Chapter I: 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 landscape 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 place for such a cultural study of geology within the University is believed to be shown by the increasing number of students who have elected the 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 Rhine, 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 character 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 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.

Regarded 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 historical division apart from the others. Again, a desire to treat the science of geology comprehensively has led some authors into including so many subjects as to render their texts unnecessarily encyclopedic and correspondingly uninteresting to the general 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 illustrate the readings by travels afield, which accounts for the prominence 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 glaciations.

Emphasis has also been placed upon the dependence of the dominant geological processes of any region upon existing climatic conditions, 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. 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 professional geologist to detect these new strands which have been drawn into the web.

WILLIAM HERBERT HOBBS.

ANN ARBOR, MICHIGAN,
October 25, 1911.

CONTENTS

CHAPTER I

THE COMPILATION OF EARTH HISTORY

PAGE

The sources of the history—Subdivisions of geology—The
study of earth features and their significance—Tabular
recapitulation—Geological processes not universal—Change, and not
stability, the order of nature—Observational geology _versus_
speculative philosophy—The scientific attitude and temper—The
value of the hypothesis—Heading references 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 _versus_ geodetic
observations—Changes of figure during contraction of a spherical
body—The earlier figures of the earth—The continents and
oceans at the close of the Paleozoic era—The flooded portions
of the present continents—The floors of the hydrosphere and
atmosphere—Reading references 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 surface shell—The essential nature of crystals—The
lithosphere a complex of interlocking crystals—Some properties of
natural crystals, minerals—The alterations of minerals—Reading
references 20

CHAPTER IV

THE ROCKS OF THE EARTH’S SURFACE SHELL

The processes by which rocks are formed—The marks of origin—The
metamorphic rocks—Characteristic textures of the igneous
rocks—The classification of rocks—Subdivisions of the sedimentary
rocks—The different deposits of 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—Reading references 30

CHAPTER V

CONTORTIONS OF THE STRATA WITHIN THE ZONE OF FLOW

The zones of fracture and flow—Experiments which illustrate
the fracture and flow of solid bodies—The arches and troughs
of the folded strata—The elements of folds—The shapes of rock
folds—The overthrust fold—Restoration of mutilated folds—The
geological map and section—Measurement of the thickness of
formations—The detection of plunging folds—The meaning of an
unconformity—Reading references 40

CHAPTER VI

THE ARCHITECTURE OF THE FRACTURED SUPERSTRUCTURE

The system of the fractures—The space intervals of joints—The
displacements 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: EARTHQUAKES AND
SEAQUAKES

Nature of earthquake shocks—Seaquakes and seismic sea waves—The
grander and the lesser earth movements—Changes in the earth’s
surface during 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: EARTHQUAKES 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

CHAPTER IX

THE RISE OF MOLTEN ROCK TO THE EARTH’S SURFACE; VOLCANIC
MOUNTAINS OF EXUDATION

Prevalent misconceptions about volcanoes—Early views concerning
volcanic mountains—The birth of volcanoes—Active and extinct
volcanoes—The earth’s volcano belts—Arrangement of volcanic
vents along 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 cinder 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
Pelé—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 rôle 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 mantle 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 contrasted—The balance between degradation and
aggradation—The accordance of tributary valleys—The grading of
the flood plain—The cycles of stream meanders—The cut-off of the
meander—Meander scars—River terraces—The delta of the river—The
levee—The sections of delta deposits 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 Hogarthian 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 references 169

CHAPTER XIV

THE TRAVELS OF THE UNDERGROUND WATER

The descent within the unsaturated zone—The trunk channels
of descending water—The caverns of limestones—Swallow holes
and limestone sinks—The sinter deposits—The growth of
stalactites—Formation of stalagmites—The Karst and its features—A
desert from the destruction of forests—The ponore and the
polje—The return of the water to the surface—Artesian wells—Hot
springs and geysers—The deposition of siliceous sinter by plant
growth—Reading references 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 weathering:
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

CHAPTER XVII

REPEATING PATTERNS IN THE EARTH RELIEF

The weathering processes under control of the fracture system—The
fracture control of the drainage lines—The repeating pattern in
drainage networks—The dividing lines of the relief patterns:
lineaments—The composite repeating patterns of the higher
orders—Reading references 223

CHAPTER XVIII

THE FORMS CARVED AND MOLDED BY WAVES

The motion of a water wave—Free waves and breakers—Effect
of the breaking wave upon a 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 barrier—The land-tied island—A barrier series—Character
profiles—Reading references 231

CHAPTER XIX

COAST RECORDS OF THE RISE OR FALL OF THE LAND

The characters in which the record has been preserved—Even
coast line the mark of uplift—A ragged coast line the mark of
subsidence—Slow uplift of the 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 movements 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 mountain barriers in initiating glaciers—Sensitiveness of
glaciers to temperature changes—The cycle of glaciation—The
advancing hemicycle—Continental and mountain glaciers
contrasted—The nourishment of glaciers—The upper and lower cloud
zones of the atmosphere 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 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—Drumlins—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
blocking—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 Hudson’s Bay
drainage basin—Reading references 320

CHAPTER XXIV

THE UPTILT OF THE LAND AT THE CLOSE OF THE ICE AGE

The response of the earth’s shell to its ice mantle—The
abandoned strands as they appear to-day—The records of uplift
about Mackinac Island—The present inclinations of the uplifted
strands—The hinge lines of uptilt—Future consequences of the
continued uptilt within the lake region—Gilbert’s prophecy of a
future outlet of the Great Lakes to the Mississippi—Geological
evidences of continued uplift—Drowning of southwestern shores of
Lakes Superior and Erie—Reading references 340

CHAPTER XXV

NIAGARA FALLS A CLOCK OF RECENT GEOLOGICAL TIME

Features in and about the Niagara gorge—The drilling of the
gorge—The present rate of recession—Future extinction of the
American Fall—The captured Canadian Fall at Wintergreen Flats—The
Whirlpool Basin excavated from the St. David’s gorge—The shaping
of the Lewiston Escarpment—Episodes of Niagara’s history and
their correlation with those of the glacial lakes—Time measures
of the Niagara clock—The horologe of late glacial time in
Scandinavia—Reading references 352

CHAPTER XXVI

LAND SCULPTURE BY MOUNTAIN GLACIERS

Contrasted sculpturing of continental and mountain glaciers—Wind
distribution of the snow which falls in mountains—The niches
which form on snowdrift sites—The augmented snowdrift moves
down the valley: birth of the glacier—The excavation of the
glacial amphitheater or cirque—Life history of the cirque—Grooved
and fretted uplands—The features carved above the glacier—The
features shaped beneath the glacier—The cascade stairway in
glacier-carved valleys—The character profiles which result from
sculpture by mountain glaciers—The sculpture accomplished by ice
caps—The Norwegian tind or beehive mountain—Reading references 367

CHAPTER XXVII

SUCCESSIVE GLACIER TYPES OF A WANING GLACIATION

Transition from the ice cap to the mountain glacier—The piedmont
glacier—The expanded-foot glacier—The dendritic glacier—The
radiating glacier—The horseshoe glacier—The inherited-basin
glacier—Summary of types of mountain glacier—Reading references 383

CHAPTER XXVIII

THE GLACIER’S SURFACE FEATURES AND THE DEPOSITS UPON ITS BED

The glacier flow—Crevasses and séracs—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

CHAPTER XXIX

A STUDY OF LAKE BASINS

Fresh water and saline lakes—Newland lakes—Basin-range
lakes—Rift-valley lakes—Earthquake lakes—Crater lakes—Coulée
lakes—Morainal lakes—Pit lakes—Glint or colk lakes—Ice-dam
lakes—Glacier-lobe lakes—Rock-basin lakes—Valley moraine
lakes—Landslide lakes—Border lakes—Ox-bow lakes—Saucer
lakes—Crescentic levee lakes—Raft lakes—Side-delta lakes—Delta
lakes—Barrier lakes—Dune lakes—Sink lakes—Karst lakes:
_poljen_—Playa lakes—Salines—Alluvial-dam lakes—Résumé—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 rôle of lakes in the economy of nature—Ice ramparts
on lake shores—Reading references 426