Chapter 6
That there should be two or three Yosemites in the Sierra not very far apart, all with the main features singularly alike, is very significant--as if this kind of valley was latent in the granite of that region--some peculiarity of rock structure that lends itself readily to these formations. The Sierra lies beyond the southern limit of the great continental ice-sheet of late Tertiary times, but it nursed and reared many local glaciers, and to the eroding power of these its Yosemites are partly due. But water was at work here long before the ice--eating down into the granite and laying open the mountain for the ice to begin its work. Ice may come, and ice may go, says the river, but I go on forever. Water tends to make a V-shaped valley, ice a U-shaped one, though in the Hawaiian Islands, where water erosion alone has taken place, the prevailing form of the valleys is that of the U-shaped. Yosemite approximates to this shape, and ice has certainly played a part in its formation. But the glacier seems to have stopped at the outlet of the great valley; it did not travel beyond the gigantic hall it had helped to excavate. The valley of the Merced from the mouth of Yosemite downward is an open valley strewn with huge angular granite rocks and shows no signs of glaciation whatever. The reason of this abruptness is quite beyond my ken. It is to me a plausible theory that when the granite that forms the Sierra was lifted or squeezed up by the shrinking of the earth, large fissures and crevasses may have occurred, and that Yosemite and kindred valleys may be the result of the action of water and ice in enlarging these original chasms. Little wonder that the earlier geologists, such as Whitney, were led to attribute the exceptional character of these valleys to exceptional and extraordinary agents--to sudden faulting or dislocation of the earth's crust. But geologists are becoming more and more loath to call in the cataclysmal to explain any feature of the topography of the land. Not to the thunder or the lightning, to earthquake or volcano, to the forces of upheaval or dislocation, but to the still, small voice of the rain and the winds, of the frost and the snow,--the gentle forces now and here active all about us, carving the valleys and reducing the mountains, and changing the courses of rivers,--to these, as Lyell taught us, we are to look in nine cases out of ten, yes, in ninety-nine out of a hundred, to account for the configuration of the continents.
The geologists of our day, while not agreeing as to the amount of work done respectively by ice and water, yet agree that to the latter the larger proportion of the excavation is to be ascribed. At any rate between them both they have turned out one of the most beautiful and stupendous pieces of mountain carving to be found upon the earth.
IV
THROUGH THE EYES OF THE GEOLOGIST
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.
II
It was the geologist that emboldened Tennyson to sing,--
"The hills are shadows and they flow From form to form and nothing stands, They melt like mists, the solid lands, Like clouds they shape themselves and go."
But some hills flow much faster than others. Hills made up of the latest or newest formations seem to take to themselves wings the fastest.
The Archaean hills and mountains, how slowly they melt away! In the Adirondacks, in northern New England, in the Highlands of the Hudson, they still hold their heads high and have something of the vigor of their prime.
The most enduring rocks are the oldest; and the most perishable are, as a rule, the youngest. It takes time to season and harden the rocks, as it does men. Then the earlier rocks seem to have had better stuff in them. They are nearer the paternal granite; and the primordial seas that mothered them were, no doubt, richer in the various mineral solutions that knitted and compacted the sedimentary deposits. The Cretaceous formations melt away almost like snow. I fancy that the ocean now, compared with the earlier condition when it must have been so saturated with mineral elements, is like thrice-skimmed milk.
The geologist is not stinted for time. He deals with big figures. It is refreshing to see him dealing out his years so liberally. Do you want a million or two to account for this or that? You shall have it for the asking. He has an enormous balance in the bank of Time, and he draws upon it to suit his purpose. In human history a thousand years is a long time. Ten thousand years wipe out human history completely. Ten thousand more, and we are probably among the rude cave-men or river-drift men. One hundred thousand, and we are--where? Probably among the simian ancestors of man. A million years, and we are probably in Eocene or Miocene times, among the huge and often grotesque mammals, and our ancestor, a little creature, probably of the marsupial kind, is skulking about and hiding from the great carnivorous beasts that would devour him.
"Little man, least of all, Among the legs of his guardians tall, Walked about with puzzled look. Him by the hand dear Nature took, Dearest Nature, strong and kind, Whispered, 'Darling, never mind! To-morrow they will wear another face, The founder thou; these are thy race!'"
I fancy Emerson would be surprised and probably displeased at the use I have made of his lines. I remember once hearing him say that his teacher in such matters as I am here touching upon was Agassiz, and not Darwin. Yet did he not write that audacious line about "the worm striving to be man"? And Nature certainly took his "little man" by the hand and led him forward, and on the morrow the rest of the animal creation "wore another face."
III
In my geological studies I have had a good deal of trouble with the sedimentary rocks, trying to trace their genealogy and getting them properly fathered and mothered. I do not think the geologists fully appreciate what a difficult problem the origin of these rocks presents to the lay mind. They bulk so large, while the mass of original crystalline rocks from which they are supposed to have been derived is so small in comparison. In the case of our own continent we have, to begin with, about two million of square miles of Archaean rocks in detached lines and masses, rising here and there above the primordial ocean; a large triangular mass in Canada, and two broken lines of smaller masses running south from it on each side of the continent, inclosing a vast interior sea between them. To end with, we have the finished continent of eight million or more square miles, of an average height of two thousand feet above the sea, built up or developed from and around these granite centres very much as the body is built up and around the bones, and of such prodigious weight that some of our later geologists seek to account for the continental submarine shelf that surrounds the continent on the theory that the land has slowly crept out into the sea under the pressure of its own weight. And all this,--to say nothing of the vast amount of rock, in some places a mile or two in thickness, that has been eroded from the land surfaces of the globe in later geological time, and now lies buried in the seas and lakes,--we are told, is the contribution of those detached portions of Archaean rock that first rose above the primordial seas. It is a greater miracle than that of the loaves and the fishes. We have vastly more to end with than we had to begin with. The more the rocks have been destroyed, the more they have increased; the more the waters have devoured them, the more they have multiplied and waxed strong.