I
How habitually we go about over the surface of the earth, delving it
or cultivating it or leveling it, without thinking that it has not
always been as we now find it, that the mountains were not always
mountains, nor the valleys always valleys, nor the plains always
plains, nor the sand always sand, nor the clay always clay. Our
experience goes but a little way in such matters. Such a thought
takes us from human time to God's time, from the horizon of place
and years to the horizon of geologic ages. We go about our little
affairs in the world, sowing and reaping and building and
journeying, like children playing through the halls of their
ancestors, without pausing to ask how these things all came about.
We do not reflect upon the age of our fields any more than we do
upon the size of the globe under our feet: when we become curious
about such matters and look upon the mountains as either old or
young, or as the subjects of birth, growth, and decay, then we are
unconscious geologists. It is to our interest in such things that
geology appeals and it is this interest that it stimulates and
guides.
What an astonishing revelation, for instance, that the soil was born
of the rocks, and is still born of the rocks; that every particle of
it was once locked up in the primitive granite and was unlocked by
the slow action of the rain and the dews and the snows; that the
rocky ribs of the earth were clothed with this fertile soil out of
which we came and to which we return by their own decay; that the
pulling-down of the inorganic meant the building-up of the organic;
that the death of the crystal meant the birth of the cell, and
indirectly of you and me and of all that lives upon the earth.
Had there been no soil, had the rocks not decayed, there had been no
you and me. Such considerations have long made me feel a keen
interest in geology, and especially of late years have stimulated my
desire to try to see the earth as the geologist sees it. I have
always had a good opinion of the ground underfoot, out of which we
all come, and to which we all return; and the story the geologists
tell us about it is calculated to enhance greatly that good opinion.
I think that if I could be persuaded, as my fathers were, that the
world was made in six days, by the fiat of a supernatural power, I
should soon lose my interest in it. Such an account of it takes it
out of the realm of human interest, because it takes it out of the
realm of natural causation, and places it in the realm of the
arbitrary, and non-natural. But to know that it was not made at all,
in the mechanical sense, but that it grew--that it is an evolution
as much as the life upon the surface, that it has an almost infinite
past, that it has been developing and ripening for millions upon
millions of years, a veritable apple upon the great sidereal tree,
ameliorating from cycle to cycle, mellowing, coloring,
sweetening--why, such a revelation adds immensely to our interest in
it.
As with nearly everything else, the wonder of the world grows the
more we grasp its history. The wonder of life grows the more we
consider the chaos of fire and death out of which it came; the
wonder of man grows the more we peer into the abyss of geologic time
and of low bestial life out of which he came.
Not a tree, not a shrub, not a flower, not a green thing growing,
not an insect of an hour, but has a background of a vast aeon of
geologic and astronomic time, out of which the forces that shaped it
have emerged, and over which the powers of chaos and darkness have
failed to prevail.
The modern geologist affords us one of the best illustrations of the
uses of the scientific imagination that we can turn to. The
scientific imagination seems to be about the latest phase of the
evolution of the human mind. This power of interpretation of
concrete facts, this Miltonic flight into time and space, into the
heavens above, and into the bowels of the earth beneath, and bodying
forth a veritable history, a warring of the powers of light and
darkness, with the triumph of the angels of light and life, makes
Milton's picture seem hollow and unreal. The creative and poetic
imagination has undoubtedly already reached its high-water mark. We
shall probably never see the great imaginative works of the past
surpassed or even equaled. But in the world of scientific discovery
and interpretation, we see the imagination working in new fields and
under new conditions, and achieving triumphs that mark a new epoch
in the history of the race. Nature, which once terrified man and
made a coward of him, now inspires him and fills him with love and
enthusiasm.
The geologist is the interpreter of the records of the rocks. From a
bit of strata here, and a bit there, he re-creates the earth as it
was in successive geologic periods, as Cuvier reconstructed his
extinct animals from fragments of their bones; and the same
interpretative power of the imagination is called into play in both
cases, only the palaeontologist has a much narrower field to work
in, and the background of his re-creations must be supplied by the
geologist.
Everything connected with the history of the earth is on such a vast
scale--such a scale of time, such a scale of power, such a scale of
movement--that in trying to measure it by our human standards and
experience we are like the proverbial child with his cup on the
seashore. Looked at from our point of view, the great geological
processes often seem engaged in world-destruction rather than in
world-building. Those oft-repeated invasions of the continents by
the ocean, which have gone on from Archaean times, and during which
vast areas which had been dry land for ages were engulfed, seem like
world-wide catastrophes. And no doubt they were such to myriads of
plants and animals of those times. But this is the way the
continents grew. All the forces of the invading waters were engaged
in making more land.
The geologist is bold; he is made so by the facts and processes with
which he deals; his daring affirmations are inspired by a study of
the features of the earth about him; his time is not our time, his
horizons are not our horizons; he escapes from our human experiences
and standards into the vast out-of-doors of the geologic forces and
geologic ages. The text he deciphers is written large, written
across the face of the continent, written in mountain-chains and
ocean depths, and in the piled strata of the globe. We untrained
observers cannot spell out these texts, because they are written
large; our vision is adjusted to smaller print; we are like the
school-boy who finds on the map the name of a town or a river, but
does not see the name of the state or the continent printed across
it. If the geologist did not tell us, how should we ever suspect
that probably where we now stand two or more miles of strata have
been worn away by the winds and rains; that the soil of our garden,
our farm, represents the ashes of mountains burned up in the slow
fires of the geologic ages.
Geology first gives us an adequate conception of time. The
limitations which shut our fathers into the narrow close of six
thousand years are taken down by this great science and we are
turned out into the open of unnumbered millions of years. Upon the
background of geologic time our chronological time shows no more
than a speck upon the sky. The whole of human history is but a mere
fraction of a degree of this mighty arc. The Christian era would
make but a few seconds of the vast cycle of the earth's history.
Geologic time! The words seem to ring down through the rocky strata
of the earth's crust; they reverberate under the mountains, and make
them rise and fall like the waves of the sea; they open up vistas
through which we behold the continents and the oceans changing
places, and the climates of the globe shifting like clouds in the
sky; whole races and tribes of animal forms disappear and new ones
come upon the scene. Such a past! the imagination can barely skirt
the edge of it. As the pool in the field is to the sea that wraps
the earth, so is the time of our histories to the cycle of ages in
which the geologist reckons the events of the earth's history.
Through the eyes of the geologist one may look upon his native hills
and see them as they were incalculable ages ago, and as they
probably will be incalculable ages ahead; those hills, so unchanging
during his lifetime, and during a thousand lifetimes, he may see as
flitting as the cloud shadows upon the landscape. Out of the dark
abyss of geologic time there come stalking the ghosts of lost
mountains and lost hills and valleys and plains, or lost rivers and
lakes, yea, of lost continents; we see a procession of the phantoms
of strange and monstrous beasts, many of them colossal in size and
fearful in form, and among the minor forms of this fearful troop of
spectres we see the ones that carried safely forward, through the
vicissitudes of those ages, the precious impulse that was to
eventuate in the human race.
Only the geologist knows the part played by erosion in shaping the
earth's surface as we see it. He sees, I repeat, the phantoms of
vanished hills and mountains all about us. He sees their shadow
forms wherever he looks. He follows out the lines of the flexed or
folded strata where they come to the surface, and thus sketches in
the air the elevation that has disappeared. In some places he finds
that the valleys have become hills and the hills have become
valleys, or that the anticlines and synclines, as he calls them,
have changed places--as a result of the unequal hardness of the
rocks. Over all the older parts of the country the original features
have been so changed by erosion that, could they be suddenly
restored, one would be lost on his home farm. The rocks have melted
into soil, as the snow-banks in spring melt into water. The rocks
that remain are like fragments of snow or ice that have so far
withstood the weather. Geologists tell us that the great Appalachian
chain has been in the course of the ages reduced almost to a base
level or peneplain, and then reelevated and its hills and mountains
carved out anew.
We change the surface of the earth a little with our engineering,
drain a marsh, level a hill, sweep away a forest, or bore a
mountain, but what are these compared with the changes that have
gone on there before our race was heard of? In my native mountains,
the Catskills, all those peaceful pastoral valleys, with their farms
and homesteads, lie two or three thousand feet below the original
surface of the land. Could the land be restored again to its first
condition in Devonian times, probably the fields where I hoed corn
and potatoes as a boy would be buried one or two miles beneath the
rocks.
The Catskills are residual mountains, or what Agassiz calls
"denudation mountains." When we look at them with the eye of the
geologist we see the great plateau of tableland of Devonian times
out of which they were carved by the slow action of the sub-aerial
forces. They are like the little ridges and mounds of soil that
remain of your garden-patch after the waters of a cloudburst have
swept over it. They are immeasurably old, but they do not look it,
except to the eye of the geologist. There is nothing decrepit in
their appearance, nothing broken, or angular, or gaunt, or rawboned.
Their long, easy, flowing lines, their broad, smooth backs, their
deep, wide, gently sloping valleys, all help to give them a look of
repose and serenity, as if the fret and fever of life were long
since passed with them. Compared with the newer mountains of uplift
in the West, they are like cattle lying down and ruminating in the
field beside alert wild steers with rigid limbs and tossing horns.
They sleep and dream with bowed heads upon the landscape. Their
great flanks and backs are covered with a deep soil that nourishes a
very even growth of beech, birch, and maple forests. Though so old,
their tranquillity never seems to have been disturbed; no
storm-and-stress period has left its mark upon them. Their strata
all lie horizontal just as they were laid down in the old seas, and
nothing but the slow gentle passage of the hand of time shows in
their contours. Mountains of peace and repose, hills and valleys
with the flowing lines of youth, coming down to us from the fore-
world of Palaeozoic time, yet only rounded and mellowed by the aeons
they have passed through. Old, oh, so old, but young with verdure
and limpid streams, and the pastoral spirit of to-day!
To the geologist most mountains are short-lived. When he finds great
sturdy ranges, like the Alps, the Andes, the Himalayas, he knows
they are young,--mere boys. When they get old, they will be cut
down, and their pride and glory gone. A few more of these geologic
years and they will be reduced to a peneplain,--only their stumps
left. This seems to hold truer of mountains that are wrinkles in the
earth's crust--squeezed up and crumpled stratified rock, such as
most of the great mountain-systems are--than of mountains of
erosion like the Catskills, or of upheaval like the Adirondacks. The
crushed and folded and dislocated strata are laid open to the
weather as the horizontal strata, and as the upheaved masses of
Archaean rock are not. Moreover, strata of unequal hardness are
exposed, and this condition favors rapid erosion.
In imagination the geologist is present at the birth of whole
mountain-ranges. He sees them gestating in the womb of their mother,
the sea. Where our great Appalachian range now stands, he sees, in
the great interior sea of Palaeozoic time, what he calls a
"geosyncline," a vast trough, or cradle, being slowly filled with
sediment brought down by the rivers from the adjoining shores. These
sediments accumulate to the enormous depth of twenty-five thousand
feet, and harden into rock. Then in the course of time they are
squeezed together and forced up by the contraction of the earth's
crust, and thus the Appalachians are born. When Mother Earth takes a
new hitch in her belt, her rocky garment takes on new wrinkles. Just
why the earth's crust should wrinkle along lines of rock of such
enormous thickness is not a little puzzling. But we are told it is
because this heavy mass of sediment presses the sea-bottom down till
the rocks are fused by the internal heat of the earth and thus a
line of weakness is established. In any case the earth's forces act
as a whole, and the earth's crust at the thickest points is so
comparatively thin--probably not much more than a heavy sheet of
cardboard over a six-inch globe--that these forces seem to go their
own way regardless of such minor differences.
The Alps and the Himalayas, much younger than our Appalachians, were
also begotten and nursed in the cradle of a vast geosyncline in the
Tertiary seas. We speak of the birth of a mountain-range in terms of
a common human occurrence, or as if it were an event that might be
witnessed, measurable in human years or days, whereas it is an event
measurable only in geologic periods, and geologic periods are marked
off only on the dial-face of eternity. The old Hebrew writer gave
but a faint image of it when he said that with the Lord a thousand
years are as one day; it is hardly one hour of the slow beat of that
clock whose hours mark the periods of the earth's development.
The whole long period during which the race of man has been rushing
about, tickling and scratching and gashing the surface of the globe,
would make but a small fraction of one of the days that make up the
periods with which the geologist deals. And the span of human life,
how it dwindles to a point in the face of the records of the rocks!
Doubtless the birth of some of the mountain-systems of the globe is
still going on, and we suspect it not; an elevation of one foot in a
century would lift up the Sierra or the Rocky Mountains in a
comparatively short geologic period.