the process of land sculpture approaches its end4 ,gradually the vigor of the stream has faded away1 and can now only be renewed through a fresh uplift of the land1 or1 what would amount to the same thing1 a depression of the base level4 ,upland and river have reached old age together1 and the approximation to a new plain but little elevated above base level is so marked that the name peneplain is applied to it4 ,scattered elevations1 which because of some favoring circumstance rise to greater heights above the general level of the peneplain1 are known as monadnocks after the type example of ,mount ,monadnock in ,new ,hampshire 7,fig4 #agi74 ,illustration3 ,,fig4 #ahj4--;,comparison of the cross sections of river valleys for the different stages of the erosion cycle4 ,the river cross sections of successive stages4--,to the successive stages of a river's life it has been common to carry over the names from the well-marked periods of a human life4 ,if neglecting for the moment the general aspect of the upland1 we fix our attention upon the characteristic cross sections of the river valley1 we find that here also there are clearly marked characters to distinguish each stage of the river's life 7,fig4 #ahj74 ,in infancy the steep1 narrow1 and sharp-angled caon is a characteristic2 with youth the wider ,v-form has already developed2 in adolescence the angles of the caon are transformed into well-rounded shoulders1 and the valley broadens so as in the lower reaches to lay down a flood plain2 in maturity the divides and the double curves of the line of beauty appear2 while in the decline of old age the valleys are extremely broad and flat and are floored by an extended flood plain4 ,the entrenchment of meanders with renewed uplift4--,upon the reduced grades which are characteristic of the declining stage of a river's life1 the current has little power to modify the surface configuration4 ,on the old land of this stage a renewed uplift starts the streams again into action4 ,this infusion of driving power into moving water1 regarded as a machine capable of accomplishing certain work1 is like winding up a clock that has run down4 ,once more the streams acquire a velocity sufficient to enable them to cut their valleys into the land surface1 and so a new erosional cycle may be inaugurated upon the old land surface--the peneplain4 ,after such an uplift has been accomplished and the rivers have sunk their early valleys within the new upland1 we may look out from this now elevated surface and the eye take in but a single horizontal line1 since we view the plain along its edge4 ,illustration3 ,,fig4 #aha4--,the ,beavertail ,bend of the ,yakima ,caon in central ,washington 7after ,george ,otis ,smith74 ,by the uplift the meanders of the earlier rivers may become entrenched in the new upland1 the wide lobes of the individual meanders being now separated by mountains where before had been plains of silt only4 ,the ,new ,river of the ,cumberland plateau and the ,yakima ,river of central ,washington 7,fig4 #aha7 furnish excellent ,american examples of intrenched meanders1 as the ,moselle ,river does in ,europe4 ,upon the course of the latter river near the town of ,zell a tunnel of the railroad a quarter of a mile in length pierces a mountain in the neck of a meander lobe in which the river itself travels a distance of more than six miles in order to make the same advance4 ,the ,kaiser ,wilhelm tunnel in the same district penetrates a larger mountain included in a double meander of the river4 ,although intrenched1 river meanders are still competent to scour and so undermine the outer bank1 and with favoring conditions they may by this process erode extended 8bottoms0 out of the plateau4 7,see ,lockport quadrangle1 ,u4 ,s4 ,g4 ,s47 ,the valley of the rejuvenated river4--,whenever a new uplift occurs before an erosional cycle has been completed1 the rivers become intrenched1 not in a peneplain1 but in the bottoms of broad valleys4 ,the sweeping curves which characterize mature landscapes may thus be brought into striking contrast with the straight lines of youthful caons which with ,v-sections descend from their lowest levels 7,fig4 #ahb74 ,the full cross section of such a valley shows a central ,v whose sharp shoulders are extended outward and upward in the softened curves of later erosion stages4 ,illustration3 ,,fig4 #ahb4--;,a rejuvenated river valley 7after a photograph by ,fairbanks74 ,the arrest of stream erosion by the more resistant rocks4--,the capacity of a river to erode and carry away the rock material that lies along its course is dependent not only upon the velocity of the current1 but also upon the hardness1 the firmness of texture1 and the solubility of the material4 ,particularly in arid and semiarid regions1 where no mantle of vegetation is at hand to mask the surfaces of the firmer rock masses1 differences of this kind are stamped deeply upon the landscape4 ,the rock terraces in the ,grand ,caon of the ,colorado together represent the stronger rock formations of the region1 while sloping talus accumulations bury the weaker beds from sight4 ,illustration3 ,,fig4 #ahc4--,plan of a river narrows4 ,each area of harder rock which rises athwart the course of a stream causes a temporary arrest in the process of valley erosion and is responsible for a noteworthy local contraction of the river valley4 ,the valley is carved less widely as well as less deeply1 and since a river can never corrade below its base1 a 8temporary base level0 is for a time established above the area of harder rock4 ,owing to the contraction of the valley under these conditions1 the locality is described as a river narrows 7,fig4 #ahc74 ,the narrows upon the ,hudson ,river occur in the ,highlands where the river leaves a broad expanse occupied by softer sediments to traverse an island-like area of hard crystalline rocks4 ,within the narrows of a river the steep walls1 characteristic of youth and the turbulent current as well1 are often retained long after other portions of the river have acquired the more restful lines of river maturity4 ,the picturesque crag and the generally rugged character of river narrows render them points of special interest upon every navigable river4 ,illustration3 ,,fig4 #ahd4--,successive diagrams to illustrate repeated river piracy and the development of 8trellis drainage01 7after ,russell74 ,the capture of one river's territory by another4--,the effect of a hard layer of rock interposed in the course of a stream is thus always to delay the advance of the erosional process at all levels above the obstruction4 ,when a stream in incising its valley degrades its channel through a veneer of softer rocks into harder materials below1 it is technically described as having discovered the harder layer4 ,where several neighboring streams flow by similar routes to their common base level1 those which discover a harder rock will advance their headwaters less rapidly into the upland and so will be at a disadvantage in extending their drainage territory4 ,a stream which is not thus hindered will in the course of time rob the others of a portion of their territory1 for it is able to erode its lower reaches nearer to base level and thus acquire for its upper reaches1 where erosion is chiefly accomplished1 an advantage in declivity4 ,the divide which separates its headwaters from those of its less favored neighbor will in consequence migrate steadily into the neighbor's territory4 ,the divide is thus a sort of boundary wall separating the drainage basins of neighboring streams1 and any migration must extend the territory of the one at the expense of the other4 ,as more and more territory is brought under the dominion of the more favored stream1 there will come a time when the divide in its migration will arrive at the channel of the stream that is being robbed1 and so by a sudden act of annexation draw off all the upper waters into its own basin4 ,by this capture the stream whose territory has been invaded is said to have been beheaded4 ,by this act of piracy the stronger stream now develops exceptional activity because of the local steep grades near the point of capture1 and with this newly acquired cutting power the invader is competent to advance still further and enter the territory of the stream that lies next beyond4 ,the type of drainage network which results from repeated captures of this kind is known as 8trellis drainage0 7,fig4 #ahd71 a type well illustrated by the rivers of the southern ,appalachians4 ,in general it may be said that1 other conditions being the same1 of two neighboring streams which have a common base level1 that one which takes the longest route will lose territory to the other1 since it must have the flatter average slope4 ,stream capture may thus come about without the discovery of hard rock layers which are more unfavorable to one stream than another4 ,illustration3 ,,fig4 #ahe4--,sketch maps to show the earlier and the present drainage condition about the ,blue ,ridge near ,harper's ,ferry4 ,water and wind gaps4--,in the ,allegheny plateau rivers cross1 the range of harder rocks in deep mountain narrows which upon the horizon appear as gateways through the barrier of the mountain wall4 ,such gateways are sometimes referred to as 8water gaps01 of which the ,delaware ,water ,gap is perhaps the best known example1 though the ,potomac crosses the ,blue ,ridge at the historic ,harper's ,ferry through a similar portal4 ,the valley of the tributary ,shenandoah has been the scene of an interesting episode in the struggle of rival streams which is typical of others in the same upland region4 ,the records which may be made out from the landscapes show clearly that in an earlier but recent period1 when the general surface stood at a higher level which has been called the ,kittatinny ,plain1 the younger ,potomac of that time and a younger but larger ancestor of ,beaverdam ,creek each crossed the ,blue ,ridge of the time through similar water gaps 7,fig4 #ahe1 map1 and ,fig4 #ahf74 ,the ,potomac of that time was1 however1 the more deeply intrenched1 and possessing an advantage in slope it was able to advance the divide at the head of its tributary1 the ,shenandoah1 into the territory of ,beaverdam ,creek4 ,thus the beheading of the ,beaverdam by the ,shenandoah was accomplished 7,fig4 #ahe1 second map7 and its upper waters annexed to the ,potomac system4 ,with the subsequent lowering of the general level of the country which yielded the present ,shenandoah ,plain1 the former water gap of ,beaverdam ,creek was abandoned of its stream at a high level in the range4 ,known as ,snickers ,gap1 it may serve as a type of the 8wind gaps0 of similar origin which are not altogether uncommon in the ,appalachian ,mountain system 7,fig4 #ahf74 ,illustration3 ,,fig4 #ahf4--,section to illustrate the history of ,snickers ,gap4 ,character profiles4--,for humid regions the landscapes possess characters which1 speaking broadly1 depend upon the stage of the erosion cycle4 ,for the earliest stages the straight line enters as almost the only element in the design2 as the cycle advances to adolescence the rounded forms begin to replace the angles of the immature stages1 and with full maturity the lines of beauty alone are characteristic4 ,as this critical stage is passed irregularity of feature and ever more flattened curves are found to correspond to the decline of the river's vital energies4 ,there are thus marks of senility in the work of rivers 7,fig4 #ahg74 ,illustration3 ,,fig4 #ahg4--;,character profiles of landscapes shaped by stream erosion in humid climates4 ,,reading ,,references ,,for ,,chapters ,,xii ,,and ,,xiii ,general3-- ,,sir ,,john ,,playfair4 ,illustrations of the ,huttonian ,theory of the ,earth4 ,edinburgh1 #ahjb1 pp4 #cej-cga4 ,j4 ,w4 ,,powell4 ,exploration of the ,colorado ,river of the ,west and its ,tributaries4 ,washington1 #ahge1 pp4 #adi-bad4 ,g4 ,k4 ,,gilbert4 ,report on the ,geology of the ,henry ,mountains4 ,washington1 #ahgg1 pp4 #ii-aej4 7,a classic upon the work of rivers47 ,c4 ,e4 ,,dutton4 ,tertiary ,history of the ,grand ,caon ,district 7with atlas71 ,mon4 #b1 ,u4 ,s4 ,geol4 ,surv41 #ahhb1 pp4 #bfd4 ,w4 ,m4 ,,davis4 ,the ,rivers and ,valleys of ,pennsylvania1 ,nat4 ,geogr4 ,mag4 vol4 #a1 #ahhi1 pp4 #bjc-bai2 ,the ,triassic ,formation of ,connecticut1 #ahth ,ann4 ,rept4 ,u4 ,s4 ,geol4 ,surv41 ,pt4 ii1 #ahih1 pp4 #add-aec4 ,,sir ,a4 ,,geikie4 ,the ,scenery of ,scotland4 ,london1 #aija1 pp4 #a-ab4 ,i4 ,c4 ,,russell4 ,rivers of ,north ,america4 ,putnam4 ,new ,york1 #ahih1 pp4 #cbg4 ,m4 ,r4 ,,campbell4 ,drainage ,modifications and their ,interpretation1 ,jour4 ,geol41 vol4 #d1 #ahif1 pp4 #efg-eha1 #feg-fgh4 ,,henry ,,gannett4 ,physiographic ,types1 ,u4 ,s4 ,geol4 ,surv41 ,topographic ,atlas1 ,folios #a-b1 #ahif1 #aijj4 ,w4 ,m4 ,,davis4 ,the ,geographical ,cycle1 ,geogr4 ,jour41 vol4 #ad1 #ahii1 pp4 #dha-ejd4 ,the flood plain3-- ,,henry ,,gannett4 ,the ,flood of ,april1 #ahig1 in the ,lower ,mississippi1 ,scot4 ,geogr4 ,mag41 vol4 #ac1 #ahig1 pp4 #dai-dba4 ,w4 ,m4 ,,davis4 ,the ,development of ,river ,meanders1 ,geol4 ,mag41 ,decade iv1 vol4 #aj1 #aijc1 pp4 #ade-adh4 ,w4 ,s4 ,,tower4 ,the ,development of ,cut-off ,meanders1 ,bull4 ,am4 ,geogr4 ,soc41 vol4 #cf1 #aijd1 pp4 #ehi-eii4 ,river terraces3-- ,w4 ,m4 ,,davis4 ,the ,terraces of the ,westfield ,river1 ,massachusetts1 ,am4 ,jour4 ,sci41 vol4 #ad1 #aijb1 pp4 #gg-id1 pl4 #d2 ,river ,terraces in ,new ,england1 ,bull4 ,mus4 ,comp4 ,zol41 vol4 #ch1 #aijb1 pp4 #bha-cdf4 ,river deltas3-- ,g4 ,k4 ,,gilbert4 ,the ,topographic ,features of ,lake ,shores1 #eth ,ann4 ,rept4 ,u4 ,s4 ,geol4 ,surv41 #ahhe1 pp4 #ajd-ajh2 ,lake ,bonneville1 ,mon4 ,i1 ,u4 ,s4 ,geol4 ,surv41 #ahij1 pp4 #aec-afg4 ,charts of ,mississippi ,river ,commission4 ,g4 ,r4 ,,credner4 ,die ,deltas1 ihre ,morphologie1 geographische ,verbreitung und ,entstehungsbedingungen1 ,pet4 ,mitt4 ,ergh4 #ef1 #ahgh1 pp4 #a-gd1 pls4 #a-c4 ,the peneplain3-- ,w4 ,m4 ,,davis4 ,plains of ,marine and ,subarial ,denudation1 ,bull4 ,geol4 ,soc4 ,am41 vol4 #g1 #ahif1 pp4 #cgg-cih2 ,the ,peneplain1 ,am4 ,geol41 vol4 #bc1 #ahii1 pp4 #bjg-bci4 ,intrenchment of meanders3-- ,w4 ,m4 ,,davis4 ,the ,seine1 the ,meuse1 and the ,moselle1 ,nat4 ,geogr4 ,mag41 vol4 #g1 #ahif1 pp4 #ahi-bjb4 ,stream capture3-- ,n4 ,h4 ,,darton4 ,examples of ,stream ,robbing in the ,catskill ,mountains1 ,bull4 ,geol4 ,soc4 ,am41 vol4 #g1 #ahif1 pp4 #eje-ejg1 pl4 #bc4 ,,collier ,,cobb4 ,a ,recapture from a ,river ,pirate1 ,science1 vol4 #bb1 #ahic1 p4 #aie4 ,,william ,h4 ,,hobbs4 ,the ,still ,rivers of ,western ,connecticut1 ,bull4 ,geol4 ,soc4 ,am41 vol4 #ac1 #aijb1 pp4 #ag-bb1 pl4 #a4 ,,isaiah ,,bowman4 ,a ,typical ,case of ,stream ,capture in ,michigan1 ,jour4 ,geol41 vol4 #ab1 #aijd1 pp4 #cbf-ccd4 ,,chapter ,,xiv ,,the ,,travels ,,of ,,the ,,underground ,,water ,the descent within the unsaturated zone4--,of the moisture precipitated from the atmosphere1 that portion which neither evaporates into the air nor runs off upon the surface1 sinks into the ground and is described as the ground water4 ,here it descends by gravity through the pores and open spaces1 and at a quite moderate depth arrives at a zone which is completely saturated with water4 ,the depth of the upper surface of this saturated zone varies with the humidity of the climate1 with the altitude of the earth's surface1 and with many other similarly varying factors4 ,within humid regions its depth may vary from a few feet to a few hundred feet1 while in desert areas the surface may lie as low as a thousand feet or more4 ,the surface of the zone of the lithosphere that is saturated with water is called the water table1 and though less accentuated it conforms in general to the relief of the country 7,fig4 #ahh74 ,its depth at any point is found from the levels of all perennial streams and from the levels at which water stands in wells4 ,illustration3 ,,fig4 #ahh4--;,diagram to show the seasonal range in the position of the water table and the cause of intermittent streams4 ,during the season of small precipitation the water table is lowered1 and if at such times it falls below the bed of a valley1 the surface stream within the valley dries up1 to be revived when1 after heavier precipitation1 the water table has in turn been raised4 ,such streams are said to be intermittent1 and are especially characteristic of semiarid regions 7,fig4 #ahh74 ,wherever in descending from the surface an impervious layer1 such as clay1 is encountered1 the further downward progress of the water is arrested4 ,now conducted in a lateral direction it issues at the surface as a spring at the line of emergence of the upper surface of the impervious layer 7,fig4 #ahi74 ,illustration3 ,,fig4 #ahi4--;,diagram to show how an impervious layer conducts the descending water in a lateral direction to issue in surface springs4 ,the trunk channels of descending water4--,while within the unconsolidated rock materials near the surface of the earth1 it is clear that water can circulate in proportion as the materials are porous and so relatively pervious4 ,as the pore spaces become minute and capillary1 the difficulty of permeation through the materials becomes very great4 ,thus in the noncoherent rocks it is the coarse gravel and the layers of sand which serve as the underground channels1 while the fine clays have the effect of an impervious wall upon the circulating waters4 ,in coarse sand as much as a third of the volume of the material is pore space for the absorption and transmission of water4 ,even under these favorable conditions the movement of the water is exceedingly slow and usually less than a fifth of a mile a year4 ,illustration3 ,,fig4 #aij4--,sketch map of the ,oucane de ,chabrires near ,chorges in the ,high ,alps1 to illustrate the corrosion of limestone along two series of vertical joints 7after ,martel74 ,within the hard rocks it is the sandstones which have the largest pore spaces1 but in nearly all consolidated rocks there are additional spaces along certain of the bedding planes1 the joint openings 7,fig4 #aij71 and the crushed zones of displacement1 so that these parting planes become the trunk channels1 so to speak1 of the circulating water4 ,it is along such crevices that in the course of time the mineral matter carried in solution by the water is deposited to produce the ore veins and the associated crystallized minerals4 ,the caverns of limestones4--,where limestone formations have a nearly flat upper surface1 a large part of the surface water enters the rock by way of the joint spaces1 which it soon widens by solution into broad crevices with well-rounded shoulders4 ,at joint intersections solution of the limestone is so favored that the water may here descend in a sort of vertical shaft until it meets a bedding plane extending laterally and offering more favorable conditions for corrosion4 ,its journey now begins in a lateral direction1 and solution of the rock continuing1 a tunnel may be etched out and extended until another joint is encountered which is favorable to its further descent into the formation4 ,by this process on alternating shafts and galleries the water descends to near the surface of the water table by a series of steps1 and is eventually discharged into the river system of the district 7,fig4 #aia74 ,within the larger caverns the water at the lowest level usually flows as a subterranean river to emerge later into the light from beneath a rock arch4 ,illustration3 ,,fig4 #aia4--;,diagram to show the relation of caverns in limestone to the river system of the district and to the 8swallow holes0 upon the surface4 ,from the plan of a system of connecting caverns it may often be observed that the galleries of the several levels are alike directed along two rectangular directions which indicate the master joint directions within the limestone formation4 ,this is especially clear from the map of the galleries in the explored portions of the ,mammoth ,cave 7,fig4 #aib74 ,swallow holes and limestone sinks4--,above the caverns of limestone formations there are selected points where the water has descended in the largest volume1 and here funnel-shaped depressions have been dissolved out from the surface of the rock4 ,in different districts such depressions have become known as 8sinks01 8swallow holes01 entonnoirs1 and ,orgeln4 ,wherever the depressions have a characteristic circular outline1 there can be little doubt that they are the product of solution by the descending water1 and have relatively small connections only with the subterranean caverns4 ,they have thus naturally collected upon their bottoms the insoluble clay which was contained in the impure limestone as well as a certain amount of slope wash from the surface4 ,inasmuch as the clays are impervious to water1 the bottoms of these swallow holes are better supplied with moisture than the surrounding rock surfaces1 and by nourishing a more vigorous plant growth are strongly impressed upon the landscape 7,fig4 #aic74 ,illustration3 ,,fig4 #aib4--,plan of a portion of ,mammoth ,cave1 ,kentucky 7after ,h4 ,c4 ,hovey74 ,illustration3 ,,fig4 #aic4--,trees and shrubs growing luxuriantly upon the bottoms of sinks within a limestone country 7after a photograph by ,h4 ,t4 ,a4 de ,l4 ,hus74 ,certain of the depressions above caverns are1 however1 less regular in outline1 and their bottoms are occupied by a mass of limestone rubble4 ,in some instances1 at least1 these depressions appear to be the result of local incaving of the cavern roofs4 ,an incaving of this nature may close up an earlier gallery in the cavern and divert the cave waters to a new course4 ,the destruction of the roofs of caverns through this process of incaving may continue until only relatively small remnants are left4 ,from long subterranean tunnels the caves are thus transformed into subarial rock bridges that have become known as 8natural bridges40 ,the best-known ,american example is the ,natural ,bridge near ,lexington1 ,virginia4 ,much grander natural bridges have been formed in sandstone by a totally different process1 and must not be confused with these limestone remnants of caverns4 ,the sinter deposits4--,just as water can dissolve the calcareous rocks with the formation of caverns1 it can under other conditions deposit the material which has thus been taken into solution4 ,its power to hold carbonate of lime in solution is dependent upon the presence of carbonic acid gas within the water4 ,water charged with gas and dissolved lime carbonate is said to be 8hard01 and if the gas be driven off by boiling or otherwise1 the dissolved lime is thrown out of solution and deposited in a form well known to all housekeepers4 ,hard water flowing in a surface stream1 if dashed into spray at a cascade1 may deposit its lime carbonate in an ever thickening veneer wherever the spray is dashed about the falls4 ,this material1 when cut in section1 has waving parallel layers and is known as travertine or calcareous sinter4 ,some of the most remarkable deposits of this nature may be seen at the cascade of ,tivoli near ,rome1 and most of the ,roman buildings have been constructed from travertine that has been quarried in the vicinity4 ,the growth of stalactites4--,water1 after percolating slowly through the crevices of limestone1 where it becomes charged with the carbonic acid gas and with dissolved carbonate of lime1 may trickle from the roof of a cavern4 ,emerging from the narrow crevice1 it may give off some of its contained gas and is usually subject to evaporation1 with the result that the lime carbonate is left adhering to the rock surface from which evaporation took place4 ,if the water collects upon the cavern roof so slowly that it can entirely evaporate before a drop can form1 the entire content of carbonate will be left adhering to the roof4 ,evaporation is most rapid near the margins and over the center of each drop as it develops1 and the deposit which is left thus takes the form of tiny white rings at those points upon the crevice where there is the easiest passage for the trickling water4 ,to the outer surface of these rings water will first adhere and then evaporate1 as it will also slowly ooze through the passage in the ring1 but here without evaporation until it reaches the lower surface4 ,a pendant structure will1 therefore1 develop1 growing outward in all directions by the deposition of concentric layers which are thickest near the roof1 and downward into the form of a rock 8icicle0 through evaporation of the water which collects near the tip4 ,these pendant sinter formations are known as stalactites and are thus formed of concentric layers arranged like a series of nested cornucopias with a perforation of nearly uniform caliber along the axis of the structure 7,fig4 #aid74 ,illustration3 ,,fig4 #aid4--;,diagrams to show the manner of formation of stalactites1 stalagmites1 and sinter columns beneath parallel crevices upon the roofs of caverns 7in part after von ,knebel74 ,formation of stalagmites4--,wherever the water percolates through the roof of the cavern so rapidly that it cannot entirely evaporate upon the roof1 a portion falls to the floor1 and1 spattering as it strikes1 builds up a relatively thick cone of sinter known as a stalagmite1 and this is accurately centered beneath a stalactite upon the roof4 ,in proportion as the cavern is high1 the dropping water is widely dispersed as it strikes the floor1 with the formation of a correspondingly thick and blunt stalagmite4 ,as this rises by growth toward the roof1 it often develops upon its summit a distinct crater-like depression 7,fig4 #aid1 lower figure74 ,when the process is long continued1 stalactites and stalagmites may grow together to form columns which may be ranged with their neighbors like the pipes of an organ1 and like them they give out clear tones when struck lightly with a mallet4 ,at other times the columns are joined to their neighbors to form hangings and draperies of the most fantastic and beautiful design 7,fig4 #aie74 ,illustration3 ,,fig4 #aie4--,sinter formations in the ,luray caverns1 ,virginia4 ,in remote antiquity limestone caverns afforded a refuge to many species of predatory birds and animals as well as to our earliest ancestors4 ,the bones of all these denizens of the caves lie entombed within the clays and the sinter formations upon the cavern floors1 and they tell the story of a fierce and long-continued warfare for the possession of these natural strongholds4 ,the evidence is clear that these cave men with their primitive weapons were able at times to drive away the cave bears1 lions1 and hyenas1 and to set up in the cavern their simple hearths1 only in their turn to be conquered by the ferocity of their enemies4 ,some of the ,european caves have yielded many wagonloads of the skeletons of these fierce predatory animals1 together with the simple weapons of the primitive man4 ,the ,karst and its features4--,most so-called limestones have a large admixture of argillaceous materials 7clays7 and of siliceous or sandy particles4 ,such impurities make up the bulk of the clays and muds which are left behind when the soluble portions of the limestone have been dissolved4 ,illustration3 ,,fig4 #aif4--,map of the dolines of the ,karst region near ,divaa4 ,swallow holes we have found to be characteristic features within such districts4 ,when limestones are more nearly pure1 as in the ,karst region east of the ,adriatic ,sea1 similar features are developed1 but upon a grander scale1 and certain additional forms are encountered4 ,in place of the sink or swallow hole1 there appears the 8karst funnel0 or doline1 a deep1 bowl-shaped depression having a flat bottom4 ,such funnels may be #cj to #cjjj feet across and from #f to #cjj feet in depth 7,fig4 #aif74 ,though in one or two instances known to be the result of the break down of cavern roofs 7,fig4 #aig71 yet like the swallow holes of other regions these larger funnels appear generally to be the work of solution by the descending waters4 ,where they have been opened in artificial cuttings along railroads or in mines1 the original rock is found intact at the bottom1 with small crevices only going down to lower levels4 ,over the bottoms of the dolines there is spread a layer of fertile red clay1 the terra rossa1 like that which is obtained as a residue when a fragment of the limestone has been dissolved in laboratory experiments4 ,illustration3 ,,fig4 #aig4--;,cross section of the doline formed by inbreak of a cavern roof4 ,the ,stara ,apnenka doline in ,carinthia 7after ,martel74 ,a desert from the destruction of forests4--,between the dolines is found a veritable desert with jutting limestone angles and little if any vegetation4 ,the water which falls upon the surface either runs off quickly or goes down to the subterranean caverns by which so much of the country is undermined4 ,hence it is that the gardens which furnish the sustenance for the scattered population are all included within the narrow limits of the doline bottoms4 ,although to-day so largely a barren waste1 we know that the ,karst upon the ,adriatic was in remote antiquity a heavily forested region and that it supplied the myriads of wooden piles upon which the city of ,venice is supported4 ,the vessels which brought to this port upon the ,adriatic its ancient prosperity were built from wood brought from this tract of modern desert4 ,in the days of ,venetian grandeur the fertile terra rossa formed a veneer upon the rock surface of the ,karst and so retained the surface waters for the support of the luxuriant forest cover4 ,after deforestation this veneer of rich soil was washed by the rains into the dolines or into the few stream courses of the region1 thus leaving a barren tract which it will be all but impossible to reclaim 7plate #f ,a74 ,illustration3 ,,fig4 #aih4--,sharp ,karren of the ,ifenplatte ,allgu 7after ,eckert74 ,upon the steeper slopes over the purer limestones1 the rain water runs away1 guided by the joints within the rock4 ,there is thus etched out a more or less complete network of narrow channels 7,fig4 #aij1 p4 #aha71 between which the remnants rise in sharp blades to produce a structure often simulated upon the fissured surface of a glacier that has been melted in the sun's rays 7,fig4 #dja74 ,these almost impassable areas of karst country are described as ,schratten or ,karrenfelder 7,fig4 #aih74 ,the ponore and the polje4--,to-day large areas of the ,karst are devoid of surface streams1 nearly all the surface water finding its way down the crevices of the limestone into caverns1 and there flowing in subterranean courses4 ,the foot traveler in the ,karst country is sometimes suddenly arrested to find a precipice yawning at his feet1 and looking down a well-like opening to the depth of a hundred feet or more1 he may see at the bottom a large river which emerges from beneath the one wall to disappear beneath the other4 ,these well-like shafts are in the ,austrian ,karst known as ,ponores1 while to the southward in ,greece they are called ,katavothren4 ,,plate #f4 ,illustration3 ,a4 ,barren ,karst landscape near the famous ,adelsberg grottoes4 7,photograph by ,i4 ,d4 ,scott47 ,illustration3 ,b4 ,surface of a limestone ledge where joints have been widened through solution4 ,syracuse1 ,n4,y4 7,photograph by ,i4 ,d4 ,scott47 ,elsewhere the karst river may emerge from its subterranean course in a broader depressed area bounded by vertical cliffs1 from which it later disappears beneath the limestone wall4 ,such depressions of the karst are known as poljen1 and appear in most cases to be above the downthrown blocks in the intricate fault mosaic of the region4 ,some of these steeply walled inclosures have an area of several hundred square miles1 and especially at the time of the spring snow melting they are flooded with water and so transformed into seasonal lakes 7,fig4 #aii and p4 #dbb74 ,it appears that at such times the cave galleries of the region with their local narrows are not able to carry off all the water which is conducted to them2 and in consequence there is a temporary impounding of the flood waters in those portions of the river's course which are open to the sky and more extended4 ,the rush of water at such times may bring the red clay into the subterranean channels in sufficient quantity to clog the passages4 ,the ,zirknitz ,lake usually has high water two or three times a year1 and exceptionally the flooding has continued for a number of years4 ,it has thus in some districts been necessary to afford relief to the population through the construction of expensive drainage tunnels4 ,illustration3 ,,fig4 #aii4--,the ,zirknitz seasonal lake within a polje of the ,karst 7after ,berghaus74 ,the conditions which are typified in the ,karst area to the east of the ,adriatic ,sea are encountered also in many other lands2 as1 for example1 in the ,vorarlberg and ,swiss ,alps1 in ,lebanon1 and in ,sicily4 ,the return of the water to the surface4--,water which has descended from the surface and been there held between impervious layers1 may be under the pressure of its own weight or 8head02 and will later find its way upward1 it may be to the surface or higher1 where a perforation is discovered in its otherwise impervious cover4 ,such local perforations are produced naturally by lines of fracture or faulting 7widened at their intersections71 and artificially through the sinking of deep wells4 ,the water1 which at ordinary times reaches the surface upon fissures1 is usually concentrated locally at the intersections of the fracture network1 where it issues in lines of fissure springs 7,fig4 #bjj72 but at the time of earthquakes the water may rise above the surface in lines of fountains 7p4 #hc71 or occasionally as sheets of water which may mount some tens of feet into the air4 ,illustration3 ,,fig4 #bjj4--;,fissure springs arranged upon lines of rock fracture at intersections1 ,pomperaug valley1 ,connecticut4 ,in contrast to the flow of surface springs1 which varies with the season through wide ranges both in its volume and in temperature of the water1 the volume of fissure springs is but slightly affected by the seasonal precipitation1 and the water temperature is maintained relatively constant4 ,rock is but a poor heat conductor1 and the seasonal temperature changes descend a few feet only into the ground4 ,thus water which rises from depths of a few hundred feet only is apt to be icy cold1 while from greater depths the effect of the earth's internal heat is apparent in a uniform but relatively higher temperature of the water4 ,such 8warm0 or thermal springs are apt to contain considerable mineral matter in solution1 both because the water is far traveled and because its higher temperature has considerably increased its solvent properties4 ,it has long been recognized that lines of junction of different rock formations at the base of mountain ranges are localities favorable for the occurrence of thermal springs4 ,these junction lines are usually within zones where by movement upon fractures the widest openings in the rock have formed1 and the catchment area of the neighboring mountain highland has supplied head for the ground water4 ,a map of the hot springs within the ,great ,basin of the western ,united ,states would present in the main a map of its principal faults4 ,artesian wells4--,from the natural fissure spring an artesian well differs in the artificial character of the perforation of the impervious cover to the water layer4 ,the water of artesian wells may flow out at the surface under pressure1 or it may require pumping to raise it from some lower level4 ,ideal conditions are furnished where the geological structure of the district is that of a broad basin or syncline4 ,the water which falls in a neighboring upland is here impounded between two parallel1 saucer-like walls and will flow under its head if the upper wall be perforated at some low level 7,fig4 #bja1 #c74 ,illustration3 ,,fig4 #bja4--,schematic diagrams to illustrate the different types of artesian wells1 7#a7 ,a non-flowing well2 7#b7 flowing wells without basin structure caused by clogging of the pervious formation2 7#c7 flowing wells in an artesian basin4 ,the dotted lines are the water levels within the pervious layers 7after ,chamberlin74 ,a monoclinal structure may furnish artesian conditions when the generally pervious layer has become clogged at a low level so as to hold back the water 7,fig4 #bdh1 #b74 ,pumping wells may be used successfully even when such clogging does not exist1 for the slow-moving underground water flows readily in the direction of all free outlets 7,fig4 #bja1 #a74 ,hot springs and geysers4--,thermal springs whose temperature approaches the boiling point of water are known as hot springs4 ,a geyser is a hot spring which intermittently ejects a column of water and steam4 ,both hot springs and geysers are to be found only in volcanic regions1 and appear to be connected with uncooled masses of siliceous lava4 ,in two of the three known geyser regions1 ,iceland and ,new ,zealand1 the volcanoes of the neighborhood are still active1 and the lavas of the ,yellowstone ,national ,park date from the quite recent geological period which immediately preceded the so-called 8,ice ,age40 ,wherever found1 geysers are in the low levels along lines of drainage where the underground water would most naturally reappear at the surface4 ,their water has penetrated to considerable depths below the surface1 but has been chiefly heated by ascending steam or other vapors4 ,the water journey has been chiefly made along fissures1 as is shown by the cool springs which often issue near them4 ,though some hot springs and geysers may disappear from a district1 others are found to be forming1 and there is no good reason to think that geysers are rapidly dying out1 as was at one time supposed4 ,the action of a geyser was first satisfactorily explained by the great ,german chemist ,bunsen after he had made studies of the ,icelandic geysers1 and the mechanics of the eruption was later strikingly illustrated in the laboratory by an artificial geyser constructed by the ,irish physicist ,tyndall4 ,in many respects this action is like that of the ,strombolian eruption within a cinder cone1 since it is connected with the viscosity of the fluid and the resistance which this opposes to the liberation of the developing vapor4 ,in the case of the geyser1 a column of heated water stands within a vertical tube and is heated near the bottom of the column4 ,illustration3 ,,fig4 #bjb4--;,cross section of ,geysir1 ,iceland1 with simultaneously observed temperatures recorded at the left1 and the boiling temperatures for the same levels at the right 7after ,campbell74 ,though the water may at its surface have the normal boiling temperature and be there in quiet ebullition1 the boiling point for all lower levels is raised by the weight of the column of superincumbent liquid1 and so for a time the formation of steam within the mass is prevented4 ,in ,fig4 #bjb is shown a cross section of the ,icelandic ,geysir from which our name for such phenomena has been derived1 and to this section have been added the actual observed temperatures of the water at the different levels as well as the temperatures at which boiling can take place at these levels4 ,from this it will be seen that at a depth of #de feet the water is but #b ,centigrade below its boiling point4 ,a slight increase of temperature at this level1 due to the constantly ascending steam1 will not only carry this layer above the boiling point1 but the expansion of the steam within the mass will elevate the upper layers of the water into zones where the boiling points are lower1 and thus bring about a sudden and violent ebullition of all these upper portions4 ,thus is explained the almost universal observation that just before geysers erupt the hot water rises in the bowls and generally overflows them4 ,illustration3 ,,fig4 #bjc4--;,apparatus for simulating geyser action in the lecture room 7by courtesy of ,professor ,b4 ,w4 ,snow74 ,the water ejected from the geyser is considerably cooled in the air2 and after its return to the tube must be again heated by the ascending vapors before another eruption can occur4 ,the measure of the cooling1 the time necessary to fill the tube1 and the supply of rising steam1 all play a part in fixing the period which separates consecutive eruptions4 ,if the top of the tube be narrowed from its average caliber1 as is commonly observed to be true of the geysers within the ,yellowstone ,national ,park1 the escape of the steam is further hindered1 and frequent geyser eruption promoted4 ,an artificial geyser for demonstration of the phenomenon in the lecture room is represented in ,fig4 #bjc4 ,the cut has been prepared from a photograph of an apparatus designed by ,professor ,b4 ,w4 ,snow of the ,university of ,wisconsin4 ,in this design the tube is contracted so as to have a top diameter one fourth only of what it is at the bottom1 where heat is directly applied by multiple ,bunsen lamps4 ,the water once sufficiently heated1 this artificial geyser erupts at regular intervals of time which are dependent upon the dimensions of the apparatus and the quantity of heat applied4 ,in case of natural geysers a considerable quantity of heat escapes between eruptions in steam which issues quietly from the bowl of the geyser4 ,if this heat be retained by plugging the mouth of the tube with a barrowful of turf1 as is sometimes done with the geyser ,strokr in ,iceland1 eruption is promoted and so takes place earlier4 ,another method of securing the same result is to increase the viscosity of the water through the addition of soap1 as was accidentally discovered by a ,chinaman who was utilizing the geyser water in the ,yellowstone ,park for laundry operations4 ,after this discovery it became a common custom to 8soap0 the ,yellowstone geysers in order to make them play2 but this method was prohibited under heavy penalty after the disastrous eruption of the ,excelsior ,geyser4 ,the deposition of siliceous sinter by plant growth4--,geysers are known only from areas of siliceous volcanic lava1 and this may perhaps have its cause in the easier solution of the geyser tube from such materials4 ,the silica dissolved in the heated waters is again deposited at the surface to form siliceous sinter or geyserite4 ,this material forms terraces surrounding the geysers or is built up into mounds which are often quite symmetrical1 such as those of the ,bee ,hive and ,lone ,star geysers of the ,yellowstone ,park 7,fig4 #bjd74 ,illustration3 ,,fig4 #bjd4--;,cone of siliceous sinter built up about the mouth of the ,lone ,star ,geyser in the ,yellowstone ,national ,park4 ,the greater part of this separation of silica from the heated geyser waters is due to the action of plants or alg that are able to grow in the boiling waters and which produce the beautiful colors in the linings to the hot springs4 ,the wonderful variety of the tints displayed is accounted for by the fact that the alg take on different colors at different temperatures4 ,the silica is deposited from the water in the gelatinous hydrated form1 which1 however1 dries in the sun to a white sand4 ,the growth within the pools goes on in a manner similar to that of a coral reef1 the alg dying below and there becoming encased in the rock lining while still continuing to grow upon the surface4 ,whereas sinter of this nature1 when deposited by evaporation alone1 can produce a maximum thickness of layer of a twentieth of an inch each year1 the growth from alga deposition within limited areas may be as much as eight inches during the same period4 ,,reading ,,references ,,for ,,chapter ,,xiv ,general3-- ,f4 ,h4 ,,king4 ,principles and ,conditions of the ,movements of ,ground ,water1 #aith ,ann4 ,rept4 ,u4 ,s4 ,geol4 ,surv41 #ahii1 ,pt4 ii1 pp4 #ei-bid1 pls4 #f-af4 ,c4 ,s4 ,,slichter4 ,the ,motions of the ,underground ,waters1 ,water ,supply ,paper ,no4 #fg1 ,u4 ,s4 ,geol4 ,surv41 #aijb1 pp4 #a-ajf1 pls4 #a-h2 ,field ,measurements of the ,rate of ,movement of ,underground ,waters1 ibid41 ,no4 #adj1 #aije1 pp4 #a-abb1 pls4 #a-ae4 ,m4 ,l4 ,,fuller4 ,occurrence of ,underground ,water1 ibid44 ,no4 #aad1 #aije1 pp4 #ah-dj1 pls4 #d2 ,bibliographic review and index of papers relating to underground waters published by the ,united ,states ,geological ,survey1 #ahgi-aijd1 ibid41 ,no4 #abj1 #aije1 pp4 #a-abh4 ,caverns3-- ,e4 ,a4 ,,martel4 ,les abimes1 les eaux souterraines1 les cavernes1 les sources1 la splologie4 ,delagrave1 ,paris1 pp4 #egh4 7,lavishly illustrated47 ,h4 ,c4 ,,hovey4 ,celebrated ,american ,caverns4 ,cincinnati1 #ahif1 pp4 #bbh2 ,the ,mammoth ,cave of ,kentucky4 ,louisville1 #ahig1 pp4 #aaa4 ,j4 ,w4 ,,beede4 ,cycle of ,subterranean ,drainage in the ,bloomington ,quadrangle1 ,proc4 ,ind4 ,acad4 ,sci41 #aiaj1 pp4 #a-ca4 ,karst conditions3-- ,j4 ,,cvijic4 ,das ,karstphnomen1 ,geogr4 ,abh41 vol4 #e1 #ahic4 ,,mile ,,chaix4 ,la topographie du desert de plat 7,hautes ,savoie71 ,le ,globe1 vol4 #cd1 #ahie1 pp4 #a-dd1 pls4 #a-af1 pp4 #bag-ccj4 ,w4 ,v4 ,,knebel4 ,hhlenkunde mit ,bercksichtigung der ,karstphnomene4 ,vieweg1 ,braunschweig1 #aijf1 pp4 #bbb4 ,a4 ,,grund4 ,die ,karsthydrographie1 ,studien aus ,westbosnien1 ,geogr4 ,abh41 vol4 #g1 ,no4 #c1 #aijc1 pp4 #bjj4 ,,mile ,,chaix-,,du ,,bois et ,,andr ,,chaix4 ,contribution a l'tude des lapies en ,carniole et au ,steinernes ,meer1 ,le ,globe1 vol4 #df1 #aijg1 pp4 #ag-ef1 pls4 #bf4 ,p4 ,,arbenz4 ,die ,karrenbildungen geschildert am ,beispiele der ,karrenfelder bei der ,frutt in ,kanton ,obwalden 7,schweiz74 ,deutsch4 ,alpenzeitung1 ,munich1 #aiji1 pp4 #a-i4 ,f4 ,,katzer4 ,karst und ,karsthydrographie4 ,sarejevo1 #aiji1 pp4 #ie4 ,m4 ,,neumayr4 ,erdgeschichte1 vol4 #a1 pp4 #ejj-eaj4 ,e4 ,,de ,,martonne4 ,trait de ,gographie ,physique1 pp4 #dfb-dgb 7excellent summaries in this and the last reference74 ,e4 ,a4 ,,martel4 ,the ,land of the ,causses1 ,appalachia1 vol4 #g1 #ahic1 pp4 #ah-adi1 pls4 #d-ac4 ,fissure springs3-- ,a4 ,c4 ,,peale4 ,natural ,mineral ,waters of the ,united ,states1 #adth ,ann4 ,rept4 ,u4 ,s4 ,geol4 ,surv41 ,pt4 ii1 #ahid1 pp4 #di-hh4 ,,william ,h4 ,,hobbs4 ,the ,newark ,system of the ,pomperaug ,valley4 ,connecticut1 #bast ,ann4 ,rept4 ,u4 ,s4 ,geol4 ,surv41 ,pt4 iii1 #aija1 pp4 #ia-ic4 ,artesian wells3-- ,t4 ,c4 ,,chamberlin4 ,requisite and ,qualifying ,conditions of ,artesian ,wells1 #eth ,ann4 ,rept4 ,u4 ,s4 ,geol4 ,surv41 #ahhe1 pp4 #aca-agc4 ,hot springs and geysers3-- ,a4 ,c4 ,,peale4 ,yellowstone ,park1 ,thermal ,springs1 #abth ,ann4 ,rept4 ,geol4 and ,geogr4 ,surv4 ,ter4 7,hayden71 ,pt4 ii1 ,sec4 ii1 pp4 #fc-ded 7many plates and maps74 ,w4 ,h4 ,,weed4 ,geysers1 ,rept4 ,smithson4 ,inst41 #ahia1 pp4 #afc-agh4 ,,arnold ,,hague and ,w4 ,h4 ,,weed 7on hot springs and geysers of ,yellowstone ,national ,park71 ,c4 ,r4 ,cong4 ,gol4 ,intern41 ,washington1 #ahia1 pp4 #cdf-cfc4 ,w4 ,h4 ,,weed4 ,formation of ,travertine and ,siliceous ,sinter by the ,vegetation of ,hot ,springs1 #ith ,ann4 ,rept4 ,u4 ,s4 ,geol4 ,surv41 #ahhi1 pp4 #fac-fgf1 pls4 #gh-hg4 ,m4 ,,neumayr4 ,erdgeschichte1 vol4 #a1 pp4 #ejj-eaj4 ,,arnold ,,hague4 ,soaping ,geysers1 ,trans4 ,am4 ,inst4 ,min4 ,eng41 vol4 #ag1 #ahhi1 pp4 #edf-eec4 ,,john ,,tyndall4 ,heat as a ,mode of ,motion1 ,new ,york1 #ahgc1 pp4 #aae-aba 7artificial geyser74 ,,chapter ,,xv ,,sun ,,and ,,wind ,,in ,,the ,,lands ,,of ,,infrequent ,,rains ,the law of the desert4--,it is well to keep ever in mind that there is no universal law which dominates ,nature's processes in all the sections of her realm4 ,those changes which1 because often observed1 are most familiar1 may not be of general application1 for the reason that the areas habitually occupied by highly civilized races together comprise but a small portion of the earth's surface4 ,in the dank tropical jungle1 upon the vast arid sand plains1 and in the cold white spaces near the poles1 ,nature has instituted peculiar and widely different processes4 ,the fundamental condition of the desert is aridity1 and this necessitates an exclusion from it of all save the exceptional rain cloud4 ,thus deserts are walled in by mountain ranges which serve as barriers to intercept the moisture-bringing clouds4 ,they are in consequence saucer-shaped depressions1 often with short mountain ranges rising out of the bottoms1 and such rain as falls within the inclosure is largely upon the borders4 ,of this rainfall none flows out from the desert1 for the water is largely returned to the atmosphere through evaporation4 ,the desert history is thus begun in isolation from the sea from which the cloud moisture is derived1 a balance being struck between inflow and evaporation4 ,yet if deserts have no outlets1 it is not true that they have no rivers4 ,these are occasionally permanent1 often periodic1 but generally ephemeral and violent4 ,the characteristic drainage of deserts comes as the immediate result of sudden cloudburst4 ,as a consequence1 the desert stream flows from the mountain wall choked with sediment1 and entering the depressed basin1 is for the most part either sucked down into the floor or evaporated and returned to the atmosphere4 ,the dissolved material which was carried in the water is eventually left in saline deposits1 and the great burden of sediment accumulates in thick stratified masses which in magnitude outstrip the largest deltas in the ocean4 ,the self-registering gauge of past climates4--,from the initiation of the desert in its isolation from the lands tributary to the sea1 its history becomes an individual and independent one4 ,an increasing quantity of rainfall will be marked by larger inflow to the basin1 and the lakes which form in its lowest depression will1 as a consequence1 rise and expand over larger areas4 ,a contrary climatic change will bring about a lowering of the lakes and leave behind the marks of former shorelines above the water level 7,fig4 #bje74 ,deserts are thus in a sense self-registering climatic gauges whose records go back far beyond the historic past4 ,from them it is learned that there have been alternating periods of larger and smaller precipitation1 which are referred to as pluvial and interpluvial periods4 ,illustration3 ,,fig4 #bje4--;,former shore lines on the mountain wall surrounding the desert of the ,great ,basin4 ,view from the temple in ,salt ,lake ,city 7after ,gilbert74 ,from such records it is learned that the ,great ,basin of the western ,united ,states was at one time occupied by two great desert lakes1 the one in the eastern portion being known as ,lake ,bonneville 7,fig4 #bjf74 ,with the desiccation which followed upon the series of pluvial periods1 which in other latitudes resulted in great continental glaciers and has become known as the ,glacial ,period1 this former desert lake dried up to the limits of ,great ,salt ,lake and a few smaller isolated basins4 ,between #ahej and #ahfi the waters of ,great ,salt ,lake were rising1 while from #ahgf to #ahij their level was falling1 though subject to periodic fluctuations1 and in recent years the waters of the lake have risen so high as to pass all records since the occupation of the country4 ,as a consequence the so-called ,salt ,lake 8cut-off0 of the ,union ,pacific ,railway1 constructed at great expense across a shallow portion of the lake1 has been overflowed by its waters4 ,the ,sawa ,lake in the ,persian ,desert1 which disappeared some five hundred years ago1 again came into existence in #ahhh so as to cover the caravan route to ,teheran4 ,illustration3 ,,fig4 #bjf4--,map of the former ,lake ,bonneville 7dotted shores71 and the boundaries of the ,great ,salt ,lake of #ahfi 7smaller area7 and that of the present 7after ,berghaus74 ,the record in the rocks of the distant past reveals the fact that in some former deserts barriers were1 in the course of time1 broken down1 with the result that an invading sea entered through the breached wall4 ,the result was the sudden destruction of land life1 the remains of which are preserved in 8bone beds01 now covered by true marine deposits4 ,a still later episode of the history was begun when the sea had disappeared and land animals again roamed above the earlier desert4 ,such an alternation of marine deposits with the remains of land plants and animals in the deposits of the ,paris ,basin1 led the great ,cuvier to his belief that geologic history was comprised of a succession of cataclysms in which life was alternately destroyed and re-created in new forms--a view which later1 under the powerful influence of ,lyell and ,darwin1 gave way to that of more gradual changes and the evolution of life forms4 ,some characteristics of the desert wastes4--,the great stretches of the arid lands have been often compared to the ocean1 and the ,bedouin's camel is known as 8the ship of the desert40 ,though a deceptive resemblance for the most part1 the comparison is not without its value4 ,both are closed basins1 and it is in this respect that the desert and the ocean may be said to most resemble each other1 for none of the water and none of the sediment is lost to either except as boundaries are1 with the progress of time1 transposed or destroyed4 ,flatness of surface and monotony of scenery both have in common1 and the waters and the sand are in each case salt2 yet the ocean1 from the tropics to the poles1 has the same salts in essentially the same proportions1 while in the desert the widest variations are found both in the salts which are present and in their relative quantities4 ,upon the borders of the ocean are found ridges of yellow sand heaped up by the wind1 but these ramparts are small in comparison to those which in deserts are found upon the borders 7plate #g ,a74 ,the desert is a land of geographic paradoxes4 ,as ,walther has pointed out1 we have rain in the desert which does not wet1 springs which yield no brooks1 rivers without mouths1 forests preserved in stone1 lakes without outlets1 valleys without streams1 lake basins without lakes1 depressions below the level of the sea yet barren of water1 intense weathering with no mantle of disintegrated rock1 a decomposition of the rocks from within instead of from without1 and valleys which branch sometimes upstream and sometimes down4 ,within the deserts curious mushroom-like remnants of erosion afford a local relief from the searching rays of the desert sun4 ,pocket-like openings large enough for a hermit's habitation are hollowed out by the wind from the disintegrated rock masses4 ,amphitheaters open out from little erosion valleys or wadi1 and isolated outliers of the mountains stand like sentinels before their massive fronts4 ,because of the general absence of clouds above a desert1 no shield such as is common in humid regions is provided against the blinding intensity of the sun's rays4 ,sun temperatures as high as #ahj ,fahrenheit have been registered over the deserts of western ,africa4 ,every one is familiar with the fact that a blanket of thick clouds is a prevention of frosts at night1 for1 with the setting of the sun and the consequent radiation of heat from the earth1 these rays are intercepted by the clouds1 returned and re-returned in many successive exchanges4 ,over desert regions the absence of any such blanket of moisture is responsible for the remarkable falls of temperature at sunset4 ,though shortly before temperatures of #ajj ,fahrenheit or greater may have been measured1 it is not uncommon for water to freeze during the following night4 ,much the same conditions of sudden temperature change with nightfall are experienced in high mountains when one has ascended above the blanketing clouds4 ,illustration3 ,,fig4 #bjg4--;,borax deposits upon the floor of ,death valley1 ,california 7after a photograph by ,fairbanks74 ,dry weathering--the red and brown desert varnish4--,in desert lands the fierce rays of the sun suck up all the available moisture1 and the water table may be hundreds of feet below the surface4 ,roots of trees a hundred feet or more in length have been found to testify to the fierce struggle of the desert plant with the arid conditions4 ,in humid regions the meteoric water dissolves the more soluble sodium salts near the surface of the rock and carries them out to the ocean1 where they add to the saltness of the sea4 ,in the desert the rare precipitations prevent an outflow1 but the sun's strong rays suck out with the moisture the salts from within the rock1 and evaporating upon the surface1 the salts are left as a coat of 8alkali01 which is in part carried away on the wind and in part washed off in one of the rare cloudbursts4 ,in either case these constituents find their way to the lowest depressions of the basin1 where they contribute to the saline deposits of the desert lakes 7,fig4 #bjg74 ,illustration3 ,,fig4 #bjh4--;,hollowed forms of weathered granite in a desert of central ,asia 7after ,walther74 ,certain of the saline constituents of the rocks1 as they are thus drawn out by the sun's rays1 fuse with the rock at the surface to form a dense brown substance with smooth surface coat1 known as desert varnish4 ,within the interior a portion of the salts crystallize within the capillary fissures1 and like water freezing within a pipe1 they rend the walls apart4 ,as a direct consequence of this disintegrating process the interior of rock masses may crumble into sand2 and if the hard shell of varnish be broken at any point1 the wind makes its entrance and removes the interior portion so as to leave a hollow shell--the characteristic 8pocket rock0 7,fig4 #bjh7 of the desert4 ,the nummulitic limestone of ,mokkatan and many of the great hewn blocks of ,egyptian limestone sound hollow under the tap of the hammer1 and when broken1 they reveal a shell a few inches only in thickness 7,fig4 #bji74 ,illustration3 ,,fig4 #bji4--;,hollow hewn blocks in a wall in the ,wadi ,guerraui 7after ,walther74 ,the brown desert varnish is one of the most characteristic marks of an arid country4 ,it is found in all deserts under much the same conditions1 and is especially apt to be present in sandstone4 ,when scratched1 the surface of the rock becomes either cherry-red1 indicating anhydrous ferric oxide1 or it is yellowish1 due to the hydrated iron oxide which we know as iron rust4 ,thus it is seen that the sands of deserts1 in contrast to those yielded by other processes within humid regions1 have a characteristic red color1 and this may vary from brownish red upon the one hand to a rich carmine upon the other4 ,the mechanical breakdown of the desert rocks4--,the chemical changes of decomposition within desert rocks are1 as we have seen1 largely due to the action of concentrated solutions of salts at high temperatures4 ,that there is a certain mechanical rending of these rocks1 due to the 8freezing0 of salts within the capillary fissures1 has been already mentioned4 ,a further strain effect arises in rocks like granite1 which are a mixture of different minerals4 ,heated to a high temperature during the day and cooled through a considerable range at night1 the different minerals alternately expand and contract at different rates and by different relative amounts1 so that strains are set up1 tending to tear them apart4 ,the effect of these strains is thus a surface crumbling of rocks4 ,but rock is1 as already pointed out1 a relatively poor conductor of heat1 and hence it is a relatively thin skin only which passes through the daily round of wide temperature range4 ,this outer shell when heated is expanded1 and so tends to peel off1 or exfoliate1 like the outer skin of an onion4 ,the process is therefore described as exfoliation4 ,in all rocks of homogeneous texture the continued action of this process results in convexly spherical surfaces1 the material scaled off in the process remaining as a slope or talus which surrounds the projecting knob 7,fig4 #baj74 ,naked1 these projecting domes rise above the rim of dbris at their bases4 ,not a particle of dust adheres to the fresh rock surface--no dirt interferes with its glaring whiteness4 ,yet close at hand lie masses of dbris into which wells may be carried to depths of more than six hundred feet without encountering either solid rock or ground water4 ,the bare walls of granite sometimes mount upwards for thousands of feet into the air1 as steep and as inaccessible as the squared towers of the ,tyrolean ,dolomites4 ,illustration3 ,,fig4 #baj4--,smooth granite domes shaped by exfoliation and surrounded by a rim of talus4 ,gebel ,karsala1 ,nubian ,desert 7after ,walther74 ,rock is such a poor conductor of heat that special strains are set up at the margin of sunlight and shade4 ,this localization of the disintegration on the margin of the shaded portions of rock masses is known as shadow weathering 7see ,fig4 #bae1 p4 #bjf74 ,there is1 however1 still another mechanical disintegrating process characteristic of the desert regions1 which is likewise dependent upon the sudden changes of temperature4 ,rains1 though they may not occur for a year or more1 come as sudden downpours of great volume and violence4 ,rock masses1 which are highly heated beneath the desert sun1 if suddenly dashed with water1 may be rent apart by the differential strains set up near the surface4 ,that rocks may be easily rent as a result of sudden chilling is well known to our ,northern farmers1 who are accustomed to rid themselves of objectionable bowlders by first building a fire about them and then dashing water upon their surface4 ,thus split into fragments1 even the larger bowlders may be handled and so removed from the farming land4 ,the natural process of rock rending by the occasional cloudburst may be described as diffission4 ,blocks as much as twenty-five feet in diameter have been observed in the desert of western ,texas1 soon after being broken into several fragments at the time of a downpour of rain 7,fig4 #baa74 ,illustration3 ,,fig4 #baa4--;,granite blocks in the ,sierra de los ,dolores of ,texas1 rent into several fragments by the dash of rain 7after ,walther74 ,the natural sand blast4--,because of the saucer-like shape1 the vast expanse1 and the absence of wind breaks1 the potency of wind as a geological agent is in desert areas not easily overestimated4 ,while most of its work is accomplished with the aid of tools1 it has been proven that even without this help1 considerable work is done through the friction of the wind alone1 particularly when moving as powerful eddies in cracks and crannies4 ,this wear of the wind1 unaided by cutting tools1 is known as deflation4 ,the greater work of the wind is1 however1 accomplished with the aid of larger or smaller rock particles1 the sand and dust1 with which it is so generally charged above the deserts4 ,unprotected by any mat of vegetation the materials of the desert surface are easily lifted and are constantly migrating with the wind4 ,the finest dust is raised high into the air1 and is carried beyond the marginal barriers1 but none of the sand or coarser materials ever passes beyond the borders4 ,illustration3 ,,fig4 #bab4--8,mushroom rock0 from a desert in ,wyoming 7after ,fairbanks74 ,the efficiency of this sand as a cutting tool when carried by the wind is directly proportioned to the size of the grain1 since with larger fragments a heavier blow is struck when carried at any given velocity4 ,these more effective grains are1 however1 not lifted far above the ground1 but advance with a squirming or hopping motion1 much as do the larger pebbles upon the bottom of a river at the time of a spring freshet4 ,to quote ,professor ,walther3 8,whoever has had the opportunity to travel over a surface of dune sand when a strong wind is blowing has found it easy to convince himself of the grinding action of the wind4 ,at such times the ground becomes alive1 everywhere the sand is creeping over the surface with snake-like squirmings1 and the eye quickly tires of these writhing movements of the currents of sand and cannot long endure the scene40 ,illustration3 ,,fig4 #bac4--,windkanten shaped by the desert sand blast 7after ,chamberlin and ,salisbury74 ,a direct consequence of this restriction of the more effective cutting tools to the layer of air just above the ground1 is the strong tendency to cut away all projecting masses near their bases4 ,the 8mushroom rocks01 which are so characteristic of desert landscapes1 have been shaped in this manner 7,fig4 #bab74 ,another product of the desert sand blast is the so-called ,windkante 7wind-edge7 or ,dreikante 7three-edge71 a pebble which is usually shaped in the form of a pyramid 7,fig4 #bac74 ,whenever a rock face1 open to direct attack by the drifting sand1 is constituted of parts which have different hardness1 the blast of sand pecks away at the softer places and leaves the harder ones in relief4 ,thus is produced the well-known 8stone lattice0 of the desert 7,fig4 #bad74 ,particularly upon the neck of the great ,sphinx have the flying sand grains1 by removing the softer layers1 brought the sedimentary structures of the sandstone into strong relief4 ,illustration3 ,,fig4 #bad4--,the 8stone lattice0 of the desert1 the work of the natural sand blast 7after ,walther74 ,when guided both by planes of sedimentation and planes of jointing1 forms of a very high degree of ornamentation are developed4 ,some of the most remarkable forms are due to the protection afforded to the sun-exposed surfaces by the shell of desert varnish4 ,in the shaded portions of projecting masses there is no such protection1 and here the sand blast insinuates itself into every crack and cranny4 ,in this it is aided by shadow weathering due to the differential strains set up at the border of the expanded sun-heated surface4 ,as a result1 projecting rock masses are sometimes etched away beneath and give the effect of a squatting animal4 ,these forms1 due to shadow erosion1 have also been likened to projecting faucets4 7,fig4 #bae74 ,illustration3 ,,fig4 #bae4--,projecting rock carved by the drifting sand into the form of a couchant animal as a result of shadow weathering and erosion4 ,cut in granite on the north ,indian ,desert 7after ,walther74 ,worn by its impact upon neighboring sand grains while in transport1 but much more as it is thrown against the ground or hard rock surfaces1 the wind-driven or eolian sand is at last worn into smoothly rounded granules which approach the form of a sphere4 ,compared to the surface which sea sand acquires by attrition1 this shaping process is much the more efficient1 since in the water the beach sand is buoyed up and is more effectively cushioned against its neighboring grains4 ,the grains of beach sand when examined under a microscope are found to be much more irregular in form and usually display the original fracture surfaces only in part abraded4 ,illustration3 ,,fig4 #baf4--;,cliffs in loess #bjj feet in height which exhibit the characteristic vertical jointing 7after von ,richtofen74 ,the dust carried out of the desert4--,when1 standing upon the mountain wall that surrounds a desert1 the traveler gazes out to windward over the great depression1 his field of view is generally obscured by the yellow haze of the dust clouds moving across the margins4 ,upon the mountain flanks and extending far outside the borders1 this cloud of dust settles as a shrouding mantle of impalpable yellow powder1 which is known as loess4 ,these deposits are continually deepening1 and have sometimes accumulated until they are hundreds or even thousands of feet in thickness4 ,before reaching its final resting place the dust of this deposit may have settled many times1 and has certainly been in part redistributed by the streams near the desert margin4 ,in it are the ingredients which are necessary for the nourishment of plants1 and it constitutes the most important of natural soils4 ,continually fed by new deposits from the desert1 and refertilized from below by a natural process so soon as the upper layers become impoverished1 it requires no artificial fertilization4 ,without artificial aids the loess of northern ,china has been tilled for thousands of years without any signs of exhaustion4 ,illustration3 ,,fig4 #bag4--;,a caon in loess worn by traffic and wind4 ,a highway in northern ,china 7after von ,richtofen74 ,though easily pulverized between the fingers1 loess is none the less characterized by a perfect vertical jointing and stands on vertical faces as does the solid rock 7,fig4 #baf71 but it is absolutely devoid of layers or bedding4 ,its capacity of standing in vertical cliffs the loess owes to a never failing content of lime carbonate which acts as a cement1 and to a peculiar porous structure caused by capillary canals that run vertically through the mass1 branching like rootlets and lined with carbonate of lime4 ,this texture once destroyed1 loess resolves itself into a common sticky clay4 ,by the feet of passing animals or by wheels of vehicles1 the loess is crushed1 and a portion is lifted and carried away by the wind4 ,thus in the course of time roadways sink deep into the mass as steep-walled caons 7,fig4 #bag74 ,a portion of the now structureless clay remaining upon the roadway is at the time of the rains transformed into a thick mud which makes traveling all but impossible1 though before its structure has been destroyed the loess is perfectly drained to the bottom of its deposits4 ,the particles which compose the loess are sharply angular quartz fragments1 so fine that all but a few grains can be rubbed into the pores of the skin4 ,fine scales of mica1 such as are easily lifted by the wind1 are disseminated uniformly throughout the mass4 ,the only inclosures which are arranged in layers consist of irregularly shaped concretions of clay4 ,these show a striking resemblance to ginger roots and are called by the ,chinese 8stone ginger01 though they are elsewhere more generally known by their ,german name of ,loessmnnchen1 or loess dolls4 ,these concretions are so disposed in the loess that their longer axes are vertical1 and they were evidently separated from the mass and not deposited with it4 ,,chapter ,,xvi ,,the ,,features ,,in ,,desert ,,landscapes ,illustration3 ,,fig4 #bah4--;,diagrams to illustrate the effects of obstructions of different types in arresting wind-driven sand4 a1 ,an unyielding obstruction which permits the wind to pass through it2 b1 a flexible and perforated obstruction2 c1 an unyielding closed barrier 7after ,schulze74 ,the wandering dunes4--,over the broad expanse of the desert1 sand and dust1 and occasionally gypsum from the saline deposits1 are ever migrating with the wind2 on quiet days in the eddying 8sand devils01 but especially during the terrifying sand storms such as in the windy season darken the air of northern ,china and southern ,manchuria4 ,this drift of the sand is halted only when an obstruction is encountered--a projecting rock1 a bush1 or a bunch of grass1 or again the buildings of a city or a town4 ,the manner in which the sand is arrested by obstacles of different kinds is of great interest and importance1 and is utilized in raising defenses against its encroachments4 ,if the obstacle is unyielding but allows some of the wind to pass through it1 no eddies are produced and the sand is deposited both to windward and to leeward of the obstruction to form a fairly symmetrical mound 7,fig4 #bah a74 ,an obstruction which yields to the wind causes the sand to deposit in a mound which is largely to leeward of the obstruction 7,fig4 #bah b74 ,a solid wall1 on the other hand1 by inducing eddies1 is at first protected from the sand and mounds deposit both to windward and to leeward 7,fig4 #bah c and ,fig4 #bai74 ,except when held up by an obstruction1 the drifting sand travels to leeward in slowly migrating mounds or ridges which are known as dunes4 ,their motion is due to the wind lifting the sand from the windward side and carrying it over the crest1 from where it slides down the leeward slope and assumes a surface which is the angle of repose of the material4 ,in contrast with this the windward slope is notably gradual1 being shaped in conformity to the wind currents4 ,illustration3 ,,fig4 #bai4--,sand accumulating both to windward and to leeward of a firm and impenetrable obstruction4 ,the wind comes from the left 7after a photograph by ,bastin74 ,the dunes which are raised upon seashores1 like those of the desert1 are constantly migrating1 those upon the shores of the ,north ,sea at the average rate of about twenty feet per year4 ,relentlessly they advance1 and despite all attempts to halt them1 have many times overwhelmed the villages along the coast4 ,upon the great barrier beach known as the ,kurische ,nehrung1 on the southeastern shore of the ,baltic ,sea1 such a burial of villages has more than once occurred1 but as in the course of time further migration of the dune has proceeded1 the ruins of the buried villages have been exhumed by this natural excavating process 7,fig4 #bbj74 ,illustration3 ,,fig4 #bbj4--,successive diagrams to show how the town of ,kunzen was buried1 and subsequently exhumed in the continued migration of a great dune upon the ,kurische ,nehrung 7after ,behrendt74 ,,plate #g4 ,illustration3 ,a4 ,ranges of dunes upon the margin of the ,colorado ,desert 7after ,mendenhall74 ,illustration3 ,b4 ,sand dunes encroaching upon the oasis of ,wed ,souf4 ,algeria 7after ,t4 ,h4 ,kearney74 ,the forms of dunes4--,the forms assumed by dunes are dependent to a very large extent upon the strength of the wind and the available supply of sand4 ,with small quantities of sand and with moderate winds1 sickle-shaped dunes known as barchans 7,fig4 #bba7 are formed1 whose convex and flatter slopes are toward the wind and whose steep concave leeward slopes are maintained at the angle of repose4 ,the barchan is shaped by the wind going both over and around the dune1 constantly removing sand from the windward side and depositing it to leeward4 ,with larger supplies of sand and winds which are not too violent a series of barchans is built up1 and these are arranged transversely to the wind direction 7,fig4 #bbb b74 ,if the winds are more violent1 the minor depressions in the crests of the dunes become wind channels1 and the sand is then trailed out along them until the arrangement of the ridges is parallel to the wind 7,fig4 #bbb c74 ,the surfaces of dunes are generally marked by beautiful ripples in the sand1 which1 seen from a little distance1 may give the appearance of watered silk 7plate #g ,a74 ,illustration3 ,,fig4 #bba4--,view of desert barchans 7after ,haug74 ,illustration3 ,,fig4 #bbb4--;,diagrams to show the relationships in form and in orientation of dunes to the supply of sand and to the strength of the wind4 a1 barchans formed by small supplies of sand and moderate winds2 b1 transverse dune ridges1 formed when supply of sand is large and winds are moderate2 c1 dune ridges formed with large sand supply and violent winds 7after ,walther and ,cornish74 ,under normal conditions dunes are not stationary but continue to wander with the prevailing winds until they have reached the outer edge of the zone of vegetation near the base of the foothills at the margin of the desert4 ,here the grasses and other desert plants arrest the first sand grains that reach them1 and they continue to grow higher as the sands accumulate4 ,some of the desert plants1 like the yuccas1 have so adapted themselves to desert conditions that they may grow upward with the sand for many feet and so keep their crowns above its surface4 ,the cloudburst in the desert4--,such clouds as enter the desert through its mountain ramparts1 and those derived from evaporation from the hot desert soil1 usually precipitate their moisture before passing out of the basin4 ,above the highly heated floor the heavy rain clouds are unable to drop their burden4 ,the rain can sometimes be seen descending1 but long before it has reached the ground it has again passed into vapor1 and through repetition of this process the clouds become so charged with moisture that when they encounter a mountain wall and are thus forced to rise1 there is a sudden downpour not equaled in the humid regions4 ,desert rains are rare1 but violent beyond comparison4 ,often for a year or more there is no rainfall upon the loose sand or porous clay1 and the few plants which survive must push their roots deep down until they have reached the zone of ground water4 ,when the clouds burst1 each small caon or wed 7pl4 wadi7 within the mountain wall is quickly occupied by a swollen current which carries a thick paste of sediment and drowns everything before it4 ,ere it has flowed a mile1 it may be that the water has disappeared entirely1 leaving a layer of mud and sand which rapidly dries out with the reappearance of the sun4 ,illustration3 ,,fig4 #bbc4--;,ideal section across the rising mountain wall surrounding a desert and a part of the neighboring slope 7after ,r4 ,w4 ,pumpelly74 ,as the mountains upon seacoasts are generally rising with reference to the neighboring sea bottom1 so the mountains which hem in the deserts are generally growing upward with reference to the inclosed desert floor4 ,the marginal dislocations which separate the two are often in evidence at the foot of the steep slope 7,fig4 #bbc71 and these may even appear as visible earthquake faults to indicate that the uplift is more accelerated than the deposition along the mountain front4 ,illustration3 ,,fig4 #bbd4--;,dry delta or alluvial fan at the foot of a mountain range upon the borders of a desert4 ,the zone of the dwindling river4--,the rapid uplift so generally characteristic of desert margins gives to the torrential streams which develop after each cloudburst such an unusual velocity that when they emerge from the mountain valleys on to the desert floor1 the current is suddenly checked and the burden of sediment in large part deposited at the mouth of the valley so as to form a coarse delta deposit which is described as a dry delta 7,fig4 #bbd74 ,dependent upon its steepness of slope1 this delta is variously referred to as an alluvial fan or apron1 or as an alluvial cone4 ,over the conical slopes of the delta surface the stream is broken up into numerous distributaries which divide and subdivide as do the roots of a tree4 ,in the ,mohammedan countries described as wadi1 these distributaries upon dry deltas are on the ,pacific coast of the ,united ,states referred to as 8washes0 7,fig4 #bbe74 ,illustration3 ,,fig4 #bbe4--,map of the distributaries of neighboring streams which emerge at the western base of the ,sierra ,nevadas in ,california 7after ,w4 ,d4 ,johnson74 ,fast losing their velocity after emerging from the mountains1 the various distributaries drop first of all the heavy bowlders1 then the large pebbles and the sand1 so that only the finer sand and the silt are carried to the margin of the delta4 ,as they enlarge their boundaries1 the neighboring deltas eventually coalesce and so form an alluvial bench or 8gravel piedmont0 at the foot of the range4 ,only the larger streams are able to entirely cross this bench of parched deposits with its coarsely porous structure1 for the water is soon sucked up by the thirsty materials4 ,encountering in its descent more clayey layers1 this water is conducted to the surface near the margin of the bench and may there appear as a line of springs4 ,at this level there develops1 therefore1 a zone of vegetation1 though there is no local rain4 ,the alluvial bench grows upward by accretion of layers which are thickest at the mountain end1 so that the steepness of the bench increases with time4 ,erosion in and about the desert4--,the violent cloudburst that is characteristic of the arid lands is a most potent agent in modeling the surface of the ground wherever the rock materials are not too firmly coherent4 ,under the dash of the rain a peculiar type of 8bad land0 topography is developed 7plate #e ,b and ,fig4 #bbf74 ,such a rain-cut surface is a veritable maze of alternating gully and ridge1 a country worthless for agricultural purposes and offering the greatest difficulty in the way of penetrating it4 ,when composed of stiff clay with scattered pebbles and bowlders1 the effect of the 8rain erosion0 is to fashion steep clay pillars each capped by a pebble and described as 8demoiselles0 7,fig4 #bbf74 ,illustration3 ,,fig4 #bbf4--;,a group of 8demoiselles0 in the 8bad lands0 7after a photograph by ,fairbanks74 ,behind the mountain front the valleys out of which the torrents are discharged are usually short with steep side walls and a relatively flat bottom1 ending headward in an amphitheater with precipitous walls 7,fig4 #bbg74 ,in the western ,united ,states such valleys are referred to as 8box caons01 but in ,mohammedan countries the name 8wed0 applies to the river valley within the mountains and to the distributaries as well4 ,characteristic features of the arid lands4--,it is characteristic of erosion and deposition within humid regions that all outlines become softened into flowing curves1 due to the protective mat of vegetation4 ,in arid lands those massive rocks which are without structural planes of separation1 partly as a consequence of exfoliation1 develop broad domes which are projected upon the horizon as great semicircles1 broken in half it may be by displacement4 ,the same massive rocks where intersected by vertical joint planes yield1 on the contrary1 sharp granite needles like those of ,harney ,peak 7plate #h ,a74 ,similarly1 schistose or bedded rocks1 when tilted at a high angle1 may yield forms which are almost identical4 ,examples of such needles are found in the ,garden of the ,gods in ,colorado4 ,at lower levels1 where the flying sand becomes effective as an eroding agent1 flat bedded rocks become etched into shelves and cornices1 and if intersected by joints1 the shelves and cornices are transformed into groups of castellated towers and pinnacles of a high degree of ornamentation4 ,these fantastic erosion remnants are usually referred to as 8chimneys0 and may be seen in numbers in the bad lands of ,dakota1 as they may in ,colorado either in ,monument ,park or in the new ,monolithic ,national ,park 7plate #h ,b74 ,illustration3 ,,fig4 #bbg4--;,amphitheater at the head of the ,wed ,beni ,sur 7after ,walther74 ,where wind erosion plays a smaller rle in the sculpture1 but where after an uplift a river has made its way1 horizontally bedded rocks are apt to be carved into broad rock terraces1 nowhere shown upon so grand a scale as about the ,grand ,caon of the ,colorado4 ,each harder layer has here produced a floor or terrace which ends in a vertical escarpment1 and this is separated from the next lower layer of more resistant rock by a slope of talus which largely hides the softer intermediate beds4 ,the great ,desert of ,sahara is shaped in a series of rock terraces or steppes which descend toward the interior of the basin4 ,a single harder layer of resistant rock comes often to form the flat capping of a plateau1 and is then known as a mesa1 or table mountain4 ,along its front1 detached outliers usually stand like sentinels before the larger mass1 and according to their relative proportions1 these are referred to either as small mesas or as the smaller buttes 7,fig4 #bbh74 ,illustration3 ,,fig4 #bbh4--,mesa and outlying butte in the ,leucite ,hills of ,wyoming 7after ,whitman ,cross1 ,u4 ,s4 ,g4 ,s474 ,the war of dune and oasis4--,in every desert the deposits are arranged in consecutive belts or zones which are alternately the work of wind and water4 ,surrounding the desert and upon the flanks of the mountain wall there is found 7#a7 the deposit of loess derived from the dust that is carried out of the desert by the wind4 ,immediately within the desert border at the base of the mountains is 7#b7 the zone of the dwindling river with its sloping bench of coarse rubble and gravel4 ,illustration3 ,,fig4 #bbi4--;,flat-bottomed basin separating dunes--bajir or takyr 7after ,ellsworth ,huntington74 ,next in order is 7#c7 the belt of the flying sand1 a zone of dune ridges often separated by narrow1 flat-bottomed basins 7,fig4 #bbi7 into which the strongest streams bring the finer sands and silt from the mountains4 ,lastly1 there is 7#d7 the central sink or sinks1 into which all water not at once absorbed within the zone of alluviation or in the zone of dunes is finally collected4 ,here are the true lacustrine deposits of clay and separated salts 7,fig4 #bcj and ,fig4 #bjg1 p4 #bja74 ,the lake deposits fill in all the original irregularities of the desert floor1 out of which the tops of isolated ranges of mountains now project like islands out of the surface of the sea4 ,the several zones of deposits in their order from the margin to the center of the desert are given schematically in ,fig4 #bca4 ,,plate #h4 ,illustration3 ,a4 ,the granite needles of ,harney ,peak in the ,black ,hills of ,south ,dakota 7after ,darton74 ,illustration3 ,b4 ,castellated erosion chimneys in ,el ,cobra ,caon1 ,new ,mexico4 7,photograph by ,e4 ,c4 ,case47 ,illustration3 ,,fig4 #bcj4--;,billowy surface of the salt crust on the central sink in the ,lop ,desert of central ,asia 7after ,ellsworth ,huntington74 ,the zone of vegetation1 as already stated1 lies near the foot of the alluvial bench1 so that here are found the oases about which have clustered the cities of the desert from the earliest records of antiquity until now4 ,just without the line of oases is the wall of dunes held back from further advance only by the vegetation which in turn is dependent upon the rains in the neighboring mountains4 ,with every diminution in the water supply1 the dunes advance and encroach upon the oases 7plate #g ,b72 while with every considerable increase in this supply of moisture the alluvial bench advances over the dunes and acquires a strip of their territory4 ,thus with varying fortunes a war is continually waged between the withering river and the flying sand1 and the alternations of climate are later recorded in the dovetailing together of the eolian and alluvial deposits at their common junction 7,fig4 #bca74 ,illustration3 ,,fig4 #bca4--,schematic diagram to show the zones of deposition in their order from the margin to the center of a desert4 ,illustration3 ,,fig4 #bcb4--,mounds upon the site of the buried city of ,nippur 7after the cast by ,muret74 ,in addition to the smaller periodic alternations of pluvial and interpluvial climate--the 8pulse of ,asia0--the record of the ,asiatic deserts indicates a progressive desiccation of the entire region1 which has now given the victory to the dune4 ,the ancient history of the cities of the plains supplies the records of many that have been buried in the dunes4 ,to-day1 where once were prosperous cities1 nothing is to be seen at the surface but a group of mounds 7,fig4 #bcb74 ,exhumed after much painstaking labor1 the walls and palaces of these ancient cities have once more been brought to the light of day1 and much has thus been learned of the civilization of these early times 7,fig4 #bcc74 ,quite recently the mounds which cover between one and two hundred buried villages have been found upon the borders of the ,tarim basin of central ,asia1 where they were lost to history when they were overwhelmed in the early centuries of the ,christian ,era4 ,illustration3 ,,fig4 #bcc4--;,exhumed structures in the buried city of ,nippur 7after ,hilprecht74 ,the origin of the high plains which front the ,rocky ,mountains4--,to the eastward of the great backbone of the ,north ,american continent stretches a vast plain gently inclined away from the range and generally known as the ,high ,plains region 7plate #i74 ,the tourist who travels westward by train ascends this slope so gradually that when he has reached the mountain front it is difficult to realize that he has climbed to an altitude of five thousand feet above the level of the sea4 ,that he has also passed through several climatic zones--a humid1 a semiarid1 and an arid--and has now entered a semiarid district1 is more easily appreciated from study of the vegetation 7,fig4 #bcd74 ,the surface of the ,high ,plains1 where not cut into by rivers1 is remarkably even1 so that it might be compared to the quiet surface of a great lake4 ,illustration3 ,,fig4 #bcd4--,section across the ,high ,plains1 showing the position of the terrace and the climatic zones above it 7after ,w4 ,d4 ,johnson74 ,the materials which compose the surface veneer of these plains are coarse conglomerates1 gravels1 and sands1 and the so-called 8mortar beds01 which are nothing but sands cemented into sandstone by carbonate of lime4 ,the pebbles in all these deposits are far-traveled and appear to have been derived from erosion of those crystalline rocks which compose the eastern front of the ,rocky ,mountains4 ,these different materials are not arranged in strictly parallel beds1 as are the deposits of a lake or sea2 but the beds are made up of long threads of lenticular cross section which are interlaced in the most intricate fashion and which extend down the slope1 or outward from the mountain front 7,fig4 #bce74 ,it is thus shown that the ,high ,plains are a bench or plain of alluviation formed at the front of the ,rocky ,mountains during an earlier series of pluvial periods1 and that subsequent uplift has produced the modern river valleys which are cut out of the plain4 ,the plexus of long threads of the coarser materials are the courses of dwindling rivers which interlaced over the former plain1 and which in time were buried under other channel deposits of the same nature but in different positions 7,fig4 #bcf74 ,the pluvial periods in which this bench was formed produced in other latitudes the great continental glaciers which wrought such marvelous changes in northern ,north ,america and in northern ,europe4 ,illustration3 ,,fig4 #bce4--,section across the great lenticular threads of alluvial deposits which compose the veneer of the ,high ,plains 7after ,w4 ,d4 ,johnson74 ,illustration3 ,,fig4 #bcf4--;,distributaries of the foothills superimposed upon an earlier series 7after ,w4 ,d4 ,johnson74 ,character profiles4--,in contrast with the profiles in the landscapes of humid regions 7see ,fig4 #ahg1 p4 #agg71 those of arid lands are marked by straighter elements 7,fig4 #bcg74 ,almost the only exception of importance is furnished by the domes of massive granite monoliths1 which are sometimes broken in half by great displacements4 ,below the horizon the secondary lines in the landscape betray the same straightness of the component elements by the gabled slopes of talus which are many times repeated so as almost to reproduce the lines in a house of cards1 since the sloping lines are maintained at the angle of repose of the materials 7,fig4 #dhb1 p4 #ddc74 ,wherever the waves of desert lakes have made an attack upon the rocks and have retired the projecting spurs1 other gables characterized by slightly different slopes are introduced into the landscape4 ,illustration3 ,,fig4 #bcg4--;,character profiles in the landscapes of arid lands4 ,,plate #i4 ,illustration3 ,,the ,,high ,,plains ,,reading ,,references ,,for ,,chapters ,,xv ,,and ,,xvi ,general3-- ,,johannes ,,walther4 ,das ,gesetz der ,wstenbildung in ,gegenwart und ,vorzeit4 ,berlin1 #aijj1 pp4 #age1 many plates4 7,this extremely valuable work is now out of print1 but both a revised edition and an ,english translation are promised for #aiab47 ,,siegfried ,,passarge4 ,die ,kalihari4 ,berlin1 #aijd1 pp4 #ffb4 ,w4 ,m4 ,,davis4 ,the ,geographic ,cycle in an ,arid ,climate1 ,jour4 ,geol41 vol4 #ac1 #aije1 pp4 #cha-djg4 ,,ellsworth ,,huntington4 ,the ,pulse of ,asia4 ,new ,york and ,boston1 #aijg1 pp4 #dae4 ,,sven ,,hedin4 ,scientific ,results of a ,journey through ,central ,asia1 #ahii-aijj4 ,stockholm1 #aijd-aije1 vols4 #a and #b1 pp4 #ebc and #gag1 pls4 #ef and #gf4 ,,joseph ,,barrell4 ,relative ,geological ,importance of ,continental1 ,littoral and ,marine ,sedimentation1 ,jour4 ,geol41 vol4 #ad1 #aijf1 pp4 #caf-cef1 #dbi-deg1 #ebd-efh4 ,e4 ,f4 ,,gautier4 tudes sahariennes1 ,ann4 de ,gogr41 vol4 #af1 #aijg1 pp4 #df-fi1 #aag-ach4 ,the self-registering gauge of past climates3-- ,g4 ,k4 ,,gilbert4 ,lake ,bonneville1 ,mon4 ,i1 ,u4 ,s4 ,geol4 ,surv41 ,chapter vi1 pp4 #bad-cah4 ,t4 ,f4 ,,jamieson4 ,the ,inland ,seas and ,salt ,lakes of the ,glacial ,period1 ,geol4 ,mag4 decade ,,iii1 vol4 #b1 #ahhe1 pp4 #aic-bjj4 ,j4 ,e4 ,,talmage4 ,the ,great ,salt ,lake1 ,present and ,past4 ,salt ,lake ,city1 #aijj1 pp4 #aaf1 plates4 ,e4 ,,huntington4 ,some ,characteristics of the ,glacial ,period in ,non-glaciated ,regions1 ,bull4 ,geol4 ,soc4 ,am41 vol4 #ah1 #aijg1 pp4 #cea-chh1 pls4 #ca-ci4 ,t4 ,c4 ,,chamberlin4 ,the ,future ,habitability of the ,earth1 ,rept4 ,smithson4 ,inst41 #aiaj1 pp4 #cga-chi4 ,the red and brown desert varnish3-- ,i4 ,c4 ,,russell4 ,subarial ,decay of ,rocks and ,origin of the ,red ,color of ,certain ,formations4 ,bull4 #eb1 ,u4 ,s4 ,geol4 ,surv41 #ahhi1 pp4 #fe1 pls4 #e4 ,erosion in the desert3-- ,j4 ,a4 ,,udden4 ,erosion1 ,transportation1 and ,sedimentation performed by the ,atmosphere1 ,jour4 ,geol41 vol4 #b1 #ahid1 pp4 #cah-cca4 ,s4 ,,passarge4 ,die pfannenfrmigen ,hohlformen der sdafrikanischen ,steppen1 ,pet4 ,mitt41 vol4 #eg1 #aiaa1 pp4 #eg-fa1 #acj-ace4 ,the dust carried out of the desert3-- ,f4 ,,von ,,richtofen4 ,china1 ,ergebnisse eigene ,reisen und darauf gegrndeten ,studien1 ,berlin1 #ahgg1 vol4 #a1 pp4 #ef-abe4 ,e4 ,,hilgard4 ,the ,loess of the ,mississippi ,valley1 ,am4 ,jour4 ,sci41 7#c71 vol4 #ah1 #ahgi1 pp4 #ajf-aab4 ,t4 ,c4 ,,chamberlin and ,r4 ,d4 ,,salisbury4 ,preliminary ,paper on the ,driftless ,area of the ,upper ,mississippi ,valley1 #fth ,ann4 ,rept4 ,u4 ,s4 ,geol4 ,surv41 #ahhe1 pp4 #bgh-cjg4 ,e4 ,e4 ,,free4 ,the movement of soil material by the wind1 with a bibliography of eolian geology by ,s4 ,c4 ,stuntz and ,e4 ,e4 ,free1 ,bull4 #fh1 ,u4 ,s4 ,bureau of ,soils1 #aiaa1 pp4 #bgb1 pls4 #e4 ,m4 ,,neumayr4 ,erdgeschichte1 vol4 #a1 pp4 #eaj-ead4 ,e4 ,,de ,,martonne4 ,gographie physique1 pp4 #ffc-ffh4 ,dunes3-- ,,vaughan ,,cornish4 ,on the ,formation of ,sand-dunes1 ,geogr4 ,jour41 vol4 #i1 #ahig1 pp4 #bgh-cji 7a most important paper74 ,f4 ,,solger and ,others4 ,dnenbuch4 ,enke1 ,stuttgart1 #aiaj1 pp4 #cgc4 ,the zone of the dwindling river3-- ,e4 ,,huntington4 ,the ,border ,belts of the ,tarim ,basin1 ,bull4 ,am4 ,geogr4 ,soc41 vol4 #ch1 #aijf1 pp4 #ia-if2 ,the ,pulse of ,asia1 pp4 #baj-bbb1 #bfb-bgi4 ,the war of dune and oasis3-- ,r4 ,,pumpelly4 ,explorations in ,turkestan1 ,expedition of #aijd1 etc41 ,pub4 #gc1 ,carneg4 ,inst41 ,washington1 vol4 #a1 pp4 #a-ac4 ,e4 ,,huntington4 ,the ,oasis of ,kharga1 ,bull4 ,am4 ,geogr4 ,soc41 vol4 #db4 #aiaj1 pp4 #fda-ffa4 ,,th4 ,h4 ,,kearney4 ,the ,country of the ,ant ,men1 ,nat4 ,geogr4 ,mag41 vol4 #bb1 #aiaa1 pp4 #cfg-chb4 ,features of the arid lands3-- ,c4 ,e4 ,,dutton4 ,tertiary ,history of the ,grand ,caon ,district1 with ,atlas1 ,mon4 ,,ii1 ,u4 ,s4 ,geol4 ,surv41 #ahhb1 pp4 #bfd1 pls4 #db1 maps #bc4 ,g4 ,,sweinfurth4 ,map ,sheets of the ,eastern ,egyptian ,desert4 ,berlin1 #aija-aijb1 #h sheets4 ,the origin of the high plains3-- ,w4 ,d4 ,,johnson4 ,the ,high ,plains and their ,utilization1 #bast ,ann4 ,rept4 ,u4 ,s4 ,geol4 ,surv41 ,pt4 iv1 #aija1 pp4 #fja-gda4 ,,chapter ,,xvii ,,repeating ,,patterns ,,in ,,the ,,earth ,,relief ,the weathering processes under control of the fracture system4--,in an earlier chapter it was learned that the rocks which compose the earth's surface shell are intersected by a system of joint fractures which in little-disturbed areas divide the surface beds into nearly square perpendicular prisms 7,fig4 #cf1 p4 #ee71 more or less modified by additional diagonal joints1 and often also by more disorderly fractures4 ,throughout large areas these fractures may maintain nearly constant directions1 though either one or more of the master series may be locally absent4 ,this distinctive architecture of the surface shell of the lithosphere has exercised its influence upon the various weathering processes1 as it has also upon the activities of running water and of other less common transporting agencies at the surface4 ,within high latitudes1 where frost action is the dominant weathering process1 the water1 by insinuating itself along the joints and through repeated freezings1 has broken down the rock in the immediate neighborhood of these fractures1 and so has impressed upon the surface an image of the underlying pattern of structure lines 7plate #aj ,a74 ,in much lower latitudes and in regions of insufficient rainfall1 the same structures are impressed upon the relief1 but by other weathering processes4 ,in the case of the less coherent deposits in these provinces1 the initial forms of their erosional surface have sometimes been determined by the dash of rain from the sudden cloudburst4 ,thus the 8bad lands0 may have their initial gullies directed and spaced in conformity with the underlying joint structures 7,fig4 #bch74 ,illustration3 ,,fig4 #bch4--,rain sculpturing under control by joints4 ,coast of southern ,california 7after a photograph by ,fairbanks74 ,in such portions of the temperate regions as are favored by a humid climate1 the mat of vegetation holds down a layer of soil1 and mat and soil in coperation are effective in preventing any such large measure of frostwork as is characteristic of the subpolar regions or of high levels in the arid lands4 ,in humid regions the rocks become a prey especially to the processes of solution and accompanying chemical decomposition1 and these processes1 although guided by the course of the percolating ground water along the fracture planes1 do not afford such striking examples of the control of surface relief4 ,those limestones which slowly pass into solution in the percolating water do1 however1 quite generally indicate a localization of the solution along the joint channels 7,fig4 #bci and plate #f ,b74 ,though in other rocks not so apparent1 yet solutions generally take their courses along the same channels1 and upon them is localized the development of the newly formed hydrated and carbonate minerals1 as is well illustrated by the phenomenon of spheroidal weathering 7,fig4 #aee1 p4 #aej74 ,illustration3 ,,fig4 #bci4--,outcrop of flaggy limestone which shows the effects of solution along neighboring joints in a sagging of the upper beds 7after ,gilbert1 ,u4 ,s4 ,g4 ,s474 ,the fracture control of the drainage lines4--,the etching out of the earth's architectural plan in the surface relief1 which we have seen begun in the processes of weathering1 is continued after the transporting agents have become effective4 ,it is often easy to see that a river has taken its course in rectangular zigzags like the elbows of a jointed stove pipe1 and that its walls are formed of joint planes from which an occasional squared buttress projects into the channel4 ,this structure is rendered in the plan of the ,abisko ,caon of northern ,lapland 7,fig4 #bdj74 ,we are later to learn that another great transporting agent1 the water wave1 makes a selective attack upon the lithosphere along the fractures of the joint system 7,fig4 #bej1 p4 #bcc and ,fig4 #bed1 p4 #bce74 ,illustration3 ,,fig4 #bdj4--,map of the joint-controlled ,abisko ,caon in northern ,lapland 7after ,otto ,sjgren74 ,where the scale of the example is large1 as in the cases which have been above cited1 the actual position and directions of the joint wall are easily compared with the near-by elements of the river's course1 so that the connection of the drainage lines with the underlying structure is at once apparent4 ,in many examples where the scale is small1 the evidence for the controlling influence of the rock structure in determining the courses of streams may be found in the peculiar character of the drainage plan4 ,to illustrate3 the course of the ,zambesi ,river1 within the gorge below the famous ,victoria ,falls1 not only makes repeated turnings at a right angle1 but its tributary streams1 instead of making the usual sharp angle where they join the main stream1 also affect the right angle in their junctions 7,fig4 #bda74 ,illustration3 ,,fig4 #bda4--,map of the gorge of the ,zambesi ,river below the ,victoria ,falls 7after ,lamplugh74 ,the repeating pattern in drainage networks4--,it is a characteristic of the joint system that the fractures within each series are spaced with approximation to uniformity4 ,if the plan of a drainage system has been regulated in conformity with the architecture of the underlying rock basement1 the same repeating rectangles of the master joints may be expected to appear in the lines of drainage--the so-called drainage network4 ,such rectangular patterns do very generally appear in the drainage network1 though they are often masked upon modern maps by what1 to the geologist1 seems impertinent intrusion of the black lines of overprinting which indicate railways1 lines of highway1 and other culture elements4 ,on river maps1 which are printed without culture1 the pattern is much more easily recognized 7,figs4 #bdb and #bdc74 ,wherever the relief is strong1 as is the case in the ,adirondack ,mountain province of the ,state of ,new ,york1 individual hills may stand in relief between the bounding streams which compose the rectangular network1 like the squared pedestals of monuments4 ,such a type of relief carved in repeating patterns has been described as 8checkerboard topography40 ,illustration3 ,,fig4 #bdb4--;,controlled drainage network of the ,shepaug ,river in ,connecticut4 ,illustration3 ,,fig4 #bdc4--;,a river network of repeating rectangular pattern4 ,near ,lake ,temiskaming1 ,ontario 7from the map by the ,dominion ,government74 ,the dividing lines of the relief patterns--lineaments4--,the repeating design outlined in the river network of the ,temiskaming district 7,fig4 #bdc7 would appear in greater perfection if we could reproduce the relief without at the same time obscuring the lines of drainage2 for where the pattern is not completely closed by the course of the stream1 there is generally found either a dry valley or a ravine to complete the design4 ,if these are not present1 a bit of straight coast line1 a visible line of fracture1 a zone of fault breccia1 or the boundary line separating different formations may one or more of them fill in the gaps of the parallel straight drainage lines which by their intersection bring out the pattern4 ,these significant lines of landscapes which reveal the hidden architecture of the rock basement are described as lineaments 7,fig4 #hb1 p4 #hg74 ,they are the character lines of the earth's physiognomy4 ,it is important to emphasize the essentially composite expression of the lineament4 ,at one locality it appears as a drainage line1 a little farther on it may be a line of coast2 then1 again1 it is a series of aligned waterfalls1 a visible fault trace1 or a rectilinear boundary between formations2 but in every case it is some surface expression of a buried fracture4 ,hidden as they so generally are1 the fracture lines must be searched out by every means at our disposal1 if we are not to be misled in accounting for the positions and the attitudes of disturbed rock masses4 ,as we have learned1 during earthquake shocks1 as at no other time1 the surface of the earth is so sensitized as to betray the position of its buried fractures4 ,as the boundaries of orographic blocks1 certain of the fractures are at such times the seats of especially heavy vibrations2 they are the seismotectonic lines of the earthquake province4 ,many lineaments are identical with seismotectonic lines1 and they therefore afford a means of to some extent determining in advance the lines of greatest danger from earthquake shock4 ,the composite repeating patterns of the higher orders4--,not only do the larger joint blocks become impressed upon the earth relief as repeating diaper patterns1 but larger and still larger composite units of the same type may1 in favorable districts1 be found to present the same characters4 ,attention has already been more than once directed to the fact that the more perfect and prominent fracture planes recur among the joints of any series at more or less regular intervals 7,fig4 #dj1 p4 #eg1 and ,fig4 #da1 p4 #eh74 ,nowhere1 perhaps1 is this larger order of the repeating pattern more perfectly exemplified than in some recent deposits in the ,syrian desert 7plate #aj ,b74 ,it is usually1 however1 in the older sediments that such structures may be recognized2 as1 for example1 in the squared towers and buttresses of the ,tyrolean ,dolomites 7,fig4 #bdd74 ,here the larger blocks appear in the thick bedded lower formation1 the dolomite1 divided into subordinate sections of large dimensions2 but in the overlying formations in blocks of relatively small size1 yet with similarly perfect subequal spacing4 ,illustration3 ,,fig4 #bdd4--,squared mountain masses which reveal a distribution of the joints in block patterns of different orders of magnitude4 ,the ,pordoi range of the ,sella group of the ,dolomites1 seen from the ,cima di ,rossi 7after ,mojsisovics74 ,the observing traveler who is privileged to make the journey by steamer1 threading its course in and out among the many islands and skerries of the ,norwegian coast1 will hardly fail to be struck by the remarkable profiles of most of the lower islands 7,fig4 #bde74 ,these profiles are generally convexly scalloped with a noteworthy regularity1 and not in one unit only1 but in at least two with one a multiple of the other 7,fig4 #bdf74 ,as the steamer passes near to the islands1 it is discovered that the smaller recognizable units in the island profiles are separated by widely gaping joints which do not1 however1 belong to the unit series1 but to a larger composite group 7,fig4 #bdf b74 ,frostwork1 which depends for its action upon open spaces within the rocks1 has here been the cause of the excessive weathering above the more widely gaping joints4 ,,plate #aj4 ,illustration3 ,a4 ,view in ,spitzbergen to illustrate the disintegration of rock under the control of joints4 7,photograph by ,o4 ,haldin47 ,illustration3 ,b4 ,composite pattern of the joint structures within recent alluvial deposits4 7,photograph by ,ellsworth ,huntington47 ,illustration3 ,,fig4 #bde4--;,island groups of the ,lofoten archipelago off the northwest coast of ,norway1 which reveal repeating patterns of the relief in two orders of magnitude 7after a photograph by ,knudsen74 ,illustration3 ,,fig4 #bdf4--;,diagrams to illustrate the composite profiles of the islands on the ,norwegian coast4 a1 distant view2 b1 near view1 showing the individual joints and the more widely gaping fractures beneath each sag in the profile4 ,high northern latitudes are thus especially favorable for revealing all the details in the architectural pattern of the lithosphere shell1 and we need not be surprised that when the modern maps of the ,norwegian coast are examined1 still larger repeating patterns than any that may be seen in the field are to be made out4 ,the ,norwegian coast was long ago shown to be a complexly faulted region1 and these larger divisions of the relief pattern1 instead of being explained as a consequence solely of selective weathering1 must be regarded as due largely to fault displacements of the type represented in our model 7plate #d ,c74 ,yet whether due to displacements or to the more numerous joints1 all belong to the same composite system of fractures expressed in the relief4 ,,reading ,,references ,,for ,,chapter ,,xvii ,,william ,h4 ,,hobbs4 ,the ,river ,system of ,connecticut1 ,jour4 ,geol41 vol4 #i1 #aija1 pp4 #dfi-dhe1 pl4 #a2 ,lineaments of the ,atlantic ,border ,region1 ,bull4 ,geol4 ,soc4 ,am41 vol4 #ae1 #aijd1 pp4 #dhc-ejf1 pls4 #de-dg2 ,the ,correlation of ,fracture ,systems and the ,evidences for ,planetary ,dislocations within the ,earth's ,crust1 ,trans4 ,wis4 ,acad4 ,sci41 etc41 vol4 #ae1 #aije1 pp4 #ae-bi2 ,repeating ,patterns in the ,relief and in the ,structure of the ,land1 ,bull4 ,geol4 ,soc4 ,am41 vol4 #bb1 #aiaa1 pp4 #abc-agf1 pls4 #g-ac4 ,,chapter ,,xviii ,,the ,,forms ,,carved ,,and ,,molded ,,by ,,waves ,the motion of a water wave4--,the motions within a wave upon the surface of a body of water may be thought of in two different ways4 ,first of all1 there is the motion of each particle of water within an orbit of its own2 and there is1 further1 the forward motion of propagation of the wave considered as a whole4 ,illustration3 ,,fig4 #bdg4--;,diagram to show the nature of the motions within a free water wave4 ,the water particle in a wave has a continued motion round and round its orbit like that of a horse circling a race course1 only that here the track is in a vertical plane1 directed along the line of propagation of the wave 7,fig4 #bdg74 ,each particle of water1 through its friction upon neighboring particles1 is able to transmit its motion both along the surface and downward into the water below4 ,the force which starts the water in motion and develops the wave1 is the friction of wind blowing over the water surface1 and the size of the orbit of the water particle at any point is proportional to the wind's force and to the stretch of water over which it has blown4 ,the wind's effect is1 therefore1 cumulative--the wave is proportional to the wind's effect upon all water particles in its rear1 added to the local wind friction4 ,the size or height of the wave is measured by the diameter of the orbit of motion of the surface particle1 and this is the difference in height between trough and crest4 ,the distance from crest to crest1 or from trough to trough1 is called the wave length4 ,though the wave motion is transmitted downward into the water there is a continued loss of energy which is here not compensated by added wind friction1 and so the orbital motion grows smaller and smaller1 until at the depth of about a wave length it has completely died out4 ,this level of no motion is called the wave base4 ,in quiet weather the level of no motion is practically at the water's surface1 and inasmuch as the geological work of waves is in large part accomplished during the great storms1 the term 8wave base0 refers to the lowest level of wave motion at the time of the heaviest storms4 ,upon the ocean the highest waves that have been measured have an amplitude of about fifty feet and a wave length of about six hundred feet4 ,free waves and breakers4--,so long as the depth of the water is below wave base1 there is obviously no possibility of interference with the wave through friction upon the bottom4 ,under these conditions waves are described as free waves1 and their forms are symmetrical except in so far as their crests are pulled over and more or less dissipated in the spray of the 8white caps0 at the time of high winds4 ,illustration3 ,,fig4 #bdh4--;,diagram to illustrate the transformation of a free wave into a breaker as it approaches the shore4 ,as a wave approaches a shore1 which generally has a gentle outward sloping surface1 there is interposed in the way of a free forward movement the friction upon the bottom4 ,this friction begins when the depth of water is less than wave base1 and its effect is to hold back the wave at the bottom4 ,carried slowly upward in the water by the friction of particle upon particle1 the effect of this holding back is a piling up of the water1 which increases the wave height as it diminishes the wave length1 and also interferes with wave symmetry 7,fig4 #bdh74 ,moving forward at the top under its inertia of motion and held back at the bottom by constantly increasing friction1 a strong turning motion or couple is started about a horizontal axis1 the immediate effect of which is to steepen the forward slope of the wave1 and this continues until it overhangs1 and1 falling1 8breaks0 into surf4 ,such a breaking wave is called a 8comber0 or 8breaker0 7plate #aa ,b74 ,,plate #aa4 ,illustration3 ,a4 ,ripple markings within an ancient sandstone 7courtesy of ,u4 ,s4 ,grant74 ,illustration3 ,b4 ,a wave breaking as it approaches the shore4 7,photograph by ,fairbanks47 ,illustration3 ,,fig4 #bdi4--,notched rock cliff cut by waves and the fallen blocks derived from the cliff through undermining4 ,profile ,rock at ,farwell's ,point near ,madison1 ,wisconsin4 ,effect of the breaking wave upon a steep rocky shore--the notched cliff4--,if the shore rises abruptly from deeper water1 the top of the breaking wave is hurled against the cliff with the force of a battering ram4 ,during storms the water of shore waves is charged with sand1 and each sand particle is driven like a stone cutter's tool under the stroke of his hammer4 ,the effect is thus both to chip and to batter away the rock of the shore to the height reached by the wave1 undermining it and notching the rock at its base 7,fig4 #bdi74 ,when the notch has been cut in this manner to a sufficient depth1 the overhanging rock falls by its own weight in blocks which are bounded by the ever present joints1 leaving the upper cliff face essentially vertical4 ,illustration3 ,,fig4 #bej4--;,a wave-cut chasm under control by joints1 coast of ,maine 7after ,tarr74 ,coves1 sea arches1 and stacks4--,it is the headland which is most exposed to the work of the waves1 since with change of wind direction it is exposed upon more than a single face4 ,the study of headlands which have been cut by waves shows that the joints within the rock play a large rle in the shaping of shore features4 ,the attack of the waves under the direction of these planes of ready separation opens out indentations of the shore 7,fig4 #bej7 or forms sea caves which1 as they extend to the top of the cliff by the process of sapping1 yield the coves which are so common a feature upon our rock-bound shores 7,fig4 #bei1 p4 #bch74 ,with continuation of this process1 the caves formed on opposite sides of the headland may be united to form a sea arch 7,fig4 #bea74 ,illustration3 ,,fig4 #bea4--,the sea arch known as the ,grand ,arch upon one of the ,apostle ,islands in ,lake ,superior 7after a photograph by the ,detroit ,photographic ,company74 ,a later stage in this selective wave carving under the control of joints is reached when the bridge above the arch has fallen in1 leaving a detached rock island with precipitous walls4 ,such an offshore island of rock with precipitous sides is known as a stack 7,fig4 #beb71 or sometimes as a 8chimney01 though this latter term is best restricted to other and similar forms which are the product of selective weathering 7p4 #cjj74 ,illustration3 ,,fig4 #beb4--,stack near the shore of ,lake ,superior4 ,whenever the rock is less firmly consolidated1 and so does not stand upon such steep planes1 the stack is apt to have a more conical form1 and may not be preceded in its formation by the development of the sea arch 7,fig4 #bfj1 p4 #bci74 ,in the reverse case1 or where the rock possesses an unusual tenacity1 the stack may be largely undermined and stand supported like a table upon thick legs or pillars of rock 7,fig4 #bec74 ,in ,fig4 #bed is seen a group of stacks upon the coast of ,california1 which show with clearness the control of the joints in their formation1 but unlike the marble of the ,south ,american example the forms are not rounded1 but retain their sharp angles4 ,illustration3 ,,fig4 #bec4--,the ,marble ,islands1 stacks in ,lake ,buenos ,aires1 southern ,andes 7after ,f4 ,p4 ,moreno74 ,the cut rock terrace4--,when waves first begin their attack upon a steep1 rocky shore1 the lower limit of the action is near the wave base4 ,the action at this depth is1 however1 less efficient1 and as the recession of the cliff is one of the most rapid of erosional processes1 the rock floor outside the receding cliff comes to slope gradually downward from the cliff to a maximum depth at the edge of the terrace1 approximately equal to wave base 7,fig4 #bee74 ,this cut terrace is extended seaward or lakeward1 as the case may be1 in a built terrace constructed from a portion of the rock dbris acquired from the cliff4 ,illustration3 ,,fig4 #bed4--,squared stacks which reveal the position of the joint planes which have controlled in the process of carving by the waves4 ,pt4 ,buchon1 ,california 7after a photograph by ,fairbanks74 ,illustration3 ,,fig4 #bee4--;,ideal section of a steep rocky shore carved by waves into a notched cliff and cut terrace1 and extended by a built terrace4 ,the broken wave1 after rising upon the terrace under the inertia of its motion until all its energy has been dissipated1 slides outward by gravity1 and though checked and overridden by succeeding breakers1 it continues its outward slide as the 8undertow0 until it reaches the end of the terrace4 ,here it suddenly enters deep water1 and losing its velocity1 drops its burden of rock1 and builds the terrace seaward after the manner of construction of an embankment4 ,as we are to see1 the larger portion of the wave-quarried material is diverted to a different quarter4 ,illustration3 ,,fig4 #bef4--,map showing the outlines of the ,island of ,heligoland at different stages in its recent history4 ,the peripheries given are in miles4 ,to gain some conception of the importance of wave cutting as an eroding process1 we may consider the late history of ,heligoland1 a sandstone island off the mouth of the ,elbe in the ,north ,sea 7,fig4 #bef74 ,from a periphery of #abj miles1 which it possessed in the ninth century of the ,christian era1 the island has reduced its outline to #de miles in the fourteenth century1 #h miles in the seventeenth1 and to about #c miles at the beginning of the twentieth century4 ,the ,german government1 which recently acquired this little remnant from ,england1 has expended large sums of money in an effort to save this last relic4 ,illustration3 ,,fig4 #beg4--;,cut and built terrace with bowlder pavement shaped by waves on a steep shore formed of loose materials4 ,the cut and built terrace on a steep shore of loose materials4--,in materials which lack the coherence of firm rock1 no vertical cliff can form2 for as fast as undermined by the waves the loose materials slide down and assume a surface of practically constant slope--the 8angle of repose0 of the materials 7,fig4 #beg74 ,the terrace below this sloping cliff will not differ in shape from that cut upon a rocky shore2 but whenever the materials of the shore include disseminated blocks too large for the waves to handle1 they collect upon the terrace near where they have been exhumed1 thus forming what has been called a 8bowlder pavement0 7,fig4 #beh74 ,illustration3 ,,fig4 #beh4--,sloping cliff and terrace with bowlder pavement exposed at low tide upon the shore at ,scituate1 ,massachusetts4 ,the edge of the cut and built terrace is1 as already mentioned1 maintained at the depth of wave base4 ,if one will study the submerged contours of any of our inland lakes1 it will be found that these basins are surrounded by a gently sloping marginal shelf1--the cut and built terrace1--and that the depth of this shelf at its outer edge is proportioned to the size of the lake4 ,upon ,lake ,mendota at ,madison1 ,wisconsin1 the large storm waves have a length of about twenty feet1 which is the depth of the outer edge of the shore terraces 7,fig4 #bfg1 p4 #bdb74 ,the shelf surrounding the continents has1 with few local exceptions1 a uniform depth of #ajj fathoms1 or about the wave base of the heaviest storm waves4 ,the work of the shore current4--,in describing the formation of the built terrace1 it was stated that the greater part of the rock material quarried upon headlands by the waves is diverted from the offshore terrace4 ,this diversion is the work of the shore current produced by the wave4 ,illustration3 ,,fig4 #bei4--,map to show the nature of the shore current and the forms which are molded by it4 ,at but few places upon a shore will the storm waves beat perpendicularly1 and then for but short periods only4 ,the broken wave1 as it crawls ever more slowly up the beach1 carries the sand with it in a sweeping curve1 and by the time gravity has put a stop to its forward movement1 it is directed for a brief instant parallel to the shore4 ,soon1 however1 the pull of gravity upon it has started the backward journey in a more direct course down the slope of the terrace2 and here encountering the next succeeding breaker1 a portion of the water and the coarser sand particles with it are again carried forward for a repetition of the zigzag journey4 ,this many times interrupted movement of the sand particles may be observed during a high wind upon any sandy lee shore4 ,the 8set0 of the water along the shore as a result of its zigzag journeyings is described as the shore current 7,fig4 #bei71 and the effect upon sand distribution is the same as though a steady current moved parallel to the shore in the direction of the average trend of the moving particles4 ,the sand beach4--,the first effect of the shore current is to deposit some portion of the sand within the first slight recess upon the shore in the lee of the cliff4 ,the earlier deposits near the cliff gradually force the shore current farther from the shore and so lay down a sand selvage to the shore1 which is shaped in the form of an arc or crescent and known as a beach 7,fig4 #bei and ,fig4 #bfj74 ,illustration3 ,,fig4 #bfj4--;,crescent-shaped beach formed in the lee of a headland4 ,santa ,catalina ,island1 ,california 7after a photograph by ,fairbanks74 ,illustration3 ,,fig4 #bfa4--;,cross section of a beach pebble4 ,the shingle beach4--,with heavy storms and an exceptional reach of the waves1 the shore currents are competent to move1 not the sand alone1 but pebbles1 the area of whose broader surface may be as great as the palm of one's hand4 ,such rock fragments are shaped by the continued wear against their neighbors under the restless breakers1 until they have a lenticular or watch-shaped form 7,fig4 #bfa74 ,such beach pebbles are described as shingle1 and they are usually built up into distinct ridges upon the shore1 which1 under the fury of the high breakers1 may be piled several feet above the level of quiet water 7,fig4 #bfb74 ,such storm beaches have a gentle forward slope graded by the shore current1 but a steep backward slope on the angle of repose4 ,most storm beaches have been largely shaped by the last great storm1 such as comes only at intervals of a number of years4 ,illustration3 ,,fig4 #bfb4--,storm beach of coarse shingle about four feet in height at the base of ,burnt ,bluff on the northeast shore of ,green ,bay1 ,lake ,michigan4 ,bar1 spit1 and barrier4--,wherever the shore upon which a beach is building makes a sudden landward turn at the entrance to a bay1 the shore currents1 by virtue of their inertia of motion1 are unable longer to follow the shore4 ,the dbris which they carry is thus transported into deeper water in a direction corresponding to a continuation of the shore just before the point of turning 7see ,fig4 #bei1 p4 #bch74 ,the result is the formation of a bar1 which rises to near the water surface and is extended across the entrance to the bay through continued growth at its end1 after the manner of constructing a railway embankment across a valley4 ,illustration3 ,,fig4 #bfc4--,spit of shingle on ,au ,train ,island1 ,lake ,superior 7after ,gilbert74 ,over the deeper water near the bar the waves are at first not generally halted and broken1 as they are upon the shore1 and so the bar does not at once build itself to the surface1 but remains an invisible bar to navigation4 ,from its shoreward end1 however1 the waves of even moderate storms are broken1 and the bar is there built above the water surface1 where it appears as a narrow cape of sand or shingle which gradually thins in approaching its apex4 ,this feature is the well-known spit 7,fig4 #bfc7 which1 as it grows across the entrance to the bay1 becomes a barrier or barrier beach 7,fig4 #bfd74 ,the continuation of the visible in the usually invisible bar1 is at the time of high winds made strikingly apparent1 for the wave base is below the crest of the bar1 and at such times its crescentic course beyond the spit can be followed by the eye in a white arc of broken water4 ,illustration3 ,,fig4 #bfd4--;,barrier beach in front of a lagoon on ,lake ,mendota at ,madison1 ,wisconsin4 ,the shallow lagoon behind the barrier is filling up and is largely hidden in vegetation4 ,the construction of a barrier across the entrance to a bay transforms the latter into a separate body of water1 a lagoon1 within which silting up and peat formation usually lead to an early extinction 7p4 #dbi74 ,the formation of barriers thus tends to straighten out the irregularities of coast lines1 and opens the way to a natural enlargement of the land areas4 ,while the coasts of the ,united ,kingdom of ,great ,britain have been losing some four thousand acres through wave erosion1 there has been a gain by growth in quiet lagoons which amounts to nearly seven times that amount4 ,as evidence of the straightening of the shore line which results from this process1 the coast of the ,carolinas or of ,nantucket 7,fig4 #dei7 may serve for illustration4 ,the land-tied island4--,we have seen that wave erosion operates to separate small islands from the headlands1 but the shore currents counteract this loss to the continents by throwing out barriers which join many separated islands to the mainland4 ,such land-tied islands are a common feature on many rocky coasts1 and upon the ,new ,england coast they usually have been given the name of 8neck40 ,the long arc of ,lynn ,beach joins the former island of ,nahant1 through its smaller neighbor ,little ,nahant1 to the coast of ,massachusetts4 ,a similar land-tied island is ,marblehead ,neck4 ,the ,rock of ,gibraltar1 formerly an island1 is now joined to ,spain by the low beach known as the 8neutral ground40 ,the ,spanish name1 tombola1 has sometimes been employed to describe an island thus connected to the shore4 ,illustration3 ,,fig4 #bfe4--;,cross section of a barrier beach with lagoon in its rear4 ,a barrier series4--,the cross section of a barrier beach1 like that of a storm beach upon the shore1 slopes gently upon the forward side1 and more steeply at the angle1 of repose upon the rear or landward margin 7,fig4 #bfe74 ,the thinning wedge of shore deposits which the barrier throws out to seaward raises the level of the lake bottom 7,fig4 #bff71 and when coast irregularities are favorable to it1 new spits will develop upon the shore outside the earlier one1 and a new bar1 and in its turn a barrier1 will be found outside the initial one1 taking a course in a direction more or less parallel to it 7,fig4 #bfg74 ,illustration3 ,,fig4 #bff4--;,cross section of a series of barriers and an outer bar4 ,illustration3 ,,fig4 #bfg4--;,formation of barrier series and an outer bar in ,university ,bay of ,lake ,mendota1 at ,madison1 ,wisconsin4 ,the water contour interval is five feet1 and the land contour interval ten feet 7based on a map by the ,wisconsin ,geological ,survey74 ,illustration3 ,,fig4 #bfh4--,series of barriers at the western end of ,lake ,superior 7after ,gilbert74 ,so soon as the first barrier is formed1 processes are set in operation which tend to transform the newly formed lagoon into land1 and so with a series of barriers1 a zone of water lilies between the outer barrier and the bar1 a bog1 and a land platform may represent the successive stages in this acquisition of territory by the lands4 ,a noteworthy example of barrier series and extension of the land behind them1 is afforded by the bay at the western end of ,lake ,superior 7,fig4 #bfh74 ,illustration3 ,,fig4 #bfi4--;,character profiles resulting from wave action upon shores4 ,character profiles4--,the character profiles yielded by the work of waves are easy of recognition 7,fig4 #bfi74 ,the vertical cliff with notch at its base is varied by the stack of sugar-loaf form carved in softer rocks1 or the steeper notched variety cut from harder masses4 ,sea caves and sea arches yield variations of a curve common to the undercut forms4 ,wherever the materials of the shore are loosely consolidated only1 the sloping cliff is formed at the angle of repose of the materials4 ,the barrier beach1 though projecting but a short distance above the waves1 shows an unsymmetrical curve of cross section with the steeper slope toward the land4 ,,reading ,,references ,,for ,,chapter ,,xviii ,g4 ,k4 ,,gilbert4 ,the ,topographic ,features of ,lake ,shores1 #eth ,ann4 ,rept4 ,u4 ,s4 ,geol4 ,surv41 #ahhe1 pp4 #fi-abc1 pls4 #c-bj2 ,lake ,bonneville1 ,mon4 ,i1 ,u4 ,s4 ,geol4 ,surv41 #ahij1 ,chapters ii-iv1 pp4 #bc-ahg4 ,,vaughan ,,cornish4 ,on ,sea ,beaches and ,sand ,banks1 ,geogr4 ,jour41 vol4 #aa1 #ahih1 pp4 #ebh-edc1 #fbh-feh4 ,f4 ,p4 ,,gulliver4 ,shore ,line ,topography1 ,proc4 ,am4 ,acad4 ,arts and ,sci41 vol4 #cd1 #ahii1 pp4 #adi-beh4 ,n4 ,s4 ,,shaler4 ,the ,geological ,history of ,harbors1 #acth ,ann4 ,rept4 ,u4 ,s4 ,geol4 ,surv41 #ahic1 pp4 #ic-bji4 ,,sir ,a4 ,,geikie4 ,the ,scenery of ,scotland1 #aija1 pp4 #df-hi4 ,w4 ,h4 ,,wheeler4 ,the ,sea ,coast4 ,longmans1 ,london1 #aijb1 pp4 #a-gh4 ,g4 ,w4 ,,von ,,zahn4 ,die zerstrende ,arbeit des ,meeres an ,steilksten nach ,beobachtungen in der ,bretagne und ,normandie in den ,jahren #aijg und #aijh1 ,mitt4 d4 ,geogr4 ,ges4 ,hamb41 vol4 #bd1 #aiaj1 pp4 #aic-bhd1 pls4 #ab-bg4 ,,chapter ,,xix ,,coast ,,records ,,of ,,the ,,rise ,,or ,,fall ,,of ,,the ,,land ,the characters in which the record has been preserved4--,the peculiar forms into which the sea has etched and molded its shores have been considered in the last chapter4 ,of these the more significant are the notched rock cliff1 the cut rock terrace1 the sea cave1 the sea arch1 the stack1 and the sloping cliff and terrace1 among the carved features2 and the barrier beach and built terrace1 among the molded forms4 ,it is important to remember that the molded forms1 by the very manner of their formation1 stand in a definite relationship to the carved features2 so that when either one has been in part effaced and made difficult of determination1 the discovery of the other in its correct natural position may remove all doubt as to the origin of the relic4 ,illustration3 ,,fig4 #bgj4--,the east coast of ,florida1 with shore line characteristic of a raised coast4 ,in studies of the change of level of the land1 it is customary to refer all variations to the sea level as a zero plane of reference4 ,it is not on this account necessary to assume that the changes measured from this arbitrary datum plane are the absolute upward or downward oscillations which would be measured from the earth's center2 for the sea1 like the land1 has been subject to its changes of level4 ,there need1 however1 be no apology for the use of the sea surface as a plane of reference2 for it is all that we have available for the purpose1 and the changes in level1 even if relative only1 are of the greatest significance4 ,it is probable that in most cases where the coast line is rising from uplift1 some portion of the sea basin not far distant is becoming deepened1 so that the visible change of level is the algebraic sum of the two effects4 ,even coast line the mark of uplift4--,it was early pointed out in this volume 7p4 #aeh7 that the floor of the sea in the neighborhood of the land presents a relatively even surface4 ,the carving by waves1 combined with the process of deposition of sediments1 tends to fill up the minor irregularities of surface and preserve only the features of larger scale1 and these in much softened outlines4 ,upon the continents1 on the contrary1 the running water1 taking advantage of every slight difference in elevation and searching out the hidden structure planes within the rock1 soon etches out a surface of the most intricate detail4 ,the effect of elevation of the sea floor into the light of day will therefore be to produce an even shore line devoid of harbors 7,fig4 #bgj74 ,if the coast has risen along visible planes of faulting near the sea margin1 the coast line1 in addition to being even1 will usually be made up of notably straight elements joined to one another4 ,illustration3 ,,fig4 #bga4--,ragged coast line of ,alaska1 the effect of subsidence4 ,a ragged coast line the mark of subsidence4--,when in place of uplift a subsidence occurs upon the coast1 the intricately etched surface1 resulting from erosion beneath the sky1 comes to be invaded by the sea along each trench and furrow1 so that a most ragged outline is the result 7,fig4 #bga74 ,such a coast has many harbors1 while the uplifted coast is as remarkable for its lack of them4 ,slow uplift of the coast--the coastal plain and cuesta4--,a gradual uplift of the coast is made apparent in a progressive retirement of the sea across a portion of its floor1 thus exposing this even surface of recent sediments4 ,the former shore land will be easily recognized by it's etched surface1 which will now come into sharp contrast with the new plain4 ,it is therefore referred to as the oldland and the newly exposed coastal plain as the newland 7,fig4 #bgb74 ,illustration3 ,,fig4 #bgb4--,portion of ,atlantic coastal plain and neighboring oldland of the ,appalachian ,mountains4 ,but the near-shore deposits upon the sea floor had an initial dip or slope to seaward1 and this inclination has been increased in the process of uplift4 ,the streams from the oldland have trenched their way across these deposits while the shore was rising4 ,but the process being a slow one1 deposits have formed upon the seaward side of the plain after the landward portion was above tide1 and the coastal plain may come to have a 8belted0 or zoned character4 ,the streams tributary to those larger ones which have trenched the plain may encounter in turn harder and softer layers of the plain deposits1 and at each hard layer will be deflected along its margin so as to enter the main streams more nearly at right angles4 ,they will also1 as time goes on1 migrate laterally seaward through undermining of the harder layers1 and thus will be shaped alternating belts of lowland separated by escarpments in the harder rock from the residual higher slopes4 ,belts of upland of this character upon a coastal plain are called cuestas 7,fig4 #bgc74 ,illustration3 ,,fig4 #bgc4--;,ideal form of cuestas and intermediate lowlands carved from a coastal plain 7after ,davis74 ,the sudden uplifts of the coasts4--,elevations of the coast which yield the coastal plain must be accounted among the slower earth movements that result in changes of level4 ,such movements1 instead of being accompanied by disastrous earthquakes1 were probably marked by frequent slight shocks only1 by subterranean rumblings1 or1 it may be1 the land rose gradually without manifestations of a sensible character4 ,upon those coasts which are often in the throes of seismic disturbance1 a quite different effect is to be observed4 ,here within the rocks we will probably find the marks of recent faulting with large displacements1 and the movements have been upon such a scale that shore features1 little modified by subsequent weathering1 stand well above the present level of the seas4 ,above such coasts1 then1 we recognize the characteristic marks of wave action1 and the evidence that they have been suddenly uplifted is beyond question4 ,illustration3 ,,fig4 #bgd4--,uplifted sea cave1 ten feet above the water upon the coast of ,california2 the monument to a former earthquake 7after a photograph by ,fairbanks74 ,illustration3 ,,fig4 #bge4--;,double-notched cliff near ,cape ,tiro1 ,celebes 7after a photograph by ,sarasin74 ,the upraised cliff4--,upon the coast of southern ,california may be found all the features of wave-cut shores now in perfect preservation1 and in some cases as much as fifteen hundred feet above the level of the sea4 ,these features are monuments to the grandest of earthquake disturbances which in recent time have visited the region 7,fig4 #bgd74 ,quite as striking an example of similar movements is afforded by notched cliffs in hard limestone upon the shore of the ,island of ,celebes 7,fig4 #bge74 ,but the coast of ,california furnishes the other characteristic coast features in the high sea arch and the stack as additional monuments to the recent uplift4 ,let one but imagine the stacks which now form the ,seal ,rocks off the ,cliff ,house at ,san ,francisco to be suddenly raised high above the sea1 and the forms which they would then present would differ but little from those which are shown in ,fig4 #bgf4 ,illustration3 ,,fig4 #bgf4--;,jasper rock stacks uplifted on the coast of ,california 7after a photograph by ,fairbanks74 ,the uplifted barrier beach4--,within the rentrants of the shore1 the wave-cut cliff is1 as we know1 replaced by the barrier beach1 which takes its course across the entrance to a bay4 ,after an uplift1 such a barrier composed of sand or shingle should be connected with the headlands1 often with a partially filled lagoon behind it4 ,its cross section should be steep in the direction of the lagoon1 but quite gradual in front 7,fig4 #bgg74 ,illustration3 ,,fig4 #bgg4--,uplifted shingle beach across the entrance to a former bay upon the coast of southern ,california 7after a photograph by ,fairbanks74 ,illustration3 ,,fig4 #bgh4--,raised beach terraces near ,elie1 ,fife1 ,scotland4 ,coast terraces4--,upon those shores where to-day high mountains front the sea1 the coast may generally be seen to rise in a series of terraces 7,fig4 #bgh74 ,this is notably true of those coasts which are to-day racked by earthquakes1 such as is the eastern margin of the ,pacific from ,alaska to ,patagonia4 ,the traveler by steamer along the coast from ,san ,francisco to ,chili has for weeks almost constantly in sight these giant steps on which the mountains have been uplifted from the sea4 ,in ,alaska we are fortunate in having the history of the later stages in this uplift 7,fig4 #bgi74 ,as described in a former chapter1 portions of this shore rose in the month of ,september of the year #ahii in some places as high as forty-seven feet1 to the accompaniment of a terrific earthquake and sea wave4 ,above the terrace which marks the beach line of #ahii there is a higher terrace of similar form now overgrown with trees1 but none the less clearly to be recognized as a shore line of the past century which preceded in the long sequence the uplift of #ahii4 ,illustration3 ,,fig4 #bgi4--,uplifted sea cliffs and terraces on the coast of ,russell ,fjord1 ,alaska 7after ,tarr and ,martin74 ,illustration3 ,,fig4 #bhj4--;,diagrams to show how excessive sinking upon the sea floor will cause the shore to migrate landward as it is uplifted4 ,illustration3 ,,fig4 #bha4--;,a drowned river mouth1 or estuary upon a coastal plain4 ,as was noted in our study of earthquakes1 the recent instrumental records of distant earthquakes tell us that the movements upon the sea floor are many times larger than those upon the continents1 and that while the mountainous coasts are generally rising1 the deeps of the sea are sinking4 ,the effect of this over-balance of sinking1 or resultant shrinking of the earth's shell1 may be to compress the mountain district and so cause the shore line to move landward at the same time that it moves upward 7,fig4 #bhj74 ,the sunk or embayed coast4--,when now1 upon the other hand1 a section of the coast line sinks with reference to the sea1 the water invades all the near-shore valleys1 thus 8drowning0 them and yielding the drowned river mouth or estuary4 ,if the relief of the shore was slight1 as it generally is upon a coastal plain1 slight depression only will produce broad estuaries1 such as ,chesapeake ,bay at the drowned mouth of the ,susquehanna 7,fig4 #bha74 ,if1 on the other hand1 the relief of the shore is strong and the subsidence is large1 the entire coast line will be transformed into an archipelago of steep-walled rocky islets which rise abruptly from the sea 7,figs4 #bhb and #bhd74 ,a plateau which is intersected by deep and steep-walled valleys of ,u-section 7p4 #cda7 under large submergence yields the fjords so characteristic of ,scandinavia or ,alaska4 ,a ragged coast line1 fringed with islands as a result of submergence1 is described as an embayed coast4 ,illustration3 ,,fig4 #bhb4--;,archipelago of steep rocky islets due to large submergence of a coast having strong relief4 ,entrance to ,esquimalt ,harbor1 ,vancouver ,island 7after a photograph by ,fairbanks74 ,illustration3 ,,fig4 #bhc4--,the submerged ,hudsonian channel which continues the ,hudson ,river across the continental shelf4 ,submerged river channels4--,the sinking of a coast of small relief be sufficient to completely submerge river valleys1 whose channels then begin to fill with sediment and whose courses can only be followed in soundings4 ,one of the most interesting of such channels is that which continues the ,hudson ,river across the continental shelf into the deeper sea 7,fig4 #bhc74 ,records of an oscillation of movement4--,because a coast is deeply embayed is no ground for assuming that a subsidence is now in progress1 or is1 in fact1 the latest movement recorded upon the coast4 ,in many cases it is easy to see that such is not the case4 ,the coast of ,maine is perhaps as typical of an embayed shore line as any that might be cited1 but a study of the river valleys in the neighborhood shows clearly that the present submergence of their mouths is a fraction only of an earlier one which has left a record of its existence in beds of marine clay which outline the earlier and far deeper indentations 7,fig4 #bhd74 ,illustration3 ,,fig4 #bhd4--,marine clay deposits near the mouths of the rivers of ,maine which preserve a record of earlier subsidence 7after ,stone74 ,if now we give a closer examination to the coast1 it is found that there are marks of recent uplift in an abandoned shore line now far above the reach of the waves4 ,there is here1 then1 the record1 first of subsidence and consequent embayment1 and1 later1 of an uplift which has reduced the raggedness of the coast outline exposed the clay deposits1 and raised the strands of the period of deep subsidence to their present position4 ,in countries which possess a more ancient civilization than our own1 the record of such oscillations in the level of the ground has sometimes been entered upon human monuments1 so that it is possible to date more or less definitely the periods of subsidence or elevation4 ,at the little town of ,pozzuoli1 upon the shore of the ,bay of ,naples1 is found one of the mos instructive of these records4 ,illustration3 ,,fig4 #bhe4--,view of the three standing columns of the temple of ,jupiter ,serapis at ,pozzuoli1 showing the dark and rough band nine feet in width affected by the rock-boring mollusks which now live in the ,bay of ,naples4 ,in the ruins of the ancient temple of ,jupiter ,serapis are three marble monoliths #dj feet in height1 curiously marked by a roughened surface between the heights of #ab and #ba feet above their pedestals 7,fig4 #bhe74 ,closer inspection shows that this roughened surface has been produced by a marine1 rock-boring mollusk1 the lithodomus1 which lives in the waters of the ,bay of ,naples1 and the shells of this animal are still to be found within the cavities upon the surface of the columns4 ,without recounting details which have been many times recited since these interesting monuments were first geologically explored by ,babbage and ,lyell1 it may be stated that a record is here preserved1 first of subsidence amounting to some #dj feet1 and of subsequent elevation1 of the low coast land on which stood the temple in the old ,roman city of ,puteoli 7,fig4 #bhf74 ,at the time of deepest submergence the top of the lithodomus zone upon the column stood at the level of the water in the ,bay of ,naples1 the smoother lower zone being buried at the time in the sand at the bottom1 and thus made inaccessible for the lithodomi4 ,it is to be added that studies made in the environs of ,pozzuoli have fully confirmed the changes of level revealed by the columns1 through the discovery of now elevated shore lines which are referable to the period of deep submergence4 ,simultaneous contrary movements upon a coast4--,in our study of the changes in the level of the ground that take place during earthquakes1 it was learned that neighboring sections of the earth's crust may be moved at different rates or even in opposite directions1 notwithstanding the fact that the general movement of the province is one of uplift4 ,thus during the ,alaskan earthquake of #ahii1 although portions of the coast line were elevated by as much as forty-seven feet1 neighboring sections were raised by smaller amounts1 and some small sections were sunk and so far submerged that the salt water and the beach sand were washed about the roots of forest trees4 ,illustration3 ,,fig4 #bhf4--,pozzuoli in the #crd1 #ith1 and #bjth ,centuries4 ,a region racked by heavy earthquakes1 where the present configuration of the ground speaks strongly for a movement of somewhat similar nature1 but with average movement of elevation much greater to the northward than in the opposite direction1 is the extended coast line of ,chili4 ,this country is characterized by a great central north and south valley which separates the coast range from the high chain of the ,cordilleras to the eastward4 ,to the southward the floor of this valley descends1 and has its continuance in the ,gulf of ,corcovado behind the island of ,chiloe and the ,chonos archipelago4 ,the known recent uplift of the coast of ,chili1 particularly in the northern sections and during the earthquakes of the eighteenth1 nineteenth1 and twentieth centuries1 lends great interest to this topographic peculiarity4 ,indications are not lacking that1 during the earthquake of ,concepcion in #ahce1 and of ,valparaiso in #aijg1 the measure of uplift was greater to the north than it was to the south4 ,illustration3 ,,fig4 #bhg4--,map of ,san ,clemente ,island1 ,california1 showing the characteristic topography of recent uplift 7after ,u4 ,s4 ,coast and ,geodetic ,survey74 ,the contrasted islands of ,san ,clemente and ,santa ,catalina4--,perhaps the most striking example of simultaneous opposite movements observable in neighboring portions of the earth's crust is furnished by the coast of southern ,california4 ,the coast itself at ,san ,pedro and the island of ,san ,clemente1 some fifty miles off this point1 in common with most portions of the neighboring coast land1 have been rising in interrupted movements from the sea1 and offer in rare perfection the characteristic coast terraces 7,fig4 #bhg and ,fig4 #bgh1 p4 #bej74 ,midway between these two rising sections of the crust1 and less than twenty-five miles distant from either1 is the island of ,santa ,catalina1 which has been sinking beneath the waves1 and apparently at a similarly rapid rate 7,fig4 #bhh74 ,the topography of the island shows the intricate detail of a maturely eroded surface1 while that of the neighboring ,san ,clemente shows only the widely spaced1 deep caons of the infantile stage of erosion 7,fig4 #afe and pl4 #ab ,a74 ,while ,santa ,catalina has been sinking1 ,san ,pedro ,hill has risen #abdj feet1 and ,san ,clemente1 #aejj feet4 ,it is characteristic of a sinking coast line that the cliff recession is abnormally rapid1 and evidence for this is furnished by the shores of ,santa ,catalina1 upon which the waves are cutting the cliffs back into the beds of caons1 and so causing small falls to develop at the caon mouths4 ,,plate #ab4 ,illustration3 ,a4 ,v-shaped caon cut in an upland recently elevated from the sea1 ,san ,clemente ,island1 ,california 7after ,w4 ,s4 ,tangier-,smith74 ,illustration3 ,b4 ,a 8hogback0 at the base of the ,bighorn ,mountains1 ,wyoming 7after ,darton74 ,illustration3 ,,fig4 #bhh4--,map of ,santa ,catalina ,island1 ,california1 showing the characteristic surface of an area which has long been above the waves1 and the entire absence of coast terraces 7after ,u4 ,s4 ,c4 and ,g4 ,s474 ,the ,blue ,grotto of ,capri4--,we may now return to the ,bay of ,naples for additional evidence that oscillations of level in neighboring portions of the same coast are not necessarily synchronous1 and that near-lying sections may even move in opposite directions at the same time1 as has already been shown for the islands off the ,california coast4 ,for the ,pozzuoli shore of the bay it was learned that within the ,christian ,era a complete cycle of downward1 followed by later upward1 movement has been largely accomplished4 ,across the bay1 and less than #bj miles distant1 is the ,blue ,grotto of ,capri1 a sea cave cut in limestone above an earlier cave of the same nature which is now deep below the water surface4 ,it is the refracted sunlight which enters the cave through this lower submerged opening and has been robbed on the way of all but its blue rays which gives to the famous grotto its special charm 7,fig4 #bhi74 ,illustration3 ,,fig4 #bhi4--;,cross section of the ,blue ,grotto on the ,island of ,capri1 showing the submerged sea cave through which most of the light enters the grotto1 and the higher artificial window now widened by wave action 7after von ,knebel74 ,it is known that the former1 and now submerged1 sea cave was in use by ,roman patricians as a cool retreat from the oppressive hot wind known as the sirocco1 and that an artificial entrance or window was cut where is now the only accessible entrance to the grotto4 ,in the ancient writings1 no mention is made1 however1 of the remarkable blue illumination for which it is now famous1 and the conditions at the time1 as we may see1 were not such as to make this possible4 ,later subsidence of the coast has brought the ancient window to the sea level1 where it has been considerably enlarged by the waves4 ,the earlier grotto1 abandoned as its entrance was closed1 was rediscovered in #ahbf by the painter and poet1 ,august ,kopisch4 ,a grotto with green illumination 7the ,grotto ,verde7 is situated upon the opposite side of the island1 and a blue grotto1 having its origin in similar conditions to those of the famous ,blue ,grotto1 is found upon the island of ,busi off the ,dalmatian coast4 ,character profiles4--,in the landscape of a coast which has been slowly uplifted the characteristic line is the profile of the cuesta1 with short perpendicular element joined to a gently sloping and longer section and continued in the horizontal portion corresponding to the lowland 7,fig4 #bij74 ,rapidly uplifted coasts offer in contrast the lines characteristic of wave erosion and deposition1 but at higher levels and in repeated sections4 ,most prominent of all is the staircase constructed of coast terraces1 with either vertical or sloping risers and with outwardly inclining and gently graded treads4 ,near the steep riser in the staircase may sometimes be seen the sugar-loaf outline of the stack cut in softer material1 or the obelisk-like pillar undercut at its base1 which is carved in firmer rock masses4 ,with excessively rapid uplift1 the double-notched cliff or the double sea arch may appear in the landscape4 ,upon a submerged coast the most significant lines in the view are those of the rock islet and the steep-walled fjord4 ,illustration3 ,,fig4 #bij4--;,character profiles in coast landscapes where there has been either elevation or depression4 ,,reading ,,references ,,for ,,chapter ,,xix ,general3-- ,,sir ,,ch4 ,,lyell4 ,principles of ,geology1 vol4 #b1 pp4 #ahj-aig4 ,,ed4 ,,suess4 ,the ,face of the ,earth1 ,clarendon ,press1 ,oxford1 #aijf1 vol4 #b1 ,chapters i and xiv1 pp4 #a-bi1 #ece-eef4 ,,robert ,,sieger4 ,seenschwankungen und ,strandverschiebungen in ,scandinavien1 ,zeit4 d4 ,gesell4 f4 ,erdk41 ,berlin1 vol4 #bh1 #ahic1 pp4 #a-ajf1 #cic-fhh1 pl4 #g4 ,elevated shore lines3-- ,f4 ,b4 ,,taylor4 ,the ,highest ,old ,shore ,line of ,mackinac ,island1 ,am4 ,jour4 ,sci41 vol4 #dc1 #ahib1 pp4 #baj-bah4 ,,thomas ,l4 ,,watson4 ,evidences of ,recent ,elevation of the ,southern ,coast of ,baffins ,land1 ,jour4 ,geol41 vol4 #e1 #ahig1 pp4 #ag-cc4 ,j4 ,w4 ,,goldthwait4 ,the ,abandoned ,shore ,lines of ,eastern ,wisconsin4 ,bull4 #ag1 ,wis4 ,geol4 and ,nat4 ,hist4 ,surv41 #aijg1 pp4 #acd1 pls4 #a-cg4 ,evidences of depression3-- ,w4 ,b4 ,,scott4 ,introduction to ,geology1 ,new ,york1 #aijg1 pp4 #cc-cf4 ,w4 ,j4 ,,mcgee4 ,the ,gulf of ,mexico as a ,measure of ,isostacy1 ,am4 ,jour4 ,sci4 7#c71 vol4 #dd1 #ahib1 pp4 #agg-aib4 ,a4 ,,lindenkohl4 ,notes on the ,submarine ,channel of the ,hudson ,river1 etc41 ,am4 ,jour4 ,sci4 7#c71 vol4 #da1 #ahia1 pp4 #dhi-dii1 pl4 #ah4 ,j4 ,w4 ,,spencer4 ,the ,submarine ,great ,caon of the ,hudson ,river1 ibid4 7#d71 vol4 #ai1 #aije1 pp4 #a-ae2 ,submarine ,valleys off the ,american ,coast and in the ,north ,atlantic1 ,bull4 ,geol4 ,soc4 ,am41 vol4 #ad1 #aijc1 pp4 #bjg-bbf1 pls4 #ai-bj4 ,f4 ,,nansen4 ,the ,bathymetrical ,features of the ,north ,polar ,sea1 with a ,discussion of the ,continental ,shelves and ,previous ,oscillations of ,shore ,line1 ,norwegian ,north ,polar ,expedition1 vol4 #d1 #aijd1 pp4 #ii-bca1 pl4 #a4 ,w4 ,v4 ,,knebel4 ,hhlenkunde1 etc41 ,braunschweig1 #aijf1 pp4 #age-agg 7the blue grotto of ,capri74 ,oscillation of movement3-- ,c4 ,,lyell4 ,principles of ,geology1 vol4 #b1 pp4 #afd-agf 7,temple of ,jupiter ,serapis74 ,e4 ,,ray ,,lankester4 ,extinct ,animals1 ,new ,york1 #aije1 pp4 #ca-db4 ,h4 ,w4 ,,fairbanks4 ,oscillations of the ,coast of ,california during the ,pliocene and ,pleistocene1 ,am4 ,geol41 vol4 #bj1 #ahig1 pp4 #bac-bde4 ,g4 ,h4 ,,stone4 ,mon4 #cd1 ,u4 ,s4 ,geol4 ,surv41 #ahii1 pp4 #ef-eh1 pl4 #b4 ,,bailey ,,willis4 ,ames ,knob1 ,north ,haven1 ,maine4 ,bull4 ,geol4 ,soc4 ,am41 vol4 #ad1 #aijc1 pp4 #bja-bjf1 pls4 #ag-ah4 ,simultaneous contrary movements on a coast3-- ,a4 ,c4 ,,lawson4 ,the ,post-,pliocene ,diastrophism of the ,coast of ,southern ,california1 ,bull4 ,univ4 ,calif4 ,dept4 ,geol41 vol4 #a1 #ahic1 pp4 #aae-afj1 pls4 #h-i4 ,w4 ,s4 ,,tangier-,,smith4 ,a ,geological ,sketch of ,san ,clemente ,island1 #ahth ,ann4 ,rept4 ,u4 ,s4 ,geol4 ,surv41 ,pt4 ii1 #ahih1 pp4 #dei-dif1 pls4 #hd-if4 ,r4 ,s4 ,,tarr and ,l4 ,,martin4 ,recent ,changes of ,level in the ,yakutat ,bay ,region1 ,alaska1 ,bull4 ,geol4 ,soc4 ,am41 vol4 #ag1 #aijf1 pp4 #bi-fd1 pls4 #ab-bc4 ,,chapter ,,xx ,,the ,,glaciers ,,of ,,mountain ,,and ,,continent ,conditions essential to glaciation4--,wherever for a sufficiently protracted period the annual snowfall of a district is in excess of the snow that is melted1 a residue must remain from each season to be added to that of succeeding ones4 ,eventually so much snow will have accumulated that under its own weight and in obedience to its peculiar properties1 a movement will begin within the mass tending to spread it and so to reduce the slope of its upper surface 7,frontispiece plate74 ,the conditions favorable to glaciation are1 therefore1 heavy precipitation and low annual temperature4 ,if the precipitation is scanty1 the small snowfall is soon melted2 and if the temperature be too high1 the moisture is precipitated not in the form of snow but as rain4 ,it is important here to keep in mind that snow is a poor heat conductor and itself protects its deeper layers from melting4 ,the snow-line4--,because of the low temperatures glaciers should be most abundant or most extensive in high latitudes and in high altitudes4 ,the largest are found in polar and subpolar regions1 and they are elsewhere encountered only at considerable elevations4 ,the largest glaciers are the vast sheets of ice which inwrap the continents of ,greenland and ,antarctica1 but glaciers of large size are to be found upon other large land masses of the ,arctic1 as well as in ,alaska1 in the southern ,andes1 and in ,new ,zealand4 ,much smaller glaciers are characteristic of certain highlands within temperate and tropical regions1 but because of specially favorable conditions both of altitude and precipitation the ,himalayas1 although in relatively low latitudes1 nourish glaciers of large proportions4 ,in general1 it may be said that the nourishing grounds of glaciers are largely restricted to those areas where snow covers the ground throughout the year4 ,the lower margin of such areas is designated the snow line1 and varies but little from the line on which the average summer temperature is at the freezing point of water--the so-called summer isotherm of #cb ,fahrenheit4 ,within the tropics this line may rise as high as #ah1jjj feet above the sea1 whereas in polar latitudes it descends to sea level4 ,importance of mountain barriers in initiating glaciers4--,the precipitation within any district depends1 however1 not alone upon the amount of moisture which is brought to it in the clouds1 but upon the amount which is abstracted before the clouds have passed over it4 ,the capacity of space to hold moisture increases with its temperature1 and hence any lowering of this temperature will reduce the capacity4 ,if lowered sufficiently1 the point of complete saturation will be reached and further cooling must result in precipitation4 ,hence1 anything which forces an air current to rise into more rarefied zones above1 will lower the pressure upon it and so bring about a cooling effect in which no heat is abstracted4 ,this so-called adiabatic refrigeration of a gas may be illustrated by the cool current which issues in a jet from a warm expanded rubber tire after the cock has been opened2 or even better1 by the instant solidification at extreme low temperatures of such normal gases as carbonic acid when they are allowed to issue under heavy pressure from a small orifice4 ,as applied to moisture-laden and near-surface winds1 the effective agents of adiabatic cooling are the upland areas upon the continents1 and especially the ranges of mountains4 ,these barriers force the moving clouds to rise1 cool1 and deposit their moisture4 ,it is1 therefore1 the highland barriers which face the oncoming1 moisture-laden winds that receive the heaviest precipitation4 ,within temperate regions1 because of the prevalence of westerly winds1 those barriers which face the western shores receive the heaviest fall4 ,within the tropics1 on the other hand1 it is the barriers facing the eastern shores which1 because of the easterly 8trades01 are most favorable to precipitation4 ,thus it is in the ,sierra ,nevadas of ,california1 and not in the ,rockies or the ,appalachians1 that the glaciers of the ,united ,states are found4 ,the highland of the ,swiss ,alps lying likewise athwart the 8westerlies0 of the temperate zone acquires the moisture for nourishment of its glaciers from the western ocean--here the ,atlantic 7,fig4 #bia74 ,within the tropics the conditions are reversed1 and it is in general the ranges which lie nearer the eastern coasts that are the more favored4 ,if no barrier is found upon this coast1 the clouds may travel over vast stretches of country before being arrested by mountains and robbed of their moisture4 ,thus in tropical ,brazil the glaciers are found in the ,andes upon the ,pacific coast though nourished by clouds from the ,atlantic4 ,illustration3 ,,fig4 #bia4--,map showing the distribution of existing glaciers1 and the two important wind poles of the earth4 ,sensitiveness of glaciers to temperature changes4--,how sensitive is the adjustment between snow precipitation and temperature may be strikingly illustrated by the statement on excellent authority that if the average annual temperature of the air within the ,scottish ,highlands should be lowered by only three degrees ,fahrenheit1 small glaciers would be the result2 and a moderate temperature fall within the region surrounding the ,laurentian lakes of ,north ,america would bring on glaciation1 otherwise expressed as a depression of the snow line of the region4 ,the cycle of glaciation4--,though to-day buried beneath its ice mantle1 it is known that ,greenland had more than once in earlier geological ages a notably mild climate1 and in some future age it may revert to this condition4 ,in other regions1 also1 we have evidence that such a rotation of climatic changes has been successively accomplished1 the climate having steadily increased in severity towards a culminating point1 and been followed by a reverse series of changes4 ,such a complete period may be called a cycle of glaciation4 ,while the climate is steadily becoming more rigorous1 we have to do with an advancing hemicycle of glaciation1 but after the culminating point has been reached1 the period of amelioration of climate is the receding hemicycle4 ,the advancing hemicycle4--,there is little reason to doubt that whatever be the cause of the climatic changes which bring on glacial conditions1 these changes come on by insensible gradations4 ,the first visible evidence of the increased severity of the climate is the longer persistence of the winter snows1 at first within the more elevated districts4 ,in such positions drifts must eventually continue throughout the warm season and so contribute to the snow accumulations of the succeeding winter4 ,this point once reached1 small glaciers are inevitable1 even should the average temperature fall no further1 for the snow left over in each season must steadily increase the depth of the deposits until the weight brings about an internal motion of the mass from higher to lower levels4 ,illustration3 ,,fig4 #bib4--;,an ,alaskan glacier spreading out at the foot of the range which nourishes it4 ,the inherited depressions of the upland--the gentle hollows at the heads of rivers--will first be filled1 and so the valleys below become the natural channels for the outflow of the early glaciers4 ,with a continued lowering of the annual temperature and consequent increased snowfall1 the early glaciers become more and more amply nourished4 ,snow and ice will1 therefore1 cover larger areas of the upland1 and the glaciers will push their fronts farther down the valleys before they are wasted in the warm air of the lower levels4 ,as the valleys become thus more completely invested by the glacier they are likewise filled to greater and greater depths1 and they may thus submerge portions of the walls that separate adjacent valleys4 ,reaching at last the front of the upland area1 the glaciers may now be so well nourished at their heads that they push out upon the flatter foreland and without restraint from retaining walls spread broadly upon it 7,fig4 #bib74 ,illustration3 ,,fig4 #bic4--,surface of a glacier whose upper layers spread with slight restraint from retaining walls4 ,surface of the ,folgefond1 an ice cap of southern ,norway4 ,the culmination of the progressive climatic change may ere this have been reached and milder conditions have ensued4 ,if1 however1 the severity of the climate should be still further increased1 the expanded fronts of neighboring glaciers will coalesce to form a common ice fan or apron along the foot of the upland 7,plate #ah ,b74 ,this could hardly take place without a still further deepening of the ice within the valleys above1 and1 probably1 a progressive submergence of the lower crests in the valley walls4 ,this may even continue until all parts of the upland area have been buried4 ,the snow and ice now take the form of a covering cap or carapace1 and the upper portions being no longer restrained at the sides1 now spread into a broad dome1 as would a viscous liquid like thick molasses when poured out upon the floor 7,fig4 #bic74 ,the lower zones of the mass and the thinner marginal portions still have their motion to a greater or less extent controlled by the irregularity of the rock floor against which they rest4 ,the reverse series of changes in the glacier is inaugurated by an amelioration of the climate1 and here1 therefore1 the advancing hemicycle becomes merged in the receding hemicycle of glaciation4 ,continental and mountain glaciers contrasted4--,the time when the rock surface becomes submerged beneath the glacier is1 as regards both the surface forms and the erosive work1 a critical point of much significance2 for the ice cap and larger continental glacier obviously protect the rock surface from the action of those chemical and mechanical processes in which the atmosphere enters as chief agent1 and which are collectively known as weathering processes4 ,until submergence is accomplished1 larger or smaller portions of the rock surface project either through or between the ice masses and are1 therefore1 exposed to direct attack by the weather 7see below1 p4 #cgj74 ,illustration3 ,,fig4 #bid4--,section through a mountain glacier 7in solid black71 showing how its surface is determined by the irregularities in the rock basement 7after ,hess74 ,snow which falls in the mountains is not allowed to remain long where it falls4 ,by the first high wind it is swept off the more elevated and exposed surfaces and collected under eddies in any existing hollows1 but especially those upon the lee slopes of the range4 ,we are to learn that glaciers carve the mountains by enlarging the hollows which they find and producing great basins for the collection of their snows2 but with the initiation of glaciation the inherited hollows are in most cases the unimportant depressions at the heads of streams4 ,whatever they may be and however formed1 the snow first fills those hollows which are sheltered from the wind1 and as it accumulates and becomes distributed as ice1 assumes a surface of its own that is dependent upon the form and the position of the basin which it occupies 7see ,fig4 #bid74 ,illustration3 ,,fig4 #bie4--,profile across the largest of the ,icelandic ice caps1 with the vertical scale greatly exaggerated 7after ,thoroddsen and ,spethmann74 ,when the quantity of accumulated snow is so great that all hollows of the rock surface are filled1 its own surface is no longer controlled by retaining rock walls1 and it now assumes a form largely independent of the irregularities in the upland4 ,experience shows that this surface is approximately that of a flat dome or shield1 and as it covers all the upland1 save where the ice thins upon its margins1 this type of glacier is called an ice cap 7,fig4 #bie74 ,all types of glacier in which rock projects above the highest levels of the ice and snow are known as mountain glaciers4 ,illustration3 ,,fig4 #bif4--;,ideal section across a continental glacier1 with the vertical scale and the projecting rock masses of the marginal zone greatly magnified4 ,the flat domes of ice which mantle the continents of ,greenland and ,antarctica1 though resembling in form the smaller ice cap1 are yet because of their vast size so distinct from them1 particularly in the manner of their nourishment1 that they belong in a separate class described as inland ice or continental glaciers4 ,though they have some affinities with ice caps1 they are most sharply differentiated from all types of mountain glaciers4 ,of them it is true that the lithosphere projects through them only in the neighborhood of their margins 7,fig4 #bif71 whereas in the case of mountain glaciers rock may project at any level but always above the highest snow surface4 ,ice caps may be regarded as intermediate between the two main classes of mountain and continental glaciers 7,fig4 #big74 ,because of the large rle which continental glaciers have played in geological history1 it is thought best to consider them first1 leaving for later discussion the no less interesting but less important mountain glaciers4 ,illustration3 ,,fig4 #big4--,view of the ,eyriks-,jkull1 an ice-cap of ,iceland 7after ,grossman74 ,the nourishment of glaciers4--,the life of a glacier is dependent upon the continued deposition of snow in aggregate amount in excess of that which is lost by melting or by other depleting processes4 ,whenever1 on the other hand1 the waste exceeds the precipitation1 the glacier is in a receding condition and must eventually disappear1 if such conditions are sufficiently long continued4 ,the source of the snow is the water of the ocean evaporated into the atmosphere and transported over the land in the form of clouds4 ,we are to learn that the changes which this moisture undergoes before its delivery to the glacier are notably different for the classes of continental and mountain glacier4 ,the upper and lower cloud zones of the atmosphere4--,before we can comprehend the nature of the processes by which glaciers are nourished1 it will be necessary to review the results of recent studies made upon the earth's atmospheric envelope4 ,it must be kept in mind that the sun's rays are chiefly effective in warming the atmosphere through being first absorbed by some solid body such as rock or water and their heat then communicated by contact to the immediately adjacent air layers4 ,the layers thus warmed being now lighter than before1 they rise and are replaced by colder air1 which in its turn is warmed and likewise set in upward motion4 ,such currents developed in the air by contact with warmer solid bodies constitute the process known as convection4 ,illustration3 ,,fig4 #bih4--,the zones of the lower atmosphere as revealed by recent kite and balloon explorations4 ,to a relatively small degree the atmosphere is heated by the direct absorption of the sun's rays which pass through it4 ,since air has weight1 it compresses the lower layers near the earth1 and hence as we ascend from the earth's surface the air becomes continually lighter4 ,convection currents must1 therefore1 adjust themselves by the air expanding as it rises4 ,but expansion of a gas always results in its cooling1 as every one must have observed who has placed his finger in the air current which escapes from the open valve of a warm rubber tire4 ,dry air is cooled a degree ,fahrenheit for every six hundred feet of ascent in the atmosphere4 ,at a height of about seven miles above the earth's surface all rising air currents have cooled to about #fh below the zero of the ,fahrenheit scale1 and exploration with balloons has shown that the currents rise no farther4 ,at this level they move horizontally1 just as rising vapor spreads out in a room beneath the ceiling4 ,above this level1 as far as exploration has gone1 or to a height of more than twelve miles1 the temperature remains nearly constant1 and this upper zone is1 therefore1 called the isothermal or the advective zone--the uniform temperature zone of the lower atmosphere4 ,beneath the convective ceiling the process of convection is characteristic1 and this zone is therefore described as the convective zone 7,fig4 #bih74 ,a large part of the moisture which rises from the ocean's surface is condensed to vapor before it has ascended three miles1 and in this form it makes its transit over land as fleecy or stratiform clouds--the so-called cumulus and stratus clouds and their many intermediate varieties 7see ,frontispiece74 ,this lower layer within the convective zone is1 therefore1 a moist one overlaid by a relatively drier middle layer of the convective zone4 ,that moisture which rises above the lower cloud layer is congealed by adiabatic cooling to fine ice needles visible as the so-called cirrus clouds which float as feathery fronds beneath the convective ceiling 7see frontispiece at right upper corner of picture74 ,thus we have within the convective zone an upper layer more or less charged with water in the form of ice needles4 ,it is the clouds of the lower zone whose moisture in the form of vapor supplies the nourishment of mountain glaciers1 and the high cirrus clouds whose congealed moisture1 after interesting transformations1 is responsible for the continued existence of continental glaciers4 ,as we are to see1 there are other noteworthy differences between continental and mountain glaciers1 in the manner of their sculpture of the lithosphere1 so that long after they have disappeared the characters of each are easily identified in their handiwork4 ,how the lower clouds are forced upward and so compelled to give up their moisture to feed the mountain glaciers1 and how the upper clouds are pulled downward to nourish the glaciers of continents1 can be best understood after the characteristics of each glacier class have been studied4 ,,chapter ,,xxi ,,the ,,continental ,,glaciers ,,of ,,polar ,,regions ,illustration3 ,,fig4 #bii4--,map of ,greenland showing the area of inland-ice and the routes of different explorers4 ,the inland ice of ,greenland4--,in ,greenland and in ,antarctica the land is almost or quite buried under a cover of snow and ice--the so-called 8inland ice0--which always assumes the surface of a very flat dome or shield4 ,in ,greenland there is found a marginal ribbon of land generally from five to twenty-five miles in width 7,fig4 #bii71 but in ,antarctica all the land1 with the exception of a few mountain peaks1 is inwrapped in a mantle of ice which is also extended upon the sea in a broad shelf of snow and ice4 ,neither of these vast glaciers has been explored except in its marginal portion1 yet such is the symmetry of the profiles along the routes traversed1 and such the flatness and monotony of the snow surface within the margins1 that there is little reason to doubt that the profile made along ,nansen's route in southern ,greenland would1 save only for magnitude1 fairly represent a section across the middle of the continent 7,fig4 #cjj74 ,the mountain rampart and its portals4--,as soon as we examine the coastal belt we observe that the 8,great ,ice0 of ,greenland is held in by a wall of mountains and so prevented from spreading out to its natural surface in the marginal portions4 ,through portals of the inclosing mountain ranges--the outlets--it sends out tongues of ice which in many respects resemble certain types of mountain glaciers4 ,illustration3 ,,fig4 #cjj4--,profile in natural proportions across the southern end of the continental glacier of ,greenland1 constructed upon an arc of the earth's surface and based upon ,nansen's profile corrected by ,hess4 ,the marginal portions of the profile are represented below upon a magnified scale in order to bring out the characters of the marginal slopes4 ,such measurements as have been made upon the inland ice of ,greenland at points back from1 but yet comparatively near to1 the outlets1 show that it has here a surface rate of motion amounting to less than an inch per day1 and it is highly probable that at moderate distances from the margin this amount diminishes to zero4 ,upon the outlets1 on the contrary1 surface rates as high as #ei feet per day have been measured1 and even #ajj feet per day has been reported4 ,we are thus justified in saying that glacier flow within the outlets is from #gjj to #ajjj times as great as it is upon the near-by inland ice1 and that the glacier is in a measure drained through the portals of the inclosing ranges4 ,back from these outlet streams of ice1 or tongues1 the surface of the inland ice is depressed to form a dimple or 8basin of exudation0 as is the surface of a reservoir above the raceway when the water is being rapidly drawn away 7,fig4 #cja74 ,,plate #ac4 ,illustration3 ,a4 ,precipitous front of the ,bryant glacier outlet of the ,greenland inland-ice 7after ,chamberlin74 ,illustration3 ,b4 ,lateral stream beside the ,benedict glacier outlet1 ,greenland 7after ,r4 ,e4 ,peary74 ,illustration3 ,,fig4 #cja4--,map of a glacier tongue1 with dimple showing above and due to indraught of the ice4 ,umanakfjord1 ,greenland 7after von ,drygalski74 ,fissures in the ice1 the so-called crevasses1 are the recognized marks of ice movement1 and these are always concentrated at the steep slopes of the ice surface in the neighborhood of its margins4 ,upon the ,greenland ice1 crevasses are restricted in their distribution to a zone which extends from seven to twenty-five miles within the ice border4 ,the marginal rock islands4--,from its margin the ice surface rises so steeply as to be climbed only with difficulty1 but this gradient steadily diminishes until at a distance of between seventy-five and a hundred miles its slope is less than two degrees4 ,where crossed by ,nansen near latitude #fd ,n4 the broad central area of ice was so nearly level as to appear to be a plain4 ,as we pass across the irregular ice margin in the direction of the interior1 larger and larger proportions of the land's surface are submerged1 until only projecting peaks rise above the ice as islands which are described as nunataks 7,fig4 #cjb74 ,though not a universal observation1 it has been often noted that the absorption of the sun's rays by rock masses projecting through the snow results in a radiation of the heat and a lowering by melting of the surrounding snow and ice4 ,for this reason nunataks are often surrounded by a deep trench due to a melting of the snow4 ,such a depression in the ice surface about the margin of a nunatak1 from its resemblance to a trench about an ancient castle1 has been designated a moat 7,fig4 #cjc74 ,for the same reason1 the outlet tongues of ice which descend in deep fjords between walls of rock are melted away from the walls and a lateral stream of water is sometimes found to flow between ice and rock 7pl4 #ac ,b74 ,illustration3 ,,fig4 #cjb4--;,edge of the ,greenland inland ice1 showing the nunataks diminishing in size toward the interior4 ,the lines upon the ice are medial moraines starting from nunataks 7after ,libbey74 ,rock fragments which travel with the ice4--,rock surfaces which are exposed to the atmosphere are in high latitudes broken down through the freezing of water within their crevices4 ,the fragments resulting from this rending process fall upon the glacier surface and are carried forward as passengers in the direction of the ice margin4 ,they are either visible as long and narrow ridges or trains following the directions of the steepest slope 7,fig4 #cjb71 or they become buried under fresh falls of snow and only again become visible where summer melting has lowered the glacier surface in the vicinity of its margin4 ,these longitudinal trains of rock fragments upon the glacier surface always have their starting point at the lower margin of one of the nunataks1 and are known as medial moraines 7,fig4 #cja1 p4 #bgc1 and ,fig4 #cjb74 ,inside the zone of nunataks the glacier surface is1 however1 clear of rock dbris except where dust has been blown on by the wind1 and this extends for a few miles only4 ,the material of the medial moraines is a collection of angular blocks whose surfaces are the result of frost rending1 for in their travel above the ice they are subjected to no abrading processes4 ,illustration3 ,,fig4 #cjc4--,moat surrounding a nunatak in ,victoria ,land 7after ,scott74 ,a contrasted type of surface moraines upon the ,greenland glacier1 instead of being parallel to the direction of ice movement1 is directed transversely or parallel to the margins4 ,the materials of these moraines are more rounded fragments of rock which have come up from the bottom layers1 and we shall again refer to the origin of such moraines after the subglacial conditions have been considered4 ,the grinding mill beneath the ice4--,if1 now1 we examine the front of a glacier tongue which goes out from the inland ice1 we find that while the upper portion is white and mainly free from rock dbris 7plate #ac ,a71 the lower zone is of a dark color and crowded with layers of pebbles and bowlders which have been planed1 polished1 and scratched in a quite remarkable manner4 ,the ice front is itself subject to forward and retrograde migrations of short period1 but it is easily seen that in the main its larger movement has been a retrograde one4 ,the ground from which it has lately withdrawn is generally a hard rock floor unweathered1 but smooth1 polished1 and scratched in the same manner as the bowlders which are imbedded within the ice4 ,it is perfectly apparent that the latter have been derived from some portion of the rock basement upon which the glacier still rests1 and that floor and bowlders have alike been ground smooth by mutual contact under pressure4 ,this erosion beneath the ice is accomplished by two processes2 namely1 plucking and abrasion4 ,wherever the rock over which the glacier moves has stood up in projecting masses and is riven by fissure planes of any kind1 the ice has found it easy to remove it in larger or smaller fragments by a quarrying process described as plucking4 ,the rock may be said to be torn away in blocks which are largely bounded by the prexisting fissure planes4 ,over relatively even surfaces plucking has little importance1 but where there are noteworthy inequalities of surface upon the glacier bed1 those sides which are away from the oncoming ice 7lee side7 are degraded by plucking in such a manner as sometimes to leave steep and ragged fracture surfaces4 ,the tools of the ice thus acquired in the process of plucking are quickly frozen into the lowest ice layers1 and being now dragged along the floor they abrade in the same manner as does a rasp or file4 ,these tools of the ice are themselves worn away in the process and are thus given their characteristic shapes4 ,just as the lapidary grinds the surface of a jewel into facets by imbedding the gem in a matrix1 first in one and then in another position1 each time wearing down the projecting irregularities through contact with the abrading surface2 so in like manner the rock fragment is held fast at the bottom of the glacier until 8soled0 or 8shod01 first upon one side and then upon another4 ,accidental contact with some obstruction upon the floor may suffice to turn the fragment and so expose a new surface to wear upon the abrading floor4 ,minor obstructions coming in contact with one side of the fragment only1 may turn it in its own plane without overturning4 ,evidence of such interruptions can be later read in the different directions of stri upon the same facet 7plate #ag ,a74 ,illustration3 ,,fig4 #cjd4--;,a glacier pavement of ,permo-,carboniferous age in ,south ,africa4 ,the stri running in the direction of the observer are prominent and a noteworthy gouging of the surface is to be noted to the right in the middle distance 7after ,davis74 ,the floor beneath the glacier is reduced by the abrading process to a more or less smooth and generally flattened or rounded surface--the so-called glacier pavement 7,fig4 #cjd74 ,to accomplish this all former mantle rock due to weathering processes must first be cleared away1 and the firm unaltered rock beneath is wherever susceptible of it given a smooth polish although locally scored and scratched by the grinding bowlders4 ,the earlier projections of the surface of the floor1 if not entirely planed away1 are at least transformed into rounded shoulders of rock1 which from their resemblance to closely crowded backs in a flock of sheep have been called 8sheep backs0 or 8roches moutonnes40 ,thus the effect of the combined action of the processes of plucking and abrasion is to reduce the accent of the relief and to mold the contours of the rock in smoothly flowing curves1 generally of large radius4 ,the lifting of the grinding tools and their incorporation within the ice4--,wherever the ice is locally held in check by the projecting nunataks1 relief is found between such obstructions1 and there the flow of the ice has a correspondingly increased velocity 7,fig4 #cje b74 ,if the obstructions are not of large dimensions1 the ice which flows around the outer edges is soon joined to that which passes between the obstructions and so normal conditions of flow are restored below the nunataks4 ,the locally rapid flow of the ice is1 therefore1 restricted to a relatively short distance1 the passageway between the nunataks1 and the conditions are thus to be likened to the fall of water at a raceway due to the sudden descent of its surface from the level of the reservoir to the level of the stream in the outlet4 ,as is well known1 there is under these conditions a prodigious scour upon the bottom which tends to dig a pit just above and below the dam--a scape colk--and carry the materials up to the surface below the pit4 ,such a tendency was well illustrated by the behavior of the water at the opening of the ,neu ,haufen dam below the city of ,vienna 7,fig4 #cje a74 ,in the case of ice1 material from the bottom may by the upward current be brought up to the surface of the glacier at the lower edge of the colk and thus produce a type of local surface moraine of horseshoe form with its direction generally transverse to the direction of ice movement 7,fig4 #cje b74 ,illustration3 ,,fig4 #cje4--;a1 ,map showing pit excavated by the current below the opening in a dam4 b1 ,nunataks and surface moraines on the ,greenland ice4 ,dalager's ,nunataks 7after ,suess74 ,any obstruction upon the pavement of the glacier apparently exerts a larger or smaller tendency to elevate the bowlders and pebbles and incorporate them within the ice4 ,rock dbris thus incorporated is described as englacial drift4 ,in the case of ,greenland glaciers this material seems at the ice front to be largely restricted to the lower #ajj feet 7plate #ac ,a74 ,near the front of the inland ice the increased slope of the upper surface greatly increases the flow of the upper ice layers in comparison with those nearer the bottom1 so that the upper layers override the lower as they would an obstruction4 ,the englacial drift is either for this reason or because of rock obstructions brought to the surface1 where it yields parallel ridges corresponding in direction to the glacier margin4 ,such transverse surface moraines are thus in many respects analogous to those which appear about the lower margins of scape colks4 ,in contrast to the longitudinal or medial surface moraines the materials of the transverse moraines are more faceted and rounded--they have been abraded upon the glacier pavement4 ,melting upon the glacier margins in ,greenland4--,during the short but warm summer season1 the margins of the ,greenland ice are subject to considerable losses through surface melting4 ,when the uppermost ice layer has attained a temperature of #cb ,fahrenheit1 melting begins and moves rapidly inward from the glacier margin4 ,in late spring the surface of the outer marginal zone is saturated with water1 and this zone of slush advances inward with the season1 but apparently never transgresses the inner border of what we have generally referred to as the marginal zone of the ice characterized by relatively steep slopes1 crevasses1 and nunataks4 ,upon the ice within this zone are found streams large enough to be designated as rivers and these are connected with pools1 lakes1 and morasses4 ,the dirt and rock fragments imbedded in the ice are melted out in the lowering of the surface1 so that late in the season the ice presents a most dirty aspect4 ,at the front of the great mountain glaciers of ,alaska1 a more vigorous operation of the same process has yielded a surface soil in which grow such rank forests as entirely to mask the presence of the ice beneath4 ,in addition to the visible streams upon the surface of the ,greenland ice1 there are others which flow beneath and can be heard by putting the ear to the surface4 ,all surface streams eventually encounter the marginal crevasses and plunge down in foaming cascades1 producing the well known 8glacier wells0 or 8glacier mills40 ,the progress of the water is now throughout in tunnels within the ice until it again makes its appearance at the glacier margin4 ,illustration3 ,,fig4 #cjf4--,marginal moraine now forming at the edge of ,greenland inland ice1 showing a smooth rock pavement outside it4 ,a small lake with a partial covering of lake ice occupies a hollow of this pavement 7after von ,drygalski74 ,the marginal moraines4--,study of both the ,greenland and ,antarctic glaciers has shown that if we disregard the smaller and short-period migrations of the ice front1 the general later movement has been a retrograde one--we live in a receding hemicycle of glaciation4 ,the earlier ,greenland glacier has now receded so as to expose large areas of the former glacier pavement4 ,in places this pavement is largely bare1 indicating a relatively rapid retirement of the ice front1 but at all points at which the ice margin was halted there is now found a ridge of unassorted rock materials which were dropped by the ice as it melted 7,fig4 #cjf74 ,such ridges1 composed of the unassorted materials described as till1 come to have a festooned arrangement largely concentric to the ice margin1 and are the marginal or terminal moraines 7see ,fig4 #ccf1 p4 #cab74 ,marginal moraines1 if of large dimensions1 usually have a hummocky surface1 and are apt to be composed of rock fragments of a wide range of size from rock flour 7clay7 to large bowlders 7plate #ag ,a71 which may represent many types since they have been plucked by the glacier or gathered in at its surface from many widely separated localities4 ,illustration3 ,,fig4 #cjg4--,small lake impounded between the ice front and a moraine which it has recently built4 ,greenland 7after von ,drygalski74 ,as the glacier front retires from the moraine which it has built up1 the water which emerges from beneath the ice is impounded behind the new dam so as to form a lake of crescentic outline 7,fig4 #cjg74 ,such lakes are particularly short-lived1 for the reason that the water finds an outlet over the lowest point in the crest of the moraine and easily cuts a gorge through the loose materials1 thus draining the lake 7,fig4 #cjh74 ,thereafter1 the escaping water flows in a braided stream across the late lake bottom and thence at the bottom of the gorge through the moraine4 ,illustration3 ,,fig4 #cjh4--,view of a drained lake bottom between the moraine-covered ice front in the foreground and an abandoned marginal moraine in the middle distance4 ,the water flows from the ice front in a braided stream and passes out through the moraine in a narrow gorge4 ,variegated glacier1 ,alaska 7after ,lawrence ,martin74 ,the outwash plain or apron4--,the water which descends from the glacier surface in the glacier wells or mills1 eventually arrives at the bottom1 where it follows a sinuous course within a tunnel melted out in the ice4 ,much of this water may issue at the ice front beneath the coarse rock materials which are found there1 and so be discovered with the ear rather than by the eye4 ,the water within the tunnels not flowing with a free surface but being confined as though it were in a pipe1 may1 however1 reach the glacier margin under a hydrostatic pressure sufficient to carry it up rising grades4 ,inasmuch as it is heavily charged with rock dbris and is suddenly checked upon arriving at the front it deposits its burden about the ice margin so as to build up plains of assorted sands and gravels1 and over this surface it flows in ever shifting serpentine channels of braided type 7,fig4 #cjh74 ,such plains of glacier outwash are described as outwash plains or outwash aprons4 ,rising as it does under hydrostatic pressure the water issuing at the glacier front may find its way upward in some of the crevasses and so emerge at a level considerably above the glacial floor4 ,it may thus come about that the outwash plain is built up about the nose of the glacier so as partially to bury it from sight4 ,when now the ice front begins a rapid retirement1 a depression or fosse 7,fig4 #cji and ,fig4 #cci1 p4 #cad7 is left behind the outwash plain and in front of the moraine which is built up at the next halting place4 ,illustration3 ,,fig4 #cji4--;,diagrams to show the manner of formation and the structure of an outwash plain1 and the position of the fosse between this and the moraine4 ,the continental glacier of ,antarctica4--,in ,victoria ,land1 upon the continent of ,antarctica1 so far as exploration has yet gone1 the continental glacier is held back by a rampart of mountains1 as has been shown to be true of the inland ice of ,greenland4 ,the same flat dome or shield has likewise been found to characterize its upper surface 7,fig4 #caj74 ,the most noteworthy differences between the inland ice masses of ,greenland and ,antarctica are to be ascribed to the greater severity of the ,antarctic climate and to the more ample nourishment of the southern glacier measured by the land area which it has submerged4 ,there is here no marginal land ribbon as in ,greenland1 but the glacier covers all the land and is1 moreover1 extended upon the sea as a broad floating terrace--the shelf ice 7,fig4 #caa74 ,this barrier at its margin puts a bar to all further navigation1 rising as it does in some cases #bhj feet above the sea and descending to even greater depths below 7plate #ae ,b74 ,illustration3 ,,fig4 #caj4--,map showing the inland ice of ,victoria ,land bordered by the shelf ice of the ,great ,ross ,barrier4 ,the arrows show the direction of the prevailing winds 7based on maps by ,scott and ,shackleton74 ,in that portion of ,antarctica which was explored by the ,german expedition1 the inland ice is not as in ,victoria ,land restrained within walls of rock1 but is spread out upon the continent so as to assume its natural ice slopes1 which are therefore much flatter than those examined in ,greenland and ,victoria ,land4 ,here in ,kaiser ,wilhelm ,land the ice rises at its sea margin in a cliff which is from #acj to #afe feet in height1 then upon a fairly steeply curving slope to an elevation of perhaps a thousand feet4 ,here the grades have become relatively level1 and on ever flatter slopes the surface appears to continue into the distant interior 7plate #ad74 ,near the ice margin numerous fissures betray a motion within the mass which exact measurements indicate to be but one foot per day1 and at a distance of a mile and a quarter from the margin even this slight value has diminished by fully one eighth4 ,it can hardly be doubted that at moderate distances only within the ice margin1 the glacier is practically without motion4 ,,plate #ad4 ,illustration3 ,view of the margin of the ,antarctic continental glacier in ,kaiser ,wilhelm ,land 7after ,e4 v4 ,drygalski74 ,rain or general melting conditions being unknown in ,antarctica1 a striking contrast is offered to the marginal zone of the ,greenland continent4 ,this is to a large extent explained by the existence upon the northern land mass of a coastland ribbon which becomes quickly heated in the sun's rays1 and both by warming the air and by radiating heat to the ice it causes melting and produces local air temperatures which in summer may even be described as hot4 ,about ,independence ,bay in latitude #hb ,n4 and near the northernmost extremity of ,greenland1 ,peary descended from the inland ice into a little valley within which musk oxen were lazily grazing and where bees buzzed from blossom to blossom over a gorgeous carpet of flowers4 ,illustration3 ,,fig4 #caa4--,sections across the inland ice of ,victoria ,land1 ,antarctica1 with the shelf ice in front 7after ,shackleton74 ,nourishment of continental glaciers4--,explorations upon and about the glaciers of ,greenland and ,antarctica have shown that the circulation of air above these vast ice shields conforms to a quite simple and symmetrical model subject to spasmodic pulsations of a very pronounced type4 ,each great ice mass with its atmospheric cover constitutes a sort of refrigerating air engine and plays an important part in the wind system of the globe4 7,see ,fig4 #bia1 p4 #bfc74 ,both the domed surface and the low temperature of the glacier are essential to the continuation of this pulsating movement within the atmosphere 7,fig4 #cab74 ,the air layer in contact with the ice is during a period of calm cooled1 contracted1 and rendered heavier1 so that it begins to slide downward and outward upon the domed surface in all directions4 ,the extreme flatness of the greater portion of the glacier surface--a fraction only of one degree--makes the engine extremely slow in starting1 but like all bodies which slide upon inclined planes1 the velocity of its movement is rapidly accelerated1 until a blizzard is developed whose vigor is unsurpassed by any elsewhere experienced4 ,illustration3 ,,fig4 #cab4--;,diagram to show the nature of the fixed glacial anticyclone above continental glaciers and the process by which their surface is shaped4 ,the effect of such centrifugal air currents above the glacier is to suck down the air of the upper currents in order to supply the void which soon tends to develop over the central portion of the glacier dome4 ,this downward vortex1 fed as it is by inward-blowing1 high-level currents1 and drained by outwardly directed surface currents1 is what is known as an anticyclone1 here fixed in position by the central embossment of the dome4 ,the air which descends in the central column is warmed by compression1 or adiabatically1 just as air is warmed which is forced into a rubber tire by the use of a pump4 ,the moisture congealed in the cirrus clouds floating in the uppermost layer of the convective zone1 is carried down in this vortex and first melted and in turn evaporated1 due to the adiabatic effect4 ,this fusion and evaporation of the ice by its transformation of latent1 to sensible1 heat1 in a measure counteracts1 and so retards1 the adiabatic elevation of temperature within the column4 ,eventually the warm air now charged with water vapor reaches the ice surface1 is at once chilled1 and its burden of moisture precipitated in the form of fine snow needles1 the so-called 8frost snow01 which in accompaniment to the sudden elevation of temperature is precipitated at the termination of a blizzard4 ,the warming of the air has1 however1 had the effect of damping as it were1 the engine stroke1 and1 as the process is continued1 to start a reverse or upward current within the chimney of the anticyclone4 ,the blizzard is thus suddenly ended in a precipitation of the snow1 which by changing the latent heat of condensation to sensible heat tends to increase this counter current4 ,illustration3 ,,fig4 #cac4--,snow deltas about the margins of the ,fan glacier outlet of ,greenland 7after ,chamberlin74 ,the glacier broom4--,during the calm which succeeds to the blizzard1 heat is once more abstracted from the surface air layer1 and a new outwardly directed engine stroke is begun4 ,the tempest which later develops acts as a gigantic centrifugal broom which sweeps out to the margins of the glacier all portions of the latest snowfall which have not become firmly attached to the ice surface4 ,the sweepings piled up about the margin of continental glaciers have been described as fringing glaciers1 or the glacial fringe4 ,the northern coast of ,greenland and ,grant ,land are bordered by a fringe of this nature 7plate #ad ,a1 and ,fig4 #cae1 p4 #bhh74 ,it is by the operation of the glacier broom that the inland ice is given its characteristic shield-like shape 7,fig4 #cab74 ,the granular nature of the snow carried by the wind is well brought out by the little snow deltas about the margins of ,greenland ice tongues 7,fig4 #cac74 ,obviously because of the presence of the vigorous anticyclone1 no snows such as nourish mountain glaciers can be precipitated upon continental glaciers except within a narrow marginal zone1 and1 as shown by ,nansen rock dust from the coastland ribbon and from the nunataks of ,greenland1 is carried by a few miles inside the western margin1 and not at all within the eastern4 ,illustration3 ,,fig4 #cad4--,sea ice of the ,arctic region in lat4 #hj #e ,n4 and long4 #b #eb ,e4 7after ,duc d',orleans74 ,field and pack ice4--,within polar regions the surface of the sea freezes during the long winter season1 the product being known as sea-ice or field-ice 7,fig4 #cad74 ,this ice cover may reach a thickness by direct freezing of eight or more feet1 and by breaking up and being crowded above and below neighboring fragments may increase to a considerably greater thickness4 ,ice thus crowded together and more or less crushed is described as pack ice or the pack4 ,the pack does not remain stationary but is continually drifting with the wind and tide1 first in one direction and then in another1 but with a general drift in the direction of the prevailing winds4 ,because of the vast dimensions of the pack1 the winds over widely separated parts may be contrary in direction1 and hence when currents blow toward each other or when the ice is forced against a land area1 it is locally crushed under mighty pressures and forced up into lines of hummocks--the so-called pressure ridges4 ,at other times1 when the winds of widely separated areas blow away from each other1 the pack is parted1 with the formation of lanes or leads of open water4 ,if seen in bird's-eye view the lines of hummocks would according to ,nansen be arranged like the meshes of a net having roughly squared angles and reaching to heights of #ae to #be1 rarely #cj1 feet above the general surface of the pack4 ,the ice within each mesh of the network is a floe1 which at the times of pressure is ground against its neighbors and variously shifted in position4 ,at the margin of the pack these floes become separated and float toward lower latitudes until they are melted4 ,the drift of the pack4--,the discovery of the drift in the ,arctic pack is a romantic chapter in the history of polar exploration1 and has furnished an example of faith in scientific reasoning and judgment which may well be compared with that of ,columbus4 ,the great figure in this later discovery is the ,norwegian explorer ,fridtjof ,nansen1 and to the final achievement the ill-fated ,jeannette expedition contributed an important part4 ,the ,jeannette carrying the ,american exploring expedition was in #ahgi caught in the pack to the northward of ,wrangel ,island 7,fig4 #cae71 and two years later was crushed by the ice and sunk to the northward of the ,new ,siberian ,islands4 ,in #ahhd various articles1 including a list of stores in the handwriting of the commander of the ,jeannette1 were picked up at ,julianehaab near the southern extremity of ,greenland but upon the western side of ,cape ,farewell4 ,nansen1 having carefully verified the facts1 concluded that the recovered articles could have found their way to ,julianehaab only by drifting in the pack across the polar sea1 and that at the longest only five years had been consumed in the transit4 ,after being separated from the pack the articles must have floated in the current which makes southward along the east coast of ,greenland and after doubling ,cape ,farewell flows northward upon the west coast4 ,it was clear that if they had come through ,smith ,sound they would inevitably have been found upon the other shore of ,baffin ,bay4 ,in confirmation of this view there was found at ,godthaab1 a short distance to the northward of ,julianehaab 7,fig4 #cae71 an ornamented ,alaskan 8throwing stick0 which probably came by the same route4 ,moreover1 large quantities of driftwood reach the shores of ,greenland which have clearly come from the ,siberian coast1 since the ,siberian larch has furnished the larger quantity4 ,illustration3 ,,fig4 #cae4--,map of the north polar regions1 showing the area of drift ice and the tracks of the ,jeannette and the ,fram 7compiled from various maps74 ,pinning his faith to these indubitable facts1 ,nansen built the ,fram in such a manner as to resist and elude the enormous pressures of the ice pack1 stocked her with provisions sufficient for five years1 and by allowing the vessel to be frozen into the pack north of the ,new ,siberian ,islands1 he consigned himself and his companions to the mercy of the elements4 ,the world knows the result as one of the most remarkable achievements in the long history of polar exploration4 ,the track of the ,fram1 charted in ,fig4 #cae1 considered in connection with that of the ,jeannette1 shows that the ,arctic pack drifts from ,bering ,sea westward until near the northeastern coast of ,greenland4 ,special casks were for experimental purposes fastened in the ice to the north of ,behring ,strait by ,melville and ,bryant1 and two of these were afterwards recovered1 the one near the ,north ,cape in northern ,norway1 and the other in northeastern ,iceland 7see map1 ,fig4 #cae74 ,peary's trips northward in #aijf and #aiji from the vicinity of ,smith ,sound have indicated that between the ,pole and the shores of ,greenland and ,grant ,land the drift is throughout to the eastward1 corresponding to the westerly wind4 ,upon this border the great area of ,arctic drift ice is in contact with great continental glaciers bordered by a glacier fringe4 ,admiral ,peary has shown that instead of consisting of frozen sea ice1 the pack is here made up of great floes from #bj to #ajj feet in thickness and that these have been derived from the glacier fringe4 ,whenever the blizzards blow off the inland ice from the south1 leads are opened at the margin of the fringe and may carry strips from the latter northward across the lead4 ,with favorable conditions these leads may be closed by thick sea ice so that with the occurrence of counter winds from the north they do not entirely return to their original position4 ,a continuance of this process may have resulted in the heavy floe ice to the northward of ,greenland1 which1 acting as an obstruction1 may have forced the thinner drift ice to keep on the ,european side of the ,arctic pack4 ,illustration3 ,,fig4 #caf4--,the shelf ice of ,coats ,land with the surrounding pack ice showing in the foreground 7after ,bruce74 ,about the ,antarctic continent there is a broad girdle of pack ice which1 while more indolent in its movements than the ,arctic pack1 has been shown by the expeditions of the ,belgica and the ,pourquoi-,pas to possess the same kind of shifting movements4 ,in the southern spring this pack floats northward and is to a large extent broken up and melted on reaching lower latitudes4 ,illustration3 ,,fig4 #cag4--,tidewater cliff at the front of a glacier tongue from which icebergs are born4 ,the ,antarctic shelf ice4--,it has been already pointed out that the inland ice of ,antarctica is in part at least surrounded by a thick snow and ice terrace floating upon the sea and rising to heights of more than #aej feet above it 7plate #ae ,b and ,fig4 #caf74 ,the visible portions of this shelf-ice are of stratified compact snow1 and the areas which have thus far been studied are found in bays from which dislodgment is less easily effected4 ,the origin of the shelf ice is believed to be a sea-ice which because not easily detached at the time of the spring 8break-up0 is thickened in succeeding seasons chiefly by the deposition of precipitated and drifted snow upon its surface1 so that it is bowed down under the weight and sunk to greater and greater depths in the water4 ,to some extent1 also1 it is fed upon its inner margin by overflow of glacier ice from the inland ice masses4 ,icebergs and snowbergs and the manner of their birth4--,greenland reveals in the character of its valleys the marks of a large subsidence of the continent--the serpentine inlets or fjords by which its coast is so deeply indented4 ,into the heads of these fjords the tongues from the inland ice descend generally to the sea level and below4 ,the glacier ice is thus directly attacked by the waves as well as melted in the water1 so that it terminates in the fjords in great cliffs of ice 7,fig4 #cag74 ,it is also believed to extend beneath the water surface as a long toe resting upon the bottom 7,fig4 #cai74 ,,plate #ae4 ,illustration3 ,a4 ,an ,antarctic ice foot with boat party landing 7after ,r4 ,f4 ,scott74 ,illustration3 ,b4 ,a near view of the front of the ,great ,ross ,barrier1 ,antarctica 7after ,r4 ,f4 ,scott74 ,illustration3 ,,fig4 #cah4--;,a ,greenlandic iceberg after a long journey in warm latitudes4 ,the exposed cliff is notched and undercut by the waves in the same manner as a rock cliff1 and the upper portions override the lower so that at frequent intervals small masses of ice from this front separate on crevasses1 and toppling over1 fall into the water with picturesque splashes4 ,such small bergs1 whose birth may be often seen at the cliff front of both the ,greenland and ,alaskan glaciers1 have little in common with those great floating islands of ice that are drifted by the winds until1 wasted to a fraction only of their former proportions1 they reach the lanes of transatlantic travel and become a serious menace to navigation 7,fig4 #cah74 ,illustration3 ,,fig4 #cai4--;,diagram showing one way in which northern icebergs may be born from the glacier tongue 7after ,russell74 ,northern icebergs of large dimensions are born either by the lifting of a separated portion of the extended glacier toe lying upon the bottom of the fjord1 or else they separate bodily from the cliff itself1 apparently where it reaches water sufficiently deep to float it4 ,in either case the buoyancy of the sea water plays a large rle in its separation4 ,if derived from the submerged glacier toe 7,fig4 #cai71 a loud noise is heard before any change is visible1 and an instant later the great mass of ice rises out of the water some distance away from the cliff1 lifting as it does so a great volume of water which pours off on all sides in thundering cascades and exposes at last a berg of the deepest sapphire blue4 ,the commotion produced in the fjord is prodigious1 and a vessel in close proximity is placed in jeopardy4 ,even larger bergs are sometimes seen to separate from the ice cliff1 in this case an instant before or simultaneously1 with a loud report1 but such bergs float away with comparatively little commotion in the water4 ,illustration3 ,,fig4 #cbj4--;,a northern iceberg surrounded by sea ice4 ,the icebergs of the south polar region are usually built upon a far grander scale than those of the ,arctic regions1 and are1 further1 both distinctly tabular in form and bounded by rectangular outlines 7,fig4 #cba74 ,whereas the large bergs of ,greenlandic origin are of ice and blue in color1 the tabular bergs of ,antarctica might better be described as snowbergs1 since they are of a blinding whiteness and their visible portions are either compacted snow or alternating thick layers of compact snow and thin ribbons of blue ice1 the latter thicker and more abundant toward the base4 ,all such bergs have been derived from the shelf ice and not from the inland ice itself4 ,blue icebergs which have been derived from the inland ice have been described from the one ,antarctic land that has been explored in which that ice descends directly to the sea4 ,illustration3 ,,fig4 #cba4--,tabular ,antarctic iceberg separating from the shelf ice 7after ,shackleton74 ,in both the northern and southern hemispheres those bergs which have floated into lower latitudes have suffered profound transformations4 ,their exposed surfaces have been melted in the sun1 washed by the rain1 and battered by the waves1 so that they lose their relatively simple forms but acquire rounded surfaces in place of the early angular ones 7,fig4 #cah1 p4 #bia74 ,sir ,john ,murray1 who had such extended opportunities of studying the southern icebergs from the deck of the ,challenger1 has thus described their beauties3 8,waves dash1 against the vertical faces of the floating ice island as against a rocky shore1 so that at the sea level they are first cut into ledges and gullies1 and then into caves and caverns of the most heavenly blue1 from out of which there comes the resounding roar of the ocean1 and into which the snow-white and other petrels may be seen to wing their way through guards of soldier-like penguins stationed at the entrances4 ,as these ice islands are slowly drifted by wind and current to the north1 they tilt1 turn and sometimes capsize1 and then submerged prongs and spits are thrown high into the air1 producing irregular pinnacled bergs higher1 possibly1 than the original table-shaped mass40 ,,reading ,,references ,,for ,,chapters ,,xx ,,and ,,xxi ,general3-- ,i4 ,c4 ,,russell4 ,glaciers of ,north ,america4 ,ginn1 ,boston1 #ahig1 pp4 #baj1 pls4 #bb4 ,,chamberlin and ,,salisbury4 ,geology1 vol4 #a1 pp4 #bcb-cjh4 ,h4 ,,hess4 ,die ,gletscher1 ,braunschweig1 #aijd1 pp4 #dbf 7illustrated74 ,,william ,h4 ,,hobbs4 ,characteristics of ,existing ,glaciers4 ,macmillan1 #aiaa1 pp4 #cja1 pls4 #cd4 ,special districts of mountain glaciers3-- ,,james ,d4 ,,forbes4 ,travels ,through the ,alps of ,savoy and other ,parts of the ,pennine ,chain with ,observations on the ,phenomena of ,glaciers4 ,edinburgh1 #ahde1 pp4 #def1 pls4 #i1 maps #b4 ,a4 ,,penck1 ,e4 ,,br,,ckner1 et ,l4 ,,du ,,pasquier4 ,le systme glaciare des alpes1 etc41 ,bull4 ,soc4 ,sc4 ,nat4 ,neuchtel1 vol4 #bb1 #ahid1 pp4 #hf4 ,e4 ,,richter4 ,die ,gletscher der ,ostalpen4 ,stuttgart1 #ahhh1 pp4 #cjf1 #g maps4 ,,james ,d4 ,,forbes4 ,norway and ,its ,glaciers1 etc4 ,edinburgh1 #ahec1 pp4 #cdi1 pls4 #aj1 map4 ,i4 ,c4 ,,russell4 ,existing ,glaciers of the ,united ,states1 #eth ,ann4 ,rept4 ,u4 ,s4 ,geol4 ,surv41 #ahhe1 pp4 #cjg-cee1 pls4 #cb-ee2 ,glaciers of ,mt4 ,ranier1 #ahth ,ann4 ,rept4 ,u4 ,s4 ,geol4 ,surv41 #ahih1 pp4 #cdi-dbc1 pls4 #fe-hb4 ,w4 ,h4 ,,sherzer4 ,glaciers of the ,canadian ,rockies and ,selkirks1 ,smith4 ,cont4 to ,knowl4 ,no4 #afib1 ,washington1 #aijg1 pp4 #ace1 pls4 #db4 ,h4 ,f4 ,,reid4 ,studies of ,muir ,glacier1 ,alaska1 ,nat4 ,geogr4 ,mag41 vol4 #d1 #ahib1 pp4 #ai-hd1 pls4 #a-af4 ,i4 ,c4 ,,russell4 ,malaspina ,glacier1 ,jour4 ,geol41 vol4 #a1 #ahic1 pp4 #bai-bde4 ,g4 ,k4 ,,gilbert4 ,harriman ,alaska ,expedition1 vol4 #c1 ,glaciers1 #aijd1 pp4 #bca1 pls4 #cg4 ,w4 ,m4 ,,conway4 ,climbing and ,exploration in the ,karakoram ,himalayas1 ,maps and ,scientific ,reports1 #ahid1 map sheets ,i-,,ii4 ,,fanny ,,bullock ,,workman and ,,william ,,hunter ,,workman4 ,the ,hispar ,glacier1 ,geogr4 ,jour41 vol4 #ce1 #aiaj1 pp4 #aje-acb1 #g pls4 and map4 ,the cycle of glaciation3-- ,,william ,h4 ,,hobbs4 ,the ,cycle of ,mountain ,glaciation1 ,geogr4 ,jour41 vol4 #cf1 #aiaj1 pp4 #adf-afc1 #bfh-bhd4 ,upper and lower cloud zones of the atmosphere3-- ,r4 ,,assmann1 ,a4 ,,berson1 and ,h4 ,,gross4 ,wissenschaftliche ,luftfahrten ausgefhrt vom deutschen ,verein zur ,frderung der ,luftschiffahrt in ,berlin1 #ahii-aijj1 #c vols4 ,e4 ,,gold and ,w4 ,a4 ,,harwood4 ,the ,present ,state of our ,knowledge of the ,upper ,atmosphere as ,obtained by the ,use of ,kites1 ,balloons1 and ,pilot-balloons1 ,rept4 ,brit4 ,assoc4 ,adv4 ,sci41 #aiji1 pp4 #a-ee4 ,w4 ,h4 ,,moore4 ,descriptive ,meteorology1 ,appleton1 ,new ,york1 #aiaj1 pp4 #ie-acf4 ,,william ,h4 ,,hobbs4 ,the ,pleistocene ,glaciation of ,north ,america ,viewed in the ,light of our ,knowledge of ,existing ,continental ,glaciers1 ,bull4 ,am4 ,geogr4 ,soc41 vol4 #db1 #aiaa1 pp4 #fdg-fej4 ,the continental glacier of ,greenland3-- ,f4 ,,nansen4 ,the ,first ,crossing of ,greenland1 #b vols1 ,longmans1 ,london1 #ahij 7the scientific results are contained in an appendix to volume #b1 pp4 #ddc-dig74 ,r4 ,e4 ,,peary4 ,a ,reconnaissance of the ,greenland ,inland ,ice1 ,jour4 ,am4 ,geogr4 ,soc41 vol4 #ai1 #ahhg1 pp4 #bfa-bhi2 ,journeys in ,north ,greenland1 ,geogr4 ,jour41 vol4 #aa1 #ahih1 pp4 #bac-bdj4 ,t4 ,c4 ,,chamberlin4 ,glacier ,studies in ,greenland1 ,jour4 ,geol41 vol4 #b1 #ahid1 pp4 #fdi-ffh1 #gfh-ghh1 vol4 #c1 pp4 #fa-fi1 #aih-bah1 #dfi-dhj1 #efe-ehb1 #ffh-fha1 #hcc-hdc1 vol4 #d1 pp4 #ehb-eib1 #gfi-haj1 vol4 #e1 pp4 #bbi-bde2 ,recent glacial studies in ,greenland 7,presidential address71 ,bull4 ,geol4 ,soc4 ,am41 vol4 #f1 #ahie1 pp4 #aii-bbj1 pls4 #c-aj4 ,r4 ,s4 ,,tarr4 ,the ,margin of the ,cornell ,glacier1 ,am4 ,geol41 vol4 #bj1 #ahig1 pp4 #aci-aef1 pls4 #f-ab4 ,r4 ,d4 ,,salisbury4 ,the ,greenland ,expedition of #ahie1 ,jour4 ,geol41 vol4 #c1 #ahie1 pp4 #hge-ijb4 ,e4 ,v4 ,,drygalski4 ,grnland ,expedition der ,gesellschaft fr ,erdkunde zu ,berlin #ahia-ahic1 ,berlin1 #ahig1 #b vols41 pp4 #eea and #ega1 pls4 #ec1 maps #aj4 ,,william ,h4 ,,hobbs4 ,characteristics of the ,inland ,ice of the ,arctic ,regions1 ,proc4 ,am4 ,phil4 ,soc41 vol4 #di1 #aiaj1 pp4 #eg-abi1 pls4 #bf-cj4 ,the ,antarctic continental glacier3-- ,r4 ,f4 ,,scott4 ,the ,voyage of the ,discovery4 ,london1 #b vols41 #aije4 ,e4 ,h4 ,,shackleton4 ,the ,heart of the ,antarctic4 ,london1 #b vols41 #aiaj4 ,e4 ,,von ,,drygalski4 ,zum ,kontinent des eisigen ,sdens1 ,deutsche ,sdpolar-,expedition1 ,fahrten und ,forschungen des 8,gauss01 #aija-aijc1 ,berlin1 #aijd1 pp4 #ffh1 pls4 #ba4 ,,otto ,,nordenski,,ld and ,j4 ,s4 ,,andersson4 ,antarctica or ,two ,years ,amongst the ,ice of the ,south ,pole4 ,london1 #aije1 pp4 #fjh1 illustrated4 ,e4 ,,philippi4 ,ueber die fnf ,landeis-,expeditionen1 etc41 ,zeit4 f4 ,gletscherk41 vol4 #b1 #aijg1 pp4 #a-ba4 ,nourishment of continental glaciers3-- ,,william ,h4 ,,hobbs4 ,characteristics of the ,inland ,ice of the ,arctic ,regions1 ,proc4 ,am4 ,phil4 ,soc41 vol4 #di1 #aiaj1 pp4 #if-aaj2 ,the ,ice ,masses on and about the ,antarctic ,continent1 ,zeit4 f4 ,gletscherk41 vol4 #e1 #aiaj1 pp4 #ajg-abj2 ,characteristics of ,existing ,glaciers4 ,new ,york1 #aiaa1 pp4 #adc-afa1 #bfa-bhi4 ,pleistocene ,glaciation of ,north ,america ,viewed in the ,light of our ,knowledge of ,existing ,continental ,glaciers1 ,bull4 ,am4 ,geogr4 ,soc41 vol4 #dc1 #aiaa1 pp4 #fda-fei4 ,field and pack ice3-- ,,emma ,,de ,,long4 ,the ,voyage of the ,jeannette1 the ship and ice journals of ,george ,w4 de ,long1 etc4 ,berlin1 #ahhd1 #b vols41 chart in back of vol4 #a4 ,,robert ,e4 ,,peary4 ,the ,discovery of the ,north ,pole 7for further references on both sea and pack ice and ,antarctic shelf ice1 consult ,hobbs's ,characteristics of ,existing ,glaciers1 pp4 #baj-bac1 #bdb-bdd74 ,icebergs3-- ,,wyville ,,thomson4 ,challenger ,report1 ,narrative1 vol4 #a1 #ahfe1 ,pt4 i1 pp4 #dca-dcb1 pls4 ,b-,d4 ,i4 ,c4 ,,russell4 ,an ,expedition to ,mt4 ,st4 ,elias1 ,nat4 ,geogr4 ,mag41 vol4 #c1 #ahia1 pp4 #aja-ajb1 fig4 #a4 ,h4 ,f4 ,,reid4 ,studies of ,muir ,glacier1 ,alaska1 ibid41 vol4 #d1 #ahib1 pp4 #dg-dh4 ,e4 ,,von ,,drygalski4 ,grnland-,expedition1 etc41 vol4 #a1 pp4 #cfg-djd4 ,m4 ,c4 ,,engell4 ,ueber die ,entstehung der ,eisberge1 ,zeit4 f4 ,gletscherk41 vol4 #e1 #aiaj1 pp4 #aab-acb4 ,,chapter ,,xxii ,,the ,,continental ,,glaciers ,,of ,,the 8,,ice ,,age0 ,earlier cycles of glaciation4--,our study of the rocks composing the outermost shell of the lithosphere tells us that in at least three widely separated periods of its history the earth has passed through cycles of glaciation during which considerable portions of its surface have been submerged beneath continental glaciers4 ,the latest of these occurred in the yesterday of geology and has often been referred to as the 8ice age01 because until quite recently it was supposed to be the only one of which a record was preserved4 ,illustration3 ,,fig4 #cbb4--,map of the globe showing the areas which were covered by the continental glaciers of the so-called 8ice-age0 of the ,pleistocene period4 ,the arrows show the directions of the centrifugal air currents in the fixed anticyclones above the glaciers4 ,illustration3 ,,fig4 #cbc4--;,glaciated granite bowlder which has weathered out of a moraine of ,permo-,carboniferous age upon which it rests4 ,south ,australia 7after ,howchin74 ,this latest ice age represents four complete cycles of glaciation1 for it is believed that the continental ice developed and then completely disappeared during a period of mild climate before the next glacier had formed in its place1 and that this alternation of climates was no less than three times repeated1 making four cycles in all4 ,at nearly or quite the same time ice masses developed in northern ,north ,america and in northern ,europe1 the embossments of the ice domes being located in ,canada and in ,scandinavia respectively 7,fig4 #cbb74 ,there appears to have been at this time no extensive glaciation of the southern hemisphere1 though in the next earlier of the known great periods of glaciation--the so-called ,permo-,carboniferous--it was the southern hemisphere1 and not the northern1 that was affected 7,fig4 #cbc and ,fig4 #cjd1 p4 #bgf74 ,from the still earlier glacial period our data are naturally much more meager1 but it seems probable that it was characterized by glaciated areas within both the northern and the southern hemispheres4 ,illustration3 ,,fig4 #cbd4--,map to show the glaciated and nonglaciated regions of ,north ,america 7after ,salisbury and ,atwood74 ,contrast of the glaciated and nonglaciated regions4--,since we have now studied in brief outline the characteristics of the existing continental glaciers1 we are in a position to review the evidences of former glaciers1 the records of which exist in their carvings1 their gravings1 and their deposits4 ,illustration3 ,,fig4 #cbe4--,map of the glaciated and nonglaciated areas of northern ,europe4 ,the strongly marked morainal belts respectively south and north of the ,baltic depression represent halting places in the retreat of the latest continental glacier 7compiled from maps by ,penck and ,leverett74 ,an observant person familiar with the aspects of ,nature in both the northern and southern portions of the central and eastern ,united ,states must have noticed that the general courses of the ,ohio and ,missouri rivers define a somewhat marked common border of areas which in most respects are sharply contrasted 7,fig4 #cbd74 ,hardly less striking is the contrast between the glaciated and the nonglaciated regions upon the continent of ,europe 7,fig4 #cbe74 ,it is the northern of the two areas which in each case reveals the characteristic evidences of glaciation1 while there is entire absence of such marks to the southward of the common border4 ,within the ,american glaciated region there is1 however1 an area surrounded like an island1 and within this district 7,fig4 #cbd7 none of the marks characteristic of glaciation are to be found4 ,this area is usually referred to as the 8driftless area01 and occupies portions of the states of ,wisconsin1 ,illinois1 ,minnesota1 and ,iowa4 ,even better than the area to the southward of the ,ohio and ,missouri rivers1 it permits of a comparison of the nonglaciated with the drift-covered region4 ,illustration3 ,,fig4 #cbf4--8,stand ,rock0 near the 8,dells0 of the ,wisconsin river1 an unstable erosion remnant characteristic of the driftless area of ,north ,america 7after ,salisbury and ,atwood74 ,the 8driftless area40--,within this district1 then1 we have preserved for our study a landscape which remains largely as it was before the several ice invasions had so profoundly transformed the general surface of the surrounding country4 ,speaking broadly1 we may say that it represents an uplifted and in part dissected plain1 which to the south and east particularly reveals the character of nearly mature river erosion 7,fig4 #agg1 p4 #agj74 ,the rock surface is here everywhere mantled by decomposed and disintegrated rock residues of local origin4 ,the soluble constituents of the rock1 such as the carbonates1 have been removed by the process of leaching1 so that the clays no longer effervesce when treated with dilute mineral acid4 ,wherever favored by joints and by an alternation of harder and softer rock layers1 picturesque unstable erosion remnants or 8chimneys0 may stand out in relief 7,fig4 #cbf74 ,furthermore1 the driftless area is throughout perfectly drained--it is without lakes or swamps--since all valleys are characterized throughout by forward grades4 ,the side valleys enter the main valleys as do the branches a tree trunk2 in other words1 the drainage is described as arborescent4 ,in so far as any portions of a plane surface now remain in the landscape1 they are found at the highest levels 7plate #af ,a74 ,the topography is thus the result of a partial removal by erosion of an upland and may be described as incised topography4 ,nowhere within the area are there found rock masses foreign to the region1 but all mantle rock is the weathered product of the underlying ledges4 ,,plate #af4 ,illustration3 ,a4 ,incised topography within the 8driftless area0 7,u4 ,s4 ,geol4 ,survey74 ,illustration3 ,b4 ,built-up topography within glaciated region 7,u4 ,s4 ,geol4 ,survey74 ,characteristics of the glaciated regions4--,the topography of the driftless area has been described as incised1 because due to the partial destruction of an uplifted plain2 and this surface is1 moreover1 perfectly drained4 ,the characteristic topography of the 8drift0 areas is by contrast built up2 that is to say1 the features of the region instead of being carved out of a plain are the result of molding by the process of deposition 7plate #af ,b74 ,in so far as a plane is recognizable1 it is to be found not at the highest1 but at the lowest level--a surface represented largely by swamps and lakes--and above this plain rise the characteristic rounded hills of various types which have been built up through deposition4 ,the process by which this has been accomplished is one easy to comprehend4 ,as it invaded the region1 the glacier planed away beneath its marginal zone all weathered mantle rock and deposited the planings within the hollows of the surface 7,fig4 #cbg74 ,the effect has been to flatten out the prexisting irregularities of the surface1 and to yield at first a gently undulating plain upon which are many undrained areas and a haphazard system of drainage 7,fig4 #cbh74 ,all unstable erosion remnants1 such as now are to be found within the driftless area1 were the first to be toppled over by the invading glacier1 and in their place there is left at best only rounded and polished 8shoulders0 of hard and unweathered rock--the well-known roches moutonnes4 ,illustration3 ,,fig4 #cbg4--;,diagram showing the manner in which a continental glacier obliterates existing valleys 7after ,tarr74 ,the glacier gravings4--,the tools with which the glacier works are never quite evenly edged1 and instead of an in all respects perfect polish upon the rock pavement1 there are left furrowings1 gougings1 and scratches4 ,of whatever sort1 these scorings indicate the lines of ice movement and are thus indubitable records graven upon the rock floor4 ,when mapped over wide areas1 a most interesting picture is presented to our view1 and one which supplements in an important way the studies of existing continental glaciers 7,fig4 #ccd1 p4 #cjh1 and ,fig4 #ccf1 p4 #cab74 ,illustration3 ,,fig4 #cbh4--,lake and marsh district in northern ,wisconsin1 the effect of glacial deposition in former valleys 7after ,fairbanks74 ,it has been customary to think of the glacier as everywhere eroding its bed1 although the only warrant for assuming degradation by flow of the ice is restricted to the marginal zone1 since here only is there an appreciable surface grade likely to induce flow4 ,both upon the advance and again during the retreat of a glacier1 all parts of the area overridden must be subjected to this action4 ,heretofore pictured in the imagination as enlarged models of ,alpine glaciers1 the vast ice mantles were conceived to have spread out over the country as the result of a kind of viscous flow like that of molasses poured upon a flat surface in cold weather4 ,the maximum thickness of the latest ,american glacier of the ice age has been assumed to have been perhaps #aj1jjj feet near the summit of its dome in central ,labrador4 ,from this point it was assumed that the ice traveled southward up the northern slope of the ,laurentian divide in ,canada1 and thence to the ,ohio river1 a distance of over #acjj miles4 ,if such a mantle of ice be represented in its natural proportions in vertical section1 to cover the distance from center to margin we may use a line six inches in length1 and only #a_/ajj of an inch thick4 ,upon a reduced scale these proportions are given in ,fig4 #cbi4 ,obviously the force of gravity acting within a viscous mass of such proportions would be incompetent to effect a transfer of material from the center to the periphery1 even though the thickness should be doubled or trebled4 ,yet until the fixed glacial anticyclone above the glacier had been proven and its efficiency as a broom recognized1 no other hypothesis than that of viscous flow had been offered in explanation4 ,the inherited conception of a universal plucking and abrasion on the bed of the glacier is thus made untenable and can be accepted for the marginal portion only4 ,illustration3 ,,fig4 #cbi4--;,cross section in approximate natural proportions of the latest ,north ,american continental glacier of ,pleistocene age from its center to its margin4 ,not only do the rock scorings show the lines of ice movement1 but the directions as well may often be read upon the rock4 ,wherever there are pronounced irregularities of surface still existing on the pavement1 these are generally found to have gradual slopes upon the side from which the ice came1 and relatively steep falls upon the lee or 8pluck0 side4 ,if1 however1 we consider the irregularities of smaller size1 the unsymmetrical slopes of these protruding portions of the floor are found to be reversed--it is the steep slope which faces the oncoming ice and the flatter slope which is upon the lee side4 ,such minor projections upon the floor usually have their origin in some harder nodule which deflects the abrading tools and causes them to pass1 some on the one side and some upon the other4 ,by this process a staple-shaped groove comes to surround the nodule1 leaving an unsymmetrical elevated ridge within1 which is steep upon the stoss side and slopes gently away to leeward4 ,illustration3 ,,fig4 #ccj4--,limestone surface at ,sibley1 ,michigan4 ,younger records over older--the glacier palimpsest4--,many important historical facts have been recovered from the largely effaced writing upon ancient palimpsests1 or parchments upon which an earlier record has been intentionally erased to make room for another4 ,in the gravings upon the glacier pavement1 earlier records have been likewise in large part effaced by later1 though in favorable localities the two may be read together4 ,thus1 as an example1 at the great limestone quarries of ,sibley1 in southeastern ,michigan1 the glaciated rock surface wherever stripped of its drift cover is a smoothly polished and relatively level floor with stri which are directed west-northwest4 ,beneath this general surface there are1 however1 a number of elliptical depressions which have their longer axes directed south-southwest1 one being from twenty-five to thirty feet long and some ten feet in depth 7,fig4 #ccj74 ,these boat-shaped depressions are clearly the remnants of an earlier more undulating surface which the latest glacier has in large part planed away1 since the bottoms of the depressions are no less perfectly glaciated but have their stri directed in general near the longer axis of the troughs4 ,palimpsest-like there are here also the records of more than one graving4 ,illustration3 ,,fig4 #cca4--,map to show the outcroppings of peculiar rock types in the region of the ,great ,lakes1 and some of the localities where 8float copper0 has been collected 7float copper localities after ,salisbury74 ,the dispersion of the drift4--,long before the 8ice age0 had been conceived in the minds of ,agassiz and his contemporaries1 it had been remarked that scattered over the ,north ,german plain were rounded fragments of rock which could not possibly have been derived from their own neighborhood but which could be matched with the great masses of red granite in ,sweden well known as the 8,swedish granite40 ,buckland1 an ,english geologist1 had in #ahae accounted for such 8erratic0 blocks of his own country1 here of ,scotch granite1 by calling in the deluge of ,noah2 but in the late thirties of the nineteenth century1 ,sir ,charles ,lyell1 with the results of ,english ,arctic explorers in mind1 claimed that such traveled blocks had been transported by icebergs emanating from the polar regions4 ,a relic of ,buckland's earlier view we have in the word 8diluvium0 still occasionally used in ,germany for glacier transported materials2 while the term 8drift0 still remains in common use to recall ,lyell's iceberg hypothesis1 even though the original meaning of the term has been abandoned4 ,drift is now a generic term and refers to all deposits directly or indirectly referable to the continental glaciers4 ,in general the place of derivation of the glacial drift may be said to be some point more distant from and within the former ice margin at the time when it was deposited2 in other words1 the dispersion of the drift was centrifugal with reference to the glacier4 ,illustration3 ,,fig4 #ccb4--,map of the 8bowlder train0 from ,iron ,hill1 ,r4 ,i4 7based upon ,shaler's map1 but with the directions of glacial stri added74 ,wherever rocks of unusual and therefore easily recognizable character can be shown to occur in place and with but limited areas1 the dispersion of such material is easy to trace4 ,the areas of red ,swedish and ,scotch granite have been used to follow out in a broad way the dispersion of drift over northern ,europe4 ,within the region of the ,great ,lakes of ,north ,america are areas of limited size which are occupied by well marked rock types1 so that the journeyings of their fragments with the continental glacier can be mapped with some care4 ,upon the northern shore of ,georgian ,bay occurs the beautiful jasper conglomerate1 whose bright red pebbles in their white quartz field attract such general notice4 ,at ,ishpeming in the northern peninsula of ,michigan is found the equally beautiful jaspilite composed of puckered alternating layers of black hematite and red jasper4 ,on ,keweenaw ,peninsula1 which protrudes into ,lake ,superior from its southern shore1 is found that remarkable occurrence of native copper within a series of igneous rocks of varied types and colors4 ,fragments of this copper1 some weighing several hundreds of pounds each and masked in a coat of green malachite1 have under the name of 8drift0 or 8float0 copper been collected at many localities within a broad 8fan0 of dispersal extending almost to the very limits of glaciation 7,fig4 #cca74 ,some miles to the north of ,providence in ,rhode ,island there is a hill known as ,iron ,hill composed in large part of black magnetite rock1 the so-called ,cumberlandite4 ,from this hill as an apex there has been dispersed a great quantity of the rock distributed as a well marked 8bowlder train0 within which the size and the frequency of the dispersed bowlders is in inverse ratio to the distance from the parent ledge 7,fig4 #ccb74 ,similar though less perfect trains of bowlders are found on the lee side of most projecting masses of resistant rocks within the area of the drift4 ,large bowlders when left upon a ledge of notably different appearance easily attract attention1 and have been described as 8perched bowlders40 ,resting as they sometimes do upon a relatively small area1 they may be nicely balanced and thus easily given a pendular or rocking motion4 ,such 8rocking stones0 are common enough1 especially among the ,new ,england hills 7plate #ag ,b74 ,many such bowlders have made somewhat remarkable peregrinations with many interruptions1 having been carried first in one direction by an earlier glacier to be later transported in wholly different directions at the time of new ice invasions4 ,,plate #ag4 ,illustration3 ,a4 ,soled glacial bowlders which show differently directed stri upon the same facet4 ,illustration3 ,b4 ,perched bowlder upon a striated ledge of different rock type1 ,bronx ,park1 ,new ,york 7after ,lungstedt74 ,illustration3 ,c4 ,characteristic knob and basin surface of a moraine4 ,the diamonds of the drift4--,of considerable popular1 even if not economic1 interest are the diamonds which have been sown in the drift after long and interrupted journeyings with the ice from some unknown home far to the northward in the wilderness of ,canada4 ,the first stone to be discovered was taken by workmen from a well opening near the little town of ,eagle in ,wisconsin in the year #ahgf4 ,its nature not being known1 it remained where it was found as a curiosity only1 and it was not until #ahhc that it was taken to ,milwaukee and sold to a jeweler equally ignorant of its value1 and for the merely nominal sum of one dollar4 ,later recognized as a diamond of the unusual weight of sixteen carats1 it was sold to the ,tiffanys and became the cause of a long litigation which did not end until the ,supreme ,court of ,wisconsin had decided that the ,milwaukee jeweler1 and not the finder1 was entitled to the price of the stone1 since he had been ignorant of its value at the time of purchase4 ,illustration3 ,,fig4 #ccc4--,shapes and approximate natural sizes of some of the more important diamonds from the ,great ,lakes region of the ,united ,states4 ,in order from left to right these figures represent the ,eagle diamond of sixteen carats1 the ,saukville diamond of six and one half carats1 the ,milford diamond of six carats1 the ,oregon diamond of four carats1 and the ,burlington diamond of a little over two carats4 ,an even larger diamond1 of twenty-one carats weight1 was found at ,kohlsville1 and smaller ones at ,oregon1 ,saukville1 ,burlington1 and ,plum ,creek in the state of ,wisconsin2 at ,dowagiac in ,michigan2 at ,milford in ,ohio1 and in ,morgan and ,brown counties in ,indiana4 ,the appearance of some of the larger stones in their natural size and shape may be seen in ,fig4 #ccc4 ,while the number of the diamonds sown in the drift is undoubtedly large1 their dispersion is such that it is little likely they can be profitably recovered4 ,the distribution of the localities at which stones have thus far been found is set forth upon ,fig4 #ccd4 ,obviously those that have been found are the ones of larger size1 since these only attract attention4 ,in #ahic1 when the finding of the ,oregon stone drew attention to these denizens of the drift1 the writer prophesied that other stones would occasionally be discovered under essentially the same conditions1 and such discoveries are certain to continue in the future4 ,illustration3 ,,fig4 #ccd4--;,glacial map of a portion of the ,great ,lakes region1 showing the unglaciated area and the areas of older and newer drift4 ,the driftless area1 the moraines of the later ice invasion1 and the distribution of diamond localities upon the latter are also shown4 ,with the aid of the directions of stri some attempt has been made to indicate the probable tracks of more important diamonds1 which tracks converge in the direction of the ,labrador peninsula4 ,tabulated comparison of the glaciated and nonglaciated regions4--,it will now be profitable to sum up in parallel columns the contrasted peculiarities of the glaciated and the unglaciated regions4 ,,unglaciated ,,region ,,glaciated ,,region ,,topography ,the topography is destructional2 ,the topography is constructional2 the remnants of a plain are found the remnants of a plain are found at the highest levels or upon the at the lowest levels in lakes and hill tops2 hills are carved out swamps2 hills are molded above a of a high plain2 unstable erosion plain in characteristic forms2 no remnants are characteristic4 unstable erosion remnants1 but only rounded shoulders of rock4 ,,drainage ,the area is completely drained1 ,the area includes undrained and the drainage network is areas1--lakes and swamps1--and arborescent4 the drainage system is haphazard4 ,,rock ,,mantle ,the exposed rock is decomposed ,no decomposed or disintegrated and disintegrated to a rock is 8in place01 but only considerable depth2 it is all of hard1 fresh surface2 loose rock local derivation and hence of few material is all foreign and of many types--homogeneous2 the fragments sizes and types--heterogeneous2 are angular2 soils are leached and rock bowlders and pebbles are hence do not contain carbonates4 faceted and polished as well as striated1 usually in several directions upon each facet2 soils are rock flour--the grist of the glacial mill4 ,,rock ,,surface ,rock surface is rough and ,rock surface is planed or grooved1 irregular4 and polished4 ,shows glacial stri4 ,unassorted and assorted drift4--,the drift is of two distinct types2 namely1 that deposited directly by the glacier1 which is without stratification1 or unassorted2 and that deposited by water flowing either beneath or from the ice1 and this like most fluid deposited material is assorted or stratified4 ,the unassorted material is described as till1 or sometimes as 8bowlder clay02 the assorted is sand or gravel1 sometimes with small included bowlders1 and is described as kame gravel4 ,to recall the parts which both the glacier and the streams have played in its deposition1 all water-deposited materials in connection with glaciers are called fluvio-glacial4 ,illustration3 ,,fig4 #cce4--,section in coarse till4 ,note the range in size of the materials1 the lack of stratification1 and the 8soled0 form of the bowlders4 ,till is1 then1 characterized by a noteworthy lack of homogeneity1 both as regards the size and the composition of its constituent parts4 ,as many as twenty different rock types of varied textures and colors may sometimes be found in a single exposure of this material1 and the entire gamut is run from the finest rock flour upon the one hand to bowlders whose diameter may be measured in feet 7,fig4 #cce74 ,in contrast with those derived by ordinary stream action1 the pebbles and bowlders of the till are faceted or 8soled01 and usually show striations upon their faces4 ,if a number of pebbles are examined1 some at least are sure to be found with striations in more than one direction upon a single facet4 ,as a criterion for the discrimination of the material this may be an important mark to be made use of to distinguish in special cases from rock fragments derived by brecciation and slickensiding and distributed by the torrents of arid and semiarid regions4 ,inasmuch as the capacity of ice for handling large masses is greater than that of water1 assorted drift is in general less coarse1 and1 as its name implies1 it is also stratified4 ,from ordinary stream gravels1 the kame gravels are distinguished by the form of their pebbles1 which are generally faceted and in some cases striated4 ,in proportion1 however1 as the materials are much worked over by the water1 the angles between pebble faces become rounded and the original shapes considerably masked4 ,features into which the drift is molded4--,though the prexisting valleys were first filled in by drift materials1 thus reducing the accent of the relief1 a continuation of the same process resulted in the superimposition of features of characteristic shapes upon the imperfectly evened surface of the earlier stages4 ,these features belong to several different types1 according as they were built up outside of1 at and upon1 or within the glacier margin4 ,the extra-marginal deposits are described as outwash plains or aprons1 or sometimes as valley trains2 the marginal are either moraines or kames2 while within the border were formed the till plain or ground moraine1 and1 locally also1 the drumlin and the esker or os4 ,these characteristic features are with few exceptions to be found only within the area covered by the latest of the ice invasions4 ,for the earlier ones1 so much time has now elapsed that the effect of weathering1 wash1 and stream erosion has been such that few of the features are recognizable4 ,marginal and extra-marginal features are extended in the direction of the margin or1 in other words1 perpendicular to the local ice movement2 while the intra-marginal deposits are as noteworthy for being perpendicular to the margin1 or in correspondence with the direction of local ice movement4 ,each of these features possesses characteristic marks in its form1 its size1 proportions1 surface molding and orientation1 as well as in its constituent materials4 ,it should perhaps be pointed out that the existing continental glaciers1 being in high latitudes1 work upon rock materials which have been subjected to different weathering processes from those characteristic of temperate latitudes4 ,moreover1 the melting of the ,pleistocene glaciers having taken place in relatively low latitudes1 larger quantities of rock dbris were probably released from the ice during the time of definite climatic changes1 and hence heavier drift accumulations have for both of these reasons resulted4 ,marginal or 8kettle0 moraines4--,wherever for a protracted period the margin of the glacier was halted1 considerable deposits of drift were built up at the ice margin4 ,these accumulations form1 however1 not only about the margin1 but upon the ice surface as well2 in part due to materials collected from melting down of the surface1 and in part by the upturning of ice layers near the margin 7see ante1 p4 #bgg74 ,illustration3 ,,fig4 #ccf4--,sketch map of portions of ,michigan1 ,ohio1 and ,indiana1 showing the festooned outlines of the moraines about the former ice lobes1 and the directions of ice movement as determined by the stri upon the rock pavement 7after ,leverett74 ,an important rle is played by the thaw water which emerges at the ice margin1 especially within the rentrants or recesses of the outline4 ,the materials of moraines are1 therefore1 till with large local deposits of kame gravel1 and these form in a series of ridges corresponding to the temporary positions of the ice front4 ,their width may range from a few rods to a few miles1 their height may reach a hundred feet or more1 and they stretch across the country for distances of hundreds or even thousands of miles1 looped in arcs or scallops which are always convex outward and which meet in sharp cusps that in a general way point toward the embossment of the former glacier 7,fig4 #ccd1 p4 #cjh1 and ,fig4 #ccf74 ,these festoons of the moraines outline the ice lobes of the latest ice invasion1 which in ,north ,america were centered over the depressions now occupied by the ,laurentian lakes4 ,there was1 thus1 a ,lake ,superior lobe1 a ,lake ,michigan lobe1 etc4 ,with the aid of these moraine maps we may thus in imagination picture in broad lines the frontal contours of the earlier glaciers4 ,at specially favorable localities where the ice front has crossed a deep valley at the edge of the ,driftless ,area1 we may1 even in a rough way1 measure the slope of the ice face4 ,thus near ,devils ,lake in southern ,wisconsin the terminal moraine crosses the former valley of the ,wisconsin ,river1 and in so doing has dropped a distance of about four hundred feet within the distance of a half mile or thereabouts 7,fig4 #ccg74 ,the characteristic surface of the marginal moraine is responsible for the name 8kettle0 moraine so generally applied to it4 ,the 8kettles0 are roughly circular1 undrained basins which lie among hummocks or knobs1 so that the surface has often been referred to as 8knob and basin0 topography 7plate #ag ,c74 ,illustration3 ,,fig4 #ccg4--,map of the vicinity of ,devils ,lake1 ,wisconsin1 located within a rentrant of the 8kettle0 moraine upon the margin of the ,driftless ,area4 ,the lake lies within an earlier channel of the ,wisconsin ,river which has been blocked at both ends1 first by the glacier and later by its moraine4 ,the stippled area upon the heights and next the moraine represents the clay deposits of a former lake 7based on map by ,salisbury and ,atwood74 ,illustration3 ,,fig4 #cch4--,moraine with outwash apron in front1 the latter in part eroded by a river4 ,westergtland1 ,sweden 7after ,h4 ,munthe74 ,illustration3 ,,fig4 #cci4--;,fosse between an outwash plain 7in the foreground7 and the moraine1 which rises to the left in the middle distance4 ,ann ,arbor1 ,michigan4 ,kames4--,within rentrants or recesses of the ice margin the drift deposits were especially heavy1 so that high hills of hummocky surface have been built up1 which are described as kames4 ,most of the higher drift hills have this origin4 ,they rarely have any principal extension along a single direction1 but are composed in large part of assorted materials4 ,in contrast with other portions of the morainal ridges they lack the prominent basins known as kettles4 ,other kames are high hills of assorted materials not in direct association with moraines and believed to have been built up beneath glacier wells or mills 7p4 #bgh74 ,outwash plains4--,upon the outer margin of the moraine is generally to be found a plain of glacial 8outwash0 composed of sand or gravel deposited by the braided streams 7,fig4 #cjh1 p4 #bhj7 flowing from the glacier margin4 ,such plains1 while notably flat 7,fig4 #cch71 slope gently away from the moraine4 ,between the outwash plain and the moraine there is sometimes found a pit1 or fosse 7,fig4 #cji1 p4 #bha71 where a part of the ice front was in part buried in its own outwash 7,fig4 #cci74 ,illustration3 ,,fig4 #cdj4--,view looking along an esker in southern ,maine 7after ,stone74 ,pitted plains and interlobate moraines4--,where glacial outwash is concentrated within a long and narrow rentrant1 separating glacial lobes1 strips of high plain are sometimes built up which overtop the other glacial deposits of the district4 ,the sand and gravel which compose such plains have a surface which is pitted by numerous deep and more or less circular lakes1 so that the term 8pitted plain0 has been applied to them4 ,the surface of such a plain steadily rises toward its highest point in the angle between the ice lobes4 ,though consisting almost entirely of assorted materials1 and built up largely without the ice margins1 such gently sloping pitted platforms are described as interlobate moraines4 ,upon a topographic map the course of such an interlobate moraine may often be followed by the belts of small pit lakes 7see ,fig4 #ccf74 ,illustration3 ,,fig4 #cda4--,outline map showing the eskers of ,finland trending southeasterly toward the festooned moraines at the margin of the ice4 ,the characteristic lakes of a glaciated region appear behind the moraines 7after ,j4 ,j4 ,sederholm74 ,illustration3 ,,fig4 #cdb4--,small sketch maps showing the relationships in size1 proportions1 and orientation of drumlins and eskers in southern ,wisconsin4 ,the eskers are in solid black 7after ,alden74 ,eskers4--,intra-morainal features1 or those developed beneath the glacier but relatively near its margin1 include the 8serpentine kame01 esker1 or1 as it is called in ,scandinavia1 the os 7plural osar7 7,fig4 #cdj74 ,these diminutive ridges have a width seldom exceeding a few rods1 and a height a few tens of feet at most1 but with slightly sinuous undulations they may be followed for tens or even hundreds of miles in the general direction of the local ice movement 7,fig4 #cda74 ,they are composed of poorly stratified1 thick-bedded sands1 gravels1 and 8worked over0 materials1 and are believed to have been formed by subglacial rivers which flowed in tunnels beneath the ice4 ,inasmuch as the deposits were piled against the ice walls1 the beds were disturbed at the sides when these walls disappeared1 and the stratification1 which was somewhat arched in the beginning1 has been altered by sliding at both margins4 ,as already stated1 eskers have not a general distribution within the glaciated area1 but are often found in great numbers at specially favored localities4 ,formed as they are beneath the ice1 it is believed that many have their materials redistributed so soon as uncovered at the glacier margin1 because of the vigorous drainage there4 ,they are thus to be found only at those favored localities where for some reason border drainage is less active1 or where the ice ended in a body of water4 ,drumlins4--,a peculiar type of small hill likewise found behind the marginal moraine in certain favored districts has the form of an inverted boat or canoe1 the long axis of which is parallel to the direction of ice movement1 as is that of the esker 7,fig4 #cdb74 ,unlike the esker1 this type of hill is composed of till1 and from being found in ,ireland it is called a drumlin1 the ,irish word meaning a little hill 7,fig4 #cdc74 ,drumlins are usually found in groups more or less radial and not far behind the outermost moraine1 to which their radiating axes are perpendicular4 ,the manner of their formation is involved in some uncertainty1 but it is clear that they have been formed beneath the margin of the glacier1 and have been given their shape by the last glacier which occupied the district4 ,the mutual relationships of nearly all the molded features resulting from continental glaciation may be read from ,fig4 #cdd4 ,illustration3 ,,fig4 #cdc4--,view of a drumlin1 showing an opening in the till4 ,near ,boston1 ,massachusetts 7after ,shaler and ,davis74 ,the shelf ice of the ice age4--,shelf ice1 such as we have become familiar with in ,antarctica as a marginal snow-ice terrace floating upon the sea1 no doubt existed during the ice age above the ,gulf of ,maine 7see ,fig4 #cbd1 p4 #bih71 and perhaps also over the deep sea to the westward of ,scotland4 ,though the inland ice probably covered the ,north ,sea1 and upon the ,american side of the ,atlantic the ,long ,island ,sound1 both these basins are so shallow that the ice must have rested upon the bottom1 for neither is of sufficient depth to entirely submerge one of the higher ,european cathedrals4 ,illustration3 ,,fig4 #cdd4--,outline map of the front of the ,green ,bay lobe of the latest continental glacier of the ,united ,states4 ,drumlins in solid black1 moraines with diagonal hachure1 outwash plains and the till plain or ground moraine in white 7after ,alden74 ,character profiles4--,all surface features referable to continental glaciers1 whether carved in rock or molded from loose materials1 present gently flowing outlines which are convex upward 7,fig4 #cde74 ,the only definite features carved from rock are the roches moutonnes1 with their flattened shoulders1 while the hillocks upon moraines and kames1 and the drumlins as well1 approximate to the same profile4 ,the esker in its cross sections is much the same1 though its serpentine extension may offer some variety of curvature when viewed from higher levels4 ,illustration3 ,,fig4 #cde4--;,character profiles referable to continental glacier4 ,,reading ,,references ,,for ,,chapter ,,xxii ,general3-- ,,james ,,geikie4 ,the ,great ,ice ,age4 #c;d ed4 ,london1 #ahid1 pp4 #hej1 maps #ah4 ,,chamberlin and ,,salisbury4 ,geology1 vol4 #c1 #aijf1 pp4 #cbg-eaf4 ,,frank ,,leverett4 ,the ,illinois ,glacial ,lobe1 ,mon4 #ch1 ,u4 ,s4 ,geol4 ,surv41 #ahii1 pp4 #hag1 pls4 #cd2 ,glacial formations and ,drainage ,features of the ,erie and ,ohio ,basins1 ,mon4 #da1 ibid41 #aijb1 pp4 #hjb1 pls4 #be2 ,comparison of ,north ,american and ,european ,glacial ,deposits1 ,zeit4 f4 ,gletscherk41 vol4 #d1 #aiaj1 pp4 #bda-cae1 pls4 #a-e4 ,former glaciations previous to ,ice ,age3-- ,a4 ,,strahan4 ,the ,glacial ,phenomena of ,paleozoic ,age in the ,varanger ,fjord1 ,quart4 ,jour4 ,geol4 ,soc41 ,london1 vol4 #ec1 #ahig1 pp4 #acg-adf1 pls4 #h-aj4 ,,bailey ,,willis and ,,eliot ,,blackwelder4 ,research in ,china1 ,pub4 #ed1 ,carnegie ,inst4 ,washington1 vol4 #a1 #aijg1 pp4 #bfg-bfi1 pls4 #cg-ch4 ,a4 ,p4 ,,coleman4 ,a ,lower ,huronian ,ice ,age1 ,am4 ,jour4 ,sci4 7#d71 vol4 #bc1 #aijg1 pp4 #ahg-aib4 ,w4 ,m4 ,,davis4 ,observations in ,south ,africa1 ,bull4 ,geol4 ,soc4 ,am41 vol4 #ag1 #aijf1 pp4 #cgg-dej1 pls4 #dg-ed4 ,,david ,,white4 ,permo-,carboniferous ,climatic ,changes in ,south ,america1 ,jour4 ,geol41 vol4 #ae1 #aijg1 pp4 #fae-fcc4 ,driftless and drift areas3-- ,t4 ,c4 ,,chamberlin and ,r4 ,d4 ,,salisbury4 ,preliminary ,paper on the ,driftless ,areas of the ,upper ,mississippi ,valley1 #fth ,ann4 ,rept4 ,u4 ,s4 ,geol4 ,surv41 #ahhe1 pp4 #aii-cbb1 pls4 #bc-bi4 ,r4 ,d4 ,,salisbury4 ,the ,drift1 its ,characteristics and ,relationships1 ,jour4 ,geol41 vol4 #b1 #ahid1 pp4 #gjh-gbd1 #hcg-hea4 ,r4 ,h4 ,,whitbeck4 ,contrasts between the ,glaciated and the ,driftless ,portions of ,wisconsin1 ,bull4 ,geogr4 ,soc41 ,philadelphia1 vol4 #i1 #aiaa1 pp4 #aad-abc4 ,glacier gravings3-- ,t4 ,c4 ,,chamberlin4 ,the ,rock ,scorings of the ,great ,ice ,invasions1 #gth ,ann4 ,rept4 ,u4 ,s4 ,geol4 ,surv41 #ahhh1 pp4 #adg-bdh1 pl4 #h4 ,the dispersion of the drift3-- ,r4 ,d4 ,,salisbury4 ,notes on the ,dispersion of ,drift ,copper1 ,trans4 ,wis4 ,acad4 ,sci41 etc41 vol4 #f1 #ahhf1 pp4 #db-ej1 pl4 ,n4 ,s4 ,,shaler4 ,the ,conditions of ,erosion beneath ,deep ,glaciers1 based upon a ,study of the ,bowlder ,train from ,iron ,hill1 ,cumberland1 ,rhode ,island1 ,bull4 ,mus4 ,comp4 ,zol4 ,harv4 ,coll41 vol4 #af1 ,no4 #aa1 #ahic1 pp4 #ahe-bbe1 pls4 #a-d and map4 ,,william ,h4 ,,hobbs4 ,the ,diamond ,field of the ,great ,lakes1 ,jour4 ,geol41 vol4 #g1 #ahii1 pp4 #cge-chh1 pls4 #b 7also ,rept4 ,smithson4 ,inst41 #aija1 pp4 #cei-cff1 pls4 #a-c74 ,glacial features3-- ,t4 ,c4 ,,chamberlin4 ,preliminary ,paper on the ,terminal ,moraine of the ,second ,glacial ,epoch1 #c;d ,ann4 ,rept4 ,u4 ,s4 ,geol4 ,surv41 #ahhc1 pp4 #bia-djb1 pls4 #bf-ce4 ,g4 ,h4 ,,stone4 ,glacial ,gravels of ,maine and their ,associated ,deposits1 ,mon4 #cd1 ,u4 ,s4 ,geol4 ,surv41 #ahii1 pp4 #dhi1 pls4 #eb4 ,w4 ,c4 ,,alden4 ,the ,delaven ,lobe of the ,lake ,michigan ,glacier of the ,wisconsin ,stage of ,glaciation and ,associated ,phenomena4 ,prof4 ,pap4 ,no4 #cd1 ,u4 ,s4 ,geol4 ,surv41 #aijd1 pp4 #ajf1 pls4 #ae2 ,the ,drumlins of ,southeastern ,wisconsin1 ,bull4 #bgc1 ,u4 ,s4 ,geol4 ,surv41 #aije1 pp4 #df1 pls4 #i4 ,w4 ,m4 ,,davis4 ,structure and ,origin of ,glacial ,sand ,plains1 ,bull4 ,geol4 ,soc4 ,am41 vol4 #a1 #ahij1 pp4 #aif-bjb1 pl4 #c2 ,the ,subglacial ,origin of ,certain ,eskers1 ,proc4 ,bost4 ,soc4 ,nat4 ,hist41 vol4 #ce1 #ahib1 pp4 #dgg-dii4 ,f4 ,p4 ,,gulliver4 ,the ,newtonville ,sand ,plain1 ,jour4 ,geol41 vol4 #a1 #ahic1 pp4 #hjc-hab4 ,,chapter ,,xxiii ,,glacial ,,lakes ,,which ,,marked ,,the ,,decline ,,of ,,the ,,last ,,ice ,,age ,illustration3 ,,fig4 #cdf4--,the ,illinois ,river where it passes through the outer moraine at ,peoria1 ,illinois1 showing the flood plain of the ancient stream as an elevated terrace into which the modern stream has cut its gorge 7after ,goldthwait74 ,interference of glaciers with drainage4--,every advance and every retreat of a continental glacier has been marked by a complex series of episodes in the history of every river whose territory it has invaded4 ,whenever the valley was entered from the direction of its divide1 the effect of the advancing ice front has generally been to swell the waters of the river into floods to which the present streams bear little resemblance 7,fig4 #cdf74 ,because of the excessive melting1 this has been even more true of the ice retreat1 but here when the ice front retired up the valley toward the divide4 ,a sufficiently striking example is furnished by the ,wabash1 ,kaskaskia1 ,illinois1 and other streams to the southward of the divide which surrounds the basin of the ,great ,lakes 7,fig4 #cdg74 ,illustration3 ,,fig4 #cdg4--;,broadly terraced valleys outside the divide of the ,st4 ,lawrence basin1 which remain to mark the floods that issued from the latest continental glacier during its retreat 7after ,leverett74 ,wherever the relief was small there occurred in the immediate vicinity of the ice front a temporary diversion of the streams by the parallel moraines1 so that the currents tended to parallel the ice front4 ,this temporary diversion known as 8border drainage0 was brought to a close when the partially impounded waters had1 by cutting their way through the moraines1 established more permanent valleys 7,fig4 #cdh74 ,temporary lakes due to ice blocking4--,whenever1 on the contrary1 the advancing ice front entered a valley from the direction of its mouth1 or a retreating ice front retired down the valley1 quite different results followed1 since the waters were now impounded by the ice front serving as a dam4 ,though the histories of such blocking of rivers are often quite complex1 the principles which underlie them are in reality simple enough4 ,of the lakes formed during advancing hemicycles of glaciation1 and of all save the latest receding hemicycle1 no satisfactory records are preserved1 for the reason that the lake beaches and the lake deposits were later disturbed and buried by the overriding ice sheets4 ,we have1 however1 every reason to suppose that the histories of each of these hemicycles were in every way as complex and interesting as that of the one which we are permitted to study4 ,illustration3 ,,fig4 #cdh4--;,border drainage about the retreating ice front south of ,lake ,erie4 ,the stippled areas are the morainal ridges and the hachured bands the valleys of border drainage 7after ,leverett74 ,as an introduction to the study of the ice-blocked lakes of ,north ,america1 and to set forth as clearly as may be the fundamental principles upon which such lakes are dependent1 we shall consider in some detail the late glacial history of certain of the ,scottish glens1 since their area is so small and the relief so strong that relationships are more easily seen2 it is1 so to speak1 a pocket edition of the history of the more extended glacial lakes4 ,illustration3 ,,fig4 #cdi4--,the 8parallel roads0 of ,glen ,roy in the southern highlands of ,scotland 7after ,jamieson74 ,the 8parallel roads0 of the ,scottish glens4--,in a number of neighboring glens within the southern highlands of ,scotland there are found faint terraces upon the glen walls which under the name of the 8parallel roads0 7,fig4 #cdi7 have offered a vexed problem to scientists4 ,of the many scientists who long attempted to explain them1 though in vain1 was ,charles ,darwin1 the father of modern evolution4 ,he offered it as his view that the 8roads0 were beaches formed at a time when the sea entered the glens and stood at these levels4 ,when1 however1 ,jamieson's studies had discovered their true history1 ,darwin1 with a frankness characteristic of some of the greatest scientists1 admitted how far astray he had been in his reasoning4 ,let us1 then1 first examine the facts1 and later their interpretation4 ,the map of ,fig4 #cej will suffice to set forth with sufficient clearness the course of the several 8roads40 ,these 8roads0 are found in a number of glens tributary to ,loch ,lochy1 and of the three neighboring valleys1 ,glen ,roy has three1 ,glen ,glaster two1 and ,glen ,spean one 8road40 ,the facts of greatest significance in arriving at their interpretation relate to their elevations with reference to the passes at the valley heads1 their abrupt terminations down-valleyward1 and the morainic accumulations which are found where they terminate4 ,the single 8road0 of ,glen ,spean is found at an elevation of #hih feet1 a height which corresponds to that of the pass or col at the head of its valley and to the lowest of the 8roads0 in both ,glens ,glaster and ,roy4 ,similarly the upper of the two 8roads0 in ,glen ,glaster is at the height of the pass at its head 7#ajge feet7 and corresponds in elevation to the middle one of the three 8roads0 in ,glen ,roy4 ,lastly1 the highest of the 8roads0 in ,glen ,roy is found at an elevation of #aaea feet1 the height of the col at the head of the ,glen4 ,in the neighboring ,glen ,gloy is a still higher 8road0 corresponding likewise in elevation to that of the pass through which it connects with ,glen ,roy4 ,illustration3 ,,fig4 #cej4--,map of ,glen ,roy and neighboring valleys of the ,scottish highlands with the so-called 8roads0 entered in heavy lines4 ,glens ,roy1 ,glaster1 and ,spean have three 8roads01 two 8roads01 and one 8road01 respectively 7after ,jamieson74 ,to come now to the explanation of the 8roads01 it may be said at the outset that they are1 as ,darwin supposed1 beach terraces cut by waves1 not as he believed of the ocean1 but of lakes which once filled portions of the glens when glaciers proceeding from ,ben ,nevis to the southwestward were blocking their lower portions4 ,the several episodes of this lake history will be clear from a study of the three successive idealistic diagrams in ,fig4 #cea4 ,illustration3 ,,fig4 #cea4--,three successive diagrams to set forth in order the late glacial lake history of the ,scottish glens4 ,to derive the principles underlying this history1 it is at once seen that all changes are initiated by the retirement of the ice front to such a point that it unblocks for the waters of a lake an outlet that is lower than the one in service at the time4 ,this is the principle which explains nearly all episodes of glacial lake history4 ,thus1 when the ice front had retired so as to open direct connections between ,glen ,roy and ,glen ,glaster1 the col at the head of ,glen ,roy was abandoned as an outlet1 and the waters fell to the level fixed for ,glen ,glaster4 ,a still further retirement at last opened direct connection between ,glen ,glaster and ,glen ,spean1 so that the lake common to ,glens ,glaster and ,roy fell to the level of the col which was the outlet of the ,spean valley at the time4 ,this stage continued until the ice front had retired so far that the waters drained naturally down the river ,spean to ,loch ,lochy and thence to the ocean4 ,illustration3 ,,fig4 #ceb4--;,harvesting time on the fertile floor of the glacial ,lake ,agassiz 7after ,howell74 ,only in their far grander scale and in the lesser relief of the land over which they formed1 do the complex histories of the great ice-blocked lakes of ,north ,america differ from these little valley lakes whose beaches may be visited and the relationships worked out1 thanks to ,jamieson1 in a single day's strolling4 ,illustration3 ,,fig4 #cec4--,map of ,lake ,agassiz 7after ,upham74 ,the glacial ,lake ,agassiz4--,the grandest of the temporary lakes referable to blocking by the continental glaciers of the ice age must be looked for in the largest valleys that lay within the territory invaded and which normally drain toward the retiring ice front4 ,in ,north ,america these rivers are the ,red ,river of the ,north in ,minnesota1 the ,dakotas1 and ,manitoba2 and the ,st4 ,lawrence ,river system4 ,to the ice dam which lay across the ,red ,river valley we owe the fertility of that vast plain of lake deposits where is to-day the most intensive wheat farming of the northwest 7,fig4 #ceb74 ,lakes ,winnipeg1 ,winnipegoosis1 and ,manitoba1 and the ,lake of the ,woods1 are all that now remain of this greatest of the glacial lakes1 which in honor of the distinguished founder of the glacial theory has been called ,lake ,agassiz 7,fig4 #cec74 ,with their natural outlet blocked by the ice in northern ,manitoba and ,keewatin1 the waters of the ,red were swollen by melting from the retiring glacier and spread over a vast area before finding a southern outlet along the course of the present ,lake ,traverse and the valley of the ,minnesota ,river4 ,along this route there flowed a mighty flood which carved out a broad valley many times too large for the ,minnesota1 its present occupant1 and this giant prehistoric river has been called the ,warren ,river 7,fig4 #ced74 ,illustration3 ,,fig4 #ced4--,map of the southern end of the ,lake ,agassiz basin1 showing the position of some of the beaches and the outlet through the former ,warren ,river 7after ,upham74 ,illustration3 ,,fig4 #cee4--,narrows of the ,warren ,river below ,big ,stone ,lake1 where it passed between jaws of hard granite and gneiss 7after ,upham74 ,illustration3 ,,fig4 #cef4--,map of the valley of the ,warren ,river in the vicinity of ,minneapolis1 with the young valley of the ,mississippi entering it at ,fort ,snelling 7after ,sardeson74 ,it is interesting to follow this ancient waterway and to discover that1 like our normal1 present-day streams1 it was held up in narrows wherever outcroppings of harder rock had constricted its channel 7,fig4 #cee74 ,the upper end of the ,warren ,river valley is now occupied by the long and relatively narrow ,lakes ,traverse and ,big ,stone1 each the result of blocking by delta deposits where a tributary stream has emerged into the valley1 but this gigantic channel continues down to and beyond ,minneapolis1 occupied as far as ,fort ,snelling by the ,minnesota ,river--a mere pygmy compared to its predecessor4 ,to the earnest student of glacial geology there can be few sights more impressive than are obtained by standing at ,fort ,snelling1 just above the confluence of the ,minnesota and the ,mississippi rivers1 and surveying first the steep and narrow valley of the ,mississippi above the junction1--a stream fitted to its valley for the simple reason that it has carved it1--and then gazing up and down that broad valley in which the great ,warren ,river once flowed majestically to the sea1 now the bed of the ,minnesota above the ,fort and of the ,mississippi below it 7,fig4 #cef74 ,illustration3 ,,fig4 #ceg4--,portion of the ,herman quadrangle of ,minnesota1 showing the position of the ,herman beach on the shore of the former ,lake ,agassiz4 ,the lake basin is to the left1 and the pitted morainal deposits appear to the right 7,u4 ,s4 ,g4 ,s474 ,just as the 8parallel roads0 of ,glen ,roy1 roads in name only1 are the beaches of earlier glacial lake stages1 so in ,lake ,agassiz we have parallel beaches of the barrier type which are often roads in fact as well as in name1 and which mark the stages of successive lakes within this vast basin4 ,the ,herman beach1 corresponding to the highest level of the lake1 is thus a sharp topographic boundary between lake deposits and morainal accumulations1 and is further itself a well-marked topographic feature composed of wave-washed and hence well-drained materials 7,fig4 #ceg74 ,farmers of the district have been quick to realize that these level and slightly elevated ridges lack the clay which would render them muddy in the wet seasons1 and are thus ideally adapted for roads4 ,they have in many sections been thus used over long stretches and are known as the 8ridge roads40 ,episodes of the glacial lake history within the ,st4 ,lawrence valley4--,within this great drainage basin it has apparently been possible to read the records of each stage in the latest lake history--complex as this has been4 ,we have only to recall the lake stages cited from the ,scottish glens and remember that each new stage was begun in a retirement of the glacier front which unblocked an outlet of lower level than the last4 ,this sequence might1 however1 have been varied by a temporary readvance of the ice1 as indeed once occurred in the ,huron-,erie lobe of the great ,north ,american glacier4 ,illustration3 ,,fig4 #ceh4--,the continental glacier of ,north ,america in an early stage of its recession1 when it covered the entire ,st4 ,lawrence drainage basin4 ,the dashed line is the approximate position of the divide 7based on a map by ,goldthwait74 ,illustration3 ,,fig4 #cei4--,outline map of the early ,lake ,maumee1 with the bordering moraine and the water-laid moraine remaining on the site of the former ice cliff4 ,the crescentic lakes of the earlier stages4--,so long as the glacier covered the entire drainage basin of the ,st4 ,lawrence ,river system1 all water was freely drained away by streams which flowed away from the ice front 7,fig4 #ceh74 ,so soon1 however1 as at any point the front had retired behind the divide1 impounding of the waters must locally have occurred4 ,lakes of this type are to-day to be seen in ,greenland and in the southern ,andes2 and though upon a diminutive scale1 some idea of their aspect may be obtained from the appearance of the ,mrjelen ,lake of ,switzerland1 here blocked by a mountain glacier 7,fig4 #ddf1 p4 #daa74 ,within all areas of small relief1 such as the prairie country surrounding the present ,laurentian lakes1 the earlier and smaller stages of such ice-blocked lakes are generally crescentic in outline4 ,this is because a moraine in most cases forms the land margin of the lake1 and because the ice cliff upon the opposite border1 although somewhat straightened1 as a consequence of wave-cutting and iceberg formation1 still retains the convex outlines characteristic of ice lobes 7,fig4 #cei74 ,illustration3 ,,fig4 #cfj4--,map to show the first stages of the ice-dammed lakes within the ,st4 ,lawrence basin 7after ,leverett and ,taylor74 ,within each of the ,great ,lake basins a crescentic lake early appeared at that end of the depression which was first uncovered by the glacier3 ,lake ,duluth in the ,superior basin1 ,lake ,chicago in the ,michigan basin1 and ,lake ,maumee in the ,huron-,erie basin 7,fig4 #cfj74 ,we may now1 with profit1 trace the successive episodes of the glacial lake history1 considering for the earlier stages those changes which occurred within the ,huron-,erie basin1 since1 these are in essential respects like those of the ,michigan and ,superior basins1 although worked out in greater detail4 ,lake ,chicago must1 however1 be brought into consideration1 since in all save the earliest and the later stages1 the waters from the ,huron-,erie depression were discharged through the ,grand ,river into this lake and thence by the so-called 8,chicago outlet0 into the ,mississippi 7plate #bj ,a74 ,the early ,lake ,maumee4--,the area1 outline1 and outlet of this lake are indicated upon ,fig4 #cfj4 ,its ancient beaches have been traced1 as well as the water-laid moraine beneath its former ice cliff2 and no observant traveler who should take his way down the ancient outlet from ,fort ,wayne1 ,indiana1 past the town of ,huntington1 could fail to be impressed by its size1 suggesting as it does the great volume of water which must once have flowed along it4 ,now a channel a mile or more in width1 its bed for the twenty-five miles between ,fort ,wayne and ,huntington may be seen from the tracks of the ,wabash ,railway as a series of swamps merely1 while at ,huntington the ,wabash river enters by a young ,v-shaped valley at the side1 much as the ,mississippi emerges into the old channel of the ,warren ,river at ,fort ,snelling1 ,minnesota 7see p4 #cbg74 ,the ,huron ,river of southern ,michigan1 which now discharges into ,lake ,erie1 then found its lower course blocked by the glacier and was thus compelled to find a southerly directed channel now easily followed to the northern horn of the crescent of ,lake ,maumee4 ,the later ,lake ,maumee4--,when the ice lobe had retired its front sufficiently1 an outlet lower than that at ,fort ,wayne was uncovered past the city of ,imlay1 ,michigan1 into the ,grand ,river1 and thence through ,lake ,chicago and its outlet into the ,mississippi4 ,this old outlet south of ,chicago follows the course of the present ,drainage ,canal and the line of the ,chicago ,alton ,railway4 ,the traveler journeying southward by train from ,chicago has thus the opportunity of observing first the beaches of the former lake1 and then the several channels which were joined in the main outlet at the station of ,sag 7plate #bj ,a74 ,illustration3 ,,fig4 #cfa4--,outline map of the later ,lake ,maumee and of its 8,imlay outlet0 to ,lake ,chicago 7after ,leverett74 ,in this stage of our history ,lake ,maumee pushed a shrunk arm up past the site of ,ypsilanti in ,michigan 7,fig4 #cfa71 the well-marked beach being found on ,summit ,street opposite the ,state ,normal ,college4 ,the ,huron ,river1 which in the first lake stage had followed the valley now occupied by the ,raisin ,river southward into ,indiana1 now discharged directly into a bay upon this arm of ,lake ,maumee1 and so formed a delta at ,ann ,arbor4 ,illustration3 ,,fig4 #cfb4--,outline map of ,lakes ,whittlesey and ,saginaw 7after ,leverett74 ,illustration3 ,,fig4 #cfc4--,map of the glacial ,lake ,warren1 the last of the lakes in the ,huron-,erie basin1 which discharged through the 8,grand ,river outlet0 into the ,mississippi 7after ,leverett74 ,lakes ,arkona and ,whittlesey4--,the ice front in the ,huron-,erie basin now retired so far that the impounded waters1 instead of following the more direct 8,imlay outlet0 to the ,grand1 passed at a lower level completely around 8the thumb0 of ,michigan into the ,saginaw basin4 ,meanwhile a crescent-shaped lake had developed in that basin1 so that now the waters of the ,maumee basin were joined to those in the ,saginaw basin as a common lake1 just as the lowering of the waters in ,glen ,roy caused a union with those of ,glen ,glaster in the example cited for illustration4 ,our records of this third ,north ,american lake stage1 referred to as ,lake ,arkona1 are however most imperfect1 for the reason that it was followed by a readvance of the ice front which closed the passage around 8the thumb0 and raised the level of the waters until an outlet was found past the town of ,ubly at a lower level than the 8,imlay outlet40 ,when the waters of a lake are thus rising1 strong beach formations result1 and those of this stage1 which is known as the ,lake ,whittlesey stage1 are much the strongest that are found within the ,huron-,erie basin4 ,traced for some three hundred miles entirely around the southern and western margins of ,lake ,erie1 this beach is for much of the distance the famous 8ridge road0 7,fig4 #cfb74 ,lake ,warren4--,as the ice advance which had produced ,lake ,whittlesey came to an end1 the normal recession was resumed and a lake once more formed as a body common to the ,saginaw and ,erie basins4 ,this lake1 known as ,lake ,warren1 extended a shrunk arm far eastward along the ice front into western ,new ,york1 though it was still blocked from entering the great ,mohawk valley 7,fig4 #cfc74 ,illustration3 ,,fig4 #cfd4--,map of the ,glacial ,lake ,algonquin 7after ,leverett74 ,lakes ,iroquois and ,algonquin4--,it must be evident that toward the close of the ,lake ,warren stage a profound change was imminent--a transfer of the glacial waters from their course to the ,mississippi and the ,gulf to the trench which crosses ,new ,york ,state and enters the ,atlantic4 ,so soon as the ice front had retired sufficiently to lay bare the bed of the ,mohawk1 an outlet was found by this route and its continuation down the ,hudson valley to the sea4 ,the ,lake ,ontario basin now became occupied by a considerably larger water body known as ,lake ,iroquois1 and the three upper lakes1 then joined as ,lake ,algonquin1 discharged their combined waters into ,lake ,iroquois at first through a great channel now strongly marked across ,ontario in the course of the ,trent ,river and ,lake ,simcoe1 the so-called 8,trent outlet40 ,at this time a smaller ,lake ,erie probably occupied the basin of that lake1 and later the ,trent outlet was abandoned for the ,port ,huron outlet 7,fig4 #cfd74 ,illustration3 ,,fig4 #cfe4--,outline map of the ,nipissing ,great ,lakes with their outlet past ,north ,bay into the ,champlain ,sea4 ,the ,nipissing ,great ,lakes4--,we have now followed the ice front step by step in its retreat across the valley of the ,st4 ,lawrence system4 ,the successive unblocking of outlets offers but one further possibility--the opening of the ,french ,river-,nipissing ,lake-,ottawa ,river1 or 8,north ,bay outlet40 ,though not so to-day1 the bed of this ancient channel was then much lower than that of the 8,mohawk outlet01 and so soon as the glacier had in its retreat uncovered this northern channel1 the waters of the upper lakes discharged through it past the site of ,ottawa and into an arm of the sea which then occupied the lower ,st4 ,lawrence valley and has been called the ,champlain ,gulf or ,sea 7,fig4 #cfe74 ,the level of the waters was lowered and the area of the lakes correspondingly reduced4 ,the reader who has had no opportunity to observe these ancient channels which carried the swollen waters of the former glacier lakes1 will find it interesting to consider that every one of them has been fixed upon by engineers for improvement as artificial waterways4 ,thus we have the ,illinois ,drainage ,canal and projected ship canal along the 8,chicago outlet01 the projected ,mississippi-,lake ,erie ,canal along the 8,fort ,wayne outlet01 the ,grand ,river canal project to connect ,lake ,michigan and ,saginaw ,bay along the course of the 8,grand ,river outlet01 the ,trent ,canal along the 8,trent outlet01 the ,erie ,canal along the 8,mohawk outlet01 and1 lastly1 the proposed ,georgian ,bay ship canal to the ocean along the 8,north ,bay0 or 8,nipissing outlet40 ,summary of lake stages4--,we have omitted in this summary of late lake history in the ,laurentian basin all the less important lake stages1 including some of a transitional nature which were represented by beaches and outlets easily traced to-day4 ,this is because it is an outline only which it seems best to present1 and the episodes of this abridged history may be tabulated as follows3 ,,episodes ,,of ,,glacial ,,lake ,,history ,,mississippi ,,drainage ,lake ,maumee 7early71 ,fort ,wayne outlet4 ,lake ,maumee 7late71 ,imlay ,city outlet4 ,lake ,arkona1 8thumb0 outlet4 ,lake ,whittlesey 7with readvance of glacier71 ,ubly outlet4 ,lake ,warren1 8thumb0 outlet4 ,,atlantic ,,drainage ,lakes ,iroquois and ,algonquin 7early71 ,trent and ,mohawk outlets4 ,lakes ,iroquois and ,algonquin 7late71 ,port ,huron and ,mohawk outlets4 ,nipissing ,great ,lakes1 ,north ,bay outlet4 ,permanent changes of drainage affected by the glacier4--,while the lake history which we have sketched is made up of episodes which endured only while the ice front lay between certain stations upon its retreat1 there were none the less brought about the profoundest of permanent modifications in the drainage of the region4 ,it is possible to restore upon maps in part only the preglacial drainage of the north central states1 but we know at least that it was as different as may be from that which we find to-day4 ,the ,missouri and the ,ohio take their courses to-day along the margin of the glaciated area as an inheritance from the border drainage of the ice age4 ,within the glaciated regions rivers have in many cases been compelled by morainal obstructions to enter upon new courses1 or even to travel in the opposite direction along their former channels4 ,in districts of considerable relief these diversions have sometimes caused the streams to plunge over the walls of deep valleys1 and it may truthfully be said that we owe much of our most beautiful scenery in part to the carving and molding of glaciers1 but especially to the cascades and waterfalls directly due to their interference with drainage4 ,illustration3 ,,fig4 #cff4--,probable preglacial drainage of the upper ,ohio region 7after ,chamberlin and ,leverett74 ,many diversions or reversals of former drainage lines1 through the influence of the continental glacier1 are at once suggested by the abnormal stream courses1 which appear upon our maps1 and the correctness of these suggestions may often be confirmed by very simple observations made upon the ground4 ,the map of ,fig4 #cff shows how different was the preglacial drainage of the upper ,ohio region from that of to-day4 ,an interesting additional example is furnished by the ,still ,river which in ,connecticut is tributary to the ,farmington1 and is no less remarkable for its abnormal northerly course and sluggish current perpetuated in its name1 than for the way in which it is joined to the ,farmington system 7,fig4 #cfg ,a74 ,a careful study of the district has shown that the ,still ,river was once a part of the ,naugatuck and flowed southward toward ,long ,island ,sound like other rivers of the district 7,fig4 #cfg ,b74 ,it possessed1 however1 an advantage in a narrow belt of softer rock along its course1 and because of this advantage it captured a portion of one of the tributaries to the ,farmington 7,fig4 #cfg ,c74 ,the continental glacier later covered the region1 and on its retreat laid down morainal obstructions directly across this river and also at the head of the severed arm of the ,farmington tributary 7,fig4 #cfg ,d74 ,the now impounded waters found their lowest outlet near ,sandy ,brook1 and in waterfalls and cascades the now reversed river falls one hundred feet to the bed of that stream4 ,with the aid of the excellent topographic maps which are now supplied by a generous government at a merely nominal price1 such bits of recent history may be read at many places within the glaciated region4 ,illustration3 ,,fig4 #cfg4--;,diagrams to illustrate the episodes in the recent history of the ,still ,river tributary to the ,farmington in ,connecticut4 ,a1 present drainage2 ,b1 early stage2 ,c1 after capture of a tributary to the ,farmington2 ,d1 after blocking by morainal obstructions of the ice age4 ,glacial ,lake ,ojibway in the ,hudson ,bay drainage basin4--,when by passing over the 8height of land0 in northern ,ontario the greatly reduced continental glacier had vacated the basin of ,st4 ,lawrence drainage1 it was in a position to impound those waters which normally drained to ,hudson ,bay4 ,the lake which then came into existence has been called ,lake ,ojibway and was the latest of the entire series4 ,though of but recent discovery in a country till lately a trackless wilderness1 its extension seems to have been that of the clay beds suited for farming4 ,the beaches and outlets remain to be mapped when the country has been made more easily accessible4 ,,reading ,,references ,,for ,,chapter ,,xxiii ,parallel roads of ,glen ,roy3-- ,,charles ,,darwin4 ,observations on the ,parallel ,roads of ,glen ,roy and of ,other ,parts of ,lochaber in ,scotland1 with an attempt to prove that they are of ,marine ,origin1 ,phil4 ,trans41 vol4 #h1 #ahci1 pp4 #ci-hb4 ,,louis ,,agassiz4 ,geological ,sketches1 ,boston1 #ahgf1 vol4 #b1 pp4 #cb-gf4 ,t4 ,t4 ,,jamieson4 ,on the ,parallel ,roads of ,glen ,roy and their ,place in the ,history of the ,glacial ,period1 ,quart4 ,jour4 ,geol4 ,soc4 ,lond41 vol4 #ai1 #ahfc1 pp4 #bce-bei4 ,glacial ,lake ,agassiz3-- ,,warren ,,upham4 ,the ,glacial ,lake ,agassiz4 ,mon4 #be1 ,u4 ,s4 ,geol4 ,surv41 pp4 #feh1 pls4 #ch4 ,f4 ,w4 ,,sardeson4 ,beginning and ,recession of ,st4 ,anthony's ,falls1 ,bull4 ,geol4 ,soc4 ,am41 vol4 #ai1 #aijh1 pp4 #bi-cf4 ,glacial lakes in the ,st4 ,lawrence valley3-- ,,chamberlin ,,and ,,salisbury4 ,geology1 vol4 #c1 pp4 #cid-dje4 ,,frank ,,leverett4 ,outline of the ,history of the ,great ,lakes 7,presidential ,address71 #abth ,rept4 ,mich4 ,acad4 ,sci41 #aiaj1 pp4 #ai-db4 ,the ,pleistocene ,features and ,deposits of the ,chicago ,area4 ,chicago1 #ahig1 pp4 #hf1 pls4 #h 7,chicago ,outlet74 ,h4 ,l4 ,,fairchild4 ,glacial ,lakes in ,western ,new ,york1 ,bull4 ,geol4 ,soc4 ,am41 vol4 #f1 #ahie1 pp4 #cec-cgd1 pls4 #ah-bc2 ,glacial ,waters in ,central ,new ,york4 ,bull4 #abg1 ,n4 ,y4 ,state ,mus41 #aiji1 pp4 #ff1 pls4 #db1 and maps in cover4 ,early lakes in the ,erie basin3-- ,,frank ,,leverett4 ,on the ,correlation of ,moraines with ,raised ,beaches of ,lake ,erie1 ,am4 ,jour4 ,sci4 7#c71 vol4 #dc1 #ahib1 pp4 #bha-cja4 ,f4 ,b4 ,,taylor4 ,the ,great ,ice ,dams of ,lakes ,maumee1 ,whittlesey1 and ,warren1 ,am4 ,geol41 vol4 #bd1 #ahii1 pp4 #f-ch1 pls4 #b-c2 ,relation of ,lake ,whittlesey to the ,arkona ,beaches1 #gth ,rept4 ,mich4 ,acad4 ,sci41 #aije1 pp4 #cj-cf4 ,,frank ,,leverett4 ,the ,ann ,arbor ,folio1 ,folio ,no4 #aee1 ,u4 ,s4 ,geol4 ,surv41 #aijh1 pp4 #aj-ab4 ,,chapter ,,xxiv ,,the ,,uptilt ,,of ,,the ,,land ,,at ,,the ,,close ,,of ,,the ,,ice ,,age ,the response of the earth's shell to its ice mantle4--,there is now good reason to believe that the earth's outer shell makes a response by oscillations of level due to the loading by ice1 on the one hand1 and to the removal of this burden upon the other4 ,we know1 at least1 that both in northern ,europe and in ,north ,america areas which have undergone depression during and elevation after the ice age1 correspond closely to the regions which were ice covered4 ,wherever in these regions there was high relief before the advent of the ice1 river valleys were drowned at the land margins and were also gouged out into troughs through erosion by the outlet tongues upon the margin of the ice sheet4 ,such furrowed and half-submerged valleys have a characteristic ,u-shaped section1 so that their walls rise precipitously from the sea4 ,from their typical occurrence in ,scandinavian countries the name fjord has been applied to them4 ,it is now no less clear that the removal of the ice blanket brought from the earth a relatively quick response in uplift1 which began before the ice front had retired across the present international boundary of the ,united ,states1 and that this uplift continued until the final disappearance of the ice4 ,a far slower elevation of a somewhat different nature has continued1 even to the present day4 ,it is obvious that at the time of their formation all shore lines referable to the work of waves must have been horizontal1 and hence any variations from a perfect level which they reveal to-day must indicate that a tilting movement of the ground has occurred since the waters departed from their basins4 ,we have thus provided for us in the positions of these ancient water planes1 particularly because of their wide extent1 a complete record the refinement of which is not easily overstated4 ,interpreting this record1 we find that it was the uptilt of the land to the northward which brought the glacial lake history to an end and inaugurated the present system of ,st4 ,lawrence drainage4 ,the outlet of the ,nipissing ,great ,lakes is to-day more than a hundred feet above the level of the outlet at ,port ,huron1 where the upper lakes are now discharging their waters1 and this difference in level can only be ascribed to an upward tilting of the land since the latest of the glacial lake stages4 ,the abandoned strands as they appear to-day4--,the traveler by steamer upon the upper lakes1 as he comes within view of each rocky headland1 may note how the profile against the horizon is notched by a series of steps or terraces 7,fig4 #cfh71 and if he has followed the discussion in previous chapters1 he will suspect that these terraces mark the now abandoned shore lines which have come to their present position through a series of uplifts of the ground accompanied by earthquake shocks4 ,as his steamer skirts the shore he may chance to note a cave within the rock cliff which represents the now elevated sea-arch of an ancient shore4 ,illustration3 ,,fig4 #cfh4--,the notched rock headland of ,boyer ,bluff between ,green ,bay and ,lake ,michigan 7after ,goldthwait74 ,disembarking from the steamer and traveling inland at any point where the shores are high1 the traveler is certain to come upon still more convincing proofs of the ancient strands2 perhaps in a storm beach of the unmistakable 8shingle01 half buried though it may be under dunes of newly drifted sand1 or possibly at higher levels the highway has been cut through a shingle barrier as fresh and unmistakable as though formed upon the present shore4 ,sometimes it is the rock cliff and terrace1 at other times barrier ridges of shingle1 or1 again1 it is the sloping cliff and terrace cut in the drift deposits2 but of whatever sort1 if studied with proper regard to the topography of the district1 the evidence is clear and unmistakable4 ,the records of uplift about ,mackinac ,island4--,nowhere are the records of the recent uplift of the lake region more easily read than about ,mackinac ,island in the straits connecting ,lake ,michigan with ,lake ,huron4 ,approaching the island by steamer from ,st4 ,ignace1 its profile upon the horizon is worthy of remark 7,fig4 #cfi74 ,from a central crest broken by minor irregularities and bounded on all sides by a cliff1 the island profile slopes gently away to a still lower cliff1 below which is another terrace4 ,illustration3 ,,fig4 #cfi4--,view of ,mackinac ,island from the direction of ,st4 ,ignace4 ,the irregular central portion is the only part of the island that was not submerged in ,lake ,algonquin4 ,the terrace at its base is the old shore line of ,lake ,algonquin1 and the lower terrace the strand of ,lake ,nipissing 7after a photograph by ,taylor74 ,illustration3 ,,fig4 #cgj4--,the 8,sugar ,loaf01 a stack near the shore of ,lake ,algonquin1 as it is seen from the observatory upon ,mackinac ,island 7after a photograph by ,taylor74 ,when we have reached the island and have climbed to the summit1 we there find the surface which is characteristic of erosion by running water1 whereas at lower levels are found the forms carved or molded by the action of waves4 ,this central 8island01 superimposed upon the larger island1 is all that rose above ,lake ,algonquin1 the earliest of the glacial lakes in this northern district2 and as we look out from the observatory upon the summit1 it is easy to call up a picture of the country when the lake stood at the base of this highest cliff4 ,to the northward one sees the 8,sugar ,loaf0 rise out of a sea of foliage1 as it formerly did from the waters of ,lake ,algonquin 7,fig4 #cgj74 ,it is a huge stack near the former island shore4 ,if we turn now to the southward and direct our gaze toward the ,fort1 we encounter a veritable succession of beach ridges formed of shingle and ranged like a series of waves within the cleared space of the 8,short ,target ,range0 7,fig4 #cga74 ,these ridges mark each a stage within a series of successive uplifts which have brought the island to its present height4 ,illustration3 ,,fig4 #cga4--,view from the observatory upon ,mackinac ,island across the 8,short ,target ,range0 toward the ,fort4 ,beach ridges appear in succession within the cleared space 7after a photograph by ,rossiter74 ,illustration3 ,,fig4 #cgb4--,notched stack of the ,nipissing ,great ,lakes at ,st4 ,ignace 7after a photograph by ,taylor74 ,illustration3 ,,fig4 #cgc4--,series of diagrams to illustrate the evolution of ideas concerning the uplift of the lake region since the ice age4 ,a1 simple northerly up-canting 7,gilbert73 ,b1 northerly acceleration of the up-canting 7,spencer and ,upham72 ,c1 northerly 8feathering out0 of beaches 7,spencer and ,upham72 ,d1 hinge1 line of up-canting found within the lake region 7,leverett72 ,e1 multiple and northwardly migrating hinge lines of up-canting 7,hobbs74 ,if now we descend from our position and visit the 8battlefield01 we find there a great ridge of level crest1 behind which the ,british force was stationed in its defense of the island in #ahab4 ,near by in the woods is ,pulpit ,rock1 a strikingly perfect stack of the ,nipissing ,lake4 ,across the straits at ,st4 ,ignace is an even finer example of the notched stack 7,fig4 #cgb74 ,other less prominent beaches1 but all later than the ,nipissing ,lakes1 intervene between this level and the present shore to mark the stages in the continued uplift of the land4 ,the present inclinations of the uplifted strands4--,it is not enough that we should have recognized the marks of former shores now at considerable elevations above the existing lakes2 if we are to know the nature of the uplift1 we must prepare accurate maps based upon measurements by precise leveling at many localities4 ,such methods are1 however1 of comparatively recent application in this field2 and1 as in the investigation of so many other problems1 the earlier observations were largely of the nature of reconnaissances with the elevation of beaches estimated by comparatively crude methods only4 ,the evolution of ideas concerning the uptilt has1 therefore1 been a gradual one4 ,illustration3 ,,fig4 #cgd4--,map of the ,great ,lakes region to show isobases and hinge lines of uptilt4 a1 isobase of the ,chicago outlet2 b1 main hinge line of the ,lake ,whittlesey beach 7,leverett72 b#a1 hinge line of the ,lake ,warren beach 7,taylor72 c1 isobase of the ,port ,huron outlet2 d1 main hinge line of highest ,algonquin beach 7,goldthwait72 e1 f1 g1 h1 additional hinge lines of ,algonquin beaches in ,door ,county peninsula 7,hobbs72 l1 isobase of the ,lake ,superior outlet for the ,algonquin beaches 7,leverett73 m1 isobase of the same outlet for the ,nipissing beaches 7,leverett74 ,it was early observed that the beaches corresponding to a given lake stage were higher to the northward and northeastward1 and the natural conclusion from this was that the earth's crust had here been canted like a trap door 7,fig4 #cgc1 ,a74 ,as we are to see1 this but half-correct assumption has led to a striking prophecy relating to future changes within the lake region which we now know to be without warrant in the facts4 ,later it was learned that the uptilt of the lake beaches is much accelerated to the northward 7,fig4 #cgc1 ,b71 and that new beaches make their appearance from beneath others as we proceed in this direction--there is a 8feathering out0 of beaches to the northward 7,fig4 #cgc1 ,c74 ,the hinge lines of uptilt4--,still later in the study of the region1 it was learned that the axis or fulcrum about which the region has been uptilted1 instead of lying to the southward of the lake district1 as had been assumed by ,gilbert1 lay within the region and about halfway up the basin of ,lake ,michigan 7,fig4 #cgc1 ,d1 and ,fig4 #cgd74 ,similarly1 in the uptilt which followed the ice retreat in northern ,europe a definite hinge line of movement has been discovered4 ,lastly1 it has been shown1 as a result of the use of precise leveling methods1 that not one but several hinge lines of movement lie within the region1 and that the separate sections into which they divide the area are each in turn characterized by increased up-cant as we proceed to the northward 7,fig4 #cgc1 ,e and ,fig4 #cgd74 ,illustration3 ,,fig4 #cge4--,series of idealistic diagrams to indicate the nature of the quick recovery of the crust by uplift in blocks unloaded of the ice in succession4 ,a further and slower uptilt1 added after the completion of the first movement1 is brought out in the last diagram 7b74 ,the beaches of ,lake ,maumee1 the earliest of the series of lakes within the ,huron-,erie lobe and within the extreme southern portion of the ,great ,lakes area1 show only the slightest possible northerly uptilt1 and the well-marked hinge line disclosed in the ,whittlesey beach is evidence that the elastic recoil1 as it were1 from the weight of the mantling glacier did not begin until after the draining of ,lake ,whittlesey4 ,the determination by ,taylor that there is a similar initial hinge line in the ,warren beach--that this strand begins its uptilt some fifteen miles farther northeast than does the ,whittlesey beach--is one of the greatest importance in obtaining a correct idea of the recent uplift2 for it shows that the draining of ,lake ,whittlesey was followed by a period of quick uplift and seismic activity1 that the stage of ,lake ,warren was one of comparative stability of the land1 and1 lastly1 that the draining of ,lake ,warren was followed by a second period of rapid uplift and earthquake disturbance4 ,the strongly marked hinge lines1 additional to the initial one indicated for the ,algonquin beaches in the profiles by ,goldthwait from the west shore of ,lake ,michigan1 when considered in the light of this northeasterly migration of the still earlier hinge line in the southern district1 are best explained through the assumption of a succession of quick recoveries of the crust by uplift1 separated by periods of relative stability1 and brought on by the removal in turn of the ice burden from successive blocks of the shell which are separated by the several hinge lines 7,fig4 #cge74 ,the elaborate study of erosion in the outlet of ,lake ,agassiz had indicated identical interruptions in the up-canting process for that basin4 ,future consequences of the continued uptilt within the lake region4--,one of the most distinguished of ,american geologists1 ,dr4 ,g4 ,k4 ,gilbert1 in order to determine whether the uptilt revealed by canted beach lines is still in progress1 carried out an elaborate study upon the gauge records preserved at the various gauging stations about the ,great ,lakes4 ,upon the basis of these studies1 he concluded that the uplift continues1 that the axes of equal uplift 7isobases7 take their course about fifteen degrees north of west1 so that the lines of greatest uptilt should be perpendicular to this direction1 or fifteen degrees east of north4 ,he further believed that the basin was undergoing an up-cant in the simple manner of a trap door1 the hinge of which lay to the southward of ,chicago1 and the study of the gauge records led him to believe that 8the rate of change is such that the two ends of a line one hundred miles long and lying in a south-southwest direction are relatively displaced four tenths of a foot in one hundred years40 ,gilbert's prophecy of a future outlet of the ,great ,lakes to the ,mississippi4--,the natural rock sill1 over which the waters of ,lake ,chicago once flowed to the ,mississippi1 is to-day but eight feet above the common mean level of ,lakes ,michigan and ,huron1 and if the tilting of the lake region were to continue upon ,gilbert's assumption of a canting plane with the hinge of the movement to the south of ,chicago1 a time must come when the 8,chicago outlet0 will again come into use and the lakes once more drain to the ,mississippi and the ,gulf4 ,upon the basis of his measurements1 ,gilbert ventured the prophecy that the first high-water discharge into the ,mississippi should occur in from five hundred to six hundred years1 and for continuous discharge in fifteen hundred years4 ,in twenty-five hundred years ,niagara ,falls should at low water stages be dry from this cause1 and in thirty-five hundred years it should have become extinct4 ,this prophecy1 emanating from a high scientific authority and relating to changes of such profound economic and commercial importance1 has been often quoted and has taken a firm hold upon the popular imagination4 ,obviously1 it depends upon the now exploded theory that the lake basin has been canted as a plane and that the axis of uptilt lies somewhere to the southward of the lake region1 or1 in any event1 to the southward of the present ,port ,huron outlet4 ,we know to-day that instead of being uniformly distributed over the entire lake region1 the uptilting goes on at a much higher rate within the northern areas1 and that since the early stage of ,lake ,whittlesey the hinge line of uplift has been steadily migrating northward with the retreat of the ice and is now well to the northward of the present outlet4 ,there is1 therefore1 no known uptilt of the district which separates the present from the former ,chicago outlet1 and there is no apparent natural cause which should result in the reoccupation of the old outlet to the ,mississippi4 ,the prophecy must be regarded as one that has been outgrown with the progress of science4 ,geological evidences of continued uplift4--,it has recently been claimed1 on the basis of a rexamination of ,gilbert's study of the lake gauge records1 that his methods are open to serious criticism and that in reality the figures afford no evidence of continued uplift of the region4 ,however this may be1 there are not lacking geological evidences which do not admit of doubt1 and these are in a striking way confirmatory of the latest conclusions upon the manner of the recent uplift4 ,if our conclusions have been correct1 the several lake basins should now be behaving in different ways as regards the changes upon their shores4 ,if it is true that the lines of greatest uptilt run north-northeasterly1 there should be1 speaking broadly1 a 8spilling over0 of waters upon the south-southwesterly shores and a laying bare of the north-northeasterly shore terraces of the basins4 ,this should1 however1 be true only of basins whose outlets are to the northeastward of the existing main hinge line of uptilt4 ,lake ,huron1 having its outlet at the southern margin of its basin1 should not have its waters encroaching upon the southern shore1 for the simple reason that any continued uptilt of the basin can only have the effect of pouring more water through the outlet4 ,lake ,michigan and ,saginaw ,bay1 which are arms of the ,huron basin1 ought1 however1 to become flooded upon their southern shores1 were it not that the hinge line of uptilt to-day lies to the northward of the outlet at ,port ,huron1 and1 further1 that the two connecting channels still have their beds lower than the sill of the outlet channel4 ,now the evidence goes to show that no encroachment of waters is occurring upon the ,chicago shore of ,lake ,michigan1 and although the shores of ,saginaw ,bay are so excessively flat as to reveal slight changes of level by large migrations of the strand1 yet the ancient meander posts fixed by the early surveys are still found near the water's edge4 ,drowning of southwestern shores of ,lakes ,superior and ,erie4--,within the basins occupied by ,lakes ,superior and ,erie1 a wholly different condition is found4 ,in each case the outlet is found to the northeastward 7,fig4 #cgd1 p4 #cde71 and the northwesterly trend of the isobases from these outlets is responsible for a continued elevation from uptilt of the outlets with reference to the western and southern shores4 ,in consequence1 the waters are encroaching upon these shores1 and rivers which there enter the lake are drowned at their mouths1 with the formation of estuaries4 ,upon ,lake ,superior these changes are very marked near ,duluth and particularly in the ,st4 ,louis ,river1 within which1 since the early treaty with the ,indians1 certain rapids have disappeared and submerged trunks of trees are now found in the channel of the river4 ,as far east as ,ontonagon essentially the same conditions are found4 ,upon the shores within the ,porcupine ,mountain district1 the waters are clearly rising4 ,here old cedar trees may be seen1 in some cases dead but still upright and standing in from six to eight inches of water a number of feet out from the present shore1 while others near the shore1 but upon the land and still living1 are washed by the waves1 and losing their lower bark in consequence4 ,an old road along the shore has had to be abandoned because of the encroaching water4 ,upon the opposite or northeastern shore of the lake1 on the other hand1 the land is everywhere rising out of the water1 and the waves are now building storm beaches well out upon the wave-cut terrace4 ,here the streams1 instead of forming estuaries by drowning1 drop down in rapids to the level of the lake4 ,illustration3 ,,fig4 #cgf4--,portion of the ,inner ,sandusky ,bay1 to afford a comparison of the shore line of #ahbj with that of to-day 7after ,moseley74 ,at the southwestern margin of ,lake ,erie there is everywhere evidence of a rapid encroachment by the water4 ,in the caves of ,south ,bass ,island stalactites1 which must obviously have formed above the lake level1 are now permanently submerged4 ,it is1 however1 about ,sandusky ,bay upon the southwest shore that the most striking observations have been made4 ,moseley has collected historical records of the killing of forest trees through a submergence which was the result of an advance of the water upon the shores4 ,it seems to be proven from his studies that the water is now rising in ,sandusky ,bay at a rate of about #b4ad feet per century4 ,in ,fig4 #cgf there is a comparison of the shores of the inner bay separated by an interval of about ninety years4 ,,reading ,,references ,,for ,,chapter ,,xxiv ,uptilt in basin of ,lake ,agassiz3-- ,,warren ,,upham4 ,the ,glacial ,lake ,agassiz1 ,mon4 #be1 ,u4 ,s4 ,geol4 ,surv41 pp4 #dgd-ebb4 ,uptilt in ,laurentian ,basin3-- ,g4 ,k4 ,,gilbert4 ,recent ,earth ,movement in the ,great ,lakes ,region1 #ahth ,ann4 ,rept4 ,u4 ,s4 ,geol4 ,surv41 #ahih1 ,pt4 ii1 pp4 #eie-fdg4 ,j4 ,w4 ,,spencer4 ,deformation of the ,algonquin ,beach1 etc41 ,am4 ,jour4 ,sci4 7#c71 vol4 #da1 #ahia1 pp4 #ad-af4 ,f4 ,b4 ,,taylor4 ,the ,highest ,old ,shore ,line of ,mackinac ,island1 ,am4 ,jour4 ,sci4 7#c71 vol4 #dc1 #ahib1 pp4 #baj-bah4 ,a4 ,c4 ,,lawson4 ,sketch of the ,coastal ,topography of the ,north ,side of ,lake ,superior1 with reference to the abandoned strands1 etc41 #bjth ,ann4 ,rept4 ,geol4 and ,nat4 ,hist4 ,surv4 ,minn41 #ahic1 pp4 #aha-bhi1 pls4 #g-ab4 ,j4 ,b4 ,,woodworth4 ,ancient ,water ,levels of the ,champlain and ,hudson ,valleys1 ,bull4 #hd1 ,n4,y4 ,state ,mus41 #aije1 pp4 #bfe1 pls4 #bh4 ,e4 ,l4 ,,moseley4 ,formation of ,sandusky ,bay and ,cedar ,point1 ,proc4 ,ohio ,state ,acad4 ,sci41 vol4 #d1 #aije1 ,pt4 v1 pp4 #agi-bch4 ,f4 ,e4 ,,wright4 ,rept4 ,geol4 ,surv4 ,mich4 for #aijc1 #aije1 p4 #cg4 ,j4 ,w4 ,,goldthwait4 ,the ,abandoned ,shore ,lines of ,eastern ,wisconsin1 ,bull4 #ag1 ,wis4 ,geol4 and ,nat4 ,hist4 ,surv41 #aijg1 pp4 #acd1 pls4 #cg2 ,a ,reconstruction of ,water ,planes of the ,extinct ,glacial ,lakes in the ,lake ,michigan ,basin1 ,jour4 ,geol41 vol4 #af1 #aijh1 pp4 #dei-dgf2 ,isobases of the ,algonquin and ,iroquois ,beaches and their ,significance1 ,bull4 ,geol4 ,soc4 ,am41 vol4 #ba1 #aiaj1 pp4 #bbg-bdh1 pl4 #e2 ,an ,instrumental ,survey of the ,shore ,lines of the ,extinct ,lakes ,algonquin and ,nipissing in ,southwestern ,ontario1 ,mem4 #aj1 ,dept4 of ,mines1 ,canada1 #aiaj1 pp4 #eg1 pls4 #d4 ,,william ,h4 ,,hobbs4 ,the ,late ,glacial and ,post-glacial ,uplift of the ,michigan ,basin1 ,pub4 #e1 ,mich4 ,geol4 and ,biol4 ,surv41 #aiaa1 pp4 #fh1 pls4 #b4 ,,lawrence ,,martin4 ,post-glacial ,modifications in and ,around the ,great ,lakes1 ,mon4 #eb1 ,u4 ,s4 ,geol4 ,surv41 #aiaa1 pp4 #dee-dei4 ,uptilt in northern ,europe3-- ,g4 ,,de ,,geer4 ,quaternary ,changes of ,level in ,scandinavia1 ,bull4 ,geol4 ,soc4 ,am41 vol4 #c1 #ahib1 pp4 #fe-fh1 pl4 #b4 ,h4 ,,munthe4 ,studies in the ,late ,quaternary ,history of ,southern ,sweden1 paper ,no4 #be1 ,livret ,guide1 ,cong4 ,gol4 ,intern41 #aiaj1 pp4 #if1 many plates and maps4 ,,chapter ,,xxv ,,niagara ,,falls ,a ,,clock ,,of ,,recent ,,geological ,,time ,features in and about the ,niagara gorge4--,a striking example of those permanent alterations of drainage which have resulted from the presence of the late continental glacier in ,north ,america is to be found in the ,niagara gorge between ,lakes ,erie and ,ontario4 ,with the aid of borings many of the now buried channels of the region have been followed out1 and in a later paragraph we shall refer to some of the stronger lines of the earlier drainage system4 ,before undertaking the study of ,niagara history1 it is essential that one become somewhat familiar with the present topography in and about the ,niagara gorge4 ,below the present cataract the river flows through a deep gorge for about seven miles before issuing at the ,lewiston ,escarpment 7,fig4 #cha1 p4 #cee74 ,this gorge has been cut in beds of rock sediments which dip at a gentle angle southward toward ,lake ,erie4 ,the capping of the rock series is a compact and relatively resistant limestone which is known as the ,niagara limestone1 beneath which there are alternating beds of shale with thinner limestone and sandstone4 ,the plain formed by the upper surface of the limestone capping terminates in the ,lewiston ,escarpment1 which is transverse to the direction of the gorge and seven miles distant below the ,falls4 ,the depth of the gorge varies markedly1 the above-water portion being represented at the upper end by the height of the cataract1 one hundred and sixty-five feet1 while at its lower end near ,lewiston it is twice that amount4 ,halfway down the gorge a sharp turn is made at an angle of more than ninety degrees1 and the upstream arm is extended to form a basin which contains the famous whirlpool4 ,this visible extension of the upper gorge is continued in a buried channel1 the ,st4 ,davids ,gorge1 which extends to the escarpment1 broadening as it does so in the form of a trumpet4 ,the materials which fill this earlier channel are notably coarse glacial deposits 7,fig4 #chi74 ,illustration3 ,,fig4 #cgg4--;,ideal cross section of the ,niagara gorge to show the marginal terrace4 ,directly above the whirlpool the ,niagara gorge is first contracted1 but almost immediately swells out into the form of a sausage1 which under the name of the ,eddy ,basin extends to the constricted channel occupied by the ,whirlpool ,rapids4 ,this ,gorge of the ,whirlpool ,rapids extends to and a little above the railroad bridges1 where it again suddenly widens and deepens and with surprisingly uniform cross section now continues as far as the cataract4 ,this uppermost section is known as the ,upper ,great ,gorge4 ,about a mile below the whirlpool is that remarkable projection into the gorge from the ,canadian wall which is known as ,wintergreen ,flats1 below which and nearer the river are ,fosters ,flats4 ,almost throughout its entire length the ,niagara gorge is bordered on either side by a narrow and gently incurving terrace eroded below the general level of the plain and meeting the gorge in a sharp angle 7,fig4 #cgg74 ,the features immediately about the cataract show that the ,falls are to-day in a condition which1 so far as we know1 has occurred but once before in their entire history--the waters of the river are divided unequally by an island1 and for this reason1 as we shall see1 the cataract enters over the side wall of the gorge instead of at its end 7,fig4 #cha71 although the turning of the channel from this cause is combined with a bend of the river4 ,illustration3 ,,fig4 #cgh4--,view of the bed of the ,niagara ,river above the cataract1 where water has been drained off in installing a power plant4 ,some separated blocks of limestone are still in place 7after ,j4 ,w4 ,spencer74 ,the drilling of the gorge4--,there appear to be two important processes which are responsible for the recession of the ,falls1 the rate of which is determined largely by the resistance of the limestone capping and the tenacity of the looser shale beneath it4 ,one of the eroding processes operates from below and undermines the cap until the unsupported cornice falls in blocks to the bottom of the gorge2 the other makes its attack directly from above1 selecting for the purpose the lines of jointing of the rock which it widens by solution and corrasion until the included blocks are in so far separated that they are torn out and go over the brink of the ,falls 7,fig4 #cgh74 ,this process of overhead attack in the powerful currents just above a cataract is even better illustrated by the ,falls of ,st4 ,anthony near ,minneapolis1 which have had a similar history of recession to that of the ,niagara ,falls 7,fig4 #cgi74 ,illustration3 ,,fig4 #cgi4--;,falls of ,st4 ,anthony1 looking westward from ,hennepin ,island in #ahea 7after ,n4 ,h4 ,winchell1 daguerreotype by ,hessler of ,chicago74 ,the blocks of the capping limestone at ,niagara ,falls are to some extent fixed in size by the joint planes present in them1 and as they fall to the bottom of the gorge1 they promote or retard the further recession of the ,falls according as they can or cannot be moved about by the churning currents beneath the cataract4 ,of the retarding effect there is an illustration in the accumulation of the blocks below the ,american and the intermediate ,luna ,falls 7plate #bc ,a71 which the weaker currents upon the ,american side find too heavy to handle4 ,illustration3 ,,fig4 #chj4--;,ideal section to show the nature of the drilling process beneath the cataract4 ,illustration3 ,,fig4 #cha4--,plan and section of the ,niagara gorge1 showing how in each section the depth is proportional to the width1 except in the lowest section where subsequent river action of the normal type has modified the bed of the channel 7plan after ,taylor and section after ,gilbert74 ,the ,canadian ,fall1 with its much greater power1 is an example of the promotion of recession through the churning about of the blocks at the base of the cataract4 ,we have here to do with a churn drill which bores its way into the bottom of the gorge with increasing radius of rotary motion with each increase in volume of the falling water4 ,under this rotary churning the soft shales are torn out near the bottom and in succession the harder layers above until the capping is reached 7,fig4 #chj74 ,the conditions appear now to be such that the effective work is largely concentrated1 as it usually has been1 near the middle of the channel2 and so the gorge recedes with a margin of the earlier river bed remaining as a terrace on either side and extending to the former river bank 7,fig4 #cgg74 ,as must have been noted1 one peculiarity of the operation of the churn drill beneath the cataract is that the depth of the gorge will bear a direct proportion to its width1 and if the volume of water has varied during the process of recession1 these changes in volume will be registered in the width and also in the depth of that section of the gorge which was drilled at the time--the cross section of the gorge at any place is proportional to the volume of the water falling in the cataract which produced it1 modified1 however1 by the competency to handle the joint blocks of definite size 7,fig4 #cha74 ,illustration3 ,,fig4 #chb4--;,comparison of a sketch of the ,canadian ,fall made with the aid of a camera lucida in #ahbg with a photograph taken from the same view point in #ahie 7after ,gilbert74 ,the present rate of recession4--,there are various sketches1 more or less accurate1 made in the early part of the nineteenth century1 and from the later period there are daguerreotypes1 photographs1 and maps1 which refer especially to the ,canadian ,fall2 and which1 taken together1 render possible a comparison of the earlier with the later brinks4 ,by comparing the earliest with the recent1 views it is seen at a glance that the ,falls are receding1 and at a quite appreciable rate 7,fig4 #chb74 ,a careful comparison of the maps made in #ahdb1 #ahge1 #ahhf1 #ahij1 and #aije of the brink of the ,canadian ,fall 7,fig4 #chc7 indicates that for the period covered the rate of recession has been about five feet per year1 and similar studies made of the ,american ,fall show that it has been receding at the rate of only three inches per year1 or one twentieth the rate of the recession of the ,canadian ,fall4 ,illustration3 ,,fig4 #chc4--,map to show the recession of the brink of the ,canadian ,fall1 based upon maps of different dates 7after ,gilbert74 ,future extinction of the ,american ,fall4--,it is because of this many times more rapid recession of the ,canadian ,fall that the ,niagara cataract1 instead of lying athwart the gorge1 enters it from its side4 ,the ,canadian ,fall is thus in reality swinging about the ,american1 and the time can already be roughly estimated when this more effective drilling tool will have brought about a capture1 so to speak1 of the ,american ,fall through the cutting off of its water supply4 ,it will then be drained and left literally 8high and dry01 an enduring witness to the geological effect of an island in making an unequal division of the waters for the work of two cataracts4 ,as already pointed out1 the inefficiency of the ,american ,fall as an eroding agent is amply attested by the wall of blocks already appearing above the water below it4 ,the tourist who a thousand years hence pays a visit to the ,niagara cataract1 provided the water flow is allowed to remain as it has been1 will find above this rampart of blocks a bare cliff in part undermined1 and surmounted by a nearly flat table surface which is cut off from the existing cataract by a higher section of the gorge 7,fig4 #chd74 ,it is quite likely that this table will furnish the most satisfactory viewpoint of the future cataract of that date4 ,illustration3 ,,fig4 #chd4--;,comparison of the present with the future falls4 ,the captured ,canadian ,fall at ,wintergreen ,flats4--,what we have predicted for the future of the present ,american ,fall will be the better understood from the study of a monument to earlier capture made long before the upper section of the gorge had been cut or the whirlpool had come into existence4 ,the tables were then turned1 for it was a fall upon the ,canadian side of the gorge that was captured by one upon the ,american4 ,the locality is known as ,wintergreen ,flats1 or sometimes as ,fosters ,flats2 though the first name properly applies to a higher surface near the brink of the gorge1 and ,fosters ,flats to a lower plain near the level of the river 7see ,fig4 #cha1 p4 #cee74 ,the peculiar topographic features at this locality are well brought out in ,gilbert's bird's-eye view of the locality 7,fig4 #che72 in fact1 in some respects better than they appear to the tourist upon the ground1 for the reason that the abandoned channel and the ,flats on the site of the since undermined island are both heavily forested and so not easy to include in a single view4 ,for one who has studied the existing cataract this early monument is full of meaning4 ,standing1 as one may1 upon the very brink of the former cataract1 it is easy to call up in imagination the grandeur of the earlier surroundings and to hear the thunder of the falling water4 ,a particularly vivid touch is added when1 in digging over the sand about the great blocks of fallen limestone underneath the brink1 one comes upon the shells of an animal still living in the ,niagara ,river1 though only in the continual spray beneath the cataract4 ,illustration3 ,,fig4 #che4--;,bird's-eye view of the captured ,canadian ,fall at ,wintergreen ,flats1 showing the section of the river bed above the cliff and the blocks of fallen ,niagara limestone strewn over the abandoned channel below 7after ,gilbert74 ,the ,whirlpool ,basin excavated from the ,st4 ,davids ,gorge4--,it has already been pointed out that a rock channel now filled with glacial deposits extends from the ,whirlpool ,basin to the edge of the escarpment at ,st4 ,davids 7,fig4 #chi1 p4 #cfc74 ,in plan this buried gorge has a trumpet form1 being more than two miles wide at its mouth and narrowing to the width of the upper gorge before it has reached the ,whirlpool4 ,near the ,whirlpool it has been in part excavated by ,bowman ,creek1 thus revealing walls that are well glaciated4 ,different opinions have been expressed concerning the origin of this channel1 one being that it is the course either of a preglacial river or one incised between consecutive glacial invasions2 and another that it is a cataract gorge drilled out between glacial invasions after the manner of the later ,niagara gorge4 ,in either case its contours have been much modified by the later glacier or glaciers1 whose work of planing1 polishing1 and widening is revealed in the exposed surfaces2 and it is not improbable that a cataract has receded along the course of an earlier river valley4 ,as we shall see1 there are facts which point rather clearly to an earlier cataract which ended its life immediately above the present ,whirlpool4 ,when the later ,niagara cataract had receded to near the upper end of the ,cove section1 or near the present ,whirlpool1 the falling water must have been separated from this older channel and its filling of till deposits by only a thin wall of rock1 and this must have been constantly weakened as its thickness was further reduced4 ,when this weakened dam at last gave way1 it must have produced a debacle grand in the extreme4 ,it is hardly to be conceived that the 8washout0 of the ancient channel to form the ,whirlpool ,basin could have occupied more than a small fraction of a day1 though it is highly probable that the broken rock partition below the ,whirlpool was not immediately removed entire4 ,the mandible-like termination of the ,eddy ,basin immediately above the ,whirlpool has led ,taylor to believe that the cataract quickly restablished itself at this point upon the last site of the extinct ,st4 ,davids cataract4 ,if reduced in power for a short interval1 as a result of the obstructions still remaining in the lately broken dam below the ,whirlpool1 the remarkable narrowing of the gorge at this point would be sufficiently accounted for4 ,being compelled to turn through more than a right angle after it enters the ,whirlpool ,basin1 the swift current of the ,niagara ,river is forced to double upon itself against the opposite bank and dive below the incoming current before emerging into the ,cove section below the ,whirlpool 7,fig4 #chf74 ,illustration3 ,,fig4 #chf4--,map of the ,whirlpool ,basin1 showing the rock side walls like those of the ,niagara ,gorge1 and the drift bank which forms the northwest wall 7after ,gilbert74 ,in tearing out the loose deposits which had filled this part of the buried ,st4 ,davids ,gorge1 many bowlders of great size were left which slid down the slope and in time produced an armor about the looser deposits beneath1 so as to protect them and prevent continued excavation4 ,thus it is found that the submerged northwestern wall of the basin is sheathed with bowlders large enough to retain their positions and so stop a natural process of placer outwashing upon a gigantic scale 7,fig4 #chf74 ,the shaping of the ,lewiston ,escarpment4--,to understand the formation of the ,lewiston ,escarpment cut in the hard ,niagara limestone1 it is necessary to consider the geology of a much larger area--that of the ,great ,lakes region as a whole4 ,to the north of the ,lakes in ,canada is found a most ancient continent which was in existence when all the area to the southward lay below the waters of the ocean4 ,in a period still very many times as long ago as the events we have under discussion1 there were laid down off the shore of this oldland a series of unconsolidated deposits which1 hardened in the course of time1 and elevated1 are now represented by the shales1 sandstone1 and limestone which we find1 one above the other1 in the ,niagara gorge in the order in which they were laid down upon the ocean floor4 ,the formations represented in the gorge are but a part of the entire series1 for other higher members are represented by rocks about ,lake ,erie and even farther to the southward4 ,these strata1 having been formed upon an outward sloping sea floor1 had a small initial dip to the southward1 and this has been probably increased by subsequent uptilt1 including the latest which we have so recently had under discussion4 ,at the present time the beds dip southward by an angle of less than four degrees1 or about thirty-five feet in each mile4 ,illustration3 ,,fig4 #chg4--,map to show the cuestas which have played so important a part in fixing the boundaries of the ,lake basins1 and also the principal preglacial rivers by which they have been trenched 7based upon a map by ,grabau74 ,when the elevation of the land in the vicinity of this shore had caused a recession of the waters1 there was formed a coastal plain on the borders of the oldland like that which is now found upon our ,atlantic border between the ,appalachians and the sea 7,fig4 #bgb1 p4 #bdf74 ,the rivers from the oldland cut their way in narrow trenches across the newland1 and because of the harder limestone formations1 their tributaries gradually became diverted from their earlier courses until they entered the trunk stream nearly at right angles and produced the type of drainage network which is called 8trellis drainage40 ,it is characteristic of this drainage that few tributaries of the second order will flow up the natural slope of the beds1 but on the contrary these natural slopes are followed in the softer rock nearly at right angles again to the tributaries of the first order of magnitude 7,fig4 #chg74 ,thus are produced a series of more or less parallel escarpments formed in the harder rock and having at their base a lowland which rises gradually in the direction of the oldland until a new escarpment is reached in the next lower of the hard formations4 ,such flat-topped uplands in series with intermediate lowlands and separated by sharp escarpments are known as cuestas 7see p4 #bdf71 and the ,lewiston ,escarpment limits that formed in ,niagara limestone 7,figs4 #chg and #chh74 ,illustration3 ,,fig4 #chh4--;,bird's-eye view of the cuestas south of ,lakes ,ontario and ,erie 7after ,gilbert74 ,episodes of ,niagara's history and their correlation with those of the ,glacial ,lakes4--,of the early episodes of ,niagara's history1 our knowledge is not as perfect as we could desire1 but the later events are fully and trustworthily recorded4 ,the birth of the ,falls is to be dated at the time when the ice front had here first retired into what is now ,canadian territory1 thus for the first time allowing the waters from the ,erie basin to discharge over the ,lewiston ,escarpment into the basin of the newly formed ,lake ,iroquois 7,fig4 #cfd1 p4 #ccd74 ,since the level of ,lake ,iroquois was far above that of the present ,lake ,ontario1 the new-born cataract was not the equivalent in height of the escarpment to-day4 ,the ,iroquois waters then bathed all the lower portion of the escarpment1 so that the foot of the ,fall was upon the borders of the ,lake4 ,in order to interpret the history of the ,niagara gorge1 we must remember that the effective drilling of this gorge was in each stage dependent mainly upon the volume of water discharged from ,lake ,erie1 a large discharge being recorded by a channel drilled both wide and deep1 while that produced by the discharge of a smaller volume was correspondingly narrow and shallow4 ,to-day the gorges of large cross section have1 moreover1 a relatively placid surface1 whereas through the constricted sections the water of the river is unable to pass without first raising its level at the upper end and under the head thus produced rushing through under an increased velocity4 ,the best illustration of such a constricted section is the ,gorge of the ,whirlpool ,rapids4 ,illustration3 ,,fig4 #chi4--,sketch map of the greater portion of the ,niagara ,gorge to show the changes in cross section in their relations to ,niagara history 7based upon a map by ,taylor74 ,our reading of the history should begin at the site of the present cataract1 since the records of later events are so much the more complete and legible1 and it should ever be our plan to proceed from the clearly written pages to those half effaced and illegible4 ,as we have learned1 the most abrupt change in the cross section of the gorge is found a little above the railroad bridges1 where the ,upper ,great ,gorge is joined to the ,gorge of the ,whirlpool ,rapids 7,fig4 #chi74 ,in view of the remarkably uniform cross section of the ,upper ,great ,gorge1 there is no reason to doubt that it has been drilled throughout under essentially the same volume of water1 and that its lower limit marks the position of the former cataract when the waters from the upper lakes were transferred from the 8,north ,bay ,outlet0 into the present or 8,port ,huron ,outlet0 and ,lake ,erie4 ,as the upper limit of the ,gorge of the ,whirlpool ,rapids thus corresponds to the closing of the 8,north ,bay ,outlet0 and the extinction of the ,nipissing ,great ,lakes1 so its lower limit doubtless corresponds to the opening of that outlet and the termination of the preceding ,algonquin stage2 for in the stage of the ,nipissing lakes the water of the upper lakes1 as we have learned1 reached the ocean through the northern outlet4 ,mr4 ,frank ,taylor1 who has given much study to the problem of ,niagaran history1 believes that the ,middle ,great ,gorge1 comprising the ,eddy ,basin and the ,cove section1 represents the gorge drilling which occurred during the later stage of ,lake ,algonquin after the 8,trent ,outlet0 had been closed and the waters of the upper lakes had been turned into the ,erie ,basin4 ,summarizing1 then1 the episodes of the lake and the gorge history are to be correlated as follows3-- ,,glacial ,,lake ,,niagara ,,gorge ,early ,lakes ,iroquois and ,algonquin4 ,drilling of the gorge from the ,lewiston ,escarpment to the ,cove section above the ,wintergreen ,flats4 ,later ,lakes ,iroquois and ,algonquin ,drilling of ,middle ,great ,gorge4 with upper lakes discharging into ,erie basin4 ,nipissing ,great ,lakes with the ,drilling of the narrow ,gorge of upper lake waters diverted from the ,whirlpool ,rapids4 ,lake ,erie4 ,recent ,st4 ,lawrence drainage ,drilling of ,upper ,great ,gorge to since the waters of the upper lakes the present cataract4 were discharged into ,lake ,erie through occupation of the ,port ,huron ,outlet4 ,time measures of the ,niagara clock4--,in primitive civilizations time has sometimes been measured by the lapse necessary to accomplish a certain task1 such1 for example1 as walking the distance between two points2 and the natural clock of ,niagara has been of this type4 ,but men possess differences in strength and speed1 and the same man is at some times more vigorous than at others1 and so does not work at a uniform rate4 ,the cataract of ,niagara1 charged with the pent-up energy of the waters of all the ,great ,lakes1 can rush its work as it is clearly unable to do at times when the greater part of this energy has been diverted4 ,units of distance measured along the gorge are therefore too unreliable for our use1 with the unique exception of the stretch from the railroad bridges to the site of the present cataract1 within which stretch the gorge cross sections are so nearly uniform as to indicate an approximation to continued application of uniform energy4 ,this energy we may actually measure in the existing cataract1 and so fix upon a unit of time that can be translated into years4 ,in order to secure the normal rate of recession of this ,upper ,great ,gorge1 we should add to the volume of water in the ,canadian ,fall that now passing over the ,american2 and for the reason that the blocks which fall from the cataract cornice and are the tools of the drilling instrument approximate to a definite size fixed by their joint planes1 the effect of this added energy it is not easy to estimate4 ,we may be sure1 however1 that the drilling action would be somewhat increased by the junction of the two ,falls1 and thus are assured that the average rate of recession within the ,upper ,great ,gorge has been somewhat in excess of the five feet per year determined by ,gilbert for the present ,canadian ,fall4 ,the ,upper ,great ,gorge is about two miles in length1 and its beginning may thus be dated near the dawning of the ,christian ,era4 ,the ,whirlpool ,gorge was cut when the ice vacated the ,north ,bay ,outlet in ,canada1 and still lay as a broad mantle over all northeastern ,canada4 ,for the earlier gorge and lake stages1 the time estimates are hardly more than guesses1 and we need not now concern ourselves with them4 ,the horologe of late glacial time in ,scandinavia4--,a glacial timepiece of somewhat different construction and of greater refinement has been made use of in ,scandinavia to derive the 8geochronology of the last #ab1jjj years40 ,instead of retreating over the land and impounding the drainage as it did so1 the latest continental glacier of ,scandinavia ended below sea level1 and as it retired1 its great subglacial river laid down a giant esker known as the ,stockholm ,os1 which was bordered by a delta and fringed on either side by water-laid moraines of the block type4 ,these recessional moraines are upon the average less than #ajjj feet apart1 and are believed to have each been formed in a single season4 ,the delta deposits which surround the esker are of thin-banded clay1 and as an additional uppermost band is found outside every moraine1 these bands are also believed to represent each the delta deposit of a single year4 ,in studies extending over many years1 ,baron de ,geer1 with the aid of a large body of student helpers1 has succeeded in completing a count of moraines and clay layers1 and so in determining the time to be #ab1jjj years since the ice front of the latest continental glacier lay across southern ,sweden4 ,the fertility of conception and the thoroughness of execution of this epoch-making investigation recommend its conclusion to the scientific reader4 ,,reading ,,references ,,for ,,chapter ,,xxv ,g4 ,k4 ,,gilbert4 ,niagara ,falls and their ,history1 ,nat4 ,geogr4 ,soc4 ,mon41 vol4 #a1 ,no4 #g1 #ahie1 pp4 #bjc-bcf4 ,f4 ,b4 ,,taylor4 ,origin of the ,gorge of the ,whirlpool ,rapids at ,niagara1 ,bull4 ,geol4 ,soc4 ,am41 vol4 #i1 #ahih1 pp4 #ei-hd4 ,a4 ,w4 ,,grabau4 ,guide to the ,geology and ,paleontology of ,niagara ,falls and ,vicinity1 ,bull4 ,n4 ,y4 ,state ,mus41 vol4 #i1 ,no4 #de1 #aija1 pp4 #a-he1 pls4 #a-aa4 ,j4 ,w4 ,,spencer4 ,the ,falls of ,niagara1 etc4 ,dept4 of ,mines1 ,geol4 ,surv4 ,branch1 ,canada1 #aijg1 pp4 #dij1 pls4 #dc4 ,g4 ,k4 ,,gilbert4 ,rate of ,recession of ,niagara ,falls1 etc4 ,bull4 #cjf1 ,u4 ,s4 ,geol4 ,surv41 #aijg1 pp4 #ca1 pls4 #aa4 ,g4 ,,de ,,geer4 ,quaternary ,sea ,bottoms of ,western ,sweden4 ,paper #bc1 ,livret ,guide ,cong4 ,gol4 ,intern41 #aiaj1 pp4 #eg1 pls4 #c4 ,,chapter ,,xxvi ,,land ,,sculpture ,,by ,,mountain ,,glaciers ,contrasted sculpturing of continental and mountain glaciers4--,in discussing in a previous chapter the rock pavement lately uncovered by the ,greenland glacier1 we learned that this surface had been lowered by the processes of plucking and abrasion1 the combined effect of which is always to reduce the irregularities of the surface1 soften its outlines1 and from sharply projecting masses to develop rounded shoulders of rock--roches moutonnes4 ,though the same processes act in much the same manner beneath mountain glaciers1 though here upon all parts of the bed1 they are1 in the earlier stages at least1 subordinated to a third process more important than the two acting together4 ,sculpture by mountain glaciers1 instead of reducing surface irregularities and softening outlines1 increases the accent of the relief and produces the most sharply rugged topography that is known4 ,in nearly all places where ,alpinists resort for difficult rock climbing1 mountain glaciers are to be seen1 or the evidence for their former presence may be read in unmistakable characters4 ,wind distribution of the snow which falls in mountains4--,until quite recently students of glaciation have concerned themselves but little with the work of the wind in lifting and redistributing the snow after it has fallen4 ,we have already seen that1 for the continental glaciers1 wind appears to be the chief transporting agent1 if we except the marginal lobes where glacier flow assumes large importance4 ,in the case of mountain glaciers1 also1 we are to find that for the earlier stages particularly wind is of the first importance as a redistributing agent4 ,in the higher levels snow is swept up from the ground by all high winds1 and does not find a resting place until it is dropped beneath an eddy in some irregularity of the surface2 and if the inherited surface be relatively smooth1 this will be found in most cases upon the lee of the mountain crest4 ,in normal cases at least the inherited irregularities of the higher zones of mountain upland are the gentle depressions which develop at the heads of streams4 ,these become1 then1 the sites of snowdrifts that are augmented in size from year to year1 though at first they melt away in the late summer4 ,illustration3 ,,fig4 #cij4--,snowdrift hollowing its bed by nivation and building a delta 7at the left74 ,quadrant ,mountain1 ,yellowstone ,national ,park4 ,the niches which form on snowdrift sites4--,wherever a drift is formed1 a process is set in operation1 the effect of which is to hollow out and lower the ground beneath it1 a process which has been called nivation4 ,the drift shown in ,fig4 #cij was photographed in late summer at an elevation of some #ijjj feet in the ,yellowstone ,national ,park4 ,the very gently sloping surface surrounding the drift is covered with grass1 but within a zone a few feet in width on the borders of the drift no grass is growing1 and in its place is found a fine brown soil which is fast becoming the prey of the moving water derived by melting of the drift4 ,this is explained by the water permeating the crevices of the rock and being rent by the nightly freezing4 ,farther from the drift the ground is dry1 and no such action is possible4 ,with each succeeding spring the augmented drift as it melts carries all finely comminuted rock material down slopes beneath the snow to emerge at the lowest margin and be there deposited in the form of a delta4 ,by the operation of this process of nivation the higher parts of the drift site are lowered as deposition goes on upon the lower4 ,the combined effect is thus to produce a niche or faintly etched amphitheater upon the slope of the mountain 7,fig4 #cia74 ,illustration3 ,,fig4 #cia4--;,amphitheater formed on a drift site in northern ,lapland 7after a photograph by ,g4 von ,zahn74 ,the augmented snowdrift moves down the valley--birth of the glacier4--,in still lower air temperatures the drifts enlarge with each succeeding year until they endure throughout the summer season4 ,from this stage on1 an increment of snow is left from each succeeding season4 ,no longer entirely wasted by melting1 the time soon comes when the upper snow layers will by their weight compress the lower into ice1 and the mass will begin to creep down the slope along the course of the inherited valley4 ,the enlarged snowdrift which feeds this ice stream is called the nv or firn4 ,against the sloping cliff which had been shaped by nivation at the upper margin of the snowdrift1 that snow which is not of sufficient depth to begin a movement towards the valley separates from the moving portion1 opening as it does so a cleft or crevasse parallel to the wall4 ,this crack in the snow is called by its ,german name ,bergschrund or ,randspalte1 and may perhaps be referred to as the marginal crevasse 7,fig4 #cib74 ,illustration3 ,,fig4 #cib4--,the marginal crevasse or ,bergschrund on the highest margin of a glacier 7after ,gilbert74 ,the excavation of the glacial amphitheater or cirque4--,it has been found that the marginal crevasse plays a most important rle in the sculpture of mountains by glaciers1 for the great amphitheater which is everywhere the collecting basin for the nourishment of mountain glaciers is not an inherited feature1 but the handiwork of the ice itself4 ,this was the discovery of ,mr4 ,w4 ,d4 ,johnson1 an ,american topographer and geologist1 who1 in order to solve the problem of the amphitheater allowed himself to be lowered into such a crevasse upon the ,mount ,lyell glacier of the ,sierra ,nevadas in ,california4 ,illustration3 ,,fig4 #cic4--,niches and cirques in the same vicinity in the ,bighorn ,mountains of ,wyoming4 ,a1 ,a1 unmodified valleys2 ,b1 ,b1 niches on drift sites2 ,c1 ,c1 cirques on small glacier sites 7after map by ,f4 ,e4 ,mathes1 ,u4 ,s4 ,g4 ,s474 ,let down a distance of a hundred and fifty feet1 he reached the bottom of the crack1 and in a drizzling rain of thaw water stood upon a floor composed of rock masses in part dislodged from a wall which extended some twenty feet upwards upon the cliff side of the crevasse4 ,it was evident that the warm air of the day produced the thaw water which was constantly dripping and which filled every crack and cranny of the rock surface4 ,with the sinking of the sun below the peaks the sudden chill1 so characteristic of the end of the day in high mountains1 causes this water to freeze and thus rend the rock along its planes of jointing4 ,broad and thin plates of ice1 loosened by melting at the walls1 could be extracted from the crevices of the rock as mute witnesses to the powerful stresses developed by this most vigorous of weathering processes4 ,illustration3 ,,fig4 #cid4--,subordinate small cirques in the amphitheater on the west face of the ,wannehorn above the ,great ,aletsch ,glacier of ,switzerland4 ,in short1 the rock wall above the glacier1 which in its initial stage was the upper wall of the niche hollowed beneath the snowdrift1 is first steepened and later continually both recessed and deepened by an intensive frost rending which is in operation at the base of the marginal crevasse4 ,the same process does not go on as rapidly above the surface of the nv for the reason that the necessary wetting of the rock surface does not there so generally result from the daily summer thaw4 ,at the bottom of the marginal crevasse alone is this condition fully realized4 ,intensive frost action where the rock is wet with thaw water daily is thus a fundamental cause1 both of the hollowing of the early drift site to form the niche1 and of the later enlargement of this niche into an amphitheater or cirque when the drift has been transformed into the nv of a glacier4 ,inasmuch as the crevasse forms where the snow and ice pull away from the rock toward the middle of the depression1 the cirque wall in its early stage has the outline of a semicircle4 ,in the ,bighorn ,mountains of ,wyoming1 all stages1 from the unmodified valley heads to the full-formed cirque1 may be seen near one another 7,fig4 #cic74 ,it will be noted that wherever a glacier has formed1 as indicated by the cirque1 there is a series of lakes which have developed in the valley below 7see p4 #dab74 ,illustration3 ,,fig4 #cie4--8;,biscuit cutting0 effect of glacial sculpture in the ,uinta ,mountains of ,wyoming 7after ,atwood74 ,illustration3 ,,fig4 #cif4--,two intersecting inverted cones representing glacial cirques of different sizes1 to show that their intersection is the arc of a hyperbola1 the curve to which the col approximates4 ,life history of the cirque4--,in its earliest stage the cirque is more or less uniformly supplied with snow from all sides1 and so it enlarges by recession in a manner to retain its early semicircular outline4 ,in a later stage a larger proportion of the snow reaches the cirque at its sides so that its further enlargement causes it to broaden and to flatten somewhat that part of its outline which represents the head of the valley 7,fig4 #chi1 p4 #cfd74 ,as the territory of the upland is still further invested by the cirques1 their nourishment becomes still more irregular1 and the circular outline gives place to a scalloped border1 as the amphitheater becomes differentiated into subordinate smaller cirques1 each of which corresponds to a scallop of the outline 7,fig4 #cih and ,fig4 #cid74 ,grooved and fretted uplands4--,the partial investment by cirques of a mountain upland yields a type of topography quite unlike that produced by any other geological process4 ,the irregularly connected remnants of the inherited upland resemble nothing so much as a layer of dough from which biscuits have been cut 7,fig4 #cie74 ,the surface as a whole1 furrowed as it is below the cirques1 may be described as a grooved upland 7plate #ai ,a74 ,a further continuation of the process removes all traces of the earlier upland1 for the cirques intersect from opposite sides and thus yield palisades of sharp rock pinnacles which rise on precipitous walls from a terraced floor4 ,this ultimate product of cirque sculpture by glaciers is called a fretted upland 7plate #ah ,a and #ai ,b74 ,,plate #ah4 ,illustration3 ,a4 ,fretted upland of the ,alps seen from the summit of ,mount ,blanc4 ,illustration3 ,b4 ,model of the ,malaspina ,glacier and the fretted upland above it 7after model by ,l4 ,martin74 ,,plate #ai4 ,illustration3 ,a4 ,contour map of a grooved upland1 ,bighorn ,mountains1 ,wyoming 7,u4 ,s4 ,geol4 ,survey74 ,illustration3 ,b4 ,contour map of a fretted upland1 ,philipsburg ,quadrangle1 ,montana 7,u4 ,s4 ,geol4 ,survey74 ,the features carved above the glacier4--,the ranges of pinnacles carved out by mountain glaciers have become known by various names of foreign derivation1 such as arte1 grat1 aiguille mountains1 8files of gendarmes01 etc4 ,they may1 perhaps1 be best referred to as comb ridges1 and according to their position they are differentiated into main and lateral comb ridges1 as will be clear from the second map of plate #ai4 ,illustration3 ,,fig4 #cig4--;,a col shaped like a hyperbola between ,mount ,sir ,donald and ,yogo ,peak in the ,selkirks 7after a plate by the ,keystone ,plate ,co474 ,with the gradual invasion of the upland upon which the cirques have made their attack1 the area from which winds may gather up the snow is steadily diminished1 and hence cirque recession is correspondingly retarded4 ,cirques which have approached each other from opposite sides of the ridge until they have become tangent at one point may1 however1 still receive nourishment at the sides and so continue to cut down the intervening rock wall to form a pass or col4 ,the theoretical curve which results from this intersection is that known as the hyperbola1 of which an illustration is afforded by ,fig4 #cif4 ,an approximation to this form is clearly furnished by most of the mountain passes in glaciated mountain districts1 and a particularly good illustration is furnished from the vicinity of ,glacier on the line of the ,canadian ,pacific ,railway 7,fig4 #cig74 ,illustration3 ,,fig4 #cih4--;,diagrams to illustrate the progressive investment of an upland by cirques with the formation of comb ridges1 cols1 and horns4 ,i1 early stage1 youth2 ,,ii1 intermediate stage2 ,,iii1 late stage1 maturity4 ,upon either side of the col the land mass is left in high relief1 rising from a more or less triangular base 7,fig4 #cih1 ,,iii7 into a sharp horn or tooth4 ,an illustration of such a horn is furnished by the ,matterhorn in the ,swiss ,alps1 or by ,mount ,sir ,donald in the ,selkirks1 though less noteworthy examples may be found in every maturely glaciated mountain district4 ,the features shaped beneath the glacier4--,those features which are carved above the glacier--the comb ridge1 the col1 and the horn--are all shaped as a result of intensive weathering upon the cirque wall4 ,the shaping at lower levels is accomplished by processes in operation below the glacier surface1 where weathering is excluded and where plucking and abrasion work together to tear away and grind off the rock surface4 ,by their joint action the valley is both deepened and widened1 directly to the height of the glacier surface1 and indirectly through undermining as far up as rock extends4 ,thus the valley is transformed into one of broad and flat bed and precipitous side walls--the ,u-shaped section illustrated by valleys of the ,swiss ,alps and in fact in all districts which have been strongly glaciated by mountain glaciers 7,fig4 #cii74 ,illustration3 ,,fig4 #cii4--,the ,u-shaped ,kern valley in the ,sierra ,nevadas of ,california 7after ,w4 ,b4 ,scott74 ,as high up in the valley as it has been occupied by the glacier1 the bed is rounded1 smoothed1 and polished1 and marked by the characteristic glacial scorings or stri which point down the valley4 ,above the level of the glacier's upper surface1 on the other hand1 erosion is accomplished through undermining or sapping1 a process which always leaves precipitous slopes of ragged surface made up of the joint planes on which the fallen blocks have separated from the cliff4 ,thus there is found a sharp line which separates the smoothly rounded rock surface below from the jagged and precipitous one above 7,fig4 #djj74 ,inasmuch as this boundary usually separates the scalable from the inaccessible slopes above1 snow is apt to lodge at this level and make it strikingly apparent4 ,illustration3 ,,fig4 #djj4--;,glaciated valley wall in the ,sierra ,nevadas of ,california1 showing the sharp line which separates the abraded from the undermined rock surface 7after a photograph by ,fairbanks74 ,illustration3 ,,fig4 #dja4--,view of the ,vale of ,chamonix from the sracs of the ,glacier des ,bossons4 ,the alb of the opposite side is well brought out4 ,if uplift of the land occurs while glaciers occupy the valleys of mountains1 an increased capacity for deepening the valley is imparted to these ice streams1 and we find1 as a result1 a deep central valley of ,u cross section excavated within a relatively broad trough visible above the shoulder on either side of the later furrow4 ,save only for its characteristic curves1 such a valley bears close resemblance to a mature stream valley which has been rejuvenated 7see p4 #agc74 ,the remnants of the earlier glacier-carved valley are1 as already stated1 gently curving high terraces so common in ,switzerland1 where they are known as albs or high mountain meadows4 ,these albs may be seen to special advantage on the sides of the ,chamonix valley 7,fig4 #dja71 the ,lauterbrunnen valley1 or in fact almost any of the larger ,alpine valleys4 ,the cascade stairway in glacier-carved valleys4--,if now1 instead of giving our attention to the cross section1 we follow the course of the valley that has been occupied by a glacier1 we find that it descends by a series of steps or terraces having many backwardly directed treads 7plate #ai71 whereas a normal and well-established river valley has only forward grades4 ,because of these backward grades the stream waters are impounded1 and so lakes are found strung along the valley in chains as the larger beads are found in a rosary1 and these are the characteristic rock basin lakes sometimes referred to as 8,paternoster ,lakes0 7see p4 #dab and ,fig4 #djb74 ,,plate #bj4 ,illustration3 ,map of the surface modeled by mountain glaciers in the ,sierra ,nevadas of ,california 7after ,i4 ,c4 ,russell74 ,when the backward grades upon the valley floor are especially steep1 the rock step becomes a rock bar1 or ,riegel1 of which nearly every ,alpine valley has its examples4 ,in a walk from the ,grimsel to ,meiringen many such bars are passed4 ,carrying in suspension the sharp rock sand from the glacier deposits along its bed1 the stream which succeeds to the glacier as it vacates its valley saws its way through these obstructions with a rapidity that is amazing1 thus producing narrow defiles1 of which the ,gorge of the ,aar near ,meiringen and that of the ,gorner near ,zermatt are such well-known examples 7,fig4 #djc74 ,illustration3 ,,fig4 #djb4--,map of an area near the continental divide in ,colorado1 showing an unglaciated surface to the west of the divide1 where the westerly winds have cleared the ground of snow1 and the glacier-carved country to the eastward4 ,note the regular forms of the youthful cirque1 the glacier stairway1 and the rock basin lakes 7,u4 ,s4 ,g4 ,s474 ,illustration3 ,,fig4 #djc4--;,gorge of the ,albula ,river near ,berkum in the ,engadine1 cut through a rock bar by the river which has succeeded to the earlier glacier4 ,illustration3 ,,fig4 #djd4--;,idealistic sketch showing both glaciated and nonglaciated side valleys tributary to a glaciated main valley 7after ,davis74 ,it is characteristic of rivers that the tributaries cut their valleys more rapidly than does the main stream within the neighboring section1 though they cannot cut lower than their outlets--the side streams enter accordantly4 ,this is easily explained because the grades of the tributary streams are the steeper1 and1 as we well know1 the corrosion of a valley is augmented at a most amazing rate for each increase of its grade4 ,no such law controls the processes of plucking and abrasion by which the glacier lowers its floor1 for these processes appear to depend for their efficiency upon the depth of the ice1 and the supply of cutting tools1 quite as much as upon the grade of the bed4 ,to apply a homely illustration1 the hollowing of flagstones upon our walks is dependent more upon the number of persons that pass over them1 and upon their size and the number of protruding nails in their boot heels1 than upon the grades upon which they are placed4 ,at all events we find that the main glacier valleys are cut deeper than the side valleys1 so that the latter become hanging valleys--they enter the main valley1 not upon its bed1 but some distance above it 7,fig4 #djd74 ,the ,u-shaped hanging valleys1 like the main valley1 are much too large for the streams which now fill them1 and these diminutive side streams plunge over the steep wall of the main valley in ribbon-like falls so thin that the wind turns them aside and disperses the water in the spray of a 8bridal veil40 ,such falls are found by the hundred in every glaciated mountain district1 imparting to it one of the greatest of its scenic charms4 ,illustration3 ,,fig4 #dje4--;,character profiles in landscapes sculptured by mountain glaciers4 ,illustration3 ,,fig4 #djf4--;,flat dome shaped under the margin of a ,norwegian ice cap with projecting rock knobs and moraines in foreground4 ,the character profiles which result from sculpture by mountain glaciers4--,the lines which are repeated in landscapes carved by mountain glaciers are easy to recognize 7,fig4 #dje74 ,the highest horizon lines are the outlines of horns which are separated by cols4 ,minaret-like palisades1 or 8files of gendarmes01 often run for long distances as the characteristic comb ridges4 ,lower down and lacking the lighter background of the sky1 we make out with less distinctness the ,u-valley1 either with or without the albs to show that the sculpturing process has been interrupted by uplift4 ,illustration3 ,,fig4 #djg4--,two views illustrating successive stages in the shaping of tinds or 8beehive0 mountains4 ,the sculpture accomplished by ice caps4--,in the case of ice caps1 the only rock exposed is found in the neighborhood of the margin--the projecting islands known as nunataks4 ,it is essential for the existence of the ice cap that the rock base should have relatively slight irregularities compared to the dimensions of the cap itself4 ,except in very high latitudes this base must be somewhat elevated1 for like mountain glaciers ice caps are nourished by the surface air currents1 and their snows are deposited above the snow line4 ,the ,norwegian tind or beehive mountain4--,within temperate or tropical climes the snow line lies so high that only the loftier mountains are able to support glaciers4 ,it follows that those which are formed flow upon relatively high grades with correspondingly high rate of movement and increased cutting power4 ,within high latitudes the snow is found nearer the sea level1 and glaciers are for the most part correspondingly sluggish in their movements as well as less active denuding agents4 ,to this condition characteristic of high latitude glaciers1 there is added in ,norway another in the peculiar shape of the basement beneath the recent and the still existing glaciers4 ,the plateau of ,norway is intersected by a network of deep and steep walled fjords1 and the glaciers have developed as small ice caps perched upon veritable pedestals of rock1 over the margins of which their outlet tongues of ice descend on steep slopes into the fjord4 ,the tops of the pedestals thus come to be shaped by the plucking and abrading processes into flat domes 7,fig4 #djf71 while the knobs of rock1 which as nunataks reach above the surface of the ice1 divide the outflowing ice tongues at the margin of the pedestal4 ,these tongues being much more active denuding agents1 because of their steep gradients1 continually lower their beds1 thus transforming the earlier knobs of rock into high and steep mountains of more or less circular base4 ,such 8beehive0 mountains upon the margins of the fjords are the characteristic ,norwegian tinds 7,fig4 #djg74 ,,reading ,,references ,,for ,,chapter ,,xxvi ,i4 ,c4 ,,russell4 ,quaternary ,history of ,mono ,valley1 ,california1 #hth ,ann4 ,rept4 ,u4 ,s4 ,geol4 ,surv41 #ahhi1 pp4 #cbi-cga1 pls4 #bg-cg4 ,f4 ,e4 ,,matthes4 ,glacial ,sculpture of the ,bighorn ,mountains1 ,wyoming1 #bast ,ann4 ,rept4 ,u4 ,s4 ,geol4 ,surv41 #aijj1 ,pt4 ii1 pp4 #agi-ahe1 pl4 #bc4 ,w4 ,d4 ,,johnson4 ,maturity in ,alpine ,glacial ,erosion1 ,jour4 ,geol41 vol4 #ab1 #aijd1 pp4 #efi-egh4 ,g4 ,k4 ,,gilbert4 ,systematic ,asymmetry of ,crest ,lines in the ,high ,sierras of ,california1 ibid41 pp4 #egi-ehh4 ,,emm4 ,,de ,,martonne4 ,sur la ,formation des ,cirques1 ,ann4 de ,gogr41 vol4 #aj1 #aija1 pp4 #aj-af4 ,w4 ,m4 ,,davis4 ,glacial ,erosion in ,north ,wales1 ,quart4 ,jour4 ,geol4 ,soc4 ,lond41 vol4 #fe1 #aiji1 pp4 #bha-cej1 pl4 #ad4 ,,ed4 ,,br,,ckner4 ,die ,glazialen ,zge im ,antlitz der ,alpen1 ,naturw4 ,wochenschr41 ,n4 ,f41 vol4 #h1 #aiji4 ,,william ,h4 ,,hobbs4 ,characteristics of ,existing ,glaciers1 pp4 #a-if4 ,,chapter ,,xxvii ,,successive ,,glacier ,,types ,,of ,a ,,waning ,,glaciation ,transition from the ice cap to the mountain glacier4--,a study of existing glaciers leads inevitably to the conclusion that although subject to short period advances and retreats1 yet1 broadly speaking1 glaciers are now gradually wasting away1 surrounded by wide areas upon which are the evidences of their recent occupation4 ,we are thus living in a receding hemicycle of glaciation4 ,illustration3 ,,fig4 #djh4--,schematic diagram to show the relationships of glacier types formed in succession during a receding hemicycle of glaciation4 ,many mountain districts which now support small glaciers only1 or none at all1 were once nearly or quite submerged beneath snow and ice4 ,if once covered by an ice carapace or cap1 our present interest in them begins at that stage of the receding hemicycle when the rock surface has made its reappearance above the surface of the snow-ice mass4 ,at this stage intensive frostwork1 the characteristic high level weathering1 begins1 and cirques develop above the scars of those earlier amphitheaters formed in the advancing hemicycle4 ,the piedmont glacier4--,in this early stage of transition from the ice cap to the mountain glacier1 the ice flows outward to the mountain front in ill-defined streams divided by the projecting ridges1 and upon reaching the mountain front these streams deploy upon it so as to coalesce in a great stagnant ice apron whose upper surface slopes gently forward at an angle of a few degrees at the most 7,fig4 #djh1 stage ,i74 ,this is the piedmont glacier1 a type found to-day in the high latitudes of ,alaska and in the southern ,andes 7,fig4 #dji and pl4 #ah ,b74 ,illustration3 ,,fig4 #dji4--,map of the ,malaspina glacier of ,alaska1 the best known of existing piedmont glaciers 7after ,russell74 ,during this stage the cirques may be but poorly defined1 and ice flows in both directions from rock divides so that the streams transect the range1 and later1 after the glaciers have disappeared1 may expose a pass smoothed and polished upon its floor and with stri directed in opposite directions from the highest point4 ,the pass of the ,grimsel in ,switzerland furnishes an excellent illustration of such earlier transection of the range4 ,illustration3 ,,fig4 #daj4--,map of the ,baltoro glacier of the ,himalayas1 a typical glacier of the dendritic type4 ,the expanded-foot glacier4--,as air temperatures continue to become milder1 the glacier streams within the mountains are less deep and hence more clearly defined1 and instead of coalescing upon the mountain foreland1 they now issue from the mountains to form individual aprons and are described as expanded-foot glaciers 7,fig4 #djh1 stage ,,ii1 and ,fig4 #bib1 p4 #bfd74 ,illustration3 ,,fig4 #daa4--,the ,triest glacier1 a hanging glacieret separated from the ,great ,aletsch glacier to which it was lately a tributary4 ,the dendritic glacier4--,still later in the hemicycle nourishment of the glaciers is diminished as depletion from melting increases1 so that the glacier streams no longer reach to the mountain front4 ,branches continue to enter the main valley from the several side valleys like the short branches of a tall tree1 and because of this arrangement such a glacier may be described as a dendritic glacier 7,fig4 #djh1 stage ,,iii1 and ,fig4 #daj74 ,inasmuch as the depletion from melting increases at a rapid rate in descending to lower levels1 the tributary glacier valleys 8hanging0 above the main valley in the lower stretches become separated1 and may continue to exist as series of hanging glacierets upon either side of the main valley below the glacier front 7,fig4 #djh1 stage ,,iii1 and ,fig4 #daa74 ,it must be clear from this that any attempt to name each separated ice stream without regard to its relationship must lead to endless confusion1 for glacier size is in such sensitive adjustment to air temperature that a fall or rise of a few degrees only in the average annual temperature of the district may prove sufficient to fuse many glaciers into one or separate one ice mass into many smaller ones4 ,when in high latitudes a dendritic glacier descends in fjords to below the level of the sea1 it is attacked by the water in the same manner as are the outlets of ,greenland glaciers1 and is then known as a 8tidewater glacier01 which may thus be a subtype or variety of the dendritic glacier 7,fig4 #dab74 ,illustration3 ,,fig4 #dab4--,the ,harriman fjord glacier of ,alaska1 a tidewater variety of dendritic glacier 7after a map by ,gannett74 ,the radiating 7,alpine7 glacier4--,in the progressive wastings of dendritic glaciers1 there comes a time when their dendritic outlines give place to radiating ones4 ,attention has already been called to the division of the cirque into subordinate basins separated by small rock artes and yielding a markedly scalloped border 7,fig4 #cid1 p4 #cga74 ,when the ice front retires from the main valley into one of these mature cirques1 the now wasted ice stream is broken up into subordinate glacierets1 each of which occupies one of the basins within the larger cirque1 and these ice streams flow together to produce a glacier whose component elements radiate like the sticks within a lady's fan 7,fig4 #djh1 stage ,,iv1 and ,fig4 #dac74 ,illustration3 ,,fig4 #dac4--,map of the ,rotmoos glacier1 a radiating glacier of ,switzerland 7after ,sonklar74 ,the horseshoe glacier4--,as the glacier draws near to its final extinction1 it is crowded hard against the wall of the amphitheater in which it has so long been nourished4 ,up to this stage it has offered a swelling front outwardly convex as a direct consequence of the laws controlling its flow4 ,no longer amply nourished1 for the first time its front is hollowed1 and it awaits its final dissolution curled up against the cirque wall 7,fig4 #djh1 stage ,v1 and ,fig4 #dad74 ,practically all the glaciers of the ,united ,states and southern ,canada are of this type4 ,the above classification is one depending directly upon glacier nourishment1 and hence also upon size1 and upon the stage of the glacial hemicycle4 ,in order to determine the type of any glacier it is necessary to know the outlines of the mountain valley--its divide--and those of the glacier or glaciers within it4 ,it is likely that the types of the advancing hemicycle of glaciation would be much the same1 save only for the new-born or nivation glacier1 which would be as different as possible from the horseshoe type1 to which in size it corresponds4 ,upon the continent of ,antarctica1 where the absence of any general melting of the ice1 even in the summer season and near the sea level1 introduces special conditions1 some additional glacier types are found1 which1 however1 it is not necessary that we consider here4 ,illustration3 ,,fig4 #dad4--,outline map of the ,asulkan glacier in the ,selkirks1 a typical horseshoe glacier4 ,the inherited-basin glacier4--,it may be1 however1 that glaciers have developed1 not upon mountains shaped in a cycle of river erosion1 nor yet in succession to an ice cap1 as in the normal cases which we have considered4 ,on the contrary1 glaciers may develop where basins of one sort or another have been inherited from the preceding period4 ,in such cases inherited depressions may become more important than the auto-sculpture of the glacier4 ,glaciers which develop under such conditions may be described as inherited-basin glaciers4 ,illustration3 ,,fig4 #dae4--,outline map of the ,illecillewaet glacier1 an inherited-basin glacier in the ,selkirks4 ,a partly closed basin between ridges may supply a collecting ground for snows carried from neighboring slopes by the wind1 and so may yield a broad nv1 approaching in size a small ice cap1 yet without developing definite ice streams except upon its border4 ,such a glacier is the ,illecillewaet glacier of the ,selkirks 7,fig4 #dae74 ,again in low latitudes the high and pointed volcanic peaks may push up beyond the snow line into the upper atmosphere1 and so become snow-capped4 ,definite cirques do not develop well under these circumstances1 and the loose materials of which such peaks are always composed are attacked in somewhat irregular fashion from the different sides4 ,this is the case of ,mount ,rainier and similar peaks of the ,cascade range of ,north ,america4 ,summary of types of mountain glacier4--,in tabular form the various types of mountain glacier may be arranged as follows3-- ,,mountain ,,glaciers ,piedmont glacier4 ,mountain valleys entirely occupied and largely submerged1 with overflow upon the foreland to form a common ice apron through coalescence of neighboring streams4 ,expanded-foot glacier4 ,valley entirely occupied and an overflow upon the foreland sufficient to produce individual ice apron4 ,dendritic glacier4 ,valley not completely occupied but with tributary ice streams ranged along the sides of the main stream1 and with hanging glacierets separated near the glacier foot4 ,radiating glacier4 ,glacier largely included in a cirque with subordinate glacierets converging below like the sticks in a lady's fan4 ,horseshoe glacier4 ,small glacier remnants hugging the cirque wall and having an incurving front4 ,inherited-basin glacier4 ,of form dependent on a basin inherited and not shaped by the glacier itself4 ,,reading ,,reference ,,for ,,chapter ,,xxvii ,,william ,h4 ,,hobbs4 ,the ,cycle of ,mountain ,glaciation1 ,geogr4 ,jour41 vol4 #cg1 #aiaj1 pp4 #bfh-bhd4 ,,chapter ,,xxviii ,,the ,,glacier',s ,,surface ,,features ,,and ,,the ,,deposits ,,upon ,,its ,,bed ,the glacier flow4--,the downward flow of the ice within a mountain glacier has been the subject of many investigations and the topic of many heated discussions since the time when ,louis ,agassiz and his companions set a line of stakes across the ,aar glacier and numbered the surface bowlders in preparation for repeated observations4 ,their first observation was that the line of stakes1 which had run straight across the glacier1 was distorted into a curve which was convex downstream 7,fig4 #daf1 ,a71 thus showing that the surface layers have more rapid motion in proportion as they are distant from the side margins4 ,summarizing these and later studies1 it may be stated that the glacier increases its rate of motion from its side margin towards its center line1 from its bed upwards towards its surface1 and below the nv the velocity is greatest where the fall is greatest and also wherever the cross section diminishes4 ,in all these particulars1 then1 the ice of the glacier behaves like a stream of water4 ,the average rate of flow of ,alpine glaciers varies from a few inches to a few feet per day1 and is greater during the warm summer season4 ,the ,muir glacier of ,alaska has been shown to move at the rate of about seven feet per day4 ,illustration3 ,,fig4 #daf4--;,diagram to illustrate the migrations of lines of stakes crossing a glacier1 due to its surface movement1 ,a1 original position of lines2 ,a1 later positions2 a and a1 original and distorted forms of a square section of the glacier surface near its margin2 r1 r1 diagonal crevasses4 ,in traveling from the nv downward to the glacier foot1 the snow not only changes into ice1 but it undergoes a granulating process with continued increase in the size of the nodules until at the foot of the glacier these may be picked out of the partially melted ice as articulating balls the size of the fist or larger4 ,glacier ice has therefore a structure quite different from that of lake ice1 since the latter is developed in parallel needles perpendicular to the freezing surface4 ,crevasses and sracs4--,prominent surface indications of glacier movement are found in the open cracks or crevasses1 which are the marks of its yielding to tensional stresses4 ,crevasses are apt to run either directly across the glacier1 wherever there is a steep descent upon its bed1 or diagonally1 running in from the margin and directed up-glacier 7r1 r1 r1 of ,fig4 #daf71 though they occasionally run longitudinally with the glacier when there is a rock terrace at the side of the valley beneath the ice4 ,the diagonal crevasses at the glacier margin are due to the more sluggish movement where the ice is held back by friction upon the walls of the valley1 as will be clear from ,fig4 #daf4 ,the square a has by this movement been distorted into the lozenge a1 so that the line xy has been extended into xy1 with the obvious tendency to open cracks in the direction ss4 ,every glacier surface below its nv is marked by steps or terraces1 which are well understood to overlie corresponding steps of the cascade stairway to be seen in all vacated glacier valleys 7plate #ai74 ,the steep risers of these steps are usually marked by parallel crevasses which cross the glacier4 ,under the rays of the sun1 which strike them more from one side than from the other1 the slices into which the ice is divided are transformed into sharpened blades and needles which are known as sracs 7,fig4 #dja1 p4 #cgf1 and ,fig4 #dag74 ,illustration3 ,,fig4 #dag4--,transverse crevasses at the fall below a glacier step transformed by unsymmetrical melting into sracs4 ,the numerous crevasses tell us that the ice is many times wrenched apart during its journey down the glacier4 ,this has been illustrated by somewhat grewsome incidents connected with accidents to ,alpinists1 but as they illustrate in some measure both the mode and the rate of motion of ,swiss glaciers1 they are worthy of our consideration4 ,bodies given up by the ,glacier des ,bossons4--,in the year #ahbj1 during one of the earlier ascents of ,mont ,blanc1 three guides were buried beneath an avalanche near the ,rochers ,rouges in the nv of the ,glacier des ,bossons 7,fig4 #dah74 ,in #aheh ,dr4 ,forbes1 who had measured the rate of flow of a number of ,alpine glaciers1 predicted that the bodies of the victims of this accident would be given up by the glacier after being entombed from thirty-five to forty years4 ,in the year #ahfa1 or forty-one years after the disaster1 the heads of the three guides1 separated from their bodies1 with some hands and fragments of clothing1 appeared at the foot of the ,glacier des ,bossons1 and in such a state of preservation that they were easily recognized by a guide who had known them in life4 ,inasmuch as these fragments of the bodies had required forty-one years to travel in the ice the three thousand meters which separate the place of the accident from the foot of the glacier1 the rate of movement was twenty centimeters1 or eight inches1 per day4 ,illustration3 ,,fig4 #dah4--,view of the ,glacier des ,bossons upon the slopes of ,mont ,blanc showing the position of accidents to ,alpinists and the place of reappearance of their bodies4 ,illustration3 ,,fig4 #dai4--,lines of flow upon the surface of the ,hintereisferner glacier in the ,alps 7after ,hess74 ,various separated parts of the body of ,captain ,arkwright1 who had been lost in #ahff upon the nv of the same glacier1 reappeared at its foot after entombment in the ice for a period of thirty-one years4 ,to-day the time of reappearance of portions of the bodies of persons lost upon ,mont ,blanc is rather accurately predicted1 so that friends repair to ,chamonix to await the giving up of its victims by the ,glacier des ,bossons4 ,illustration3 ,,fig4 #dbj4--,lateral and medial moraines of the ,mer de glace and its tributary ice streams4 ,the moraines4--,the horns and comb ridges which rise above the glacier surface are continually subject to frost weathering1 and from time to time drop their separated fragments upon the glacier4 ,falling as these do from considerable heights1 they reach the ice under a high velocity1 and rebounding1 sometimes travel well out upon its surface before coming to a temporary rest4 ,upon a fresh snow surface of the nv their tracks may sometimes be followed with the eye for considerable distances1 and their fall is a constant menace to ,alpine climbers4 ,below the nv the larger number of such fragments remain near the cliff1 and the lines of flow of the ice within the glacier surface are such that blocks which reach points farther out upon the glacier are later gathered in beneath the cliff at the side 7,fig4 #dai74 ,the ridge of angular rock dbris which thus forms at the side of the glacier is called a lateral moraine 7see ,fig4 #daa1 p4 #che1 and ,fig4 #dbj74 ,at the junction of two glacier streams1 the lateral moraines are joined1 and there move out upon the ice surface of the resultant glacier as a medial moraine4 ,thus from the number of medial moraines upon a glacier surface it is possible to say that the important tributary glaciers number one more 7,fig4 #dbj74 ,illustration3 ,,fig4 #dba4--;,ideal cross-section of a mountain glacier to show the position of moraines and other peculiarities characteristic of the surface of the bed4 ,the plucking and abrading processes in operation beneath the glacier1 quarry the rock upon its bed1 and after shaping and smoothing the separated rock fragments1 these are incorporated within the lower layers of the ice as englacial rock dbris4 ,in spaces favorable for its accumulation1 a portion of this material1 together with much finer dbris and rock flour1 is left behind as a ground moraine upon the bed of the glacier 7see ,fig4 #dba74 ,illustration3 ,,fig4 #dbb4--;,fragments of rock of different sizes1 to bring out their different effects upon the melting of the glacier surface4 ,at the foot of the glacier the relatively angular rock dbris1 which has been carried upon the surface1 and the soled and polished englacial material from near the bottom1 are alike deposited in a common marginal ridge known as the terminal or end moraine 7plate #ba ,b74 ,,plate #ba4 ,illustration3 ,a4 ,view of the ,harvard ,glacier1 ,alaska1 showing the characteristic terraces 7after ,u4 ,s4 ,grant74 ,illustration3 ,b4 ,the terminal moraine at the foot of a mountain glacier 7after ,george ,kinney74 ,selective melting upon the glacier surface4--,the white surface of the glacier generally reflects a large proportion of the sun's rays which reach it1 and its more rapid melting is largely accomplished through the agency of rock fragments spread upon its surface4 ,such fragments1 however1 promote or retard the melting process in inverse proportion to their size up to a certain limit1 and above that size their action is always to protect the glacier from the sun4 ,this nice adjustment to the size of the rock fragments will be clear from examination of ,fig4 #dbb1 for rock is a poor conductor of heat1 and in even the longest summer day a thin outer layer only is appreciably warmed4 ,large rock blocks1 grouped in the medial and lateral moraines1 hold back the process of lowering the glacier surface during the summer1 so that late in the season these moraines stand fifty feet or more above the glacier as armored ice ridges4 ,illustration3 ,,fig4 #dbc4--,small glacier table upon the surface of the ,great ,aletsch glacier in #aijh4 ,isolated and large rock slabs1 as the season advances1 may come to form the capping of an ice pedestal which they overhang and are known as glacier tables 7,fig4 #dbc74 ,such tables the sun attacks more upon one side than upon the other1 so that the slab inclines more and more to the south and may eventually slip down until its edges rest against the glacier surface4 ,rounded bowlders1 which less frequently become perched upon ice pedestals1 may1 from a similar process1 slide down upon the southern side and leave a pyramid of ice furrowed upon this side and known as an ice pyramid4 ,fine dirt when scattered over the glacier surface is1 on the other hand1 most effective in lowering its level by melting4 ,use was made of this knowledge to lower the great drifts of snow which had to be removed each season during the construction of the new ,bergen railway of southern ,norway4 ,each dirt particle1 being warmed throughout by the sun's rays1 melts its way rapidly into the glacier surface until the dust well which it has formed is so deep that the slanting rays of the sun no longer reach it4 ,when the dirt particles are near together1 the thin walls which separate the dust wells are attacked from the sides in the warm air of summer days1 thus producing from a patch of dirt upon the glacier surface a bath tub 7,fig4 #dbd d74 ,at night the water which fills these basins is frozen to form a lining of ice needles projecting inward from the wall1 and this1 repeated in succeeding nights1 may entirely close the basin with water ice and produce the familiar glacier star 7,fig4 #dbd c74 ,illustration3 ,,fig4 #dbd4--;,effects of differential melting and subsequent refreezing upon the glacier surface4 a1 dust wells2 b1 glacier tub produced by melting about a group of scattered dust particles2 c1 glacier star produced when the inclosed water of the glacier well has frozen in successive nights2 d1 8bath tub40 ,if the dirt upon the glacier surface1 instead of being scattered1 is so disposed as to make a patch completely covering the ice to the thickness of an inch or more1 the effect is altogether different4 ,protecting as it now does the ice below1 a local ice hillock rises upon its site as the surrounding surface is lowered1 and as this grows in height its declivities increase and a portion of the dirt slides down the side4 ,the final product of this shaping is an almost perfectly conical ice hill encased in dirt and known as a dbris1 sand1 or dirt cone 7,fig4 #dbe74 ,the novice in glacier study is apt to assume that these black cones contain only dirt1 but is rudely awakened to the reality when he attempts to kick them to pieces4 ,both glacier tubs and dbris cones may assume large dimensions2 as1 for example1 in ,alaska1 where they may be properly described as lakes and hills4 ,illustration3 ,,fig4 #dbe4--;,dirt cone and one with its casing in part removed4 ,victoria glacier 7after ,sherzer74 ,a patch of hard and dense snow which is less easily melted than that upon which it rests may lead to the formation of snow cones upon the glacier surface similar in size and shape to the better known dbris cones4 ,such cones of snow have1 with doubtful propriety1 been designated 8penitents01 for it is pretty clear that the interesting bowed snow figures1 which really resemble penitents and which were first described from the southern ,andes under the name of nieves penitentes1 are of somewhat different character4 ,illustration3 ,,fig4 #dbf4--,schematic diagram to show the manner of formation of glacier cornices4 ,one further ice feature shaped by differential melting around rock particles remains to be mentioned4 ,wherever the seasonal snowfalls of the nv are exposed in crevasses1 they are generally found to be separated by layers of dirt1 and lines of pebbles similarly separate those ice layers which are revealed at the foot of the glacier4 ,in either case1 if the sun's rays can reach these layers in an opened crevasse1 the half-buried rock fragments are warmed by the sun upon their exposed surfaces and slowly melt their way down the ice surface1 thus removing from it a thin layer of snow or ice and causing that part above the pebble layer to project like a cornice4 ,this process will go on until the overhanging cornice protects the pebbles from any further warming by the sun1 but each lower pebble layer that is reached by the sun will produce an additional cornice1 so that the original surface may at the bottom have been retired by the process a number of inches4 ,these features are described as glacier cornices 7,fig4 #dbf74 ,illustration3 ,,fig4 #dbg4--,superglacial stream upon the ,great ,aletsch glacier4 ,glacier drainage4--,already in the early morning of every warm summer day1 active melting has begun upon the surface of the ,swiss glaciers4 ,rills of icy water soon make their way along depressions upon the surface1 and are joined to one another so that they sometimes form brooks of considerable size 7,fig4 #dbg74 ,such streams continue their serpentine courses until these are intersected by a crevasse down which the waters plunge in a whirling vortex which soon develops a vertical shaft of circular section within the ice4 ,such shafts with their descending columns of whirling water are the well-known moulins1 or 8mills01 which may be detected from a distance by their gurgling sounds4 ,the first plunge of the water may not reach to the bottom of the glacier1 in which case the stream finds a passageway below the surface but above the floor until another crevasse is encountered and a new plunge made1 here perhaps to the bottom4 ,once upon the valley floor the stream is joined by others1 and pursues its course within an ice tunnel of its own making 7,fig4 #dba1 p4 #cid7 until it issues at the glacier front4 ,the coarser of the rock dbris which was gathered up by the stream upon the glacier surface is deposited within the tunnel in imperfect assortment 7gravel and sand71 while all finer material and that lifted from the floor 7rock flour7 is retained in suspension and gives to the escaping stream its opaque white appearance4 ,this glacier milk may generally be traced far down the valleys or out upon the foreland1 and is often the traveler's first indication that a range which he is approaching supports glaciers4 ,illustration3 ,,fig4 #dbh4--;,ideal form of the surface left on the site of the apron of a piedmont glacier4 ,m1 moraine2 ,t1 outwash2 ,c1 basin usually occupied by a lake2 ,d1 drumlins 7after ,penck74 ,deposits within the vacated valley4--,for every excavation of the higher portions of the upland through glacial sculpture1 there is a corresponding deposit of the excavated materials in lower levels4 ,so far as these materials are deposited directly by the ice1 they form the lateral1 medial1 ground1 and terminal moraines already described4 ,a considerable proportion of them are1 however1 deposited by the water outside the terminal moraine2 but as with the shrinking glacier the ice front retires in halting movements over the area earlier ice-covered1 the terminal moraines are ranged along the vacated valley as recessional moraines1 each with a valley train of outwash below4 ,about the apron of the piedmont glacier1 such deposits are particularly heavy 7,fig4 #dbh74 ,during the 8ice age0 the ,swiss glaciers extended down the valleys below the existing ice remnants and spread upon the ,swiss foreland as great piedmont glaciers such as may now be seen in ,alaska4 ,to-day we find there moraines and glacial outwash1 a lake in the middle of the apron site1 and sometimes a group of radiating drumlins like those found within the ice lobes of the continental glacier in southern ,wisconsin 7,fig4 #dbi1 and ,fig4 #cdd1 p4 #cag74 ,illustration3 ,,fig4 #dbi4--,moraines and drumlins about ,lake ,constance upon the site of the earlier piedmont glacier of the ,upper ,rhine4 ,the white area outside the outermost moraine is buried in glacial outwash 7after ,penck and ,brckner74 ,behind the recessional moraines within the glaciated valley are found the valley moraine lakes 7,fig4 #ddh1 p4 #dac71 in association with the rock basin lakes due to glacial sculpture 7,fig4 #ddg1 p4 #dab74 ,after the glacier has vacated its valley1 the precipitous side walls become the prey of frostwork and are the scenes of disastrous avalanches or landslides4 ,within the cirques1 drifts of snow are nourished long after the ice has disappeared1 and as a consequence the amphitheater walls succumb to the process of solifluxion 7p4 #aec74 ,diversions and reversals of drainage1 which are so characteristic of the work of continental glaciers1 are hardly less common to glaciated mountain districts4 ,many of our most beautiful waterfalls have resulted from either the temporary or permanent obstruction of earlier valleys above the falls4 ,the famous ,yosemite ,falls offers an interesting illustration of the shifting of an earlier waterfall1 itself no doubt due to ice blocking in a still earlier glaciation 7plate #bb ,b74 ,marks of the earlier occupation of mountains by glaciers4--,it is well that we should now bring together within a small compass those evidences by which the existence of earlier mountain glaciers may be proven in any district4 ,these marks are so deeply stamped upon the landscape that no one need err in their interpretation4 ,,marks ,,of ,,mountain ,,glaciers ,high-level sculpture4 ,the grooved upland with its cirques1 or the fretted upland with its cirques1 cols1 horns1 and comb ridges4 ,low-level sculpture4 ,the ,u-shaped main valley1 the hanging side valleys with their ribbon falls1 the glacier staircase with its rock bars and gorges1 the rounded1 polished1 and striated rock floor4 ,deposits4 ,the recessional moraines of till and the valley trains of sand and gravel1 the soled erratic blocks derived always from higher levels of the valley4 ,lakes4 ,the valley moraine lakes and the chains of rock basin lakes4 ,,reading ,,references ,,for ,,chapter ,,xxviii ,glacier movement3-- ,l4 ,,agassiz4 ,nouvelles tudes et ,expriences sur les ,glaciers ,actuels1 etc41 ,paris1 #ahdg1 pp4 #dce-eci4 ,h4 ,,hess4 ,die ,gletscher1 ,braunschweig1 #aijd1 pp4 #aae-aej4 ,h4 ,f4 ,,reid4 ,the ,mechanics of ,glaciers1 ,jour4 ,geol41 vol4 #d1 #ahif1 pp4 #iab-ibh2 ,glacier ,bay and ,its ,glaciers1 #afth ,ann4 ,rept4 ,u4 ,s ,geol4 ,surv41 ,pt4 i1 #ahih1 pp4 #dde-ddh4 ,,plate #bb4 ,illustration3 ,a4 ,model of the vicinity of ,chicago1 showing the position of the ancient beaches and the outlet of the former ,lake ,chicago4 ,illustration3 ,b4 ,map of ,yosemite ,falls and its earlier site near ,eagle ,peak 7after ,f4 ,e4 ,matthes74 ,,chapter ,,xxix ,a ,,study ,,of ,,lake ,,basins ,freshwater and saline lakes4--,lakes require for their existence a basin within which water may be impounded1 and a supply of water more than sufficient to meet the losses from seepage and evaporation4 ,if there is a surplus beyond what is needed to meet these losses1 lakes have outlets and remain fresh2 their content of mineral matter is then too slight to be detected by the palate4 ,if1 on the other hand1 supply is insufficient for overflow1 continued evaporation results in a concentration of the mineral content of the water1 subject as it is to continual augmentation from the inflowing streams4 ,as we have seen1 there are in areas of small rainfall special weathering processes which tend to bring out the salts from the interior of rock masses1 these concentrated salts generally first appearing as a surface efflorescence which is ultimately transferred through the agency of wind and cloudburst to the characteristically saline desert lakes4 ,lake basins may be formed in many ways4 ,depressions of the land surface may result from tectonic movements of the crust2 they may be formed by excavating processes2 but in by far the greater number of instances they result from the obstruction in some manner of valleys which were before characterized by uniformly forward grades4 ,in relatively few cases loose materials are heaped up in such a manner as to produce fairly symmetrical basins4 ,illustration3 ,,fig4 #dcj4--,map and diagram to bring out the characteristics of newland lakes4 ,newland lakes4--,on land recently elevated from the sea1 basins of lakes may be merely the inherited slight irregularities of the earlier sea floor1 in which case they may be assumed to be largely the result of an irregular distribution of deposits derived from the land4 ,lakes of this type are especially well exhibited in ,florida1 and are known as newland lakes 7,fig4 #dcj74 ,such lakes are exceptionally shallow1 and are apt to have irregular outlines and extremely low banks4 ,under these circumstances1 they are soon filled with a rank growth of vegetation1 so that it is sometimes difficult to properly distinguish lake and marsh4 ,illustration3 ,,fig4 #dca4--,view of the ,warner ,lakes1 ,oregon 7after ,russell74 ,illustration3 ,,fig4 #dcb4--,schematic diagrams to illustrate the characteristics of basin-range lakes4 ,basin-range lakes4--,newland lakes may be said to have their origin in an uplift of the land and sea floor near their common margin4 ,a lake type dependent upon movements of the earth's crust but within interior areas has been described as the basin-range type and is exemplified by the ,warner ,lakes of ,oregon4 ,in this district great rectangular blocks of the earth's crust1 which in their upper portions at least are composed of basaltic lavas1 have undergone vertical adjustments in level and have been tilted so that the corresponding corners of neighboring blocks have been given a similar degree of down-tilt 7,fig4 #dca74 ,lakes formed in this way are of triangular outline1 are bounded on the two shorter sides by cliffs1 but have extremely flat shores on their longest side4 ,from this shore the water increases gradually in depth and attains a maximum depth at or near the opposite angle4 ,such lakes naturally betray a tendency to appear in series 7,fig4 #dcb71 and are unfortunately much too often illustrated on a small scale after a shower by the tilted blocks of imperfectly made cement sidewalks4 ,illustration3 ,,fig4 #dcc4--,schematic diagrams of rift-valley lakes1 and the rift valley of the ,jordan with the ,dead ,sea and the ,sea of ,galilee as remnants of a larger lake in which their basins were included4 ,rift-valley lakes4--,another type of lake basin which has its origin in faulted block movements is known as the rift-valley lake1 and is best exemplified by the great lakes of east ,central ,africa4 ,in this type a strip of crust1 many times as long as it is wide1 has been relatively sunk between the blocks on either side so as to produce a deep rift1 or what in ,germany is known as a ,graben 7trench74 ,such a basin when occupied by water yields a lake which is long1 straight1 deep1 and narrow1 and is in addition bounded on the sides by steep rock cliffs4 ,at the ends the shores are generally by contrast decidedly low4 ,if the hard rock at the bottom of the lake could be examined1 it would be found to be of the same type as that exposed near the top of the side cliffs4 ,the valley of the ,jordan in ,palestine is a rift of this character and was at one time occupied by a long and narrow lake of which the ,dead ,sea and the ,sea of ,galilee are the existing remnants 7,fig4 #dcc74 ,illustration3 ,,fig4 #dcd4--,map showing the rift valley lakes of east ,central ,africa4 ,one of the most striking examples of a rift valley lake is ,lake ,tanganyika1 while ,albert ,nyanza1 ,nyassa1 and ,rudolf in the same region are similar 7,fig4 #dcd74 ,illustration3 ,,fig4 #dce4--;,earthquake lakes which were formed in the flood plain of the lower ,mississippi during the earthquake of #ahaa 7after ,humphreys74 ,earthquake lakes4--,the complex adjustments in level of the surface of the ground at the time of sensible earthquakes are many of them made apparent in no other way than by the derangements of the surface water4 ,this is at such times impounded either in pools or in broad lakes1 which inasmuch as they date from known earthquakes have been called 8earthquake lakes01 even though in a strict sense any lake which has originated in earth movements might properly be regarded as an earthquake lake4 ,to avoid unnecessary confusion1 the term must1 however1 be restricted to those lakes which are known to have been formed at the time of definite earthquakes 7,fig4 #dce74 ,reelfoot ,lake in ,tennessee1 which in late years has acquired undesirable notoriety because of the feuds between the fishermen of the district and the constituted authorities1 is a lake more than twenty miles across and came into existence during the great earthquake of the lower ,mississippi valley in #ahaa4 ,crater lakes4--,the craters of volcanic mountains are natural basins in which surface waters are certain to be collected1 provided only the supply is sufficient and seepage into the loose materials is not excessive4 ,some craters1 still visibly more or less active1 are occupied by lakes 7,fig4 #dcf74 ,illustration3 ,,fig4 #dcf4--,view of lake in ,poas ,crater in ,costa ,rica1 a volcanic crater more than half a mile across and with walls #hjj feet deep4 ,at intervals there is an ejection of steam mixed with mud and ash after the manner of a geyser 7after ,h4 ,pittier74 ,in the larger number of cases in which craters become occupied by lakes1 the evidence of continued activity is lacking1 and it would appear in such cases that the lava of the chimney had consolidated into a volcanic plug1 closing the bottom of the crater4 ,notable groups of crater lakes are the ,caldera of the ,roman ,campagna 7,fig4 #dcg7 and the so-called maare of the ,eifel about the ,lower ,rhine4 ,crater lakes are easy to recognize by their circular plan1 their steep walls of volcanic materials1 and their considerable depth with a maximum near the center4 ,one of the most remarkable of these water-filled basins is ,crater ,lake in ,oregon1 which has a diameter of about six miles and is believed to have resulted from the incaving of a great volcanic cone in the latest stage of its activity4 ,this remarkable feature has now been made a national park and will soon be conveniently reached by tourists and counted one of the greatest nature wonders of the ,pacific slope4 ,illustration3 ,,fig4 #dcg4--;,diagrams to illustrate the characteristics of crater lakes4 ,the ,roman ,campagna is a plain formed of volcanic ash1 with the crater lakes of ,bracciano1 ,vico1 and ,bolseno arranged on a line traversing it4 ,coule lakes4--,far more important as lakes are those volcanic basins which arise from the flow of a stream of lava across the valley of a river so as to impound its waters 7,fig4 #dch74 ,at the time of the great eruption under ,skaptr ,jkull in #aghc the river ,skaptr and many of its tributaries were blocked by the flow of lava1 which it is estimated exceeded in bulk the mass of ,mont ,blanc4 ,illustration3 ,,fig4 #dch4--,view of ,snag ,lake1 a coule lake with lava dam shown in middle distance 7after ,fairbanks74 ,morainal lakes4--,as we have learned1 the obstruction of drainage1 due to the distribution of rock dbris by continental glaciers1 has yielded lakes in almost countless numbers4 ,probably ninety per cent or more of the known lakes have had this origin1 and the type is so common within the once glaciated regions that it forms perhaps the best distinguishing mark of former glaciation4 ,the hummocky surface of morainal deposits is so characteristic that the lakes of this type are never very large and are correspondingly irregular in outline4 ,they have often numerous islands1 and their banks are formed of the combination of rock flour and ice-worn materials known as till 7,fig4 #dci74 ,the smallest of the morainal lakes are mere kettles on the marginal moraine1 and these rapidly become replaced by peat bogs4 ,in contrast with pit lakes1 morainal lakes lack the steep surrounding slopes and the encircling plain4 ,illustration3 ,,fig4 #dci4--;,diagrams to illustrate the characteristics of morainal lakes1 and a sample map of such lakes from the glaciated region of ,north ,america4 ,pit lakes4--,the so-called pit lakes have their origin in continental glaciation1 and are found in groups within broad plains of glacial outwash 7mainly sand and gravel71 which are for this reason described as 8pitted plains0 7see p4 #cad74 ,those areas which lay between neighboring lobes of the ice sheet were subject to particularly heavy deposits of outwash material1 and are1 in consequence1 particularly likely to be occupied by pit lakes4 ,as has been pointed out in an earlier section1 the water derived from surface melting within the marginal portions of a continental glacier descends to the bottom in the crevasses and thereafter flows in an ice tunnel under the same conditions as water flowing in a pipe4 ,having in most cases a considerable head at the outer margin of the ice1 this water may rise and issue well above the lower ice layers and so cover a portion of the ice margin beneath sand and gravel 7,fig4 #ddj74 ,separated blocks1 often of massive proportions1 are thus buried beneath nonconducting materials by which they are long protected from further melting4 ,eventually1 however1 with the approach of still milder climates they disappear1 thus causing the overlying sand and gravel to descend and form a pit of steep walls similar to the sawdust pits over melted ice blocks within our storehouses4 ,illustration3 ,,fig4 #ddj4--;,diagram to show the manner of formation of pit lakes4 ,pit lakes are thus easily recognized by their occurrence usually in groups within a plain of glacial outwash and by their characteristic banks inclined at the angle of repose of such materials 7,fig4 #dda74 ,illustration3 ,,fig4 #dda4--;,diagrams to illustrate the characteristics of pit lakes and a sample map from the glaciated region of ,north ,america4 ,glint or colk lakes4--,it has been found to be true of existing continental glaciers that where their mass has been held back by a mountain wall1 their current at the portals within this rampart becomes greatly accelerated4 ,though the upper layers of the glacier in the vicinity may move forward with a velocity of but an inch per day1 the current within the outlet may be as much as seven hundred or a thousand times as great4 ,in many respects these conditions are similar to those about the raceway of a reservoir where the near-by surface of the water is lowered by the indraught of the outlet and the current in the raceway is so accelerated that1 unless protected1 the bottom of the race is carried away and a basin excavated which extends a short distance both above and below the position of the dam4 ,in ,holland such basins hollowed out beneath breaks in the dykes are known as colks4 ,basins which were excavated beneath the glacier outlets by a similar process would not be open to our inspection until after the ice had disappeared from the region2 but it is most significant that in ,scandinavia1 where the ,pleistocene continental glacier1 advancing westward from the ,baltic1 was held in check by the escarpment at the ,norwegian boundary 7the glint71 lake basins have been excavated in hard rock whose walls show the abrading and polishing which are characteristic of glacial sculpture1 and whose positions are such that they lie beneath the former outlets partly above and in part below the line of the escarpment4 ,their position in reference to the rampart and to the former outlets is brought out in ,fig4 #ddb4 ,the largest of the glint lakes of this series is ,tornetrsk in northern ,lapland 7see p4 #bgg and ,fig4 #ddc74 ,illustration3 ,,fig4 #ddb4--;,diagram to show the manner of formation of glint or outlet lakes where the continental glacier of ,scandinavia issued from the ,baltic depression through portals in its mountain rampart4 ,illustration3 ,,fig4 #ddc4--,map showing a series of glint lakes which lie across the international boundary of ,sweden and ,norway4 ,ice-dam lakes4--,whenever a continental glacier1 either in advancing its front or in retiring1 lies across the lines of drainage upon their downstream side1 water is impounded along the ice front so as to form ice-dam lakes4 ,such lakes are found to-day in ,greenland and in the southern ,andes1 and similar bodies of water of far greater size and importance came into existence in ,pleistocene times each time that the continental glaciers of northern ,north ,america and ,europe advanced upon or retired from suitably directed river systems4 ,thus above the ,baltic depression1 when the ice front lay to the eastward of the main watershed1 each easterly sloping valley was obstructed by the ice and occupied by an ice-dam lake 7,fig4 #ddd71 the beaches of which may all be traced to-day 7,fig4 #dde74 ,illustration3 ,,fig4 #ddd4--;,ice-dam lakes 7in black7 between the front of the late ,pleistocene glacier of northern ,europe and the divide near the ,norwegian boundary 7after ,g4 de ,geer74 ,one side of each ice-dam lake is formed by an ice cliff at the glacier front1 and if the region is relatively flat1 the remaining shores are likely to be formed by a marginal moraine which the glacier has abandoned in its retreat4 ,in their smaller stages1 therefore1 ice-dam lakes on prairie country have the form of a crescent1 which is the more pronounced because the waves by their attack upon the ice front flatten the curvature of its outline 7see ,fig4 #cfj1 p4 #ccj74 ,the life of an ice-dam lake is begun and ended in important changes of glacier outline1 and after the draining of lakes by this process the land shores may be traced in beaches1 and the ice margin by a water-laid moraine of low relief 7,fig4 #cei1 p4 #ccj74 ,a much smaller but in many respects similar ice-dam lake is to-day to be seen at the side of the ,great ,aletsch glacier1 a mountain glacier of ,switzerland4 ,the traveler who makes the easy ascent of the ,eggishorn may look directly down upon this crescent-shaped lake with its ice cliff on the glacier side 7see ,fig4 #ddf74 ,illustration3 ,,fig4 #dde4--,wave-cut terrace at an elevation of #agg4e meters above sea on the southern slope of the northern ,dala valley north of ,baggedalen in ,sweden4 ,to the right in the foreground is a peat bog 7after ,munthe74 ,illustration3 ,,fig4 #ddf4--,view of the ,mrjelen ,lake at the side of the ,great ,aletsch glacier1 seen looking directly down from the summit of the ,eggishorn 7after a photograph by ,i4 ,d4 ,scott74 ,glacier lobe lakes4--,upon the sites of the former lobes of the ,pleistocene glacier of ,north ,america are found the basins of the ,laurentian ,river system1 the largest freshwater lakes in the world4 ,there has been much controversy concerning the manner of formation of these lakes1 but the view which has seemed to have the largest following is that they were excavated by the eroding action of the continental glacier over the drainage basins of former rivers4 ,it is but one phase of the long controversy between opposing schools1 which have advocated on the one hand the efficiency of glacier ice as an eroding agent1 and upon the other its supposed protection from the weathering processes4 ,the positions and the outlines of the several lakes of the series sufficiently proclaim their connection with the former glacial lobes1 and the name which we have adopted leaves the exact manner of their formation a still open question4 ,the recognition of the importance of the glacial anticyclone1 in giving shape to the glacier surface and in effecting a transfer of snow from the central to the marginal portions1 has had the effect of emphasizing the relative importance of erosion under the marginal and lobate portions4 ,thus the importance of ice lobes has been greatly accentuated1 though this applies only to the shaping of the basins and not in any important way to the impounding of the present waters4 ,the present ,laurentian ,lakes owe their existence to the elevation by successive uplifts of the country to the northward and eastward1 since the glacier retired from the lake region4 ,when the ice front lay to the northward of the ,ottawa ,river1 the discharge of the upper lakes was by a channel through ,nipissing ,river and ,lake and thence down the ,ottawa ,river to a gulf in the lower ,st4 ,lawrence4 ,the uplift of the land has had the effect of raising a barrier where the former outlet existed1 and diverting the waters to a roundabout channel by way of ,detroit and ,lake ,erie 7see ,fig4 #cfe1 p4 #cce74 ,illustration3 ,,fig4 #ddg4--;,diagrams to illustrate the arrangement and the characters of rock-basin lakes1 together with a map of such lakes from the ,bighorn ,mountains in ,wyoming4 ,rock-basin lakes4--,the reversed grades which develop in a valley deepened by mountain glaciers--the back-tilted treads of the cascade stairway 7see p4 #cgf7--;furnish a series of basins hollowed in rock which are strung along the course of the valley like pearls upon a thread1 or1 far better1 like the larger beads in a rosary 7,fig4 #ddg74 ,this characteristic arrangement accounts for the name 8,paternoster ,lakes0 which has sometimes been applied to them in ,europe4 ,their positions in series within ,u-shaped mountain valleys1 and their rock shores with characteristically smoothed and striated surfaces1 make them easy of determination4 ,in the higher portions of the valley1 where the treads of the cascade stairway are relatively narrow1 such lakes are often approximately circular in outline1 but in the lower levels and upon wider treads they may be ribbon-like1 though lakes of this type are to a large extent replaced in the lower levels by the valley moraine type or a combination of the two4 ,illustration3 ,,fig4 #ddh4--;,convict ,lake1 a lake behind a moraine dam within a glaciated valley of the ,sierra ,nevadas1 ,california 7after a photograph by ,fairbanks74 ,valley moraine lakes4--,the recessional moraines which mark the halting stations of mountain glaciers1 while retiring up their valleys1 form dams in the later river and so produce a type of lake which is in contrast with the morainal lakes which result from continental glaciation4 ,they may1 therefore1 be distinguished by the name valley moraine lakes4 ,their positions on the bed of a ,u-shaped mountain valley1 and the glacial materials which compose the dams1 are sufficient for their identification 7,fig4 #ddh74 ,moraine ,lake and ,lake ,louise in the ,canadian ,rockies are typical examples4 ,rock basin and valley moraine lakes may occur in alternation or combined in mountain valleys4 ,illustration3 ,,fig4 #ddi4--,lake basins produced by successive slides from the steep walls of a glaciated mountain valley 7after ,russell74 ,landslide lakes4--,the sheer-walled valleys which are carved by mountain glaciers are too steep to long retain their perpendicularity when the support of the glacier has been removed4 ,aided by the ever present joint planes1 which admit water to the rock1 they succumb to frost action1 and further give way in avalanches whenever the rock is of sufficiently porous material to become saturated with water4 ,landslides sometimes occur successively until the original valley wall has been replaced by a terraced slope4 ,the treads of the steps in this terrace have generally a backward-sloping grade1 so that basins are formed to be filled by relatively long and narrow lakes or by successions of small pools 7,fig4 #ddi and plate #bc ,b74 ,illustration3 ,,fig4 #dej4--,lake ,garda1 a border lake upon the site of a piedmont apron at the margin of the ,alpine highland 7after ,penck and ,brckner74 ,when the avalanched material is so disposed as to dam the valley1 much larger lakes of this type come into existence4 ,during an earthquake which occurred on ,january #be1 #acdh1 there was a landslide within the valley of the ,gail1 ,carinthia1 which destroyed seventeen villages and produced a lake which even to-day is represented by a great marsh4 ,border lakes4--,whenever mountain glaciers push out their fronts beyond the borders of the mountain range by which they are nourished1 they spread upon the foreland in broad aprons about which morainic accumulations are particularly heavy4 ,this elevation of morainal walls about the margins of the aprons yields natural basins that are occupied by lakes so soon as the glacier retires its front within the valley4 ,because such lakes are found at the borders of upland districts they have been called border lakes4 ,the beautiful ,lakes ,constance1 ,lucerne1 ,maggiore1 ,lugano1 ,como1 and ,garda 7,fig4 #dej71 on the borders of the ,alpine highland1 are all of this type4 ,,plate #bc4 ,illustration3 ,a4 ,view of the ,american ,fall at ,niagara1 showing the accumulation of rocks beneath 7after ,grabau74 ,illustration3 ,b4 ,crystal ,lake1 a landslide lake in ,colorado4 7,photograph by ,howland ,bancroft47 ,ox-bow lakes4--,the cutting off of a meander within the flood plain of a river yields a lake which is of horseshoe 7ox-bow7 outline and lies generally with low banks within a plain composed of river silt4 ,before separating from the parent stream the meander had begun to silt up1 especially at the ends4 ,ox-bow lakes are1 however1 relatively deep near the convex shore and correspondingly shallow toward the concave margin 7,fig4 #dea74 ,illustration3 ,,fig4 #dea4--;,diagrams to bring out the characteristics of ox-bow lakes1 together with a map of such lakes from the flood plain of the ,arkansas ,river4 ,illustration3 ,,fig4 #deb4--;,diagrammatic section to illustrate the formation of saucer-like basins between the levees of streams flowing in a flood plain4 ,saucer lakes4--,as we have learned1 a river meandering in its flood plain has banks which are higher than the average level of the plain1 for the reason that at flood time the main current of the stream still persists in the channel1 thus allowing the burden of sediment to be dropped in the relatively slack water upon its margin4 ,because of these natural embankments or levees1 tributary streams are often compelled to flow long distances in nearly parallel direction before effecting a junction4 ,between the trunk stream and its tributaries1 likewise bounded by levees1 and between streams and the valley walls1 there thus exist low basins which are more or less saucer-shaped 7,fig4 #deb74 ,at flood time1 when the levees are overflowed or crevassed1 water enters these depressions1 and an additional supply may be derived from the walls of the valley4 ,good illustrations of such lakes are furnished by the flood plain of the former river ,warren near the banks of the present ,minnesota ,river 7,fig4 #dec74 ,illustration3 ,,fig4 #dec4--,saucer lakes upon the bed of the former river ,warren 7from the ,minneapolis sheet1 ,u4 ,s4 ,g4 ,s474 ,crescentic levee lakes4--,as we approach the delta of a river1 the size and importance of the levee increases1 and here a new type of levee lake may develop in series 7,fig4 #ded74 ,at flood time the levee is breached near the point of sharpest curvature on the convex side 7,fig4 #ded a74 ,when the waters are subsiding1 the current is kept away from the old channel by the rising grade of the levee as well as by the inertia of the current1 and an entrance to the old channel is first found below the next change in curvature of the meander1 since here scour becomes effective in cutting through the levee4 ,the new channel is thus established in the form of a loop inclosing the old one1 and the process of levee building now erects a wall about the territory newly acquired by the meander4 ,this territory has the form of a crescent1 and when occupied by water produces a crescentic levee lake often joined to its neighbors in series4 ,the abandoned channel now closed at both ends by levees may be occupied by water to produce a subordinate ribbon type of curving trench 7,fig4 #ded b1 c74 ,the importance of levees in obstructing drainage to form lakes is only beginning to be appreciated4 ,it has quite recently been shown that when trunk streams are greatly swollen and burdened with sediment while flowing from a receding continental glacier1 they may build such high levees as to aggrade their tributary streams above the junctions1 even producing reversed grades and so impounding the waters to form extensive lakes4 ,during the 8ice age0 lakes of this type were formed in ,illinois and ,kentucky rivers just above their junctions with the ,ohio4 ,the old lake floor with its eastern shore line and its protruding islands is easily made out upon the new topographic maps of ,kentucky4 ,illustration3 ,,fig4 #ded4--,levee lakes developed concentrically in series within meanders of a stream tributary to the ,mississippi and flowing upon its delta plain4 b and c are examples of the ribbon type of levee lake due to occupation of the abandoned river channel4 ,the larger number of lakes1 of which ,sip ,lake and ,texas ,lake are examples1 have the form of crescents and lie between abandoned levees 7from recent map of ,u4 ,s4 ,g4 ,s474 ,raft lakes4--,within humid regions the flood plains of our larger rivers are generally forested1 and as the river swings from side to side in its perpetual meanderings1 the timber which grows upon the convex side of each meander is progressively undermined by the river and felled upon its bank4 ,the prostrate trees remain upon the banks during the low water of the summer season1 to be gathered up at the time of flood in the next spring season4 ,it is log jams thus acquired which so generally block the main channel of a river and turn the current across the neck of the meander when cut-offs occur with the formation of ox-bow lakes4 ,when the mass of timber thus gathered up by the river is excessive1 as1 for example1 within the flood plain of the ,red ,river of ,arkansas and ,louisiana1 huge log rafts are produced which dam up the river so effectively as to produce temporary lakes4 ,the impounded waters soon find an outlet over the levee at some point higher up the river1 and the waters flowing off through the timbered bottom lands1 other logs are caught by the standing timber as in a weir4 ,a second dam is thus formed which is separated from the initial one by open water1 and in this way the driftwood dam acquires enormous proportions as it gradually moves up the river4 ,after a period of perhaps a century or more1 the lower sections of the jam become decayed and dislodged so as to float down the river4 ,illustration3 ,,fig4 #dee4--,raft lakes along the banks of the ,red ,river in ,arkansas and ,louisiana at their fullest recorded development 7after ,a4 ,c4 ,veatch1 ,u4 ,s4 ,g4 ,s474 ,in the lower ,red ,river a great raft of alternating jams and open water reached a length of about one hundred and sixty miles and moved up the river at the average rate of something less than a mile per year4 ,within the limits of the dam all tributary streams were blocked1 so that secondary lakes were formed in a double fringe about the main river 7,fig4 #dee74 ,the great raft which formed here in the latter part of the fifteenth century has now at the beginning of the twentieth been largely removed and measures have been adopted to prevent its re-formation4 ,illustration3 ,,fig4 #def4--,the ,swiss lakes ,thun and ,brienz1 formed by deltas at the junction of streams tributary to a steep-walled valley4 ,side-delta lakes4--,it is characteristic of river drainage that the tributary streams enter the main valley on steeper gradients than the trunk stream at the point of junction4 ,wherever the difference in velocity of the two streams at the junction is large1 and the side stream is charged with sediment1 a delta will be formed at the mouth of the tributary stream4 ,such deltas push out from the shore and may eventually block the main channel so as to form a more or less sausage-shaped expansion of the river--a side-delta lake4 ,traverse and ,big ,stone ,lakes in the valley of the ,warren ,river in ,minnesota have been formed in this way 7,fig4 #ced1 p4 #cbf74 ,lakes ,thun and ,brienz in the ,swiss ,alps are of similar origin1 the beautiful city of ,interlaken being built upon the delta plain over the valley of the earlier river 7,fig4 #def74 ,the ,mississippi has similarly been expanded to form ,lake ,pepin above the delta at the mouth of the ,chippewa ,river4 ,illustration3 ,,fig4 #deg4--;,delta lakes formed at the mouth of the ,mississippi through the junction of the levees of radiating distributaries with the shore of the estuary 7after ,berghaus74 ,delta lakes4--,a somewhat different type of delta lake has been formed in ,louisiana1 where the 8father of waters0 discharges into the gulf4 ,here the various distributaries radiate from the main channel to produce the 8bird-foot0 delta type and the toes in this foot by their junction with the banks which outline the ancient estuary1 have separated in succession a series of basins that before were in direct connection with the sea 7,fig4 #deg74 ,lake ,pontchartrain is the largest of this series1 while the so-called ,lake ,borgne is in process of separation4 ,where large deltas push out from the shore into the open sea1 the levees which border the individual distributaries are attacked by the waves and their materials are transported by the shore currents and built into barriers4 ,these barriers cut off the re-entrants between neighboring distributaries so as to produce lagoons or lakes 7,fig4 #deh74 ,illustration3 ,,fig4 #deh4--;,a type of delta lakes formed by levees in part destroyed and built into barriers on the margin of the delta of the ,nile 7after ,supan74 ,a type of delta lake1 which more resembles the side-delta lake above described1 has formed at the mouth of the ,colorado ,river1 where it enters the ,gulf of ,lower ,california4 ,the ,imperial ,valley lying to the north of this delta is the desiccated floor of the earlier ,gulf of ,lower ,california which has been captured from the sea by the delta of the ,colorado4 ,the rampart of mountains1 by which this valley is surrounded1 has cut it off from any water supply derived from clouds1 and its waters being no longer renewed from the sea1 the region has passed through a period of desiccation which has left the ,salton ,sink as the only existing remnant of the earlier lagoon4 ,it will be remembered that careless operations in diverting distributaries of the ,colorado recently reversed this process so that the waters rose in the valley1 and expensive emergency operations were necessary in order to again turn the waters of the ,colorado into their accustomed channels4 ,illustration3 ,,fig4 #dei4--;,diagrams to illustrate the characteristics of barrier lakes1 with an example from the southern coast of the ,island of ,nantucket4 ,barrier lakes4--,the ,salton ,sink illustrates a type of lake which is formed at the border of the sea through the erection of some kind of barrier which captures a small area of the ocean's surface4 ,though such lakes may be properly described as strand lakes1 it is usually at the mouth of a river that the process becomes effective4 ,the common type of barrier lakes is found developed on most ragged coast lines where the shore currents have formed first bars and later barriers at the mouths of the estuaries 7,fig4 #dei74 ,such embankments are usually gently curving or crescent shaped and are composed of sand or shingle which presents a steep landward and a gradual seaward slope4 ,illustration3 ,,fig4 #dfj4--;,dune lakes on the coast of ,france 7after ,berghaus74 ,dune lakes4--,within the narrow strips of shore in which all the fine soil that could be available for plant life has been washed away by the waves1 beach sand is exposed to the direct action of the winds4 ,in time of storm the sand is picked up and after drifting in the wind is collected in long ridges parallel to the shore4 ,constantly traveling along shore1 these dunes block the mouths of rivers and thus produce a series of lakes such as are indicated in ,fig4 #dfj4 ,sink lakes4--,another class of lakes are due either directly or indirectly to the work of underground waters4 ,in districts which are underlain by limestone1 the surface water descending along the joints of the limestone may widen these passageways through solution of the rock and at lower levels flow on the floors of caverns eaten out by the same process on bedding planes of the formation4 ,at the intersections of joints1 more or less circular shafts known as 8swallow-holes0 go down to the caves from the surface4 ,locally1 also the cavern roofs give way so as to choke the galleries with rubble and leave a basin at the surface which has an irregular but generally a more or less oval outline4 ,if sufficiently clogged at the bottom by finer rock dbris1 these basins become occupied by small lakes which are known as sinks1 and constitute one of the best surface indications of a limestone country4 ,illustration3 ,,fig4 #dfa4--,sink lakes in ,florida1 with a schematic diagram to illustrate the manner of their formation 7map from ,u4 ,s4 ,g4 ,s474 ,karst lakes--poljen4--,in the limestone country to the north and east of the ,adriatic ,sea--the so-called ,karst region--there are many interesting features which are directly traceable to the solution of the country rock4 ,here all the surface water descends in certain districts along the widened joint planes so that the drainage is largely subterranean4 ,the so-called dolines or sinks of very regular and symmetrical forms resembling deep bowls cover a large part of the surface4 ,the entire country is1 moreover1 faulted in the most intricate fashion into many rift valleys4 ,the drainage being so largely subterranean1 these downthrown blocks of crust1 the so-called poljen1 become flooded at certain seasons of the year when the subterranean passages become choked or are too small to carry away all the water4 ,a seasonal lake of this character is the ,zirknitz ,lake 7p4 #ahi74 ,playa lakes4--,it is the law of the desert that the arid region be walled in by mountains4 ,this encircling rampart forces the clouds to rise1 and by robbing them of their moisture leaves the desert dry and barren4 ,those waters which fall upon the inner margin of the ranges drain toward the interior of this pan-like depression and are not returned to the sea--the desert is without an outlet4 ,infrequent though they be1 the desert rains are of the cloudburst type and in the hills develop torrents whose waters1 emerging upon the desert floor1 develop lakes in the space of a few minutes or at most hours4 ,in the hot and dry atmosphere the waters of these shallow basins may be sucked up in the space of a few hours but reappear in the same basins at the time of the next succeeding cloudburst4 ,such ephemeral lakes are known as playas4 ,salines4--,desert lakes more favored in their supply of water may be relatively long lived and persist for periods measured in years or centuries4 ,such lakes are1 however1 extremely sensitive to climatic changes 7see p4 #aih74 ,for the reason that they have no outlet the waters of desert lakes become salt through continued evaporation4 ,they are1 therefore1 spoken of as salines4 ,lake ,bonneville1 so long as it discharged its waters over the sill of the ,red ,rock ,pass1 must have remained fresh2 but when the level of its waters had fallen below this outlet1 its waters became salt and the content increased as the volume diminished4 ,the shallow basins upon the floors of desert lakes may have come into existence in various ways2 but it would appear that the irregular removal of the soil by the winds1 modified as this is by differences in composition of the rock materials and by vegetable growth1 and the deposition of sand by the same agent1 are by far the most important4 ,many of the types of tectonic and volcanic lakes which have been described are characteristic of humid and arid regions alike4 ,alluvial-dam lakes4--,within the mountains upon the desert borders1 the alluvial fans which form at the mouths of valleys1 because of the characteristic cloudburst1 sometimes obstruct a main valley at the junction with its tributaries4 ,by this process the waters of the main river are impounded in essentially the same manner as are the rivers of humid regions by the deltas of their tributaries4 ,rsum4--,the types of lakes which we have now considered are arranged below in tabular form so as to show their relationship to important geological processes4 ,while not complete1 the list includes the more important classes1 as well as others which1 while not of common occurrence1 are yet of interest in giving further illustration to the processes which have been treated in earlier chapters4 ,by giving careful attention to criteria which have been above suggested1 it should be possible in the greater number of instances at least to determine whether any lake which is visited has had its origin in one or another of the processes described4 ,,classification ,,of ,,lakes ,tectonic ,lakes ,volcanic ,lakes ,newland lakes ,crater lakes ,basin-range lakes ,coule lakes ,rift-valley lakes ,earthquake lakes ,continental ,glaciation ,lakes ,mountain ,glaciation ,lakes ,morainal lakes ,rock-basin lakes ,pit lakes ,valley moraine lakes ,glint or colk lakes ,landslide lakes ,ice-dam lakes ,border lakes ,glacier-lobe lakes ,river ,lakes ,strand ,lakes ,ox-bow lakes ,barrier lakes ,saucer lakes ,dune lakes ,crescentic levee lakes ,raft lakes ,side-delta lakes ,delta lakes ,ground ,water ,lakes ,desert ,lakes ,sink lakes ,playa lakes ,karst lakes--poljen ,salines ,alluvial dam lakes4 ,,reading ,,references ,,for ,,chapter ,,xxix ,general3-- ,i4 ,c4 ,,russell4 ,lakes of ,north ,america4 ,boston1 #ahie1 pp4 #abe1 pls4 #bc4 ,a4 ,p4 ,,brigham4 ,lakes1 ,a ,study for ,teachers1 ,jour4 ,sch4 ,geogr41 vol4 #a1 #ahig1 pp4 #fe-gb4 ,n4 ,m4 ,,fenneman4 ,the ,lakes of ,southeastern ,wisconsin1 ,bul4 #h1 ,wis4 ,geol4 and ,nat4 ,hist4 ,surv41 #aijb 7,rev4 ,ed41 #aiaj71 pp4 #ahh1 pls4 #cg4 ,a4 ,,delebecque4 ,les ,lacs ,franais 7with ,atlas74 ,paris1 #ahih4 7,work crowned by the ,society of ,geology of ,paris47 ,h4 ,r4 ,,mill4 ,bathymetrical ,survey of the ,english ,lakes1 ,geogr4 ,jour41 vol4 #f1 #ahie1 pp4 #df-gc1 #ace-aff4 ,a4 ,,supan4 ,grundzge der ,physischen ,erdkunde4 ,leipzig1 #ahif1 pp4 #eca-edh4 ,h4 ,,berghaus4 ,atlas der ,hydrographie4 ,gotha1 #ahia1 pl4 #c4 ,r4 ,d4 ,,salisbury4 ,physiography4 #aijg1 pp4 #bib-cbg4 ,,charles ,,rabot4 ,revue de limnologie1 ,la ,gographie1 ,vol4 #d1 #aija1 pp4 #aaj-aai1 #agb1 #ahi4 ,i4 ,c4 ,,russell4 ,a ,geological ,reconnaissance in ,southern ,oregon1 #dth ,ann4 ,rept4 ,u4 ,s4 ,geol4 ,surv41 #ahhd1 pp4 #ddb-ddg4 7,basin range lakes47 ,,ed4 ,,suess4 ,the ,face of the ,earth1 vol4 #d1 #aiji1 pp4 #bfh-bhf4 7,rift valley lakes47 ,j4 ,s4 ,,diller4 ,crater ,lake1 ,nat4 ,geogr4 ,mag41 vol4 #h1 #ahig1 pp4 #cc-dh1 pl4 #a2 ,geology of ,lassen ,peak ,quadrangle1 ,california1 ,geol4 ,fol4 #ae1 ,u4 ,s4 ,geol4 ,surv41 #ahie4 7,coule lakes47 ,n4 ,m4 ,,fenneman4 ,lakes of ,southeastern ,wisconsin1 l4c41 pp4 #d-f4 7,pit lakes47 ,,ed4 ,,suess4 ,the ,face of the ,earth1 vol4 #b1 #aijf1 pp4 #cdj-cdf1 pl4 #g4 7,glint lakes47 ,i4 ,c4 ,,russell4 ,a ,preliminary ,paper on the ,geology of the ,cascade ,mountains in ,northern ,washington1 #bjth ,ann4 ,rept4 ,u4 ,s4 ,geol4 ,surv4 ,pt4 ii1 #aijj1 pl4 #ad4 7,view of a rock-basin lake47 ,e4 ,w4 ,,shaw4 ,preliminary ,statement concerning a ,new ,system of ,quaternary ,lakes in the ,mississippi ,basin1 ,jour4 ,geol41 #aiaa1 pp4 #dha-dia4 7,new type of levee lakes47 ,a4 ,c4 ,,veatch4 ,formation and ,destruction of the ,lakes of the ,red ,river ,valley1 ,prof4 ,pap4 ,no4 #df1 ,u4 ,s4 ,geol4 ,surv41 pp4 #fj-fb1 pls4 #bi-cc4 7,raft lakes47 ,m4 ,,neumeyer4 ,erdgeschichte1 vol4 #a1 pp4 #eie-eif4 7,poljen47 ,,chapter ,,xxx ,,the ,,ephemeral ,,existence ,,of ,,lakes ,lakes as settling basins4--,of all the processes which conspire to blot out the lakes with which our northern landscapes are dotted1 the one of greatest importance is in most cases a process of filling by the sediments brought in by tributary streams4 ,the carrying of sediment in suspension depends1 as we know1 upon the velocity of the current1 and as this is checked where it reaches the lake margin1 all coarser material is at once deposited to form a delta1 while the finer sediments are held longer in suspension and finally settle in thin layers over the entire bottom of the lake4 ,clay deposits surrounded by coarser sediments are thus characteristic of filled lake basins4 ,illustration3 ,,fig4 #dfb4--,map of the ,arve and the upper ,rhone to show the importance of ,lake ,geneva as a settling basin of the larger stream4 ,how waters are clarified by their passage through a lake is indicated by a comparison of a river system such as the ,st4 ,lawrence1 with a river like the ,missouri and ,mississippi4 ,not only are the lower stretches of the ,st4 ,lawrence in striking contrast with the muddy floods of the ,missouri and ,mississippi2 but the delta1 which is so remarkable a feature in the ,mississippi1 has no counterpart in the northern river4 ,the most noteworthy examples of settling are1 however1 furnished by the lakes of ,switzerland1 for the reason that ,,swiss rivers are heavily charged with rock flour produced beneath the numerous glaciers at the valley heads1 and1 further1 because these rivers descend with turbulent currents to near the borders of the larger lakes4 ,to look out upon the murky waters of the upper ,rhone1 where they enter ,lake ,geneva near ,villeneuve1 and then to watch the flood of crystal water which issues from the lake and passes under the bridge at ,geneva1 is an object lesson which no traveling student should miss 7,fig4 #dfb74 ,yet even more instructive is a visit to the ,bois de la ,btie at the junction of this clear stream with the ,arve1 a half hour's walk only below ,geneva4 ,the waters of the ,arve have come on a steep descent directly from the glaciers of the ,mont ,blanc district1 and as they meet the cleared waters of the ,rhone1 they flow beside them down the common valley without mingling4 ,dull and opaque1 the ,arve waters can be discerned for a long distance as a white belt against the left bank of the river1 sharply defined against the blue reflecting surface of the ,rhone waters 7,fig4 #dfc74 ,upon the banks of the ,arve1 just above its junction1 a cement manufactory has been established to utilize the clays which are here deposited4 ,illustration3 ,,fig4 #dfc4--,view looking upstream across the opaque waters of the ,arve to the clear reflecting surface of the ,rhone4 ,to the right across the ,arve is seen the cement works for recovering the ,arve sediments4 ,wherever lakes are contained in long and narrow valleys1 the greater part of the tributary drainage enters at the upper end1 and the delta which there forms extends from bank to bank4 ,as it continues to advance into the lake1 the earlier water basin is gradually transformed into a level plain of delta deposit1 a feature so common as to be deserving of a special name4 ,the ,scottish lochs1 which are lakes of this type1 are each extended in a longer or shorter delta plain described as a strath1 and this local term may well be given a general application 7frontispiece74 ,the city of ,ithaca1 the seat of ,cornell ,university1 is built upon a strath at the head of ,lake ,cayuga1 and numberless ,scottish and ,swiss hamlets have been located upon such fertile plains 7,fig4 #dfd74 ,illustration3 ,,fig4 #dfd4--,the village of ,poschiavo in eastern ,switzerland1 built upon a strath at the head of ,lake ,poschiavo4 ,drawing off of water by erosion of outlet4--,next in importance to the filling up of lake basins as a factor in their early extinction is the cutting down of their channels of outflow4 ,whenever the walls of the outlet are cut in rock1 this draining process is apt to be slow1 for the reason that the outlet stream is of filtered water and so lacks the necessary cutting tools4 ,by far the larger number of lakes are1 however1 held back by dams of loose drift deposits laid down by the earlier continental glaciers2 and so the very clarity of the water promotes the erosion of the outlet by allowing the stream's full burden of sediment to be lifted and then removed from the channel4 ,the pulling in of headlands and the cutting off of bays4--,the removal of projecting headlands by wave action1 though it increases the area of the lake1 yet it decreases directly the volume of lake water through formation of the built terrace1 and indirectly in far larger measure through the transformation of bays into quiet lagoons within which the extinguishing process of peat growth is set in operation4 ,lake extinction by peat growth4--,the first condition for the growth of lake vegetation is quiet water4 ,within small lakes1 such as the kettle basins upon moraines1 aquatic vegetation develops rapidly1 and bogs of peat might almost be included among the most important distinguishing marks of a glaciated country4 ,within larger lakes it is only after barrier beaches have been thrown across the mouths of the bays to form natural breakwaters for the waves that this process of lake extinction by peat growth can become effective4 ,illustration3 ,,fig4 #dfe4--,view of the floating bog and surrounding zones of vegetation in a small glacial lake of the ,yellowstone ,national ,park 7after a photograph by ,fairbanks74 ,many erroneous notions are still held concerning the prime importance of sphagnum in peat formation1 owing to the peculiar local conditions under which the early studies were made4 ,within the glaciated districts of the ,united ,states1 the formation of peat involves the successive growths of a number of zones of vegetation and the formation of a floating bog which advances into the lake from the shores1 followed in turn by belts of low shrubs1 tamaracks1 and lastly deciduous trees 7,fig4 #dfe74 ,in most cases the first plants to develop in a quiet lake are the water lilies1 though these are sometimes preceded by chara and floating bladderwort4 ,next behind the water lilies come the sedges1 which form a mat of floating bog by their grasslike stems sinking down in the water and being there interwoven with the rhizomes below4 ,this mat of sedge is often so firm that cattle may advance upon it to the water's edge1 but it is separated by a layer of water from the bed of growing peat at the bottom of the lake 7,fig4 #dff74 ,this bed of peat appears to grow upward toward the surface and become joined to the shore end of the floating bog by decaying vegetation which is dropped from the bottom of the mat above4 ,illustration3 ,,fig4 #dff4--;,diagram to show how small lakes are transformed into peat bogs 7after ,c4 ,a4 ,davis74 ,in order behind the floating bog come the advanced plants of the conifer group1 with sphagnum and low shrub here upon a peat base extending to the lake bottom4 ,behind the belt of shrubs arise the tamaracks and spruces1 and lastly1 toward the shore1 come the deciduous trees and especially poplars1 maples1 and marginal willows4 ,upon the margin of the basin there is usually a low trench1 or 8fosse01 filled with water during wet seasons1 as a result1 no doubt1 of seasonal inwash that does not reach the residual lake toward the center of the basin4 ,extinction of lakes in desert regions4--,in arid regions there are special causes of lake extinction4 ,thus the blowing in of sand and dust carried for long distances in the air1 a by no means negligible factor even in humid regions1 here assumes large importance4 ,the now exposed basins of extinct desert lakes afford the evidence1 however1 of an even greater factor of extinction1 in climatic change4 ,the clouds1 which at one time found their way into the drainage basin of a lake1 may later through the rise of a mountain barrier be cut off1 and so with reduced water supply a period of lake desiccation is begun4 ,when1 in this process of drying up1 the lake level has fallen below that of the outlet1 the saline content of the waters begins to increase1 and later a stage is reached1 as in ,great ,salt ,lake1 when the sodium salts are precipitated4 ,when the lake has become extinct1 these deposits remain as a witness to the changed climatic condition4 ,the rle of lakes in the economy of nature4--,it is natural1 in considering the extinction of lakes1 to give some attention to the rle which they play in the economy of nature4 ,that lakes filter the water of rivers1 and prevent the formation of important delta deposits1 has already been noticed4 ,a curious exception to this general rule is furnished by the great delta at the head of ,lake ,st4 ,clair1 just below the outlet of ,lake ,huron4 ,this anomaly is1 however1 explained by the peculiar currents of ,lake ,huron1 which are so directed as to sweep the beach sand into the swift current of the outlet1 to be deposited in the quiet waters of ,lake ,st4 ,clair 7,fig4 #dfg74 ,illustration3 ,,fig4 #dfg4--,map to show anomalous position of the delta in ,lake ,st4 ,clair1 due to the peculiar currents in ,lake ,huron 7after maps by ,cole74 ,as regulators of the flow of rivers1 lakes perform an important function4 ,such disastrous floods as are characteristic of the spring season within the basin of the lower ,mississippi could not occur in the lower ,st4 ,lawrence1 for the reason that the great basins of the lakes serve as distributing reservoirs4 ,the annual floods1 upon which the agriculture of ,egypt depends1 are explained by the flood waters from the high mountains of ,abyssinia entering the ,nile below the lakes of its upper basin4 ,in one further respect large inland bodies of water have an important function as regulators4 ,it is the property of water to respond but slowly to the variations in the quantity of heat which reaches the earth's surface from the sun4 ,a larger quantity of heat must be added to or abstracted from a body of water1 in order to change its temperature by one degree1 than would be required for a like change in the same bulk of earth or rock4 ,thus bodies of water by more slowly acquiring the summer's heat retard the coming spring1 and by storing up this energy and carrying it over into the autumn the warm season is prolonged and early frosts prevented4 ,the fruit belts about the lower ,great ,lakes are thus dependent upon this regulating property of the lake waters4 ,the discomfort of the long spring of raw weather is thus compensated by an unusually salubrious harvest season4 ,ice ramparts on lake shores4--,small ridges known as ice ramparts are formed upon lake shores by the action of lake ice1 though subject to so many qualifying conditions that the range of their occurrence is somewhat limited4 ,within districts where a winter ice cover of some thickness is formed1 the shores of lakes are apt to present ridges of bowlders parallel to and near the water's edge1 and such lakes have sometimes become known as 8wall lakes0 7,fig4 #dfh74 ,illustration3 ,,fig4 #dfh4--;,a bowlder wall upon the shore of a small lake in the ,adirondacks of ,new ,york4 ,in many cases these small ridges have been formed at the time of the spring 8break up0 of the ice2 for the ice cover1 when once loosened1 is drifted in great rafts first against one shore1 and later1 with a change of wind direction1 against another4 ,under the impact of such heavy rafts1 the half-submerged bowlders near the shore are forced up the beach until they lie in a ridge or bowlder wall4 ,at other times such bowlder walls1 and far more interesting ridges as well1 result from a kind of ice shove independent of the wind1 but caused by expansion within the ice itself during a sudden rise of temperature of the surrounding air4 ,such ice ramparts require for their explanation a consideration of the sequence of events from the time the ice cover closes the lakes4 ,illustration3 ,,fig4 #dfi4--;,diagrams to show the effect of ice shove in producing ice ramparts upon the shores of lakes 7after ,buckley with a slight modification74 ,the first lake ice of early winter forms in most cases with air temperatures a few degrees only below the freezing point of the water4 ,when later a severe 8cold wave0 arrives1 the ice cover is contracted and becomes too small for the lake surface4 ,to this contraction it yields and opens cracks up which the water rises1 and in the prevailing low temperature this water is quickly frozen and the lake cover again made complete4 ,skaters are familiar with the opening of these cracks and the loud 8roaring0 which accompanies it on cold mornings1 the sharp skate runners sometimes starting a crack in the strained ice1 as does a light scratch upon glass that is in a similar strained condition4 ,illustration3 ,,fig4 #dgj4--,various forms of ice ramparts 7after ,buckley74 ,the original ice cover of the lake1 which was formed at near-freezing temperatures1 has now received a number of inserted wedges of new ice at a time when its contracted volume has made this possible4 ,if now a 8warm wave0 succeeds to the 8cold wave0 in the air1 the ice cover expands at a rate corresponding to its rate of contraction1 so that a strong pressure is exerted against the shore 7,fig4 #dfi74 ,sliding up the sloping surface of the cut and built terrace1 the force of this shove may be deflected upward against the cliff1 and if this is of loose materials1 the effect may be to ram bowlders into the bank1 to push up ramparts or ridges1 to overturn trees1 etc4 7,fig4 #dgj74 ,in marsh land the frozen surface layer may slide over its unfrozen base and be forced up into broken folds 7lower diagram of ,figs4 #dfi and #dgj74 ,illustration3 ,,fig4 #dga4--,map of ,lake ,mendota at ,madison1 ,wisconsin1 showing the position of the ridge which forms from ice expansion1 and the ice ramparts about the shores of the bays 7based on ,buckley's map74 ,in order that ice ramparts may be formed1 it is necessary that the winter climate of the district be severe and characterized by alternating cold and warm waves1 involving considerable range of air temperature below the freezing point4 ,if the lake is small1 the push of the ice will be through so small a distance as not to yield appreciable ramparts4 ,if1 on the other hand1 the lake is too large1 the ice cover is not rigid enough to transmit the push to the distant shore1 but1 like a long beam employed in the same manner to transmit a compressive stress1 it is bent out of a straight line and later broken4 ,thus in a broad lake1 with the coming of a 8warm wave01 the ice cover opens in a crack from shore to shore and finds relief from the stress by pushing up a ridge above the crack4 ,on such lakes ice ramparts are found only about the shores of bays whose expanse does not greatly exceed a mile 7,fig4 #dga74 ,when there is heavy snowfall1 ice ramparts either do not form or are of smaller dimensions1 probably in part because the ice is blanketed by the snow and so prevented from sudden elevation of temperature during the 8warm wave01 but even more because the ice cover is sensibly bowed down under its load and so rendered incompetent to transmit the developed stresses to the shores4 ,,reading ,,references ,,for ,,chapter ,,xxx ,lake extinction by peat growth3 ,c4 ,a4 ,,davis4 ,peat1 ,essays on its ,origin1 ,uses1 and ,distribution in ,michigan1 ,ann4 ,rept4 ,mich4 ,geol4 ,surv4 for #aijf1 #aijg1 pp4 #aje-ahb2 ,peat ,deposits as ,geological ,records1 #ajth ,rept4 ,mich4 ,acad4 ,sci41 #aijh1 pp4 #ajg-aab4 ,g4 ,p4 ,,burns4 ,bog ,studies4 ,ann ,arbor1 #aijf1 pp4 #ac4 ,ice ramparts3 ,c4 ,h4 ,,hitchcock4 ,shore ,ramparts in ,vermont1 ,proc4 ,am4 ,assoc4 ,adv4 ,sci41 vol4 #ac1 #ahfi1 pp4 #cce-ccg4 ,g4 ,k4 ,,gilbert4 ,lake ,bonneville1 ,mon4 #a1 ,u4 ,s4 ,geol4 ,surv41 #ahij1 pp4 #ga-gb4 ,e4 ,r4 ,,buckley4 ,ice ,ramparts1 ,trans4 ,wis4 ,acad4 ,sci41 etc41 vol4 #ac1 #aijj1 pp4 #ada-afb1 pls4 #a-ah4 ,,william ,h4 ,,hobbs4 ,requisite ,conditions for the ,formation of ,ice ,ramparts1 ,jour4 ,geol41 vol4 #ai1 #aiaa1 pp4 #aeg-afj4 ,,chapter ,,xxxi ,,the ,,origin ,,and ,,the ,,forms ,,of ,,mountains ,a mountain defined4--,as ordinarily understood1 mountains are elevations upon the earth's surface which rise above the general level of the country4 ,their summits need not be at great heights above the sea1 but it is essential that they project above the average level of the surrounding country by at least a quarter of a mile4 ,lower elevations are described as hills4 ,on the other hand1 the elevation of a plateau like the 8,high ,plains0 of the western ,united ,states may be as much as a mile1 but the vast expanse of nearly level surface precludes the use of the term 8mountain40 ,the word is thus applied to a feature of the earth and not merely to an elevated tract4 ,in a collective sense1 though more often in the plural form1 the term is properly applied to groups of similar features which have a common origin in local uplift of the land4 ,the origin of mountains used in this sense of mountain complexes is thus connected with some essentially local uplift of the earth's surface4 ,this may take place by the processes of folding and superincumbent fault displacement1 by volcanic extravasations or ejections1 or by a deeper seated and essentially hydrostatic elevation of rock beds over molten rock material4 ,the existing forms of mountains1 as we are to see1 are largely shaped by the erosional processes which are set in operation by the uplift itself1 though often completed long subsequent to it4 ,the festoons of mountain arcs4--,from our earliest studies of school geographies1 we have become familiar with the arrangement of the more important mountains in long chains or systems4 ,comparatively few persons have given any further attention to the arrangement of the chains1 though over large areas of the earth's surface the distribution of mountain ranges is deeply significant4 ,the map of ,asia in particular presents a series of great sweeping arcs or crescents which are grouped as though hung upon the map in festoons with knots or vertexes to separate neighboring groups 7,fig4 #dgd1 p4 #dch1 and ,fig4 #dgb74 ,illustration3 ,,fig4 #dgb4--,the great multiple mountain arc of ,sewestan1 ,british ,india 7after de ,saint ,martin and ,schrader74 ,the significance of these mountain groupings in the evolution of the earth's surface has been pointed out by the great ,viennese geologist ,suess1 to whom we are indebted for focusing upon the plan of the earth an amount of attention which before had been largely given to the preparation of hypothetical sections of strata which were largely buried from sight beneath the earth's surface4 ,broadly speaking1 the mountain arcs may be said to be grouped about those shields of older rock which geological studies have shown to be the oldest land masses upon the globe4 ,within the northern hemisphere these original continents are represented by the areas of crystalline rock centered over ,hudson ,bay1 the ,baltic ,sea1 and an area in northeastern ,siberia known to geologists as ,angara ,land4 ,in our study of the figure of the earth 7,chapter ,,ii7 it was found that these shields represent the truncated angles of the rounded tetrahedral form toward which the planet is tending 7,fig4 #c1 p4 #ab74 ,theories of origin of the mountain arcs4--,the mountain arcs1 when studied in detail1 are found to be composed of closely folded rock strata1 the flexures of which are generally so overturned that their axial planes dip toward the center of the arc 7,fig4 #dgc74 ,it was the view of ,suess that these arcs are to be explained by a pushing outward of the rock strata from the center of the arc toward its periphery1 thus causing a wrinkling of the surface strata and an overriding of the surrounding formations1 which upon this hypothesis opposed a greater resistance to the sliding movement4 ,the folding together of the strata due to the sliding naturally involves a very considerable diminution of the surface area presented by the strata 7,fig4 #bb1 p4 #db74 ,in the case of the ,alpine chains it has been estimated that a flat land area1 four hundred to eight hundred miles across1 has by the folding process been reduced to a width of only about one hundred miles1 or from a fourth to an eighth of its former width4 ,illustration3 ,,fig4 #dgc4--;a1 diagram to illustrate the ,suess' theory of the origin of mountain arcs2 b1 the author's modification of this view4 ,the weakness of ,professor ,suess' theory lies in the fact that such compression as it implies is assumed to be due to an outward movement of the relatively small area of the earth's outer shell which is included within the arc4 ,it must be obvious that such a movement1 being from a center toward three sides at once1 would for this circumscribed area involve enormous proportionate reduction in superficial area of the strata and could only result in a hiatus near the center of the arc4 ,no such gap is to be found1 and one would1 moreover1 be difficult to account for upon any plausible hypothesis4 ,on the other hand1 the general contraction of the planet as a whole1 involving as it does reduction of surface over large areas1 is a well-recognized fact2 and if it be true that the shields formed by the older continents are less subject to contraction than the remaining portions of the surface1 it is easy to understand why the earth's outer skin should be wrinkled by underfolding and thrusting about these continental margins4 ,the contrast of this view with that of ,professor ,suess is expressed in the diagrams of ,fig4 #dgc4 ,illustration3 ,,fig4 #dgd4--;,festoons of mountain arcs about the borders of the ,pacific ,ocean--,pacific type of coast 7based upon ,suess74 ,we may illustrate this conception by a stretched sheet of rubber cloth such as is in common use by dentists1 upon which a thin layer of hot ,canada balsam has been spread4 ,this substance congeals upon cooling to near-normal temperatures1 and if a small local area of the balsam layer be chilled and the tension upon the rubber then released1 the viscous balsam of the unchilled portion of the layer is thrown into wrinkles about the cooled and more resistant areas4 ,these more resistant portions of the stratum may thus represent the ancient continental shields of our planet4 ,the ,atlantic and ,pacific coasts contrasted4--,in his studies of mountain arcs in their relation to the plan of the earth1 ,professor ,suess has shown how the arrangements of the mountain chains about the two larger oceans represent two strongly contrasted types4 ,whereas about the ,pacific margin the mountain arcs are1 as it were1 strung in festoons which trend parallel to and are convex toward the coast1 or else lie in fringing garlands of islands in the same attitude 7,fig4 #dgd72 the mountain chains about the ,atlantic become sharply truncated as they reach the coast1 and thus indicate that the basin of this ocean has been produced by an inthrow or depression between great marginal displacements in some period subsequent to the formation of the mountains4 ,illustration3 ,,fig4 #dge4--,the interrupted system of the ,armorican ,mountains common to western ,europe and eastern ,north ,america 7after ,arldt74 ,thus the mountain folds of the ,appalachian system are in ,newfoundland cut off abruptly at the coast line1 and the same beds1 similarly truncated1 are encountered again across the expanse of ocean in the folds at the coast of western ,europe 7,fig4 #dge74 ,in discontinuous remnants this ancient mountain chain may be traced in an east and west direction across western and central ,europe4 ,we have thus here to do with a single mountain system which extends from central ,europe to northern ,alabama1 out of which a great link has been taken by the subsequent sinking in of the basin of the ,atlantic ,ocean4 ,illustration3 ,,fig4 #dgf4--,schematic representation of a 8zone of diverse displacement0 in the ,great ,basin of the western ,united ,states 7after ,powell74 ,the block type of mountain4--,the inclusion of most elevations in mountain chains and arcs is one of the most obvious facts to any one who has examined world atlases with this subject in mind4 ,such chains are almost invariably composed of folded rocks1 thus indicating that erosion has removed great superincumbent masses of strata since the crustal compression produced the folds at considerable depths below the then surface4 ,there are1 however1 large elevated tracts upon the earth's surface which are intersected by deep valleys1 but where no arrangement of the elevated portions within chains or ranges is to be detected4 ,in such cases the distribution of mountain and valley may bear a resemblance to a mosaic of disturbed parts which stand at different levels 7,fig4 #dgf74 ,illustration3 ,,fig4 #dgg4--,section of an ,east ,african block mountain 7after ,j4 ,w4 ,gregory74 ,such block mountain districts are to be found in many parts of the earth's surface1 but notably within the ,great ,basin of the western ,united ,states1 and in the land area which borders the ,indian ,ocean upon the west and northwest4 ,in contrast with the mountain arcs1 so strikingly exemplified by the continent of ,asia as a whole1 its extreme southwestern portion is made up of an alternation of plateau and rift valley separated from each other by great displacements4 ,though modified to some extent by erosion1 the elevations seem generally to represent the displaced crust blocks which in mutual adjustments have been left at the highest levels 7,fig4 #dgg74 ,the valley of the ,jordan1 with the mountains of ,lebanon rising above it1 is near the northern extremity of this faulted mountain region 7,fig4 #dcd1 p4 #djd71 while the ,great ,rift valley1 crossing east ,central ,africa1 and the many neighboring rifts to the east and west1 are graven in lines so deep that an observer upon a neighboring planet might perhaps detect them4 ,it is not necessary in all cases to assume that the block mountains of a faulted district represent the blocks which in the adjustments were left the highest4 ,erosion in the course of time accomplishes marvels of transformation1 and it may result that heavy masses of more resistant rock eventually project the highest1 even though they may represent the downthrown blocks in the fault mosaic 7,fig4 #dc1 p4 #fj74 ,illustration3 ,,fig4 #dgh4--,tilted crust blocks in the ,queantoweap valley4 ,where in addition to undergoing changes of level the earth blocks have been tilted1 the features long since described from our western interior basin as 8,basin ,range structure0 are developed4 ,here the upper surface of the disturbed earth blocks betrays the evidence of a definite tilt in some one direction 7,fig4 #dgh1 and ,fig4 #dca1 p4 #djb74 ,mountains of outflow or upheap4--,an important type of mountain1 generally described as volcanic1 may be due either to the outflow of lava at the earth's surface1 or to accumulations of separated fragments of lava1 first thrown into the air1 and then deposited by gravity or admixed with water as volcanic mud4 ,such mountains1 both before and after modification by erosion1 assume the strikingly characteristic forms which have been fully discussed in ,chapters ,,ix and ,x4 ,the dominant types are the lava dome and the puy1 the cinder cone1 and the more complex composite cone4 ,excepting only the surface produced by the few great fissure eruptions and the semivolcanic mesa type1 the individual mountains of volcanic origin develop features with notably circular bases4 ,illustration3 ,,fig4 #dgi4--,pen drawing of the laccolite of the ,carriso ,mountain by ,w4 ,h4 ,holmes1 which shows the jagged surface of the igneous rock core and the sloping tables which still remain of the roof of sedimentary rocks 7after ,cross74 ,illustration3 ,,fig4 #dhj4--,map of laccolitic mountains4 ,a portion of the ,judith ,mountains1 ,montana4 ,the intrusive igneous rock is shown in black 7after ,weed74 ,domed mountains of uplift--laccolites4--,at a considerable number of widely separated localities upon the earth's surface1 mountainous regions are encountered1 the central areas or cores of which are composed of intrusive igneous rock such as granite1 and about this core the sediments dip away in all directions as though they had once formed a continuous roof above it and had been forced into this dome by hydrostatic pressure of the once viscous material beneath 7,fig4 #aeb1 p4 #adc1 and ,figs4 #dgi and #dhj74 ,examples of such domed mountains of uplift were first described by ,gilbert from the ,henry ,mountains of ,utah1 but instances are furnished by many elevated tracts1 especially within the western ,united ,states4 ,such mountains are known as laccolites1 but when one margin at least of the igneous core corresponds to a displacement1 the mountain is described as a bysmalite 7,fig4 #dha74 ,illustration3 ,,fig4 #dha4--;,ideal sections of laccolite and bysmalite4 ,when subjected to long-continued erosion1 the generally fissured granitic core of the laccolite weathers in a wholly different manner from the bedded sediments which surround and still in part mount over it4 ,the former usually presents a more or less jagged surface which contrasts sharply with the gently sloping tables of the latter 7,fig4 #dgi74 ,about the high granite core of the mountain1 the several strata of the uptilted formations present each a steep slope toward this higher land1 and a gentler slope in the opposite direction4 ,such unsymmetrical ridges which surround the mountain area are often referred to as 8hog backs0 7plate #ab ,b74 ,the arrangement of the strata in the hog backs thus presents an overlapping series like the shingles upon a roof1 except that the overlapping is here from the bottom instead of the top1 and the exposed ends thus face toward the crest4 ,unlike a shingle roof the hog backs do not shed the water which descends to them from the higher levels1 but1 on the contrary1 they cause it to flow in troughs parallel to the base of the slope except where outlets are found through them4 ,mountains carved from plateaus4--,in the mountain types thus far discussed1 the local uplifting of the land has itself developed features which in the aggregate may be referred to as mountains1 even though the characters of the original surface are soon destroyed by erosive processes of one sort or the other4 ,erosive processes are1 however1 quite competent to produce mountain forms from a featureless plateau1 and particularly through the incision by streams of running water1 the best studied process of mountain sculpture 7see ,chapters ,,xi-,,xiii74 ,this process of throwing valleys about an elevated section of the earth's surface1 and so carving out mountains1 is sometimes described as circumvallation2 and if the term 8mountain0 be applied in its ordinary sense to describe an individual feature1 it is clear that most mountains have been formed in this way4 ,to discuss the characteristic shapes of such mountains would be largely to review the contents of this book1 and especially those portions which discuss the character profiles resulting from the action of each sculpturing or molding agent4 ,the work of frost and other weathering agencies1 of running water1 of mountain and of continental glacier1 would all have to be considered in order to evolve the history of each mountain4 ,in addition to discovering the agents which were chiefly responsible for the shaping of the mountain1 we may1 further1 in many cases determine at what stage the work of one agent has been succeeded by that of another1 and at least at what stage of its complete cycle of activity the latest agent is now at work4 ,illustration3 ,,fig4 #dhb4--,the gabled faade so largely developed in desert landscapes and sharply contrasted with the recurring curves in the landscapes of humid districts 7from a painting of the ,grand ,caon of the ,colorado by ,moran74 ,the climatic conditions of the mountain sculpture4--,since the different geological agencies operate either in a different manner or with differences in vigor according to the varying climatic conditions1 the mountains of arid regions may in most cases be readily differentiated from those of the more habitable humid sections of country4 ,in broad lines these differences may be summed up in the greater prevalence of the curving line within the landscapes of humid districts4 ,this may be largely ascribed to the influence of the mat of vegetation1 which protects the rock surface from more rapid mechanical degeneration1 and arrests the sliding movements within the already loosened rock dbris4 ,in place of the reversed curves of the lines of beauty1 so generally observed in the landscapes of well-watered regions1 the desert lands present ever a repetition of the vertical cliff alternating with a sort of many gabled faade which is occasionally due to truncation of mountain spurs by the waves of former lakes1 but far more often the outlines of dbris cones built up beneath each prominent joint of the cliff walls 7,fig4 #dhb74 ,the effect of the resistant stratum4--,in a striking manner mountain landscapes may disclose the influence of the diversified rock materials and of the rock structures as well4 ,after prolonged erosion there is likely to be little correspondence between the positions of the anticlinal folds and the crests of the higher mountains4 ,such mountains are1 in fact1 much more likely to rise over synclines than upon the site of anticlines4 ,the traveler who enters the ,alps by any of the several railways1 or who journeys by steamer over the beautiful lake of ,lucerne1 has a most favorable opportunity to study the position of the rock folds in the mountain sections that are unrolled in succession before him4 ,rarely indeed will he find a definite anticline in correspondence with a mountain peak1 for the layers which are most resistant have developed the peaks1 and it is because the outer layers of the anticlines open by local tension 7see ,fig4 #bf1 p4 #de7 that they were first cut away by erosion1 so that the hard layers within the synclines are likely to constitute the peaks within the existing surface4 ,illustration3 ,,fig4 #dhc4--,the ,mythen1 composed of ,jurassic and ,cretaceous sediments1 and resting upon softer ,tertiary formations4 ,view from a balloon 7after a photograph by ,c4 ,schmidt74 ,when1 as sometimes happens1 an older and likewise more resistant bed has been folded back upon younger and softer formations1 an isolated remnant may be found 8unrooted0 to its base1 upon which it appears as though floating within a billowy sea of the softer formations 7,fig4 #dhc74 ,the mark of the rift in the eroded mountains4--,applying the term 8mountain0 in its collective sense for a circumscribed area of uplifted crust1 whether represented to-day by a folded or a faulted complex1 a lava mass1 or a granite dome2 the period of uplift has marked the beginning of the activity of sculpturing agencies4 ,by these the mass is pared down as it is shaped into a more or less intricate design of component and essentially repeating units4 ,in the vernacular the word 8mountain0 is applied to these units into which the larger mountain mass is subdivided4 ,illustration3 ,,fig4 #dhd4--,the battlement type of erosion mountains4 ,die ,drei ,zinnen 7,three ,battlements7 in the ,dolomites 7after ,marr74 ,it has been one of the main objects of this work to point out that the peculiar shapes of these elementary mountains are each characteristic of the erosive agents which produced them1 and that each surface has marks which may be recognized in those lines of profile which recur within the landscape--the character profiles4 ,in the subdivision of the larger mass--the genetical mountain--to form the numerous smaller masses--the erosional or circumvallational mountains--there is disclosed a pattern of fractures which has guided the erosional agents in their incisional operations 7see ,chapter ,,xvii74 ,in high altitudes1 where the action of frost is so potent in prying at the wider fractures1 this subdivision of the mass may be revealed by the sculpturing of squared towers or battlements 7,fig4 #dhd74 ,illustration3 ,,fig4 #dhe4--,symmetrically formed low islands repeated in ranks upon ,temagami ,lake1 ,ontario4 ,for other examples in which the sculptured surface is largely the handiwork of a single erosional agent1 as over vast areas in the ,canadian wilderness1 the revelation of the fracture design is no less apparent4 ,here a series of crystalline rocks underlie broad expanses of territory and are without noteworthy variations of hardness and almost bare of surface dbris4 ,sculptured beneath a mantling ice sheet1 excavation has naturally been concentrated above the more widely gaping fissures of the joint-fault system1 doubtless already marked out in the river network which the glacier overrode4 ,the result has been a division of the surface into a series of low1 oval ridges or hummocks1 which over vast areas are repeated with monotonous regularity4 ,wherever the lower levels have been flooded1 symmetrical low islands of nearly uniform elevation rise from the expanse of water and may be counted by thousands4 ,though the smaller islands have notably regular shore lines1 the larger ones disclose their composition from smaller units by the breaking of their shores into similar bays spaced with regular intervals 7,fig4 #dhe1 and ,figs4 #bdc and #bde1 p4 #bbi74 ,the ever repeating fracture design of the earth's crust is not restricted to the mountain masses which it has broken up1 and the unity of which it has done so much to conceal4 ,it extends far outside the margin of these masses1 and is in fact common to whole continents and perhaps even to the planet as a whole4 ,the part played by this design of fractures in the control of the sculpture of landscapes it would be hard to overestimate4 ,through its influence the striking features molded by one agent have been merged in the contrasted shapes developed by another4 ,it is the great outline blender in the creation of nature's masterpieces of form and color4 ,thus the lines of this mysterious fracture network1 though stamped in indelible characters upon our landscapes1 are generally lost in the ensemble effect and may long remain undiscovered4 ,like a moss-grown inscription upon a slab of marble1 though veiled1 it may yet be deciphered2 and if the veil be withdrawn1 the runic characters are disclosed1 and one of nature's laws lies open before us4 ,,reading ,,references ,,for ,,chapter ,,xxxi ,mountain arcs or festoons3-- ,,ed4 ,,suess4 ,the ,face of the ,earth1 vol4 #b1 #aijf1 pp4 #bja-bjg2 vol4 #d1 #aiji1 pp4 #dih-edb4 ,block mountains3-- ,g4 ,k4 ,,gilbert4 ,surveys ,west of the #ajjth ,meridian 7,wheeler71 vol4 #c1 ,geology1 ,washington1 #ahge1 ,pt4 #a1 pp4 #ai et seq41 #dh4 ,j4 ,w4 ,,powell4 ,report on the ,geology of the ,eastern ,portion of the ,uinta ,mountains and a ,region of ,country ,adjacent thereto1 ,u4 ,s4 ,geol4 and ,geogr4 ,surv4 ,ter41 ,,ii ,div4 ,washington1 #ahgf1 pp4 #bah4 ,,john ,w4 ,,gregory4 ,the ,great ,rift ,valley4 ,london1 #ahif1 pp4 #dbb4 ,laccolites and bysmalites3-- ,g4 ,k4 ,,gilbert4 ,report on the ,geology of the ,henry ,mountains1 ,u4 ,s4 ,geol4 and ,geogr4 ,surv4 ,ter41 #ahgg1 pp4 #ah-ih4 ,,whitman ,,cross4 ,the ,laccolitic ,mountain ,groups of ,colorado1 ,utah1 and ,arizona1 #adth ,ann4 ,rept4 ,u4 ,s4 ,geol4 ,surv41 #ahie1 pp4 #aeg-bda1 pls4 #g-af4 ,w4 ,h4 ,,weed and ,l4 ,v4 ,,pirsson4 ,geology and ,mineral ,resources of the ,judith ,mountains of ,montana1 #ahth ,ann4 ,rept4 ,u4 ,s4 ,geol4 ,surv41 ,pt4 iii1 #ahih1 pp4 #dhe-eef1 pl4 #ge4 ,w4 ,h4 ,,weed4 ,geology of the ,little ,belt ,mountains1 ,montana1 etc41 #bjth ,ann4 ,rept4 ,u4 ,s4 ,geol4 ,surv41 ,pt4 iii1 #aijj1 pp4 #chg-djj4 ,,vera ,,de ,,derwies4 ,recherches gologiques et ptrographiques sur les loccolithes des environs de ,piatigorsk 7,caucase du ,nord74 ,geneva1 #aije1 pp4 #hd1 pls4 #c4 ,r4 ,a4 ,,daly4 ,the ,mechanics of ,igneous ,intrusion1 ,am4 ,jour4 ,sci4 7#d71 vol4 #ae1 #aijc1 pp4 #bfi-bgh2 vol4 #af1 #aijc1 pp4 #ajg-abf4 ,,joseph ,,barrell4 ,geology of the ,marysville ,mining ,district1 ,montana4 ,a study of ,igneous ,intrusion and ,contact ,metamorphism4 ,prof4 ,pap4 #eg1 ,u4 ,s4 ,geol4 ,surv41 #aijg1 pp4 #aea-agh4 ,climatic condition in relation to land sculpture3-- ,c4 ,e4 ,,dutton4 ,tertiary ,history of the ,grand ,canyon ,district1 ,mon4 #b1 ,u4 ,s4 ,geol4 ,surv41 #ahhb1 pp4 #bfd1 pls4 #db4 ,,appendix ,a ,,the ,,quick ,,determination ,,of ,,the ,,common ,,minerals ,before one may gain a knowledge of rocks or the architecture of their arrangement within the earth's crust1 it is quite essential that some familiarity should be acquired with the appearance and properties of the commonest minerals1 and particularly those which enter as essential constituents into the more abundant rocks4 ,to be a competent mineralogist1 one must have a rather extended knowledge both of inorganic chemistry and of the science of crystallography1 which1 fascinating as it is to study1 involves some technical knowledge of mathematics and much laboratory experience4 ,though necessary to any one who contemplates making a career as a geologist1 this special study is not essential to a cultural course like the present one4 ,the attempt will here be made to bring together a body of fact1 from the study of which the student may quickly learn to recognize the commonest minerals in their usual varieties4 ,the tests he is to apply are mainly physical1 and in place of an elaborate discussion of crystal symmetry1 pictures only can be supplied4 ,to the beginner the usual textbook of mineralogy is difficult to read intelligently1 for the reason that for each mineral species it sets before him a catalogue of each physical property in its turn1 with little indication of those data which in the individual case have special diagnostic value4 ,none the less1 however1 the student is advised to consider the several properties of each mineral in a definite order1 and the following may serve as well as any3 crystal or other form1 cleavage1 fracture1 luster1 color1 streak1 transparency1 tenacity1 hardness1 magnetism1 and specific gravity4 ,in endeavoring to connect the specific values of these properties with individual mineral species1 the chemical composition and the manner of occurrence are not to be forgotten4 ,it is well for the student to be supplied with a small pocket lens and with a pocket knife the blade of which has been magnetized4 ,crystal form4--,some mineral species generally occur in more or less definite crystals--are bounded by definite plane surfaces developed when the mineral was formed2 others in groups of interfering crystals or aggregates1 in which case the mineral is said to be crystalline2 while still others are rarely found crystallized at all4 ,thus in a given case crystal form may1 or may not1 be important for the diagnosis of the substance4 ,if a mineral species is usually to be found in crystals1 the student should be aware of the fact1 and if possible should have a mental picture of the common crystal shape or shapes4 ,without an extended knowledge of crystallography1 this must be supplied him by drawings4 ,since crystals of most species are apt to be distorted1 owing to the fact that some planes within the same group appear upon the crystal with a larger development than others1 it is convenient to remember that markings1 such as lines or etchings upon the crystal faces1 are the same throughout the same group of planes1 and in the text figures such groups of planes are indicated by the use of a common letter4 ,for crystalline aggregates such terms as fibrous1 radiating1 massive1 or granular have their usual meanings4 ,cleavage4--,it is characteristic of most crystals that they break or cleave along certain directions so as to leave plane or nearly plane surfaces1 and the luster of the cleaved surface measures the perfection of the cleavage property4 ,it is important always to note how many such directions of cleavage are present1 and1 roughly at least1 at what angles they intersect--whether they are perpendicular to each other or inclined at some other angle4 ,further1 it should be noted whether a given cleavage is perfect1 that is1 easy1 which will be indicated by the thinness of the plates which can be secured4 ,an extremely perfect cleavage is possessed by the mineral mica1 whose plates are thinner than the thinnest paper4 ,in the case of imperfect or interrupted cleavage1 the fracture surfaces are not plane throughout1 but interrupted1 the surface 8jumping0 from one plane to a neighboring parallel one4 ,it is especially important to note whether1 in the case of several cleavages possessed by a crystal1 all have the same degree of perfection1 or whether they exhibit differences4 ,fracture4--,in minerals with poorly developed cleavage1 the fracture surface is described as fracture4 ,fracture is thus perfect in proportion as cleavage is imperfect4 ,the fracture is described as conchoidal when it shows waving spherical surfaces like broken glass4 ,for fine aggregates the fracture is described as even1 uneven1 earthy1 etc41 names which are generally intelligible4 ,luster4--,this term is applied especially to the manner in which light is reflected from mineral surfaces4 ,the most important distinction is made between those minerals which have a metallic luster and those which have not1 the former being always opaque4 ,other characteristic lusters are adamantine 7like oiled glass71 vitreous 7glassy71 resinous1 waxy1 etc4 ,color4--,for minerals which possess metallic luster the color is always practically the same1 and hence it becomes a valuable diagnostic property4 ,of minerals which have nonmetallic luster1 the color may be always the same and hence characteristic1 but in the case of many minerals it ranges between wide limits and sometimes runs almost the entire gamut of hues1 yet without appreciable changes in the chemical composition of the mineral4 ,streak4--,this term is applied to the color of the mineral powder1 and is usually fairly constant1 even when the surface color of different specimens may vary within wide limits4 ,in the case of fairly soft minerals the streak is best examined by making a mark on a piece of unglazed porcelain 7streak stone74 ,transparency 7diaphaneity74--,the terms 8transparent01 8translucent01 8subtranslucent01 and 8opaque0 are used to describe decreasing grades of permeability by light rays4 ,through transparent bodies print may be read1 while translucent bodies allow the light to be transmitted in considerable quantity through them1 though without rendering the image of objects4 ,tenacity4--,this comprehensive term includes such properties as brittleness1 flexibility1 elasticity1 malleability1 etc4 ,hardness4--,quite erroneous notions are held concerning the meaning of this very common word1 which properly implies a resistance offered to abrasion4 ,it is one of the most valuable properties for the quick determination of minerals1 since minerals range from diamond upon the one hand--the hardest of substances--to talc and graphite1 which are so soft as to be deeply scratched by the thumb nail4 ,for practical purposes it is sufficient to make use of a rough scale of hardness made up from common or well-known minerals4 ,if we exclude the gem minerals1 this scale need include but seven numbers1 which are3 talc1 #a2 gypsum1 #b2 calcite1 #c2 fluor spar1 #d2 apatite1 #e2 feldspar1 #f2 and quartz1 #g4 ,a given mineral is softer than a mineral in the scale when it can be visibly scratched by a scale mineral1 but will not leave a scratch when the conditions are reversed4 ,if each will scratch the other with equal readiness1 the two minerals have the same hardness4 ,since it may often be desirable to test mineral hardness when no scale is at hand1 the following substitutes may be made use of3 #a1 greasy feel and easily scratched by the thumb nail2 #b1 takes a scratch from the thumb nail1 but much less readily2 #c1 scratched by a copper coin and very easily by a pocket knife2 #d1 scratched without difficulty by a knife2 #e1 scratched with difficulty by a knife1 but easily by window glass2 #f1 scratched by window glass2 #g1 scratches window glass with readiness1 but a grain of sand may be substituted to represent quartz in the scale4 ,magnetism4--,though nearly all minerals which contain important quantities of the elements iron1 cobalt1 or nickel may be attracted to a strong electromagnet1 there are but two common minerals1 and these of widely different appearance1 whose powder is lifted by a common magnet4 ,others are1 however1 lifted after strong heating in the air 7ignition71 and this is a valuable test4 ,specific gravity4--,rough tests of relative weight1 or specific gravity1 may be made by lifting fair-sized specimens in the hand4 ,better determinations require the use of a spring balance4 ,treatment with acid4--,the carbonate minerals react with warm and dilute mineral acid so as to give a boiling effect 7effervescence71 since carbonic acid gas escapes into the air in the process4 ,,properties ,,of ,,the ,,common ,,minerals ,the more important common minerals fall into two classes according as they have large economic importance as ores1 or enter in an important way into the composition of rocks4 ,i4 ,the ,minerals of ,economic ,importance ,hematite4--,the sesquioxide of iron1 ,fe#b,o#c1 and by far the most important ore of iron4 ,rarely in good crystals1 but sometimes in thin opaque scales bearing some resemblance to mica and known as micaceous or specular iron ore4 ,at other times in nodules built up from radial needles 7needle ore72 in hard masses mixed with fine quartz grains 7hard hematite72 or in soft reddish brown earth 7soft hematite74 ,color1 black to cherry red4 ,the powdered mineral always cherry red or reddish brown1 and easily lifted by the magnet after ignition4 ,hardness #e4e-f4e2 specific gravity #e4 ,magnetite4--,the magnetic oxide of iron1 ,fe#c,o#d1 often in crystals like ,fig4 #dhf1 #a-b4 ,black and opaque with a metallic luster4 ,streak black4 ,lifted by a magnet and sometimes itself capable of lifting filings of soft iron 7lodestone74 ,hardness #e4e-f4e4 ,specific gravity #e4 ,limonite4--,the most abundant and most valuable of the hydrated iron ores1 #b ,fe#b,o#c4 #c ,h#b,o4 ,chemical composition the same as iron rust1 with which in the earthy form it is identical4 ,never in crystals1 but often in mammillary or rounded pendant forms resembling icicles1 or sometimes clusters of grapes4 ,its yellow 7rust7 streak is its best diagnostic property4 ,ignited it gives off water and becomes magnetic4 ,the streak and its notably lower specific gravity distinguish it from certain forms of hematite which it outwardly resembles4 ,hardness #e-e4e4 ,specific gravity #c4f-d4 ,pyrite1 iron pyrites1 or 8fool's gold40--,the sulphide of iron1 ,fe,s#b4 ,the most widely distributed sulphide mineral and now a chief source of the great chemical reagent1 sulphuric acid or vitriol4 ,often1 but not always1 in crystals 7,fig4 #dhf1 #c-e7 which have peculiar stri upon their faces4 ,at other times the mineral is found massive or in radiated needles4 ,bright metallic luster with the color of new brass1 though often tarnished or altered upon the surface to limonite4 ,hard and brittle1 and so distinguished from gold1 which is soft and malleable and of the color of the paler old brass 7which contained a larger percentage of zinc74 ,gold is1 further1 about four times as heavy as pyrite4 ,hardness #f-f4e4 ,specific gravity #e4 ,chalcopyrite1 copper pyrites4--,a mixed sulphide of copper and iron4 ,if in crystals1 like ,fig4 #dhf1 #f2 otherwise massive or compact4 ,luster metallic4 ,color orange-yellow1 often with local blue and green iridescence like a pigeon's throat4 ,distinguished from pyrite by the deeper color and lower hardness1 and from gold1 particularly1 by its brittleness and lower specific gravity4 ,hardness #c4e-d4 ,specific gravity #d4 ,galenite1 galena4--,sulphide of lead1 ,pb,s4 ,the chief ore of lead1 and1 from admixture of a silver mineral1 of silver as well4 ,usually found in crystals 7,fig4 #dhf1 #g74 ,always cleaves into blocks bounded by six very perfect rectangular faces which1 when freshly broken1 show a bright silvery luster and quickly tarnish to a peculiarly 8leaden0 surface4 ,very heavy4 ,color and streak lead-gray4 ,hardness #b4e4 ,specific gravity #g4e4 ,sphalerite1 zinc blende4--,sulphide of zinc1 ,zn,s1 usually with considerable admixture of sulphide of iron4 ,the great ore of zinc4 ,not infrequently in crystals 7,fig4 #dhf1 #h-i71 but more often in cleavable crystalline aggregates4 ,the cleavage in fine aggregates is sometimes difficult to make out1 but in coarse-grained masses it is seen to be equally and highly perfect in six different directions1 so that a symmetrical twelve-faced form may sometimes be broken out 7dodecahedron74 ,luster like that of rosin 7rosin jack71 though when with large iron admixture the color may approach black 7black jack74 ,the lighter colored varieties are translucent4 ,hardness #c4e-d4 ,specific gravity #d4 ,malachite4--,hydrated 7basic7 copper carbonate4 ,the green copper ore and the common surface alteration product of other copper minerals4 ,usually has a microscopic structure made up of fine needle-like crystals1 but generally massive in various imitative shapes not unlike those of the iron ores4 ,sometimes earthy4 ,its color is bright green1 and it is usually found in association with other characteristic copper ores1 such as chalcopyrite and azurite4 ,when relatively pure and in large masses1 it is a beautiful ornamental stone4 ,effervesces with acid4 ,hardness #c4e-d4 ,specific gravity #d4 ,illustration3 ,,fig4 #dhf4--;,forms of ,crystals3 #a-b1 magnetite2 #c-e1 pyrite2 #f1 chalcopyrite2 #g1 galenite2 #h-i1 sphalerite2 #aj-ac1 calcite4 ,azurite4--,hydrated 7basic7 copper carbonate1 less hydrated than malachite1 and known as the blue carbonate of copper4 ,generally in very minute and quite complex crystals1 but also in imitative shapes similar to those of malachite1 and at other times earthy4 ,slightly lighter in weight than malachite1 from which it is easily distinguished1 as from most other minerals1 by its bright azure blue color and its somewhat lighter blue streak4 ,effervesces with nitric acid4 ,hardness #c4e-d4 ,specific gravity #c4g-c4h4 ,calcite4--,calcium carbonate1 ,ca,c,o#c4 ,almost always in crystals 7,fig4 #dhf1 #aj-ac71 or in confused crystal aggregates1 though rarely fibrous or dull and earthy4 ,some of the forms of the crystals are described as 8dog-tooth spar01 others as 8nail-head spar01 while still others are modified hexagonal prisms4 ,there is a beautifully perfect cleavage of the mineral along three directions which make angles of about #aje with each other1 so that under the hammer the substance breaks into blocks which are shaped like the crystal of ,fig4 #dhf1 #aj4 ,usually white or gray1 but occasionally faintly tinted4 ,streak white4 ,effervesces with cold and dilute mineral acids4 ,an associate of many ores and the chief mineral of limestone4 ,a similar mineral--dolomite--contains in addition magnesium carbonate1 has simpler crystals 7like the drawing of ,fig4 #dhf1 #aj1 but often with rounded faces71 and effervesces only when the acid is warmed4 ,hardness #c4 ,specific gravity #b4g4 ,gypsum4--,hydrated calcium sulphate1 ,ca,s,o#d4b ,h#b,o1 and the source of plaster of ,paris4 ,often in simple crystals 7,fig4 #dhg1 #a7 or else 8swallow tail01 like ,fig4 #dhg1 #b2 in which case the mineral is generally either transparent or translucent and is described as selenite4 ,such crystals show a cleavage approaching in perfection that of the micas1 but1 unlike the mica lamin1 those produced by cleavage in gypsum though flexible are not elastic4 ,there are also fibrous forms of gypsum 7satin spar71 a fine-grained form 7alabaster71 and the impure earthy form 7rock gypsum74 ,very soft1 light in weight1 and difficultly fusible4 ,color usually white1 gray1 or pale yellow4 ,hardness #b4 ,specific gravity #b4c4 ,copper glance4--,a sulphide of copper1 ,cu#b,s4 ,not usually well crystallized1 but generally massive and associated or variously admixed with other copper ores such as chalcopyrite1 malachite1 etc4 ,fracture conchoidal1 luster metallic1 color and streak blackish lead-gray1 though often tarnished blue or green from surface alterations to the copper carbonates4 ,softer and heavier than chalcopyrite4 ,blowpipe or chemical tests are necessary for its identification4 ,hardness #b4e-c4 ,specific gravity #e4e-e4h4 ,cerussite4--,the white or carbonate lead ore1 ,pb,c,o#c1 and an important ore of silver as well4 ,often in crystals of considerable complexity1 though ,fig4 #dhg1 #c-d1 shows some common shapes4 ,often granular1 massive1 or earthy 7gray carbonate ore74 ,very brittle and with conchoidal fracture4 ,the luster is adamantine or like that of oiled glass4 ,color generally white or gray4 ,very heavy1 the heaviest of light colored and nonmetallic minerals4 ,dissolves in nitric acid with effervescence4 ,hardness #c-c4e4 ,specific gravity #f4e4 ,siderite4--,the carbonate or 8spathic0 ore of iron1 ,fe,c,o#c4 ,either in crystals resembling in form ,fig4 #dhf1 #aj1 but with rounded faces1 or cleavable massive to finely granular and earthy4 ,the crystalline varieties cleave easily into smaller blocks of the same form as those of calcite4 ,color usually gray or brown and streak white4 ,on strongly igniting1 the white powder becomes black and magnetic4 ,lighter in both color and weight than the other iron ores1 and unlike them siderite effervesces with acid4 ,distinguished from calcite by its higher specific gravity and its change upon being ignited4 ,hardness #c4e-d4 ,specific gravity #c4i4 ,smithsonite4--,carbonate of zinc1 ,zn,c,o#c1 and an important ore of that metal4 ,seldom found in crystals except as a replacement of calcite crystals1 in which case it shows the forms characteristic of the latter mineral4 ,usually kidney-shaped1 stalactitic1 or else in incrustations upon other minerals4 ,sometimes granular or earthy4 ,brittle4 ,luster vitreous1 color white or greenish gray1 though often stained yellow with iron rust4 ,streak white except when the mineral is stained with iron4 ,effervesces with warm acid4 ,hardness #e4 ,specific gravity #d4d4 ,pyrolusite4--,black oxide of manganese1 ,mn,o#b1 though generally impure from admixture with other manganese oxides4 ,usually in intricate aggregates which may be columnar1 fibrous1 mammillary1 earthy1 etc4 ,opaque1 with color and streak both black4 ,soft and easily soils the fingers4 ,with hydrochloric acid gives off the choking fumes of chlorine4 ,hardness #b-b4e4 ,specific gravity #d4h4 ,,ii4 ,the ,minerals important as ,rock ,makers ,these minerals are in most cases complex silicates of one or more of a certain number of metals such as aluminium1 calcium1 magnesium1 iron1 sodium1 potassium1 or hydroxyl 7,,oh74 ,for their identification an examination of the physical properties is usually sufficient1 whereas of the typical ore minerals already considered1 additional chemical tests may be necessary4 ,feldspars4--,a group of similar alumino-silicates of potassium1 sodium1 and calcium4 ,the most important of all rock-making minerals4 ,although with wide variation in chemical composition1 the feldspars are yet broadly divided into two classes2 the one striated1 and the other an unstriated potash or orthoclase variety4 ,the pocket lens is usually necessary in order to make out the striations upon the crystal or cleavage surfaces4 ,when formed in veins1 feldspar appears in crystals 7,fig4 #dhg1 #e-f71 but as a rock constituent the mutual interference of crystals prevents the development of bounding faces4 ,two cleavage directions1 nearly or quite perpendicular to each other1 are notably different in their perfection4 ,hard enough to scratch glass1 but easily scratched by sand4 ,color pink 7usually orthoclase or microline71 white 7often albite7 to gray4 ,sometimes with beautiful 8pigeon's throat0 effect of iridescence 7labradorite74 ,low specific gravity4 ,hardness #f4 ,specific gravity #b4e-b4h4 ,illustration3 ,,fig4 #dhg4--;,forms of ,crystals3 #a-b1 gypsum2 #c-d1 cerussite2 #e-f1 feldspar2 #g1 quartz2 #h1 pyroxene 7cross section72 #i1 hornblende 7cross section72 #aj1 garnet2 #aa1 nephelite2 #ab-ad1 staurolite2 #ae-af1 tourmaline 7cross sections72 #ag1 olivine4 ,quartz4--,oxide of silicon or silica1 ,si,o#b4 ,both an important vein mineral associated with the ores and a rock maker4 ,in the former case particularly1 often in crystals of notably simple forms 7,fig4 #dhg1 #g74 ,few minerals which are not gems are so hard4 ,remarkable freedom from cleavage so that the mineral breaks much like window glass--conchoidal fracture4 ,wide range in both transparency and color4 ,transparent and colorless crystalline variety 7rock crystal71 brown translucent 7smoky quartz71 turbid white 7milky quartz71 and various colored varieties 7carnelian1 jasper1 jet1 etc474 ,insoluble in acids and infusible4 ,hardness #g4 ,specific gravity #b4f4 ,micas4--,like the feldspars a group of complex silicates1 but here chiefly of potassium1 magnesium1 iron1 and hydroxyl4 ,abundant as rock makers1 the micas are all characterized by the thinnest and toughest of elastic cleavage plates1 such as are generally known as isinglass4 ,when a needle is driven sharply through a thin scale of mica1 a six-rayed puncture star forms about the needle point4 ,the darker common variety of mica is rich in iron and magnesium and is called biotite1 and the lighter colored alkaline variety1 muscovite4 ,hardness #b4e-c4a4 ,specific gravity #b4g-c4a4 ,chlorite4--,generally an intricate mixture of more or less similar microscopic crystals having varying and rather complex chemical compositions and related to the micas1 but all characterized by a peculiar leaf green color4 ,these minerals are a common product of hydration weathering in rocks which are rich in magnesium and iron--especially those that contain biotite1 pyroxene1 or hornblende 7see below74 ,hardness #a-b4e4 ,specific gravity #b4e-c4 ,pyroxenes4--,an important group of related rock-making minerals all of which are silicates of the bases magnesium1 calcium1 aluminium1 iron1 and manganese4 ,quite generally developed either in columnar or needle-like crystals which are uniformly shaped in cross section like ,fig4 #dhg1 #h4 ,two rather imperfect cleavages are directed parallel to the longer axis of the crystal and nearly at right angles to each other4 ,the colors of all but the lime varieties are dark and generally green1 dark brown1 bronze1 or black4 ,the lime varieties are white1 gray1 or pale green4 ,a dark colored and common iron variety is known as augite4 ,streak generally either white or lightly tinted4 ,hardness #e-f4 ,specific gravity #c4b-c4f4 ,amphiboles4--,a group of minerals of the same chemical composition as the pyroxenes1 with which also in most physical properties they agree4 ,the principal distinction is found in the shape of the cross section and in the cleavage 7,fig4 #dhg1 #i74 ,whereas the cross sections of pyroxenes are generally eight sided1 those of the amphiboles have six sides1 and whereas the cleavage directions of pyroxenes are nearly at right angles to each other 7#hg71 the similar but much more perfect cleavage directions of the amphiboles are inclined at an obtuse angle 7#abd74 ,owing to the obliquity of the amphibole cleavage1 fractured surfaces of the mineral appear splintery1 which is not in the same measure true of the pyroxenes4 ,a fibrous variety of amphibole1 and occasionally other varieties of the mineral1 is a not uncommon product of weathering of pyroxenes4 ,other physical properties of the amphiboles are in the main almost identical with those of the pyroxenes4 ,garnet4--,complex alumino-silicates or ferro-silicates of calcium1 magnesium1 iron1 or manganese1 or several of these combined4 ,nearly always in crystals1 and usually found in mica schist 7see below74 ,the crystals usually have twelve similar faces1 each a lozenge 7dodecahedron71 or else twenty-four similar faces1 or the two forms combined 7,fig4 #dhg1 #aj74 ,brittle4 ,from any but the gem minerals garnet is easily distinguished by its hardness1 which in different varieties ranges from somewhat below to somewhat above that of quartz4 ,the luster is vitreous1 and the color runs the gamut of reds1 browns1 and greens1 but with the common hue dark red to black4 ,streak white4 ,hardness #f4e-g4e4 ,specific gravity #c4a-d4c4 ,nephelite 7nephelene74--,an alumino-silicate of sodium and potassium4 ,in certain special provinces this mineral is developed in abundance as an essential constituent of igneous rocks1 but elsewhere practically unknown4 ,the rare crystals are hexagonal prisms 7,fig4 #dhg1 #aa71 but the mineral is most easily determined by its general resemblance to feldspar1 but with the differences of cleavage1 luster1 and reaction with acid4 ,whereas the feldspars have two cleavages1 either nearly or quite perpendicular to each other and of different degrees of perfection1 nephelite has three equal cleavages inclined #fj and #abj to each other and of less perfection than either feldspar cleavage4 ,the luster of nephelite is perhaps the best clew to its identity1 since this is greasy and simulated by but few minerals4 ,the fine powder of the mineral treated for some time with strong hydrochloric acid forms a perfect jelly of silicic acid1 whereas the feldspars do not4 ,though itself gray or white and unobtrusive1 nephelite is usually associated with brightly colored minerals1 which are often the first clew to its presence in a rock4 ,hardness #e4e-f4 ,specific gravity #b4e-b4f4 ,talc 7soapstone74--,a silicate of magnesium and hydroxyl which is an important alteration product through weathering of certain pyroxene rocks especially4 ,usually a foliated mass1 this product is occasionally fibrous or even granular4 ,talc is one of the softest of minerals1 having a greasy feel and being easily scratched with the thumb nail4 ,the luster of the foliated varieties is apt to be pearly1 and the color apple-green to white1 though sometimes stained brown from oxide of iron4 ,the streak of the mineral is white except when stained by iron4 ,although the rocks which are composed mainly of talc 7soapstone7 are exceedingly soft1 they are very tough and remarkably resistant4 ,hardness #a-a4e4 ,specific gravity #b4g-b4h4 ,serpentine4--,like talc1 serpentine is a silicate of magnesium and hydroxyl1 and an important product of the breaking down of magnesium minerals in the process of weathering4 ,the mineral is usually found as a fine web of microscopic needle-like fibers1 and is best roughly diagnosed by its color and its associated minerals4 ,like talc it is usually developed within those igneous rocks from which feldspar is lacking1 but where either pyroxene or olivine is found in abundance or was previous to alteration4 ,the characteristic color of serpentine is leek-green4 ,the rock largely composed of serpentine is called by the same name1 and being exceedingly tough and unchanging is1 in spite of its softness1 a valuable building and ornamental stone4 ,a red magnesium garnet is apt to be associated with such serpentine masses4 ,hardness #b4e-d1 because of impurities4 ,specific gravity #b4e-b4f4 ,staurolite4--,a silicate of aluminium1 iron1 and hydroxyl4 ,found in metamorphic rocks usually in association with garnet4 ,always in crystals bounded by simple forms generally crossed1 as shown in ,fig4 #dhg1 #ab-ad4 ,the color is dark reddish brown1 and the streak is colorless to grayish4 ,the hardness is exceptional and higher than that of quartz4 ,hardness #g-g4e4 ,specific gravity #c4f-c4g4 ,tourmaline4--,an exceptionally complex silicate of boron and aluminium as well as iron1 magnesium1 and the alkalies4 ,found in metamorphic rocks and always crystallized4 ,the crystals are columns or needles whose cross section is the best guide to their identity1 since this is a modified triangle unlike that of any other mineral 7,fig4 #dhg1 #ae-af74 ,additional diagnostic properties are the characteristic striations which run lengthwise of the crystals upon prism faces1 and the lack of any cleavage 7difference from hornblende74 ,the hardness is also a valuable property1 since this is greater than that of quartz4 ,the mineral is brittle and the fracture subconchoidal4 ,the range in color is as great as1 or greater than1 that of garnet1 though the common forms are jet black4 ,streak uncolored4 ,hardness #g-g4e4 ,specific gravity #c-c4b4 ,olivine4--,a silicate of magnesium and iron and a rock-making mineral found only in those igneous rocks which have little or no feldspar4 ,it easily suffers alteration by weathering and passes into serpentine1 and in fact is seldom found except when at least partially altered to the fibrous webs of that mineral4 ,the form of the unaltered crystals within the rocks is shown in ,fig4 #dhg1 #ag1 and1 cut in sections1 the mineral appears in more or less elongated hexagons4 ,the hardness of the unaltered mineral is about that of quartz4 ,it has rather imperfect cleavages in two rectangular directions1 and is usually translucent1 with a vitreous luster and a color which is olive-green when not stained brown by oxide of iron4 ,streak uncolored4 ,hardness #f4e-g4 ,specific gravity #c4b-c4c4 ,,appendix ,b ,,short ,,descriptions ,,of ,,some ,,common ,,rocks ,in ,chapter ,,iv the classification and the structure of rocks have been briefly discussed4 ,below are added brief descriptions of the more important common rocks4 ,for rocks as for minerals it is1 however1 essential that a collection of well-chosen specimens be studied for purposes of comparison4 ,a small pocket lens is a valuable aid in making out the component minerals and the textures of the finer grained rocks4 #a4 ,intrusive ,rocks ,granite4--,of granitic texture1 though sometimes porphyritic as well4 ,the most abundant mineral constituent is a pink or white feldspar1 usually without visible striations1 with which there is usually in subordinate quantity a white striated feldspar4 ,next in importance to the feldspar is quartz1 which because of its lack of cleavage shows a peculiar gray surface resembling wet sugar4 ,in addition to feldspar and quartz there is generally1 though not universally1 a dark colored mineral1 either mica or hornblende4 ,the mica is usually biotite1 though often associated with muscovite4 ,syenite4--,like granite1 but without quartz1 with more striated feldspar1 and generally also the rock has a darker average tint4 ,while biotite is the commonest dark colored constituent of granite1 hornblende is more apt to take its place in syenite4 ,less common than granite1 to which it is closely related in origin and in composition4 ,gabbro4--,a dark colored rock of granitic texture composed of striated feldspar with broad cleavage surfaces and usually an abundance of pyroxene4 ,in contrast to the feldspars of granite1 those of gabbroes are often dull and colored grayish yellow or greenish4 ,the pyroxene is often in part changed to fibrous amphibole4 ,magnetite may be an abundant accessory mineral4 ,diabase4--,in color dark like gabbro1 and of similar constitution4 ,in diabase1 however1 the feldspar crystals1 instead of being broad and of irregularly interrupted outline1 are relatively long 78lath-shaped071 and the pyroxene acts as a filler of the residual space between them4 ,peridotite4--,a heavy and dark colored rock of granitic texture which is nearly or quite devoid of feldspar but contains olivine4 ,when altered1 as it generally is1 it is largely a mass of serpentine1 talc1 and chlorite1 surrounding cores1 it may be1 of still unaltered pyroxene and olivine4 ,magnetite is an abundant constituent1 and a red garnet is apt to be present4 #b4 ,extrusive ,rocks ,obsidian4--,a rock glass rich in silica4 ,it is usually black and breaks with a perfect conchoidal fracture4 ,it often passes over through insensible gradations into pumice1 which differs only in its vesicular structure4 ,as regards chemical composition1 obsidian and pumice are not notably different from rhyolite 7below74 ,rhyolite4--,a light colored rock of porphyritic texture1 often also with fluxion or spherulitic textures1 or both combined4 ,the porphyritic appearance is given the rock by large crystals of a glassy1 unstriated feldspar and crystals of quartz4 ,rhyolite is a very siliceous lava containing rather more silica than granite1 to which of the intrusive rocks it is most closely related1 and from which it differs in its texture and in the manner of its occurrence in nature4 ,whereas granite is found in great batholites1 laccolites1 and bysmalites1 and consolidated in most cases beneath the earth's surface1 rhyolite generally occurs in sheets1 flows1 or dikes1 and consolidated either above or in fissures near to the surface4 ,trachyte4--,similar to rhyolite1 but usually with a peculiar gray aspect from the greater abundance of feldspar crystals4 ,the rock is less siliceous than rhyolite1 contains no quartz crystals1 and approaches a feldspar in its average composition4 ,andesite4--,similar to rhyolite in appearance and in origin1 but more basic and correspondingly dark in color4 ,the porphyritic crystals are of lath-shaped1 striated feldspar1 with which are associated crystals of either biotite or hornblende or both4 ,a fluxion texture is particularly characteristic of this type of extrusive rock4 ,basalt4--,a dark colored or black basic rock of porphyritic texture which differs but little from diabase4 ,it may show under the lens fine lath-shaped crystals of striated feldspar associated with crystals of augite1 but more frequently the rock is dense and without visible mineral constituents4 ,it is particularly likely to occur divided up into columns six inches to a foot in diameter and known as basaltic columns4 ,especially fine examples are known from the ,giant's ,causeway and other localities in the western ,british ,isles4 #c4 ,sedimentary ,rocks of ,mechanical ,origin ,conglomerate 78pudding stone074--,a rock made up from pebbles which are cemented together with sand and finer materials4 ,the pebbles are usually worn by work of the waves upon a shore1 and may vary in size from a pea to large bowlders4 ,they may consist of almost any hard mineral or rock1 though the sand about them is largely quartz4 ,sandstone4--,a rock composed of sand cemented together either by calcareous1 siliceous1 or ferruginous materials4 ,sandstones are described as friable when their surface grains are easily rubbed off1 or as compact when they are more firmly cemented4 ,sandstones are often distinctly banded and are sometimes variously stained with oxide of iron4 ,those sandstones which have been formed upon a seacoast are known as marine sandstones1 while those derived from accumulations collected by the wind in deserts are distinguished as continental deposits4 ,sandstones form much thicker formations than conglomerates1 the latter usually constituting a basal layer only of the sandstone formation 7basal conglomerate74 ,shale4--,a consolidated mud stone which is probably the most abundant rock formation4 ,in large part clay admixed in varying proportions with extremely fine sandy grains4 #d4 ,sedimentary ,rocks of ,chemical ,precipitation ,calcareous tufa 7travertine74--,not to be confused with tuff1 which is a fragmental extrusive or volcanic rock4 ,calcareous tufa is formed when waters which contain carbonic acid gas and lime carbonate in solution1 give off the gas and with it the power to hold the lime in solution4 ,such a liberation of the gas may occur when the stream is dashed into spray above a cascade1 and the lime is then deposited about the site of the falls4 ,travertine is generally porous and formed of more or less concentric layers or incrustations4 ,a remarkable illustration is furnished by the travertine deposits of ,tivoli and other localities near ,rome1 since here the material supplies a valuable building stone4 ,olitic limestone 7oolite74--,this rock is made up of spherical nodules and so has the appearance of fish roe4 ,broken apart1 each grain reveals in its center a core of siliceous sand about which carbonate of lime has been deposited in concentric layers4 ,it is thought that waters charged with carbonate of lime1 in issuing from a river near a sea beach1 coat the sand grains of the latter with successive thin films of lime carbonate due to the rhythmic ebb and flow of the tides1 evaporation of the adhering water taking place when the sands are exposed at low tide4 #e4 ,sedimentary ,rocks of ,organic ,origin ,limestone4--,a generally white or gray rock composed of carbonate of lime with varying proportions of clay1 silica1 and other impurities4 ,the lime carbonate is usually derived from the hard parts of marine organisms1 and the argillaceous and siliceous impurities from the finer land-derived sediments which descend with them to the bottom4 ,dolomite 7dolomitic or magnesium limestone74--,differs from limestone in containing varying proportions of the mineral dolomite 7ante1 p4 #dee71 which is made up of equal parts of calcium and magnesium carbonates4 ,difficult to distinguish from limestone unless a chemical test is made for magnesium1 though it may be said in general that dolomite is less soluble in cold mineral acids4 ,peat4--,an accumulation of decomposed vegetable matter within small lakes and in lagoons separated from larger ones 7ante1 p4 #dbi74 ,peat represents the first stage in the formation of coal from vegetable matter1 and differs from the coals by its larger proportion of contained water4 ,because of this water its fuel value is correspondingly small4 ,it is usually dark brown or black and reveals something of the structure of the plants out of which it was formed4 #f4 ,metamorphic ,rocks ,gneiss4--,a generally more or less banded 7gneissic7 metamorphic rock with a mineral constitution similar to granite1 and often developed by metamorphic processes from that rock4 ,it may at other times1 by processes not essentially different1 be derived from sedimentary formations4 ,it usually contains as important constituents unstriated feldspar and quartz1 but in addition it may include a striated feldspar1 biotite1 muscovite1 or hornblende1 or several of these combined4 ,in proportion as mica or hornblende is abundant1 it has a marked banded texture1 but it differs from mica schist 7see below7 not only in the presence of its feldspar1 but in the smaller proportion of mica4 ,biotite gneiss1 hornblende gneiss1 etc41 are terms used to designate varieties in which one or the other of the dark colored constituents predominate4 ,mica schist4--,a metamorphic rock without feldspar and mainly composed of quartz and light colored mica 7muscovite74 ,the abundant mica lends to the rock its characteristic schistose texture1 which differs from the usual gneissic texture4 ,in some cases the mica is wrapped about the grains of quartz1 but at other times it forms a series of almost continuous membranes separating layers of quartz4 ,sericite schist4--,a variety of schist which is characterized by an abundance of a peculiar silvery mica rich in the element group hydroxyl4 ,the mica scales are often microscopic and wrought into an intricate web with the quartz constituent4 ,talc schist4--,a schist made up largely of talc1 but with varying proportions of quartz1 magnetite1 etc4 ,from the abundance of the talc it is usually pale green or white4 ,chlorite schist4--,a greenish1 fine-grained metamorphic rock in which chlorite is the principal mineral1 but in which magnetite is a quite characteristic accessory constituent4 ,staurolitic garnetiferous mica schist4--,a mica schist in which garnet and staurolite are so abundant as to be essential constituents4 ,clay slate4--,a metamorphosed mud stone or shale4 ,in the process of metamorphism the rock has been hardened1 given a slaty cleavage1 and innumerable minute scales of mica have developed to produce a silky luster upon the cleavage faces4 ,the color may be gray1 green1 purple1 or black4 ,quartzite4--,a metamorphosed sandstone in which the sand grains have become enlarged by accretion of silica4 ,whereas a sandstone fractures about its constituent grains1 a break in quartzite is continued through the grains and the cement alike4 ,in contrast to sandstones1 the quartzites derived from them are usually lighter in color and often nearly white4 ,marble 7crystalline limestone74--,the result of metamorphism upon limestones4 ,usually white in color but sometimes gray1 blue gray1 or yellow1 and sometimes variously broken or brecciated and stained with iron oxide4 ,effervesces with cold dilute acid4 ,coals4--,under the head of peat the first stage in the formation of coals from vegetable matter has been briefly described4 ,lignite1 or brown coal1 represents a further stage and one in which the vegetable structure is still recognizable4 ,it is usually brownish black or black in color and contains a considerable proportion of water4 ,with increased pressure or dynamic metamorphism1 further percentages of the volatile constituents are eliminated1 and when from seventy-five to ninety per cent of carbon remains1 the material burns with a yellow flame and is known as bituminous coal4 ,this is the great fuel for the production of steam4 ,a continuation of the metamorphic processes carries off a further proportion of the volatile matter and leaves a dense1 hard1 black substance with sometimes as much as ninety-five per cent of carbon4 ,this is the so-called 8hard coal0 or anthracite generally used for fuel in our houses1 for which purpose it is so well adapted because it burns with a production of much heat and almost without smoke4 ,,appendix ,c ,,the ,,preparation ,,of ,,topographical ,,maps ,topographical maps a library of physiography4--,for the satisfactory working out in detail of the geology of any region of complex structure1 an accurate topographical map is prerequisite4 ,this is so much the more true because nearly all complexly folded or faulted rock masses are to be found in mountainous1 or at least in hilly regions4 ,the making of the topographical map must1 therefore1 precede that of the geological map1 and in modern usage the latter is a topographical and a geological map combined in one4 ,within certain narrow limits1 predictions concerning the geological history of a province may often be made by an expert geologist from examination of an accurate topographical map4 ,just as in forecasting the weather upon the basis of the usual weather maps1 such predictions can sometimes be made with entire confidence in their accuracy1 while at other times a guess only may be hazarded4 ,the great value of the modern topographical map is becoming1 however1 universally acknowledged1 and every highly civilized nation has either completed or has in preparation sectional topographical maps of its domain on such a scale as is warranted by its financial condition and its state of development4 ,thus there is now being accumulated a vast library of geographical and to some extent geological information1 of which the student of geology must be prepared to make use4 ,the nature of a contour map4--,more and more the contour map is replacing the earlier and less scientific methods of representing topography on the large scale sectional maps1 and hence this type only need here be considered4 ,in the contour map1 the relief of the land is represented by a series of curving lines1 each the intersection of a particular horizontal plane with the land surface1 and the several planes separated by uniform differences of elevation4 ,this altitude interval is known as the contour interval4 ,its choice is a matter of considerable importance1 for though regions of relatively simple topography may be adequately represented upon a map of large contour interval1 say one hundred feet1 another district may require an interval as short as five feet4 ,a contour map with this interval may be conceived to have been made by flooding the region which it represents and preparing maps of the shore lines for each rise of five feet of the water surface1 and superimposing the several maps thus derived with accurate registration one above the other4 ,wherever the land slopes are steep1 the shore lines of the several maps will be crowded closely together and give the effect of a relatively dark local shade2 where1 upon the other hand1 the surface is relatively flat1 the several shores will be widely spaced and the effect will be to produce a white area upon the map4 ,thus in contour maps dark tones indicate steep gradients and pale tones a flatness of surface4 ,the selection of scale and contour interval4--,with the use of the small scale in the contour map1 the tones of the map will be correspondingly dark1 though the relative differences in tone will remain the same4 ,with the use of a closer contour interval the tones will deepen throughout4 ,the adjustment of scale and contour interval to any given region is a matter requiring experience in topographical mapping1 and in addition a knowledge of the geological significance of topographic features4 ,unfortunately1 the element of expense and the special commercial objects held in view1 conspire to select scales and contour intervals which are often little adapted to the districts surveyed4 ,the method of preparing a topographical map4--,having fixed upon the scale and the contour interval which is to be employed1 the task of the topographical surveyor is next to fix accurately the positions and the elevations of a sufficient number of points to control the map1 and then to hang1 as it were1 upon these points as attachments the design represented by the relief4 ,were the surface of the ground to be represented by a flexible fabric1 the map maker might raise from a flat base a series of stout posts of the heights and in the positions which he has determined1 and upon these supports arrange the slopes of the fabric much as drapery is adjusted4 ,the determination of the exact positions and the elevations of his control stations is1 therefore1 a process coldly precise and formal2 whereas in the shaping of the surfaces his attention should be fixed more upon correctly reproducing the shapes than upon fixing accurately the position of every point4 ,as a matter of fact1 the position of the average point will be most accurately fixed when the shapes of the features are most clearly comprehended4 ,to some extent1 therefore1 the topographer should be familiar with the geological significance of the earth features which he is representing4 ,laboratory exercises in the preparation of topographical maps4--,the principles which underlie the surveyor's method for preparing a topographical map may be learned in the laboratory by the use of models and the simple device shown in plate #bd ,a and ,b4 ,to represent the section of country to be mapped a model in plaster of ,paris is substituted1 and this is placed within a rectangular tank to which locating carriages and altitude gauges are attached that allow the student to fix the position and the elevation of any point upon the surface of the model4 ,,plate #bd4 ,illustration3 ,a4 ,apparatus for exercise in the preparation of topographic maps4 ,illustration3 ,b4 ,the same apparatus in use for testing the contours of a map4 ,illustration3 ,c4 ,modeling apparatus in use4 ,upon each model the student 8locates01 or fixes1 the position of a sufficient number of points for the control of his map1 entering upon an appropriate map base for each position the altitude which was read from the gauges4 ,now with the map always before him he 8sketches in0 the forms of the surface by means of contour lines4 ,for this purpose it is often desirable to fix roughly the direction of the steepest slope at a number of places1 and noting the differences in elevation between control stations1 divide up the distance in accordance with the curves of slope and start the contours at right angles to the slope4 ,afterwards such sections are connected by sketching in with the model always in view for control 7,fig4 #dhh74 ,illustration3 ,,fig4 #dhh4--;,a student's map prepared from a model by the use of the contour apparatus represented in plate #bd ,a4 ,the verification of the map4--,the map prepared1 its accuracy may be tested by a simple method which is denied the topographer who has to do with the actual surface of the ground4 ,the locating carriages and altitude gauges are removed from the tank1 which is next filled with water and leveled by means of guide marks upon the interior4 ,a few drops of milk or of ordinary clothes blueing are added to the water to render it opaque1 and it is then drawn off at the faucet in successive installments1 so that the surface drops by layers corresponding in thickness to the contour interval of the map1 plate #bd ,b4 ,as each layer is withdrawn1 that contour of the map to which the shore line should correspond is carefully examined and corrected4 ,by such corrections the nature of the first errors made is soon appreciated1 and the method of procedure is thus more easily acquired4 ,at the same time the significance of the design of the map is more quickly learned than by a mere examination of the standard government maps4 ,the work above outlined calls for waterproofed models of suitable form and size1 and a series1 each of which sets forth some typical feature or series of features1 has been designed by ,mr4 ,irving ,d4 ,scott4#b ,the preparation of physiographic models4--,the apparatus used to prepare the topographic map is adapted also for preparing a physiographic model from a standard topographical map4 ,for this purpose the method is essentially reversed1 though the tank is replaced to advantage by a light metal frame elevated upon one side so as to permit a free use of the hands in modeling the clay4 ,the material used in preparing the model is artists' modeling clay#c which has a base of beef suet1 and hence does not dry out and crack as does ordinary clay4 ,its form is1 therefore1 retained indefinitely1 and it may be used again and again4 ,most maps must be enlarged in modeling1 and the simplest way is often to photographically or by pantograph enlarge the map to the scale of the model4 ,the map prepared1 it is covered by a thin celluloid plate which has cut upon it a series of crossed lines spaced in inches and larger subdivisions to correspond to those of the locating carriages 7plate #bd ,c74 ,the enlargement of the map is not essential to experienced workers1 and the standard map may be covered in similar manner by a transparent plate with 8checkerboard0 design1 the squares of which bear some simple relation in size to the larger divisions of the locating carriages 7,plate #bd ,c1 rear74 ,the method of preparing the model is comparatively simple4 ,beginning at any point upon the map1 the intersection of a heavy contour line with one of the guide lines of the celluloid 8position plate0 is carefully noted4 ,both the position and the elevation of this point are fixed by the point of the altitude gauge of the modeling frame1 and the clay built up beneath it to that height4 ,with the fingers the clay is now roughly shaped in various directions from this point1 the altitude gauge is advanced by the locating carriage so as to correspond in position to the intersection of the next heavy contour line with the same guide line of the position plate1 and the elevation for this point similarly adjusted upon the model4 ,as before1 the surface of the clay is roughly shaped in advance and upon the sides so as to conform to the indications of the map2 and this process is repeated until the work is finished4 ,corrections for intermediate positions may be carried to any desired degree of refinement which the scale and the accuracy of the map permit4 ,models which are larger than the area of the modeling frame are prepared by making a square foot at a time by the above described process1 and then moving the frame forward and adjusting in a new position by means of the sharp pins in the legs of the apparatus4 ,,reading ,,references ,,william ,h4 ,,hobbs1 ,new ,laboratory ,methods for ,instruction in ,geography1 ,journal of ,geography1 vol4 #g1 #aiji1 pp4 #ig-ajd4 ,also ,scot4 ,geogr4 ,mag41 vol4 #bd1 #aijh1 pp4 #fdc-feb4 ,the ,modeling of ,physiographic ,forms in the ,laboratory1 ibid41 vol4 #h1 #aiaj1 pp4 #bbe-bbh4 ,,appendix ,d ,,laboratory ,,models ,,for ,,study ,,in ,,the ,,interpretation ,,of ,,geological ,,maps ,illustration3 ,,fig4 #dhi4--,models to represent outcrops of rock4 ,the laboratory models which have been described on page #fc1 and are used to represent outcrops in the study of geological maps1 are shown in ,fig4 #dhi4 ,the drum-shaped blocks serve to represent massive rocks which occur in irregularly shaped masses such as batholites and flows4 ,the long1 narrow strips are for intrusive rocks in the form of dikes1 while the larger blocks provided with a swivel joint are used for outcrops of sedimentary rocks1 and after adjustment they give the dip and strike of the exposure4 ,the wing bolts used in their construction should be of bronze1 because of the effect of iron upon the compass4 ,for the same reason tables should not be placed near iron beams or columns4 ,all these blocks can be made by an ordinary carpenter1 and should be available in sufficient numbers to arrange problems like those of ,figs4 #dg1 #dh1 and #dij4 ,with a view to supplying suggestions for other problems of the same general nature1 the three additional field maps of ,fig4 #dia have been introduced4 ,illustration3 ,,fig4 #dij4--,special laboratory table set with a problem in geological mapping which is solved in ,figs4 #dg and #dh4 ,illustration3 ,,fig4 #dia4--,three field maps to be used as suggestions in arranging laboratory tables for problems in the preparation of areal geological maps4 ,the list of questions given below is intended to indicate the nature of some of the problems which the student should be asked to solve in the preparation of each map4 ,the numbers in parentheses refer to pages in this book where further information is given3-- ,,stratigraphical #a4 ,of the formations represented what ones are sedimentary and what igneous 7,chap4 ,,iv1 ,app4 ,b78 #b4 ,which formations1 if any1 are separated by unconformities 7#ea-ec78 #c4 ,what is the order of age of the sedimentary formations 7#fe78 #d4 ,what are the exposed thicknesses of each of these formations 7#dh-di78 #e4 ,do any of these values represent full thickness of the formation1 and if so1 which ones8 #f4 ,what is the age in terms of the sedimentary formations of each of the igneous rock masses 7#fe78 #g4 ,which igneous rocks1 if any1 occur in batholites 7#adc1 #dda78 ,which1 if any1 in dikes 7#adj78 ,,structural #h4 ,what formations1 if any1 have monoclinal dip 7#db78 #i4 ,indicate upon the map by dashed lines the crests of all anticlines and the trough lines of synclines4 #aj4 ,indicate by arrows the direction of pitch of all plunging anticlines and synclines wherever disclosed by changes of dip and strike 7#dc74 #aa4 ,indicate the approximate position of all faults whose position is disclosed 7#eh-fa71 and1 if possible1 state which limb is the one downthrown4 #ab4 ,prepare suitable geological sections4 ,,reading ,,reference ,,william ,h4 ,,hobbs4 ,apparatus for ,instruction in ,geography and ,structural ,geology4 ,,iii4 ,the ,interpretation of ,geologic ,maps4 ,school ,science and ,mathematics1 vol4 #i1 #aiji1 pp4 #fdd-fec4 ,,appendix ,e ,,suggested ,,itineraries ,,for ,,pilgrimages ,,to ,,study ,,earth ,,features ,the chief value of the laboratory studies discussed in the preceding appendices is as a preparation for observations made in the field--the laboratory par excellence of the geologist4 ,the pilgrimages whose itineraries are here suggested have been planned especially for impressing by observation the lessons of this book4 ,such journeys are best interrupted at a relatively small number of localities which1 because already studied in some detail1 are specially adapted to serve as centers for local excursions4 ,these localities will in most cases be the great scenic places to which tourists resort1 or the seats of universities near which specially detailed explorations have been often made4 ,within the ,united ,states a few local geological guides have been published1 and the ,geologic ,folios published by the ,united ,states ,geological ,survey are already available for a number of such centers4 ,for one long geological pilgrimage we are fortunate in having a carefully prepared guide1 namely1 from ,new ,york to the ,yellowstone ,national ,park and back1 with a side trip to the ,grand ,caon of the ,colorado4 ,except for the side trip this route1 in large measure1 corresponds with one here chosen1 and for the return journey especially the student is referred to it for information 7,geological ,guide ,book of the ,rocky ,mountain ,excursion1 edited by ,samuel ,franklin ,emmons4 ,comte ,rendu de la ,congrs ,gologique ,internationale1 #eme ,session1 ,washington1 #ahia1 #ahic1 pp4 #bec-dhg1 map and plates #ac1 figs4 #cb74 ,our journey is begun at ,new ,york ,city1 which is built about the deeply submerged channels of an estuary choked with glacial deposits1 though the channel may be followed as a deep caon across the continental shelf to its margin 7#beb1d pl4 #ag ,b74 ,new ,york ,city is also upon the margin of the glaciated area1 the outer terminal moraine of which is well represented on ,long ,island 7#bih74 ,across the ,hudson in ,new ,jersey is the great ,coastal ,plain which meets the oldland in a well-defined margin 7#aei1 #bdf1 #bdg74 ,a local geological guide of the vicinity of the metropolis has been written by ,gratacap 7,geology of the ,city of ,new ,york1 ,greater ,new ,york4 ,brentanos1 ,new ,york1 #aijd1 pp4 #aai1 pls4 and map74 ,traveling by the ,new ,york ,central ,railway1 we follow up the ,mohawk outlet of the glacial lakes ,iroquois and ,algonquin 7#ccd71 first skirting upon the east the great sills of intrusive basalt known as the ,palisades1 with their markedly columnar jointing and intersections by numerous faults4 ,above ,peekskill we enter the picturesque narrows of the river 7#agd71 cut in the hard crystalline rocks of the ,highlands4 ,entering the ,mohawk ,valley1 we pass ,syracuse with limestone caverns and well-oriented joints widened by solution through the agency of the descending ground water 7#aha1 pl4 #f ,b74 ,a branch line to the southwest reaches the vicinity of ,cayuga ,lake and ,ithaca1 where are well-oriented joints which have controlled the drainage directions1 and there is also a typical strath 7#ee1 #hg1 #dbh74 ,to ,niagara ,falls at least a day should be allotted for the 8gorge ride0 by trolley car1 thus making the complete circuit of the brink of the gorge with interruptions and local studies at all important points 7#ceb-cff1 pl4 #bc ,a74 ,from ,niagara ,falls over the ,michigan ,central ,railway we reach ,detroit on the present outlet of the upper ,great ,lakes as well as of the later ,lake ,algonquin 7#ccd74 ,from this city as a center a trip is made by electric railway to ,ypsilanti and ,ann ,arbor1 across the bottoms of the early glacial lakes from the first ,maumee to ,warren 7#ccj-ccc74 ,the strong ,whittlesey beach is encountered at the little station of ,ridge ,road1 and one of the ,maumee beaches on ,summer ,street in ,ypsilanti4 ,the city of ,ypsilanti is built upon a terrace 7#afe7 of the ,huron ,river1 and another terrace in the same series is crossed by the electric line4 ,in an excursion of a few miles down the river1 passing meanders 7#afd-afe7 and ox-bow lakes 7#afe1 #dae71 is found an interesting case of stream capture near the little village of ,rawsonville 7#age4 ,see ,isaiah ,bowman1 ,jour4 ,geol41 ,vol4 #ab1 #aijd1 pp4 #cbf-ccd74 ,continuing our journey from ,ypsilanti over a high moraine 7#cab71 ,ann ,arbor is reached1 built upon the level plain of outwash with fosses sometimes separating it from the moraine 7#bha1 #cad74 ,upon the campus of the university are great bowlders of jasper conglomerate and jaspilite1 which were transported from the north by the continental glacier 7#cje74 ,across the river from the ,michigan ,central station and behind the little church is a delta formed in one of the glacial lakes ,maumee and here opened in section 7#afh74 ,west of the city is a great valley which was the former course of the ,huron ,river when thus diverted by the continental glacier lying to the eastward of ,ann ,arbor--border drainage 7see ,ann ,arbor folio by the ,u4 ,s4 ,g4 ,s41 and1 further1 ,r4 ,c4 ,allen and ,i4 ,d4 ,scott1 ,an ,aid to ,geological ,field ,studies in the ,vicinity of ,ann ,arbor1 ,george ,wahr1 publisher1 ,ann ,arbor74 ,returning to ,detroit 7,m4 ,c4 ,ry471 the great ,sibley quarries in limestone near ,trenton may be visited4 ,they display perfect jointing1 numerous fossils1 and especially well-glaciated surfaces interrupted by deep troughs and showing stri of several glaciations 7#cjd74 ,from ,detroit the journey is continued by steamer to ,mackinac ,island in the strait connecting ,lakes ,michigan and ,huron1 passing on the way through the peculiar delta of the ,st4 ,clair ,river 7#dca71 and coming in view of the notched headlands1 which are a monument to the post-glacial uplift of the glaciated area 7#bej1 #cda74 ,a day is spent at ,mackinac ,island and ,st4 ,ignace in order to study with some care these uplifted strands of the late glacial lakes 7#cda-cdd74 ,chicago may now be reached either by steamer or by rail1 and in its vicinity we may see the elevated beaches and the ancient outlet of ,lake ,chicago 7#cca-ccb1 #cdg1 pl4 #bb ,a4 ,see ,chicago ,folio1 ,u4 ,s4 ,g4 ,s474 ,by the ,chicago and ,northwestern ,railway the area of recessional moraines and intermediate outwash plains1 and later that of the drumlins1 are crossed in journeying to ,madison1 ,wisconsin4 ,by examination of the maps on pages #cjh and #cag in connection with the larger scale atlas sheets of the ,united ,states ,geological ,survey 7,janesville1 ,evansville1 and ,madison sheets71 this car journey can be made most instructive in gaining familiarity with the characteristic glacial features1 and this study is continued to special advantage in excursions about ,madison as a center 7#caf-cag1 #djg74 ,this is the more true since at numerous localities in the vicinity of ,madison the well-striated glacier pavement is exposed for comparison of the stri as regards direction with the axes of the several types of glacial features4 ,an especially instructive excursion may be made by carriage in a single day to the 8driftless area0 some twelve miles west of the city4 ,before reaching it we cross in alternation a series of recessional terminal moraines 7pl4 #ag ,c7 and outwash plains1 and near ,cross ,plains encounter the partially dissected upland with its arborescent drainage and even sky line 7#bih1 #cjj-cja1 #cab-cac1 pl4 #af ,a and ,b74 ,typical shore formations 7#bcc1 #bda1 #bdb7 are studied to advantage about ,lake ,mendota in a walking trip to and beyond ,picnic ,point1 where are found the best ice ramparts 7#dca-dcd4 ,see ,buckley1 ,trans4 ,wis4 ,acad4 ,sci41 ,vol4 #ac1 pp4 #ada-afb1 pls4 #ah74 ,our journey is now continued over the ,chicago and ,northwestern ,railway to ,devils ,lake near ,baraboo1 where we cross a salient of the driftless area1 within which lies ,devils ,lake1 imprisoned in a former valley of the ,wisconsin ,river1 since diverted to another course as a result of the glacial invasion 7#cab-cac74 ,the valley here is a former narrows in hard quartzite 7#dff71 which towers above the lake in unstable chimneys 7#cjj71 such as the ,devils ,tower1 but such remnants are not found on the other side of the moraine1 being there replaced by rounded rock shoulders4 ,just north of the lake the marginal moraine which blocks the valley is so characteristic as to merit special study 7pl4 #ag ,c74 ,only a few miles northward along the railway from ,devils ,lake is ,ableman1 where1 exposed in a high cliff1 the hard purple quartzite with beautiful ripple marks to reveal its plane of sedimentation 7pl4 #aa ,a7 dips vertically1 and is overlain by horizontally bedded yellow sandstone4 ,the marked angular unconformity which is thus displayed is further made evident by a basal layer of conglomerate 7#dfc7 in the sandstone 7#ea-ec74 ,here also are deposits of loess along the river1 which display their vertical joint surfaces 7#bjg74 ,an excellent geological guide to this interesting district and that of the neighboring 8,dalles0 of the ,wisconsin ,river has been written by ,salisbury and ,atwood 7,the ,geography of the ,region about ,devils ,lake and the ,dalles of the ,wisconsin1 etc41 ,bull4 #e1 ,wis4 ,geol4 and ,nat4 ,hist4 ,surv41 #aijj1 pp4 #aea1 pls4 #ch1 figs4 #dg74 ,if we have taken a conveyance at ,devils ,lake for ,ableman1 we may continue in the same manner to ,kilbourn1 where begin the picturesque ,dalles of the ,wisconsin ,river--here a young gorge cut in sandstone1 because the ,wisconsin was diverted from its old valley to border drainage at the edge of the driftless area 7#cjj1 #cba74 ,the side caons of the river1 through their abrupt zigzags1 reveal the control of their courses by the joint system 7#bbd74 ,in the journey up the rapids by steamer to inspect the ,dalles1 we observe many beautiful examples of cross bedding in the sandstone 7#cg74 ,from ,kilbourn we continue our journey to ,minneapolis over the ,chicago1 ,milwaukee1 and ,st4 ,paul ,railway1 and near ,camp ,douglas are over a peneplain1 out of which rise prominent monadnocks 7#aga74 ,at ,la ,crosse the ,mississippi ,river is reached1 flowing beneath bluffs of sandstone which are capped by loess 7#bjg74 ,the meanderings and the numerous cut-offs of the ,mississippi may be observed to the left 7#dae74 ,lake ,pepin is a side-delta lake blocked by the deposits of the ,chippewa ,river 7#dai74 ,from ,minneapolis an excursion is made to ,fort ,snelling to view the young gorge of the ,mississippi1 cut by the ,falls of ,st4 ,anthony for a distance of about eight miles in manner similar to that of the seven miles of ,niagara gorge 7#ced71 and to compare this narrow gorge with the broad valley of the ,warren ,river which drained ,lake ,agassiz 7#cbg74 ,somewhat farther up the ,warren ,river are examples of saucer lakes 7#daf74 ,from ,minneapolis the journey may be continued by the ,great ,northern ,railway to ,livingston1 ,montana1 thus crossing between the stations of ,muscoda and ,buffalo the bed of ,lake ,agassiz and its marginal beaches 7#cbe-cbh4 ,for local geology of ,minnesota consult ,c4 ,w4 ,hall1 ,geology of ,minnesota1 ,vol4 #a1 ,minneapolis1 #aijc74 ,the ,yellowstone ,park is entered from ,livingston 7,livingston ,geological ,folio1 ,u4 ,s4 ,g4 ,s47 and departure from it made at the relatively new ,union ,pacific terminal at the southwest margin4 ,the regular trip through the ,park includes visits to the several geyser basins 7#aia-aid71 ,obsidian ,cliff 7#cc1 #dfc71 the ,caon of the ,yellowstone1 etc4 ,good climbers can make a side trip from near the ,mammoth ,hot ,springs to the top of ,quadrant ,mountain1 the remnant of a 8biscuit cut0 upland 7#cgb71 and there study the nivation process 7#cfh1 ,yellowstone ,national ,park ,folio1 ,u4 ,s4 ,g4 ,s474 ,the trip from the ,park to ,salt ,lake ,city1 over the ,union ,pacific ,railway1 passes through the ,red ,rock ,pass1 the former outlet of ,lake ,bonneville 7#dbc71 into the desert of the ,great ,basin 7,chaps4 ,,xv and ,,xvi74 ,great ,salt ,lake is a saline lake or sink with an interesting record of climatic changes 7#aih1 #dja74 ,the front of the ,wasatch ,range1 in view and easily reached from ,salt ,lake ,city1 is deeply scored by the horizontal shore terraces of ,lake ,bonneville 7#aih1 #aii71 and these terraces are extended at every rentrant by barrier beaches of great perfection4 ,in the ,pleistocene period mountain glaciers in part occupied the valleys of this range1 though they did not always extend as far as the mountain front4 ,big ,cottonwood ,caon1 which realizes this condition1 and the neighboring ,little ,cottonwood ,caon1 from whose front its glacier spread into an expanded foot 7#bfd71 thus show for comparison in a single view the ,v and the low ,u sections respectively 7#agb1 #cgf74 ,here are also alluvial fans 7#bac7 and recent faults which intersect them4 ,from ,salt ,lake ,city the return to ,new ,york may be made by the ,denver and ,rio ,grande ,railway across deserts and through the ,royal ,gorge1 the caon of the ,arkansas ,river4 ,a full itinerary of the points of geological interest along this route1 and continued to ,chicago1 ,washington1 and ,new ,york1 is supplied in much detail in the guide of the geological excursion to the ,rocky ,mountains above cited4 ,this the traveling geologist should not fail to study4 ,some references to points along this journey will be found on preceding pages of this book 7#bai-bbj1 ,high ,plains2 #agj1 ,allegheny ,plateau in ,west ,virginia2 #agf1 water gap of ,harper's ,ferry2 #agf-agg1 #ahd-ahf1 side trip up the ,shenandoah ,valley to ,luray ,caverns and ,snickers ,gap2 #bea1 ,chesapeake ,bay74 ,instead of returning directly from ,salt ,lake ,city1 the traveler1 if he has sufficient time at his disposal1 may extend his journey southwestward across the ,great ,basin to ,los ,angeles4 ,a branch line from this route leaves the ,vegas ,valley and passes within reach of the famous ,death ,valley 7#bja7 to ,tonopah 7#gi7 and the ,owens ,valley 7#gg-gh1 #ib71 where are many surface faults dating from the earthquake of #ahgb and other less recent disturbances4 ,returning to the junction point1 the route continues across the ,colorado and ,mohave deserts to ,los ,angeles4 ,from ,los ,angeles as a center the exceptionally interesting terraces1 caves1 and stacks of an uplifted coast are to be seen to best advantage near ,pt4 ,harford 7,chap4 ,,xix74 ,the islands of ,san ,clemente and ,santa ,catalina may also be reached from ,los ,angeles 7#bci1 #bdh1 #bdi1 #bej1 #bef1 #beg1 pls4 #e ,b1 #g ,a1 #ab ,a74 ,the return to the ,east1 if made by the ,santa ,fe ,railway1 permits of a visit to the ,grand ,caon 7#agd1 #ddc7 from the station of ,williams4 ,from that point eastward the geology of the route is fully covered in ,emmons' ,guide to the ,rocky ,mountain ,excursion already cited4 99 99 99 99 99 ,for the benefit of those who are privileged to travel in ,europe1 and the number increases yearly1 a pilgrimage is suggested which may easily be made to correspond with plans laid out on the basis of historical1 artistic1 and scenic points of interest4 ,the only popular guide of a general nature written for geologists traveling abroad appears to be a brief but valuable little paper by ,professor ,lane 7,the ,geological ,tourist in ,europe1 ,popular ,science ,monthly1 ,vol4 #cc1 #ahhh1 pp4 #baf-bbi74 ,the publishing house of ,gebrder ,borntrger in ,berlin is now publishing a quite valuable series of geological guides dealing with special districts and written by well-known authorities 7,sammlung ,geologischer ,fhrer74 ,of this series some thirteen numbers have already been issued4 ,many other valuable local guides of a geological nature are the ,livrets ,guides of the ,international ,geological and ,geographical ,congresses1 and the similar pamphlets supplied in connection with annual meetings of national or provincial geological societies4 ,passengers on steamships sailing from the harbor of ,new ,york pass out over a deeply submerged caon 7#beb7 largely filled with glacial deposits1 through the ,narrows 7#agd71 and in sight of ,sandy ,hook1 a modified spit 7#bch1 #bdj74 ,to the left are seen the great morainic accumulations at the border of the glaciated area on ,long ,island 7#bih74 ,in the course of the trans-,atlantic voyage a much-rounded iceberg may be encountered 7#bia71 though this is much more apt to occur upon the northern routes from ,quebec1 and late in the season4 ,upon entering the ,english ,channel the land on both coasts rises in steep cliffs1 where are found all the common shore features well developed 7,chap4 ,,xviii74 ,the ,german steamships pass in sight of ,heligoland1 that last remnant of wave erosion 7#bcf74 ,while traveling in ,europe1 the student should consult a map of the glaciated area 7#bii71 and so learn to recognize its peculiarities1 and carefully mark its marginal moraine 7#caa7 and other strongly marked features4 ,if the ,british ,isles are visited and the more rugged areas are selected1 one may study the cirques and other characteristic features due to the presence of mountain glaciers about ,snowdon 7,chap4 ,,xxvi74 ,more mature stages of the same processes are to be found in the ,scottish ,highlands and the ,inner ,hebrides1 but especially upon the ,island of ,skye 7,fig4 #dib74 ,a very valuable aid to excursions in this district is ,baddeley's ,scotland 7part ,i1 ,dulau1 ,london7 and ,sir ,archibald ,geikie's ,explanatory ,notes to accompany ,bartholomew's ,geological ,map of ,scotland 7map and notes in cover1 ,edinburgh1 #ahib1 pp4 #bc74 ,illustration3 ,,fig4 #dib4--,sketch map of ,western ,scotland and the ,inner ,hebrides to show location of some points of special geological interest4 ,it is from ,oban1 the 8,charing ,cross of the ,highlands01 that one should start out upon the summer steamers in order to reach both ,skye and ,staffa1 the latter with fine basaltic columns 7#dfc71 and ,fingal's ,cave4 ,in sailing to ,skye one passes upon either shore of the narrow fjords many relics left in the dissection of volcanoes 7#aci-adc and ,sir ,a4 ,geikie1 ,ancient ,volcanoes of ,great ,britain1 ,vol4 ,,ii72 also rocky islands and skerries marking submergence 7#beb71 and the coast terraces which register a later uplift 7#bej74 ,skye is a complex of many intrusive and volcanic rocks of such markedly different colors as to appear as tints in the landscape4 ,in the ,cuchillin ,hills of dark green rises the massive gabbro 7#dfb7 cut by cirques into the jagged pinnacles of horns and comb ridges 7#cgc72 while lower down and to the east are rounded domes of rhyolite 7#dfc7 abraded beneath the glaciers and of a delicate salmon tint4 ,still lower and to the westward are flat mesas composed of horizontal layers of black basalt under a rich carpeting of the brightest verdure4 ,eastward across the channel are seen the purplish walls of an ancient sandstone4 ,the jagged gabbro core of the island thus represents a fretted upland 7#cgb7 and is now the training ground of the ,alpinist 7,abraham1 ,rock ,climbing in ,skye1 ,longmans1 ,london1 #aijh71 while nestled in one of the bottoms of a ,u-valley is ,loch ,coruisk1 a typical rock-basin lake 7#dab71 its shores of hard rock planed and scored4 ,from ,skye we may go to study the remarkable thrusts 7#de7 on the north shore of ,loch ,maree1 a marked lineament1 and one directed at right angles to that on the course of the ,caledonian ,canal connecting ,loch ,linne with ,loch ,ness4 ,this northeast wall of ,loch ,maree is a strikingly rectilinear fault represented by an escarpment1 up which we climb to find at the top the crushed and fluted thrust planes of movement dipping southeastward at a flat angle4 ,here also are beautiful rock-basin lakes1 lying in hollows molded beneath the continental glacier4 ,on our way from ,skye we have passed up ,loch ,carron1 a sea loch or fjord 7#beb71 and along the strath at its head known as ,strathcarron 7#dbh74 ,returning now to ,oban1 it is but a short trip by steamer up ,loch ,linne to ,fort ,william along the striking lineament 7#bbf7 which continues to ,loch ,ness and beyond 7,fig4 #dib71 and thence by rail to ,glen ,roy and the neighboring glens of ,lochaber 7#cbb-cbe74 ,from ,paris as a starting point1 we may visit in a most picturesque region the beautifully preserved craters of extinct volcanoes in the ,auvergne of ,central ,france 7#aje1 #abd1 #ade71 which district is entered from ,clermont-,ferrand4 ,here are found the characteristic puys1 steep lava domes of viscous lava 7#aje71 which figured largely in the early controversies of geologists concerning the origin of rocks4 ,illustration3 ,,fig4 #dic4--,outline map of a geological pilgrimage across the continent of ,europe4 ,the rest of our pilgrimage will be so planned as to enter the noble river ,rhine at its mouth 7,fig4 #dic71 ascend its course to its birthplace in the snows of ,switzerland1 and after further exploration of the features of this fretted upland1 traverse northern and central ,italy so as to make our departure for ,america by the southern route4 ,entering then upon this course in the ,low ,countries1 we have first the opportunity of observing the characteristics of a great delta with natural levees artificially strengthened as dikes 7#afe-afh74 ,here also are found dunes of beach material which has been raised by the wind into a great rampart near the shore 7#bji-baa74 ,such a wall of dune sand is well displayed at the bathing resort at ,scheveningen near the ,hague 7#dba74 ,the flood plain of the ,rhine 7#afb-afe7 may be studied in a journey up the river to the university town of ,bonn1 from whence a day's excursion should be devoted to the relics of volcanoes known as the ,seven ,mountains 7,h4 von ,dechen1 ,geognostischer ,fhrer in das ,siebengebirge1 ,bonn1 #ahfa74 ,as a preparation for this trip and others in the volcanic ,eifel higher up the river1 a visit should be made to the mineral and rock collections of the ,poppelsdorfer ,schloss at the ,university4 ,in the volcanic ,eifel are found some of the most interesting of crater lakes 7#dje71 the largest being ,lake ,laach with its somewhat peculiar volcanic ejectamenta and its picturesque abbey 7see von ,dechen1 ,geognostischer ,fhrer zu der ,vulkanreihe der ,vorder-,eifel1 etc41 ,bonn1 #ahhf4 ,consult also ,lane1 ,a ,geological ,tourist in ,europe1 l4c474 ,continuing our course up the river from ,bonn1 we soon enter the gorge of the ,rhine cut in an uplifted peneplain 7#afi1 #aga1 #agd74 ,from ,coblenz1 where the ,moselle enters the ,rhine1 a side trip may be made up this tributary river past ,zell with its entrenched meanders 7#agc7 to the ancient ,roman city of ,treves4 ,above ,bingen on the ,rhine we leave behind us the narrow gorge and rapid current of the river and continue over the broad floor at the bottom of a rift valley 7#djc71 lying between the forest of ,odin and the ,black ,forest on the east and the 8,blue ,alsatian ,mountains0 far away to the west4 ,at the margins of this plain are beds of loess with their characteristic joint structures and inclusions 7#bjg71 and in the higher hills on either hand a wealth of intrusive igneous rocks4 ,at the entrance of the ,neckar ,river to this broad plain is nestled the picturesque castle and university town of ,heidelberg1 a convenient center for excursions 7,julius ,ruska1 ,geologische ,streifzge in ,heidelbergs ,umgebung1 etc41 ,ngele1 ,leipzig1 #aijh1 pp4 #bjh1 map74 ,at ,strassburg 7,schwarzwaldstrasse #ab7 is located the ,german ,chief ,station for ,earthquake ,study1 with a particularly large set of modern seismographs4 ,in the university cabinet is also one of the largest and most representative mineral collections in ,europe4 ,for excursions in the neighborhood consult ,benecke1 ,sammlung ,geognostische ,fhrer1 ,vol4 #e1 ,elsass1 #aijj4 ,from ,strassburg we may go by the ,black ,forest ,railway to the ,hegau with its volcanic plugs 7#adj71 each surmounted by a picturesque castle4 ,we enter next the broadly extended piedmont apron site1 above which ,lake ,constance still remains as a border lake 7#cii74 ,outwash aprons 7#cad71 moraines 7#caa71 and drumlins 7#cag7 are each in turn encountered4 ,still continuing our course up the ,rhine from ,bregenz1 we enter the fretted upland 7#cgb7 of the ,alps1 mountains composed of great folds and thrusts about a core of intrusive rock 7,rothpletz1 ,sammlung ,geologische ,fhrer1 ,vol4 #aj1 #aijb1 ,thrusts in the ,alps between ,lake ,constance and the ,engadine74 ,some fourteen miles above ,chur we pass the terrace produced by successive landslides 7#dad71 known far and wide as the ,flimser ,bergstrz4 ,the further assent of the cascade stairway of this glacier-carved valley brings us to the ,furka ,pass1 from which point magnificent views of the fretted upland are obtained4 ,at the ,knzli1 a mile from the hotel1 one may view the nv of the ,rhone ,glacier1 which may also be easily visited4 ,we have now followed a great river from its mouth in the sands of ,holland to its source in the snows of the higher ,alps4 ,passing over the divide and descending to ,gletsch1 we may observe the lower end1 or foot1 of the ,rhone glacier and the crevasses and sracs 7#cia7 on the steep descent of this radiating glacier 7#chc1 #chf74 ,the response which glaciers make to climatic changes is here well illustrated by the recession of the glacier front from near the hotel 7its position in the '#ejs of the nineteenth century7 to its present position about a mile farther up the valley4 ,the characteristics of a glaciated mountain valley may be further illustrated by climbing to the ,grimsel ,pass1 which is scratched and striated 7#cgg1 #che71 and then descending the valley of the ,aar to ,meyringen 7#cgg74 ,near the ,grimsel ,hospice are the characteristic rock basin lakes 7#dab71 and upon the ,aar ,glacier to our left were carried out the epoch-making researches of ,louis ,agassiz1 the founder of the glacial theory for explaining the drift4 ,we encounter some thirteen rock bars 7#cgg74 ,just before reaching ,meyringen we pass the last of these1 the ,gorge of the ,aar1 cut by the stream through limestone4 ,interlaken 7#dai7 may be made the center for additional excursions up the ,lauterbrunnen ,valley1 with its prominent albs 7#cgf7 and its ribbon fall of the ,staubbach 7#cgh74 ,by the ,jungfrau ,mountain railway we may now ascend partly in tunnels of the rock to the ,ewigeismeer1 and look down upon the nv and bergschrunds of the ,great ,aletsch ,glacier 7#cgj1 see ,baltzer1 ,sammlung ,geologische ,fhrer1 ,vol4 #aj1 ,bernese ,oberland1 #aijf74 ,returning to ,interlaken by way of ,grindelwald1 one may study the foot of a radiating glacier1 the ,untergrindelwald glacier1 with its tunnel and its milky and braided stream4 ,crossing now the ,alpine foreland to ,villeneuve at the upper end of ,lake ,geneva and upon a well-developed strath 7#dbf1 #dbh71 we may look out upon the turbid waters extending far from the shore of the lake4 ,journeying to ,geneva by steamer we note the gradual clearing of the water until at the outlet of the lake it is as clear as crystal4 ,a walking trip from ,geneva takes us to the ,bois de la ,btie1 where the ,arve with turbid waters meets this clear stream 7#dbg74 ,the railroad to ,chamonix ascends another cascade stairway 7#cgf71 affords views of complexly folded sedimentary rocks 7#dc71 and at ,chamonix itself the mer de glace supplies opportunities for the study of moraines 7#chf1 #cic7 and glacial movement 7#cij-cib74 ,to experienced ,alpinists the summit of ,mount ,blanc offers a remarkably extended outlook over the fretted upland of the ,alps 7pl4 #ah ,a74 ,from the station of ,le,fayet below ,chamonix1 one may ascend to the ,dsert de la ,plat1 where are ,schratten in limestone due to solution 7#ahh74 ,crossing by one of the passes to the valley of the ,rhone at ,martigny we may reach ,zermatt1 to-day the climbing center of the ,alps4 ,from the subordinate cirques surrounding this village descend the ,gorner1 ,findelen1 ,st4 ,theodul1 and other components of this radiating glacier4 ,a black tooth of rock1 the ,matterhorn1 towers above the other peaks and shows to greatest advantage this feature of glacial sculpture 7#cgd71 while the ,gorge of the ,gorner is a severed rock bar like that of the ,aar 7#cgg74 ,either on foot or over the mountain railway we may ascend to the ,gorner ,grat1 a subordinate comb ridge 7#cgc7 which affords one of the most magnificent and instructive views of radiating glaciers4 ,from ,brig1 farther up the ,rhone ,valley1 an excursion is made to the ,eggishorn ,hotel1 a center for study on and about the ,great ,aletsch ,glacier 7#cbi1 #cga1 #che1 #chh1 #cie1 #daj74 ,the easy ascent of the ,eggishorn is rewarded by a view almost directly downward upon the ice-dammed ,mrjelen ,lake 7#cbi1 #daa74 ,from ,brig one may make his entry into ,italy1 either over the picturesque ,simplon route afoot or by diligence1 or else beneath it through the railway tunnel4 ,by an alternation of short steamboat and rail trips the journey is continued in a direction transverse to the longer axes of the border lakes ,maggiore1 ,lugano1 and ,como1 and later southward to ,milan4 ,in leaving the village of ,como we pass over heavy morainic deposits on the apron borders of the expanded-foot glacier 7#chc1 #che7 which once occupied the valley above4 ,on the journey from ,milan to ,venice1 over the fertile plains of ,lombardy1 the similar accumulations about ,lake ,garda 7#dad7 are first encountered at the little station of ,lonato and left behind at ,somma ,campagna 7,tornquist1 ,sammlung ,geologische ,fhrer1 ,vol4 #i1 ,northern ,italy1 #aijb74 ,the city of ,venice is built upon pile foundations in the lagoon behind the barrier beach known as the ,lido 7#bdb1 #dbh-dbi74 ,from here we may reach the ,karst country by way of ,trieste1 some of the more interesting and typical features being found near ,divaa 7#ahg-ahi1 #dbb1 pl4 #f ,a74 ,in a different direction from ,venice by way of ,belluno we enter the ,dolomites with their patterned relief and battlemented towers 7#bbh1 #dde74 ,additional centers for geological excursions on the route to our point of departure from ,italy are ,rome and ,naples4 ,at the ,italian capitol and in its neighborhood we may study the volcanic ,campagna with its beds of tuff 7#aje7 and its crater lakes 7#dje4 ,see ,sir ,a4 ,geikie1 ,the ,roman ,campagna1 ,landscape in ,history and other ,essays1 ,macmillan1 #aije1 pp4 #cjh-ceb2 also ,deecke1 ,sammlung ,geologische ,fhrer1 ,vol4 #h1 ,campagna1 #aija74 ,from ,rome it is an easy journey to the cataract of ,tivoli with its deposits of travertine 7#ahd74 ,in the opposite direction from ,rome across the ,campagna rise the ,alban ,hills1 ruins of a composite cone with several crater lakes on the sites of former vents4 ,on the summit of the encircling crater rim1 like the ,monte ,somma of the ,vesuvian ,mountain now a crescent only1 is located the chief ,italian station for earthquake study4 ,from ,naples we may reach in short excursions and study with some care still active volcanic mountains4 ,to the east is ,mount ,vesuvius 7#id1 #ig1 #abb1 #abd1 #abg-acg71 which was in grand eruption in ,april1 #aijf4 ,westward from ,naples are the ,campi ,phlegraeii1 or burning fields1 with many craters4 ,of these ,astroni offers a fine example of a large-cratered cinder cone 7#aje74 ,in the same vicinity are ,monte ,nuovo 7#if7 and the ,solfatara 7#ig71 the latter a type of volcano which no longer erupts lava1 but in its place emits carbon dioxide and other gaseous emanations 7,grotto del ,cane74 ,the starting point for excursions in the ,phlegran fields is ,pozzuoli with its ,temple of ,jupiter ,serapis 7#bed-bee71 reached from ,naples by an electric line which pierces the wall of an immense crater 7,posilippo7 composed of fine yellow volcanic ash known as ,pozzuolan4 ,from ,naples steamers make short excursions to ,sorrento with its deep ash deposits1 and to ,capri with its blue grotto 7#beg-beh74 ,herculaneum 7#aci7 and ,pompeii 7#abb71 buried during the eruption of #gi ,a4,d41 are on the line of the ,circum-,vesuvian ,railway4 ,steamships to ,new ,york from ,naples call at ,gibraltar1 the land-tied island par excellence 7#bda74 ,most steamships of the southern route pass through or near the volcanic islands of the ,azores1 and certain boats touch at ,algiers1 from which a line of railway gives access to ,biskra on the borders of the ,desert of ,sahara4 ,throughout these pilgrimages the traveler should be on the alert to note not only the agent responsible for the features which come under his observation1 but1 especially where this is the common sculpturing agent of running water1 he should not fail to notice the stage of the erosion cycle which is represented 7,chapter ,,xiii74 ,,index ,abrasion1 beneath glaciers1 #bge4 ,abyssinia1 fissure eruptions in1 #aja4 ,accordance1 of tributary valleys1 #afb4 ,adiabatic refrigeration1 in relation to glaciers1 #bfb4 ,adolescence1 in cycle of erosion1 #afi4 ,advancing hemicycle of glaciation1 #bfc-bff4 ,advective zone1 of atmosphere1 #bgj4 ,aftershocks1 of earthquakes1 #hc4 ,agassiz1 glacial lake1 #cbe-cbh4 ,agassiz1 ,louis1 cited1 #cci1 #djj4 ,age1 of strata1 #ch1 #eb4 ,aggradation1 #afb4 ,aktian deposits1 #cf4 ,alaskan coast1 map of1 #gi4 ,albs1 #cgf4 ,alden1 ,w4 ,c41 cited1 #caf1 #cah1 #cai4 ,alg1 growth of1 in hot springs1 #aid4 8,alkali0 in deserts1 #bja4 ,alluvial bench1 #bad4 ,alluvial cone1 #bac4 ,alluvial-dam lakes1 #dbc4 ,alluvial fan1 #bac4 ,alpine glaciers1 #chc1 #chf4 ,alterations of minerals1 #bg4 ,altitude1 of different parts of lithosphere1 #ah4 ,american ,falls1 future extinction of1 #ceg4 ,amphiboles1 #dei4 ,amphitheaters1 formed on drift sites1 #cfi4 ,amundsen1 ,r41 cited1 #bc4 ,analysis1 of folds1 #ed4 ,anderson1 ,tempest1 cited1 #adf1 #adg4 ,andersson1 ,j4 ,g41 cited1 #aeg1 #bie4 ,andesite1 #dfc4 ,angular unconformity1 #ec4 ,antarctica1 #aed1 #bha4 ,antarctic protuberance1 #ag4 ,antarctic shelf ice1 #bhi1 #bij4 ,anticlinal folds1 #db4 ,anticlines1 #db2 tension in1 #de4 ,anticyclone1 glacial1 #bhd4 ,ants1 factor in rock decomposition1 #aef4 ,apron1 alluvial1 #bac4 ,aprons1 outwash1 #bhj1 #bha4 ,arbenz1 ,p41 cited1 #aie4 ,arches1 of folded strata1 #db2 sea1 #bcc1 #bcd4 ,architecture1 of fractured earth superstructure1 #ee4 ,arctic depression1 #ag4 ,areal geological map1 #fb4 ,artes1 #cgc4 ,arldt1 ,theodore1 cited1 #aa1 #ai1 #dch4 ,arnold1 ,ralph1 cited1 #aeg4 ,arrangement of oceans and continents1 #aj4 ,artesian wells1 #aij1 #aia1 #aif4 ,ash1 volcanic1 #abb4 ,askja1 eruption of1 in #ahge1 #aja4 ,assmann1 ,r41 cited1 #bid4 ,astronomical vs4 geodetic observations1 #ab4 ,atlantis1 ,north1 #af4 ,atmosphere1 compressibility of1 #h4 ,attack1 of the weather1 #adi4 ,atwood1 ,w4 ,w41 cited1 #g1 #afj1 #bih1 #cjj1 #cac1 #cgb4 ,axial plane1 of folds1 #db4 ,axis1 of folds1 #db4 ,azurite1 #dec4 ,bacteria1 part taken in weathering1 #aef4 8,bad ,lands01 control of relief in1 #bbc1 #bbd4 8,bad ,land0 topography1 #bad4 ,bajir1 #baf4 ,balance1 between degradation and aggradation1 #afa4 ,bandai-san1 dissection of1 #ada4 ,barchans1 #baa4 ,barrancoes1 #aci4 ,barrell1 ,j41 cited1 #bba1 #ddg4 ,barrier beaches1 #bdj2 sections of1 #bdb2 uplifted1 #bdi1 #bej4 ,barrier lakes1 #dbj4 ,barriers1 #bdj2 mountain1 in relation to glaciers1 #bfb4 ,bars1 #bdj4 ,basal conglomerate1 #cg1 #ec4 ,basalt1 #dfc2 faulted blocks of1 #eh2 of ,hawaii1 #aje4 ,base level1 #aei4 ,basin-range lakes1 #djb1 #djc4 ,basin ,range structure1 #ddj4 ,basins1 flat bottomed1 separating dunes1 #baf2 of exudation1 #bgb2 of sedimentation1 earlier1 #ch4 ,bastin1 ,e4 ,s41 cited1 #baj4 ,batholites1 #adc4 8,bath tubs01 #cie4 ,beach pebbles1 #bci4 ,beach sand1 #bjf1 #bch4 ,beaches1 remaining from ice-dam lakes1 #daj2 shingle1 #bci2 storm1 #bdj2 uplifted1 8feathering out0 of1 #cdd4 ,bedded structure of rocks1 #ca4 ,beede1 ,j4 ,w41 cited1 #aie4 8,bee-hive0 mountains1 #chj1 #cha4 ,belgica expedition1 #bhi4 ,belt of sea which divides land masses1 #aa4 ,berghaus1 ,h41 cited1 #dbd4 ,bergschrund1 #cgj4 ,berson1 ,a41 cited1 #bid4 ,berthaut1 ,general1 cited1 #g4 8,bird-foot0 delta1 #afg4 8,biscuit cutting0 effect of glacial sculpture1 #cgb4 ,blackwelder1 ,e41 cited1 #cah4 ,block mountains1 #ddf4 ,blocks1 orographic1 #eh4 ,bocchi1 #abe4 ,bog1 floating1 #dbi4 ,bogs1 of peat1 #dbi1 #dcj4 ,bonney1 ,t4 ,g41 cited1 #adf4 ,borax deposits1 in deserts1 #bja4 ,border drainage1 about glaciers1 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,indies1 seismotectonic lines of1 #hh4 ,wheeler1 ,w4 ,h41 cited1 #bdd4 ,whirlpool basin1 at ,niagara1 #cei2 excavation of1 #cfj4 ,whitbeck1 ,r4 ,h41 cited1 #cai4 ,white1 ,david1 cited1 #cah4 ,willis1 ,bailey1 cited1 #de1 #ed1 #aeg1 #bfj1 #cah4 ,winchell1 ,n4 ,h41 cited1 #ced4 ,wind1 in relation to location of glaciers1 #cgg2 in relation to mountain glaciers1 #cfg4 ,wind distribution of snow1 #cfg4 ,wind gaps1 #agf4 ,windkanten1 #bje4 ,wind poles1 of the earth1 #bfc2 of earth1 earlier1 #big4 ,wintergreen ,flats1 site of captured fall1 #ceh4 ,wisconsin diamonds1 #cjg1 #cjh4 ,woodworth1 ,j4 ,b41 cited1 #gd1 #cea4 ,worcester1 ,dean ,c41 cited1 #if4 ,working hypothesis1 #f4 ,workman1 ,fanny ,bullock1 cited1 #bid4 ,workman1 ,w4 ,h41 cited1 #bid4 ,wright1 ,f4 ,e41 cited1 #cea4 ,yellowstone ,national ,park1 #cc1 #aia1 #aic1 #aid4 ,yosemite ,valley1 #ei1 #aeb4 ,young rivers1 #aei1 #afj4 ,zahn1 ,g4 ,w4 von1 cited1 #bdd4 ,zigzag ranges1 due to plunging folds1 #ea4 ,zittel1 ,k4 v41 cited1 #ai4 ,zone of diverse displacement1 #dci4 ,zone of flow1 #dj1 #adc4 ,zone of fracture1 #dj1 #df4 ,zones1 of deposition1 surrounding desert1 #baf1 #bag2 upper and lower cloud1 #bfh1 #bfi4 ,printed in the ,united ,states of ,america4 ,,footnotes3 #a ,italian for mouth2 plural bocchi4 #b ,these models and the contouring apparatus are now manufactured for the use of schools and colleges by ,eberbach and ,son1 ,ann ,arbor1 ,mich4 #c ,this clay is manufactured by the ,a4 ,h4 ,abbott ,company1 art dealers1 ,wabash ,avenue1 ,chicago4 #d ,numbers in parenthesis refer to pages in this book1 where further information is to be found4 99 99 99 99 99 99 ,transcriber's note3 --,obvious typographical errors have been silently corrected4 ,all other variations in spelling punctuation and accents have been left unchanged4 --,a border has been added to plates4