Transcriber's Note
Italic text is denoted by _underscores_ and bold text by =equal signs=.
Whole and partial numbers are displayed as 2-1/2.
[Illustration: Photo, Ridge Studio; Courtesy Ogden Chamber of
Commerce]
_A great ledge in Ogden Canyon near Ogden, Utah. The rock, still
retaining its stratification, was deposited layer upon layer
horizontally mostly as sand upon the floor of a sea which covered the
region fully 25,000,000 years ago. That the sea was of very early
Paleozoic (i.e., Cambrian) age has been proved by fossils in associated
strata. Long after their deep burial and consolidation within the
earth, the strata were subjected to tremendous mountain-making
pressure, notably altered to a rock called "Quartzite," raised high
above sea level, and tilted almost vertically. Then through long ages
(millions of years) overlying rocks of great thickness have been cut
away (eroded) by weathering and stream action, laying bare the ledge as
we see it to-day._
Popular Science Library
EDITOR-IN-CHIEF
GARRETT P. SERVISS
AUTHORS
WILLIAM J. MILLER HIPPOLYTE GRUENER A. RUSSELL BOND
D. W. HERING LOOMIS HAVEMEYER ERNEST G. MARTIN
ARTHUR SELWYN-BROWN ROBERT CHENAULT GIVLER
ERNEST INGERSOLL WILFRED MASON BARTON
WILLIAM B. SCOTT ERNEST J. STREUBEL
NORMAN TAYLOR DAVID TODD
CHARLES FITZHUGH TALMAN
ROBIN BEACH
ARRANGED IN SIXTEEN VOLUMES
WITH A HISTORY OF SCIENCE, GLOSSARIES
AND A GENERAL INDEX
_ILLUSTRATED_
[Illustration]
VOLUME THREE
P. F. COLLIER & SON COMPANY
NEW YORK
Copyright 1922
By P. F. Collier & Son Company
MANUFACTURED IN U. S. A.
GEOLOGY
The Science of the Earth's Crust
BY
WILLIAM J. MILLER
Professor of Geology, Smith College
[Illustration]
P. F. COLLIER & SON COMPANY
NEW YORK
PREFACE
In the preparation of this book the author has attempted to present, in
popular form, the salient points of a general survey of the whole great
science of geology, the science which deals with the history of the
earth and its inhabitants as revealed in the rocks.
The use of technical and unusual terms has been reduced to a minimum
compatible with a reasonable understanding of the subject by the
layman. Each of the relatively few scientific terms is explained where
first used in the text, and a glossary of common geological terms has
been appended.
The matter of illustrations has received very careful attention, and
only pictures, maps, and diagrams are used which actually illustrate
important features of the text. A special point has been made to
introduce only cuts of simple construction comparatively free from
technicalities. Nearly every illustration is accompanied by a really
explanatory title.
A number of the pictures are from the author's collection of
photographs, and many of the line-cuts have either been made or
considerably modified by the author. Among the numerous sources of
illustrations, special mention should be made of the United States
Geological Survey, the New York State Museum, the American Museum
of Natural History, the University of Chicago Press, and various
individuals, full credit being given wherever due.
William J. Miller.
Northampton, Mass.
CONTENTS
CHAPTER PAGE
I. Introduction 9
II. Weathering and Erosion 22
III. Stream Work 30
IV. The Sea and Its Work 51
V. Glaciers and Their Work 59
VI. The Action of Wind 71
VII. Instability of the Earth's Crust 76
VIII. Volcanoes and Igneous Rocks 99
IX. Waters Within the Earth 113
X. How Mountains Come and Go 130
XI. A Study of Lakes 142
XII. How the Earth May Have Originated 158
XIII. Very Ancient Earth History 164
XIV. Ancient Earth History 179
XV. Medieval Earth History 208
XVI. Modern Earth History 221
XVII. Evolution of Plants 249
XVIII. Geological History of Animals (Excluding
Vertebrates) 259
XIX. Geological History of Vertebrate Animals
(Including Man) 281
XX. Mineralogy 307
XXI. Economic Geology 342
Glossary of Common Geological Terms 377
LIST OF ILLUSTRATIONS
Ledge of Rock with Nearly Vertical Strata _Frontispiece_
PLATE FACING PAGE
1 Granite Weathering to Soil Leaving Residual
Cores of Joint Blocks (_Upper picture_) 32
Looking-Glass Rock, Utah. Stratified Sandstone
Sculptured by Wind Erosion (_Lower picture_) 32
2 Grand Canyon of the Yellowstone River. A
Channel Worn by Erosion 33
3 Gorge of the Niagara River Below the Falls.
A Sample of Recent Erosion 64
4 Winding Stream in the St. Lawrence Valley
with Flood Plain (_Upper picture_) 65
Davidson Glacier, Alaska, Showing Action on
the Valley's Walls and Floor (_Lower picture_) 65
5 Swift Current Valley in Glacier National
Park, Formed by Stream and Glacier Action 96
6 Yosemite Valley from Western Entrance. The
Result of Glacial Action 97
7 An Upbend Fold or Anticline in Maryland 128
8 Ledge of Igneous Rock Showing Joints
(_Upper picture_) 129
Fault Fracture in Limestone Formations
(_Lower pictures_) 129
9 Molten Lava Flowing Over a Cliff in Hawaii
(_Upper picture_) 160
Dikes of Granite Cutting Old Rock
(_Lower picture_) 160
10 Lassen Peak, California, in Eruption
(_Left picture_) 161
Devil's Tower, Wyoming, Once a Mass of Molten
Rock Forced Through Strata (_Right picture_) 161
11 Mammoth Hot Springs Terrace in Yellowstone
National Park (_Upper picture_) 224
Crater Lake, Oregon, Formed by the Subsidence
of a Volcano (_Lower picture_) 224
12 Archeozoic Rock, Oldest Known Rock Formation
on Earth (_Upper picture_) 225
Twisted Mass of Stratified Limestone, Surrounded
by Granite (_Lower picture_) 225
13 Paleozoic Rock, Covered with Oldest Known
Animal Remains 256
14 "Stone-Lily" Stems in Ordovician Strata (_Upper
left picture_) 257
Various Brachiopods in Ordovician Strata (_Upper
right picture_) 257
Stratified Limestone of Middle Ordovician Era
Containing Fossils (_Lower picture_) 257
15 A Landscape of the Coal Age (_Upper picture_) 288
Fossil Fern on a Piece of Shale (_Lower picture_) 288
16 Restoration of Huge Animals of the Mesozoic Era 289
17 Skeleton of Two-Legged Carnivorous Dinosaur
(_Large picture_) 320
Earliest Known Bird Form (_Insert_) 320
18 Skeleton of Large Flying Reptile (_Upper picture_) 321
Skeleton of a Swimming Reptile of the Mesozoic
Era (_Lower picture_) 321
19 Appalachians Along New River, Peneplain Upraised Again 352
20 Glacial Bowlder Left by Ice Sheet (_Upper picture_) 353
Esker, Deposited by a Stream in the Great
Glacier (_Lower picture_) 353
CHAPTER I
INTRODUCTION
Earth features are not fixed. The person of ordinary intelligence,
surrounded as he is by a great variety of physical features, is, unless
he has devoted some study to the subject, very likely to regard those
features as practically unchangeable, and to think that they are now
essentially as they were in the beginning of the earth's history. Some
of the most fundamental ideas taught in this book are that the physical
features of the earth, as we behold them to-day, represent but a single
phase of a very long-continued history; that significant changes
are now going on all around us; and that we are able to interpret
present-day earth features only by an understanding of earth changes in
the past.
_Geology_, meaning literally "earth science," deals with the history of
the earth and its inhabitants as revealed in the rocks. The science is
very broad in its scope. It treats of the processes by which the earth
has been, and is now being, changed; the structure of the earth; the
stages through which it has passed; and the evolution of the organisms
which have lived upon it.
_Geography_ deals with the distribution of the earth's physical
features, in their relation to one another, to the life of sea and
land, and human life and culture. It is the present and outward
expression of geological effects.
As a result of the work of many able students of geology during the
past century and a quarter, it is now well established that our planet
has a definitely recorded history of many millions of years, and that
during the lapse of those eons, revolutionary changes in earth features
have occurred, and also that there has been a vast succession of
living things which, from very early times, have gradually passed from
simple into more and more complex forms. The physical changes and the
organisms of past ages have left abundant evidence of their character,
and the study of the rock formations has shown that within them we have
a fairly complete record of the earth's history. Although very much yet
remains to be learned about this old earth, it is a remarkable fact
that man, through the exercise of his highest faculty, has come to know
so much concerning it.
The following words, by the late Professor Barrell, admirably summarize
the significance of geological history. "The great lesson taught by the
study of the outer crust is that the earth mother, like her children,
has attained her present form through ceaseless change, which marks
the pulse of life and which shall cease only when her internal forces
slumber and the cloudy air and surf-bound ocean no more are moving
garments. The flowing landscapes of geologic time may be likened to a
kinetoscopic panorama. The scenes transform from age to age, as from
act to act; seas and plains and mountains of different types follow and
replace each other through time, as the traveler sees them succeed each
other in space. At times the drama hastens, and unusual rapidity of
geologic action has, in fact, marked those epochs since man has been
a spectator upon the earth. Science demonstrates that mountains are
transitory forms, but the eye of man through all his lifetime sees no
change, and his reason is appalled at the conception of a duration so
vast that the milleniums of written history have not accomplished the
shifting of even one of the fleeting views which blend into the moving
picture."[A]
[A] Central Connecticut in the Geologic Past, pp. 1-2.
Or in the words of Tennyson:
There rolls the deep where grew the tree.
O, earth, what changes hast thou seen!
There where the long street roars, hath been
The stillness of the central sea.
The hills are shadows, and they flow
From form to form, and nothing stands;
They melt like mist, the solid lands,
Like clouds they shape themselves and go.
The following statement of some of the more definite important
conclusions regarding earth changes may serve to make still clearer the
general scope of the science of geology. The evidences upon which these
conclusions are based are discussed in various parts of this book. For
untold millions of years the rocks at and near the earth's surface
have been crumbling; streams have been incessantly sawing into the
lands; the sea has been eating into continental masses; the winds have
been sculpturing desert lands; and, more intermittently and locally,
glaciers have plowed through mountain valleys, and even great sheets of
ice have spread over considerable portions of continents. Throughout
geologic time, the crust of the earth has shown marked instability.
Slow upward and downward movements of the lands relative to sea level
have been very common, in many cases amounting to even thousands of
feet. Various parts of the earth have been notably affected by sudden
movements (resulting in earthquakes) along fractures in the outer
crust. During millions of years molten materials have, at various
times, been forced into the earth's crust, and in many cases to its
surface. Mountain ranges have been brought forth and cut down. The site
of the Appalachian Mountains was, millions of years ago, the bottom of
a shallow sea. Lakes have come and gone. The Great Lakes have come into
existence very recently (geologically), that is to say, since the great
Ice Age. A study of stratified rocks of marine origin shows that all,
or nearly all, of the earth's surface has at some time, or times, been
covered by sea water. Over certain districts the sea has transgressed
and retrogressed repeatedly. Organisms have inhabited the earth for
many millions of years. In earlier known geologic time, the plants and
animals were comparatively simple and low in the scale of organization,
and through the succeeding ages higher and more complex types were
gradually evolved until the highly organized forms of the present time,
including the human race, were produced.
The rocks of the earth constitute the special field of study for the
geologist because they contain the records of events through which the
earth and its inhabitants have passed during the millions of years of
time until their present conditions have been reached. All the rocks of
the earth's crust may be divided into three great classes: _igneous_,
_sedimentary_, and _metamorphic_.
_Igneous_ rocks comprise all those which have ever been in a molten
condition, and of these we have the _volcanic_ rocks (for example,
lavas), which have cooled at or near the surface; _plutonic_ rocks (for
example, granites), which have cooled in great masses at considerable
depths below the surface; and the _dike_ rocks which, when molten, have
been forced into fissures in the earth's crust and there cooled.
_Sedimentary_ rocks comprise all those which have been deposited under
water, except some wind-blown deposits, and they are nearly always
arranged in layers (stratified). Such rocks are called strata. They may
be of mechanical origin such as clay or mud which hardens to _shale_;
sand, which consolidates into _sandstone_; and gravel, which when
cemented becomes _conglomerate_. They may be of organic origin such as
limestone, most of which is formed by the accumulation of calcareous
shells; _flint_ and _chert_, which are accumulations of siliceous
shells; or _coal_, which is formed by the accumulation of partly
decayed organic matter. Or, finally, they may be formed by chemical
precipitation, as beds of _salt_, _gypsum_, _bog iron ore_, etc.
_Metamorphic_ rocks include both sedimentary and igneous rocks which
have been notably changed from their original condition. Traces or
remains of plants and animals preserved in the rocks are known as
fossils. The term originally meant anything dug out of the earth,
whether organic or inorganic, but for many years it has been strictly
applied to organic remains. Many thousands of species of fossils are
known from rocks of all ages except the oldest, and more are constantly
being brought to light, but these represent only a small part of
the life of past ages because relatively few organic remains were
deposited under conditions favorable for preservation in fossil form.
The fossils in the rocks are, however, a fair average of the groups of
organisms to which they belong. It is really remarkable that such a
vast number of fossils are imbedded in the rocks, and from a study of
these many fundamental conclusions regarding the history of life on our
planet may be drawn.
As early as the fifth century B. C., Xenophanes is said to have
observed fossil shells and plants in the rocks of Paros, and to
have attributed their presence to incursions of the sea over the
land. Herodotus, about a century later, came to a similar conclusion
regarding fossil shells in the mountains of Egypt. None of the
ancients, however, seemed to have the slightest conception of the
significance of fossils as time markers in the history of the earth.
(See discussion below.)
In the Middle Ages, distinguished writers held curious views regarding
fossils. Thus Avicenna (980-1037) believed that fossils represented
unsuccessful attempts on the part of nature to change inorganic
materials into organisms within the earth by a peculiar creative force
(_vis plastica_). About two centuries later, Albertus Magnus held
a somewhat similar view. Leonardo da Vinci (1452-1519), the famous
artist, architect, and engineer, while engaged in canal building in
northern Italy, saw fossils imbedded in the rocks, and concluded
that these were the remains of organisms which actually lived in
sea water which spread over the region. During the seventeenth and
eighteenth centuries, many correctly held that fossils were really
of organic origin, but it was commonly taught that all fossils
represented remains of organisms of an earlier creation which were
buried in the rocks during the great Deluge (Noah's Flood). William
Smith (1769-1839), of England, was, however, the first to recognize
the fundamental significance of fossils for determining the relative
ages of sedimentary rocks. This discovery laid the foundation for the
determination of earth chronology which is of great importance in the
study of the history of the earth. (See discussions below.)
Organic remains, dating as far back as tens of millions of years, have
been preserved in the rocks of the earth in various ways. A very common
kind of fossilization is the preservation of only the hard parts of
organisms. Thus the soft parts have disappeared by decomposition, while
the hard parts, such as bones, shells, etc., remain. In many cases
practically complete skeletons of large and small animals which lived
millions of years ago have been found intact in the rocks. Fossils
which show none of the original material, but only the shape or form,
are also very abundant. When sediment hardens around an imbedded
organism, and the organism then decomposes or dissolves away, a cavity
or fossil mold only is left. Casts of organisms or parts of them are
formed by filling shells or molds with sediment or with mineral matter
carried in solution by underground water. Only rarely have casts of
wholly soft animals been found in ancient rocks. In other cases both
original form and structure are preserved, but none of the original
material. This is known as petrifaction which takes place when a plant
or hard part of an animal has been replaced, particle by particle,
by mineral matter from solution in underground water. Not uncommonly
organic matter, such as wood, or inorganic matter, such as carbonate
of lime shells, has been so perfectly replaced that the original
structures are preserved almost as in life. The popular idea that
petrified wood is wood which has been changed into stone is, of course,
incorrect. It is doubtful if flesh has ever been truly petrified. In
many cases mainly the carbon only of organisms has been preserved.
This is also true of plants where, under conditions of slow chemical
change or decomposition, the hydrogen and oxygen mostly disappear,
leaving much of the carbon with original structures often remarkably
preserved. Fine examples are fossil plants in the great coal-bearing
strata. Much more rarely entire organisms have been preserved either
by freezing or by natural embalmment. Most remarkable are the species
of mammoths and rhinoceroses, extinct for thousands of years, bodies
of which, with flesh, hide, and hair still intact, have been held in
cold storage in the frozen soils of Siberia, or other cases. Insects
have been perfectly preserved in amber, as, for example, in the Baltic
region. This amber is a hardened resin in which the insects were
caught while it was still soft and exuding from the trees. Finally, we
should mention the preservation of tracks and trails of land and water
animals. Thousands of tracks of long-extinct great reptiles occur in
the sandstones and shales of the Connecticut Valley of Massachusetts.
The footprints were made in soft sandy mud which hardened and then
became covered with more sediment.
Few fossils occur in other than the sedimentary rocks. Most numerous,
by far, are fossils in rocks of marine origin, because on relatively
shallow sea bottoms, where sediments of the geologic ages have
largely accumulated, the conditions for fossilization have been
most favorable. Among the many conditions which have produced great
diversity in numbers and distribution of marine organisms during
geologic time are temperature, depth of water, clearness of water,
nature of sea bottom, degree of salinity, and food supply. River
and lake deposits also not uncommonly contain remains of organisms
which inhabited the waters, but also others which were carried in.
"Surrounding trees drop their leaves, flowers, and fruit upon the mud
flats, insects fall into the quiet waters, while quadrupeds are mired
in mud or quicksand and soon buried out of sight. Flooded streams bring
in quantities of vegetable debris, together with carcasses of land
animals drowned by the sudden rise of the flood" (W. B. Scott).
In the study of the many changes which have taken place in the history
of the earth, a fundamental consideration is the determination of
the relative ages of the rocks, especially the strata. How can the
geologist assign a rock formation of any part of the earth to a
particular age in the history of the earth? How can it be proved that
certain rock formations in various parts of the earth originated
practically at the same time? There are two important criteria.
First, in any region where the strata have not been disturbed from
their normal order, the older strata underlie the younger because the
underlying sediments must have been deposited first. Now, the total
thickness of the stratified series of the earth has been estimated to
be no less than 200,000 feet and only a small part of this is actually
present in any given locality or region. It is, therefore, evident
that the order of superposition of strata is in itself not sufficient
for the determination of the relative ages of all the strata in even
a considerable portion of a single continent, not to mention its utter
inadequacy in building up the geological column of the whole earth.
When, however, the second criterion, namely, the fossil content of the
strata, is used in direct connection with the order of superposition,
we have the real basis for determining the relative ages of strata for
all parts of the earth. The discovery of this method was very largely
due to the painstaking field work in England by William Smith about the
beginning of the nineteenth century.
It is a well-established fact that organisms have inhabited the earth
for many millions of years and that, through the geologic ages,
they have continuously changed, with gradual development of higher
and higher types. Tens of thousands of species have come and gone.
Accepting this fact, it is then clear that strata which were formed
at notably different times must contain notably different fossils,
while strata which accumulated at practically the same time contain
similar fossils, allowing, of course, for reasonable differences in
geographical distribution of organisms as at the present time. Each
epoch of earth history or series of strata has its characteristic
assemblage of organisms. In short, "a geological chronology is
constructed by carefully determining, first of all, the order of
superposition of the stratified rocks, and next by learning the fossils
characteristic of each group of strata.... The order of succession
among the fossils is determined from the order of superposition of
the strata in which they occur. When that succession has been thus
established, it may be employed as a general standard" (W. B. Scott).
It should, however, be borne in mind that precise contemporaneity of
strata in widely separated districts can rarely, if ever, be determined
because of the very great length of geologic time and the general
slowness of the evolution of organisms. Rocks carrying remarkably
similar fossils may really be several thousand years different in age;
but this is, indeed, a very small limit of error when one considers the
vast antiquity of the earth. Much very accurate and satisfactory work
has been done, especially in Europe and North America, in correlating
strata and assigning them to their places in the geological time table
(see below), but a vast amount of work yet remains to be done before
the task is complete.
Certain types or species of organisms are much more useful than others
in the determination of earth chronology. Best of all for world-wide
correlations are species which were widely distributed and which
persisted for relatively short times. Thus any species which lived in
the surface waters of the ocean and was easily distributed over wide
areas, while, at the same time, it existed as such only a short time,
is the best type of chronologic indicator.
The known history of the earth has been more or less definitely divided
into great eras and lesser periods and epochs, constituting what may
be called the geologic time scale. In the accompanying table the era
and period names, except those representing earlier time, are mostly
world-wide in their usage. Epoch names, being more or less locally
applied, are omitted from the table. Very conservative estimates of
the length of time represented by the eras and the most characteristic
general features of the life of the main divisions are also given.
PRINCIPAL DIVISIONS OF GEOLOGIC TIME
(Modified after U. S. Geological Survey.)
=========================================================================
| | |Millions
Era. | Period. | Characteristic life. |of years
| | |estimated
-----------+--------------+------------------------------------+---------
| |"Age of man." Animals and plants |
|Quaternary. |of modern types. |
+--------------+------------------------------------+
Cenozoic | |"Age of mammals." Rise of highest |3 to 5.
|Tertiary. |animals except man. Rise and |
| |development of highest orders of |
| |plants. |
-----------+--------------+------------------------------------+---------
| |"Age of reptiles." Rise and |
|Cretaceous. |culmination of huge land reptiles |
| |(dinosaurs), of shellfish with |
| |complexly partitioned coiled |
+--------------+shells (ammonites), and of great |
| |flying reptiles. First appearance |
Mesozoic |Jurassic. |(in Jurassic) of birds and mammals; |5 to 10.
| |of cycads, an order of palm-like |
+--------------|plants (in Triassic); and of |
| |angiospermous plants, among |
|Triassic. |which are palms and hardwood |
| |trees (in Cretaceous). |
-----------+--------------+------------------------------------+---------
| |"Age of amphibians." Dominance of |
|Permian. |club mosses (lycopods) and plants |
+--------------+of horsetail and fern types. |
| |Primitive flowering plants and |
|Pennsylvanian.|earliest cone-bearing trees. |
| |Beginnings of back-boned land |
+--------------+animals (land vertebrates). Insects.|
|Mississippian.|Animals with nautiluslike coiled |
| |shells (ammonites) and sharks |
| |abundant. |
+--------------+------------------------------------+
| |"Age of fishes." Shellfish |
|Devonian. |(mollusks) also abundant. Rise of |
| |amphibians and land plants. |
+--------------+------------------------------------|
| A {|Shell-forming sea animals dominant, |
| g {|especially those related to |
| e {|the nautilus (cephalopods). Rise |
Paleozoic | {|and culmination of the marine |17 to 25.
|Silurian. o {|animals sometimes known as sea |
| f {|lilies (crinoids) and of giant |
| {|scorpionlike crustaceans |
| I {|(eurypterids). Rise of fishes and |
| n {|of reef-building corals. |
+-----------n-{+------------------------------------+
| v {|Shell-forming sea animals, |
| e {|especially cephalopods and |
|Ordovician.r {|mollusk-like brachiopods, abundant. |
| t {|Culmination of the buglike marine |
| e {|crustaceans known as trilobites. |
+-----------b-{+------------------------------------+
| r {|Trilobites and brachiopods most |
|Cambrian. a {|characteristic animals. Seaweeds |
| t {|(algæ) abundant. No trace of |
| e {|land animals found. |
-----------+-----------s-{+------------------------------------+---------
| |First life that has left distinct |
Proterozoic|Algonkian. |record. Crustaceans, brachiopods, |
| |and seaweeds. |
-----------+--------------+------------------------------------+
| |Organic matter in form of graphite |25 to 50+
Archeozoic |Archean. |(black lead), but no determinable |
| |fossils found. |
-----------+--------------+------------------------------------+---------
The length of time represented by human history is very short compared
to the vast time of known geological history. The one is measured
by thousands of years, while the other must be measured by tens of
millions of years. Just as we may roughly divide human history into
certain ages according to some notable person, nation, principle, or
force as, for example, the "Age of Pericles," the "Roman Period,"
the "Age of the French Revolution," or the "Age of Electricity," so
geologic history may be subdivided according to great predominant
physical or organic phenomena, such as "the Appalachian Mountain
Revolution" (toward the end of the Paleozoic era), the "Age of Fishes"
(Devonian period), or the "Age of Reptiles" (Mesozoic era).
In the study of earth history, as in the study of human history, it
is important to distinguish between events and records of events.
Historical events are continuous, but they are by no means all
recorded. Records of events are often interrupted and seemingly sharply
separated from each other.