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Digitized by the Internet Archive 
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 The Library of Congress 
 
 http://www.archive.org/details/earthfeaturestheOOhobb 
 
EARTH FEATURES AND THEIR MEANING 
 
THE MACMILLAN COMPANY 
 
 NEW YORK • BOSTON • CHICAGO 
 DALLAS • SAN FRANCISCO 
 
 MACMILLAN & CO., Limited 
 
 LONDON • BOMBAY ■ CALCUTTA .^.^ 
 MELBOURNE 
 
 THE MACMILLAN CO. OF CANADA, Ltd. 
 
 TORONTO 
 
Plate 1. 
 
 Mount Balfour and the Balfour Glacier in the Selkirks. 
 
EARTH FEATUEES 
 
 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 " EARTHQUAKES, AN INTRODUCTION TO 
 
 SEISMIC geology"; "CHARACTERISTICS OF 
 
 EXISTING GLACIERS " : ETC. 
 
 N£to gork 
 
 THE MACMILLAN COMPANY 
 
 1912 
 
 All rights reserved 
 

 Copyright, 1912, 
 
 bt the macmillan company. 
 
 Set up and electrotyped. Published March, iqi2. 
 
 J. S. Gushing Co. — Berwick & Smith Co. 
 Norwood, Mass., U.S.A. 
 
 sQ.CI.A300538 
 
-^ 'ff 
 
 T@ THE MEM©RY 
 
 0F . / 
 
 y 
 GE©RGE 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 Michigan. 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 them. Such a geological examination of land- 
 scape is replete with fascinating revelations, and it lends to the 
 study of Nature a deep meaning which cannot but enhance the 
 enjoyment of her varied aspects. 
 
 That there is a real JDlace 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 work. Even more than 
 in former years the American travels afar by car or steamship, and 
 the earth's surface features in all their manifold diversity are thus 
 one after the other unrolled before him. The thousands who each 
 year cross the Atlantic to roam over European countries may by 
 historical, literary, or artistic studies prepare themselves to derive 
 an exquisite pleasure as they visit places identified with past 
 achievement of one form or another. Yet the Channel coast, the 
 gorge of the Ehine, the glaciers of Switzerland, and the wild scenery 
 of Norway or Scotland have each their fascinating story to tell 
 of a history far more remote and varied. To read this history, the 
 runic characters in which it is written must first of all be mastered ; 
 for in every landscape there are strong individual lines of char- 
 acter such as the pen artist would skillfully extract for an outline 
 sketch. Such character profiles are often many times repeated in 
 each landscape, and in them we have a key to the historical record. 
 
 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 Nature. In the landscapes which 
 
viii PREFACE 
 
 have been represented, the aim has been to draw as far as possible 
 upon localities well known to travelers and likely to be visited, 
 either because of their historical interest or their purely scenic 
 attractions. It should thus be possible for a tourist in America 
 or Europe to pursue his landscape studies whenever he sets out 
 upon his travels. The better to aid him in this endeavor, some 
 suggestions concerning the itinerary of journeys have been supplied 
 in an appendix. 
 
 Eegarded as a textbook of geology, the present work offers some 
 departures from existing examples. Though it has been customary 
 to combine in a single text historical with dynamical and structural 
 geology, a tendency has already become apparent to treat the his- 
 torical division apart from the others. Again, a desire to treat the 
 science of geology comprehensively has led some authors into in- 
 cluding so many subjects as to render their texts unnecessarily 
 encyclopedic and correspondingly uninteresting to the general 
 reader. It is the author's belief that there is a real need for a book 
 which may be read intelligently by the general public, and it must 
 be recognized that the beginner in the subject cannot cover the 
 entire field by a single course of readings. The present work has, 
 therefore, been prepared with a view to selecting for study those 
 dominant geological processes which are best illustrated by features 
 in northern North America and Europe. It is this desire to illus- 
 trate the readings by travels afield, which accounts for the promi- 
 nence given to the subject of glaciation ; for the larger number of 
 colleges and universities in both America and Europe are surrounded 
 by the heavy accumulations that have resulted from former glacia- 
 tions. 
 
 Emphasis has also been placed upon the dependence of the domi- 
 nant geological processes of any region upon existing climatic con- 
 ditions, a fact to which too little attention has generally been given. 
 This explains the rather full treatment of desert regions, of which, 
 in our own country particularly, much may be illustrated upon the 
 transcontinental railway journeys. 
 
 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 text. For such success as has been 
 reached in this endeavor, the author is greatly indebted to two 
 students of the University of Michigan, — Mr. James H. Meier, 
 who has prepared the line drawings of landscapes, and Mr. Hugh M. 
 
PREFACE ix 
 
 Pierce, who has draughted the diagrams. Though credit has in 
 most cases been given where illustrations have been made from 
 another's photographs, yet especial mention should here be made 
 of the debt to Dr. H. W. Fairbanks of Berkeley, California, whose 
 beautiful and instructive photographs are reproduced upon many 
 a page. 
 
 As given at the University of Michigan, 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 rocks, and to read intelligently the usual 
 topographical and geological maps. In the appendices the means 
 for carrying out such studies, in part with newly devised apparatus, 
 have been indicated. 
 
 The scope of the book precludes the possibility of furnishing the 
 reader with the sources for the body of fact and theory which is 
 presented, although much may be inferred from the names which 
 appear beneath the illustrations, and more definite knowledge will 
 be found in the references to literature supplied at the ends of 
 chapters. A large amount of original and unpublished material 
 is for a similar reason unlabeled, and it has been left for the pro- 
 fessional geologist to detect these new strands which have been 
 
 drawn into the web. 
 
 WILLIAM HERBEET HOBBS. 
 Ann Arbor, Michigan, 
 October 25, 1911. 
 
CONTENTS 
 
 CHAPTER I 
 The Compilation of Eakth History 
 
 PAGE 
 
 The sources of the history — Subdivisions of geology — T}je.,study o^ earth 
 f eatijEes_aBd-4±L£dlL^igilJJflcance — Tabular recapitulation — Geological 
 processes not universal — .Change, and not stability, the order of nature 
 
 — Observational geology versus speculative philosophy — The scientific 
 attitude and temper — The value of the hypothesis — Reading refer- 
 ences 1 
 
 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 vei'sus geodetic observations — Changes of figure dur- 
 ing 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 hydro- 
 sphere and atmosphere — Reading references 8 
 
 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 sur- 
 face shell — The essential nature of crystals — The lithosphere a com- 
 plex of interlocking crystals ^ Some properties of natural crystals, 
 minerals — The alterations of minerals — Reading references . . 20 
 
 CHAPTER IV 
 
 The Eocks 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 
 
xii CONTENTS 
 
 PAGE 
 
 — The different deposits of ocean, lake, 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 — Heading references 30 
 
 CHAPTER V 
 
 Contortions of the Strata within the Zone of Flow 
 
 The zones of fracture and flow — Experiments which illustrate the frac- 
 ture and flow of solid bodies — The arches and troughs of the folded 
 strata — The elements of folds — The shapes of rock folds — The over- 
 thrust 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 refer- 
 ences 40 
 
 CHAPTER VI 
 
 The Architecture of the Fractured Superstructure 
 
 The system of the fractures — The space intervals of joints — The dis- 
 placements upon joints: 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 vs. fault topography — Reading references 55 
 
 CHAPTER VII 
 
 The Interrupted Character of Earth Movements : Earth- 
 quakes 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 earthquakes : 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 1899 67 
 
 CHAPTER VIII 
 
 The Interrupted Character of Earth Movements : Earth- 
 quakes AND Seaquakes (concluded) 
 
 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 ... 81 
 
CONTENTS xiii 
 
 CHAPTER IX 
 
 The Rise of Molten Rock to the Earth's Surface ; Volcanic 
 Mountains of Exudation 
 
 FAGE 
 
 Prevalent misconceptions about volcanoes — Early views concerning vol- 
 canic mountains — The birth of volcanoes — Active and extinct vol- 
 canoes — The earth's volcano belts — Arrangement of volcanic vents 
 along fissures, 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 . 94 
 
 CHAPTER X 
 
 The Rise of Molten Rock to the Earth's Surface ; Volcanic 
 Mountains of Ejected Materials 
 
 The mechanics of crater explosions — Grander volcanic eruptions of cinder 
 cones — The eruption of Volcano in 1888 — The eruption of Taal 
 volcano on January 30, 1911 — The materials and the structure of cin- 
 der cones — The profile lines of cinder cones — The composite cone — 
 The caldera of composite cones — The eruption of Vesuvius in 1906 
 
 — The sequence of events within the chimney — The spine of Vel6 
 
 — The aftermath of mud flows — The dissection of volcanoes — The 
 formation of lava reservoirs — Character profiles — Reading references 115 
 
 CHAPTER XI 
 
 The Attack of the Weather 
 
 The two contrasted processes of weathering — The r61e of the percolating 
 water — Mechanical results of decomposition: 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 man- 
 tle and its shield in the mat of vegetation — Reading references . . 149 
 
 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 con- 
 trasted — The balance between degradation and aggradation — The 
 accordance of tributary valleys — The grading of the flood plain — 
 
xiv CONTENTS 
 
 PAGE 
 
 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 158 
 
 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 Hogai'thian line of beauty — 
 The final product of river sculpture : 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 refer- 
 ences 169 
 
 CHAPTER XIV 
 
 The Travels of the Underground Water 
 
 The descent within the unsaturated zone — The trunk channels of descend- 
 ing 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 180 
 
 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 weatherin g : the red and 
 brown desert varnish — The mechanical breakdown of the desert rocks 
 
 — The natural_sand blast — The dust carried out of the desert . . 197 
 
 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 .... 209 
 
CONTENTS XV 
 
 CHAPTER XVII 
 Repeating Patterns in the Earth Relief 
 
 PAGE 
 
 The ■weathering processes under control of the fracture system — The 
 fracture control of the drainage lines — The repeating pattern in drain- 
 age networks — The dividing lines of the relief patterns : lineaments 
 
 — The composite repeating patterns of the higher orders — Reading 
 references . . ' 223 
 
 CHAPTER XVIII 
 
 The Forms carved and molded by Waves i/- 
 
 The motion of a water wave — Free waves and breakers — Effect of the 
 breaking wave upon a steep, rocky shore : the notched cliff — Coves, 
 sea arches, 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 — Bar, spit, and bar- 
 rier — The land-tied island — A barrier series — Character profiles — 
 Reading references 231 
 
 CHAPTER XIX 
 
 Coast Records of the Rise or Fall or 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 coasts ; 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 move- 
 ments upon a coast — The contrasted islands of San Clemente and 
 Santa Catalina — The Blue Grotto of Capri — Character profiles — 
 Reading references 245 
 
 CHAPTER XX 
 
 The Glaciers of Mountain and Continent 
 
 Conditions essential to glaciation — The snow-line — Importance of moun- 
 tain barriers in initiating glaciers — Sensitiveness of glaciers to tem- 
 perature 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 . 261 
 
 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 
 
Xvi CONTENTS 
 
 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 .... 271 
 
 CHAPTER XXII 
 
 The Continental Glaciers of the "Ice Age" 
 
 Earlier cycles of glaciation — Contrast of the glaciated and nonglaciated 
 regions — The "driftless area" — Characteristics of the glaciated 
 regions — The glacier gravings — Younger records over older : 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 "kettle" moraines — Outwash plains — 
 Pitted plains and interlobate moraines — Eskers — Drumlius — The 
 shelf ice of the ice age — Character profiles 297 
 
 CHAPTER XXIII 
 
 Glacial Lakes which marked the Decline of the Last Ice Age 
 
 Interference of glaciers with drainage — Temporary lakes due to ice block- 
 ing — The "parallel roads" of the Scottish glens — The glacial Lake 
 Agassiz — Episodes of the glacial lake history within the St. 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 Hud- 
 son's Bay drainage basin — Reading references 320 
 
 CHAPTER XXIV 
 
 The Uptiiv of the Land at the Close of the Ice Age 
 
 The response of th h's shell to its ice mantle — The abandoned strands 
 as they appear / — 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 refer- 
 ences 340 
 
CONTENTS xvii 
 
 CHAPTER XXV 
 
 Niagara Falls a Clock of Recent Geological Time 
 
 PAGE 
 
 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 St. David's gorge — The shaping of the 
 Levdston Escarpment — Episodes of Niagara's history and their corre- 
 lation with those of the glacial lakes — Time measures of the Niagara 
 clock — The horologe of late glacial time in Scandinavia — Reading 
 references 352 
 
 CHAPTER XXVI 
 
 Land Sculpture by Mountain Glaciers 
 
 Contrasted sculpturing of continental and mountain glaciers — Wind dis- 
 tribution of the snow which falls in mountains — The niches which 
 form on snowdrift sites — The augmented snowdrift moves down the 
 valley: birth of the glacier — The excavation of the glacial amphi- 
 theater 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 ...... 367 
 
 CHAPTER XXVII 
 
 Successive Glacier Types of a Waning Glaciation 
 
 Transition from the ice cap to the mountain glacier — The piedmont 
 glacier — The expanded-f oot glacier — The dendritic glacier — The 
 radiating glacier — The horseshoe glacier — The inherited -basin glacier 
 
 — Summary of types of mountain glacier — Reading references . . 383 
 
 CHAPTER XXVIII 
 
 The Glacier's Surface Features and the Df,. / o upon its Bed 
 
 The glacier flow — Crevasses and s^racs — 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 390 
 
xviii CONTENTS 
 
 CHAPTER XXIX 
 A Study of Lake Basins 
 
 PAGE 
 
 Fresh water and saline lakes — Newland lakes — Basin-range lakes — Rift- 
 valley lakes — Earthquake lakes — Crater lakes — Coulee lakes — 
 Morainal lakes — Pit lakes — Glint or colk lakes — Ice-dam lakes — 
 Glacier-lobe lakes — Rock-basin lakes — Valley moraine lakes — Land- 
 slide lakes — Border lakes — Ox-bow I'akes — Saucer lakes — Crescentic 
 levee lakes — Raft lakes — Side-delta lakes — Delta lakes — Barrier 
 lakes — Dune lakes — Sink lakes — Karst lakes : poljen — Playa lakes 
 — Salines — Alluvial-dam lakes — R^sum6 — Reading references . 401 
 
 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 role of 
 lakes in the economy of nature — Ice ramparts on lake shores — Read- 
 ing references 426 
 
 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 uplift ; 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 435 
 
 APPENDICES 
 
 A. The quick determination of the common minerals .... 449 
 
 B. Short descriptions of some common rocks 462 
 
 C. The preparation of topographical maps 467 
 
 D. Laboratory models for study in the interpretation of geological maps . 472 
 
 E. Suggested itineraries for pilgrimages to study earth features . . 475 
 
 Index 489 
 
LIST OF PLATES 
 
 PLATE 
 
 1. Mount Balfour and the Balfour Glacier in the Selkirks . Frontispiece 
 
 FACING PAGE 
 
 2. A. Layers compressed in experiments and showing the effect of a com- 
 
 petent layer in the process of folding 44 
 
 B. Experimental production of a series of parallel thrusts within 
 
 closely folded strata ......... 44 
 
 C. Apparatus to illustrate shearing action within the overturned limb 
 
 of a fold 44 
 
 3. A. An earthquake fault opened in Formosa in 1906 with vertical and 
 
 lateral displacements combined 72 
 
 B. Earthquake faults opened in Alaska in 1889 on which vertical 
 
 slices of the earth's shell have undergone individual adjustments 72 
 
 4. A. Experimental tank to illustrate the earth movements which are 
 
 manifested in earthquakes. The sections of the earth's shell are 
 here represented before adjustment has taken place ... 82 
 
 B. The same apparatus after a sudden adjustment . . . .82 
 
 C. Model to illustrate a block displacement in rocks which are inter- 
 
 sected by master joints 82 
 
 5. A. Once wooded region in China now reduced to desert through de- 
 
 forestation ........... 156 
 
 B. " Bad Lands " in the Colorado Desert ...... 156 
 
 6. A. Barren Karst landscape near the famous Adelsberg grottoes . . 188 
 B. Surface of a limestone ledge where joints have been widened through 
 
 solution 188 
 
 7. A. Eanges of dunes upon the margin of the Colorado Desert . . 210 
 B. Sand dunes encroaching upon the oasis of Oued Souf, Algeria . 210 
 
 8. A. The granite needles of Harney Peak in the Black Hills of South 
 
 Dakota 216 
 
 B. Castellated erosion chimneys in El Cobra Caiion, New Mexico . 216 
 
 9. Map of the High Plains at the eastern front of the Rocky Mountains . 220 
 
 10. A. View in Spitzbergen to illustrate the disintegration of rock under 
 
 the control of joints , . ... 228 
 
 B. Composite pattern of the joint structures within recent alluvial 
 
 deposits of the Syrian Desert 228 
 
 11. A. Hippie markings within an ancient sandstone .... 232 
 B. Wave breaking as it approaches the shore 232 
 
 xix 
 
XX LIST OF PLATES 
 
 I'T.ATE FACING PA.GS 
 
 12. A. V-shaped canon cut in an upland recently elevated from the sea, 
 
 San Clemente Island, California 256 
 
 B. A "hogback" at the base of the Bighorn Mountains, Wyoming . 256 
 
 13. A. Precipitous front of the Bryant Glacier outlet of the Greenland 
 
 inland ice 272 
 
 B. Lateral stream beside the Benedict Glacier outlet, Greenland . 272 
 
 14. View of the margin of the Antarctic continental glacier in Kaiser 
 
 Wilhelm Laud 282 
 
 15. A. An Antarctic ice foot with boat party landing .... 290 
 B. A near view of the front of the Great Ross Barrier, Antarctica . 290 
 
 16. A. Incised topography within the " driftless area " .... 300 
 B. Built-up topography within the glaciated region .... 300 
 
 17. A. Soled glacial bowlders which show differently directed strise upon 
 
 the same facet 306 
 
 B. Perched bowlder upon a striated ledge of different rock type, Bronx 
 
 Park, New York , .... 306 
 
 C. Characteristic knob and basin surface of a moraine . . . 306 
 
 18. A. Fretted upland of the Alps seen from the summit of Mount Blanc 372 
 B. Model of the Malaspina Glacier and the fretted upland above it . 372 
 
 19. A. Contour map of a grooved upland, Bighorn Mountains, Wyoming 372 
 B. Contour map of a fretted upland, Philipsburg Quadrangle, Mon- 
 tana .... 372 
 
 20. Map of the surface modeled by mountain glaciers in the Sierra Nevadas 
 
 of California .......... 376 
 
 21. A. View of the Harvard Glacier, Alaska, showing the characteristic 
 
 terraces 394 
 
 B. The terminal moraine at the foot of a mountain glacier . . . 394 
 
 22. A. Model of the vicinity of Chicago, showing the position of the 
 
 outlet of the former Lake Chicago 400 
 
 B. Map of Yosemite Falls and its earlier site near Eagle Peak . . 400 
 
 23. A. View of the American Fall at Niagara, showing the accumulation 
 
 of blocks beneath 414 
 
 B. Crystal Lake, a landslide lake in Colorado 414 
 
 24. A. Apparatus for exercise in the preparation of topographic maps . 468 
 
 B. The same apparatus in use for testing the contours of a map . . 468 
 
 C. Modeling apparatus in use 468 
 
ILLUSTRATIONS IN THE TEXT 
 
 FIG. PAGE 
 
 1. Diagram to show the measure of the earth's surface irregularities . 11 
 
 2. Map to show the reciprocal relation of areas of land and sea . . 11 
 
 3. The tetrahedral form toward which the earth is tending ... 12 
 
 4. A truncated tetrahedron to show the reciprocal relation of projection 
 
 and depression upon the surface ....... 13 
 
 5. Approximations to earlier and present figures of the earth ... 15 
 
 6. Diagrams for comparison of coasts upon an upright and upon an in- 
 
 verted tetrahedron . . . . ...... 17 
 
 7. The continents, including submerged portions ..... 18 
 
 8. Diagram to indicate the altitude of different parts of the lithosphere 
 
 surface 18 
 
 9. Diagram to show how the terrestrial rocks grade into the meteorites . 22 
 
 10. Comparison of a crystalline with an amorphous substance ... 24 
 
 11. " Light figure " seen upon etched surface of calcite . . . . 25 
 
 12. Battered sand grains which have developed crystal faces ... 26 
 
 13. Unassimilated grains of quartz within a garnet crystal ... 28 
 
 14. New minerals developed about the core of an augite crystal . . 28 
 
 15. A common rim of new mineral developed by reaction where earlier 
 
 minerals come into contact ........ 28 
 
 16. Laminated structure of a sedimentary rock 30 
 
 17. Characteristic textures of igneous rocks 33 
 
 18. Diagram to show the order of sediments laid down during a trans- 
 
 gression of the sea 37 
 
 19. Fractures produced by compression of a block of molder's wax . . 41 
 
 20. Apparatus to illustrate the folding of strata 41 
 
 21. Diagrams of fold types 42 
 
 22. Diagrams to illustrate crustal shortening 42 
 
 23. Anticlinal and synclinal folds . " . . . . . . .43 
 
 24. Diagrams to illustrate the shapes of rock folds 44 
 
 25. Secondary and tertiary flexures superimposed upon the primary ones 44 
 
 26. A. bent stratum to illustrate tension and compression upon opposite 
 
 sides 45 
 
 27. A geological section with truncated arches restored .... 47 
 
 28. Diagram to illustrate the nature of strike and dip . . . .47 
 
 29. Diagram to show the use of T symbols for strike and dip observation . 48 
 
 30. Diagram to show how the thickness of a formation is determined . 49 
 
 31. A plunging anticline 50 
 
 xxi 
 
xxii ILLUSTRATIONS IN THE TEXT 
 
 FIG. PAGE 
 
 32. A plunging syncline '. . . . .50 
 
 33. An unconformity upon the coast of California 51 
 
 34. Series of diagrams to illustrate the episodes involved in the production 
 
 of an angular unconformity ........ 52 
 
 35. Types of deceptive or erosional unconformities ..... 53 
 
 36. A set of master joints in shale 55 
 
 37. Diagram to show the manner of replacement of one set of joints by 
 
 another 56 
 
 38. Diagram to show the different combinations of joint series ... 56 
 
 39. View of the shore in West Greenland 57 
 
 40. View in Iceland which shows joint intervals of more than one order . 57 
 
 41. Faulted blocks of basalt near Woodbury, Connecticut .... 58 
 
 42. A fault in previously disturbed strata 59 
 
 43. Diagram to show the effect of erosion upon a fault .... 60 
 
 44. A fault plane exhibiting drag 60 
 
 45. Map to show how a fault may be indicated by abrupt changes in strike 
 
 and dip 61 
 
 46. A series of parallel faults revealed by offsets 61 
 
 47. Pield map prepared from the laboratory table ..... 64 
 
 48. Areal geological map based upon the field map 64 
 
 49. A portion of the ruins of Messina ........ 67 
 
 50. Ruins of the Carnegie Palace of Peace at Cartaga, Costa Rica . . 68 
 
 51. Overturned bowlders from Assam earthquake of 1897 .... 69 
 62. Post sunk into ground during Charleston earthquake .... 69 
 
 53. Map showing localities where shocks have been reported at sea off 
 
 Cape Mendocino, California ........ 70 
 
 54. Effect of seismic water wave in Japan 70 
 
 55. A fault of vertical displacement . . . . . . . . 71 ' 
 
 56. Escarpment produced by an earthquake fault in India ... 72 
 
 57. A fault of lateral displacement ........ 72 
 
 58. Fence parted and displaced by lateral displacement on fault during 
 
 California earthquake ......... 72 
 
 59. Fault with vertical and lateral displacements combined ... 72 
 
 60. Diagram to show how small faults may be masked at the earth's sur- 
 
 face 73 
 
 61. " Mole hill " effect above buried earthquake fault .... 73 
 
 62. Post-glacial earthquake faults 74 
 
 63. Earthquake cracks in Colorado desert 74 
 
 64. Railway tracks broken or buckled at time of earthquake ... 75 
 
 65. Railroad bridge in Japan damaged by earthquake .... 75 
 
 66. Diagrams to show contraction of earth's crust during an earthquake . 76 
 
 67. Map of the Chedrang fault of India 76 
 
 68. Displacements along earthquake fault in Alaska 77 
 
 69. Abrupt change in direction of throw upon an earthquake fault . . 77 
 
 70. Map of faults in the Owens Valley, California, formed during earth- 
 
 quake of 1872 78 
 
ILLUSTRATIONS IN THE TEXT xxiii 
 
 TIG. PAGE 
 
 71. Marquetry of the rock floor in the Tonopah district, Nevada . . 79 
 
 72. Map of Alaskan coast to show adjustments of level during an earth- 
 
 quake 79 
 
 73. An Alaskan shore elevated seventeen feet during the earthquake of 
 
 1899 .80 
 
 74. Partially submerged forest from depression of shore in Alaska during 
 
 earthquake ........... 80 
 
 75. Effect of settlement of the shore at Port Royal during earthquake of 
 
 1907 80 
 
 76. Diagrams to illustrate the draining of lakes during earthquakes . . 83 
 
 77. Diagram to illustrate the derangements of water flow during an 
 
 earthquake 84 
 
 78. Mud cones aligned upon an eartliquake fissure in Servia ... 84 
 
 79. Craterlet formed near Charleston, South Carolina, during the earth- 
 
 quake of 1886 85 
 
 80. Cross section of a craterlet 85 
 
 SI. Map of the island of Ischia to show the concentration of earthquake 
 
 shocks 87 
 
 82. A line of earth fracture revealed in the plan of the relief ... 87 
 
 S3. Seismotectonic lines of the West Indies 88 
 
 84. Device to illustrate the different effects of earthquakes in firm rock 
 
 and in loose materials 88 
 
 85. House wrecked in San Francisco earthquake . . . . .90 
 
 86. Building wrecked in California earthquake by roof and upper floor 
 
 battering down the upper walls 91 
 
 87. Breached volcanic cone in New Zealand showing the bending down 
 
 of the strata near the vent '. 96 
 
 88. View of the new Camiguin volcano formed in 1871 in the Philippines 97 
 
 89. Map to show the belts of active volcanoes . ..... 98 
 
 90. A portion of the " fire girdle " of the Pacific 98 
 
 91. Volcanic cones formed in 1783 above the Skaptar fissure in Iceland . 99 
 
 92. Diagrams to illustrate the location of volcanic vents upon fissure lines 100 
 
 93. Outline map showing the arrangement of volcanic vents upon the 
 
 island of Java 100 
 
 94. Map showing the migration of volcanoes along a fissure . . . 101 
 
 95. Basaltic plateau of the northwestern United States due to fissure 
 
 eruptions of lava 102 
 
 96. Lava plains about the Snake River in Idaho 102 
 
 97. Characteristic profiles of lava volcanoes . . . . . . 103 
 
 98. A driblet cone 104 
 
 99. Lefiingwell Crater, a cinder cone in the Owens Valley, California . 104 
 
 100. Map of Hawaii and its lava volcanoes ...... 106 
 
 101. Section through Mauna Loa and Kilauea 106 
 
 102. Schematic diagram to illustrate the moving platform in the crater of 
 
 Kilauea. ........... 107 
 
 103. View of the open lava lake of Halemaumau . „ ... 108 
 
xxiv ILLUSTRATIONS IN THE TEXT 
 
 FIG. PAGE 
 
 104. Map to show the manner of outflow of the lava from Kilauea in the 
 
 eruption of 1840 109 
 
 105. Lava of Matavanu flowing down to the sea during the eruption of 
 
 1906 110 
 
 106. Lava stream discharging into the sea from a lava tunnel . . . Ill 
 
 107. Diagrammatic representation of the structure of lava volcanoes as a 
 
 result of the draining of frozen lava streams . . . .112 
 
 108. Diagram to show the formation of mesas by outflow of lava in valleys 
 
 and subsequent erosion 112 
 
 109. Surface of lava of the Pahoehoe type 113 
 
 110. Three successive views to show the growth of the island of Savaii, 
 
 from lava outflow in 1906 113 
 
 111. View of the volcano of Stromboli showing the excentric position of 
 
 the crater ........... 116 
 
 112. Diagrams to illustrate the eruptions within the crater of Stromboli . 117 
 
 113. Map of Volcano in the ^olian Islands 118 
 
 114. " Bread-crust " lava projectile from the eruption of Volcano in 1888 . 119 
 
 115. "Cauliflower cloud" of steam and ash rising above the cinder cone 
 
 of Volcano 120 
 
 116. Eruption of Taal volcano in 1911 seen from a distance of six miles . 120 
 
 117. The thick mud veneer upon the island of Taal (after a photograph 
 
 by Deniston) . . . 121 
 
 118. A pear-shaped lava projectile . ■ 121 
 
 119. Artificial production of a cinder cone . . . . . . .122 
 
 120. Diagram to show the contrast between a lava dome and a cinder cone 123 
 
 121. Mayon volcano on the island of Luzon, Philippine Islands . . . 123 
 
 122. A series of breached cinder cones due to migration of the eruption 
 
 along a fissure 124 
 
 123. The mouth upon the inner cone of Mount Vesuvius from which flowed 
 
 the lava of 1872 124 
 
 124. A row of parasitic cones raised above a fissure opened on the flanks 
 
 of Etna in 1892 125 
 
 125. View of Etna, showing the parasitic cones upon its flanks . . . 125 
 
 126. Sketch map of Etna to show the areas covered by lava and tuff re- 
 
 spectively 126 
 
 127. Panum crater showing the caldera ....... 126 
 
 128. View of Momit Vesuvius before the eruption of 1906 . . . .127 
 
 129. Sketches of the summit of the Vesuvian cone to bring out the changes 
 
 in its outline ........... 128 
 
 130 Night view of Vesuvius from Naples before the outbreak of 1906, 
 
 showing a small lava stream descending the central cone . . 129 
 
 131. Scoriaceous lava encroaching upon the tracks of the Vesuvian railway 130 
 
 132. Map of Vesuvius, showing the position of the lava mouths opened 
 
 upon its flanks during the eruption of 1906 131 
 
 133. The ash curtain over Vesuvius lifting and disclosing the outlines of 
 
 the mountain 132 
 
ILLUSTRATIONS IN THE TEXT XXV 
 
 riG. PAGE 
 
 134. The central cone of Vesuvius as it appeared after the eruption of 1906 132 
 
 135. A sunken road upon Vesuvius filled with indrifted ash . . . 133 
 
 136. View of Vesuvius from the southwest during the waning stages of 
 
 the eruption ........... 133 
 
 137. The main lava stream advancing upon Boscotrecase .... 133 
 
 138. A pine snapped off by the lava and carried forward upon its surface . 133 
 
 139. Lava front pushing over and running around a wall in its path . . 134 
 
 140. One of the ruined villas in Boscotrecase ...... 134 
 
 141. Three diagrams to illustrate the sequence of events during the cone- 
 
 building and crater-producing periods 135 
 
 142. The spine of Pel6 rising above the chimney of the volcano after the 
 
 eruption of 1902 136 
 
 143. Successive outlines of the Pel6 spine 137 
 
 144. Corrugated surface of the Vesuvian cone due to the mud flows which 
 
 followed the eruption of 1906 138 
 
 145. View of the Kammerbiihl near Eger in Bohemia .... 139 
 
 146. Volcanic plug exposed by natural dissection of a volcanic cone in 
 
 Colorado 140 
 
 147. A dike cutting beds of tuff in a partly dissected volcano of south- 
 
 western Colorado 140 
 
 148. Map and general view of St. Paul's rocks, a volcanic cone dissected 
 
 by waves ........... 141 
 
 149. Dissection by explosion of Little Bandai-san in 1888 .... 141 
 
 150. The half -submerged volcano of Krakatoa before and after the erup- 
 
 tion of 1883 . 142 
 
 151. The cicatrice of the Banat 142 
 
 152. Diagram to illustrate a probable cause of formation of lava reservoirs 
 
 and the connection with volcanoes upon the surface . . . 143 
 
 153. Effect of relief of load upon rocks by arching of a competent forma- 
 
 tion 144 
 
 154. Character profiles connected with volcanoes 146 
 
 155. Diagrams to show the effect of decomposition in producing spheroidal 
 
 bowlders 150 
 
 156. Spheroidal weathering of an igneous rock 151 
 
 157. Dome structure in granite mass 152 
 
 158. Talus slope beneath a cliff . . . . . . . . .153 
 
 159. Striped ground from soil flow ........ 154 
 
 160. Pavement of horizontal surface due to soil flow 154 
 
 161. Tree roots prying rock apart on fissure 154 
 
 162. Bowlder split by a growing tree 155 
 
 163. Rock mantle beneath soil and vegetable mat 165 
 
 164. Diagram to show the varying thickness of mantle rock upon the 
 
 different portions of a hill surface 156 
 
 165. Gullies from earliest stage of a river's life 160 
 
 166. Partially dissected upland 160 
 
 167. Longitudinal sections of upper portion of a river valley . . . 161 
 
XXVi ILLUSTRATIONS IN THE TEXT 
 
 riG. PAGE 
 
 168. Map and sections of a stream meander 163 
 
 169. Tree undermined on the outer bank of a meander .... 164 
 
 170. Diagrams to show the successive positions of stream meanders . . 164 
 
 171. An ox-bow lake in the flood plain of a river 165 
 
 172. Schematic representation of a series of river terraces . . . . 165 
 
 173. " Bird-foot " delta of the Mississippi Kiver 167 
 
 174. Diagrams to show the nature of delta deposits as exhibited in sec- 
 
 tions 168 
 
 175. Gorge of the River Rhine near St. Goars 169 
 
 176. Valley with rounded shoulders characteristic of the stage of adoles- 
 
 cence 170 
 
 177. View of a maturely dissected upland 170 
 
 178. Hogarth's line of beauty 171 
 
 179. View of the oldland of New England, with Mount Monadnock rising 
 
 in the distance .......... 171 
 
 180. Comparison of the cross sections of river valleys of different stages . 172 
 
 181. The Beavertail Bend of the Yakima River 173 
 
 182. A rejuvenated river valley 174 
 
 183. Plan of a river narrows 174 
 
 184. Successive diagrams to illustrate the origin of " trellis drainage" . 175 
 
 185. Sketch maps to show the earlier and present drainage near Harper's 
 
 Ferry 176 
 
 186. Section to illustrate the history of Snickers Gap 177 
 
 187. Character profiles of landscapes shaped by stream erosion in humid 
 
 climates 177 
 
 188. Diagram to show the seasonal range in the position of the water table 180 
 
 189. Diagram to show the effect of an impervious layer upon the descend- 
 
 ing water 181 
 
 190. Sketch map to illustrate corrosion of limestone along two series of 
 
 vertical joints 181 
 
 191. Diagram to show the relation of limestone caverns to the river system 
 
 of the district 182 
 
 192. Plan of a portion of Mammoth Cave, Kentucky 183 
 
 193. Trees and shrubs growing upon the bottoms of limestone sinks . . 183 
 
 194. Diagrams to show the manner of formation of stalactites and stalag- 
 
 mites ............ 185 
 
 195. Sinter formations in the Luray caverns 186 
 
 196. Map of the dolines of the Karst region ...... 187 
 
 197. Cross section of a doline formed by inbreak 187 
 
 198. Sharp Karren of the Ifenplatte ........ 188 
 
 199. The Zirknitz seasonal lake 189 
 
 200. Fissure springs arranged at intersections of rock fi'actures . . . 190 
 
 201. Schematic diagrams to illustrate the different types of artesian wells . 191 
 
 202. Cross section of Geysir, Iceland 192 
 
 203. Apparatus for simulating geyser action ...... 193 
 
 204. Cone of siliceous sinter about the Lone Star Geyser .... 194 
 
ILLUSTRATIONS IN THE TEXT xxvii 
 
 TIG. PAGE 
 
 205. Former shore lines in the Great Basin 198 
 
 206. Map of the former Lake Bonneville 199 
 
 207. Borax deposits in Death Valley, California 201 
 
 208. Hollowed forms of weathered granite in a desert of Central Asia . 201 
 
 209. Hollow hewn blocks in a wall in the Wadi Guerraui .... 202 
 
 210. Smooth granite domes shaped by exfoliation 203 
 
 211. Granite blocks rent by diffission 204 
 
 212. " Mushroom Rock " from a desert in Wyoming .... 205 
 
 213. Windkanten shaped by sand blast in the desert 205 
 
 214. The " stone lattice " of the desert 206 
 
 215. Shadow erosion in the desert 206 
 
 216. Cliffs in loess with characteristic vertical jointing . . . . 207 
 
 217. A canon in loess worn by traffic and wind 207 
 
 218. Diagrams to illustrate the effects of obstructions in arresting wind- 
 
 driven sand 209 
 
 219. Sand accumulating on either side of a firm and impenetrable obstruc- 
 
 tion , 210 
 
 220. Successive diagrams to illustrate the history of the town of Kunzeu 
 
 upon the Kurische Nehrung ........ 210 
 
 221. View of desert barchans 211 
 
 222. Diagrams to show the relationships of dunes to sand supply and wind 
 
 dii'ection ........... 211 
 
 223. Ideal section showing the rising mountain wall about a desert and 
 
 the neighboring slope 212 
 
 224. Dry delta at the foot of a range upon the borders of a desert . .213 
 
 225. Map of distributaries of streams which issue at the western base of 
 
 the Sierra Nevadas 213 
 
 226. A group of " demoiselles " in the " bad lands " 214 
 
 227. Amphitheater at the head of the Wadi Beni Sur .... 215 
 
 228. Mesa and outlier in the Leucite Hills of Wyoming .... 216 
 
 229. Flat-bottomed basin separating dunes . . . . . .216 
 
 230. Billowy surface of the salt crust on the central sink of the desert of 
 
 Lop 217 
 
 231. Schematic diagram to show the zones of deposition in their order 
 
 from the margin to the center of a desert ..... 217 
 
 232. Mounds upon the site of the buried city of Nippur .... 218 
 
 233. Exhumed structures in the buried city of Nippur .... 218 
 
 234. Section across the High Plains 219 
 
 235. Section across the lenticular threads of alluvial deposits of the High 
 
 Plains 220 
 
 236. Distributaries of the foot hills superimposed upon an earlier series . 220 
 
 237. Character profiles in the landscapes of arid lands .... 220 
 
 238. Eain sculpturing under control by joints 224 
 
 239. Sagging of limestone above joints 224 
 
 240. Map of the joint-controlled Abisko Canon in Northern Lapland . 225 
 
 241. Map of the gorge of the Zambesi River below Victoria Falls . . 225 
 
xxviii ILLUSTRATIONS IN THE TEXT 
 
 FIG. PAGE 
 
 242. Controlled drainage network of the Shepaug River in Connecticut . 226 
 
 243. A river network of repeating rectangular pattern .... 226 
 
 244. Squared mountain masses which reveal a distribution of joints in 
 
 block patterns of different orders 228 
 
 245. Island groups of the Lofoten Archipelago 229 
 
 246. Diagrams to illustrate the composite profiles of the islands on the 
 
 Norwegian coast . 229 
 
 247. Diagram to show the nature of the motions within a free water wave 231 
 
 248. Diagram to illustrate the transformation of a free wave into a breaker 232 
 
 249. Notched rock cliff and fallen blocks 233 
 
 250. A wave-cut chasm under control by joints 233 
 
 251. Grand Arch upon one of the Apostle Islands in Lake Superior . . 234 
 
 252. Stack near the shore of Lake Superior 234 
 
 253. The Marble Islands, stacks in a lake of the southern Andes . . 235 
 
 254. Squared stacks revealing the position of the joint planes on which 
 
 they were carved 335 
 
 255. Ideal section cut by waves upon a steep rocky shore .... 236 
 
 256. Map showing the outlines of the island of Heligoland at different 
 
 stages in its history 236 
 
 257. Ideal section carved by waves upon a steep shore of loose materials . 237 
 
 258. Sloping cliff and boulder pavement at Scituate, Massachusetts . . 237 
 
 259. Map to show the nature of the shore current and the forms which are 
 
 molded by it 238 
 
 . 239 
 
 . 239 
 
 . 240 
 
 . 240 
 
 . 241 
 
 . 242 
 
 . 242 
 
 260. Crescent-shaped beach in the lee of a headland . 
 
 261. Cross section of a beach pebble ..... 
 
 262. A storm beach on the northeast shore of Green Bay . 
 
 263. Spit of shingle on Au Train Island, Lake Superior 
 
 264. Barrier beach in front of a lagoon .... 
 
 265. Cross section of a barrier beach with lagoon in its rear 
 
 266. Cross section of a series of barriers and an outer bar . 
 
 267. A barrier series and an outer bar on Lake Mendota at Madison, 
 
 Wisconsin ........... 242 
 
 268. Series of barriers at the western end of Lake Superior . . . 243 
 
 269. Character profiles resulting from wave action upon shores . . . 243 
 
 270. The even shore line of a raised coast ....... 246 
 
 271. The ragged coast line produced by subsidence 246 
 
 272. Portion of the Atlantic coastal plain at the base of the oldland . . 246 
 
 273. Ideal form of cuestas and intermediate lowlands carved from a coastal 
 
 plain ............ 247 
 
 274. Uplifted sea cave on the coast of California 248 
 
 275. Double-notched cliff near Cape Tiro, Celebes 248 
 
 276. Uplifted stacks on the coast of California 249 
 
 277. Uplifted shingle beach across the entrance to a former bay upon the 
 
 coast of California 250 
 
 278. Raised beach terraces near Elie, Fife, Scotland 250 
 
 279. Uplifted sea cliffs and terraces on the Alaskan coast .... 250 
 
ILLUSTRATIONS IN THE TEXT Xxix 
 
 FIG. PAGE 
 
 280. Diagrams to show how excessive sinking upon the sea floor will cause 
 
 the shore to migrate landward 251 
 
 281. A drowned river mouth or estuary upon a coastal plain , . . 251 
 
 282. Archipelago of steep rocky islets due to submergence . . . 252 
 
 283. The submerged Hudsonian channel which continues the Hudson 
 
 River across the continental shelf 262 
 
 284. Marine clay deposits near the mouths of the Maine rivers which pre- 
 
 serve a record of earlier subsidence and later elevation . . 253 
 
 285. View of the three standing columns of the Temple of Jupiter Serapis, 
 
 at Pozzuoli 254 
 
 286. Three successive views to set forth the recent oscillations of level on 
 
 the northern shore of the Bay of Naples 255 
 
 287. Belief map of San Clemente Island, California 256 
 
 288. Relief map of Santa Catalina Island, California ..... 257 
 
 289. Cross section of the Blue Grotto, on the island of Capri . . . 258 
 
 290. Character profiles of coast elevation and subsidence .... 259 
 
 291. Map showing the distribution of existing glaciers and the two impor- 
 
 tant wind poles of the earth ........ 263 
 
 292. An Alaskan glacier spreading out at the foot of the range which 
 
 nourishes it .......... . 264 
 
 293. Surface of a glacier whose upper layers spread with but slight restraint 
 
 from retaining walls ......... 265 
 
 294. Section through a mountain glacier 267 
 
 295. Profile across the largest of the Icelandic ice caps .... 267 
 
 296. Ideal section across a continental glacier 267 
 
 297. View of the Eyriks JokuU, an ice cap of Iceland .... 268 
 
 298. The zones of the lower atmosphere as revealed by recent kite and 
 
 balloon exploration ......... 269 
 
 299. Map of Greenland, showing the area of inland ice and the routes of 
 
 explorers 271 
 
 300. Profile in natural proportions across the southern end of the conti- 
 
 nental glacier of Greenland 272 
 
 301. Map of a glacier tongue with dimple above 273 
 
 302. Edge of the Greenland inland ice, showing the nunataks diminishing 
 
 in size toward the interior 274 
 
 303. Moat surrounding a nunatak in Victoria Land 274 
 
 304. A glacier pavement of Permo-Carboniferous age in South Africa . 276 
 •305. Diagrams to illustrate the manner of formation of scape colks . . 277 
 
 306. Marginal moraine now forming at the edge of the continental glacier 
 
 of Greenland 279 
 
 307. Small lake between the ice front and a moraine which it has recently 
 
 built 279 
 
 308. View of a drained lake bottom between the ice front and an aban- 
 
 doned moraine .......... 280 
 
 309. Diagrams to show the manner of foi'mation and the structure of an 
 
 outwash plain and fosse 280 
 
XXX ILLUSTRATIONS IN THE TEXT 
 
 FIG. TAGE 
 
 310. Map of the ice masses of Victoria Land, Antarctica .... 282 
 
 311. Sections across the inland ice and the shelf ice of Antarctica . . 283 
 
 312. Diagram to show the nature of the fixed glacial anticyclone above . 
 
 continental glaciers 284 
 
 313. Snow deltas about the margins of a glacier tongue in Greenland . 285 
 
 314. View of the sea ice of the Arctic region 286 
 
 315. Map of the north polar regions, showing the area of drift ice and the 
 
 tracks of the Jeannette and the Fram 288 
 
 316. The shelf ice of Coats Land with surrounding pack ice . . . 290 
 
 317. Tide-water cliff on a glacier tongue from which icebergs are born . 290 
 
 318. A Greenlandic iceberg after a long journey in warm latitudes . . 291 
 
 319. Diagram showing one way in which northern icebergs are born from 
 
 the glacier tongue 291 
 
 320. A northern iceberg surrounded by sea ice 292 
 
 321. Tabular Antarctic iceberg separating from the shelf ice . . . 29S 
 
 322. Map of the globe, showing the areas covered by continenual glaciers 
 
 during the " ice age " 297 
 
 323. Glaciated granite bowlder weathered out of a moraine of Permo- 
 
 Carboniferous age. South Australia 298 
 
 324. Map to show the glaciated and nonglaciated regions of North 
 
 America ........... 298 
 
 325. Map of the glaciated and nonglaciated areas of northern Europe . 299 
 
 326. An unstable erosion remnant characteristic of the " driftless area " . 300 
 
 327. Diagram showing the manner in which a continental glacier obliter- 
 
 ates existing valleys 301 
 
 328. Lake and marsh district in northern Wisconsin 302 
 
 329. Cross section in natural proportion of the latest North American 
 
 continental glacier 303 
 
 330. Diagram showing the earlier and the later glacier records together 
 
 upon the same limestone surface 304 
 
 331. Map to show the outcroppings of peculiar rock types in the region 
 
 of the Great Lakes, and some localities where "drift copper" 
 
 has been collected 305 
 
 332. Map of the "bowlder train " from Iron Hill, Rhode Island . . 306 
 
 333. Shapes and approximate natural sizes of some of the diamonds from 
 
 the Great Lakes region 307 
 
 334. Glacial map of a portion of the Great Lakes region .... 308 
 
 335. Section in coarse till .......... 310 
 
 336. Sketch map of portions of Michigan, Ohio, and Indiana, showing the 
 
 distribution of moraines 312 
 
 337. Map of the vicinity of Devil's Lake, Wisconsin, partly covered by 
 
 the continental glacier 31S 
 
 338. Moraine with outwash apron in front 313 
 
 339. Fosse between an outwash plain and a moraine 314 
 
 340. View along an esker in southern Maine 315 
 
 341. Outline map of moraines and eskers in Finland 315 
 
ILLUSTRATIONS IN THE TEXT XXxi 
 
 FIQ. PAGE 
 
 342. Sketch maps showing the relationships of drumlins and eskers . . 31(> 
 
 343. View of a drumlin, showing an opening in the till .... 317 
 
 344. Outline map of the front of the Green Bay lobe to show the relation- 
 
 ships of drumlins, moraines, outwash plains, and ground moraine 317 
 
 345. Character profiles referable to continental glacier .... 318 
 
 346. View of the flood plain of the ancient Illinois River near Peoria . 320 
 
 347. Broadly terraced valleys which mark the floods that once issued from 
 
 the continental glacier of North America ..... 321 
 
 348. Border drainage about the retreating ice front south of Lake Erie . 321 
 
 349. The " parallel roads " of Glen Roy in the Scottish Highlands . . 322 
 
 350. Map of Glen Roy and neighboring valleys of the Scottish Highlands . 322 
 
 351. Three successive diagrams to set forth the late glacial lake history of 
 
 the Scottish glens 324 
 
 352. Harvesting time on the fertile floor of the glacial Lake Agassiz . . 325 
 
 353. Map of Lake Agassiz 325 
 
 354. Map showing some of the beaches of Lake Agassiz and its outlet . 326 
 
 355. Narrows of the Warren River where it passed between jaws of granite 
 
 and gneiss 327 
 
 356. Map of the valley of the Warren River near Minneapolis . . . 327 
 367. Portion of the Herman beach on the shore of the former Lake Agassiz 328 
 
 358. Map of the continental glacier of North America when it covered the 
 
 entire St. Lawrence basin 329 
 
 359. Outline map of the early Lake Maumee 330 
 
 360. Map to show the first stages of the ice-dammed lakes within the 
 
 St. Lawrence basin . 330 
 
 361. Outline map of the later Lake Maumee and its outlet . . . 332 
 
 362. Outline map of lakes Whittlesey and Saginaw 333 
 
 363. Map of the glacial Lake Warren 333 
 
 364. Map of the glacial Lake Algonquin 334 
 
 366. Outline map of the Nipissing Great Lakes . . . . . . 335 
 
 366. Probable preglacial drainage of the upper Ohio region . . . 337 
 
 367. Diagrams to illustrate the episodes in the recent history of a Con- 
 
 necticut river .......... 338 
 
 368. The notched rock headland of Boyer Bluff on Lake Michigan . . 341 
 
 369. View of Mackinac Island from the direction of St. Ignace . . . 342 
 
 370. The " Sugar Loaf," a stack of Lake Algonquin upon Mackinac Island 342 
 
 371. Beach ridges in series on Mackinac Island 343 
 
 372. Notched stack of the Nipissing Great Lakes at St. Ignace . . .343 
 
 373. Series of diagrams to illustrate the evolution of ideas concerning the 
 
 uplift of the lake region since the Ice Age 344 
 
 374. Map of the Great Lakes region to show the isobases and hinge lines of 
 
 uptilt 345 
 
 375. Series of diagrams to indicate the nature of the recovery of the crust 
 
 by uplift when unloaded of an ice mantle 346 
 
 376. Portion of the Inner Sandusky Bay, for comparison of the shore line 
 
 of 1820 with that of to-day 350 
 
XXxii ILLUSTRATIONS IN THE TEXT 
 
 FIG. PAGE 
 
 377 . Ideal cross section of the Niagara Gorge to show the marginal terrace 353 
 
 378. View of the bed of the Niagara River above the cataract where water 
 
 has been drained off ........ . 353 
 
 379. View of the Falls of St. Anthony in 1851 354 
 
 380. Ideal section to show the nature of the drilling process beneath the 
 
 cataract ........... 355 
 
 381. Plan and section of the gorge, showing how the depth is proportional 
 
 to the width 355 
 
 382. Comparative views of the Canadian Falls in 1827 and 1895 . . 3-56 
 
 383. Map to show the recession of the Canadian Fall .... 357 
 
 384. Comparison of the present with the future falls .... 358 
 
 385. Bird's-eye view of the captured Canadian Fall at Wintergreen Flats 368 
 
 386. Map of the Whirlpool Basin 360 
 
 387. Map of the cuestas which have played so important a part in fixing 
 
 the boundaries of the lake basins 361 
 
 388. Bird's-eye view of the cuestas south of Lakes Ontario and Erie . . 362 
 
 389. Sketch map of the greater portion of the Niagara Gorge to illustrate 
 
 Niagara history .......... 363 
 
 390. Snowdrift hollowing its bed by nivation 368 
 
 391. Amphitheater formed upon a drift site in northern Lapland . . 369 
 
 392. The marginal crevasse on the highest margin of a glacier . . . 370 
 
 393. Niches and cirques in the Bighorn Mountains of Wyoming . . 371 
 
 394. Subordinate cirques in the amphitheater on the west face of the 
 
 Wannehorn 371 
 
 395. "Biscuit cutting" effect of glacial sculpture in the Uinta Mountains 
 
 of Wyoming ........... 372 
 
 396. Diagram to show the cause of the hyperbolic curve of cols . . . 372 
 
 397. A col in the Selkirks 373 
 
 398. Diagrams to illustrate the formation of comb ridges, cols, and horns . 374 
 
 399. The U-shaped Kern Valley in the Sierra Nevadas of California . . 375 
 
 400. Glaciated valley wall, showing the sharp line which separates the 
 
 abraded from the undermined rock surface 375 
 
 401. View of the Vale of Chamonix from the seracs of the Glacier des 
 
 Bossons ........... 376 
 
 402. Map of an area near the continental divide in Colorado . . . 377 
 
 403. Gorge of the Albula River in the Engadine cut through a rock bar . 378 
 
 404. Idealistic sketch, showing glaciated and nonglaciated side valleys . 378 
 
 405. Character profiles sculptured by mountain glaciers .... 379 
 
 406. FlPot dome shape( nder the margin of a Norwegian ice cap . . 379 
 
 407. Two views which .strate successive stages in the shaping of tinds . 380 
 
 408. Schematic diagra- to bring out the relationships of the various types 
 
 of mountain glaciers ......... 383 
 
 409. Map of the Malaspina Glacier of Alaska 384 
 
 410. Map of the Baltoro Glacier of the Himalayas 385 
 
 411. View of the Triest Glacier, a hanging glacieret ..... 385 
 412 Map of the Harriman Fjord Glacier of Alaska 386 
 
ILLUSTRATIONS IN THE TEXT XXXlil 
 
 no. PAGE 
 
 413. Map of the Rotmoos Glacier, a radiating glacier of Switzerland . . 386 
 
 414. Outline map of the Asulkan Glacier in the Selkirks, a horseshoe 
 
 glacier 387 
 
 415. Outline map of the lUecillewaet Glacier of the Selkirks, an inherited- 
 
 basin glacier 388 
 
 416. Diagram to illustrate the surface flow of glaciers .... 390 
 
 417. Diagram to show the transformation of crevasses into seracs . . 391 
 
 418. View of the Glacier des Bossons, showing the position of accidents 
 
 to Alpinists ........... 392 
 
 419. Lines of flow upon the surface of the Hintereisferner Glacier in the 
 
 Alps 393 
 
 420. Lateral and medial moraines of the Mer de Glace and its tributaries . 393 
 
 421. Ideal cross section of a mountain glacier 394 
 
 422. Diagrams to illustrate the melting effects upon glacier ice of rock 
 
 fragments of different sizes ........ 394 
 
 423. Small glacier table upon the Great Aletsch Glacier .... 395 
 
 424. Effects of differential melting and subsequent re-freezing upon a glacier 
 
 surface 396 
 
 425. Dirt cone with its casing in part removed ...... 396 
 
 426. Schematic diagram to show the manner of formation of glacier cornices 397 
 
 427. Superglacial stream upon the Great Aletsch Glacier .... 398 
 
 428. Ideal form of the surface left on the site of a piedmont glacier apron 399 
 
 429. Map of the site of the earlier piedmont glacier of the Upper Rhine . 399 
 
 430. Diagram and map to bring out the characteristics of newland lakes . 402 
 
 431. View of the Warner Lakes, Oregon ....... 402 
 
 432. Schematic diagram to illustrate the characteristics of basin-range lakes 403 
 
 433. Schematic diagram of rift-valley lakes and the valley of the Jordan . 403 
 
 434. Map of the rift-valley lakes of East Central Africa .... 404 
 
 435. Earthquake lakes formed in 1811 in the flood plain of the Lower 
 
 Mississippi ........... 404 
 
 436. View of a crater lake in Costa Rica 405 
 
 437. Diagrams to illustrate the characteristics of crater lakes . . . 406 
 
 438. View of Snag Lake, a coulee lake in California ..... 406 
 4.39. Diagrams to illustrate the characteristics of morainal lakes . . 407 
 
 440. Diagram to show the manner of formation of pit lakes . , . 408 
 
 441. Diagrams to illustrate the characteristics of pit lakes ..... 408 
 
 442. Diagram to show the manner of formation of glint lakes . . . 409 
 
 443. Map of a series of glint lakes on the boundary of Sweden and Norway 409 
 
 444. Map of ice-dam lakes near the Norwegian boundar^' f Sweden . . 410 
 
 445. Wave-cut terrace of a former ice-dam lake in Swe. .... 410 
 
 446. View of the Marjelen Lake from the summit of the jfggishorn . . 411 
 
 447. Diagrams to illustrate the arrangement and the characters of rock- 
 
 basin lakes 412 
 
 448. Convict Lake, a valley-moraine lake of California .... 413 
 
 449. Lake basins produced by successive slides from the steep walls of a 
 
 glaciated mountain valley 414 
 
XXxiv ILLUSTRATIONS IN THE TEXT 
 
 FIG. PAGE 
 
 450. Lake Garda, a border lake upon the site of a piedmont apron , . 414 
 
 451. Diagrams to bring out the characteristics of ox-bow lakes . . . 415 
 
 452. Diagramatic section to illustrate the formation of saucer-like basins 
 
 between the levees of streams on a flood plain .... 415 
 
 453. Saucer lakes upon the bed of the former river Warren . . .416 
 
 454. Levee lakes developed in series within meanders in a delta plain . 417 
 
 455. Kaft lakes along the banks of the Red River in Arkansas and Louisiana 418 
 
 456. Map of the Swiss lakes Thun and Brienz 419 
 
 457. Delta lakes formed at the mouth of the Mississippi .... 419 
 
 458. Delta lakes at the margin of the Nile delta ...... 420 
 
 459. Diagrams to illustrate the characteristics of barrier lakes . . . 420 
 
 460. Dune lakes on the coast of France 421 
 
 461. Sink lakes in Florida, with a schematic diagram to illustrate the 
 
 manner of their formation ........ 421 
 
 462. Map of the Arve and the Upper Rhone 426 
 
 463. View of the Arve and the Rhone at their junction .... 427 
 
 464. A village in Switzerland built upon a strath at the head of Lake 
 
 Poschiavo 428 
 
 465. View of the floating bog and surrounding zones of vegetation in a 
 
 small glacial lake 429 
 
 466. Diagram to show how small lakes are transformed into peat bogs . 430 
 467- Map to show the anomalous position of the delta in Lake St. Clair . 431 
 
 468. A bowlder wall upon the shore of a small lake 432 
 
 469. Diagrams to show the effect of ice shove in producing ice ramparts 
 
 upon the shores of lakes ........ 433 
 
 470. Various forms of ice ramparts 433 
 
 471. Map of Lake Mendota, showing the position of the ridge which forms 
 
 from ice expansion and the ice ramparts upon the shores . . 434 
 
 472. The great multiple mountain arc of Sewestan, British India . . 436 
 
 473. Diagrams to illustrate the theories of origin of mountain arcs . . 437 
 
 474. Festoons of mountain arcs about the borders of the Pacific Ocean . 438 
 
 475. The interrupted Armorican Mountains common to western Europe 
 
 and eastern North America ........ 438 
 
 476. A zone of diverse displacement in the western United States . . 439 
 
 477. Section of an East African block mountain 439 
 
 . 440 
 
 . 441 
 
 . 441 
 
 . 442 
 
 . 443 
 
 . 444 
 
 . 445 
 
 Temagami 
 
 . 445 
 
 . 454 
 
 . 457 
 
 478. Tilted crust blocks in the Queautoweap valley . 
 
 479. View of the laccolite of the Carriso Mountain . 
 
 480. Map of laccolitic mountains ..... 
 
 481. Ideal sections of laccolite and bysmalite 
 
 482. The gabled faQade largely developed in desert landscapes 
 
 483. Balloon view of the Mythen in Switzerland 
 
 484. The battlement type of erosion mountain . 
 
 485. Symmetrically formed low islands repeated in ranks upon 
 
 Lake, Ontario ....... 
 
 486. Forms of crystals of a number of minerals . 
 
 487. Forms of crystals of a number of minerals . 
 
ILLUSTRATIONS IN THE TEXT XXXV 
 
 FIG. PAGE 
 
 488. A student's contour map 469 
 
 489. Models to represent outcrops of rock 472 
 
 490. Special laboratory table set with a problem in geological mapping 
 
 which is solved in Figs, 47 and 48 ..... . 472 
 
 491. Three field maps to be used as suggestions in arranging laboratory- 
 
 table for problems in the preparation of areal geological maps . 473 
 
 492. Sketch map of Western Scotland and the Inner Hebrides to show 
 
 location of some points of special geological interest . . .481 
 
 493. Outline map of a geological pilgrimage across the continent of Europe 483 
 
EXPLANATORY LIST OF ABBREVIATIONS FOR 
 JOURNAL NAMES IN READING REFERENCES 
 
 Am. Geol. : American Geologist. 
 
 Am. Jour. Sci. : American Journal of Science, New Haven. 
 
 Ann. de G^ogr. : Annales de Geographic, Paris. 
 
 Ann. Eept. Geol. and Geogr. Surv. Ter. : Annual Eeport of the Geological and 
 Geographical Survey of the Territories (Hay den), Washington. 
 
 Ann. Kept. Geol. and Nat. Hist. Surv. Minn. : Annual Report of the Geological 
 and Natural History Survey of Minnesota, Minneapolis. 
 
 Ann. Kept. Mich. Geol. Surv. : Annual Report of the Michigan Geological Sur- 
 vey, Lansing. 
 
 Ann. Rept. U. S. Geol. Surv. : Annual Report of the United States Geological 
 Survey, Washington. 
 
 Bull. Am. Geogr. Soc. : Bulletin of the American Geographical Society, New 
 York. 
 
 Bull. Earthq. Inv. Com. Japan : Bulletin of the Earthquake Investigation Com- 
 mittee of Japan, Tokyo. 
 
 Bull. Geogr. Soc. Philadelphia : Bulletin of the Geographical Society of Phila- 
 delphia. 
 
 Bull. Geol. Soc. Am. : Biilletin of the Geological Society of America. 
 
 Bull. Mus. Comp. Zool. : Bulletin of the Museum of Comparative Zoology, 
 Harvard College, Cambridge. 
 
 Bull. N. Y. State Mus. : Bulletin of the New York State Museum, Albany. 
 
 Bull. Soc. Beige d' Astronomic : Bulletin de la Soci6t6 Beige d' Astronomic, 
 Brussels. 
 
 Bull. Soc. Beige G60I. : Bulletin de la Soci6t6 Beige de Geologic, Brussels. 
 
 Bull. Soc. Sc. Nat. Neuchatel : Bulletin de la Soci^t^ des Sciences Naturelles de 
 Neuchatel. 
 
 Bull. Univ. Calif. Dept. Geol. : Bulletin of the University of California, Depart- 
 ment of Geology, Berkeley. 
 
 Bull, U. S. Geol. Surv. : Bulletin of the United States Geological Survey, 
 Washington. 
 
 Bull. Wis. Geol. and Nat. Hist. Surv. : Bulletin of the Wisconsin Geological and 
 Natural History Survey, Madison. 
 
 C. R. Cong. Geol. Intern. : Comptes Rendus de la Congres G^ologique Inter- 
 nationale. 
 
 Dept. of Mines, Geol. Surv. Branch, Canada : Department of Mines, Geological 
 Survey Branch, Canada. 
 
 xxxvii 
 
XXXVm EXPLANATORY LIST OF ABBREVIATIONS 
 
 Geogr. Abh. : Geographiscbe Abhandlungen. 
 
 Geogr. Jour. : Geographical Journal, London. 
 
 Geol. Folio U. S. Geol. Surv. : Geological Folio of the United States Geological 
 Survey. 
 
 Geol. Mag. : Geological Magazine, London (sections designated by decades). 
 
 Jour. Am. Geogr. Soc. : Journal of the American Geographical Society, New- 
 York. 
 
 Jour. Coll. Sci. Imp. Univ. Tokyo : Journal of the College of Science of the 
 Imperial University, Tokyo, Japan. 
 
 Jour. Geol. : Journal of Geology, Chicago. 
 
 Jour. Sch. Geogr. : Journal of School Geography. 
 
 Livret Guide Cong. G60I. Intern. : Livret Guide Congrfes G^ologique Inter- 
 nationale. 
 
 Mem. Geol. Surv. India : Memoirs of the Geological Survey of India, Calcutta. 
 
 Mitt. Geogr. Ges. Hamb. : Mitteilungen der Geographiscbe Gesellschaft, Ham- 
 burg. 
 
 Mon. U. S. Geol. Surv. : Monograph of the United States Geological Survey, 
 "Washington. 
 
 Nat. Geogr. Mag. : National Geographic Magazine, Washington. 
 
 Nat. Geogr. Mon. : National Geographic Monographs, American Book Com- 
 pany, New York. 
 
 Naturw. Wochenschr. : Naturwissenschaftliche Wochenschrift. 
 
 Pet. Mitt. : Petermanns Mittheilungen aus Justus Perthes' Geographischer 
 Anstalt, Gotha. 
 
 Pet. Mitt., Erganzungsh. or Erg. : Petermanns Mittheilungen, Gotha (Ergan- 
 zungsheft or Supplementary Paper). 
 
 Phil. Jour. Sci. : Philippine Journal of Science, Manila. 
 
 Phil. Trans. : Philosophical Transactions of the Royal Society, London. 
 
 Proc. Am. Acad. Arts and Sci. : Proceedings of the American Academy of Arts 
 and Sciences. 
 
 Proc. Am. Assoc. Adv. Sci. : Proceedings of the American Association for the 
 Advancement of Science. 
 
 Proc. Am. Phil. Soc. : Proceedings of the American Philosophical Society, 
 Philadelphia. 
 
 Proc. Bost. Soc. Nat. Hist. : Proceedings of the Boston Society of Natural 
 History, Boston. 
 
 Proc. Ind. Acad. Sci. : Proceedings of the Indiana Academy of Science. 
 
 Proc. Linn. Soc. New South Wales : Proceedings of the Linnean Society of 
 New South Wales. 
 
 Proc. Ohio State Acad. Sci. : Proceedings of the Ohio State Academy of Science. 
 
 Prof. Pap. U. S. Geol. Surv. : Professional Paper of the United States Geologi- 
 cal Survey, Washington. 
 
 Pub. Carneg. Inst. : Publication of the Carnegie Institution of Washington. 
 
 Pub. Mich. Geol. and Biol. Surv. : Publication of the Michigan Geological and 
 Biological Survey, Lansing. 
 
 Quart. Jour. Geol. Soc. Lond. : Quarterly Journal of the Geological Society, 
 London. 
 
EXPLANATORY LIST OF ABBREVIATIONS XXXIX 
 
 Kept. Brit. Assoc. Adv. Sci. : Report of the British Association for the Advance- 
 ment of Science. 
 
 Kept. Geol. Surv. Mich. : Report of the Geological Survey of Michigan, Lansing. 
 
 Rept. Mich. Acad. Sci. : Report of the Michigan Academy of Science, Lansing. 
 
 Rept. Nat. Conserv. Com. : Report of the National Conservation Commission, 
 Washington. 
 
 Rept. Smithson. Inst. : Report of the Smithsonian Institution, Washington. 
 
 Sci. Bull. Brooklyn Inst. Arts and Sci. : Science Bulletin of the Brooklyn Insti- 
 tute of Arts and Sciences. 
 
 Scot. Geogr. Mag. : Scottish Geographic Magazine, Edinburgh. 
 
 Smith. Cont. to Knowl. : Smithsonian Contributions to Knowledge, Washington. 
 
 Tech. Quart. : Technology Quarterly of the Massachusetts Institute of Tech- 
 nology, Boston. 
 
 Trans. Am. Inst. Min. Eng. : Transactions of the American Institute of Mining 
 Engineers, New York. 
 
 Trans. Roy. Dublin Soc. : Transactions of the Royal Dublin Society. 
 
 Trans. Seis. Soc. Japan : Transactions of the Seismological Society of Japan, 
 Tokyo. 
 
 Trans. Wis. Acad, Sci. : Transactions of the Wisconsin Academy of Sciences, 
 Arts, and Letters, Madison. 
 
 U. S. Geogr. and Geol. Surv. Rocky Mt. Region : United States Geographical 
 and Geological Survey of the Rocky Mountain Region (Powell), Wash- 
 ington. 
 
 Zeit. d. Gesell. f . Erdk. z. Berlin : Zeitschrift der Gesellschraft fur Erdkunde 
 zu Berlin. 
 
 Zeit. f. Gletscherk : Zeitschrift fiir Gietscherkunde, Berlin. 
 
EAETH FEATURES AND THEIE MEANING 
 
 CHAPTER I 
 THE COMPILATION OF EARTH HISTORY 
 
 The sources of the history. — The science which deals with the 
 chapters of earth history that antedate the earliest human writ- 
 ings is geology. The pages of the record are the layers of rock 
 which make up the outer shell of our world. Here as in old 
 manuscripts pages are sometimes found to be missing, and on 
 others the writing is largely effaced so as to be indistinct or even 
 illegible. An intelligent interpretation of this record requires a 
 knowledge of the materials and the structure of the earth, as 
 well as a proper conception of the agencies which have caused 
 change and so developed the history. These agencies in opera- 
 tion are physical and chemical processes, and so the sciences of 
 physics and chemistry are fundamental in any extended study of 
 geology. Not only is geology, so to speak, founded upon chemis- 
 try and physics, but its field overlaps that of many other im- 
 portant sciences. The earliest earth history has to do with the 
 form, size, and physical condition of a minor planet in the solar 
 system. The earliest portion of the story belongs therefore to 
 astronomy, and no sharp line can be drawn to separate this chap- 
 ter from those later ones which are more clearly within the domain 
 of geology. 
 
 Subdivisions of geology. — The terms "cosmic geology" and 
 "astronomic geology" have sometimes been used to cover the 
 astronomy of the earth planet. The later earth history develops, 
 among other things, the varied forms of animal and vegetable life 
 which have had a definite order of appearance. Their study is 
 to a large extent zoology and botany, though here considered 
 from an essentially different viewpoint. This subdivision of our 
 science is called paleontological geology or paleontology, which 
 
2 EARTH FEATURES AND THEIR MEANING 
 
 in common usage includes the plant as well as the animal world, 
 or what is sometimes called paleobotany. In order to fix the 
 order of events in geological history, these biological studies are 
 necessary, for the pages of the record have many of them been 
 misplaced as a result of the vicissitudes of earth history, and the 
 remains of life in the rock layers supply a pagination from which 
 it is possible to correctly rearrange the misplaced pages. As com- 
 piled into a consecutive history of the earth since life appeared 
 upon it, we have the division of historical geology ; though this 
 differs but little from stratigraphical geology, 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 
 record. 
 
 So far as they are known to us, the materials of which the 
 earth is composed are minerals grouped into various characteristic 
 aggregates known as rocks. Here the science is founded upon 
 mineralogy as well as chemistry, and a study of the rock materials 
 of the earth is designated petrographical geology or petrography. 
 The various rocks which enter into the composition of the earth's 
 outer shell — the only portion known to us from direct observa- 
 tion — are built into it in an architecture which, when carefully 
 studied, discloses important events in the earth's history. The 
 division of the science which is concerned with earth architecture 
 is geotectonic or structural geology. 
 
 The study of earth features and their significance. — The 
 features upon the surface of the earth have all their deep sig- 
 nificance, and if properly understood, a flood of light is thrown, 
 not only upon present conditions, but upon many chapters of the 
 earth's earlier history. Here the relation of our study to topog- 
 raphy and geography is very close, so that the lines of separa- 
 tion are but ill defined. The terms " physiographical geology," 
 "physiography," and " geomorphology " are concerned with the 
 configuration of the earth's surface — its physiognomy — and with 
 the genesis of its individual surface features. It is this ge- 
 netical side of physiography which separates it from topography 
 and lends it an absorbing interest, though it causes it to largely 
 overlap the division of dynamical geology or the study of 
 geplogical processes. In fact, the difference between dynamical 
 geology and physiography is largely one of emphasis, the stress 
 
THE COMPILATION OF EARTH HISTORY 3 
 
 being laid upon the processes in the former and upon the result- 
 ant features in the latter. 
 
 Under dynamical geology are included important subdivisions, 
 such as seismic geology, or the study of earthquakes, and vul- 
 canology, or the studj^ of volcanoes. Another large subject, 
 glacial geology, belongs within the broad frontier common to both 
 dynamical geology and physiography. A relatively new sub- 
 division of geological science is orientational geology, which is 
 concerned with the trend of earth features, and is closely related 
 both to physiography and to dynamical and structural geology. 
 
 Tabular recapitulation. — In a slightly different arrangement 
 from the above order of mention, the subdivisions of geology are 
 as follows : — 
 
 Subdivisions of Geology 
 
 Petrographical Geology. Materials of the earth. 
 
 Geotectonic Geology. Architecture of the earth's outer 
 
 shell. 
 Dynamical Geology. Earth processes. 
 
 Seismic Geology — earthquakes. 
 Vulcanology — volcanoes. Glacial 
 Geology — glaciers, etc. 
 Physiographical Geology. Earth physiognomy and its 
 
 genesis. 
 Orientational Geology. The arrangement an4_the-..trend. 
 
 '- ~~ ~ " of earth features. 
 
 In one way or another all of the above subdivisions of geology 
 are in some way concerned in the genesis of earth physiognomy, 
 and they must therefore be given consideration in a work which 
 is devoted to a study of the meaning of earth features. The 
 compiled record of the rocks is, however, something quite apart 
 and without pertinence to the present work. As already indicated 
 its subdivisions are : — 
 
 Astronomic Geology. Planetary history of the earth. 
 
 Statigraphic Geology. The pagination of earth records. 
 
 Historical Geology. The compiled record and its inter- 
 
 pretation. 
 Paleontological Geology. The evolution of life upon the earth. 
 
 In every attempt at systematic arrangement difficulties are 
 encountered, usually because no one consideration can be used 
 throughout as the basis of classification. Such terms as " eco- 
 
4 EARTH FEATURES AND THE-IR MEANING 
 
 nomic geology " and " mining geology " have either a pedagogical 
 or a commercial significance, and so would hardly fit into the 
 system which we have outlined. 
 
 Geological processes not universal. — It is inevitable that the 
 geology of regions which are easily accessible for study should 
 have absorbed the larger measure of attention; but it should not 
 be forgotten that geology is concerned with the history of the 
 entire world, and that perspective will be lost and erroneous 
 conclusions drawn if local conditions are kept too often before 
 the eyes. To illustrate by a single instance, the best studied 
 regions of the globe are those in which fairly abundant precipita- 
 tion in the form of rain has fitted the land for easy conditions of 
 life, and has thus permitted the development of a high civilization. 
 In degree, and to some extent also in kind, geologic processes 
 are markedly different within those widely extended regions which, 
 because either arid or cold, have been but ill fitted for human 
 habitation. Yet in the historical development of the earth, those 
 geologic processes which obtain in desert or polar regions are none 
 the less important because less often and less carefully observed. 
 
 Change, and not stability, the order of nature. — Man is ever 
 prone to emphasize the importance of apparent facts to the dis- 
 advantage of those less clearly revealed though equally potent. 
 The ancient notion of the terra firma, the safe and solid ground, 
 arose because of its contrast \\dth the far more mobile bodies of 
 water ; but this illusion is quickly dispelled with the sudden quak- 
 ing of the ground. Experience has clearly shown that, both upon 
 and beneath the earth's surface, chemical and physical changes 
 are going on, subject to but little interruption. " The hills rock- 
 ribbed and ancient as the sun" is a poetical metaphor; for the 
 Himalayas, the loftiest mountains upon the globe, were, to speak 
 in geological terms, raised from the sea but yesterday. Even 
 to-day they are pushing up their heads, only to be relentlessly 
 planed down through the action of the atmosphere, of ice, and of 
 running water. Even more than has generally been supposed, the 
 earth suffers change. Often Avithin the space of a few seconds, 
 to the accompaniment of a heavy earthquake, many square miles 
 of territory are bodily uplifted, while neighboring areas may be 
 relatively depressed. Thus change, and not stability, is the order 
 of nature. ~ "^ 
 
THE COMPIIATION OF EARTH HISTORY 5 
 
 Observational geology versus speculative philosophy. — 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 next ; and this is apt to lead to the belief that little is really 
 known and that much is largely guessed. Some ground there 
 undoubtedly is for such skepticism, though much of it may be 
 accounted for by a general failure among scientists, as well as 
 others, to clearly differentiate that which is essentially speculative 
 from what is based broadly upon observed facts. Even with 
 extended observation, the possibility of explaining the facts in 
 more than one way is not excluded ; but the line is nevertheless 
 a broad one which separates this entire field of observation from 
 what is essentially speculative philosophy. To illustrate : the 
 mechanics of the action which goes on within volcanic craters is 
 now fairly well understood as a result of many and extended 
 observations, and it is little likely that future generations of 
 geologists will discredit the main conclusions which have been 
 reached. The cause of the rise of the lava to the earth's surface 
 is, on the other hand, much less clearly demonstrated, and the 
 views which are held express rather the differing opinions than 
 any clear deductions from observation. Again, and similarly, the 
 physical history of the great continental glaciers of the so-called 
 " ice age "is far more thoroughly known than that of any existing 
 glacier of the same type; but the cause of the climatic changes 
 which brought on the glaciation is still largely a matter for specu- 
 lation. 
 
 In the present work, the attempt will be, so far as possible, to 
 give an exposition of geologic processes and the earth features 
 which result from them, with hints only at those ultimate causes 
 which lie hidden in the background. 
 
 The scientific attitude and temper. — The student of science 
 should make it his aim, not only clearly to separate in his studies 
 the proximate from the ultimate causes of observed phenomena, 
 but he should keep his mind always open for reaching individual 
 conclusions. No doctrines should be accepted finally upon faith 
 merely, but subject rather to his own reasoning processes. 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 authorities; but his acceptance of any theory should 
 
6 EARTH FEATURES AND THEIR MEANING 
 
 be subject to review so soon as his own horizon has been sufficiently 
 enlarged. False theories could hardly have endured so long in the 
 past, had not too great respect been given to authorities, and in- 
 dividual reasoning processes been held too long in subjection. 
 
 The value of the hypothesis. — Because all the facts necessary 
 for a full interpretation of observed phenomena are not at one's 
 hand, this should not be made to stand in the way of provisional 
 explanations. If science is to advance, the use of hypothesis is 
 absolutely essential ; 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 it. Thus 
 regarded with an open mind, inadequate hypotheses are eventu- 
 ally found to be untenable, whereas correct explanations of the 
 facts by the same process are confirmed. Most hypotheses of 
 science are but partially correct, for we now " see through a glass 
 darkly " ; but even so, if properly tested, the false elements in the 
 hypothesis are one after the other eliminated as the embodied 
 truth is confirmed and enlarged. Thus "working hypothesis" 
 passes into theory and becomes an integral part of science. 
 
 Reading References for Chapter I 
 
 The most comprehensive of general geological texts written in English is 
 Chamberlin and Salisbury's " Geology " in three volumes (Henry Holt, 
 1904-1906), the first volume of which is devoted exclusively to geological 
 processes and their results. An abridged one-volume edition of the work 
 intended for use as a college text was issued in 1906 (CoUege Geology, 
 Henry Holt). Other standard texts are : — 
 
 Sir Archibald Geikie. Text-book of Geology, 4th ed. 2 vols. Lon- 
 don, 1902, pp. 1472. 
 
 W. B. Scott. An Introduction to Geology. 2d^ ed. Macmhlan, 1907, 
 pp. 816. 
 
 J. D. Dana. Manual of Geology. New edition. American Book Com- 
 pany, 1895, pp. 1087. 
 
 Joseph LeConte. Elements of Geology. (Revised by Faircbild.) 
 Appleton, 1905, pp. 667. 
 
 A very valuable guide to the recent literature of dynamical and struc- 
 tural geology is Branner's "SyUabus of a Course of Lectures on Elemen- 
 tary Geology" (Stanford University, 1908). 
 
 On the relation of geology to landscape, a number of interesting books 
 have been written : — 
 
 James Geikie. Earth Sculpture or the Origin of Land-Forms. New 
 York and London, 1896, pp. 397. 
 
THE COMPILATION OF EARTH HISTORY 7 
 
 John E. Marr. The Scientific Study of Scenery. Methuen, London, 
 
 1900, pp. 368. 
 
 Sir a. Geikie. The Scenery of Scotland. 3d ed. Macmillan, London, 
 
 1901, pp. 540. 
 
 Sir John Lubbock. The Scenery of Switzerland and the Causes to which 
 it is Due. Macmillan, London, 1896, pp. 480. 
 
 Lord Avebury. The Scenery of England. Macmillan, London, 1902, 
 pp. 534. 
 
 Sir a. Geikie. Landscape in History, and Other Essays. Macmillan, 
 London, 1905, pp. 352. 
 
 N. S. Shaler. Aspects of the Earth. Scribners, New York, 1889, pp. 344. 
 
 G. DE La Noe et Emm. de Margerie. Les Formes du Terrain, Service 
 Geographique de I'Armee. Paris, 1888, pp. 205, pis. 48. 
 
 W. M. Davis. Practical Exercises in Physical Geography, with Accom- 
 panying Atlas. Ginn and Co., Boston, 1908, pp. 148, pis. 45. 
 
 JohnMuir. The Mountains of Calif ornia. Unwin, London, 1894, pp. 381. 
 
 Upon the use and interpretation of topographic maps in illustration of 
 characteristic earth features, the following are recommended : — 
 R. D. Salisbury and W. W. Atwood. The Interpretation of Topo- 
 graphic Maps, Prof. Pap., 60 U.S. Geol. Surv., pp. 84, pis. 170. 
 D. W. Johnson and F. E. Matthes. The Relation of Geology to 
 Topography, in Breed and Hosmer's Principles and Practice of Sur- 
 veying, vol. 2. Wiley, New York, 1908. 
 General Berth aut. Topologie, Etude du Terrain, Service Geogra- 
 phique de I'Armee. Paris, 1909, 2 vols., pp. 330 and 674, pis. 265. 
 
 The United States Geological Survey issues free of charge a list of 
 100 topographic altas sheets which illustrate the more important physi- 
 ographic types. In his " Traite de Geographie Physique," Professor E. de 
 Martonne has given at the end of each chapter the important foreign 
 maps which illustrate the physiographic types there described. 
 
 " The Principles of Geology," by Sir Charles Lyell, published first in three 
 volumes, appeared in the years 1830-1833, and may be said to mark the 
 beginning of modern geology. Later reduced to two volumes, an eleventh 
 edition of the work was issued in 1872 (Appleton) and may be profitably 
 read and studied to-day by all students of geology. Those familiar with 
 the German language will derive both pleasure and profit from a perusal 
 of Neumayr's " Erdgeschichte " (2d ed. revised by Uhlig. Leipzig and 
 Vienna, 2 vols., 1895-1897), and especially the first volume, "Allgemeine 
 Geologie." A recent French work to be recommended is Haug's "Traite 
 de Geologie" (Paris, 1907). 
 
 Some texts of physical geography may well be consulted, especially 
 Emm. de Martonne's " Traite de Geographie Physique." Colin, Paris, 
 1909, pp. 910, pis. 48, and figs. 396. 
 
 Note. An explanatory list of abbreviations used in the reading refer- 
 ences follows the List of Illustrations. 
 
CHAPTER II 
 THE FIGURE OF THE EARTH 
 
 The lithosphere and its envelopes. — The stony part of the 
 earth is known as the lithosphere, of which only a thin surface 
 shell is known to us from direct observation. The relatively un- 
 known central portion, or '/ core," is sometimes referred to as the 
 centrosphere. Inclosing the lithosphere is a water envelope, the 
 hydrosphere, which comprises the oceans and inland bodies of 
 water, "and has a mass 45V0 that of the lithosphere. If uniformly 
 distributed, the hydrosphere would cover the lithosphere to the 
 depth of about two miles, instead of being collected in basins as it 
 now is. Though apparently not continuous, if we take into account 
 the zone of underground water upon the continents, the hydro- 
 sphere may properly be considered as a continuous film about the 
 lithosphere. It is a fact of much significance that all the ocean 
 basins are connected, so that the levels are adjusted to furnish a 
 common record of deposits over the entire surface that is sea- 
 covered. 
 
 Enveloping the hydrosphere is the gaseous envelope, the atmos- 
 phere, with a mass ttt^o'o that of the lithosphere. The atmos- 
 phere is a mixture of the gases oxygen and nitrogen in parts by 
 volume of one of the former to four of the latter, with a relatively 
 small percentage of carbon dioxide. Locally, and at special 
 seasons, the atmosphere may be charged with relatively large 
 percentages of water vapor ; 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 climate. Unlike 
 the water which composes the hydrosphere, the gases of the 
 atmosphere are compressible. Forced down by the weight of 
 superincumbent gas, the layers of the atmosphere at the level of 
 the sea sustain a pressure of about fifteen pounds to the square 
 inch ; but this pressure steadily decreases in ascending to higher 
 levels. From direct instrumental observation, the air has now 
 
 8 
 
THE FIGURE OF THE EARTH 9 
 
 been investigated to a height of more than twelve miles from the 
 earth's surface. 
 
 The evolution of ideas concerning the earth's figure. — The 
 ideas which in all ages have been promulgated concerning the 
 figure of the earth have been many and varied. Though among 
 them are not wanting the purely speculative and fantastic, it will 
 be interesting to pass in review such theories as have grown directly 
 out of observation. 
 
 The ancient Hebrews and the Babylonians were dwellers of the 
 desert, and in the mountains which bounded their horizon they 
 saw the confines of the earth. Pushing at last westward beyond 
 the mountains, they found the Mediterranean, and thus arrived at 
 the view that the earth was a disk with a rim of mountains which 
 was floated upon water. 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 '' windows of heaven " 
 the water " which is above the earth " was poured out upon the 
 earth's surface. Fantastic as this theory may seem to-day, it 
 was founded upon observation, and it well illustrates the dangers 
 of reasoning from observation within too limited a field. 
 
 As soon as men began to sail the sea, it was noticed that the 
 water surface is convex, for the masts of ships were found to remain 
 visible long after their hulls had disappeared below the horizon. 
 It is difficult to say how soon the idea of the earth's rotundity was 
 acquired, but it is certainly of great antiquity. The Dominican 
 monk Vincentius of Beauvais, in a work completed in 1244, declared 
 that the surfaces of the earth and the sea were both spherical. 
 The poet Dante made it clear that these surfaces were one, and 
 in his famous address upon " The Water and the Land," which 
 was delivered in Verona on the 20th of January, 1320, he added 
 a statement that the continents rise higher than the ocean. His 
 explanation of this was that the continents are pulled up by the 
 attraction of the fixed stars after the manner of attraction of 
 magnets, thus giving an early hint of the force of gravitation. 
 
 The earth's rotundity may be said to have been first proven 
 when Magellan's ships in 1521 had accomplished the circumnavi- 
 gation of the globe. Circumnavigation, soon after again carried 
 
10 EARTH FEATURES AND THEIR MEANING 
 
 out by Sir Francis Drake, proved that the earth is a closed body 
 bounded by curving surfaces in part enveloped by the oceans and 
 everywhere by the atmosphere. The great discovery of Copernicus 
 in 1530 that the earth, like Venus, Mars, and the other planets, 
 revolves about the sun as a part of a system, left little room for 
 doubt that the figure of the earth was essentially that of a sphere. 
 
 The oblateness of the earth. — Every schoolboy is to-day fa- 
 miliar with the fact that the earth departs from a perfect spherical 
 figure by being flattened at the ends of its axis of rotation. The 
 polar diameter is usually given as 2^^ shorter than the equatorial 
 one. 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 latitudes. 
 
 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 plastic, and hence more re- 
 sponsive to deformation. An elastic hoop rotating rapidly about 
 an axis in its plane appears to the eye as a solid, and becomes 
 flattened at the ends of its axis in proportion as the velocity of 
 rotation is increased. Like the earth, the other planets in the 
 solar system are similarly oblate and by amounts dependent on the 
 relative velocities of rotation. 
 
 The departure of the geoid from the spherical surface, owing to 
 its oblateness, is so small that in the figures which we shall use for 
 illustration it would be less than the thickness of a line. Since it 
 is well recognized and not important in our present consideration, 
 we shall for the time being speak of the figure of the earth in terms 
 of departures from a standard spherical surface. 
 
 The arrangement of oceans and continents. — There are other 
 departures from a spherical surface than the oblateness just re- 
 ferred to, and these departures, while not large, are believed to be 
 full of significance. Lest the reader should gain a wrong impres- 
 sion of their magnitude, it may be well to introduce a diagram 
 drawn to scale and representing prominent elevations and depres- 
 sions of the earth (Fig. 1). 
 
 Wrong impressions concerning the figure of the lithosphere are 
 sometimes gained because its depressions are obliterated by the 
 oceans. The oceans are, indeed, useful to us in showing where 
 the depressions are located, but the figure of the earth which we 
 
THE FIGURE OF THE EARTH 
 
 11 
 
 Gr-ea-Z-esf- c/eejos 
 
 VepT/j ci!^7^t^_eqrt;/7's_r^^ius_ 
 
 a 
 
 Fig. 1. — Diagrams to afford 
 a correct impression of the 
 measure of the iuequalities 
 upon the earth's surface com- 
 pared to the earth's radius. 
 The shell represented in h is 
 1J5 of the earth's radius, and 
 in a this zone is magnified 
 for comparison with surface 
 inequalities. 
 
 are considering is the naked surface of the rock. In a broad way, 
 the earth's shape will be given by the arrangement of the oceans 
 and the continents. As 
 soon as we take up the 
 study of this arrangement, 
 we find that quite signifi- 
 cant facts of distribution 
 are disclosed. 
 
 One of the most signifi- 
 cant facts involved in the 
 distribution of land and 
 sea, is a concentration of 
 the land areas within the 
 northern and the seas 
 within the southern hemi- 
 sphere. The noteworthy 
 exception is the occurrence 
 of the great and high 
 Antarctic continent cen- 
 tered near the earth's 
 
 south pole ; and there are extensions of the northern 
 continent as narrowing land masses to the southward 
 of the equator. Hardly less significant than the ex- 
 istence of land and water hemispheres is the reciprocal 
 or antipodal distribution of land and sea (Fig. 2). 
 A third fact of significance is a dovetailing together of sea and 
 
 land along an east- 
 and-west direction. 
 While the seas are 
 generally A-shaped 
 and narrow north- 
 ward, the land masses 
 are V-shaped and nar- 
 row southward, hut 
 this occurs mainly in 
 the southern hemi- 
 sphere. Lastly, there 
 is some indication of 
 a belt of sea dividing 
 
 Fig. 2. — Map on Mercator's projection to show the 
 reciprocal relation of the land and sea areas (after 
 Gregory and Arldt). 
 
12 
 
 EARTH FEATURES AND THEIR MEANING 
 
 Angara 
 
 the land masses into northern and southern portions along the 
 course of a great circle which makes a small angle with the earth's 
 equator. Thus the western continent is nearly divided by a 
 mediterranean sea, — the Caribbean, — and the eastern is in part 
 so divided by the separation of Europe from Africa. 
 
 The figure toward which the earth is tending. — Thus far in 
 our discussion of the earth's figure we have been guided entirely 
 
 by the present dis- 
 tribution of land and 
 water. There are, 
 however, depres- 
 sions upon the sur- 
 face of the land, in 
 some cases extend- 
 ing below the level 
 of the sea, which are 
 not to-day occupied 
 by water. By far 
 the most notable of 
 these is the great 
 Caspian Depression, 
 which with its ex- 
 tension divides cen- 
 tral and eastern Asia 
 upon the east from Africa and Europe upon the west. This 
 depression was quite recently occupied by the sea, and when 
 added to the present ocean basins to indicate depressions of the 
 lithosphere, it shows that the earth's figure departs from the 
 standard spheroid in the direction of the form represented in 
 Fig. 3. This form approximates to a tetrahedron, a figure bounded 
 by four equal triangular faces, here with symmetrically truncated 
 angles. Of all regular figures with plane surfaces the tetrahedron 
 has the smallest volume for a given surface, and it presents more- 
 over a reciprocal relation of projection to depression. Every 
 line passing through its center thus finds the surface nearer than 
 the average distance upon one side and correspondingly farther 
 upon the other (Fig. 4). 
 
 Astronomical versus geodetic observations. — Confirmation of 
 the conclusions arrived at from the arrangement of oceans and 
 
 Fig. 3. — The form toward which the figure of the earth 
 is tending, a tetrahedron with symmetrically truncated 
 angles. 
 
THE FIGURE OF THE EARTH 
 
 13 
 
 continents has been secured in other fields. 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 latitudes, the degree being found longer as the pole is 
 approached. Any variation from the spherical surface must ob- 
 viously increase the size of the measured degree of latitude in 
 proportion to the departure from the standard form, 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 hemisphere. This 
 has been found by measure- 
 ment to be the case, and the 
 result is further confirmed by 
 pendulum studies upon the 
 distribution of the earth's at- 
 traction or gravity. If less of 
 the mass of the earth is con- 
 centrated in the southern 
 hemisphere, its attraction as 
 measured in vibrations of 
 the pendulum should be cor- 
 respondingly smaller. 
 
 Other confirmations of the tetrahedral figure of the earth have 
 been derived from a comparison of astronomical data, which assume 
 the earth to be a perfect spheroid, with geodetic measurements, 
 which are based upon direct measurements. Thus the arc meas- 
 ured in an east-and-west direction across Europe revealed a differ- 
 ent curvature near the angle of the tetrahedral figure from what 
 was found farther to the eastward. 
 
 Changes of figure during contraction of a spherical body. — If 
 we inquire why the earth in cooling should tend to approach the 
 tetrahedral figure, an answer is easily found. When formed, 
 the earth appears to have been a but slightly oblate spheroid, 
 or practically a sphere — the shape which of all incloses the 
 piost space for a given surface. Cooled and solidified at the sur- 
 face to the temperature of the surrounding air, and the core 
 still hot and continuing to lose heat, the core must continue to 
 
 Fig. 4. — A truncated tetrahedron, showing 
 how the depression upon one side of the cen- 
 ter is balanced by the opposite projection. 
 
14 EARTH FEATURES AND THEIR MEANING 
 
 contract though the outer shell is no longer able to do so. The 
 superficial area being thus maintained constant while the volume 
 continues to diminish, the figure must change from the initial one 
 of greatest bulk to others of smaller volume, and ultimately, if the 
 process should continue indefinitely, to the tetrahedron, which of 
 all regular figures has the minimum volume for a given surface. 
 
 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 balloons, as well as by experiments 
 upon the exhaustion of air contained in hollow metal spheres of 
 only moderate strength. In all these instances, the ultimate 
 form produced indicates an indenting of four sides of the sphere 
 which have the positions of the faces of a tetrahedron. The late 
 Professor Prinz of Brussels secured some extremely interesting 
 results in which he obtained intermediate forms with six angles, 
 but unfortunately these studies were not prepared for publication 
 at the time of his death. 
 
 The earth's departure from the spheroid in the direction of the 
 modified tetrahedron is, as we have seen, no hypothesis, but ob- 
 served fact revealed in (1) the concentration of the land about 
 a central ocean in the northern hemisphere; in (2) the antipodal 
 relation of the land to the water areas, and in (3) the threefold 
 subdivision of the surface into north and south belts by the two 
 greater oceans and the Caspian Depression. 
 
 The earlier figures of the earth. — The manner in which conti- 
 nent 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 described. Closer examination 
 shows that instead of being in harmony with this figure, it indi- 
 cates a departure from it, and, as we shall see, a significant depar- 
 ture which undoubtedly has its origin in the earlier history of 
 the planet. The mediterranean seas of both the eastern and the 
 western hemispheres likewise interfere with the perfection of the 
 tetrahedral figure and require an explanation. 
 
 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 change. It is now well 
 known that there have been three major periods of great deforma- 
 tion of the earth's shell. The fi^rst of these of which we have 
 
THE FIGURE OF THE EARTH 
 
 15 
 
 record came at the end of the first great era of geologic history, 
 the so-called Eozoic era; a second great transformation came at 
 the close of the second or Paleozoic era ; and a third began at the 
 end of the next or Mesozoic era, an adjustment which is apparently 
 continuing to-day. Each of these great surface deformations was 
 accompanied by great volcanic eruptions of which we have the 
 evidence in the lavas remaining for our inspection, and each was 
 followed by the formation of great glaciers which spread over 
 large areas of the existing continents. 
 
 Before the earliest of these great changes, the earth appears to 
 have approximated in its figure somewhat closely to the ideal 
 spheroid, for it was everywhere enveloped in the hydrosphere as a 
 universal ocean. Toward the close of this period came the adjust- 
 ments which brought the lithosphere to protrude through the 
 hydrosphere in shield-like continents whose distribution, as shown 
 by the rocks of this period, is of great significance. Within the 
 northern hemisphere rose three land shields spaced at nearly 
 equal intervals and at nearly equal distances from the northern 
 pole. One of these was centered where now is Hudson Bay, 
 another about the present Baltic Sea, and the relics of the third 
 are found in northeastern Siberia. These earliest continents 
 have been referred to as the Laurentian, Baltic, and Angara shields. 
 Within the southern hemisphere shields appear to have developed 
 
 At e/YO or £^o20/c ^fiA 
 
 Wr £/VO Of FiA^EOZOiC Ef^A 
 
 T/f£: f'/=l£^£tlT 
 
 Fig. 5. — Approximations to earlier and present figures of the earth. 
 
 in somewhat similar grouping, namely, in South America, in South 
 Africa, and in Australia (Figs. 3 and 5). 
 
 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 time, and have been enlarged 
 by the growth of sediments about them as well as by the later 
 
16 EARTH FEATURES AND THEIR MEANING 
 
 elevation and wrinkling of these deposits into marginal mountain 
 ranges. 
 
 The continents and oceans which arose at the close of the 
 Paleozoic era. — At the close of the second great era in the recorded 
 
 history of the earth, the now somewhat enlarged continents were 
 profoundly altered during a series of convulsive movements within 
 the surface shell of the lithosphere. When these convulsions were 
 over, there was a new disposition of land and sea, but one quite 
 different from the present arrangement. Instead of being ex- 
 tended in north-south belts, as they are at present, the continents 
 stretched out in broad east-west zones, one in the northern and 
 the other in the southern hemisphere. To the broad southern 
 continent of which so little now remains, the name " Gondwana 
 Land " has been given, and to the sea which divided the northern 
 from the southern continent the name "Ocean of Tethys." The 
 northern continent stretched across the site of the present Atlantic 
 Ocean as the '' North Atlantis," its northern shore to the west- 
 ward being somewhat farther south than the present northern 
 coast of North America, since life forms migrated in the north- 
 ern ocean from the site of Behring Sea to that of the present 
 North Atlantic. 
 
 This arrangement of land and water during the middle period 
 of the earth's recorded history, when considered with reference 
 both to its earlier and to its later evolution, may perhaps be best 
 accounted for by the assumption that the lithosphere was then 
 shaped like Fig. 5 (middle). In this figure two truncated tetra- 
 hedrons are joined in a common plane of contact which may be 
 described as the twin plane. This medial depression upon the 
 lithosphere was occupied by the intercontinental sea, the Ocean of 
 Tethys. 
 
 Near the close of this second great era of the earth's conti- 
 nental history, crustal convulsions, which were perhaps the most 
 remarkable in the entire record, resulted in the almost complete 
 disappearance of the southern continent and a concentration of 
 the land within the northern hemisphere as a somewhat inter- 
 rupted belt surrounding a central polar ocean (Figs. 3 and 5). 
 
 Upon the assumption of twin tetrahedrons in the intermediate 
 era of continental evolution, both the Ocean of Tethys of that 
 time and its present remnants, the Caribbean and Mediterranean 
 
THE FIGURE OF THE EARTH 
 
 17 
 
 Terra he cfra/ /^ces mth A/oejr fo Sou/-/? 
 
 seas, are accounted for. The V-shaped continent extensions 
 and the A-shaped oceans of the southern hemisphere (Fig. 2) may 
 likewise be considered as rehcs of the now largely submerged tet- 
 rahedron of the southern hemisphere, since this had its apex to the 
 northward (Fig. 6). 
 
 Thus we see that the lithosphere can scarcely be regarded as a 
 perfect spheroid, since in the course of geologic ages it has under- 
 gone successive de- 
 partures from this 
 original form. In 
 its present state it 
 has been described 
 as tetrahedral, 
 though we must 
 keep in mind that 
 the sharp angles 
 of that figure are 
 deeply truncated. 
 The soundings 
 first by Nansen 
 and more recently 
 by Peary in the 
 Arctic basin, far 
 to the north of the 
 continental bor- 
 der, showed that this depression is characterized by profound 
 depths, and so have afforded confirmation of the tetrahedral fig- 
 ure. To match this depression at the northern extremity of the 
 earth's axis, a high continent reaching to elevations in excess of 
 10,000 feet has been penetrated by Sir Ernest Shackleton at the 
 opposite extremity of this polar diameter. Considering its size 
 and its elevation, the Antarctic continent with its glacier mantle 
 is the largest protuberance upon the surface of the lithosphere. 
 
 In our study of the departures of the earth from the standard 
 spheroidal surface, we might even go a step farther and show how 
 the tetrahedron, which best represents the symmetry of the present 
 figure, is somewhat deformed by a flattening perpendicular to the 
 Pacific Ocean. To draw attention to this flattening of the earth, 
 it has sometimes been described as '' potato-shaped," since the 
 
 7er/~ahBe/ra/ Fiices y^/^/r ^pejr to AAsfth 
 Actifo/ //»es //? <SeH/f/7ern H'em/'Sjo/;ere. 
 
 Fig. 6. — Diagrams for comparison of shore lines upon 
 tetrahedrons which have an angle, the first at the south 
 and the second at the north. 
 
18 
 
 EARTH FEATURES AND THEIR MEANING 
 
 outline perpendicular to this face is imperfectly heart-shaped or 
 like a flattened " peg top." 
 
 The flooded portions of the present continents. — We are accus- 
 tomed to think of the continents as ending at the shores of the 
 
 oceans. If, however, we 
 are to regard them as 
 platforms which rise 
 from the ocean depres- 
 sions, their margins 
 should be considerably 
 extended, for a sub- 
 merged shelf now prac- 
 tically surrounds all the 
 continents to a nearly 
 uniform depth of 100 
 fathoms or 600 feet. 
 The oceans thus more than fill their basins and may be thought of 
 as spilling over upon the continents. In Fig. 7, the submerged por- 
 tions of the continents have been joined to those usually represented, 
 thus adding about 10,000,000 square miles to their area, and giving 
 them one third, instead of one fourth, of the lithosphere surface. 
 
 The floors of the hydrosphere and atmosphere. — The highest 
 altitudes upon the continents and the profoundest deeps of the 
 
 '3QOaOFf: 
 
 
 
 /r/~/ 
 
 — ' i\ 
 
 / / /\ 
 
 ^x^ 
 
 W'i/ 
 
 PviA 
 
 
 _Wh 
 
 AW^ 
 
 ~4U?J 
 
 
 ~^gy 
 
 \Vc 
 
 ~i^M/ 
 
 
 ^^^ 
 
 ^^ 
 
 ^^^ 
 
 Fig. 7. 
 
 ■The continents with submerged portions 
 added (after Gilbert). 
 
 wo.ooo 
 
 -20,000 
 
 •JiiOOO/h 
 Fig. 8. 
 
 1 h i 
 
 
 \^__J_^ 
 
 
 
 /: J. 
 
 : .JO 
 
 ■Diagram to indicate the altitude of different parts of the 
 lithosphere surface. 
 
 ocean are each removed about 30,000 feet, or nearly 6 miles, 
 from the level of the sea. In comparison with the entire surface 
 of the lithosphere, these extremes of elevation represent such 
 
 small areas as to be almost inappreciable. 
 
 Only about -^ 
 
 of the 
 
THE FIGURE OF THE EARTH 19 
 
 lithosphere surface rises more than 6000 feet above sea level, 
 and about the same proportion lies deeper than 18,000 feet below 
 the same datum plane (Fig. 8). Almost the entire area of the 
 lithosphere is included either in the so-called continental plateau 
 or platform, in the oceanic platform, or in the slope which separates 
 the two. The continental platform includes the continental shelf 
 above referred to, and represents about one third of the entire 
 area of the planet. This platform has a range of elevation from 
 6000 feet above to 600 feet below sea level and has an average 
 altitude of about 2300 feet. The oceanic platform slopes more 
 steeply, ranges in depth from 12,000 to 18,000 feet below sea level, 
 and comprises about one half the lithosphere surface. The 
 remaining portion of the surface, something less than one eighth 
 of all, is included in the steep slopes between the two platforms, 
 between 600 and 12,000 feet below sea. The two platforms and 
 the slope between them must not, however, be thought of as 
 continuous features upon the surface, but merely as representing 
 the average elevations of portions of the lithosphere. 
 
 Reading References for Chapter II 
 On the evolution of ideas concerning the earth's figure : — 
 SuEss. The Face of the Earth (Clarendon Press, 1906), vol. 2, Chapter 1. 
 V. ZiTTEL. History of Geology and Paleontology (Walter Scott, Lon- 
 don, 1901), Chapters 1-2. 
 
 The departure of the spheroid toward the tetrahedron : — 
 
 W. LowTHiAN Green. Vestiges of the Molten Globe, Part 1. London, 1875„ 
 (Now a rare work, but it contains the original statement of the idea.) 
 
 J. W. Gregory. The Plan of the Earth and Its Causes, Geogr. Jour., 
 vol. 13, 1899, pp. 225-251 (the best general statement of the argu- 
 ments for a tetrahedral form). 
 
 W. Prinz. L'echelle reduite des experiences geologiques, Bull. Soc. Beige 
 d'Astronomie, 1899. 
 
 B. K. Emerson. The Tetrahedral Earth and Zone of the Interconti- 
 nental Seas, Bull. Geol. Soc. Am., vol. 11, 1911, pp. 61-106, pis. 9-14. 
 
 M. P. RuDSKi. Physik der Erde (Tauchnitz, Leipzig, 1911), Chapters 
 1-3 (the best discussion of the geoid from the purely mathematical 
 standpoint, so far as the spheroid is concerned). 
 
 The earlier figures of the earth : — • 
 Th. Arldt. Die Entwicklung der Kontinente und ihrer Lebewelt. Engel- 
 mann, Leipzig, 1907. (Contains a valuable series of map plates, 
 showing the probable boundaries of the continents in the different 
 geological periods). 
 
CHAPTER III 
 THE NATURE OF THE MATERIALS IN THE LITHOSPHERE 
 
 The rigid quality of our planet. — For a long time it was sup- 
 posed that the solid earth constituted a crust only which was 
 floated upon a liquid interior. This notion was clearly an out- 
 growth of the then generally accepted Laplacian hypothesis of 
 the origin of the universe, which assumed fluid interiors for the 
 planets, the crust being suggested by the winter crust of frozen 
 water upon the surface of our inland lakes. To-day the nebular 
 hypothesis in the Laplacian form is fast giving place to quite 
 different conceptions, in which solid particles, and not gaseous 
 ones, are conceived to have built up the lithosphere. The analogy 
 with frozen water has likewise been abandoned with the discovery 
 that frozen rock, instead of floating, sinks in its molten equivalent. 
 
 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 bodies. Provisionally, therefore, we 
 may regard the earth's core as rigid and essentially solid. It was 
 long ago pointed out by the late Lord Kelvin that if our litho- 
 sphere were not more rigid than a ball of glass of the same size, it 
 would be constantly passing through periodic six-hourly distortions 
 of great amplitude in response to the varying attractions of the 
 moon. An equally striking argument emanating from the same 
 high authority is furnished by the well-known egg-spinning demon- 
 stration. For illustration, Kelvin was accustomed to take two 
 eggs, one boiled and the other raw, and attempt to spin them 
 upon their ends. For the boiled, and essentially solid, egg this is 
 easily accomplished, but internal friction of the liquid contents of 
 the raw egg quickly stops any rotary motion which is imparted to 
 it. Upon the same grounds it is argued that had the earth's 
 interior possessed the properties of a liquid, rotation must long 
 since have ceased. 
 
 20 
 
NATURE OF THE MATERIALS IN THE LITHOSPHERE 21 
 
 A stronger proof of earth rigidity than either of these has been 
 lately furnished by the instrumental study of earthquakes. With 
 the delicate apparatus which is now installed for the purpose, 
 heavy earthquakes may be sensed which have occurred anywhere 
 upon the earth's surface, the earth movement sending its own 
 message by the shortest route through the core of the earth to the 
 observing station. A heavy shock which occurs in New Zealand 
 is recorded in England, almost diametrically opposite, in about 
 twenty-one minutes after its occurrence. The laws of wave 
 propagation and their relation to the properties of the transmitting 
 medium are well known, 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 steel. 
 
 Probable composition of the earth's core. — In deriving views 
 concerning the nature of the earth's interior we are greatly aided 
 by astronomical studies. 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 spectroscope. 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 bodies. 
 Again, the group of planets of the solar system which are nearest 
 to the sun — Mercury, Venus, the Earth, and Mars — have each 
 a high density, all except Mars, the most distant, having specific 
 gravities very closely 5|, that of Mars being about 4. This 
 average specific gravity is also that of the solid bodies, the so-called 
 meteorites, which reach the surface of our planet from the sur- 
 rounding space. Yet though the earth as a whole is thus found 
 to have a specific gravity five and a half times that of water, its 
 surface shell has an average density of less than half this value, 
 or 2.7. 
 
 The study of meteorites has given us a possible clew to the 
 nature of the earth's interior; for when both terrestrial and 
 celestial rock types are classified and placed in orderly arrange- 
 ment, it is found that the chemical elements which compose the 
 two groups are identical, and that these are united according to 
 the same physical and chemical laws. No new element has been 
 discovered in the one group that has not been found in the other, 
 and though some compounds of these elements, the minerals, oc- 
 cur in the earth's crust that have not been found in meteorites, 
 
22 
 
 EARTH FEATURES AND THEIR MEANING 
 
 and though some occur in meteorites which are not known from 
 the earth, yet of those which are common to both bodies there is 
 agreement, even to the minor details (Fig. 9). It is found, how- 
 ever, that the commonest of the minerals in the earth's shell are 
 absent from meteorites, as the commoner constituents of meteor- 
 ites are wanting in the earth's crust. This observation would go 
 far to show that we may in the two cases be examining different 
 
 TerresTr/cr/ /^gc/fs. 
 
 a 
 
 A/eteor/Tes anc^ rarer Terrestr/a/ ffocAe. 
 
 Fig. 9. — Diagram to show how terrestrial rocks grade into those of the meteorites. 
 1, oxygen ; 2, silicon ; 3, aluminium ; 4, alkali metals; 5, alkaline earth metals; 
 6, iron, nickel, cobalt, etc. ; a, granites and rhyolites ; 6, syenites and trachytes ; 
 c, diorites and andesites ; d, gabbros and basalts ; e, ultra-basic rocks ; /, basic 
 inclosures in basalt, etc. ; g, iron basalts of west Greenland ; h, iron masses of 
 Ovifak, west Greenland ; a'-d', meteorites in order of density (after Judd) . 
 
 portions of quite similar bodies ; and this view is strikingly con- 
 firmed when the rocks of the two groups are arranged in the order 
 of their densities (Fig. 9) . 
 
 In a broad way, density, structure, and chemical composition 
 are all similarly involved in the gradations illustrated by the 
 diagram ; and it is significant that while there are terrestrial rocks 
 not represented by meteorites, the densest and the most unusual 
 of the terrestrial rocks are chemically almost identical with the 
 less dense of the celestial bodies. 
 
NATURE OF THE MATERIALS IN THE LITHOSPHERE 23 
 
 The earth a magnet. — The denser, and likewise the more 
 common, of the meteorite rocks — the so-called meteoric irons — 
 are composed almost entirely of the elements iron, nickel, and 
 cobalt. Such aggregates are not known as yet from terrestrial 
 sources, although transitional types appear to exist upon the 
 island of Disco off the west coast of Greenland. If it were pos- 
 sible to explore the earth's interior, would such combinations of 
 the iron minerals be encountered? Apart from the surprising 
 velocity of transmission of earthquake waves, the strongest argu- 
 ment for an iron core to the lithosphere is found in the magnetic 
 property of the earth as a whole. The only magnetic elements 
 known to us are those of the heavy meteorites — iron, nickel, 
 and cobalt, — and the earth is, as we know, a great magnet whose 
 northern pole in British America and whose southern pole in 
 Antarctica have at last been visited by Amundsen and David, 
 respectively. The specific gravity of iron is 7.15, and those of 
 nickel and cobalt, which in the meteorites are present in relatively 
 small amounts, are 7.8 and 7.5, respectively. Considering that 
 the surface shell of the earth has a specific gravity of 2.7, these 
 values must be regarded as agreeing well with the determined 
 density of the earth (5.6) and the other planets of its group (Mer- 
 cury 5.7, Venus 5.4, Mars 4). 
 
 The chemical constitution of the earth's surface shell. — The 
 number of the so-called chemical elements which enter into the 
 earth's composition is more than eighty, but few of these figure 
 as important constituents of the portion known to us. Nearly 
 one half of the mass of this shell is oxygen, and more than a quarter 
 is silicon. The remaining quarter is largely made up of aluminium, 
 iron, calcium, magnesium, and the alkalies sodium and potassium, 
 in the order named. These eight constituent elements are thus 
 the only ones which play any important role in the composition 
 of the earth's surface shell. They are not found there in the free 
 condition, but combined in the definite proportions characteristic 
 of chemical compounds, and as such they are known as minerals. 
 
 The essential nature of crystals. — A crystal we are accus- 
 tomed to think of as something transparent bounded by sharp 
 edges and angles, our ideas having been obtained largely from the 
 gem minerals. This outward symmetry of form is, however, but 
 an expression of a power which resides, so to speak, in the heart 
 
24 
 
 EARTH FEATURES AND THEIR MEANING 
 
 Just as the real nature of a 
 
 Crystal CQvartz) Amorphous Substance 
 (Glass) 
 
 or soul of the crystal individual — it has its own structural make- 
 up, its individuality. No more correct estimates of the compari- 
 son 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 clothing. Too often 
 this outward dress tells only of the conditions by which both men 
 and crystals have been surrounded, and but little of the power 
 inherent in the individual. Many a battered mineral fragment 
 with little beauty to recommend it, when placed under suitable 
 conditions for its development, has grown into a marvel of beauty. 
 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 shapeless. 
 
 person is first disclosed by his 
 behavior under trying circum- 
 stances, so of a crystal it is its 
 conduct under stress of one sort 
 or another which brings out 
 its real character. 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 bat- 
 tered fragment — and then pre- 
 pare a sphere of similar size and 
 shape from a noncrystalline or 
 amorphous substance like glass. 
 If now these two spheres be in- 
 troduced into a bath of oil and 
 raised to a higher temperature, 
 the glass globe undergoes an 
 Fig. 10?- Comparison of a crystalline enlargement without change of 
 
 with an amorphous substance when ex- its form ; but the Crystal ball 
 
 panded by heat and when attacked by reveals its individuality by ex- 
 panding into a spheroid in 
 which each new dimension is nicely adjusted to this more complex 
 figure (Fig. 10). 
 
 We may, instead of submitting the two balls to the " trial by 
 
 Expansion by heat 
 
/'■' 
 
 NATURE OF THE MATERIALS IN THE LITHOSPHERE 25 
 
 fire," allow each to be attacked by the powerful reagent, hydro- 
 fluoric acid. The common glass under the attack of the acid 
 remains as it was before, a sphere, but with shrunken dimensions. 
 The crystal, on the other hand, is able to control the action of the 
 solvent, 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 revealed. This glimpse into the nature of the crystal, so as 
 to reveal its structural beauty, is still more surprising when the 
 crystal is taken from the acid in the 
 early stages of the action and held '■■:^}-h^\\t^'^y 
 close beneath the eye. Now the ht- 
 tle etchings upon the surface display 
 
 each the individuality of the sub- .• ,/ \ " 
 
 stance, and joining with their neigh- ■ ■ '^ b^'^^ -^ 
 bors they send out a beautifully 
 
 symmetrical and entirely character- .: Y /1;^-.. ./^*K, 
 istic picture (Fig. 11). ( ;| M^^' 
 
 The lithosphere a complex of 
 interlocking crystals. — To the lay- 
 man the crystal is something rare Fig. ii. — " Light figure" seen upon 
 
 and expensive, to be obtained from an etched surface of a crystal of 
 
 a jeweler or to be seen displayed in ^^/°'*^ , ^^^*'^'" Goldschmidt and 
 
 , , Wright). 
 
 the show cases of the great muse- 
 ums. Yet the one most striking quality of the lithosphere which 
 separates it from the hydrosphere and the atmosphere is its crys- 
 talline structure, — a structure belonging also to the meteorite, and 
 with little doubt to all the planets of the earth group. A snowflake 
 caught during its fall from the sky reveals all the delicate tracery 
 of crystal boundary; collected from a thick layer lying upon the 
 ground, it appears as an intricate aggregate of broken fragments 
 more or less firmly cemented together. And so it is of the litho- 
 sphere, for the myriads of individuals are either the ruins of former 
 crystals, or they are grown together in such a manner that crystal 
 facets had no opportunity to develop. 
 
 Such mineral individuals as once possessed the crystal form may 
 have been broken and their surfaces ground away by mutual attri- 
 tion under the rhythmic beating of the waves upon a shore or in 
 the continuous rolling of pebbles on a stream bed, until as bat- 
 
26 
 
 EARTH FEATURES AND THEIR MEANING 
 
 tered relics they are piled away together in a bed of sand. Yet 
 no amount of such rough handling is sufficient to destroy the crys- 
 tal individuality, and if they are now surrounded with conditions 
 which are suitable for their growth, their individual nature again 
 becomes revealed in new crystal outlines. Many of our sand- 
 stones when turned in the bright sunlight send out flashes of light 
 to rival a bank of snov/ in early spring. These bright flashes 
 proceed from the facets of minute crystals formed about each 
 rounded grain of the sand, and if we examine them under a lens, 
 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 (Fig. 12). 
 
 Fig. 12. — Battered sand grains which have taken on a new lease of life and have 
 developed a crystal form, a, a single grain grown into an individual crystal ; b, 
 a parallel growth about a single grain ; c, growth of neighboring grains until they 
 have mutually interfered and so destroyed the crystal facets — the common con- 
 dition within the mass of a rock (after Irving and Van Hise). 
 
 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 " crystal molecules." The crystal quality 
 belongs to the chemical elements and to their compounds in the 
 solid condition, but not to ordinary mixtures of them. 
 
 Some properties of natural crystals, minerals. — No two mineral 
 species appear in crystals of the same appearance, any more 
 than two animal species have been given the same form ; and so 
 minerals may be recognized by the individual peculiarities of their 
 crystals. Yet for the reason that crystals have so generally been 
 prevented from developing or retaining their characteristic faces, 
 
NATURE OF THE MATERIALS IN THE LITHOSPHERE 27 
 
 in the vast number of instances it is the behavior, and not the 
 appearance, of the mineral substance which is made use of for iden- 
 tification. 
 
 When a mineral is broken under the blow of a hammer, in- 
 stead of yielding an irregular fracture, like that of glass, it generally 
 tends to part along one or more directions so as to leave plane 
 surfaces. This property of cleavage is strikingly illustrated for 
 a single direction in the mineral mica, for two directions in feld- 
 spar, and for three directions in calcite or Iceland spar. Other 
 properties of minerals, such as hardness, specific gravity, luster, 
 color, fusibility, etc., are all made use of in rough determinations 
 of the minerals. Far more delicate methods depend upon the 
 behavior of minerals when observed in polarized light, and such 
 behavior is the basis of those branches of geological science known 
 as optical mineralogy and as microscopical petrography. An out- 
 line description of some of the common minerals and the means 
 for identifying them will be found in appendix A. 
 
 The alterations of minerals. — By far the larger number of 
 minerals have been formed in the cooling and consequent con- 
 solidation of molten rock material such as during a volcanic erup- 
 tion reaches the earth's surface as lava. Beginning their growth 
 at many points within the viscous mass, the individual crystals 
 eventually may grow together and so prevent a development of 
 their crystal faces. 
 
 Another class of minerals are deposited from solution in water 
 within the cavities and fissures of the rocks ; and if this process 
 ceases before the cavities have been completely closed, the minerals 
 are found projecting from the walls in a beautiful lining of crys- 
 tal — the Krystallkeller or "crystal cellar." It is from such 
 pockets or veins within the rocks that the valuable ores are ob- 
 tained, as are the crystals which are displayed in our mineral 
 cabinets. 
 
 There is, however, a third process by which minerals are formed, 
 and minerals of this class are produced within the solid rock as 
 a product of the alteration of preexisting minerals. Under the 
 enormous pressures of the rocks deep below the earth's surface, 
 they are as permeable to the percolating waters as is a sponge 
 at the surface. Under these conditions certain minerals are 
 dissolved and their material redeposited after traveling in the 
 
28 
 
 EARTH FEATURES AND THEIR MEANING 
 
 quartz i n- 
 cluded be- 
 cause not as- 
 similated. 
 
 ,fCw^' 
 
 solution, or solution and redeposition of mineral matter may go 
 on together within the mass of the same rock. One new mineral 
 may have been produced from the dissolved materials of a num- 
 ber of earlier species, or several new minerals may 
 be the result of the alteration of a preexisting min- 
 eral with a more complex chemical structure. Where 
 the new mineral has been formed " in place," it has 
 sometimes been able to utilize the materials of all 
 the minerals which before existed there, or it may 
 Fig. 13.— Crys- have been obliged to inclose within itself those earlier 
 a o garnet constituents which it could not assimilate in its own. 
 
 developed in 
 
 a schist with structure (Fig. 13). 
 
 grains of At other times a crystal which is imbedded in 
 rock has been attacked upon its surface by the per- 
 colating solutions, and the dissolved 
 materials have been deposited in place 
 as a crowTi of new minerals which steadily widens its 
 zone until the center is reached and the original 
 crystal has been entirely transformed (Fig. 14). 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 min- 
 erals. In rocks which are 
 aggregates of several min- 
 FiG. 15. — A new mineral eral species, a newly formed 
 
 mineral may appear only at 
 the common margin of cer- 
 tain of these species, thus showing that 
 they supply those chemical elements which 
 were necessary to the formation of the 
 new substance (Fig. 15). Thus it is seen 
 that below the earth's surface chemical reactions are constantly 
 going on, and the earlier rocks are thus locally being transformed 
 into others of a different mineral constitution. 
 
 (hornblende) forming as an 
 intermediate "reaction 
 rim" between the mineral 
 having irregular fractures 
 (olivine) and the dusty 
 white mineral (lime-soda 
 feldspar) . 
 
 %/■ 
 
 Fig. 14. — a 
 crystal of aug- 
 ite within the 
 mass of a rock 
 altered in part 
 to form a rim 
 of the min- 
 erals horn- 
 blende and 
 magnetite. 
 Note the orig- 
 inal outline of 
 the augite 
 crystal. 
 
NATURE OF THE MATERIALS IN THE LITHOSPHERE 29 
 
 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 hthosphere into carbonates, hydrates, 
 and oxides. These compounds are more soluble than are the 
 minerals out of which they were formed, and they are also more 
 bulky and so tend to crack off from the parent mass on which 
 they were formed. As we are to see, for both of these reasons 
 the surface rocks of the lithosphere succumb to this attack from 
 the atmosphere. 
 
 In connection with those wrinklings of the surface shell of the 
 lithosphere from which mountains result, the underlying rocks 
 are subjected to great strains, and even where no visible partings 
 are produced, the rocks are deformed so that individual minerals 
 may be bent into crescent-shaped or S-shaped forms, or they are 
 parted into one or more fragments which remain imbedded within 
 the rock. 
 
 Reading References for Chapter III 
 
 Theories of origin of the earth : — 
 
 Thomson and Tait. Natural Philosophy. 2d ed. Cambridge, 1883, 
 
 pp. 422. 
 T. C. Chamberlin. Chamberlin and Salisbury's Geology, vol. 2, pp. 1-81. 
 
 Rigidity of the earth : — 
 
 Lord Kelvin. The Internal Condition of the Earth as to Temperature, 
 
 Fluidity, and Rigidity, Popular Lectures and Addresses, vol. 2, pp. 
 
 299-318 ; Review of evidence regarding the physical condition of 
 
 the earth, ibid., pp. 238-272. 
 HoBBs. Earthquakes (Appleton, New York, 1907), Chapters xvi and 
 
 xvii. 
 
 Composition of the earth's core and shell : — 
 
 O. C. Farrington. The Preterrestrial History of Meteorites, Jour. 
 
 GeoL, vol. 9, 1901, pp. 623-236. 
 E. S. Dana. Minerals and How to Study Them (a book for beginners 
 
 in mineralogy). Wiley, New York, 1895. 
 
 On the nature of crystals : — 
 
 Victor Goldschmidt. Ueber das Wesen der Krystalle, Ostwalds Annalen 
 der Naturphilosophie, vol. 9, 1909-1910, pp. 120-139, 368-419. 
 
CHAPTER IV 
 
 THE ROCKS OF THE EARTH'S SURFACE SHELL 
 
 The processes by which rocks are formed. — Rocks may be 
 formed in any one of several ways. When a portion of the molten 
 lithosphere, so-called magma, cools and consolidates, the product 
 is igneous rock. Either igneous or other rock may become dis- 
 integrated at the earth's surface, and after more or less extended 
 travel, either in the air, in water, or in ice, be laid down as a sedi- 
 ment. Such sediments, whether cemented into a coherent mass 
 or not, are described as sedwientary or clastic rocks. If the fluid 
 from which they were deposited was the atmosphere, they are 
 known as suhaerial or eolian sediments ; but if water, they are 
 known as subaqueous deposits. Still another class are ice-deposited 
 and are known as glacial deposits. 
 
 But, as we have learned, rocks may undergo transformations 
 through mineral alteration, in which case they are known as 
 
 metamorphic rocks. 
 When these changes 
 consist chiefly in the 
 production of more 
 soluble minerals at 
 the surface, accom- 
 panied by thorough 
 disintegration, due 
 to the direct attack 
 of the atmosphere, 
 the resulting rocks 
 are called residual 
 
 Fig. 16. — Laminated structure of sedimentary rock, rOcks. 
 Western Kansas (after a photograph by E. S. jj^^ marks of ori- 
 
 Tucker). 
 
 gin. — Each of the 
 three great classes of rocks, the igneous, sedimentary, and meta- 
 morphic, is characterized by both coarser and finer structures, in 
 the examination of which they may be identified. The igneous 
 
 30 
 
 *W',4j-''.sS'.t>',..(,W 
 
THE ROCKS OF THE EARTH'S SURFACE SHELL 31 
 
 rocks havinlg been produced from magmas, which are essentially 
 homogeneous, are usually without definite directional structures 
 due to an arrangement of their constituents, and are said to have 
 a massive structure. Sedimentary rocks, upon the other hand, 
 have been formed by an assorting process, the larger and heavier 
 fragments having been laid down when there was high velocity of 
 either wind or water current, and the smaller and lighter frag- 
 ments during intermediate periods. They are therefore more or 
 less banded, and are said to have a hedded or laminated structure 
 (Fig. 16). 
 
 Again, igneous rocks, being due to a process of crystallization, 
 are composed of mineral individuals which are bounded either 
 by crystal planes or by irregular surfaces along which neighboring 
 crystals have interfered with each other ; but in either case the 
 grains possess sharply angular boundaries. Quite different has 
 been the result of the attrition between grains in the transpor- 
 tation and deposition of sediments, for it is characteristic of the 
 sedimentary rocks that their constituent grains are well rounded. 
 Eolian sediments have usually more perfectly rounded grains than 
 subaqueous deposits. 
 
 Glacial deposits, if laid down directly by the ice, are unstrati- 
 fied, relatively coarse, and contain pebbles which are both faceted 
 and striated. Such deposits are described as till or tillite. If 
 glacier-derived material is taken up by the streams of thaw 
 water and is by them redeposited, the sediments are assorted 
 or stratified, and they are described as fluvio-glacial deposits. 
 
 The metamorphic rocks. — Both the coarser structures and 
 the finer textures of the metamorphic rocks are intermediate 
 between those of the igneous and the sedimentary classes. A 
 metamorphosed sedimentary rock, in proportion to its alteration, 
 loses the perfect lamination and the rounded grain which were 
 its distinguishing characters ; while an igneous rock takes on in 
 the process an imperfect banding, and the sharp angles of its 
 constituent grains become rounded off by a sort of peripheral 
 crushing or granulation. Metamorphic rocks are therefore 
 characterized by an imperfectly banded structure described as 
 schistosity or gneiss banding, and the constituent grains may be 
 either angular or rounded. If the metamorphism has not been 
 too intense or too long continued, it is generally possible to deter- 
 
32 EARTH FEATURES AND THEIR MEANING 
 
 mine, particularly with the aid of the polarizing microscope, 
 whether the original rock from which it was derived was of igneous 
 or of sedimentary origin. There are, however, many examples 
 which have defied a reliable verdict concerning their origin. 
 
 Characteristic textures of the igneous rocks. — In addition to 
 the massiveness of their general aspect and the angular bound- 
 aries of their constituents, there are many additional textures 
 which are characteristic of the igneous rocks. While those that 
 have consolidated below the earth's surface, the intrusive rocks, 
 are notably compact, 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 them, or upon the conditions of flow over the earth's sur- 
 face. Magmas which thus reach the surface of the earth are de- 
 scribed as lavas, and the rocks produced by their consolidation 
 are extrusive or volcanic rocks. The steam included in the lava 
 expands into bubbles or vesicles which may be large or small, 
 few or many. According to the number and the size of these 
 cavities, the rock is said to have a vesicular, scoriaceous, or pumi- 
 ceous texture. 
 
 Most lavas, when they arrive at the earth's surface, contain 
 crystals which are more or less disseminated throughout the 
 molten mass. 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 leucite, each bounded by 
 twenty-four crystal faces. It is clear that these crystals must 
 have developed by a slow growth within the magma while it was 
 still below the surface, and when the inclosing lava has con- 
 solidated, these earlier crystals lie scattered within a groundmass 
 of glassy or minutely crystalline material. 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 crystallization, and the texture which results is 
 described as porphyritic (Fig, 17 6), Should the lava arrive at 
 the surface before any crystals have been generated and consoli- 
 date rapidly as a rock glass, its texture is described as glassy 
 (Fig. 17 c). 
 
 When the crystals of the earlier generation are numerous and 
 
THE ROCKS OF THE EARTH'S SURFACE SHELL 
 
 33 
 
 needle-like in form, as is very often the case, they arrange them- 
 selves " end on " during the rock flow, so that when consolida- 
 tion has occurred, the rock has a kind of puckered lamination which 
 is the characteristic of the fluxion or flow texture. This texture 
 has sometimes been confused with the lamination of the sedi- 
 mentary rocks, so that wrong conclusions have been reached 
 
 '^s.j^^l:^: 
 
 Pig. 17. — Characteristic textures of igneous rocks, a, granitic texture characteristic 
 of the deep-seated intrusive rocks ; b, porphyritic texture characteristic of the ex- 
 trusive and of the near-surface intrusive rocks ; c, glassy texture of an extrusive rock. 
 
 regarding origin. At other times the same needle-like crystals 
 within the lava have grouped themselves radially to form rounded 
 nodules called spherulites. Such nodules give to the rock a 
 spheruUtic texture, which is nowhere better displayed than in the 
 beautiful glassy lavas of Obsidian Cliff in the Yellowstone Na- 
 tional Park. 
 
 Those intrusive rocks which consolidate deep below the earth's 
 surface, part with their heat but slowly, and so the process of 
 crystallization is continued without interruption. Starting from 
 many centers, the crystals continue to grow until they mutually 
 intersect in an interlocking complex known as the granitic tex- 
 ture (Fig. 17 a). 
 
 Classification of rocks. — In tabular form rocks may thus be 
 classified as follows : — 
 
 Igneous. 
 
 .|^, . , r Intrusive. Granitic or porphyritic texture. 
 
 .,, 1 , , J Extrusive. Glassy or porphyritic texture ; 
 
 with sharply angular i „^ , -xi. • i • 
 
 orten also with vesicular, scoriaceous, pumi- 
 
 >- ceous, fluxion, or spherulitic textures. 
 
34 
 
 EARTH FEATURES AND THEIR MEANING 
 
 Sedimentary. Laminated 
 and with rounded 
 grains. 
 
 Subaerial. Sands and loess. 
 
 Subaqueous. (See below.) 
 
 Glacial. Coarse, unstratified deposits with 
 
 faceted pebbles. Till and tillite. 
 Fluvio-glacial. Stratified sands and gravels 
 
 with "worked over" glacial characters. 
 
 M etamorphic. Schistose (Metamorphic proper. Due to below surface 
 and with grains either j changes, 
 angular or rounded. [Residual. Disintegrated at or near surface. 
 
 Subdivisions of the sedimentary rocks. — While the eolian 
 sediments are all the product of a purely mechanical process of 
 lifting, transportation, and deposition of rock particles, this is 
 not always the case with the subaqueous sediments, since water 
 has the power of dissolving mineral substance, as it has also of 
 furnishing a home for animal and vegetable life. Deposited 
 materials which have been in solution in water are described as 
 chemical deposits, and those which have played a part in the life 
 process as organic deposits. The organic deposits from vege- 
 table sources are peat and the coals, while limestones and marls 
 are the chief depositories of the remains of the animal life of the 
 water. The tabular classification of the sediments is as follows : — 
 
 Classification of Sediments. 
 
 Mechanical 
 
 Chemical 
 
 Organic 
 
 Subaqueous 
 
 Conglomerate, sand- 
 
 Deposited by water. 
 
 stone and shale. 
 
 Subaerial or Eolian 
 
 Sandstone and loess. 
 
 Deposited by wind. 
 
 
 Glacial 
 
 Till and tillite. 
 
 Deposited by ice. - 
 
 
 Fluvio-glacial 
 
 Sands and gravels. 
 
 . Glacier-water deposit 
 
 s. 
 
 Calcareous tufa 
 
 Deposited in springs 
 
 
 and rivers. 
 
 Oolitic limestone 
 
 Deposited at the 
 
 
 mouths of rivers 
 
 
 between high and 
 
 
 low tide. 
 
 Formed of plant re- 
 
 Peats and coals. 
 
 mains. 
 
 
 Formed of animal re- 
 
 Limestones and 
 
 mains. 
 
 marls. 
 
THE ROCKS OF THE EARTH'S SURFACE SHELL 35 
 
 Winds are under favorable conditions capable of transporting 
 both dust and sand, but not the larger rock fragments. The dust 
 deposits are found accumulating outside the borders of des- 
 erts as the so-called loess (Fig. 216), though the sand is never 
 carried beyond the desert border, near which it collects in wide 
 belts of ridges described as dunes. When this sand has been 
 cemented into a coherent mass, it is known as eolian sandstone. 
 A section of the appendix (B) is devoted to an outline description 
 •of some of the commoner rock types. 
 
 The different deposits of ocean, lake, and river. — Of the sub- 
 aqueous sediments, there are three distinct types resulting : 
 (1) from sedimentation in rivers, the fluviatile deposits ; (2) from 
 sedimentation in lakes, the lacustrine deposits ; and (3) from sed- 
 imentation in the ocean, marine deposits. Again, the widest 
 range of character is displayed by the deposits which are laid 
 down in the different parts of the course of a stream. Near the 
 source of a river, coarse river gravels may be found ; in the middle 
 course the finer silts ; and in the mouth or delta region, where the 
 deposits enter the sea or a lake, there is found an assortment of 
 silts and clays. Except within the delta region, where the area 
 of deposition begins to broaden, the deposits of rivers are stretched 
 out in long and relatively narrow zones, and are so distinguished 
 from the far more important lacustrine and marine deposits. 
 
 Lakes and oceans have this in common that both are bodies 
 of standing as contrasted with flowing water ; and both are sub- 
 ject to the periodical rhythmic motions and alongshore currents 
 due to the waves raised by the wind. About their margins, the 
 deposits of lake and ocean are thus in large part wrested by the 
 waves from the neighboring land. Their distribution is always 
 such that the coarsest materials are laid down nearest to the shore, 
 a,nd the deposits become ever finer in the direction of deeper 
 water. Relatively far from shore may be found the finest sands 
 and muds or calcareous deposits, while near the shore are sands, 
 and, finally, along the beach, beds of beach pebbles or shingle. 
 When cemented into coherent rocks, these deposits become shales 
 or limestones, sandstones, and conglomerates, respectively. 
 
 As regards the limestones, their origin is involved in consid- 
 erable uncertainty. Some, like the shell limestone or coquina 
 ■of the Florida coast, are an aggregation of remains of mollusks 
 
36 EARTH FEATURES AND THEIR MEANING 
 
 which Hve near the border of the sea. Other hmestones are de- 
 posited directly from carbonate of lime in solution in the water, 
 A deposit of this nature is forming in southern Florida, both as 
 a flocculent calcareous mud and as crystals of lime carbonate 
 upon a limestone surface. Again, there is the reef limestone 
 which is built up of the stony parts of the coral animal, and^ 
 lastly, the calcareous ooze of the deep-sea deposits. 
 
 The marine sediments which are derived from the conti- 
 nents, the so-called terrigenous deposits, are found only upon the 
 continental shelf and upon the continental slope just outside it. 
 Of these terrigenous deposits, it is customary to distinguish : 
 (I) littoral or alongshore deposits, which are laid down between" 
 high and low tide levels ; (2) shoal water deposits, which are found 
 between low-water mark and the edge of the continental shelf ; and 
 (3) aktian or offshore deposits, which are found upon the conti- 
 nental slope. The littoral and shoal water deposits are mainly 
 gravels and sands, while the offshore deposits are principally 
 muds or lime deposits. 
 
 Special marks of littoral deposits. — The marks of ripples are 
 often left in the sand of a beach, and may be preserved in the sand- 
 stone which results from the cementation of such deposits (pi. 11 A). 
 Very similar markings are, however, quite characteristic of the 
 surface of wind-blown sand. For the reason that deposits are 
 subject to many vicissitudes in their subsequent history, so that 
 they sometimes stand at steep angles or are even overturned, 
 it is important to observe the curves of sand ripples so as to dis- 
 tinguish the upper from the lower surface. 
 
 In the finer sands and muds of sheltered tidal flats may be pre- 
 served the impressions from raindrops or of the feet of animals 
 which have wandered over the flat during an ebb tide. When 
 the tide is at flood, new material is laid down upon the surface 
 and the impressions are filled, but though hardened into rock, 
 these surfaces are those upon which the rock is easily parted, 
 and so the impressions are preserved. In the sandstones of the 
 Connecticut valley there has been preserved a quite remarkable 
 record in the footprints of animals belonging to extinct species, 
 which at the time these deposits were laid down must have been 
 abundant upon the neighboring shores. 
 
 Between the tides muds may dry out and crack in intersecting 
 
THE ROCKS OF THE EARTH'S SURFACE SHELL 37 
 
 lines like the walls of a honeycomb, and when the cracks have been 
 filled at high tide, a structure is produced which may later be 
 recognized and is usually referred to as " mud-crack " structure. 
 This structure is of special service in distinguishing marine de- 
 posits from the subaerial or continental deposits. 
 
 A variation in the direction of winds of successive storms 
 may be responsible for the piling up of the beach sand in a pecul- 
 iar " plunge and flow " or " cross-bedded " structure, a structure 
 which is extremely common in littoral deposits, though simu- 
 lated in rocks of eolian origin. 
 
 The order of deposition during a transgression of the sea. — 
 Many shore lines of the continents are almost constantly migrat- 
 ing either landward or seaward. When the shore line advances 
 
 S eo 1— «■ 
 
 Fig. 18. — Diagram to show the order of the sediments laid down during a trans- 
 gression of the sea. 
 
 over the land, the coast is sinking, and marine deposits will be 
 formed directly above what was recently the " dry land." Such 
 an invasion of the land by the sea, due to a subsidence of the coast, 
 is called a transgression of the sea, or simply a transgression. 
 Though at any moment the littoral, shoal water, and offshore 
 deposits are each being laid down in a particular zone, it is evi- 
 dent that each must advance in turn in the direction of the shore 
 and so be deposited above the zones nearer shore. Thus there 
 comes to be a definite series of continuous beds, one above the other, 
 provided only that the process is continued (Fig. 18). At the 
 very bottom of this series there will usually be found a thin bed 
 of pebbly beach materials, which later will harden into the so- 
 called hasal conglomerate. If the size of the pebbles is such as to 
 make possible an identification, it will generally be found that these 
 represent the ruins of the rock over which the sea has advanced 
 upon the land. 
 
 Next in order above the basal conglomerate, will follow the 
 coarser and then the finer sands, upon which in turn will be laid 
 down the offshore sediments — the muds and the lime deposits. 
 
38 EARTH FEATURES AND THEIR MEANING 
 
 Later, when cemented together, these become in order, coarser 
 and finer sandstones, shales, and limestones. The order of super- 
 position, reading from the bottom to the top, thus gives the order 
 of decreasing age of the formations. 
 
 A subsequent uplift of the coast will be accompanied by a 
 recession of the sea, and when later dissected by nature for our 
 inspection, the order of superposition and the individual character 
 of each of the deposits may be studied at leisure. 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 Crustacea. These 
 so-called fossils represent animals which were gradually developed 
 from simpler to more and more complex forms ; and they thus 
 serve the purpose of successive page numbers in arranging the 
 order of disturbed strata, at the same time that they supply 
 the most secure foundation upon which rests the great doctrine 
 of evolution. 
 
 The basins of earlier ages. — It was the great Viennese geolo- 
 gist, Professor Suess, who first pointed out that in mountain regions 
 there are found the thickest and the most complete series of the 
 marine deposits ; whereas outside these provinces the forma- 
 tions are separated by wide gaps representing periods when no 
 deposits were laid down because the sea had retired from the 
 region. 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-day, were for long preceding ages 
 the basins for deposition of terrigenous sediments. 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 uplift. 
 
 The deposits of the deep sea. — Outside the continental slope, 
 whose base marks the limit of the terrigenous deposits, lies the 
 deeper sea, for the most part a series of broad plains, but varied by 
 more profound steep-walled basins, the so-called " deeps " of the 
 ocean. As shoAvn by the dredgings of the Challenger expedi- 
 tion and others of more recent date, the deposits upon the ocean 
 floor are of a wholly different character from those which are 
 derived from the continents. Except in the great deeps, or 
 between depths of five hundred and fifteen hundred fathoms, 
 
THE ROCKS OF THE EARTH'S SURFACE SHELL 39 
 
 these deposits are the so-called " ooze," composed of the cal- 
 careous or chitinous parts of algae and of minute animal organisms. 
 The pelagic or surface waters of the ocean are, as it were, a great 
 meadow of these plant forms, upon which the minute Crustacea, 
 such as globigerina, foraminifera, and the pteropods, feed in count- 
 less myriads. The hard parts of both plant and animal organisms 
 descend to the bottom and there form the ooze in which are some- 
 times found the ear bones of whales and the teeth of sharks. 
 
 In the deeps of the ocean, none of these vegetable or animal 
 deposits are being laid down, but only the so-called " red clay," 
 which is believed to represent decomposed volcanic material 
 deposited by the winds as fine dust on the surface of the ocean, or 
 the product of submarine volcanic eruption. From the absence 
 of the ooze in these profound depths, 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 water. 
 
 Reading References for Chapter IV 
 
 J. S. DiLLER. The Educational Series of Rock Specimens collected and 
 
 distributed by the United States Geological Survey, Bull. 150 
 
 U. S. Geol. Surv., 1898, pp. 1-400. 
 L. V. PiRSsoN. Rocks and Rock Minerals. Wiley, New York, 1908. 
 Sir John Murray. Deep-sea Deposits, Reports of the Challenger 
 
 expedition, Chapter iii. 
 L. W. Collet. Les depots marins. Doin, Paris, 1907 (Encyclopedia 
 
 Scientifique). 
 
CHAPTER V 
 
 CONTORTIONS OF THE STRATA WITHIN THE ZONE OF 
 
 FLOW 
 
 The zones of fracture and flow. — It is easy to think of the 
 atmosphere and the hydrosphere as each sustaining at any point 
 the load of the superincumbent material. At the sea level the 
 weight of air upon each square inch of surface is about fifteen 
 pounds, whereas upon the floor of the hydrosphere in the more 
 profound deeps the load upon the square inch must be measured 
 in tons. Near the lithosphere surface the rocks support by their 
 strength the load of rock above them, but at greater depths they 
 are unable to do this, 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 surface. The average 
 specific gravity of rock is 2.7, 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 rock. At the depth repre- 
 sented by the length of such a column, rocks cannot yield to pres- 
 sure by fracture, for the opening of a crack implies that the rock 
 upon either side is strong enough to prevent the walls from clos- 
 ing. At this depth, rock must therefore yield to pressure not by 
 fracture, as it would at the surface, but by flow after the manner 
 of a liquid ; and so the zone below this critical level is referred to 
 as the zone of flow. 
 
 In contrast, the near-surface zone is called the zone of fracture. 
 But different rocks possess different strengths, and these are 
 subject to modifications from other conditions, such, for example, 
 as the proximity of an uncooled magma. The zone of flow is 
 therefore joined to the zone of fracture, not upon a definite surface, 
 but in an intermediate zone described as the zone of fracture and 
 flow. 
 
 Experiments which illustrate the fracture and flow of solid 
 bodies. — A prismatic block prepared from stiff molders' wax, 
 if crushed between the jaws of a testing machine, yields a system 
 
 40 
 
CONTORTIONS OF THE STRATA 
 
 41 
 
 of intersecting fractures which are perpendicular to the free sur- 
 faces of the block and take two directions each inclined by half 
 of a right angle to the direction of compression 
 (Fig. 19). This experiment may illustrate the 
 manner in which fractures are produced by 
 the compression within the zone of fracture 
 of the lithosphere, as its core continues to 
 contract. 
 
 To reproduce the conditions within the zone 
 of flow, it will be necessary to load the lateral 
 surfaces of the block instead of leaving them 
 unconstrained as in the above-described ex- 
 periment. The experiment is best devised as 
 in Fig. 20. Here a series of layers having 
 varying degrees of rigidity is prepared from 
 beeswax as a base, either stiffened by ad- 
 mixture of varying proportions of plaster of 
 Paris, or weakened by the use of Venice turpen- 
 tine. Such a series of layers may represent 
 rocks of as widely different characters as lime- 
 stone and shale. The load which is to rep- 
 resent superincumbent rock is supplied in the 
 experiment by a deep layer of shot. 
 
 When compression is applied to the layers 
 from the ends, these normally solid materials, 
 instead of fracturing, are bent into a series 
 of folds. The stiffer, or more competent, layers are found to be 
 less contorted than are the weaker layers, particularly if the 
 
 Fig. 19. — Two inter- 
 secting parallel series 
 of fractures produced 
 upon each free sur- 
 face of a prismatic 
 block of stiff molders' 
 wax when broken by 
 compression from the 
 ends (after Daubree 
 and Tresca). 
 
 SecOan on Uru, ab Section on Une cd 
 
 Fig. 20. — Apparatus to illustrate the folding of strata within the zone of flow 
 
 (after Willis). 
 
42 
 
 EARTH FEATURES AND THEIR MEANING 
 
 Fig. 21. — Diagrams representing a, an 
 anticline ; b, a syncline ; and c, a mono- 
 cline. 
 
 CF 
 
 latter have been protected under an arch of the more competent 
 layer (pi. 2 A). 
 
 The arches and troughs of the folded strata. — Every series 
 of folds is made up of alternating arches and troughs. The arches 
 of the strata the geologist calls anticlines or anticlinal folds, and 
 the troughs he calls synclines or synclinal folds (Fig. 21), When a 
 
 stratum is merely dropped in a 
 bend to a lower level without 
 producing a complete arch or a 
 complete trough, this half fold 
 is termed a monocline. 
 
 Any flexuring of the strata 
 implies a reduction of their 
 surface area, or, considering a 
 single section, a shortening. If the arches and troughs are low 
 and broad, the deformation of the strata is slight, the shorten- 
 ing is comparatively small, and the folds are described as open 
 (Fig. 22 b). If they be relatively both 
 high and narrow, the deformation is 
 considerable, a larger amount of crustal 
 shortening has gone on, and the folds 
 are described as close (Fig. 22 c). This 
 closing up of the folds may continue 
 until their sides have practically the 
 same slope, in which case they are said 
 to be isoclinal (Fig. 22 d). 
 
 The elements of folds. — Folds must 
 always be thought of as having ex- 
 tension in each of the three dimensions 
 of space (Fig. 23), and not as properly 
 included within a single plane like the 
 cross sections which we so often use in 
 illustration. 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 trough, 
 and is called the axial plane. The line in which this plane inter- 
 sects the arch or the trough is the axis, which may be called the 
 Crestline in an anticline, and the troughline in a syncline. 
 
 In the case of many open folds the axis is practically hori- 
 
 FiG? 22. — A comparison of 
 folds to express increasing 
 degrees of crustal shortening 
 or progressive deformation 
 within the zone of flow : a, 
 stratum before folding ; b, 
 open folds ; c, close folds ; 
 d, isoclinal folds. 
 
CONTORTIONS OF THE STRATA 
 
 43 
 
 zontal, but in more complexly folded regions this is seldom true. 
 The departure of the axis from the horizontal is called the pitch, 
 and folds of this type are described as pitching folds or plunging 
 
 ^ PITCH. 
 
 Fig. 23. — Anticlinal and synclinal folds in strata (after Willis). 
 
 folds. The axis is in reality in these cases thrown into a series 
 of undulations or " longitudinal folds," and hence pitch will 
 vary along the axis. 
 
 The shapes of rock folds. — By the axial plane each fold is 
 divided into two parts which are called its limbs, which may have 
 either the same or different average inclinations. To describe 
 now the shapes of rock folds and not the degree of compression of 
 the district, some additional terms are necessary. Anticlines 
 or synclines whose limbs have about the same inclinations are 
 known as upright or symmetrical folds. The axial plane of the 
 symmetrical fold is vertical (Fig. 24). If this plane is inclined to 
 the vertical, the folds are unsymmetrical. So soon as the steeper 
 ,of the two limbs has passed the vertical position and inclines in 
 the same direction as the flatter limb, the fold is said to be over- 
 turned. The departure from symmetry may go so far that the 
 axial plane of the fold lies at a very flat angle, and the fold is then 
 said to be recumbent. 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 folds, as he may also, 
 
44 
 
 EARTH FEATURES AND THEIR MEANING 
 
 ■Symme t/-/co/ 
 
 (yn^ymmetr/ca/ 
 
 \ 
 
 though generally less easily, in passing through the Appalachian 
 
 Mountains. 
 
 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 them, and these in turn may 
 show crumplings of still lower orders. 
 It has been found that the folds of 
 the smaller orders of magnitude pos- 
 sess the shapes of the larger flexures, 
 and much is therefore to be learned 
 from their careful study (Fig. 25). 
 It is also quite generally discovered 
 that parallel planes of ready parting, 
 which are described as roch cleavage, 
 take their course parallel to the axial 
 plane within each minor fold. As 
 was long ago shown by the pioneer 
 British geologists, these planes of 
 cleavage are essentially parallel and 
 follow the fold axes throughout large 
 areas. 
 
 The overthrust fold. — Whenever 
 a stratum is bent, there is a tendency for its particles to be 
 separated upon the convex side of the bend, at the same time 
 that those upon the con- , 
 
 cave side are crowded ♦ ovj"//. «>/ 
 
 closer together — there ^ 
 
 is tension in the former 
 case and compression 
 in the latter (Fig. 26). 
 Within an unsymmet- 
 rical or an overturned 
 fold, the peculiar dis- 
 tortions in the different 
 sections of the stratum 
 are less simple and are 17 ok o ^ a ^ ^- a 
 
 ^ Fig. 25. — Secondary and tertiary flexures supenm- 
 
 best illustrated by posed upon the primary ones. 
 
 f?ecumbeni- 
 
 Fig. 24. — Diagrams to illustrate 
 the different shapes of rock folds. 
 
Platk 2. 
 
 A. Layers compressed in experiments and showing the effect of a competent layer 
 in the process of folding (after Willis). 
 
 B. Experimental production of a series of parallel thrusts within closely folded strata 
 
 (after Willis). 
 
 C. Apparatus to illustrate shearing action vvithui the overturned limb of a fold. 
 
CONTORTIONS OF THE STRATA 45 
 
 pi. 2 C. This apparatus shows two similar piles of paper sheets^ 
 upon the edges of each of which a series of circles has been drawn. 
 When now one of the piles is bent into an unsymmetrical fold, it. 
 is seen that through an accommodation by the paper sheets sliding 
 each over its neighbor large distortions of the circles have occurred. 
 In that steeper limb which with closer folding will be overturned 
 the circles have been drawn 
 
 out into long and narrow ^-^oMTT'^^T^^V ^'^77'f^ 
 
 ellipses, and this indicates 
 that those rock particles 
 which before the bending 
 were included in the circle 
 
 have been moved past each ^^°- 26.— A bent stratum to illustrate tension 
 ., • ,1 (. , 1 upon the convex and compression upon the 
 
 Other m the manner of the concave side (after Van Hise). 
 
 blades of a pair of shears. 
 
 Such extreme " shearing " action is thus localized in the under- 
 turned limb of the fold, 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 anticline. Such structures prob- 
 ably occur in the zone of combined fracture and flow, up into 
 which the beds are forced in cases of close compression. Relief 
 thus being found upon this plane of fracture, the upper portion 
 of the fold will now ride over the lower, and the displacement is 
 described as a thrust or overthrust. 
 
 In the long series of experiments conducted by Mr. Bailey 
 Willis of the United States Geological Survey, all the stages be- 
 tween the overturned fold and the overthrust fold were reproduced. 
 Where a series of folds was closely compressed, a parallel series of 
 thrusts developed (pi. 2 B), so that a series of shces cutting across 
 neighboring strata was slid in succession, each over the other, 
 like the scales upon a fish or the shingles upon a roof. Quite 
 remarkable structures of this kind have been discovered in rocks 
 of such closely folded districts as the Northwest Highlands of Scot- 
 land, where the overriding is measured in miles. Near the thrust 
 planes the rocks show a crushing of the grains, and the planes them- 
 selves are sometimes corrugated and polished by the movement. 
 
 Restoration of mutilated folds. — Since fiexuring of the rocks 
 takes place within the zone of flow at a distance of several miles 
 
46 EARTH FEATURES AND THEIR MEANING 
 
 below the earth's surface, it is quite obvious that the results of the 
 process can be studied only after some thousands of feet of super- 
 incumbent strata have been removed. We are a little later to see 
 by what processes this lowering of the surface is accomplished, 
 but for the present it may be sufficient to accept the fact, realizing 
 that before foldings in the strata can reach the surface, they must 
 have passed through the upper zone of fracture. 
 
 It might perhaps be supposed that the anticlines would appear 
 as the mountains upon the surface, and occasionally this is true ; 
 as, for example, in the folded Jura Mountains of western Europe. 
 More generally, the mountains have a synclinal structure and the 
 valleys an anticlinal one ; but as no general rule can be applied, 
 it is necessary to make a restoration of the truncated folds in each 
 district before their character can be known. 
 
 The geological map and section. — The earth's surface is in 
 most regions in large part covered with soil or with other inco- 
 herent rock material, so that over considerable areas the hard rocks 
 are hidden from view. Each locality at which the rock is found 
 at the earth's surface " in place " is described as an outcropping 
 or expositive. In a study of the region each such exposure must 
 be examined to determine the nature of the rock, especially for 
 the purpose of correlation with neighboring exposures, and, in 
 addition, both the probable direction in which it is continued along 
 the surface — the strike — and the inclination of its beds — 
 the dip. If the outcroppings are sufficiently numerous, and rock 
 type, strike and dip, may all be determined, the folds of the dis- 
 trict may be restored with almost as much "accuracy as though 
 their curves were everywhere exposed to view. 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 (Fig. 27). A 
 map upon which the data have been entered in their correct loca- 
 tions, either with or without assumptions concerning the covered 
 areas, is known as a geological map. 
 
 If the axes of folds are absolutely horizontal, and the surface 
 of the earth be represented as a plain, the lines of intersection of 
 the truncated strata with the ground, or with any horizontal sur- 
 face, will give the directions of continuation of the individual 
 strata. This strike direction is usually determined at each expo- 
 
CONTORTIONS OF THE STRATA 
 
 47 
 
 sure by use of a compass provided with a spirit level. When that 
 edge of the leveled compass which is parallel to the north-south 
 line upon the dial is held against the sloping rock stratum, the 
 
 Fig. 27. — A geological section based upon observations at outcrops, but with 
 the truncated arches restored. 
 
 angle of strike is measured in degrees by the compass needle. If 
 the cardinal directions have been placed in their correct positions 
 upon the compass dial, the needle will point to the northwest 
 when the strike is northeast, and vice versa (Fig. 28 a). Upon 
 
 Fig. 28. — Diagram to illustrate the manner of determining the strike of rock beds 
 at an outcropping, a, a compass which has the cardinal directions in their 
 natural positions ; b, a compass with the east and west initials reversed upon the 
 dial ; c, home-made clinometer in position to determine the dip. 
 
 the geologist's compass it is therefore customary to reverse the 
 initials which represent the east and west directions, in order that 
 the correct strike may be read directly from-^the dial (Fig. 28 6). 
 
 By the dip is meant the inclination of the stratum at any expo- 
 sure, and this must obviously be measured in a vertical plane 
 
48 EARTH FEATURES AND THEIR MEANING 
 
 along the steepest line in the bedding plane. The dip angle is 
 always referred to a horizontal plane, and hence vertical beds have 
 a dip of 90°. The device for measuring this angle of dip, the 
 clinometer, is merely a simple pendulum which serves as an indi- 
 cator and is centered at the corner of a graduated quadrant. A 
 home-made variety is easily constructed from a square piece of 
 board and an attached paper quadrant (Fig. 28 c), but the geolo- 
 gist's compass is always provided with a clinometer attachment 
 to the dial. 
 
 Since the strike is the intersection of the bedding plane with a 
 horizontal surface, and the dip is the intersection with that partic- 
 ular vertical plane which gives the steepest inclination, the strike 
 and dip are perpendicular to each other. To represent them 
 upon maps, it is more or less customary to use the so-called T 
 symbols, the top of the T giving the direction of the strike and the 
 shank that of the dip. If meridians are drawn upon the map, the 
 direction or attitude of the T can be found by the use of a simple 
 protractor; and when entered upon the map, the exact angle of 
 the strike may be supplied by a figure near the top of the T, and 
 the dip angle by a figure at the end of the shank. It is the custom, 
 also, to make the length of the shank inversely proportional to 
 the steepness of the dip, so that in a broad way the attitudes of 
 the strata may be taken in at a glance (Fig. 29). It is further of 
 
 advantage to make the top of the 
 I T a double line, so that some 
 
 symbol or color may show the 
 
 C^^^ correlations of the different expo- 
 
 ^^*^ sures. To illustrate, in Fig. 29, 
 
 the symbol marked a represents 
 
 an outcrop of limestone, the strike 
 \5 of which is 50° east of north (N. 
 
 50° E.), and the dip of which is 
 Fig. 29. — Diagram to show the use 45° southeast. In the same figure 
 of T symbols to indicate the dip and & represents a shale outcrop in hori- 
 
 strike of outcroppings. . i i i i • i i 
 
 zontal beds, which have m conse- 
 quence a universal strike and a dip of 0°. An exposure of limestone 
 in vertical beds which strike N. 60° E. is shown at c, etc. 
 
 Measurement of the thickness of formations. — When forma- 
 tions still lie in horizontal beds, we may sometimes learn their 
 
 x: 
 
CONTORTIONS OF THE STRATA 
 
 49 
 
 of I 
 
 OuTcrop \ 
 
 ijhickness directly either from the depth of borings to the under- 
 lying rock, or by measurements upon steep canon walls. If the 
 beds stand vertically, the matter is exceedingly simple, for in this 
 case the thickness is the width of the outcrops of the formation 
 between the beds which bound it upon either side. In the general 
 case, in which the beds are 
 neither horizontal nor ver- 
 tical, the thickness must be 
 obtained indirectly from the 
 width of the exposures and 
 the angle of the dip. The 
 factor by which the ex- 
 posure width must be mul- 
 tiplied is known as the sine Fiq. 30. —Diagram to show how the thickness 
 of the dip angle (Fig. 30), of a formation may be obtained from the 
 
 which is given with sufficient 
 
 accuracy for most purposes 
 
 in the following table. 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 other. 
 
 angle of the dip and the width of the ex- 
 posures. 
 
 
 
 Natural 
 
 Sines 
 
 
 
 0° 
 
 .00 
 
 35° 
 
 .57 
 
 70° 
 
 .94 
 
 5° 
 
 .09 
 
 40° 
 
 .64 
 
 75° 
 
 .97 
 
 10° 
 
 .17 
 
 45° 
 
 .71 
 
 80° 
 
 .98 
 
 15° 
 
 .26 
 
 50° 
 
 .77 
 
 85° 
 
 1.00 
 
 20° 
 
 .3-4 
 
 55° 
 
 .82 
 
 90° 
 
 1.00 
 
 25° 
 
 .42 
 
 60° 
 
 .87 
 
 
 
 30° 
 
 .50 
 
 65° 
 
 .91 
 
 
 
 The detection of plunging folds. — When the axis of a fold is 
 horizontal, its outcrops upon a plain will continue to have the same 
 strike until the formation comes to an end. Upon a generally 
 level surface, therefore, any regular progressive variation in the 
 strike direction is an indication that the folds have a plunging 
 or pitching character. Many serious mistakes of interpretation 
 have been made because of a failure to recognize this evidence of 
 plunging folds. The way in which the strikes are progressively 
 modified will be made clear by the diagrams of Figs. 31 and 32, 
 
50 
 
 EARTH FEATURES AND THEIR MEANING 
 
 the first representing a pitching antichne and the second a pitch- 
 ing synchne. In both these reciprocal cases the strikes of the 
 
 Fig. 31. — Combined surface and sectional views of a plunging anticline (after Willis). 
 
 beds undergo the same changes, and the dip directions serve to 
 distinguish which of the two structures is present in a given case. 
 There is, however, one further difference in that the hard layers 
 
 Fig. 32. — Combined aurf ace and sectional views of a plunging syncline (after Willis). 
 
CONTORTIONS OF THE STRATA 
 
 51 
 
 of the plunging anticline, where they disappear below the surface 
 in the axis, will present a domed surface sloping forward like the 
 back of a whale as it rises above the surface of the sea. 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 surface. Such features are encountered in 
 eastern Pennsylvania, where the hard formations of the Appala- 
 chian Mountain system plunge northeastward under the later 
 formations. The pitch of the larger fold is often disclosed by that 
 of the minor puckerings superimposed upon it. 
 
 The meaning of an unconformity. — The rock beds, which are 
 deposited one above the other during a transgression of the sea, 
 
 Fig. 33. — Unconformity between a lower and an upper series of beds upon the coast 
 of California. Note how the hard layer stands in relief upon the connecting 
 surface (after Fairbanks). 
 
 are usually parallel and thus represent a continuous process of 
 deposition. Such beds are said to be conformable. Where, upon 
 the other hand, two series of deposits which are not parallel to 
 each other are separated by a break, they are said to form un- 
 conformable series, and the break or surface of junction is an un- 
 conformity (Fig. 33). 
 
52 
 
 EARTH FEATURES AND THEIR MEANING 
 
 Here it is evident that the sediments which compose the lower 
 series of beds have been folded in the zone of flow, though the 
 upper series has evidently escaped this vicissitude. Furthermore, 
 the surface which delimits the lower series from the upper is some- 
 what irregular and shows a hard layer standing in relief, as it 
 would if it had opposed greater resistance to the attacks of the 
 atmosphere upon it. 
 
 In reality, an unconformity between formations must be in- 
 terpreted to mean that the lower series is not only older than the 
 upper, as shown by the order of superposition, 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 series. The 
 stages or episodes in the history of the beds represented in 
 Fig. 33 may be read as follows (see Fig. 34 a-e) : — 
 
 (a) Deposition 
 of the lower series 
 during a transgres- 
 sion of the sea. 
 
 (6) Continued 
 subsidence and 
 burial of the lower 
 series beneath 
 overlying sedi- 
 ments, and flexur- 
 ing in the zone of 
 flow. 
 
 (c) Elevation of 
 the combined de- 
 posits to and far 
 above sea level and 
 ^ ^^ _, . ^ removal by erosion 
 
 ±IG. 34. — Series of diagrams to illustrate in succession the » j. j.i • i 
 
 episodes involved in the historical development of an ^^ ^^^^ tniCKUeSSeS 
 
 angular unconformity. The vertical arrows indicate of the Upper SCdi- 
 
 the direction of movement of the land, and the horizontal nients 
 arrows the direction of shore migration. / 7x ' » i 
 
 (a) A new sub- 
 sidence of the truncated lower series and deposition of the upper 
 series across its eroded surface. 
 
 (e) A new elevation of the double series to its present position 
 above sea level. 
 
CONTORTIONS OF THE STRATA 
 
 53 
 
 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 elevation, a smaller subsidence followed by elevation. 
 The time interval which must have been represented by these re- 
 peated operations is so vast as at first to stagger the mind in con- 
 templating it. When, as in this instance, the dips of the lower 
 .series of beds differ from those of the upper, we have to do with 
 an angular unconformity. It may be, however, that the lower 
 series was not so far depressed as to enter the zone of flow, and 
 that its beds meet those of the upper series with apparent con- 
 formity. Such an unconformity is often extremely difficult to 
 recognize, and it is described as a deceptive or erosional uncon- 
 formity. 
 
 With a deceptive unconformity the clew to its real nature is 
 usually some fact which indicates that the lower series of sedi- 
 ments had been raised above the 
 level of the sea before the upper 
 series was deposited upon it. 
 This may be apparent either in 
 the irregularity of the surface on 
 which the two series are joined, 
 in some evidence of the action 
 of waves such as would be fur- 
 nished by a basal conglomerate 
 in the upper series, or some in- 
 dication of different resistance of 
 different rocks of the lower series 
 to attacks of the atmosphere 
 upon them (Figs. 33 and 35 a-c). 
 
 In most cases, at least, the 
 lowest member of the upper 
 series will be a different type of 
 rock from the uppermost mem- 
 ber of the lower series, hence the 
 
 frequent occurrence of the dis- Fig. 35. — Types of deceptive or erosional 
 
 cordant cross bedding in sand- uncon ormi les. 
 
 stone should not deceive even the novice into the assumption 
 
 of an unconformity. 
 
 ^. B///ouvy Surface. 
 
 m 
 
 z 
 
 S. jBoso/ Con^/omerate. 
 
 C Depression of surface oi^er 
 a. — wtfoA- rock, ondfiro/ecf/or? oi^er 
 fy— strong rock. 
 
54 EARTH FEATURES AND THEIR MEANING 
 
 Reading References to Chapter V 
 
 The zones of fracture and flow : — 
 C. R. Van Hise. Principles of North American Precambrian Geology, 
 
 16th Ann. Rept. U.S. Geol. Surv., 1895, Pt. I, pp. 581-603. 
 Bailey Willis. Mechanics of Appalachian Structure, 13th Ann. Rept> 
 
 U.S. Geol. Surv., 1893, Pt. II, pp. 217-253. 
 A. Daubree. Etudes Synthetiques de Geologie Experimentale. Paris, 
 
 1879, pp. 306-328, pi. II. 
 W. Prinz. Quelques remarques generales a propos de I'essai de carte 
 
 tectonique de la belgique, etc., Bull. Soc. Beige Geol., vol. 18, 1904, 
 
 p. 143, pi. V. 
 
 Analysis of folds : — 
 Van Hise and Willis as above ; de Margerie et Heim ; Les disloca- 
 tions de I'ecorce terrestre (in French and German langu?ges). Zurich, 
 
 1888. 
 
 Geological maps : — 
 Wm. H. Hobbs. The Mapping of the Crystalline Schists, Jour. Geol.» 
 vol. 10, 1902, pp. 780-792, 858-890. 
 
CHAPTER VI 
 
 THE ARCHITECTURE OF THE FRACTURED SUPER- 
 STRUCTURE 
 
 The system of the fractures. — In referring to experiments made 
 upon the fracture of solid blocks under compression (p. 41), it was 
 shown that two series of parallel fractures develop perpendicular 
 to each free surface of 
 the block, and that 
 these series are each of 
 them inclined by half 
 of a right angle to the 
 direction of compres- 
 sion, and thus perpen- 
 dicular to each other. 
 The fragments into 
 which a block with one 
 free surface would thus 
 tend to be divided 
 should be square prisms 
 perpendicular to the 
 free surface. It would 
 be interesting, if it were 
 practicable, to learn 
 from experiment how 
 these prisms would be 
 further fractured by a 
 continuation of the com- 
 pression. From me- 
 chanical considerations involving the resolution of forces with refer- 
 ence to the ready-formed fractures, it seems probable that the next 
 series of fractures to form would bisect the angles of the first double 
 series or set. Wherever rocks are found exposed in their original 
 
 55 
 
 B^^m' 
 
 
 Fig. 36. — A set of master joints developed in shale 
 upon the shores of Cayuga Lake near Ithaca, 
 New York (after U. S. G. S.). 
 
56 
 
 EARTH FEATURES AND THEIR MEANING 
 
 Fig. 37. — Diagram to show how sets of master joints 
 differing in direction by half a right angle may 
 abruptly replace each other. 
 
 omnipresent double series or 
 set of joints is the well-known 
 set of master joints, and very 
 often it is found developed 
 practically alone (Fig. 36). 
 Over large areas, the direction 
 of the set of master joints 
 may remain practically con- 
 stant, or this set may quite 
 suddenly give place to a sim- 
 ilar set which is, however, 
 turned through half a right 
 angle from the first (Fig. 
 37). Not infrequently two 
 such sets of master joints 
 are found together bisecting 
 each other's angles within the 
 same rocks, and to them 
 
 attitudes, they are, in 
 fact, seen to be inter- 
 sected by two parallel 
 series of fractures 
 which are perpendicu- 
 lar to the earth's sur- 
 face and to each other 
 and are described as 
 joints. In many cases 
 more than two series of 
 such fractures are 
 found, 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 surface. This 
 
 Fig. 38. — Diagram to show the different 
 combinations of the series composing two 
 double sets of master joints, and in a, a, a 
 additional disorderly fractures. 
 
ARCHITECTURE OF FRACTURED SUPERSTRUCTURE 57 
 
 are sometimes added additional thougii less perfect series of joint 
 planes. 
 
 Studied throughout a considerable district, the various series 
 which make up these two sets of master joints may be seen locally 
 
 ^^.^^^i^:<^-:^-^J^^i ■" ^-^— I 
 
 -<k,k,..^^^i'r^ 
 
 Fig. 39. 
 
 •View on the shore at Holstensborg, West Greenland, to show the sub- 
 equal spacing of the joints (after Kornerup). 
 
 developed in different combinations as well as in association with 
 additional fissure planes which are not easily reduced to any simple 
 law of arrangement 
 (Fig. 38 a, a, a). 
 Only rarely are reg- 
 ular joint series ob- 
 served which do not 
 stand perpendicular 
 to the original atti- 
 tude of the rock 
 beds. In a few local- 
 ities, however, rec- 
 tangular joint sets 
 have been discov- 
 ered 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 angle. 
 Where the rock beds have been much disturbed, the complex of 
 
 Fig. 40. — 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 (after Thoroddsen). 
 
58 
 
 EARTH FEATURES AND THEIR MEANING 
 
 joints may be such as to defy all attempts at orderly arrange- 
 ment. 
 
 The space intervals of joints. The same kind of subequal spac- 
 ing which characterizes the fractures near the surface of the block 
 in Daubr^e's experiment (Fig. 19, p. 41) is found simulated by the 
 rock joints (Fig. 39). Such unit intervals between fractures may 
 be grouped together into larger units which are separated by frac- 
 tures of unusual perfection. We may think of such larger space 
 units as having the smaller ones superimposed upon them (Fig. 40). 
 
 The displacements upon joints — faults. — In the vast majority 
 of cases, the joint fractures when carefully examined betray no 
 evidence of any appreciable movement of the two walls upon each 
 other. Generally the rock layers are seen to cross the joints with- 
 out apparent displacement. Joints are therefore planes of dis- 
 junction only, and not planes of displacement. 
 
 Within many districts, however, a displacement may be seen 
 to have occurred upon certain of the joint planes, and these are 
 then described as faults. Such displacements of necessity imply 
 
 Fig. 41. — Faulted .blocks of basalt divided by joints near Woodbury, Connecticut. 
 To show the structure of the rock, some of the foliage has been removed in prepar- 
 ing the sketch from a photograph. 
 
 a differential movement of sections or blocks of the earth's crust, 
 the so-called orographic blocks, which are bounded by the joint 
 planes and play individual roles in the movement. A simple case 
 of such displacements in rocks intersected by a single set of mas- 
 ter joints is represented in the model of plate 4 C. The most promi- 
 nent fault represented by this model runs lengthwise through the 
 middle, and the displacement which is measured upon it not only 
 varies between wide limits, but is marked b}'' abrupt changes at 
 the margins of the larger blocks. This vertical displacement upon 
 
ARCHITECTURE OF FRACTURED SUPERSTRUCTURE 59 
 
 the fault is called its throw. Though not illustrated by the model, 
 horizontal displacements may likewise occur, and these will be 
 more fully discussed when the subject of earthquakes is considered 
 in the following chapter. An actual example of blocks displaced 
 by vertical adjustment is represented in Fig. 41, a simple type of 
 faulting which has taken place in rocks but slightly disturbed from 
 their original attitude, but intersected by a relatively simple sys- 
 tem of master joints. In those regions where the beds have been 
 folded and perhaps overthrust before their elevation into the zone 
 of fracture, and which are further intersected by disorderly fissure 
 planes, the results are far more complex. In such cases the 
 planes of individual displacement may not be vertical, though 
 they are generally steeper than 45°. For their description it is 
 necessary to make use of addi- 
 tional technical terms (Fig. 42). 
 The inclination of a sloping fault 
 plane measured against the ver- 
 tical is called the hade of the fault. 
 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 Fig. 42.— A fault in previously dis- 
 
 the other. The additional terms turbed strata. AB, displacement; 
 
 1 ax • u.^ ^ u xu AC, throw ; fiZ), stratigraphic throw ; 
 
 are made sumciently clear by the r>^ , i ^ < d u j 
 
 •^ "^ BC, heave ; angle CAB, hade. 
 
 diagram. 
 
 Methods of detecting faults. — The first effect of a fault is usually 
 to produce a crack at the surface of the earth ; and, provided there 
 is a vertical displacement or throw, an escarpment which rises 
 upon the upthrown side of the fault. In general it may be said 
 that escarpments which appear at the earth's surface as plane 
 surfaces probably represent planes of fracture, though not neces- 
 sarily planes of faulting. In many cases the actual displacements 
 lie buried under loose rock debris near to and paralleling the es- 
 carpment, and in some cases as a result of the erosional processes 
 working upon alternately hard and soft layers of rock, the escarp- 
 ment may later appear upon the downthrown side or limb of the 
 fault (Fig. 43). As an illustration of a fault escarpment, the 
 fagade of El Capitan and many other rock faces of the Yosemite 
 valley may be instanced. 
 
60 
 
 EARTH FEATURES AND THEIR MEANING 
 
 Fig. 43. — Diagrams to show how 
 an escarpment originally on the 
 upthrown side of the fault may, 
 through erosion, appear upon the 
 downthrown side. 
 
 When we have further studied the erosional processes at the 
 earth's surface, it will be appreciated that faults tend to quickly 
 
 bury themselves from sight, where- 
 as fold structures will long remain 
 in evidence Many faults will thus 
 be overlooked, and too great weight 
 is likely to be ascribed to the folds 
 in accounting for the existing atti- 
 tudes and positions of the rock 
 masses. Faults must therefore be 
 sought out if mistakes of interpreta- 
 tion are to be avoided. 
 
 The most satisfactory evidence of 
 a fault is the disL^overy of a rock bed 
 which may be easily identified, and 
 which is actually seen displaced on 
 a plane of fracture which intersects 
 it (Fig. 42, p. 59). When such an 
 easily recognizable layer is not to be 
 found, 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 water. Such a fractured rock zone which 
 follows a plane of faulting is 
 a fault breccia. If the fault 
 breccia, or vein rock, is much 
 stronger than the rock on 
 either side, it may eventually 
 stand in relief at the surface 
 like a dike or wall. At other 
 times the displacement pro- 
 duces little fracture of the 
 walls, but they slide over each 
 other in such a manner as to 
 yield either a smoothly cor- 
 rugated or an evenly polished 
 surface which is described as 
 
 " sHckensides. ' It may be, Fiq. 44. — a fault plane exhibiting "drag.", 
 however, that during the move- The opening is artificial (after Scott) . 
 
ARCHITECTURE OF FRACTURED SUPERSTRUCTURE 61 
 
 ment either one or both of the walls have " dragged," and so are 
 curled back in the immediate neighborhood of the fault plane 
 (Fig. 44). 
 
 When, as is quite generally the case, the actual plane of dis- 
 placement of a fault is not open to inspection, the movement may 
 be proven by the observation of 
 abrupt, as contrasted with grad- 
 ual, changes in the strikes and dips 
 of neighboring exposures (Fig. 45) ; 
 or by noting that some easily rec- 
 ognized formation has been 
 sharply offset in its outcrops (Fig. 
 46). 
 
 There are in addition many in- 
 dications rather than proofs of the 
 presence of faults, which must be 
 taken account of in every general 
 study of the geology of a district. 
 Thus the outcrops of all neighbor- 
 ing formations may terminate 
 abruptly upon a straight line which 
 intersects all alike. Deep-seated 
 fissure springs may be aligned in 
 a striking manner, and so indicate 
 
 the course of a prominent fracture, 
 though not necessarily of a fault. 
 Much the same may be said of the 
 dikes of cooled magma which have 
 been injected along preexisting frac- 
 tures. 
 
 The base of the geological map. — 
 Modern topographic maps form an im- 
 portant part of the library of the serious 
 student of physiography; they are the 
 gazetteer of this branch of science. 
 Every civilized nation has to-day either completed a topographic 
 atlas of its territory, or it is vigorously prosecuting a survey to 
 furnish maps which represent the relief with some detail, and pub- 
 lishing the results in the form of an atlas of quadrangles. Thus 
 
 Fig. 45. — Map to show how a fault 
 may be indicated in abrupt changes 
 of the strike and dip of neighboring 
 exposures. 
 
 Fig. 46. — A series of parallel 
 faults indicated by successive 
 offsets in the course of an 
 easily recognizable rock for- 
 mation. 
 
62 EARTH FEATURES AND THEIR MEANING 
 
 a relief map will erelong be obtainable of any part of the civilized 
 world, and may be purchased in separate sections. Nowhere is this 
 work being taken up with greater vigor than in the United States, 
 where a vast domain representing every type of topographic pecul- 
 iarity is being attacked from many centers. Here and elsewhere 
 the relief of the land is being expressed by so-called contours or 
 lines of equal altitude upon the earth's surface. It is as though 
 a series of horizontal planes, separated by uniform intervals of 20 
 or 40 or 100 feet, had been made to intersect the surface, and the 
 intersection curves, after consecutive numeration, had been dropped 
 into a single plane for printing. 
 
 Where the slopes are steep, the contour lines in the topographic 
 map will appear crowded together and so produce a deep shade 
 upon the map ; whereas with relatively flat surfaces white patches 
 will stand out prominently upon the map. More and more the 
 topographic map is coming into use, and for the student of nature 
 in particular it is important to acquire facility in interpreting the 
 relief from the topographic map. To further this end, a special 
 model has been devised, and its use is described in appendix C. 
 Usually before any satisfactory geological map can be prepared, 
 a contoured topographic map of the district to be studied must 
 be available. 
 
 The field map and the areal geological map. — As the atlas of 
 topographic maps is the physiographic gazetteer, so geological 
 maps together constitute the reference dictionary of descriptive 
 geology. Not only are topographic maps of many districts now 
 generally available, but more and more it has become the policy 
 of governments to supply geological maps in ^:he same quadrangle 
 form which is the unit of the topographic map. The geological 
 map is, however, a complex of so many conventional symbols, 
 that without some practical experience in the actual preparation 
 of one, it is exceedingly difficult for the student to comprehend 
 its significance. A modern geological map is usually a rectangular 
 sheet printed in color, upon which are many irregular areas of in- 
 dividual hue joined to each other like the parts of a child's pic- 
 ture puzzle. 
 
 The colored areas upon the geological map are each supposed 
 to indicate where a certain rock type or formation lies immediately 
 below the surface, and this distribution represents the best judg- 
 
ARCHITECTURE OF FRACTURED SUPERSTRUCTURE 63 
 
 ment of the geologist who, after a study of the district, has prepared 
 the map. Unfortunately the conventions in use are such that his 
 observation and his theory have been hopelessly intermingled 
 in the finished product. Armed with the geological map, the 
 student who visits the district finds spread out before him, it may 
 be, a landscape of hill and valley, of green forest and brown farming 
 land, which is as different as may be from the colored puzzle which 
 he holds in his hand. 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 map. Ex- 
 perience 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 
 necessary. We shall therefore describe, with the aid of laboratory 
 models, the various stages necessary to the preparation of a geo- 
 logical map, and every student should be advised to follow this by 
 practical study of some small area where rocks are found in out- 
 crop. 
 
 Though the published areal geological map represents both fact 
 and theory, the map maker retains an unpublished field map or 
 map of observations, upon which the final map has been based. 
 This field map shows the location of each outcrop that has been 
 studied, with a record of the kind of rock and of such observations 
 as strike, dip, and pitch. Our task will therefore be to prepare : 
 (1) a field map ; (2) an areal geological map ; and (3) some typical 
 geological sections. 
 
 Laboratory models for the study of geological maps. — In order 
 to represent in the laboratory the disposition of rock outcrops 
 in the field, special laboratory tables are prepared with removable 
 covers and with fixed tops, which are divided into squares num- 
 bered like the township sections of the national domain (Fig. 47). 
 To represent the rock outcrops, blocks are prepared which may 
 be fixed in any desired position by fitting a pin into a small augur 
 hole bored through the table. The outcrop blocks for the sedi- 
 mentary rock types are so constructed as to show the strike and 
 dip of the beds. (See Appendix D.) 
 
 The method of preparing the map. — To prepare the map, use 
 is made of a geological compass with clinometer attachment, a 
 protractor, and a map base divided into sections like the top of 
 
64 
 
 EARTH FEATURES AND THEIR MEANING 
 
 the table, and on the scale of one inch to the foot. Each exposure 
 represented upon the table is " visited " and then located upon the 
 base map in its proper position and attitude. The result is the 
 field map (Fig. 47), which thus represents the facts only, unless 
 
 t 
 
 -^ 
 
 ~o 
 
 o 
 
 o 
 
 T 
 
 too 
 
 4. 
 
 o 
 
 jb^. 
 
 C) 
 
 3^ 
 
 f. 
 
 ■=5, 
 
 h 
 
 I. 
 
 .£ 
 
 oSf ¥^ 
 
 ^ 
 
 o 
 
 w 
 
 I 
 
 7-.^ 
 
 pii 
 
 t 
 
 K '' 
 
 ^ «, 
 
 tK-^ 
 
 r 
 
 X 
 
 'rf 
 
 -^- 
 
 'r 
 
 
 m^ 
 
 -4^ 
 
 ^ 
 
 Fig. 47. — Field map prepared from a laboratory table. 
 
 there have been uncertainties in the correlation of exposures or 
 in determining the position of the bedding plane. 
 
 To prepare the areal geological map from the field map, it is 
 first necessary to fix the boundaries which separate formations at 
 
 Fig. 48. — Areal geological map constructed from the field map of Fig. 47, with two 
 selected geological sections. 
 
 the surface ; and now perhaps for the first time it is realized how 
 large an element of uncertainty may enter if the exposures were 
 widely separated. It is clear that no two persons will draw these 
 lines in the same positions throughout, though certain portions 
 
ARCHITECTURE OF FRACTURED SUPERSTRUCTURE 65 
 
 of them — where the facts are more nearly adequate — may cor- 
 respond. In Fig. 48 is represented the areal geological map con- 
 structed from the field map, with the doubtful area at one side left 
 blank. 
 
 Some conclusions from this map may now be profitably con- 
 sidered. The complexly folded sandstone formation at the left 
 of the map appears as the oldest member represented, since its 
 area has been cut through by the intrusive granite which does not 
 intrude other formations, and is unconformably overlaid by the 
 limestone and its basal layer of conglomerate. The limestone in 
 turn is unconformably overlaid by the merely tilted sandstone 
 beds at the right of the map. These three sedimentary forma- 
 tions clearly represent decreasing amounts of close folding, from 
 which it is clear that each earlier formation has passed through 
 an episode not shared by that of next younger age. Of the other 
 intrusive rocks, the dike of porphyry is younger than all the other 
 formations, with the possible exception of the upper sandstone. 
 Offsetting of the formations has disclosed the course of a fault, 
 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 
 faulting. 
 
 The dashed lines upon the map (AB and CD) have been selected 
 as appropriate lines along which to construct geological sections 
 (Fig. 48, below map), and from these sections the exposed thick- 
 nesses of the different formations may be calculated. In one in- 
 stance only, that of the conglomerate, can we be sure that this 
 exposed thickness measures the entire formation. 
 
 Fold versus fault topography. — The more resistant or " stronger " 
 rock beds, as regards attacks of the atmosphere, in the course 
 of time come to stand in relief, separated by depressions which 
 overlie the " weaker " formations. . Simple open folds which are 
 not plunging exercise an influence upon topography by producing 
 generally long and straight ridges. More complex flexures, since 
 they generally plunge, make themselves apparent by features 
 which in the map are represented by curves. Fracture structures, 
 and especially block displacements, are differentiated from these 
 curving features by the dominance of straight or nearly rectilinear 
 lines upon the map. The effect of erosion is to reduce the asperity 
 of features and to mold them with flowing curves. The frac- 
 
66 EARTH FEATURES AND THEIR MEANING 
 
 ture structures are for this reason much more likely to be over- 
 looked, and if they are not to elude the observer, they must be 
 sought out with care. Fold and fracture structures may both be 
 revealed upon the same map. 
 
 Reading References to Chapter VI 
 
 Joint systems : — 
 
 John Phillips. Observations made in the Neighborhood of Ferrybridge 
 in the Years 1826-1828, Phil. Mag., 2d ser., vol. 4, 1828, pp. 401-409 ; 
 Illustrations of the geology of Yorkshire, Pt. II, The Limestone Dis- 
 trict. London, 1836, pp. 90-98. 
 
 Samuel Haughton. On the Physical Structure of the Old Red Sand- 
 stone of the County of Waterford, considered with reference to cleav- 
 age, joint surfaces, and faults. Trans. Roy. Soc. London, vol. 148, 
 1858, pp. 333-348. 
 
 W. C. Brogger. Spaltenverwerfungen in der Gegend Langesund-Skien, 
 Nyt Magazin for Naturvidernskaberne, vol. 28, 1884, pp. 253-419. 
 
 Wm. H. Hobbs. The Newark System of the Pomperaug Valley, Con- 
 necticut, 21st Ann. Rept. U. S. Geol. Surv., Pt. Ill, 1901, pp. 85-143. 
 
 Geological map : — 
 Wm. H. Hobbs. The Interpretation of Geological Maps, School Science 
 and Mathematics, vol. 9, 1909, pp. 644-653. 
 
CHAPTER VII 
 
 THE INTERRUPTED CHARACTER OF EARTH MOVE- 
 MENTS: EARTHQUAKES AND SEAQUAKES 
 
 Nature of earthquake shocks. — Man's belief in the stability of 
 Mother Earth — the terra firma — is so inbred in his nature that 
 even a hght shock of earthquake brings a rude awakening. The 
 terror which it inspires is no doubt largely to be explained by this 
 
 Pig. 49. — View of "a portion of the ruing of Messina after the earthquake of 
 December 28, 1908. 
 
 disillusionment from the most fundamental of his beliefs. Were 
 he better advised, the long periods of quiet which separate earth- 
 quakes, and not the lighter shocks which follow all grander dis- 
 turbances, would occasion him concern. 
 
 67 
 
68 
 
 EARTH FEATURES AND THEIR MEANING 
 
 Earthquakes are the sensible manifestations of changes in level 
 or of lateral adjustments of portions of the continents, and the 
 seismic disturbances upon the sea — seaquakes and seismic sea 
 waves — relate to similar changes upon the floor of the ocean. 
 
 During the grander or catastrophic earthquakes, the changes 
 are indeed terrifying, and have usually been accompanied by losses 
 to life and property, which are only to be compared with those of 
 great conflagrations or of inundations on thickly populated plains. 
 The conflagration has all too frequently been an aftermath of 
 the great historic earthquakes. The earthquake of December 28, 
 1908, in southern Italy, destroyed almost the entire population of 
 a great city, and left of its massive buildings only a confused heap 
 of rubble (Fig. 49). Two years later a heavy earthquake resulted 
 in great damage to cities in Costa Rica (Fig. 50), while two years 
 
 Fig. 50. — Ruins of the Carnegie Palace of Peace at Cartago, Costa Rica, de- 
 stroyed when almost completed by the great earthquake of May 4, 1910 (after 
 a photograph by Rear-Admiral Singer, U.S.N.). 
 
 earlier our own country was first really awakened to the danger 
 in which it stands from these convulsive earth throes; though, as 
 we shall see, these dangers can be largely met through proper 
 methods of construction. 
 
 Earthquakes are usually preceded for a brief instant bj^ sub- 
 terranean rumblings whose intensity appears to bear no relation 
 to the shocks which follow. The ground then rocks in wavelike 
 
EARTHQUAKES AND SEAQUAKES 
 
 69 
 
 motions, which, if of large amplitude, may induce nausea, prevent 
 animals from keeping upon their feet, and wreck all structures 
 not specially adapted to withstand them. Heavy bodies are some- 
 times thrown up from the ground (Fig. 51), and at other times 
 
 Fig. 51. — Bowlders thrown into the an- and overturned during the Assam 
 earthquake of 1897 (after R. D. Oldham). 
 
 similar heavy masses are, apparently because of their inertia, more 
 
 deeply imbedded in the earth. 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 (Fig. 52). 
 
 When bodies are thrown upward, it _____ p_ ^^ ^ ^ f.! 
 
 would imply that a quick upward ^ ' _ - . 
 
 movement of the ground had been fig. 52. — Heavy post sunk deeper 
 
 suddenly arrested, while the burial into the ground during the 
 
 of heavy bodies in the earth is prob- ':^^!i':^°'' l^'^^T^"^ ^"^"'* 
 
 31, 1886 (after Dutton). 
 
 ably due to a movement which 
 
 begins suddenly and is less abruptly terminated. 
 
 Seaquakes and seismic sea waves. — 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 shoal, though in most instances there is no visible commotion in 
 
70 
 
 EARTH FEATURES AND THEIR MEANING 
 
 the water. The distribution of these shocks, as indicated either 
 by the experiences of neighboring ships at the time of a particular 
 shock, or by the records of vessels which at different times have 
 sailed over an area of frequent seismic disturbance, appears to be 
 
 limited to narrow zones or lines (Fig. 
 53). The same tendency of under-sea 
 disturbances to be localized upon defi- 
 nite straight lines has been often illus- 
 trated 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 
 ■r, r<3 A/r T, • *v, 1 ranged upon a straight line. 
 
 Fig. 53. — Map showing the lo- ° ^ ° 
 
 caiities at which shocks have Far grander disturbances upon the 
 been reported at sea off Cape floor of the ocean have been revealed 
 
 Mendocino, California. -l j.i- j. j.i- n i 
 
 by the great sea waves — the so-called 
 " tidal waves," properly referred to as tsunamis — which recur in 
 those sea districts which adjoin the special earthquake zones upon 
 the continents (p. 86) . The forerunner of such a sea wave approach- 
 
 FiG. 54. — Effect of a seismic water wave at Kamaishi, Japan, in 1896 (after E. R. 
 
 Scidmore). 
 
 ing the shore is usually a sudden withdrawal of the water so as to 
 lay bare a portion of the bottom, 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 coun- 
 
EARTHQUAKES AND SEAQUAKES 
 
 71 
 
 try and encountered a mountain wall. Such seismic waves have 
 been especially common upon the Pacific shore of South America 
 and upon the Japanese littoral (Fig. 54). These waves proceed 
 from above the great deeps upon the ocean bottom, and clearly 
 result from the grander earth movements to which these depres- 
 sions owe their exceptional depth. 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 draw- 
 ing-in of the ocean surface above. 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 
 depression. 
 
 The grander and the lesser earth movements. — Upon the 
 land the grander and so-called catastrophic earthquakes are 
 usually the accompaniment of important changes in the sur- 
 face of the . ground that will be discussed in later sections. 
 Those shocks which do little damage to structures produce no 
 visible changes in the earth's surface, except, it may be, to shake 
 down some water-soaked masses of earth upon the steeper slopes. 
 Still other movements, and these too slight to be felt even in 
 the night when the animal world is at rest, may yet be distin- 
 guished by their sounds, the unmistakable rumblings which are 
 characteristic alike of the heaviest and the lightest of earth- 
 quake shocks. 
 
 Changes in the earth's surface during earthquakes — faults and 
 fissures. — 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 intense. 
 A section of the ground is usually'' 
 found to have moved with reference to 
 another upon the other side of a verti- 
 cal plane which is usually to be seen; 
 we have here to do with the actual 
 making of a fault or displacement such 
 as we find the fossil examples of within 
 the rocks. The displacement, or throw, 
 upon the fault plane may be either upward or downward or 
 laterally in one direction or the other, or these movements may be 
 
 Fig. 
 
 55. — A fault of vertical 
 displacement. 
 
72 
 
 EARTH FEATURES AND THEIR MEANING 
 
 combined. A movement of adjacent sections of the ground 
 
 upward or downward withi refer- 
 ence to each other (Fig. 55) has 
 been often observed, notably 
 at Midori after the great Jap- 
 anese earthquake of 1891, and 
 in the Chedrang valley of Assam 
 after the earthquake of 1897 
 (Fig. 56). 
 
 A lateral throw, unaccom- 
 panied by appreciable vertical 
 displacement (Fig. 57), is espe- 
 cially well illustrated by the 
 fault in California which was 
 formed during the earthquake 
 of 1906 (Fig. 58). A combination of the two types of displace- 
 ment in one (Fig. 59) is exempli- 
 
 FiG. 56. — Escarpment produced by an 
 earthquake fault of vertical displace- 
 ment which cut across the Chedrang 
 River and thus produced a waterfall, 
 Assam earthquake of 1897 (after R. D. 
 Oldham). 
 
 Fig. 57. — A fault of lateral displacement. 
 
 fied by the Baishiko fault of 
 Formosa at the place shown in 
 plate 3 A. 
 
 The measure of displacement. — To 
 afford some measure of the displacements 
 which have been observed upon earth- 
 quake faults, it may be stated that the 
 maximum vertical throw measured upon 
 the fault in the Neo valley of Japan (1891) 
 was 18 feet, in the Chedrang valley of 
 Assam (1897) 35 feet, and of the Alaskan 
 coast (1899) 47 feet. Large sections of 
 land were bodily uplifted in these cases 
 within the space of a few seconds, or 
 
 Fig. 58. — Fence parted and displaced 
 fifteen feet by a transverse fault 
 formed during the California earth- 
 quake of 1906 (after W. B. Scott). 
 
 Fig. 59. — Fault with verti- 
 cal and lateral displace- 
 ments combined. 
 
Plate 3. 
 
 A. An earthquake fault opened in Formosa in 1906, with vertical and lateral dis- 
 placements combined (after Omori). 
 
 B. Earthquake faults opened in Alaska in 1889, on which vertical slices of the 
 earth's shell have undergone individual adjustments (after Tarr and Martin). 
 
EARTHQUAKES AND SEAQUAKES 
 
 73 
 
 at most a few minutes, by the amounts given. The largest re- 
 corded lateral displacement measured upon an earthquake fault 
 is about 21 feet upon the California ^ 
 rift after the earthquake of 1906 ; 
 though an amount only slightly less 
 than this is indicated in the shifting 
 of roads and arroyas dating from the 
 earthquake of 1872 in the Owens valley, 
 California. Fault lines once established 
 are planes of special weakness and 
 become later the seat of repeated 
 movements of the same kind. 
 
 The greater number of earthquake 
 faults are found in the loose rock cover 
 Avhich so generally mantles the firmer ^^o- ^O- - Diagram to show how 
 
 . , small faults in the rock base- 
 
 rock basement, and it is almost certain ^^^^ j^ay be masked at the 
 
 that the throws within the solid rock surface through adjustments 
 
 are considerably larger than those within the loose rock mantle, 
 which are here measured at the surface, owing to the adjustments 
 which so readily take place in the looser materials. Those lighter 
 shocks of earthquake which are accompanied by no visible dis- 
 placements at the surface do, 
 however, in some instances affect 
 in a measure the flow of water 
 upon the surface, and thus indi- 
 cate that small changes of sur- 
 face level have occurred without 
 breaks sufficiently sharp to be 
 perceived (Fig. 60). Intermedi- 
 ate between the steep escarpment 
 and the masked displacement 
 just described is the so-called 
 "mole-hill" effect, — a rounded 
 Fig. 61. — Diagram to show the appear- and variously cracked slope or 
 
 ance of a "mole hill" above a buried ridge aboVC the pOSition of a 
 
 earthquake fault (after Koto). 
 
 buried fault (Fig. 61). 
 
 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 most ; for because of their verticality 
 
74 
 
 EARTH FEATURES AND THEIR MEANING 
 
 they must gradually disappear in rounded slopes under the action 
 of the elements. Smaller displacements within a rock which 
 
 rapidly disintegrates under 
 
 r.^ife''#^^ 
 
 
 
 
 v;g|i^i^|^ 
 
 
 \ 
 
 the action of frost and sun 
 will likewise before long be 
 effaced. In those excep- 
 tional instances where a 
 resistant rock type has had 
 all altered upper layers 
 planed away until a fresh 
 and hard surface is ex- 
 posed, and has further 
 -^.° ■" s_ "-X. been protected from the 
 
 Fig. 62. — Post-glacial earthquake faults of small frost and SUn beneath a 
 but cumulative displacement, eastern New thin layer of Soil, its Origi- 
 York (after Woodworth). i ,. 
 
 nal surface may be re- 
 tained unaltered for many centuries. Upon such a surface the 
 lightest of sensible shocks, or even the smaller earth movements 
 which are not perceived at the time, may leave an almost indelible 
 record. Such records particu- 
 larly show that the movements 
 which they register occur upon 
 the planes of jointing within the 
 rock, and that these ready 
 formed cracks have probably 
 been the seats of repeated and 
 cumulative adjustments (Fig. 
 62). 
 
 Contraction of the earth's 
 surface during earthquakes. — 
 The wide variations in the 
 amount of the lateral displace- 
 ment upon earthquake faults, 
 hke those opened in California 
 in 1906, show that at the time of 
 
 a heavy earthquake there must Fig- 63. — Earthquake cracks in Colorado 
 , , 111 .1 desert (after a photograph by Sauerven). 
 
 be large local changes m the 
 
 density of the surface materials. Literally, thousands of fis- 
 sures may appear in the lowlands, many of them no doubt a 
 
EARTHQUAKES AND SEAQUAKES 
 
 75 
 
 secondary effect of the shaking, but others, Hke the quebradas of 
 the southern Andes or the " earthquake cracks " in the Colorado 
 desert (Fig. 63), may have a deeper-seated origin. Many facts 
 go to show, however, that though local expansion does occur in 
 
 Fig. 
 
 64. — Diagrams to show how railway tracks are either broken or buckled 
 locally within the district visited by an earthquake. 
 
 some localities, a surface contraction is a far more general conse- 
 quence of earth movement. In civilized countries of high indus- 
 trial development, where lines of metal of one kind or another run 
 for long distances beneath or upon the surface of the ground, such 
 general contraction of the surface may be easily proven. Com- 
 
 FiG. 65. 
 
 ■The Biwajima railroad bridge in Japan after the earthquake of 1891 
 (after Milne and Burton). 
 
 paratively seldom are lines of metal pulled apart in such a way 
 as to show an expansion of the surface ; whereas bucklings and 
 kinkings of the lines appear in many places to prove that the area 
 within which they are found has, as a whole, been reduced. 
 
 Water pipes laid in the ground at a depth of some feet may be 
 bowed up into an arch which appears above the surface ; lines of 
 
76 
 
 EARTH FEATURES AND THEIR MEANING 
 
 curbing are raised into broken arches, and the tracks of railways 
 are thrown into local loops and kinks which imply a very consid- 
 erable local contraction of the surface (Fig. 64). With unvarying 
 regularity railway or other bridges which cross rivers or ravines, 
 if the structures are seriously damaged, indicate that the river 
 banks have drawn nearer together at the time of the disturbance. 
 In such cases, whenever 
 
 „ ^ ,, ,, - - - -.- " ^.^/^i V/^ ^- ' ' ■ ■■■" • abutments, these have 
 
 T7-i^Y^^ either been broken or back- 
 
 B tilted as a whole in such a 
 
 Fig. 66. — Diagrams to show how the compres- 
 sion of a district and its consequent contraction 
 during an earthquake may close up the joint 
 spaces within the rock basement and concen- 
 trate the contraction of the overlying mantle 
 where this is partially cut through and so 
 weakened in the valley sections. 
 
 manner as to indicate an 
 approach of the founda- 
 tions which was prevented 
 at the top by the stiffness 
 of the girder (Fig. 65). 
 The simplest explana- 
 tion 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 rock, and an adjust- 
 ment of the mantle upon the floor mainly in the valley sections 
 (Fig. 66). 
 
 The plan of an earthquake fault. — In our consideration of earth- 
 quake faults we have thus far given our attention to the displace- 
 
 FiG. 67. — Map of the Chedrang fault which made its appearance during the Assam 
 earthquake of 1897. The figures give the amounts of the local vertical displace- 
 ment measured in feet (after R. D. Oldham). < 
 
 ment as viewed at a single locality only. Such displacements are, 
 however, continued for many miles, and sometimes for hundreds 
 of miles ; and when now we examine a map or plan of such a line 
 of faulting, new facts of large significance make their appearance. 
 This may be well illustrated by a study of the plan of the Chedrang 
 
EARTHQUAKES AND SEAQUAKES 
 
 77 
 
 fault which appeared at the time of the Assam earthquake of 
 1897 (Fig. 67). From this map it will be noticed that the upward 
 or downward displacement upon the perpendicular plane of the- 
 fault is not uniform, but is subject to large and sudden changes* 
 Thus in order the measurements in feet 
 are 32, 0, 18, 35, 0, 8, 25, 12, 8, 2, 0. 
 The fault formed in 1899 upon the 
 shores of Russell Fjord in Alaska (Fig. 
 68) reveals similar sudden, changes of 
 throw, only that here the direction of 
 the movement is often reversed; or, 
 otherwise expressed, the upthrow is 
 suddenly transferred from one side of 
 the fault to the other. Such abrupt 
 changes in the direction of the dis- 
 placement have been observed upon 
 
 Fig. 69. — Abrupt change in the direction 
 of throw upon an earthquake fault which 
 was formed in the Owens valley, Califor- 
 nia, in 1872. 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 (after a 
 photograph by W. D. Johnson). 
 
 M I LE£. 
 
 Fig. 68. — Map giving the 
 displacements in feet 
 measured along an earth- 
 quake fault formed in 
 Alaska in 1899 (after Tarr 
 and Martin). 
 
 many earthquake faults, and a particularly striking one is repre- 
 sented in Fig. 69. 
 
 The block movements of the disturbed district. — The displace- 
 ments upon earthquake faults are thus seen to be subdivided into 
 sections, each of which differs from its neighbors upon either side 
 and is sharply separated from them, at least in many instances. 
 These points of abrupt change of displacement are, in many cases 
 at least, the intersection points with transverse faults (Fig. 69). 
 
78 
 
 EARTH FEATURES AND THEIR MEANING 
 
 Such points of abrupt change in the degree or in the direction of 
 the displacement may be, when looked at from above, abrupt 
 
 turning points in the direction 
 of extension of the fault, whose 
 course upon the map appears as 
 a zigzag line made up of straight 
 sections connected by sharp 
 elbows (Fig. 70). 
 
 Such a grouping of surface 
 faults as are represented upon 
 the map is evidence that the 
 area of the earth's shell, which 
 is included, has at the time of 
 the earthquake been subject to 
 adjustments as a series of sepa- 
 rate units or blocks, certain of 
 the boundaries of which are the 
 fault lines represented. The 
 changes in displacement meas- 
 ured upon the larger faults 
 make it clear that the observed 
 faults can represent but a frac- 
 tion of the total number of 
 lines of displacement, the others 
 being masked by variations in 
 the compactness of the loose 
 mantling deposits. Could we 
 but have this mantle removed, 
 we should doubtless find a rock 
 floor separated into parts like 
 an ancient Pompeiian pavement, 
 the individual blocks in which 
 have been thro'wn, some upward 
 and some downward, by vary- 
 ing amounts. Less than a 
 hundred miles away to the east- 
 ward from the Owens valley, a 
 portion of this pavement has 
 been uncovered in the extensive 
 
 Fig. 70. — Map of the faults within an area 
 of the Owens valley, California, formed 
 in part during the earthquake of 1872, 
 and in part due to early disturbances. 
 In the western portions the displace- 
 ments cut across firm rock and alluvial 
 deposits alike without deviation of di- 
 rection (after a map by W. D. Johnson). 
 
EARTHQUAKES AND SEAQUAKES 
 
 79 
 
 operations of the Tonapah Min- 
 ing District, so that there we 
 may study in all its detail the 
 elaborate pattern of earth mar- 
 quetry (Fig. 71) which for the 
 floor of the Owens valley is as 
 yet denied us. 
 
 The earth blocks adjusted 
 during the Alaskan earthquake 
 of 1899. — For a study of the 
 adjustments which take place 
 between neighboring earth blocks 
 during a great earthquake, the 
 recent Alaskan disturbance has 
 
 Fig. 72. — Map of a portion of the Alaskan coast to 
 show the adjustments in level during the earth- 
 quake of 1899 (after Tarr and Martin). 
 
 Fig. 71. — Marquetry of the rock floor 
 of the Tonapah Mining District, 
 Nevada (after Spurr). 
 
 offered the advantage 
 that the most affected 
 district was upon the 
 seacoast, where changes 
 of level could be referred 
 to the datum of the sea's 
 surface. Here a great 
 island and large sections 
 of the neighboring shore 
 underwent movements 
 both as a whole in large 
 blocks and in adjust- 
 ments of their subordi- 
 nate parts among them- 
 selves (Fig. 72). Some 
 sections of the coast were 
 here elevated by as much 
 as 47 feet, while neigh- 
 boring sections were up- 
 lifted by smaller amounts 
 (Fig. 73), and certain 
 smaller sections were 
 even dropped below the 
 level of the sea. The 
 amount of such subsid- 
 
80 
 
 EARTH FEATURES AND THEIR MEANING 
 
 ence is, however, difficult to ascertain, for the reason that the 
 former shore features are now covered with water and thus removed 
 
 from observation. In favor- 
 able localities the minimum 
 amount of submergence may 
 sometimes be measured upon 
 forest trees which are now 
 flooded with sea water. In 
 Fig. 74 a portion of the 
 coast is represented where 
 the beach sand is now ex- 
 tended back into the spruce 
 forest, a distance of a hun- 
 dred feet or more, and where 
 
 
 Fig. 73. — View on Haencke Island, Disen- 
 chantment Bay, Alaska, revealing the shore 
 that rose seventeen feet above the sea during 
 the earthquake of 1899, and was found with Scdgy bcach graSS is growing 
 barnacles still clinging to the rock (after ^mong trees whose rOOts are 
 Tarr and Martin). 7 i • i 
 
 now laved m salt water. 
 At the front of this forest the great storm waves overturn the 
 trees and pile the wreckage in front of those that still remain 
 standing. 
 
 Upon the glaciated rock surfaces of the Alaskan coast, excep- 
 tionally favorable opportunities are found for study of the intricate 
 
 Fig. 74. — Partially submerged forest 
 upon the shore of Knight Island, Alaska, 
 due to the sinking of a section of the 
 coast during the earthquake of 1899 
 (after Tarr and Martin). 
 
 ■ Settlement of a section of the 
 shore at Port Royal, Jamaica, during 
 the earthquake of January 14, 1907, 
 adjacent to a similar but larger settle- 
 ment of the near shore during the 
 earthquake of 1692 (after a photo- 
 graph by Brown). 
 
 pattern of the earth mosaic which is under adjustment at the time 
 of an earthquake. Upon Gannett Nunatak the surface was found 
 divided by parallel faults into distinct slices which individually 
 underwent small changes of level (plate 3B). 
 
CHAPTER VIII 
 
 THE INTERRUPTED CHARACTER OF EARTH MOVE- 
 MENTS: EARTHQUAKES AND SEAQUAKES (Concluded) 
 
 Experimental demonstration of earth movements. — The study 
 of the Alaskan earthquake of 1899 showed that during this adjust- 
 ment within the earth's shell some of the local blocks moved up- 
 ward and by larger amounts than their neighbors, and that still 
 others were actually depressed so that the sea flowed over them. 
 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 it. From under 
 those strips of coast land which were depressed, material must 
 have been moved so as to fill the void which would otherwise have 
 formed beneath the sections that were uplifted. If we take into 
 consideration much larger fractions upon the surface of our planet, 
 we are taught by the great seaquakes which are now registered 
 upon earthquake instruments at distant stations that large down- 
 ward 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 mountains. From 
 under the offshore deeps of the ocean to beneath the growing 
 mountains upon the shore, a transfer of earth material must be 
 assumed to take place when disturbances are registered. 
 
 Within the time interval that separates the sudden adjustments 
 of the surface which are manifested in earthquakes, the condition 
 of strain which brings them about is steadily accumulating, due, 
 as we generally assume, to earth contraction through loss of its 
 heat. It seems probable that the resistance to an immediate ad- 
 justment is found in the rigidity of the shell because of the com- 
 pression to which it is subjected. To illustrate : a row of blocks 
 well fitted to each other may be held firmly as a bridge between 
 the jaws of a vice, because so soon as each block starts to fall a 
 large resistance from friction upon its surface is called into exist- 
 ence, a force which increases with the degree of compression. 
 G 81 
 
82 EARTH FEATURES AND THEIR MEANING 
 
 It is thus possible upon this assumption crudely to demonstrate 
 the adjustment of earth blocks by the simple device represented in 
 plate 4 A. The construction of this experimental tank is so simple 
 that little explanation is necessary. Wooden blocks of different 
 heights are supported in water within a tank having a glass front, 
 and are kept in a strained condition at other than their natural 
 positions of flotation by the compression of a simple vice at the 
 top. Held firmly in this position, they may thus represent the 
 neighboring blocks within the earth's outer shell which are sup- 
 ported upon relatively yielding materials beneath, and prevented 
 from at once adjusting themselves to their natural positions through 
 the compression to which they are subjected. Held as they now 
 are, the water near the ends of the tank is forced up beneath the 
 blocks to higher than its natural level, and thus tends to flow from 
 both ends toward the center. Such a movement would permit 
 the end blocks to drop and force the middle ones to rise. The end 
 blocks are, let us say, the sections of Alaskan coast line which sunk 
 during the earthquake, as the center blocks are the sections which 
 rose the full measure of 47 feet. Upon a larger scale the end blocks 
 may equally well be considered as the floor of the great deeps off 
 the Alaskan coast, whose sinking at the time of the earthquake 
 was the cause of the great sea wave. Upon this assumption the 
 center blocks would represent the Alaskan coast regarded as a 
 whole, which underwent a general uplift. 
 
 Though we may not, in our experiment, vary the tendency to 
 adjustment by any contractional changes in either the water or 
 the blocks, we may reduce the compression of the vice, which leads 
 to the same general result. As the compression of the vice is 
 slowly relaxed, a point is at last reached at which friction upon 
 the block surfaces is no longer sufficient to prevent an adjustment 
 taking place, and this now suddenly occurs with the result shown in 
 plate 4 B. In the case of the earth blocks, this sudden adjustment 
 is accompanied by mass movements of the ground separated by 
 faults, and these movements produce successional vibrations that 
 are particularly large near the block margins, and other frictional 
 vibrations of such small measure as to be generally appreciated by 
 sounds only. The jolt of the adjustments has thrown some blocks 
 beyond their natural position of rest, and these sink and rise sub- 
 sequently in order to readjust themselves with lighter vibrations, 
 
Plate 4. 
 
 P 
 
 A. Experimental tank to illustrate the earth movements which are 
 manifested in earthquakes. The sections of the earth's shell are here 
 represented before adjustment has taken place. 
 
 B. The same apparatus after a sudden adjustment. 
 
 ^^^^^KS^v -"„3E^ 
 
 C. Model to illustrate a block displacement in rocks which are intersected 
 by master joints. 
 
EARTHQUAKES AND SEAQUAKES 
 
 83 
 
 /^ 
 
 £~/ns 
 
 which may be repeated and continued for some time. In the case 
 of the earth these later adjustments are the so-called aftershocks 
 which usually continue throughout a considerable period follow- 
 ing every great earthquake. Gradually they fall off in intensity 
 and frequency until they can no longer be felt, and are thereafter 
 continued for a time as rumblings only. 
 
 Derangement of water flow by earth movement. — 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 fracture. The surface water layers in the tank may, how- 
 ever, be considered in a different 
 way, since their behavior is remark- 
 ably like that of the water within 
 and upon the earth's surface during 
 an earth adjustment. At the instant 
 when adjustment takes place in the 
 tank, water frequently spurts upward 
 from the cracks between the sinking 
 end blocks ; 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 tank, a " lake " will 
 be formed above it. When the ad- 
 justment occurs, this lake is im- 
 mediately drained by outflow of the water at its bottom along 
 one of the cracks between the blocks (Fig. 76). 
 
 Such derangements of water flow as have been illustrated by 
 the experiment are among the commonest of the phenomena 
 which accompany earthquakes. Lakes and swamp lands have 
 during earthquakes been suddenly drained, 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 suck- 
 ing down of the water with later readjustment. During the great 
 earthquake of the lower Mississippi valley in 1811, known as the 
 New Madrid earthquake, the earlier Lake Eulalie was completely 
 drained, and upon the now exposed bed there appeared parallel 
 fissures on which were ranged funnel-like openings down which 
 the water had been sucked. In other sections of the affected 
 region the water shot up in sheets along fissures to the tops of high 
 
 
 
 
 
 
 
 
 
 
 
 mmi 
 
 -mm/ziK. 
 
 
 
 B 
 
 mm/Ay 
 
 
 
 mmy//. 
 
 
 Fig. 76. — Diagrams to illustrate 
 the draining of lakes during 
 earthquakes. 
 
84 
 
 EARTH FEATURES AND THEIR MEANING 
 
 trees. Areas where such spurting up of the water has been ob- 
 served have in most cases been shown to correspond to areas of 
 depression, and such areas have sometimes been left flooded with 
 water. During the Indian earthquake of 1819 an area of some 
 200 square miles suddenly sank and was transformed into a lake. 
 Sand or mud cones and craterlets. — From a very moderate 
 depth below the surface to that of several miles, all pore spaces 
 
 EovVhqwake SpKingSjfouti- 
 .F^V-r^er Lakedr-a;nei.,,_^^'>'"S.S«"'«o"!**'^''°^*'''®^' Swamp drained 
 
 rn>^ ' ^ '* '"* *"* 'v 'i^ 't* ^'''c^'^Tr^^'SiCL" i-zz^ 
 
 Fig. 77. — Diagram to illustrate the derangements of flow of water at the time of 
 an earthquake ; water i ssuing at the surface over down thrown rocks, and being 
 sucked down in upthrown blocks. 
 
 and all larger openings within the rock are completely filled with 
 water, the " trunk lines " of whose circulation is by way of the 
 joints or along the bedding planes of the rocks. The principal 
 reservoirs, so to speak, of this water inclosed within the rock are 
 
 Fig. 78. — Mud cones aligned upon a fissure opened at Moraza, Servia, during 
 the earthquake of April 4, 1904 (after Michailovitch). 
 
 the porous sand formations. When, now, during an earthquake a 
 block of the earth's shell is suddenly sunk and as suddenly arrested 
 
EARTHQUAKES AND SEAQUAKES 
 
 85 
 
 in its downward movement, the effect is to compress the porous 
 layers and so force the contained water upward along the joints to 
 the surface, carrying with it large quantities of the sand (Fig. 77). 
 
 wm 
 
 Fig. 79. — One of the many craterlets formed near Charleston, South Carolina, 
 during the earthquake of August 31, 1886. The opening is twenty feet across, 
 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 (after Button). 
 
 Ejected at the surface this water appears in fountains usually 
 arranged in line over joints, or even in continuous sheets, and the 
 sand collecting about 
 the jets builds up lines ^'^"^^' 
 
 of sand or mud cones 
 sometimes described as 
 "mud volcanoes" (Fig. 
 78). The amount of 
 sand thus poured out 
 is sometimes so great 
 that blankets of quick- 
 sand are spread over 
 large sections of the 
 country. Most fre- 
 quently, however, the sand is not built above the general level 
 of the surface, but forms a series of craterlets which are largely 
 
 Fig. 80. — Cross section of a craterlet to show the 
 trumpet-like form of the sand column. 
 
86 EARTH FEATURES AND THEIR MEANING 
 
 shaped as the water is sucked down at the time of the readjustment 
 with which the play of such earthquake fountains is terminated 
 (Fig. 79). Subsequent excavations made about such craterlets 
 have shown them to have the form of a trumpet, 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 hetero- 
 geneous materials of the sand layers and carried upward in the 
 rush of water to the surface (Fig. 80). 
 
 The earth's zones of heavy earthquake. — Since earthquakes 
 give notice of a change of level of the ground, the special danger 
 zones from this source are the growing mountain systems which 
 are usually found near the borders of the sea. Such lines of moun- 
 tains are to-day rising where for long periods in the past were the 
 basins of deposition of former seas. 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 level. 
 
 By far the most unstable belt upon the earth's surface is the 
 rim surrounding the Pacific Ocean, within which margin it has 
 been estimated that about 54 per cent of the recorded shocks of 
 earthquake have occurred. Next in importance for seismic in- 
 stability is the zone which borders both the Mediterranean Sea 
 and the Caribbean — the American Mediterranean — and is ex- 
 tended across central Asia through the Himalayas into Malaysia. 
 Both zones approximate to great circles upon the earth's surface 
 and intersect each other at an angle of about 67°. It has been 
 estimated that about 95 per cent of the recorded continental earth- 
 quakes have emanated from these belts. 
 
 The special lines of heavy shock. — Within any earthquake 
 district the shocks are not felt with equal severity at all places, 
 but there are, on the contrary, definite lines which the disturbance 
 seems to search out for special damage. From their relations to 
 the relief of the land these fines would appear to be lines of fracture 
 upon the boundaries of those sections of the crust that play in- 
 dividual roles in the block adjustment which takes place. More 
 or less masked as these lines are beneath the rounded curves of 
 the landscape, they are given an altogether unenviable prominence 
 with each succeeding earthquake. At such times we may think 
 of the earth's surface as specially sensitized for laying bare its 
 
EARTHQUAKES AND SEAQUAKES 
 
 87 
 
 hidden structure, as is the sensitized plate under the magical in- 
 fluence of the X rays. 
 
 When, at the time of an earthquake, blocks are adjusted with 
 reference to their neighbors, the movements of oscillation are 
 greatest in those marginal portions 
 of direct contact. Corners of blocks 
 — the intersecting points of the im- 
 portant faults — should for the same 
 reason be shaken with a double 
 violence, and this assumption ap- 
 pears to be confirmed by observation. 
 J Upon the island 
 
 of Ischia, off the 
 Bay of Naples, 
 the shocks from 
 recent earth- 
 quakes have 
 been strangely 
 concentrated 
 near the town of 
 Casamicciola, 
 
 which was last destroyed in 1883. This un- 
 fortunate city lies at the crossing point of 
 important fractures whose course upon the 
 island is marked by numerous springs and 
 suffioni (Fig. 81). 
 
 Seismotectonic lines. — The lines of im- 
 portant earth fractures, as will be more clearly 
 shown in the sequel (p. 227), are often indi- 
 cated with some clearness by straight lines in 
 the plan of the surface relief (Fig. 82). Lines 
 of this nature are easily made out upon the 
 map of the West Indies, and if we represent 
 
 .——Epicenlrum of I883. 
 
 Intense cfestrucUve Area 1796 
 
 Fig. 81. — Map of the island of 
 Ischia to show how the shocks 
 of recent earthquakes have been 
 concentrated at the crossing 
 point of two fractures (after 
 Mercalli and Johnston-Lavis). 
 
 ScaZe. 
 
 SSMUes 
 
 Fig. 82. — a line of earth 
 fracture indicated in 
 the plan of the relief, 
 
 which may at any time upon it by circles of different diameters the 
 
 become the seat of combined intensities of the recorded earth- 
 movement and result- , • ,^ ■ • , • • , , i , 
 ant shock. quakes m the various cities, it appears that 
 
 the heavily shaken localities are ranged upon 
 
 lines stamped out in the relief, with the most severely damaged 
 
 places at their intersections (Fig. 83). These lines of exceptional 
 
88 
 
 EARTH FEATURES AND THEIR MEANING 
 
 
 :^^'^>^^4 
 
 
 Fig. 83. — Seismotectooic lines of the West Indies. 
 
 instability are known as seismotedonic lines — earthquake struc- 
 ture lines. 
 
 The heavy shocks above loose foundations. — It is character- 
 istic of faults that they soon bury themselves from sight under 
 loose materials, and are thus made difficult of inspection. The 
 escarpment which is the direct consequence of a vertical displace- 
 ment upon a fault tends to migrate from the place of its formation, 
 rounding the surface as it does so and burying the fault line beneath 
 its deposits (Fig. 43, p. 60). 
 
 This is not, however, the sole reason why loose foundations 
 should be places of special danger at the time of earth shocks, for 
 the reason that earthquake waves are sent out in all directions 
 from the surfaces of displacement through the medium of the un- 
 derlying rock. These waves travel 
 within the firm rock for considerable 
 distances with only a gradual dissipa- 
 tion of their energy, but with their 
 entry into the loose surface deposits 
 their energy is quickly used up in 
 local vibratiohs of large amplitude, 
 and hence destructive to buildings. 
 
 The essential difference between 
 firm rock and such loose materials as 
 are found upon a river bottom or in 
 the " made land " about our cities 
 may be illustrated Vy the simple 
 device which is represented in Fig. 84. Two similar metal pans 
 are suspended from a firm support by bands of steel and "elastic" 
 braid of similar size and shape, and carry each a small block of 
 wood standing upon its end. Similar light blows are now admin- 
 istered directly to the pans with the effect of upsetting that block 
 
 Fig. 84. — Devnce to illustrate the 
 different effects upon the trans- 
 mission and the character of 
 shocks which are produced by 
 firm rock and by loose materials. 
 
EARTHQUAKES AND SEAQUAKES 89 
 
 which is supported by the loose braid because of the large range 
 or amplitude of movement that is imparted to the pan. The 
 " elastic " braid, because of these large vibrations of which it is 
 susceptible, may represent the loose materials when an earthquake 
 wave passes into them. In the case of the steel support, the 
 energy of the blow, instead of being dissipated in local swingings 
 of the pan, is to a large extent transmitted through the elastic 
 metal to materials beyond. The steel thus resembles in its high 
 elasticity the firmer rock basement, which receives and transmits 
 the earthquake shocks, but except when ruptured in a fault is 
 subject to vibrations of small amplitude only. 
 
 Construction in earthquake regions. — Wherever earthquakes 
 have been felt, they are certain to occur again; and wherever 
 mountains are growing or changes of level are in progress, there 
 no record of past earthquakes is required in order to forecast the 
 future seismic history. Although the future earthquakes may be 
 predicted, the time of their coming is, fortunately or unfortunately, 
 still hidden from us. If one's lot is to be cast in an earthquake 
 country, the only sane course to pursue is to build with due regard 
 to future contingencies. 
 
 The danger from destructive fires may to-day be largely met 
 by methods of construction which levy an additional burden of 
 cost. Though the danger from seismic disturbances can hardly 
 be met as fully as that from fire, 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 displacement. Here, 
 also, a considerable additional expense is involved in the method 
 of construction, in the case of residences particularly. 
 
 From what has been said, 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 foundation. 
 The choice of building materials is next of importance. Those 
 buildings which succumb to earthquakes' are in most cases racked 
 or shaken apart, and thus they become a prey to their own inherent 
 properties of inertia. Each part of a structure may be regarded 
 as a weight which is balanced upon a stiff rod and pivoted upon 
 the ground. When shocks arrive, each part tends to be thrown 
 into vibration after the manner of an inverted pendulum. In 
 proportion, therefore, as the weights are large and rest upon long 
 
90 
 
 EARTH FEATURES AND THEIR MEANING 
 
 supports, the danger of overthrow and of tearing apart is increased. 
 In general, structures are best constructed of light materials whose 
 weight is concentrated near the ground. Masonry structures, 
 and especially high ones, are, therefore, the least suited for resisting 
 earthquakes, of which the late complete destruction of the city 
 of Messina is a grewsome reminder. Despite repeated warnings 
 in the past, the buildings of that stricken city were generally con- 
 structed of heavy rubble, which in addition had been poorly ce- 
 mented (Fig. 49, p. 67). Such structures are usually first ruptured 
 at the edges and corners, since here the vibrations which tend to 
 
 
 FiG. 85. — House wrecked in San Francisco earthquake of 1906 because the floors 
 and partitions were not securely fastened to the walls (after R. L. Humphrey). 
 
 tear the building asunder are resisted by no supports and are 
 reenforced from neighboring walls. 
 
 An advantage of the first importance is evidently secured if the 
 rods of the pendulum, of which the building is conceived to be com- 
 posed, have sufficient elasticity to be considerably distorted with- 
 out rupture and to again recover their original position. This is 
 the supreme advantage of structural steel for all large buildings, 
 which is coupled, however, with the disadvantage that the 
 riveted fastenings are apt to be quickly sheered off under the 
 vibrations. Large and high buildings, when sufficiently elastic, 
 have fortunately the property of destroying the earth waves 
 by interference before they have traveled above the lower 
 stories. 
 
 For large structures in which wood cannot be used, strongly 
 
EARTHQUAKES AND SEAQUAKES 
 
 91 
 
 reenforced concrete is well adapted, for it has in general the same 
 advantages as steel with somewhat reduced elasticity-, but with a 
 more effective binding together of the parts. This requirement 
 of thorough bracing and tying together of the several parts of a 
 building causes it to vibrate, not as many pendulums, but as one 
 body. If met, it removes largely the danger from racking strains, 
 and for small structures particularly it is the requirement which 
 is most easily complied with. For such buildings it is therefore 
 necessary that the framework should be built in a close network 
 
 Fig. 86. — Building wrecked at San Mateo, California, during the late earth- 
 quake. The heavy roof and upper floor, acting as a unit, have battered down 
 the upper walla (after J. C. Branner). 
 
 with every joint firmly braced and with all parts securely tied to- 
 gether. Especial attention should be given to the fastenings of 
 floor and partition ends. The house shown in Fig. 85 could not 
 have been subjected to heavy shocks, for though the walls are 
 thrown down, the floors and partitions have been left near their 
 original positions. 
 
 This tendency of the walls, floors, partitions, and roof to act 
 as individual units in the vibration, is one that must be reckoned 
 with and be met by specially effective bracing and tying at the 
 junctions. Otherwise these larger parts of the structure may act 
 like battering rams to throw over the walls or portions of them 
 (Fig. 86). 
 
92 EARTH FEATURES AND THEIR MEANING 
 
 Reading References for Chapters VII and VIII 
 
 General works : — 
 John Milne. Seismology. London, 1898, pp. 320. 
 C E. DuTTON. Earthquakes in the Light of the New Seismology. Put- 
 nam, New York, 1904, pp. 314. 
 
 A. Sieberg. Handbuch der Erdbebenkunde. Braunschweig, 1904, pp. 
 
 362. 
 Count F. de Montessus de Ballore. Les Tremblements de Terre, 
 
 Geographie Seismologique. Paris, 1906, pp. 475 ; La Science Seismo- 
 
 logique. Paris, 1907, pp. 579. 
 William Herbert Hobbs. Earthquakes, an Introduction to Seismic 
 
 Geology. Appleton, New York, 1907, pp. 336. 
 C. G. Knott. The Physics of Earthquake Phenomena. Clarendon Press, 
 
 Oxford, 1908, pp. 283. 
 E. Rudolph. Ueber Submarine Erdbeben und Eruptionen, Beitrage zur 
 
 Geophysik, vol. 1, 1887, pp. 133-365 ; vol. 2, 1895, pp. 537-666 ; vol. 3, 
 
 1898, pp. 273-536. 
 
 Descriptive reports of some important earthquakes : — 
 
 C. E. DuTTON. The Charleston Earthquake of August 31, 1886, 9th 
 Ann. Rept. U. S. Geol. Surv., 1889, pp. 203-528. 
 
 B. Koto. On the Cause of the Great Earthquake in Central Japan, 1891, 
 
 Jour. Coll. Sci. Imp. Univ., Tokyo, Japan, vol. 5, 1893, pp. 295-353, 
 
 pis. 28-35. 
 John Milne and W. K. Burton. The Great Earthquake of Central 
 
 Japan. 1891, pp. 10, pis. 30. 
 R. D. Oldham. Report on the Great Earthquake of 12th June, 1897, 
 
 Mem. Geol. Surv. India. Vol. 29, 1899, pp. 379, pis. 42. 
 A. C. Lawson, and others. The California Earthquake of April 18, 1906, 
 
 Report of the State Earthquake Investigation Commission, three 
 
 quarto vols. (Carnegie Institution of Washington) ; many plates and 
 
 figures. 
 Italian Photographic Society, Messina and Reggio before and after the 
 
 Earthquake of December 28, 1908 (an interesting coUeetion of pic- 
 tures). Florence, 1909. 
 R. S. Tarr and L. Martin. Recent Changes of Level in the Yakutat 
 
 Bay Region, Alaska, Bull. Geol. Soc. Am., vol. 17, 1906, pp. 29-64, 
 
 pis. 12-23. 
 William Herbert Hobbs. The Earthquake of 1872 in the Owens 
 
 Valley, California, Beitrage zur Geophysik, vol, 10, 1910, pp. 352- 
 
 385, pis, 10-23. 
 
 Faults in connection with earthquakes : — 
 
 William H. Hobbs. On Some Principles of Seismic Geology, Beitrage zur 
 Geophysik, vol. 8, 1907, Chapters iv-v. 
 
EARTHQUAKES AND SEAQUAKES 93 
 
 Expansion or contraction of the earth's surface during earthquakes : — 
 
 William H. Hobbs. A Study of the Damage to Bridges during Earth- 
 quakes, Jour. Geol., vol. 16, 1908, pp. 636-653 ; The Evolution and 
 the Outlook of Seismic Geology, Proc. Am. Phil. Soc, vol. 48, 1909, 
 pp. 27-29. 
 
 Earthquake construction : — 
 
 John Milne. Construction in Earthquake Countries, Trans. Seis. Soc, 
 Japan, vol. 14, 1889-1890, pp. 1-246. 
 
 F. DE MoNTESSus DE Ballorb. L'art de batir dans les pays a tremble- 
 ments de terre (34th Congress of French Architects), L' Architecture, 
 193 Annee, 1906, pp. 1-31. 
 
 Gilbert, Humphrey, Sewell, and Soule. The San Francisco Earth- 
 quake and Fire of April 18, 1906, and their Effects on Structures and 
 Structural Materials, BuU. 324, U. S. Geol. Surv., 1907, pp. 1-170, 
 pis. 1-57. 
 
 William H. Hobbs. Construction in Earthquake Countries, The En- 
 gineering Magazine, vol. 37, 1909, pp. 1-19. 
 
 Lewis Alden Estes. Earthquake-proof Construction, a discussion of the 
 effects of earthquakes on building construction with special reference 
 to structures of reenforced concrete, published by Trussed Concrete 
 Steel Company. Detroit, 1911, pp. 46. 
 
CHAPTER IX 
 
 THE RISE OF MOLTEN ROCK TO THE EARTH'S 
 SURFACE 
 
 VOLCANIC MOUNTAINS OF EXUDATION 
 
 Prevalent misconceptions about volcanoes. — The more or less 
 common impression that a volcano is a " burning mountain " 
 or a " smoking mountain " has been much fostered by the school 
 texts in physical geography in use during an earlier period. The 
 best introduction to a discussion of volcanoes is, therefore, a disil- 
 lusionment from this notion. Far from being burning or smoking, 
 there is normally no combustion whatever in connection with a 
 volcanic eruption. The unsophisticated tourist who, looking out 
 from Naples, sees the steam cap which overhangs the Vesuvian 
 crater tinged with brown, easily receives the impression that the 
 material of the cloud is smoke. Even more at night, when a bright 
 glow is reflected to his eye and soon fades away, only to again glow 
 brightly after a few moments have passed, is it difficult to remove 
 the impression that one is watching an intermittent combustion 
 within the crater. The cloud which floats away from the crest of 
 the mountain is in reality composed of steam with which is ad- 
 mixed a larger or smaller proportion of fine rock powder which 
 gives to the cloud its brownish tone. The glow observed at night 
 is only a reflection from molten lava within the crater, and the 
 variation of its brightness is explained by the alternating rise and 
 fall of the lava surface by a process presently to be explained. 
 
 Not only is there no combustion in connection with volcanic 
 eruptions, but so far as the volcano is a mountain it is a product 
 of its own action. The grandest of volcanic eruptions have pro- 
 duced no mountains whatever, but only vast plains or plateaus 
 of consolidated molten rock, and every volcanic mountain at 
 some time in its history has risen out of a relatively level surface. 
 
 When the traditional notions about volcanoes grew up, it was 
 supposed that the solid earth was merely a " crust " enveloping 
 still molten material. As has already been pointed out in an ear- 
 
 94 
 
RISE OF MOLTEN ROCK TO THE EARTH'S SURFACE 95 
 
 lier chapter, this view is no longer tenable, for we now know that the 
 condition of matter within the earth's interior, while perhaps not 
 directly comparable to any that is known, yet has properties most 
 resembling known matter in a solid state; it is much more rigid 
 than the best tool steel. While there must be reservoirs of molten 
 rock beneath active volcanoes, it is none the less clear that they 
 are small, local, and temporary. This is shown by the compara- 
 tive study of volcanic outlets within any circumscribed district. 
 
 It is perhaps not easy to frame a definition of a volcano, but 
 its essential part, instead of being a mountain, is rather a vent or 
 channel which opens up connection between a subsurface reservoir 
 of molten rock and the surface of the earth. An eruption occurs 
 whenever there is a rise of this material, together with more or less 
 steam and admixed gases, to the surface. Such molten rock ar- 
 riving at the surface is designated lava. The changes in pressure 
 upon this material during its elevation induce secondary phenom- 
 ena as the surface is approached, and these manifestations are 
 often most awe inspiring. While often locally destructive, the 
 geological importance of such phenomena is by reason of their 
 terrifying aspect likely to be greatly exaggerated. 
 
 Early views concerning volcanic mountains. — As already pointed 
 out, a volcano at its birth is not a mountain at all, but only, so to 
 speak, a shaft or channel of communication between the surface 
 and a subterranean reservoir of molten rock. By bringing this 
 melted rock to the surface there is built up a local elevation which 
 may be designated a mountain, except where the volume of the 
 material is so large and is spread to such distances as to produce a 
 plain (see fissure eruptions below). 
 
 In the early history of geology it was the view of the great Ger- 
 man geologist von Buch and his friend and colleague von Hum- 
 boldt, that a volcanic mountain was produced in much the same 
 manner as is a blister upon the body. 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 crater. This 
 ^' elevation-crater " theory of volcanoes long held the stage in 
 geological science, although it ignored the very patent fact that 
 the layers on the flanks of volcanic cones are not of sedimentary 
 rock at all, but, on the contrary, of the volcanic materials which 
 
96 
 
 EARTH FEATURES AND THEIR MEANING 
 
 Fig. 87. — Breached volcanic cone near 
 Auckland, New Zealand, showing the 
 bending down of the sedimentary strata 
 in the neighborhood of the vent (after 
 Heaphy and Scrope). 
 
 are brought up to the surface during the eruption. The observa- 
 tional phase of science was, however, daw^ning, and the Enghsh 
 
 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 ejected. 
 Making use of data derived 
 from New Zealand, Scrope 
 showed that, instead of being 
 elevated during the formation 
 of a volcanic mountain, the sedimentary strata of the vicinity 
 may be depressed near the volcanic vent (Fig. 87). 
 
 The birth of volcanoes. — To confirm the impression that the 
 formation of the volcanic mountain is in reality a secondary phe- 
 nomenon connected with eruptions, we may cite the observed birth 
 of a number of volcanoes. On the 20th of September, 1538, a 
 new volcano, since known as Monte Nuovo (new mountain), rose 
 on the border of the ancient Lake Lucrinus to the westward of 
 Naples. This small mountain attained a height of 440 feet, and 
 is still to be seen on the shore of the bay of Naples. From Mexico 
 have been recorded the births of several new volcanoes: Jorullo 
 in 1759, Pochutla in 1870, and in 1881 a new volcano in the Ajusco 
 Mountains about midway between the Gulf of Mexico and the 
 Pacific Ocean. The latest of new volcanoes is that raised in Japan 
 on November 9, 1910, in connection with the eruption of Usu-san. 
 This " New Mountain " reached an elevation of 690 feet. 
 
 As described by von Humboldt, Jorullo rose in the night of the 
 28th of September, 1759, from a fissure which opened in a broad 
 plain at a point 35 miles distant from any then existing volcano. 
 The most remarkable of new volcanoes rose in 1871 on the island 
 of Camiguin northward from Mindanao in the Philippine archi- 
 pelago. This mountain was visited by the Challenger expedition 
 in 1875, and was first ascended and studied thirty years later 
 by a party under the leadership of Professor Dean C. Worcester, 
 the Secretary of the Interior of the Philippine Islands, to whom 
 the writer is indebted for this description and the accompanying 
 
RISE OF MOLTEN ROCK TO THE EARTH'S SURFACE 97 
 
 illustration of this largest and most interesting of new-born vol- 
 canoes. As in the case of Jorullo, the eruption began with the 
 formation of a fissure in a 
 level plain, some 400 yards 
 distant from the town of 
 Catarman (Fig. 88). The 
 eruption continued for four 
 years, at the end of which • -- "■^- " ::^=r=^ 
 
 time the height of the sum- Fig. 88. — View of the new Camiguin volcano 
 ., J.- J. 1 T_ J.1 from the sea. It was formed in 1871 over 
 
 mit was estimated by the , , , , . t.. + c r^ . 
 
 _ '^ a nearly level plain. The town of Catarman 
 
 Challenger expedition to be appears at the right near the shore (after an 
 1900 feet. At the time of unpublished photograph by Professor Dean 
 
 the first ascent in 1905, ' ^^^^^ 
 
 the height was determined by aneroid as 1750 feet, with sharp 
 
 rock pinnacles projecting some 50 or 75 feet higher. 
 
 Active and extinct volcanoes. — The terms '' active " and 
 " extinct " have come into more or less common use to describe 
 respectively those volcanoes which show signs of eruptive activity, 
 and those which are not at the time active. The term " dormant " 
 is applied to volcanoes recently active and supposed to be in a 
 doubtfully extinct condition. From a well-known volcano in 
 the vicinity of Naples, volcanoes which no longer erupt lava or 
 cinder, but show gaseous emanations (fumeroles) are said to be in 
 the solfatara condition, or to show solfataric activity. 
 
 Experience shows that the term " extinct," while useful, must 
 alwaj^s be interpreted to mean apparently extinct. This may be 
 illustrated by the history of Mount Vesuvius, which before the 
 Christian era was forested in the crater and showed no signs of 
 activity ; and in fact it is known that for several centuries no erup- 
 tion of the volcano had taken place. Following a premonitory 
 earthquake felt in the year 63, the mountain burst out in grand 
 explosive eruption in 79 a.d. This eruption profoundly altered 
 the aspect of the mountain and buried the cities of Pompeii, Stabeii, 
 and Herculaneum from sight. Once more, this time during the 
 middle ages, for nearly five centuries (1139 to 1631) there was 
 complete inactivity, if we except a light ash eruption in the year 
 1500. During this period of rest the crater was again forested, 
 but the repose was suddenly terminated by one of the grandest 
 eruptions in the mountain's history. 
 
98 
 
 EARTH FEATURES AND THEIR MEANING 
 
 The earth's volcano belts. — The distribution of volcanoes is 
 not uniform, but, on the contrary, volcanic vents appear in definite 
 zones or belts, either upon the margins of the continents or included 
 within the oceanic areas (Fig. 89). The most important of these 
 
 Fig. 89. — Map showing the location of the belts of active volcanoes. 
 
 belts girdles the Pacific Ocean, and is represented either by chains 
 or by more widely spaced volcanic mountains throughout the 
 Cordilleran Mountain system of South and Central America and 
 Mexico, by the volcanoes of the Coast and Cascade ranges of North 
 America, the festooned volcanic chain of the Aleutian Islands, and 
 the similar island arcs off the eastern coast of the Eurasian con- 
 tinent. The belt is further continued through the islands of 
 Malaysia to New Zealand, and on the Pacific's southern margin 
 are found the volcanoes of Victoria Land, King Edward Land, 
 and West Antarctica. 
 
 This volcano girdle is by no means a perfect one, for in addi- 
 tion to the principal festoons of the western border there are many 
 
 Fig. 90. — a portion of the "fire girdle" of the Pacific, showing the relation of the 
 chains of volcanic mountains to the deeps of the neighboring ocean floor. 
 
RISE OF MOLTEN ROCK TO THE EARTH'S SURFACE 99 
 
 secondary ones, and still other arcs are found well toward the 
 center of the oceanic area. Another broad belt of volcanoes bor- 
 ders the Mediterranean Sea, and is extended westward into the 
 Atlantic Ocean. Narrower belts are found in both the northern 
 and southern portions of the Atlantic Ocean, on the margins of 
 the Caribbean Sea, etc. 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 (Fig. 90). As has been already pointed 
 out in the chapter upon earthquakes, it is just such places as these 
 which are the seat of earthquakes; these are zones of the earth's 
 crust which are undergoing the most rapid changes of level at the 
 present time. Thus the rise of the land in mountains is proceeding 
 simultaneously with the sinking of the sea floor to form the neigh- 
 boring deeps. 
 
 Arrangement of volcanic vents along fissures and especially at 
 their intersections. — Within those districts in which volcanoes 
 
 Fig. 91. — Volcanic cones formed in 1783 above the Skaptar fissure in Iceland 
 
 (after Helland). 
 
 are widely separated from their neighbors, the law of their arrange- 
 ment is difficult to decipher, but the view that volcanic vents are 
 aligned over fissures is now supported by so much evidence that 
 illustrations may be suppHed from many regions. An excep- 
 tionally perfect fine of small cones is found along the Skaptar 
 cleft in Iceland, upon which stands the large volcano of Laki. 
 This fissure reopened in 1783, and great volumes of lava were 
 exuded. Over the cleft there was left a long fine of volcanic 
 cones (Fig. 91). There are in Iceland two dominating series of 
 parallel fissures of the same character which take their directions 
 respectively northeast-southwest and north-south. Many such 
 fissures are traceable at the surface as deep and nearly straight 
 clefts or gjds, usually a few yards in width, but extending for many 
 miles. The Eldgja has a length of more than 18 EngHsh miles 
 and a depth varying from 400 to 600 feet. On some of these 
 fissures no lava has risen to the surface, whereas others have at 
 numerous points exuded molten rock. Sometimes one end only 
 of a fissure, the more widely gaping portion, has supplied the 
 
100 
 
 EARTH FEATURES AND THEIR MEANING 
 
 -^ 
 
 -^ 
 
 *- 
 
 4- 
 
 conduits for the molten lava. This is well illustrated by the 
 cratered monticules raised by the common ant over the cracks 
 
 _^ _^ which separate the blocks of cement 
 
 sidewalk, the hillocks being located 
 where the most favorable channel was 
 found for the elevation of the mate- 
 rials. 
 
 Those places upon fissures which be- 
 come lava conduits appear to be the 
 ones where the cleft gapes widest so as 
 to furnish the widest channel. Wher- 
 ever a differential lateral movement of 
 the walls has occurred, openings will 
 be found in the neighborhood of each minor variation from a 
 straight line (Fig. 92a). Wherever there are two or more series 
 of fissures, and this would appear to be the normal condition, 
 places favorable for lava conduits occur at fissure intersections. 
 Within such veritable volcano gardens as are to be found in Ma- 
 laysia, the law of volcano distribution became apparent so soon as 
 
 Fig. 92. — Diagrams to illustrate 
 the location of volcanic vents 
 upon fissure lines, a, openings 
 caused by lateral movement of 
 fissure walls ; 6, openings formed 
 at fissure intersections. 
 
 Fig. 93. — Outline map of the eastern portion of the island of Java, displaying the ar- 
 rangement of volcanic vents in alignment upon fissures with the larger mountains 
 at fissure intersections (after Verbeek). 
 
 accurate maps had been prepared. Thus the outline map of a por- 
 tion of the island of Java (Fig. 93) shows us that while the vol- 
 canoes of the island present at first sight a more or less irregular 
 band or zone, there are a number of fissures intersecting in a net- 
 work, and that the volcanoes are aligned upon the fissures with 
 the larger cones located at the intersections. So also in Iceland, 
 
RISE OF MOLTEN ROCK TO THE EARTH'S SURFACE 101 
 
 the great eruption of Askja in 1875 occurred at the intersection 
 of two hnes of fissure. 
 
 Outside these closely packed volcanic regions, similar though 
 less marked networks are indicated; as, for example, in and near 
 the Gulf of Guinea. If now, instead of reducing the scale of our 
 volcano maps, we increase it, the same law of distribution is no 
 less clearly brought out. The monticules or small volcanic cones 
 which form upon the flanks of larger volcanic mountains are like- 
 wise built up over fissures which on numerous occasions have 
 been observed to open and the cones to form upon them. 
 
 Still further reducing now 
 the area of our studies and 
 considering for the moment the 
 " frozen " surface of the boil- 
 ing lava within the caldron of 
 Kilauea, this when observed at 
 night reveals in great perfec- 
 tion the sudden formation of ., ,, 
 fissures in the crust with the ^ „, ,, ^ ., ^ ^. 
 
 . . Fig. 94. — Map of the Puy Panou in the 
 
 appearance of mmiature vol- Auvergne of central France. The seat of 
 canoes rising successively at eruption has migrated along the fissure 
 
 more or less regular intervals "p°° ^^^^ *^,^ ^^"^f "■ "°^^ ^^^ ^^^° 
 
 built up (after Scrope). 
 
 along them. 
 
 It not infrequently happens that after a volcanic vent has 
 become established above some conduit in a fissure, the conduit 
 migrates along the fissure, thus establishing a new cone with more 
 or less complete destruction of the old one (Fig. 94). 
 
 The so-called fissure eruptions. — 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 lava. 
 Such grander eruptions have been for the most part prehistoric, 
 and in later geologic history have occurred chiefly in India, in 
 Abyssinia, in northwestern Europe, and in the northwestern 
 United States. In western India the singularly horizontal pla- 
 teaus of basaltic lava, the Dekkan traps, cover some 200,000 
 square miles and are more than a mile in depth. 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 
 material. No cones or definite vents have been found. 
 
102 
 
 EARTH FEATURES AND THEIR MEANING 
 
 The larger portion of the northwestern British Isles would 
 appear to have been at one time similarly blanketed by nearly 
 horizontal beds of basaltic lava, which beds extended north- 
 westward across the sea through the Orkney and Faroe islands 
 to Iceland. Remnants of this vast plateau are to-day found in all 
 the island groups as well as in large areas of northeastern Ireland, 
 and fissure fillings of the same material occur throughout large 
 areas of the British Isles. In many cases these dikes represent 
 
 once molten rock which may never 
 have communicated with the surface 
 at the time of the lava outpouring, yet 
 they well illustrate what we might ex- 
 pect to find if the ba3alt sheets of 
 Iceland or Ireland were to be removed. 
 The floods of basaltic lava which in 
 the northwestern United States have 
 yielded the barren plateau of the Cas- 
 cade Mountains (Fig. 95) would appear 
 to offer another example of fissure erup- 
 tion, though cones appear upon the 
 surface and perhaps indicate the position of lava outlets during the 
 later phases of the eruptive period. The barrenness and desola- 
 tion of these lava plains is suggested by Fig. 96. 
 
 Fig. 95. — Basaltic plateau of the 
 northwestern United States due 
 to fissure eruptions of lava. 
 
 '«•<=: An- =••" 
 
 . ■ .' '«' -£>=. • • _ ' .J, 
 
 FiQ. 96. — Lava plains about the Snake River in Idaho. 
 
 Though the greater effusions of lava have occurred in pre- 
 historic times, 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 regions, yet in 
 
RISE OF MOLTEN ROCK TO THE EARTH'S SURFACE 103 
 
 Iceland we are able to observe the connection between the dikes 
 and the lava outflows. Professor Thoroddsen has stated that in 
 the great basaltic plateau of Iceland, lava has welled out quietly 
 from the whole length of fissures and often on both sides without 
 giving rise to the formation of cones. At three wider portions of 
 the great Eld cleft, lava welled out quietly without the formation 
 of cones, though here in the southern prolongation of the fissure, 
 where it was narrower, a row of low slag cones appeared. Where 
 the lava outwellings occurred, an area of 270 square miles was 
 flooded. 
 
 The composition and the properties of lava. — In our study of 
 igneous rocks (Chapter IV) it was learned that they are com- 
 posed for the most part of silicate minerals, and that in their 
 chemical composition they represent various proportions of silica, 
 
 Fig. 97. — Characteristic profiles of lava volcanoes. 1, basaltic lava mountain; 
 2, mountain of siliceous lava (after Judd). 
 
 alumina, iron, magnesia, lime, potash, and soda. The more 
 abundant of these constituents is silica, which varies from 35 to 
 70 per cent of the whole. Whenever the content of silica is rela- 
 tively low, — basic or basaltic lava, — the cooled rock is dark in 
 color and relatively heavy. It melts at a relatively low tempera- 
 ture, and is in consequence relatively fluid at the temperatures 
 which lavas usually have on reaching the earth's surface. Further- 
 more, from being more fluid, the water which is nearly always 
 present in large quantity within the lava more readily makes its 
 escape upon reaching the surface. Eruptions of such lava are 
 for this reason without the violent aspects which belong to extru- 
 sions of more siliceous (more " acidic ") lavas. For the same 
 
104 
 
 EARTH FEATURES AND THEIR MEANING 
 
 reason, also, basaltic lava flows more freely and can spread much 
 farther before it has cooled sufficiently to consolidate. This is 
 equivalent to saying that its surface will assume a flatter angle of 
 slope, which in the case of basaltic lava seldom exceeds ten degrees 
 and may be less than one degree (Fig. 97). 
 
 Siliceous lavas, on the other hand, are, when consolidated, rela- 
 tively light both in color and weight and melt at relatively high 
 temperatures. They are, therefore, usually but partly fused and 
 of a viscous consistency when, they arrive at the earth's surface. 
 Because of this viscosity they offer much resistance to the libera- 
 tion of the contained water, which therefore is released only to 
 the accompaniment of more or less violent explosions. The lava 
 is blown into the air and usually falls as consolidated fragments 
 of various degrees of coarseness. 
 
 It must not, however, be assumed that the temperature of lava 
 is always the same when it arrives at the surface, and hence it 
 may happen that a siliceous lava is exuded 
 at so high a temperature that it behaves 
 like a normal basaltic lava. On the other 
 hand, basaltic lavas may be extruded at 
 unusually low temperatures, in which case 
 their behavior may resemble that of the 
 normal siliceous lavas. If, however, as is 
 generally the case, the energy of explosion 
 of a basaltic lava is relatively small, any 
 ejected portions of the liquid lava travel 
 to a moderate height only in the air, 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 
 "spatter cones" or 
 " driblet cones " (Fig. 
 98). When, on the other 
 hand, the energy of ex- 
 plosion is great, as is nor- 
 mally the case with sili- ^^°- ^^—J'Z ""^ ^^^^^^f^'^^'!' f /'^^^'^ 
 
 , cone in the Owens valley, California (after an 
 
 CeOUS lavas, the portions unpublished photograph by W. D. Johnson). 
 
 Fig. 98. — A driblet cone 
 (after J. D. Dana). 
 
RISE OF MOLTEN ROCK TO THE EARTH'S SURFACE 105 
 
 of ejected lava have been fully consolidated before their fall to the 
 surface, so that they build up the same type of accumulation as 
 would sand falling in the same manner. The structures which 
 they form are known as tuff, cinder, or ash cones (Fig. 99). 
 
 Whenever the contained water passes off from siUceous lavas 
 without violent explosions, the lava may flow from the vent, but 
 in contrast to basaltic lavas it travels a short distance only before 
 consoHdating. The resulting mountain is in consequence propor- 
 tionately high and steep (Fig. 97). Eruptions characterized by 
 violent explosions accompanied by a fall of cinder are described 
 as explosive eruptions. Those which are relatively quiet, and in 
 which the chief product is in the form of streams of flowing lava, 
 are spoken of as convulsive eruptions. 
 
 The three main types of volcanic mountain. — If the eruptions 
 at a volcanic vent are exclusively of the explosive type, the ma- 
 terial of the mountain which results is throughout tuff or cinder, 
 and the volcano is described as a cinder cone. If, on the other 
 hand, the vent at every eruption exudes lava, a mountain of solid 
 rock results which is a lava dome. It is, however, the exception 
 for a volcano which has a long history to manifest but a single 
 kind of eruption. At one time exuding lava comparatively 
 quietly, at another the violence with which the steam is liberated 
 yields only cinder, and the mountain is a composite of the two 
 materials and is known as a composite volcanic cone. 
 
 The lava dome. — When successive lava flows come from a 
 crater, the structure which results has the form of a more or less 
 perfect dome. If the lava be of the basaltic or fluid type, the 
 slopes are flat, seldom making an angle of as much as ten degrees 
 with the horizon and flatter toward the summit (Fig. 101, p. 106). 
 If of siliceous or viscous lava, on the other hand, the slopes are 
 correspondingly steep and in some cases precipitous. To this 
 latter class belong some of the Kuppen of Germany, the puys of 
 central France, and the mamelons of the Island of Bourbon. 
 
 The basaltic lava domes of Hawaii. — At the " crossroads of 
 the Pacific " rises a double line of lava volcanoes which reach 
 from 20,000 to 30,000 feet above the floor of the ocean, some 
 of them among the grandest volcanic mountains that are known. 
 More than half the height and a much larger proportion of the 
 bulk of the largest of these are hidden beneath the ocean's surface. 
 
106 
 
 EARTH FEATURES AND THEIR MEANING 
 
 The two great active vents are Mokuaweoweo (on Mauna Loa) 
 and Kilauea, distinct volcanoes notwithstanding the fact that their 
 lava extravasations have been merged in a single mass. The rim 
 of the crater of Mauna Loa is at an elevation of 13,675 feet above 
 
 the sea, whereas that of Kilauea 
 is less than 4000 feet and ap- 
 pears to rest upon the flank of 
 the larger mountain (Figs. lOQ 
 and 101). Although one crater 
 is but 20 miles distant from the 
 other and nearly 10,000 feet 
 lower, their eruptions have ap- 
 parently been uiisympathetic. 
 Nowhere have still active lava 
 mountains been subjected to 
 such frequent observations ex- 
 tending throughout a long pe- 
 riod, and the dynamics of their 
 Fig. 100. — Map of Hawaii and the lava eruptions are fairly well under- 
 stood. To put this before the 
 reader, it will be best to con- 
 sider both mountains, for 
 though they have much in common, the observations from one are 
 strangely complementary to those of the other. The lower crater 
 
 Scafe of Mffes. 
 
 Fig. 101. — Section through Mauna Loa and Kilauea. 
 
 being easily accessible, Kilauea has been often visited, and there 
 exists a long series of more or less consecutive observations upon 
 it, which have been assembled and studied by Dana and Hitch- 
 cock. The place of outflow of the Kilauea lavas has not generally 
 been visible, whereas Mokuaweoweo has slopes rising nearly 14,000 
 feet above the sea and displays the records of outflow of manj^ 
 eruptions, some of which were accompanied by the grandest of 
 volcanic phenomena. 
 
 Lava movements within the caldron of Kilauea. — The craters 
 of these mountains are the largest of active ones, each being in 
 
 volcanoes of Mokuaweoweo (Mauna 
 Loa) and Kilauea (after the government 
 map by Alexander) . 
 
RISE OF MOLTEN ROCK TO THE EARTH'S SURFACE 107 
 
 excess of seven miles in circumference. In shape they are irregu- 
 larly elliptical and consist of a series of steps or terraces descend- 
 ing to a pit at the bottom, in which are open lakes of boiling lava. 
 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 surface. The cliff below the so-called '' black 
 ledge " was produced by the falling in of the frozen lava surface 
 at the time of the outflow of 1840, the lava issuing upon the 
 eastern flank of the mountain and pouring into the sea near 
 Nanawale. 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 (Fig. 102). The floor has, however, never been complete, 
 for one or more open lakes are ^^^^ ^^ 
 
 always to be seen, that of Hale- 
 maumau located near the south- 
 western margin having been much 
 the most persistent. Within the 
 
 , , ji 1 •!• 1 • Fig. 102. — Schematic diagram to illus- 
 
 open lakes the boihng lava is ap- ^,^^6 the moving platform of frozen 
 parently white hot at the depth lava which rises and falls in the crater 
 
 of but a few inches below the of Kilauea. 
 surface, and in the overturnings of the mass these hotter portions 
 are brought to the surface and appear as white streaks marking 
 the redder surface portions. From time to time the surface 
 freezes over, then cracks open and erupt at favored points along 
 the fissures, sending up jets and fountains of lava, the material of 
 which falls in pasty fragments that build up driblet cones. Small 
 fluid clots are shot out, carrying a threadlike line of lava glass 
 behind them, the well-known " Pele's hair." Sometimes the open 
 lakes build up congealed walls, rising above the general level of 
 the pit, and from their rim the lava spills over in cascades to 
 spread out upon the frozen floor, thus increasing its thickness from 
 above (Fig. 103). At other times a great dome of lava has been 
 pushed up from the pit of Halemaumau under a frozen shell, the 
 molten lava shining red through cracks in its surface and exuding 
 so as to heal each widely opened fissure as it forms. 
 
 At intervals of from a few years to nine or ten years the crater 
 has been periodically drained, at which times the moving plat- 
 
108 
 
 EARTH FEATURES AND THEIR MEANING 
 
 form of frozen lava has sunk more or less rapidly to levels far 
 below the black ledge and from 900 to 1700 feet below the crater 
 rim. Following this descent a slow progressive rise is inaugurated, 
 which has sometimes gone on at a rate of more than a hundred 
 feet per year, though it is usually much slower than this. When 
 
 Fig. 103. — View of the open lava lake of Halemaumau within the crater of 
 Kilauea, the molten lava shown cascading over the raised lava walls on to the 
 floor of the pit (after Pavlow) . 
 
 the platform has reached a height varying from 700 to 350 feet 
 below the crater rim, another sudden settlement occurs which 
 again carries the pit floor downward a distance of from 300 to 700 
 feet. 
 
 The draining of the lava caldrons. — The changes which go on 
 within the crater of Mokuaweoweo, though less studied than 
 those of Kilauea, appear to be in some respects different. Here 
 every eruption seems to be preceded by a more or less rapid influx 
 of melted lava to the pit of the crater, this phenomenon being 
 observed from a distance as a brilliant light above the crater — 
 the reflection of the glow from overhanging vapor clouds. The 
 uprising of the lava has often been accompanied by the formation 
 of high lava fountains upon the surface, and the molten lava 
 sometimes appears in fissures near the crater rim at levels well 
 above the lava surface within the pit. 
 
RISE OF MOLTEN ROCK TO THE EARTH'S SURFACE 109 
 
 anawale 
 
 Although in many cases the lava which has thus flooded the 
 crater has suddenly drained away without again becoming visible, 
 it is probable that in such cases an outlet has been found to some 
 submarine exit, since under-ocean discharge effects have been 
 observed in connection with eruptions of each of the volcanoes. 
 
 Inasmuch as no earthquakes are felt in connection with such 
 outflows as have been described, it is probable that the hot lava 
 fuses a passageway for itself into some open channel underneath 
 the flanks of the mountain. Such a course is well illustrated by 
 the outflow of Kilauea 
 in 1840, when, it will 
 be remembered, oc- 
 curred the great down- 
 plunge of the crater 
 that yielded the pit 
 below the black ledge. 
 At this time the lava 
 first made its appear- 
 ance 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 
 (Fig. 104). Within 
 this new crater the 
 lava rose, and small ejections soon followed from fissures formed in 
 its neighborhood. Some time after, the lava sank in the first new 
 crater, only to reappear successively at other small openings (Fig. 
 104, B, C, m, n) 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 sea. Only the slightest earth 
 tremors were felt, and as no rumblings were heard, it is evident 
 that the lava fused its way along a buried channel largely open at 
 the time (see below, p. 112). 
 
 In a majority of the eruptions of Mokuaweoweo, when the 
 outflowing lavas have become visible, the molten rock has ap- 
 parently fused its way out to the surface of the mountain at 
 
 Fig. 104. — Map showing the manner of outflow of 
 lava from Kilauea during the eruption of 1840. 
 The outflowing lava made its appearance succes- 
 sively at the points A, B, C, m, n, and finally at a 
 point below n, from whence it issued in volume and 
 flowed down to the sea at Nanawale (after J. D. 
 Dana). 
 
110 EARTH FEATURES AND THEIR MEANING 
 
 points from 1000 to 3000 feet below the bottom of the crater, 
 and this discharge has corresponded in time to the lowering 
 of the lava surface within the crater. There are, however, 
 three instances upon record in which the lava issued from definite 
 rents which were formed upon the mountain flanks at compara- 
 tively low levels. In contrast to the formation of fused outlets, 
 these ruptures of a portion of the mountain's flank were always 
 accompanied by vigorous local earthquakes of short duration. In 
 one instance (the eruption of 1851) such a rent appeared under 
 the same conditions but at an elevation of 12,500 feet, or near 
 the level of the lava in the crater. 
 
 The outflow of the lava floods. — In order to properly com- 
 prehend these and many otherwise puzzling phenomena connected 
 
 Fig. 105. — Lava of Matavanu upon the Island of Savaii flowing down to the 
 sea during the eruption of 1906. 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 (after H. I. Jensen). 
 
 with volcanoes, it is necessary to keep ever in mind the quite 
 remarkable heat-insulating property of congealed lava. So soon 
 as a thin crust has formed upon the surface of molten rock, the 
 heat of the underlying fluid mass is given off with extreme slow- 
 ness, so that lava streams no longer connected with their internal 
 lava reservoirs may remain molten for decades. 
 
 We have seen that for Mokuaweoweo and Kilauea, lava either 
 ■quietly melts its way to the surface at the time of outflow, or 
 else produces a rent for its egress to the accompaniment of vigor- 
 '.ous local earthquakes. In either case if the lava issues at a point 
 
RISE OF MOLTEN ROCK TO THE EARTH'S SURFACE 111 
 
 far below the crater, gigantic lava fountains arise at the point of 
 outflow, the fluid rock shooting up to heights which range from 
 250 to 600 or more feet above the surface. A certain proportion 
 of this fluid lava is sufficiently cooled to consolidate while travel- 
 ing in the air, and falling, it builds up a cinder cone which is left 
 as a location monument for the place of discharge. From this 
 outlet the molten lava begins its journey down the slope of the 
 mountain, and quickly freezes over to produce a tunnel, beneath 
 the roof of which the fluid lava flows with comparatively slow 
 further loss of heat. Save for occasional steam jets issuing from 
 its surface, it may give little indication of its presence until it has 
 reached the sea (Fig. 105). 
 
 If sufficient in volume and the shore be not too distant, the 
 stream of lava arrives at the sea, where, discharging from the 
 
 Fig. 106 
 
 a lava tunnel 
 
 Lava stream discharging into the sea from beneath the frozen roof of 
 Eruption of Matavanu on Savaii in 1906 (after Sapper). 
 
 mouth of its tunnel, it throws up vast volumes of steam and in- 
 duces ebullition of the water over a wide area (Fig. 106). Pro- 
 fessor Dana, who visited Hawaii a few months only after the 
 great outflow of 1840, states that the lava, upon reaching the 
 
112 
 
 EARTH FEATURES AND THEIR MEANEsTG 
 
 Fig. 107. — Diagrammatic repre- 
 sentation of the structure of the 
 flanks of lava volcanoes as a re- 
 sult of the draining of frozen lava 
 streams. 
 
 ocean, was shivered like melted glass and thrown up in millions of 
 particles which darkened the sky and fell like hail over the sur- 
 rounding country. The light was so bright that at a distance of 
 forty miles fine print could be read at midnight. 
 
 Protected from any extensive consohdation by its congealed 
 cover, the lava within a stream may all drain away, leaving behind 
 
 an empty lava tunnel, which in the 
 case of the Hawaiian volcanoes 
 sometimes has its roof hung with 
 beautiful lava stalactites and its 
 floor studded with thin lava spines. 
 Later lava outflows over the same 
 or neighboring courses bury such 
 tunnels beneath others of similar 
 nature, giving to the mountain flanks an elongated cellular struc- 
 ture illustrated schematically in Fig. 107. These buried channels 
 may in the future be again utilized for outflows similar in char- 
 acter to that of Kilauea in 1840. 
 
 While the formation of lava stalactites of such perfection and 
 beauty is peculiar to the Hawaiian lava tunnels, the formation of 
 the tunnel in connection with lava outflow is the rule wherever a dis- 
 sipation at the end has permitted of drainage. A few hours only 
 after the flow has begun, the frozen surface has usually a thickness 
 of a few inches, and this cover may be walked over with the lava still 
 molten below. At first in part supported by the molten lava, the 
 tunnel roof sometimes caves in so soon as drainage has occurred. 
 
 Wherever basaltic lava has spread out in valleys on the surface 
 of more easily eroded 
 
 h 
 
 material, either cinder 
 or sedimentary forma- 
 tions, the softer inter- 
 vening ridges are first 
 carried away by the 
 eroding agencies, leav- 
 ing the lava as cappings 
 upon residual eleva- 
 tions. Thus are derived a type of table mountain or mesa of the 
 sort well illustrated upon the western slopes of the Sierra Ne- 
 vadas in California (Fig. 108). 
 
 Fig. 108. — Diagram to show the manner of forma- 
 tion of mesas or table mountains by the outflow 
 of lava in valleys and the subsequent more rapid 
 erosion of the intervening ridges. R, earlier river 
 valley ; R'R', later valleys. 
 
RISE OF MOLTEN ROCK TO THE EARTH'S SURFACE 113 
 
 Fig. 109. — Surface of lava of the Pahoehoe tjrpe. 
 
 The surface which flowing lava assumes, while subject to con- 
 siderable variation, may yet be classified into two rather distinct 
 types. On the one hand there is the billowy surface in which 
 ellipsoidal or kidney-shaped masses, each with dimensions of from 
 one to several feet, lie merged 
 in one another, not unlike an 
 irregular collection of sofa 
 pillows. This type of lava has 
 become known as the Pahoehoe, 
 from the Hawaiian occurrence 
 (Fig. 109). A variation from 
 this type is the '' corded " or 
 " ropy " lava, the surface of 
 which much resembles rope as 
 it is coiled along the deck of 
 a vessel, the coils being here the 
 lines of scum or scoriae arranged 
 in this manner by the currents 
 at the surface of the stream 
 (Fig. 123, p. 124). A quite 
 different type is the block lava 
 {Aa type) which usually has a 
 ragged scoriaceous surface and 
 consists of more or less separate 
 fragments of cooled lava (Fig. 
 131, p. 130). 
 
 Fig. 110. — Three successive views to 
 illustrate the growth of the Island of 
 Savaii from the outflow of lava at 
 Matavanu in the year 1906. a, near the 
 beginning of the outflow ; h, some weeks 
 later than a ; c, some weeks later than 
 6 (after H. I. Jensen). 
 
114 EARTH FEATURES AND THEIR MEANING 
 
 Wherever lava flows into the sea in quantity, it extends the 
 margin of the shore, often by considerable areas. The outflow of 
 Kilauea in 1840 extended the shore of Hawaii outward for the 
 distance of a quarter of a mile, and a more recent illustration of 
 such extension of land masses is furnished by Fig. 110, 
 
CHAPTER X 
 
 THE RISE OF MOLTEN ROCK TO THE EARTH'S 
 SURFACE 
 
 VOLCANIC MOUNTAINS OF EJECTED MATERIALS 
 
 The mechanics of crater explosions. — If we now turn from 
 the lava volcano to the active cinder cone, we encounter an entire 
 change of scene. In place of the quiet flow and convulsive move- 
 ments of the molten lava, we here meet with repeated explosions 
 of greater or less violence. If we are to profitably study the 
 manner of the explosions, considering the volcanic vent as a great 
 experimental apparatus, it would be well to select for our purpose 
 a volcano which is in a not too violent mood. The well-known 
 cinder cone of Stromboli in the Eolian group of islands north of 
 Sicily has, with short and unimportant interruptions, remained in 
 a state of light explosive activity since the beginning of the Chris- 
 tian era. Rising as it does some three thousand feet directly out 
 of the Mediterranean, and displaying by day a white steam cap 
 and an intermittent glow by night, its summit can be seen for a 
 distance of a hundred miles at sea and it has justly been called 
 the '' Lighthouse of the Mediterranean." The " flash " interval 
 of this beacon may vary from one to twenty minutes, and it may 
 show, furthermore, considerable variation of intensity. 
 
 For the reason that the crater of the mountain is located at 
 one side and at a considerable distance below the actual summit, 
 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 (Fig. 111). Long ago the 
 Itahan vulcanologist Spallanzani undertook to make observations 
 from above the crater, and many others since his day have profited 
 by his example. 
 
 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 issuing, Here, as in the Kilauea crater, there are 
 open pools of boiling lava. From some of these, lava is seen 
 
 115 
 
116 
 
 EARTH FEATURES AND THEIR MEANING 
 
 welling out to overflow the frozen surface ; from others, steam is 
 ejected in puffs as though from the stack of a locomotive. Within 
 others lava is seen heaving up and down in violent ebullition, and 
 at intervals a great bubble of steam is ejected with explosive vio- 
 lence, carrying up with it a considerable quantity of the still 
 molten lava, together with its scumlike surface, to fall outside the 
 crater and rattle down the mountain's slope into the sea. Fol- 
 lowing this explosion the lava surface in the pool is lowered and 
 the agitation is renewed, to culminate after the further lapse of a 
 few minutes in a second explosion of the same nature. The rise 
 
 of the lava which 
 precedes the ejection 
 appears at night as a 
 brighter reflection or 
 glow from the over- 
 hanging steam cloud 
 — the flash seen by 
 the mariner from his 
 vessel. 
 
 What is going on 
 within the crater of 
 Stromboli we may 
 perhaps best illus- 
 trate by the boiling 
 of a stiff porridge 
 over a hot fire. 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 meal, it is' necessary to stir the 
 mass with redoubled vigor if anything is to be retained within the 
 kettle. 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 spoon. If the stirring motion be stopped for a 
 moment, the steam expands to form great bubbles which soon 
 eject the pasty mass from the kettle. 
 
 For the crater of Stromboli this process is illustrated by the 
 series of diagrams in Fig. 112. As the lava rises toward the 
 surface, presumably as a result of convectional currents within 
 the chimney of the volcano, the contained steam is relieved from 
 
 Fig. 111. — The volcano of Stromboli, showing the 
 excentric position of the crater (after a sketch by 
 Judd). 
 
RISE OF MOLTEN ROCK TO THE EARTH'S SURFACE 117 
 
 pressure, so that at some depth below the surface it begins to 
 separate out in minute vesicles or bubbles, which, expanding as 
 they rise, acquire a rapidly accelerating velocity. Soon they flow 
 together with a quite sudden increase of their expansive energy, 
 and now shooting upward with further accelerated velocity, a 
 layer of liquid lava with its cover of scum is raised on the surface 
 of a gigantic bubble and thrown high into the air. Cooled during 
 their flight, the quickly congealed lava masses become the tuff or 
 volcanic ash which is the material of the cinder cone. 
 
 
 a b c 
 
 Fig. 112. — Diagrams to illustrate the nature of eruptions within the crater of 
 
 Stromboli. 
 
 Grander volcanic eruptions of cinder cones. — Most cinder and 
 composite cones, in the intervals between their grander eruptions, 
 if not entirely quiescent, lapse into a period of light activity 
 during which their crater eruptions appear to be in all essential 
 respects like the habitual explosions within the Strombolian 
 crater. This phase of activity is, therefore, described as Strom- 
 bolian. By contrast, the occasional grander eruptions which have 
 punctuated the history of all larger volcanoes are described in 
 the language of Mercalli as Vulcanian eruptions, from the best 
 studied example. 
 
 Just what it is that at intervals brings on the grander Vul- 
 canian outburst within a volcano is not known with certainty; 
 but it is important to note that there is an approach to periodicity 
 
118 
 
 EARTH FEATURES AND THEIR MEANING 
 
 in the grander eruptions. It is generally possible to distinguish 
 eruptions of at least two orders of intensity greater than the 
 Strombolian phase ; a grander one, the examples of which may 
 be separated by centuries, and one or more orders of relatively 
 moderate intensity which recur at intervals perhaps of decades, 
 their time intervals subdividing the larger periods marked off by 
 the eruptions of the first order. 
 
 The eruption of Volcano in 1888. — In the Eolian Islands to 
 the north of Sicily was located the mythical forge of Vulcan. 
 From this locality has come our word '' volcano," and both the 
 island and the mountain bear no other 
 name to-day (Fig. 113). There is in the 
 structure of the island the record of a 
 somewhat complex volcanic history, but 
 the form of the large central cinder cone 
 was, according to Scrope, acquired during 
 the eruption of 1786, at which time the 
 crater is reported to have vomited ash for 
 a period of fifteen days. Passing after 
 this eruption into the solfatara condition, 
 with the exception of a fight eruption in 
 1873, the volcano remained quiet until 
 1886. So active had been the fumeroles 
 within the crater during the latter part of 
 this period that an extensive plant had 
 been estabfished there for the collection 
 especially of boracic acid. In 1886 occurred 
 a slight eruption, sufficient to clear out the 'bottom of the crater, 
 though not seriously to disturb the English planter whose vine- 
 yards and fig orchards were in the valley or atrio near the point d 
 upon the map (Fig. 113), nearly a mile from the crater rim. On 
 the 3d of August, 1888, came the opening discharge of an eruption, 
 which, while not of the first order of magnitude, was yet the greatest 
 in more than a century of the mountain's history, and may serve us 
 to illustrate the Vulcanian phase of activity within a cinder cone. 
 During the day, to the accompaniment of explosions of consider- 
 able violence, projectiles fell outside the crater rim and rolled 
 down the steep slopes toward the at7'io. These explosions were 
 repeated at intervals of from twenty to thirty minutes, each 
 
 Sca/e ofMi/es. 
 
 o ■* 
 
 Fig. 113. — Map of Vol- 
 cano in the Eolian group 
 of islands. The smaller 
 craters partially dissected 
 by the waves belong to 
 Vulcanello (after Judd). 
 
RISE OF MOLTEN ROCK TO THE EARTH'S SURFACE 119 
 
 beginning in a great upward rush of steam and ash, accompanied 
 by a low rumbling sound. During the following night the erup- 
 tions increased in violence, and the anxious planter remained on 
 watch in his villa a mile from the crater. Falling asleep toward 
 morning, he was rudely awakened by a rain of projectiles falling 
 upon his roof. Hastily snatching up his two children he ran 
 toward the door just as a red hot projectile, some two feet in di- 
 ameter, descended through the roof, ceiling, and floor of the drawing 
 room, setting fire to the building. A second projectile similar to 
 the first was smashed into fragments at his feet as he was emerg- 
 ing from the house, burning one of the children. Making his 
 escape to Vulcanello at the extremity of the island, the remainder 
 of the night and the following day, until rescue came from Lipari, 
 were spent just beyond the range 
 of the falHng masses. ^^ 
 
 When the writer visited the ^^•^^^^^^^-'""^-^"^^^W 
 
 island some months later, the .^-^^^^'^^^^^^^^^^-^^ | 
 
 eruption was still so vigorous that jUmf^^'' ^ '^'^^■^^3^'^-^M M^l 
 the crater could not be reached. ■K'/,\ "H'^^^^^^^^^ 
 
 The ruined villa, smashed and '■'"''^ 
 
 1 1 J. 1 -xi, -x. ^^ I, ^2 FiGf- 114. — "Bread-crust" lava pro- 
 
 charred, stood with its walls halt . , ., . ,, , . . ^r , 
 
 ' _ jectile from the eruption of Volcano 
 
 buried in ash and lapilh, among in 1888 (after Mercalii). 
 which were partly smashed pumi- 
 
 ceous lava projectiles. 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 (Fig. 114). The larger of these exhibited the peculiar 
 '' bread-crust " 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 ground. One of these projectiles fully 
 three feet in diameter was found at the distance of a mile and a 
 half from the crater. Though diminished considerably in inten- 
 sity, the rhythmic explosions within the crater still recurred at 
 intervals varying from four minutes to half an hour, and were 
 accompanied by a dull roar easily heard at Lipari on a neighboring 
 island six miles away. Simultaneously, a dark cloud of ''smoke/' 
 the peculiar " cauliflower cloud " or 'pino mounted for a couple 
 of miles above the crater (Fig. 115), and the rise was succeeded 
 by a rain of small lava fragments or lapilli outside the crater rim. 
 
120 
 
 EARTH FEATURES AND THEIR MEANING 
 
 ^-:^: 
 
 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 Stromboh, if we 
 except the elevation of a con- 
 siderable quantity of acces- 
 sory and older tuff which is 
 Fig. 115. -Peculiar "cauliflower cloud" derived from the inner walls 
 
 or vino composed of steam and ash, of the crater and Carried up- 
 rising above the cinder cone of Volcano ^^j.^ -j^^Q ^Yie air together 
 during the waning phases of the explo- 
 
 sive eruption of 1888 (after a photo- With the pasty cakes of fresh 
 graph by B. Hobson). lava derived from the chimney. 
 
 It is this accessory material 
 which gives to the 'pino its dark or even black appearance. 
 The eruption of Taal volcano on January 30, 191 1. — The 
 recent eruption of the cinder - • 
 
 cone known as Taal volcano ^■^ -1 .;^'.^::,- .. • '•. / 
 
 is of interest, not only because '' v •/..■•" ;' ' 
 
 so fresh in mind, but because 
 two neighboring vents erupted 
 simultaneously with explosions 
 of nearly equal violence (Fig. 
 116). This PhiUppine vol- 
 cano lies near the center of a 
 lake some fifteen miles in 
 diameter and about fifty miles 
 south of the city of Manila. 
 After a period of rest extend- 
 ing over one hundred and fifty 
 years, the symptoms of the 
 coming eruption developed 
 rapidly, and on the morning 
 of January 30 grand explo- 
 sions of steam and ash oc- -».--•"' * . '■'-'■'r •-,•>•• ^^ 
 curred simultaneously in the "^ "•' •■ " ' " 
 
 neighboring craters, and the Fig. II6. -Double explosive eruption of 
 ' Taal volcano on the morning of January 
 
 condensed moisture brought 30, 1911. 
 
 V'- 
 
RISE OF MOLTEN ROCK TO THE EARTH'S SURFACE 121 
 
 down the ash in an avalanche of scalding mud which buried the 
 entire island. Almost the entire population of the island, num- 
 bering several hundreds, 
 was hterally buried in the 
 blistering mud (Fig. 117); 
 and the gases from the ex- 
 plosions carried to the dis- 
 tant shores of the lake 
 added to this number many 
 hundred victims. 
 
 The shocks which accom- 
 panied the explosions raised 
 a great wave upon the sur- 
 face of the lake, which, ad- 
 vancing upon the shores, 
 washed away structures for 
 a distance of nearly a half 
 mile. 
 
 The materials and the 
 structure of cinder cones. 
 — Obviously the materials 
 which compose cinder cones 
 are the cooled lava frag- 
 ments of various degrees of 
 
 coarseness which have been ejected from the crater. If larger 
 than a finger joint, such fragments are referred to as volcanic 
 projectiles, or, incorrectly, as " volcanic bombs." Of the larger 
 masses it is often true that the force of expulsion has not been 
 
 applied opposite the cen- 
 ter of mass of the body. 
 ////' ^. ^-^^^ ■ ■ Thus it follows that they 
 
 '""' ' ^^^ undergo complex whirl- 
 
 ing motions during their 
 flight, and being still 
 semiliquid, they develop 
 curious pear-shaped or 
 less regular forms (Fig. 
 118). When crystals 
 Fig. 118.— A pear-shaped lava projectile. have already separated 
 
 Fig. 117. — The thick mud veneer upon the 
 island of Taal (after a photograph by 
 Deniston) . 
 
122 
 
 EARTH FEATURES AND THEIR MEANING 
 
 out in the lava before its rise in the chimney of the volcano, the 
 surrounding fluid lava may be blown to finely divided volcanic 
 dust which floats away upon the wind, thus leaving the crystals 
 intact to descend as a crystal rain about the crater. Such a 
 shower occurred in connection with the eruption of Etna in 1669, 
 and the black augite crystals may to-day be gathered by the 
 handful from the slopes of the Monti Rossi (Fig. 125, p. 125). 
 
 The term lapilli, or sometimes rapilli, is applied to the ejected 
 lava fragments when of the average size of a finger joint. This is 
 
 the material which still 
 partially covers the un- 
 exhumed portions of the 
 city of Pompeii. Vol- 
 canic sajid, ash, and dust 
 are terms applied in 
 order to increasingly 
 fine particles of the 
 ejected lava. The finest 
 material, the volcanic 
 dust, is often carried 
 for hundreds and some- 
 times even for thou- 
 sands of miles from the 
 crater in the high-level 
 currents of the atmos- 
 phere. Inasmuch as 
 this material is de- 
 posited far from the 
 crater and in layers 
 more or less horizontal, 
 such material plays a small role in the formation of the cinder 
 cone. The coarser sands and ash, on the other hand, are the 
 materials from which the cinder cone is largely constructed. 
 
 The manner of formation and the structure of cinder cones 
 may be illustrated by use of a simple laboratory apparatus (Fig. 
 119). Through an opening in a board, first white and then 
 colored sand is sent up in a light current of air or gas supplied 
 from suitable apparatus. The alternating layers of the sand 
 form in the attitudes shown; that is to say, dipping inward or 
 
 
 Fig. 119. — Artificial production of the structure of 
 a cinder cone with use of colored sands carried up 
 in alternation by a current of air (after G. Linck). 
 
RISE OF MOLTEN ROCK TO THE EARTH'S SURFACE 123 
 
 toward the chimney of the volcano at all points within the crater 
 rim, and outward or away from it at all points outside (Fig. 119). 
 If the experiment is carried so far that at its termination sand 
 slides down the crater walls into the chimney below, the inward 
 dipping layers will be truncated, or even removed entirely, as 
 shown in Fig. 119 6. 
 
 The profile lines of cinder cones. — The shapes of cinder cones 
 are notably different from those of lava mountains. While the 
 
 ^ A ^ 
 
 Fig. 120. — Diagram to show the contrast between a lava dome and a cinder cone. 
 AAA, cinder cone ; BabC, lava dome ; DE, line of low cinder cones above a fissure 
 (after Thoroddsen). 
 
 latter are domes, the mountains constructed of cinder are conical 
 and have curves of profile that are concave upward instead of 
 convex (Fig. 120). In the earlier stages of its growth the cinder 
 cone has a crater which in proportion to the height of the moun- 
 tain is relatively broad (Fig. 99, p. 104). 
 
 Speaking broadly, the diameter of the crater is a measure of 
 the violence of the explosions within the chimney. A single series 
 of short and violent explosive 
 eruptions builds a low and 
 broad cinder cone. A long- 
 continued succession of moder- 
 ately violent explosions, on the 
 other hand, builds a high cone 
 with crater diameter small if 
 compared with the mountain's 
 altitude, and the profile afforded 
 is a remarkably beautiful sweep- 
 ing curve (Fig. 121). Toward 
 the summit of such a cone the 
 loose materials of which it is composed are at as steep an angle 
 as they can lie, the so-called angle of repose of the material ; 
 whereas lower down the flatter slopes have been determined by the 
 distribution of the cinder during its fall from the air. When one 
 
 Fig. 121. — Mayon volcano on the island 
 of Luzon, P.I. A remarkably perfect 
 high cinder cone. 
 
124 
 
 EARTH FEATURES AND THEIR MEANING 
 
 Fig. 122. — A series of breached 
 cinder cones where the place of 
 eruption has migrated along the 
 
 makes the ascent of such a mountain, he encounters continually 
 steeper grades, with the most difficult slope just below the crest. 
 
 The composite cone. — 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 
 underij.-ing fissure. The Puys with explosions, and where, therefore, 
 Noir, Solas, and La Vache in the ^^xe structure of the mountain repre- 
 
 Mont Dore Province of central . i • i 
 
 France (after Scrope). sents a composite ot lava and cmder. 
 
 Such composite cones possess a skele- 
 ton of solid rock upon which have been built up alternate sloping 
 layers of cinder and lava. In most respects such cones stand in 
 an intermediate position be- 
 tween lava domes and cinder 
 cones. 
 
 Regarded as a retaining wall 
 for the lava which mounts in 
 the chimney, the cinder cone 
 is obviously the weakest of 
 all. Should lava rise in a 
 cinder cone without an ex- 
 plosion occurring, the cone is 
 at once broken through upon 
 one side by the outwelling 
 of the lava near the base. 
 Thus arises the characteristic 
 breached cone of horseshoe 
 form (Fig. 122). 
 
 Quite in contrast with the 
 weak cinder cone is the lava 
 dome with its rock walls and 
 relatively flat slopes. Con- 
 sidered as a retaining wall for 
 lava it is much the strongest 
 type of volcanic mountain, 
 and it is likely that the hydrostatic pressure of the lava within 
 the crater would seldom suffice to rupture the walls, were it not 
 
 Fig. 123. — The bocca or mouth upon the 
 inner cone of Mount Vesu-vius from which 
 flowed the lava stream of 1872. This 
 lava stream appears in the foreground 
 with its characteristic "ropy" surface. 
 
RISE OF MOLTEN ROCK TO THE EARTH'S SURFACE 125 
 
 that the molten rock first fuses its way into old stream tunnels 
 buried under the mountain slopes (see ante, p. 112). Composite 
 cones have a strength as retaining walls for lava which is inter- 
 mediate between that of the 
 
 other types. Their Vulcanian 
 eruptions of the convulsive 
 type are initiated by the forma- 
 tion of a rent or fissure upon 
 the mountain flanks at eleva- 
 tions well above the base, the 
 opening of the fissure being 
 generally accompanied by a 
 local earthquake of greater or 
 less violence. 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 cone, referred to as a " mouth," or hocca ^ 
 (Fig. 123), or one or more cinder cones which from their position 
 upon the flanks of the larger volcano are referred to as parasitic 
 
 '%-l. 
 
 Fig. 124. — A row of parasitic cones raised 
 above a fissure which was opened upon 
 the flanks of Mount Etna during the 
 eruption of 1892 (after De Lorenzo) . 
 
 
 Fig. 125. — View looking toward the summit of Etna from a position upon the 
 southern flank near the village of Nicolosi. The two breached parasitic cones 
 seen behind this village are the Monti Rossi which were thrown up in 1669 and 
 from which flowed the lava which overran Catania (after a photograph by 
 Sommer) . 
 
 cones (Fig. 124). The lava of Vesuvius more frequently yields 
 bocchi at the place of outflow, whereas the flanks of Etna are 
 
 1 Italian for mouth ; plural bocchi. 
 
126 
 
 EARTH FEATURES AND THEIR MEANING 
 
 pimpled with great numbers of parasitic cinder cones, each the 
 monument to some earlier eruption (Fig. 125). 
 
 It is generally the case that a single 
 eruption makes but a relatively small 
 contribution to the bulk of the mountain. 
 From each new cone or bocca there pro- 
 ceeds a stream of lava spread in a rela- 
 tively narrow stream extending down the 
 slopes (Fig. 126). 
 
 The caldera of composite cones. — 
 Because of the varied episodes in the 
 Fig. 126. — Sketch map of history of Composite cones, they lack the 
 Etna, showing the indi- regular liues characteristic of the two 
 
 vidual surface lava streams . , , mi i i c i i 
 
 (in black) and the tuff Simpler types. The larger number of the 
 covered surface (stippled), more important composite cones have 
 been built up within an outer crater of 
 relatively large diameter, the Somma cone or caldera, which 
 surrounds them like a gigantic ruff or collar. This caldera is 
 clearly in most cases at least the relic of an earlier explosive 
 crater, after which successive eruptions of lesser violence have 
 built a more sharply conical structure. This can only be inter- 
 preted to mean that most larger and long-active volcanoes have 
 
 
 
 i^Uff'^ 
 
 Fig. 127. — Panum crater, showing the caldera and the later interior cones 
 (after Russell) . 
 
 been born in the grandest throes of their life history, and that a 
 larger or smaller lateral migration of the vent has been responsible 
 for the partial destruction of the explosion crater. Upon Vesu- 
 
RISE OF MOLTEN ROCK TO THE EARTH'S SURFACE 127 
 
 vius we find the crescent-like rim of Monte Somma; on Etna it 
 is the Val del Bove, etc. It is this caldera of composite cones 
 which gave rise to the theory of the " elevation crater " of von 
 Buch (see ante, p. 95, and Fig. 127). 
 
 The eruption of Vesuvius in 1906. — The volcano Vesuvius 
 rises on the shores of the beautiful bay of Naples only about ten 
 miles distant from the city of Naples. The mountain consists of 
 the remnant of an earlier broad-mouthed explosion crater, the 
 Monte Somma, and an inner, more conical elevation, the Monte 
 Vesuvio. Before the eruption of 1906 this central cone was sharply 
 conical and rose to ^ 
 
 a height of about 
 4300 feet above 
 the surface of the 
 bay, or above the 
 highest point of the 
 ancient caldera. 
 The base of this 
 inner cone is at an 
 elevation of some- 
 thing less than half 
 that of the entire 
 mass, and is sepa- 
 rated from the en- 
 circling ring wall of the old crater by the atrio, to which corre- 
 sponds in height a perceptible shelf or piano upon the slope toward 
 the bay of Naples (Fig. 128). 
 
 An active composite cone like that of Vesuvius is for the greater 
 part of the time in the Strombolian condition ; that is to say, light 
 ■crater explosions continue with varying intensity and interval, 
 except when the mountain has been excited to the periodic Vul- 
 canian outbreaks with which its history has been punctuated. 
 The Strombolian explosions have sufficient violence to eject small 
 fragments of hot lava, which, falling about the crater, slowly built 
 up a rather sharp cone. The period of Strombolian activity has, 
 therefore, been called the cone-producing period. Just before each 
 new outbreak of the Vulcanian type, the altitude of the mountain 
 has, therefore, reached a maximum, and since the larger explosive 
 eruptions remove portions of this cone at the same time that 
 
 Fig. 128. — View of Mount Vesuvius as it appeared from 
 the Bay of Naples shortly before the eruption of 1906 
 The horn to the left is Monte Somma. 
 
128 
 
 EARTH FEATURES AND THEIR MEANING 
 
 Before tfie£ruptJon 
 
 July e'-' 
 
 Aug. ff • 
 
 Septa'' 
 
 they increase the dimensions of the crater, the Vulcanian stage in 
 contrast to the other has been called the crater-producing period. 
 In this period, then, the material ejected during the explosions does 
 not consist solely of fresh lava cakes, but in part of the older debris 
 derived from the crater walls, whence it is avalanched upon the 
 chimney after each larger explosion. The over- 
 hanging cloud, which during the Strombolian 
 period has consisted largely of steam and is 
 noticeably white, now assumes a darker tone, 
 the " smoke " which characterizes the Vulcanian 
 eruption. 
 
 On several historical occasions the cone of 
 Vesuvius has been lowered by several hundred 
 feet, the greatest of relatively recent truncations 
 having occurred in 1822 and in 1906. Between 
 Vulcanian eruptions the. Strombolian activity is 
 by no means uniform, and so the upward growth 
 of the cone is subject to lesser interruptions and 
 truncations (Fig. 129). 
 
 The Vesuvian eruption of 1906 has been 
 selected as a type of the larger Vulcanian erup- 
 tion of composite cones, because it combined the 
 explosive and paroxysmal elements, and because 
 it has been observed and studied with greater 
 thoroughness than any other. The latest pre- 
 vious eruption of the Vulcanian order had 
 occurred in 1872. Some two years later the 
 period of active cone building began and pro- 
 ceeded with such rapidity that by 1880 the new 
 cone began to appear above the rim of the crater 
 of 1872. From this time on occasional hght 
 eruptions interrupted the upbuilding process, 
 and as the repairs were not in all cases com- 
 pleted before a new interruption, a nest of cones, each smaller 
 than the last, arose in series like the outdrawn sections of an old- 
 time spyglass. At one time no less than five concentric craters 
 were to be seen. 
 
 For a brief period in the fall of 1904 Vesuvius had been in almost 
 absolute repose, but soon thereafter the Strombolian crater ex- 
 
 FiG. 129. — A series 
 of consecutive 
 sketches of the 
 summit of the 
 Vesuvian cone, 
 showing the modi- 
 fications in its out- 
 line (after Sir Wil- 
 liam Hamilton). 
 
RISE OF MOLTEN ROCK TO THE EARTH'S SURFACE 129 
 
 plosions were resumed. On May 25, 1905, a small stream of lava 
 began to issue from a fissure high up upon the central cone, and 
 from this time on the lava continued to flow down to the valley or 
 atrio, separating the inner cone from the caldera remnant of Monte 
 Somma. Seen in the night, this stream of lava appeared from 
 
 Fig. 130. — Night view of Vesuvius from Naples before 
 the outbreak of 1906. A small lava stream is seen 
 descending from a high point upon the central cone 
 (after Mercalli). 
 
 Naples like a red hot wire laid against the mountain's side (Fig. 
 130). With gradual augmentation of Strombolian explosions 
 and increase in volume of the flowing lava stream, the same condi- 
 tion continued until the first days of April in 1906. The flowing 
 lava had then overrun the tracks of the mountain railway and 
 accumulated in considerable quantity within the atrio (Fig. 131). 
 On the morning of April 4, a preliminary stage of the eruption 
 was inaugurated by the opening of a new radial fissure about 500 
 
130 
 
 EARTH FEATURES AND THEIR MEANING 
 
 feet below the summit of the cone (Fig. 132 a), and by early after- 
 noon the cone-destroying stage began with the rise of a dark " cauli- 
 flower cloud " or pino to replace the hghter colored steam cloud. 
 The cone was beginning to fall into the crater, and old lava debris 
 was mingled in the ejections with the lava clots blown from the 
 still fluid material within the chimney. From now on short and 
 snappy lightning flashes played about the black cloud, giving out 
 a sharp staccato " tack-a-tack." The volume and density of the 
 cloud and the intensity of the crater explosions continued to in- 
 crease until the culmination on April 7. On April 5 at midnight a 
 
 Fig. 131. — Scoriaceous lava encroaching upon the tracks of the Vesuviau railway 
 (after a photograph by Sommer). 
 
 new lava mouth appeared upon the same fissure which had opened 
 near the summit, but now some 300 feet lower (Fig. 132 6). The 
 lava now welled out in larger volume corresponding to its greater 
 head, and the stream which for ten months had been flowing from 
 the highest outlet upon the cone now ceased to flow. The next 
 morning, April 6, at about 8 o'clock, lava broke out at several 
 points some distance east of the opening h, and evidently upon 
 another fissure transverse to the first (Fig. 132 c). The lava sur- 
 face within the chimney must still have remained near its old 
 level, — effective draining had not yet begun, -:— 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 higher. 
 
RISE OF MOLTEN ROCK TO THE EARTH'S SURFACE 131 
 
 The culmination of the eruption came in the evening of April 7, 
 when, to the accompaniment of light earthquakes felt as far as 
 Naples, lava issued for the first time in great volume from a mouth 
 more than halfway 
 
 down the mountain side 
 (Fig. 132 /), and thus 
 began the drainage of 
 the chimney. At about 
 the same time with loud 
 detonations a huge 
 black cloud rose above 
 the crater in connection 
 with heavy explosions, 
 and a rain of cinder was 
 general in the region 
 about the mountain but 
 especially within the 
 northeast quadrant. 
 Those who were so for- 
 tunate as to be in Pom- 
 peii had a clear view of 
 the mountain's summit 
 where red hot masses of 
 lava were thrown far 
 into the air. The direc- 
 tion of these projections 
 was reported to have 
 been not directly up- 
 ward, but inclined 
 toward the northeast 
 quadrant of the moun- 
 tain ; but since with a 
 northeast surface wind 
 the heaviest deposit of 
 ash and dust should 
 have been upon the southwestern quadrant of the mountain, it 
 is evident that the. material was carried upward until it reached 
 the contrary upper currents of the atmosphere, to be by them dis- 
 tributed. 
 
 Fig. 132. — Map of Vesuvius, showing the position 
 and order of formation of the lava mouths upon 
 its flanks during the eruption of 1906 (after 
 Johnston-Lavis) . 
 
132 
 
 EARTH FEATURES AND THEIR MEANING 
 
 When the heavy curtain of ash, which now for a number of 
 succeeding days overhung all the circum-Vesuvian country, began 
 
 Fig. i;:!:;. — 
 
 ho ash curtain which had o\- 
 
 
 Vesuvius lifting and 
 
 j^mg 
 
 the outlines of the mountain on April 10, 1911 (after De Lorenzo). 
 
 to lift (Fig. 133), it was seen that the summit of the cone had been 
 truncated an average of some 500 feet (Fig. 134). 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 feet, where it had 
 drifted into all the hollow 
 ways so as almost to 
 efface them (Fig. 135). 
 More than thrice as 
 heavy as water, the weak 
 roof timbers of the houses 
 at the base of the moun- 
 tain gave way beneath 
 the added load upon 
 them, thus making many 
 victims. Inasmuch, how- 
 ever, as the ash-fall par- 
 takes of the same general characters as in eruptions from cinder 
 cones, we may here give our attention especially to the streams of 
 
 Fig. 134. — The central cone of Vesuvius as it 
 appeared after the eruption of 1906, but with 
 the earlier profile indicated. The truncation 
 represents a lowering of the summit by some 
 five hundred feet, with corresponding increase in 
 the diameter of the crater (after Johnston- 
 Lavis) . 
 
RISE OF MOLTEN ROCK TO THE EARTH'S SURFACE 133 
 
 .'i^y--^ 
 
 Fig. 135. — A sunken road filled with in- 
 drifted cocoa-colored ash from the Vesu- 
 vian eruption of 1906. 
 
 ^-,&^^ 
 
 lava which issued upon the 
 opposite flank of the moun- 
 tain (Fig. 136). 
 
 The main lava stream 
 descended the first steep 
 slopes with the velocity of a 
 mile in twenty-five minutes, 
 about the strolling speed of 
 a pedestrian, but this rate 
 was gradually reduced as 
 the stream advanced far- 
 ther from the mouth. Tak- 
 ing advantage of each depression of the surface, the black stream 
 advanced slowly but relentlessly toward the cities at the south- 
 west base of the mountain. With a motion not unlike that of a 
 heap of coal falling over itself down a slope, the block lava 
 
 Fig. 136. — View of Vesuvius taken from the 
 southwest during the waning stages of the 
 eruption of 1906. In the middle distance 
 may be discerned the several lava mouths 
 aligned upon a fissure, and the courses of 
 the streams which descend from them. In 
 the foreground is the main lava stream with 
 scoriaceous surface (after W. Prinz). 
 
 Fig. 137. — The main lava stream of 
 1906 advancing upon the village of 
 Boscotrecase. 
 
 Fig. 138. — An Italian pine snapped off 
 by the lava and carried forward upon 
 its surface as a passenger (after Haug). 
 
134 
 
 EARTH FEATURES AND THEIR MEANING 
 
 Fig. 139. — Lava front both pushing over and 
 running around a wall which lies athwart its 
 course (after Johnston-Lavis). 
 
 advances without burning 
 the objects in its path 
 (Fig. 137). The beautiful 
 pines are merely charred 
 where snapped off and 
 are carried forward upon 
 the surface of the stream 
 (Fig. 138). When a real 
 obstruction, such as a 
 bridge or a villa, is en- 
 countered, the stream is 
 at first halted, but the 
 rear crowding upon the 
 van, unless a passage is found at the side, the lava front rises 
 higher and higher until by its weight the obstruction is forced to 
 give way (Figs. 139 and 140). 
 
 The sequence of events within the chimney. — 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 volcano, both 
 before and during the erup- 
 tion. Anticipating some 
 conclusions derived from the 
 observed dissection of vol- 
 canoes, which will be dis- 
 cussed below, it may be 
 stated that what might be 
 termed the core of the com- 
 posite cone — the chimney 
 — is a more or less cylin- 
 drical plug of cooled lava 
 which during the active 
 period of the vent has an 
 interior bore of probably variable caliber. This plug in its 
 lower section appears in solid black in all the diagrams of Fig. 
 141. During the cone-building period (Fig. 141 a and 6) the plug 
 is obviously built upward along with the cone, for lava often flows 
 out at a level a few hundred feet only below the crater rim. By 
 
 :^ 
 
 
 
 J 
 
 
 
 
 '."-.- 
 
 -'J^-: 
 
 ^^-"'^ _^— -— -^ — > ^ 
 
 n' 
 
 
 \^.Al^. ._ 't 
 
 
 
 
 "" '':'i^,^3^^^' - 
 
 
 
 Fig. 140. — One of the \'illas in Boscotrecase 
 which was ruined by the Vesu\aan lava flow 
 of 1906. The fragments of masonry from 
 the ruined walls traveled upon the lava 
 current, where they sometimes became 
 incased in lava. 
 
RISE OF MOLTEN ROCK TO THE EARTH'S SURFACE 135 
 
 what process this chimney 
 building goes on is not well 
 understood, though some light 
 is thrown upon it by the post- 
 eruption stage of Mont Pele in 
 1902-1903 (see below). 
 
 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 tuff; and 
 they are, therefore, in a condi- 
 tion not unlike that of the 
 inner barrel of a great gun over 
 which sleeves of metal have 
 been shrunk so as to give sup- 
 port against bursting pressures. 
 On the other hand, when not 
 sustaining the hydrostatic pres- 
 sure of the liquid lava within, 
 the chimney would tend to be 
 crushed in by the pressure 
 of the surrounding tuff. Its 
 strength to withstand bursting 
 pressures is dependent not 
 alone upon the thickness of its 
 rock walls, but also upon its 
 internal diameter or caliber. 
 A steam cylinder of given 
 thickness of wall, as is well 
 known, can resist bursting 
 pressures in proportion as its 
 internal diameter is small. So 
 in the volcanic chimney, any 
 tendency to remelt from within 
 the chimney walls must weaken 
 them in a twofold ratio, 
 
 We are yet without accurate 
 
 
 ^^^r"? 
 
 Fig. 141. — Three diagrams to illustrate 
 the sequence of events within the crater 
 of a composite cone during the cone- 
 building and crater-producing periods. 
 a and h, two successive stages of the 
 cone building or Strombolian period ; 
 c, enlargement of the crater, truncation 
 of the cone, and destruction of the upper 
 chimney [luring the relatively brief 
 crater-producing or Vulcanian period. 
 
136 
 
 EARTH FEATURES AND THEIR MEANING 
 
 temperature observations upon the lava in volcanic chimneys, 
 but it seems almost certain that these temperatures rise as the 
 Vulcanian stage is approaching, and such elevation of temperature 
 must be followed by a greater or less re-fusion of the chimney 
 walls. The sequence of events during the late Vesuvian eruption 
 
 fc:? 
 
 '■•i^^i^^m^Sf'- 
 
 Fig. 142. — The spine of Pele rising above the chimney of the volcano after 
 the eruption of 1902 (after Hovey). 
 
 is, then, naturally explained by progressive re-fusion and conse- 
 quent weakening of the chimney walls, thus permitting a radial 
 fissure to open near the top and gradually extend downwards. 
 Thus at first small and high outlets were opened insufficient to 
 drain the chimney, but later, on April 7, after this fissure had 
 
RISE OF MOLTEN ROCK TO THE EARTH'S SURFACE 137 
 
 been much extended and a new and larger one had opened at a 
 lower level, the draining began and the surface of lava commenced 
 rapidly to sink. 
 
 When the rapid sinking of the lava surface occurred, the lower 
 lava layers were almost immediately relieved of pressure, thus 
 causing a sudden expansion of the contained steam and resulting 
 in grand crater explosions. The partially re-fused and fissured 
 upper chimney, now unable to withstand the inward pressure of 
 
 Fig. 143. — Outlines of the Pele spine upon successive dates. The full line repre- 
 sents its outline on December 26, 1902 ; the dotted-dashed line is a profile of 
 January 3, 1902 ; while the dotted line is that of January 9, 1903. The dark 
 line is a fissure( after E. O. Hovey). 
 
 the surrounding tuff walls, since outward pressures no longer 
 existed, 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 (Fig. 141 c). In outline, then, 
 these seem to be the conditions which are indicated by the 
 sequence of observed events in connection with the late Vesuvian 
 outbreak. 
 
 The spine of Pele. — The disastrous eruption of Mont Pele 
 upon Martinique in the year 1902 is of importance in connection 
 with the interesting problem of the upward growth of volcanic 
 chimneys during the cone-building period of a volcano. After 
 the conclusion of this great Vulcanian eruption, a spine of lava 
 
138 EARTH FEATURES AND THEIR MEANING 
 
 grew upward from the chimney of the main crater until it had 
 reached an elevation of more then a thousand feet above its base, 
 a figure of the same order of magnitude as the probable height of 
 the upper section of the Vesuvian chimney previous to the erup- 
 tion of 1906. The Pele spine (Fig. 142) did not grow at a uniform 
 rate, but was subject to smaller or larger truncations, but for a 
 period of 18 days the upward growth was at t-he rate of about 41 
 feet per day. Later, the mass split upon a vertical plane reveahng 
 a concave inner surface, and was somewhat rapidly reduced in 
 altitude to 600 feet (Fig. 143), only to rise again to its full height 
 of about 1000 feet some three months later. 
 
 While apparently unique as an observed phenomenon, and not 
 free from uncertainty as to its interpretation, 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 pressures. 
 
 The aftermath of mud flows. — When the late Vulcanian ex- 
 plosions of Vesuvius had come to an end, all slopes of the moun- 
 tain, but especially 
 the higher ones, 
 were buried in 
 thick deposits of 
 the cocoa-colored 
 ash, included in 
 which were larger 
 and smaller pro- 
 jectiles. As this 
 
 Fig. 144. — Corrugated surface of the Vesu\-ian cone material is ex- 
 after the mud flows which followed the eruption in 1906 , i •, 
 
 . ., T , , T • ^ tremely porous, it 
 
 (after Johnston-La vis). . 
 
 greedily sucks up 
 the water which falls during the first succeeding rains. When 
 nearly saturated, it begins to descend the slopes of the mountain 
 and soon develops a velocity quite in contrast with that of the 
 slow-moving lava. The upper slopes are thus denuded, while 
 the fields and even the houses about the base are invaded by these 
 torrents of mud (lava d' acqiia). Inasmuch as these mud flows are 
 the inevitable aftermath of all grander explosive eruptions, the 
 Italian government has of late spent large sums of money in the 
 construction of dikes intended to arrest their progress in the future. 
 
RISE OF MOLTEN ROCK TO THE EARTH'S SURFACE 139 
 
 It was streams of this sort that buried the city of Hereulaneum 
 after the explosive eruption of 79 a.d. 
 
 After the mud flows have occurred, the Vesuvian cone, like all 
 similar volcanic cones under the same conditions, is found with 
 deep radial corrugations (Fig. 144), such as were long ago de- 
 scribed as '' barrancoes " and supposed to support the *' elevation 
 crater " theory of volcano formation. 
 
 The dissection of volcanoes. — To the uninitiated it might ap- 
 pear a hopeless undertaking to attempt to learn by observation 
 the internal structure of a volcano, and especially of a complex 
 volcano of the composite type. The earliest successful attempt 
 appears to have been made by Count Caspar von Sternberg in 
 order to prove the cor- 
 rectness of the theory 
 of his friend, the poet 
 Goethe. Goethe had 
 claimed that a little 
 hill in the vicinity of 
 Eger, on the borders 
 of Bohemia, was an ex- 
 tmct volcano, though 
 the foremost geologist 
 of the time, the fa- 
 mous Werner, had pro- 
 mulgated the doctrine 
 that this hill, in common with others of similar aspect, originated 
 in the combustion of a bed of coal. The elevation in question, 
 which is known -as the Kammerbiihl, consists mainly of cinder, 
 and Goethe had maintained that if a tunnel were to be driven 
 horizontally into the mountain from one of its slopes, a core or 
 plug of lava would be encountered beneath the summit. The 
 excavations, which were completed in 1837, fully verified the 
 poet's view, 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 (Fig. 145). 
 
 It is not, however, to such expensive projects that reference 
 is here made, but rather to processes which are continually going 
 on in nature, and on a far grander scale. The most important 
 dissecting agent for our purpose is running water, which is con- 
 
 FiG. 145. — The Kammerbiihl near Eger, showing 
 the tunnel completed in 1837 which proved the 
 volcanic nature of the mountain (after Judd) . 
 
140 
 
 EARTH FEATURES AND THEIR MEANING 
 
 tinually paring down the earth's surface and disclosing its buried 
 structures. How much more convincing than any results of 
 
 ..--_._^vsi!? 
 
 Fig. 146. — Volcanic plug exposed by natural dissection of a 
 volcanic cone in Colorado (U. S. G. S.). 
 
 artificial excavation, as evidence of the internal structure of a 
 volcano, is the monument represented in Fig. 146, since here the 
 
 lava plug stands in relief like a 
 gigantic thumb still surrounded by 
 a remnant of cinder deposits. Such 
 exposed chimneys of former volcanoes 
 are found in many regions, and have 
 become known as volcanic necks, 
 pipes, or plugs. 
 
 Not infrequently the beds of tuff 
 composing the flanks of the volcano, 
 upon dissection by the same process, 
 bring to light walls of cooled lava 
 standing in relief (Fig. 147) — the 
 filling of the fissure which gave outlet 
 to the flanks of the mountain at the 
 time of the eruption. Study of ex- 
 posed dikes formed in connection 
 with recent eruptions of Vesuvius 
 has shown that in many instances they are still hollow, the lava 
 having drained from them before complete consolidation. 
 
 i lu. 147. — A dike cutting beds of 
 tuff in a partly dissected volcano 
 of southwestern Colorado (after 
 Howe, U. S. G. S.). 
 
RISE OF MOLTEN ROCK TO THE EARTH'S SURFACE 141 
 
 Fig. 148. — Map and gen- 
 eral view of St. Paul's 
 Rocks, a volcanic cone 
 dissected by waves. 
 
 Another agent which is effective in uncovering the buried struc- 
 tures of volcanoes is the action of waves on shores. Always a 
 relatively vigorous erosive agency, the softer structures of vol- 
 canic cones are removed with especial facility by this agent. On 
 the shores of the island of Volcano, the little 
 cone of Vulcanello has been nearly half 
 carried away by the waves, so as to reveal 
 with especial perfection the structure of the 
 cinder beds as well as the internal rock 
 skeleton of the mass. Here the character- 
 istic dips of lava streams, intercalated as 
 they now are between tuff deposits and the 
 lava which consoHdated in fissures, are both 
 revealed. 
 
 In mid-Atlantic a quite perfect crater, the 
 St. Paul's Rocks, has been cut nearly in 
 half so as to produce a natural harbor 
 (Fig. 148). 
 
 In still other instances we may thank the 
 volcano itself for opening up the interior of 
 
 the mountain for our inspection. The eruption in 1888 of the 
 Japanese volcano of Bandai-san, by removing a considerable part 
 of the ancient cone, has afforded us a section completely through 
 the mountain. The summit and one side of the small Bandai was 
 carried completely away, and there was substituted a yawning 
 crater eccentric to the former mountain and having its highest 
 ,, — ^ wall no less than 1500 
 
 feet in height (Fig. 149). 
 In two hours from the 
 first warning of the ex- 
 plosion the catastrophe 
 was complete and the 
 eruption over. 
 
 The eruption of Kra- 
 katoa in 1883, probably 
 the grandest observed volcanic explosion in historic times, left 
 a volcanic cone divided almost in half and open to inspection 
 (Fig. 150). Rakata, Danan, and Perbuatan had before con- 
 stituted a line of cones built up round individual craters sub- 
 
 Fig. 
 
 149. — Dissection by explosion of Little 
 Bandai-san in 1888 (after Sekiya). 
 
142 
 
 EARTH FEATURES AND THEIR MEANING 
 
 sequent to the partial destruction of an earlier caldera, portions 
 of which were still existent in the islands Verlaten and Lang. 
 By the eruption of 1883 all the exposed parts and considerable 
 submerged portions of the two smaller cones were entirely de- 
 stroyed, and the larger one, known as Rakata, was divided just 
 outside the plug so as to leave a precipitous wall rising directly 
 
 from the sea and 
 
 ^^K^(}'^''' 
 
 jtnirAr'^ 
 
 '^iJa^ait 
 
 Fig. 150. — The half-submerged volcano of Krakatoa 
 in the Sunda Straits before and after the eruption of 
 1883 (after Verbeek). 
 
 sho^vang lava streams 
 r"^^ ' in alternation with 
 somewhat thicker 
 tuff layers, the whole 
 knit together by nu- 
 merous lava dikes. 
 
 In order to carry 
 our dissecting pro- 
 cess dowm to levels 
 below the base of the volcanic mountain, it is usually necessary to 
 inspect the results of erosion by running water. Here the plug or 
 chimney, instead of being surrounded b}^ tuff, is inclosed by the 
 country rock of the region, which is commonly a sedimentary 
 formation. Such exposed lower sections of volcanic chimneys are 
 numerous along the northwestern shores of the British Isles. 
 Where aligned upon 
 a dislocation or note- 
 worthy fissure in the 
 rocks, the group of 
 plugs has been re- 
 ferred to as a scar or 
 cicatrice (Fig. 151). 
 Associated with the 
 plugs of the cicatrice 
 are not infrequently 
 
 dikes, or, it may be, sheets of lava extended between layers of 
 sediment and known as sills. 
 
 If we are able to continue the dissection process to still greater 
 depths, 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 uninterrupted. This rock 
 is found in masses of larger dimensions, and though generally of 
 
 MB ErupT/ve ffocA 
 Wii^ Mero/r>oro/j/c Zone 
 
 fi// ono Mez for/nor/or^ 
 Cry^ta///ne Sc/i/srs 
 
 Fig. 151. — The cicatrice of the Banat (after Suess). 
 
RISE OF MOLTEN ROCK TO THE EARTH'S SURFACE 143 
 
 more or less irregular form, no one dimension is of a different order 
 of magnitude from the others. Such masses are commonly de- 
 scribed as bosses, or, if especially large, as hathoUtes (Fig. 152). 
 Wherever the rock beds appear as though they had been forced 
 up by the upward pressure of the igneous mass, the latter takes 
 the form of a mushroom and has been described as a laccoUte 
 (Figs. 479-481, pp. 441-442). Evidence seems, however, to accumu- 
 late that in the greater number of cases the molten rock has fused 
 its way upward, in part assimilating and in part inclosing the rock 
 which it encountered. This pro- ^ , 
 
 cess of upward fusion has been 
 likened to the progress of a red 
 hot iron burning its waj^ through 
 a board. 
 
 The formation of lava reser- 
 voirs. — The discarding of the 
 earlier notion that the earth has 
 a liquid interior makes it proper 
 in discussing the subject of vol- 
 canoes to at least touch upon 
 the origin of the molten rock 
 material. As already pointed 
 out, such reservoirs as exist 
 must be local and temporary, 
 or it would be difficult to see 
 how the existing condition of 
 earth rigidity could be main- 
 tained. From the rate at which rock temperatures rise, at 
 increasing depths below the surface, it is clear that all rocks would 
 be melted at very moderate depths only, if they were not kept in a 
 solid state by the prodigious loads which they sustain. Any relief 
 from this load should at once result in fusion of the rock. 
 
 Now the restriction of active volcanoes to those zones of the 
 earth's surface within which mountains are rising, and where 
 in consequence earthquakes are felt, has furnished us at least a 
 clew to the origin of the lava. Regarded as a structure capable 
 of sustaining a load, the competency of an arch is something quite 
 remarkable, so that the arching up of strong rock formations into 
 anticlines within the upper layers of the zone of flow, or of com- 
 
 — > —SonC/sTofie- ■■ — - — . 
 
 I IG 152 — Dia^r xm 1 o illu'^trate a pi ob- 
 
 ablc L;a,uoe of fi_.rnicitiuii yj{ lava TcacP- 
 
 voirs, and to show the connection 
 between such reservoirs and the vol- 
 canoes at the surface. 
 
144 
 
 EARTH FEATURES AND THEIR MEANING 
 
 bined fracture and flow, would be sufficient to remove the load 
 from relatively weak underlying beds, which in consequence would 
 be fused and form local reservoirs of lava (Figs. 152 and 153). 
 
 It has been further quite generally observed that lines of vol- 
 canoes, in so far as they betray any relation in position to neigh- 
 boring mountain ranges, tend to appear upon the rear or flatter 
 limb of unsymmetrical arches, or where local tension would favor 
 the opening of channels toward the surface. Moreover, wherever 
 recent block movements of surface portions of the earth's shell 
 have been disclosed in the neighborhood of volcanoes, the latter 
 appear to be connected with downthrowT.1 blocks, as though the lava 
 
 had, so to speak, been squeezed out from 
 beneath the depressed block or blocks. 
 
 We must not, however, forget that the 
 igneous rocks are greatly restricted in the 
 range of their chemical composition. No 
 igneous rock type is known which could 
 be formed by the fusion of any of the 
 carbonate rocks such as limestone or 
 dolomite, or of the more siliceous rocks, 
 such as sandstone or quartzite. There 
 remains only the argillaceous class of 
 sediments, the shales and slates, 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 rocks. 
 For purposes of comparison there is given below the composite or 
 average constitution of igneous rocks in parallel column, with the 
 average attained by combining the analyses of-56 slates and shales, 
 the latter recalculated with water excluded: 
 
 Fig. 153. — Result of experi- 
 ment with layers of com- 
 position to illustrate the 
 effect of relief of load upon 
 rocks by arching of com- 
 petent formation (after 
 WiUis). 
 
 
 Average Igneous Rock 
 
 Average Shale 
 
 
 (Clark) 
 
 (Washington) 
 
 810-2 
 
 61.25 
 
 61.69 
 
 63.34 
 
 AI2O3 
 
 15.81 
 
 15.94 
 
 16.56 
 
 FeaOs 
 
 FeO 
 
 3.61 ) 6-31 
 
 21!} 4-53 
 
 !:4lr-89 
 
 MgO 
 
 4.47 
 
 4.90 
 
 3.54 
 
 CaO 
 
 5.03 
 
 5.02 
 
 3.33 
 
 NaoO 
 
 3.64 
 
 4.09 
 
 1.29 
 
 K2O 
 
 2.87 
 
 3.35 
 
 3.52 
 
 TiOa 
 
 .62 
 
 .48 
 
 .53 
 
 
 100.00 
 
 100.00 
 
 100.00 
 
RISE OF MOLTEN ROCK TO THE EARTH'S SURFACE 145 
 
 This close resemblance is probably of deep significance, for the 
 reason that shales and slates are structurally the weakest of all 
 rocks and for the further reason that they rather generally di- 
 rectly underhe the carbonate rocks, which are by contrast the 
 ' strongest (see ante, p. 37). 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 flow. If this view is well founded, lavas and other igneous 
 rocks are in large part fused argillaceous sediments formed in con- 
 nection with the process of folding, or are refused rocks of igneous 
 origin and similar composition. 
 
 Character profiles. — The character profiles of features con- 
 nected in their origin w"ith volcanoes are particularly easy to 
 recognize, and in a few cases in which they might be confused with 
 others of a different origin, an examination of the materials of 
 the features should lead to a definitive judgment. 
 
 The lava plains which result from massive outflows of basalt 
 might perhaps strictly be regarded as lack of feature, so great may 
 be their continuous extent. Wherever definite vents exist, a 
 broad flat dome is the usual result of the extravasation of a basal- 
 tic lava. The puys of France and many of the Kuppen of Ger- 
 many, being formed from less fluid lava, have afforded profiles 
 with relatively small radius of curvature. 
 
 In its youthful stage, the cinder cone usually presents a broad 
 summit sag and relatively short side slopes, 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 increas- 
 ing rapidly toward the summit. In contrast, too, with the earlier 
 stage, the crest is relatively small. A marked reduction in the 
 high symmetry of such profiles is noted wherever a breaching by 
 lava outflow has occurred (Fig. 154). 
 
 With the composite cone, complexity and corresponding lack 
 of symmetry is introduced, especially in the partially ruined 
 caldera, and by the more or less accidental distribution of parasitic 
 cones, as well as by migrations of the central cone. Peculiarly 
 similar acuminated profiles result from spatter-cone formation, 
 from the formation of a superchimney spine, and by the uncover- 
 ing of the chimney through denudational processes — the volcanic 
 neck. 
 
146 
 
 EARTH FEATURES AND THEIR MEANING 
 
 Another important feature resulting from denudation is the 
 Mesa or table mountain with its protecting basalt cap above softer 
 rocks. Its profile most resembles that of table mountains due to 
 differential erosion of alternately strong and weak horizontally 
 
 3oso/y- /^/o/n 
 
 Fig. 154. — Character profiles connected with volcanoes. 
 
 bedded rocks, such as compose the upper portion of the section in 
 the Grand Canon of the Colorado. Here, however, 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 profile. 
 
 Reading References to Chapters IX and X 
 General works : — 
 
 Paulett Scrope. The Geology of the Extinct Volcanoes of Central 
 France. John Murray, London, 1858, pp. 258. (An epoch-making 
 work of early date which, like the following reference, may be studied 
 to advantage to-day.) 
 
 Sir Charles Lyell. Principles of Geology, vol. 1, Chapters xxiii-xxv. 
 
 Melchior Neumatr. Erdgeschichte, vol. 1, Allgemeine Geologic, revised 
 edition by v. Uhlig, 1897, pp. 133-277 (a storehouse of valuable infor- 
 mation clearly presented). 
 
 J. D. Dana. Characteristics of Volcanoes, with Contributions of Facts 
 and Principles from the Hawaiian Islands. Dodd, Mead, and Com- 
 pany, New York, 1890, pp. 397. 
 
 Tempest Anderson. Volcanic Studies in Many Lands, being reproduc- 
 tions of photographs by the author with explanatory notes. John 
 Murray, London, 1903, pp. 200, pis. 105. 
 
 T. G. Bonnet. Volcanoes, their Structure and Significance. John 
 Murray, London, 1899, pp. 331. 
 
RISE OF MOLTEN ROCK TO THE EARTH'S SURFACE 147 
 
 I. C. Russell. Volcanoes of North America. Maemillan, New York, 
 1897, pp. 346. 
 
 Elisee Reclus. Les voleans de la terre, Belgian Society of Astronomy. 
 Meteorology, and Physics of the Globe, 1906-1910 (a valuable de- 
 scriptive geographical and bibliographical work of reference). 
 
 G. Mbrcalli. I vulcani attivi della terre. Hoepli, Milan, 1907, pp. 421. 
 (A most valuable work, beautifully illustrated, but in the Italian 
 language.) 
 Arrangement of volcanic vents : — 
 
 Th. Thoroddsen. Die Bruchlinien und ihre Beziehungen zu den Vul- 
 kanen, Pet. Mitt., vol. 51, 1905, pp. 1-5, pi. 5. 
 
 R. D. M. Verbeek. Various volumes and atlases of maps covering the 
 Dutch East Indies and fully cited in the following reference (p. 21). 
 
 William H. Hobbs. The Evolution and the Outlook of Seismic Geology, 
 Proc. Am. Phil. Soc, vol. 48, 1909, pp. 17-27. 
 Birth of volcanoes : — 
 
 F. Omori. The Usu-san Eruption and Earthquake and Elevation Phe- 
 nomena, Bull. Earthq. Inv. Com., Japan, vol. 5, No. 1, 1911, pp. 1-37, 
 pis. 1-13. 
 Fissure eruptions : — 
 
 Th. Thoroddsen. Island, IV, Vulkane, Pet. Mitt., Erganzungsh. 153, 
 1906, pp. 108-111. 
 
 A. Geikie. Text-book of Geology, 4th ed., pp. 342-346. 
 
 Lava domes of Hawaii : — 
 J. D. Dana. Characteristics of Volcanoes (as above). 
 C. H. Hitchcock. Hawaii and Its Volcanoes. Honolulu, 1909, pp. 314. 
 
 Eruption of Matavanu volcano in 1906 : — 
 Karl Sapper. Der Matavanu-Ausbruch auf Savaii, 1905-1906, Zeit. 
 
 d. Gesell. f. Erdk. z. BerHn, vol. 19, 1906, pp. 686-709, 4 pis. 
 H. J. Jensen. The Geology of Samoa, and the Eruptions in Savaii, Proc. 
 
 Linn. Soc, New South Wales, vol. 31, 1906, pp. 641-672, pis. 54-64. 
 Tempest Anderson. The Volcano of Matavanu in Savaii, Quart. Jour. 
 
 Geol. Soc, London, vol. 66, 1910, pp. 621-639, pis. 45-52. 
 
 Eruption of Volcano in 1888 : — 
 H. J. Johnston-Lavis. The South Italian Volcanoes. Naples, 1891, 
 pp. 342, pis. 16. 
 Eruption of Taal volcano in 1911 : — 
 W. E. Pratt. The Eruption of Taal Volcano, January 30, 1911, Phil. 
 Jour. Sci., vol. 6, No. 2, Sec A, 1911,- pp. 63-86, pis. 1-14. 
 
 F. H. Noble. Taal Volcano, album of views of 1911 eruption, Manila, 
 
 1911, pp. 1-48. 
 The volcano of Etna : — 
 
 G. voM Rath. Der Aetna. Bonn, 1872, pp. 1-33. (A beautiful piece of 
 
 descriptive writing from both the geological and scenic standpoints.) 
 
148 EARTH FEATURES AND THEIR MEANING 
 
 Sartorius von Waltershausen. Der Aetna. Leipzig, 1880, 2 quarta 
 
 vols., pp. 371 and 548. 
 The eruption of Vesuvius in 1906 : — 
 H. J. Johnston-Lavis. Geological Map of Monte Somma and Vesuvius, 
 
 with a short and concise account, etc. Geo. Philip & Son, London, 
 
 1891. 
 H. J. Johnston-Lavis. The Eruption of Vesuvius in April, 1906, Trans. 
 
 Roy. Dublin Soc, vol. 9, 1909, Pt. VIII, pp. 139-200, pis. 3-23 (the 
 
 most authoritative work upon the subject). 
 T. A. Jaggar, Jr. The Volcano Vesuvius in 1906, Tech. Quart., vol. 19, 
 
 1906, pp. 105-115. 
 W. Prinz. L'eruption du Vesuv d'avril, 1906, Ciel et Terre, 27e Annee, 
 
 1906, pp. 1-49. 
 Frank A. Perret. Notes on the Electrical Phenomena of the Vesuvian 
 
 Eruption, April, 1906, Sei. Bull., Brooklyn Inst. Arts and Sei., vol. 1, 
 
 No. 11, pp. 307-312; Vesuvius, Characteristics and Phenomena of 
 
 the Present Repose Period, Am. Jour. Sei., vol. 28, 1909, pp. 413-430. 
 William H. Hobbs. The Grand Eruption of Vesuvius in 1906, Jour. 
 
 GeoL, vol. 14, 1906, pp. 636-655. 
 The spine of Pelee : — 
 E. O. Hovey. The New Cone of Mont Pele and the Gorge of the Riviere 
 
 Blanche, Martinique, Am. Jour. Sei., vol. 16, 1903, pp. 269-281, pis. 
 
 11-14. 
 A. Heilprin. The Tower of Pelee. Philadelphia, 1904, pp. 62, pis. 22. 
 A. Lacroix. La montagne Pelee et ses eruptions, Acad, des Sciences, 
 
 Paris, 1904, Chapter iii. 
 Karl Sapper. In den Vulkangebieten Mittelamerikas und Westindiens, 
 
 Stuttgart, 1905, pp. 172-178. 
 A. C. Lane. Absorbed Gases of Vulcanism, Science, N.S., vol. 18, 1903, 
 
 p. 760. 
 G. K. Gilbert. The Mechanism of the Mont Pelee Spine, ibid., vol. 19, 
 
 1904, pp. 927-928. 
 I. C. Russell. Pele Obelisk once More, ibid., voF. 21, 1905, pp. 924-931. 
 
 The dissection of volcanoes : — ■ 
 J. W. JuDD. Volcanoes, Chapter v. 
 S. Sekya and Y. Kikuchi. The Eruption of Bandai-San, Trans. Seis. 
 
 Soc, Japan, vol. 13, Pt. 2, 1890, pp. 140-222, pis. 1-9. 
 R. D. M. Verbeek. Krakatau. Batavia, 1885, pp. 557, pis. 25. 
 Royal Society, The Eruption of Krakatoa and Subsequent Phenomena. 
 
 London, 1888, pp. 494. 
 G. K. Gilbert. Report on the Geology of the Henry Mountains, U.S. 
 
 Geogr. and Geol. Surv., Rocky Mt. Region, Washington, 1877, pp. 
 
 22-60. 
 Sir a. Geikie. Ancient Volcanoes of Great Britain, vol. 2 especially. 
 D. W. Johnson. Volcanic Necks of the Mount Taylor Region, New 
 
 Mexico, BuU. GeoL Soc. Am., vol. 18, 1907, pp. 303-324, pis. 25-30. 
 
CHAPTER XI 
 THE ATTACK OF THE WEATHER 
 
 The two contrasted processes of weathering. — It has already 
 been pointed out that change and not stability is the order of 
 nature. Within the earth's outer shell and upon it rock altera- 
 tion goes on continually, and from some portions of its surface the 
 changed material is as constantly migrating to neighboring or 
 even far distant regions. Before such transportation can begin 
 the hard rock must first be broken down and reduced to fragments 
 which the transporting agencies are competent to move. 
 
 To accomplish this breaking down, or degeneration, of the rock 
 masses, either a wide range in temperature or chemical reaction is 
 essential. In the atmosphere are found such active chemical 
 agents as oxygen and carbon dioxide, the so-called carbonic acid 
 gas ; 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 carbonates, which are lighter in weight and more 
 soluble. This chemical attack upon the outer shell of the litho- 
 sphere is described as decomposition. 
 
 On the other hand the rock may succumb to changes which are 
 purely mechanical and are due either to the stresses set up by dif- 
 ferences between surface and interior temperatures, or to the prying 
 action of the frost in the crevices. Such purely mechanical de- 
 generation of the rocks is in contrast with decomposition and is 
 described as disintegration. The two processes of decomposition 
 and disintegration may, however, go on together ; and the changes 
 of volume that are caused by decomposition may result directly 
 in considerable disintegration, as we are to see. 
 
 The rdle of the percolating water. — In order to effect chemical 
 change or reaction, 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 solution. The 
 chemical reactions which go on between the gaseous atmosphere 
 and the solid lithosphere are accomplished through solution of the 
 
 149 
 
150 
 
 EARTH FEATURES AND THEIR MEANING 
 
 gases in water. This water, derived from rain or snow, percolates 
 into the ground or descends along the crevices in the rocks, carry- 
 ing with it a certain measure of dissolved air. This air differs 
 from that of the surrounding atmospheric envelope by containing 
 
 relatively large amounts of oxygen and 
 of the other active element carbon diox- 
 ide. It follows from the important role 
 thus performed by the percolating water 
 that the process of decomposition will 
 be relatively important in humid re- 
 gions where the atmospheric precipita- 
 tion is sufficient for the purpose. 
 
 Within hot and dry regions there is 
 a larger measure of rock disintegration, 
 and distinct chemical changes unlike 
 those of humid regions take place in the 
 higher temperatures and with the more 
 concentrated saline solutions. The dis- 
 cussion of such changes will be deferred 
 until desert conditions are treated in 
 another chapter. 
 
 Mechanical results of decomposition 
 — spheroidal weathering. — 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 prisms. It is these 
 joints which offer relatively easy paths 
 for the descent of the water into the 
 rocks. In rocks of sedimentary origin 
 there are found, in addition to the vertical joints, planes of bed- 
 ding originally horizontal, and in the intrusive and volcanic rocks 
 a somewhat similar parting, likewise parallel to the surface of the 
 ground. 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 (Fig. 155, upper figure) which stand 
 in vertical columns. 
 
 Fig. 155. — Successive dia- 
 grams to show the effect of 
 decomposition and resulting 
 disintegration upon joint 
 blocks so as to produce 
 spheroidal bowlders by 
 weathering. 
 
THE ATTACK OF THE WEATHER 
 
 151 
 
 The water which percolates downward upon the joints, finds 
 its way laterally along the parting planes, and so subjects the en- 
 tire surface of each block to simultaneous attack by its reagents. 
 Though all parts of the surface of each block are alike subject to 
 attack, it is the angles and the edges which are most vigorously 
 acted upon. In the narrow crevices the solutions move but slug- 
 gishly, and as they are soon impoverished of their reagents in the 
 attack upon the rock, fresh solution can reach the middle of the 
 faces from relatively few directions. The edges are at the same 
 time being reached from many more directions, and the corners 
 from a still larger number. 
 
 The minerals newly formed by these chemical processes of 
 hydration and carbonization are notably lighter, and hence more 
 bulky than the minerals from whose constituents they have been 
 largely formed. Strains are thus set up which tend to separate 
 the bulkier new material from the core of unaltered rock below. 
 As the process continues, distinct channels for the moving waters 
 are developed favorable to action at the edges and corners of the 
 blocks. Eventually, the squared block is by this process trans- 
 formed into a spheroidal core of still unaltered rock wrapped in 
 layers of decomposed material, like the outer wrappings of an onion. 
 These in turn are usually imbedded in more thoroughly disinte- 
 grated material from which 
 
 the shell structure has dis- 
 appeared (Fig. 156). 
 
 Exfoliation or scaling. — A 
 fact of much importance to 
 geologists, but one far too 
 often overlooked, is that rocks 
 are but poor, conductors for 
 heat. It results from this 
 that in the bright sun of a 
 'summer's day a thin skin, as 
 it were, upon the rock surface may be heated to a relatively high 
 temperature, although the layer immediately below it is prac- 
 tically unaffected. The consequent expansion of the surface layer 
 causes stresses that tend to scale it off from the layer below, 
 which, uncovered in its turn, develops new strains of the same 
 sort. This process of exfoliation acquires exceptional importance 
 
 Fig. 15G. 
 
 Spheroidal weathering of an 
 igneous rock. 
 
152 
 
 EARTH FEATURES AND THEIR MEANING 
 
 Fig. 157. — Dome structure in granite 
 mass, Yosemite valley, California 
 (after a photograph by Sinclair) . 
 
 in desert regions where tiie rock surfaces are daily elevated to 
 excessively high temperatures (see Chapter XV). 
 
 Dome structure in granite masses. — In large granite masses, 
 such as are to be found in the ranges of the Sierra Nevada of Cali- 
 fornia, a peculiar dome structure is sometimes found developed 
 upon a large scale, and has had an important influence upon the 
 
 breaking down of the rock and 
 upon the shaping of the mountain 
 (Fig. 157). Such a structure, made 
 up as it is of prodigious layers, 
 can have little in common with 
 the veneers of weathered miner- 
 als which are the result of exfoli- 
 ation, 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 them, but has been carried away by erosion since the uplift 
 of the range. 
 
 The prying work of frost. — In all countries where winter tem- 
 peratures range below the freezing point of water, a most potent 
 agent of rock disintegration is the frost which pries at every crevice 
 and cranny of the surface rock. Important in the temperate zones, 
 in the polar regions it becomes almost the sole effective agent of 
 rock weathering. There, as elsewhere, its efficiency as a disinte- 
 grating agent is directly dependent upon the nature of the crevices 
 within the rock, so that the omnipresent joints are able to exer- 
 cise a degree of control over the sculpturing of the surface features 
 which is hardly. to be looked for elsewhere (see plate 10 A). 
 
 Talus. — Wherever the earth's surface rises in steep cliffs, the 
 rock fragments derived from frost action, or by other processes of 
 disintegration, as they become detached either fall or slide rapidly 
 downward until arrested upon a flatter slope. Upon the earlier 
 accumulations of this kind, the later ones are deposited, until their 
 surface slopes up to the cliff face as steeply as the material will lie 
 — the angle of repose. Such debris accumulations at the base of 
 a cliff (Fig. 158) are known as talus, and the slope is described as 
 a talus slope, or in Scotland as a " scree." 
 
THE ATTACK OF THE WEATHER 
 
 153 
 
 Soil flow in the continued presence of thaw water. — So soon 
 as the rocks are broken down by the weathering processes, they are 
 easily moved, usually to lower levels. In part this transportation 
 may be accomplished by gravity slowly acting upon the disinte- 
 grated rock and causing 
 it to creep down the slope. 
 Yet even in such cases 
 water is usually present 
 in quantity sufficient to fill 
 the spaces between the 
 grains, and so act as a 
 lubricant to facilitate the 
 migration. 
 
 Upon a large scale rocks 
 which were either origi- 
 nally incoherent or have 
 been made so by weather- 
 ing, after they have be- 
 come saturated with F^^- ^^^- — ^alus slope beneath a cliff. . 
 
 water, may start into sudden motion as great landslides or ava- 
 lanches, which in the space of a few moments materially change the 
 face of the country, and by burying the bottom lands leave dis- 
 aster and misery in their wake. 
 
 Within the subpolar regions, where a large part of the surface 
 is for much of the year covered with snow, the underlying rocks 
 are for long periods saturated with thaw water, and in alternation 
 are repeatedly frozen and thawed. Essentially similar conditions 
 are met with in the high, snow-capped mountains of temperate or 
 torrid regions. For the subpolar regions particularly it is now 
 generally recognized that somewhat special processes of soil flow, 
 described under the name solifluction, are characteristic. The 
 exact nature of these processes is as yet imperfectly understood, but 
 there can be little doubt concerning the large role which they have 
 played in the transportation of surface materials. Such soil flow 
 is clearly manifested under different aspects, and it is likely that 
 by this comprehensive term distinct processes have been brought 
 together. 
 
 Possibly the most striking aspect of the soil flow in subpolar 
 regions is furnished by the remarkable " stone rivers " and " rock 
 
154 
 
 EARTH FEATURES AND THEIR MEANING 
 
 Fig. 159. — Striped ground from soil flow 
 of chipped rock fragments upon a slope, 
 Snow Hill Island, West Antarctica (after 
 Otto Nordenskiold). 
 
 glaciers " ; 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 
 materials. 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 (Fig. 
 159). The direction of the furrows is always up and down the 
 slope, and the striping is marked in pro- 
 portion as the slope is steep. Where the 
 bottom is reached, the furrows are re- 
 placed by a sort of mosaic pavement 
 of hexagonal repeating figures, each of 
 which may be an area of the surface six 
 feet or more across (Fig. 160, and Fig. 
 390, p. 368). The depressions which 
 separate the " blocks " of the pavement 
 are often filled with clay, while the in- 
 closed surfaces are made up of coarsely 
 chipped stone. 
 
 The splitting wedges of roots and trees. — In the mechanical 
 
 breakdown of the rocks 
 within humid regions a 
 not 'unimportant part is 
 sometimes taken by the 
 trees, which insinuate the 
 tenuous extremities of their 
 rootlets into the smallest 
 cracks, and by continued 
 gro\\'th slowly wedge even 
 the firmer rocks apart (Fig. 
 161). In a similar manner 
 the small tree trunk grow- 
 ing within a crevice of the 
 
 Fig. 160. — Pavement of hori- 
 zontal surface due to soil 
 flow, Spitzbergen (after Otto 
 Nordenskiold). 
 
 Fig. 161. — Tree roots entering fissured rock and 
 prying its sections apart. 
 
 rock may in time split its parts asunder (Fig. 162). 
 
THE ATTACK OF THE WEATHER 
 
 155 
 
 Fig. 162. — A large glacial bowlder 
 split by a growing tree near East 
 Lansing, Michigan (after a pho- 
 tograph by Bertha Thompson). 
 
 The rock mantle and its shield in the mat of vegetation. — 
 
 Through the action of weathering, the rocks, as we have seen, 
 
 lose their integrity within a surface layer, which, though it may be 
 
 as much as a hundred feet or more 
 
 in thickness, must still be accounted 
 
 a mere film above the underlying bed 
 
 rock. The mechanical agents of the 
 
 breakdown operate only within a few 
 
 feet of the surface, and the agents of 
 
 rock decomposition, derived as they 
 
 are from the atmosphere, become 
 
 inert before they have descended to 
 
 any considerable depth. The surface 
 
 layer of incoherent rock is usually 
 
 referred to as the rock mantle (Fig. 
 
 163). Where the rock mantle is rel- 
 atively deep, as it is in the states 
 
 south of the Ohio in the eastern 
 
 United States, there is found, deep 
 
 below the outer layer of soil, a partially decomposed and disin- 
 tegrated rock, 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 associates. While thus 
 in a certain sense possessing the 
 original structure, this altered ma- 
 terial is essentially incoherent and 
 easily succumbs to attack by the 
 pick and spade, so that it is only 
 at considerably greater depths 
 that the unaltered rock is en- 
 countered. 
 
 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 (Fig. 164). 
 
 In the transformation of the upper portion of the mantle rock 
 
 into soil, additional chemical processes to those of weathering, 
 
 Fig. 163. — Rock mantle consisting of 
 broken rock, above which is soil and 
 a vegetable mat. Coast of California 
 (after a photograph by Fairbanks). 
 
ffi^^^^t^ 
 
 156 EARTH FEATURES AND THEIR MEANING 
 
 are carried through by the agency of earthworms, bacteria, and 
 other organisms, and by the action of humus and other acids de- 
 rived from the decomposition of vegetation. The bacteria par- 
 ticularly play a part in the formation of carbonates, as they do 
 
 also in changing 
 the nitrogen of 
 the air into ni- 
 trates which be- 
 come available 
 
 Fig. 164. — Diagram to show the varying thickness of aS plant food. 
 mantle rock upon the different portions of a hill surface "^ ithin the 
 (after Chamberlin and Salisbury). , • i . • i 
 
 humid tropical 
 regions ants and other insects enter as a large factor in rock 
 decomposition, as they do also in producing not unimportant 
 surface irregularities. 
 
 How important is the cover of vegetation in retaining the rock 
 mantle and the upper soil layer in their respective positions, as 
 required for agricultural purposes, may be best illustrated by the 
 disastrous consequences of allowing it to be destroyed. Wherever, 
 by the destruction of forests, by the excessive grazing of animals, 
 or by other causes, the mat of turf has been destroyed, the sur- 
 face is opened in gullies by the first hard rain, and the fertile layer 
 of soil is carried from the slopes and distributed with the coarser 
 mantle upon the bottom lands. 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 (plate 5 A). The soil once washed away is not again 
 renewed, for the continuation of the gullying process now effec- 
 tively prevents its accumulation. 
 
 Reading Refeeences to Chapter XI 
 Decomposition alid disintegration : — 
 George P. Merrill. The Principles of Rock Weathering, Jour. Geol., 
 vol. 4, 1896, pp. 704-724, 850-871. Rocks, Rock Weathering, and 
 Soils. Macmillan, New York, 1897, Pt. iii, pp. 172-411. 
 Alexis A. Julien. On the Geological Action of the Humus Acids, Proc. 
 Am. Assoc. Adv. Sci., vol. 28, 1879, pp. 311-410. 
 
 Corrosion of rocks : — 
 ^C. W. Hayes. Solution of Silica under Atmospheric Conditions, Bull. 
 Geol. Soc. Am., vol. 8, 1897, pp. 213-220, pis. 17-19. 
 
Plate 5 
 
 A. Once wooded region in China now reduced to desert through deforestation 
 
 (after Willis). 
 
 B. "Bad Lands" in the Colorado Desert (after Mendenhall). 
 
THE ATTACK OF THE WEATHER 157 
 
 M. L. Fuller. Etching of Quartz in the Interior of Conglomerates, 
 
 Jour. GeoL, vol. 10, 1902, pp. 815-821. 
 C. H. Smyth, Jr. Replacement of Quartz by Pyrites and Corrosion of 
 
 Quartz Pebbles, Am. Jour. Sci. (4), vol. 19, 1905, pp. 282-285. 
 
 Dome structure of granite masses : — 
 
 G. K. Gilbert. Domes and Dome Structure of the High Sierra, Bull. 
 
 Geol. Soc. Am., vol. 15, 1904, pp. 29-36, pis. 1-4. 
 Ralph Arnold. Dome Structure in Conglomerate, ibid., vol. 18, 1907, 
 
 pp. 615-616. 
 
 Soil flow : — 
 
 J. Gtinnar Andersson. Solifluction, a Component of Subaerial Denuda- 
 tion, Jour. Geol., vol. 14, 1906, pp. 91-112. 
 
 Otto Nordenskiold. Die Polarwelt und ihre Naehbarlander, Leipzig, 
 1909, pp. 60-65. 
 
 Ernest Howe. Landslides in the San Juan Mountains, Colorado, etc.. 
 Prof. Pap., 67 U. S. Geol. Surv., 1909, pp. 1-58, pis. 1-20. 
 
 G. E. Mitchell. Landslides and Rock Avalanches, Nat. Geogr. Mag., 
 vol. 21, 1910, pp. 277-287. 
 
 William H. Hobbs. Soil Stripes in Cold Humid Regions and a Kindred 
 Phenomenon, 12th Rept. Mich. Acad. Sci., 1910, pp. 51-53, pis. 1-2. 
 
 Relation of deforestation to erosion : — 
 
 N. S. Shaler. Origin and Nature of Soils, 12th Ann. Rept. U. S. Geol. 
 
 Surv., 1891, Pt. 1, pp. 268-287. 
 W J McGee. The Lafayette Formation, ibid., pp. 430-448. 
 F. H. King. Soils. Macmillan, New York, 1908, pp. 50-54. 
 Bailey Willis. Water Circulation and Its Control, Rept. Nat. Conserv. 
 
 Com., 1909, vol. 2, pp. 687-710. 
 W J McGee. Soil erosion, Bull. 71, U. S. Bureau of Soils, 1911. pp, 60, 
 
 pis. 33. 
 
CHAPTER XII 
 THE LIFE HISTORIES OF RIVERS 
 
 The intricate pattern of river etchings. — The attack of the 
 weather upon the solid lithosphere destroys the integrity of its 
 surface layer, and through reducing it to rock debris makes it the 
 natural prey of any agent competent to carry it along the surface. 
 We have seen how, for short distances, gravity unaided may pile 
 up the debris in accumulations of talus, and how, when assisted by 
 thaw water which has soaked into the material, it may accomplish 
 a slow migration by a peculiar type of soil flow. Yet far more 
 potent transporting agencies are at work, and of these the one of 
 first importance is running water. 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 heard. 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 surface. It is this 
 etching out of the continents in an intricate pattern of anastomos- 
 ing valleys which constitutes the chief difference between the land 
 surface and the relatively even floor of the oceans. 
 
 The motive power of rivers. — Every river is born in throes 
 of Mother Earth by which the land is uplifted and left at a higher 
 level than it was before. 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 lower. This natural " head " due to 
 differences of elevation is the motive power of the local streams, 
 and for each increase in elevation there is an immediate response 
 in renewed vigor of the streams. The elevated area off which the 
 rivers flow is here termed an upland. 
 
 The velocity of a stream will be dependent not only upon the 
 difference in altitude between its source and its mouth, but upon 
 the distance which separates them, since this will determine the 
 grade. The level of the mouth being the lowest which the stream 
 
 158 
 
THE LIFE HISTORIES OF RIVERS 159 
 
 can reach is termed the base level, and the current is fixed by the 
 slope or decHvity. The capacity to Hft and transport rock debris 
 is augmented at a quite surprising rate with every increase in 
 current velocity, the law being that the weight of the heaviest 
 transportable fragment varies with the sixth power of the velocity 
 of the current. Thus if one stream flows twice as rapidly as 
 another, it can transport fragments which are sixty-four times as 
 heavy. 
 
 Old land and new land. — The uplifts of the continents may 
 proceed without changes in the position of the shore lines, in 
 which case areas, already carved by streams but no longer actively 
 modified by them, are worked upon by tools freshly sharpened 
 and driven by greater power. The land thus subjected to active 
 stream cutting is described as old land, and has already had 
 engraved upon it the characteristic pattern of river etchings, 
 albeit the design has been in part effaced. 
 
 If, upon the other hand, the shore line migrates seaward with 
 the uplift, a portion of the relatively even sea floor, or new land, 
 is elevated and laid under the action of the running water. 
 As we are to see, stream cutting is to some extent modified when 
 a river pattern is inherited from the uplift. The uplift, whether 
 of old land only or of both old land and new land, marks the 
 starting point of a new river history, usually described as an 
 erosion cycle. 
 
 The earlier aspects of rivers. — Though geologists have some- 
 times regarded the uplift of the continents as a sort of upwarping 
 in a continuous curved surface, 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 ele- 
 vated area meets the lower lying country or the sea in a more or 
 less definite escarpment. The first rivers to develop after the 
 uplift may be described as gulhes shaped by the sudden down- 
 rush of storm waters and spaced more or less regularly along the 
 margin of the escarpment (Fig. 165). These gullies are relatively 
 short, straight, and steep ; they have precipitous walls and few, 
 if any, tributaries. 
 
 With time the gully heads advance into the upland as they 
 take on tributaries ; and so at length they in part invest it and 
 dissect it into numerous irregularly bounded and flat-topped 
 
160 
 
 EARTH FEATURES AND THEIR MEANING 
 
 tables which are separated by canons (Fig. 166). At the same 
 time the grade of the channel is becoming flatter, and its precipi- 
 tous walls are being replaced by curving slopes, as will be more 
 
 Fig. 165. — Two successive forms of gullies from the earliest stage of a 
 river's life (after Salisbury and Atwood). 
 
 fully described in the sequel. 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 history. The 
 
 Fig. 166. 
 
 ■Partially dissected upland (after Salisbury and 
 Atwood). 
 
 water then rushes down the steep grades in rapids, and is often 
 at times opened out in some basin to form a lake where differ- 
 ences of uplift have been characteristic of neighboring sections. 
 
THE LIFE HISTORIES OF RIVERS 161 
 
 For several reasons such basins in the course of a stream are rela- 
 tively short lived (Chapter XXX), and they disappear with the 
 earlier stages of the river history. 
 
 The meshes of the river network. — From the continued throw- 
 ing out of new tributaries by the streams, the meshes in the 
 river network draw more closely together as the stages of its his- 
 tory advance. The closeness of texture which is at last developed 
 upon the upland is in part determined by the quantity of rainfall, 
 so that in New Jersey with heavy annual precipitation the meshes 
 in the network are much smaller than they are, for example, 
 upon the semiarid or arid plains of the western United States. 
 Its design will, however, in either case more or less clearly express 
 the plan of rock architecture which is hidden beneath the surface 
 (Chapter XVII). 
 
 The upper and lower reaches of a river contrasted. — From 
 the fact that the river progressively invades new portions of the 
 upland and lays the acquired sections under more and more 
 thorough investment, 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 
 stage. The newly acquired sections of river valley may thus 
 possess the steep grade and precipitous walls which are charac- 
 teristic of early guUies and canons and are in contrast with 
 the more rounded and flat-bottomed sections below. Lateral 
 streams, from the fact that they are newer than the main or trunk 
 
 Fig. 167. — Characteristic longitudinal sections of the upper portion of a river 
 valley and its tributaries (after scaled sections by Nussbaum). 
 
 stream to which they are tributary, likewise descend upon somewhat 
 steeper grades (Fig. 167). 
 
 The balance between degradation and aggradation. — We have 
 seen that the power to transport rock fragments is augmented at 
 a most surprising rate with every increase in the current velocity. 
 While the lighter particles of rock may be carried as high up as 
 the surface of the water, the heavier ones are moved forward 
 upon the bottom with a combined rolling and hopping motion 
 aided by local eddies. Those particles which come in contact 
 
162 EARTH FEATURES AND THEIR MEANING 
 
 with the bottom or sides of the channel abrade its surface so as 
 ever to deepen and widen the valley. This cutting accomplished 
 by partially suspended debris in rapidly moving currents of water is 
 known as corrasion and the stream is said to he incising its valley. -/«. 
 
 As the current is checked upon the lower and flatter grades, 
 some of its load of sediment, and especially the coarser portion, 
 will be deposited and so partially fill in the channel. A nice 
 balance is thus established between degradation and the con- 
 trasted process known as aggradation. The older the river valley 
 the flatter become the grades at any section of its course, and 
 thus the point which separates the lower zone of aggradation 
 from the upper one of degradation moves steadily upstream with 
 the lapse of time. 
 
 The accordance of tributary valleys. — 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 accordantly. Each has carved its own valley, 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 stream. 
 
 The grading of the flood plain. — All rivers are subject to 
 seasonal variations in the volume of their waters. Where there 
 are wet and dry seasons these differences are greatest, and for a 
 large part of the year the valleys in such regions may be empty 
 of water, and are in fact often utilized for thoroughfares. In the 
 temperate climates of middle latitudes rivers_ are generally flooded 
 in the spring when the winter snows are melted, though they 
 may dwindle to comparatively small streams during the late 
 summer. In the upper reaches of the river the current velocities 
 are such that the usual river channel may carry all the water of 
 flood time ; but lower down and in the zone of aggradation, where 
 the current has been checked, the level of the water rises in flood 
 above the banks of its usual channel and spreads over the sur- 
 rounding lowlands. As a deposit of sediment is spread upon the 
 surface, the succession of the annual deposits from this source 
 raises the general level as a broad floor described as the flood plain j 
 of the river. / 
 
THE LIFE HISTORIES OF RIVERS 
 
 163 
 
 The cycles of stream meanders. — The annual flooding with 
 water and simultaneous deposition of silt is not, however, the 
 only grading process which is in operation upon the flood plain. 
 It is characteristic of swift currents that their course is main- 
 tained in relatively straight lines because of the inertia of the 
 rapidly moving water. In proportion as their currents become 
 sluggish, rivers are turned aside by the smallest of obstructions ; 
 and once diverted from their straight course, a law of nature 
 becomes operative which increases the curvature of the stream 
 at an accelerated rate up to a critical point, when by a change, 
 sudden and catastrophic, a new and direct course is taken, to be 
 in its turn carried through a similar cycle of changes. This 
 so-called meanderifig 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 other. Inasmuch as the later meanders 
 cross the earlier ones and in time occupy all portions of the plain 
 to the same average extent, a process of rough grading is accom- 
 plished to which the annual overflow deposit is supplementary. 
 
 The course of the current in consecutive meanders and the 
 cross sections of the channel which result directly from the mean- 
 dering process will be made clear from examination of Fig. 168. 
 So soon as diverted from its direct course, the current, by its 
 inertia of motion, is 
 thrown against the 
 outer or convex side 
 so as to scour or 
 corrade that bank. 
 Upon the concave 
 or inner side of the 
 curve there is in con- 
 sequence an area of 
 slack water, and here 
 
 the silt scoured from higher meanders is deposited. 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 unsym- 
 metrical character (Fig. 168 ah). Between meanders near the 
 point of inflection of the curve, and there only, the current is cen- 
 tered in the middle of the channel and the cross section is sym- 
 metrical (Fig. 168 cd). 
 
 Fig. 168. — Map and sections of a stream meander. 
 The course of the main current is indicated by the 
 dashed line. 
 
164 
 
 EARTH FEATURES AND THEIR MEANING 
 
 •^^* 
 
 jvimmMB'«u>>(i.'iiii\v;.'.'.V'.,i'vi'F;!'*;'.':-.''''''"''' ' 
 
 Fig. 169. — Tree in part undermined 
 upon the outer bank of a meander. 
 
 The scour upon the convex side of a meander causes the river 
 to swing ever farther in that direction, and through invasion of 
 the silted flood plain to migrate across it. Trees which He in its 
 
 path are undermined and fall out- 
 ward in the stream with tops di- 
 rected with the current (Fig. 169). 
 Whenever the flood plain is for- 
 ested, the fallen trees may be so 
 numerous as to lie in ranks along 
 the shore, and at the time of the 
 next flood they are carried down- 
 stream to jam in narrow places 
 along the channel and give the er- 
 roneous impression that the flood 
 has itself uprooted a section of for- 
 est (see p. 418). 
 
 The cut-off of the meander. — 
 As the meander swings toward its extreme position it becomes 
 more and more closely looped. Adjacent loops thus approach 
 nearer and nearer to each other, but in the successive positions 
 a nearly stationary point is established near where the river 
 makes its sharpest turn (Fig. 170, G, and 
 Fig. 454, p. 417). 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 neck, and once started in the new 
 direction a channel is scoured out in t^e 
 soft silt. Thus by a breaking through of 
 the bank of the stream, a so-called " cre- 
 vasse," the river suddenly straightens its 
 course, though up to this time it has steadily 
 become more and more sharply serpentine. 
 After the cut-off has occurred, the old chan- 
 nel may for a time continue to be used by the 
 stream in common with the new one, but the advantage in velocity 
 of current being with the cut-off, the old channel contains slacker 
 water and so begins to fill with silt both at the beginning and 
 the end of the loop. Eventually closed up at both ends, this loop 
 
 Fig. 170. — Diagrams to 
 show the successive 
 positions of stream 
 meanders and the 
 relatively stationary- 
 point near the sharp- 
 est curvature. 
 
THE LIFE HISTORIES OF RIVERS 
 
 165 
 
 or " oxbow " is entirely separated from the new channel, and 
 once abandoned of the stream is transformed into an oxbow 
 lake (Fig. 171 and p. 415). 
 
 Meander scars. — Swinging as it occasionally does in its 
 meanderings quite across the flood plain and against the bank of 
 the earlier degrading river in 
 this section, the meander at 
 times scours the high bank 
 which bounds the flood plain, 
 and undermining it in the same 
 manner, it excavates a recess 
 of amphitheatral form which is 
 known as a meander scar (Fig. 
 1 72) . At length the entire bank 
 is scarred in this manner so as 
 
 
 mm 
 
 
 1 
 
 ^^ 
 
 
 Fig. 171. — An oxbow lake in the flood 
 plain of a river. 
 
 to present to the stream a series of concave scallops separated by 
 sharp intermediate salients of cuspate form. 
 
 River terraces. — Whenever the river's history is interrupted 
 by a small uplift, or the base level is for any reason lowered, the 
 stream at once begins to sink its channel into the flood plain. 
 Once more flowing upon a low grade, it again meanders, and so 
 produces new walls at a lower level, but formed, like the first, of 
 intersecting meander scars. Thus there is produced a new flood 
 
 plain with cliff and ter- 
 race above, which is 
 known as a river terrace. 
 A succession of uplifts 
 or of depressions of the 
 base level yields terraces 
 in series, as they appear 
 schematically represented 
 in Fig. 172. Such ter- 
 races are to be found well developed upon most of our larger 
 rivers to the northward of the Ohio and Missouri. The highest 
 terrace is obviously the remnant of the earliest flood plain, as the 
 lowest represents the latest. 
 
 The delta of the river. — As it approaches its mouth the river 
 moves more and more sluggishly over the flat grades, and swings 
 in broader meanders as it flows. Yet it still carries a quantity 
 
 Fig. 172. — Schematic representation of a series 
 of river terraces, a, b, c, e, successive terraces 
 in order of age. d, d, d, d, terrace slopes formed 
 of meander scars. 
 
166 EARTH FEATURES AND THEIR MEANING 
 
 of silt which is only laid down after its current has been stopped 
 on meeting the body of standing water into which it discharges. 
 If this be the ocean, the sahnity of the sea water greatly aids in a 
 quick precipitation of the finest material. This clarifying effect 
 upon the water of the dissolved salt may be strikingly illustrated 
 by taking two similar jars, the one filled with fresh and the other 
 with salt water, and stirring the same quantity of fine clay into 
 each. The clay in the salt water is deposited and the water 
 cleared long before the murkiness of the other has disappeared. 
 
 By the laying down of the residue of its burden of sediment 
 where it meets the sea, 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 sea. Whereas in its upper 
 reaches the river with its tributary streams appears in the plan 
 like a tree and its branches, in the delta region the stream, by 
 dividing into diverging channels called distributaries (Fig. 458, 
 p. 420), completes the resemblance to the tree by adding the 
 roots. From the divergence of the distributaries upon the delta 
 plain the Greek capital letter A is suggested and has supplied the 
 name for these .deposits. Of great fertility, the delta plains of 
 rivers have become the densely populated regions of the globe, 
 among which it is necessary to mention only the delta of the 
 Nile in Egypt, those of the Ganges and Brahmaputra in India, 
 and those of the Hoang and Yangtse rivers in China. 
 
 The levee. — When the snows thaw upon the mountains at 
 the headwaters of large rivers, freshets result and the delta regions 
 are flooded. At such times heavily charged with sediment, a 
 thin deposit of fertile soil is left upon the surface of the delta 
 plain, and in Egypt particularly this is depended upon for the 
 annual enrichment of the cultivated fields. Though at this time 
 the waters spread broadly over the plain, the current still continues 
 to flow largely within the normal channel, so that the slack water 
 upon either side becomes the locus for the main deposit of the 
 sediment. There is thus built up on either side of the channel a 
 ridge of silt which is known as a levee, and this bank is steadily 
 increased in height from year to year (Fig. 452). 
 
 To prevent the danger of floods upon the inhabited plains, 
 artificial levees are usually raised upon the natural ones, and in a 
 country like Holland, such levees (dikes) involve a large expendi- 
 
THE LIFE HISTORIES OF RIVERS 
 
 167 
 
 Fig. 173. — "Bird-foot" delta, 
 of the Mississippi River. 
 
 ture of money and no small degree of engineering skill and ex- 
 perience to construct. So important to the life of the nation is 
 the proper management of its dikes, that in the past history of 
 China each weak administration has been marked by the develop- 
 ment of graft in this important department and by floods which 
 have destroyed the lives of hundreds of thousands of people. 
 
 Wherever there has been a markedly rapid sinking upon a 
 delta region, and depressions are common in delta territory, no- 
 doubt as a result of the loading down 
 of the crust, the river may present the 
 paradoxical condition of flowing at a 
 higher level than the surrounding coun- 
 try. Between the levees of neighboring 
 distributaries there are peculiar saucer- 
 shaped depressions of the country which 
 easily become filled with water. At the 
 extremity of the delta the levee may be 
 the only land which shows above the 
 ocean surface, and so present the pecul- 
 iar '' bird-foot " outline which is characteristic of the extremity 
 of the Mississippi delta, though other processes than the mere 
 sinking of the deposits may contribute to this result (Fig. 173). 
 
 The sections of delta deposits. — If now we leave the plan of 
 the delta to consider the section of its deposits, we find them so 
 characteristic as to be easily recognized. Considered broadly, 
 the delta advances seaward after the manner of a railroad embank- 
 ment which is being carried across a lake. Though the greater 
 portion of the deposit is unloaded upon a steep slope at the front, 
 a smaller amount of material is dropped along the way, and a 
 laj^er of extremely fine material settles in advance as the water 
 clears of its finely suspended particles (Fig. 174). Simultaneous 
 deposits within a delta thus comprise a nearly horizontal layerj 
 of coarser materials, the so-called top-set bed ; the bulk of the' 
 deposit in a forward sloping layer, the so-called f ore-s et bed; 
 and a thin film of clay which is extended far in advance, the 
 bottom-set bed (Fig. 174, 2). If at any point a vertical section is 
 made through the deposits, beds deposited in different periods 
 are encountered ; the oldest at the bottom in a horizontal posi- 
 tion, the next younger above them and with forward dip, and the 
 
168 
 
 EARTH FEATURES AND THEIR MEANING 
 
 youngest and coarsest upon the top in nearly horizontal position 
 (Fig. 174, 3). 
 
 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 760 years. 
 
 
 I. P'/m^/e of o £?e/r<7. 
 
 Z. Bigds /br/7?ec/ or arye r//77e. 
 
 Sor-fo/rj set i^ 
 
 
 7o/>ee-f- &ei/s 
 
 fore set Aeds 
 
 Sof^tyn seT Jiteda 
 
 The derived ma- 
 terial is being 
 deposited in the 
 flood plain and 
 delta regions of its 
 principal rivers. 
 Some 513 million 
 tons of suspended 
 matter is in the 
 United States car- 
 ried to tidewater 
 each year, and 
 about half as much 
 more goes out to 
 sea as dissolved 
 matter. If this 
 material were re- 
 moved from the 
 
 3. l/krr/ce7/ Sect/o/? across The jbea(s. 
 
 Fig. 174. — Diagrams to show the nature of delta de- 
 posits as exhibited in section. 
 
 Panama Canal cutting, an 85-foot sea-level canal would be ex- 
 cavated in about 73 days. The Mississippi River alone carries 
 annually to the sea 340 million tons of suspended matter, or 
 two thirds of the entire amount removed from the area of the 
 United States as a whole. It is thus little wonder that great 
 deltas have extended their boundaries so rapidly and that the 
 crust is so generally sinking beneath the load. 
 
CHAPTER XIII 
 
 EARTH FEATURES SHAPED BY RUNNING WATER 
 
 The newly incised upland and its sharp salients. — The suc- 
 cessive stages of incising, sculpturing, and finally of reducing an 
 uplifted land area, are each of them possessed of distinctive 
 characters which are all to be read either from the map or in the 
 lines of the landscape. Upon the newly uplifted plain the incis- 
 ing by the young rivers is to be found chiefly in the neighbor- 
 hood of the margins. In this stage the vallej^s are described as 
 V-shaped canons, for the valley wall meets the upland surface 
 in sharp salients (plate 12 A), and the lines of the landscape are 
 throughout made up from straight elem_ents. Though the land- 
 scapes of this stage present the grandest scenery that is known 
 and may be cut out in massive proportions, often with rushing 
 river or placid lake to enhance the effect of crag and gorge, they 
 lack the softness and grace of 
 outline which belong only to the 
 maturer erosion stages. The 
 grand canon of the Colorado 
 presents the features character- 
 istic of this stage in the grandest 
 and most subhme of all exam- 
 ples, and the castled Rhine is a 
 gorge of rugged beauty, carved 
 out from the newly elevated 
 plateau of western Prussia, 
 through which the water swirls in eddying rapids (Fig. 175). 
 
 The stage of adolescence. — As the upland becomes more 
 largely invaded as a consequence of the headward advance of 
 the canons and their sending out of tributary side canons, the 
 sharp angles in which the canon walls intersect the plain become 
 gradually replaced by well-rounded shoulders. Thus the lines in 
 the landscape of this stage are a combination of the straight 
 
 169 
 
 Fig. 175. — Gorge of the River Rhine 
 near St. Goars, incised within an up- 
 lifted plain which forms the hill tops. 
 
170 EARTH FEATURES AND THEIR MEANING 
 
 line with a simple curve convex toward the sky (Fig. 176). In 
 this stage large sections of the original plateau remain, though 
 
 cut into small areas by the ex- 
 
 , . tensions of the tributary valleys. 
 
 ^ r-^'-f The maturely dissected up- 
 
 "^^uS?"*?^^' land. — Continued ramifications 
 
 "'''^^. ^ by the rivers eventually divide 
 
 '""'•■^^■5,-' ' ' the entire upland area into sep- 
 
 FiG. 176. — V-shaped valley with well- arated parts, and the rounding 
 
 rounded shoulders characteristic of of the shoulders of Vallcj^S pro- 
 the stage of adolescence. Allegheny ceeds simultaneously until of the 
 plateau m West Virginia. . . ^ , 
 
 original upland no easily recog- 
 nizable compartments are to be found. Where before were flat 
 hilltops are now ridges or watersheds, the well-known divides. 
 The upland is now said to be completely dissected or to have 
 arrived at maturity. The streams are still vigorous, for they 
 make the full descent from the upland level to base level, and 
 yet a critical turning point of 
 their history has been reached, 
 and from now on they are to 
 show a steady falling off in effi- ■"' +r«**-- ... 
 
 ciency as sculpturing agents. *"*^^*Hr'"' *^ 
 
 Viewed from one of the hill- Fig. 177.— View of a maturely dissected 
 tops, the landscape of this stage upland from one of its hilltops, Kla- 
 bears a marked resemblance to ^f *^ Mountains, California (after a 
 
 photograph by Fairbanks). 
 
 a sea m which the numberless 
 
 divides are the crests of billows, and these, as distance reduces 
 their importance in the landscape, fade away into the even line 
 of the horizon (Fig. 177). 
 
 The Hogarthian line of beauty. — Since the youthful stage of 
 the upland, when the lines of its landscape were straight, its 
 character rugged, and its rivers wild and turbulent, there has 
 been effected a complete transformation. The only straight line 
 to be seen is the distant horizon, for the landscape is now molded 
 in softened outlines, among which there is a repeated recurrence 
 of the line of beauty made famous by Hogarth in his " Analysis of 
 Beauty." As well known to all art students, this is a sinuous 
 line of reversed or double curvature — a curve which passes 
 insensibly at a point of inflection from convex to concave (Fig. 
 
EARTH FEATURES SHAPED BY RUNNING WATER 171 
 
 Point of 
 Inflection 
 
 — Hogarth's line of 
 beauty. 
 
 178). The curve of beauty is now found in every section of the 
 hills, and it imparts to the landscape a gracefulness and a measure 
 of restfulness as well, which are not to be found in the landscapes 
 of earlier stages in the erosion cycle. 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 som- 
 ber background of the hills. 
 
 Considered from the commercial Fig- 178. 
 viewpoint, the mature upland is one 
 of the least adaptable as a habitation for highly civilized man. 
 Direct lines of communication run up hill and down dale in 
 monotonous alternation, and almost the only way of carrying a 
 railroad through the region, without an expenditure for trestles 
 which would be prohibitive, is to follow the tortuous crest of a 
 main divide or the equally winding bed of one of the larger valleys. 
 The final product of river sculpture — the peneplain. — When 
 maturity has been reached in the history of a river, its energies 
 are devoted to a paring down of the valley slopes and crests so 
 as to reduce the general level. From this time on hill summits 
 no longer fall into a common level - — that of the original upland 
 — for some mount notably higher than others, and with increas- 
 ing age such differences become accentuated. There is now also 
 a larger aggradation of the valleys to form the level floors of 
 flood plains, out of which at length the now slight elevations rise 
 upon such gentle slopes that the process of land sculpture ap- 
 proaches its end. Gradually 
 the vigor of the stream has 
 faded away, and can now only 
 be renewed through a fresh 
 uplift of the land, or, what 
 would amount to the same 
 thing, a depression of the base 
 level. Upland and river have 
 reached old age together, and 
 the approximation to a new 
 plain but little elevated above base level is so marked that the 
 name peneplain is apphed to it. Scattered elevations, which be- 
 
 FiG. 179. — View of the old land of New 
 England, with Mount Monadnock rising 
 in the distance. 
 
172 
 
 EARTH FEATURES AND THEIR MEANING 
 
 cause of some favoring circumstance rise to greater heights above 
 the general level of the peneplain, are known as monadnocks after 
 the type example of Mount Monadnock in New Hampshire (Fig. 
 179). 
 
 The river cross sections of successive stages. — To the suc- 
 cessive stages of a river's life it has been common to carry over 
 the names from the well-marked periods of a human life. If 
 neglecting for the moment the general aspect of the upland, we 
 
 fix our attention up- 
 on the characteristic 
 cross sections of the 
 river valley, we find 
 that here also there 
 are clearly marked 
 characters to distin- 
 guish each stage of the 
 river's life (Fig. 180). 
 In infancy the steep, 
 narrow, and sharp- 
 angled canon is a char- 
 acteristic ; with youth 
 the wider V-form has already developed ; in adolescence the angles 
 of the canon are transformed into well-rounded shoulders, and the 
 valley broadens so as in the lower reaches to lay down a fiood 
 plain ; in maturity the divides and the double curves of the line 
 of beauty appear ; while in the decline of old age the valleys are 
 extremely broad and flat and are floored by an extended flood 
 plain. 
 
 The entrenchment of meanders with renewed upHft. — Upon 
 the reduced grades which are characteristic of the declining stage 
 of a river's life, the current has little power to modify the surface 
 configuration. On the old land of this stage a renewed uplift 
 starts the streams again into action, This infusion of driving 
 power into moving water, regarded as a machine capable of ac- 
 complishing certain work, is like winding up a clock that has 
 run down. Once more the streams acquire a velocity sufficient 
 to enable them to cut their valleys into the land surface, and 
 so a new erosional cycle may be inaugurated upon the old land 
 surface — the peneplain. After such an uplift has been accom- 
 
 0/<y Affe Co/77/?ar/\5on 
 
 Fig. 180. — Comparison of the cross sections of river 
 valleys for the different stages of the erosion cycle. 
 
EARTH FEATURES SHAPED BY RUNNING WATER 173 
 
 plished and the rivers have sunk their early valleys within the 
 new upland, we may look out from this now elevated surface 
 and the eye take in but a single horizontal line, since we view 
 the plain along its edge. 
 
 By the uplift the meanders of the earlier rivers may become 
 entrenched in the new upland, the wide lobes of the individual 
 meanders being now separated by mountains where before had 
 been plains of silt only. The New River of the Cumberland 
 plateau and the Yakima River of central Washington (Fig. 181) 
 furnish excellent American examples of intrenched meanders, as 
 
 Fig. 181. — The Beavertail Bend of the Yakima Canon in central Washington 
 (after George Otis Smith). 
 
 the Moselle River does in Europe. 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 advance. The Kaiser Wilhelm 
 tunnel in the same district penetrates a larger mountain included 
 in a double meander of the river. Although intrenched, river 
 meanders are still competent to scour and so undermine the 
 outer bank, and with favoring conditions they may by this process 
 erode extended " bottoms " out of the plateau. (See Lockport 
 quadrangle, U. S. G. S.) 
 
 The valley of the rejuvenated river. — Whenever a new uplift 
 occurs before an erosional cycle has been completed, the rivers 
 become intrenched, not in a peneplain, but in the bottoms of 
 broad valleys. The sweeping curves which characterize mature 
 
174 
 
 EARTH FEATURES AND THEIR MEANING 
 
 Fig. 182. — A rejuvenated river valley (after a 
 photograph by Fairbanks). 
 
 landscapes may thus be brought into striking contrast with the 
 straight Hnes of youthful canons which with V-sections descend 
 
 from their lowest levels 
 (Fig. 182). The full 
 cross section of such a 
 valley shows a central V 
 whose sharp shoulders 
 are extended outward 
 and upward in the soft- 
 ened curves of later ero- 
 sion stages. 
 
 The arrest of stream 
 erosion by the more re- 
 sistant rocks. — The ca- 
 pacity of a river to erode and carry away the rock material 
 that lies along its course is dependent not only upon the ve- 
 locity of the current, but also upon the hardness, the firmness 
 of texture, and the solubility of the material. Particularly in 
 arid and semiarid regions, where no mantle of vegetation is at 
 hand to mask the surfaces of the firmer rock masses, differences 
 of this kind are stamped deeply upon the landscape. The rock 
 terraces in the Grand Canon of the Colorado together represent 
 the stronger rock formations of the region, while sloping talus 
 accumulations bury the weaker beds from sight. 
 
 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 
 valley. The valley is carved less widely as well as less deeply, 
 and since a river can never corrade 
 below its base, a " temporary base 
 level " is for a time established 
 above the area of harder rock. 
 Owing to the contraction of the 
 valley under these conditions, the 
 locality is described as a river 
 narrows (Fig. 183). 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 crystal- 
 
 *-^-«'f«&^'.:^/;,?-«"^, 
 
 „f''/h^ 
 
 
 
 Fig. 183. — Plan of 
 
 nver narrows. 
 
EARTH FEATURES SHAPED BY RUNNING WATER 175 
 
 line rocks. Within the narrows of a river the steep walls, charac- 
 teristic of youth and the turbulent current as well, are often retained 
 long after other portions of the river have acquired the more restful 
 lines of river maturity. The picturesque crag and the generally 
 rugged character of river narrows render them points of special 
 interest upon every navigable river. 
 
 The capture of one river's territory by another. — 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 obstruction. When a stream in incising its 
 valley degrades its channel through a veneer of softer rocks into 
 harder materials below, it is technically described as having dis- 
 covered the harder layer. Where several neighboring streams flow 
 by similar routes to their common base level, those which dis- 
 cover a harder rock will advance their headwaters less rapidly 
 into the upland and so will be at a disadvantage in extending 
 their drainage territory. A stream 
 which is not thus hindered mil in the 
 course of time rob the others o'f a por- 
 tion of their territory, for it is able to 
 erode its lower reaches nearer to base 
 level and thus acquire for its upper 
 reaches, where erosion is chiefly accom- 
 plished, an advantage in declivity. The 
 divide which separates its headwaters 
 from those of its less favored neighbor 
 will in consequence migrate steadily in- 
 to the neighbor's territory. The divide 
 is thus a sort of boundary wall separat- 
 ing the drainage basins of neighboring 
 streams, and any migration must extend 
 the territory of the one at . the expense 
 of the other. As more and more terri- 
 tory is brought under the dominion of 
 the more favored stream, there will come 
 a time when the divide in its migration 
 will arrive at the channel of the stream that is being robbed, and. 
 so by a sudden act of annexation draw off all the upper waters 
 into its own basin. By this capture the stream whose territory has 
 
 Fig. 184. — Successive dia- 
 grams to illustrate repeated 
 river piracy and the devel- 
 opment of ' ' trellis drainage, ' ' 
 (after Russell). 
 
176 
 
 EARTH FEATURES AND THEIR MEANING 
 
 been invaded is said to have been beheaded. By this act of piracy 
 the stronger stream now develops exceptional activity because of 
 the local steep grades near the point of capture, and with this 
 newly acquired cutting power the invader is competent to ad- 
 vance still further and enter the territory of the stream that lies 
 next beyond. The type of drainage network which results from 
 repeated captures of this kind is known as " trellis drainage " 
 (Fig. 184), a type well illustrated by the rivers of the southern 
 Appalachians. 
 
 In general it may be said that, other conditions being the 
 same, of two neighboring streams which have a common base 
 level, that one which takes the longest route will lose territory 
 to the other, since it must have the flatter average slope. Stream 
 capture may thus come about without the discovery of hard 
 rock layers which are more unfavorable to one stream than an- 
 other. 
 
 Water and wind gaps. — In the Allegheny plateau rivers cross 
 the range of harder rocks in deep mountain narrows which upon 
 the horizon appear as gateways through the barrier of the moun- 
 tain wall. Such gate- 
 // -^ ^) -'?* ways are sometimes 
 
 referred to as "water 
 gaps," of which the 
 Delaware Water Gap 
 is perhaps the best 
 known example, 
 though the Potomac 
 crt)sses the Blue 
 Ridge at the historic 
 Harper's Ferry through 
 a similar portal. 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 region. The records which may be made out from the 
 landscapes show clearly that in an earlier but recent period, 
 when the general surface stood at a higher level which has been 
 called the Kittatinny Plain, the younger Potomac of that time 
 and a younger but larger ancestor of Beaverdam Creek each 
 
 Fig. 185. — Sketch maps to show the earlier and the 
 present drainage condition about the Blue Ridge 
 near Harper's Ferry. 
 
EARTH FEATURES SHAPED BY RUNNING WATER 177 
 
 ■ /^ormer ^^/ei^e/ of /f/rr/^r/A/V 
 
 
 Fig. 186. — Section to illustrate the history of Snickers 
 Gap. 
 
 crossed the Blue Ridge of the time through similar water gaps 
 (Fig. 185, map, and Fig. 186). The Potomac of, that time was, 
 however, the more 
 
 deeply intrenched, §^ |*|; 
 
 and possessing an 
 advantage in slope 
 it was able to 
 advance the divide 
 at the head of its 
 tributary, the 
 Shenandoah, into 
 the territory of Beaverdam Creek. Thus the beheading of the 
 Beaverdam by the Shenandoah was accomplished (Fig. 185, second 
 map) and its upper waters annexed to the Potomac system. 
 With the subsequent lowering of the general level of the country 
 which yielded the present Shenandoah Plain, the former water gap 
 of Beaverdam Creek was abandoned of its stream at a high level 
 in the range. Known as Snickers Gap, it may serve as a type of 
 the " wind gaps " of similar origin which are not altogether un- 
 common in the Appalachian Mountain system (Fig. 186). 
 
 Character profiles. — For humid regions the landscapes possess 
 characters which, speaking broadly, depend upon the stage of the 
 erosion cycle. For the earliest stages the straight line enters 
 as almost the only element in the design ; as the cycle advances 
 to adolescence the rounded forms begin to replace the angles of 
 
 Youth 
 
 Adolescence 
 
 REJU\/E/\/yA Tl ON 
 Fig. 187. — Character profiles of landscapes shaped by stream erosion in humid 
 
 climates. 
 
178 EARTH FEATURES AND THEIR MEANING 
 
 the immature stages, and with full maturity the lines of beauty 
 alone are characteristic. As this critical stage is passed irregu- 
 larity of feature and ever more flattened curves are found to cor- 
 respond to the decline of the river's vital energies. There are 
 thus marks of senility in the work of rivers (Fig. 187). 
 
 Reading References for Chapters XII and XIII 
 
 General : — 
 Sir John Playfair. Illustrations of the Huttonian Theory of the Earth. 
 
 Edinburgh, 1802, pp. 350-371. 
 J. W. Powell. Exploration of the Colorado River of the West and its 
 
 Tributaries. Washington, 1875, pp. 149-214. 
 G. K. Gilbert. Report on the Geology of the Henry Mount?ins. Wash- 
 ington, 1877, pp. 99-150. (A classic upon the work of rivers.) 
 C. E. DuTTON. Tertiary History of the Grand Canon District (with 
 
 atlas), Mon. 2, U. S. Geol. Surv., 1882, pp. 264. 
 W. M. Davis. The Rivers and Valleys of Pennsylvania, Nat. Geogr. Mag. 
 
 vol. 1, 1889, pp. 203-219 ; The Triassic Formation of Connecticut, 
 
 18th Ann. Rept. U. S. Geol. Surv., Pt. ii, 1898, pp. 144-153. 
 Sir a. Geikie. The Scenery of Scotland. London, 1901, pp. 1-12. 
 I. C. Russell. Rivers of North America. Putnam. New York, 1898, 
 
 pp. 327. 
 M. R. Campbell. Drainage Modifications and their Interpretation, 
 
 Jour. Geol., vol. 4, 1896, pp. 567-581, 657-678. 
 Henry Gannett. Physiographic Types, U. S. Geol. Surv., Topographic 
 
 Atlas, Folios 1-2, 1896, 1900. 
 W. M. Davis. The Geographical Cycle, Geogr. Jour., vol. 14, 1899, 
 
 pp. 481-504. 
 
 The flood plain : — 
 Henry Gannett. The Flood of April, 1897, in *the Lower Mississippi, 
 
 Scot. Geogr. Mag., vol. 13, 1897, pp. 419-421. 
 W. M. Davis. The Development of River Meanders, Geol. Mag., Decade 
 
 iv, vol. 10, 1903, pp. 145-148. 
 W. S. Tower. The Development of Cut-off Meanders, Bull. Am. Geogr. 
 
 Soc, vol. 36, 1904, pp. 589-599. 
 
 River terraces : — 
 W. M. Davis. The Terraces of the Westfield River, Massachusetts, Am. 
 Jour. Sci., vol. 14, 1902, pp. 77-94, pi. 4 ; River Terraces in New Eng- 
 land, Bull. Mus. Comp. Zool., vol. 38, 1902, pp. 281-346. 
 
 River deltas : — 
 G. K. Gilbert. The Topographic Features of Lake Shores, 5th Ann. 
 
EARTH FEATURES SHAPED BY RUNNING WATER 179 
 
 Rept. U. S. Geol. Surv., 1885, pp. 104-108 ; Lake Bonneville, Mon. I, 
 
 U. S. Geol. Surv., 1890, pp. 153-167. 
 Charts of Mississippi River Commission. 
 G. R. Credner. Die Deltas, ihre Morphologie, geographische Ver- 
 
 breitung und Entstehungsbedingungen, Pet. Mitt. Ergh. 56, 1878, 
 
 pp. 1-74, pis. 1-3. 
 
 The peneplain : — 
 W. M. Davis. Plains of Marine and Subaerial Denudation, Bull. Geol. 
 Soe. Am., vol. 7, 1896, pp. 377-398; The Peneplain, Am. Geol., vol. 
 23, 1899, pp. 207-239. 
 
 Intrenchment of meanders : — 
 W. M. Davis. The Seine, the Meuse, and the Moselle, Nat. Geogr. Mag., 
 vol. 7, 1896, pp. 189-202. 
 
 Stream capture : — 
 N. H. Darton. Examples of Stream Robbing in the Catskill Mountains, 
 
 Bull. Geol. Soe. Am., vol. 7, 1896, pp. 505-507, pi. 23. 
 Collier Cobb. A Recapture from a River Pirate, Science, vol. 22, 1893, 
 
 p. 195. 
 William H. Hobbs. The Still Rivers of Western Connecticut, Bull. 
 
 Geol. Soe. Am., vol. 13, 1902, pp. 17-22, pi. 1. 
 Isaiah Bowman. A Typical Case of Stream Capture in Michigan, Jour. 
 
 Geol., vol. 12, 1904, pp. 326-334. 
 
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EARTH FEATURES SHAPED BY RUNNING WATER 179 
 
 Rept. U. S. Geol. Surv., 1885, pp. 104-108 ; Lake Bonneville, Mon. I, 
 
 U. S. Geol. Surv., 1890, pp. 153-167. 
 Charts of Mississippi River Commission. 
 G. R. Credner. Die Deltas, ihre Morphologie, geographische Ver- 
 
 breitung und Entstehungsbedingungen, Pet. Mitt. Ergh. 56, 1878, 
 
 pp. 1-74, pis. 1-3. 
 
 The peneplain : — 
 W. M. Davis. Plains of Marine and Subaerial Denudation, Bull. Geol. 
 Soe. Am., vol. 7, 1896, pp. 377-398; The Peneplain, Am. Geol., vol. 
 23, 1899, pp. 207-239. 
 
 Intrenchment of meanders : — 
 W. M. Davis. The Seine, the Meuse, and the Moselle, Nat. Geogr. Mag., 
 vol. 7, 1896, pp. 189-202. 
 
 Stream capture : — 
 N. H. Darton. Examples of Stream Robbing in the Catskill Mountains, 
 
 Bull. Geol. Soe. Am., vol. 7, 1896, pp. 505-507, pi. 23. 
 Collier Cobb. A Recapture from a River Pirate, Science, vol. 22, 1893, 
 
 p. 195. 
 William H. Hobbs. The Still Rivers of Western Connecticut, Bull. 
 
 Geol. Soe. Am., vol. 13, 1902, pp. 17-22, pi. 1. 
 Isaiah Bowman. A Typical Case of Stream Capture in Michigan, Jour. 
 
 Geol., vol. 12, 1904, pp. 326-334. 
 
CHAPTER XIV 
 THE TRAVELS OF THE UNDERGROUND WATER 
 
 The descent within the unsaturated zone. — Of the moisture 
 precipitated from the atmosphere, that portion which neither 
 evaporates into the air nor runs off upon the surface, sinks into 
 the ground and is described as the ground water. Here it descends 
 by gravity through the pores and open spaces, and at a quite 
 moderate depth arrives at a zone which is completely saturated 
 with water. The depth of the upper surface of this saturated zone 
 varies with the humidity of the chmate, with the altitude of the 
 earth's surface, and with many other similarly varying factors. 
 Within humid regions its depth may vary from a few feet to a few 
 hundred feet, while in desert areas the surface may lie as low as a 
 thousand feet or more. 
 
 The surface of the zone of the lithosphere that is saturated 
 with water is called the water table, and though less accentuated it 
 conforms in general to the relief of the country (Fig. 188). Its 
 
 Fig. 188. — Diagram to show the seasonal range in the position of the water table 
 and the cause of intermittent streams. 
 
 depth at any point is found from the levels of all perennial streams 
 and from the levels at which water stands in wells. 
 
 During the season of small precipitation the water table is 
 lowered, and if at such times it falls below the bed of a valley, 
 the surface stream within the valley dries up, to be revived when, 
 after heavier precipitation, the water table has in turn been raised. 
 Such streams are said to be intermittent, and are especially char- 
 acteristic of semiarid regions (Fig. 188). 
 
 180 
 
THE TRAVELS OF THE UNDERGROUND WATER 181 
 
 Wherever in descending from the surface an impervious layer, 
 such as clay, is encountered, the further downward progress of the 
 water is arrested. Now conducted in a lateral direction it issues 
 at the surface as a spring at the line of emergence of the upper sur- 
 face of the impervious layer (Fig. 189). 
 
 S/o/'/'n^ 
 
 Tig. 189. — Diagram to show how an impervious layer conducts the descending 
 water in a lateral direction to issue in surface springs. 
 
 The trunk channels of descending water. — While within the 
 unconsolidated rock materials near the surface of the earth, it is 
 clear that water can circulate in proportion as the materials are 
 porous and so relatively pervious. As the pore spaces become 
 minute and capillary, the difficulty of permeation through the 
 materials becomes very great. Thus in the noncoherent rocks 
 it is the coarse gravel and the layers of sand which serve as the 
 underground channels, while the fine clays have the effect of an 
 impervious wall upon the circulating waters. In coarse sand as 
 much as a third of the volume of the material is pore space for the 
 absorption and transmission of water. Even under these favor- 
 able conditions the movement of the water is exceedingly slow 
 and usually less than a fifth of a mile a year. 
 
 Within the hard rocks it is the sandstones which have the largest 
 pore spaces, but in 
 nearly all consolidated 
 rocks there are addi- 
 tional spaces along 
 certain of the bedding 
 planes, the joint open- 
 ings (Fig. 190), and 
 the crushed zones of 
 displacement, so that 
 these parting planes 
 become the trunk 
 
 channels so to SOeak -^^^^ ^^^- — Sketch map of the Oucane de Chabriferes 
 
 p ,1 . 1 X • near Chorges in the High Alps, to illustrate the cor- 
 
 OI tne circulating rosion of limestone along two series of vertical joints 
 
 water. It is along (after Martel). 
 
182 EARTH FEATURES AND THEIR MEANING 
 
 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 minerals. 
 
 The caverns of limestones. — Where limestone formations have 
 a nearly flat upper surface, a large part of the surface water enters 
 the rock by way of the joint spaces, which it soon widens by solu- 
 tion into broad crevices with well-rounded shoulders. 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 corrosion. Its journey now begins in a lateral direction, and 
 solution of the rock continuing, a tunnel may be etched out and 
 extended until another joint is encountered which is favorable to 
 its further descent into the formation. By this process on alter- 
 nating shafts and galleries the water descends to near the surface 
 of the water table by a series of steps, and is eventually discharged 
 into the river system of the district (Fig. 191). Within the larger 
 
 caverns the water at the lowest level 
 usually flows as a subterranean river 
 to emerge later into the light from be- 
 neath a rock arch. 
 
 FiG.lQl.-Diagramtoshowthe ^^Om the plan of a System of con- 
 
 relation of caverns in limestone necting caverns it may often be ob- 
 to the river system of the dis- served that the galleries of the several 
 
 trict and to the "swallow ■, ■, ti t ■ i i i 
 
 holes" upon the surface. ^^vels are alike directed along two 
 
 rectangular directions which indicate 
 the master joint directions within the limestone formation. This 
 is especially clear from the map of the galleries in the explored 
 portions of the Mammoth Cave (Fig. 192). 
 
 Swallow holes and limestone sinks. — Above the caverns of 
 limestone formations there are selected points where the water 
 has descended in the largest volume, and here funnel-shaped 
 depressions have been dissolved out from the surface of the rock. 
 In different districts such depressions have become known as 
 " sinks," " swallow holes," entonnoirs, and Orgeln. Wherever the 
 depressions have a characteristic circular outline, there can be 
 little doubt that they are the product of solution by the descend- 
 ing water, and have relatively small connections only with the 
 subterranean caverns. They have thus naturally collected upon 
 
THE TRAVELS OF THE UNDERGROUND WATER 183 
 
 their bottoms the insoluble clay which was contained in the impure 
 limestone as well as a certain amount of slope wash from the sur- 
 
 FiG. 192. — Plan of a portion of Mammoth Cave, Kentucky (after H. C Hovey). 
 
 face. Inasmuch as the clays are impervious to water, the bottoms 
 of these swallow holes are better supplied with moisture than the 
 surrounding rock surfaces, and 
 by nourishing a more vigorous 
 plant growth are strongly im- 
 pressed upon the landscape 
 (Fig. 193). 
 
 Certain of the depressions 
 above caverns are, however, 
 less regular in outline, and their ^ " 
 
 bottoms are occupied by a F^g- 193. — Trees and shrubs growing 
 ^^ r T J. Ill T luxuriantly upon the bottoms of sinks 
 
 mass 01 limestone rubble. In .,, • "i- + + / f+„ „ 
 
 within a limestone country (after a 
 
 some instances, at least, these photograph by H. t. a. de L. Hus). 
 
184 EARTH FEATURES AND THEIR MEANING 
 
 depressions appear to be the result of local incaving of the cavern 
 roofs. An incaving of this nature may close up an earlier gallery in 
 the cavern and divert the cave waters to a new course. The de- 
 struction of the roofs of caverns through this process of incaving may 
 continue until only relatively small remnants are left. From long 
 subterranean tunnels the caves are thus transformed into subaerial 
 rock bridges that have become known as " natural bridges." The 
 best-known American example is the Natural Bridge near Lex- 
 ington, Virginia. Much grander natural bridges have been formed 
 in sandstone by a totally different process, and must not be con- 
 fused with these limestone remnants of caverns. 
 
 The sinter deposits. — Just as water can dissolve the calcare- 
 ous rocks with the formation of caverns, it can under other con- 
 ditions deposit the material which has thus been taken into solu- 
 tion. Its power to hold carbonate of lime in solution is dependent 
 upon the presence of carbonic acid gas within the water. Water 
 charged with gas and dissolved lime carbonate is said to be " hard," 
 and if the gas be driven off by boiling or otherwise, the dissolved 
 lime is thrown out of solution and deposited in a form well known 
 to all housekeepers. 
 
 Hard water flowing in a surface stream, if dashed into spray 
 at a cascade, may deposit its lime carbonate in an ever thickening 
 veneer wherever the spray is dashed about the falls. This material, 
 when cut in section, has waving parallel layers and is known as 
 travertine or calcareous sinter. Some of the most remarkable de- 
 posits of this nature may be seen at the cascade of Tivoli near 
 Rome, and most of the Roman buildings have been constructed 
 from travertine that has been quarried in the vicinity. 
 
 The growth of stalactites. — Water, after percolating slowly 
 through the crevices of limestone, where it becomes charged with 
 the carbonic acid gas and with dissolved carbonate of lime, may 
 trickle from the roof of a cavern. Emerging from the narrow 
 crevice, it may give off some of its contained gas and is usually 
 subject to evaporation, with the result that the lime carbonate is 
 left adhering to the rock surface from which evaporation took 
 place. If the water collects upon the cavern roof so slowly that 
 it can entirely evaporate before a drop can form, the entire content 
 of carbonate will be left adhering to the roof. Evaporation is 
 most rapid near the margins and over the center of each drop as it 
 
THE TRAVELS OP THE UNDERGROUND WATER 185 
 
 -i^.^0^^^^M: 
 
 develops, 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 water. To the outer surface of 
 these rings water will first adhere and then evaporate, as it will 
 also slowly ooze through the passage in the ring, but here without 
 evaporation until it reaches the lower surface. A pendant struc- 
 ture will, therefore, develop, growing outward in all directions by 
 the deposition of concentric layers which are thickest near the roof, 
 and downward into the form of a rock " icicle " through evapora- 
 tion of the water which collects near the tip. 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 struc- 
 ture (Fig. 194). 
 
 Formation of stalagmites. — Wherever the water percolates 
 through the roof of the cavern so rapidly that it cannot entirely 
 evaporate upon the roof, a portion 
 falls to the floor, and, spattering as 
 it strikes, builds up a relatively 
 thick cone of sinter known as a 
 stalagmite, and this is accurately 
 centered beneath a stalactite upon 
 the roof. In proportion as the 
 cavern is high, the dropping water 
 is widely dispersed as it strikes the 
 floor, with the formation of a corre- 
 spondingly thick and blunt stalag- 
 mite. As this rises by growth to- 
 ward the roof, it often develops 
 upon its summit a distinct crater- 
 like depression (Fig. 194, lower figure). When the process is 
 long continued, stalactites and stalagmites may grow together 
 to form columns which may be ranged with their neighbors 
 like the pipes of an organ, and like them they give out clear 
 tones when struck lightly with a mallet. At other times the 
 columns are joined to their neighbors to form hangings and dra- 
 peries of the most fantastic and beautiful design (Fig. 195). 
 
 In remote antiquity limestone caverns afforded a refuge to many 
 species of predatory birds and animals as well as to our earliest 
 
 lA'fv'.Vi'rfVivi^XwC'JOi; 
 
 .vXv^xJKc'-^^vv.-; 
 
 Fig. 194. — Diagrams to show the 
 manner of formation of stalactites, 
 stalagmites, and sinter columns 
 beneath parallel crevices upon the 
 roofs of caverns (in part after von 
 Knebel). 
 
186 
 
 EARTH FEATURES AND THEIR MEANING 
 
 ancestors. The bones of all these denizens of the caves lie en- 
 tombed -within the clays and the sinter formations upon the cavern 
 floors, and they tell the story of a fierce and long-continued war- 
 fare for the possession of these natural strongholds. The evidence 
 is clear that these cave men with their primitive weapons were 
 
 
 
 
 Fig. 195. — Sinter formations in the Luray caverns, Virginia. 
 
 able at times to drive away the cave bears, lions, and h3^enas, and 
 to set up in the cavern their simple hearths, only in their turn to 
 be conquered by the ferocity of their enemies: Some of the Euro- 
 pean caves have yielded many wagonloads of the skeletons of 
 these fierce predatory animals, together with the simple weapons 
 of the primitive man. 
 
 The Karst and its features. — Most so-called limestones have a 
 large admixture of argillaceous materials (claj^s) and of siliceous 
 or sanely particles. Such impurities make up the bulk of the clays 
 and muds which are left behind when the soluble portions of the 
 limestone have been dissolved. 
 
 Swallow holes we have found to be characteristic features -^^dthin 
 such districts. When limestones are more nearly pure, as in the 
 
THE TRAVELS OF THE UNDERGROUND WATER 187 
 
 O 
 
 /Scalff. 
 
 ^/^JkTs. 
 
 Fig. 196. — Map of the dolines of the Karst re- 
 gion near Divaca. 
 
 Karst region east of the Adriatic Sea, similar features are devel- 
 oped, but upon a grander scale, and certain additional forms are. 
 
 encountered. In place of 
 
 ^^ .... N\#;%,#7 
 
 the sink or swallow hole, 
 
 there appears the " karst 
 
 funnel " or doline, a deep, 
 
 bowl-shaped depression 
 
 having a flat bottom. 
 
 Such funnels may be 30 
 
 to 3000 feet across and 
 
 from 6 to 300 feet in depth 
 
 (Fig. 196). Though in 
 
 one or two instances 
 
 known to be the result 
 
 of the break down of 
 
 cavern roofs (Fig. 197), 
 
 yet like the swallow holes 
 
 of other regions these 
 
 larger funnels appear gen- 
 erally to be the work of 
 
 solution by the descending waters. Where they have been opened 
 
 in artificial cuttings along railroads or in mines, the original rock 
 
 is found intact at the bottom, with 
 small crevices only going down to 
 lower levels. Over the bottoms of 
 the dolines there is spread a layer 
 of fertile red clay, the terra rossa, 
 like that which is obtained as a 
 residue when a fragment of the 
 limestone has been dissolved in 
 laboratory experiments. 
 
 A desert from the destruction of 
 forests. — Between the dolines is 
 
 found a veritable desert with jutting limestone angles and little 
 
 if any vegetation. 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 undermined. Hence it is that the gar 
 
 dens which furnish the sustenance for the scattered population 
 
 are all included within the narrow limits of the doline bottoms. 
 
 Fig. 197. — Cross section of the do- 
 line formed by inbreak of a cavern 
 roof. The Stara Apnenka dohne 
 in Carinthia (after Martel). 
 
188 
 
 EARTH FEATURES AND THEIR MEANING 
 
 Although to-day so largely a barren waste, we know that the Karst 
 upon the Adriatic was in remote antiquity a heavily forested re- 
 gion and that it supplied the myriads of wooden piles upon which 
 the city of Venice is supported. The vessels which brought to 
 this port upon the Adriatic its ancient prosperity were built from 
 wood brought from this tract of modern desert. 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 cover. After deforestation 
 this veneer of rich soil was washed by the rains into the dolines 
 or into the few stream courses of the region, thus leaving a barren 
 tract which it will be all but impossible to reclaim (plate 6 A). 
 
 Upon the steeper slopes 
 v4^,'S-""^V^/S''*^ x'/ over the purer limestones, 
 
 the rain water runs away, 
 guided by the joints within 
 the rock. There is thus 
 etched out a more or less 
 complete network of nar- 
 row channels (Fig. 190, 
 p. 181), between which the 
 remnants rise in sharp 
 blades to produce a struc- 
 ture often simulated upon 
 the fissured surface of a 
 glacier that has been melted in the sun's rays (Fig. 401). These 
 almost impassable areas of karst country are described as Schratten 
 or Karrenfelder (Fig. 198). 
 
 The ponore and the polje. — To-day large areas of the Karst 
 are devoid of surface streams, nearly all the surface water finding 
 its way down the crevices of the limestone into caverns, and there 
 flowing in subterranean courses. The foot traveler in the Karst 
 country is sometimes suddenly arrested to find a precipice yawn- 
 ing at his feet, and looking down a well-like opening to the depth 
 of a hundred feet or more, he may see at the bottom a large river 
 which emerges from beneath the one wall to disappear beneath 
 the other. These well-like shafts are in the Austrian Karst knov/n 
 as Ponores, while to the southward in Greece they are called 
 Katavothren. 
 
 Fig. 
 
 198. — Sharp Karren of the Ifenplatte in 
 Allgau (after Eekert). 
 
Plate 6. 
 
 A. Barren Karst landscape near the famous Adelsberg grottoes. 
 {Photograph by 1. D. Scott.) 
 
 B. Surface of u limestone ledge where joints have been widened througli solution. 
 
 Syracuse, N.Y. 
 {Photograph by I. D. Scott.) 
 
THE TRAVELS OF THE UNDERGROUND WATER 189 
 
 Elsewhere the karst river may emerge from its subterranean 
 course in a broader depressed area bounded by vertical cliffs, from 
 which it later disappears beneath the limestone wall. Such de- 
 pressions of the karst are known as poljen, and appear in most 
 cases to be above the downthrown blocks in the intricate fault 
 mosaic of the region. Some of these steeply walled inclosures 
 have an area of several hundred square miles, and especially at 
 the time of the spring snow melting they are flooded with water 
 and so transformed into seasonal lakes (Fig. 199 and p. 422). 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 them ; 
 and in consequence there is a tempo- 
 rary impounding of the flood waters in 
 those portions of the river's course 
 which are open to the sky and more 
 extended. The rush of water at such 
 times may bring the red clay into the 
 subterranean channels in sufficient 
 quantity to clog the passages. The 
 Zirknitz Lake usually has high water 
 two or three times a year, and exceptionally the flooding has con- 
 tinued for a number of years. It has thus in some districts been 
 necessary to afford relief to the population through the construc- 
 tion of expensive drainage tunnels. 
 
 The conditions which are typified in the Karst area to the east 
 of the Adriatic Sea are encountered also in many other lands; as, 
 for example, in the Vorarlberg and Swiss Alps, in Lebanon, and 
 in Sicily. 
 
 The return of the water to the surface. — Water which has de- 
 scended from the surface and been there held between impervious 
 layers, may be under the pressure of its own weight or '' head " ; 
 and will later find its way upward, it may be to the surface or 
 higher, where a perforation is discovered in its otherwise imper- 
 vious cover. Such local perforations are produced naturally by 
 lines of fracture or faulting (widened at their intersections), 
 and artificially through the sinking of deep wells. The water, 
 which at ordinary times reaches the surface upon fissures, is usually 
 
 Fig. 199. — The Zirknitz seasonal 
 lake within a polje of the Karst 
 (after Berghaus) . 
 
190 
 
 EARTH FEATURES AND THEIR MEANING 
 
 concentrated locally at the intersections of the fracture network, 
 where it issues in lines of fissure springs (Fig. 200) ; but at the time 
 of earthquakes the water may rise above the surface in lines of 
 fountains (p. 83), or occasionally as sheets of water which may 
 mount some tens of feet into the air. 
 
 In contrast to the flow of surface springs, which varies with the 
 season through wide ranges both in its volume and in temperature 
 
 of the water, the volume of 
 fissure springs is but slightly 
 affected by the seasonal pre- 
 cipitation, and the water tem- 
 perature is maintained rela- 
 tively constant. Rock is but 
 a poor heat conductor, and the 
 seasonal temperature changes 
 descend a few feet only into the 
 ground. Thus water which 
 rises from depths of a few hun- 
 dred feet only is apt to be icy 
 cold, while from greater depths 
 the effect of the earth's internal 
 heat is apparent in a uniform 
 but relatively higher temperature of the water. Such " warm " 
 or thermal springs are apt to contain considerable mineral matter 
 in solution, both because the water is far traveled and because its 
 higher temperature has considerably increased its solvent properties. 
 It has long been recognized that lines of junction of different 
 rock formations at the base of mountain ranges are localities fa- 
 vorable for the occurrence of thermal springs. These junction 
 lines are usually within zones where by movement upon fractures 
 the widest openings in the rock have formed, and the catchment 
 area of the neighboring mountain highland has supplied head for 
 the ground water. 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 faults. 
 
 Artesian wells. — From the natural fissure spring an artesian 
 well differs in the artificial character of the perforation of the im- 
 pervious cover to the water layer. The water of artesian wells 
 may flow out at the surface under pressure, or it may require 
 
 Fig. 200. — Fissure springs arranged upon 
 lines of rock fracture at intersections, 
 Pomperaug valley, Connecticut. 
 
THE TRAVELS OF THE UNDERGROUND WATER 191 
 
 pumping to raise it from some lower level. Ideal conditions are 
 furnished where the geological structure of the district is that of a 
 broad basin or syncline. The water which falls in a neighboring 
 upland is here impounded between two parallel, saucer-like walls 
 and will flow under its head if the upper wall be perforated at 
 some low level (Fig. 201, 3). 
 
 Fig. 201. — Schematic diagrams to illustrate the different types of artesian wells, 
 (1) A non-flowing well; (2) flowing wells without basin structure caused by 
 clogging of the pervious formation ; (3) flowing wells in an artesian basin. The 
 dotted lines are the water levels within the pervious layers (after Chamberlin). 
 
 A monoclinal structure may furnish artesian conditions when 
 the generally pervious layer has become clogged at a low level so 
 as {o hold back the water (Fig. 248, 2). Pumping wells may be 
 used successfully even when such clogging does not exist, for the 
 slow-moving underground water flows readily in the direction of 
 all free outlets (Fig. 201, 1). 
 
 Hot springs and geysers. — Thermal springs whose temperature 
 approaches the boiling point of water are known as hot springs. 
 A geyser is a hot spring which intermittently ejects a column of 
 water and steam. Both hot springs and geysers are to be found 
 only in volcanic regions, and appear to be connected with uncooled 
 masses of siliceous lava. In two of the three known geyser regions, 
 Iceland and New Zealand, the volcanoes of the neighborhood are 
 still active, and the lavas of the Yellowstone National Park date 
 from the quite recent geological period which immediately pre- 
 ceded the so-called " Ice Age." 
 
 Wherever found, geysers are in the low levels along lines of drain- 
 
192 
 
 EARTH FEATURES AND THEIR MEANING 
 
 age where the underground water would most naturally reappear 
 at the surface. Their water has penetrated to considerable depths 
 below the surface, but has been chiefly heated by ascending steam 
 or other vapors. The water journey has been chiefly made along 
 fissures, as is shown by the cool springs which often issue near 
 them. Though some hot springs and geysers may disappear from 
 a district, others are found to be forming, and there is no good 
 reason to think that geysers are rapidly dying out, as was at 
 one time supposed. 
 
 The action of a geyser was first satisfactorily explained by the 
 great German chemist Bunsen after he had made studies of the 
 Icelandic geysers, and the mechanics of the eruption was later 
 strikingly illustrated in the laboratory by an artificial geyser con- 
 structed by the Irish physicist Tyndall. In many respects this 
 action is like that of the Strombolian eruption within a cinder 
 cone, since it is connected with the viscosity of the fluid and the 
 resistance which this opposes to the liberation of the developing 
 vapor. In the case of the geyser, a column of heated water stands 
 within a vertical tube and is heated near the bottom of the column. 
 Though the water may at its surface have the normal boiling 
 temperature and be there in quiet ebullition, the boiling point 
 
 for all lower levels is raised by the 
 weight of the column of superin- 
 cumbent liquid, and so for a time 
 the formation of steam within the 
 mass is prevented. In Fig. 202 
 is shown a cross section of the 
 Icelandic Gcysir from which our 
 name for such phenomena has been 
 derived, and to this section have 
 been added the actual observed 
 temperatures of the water at the 
 different levels as well as the tem- 
 peratures at which boiling can 
 
 From 
 
 OAserveef 
 Temp. 
 
 j/o°c - 
 
 Fig. 202. — Cross section of Geysir, 
 Iceland, with simultaneously ob- 
 served temperatures recorded at the 
 left, and the boiling temperatures for 
 the same levels at the right (after take place at these levels. 
 
 ^™^ ^ this it will be seen that at a depth 
 
 of 45 feet the water is but 2° Centigrade below its boiling point. 
 A slight increase of temperature at this level, due to the con- 
 stantly ascending steam, will not only carry this layer above the 
 
THE TRAVELS OF THE UNDERGROXJND WATER 193 
 
 fs 
 
 boiling point, but the expansion of the steam within the mass will 
 elevate the upper layers of the water into zones where the boiling 
 points are lower, and thus bring about a sudden and violent ebul- 
 lition of all these upper portions. Thus is explained the almost 
 universal observation that just before geysers erupt the hot water 
 rises in the bowls and generally overflows them. 
 
 The water ejected from the geyser is considerably cooled in the 
 air, and after its return to the tube must be again heated by the 
 ascending vapors before another eruption can 
 occur. The measure of the cooling, the time 
 necessary to fill the tube, and the supply of 
 rising steam, all play a part in fixing the period 
 which separates consecutive eruptions. If the 
 top of the tube be narrowed from its average 
 caliber, as is commonly observed to be true of 
 the geysers within the Yellowstone National 
 Park, the escape of the steam is further hin- 
 dered, and frequent geyser eruption promoted. 
 
 An artificial geyser for demonstration of the 
 phenomenon in the lecture room is represented 
 in Fig. 203. The cut has been prepared from 
 a photograph of an apparatus designed by 
 Professor B. W. Snow of the University of 
 Wisconsin. In this design the tube is con- 
 tracted so as to have a top diameter one fourth 
 only of what it is at the bottom, where heat is 
 directly applied by multiple Bunsen lamps. 
 The water once sufficiently heated, this arti- 
 ficial geyser erupts at regular intervals of time 
 which are dependent upon the dimensions of 
 the apparatus and the quantity of heat applied. 
 
 In case of natural geysers a considerable 
 quantity of heat escapes between eruptions in 
 steam which issues quietly from the bowl of 
 the geyser. If this heat be retained by plugging the mouth 
 of the tube with a barrowful of turf, as is sometimes done 
 with the geyser Strokr in Iceland, eruption is promoted and so 
 takes place earlier. Another method of securing the same result 
 is to increase the viscosity of the water through the addition of 
 
 Fig. 203. —Apparatus 
 for simulating gey- 
 ser action in the lec- 
 ture room (by cour- 
 tesy of Professor B. 
 W. Snow). 
 
194 
 
 EARTH FEATURES AND THEIR MEANING 
 
 soap, as was accidentally discovered by a Chinaman who was uti- 
 lizing the geyser water in the Yellowstone Park for laundry opera- 
 tions. After this discovery it became a common custom to 
 "soap" the Yellowstone geysers in order to make them play; 
 but this method was prohibited under heavy penalty after the dis- 
 astrous eruption of the Excelsior Geyser. 
 
 The deposition of siliceous sinter by plant growth. — Geysers 
 are known only from areas of siliceous volcanic lava, and this may 
 
 perhaps have its cause in the easier 
 solution of the geyser tube from 
 such materials. The silica chs- 
 solved in the heated waters is 
 again deposited at the surface to 
 form siliceous sinter or geyserite. 
 This material forms terraces sur- 
 rounding the geysers or is built up 
 into mounds which are often quite 
 symmetrical, such as those of the 
 Bee Hive and Lone Star geysers 
 of the Yellowstone Park (Fig. 204). 
 The greater part of this sepa- 
 ration of silica from the heated 
 geyser waters is due to the action 
 of plants or algae that are able 
 to grow in the boiling waters and which produce the beautiful 
 colors in the linings to the hot springs. The wonderful variety 
 of the tints displayed is accounted for by the fact that the algse 
 take on different colors at different temperatures. The silica 
 is deposited from the water in the gelatinous hydrated form, which, 
 however, dries in the sun to a white sand. The growth within the 
 pools goes on in a manner similar to that of a coral reef, the algse 
 dying below and there becoming encased in the rock lining while 
 still continuing to grow upon the surface. Whereas sinter of this 
 nature, when deposited by evaporation alone, can produce a maxi- 
 mum thickness of layer of a twentieth of an inch each year, the 
 growth from alga deposition within limited areas may be as much 
 as eight inches during the same period. 
 
 Fig. 204. — Cone of siliceous sinter 
 built up about the mouth of the 
 Lone Star Geyser in the Yellow- 
 stone National Park. 
 
THE TRAVELS OF THE UNDERGROUND WATER 195 
 
 Reading Referencks for Chapter XIV 
 General : — 
 
 P. H. King. Principles and Conditions of the Movements of Ground 
 Water, 19th Ann. Rept. U. S. Geol. Surv., 1899, Pt. ii, pp. 59-294, 
 pis. 6-16. 
 
 C. S. Slighter. The Motions of the Underground Waters, Water Supply 
 Paper No. 67, U.S. Geol. Surv., 1902, pp. 1-106, pis. 1-8; Field 
 Measurements of the Rate of Movement of Underground Waters, 
 ibid., No. 140, 1905, pp. 1-122, pis. 1-15. 
 
 M. L. Fuller. Occurrence of Underground Water, ibid., No. 114, 1905, 
 pp. 18-40, pis. 4 ; Bibliographic review and index of papers relating 
 to underground waters published by the United States Geological 
 Survey, 1879-1904, ibid.. No. 120, 1905, pp. 1-128. 
 
 Caverns : — - 
 
 E. A. Martel. Les abimes, les eaux souterraines, les cavernes, les 
 
 sources, la spelseologie. Delagrave, Paris, pp. 578. (Lavishly illus- 
 trated.) 
 
 H. C. HovEY. Celebrated American Caverns. Cincinnati, 1896, pp. 228 ; 
 The Mammoth Cave of Kentucky. Louisville, 1897, pp. 111. 
 
 J. W. Beede. Cycle of Subterranean Drainage in the Bloomington 
 Quadrangle, Proc. Ind. Acad. Sci., 1910, pp. 1-31. 
 
 Karst conditions : — - 
 J. CviJic. Das Karstphanomen, Geogr. Abh., vol. 5, 1893. 
 Emile Chaix. La topographic du desert de plate (Hautes Savoie), Le 
 
 Globe, vol. 34, 1895, pp. 1-44, pis. 1-16, pp. 217-330. 
 W. V. Knebel. Hohlenkunde mit Bertieksichtigung der Karstphano- 
 
 mene. Vieweg, Braunschweig, 1906, pp. 222. 
 A. Grund. Die Karsthydrographie, Studien aus Westbosnien, Geogr. 
 
 Abh., vol. 7, No. 3, 1903, pp. 200. 
 Emile Chaix-du Bois et Andre Chaix. Contribution a I'etude des 
 
 lapies en Carniole et au Steinernes Meer, Le Globe, vol. 46, 1907, 
 
 pp. 17-56, pis. 26. 
 P. Arbenz. Die Karrenbildungen geschildert am Beispiele der Karren- 
 
 f elder bei der Frutt in Kanton Obwalden (Schweiz). Deutsch. Alpen- 
 
 zeitung, Munich, 1909, pp. 1-9. 
 
 F. Katzer. Karst und Karsthydrographie. Sarejevo, 1909, pp. 95. 
 M. Neumayr. Erdgesehichte, vol. 1, pp. 500-510. 
 
 E. DE Martonne. Traite de Geographic Physique, pp. 462-472 (excel- 
 lent summaries in this and the last reference). 
 
 E. A. Martel. The Land of the Causses, Appalachia, vol. 7, 1893, pp. 
 18-149, pis. 4-13. 
 
 Fissure springs : — 
 A. C. Peale. Natural Mineral Waters of the United States, 14th Ann. 
 Rept. U. S. Geol. Surv., Pt. ii, 1894, pp. 49-88. 
 
196 EARTH FEATURES AND THEIR MEANING 
 
 William H. Hobbs. The Newark System of the Pomperaug Valley, 
 Connecticut, 21st Ann. Rept. U. S. Geol. Surv., Pt. iii, 1901, pp. 91-93. 
 
 Artesian wells : — 
 T. C. Chamberlin. Requisite and Qualifying Conditions of Artesian 
 WeUs, 5tli Ann. Rept. U. S. Geol. Surv., 1885, pp. 131-173. 
 
 Hot springs and geysers : — 
 A, C. Peale. Yellowstone Park, Thermal Springs, 12th Ann. Rept. 
 
 Geol. and Geogr. Surv. Ter. (Hayden), Pt. ii, Sec. ii, pp. 63-454 
 
 (many plates and maps). 
 W. H. Weed. Geysers, Rept. Smithson. Inst., 1891, pp. 163-178. 
 Arnold Hague and W. H. Weed (on hot springs and geysers of Yellow- 
 stone National Park), C. R. Cong. Geol. Intern., Washington, 1891, 
 
 pp. 346-363. 
 W. H. Weed. Formation of Travertine and Siliceous Sinter by the 
 
 Vegetation of Hot Springs, 9th Ann. Rept. U. S. Geol. Surv., 1889, 
 
 pp. 613-676, pis. 78-87. 
 M. Neumatr. Erdgesehichte, vol. 1, pp. 500-510. 
 Arnold Hague. Soaping Geysers, Trans. Am. Inst. Min. Eng., vol. 17, 
 
 1889, pp. 546-553. 
 John Ttndall. Heat as a Mode of Motion, New York, 1873, pp. 115— 
 
 121 (artificial geyser). 
 
CHAPTER XV 
 
 SUN AND WIND IN THE LANDS OF INFREQUENT 
 
 RAINS 
 
 The law of the desert. — 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 realm. Those changes which, because often 
 observed, are most familiar, may not be of general application, 
 for the reason that the areas habitually occupied by highly civi- 
 lized races together comprise but a small portion of the earth's 
 surface. In the dank tropical jungle, upon the vast arid sand 
 plains, and in the cold white spaces near the poles, Nature has 
 instituted peculiar and widely different processes. 
 
 The fundamental condition of the desert is aridity, and this 
 necessitates an exclusion from it of all save the exceptional rain 
 cloud. Thus deserts are walled in by mountain ranges which 
 serve as barriers to intercept the moisture-bringing clouds. They 
 are in consequence saucer-shaped depressions, often with short 
 mountain ranges rising out of the bottoms, and such rain as falls 
 within the inclosure is largely upon the borders. Of this rainfall 
 none flows out from the desert, for the water is largely returned 
 to the atmosphere through evaporation. 
 
 The desert history is thus begun in isolation from the sea from 
 which the cloud moisture is derived, a balance being struck be- 
 tween inflow and evaporation. Yet if deserts have no outlets, 
 it is not true that they have no rivers. These are occasionally 
 permanent, often periodic, but generally ephemeral and violent. 
 The characteristic drainage of deserts comes as the immediate 
 result of sudden cloudburst. As a consequence, the desert stream 
 flows from the mountain wall choked with sediment, and entering 
 the depressed basin, is for the most part either sucked down into the 
 floor or evaporated and returned to the atmosphere. The dis- 
 solved material which was carried in the water is eventually left 
 
 197 
 
198 
 
 EARTH FEATURES AND THEIR MEANING 
 
 in saline deposits, and the great burden of sediment accumulates 
 in thick stratified masses which in magnitude outstrip the largest 
 deltas in the ocean. 
 
 The self-registering gauge of past climates. — From the ini- 
 tiation of the desert in its isolation from the lands tributary to the 
 sea, its history becomes an individual and independent one. An 
 increasing quantity of rainfall will be marked by larger inflow to 
 the basin, and the lakes which form in its lowest depression will, 
 as a consequence, rise and expand over larger areas. A contrary 
 climatic change will bring about a lowering of the lakes and leave 
 behind the marks of former shorelines above the water level (Fig. 
 205). Deserts are thus in a sense self-registering climatic gauges 
 whose records go back far beyond the historic past. From them 
 
 Fig. 205. — Former shore lines on the mountain wall surrounding the desert of the 
 Great Basin. View from the temple in Salt Lake City (after Gilbert). 
 
 it is learned that there have been alternating periods of larger and 
 smaller precipitation, which are referred to as pluvial and inter- 
 pluvial periods. 
 
 From such records it is learned that the Great Basin of the 
 western United States was at one time occupied by two great desert 
 lakes, the one in the eastern portion being known as Lake Bonne- 
 ville (Fig. 206). With the desiccation which followed upon the 
 series of pluvial periods, which in other latitudes resulted in great 
 continental glaciers and has become known as the Glacial Period, 
 this former desert lake dried up to the limits of Great Salt Lake and 
 a few smaller isolated basins. Between 1850 and 1869 the waters 
 of Great Salt Lake were rising, while from 1876 to 1890 their level 
 was falling, though subject to periodic fluctuations, and in recent 
 years the waters of the lake have risen so high as to pass all records 
 since the occupation of the country. As a consequence the so- 
 called Salt Lake '' cut-off " of the Union Pacific Railway, con- 
 structed at great expense across a shallow portion of the lake, has 
 
SUN AND WIND IN LANDS OF INFREQUENT RAINS 199 
 
 
 been overflowed by its waters. The Sawa Lake in the Persian 
 Desert, which disappeared some five hundred years ago, again 
 came into existence in 1888 so as to cover the caravan route to 
 Teheran. 
 
 The record in the rocks of the distant past reveals the fact that 
 in some former deserts barriers were, in the course of time, broken 
 down, with the result that an invading 
 sea entered through the breached wall. 
 The result was the sudden destruction 
 of land life, the remains of which are 
 preserved in " bone beds," now covered 
 by true marine deposits. A still later 
 episode of the history was begun when 
 the sea had disappeared and land ani- 
 mals again roamed above the earlier 
 desert. Such an alternation of marine 
 deposits with the remains of land plants 
 and animals in the deposits of the Paris 
 Basin, led the great Cuvier to his belief 
 that geologic history was comprised of 
 a succession of cataclysms in which life 
 wa^ alternately destroyed and re-created 
 in new forms — a view which later, under 
 the powerful influence of Lyell and 
 Darwin, gave way to that of more 
 gradual changes and the evolution of 
 life forms. 
 
 Some characteristics of the desert 
 wastes. — The great stretches of the 
 arid lands have been often compared to 
 the ocean, and the Bedouin's camel is 
 known as " the ship of the desert." Though a deceptive resem- 
 blance for the most part, the comparison is not without its value. 
 Both are closed basins, and it is in this respect that the desert and 
 the ocean may be said to most resemble each other, for none of 
 the water and none of the sediment is lost to either except as 
 boundaries are, with the progress of time, transposed or destroyed. 
 Flatness of surface and monotony of scenery both have in common, 
 and the waters and the sand are in each case salt ; yet the ocean, 
 
 3Vfile;S. 
 
 80 
 
 Fig. 206. — Map of the former 
 Lake Bonneville (dotted 
 shores), and the boundaries 
 of the Great Salt Lake of 
 1869 (smaller area) and that 
 of the present (after Berg- 
 haus) . 
 
200 EARTH FEATURES AND THEIR MEANING 
 
 from the tropics to the poles, has the same salts in essentially the 
 same proportions, while in the desert the widest variations are 
 fomid both in the salts which are present and in their relative 
 quantities. 
 
 Upon the borders of the ocean are found ridges of yellow sand 
 heaped up by the wind, but these ramparts are small in comparison 
 to those which in deserts are found upon the borders (plate 7 A) . 
 
 The desert is a land of geographic paradoxes. As Walther has 
 pointed out, we have rain in the desert which does not wet, springs 
 which yield no brooks, rivers without mouths, forests preserved 
 in stone, lakes without outlets, valleys without streams, lake basins 
 without lakes, depressions below the level of the sea yet barren 
 of water, intense weathering with no mantle of disintegrated rock, 
 a decomposition of the rocks from within instead of from without, 
 and valleys which branch sometimes upstream and sometimes 
 down. 
 
 Within the deserts curious mushroom-like remnants of erosion 
 afford a local relief from the searching rays of the desert sun. 
 Pocket-like openings large enough for a hermit's habitation are 
 hollowed out by the wind from the disintegrated rock masses. 
 Amphitheaters open out from little erosion valleys or wadi, and 
 isolated outliers of the mountains stand like sentinels before their 
 massive fronts. 
 
 ' Because of the general absence of clouds above a desert, no 
 shield such as is common in humid regions is provided against the 
 blinding intensity of the sun's rays. Sun temperatures as high 
 as 180° Fahrenheit have been registered over the deserts of 
 western Africa. Every one is familiar with the fact that a 
 blanket of thick clouds is a prevention of frosts at night, for, with 
 the setting of the sun and the consequent radiation of heat from 
 the earth, these rays are intercepted by the clouds, returned and 
 re-returned in many successive exchanges. Over desert regions 
 the absence of any such blanket of moisture is responsible for the 
 remarkable falls of temperature at sunset. Though shortly before 
 temperatures of 100° Fahrenheit or greater may have been 
 measured, it is not uncommon for water to freeze during the 
 following night. Much the same conditions of sudden tempera- 
 ture change with nightfall are experienced in high mountains when 
 one has ascended above the blanketing clouds. '< 
 
SUN AND WIND IN LANDS OF INFREQUENT RAINS 201 
 
 Fig. 207. — Borax deposits upon the floor 
 of Death valley, California (after a pho- 
 tograph by Fairbanks). 
 
 1 Dry weathering — the red and brown desert varnish. — In 
 desert lands the fierce rays of the sun suck up all the available 
 moisture, and the water table may be hundreds of feet below the 
 surface. 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 conditions | 
 In humid regions the meteoric 
 water dissolves the more 
 soluble sodium salts near the 
 surface of the rock and carries 
 them out to the ocean, where 
 they jadd to the saltness of the 
 sea. 'I In the desert the rare 
 precipitations prevent an out- 
 flow, but the sun's strong rays suck out with the moisture the 
 salts from within the rock, and evaporating upon the surface, the 
 salts are left as a coat of " alkali," which is in part carried away on 
 the wind and in part washed off in one of the rare cloudbursts. 
 In either case these constituents find their way to the lowest de- 
 pressions of the basin, 
 where they contribute 
 to the saline deposits 
 of the desert lakes (Fig, 
 207). 
 
 Certain of the saline 
 constituents of the 
 rocks, as they are thus 
 drawn out by the sun's 
 rays, fuse with the rock 
 at the surface to form a 
 dense brown substance 
 with smooth surface 
 coat, known as desert 
 varnish. Within the interior a portion of the salts crystallize 
 within the capillary fissures, and like water freezing within a pipe, 
 they rend the walls apart. As a direct consequence of this 
 disintegrating process the interior of rock masses may crumble 
 into sand ; and if the hard shell of varnish be broken at any 
 
 Fig. 208. — Hollowed forms of weathered granite in 
 a desert of central Asia (after Walther). 
 
202 EARTH FEATURES AND THEIR MEANING 
 
 point, the wind makes its entrance and removes the interior por- 
 tion so as to leave a hollow sh^ll — the characteristic " pocket 
 rock" (Fig. 208) of the desert. \ The nummulitic limestone of 
 Mokkatan and many of the great hewn blocks of Egyptian lime- 
 stone sound hollow under the tap of the hammer, and when 
 broken, they reveal a shell a few inches only in thickness (Fig. 
 209). 
 
 '\ The brown desert varnish is one of the most characteristic 
 marks of an arid country. It is found in all deserts under much 
 
 the same conditions, and 
 is especially apt to be pres- 
 ent in sandstone. When 
 scratched, the surface of 
 the rock becomes either 
 cherry-red, indicating an- 
 
 -=^.- K jij-.— ^"--i. .-".— -^- -. ^^ hydrous lerric oxide, or it 
 
 "':., ^ "- y .-ul^S is yellowish, due to the 
 
 ""^-'*' hydrated iron oxide which 
 
 Fig. 209. — Hollow hewn blocks in a wall in the , 
 
 WadiGuerraui (after Walther). ^e knOW as iron rust. 
 
 Thus it is seen that the 
 sands of deserts, in contrast to those yielded by other processes 
 within humid regions, have a characteristic red color, and this 
 may vary from brownish red upon the one hand to a rich carmine 
 upon the other/ 
 
 The mechanical breakdown of the desert rocks. — The chemi- 
 cal changes of decomposition within desert rocks are, as we have 
 seen, largely due to the action of concentrated solutions of salts 
 at high temperatures. That there is a certain, mechanical rending 
 of these rocks, due to the " freezing " of salts within the capil- 
 lary fissures, has been already mentioned. A further strain 
 effect arises in rocks like granite, which are a mixture of different 
 minerals. Heated to a high temperature during the day and 
 cooled through a considerable range at night, the different minerals 
 alternately expand and contract at different rates and by dif- 
 ferent relative amounts, so that strains are set up, tending to 
 tear them apart. The effect of these strains is thus a surface 
 crumbling of rocks. 
 
 But rock is, as already pointed out, a relatively poor conductor 
 of heat, and hence it is a relatively thin skin only which passes 
 
SUN AND WIND IN LANDS OF INFREQUENT RAINS 203 
 
 through the daily round of wide temperature range. This outer 
 shell when heated is expanded, and so tends to peel off, or ex- 
 foliate, like the outer skin of an onion. The process is therefore 
 described as exfoliation. In all rocks of homogeneous texture the 
 continued action of this process results in convexly spherical sur- 
 faces, the material scaled off in the process remaining as a slope 
 or talus which surrounds the projecting knob (Fig. 210). Naked, 
 
 
 Fig. 210. — Smooth granite domes shaped by exf ohation and surrounded by a rim of 
 talus. Gebel Karsala, Nubian Desert (after Walther). 
 
 these projecting domes rise above the rim of debris at their bases. 
 Not a particle of dust adheres to the fresh rock surface — no 
 dirt interferes with its glaring whiteness. Yet close at hand lie 
 masses of debris into which wells may be carried to depths of 
 more than six hundred feet without encountering either solid 
 rock or ground water. The bare walls of granite sometimes mount 
 upwards for thousands of feet into the air, as steep and as inac- 
 cessible as the squared towers of the Tyrolean Dolomites. 
 
 Rock is such a poor conductor of heat that special strains are 
 set up at the margin of sunlight and shade. This localization of 
 the disintegration on the margin of the shaded portions of rock 
 masses is known as shadow weathering (see Fig. 215, p. 206). 
 
 There is, however, still another mechanical disintegrating 
 process characteristic of the desert regions, which is likewise 
 dependent upon the sudden changes of temperature. Rains, 
 
204 EARTH FEATURES AND THEIR MEANING 
 
 though they may not occur for a year or more, come as sudden 
 downpours of great volume and violence. Rock masses, which 
 are highly heated beneath the desert sun, if suddenly dashed 
 with water, may be rent apart by the differential strains set up 
 near the surface. That rocks may be easily rent as a result of 
 sudden chilling is well known to our Northern farmers, who are 
 accustomed to rid themselves of objectionable bowlders by first 
 building a fire about them and then dashing water upon their 
 surface. Thus split into fragments, even the larger bowlders 
 may be handled and so removed from the farming land. The 
 natural process of rock rending by the occasional cloudburst may 
 be described as diffission. Blocks as much as twenty-five feet in 
 
 diameter have been observed 
 in the desert of western 
 Texas, soon after being 
 broken into several frag- 
 ments at the time of a down- 
 pour of rain (Fig. 211). 
 
 ! The natural sand blast. — 
 Because of the saucer-like 
 shape, the vast expanse, and 
 
 Fig. 211. — Granite blocks in the Sierra de the absence of wind breaks, 
 los Dolores of Texas, rent into several the potency of wind aS a 
 fragments by the dash of rain (after i • i . • • i . 
 
 Waither). geological agent is m desert 
 
 areas not easily overesti- 
 mated. While most of its work is accomplished with the aid of 
 tools, it has been proven that even without this help, considerable 
 work is done through the friction of the wind, alone, particularly 
 when moving as powerful eddies in cracks and crannies. This 
 wear of the wind, unaided by cutting tools, is known as deflation. 
 The greater work of the wind is, however, accomplished with 
 the aid of larger or smaller rock particles, the sand and dust, 
 with which it is so generally charged above the deserts. Un- 
 protected by any mat of vegetation the materials of the desert 
 surface are easily lifted and are constantly migrating with the 
 wind. The finest dust is raised high into the air, and is carried 
 beyond the marginal barriers, but none of the sand or coarser 
 materials ever passes beyond the borders. 
 
 The efficiency of this sand as a cutting tool when carried by the 
 
SUN AND WIND IN LANDS OF INFREQUENT RAINS 205 
 
 Fig. 212. — "Mushroom rock" from a 
 desert in Wyoming (after Fairbanks) . 
 
 wind is directly proportioned to the size of the grain, since with 
 larger fragments a heavier blow is struck when carried at any- 
 given velocity. These more effective grains are, however, not lifted 
 far above the ground, but advance with a squirming or hopping 
 motion, much as do the larger pebbles upon the bottom of a river 
 at the time of a spring freshet. \ To quote Professor Walther: 
 '' Whoever has had the oppor- 
 tunity 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 wind. At such 
 times the ground becomes alive, 
 everywhere the sand is creeping 
 over the surface with snake-hke 
 squirmings, and the eye quickly 
 
 tires of these writhing movements of the currents of sand and 
 cannot long endure the scene." 
 
 (,A ditect consequence of this restriction of the more effective 
 cutting tools to the layer of air just above the ground, is the 
 strong tendency to cut away all projecting masses near their 
 bases. The " mushroom rocks," which are so characteristic of 
 desert landscapes, have been shaped in this manner (Fig. 212). 
 
 Another product of the desert 
 sand blast is the so-called Wind- 
 kante (wind-edge) or Dreikante 
 (three-edge), a pebble which is 
 usually shaped in the form of 
 a pyramid (Fig. 213). 
 
 Whenever a rock face, open 
 to direct attack by the drifting 
 sand, is constituted of parts 
 which have different hardness, 
 the blast of sand pecks away 
 at the softer places and leaves the harder ones in relief. Thus is 
 produced the well-known " stone lattice " of the desert (Fig. 214). 
 Particularly upon the neck of the great Sphinx have the flying 
 sand grains, by removing the softer layers, brought the sedi- 
 mentary structures of the sandstone into strong rehef . ' 
 
 Fig. 213. — Windkanten shaped by the 
 desert sand blast (after Chamberlin and 
 Salsbury) . 
 
206 
 
 EARTH FEATURES AND THEIR MEANING 
 
 Fig. 214. — The "stone lattice" of the 
 desert, the work of the natural sand 
 blast (after Walther). 
 
 When guided both by planes of sedimentation and planes of joint- 
 ing, forms of a very high degree? of ornamentation are developed. 
 Some of the most remarkable forms are due to the protection af- 
 forded to the sun-exposed surfaces by the shell of desert varnish. 
 In the shaded portions of projecting masses there is no such pro- 
 tection, and here the sand blast insinuates itself into every crack 
 
 and cranny. In this it is aided 
 by shadow weathering due to 
 the differential strains set up at 
 the border of the expanded sun- 
 heated surface. As a result, 
 projecting rock masses are some- 
 times etched away beneath and 
 give the effect of a squatting 
 animal. These forms, due to 
 shadow erosion, have also been 
 likened to projecting faucets. 
 (Fig. 215). 
 
 \Worn by its impact upon neighboring sand grains while in trans- 
 port, but much more as it is thrown against the ground or hard 
 rock surfaces, the wind-driven or eolian sand is at last worn into 
 smoothly rounded granules which approach the form of a sphere. 
 Compared to the sur- 
 face which sea sand 
 acquires by attrition, 
 this shaping process is 
 much the more effi- 
 cient, since in the 
 water the beach sand 
 is buoyed up and is 
 more effectively cush- 
 ioned against its neigh- 
 boring grains. 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 abraded. 
 
 I The dust carried out of the desert. — When, standing upon the 
 
 mountain wall that surrounds a desert, the traveler gazes out to 
 
 
 Fig 215 — Projecting rock carved by the drifting 
 sand into the form of a couchant animal as a result 
 of shadow weathering and erosion. Cut in granite 
 on the north Indian Desert (after Walther). 
 
SUN AND WIND IN LANDS OF INFREQUENT RAINS 207 
 
 windward over the great depression, his field of view is generally 
 obscured by the yellow haze of the dust clouds moving across 
 the margins. Upon the mountain 
 flanks and extending far outside 
 the borders, this cloud of dust 
 settles as a shrouding mantle of 
 impalpable yellow powder, which 
 is known as loess. These deposits 
 are continually deepening, and 
 have sometimes accumulated until 
 they are hundreds or even thou- 
 sands of feet in thickness. Before 
 reaching its final resting place the 
 dust of this deposit may have 
 settled many times, and has cer- 
 tainly been in part redistributed ^.^^ 216.- Cliffs in loess 200 feet in 
 
 height which exhibit the characteris- 
 tic vertical jointing (after von Rich- 
 tofen). 
 
 by the streams near the desert 
 margin. In it are the ingredients 
 which are necessary for the nour- 
 ishment of plants, and it constitutes the most important of natural 
 soils. Continually fed by new deposits from 
 the desert, and refertilized from below by a 
 natural process so soon as the upper layers 
 become impoverished, it requires no artificial 
 fertilization. Without artificial aids the loess 
 of northern China has been tilled for thousands 
 of years without any signs of exhaustion. 
 
 Though easily pulverized between the fingers, 
 loess is none the less characterized by a perfect 
 vertical jointing and stands on vertical faces 
 as does the solid rock (Fig. 216), but it is ab- 
 solutely devoid of layers or bedding. Its ca- 
 pacity of standing in vertical cliffs the loess owes 
 to a never failing content of hme^ carbonate 
 which acts as a cement, and to a peculiar porous 
 structure caused by capillary canals that run 
 vertically through the mass, branching like 
 rootlets and lined with carbonate of lime. This texture once 
 destroyed, loess resolves itself into a common sticky clay. 
 
 Fig. 217. — A canon 
 in loess worn by 
 traffic and wind. A 
 highway in north- 
 ern China (after 
 von Richtofen). 
 
208 EARTH FEATURES AND THEIR MEANING 
 
 By the feet of passing animals or by wheels of vehicles, the loess 
 is crushed, and a portion is lifted and carried away by the wind. 
 Thus in the course of time roadways sink deep into the mass as 
 steep-walled canons (Fig. 217). A portion of the now structure- 
 less clay remaining upon the roadway is at the time of the rains 
 transformed into a thick mud which makes traveling all but 
 impossible, though before its structure has been destroyed the 
 loess is perfectly drained to the bottom of its deposits. 
 
 The particles which compose the loess are sharply angular 
 quartz fragments, so fine that all but a few grains can be rubbed 
 into the pores of the skin. Fine scales of mica, such as are easily 
 lifted by the wind, are disseminated uniformly throughout the 
 mass. The only inclosures which are arranged in layers consist 
 of irregularly shaped concretions of clay. These show a striking 
 resemblance to ginger roots and are called by the Chinese "stone 
 ginger," though they are elsewhere more generally known by 
 their German name of Loessmdnnchen, or loess dolls. These 
 concretions are so disposed in the loess that their longer axes are 
 vertical, and they were evidently separated from the mass and 
 not deposited with it. 
 
CHAPTER XVI 
 
 THE FEATURES IN DESERT LANDSCAPES 
 
 The wandering dunes. — Over the broad expanse of the desert, 
 sand and dust, and occasionally gypsum from the sahne deposits, 
 are ever migrating with the wind ; on quiet days in the eddying 
 " sand devils," but especially during the terrifying sand storms 
 such as in the windy season darken the air of northern China and 
 southern Manchuria. This drift of the sand is halted only when 
 an obstruction is encountered — a projecting rock, a bush, or a 
 bunch of grass, or again the buildings of a city or a town. The 
 manner in which the sand is ar- 
 rested by obstacles of different 
 kinds is of great interest and im- 
 portance, and is utilized in raising 
 defenses against its encroachments. 
 If the obstacle is unyielding but 
 allows some of the wind to pass 
 through it, no eddies are produced 
 and the sand is deposited both to 
 windward and to leeward of the 
 obstruction to form a fairly sym- 
 metrical mound (Fig, 218 a). An 
 obstruction which yields to the 
 wind causes the sand to deposit 
 in a mound which is largely to 
 leeward of the obstruction (Fig. 
 218 b). A solid wall, on the other 
 hand, by inducing eddies, is at 
 first protected from the sand and mounds deposit both to wind- 
 ward and to leeward (Fig. 218 c and Fig. 219). 
 
 Except when held up by an obstruction, the drifting sand travels 
 to leeward in slowly migrating mounds or ridges which are known 
 as dunes. Their motion is due to the wind lifting the sand from 
 p 209 
 
 Fig. 218. — Diagrams to illustrate the 
 effects of obstructions of different 
 types in arresting wind-driven sand. 
 
 a. An unyielding obstruction which 
 permits the wind to pass through it ; 
 
 b, a flexible and perforated obstruc- 
 tion ; c, an unyielding closed barrier 
 (after Schulze). 
 
210 
 
 EARTH FEATURES AND THEIR MEANING 
 
 the windward side and carrying it over the crest, from where it 
 slides down the leeward slope and assumes a surface which is 
 the angle of repose of the material. In contrast with this the 
 
 windward slope is 
 
 notably gradual, be- 
 ing shaped in con- 
 formity to the wind 
 currents. 
 
 The dunes which 
 are raised upon sea- 
 shores, like those of 
 the desert, are con- 
 stantly migrating, 
 those upon the shores 
 of the North Sea at 
 the average rate of 
 about twenty feet per year. Relentlessly they advance, and de- 
 spite all attempts to halt them, have many times overwhelmed 
 the villages along the coast. Upon the great barrier beach known 
 as the Kurische Nehrung, on the southeastern shore of the Baltic 
 Sea, such a burial of villages has more than once occurred, but 
 as in the course of time further migration of the dune has pro- 
 ceeded, the ruins of the buried villages have been exhumed by 
 this natural excavating process (Fig, 220), 
 
 Fig. 219. — Sand accumulating both to windward and 
 to leeward of a firm and impenetrable obstruction. 
 The wind comes from the left (after a photograph 
 by Bastin). 
 
 C^OO/7 
 
 /86£> 
 Sco/e of Miles. 
 
 Fig. 220. — Successive diagrams to show how the town of Kunzen was buried, and 
 subsequently exhumed in the continued migration of a great dune upon the 
 Kurische Nehrung (after Behrendt). 
 
 The forms of dunes. — The forms assumed by dunes are de- 
 pendent to a very large extent upon the strength of the wind 
 and the available supply of sand. With small quantities of 
 
Plate 7. 
 
 A. Ranges of dunes upon the margin of the Colorado Desert (after Mendenhall) 
 
 B. Sand dunes encroaching upon the oasis of Wed Souf, Algeria (after T. H. 
 
 Kearney) . 
 
THE FEATURES IN DESERT LANDSCAPES 
 
 211 
 
 ■sand and with moderate winds, sickle-shaped dunes known as 
 barchans (Fig. 221) are formed, whose convex and flatter slopes 
 are toward the wind and whose steep concave leeward slopes are 
 
 Fig. 221. — -View of desert barchans (after Haug). 
 
 maintained at the angle of repose. The barchan is shaped by the 
 wind going both over and around the dune, constantly removing 
 sand from the windward side and depositing it to leeward. With 
 larger supplies of sand and winds which are not too violent a 
 series of barchans is built up, and these are arranged transversely 
 to the wind direction] (Fig. 222 6). If the winds are more violent, 
 the minor depressions in the crests of the dunes become wind 
 channels, and the sand is then trailed out along them until the 
 arrangement of the ridges is parallel to the wind (Fig. 222 c). 
 The surfaces of dunes are 
 generally marked by beau- 
 tiful ripples in the sand, 
 which, seen from a little 
 distance, may give the ap- 
 pearance of watered silk 
 (plate 7 A). 
 
 Under normal condi- 
 tions dunes are not sta- 
 tionary but continue to 
 wander with the prevail- 
 ing winds until they have 
 reached the outer edge of 
 the zone of vegetation 
 near the base of the foot- 
 hills at the margin of the desert. Here the grasses and other 
 desert plants arrest the first sand grains that reach them, and 
 they continue to grow higher as the sands accumulate. Some of 
 
 Fig. 222. — Diagrams to show the relationships 
 in form and in orientation of dunes to the sup- 
 ply of sand and to the strength of the wind. 
 a, barchans formed by small supplies of sand 
 and moderate winds ; b, transverse dune ridges, 
 formed when supply of sand is large and winds 
 are moderate ; c, dune ridges formed with large 
 sand supply and violent winds (after Walther 
 and Cornish). 
 
212 ; EARTH FEATURES AND THEIR MEANING 
 
 the desert plants, like the yuccas, 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 surface. 
 
 The cloudburst in the desert. — Such clouds as enter the 
 desert through its mountain ramparts, and those derived from 
 evaporation from the hot desert soil, usually precipitate their 
 moisture before passing out of the basin. Above the highly 
 heated floor the heavy rain clouds are unable to drop their bur- 
 den. The rain can sometimes be seen descending, but long 
 before it has reached the ground it has again passed into vapor, 
 
 Fig. 223. — Ideal section across the rising mountain wall surrounding a desert 
 and a part of the neighboring slope (after R. W. Pumpelly). 
 
 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 rise, there is a sudden downpour not equaled 
 in the humid regions. Desert rains are rare, but violent beyond 
 comparison. Often for a year or more there is no rainfall upon 
 the loose sand or porous clay, and the few plants which survive 
 must push their roots deep down until they have reached the 
 zone of ground water. When the clouds burst, each small canon 
 or wed (pi. wadi) within the mountain wall is quickly occupied 
 by a swollen current which carries a thick paste of sediment and 
 drowns everything before it. Ere it has flowed a mile, it may 
 be that the water has disappeared entirely, leaving a layer of mud 
 and sand which rapidly dries out with the reappearance of the sun. 
 As the mountains upon seacoasts are generally rising with 
 reference to the neighboring sea bottom, so the mountains which 
 hem in the deserts are generally growing upward with reference 
 to the inclosed desert floor. The marginal dislocations which 
 separate the two are often in evidence at the foot of the steep 
 slope (Fig. 223), and these may even appear as visible earth- 
 
THE FEATURES IN DESERT LANDSCAPES 
 
 213 
 
 quake faults to indicate that the uplift is more accelerated than 
 the deposition along the mountain front. 
 
 The zone of the dwindling river. — The rapid uplift so generally 
 characteristic of desert margins gives to the torrential streams 
 which develop after each cloud- 
 burst such an unusual velocity 
 that v^hen they emerge from the 
 mountain valleys on to the desert 
 floor, the current is suddenly 
 checked and the burden of sedi- 
 m-cnt 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 (Fig. 224). Dependent upon its steep- 
 ness of slope, this delta is variously referred to as an alluvial fan 
 or apron, or as an alluvial cone. 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 tree. In the 
 Mohammedan countries described as wadi, these distributaries 
 
 Fig. 224. — Dry delta or alluvial fan at 
 the foot of a mountain range upon 
 the borders of a desert. 
 
 , Scale, of Miles. 
 
 Pig. 225. — Map of the distributaries of neighboring streams which emerge at the 
 western base of the Sierra Nevadas in California (after W. D. Johnson). 
 
 upon dry deltas are on the Pacific coast of the United States 
 referred to as '' washes " (Fig. 225). 
 
 Fast losing their velocity after emerging from the mountains, 
 the various distributaries drop first of all the heavy bowlders, 
 
214 
 
 EARTH FEATURES AND THEIR MEANING 
 
 then the large pebbles and the sand, so that only the finer sand 
 and the silt are carried to the margin of the delta. As they 
 enlarge their boundaries, the neighboring deltas eventually 
 coalesce and so form an alluvial bench or " gravel piedmont " at 
 the foot of the range. Only the larger streams are able to entirely 
 cross this bench of parched deposits with its coarsely porous 
 structure, for the water is soon sucked up by the thirsty ma- 
 terials. Encountering in its descent more clayey layers, this water 
 is conducted to the surface near the margin of the bench and 
 may there appear as a line of springs. At this level there develops^ 
 therefore, a zone of vegetation, though there is no local rain. 
 
 The alluvial bench grows upward by accretion of layers which 
 are thickest at the mountain end, so that the steepness of the 
 bench increases with time. 
 
 Erosion in and about the desert. — The violent cloudburst that 
 is characteristic of the arid lands is a most potent agent in model- 
 ing the surface of the ground wherever the rock materials are 
 not too firmly coherent. Under the dash of the rain a peculiar 
 type of " bad land " topography is developed (plate 5B and Fig. 226). 
 Such a rain-cut surface is a veritable maze 
 of alternating gully and ridge, a country 
 worthless for agricultural purposes and offer- 
 ing the greatest difficulty in the way of pene- 
 trating it. When composed of stiff clay with 
 scattered pebbles and bowlders, the effect of 
 the " rain erosion " is to fashion steep clay 
 pillars each capped by a pebble and described 
 as " demoiselles " (Fig. 226). 
 
 Behind the mountain front the valleys out 
 of which the torrents are discharged are usu- 
 ally short with steep side walls and a rela- 
 tively flat bottom, ending head ward in an 
 amphitheater with precipitous walls (Fig. 
 227). In the western United States such 
 valleys are referred to as " box canons," but 
 in Mohammedan countries the name "wed" applies to the river 
 valley within the mountains and to the distributaries as well. 
 
 Characteristic features of the arid lands. — It is characteristic 
 of erosion and deposition within humid regions that all outlines 
 
 Fig. 226. — A group of 
 "demoiselles" in the 
 "bad lands" (after a 
 photograph by Fair- 
 banks) . 
 
THE FEATURES IN DESERT LANDSCAPES 
 
 215 
 
 become softened into flowing curves, due to the protective mat 
 of vegetation. In arid lands those massive rocks which are 
 without structural planes of separation, partly as a consequence 
 of exfoliation, develop broad domes which are projected upon 
 the horizon as great semicircles, 
 broken in half it may be by 
 displacement. The same massive 
 rocks where intersected by vertical 
 joint planes yield, on the contrary, 
 sharp granite needles like those of 
 Harney Peak (plate 8 A). Similarly, 
 schistose or bedded rocks, when tilted 
 at a high angle, may yield forms 
 which are almost identical. Ex- 
 amples of such needles are found in 
 the Garden of the Gods in Colorado. 
 
 At lower levels, where the flying 
 sand becomes effective as an erod- 
 ing agent, flat bedded rocks become 
 etched into shelves and cornices, and 
 if intersected by joints, the shelves 
 
 and cornices are transformed into groups of castellated towers and 
 pinnacles of a high degree of ornamentation. These fantastic 
 erosion remnants are usually referred to as ''chimneys" and may 
 be seen in numbers in the bad lands of Dakota, as they may in 
 Colorado either in Monument Park or in the new Monolithic 
 National Park (plate 8 B). 
 
 Where wind erosion plays a smaller role in the sculpture, but 
 where after an uplift a river has made its way, horizontally bedded 
 rocks are apt to be carved into broad rock terraces, nowhere shown 
 upon so grand a scale as about the Grand Canon of the Colorado. 
 Each harder layer has here produced a floor or terrace which 
 ends in a vertical escarpment, and this is separated from the 
 next lower layer of more resistant rock by a slope of talus which 
 largely hides the softer intermediate beds. The great Desert of 
 Sahara is shaped in a series of rock terraces or steppes which 
 descend toward the interior of the basin. 
 
 A single harder layer of resistant rock comes often to form 
 the flat capping of a plateau, and is then known as a mesa, or 
 
 Fig. 227. — Amphitheater at the 
 head of the Wed Beni Sur (after 
 Walther). 
 
216 
 
 EARTH FEATURES AND THEIR MEANING 
 
 table mountain. Along its front, detached outliers usually stand 
 like sentinels before the larger mass, and according to their rela- 
 tive proportions, these are referred to either as small mesas or 
 as the smaller huttes (Fig. 228). 
 
 1ii|BI,llS*'Si!Sij«*f|r»' 
 
 ;^»i"mi)sijjf3llj^ 
 
 
 .~^-.£??^? 
 
 '■.dis??^'' ■" 
 
 Fig. 228. — Mesa and outlying butte in the Leucite Hills of Wyoming Rafter Whit- 
 man Cross, U. S. G. S.). 
 
 The war of dune and oasis. — In every desert the deposits 
 are arranged in consecutive belts or zones which are alternately 
 the work of wind and water. Surrounding the desert and upon 
 the flanks of the mountain wall there is found (1) the deposit of 
 loess derived from the dust that is carried out of the desert by 
 the wind. Immediately within the desert border at the base of 
 the mountains is (2) the zone of the dwindling river with its 
 sloping bench of coarse rubble and gravel. Next in order is 
 (3) the belt of the flying sand, a zone of dune ridges often sepa- 
 rated by narrow, flat-bottomed basins (Fig. 229) into which the 
 
 Fig. 229 
 
 -Flat-bottomed basm separating dunes- 
 worth Huntington). 
 
 bajir or takyr (after Ells- 
 
 strongest streams bring the finer sands and silt from the moun- 
 tains. Lastly, there is (4) the central sink or sinks, into which 
 all water not at once absorbed within the zone of alluviation or 
 in the zone of dunes is finally collected. Here are the true lacus- 
 
Plate 8. 
 
 .•1. The granite needles of Harney Peak in the Black Hills of South Dakota (after 
 
 Darton). 
 
 
 B. Castellated erosion chimneys in El Cobra Canon, New Mexico. 
 (Photograph by E. C. Case.) 
 
THE FEATURES IN DESERT LANDSCAPES 
 
 217 
 
 trine deposits of clay and separated salts (Fig. 230 and Fig. 207, 
 p. 201). The lake deposits fill in all the original irregularities 
 of the desert floor, out of which the tops of isolated ranges of 
 mountains now project like islands out of the surface of the sea. I 
 The several zones of de- 
 posits in their order from 
 the margin to the center 
 of the desert are given 
 schematically in Fig. 231. 
 , The zone of vegetation, 
 as already stated, lies near 
 the foot of the alluvial 
 bench, so that here are 
 found the oases about 
 which have clustered the 
 cities of the desert from 
 the earliest records of antiquity until now. 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 mountains. With every diminution in the water 
 supply, the dunes advance and encroach upon the oases (plate 7 B) ; 
 while with every considerable increase in this supply of moisture 
 
 ^:fti^;4: 
 
 Fig. 230. — Billowy surface of the salt crust on 
 the central sink in the Lop Desert of central 
 Asia (after Ellsworth Huntington). 
 
 L acustnne 
 
 Fig. 231. — Schematic diagram to show the zones of deposition in their order from 
 the margin to the center of a desert. 
 
 the alluvial bench advances over the dunes and acquires a strip 
 of their territory. Thus with varying fortunes a war is con- 
 tinually waged between the withering river and the flying sand, 
 and the alternations of climate are later recorded in the dove- 
 
218 
 
 EARTH FEATURES AND THEIR MEANING 
 
 Fig. 232. — Mounds upon the site of the buried 
 city of Nippur (after the cast by Muret). 
 
 tailing together of the eohan and alluvial deposits at their com- 
 mon junction (Fig. 231). 
 
 In addition to the smaller periodic alternations of pluvial and 
 
 interpluvial climate — 
 the " pulse of Asia " — 
 the record of the Asiatic 
 deserts indicates a pro- 
 gressive desiccation of 
 the entire region, which 
 has now given the vic- 
 tory to the dune! The 
 ancient history of the 
 cities of the plains sup- 
 plies the records of many 
 that have been buried 
 in the dunes. To-day, 
 where once were pros- 
 perous cities, nothing is 
 to be seen at the surface but a group of mounds (Fig. 232). Ex- 
 humed after much painstaking labor, the walls and palaces of 
 
 these ancient cities 
 
 have once more been 
 brought to the light 
 of clay, and much 
 has thus been 
 learned of the civi- 
 lization of these 
 early times (Fig. 
 233). Quite re- 
 cently the mounds 
 which cover be- 
 tween one and two 
 hundred buried vil- 
 lages have been 
 found upon the bor- 
 ders of the Tarim 
 basin of central Asia, where they were lost to history when 
 they were overwhelmed in the early centuries of the Christian 
 Era. 
 
 Fig. 233. — Exhumed structures in the buried city of 
 Nippur (after Hilprecht). 
 
THE FEATURES IN DESERT LANDSCAPES 
 
 219 
 
 C0L:HAM30Ut/0JiR)r 
 
 The origin of the high plains which front I 
 the Rocky Mountains. — To the eastward of 
 the great backbone of the North American 
 continent stretches a vast plain gently in- 
 clined away from the range and generally c*. ^^^fiocKyMrFffoirr 
 known as the High Plains region (plate 9). 
 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 c 
 of five thousand feet above the level of the 
 sea. That he has also passed through several 
 climatic zones — a humid, a semiarid, and 
 an arid — and has now entered a semiarid 
 district, is more easily appreciated from study ' 
 of the vegetation (Fig. 234). The surface of 
 the High Plains, where not cut into by rivers, 
 is remarkably even, so that it might be com- 
 pared to the quiet surface of a great lake. 
 
 The materials which compose the surface 
 veneer of these plains are coarse conglomer- 
 ates, gravels, and sands, and the so-called 
 '^ mortar beds," which are nothing but sands 
 cemented into sandstone by carbonate of lime. 
 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 
 Mountains. These different materials are 
 not arranged in strictly parallel beds, as are 
 the deposits of a lake or sea; 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 
 slope, or outward from the mountain front 
 (Fig. 235). 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 periods, and that subsequent 
 
 |/CCv-/*to SoiwOA/fy 
 
220 
 
 EARTH FEATURES AND THEIR MEANING 
 
 uplift has produced the modern river valleys which are cut out of 
 the plain. The plexus of long threads of the coarser materials are 
 the courses of dwindling rivers which interlaced over the former 
 
 Fig. 235. — iSection across the great lenticular threads of aLIu\'ial deposits which 
 compose the veneer of the High Plains (after W. D. Johnson). 
 
 plain, and which in time were buried under other channel deposits 
 of the same nature but in different positions (Fig. 236). 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 
 Europe. 
 
 Character profiles. — In 
 contrast with the profiles in the landscapes of humid regions (see 
 Fig. 187, p. 177), those of arid lands are marked by straighter 
 
 Fig. 236. — Distributaries of the foothills 
 superimposed upon an earlier series (after 
 W. D. Johnson). 
 
 Bench 
 
 Fig. 237. — Character profiles in the landscapes of arid lands. 
 
Plate 9. 
 
 THE HIGH PLAINS 
 
 Scale of miles i 
 
 30 U>0 ISO 
 
THE FEATURES IN DESERT LANDSCAPES 221 
 
 elements (Fig. 237). Almost the only exception of importance is 
 furnished by the domes of massive granite monoliths, which are 
 sometimes broken in half by great displacements. 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 repro- 
 duce the lines in a house of cards, since the sloping lines are 
 maintained at the angle of repose of the materials (Fig. 482, p. 443). 
 Wherever the waves of desert lakes have made an attack upon the 
 rocks and have retired the projecting spurs, other gables charac- 
 terized by slightly different slopes are introduced into the landscape. 
 
 Reading References for Chapters XV and XVI 
 General : — 
 
 Johannes Walther. Das Gesetz der Wiistenbildung in Gegenwart und 
 Vorzeit. Berlin, 1900, pp. 175, many plates. (This extremely valua- 
 ble work is now out of print, but both a revised edition and an Eng- 
 lish translation are promised for 1912.) 
 
 Siegfried Passarge. Die Kalihari. Berlin, 1904, pp. 662. 
 
 W. M. Davis. The Geographic Cycle in an Arid Climate, Jour. Geol., 
 vol. 13, 1905, pp. 381-407. 
 
 Ellsworth Huntington. The Pulse of Asia. New York and Boston, 
 1907, pp. 415. 
 
 SvEN Hedin. Scientific Results of a Journey through Central Asia, 1899- 
 1900. Stockholm, 1904-1905, vols. 1 and 2, pp. 523 and 717, pis. 
 56 and 76. 
 
 Joseph Barrell. Relative Geological Importance of Continental, Lit- 
 toral and Marine Sedimentation, Jour. Geol., vol. 14, 1906, pp. 316- 
 356, 429-457, 524-568. 
 
 E. F. Gautier. Etudes sahariennes, Ann. de Geogr., vol. 16, 1907, pp. 
 46-69, 117-138. 
 
 The self -registering gauge of past climates : — 
 
 G. K. Gilbert. Lake Bonneville, Mon. I, U. S. Geol. Surv., Chapter vi, 
 pp. 214-318. 
 
 T. F. Jamieson. The Inland Seas and Salt Lakes of the Glacial Period, 
 Geol. Mag. decade III, vol. 2, 1885, pp. 193-200. 
 
 J. E. Talmage. The Great Salt Lake, Present and Past. Salt Lake City, 
 1900, pp. 116, plates. 
 
 E. Huntington. Some Characteristics of the Glacial Period in Non- 
 glaciated Regions, Bull. Geol. Soc. Am., vol. 18, 1907, pp. 351-388, 
 pis. 31-39. 
 
 T. C. Chamberlin. The Future Habitability of the Earth, Rept. 
 Smithson. Inst., 1910, pp. 371-389. 
 
222 EARTH FEATURES AND THEIR MEANING 
 
 The red and brown desert varnish : — 
 I. C. Russell. Subaerial Decay of Rocks and Origin of the Red Color 
 of Certain Formations. Bull. 52, U. S. Geol. Surv., 1889, pp. 65, pis. 5. 
 
 Erosion in the desert : — 
 J. A. Udden. Erosion, Transportation, and Sedimentation performed by 
 
 the Atmosphere, Jour. Geol., vol. 2, 1894, pp. 318-331. 
 S. Passarge. Die pfannenformigen Hohlformen der siidafrikanischen 
 
 Steppen, Pet. Mitt., vol. 57, 1911, pp. 57-61, 130-135. 
 
 The dust carried out of the desert : — 
 
 F. VON RicHTOFEN. China, Ergebnisse eigene Reisen und darauf ge- 
 griindeten Studien, Berlin, 1877, vol. 1, pp. 56-125. 
 
 E. HiLGARD. The Loess of the Mississippi Valley, Am. Jour. Sei., (3), 
 vol. 18, 1879, pp. 106-112. 
 
 T. C. Chamberlin and R. D. Salisbury. Preliminary Paper on the 
 Driftless Area of the Upper Mississippi VaUey, 6th Ann. Rept. U. S. 
 Geol. Surv., 1885, pp. 278-307. 
 
 E. E. Free. The movement of soil material by the wind, with a bibli- 
 ography of eolian geology by S. C. Stuntz and E. E. Free, Bull. 68, 
 U. S. Bureau of Soils, 1911, pp. 272, pis. 5. 
 
 M. Neumayr. Erdgeschichte, vol. 1, pp. 510-514. 
 
 E. DE Martonne. Geographie physique, pp. 663-668. 
 
 Dunes : — 
 Vaughan Cornish. On the Formation of Sand-dunes, Geogr. Jour., 
 vol. 9, 1897, pp. 278-309 (a most important paper). 
 
 F. Solger and Others. Diinenbueh. Enke, Stuttgart, 1910, pp. 373. 
 
 The zone of the dwindling river : — 
 E. Huntington. The Border Belts of the Tarim Basin, Bull. Am. Geogr. 
 Soc, vol. 38, 1906, pp. 91-96 ; The Pulse of Asia, pp. 210-222, 262-279. 
 
 The war of dune and oasis : — 
 R. PuMPELLY. Explorations in Turkestan, Expedition of 1904, etc., 
 
 Pub. 73, Carneg. Inst., Washington, vol. 1, pp. 1-13. 
 E. Huntington. The Oasis of Kharga, Bull. Am. Geogr. Soc, vol. 42. 
 
 1910, pp. 641-661. 
 Th. H. Kearney. The Country of the Ant Men, Nat. Geogr. Mag., vol. 
 
 22, 1911, pp. 367-382. 
 
 Features of the arid lands : — 
 C. E. DuTTON. Tertiary History of the Grand Canon District, with 
 Atlas, Mon. II, U. S. Geol. Surv., 1882, pp. 264, pis. 42, maps 23. 
 
 G. SwEiNFURTH. Map Sheets of the Eastern Egyptian Desert. BerUn, 
 
 1901-1902, 8 sheets. 
 
 The origin of the high plains : — 
 W. D. Johnson. The High Plains and their Utilization, 21st Ann. Rept. 
 U. S. Geol. Surv., Pt. iv, 1901, pp. 601-741. 
 
CHAPTER XVII 
 REPEATING PATTERNS IN THE EARTH RELIEF 
 
 The weathering processes under control of the fracture system. 
 — In an earlier chapter it was learned that the rocks which com- 
 pose 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 (Fig. 36, p. 55), 
 more or less modified by additional diagonal joints, and often 
 also by more disorderly fractures. Throughout large areas these 
 fractures may maintain nearly constant directions, though either 
 one or more of the master series may be locally absent. This 
 distinctive architecture of the surface shell of the lithosphere has 
 exercised its influence upon the various weathering processes, as it 
 has also upon the activities of running water and of other less 
 common transporting agencies at the surface. 
 
 Within high latitudes, where frost action is the dominant 
 weathering process, the water, by insinuating itself along the 
 joints and through repeated freezings, has broken down the rock 
 in the immediate neighborhood of these fractures, and so has 
 impressed upon the surface an image of the underlying pattern 
 of structure lines (plate 10 A). 
 
 In much lower latitudes and in regions of insufficient rainfall, 
 the same structures are impressed upon the relief, but by other 
 weathering processes. In the case of the less coherent deposits 
 in these provinces, the initial forms of their erosional surface have 
 sometimes been determined by the dash of rain from the sudden 
 cloudburst. Thus the " bad lands " may have their initial guUies 
 directed and spaced in conformity with the underlying joint struc- 
 tures (Fig. 238). 
 
 In such portions of the temperate regions as are favored by a 
 humid climate, the mat of vegetation holds down a layer of soil, 
 and mat and soil in cooperation are effective in preventing any 
 
 223 
 
224 
 
 EARTH FEATURES AND THEIR MEANING 
 
 such large measure of frostwork as is characteristic of the sub- 
 polar regions or of high levels in the arid lands. In humid regions 
 
 the rocks become a prey espe- 
 cially to the processes of solu- 
 tion and accompanying chemi- 
 cal decomposition, and these 
 processes, although guided by 
 the course of the percolating 
 ground water along the frac- 
 ture planes, do not afford such 
 striking examples of the con- 
 trol of surface relief. 
 
 Those limestones which 
 slowly pass into solution in 
 the percolating water do, how- 
 ever, quite generally indicate 
 a localization of the solution 
 along the joint channels (Fig. 
 
 Fig. 238. — Rain sculpturing under control 239 and plate 6 B). Though 
 by joints. Coast of southern California in other rocks not SO apparent, 
 
 (after a photograph by Fairbanks). ^^^ solutions generally take 
 
 their courses along the same channels, and upon them is localized 
 the development of the newly formed hydrated and carbonate 
 minerals, as is well illustrated by 
 the phenomenon of spheroidal 
 weathering (Fig. 155, p. 150). 
 
 The fracture control of the drain- 
 age lines. — The etching out of 
 the earth's architectural plan in 
 the surface relief, which we have 
 seen begun in the processes of 
 weathering, is continued after the 
 transporting agents have become 
 effective. It is often easy to see 
 that a river has taken its course 
 in rectangular zigzags like the 
 elbows of a jointed stove pipe, and that its walls are formed 
 of joint planes from which an occasional squared buttress pro- 
 jects into the channel. This structure is rendered in the plan of 
 
 ^«iir 
 
 !f>i=^ '■-V „'=*:,' ^ ^ ..%j^ 
 
 cj'tt^'' 
 
 Fig. 239. — Outcrop of flaggy limestone 
 which shows the effects of solution 
 along neighboring joints in a sagging 
 of the upper beds (after Gilbert, U. 
 S. G. S.). 
 
REPEATING PATTERNS IN THE EARTH RELIEF 225 
 
 Fig. 240. — Map of the 
 joint-controlled Abisko 
 Canon in northern Lap- 
 land (after Otto Sjogren). 
 
 the Abisko Canon of northern Lapland (Fig. 240). We are later 
 to learn that another great transporting agent, the water wave, 
 makes a selective attack upon the litho- , . • . 
 
 sphere along the fractures of the joint 
 system (Fig. 250, p. 233 and Fig. 254, 
 p. 235). 
 
 Where the scale of the example is large, 
 as in the cases which have been above 
 cited, the actual position and directions 
 of the joint wall are easily compared with 
 the near-by elements of the river's course, 
 so that the connection of the drainage 
 lines with the underlying structure is at 
 once apparent. In many examples where 
 the scale is small, the evidence for the con- 
 trolling influence of the rock structure in 
 determining the courses of streams may 
 be found in the peculiar character of the drainage plan. To 
 illustrate : the course of the Zambesi River, within the gorge below 
 the famous Victoria Falls, not only makes repeated turnings at a 
 right angle, but its tributary streams, instead of making the usual 
 ^ sharp angle where they join the 
 
 main stream, also affect the right 
 angle in their junctions (Fig. 241). 
 The repeating pattern in drainage 
 networks. — It is a characteristic of 
 the joint system that the fractures 
 within each series are spaced with 
 approximation to uniformity. If 
 the plan of a drainage system has 
 been regulated in conformity with 
 the ' architecture of the underlying 
 rock basement, the same repeating 
 rectangles of the master joints may 
 be expected to appear in the lines of drainage — the so-called 
 drainage network. 
 
 Such rectangular patterns do very generally appear in the 
 drainage network, though they are often masked upon modern 
 maps by what, to the geologist, seems impertinent intrusion of the 
 
 Fig. 241. — Map of the gorge of the 
 Zambesi River below the Victoria 
 Falls (after Lamplugh). 
 
226 
 
 EARTH FEATURES AND THEIR MEANING 
 
 black lines of overprinting which indicate railways, lines of high- 
 way, and other culture elements. On river maps, which are 
 printed without culture, the pattern is much more easily recog- 
 nized (Figs. 242 and 243). Wherever the relief is strong, as is 
 
 Smites 
 Pig. 242. — Controlled 
 drainage network of 
 the Shepaug River 
 in Connecticut. 
 
 Fig. 243. — A river network of repeating rectangular pat- 
 tern. Near Lake Temiskaming, Ontario (from the map 
 by the Dominion Government) . 
 
 the case in the Adirondack Mountain province of the State of 
 New York, individual hills may stand in relief between the bound- 
 ing streams which compose the rectangular network, like the 
 squared pedestals of monuments. Such a type of relief carved in 
 repeating patterns has been described as " checkerboard topog- 
 raphy." 
 
 The dividing lines of the relief patterns — lineaments. — The 
 repeating design outlined in the river network of the Temiska- 
 ming district (Fig. 243) would appear in greater perfection if we 
 could reproduce the relief without at the same time obscuring 
 
REPEATING PATTERNS IN THE EARTH RELIEF 227 
 
 the lines of drainage ; for where the pattern is not completely 
 closed by the course of the stream, there is generally found either 
 a dry valley or a ravine to complete the design. If these are 
 not present, a bit of straight coast line, a visible line of frac- 
 ture, a zone of fault breccia, 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 pattern. These significant lines of landscapes 
 which reveal the hidden architecture of the rock basement are 
 described as lineaments (Fig. 82, p. 87). They are the character 
 lines of the earth's physiognomy. 
 
 It is important to emphasize the essentially composite ex- 
 pression of the lineament. At one locality it appears as a drain- 
 age line, a little farther on it may be a line of coast; then, again, 
 it is a series of aligned waterfalls, a visible fault trace, or a recti- 
 linear boundary between formations ; but in every case it is some 
 surface expression of a buried fracture. Hidden as they so gen- 
 erally are, the fracture lines must be searched out by every means 
 at our disposal, if we are not to be misled in accounting for the 
 positions and the attitudes of disturbed rock masses. 
 
 As we have learned, during earthquake shocks, as at no other 
 time, the surface of the earth is so sensitized as to betray the 
 position of its buried fractures. As the boundaries of orographic 
 blocks, certain of the fractures are at such times the seats of 
 especially heavy vibrations; they are the seismotectonic lines 
 of the earthquake province. Many lineaments are identical 
 with seismotectonic lines, and they therefore afford a means of 
 to some extent determining in advance the lines of greatest dan- 
 ger from earthquake shock. 
 
 The composite repeating patterns of the higher orders. — Not 
 only do the larger joint blocks become impressed upon the earth 
 relief as repeating diaper patterns, but larger and still larger com- 
 posite units of the same type may, in favorable districts, be found 
 to present the same characters. 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 (Fig. 40, p. 57, and Fig. 41, p. 58). 
 Nowhere, perhaps, is this larger order of the repeating pattern 
 more perfectly exemplified than in some recent deposits in the 
 
228 
 
 EARTH FEATURES AND THEIR MEANING 
 
 Syrian desert (plate 10 B). It is usually, however, in the older 
 sediments that such structures may be recognized; as, for ex- 
 ample, in the squared towers and buttresses of the Tyrolean 
 Dolomites (Fig. 244). Here the larger blocks appear in the thick 
 
 Fig. 244. — Squared mountain masses which reveal a distribution of the joints in 
 block patterns of different orders of magnitude. The Pordoi range of the Sella 
 group of the Dolomites, seen from the Cima di Rossi (after Mojsisovics). 
 
 bedded lower formation, the dolomite, divided into subordinate 
 sections of large dimensions ; but in the overlying formations 
 in blocks of relatively small size, yet with similarly perfect sub- 
 equal spacing. 
 
 The observing traveler who is privileged to make the journey 
 by steamer, threading its course in and out among the many is- 
 lands and skerries of the Norwegian coast, will hardly fail to be 
 struck by the remarkable profiles of most of the lower islands 
 (Fig. 245) . These profiles are generally convexly scalloped with a 
 noteworthy regularity, and not in one unit only, but in at least two 
 with one a multiple of the other (Fig. 246). As the steamer passes 
 near to the islands, it is discovered that the smaller recognizable 
 units in the island profiles are separated by widely gaping joints 
 which do not, however, belong to the unit series, but to a larger 
 composite group (Fig. 246 b). Frostwork, which depends for its 
 
Plate 10. 
 
 A. View in Spitzbergen to illustrate the disintegration of rock under the control of 
 
 joints. 
 (Photograph by 0. Haldin.) 
 
 B. Composite pattern of the joint structures within recent alluvial deposits. 
 (Photograph by Ellsworth Huntington.) 
 
EEPEATING PATTERNS IN THE EARTH RELIEF 229 
 
 action upon open spaces within the rocks, has here been the cause 
 of the excessive weathering above the more widely gaping joints. 
 High northern latitudes are thus especially favorable for re- 
 vealing all the details in the architectural pattern of the litho- 
 
 FiG. 245. — Island groups of the Lofoten archipelago off the northwest coast of 
 Norway, which reveal repeating patterns of the relief in two orders of magnitude 
 (after a photograph by Knudsen). 
 
 sphere shell, and we need not be surprised that when the modern 
 maps of the Norwegian coast are examined, still larger repeating 
 patterns than any 
 that may be seen 
 in the field are to 
 be made out. The 
 Norwegian coast 
 was long ago shown 
 
 to be a complexly Fiq. 246. — Diagrams to illustrate the composite profiles 
 faulted region, and of the islands on the Norwegian coast, a, distant view ; 
 
 these larger divi- 
 sions of the relief 
 pattern, instead of being explained as a consequence solely of 
 selective weathering, must be regarded as due largely to fault 
 displacements of the type represented in our model (plate 4 C). 
 Yet whether due to displacements or to the more numerous 
 joints, all belong to the same composite system of fractures 
 expressed in the relief. 
 
 b, near view, showing the individual joints and the more 
 widely gaping fractures beneath each sag in the profile. 
 
230 EARTH FEATURES AND THEIR MEANING 
 
 Reading References for Chapter XVII 
 
 William H. Hobbs. The River System of Connecticut, Jour. GeoL, 
 vol. 9, 1901, pp. 469-485, pi. 1 ; Lineaments of the Atlantic Border 
 Region, Bull. Geol. Soc. Am., vol. 15, 1904, pp. 483-506, pis. 45-47 ; 
 The Correlation of Fracture Systems and the Evidences for Plan- 
 etary Dislocations within the Earth's Crust, Trans. Wis. Acad. Sci., 
 etc., vol. 15, 1905, pp. 15-29 ; Repeating Patterns in the Relief and 
 in the Structure of the Land, Bull. Geol. Soc. Am., vol. 22, 1911, pp. 
 123-176, pis. 7-13. 
 
CHAPTER XVIII 
 
 THE FORMS CARVED AND MOLDED BY WAVES 
 
 The motion of a water wave. — The motions within a wave 
 upon the surface of a body of water may be thought of in two 
 different ways. First of all, there is the motion of each particle 
 of water within an orbit of its own ; and there is, further, the for- 
 ward motion of propagation of the wave considered as a whole. 
 
 The water particle in a wave has a continued motion round and 
 round its orbit like that of a horse circling a race course, only that 
 here the track is in a 
 vertical plane, directed 
 along the line of propa- 
 gation of the wave (Fig. 
 247). Each particle of 
 water, through its fric- 
 tion upon neighboring 
 particles, is able to 
 transmit its motion both 
 along the surface and 
 downward into the water 
 below. The force which 
 starts the water in mo- 
 tion and develops the 
 wave, is the friction of 
 wind blowing over the 
 
 water surface, 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 blown. The wind's effect is, therefore, 
 cumulative — the wave is proportional to the wind's effect upon 
 all water particles in its rear, added to the local wind friction. 
 
 The size or height of the wave is measured by the diameter of the 
 orbit of motion of the surface particle, and this is the difference 
 in height between trough and crest. The distance from crest 
 to crest, or from trough to trough, is called the wave length. 
 Though the wave motion is transmitted downward into the water, 
 
 231 
 
 l/Vai^e Base 
 Fig. 247. — Diagram to show the nature of the 
 motions within a free water wave. 
 
232 
 
 EARTH FEATURES AND THEIR MEANING 
 
 there is a continued loss of energy which is here not compensated 
 by added wind friction, and so the orbital motion grows smaller and 
 smaller, until at the depth of about a wave length it has completely 
 died out. This level of no motion is called the wave base. In 
 quiet weather the level of no motion is practically at the water's 
 surface, and inasmuch as the geological work of waves is in large 
 part accomplished during the great storms, the term ''wave base" 
 refers to the lowest level of wave motion at the time of the heavi- 
 est storms. 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 feet. 
 
 Free waves and breakers. — So long as the depth of the water 
 is below wave base, there is obviously no possibility of interfer- 
 ence with the wave through friction upon the bottom. Under 
 these conditions waves are described as free waves, 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 " white caps " at 
 the time of high winds. 
 
 As a wave approaches a shore, which generally has a gentle 
 outward sloping surface, there is interposed in the way of a free 
 forward movement the friction upon the bottom. This friction 
 begins when the depth of water is less than wave base, and its 
 effect is to hold back the wave at the bottom. Carried slowly 
 
 Fig. 248. — Diagram to illustrate the transformation of a free wave into a breaker 
 as it approaches the shore. 
 
 upward in the water by the friction of particle upon particle, 
 the effect of this holding back is a piling up of the water, which in- 
 creases the wave height as it diminishes the wave length, and also 
 interferes with wave symmetry (Fig. 248). Moving forward 
 at the top under its inertia of motion and held back at the bottom 
 
Plate 11. 
 
 A. Ripple markings within an ancient sandstone (courtesy of U. S. Grant). 
 
 B. A wave breaking as it approaches the shore. 
 {Photograph by Fairbanks.) 
 
THE FORMS CARVED AND MOLDED BY WAVES 233 
 
 Fig. 249. — Notched rock cliff cut by waves and 
 the fallen blocks derived from the cliff through 
 undermining. Profile Rock at Farwell's 
 Point near Madison, Wisconsin. 
 
 by constantly increasing friction, a strong turning motion or 
 couple is started about a horizontal axis, the immediate effect 
 of which is to steepen the forward slope of the wave, and this con- 
 tinues until it overhangs, 
 and, falling, " breaks " into 
 surf. Such a breaking 
 wave is called a " comber " 
 or " breaker " (plate 11 B). 
 Effect of the breaking 
 wave upon a steep rocky 
 shore — the notched cliff. — 
 If the shore rises abruptly 
 from deeper water, the top 
 of the breaking wave is 
 hurled against the cliff with 
 the force of a battering ram. 
 During storms the water of 
 shore waves is charged with sand, and each sand particle is driven 
 like a stone cutter's tool under the stroke of his hammer. The effect 
 is thus both to chip and to batter away the rock of the shore to 
 the height reached by the wave, undermining it and notching 
 the rock at its base (Fig. 249). When the notch has been cut 
 in this manner to a sufficient depth, the overhanging rock falls 
 
 by its own weight in blocks which 
 are bounded by the ever present 
 joints, leaving the upper cliff face 
 essentially vertical. 
 
 Coves, sea arches, and stacks. 
 — It is the headland which is 
 most exposed to the work of the 
 waves, since with change of wind 
 direction it is exposed upon more 
 than a single face. The study of 
 headlands which have been cut 
 by waves shows that the joints 
 within the rock play a large role 
 in the shaping of shore features. 
 
 Fig. 250. — A wave-cut chasm under mi j.j. i r xi i 
 
 control byjoints,coastof Maine (after The attack of the waves under 
 
 Tarr). the direction of these planes of 
 
234 
 
 EARTH FEATURES AND THEIR MEANING 
 
 Fig. 251. — The sea arch known as the 
 Grand Arch upon one of the Apostle 
 Islands in Lake Superior (after a pho- 
 tograph by the Detroit Photographic 
 Company). 
 
 ready separation opens out indentations of the shore (Fig. 250) or 
 
 forms sea caves which, as they extend to the top of the cHff by the 
 
 process of sapping, yield the coves which are so common a feature 
 
 upon our rock-bound shores 
 (Fig. 259, p. 238) . With contin- 
 uation of this process, the caves 
 formed on opposite sides of the 
 headland may be united to form 
 a sea arch (Fig. 251). 
 
 A later stage in this selective 
 wave carving under the control 
 of joints is reached when the 
 bridge above the arch has 
 fallen in, leaving a detached 
 rock island with precipitous 
 walls. Such an offshore island 
 of rock with precipitous sides 
 is known as a stack (Fig. 
 252), or sometimes as a 
 " chimney," though this latter 
 
 term is best restricted to other and similar forms which are the 
 
 product of selective weathering (p. 300). 
 
 Whenever the rock is less firmly consolidated, and so does not 
 
 stand upon such steep planes, 
 
 the stack is apt to have a 
 
 more conical form, and may 
 
 not be preceded in its forma- 
 tion by the development of 
 
 the sea arch (Fig. 260, p. 239). 
 
 In the reverse case, or where 
 
 the rock possesses an unusual 
 
 tenacity, the stack may be 
 
 largely undermined and stand 
 
 supported like a table upon 
 
 thick legs or pillars of rock 
 
 (Fig. 253). In Fig. 254 is 
 
 seen a group of stacks upon the coast of California, which show 
 
 with clearness the control of the joints in their formation, but 
 
 unlike the marble of the South American example the forms 
 
 Fig. 252. 
 
 ■Stack near the shore of Lake 
 Superior. 
 
THE FORMS CARVED AND MOLDED BY WAVES 235 
 
 are not rounded, but retain 
 their sharp angles. 
 
 The cut rock terrace. — 
 
 When waves first begin their 
 
 attack upon a steep, rocky 
 
 shore, the lower limit of the 
 
 action is near the wave base. 
 
 The action at this depth is, 
 
 however, less efficient, and as 
 
 the recession of the cliff is one 
 
 of the most rapid of erosional 
 
 processes, the rock floor outside the receding cliff comes to slope 
 
 gradually downward from the cliff to a maximum depth at the 
 
 Fig. 253. — The Marble Islands, stacks in 
 Lake Buenos Aires, southern Andes 
 (after F. P. Moreno). 
 
 Fig. 254. — Squared stacks which reveal the position of the joint planes which have 
 controlled in the process of carving by the waves. Ft. Buchon, California 
 (after a photograph by Fairbanks). 
 
 edge of the terrace, approximately equal to wave base (Fig. 255). 
 This cut terrace is extended seaward or lakeward, as the case may 
 be, in a huilt terrace constructed from a portion of the rock debris 
 acquired from the cliff. 
 
236 
 
 EARTH FEATURES AND THEIR MEANING 
 
 The broken wave, after rising upon the terrace under the inertia 
 of its motion until all its energy has been dissipated, slides out- 
 ward by gravity, and though 
 checked and overridden by 
 succeeding breakers, it con- 
 tinues its outward slide as 
 the " undertow " until it 
 reaches the end of the ter- 
 race. Here it suddenly en- 
 ters deep water, and losing 
 
 Fig. 255. -Ideal section of a steep rocky ^^^ velocity, drops its burden 
 shore carved by waves into a notched cliff of rock, and builds the ter- 
 
 and cut terrace, and extended by a built race seaward after the man- 
 ner of construction of an 
 embankment. As we are to see, the larger portion of the wave- 
 quarried material is diverted to a different quarter. 
 
 To gain some conception of the importance of wave cutting 
 as an eroding process, we may consider the late history of Heli- 
 goland, a sandstone island off the mouth of the Elbe in the North 
 Sea (Fig. 256). From a periphery of 120 miles, which it possessed 
 in the ninth cen- 
 tury of the Chris- 
 tian era, the 
 island has reduced 
 its outline to 45 
 miles in the four- 
 teenth century, 8 
 miles in the seven- 
 teenth, and to 
 about 3 miles at 
 the beginning of 
 the twentieth cen- 
 tury. The German 
 government, which 
 recently acquired 
 this little remnant 
 from England, has 
 expended large 
 sums of money in an effort to save this last relic. 
 
 Fig. 256. — Map showing the outlines of the Island of 
 Heligoland at different stages in its recent history. The 
 peripheries given are in miles. 
 
THE FORMS CARVED AND MOLDED BY WAVES 237 
 
 The cut and built terrace on a steep shore of loose materials. 
 
 ■ — In materials which lack the coherence of firm rock, no vertical 
 cliff can form ; for as fast as undermined by the waves the loose 
 
 materials slide down 
 
 /■"/■. 
 
 and assume a surface 
 of practically constant 
 slope — the " angle of 
 repose " of the mate- 
 rials (Fig. 257). The 
 terrace below this 
 sloping cliff will not 
 differ in shape from 
 that cut upon a rocky shore; but whenever the materials of the 
 shore include disseminated blocks too large for the waves to handle, 
 they collect upon the terrace near where they have been exhumed, 
 thus forming what has been called a " bowlder pavement " (Fig. 
 258). 
 
 The edge of the cut and built terrace is, as already mentioned, 
 maintained at the depth of wave base. If one will study the sub- 
 . merged contours of any of our 
 
 Fig. 257. — Cut and built terrace with bowlder pave- 
 ment shaped by waves on a steep shore formed of 
 loose materials. 
 
 inland lakes, it will be found 
 that these basins are sur- 
 rounded bj^ a gently sloping 
 marginal shelf, — the cut and 
 built terrace, — and that the 
 depth of this shelf at its outer 
 edge is proportioned to the 
 size of the lake. Upon Lake 
 Mendota at Madison, Wiscon- 
 sin, the large storm waves have 
 a length of about twenty feet, 
 which is the depth of the outer 
 edge of the shore terraces (Fig. 
 267, p. 242). The shelf sur- 
 rounding the continents has, 
 
 with few local exceptions, a uniform depth of 100 fathoms, or about 
 
 the wave base of the heaviest storm waves. 
 
 The work of the shore current. — In describing the formation 
 
 of the built terrace, it was stated that the greater part of the rock 
 
 Fig. 258. — Sloping cliff ana terrace with 
 bowlder pavement exposed at low tide 
 upon the sea shore at Scituate, Mass- 
 achusetts. 
 
238 
 
 EARTH FEATURES AND THEIR MEANING 
 
 material quarried upon headlands by the waves is diverted from 
 the offshore terrace. This diversion is the work of the shore cur- 
 rent produced by the wave. 
 
 At but few places upon a shore will the storm waves beat per- 
 pendicularly, and then for but short periods only. The broken 
 wave, as it crawls ever more slowly up the beach, carries the sand 
 with it in a sweeping curve, and by the time gravity has put a stop 
 to its forward movement, it is directed for a brief instant parallel 
 to the shore. Soon, however, the pull of gravity upon it has started 
 the backward journey in a more direct course down the slope of 
 
 Fig. 259. 
 
 ^D/rcct/o^ of 
 
 ■ Map to show the nature of the shore current and the forms which are 
 molded by it. 
 
 the terrace; and here encountering the next succeeding breaker, 
 a portion of the water and the coarser sand particles with it are 
 again carried forward for a repetition of the zigzag journey. This 
 many times interrupted movement of the sand particles may be 
 observed during a high wind upon any sandy lee shore. The " set " 
 of the water along the shore as a result of its zigzag journejdngs 
 is described as the shore current (Fig. 259), 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 particles. 
 
 The sand beach. — 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 cliff. The earlier deposits near the cliff 
 
THE FORMS CARVED AND MOLDED BY WAVES 239 
 
 gradually force the shore current farther from the shore and 
 so lay down a sand selvage to the shore, which is shaped in the 
 form of an arc or crescent and known as a beach (Fig. 259 and 
 Pig. 260). 
 
 - > >• 
 
 \.. 
 
 
 'Fig. 260. — Crescent-shaped beach formed in the lee of a headland. Santa 
 Catalina Island, California (after a photograph by Fairbanks). 
 
 The shingle beach. — With heavy storms and an exceptional 
 Teach of the waves, the shore currents are competent to move, not 
 the sand alone, but pebbles, the area of whose broader surface may 
 be as great as the palm of one's hand. Such rock fragments are 
 shaped by the continued wear against their neighbors under the 
 restless breakers, until they have a len- 
 ticular or watch-shaped form (Fig. 261). 
 Such beach pebbles are described as shingle, 
 and they are usually built up into distinct 
 ridges upon the shore, which, under the 
 fury of the high breakers, may be piled several feet above the level 
 of quiet water (Fig. 262). Such storm beaches have a gentle 
 
 Fig. 261. — Cross section 
 of a beach pebble. 
 
240 
 
 EARTH FEATURES AND THEIR MEANING 
 
 Fig. 262. — Storm beach of coarse 
 shingle about four feet in height at 
 the base of Burnt Bluff on the north- 
 east shore of Green Bay, Lake 
 Michigan. 
 
 forward slope graded by the shore current, but a steep back- 
 ward slope on the angle of repose. Most storm beaches have 
 been largely shaped by the last great storm, such as comes only 
 
 at intervals of a number of years. 
 Bar, spit, and barrier. — 
 Wherever the shore upon which 
 a beach is building makes a 
 sudden landward turn at the en- 
 trance to a bay, the shore cur- 
 rents, by virtue of their inertia 
 of motion, are unable longer to 
 follow the shore. The debris 
 which they carry is thus trans- 
 ported into deeper water in a 
 direction corresponding to a con- 
 tinuation of the shore just before 
 the point of turning (see Fig. 259, p. 238). The result is the 
 formation of a bar, which rises to near the water surface and is ex- 
 tended across the entrance to the bay through continued growth 
 at its end, after the manner of constructing a railway embank- 
 ment across a valley. 
 
 Over the deeper water near the bar the waves are at first not 
 generally halted and broken, as they are upon the shore, and so 
 the bar does not at once 
 build itself to the surface, 
 but remains an invisible 
 bar to navigation. From 
 its shoreward end, how- 
 ever, the waves of even 
 moderate storms are 
 broken, and the bar is 
 there built above the water 
 surface, where it appears 
 as a narrow cape of sand 
 or shingle which gradually 
 thins in approaching its 
 
 apex. This feature is the well-known spit (Fig. 263) which, as it 
 grows across the entrance to the bay, becomes a barrier or barrier 
 beach (Fig. 264). 
 
 i^^<^^^£~ 
 
 <^_ 
 
 Fig. 263. — Spit of shingle on Au Train Island, 
 Lake Superior (after Gilbert). 
 
THE FORMS CARVED AND MOLDED BY WAVES 241 
 
 The continuation of the visible in the usually invisible bar, is 
 at the time of high winds made strikingly apparent, for the wave, 
 base is below the crest of the bar, and at such times its crescentic 
 course beyond the spit can be followed by the eye in a white arc 
 of broken water. 
 
 The construction of a barrier across the entrance to a bay trans- 
 forms the latter into a separate body of water, a lagoon, within 
 which silting up and peat 
 formation usually lead to an 
 early extinction (p. 429) . The 
 formation of barriers thus 
 tends to straighten out the 
 irregularities of coast lines, 
 and opens the way to a 
 natural enlargement of the 
 land areas. While the coasts 
 of the United Kingdom of 
 Great Britain have been 
 losing some four thousand 
 acres through wave erosion, 
 there has been a gain by 
 gro^^iih in quiet lagoons which 
 amounts to nearly seven 
 
 times that amount. As evidence of the straightening of the shore 
 line which results from this process, the coast of the Carolinas or 
 of Nantucket (Fig. 459) may serve for illustration. 
 
 The land-tied island. — We have seen that wave erosion oper- 
 ates to separate small islands from the headlands, but the shore 
 currents counteract this loss to the continents by throwing out 
 barriers which join many separated islands to the mainland. Such 
 land-tied islands are a common feature on many rocky coasts, 
 and upon the New England coast they usually have been given the 
 name of " neck." The long arc of Lynn Beach joins the former 
 island of Nahant, through its smaller neighbor Little Nahant, 
 to the coast of Massachusetts. A similar land-tied island is 
 Marblehead Neck. The Rock of Gibraltar, formerly an island, 
 is now joined to Spain by the low beach known as the '' neutral 
 ground." The Spanish name, tombola, has sometimes been em- 
 ployed to describe an island thus connected to the shore. 
 
 Fig. 264. • — Barrier beach in front of alagoon 
 on Lake Mendota at Madison, Wisconsin. 
 The shallow lagoon behind the barrier is 
 filling up and is largely hidden in vege- 
 tation. 
 
242 
 
 EARTH FEATURES AND THEIR MEANING 
 
 A barrier series. — The cross section of a barrier beach, like 
 that of a storm beach upon the shore, slopes gently upon the for- 
 ward side, and more steeply 
 at the angle of repose upon 
 the rear or landward margin 
 (Fig. 265). The thinning 
 wedge of shore deposits which 
 the barrier throws out to sea- 
 ward raises the level of the 
 lake bottom (Fig. 266), and when coast irregularities are favor- 
 able to it, new spits will develop upon the shore outside the 
 
 Fig. 265. — Cross section of a barrier beach 
 with lagoon in its rear. 
 
 Fig. 266. — Cross section of a series of barriers and an outer bar. 
 
 earlier one, and a new bar, and in its turn a barrier, will be found 
 outside the initial one, taking a course in a direction more or less 
 parallel to it (Fig. 267), 
 
 Fig. 267. — Formation of barrier series and an outer bar in University Bay of 
 Lake Mendota, at Madison, Wisconsin. The water contour interval is five feet, 
 and the land contour interval ten feet (based on a map by the Wisconsin Geologi- 
 cal Survey). 
 
THE FORMS CARVED AND MOLDED BY WAVES 243 
 
 Fig. 268. — Series of barriers at the western end 
 of Lake Superior (after Gilbert). 
 
 So soon as the first barrier is formed, processes are set in opera- 
 tion which tend to trans- 
 form the newly formed la- 
 goon into land, and so with 
 a series of barriers, a zone 
 of water lilies between the 
 outer barrier and the bar, 
 a bog, and a land platform 
 may represent the succes- 
 sive stages in this acquisi- J 
 tion of territory by the 
 lands. A noteworthy ex- 
 ample of barrier series 
 and extension of the land 
 behind them, is afforded by 
 the bay at the western end 
 of Lake Superior (Fig. 268). 
 
 Character profiles. — The character profiles yielded by the 
 work of waves are easy of recognition (Fig. 269). The vertical 
 
 cliff with notch at its 
 base is varied by the 
 stack of sugar-loaf 
 form carved in softer 
 rocks, or the steeper 
 notched variety cut 
 from harder masses. 
 Sea caves and sea 
 arches yield varia- 
 tions of a curve com- 
 mon to the undercut 
 forms . Wherever the 
 materials of the shore 
 are loosely consoli- 
 dated only, the slop- 
 ing cliff is formed at the angle of repose of the materials. The 
 barrier beach, though projecting but a short distance above the 
 waves, shows an unsymmetrical curve of cross section with the 
 steeper slope toward the land. 
 
 Fig. 269. — Character profiles resulting from wave 
 action upon shores. 
 
244 EARTH FEATURES AND THEIR MEANING 
 
 Reading References for Chapter XVIII 
 
 G. K. Gilbert. The Topographic Features of Lake Shores, 5th Ann. 
 Rept. U.S. Geol. Surv., 1885, pp. 69-123, pis. 3-20; Lake Bonne- 
 ville, Mon. I, U. S. Geol. Surv., 1890, Chapters ii-iv, pp. 23-187. 
 
 Vaughan Cornish. On Sea Beaches and Sand Banks, Geogr. Jour., vol. 
 11, 1898, pp. 528-543, 628-658. 
 
 F. P. GtJLLivER. Shore Line Topography, Proc. Am. Acad. Arts and 
 
 Sci., vol. 34, 1899, pp. 149-258. 
 N. S. Shaler. The Geological History of Harbors, 13th Ann. Rept. U. S. 
 
 Geol. Surv., 1893, pp. 93-209. 
 Sir A. Geikie. The Scenery of Scotland, 1901, pp. 46-89. 
 W. H. Wheeler. The Sea Coast. Longmans, London, 1902, pp. 1-78. 
 
 G. W. von Zahn. Die zerstorende Arbeit des Meeres an Steilkiisten nach 
 
 Beobachtungen in der Bretagne und Normandie in den Jahren 1907 
 und 1908, Mitt. d. Geogr. Ges. Hamb., vol. 24, 1910, pp. 193-284, 
 pis. 12-27. 
 
CHAPTER XIX 
 
 COAST RECORDS OF THE RISE OR FALL OF THE 
 
 LAND 
 
 The characters in which the record has been preserved. — 
 
 The peculiar forms into which the sea has etched and molded its 
 shores have been considered in the last chapter. Of these the 
 more significant are the notched rock cliff, the cut rock terrace, 
 the sea cave, the sea arch, the stack, and the sloping cliff and ter- 
 race, among the carved features ; and the barrier beach and built 
 terrace, among the molded forms. It is important to remember 
 that the molded forms, by the very manner of their formation, 
 stand in a definite relationship to the carved features ; so that 
 when either one has been in part effaced and made difficult of de- 
 termination, the discovery of the other in its correct natural posi- 
 tion may remove all doubt as to the origin of the relic. 
 
 In studies of the change of level of the land, it is customary to 
 refer all variations to the sea level as a zero plane of reference. 
 It is not on this account necessary to assume that the changes 
 measured from this arbitrary datum plane are the absolute up- 
 ward or downward oscillations which would be measured from the 
 earth's center ; for the sea, like the land, has been subject to its 
 changes of level. There need, however, be no apology for the 
 use of the sea surface as a plane of reference ; for it is all that we 
 have available for the purpose, and the changes in level, even if 
 relative only, are of the greatest significance. It is probable that 
 in most cases where the coast line is rising from uplift, some por- 
 tion of the sea basin not far distant is becoming deepened, so that 
 the visible change of level is the algebraic sum of the two effects. 
 
 Even coast line the mark of uplift. — It was early pointed out 
 in this volume (p. 158) that the floor of the sea in the neighborhood 
 of the land presents a relatively even surface. The carving by 
 waves, combined with the process of deposition of sediments, tends 
 to fill up the minor irregularities of surface and preserve only the 
 
 245 
 
246 
 
 EARTH FEATURES AND THEIR MEANING 
 
 Capehfahbar 
 
 features of larger scale, and these in much softened outlines. Upon 
 the continents, on the contrary, the running water, taking advan- 
 tage of every slight difference in elevation and 
 searching out the hidden structure planes 
 within the rock, soon etches out a surface of the 
 most intricate detail. The effect of elevation 
 of the sea floor into the light of day will there- 
 fore be to produce an even shore line devoid of 
 harbors (Fig. 270). If the coast has risen 
 along visible planes of faulting near the sea, 
 margin, the coast line, in addition to being even, 
 will usually be made up of notably straight ele- 
 ments joined to one another. 
 
 A ragged coast line the mark of subsid- 
 ence. — When in place of uplift a subsidence 
 occurs upon the coast, 
 the intricately etched 
 surface, resulting from 
 erosion beneath the 
 sky, comes to be in- 
 vaded by the sea 
 along each trench and 
 furrow, so that a most 
 ragged outline is the result (Fig. 271). 
 
 Such a coast 
 has many 
 harbors, 
 while the 
 
 uplifted coast is as remarkable for its 
 lack of them. 
 
 Slow upUft of the coast — the 
 coastal plain and cuesta. — A gradual 
 uplift of the coast is made apparent 
 in a progressive retirement of the sea 
 across a portion of its floor, thus ex- 
 posing this even surface of recent 
 Atlantic sediments. The former shore land 
 will be easily recognized by its etched 
 surface, which will now come into 
 
 Fig. 270. — The east 
 coast of Florida, with 
 even shore line char- 
 acteristic of a raised 
 coast. 
 
 Fig. 271. — Ragged coast line 
 of Alaska, the effect of sub- 
 sidence. 
 
 Fig. 272. — Portion of 
 
 coastal plain and neighboring old 
 land of the Appalachian Moun- 
 tains. 
 
COAST RECORDS OF THE RISE OR FALL OF LAND 247 
 
 sharp contrast with the new plain. It is therefore referred to as 
 the oldland and the newly exposed coastal plain as the newland 
 (Fig. 272). 
 
 But the near-shore deposits upon the sea floor had an initial 
 dip or slope to seaward, and this inclination has been increased 
 in the process of uplift. The streams from the oldland have 
 trenched their way across these deposits while the shore was ris- 
 ing. But the process being a slow one, deposits have formed 
 upon the seaward side of the plain after the landward portion was 
 above tide, and the coastal plain may come to have a " belted " 
 or zoned character. The streams tributary to those larger ones 
 which have trenched the plain may encounter in turn harder and 
 softer layers of the plain deposits, and at each hard layer will be 
 deflected along its margin so as to 
 enter the main streams more nearly 
 at right angles. They will also, as 
 time goes on, migrate laterally sea- 
 ward through undermining of the 
 harder layers, and thus will be Fig. 273. — ideal form of cuestas 
 
 shaped alternating belts of lowland ^"^ intermediate lowlands carved 
 
 . from a coastal plain (after Davis). 
 
 separated by escarpments m the 
 
 harder rock from the residual higher slopes. Belts of upland of 
 
 this character upon a coastal plain are called cuestas (Fig. 273). 
 
 The sudden uplifts of the coasts. — Elevations of the coast 
 which yield the coastal plain must be accounted among the 
 slower earth movements that result in changes of level. Such 
 movements, instead of being accompanied by disastrous earth- 
 quakes, were probably marked by frequent slight shocks only, 
 by subterranean rumblings, or, it may be, the land rose gradually 
 without manifestations of a sensible character. 
 
 Upon those coasts which are often in the throes of seismic dis- 
 turbance, a quite different effect is to be observed. Here within 
 the rocks we will probably find the marks of recent faulting with 
 large displacements, and the movements have been upon such a 
 scale that shore features, little modified by subsequent weathering, 
 stand well above the present level of the seas. Above such coasts, 
 then, we recognize the characteristic marks of wave action, and 
 the evidence that they have been suddenly uplifted is beyond 
 question. 
 
248 
 
 EARTH FEATURES AND THEIR MEANING 
 
 Fig. 274. — Uplifted sea cave, ten feet above the water upon the coast of Califor- 
 nia ; the monument to a former earthquake (after a photograph by Fairbanks). 
 
 Fig. 275. — Double-notched cliff near Cape Tiro, Celebes (after a photograph by 
 
 Sarasin). 
 
COAST RECORDS OF THE RISE OR FALL OF LAND 249 
 
 The upraised cliff. — Upon the coast of southern California 
 may be found all the features of wave-cut shores now in perfect 
 preservation, and in some cases as much as j&fteen hundred feet 
 above the level of the sea. These features are monuments to the 
 grandest of earthquake disturbances which in recent time have 
 visited the region (Fig. 274). Quite as striking an example of 
 similar movements is afforded by notched cliffs in hard limestone 
 upon the shore of the Island of Celebes (Fig. 275). 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 
 
 IFiG. 276. — Jasper rock stacks uplifted on the coast of California (after a photo- 
 graph by Fairbanks). 
 
 uplift. 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 sea, and the forms which they would then present 
 would differ but little from those which are shown in Fig. 276. 
 
 The uplifted barrier beach. — Within the reentrants of the 
 shore, the wave-cut cliff is, as we know, replaced by the barrier 
 beach, which takes its course across the entrance to a bay. After 
 an uplift, such a barrier composed of sand or shingle should be 
 connected with the headlands, often with a partially filled lagoon 
 behind it. Its cross section should be steep in the direction of 
 the lagoon, but quite gradual in front (Fig. 277). 
 
250 
 
 EARTH FEATURES AND THEIR MEANING 
 
 [Fig. 277. — Uplifted shingle beach across the entrance to a former bay upon 
 the coast of southern California (after a photograph by Fairbanks). 
 
 Coast terraces. — Upon those shores where to-day high moun- 
 tains front the sea, the coast may generally be seen to rise in a series 
 
 of terraces (Fig. 278). This 
 is notably true of those coasts 
 which are to-day racked by 
 earthquakes, such as is the 
 eastern margin of the Pacific 
 from Alaska to Patagonia. 
 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 sea. In 
 
 Fig. 278. — Raised beach terraces near Elie, 
 Fife, Scotland. 
 
 ,cu.o iVA)/i^-cc/r oj/nr 
 
 iy/^RAISED BEACH OF /a99 
 MODERN BEACH 
 
 OLD rffEE-COt^OiCO 
 BSACH 
 
 Fig. 279. 
 
 ■Uplifted sea clifTs and terraces on the coast of Russell Fjord, Alaska 
 (after Tarr and Martin). 
 
 Alaska we are fortunate in having the history of the later stages in 
 this uplift (Fig. 279). As described in a former chapter, portions 
 of this shore rose in the month of September of the year 1899 in 
 
COAST RECORDS OF THE RISE OR FALL OF LAND 251 
 
 some places as high as forty-seven feet, to the accompaniment of 
 a terrific earthquake and sea wave. Above the terrace which 
 
 Pig. 280. ■ 
 
 ■Diagrams to show how excessive sinking upon the sea floor will cause 
 the shore to migrate landward as it is uplifted. 
 
 marks the beach fine of 1899 there is a higher terrace of similar 
 form now overgrown with trees, but none the less clearly to be rec- 
 ognized as a shore line of the past century 
 which preceded in the long sequence the 
 uplift of 1899. 
 
 As was noted in our study of earth- 
 quakes, the recent instrumental records of 
 distant earthquakes tell us that the move- 
 ments upon the sea floor are many times 
 larger than those upon the continents, and 
 that while the mountainous coasts are gen- 
 erally rising, the deeps of the sea are sink- 
 ing. The effect of this over-balance of 
 sinking, or resultant shrinking of the earth's 
 shell, may be to compress the mountain 
 district and so cause the shore line to move 
 landward at the same time that it moves 
 upward (Fig. 280). 
 
 The sunk or embayed coast. — When 
 now, upon the other hand, a section of the 
 coast line sinks with reference to the sea, 
 the water invades all the near-shore val- 
 leys, thus " drowning " them and yielding 
 the " drowned river mouth " or estuary. 
 If the relief of the shore was slight, as it generally is upon a 
 coastal plain, slight depression only will produce broad estuaries, 
 
 .^:^^ 
 
 Fig. 281. — A drowned river 
 mouth or estuary upon a 
 coastal plain. 
 
252 EARTH FEATURES AND THEIR MEANING 
 
 Fig. 282. — Archipelago of steep rocky islets due to large submergence of a coast 
 having strong relief. Entrance to Esquimalt Harbor, Vancouver Island (after 
 a photograph by Fairbanks). 
 
 such as Chesapeake Bay at the 
 drowned mouth of the Susque- 
 hanna (Fig. 281). 
 
 If, on the other hand, the rehef 
 of the shore is strong and the sub- 
 sidence is large, the entire coast 
 hne will be transformed into an 
 archipelago of steep-walled rocky- 
 islets which rise abruptly from the 
 sea (Figs. 282 and 284) . A plateau 
 which is intersected by deep and 
 steep-walled valleys of U-section 
 (p. 341) under'large submergence 
 yields the fjords so characteristic 
 of Scandinavia or Alaska. A rag- 
 ged coast line, fringed with islands 
 as a result of submergence, is de- 
 scribed as an embayed coast. 
 
 Submerged river channels. — 
 The sinking of a coast of small 
 
 Fig. 283. -The submerged Hudso- ^^^^^^ ^e Sufficient to COm- 
 
 man channel which continues the 
 
 Hudson River across the continental pletely Submerge river valleys, 
 
 whose channels then begin to fill 
 
 shelf. 
 
COAST RECORDS OF THE RISE OR FALL OF LAND 253 
 
 with sediment and whose courses can only be followed in sound- 
 ings. One of the most interesting of such channels is that which 
 continues the Hudson River across the continental shelf into the 
 deeper sea (Fig. 283). 
 
 Records of an oscillation of movement. — Because a coast 
 is deeply embayed is no ground for assuming that a subsidence 
 is now in prog- 
 ress, or is, in 
 fact, the latest 
 movement re- 
 corded upon the 
 coast. In many 
 cases it is easy 
 to see that such 
 is not the case. 
 The coast of 
 Maine is per- 
 haps as typical 
 of an embayed 
 shore line as 
 any that might 
 be cited, but a 
 study of the 
 river valleys in 
 the neighbor- 
 hood 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 (Fig. 284). 
 
 If now we give a closer examination to the coast, it is found 
 that there are marks of recent uplift in an abandoned shore line 
 now far above the reach of the waves. There is here, then, the 
 record, first of subsidence and consequent embayment, and, later, 
 of an uplift which has reduced the raggedness of the coast outline, 
 exposed the clay deposits, and raised the strands of the period of 
 deep subsidence to their present position. 
 
 In countries which possess a more ancient civilization than our 
 own, the record of such oscillations in the level of the ground has 
 sometimes been entered upon human monuments, so that it is 
 
 Fig. 284. — Marine clay deposits near the mouths of the rivers 
 of Maine which preserve a record of earlier subsidence (after 
 Stone) . 
 
254 
 
 EARTH FEATURES AND THEIR MEANING 
 
 possible to date more or less definitely the periods of subsidence 
 or elevation. At the little town of Pozzuoli, upon the shore of 
 the Bay of Naples, is found one of the most instructive of these 
 records. 
 
 In the ruins of the ancient temple of Jupiter Serapis are three 
 marble monoliths 40 feet in height, curiously marked by a 
 
 roughened surface between the 
 heights of 12 and 21 feet above 
 their pedestals (Fig. 285) . Closer 
 inspection shows that this rough- 
 ened surface has been produced 
 by a marine, rock-boring mollusk, 
 the lithodomus, which lives in the 
 waters of the Bay of Naples, and 
 the shells of this animal are still 
 to be found within the cavities 
 
 Fig 285. -View of the three standing ^^^ ^^^.^^^^ ^f ^^^ columns. 
 
 columns of the temple of Jupiter Se- 
 
 rapis at PozzuoH, showing the dark Without recounting details which 
 and rough band nine feet in width have been many times recited 
 
 affected by the rock-boring mollusks g-^^g ^^^^^ interesting monu- 
 which now live in the Bay of Naples. . 
 
 ments were first geologically ex- 
 plored by Babbage and Lyell, it may be stated that a record is 
 here preserved, first of subsidence amounting to some 40 feet, and 
 of subsequent elevation, of the low coast land on which stood the 
 temple in the old Roman city of Puteoli (Fig. 286). 
 
 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 
 Naples, the smoother lower zone being buried, at the time in the 
 sand at the bottom, and thus made inaccessible for the lithodomi. 
 It is to be added that studies made in the environs of Pozzuoli 
 have fully confirmed the changes of level revealed by the columns, 
 through the discovery of now elevated shore lines which are re- 
 ferable to the period of deep submergence. 
 
 Simultaneous contrary movements upon a coast. — In our 
 study of the changes in the level of the ground that take place 
 during earthquakes, it was learned that neighboring sections of 
 the earth's crust may be moved at different rates or even in op- 
 posite directions, notwithstanding the fact that the general move- 
 ment of the province is one of uplift. Thus during the Alaskan 
 
■''^. 
 
 :tjr^- 
 
 ''-^S. 
 
 
 -■ '///'■ 
 
 Fig. 286. — Pozzuoli in the 3rd, 9th, and 20th Centuries. 
 
256 EARTH FEATURES AND THEIR MEANING 
 
 earthquake of 1899, although portions of the coast line were elevated 
 by as much as forty-seven feet, neighboring sections were raised by 
 smaller amounts, 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 trees. 
 
 A region racked by heavy earthquakes, where the present con- 
 figuration of the ground speaks strongly for a movement of some- 
 what similar nature, but with average movement of elevation much 
 greater to the northward than in the opposite direction, is the ex- 
 tended coast line of Chili. 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 eastward. To 
 the southward the floor of this valley descends, and has its con- 
 tinuance in the Gulf of Corcovado behind the island of Chiloe and 
 the Chonos archipelago. The known recent uplift of the coast of 
 Chili, particularly in the northern sections and during the earth- 
 quakes of the eighteenth, nineteenth, and twentieth centuries, 
 lends great interest to this topographic peculiarity. Indications 
 are not lacking that, during the earthquake of Concepcion in 
 1835, and of Valparaiso in 1907, the measure of uplift was greater 
 to the north than it was to the south. 
 
 The contrasted islands of San Clemente and Santa Catalina. — 
 Perhaps the most striking example of simultaneous opposite move- 
 
 
 1^^^ 
 
 
 
 ^ 
 
 ^ 
 
 '^ 
 
 ^ 
 
 ^ 
 
 ^^ 
 
 Fig. 287. — Map of San Clemente Island, California, showing the characteristic 
 topography of recent uplift (after U. S. Coast and Geodetic Survey). 
 
 ments observable in neighboring portions of the earth's crust 
 is furnished by the coast of southern California. The coast itself 
 at San Pedro and the island of San Clemente, some fifty miles off 
 this point, in common with most portions of the neighboring coast 
 land, have been rising in interrupted movements from the sea, and 
 offer in rare perfection the characteristic coast terraces (Fig. 287 
 
Plate 12. 
 
 A. V-ahaped canon cut in an upland recently elevated from the sea, San Clemente 
 Island, California (after W. S. Tangier-Smith). 
 
 B. A "hogback" at the base of the Bighorn Mountains, Wyoming (after Darton). 
 
COAST RECORDS OF THE RISE OR FALL OF LAND 257 
 
 and Fig. 278, p. 250). Midway between these two rising sections 
 of the crust, and less than twenty-five miles distant from either, is 
 the island of Santa Catalina, which has been sinking beneath the 
 waves, and apparently at a similarly rapid rate (Fig. 288). The 
 
 Fig. 288. — Map of Santa Catalina Island, California, showing the characteristic 
 surface of an area which has long been above the waves, and the entire absence of 
 coast terraces (after U. S. C. and G. S.). 
 
 topography of the island shows the intricate detail of a maturely 
 eroded surface, while that of the neighboring San Clemente shows 
 only the widely spaced, deep canons of the infantile stage of erosion 
 (Fig. 165 and pi. 12 A). While Santa Catalina has been sinking, 
 San Pedro Hill has risen 1240 feet, and San Clemente, 1500 feet. 
 It is characteristic of a sinking coast line that the cliff recession is 
 abnormally rapid, and evidence for this is furnished by the shores 
 of Santa Catalina, upon which the waves are cutting the cliffs 
 back into the beds of canons, and so causing small falls to develop 
 at the caiion mouths. 
 
 The Blue Grotto of Capri. — 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 syn- 
 chronous, and that near-lying sections may even move in opposite 
 directions at the same time, as has already been shown for the isl- 
 ands off the California coast. For the Pozzuoli shore of the bay 
 it was learned that within the Christian Era a complete cycle of 
 downward, followed by later upward, movement has been largely 
 accomplished. Across the bay, and less than 20 miles distant, is 
 the Blue Grotto of Capri, a sea cave cut in limestone above an 
 earlier cave of the same nature which is now deep below the water 
 surface. It is the refracted sunlight which enters the cave through 
 
258 EARTH FEATURES AND THEIR MEANING 
 
 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 (Fig. 289). 
 
 It is known that the former, and now submerged, sea cave was 
 
 . in use by Roman patricians as a 
 
 ^'"'^'Hv- I cool retreat from the oppressive 
 
 seo ^B^e/ _^^'^~-":^s^^£^ hot wind known as the sirocco, 
 
 \ \ and that an artificial entrance or 
 
 ^"^ ^ window was cut where is now the 
 
 ^r-rr?er Sea Co^^ J 
 
 "^ only accessible entrance to the 
 
 ^ grotto. In the ancient writings, 
 
 ^^--^^"^^^ no mention is made, however, of 
 
 Fig. 289. — Cross section of the Blue the remarkable blue illumination 
 
 Grotto on the Island of Capri, show- for which it is noW famOUS, and 
 ing the submerged sea cave through ,i ■,.,. , ,, ,. 
 
 which most of the light enters the ^^e conditions at the time, as we 
 grotto, and the higher artificial win- may See, Were not such as to make 
 dow now widened by wave action this possible. Later subsidence 
 
 (after von Knebel). r xi j. i i, t_x j.t. 
 
 01 the coast has brought the 
 ancient window to the sea level, where it has been considerably 
 enlarged by the waves. The earlier grotto, abandoned as its 
 entrance was closed, was rediscovered in 1826 by the painter and 
 poet, August Kopisch. 
 
 A grotto with green illumination (the Grotto Verde) is situated 
 upon the opposite side of the island, and a blue grotto, having its 
 origin in similar conditions to those of the famous Blue Grotto, 
 is found upon the island of Busi off the Dalmatian coast. 
 
 Character profiles. — In the landscape of a coast which has been 
 slowly uplifted the characteristic line is the profile of the cuesta, 
 with short perpendicular element joined to a gently sloping and 
 longer section and continued in the horizontal portion correspond- 
 ing to the lowland (Fig. 290). Rapidly uplifted coasts offer in 
 contrast the lines characteristic of wave erosion and deposition, 
 but at higher levels and in repeated sections. Most prominent 
 of all is the staircase constructed of coast terraces, with either 
 vertical or sloping risers and with outwardly inclining and gently 
 graded treads. Near the steep riser in the staircase may some- 
 times be seen the sugar-loaf outline of the stack cut in softer ma- 
 terial, or the obelisk-like pillar undercut at its base, which is carved 
 in firmer rock masses. With excessively rapid uplift, the double- 
 
COAST RECORDS OF THE RISE OR FALL OF LAND 259 
 
 notched cliff or the double sea arch may appear in the landscape. 
 Upon a submerged coast the most significant lines in the view 
 are those of the rock islet and the steep-walled fjord. 
 
 Ooub/ 
 
 
 
 1 CD l^vl 
 
 subsideince: 
 
 subs.deivjce:. '-^■^^" eIevat.on. 
 
 Fig. 290. — Character profiles in coast landscapes where there has been either 
 elevation or depression. 
 
 Reading References for Chapter XIX 
 General : — 
 Sir Ch. Lyell. Principles of Geology, vol. 2, pp. 180-197. 
 Ed. Suess. The Face of the Earth, Clarendon Press, Oxford, 1906, voL 
 
 2, Chapters i and xiv, pp. 1-29, 535-556. 
 Robert Sieger. Seenschwankungen und Strandversehiebungen in Sean- 
 dinavien, Zeit. d. Gesell. f. Erdk., Berlin, vol. 28, 1893, pp. 1-106, 
 393-688, pi. 7. 
 
 Elevated shore lines : — 
 F. B. Taylor. The Highest Old Shore Line of Mackinac Island, Am. 
 
 Jour. Sei., vol. 43, 1892, pp. 210-218. 
 Thomas L. Watson. Evidences of Recent Elevation of the Southern 
 
 Coast of BafSns Land, Jour. Geol., vol. 5, 1897, pp. 17-33. 
 J. W. GoLDTHWAiT. The Abandoned Shore Lines of Eastern Wisconsin. 
 
 Bull. 17, Wis. Geol. and Nat. Hist. Surv., 1907, pp. 134, pis. 1-37. 
 
 Evidences of depression : — 
 W. B. Scott. Introduction to Geology, New York, 1907, pp. 33-36. 
 W J McGee. The Gulf of Mexico as a Measure of Isostacy, Am, 
 Jour. Sci. (3), vol. 44, 1892, pp. 177-192. 
 
260 EARTH FEATURES AND THEIR MEANESTG 
 
 A. LiNDENKOHL. Notes on the Submarine Channel of the Hudsoa 
 River, etc., Am. Jour. Sci. (3), vol. 41, 1891, pp. 489-499, pi. 18. 
 
 J. W. Spencer. The Submarine Great Canon of the Hudson River, 
 ibid. (4), vol. 19, 1905, pp. 1-15; Submarine Valleys off theAmericaii 
 Coast and in the North Atlantic, Bull. Geol. Soc. Am., vol. 14, 1903, 
 pp. 207-226, pis. 19-20. 
 
 F. Nansen. The Bathymetrical Features of the North Polar Sea, with a 
 
 Discussion of the Continental Shelves and Previous Oscillations of 
 Shore Line, Norwegian North Polar Expedition, vol. 4, 1904, pp. 99- 
 231, pi. 1. 
 W. V. Knebel. Hohlenkunde, etc., Braunschweig, 1906, pp. 175-177 
 (the blue grotto of Capri). 
 
 Oscillation of movement : — 
 C. Lyell. Principles of Geology, vol. 2, pp. 164-176 (Temple of Jupiter 
 
 Serapis). 
 E. Ray Lankester. Extinct Animals, New York, 1905, pp. 31-42. 
 H. W. Fairbanks. Oscillations of the Coast of California during the 
 Pliocene and Pleistocene, Am. Geol., vol. 20, 1897, pp. 213-245. 
 
 G. H. Stone. Mon. 34, U. S. Geol. Surv., 1899, pp. 56-58, pi. 2. 
 Bailey Willis. Ames Knob, North Haven, Maine. Bull. Geol. Soc. 
 
 Am., vol. 14, 1903, pp. 201-206, pis. 17-18. 
 
 Simultaneous contrary movements on a coast : — 
 A. C. Lawson. The Post-PKocene Diastrophism of the Coast of Southern 
 
 California, Bull. Univ. Calif. Dept. Geol., vol. 1, 1893, pp. 115-160, 
 
 pis. 8-9. 
 W. S. Tangier-Smith. A Geological Sketch of San Clemente Island, 
 
 18th Ann. Rept. U. S. Geol. Surv., Pt. ii, 1898, pp. 459-496, pis. 84-96. 
 R. S. Tarr and L. Martin. Recent Changes of Level in the Yakutat 
 
 Bay Region, Alaska, Bull. Geol. Soe. Am., vol. 17, 1906, pp. 29-64, 
 
 pis. 12-23. 
 
CHAPTER XX 
 THE GLACIERS OF MOUNTAIN AND CONTINENT 
 
 Conditions essential to glaciation. — Wherever for a suffi- 
 ciently protracted period the annual snowfall of a district is in 
 excess of the snow that is melted, a residue must remain from 
 each season to be added to that of succeeding ones. Eventually 
 so much snow will have accumulated that under its own weight 
 and in obedience to its peculiar properties, a movement will begin 
 within the mass tending to spread it and so to reduce the slope 
 of its upper surface (Frontispiece plate) . The conditions favorable 
 to glaciation are, therefore, heavy precipitation and low annual 
 temperature. If the precipitation is scanty, the small snowfall 
 is soon melted ; and if the temperature be too high, the moisture 
 is precipitated not in the form of snow but as rain. It is impor- 
 tant here to keep in mind that snow is a poor heat conductor 
 and itself protects its deeper layers from melting. 
 
 The snow-line. — Because of the low temperatures glaciers 
 should be most abundant or most extensive in high latitudes and 
 in high altitudes. The largest are found in polar and sub-polar 
 regions, and they are elsewhere encountered only at considerable 
 elevations. The largest glaciers are the vast sheets of ice which 
 inwrap the continents of Greenland and Antarctica, but glaciers 
 of large size ate to be found upon other large land masses of the 
 Arctic, as well as in Alaska, in the southern Andes, and in New 
 Zealand. Much smaller glaciers are characteristic of certain 
 highlands within temperate and tropical regions, but because 
 of specially favorable conditions both of altitude and precipi- 
 tation the Himalayas, although in relatively low latitudes, nourish 
 glaciers of large proportions. In general, it may be said that 
 the nourishing grounds of glaciers are largely restricted to those 
 areas where snow covers the ground throughout the year. The 
 lower margin of such areas is designated the snow line, and varies 
 but little from the line on which the average summer tempera- 
 ture is at the freezing point of water — the so-called summer 
 
 261 
 
262 EARTH FEATURES AND THEIR MEANING 
 
 isotherm of 32° Fahrenheit. Within the tropics this line may 
 rise as high as 18,000 feet above the sea, whereas in polar lati- 
 tudes it descends to sea level. 
 
 Importance of mountain barriers in initiating glaciers. — The 
 precipitation within any district depends, however, not alone 
 upon the amount of moisture which is brought to it in the clouds, 
 but upon the amount which is abstracted before the clouds have 
 passed over it. The capacity of space to hold moisture increases 
 with its temperature, and hence any lowering of this temperature 
 will reduce the capacity. If lowered sufficiently, the point of 
 complete saturation will be reached and further cooling must 
 result in precipitation. Hence, anything which forces an air 
 current to rise into more rarefied zones above, will lower the pres- 
 sure upon it and so bring about a cooling effect in which no heat 
 is abstracted. This so-called adiahatic 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 opened ; or 
 even better, by the instant solidification at extreme low tempera- 
 tures of such normal gases as carbonic acid when they are allowed 
 to issue under heavy pressure from a small orifice. 
 
 As applied to moisture-laden and near-surface winds, the 
 effective agents of adiabatic cooling are the upland areas upon 
 the continents, and especially the ranges of mountains. These 
 barriers force the moving clouds to rise, cool, and deposit their 
 moisture. It is, therefore, the highland barriers which face the 
 on-coming, moisture-laden winds that receive the heaviest pre- 
 cipitation. Within temperate regions, because of the prevalence 
 of westerly winds, those barriers which face the western shores 
 receive the heaviest fall. Within the tropics, on the other hand, 
 it is the barriers facing the eastern shores which, because of the 
 easterly " trades," are most favorable to precipitation. 
 
 Thus it is in the Sierra Nevadas of California, and not in the 
 Rockies or the Appalachians, that the glaciers of the United States 
 are found. The highland of the Swiss Alps lying likewise athwart 
 the " westerlies" of the temperate zone acquires the moisture 
 for nourishment of its glaciers from the western ocean • — here 
 the Atlantic (Fig. 291). Within the tropics the conditions are 
 reversed, and it is in general the ranges which lie nearer the eastern 
 coasts that are the more favored. If no barrier is found upon 
 
THE GLACIERS OF MOUNTAIN AND CONTINENT 263 
 
 this coast, the clouds may travel over vast stretches of country 
 before being arrested by mountains and robbed of their moisture. 
 Thus in tropical Brazil the glaciers are found in the Andes upon 
 the Pacific coast though nourished by clouds from the Atlantic. 
 
 Fig. 291. — Map showing the distribution of existing glaciers, and the two im- 
 portant wind poles of the earth. 
 
 Sensitiveness of glaciers to temperature changes. — How 
 
 sensitive is the adjustment between snow precipitation and tem- 
 perature may be strikingly illustrated by the statement on ex- 
 cellent authority that if the average annual temperature of the air 
 within the Scottish Highlands should be lowered by only three 
 degrees Fahrenheit, small glaciers would be the result; and a 
 moderate temperature fall within the region surrounding the 
 Laurentian lakes of North America would bring on glaciation, 
 otherwise expressed as a depression of the snow line of the region. 
 The cycle of glaciation. — Though to-day buried beneath its 
 ice mantle, it is known that Greenland had more than once in earlier 
 geological ages a notably mild climate, and in some future age 
 it may revert to this condition. In other regions, also, we have 
 evidence that such a rotation of climatic changes has been suc- 
 cessively accomplished, the climate having steadily increased in 
 severity towards a culminating point, and been followed by a 
 reverse series of changes. Such a complete period may be called 
 a cycle of glaciation. While the climate is steadily becoming 
 more rigorous, we have to do with an advancing hemicycle of 
 
264 
 
 EARTH FEATURES AND THEIR MEANING 
 
 glaciation, but after the culminating point has been reached, the 
 period of amelioration of climate is the receding hemicycle. 
 
 The advancing hemicycle. — There is little reason to doubt 
 that whatever be the cause of the climatic changes which bring 
 on glacial conditions, these changes come on by insensible grada- 
 tions. The first visible evidence of the increased severity of 
 the climate is the longer persistence of the winter snows, at first 
 
 Fig. 292. — An Alaskan glacier spreading out at the foot of the range which 
 
 nourishes it. 
 
 within the more elevated districts. In such positions drifts must 
 eventually continue throughout the warm season and so con- 
 tribute to the snow accumulations of the succeeding winter. This 
 point once reached, small glaciers are inevitable, even should the 
 average temperature fall no further, 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 levels. 
 
 The inherited depressions of the upland — the gentle hollows 
 at the heads of rivers — will first be filled, and so the valleys 
 
THE GLACIERS OF MOUNTAIN AND CONTINENT 265 
 
 below become the natural channels for the outflow of the early 
 glaciers. With a continued lowering of the annual temperature 
 and consequent increased snowfall, the early glaciers become 
 more and more amply nourished. Snow and ice will, therefore, 
 cover larger areas of the upland, and the glaciers will push their 
 fronts farther down the valleys before they are wasted in the 
 warm air of the lower levels. As the valleys become thus more 
 completely invested by the glacier they are likewise filled to greater 
 and greater depths, and they may thus submerge portions of the 
 walls that separate adjacent valleys. Reaching at last the front 
 of the upland area, the glaciers may now be so well nourished at 
 their heads that they push out upon the flatter foreland and with- 
 out restraint from retaining walls spread broadly upon it (Fig. 292). 
 The culmination of the progressive climatic change may ere 
 this have been reached and milder conditions have ensued. If, 
 however, the severity of the climate should be still further in- 
 creased, the expanded fronts of neighboring glaciers will coalesce 
 to form a common ice fan or apron along the foot of the upland 
 (Plate 18 B). This could hardly take place without a stiU further 
 deepening of the ice within the valleys above, and, probably, a 
 progressive submergence of the lower crests in the valley walls. 
 
 Fig. 293. — Surface of a glacier whose upper layers spread with slight restraint 
 from retaining walls. Surface of the Folgefond, an ice cap of southern Norway. 
 
266 EARTH FEATURES AND THEIR MEANING 
 
 This may even continue until all parts of the upland area have 
 been buried. The snow and ice now take the form of a covering 
 cap or carapace, and the upper portions being no longer restrained 
 at the sides, now spread into a broad dome, as would a viscous 
 liquid like thick molasses when poured out upon the floor (Fig. 
 293). The lower zones of the mass and the thirmer marginal 
 portions still have their motion to a greater or less extent con- 
 trolled by the irregularity of the rock floor against which they rest. 
 
 The reverse series of changes in the glacier is inaugurated by an 
 amelioration of the climate, and here, therefore, the advancing 
 hemicycle becomes merged in the receding hemi cycle of glacia- 
 tion. 
 
 Continental and mountain glaciers contrasted. — The time 
 when the rock surface becomes submerged beneath the glacier 
 is, as regards both the surface forms and the erosive work, a criti- 
 cal point of much significance ; for the ice cap and larger conti- 
 nental glacier obviously protect the rock surface from the action 
 of those chemical and mechanical processes in which the atmosphere 
 enters as chief agent, and which are collectively known as weath- 
 ering processes. Until submergence is accomplished, larger or 
 smaller portions of the rock surface project either through or 
 between the ice masses and are, therefore, exposed to direct 
 attack by the weather (see below, p. 370). 
 
 Snow which falls in the mountains is not allowed to remain 
 long where it falls. By the first high wind it is swept off the 
 more elevated and exposed surfaces and collected under eddies in 
 any existing hollows, but especially those upon the lee slopes of 
 the range. 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 snows ; but with the initiation of gla- 
 ciation the inherited hollows are in most cases the unimportant 
 depressions at the heads of streams. Whatever they may be 
 and however formed, the snow first fills those hollows which are 
 sheltered from the wind, and as it accumulates and becomes 
 distributed as ice, assumes a surface of its own that is dependent 
 upon the form and the position of the basin which it occupies 
 (see Fig. 294). 
 
 When the quantity of accumulated snow is so great that all 
 hollows of the rock surface are filled, its own surface is no longer 
 
THE GLACIERS OF MOUNTAIN AND CONTINENT 267 
 
 controlled by retaining rock walls, and it now assumes a form 
 largely independent of the irregularities in the upland. Expe- 
 
 Fig. 294. — Section through a mountain glacier (in solid black), showing how its 
 surface is determined by the irregularities in the rock basement (after Hess) . 
 
 rience shows that this surface is approximately that of a flat dome 
 or shield, and as it covers all the upland, save where the ice thins 
 upon its margins, this type of glacier is called an ice cap (Fig. 
 295). All types of glacier in which rock projects above the 
 highest levels of the ice and snow are known as mountain glaciers. 
 
 2000- 
 ■1SC0 - 
 ■1000- 
 
 FiG. 295. — Profile across the largest of the Icelandic ice caps, with the vertical 
 scale greatly exaggerated (after Thoroddsen and Spethmann). 
 
 The flat domes of ice which mantle the continents of Green- 
 land and Antarctica, though resembling in form the smaller ice 
 cap, are yet because of their vast size so distinct from them, par- 
 ticularly in the manner of their nourishment, that they belong in 
 a separate class described as inland ice or continental glaciers. 
 Though they have some affinities with ice caps, they are most 
 sharply differentiated from all types of mountain glaciers. Of them 
 it is true that the lithosphere projects through them only in the 
 neighborhood of their margins (Fig. 296), whereas in the case of 
 
 ^^•N 
 
 Fig. 296. — Ideal section across a continental glacier, with the vertical scale and 
 the projecting rock masses of the marginal zone greatly magnified. 
 
268 EARTH FEATURES AND THEIR MEANING 
 
 mountain glaciers rock may project at any level but always above 
 the highest snow surface. Ice caps may be regarded as interme- 
 diate between the two main classes of mountain and continental 
 glaciers (Fig. 297) . Because of the large role which continental 
 
 Fig. 297. — View of the Eyriks-Jokull, aa ice-cap of Iceland (after Grossman). 
 
 glaciers have played in geological history, it is thought best to con- 
 sider them first, leaving for later discussion the no less mterest- 
 ing but less important mountain glaciers. 
 
 The nourishment of glaciers. — The life of a glacier is depend- 
 ent upon the continued deposition of snow in aggregate amount 
 in excess of that which is lost by melting or by other depleting 
 processes. Whenever, on the other hand, the waste exceeds the 
 precipitation, the glacier js in a receding condition and must 
 eventually disappear, if such conditions are sufficiently long con- 
 tinued. The source of the snow is the water of the ocean evapo- 
 rated into the atmosphere and transported over the land in the 
 form of clouds. 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 glacier. 
 
 The upper and lower cloud zones of the atmosphere. — Be- 
 fore we can comprehend the nature of the processes by which gla- 
 ciers are nourished, it will be necessary to review the results of 
 recent studies made upon the earth's atmospheric envelope. 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 layers. The layers thus 
 warmed being now lighter than before, they rise and are replaced 
 by colder air, which in its turn is warmed and likewise set in up- 
 ward motion. Such currents developed in the air by contact 
 with warmer solid bodies constitute the process known as con- 
 vection. 
 
THE GLACIERS OF MOUNTAIN AND CONTINENT 269 
 
 To a relatively small degree the atmosphere is heated by the 
 direct absorption of the sun's rays which pass through it. Since 
 air has weight, it compresses the lower layers near the earth, and 
 hence as we ascend from the earth's surface the air becomes con- 
 tinually lighter. Convection currents must, therefore, adjust 
 themselves by the air expanding as it rises. But expansion of a 
 gas always results in its cooling, as every one must have observed 
 
 KILOMETERS 
 
 CENTIGRADE 
 
 ■54 
 '55 1^ 
 
 ISOTHERMAL 
 o R 
 
 ADVECTIVE 
 
 ZONE 
 
 Ce/7/ng of iconvective zone 
 
 sea 
 
 Fig. 298. — The zones of the lower atmosphere as revealed by recent kite and 
 balloon explorations. 
 
 who has placed his finger in the air current which escapes from 
 the open valve of a warm rubber tire. Dry air is cooled a degree 
 Fahrenheit for every six hundred feet of ascent in the atmos- 
 phere. At a height of about seven miles above the earth's sur- 
 face all rising air currents have cooled to about 68° below the 
 zero of the Fahrenheit scale, and exploration with balloons has 
 shown that the currents rise no farther. At this level they 
 
270 EARTH FEATURES AND THEIR MEANING 
 
 move horizontally, just as rising vapor spreads out in a room be- 
 neath the ceiling. Above this level, as far as exploration has gone, 
 or to a height of more than twelve miles, the temperature remains 
 nearly constant, and this upper zone is, therefore, called the iso- 
 thermal or the advective zone — the uniform temperature zone 
 of the lower atmosphere. Beneath the convective ceiling the 
 process of convection is characteristic, and this zone is therefore' 
 described as the convective zone (Fig. 298). 
 
 A large part of the moisture which rises from the ocean's sur- 
 face is condensed to vapor before it has ascended three miles, 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 (see Frontispiece). This lower layer within 
 the convective zone is, therefore, a moist one overlaid by a rela- 
 tively drier middle layer of the convective zone. That mois- 
 ture which rises above the lower cloud layer is congealed by adia- 
 batic cooling to fine ice needles visible as the so-called cirrus 
 clouds which float as feathery fronds beneath the convective 
 ceiling (see frontispiece at right upper corner of picture). Thus 
 we have within the convective zone an upper layer more or less 
 charged with water in the form of ice needles. It is the clouds 
 of the lower zone whose moisture in the form of vapor supplies 
 the nourishment of mountain glaciers, and the high cirrus clouds 
 whose congealed moisture, after interesting transformations, is 
 responsible for the continued existence of continental glaciers. 
 
 As we are to see, there are other noteworthy differences be- 
 tween continental and mountain glaciers, in the manner of their 
 sculpture of the lithosphere, so that long after they have disap- 
 peared the characters of each are easily identified in their handi- 
 work. How the lower clouds are forced upward and so compelled 
 to give up their moisture to feed the mountain glaciers, and how 
 the upper clouds are pulled downward to nourish the glaciers of 
 continents, can be best understood after the characteristics of 
 each glacier class have been studied. 
 
CHAPTER XXI 
 
 THE CONTINENTAL GLACIERS OF POLAR REGIONS 
 
 The inland ice of Greenland. — In Greenland and in Antarc- 
 tica the land is almost or quite buried under a cover of snow and 
 ice — the so-called "inland ice" 
 — which always assumes the 
 surface of a very flat dome or 
 shield. In Greenland there is 
 found a marginal ribbon of 
 land generally from five to 
 twenty-five miles in width 
 (Fig. 299), but in Antarctica 
 all the land, with the excep- 
 tion of a few mountain peaks, 
 is inwrapped in a mantle of 
 ice which is also extended upon 
 the sea in a broad shelf of snow 
 and ice. Neither of these vast 
 glaciers has been explored ex- 
 cept in its marginal portion, 
 yet such is the symmetry of 
 the profiles along the routes 
 traversed, and such the flat- 
 ness and monotony of the snow 
 surface within the margins, 
 that there is little reason to 
 
 doubt that the profile made Fig. 299. — Map of Greenland showing the 
 along Nansen's route in south- ^^f °^ inland-ice and the routes of differ- 
 ^ ent explorers. 
 
 ern Greenland would, save only 
 
 for magnitude, fairly represent a section across the middle of the 
 
 continent (Fig. 300). 
 
 The mountain rampart and its portals. — As soon as we ex- 
 amine the coastal belt we observe that the " Great Ice " of 
 
 271 
 
272 EARTH FEATURES AND THEIR MEANING 
 
 Greenland is held in by a wall of mountains and so prevented from 
 spreading out to its natural surface in the marginal portions. 
 Through portals of the inclosing mountain ranges — the out- 
 lets — it sends out tongues of ice which in many respects resemble 
 certain types of mountain glaciers. 
 
 I ^i^heotf^x^ 
 
 ■^ ^* <^' 
 
 Fig. 300. — Profile in natural proportions across the southern end of the continental 
 glacier of Greenland, constructed upon an arc of the earth's surface and based 
 upon Nansen's profile corrected by Hess. The marginal portions of the profile 
 are represented below upon a magnified scale in order to bring out the characters 
 of the marginal slopes. 
 
 Such measurements as have been made upon the inland ice 
 of Greenland at points back from, but yet comparatively near to, 
 the outlets, show that it has here a surface rate of motion amount- 
 ing to less than an inch per day, and it is highly probable that at 
 moderate distances from the margin this amount diminishes to 
 zero. Upon the outlets, on the contrary, surface rates as high as 
 59 feet per day have been measured, and even 100 feet per day has 
 been reported. We are thus justified in saying that glacier flow 
 within the outlets is from 700 to 1000 times as great as it is upon 
 the near-by inland ice, and that the glacier is in a measure drained 
 through the portals of the inclosing ranges. Back from these 
 outlet streams of ice, or tongues, the surface of the inland ice is 
 depressed to form a dimple or " basin of exudation " as is the sur- 
 face of a reservoir above the raceway when the water is being rapidly 
 drawn away (Fig. 301). 
 
 Fissures in the ice, the so-called crevasses, are the recognized 
 marks of ice movement, and these are always concentrated at the 
 steep slopes of the ice surface in the neighborhood of its margins. 
 Upon the Greenland ice, crevasses are restricted in their distribu- 
 tion to a zone which extends from seven to twenty-five miles 
 within the ice border. 
 
 The marginal rock islands. — From its margin the ice surface 
 rises so steeply as to be climbed only with difficulty, but this 
 
Plate 13. 
 
 A. Precipitous front of the Bryant glacier outlet of the Greenland inland-ice (after 
 
 Chamberlin). 
 
 B. Lateral stream beside the Benedict glacier outlet, Greenland (after R. E. Peary). 
 
THE CONTINENTAL GLACIERS OF POLAR REGIONS 273 
 
 gradient steadily diminishes until at a distance of between seventy- 
 five and a hundred miles its slope is less than two degrees. Where 
 crossed by Nansen near latitude 64° N. the broad central area of 
 ice was so nearly level as to 
 appear to be a plain. T 
 
 As we pass across the irregu- 
 lar ice margin in the direction 
 of the interior, larger and larger 
 proportions of the land's sur- 
 face are submerged, until only 
 projecting peaks rise above 
 the ice as islands which are 
 described as nunataks (Fig. 
 302). 
 
 Though not a universal ob- 
 servation, 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 
 ice. For this reason nunataks 
 are often surrounded by a deep 
 trench due to a melting of the 
 snow. Such a depression in 
 the ice surface about the mar- 
 gin of a nunatak, from its re- 
 semblance to a trench about 
 an ancient castle, has been 
 designated a 7noat (Fig. 303). 
 For the same reason, the out- 
 let 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 
 (pi. 13B). 
 
 T 
 
 ice 
 
 land 
 
 Fig. 301. — Map of a glacier tongue, with 
 dimple showing above and due to in- 
 draught of the ice. Umanakf j ord, Green- 
 land (after von Drygalski). 
 
274 
 
 EARTH FEATURES AND THEIR MEANING 
 
 Tig. 302. — Edge of the Greenland inland ice, 
 showing the nunataks diminishing in size toward 
 the interior. The lines upon the ice are medial 
 moraines starting from nunataks (after Libbey). 
 
 Rock fragments which travel with the ice. — Rock surfaces 
 which are exposed to the atmosphere are in high latitudes broken 
 
 down through the freez- 
 ing of water within their 
 crevices. The frag- 
 ments resulting from 
 this rending process fall 
 upon the glacier surface 
 and are carried forward 
 as passengers in the di- 
 rection of the ice mar- 
 gin. They are either 
 visible as long and nar- 
 row ridges or trains fol- 
 lowing the directions of 
 the steepest slope (Fig. 
 302), 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 margin. These longitudinal trains of 
 rock fragments upon the glacier surface always have their starting 
 point at the lower margin of one of the nunataks, and are known 
 as medial moraines (Fig. 301, p. 273, and Fig. 302). Inside 
 the zone of nunataks the glacier surface is, however, clear of rock 
 debris except where dust has 
 been blown on by the wind, 
 and this extends for a few 
 miles only. The material of 
 the medial moraines is a col- 
 lection of angular blocks whose 
 surfaces are the result of frost 
 rending, for in their travel 
 above the ice they are sub- 
 jected, to no abrading pro- 
 cesses. 
 
 A contrasted type of surface 
 moraines upon the Greenland 
 glacier, instead of being par- 
 allel to the direction of ice movement, is directed transversely or 
 parallel to the margins. The materials of these moraines are 
 
 Fig. 303. — Moat surrounding a nunatak in 
 Victoria Land (after Scott). 
 
THE CONTINENTAL GLACIERS OF POLAR REGIONS 275 
 
 more rounded fragments of rock which have come up from the 
 bottom layers, and we shall again refer to the origin of such 
 moraines after the subglacial conditions have been considered. 
 
 The grinding mill beneath the ice. — If, now, we examine the 
 front of a glacier tongue which goes out from the inland ice, we 
 find that while the upper portion is white and mainly free from rock 
 debris (plate 13 A), the lower zone is of a dark color and crowded 
 with layers of pebbles and bowlders which have been planed, 
 polished, and scratched in a quite remarkable manner. The ice 
 front is itself subject to forward and retrograde migrations of short 
 period, but it is easily seen that in the main its larger movement 
 has been a retrograde one. The ground from which it has lately 
 withdrawn is generally a hard rock floor unweathered, but smooth, 
 polished, and scratched in the same manner as the bowlders which 
 are imbedded within the ice. It is perfectly apparent that the 
 latter have been derived from some portion of the rock basement 
 upon which the glacier still rests, and that floor and bowlders have 
 alike been ground smooth by mutual contact under pressure. 
 
 This erosion beneath the ice is accomplished by two processes; 
 namely, -plucking and abrasion. Wherever the rock over which 
 the glacier moves has stood up in projecting masses and is riven 
 by fissure planes of any kind, the ice has found it easy to remove 
 it in larger or smaller fragments by a quarrying process described 
 as plucking. The rock may be said to be torn away in blocks which 
 are largely bounded by the preexisting fissure planes. Over rela- 
 tively even surfaces plucking has little importance, but where 
 there are noteworthy inequalities of surface upon the glacier bed, 
 those sides which are away from the oncoming ice {lee side) are 
 degraded by plucking in such a manner as sometimes to leave 
 steep and ragged fracture surfaces. The tools of the ice thus ac- 
 quired in the process of plucking are quickly frozen into the lowest 
 ice layers, and being now dragged along the floor they abrade in 
 the same manner as does a rasp or file. These tools of the ice are 
 themselves worn away in the process and are thus given their 
 characteristic shapes. Just as the lapidary grinds the surface of 
 a jewel into facets by imbedding the gem in a matrix, first in one 
 and then in another position, each time wearing down the pro- 
 jecting irregularities through contact with the abrading surface ; 
 so in like manner the rock fragment is held fast at the bottom of 
 
276 
 
 EARTH FEATURES AND THEIR MEANING 
 
 -\ 
 
 -*V 
 
 ■\ 
 
 the glacier until " soled " or " shod," first upon one side and then 
 upon another. Accidental contact with some obstruction upon 
 the floor may suffice to turn the fragment and so expose a new sur- 
 face to wear upon the abrading floor. Minor obstructions com- 
 ing in contact with one side of the fragment only, may turn it in 
 its own plane without overturning. Evidence of such interrup- 
 tions can be later read in the different directions of striae upon 
 the same facet (plate 17 A). 
 
 The floor beneath the glacier is reduced by the abrading process 
 to a more or less smooth and generally flattened or rounded sur- 
 face — the so-called glacier 'pavement (Fig. 304) . To accomplish 
 
 this all former mantle rock 
 
 due to weathering processes 
 must first be cleared away, 
 and the firm unaltered rock 
 beneath is wherever suscep- 
 tible of it given a smooth 
 polish although locally 
 scored and scratched by the 
 grinding bowlders. The 
 earlier projections of the 
 surface of the floor, if not 
 entirely planed away, are 
 at least transformed into 
 rounded shoulders of rock, 
 which from their resem- 
 blance to closely crowded backs in a flock of sheep have been 
 called "sheep backs" or "roches moutonnees." 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 curves, generally of large radius. 
 
 The lifting of the grinding tools and their incorporation 
 within the ice. — Wherever the ice is locally held in check by the 
 projecting nunataks, relief is found between such obstructions, 
 and there the flow of the ice has a correspondingly increased ve- 
 locity (Fig. 305 6). If the obstructions are not of large dimensions, 
 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 nunataks. The locally rapid flow 
 
 Fig. 304. — A glacier pavement of Permo-Car- 
 boniferous age in South Africa. The striae 
 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 (after Davis). 
 
THE CONTINENTAL GLACIERS OF POLAR REGIONS 277 
 
 of the ice is, therefore, restricted to a relatively short distance, the 
 passageway between the nunataks, 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 outlet. As is well known, there is under these 
 conditions a prodigious scour upon the bottom which tends to dig 
 a pit just above and below the dam — a scaye colk — and carry 
 the materials up to the surface below the pit. 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 (Fig. 305 a). In 
 
 L. 
 
 Scilel :6760(l-.8O- 
 
 a 
 
 Fig. 305. — a, Map showing pit excavated by the current below the opening in a 
 dam. b, Nunataks and surface moraines on the Greenland ice. Dalager's 
 Nunataks (after Suess). 
 
 the case of ice, material from the bottom may by the upward cur- 
 rent 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 direc- 
 tion of ice movement (Fig. 305 5). 
 
 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 ice. Rock debris thus 
 incorporated is described as englacial drift. In the case of Green- 
 land glaciers this material seems at the ice front to be largely re- 
 stricted to the lower 100 feet (plate 13 A). 
 
 Near the front of the inland ice the increased slope of the upper 
 surface greatly increases the flow of the upper ice layers in com- 
 
278 EARTH FEATURES AND THEIR MEANING 
 
 parison with those nearer the bottom, so that the upper layers 
 override the lower as they would an obstruction. The englacial 
 drift is either for this reason or because of rock obstructions 
 brought to the surface, where it yields parallel ridges corresponding 
 in direction to the glacier margin. Such transverse surface mo- 
 raines are thus in many respects analogous to those which ap- 
 pear about the lower margins of scape colks. In contrast to the 
 longitudinal or medial surface moraines the materials of the trans- 
 verse moraines are more faceted and rounded — they have been 
 abraded upon the glacier pavement. 
 
 Melting upon the glacier margins in Greenland. — During the 
 short but warm summer season, the margins of the Greenland ice 
 are subject to considerable losses through surface melting. When 
 the uppermost ice layer has attained a temperature of 32° Fahren- 
 heit, melting begins and moves rapidly inward from the glacier 
 margin. In late spring the surface of the outer marginal zone is 
 saturated with water, and this zone of slush advances inward T\dth 
 the season, 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 slopes, crevasses, and nunataks. 
 Upon the ice within this zone are found streams large enough to be 
 designated as rivers and these are connected with pools, lakes, and 
 morasses. The dirt and rock fragments imbedded in the ice are 
 melted out in the lowering of the surface, so that late in the season 
 the ice presents a most dirty aspect. At the front of the great 
 mountain glaciers of Alaska, 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 beneath. 
 
 In addition to the visible streams upon the surface of the Green- 
 land ice, there are others which flow beneath and can be heard by 
 putting the ear to the surface. All surface streams eventually 
 encounter the marginal crevasses and plunge down in foaming 
 cascades, producing the well known " glacier wells " or " glacier 
 mills." The progress of the water is now throughout in tunnels 
 within the ice until it again makes its appearance at the glacier 
 margin. 
 
 The marginal moraines. — Study of both the Greenland and 
 Antarctic glaciers has shown that if we disregard the smaller and 
 short-period migrations of the ice front, the general later move- 
 
THE CONTINENTAL GLACIERS OF POLAR REGIONS 279 
 
 ment has been a retrograde one — we live in a receding hemicycle 
 of glaciation. The earher Greenland glacier has now receded so 
 as to expose large areas of 
 the former glacier pave- 
 ment. In places this 
 pavement is largely bare, 
 indicating a relatively rapid 
 retirement of the ice front, 
 but at all points at which 
 the ice margin was halted 
 there is now found a ridge 
 of unassorted rock mate- 
 rials which were dropped 
 by the ice as it melted (Fig. 
 306). Such ridges, com- 
 posed of the unassorted 
 materials described as till, 
 
 ^^^S, 
 
 
 Fig. 306. — Marginal moraine now forming at 
 the edge of Greenland inland ice, showing a 
 smooth rock pavement outside it. A small 
 lake with a partial covering of lake ice occu- 
 pies a hollow of this pavement (after von 
 Drygalski) . 
 
 come to have a festooned arrangement largely concentric to the ice 
 margin, and are the marginal or terminal moraines (see Fig. 336, 
 p. 312). Marginal moraines, if of large dimensions, usually have a 
 hummocky surface, and are apt to be composed of rock fragments 
 of a wide range of size from rock flour (clay) to large bowlders 
 (plate 17 A), which may represent many types since they have 
 
 been plucked by the glacier 
 or gathered in at its surface 
 from many widely separated 
 localities. 
 
 As the glacier front retires 
 from the moraine which it 
 has built up, the water which 
 emerges from beneath the 
 ice is impounded behind the 
 new dam so as to form a 
 lake of crescentic outline 
 (Fig. 307). Such lakes are 
 particularly short-lived, 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 materials, thus draining 
 
 Fig. 307. — Small lake impounded between 
 the ice front and a moraine which it has 
 recently buUt. Greenland (after von Dry- 
 galski) . 
 
280 
 
 EARTH FEATURES AND THEIR MEANING 
 
 the lake (Fig. 308). Thereafter, the escaping water flows in a 
 braided stream across the late lake bottom and thence at the 
 bottom of the gorge through the moraine. 
 
 . .•.::^^. 
 
 Pig. 308. — View of a drained lake bottom between the nioraine-covered ice front 
 in the foreground and an abandoned marginal moraine in the middle distance. The 
 water flows from the ice front in a braided stream and passes out through the mo- 
 raine in a narrow gorge. Variegated glacier, Alaska (after Lawrence Martin). 
 
 The outwash plain or apron. — The water which descends from 
 the glacier surface in the glacier wells or mills, eventually arrives 
 at the bottom, where it follows a sinuous course within a tunnel 
 melted out in the ice. Much of this water may issue at the ice 
 front beneath the coarse rock materials which are found there, 
 and so be discovered with the ear rather than by the eye. The 
 water within the tunnels not flowing with a free surface but being 
 confined as though it were in a pipe, may, however, reach the 
 glacier margin under a hydrostatic pressure sufficient to carry it 
 up rising grades. Inasmuch as it is heavily charged with rock 
 debris and is suddenly checked upon arriving at the front it de- 
 posits its burden about the ice margin so as to build up plains of 
 assorted sands and gravels, and over this surface it flows in ever 
 shifting serpentine channels of braided type (Fig. 308). Such 
 plains of glacier outwash are described as outwash plains or out- 
 wash aprons. 
 
 Rising as it does under hydrostatic pressure the water issuing 
 at the glacier front may find its way upward in some of the ere- 
 
THE CONTINENTAL GLACIERS OF POLAR REGIONS 281 
 
 vasses and so emerge at a level considerably above the glacial 
 floor. 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 
 
 
 Fig. 309. — Diagrams to show the manner of formation and the structure of an 
 outwash plain, and the position of the fosse between this and the moraine. 
 
 sight. When now the ice front begins a rapid retirement, a de- 
 pression or fosse (Fig. 309 and Fig. 339, p. 314) is left behind the 
 outwash plain and in front of the moraine which is built up at the 
 next halting place. 
 
 The continental glacier of Antarctica. — In Victoria Land, upon 
 the continent of Antarctica, so far as exploration has yet gone, 
 the continental glacier is held back by a rampart of mountains, 
 as has been shown to be true of the inland ice of Greenland. The 
 same flat dome or shield has likewise been found to characterize 
 its upper surface (Fig. 310). 
 
 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 nourish- 
 ment of the southern glacier measured by the land area which it 
 has submerged. There is here no marginal land ribbon as in Green- 
 land, but the glacier covers all the land and is, moreover, extended 
 upon the sea as a broad floating terrace — the shelf ice (Fig. 311). 
 This barrier at its margin puts a bar to all further navigation, 
 rising as it does in some cases 280 feet above the sea and descend- 
 ing to even greater depths below (plate 15 B). 
 
 In that portion of Antarctica which was explored by the German 
 expedition, the inland ice is not as in Victoria Land restrained 
 within walls of rock, but is spread out upon the continent so as to 
 assume its natural ice slopes, which are therefore much flatter 
 
282 
 
 EARTH FEATURES AND THEIR MEANING 
 
 than those examined in Greenland and Victoria Land. Here in 
 Kaiser Wilhelm Land the ice rises at its sea margin in a chff which 
 is from 130 to 165 feet in height, then upon a fairly steeply curving 
 
 c^*^ 
 
 ^"^"' 
 
 ^^''.^y- 
 
 ^ 
 
 X 
 
 w 
 
 ^"^ Ross Barrier 
 
 
 Fig. 310. — Map showing the inland ice of Victoria Land bordered by the shelf 
 ice of the Great Ross Barrier. The arrows show the direction of the prevailing 
 winds (based on maps by Scott and Shackleton). 
 
 slope to an elevation of perhaps a thousand feet. Here the grades 
 have become relatively level, and on ever flatter slopes the surface 
 appears to continue into the distant interior (plate 14). Near 
 the ice margin numerous fissures betray a motion within the mass 
 
Plate 14. 
 
THE CONTINENTAL GLACIERS OP POLAR REGIONS 283 
 
 which exact measurements indicate to be but one foot per day, and 
 at a distance of a mile and a quarter from the margin even this 
 sHght value has diminished by fully one eighth. It can hardly 
 be doubted that at moderate distances only within the ice margin^ 
 the glacier is practically without motion. 
 
 Rain or general melting conditions being unknown in Antarctica, 
 a striking contrast is offered to the marginal zone of the Greenland 
 continent. This is to a large extent explained by the existence 
 
 Furtheri 'south 
 
 79" Tfl" 
 
 ^icai Scate cf Fesf 
 
 b 
 
 Ut72» fig's Long. 155* t6' 
 
 Sou^'h Magnetic 
 
 Fig. 311. 
 
 ■ Sections across the inland ice of Victoria Land, Antarctica, witli the 
 shelf ice in front (after Shackleton). 
 
 upon the northern land mass of a coast-land ribbon which becomes 
 quickly heated in the sun's rays, 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 hot. 
 About Independence Bay in latitude 82° N. and near the north- 
 ernmost extremity of Greenland, Peary descended from the in- 
 land 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 flowers. 
 
 Nourishment of continental glaciers. — Explorations upon and 
 about the glaciers of Greenland and Antarctica have shown tha,t 
 the circulation of air above these vast ice shields conforms to a 
 quite simple and symmetrical model subject to spasmodic pulsa- 
 
284 EARTH FEATURES AND THEIR MEANING 
 
 tions of a very pronounced type. 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 globe. 
 (See Fig. 291, p. 263). Both the domed surface and the low tem- 
 perature of the glacier are essential to the continuation of this 
 pulsating movement within the atmosphere (Fig. 312). The air 
 layer in contact with the ice is during a period of calm cooled, con- 
 tracted, and rendered heavier, so that it begins to slide downward 
 and outward upon the domed surface in all directions. The ex- 
 treme flatness of the greater portion of the glacier surface — a 
 
 G- U AC I A L .••■ ^.•••• 
 
 A N T I C Y C L O.N E 
 
 CONTINENTAL OI.AOIER 
 
 Fig. 312. — Diagram to show the nature of the fixed glacial anticyclone above 
 continental glaciers and the process by which their surface is shaped. 
 
 fraction only of one degree — makes the engine extremely slow 
 in starting, but like all bodies which slide upon inclined planes, 
 the velocity of its movement is rapidly accelerated, until a blizzard 
 is developed whose vigor is unsurpassed by any elsewhere experi- 
 enced. 
 
 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 dome. This downward vortex, fed as it is by inward-blow- 
 ing, high-level currents, and drained by outwardly directed sur- 
 face currents, is what is known as an anticyclone, here fixed in 
 position by the central embossment of the dome. 
 
 The air which descends in the central column is warmed by 
 compression, or adiabatically, just as air is v»rarmed which is forced 
 into a rubber tire by the use of a pump. The moisture congealed 
 in the cirrus clouds floating in the uppermost layer of the convec- 
 tive zone, is carried down in this vortex and first melted and in 
 turn evaporated, due to the adiabatic effect. This fusion and 
 evaporation of the ice by its transformation of latent, to sensible, 
 heat, in a measure counteracts, and so retards, the adiabatic ele- 
 
THE CONTINENTAL GLACIERS OF POLAR REGIONS 285 
 
 vation of temperature within the column. Eventually the warm 
 air now charged with water vapor reaches the ice surface, is at 
 once chilled, and its burden of moisture precipitated in the form of 
 fine snow needles, the so-called '' frost snow," which in accompani- 
 ment to the sudden elevation of temperature is precipitated at the 
 termination of a blizzard. 
 
 The warming of the air has, however, had the effect of damping 
 as it were, the engine .stroke, and, as the process is continued, to 
 start a reverse or upward current within the chimney of the anti- 
 cyclone. The blizzard is thus suddenly ended in a precipitation 
 of the snow, which by changing the latent heat of condensation 
 to sensible heat tends to increase this counter current. 
 
 The glacier broom. — During the calm which succeeds to the 
 blizzard, heat is once more abstracted from the surface air layer, 
 and a new outwardly directed engine stroke is begun. The tem- 
 pest which later develops acts as a gigantic centrifugal broom which 
 
 -"i;^ 
 
 Fig. 313. — Snow deltas about the margins of the Fan glacier outlet of Greenland 
 
 (after Chamberlin) . 
 
 sweeps out to the margins of the glacier all portions of the latest 
 snowfall which have not become firmly attached to the ice surface. 
 The sweepings piled up about the margin of continental glaciers 
 have been described as fringing glaciers, or the glacial fringe. The 
 northern coast of Greenland and Grant Land are bordered by a 
 fringe of this nature (plate 14 A, and Fig. 315, p. 288). It is by the 
 
286 EARTH FEATURES AND THEIR MEANING 
 
 operation of the glacier broom that the inland ice is given its charac- 
 teristic shield-Hke shape (Fig. 312). 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 (Fig. 313). 
 Obviously because of the presence of the vigorous anticyclone, no 
 snows such as nourish mountain glaciers can be precipitated upon 
 continental glaciers except within a narrow marginal zone, and, 
 as shown by Nansen rock dust from the coastland ribbon and 
 
 from the nunataks 
 .■.■;:;■;•.■:. 'v^^^^^ .' of Greenland, is car- 
 
 .... ...V. :■: ■.>.;.•:.• .■ ried by a few miles 
 
 inside the western 
 margin, and not 
 at all within the 
 eastern. 
 ''^^»H«™ii?^_ Field ^and pack 
 
 ice. — Within polar 
 regions the surface 
 ~ "T~ of the sea freezes 
 
 Fig. 314. — Sea ice of the Arctic region in lat. 80° 5' N. . 
 
 and long. 2° 52' E. (after Due d'Orleans). during the long 
 
 winter season, the 
 product being known as sea-ice or field-ice (Fig. 314). This ice 
 cover may reach a thickness by direct freezing of eight or more 
 feet, and by breaking up and being crowded above and below 
 neighboring fragments may increase to a considerably greater 
 thickness. Ice thus crowded together and more or less crushed is 
 described as pack ice or the pack. 
 
 The pack does not remain stationary but is continually drifting 
 with the wind and tide, first in one direction and then in another, 
 but with a general drift in the direction of the prevailing winds. 
 Because of the vast dimensions of the pack, the winds over widely 
 separated parts may be contrary in direction, and hence when cur- 
 rents blow toward each other or when the ice is forced against a 
 land area, it is locally crushed under mighty pressures and forced 
 up into lines of hummocks — the so-called pressure ridges. At 
 other times, when the winds of widely separated areas blow away 
 from each other, the pack is parted, with the formation of lanes or 
 leads of open water. 
 
 If seen in bird's-eye view the lines of hummocks would accord- 
 
THE CONTINENTAL GLx\CIERS OF POLAR REGIONS 287 
 
 ing to Nansen be arranged like the meshes of a net having roughly 
 squared angles and reaching to heights of 15 to 25, rarely 30, feet 
 above the general surface of the pack. The ice within each mesh of 
 the network is a floe, which at the times of pressure is ground against 
 its neighbors and variously shifted in position. At the margin of 
 the pack these floes become separated and float toward lower lati- 
 tudes until they are melted. 
 
 The drift of the pack. — The discovery of the drift in the Arctic 
 pack is a romantic chapter in the history of polar exploration, and 
 has furnished an example of faith in scientific reasoning and judg- 
 ment which may well be compared with that of Columbus. The 
 great figure in this later discovery is the Norwegian explorer 
 Fridtjof Nansen, and to the final achievement the ill-fated Jean- 
 nette expedition contributed an important part. 
 
 The Jeannette carrying the American exploring expedition 
 was in 1879 caught in the pack to the northward of Wrangel Island 
 (Fig. 315), and two years later was crushed by the ice and sunk to 
 the northward of the New Siberian Islands. In 1884 various 
 articles, including a list of stores in the handwriting of the com- 
 mander of the Jeannette, were picked up at Julianehaab near the 
 southern extremity of Greenland but upon the western side of 
 Cape Farewell. Nansen, having carefully verified the facts, 
 concluded that the recovered articles could have found their way 
 to Julianehaab only by drifting in the pack across the polar sea, 
 and that at the longest only five years had been consumed in the 
 transit. 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 north- 
 ward upon the west coast. It was clear that if they had come 
 through Smith Sound they would inevitably have been found 
 upon the other shore of Baffin Bay. In confirmation of this view 
 there was found at Godthaab, a short distance to the northward 
 of Julianehaab (Fig. 315), an ornamented Alaskan " throwing 
 stick " which probably came by the same route. Moreover, 
 large quantities of driftwood reach the shores of Greenland which 
 have clearly come from the Siberian coast, since the Siberian 
 larch has furnished the larger quantity. 
 
 Pinning his faith to these indubitable facts, Nansen built the 
 Fram in such a manner as to resist and elude the enormous pres- 
 
288 EARTH FEATURES AND THEIR MEANING 
 
 Fig. 315. — Map of the north polar regions, showing the area of drift ice and the 
 tracks of the Jeannette and the Fram (compiled from various maps) . 
 
THE CONTINENTAL GLACIERS OF POLAR REGIONS 289 
 
 sures of the ice pack, stocked her with provisions sufficient for 
 five years, and by allowing the vessel to be frozen into the pack 
 north of the New Siberian Islands, he consigned himself and 
 his companions to the mercy of the elements. The world knows 
 the result as one of the most remarkable achievements in 
 the long history of polar exploration. The track of the Fram, 
 charted in Fig. 315, considered in connection with that of the 
 Jeannette, shows that the Arctic pack drifts from Bering Sea west- 
 ward until near the northeastern coast of Greenland. 
 
 Special casks were for experimental purposes fastened in the 
 ice to the north of Behring Strait by Melville and Bryant, and two 
 of these were afterwards recovered, the one near the North Cape 
 in northern Norway, and the other in northeastern Iceland (see 
 map, Fig. 315). Peary's trips northward in 1906 and 1909 from 
 the vicinity of Smith Sound have indicated that between the Pole 
 and the shores of Greenland and Grant Land the drift is through- 
 out to the eastward, corresponding to the westerly wind. Upon 
 this border the great area of Arctic drift ice is in contact with 
 great continental glaciers bordered by a glacier fringe. Admiral 
 Peary has shown that instead of consisting of frozen sea ice, the 
 pack is here made up of great floes from 20 to 100 feet in thickness 
 and that these have been derived from the glacier fringe. 
 
 Whenever the blizzards blow off the inland ice from the south, 
 leads are opened at the margin of the fringe and may carry strips 
 from the latter northward across the lead. With favorable con- 
 ditions 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 position. A continuance of this process 
 may have resulted in the heavy floe ice to the northward of Green- 
 land, which, acting as an obstruction, may have forced the thinner 
 drift ice to keep on the European side of the Arctic pack. 
 
 About the Antarctic continent there is a broad girdle of pack 
 ice which, while more indolent in its movements than the Arctic 
 pack, has been shown by the expeditions of the Belgica and the 
 Pourquoi-Pas to possess the same kind of shifting movements. 
 In the southern spring this pack floats northward and is to a large 
 extent broken up and melted on reaching lower latitudes. 
 
 The Antarctic shelf ice. — It has been already pointed out 
 that the inland ice of Antarctica is in part at least surrounded by 
 
290 
 
 EARTH FEATURES AND THEIR MEANING 
 
 a thick snow and ice terrace floating upon the sea and rising to 
 heights of more than 150 feet above it (plate 15 Band Fig. 316). 
 The visible portions of this shelf-ice are of stratified compact 
 
 Fig. 316. — The shelf ice of Coats Land with the surrounding pack ice showing 
 in the foreground (after Bruce). 
 
 snow, and the areas which have thus far been studied are found 
 in bays from which dislodgment is less easily effected. The origin 
 of the shelf ice is believed to be a sea-ice which because not easily 
 detached at the time of the spring " break-up " is thickened in 
 succeeding seasons chiefly by the deposition of precipitated and 
 
 drifted snow upon its 
 surface, so that it is 
 bowed down under 
 the weight and sunk 
 to greater and greater 
 depths in the water. 
 To some extent, also, 
 it is fed upon its inner 
 margin by overflow 
 of glacici- ice from 
 the inland ice masses. 
 Icebergs and snowbergs and the manner of their birth. — Green- 
 land reveals in the character of its valleys the marks of a large 
 subsidence of the continent — the serpentine inlets or fjords by 
 
 Crm-< 
 
 Fig. 317. — Tidewater cliff at the front of a glacier 
 tongue from which icebergs are born. 
 
Plate 15. 
 
 'f 4 
 
 
 A. An Antarctic ice foot with boat party landing (after R. F. Scott) 
 
 B. A near view of the front of the Great Ross Barrier, Antarctica (after R. F. Scott). 
 
THE CONTINENTAL GLACIERS OF POLAR REGIONS 291 
 
 which its coast is so deeply indented. Into the heads of these fjords 
 the tongues from the inland ice descend generally to the sea level 
 and below. The glacier ice is thus directly attacked by the waves 
 as well as melted in the water, so that it terminates in the fjords 
 in great cliffs of ice (Fig. 317). It is also believed to extend 
 beneath the water surface as 
 a long toe resting upon the 
 bottom (Fig. 319). 
 
 The exposed cliff is notched 
 and undercut by the waves in 
 the same manner as a rock cliff, 
 and the upper portions override 
 the lower so that at frequent in- 
 tervals small masses of ice from 
 this front separate on crevasses, 
 water with picturesque splashes. 
 
 Fig. 318. — A Greenlandic iceberg after a 
 long journey in warm latitudes. 
 
 and toppling over, fall into the 
 Such small bergs, whose birth 
 may be often seen at the cliff front of both the Greenland and 
 Alaskan glaciers, have little in common with those great floating 
 islands of ice that are drifted by the winds until, wasted to a frac- 
 tion only of their former proportions, they reach the lanes of trans- 
 atlantic travel and become a serious menace to navigation (Fig. 318). 
 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 fjord, or else they separate bodily from the cliff 
 
 Fig. 319. 
 
 ■ Diagram showing one way in which northern icebergs may be born 
 from the glacier tongue (after Russell). 
 
 itself, apparently where it reaches water sufficiently deep to float it. 
 In either case the buoyancy of the sea water plays a large role in its 
 separation. 
 
 If derived from the submerged glacier toe (Fig. 319), a loud' noise 
 is heard before any change is visible, and an instant later the great 
 
292 
 
 EARTH FEATURES AND THEIR MEANING 
 
 mass of ice rises out of the water some distance away from the 
 cliff, 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 blue. The commotion produced in the fjord is 
 prodigious, and a vessel in close proximity is placed in jeopardy. 
 
 Even larger bergs are sometimes seen to separate from the ice 
 cliff, in this case an instant before or simultaneously, with a loud 
 report, but such bergs float away with comparatively little com- 
 motion in the water. 
 
 The icebergs of the south polar region are usually built upon a 
 far grander scale than those of the Arctic regions, and are, further, 
 both distinctly tabular in form and bounded by rectangular out- 
 lines (Fig. 321). Whereas the large bergs of Greenlandic origin 
 are of ice and blue in color, the tabular bergs of Antarctica might 
 better be described as snowbergs, since they are of a blinding white- 
 
 FiG. 320. — A northern iceberg surrounded by sea ice. 
 
 ness and their visible portions are either compacted snow or alter- 
 nating thick layers of compact snow and thin ribbons of blue ice, 
 the latter thicker and more abundant toward the base. All such 
 bergs have been derived from the shelf ice and not from the inland 
 ice itself. 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 sea. 
 
THE CONTINENTAL GLACIERS OF POLAR REGIONS 293 
 
 In both the northern and southern hemispheres those bergs 
 which have floated into lower latitudes have suffered profound 
 transformations. Their exposed surfaces have been melted in the 
 sun, washed by the rain, and battered by the waves, so that they 
 lose their relatively simple forms but acquire rounded surfaces in 
 place of the early angular ones (Fig. 318, p. 291). Sir John Murray, 
 who had such extended opportunities of studying the southern ice- 
 
 FiG. 321 . — Tabular Antarctic iceberg separating from the shelf ice (after Shackleton) . 
 
 bergs from the deck of the Challenger, has thus described their 
 beauties : 
 
 "Waves dash against the vertical faces of the floating ice island as 
 against a rocky shore, so that at the sea level they are first cut into ledges 
 and gullies, and then into caves and caverns of the most heavenly blue, 
 from out of which there comes the resounding roar of the ocean, 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 entrances. As 
 these ice islands are slowly drifted by wind and current to the north, they 
 tilt, turn and sometimes capsize, and then submerged prongs and spits are 
 thrown high into the air, producing irregular pinnacled bergs higher, pos- 
 sibly, than the original table-shaped mass." 
 
 Reading References for Chapters XX and XXI 
 General : — 
 I. C. Russell. Glaciers of North America. Ginn, Boston, 1897, pp. 
 
 210, pis. 22. 
 Chamberlin and Salisbury. Geology, vol. 1, pp. 232-308. 
 
294 EARTH FEATURES AND THEIR MEANING 
 
 H. Hess. Die Gletscher, Braunseh.weig, 1904, pp. 426 (illustrated). 
 William H. Hobbs. Characteristics of Existing Glaciers. Macmillan, 
 1911, pp. 301, pis. 34. 
 
 Special districts of mountain glaciers : — 
 James D. Forbes. Travels Through the Alps of Savoy and other Parts 
 
 of the Pennine Chain with Observations on the Phenomena of Glaciers. 
 
 Edinburgh, 1845, pp. 456, pis. 9, maps 2. 
 A. Penck, E. Brtjckner, et L. du Pasquier. Le systeme glaciare des 
 
 alpes, etc., Bull. Soe. Sc. Nat. Neuchatel, vol. 22, 1894, pp. 86. 
 E. RicHTER. Die Gletscher der Ostalpen. Stuttgart, 1888, pp. 306, 
 
 7 maps. 
 James D. Forbes. Norway and Its Glaciers, etc. Edinburgh, 1853, pp. 
 
 349, pis. 10, map. 
 I. C. Russell. Existing Glaciers of the United States, 5th Ann. Rept. 
 
 U.S. Geol. Surv., 1885, pp. 307-355, pis. 32-55; Glaciers of Mt. 
 
 Ranier, 18th Ann. Rept. U. S. Geol. Surv., 1898, pp. 349-423, pis. 
 
 65-82. 
 W. H. Sherzer. Glaciers of the Canadian Rockies and Selkirks, Smith. 
 
 Cont. to Knowl. No. 1692, Washington, 1907, pp. 135, pis. 42. 
 H. F. Reid. Studies of Muir Glacier, Alaska, Nat. Geogr. Mag., vol. 4, 
 
 1892, pp. 19-84, pis. 1-16. 
 I. C. Russell. Malaspina Glacier, Jour. Geol., vol. 1, 1893, pp. 219- 
 
 245. 
 G. K. Gilbert. Harriman Alaska Expedition, vol. 3, Glaciers, 1904, 
 
 pp. 231, pis. 37. 
 W. M. Conway. Climbing and Exploration in the Karakoram Hima- 
 layas, Maps and Scientific Reports, 1894, map sheets I-II. 
 Fanny Bullock Workman and William Hunter Workman. The His- 
 
 par Glacier, Geogr. Jour., vol. 35, 1910, pp. 105-132, 7 pis. and map. 
 
 The cycle of glaeiation : — - 
 William H. Hobbs. The Cycle of Mountain Glaeiation, Geogr. Jour., 
 vol. 36, 1910, pp. 146-163, 268-284. 
 
 Upper and lower cloud zones of the atmosphere : — 
 R. Assmann, a. Berson, and H. Gross. Wissenschaftliche Luftfahrten 
 
 ausgefiihrt vom deutschen Verein zur Forderung der Luftsehiffahi't 
 
 in Berlin, 1899-1900, 3 vols. 
 E. Gold and W. A. Harwood. The Present State of our Knowledge of 
 
 the Upper Atmosphere as Obtained by the Use of Kites, Balloons, 
 
 and Pilot-ballons, Rept. Brit. Assoc. Adv. Sci., 1909, pp. 1-55. 
 W. H. Moore. Descriptive Meteorology, Appleton, New York, 1910, 
 
 pp. 95-136. 
 William H. Hobbs. The Pleistocene Glaeiation of North America 
 
 Viewed in the Light of our Knowledge of Existing Continental 
 
 Glaciers, Bull. Am. Geogr. Soc, vol. 42, 1911, pp. 647-650. 
 
THE CONTINENTAL GLACIERS OF POLAR REGIONS 295 
 
 The continental glacier of Greenland : — 
 
 F. Nansen. The First Crossing of Greenland, 2 vols, Longmans, Lon- 
 don, 1890 (the scientific results are contained in an appendix to 
 volume 2, pp. 443-497). 
 
 R. E. Peary. A Reconnaissance of the Greenland Inland Ice, Jour. Am. 
 Geogr. Soc, vol. 19, 1887, pp. 261-289 ; Journeys in North Green- 
 land, Geogr. Jour., vol. 11, 1898, pp. 213-240. 
 
 T. C. Chamberlin. Glacier Studies in Greenland, Jour. Geol., vol. 2, 
 
 1894, pp. 649-668, 768-788, vol. 3, pp. 61-69, 198-218, 469-480, 565- 
 582, 668-681, 833-843, vol. 4, pp. 582-592, 769-810, vol. 5, pp. 229- 
 245; Recent glacial studies in Greenland (Presidential address). 
 Bull. Geol. Soc. Am., vol. 6, 1895, pp. 199-220, pis. 3-10. 
 
 R. S. Tarr. The Margin of the Cornell Glacier, Am. Geol., vol. 20, 1897, 
 
 pp. 139-156, pis. 6-12. 
 R. D. Salisbury. The Greenland Expedition of 1895, Jour. Geol., vol. 3, 
 
 1895, pp. 875-902. 
 
 E. V. Drygalski. Gronland Expedition der Gesellschaft fiir Erdkunde zu 
 Berhn 1891-1893, Berlin, 1897, 2 vols., pp. 551 and 571, pis. 53, 
 maps 10. 
 
 William H. Hobbs. Characteristics of the Inland Ice of the Arctic 
 Regions, Proe. Am. Phil. Soc, vol. 49, 1910, pp. 57-129, pis. 26-30. 
 
 The Antarctic continental glacier : — 
 
 R. F. Scott. The Voyage of the Discovery. London, 2 vols., 1905. 
 
 E. H. Shackleton. The Heart of the Antarctic. London, 2 vols., 1910. 
 
 E. VON Drygalski. Zum Kontinent des eisigen Siidens, Deutsche Siid- 
 polar-Expedition, Fahrten und Forschungen des "Gauss," 1901-1903, 
 Berlin, 1904, pp. 668, pis. 21. 
 
 Otto Nordenseiold and J. S. Andersson. Antarctica or Two Years 
 Amongst the Ice of the South Pole. London, 1905, pp. 608, illus- 
 trated. 
 
 E. Philippi. Ueber die fiinf Landeis-Expeditionen, etc., Zeit. f. Glet- 
 scherk., vol. 2, 1907, pp. 1-21. 
 
 Nourishment of continental glaciers : — 
 William H. Hobbs. Characteristics of the Inland Ice of the Arctic 
 Regions, Proc. Am. Phil. Soc, vol. 49, 1910, pp. 96-110; The Ice 
 Masses on and about the Antarctic Continent, Zeit. f. Gletseherk., 
 vol. 5, 1910, pp. 107-120 ; Characteristics of Existing Glaciers. New 
 York, 1911, pp. 143-161, 261-289. Pleistocene Glaeiation of North 
 America Viewed in the Light of our Knowledge of Existing Con- 
 tinental Glaciers, Bull. Am. Geogr. Soc, vol. 43, 1911, pp. 641-659. 
 
 Field and pack ice : — 
 Emma de Long. The Voyage of the Jeannette, the ship and ice joui-nals 
 of George W. de Long, etc Berlin, 1884, 2 vols., chart in back of 
 vol. 1. 
 
296 EARTH FEATURES AND THEIR MEANING 
 
 Robert E. Peary. The Discovery of the North Pole (for further refer- 
 ences on both sea and pack ice and Antarctic shelf ice, consult Hobbs's 
 Characteristics of Existing Glaciers, pp. 210-213, 242-244. 
 
 Icebergs : — 
 Wyville Thomson. Challenger Report, Narrative, vol. 1, 1865, Pt. i, 
 
 pp. 431-432, pis. B-D. 
 I. C. Russell. An Expedition to Mt. St. Elias, Nat. Geogr. Mag., vol. 3, 
 
 1891, pp. 101-102, fig. 1. 
 H. F. Reid. Studies of Muir Glacier, Alaska, ibid., vol. 4, 1892, pp. 47- 
 
 48. 
 E. VON Drygalski. Gronland-Expedition, etc., vol. 1, pp. 367-404. 
 M. C. Engell. Ueber die Entstehung der Eisberge, Zeit. f. Gletscherk., 
 
 vol. 5, 1910, pp. 112-132. 
 
CHAPTER XXII 
 
 THE CONTINENTAL GLACIERS OF THE " ICE AGE " 
 
 Earlier cycles of glaciation. — Our study of the rocks compos- 
 ing 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 glaciers. 
 The latest of these occurred in the yesterday of geology and has 
 
 Fig. 322. Map of the globe showing the areas which were covered by the con- 
 tinental glaciers of the so-called "ice-age" of the Pleistocene period. The arrows 
 show the directions of the centrifugal air currents in the fixed anticyclones above the 
 glaciers. 
 
 often been referred to as the " ice age," because until quite re- 
 cently it was supposed to be the only one of which a record was 
 preserved. 
 
 This latest ice age represents four complete cycles of glaciation, 
 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 place, and that this alternation of 
 climates was no less than three times repeated, making four cycles 
 in all. At nearly or quite the same time ice masses developed in 
 
 297 
 
298 
 
 EARTH FEATURES AND THEIR MEANING 
 
 
 northern North America and 
 in northern Europe, the em- 
 bossments of the ice domes 
 being located in Canada and 
 in Scandinavia respectively 
 (Fig. 322). There appears to 
 have been at this time no ex- 
 tensive glaciation of the south- 
 ern hemisphere, though in the 
 next earlier of the known great 
 periods of glaciation — the so- 
 called Permo-Carboniferous — it was the southern hemisphere, and 
 not the northern, that was affected (Fig. 323 and Fig. 304, p. 276). 
 
 Fig 323 — Glaciated granite bowlder 
 which has weathered out of a moraine 
 of Permo-Carboniferous age upon which 
 it rests. South Australia (after How- 
 chin). 
 
 Fig. 324. — Map to show the glaciated and nonglaciated regions of North America 
 (after Salisbury and At wood). 
 
THE CONTINENTAL GLACIERS OF THE "ICE AGE" 299 
 
 From the still earlier glacial period our data are naturally much 
 more meager, but it seems probable that it was characterized by 
 glaciated areas within both the northern and the southern hemi- 
 spheres. 
 
 Contrast of the glaciated and nonglaciated regions. — Since 
 we have now studied in brief outline the characteristics of the exist- 
 ing continental glaciers, we are in a position to review the evidences 
 
 Fig. 325. — Map of the glaciated and nonglaciated areas of northern Europe. The 
 strongly marked morainal belts respectively south and north of the Baltic depres- 
 sion represent halting places in the retreat of the latest continental glacier (com- 
 piled from maps by Penck and Leverett). 
 
 of former glaciers, the records of which exist in their carvings, their 
 gravings, and their deposits. 
 
 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 (Fig. 324). 
 Hardly less striking is the contrast between the glaciated and the 
 nonglaciated regions upon the continent of Europe (Fig. 325) . 
 
 It is the northern of the two areas which in each case reveals the 
 characteristic evidences of glaciation, while there is entire absence 
 
300 
 
 EARTH FEATURES AND THEIR MEANING 
 
 of such marks to the southward of the common border. Within 
 the American glaciated region there is, however, an area surrounded 
 Hke an island, and within this district (Fig. 324) none of the marks 
 characteristic of glaciation are to be found. This area is usually 
 referred to as the " driftless area," and occupies portions of the 
 states of Wisconsin, Illinois, Minnesota, and Iowa. Even better 
 than the area to the southward of the Ohio and Missouri rivers, it 
 permits of a comparison of the nonglaciated with the drift-cov- 
 ered region. 
 
 The " driftless area." — Within this district, then, we have 
 preserved for our study a landscape which remains largely as it was 
 
 before the several ice 
 invasions had so pro- 
 foundly transformed the 
 general surface of the 
 surrounding country. 
 Speaking broadly, we 
 may say that it rep- 
 resents an uplifted and 
 in part dissected plain, 
 which to the south and 
 east particularly reveals 
 the character of nearly 
 mature river erosion 
 (Fig. 177, p. 170). The 
 rock surface is here 
 everywhere mantled by 
 decomposed and disin- 
 tegrated rock residues 
 of local origin. The 
 soluble constituents of 
 the rock, such as the 
 carbonates, have been 
 removed by the process of leaching, so that the clays no longer 
 effervesce when treated with dilute mineral acid. 
 
 Wherever favored by joints and by an alternation of harder 
 and softer rock layers, picturesque unstable erosion remnants or 
 " chimneys " may stand out in relief (Fig. 326). Furthermore, the 
 driftless area is throughout perfectly drained — it is without lakes 
 
 Fig. 320. — "Stand Rock" near the "Dells" of the 
 Wisconsin river, an unstable erosion remnant char- 
 acteristic of the driftless area of North America 
 (after Salisbury and Atwood) . 
 
Plate 16. 
 
 Scale. 
 
 5MHm. 
 
 A. Incised topography within the " driftless area " (U. S. Geol. Survey). 
 
 Scale. 
 
 3 Miles. 
 
 B. Built-up topography within glaciated region (U. S. Geol. Survey). 
 
THE CONTINENTAL GLACIERS OF THE "ICE AGE" 301 
 
 or swamps — since all valleys are characterized throughout by- 
 forward grades. The side valleys enter the main valleys as do the 
 branches a tree trunk ; in other words, the drainage is described a& 
 arborescent. In so far as any portions of a plane surface now remain 
 in the landscape, they are found at the highest levels (plate 16 A), 
 The topography is thus the result of a partial removal by erosion 
 of an upland and may be described as incised tocography. Nowhere 
 within the area are there found rock masses foreign to the region, 
 but all mantle rock is the weathered product of the underlying 
 ledges. 
 
 Characteristics of the glaciated regions. — The topography of 
 the driftless area has been described as incised, because due to the 
 partial destruction of an uphfted plain ; and this surface is, more- 
 over, perfectly drained. The 
 characteristic topography of the 
 '' drift " areas is by contrast hiiilt 
 up; that is to say, the features of 
 the region instead of being carved 
 out of a plain are the result of 
 
 Fig. 327. -Diagram showing the man- 'rrjolding by the prOCeSS of deposi- 
 ner in which a continental glacier ob- tion (plate 16 B). In SO far aS a 
 literates existing valleys (after Tarr). plane is recognizable, it is to be 
 
 found not at the highest, 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 huilt up through deposition. The 
 process by which this has been accomplished is one easy to compre- 
 hend. As it invaded the region, the glacier planed away beneath 
 its marginal zone all weathered mantle rock and deposited the 
 planings within the hollows of the surface (Fig. 327). The 
 effect has been to flatten out the preexisting irregularities of the 
 surface, and to yield at first a gently undulating plain upon which 
 are many undrained areas and a haphazard system of drainage 
 (Fig. 328). All unstable erosion remnants, such as now are to be 
 found within the driftless area, were the first to be toppled over by 
 the invading glacier, and in their place there is left at best only 
 rounded and polished " shoulders " of hard and unweathered rock 
 - — the well-known roches moutonnees. 
 
 The glacier gravings. — The tools with which the glacier works 
 
302 
 
 EARTH FEATURES AND THEIR MEANING 
 
 are never quite evenly edged, and instead of an in all respects 
 perfect polish upon the rock pavement, there are left furrowings, 
 gougings, and scratches. Of whatever sort, these scorings indi- 
 cate the lines of ice movement and are thus indubitable records 
 graven upon the rock floor. When mapped over wide areas, a 
 
 Fig. 328. — Lake and marsh district in northern Wisconsin, the effect of glacial 
 deposition in former valleys (after Fairbanks). 
 
 most interesting picture is presented to our view, and one which 
 supplements in an important way the studies of existing continental 
 glaciers (Fig. 334, p. 308, and Fig. 336, p. 312). 
 
 It has been customary to think of the glacier as everywhere 
 eroding its bed, although the only warrant for assuming degra- 
 dation by flow of the ice is restricted to the marginal zone, since 
 here only is there an appreciable surface grade likely to induce 
 flow. Both upon the advance and again during the retreat of a 
 glacier, all parts of the area overridden must be subjected to this 
 action. Heretofore pictured in the imagination as enlarged 
 models of Alpine glaciers, 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 
 weather. The maximum thickness of the latest American glacier 
 of the ice age has been assumed to have been perhaps 10,000 feet 
 near the summit of its dome in central Labrador. From this 
 
THE CONTINENTAL GLACIERS OF THE "ICE AGE" 303 
 
 point it was assumed that the ice traveled southward up the 
 northern slope of the Laurentian divide in Canada, and thence 
 to the Ohio river, a distance of over 1300 miles. If such a mantle 
 of ice be represented in its natural proportions in vertical section, 
 to cover the distance from center to margin we may use a line 
 six inches in length, and only j^^ of an inch thick. Upon a reduced 
 scale these proportions are given in Fig. 329. Obviously the 
 force of gravity acting within a viscous mass of such proportions 
 
 Fig. 329. — Cross section in approximate natural proportions of the latest North 
 American continental glacier of Pleistocene age from its center to its margin. 
 
 would be incompetent to effect a transfer of material from the 
 center to the periphery, even though the thickness should be 
 doubled or trebled. Yet until the fixed glacial anticyclone above 
 the glacier had been proven and its efficiency as a broom recog- 
 nized, no other hypothesis than that of viscous flow had been 
 offered in explanation. The inherited conception of a universal 
 plucking and abrasion on the bed of the glacier is thus made un- 
 tenable and can be accepted for the marginal portion only. 
 
 Not only do the rock scorings show the lines of ice movement, 
 but the directions as well may often be read upon the rock. Wher- 
 ever there are pronounced irregularities of surface still existing on 
 the pavement, these are generally found to have gradual slopes 
 upon the side from which the ice came, and relatively steep falls 
 upon the lee or " pluck " side. If, however, we consider the irregu- 
 larities of smaller size, 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 side. Such minor projections upon the floor usually have their 
 origin in some harder nodule which deflects the abrading tools and 
 causes them to pass, some on the one side and some upon the other. 
 By this process a staple-shaped groove comes to surround the 
 nodule, leaving an unsymmetrical elevated ridge within, which is 
 steep upon the stoss side and slopes gently away to leeward. 
 
 Younger records over older — the glacier palimpsest. — Many 
 important historical facts have been recovered from the largely 
 effaced writing upon ancient palimpsests, or parchments upon 
 which an earlier record has been intentionally erased to make room 
 
304 
 
 EARTH FEATURES AND THEIR MEANING 
 
 for another. In the gravings upon the glacier pavement, earlier 
 records have been likewise in large part effaced by later, though in 
 favorable localities the two may be read together. Thus, as an 
 example, at the great limestone quarries of Sibley, in south- 
 eastern Michigan, the glaciated rock surface wherever stripped of 
 its drift cover is a smoothly polished and relatively level floor 
 with striae which are directed west-northwest. Beneath this gen- 
 eral surface there are, however, a number of elliptical depres- 
 sions which have their longer axes directed south-southwest, one 
 being from twenty-five to thirty feet long and some ten feet in 
 depth (Fig. 330). These boat-shaped depressions are clearly the 
 
 remnants of an earlier 
 more undulating sur- 
 face which the latest 
 glacier has in large 
 part planed away, 
 since the bottoms of 
 the depressions are no 
 less perfectly glaciated 
 but have their strise 
 directed in general 
 near the longer axis of 
 the troughs. Palimp- 
 sest-like there are 
 here also the records 
 of more than 
 
 one 
 
 Fig. 330. — Limestone surface at Sibley, Michigan. 
 
 graving. 
 The dispersion of the drift. — Long before the " ice age " had 
 been conceived in the minds of Agassiz and his contemporaries, 
 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 
 " Swedish granite." Buckland, an English geologist, had in 1815 
 accounted for such '' erratic " blocks of his own countrj^, here of 
 Scotch granite, by calling in the deluge of Noah ; but in the late 
 thirties of the nineteenth century, Sir Charles Lj^ell, with the results 
 of English Arctic explorers in mind, claimed that such traveled 
 blocks had been transported by icebergs emanating from the polar 
 
THE CONTINENTAL GLACIERS OF THE "ICE AGE" 305 
 
 tx/^ 
 
 regions. A relic of Buckland's earlier view we have in the word 
 " diluvium " still occasionally used in Germany for glacier trans- 
 ported materials ; while the term " drift " still remains in common 
 use to recall LyelFs iceberg hypothesis, even though the original 
 meaning of the term has been abandoned. Drift is now a generic 
 term and refers to all deposits directly or indirectly referable to the 
 continental glaciers. 
 
 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 mar- 
 gin at the time 
 when it was de- 
 posited ; in other 
 words, the dis- 
 persion of the 
 drift was cen- 
 trifugal with ref- 
 erence to the 
 glacier. 
 
 Wherever 
 rocks of unusual 
 and therefore 
 easily recogniz- 
 able character 
 can be shown to 
 occur in place 
 and with but lim- 
 ited areas, the 
 dispersion of 
 such material is 
 easy to trace. 
 
 The areas of red Swedish and Scotch granite have been used to 
 follow out in a broad way the dispersion of drift over northern 
 Europe. Within the region of the Great Lakes of North America 
 are areas of limited size which are occupied by well marked rock 
 types, so that the journey ings of their fragments with the conti- 
 nental glacier can be mapped with some care. Upon the northern 
 shore of Georgian Bay occurs the beautiful jasper conglomerate, 
 whose bright red pebbles in their white quartz field attract such 
 general notice. At Ishpeming in the northern peninsula of Michi- 
 
 FiG. 331. — Map to show the outcroppings of peculiar rock 
 types in the region of the Great Lakes, and some of the 
 localities where "float copper" has been collected (float 
 copper localities after Salisbury) . 
 
306 
 
 EARTH FEATURES AND THEIR MEANING 
 
 gan is found the equally beautiful jaspilite composed of puckered 
 alternating layers of black hematite and red jasper. On Keweenaw 
 Peninsula, which protrudes into Lake Superior from its southern 
 shore, is found that remarkable occurrence of native copper within 
 a series of igneous rocks of varied types and colors. Fragments 
 
 of this copper, some weighing several 
 hundreds of pounds each and masked 
 in a coat of green malachite, have under 
 the name of " drift " or " float " copper 
 been collected at many localities within 
 a broad " fan " of dispersal extending 
 almost to the very limits of glaciation 
 (Fig. 331). 
 
 Some miles to the north of Provi- 
 dence in Rhode Island there is a hill 
 known as Iron Hill composed in large 
 part of black magnetite rock, the so- 
 called Cumberlandite. From this hill 
 as an apex there has been dispersed a 
 great quantity of the rock distributed 
 as a well marked " bowlder train " 
 within which the size and the fre- 
 quency of the dispersed bowlders is in 
 inverse ratio to the distance from the 
 parent ledge (Fig. 332). Similar 
 though less perfect trains of bowlders 
 are found on the lee side of most pro- 
 j ecting masses of resistant rocks within 
 the area of the drift. 
 
 Large bowlders when left upon a 
 ledge of notably different appearance 
 easily attract attention, and have been 
 described as " perched bowlders." Resting as they sometimes do 
 upon a relatively small area, they may be nicely balanced and 
 thus easily given a pendular or rocking motion. Such " rocking 
 stones " are common enough, especially among the New England 
 hills (plate 17 B). Many such bowlders have made somewhat 
 remarkable peregrinations with many interruptions, having been 
 carried first in one direction by an earlier glacier to be later trans- 
 
 FiG. 332. — Map of the "bowlder 
 train" from Iron Hill, R.I. 
 (based upon Shaler's map, but 
 with the directions of glacial 
 striae added). 
 
Plate 17. 
 
 A. Soled glacial bowlders which show differently directed strise upon the same facet. 
 
 B. Perched bowlder upon a striated ledge of different rock type, Bronx Park, New 
 York (after Lungstedt). 
 
 C. Characteristic knob and basin surface of a moraine. 
 
THE CONTINENTAL GLACIERS OF THE "ICE AGE" 307 
 
 ported in wholly different directions at the time of new ice inva- 
 sions. 
 
 The diamonds of the drift. — Of considerable popular, even if 
 not economic, 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 Canada. The first stone to be discovered was taken by work- 
 men from a well opening near the little town of Eagle in Wisconsin 
 in the year 1876. Its nature not being known, it remained where 
 it was found as a curiosity only, and it was not until 1883 that it 
 was taken to Milwaukee and sold to a jeweler equally ignorant 
 of its value, and for the merely nominal sum of one dollar. Later 
 recognized as a diamond of the unusual weight of sixteen carats, 
 
 Fig. 333. — Shapes and approximate natural sizes of some of the more important 
 diamonds from the Great Lakes region of the United States. In order from left 
 to right these figures represent the Eagle diamond of sixteen carats, the Saukviile 
 diamond of six and one half carats, the Milford diamond of six carats, the Oregon 
 diamond of four carats, and the Burlington diamond of a little over two carats. 
 
 it was sold to the Tiffanys and became the cause of a long litiga- 
 tion which did not end until the Supreme Court of Wisconsin had 
 decided that the Milwaukee jeweler, and not the finder, was en- 
 titled to the price of the stone, since he had been ignorant of its 
 value at the time of purchase. 
 
 An even larger diamond, of twenty-one carats weight, was found 
 at Kohlsville, and smaller ones at Oregon, Saukviile, Burlington, 
 and Plum Creek in the state of Wisconsin ; at Dowagiac in Michi- 
 gan; at Milford in Ohio, and in Morgan and Brown counties in 
 Indiana. The appearance of some of the larger stones in their 
 natural size and shape may be seen in Fig. 333. 
 
 While the number of the diamonds sown in the drift is undoubt- 
 edly large, their dispersion is such that it is little likely they 
 can be profitably recovered. The distribution of the localities at 
 which stones have thus far been found is set forth upon Fig. 334. 
 Obviously those that have been found are the ones of larger size, 
 
Fig. 334. — Glacial map of a portion of the Great Lakes region, showing the ungla- 
 ciated area and the areas of older and newer drift. The driftless area, the mo- 
 raines of the later ice invasion, and the distribution of diamond localities upon 
 the latter are also shown. With the aid of the directions of striae some attempt 
 has been made to indicate the probable tracks of more important diamonds, wiiich 
 tracks converge in the direction of the Labrador peninsula. 
 
 308 
 
THE CONTINENTAL GLACIERS OF THE "ICE AGE" 309 
 
 since these only attract attention. In 1893, when the finding of 
 the Oregon stone drew attention to these denizens of the drift,, 
 the writer prophesied that other stones would occasionally be dis- 
 covered under essentially the same conditions, and such discoveries 
 are certain to continue in the future. 
 
 Tabulated comparison of the glaciated and nonglaciated re- 
 gions. — It will now be profitable to sum up in parallel columns 
 the contrasted peculiarities of the glaciated and the unglaciated 
 regions. 
 
 Unglaciated Region Glaciated Region 
 
 topography 
 
 The topography is destructional ; The topography is constructional; 
 
 the remnants of a plain are found at the remnants of a plain are found 
 
 the highest levels or upon the hill at the lowest levels in lakes and 
 
 tops ; hills are carved out of a high swamps ; hills are molded above a 
 
 plain ; unstable erosion remnants are plain in characteristic forms ; no 
 
 characteristic. unstable erosion remnants, but only 
 
 rounded shoulders of rock. 
 
 DRAINAGE 
 
 The area is completely drained, The area includes undrained 
 and the drainage network is arbores- areas, — lakes and swamps, — and 
 cent. the drainage system is haphazard. 
 
 ROCK MANTLE 
 
 The exposed rock is decomposed No decomposed or disintegrated 
 and disintegrated to a considerable rock is "in place," but only hard, 
 depth ; it is all of local derivation fresh surface ; loose rock material 
 and hence of few types — homogene- is all foreign and of many sizes and 
 oris ; the fragments are angular ; types — heterogeneous ; rock bowl- 
 soils are leached and hence do not ders and pebbles are faceted and 
 contain carbonates. polished as well as striated, usually 
 
 in several directions upon each 
 facet ; soils are rock flour — the 
 grist of the glacial mill. 
 
 ROCK SURFACE 
 
 Rock surface is rough and irreg- Rock surface is planed or grooved, 
 ular. and polished. Shows glacial striae. 
 
 Unassorted and assorted drift. — The drift is of two distinct 
 types; namely, that deposited directly by the glacier, which is 
 
310 EARTH FEATURES AND THEIR MEANING 
 
 without stratification, or unassorted ; and that deposited by water 
 flowing either beneath or from the ice, and this hke most fluid de- 
 posited material is assorted or stratified. The unassorted material 
 is described as till, or sometimes as " bowlder clay " ; the as- 
 sorted is sand or gravel, sometimes with small included bowlders, 
 and is described as kame gravel. To recall the parts which both 
 the glacier and the streams have played in its deposition, all water- 
 deposited materials in connection with glaciers are called fluvio- 
 glacial. 
 
 Till is, then, characterized by a noteworthy lack of homogeneity^ 
 both as regards the size and the composition of its constituent 
 
 parts. As many as twenty 
 
 '""'-'"■ < " r.*"^ different rock types of varied 
 
 ^ 3 textures and colors may some- 
 
 ^ *^-* ^ -, times be found in a single 
 
 ^ "^ ' "■ > exposure of this material, and 
 
 - V ^ the entire gamut is run from 
 
 the finest rock flour upon the 
 one hand to bowlders whose 
 diameter may be measured 
 in feet (Fig. 335). 
 « -^ ' * ' i^^ contrast with those de- 
 
 ^^ ' ^^x^./--^' rived by ordinary stream 
 
 Fig 335 —becti on m coarse till Note the action, the pebbles and 
 range in size of the materials, the lack of bowlders of the till are fac- 
 stratification, and the "soled" form of the 
 
 bowlders. eted or soled, and usually 
 
 show striations upon their 
 faces. If a number of pebbles are examined, some at least are sure 
 to be found with striations in more than one direction upon a 
 single facet. 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 
 regions. 
 
 Inasmuch as the capacity of ice for handling large masses is 
 greater than that of water, assorted drift is in general less coarse, 
 and, as its name implies, it is also stratified. From ordinary 
 stream gravels, the kame gravels are distinguished by the form of 
 their pebbles, which are generally faceted and in some cases 
 
TPIE CONTINENTAL GLACIERS OF THE "ICE AGE" 311 
 
 striated. In proportion, however, as the materials are much 
 worked over by the water, the angles between pebble faces be- 
 come rounded and the original shapes considerably masked. 
 
 Features into which the drift is molded. — Though the pre- 
 existing valleys were first filled in by drift materials, thus reducing 
 the accent of the relief, a continuation of the same process resulted 
 in the superimposition of features of characteristic shapes upon 
 the imperfectly evened surface of the earlier stages. These 
 features belong to several different types, according as they were 
 built up outside of, at and upon, or within the glacier margin. 
 The extra-marginal deposits are described as outwash plains or 
 aprons, or sometimes as valley trains; the marginal are either 
 moraines or kames; while within the border were formed the till 
 plain or ground moraine, and, locally also, the drumlin and the 
 esker or os. These characteristic features are with few exceptions 
 to be found only within the area covered by the latest of the ice 
 invasions. For the earlier ones, so much time has now elapsed 
 that the effect of weathering, wash, and stream erosion has been 
 such that few of the features are recognizable. 
 
 Marginal and extra-marginal features are extended in the direc- 
 tion of the margin or, in other words, perpendicular to the local 
 ice movement ; while the intra-marginal deposits are as note- 
 worthy for being perpendicular to the margin, or in correspondence 
 with the direction of local ice movement. Each of these features 
 possesses characteristic marks in its form, its size, proportions, 
 surface molding and orientation, as well as in its constituent 
 materials. It should perhaps be pointed out that the existing 
 continental glaciers, being in high latitudes, work upon rock ma- 
 terials which have been subjected to different weathering processes 
 from those characteristic of temperate latitudes. Moreover, the 
 melting of the Pleistocene glaciers having taken place in relatively 
 low latitudes, larger quantities of rock debris were probably released 
 from the ice during the time of definite climatic changes, and hence 
 heavier drift accumulations have for both of these reasons resulted. 
 
 Marginal or " kettle " moraines. — Wherever for a protracted 
 period the margin of the glacier was halted, considerable deposits 
 of drift were built up at the ice margin. These accumulations 
 form, however, not only about the margin, but upon the ice sur- 
 face as well ; in part due to materials collected from melting down 
 
312 
 
 EARTH FEATURES AND THEIR MEANING 
 
 of the surface, and in part by the upturning of ice layers near the 
 margin (see ante, p. 277). 
 
 An important role is played by the thaw water which emerges 
 at the ice margin, especially within the reentrants or recesses of 
 the outline. The materials of moraines are, therefore, till with 
 large local deposits of kame gravel, and these form in a series of 
 ridges corresponding to the temporary positions of the ice front. 
 Their width may range from a few rods to a few miles, their height 
 
 may reach a hundred feet or more, 
 and they stretch across the country 
 for distances of hundreds or even 
 thousands of miles, 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 (Fig. 334, p. 308, and 
 Fig. 336). These festoons of the 
 moraines outline the ice lobes of 
 the latest ice invasion, which in 
 North America were centered over 
 the depressions now occupied by the 
 Laurentian lakes. There was, thus, 
 a Lake Superior lobe, a Lake Mich- 
 igan lobe, etc. With the aid of 
 these moraine maps we may thus 
 in imagination picture in broad lines 
 the frontal contours of the earlier 
 glaciers. At specially favorable lo- 
 calities where the ice front has 
 crossed a deep vallej^ at the edge of 
 the Driftless Area, we may, even in a rough way, measure the slope 
 of the ice face. Thus near Devils Lake in southern Wisconsin the 
 terminal moraine crosses the former valley of the AVisconsin River, 
 and in so doing has dropped a distance of about four hundred feet 
 within the distance of a half mile or thereabouts (Fig. 337). 
 
 The characteristic surface of the marginal moraine is responsible 
 for the name " kettle " moraine so generally applied to it. The 
 " kettles " are roughly circular, undrained basins which lie among 
 
 Fig 336 — Sketch map of portions 
 of Michigan, Ohio, and Indiana, 
 showing the festooned outhnes of 
 the moraines about the former ice 
 lobes, and the directions of ice 
 movement as determined by the 
 striae upon the rock pavement 
 (after Leverett) . 
 
THE CONTINENTAL GLACIERS OF THE "ICE AGE" 313 
 
 Pig. 337. — Map of the vicinity of Devils Lake, Wisconsin, located within a reen- 
 trant of the "kettle" moraine upon the margin of the Driftless Area. The lake 
 lies within an earlier channel of the Wisconsin River which has been blocked at 
 both ends, first by the glacier and later by its moraine. The stippled area upon 
 the heights and next the moraine represents the clay deposits of a former lake 
 {based on map by Salisbury and Atwood). 
 
 Tig. 338. — Moraine with outwash apron in front, the latter in part eroded by a 
 river. Westergotland, Sweden (after H. Munthe). 
 
fiM 
 
 tlti' 
 
 314 EARTH FEATURES AND THEIR MEANESTG 
 
 hummocks or knobs, so that the surface has often been referred 
 to as " knob and basin " topography (plate 17 C). 
 
 Karnes. — Within reentrants or recesses of the ice margin the 
 drift deposits were especially heavy, so that high hills of hummocky 
 surface have been built up, which are described as kames. Most 
 of the higher drift hills have this origin. They rarely have any 
 principal extension along a single direction, but are composed in 
 large part of assorted materials. In contrast with other portions 
 of the morainal ridges they lack the prominent basins known as 
 kettles. Other kames are high hills of assorted materials not in 
 
 direct association with mo- 
 raines and believed to have 
 been built up beneath glacier 
 wells or mills (p. 278). 
 
 Outwash plains. — Upon the 
 outer margin of the moraine 
 is generally to be found a plain 
 of glacial " outwash " com- 
 ^^^■^?^ -'^^^^^^^^= ^IjE^g ^:^,9^?^-' posed of sand or gravel de- 
 FiG. 339. — Fosse between an outwash plain posited by the braided streams 
 
 (in the foreground) and the moraine, {Y\g. 308, p. 280) flowing from 
 which rises to the left in the middle dis- , , , . • r\ ^ 
 
 tance. Ann Arbor, Michigan. t^^e glaCier margin. Such 
 
 plains, while notably flat (Fig. 
 338), slope gently away from the moraine. Between the outwash 
 plain and the moraine there is sometimes found a pit, or fosse 
 (Fig. 309, p. 281), where a part of the ice front was in part buried 
 in its own outwash (Fig. 339). 
 
 Pitted plains and interlobate moraines. — Where glacial outwash 
 is concentrated within a long and narrow reentrant, separating 
 glacial lobes, strips of high plain are sometimes built up which 
 overtop the other glacial deposits of the district. The sand and 
 gravel which compose such plains have a surface which is pitted by 
 numerous deep and more or less circular lakes, so that the term 
 "pitted plain " has been applied to them. The surface of such a 
 plain steadily rises toward its highest point in the angle between 
 the ice lobes. Though consisting almost entirely of assorted 
 materials, and built up largely without the ice margins, such 
 gently sloping pitted platforms are described as interlobate mo- 
 raines. Upon a topographic map the course of such an inter- 
 
THE CONTINENTAL GLACIERS OF THE "ICE AGE 
 
 315 
 
 lobate moraine may often be followed by the belts of small pit 
 lakes (see Fig. 336). 
 
 Eskers. — Intra-morainal features, or those developed beneath 
 the glacier but relatively near its margin, include the " serpentine 
 kame," esker, or, 
 as it is called in 
 Scandinavia, the os 
 (plural osar) (Fig. 
 340). These di- 
 minutive ridges 
 have a width sel- 
 dom exceeding a 
 few rods, and a 
 height a few tens 
 of feet at most, 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 (Fig. 341). They are composed of 
 
 Fig. 340. — View looking along an esker in southern 
 'Maine (after Stone). 
 
 Fig. 341. — Outline map showing the eskers of Finland trending southeasterly to- 
 ward the festooned moraines at the margin of the ice. The characteristic lakes, 
 of a glaciated region appear behind the moraines (after J. J. Sederholm) . 
 
316 
 
 EARTH FEATURES AND THEIR MEANING 
 
 poorly stratified, thick-bedded sands, gravels, and '' worked over " 
 materials, and are believed to have been formed by subglacial 
 rivers which flowed in tunnels beneath the ice. Inasmuch as the 
 deposits were piled against the ice walls, the beds were disturbed 
 
 at the sides when these walls disap- 
 peared, and the stratification, which 
 was somewhat arched in the beginning, 
 has been altered by sliding at both 
 margins. As already stated, eskers 
 have not a general distribution within 
 the glaciated area, but are often found 
 in great numbers at specially favored 
 localities. Formed as they are beneath 
 the ice, it is believed that many have 
 their materials redistributed so soon as 
 uncovered at the glacier margin, be- 
 cause of the vigorous drainage there. 
 They are thus to be found only at those 
 favored localities where for some reason 
 border drainage is less active, or where 
 the ice ended in a body of water. 
 
 Drumlins. — A peculiar type of small 
 hill likewise found behind the marginal 
 moraine in certain favored districts has 
 the form of an inverted boat or canoe, 
 the long axis of which is parallel to 
 _ the direction of ice movement, as is 
 ^antQ";7inte7vVi20feet " that of the esker (Fig. 342). Unlike 
 
 Fig. 342. — Small sketch maps ^he esker, this type of hill is composed 
 
 showing the relationships in p , -n i j. i • p j • t i j 
 
 ,. , . , 01 till, and from bemg found m Ireland 
 
 size, proportions, and orienta- ' ° 
 
 tion of drumhns and eskers in it is Called a drumlin, the Irish word 
 
 meaning a little hill (Fig. 343) . Drum- 
 lins are usually found in groups more 
 or less radial and not far behind the 
 outermost moraine, to which their radiating axes are perpendicular. 
 The manner of their formation is involved in some uncertainty, 
 but it is clear that they have been formed beneath the margin of 
 the glacier, and have been given their shape by the last glacier 
 which occupied the district. 
 
 Scale 
 
 southern Wisconsin. The es- 
 kers are in solid black (after 
 Alden). 
 
THE CONTINENTAL GLACIERS OF THE "ICE AGE" 317 
 
 The mutual relationships of nearly all the molded features 
 resulting from continental glaciation may be read from Fig. 344. 
 
 The shelf ice of the ice age. — Shelf ice, such as we have become 
 familiar with in Antarctica as a marginal snow-ice terrace floating 
 
 Fig. 343. — View of a drumlin, showing an opening m the till Near Boston, Mas- 
 sachusetts (after Shaler and Davis). 
 
 upon the sea, no doubt existed during the ice age above the Gulf 
 of Maine (see Fig. 324, p. 298), and perhaps also over the deep sea 
 to the westward of Scotland. Though the inland ice probably 
 covered the North Sea, and upon the American side of the Atlantic 
 
 " - -i—KiMr^^ LI 
 Fig. 344. — Outline map of the front of the Green Bay lobe of the latest continental 
 glacier of the United States. Drumlins in solid black, moraines with diagonal 
 hachure, outwash plains and the till plain or ground moraine in white (after 
 Alden). 
 
 the Long Island Sound, both these basins are so shallow that 
 the ice must have rested upon the bottom, for neither is of 
 sufficient depth to entirely submerge one of the higher European 
 cathedrals. 
 
318 
 
 EARTH FEATURES AND THEIR MEANING 
 
 Character profiles. — All surface features referable to continental 
 
 glaciers, whether carved in rock or molded from loose materials, 
 present gently flowing outlines which are convex upward (Fig, 
 345). The only definite features carved from rock are the roches 
 moutonnees, with their flattened shoulders, while the hillocks upon 
 
 Fig. 345. — Character profiles referable to continental glacier. 
 
 moraines and kames, and the drumlins as well, approximate to 
 the same profile. The esker in its cross sections is much the same, 
 though its serpentine extension may offer some variety of curvature 
 when viewed from higher levels. 
 
 Reading References for Chapter XXII 
 General : — 
 
 James Geikie. The Great lee Age. 3d ed. London, 1894, pp. 850, 
 
 maps 18. 
 Chamberlin and Salisbury. Geology, vol. 3, 1906, pp. 327-516. 
 Frank Leverett. The Illinois Glacial Lobe, Mon. 38, U. S. Geol. Surv., 
 
 1899, pp. 817, pis. 34 ; Glacial formations and Drainage Features of 
 
 the Erie and Ohio Basins, Mon. 41, iUd., 1902, pp. 802, pis. 25; 
 
 Comparison of North American and European Glacial Deposits, Zeit. 
 
 f. Gletscherk., vol. 4, 1910, pp. 241-315, pis. 1-5. 
 
 Former glaciations previous to Ice Age : — 
 
 A. Strahan. The Glacial Phenomena of Paleozoic Age in the Varanger 
 
 Fjord, Quart. Jour. Geol. Soc, London, vol. 53, 1897, pp. 137-146, pis. 
 
 8-10. 
 Bailey Willis and Eliot Blackwelder. Research in China, Pub. 54, 
 
 Carnegie Inst. Washington, vol. 1, 1907, pp. 267-269, pis. 37-38. 
 A. P. Coleman. A Lower Huronian Ice Age, Am. Jour. Sci. (4), vol. 23, 
 
 1907, pp. 187-192. 
 W. ]\I. Davis. Observations in South Africa, Bull. Geol. Soc. Am., vol. 
 
 17, 1906, pp. 377-450, pis. 47-54. 
 David White. Permo-Carboniferous Climatic Changes in South America, 
 
 Jour. Geol., vol. 15, 1907, pp. 615-633. 
 
THE CONTINENTAL GLACIERS OF THE "ICE AGE" 319 
 
 Drif tless and drift areas : — 
 T. C. Chamberlin and R. D. Salisbury. Preliminary Paper on the 
 
 Driftless Areas of the Upper Mississippi Valley, 6th Ann. Rept. U. S. 
 
 Geol. Surv., 1885, pp. 199-322, pis. 23-29. 
 R. D. Salisbury. The Drift, its Characteristics and Relationships, 
 
 Jour. Geol., vol. 2, 1894, pp. 708-724, 837-851. 
 R. H. Whitbsck. Contrasts between the Glaciated and the Driftless 
 
 Portions of Wisconsin, BuU. Geogr. Soc, Philadelphia, vol. 9, 1911, 
 
 pp. 114-123. 
 
 Glacier gravings : — 
 T. C. Chamberlin. The Rock Scorings of the Great Ice Invasions, 7th 
 Ann. Rept. U. S. Geol. Surv., 1888, pp. 147-248, pi. 8. 
 
 The dispersion of the drift : — 
 R. D. Salisbury. Notes on the Dispersion of Drift Copper, Trans. Wis. 
 
 Acad. Sci., etc., vol. 6, 1886, pp. 42-50, pi. 
 N. S. Shaler. The Conditions of Erosion beneath Deep Glaciers, 
 
 based upon a Study of the Bowlder Train from Iron Hill, Cumberland, 
 
 Rhode Island, Bull. Mus. Comp. Zool. Harv. Coll., vol. 16, No. 11, 
 
 1893, pp. 185-225, pis. 1-4 and map. 
 William H. Hobbs. The Diamond Field of the Great Lakes, Jour. 
 
 Geol., vol. 7, 1899, pp. 375-388, pis. 2 (also Rept. Smithson. Inst., 
 
 1901, pp. 359-366, pis. 1-3). 
 
 Glacial features : — 
 T. C. Chamberlin. Preliminary Paper on the Terminal Moraine of the 
 
 Second Glacial Epoch, 3d Ann. Rept. U. S. Geol. Surv., 1883, pp. 
 
 291-402, pis. 26-35. 
 G. H. Stone. Glacial Gravels of Maine and their Associated Deposits, 
 
 Mon. 34, U. S. Geol. Surv., 1899, pp. 489, pis. 52. 
 W. C. Alden. The Delaven Lobe of the Lake Michigan Glacier of the 
 
 Wisconsin Stage of Glaciation and Associated Phenomena. Prof. Pap. 
 
 No. 34, U. S. Geol. Surv., 1904, pp. 106, pis. 15 ; The Drumlins of 
 
 Southeastern Wisconsin, Bull. 273, U. S. Geol. Surv., 1905, pp. 46, 
 
 pis. 9. 
 W. M. Davis. Structure and Origin of Glacial Sand Plains, Bull. Geol. 
 
 Soc. Am., vol. 1, 1890, pp. 196-202, pi. 3; The Subglaeial Origin 
 
 of Certain Eskers, Proc. Bost. Soc. Nat. Hist., vol. 35, 1892, pp. 477- 
 
 499. 
 F. P. Gulliver. The Newtonville Sand Plain, Jour. Geol., vol. 1, 1893, 
 
 pp. 803-812. 
 
CHAPTER XXIII 
 
 GLACIAL LAKES WHICH MARKED THE DECLINE OF 
 THE LAST ICE AGE 
 
 
 Interference of glaciers with drainage. — Every advance and 
 every retreat of a continental glacier has been marked by a com- 
 plex series of episodes in the history of every river whose territory 
 it has invaded. Whenever the valley was entered from the direc- 
 tion of its divide, the 
 effect of the advanc- 
 ing ice front has gen- 
 erally been to swell 
 the waters of the river 
 into floods to which 
 the present streams 
 bear little resemblance 
 (Fig. 346). Because 
 of the excessive melt- 
 ing, this has been even 
 more true of the ice 
 retreat, but here when 
 the ice front retired up the valley toward the divide. A sufficiently 
 striking example is furnished by the Wabash, Kaskaskia, Illinois, 
 and other streams to the southward of the divide which surrounds 
 the basin of the Great Lakes (Fig. 347). 
 
 Wherever the relief was small there occurred in the immediate 
 vicinity of the ice front a temporary diversion of the streams by the 
 parallel moraines, so that the currents tended to parallel the ice 
 front. This temporary diversion known as " border drainage " 
 was brought to a close when the partially impounded waters had, 
 by cutting their way through the moraines, established more perma- 
 nent valleys (Fig. 348). 
 
 320 
 
 Fig. 346. — The Illi.iois River where it passes through 
 the outer moraine at Peoria, lUinois, showing the 
 flood plain of the ancient stream as an elevated 
 terrace into which the modern stream has cut its 
 gorge (after Goldthwait). 
 
GLACIAL LAKES 
 
 321 
 
 Temporary lakes due to ice blocking. — Whenever, on the con- 
 trary, the advancing ice front entered a valley from the direction 
 of its mouth, or a re- 
 treating ice front retired 
 down the valley, quite 
 different results fol- 
 lowed, since the waters 
 were now impounded 
 by the ice front serving 
 as a dam. Though the 
 histories of such block- 
 ing of rivers are often 
 quite complex, the prin- 
 ciples which underlie 
 them are in reality sim- 
 ple enough. Of the 
 lakes formed during ad- 
 vancing hemicycles of 
 glaciation, and of all 
 save the latest reced- 
 ing hemicycle, no satis- 
 factory records are pre- 
 served, for the reason 
 that the lake beaches and the lake deposits were later disturbed 
 and buried by the overriding ice sheets. We have, however, every 
 
 Fig. 347. — Broadly terraced valleys outside the 
 divide of the St. Lawrence basin, which remain to 
 mark the floods that issued from the latest con- 
 tinental glacier during its retreat (after Leverett). 
 
 Fig. 348. — Border drainage about the retreating ice front south of Lake Erie. 
 The stippled areas are the morainal ridges and the hachured bands the valleys 
 of border drainage (after Leverett). 
 
 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 study. 
 
322 
 
 EARTH FEATURES AND THEIR MEANING 
 
 As an introduction to the study of the ice-blocked lakes of North 
 America, and to set forth as clearly as may be the fundamental 
 principles upon which such lakes are dependent, we shall consider 
 in some detail the late glacial history of certain of the Scottish 
 
 glens, since their area is so small 
 and the relief so strong that rela- 
 tionships are more easily seen ; it 
 is, so to speak, a pocket edition 
 of the history of the more ex- 
 tended glacial lakes. 
 
 The " parallel roads " of the 
 Scottish glens. — 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 " parallel roads " (Fig. 349) have offered a vexed 
 problem to scientists. Of the many scientists who long attempted 
 to explain them, though in vain, was Charles Darwin, the father 
 of modern evolution. He offered it as his view that the " roads " 
 
 Fig. 349. — The "parallel roads" of 
 Glen Roy in the southern highlands 
 of Scotland (after Jamieson). 
 
 Fig. 350. — Map of Glen Roy and neighboring valleys of the Scottish highlands with 
 the so-called "roads" entered in heavy lines. Glens Roy, Glaster, and Spean 
 have three "roads," two "roads," and one "road," respectively (after Jamieson). 
 
 were beaches formed at a time when the sea entered the glens 
 and stood at these levels. When, however, Jamieson's studies 
 had discovered their true history, Darwin, with a frankness char- 
 acteristic of some of the greatest scientists, admitted how far astray 
 
GLACIAL LAKES 323 
 
 he had been in his reasoning. Let us, then, first examine the facts, 
 and later their interpretation. The map of Fig, 350 will suffice 
 to set forth with sufficient clearness the course of the several 
 " roads." These " roads " are found in a number of glens tribu- 
 tary to Loch Lochy, and of the three neighboring valleys, Glen 
 Roy has three, Glen Glaster two, and Glen Spean one " road." 
 The facts of greatest significance in arriving at their interpretation 
 relate to their elevations with reference to the passes at the valley 
 heads, their abrupt terminations down-valleyward, and the mo- 
 rainic accumulations which are found where they terminate. The 
 single " road " of Glen Spean is found at an elevation of 898 
 feet, a height which corresponds to that of the pass or col at the 
 head of its valley and to the lowest of the " roads " in both Glens 
 Glaster and Roy. Similarly the upper of the two " roads " in 
 Glen Glaster is at the height of the pass at its head (1075 feet) 
 and corresponds in elevation to the middle one of the three " roads " 
 in Glen Roy. Lastly, the highest of the "roads " in Glen Roy is 
 found at an elevation of 1151 feet, the height of the col at the head 
 of the Glen. In the neighboring Glen Gloy is a still higher " road " 
 corresponding likewise in elevation to that of the pass through 
 which it connects with Glen Roy. 
 
 To come now to the explanation of the " roads," it may be said 
 at the outset that they are, as Darwin supposed, beach terraces 
 cut by waves, not as he believed of the ocean, but of lakes which 
 once filled portions of the glens when glaciers proceeding from 
 Ben Nevis to the southwestward were blocking their lower por- 
 tions. The several episodes of this lake history will be clear from 
 a study of the three successive idealistic diagrams in Fig. 351. 
 
 To derive the principles underlying this history, 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 time. This is the principle 
 which explains nearly all episodes of glacial lake history. Thus, 
 when the ice front had retired so as to open direct connections 
 between Glen Roy and Glen Glaster, the col at the head of Glen 
 Roy was abandoned as an outlet, and the waters fell to the level 
 fixed for Glen Glaster. A still further retirement at last opened 
 direct connection between Glen Glaster and Glen Spean, so that 
 the lake common to Glens Glaster and Roy fell to the level of the 
 
324 EARTH FEATURES AND THEIR MEANING 
 
 
 Fig. 351. — Three successive diagrams to set forth in order the late glacial lake 
 history of the Scottish glens. 
 
GLACIAL LAKES 
 
 325 
 
 €ol which was the outlet of the Spean valley at the time. 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 ocean. 
 
 Only in their far grander scale and in the lesser relief of the land 
 over which they formed, do the complex histories of the great 
 
 l-imm 
 
 ..^sr ^ter..-^-=*- 
 
 
 
 Fig. 352. — Harvesting time on the fertile floor of the glacial Lake Agassiz (after 
 
 Howell). 
 
 ice-blocked lakes of North America differ from these little valley 
 lakes whose beaches may be visited and the relationships worked 
 out, thanks to Jamieson, in a single day's strolling. 
 
 The glacial Lake Agassiz. — 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 terri- 
 tory invaded and which normally 
 drain toward the retiring ice front. 
 In North America these rivers are 
 the Red River of the North in 
 Minnesota, the Dakotas, and Mani- 
 toba; and the St. Lawrence River 
 system. 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 (Fig. 352). Lakes Winnipeg, Winnipegoosis, and 
 Manitoba, and the Lake of the Woods, are all that now remain of 
 this greatest of the glacial lakes, which in honor of the distinguished 
 founder of the glacial theory has been called Lake Agassiz (Fig. 
 353). With their natural outlet blocked by the ice in northern 
 
 
 Fig. 353. 
 
 Map of Lake Agassiz (after 
 Upham). 
 
326 
 
 EARTH FEATURES AND THEIR MEANING 
 
 Manitoba and Keewatin, 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 River. Along this route 
 
 Fig. 354. — Map of the southern end of the Lake Agassiz basin, showing the position 
 of some of the beaches and the outlet through the former Warren River (after 
 
 Upham). 
 
 there flowed a mighty flood which carved out a broad valley many- 
 times too large for the Minnesota, its present occupant, and this 
 giant prehistoric river has been called the Warren River (Fig. 354) . 
 
GLACIAL LAKES 
 
 327 
 
 It is interesting to follow this ancient waterway and to discover 
 that, like our normal, present-day streams, it was held up in narrows 
 wherever outcroppings of harder rock had constricted its channel 
 (Fig. 355). The upper end of the Warren River valley is now 
 
 
 ^ 
 
 A R B 
 
 *5ero/e 07* A^j/cs. 
 
 Fig. 355. — Narrows of the Warren River below Big Stone Lake, where it passed 
 between jaws of hard granite and gneiss (after Upham). 
 
 occupied by the long and relatively narrow Lakes Traverse and 
 Big Stone, each the result of blocking by delta deposits where a 
 tributary stream has emerged into the valley, but this gigantic 
 channel continues down to and beyond Minneapolis, occupied as 
 far as Fort Snelling by the 
 Minnesota River — a mere 
 pygmy compared to its prede- 
 cessor. To the earnest student 
 of glacial geology there can be 
 few sights more impressive than 
 are obtained by standing at 
 Fort Snelling, just above the 
 confluence of the Minnesota 
 and the Mississippi rivers, and 
 surveying first the steep and 
 narrow valley of the Missis- ^/ 
 sippi above the junction, — a 
 
 stream fitted to its valley for Fig. 356. — Map of the valley of the Warren 
 
 the simple reason that it has River in the vicinity of Minneapolis, with 
 
 1 .. , ., . the young valley of the Mississippi enter- 
 
 carved it, — and then gazmg j^^ j, ^^ ^^^^ S^^Ui^g ^^^ ^^^ Sardeson) . 
 up and down that broad valley 
 
 in which the great Warren River once flowed majestically to the 
 sea, now the bed of the Minnesota above the Fort and of the Mis- 
 sissippi below it (Fig. 356). 
 
328 
 
 EARTH FEATURES AND THEIR MEANING 
 
 Just as the " parallel roads " of Glen Roy, roads in name only, 
 are the beaches of earlier glacial lake stages, so in Lake Agassiz 
 we have parallel beaches of the barrier type which are often roads 
 in fact as well as in name, and which mark the stages of successive 
 lakes within this vast basin. The Herman beach, corresponding 
 to the highest level of the lake, is thus a sharp topographic bound- 
 ary between lake deposits and morainal accumulations, and is 
 
 Fig. 357. — Portion of the Herman quadrangle of Minnesota, showing the position 
 of the Herman beach on the shore of the former Lake Agassiz. The lake basin is 
 to the left, and the pitted morainal deposits appear to the right (U. S. G. S.). 
 
 further itself a well-marked topographic feature composed of wave- 
 washed and hence well-drained materials (Fig. 357). 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 seasons, and are thus ideally adapted for roads. They 
 have in many sections been thus used over long stretches and are 
 known as the "ridge roads." 
 
GLACIAL LAKES 
 
 329 
 
 Episodes of the glacial lake history within the St. Lawrence 
 valley. — 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 been. 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 un- 
 blocked an outlet of lower level than the last. This sequence 
 might, however, have been varied by a temporary readvance of the 
 ice, as indeed once occurred in the Huron-Erie lobe of the great 
 North American glacier. 
 
 The crescentic lakes of the earlier stages. — So long as the 
 glacier covered the entire drainage basin of the St. Lawrence 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 ^v^ 
 
 
 
 
 
 
 
 
 >"- 
 
 ~,~^r'^'' ' 
 
 
 
 
 
 
 
 ,''' 
 
 .-•■--■ 
 
 ' ^v 
 
 
 - 
 
 
 
 
 
 ,,-'V'' 
 
 
 'F~ 
 
 '€ 
 
 ^'-. 
 
 
 ^ *N 
 
 ^i''?^f 
 
 ■if' '] 
 
 \ 
 
 ^j' 
 
 
 
 ,/ 
 
 1. 
 
 i'^yjo I 
 
 
 / 
 
 
 ..-- 
 
 --■-,^' 
 
 
 
 
 y 
 
 .--' 
 
 
 -% 
 
 T 
 
 X 
 
 j' 
 
 
 "' C^. 
 
 
 ^®^^^--v 
 
 y' ..■■•" 
 
 '""^M^ 
 
 
 s 
 
 
 
 
 -N^ 
 
 \ .■ 
 
 fe 
 
 
 i\ 
 
 
 
 ...v.-/ 
 
 1 ' — 
 
 ~ ~, 
 
 , -■ ^ 
 
 ,j-> V 
 
 !■ - 
 
 7 
 
 1 "^^^^ 
 
 ./- 
 
 
 
 
 
 ( 
 
 ^ 
 
 1 •■>. 
 
 
 
 
 ;? 
 
 
 Fig. 358. — The continental glacier of North America in an early stage of its reces- 
 sion, when it covered the entire St. Lawrence drainage basin. The dashed line 
 is the approximate position of the divide (based on a map by Goldthwait). 
 
 River system, all water was freely drained away by streams which 
 flowed away from the ice front (Fig. 358). So soon, however, 
 as at any point the front had retired behind the divide, impound- 
 ing of the waters must locally have occurred. Lakes of this type 
 are to-day to be seen in Greenland and in the southern Andes ; 
 and though upon a diminutive scale, some idea of their aspect may 
 be obtained from the appearance of the Marjelen Lake of Smt- 
 zerland, here blocked by a mountain glacier (Fig. 446, p. 411). 
 
330 
 
 EARTH FEATURES AND THEIR MEANING 
 
 ScalA 
 
 Fig. 359. — Outline map of the 
 early Lake Maumee, with the 
 bordering moraine and the 
 water-laid moraine remaining 
 on the site of the former ice cliff. 
 
 Within each of the Great 
 peared at that end of the 
 
 Within all areas of small relief, such as 
 the prairie country surrounding the 
 present Laurentian lakes, the earlier 
 and smaller stages of such ice-blocked 
 lakes are generally crescentic in out- 
 line. This is because a moraine in 
 most cases forms the land margin of 
 the lake, and because the ice chff 
 upon the opposite border, although 
 somewhat straightened, as a conse- 
 quence of wave-cutting and iceberg 
 formation, still retains the convex 
 outlines characteristic of ice lobes 
 (Fig. 359). 
 
 Lake basins a crescentic lake early ap- 
 depression which was first uncovered 
 
 
 
 Fig. 360. — Map to show the first stages of the ice-dammed lakes within the 
 St. Lawrence basin (after Leverett and Taylor). 
 
GLACIAL LAKES 331 
 
 by the glacier : Lake Duluth in the Superior basin, Lake Chicago 
 in the Michigan basin, and Lake Maumee in the Huron-Erie 
 basin (Fig. 360). 
 
 We may now, with profit, trace the successive episodes of the 
 glacial lake history, considering for the earlier stages those changes 
 which occurred within the Huron-Erie basin, since, these are in 
 essential respects like those of the Michigan and Superior basins, 
 although worked out in greater detail. Lake Chicago must, 
 however, be brought into consideration, since in all save the earli- 
 est and the later stages, the waters from the Huron-Erie depression 
 were discharged through the Grand River into this lake and 
 thence by the so-called " Chicago outlet " into the Mississippi 
 (plate 20 A). 
 
 The early Lake Maumee. — The area, outline, and outlet of 
 this lake are indicated upon Fig. 360. Its ancient beaches have 
 been traced, as well as the water-laid moraine beneath its former 
 ice cliff; and no observant traveler who should take his way 
 down the ancient outlet from Fort Wayne, Indiana, past the town 
 of Huntington, could fail to be impressed by its size, suggesting 
 as it does the great volume of water which must once have flowed 
 along it. Now a channel a mile or more in width, 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 
 merel}'', while at Huntington the Wabash river enters by a young 
 V-shaped valley at the side, much as the Mississippi emerges into 
 the old channel of the Warren River at Fort Snelling, Minnesota 
 (seep. 327). 
 
 The Huron River of southern Michigan, which now discharges 
 into Lake Erie, 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 
 Maumee. 
 
 The later Lake Maumee. — When the ice lobe had retired its 
 front sufficiently, an outlet lower than that at Fort Wayne was 
 uncovered past the city of Imlay, Michigan, into the Grand 
 River, and thence through Lake Chicago and its outlet into the 
 Mississippi. This old outlet south of Chicago follows the course 
 of the present Drainage Canal and the line of the Chicago & 
 Alton Railway. The traveler journeying southward by train from 
 
332 
 
 EARTH FEATURES AND THEIR MEANING 
 
 Chicago has thus the opportunity of observing first the beaches 
 of the former lake, and then the several channels which were 
 joined in the main outlet at the station of Sag (plate 20 A). 
 
 In this stage of our history Lake Maumee pushed a shrunk 
 arm up past the site of Ypsilanti in Michigan (Fig. 361), the well- 
 marked beach being found on Summit Street opposite the State 
 Normal College. The Huron River, which in the first lake stage 
 
 Fig. 361. — Outline map of the later Lake Maumee and of its "Imlay outlet" to 
 Lake Chicago (after Leverett). 
 
 had followed the valley now occupied by the Raisin River south- 
 ward into Indiana, now discharged directly into a bay upon this 
 arm of Lake Maumee, and so formed a delta at Ann Arbor. 
 
 Lakes Arkona and "Whittlesey. — The ice front in the Huron- 
 Erie basin now retired so far that the impounded waters, instead 
 of following the more direct " Imlay outlet " to the Grand, passed 
 at a lower level completely around '' the thumb " of Michigan 
 into the Saginaw basin. Meanwhile a crescent-shaped lake had 
 developed in that basin, so that now the waters of the Maumee 
 basin were joined to those in the Saginaw basin as a common 
 lake, just as the lowering of the waters in Glen Roy caused a 
 union with those of Glen Glaster in the example cited for illus- 
 
GLACIAL LAKES 
 
 333 
 
 tration. Our records of this third North American lake stage, 
 referred to as Lake Arkona, are however most imperfect, for the 
 reason that it was followed by a readvance of the ice front which 
 
 Fig. 362. — Outline map of Lakes Whittlesey and Saginaw (after Leverett). 
 
 closed the passage around " the thumb " and raised the level of 
 the waters until an outlet was found past the town of Ubly at a 
 lower level than the " Imlay outlet." When the waters of a 
 
 Fig. 363. — Map of the glacial Lake Warren, the last of the lakes in the Huron-Erie 
 basin, which discharged through the "Grand River outlet "into the Mississippi 
 (after Leverett). 
 
 lake are thus rising, strong beach formations result, and those of 
 this stage, which is known as the Lake Whittlesey stage, are much 
 the strongest that are found within the Huron-Erie basin. Traced 
 
334 
 
 EARTH FEATURES AND THEIR MEANING 
 
 for some three hundred miles entirely around the southern and 
 western margins of Lake Erie, this beach is for much of the dis- 
 tance the famous " ridge road " (Fig. 362). 
 
 Lake Warren. — As the ice advance which had produced Lake 
 Whittlesey came to an end, the normal recession was resumed 
 and a lake once more formed as a body common to the Saginaw 
 and Erie basins. This lake, known as Lake Warren, extended 
 a shrunk arm far eastward along the ice front into western New 
 York, though it was still blocked from entering the great Mo- 
 3aawk valley (Fig. 363). 
 
 Lakes Iroquois and Algonquin. — It must be evident that 
 toward the close of the Lake Warren stage a profound change was 
 
 Fig. 364. — Map of the Glacial Lake Algonquin (after Leverett). 
 
 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 Atlantic. So soon as the ice front had 
 retired sufficiently to lay bare the bed of the Mohawk, an outlet 
 was found by this route and its continuation down the Hudson 
 valley to the sea. The Lake Ontario basin now became occupied 
 ,by a considerably larger water body known as Lake Iroquois, and 
 
GLACIAL LAKES 
 
 335 
 
 the three upper lakes, then joined as Lake Algonquin, 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 Simcoe, the so-called " Trent outlet." 
 At this time a smaller Lake Erie probably occupied the basin of. 
 that lake, and later the Trent outlet was abandoned for the Port 
 Huron outlet (Fig. 364). 
 
 The Nipissing Great Lakes. — We have now followed the ice 
 front step by step in its retreat across the valley of the St. Law- 
 rence system. The successive unblocking of outlets offers but 
 one further possibility — the opening of the French River-Nip- 
 
 
 
 
 
 
 ">,ji 
 
 
 
 
 
 "\ ^2/2^^"^^ 
 
 
 
 
 
 ^^>^ V. 
 
 
 
 
 
 /0^l^'^^& 
 
 V 
 
 '», 
 
 
 
 /"'•^?s?'f2^,„.'— '"'^ i,^^ 
 
 ^ 
 
 s 
 
 
 
 ' ~'^- V^rCr"'"'^ 
 
 IZ 
 
 
 
 
 /' ^•-^. 
 
 ^'■^s-—^ 
 
 
 
 
 
 ^^^ 
 
 ■^'^^^'^ 
 
 "^^ 
 
 
 ^(^r 
 
 \ ^ /i 
 
 As^ 
 
 
 / 
 
 
 //v«/ 
 
 
 >-^ 
 
 ?■ 
 
 \*/ 
 
 ^^ 
 
 •^^^•rr^' 
 
 
 \ ,^ / 
 
 PJ^ 
 
 ^ 
 
 
 
 
 -, — ^^^^ 
 
 i 
 
 
 " \ 
 
 / i 
 
 1 
 
 i 
 
 
 
 Fig. 365. — Outline map of the Nipissing Great Lakes witii their outlet past North 
 Bay into the Champlain Sea. 
 
 issing Lake-Ottawa River, or " North Bay outlet." Though not 
 so to-day, the bed of this ancient channel was then much lower 
 than that of the '' Mohawk outlet," and so soon as the glacier 
 had in its retreat uncovered this northern channel, 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 St. 
 Lawrence valley and has been called the Champlain Gulf or Sea 
 
336 EARTH FEATURES AND THEIR MEANING 
 
 (Fig. 365). The level of the waters was lowered and the area 
 of the lakes correspondingly reduced. 
 
 The reader who has had no opportunity to observe these an- 
 cient channels which carried the swollen waters of the former 
 glacier lakes, will find it interesting to consider that every one of 
 them has been fixed upon by engineers for improvement as arti- 
 ficial waterways. Thus we have the Illinois Drainage Canal 
 and projected ship canal along the " Chicago outlet," the pro- 
 jected Mississippi-Lake Erie Canal along the " Fort Wajoie out- 
 let," the Grand River canal project to connect Lake Michigan and 
 Saginaw Bay along the course of the " Grand River outlet," the 
 Trent Canal along the " Trent outlet," the Erie Canal along the 
 " Mohawk outlet," and, lastly, the proposed Georgian Bay ship 
 canal to the ocean along the " North Bay" or " Nipissing outlet." 
 
 Summary of lake stages. — We have omitted in this sum- 
 mary of late lake history in the Laurentian basin all the less 
 important lake stages, including some of a transitional nature 
 which were represented by beaches and outlets easily traced to- 
 day. This is because it is an outline only which it seems best to 
 present, and the episodes of this abridged history may be tabu- 
 lated as follows : 
 
 EPISODES OF GLACIAL LAKE HISTORY 
 
 Mississippi Drainage 
 
 Lake Maumee (early X Fort Wayne outlet. 
 
 Lake Maumee (late), Imlay City outlet. 
 
 Lake Arkona, "thumb" outlet. 
 
 Lake Whittlesey (with readvanee of glacier), Ubly outlet. 
 
 Lake Warren, "thumb" outlet. 
 
 Atlantic Drainage 
 
 Lakes Iroquois and Algonquin (early) , Trent and Mohawk outlets. 
 Lakes Iroquois and Algonquin (late) , Port Huron and Mohawk 
 
 outlets. 
 Nipissing Great Lakes, North Bay outlet. 
 
 Permanent changes of drainage affected by the glacier. — While 
 the lake history which we have sketched is made up of episodes 
 which endured only while the ice front lay between certain sta- 
 tions upon its retreat, there were none the less brought about the 
 
GLACIAL LAKES 
 
 337 
 
 profoundest of permanent modifications in the drainage of the 
 region. It is possible to restore upon maps in part only the pre- 
 glacial drainage of the north central states, but we know at least 
 that it was as different as may be from that which we find to-day. 
 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 age. Within the glaciated regions rivers 
 have in many cases been compelled by morainal obstructions to 
 enter upon new courses, or even to travel 
 in the opposite direction along their 
 former channels. In districts of con- 
 siderable relief these diversions have 
 sometimes caused the streams to plunge 
 over the walls of deep valleys, and it 
 may truthfully be said that we owe 
 much of our most beautiful scenery in 
 part to the carving and molding of 
 glaciers, but especially to the cascades 
 and waterfalls directly due to their in- 
 terference with drainage. 
 
 Many diversions or reversals of former 
 drainage lines, through the influence of 
 the continental glacier, are at once sug- 
 gested by the abnormal stream courses, 
 which appear upon our maps, and the 
 correctness of these suggestions may 
 often be confirmed by very simple ob- 
 servations made upon the ground. 
 The map of Fig. 366 shows how differ- 
 ent was the preglacial drainage of the upper Ohio region from 
 that of to-day. 
 
 An interesting additional example is furnished by the Still 
 River which in Connecticut is tributary to the Farmington, and 
 is no less remarkable for its abnormal northerly course and sluggish 
 current perpetrated in its name, than for the way in which it is joined 
 to the Farmington system (Fig. 367 A). A careful study of the 
 district has shown that the Still Kiver was once a part of the 
 Naugatuck and flowed southward toward Long Island Sound like 
 other rivers of the district (Fig. 367 B). It possessed, however, 
 
 Fig. 366. — Probable preglacial 
 drainage of the upper Ohio 
 region (after Chamberlin and 
 Leverett) . 
 
338 
 
 EARTH FEATURES AND THEIR MEANING 
 
 an advantage in a narrow belt of softer rock along its course, and 
 because of this advantage it captured a portion of one of the tribu- 
 taries to the Farmington (Fig. 367 C). The continental glacier 
 later covered the region, 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 (Fig. 367 D). The now 
 impounded waters found their lowest outlet near Sandy Brook, 
 and in waterfalls and cascades the now reversed river falls one 
 
 f 
 
 G/oc/er 
 /?et/re/r>ent 
 
 Fig. 367. — Diagrams to illustrate the episodes in the recent history of the Still 
 River tributary to the Farmington in Connecticut. A, present drainage ; B, early 
 stage ; C, after capture of a tributary to the Farmington ; Z), after blocking by 
 morainal obstructions of the ice age. 
 
 hundred feet to the bed of that stream. With the aid of the 
 excellent topographic maps which are now supplied by a generous 
 government at a merely nominal price, such bits of recent history 
 may be read at many places within the glaciated region. 
 
 Glacial Lake O jib way in the Hudson Bay drainage basin. — 
 When by passing over the " height of land " in northern Onta- 
 rio the greatly reduced continental glacier had vacated the basin 
 of St. Lawrence drainage, it was in a position to impound those 
 waters which normally drained to Hudson Bay. The lake which 
 then came into existence has been called Lake Ojibway and was the 
 latest of the entire series. Though of but recent discovery in 
 a country till lately a trackless wilderness, its extension seems to 
 have been that of the clay beds suited for farming. The beaches 
 and outlets remain to be mapped when the country has been 
 made more easily accessible. 
 
GLACIAL LAKES 339 
 
 Reading References for Chapter XXIII 
 
 Parallel roads of Glen Roy : — 
 Charles Darwin. Observations on the Parallel Roads of Glen Roy 
 
 and of Other Parts of Lochaber in Scotland, with an attempt to prove 
 
 that they are of Marine Origin, Phil. Trans., vol. 8, 1839, pp. 39-82. 
 Louis Agassiz. Geological Sketches, Boston, 1876, vol. 2, pp. 32-76. 
 T. T. Jamieson. On the Parallel Roads of Glen Roy and their Place in 
 
 the History of the Glacial Period, Quart. Jour. Geol. Soe. Lond., 
 
 vol. 19, 1863, pp. 235-259. 
 
 Glacial Lake Agassiz : — 
 
 Warren Upham. The Glacial Lake Agassiz. Mon. 25, U. S. Geol. Surv., 
 
 pp. 658, pis. 38. 
 F. W. Sardeson. Beginning and Recession of St. Anthony's Falls, 
 
 Bull. Geol. Soe. Am., vol. 19, 1908, pp. 29-36. 
 
 Glacial lakes in the St. Lawrence valley : — 
 
 Chamberlin and Salisbury. Geology, vol. 3, pp. 394-405. 
 
 Frank Leverett. Outline of the History of the Great Lakes (Presi- 
 dential Address), 12th Rept. Mich. Acad. Sci., 1910, pp. 19-42. The 
 Pleistocene Features and Deposits of the Chicago Area. Chicago, 
 1897, pp. 86, pis. 8 (Chicago Outlet). 
 
 H. L. Fairchild. Glacial Lakes in Western New York, Bull. Geol. Soe. 
 Am., vol. 6, 1895, pp. 353-374, pis. 18-23 ; Glacial Waters in Central 
 New York. Bull. 127, N. Y. State Mus., 1909, pp. 66, pis. 42, and 
 maps in cover. 
 
 Early lakes in the Erie basin : — 
 Frank Leverett. On the Correlation of Moraines with Raised Beaches 
 
 of Lake Erie, Am. Jour. Sci. (3), vol. 43, 1892, pp. 281-301. 
 F. B. Taylor. The Great Ice Dams of Lakes Maumee, Whittlesey, and 
 
 Warren, Am. Geol., vol. 24, 1899, pp. 6-38, pis. 2-3; Relation of 
 
 Lake Whittlesey to the Arkona Beaches, 7th Rept. Mich. Acad. Sci., 
 
 1905, pp. 30-36. 
 Frank Leverett. The Ann Arbor Folio, Folio No. 155, U. S. Geol. Surv., 
 
 1908, pp. 10-12. 
 
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. — 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 ice, on the 
 one hand, and to the removal of this burden upon the other. We 
 know, at least, that both in northern Europe and in North America 
 areas which have undergone depression during and elevation after 
 the ice age, correspond closely to the regions which were ice cov- 
 ered. Wherever in these regions there was high relief before the 
 advent of the ice, 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 sheet. Such furrowed 
 and half-submerged valleys have a characteristic U-shaped sec- 
 tion, so that their walls rise precipitously from the sea. From 
 their typical occurrence in Scandinavian countries the name fjord 
 has been applied to them. 
 
 It is now no less clear that the removal of the ice blanket brought 
 from the earth a relatively quick response in uphft, which began 
 before the ice front had retired across the present international 
 boundary of the United - States, and that this uplift continued 
 until the final disappearance of the ice. A far slower elevation of 
 a somewhat different nature has continued, even to the present 
 day. 
 
 It is obvious that at the time of their formation all shore lines 
 referable to the work of waves must have been horizontal, 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 basins. We have thus 
 provided for us in the positions of these ancient water planes, 
 particularly because of their wide extent, a complete record the 
 refinement of which is not easily overstated. Interpreting this 
 
 340 
 
UPTILT OF LAND AT CLOSE OF ICE AGE 341 
 
 record, 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 St. Lawrence drainage. The outlet of the 
 Nipissing Great Lakes is to-day more than a hundred feet above 
 the level of the outlet at Port Huron, where the upper lakes are 
 now discharging their waters, and this difference in level can 
 only be ascribed to an upward tilting of the land since the latest 
 of the glacial lake stages. 
 
 The abandoned strands as they appear to-day. — The traveler 
 by steamer upon the upper lakes, as he comes within view of 
 each rocky headland, may note 
 how the profile against the ho- 
 rizon is notched by a series of 
 steps or terraces (Fig. 368), 
 and if he has followed the dis- 
 cussion in previous chapters, 
 
 he will suspect that these ter- Fig. 368. — The notched rock headland 
 
 races mark the now abandoned ^^ ^'^y^'; ^}^^ between Green Bay and 
 
 Lake Michigan (after Goldthwait). 
 
 shore Imes which have come 
 
 to their present position through a series of uplifts of the ground 
 accompanied by earthquake shocks. 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 shore. 
 
 Disembarking from the steamer and traveling inland at any 
 point where the shores are high, the traveler is certain to come 
 upon still more convincing proofs of the ancient strands; perhaps 
 in a storm beach of the unmistakable '' shingle," half buried though 
 it may be under dunes of newly drifted sand, or possibly at higher 
 levels the highway has been cut through a shingle barrier as 
 fresh and unmistakable as though formed upon the present shore. 
 Sometimes it is the rock cliff and terrace, at other times barrier 
 ridges of shingle, or, again, it is the sloping cliff and terrace cut 
 in the drift deposits; but of whatever sort, if studied with proper 
 regard to the topography of the district, the evidence is clear 
 and unmistakable. 
 
 The records of uplift about Mackinac Island. — Nowhere are 
 the records of the recent uplift of the lake region more easily read 
 than about Mackinac Island in the straits connecting Lake Michi- 
 gan with Lake Huron. Approaching the island by steamer from 
 
342 
 
 EARTH FEATURES AND THEIR MEANING 
 
 St. Ignace, its profile upon the horizon is worthy of remark (Fig. 
 369). From a central crest broken by minor irregularities and 
 bounded on all sides by a cliff, the island profile slopes gently 
 away to a still lower clijEf, below which is another terrace. 
 
 Fig. 369. — View of Mackinac Island from the direction of St. Ignace. The ir- 
 regular central portion is the only part of the island that was not submerged in 
 Lake Algonquin. The terrace at its base is the old shore line of Lake Algon- 
 quin, and the lower terrace the strand of Lake Nipissing (after a photograph by 
 Taylor). 
 
 When we have reached the island and have climbed to the 
 summit, we there find the surface which is characteristic of erosion 
 by running water, whereas at lower levels are found the forms 
 carved or molded by the action of waves. This central " island," 
 superimposed upon the larger island, is all that rose above Lake 
 Algonquin, the earliest of the glacial lakes in this northern dis- 
 trict ; and as we look out from the observatory upon the summit, 
 
 it is easy to call up a picture of 
 the country when the lake stood 
 at the base of this highest cliff. 
 To the northward one sees the 
 " Sugar Loaf " rise out of a sea, 
 of foliage, as it formerly did 
 from the waters of Lake Algon- 
 quin (Fig. 370). It is a huge 
 stack near the former island 
 shore. If we turn now to the 
 southward and direct our gaze 
 toward the Fort, we encounter 
 a veritable succession of beach ridges formed of shingle and ranged 
 like a series of waves within the cleared space of the " Short 
 Target Range " (Fig. 371). These ridges mark each a stage within 
 
 TiG. 370. — The "Sugar Loaf," a stack 
 near the shore of Lake Algonquin, as 
 it is seen from the observatory upon 
 Mackinac Island (after a photograph 
 by Taylor). 
 
UPTILT OF LAND AT CLOSE OF ICE AGE 
 
 343 
 
 a series of successive uplifts which have brought the island to 
 its present height. 
 
 Fig. 371. — View from the observatory upon Mackinac Island across the "Short 
 Target Range" toward the Fort. Beach ridges appear in succession within the 
 cleared space (after a photogi-aph by Rossi ter). 
 
 Fig. 372. — Notched stack of the Nipissing Great Lakes at St. Ignace 
 (after a photograph by Taylor). ' 
 
344 
 
 EARTH FEATURES AND THEIR MEANING 
 
 If now we descend from our position and visit the " battle- 
 field," we find there a great ridge of level crest, behind which 
 the British force was stationed in its defense of the island in 
 1812. Near by in the woods is Pulpit Rock, a strikingly perfect 
 stack of the Nipissing Lake. Across the straits at St. Ignace is an 
 
 even finer example of the notched 
 stack (Fig. 372). Other less prom- 
 inent beaches, but all later than the 
 Nipissing Lakes, intervene between 
 this level and the present shore to 
 mark the stages in the continued up- 
 lift of the land. 
 
 The present inclinations of the up- 
 lifted strands. — It is not enough that 
 we should have recognized the marks 
 of former shores now at considerable 
 elevations above the existing lakes; 
 if we are to know the nature of the 
 uplift, we must prepare accurate maps 
 based upon nieasurements by precise 
 leveling at many localities. Such 
 methods are, however, of compara- 
 tively recent application in this field ; 
 and, as in the investigation of so many 
 other problems, the earlier observa- 
 tions were largely of the nature of 
 reconnaissances with the elevation of 
 beaches estimated by comparatively 
 crude methods only. The evolution 
 of ideas concerning the uptilt has, 
 therefore, been a gradual one. 
 
 It was early observed that the 
 beaches corresponding to a given lake 
 stage were higher to the northward 
 and northeastward, and the natural 
 conclusion from this was that the 
 earth's crust had here been canted 
 like a tf'ap door (Fig. 373, A). As we are to see, this but half- 
 con ect a\ssumption has led to a striking prophecy relating to future 
 
 F G. 373. — Series of diagrams to 
 . "lustrate the evolution of ideas 
 c ^ncerning the uplift of the lake 
 n ?ion since the ice age. A, 
 siinple northerly up-canting 
 (Ciilbert) ; B, northerly acceler- 
 ation of the up-canting (Spen- 
 cer and Upham) ; C, northerly 
 "feathering out" of beaches 
 (Spencer and Upham) ; D, hinge 
 line of up-canting found within 
 the I'ake region (Leverett) ; E, 
 multi pie and northwardly mi- 
 gratin g hinge lines of up-canting 
 (Hobbs). 
 
UPTILT OF LAND AT CLOSE OF ICE AGE 
 
 345 
 
 changes within the lake region which we now know to be with- 
 out warrant in the facts. Later it was learned that the uptilt 
 of the lake beaches is much accelerated to the northward (Fig. 
 373, B), and that new beaches make their appearance from be- 
 neath others as 
 we proceed in 
 this direction — 
 there is a " feath- 
 ering out " of 
 beaches to the 
 northward (Fig. 
 373, C). 
 
 The hinge 
 lines of uptilt. 
 — Still later in 
 the study of the 
 region, it was 
 learned that the 
 axis or fulcrum 
 about which the 
 region has been 
 uptilted, instead 
 of lying to the 
 southwa^rd of the 
 lake district, as 
 had been as- 
 
 FiG. 374. — Map of the Great Lakes region to show iso- 
 bases and hinge Hnes of uptilt. a, isobase of the Chicago 
 outlet ; b, main hinge line of the Lake Whittlesey beach 
 (Leverett) ; b^, hinge line of the Lake Warren beach (Tay- 
 lor) ; c, isobase of the Port Huron outlet ; d, main hinge 
 line of liighest Algonquin beach (Goldthwait) ; e, f, g, h, 
 additional hinge lines of Algonquin beaches in Door County 
 peninsula (Hobbs) ; I, isobase of the Lake Superior outlet 
 for the Algonquin beaches (Leverett) ; m, isobase of the 
 same outlet for the Nipissing beaches (Leverett). 
 
 sumed by Gilbert, lay within the region and about halfway up 
 the basin of Lake Michigan (Fig. 373, D, and Fig. 374). Simi- 
 larly, in the uptilt which followed the ice retreat in northern 
 Europe a definite hinge line of movement has been discovered. 
 
 Lastly, it has been shown, as a result of the use of precise level- 
 ing methods, that not one but several hinge lines of movement 
 lie within the region, 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 (Fig. 373, E and Fig. 374). 
 
 The beaches of Lake Maumee, the earliest of the series of lakes 
 within the Huron-Erie lobe and within the extreme southern 
 portion of the Great Lakes area, show only the slightest possible 
 northerly uptilt, and the well-marked hinge line disclosed in the 
 
346 
 
 EARTH FEATURES AND THEIR MEANING 
 
 Whittlesey beach is evidence that the elastic recoil, as it were, 
 from the weight of the mantling glacier did not begin until after 
 the draining of Lake Whittlesey. 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 north- 
 east than does the Whittlesey beach — is one of the greatest im- 
 portance in obtaining a correct idea of the recent uplift ; for it 
 
 S.S.fVf 
 
 n.n.e:. 
 
 Fig. 375. — Series of idealistic diagrams to indicate the nature of the quick recovery 
 of the crust by uplift in blocks unloaded of the ice in succession. A further and 
 slower uptilt, added after the completion of the first movement, is brought out in 
 the last diagram (6')- 
 
 shows that the draining of Lake Whittlesey was followed by 
 a period of quick uplift and seismic activity, that the stage of 
 
UPTILT OF LAND AT CLOSE OF ICE AGE 347 
 
 Lake Warren was one of comparative stability of the land, 
 and, lastly, that the draining of Lake Warren was followed by a 
 second period of rapid uplift and earthquake disturbance. 
 The strongly marked hinge lines, additional to the initial one 
 indicated for the Algonquin beaches in the profiles by Gold- 
 thwait from the west shore of Lake Michigan, when considered in 
 the light of this northeasterly migration of the still earlier hinge 
 line in the southern district, are best explained through the as- 
 sumption of a succession of quick recoveries of the crust by up- 
 lift, separated by periods of relative stability, 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 (Fig. 375). 
 
 The elaborate study of erosion in the outlet of Lake Agassiz 
 had indicated identical interruptions in the up-canting process 
 for that basin. 
 
 Future consequences of the continued uptilt within the lake 
 region. — One of the most distinguished of American geologists, 
 Dr. G. K. Gilbert, in order to determine whether the uptilt revealed 
 by canted beach lines is still in progress, carried out an elaborate 
 study upon the gauge records preserved at the various gauging 
 stations about the Great Lakes. Upon the basis of these studies, 
 he concluded that the uplift continues, that the axes of equal 
 uplift (isobases) take their course about fifteen degrees north of 
 west, so that the lines of greatest uptilt should be perpendicular to 
 this direction, or fifteen degrees east of north. He further believed 
 that the basin was undergoing an up-cant in the simple manner of 
 a trap door, the hinge of which lay to the southward of Chicago, 
 and the study of the gauge records led him to believe that " the 
 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 dis- 
 placed four tenths of a foot in one hundred years." 
 
 Gilbert's prophecy of a future outlet of the Great Lakes to 
 the Mississippi. — The natural rock sill, over which the waters 
 of Lake Chicago once flowed to the Mississippi, is to-day but 
 eight feet above the common mean level of Lakes Michigan and 
 Huron, 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 Chicago, a time must come when the 
 " Chicago outlet" will again come into use and the lakes once 
 
B48 EARTH FEATURES AND THEIR MEANING 
 
 more drain to the Mississippi and the Gulf. Upon the basis of 
 his measurements, Gilbert ventured the prophecy that the first 
 high-water discharge into the Mississippi should occur in from 
 five hundred to six hundred years, and for continuous discharge 
 in fifteen hundred years. In twenty-five hundred years Niagara 
 Falls should at low water stages be dry from this cause, and in 
 thirty-five hundred years it should have become extinct. 
 
 This prophecy, emanating from a high scientific authority and 
 relating to changes of such profound economic and commercial 
 importance, has been often quoted and has taken a firm hold upon 
 the popular imagination. Obviously, 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 region, or, in any event, to the southward of the present 
 Port Huron outlet. We know to-day that instead of being uni- 
 formly distributed over the entire lake region, the uptilting goes 
 on at a much higher rate within the northern areas, 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 outlet. There 
 is, therefore, no known uptilt of the district which separates 
 the present from the former Chicago outlet, and there is no ap- 
 parent natural cause which should result in the reoccupation of 
 the old outlet to the Mississippi. The prophecy must be regarded 
 as one that has been outgrown with the progress of science. 
 
 Geological evidences of continued uplift. — It has recently 
 been claimed, on the basis of a reexamination of Gilbert's study 
 of the lake gauge records, that his methods are open to serious 
 criticism and that in reality the figures afford no evidence of con- 
 tinued uplift of the region. However this may be, there are not 
 lacking geological evidences which do not admit of doubt, and 
 these are in a striking way confirmatory of the latest conclusions 
 upon the manner of the recent uplift. 
 
 If our conclusions have been correct, the several lake basins 
 should now be behaving in different ways as regards the changes 
 upon their shores. If it is true that the lines of greatest uptilt 
 run north-northeasterly, there should be, speaking broadly, a 
 '' spilling over" of waters upon the south-southwesterly shores 
 and a laying bare of the north-northeasterly shore terraces of the 
 
UPTILT OF LAND AT CLOSE OF ICE AGE 349 
 
 basins. This should, however, be true only of basins whose 
 outlets are to the northeastward of the existing main hinge line 
 of uptilt. Lake Huron, having its outlet at the southern margin 
 of its basin, should not have its waters encroaching upon the 
 southern shore, for the simple reason that any continued uptilt 
 of the basin can only have the effect of pouring more water through 
 the outlet. Lake Michigan and Saginaw Bay, which are arms of 
 the Huron basin, ought, however, to become flooded upon their 
 southern shores, were it not that the hinge line of uptilt to-day lies 
 to the northward of the outlet at Port Huron, and, further, that the 
 two connecting channels still have their beds lower than the sill of 
 the outlet channel. Now the evidence goes to show that no en- 
 croachment of waters is occurring upon the Chicago shore of Lake 
 Michigan, and although the shores of Saginaw Bay are so exces- 
 sively flat as to reveal slight changes of level by large migrations 
 of the strand, yet the ancient meander posts fixed by the early 
 surveys are still found near the water's edge. 
 
 Drowning of southwestern shores of Lakes Superior and Erie. — 
 Within the basins occupied by Lakes Superior and Erie, a wholly 
 different condition is found. In each case the outlet is found 
 to the northeastward (Fig. 374, p. 345), 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 shores. In consequence, the waters are encroach- 
 ing upon these shores, and rivers which there enter the lake are 
 drowned at their mouths, with the formation of estuaries. Upon 
 Lake Superior these changes are very marked near Duluth and par- 
 ticularly in the St. Louis River, within which, since the early treaty 
 with the Indians, certain rapids have disappeared and submerged 
 trunks of trees are now found in the channel of the river. As 
 far east as Ontonagon essentially the same conditions are found. 
 
 Upon the shores within the Porcupine Mountain district, the 
 waters are clearly rising. Here old cedar trees may be seen, 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 shore, 
 while others near the shore, but upon the land and still living, are 
 washed by the waves, and losing their lower bark in consequence. 
 An old road along the shore has had to be abandoned because of 
 the encroaching water. 
 
350 
 
 EARTH FEATURES AND THEIR MEANING 
 
 ^::c 
 
 Pi>rt CUnTon 
 
 Upon the opposite or northeastern shore of the lake, on the 
 other hand, the land is everywhere rising out of the water, and 
 the waves are now building storm beaches well out upon the wave- 
 cut terrace. Here the streams, instead of forming estuaries by- 
 drowning, drop dowa 
 
 in rapids to the level 
 of the lake. 
 
 At the southwest- 
 ern margin of Lake 
 Erie there is every- 
 where evidence of a 
 rapid encroachment 
 by the water. In the 
 caves of South Bass 
 Island stalactites, 
 which must obviously 
 have formed above 
 the lake level, are 
 now permanently sub- 
 
 FiG. 376. — Portion of the Inner Sandusky Bay, to 
 afford a comparison of the shore line of 1820 with 
 that of to-day (after Moseley). 
 
 merged. It is, however, about Sandusky Bay upon the south- 
 west shore that the most striking observations have been made. 
 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 shores. It seems to be proven from his 
 studies that the water is now rising in Sandusky Bay at a rate of 
 about 2.14 feet per century. In Fig. 376 there is a comparison 
 of the shores of the inner bay separated by an interval of about 
 ninety years. 
 
 Reading References for Chapter XXIV 
 Uptilt in basin of Lake Agassiz : — 
 Warren Upham. The Glacial Lake Agassiz, Mon. 25, U. S. Geol. Surv., 
 pp. 474-522. 
 
 Uptilt in Laurentian Basin : — 
 G. K. Gilbert. Recent Earth Movement in the Great Lakes Region, 
 
 18th Ann. Rept. U. S. Geol. Surv., 1898, Pt. ii, pp. 595-647. 
 J. W. Spencer. Deformation of the Algonquin Beach, etc., Am. Jour. 
 
 Sci. (3), vol. 41, 1891, pp. 14-16. 
 F. B. Taylor. The Highest Old Shore Line of Mackinac Island, Am. 
 
 Jour. Sci. (3), vol. 43, 1892, pp. 210-218. 
 
XJPTILT OF LAND AT CLOSE OF ICE AGE 351 
 
 A. C. Lawson. Sketch of the Coastal Topography of the North Side of 
 Lake Superior, with reference to the abandoned strands, etc., 20th 
 Ann. Rept. Geol. and Nat. Hist. Surv. Minn., 1893, pp. 181-289, 
 pis. 7-12. 
 
 J. B. WooDwoRTH. Ancient Water Levels of the Champlain and Hudson 
 Valleys, Bull. 84, N.Y. State Mus., 1905, pp. 265, pis. 28. 
 
 E. L. MosELEY. Formation of Sandusky Bay and Cedar Point, Proe. 
 
 Ohio State Acad. Sei., vol. 4, 1905, Pt. v, pp. 179-238. 
 
 F. E. Wright. Rept. Geol. Surv. Mich, for 1903, 1905, p. 37. 
 
 J. W. GoLDTHWAiT. The Abandoned Shore Lines of Eastern Wisconsin, 
 Bull. 17, Wis. Geol. and Nat. Hist. Surv., 1907, pp. 134, pis. 37; A 
 Reconstruction of Water Planes of the Extinct Glacial Lakes in the 
 Lake Michigan Basin, Jour. Geol., vol. 16, 1908, pp. 459-476 ; Iso- 
 bases of the Algonquin and Iroquois Beaches and their Significance, 
 Bull. Geol. Soc. Am., vol. 21, 1910, pp. 227-248, pi. 5; An Instru- 
 mental Survey of the Shore Lines of the Extinct Lakes Algonquin and 
 Nipissing in Southwestern Ontario, Mem. 10, Dept. of Mines, Canada, 
 1910, pp. 57, pis. 4. 
 
 William H. Hobbs. The Late Glacial and Post-glacial Uplift of the 
 Michigan Basin, Pub. 5, Mich. Geol. and Biol. Surv., 1911, pp. 68, 
 pis. 2. 
 
 Lawrence Martin. [Postglacial Modifications in and Around the Great 
 Lakes], Mon. 52, U. S. Geol. Surv., 1911, pp. 455-459. 
 
 Uptilt in northern Europe : — 
 
 G. DE Geer. Quaternary Changes of Level in Scandinavia, Bull. Geol. 
 
 Soc. Am., vol. 3, 1892, pp. 65-68, pi. 2. 
 H. Munthe. Studies in the Late Quaternary History of Southern 
 Sweden, paper No. 25, Livret Guide, Cong. Geol. Intern., 1910, pp. 
 96, many plates and maps. 
 
CHAPTER XXV 
 
 NIAGARA FALLS A CLOCK OF RECENT GEOLOGICAL 
 
 TIME 
 
 Features in and about the Niagara gorge. — A striking ex- 
 ample 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 Ontario. With the aid of borings many of the now buried 
 channels of the region have been followed out, and in a later para- 
 graph we shall refer to some of the stronger lines of the earlier 
 drainage system. Before undertaking the study of Niagara his- 
 tory, it is essential that one become somewhat familiar with the 
 present topography in and about the Niagara gorge. 
 
 Below the present cataract the river flows through a deep gorge 
 for about seven miles before issuing at the Lewiston Escarpment 
 (Fig. 381, p. 355). This gorge has been cut in beds of rock sedi- 
 ments which dip at a gentle angle southward toward Lake Erie. 
 The capping of the rock series is a compact and relatively resist- 
 ant limestone which is known as the Niagara limestone, beneath 
 which there are alternating beds of shale with thinner limestone 
 and sandstone. The plain formed by the upper surface of the 
 limestone capping terminates in the Lewiston Escarpment, which 
 is transverse to the direction of the gorge and ^even miles distant 
 below the Falls. The depth of the gorge varies markedly, the 
 above-water portion being represented at the upper end by the 
 height of the cataract, one hundred and sixty-five feet, while at 
 its lower end near Lewiston it is twice that amount. Halfway 
 down the gorge a sharp turn is made at an angle of more than 
 ninety degrees, and the upstream arm is extended to form a 
 basin which contains the famous whirlpool. This visible exten- 
 sion of the upper gorge is continued in a buried channel, the St. 
 Davids Gorge, which extends to the escarpment, broadening as 
 it does so in the form of a trumpet. The materials which fill 
 this earlier channel are notably coarse glacial deposits (Fig. 389). 
 
 352 
 
A CLOCK OF RECENT GEOLOGICAL TIME 
 
 353 
 
 GcutcoF 
 
 Fig. 377. — Ideal cross section 
 of the Niagara gorge to show 
 the marginal terrace. 
 
 Directly above the whirlpool the Niagara gorge is first con- 
 tracted, but almost immediately swells out into the form of a 
 sausage, which under the name of the Eddy Basin extends to the 
 constricted channel occupied by the Whirlpool Rapids. This Gorge 
 of the Whirlpool Rapids extends to and a little above the railroad 
 bridges, where it again suddenly widens and deepens and with 
 surprisingly uniform cross section now continues as far as the cat- 
 aract. This uppermost section is known as the Upper Great 
 Gorge. About a mile below the whirl- 
 pool is that remarkable projection into 
 the gorge from the Canadian wall which 
 is known as Wintergreen Flats, below 
 which and nearer the river are Fosters 
 Flats. Almost throughout its entire 
 length the Niagara gorge is bordered 
 on either side by a narrow and gently 
 incurving terrace eroded below the gen- 
 eral level of the plain and meeting the 
 gorge in a sharp angle (Fig. 377). 
 
 The features immediately about the cataract show that the Falls 
 are to-day in a condition which, so far as we know, has occurred 
 but once before in their entire history — ■ the waters of the river 
 are divided unequally by an island, and for this reason, as we shall 
 see, the cataract enters over the side wall of the gorge instead of 
 at its end (Fig. 381), although the turning of the channel from this 
 cause is combined with a bend of the river. 
 
 The drilling of the gorge. — There appear to be two important 
 
 processes which are responsible 
 for the recession of the Falls, 
 the rate of which is determined 
 largely by the resistance of the 
 limestone capping and the tena- 
 city of the looser shale beneath 
 it. One of the eroding processes 
 Fig. 378. -View of the bed of the Niagara Operates from below and under- 
 
 River above the cataract, where water minCS the Cap Until the UnSUp- 
 has been drained off in installing a power ported COrnice falls in blocks 
 
 to the bottom of the gorge ; 
 the other makes its attack di- 
 
 plant. Some separated blocks of lime- 
 stone are still in place (after J. W. 
 Spencer). 
 
 2a 
 
354 
 
 EARTH FEATURES AND THEIR MEANING 
 
 rectly from above, 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 (Fig. 378). This process of over- 
 head attack in the powerful currents just above a cataract is even 
 
 , -N M'-? . .., ,x.>»"--- 
 
 :- :-. ■ : - .:J 
 
 Fig. 379. — Falls of St. Anthony, looking westward from Hennepin Island in 1851 
 (after N. H. Winchell, daguerreotype by Hessler of Chicago). 
 
 better illustrated by the Falls of St. Anthony near Minneapolis, 
 which have had a similar history of recession to that of the Niagara 
 Falls (Fig. 379). 
 
 The blocks of the capping limestone at Niagara Falls are to 
 some extent fixed in size by the joint planes present in them, and 
 as they fall to the bottom of the gorge, 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 cataract. Of 
 the retarding effect there is an illustration in the accumulation of 
 the blocks below the American and the intermediate Luna Falls 
 (plate 23 A), which the weaker currents upon the American side 
 find too heavy to handle. The Canadian Fall, with its much greater 
 power, is an example of the promotion of recession through the 
 churning about of the blocks at the base of the cataract. We have 
 here to do with a churn drill which bores its way into the bottom 
 
A CLOCK OF RECENT GEOLOGICAL TIME 
 
 355 
 
 of the gorge with increasing radius of rotary motion with each in- 
 crease in volume of the falling water. Under this rotary churning 
 the soft shales are torn out near the bottom and in suc- 
 
 
 Fig.' 380. — Ideal section to show 
 the nature of the drilling process 
 beneath the cataract. 
 
 cession the harder layers 
 above until the capping is 
 reached (Fig. 380) . The con- 
 ditions appear now to be such 
 that the effective work is 
 largely concentrated, as it 
 usually has been, near the 
 middle of the channel, 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 (Fig. 
 377). 
 
 As must have been noted, 
 one peculiarity of the opera- 
 tion of the churn drill beneath 
 the cataract is that the depth 
 of the gorge will bear a direct 
 proportion to its width, and 
 
 Fig. 381. — Plan and section of the Niagara 
 gorge, showing how in each section the 
 depth is proportional to the width, except 
 in the lowest section where subsequent river 
 action of the normal type has modified the 
 bed of the channel (plan after Taylor and 
 section after Gilbert). 
 
356 
 
 EARTH FEATURES AND THEIR MEANING 
 
 if the volume of water has varied during the process of recession^ 
 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 
 it, modified, however, by the competency to handle the joint blocks 
 of definite size (Fig. 381). 
 
 The present rate of recession. — There are various sketches, 
 more or less accurate, made in the early part of the nineteenth. 
 
 -Jrtixn 
 
 Fig. 382. — Comparison of a sketch of the Canadian Fall made with the aid of a 
 ' camera lucida in 1827 with a photograph taken from the same view point in 1895 
 (after Gilbert). 
 
 century, and from the later period there are daguerreotypes, photo- 
 graphs, and maps, which refer especially to the Canadian Fall; and 
 which, taken together, render possible a comparison of the earlier 
 with the later brinks. By comparing the earliest with the recent 
 views it is seen at a glance that the Falls are receding, and at a 
 quite appreciable rate (Fig. 382). A careful comparison of the 
 
A CLOCK OF RECENT GEOLOGICAL TIME 
 
 357 
 
 maps made in 1842, 1875, 1886, 1890, and 1905 of the brink of 
 
 the Canadian Fall (Fig. 383) indicates that for the period covered 
 
 the rate of recession has been about five feet per year, and similar 
 
 studies made of the 
 
 American Fall show that 
 
 it has been receding at 
 
 the rate of only three 
 
 inches per year, or one 
 
 twentieth the rate of the 
 
 recession of the Canadian 
 
 Fall. 
 
 Future extinction of the 
 American Fall. — It is 
 because of this many 
 times more rapid reces- 
 sion of the Canadian 
 Fall that the Niagara 
 cataract, instead of lying 
 athwart the gorge, enters 
 it from its side. The 
 Canadian Fall is thus in 
 reality swinging about 
 the American, and the 
 time can already be 
 
 roughly estimated when Fig. 383. — Map to show the recession of the brink 
 this more effective drill- of t^® Canadian Fall, based upon maps of differ- 
 
 ing tool will have brought "°* ^^**^' ^^^*'' ^"^''■*^- 
 about a capture, so to speak, of the American Fall through the 
 cutting off of its water supply. It will then be drained and left 
 literally " high and dry," an enduring witness to the geological 
 effect of an island in making an unequal division of the waters for 
 the work of two cataracts. 
 
 As already pointed out, the inefficiency of the American Fall 
 as an eroding agent is amply attested by the wall of blocks 
 already appearing above the water below it. The tourist who a 
 thousand years hence pays a visit to the Niagara cataract, pro- 
 vided the water flow is allowed to remain as it has been, will find 
 above this rampart of blocks a bare cliff in part undermined, and 
 surmounted by a nearly flat table surface which is cut off from the 
 
358 
 
 EARTH FEATURES AND THEIR MEANING 
 
 existing cataract by a higher section of the gorge (Fig. 384). It 
 is quite hkely that this table will furnish the most satisfactory 
 viewpoint of the future cataract of that date. 
 
 Fig. 384. — Comparison of the present with the future fal's. 
 
 The captured Canadian Fall at Wintergreen Flats. — What we 
 have predicted for the future of the present American Fall will 
 be the better understood from the study of a monument to ear- 
 lier capture made long before the upper section of the gorge had 
 been cut or the whirlpool had come into existence. The tables 
 were then turned, for it was a fall upon the Canadian side of the 
 gorge that was captured by one upon the American. The locality 
 is known as Wintergreen Flats, or sometimes as Fosters Flats; 
 though the first name properly applies to a higher surface near the 
 
 Fig. 3S5. — Bird's-eye view of the captured Canadian Fall at Wintergreen Flats, 
 showing the section of the river bed above the cliii and the blocks of fallen Niagara 
 limestone strewn over the abandoned channel below (after Gilbert). 
 
A CLOCK OF RECENT GEOLOGICAL TIME 359 
 
 brink of the gorge, and Fosters Flats to a lower plain near the level 
 of the river (see Fig. 381, p. 355). The peculiar topographic fea- 
 tures at this locality are well brought out in Gilbert's bird's-eye 
 view of the locality (Fig. 385) ; in fact, in some respects better 
 than they appear to the tourist upon the ground, 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 view. For one who has studied the existing 
 cataract this early monument is full of meaning. Standing, as 
 one may, upon the very brink of the former cataract, it is easy 
 to call up. in imagination the grandeur of the earlier surroundings 
 and to hear the thunder of the falling water. A particularly vivid 
 touch is added when, in digging over the sand about the great 
 blocks of fallen limestone underneath the brink, one comes upon 
 the shells of an animal still living in the Niagara River, though only 
 in the continual spray beneath the cataract. 
 
 The Whirlpool Basin excavated from the St. Davids Gorge. — 
 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 St. Davids (Fig. 389, p. 363). In plan this 
 buried gorge has a trumpet form, being more than two miles wide 
 at its mouth and narrowing to the width of the upper gorge before 
 it has reached the Whirlpool. Near the Whirlpool it has been in 
 part excavated by Bowman Creek, thus revealing walls that are 
 well glaciated. Different opinions have been expressed concerning 
 the origin of this channel, one being that it is the course either of 
 a preglacial river or one incised between consecutive glacial in- 
 vasions ; and another that it is a cataract gorge drilled out between 
 glacial invasions after the manner of the later Niagara gorge. In 
 either case its contours have been much modified by the later 
 glacier or glaciers, whose work of planing, polishing, and widening 
 is revealed in the exposed surfaces ; and it is not improbable that 
 a cataract has receded along the course of an earlier river valley. 
 
 As we shall see, there are facts which point rather clearly to an 
 earlier cataract which ended its life immediately above the present 
 Whirlpool. When the later Niagara cataract had receded to near 
 the upper end of the Cove section, or near the present Whirlpool, 
 the falling water must have been separated from this older channel 
 and its filling of till deposits by only a thin wall of rock, and this 
 
360 
 
 EARTH FEATURES AND THEIR MEANING 
 
 must have been constantly weakened as its thickness was further 
 reduced. 
 
 When this weakened dam at last gave way, it must have pro- 
 duced a debacle grand in the extreme. It is hardly to be conceived 
 that the " washout " of the ancient channel to form the Whirl- 
 pool Basin could have occupied more than a small fraction of a 
 day, though it is highly probable that the broken rock partition 
 below the Whirlpool was not immediately removed entire. The 
 manible-like termination of the Eddy Basin immediately above 
 the Whirlpool has led Taylor to believe that the cataract quickly 
 reestablished itself at this point upon the last site of the extinct 
 St. Davids cataract. If reduced in power for a short interval, as a 
 result of the obstructions still remaining in the lately broken dam 
 below the Whirlpool, the remarkable narrowing of the gorge at 
 this point would be sufficiently accounted for. 
 
 Being compelled to turn through more than a right angle after 
 it enters the Whirlpool Basin, 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 (Fig. 386). 
 
 In tearing out the loose deposits which had filled this part of 
 
 the buried St. Davids Gorge, 
 many bowlders of great size 
 were left which slid down the 
 slope and in time produced an 
 armor about the looser deposits 
 beneath, so as to protect them 
 and prevent continued excava- 
 tion. Thus it is found that the 
 submerged northwestern wall 
 of the basin is sheathed with 
 bowlders large enough to retain 
 
 Fig. 386. — Map of the Whirlpool Basin, ,, .... j j. 
 
 ,.,,,., „ ,., ,, ; their positions and so stop a 
 
 showing the rock side walls like those of ^ ^ 
 
 the Niagara Gorge, and the drift bank natural prOCCSS of placer OUt- 
 which forms the northwest wall (after washing Upon a gigantic SCale 
 
 ^^^^^^*)- (Fig. 386). 
 
 The shaping of the Lewiston Escarpment. — To understand 
 the formation of the Lewiston Escarpment cut in the hard Niagara 
 limestone, it is necessary to consider the geology of a much larger 
 
A CLOCK OF RECENT GEOLOGICAL TIME 
 
 361 
 
 area — that of the Great Lakes region as a whole. 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 ocean. In a period still very many times as long 
 ago as the events we have under discussion, there were laid down 
 off the shore of this oldland a series of unconsolidated deposits 
 which, hardened in the course of time, and elevated, are now repre- 
 sented by the shales, sandstone, and limestone which we find, one 
 above the other, in the Niagara gorge in the order in which they 
 were laid down upon the ocean floor. The formations represented 
 
 Fig. 387. — Map- to show the cuestas which have played so important a part in 
 fixing the boundaries of the Lake basins, and also the principal preglacial rivers 
 by which they have been trenched (based upon a map by Grabau). 
 
 in the gorge are but a part of the entire series, for other higher mem- 
 bers are represented by rocks about Lake Erie and even farther 
 to the southward. These strata, having been formed upon an out- 
 ward sloping sea floor, had a small initial dip to the southward, 
 and this has been probably increased by subsequent uptilt, including 
 the latest which we have so recently had under discussion. At 
 the present time the beds dip southward by an angle of less than 
 four degrees, or about thirty-five feet in each mile. 
 
362 
 
 EARTH FEATURES AND THEIR MEANING 
 
 When the elevation of the land in the vicinity of this shore had 
 caused a recession of the waters, 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 (Fig. 
 272, p. 246), The rivers from the oldland cut their way in narrow 
 trenches across the newland, and because of the harder limestone 
 formations, 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 " trellis drainage." 
 It is characteristic of this drainage that 
 few tributaries of the second order will 
 flow up the natural slope of the beds, 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 (Fig. 387). 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 formations. Such 
 
 Tig. 388. — Birds-eye view i i i • • • i • 
 
 of the cuestas south of flat-topped uplands m series with mter- 
 
 Lakes Ontario and Erie mediate lowlands and separated by sharp 
 
 (after Gilbert). escarpments are known as cuestas (see p. 
 
 246), and the Lewiston Escarpment limits that formed in Niagara 
 
 Umestone (Figs. 387 and 388). 
 
 Episodes of Niagara's history and their correlation with those 
 of the Glacial Lakes. — Of the early episodes of Niagara's history, 
 our knowledge is not as perfect as we could desire, but the later 
 events are fully and trustworthily recorded. 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 territory, thus for the first time 
 allowing the waters from the Erie basin to discharge over the Lewis- 
 ton Escarpment into the basin of the newl}'^ formed Lake Iroquois 
 (Fig. 364, p. 334). Since the level of Lake Iroquois was far above 
 that of the present Lake Ontario, the new-born cataract was not 
 the equivalent in height of the escarpment to-day. The Iroquois 
 
A CLOCK OF RECENT GEOLOGICAL TIME 
 
 303 
 
 Our/et onef 7*« 
 o/aenmff ofouf-/e-f- 
 into £r/9 bas/n. 
 
 waters then bathed all the lower portion of the escarpment, so 
 that the foot of the Fall was upon the borders of the Lake. 
 
 In order to interpret the history of the Niagara gorge, we must 
 remember that the effective drilling of this gorge was in each stage 
 dependent mainly upon 
 the volume of water dis- 
 charged from Lake Erie, 
 a large discharge being 
 recorded by a channel 
 drilled both wide and 
 deep, while that pro- 
 duced by the discharge 
 of a smaller volume was 
 correspondingly narrow 
 and shallow. To-day 
 the gorges of large cross 
 section have, moreover, 
 a relatively placid sur- 
 face, whereas through the 
 constricted sections the 
 water of the river is un- 
 able to pass without first 
 raising its level at the 
 upper end and under the 
 head thus produced rush- 
 ing through under an in- 
 creased velocity. The 
 
 Fig. 389. — Sketch map of the greater portion of 
 the Niagara Gorge to show the changes in cross 
 section in their relations to Niagara history 
 (based upon a map by Taylor). 
 
 best illustration of such a constricted section is the Gorge of the 
 Whirlpool Rapids. 
 
 Our reading of the history should begin at the site of the present 
 cataract, since the records of later events are so much the more 
 complete and legible, and it should ever be our plan to proceed 
 from the clearly written pages to those half effaced and illegible. 
 
 As we have learned, the most abrupt change in the cross section 
 of the gorge is found a little above the railroad bridges, where the 
 Upper Great Gorge is joined to the Gorge of the Whirlpool 
 Rapids (Fig. 389). In view of the remarkably uniform cross 
 section of the Upper Great Gorge, there is no reason to doubt that 
 it has been drilled throughout under essentially the same volume 
 
364 EARTH FEATURES AND THEIR MEANING 
 
 of water, and that its lower limit marks the position of the former 
 cataract when the waters from the upper lakes were transferred 
 from the " North Bay Outlet " into the present or " Port Huron 
 Outlet " and Lake Erie. As the upper limit of the Gorge of the 
 Whirlpool Rapids thus corresponds to the closing of the " North 
 Bay Outlet " and the extinction of the Nipissing Great Lakes, 
 so its lower limit doubtless corresponds to the opening of that outlet 
 and the termination of the preceding Algonquin stage ; for in the 
 stage of the Nipissing lakes the water of the upper lakes, as we 
 have learned, reached the ocean through the northern outlet. 
 
 Mr. Frank Taylor, who has given much study to the problem 
 of Niagaran history, believes that the Middle Great Gorge, com- 
 prising the Eddy Basin and the Cove section, represents the gorge 
 drilling which occurred during the later stage of Lake Algonquin 
 after the " Trent Outlet " had been closed and the waters of the 
 upper lakes had been turned into the Erie Basin. 
 
 Summarizing, then, the episodes of the lake and the gorge history 
 are to be correlated as follows: — 
 
 Glacial Lake Niagara Gorge 
 
 Early Lakes Iroquois and Algon- Drilling of the gorge from the 
 quin. Lewiston Escarpment to the Cove 
 
 section above the Wintergreen Flats. 
 
 Later Lakes Iroquois and Algon- Drilling of Middle Great Gorge, 
 quin with upper lakes discharging 
 into Erie basin. 
 
 Nipissing Great Lakes with the Drilling of the narrow Gorge of 
 upper lake waters diverted from the Whirlpool Rapids. 
 Lake Erie. 
 
 Recent St. Lawrence drainage Drilling of Upper Great Gorge to 
 since the waters of the upper lakes the present cataract, 
 were discharged into Lake Erie 
 through occupation of the Port 
 Huron Outlet. 
 
 Time measures of the Niagara clock. — In primitive civiliza- 
 tions time has sometimes been measured by the lapse necessary 
 to accomplish a certain task, such, for example, as walking the 
 distance between two points ; and the natural clock of Niagara 
 has been of this type. But men possess differences in strength 
 and speed, and the same man is at some times more vigorous than 
 
A CLOCK OF RECENT GEOLOGICAL TIME 365 
 
 at others, and so does not work at a uniform rate. The cataract 
 of Niagara, charged with the pent-up energy of the waters of all 
 the Great Lakes, can rush its work as it is clearly unable to do at- 
 times when the greater part of this energy has been diverted.. 
 Units of distance measured along the gorge are therefore too un- 
 reliable for our use, with the unique exception of the stretch from 
 the railroad bridges to the site of the present cataract, within 
 which stretch the gorge cross sections are so nearly uniform as to 
 indicate an approximation to continued application of uniform 
 energy. This energy we may actually measure in the existing 
 cataract, and so fix upon a unit of time that can be translated into 
 years. 
 
 In order to secure the normal rate of recession of this Upper 
 Great Gorge, we should add to the volume of water in the Canadian 
 Fall that now passing over the American; 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 planes, the effect of this added energy it is not easy 
 to estimate. We may be sure, however, that the drilling action 
 would be somewhat increased by the junction of the two Falls, 
 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 Fall. 
 The Upper Great Gorge is about two miles in length, and its begin- 
 ning may thus be dated near the dawning of the Christian Era. 
 The Whirlpool Gorge was cut when the ice vacated the North Bay 
 Outlet in Canada, and still lay as a broad mantle over all north- 
 eastern Canada. For the earlier gorge and lake stages, the time 
 estimates are hardly more than guesses, and we need not now con- 
 cern ourselves with them. 
 
 The horologe of late glacial time in Scandinavia. — A glacial 
 timepiece of somewhat different construction and of greater refine- 
 ment has been made use of in Scandinavia to derive the " geo- 
 chronology of the last 12,000 years." Instead of retreating over 
 the land and Impounding the drainage as it did so, the latest con- 
 tinental glacier of Scandinavia ended below sea level, and as it 
 retired, its great subglacial river laid down a giant esker known as 
 the Stockholm Os, which was bordered by a delta and fringed on 
 either side by water-laid moraines of the block type. These re- 
 
366 EARTH FEATURES AND THEIR MEANING 
 
 cessional moraines are upon the average less than 1000 feet apart, 
 and are believed to have each been formed in a single season. The 
 delta deposits which surround the esker are of thin-banded clay, 
 and as an additional uppermost band is found outside every mo- 
 raine, these bands are also believed to represent each the delta 
 deposit of a single year. In studies extending over many years. 
 Baron de Geer, with the aid of a large body of student helpers, 
 has succeeded in completing a count of moraines and clay layers, 
 and so in determining the time to be 12,000 years since the ice 
 front of the latest continental glacier lay across southern Sweden. 
 The fertility of conception and the thoroughness of execution of 
 this epoch-making investigation recommend its conclusion to the 
 scientific reader. 
 
 Reading References for Chapter XXV 
 
 G. K. Gilbert. Niagara Falls and their History, Nat. Geogr. Soc. 
 Mon., vol. 1, No. 7, 1895, pp. 20.3-236. 
 
 F. B. Taylor. Origin of the Gorge of the Whirlpool Rapids at Niagara, 
 
 Bull. Geol. Soc. Am., vol. 9, 1898, pp. 59-84. 
 A. W. Grabau. Guide to the Geology and Paleontology of Niagara 
 
 Falls and Vicinity, Bull. N. Y. State Mus., vol. 9, No. 45, 1901, pp. 
 
 1-85, pis. 1-11. 
 J. W. Spencer. The Falls of Niagara, ete. Dept. of Mines, Geol. Surv. 
 
 Branch, Canada, 1907, pp. 490, pis. 43. 
 
 G. K. Gilbert. Rate of Recession of Niagara Falls, ete. Bull. 306, U. S. 
 
 Geol. Surv., 1907, pp. 31, pis. 11. 
 G. DE Geer. Quaternary Sea Bottoms of Western Sweden. Paper 23, 
 Livret Guide Cong. Geol. Interri., 1910, pp. 57, pis. 3. 
 
CHAPTER XXVI 
 LAND SCULPTURE BY MOUNTAIN GLACIERS 
 
 Contrasted sculpturing of continental and mountain glaciers. — 
 In discussing in a previous chapter the rock pavement lately un- 
 covered by the Greenland glacier, we learned that this surface had 
 been lowered by the processes of plucking and abrasion, the com- 
 bined effect of which is always to reduce the irregularities of the 
 surface, soften its outlines, and from sharply projecting masses to 
 develop rounded shoulders of rock — roches moutonnees. 
 
 Though the same processes act in much the same manner beneath 
 mountain glaciers, though here upon all parts of the bed, they are, 
 in the earlier stages. at least, subordinated to a third process more 
 important than the two acting together. Sculpture by mountain 
 glaciers, instead of reducing surface irregularities and softening 
 outlines, increases the accent of the relief and produces the most 
 sharply rugged topography that is known. In nearly all places 
 where Alpinists resort for difficult rock climbing, mountain gla- 
 ciers are to be seen, or the evidence for their former presence may 
 be read in unmistakable characters. 
 
 Wind distribution of the snow which falls in mountains. — 
 Until quite recently students of glaciation have concerned them- 
 selves but little with the work of the wind in lifting and redis- 
 tributing the snow after it has fallen. We have already seen that, 
 for the continental glaciers, wind appears to be the chief trans- 
 porting agent, if we except the marginal lobes where glacier flow 
 assumes large importance. In the case of mountain glaciers, also, 
 we are to find that for the earlier stages particularly wind is of the 
 first importance as a redistributing agent. In the higher levels 
 snow is swept up from the ground by all high winds, and does not 
 find a resting place until it is dropped beneath an eddy in some 
 irregularity of the surface; and if the inherited surface be rela- 
 
 367 
 
368 
 
 EARTH FEATURES AND THEIR MEANING 
 
 lively smooth, this will be found in most cases upon the lee of the 
 mountain crest. 
 
 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 streams. These become, then, the sites of snow- 
 drifts that are augmented in size from year to year, though at 
 first they melt away in the late summer. 
 
 The niches which form on snowdrift sites. — Wherever a drift 
 is formed, a process is set in operation, the effect of which is to 
 hollow out and lower the ground beneath it, a process which has 
 been called nivation. The drift shown in Fig. 390 was photo- 
 graphed in late summer at an elevation of some 9000 feet in the 
 Yellowstone National Park. The very gently sloping surface 
 
 Fig. 390. 
 
 ■ Snowdrift hollowing its bed by nivation and building a delta (at the 
 left). Quadrant Mountain, Yellowstone National Park. 
 
 surrounding the drift is covered with grass, but within a zone a 
 few feet in width on the borders of the drift no grass is growing, 
 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 drift. 
 This is explained by the water permeating the crevices of the rock 
 and being rent by the nightly freezing. Farther from the drift 
 the ground is dry, and no such action is possible. With each suc- 
 ceeding 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 delta. 
 By the operation of this process of nivation the higher parts of the 
 
LAND SCULPTURE BY MOUNTAIN GLACIERS 369 
 
 drift site are lowered as deposition goes on upon the lower. The 
 combined effect is thus to produce a niche or faintly etched amphi- 
 theater upon the slope of the mountain (Fig. 391). 
 
 Fig. 391. 
 
 ■Amphitheater formed on a drift site in northern Lapland (after a 
 photograph by G. von Zahn). 
 
 The augmented snowdrift moves down the valley — birth of 
 the glacier. — In still lower air temperatures the drifts enlarge with 
 each succeeding year until they endure throughout the summer 
 season. From this stage on, an increment of snow is left from each 
 succeeding season. No longer entirely wasted by melting, the 
 time soon comes when the upper snow layers will by their weight 
 compress the lower into ice, and the mass will begin to creep down 
 the slope along the course of the inherited valley. The enlarged 
 snowdrift which feeds this ice stream is called the neve or firn. 
 
 Against the sloping cliff which had been shaped by nivation 
 at the upper margin of the snowdrift, that snow which is not of 
 sufficient depth to begin a movement towards the valley separates 
 from the moving portion, opening as it does so a cleft or crevasse 
 
 2b 
 
370 
 
 EARTH FEATURES AND THEIR MEANING 
 
 parallel to the wall. This crack in the snow is called by its Ger- 
 man name Bergschrund or Randspalte, and may perhaps be re- 
 ferred to as the marginal crevasse 
 (Fig. 392). 
 
 The excavation of the glacial 
 amphitheater or cirque. — It has 
 been found that the marginal cre- 
 vasse plays a most important role 
 in the sculpture of mountains by 
 glaciers, for the great amphitheater 
 which is everywhere the collecting 
 basin for the nourishment of moun- 
 tain glaciers is not an inherited 
 feature, but the handiwork of the 
 ice itself. This was the discovery 
 of Mr. W. D. Johnson, an American 
 topographer and geologist, who, 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 California. 
 Let down a distance of a hundred and fifty feet, he reached the 
 bottom of the crack, 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 
 crevasse. 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 surface. 'With the sinking of 
 the sun below the peaks the sudden chill, so characteristic of the 
 end of the day in high mountains, causes this water to freeze and 
 thus rend the rock along its planes of jointing. Broad and thin 
 plates of ice, loosened by melting at the walls, could be extracted 
 from the crevices of the rock as mute witnesses to the powerful 
 stresses developed by this most vigorous of weathering processes. 
 
 In short, the rock wall above the glacier, which in its initial 
 stage was the upper wall of the niche hollowed beneath the snow- 
 drift, is first steepened and later continually both recessed and 
 deepened by an intensive frost rendmg which is m operation at 
 
 Pig. 392. — The marginal crevasse or 
 Bergschrund on the highest margin 
 of a glacier (after Gilbert). 
 
LAND SCULPTURE BY MOUNTAIN GLACIERS 371 
 
 O 
 
 Scale. 
 
 ^Miles. 
 
 Fig. 393. — Niches and cirques in the same 
 vicinity in the Bighorn Mountains of 
 Wyoming. A, A, unmodified valleys; 
 B, B, niches on drift sites ; C, C, cirques 
 on small glacier sites (after map by 
 F. E. Mathes, U. S. G. S.). 
 
 the base of the marginal crevasse. The same process does not go 
 on as rapidly above the surface of the neve for the reason that the 
 necessary wetting of the rock surface does not there so generally result 
 from the daily summer thaw. 
 At the bottom of the marginal 
 crevasse alone is this condition 
 fully realized. Intensive frost 
 action where the rock is wet with 
 thaw water daily is thus a 
 fundamental cause, both of the 
 hollowing of the early drift site 
 to form the niche, and of the 
 later enlargement of this niche 
 into an amphitheater or cirque 
 when the drift has been trans- 
 formed into the neve of a 
 glacier. Inasmuch as the cre- 
 vasse forms where the snow and 
 ice pull away from the rock 
 toward the middle of the depression, the cirque wall in its early 
 stage has the outline of a semicircle. In the Bighorn Mountains 
 of Wyoming, all stages, from the unmodified valley heads to the 
 
 full-formed cirque, may be seen near 
 one another (Fig. 393). It will be 
 noted that wherever a glacier has 
 formed, as indicated by the cirque, 
 there is a series of lakes which have 
 developed in the valley below (see 
 p. 412). 
 
 Life history of the cirque. — In its 
 earliest stage the cirque is more or 
 less uniformly supplied with snow 
 from all sides, and so it enlarges by 
 recession in a manner to retain its 
 early semicircular outline. In a later 
 Fig. 394. — Subordinate small cir- stage a larger proportion of the snow 
 ques in the amphitheater on the reaches the cirque at its sides so that 
 
 west face of the Wannehorn ., « ,i , ... 
 
 above the Great Aietsch Glacier ^^^ further enlargement causes it to 
 of Switzerland. broaden and to flatten somewhat that 
 
372 
 
 EARTH FEATURES AND THEIR MEANING 
 
 Fig. 395. — "Biscuit cutting" effect of glacial sculpture in the Uinta Mountains of 
 Wyoming (after Atwood) . 
 
 part of its outline which represents the head of the valley (Fig. 
 
 398, p. 364). As the territory of the upland is still further invested 
 
 by the cirques, their nourish- 
 ment becomes still more irreg- 
 ular, and the circular outline 
 gives place to a scalloped 
 border, as the amphitheater 
 becomes differentiated into 
 subordinate smaller cirques, 
 each of which corresponds to a 
 scallop of the outhne (Fig. 398 
 and Fig. 394). 
 
 Grooved and fretted up- 
 lands. — ,The partial invest- 
 ment by cirques of a mountain 
 upland yields a type of topog- 
 raphy quite unlike that pro- 
 duced by any other geological 
 process. The irregularly con- 
 nected remnants of the inher- 
 ited upland resemble nothing 
 
 Fig. 396. — Two intersecting inverted SO much aS a layer of dough 
 
 cones representing glacial cirques of dif- from which bisCuits have been 
 ferent sizes, to show that their intersec- , /tt or>r\ mi e 
 
 tion is the arc of a hyperbola, the curve ^^* ^^^S" ^^5) • The SUrf ace aS 
 
 to which the col approximates. a whole, furrowed as it is below 
 
Plate 18. 
 
 A. Fretted upland of the Alps seen from the summit of Mount Blanc. 
 
 B. Model of the Malaspiua GLieier aiiJ A.^ l.^^ud ^^^iand above it (after model by 
 
 L. Martin). 
 
Plate 19. 
 
 A. Contour map of a grooved upland, Bighorn Mountains, Wyoming 
 (U. S. Geol. Survey). 
 
 B. Contour map of a fretted upland, Philipsburg Quadrangle, Montana 
 (U. S. Geol. Survey). 
 
LAND SCULPTURE BY MOUNTAIN GLACIERS 373 
 
 the cirques, may be described as a grooved upland (plate 19 A). 
 A further continuation of the process removes all traces of the 
 earlier upland, for the cirques intersect from opposite sides and 
 thus yield palisades of sharp rock pinnacles which rise on pre- 
 cipitous walls from a terraced floor. This ultimate product of 
 cirque sculpture by glaciers is called a fretted upland (plate 18 
 A and 19 B). 
 
 The features carved above the glacier. — The ranges of pin- 
 nacles carved out by mountain glaciers have become known by 
 various names of foreign derivation, such as arete, grat, aiguille 
 
 Fig. 397. — A col shaped like a hyperbola between Mount Sir Donald and Yogo 
 Peak in the Selkirks (after a plate by the Keystone Plate Co.). 
 
 mountains, " files of gendarmes," etc. They may, perhaps, be 
 best referred to as comb ridges, and according to their position they 
 are differentiated into main and lateral comb ridges, as will be 
 clear from the second map of plate 19. 
 
 With the gradual invasion of the upland upon which the cirques 
 have made their attack, the area from which winds may gather 
 
374 
 
 EARTH FEATURES AND THEIR MEANING 
 
 Groo\/£d Upuund 
 
 (Youth) 
 
 up the snow is steadily diminished, and hence cirque recession is 
 correspondingly retarded. Cirques which have approached each 
 other from opposite sides of the ridge until they have become tan- 
 gent at one point may, however, still receive nourishment at the 
 sides and so continue to cut down the intervening rock wall to 
 form a pass or col. The theoretical curve which results from 
 
 this intersection is that 
 known as the hyperbola, 
 of which an illustration 
 is afforded by Fig. 396. 
 An approximation to this 
 form is clearly furnished 
 by most of the mountain 
 passes in glaciated moun- 
 tain districts, and a par- 
 ticularly good illustration 
 is furnished from the 
 vicinity of Glacier on the 
 line of the Canadian Pa- 
 cific Railway (Fig. 397). 
 Upon either side of the 
 col the land mass is left 
 in high relief, rising from 
 a more or less triangular 
 base (Fig. 398, III) into a sharp horn or tooth. An illustration 
 of such a horn is furnished by the Matterhorn in the Swiss Alps, 
 or by Mount Sir Donald in the Selkirks, though less noteworthy 
 examples may be found in every maturely .glaciated mountain 
 district. 
 
 The features shaped beneath the glacier. — Those features 
 which are carved above the glacier — the comb ridge, the col, 
 and the horn — are all shaped as a result of intensive weathering 
 upon the cirque wall. The shaping at lower levels is accomplished 
 by processes in operation below the glacier surface, where weather- 
 ing is excluded and where plucking and abrasion work together 
 to tear away and grind off the rock surface. By their joint action 
 the valley is both deepened and widened, directly to the height of 
 the glacier surface, and indirectly through undermining as far up 
 as rock extends. Thus the valley is transformed into one of broad 
 
 # 
 
 M 
 
 ('Ma^-ur/ryJ 
 
 Fig. 398. — Diagrams to illustrate the progres- 
 sive investment of an upland by cirques with 
 the formation of comb ridges, cols, and horns. 
 I, early stage, youth ; II, intermediate stage ; 
 III, late stage, maturity. 
 
LAND SCULPTURE BY MOUNTAIN GLACIERS 375 
 
 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 (Fig. 
 399). 
 
 As high up in the valley as it has been occupied by the glacier, 
 the bed is rounded, smoothed, and polished, and marked by the 
 characteristic glacial scorings or 
 striae which point down the val- "\. 
 ley. Above the level of the gla- 
 cier's upper surface, on the other 
 hand, erosion is accomplished 
 through undermining or sapping, 
 a process which always leaves 
 precipitous slopes of ragged sur- 
 face made up of the joint planes 
 on which the fallen blocks have 
 separated from the cliff. Thus 
 there is found a sharp line which separates the smoothly rounded 
 
 Fig. 399. — The U-shaped Kern valley 
 in the Sierra Nevadas of California 
 (after W. B. Scott). 
 
 Fig. 400. — Glaciated vallej' wall in the Sierra Nevadas of California, showing the 
 sharp line which separates the abraded from the undermined rock surface (after 
 a photograph by Fairbanks). 
 
376 
 
 EARTH FEATURES AND THEIR MEANING 
 
 rock surface below from the jagged and precipitous one above 
 (Fig. 400). Inasmuch as this boundary usually separates the 
 scalable from the inaccessible slopes above, snow is apt to lodge 
 at this level and make it strikingly apparent. 
 
 If uplift of the land occurs while glaciers occupy the valleys of 
 mountains, an increased capacity for deepening the valley is im- 
 parted to these ice 
 streams, and we find, 
 as a result, a deep 
 central valley of U 
 cross section exca- 
 vated within a rela- 
 tively broad trough 
 visible above the 
 shoulder oneither side 
 of the later furrow. 
 Save only for its 
 characteristic curves, 
 such a valley bears 
 close resemblance to 
 a mature stream val- 
 ley which has been rejuvenated (see p. 173). The remnants of the 
 earlier glacier-carved valley are, as already stated, gently curving 
 high terraces so common in Switzerland, where they are known as 
 albs or high mountain meadows. These albs may be seen to special 
 advantage on the sides of the Chamonix valley (Fig. 401), the 
 Lauterbrunnen valley, or in fact almost any of the larger Alpine 
 valleys. 
 
 The cascade stairway in glacier-carved valleys. — If now, instead 
 of giving our attention to the cross section, we follow the course 
 of the valley that has been occupied by a glacier, we find that it 
 descends by a series of steps or terraces having many backwardly 
 directed treads (plate 19), whereas a normal and well-established 
 river valley has only forward grades. Because cf these back- 
 ward grades the stream waters are impounded, and so lakes 
 are found strung along the valley in chains as the larger beads 
 are found in a rosary, and these are the characteristic rock basin 
 lakes sometimes referred to as " Paternoster Lakes " (see p. 412 
 and Fig. 402). 
 
 Fig. 401. — View of the Vale of Chamonix from the 
 s^racs of the Glacier des Bossons. The alb of the 
 opposite side is well brought out. 
 
Plate 20. 
 
 Map of the surface modeled by mountain glaciers in the Sierra Nevadas of California 
 
 (after I. C. Russell). 
 
LAND SCULPTURE BY MOUNTAIN GLACIERS 377 
 
 When the backward grades upon the valley floor are especially 
 steep, the rock step becomes a rock bar, or Riegel, of which nearly 
 every Alpine valley has its examples. In a walk from the Grimsel 
 to Meiringen many such bars are passed. Carrying in suspension 
 the sharp rock sand from the glacier deposits along its bed, the 
 
 Fig. 402. — Map of an area near the continental divide in Colorado, showing an 
 unglaciated surface to the west of the divide, where the westerly winds have cleared 
 the ground of snow, and the glacier-carved country to the eastward. Note the 
 regular forms of the youthful cirque, the glacier stairway, and the rock basin lakes 
 (U. S. G. S.). 
 
 stream which succeeds to the glacier as it vacates its valley saws 
 its way through these obstructions with a rapidity that is amazing, 
 thus producing narrow defiles, of which the Gorge of the Aar near 
 Meiringen and that of the Corner near Zermatt are such well- 
 known examples (Fig. 403). 
 
 It is characteristic of rivers that the tributaries cut their val- 
 leys more rapidly than does the main stream within the neighbor- 
 ing section, though they cannot cut lower than their outlets — 
 the side streams enter accordantly. This is easily explained be- 
 cause the grades of the tributary streams are the steeper, and, as 
 we well know, the corrasion of a valley is augmented at a most 
 
378 
 
 EARTH FEATURES AND THEIR MEANING 
 
 amazing rate for each increase of its grade. No such law controls 
 
 the processes of plucking and abrasion by which the glacier lowers 
 
 its floor, for these processes 
 appear to depend for their 
 efficiency upon the depth of 
 the ice, and the supply of 
 cutting tools, quite as much 
 as upon the grade of the 
 bed. To apply a homely 
 illustration, the hollowing 
 of flagstones upon our walks 
 is dependent more upon the 
 number of persons ohat pass 
 over them, and upon their 
 size and the number of pro- 
 truding nails in their boot 
 heels, than upon the grades 
 upon which they are placed. 
 At all events we find that 
 the main glacier valleys are 
 cut deeper than the side 
 valleys, so that the latter 
 become hanging valleys — 
 they enter the main valley, 
 not upon its bed, but some 
 distance above it (Fig. 404) . 
 The U-shaped hanging valleys, like the main valley, are much 
 
 too large for the 
 
 streams which now fill 
 
 them, and these di- 
 minutive 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 " bridal 
 
 veil." Such falls are 
 
 Fig. 404. — Idealistic sketch showing both glaciated 
 and non-glaciated side valleys tributary to a glaci- 
 ated main valley (after Davis). 
 
 Fig. 403. — Gorge of the Albula Rivernear 
 Berkum in the Engadine, cut through a rock 
 bar by the river which has succeeded to the 
 earlier glacier. 
 
LAND SCULPTURE BY MOUNTAIN GLACIERS 
 
 ;79 
 
 found by the hundred in every glaciated mountain district, impart- 
 ing to it one of the greatest of its scenic charms. 
 
 Fig. 405. — Character profiles in landscapes sculptured by mountain glaciers. 
 
 The character profiles which result from sculpture hy mountain 
 glaciers. — The lines which are repeated in landscapes carved by 
 mountain glaciers are easy to recognize (Fig. 405). The highest 
 horizon lines are the outlines of horns which are separated by cols. 
 
 "^-^ 
 
 Fig. 406. — Flat dome shaped under the margin of a Norwegian ice cap with pro- 
 jecting rock knobs and moraines in foreground. 
 
 Minaret-like palisades, or ''files of gendarmes,''^ often run for long 
 distances as the characteristic comb ridges. Lower down and 
 
380 EARTH FEATURES AND THEIR MEANING 
 
 lacking the lighter background of the sky, we make out with less 
 distinctness the U-valley, either with or without the albs to show 
 that the sculpturing process has been interrupted by uplift. 
 
 The sculpture accomplished by ice caps. — In the case of ice 
 caps, the only rock exposed is found in the neighborhood of the 
 
 JFiG. 407. — Two views illustrating successive stages in the shaping of tinds 
 or "bee-hive" mountains. 
 
 margin — the projecting islands known as nunataks. It is es- 
 sential for the existence of the ice cap that the rock base should 
 
LAND SCULPTURE BY MOUNTAIN GLACIERS 381 
 
 have relatively slight irregularities compared to the dimensions of 
 the cap itself. Except in very high latitudes this base must be 
 somewhat elevated, for like mountain glaciers ice caps are nour- 
 ished by the surface air currents, and their snows are deposited 
 above the snow line. 
 
 The Norwegian tind or beehive mountain. — Within temperate 
 or tropical climes the snow line lies so high that only the loftier 
 mountains are able to support glaciers. It follows that those 
 which are formed flow upon relatively high grades with corre- 
 spondingly high rate of movement and increased cutting power. 
 Within high latitudes the snow is found nearer the sea level, and 
 glaciers are for the most part correspondingly sluggish in their 
 movements as well as less active denuding agents. 
 
 To this condition characteristic of high latitude glaciers, there 
 is added in Norway another in the peculiar shape of the basement 
 beneath the recent and the still existing glaciers. The plateau of 
 Norway is intersected by a network of deep and steep walled fjords, 
 and the glaciers have developed as small ice caps perched upon 
 veritable pedestals of rock, over the margins of which their out- 
 let tongues of ice descend on steep slopes into the fjord. The tops 
 of the pedestals thus come to be shaped by the plucking and abrad- 
 ing processes into flat domes (Fig. 406), while the knobs of rock, 
 which as nunataks reach above the surface of the ice, divide the 
 outflowing ice tongues at the margin of the pedestal. These 
 tongues being much more active denuding agents, because of their 
 steep gradients, continually lower their beds, thus transforming 
 the earlier knobs of rock into high and steep mountains of more or 
 less circular base. Such " beehive " mountains upon the margins 
 of the fjords are the characteristic Norwegian tinds (Fig. 407). 
 
 Reading References for Chapter XXVI 
 
 I. C. Russell. Quaternary History of Mono Valley, California, 8th 
 Ann. Rept. U. S. Geol. Surv., 1889, pp. 329-371, pis. 27-37. 
 
 F. E. Matthes. Glacial Sculpture of the Bighorn Mountains, Wy- 
 
 oming, 2l3t Ann. Rept. U. S. Geol. Surv., 1900, Pt. ii, pp. 179-185, 
 pi. 23. 
 W. D. Johnson. Maturity in Alpine Glacial Erosion, Jour. Geol., vol. 12, 
 1904, pp. 569-578. 
 
 G. K. Gilbert. Systematic Asymmetry of Crest Lines in the High 
 Sierras of California, ibid., pp. 579-588. 
 
382 EARTH FEATURES AND THEIR MEANING 
 
 Emm. de Martonne. Sur la Formation des Cirques, Ann. de Geogr., 
 
 vol. 10, 1901, pp. 10-16. 
 W. M. Davis. Glacial Erosion in North Wales, Quart. Jour. Geol. Soc. 
 
 Lond., vol. 65, 1909, pp. 281-350, pi. 14. 
 Ed. Brtjckner. Die Glazialen Ziige im Antlitz der Alpen, Naturw. 
 
 Woehensehr., N. F., vol. 8, 1909. 
 William H. Hobbs. Characteristics of Existing Glaciers, pp. 1-96. 
 
CHAPTER XXVII 
 
 SUCCESSIVE GLACIER TYPES OF A WANING 
 GLACIATION 
 
 Transition from the ice cap to the mountain glacier. — A study 
 of existing glaciers leads inevitably to the conclusion that although 
 subject to short period advances and retreats, yet, broadly speak- 
 
 ffAOMT//VG 
 
 Dendritic Glac/ers Horseshoe 
 
 Glac/er Glac/ers 
 
 Fig. 408. — Schematic diagram to show the relationships of glacier types formed 
 
 in succession during a receding hemi cycle of glaciation. 
 
 ing, glaciers are now gradually wasting away, surrounded by wide 
 areas upon which are the evidences of their recent occupation. 
 We are thus living in a receding hemicycle of glaciation. 
 
 383 
 
384 
 
 EARTH FEATURES AND THEIR MEANING 
 
 Many mountain districts which now support small glaciers only, 
 or none at all, were once nearly or quite submerged beneath snow 
 and ice. If once covered by an ice carapace or cap, 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 mass. At this stage intensive frostwork, the charac- 
 teristic high level weathering, begins, and cirques develop above 
 the scars of those earlier amphitheaters formed in the advancing 
 hemicycle. 
 
 The piedmont glacier. — In this early stage of transition from 
 the ice cap to the mountain glacier, the ice flows outward to the 
 mountain front in ill-defined streams divided by the projecting 
 ridges, 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 (Fig. 408, stage I). This is the piedmont glacier, a type 
 
 Fig. 409. — Map of the Malaspina glacier of Alaska, the best known of existing 
 piedmont glaciers (after Russell) . 
 
 found to-day in the high latitudes of Alaska and in the southern 
 Andes (Fig. 409 and pi. 18 B). 
 
 During this stage the cirques may be but poorly defined, and 
 ice flows in both directions from rock divides so that the streams 
 transect the range, and later, after the glaciers have disappeared, 
 may expose a pass smoothed and polished upon its floor and with 
 
GLACIER TYPES OF A WANING GLACIATION 385 
 
 Fig. 410. — Map of the Baltoro glacier of the 
 Himalayas, a typical glacier of the dendritia 
 type. 
 
 striae directed in opposite directions from the highest point. The 
 pass of the Grimsel in Switzerland furnishes an excellent illustra- 
 tion of such earlier transection of the range. 
 
 The expanded-foot glacier. — As air temperatures continue to be- 
 come milder, the glacier streams within the mountains are less deep 
 and hence more clearly 
 defined, and instead of 
 coalescing upon the moun- 
 tain foreland, they now 
 issue from the mountains 
 to form individual aprons 
 and are described as ex- 
 panded-foot glaciers (Fig. 
 408, stage II, and Fig. 
 292, p. 264). 
 
 The dendritic glacier. 
 — Still later in the hemicycle nourishment of the glaciers is di- 
 minished as depletion from melting increases, so that the glacier 
 streams no longer reach to the mountain front. Branches con- 
 tinue to enter the main valley from 
 the several side valleys like the short 
 branches of a tall tree, and because of 
 this arrangement such a glacier may 
 be described as a dendritic glacier 
 (Fig. 408, stage III, and Fig. 410). 
 
 Inasmuch as the depletion from 
 melting increases at a rapid rate in 
 descending to lower levels, the tribu- 
 tary glacier valleys " hanging " above 
 the main valley in the lower stretches 
 become separated, and may continue 
 to exist as series of hanging glacierets 
 upon either side of the main valley be- 
 low the glacier front (Fig. 408, stage 
 III, and Fig. 411). It must be clear 
 from this that any attempt to name 
 
 Fig. 411.— The Triest glacier, a each separated ice stream without- 
 hanging glacieret separated from JJ.-X IJ." I,* J-1J 
 
 ,, „ \ ., ^ , , . ^ regard to its relationship must lead 
 
 the Great Aletsch glacier to ° ^ 
 
 which it was lately a tributary, to endless confusion, for glacier size 
 
 2o 
 
586 
 
 EARTH FEATURES AND THEIR MEANING 
 
 Fig. 412. — The Harriman fjord glacier of Alaska, 
 a tidewater variety of dendritic glacier (after a 
 map by Gannett). 
 
 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 dis- 
 trict may prove sufficient to fuse many glaciers into one or separate 
 one ice mass into many smaller ones. 
 
 When in high latitudes a dendritic glacier descends in fjords 
 to below the level of the sea, it is attacked by the water in the same 
 manner as are the outlets of Greenland glaciers, and is then known 
 
 as a " tidewater glacier," 
 which may thus be a 
 subtype or variety of the 
 dendritic glacier (Fig. 
 412). 
 
 The radiating (Alpine) 
 glacier. — In the pro- 
 gressive wastings of 
 dendritic glaciers, there 
 comes a time when their 
 dendritic outlines give 
 place to radiating ones. Attention has already been called to the 
 division of the cirque into subordinate basins separated by small 
 rock aretes and yielding a markedly scalloped border (Fig. 394, 
 p. 371). When the ice front retires from the main valley into one 
 of these mature cirques, the now wasted ice stream is broken up 
 into subordinate glacierets, each of which occupies one of the 
 basins within the larger cirque, and these ice streams 
 flow together to produce a glacier whose compo- 
 nent elements radiate like the sticks within a lady's 
 fan (Fig. 408, stage IV, and Fig. 413). 
 
 The horseshoe glacier. — As the glacier 'draws 
 near to its final extinction, it is crowded hard 
 against the wall of the amphitheater in which it 
 has so long been nourished. Up to this stage it 
 has offered a swelling front outwardly convex as a 
 direct consequence of the laws controlling its flow. 
 No longer amply nourished, for the first time its 
 front is hollowed, and it awaits its final dissolu- 
 tion curled up against the cirque wall (Fig. 408, 
 stage V, and Fig. 414). Practically all the glaciers of the United 
 States and southern Canada are of this type. 
 
 Fig. 413. — Map 
 of the Rotmoos 
 glacier, a radi- 
 ating glacier 
 of Switzerland 
 (after Sonklar). 
 
GLACIER TYPES OF A WANING GLACIATION 
 
 387 
 
 The above classification is one depending directly upon glacier 
 nourishment, and hence also upon size, and upon the stage of the 
 glacial hemicycle. In order to determine the type of any gla- 
 cier it is necessary to know the outlines of the mountain valley 
 
 mifes 
 
 _j L_ 
 
 Fig. 414. — Outline map of the Asulkan glacier in the Selkirks, a typical horseshoe 
 
 glacier. 
 
 — its divide — and those of the glacier or glaciers within it. It 
 is likely that the types of the advancing hemicycle of glaciation 
 would be much the same, save only for the new-horn or nivation 
 glacier, which would be as different as possible from the horse- 
 shoe type, to which in size it corresponds. Upon the continent 
 of Antarctica, where the absence of any general melting of the ice, 
 even in the summer season and near the sea level, introduces special 
 conditions, some additional glacier types are found, which, how- 
 ever, it is not necessary that we consider here. 
 
 The inherited-basin glacier. — It may be, however, that gla- 
 ciers have developed, not upon mountains shaped in a cycle of 
 river erosion, nor yet in succession to an ice cap, as in the nor- 
 mal cases which we have considered. On the contrary, glaciers 
 
388 
 
 EARTH FEATURES AND THEIR MEANING 
 
 may develop where basins of one sort or another have been 
 inherited from the preceding period. In such cases inherited de- 
 pressions may become more important than the auto-sculpture of 
 
 Milea 
 
 Fig. 416. — Outline map of the Illecillewaet glacier, an inherited-basin glacier in 
 
 the Selkirks. 
 
 the glacier. Glaciers which develop under such conditions may 
 be described as inherited-basin glaciers. 
 
 A partly closed basin between ridges may supply a collecting 
 ground for snows carried from neighboring slopes by the wind, 
 
GLACIER TYPES OF A WANING GLACIATION 389 
 
 and so may yield a broad neve, approaching in size a small ice cap, 
 yet without developing definite ice streams except upon its border. 
 Such a glacier is the Illecillewaet glacier of the Selkirks (Fig. 415). 
 
 Again in low latitudes the high and pointed volcanic peaks 
 may push up beyond the snow line Into the upper atmosphere, 
 and so become snow-capped. Definite cirques do not develop well 
 under these circumstances, and the loose materials of which such 
 peaks are always composed are attacked in somewhat irregular 
 fashion from the different sides. This is the case of Mount Ranier 
 and similar peaks of the Cascade range of North America. 
 
 Summary of types of mountain glacier. — In tabular form the 
 various types of mountain glacier may be arranged as follows : — 
 
 MOUNTAIN GLACIERS 
 
 Piedmont glacier. Mountain valleys entirely occupied and largely 
 submerged, with overflow upon the foreland to form a common ice apron 
 through coalescence of neighboring streams. 
 
 Expanded-foot glacier. Valley entirely occupied and an overflow upon 
 the foreland sufficient to produce individual ice apron. 
 
 Dendritic glacier. Valley not completely occupied but with tributary 
 ice streams ranged along the sides of the main stream, and with hanging 
 glacierets separated near the glacier foot. 
 
 Radiating glacier. Glacier largely included in a cirque with subordi- 
 nate glacierets converging below like the sticks in a lady's fan. 
 
 Horseshoe glacier. Small glacier remnants hugging the cirque wall 
 and having an incurving front. 
 
 Inherited-basin glacier. Of form dependent on a basin inherited and 
 not shaped by the glacier itself. 
 
 Reading Reference for Chapter XXVII 
 
 William H. Hobbs. The Cycle of Mountain Glaciation, Geogr. Jour., 
 vol. 37, 1910, pp. 268-284. 
 
CHAPTER XXVIII 
 
 THE GLACIER'S SURFACE FEATURES AND THE 
 DEPOSITS UPON ITS BED 
 
 The glacier flow. — 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 observations. Their 
 first observation was that the line of stakes, 
 which had run straight across the glacier, was 
 distorted into a curve which was convex down- 
 stream (Fig. 461, A'), thus showing that the 
 surface layers have more rapid motion in pro- 
 portion as they are distant from the side mar- 
 gins. Summarizing these and later studies, it 
 may be stated that the glacier increases its rate 
 of motion from its side margin towards its cen- 
 ter line, from its bed upwards towards its sur- 
 face, and below the neve the velocity is greatest 
 where the fall is greatest and also wherever the 
 cross section diminishes.' In all these particu- 
 lars, then, the ice of the glacier behaves like a 
 stream of water. The average rate of flow of 
 Alpine glaciers varies from a few inches to a few 
 feet per day, and is greater during the warm 
 summer season. The Muir glacier of Alaska 
 has been shown to move at the rate of about 
 seven feet per day. 
 
 In traveling from the neve downward to the 
 glacier foot, the snow not only changes into 
 ice, but it undergoes a granulating process with continued increase 
 in the size of the nodules until at the foot of the glacier these may 
 
 390 
 
 '- 1 
 
 1 ;x 
 
 /' 1 
 
 ' 
 
 X A 
 
 y 
 
 i-^ 
 
 Fig. 416. — Diagram 
 to illustrate the mi- 
 grations of lines of 
 stakes crossing a 
 glacier, due to its 
 surface movement, 
 A, original position 
 of lines ; A' , later 
 positions ; a and a', 
 original and dis- 
 torted forms of a 
 square section of 
 the glacier surface 
 near its margin ; r, 
 r', diagonal cre- 
 vasses. 
 
THE GLACIER'S SURFACE FEATURES 391 
 
 be picked out of the partially melted ice as articulating balls the 
 size of the fist or larger. Glacier ice has therefore a structure 
 quite different from that of lake ice, since the latter is developed 
 in parallel needles perpendicular to the freezing surface. 
 
 Crevasses and seracs. — Prominent surface indications of gla- 
 cier movement are found in the open cracks or crevasses, which 
 are the marks of its yielding to tensional stresses. Crevasses 
 are apt to run either directly across the glacier, wherever there is 
 a steep descent upon its bed, or diagonally, running in from the 
 margin and directed up-glacier (r, r, r, of Fig. 416), though they 
 occasionally run longitudinally with the glacier when there is 
 a rock terrace at the side of the valley beneath the ice. 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 valley, as will be clear from Fig. 416. The square a 
 has by this movement been distorted into the lozenge a', so that 
 the line xy has been extended into x'y', with the obvious tendency 
 to open cracks in the direction ss. 
 
 Every glacier surface below its neve is marked by steps or 
 terraces, which are well understood to overlie corresponding steps 
 of the cascade stairway to be seen in all vacated glacier valleys 
 (plate 19). The steep risers of these steps are usually marked 
 by parallel crevasses which cross the glacier. Under the rays 
 of the sun, which strike them more from one side than from 
 the other, the slices into which the ice 
 is divided are transformed into sharp- 
 ened blades and needles which are 
 known as seracs (Fig. 401, p. 376, and 
 Fig. 417). 
 
 The numerous crevasses tell us that Fig. 417.— Transverse crevasses 
 
 the ice is many times wrenched apart at the fail below a glacier step 
 
 during its journey down the glacier. transformed by unsymmetri- 
 
 rr\T . T , .^^ cal meltmg into seracs. 
 
 - 1 his has been illustrated by some- 
 what grewsome incidents connected with accidents to Alpinists, 
 but as they illustrate in some measure both the mode and the rate 
 of motion of Swiss glaciers, they are worthy of our consideration. 
 
 Bodies given up by the Glacier des Bossons. — In the year 
 1820, during one of the earlier ascents of Mont Blanc, three guides 
 were buried beneath an avalanche near the Rochers Rouges in 
 
392 
 
 EARTH FEATURES AND THEIR MEANING 
 
 the neve of the Glacier des Bossons (Fig. 418). In 1858 Dr. 
 Forbes, who had measured the rate of flow of a number of Alpine 
 glaciers, 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 years. In the year 1861, or forty-one years after the 
 
 Fig. 418. — View of the Glacier des Bossons upon the slopes of Mont Blanc show- 
 ing the position of accidents to Alpinists and the place of reappearance of their 
 bodies. 
 
 disaster, the heads of the three guides, separated from their bodies, 
 with some hands and fragments of clothing, appeared at the foot 
 of the Glacier des Bossons, and in such a state of preservation that 
 they were easily recognized by a guide who had known them in 
 life. 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 
 glacier, the rate of movement was twenty centimeters, or eight 
 inches, per day. 
 
 Various separated parts of the body of Captain Arkwright, who 
 had been lost in 1866 upon the neve of the same glacier, reap- 
 peared at its foot after entombment in the ice for a period of thirty- 
 one years. To-day the time of reappearance of portions of the 
 bodies of persons lost upon Mont Blanc is rather accurately pre- 
 dicted, so that friends repair to Chamonix to await the giving up 
 of its victims by the Glacier des Bossons. 
 
THE GLACIER'S SURFACE FEATURES 
 
 393 
 
 Fig. 419. — Lines of flow upon the surface of the 
 Hintereisferner glacier in the Alps (after Hess) . 
 
 The moraines. — The horns and comb ridges which rise above 
 the glacier surface are continually subject to frost weathering, 
 and from time to time drop their separated fragments upon the 
 glacier. Falling as these do from considerable heights, they reach 
 the ice under a high velocity, and rebounding, sometimes travel 
 well out upon its surface before coming to a temporary rest. Upon 
 a fresh snow surface of the neve their tracks may sometimes be 
 followed with the eye for considerable distances, and their fall 
 is a constant menace to Alpine climbers. Below the neve the 
 larger number of such frag- 
 ments remain near the 
 cliff, and the lines of flow 
 of the ice within the gla- 
 cier surface are such that 
 blocks which reach points 
 farther out upon the gla- 
 cier are later gathered in 
 beneath the cliff at the side (Fig. 419). The ridge of angular rock 
 debris which thus forms at the side of the glacier is called a 
 lateral moraine (see Fig. 411, p. 385, and Fig. 420). 
 
 At the junction of two glacier 
 streams, the lateral moraines are joined, 
 and there move out upon the ice sur- 
 face of the resultant glacier as a medial 
 moraine. Thus from the number of 
 medial moraines upon a glacier sur- 
 face it is possible to say that the im- 
 portant tributary glaciers number one 
 more (Fig. 420). 
 
 The plucking and abrading processes 
 in operation beneath the glacier, quarry 
 the rock upon its bed, and after shap- 
 ing and smoothing the separated rock 
 fragments, these are incorporated with- 
 in the lower layers of the ice as engla- 
 cial rock debris. In spaces favorable 
 for its accumulation, a portion of this material, together with much 
 finer debris and rock flour, is left behind as a ground moraine 
 upon the bed of the glacier (see Fig. 421). 
 
 Fig. 420. — Lateral and medial 
 moraines of the Mer de glace 
 and its tributary ice streams. 
 
394 
 
 EARTH FEATURES AND THEIR MEANING 
 
 At the foot of the glacier the relatively angular rock debris, 
 which has been carried upon the surface, and the soled and polished 
 englacial material from near the bottom, are alike deposited in a 
 common marginal ridge known as the terminal or end moraine 
 (plate 21 B). 
 
 Selective melting upon the glacier surface. — The white sur- 
 face of the glacier generally reflects a large proportion of the sun's 
 
 Fig. 421. — Ideal cross-section of a mountain glacier to show the position of 
 moraines and other peculiarities characteristic of the surface of the bed. 
 
 rays which reach it, and its more rapid melting is largely accom- 
 plished through the agency of rock fragments spread upon its 
 surface. Such fragments, however, promote or retard the melting 
 process in inverse proportion to their size up to a certain limit, 
 
 : Ldyeriwarmed by ■s\ir\„ 
 
 Fig. 422. — Fragments of rock of different sizes, to bring out their different 
 effects upon the melting of the glacier surface. 
 
Plate 21. 
 
 |4. View of the Harvard Glacier, Alaska, showing the characteristic terraces (after 
 
 U. S. Grant). 
 
 B. The terminal moraine at the foot of a mountain glacier (after George Kinney^. 
 
THE GLACIER'S SURFACE FEATURES 
 
 395 
 
 Fig. 423. — Small glacier table upon 
 the surface of the Great Aletsch 
 glacier in 1908. 
 
 and above that size their action is always to protect the glacier 
 from the sun. This nice adjustment to the size of the rock frag- 
 ments will be clear from examination of Fig. 422, for rock is a 
 poor conductor of heat, and in even the longest summer day a 
 thin outer layer only is appreci- 
 ably warmed. Large rock blocks, 
 grouped in the medial and lateral 
 moraines, hold back the process of 
 lowering the glacier surface during 
 the summer, so that late in the 
 season these moraines stand fifty 
 feet or more above the glacier as 
 armored ice ridges. 
 
 Isolated and large rock slabs, as 
 the season advances, may come to 
 form the capping of an ice pedestal 
 which they overhang and are known 
 as glacier tables (Fig. 423). Such 
 tables the sun attacks more upon one side than upon the other, 
 so that the slab inclines more and more to the south and may 
 eventually slip down until its edges rest against the glacier sur- 
 face. Rounded bowlders, which less frequently become perched 
 upon ice pedestals, may, from a similar process, slide down upon 
 the southern side and leave a pyramid of ice furrowed upon this 
 side and known as an ice pyramid. 
 
 Fine dirt when scattered over the glacier surface is, on the other 
 hand, most effective in lowering its level by melting. 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 Norway. Each dirt particle, 
 being warmed throughout by the sun's rays, 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 it. When 
 the dirt particles are near together, the thin walls which separate 
 the dust wells are attacked from the sides in the warm air of sum- 
 mer days, thus producing from a patch of dirt upon the glacier 
 surface a hath tub (Fig. 424 d) . At night the water which fills these 
 basins is frozen to form a lining of ice needles projecting inward 
 from the wall, and this, repeated in succeeding nights, may 
 
396 
 
 EARTH FEATURES AND THEIR MEANING 
 
 entirely close the basin with water ice and produce the familiar 
 glacier star (Fig. 424 c). 
 
 If the dirt upon the glacier surface, instead of being scattered, 
 is so disposed as to make a patch completely covering the ice to 
 
 \ c e. 
 
 ...... -E><£5.^ no I T- e 
 
 c " 
 
 Fig. 424. — Effects of differential melting and subsequent refreezing upon the 
 glacier surface, a, dust wells ; h, glacier tub produced by melting about a group of 
 scattered dust particles ; c, glacier star produced when the inclosed water of the 
 glacier well has frozen in successive nights; d, "bath tub." 
 
 the thickness of an inch or more, the effect is altogether different. 
 Protecting as it now does the ice below, a local ice hillock rises 
 upon its site as the surrounding surface is lowered, and as this 
 
 Fig. 425. — Dirt cone and one with its casing in part removed. Victoria glacier 
 
 (after Sherzer). 
 
 grows in height its declivities increase and a portion of the dirt 
 slides down the side. The final product of this shaping is an 
 almost perfectly conical ice hill encased in dirt and known as a 
 
THE GLACIER'S SURFACE FEATURES 397 
 
 debris, sand, or dirt cone (Fig. 425). The novice in glacier study 
 is apt to assume that these black cones contain only dirt, but is 
 rudely awakened to the reality when he attempts to kick them to 
 pieces. Both glacier tubs and debris cones may assume large 
 dimensions ; as, for example, in Alaska, where they may be properly 
 described as lakes and hills. 
 
 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 debris cones. Such cones of snow have, with 
 doubtful propriety, been designated " penitents," for it is pretty 
 clear that the interesting bowed snow figures, which really re- 
 semble penitents and which were first described from the southern 
 Andes under the name of nieves penitentes, are of somewhat dif- 
 ferent character. 
 
 One further ice feature shaped by differential melting around 
 rock particles remains to be mentioned. Wherever the seasonal 
 snowfalls of the neve are exposed in crevasses, they are generally 
 found to be separated by layers of dirt, and lines of pebbles simi- 
 larly separate those ice layers which are revealed at the foot 
 of the glacier. In either case, if the sun's rays can reach these 
 
 layers in an opened crevasse, the half-buried 
 
 rock fragments are warmed by the sun upon 
 
 their exposed surfaces and slowly melt their '-|S.5_^.-.-? 
 
 way down the ice surface, thus removing from I 
 
 it a thin layer of snow or ice and causing that p''^ 
 
 part above the pebble layer to project like S?.r-.- 
 
 a cornice. This process will go on until the [ 
 
 overhanging cornice protects the pebbles from ___*e^^^^^^ 
 
 any further warming by the sun, but each fig. 426. — Schematic 
 
 lower pebble layer that is reached by the sun diagram to show the 
 
 will produce an additional cornice, so that manner of formation 
 
 ^ . . . j^i 1 j^. 1 01 glacier cormces. 
 
 the origmal surface may at the bottom have 
 
 been retired by the process a number of inches. These features. 
 
 are described as glacier cornices (Fig. 426). 
 
 Glacier drainage. — Already in the early morning of every 
 warm summer day, active melting has begun upon the surface of 
 the Swiss glaciers. Rills of icy water soon make their way along 
 depressions upon the surface, and are joined to one another so that 
 
398 EARTH FEATURES AND THEIR MEANING 
 
 they sometimes form brooks of considerable size (Fig. 427). Such 
 streams continue their serpentine courses until these are inter- 
 sected by a crevasse down which the waters plunge in a whirling 
 vortex which soon develops a vertical shaft of circular section 
 within the ice. Such shafts with their descending columns of 
 
 whirling water are the 
 y^ ^ y^^ ,-. ^. ^y'^ well-known' moulins, 
 
 or " mills," which 
 may be detected from 
 a distance by their 
 gurgling sounds. The 
 first plunge of the 
 water may not reach 
 to the bottom of the 
 glacier, in which case 
 _ the stream finds a 
 
 '~ passageway below the 
 
 Fig. 427. - Superglacial stream upon the Great g^rf ace but above the 
 
 Aletseh glacier. 
 
 floor until another 
 crevasse is encountered and a new plunge made, here perhaps to 
 the bottom. Once upon the vallej^ floor the stream is joined by 
 others, and pursues its course within an ice tunnel of its own 
 making (Fig. 421, p. 394) until it issues at the glacier front. 
 
 The coarser of the rock debris which was gathered up by the 
 stream upon the glacier surface is deposited within the tunnel in 
 imperfect assortment (gravel and sand) , while all finer material 
 and that lifted from the floor (rock flour) is retained in suspension 
 and gives to the escaping stream its opaque white appearance. 
 This glacier milk may generally be traced far down the valleys or 
 out upon the foreland, and is often the traveler's first indication 
 that a range which he is approaching supports glaciers. 
 
 Deposits within the vacated valley. — For every excavation 
 of the higher portions of the upland through glacial sculpture, 
 there is a corresponding deposit of the excavated materials in 
 lower levels. So far as these materials are deposited directly by 
 the ice, they form the lateral, medial, ground, and terminal moraines 
 already described. A considerable proportion of them are, how- 
 ever, deposited by the water outside the terminal moraine; but 
 ;as with the shrinking glacier the ice front retires in halting move- 
 
THE GLACIER'S SURFACE FEATURES 
 
 399 
 
 ments over the area earlier ice-covered, the terminal moraines are 
 ranged along the vacated valley as recessional moraines, each with 
 a valley train of outwash below. About the apron of the piedmont 
 glacier, such deposits are particularly heavy (Fig. 428). During 
 
 Fig. 428. — Ideal form of the surface left on tlio site of the apron of a piedmont 
 glacier. M, moraine ; T, outwash ; C, basin usually occupied by a lake ; D, drum- 
 lins (after Penck). 
 
 the "ice age " 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 Alaska. To- 
 day we find there moraines and glacial outwash, a lake in the 
 middle of the apron site, and sometimes a group of radiating drum- 
 lins like those found within the ice lobes of the continental glacier 
 in southern Wisconsin (Fig. 429, and Fig. 344, p. 317). 
 
 Tig. 429. — Moraines and drumlins about Lake Constance upon the site of the 
 earlier piedmont glacier of the Upper Rhine. The white area outside the outer- 
 most moraine is buried in glacial outwash (after Penck and Bruckner). 
 
400 EARTH FEATURES AND THEIR MEANING 
 
 Behind the recessional moraines within the glaciated valley are 
 found the valley moraine lakes (Fig. 448, p. 413), in association 
 with the rock basin lakes due to glacial sculpture (Fig. 447, p. 412). 
 After the glacier has vacated its valley, the precipitous side walls 
 become the prey of frostwork and are the scenes of disastrous 
 avalanches or landslides. Within the cirques, drifts of snow are 
 nourished long after the ice has disappeared, and as a consequence 
 the amphitheater walls succumb to the process of solifluxion 
 (p. 153). 
 
 Diversions and reversals of drainage, which are so characteristic 
 of the work of continental glaciers, are hardly less common to 
 glaciated mountain districts. Many of our most beautiful water- 
 falls have resulted from either the temporary or permanent ob- 
 struction of earlier valleys above the falls. The famous Yosemite 
 Falls offers an interesting illustration of the shifting of an earlier 
 waterfall, itself no doubt due to ice blocking in a still earlier glacia- 
 tion (plate 22 B). 
 
 Marks of the earlier occupation of mountains by glaciers. — 
 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 district. These marks are so deeply stamped 
 upon the landscape that no one need err in their interpretation. 
 
 MARKS OF MOUNTAIN GLACIERS 
 
 High-level sculpture. The grooved upland with its cirques, or the fretted 
 upland with its cirques, cols, horns, and comb ridges. 
 
 Low-level sculpture. The U-shaped main valley, the hanging side 
 valleys with their ribbon falls, the glacier staircase with its rock bars and 
 gorges, the rounded, polished, and striated rock floor. 
 
 Deposits. The recessional moraines of till and' the valley trains of 
 sand and gravel, the soled erratic blocks derived always from higher 
 levels of the valley. 
 
 Lakes . The valley moraine lakes and the chains of rock basin lakes. 
 
 Reading References for Chapter XXVIII 
 Glacier movement : — 
 L. Agassiz. Nouvelles Etudes et Experiences sur les Glaciers Actuels, 
 
 etc., Paris, 1847, pp. 435-539. 
 H. Hess. Die Gletscher, Braunschweig, 1904, pp. 115-150. 
 H. F. Reid. The Mechanics of Glaciers, Jour. Geol., vol. 4, 1896, pp. 912- 
 928; Glacier Bay and Its Glaciers, 16th Ann. Rept. U. S Geol. 
 Surv., Pt. i, 1898, pp. 445-448. 
 
Plate 22. 
 
 \ 
 
 
 <D 
 
 
 
 a 
 
 > 
 
 
 1^ 'ai 
 
 
 
 X. ^ 
 
 
 
 
 
 ^1 
 
 
 ^ 
 
 m 2 
 
 
 
 
 
 
 
 
 5 
 
 -o a 
 
 ■c 
 
 3] 
 
 C3 En 
 
 o; 
 
 
 - ^-^ 
 
CHAPTER XXIX 
 A STUDY OF LAKE BASINS 
 
 Freshwater and saline lakes. — Lakes require for their exist- 
 ence a basin within which water may be impounded, and a supply 
 of water more than sufficient to meet the losses from seepage and 
 evaporation. If there is a surplus beyond what is needed to meet 
 these losses, lakes have outlets and remain fresh; their content 
 of mineral matter is then too slight to be detected by the palate. 
 If, on the other hand, supply is insufficient for overflow, continued 
 evaporation results in a concentration of the mineral content of 
 the water, subject as it is to continual augmentation from the in- 
 flowing streams. 
 
 As we have seen, there are in areas of small rainfall special 
 weathering processes which tend to bring out the salts from the 
 interior of rock masses, these concentrated salts generally first 
 appearing as a surface efflorescence which is ultimately transferred 
 through the agency of wind and cloudburst to the characteristi- 
 cally saline desert lakes. 
 
 Lake basins may be formed in many ways. Depressions of 
 the land surface may result from tectonic movements of the crust ; 
 they may be formed by excavating processes ; but in by far the 
 greater number of instances they result from the obstruction in 
 some manner of valleys which were before characterized by uni- 
 formly forward grades. In relatively few cases loose materials 
 are heaped up in such a manner as to produce fairly symmetrical 
 basins. 
 
 Newland lakes. — On land recently elevated from the sea, 
 basins of lakes may be merely the inherited slight irregularities 
 of the earlier sea floor, in which case they may be assumed to be 
 largely the result of an irregular distribution of deposits derived 
 from the land. Lakes of this type are especially well exhibited 
 in Florida, and are known as newland lakes (Fig. 430). Such 
 lakes are exceptionally shallow, and are apt to have irregular out- 
 2d 401 
 
402 
 
 EARTH FEATURES AND THEIR MEANING 
 
 lines and extremely low banks. Under these circumstances, they 
 are soon filled with a rank growth of vegetation, so that it is some- 
 times difficult to properly distinguish lake and marsh. 
 
 Lakes o/^c/ Afarsh 
 
 ,. ii ..B>T— unrTinwa im ^^-^.^^ ^ ^r, ,t\v ~ j0'^—- ■ ;i-riT iiii,|.._ 
 
 Fig. 430. — Map and diagram to bring out the characteristics of newland lakes. 
 
 Basin-range lakes. — Newland lakes may be said to have their 
 origin in an uplift of the land and sea floor near their common 
 margin. A lake type dependent upon movements of the earth's crust 
 
 Fig. 431. — View of the Warner Lakes, Oregon (after Russell). 
 
 but within interior areas has been described as the basin-range 
 type and is exemplified by the Warner Lakes of Oregon. In this 
 
A STUDY OF LAKE BASINS 
 
 403 
 
 district great rectangular blocks of the earth's crust, which in their 
 upper portions at least are composed of basaltic lavas, have under- 
 gone 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 (Fig. 431). Lakes 
 formed in this way are 
 of triangular outline, are 
 bounded on the two 
 shorter sides by cliffs, 
 but have extremely flat 
 shores on their longest 
 side. From this shore the 
 water increases gradually 
 in depth and attains a 
 maximum depth at or 
 near the opposite angle. 
 Such lakes naturally be- 
 tray a tendency to appear 
 in series (Fig. 432), and are unfortunately much too often illus- 
 trated on a small scale after a shower by the tilted blocks of 
 imperfectly made cement sidewalks. 
 
 Rift-valley lakes. — Another type of lake basin which has its 
 origin in faulted block movements is known as the rift-valley lake, 
 
 Fig. 432. — Schematic diagrams to illustrate the 
 characteristics of basin-range lakes. 
 
 Fig. 433. — Schematic diagrams of rift-valley lakes, 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 included. 
 
 and is best exemplified by the great lakes of east Central Africa. 
 In this type a strip of crust, many times as long as it is wide, has 
 been relatively sunk between the blocks on either side so as to 
 produce a deep rift, or what in Germany is known as a Graben 
 
404 
 
 EARTH FEATURES AND THEIR MEANING 
 
 (trench) . Such a basin when occupied by water yields a lake which 
 is long, straight, deep, and narrow, and is in addition bounded on 
 the sides by steep rock cliffs. At the ends the 
 shores are generally by contrast decidedly low. 
 If the hard rock at the bottom of the lake 
 could be examined, it would be found to be of 
 the same type as that exposed near the top of 
 the side cliffs. 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 (Fig, 433), 
 
 One of the most striking examples of a rift 
 valley lake is Lake Tanganyika, while Albert 
 Nyanza, Nyassa, and 
 Rudolf in the same 
 region are similar 
 (Fig, 434). 
 
 Earthquake lakes, — 
 The complex adjust- 
 ments 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 
 water. This is at such times impounded 
 either in pools or in broad lakes, which 
 inasmuch as they date from known earth- 
 quakes have been called " earthquake 
 lakes," even though in a strict sense any 
 lake which has originated in earth move- 
 ments might properly be regarded as an 
 earthquake lake. To avoid unnecessary 
 confusion, the term must, however, be re- 
 stricted to those lakes which are known to 
 have been formed at the time of definite earthquakes (Fig, 435). 
 Reelfoot Lake in Tennessee, which in late years has acquired 
 undesirable notoriety because of the feuds between the fishermen 
 
 Fig. 434. — Map show- 
 ing the rift-valley 
 lakes of east Central 
 Africa. 
 
 Fig. 435. — Earthquake 
 lakes which were formed 
 in the flood plain of the 
 lower Mississippi during 
 the earthquake of 1811 
 (after Humphreys). 
 
A STUDY OF LAKE BASINS 
 
 405 
 
 of the district and the constituted authorities, is a lake more than 
 twenty miles across and came into existence during the great 
 earthquake of the lower Mississippi valley in 1811. 
 
 Crater lakes. — The craters of volcanic mountains are natural 
 basins in which surface waters are certain to be collected, provided 
 only the supply is sufficient and seepage into the loose materials is 
 
 Fig. 436. — View of lake in Poas Crater in Costa Rica, a volcanic crater more 
 than half a mile across and with walls 800 feet deep. At intervals there is an 
 ejection of steam mixed with mud and ash after the manner of a geyser (after 
 H. Pittier). 
 
 not excessive. Some craters, still visibly more or less active, are 
 occupied by lakes (Fig. 436). 
 
 In the larger number of cases in which craters become occupied 
 by lakes, the evidence of continued activity is lacking, and it would 
 appear in such cases that the lava of the chimney had consolidated 
 into a volcanic plug, closing the bottom of the crater. Notable 
 groups of crater lakes are the Caldera of the Roman Campagna 
 (Fig. 437) and the so-called maare of the Eifel about the Lower 
 Rhine. Crater lakes are easy to recognize by their circular plan, 
 
406 
 
 EARTH FEATURES AND THEIR MEANING 
 
 their steep walls of volcanic materials, and their considerable 
 depth with a maximum near the center. 
 
 One of the most remarkable of these water-filled basins is Crater 
 Lake in Oregon, which has a diameter of about six miles and is 
 
 Fig. 437. — Diagrams to illustrate the characteristics of crater lakes. The Roman 
 Campagna is a plain formed of volcanic ash, with the crater lakes of Bracciano, 
 Vico, and Bolseno arranged on a line traversing it. 
 
 believed to have resulted from the incaving of a great volcanic 
 cone in the latest stage of its activity. 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 slope. 
 
 Coulee lakes. - — Far more important as lakes are those volcanic 
 basins which arise from the flow of a stream of lava across the val- 
 ley of a river so as to impound its 
 waters (Fig. 438). 
 
 At the time of the great erup- 
 tion under SJcaptar Jokull in 1783 
 the river Skaptar and many of 
 its tributaries were blocked by 
 the flow of lava, which it is esti- 
 mated exceeded in bulk the mass 
 of Mont Blanc. 
 
 Morainal lakes. — As we have 
 learned, the obstruction of drain- 
 age, due to the distribution of 
 rock debris by continental glaciers, 
 has yielded lakes in almost countless numbers. Probably ninety 
 per cent or more of the known lakes have had this origin, and the 
 
 1 iG. 438. — View of Snag Lake, a coulee 
 lake with lava dam shown in middle 
 distance (after Fairbanks). 
 
A STUDY OF LAKE BASINS 
 
 407 
 
 type is so common within the once glaciated regions that it forms 
 perhaps the best distinguishing mark of former glaciation. The 
 hummocky surface of morainal deposits is so characteristic that 
 the lakes of this type are never very large and are correspondingly 
 irregular in outline. They have often numerous islands, and their 
 banks are formed of the combination of rock flour and ice-worn ma- 
 terials known as till (Fig. 439). The smallest of the morainal 
 lakes are mere kettles on the marginal moraine, and these rapidly 
 
 "' '"^""^^ "'Vi^i^'i^ v.v^i\ i'-" ■ 
 
 Fig. 439. — [Diagrams to illustrate the characteristics of morainal lakes, and a 
 ! sample map of such lakes from the glaciated region of North America. 
 
 become replaced by peat bogs. In contrast with pit lakes, mo- 
 rainal lakes lack the steep surrounding slopes and the encircling 
 plain. 
 
 Pit lakes. — The so-called pit lakes have their origin in con- 
 tinental glaciation, and are found in groups within broad plains 
 of glacial outwash (mainly sand and gravel), which are for this 
 reason described as " pitted plains " (see p. 314). Those areas 
 which lay between neighboring lobes of the ice sheet were subject 
 to particularly heavy deposits of outwash material, and are, in 
 consequence, particularly likely to be occupied by pit lakes. As 
 has been pointed out in an earlier section, 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 pipe. Having in most cases a considerable head at the outer 
 margin of the ice, this water may rise and issue well above the lower 
 ice layers and so cover a portion of the ice margin beneath sand 
 
408 
 
 EARTH FEATURES AND THEIR MEANING 
 
 and gravel (Fig. 440). Separated blocks, often of massive pro- 
 portions, are thus buried beneath nonconducting materials by 
 which they are long protected from further melting. Eventually, 
 however, with the approach of still milder climates they disappear, 
 
 Fig. 440. — Diagram to show the manner of formation 
 of pit lakes. 
 
 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 storehouses. 
 
 Pit lakes are thus easily recognized by their occurrence usually 
 in groups within a plain of glacial out wash and by their charac- 
 
 Z.eif'e/ 
 
 '/^Vff-ed' 
 
 /='/a/n 
 
 
 Fig. 441.- 
 
 ■ Diagrams to illustrate the characteristics of pit lakes and a sample 
 map from the glaciated region of North America. 
 
 teristic banks inclined at the angle of repose of such materials 
 (Fig. 441). 
 
 Glint or colk lakes. — It has been found to be true of existing 
 continental glaciers that where their mass has been held back by a 
 mountain wall, their current at the portals within this rampart 
 becomes greatly accelerated. Though the upper layers of the 
 
A STUDY OF LAKE BASINS 
 
 409 
 
 glacier in the vicinity may move forward with a velocity of but an 
 inch per day, the current within the outlet may be as much as 
 seven hundred or a thousand times as great. In many respects 
 
 
 1 
 NOBW. Plateau .rrS? 
 
 ^o e e >>.i-~i 
 
 X' _.^:45^ 
 
 Fig. 442. — 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 rampart. 
 
 these conditions are similar to those about the raceway of a reser- 
 voir where the near-by surface of the water is lowered by the in- 
 draught of the outlet and the current in the raceway is so acceler- 
 ated that, unless protected, 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 dam. In Holland such basins hol- 
 lowed out beneath breaks in the dykes are known as colks. Basins 
 which were excavated beneath the glacier outlets by a similar pro- 
 cess would not be open to our 
 inspection until after the ice had 
 disappeared from the region; 
 but it is most significant that in 
 Scandinavia, where ^the Pleisto- 
 cene continental glacier, advanc- 
 ing westward from the Baltic, 
 was held in check by the escarp- 
 ment at ^the Norwegian bound- 
 ary (the glint), lake basins have 
 been excavated in hard rock 
 whose walls show the abrading 
 and polishing which are charac- 
 teristic of glacial sculpture, and 
 whose positions are such that 
 they lie beneath the former out- 
 lets partly above and in part 
 
 below the line of the escarpment. Their position in reference to 
 the rampart and to the former outlets is brought out in Fig. 442. 
 The largest of the glint lakes of this series is Tornetrask in 
 northern Lapland (see p. 277 and Fig. 443). 
 
 Fig. 443. — Map showing a series of 
 glint lakes which lie across the inter- 
 national boundary of Sweden and 
 Norway. 
 
410 
 
 EARTH FEATURES AND THEIR MEANING 
 
 Ice-dam lakes. — Whenever a continental glacier, either in ad- 
 vancing its front or in retiring, lies across the lines of drainage upon 
 their downstream side, water is impounded along the ice front 
 
 so as to form ice-dam lakes. Such lakes 
 are found to-day in Greenland and in 
 the southern Andes, and similar bodies 
 of water of far greater size and impor- 
 tance 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 systems. 
 Thus above the Baltic depression, when 
 the ice front lay to the eastward of the 
 main watershed, each easterly sloping 
 valley was obstructed by the ice and 
 of northern Europe and the occupied by an ice-dam lake (Fig. 444), 
 divide near the Norwegian ^^.q beaches of which may all be traced 
 
 boundary (after G. de Geer). , ,_,. ^ 
 
 to-day (Fig. 445). 
 One side of each ice-dam lake is formed by an ice cliff at the 
 glacier front, and if the region is relatively flat, the remaining 
 shores are likely to be formed by a marginal moraine which the 
 glacier has abandoned in its retreat. In their smaller stages, 
 therefore, ice-dam lakes on prairie country have the form of a 
 
 Fig. 444. — Ice-dam lakes (in 
 black) betv.'een the front of 
 the late Pleistocene glacier 
 
 ■' Z:'W^,^^^'"'.SM^ 
 
 '^=^==^^%y^ 
 
 Fig. 445. — Wave-cut terrace at an elevation of 177.5 meters above sea on the 
 southern slope of the northern Dala valley north of Baggedalen in Sweden. To 
 the right in the foreground is a peat bog (after Munthe). 
 
 crescent, which is the more pronounced because the waves by their 
 attack upon the ice front flatten the curvature of its outline (see 
 Fig. 360, p. 330). 
 
A STUDY OF LAKE BASINS 
 
 411 
 
 The life of an ice-dam lake is begun and ended in important 
 changes of glacier outline, and after the draining of lakes by this 
 process the land shores may be traced in beaches, and the ice mar- 
 gin by a water-laid moraine of low relief (Fig. 359, p. 330). 
 
 A much smaller but in many respects similar ice-dam lake is. 
 to-day to be seen at the side of the Great Aletsch glacier, a moun- 
 tain glacier of Switzerland. 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 (see Fig. 446) . 
 
 Fig. 446. — View of the Marjelen Lake at the side of the Great Aletsch glacier, 
 seen looking directly down from the summit of the Eggishorn (after a photo- 
 graph by I. D. Scott). 
 
 Glacier lobe lakes. — Upon the sites of the former lobes of the 
 Pleistocene glacier of North America are found the basins of the 
 Laurentian River system, the largest freshwater lakes in the world. 
 There has been much controversy concerning the manner of for- 
 mation of these lakes, but the view which has seemed to have the 
 largest following is that they were excavated by the eroding ac- 
 tion of the continental glacier over the drainage basins of former 
 rivers. It is but one phase of the long controversy between op- 
 posing schools, which have advocated on the one hand the efficiency 
 of glacier ice as an eroding agent, and upon the other its supposed 
 protection from the weathering processes. The positions and the 
 outlines of the several lakes of the series sufficiently proclaim their 
 connection with the former glacial lobes, and the name which we 
 have adopted leaves the exact manner of their formation a still. 
 
412 
 
 EARTH FEATURES AND THEIR MEANING 
 
 open question. The recognition of the importance of the glacial 
 anticyclone, in giving shape to the glacier surface and in effecting 
 a transfer of snow from the central to the marginal portions, has 
 had the effect of emphasizing the relative importance of erosion 
 under the marginal and lobate portions. Thus the importance of ice 
 lobes has been greatly accentuated, though this applies only to 
 the shaping of the basins and not in any important way to the im- 
 pounding of the present waters. The present Laurentian Lakes 
 owe their existence to the elevation by successive uplifts of the 
 country to the northward and eastward, since the glacier retired 
 from the lake region. When the ice front lay to the northward of 
 the Ottawa River, the discharge of the upper lakes was by a chaimel 
 through Nipissing River and Lake and thence down the Ottawa 
 River to a gulf in the lower St. Lawrence. The uplift of the land 
 has had the effect of raising a barrier where the former outlet 
 existed, and diverting the waters to a roundabout channel by way 
 ■of Detroit and Lake Erie (see Fig. 365, p. 335). 
 
 Rock-basin lakes. — The reversed grades which develop in a 
 valley deepened by mountain glaciers — the back-tilted treads of 
 
 Fig. 447. — Diagrams to illustrate the arrangement and the characters of rock- 
 basin lakes, together with a map of such lakes from the Bighorn Mountains in 
 Wyoming. 
 
 the cascade stairway (see p. 376) — furnish a series of basins 
 hollowed in rock which are strung along the course of the valley 
 like pearls upon a thread, or, far better, like the larger beads in a 
 rosary (Fig. 447). This characteristic arrangement accounts for 
 the name " Paternoster Lakes " which has sometimes been applied 
 to them in Europe. Their positions in series within U-shaped 
 mountain valleys, and their rock shores with characteristically 
 
A STUDY OF LAKE BASINS 
 
 413 
 
 smoothed and striated surfaces, make them easy of determina- 
 tion. In the higher portions of the valley, where the treads of the 
 cascade stairway are relatively narrow, such lakes are often ap- 
 proximately circular in outline, but in the lower levels and upon 
 wider treads they may be ribbon-like, 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 two. 
 
 Valley moraine lakes. — The recessional moraines which mark 
 the halting stations of mountain glaciers, while retiring up their 
 
 ■^^'^-A^V.^; 
 
 Fig. 448. — Convict Lake, a lake behind a moraine dam within a glaciated valley 
 of the Sierra Nevadas, California (after a photograph by Fairbanks). 
 
 valleys, 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 glaciation. They may, therefore, be distinguished 
 by the name valley moraine lakes. Their positions on the bed of a 
 U-shaped mountain valley, and the glacial materials which com- 
 pose the dams, are sufficient for their identification (Fig. 448). 
 Moraine Lake and Lake Louise in the Canadian Rockies are typi- 
 cal examples. Rock basin and valley moraine lakes may occur 
 in alternation or combined in mountain valleys. 
 
414 
 
 EARTH FEATURES AND THEIR MEANING 
 
 i^^iG. 449. — Lake basins produced by successive slides 
 from the steep walls of a glaciated mountain valley 
 (atte\ Russell). 
 
 Landslide lakes. — The sheer-walled valleys which are carved 
 by mountain glaciers are too steep to long retain their perpendic- 
 ularitv when the support of the glacier has been removed. Aided 
 by the ever present joint planes, which admit water to* the rock, 
 they succumb to frost action, and further give way in avalanches 
 
 whenever the rock 
 is of sufficiently 
 porous material to 
 become saturated 
 with water. Land- 
 slides sometimes 
 occur successively 
 until the original valley wall has been replaced by a terraced slope. 
 The treads of the steps in this terrace have generally a backward- 
 sloping grade, so that basins are formed to be filled by relatively 
 long and narrow lakes or by successions of small pools (Fig. 449 
 and plate 23 B). 
 
 When the avalanched material is so disposed as to dam the val- 
 ley, much larger lakes of this type come into existence. During 
 an earthquake which occurred on January 25, 1348, there was a 
 landslide within the valley of the Gail, 
 Carinthia, which destroyed seventeen 
 villages and produced a lake which 
 tven to-day is represented by a great 
 marsh. 
 
 Border lakes. — Whenever moun- 
 tain glaciers push out their fronts 
 beyond the borders of the mountain 
 range by which they are nourished, 
 they spread upon the foreland in 
 broad aprons about which morainic 
 accumulations are particularly heavy. 
 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 valley. Because such lakes 
 are found at the borders of upland districts they have been called 
 border lakes. The beautiful Lakes Constance, Lucerne, Maggiore, 
 
 Fig. 450. — Lake Garda, a 
 border lake upon the site of a 
 piedmont apron at the mar- 
 gin of the Alpine highland 
 (after Penck and Briickner). 
 
Plate 23. 
 
 A. View of the American Fall at Niagara, showing the accumulation of rocks beneath 
 
 (after Grabau). 
 
 B. Crystal Lake, a landslide lake in Colorado. 
 (Photograph by Howland Bancroft.) 
 
A STUDY OF LAKE BASINS 
 
 415 
 
 Lugano, Como, and Garda (Fig. 450) , on the borders of the Alpine 
 highland, are all of this type. 
 
 Ox-bow lakes. — The cutting off of a meander within the flood 
 plain of a river yields a lake which is of horseshoe (ox-bow) out- 
 line and lies generally with low banks within a plain composed of 
 
 Fig. 451. — Diagrams to bring out the characteristics of ox-bow lakes, together 
 with a map of such lakes from the flood plain of the Arkansas River. 
 
 river silt. Before separating from the parent stream the meander 
 had begun to silt up, especially at the ends. Ox-bow lakes are, 
 however, relatively deep near the convex shore and correspond- 
 ingly shallow toward the concave margin (Fig. 451). 
 
 Saucer lakes. — As we have learned, a river meandering in its 
 flood plain has banks which are higher than the average level of 
 the plain, for the reason that at flood time the main current of the 
 stream still persists in the channel, thus allowing the burden of 
 sediment to be dropped in the 
 relatively slack water upon its 
 margin. Because of these natural 
 embankments or levees, tributary 
 streams are often compelled to 
 flow long distances in nearly par- 
 allel direction before effecting a 
 junction. Between the trunk 
 stream and its tributaries, likewise bounded by levees, and be- 
 tween streams and the valley walls, there thus exist low basins 
 which are more or less saucer-shaped (Fig. 452). At flood time, 
 when the levees are overflowed or crevassed, water enters these 
 depressions, and an additional supply may be derived from the 
 walls of the valley. Good illustrations of such lakes are furnished 
 
 Fig. 452. — Diagrammatic section to 
 illustrate the formation of saucer- 
 like basins between the levees of 
 streams flowing in a flood plain. 
 
416 EARTH FEATURES AND THEIR MEANING 
 
 by the flood plain of the former river Warren near the banks of 
 the present Minnesota River (Fig. 453). 
 
 of Warren Rii^er 
 
 Scale of Miles 
 
 Fig. 453. — Saucer lakes upon the bed of the former river Warren (from the 
 Minneapolis sheet, U. S. G. S.). 
 
 Crescentic levee lakes. — As we approach the delta of a river, 
 the size and importance of the levee increases, and here a new type 
 of levee lake may develop in series (Fig. 454). At flood time the 
 levee is breached near the point of sharpest curvature on the con- 
 vex side (Fig. 454 a). When the waters are subsiding, the cur- 
 rent is kept away from the old channel by the rising grade of the 
 levee as well as by the inertia of the current, and an entrance to 
 the old channel is first found below the next change in curvature 
 of the meander, since here scour becomes effective in cutting 
 through the levee. The new channel is thus established in the 
 form of a loop inclosing the old one, and the process of levee build- 
 ing now erects a wall about the territory newly acquired by the 
 meander. This territory has the form of a crescent, and when 
 occupied by water produces a crescentic levee lake often joined 
 to its neighbors in series. The abandoned channel now closed 
 at both ends by levees may be occupied by water to produce a 
 subordinate ribbon type of curving trench (Fig. 454 &, c). 
 
 The importance of levees in obstructing drainage to form lakes 
 is only beginning to be appreciated. It has quite recently been 
 shown that when trunk streams are greatly swollen and burdened 
 with sediment while flowing from a receding continental glacier, 
 they may build such high levees as to aggrade their tributary 
 streams above the junctions, even producing reversed grades 
 and so impounding the waters to form extensive lakes. During 
 the " ice age " lakes of this type were formed in Illinois and Ken- 
 
A STUDY OF LAKE BASINS 
 
 417 
 
 Fig. 454. — Levee lakes developed concentrically in series within meanders of a 
 stream tributary to the Mississippi and flowing upon its delta plain, b and c are 
 examples of the ribbon type of levee lake due to occupation of the abandoned 
 river channel. The larger number of lakes, of which Sip Lake and Texas Lake 
 are examples, have the form of crescents and lie between abandoned levees (from 
 recent map of U. S. G. S.). 
 
 tucky rivers just above their junctions with the Ohio. The old 
 lake floor with its eastern shore line and its protruding islands is 
 easily made out upon the new topographic maps of Kentucky. 
 Raft lakes. — Within humid regions the flood plains of our larger 
 rivers are generally forested, and as the river swings from side to 
 
 2 E 
 
418 EARTH FEATURES AND THEIR MEANING 
 
 side in its perpetual meanderings, the timber which grows upon 
 the convex side of each meander is progressively undermined by 
 the river and felled upon its bank. The prostrate trees remain 
 upon the banks during the low water of the summer season, to be 
 gathered up at the time of flood in the next spring season. It 
 is log jams thus acquired which so generally block the main chan- 
 nel of a river and turn the current across the neck of the meander 
 when cut-offs occur with the formation of ox-bow lakes. When 
 the mass of timber thus gathered up by the river is excessive, as, 
 for example, within the flood plain of the Red River of Arkansas 
 
 and Louisiana, huge log rafts are pro- 
 duced which dam up the river so effec- 
 tively as to produce temporary lakes. 
 The impounded waters soon find an 
 outlet over the levee at some point 
 higher up the river, and the waters 
 flowing off through the timbered 
 bottom lands, other logs are caught 
 by the standing timber as in a weir. 
 A second dam is thus formed which is 
 separated from the initial one by open 
 
 Fig. 455. — Raft lakes along i • ,i • J_^ i ■(•! i 
 
 the banks of the Red River in Water, and^ m this way the driftwood 
 Arkansas and Louisiana at dam acquires enormous proportions 
 their fullest recorded develop- ^s it gradually moves up the river. 
 
 ment (after A. C. Veatch, . „ • i c i 
 
 U. S. G. s.). Alter a period of perhaps a century 
 
 or more, the lower sections of the 
 jam become decayed and dislodged so as to float down the river. 
 
 In the lower Red River a great raft of alternating jams and 
 open water reached a length of about one hundred and sixtj'' miles 
 and moved up the river at the average rate of something less 
 than a mile per year. Within the limits of the dam all tributary 
 streams were blocked, so that secondary lakes were formed in a 
 double fringe about the main river (Fig. 455). 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-formation. 
 
 Side-delta lakes. — 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 junction. Wherever the 
 
A STUDY OF LAKE BASINS 
 
 419 
 
 Fig. 456. — The Swiss lakes Thun and Briena, 
 formed by deltas at the junction of streams 
 tributary to a steep-walled valley. 
 
 difference in velocity of the two streams at the junction is large, 
 and the side stream is charged with sediment, a delta will be 
 formed at the mouth of . 
 the tributary stream. ^■- 
 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 lake. 
 Traverse and Big Stone 
 Lakes in the valley of the 
 Warren River in Minne- 
 sota have been formed in 
 this way (Fig. 354, p. 326). Lakes Thun and Brienz in the Swiss 
 Alps are of similar origin, the beautiful city of Interlaken being 
 built upon the delta plain over the valley of the earlier river 
 (Fig. 456). The Mississippi has similarly been expanded to form 
 Lake Pepin above the delta at the mouth of the Chippewa River. 
 
 Delta lakes. — A somewhat dif- 
 ferent type of delta lake has been 
 formed in Louisiana, where the 
 "father of waters" discharges into 
 the gulf. Here the various dis- 
 tributaries radiate from the main 
 channel to produce the " bird-foot " 
 delta type and the toes in this foot 
 by their junction with the banks 
 which outline the ancient estuary, 
 have separated in succession a series 
 of basins that before were in direct 
 connection with the sea (Fig. 457). 
 Lake Pontchartrain is the largest 
 of this series, while the so-called 
 Lake Borgne is in process of 
 separation. 
 
 Where large deltas push out from the shore into the open sea, 
 the levees which border the individual distributaries are attacked 
 
 Fig. 457. — Delta lakes formed at 
 the mouth of the Mississippi 
 through the junction of the levees 
 of I radiating distributaries with 
 the shore of the estuary (after 
 Berghaus). 
 
420 
 
 EARTH FEATURES AND THEIR MEANING 
 
 by the waves and their materials are transported by the shore 
 currents and built into barriers. These barriers cut off the re- 
 entrants between neighboring distributaries so as to produce 
 lagoons or lakes (Fig. 458). 
 
 A type of delta lake, which more resembles the side-delta lake 
 above described, has formed at the mouth of the Colorado River, 
 
 where it enters the Gulf of Lower 
 California. 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 Colorado. The rampart 
 of mountains, by which this valley 
 is surrounded, has cut it off from 
 any water supply derived from 
 clouds, and its waters being no 
 longer renewed from the sea, the 
 region has passed through a period 
 of desiccation which has left the 
 Salton Sink as the only existing remnant of the earlier lagoon. It 
 will be remembered that careless operations in diverting distribu- 
 taries of the Colorado recently reversed this process so that the 
 waters rose in the valley, and expensive emergency operations 
 were necessary in order to again turn the waters of the Colorado 
 into their accustomed channels. 
 
 Barrier lakes. — The Salton Sink illustrates a type of lake 
 which is formed at the border of the sea through the erection of 
 
 Fig. 458. — A type of delta lakes 
 formed by levees in part de- 
 stroyed and built into barriers 
 on the margin of the delta of the 
 Nile (after Supan). 
 
 <3ca/e ctf* rrf//A3 
 
 Fig. 459. — Diagrams to illustrate the characteristics of barrier lakes, with an 
 example from the southern coast of the Island of Nantucket. 
 
A STUDY OF LAKE BASINS 
 
 421 
 
 some kind of barrier which captures a small area of the ocean's 
 surface. Though such lakes may be properly described as strand 
 lakes, it is usually at the mouth of a river that the process be- 
 comes effective. 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 (Fig. 459) . 
 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 slope. 
 
 Dune lakes. — 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 waves, beach sand is exposed to the direct fig. 460. — Dune 
 action of the winds. In time of storm the sand lakes on the coast 
 is picked up and after drifting in the wind is ^^^ ]^^s) ^^■ 
 collected in long ridges parallel to the shore. 
 Constantly traveling along shore, these dunes block the mouths 
 of rivers and thus produce a series of lakes such as are indicated 
 in Fig. 460. 
 
 Sink lakes. — Another class of lakes are due either directly 
 or indirectly to the work of underground waters. In districts 
 which are underlain by limestone, the surface water descending 
 
 Fig. 461. 
 
 - Sink lakes in Florida, with a schematic diagram to illustrate the 
 manner of their formation (map from U. S. G. S.). 
 
422 EARTH FEATURES AND THEIR MEANING 
 
 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 
 formation. At the intersections of joints, more or less circular 
 shafts known as " swallow-holes " go down to the caves from the 
 surface. Locally, 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 outline. If 
 sufficiently clogged at the bottom by finer rock debris, these basins 
 become occupied by small lakes which are known as sinks, and 
 constitute one of the best surface indications of a limestone 
 country. 
 
 Karst lakes — poljen. — 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 rock. Here all the surface water descends 
 in certain districts along the widened joint planes so that the 
 drainage is largely subterranean. The so-called dolines or sinks of 
 very regular and symmetrical forms resembling deep bowls cover 
 a large part of the surface. 
 
 The entire country is, moreover, faulted in the most intricate 
 fashion into many rift valleys. The drainage being so largely 
 subterranean, these down-thrown blocks of crust, the so-called 
 poljen, become flooded at certain seasons of the year when the 
 subterranean passages become choked or are too small to carry 
 away all the water. A seasonal lake of this character is the 
 Zirknitz Lake (p. 189). 
 
 Playa lakes. — It is the law of the desert that the arid region 
 be walled in by mountains. This encircling rampart forces the 
 clouds to rise, and by robbing them of their moisture leaves the 
 desert dry and barren. Those waiters 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 outlet. Infrequent though they be, the desert rains are of 
 the cloudburst type and in the hills develop torrents whose waters, 
 emerging upon the desert floor, develop lakes in the space of a 
 few minutes or at most hours. 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 
 
A STUDY OF LAKE BASINS 423 
 
 next succeeding cloudburst. Such ephemeral lakes are known 
 as pi ay as. 
 
 Salines. — Desert lakes more favored in their supply of water 
 may be relatively long lived and persist for periods measured in 
 years or centuries. Such lakes are, however, extremely sensi- 
 tive to climatic changes (see p. 198). 
 
 For the reason that they have no outlet the waters of desert 
 lakes become salt through continued evaporation. They are, 
 therefore, spoken of as salines. Lake Bonneville, so long as it 
 discharged its waters over the sill of the Red Rock Pass, must 
 have remained fresh ; but when the level of its waters had fallen 
 below this outlet, its waters became salt and the content increased 
 as the volume diminished. 
 
 The shallow basins upon the floors of desert lakes may have 
 come into existence in various ways; but it would appear that 
 the irregular removal of the soil by the winds, modified as this is by 
 differences in composition of the rock materials and by vegetable 
 growth, and the deposition of sand by the same agent, are by far 
 the most important. Many of the types of tectonic and volcanic 
 lakes which have been described are characteristic of humid and 
 arid regions alike. 
 
 Alluvial-dam lakes. — Within the mountains upon the desert 
 borders, the alluvial fans which form at the mouths of valleys, 
 because of the characteristic cloudburst, sometimes obstruct a 
 main valley at the junction with its tributaries. 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 tributaries. 
 
 Resume. — The types of lakes which we have now considered 
 are arranged below in tabular form so as to show their relation- 
 ship to important geological processes. While not complete, 
 the list includes the more important classes, as well as others 
 which, while not of common occurrence, are yet of interest in giv- 
 ing further illustration to the processes which have been treated 
 in earlier chapters. 
 
 By giving careful attention to criteria which have been above 
 suggested, 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 described. 
 
424 
 
 EARTH FEATURES AND THEIR MEANING 
 
 CLASSIFICATION OF LAKES 
 
 Tectonic Lakes 
 Newland lakes 
 Basin-range lakes 
 Rift-valley lakes 
 Earthquake lakes 
 
 Volcanic Lakes 
 Crater lakes 
 Coulee lakes 
 
 Continental Glaciation Lakes 
 Morainal lakes 
 Pit lakes 
 
 Glint or colk lakes 
 Ice-dam lakes 
 Glacier-lobe lakes 
 
 Mountain Glaciation Lakes 
 Rock-basin lakes 
 Valley moraine lakes 
 Landslide lakes 
 Border lakes 
 
 River Lakes 
 Ox-bow lakes 
 Saucer lakes 
 Crescentic levee lakes 
 Raft lakes 
 Side-delta lakes 
 Delta lakes 
 
 Strand Lakes 
 Barrier lakes 
 Dune lakes 
 
 Ground Water Lakes 
 Sink lakes 
 Karst lakes — poljen 
 
 Desert Lakes 
 Playa lakes 
 Salines ^ 
 Alluvial dam lakes. 
 
 Reading References for Chapter XXIX 
 
 General : — 
 
 I. C. Russell. Lakes of North America. Boston, 1895, pp. 125, pis. 23, 
 A. P. Brigham. Lakes, A Study for Teachers, Jour. Sch. Geogr., vol. 1, 
 
 1897, pp. 65-72. 
 N. M. Fenneman. The Lakes of Southeastern Wisconsin, Bui. 8, Wis. 
 
 Geol. and Nat. Hist. Surv., 1902 (Rev. Ed., 1910), pp. 188, pis. 37. 
 A. Delebecque. Les Lacs Frangais (with Atlas). Paris, 1898. (Work 
 
 crowned by the Society of Geology of Paris.) 
 H. R. Mill. Bathymetrical Survey of the English Lakes, Geogr. Jour., 
 
 vol. 6, 1895, pp. 46-73, 135-166. 
 A. Supan. Grundziige der Physisehen Erdkunde. Leipzig, 1896, pp. 
 
 531-548. 
 H. Berghaus. Atlas der Hydrographie. Gotha, 1891, pi. 3. 
 R. D. Salisbury. Physiography. 1907, pp. 292-327. 
 Charles Rabot. Revue de limnologie, La Geographie, Vol. 4, 1901, 
 
 pp. 110-119, 172, 189. 
 
A STUDY OF LAKE BASINS 425 
 
 I. C. Russell. A Geological Reconnaissance in Southern Oregon, 4th 
 
 Ann. Rept. U. S. Geol. Surv., 1884, pp. 442-447. (Basin range 
 
 lakes.) 
 Ed. Suess. The Face of the Earth, vol. 4, 1909, pp. 268-286. (Rift valley 
 
 lakes.) 
 J. S. DiLLER. Crater Lake, Nat. Geogr. Mag., vol. 8, 1897, pp. 33-48, 
 
 pi. 1 ; Geology of Lassen Peak Quadrangle, California, Geol. Fol. 15, 
 
 U. S. Geol. Surv., 1895. (Coulee lakes.) 
 N. M. Fenneman. Lakes of Southeastern Wisconsin, I.e., pp. 4-6. (Pit 
 
 lakes.) 
 Ed. Suess. The Face of the Earth, vol. 2, 1906, pp. 340-346, pi. 7. (Glint 
 
 lakes.) 
 I. C. Russell. A Preliminary Paper on the Geology of the Cascade 
 
 Mountains in Northern Washington, 20th Ann. Rept. U. S. Geol. Surv. 
 
 Pt. ii, 1900, pi. 14. (View of a rock-basin lake.) 
 E. W. Shaw. Preliminary Statement concerning a New System of 
 
 Quaternary Lakes in the Mississippi Basin, Jour. Geol., 1911, pp. 481- 
 
 491. (New type of levee lakes.) 
 A. C. Veatch. Formation and Destruction of the Lakes of the Red 
 
 River Valley, Prof. Pap. No. 46, U. S. Geol. Surv., pp. 60-62, pis. 29- 
 
 33. (Raft lakes.) 
 M. Neumeyer. Erdgeschichte, vol. 1, pp. 595-596. (Poljen.) 
 
^1 
 
 CHAPTER XXX 
 
 THE EPHEMERAL EXISTENCE OF LAKES 
 
 Lakes as settling basins. — Of all the processes which conspire 
 to blot out the lakes with which our northern landscapes are 
 dotted, the one of greatest importance is in most cases a process 
 of filling by the sediments brought in by tributary streams. The 
 carrying of sediment in suspension depends, as we know, upon the 
 velocity of the current, and as this is checked where it reaches 
 the lake margin, all coarser material is at once deposited to form 
 
 Fig. 462. — Map of the Arve and the upper Rhone to show the importance of 
 Lake Geneva as a settling basin of the larger stream. 
 
 a delta, while the finer sediments are held longer in suspension and 
 finally settle in thin layers over the entire bottom of the lake. 
 Clay deposits surrounded by coarser sediments are thus charac- 
 teristic of filled lake basins. 
 
 How waters are clarified by their passage through a lake . is 
 indicated by a comparison of a river system such as the St. Law- 
 rence, with a river like the Missouri and Mississippi. Not only 
 are the lower stretches of the St. Lawrence in striking contrast 
 with the muddy floods of the Missouri and Mississippi ; but the 
 delta, which is so remarkable a feature in the Mississippi, has 
 no counterpart in the northern river. 
 
 426 
 
THE EPHEMERAL EXISTENCE OF LAKES 
 
 427 
 
 The most noteworthy examples of setthng are, however, fur- 
 nished by the lakes of Switzerland, for the reason that Swiss 
 rivers are heavily charged with rock flour produced beneath the 
 numerous glaciers at the valley heads, and, further, because these 
 rivers descend with turbulent currents to near the borders of the 
 larger lakes. To look out upon the murky waters of the upper 
 Rhone, where they enter Lake Geneva near Villeneuve, and then 
 to watch the flood of crystal water which issues from the lake 
 and passes under the bridge at Geneva, is an object lesson which 
 no traveling student should miss (Fig. 462). Yet even more in- 
 structive is a visit to the Bois de la Bdtie at the junction of this 
 clear stream with the Arve, a half hour's walk only below Geneva. 
 
 Fig. 463. — View looking upstream across the opaque waters of the Arve to the 
 clear reflecting surface of the Rhone. To the right across the Arve is seen the 
 cement works for recovering the Arve sediments. 
 
 The waters of the Arve have come on a steep descent directly 
 from the glaciers of the Mont Blanc district, and as they meet 
 the cleared waters of the Rhone, they flow beside them down 
 the common valley without mingling. Dull and opaque, the 
 Arve waters can be discerned for a long distance as a white belt 
 against the left bank of the river, sharply defined against the blue 
 reflecting surface of the Rhone waters (Fig. 463). Upon the 
 banks of the Arve, just above its junction, a cement manufactory 
 has been established to utilize the clays which are here deposited. 
 
428 
 
 EARTH FEATURES AND THEIR MEANING 
 
 Fig. 464. — The village of Poschiavo 
 in eastern Switzerland, built upon 
 a strath at the head of Lake Pos- 
 chiavo. 
 
 Wherever lakes are contained in long and narrow valleys, the 
 greater part of the tributary drainage enters at the upper end, 
 
 and the delta which there forms 
 extends from bank to bank. As 
 it continues to advance into the 
 lake, the earlier water basin is 
 gradually transformed into a level 
 plain of delta deposit, a feature 
 so common as to be deserving of a 
 special name. The Scottish lochs, 
 which are lakes of this type, are 
 each extended in a longer or shorter 
 delta plain described as a strath, 
 and this local term may well be 
 given a general application (fron- 
 tispiece). The city of Ithaca, the 
 seat of Cornell University, is built 
 upon a strath at the head of Lake Cayuga, and numberless Scot- 
 tish and Swiss hamlets have been located upon such fertile plains 
 (Fig. 464). 
 
 Drawing off of water by erosion of outlet. — Next in impor- 
 tance to the filling up of lake basins as a factor in their early 
 extinction is the cutting down of their channels of outflow. 
 Whenever the walls of the outlet are cut in rock, this drain- 
 ing process is apt to be slow, for the reason that the outlet 
 stream is of filtered water and so lacks the necessary cutting 
 tools. By far the larger number of lakes are, however, held 
 back by dams of loose drift deposits laid down by the earlier 
 continental glaciers; and so the very clarity of the water pro- 
 motes the erosion of the outlet by allowing the stream's full 
 burden of sediment to be lifted and then removed from the 
 channel. 
 
 The pulling in of headlands and the cutting off of bays. — The 
 removal of projecting headlands by wave action, though it in- 
 creases the area of the lake, yet it decreases directly the volume 
 of lake water through formation of the built terrace, and indi- 
 rectly in far larger measure through the transformation of bays 
 into quiet lagoons within which the extinguishing process of peat 
 growth is set in operation. 
 
THE EPHEMERAL EXISTENCE OF LAKES 
 
 429 
 
 Lake extinction by peat growth. — The first condition for the 
 growth of lake vegetation is quiet water. Within small lakes, 
 such as the kettle basins upon moraines, aquatic vegetation de- 
 velops rapidly, and bogs of peat might almost be included among 
 the most important distinguishing marks of a glaciated country. 
 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 effective. 
 
 Many erroneous notions are still held concerning the prime 
 importance of sphagnum in peat formation, owing to the pecul- 
 iar local conditions 
 under which the 
 early studies were 
 made. Within the 
 glaciated districts of 
 the United States, 
 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 
 shores, followed in 
 turn by belts of low shrubs, tamaracks, and lastly deciduous 
 trees (Fig. 465). 
 
 In most cases the first plants to develop in a quiet lake are the 
 water lilies, though these are sometimes preceded by chara and 
 floating bladderwort. Next behind the water lilies come the 
 sedges, which form a mat of floating bog by their grasslike stems 
 sinking down in the water and being there interwoven with the 
 rhizomes below. This mat of sedge is often so firm that cattle 
 may advance upon it to the water's edge, but it is separated 
 by a layer of water from the bed of growing peat at the bottom 
 of the lake (Fig. 466). This bed of peat appears to grow upward 
 toward the surface and become joined to the shore end of the 
 
 Fig. 465. — View of the floating bog and surrounding 
 zones of vegetation in a small glacial lake of the Yel- 
 lowstone National Park (after a photograph by Fair- 
 banks). 
 
430 
 
 EARTH FEATURES AND THEIR MEANING 
 
 floating bog by decaying vegetation which is dropped from the 
 bottom of the mat above. 
 
 In order behind the floating bog come the advanced plants 
 of the conifer group, with sphagnum and low shrub here upon a 
 peat base extending to the lake bottom. Behind the belt of 
 shrubs arise the tamaracks and spruces, and lastly, toward the 
 shore, come the deciduous trees and especially poplars, maples, 
 and marginal willows. Upon the margin of the basin there is 
 
 Fig. 466. 
 
 • Diagram to show how small lakes are transformed into peat bogs 
 (after C. A. Davis). 
 
 usually alow trench, or '' fosse," filled with water during wet sea- 
 sons, as a result, no doubt, of seasonal inwash that does not reach 
 the residual lake toward the center of the basin. 
 
 Extinction of lakes in desert regions. — In arid regions there 
 are special causes of lake extinction. Thus the blowing in of 
 sand and dust carried for long distances in the air, a by no 
 means negligible factor even in humid regions, here assumes 
 large importance. The now exposed basins of extinct desert 
 lakes afford the evidence, however, of an even greater factor 
 of extinction, in climatic change. The clouds, which at one 
 time found their way into the drainage basin of a lake, may 
 later through the rise of a mountain barrier be cut off, and 
 so with reduced water supply a period of lake desiccation 
 is begun. When, in this process of drying up, the lake level 
 has fallen below that of the outlet, the saline content of the 
 waters begins to increase, and later a stage is reached, as in 
 Great Salt Lake, when the sodium salts are precipitated. When 
 the lake has become extinct, these deposits remain as a witness 
 to the changed climatic condition. 
 
 The role of lakes in the economy of nature. — It is natural, 
 in considering the extinction of lakes, to give some attention to 
 the role which they play in the economy of nature. That lakes 
 
THE EPHEMERAL EXISTENCE OF LAKES 
 
 431 
 
 filter the water of rivers, and prevent the formation of important 
 delta deposits, has already been noticed. A curious exception 
 to this general rule is furnished by the great delta at the head of 
 Lake St. Clair, just below the outlet of Lake Huron. This anomaly 
 is, however, explained by the peculiar currents of Lake Huron, 
 which are so directed as to sweep the beach sand into the swift 
 current of the outlet, to be deposited in the quiet 
 waters of Lake St. Clair (Fig. 467). 
 
 As regulators of the flow of rivers, lakes perform 
 an important function. Such disastrous floods as 
 are characteristic of the spring season within the 
 basin of the lower Mississippi could not occur in 
 the lower St. Lawrence, for the reason that the 
 great basins of the lakes serve as distributing reser- 
 voirs. The annual floods, upon which the agri- 
 culture of Egypt depends, are explained by the 
 flood waters from the high mountains of Abyssinia 
 entering the Nile below the lakes of its upper basin. 
 
 In one further respect large inland bodies of 
 water have an important function as regulators. 
 It is the property of water to respond but slowly 
 to the variations in the quantity of heat which 
 Teaches the earth's surface from the sun. A larger 
 quantity of heat must be added to or abstracted 
 from a body of water, in order to change its tem- 
 perature by one degree, than would be required for a like change 
 in the same bulk of earth or rock. Thus bodies of water by more 
 slowly acquiring the summer's heat retard the coming spring, and 
 by storing up this energy and carrying it over into the autumn 
 the warm season is prolonged and early frosts prevented. The 
 fruit belts about the lower Great Lakes are thus dependent upon 
 this regulating property of the lake waters. The discomfort of 
 the long spring of raw weather is thus compensated by an un- 
 usually salubrious harvest season. 
 
 Ice ramparts on lake shores. — Small ridges known as ice ram- 
 parts are formed upon lake shores by the action of lake ice, though 
 subject to so many qualifying conditions that the range of their 
 occurrence is somewhat limited. Within districts where a winter 
 ice cover of some thickness is formed, the shores of lakes are apt 
 
 Fig. 467. — Map 
 to show anom- 
 alous position 
 of the delta in 
 Lake St. Clair, 
 due to the pe- 
 culiar currents 
 in Lake Huron 
 (after maps by 
 Cole). 
 
432 
 
 EARTH FEATURES AND THEIR MEANING 
 
 to present ridges of bowlders parallel to and near the water's 
 edge, and such lakes have sometimes become known as " wall 
 lakes" (Fig. 468). 
 
 In many cases these small ridges have been formed at the time 
 of the spring " break up " of the ice ; for the ice cover, when once 
 
 loosened, is drifted in great 
 
 rafts first against one shore, 
 and later, with a change of 
 wind direction, against an- 
 other. Under the impact of 
 such heavy rafts, the half- 
 submerged bowlders near the 
 shore are forced up the beach 
 until they lie in a ridge or 
 
 Fig. 468.— a bowlder wall upon the shore bowlder wall. 
 
 of a small lake in the Adirondacks of New At other times SUCh bowlder 
 
 walls, and far more interesting 
 ridges as well, result from a kind of ice shove independent of the 
 wind, but caused by expansion within the ice itself during a sud- 
 den rise of temperature of the surrounding air. Such ice ramparts 
 require for their explanation a consideration of the sequence of 
 events from the time the ice cover closes the lakes. 
 
 The first lake ice of early winter forms in most cases with air 
 temperatures a few degrees only below the freezing point of the 
 water. When later a severe " cold wave " arrives, the ice cover 
 is contracted and becomes too small for the lake surface. To this 
 contraction it yields and opens cracks up which the water rises, 
 and in the prevailing low temperature this water is quickly frozen 
 and the lake cover again made complete. Skaters are familiar 
 with the opening of these cracks and the loud "roaring " which 
 accompanies it on cold mornings, the sharp skate runners some- 
 times starting a crack in the strained ice, as does a light scratch 
 upon glass that is in a similar strained condition. 
 
 The original ice cover of the lake, which was formed at near- 
 freezing temperatures, has now received a number of inserted 
 wedges of new ice at a time when its contracted volume has made 
 this possible. If now a " warm wave " succeeds to the " cold 
 wave " in the air, the ice cover expands at a rate corresponding 
 to its rate of contraction, so that a strong pressure is exerted 
 
THE EPHEMERAL EXISTENCE OF LAKES 
 
 433 
 
 against the shore (Fig. 469). Sliding up the sloping surface of 
 the cut and built terrace, the force of this shove may be deflected 
 
 Fig. 469. — Diagrams to show the effect of ice shove in producing ice ramparts 
 upon the shores of lakes (after Buckley with a slight modification). 
 
 upward against the cliff, and if this is of loose materials, the effect 
 may be to ram bowlders into the bank, to push up ramparts or 
 ridges, to overturn trees, etc. (Fig. 470). In marsh land the 
 
 
 frozen surface layer may slide over 
 its unfrozen base and be forced up 
 into broken folds (lower diagram 
 of Figs. 469 and 470). 
 
 In order that ice ramparts may 
 be formed, it is necessary that the 
 winter climate of the district be 
 severe and characterized by alter- 
 nating cold and warm waves, in- 
 volving considerable range of air temperature below the freezing 
 point. If the lake is small, the push of the ice will be through so 
 small a distance as not to yield appreciable ramparts. If, on the 
 other hand, the lake is too large, the ice cover is not rigid enough 
 to transmit the push to the distant shore, but, like a long beam 
 2f 
 
 Fig. 470. — Various forms of ice 
 ramparts (after Buckley) . 
 
434 
 
 EARTH FEATURES AND THEIR MEANING 
 
 Pig. 471. — Map of Lake Mendota at Madison, Wis- 
 consin, showing the position of the ridge which forms 
 from ice expansion, and the ice ramparts about the 
 shores of the bays (based on Buckley's map). 
 
 employed in the same manner to transmit a compressive stress, 
 it is bent out of a straight hne and later broken. Thus in a broad 
 lake, with the coming of a "warm wave," the ice cover opens in 
 
 a crack from shore 
 to shore and finds 
 relief from the stress 
 by pushing up a ridge 
 above the crack. On 
 such lakes ice ram- 
 parts are found only 
 about the shores of 
 bays whose expanse 
 does not greatly ex- 
 ceed a mile (Fig. 471) . 
 When there is 
 heavy snowfall, ice 
 ramparts either do 
 not form or are of 
 smaller dimensions, probably in part because the ice is blanketed 
 by the snow and so prevented from sudden elevation of tempera- 
 ture during the " warm wave," 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 shores. 
 
 Reading References for Chapter XXX 
 Lake extinction by peat growth : 
 
 C A. Davis. Peat, Essays on its Origin, Uses, and Distribution in Michi- 
 gan, Ann. Rept. Mich. Geol. Surv. for 1906; 1907, pp. 105-182; 
 Peat Deposits as Geological Records, 10th Rept. Mich. Acad. Sci., 
 1908, pp. 107-112. 
 
 G. P. Burns. Bog Studies. Ann Arbor, 1906, pp. 13. 
 
 Ice ramparts : 
 
 C H. Hitchcock. Shore Ramparts in Vermont, Proe. Am. Assoc. Adv. 
 
 Sci., vol. 13, 1869, pp. 335-337. 
 G. K. Gilbert. Lake Bonneville, Mon. 1, U. S. Geol. Surv., 1890, pp. 71- 
 
 72. 
 E. R. Buckley. Ice Ramparts, Trans. Wis. Acad. Sci., etc., vol. 13, 1900, 
 
 pp. 141-162, pis. 1-18. 
 William H. Hobbs. Requisite Conditions for the Formation of lee 
 
 Ramparts, Jour. Geol., vol. 19, 1911, pp. 157-160. 
 
CHAPTER XXXI 
 THE ORIGIN AND THE FORMS OF MOUNTAINS 
 
 A mountain defined. — As ordinarily understood, mountains 
 are elevations upon the earth's surface which rise above the 
 general level of the country. Their summits need not be at great 
 heights above the sea, but it is essential that they project above 
 the average level of the surrounding country by at least a quarter 
 of a mile. Lower elevations are described as hills. On the other 
 hand, the elevation of a plateau like the " High Plains " of the 
 western United States may be as much as a mile, but the vast 
 expanse of nearly level surface precludes the use of the term 
 ''mountain." The word is thus applied to a feature of the earth 
 ^and not merely to an elevated tract. 
 
 In a collective sense, though more often in the plural form, 
 the term is properly applied to groups of similar features which 
 have a common origin in local uplift of the land. The origin of 
 mountains used in this sense of mountain complexes is thus 
 connected with some essentially local uplift of the earth's surface. 
 This may take place by the processes of folding and superin- 
 cumbent fault displacement, by volcanic extravasations or ejec- 
 tions, or by a deeper seated and essentially hydrostatic elevation 
 of rock beds over molten rock material. 
 
 The existing forms of mountains, as we are to see, are largely 
 shaped by the erosional processes which are set in operation 
 by the uplift itself, though often completed long subsequent 
 to it. 
 
 The festoons of mountain arcs. — From our earliest studies 
 of school geogTaphies, we have become familiar with the arrange- 
 ment of the more important mountains in long chains or systems. 
 Comparatively few persons have given any further attention to 
 the arrangement of the chains, though over large areas of the 
 earth's surface the distribution of mountain ranges is deeply sig- 
 nificant. The map of Asia in particular presents a series of great 
 sweeping arcs or crescents which are grouped as though hung 
 
 435 
 
436 
 
 EARTH FEATURES AND THEIR MEANING 
 
 upon the map in festoons with knots or vertexes to separate 
 neighboring groups (Fig. 474, p. 438, and Fig. 472). 
 
 The significance of these mountain groupings in the evolution 
 of the earth's surface 
 
 has been pointed out 
 by the great Viennese 
 geologist Suess, to whom 
 we are indebted for fo- 
 cusing 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 sur- 
 
 FiG. 472. — The great multiple mountain arc of face. Broadly speaking, 
 Sewestan, British India (aftei* de Saint Martin -j^J^g mountain arCS mav 
 and Schrader). , • i . i j 
 
 be said to be grouped 
 about those shields of older rock which geological studies have 
 shown to be the oldest land masses upon the globe. Within the 
 northern hemisphere these original continents are represented by 
 the areas of crystalline rock centered over Hudson Bay, the Baltic 
 Sea, and an area in northeastern Siberia known to geologists as 
 Angara Land. In our study of the figure of the earth (Chapter II) 
 it was found that these shields represent the truncated angles of 
 the rounded tetrahedral form toward which, the planet is tending 
 (Fig. 3, p. 12). 
 
 Theories of origin of the mountain arcs. — The mountain 
 arcs, when studied in detail, are found to be composed of closely 
 folded rock strata, the flexures of which are generally so overturned 
 that their axial planes dip toward the center of the arc (Fig. 473) . 
 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 periphery, thus causing a wrinkling of the surface 
 strata and an overriding of the surrounding formations, which 
 upon this hypothesis opposed a greater resistance to the sliding 
 movement. The folding together of the strata due to the sliding 
 
THE ORIGIN AND THE FORMS OF MOUNTAINS 437 
 
 Acr/VB/y Moi/trtg Ar-ea 
 
 Afo/v res/sy-onr ro Q//c//nc 
 
 (a) 
 
 naturally involves a very considerable diminution of the surface 
 area presented by the strata (Fig. 22, p. 42). In the case of the 
 Alpine chains it has been estimated that a flat land area, four 
 hundred to eight hundred miles across, has by the folding process 
 been reduced to a width of only about one hundred miles, or from 
 a fourth to an eighth of its former width. 
 
 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 arc. It 
 must be obvious that such a move- 
 ment, being from a center toward three 
 sides at once, would for this circum- 
 scribed area involve enormous pro- 
 portionate reduction in superficial area 
 of the strata and could only result in 
 a hiatus near the center of the arc. 
 No such gap is to be found, and one 
 would, moreover, be difficult to account 
 for upon any plausible hypothesis. On 
 the other hand, the general contraction 
 of the planet as a whole, involving 
 as it does reduction of surface over 
 large areas, is a well-recognized fact ; 
 and if it be true that the shields 
 
 formed by the older continents are less subject to contraction than 
 the remaining portions of the surface, it is easy to understand why 
 the earth's outer skin should be wrinkled by underfolding and 
 thrusting about these continental margins. The contrast of this 
 view with that of Professor Suess is expressed in the diagrams of 
 Fig. 473. 
 
 We may illustrate this conception by a stretched sheet of rub- 
 ber cloth such as is in common use by dentists, upon which a 
 thin layer of hot Canada balsam has been spread. This substance 
 congeals upon cooling to near-normal temperatures, and if a small 
 local area of the balsam layer be chilled and the tension upon the 
 rubber then released, the viscous balsam of the unchilled portion 
 of the layer is thrown into wrinkles about the cooled and more 
 
 Act'/Ve/y Mot^//?g Area 
 
 (&) 
 
 Fig. 473. — a, diagram to illus- 
 trate the Suess' theory of the 
 origin of mountain arcs ; h, the 
 author's modification of thia 
 
438 
 
 EARTH FEATURES AND THEIR MEANING 
 
 resistant areas. These more resistant portions of the stratum 
 may thus represent the ancient continental shields of our planet. 
 
 The Atlantic and 
 Pacific coasts con- 
 trasted. — In his 
 studies of moun- 
 tain arcs in their 
 relation to the 
 plan of the earth, 
 Professor Suess 
 has shown how 
 the arrangements 
 of the mountain 
 chains about the 
 two larger oceans 
 represent two 
 strongly con- 
 
 FiG. 474. — Festoons of mountain arcs about the borders trasted types, 
 of the Pacific Ocean — Pacific type of coast (based upon w v, pr-po o about 
 
 the Pacific margin 
 the mountain arcs are, as it were, strung in festoons which trend 
 parallel to and are convex toward the coast, or else lie in fringing 
 garlands of islands in the same attitude (Fig. 474) ; the mountain 
 chains about the Atlantic become sharply truncated as they reach 
 the coast, and thus indicate 
 that the basin of this ocean 
 has been produced by an in- 
 throw or depression between 
 great marginal displace- 
 ments in some period sub- 
 sequent to the formation of 
 the mountains. 
 
 Thus the mountain folds 
 of the Appalachian system 
 are in Newfoundland cut 
 off abruptly at the coast 
 
 line, and the same beds, Fig. 475. — The interrupted system of the 
 c;,^;i«^Ur +™.«„ 4- J Armorican Mountains common to western 
 
 similarly truncated, are en- „ j ^ xt ^u a • ^ f<- 
 
 '' _ ' Europe and eastern North America (after 
 
 countered again across the Aridt). 
 
THE ORIGIN AND THE FORMS OF MOUNTAINS 439 
 
 Fig. 476. — Schematic representa- 
 tion of a "zone of diverse dis- 
 placement" in the Great Basin of 
 the western United States (after 
 Powell). 
 
 expanse of ocean in the folds at the coast of western Europe (Fig. 
 475). In discontinuous remnants this ancient mountain chain may 
 be traced in an east and west direction across western and central 
 Europe. We have thus here to do with a single mountain 
 system which extends from central Europe to northern Alabama, 
 out of which a great link has been taken by the subsequent 
 sinking in of the basin of the Atlantic Ocean. 
 
 The block type of mountain. — The inclusion of most eleva- 
 tions in mountain chains and arcs is one of the most obvious 
 facts to any one who has examined 
 world atlases with this subject in 
 mind. Such chains are almost in- 
 variably composed of folded rocks, 
 thus indicating that erosion has 
 removed great superincumbent 
 masses of strata since the crustal 
 compression produced the folds at 
 considerable depths below the then 
 surface. 
 
 There are, however, large elevated tracts upon the earth's sur- 
 face which are intersected by deep valleys, but where no arrange- 
 ment of the elevated portions within chains or ranges is to be 
 detected. In such cases the distribution of mountain and valley 
 may bear a resemblance to a mosaic of disturbed parts which 
 
 stand at different levels 
 
 Ait tn 
 
 (Fig. 476). 
 
 Such block mountain dis- 
 tricts are to be found in 
 many parts of the earth's 
 surface, but notably within 
 the Great Basin of the 
 western United States, and 
 in the land area which 
 borders the Indian Ocean 
 upon the west and north- 
 west. In contrast with the 
 mountain arcs, so strikingly 
 exemplified by the continent of Asia as a whole, its extreme south- 
 western portion is made up of an alternation of plateau and rift 
 
 Lake 
 Bannqo 
 
 1 
 
 F 
 
 5 
 
 j 
 
 
 
 
 
 
 
 
 
 20 
 
 io 
 
 Fig. 477. — Section of an East African block 
 mountain (after J. W. Gregory). 
 
440 EARTH FEATURES AND THEIR MEANING 
 
 valley separated from each other by great displacements. Though 
 modified to some extent by erosion, the elevations seem generally 
 to represent the displaced crust blocks which in mutual adjust- 
 ments have been left at the highest levels (Fig. 477). The valley 
 of the Jordan, with the mountains of Lebanon rising above it, is 
 near the northern extremity of this faulted mountain region (Fig. 
 434, p. 404), while the Great Rift valley, crossing east Central 
 Africa, and the many neighboring rifts to the east and west, are 
 graven in lines so deep that an observer upon a neighboring planet 
 might perhaps detect them. 
 
 It is not necessary in all cases to assume that the block moun- 
 tains of a faulted district represent the blocks which in the ad- 
 justments were left the highest. Erosion in the course of time 
 accomplishes marvels of transformation, and it may result that 
 heavy masses of more resistant rock eventually project the high- 
 est, even though they may represent the downthrown blocks in 
 the fault mosaic (Fig. 43, p. 60). 
 
 Where in addition to undergoing changes of level the earth 
 blocks have been tilted, the features long since described from our 
 
 Fig. 478. — Tilted crust blocks in the Queantoweap valley. 
 
 western interior basin as " Basin Range strupture " are developed. 
 Here the upper surface of the disturbed earth blocks betrays the 
 evidence of a definite tilt in some one direction (Fig. 478, and Fig. 
 431, p. 402). 
 
 Mountains of outflow or upheap. — An important type of moun- 
 tain, generally described as volcanic, may be due either to the out- 
 flow of lava at the earth's surface, or to accumulations of separated 
 fragments of lava, first thrown into the air, and then deposited 
 by gravity or admixed with water as volcanic mud. Such moun- 
 tains, both before and after modification by erosion, assume the 
 strikingly characteristic forms which have been fully discussed in 
 Chapters IX and X. The dominant types are the lava dome and 
 
THE ORIGIN AND THE FORMS OF MOUNTAINS 441 
 
 the puy, the cinder cone, and the more complex composite cone. 
 Excepting only the surface produced by the few great fissure erup- 
 tions and the semivolcanic mesa type, the individual mountains 
 of volcanic origin develop features with notably circular bases. 
 
 Domed mountains of uplift — laccolites. — At a considerable 
 number of widely separated localities upon the earth's surface, 
 mountainous regions are encountered, the central areas or cores 
 
 Pig. 479. — Pen drawing of the laccolite of the Carriso Mountain by W. H. 
 Holmes, which shows the jagged surface of the igneous rock core and the slop- 
 ing tables which still remain of the roof of sedimentary rocks (after Cross). 
 
 of which are composed of intrusive igneous rock such as granite, 
 and about this core the sediments dip away in all directions as 
 though they 
 had once 
 formed a con- 
 tinuous roof 
 above it and 
 had been 
 forced into 
 this dome by 
 hydrostatic 
 pressure of 
 the once vis- 
 cous material 
 beneath (Fig. 
 152, p. 143, 
 and Figs. 479 
 and 480). Ex- 
 amples of such 
 domed moun- 
 tains of uplift g JSd€zi& <if J^iLes. s 
 were first de- ""^ ^ ' 
 
 • 1 1 1 Fig. 480. — Map of laccolitic mountains. A portion of the 
 
 scribeQDV • • • • • 
 
 •^ Judith Mountains, Montana. The intrusive igneous rock is 
 Gilbert from shown in black (after Weed). 
 
442 
 
 EARTH FEATURES AND THEIR MEANING 
 
 Fig. 
 
 481. — Ideal sections of lac- 
 colite and bysmalite. 
 
 the Henry Mountains of Utah, but instances are furnished by 
 many elevated tracts, especially within the western United States. 
 
 , Such mountains are known as lac- 
 
 colites, but when one margin at least 
 of the igneous core corresponds to 
 a displacement, the mountain is de- 
 scribed as a bysmalite (Fig. 481). 
 
 When subjected to long-continued 
 erosion, 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 it. The former usually presents a 
 more or less jagged surface which contrasts sharply with the gently 
 sloping tables of the latter (Fig. 479) . About the high granite core 
 of the mountain, the several strata of the uptilted formations pre- 
 sent each a steep slope toward this higher land, and a gentler slope 
 in the opposite direction. Such unsymmetrical ridges which sur- 
 round the mountain area are often referred to as " hog backs " 
 (plate 12 B). The arrangement of the strata in the hog backs thus 
 presents an overlapping series like the shingles upon a roof, ex- 
 cept that the overlapping is here from the bottom instead of the 
 top, and the exposed ends thus face toward the crest. Unlike a 
 shingle roof the hog backs do not shed the water which descends to 
 them from the higher levels, but, on the contrary, they cause it to 
 flow in troughs parallel to the base of the slope except where outlets 
 are found through them. 
 
 Mountains carved from plateaus. — In the mountain tj^^es 
 thus far discussed, the local uplifting of the land has itself developed 
 features which in the aggregate may be referred to as mountains, 
 even though the characters of the original surface are soon de- 
 stroyed by erosive processes of one sort or the other. Erosive 
 processes are, however, quite competent to produce mountain 
 forms from a featureless plateau, and particularly through the 
 incision by streams of running water, the best studied process of 
 mountain sculpture (see Chapters XI-XIII). This process of 
 throwing valleys about an elevated section of the earth's surface, 
 and so carving out mountains, is sometimes described as circum- 
 vallation; and if the term "mountain" be applied in its ordinary 
 
THE ORIGIN AND THE FORMS OF MOUNTAINS 443 
 
 sense to describe an individual feature, it is clear that most moun- 
 tains have been formed in this way. 
 
 To discuss the' characteristic shapes of such mountains would 
 be largely to review the contents of this book, and especially those 
 portions which discuss the character profiles resulting from the 
 action of each sculpturing or molding agent. The work of frost 
 and other weathering agencies, of running water, of mountain and 
 of continental glacier, would all have to be considered in order to 
 evolve the history of each mountain. 
 
 In addition to discovering the agents which were chiefly re- 
 sponsible for the shaping of the mountain, we may, further, in 
 many cases determine at what stage the work of one agent has 
 been succeeded by that of another, and at least at what stage 
 of its complete cycle of activity the latest agent is now at work. 
 
 The climatic conditions of the mountain sculpture. — Since 
 the different geological agencies operate either in a different man- 
 
 FiG. 482. — The gabled fagade so largely developed in desert landscapes and 
 sharply contrasted with the recurring curves in the landscapes of humid districts 
 (from a painting of the Grand Canon of the Colorado by Moran) . 
 
 ner or with differences in vigor according to the varying climatic 
 conditions, the mountains of arid regions may in most cases be 
 readily differentiated from those of the more habitable humid sec- 
 tions of country. In broad lines these differences may be summed 
 up in the greater prevalence of the curving line within the land- 
 scapes of humid districts. This may be largely ascribed to the 
 influence of the mat of vegetation, which protects the rock sur- 
 face from more rapid mechanical degeneration, and arrests the 
 sliding movements within the already loosened rock debris. In 
 place of the reversed curves of the lines of beauty, so generally 
 observed in the landscapes of well-watered regions, the desert 
 lands present ever a repetition of the vertical cliff alternating with 
 
444 EARTH FEATURES AND THEIR MEANING 
 
 a sort of many gabled fagade which is occasionally due to trunca- 
 tion of mountain spurs by the waves of former lakes, but far more 
 often the outlines of debris cones built up beneath each prominent 
 joint of the chff walls (Fig. 482). 
 
 The effect of the resistant stratum. — In a striking manner 
 mountain landscapes may disclose the influence of the diversified 
 rock materials and of the rock structures as well. After prolonged 
 erosion there is likely to be little correspondence between the posi- 
 tions of the anticlinal folds and the crests of the higher mountains. 
 Such mountains are, in fact, much more likely to rise over syn- 
 clines than upon the site of anticlines. The traveler who enters 
 the Alps by any of the several railways, or who journeys by steamer 
 over the beautiful lake of Lucerne, has a most favorable oppor- 
 tunity to study the position of the rock folds in the mountain 
 sections that are unrolled in succession before him. Rarely in- 
 deed will he find a definite anticline in correspondence with a moun- 
 tain peak, for the layers which are most resistant have developed 
 the peaks, and it is because the outer layers of the anticlines open 
 by local tension (see Fig. 26, p. 45) that they were first cut away 
 
 -v:-r.,, -.■:,. .i-->A.:^- -■ by erosion, so that the hard 
 
 ""V ■. ,rrz. ,l-^;V!^S^^vr /'■ layers within the synclines 
 
 are likely to constitute the 
 .-:" peaks within the existing sur- 
 
 "■■■'"7:r:';'. ,, j-' •' face. 
 
 When, as sometimes hap- 
 
 FiG. 483. — The Mythen, composed of Juras- ■• ^ i ti 
 
 sic and Cretaceous sediments, and resting P^nS, an_ older and llkcwiSB 
 
 upon softer Tertiary formations. View more rCsistant bed haS been 
 
 from a balloon (after a photograph by C. folded back upon younger and 
 
 ^ °^^ softer formations, an isolated 
 
 remnant may be found '' unrooted " to its base, upon which it ap- 
 pears as though floating within a billowy sea of the softer forma- 
 tions (Fig. 483). 
 
 The mark of the rift in the eroded mountains. — Applying 
 the term "mountain" in its collective sense for a circumscribed 
 area of uplifted crust, whether represented to-day by a folded or 
 a faulted complex, a lava mass, or a granite dome ; the period of 
 uplift has marked the beginning of the activity of sculpturing 
 agencies. By these the mass is pared down as it is shaped into 
 a more or less intricate design of component and essentially 
 
 ni-v 
 
THE ORIGIN AND THE FORMS OF MOUNTAINS 445 
 
 repeating units. In the vernacular the word "mountain" is 
 applied to these units into which the larger mountain mass is 
 subdivided. 
 
 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 them, and that 
 each surface has marks which may be recognized in those lines of 
 profile which recur within the land- 
 scape — the character profiles. In 
 the subdivision of the larger mass 
 — the genetical mountain — to form 
 the numerous smaller masses — the 
 erosional or circumvallational moun- ,,.^ ,;, ; 
 tains — there is disclosed a pattern ^ l^--'^?" ^ ^' " • ' 
 of fractures which has guided the *^'^'*^ -/...- '- 
 erosional agents in their incisional fig. 484. — The battlement type of 
 
 operations (see Chapter XVII). In erosion mountains. DieDreiZin- 
 
 high altitudes, where the action of 
 
 frost is so potent in prying at the 
 
 wider fractures, this subdivision of the mass may be revealed by 
 
 the sculpturing of squared towers or battlements (Fig. 484). 
 
 For other examples in which the sculptured surface is largely 
 the handiwork of a single erosional agent, as over vast areas in the 
 Canadian wilderness, the revelation of the fracture design is no 
 less apparent. Here a series of crystalline rocks underlie broad 
 expanses of territory and are without noteworthy variations of 
 
 nen (Three Battlements) 
 Dolomites (after Marr). 
 
 the 
 
 
 
 Fig. 485. — Symmetrically formed low islands repeated in ranks upon Temagami 
 
 Lake, Ontario. 
 
 hardness and almost bare of surface debris. Sculptured beneath a 
 mantling ice sheet, excavation has naturally been concentrated 
 
446 EARTH FEATURES AND THEIR MEANING 
 
 above the more widely gaping fissures of the joint-fault system, 
 doubtless already marked out in the river network which the 
 glacier overrode. The result has been a division of the surface 
 into a series of low, oval ridges or hummocks, which over vast areas 
 are repeated with monotonous regularity. Wherever the lower 
 levels have been flooded, symmetrical low islands of nearly uni- 
 form elevation rise from the expanse of water and may be counted 
 by thousands. Though the smaller islands have notably regular 
 shore lines, the larger ones disclose their composition from smaller 
 units by the breaking of their shores into similar bays spaced with 
 regular intervals (Fig. 485, and Figs. 24.3 and 245, p. 229). 
 
 The ever repeating fracture design of the earth's crust is not 
 restricted to the mountain masses which it has broken up, and the 
 unity of which it has done so much to conceal. It extends far 
 outside the margin of these masses, and is in fact common to whole 
 continents and perhaps even to the planet as a whole. The part 
 played by this design of fractures in the control of the sculpture 
 of landscapes it would be hard to overestimate. Through its 
 influence the striking features molded by one agent have been 
 merged in the contrasted shapes developed by another. It is the 
 great outline blender in the creation of nature's masterpieces of 
 form and color. Thus the lines of this mysterious fracture net- 
 work, though stamped in indelible characters upon our landscapes, 
 are generally lost in the ensemble effect and may long remain un- 
 discovered. Like a moss-grown inscription upon a slab of marble, 
 though veiled, it may yet be deciphered ; and if the veil be with- 
 drawn, the runic characters are disclosed, and one of nature's laws 
 lies open before us. 
 
 Reading References for Chapter XXXI 
 Mountain arcs or festoons : — 
 Ed. Suess. The Face of the Earth, vol, 2, 1906, pp. 201-207 ; vol. 4, 1909, 
 pp. 498-542. 
 
 Block mountains : — 
 G. K. Gilbert. Surveys West of the 100th Meridian (Wheeler), vol. 3, 
 
 Geology, Washington, 1875, Pt. 1, pp. 19 et seq., 48. 
 J. W. Powell. Report on the Geology of the Eastern Portion of the 
 
 Uinta Mountains and a Region of Country Adjacent thereto, U. S. 
 
 Geol. and Geogr. Surv. Ter., II Div. Washington, 1876, pp. 218. 
 John W. Gregory. The Great Rift Valley. London, 1896, pp. 422. 
 
THE ORIGIN AND THE FORMS OF MOUNTAINS 447 
 
 Laccolites and bysmalites : — 
 
 G. K. Gilbert. Report on the Geology of the Henry Mountains, U. S. 
 
 Geol. and Geogr. Surv. Ter., 1877, pp. 18-98. 
 Whitman Cross. The Laccolitic Mountain Groups of Colorado, Utah, 
 
 and Arizona, 14th Ann. Rept. U. S. Geol. Surv., 1895, pp. 157-241, 
 
 pis. 7-] 6. 
 W. H. Weed and L. V. Pirsson. Geology and Mineral Resources of the 
 
 Judith Mountains of Montana, 18th Ann. Rept. U. S. Geol. Surv., 
 
 Pt. iii, 1898, pp. 485-556, pi. 75. 
 W. H. Weed. Geology of the Little Belt Mountains, Montana, etc., 
 
 20th Ann. Rept. U. S. Geol. Surv., Pt. iii, 1900, pp. 387-400. 
 Vera de Derwies. Recherches geologiques et petrographiques sur les 
 
 loecolithes des environs de Piatigorsk (Caucase du Nord). Geneva, 
 
 1905, pp. 84, pis. 3. 
 R. A. Daly. The Mechanics of Igneous Intrusion, Am. Jour. Sci. (4), vol. 
 
 ]5, 1903, pp. 269-278 ; vol. 16, 1903, pp. 107-126. 
 Joseph Barrell. Geology of the Marysville Mining District, Montana. 
 
 A study of Igneous Intrusion and Contact Metamorphism. Prof. 
 
 Pap. 57, U. S. Geol. Surv., 1007, pp. 151-178. 
 
 Climatic condition in relation to land sculpture : — 
 C. E. Dutton. Tertiary History of the Grand Canyon District, Mon. 2, 
 U. S. Geol. Surv., 1882, pp. 264, pis. 42. 
 
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 crust, it is quite essential that some fa- 
 miliarity should be acquired with the appearance and properties of the 
 commonest minerals, and particularly those which enter as essential 
 constituents into the more abundant rocks. To be a competent mineralo- 
 gist, one must have a rather extended knowledge both of inorganic chem- 
 istry and of the science of crystallography, which, fascinating as it is to 
 study, involves some technical knowledge of mathematics and much 
 laboratory experience. Though necessary to any one who contemplates 
 making a career as a geologist, this special study is not essential to a 
 cultural course like the present one. The attempt will here be made to 
 bring together a body of fact, from the study of which the student may 
 quickly learn to recognize the commonest minerals in their usual va- 
 rieties. The tests he is to apply are mainly physical, and in place of an 
 elaborate discussion of crystal symmetry, pictures only can be supplied. 
 
 To the beginner the usual textbook of mineralogy is difficult to read 
 intelligently, for the reason that for each mineral species it sets before him 
 a catalogue of each physical property in its turn, with little indication of 
 those data which in the individual case have special diagnostic value. 
 None the less, however, the student is advised to consider the several 
 properties of each mineral in a definite order, and the following may serve 
 as well as any: crystal or other form, cleavage, fracture, luster, color, 
 streak, transparency, tenacity, hardness, magnetism, and specific gravity. 
 In endeavoring to connect the specific values of these properties with 
 individual mineral species, the chemical composition and the manner of 
 occurrence are not to be forgotten." 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 magnetized. 
 
 Crystal form. — Some mineral species generally occur in more or less 
 definite crystals — are bounded by definite plane surfaces developed when 
 the mineral was formed ; others in groups of interfering crystals or aggre- 
 gates, in which case the mineral is said to be crystalline ; while still others 
 are rarely found crystallized at all. Thus in a given case crystal form 
 may, or may not, be important for the diagnosis of the substance. If 
 2 a 449 
 
450 APPENDIX A 
 
 a mineral species is usually to be found in crystals, the student should 
 be aware of the fact, and if possible should have a mental picture of the 
 common crystal shape or shapes. Without an extended knowledge of 
 crystallography, this must be supplied him by drawings. Since crys- 
 tals of most species are apt to be distorted, owing to the fact that some 
 planes within the same group appear upon the crystal with a larger de- 
 velopment than others, it is convenient to remember that markings, such 
 as lines or etchings upon the crystal faces, are the same throughout the 
 same group of planes, and in the text figures such groups of planes are 
 indicated by the use of a common letter. For crystalline aggregates 
 such terms as fibrous, radiating, massive, or granular have their usual 
 meanings. 
 
 Cleavage. — It is characteristic of most crystals that the}'' break or 
 cleave along certain directions so as to leave plane or nearly plane surfaces, 
 and the luster of the cleaved surface measures the perfection of 'the cleav- 
 age property. It is important always to note how many such directions 
 of cleavage are present, and, roughly at least, at what angles thej"- inter- 
 sect — whether they are perpendicular to each other or inchned at some 
 other angle. Further, it should be noted whether a given cleavage is 
 perfect, that is, easy, which will be indicated by the thinness of the plates 
 which can be secured. An extremely perfect cleavage is possessed by 
 the mineral mica, whose plates are thinner than the thinnest paper. In 
 the case of imperfect or interrupted cleavage, the fracture surfaces are 
 not plane throughout but interrupted, the surface "jumping" from one 
 plane to a neighboring parallel one. It is especially important to note 
 whether, in the case of several cleavages possessed by a crystal, all have 
 the same degree of perfection, or whether they exhibit differences. 
 
 Fracture. — In minerals with poorly developed cleavage, the frac- 
 ture surface is described as fracture. Fracture is thus perfect in pro- 
 portion as cleavage is imperfect. The fracture is described as conchoi- 
 dal when it shows waving spherical surfaces like broken glass. For 
 fine aggregates the fracture is described as even, uneven, earthy, etc., 
 names which are generally intelligible. 
 
 Luster. — This term is applied especially to the manner in which light 
 is reflected from mineral surfaces. The most important distinction 
 is made between those minerals which have a metallic luster and those 
 which have not, the former being always opaque. Other characteristic 
 lusters are adamantine (hke oiled glass), vitreous (gla^jy), resinous, 
 waxy, etc. 
 
 Color. — For minerals which possess metallic luster the color is alwaA^'S 
 practically the same, and hence it becomes a valuable diagnostic property. 
 Of minerals which have nonmetallic luster, the color maj' be alwaj^s 
 
APPENDIX A 451 
 
 the same and hence characteristic, but in the case of many minerals it 
 ranges between wide limits and sometimes runs almost the entire gamut 
 of hues, yet without appreciable changes in the chemical composition of 
 the mineral. 
 
 Streak. — This term is applied to the color of the mineral powder, 
 and is usually fairly constant, even when the surface color of different 
 specimens may vary within wide limits. In the case of fairly soft minerals 
 the streak is best examined by making a mark on a piece of unglazed 
 porcelain (streak stone). 
 
 Transparency (diaphaneity).— The terms "transparent," "translucent," 
 "subtranslucent," and "opaque" are used to describe decreasing grades 
 of permeability by light rays. Through transparent bodies print may 
 be read, while translucent bodies allow the light to be transmitted in 
 considerable quantity through them, though without rendering the image 
 of objects. 
 
 Tenacity. — This comprehensive term includes such properties as 
 brittleness, flexibility, elasticity, malleability, etc. 
 
 Hardness. — Quite erroneous notions are held concerning the mean- 
 ing of this very common word, which properly implies a resistance offered 
 to abrasion. It is one of the most valuable properties for the quick de- 
 termination of minerals, since minerals range from diamond upon the one 
 hand — the hardest of substances — to talc and graphite, which are so 
 soft as to be deeply scratched by the thumb nail. For practical pur- 
 poses it is sufficient to make use of a rough scale of hardness made up 
 from common or well-known minerals. If we exclude the gem minerals, 
 this scale need include but seven numbers, which are : talc, 1 ; gypsum, 2 ; 
 calcite, 3 ;'! fluor spar, 4 ; apatite, 5 ; feldspar, 6 ; and quartz, 7. A given 
 mineral is softer than a mineral in the scale when it can be visibly scratched 
 by a scale mineral, but will not leave a scratch when the conditions are 
 reversed. If each will scratch the other with equal readiness, the two 
 minerals have the same hardness. 
 
 Since it may often be desirable to test mineral hardness when no scale 
 is at hand, the following substitutes may be made use of : 1, greasy feel 
 and easily scratched by the thumb nail ; 2, takes a scratch from the thumb 
 nail, but much less readily ; 3, scratched by a copper coin and very 
 easily by a pocket knife; 4, scratched without difficulty by a knife; 
 
 5, scratched with difficulty by a knife, but easily by window glass; 
 
 6, scratched by window glass ; 7, scratches window glass with readiness, 
 but a grain of sand may be substituted to represent quartz in the scale. 
 
 Magnetism. — Though nearly all minerals which contain important 
 quantities of the elements iron, cobalt, or nickel may be attracted to a 
 strong electromagnet, there are but two common minerals, and these 
 
452 APPENDIX A 
 
 of widely different appearance, whose powder is lifted by a common 
 magnet. Others are, however, lifted after strong heating in the air 
 (ignition), and this is a valuable test. 
 
 Specific gravity. — Rough tests of relative weight, or specific gravity, 
 may be made by lifting fair-sized specimens in the hand. Better deter- 
 minations require the use of a spring balance. 
 
 Treatment with acid. — The carbonate minerals react with warm 
 and dilute mineral acid so as to give a boiling effect (effervescence), 
 since carbonic acid gas escapes into the air in the process. 
 
 PROPERTIES OF THE COMMON MINERALS 
 
 The more important common minerals fall into two classes according 
 as they have large economic importance as ores, or enter in an impor- 
 tant way into the composition of rocks. 
 
 I. The Minerals of Economic Importance 
 
 Hematite. — The sesquioxide of iron, Fe203, and by far the most impor- 
 tant ore of iron. Rarely in good crystals, but sometimes in thin opaque 
 scales bearing some resemblance to mica and known as micaceous or 
 specular iron ore. At other times in nodules built up from radial needles 
 (needle ore) ; in hard masses mixed with fine quartz grains (hard hema- 
 tite) ; or in soft reddish brown earth (soft hematite). Color, black to 
 cherry red. The powdered mineral always cherry red or reddish brown, 
 and easily lifted by the magnet after ignition. Hardness 5.5-6.5; 
 specific gravity 5. 
 
 Magnetite. — The magnetic oxide of iron, re304, often in crystals like 
 Fig. 486, 1-2. Black and opaque with a metallic luster. Streak black. 
 Lifted by a magnet and sometimes itself capable of lifting filings of 
 soft iron (lodestone). Hardness 5.5-6.5. Specific gravity 5. 
 
 Limonite. — The most abundant and most valuable of the hj^drated 
 iron ores, 2 Fe203 . 3 H2O. Chemical composition the same as iron rust, 
 with which in the earthy form it is identical. Never in crystals, but often 
 in mammillary or rounded pendant forms resembling icicles, or some- 
 times clusters of grapes. Its j^ellow (rust) streak is its best diagnostic 
 property. Ignited it gives off water and becomes magnetic. The streak 
 and its notably lower specific gravity distinguish it from certain forms of 
 hematite which it outwardly resembles. Hardness 5-5.5. Specific 
 gravity 3.6-4. 
 
 Pyrite, iron pyrites, or "fool's gold." — The sulphide of iron, FeS^. 
 The most widely distributed sulphide mineral and now a chief source of 
 
APPENDIX A 453 
 
 the great chemical reagent, sulphuric acid or vitriol. Often, but not al- 
 ways, in crystals (Fig. 486, 3-5) which have peculiar striae upon their 
 faces. At other times the mineral is found massive or in radiated needles. 
 Bright metallic luster with the color of new brass, though often tarnished 
 or altered upon the surface to limonite. Hard and brittle, and so dis- 
 tinguished from gold, which is soft and malleable and of the color of the 
 paler old brass (which contained a larger percentage of zinc). Gold is, 
 fmther, about four times as heavy as pyrite. Hardness 6-6.5. Specific 
 gravity 5. 
 
 Chalcopyrite, copper pyrites. — A mixed sulphide of copper and iron. 
 If in crystals, like Fig. 486, 6 ; otherwise massive or compact. Luster me- 
 tallic. Color orange-yellow, often with local blue and green iridescence 
 hke a pigeon's throat. Distinguished from pyrite by the deeper color 
 and lower hardness, and from gold, particularly, by its brittleness and 
 lower specific gravity. Hardness 3.5-4. Specific gravity 4. 
 
 Galenite, galena. — Sulphide of lead, PbS. The chief ore of lead, and, 
 from admixture of a silver mineral, of silver as well. Usually found in 
 crystals (Fig. 486, 7). Always cleaves into blocks bounded by six very 
 perfect rectangular faces which, when fresTily broken, show a bright sil- 
 very luster and quickly tarnish to a peculiarly " leaden " surface. Very 
 heavy. Color and streak lead-gray. Hardness 2.5. Specific gravity 7.5. 
 
 Sphalerite, zinc blende. — Sulphide of zinc, ZnS, usually with considerable 
 admixture of sulphide of iron. The great ore of zinc. Not infrequently 
 in crystals (Fig. 286, 8-9), but more often in cleavable crystalline 
 aggregates. The cleavage in fine aggregates is sometimes difficult to 
 make out, but in coarse-grained masses it is seen to be equally and highly 
 perfect in six different directions, so that a symmetrical twelve-faced form 
 may sometimes be broken out (dodecahedron). Luster like that of rosia 
 (rosin jack), though when with large iron admixture the color may approach 
 black (black jack). The lighter colored varieties are translucent. Hard- 
 ness 3.5-4. Specific gravity 4. 
 
 Malachite. — Hydrated (basic) copper carbonate. The green copper 
 ore and the common surface alteration product of other copper minerals. 
 Usually has a microscopic structure niade up of fine needle-like crystals, 
 but generally massive in various imitative shapes not unlike those of the 
 iron ores. Sometimes earthy. Its color is bright green, and it is usually 
 found in association with other characteristic copper ores, such as chal- 
 copyrite and azurite. When relatively pure and in large masses, it is 
 a beautiful ornamental stone. Effervesces with acid. Hardness 3.5-4. 
 Specific gravity 4. 
 
 Azurite. — Hydrated (basic) copper carbonate, less hydrated than 
 malachite, and known as the blue carbonate of copper. Generally in 
 
454 
 
 APPENDIX A 
 
 Fig. 486. — Forms of Crystals : 1-2, magnetite ; 3-5, pyrite ; 6, chalcopyrite ; 
 7, galenite ; S-9, sphalerite ; 10-13, calcite. 
 
APPENDIX A 455 
 
 very minute and quite complex crystals, but also in imitative shapes 
 similar to those of malachite, and at other times earthy. Slightly lighter 
 in weight than malachite, from which it is easily distinguished, as from 
 most other minerals, by its bright azure blue color and its somewhat 
 lighter blue streak. Effervesces with nitric acid. Hardness 3.5-4. 
 Specific gravity 3.7-3.8. 
 
 Calcite. — Calcium carbonate, CaCOa. Almost always in crystals (Fig. 
 286, 10-13), or in confused crystal aggregates, though rarely fibrous or 
 dull and earthy. Some of the forms of the crystals are described as 
 " dog-tooth spar," others as "nail-head spar," while still others are modi- 
 fied hexagonal prisms. There is a beautifully perfect cleavage of the 
 mineral along three directions which make angles of about 105° with each 
 other, so that under the hammer the substance breaks into blocks which 
 are shaped like the crystal of Fig. 486, 10. Usually white or gray, but 
 occasionally faintly tinted. Streak white. Effervesces with cold and 
 dilute mineral acids. An associate of many ores and the chief mineral 
 of limestone. A similar mineral — dolomite — contains in addition mag- 
 nesium carbonate, has simpler crystals (like the drawing of Fig. 486, 10^ 
 but often with rounded faces), and effervesces only when the acid is warmed. 
 Hardness 3. Specific gravity 2.7. 
 
 Gypsum. — Hydrated calcium sulphate, CaS04 . 2 H2O, and the source 
 of plaster of Paris. Often in simple crystals (Fig. 487, 1) or else " swal- 
 low tail," like Fig. 487, 2^ in which case the mineral is generally either 
 transparent or translucent and is described as selenite. Such crystals 
 show a cleavage approaching in perfection that of the micas, but, unlike 
 the mica laminae, those produced by cleavage in gypsum though flexible 
 are not elastic. There are also fibrous forms of gypsum (satin spar), 
 a fine-grained form (alabaster), and the impure earthy form (rock gyp- 
 sum). Very soft, light in weight, and difl&cultly fusible. Color usually 
 white, gray, or pale yellow. Hardness 2. Specific gravity 2.3. 
 
 Copper glance. — A sulphide of copper, CU2S. Not usually well crj^stal- 
 lized, but generally massive and associated or variously admixed with 
 other copper ores such as chalcopyrite, malachite, etc. Fracture con- 
 choidal, luster metallic, color and streak blackish lead-gray, though often 
 tarnished blue or green from surface alterations to the copper carbonates. 
 Softer and heavier than chalcopyrite. Blowpipe or chemical tests are nec- 
 essary for its identification. Hardness 2.5-3. Specific gravity 5.5-5.8. 
 
 Cerussite. — The white or carbonate lead ore, PbCOg, and an important 
 ore of silver as well. Often in crystals of considerable complexity, though 
 Fig. 487, 3-4, shows some common shapes. Often granular, massive, or 
 earthy (gray carbonate ore). Very brittle and with conchoidal fracture. 
 The luster is adamantine or like that of oiled glass. Color generally 
 
456 APPENDIX A 
 
 white or gray. Very heavy, the heaviest of hght colored and nonmetaUic 
 minerals. Dissolves in nitric acid with effervescence. Hardness 3-3.5. 
 Specific gravity 6.5. 
 
 Siderite. — The carbonate or " spathic " ore of u-on, FeCOg. Either 
 in crystals resembhng in form Fig. 486, 10, but with rounded faces, or 
 cleavable massive to finely granular and earthy. The crystalline varieties 
 cleave easily into smaller blocks of the same form as those of calcite. Color 
 usually gray or brown and streak white. On strongly igniting, the white 
 powder becomes black and magnetic. Lighter in both color and weight 
 than the other iron ores, and unlike them siderite effervesces with acid. 
 Distinguished from calcite by its higher specific gravity and its change 
 upon being ignited. Hardness 3.5-4. Specific gravity 3.9. 
 
 Smithsonite. — Carbonate of zinc, ZnCOg, and an important ore of 
 that metal. Seldom found in crystals except as a replacement of calcite 
 crystals, in which case it shows the forms characteristic of the latter min- 
 eral. Usually kidney-shaped, stalactitic, or else in incrustations upon 
 other minerals. Sometimes granular or earthy. Brittle. Luster vitre- 
 ous, color white or greenish gray, though often stained yellow with iron 
 rust. Streak white except when the mineral is stained with iron. Ef- 
 fervesces with warm acid. Hardness 5. Specific gravity 4.4. 
 
 Pyrolusite. — Black oxide of manganese, MnOg, though generally im- 
 pure from admixture with other manganese oxides. Usually in intricate 
 aggregates which may be columnar, fibrous, mammillary, earthy, etc. 
 Opaque, with color and streak both black. Soft and easily soils the fingers. 
 With hydrochloric acid gives off the choking fumes of chlorine. Hard- 
 ness 2-2.5. Specific gravity 4.8. 
 
 II. 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 aluminium, calcium, magnesium, iron, 
 sodium, potassium, or hydroxyl (OH). For their identification an ex- 
 amination of the physical properties is usually sufficient, whereas of the 
 typical ore minerals already considered, additional chemical tests may be 
 necessary. 
 
 Feldspars. — A group of similar aJumino-silicates of potassium, sodium, 
 and calcium. The most important of all rock-making minerals. Although 
 with wide variation in chemical composition, the feldspars are yet broadly 
 divided into two classes ; the one striated, and the other an unstriated 
 potash or orthoclase variety. The pocket lens is usually necessary in order 
 to make out the striations upon the crystal or cleavage surfaces. When 
 formed in veins, feldspar appears in crystals (Fig. 487, 5-6), but as a rock 
 constituent the mutual interference of crystals prevents the development 
 
APPENDIX A 
 
 457 
 
 IS i6 
 
 Fig. 487. — Forms of Crystals : 1-2, gypsum ; 3-4, cerussite ; 5-6, feldspar ; 7, 
 quartz ; 8, pyroxene (cross section) ; 9, hornblende (cross section) ; 10, garnet ; 
 11, nephelite; 12-14, staurolite ; 15-16, tourmaline (cross sections) ; 17, olivine. 
 
458 APPENDIX A 
 
 of bounding faces. Two cleavage directions, nearly or quite perpendicular 
 to each other, are notably different in their perfection. Hard enough 
 to scratch glass, but easily scratched by sand. Color pink (usually ortho- 
 clase or microline), white (often albite) to gray. Sometimes with beauti- 
 ful " pigeon's throat " effect of iridescence (labradorite). Low specific 
 gravity. Hardness 6. Specific gravity 2.5-2.8. 
 
 Quartz. — Oxide of silicon or silica, SiOg. Both an important vein 
 mineral associated with the ores and a rock maker. In the former case 
 particularly, often in crystals of notably simple forms (Fig. 487, 7). Few 
 minerals which are not gems are so hard. Remarkable freedom from 
 cleavage so that the mineral breaks much like window glass — conchoidal 
 fracture. Wide range in both transparency and color. Transparent and 
 colorless crystalline variety (rock crystal), brown translucent (smoky 
 quartz), turbid white (milky quartz), and various colored varieties (car- 
 nelian, jasper, jet, etc.). Insoluble in acids and infusible. Hardness 7. 
 Specific gravity 2.6. 
 
 Micas. — Like the feldspars a group of complex silicates, but here 
 chiefly of potassium, magnesium, iron, and hydroxyl. Abundant as rock 
 makers, the micas are all characterized by the thinnest and toughest 
 of elastic cleavage plates, such as are generally known as isinglass. When 
 a needle is driven sharply through a thin scale of mica, a six-rayed punc- 
 ture star forms about the needle point. The darker common variety of 
 mica is rich in iron and magnesium and is called biotite, and the lighter 
 colored alkaline variety, muscovite. Hardness 2.5-3.1. Specific grav- 
 ity 2.7-3.1. 
 
 Chlorite. — Generally an intricate mixture of more or less similar 
 microscopic crystals having varying and rather complex chemical composi- 
 tions and related to the micas, but all characterized by a peculiar leaf 
 green color. These minerals are a common product of hydration weather- 
 ing in rocks which are rich in magnesium and iron — especially those that 
 contain biotite, pyroxene, or hornblende (see below). Hardness 1-2.5. 
 Specific gravity 2.5-3. 
 
 Pyroxenes. — An important group of related rock-making minerals all 
 of which are silicates of the bases magnesium, calcium, aluminium, iron, 
 and manganese. Quite generally developed either in columnar or needle- 
 like crystals which are uniformly shaped in cross section like Fig. 487, 8. 
 Two rather imperfect cleavages are directed parallel to the longer axis 
 of the crystal and nearly at right angles to each other. The colors of aU 
 but the lime varieties are dark and generally green, dark brown, bronze, 
 or black. The lime varieties are white, gray, or pale green. A dark 
 colored and common iron variety is known as augite. Streak generally 
 either white or lightly tinted. Hardness 5-6. Specific gravity 3.2-3.6. 
 
APPENDIX A 459 
 
 Amphiboles. ■ — A group of minerals of the same chemical composition 
 as the pyroxenes, with which also in most physical properties they agree. 
 The principal distinction is found in the shape of the cross section and in 
 the cleavage (Fig. 487, 9). Whereas the cross sections of pyroxenes are 
 generally eight sided, those of the amphiboles have six sides, and whereas 
 the cleavage directions of pyroxenes are nearly at right angles to each 
 other (87°), the similar but much more perfect cleavage directions of 
 the amphiboles are inclined at an obtuse angle (124^°). Owing to the 
 obliquity of the amphibole cleavage, fractured surfaces of the mineral 
 appear splintery, which is not in the same measure true of the pyroxenes. 
 A fibrous variety of amphibole, and occasionally other varieties of the 
 mineral, is a not uncommon product of weathering of pyroxenes. Other 
 physical properties of the amphiboles are in the main almost identical with 
 those of the pyroxenes. 
 
 Garnet. — Complex alumino-silicates or ferro-silicates of calcium, 
 magnesium, iron, or manganese, or several of these combined. Nearly 
 always in crystals, and usually found in mica schist (see below). The 
 crystals usually have twelve similar faces, each a lozenge (dodecahedron), 
 or else twenty -four similar faces, or the two forms combined (Fig. 
 487, 10). Brittle. From any but the gem minerals garnet is easily 
 distinguished by its hardness, which in different varieties ranges from 
 somewhat below to somewhat above that of quartz. The luster is vitre- 
 ous, and the color runs the gamut of reds, browns, and greens, but with 
 the common hue dark red to black. Streak white. Hardness 6.5-7.5. 
 Specific gravity 3.1-4.3. 
 
 Nephelite (nephelene). — An alumino-silicate of sodium and potassium. 
 In certain special provinces this mineral is developed in abundance as an 
 essential constituent of igneous rocks, but elsewhere practically unknown. 
 The rare crystals are hexagonal prisms (Fig. 487, 11), but the mineral is most 
 easily determined by its general resemblance to feldspar, but with the dif- 
 ferences of cleavage, luster, and reaction with acid. Whereas the feldspars 
 have two cleavages, either nearly or quite perpendicular to each other 
 and of different degrees of perfection, nephelite has three equal cleavages 
 inclined 60° and 120° to each other and of less perfection than either 
 feldspar cleavage. The luster of nephelite is perhaps the best clew 
 to its identity, since this is greasy and simulated by but few minerals. 
 The fine powder of the mineral treated for some time with strong hy- 
 drochloric acid forms a perfect jelly of silicic acid, whereas the feld- 
 spars do not. Though itself gray or white and unobtrusive, nephelite 
 is usually associated with brightly colored minerals, which are often the 
 first clew to its presence in a rock. Hardness 5.5-6. Specific gravity 
 2.5-2.6. 
 
460 APPENDIX A 
 
 Talc (soapstone). — A silicate of magnesium and hydroxyl which is 
 an important alteration product through weathering of certain pyroxene 
 rocks especially. Usually a fohated mass, this product is occasionally 
 fibrous or even granular. Talc is one of the softest of minerals, ha\ang a 
 greasy feel and being easily scratched with the thumb nail. The luster 
 of the foliated varieties is apt to be pearly, and the color apple-green to 
 white, though sometimes stained brown from oxide of iron. The streak 
 of the mineral is white except when stained by iron. Although the 
 rocks which are composed mainly of talc (soapstone) are exceedingly 
 soft, they are very tough and remarkably resistant. Hardness 1-1.5. 
 Specific gravity 2.7-2.8. 
 
 Serpentine. — Like talc, serpentine is a silicate of magnesium and 
 hydroxyl, and an important product of the brealdng down of magnesium 
 minerals in the process of weathering. The mineral is usually found as a 
 fine web of microscopic needlelike fibers, and is best rouglily diagnosed 
 by its color and its associated minerals. Like talc it is usually developed 
 within those igneous rocks from which feldspar is lacking, but where either 
 pyroxene or olivine is found in abundance or was previous to alteration. 
 The characteristic color of serpentine is leek-green. The rock largely 
 composed of serpentine is called by the same name, and being exceedingly 
 tough and unchanging is, in spite of its softness, a valuable building and 
 ornamental stone. A red magnesium garnet is apt to be associated with 
 such serpentine masses. Hardness 2.5-4, because of impurities. Specific 
 gravity 2.5-2.6. 
 
 Staurolite. — A silicate of aluminium, iron, and hj^droxyl. Found in 
 metamorphic rocks usually in association with garnet. Always in crys- 
 tals bounded by simple forms generally crossed, as shown in Fig. 487, 12-14. 
 The color is dark reddish brown, and the streak is colorless to grayish. 
 The hardness is exceptional and higher than that of quartz. Hardness 
 7-7.5. Specific gravity 3.6-3.7. 
 
 Tourmaline. — An exceptionally complex silicate of boron and alu- 
 minium as well as iron, magnesium, and the alkalies. Found in metamor- 
 phic rocks and always crystallized. The crystals are columns or needles 
 whose cross section is the best guide to their identity, since this is a modi- 
 fied triangle unhke that of any other mineral (Fig. 487, 15-16). Additional 
 diagnostic properties are the characteristic striations which run lengthwise 
 of the crystals upon prism faces, and the lack of any cleavage (difference 
 from hornblende). The hardness is also a valuable property, since this 
 is greater than that of quartz. The mineral is brittle and the fracture 
 subconchoidal. The range in color is as great as, or greater than, that of 
 garnet, though the common forms are jet black. Streak uncolored. 
 Hardness 7-7.5. Specific gravity 3-3.2. 
 
APPENDIX A 461 
 
 Olivine. — A silicate of magnesium and iron and a rock-making min- 
 eral found only in those igneous rocks which have little or no feldspar. 
 It easily suffers alteration by weathering and passes into serpentine, and 
 in fact is seldom found except when at least partially altered to the fibrous^ 
 webs of that mineral. The form of the unaltered crystals within the 
 rocks is shown in Fig. 487, 17, and, cut in sections, the mineral appears 
 in more or less elongated hexagons. The hardness of the unaltered min- 
 eral is about that of quartz. It has rather imperfect cleavages in two 
 rectangular directions, and is usually translucent, with a vitreous luster 
 and a color which is olive-green when not stained brown by oxide of 
 iron. Streak uncolored. Hardness 6.5-7. Specific gravity 3.2-3.3. 
 
APPENDIX B 
 
 SHORT DESCRIPTIONS OF SOME COMMON ROCKS 
 
 In Chapter IV the classification and the structure of rocks have been 
 briefly discussed. Below are added brief descriptions of the more im- 
 portant common rocks. For rocks as for minerals it is, however, essen- 
 tial that a collection of well-chosen specimens be studied for purposes of 
 comparison. A small pocket lens is a valuable aid in making out the 
 component minerals and the textures of the finer grained rocks. 
 
 I. Intrusive Rocks 
 
 Granite. — Of granitic texture, though sometimes porphyritic as well. 
 The most abundant mineral constituent is a pink or white feldspar, usu- 
 ally without visible striations, with which there is usually in subordinate 
 quantity a white striated feldspar. Next in importance to the feldspar 
 is quartz, which because of its lack of cleavage shows a peculiar gray 
 surface resembling wet sugar. In addition to feldspar and quartz there is 
 generally, though not universall}'-, a dark colored mineral, either mica or 
 hornblende. The mica is usually biotite, though often associated with 
 muscovite. 
 
 Syenite. — Like granite, but without quartz, with more striated feld- 
 spar, and generally also the rock has a darker average tint. While biotite 
 is the commonest dark colored constituent of granite, hornblende is more 
 apt to take its place in syenite. Less common than granite, to which it is 
 closely related in origin and in composition. 
 
 Gabbro. — A dark colored rock of granitic texture composed of striated 
 feldspar with broad cleavage surfaces and usually an abundance of pyrox- 
 ene. In contrast to the feldspars of granite, those of gabbroes are often 
 dull and colored grayish yellow or greenish. The pyroxene is often in 
 part changed to fibrous amphibole. Magnetite may be an abundant 
 accessory mineral. 
 
 Diabase. — In color dark like gabbro, and of similar constitution. In 
 diabase, however, the feldspar crystals, instead of being broad and of 
 irregularly interrupted outline, are relatively long (" lath-shaped "), and 
 the pyroxene acts as a filler of the residual space between them. 
 
 Peridotite. — A heavy and dark colored rock of granitic texture which 
 is nearlj' or quite devoid of feldspar but contains oli\'ine. When altered, 
 
 462 
 
APPENDIX B 463 
 
 as it generally is, it is largely a mass of serpentine, talc, and chlorite, sur- 
 rounding cores, it may be, of still unaltered pyroxene and olivine. Mag- 
 netite is an abundant constituent, and a red garnet is apt to be present. 
 
 2. Extrusive Rocks 
 
 Obsidian. — A rock glass rich in silica. It is usually black and breaks 
 with a perfect conchoidal fracture. It often passes over through insen- 
 sible gradations into pumice, which differs only in its vesicular structure. 
 As regards chemical composition, obsidian and pumice are not notably 
 different from rhyolite (below). 
 
 Rhyolite. — A light colored rock of porphyritic texture, often also with 
 fluxion or spherulitic textures, or both combined. The porphyritic ap- 
 pearance is given the rock by large crystals of a glassy, unstriated feldspar 
 and crystals of quartz. Rhyolite is a very siliceous lava containing rather 
 more silica than granite, to which of the intrusive rocks it is most closely 
 related, and from which it differs in its texture and in the manner of its 
 occurrence in nature. Whereas granite is found in great batholites, 
 laccolites, and bysmalites, and consolidated in rriost cases beneath the 
 earth's surface, rhyolite generally occurs in sheets, flows, or dikes, and 
 consolidated either above or in fissures near to the surface. 
 
 Trachyte. — Similar to rhyolite, but usually with a peculiar gray aspect 
 from the greater abundance of feldspar crystals. The rock is less sili- 
 ceous than rhyolite, contains no quartz crystals, and approaches a feldspar 
 in its average composition. 
 
 Andesite. — Similar to rhyolite in appearance and in origin, but more 
 basic and correspondingly dark in color. The porphyritic crystals are of 
 lath-shaped, striated feldspar, with which are associated crystals of either 
 biotite or hornblende or both. A fluxion texture is particularly char- 
 acteristic of this type of extrusive rock. 
 
 Basalt. — A dark colored or black basic rock of porphyritic texture 
 which differs but little from diabase. It may show under the lens fine 
 lath-shaped crystals of striated feldspar associated with crystals of augite, 
 but more frequently the rock is dense and without visible mineral con- 
 stituents. It is particularly likely to occur divided up mto columns six 
 inches to a foot in diameter and known as basaltic columns. Especially 
 fine examples are known from the Giant's Causeway and other localities 
 in the western British Isles. 
 
 > 3. Sedimentary Rocks of Mechanical Origin 
 
 Conglomerate ("pudding stone"). — A rock made up from pebbles 
 which are cemented together with sand and finer materials. The pebbles 
 are usually worn by work of the waves upon a shore, and may vary in 
 
464 APPENDIX B 
 
 size from a pea to large bowlders. They may consist of almost any hard 
 mineral or rock, though the sand about them is largely quartz. 
 
 Sandstone. — A rock composed of sand cemented together either by 
 calcareous, siliceous, or ferruginous materials. Sandstones are described 
 as friable when their surface grains are easily rubbed off, or as compact 
 when they are more firmly cemented. Sandstones are often distinctly 
 banded and are sometimes variously stained with oxide of iron. Those 
 sandstones which have been formed upon a seacoast are known as marine 
 sandstones, while those derived from accumulations collected by the wind 
 in deserts are distinguished as continental deposits. Sandstones form 
 much thicker formations than conglomerates, the latter usually consti- 
 tuting a basal layer only of the sandstone formation (basal conglomerate). 
 
 Shale. — A consolidated mud stone which is probably the most abun- 
 dant rock formation. In large part clay admixed in varying proportions 
 with extremely fine sandy grains. 
 
 4. Sedimentary Rocks of Chemical Precipitation 
 
 Calcareous tufa (travertine). — Not to be confused with tuff, which 
 is a fragmental extrusive or volcanic rock. Calcareous tufa is formed 
 when waters which contain carbonic acid gas and lime carbonate in solu- 
 tion, give off the gas and with it the power to hold the lime in solution. 
 Such a liberation of the gas may occur when the stream is dashed into 
 spray above a cascade, and the lime is then deposited about the site of the 
 falls. Travertine is generally porous and formed of more or less concen- 
 tric layers or incrustations. A remarkable illustration is furnished by the 
 travertine deposits of Tivoli and other localities near Rome, since here 
 the material supplies a valuable building stone. 
 
 Oolitic limestone (oolite). — This rock is made up of spherical nodules 
 and so has the appearance of fish roe. Broken apart, each grain reveals 
 in its center a core of siliceous sand about which carbonate of lime has been 
 deposited in concentric layers. It is thought that waters charged with 
 carbonate of lime, in issuing from a river near a sea beach, coat the sand 
 grains of the latter with successive thin films of lime carbonate due to the 
 rhythmic ebb and flow of the tides, evaporation of the adhering water 
 taking place when the sands are exposed at low tide. 
 
 5. Sedimentary Rocks of Organic Origin 
 
 Limestone. — A gener^-Uy white or gray rock composed of carbonate 
 of lime with var3"ing proportions of clay, silica, and other impurities. The 
 lime carbonate is usually derived from the hard parts of marine organisms, 
 and the argillaceous and siliceous impurities from the finer land-derived 
 sediments which descend with them to the bottom. 
 
APPENDIX B 465 
 
 Dolomite (dolomitic or magnesium limestone). — Differs from lime- 
 stone in containing varying proportions of the mineral dolomite {ante, 
 p. 455), which is made up of equal parts of calcium and magnesium car- 
 bonates. Difficult to distinguish from limestone unless a chemical test 
 is made for magnesium, though it may be said in general that dolomite 
 is less soluble in cold mineral acids. 
 
 Peat. — An accmnulation of decomposed vegetable matter within 
 small lakes and in lagoons separated from larger ones {ante, p. 429). 
 Peat represents the first stage in the formation of coal from vegetable mat- 
 ter, and differs from the coals by its larger proportion of contained water. 
 Because of this water its fuel value is correspondingly small. It is usu- 
 ally dark brown or black and reveals something of the structure of the 
 plants out of which it was formed. 
 
 6. Metamorphic Rocks 
 
 Gneiss. — A generally more or less banded (gneissic) metamorphic 
 rock with a mineral constitution similar to granite, and often developed 
 by metamorphic processes from that rock. It may at other times, by pro- 
 cesses not essentially different, be derived from sedimentary formations. 
 It usually contains as important constituents unstriated feldspar and 
 quartz, but in addition it may include a striated feldspar, biotite, mus- 
 covite, or hornblende, or several of these combined. In proportion as 
 mica or hornblende is abundant, it has a marked banded texture, but it 
 differs from mica schist (see below) not only in the presence of its feldspar, 
 but in the smaller proportion of mica. Biotite gneiss, hornblende gneiss, 
 etc., are terms used to designate varieties in which one or the other of the 
 dark colored constituents predominate. 
 
 Mica schist. — A metamorphic rock without feldspar and mainly 
 composed of quartz and light colored mica (muscovite). The abundant 
 mica lends to the rock its characteristic schistose texture, which differs 
 from the usual gneissic texture. In some cases the mica is wrapped about 
 the grains of quartz, but at other times it forms a series of almost contin- 
 uous membranes separating layers of quartz. 
 
 Sericite schist. — A variety of schist which is characterized by an 
 abundance of a peculiar silvery mica rich in the element group hydroxyl. 
 The mica scales are often miscroscopic and wrought into an intricate 
 web with the quartz constituent. 
 
 Talc schist. — A schist made up largely of talc, but with varying 
 proportions of quartz, magnetite, etc. From the abundance of the talc 
 it is usually pale green or white. 
 
 Chlorite schist. — A greenish, fine-grained metamorphic rock in which 
 chlorite is the principal mineral, but in which magnetite is a quite charac- 
 teristic accessory constituent. 
 2h 
 
466 APPENDIX B 
 
 Staurolitic garnetiferous mica schist. — A mica schist in which gar- 
 net and staurolite are so abundant as to be essential constituents. 
 
 Clay slate. — A metamorphosed mud stone or shale. In the process 
 of metamorphism the rock has been hardened, given a slaty cleavage, 
 and innumerable minute scales of mica have developed to produce a 
 silky luster upon the cleavage faces. The color may be gray, green, 
 purple, or black. 
 
 Quartzite. — A metamorphosed sandstone in which the sand grains 
 have become enlarged by accretion of silica. Whereas a sandstone frac- 
 tures about its constituent grains, a break in quartzite is continued through 
 the grains and the cement alike. In contrast to sandstones, the quartz- 
 ites derived from them are usually lighter in color and often nearly white. 
 
 Marble (crystalline limestone). — The result of metamorphism upon 
 limestones. Usually white in color but sometimes gray, blue gray, or 
 yellow, and sometimes variously broken or brecciated and stained with 
 iron oxide. Effervesces with cold dilute acid. 
 
 Coals. — Under the head of peat the first stage in the formation of 
 coals from vegetable matter has been briefly described. Lignite, or 
 brown coal, represents a further stage and one in which the vegetable 
 structure is still recognizable. It is usually brownish black or black 
 in color and contains a considerable proportion of water. With increased 
 pressure or dynamic metamorphism, further percentages of the vola- 
 tile constituents are eliminated, and when from seventy-five to ninety 
 per cent of carbon remains, the material burns with a yellow flame and 
 is known as bituminous coal. This is the great fuel for the production 
 of steam. A continuation of the metamorphic processes carries off a 
 further proportion of the volatile matter and leaves a dense, hard, black 
 substance with sometimes as much as ninety-five per cent of carbon. 
 This is the so-called " hard coal " or anthracite generally used for fuel 
 in our houses, for which purpose it is so well adapted because it burns 
 with a production of much heat and almost without smoke. 
 
APPENDIX C 
 
 THE PREPARATION OF TOPOGRAPHICAL MAPS 
 
 Topographical maps a library of physiography. — For the satisfactory- 
 working out in detail of the geology of any region of complex structure, 
 an accurate topographical map is prerequisite. This is so much the more 
 true because nearly all complexly folded or faulted rock masses are to be 
 found in mountainous, or at least in hilly regions. The making of the 
 topographical map must, therefore, precede that of the geological map, 
 and in modern usage the latter is a topographical and a geological map 
 combined in one. 
 
 Within certain narrow limits, predictions concerning the geological 
 history of a province may often be made by an expert geologist from 
 examination of an accurate topographical map. Just as in forecasting 
 the weather upon the basis of the usual weather maps, such predictions 
 can sometimes be made with entire confidence in their accuracy, while 
 at other times a guess only may be hazarded. The great value of the 
 modern topographical map is becoming, however, universally acknowl- 
 edged, 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 development. 
 Thus there is now being accumulated a vast library of geographical and 
 to some extent geological information, of which the student of geology 
 must be prepared to make use. 
 
 The nature of a contour map. — More and more the contour map is 
 replacing the earlier and less scientific methods of representing topog- 
 raphy on the large scale sectional maps, and hence this type only need 
 here be considered. In the contour map, the relief of the land is repre- 
 sented by a series of curving lines, each the intersection of a particular 
 horizontal plane with the land surface, and the several planes separated 
 by uniform differences of elevation. This altitude interval is known as 
 the contour interval. Its choice is a matter of considerable importance, 
 for though regions of relatively simple topography may be adequately 
 represented upon a map of large contour interval, say one hundred feet, 
 another district may require an interval as short as five feet. A contour 
 map with this interval may be conceived to have been made by flooding 
 
 467 
 
468 APPENDIX C 
 
 the region which it represents and preparing maps of the shore lines for 
 each rise of five feet of the water surface, and superimposing the several 
 maps thus derived with accurate registration one above the other. Wher- 
 ever the land slopes are steep, the shore lines of the several maps wdll be 
 crowded closely together and give the effect of a relatively dark local 
 shade; where, upon the other hand, the surface is relatively flat, the 
 several shores will be widely spaced and the effect will be to produce a 
 white area upon the map. Thus in contour maps dark tones indicate 
 steep gradients and pale tones a flatness of surface. 
 
 The selection of scale and contour interval. — With the use of the 
 small scale in the contour map, the tones of the map will be correspond- 
 ingly dark, though the relative differences in tone will remain the same. 
 With the use of a closer contour interval the tones will deepen throughout. 
 The adjustment of scale and contour interval to any given region is a 
 matter requiring experience in topographical mapping, and in addition 
 a knowledge of the geological significance of topographic features. Un- 
 fortunately, the element of expense and the special commercial objects 
 held in view, conspire to select scales and contour intervals which are 
 often little adapted to the districts surveyed. 
 
 The method of preparing a topographical map. — Having fixed upon 
 the scale and the contour interval which is to be employed, 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 map, and then 
 to hang, as it were, upon these points as attachments the design repre- 
 sented by the relief. Were the surface of the ground to be represented 
 by a flexible fabric, the map maker might raise from a flat base a series of 
 stout posts of the heights and in the positions which he has determined, 
 and upon these supports arrange the slopes of the fabric much as drapery 
 is adjusted. The determination of the exact positions and the elevations 
 of his control stations is, therefore, a process coldly precise and formal ; 
 whereas in the shaping of the surfaces his atte'ntion should be fixed 
 more upon correctly reproducing the shapes than upon fixing accurately 
 the position of every point. As a matter of fact, the position of the 
 average point will be most accurately fixed v\rhen the shapes of the fea- 
 tures are most clearlj^ comprehended. To some extent, therefore, the 
 topographer should be familiar with the geological significance of the 
 earth features which he is representing. 
 
 Laboratory exercises in the preparation of topographical maps. — The 
 principles which underlie the surveyor's method for preparing a topo- 
 graphical map may be learned in the laboratory by the use of models and 
 the simple device shown in plate 24 A and B. To represent the section 
 of country to be mapped a model in plaster of Paris is substituted, and this 
 
Plate 24. 
 
 A. Apparatus for exercise in the preparation of topographic maps. 
 
 B. The same apparatus in use for testing the contours of a map. 
 
 C. Modeling apparatus in use. 
 
APPENDIX C 
 
 469 
 
 is placed within a rectangular tank to which locating carriages and alti- 
 tude gauges are attached that allow the student to fix the position and the 
 elevation of any point upon the surface of the model. 
 
 Upon each model the student " locates," or fixes, the position of a 
 sufficient number of points for the control of his map, entering upon an 
 appropriate map base for each position the altitude which was read from 
 the gauges. Now with the map always before him he " sketches in " the 
 forms of the surface by means of contour lines. For this purpose it 
 is often desirable to fix roughly the direction of the steepest slope at a 
 
 Pig. 
 
 ■A student's map prepared from a model by the use of the contour 
 apparatus represented in plate 24 A. 
 
 number of places, and noting the differences in elevation between control 
 stations, divide up the distance in accordance with the curves of slope 
 and start the contours at right angles to the slope. Afterwards such 
 sections are connected by sketching in with the model always in view 
 for control (Fig. 488). 
 
 The verification of the map. — The map prepared, its accuracy may 
 be tested by a simple method which is denied the topographer who has 
 to do with the actual surface of the ground. The locating carriages 
 and altitude gauges are removed from the tank, which is next filled with 
 
470 APPENDIX C 
 
 water and leveled by means of guide marks upon the interior. A few 
 drops of milk or of ordinary clothes blueing are added to the water to 
 render it opaque, and it is then drawn off at the faucet in successive in- 
 stallments, so that the surface drops by layers corresponding in thick- 
 ness to the contour interval of the map, plate 24 B. As each laj^er is with- 
 drawn, that contour of the map to which the shore line should correspond 
 is carefully examined and corrected. By such corrections the nature of 
 the first errors made is soon appreciated, and the method of procedure 
 is thus more easily acquired. 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 maps. 
 
 The work above outlined calls for waterproofed models of suitable 
 form and size, and a series, each of which sets forth some typical feature 
 or series of features, has been designed by Mr. Irving D. Scott. ^ 
 
 The preparation of physiographic models. — The apparatus used to 
 prepare the topographic map is adapted also for preparing a physio- 
 graphic model from a standard topographical map. For this purpose 
 the method is essentially reversed, though the tank is replaced to advan- 
 tage by a light metal frame elevated upon one side so as to permit a free 
 use of the hands in modeling the clay. 
 
 The material used in preparing the model is artists' modeling clay* 
 which has a base of beef suet, and hence does not dry out and crack as 
 does ordinary clay. Its form is, therefore, retained indefinitely, and it 
 may be used again and again. Most maps must be enlarged in model- 
 ing, and the simplest way is often to photographically or by panto- 
 graph enlarge the map to the scale of the model. The map prepared, 
 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 (plate 24 C). 
 
 The enlargement of the map is not essential to experienced workers, 
 and the standard map may be covered in similar manner by a transpar- 
 ent plate with " checkerboard " design, the squares of which bear some 
 simple relation in size to the larger divisions of the locating carriages 
 (Plate 24 C, rear). 
 
 The method of preparing the model is comparatively simple. Be- 
 ginning at any point upon the map, the intersection of a heavy contour 
 line with one of the guide lines of the celluloid " position plate " is care- 
 fully noted. Both the position and the elevation of this point are fixed by 
 the point of the altitude gauge of the modeling frame, and the clay built 
 
 1 These models and the contouring apparatus are now manufactured for the use 
 of schools and colleges by Eberbach and Son, Ann Arbor, Mich. 
 
 ^ This clay is manufactured by the A. H. Abbott Company, art dealers, Wabash 
 Avenue, Chicago. 
 
APPENDIX C 471 
 
 up beneath it to that height. With the fingers the clay is now roughly- 
 shaped in various directions from this point, the altitude gauge is ad- 
 vanced 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 plate, and the elevation for this point similarly adjusted 
 upon the model. As before, the surface of the clay is roughly shaped in 
 advance and upon the sides so as to conform to the indications of the 
 map ; and this process is repeated until the work is finished. Correc- 
 tions for intermediate positions may be carried to any desired degree of 
 refinement which the scale and the accuracy of the map permit. 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 process, and then 
 moving the frame forward and adjusting in a new position by means 
 of the sharp pins in the legs of the apparatus. 
 
 Reading References 
 
 William H. Hobbs, New Laboratory Methods for Instruction in Geog- 
 raphy, Journal of Geography, vol. 7, 1909, pp. 97-104. Also Scot. 
 Geogr. Mag., vol. 24, 1908, pp. 643-652. The Modeling of Physi- 
 ographic Forms in the Laboratory, ibid., vol. 8, 1910, pp. 225-228. 
 
APPENDIX D 
 
 LABORATORY MODELS FOR STUDY IN THE INTERPRETATION 
 OF GEOLOGICAL MAPS 
 
 The laboratory models which have been described on page 63, and are 
 used to represent outcrops in the study of geological maps, are shown 
 in Fig. 489. The drum-shaped blocks serve to represent massive rocks 
 
 which occur in irregularly 
 
 shaped masses such as batho- 
 lites and flows. The long, 
 narrow strips are for intru- 
 sive rocks in the form of 
 dikes, while the larger blocks 
 provided with a swivel joint 
 are used for outcrops of sedimentary rocks, and after adjustment they 
 give the dip and strike of the exposure. The wing bolts used in their 
 construction should be of bronze, because of the effect of iron upon the 
 compass. For the same reason tables should not be placed near iron 
 
 Fig. 489. — Models to represent outcrops of rock. 
 
 Fig. 
 
 490. — Special laboratory table set with a problem in geological mapping 
 which is solved in Figs. 47 and 48. 
 
 beams or columns. All these blocks can be made by an ordinary car- 
 penter, and should be available in sufficient numbers to arrange problems 
 like those of Figs. 47, 48, and 490. With a view to supplying suggestions 
 for other problems of the same general nature, the three additional field 
 maps of Fig. 491 have been introduced. 
 
 472 
 
APPENDIX D 
 
 473 
 
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 Fig. 491. — Three field maps to be used as suggestions in arranging laboratory 
 tables for problems in the preparation of areal geological maps. 
 
474 APPENDIX D 
 
 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 map. The numbers in parentheses refer to pages in 
 this book where further mformation is given : — 
 
 Stkatigraphical 
 
 1. Of the formations represented what ones are sedimentary and what 
 igneous (Chap. IV, App. B)? 
 
 2. Which formations, if any, are separated by unconformities (51-53) T 
 
 3. What is the order of age of the sedimentary formations (65) ? 
 
 4. What are the exposed thicknesses of each of these formations (48- 
 49)? 
 
 5. Do any of these values represent full thickness of the formation, 
 and if so, which ones? 
 
 6. What is the age in terms of the sedimentary formations of each of 
 the igneous rock masses (65) ? 
 
 7. Which igneous rocks, if any, occur in batholites (143, 441) ? Which, 
 if any, in dikes (140)? 
 
 Steuctural 
 
 8. What formations, if any, have monoclinal dip (42) ? 
 
 9. Indicate upon the map by dashed lines the crests of all anticlines 
 and the trough lines of synclines. 
 
 10. Indicate by arrows the direction of pitch of all plunging anticlines 
 and synclines wherever disclosed by changes of dip and strike (43) . 
 
 11. Indicate the approximate position of all faults whose position is 
 disclosed (58-61), and, if possible, state which limb is the one downthrown. 
 
 12. Prepare suitable geological sections. 
 
 Reading Reference 
 
 William H. Hobbs. Apparatus for Instruction in Geography and Struc- 
 tural Geology. III. The Interpretation of Geologic Maps. School 
 Science and Mathematics, vol. 9, 1909, pp. 644-653. 
 
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 geologist. The pilgrimages whose itiner- 
 aries are here suggested have been planned especially for impressing by 
 observation the lessons of this book. Such journeys are best interrupted 
 at a relatively small number of localities which, because already studied 
 in some detail, are specially adapted to serve as centers for local excursions. 
 These localities will in most cases be the great scenic places to which 
 tourists resort, or the seats of universities near which speciall}^ detailed 
 explorations have been often made. 
 
 Within the United States a few local geological guides have been pub- 
 lished, and the Geologic Folios published by the United States Geological 
 Survey are already available for a number of such centers. For one long 
 geological pilgrimage we are fortunate in having a carefully prepared 
 guide, namely, from New York to the Yellowstone National Park and 
 back, with a side trip to the Grand Canon of the Colorado. Except for 
 the side trip this route, in large measure, corresponds with one here chosen, 
 and for the return journey especially the student is referred to it for in- 
 formation (Geological Guide Book of the Rocky Mountain Excursion, 
 edited by Samuel Franklin Emmons. Comte Rendu de la Congres 
 Geologique Internationale, 5me Session, Washington, 1891, 1893, pp. 253- 
 487, map and plates 13, figs. 32). 
 
 Our journey is begun at New York City, which is built about the deeply 
 submerged channels of an estuary choked with glacial deposits, though 
 the channel may be followed as a deep canon across the continental shelf 
 to its margin (252, ^ pi. 17 B). New York City is also upon the margin 
 of the glaciated area, the outer terminal moraine of which is well repre- 
 sented on Long Island (298). Across the Hudson in New Jersey is the 
 great Coastal Plain which meets the oldland in a well-defined margin (159, 
 246, 247). A local geological guide of the vicinity of the metropolis has 
 been written by Gratacap (Geology of the City of New York, Greater New 
 York. Brentanos, New York, 1904, pp. 119, pis. and map). 
 
 1 Numbers in parenthesis refer to pages in this book, where further information is 
 to be found. 
 
 475 
 
476 APPENDIX E 
 
 Traveling by the New York Central Railway, we follow up the Mohawk 
 outlet of the glacial lakes Iroquois and Algonquin (334), first skirting upon 
 the east the great sills of intrusive basalt known as the Palisades, with 
 their markedly columnar jointing and intersections by numerous faults. 
 Above Peekskill we enter the picturesque narrows of the river (174), cut 
 in the hard crystalline rocks of the Highlands. Entering the Mohawk 
 Valley, we pass Syracuse with limestone caverns and well-oriented joints 
 widened by solution through the agency of the descending ground water 
 (181, pi. 6 B). A branch line to the southwest reaches the vicinity of 
 Cayuga Lake and Ithaca, where are well-oriented joints which have con- 
 trolled the drainage directions, and there is also a typical strath (55, 87, 
 428). 
 
 To Niagara Falls at least a day should be allotted for the " gorge ride " 
 by trolley car, thus making the complete circuit of the brink of the gorge 
 with interruptions and local studies at all important points (352-366, pi. 
 23 A). 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 (334) . From this city as a center a trip is made by 
 electric railway to Ypsilanti and Ann Arbor, across the bottoms of the 
 early glacial lakes from the first Maumee to Warren (330-333). The 
 strong Whittlesey beach is encountered at the little station of Ridge 
 Road, and one of the Maumee beaches on Summer Street in Ypsilanti. 
 The city of Ypsilanti is built upon a terrace (165) of the Huron River, 
 and another terrace in the same series is crossed by the electric line. In 
 an excursion of a few miles down the river, passing meanders (164-165) 
 and ox-bow lakes (165, 415), is found an interesting case of stream capture 
 near the little village of Rawson\alle (175. See Isaiah Bowman, Jour. 
 GeoL, Vol. 12, 1904, pp. 326-334). 
 
 Continuing our journey from Ypsilanti over a high moraine (312), Ann 
 Arbor is reached, built upon the level plain of outwash with fosses some- 
 times separating it from the moraine (281, 314).' Upon the campus of 
 the university are great bowlders of jasper conglomerate and jaspilite, 
 which were transported from the north by the continental glacier (305). 
 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 (168). 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 (see Ann 
 Arbor folio by the U. S. G. S., and, further, R. C. Allen and I. D. Scott, 
 An Aid to Geological Field Studies in the Vicinity of Ann Arbor, George 
 Wahr, publisher, Ann Arbor). 
 
 Returning to Detroit (M. C. Ry.), the great Sibley quarries in limestone 
 
APPENDIX E 477 
 
 near Trenton may be visited. They display perfect jointing, numerous 
 fossils, and especially well-glaciated surfaces interrupted by deep troughs 
 and showing strise of several glaciations (304). From Detroit the journey 
 is continued by steamer to Mackinac Island in the strait connecting Lakes 
 Michigan and Huron, passing on the way through the peculiar delta of 
 the St. Clair River (431), and coming in view of the notched headlands, 
 which are a monument to the post-glacial uplift of the glaciated area (250, 
 341). A day is spent at Mackinac Island and St. Ignace in order to study 
 with some care these uplifted strands of the late glacial lakes (341-344). 
 Chicago may now be reached either by steamer or by rail, and in its vicinity 
 we may see the elevated beaches and the ancient outlet of Lake Chicago 
 (331-332, 347, pi. 22 A. See Chicago Folio, U. S. G. S.). By the 
 Chicago and Northwestern Railway the area of recessional moraines and 
 intermediate outwash plains, and later that of the drumlins, are crossed in 
 journeying to Madison, Wisconsin. By examination of the maps on 
 pages 308 and 317 in connection with the larger scale atlas sheets of the 
 United States Geological Survey (Janesville, Evansville, and Madison 
 sheets), this car journey can be made most instructive in gaining familiar- 
 ity with the characteristic glacial features, and this study is continued to 
 special advantage in excursions about Madison as a center (316-317,407). 
 This is the more true since at numerous localities in the vicinity of Madi- 
 son the well- striated glacier pavement is exposed for comparison of the 
 strise as regards direction Avith the axes of the several types of glacial 
 features. 
 
 An especially instructive excursion may be made by carriage in a single 
 day to the " driftless area " some twelve miles west of the city. Before 
 reaching it we cress in alternation a series of recessional terminal moraines 
 (pi. 17 C) and outwash plains, and near Cross Plains encounter the par- 
 tially dissected upland with its arborescent drainage and even sky line (298, 
 300-301, 312-313, pi. 16 A and B). Typical shore formations (233, 241, 
 242) are studied to advantage about Lake Mendota in a walking trip to 
 and beyond Picnic Point, where are found the best ice ramparts (431-434. 
 See Buckley, Trans. Wis. Acad. Sci., Vol. 13, pp. 141-162, pis. 18). 
 
 Our journey is now continued over the Chicago and Northwestern 
 Railway to Devils Lake near Baraboo, where we cross a salient of the 
 driftless area, within which lies Devils Lake, imprisoned in a former valley 
 of the Wisconsin River, since diverted to another course as a result of the 
 glacial invasion (312-313). The valley here is a former narrows in hard 
 quartzite (466), which towers above the lake in unstable chimneys (300), 
 such as the Devils Tower, but such remnants are not found on the other 
 side of the moraine, being there replaced by rounded rock shoulders. Just 
 north of the lake the marginal moraine which blocks the valley is so 
 
478 APPENDIX E 
 
 characteristic as to merit special study (pi. 17 C) . Only a few miles north- 
 ward along the railway from Devils Lake is Ableman, where, exposed in 
 a high cliff, the hard purple quartzite with beautiful ripple marks to reveal 
 its plane of sedimentation (pi. 11 A) dips vertically, and is overlain by 
 horizontally bedded yellow sandstone. The marked angular unconformity 
 which is thus displayed is further made evident by a basal layer of con- 
 glomerate (463) in the sandstone (51-53). Here also are deposits of loess 
 along the river, which display their vertical joint surfaces (207). An 
 excellent geological guide to this interesting district and that of the neigh- 
 boring " Dalles " of the Wisconsin River has been written by Salisbury 
 and Atwood (The Geography of the Region about Devils Lake and the 
 Dalles of the Wisconsin, etc.. Bull. 5, Wis. Geol. and Nat. Hist. Surv., 1900, 
 pp. 151, pis. 38, figs. 47). 
 
 If we have taken a conveyance at Devils Lake for Ableman, we may 
 continue in the same manner to Kilbourn, where begin the picturesque 
 Dalles of the Wisconsin River — here a young gorge cut in sandstone, 
 because the Wisconsin was diverted from its old valley to border drainage 
 at the edge of the driftless area (300, 321). The side canons of the river, 
 through their abrupt zigzags, reveal the control of their courses by the joint 
 system (224). In the journey up the rapids by steamer to inspect the 
 Dalles, we observe many beautiful examples of cross bedding in the sand- 
 stone (37). 
 
 From Kilbourn we continue our journey to Minneapolis over the Chicago, 
 Milwaukee, and St. Paul Railway, and near Camp Douglas are over a pene- 
 plain, out of which rise prominent monadnocks (171). At La Crosse the 
 Mississippi River is reached, flowing beneath bluffs of sandstone which are 
 capped by loess (207). The meanderings and the numerous cut-offs of 
 the Mississippi may be observed to the left (415). Lake Pepin is a side- 
 delta lake blocked by the deposits of the Chippewa River (419). 
 
 From Minneapolis an excursion is made to Fort Snelling to view the 
 young gorge of the Mississippi, cut by the Falls of St. Anthony for a distance 
 of about eight miles in mamier similar to that of the seven miles of Niagara 
 gorge (354), and to compare this narrow gorge with the broad valley of the 
 Warren River which drained Lake Agassiz (327). Somewhat farther up 
 the Warren River are examples of saucer lakes (416). 
 
 From Minneapolis the journey may be continued by the Great Northern 
 Railway to Livingston, Montana, thus crossing between the stations of 
 Muscoda and Buffalo the bed of Lake Agassiz and its marginal beaches 
 (325-328. For local geology of Minnesota consult C. W. Hall, Geology 
 of Minnesota, Vol. 1, Minneapolis, 1903). 
 
 The Yellowstone Park is entered from Livingston (Livingston Geologi- 
 cal Folio, U. S. G. S.) and departure from it made at the relatively new 
 
APPENDIX E 479 
 
 Union Pacific terminal at the southwest margin. The regular trip 
 through the Park includes visits to the several geyser basins (191-194), 
 ObsidianCliff (33, 463), the Canon of the Yellowstone, etc. Good climbers 
 ■can make a side trip from near the Mammoth Hot Springs to the top of 
 Quadrant Mountain, the remnant of a " biscuit cut " upland (372), and 
 there study the nivation process (368, Yellowstone National Park Folio, 
 V. S. G. S.). 
 
 The trip from the Park to Salt Lake City, over the Union Pacific Rail- 
 way, passes through the Red Rock Pass, the former outlet of Lake Bonne- 
 ville (423), into the desert of the Great Basin (Chaps. XV and XVI). 
 Great Salt Lake is a saline lake or sink with an interesting record of cli- 
 matic changes (198, 401). The front of the Wasatch Range, in view and 
 easily reached from Salt Lake City, is deeply scored by the horizontal 
 shore terraces of Lake Bonneville (198, 199), and these terraces are ex- 
 tended at every reentrant by barrier beaches of great perfection. In the 
 Pleistocene period mountain glaciers in part occupied the valleys of this 
 range, though they did not always extend as far as the mountain front. 
 Big Cottonwood Canon, which realizes this condition, and the neighbor- 
 ing Little Cottonwood Canon, from whose front its glacier spread into an 
 expanded foot (264), thus show for comparison in a single view the V 
 and the low U sections respectively (172, 376). Here are also alluvial 
 fans (213) and recent faults which intersect them. 
 
 From Salt La]-:e City the return to New York may be made by the 
 Denver and Rio Grande Railway across deserts and through the Royal 
 Gorge, the canon of the Arkansas River. A full itinerary of the points 
 of geological interest along this route, and continued to Chicago, Washing- 
 ton, and New York, is supplied in much detail in the guide of the geological 
 excursion to the Rocky Mountains above cited. This the traveling geol- 
 ogist should not fail to study. Some references to points along this 
 journey will be found on preceding pages of this book (219-220, High 
 Plains; 170, Allegheny Plateau in West Virginia; 176, water gap of 
 Harper's Ferry ; 176-177, 184-186, side trip up the Shenandoah Valley 
 to Luray Caverns and Snickers Gap; 251, Chesapeake Bay). 
 
 Instead of returning directly from Salt Lake Citj^, the traveler, if he 
 has sufficient time at his disposal, may extend his journey southwestward 
 across the Great Basin to Los Angeles. A l^ranch line from this route 
 leaves the Vegas Valley and passes within reach of the famous Death 
 Valley (201) to Tonopah (79) and the Owens Valley (77-78, 92), where are 
 many surface faults dating from the earthquake of 1872 and other less 
 recent disturbances. Returning to the junction point, the route continues 
 across the Colorado and Mohave deserts to Los Angeles. From Los Angeles 
 as a center the exceptionally interesting terraces, caves, and stacks of an 
 
480 APPENDIX E 
 
 uplifted coast are to be seen to best advantage near Pt. Harford (Chap. 
 XIX). The islands of San Clemente and Santa Catalina may also be 
 reached from Los Angeles (239, 248, 249, 250, 256, 257, pis. 5 B, 7 A, 
 12 A). . The return to the East, if made by the Santa Fe Railway, per- 
 mits of a visit to the Grand Canon (174, 443) from the station of Williams. 
 From that point eastward the geology of the route is fully covered in Em- 
 mons' Guide to the Rocky Mountain Excursion already cited. 
 
 For the benefit of those who are privileged to travel in Europe, and the 
 number increases yearly, a pilgrimage is suggested which may easily be 
 made to correspond with plans laid out on the basis of historical, artistic, 
 and scenic points of interest. 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 (The Geological Tourist in Europe, Popular 
 Science Monthly, Vol. 33, 1888, pp. 216-229). The pubhshing house of 
 Gebriider Borntrager in Berlin is now publishing a quite valuable series 
 of geological guides dealing with special districts and written by well- 
 known authorities (Sammlung Geologischer Fiihrer) . Of this series some 
 thirteen numbers have already been issued. Many other valuable local 
 guides of a geological nature are the Livrets Guides of the International 
 Geological and Geographical Congresses, and the similar pamphlets sup- 
 plied in connection with annual meetings of national or provincial geo- 
 logical societies. 
 
 Passengers on steamships sailing from the harbor of New York pass out 
 over a deeply submerged canon (252) largely filled with glacial deposits, 
 through the Narrows (174), and in sight of Sandy Hook, a modified spit 
 (238, 240). To the left are seen the great morainic accumulations at the 
 border of the glaciated area on Long Island (298). In the course of the 
 trans- Atlantic voyage a much- rounded iceberg may be encountered (291), 
 though this is much more apt to occur upon the northern routes from 
 Quebec, and late in the season. Upon entering the English Channel the 
 land on both coasts rises in steep cliffs, where are found all the conmion shore 
 features well developed (Chap. XVIII). The German steamships pass 
 in sight of Heligoland, that last remnant of wave erosion (236). 
 
 While traveling in Europe, the student should consult a map of the 
 glaciated area (299), and so learn to recognize its peculiarities, and care- 
 fully mark its marginal moraine (311) and other strongly marked features. 
 
 If the British Isles are visited and the more rugged areas are selected, 
 one may study the cirques and other characteristic features due to the 
 presence of mountain glaciers about Snowdon (Chap. XXVI). More 
 mature stages of the same processes are to be found in the Scottish High- 
 
APPENDIX E 
 
 481 
 
 lands and the Inner Hebrides, but especially upon the Island of Skye (Fig. 
 492). A very valuable aid to excursions in this district is Baddeley's 
 Scotland (part I, Dulau, London) and Sir Archibald Geikie's Explana- 
 
 ■Strnthearron. 
 
 Fig. 492. — Sketch map of Western Scotland and the Inner Hebrides to show 
 location of some points of special geological interest. 
 
 tory Notes to accompany Bartholomew's Geological Map of Scotland 
 (map and notes in cover, Edinburgh, 1892, pp. 23). 
 
 It is from Oban, the " Charing Cross of the Highlands," that one should 
 start out upon the summer steamers in order to reach both Skye and 
 Staffa, the latter with fine basaltic columns (463), and Fingal's Cave. In 
 sailing to Skj^e one passes upon either shore of the narrow fjords many 
 relics left in the dissection of volcanoes (139-143 and Sir A. Geikie, Ancient 
 Volcanoes of Great Britain, Vol. II) ; also rocky islands and skerries 
 marking submergence (252), and the coast terraces which register a later 
 uplift (250). Skye is a complex of many intrusive and volcanic rocks of 
 
 2i 
 
482 APPENDIX E 
 
 such markedly different colors as to appear as tints in the landscape. In 
 the Cuchillin Hills of dark green rises the massive gabbro (462) cut by 
 cirques into the jagged pinnacles of horns and comb ridges (373) ; while 
 lower down and to the east are rounded domes of rhyolite (463) abraded 
 beneath the glaciers and of a delicate salmon tint. Still lower and to the 
 westward are flat mesas composed of horizontal layers of black basalt 
 under a rich carpeting of the brightest verdure. Eastward across the 
 channel are seen the purplish walls of an ancient sandstone. The jagged 
 gabbro core of the island thus represents a fretted upland (372) and is 
 now the training ground of the Alpinist (Abraham, Rock Climbing in 
 Skye, Longmans, London, 1908), while nestled in one of the bottoms of a 
 U -valley is Loch Coruisk, atypical rock-basin lake (412), its shores of hard 
 rock planed and scored. 
 
 From Skye we may go to study the remarkable thrusts (45) on the north 
 shore of Loch Maree, a marked lineament, and one directed at right angles 
 to that on the course of the Caledonian Canal connecting Loch Linne with 
 Loch Ness. Tliis northeast wall of Loch IMaree is a strikingly rectilinear 
 fault represented by an escarpment, up which we climb to find at the top 
 the crushed and fluted thrust planes of movement dipping southeastward 
 at a flat angle. Here also are beautiful rock-basin lakes, lying in hollows 
 molded beneath the continental glacier. On our way from Skye we have 
 passed up Loch Carron, a sea loch or fjord (252), and along the strath at its 
 head known as Strathcarron (428). 
 
 Returning now to Oban, it is but a short trip by steamer up Loch Linne 
 to Fort William along the striking lineament (226) which continues to 
 Loch Ness and beyond (Fig. 492), and thence by rail to Glen Roy and the 
 neighboring glens of Lochaber (322-325). 
 
 From Paris as a starting point, we may visit in a most picturesque region 
 the beautifully preserved craters of extinct volcanoes in the Auvergne of 
 Central France (105, 124, 145), which district is entered from Clermont- 
 Ferrand. Here are found the characteristic puys, steep lava domes of 
 viscous lava (105), which figured largely in the early controversies of geol- 
 ogists concerning the origin of rocks. 
 
 The rest of our pilgrimage will be so planned as to enter the noble river 
 Rhine at its mouth (Fig. 493), ascend its course to its birthplace in the 
 snows of Switzerland, and after further exploration of the features of this 
 fretted upland, traverse northern and central Italy so as to make our 
 departure for America by the southern route. Entering then upon this 
 course in the Low Countries, we have first the opportunity of observ- 
 ing the characteristics of a great delta with natural levees artificially 
 strengthened as dikes (165-168). Here also are found dunes of beach 
 material which has been raised bj' the wind into a great rampart near the 
 
APPENDIX E 
 
 483 
 
 shore (209-211). Such a wall of dune sand is well displayed at the bathing 
 resort at Scheveningen near the Hague (421). The flood plain of the 
 Khine (162-165) may be studied in a journey up the river to the uni- 
 
 JTansf 
 
 Fig. 493. — Outline map of a geological pilgrimage across the continent of Europe. 
 
 versity town of Bonn, from whence a day's excursion should be devoted 
 to the relics of volcanoes known as the Seven Mountains (H. von Dechen, 
 Geognostischer Fiihrer in das Siebengebirge, Bonn, 1861). As a prepara- 
 tion for this trip and others in the volcanic Eifel higher up the river, a visit 
 
484 APPENDIX E 
 
 should be made to the mineral and rock collections of the Poppelsdorfer 
 Schloss at the University. In the volcanic Eifel are found some of the 
 most interesting of crater lakes (405), the largest being Lake Laach with 
 its somewhat peculiar volcanic ejectamenta and its picturesque abbey (see 
 von Dechen, Geognostischer Fiihrer zu der Vulkanreihe der Vorder-Eifel, 
 etc., Bonn, 1886. Consult also Lane, A Geological Tourist in Europe, I.e.). 
 
 Continuing our course up the river from Bonn, we soon enter the gorge 
 of the Rhine cut in an uplifted peneplain (169, 171, 174). From Coblenz, 
 where the Moselle enters the Rhine, a side trip may be made up this trib- 
 utary river past Zell with its entrenched meanders (173) to the ancient 
 Roman city of Treves. 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 (403), lying between the forest of Odin 
 and the Black Forest on the east and the " Blue Alsatian Mountains " 
 far away to the west. At the margins of this plain are beds of loess with 
 their characteristic joint structures and inclusions (207), and in the higher 
 hills on either hand a wealth of intrusive igneous rocks. 
 
 At the entrance of the Neckar River to this broad plain is nestled the 
 picturesque castle and university town of Heidelberg, a convenient center 
 for excursions (Julius Ruska, Geologische Streifziige in Heidelbergs 
 Umgebung, etc., Nagele, Leipzig, 1908, pp. 208, map). At Strassburg 
 (Schwarzwaldstrasse 12) is located the German Chief Station for Earth- 
 quake Study, with a particularly large set of modern seismographs. In 
 the university cabinet is also one of the largest and most representative 
 mineral collections in Europe. For excursions in the neighborhood con- 
 sult Benecke, Sammlung Geognostische Fiihrer, Vol. 5, Elsass, 1900. 
 
 From Strassburg we may go by the Black Forest Raihvay to the Hegau 
 with its volcanic plugs (140), each surmounted by a picturesque castle. 
 We enter next the broadly extended piedmont apron site, above which 
 Lake Constance still remains as a border lake (399). Outwash aprons 
 (314), moraines (311), and drumlins (317) are each in turn encountered. 
 Still continuing our course up the Rhine from Bregenz, we enter the fretted 
 upland (372) of the Alps, mountains composed of great folds and thrusts 
 about a core of intrusive rock (Rothpletz, Sammlung Geologische Fiihrer, 
 Vol. 10, 1902, Thrusts in the Alps between Lake Constance and the 
 Engadine). Some fourteen miles above Chur we pass the terrace pro- 
 duced by successive landslides (414), known far and wide as the Flimser 
 Bergstiirz. The further assent of the cascade stairway of this glacier- 
 carved valley brings us to the Furka Pass, from which point magnificent 
 views of the fretted upland are obtained. At the Kanzli, a mile from 
 the hotel, one may view the n6v6 of the Rhone Glacier, which may also 
 be easily visited. 
 
APPENDIX E 485 
 
 We have now followed a great river from its mouth in the sands of 
 Holland to its source in the snows of the higher Alps. Passing over the 
 divide and descending to Gletsch, we may observe the lower end, or foot, 
 of the Rhone glacier and the crevasses and s^racs (391) on the steep descent 
 of this radiating glacier (383, 386). The response which glaciers make to 
 climatic changes is here well illustrated by the recession of the glacier 
 front from near the hotel (its position in the '50s of the nineteenth century) 
 to its present position about a mile farther up the valley. 
 
 The characteristics of a glaciated mountain valley may be further 
 illustrated by climbing to the Grimsel Pass, which is scratched and striated 
 (377, 385), and then descending the valley of the Aar to Meyringen (377). 
 Near the Grimsel Hospice are the characteristic rock basin lakes (412), 
 and upon the Aar Glacier to our left were carried out the epoch-making 
 researches of Louis Agassiz, the founder of the glacial theory for explain- 
 ing the drift. We encounter some thirteen rock bars (377). Just before 
 reaching Meyringen we pass the last of these, the Gorge of the Aar, cut 
 by the stream through limestone. 
 
 Interlaken (419) may be made the center for additional excursions up 
 the Lauterbrunnen Valley, with its prominent albs (376) and its ribbon 
 fall of the Staubbach (378). By the Jungfrau Mountain railway we may 
 now ascend partly in tunnels of the rock to the Ewigeismeer, and look 
 down upon the neve and bergschrunds of the Great Aletsch Glacier (370, 
 see Baltzer, Sammlung Geologische Fiihrer, Vol. 10, Bernese Oberland, 
 1906). Returning to Interlaken by way of Grindelwald, one may study 
 the foot of a radiating glacier, the Untergrindelwald glacier, with its tunnel 
 and its milky and braided stream. 
 
 Crossing now the Alpine foreland to Villeneuve at the upper end of Lake 
 Geneva and upon a well-developed strath (426, 428), we may look out 
 upon the turbid waters extending far from the shore of the lake. Journey- 
 ing to Geneva by steamer we note the gradual clearing of the water until 
 at the outlet of the lake it is as clear as crystal. A walking trip from 
 Geneva takes us to the Bois de la Batie, where the Arve with turbid waters 
 meets this clear stream (427). 
 
 The railroad to Chamonix ascends another cascade stairway (376), 
 affords views of complexly folded sedimentary rocks (43), and at Chamonix 
 itself the mer de glace supplies opportunities for the study of moraines 
 (386, 393) and glacial movement (390-392). To experienced Alpinists 
 the summit of Mount Blanc offers a remarkably extended outlook over the 
 fretted upland of the Alps (pi. 18 A). From the station of LeFayet below 
 Chamonix, one may ascend to the Desert de la Plate, where are Schratten 
 in limestone due to solution (188). 
 
 Crossing by one of the passes to the valley of the Rhone at Martigny 
 
486 APPENDIX E 
 
 we may reach Zermatt, to-day the climbing center of the Alps. From the 
 subordinate cirques surrounding this village descend the Gomer, Findelen, 
 St. Theodul, and other components of this radiating glacier. A black 
 tooth of rock, the Matterhorn, towers above the other peaks and shows to 
 greatest advantage this feature of glacial sculpture (374), while the Gorge 
 of the Gorner is a severed rock bar like that of the Aar (377). Either on 
 foot or over the mountain railway we may ascend to the Gorner Grat, 
 a subordinate comb ridge (373) which affords one of the most magnificent 
 and instructive views of radiating glaciers. 
 
 From Brig, farther up the Rhone Valley, an excursion is made to the 
 Eggishorn Hotel, a center for studj^ on and about the Great Aletsch 
 Glacier (329, 371, 385, 388, 395, 410). The easy ascent of the Eggishorn 
 is rewarded by a view almost directly downward upon the ice-dammed 
 M^rjelen Lake (329, 411). 
 
 From Brig one may make his entry into Italy, either over the pictur- 
 esque Simplon route afoot or by diligence, or else beneath it through the 
 railway tunnel. 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 Maggiore, Lugano, and Como, and later southward to INIilan. 
 In leaving the village of Como we pass over hea^'y morainic deposits on 
 the apron borders of the expanded-foot glacier (383, 385) which once 
 occupied the valley above. On the journey from iVIilan to Venice, over 
 the fertile plains of Lombardy, the similar accmnulations about Lake 
 Garda (414) are first encountered at the little station of Lonato and left 
 behind at Somma Campagna (Tornquist, Sammlung Geologische Fiihrer, 
 Vol. 9, Northern Italy, 1902). 
 
 The city of Venice is built upon pile foundations in the lagoon behind 
 the barrier beach known as the Lido (242, 428-429) . From here we may 
 reach the Karst country by way of Trieste, some of the more interesting 
 and typical features being found near Divaca (187-189, 422, pi. 6 A). In 
 a different direction from Venice by weby of Bellu'no we enter the Dolo- 
 mites with their patterned relief and battlemented towers (228, 445). 
 
 Additional centers for geological excursions on the route to our point of 
 departure from Italy are Rome and Naples. At the Italian capitol and 
 in its neighborhood we may study the volcanic Campagna with its beds 
 of tuff (105) and its crater lakes (405. See Sir A. Geikie, The Roman Cam- 
 pagna, Landscape in History and other Essays, Macmillan, 1905, pp. 308- 
 352 ; also Deecke, Sammlung Geologische Fiihrer, Vol. 8, Campagna, 1901) . 
 From Rome it is an easy journey to the cataract of Tivoli with its deposits 
 of travertine (184). In the opposite direction from Rome across the 
 Campagna rise the Alban Hills, ruins of a composite cone with several 
 crater lakes on the sites of former vents. On the summit of the encircling 
 
APPENDIX E 487 
 
 crater rim, like the Monte Somma of the Vesuvian Mountain now a cres- 
 cent only, is located the chief Italian station for earthquake study. 
 
 From Naples we may reach in. short excursions and study with some care 
 still active volcanic mountains. To the east is Mount Vesuvius (94, 97, 
 122,124, 127-137), which was in grand eruption in April, 1906. Westward 
 from Naples are the Campi Phlegraeii, or burning fields, with many craters. 
 Of these Astroni offers a fine example of a large-cratered cinder cone (105). 
 In the same vicinity are Monte Nuovo (96) and the Solfatara (97), the 
 latter a type of volcano which no longer erupts lava, but in its place emits 
 carbon dioxide and other gaseous emanations (Grotto del Cane). The 
 starting point for excursions in the Phlegrsean fields is Pozzuoli with its 
 Temple of Jupiter Serapis (254-255), reached from Naples by an electric 
 line which pierces the wall of an immense crater (Posilippo) composed of 
 fine j^ellow volcanic ash known as Pozzuolan. 
 
 From Naples steamers make short excursions to Sorrento with its deep 
 ash deposits, and to Capri with its blue grotto (257-258), Herculaneum 
 (139) and Pompeii (122), buried during the eruption of 79 a.d., are on the 
 line of the Circum- Vesuvian Railway. 
 
 Steamships to New York from Naples call at Gibraltar, the land-tied 
 island par excellence (241). Most steamships of the southern route pasa 
 through or near the volcanic islands of the Azores, and certain boats touch 
 at Algiers, from which a line of railway gives access to Biskra on the 
 borders of the Desert of Sahara. 
 
 Tliroughout these pilgrimages the traveler should be on the alert to 
 note not only the agent responsible for the features which come under his 
 observation, but, especially where this is the cormnon sculpturing agent 
 of running water, he should not fail to notice the stage of the erosion 
 cycle which is represented (Chapter XIII). 
 
INDEX 
 
 Abrasion, beneath glaciers, 275. 
 Abyssinia, fissure eruptions in, 101. 
 Accordance, of tributary valleys, 162. 
 Adiabatic refrigeration, in relation to 
 
 glaciers, 262. 
 Adolescence, in cycle of erosion, 169. 
 Advancing hemicycle of glaciation, 263- 
 
 266. 
 Advective zone, of atmosphere, 270. 
 Aftershocks, of earthquakes, 83. 
 Agassiz, glacial lake, 325-328. 
 Agassiz, Louis, cited, 339, 400. 
 Age, of strata, 38, 52. 
 Aggradation, 162. 
 Aktian deposits, 36. 
 Alaskan coast, map of, 79. 
 Albs, 376. 
 
 Alden, W. C, cited, 316, 318, 319. 
 Algse, growth of, in hot springs, 194. 
 "Alkali" in deserts, 201. 
 Alluvial bench, 214. 
 Alluvial cone, 213. 
 Alluvial-dam lakes, 423. 
 Alluvial fan, 213. 
 Alpine glaciers, 383, 386. 
 Alterations of minerals, 27. 
 Altitude, of different parts of lithosphere, 
 
 18. 
 American Falls, future extinction of, 357. 
 Amphiboles, 459. 
 Amphitheaters, formed on drift sites, 
 
 369. 
 Amundsen, R., cited, 23. 
 Analysis, of folds, 54. 
 Anderson, Tempest, cited, 146, 147. 
 Andersson, J. G., cited, 157, 295. 
 Andesite, 463. 
 Angular unconformity, 53. 
 Antarctica, 154, 281. 
 Antarctic protuberance, 17. 
 Antarctic shelf ice, 289, 290. 
 Anticlinal folds, 42. 
 Anticlines, 42 ; tension in, 45. 
 Anticyclone, glacial, 284. 
 Ants, factor in rock decomposition, 156. 
 Apron, alluvial, 213. 
 Aprons, outwash, 280, 281. 
 Arbenz, P., cited, 195. 
 Arches, of folded strata, 42 ; sea, 233, 
 
 234. 
 
 Architecture, of fractured earth super- 
 structure, 55. 
 
 Arctic depression, 17. 
 
 Areal geological map, 62. 
 
 Aretes, 373. 
 
 Arldt, Theodore, cited, 11, 19, 438. 
 
 Arnold, Ralph, cited, 157. 
 
 Arrangement of oceans and continents, 
 10. 
 
 Artesian wells, 190, 191, 196. 
 
 Ash, volcanic, 122. 
 
 Askja, eruption of, in 1875, 101. 
 
 Assmann, R., cited, 294. 
 
 Astronomical vs. geodetic observations, 
 12. 
 
 Atlantis, North, 16. 
 
 Atmosphere, compressibility of, 8. 
 
 Attack, of the weather, 149. 
 
 Atwood, W. W., cited, 7, 160, 298, 300, 
 313, 372. 
 
 Axial plane, of folds, 42. 
 
 Axis, of folds, 42. 
 
 Azurite, 453. 
 
 Bacteria, part taken in weathering, 156. 
 
 "Bad Lands," control of relief in, 223, 
 224. 
 
 "Bad Land" topography, 214. 
 
 Bajir, 216. 
 
 Balance, between degradation and aggra- 
 dation, 161. 
 
 Bandai-san, dissection of, 141. 
 
 Barchans, 211. 
 
 Barrancoes, 139. 
 
 Barren, J., cited, 221, 447. 
 
 Barrier beaches, 240 ; sections of, 242 ; 
 uplifted, 249, 250. 
 
 Barrier lakes, 420. 
 
 Barriers, 240 ; mountain, in relation to 
 glaciers, 262. 
 
 Bars, 240. 
 
 Basal conglomei *-e, 37, 53. 
 
 Basalt, 463 ; faulted blocks of, 58 ; 
 of Hawaii, 105. 
 
 Base level, 159. 
 
 Basin-range lakes, 402, 403. 
 
 Basin Range structure, 440. 
 
 Basins, flat bottomed, separating dunes, 
 216 ; of exudation, 272 ; of sedimen- 
 tation, earlier, 38. 
 
 489 
 
490 
 
 INDEX 
 
 Bastin, E. S., cited, 210. 
 
 Batholites, 143. 
 
 "Bath tubs," 395. 
 
 Beach pebbles, 239. 
 
 Beach sand, 206, 238. 
 
 Beaches, remaining from ice-dam lakes, 
 
 410; shingle, 239; storm, 240; 
 
 uplifted, "feathering out" of, 344. 
 Bedded structure of rocks, 31. 
 Beede, J. W., cited, 195. 
 "Bee-hive" mountains, 380, 381. 
 Belgica expedition, 289. 
 Belt of sea which divides land masses, 
 
 11. 
 Berghaus, H., cited, 424. 
 Bergschrund, 370. 
 Berson, A., cited, 294. 
 Berthaut, General, cited, 7. 
 "Bird-foot" delta, 167. 
 "Biscuit cutting" effect of glacial sculp- 
 ture, 372. 
 Blackwelder, E., cited, 318. 
 Block mountains, 446. 
 Blocks, orographic, 58. 
 Bocchi, 125. 
 Bog, floating, 429. 
 Bogs, of peat, 429, 430. 
 Bonney, T. G., cited, 146. 
 Borax deposits, in deserts, 201. 
 Border drainage, about glaciers, 316, 
 
 320, 321. 
 Border lakes, 399, 414. 
 Bosses, 143. 
 "Bottoms," from entrenched meanders, 
 
 173. , 
 "Bowlder clay," 310. 
 "Bowlder pavement," 237. 
 Bowlders, faceted, 310; glacial, 298; 
 
 "soled," 276, 310; thrown up during 
 
 earthquakes, 69. 
 Bowlder trains, 306. 
 Bowman, Isaiah, cited, 179. 
 Box caiions, 214. 
 Braided streams, 280. 
 Branner, J. C., cited, 6, 91. 
 "Bread-crust" lava projectiles, 119. 
 Breakers, 232. 
 Breccia, fault, 60. 
 Bridges, nature of damage to, during 
 
 earthquakes, 75, 76. 
 Brigham, A. P., cited, 424. 
 Brogger, W. C., cited, 66. 
 Bruce, W. S., cited, 290, 382, 399, 414. 
 Bryant, H. G., cited, 289. 
 Buckley, E. R., cited, 433, 434. 
 Built terraces, 235. 
 Bunsen, cited, 192. 
 Burns, G. P., cited, 434. 
 
 Burton, W. K., cited, 92. 
 Buttes, 216. 
 Bysmalite, 442, 447. 
 
 Calcareous ooze, 36. 
 
 Calcareous sinter, 184. 
 
 Calcareous tufa, 464. 
 
 Calcite, 455. 
 
 Caldera, 405, of composite volcanic 
 
 cones, 126. 
 Camiguin volcano, birth of, 96, 97. 
 Campbell, M. R., cited, 178. 
 Caiions, 160; box, 214. 
 Capri, blue grotto of, 257, 258. 
 Capture, river, 175, 176, 179. 
 Carbonization, 151. 
 Cascade Movmtains, fissure eruptions of, 
 
 102. 
 Cascade stairway, 376. 
 Caspian Depression, 14. 
 Cauliflower cloud, 130. 
 Caverns, galleries directed by joints, 
 182 ;, of limestone, 182, 195 ; refuge of 
 predatory animals, 185. 
 Caves, sea, 234. 
 
 Cellular structure, of lava domes, 112. 
 Centers of dispersion, of North American 
 
 Pleistocene glaciers, 298. 
 Centrosphere, 8. 
 Cerussite, 455. 
 Chaix, A., cited, 195. 
 Chaix, E., cited, 195. 
 Chalcopyrite, 453. 
 
 Challenger expedition, 38, 96, 97, 293. 
 Chamberlin, T. C, cited, 29, 156, 191, 
 196, 205, 221, 222, 293, 295, 318, 319, 
 337, 339. 
 Character profiles, coast, due to uplift 
 or depression, 259 ; composite, 229 ; 
 directly due to volcanic agencies, 145. 
 146 ; from stream erosion in humid 
 climates, 177; of arid lands, 220; of 
 shore features, 243 ; referable to 
 continental glaciers, 318; referable t» 
 mountain glaciers, 379. 
 " Checkerboard topography," 226. 
 Chemical sediments, 34. 
 Chicago outlet, 331. 
 Chimneys, in "driftless area," 300. 
 Chimneys, shore feature, 234. 
 China, loess of, 207. 
 Chlorite, 458. 
 Chlorite schist, 465. 
 Cicatrice, from dissection of volcanoes, 
 
 142. 
 Cinder cones, 105; corrugations upon, 
 138 ; diameter of crater in relation ta 
 violence of explosions, 123; grander 
 
INDEX 
 
 491 
 
 eruptions of, 117; pi'ofiles of, 123; 
 secondary. 111. 
 
 Cinder eruptions, artificially simulated, 
 122. 
 
 Cirques, 371 ; life history of, 371; subor- 
 dinate, 371. 
 
 Cities, destruction of, by drifting sand, 
 218. 
 
 Clastic rocks, 30. 
 
 Clay slate, 466. 
 
 Cleavage, mineral, 27, 450; rock, 44. 
 
 Clefts, volcanic, in Iceland, 99. 
 
 Cliffs, notched, 233. 
 
 Climatic conditions, in relation to moun- 
 tain sculpture, 443. 
 
 Clinometer, 48. 
 
 Cloudbursts, in deserts, 201, 212. 
 
 Cloud zones, 268, 269, 294. 
 
 Coals, 466. 
 
 Coast, Dalmatian, grottoes of, 258. 
 
 Coast, elevation of, during earthquakes, 
 80 ; submergences of, during earth- 
 quakes, 80. 
 
 Coastal plains, 246; belted, 247. 
 
 Coast lines, even, 246 ; indicative of up- 
 lift or submergence, 245, 246 ; ragged, 
 246. 
 
 Coast records, 245. 
 
 Coasts, Atlantic and Pacific contrasted, 
 438; embayed, 251. 
 
 Coast terraces, 80, 250, 241; uplift, 
 effect of, on sediments, 38. 
 
 Coats Land, shelf ice of, 290. 
 
 Cobalt, in meteorites, 23. 
 
 Cobb, Collier, cited, 179. 
 
 Coigns, of earth's tetrahedral figure, 15. 
 
 Coleman, A. P., cited, 318. 
 
 Colk lakes, 408, 409. 
 
 Colks, scape, 277. 
 
 Collet, L. W., cited, 39. 
 
 Colorado desert, 74. 
 
 Color, of minerals, 450. 
 
 Cols, 374 ; origin of in cirque intersection, 
 372. 
 
 Comb ridges, 373. 
 
 Compass, geologist's, 47, 48. 
 
 Competent layer, 42; in relation to lava, 
 reservoirs, 144. 
 
 Composite cones, caldera of, 126, 127. 
 
 Composite groups of joints, 57. 
 
 Composite volcanic cones, 105. 
 
 Composition of earth, 29. 
 
 Composition of the earth's core, 21. 
 
 Compression of a district during earth- 
 quakes, 76. 
 
 Cones, alluvial, 213; cinder, 105; conr-- 
 posite volcanic, 105. 
 
 Conformable series, 51. 
 
 Conglomerate, 34, 463 ; basal, 37; 53. 
 
 Constructional topography, 309. 
 
 Construction of buildings, in earth- 
 quake regions, 89-91. 
 
 Continental glacier, behind rampart, 281; 
 in Victoria Land, 280-285; of An- 
 tarctica, literature of, 295 ; of Green- 
 land, 271 ; of Greenland, melting on 
 margin of, 278 ; of Greenland, litera- 
 ture, 295. 
 
 Continental glaciers, contrasted with 
 mountain glaciers, 266-268 ; defined, 
 266-267; of "ice age," 297; of ice 
 age, cross section of, 302 ; nourish- 
 ment of, 283, 286, 295 ; profiles of, 267. 
 
 Continental platform, 19. 
 
 Continental shelves, 18, 19; origin, 232. 
 
 Continents, arrangement of, 10 ; devel- 
 opment of, 14 ; increase in area of, 
 through wave action, 241 ; past 
 history of, 14. 
 
 Contortions of the strata, 40. 
 
 Contours, of topographic maps, 62. 
 
 Contraction of earth's surface, during 
 earthquakes, 74. 
 
 Contrary movements upon coasts, 254, 
 257. 
 
 Convective zone, of atmosphere, 270. 
 
 Conway, W. M., cited, 294. 
 
 Copernicus, cited, 10. 
 
 Copper glance, 455. 
 
 Coquina, 35. 
 
 Cornish, Vaughan, cited, 211, 222, 244. 
 
 Corrasion, 162. 
 
 Corrosion, of rocks, 156. 
 
 Coulee lakes, 406. 
 
 Coves, 233, 234. 
 
 Cracks, earthquake, 74. 
 
 Crater, evolution of form of, 128. 
 
 Crater lakes, 405, 406. 
 
 Craterlets, 84; sections of, 85. 
 
 Craters, mechanics of explosions in, 
 115. 
 
 Crater, volcanic, 95. 
 
 Credner, G. R., cited, 179. 
 
 Crescentic levee lakes, 416, 417. 
 
 Crestline, of an anticline, 42. 
 
 Crevasse, marginal, on mountain glaciers, 
 370. 
 
 Crevasses, in connection with river 
 cut-offs, 164; on glaciers, 391. 
 
 Cross, Whitman, cited, 216, 441, 447. 
 
 Cross-bedded structure, 37. 
 
 "Crystal cellars," 27. 
 
 Crystal form, of minerals, 449. 
 
 Crystals, behavior under special treat- 
 ment, 24, 25 ; essential nature of, 23 ; 
 forms of, 454, 457 ; individuality of. 
 
492 
 
 INDEX 
 
 24 ; mutilated, later growth of, 26 ; 
 
 symmetry of form of, 23. 
 Crustal shortening, 42. 
 Cuestas, 246, 247 ; south of Lake 
 
 Ontario, 361, 362. 
 Cut and built terrace, on steep shore of 
 
 loose materials, 237. 
 Cut-offs, of meanders, 164. 
 Cut rock terraces, 235. 
 Cuvier, cited, 199. 
 Cvijic, J., cited, 195. 
 Cycle of glaciation, 263, 294. 
 Cycles, of glaciation. Pleistocene, 297 ; 
 
 of stream meanders, 163. 
 
 Dana, J. D., cited, 6, 104, 106, 109, 111, 
 
 146, 147. 
 Dana, E. S., cited, 29. 
 Daly, R. A., cited, 447. 
 Dante, cited, 9. 
 Darton, N. H., cited, 179. 
 Darwin, Charles, cited, 199, 322, 323, 
 
 339. 
 Daubree, A., cited, 54. 
 David, T. W. E., cited, 23. 
 Davis, C. A.,' cited, 434. 
 Davis, W. M., cited, 7, 178, 179, 221, 
 
 247, 276, 317-319, 378, 382. 
 Deceptive unconformity, 53. 
 Decomposition, 149, 156 ; mechanical 
 
 results of, 150. 
 Debris cones, 395. 
 Deep sea deposits, 36, 38. 
 Deflation, 204. 
 Deforestation, in relation to agriculture, 
 
 156 ; of Karst region, 188 ; relation to 
 
 erosion, 157. 
 Degeneration, 149. 
 De Geer, G., cited, 351, 366, 410. 
 Degradation, 161, 162. 
 Dekkan, fissure eruptions of, 101. 
 Delebecque, A., cited, 424. 
 De Lorenzo, cited, 125, 132. 
 Delta, "Bird-foot," 167; bottom-set 
 
 beds, 167 ; dry, 213 ; of Mississippi 
 
 River, rate of growth of, 168. 
 Delta deposits, manner of growth of, 167. 
 Delta lakes, 419, 420. 
 Delta region, of a river, 35. 
 Deltas, abnormal, below outlets of lakes, 
 
 431 ; in relation to agriculture, 166 ; 
 
 in relation to population, 166; lake, 
 
 428 ; of rivers, 165, 166, 179 ; sections 
 
 of, 168. 
 Dendritic glaciers, 383, 385, 386. 
 Deniston, cited, 121. 
 Deposition, in zones about desert, 216, 
 
 217. 
 
 Deposits, aktian, 36 ; chemical, 34 ; 
 continental, 37 ; deep sea, 36, 38 ; 
 delta, manner of growth of, 167 ; 
 fluviatile, 35; fluvio-glacial, 31, 310; 
 in valley vacated by glacier, 398; 
 glacial, 31 ; lacustrine, 35, 217 ; 
 littoral, 36 ; marine, 35 ; mechanical, 
 34 ; organic, 34 ; salt, 217 ; shoal 
 water, 26 ; sinter, 184 ; terrigenous, 
 36. 
 
 Derangement of water flow, during 
 earthquakes, 83, 84. 
 
 Derwies, V. de, cited, 447. 
 
 Descent of ground water, 180. 
 
 Desert, due to deforestation, 156; ero- 
 sion in, 214, 222; law of, 197. 
 
 Desert lakes, 423. 
 
 Desert landscapes, features in, 209. 
 
 Desert rains, 212. 
 
 Desert rocks, red color of, 222. 
 
 Desert varnish, 201, 222. 
 
 Deserts, former shore lines in, 198; 
 self-registering gauge of past climates, 
 198. 
 
 Destructional topography, 309. 
 
 Detection of plunging folds, 49, 50. 
 
 Detonations, during Vulcanian erup- 
 tions, 131. 
 
 Device, to simulate building of cinder 
 cones, 122. 
 
 Diabase, 462. 
 
 Diagram, to illustrate formation of lava 
 reservoirs, 143. 
 
 Diagrams for comparison of fold types, 
 42 ; to show the effect of spheroidal 
 weathering, 150. 
 
 Diamonds, in the drift, 307. 
 
 Diffission, 204. 
 
 Dikes, hollow, 140; in China, 167; in 
 Holland, 166 ; from volcanic dissec- 
 tion, 140. 
 
 Diller, J. S., cited, 39, 425. 
 
 "Diluvium," 305. 
 
 Dimples, on margin of continental 
 glaciers, 272. 
 
 Dip, 46. 
 
 Dirt cones, 396. 
 
 Disintegration, 156 ; of rocks in deserts, 
 202 ; through root expansion, 154 ; 
 through tree growth, 154, 155. 
 
 Dislocations, marginal, about deserts, 
 212. 
 
 Dispersion of the drift, 304-309, 319. 
 
 Displacement, total, on faults, 59. 
 
 Dissection of volcanoes, 139. 
 
 Distributaries, on allu\'ial fans, 213, 220. 
 
 Divides, 170 ; migration of, 175. 
 
 Dolines, of Karst region, 187, 422. 
 
INDEX 
 
 49S 
 
 Dolomite, 465. 
 
 Dolomites, 203, 228, 445. 
 
 Domed mountains of uplift, 441. 
 
 Dome structure, of granite masses, 152, 
 157. 
 
 Domes, lava, 105. 
 
 Dovetailing, of sea and land, 11, 17. 
 
 Drainage, changes of, due to glaciation, 
 336-338 ; haphazard, of glaciated 
 area, 301 ; interference of glaciers 
 with, 320 ; of glaciers, 397 ; reversals 
 of, due to glaciation, 337, 338 ; trellis, 
 175. 
 
 Drainage lines, control of, by fractures, 
 224. 
 
 Drainage networks, controlled by frac- 
 tures, 225, 226 ; repeating pattern in, 
 225. 
 
 Drake, Sir Francis, circumna\'igation of 
 the globe, 10. 
 
 Dreikanten, 205. 
 
 Driblet cones, 104, 125 ; of Kilauea, 107. 
 
 "Drift," 305. 
 
 Drift, assorted, 309 ; dispersion of, 304- 
 309 ; englacial, 277, 278 ; unassorted, 
 309. 
 
 "Driftless area," 300, 313, 318. 
 
 Driftless area, map of, 298. 
 
 Drift sites, 368, 369. 
 
 Drowned rivers, 251. 
 
 Drumlins, 311, 316, 317, 399. 
 
 Drv deltas, 213. 
 
 Drygalski, E. von, cited, 273, 279, 295, 
 296. 
 
 Dry weathering, in deserts, 201. 
 
 Dune, war with oasis, 216. 
 
 Dune lakes, 421. 
 
 Dunes, 222 ; forms of, 210, 211 ; in rela- 
 tion to obstructions, 209, 210 ; stopped 
 by vegetation, 211 ; wandering, 209, 
 211. 
 
 Dust, carried out of desert, 206, 222; 
 volcanic, 122. 
 
 Dust wells, 395. 
 
 Dutton, C. E., cited, 85, 92, 178, 200, 
 222, 447. 
 
 Earlier figures of the earth, 14. 
 
 Earth, a magnet, 23 ; composition of, 
 20 ; oblateness of, 10 ; rigidity of, 
 20, 21, 29; scale of its elevations, 10, 
 11; theories of origin of, 20, 29; 
 surface shell, chemical constitution of, 
 23 ; surface shell, response to load, 340. 
 
 Earth features, shaped by running water, 
 169. 
 
 Earth figure, evolution of ideas concern- 
 ing, 9. 
 
 Earthquake cracks, 74. 
 
 Earthquake fountains, 190. 
 
 Earthquake lakes, 404. 
 
 Earthquake, of Alaska, 1899, 72, 77, 79, 
 80, 81 ; of Assam, 1897, 72, 77 ; of 
 California, 1906, 70, 72, 73, 74, 90, 91 ; 
 of Casamicciola, 1883, 87 ; of Costa 
 Rica, 1910, 68; of India, 1819, 84; 
 of Jamaica, 1692, 80 ; of Jamaica, 
 1907, 80; of Japan, 1891, 72, 75; 
 of lower Mississippi Valley, 1811, 83; 
 of Messina, 1908, 68; of Owens 
 Valley, California, 1872, 73, 77, 78, 
 79; of Servia, 1904, 84; of South 
 Carolina, 1886, 85. 
 
 Earthquake shocks, heavy over loose 
 foundations, 88. 
 
 Earthquakes, aftershocks of, ' 83 ; asso- 
 ciated with growing mountains, 86 
 changes in earth's surface during, 71 
 connected with lines of fracture, 86 
 descriptive reports upon, 92 ; due 
 to adjustments between blocks of 
 shell, 78, 79 ; faults and fissures, 71 ; 
 focused at fault intersections, 87 ; 
 fountains during, 83, 86 ; localized at 
 corners of earth blocks, 87 ; manifes- 
 tations of changes in level, 68 ; nature 
 of shocks, 67 ; of Ischia, localization 
 of, 87 ; shown by coast terraces, 250 ; 
 special lines of heavy shock, 86 ; in 
 unstable areas of earth's crust, 86 ; 
 wave motions of, 68 ; zones in distri- 
 bution of, 86. 
 
 Earth relief, repeating patterns in, 223. 
 
 Eckert, cited, 188. 
 
 Effect of contraction upon a spherical 
 body, 13. 
 
 Egg-spinning demonstration of earth 
 rigidity, 20. 
 
 "Elevation-crater" theory of volcanoes, 
 95, 139. 
 
 Embankments, shore, 240. 
 
 Embayed coasts, 251. 
 
 Emerson, B. K., cited, 19. 
 
 End moraines, 394. 
 
 Engell, M. C, cited, 296. 
 
 Englacial debris, 393. 
 
 Englacial drift, 277, 278. 
 
 Entonnoirs, 182. 
 
 Entrenchment of meanders, 172, 173^ 
 179. 
 
 Eolian sand, 206. 
 
 Eolian sediments, 30. 
 
 Erosional unconformity, 53. 
 
 Erosion cycle, 159. 
 
 Erosion, effect of, in adding curves tO' 
 landscape, 65 ; glacial, in contrast 
 
494 
 
 INDEX 
 
 with normal weathering, 377 ; in 
 
 desert, 214 ; shadow, 206 ; stream, as 
 
 modified by resistant rocks, 174. 
 "Erratic blocks," 304. 
 Eruptions, Strombolian, 117; Vulcanian, 
 
 117, 125. 
 Escarpments, from faults, 59. 
 Eskers, 311, 315, 316, 363. 
 Estes, L. A., cited, 93. 
 Estuaries, 251. 
 Etna, eruption of 1669, 122. 
 Evolution, doctrine of, in connection 
 
 with fossils, 38. 
 Evolution of ideas concerning the earth's 
 
 figure, 9. 
 Exfoliation, 151, 203. 
 Expanded foot glaciers, 383, 385. 
 Experiment, to illustrate relation of 
 
 earthquake shocks to foundations, 88. 
 Experiments, on fracture and flow, 40, 
 
 41 ; for demonstra;tion of earthquakes, 
 
 81, 82. 
 Exposures, rock, 46. 
 Extrusive rocks, 463. 
 
 Fairbanks, H. W., cited, 155, 170, 174, 
 201, 205, 214, 224, 248, 249 250, 260, 
 302, 375, 406, 413, 429. 
 
 Fairchild, H. L., cited, 339. 
 
 Falls, "Bridal veil," 378. 
 
 Falls, ribbon, 378. 
 
 Fan, alluvial, 213. 
 
 Farrington, O. C, cited, 29. 
 
 Fault, drag upon, 60. 
 
 Fault breccia, 60. 
 
 Fault topography, 65. 
 
 Faults, 58, 440 ; during earthquakes, 71 ; 
 earthquake, change in throw upon, 76, 
 77, 78 ; earthquake, disappear in loose 
 materials, 73 ; earthquake, of small 
 displacements, 74 ; earthquake, plan 
 of, 76, 78 ; illusory nature of, 59 ; 
 methods of detecting, 59 ; post-glacial, 
 74 ; relation of escarpments to, 60 ; 
 shown by changes in strike and dip, 61 ; 
 shown by offsets, 61. 
 
 Feldspars, 456. 
 
 Fenneman, N. M., cited, 424, 425. 
 
 Festoons of mountain arcs, 435, 436. 
 
 Field ice, 286. 
 
 Field map, geological, 62, 63. 
 
 Figure of the earth, the, 8. 
 
 Figures, earlier, of the earth, 14 ; earth, 
 evolution of, 15. 
 
 Figure toward which the earth is tend- 
 ing, 12. 
 
 "Fire girdle" of the Pacific, 98. 
 
 Firn, 369. 
 
 Fracture control, of drainage lines, 224. 
 
 Fissure eruptions, of volcanoes, 101. 
 
 Fissures, during earthquakes, 71 ; earth- 
 quake, 74 ; in connection with vol- 
 canoes, 99-101. 
 
 Fissure springs, 61, 190, 195. 
 
 Fjords, 290 340. 
 
 "Float copper," 305. 
 
 Flooded portions of continents, 18. 
 
 Flood plain, 178 ; manner of grading of, 
 162. 
 
 Floors of hydrosphere and atmosphere, 
 18. 
 
 Flow, experiments on, 41 ; zone of, 40. 
 
 Flow texture, of extrusive rocks, 33. 
 
 Flu\'iatile deposits, 35. 
 
 Fluvio-glacial deposits, 31. 
 
 Fluxion texture, of extrusive rocks, 33. 
 
 Folds, analysis of, 54 ; comparison of 
 shapes of, 44 ; mutilated, restoration 
 of, 45 ; pitching, 43 ; secondary, 44 ; 
 shapes of, 43. 
 
 Fold topography, 65. 
 
 Forbes, J. D., cited, 294. 
 
 Fore-set beds, 167. 
 
 Forest, destruction of, in relation to 
 agriculture, 156. 
 
 Formation of lava reservoirs, 143. 
 
 Formations, measurement of thickness 
 of, 48, 49. 
 
 Fort Snelling, on Warren River, 327, 331. 
 
 Fosses, glacial, 281, 314; in connection 
 with peat bogs, 430. 
 
 Fracture, experiments on, 41; of min- 
 erals, 450 ; zone of, 40, 46. 
 
 Fractures, in rocks, shown by rectilinear 
 lines on map, 65 ; system of, 55. 
 
 Free, E. E., cited, 222. 
 
 Free waves, 232. 
 
 Fretted upland, 372, 373. 
 
 Frost, prying wiork of, 152. 
 
 Frost action, 223. 
 
 Frost snow, 285. 
 
 Fuller, M. L., cited, 157, 195. 
 
 Fumeroles, 97. 
 
 Gabbro, 462. 
 
 Gabled facade, in desert landscapes, 221, 
 
 443. 
 Galenite, 453. 
 
 Gannett, Henry, cited, 178, 386. 
 Gaps, water, 176 ; wind, 176. 
 Garnet, 459. 
 
 Gautier, E. F., cited, 221. 
 Geikie, A., cited, 6, 7, 148, 178, 244, 318. 
 Geikie, James, cited, 6, 318. 
 Geoid, departure from spherical surface 
 
 of, 10. 
 
INDEX 
 
 495 
 
 'Geological map, 46, 54 ; areal, 62, 63 ; 
 base of, 61 ; field, 62, 63. 
 
 Geological section, 46, 47. 
 
 Geology, defined, 1. 
 
 Geyserite, 194. 
 
 Geysers, 191-194 ; effect of plugging 
 with sod, 193 ; in relation to drainage 
 lines, 191 ; soaping of, 194. 
 
 Geysir, 192. 
 
 Gilbert, G. K., cited, 93, 148, 157, 178, 
 179,' 198, 221, 224, 240, 244, 294, 344, 
 345, 347, 350, 355, 356, 357, 358, 359, 
 362, 366, 370, 381, 434, 446, 447. 
 
 Gjds, volcano fissures in Iceland, 99. 
 
 Glacial anticyclone, 284. 
 
 Glacial deposits, 30, 31. 
 
 Glacial fringe, of Grant Land, 285. 
 
 Glacial Lake Agassiz, 325-328, 339. 
 
 Glacial lakes, at close of ice age, 320 ; 
 of St. Lawrence Valley, 329. 
 
 Glaciated regions, aspects of, 302 ; 
 characteristics of, 301 ; contrasted 
 with nonglaciated, 299, 309. 
 
 Glaciation, conditions essential to, 261 ; 
 cycle of, 263 ; Permo-Carboniferous, 
 298. 
 
 Glaciations, following changes in earth's 
 figure, 15; previous to "ice age," 
 literature of, 318. 
 
 Glacier broom, over continental ice, 285. 
 
 Glacier cornices, 397. 
 
 Glacier deposits, upon its bed, 390. 
 
 Glacier drainage, 397. 
 
 Glacier flow, 390, 400 ; data from acci- 
 dents to Alpinists, 392. 
 
 Glacier gravings, 301, 319; miiltiple 
 records, 304. 
 
 Glacier lobe lakes, 411. 
 
 Glacier milk, 398. 
 
 Glacier mills, 278. 
 
 Glacier pavement, 276. 
 
 Glaciers, birth of, 369 ; crevasses on, 
 391 ; dendritic, 383, 385, 386 ; grind- 
 ing tools of, 276 ; horseshoe, 383, 386, 
 387; inherited basin, 387-389; ini- 
 tiation of, 262 ; in relation to wind 
 direction, 262 ; main types of, 266 
 mountain, cross sections of, 394 
 mountain, expanded-foot type, 264 
 mountain, land sculpture by, 367 
 mountain, successive stages, . 383 
 nivation, 387 ; nourishment of, 268- 
 270; piedmont, 383, 384; radiating, 
 383, 386; sensitiveness to temperature 
 changes, 263 ; s^racs, 391 ; surface 
 features of, 390 ; tide water, 290, 386. 
 Glacier stars, 395. 
 Glacier tables, 395. 
 
 Glacier types, successive, during waning 
 
 glaciation, 383. 
 Glacier wells, 278. 
 
 Glassy texture, of extrusive rocks, 32. 
 Glen Roy, 322, 339. 
 Glint, 409. 
 
 Glint lakes, 408, 409. 
 Gneiss, 465. 
 Gneiss banding, 31. 
 
 Goethe, cited on volcano structure, 139. 
 Gold, E., cited, 294. 
 Goldthwait, J. W., cited, 259, 320, 341, 
 
 345, 351. 
 Gondwana Land, 16. 
 Gorges, through rock bars, 378. 
 Grabau, A. W., cited, 361, 366. 
 Grading of flood plain, 162. 
 Grand Caiion of the Colorado, 146, 169, 
 
 174, 215, 443. 
 Grand River outlet, 333. 
 Granite, 462; dome structure in, 152, 157. 
 Granite domes, 221. 
 Granitic texture, of igneous rocks, 33. 
 Grats, 373. 
 Gravel, kame, 310. 
 "Gravel piedmont," 214. 
 Great Basin, 190, 198, 439. 
 Great Lakes, probable future of, 347, 
 
 348 ; submergence of certain shores of, 
 
 349, 350. 
 Great Ross Barrier, 282. 
 Great Salt Lake, 199; fluctuations of 
 
 level of, 198. 
 Green, W. Lowthian, cited, 19. 
 Gregory, J. W., cited, 11, 19, 439, 446. 
 Grooved upland, 372, 373. 
 Gross, H., cited, 294. 
 Grossman, cited, 268. 
 Grottoes, sea, colors of, 258. 
 Ground water, 180 ; descent of, in 
 
 relation to joints, 181. 
 Ground water lakes, 424. 
 Grund, A., cited, 195. 
 Gullies, early stages of, 160. 
 Gulliver, F. P., cited, 244, 319. 
 GuUsdng process, started by deforesta- 
 tion, 156. 
 Gypsum, 455. 
 
 Hade, on faults, 59. 
 Hague, Arnold, cited, 196. 
 Halemaumau, Kilauea, 107, 108. 
 Hamilton, Sir William, cited, 128. 
 Hanging valleys, 378. 
 Hardness, of minerals, 451. 
 Harwood, W. A., cited, 294. 
 Haug, E., cited, 7, 133, 211. 
 Haughton, Samuel, cited, 56. 
 
496 
 
 INDEX 
 
 Hawaii, lava domes of, 105 ; lava sur- 
 faces of, 113; map of, 106; section 
 through, 106. 
 
 Hayes, C. W., cited, 156. 
 
 Headlands, notched, 341. 
 
 Heave, of faults, 59. 
 
 Hebrews, conception of the universe, 9. 
 
 Hedin, Sven, cited, 221. 
 
 Heilprin, A., cited, 148. 
 
 Heim, A., cited, 54. 
 
 Heligoland, 236. 
 
 Helland, A., cited, 99. 
 
 Hematite, 452. 
 
 Hemicycles, of glaciation, 263, 264. 
 
 Herculaneum, buried beneath mud 
 flows, 139. 
 
 Hess, H., cited, 267, 272, 294, 393, 400. 
 
 High plains, 435 ; origin of, 219. 
 
 Hilgard, E., cited, 222. 
 
 Hinge lines, of uptilt, 344-.347. 
 
 Hitchcock, C. H., cited, 106, 147, 434. 
 
 Hobson, B., cited, 120. 
 
 Hogarth, William, cited, 170. 
 
 Hogarthian line of beauty, in landscapes, 
 170-171. 
 
 "Hog backs," 442. 
 
 Holmes, W. H., cited, 441. 
 
 Horns, 374. 
 
 Horseshoe glaciers, 383, 386, 387. 
 
 Hot springs, 191; colors in,due to algae, 194. 
 
 Hovey, E. O., cited, 136, 137, 148. 
 
 Hovey, H. C, cited, 183, 195. 
 
 Howchin, W., cited, 298. 
 
 Howe, E., cited, 140. 
 
 Howell, cited, 325. 
 
 Hudson River, narrows of, 174. 
 
 Hudsonian channel, 252. 
 
 Hummocks, on pack ice, 286. 
 
 Humphrey, R. L., cited, 90, 93. 
 
 Humphreys, cited, 404. 
 
 Humus, in relation to weathering, 156. 
 
 Huntington, Ellsworth, cited, 216, 217, 
 221 222. 
 
 Hus, H. T. A. de L., cited, 183. 
 
 Hydration, 151. 
 
 Hydrosphere, 8. 
 
 Hypothesis, the value of, 6 ; Laplacian, 
 of the universe, 20. 
 
 Icebergs, 296 ; Antarctic, 292, 293 ; 
 Antarctic, formation of, 292 ; blue, 
 292; manner of formation of, 291, 
 292; northern, 291. 
 
 Ice caps, profiles of, 267, 268 ; sculp- 
 ture, 380. 
 
 Ice-dammed lakes, 321, 323, 410, 411; 
 in St. Lawrence Valley, 339 ; of Scot- 
 tish glens, 322. 
 
 Ice floes, 287. 
 
 Iceland, fissure eruptions of, 102. 
 
 Ice pyramids, 395. 
 
 Ice ramparts, 431-434; manner of forma- 
 tion of, 433. 
 
 Igneous rocks, 30 ; textures of, 32. 
 
 Imlay outlet, 332. 
 
 Inbreak, of lava surface, 107. 
 
 Incised topography, 301. 
 
 Inherited basin glacier, 387-389. 
 
 Interlobate moraines, 314. 
 
 Inter-pluvial periods, 198. 
 
 Intricate pattern of river etchings, 158. 
 
 Intrusive rocks, 32, 402. 
 
 Islands, land-tied, 241 ; steep rocky, 
 due to submergence, 252. 
 
 Isobases, 347. 
 
 Isoclinal folds, 42. 
 
 Isothermal zone of atmosphere, 270. 
 
 Jagger, T. A., Jr., cited, 148. 
 
 Jamieson, T. F., cited, 221, 322, .339. 
 
 Jeannette exploring expedition, 287, 295. 
 
 Jensen, H. I., cited, 110, 113, 147. 
 
 Johnson, D. W., cited, 7, 148. 
 
 Johnson, W. D., cited, 77, 213, 219, 220, 
 222, 370, 381. 
 
 Johnston-Lavis, H. J., cited, 87, 131,. 
 132, 134, 138, 147, 148. 
 
 Joint blocks, in Niagara limestone, 353. 
 
 Joint plane, seat of frost action, 370. 
 
 Joints, 56 ; effect on surface features, 57 ; 
 closed during earthquakes, 76 ; com- 
 posite nature of, 58 ; composite groups 
 of, 57 ; disorderly, 57 ; displacements 
 upon, 58 ; master, 56 ; space intervals 
 of, 58 ; sets of, 55 ; system of, 55. 
 
 Joint series, combinations of, 56. 
 
 Joint systems, 66. 
 
 Jorullo, birth of, 96. 
 
 Judd, John W., cited, 116, 118, 139, 148. 
 
 Julien, A. A., 156^ 
 
 Jura Mountains, 46. 
 
 Kame gravel, 310. 
 
 Kames, 311, 314. 
 
 Kammerbiihl, 139. 
 
 Karrenfelder, 188. 
 
 Karst, characters of, 186-187 ; once 
 
 forested, 188. 
 Karst conditions, 195. 
 Karst lakes, 422. 
 Katavothren, 188. 
 Katzer, F., cited, 195. 
 Kearney, Th. H., cited, 222. 
 Kelvin, Lord, cited, 20, 29. 
 "Kettle moraines," 311-314. 
 "Kettles" on moraines, 312. 
 
INDEX 
 
 497 
 
 Kikuchi, Y., cited, 148. 
 
 Kilauea, 101, 106; draining of lava in 
 crater of, 108 ; eruption of 1840, 109, 
 111, 112; lava movements in, 106, 
 107 ; moving platform in crater, 107 ; 
 range in height of lava in, 107. 
 
 King, F. H., cited, 157, 195. 
 
 Knebel, W. von, cited, 185, 195, 258, 
 260. 
 
 "Knob and basin" topography, 314. 
 
 Knott, C. G., cited, 92. 
 
 Kopisch, August, cited, 258. 
 
 Koto, B., cited, 92. 
 
 Krakatoa, dissected by eruption, 142. 
 
 Krakatoa, eruption of 1883, 141, 142. 
 
 Kuppen, 105. 
 
 Kurische Nehrung, wandering dunes of, 
 210. 
 
 Laboratory apparatus, for simulation of 
 cinder eruptions, 122. 
 
 Laboratory models, for study of geo- 
 logical maps, 63. 
 
 Laccolites, 143, 441, 442, 447. 
 
 Lacroix, A., cited, 148. 
 
 Lacustrine deposits, 35. 
 
 Lake Agassiz, glacial, 325-328. 
 
 Lake Algonquin, 334, 342. 
 
 Lake Arkona, 332, 333. 
 
 Lake basins, study of, 401. 
 
 Lake Bonneville, 199. 
 
 Lake Chicago, 330, 332, 333. 
 
 Lake Eulalie, draining of, during earth- 
 quake, 83. 
 
 Lake Iroquois, 334, 335. 
 
 Lake Maumee, 330, 331, 332, 345. 
 
 Lake Ojibway, glacial, 338. 
 
 Lake stages, in St. Lawrence Valley, 
 336. 
 
 Lake Warren, 333, 334. 
 
 Lake Whittlesey, 332, 333. 
 
 Lakes, alluvial dam, 423 ; as regulators 
 of air temperature, 431 ; as regulators 
 of river flow, 431 ; as settling basins, 
 426-428 ; barrier, 420 ; basin range, 
 402, 403 ; become extinct through 
 wave action, 428 ; border, 399, 414 ; 
 classification of, 424 ; colk, 408, 409 ; 
 continental glaciation, 424 ; coulee, 
 406 ; crater, 405, 406 ; crescentic, 
 329, 330 ; crescentic levee, 416, 417 ; 
 currents in, 431; delta, 419, 420; 
 desert, 424 ; drained by cutting down 
 of outlet, 428 ; dune, 421 ; drained 
 during earthquakes, explanation of, 
 83 ; earthquake, 404 ; ephemeral 
 existence of, 426 ; extinction by peat 
 growth, 429-430 ; extinction of, in 
 2k 
 
 desert regions, 430 ; fresh water, 401 ; 
 glacier lobe, 411; glint, 408, 409; 
 ground water, 424 ; ice dam, 410, 411 ; 
 intramorainal, about continental gla- 
 ciers, 279, 280 ; karst, 422 ; landslide, 
 414; morainal, 315, 406, 407; moun- 
 tain glaciation, 424; newland, 401, 
 402; ox-bow, 165, 415; pit, 315, 407, 
 408 ; playa, 422 ; raft, 417, 418 ; rift- 
 valley, 403, 404 ; river, 424 ; rock 
 basin, 376, 377, 400, 412 ; rock basin 
 about continental glaciers, 279 ; role 
 of, in economy of nature, 430 ; saline, 
 401 ; salines, 423 ; saucer, 415, 416 ; 
 seasonal, 189, 422; side delta, 326, 
 327, 418, 419 ; sink, 421 ; strand, 424 ; 
 tectonic, 424 ; valley moraine, 400, 
 413; volcanic, 424 ; "wall," 432. 
 
 Laki, eruption in 1783, 99. 
 
 Laminated structure, of rocks, 31. 
 
 Lamplugh, G. W., cited, 225. 
 
 Land, growth of, from volcanic outflow, 
 113, 114; sliced during earthquake, 
 80 ; uptUt of, at close of ice age, 340. 
 
 Land areas, concentration of, in northern 
 hemisphere, 11. 
 
 Land sculpture, by mountain glaciers, 
 367 ; in relation to climatic conditions, 
 443 ; referable to ice caps, 380. 
 
 Land shields, 15. 
 
 Landslide lakes, 414. 
 
 Land-tied islands, 241. 
 
 Lane, A. C., cited, 148. 
 
 Lankester, E. Ray, cited, 260. 
 
 La Noe, G. de, cited, 7. 
 
 Lapilli, 119, 122. 
 
 Laplacian hypothesis of the universe, 20. 
 
 Lateral moraines, 393. 
 
 Lateral movements, deep seated, during 
 earthquakes, 81. 
 
 Lava, 32 ; block, 113 ; composition and 
 properties of, 103 ; discharging from 
 tunnel. 111 ; fluidity of basic, 103. 
 movements, in caldron of Kilauea, 
 107 ; probable origin from shale, 144 ; 
 ropy, 113; viscosity of siliceous, 103. 
 
 Lava domes, probable structure of walls 
 of, 112; slopes of, 103, 104, 105. 
 
 Lava projectiles, pear-shaped type, 121. 
 
 Lava reservoirs, formation of, 143. 
 
 Lava streams, appearance of, 133, 134. 
 
 Lava surface, 113, 124. 
 
 Law of the desert, 197. 
 
 Lawson, A. C., cited, 92, 260, 351. 
 
 Leads, in pack ice, 286. 
 
 Le Conte, Joseph, cited, 6. 
 
 Leffingwell crater, California, 104. 
 
 Levees, 166. 
 
498 
 
 INDEX 
 
 Leverett, Frank, cited, 6, 104, 166, 312, 
 318, 321, 330, 332, 333, 334, 337, 339, 
 344, 345. 
 
 Lewiston escarpment, at Niagara, shap- 
 ing of, 360-362. 
 
 Libbey, W., cited, 274. 
 
 Life histories, of rivers, 158. 
 
 Light figure, from surface of crystal, 25. 
 
 Lightning, in connection with volcanic 
 eruptions, 130. 
 
 Limbs of faults, 59; of folds, 43. 
 
 Limestone, 464; origin of, 36; sinks, 
 182. 
 
 Limestone, caverns of, 182. 
 
 Limonite, 452. 
 
 Linck, G., cited, 122. 
 
 Lindenkohl, A., cited, 260. 
 
 Lineaments, 87, 226, 227. 
 
 Line of beauty, Hogarthian, in land- 
 scapes, 170, 171. 
 
 Lithodomus, borings of, in records of 
 oscillation, 254. 
 
 Lithosphere, a complex of interlocking 
 crystals, 25 ; and its envelopes, 8. 
 
 Littoral deposits, 36. 
 
 Loess, 35, 207; erosion of, 208. 
 
 Loessmannchen, 208. 
 
 Lubbock, Sir John, cited, 7. 
 
 Luray caverns, Virginia, 186. 
 
 Luster, of minerals, 450. 
 
 Lyell, Sir Charles, cited, 7, 96, 146, 199, 
 259, 260, 304. 
 
 Maare, 405. 
 
 McGee, W J, cited, 157, 259. 
 
 Mackinac Island, records of uplift of, 
 341-344. 
 
 Madison, Wisconsin, 233, 237, 241, 317, 
 434. 
 
 Magellan, circumnavigation of globe, 9. 
 
 Magma, defined, 30. 
 
 Magnetism, of minerals, 451. 
 
 Magnetite, 452. 
 
 Malachite, 453. 
 
 Mamelons, 105. 
 
 Mammoth Cave, 182, 183. 
 
 Mantle, rock, 155. 
 
 Map, contour, nature of, 467 ; of 
 Armorican mountains, 438 ; of barrier 
 beaches, 242-243 ; of bowlder train 
 from Iron Hill, 306 ; of cirques and 
 niches, in Bighorn Mountains, 371 ; 
 of coast lines, 246 ; geological, 54, 
 61 ; geological, method of preparing, 
 46, 63 ; of continental divide in 
 Colorado, 377 ; of continental glacier 
 in Victoria Land, 282 ; of Dalager's 
 nunataks, 277 ; of expanded foot 
 
 glaciers, 264 ; of front of Green Bay 
 lobe, 317 ; of glacial features. South- 
 ern Finland, 315 ; of glacial Lake 
 Agassiz, 325, 326, 328; of glaciated 
 area, Europe, 299 ; of glaciated area. 
 North America, 298 ; of ice ramparts 
 on Lake Mendota, 434 ; of inner San- 
 dusky Bay, 350 ; of Kilauea and neigh- 
 boring slopes, 109 ; of Lake Chicago 
 and later Lake Maumee, 332 ; of 
 Lake Maumee, 330 ; of Lakes Whittle- 
 sey and Saginaw, 333 ; of lava out- 
 flows on Vesuvius, 1906, 131 ; of lava 
 streams on Mauna Loa, 126 ; of 
 marginal moraines, 312 ; of moun- 
 tain arcs of Eastern Asia, 438 ; of 
 mountain arc of Sewestan, 436 ; of 
 North Polar regions, 288 ; of part 
 of "fire girdle" of the Pacific, 98; of 
 Scottish glens, 322-324; of Volcano, 
 118; of volcano belts, 98; of Warren 
 River, 326, 327 ; topographical, 61 ; 
 topographical, preparation of, 467, 
 468; topographical, verification of, 
 469; to show dispersion of diamonds 
 in Lake region, 308 ; to show disper- 
 sion of peculiar rocks, 305 ; to show 
 distribution of existing glaciers, 263 ; 
 to show formation of shore features, 
 238 ; to show glaciated areas of 
 Pleistocene period, 297 ; to show 
 reciprocal relation of land and sea, 11. 
 
 Marble, 466. 
 
 Margerie, Emm. de, cited, 7, 54. 
 
 Marginal moraines, 278-280, 311-314. 
 
 Marine clays, as marks of uplift, 253. 
 
 Marine deposits, 35. 
 
 Marjelen Lake, 329, 411. 
 
 Marks, of origin of rocks, 30 ; of uplift, 
 on coasts, 245. 
 
 Marr, John E.„ cited, 7, 445. 
 
 Martel, E. A., cited, 181, 187, 195. 
 
 Martin, Lawrence, cited, 77, 92, 260, 
 280, 351. 
 
 Martonne, E. de, cited, 7, 195, 222, 382. 
 
 Massive structure, of rocks, 31. 
 
 Master joints, 56. 
 
 Matavanu, eruption in 1906, 110, 113, 
 147. 
 
 Mat of vegetation, shield to lithosphere, 
 155. 
 
 Matthes, F. E., cited, 7, 371, 381. 
 
 Maturity, of upland, 170. 
 
 Mauna Loa, 106 ; eruptions of, 109. 
 
 Meander scars, 165. 
 
 Meanders, entrenchment of, 172, 173, 
 179 ; stream, 163 ; stream, under- 
 mining by, 164. 
 
INDEX 
 
 499 
 
 Measurement of thickness, of formations, 
 48, 49. 
 
 Mechanical sediments, 34. 
 
 Medial moraines, 393 ; from nunataks, 
 274. 
 
 Mediterranean seas, 14. 
 
 Melting, selective, on glacier surface, 
 394. 
 
 Melville, G. W., cited, 289. 
 
 MercalH, G., cited, 89, 117, 119, 147. 
 
 Merrill, George P., cited, 156. 
 
 Mesa, 215, 216; origin of, 112. 
 
 Metamorphic rocks, 30, 31, 465. 
 
 Meteorites, compared with earth, 22 ; 
 composition of, 21, 23. 
 
 Mica, 458. 
 
 Mica schist, 465. 
 
 Michailovitch, J., cited, 84. 
 
 Microscopical petrography, 27. 
 
 Migration, of divides, 175. 
 
 Mill, H. R., cited, 424. 
 
 Mills, glacier, 398. 
 
 Milne, John, cited, 75, 92, 93. 
 
 Mineral fragments, possibility of growth 
 of, 24. 
 
 Minerals, alterations of, 27, 28 ; common, 
 properties of, 452-461 ; of economic 
 importance, 452-456 ; important as 
 rock makers, 456-461 ; properties of, 
 26, 27 ; quick determination of, 449. 
 
 Mississippi River, 167. 
 
 Mitchell, G. E., cited, 157. 
 
 Moats, about nunataks, 273, 274. 
 
 Models, laboratory, for study of geologi- 
 cal maps, 63. 
 
 Mojsisovics von Mojsvdr, E., cited, 228. 
 
 Mokuaweoweo, crater of, 106. 
 
 "Mole-hill" effect, after earthquakes, 
 73. 
 
 Molten rock, rise to earth's surface, 
 94. 
 
 Monadnocks, 172. 
 
 Monte Nuovo, 96. 
 
 Monte Somma. caldera of, 127. 
 
 Montessus de Ballore, de F., cited, 92, 
 93. 
 
 Monti Rossi, crystal rain from, 122 ; 
 parasitic cones of, 125. 
 
 Mont Pele, post-eruption stage of, 135- 
 138 ; spine of, 136, 137, 138. 
 
 Moore, W. H., cited, 294. 
 
 Morainal lakes, 315, 406, 407. 
 
 Moraines, interlobate, 314; lateral, 393; 
 marginal, 278-280; medial, 393; 
 medial, from nunataks, 274 ; of moun- 
 tain glaciers, 393, 394 ; recessional, 
 399; surface, 277; terminal, 311- 
 314, 394; waterlaid, 330. 
 
 Moreno, F. P., cited, 235. 
 
 Moseley, E. L., cited, 350, 351. 
 
 Moselle River, with entrenched mean- 
 ders, 173. 
 
 Motive power, of rivers, 158. 
 
 Moulins, 398. 
 
 Mountain arcs, festoons of, 435, 436 ; 
 theories of origin of, 436, 437. 
 
 Mountain glaciation lakes, 424. 
 
 Mountain glaciers, contrasted with 
 continental glaciers, 266-268 ; de- 
 fined, 266-268; dendritic, 383, 385, 
 386 ; expanded-foot type, 264 ; horse- 
 shoe, 383, 386, 387; land sculpture 
 by, 367 ; marks of, 400 ; piedmont, 
 383, 384; profiles of, 267; radiating, 
 383, 386; studies of special districts, 
 294 ; summary of types of, 389. 
 
 Mountain ramparts, about continental 
 glaciers, 271. 
 
 Mountains, battlement type, 228, 445 ; 
 block type, 439 ; carved from pla- 
 teaux, 442 ; of circumvallation, 442, 
 445 ; defined, 435 ; domed, of uplift, 
 441 ; erosional, 445 ; evidence for 
 occupation by mountain glaciers, 400 ; 
 genetical, 445 ; largely shaped by 
 erosion, 435 ; of outflow and upheap, 
 440 ; origin and forms of, 435 ; trun- 
 cated at coast lines, 438. 
 
 Mt. Etna, 125, 126. 
 
 Mt. Vesuvius, 94 ; appearance of, from 
 Naples at night, 129 ; ash curtain, 
 during eruption, 132 ; ash-fall over, 
 1906, 133; "cauliflower" cloud over, 
 133 ; changed appearance after erup- 
 tion of 1906, 132 ; eruption of 79 a.d., 
 97; eruption of 1872, 124; eruption 
 of 1906, 127-137; history of, 97; 
 lavas of, 32. 
 
 Mud cones, 84 ; aligned upon a fissure, 
 84. . 
 
 Mud-crack structure, 37. 
 
 Mud, flocculent calcareous, of Florida, 
 36. 
 
 Mud flows, which destroyed Hercula- 
 neum, 139. 
 
 Mud veneer, from eruption of Taal, 121. 
 
 Muir, John, cited, 7. 
 
 Munthe, H., cited, 313, 351, 410. 
 
 Murray, Sir John, cited, 39, 293. 
 
 "Mushroom rocks," 205. 
 
 Nansen, F., cited, 17, 260, 271, 272, 
 
 287, 295. 
 Narrows, river, 174, 327. 
 Natural Bridge, near Lexington, Vip 
 
 ginia, 184. 
 
500 
 
 INDEX 
 
 Natural bridges, 184. 
 
 Natural sand blast, 204. 
 
 Nature of materials in the lithosphere, 
 20. 
 
 Necks, volcanic, 140. 
 
 Nephelite, 459. 
 
 Neumayr, Melchior, cited, 7, 146, 195, 
 196, 222, 425. 
 
 Neve, 369. 
 
 Newborn glacier, .387. 
 
 Newland, 159, 247. 
 
 Newland lakes, 401, 402. 
 
 New Madrid earthquake, 83. 
 
 New River, of Cumberland plateau, 173. 
 
 Niagara Falls, 352-366 ; episodes in 
 history of, 362-365; the clock of 
 recent geological time, 364. 
 
 Niagara gorge, 352-366 ; drilling of, 353, 
 355 ; episodes in history of, in connec- 
 tion with glacial lakes, 364 ; plan and 
 section of, 355; rate of recession of, 356. 
 
 Niches, 371; beneath snowdrift sites, 
 368, 369. 
 
 Nickel, in meteorites, 23. 
 
 Nieves penitentes, 397. 
 
 Nipissing Great Lakes, 335, 342. 
 
 Nipissing outlet, 335, 336. 
 
 Nippur, sand mounds over, 218. 
 
 Nivation, 368. 
 
 Nivation glacier, 387. 
 
 Noble, F. H., cited, 147. 
 
 Nordenskiold, Otto, cited, 154, 157, 295. 
 
 North Atlantis, 16. 
 
 North Bay outlet, 335. 
 
 Northwest Highlands of Scotland, 
 thrusts of, 45. 
 
 Norway, repeating patterns of, 229. 
 
 Notched cliffs, 233 ; elevated, 248. 
 
 Nourishment of continental glaciers, 295. 
 
 Nunataks, 272, 274, 277. 
 
 Nussbaum, F., cited, 161. 
 
 Oasis, 216. 
 
 Oblateness, of the earth, 10. 
 
 Observational geology vs. speculative 
 
 philosophy, 5. 
 Obsidian, 463. 
 Obsidian Cliff, 33. 
 Ocean of Tethys, 16. 
 Oceanic platform, 19. 
 Oceans, arrangement of, 10. 
 Oldham, R. D., cited, 72, 76, 92. 
 Oldland, 159, 247. 
 Olivine, 461. 
 Omori, F., cited, 147. 
 OoUte, 464. 
 Oolitic limestone, 464. 
 Ooze, calcareous, 36 ; composition of, 39. 
 
 Optical mineralogy, 27. 
 
 Order of deposition, during marine 
 transgression, 37. 
 
 Order of superposition, of strata, 52. 
 
 Organic sediments, 34. 
 
 Orgeln, 182. 
 
 Orleans, Due d', cited, 286., 
 
 Orographic blocks, 58. 
 
 Osar, 311, 315, 316. 
 
 Oscillations of movement, on coasts, 253. 
 
 Outcrop blocks, for study of maps, 63. 
 
 Outcroppings, 46. 
 
 Outlets, from continental glaciers, 271 ; 
 of glacial lakes, 326, 327. 
 
 Outwash plains, 280, 281, 311, 313, 314, 
 399, 408. 
 
 Overthrust, 45. 
 
 Owens Valley, California, map of earth- 
 quake faults in, 78. 
 
 "Ox-bow," of river, 165. 
 
 Ox-bow lakes, 165, 415. 
 
 Pack, drift of, 287 ; the, 286. 
 
 Pack ice, 286. 
 
 Pagination, of the earth record, 38. 
 
 Pahoehoe tj'pe of lava surface, 113. 
 
 Pan form of deserts, 197. 
 
 Panum crater, caldera of, 126. 
 
 "Parallel roads," of Scottish glens, 322— 
 
 325, 328, 339. 
 Partially dissected upland, 160. 
 Passarge, S., cited, 221, 222. 
 "Paternoster lakes," 376. 
 Pattern, of river etchings, 158. 
 Patterns, repeating, 223. 
 Pavement, bowlder, 237 ; glacier, 276 ; 
 
 tessellated from soil flow, 154. 
 Pavlow, A. P., cited, 108. 
 Peale, A. C, cited, 195, 196. 
 Peary, R. E., cited, 17, 283, 289, 295, 296. 
 Peat, 465; formation of, 429, 430. 
 Peat bogs, 429. 
 "Pele's Hair," 107. 
 Pele, spine of, 148. 
 Penck, A., cited, 294, 399, 414. 
 Peneplain, 171, 179. 
 " Penitents," 397. 
 "Perched bowlders," 306. 
 Peridotite, 462. 
 
 Periods, inter- pluA-ial, 198; pluvial, 198. 
 Peripheral granulation, 31. 
 Perret, F. A., cited, 148. 
 Philippi, E., cited, 295. 
 Phillips, John, cited, 56. 
 Physiographic models, preparation of, 
 
 470. 
 Piedmont glaciers, 383, 384. 
 Pino, 119, 130. 
 
INDEX 
 
 501 
 
 Pipes, volcanic, 140. 
 
 Piracy, river, 175, 176. 
 
 Pirsson, L. V., cited, 39, 447. 
 
 Pitch, 43. 
 
 Pitching folds, 43. 
 
 Pit lakes, 315, 407, 408. 
 
 Pitted plains, 314, 407, 408. 
 
 Pittier, H., cited, 405. 
 
 Plains, flood, 178 ; coastal, 246 ; out- 
 wash, 280, 281 ; pitted, 314, 407, 408. 
 
 Platform, continental, 18, 19 ; oceanic, 
 -;^ 18, 19. 
 
 Playa lakes, 422. 
 
 Playfair, Sir John, cited, 178. 
 
 Plucking, beneath glaciers, 275. 
 
 Plugs, volcanic, 140. 
 
 Plunge and flow structure, 37. 
 
 Plunging folds, 43 ; detection of, 49, 50. 
 
 Pluvial periods, 198. 
 
 Pocket rocks, in desert, 200, 201, 202. 
 
 Poles, wind, of the earth, 263 ; earlier, 297. 
 
 Poljen, 189, 422. 
 
 Pompeii, destruction of, 97 ; volcanic 
 materials over, 122. 
 
 Ponores, 188. 
 
 Porphyritic texture, of certain igneous 
 rocks, 32. 
 
 Portals, in mountain rampart, surround- 
 ing continental glaciers, 271. 
 
 Potato shape, of earth, 7. 
 
 Pourquoi-Pas expedition, 289. 
 
 Powell. J. W., cited, 178, 439, 446. 
 
 Pratt, W. E., cited, 147. 
 
 Precipitation, in relation to glaciation, 
 261. 
 
 Pressure ridges, on pack ice, 286. 
 
 Prinz, cited, 14, 19, 54, 133, 148. 
 
 Processes by which rocks are formed, 30. 
 
 Profile, cut by waves on steep rocky 
 shore, 236. 
 
 Profiles, character, 177, 318 ; character, 
 directly due to volcanic agencies, 145, 
 146 ; character, coast, due to uplift or 
 depression, 259 ; character, of arid 
 lands, 220 ; character, of shore fea- 
 tures, 243 ; character, referable to 
 mountain glaciers, 379-; of cinder- 
 cones, 123. 
 
 Projectiles, lava, "bread-crust" type, 
 119; volcanic, 121. 
 
 Prying work of frost, 152. 
 
 "Pudding stone," 463. 
 
 Pumiceous texture, of extrusive rocks, 
 32. 
 
 Pumpelly, Raphael, cited, 222. 
 
 Pumpelly, R. W., cited, 212. 
 
 Puys, 105. 
 
 Puys of Auvergne, 124. 
 
 Pyrite, 452. 
 Pyrolusite, 456. 
 Pyroxenes, 458. 
 
 Quartz, 458. 
 Quartzite, 466. 
 Quebradas, 75. 
 
 Rabot, C, cited, 424. 
 
 Radiating glaciers, 383, 386. 
 
 Raft lakes, 417, 418. 
 
 Rafts, log, in Red River, 418. 
 
 Railway tracks, buckled, during earth- 
 quakes, 75. 
 
 Rain erosion, 214. 
 
 Rainfall, infrequent in deserts, 197. 
 
 Raised beaches, 326, 328. 
 
 Ramparts, ice, 431-434. 
 
 Randspalte, 370. 
 
 Rapids, in Rhine gorge, 169. 
 
 Rapilli, 122. 
 
 Rath, G. vom, cited, 147. 
 
 Reaction rims, about minerals, 28. 
 
 Receding hemicycle of glaciation, 264. 
 
 Recessional moraines, 399. 
 
 Reciprocal relation, of land and sea, 
 map to show, 11. 
 
 RMus, E., cited, 147. 
 
 Records, of rise or fall of land, 245. 
 
 Red clay, of the deep sea, 39. 
 
 Red color, of desert rocks, 202. 
 
 Reid, H. F., cited, 294, 296, 400. 
 
 Rejuvenated rivers, 173, 174. 
 
 Relief forms, carved by waves, 213. 
 
 Relief patterns, dividing lines of, 226. 
 
 Repeating patterns, in earth relief, 223 ; 
 composite, 227. 
 
 Reservoirs, of lava, local, 95. 
 
 Residual rocks, 30. 
 
 Resistant rocks, in relation to erosion, 
 174. 
 
 Rhine, gorge of, 169. 
 
 Rhvolite, 463. 
 
 Ribbon falls, 378. 
 
 Richter, E., cited, 294. 
 
 Richtofen, Freiherr von, cited, 207, 222. 
 
 "Ridge roads," 328. 
 
 Riegel, 377. 
 
 Rifting, in eroded mountains, 444. 
 
 Rift-valley lakes, 403, 404. 
 
 Rift valleys, 440. 
 
 Rigidity of the earth, 20, 29. 
 
 Ripple markings, 36. 
 
 River, zone of the dwindling, 213. 
 
 River capture, 175. 
 
 River deltas, 179. 
 
 River etchings, intricate pattern of, 158. 
 I River lakes, 424. 
 
502 
 
 INDEX 
 
 River narrows, 174, 327. 
 
 River networks, in relation to precipita- 
 tion, 161 ; in relation to rock archi- 
 tecture, 161 ; meshes of, 161. 
 
 Rivers, braided, 280 ; cross sections of, 
 in successive stages, 172 ; drowned, 
 251, 340; early aspects of, 159; Hfe 
 begun in uplift, 159; life histories of, 
 158; motive power of, 158; rejuve- 
 nated, 173, 174; submerged channels 
 of, 252 ; swollen during melting of 
 continental glaciers, 320 ; tributary, 
 accordant, 377 ; young, 159, 160. 
 
 River terraces, 165, 178. 
 
 River valley, longitudinal section of, 161. 
 
 Roches moutonnees , 276, 301, 367. 
 
 Rock bars, 377 ; cut through by gorges, 
 378. 
 
 Rock basin lakes, 376, 377, 400, 412. 
 
 Rock cleavage, 44. 
 
 " Rock glaciers," 153. 
 
 " Rocking stones," 306. 
 
 Rock mantle, 155 ; relation to topog- 
 raphy, 156. 
 
 Rock pedestals, 381. 
 
 Rock terraces, 215. 
 
 Rocks, clastic, 30; corrosion of, 156; 
 description of some common, 462-466 ; 
 extrusive, 32, 463 ; igneous, 30 ; 
 igneous, textures of, 32 ; igneous, 
 massive structure of, 31 ; intrusive, 
 32, 462, 463 ; laminated structure of, 
 31 ; marks of origin of, 30 ; meta- 
 morphic, 30, 31, 465; residual, 30; 
 sedimentary, 30 ; sedimentary, of 
 
 . chemical precipitation, 464 ; sedimen- 
 tary, of mechanical origin, 463 ; 
 sedimentary, of organic origin, 464 ; 
 sedimentary, rounded grains of, 31 ; 
 volcanic, 32. 
 
 Ross Barrier, 282. 
 
 Rudolph, E., cited, 92. 
 
 Rudski, M. P., cited, 19. 
 
 Russell, I. C, cited, 126, 147, 148, 175, 
 178, 222, 293, 294, 296, 381, 384, 414, 
 424, 425. 
 
 St. Anthony Falls, recession of, 327, 354. 
 St. David's gorge, near Niagara, 352, 
 
 359, 360, 363. 
 St. Goars, on Rhine, 169. 
 Saint Martin, cited, 436. 
 St. Paul's rocks, a dissected volcano, 141. 
 Salients, of newly incised upland, 169. 
 Salines, 423. 
 Salisbury, R. D., cited, 156, 160, 205, 
 
 222, 293, 295, 298, 300, 305, 313, 318, 
 
 319, 339, 424. 
 
 Salton sink, 420. 
 
 Sand, beach, 206; eolian, 206 ; volcanic, 
 122. 
 
 Sand blast, natural, 204. 
 
 Sand cones, 84. 
 
 "Sand devils," 209. 
 
 Sandstone, 464. 
 
 Sand storms, 209. 
 
 Santa Catalina, 239, 257- 
 
 Sapper, K., cited, 111, 147, 148. 
 
 Sarasin, P. and F., cited, 248. 
 
 Sardeson, F. W., cited, 327, 339. 
 
 Saucer lakes, 415, 416. 
 
 Sawa Lake, of Persian desert, 199. 
 
 Scaling, 151. 
 
 Scape colks, 277. 
 
 Scars, from dissection of volcanoes, 142 ; 
 meander, 165. 
 
 Schist, chlorite, 465 ; mica, 465 ; seri- 
 cite, 465 ; talc, 465. 
 
 Schistosity, 31. 
 
 Schrader, cited, 436. 
 
 Schratten, 188. 
 
 Scidmore, E. R., cited, 70. 
 
 Scoriaceous texture, of extrusive rocks,, 
 32. 
 
 Scott, I. D., cited, 411, 470. 
 
 Scott, R. F., cited, 282, 295. 
 
 Scott, W. B., cited, 6, 60, 72, 259, 274, 
 375. 
 
 "Scree," 152. 
 
 Scrope, P., cited, 96, 124, 146. 
 
 Sea caves, 234 ; elevated, 248. 
 
 Sea coves, 233. 
 
 Sea ice, 286, 292. 
 
 Seaquakes, 69 ; distribution of, 70 ; 
 downward movement of sea floor dur- 
 ing, 81 ; number and magnitude of, 81. 
 
 Seasonal lakes, 189, 422. 
 
 Section, geological, 46, 47; across moun- 
 tain wall about desert, 212. 
 
 Sederholm, J. J^ cited, 315. 
 
 Sedimentary rocks, 30 ; of chemical 
 precipitation, 464 ; of mechanical ori- 
 gin, 463; of organic origin, 464. 
 
 Seismic sea wave, 69 ; Japan, 1896, 70. 
 
 Seismotectonic lines, 87. 
 
 Sckiya, S., cited, 141, 148. 
 
 Seracs, 391. 
 
 Serapeum, at Pozzuoli, 254. 
 
 Sericite schist, 465. 
 
 Series, conformable, 51 ; unconformable, 
 51. 
 
 Serpentine, 460. 
 
 Shackleton, Sir Ernest, cited, 17, 282, 
 283, 292, 295. 
 
 Shadow erosion, 206. 
 
 Shadow weathering, 203. 
 
INDEX 
 
 503 
 
 Shale, 464. 
 
 Shaler, N. S., cited, 7, 157, 244, 306, 317, 
 
 319. 
 Shapes of rock folds, 43. 
 Shaw, E. W., cited, 425. 
 Shearing, in folds, 45. 
 "Sheep backs," 276. 
 Shelf, continental, 18, 19. 
 Shelf ice, 281, 282, 283 ; Antarctic, 289, 
 
 290; of ice age, 317. 
 Sherzer, W. H., cited, 294. 
 Shields, of lithosphere, 436. 
 Shingle, 239. 
 Shoal water deposits, 36. 
 Shore current, work of, 237, 238. 
 Shore lines, elevated, 340 ; migration of 
 
 landward with uplift, 251. 
 Side delta lakes, 418, 419. 
 Siderite, 456. 
 Sieberg, A., cited, 92. 
 Sieger, R., cited, 259. 
 Siliceous lava, viscous, 103. 
 Siliceous sinter, 194. 
 Sills, 142. 
 
 Sinclair, W. J., cited, 152. 
 Sink lakes, 421. 
 Sinks, in limestone, 182. 
 Sinter, calcareous, 184 ; siliceous, 194. 
 Sinter columns, formation of, 185. 
 Sinter deposits, 184. 
 Sjogren, Otto, cited, 225. 
 Skaptar fissure in Iceland, 99. 
 Skyline, straight, of mature upland, 
 
 170. 
 Slate, clay, 466. 
 Slichter, C. S., cited, 195. 
 Slickensides, on fault, 60. 
 Smith, George Otis, cited, 173. 
 Smithsonite, 456. 
 
 "Smoke" of volcanoes, nature of, 128. 
 Smyth, C. H., Jr., cited, 157. 
 Snake river, Idaho, lava plains of, 
 
 102. 
 Snickers Gap, 177. 
 Snow, B. W., cited, 193. 
 Snowbergs, 292, 293. 
 Snowdrift sites, 368. 
 Snow line, 261. 
 Soil flow, 153, 157. 
 Soil striping, 154. 
 
 Solfatara condition of volcanoes, 97. 
 Solger, F., cited, 222. 
 Solifluxion, 153, 157. 
 Sonklar, cited, 386. 
 Spallanzani, cited, 115. 
 Spatter cones, 104. 
 Speculative philosophy vs. observational 
 
 geology, 5. 
 
 Spencer, J. W., cited, 260, 344, 350, 353, 
 
 366. 
 Spethmann, H., cited, 267. 
 Sphalerite, 453. 
 Spherulites, 33. 
 Spherulitic texture, of igneous rocks, 
 
 33. 
 Sphinx, erosion by natural sand blast, 
 
 205. 
 Spits, 240. 
 Spitzbergen, 154. 
 Springs, fissure, 190, 195 ; surface, 181 ; 
 
 thermal, 190. 
 Stability, not the order of nature, 4. 
 Stacks, 233 ; elevated, 249, 343. 
 Stage of adolescence, 169, 170. 
 Stairway, cascade, 376. 
 Stalactites, growth of, 184. 
 Stalagmites, formation of, 185. 
 Staurolite, 460. 
 Steppes, 215. 
 Still river, of Connecticut, history of, 
 
 338. 
 Stone, G. -H., cited, 253, 260, 315, 
 
 319. 
 "Stone ginger," 208. 
 "Stone lattice," 205, 206. 
 "Stone rivers," 153. 
 Strahan, A., cited, 318. 
 Strand lakes, 424. 
 Strata, conformable, 51 ; contortions of, 
 
 40. 
 Straths, 428. 
 Streak, of minerals, 451. 
 Stream capture, 179. 
 Stream, meandering, cross section of, 
 
 163; braided, 280; intermittent, 
 
 180. 
 Stream velocity, determined by gradient, 
 
 158. 
 Strike, 46. 
 
 Striped ground, 154. 
 Strokr, 193. 
 
 Strombolian eruptions, 117. 
 Stromboli, cinder cone of, 115; ex- 
 centric crater of, 115; explanation of 
 
 eruptions in, 116, 117. 
 Structure, cross-bedded, 37. 
 Submerged channels, of rivers, 252. 
 Submergence of land, during earth- 
 quakes, 80. 
 Suess, E., cited, 19, 142, 259, 277, 425, 
 
 436, 437, 438, 446. 
 Suffioni, arrangement on faults, 87. 
 Supan, A., 420, 424. 
 Surface moraines, 277. 
 Surface springs, 181. 
 "Swallow holes," 182, 422. 
 
504 
 
 INDEX 
 
 Swamp lands, drained during earth- 
 quakes, 83. 
 Sweinfurth, G., cited, 222. 
 Syenite, 462. 
 
 Symbols, T., to express strike and dip, 48. 
 Synclinal folds, 42. 
 Synclines, 42. 
 System of fractures, 55. 
 
 Taal volcano, double explosive eruption 
 
 of 1911, 120, 121. 
 Table mountains, origin of, 112. 
 Takyr, 216. 
 Talc, 460. 
 Talc schist, 465. 
 Talmage, J. E., cited, 221. 
 Talus, 152, 153, 215. 
 Tangier-Smith, W. S., cited, 260. 
 Tarr, R. S., cited, 77, 92, 233, 260, 295, 
 
 301. 
 Taylor, F. B., cited, 259, 330, 339, 342, 
 
 343, 346, 350, 355, 366. 
 Tectonic lakes, 424. 
 Temperature, diurnal changes of, in 
 
 deserts, 202. 
 Temple of Jupiter Serapis, oscillations of 
 
 level of, 254, 255. 
 Terminal moraine, of Pleistocene glacia- 
 
 tions, 298, 299. 
 Terminal moraines, of mountain glaciers, 
 
 394. 
 Terraced valleys, 320, 321. 
 Terraces, built, 235; coast, 80, 235, 
 
 341 ; river, 165, 178, 320, 321 ; rock, 
 
 215. 
 Terra Rossa, of Karst region, 188. 
 Tessellated pavement, from soil flow, 
 
 154. 
 Tethys, ocean of, 16. 
 Tetrahedron, reciprocal relations of an- 
 tipodal parts, 13 ; truncated, toward 
 
 which earth is tending, 12. 
 Tetrahedrons, twin, 16. 
 Thaw water, soil flow in presence of, 
 
 153. 
 Theory, evolved from working hypoth- 
 esis, 6 ; mixture with observation, on 
 
 maps, 63. 
 Thermal springs, 190. 
 Thickness of formations, 65. 
 Thompson, Bertha, cited, 155. 
 Thomson and Tait, cited, 29. 
 Thomson, Wyville, cited, 296. 
 Thoroddsen, Th., cited, 103, 123, 147, 
 
 267. 
 Throw, on faults, 59. 
 Thrusts, 45. 
 "Tidal waves," 70. 
 
 Tides, effect on a fluid earth, 20. 
 
 Tidewater glaciers, 290, 386. 
 
 Till, 31, 310. 
 
 Tillite, 31. 
 
 Till plains, 311. 
 
 Tinds, 380, 381. 
 
 Tivoli, travertine of, 184. 
 
 Tombolas, 241. 
 
 Tongues, ice, on margin of continental 
 glaciers, 272. 
 
 Topographic maps, 61 ; preparation of, 
 467. 
 
 Topography, built up, 301 ; construc- 
 tional, 309 ; destructional, 309 ; fault, 
 65 ; fold, 65 ; incised, 301 ; knob and 
 basin, 314. 
 
 Top-set beds, 167. 
 
 Tourmaline, 460. 
 
 Tower, W. S., cited, 178. 
 
 Trachyte, 463. 
 
 Transgression, of the sea, 37. 
 
 Transparency, of minerals, 451. 
 
 Travertine, 184, 464. 
 
 Trees, how affected by advancing lava, 
 133 ; undermined on stream meanders, 
 164. 
 
 "Trellis drainage," 175. 
 
 Troughline, of a syncline, 42. 
 
 Trunk channels of descending water, 
 181. 
 
 Tsunamis, 70. 
 
 T symbols, to express strike and dip, 
 48. 
 
 Tufa, calcareous, 464. 
 
 Tunnels, lava. 111, 112, 125. 
 
 Twin tetrahedrons, 16. 
 
 Tyndall, John, cited, 192, 196. 
 
 Udden, J. A., cited, 222. 
 
 Unconformable series, 51. 
 
 Unconformity, 65 ; episodes in history 
 of, 52; meaning of, 51. 
 
 Underfolding, of earth's shell, 437. 
 
 Underground water, 180. 
 
 Undertow, 236. 
 
 Unstable erosion remnants, in "driftless 
 area," 300. 
 
 Upham, Warren, cited, 325, 327, 339, 
 344, 350. 
 
 Upland, fretted, 372, 373 ; grooved, 372, 
 373 ; maturely dissected, 170 ; ma- 
 ture, unfavorable to commercial de- 
 velopment, 171 ; newly incised, 169 ; 
 partially dissected, 160 ; progressive 
 investment of, by cirques, 374. 
 
 Uplift, marks of, on coasts, 245 ; sudden, 
 of coasts, 247. 
 
 Upraised cliffs, 249. 
 
INDEX 
 
 505 
 
 Uptilt, in basin of Lake Agassiz, 350 ; 
 of glaciated area, evidence that it 
 continues, 348-350 ; of glaciated area, 
 supposed nature of, 344-347. 
 
 U-shaped valleys, 374. 
 
 Usu-san (New Mountain), birth of, 96. 
 
 Valley moraine lakes, 400, 413. 
 
 Valleys, hanging, 378; of V-form, 172;. 
 U-shaped, 374. 
 
 Valley trains, 311, 399. 
 
 Van Hise, C. R., cited, 54. 
 
 Varnish, desert, 201. 
 
 Veatch, A. C, cited, 418, 425. 
 
 Verbeek, R. D. M., cited, 100, 142, 147, 
 148. 
 
 Vesicular texture, of extrusive rocks, 
 32. 
 
 Victoria Falls, 225. 
 
 Vincentius of Beauvais, cited, 9. 
 
 Volcanic ash, 122. 
 
 "Volcanic bombs," 121. 
 
 Volcanic dust, 122. 
 
 Volcanic eruptions, during changes in 
 earth's figure, 15. 
 
 Volcanic lakes, 424. 
 
 Volcanic mountains, of ejected materials, 
 115; of exudation, 94. 
 
 Volcanic necks, 140. 
 
 Volcanic pipes, 140. 
 
 Volcanic plugs, 139, 140. 
 
 Volcanic projectiles, 121. 
 
 Volcanic rocks, 32. 
 
 Volcanic sand, 122. 
 
 Volcano belts, of the earth, 98. 
 
 Volcano, definition of, 95. 
 
 Volcano, eruption in 1888, 118, 120, 147; 
 history of, 118, 119. 
 
 Volcanoes, active, 97 ; arrangement over 
 fissures, 99 ; birth of, 96 ; cone-pro- 
 ducing period of, 127 ; convulsive 
 eruptions of, 105 ; crater-producing 
 period of, 128 ; dissection of, 139, 148 ; 
 dormant, 97 ; early views concerning, 
 95; "elevation-crater" theory of, 95; 
 explosive eruptions of, 105 ; extinct, 
 97 ; fissure eruptions of, 101 ; location 
 at fissure intersections, 100 ; map of, 
 in Java, 100 ; migration of vent along 
 fissure, 101, 124; misconceptions con- 
 cerning, 94 ; mud flows after eruptions, 
 138 ; of Gulf of Guinea, 101 ; regarded 
 as retaining walls, 124, 125 ; relation 
 to mountain ranges, 144; sequence of 
 events within chimney of, during erup- 
 tion, 134, 135 ; solfataric activity of, 
 97 ; three types of, 105. 
 
 V-shaped valley, 172. 
 
 Vulcanello, 119. 
 
 Vulcanian eruptions, 117, 125. 
 
 Waltershausen, S. von, cited, 148. 
 
 Walther, Johannes, cited, 201, 202, 203, 
 204, 205, 206, 211, 215, 221. 
 
 Wandering dunes, 209. 
 
 Warren river, 416. 
 
 "Washes," 213. 
 
 Water, derangement of flow during earth - 
 quakes, 83 ; ground, 180 ; percolat- 
 ing, role of, 149 ; running, earth fea- 
 tures shaped by, 169 ; shot up in 
 sheets during earthquake, 83 ; thaw, 
 soil flow in presence of, 153. 
 
 Water gaps, 176. 
 
 Water pipes, buckled in ground, during 
 earthquakes, 75. 
 
 Water table, 180 ; extreme depth of, 
 201, 203. 
 
 Water wave, effect of breaking on shore, 
 233 ; free, 232 ; motion of, 231. 
 
 Watson, T. L., cited, 259. 
 
 Wave, water, the motion of, 231. 
 
 Wave base, 232. 
 
 Wave length, 231. 
 
 Weathering, carbonization, 151 ; chemi- 
 cal, 149 ; chemical agents of, 149 ; 
 dry, 201 ; exfoliation, 151 ; frost 
 action, 152 ; hydration, 151 ; in rela- 
 tion to climate, 150 ; internal, in 
 deserts, 201 ; mechanical, 149 ; of 
 lithosphere surface, 29 ; shadow, 203 ; 
 spheroidal, 150, 151 ; two contrasted 
 processes of, 149. 
 
 Wed (Wadi), 212, 213, 214. 
 
 Weed, W. H., cited, 196, 441, 447. 
 
 West Indies, seismotectonic lines of, 
 88. 
 
 Wheeler, W. H., cited, 244. 
 
 Whirlpool basin, at Niagara, 359; exca- 
 vation of, 360. 
 
 Whitbeck, R. H., cited, 319. 
 
 White, David, cited, 318. 
 
 Willis, Bailey, cited, 45, 54, 157, 260, 
 318 
 
 Winchell, N. H., cited, 354. 
 
 Wind, in relation to location of glaciers, 
 377 ; in relation to mountain glaciers, 
 367. 
 
 Wind distribution of snow, 367. 
 
 Wind gaps, 176. 
 
 Windka7iten, 205. 
 
 Wind poles, of the earth, 263 ; of earth, 
 earlier, 297. 
 
 Wintergreen Flats, site of captured fall, 
 358. 
 
 Wisconsin diamonds, 307, 308. 
 
506 
 
 INDEX 
 
 Woodworth, J. B., cited, 74, 351. 
 Worcester, Dean C, cited, 96. 
 Working hypothesis, 6. 
 Workman, Fanny Bullock, cited, 294. 
 Workman, W. H., cited, 294. 
 Wright, F. E., cited, 351. 
 
 Yellowstone National Park, 33, 191, 193, 
 
 194. 
 Yosemite Valley, 59, 152. 
 Young rivers, 159, 160. 
 
 Zahn, G. W. von, cited, 244. 
 
 Zigzag ranges, due to plunging folds^ 
 
 51. 
 Zittel, K. v., cited, 19. 
 Zone of diverse displacement, 439. 
 Zone of flow, 40, 143. 
 Zone of fracture, 40, 46. 
 Zones, of deposition, surrounding desert, 
 
 216, 217 ; upper and lower cloud, 268,. 
 
 269. 
 
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