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[Illustration: _Dunes at Ipswich Light, Massachusetts. Note the
effect of bushes in arresting the movement of the wind-blown sand._]
OUTLINES OF THE
EARTH'S HISTORY
A POPULAR STUDY
IN PHYSIOGRAPHY
BY
NATHANIEL SOUTHGATE SHALER
PROFESSOR OF GEOLOGY IN HARVARD UNIVERSITY
DEAN OF LAWRENCE SCIENTIFIC SCHOOL
ILLUSTRATED WITH INDEX
NEW YORK AND LONDON
D. APPLETON AND COMPANY
1898, 1910
PREFACE.
The object of this book is to provide the beginner in the study of the
earth's history with a general account of those actions which can be
readily understood and which will afford him clear understandings as
to the nature of the processes which have made this and other
celestial spheres. It has been the writer's purpose to select those
series of facts which serve to show the continuous operations of
energy, so that the reader might be helped to a truer conception of
the nature of this sphere than he can obtain from ordinary text-books.
In the usual method of presenting the elements of the earth's history
the facts are set forth in a manner which leads the student to
conceive that history as in a way completed. The natural prepossession
to the effect that the visible universe represents something done,
rather than something endlessly doing, is thus re-enforced, with the
result that one may fail to gain the largest and most educative
impression which physical science can afford him in the sense of the
swift and unending procession of events.
It is well known to all who are acquainted with the history of geology
that the static conception of the earth--the idea that its existing
condition is the finished product of forces no longer in action--led
to prejudices which have long retarded, and indeed still retard, the
progress of that science. This fact indicates that at the outset of a
student's work in this field he should be guarded against such
misconceptions. The only way to attain the end is by bringing to the
understanding of the beginner a clear idea of successions of events
which are caused by the forces operating in and on this sphere. Of all
the chapters of this great story, that which relates to the history of
the work done by the heat of the sun is the most interesting and
awakening. Therefore an effort has been made to present the great
successive steps by which the solar energy acts in the processes of
the air and the waters.
The interest of the beginner in geology is sure to be aroused when he
comes to see how very far the history of the earth has influenced the
fate of men. Therefore the aim has been, where possible, to show the
ways in which geological processes and results are related to
ourselves; how, in a word, this earth has been the well-appointed
nursery of our kind.
All those who are engaged in teaching elementary science learn the
need of limiting the story they have to tell to those truths which can
be easily understood by beginners. It is sometimes best, as in stating
such difficult matters as those concerning the tides, to give
explanations which are far from complete, and which, as to their mode
of presentation, would be open to criticism were it not for the fact
that any more elaborate statements would most likely be
incomprehensible to the novice, thus defeating the teacher's aim.
It will be observed that no account is here given of the geological
ages or of the successions of organic life. Chapters on these subjects
were prepared, but were omitted for the reason that they made the
story too long, and also because they carried the reader into a field
of much greater difficulty than that which is found in the physical
history of the earth.
N.S.S.
_March, 1898._
CONTENTS.
CHAPTER PAGE
I.--INTRODUCTION TO THE STUDY OF NATURE 1
II.--WAYS AND MEANS OF STUDYING NATURE 9
III.--THE STELLAR REALM 31
IV.--THE EARTH 81
V.--THE ATMOSPHERE 97
VI.--GLACIERS 207
VII.--THE WORK OF UNDERGROUND WATER 250
VIII.--THE SOIL 313
IX.--THE ROCKS AND THEIR ORDER 349
LIST OF FULL-PAGE ILLUSTRATIONS.
FACING PAGE
Dunes at Ipswich Light, Massachusetts _Frontispiece_
Seal Rocks near San Francisco, California 33
Lava stream, in Hawaiian Islands, flowing into the sea 72
Waterfall near Gadsden, Alabama 90
South shore, Martha's Vineyard, Massachusetts 121
Pocket Creek, Cape Ann, Massachusetts 163
Muir Glacier, Alaska 207
Front of Muir Glacier 240
Mount Ætna, seen from near Catania 201
Mountain gorge, Himalayas, India 330
OUTLINES OF THE EARTH'S HISTORY.
CHAPTER I.
AN INTRODUCTION TO THE STUDY OF NATURE.
The object of this book is to give the student who is about to enter
on the study of natural science some general idea as to the conditions
of the natural realm. As this field of inquiry is vast, it will be
possible only to give the merest outline of its subject-matter, noting
those features alone which are of surpassing interest, which are
demanded for a large understanding of man's place in this world, or
which pertain to his duties in life.
In entering on any field of inquiry, it is most desirable that the
student should obtain some idea as to the ways in which men have been
led to the knowledge which they possess concerning the world about
them. Therefore it will be well briefly to sketch the steps by which
natural science has come to be what it is. By so doing we shall
perceive how much we owe to the students of other generations; and by
noting the difficulties which they encountered, and how they avoided
them, we shall more easily find our own way to knowledge.
The primitive savages, who were the ancestors of all men, however
civilized they may be, were students of Nature. The remnants of these
lowly people who were left in different parts of the world show us
that man was not long in existence before he began to devise some
explanation concerning the course of events in the outer world.
Seeing the sun rise and set, the changes of the moon, the alternation
of the seasons, the incessant movement of the streams and sea, and the
other more or less orderly successions of events, our primitive
forefathers were driven to invent some explanation of them. This,
independently, and in many different times and places, they did in a
simple and natural way by supposing that the world was controlled by a
host of intelligent beings, each of which had some part in ordering
material things. Sometimes these invisible powers were believed to be
the spirits of great chieftains, who were active when on earth, and
who after death continued to exercise their power in the larger realms
of Nature. Again, and perhaps more commonly, these movements of Nature
were supposed to be due to the action of great though invisible
beasts, much like those which the savage found about him. Thus among
our North American Indians the winds are explained by the supposition
that the air is fanned by the wings of a great unseen bird, whose duty
it is to set the atmosphere into motion. That no one has ever seen the
bird doing the work, or that the task is too great for any conceivable
bird, is to the simple, uncultivated man no objection to this view. It
is long, indeed, before education brings men to the point where they
can criticise their first explanations of Nature.
As men in their advance come to see how much nobler are their own
natures than those of the lower animals, they gradually put aside the
explanation of events by the actions of beasts, and account for the
order of the world by the supposition that each and every important
detail is controlled by some immortal creature essentially like a man,
though much more powerful than those of their own kind. This stage of
understanding is perhaps best shown by the mythology of the Greeks,
where there was a great god over all, very powerful but not
omnipotent; and beneath him, in endless successions of command,
subordinate powers, each with a less range of duties and capacities
than those of higher estate, until at the bottom of the system there
were minor deities and demigods charged with the management of the
trees, the flowers, and the springs--creatures differing little from
man, except that they were immortal, and generally invisible, though
they, like all the other deities, might at their will display
themselves to the human beings over whom they watched, and whose path
in life they guided.
Among only one people do we find that the process of advance led
beyond this early and simple method of accounting for the processes of
Nature, bringing men to an understanding such as we now possess. This
great task was accomplished by the Greeks alone. About twenty-five
hundred years ago the philosophers of Greece began to perceive that
the early notion as to the guidance of the world by creatures
essentially like men could not be accepted, and must be replaced by
some other view which would more effectively account for the facts.
This end they attained by steps which can not well be related here,
but which led them to suppose separate powers behind each of the
natural series--powers having no relation to the qualities of mankind,
but ever acting to a definite end. Thus Plato, who represents most
clearly this advance in the interpretation of facts, imagined that
each particular kind of plant or animal had its shape inevitably
determined by something which he termed an idea, a shape-giving power
which existed before the object was created, and which would remain
after it had been destroyed, ever ready again to bring matter to the
particular form. From this stage of understanding it was but a short
step to the modern view of natural law. This last important advance
was made by the great philosopher Aristotle, who, though he died about
twenty-two hundred years ago, deserves to be accounted the first and
in many ways the greatest of the ancient men of science who were
informed with the modern spirit.
With Aristotle, as with all his intellectual successors, the
operations of Nature were conceived as to be accounted for by the
action of forces which we commonly designate as natural laws, of which
perhaps the most familiar and universal is that of gravitation, which
impels all bodies to move toward each other with a degree of intensity
which is measured by their weight and the distance by which they are
separated.
For many centuries students used the term law in somewhat the same way
as the more philosophical believers in polytheism spoke of their gods,
or as Plato of the ideas which he conceived to control Nature. We see
by this instance how hard it is to get rid of old ways of thinking.
Even when the new have been adopted we very often find that something
of the ancient and discarded notions cling in our phrases. The more
advanced of our modern philosophers are clear in their mind that all
we know as to the order of Nature is that, given certain conditions,
certain consequences inevitably follow.
Although the limitations which modern men of science perceive to be
put upon their labours may seem at first sight calculated to confine
our understanding within a narrow field of things which can be seen,
or in some way distinctly proved to exist, the effect of this
limitation has been to make science what it is--a realm of things
known as distinct from things which may be imagined. All the
difference between ancient science and modern consists in the fact
that in modern science inquirers demand a businesslike method in the
interpretation of Nature. Among the Greeks the philosopher who taught
explanations of any feature in the material world which interested him
was content if he could imagine some way which would account for the
facts. It is the modern custom now to term the supposition of an
explanation a _working hypothesis_, and only to give it the name of
theory after a very careful search has shown that all the facts which
can be gathered are in accordance with the view. Thus when Newton made
his great suggestion concerning the law of gravitation, which was to
the effect that all bodies attracted each other in proportion to
their masses, and inversely as the square of their distance from each
other, he did not rest content, as the old Greeks would have done,
with the probable truth of the explanation, but carefully explored the
movements of the planets and satellites of the solar system to see if
the facts accorded with the hypothesis. Even the perfect
correspondence which he found did not entirely content inquirers, and
in this century very important experiments have been made which have
served to show that a ball suspended in front of a precipice will be
attracted toward the steep, and that even a mass of lead some tons in
weight will attract toward itself a small body suspended in the manner
of a pendulum.
It is this incessant revision of the facts, in order to see if they
accord with the assumed rule or law, which has given modern science
the sound footing that it lacked in earlier days, and which has
permitted our learning to go on step by step in a safe way up the
heights to which it has climbed. All explanations of Nature begin with
the work of the imagination. In common phrase, they all are guesses
which have at first but little value, and only attain importance in
proportion as they are verified by long-continued criticism, which has
for its object to see whether the facts accord with the theory. It is
in this effort to secure proof that modern science has gathered the
enormous store of well-ascertained facts which constitutes its true
wealth, and which distinguishes it from the earlier imaginative and to
a great extent unproved views.
In the original state of learning, natural science was confounded with
political and social tradition, with the precepts of duty which
constitute the law of the people, as well as with their religion, the
whole being in the possession of the priests or wise men. So long as
natural action was supposed to be in the immediate control of numerous
gods and demigods, so long, in a word, as the explanation of Nature
was what we term polytheistic, this association of science with other
forms of learning was not only natural but inevitable. Gradually,
however, as the conception of natural law replaced the earlier idea as
to the intervention of a spirit, science departed from other forms of
lore and came to possess a field to itself. At first it was one body
of learning. The naturalists of Aristotle's time, and from his day
down to near our own, generally concerned themselves with the whole
field of Nature. For a time it was possible for any one able and
laborious man to know all which had been ascertained concerning
astronomy, chemistry, geology, as well as the facts relating to living
beings. The more, however, as observation accumulated, and the store
of facts increased, it became difficult for any one man to know the
whole. Hence it has come about that in our own time natural learning
is divided into many distinct provinces, each of which demands a
lifetime of labour from those who would know what has already been
done in the field, and what it is now important to do in the way of
new inquiries.
The large divisions which naturalists have usually made of their tasks
rest in the main on the natural partitions which we may readily
observe in the phenomenal world. First of all comes astronomy,
including the phenomena exhibited in the heavens, beyond the limits of
the earth's atmosphere. Second, geology, which takes account of all
those actions which in process of time have been developed in our own
sphere. Third, physics, which is concerned with the laws of energy, or
those conditions which affect the motion of bodies, and the changes
which are impressed upon them by the different natural forces. Fourth,
chemistry, which seeks to interpret the principles which determine the
combination of atoms and the molecules which are built of them under
the influence of the chemical affinities. Fifth, biology, or the laws
of life, a study which pertains to the forms and structures of animals
and plants, and their wonderful successions in the history of the
world. Sixth, mathematics, or the science of space and number, that
deals with the principles which underlie the order of Nature as
expressed at once in the human understanding and in the material
universe. By its use men were made able to calculate, as in
arithmetic, the problems which concern their ordinary business, as
well as to compute the movements of the celestial bodies, and a host
of actions which take place on the earth that would be inexplicable
except by the aid of this science. Last of all among the primary
sciences we may name that of psychology, which takes account of mental
operations among man and his lower kindred, the animals.
In addition to the seven sciences above mentioned, which rest in a
great measure on the natural divisions of phenomena, there are many,
indeed, indefinitely numerous, subdivisions which have been made to
suit the convenience of students. Thus astronomy is often separated
into physical and mathematical divisions, which take account either of
the physical phenomena exhibited by the heavenly bodies or of their
motions. In geology there are half a dozen divisions relating to
particular branches of that subject. In the realm of organic life, in
chemistry, and in physics there are many parts of these sciences which
have received particular names.
It must not be supposed that these sciences have the independence of
each other which their separate names would imply. In fact, the
student of each, however, far he may succeed in separating his field
from that of the other naturalists, as we may fitly term all students
of Nature, is compelled from time to time to call in the aid of his
brethren who cultivate other branches of learning. The modern
astronomer needs to know much of chemistry, or else he can not
understand many of his observations on the sun. The geologists have to
share their work with the student of animal and vegetable life, with
the physicists; they must, moreover, know something of the celestial
spheres in order to interpret the history of the earth. In fact, day
by day, with the advance of learning, we come more clearly to
perceive that all the processes of Nature are in a way related to each
other, and that in proportion as we understand any part of the great
mechanism, we are forced in a manner to comprehend the whole. In other
words, we are coming to understand that these divisions of the field
of science depend upon the limitations of our knowledge, and not upon
the order of Nature itself. For the purposes of education it is
important that every one should know something of the great truths
which each science has disclosed. No mortal man can compass the whole
realm of this knowledge, but every one can gain some idea of the
larger truths which may help him to understand the beauty and grandeur
of the sphere in which he dwells, which will enable him the better to
meet the ordinary duties of life, that in almost all cases are related
to the facts of the world about us. It has been of late the custom to
term this body of general knowledge which takes account of the more
evident facts and important series of terrestrial actions
physiography, or, as the term implies, a description of Nature, with
the understanding that the knowledge chosen for the account is that
which most intimately concerns the student who seeks information that
is at once general and important. Therefore, in this book the effort
is made first to give an account as to the ways and means which have
led to our understanding of scientific problems, the methods by which
each person may make himself an inquirer, and the outline of the
knowledge that has been gathered since men first began to observe and
criticise the revelations the universe may afford them.