Time and Change Part 8

About nine o'clock we rode back, facing a cold, driving mist, the back of each rider, protected by the shining yellow "slickers,"

glowing to the one behind him, in the volcano's light, till we were a mile or more away.

The next morning came clear, and the sight of the mighty slope of Mauna Loa, lit up by the rising sun, was a grand spectacle. It looked gentle and easy of ascent, wooded here and there, and here and there showing broad, black streaks from the lava overflows at the summit in recent years; but remembering that it was nearly four thousand feet higher than Haleakala, I had no desire to climb it.

This mountain and its companion, Mauna Kea, are the highest island mountains in the world.

The stage rolled us back through the fern forest to the railway station and thence on to Hilo again, where in good time, in the afternoon, we went aboard the steamer; and the next morning we were again in the harbor of Honolulu, glad we had made the inter-island trip, and above all glad that we had seen Haleakala.

VI

THE OLD ICE-FLOOD

I

He was a bold man who first conceived the idea of the great continental ice-sheet which in Pleistocene times covered most of the northern part of the continent, and played such a part in shaping the land as we know it. That bold man was Aga.s.siz, who, however, was not bold enough to accept the theory of evolution as propounded by Darwin. The idea of the great glacier did not conflict with Aga.s.siz's religious predilections, and the theory of evolution did.

It was a bold generalization, this of the continental ice-sheet, one of the master-strokes of the scientific imagination. It was about the year 1840 that Aga.s.siz, fresh from the glaciers of the Alps, went to Scotland looking for the tracks of the old glaciers, and he found them at once when he landed near Glasgow. We can all find them now on almost every walk we take to the fields and hills; but until our eyes are opened, how blind we are to them! We are like people who camp on the trail of an army and never suspect an army has pa.s.sed, though the ruts made by their wagons and artillery and the ruins of their intrenchments are everywhere visible.

When I was a boy on the farm we never asked ourselves questions about the stones and rocks that enc.u.mbered the land--whence they came, or what the agency was that brought them. The farmers believed the land was created just as we saw it--stones, boulders, soil, gravel-pits, hills, mountains, and all--and doubtless wished in their hearts that the Creator had not been so particular about the rocks and stones, or had made an exception in favor of their own fields. Rocks and stones were good for fences and foundations, and for various other uses, but they were a great hindrance to the cultivation of the soil. I once heard a farmer boast that he had very strong land--it had to be strong to hold up such a crop of rocks and stones. When the Eastern farmer moved west into the prairie states, or south into the cotton-growing states, he probably never asked himself why the Creator had not c.u.mbered the ground with rocks and stones in those sections, as he had in New York and New England. South of the line that runs irregularly through middle New Jersey, Pennsylvania, Ohio, Indiana, Illinois, Iowa, and so on to the Rockies, he will find few loose stones scattered over the soil, no detached boulders sitting upon the surface, no hills or mounds of gravel and sand, no clay banks packed full of rounded stones, little and big, no rocky floors under the soil which look as if they had been dressed down by a huge but dulled and nicked jack-plane. The reason is that the line I have indicated marks the limit of the old ice-sheet which more than a hundred thousand years ago covered all the northern part of the continent to a depth of from two to four thousand feet, and was the chief instrument in rounding off mountain-tops, scattering rock-fragments, little and big, over our landscapes, grinding down and breaking off the protruding rock strata, building up our banks of mingled clay and stone, changing the courses of streams and rivers, deepening and widening our valleys, transplanting boulders of one formation for hundreds of miles, and dropping them upon the surface of another formation. When it began to melt and retreat, it was the chief agent in building up our river terraces, and our long, low, rounded hills of sand and gravel and clay, called kames and drumlins. In many of our valleys its flowing waters left long, low ridges, gentle in outline, made up entirely of sand and gravel, or of clay. In other places it left moraines made up of earth, gravel, and rock-fragments that make a very rough streak through the farmer's land. All those high, level terraces along the Hudson, such as that upon which West Point stands, were the work of the old ice-sheet that once filled the river valley. The melting ice was also the chief agent in building up the enormous clay-banks that are found along the sh.o.r.es of the Hudson. The clay formed in very still waters, the sand and gravel in more active waters.

This great ice-sheet not only covered our northern farms with rocks and stones, and packed the soil with rounded boulders, but it also carried away much of the rock decay that goes to the making of the soil, so that the soil is of greater depth in the non-glaciated than in the glaciated areas of the country. The New-Englander or New-Yorker in traveling in the Southern States may note the enormous depth of soil as revealed by the water-courses or railroad cuts. The ice-sheet was a huge mill that ground up the rocks in the North probably as fast or faster than the rains and the rank vegetation reduced them in the South, but the floods of water which it finally let loose carried a great deal of the rock-waste into the sea.

The glacier milk which colors the streams that flow from beneath it finally settles and makes clay. Off the great Malaspina Glacier in Alaska the ocean is tinged by the glacier milk for nearly fifty miles from the sh.o.r.es. Very few country people, even among the educated, are ready to believe that this enormous ice-sheet ever existed. To make them believe that it is just as much a fact in the physical history of this continent as the war of the Revolution is a fact in our political history is no easy matter. It certainly is a crushing proposition. It so vastly transcends all our experience with ice and snow, or the experience of the race since the dawn of history, that only the scientific imagination and faith are equal to it. The belief in it rests on indubitable evidence, its record is written all over our landscape, but it requires, I say, the scientific imagination to put the facts together and make a continuous history.

Three or four hundred feet above my cabin, five or six hundred feet above tidewater, there is a bold rocky point upon which the old ice-sheet bore heavily. It has rubbed it down and flattened it as a hand pa.s.sing over a k.n.o.b of soft putty might do. The great hand in this case moved from the northeast and must have fairly made this rocky prominence groan with its weight. The surface, scratched and grooved and planed by the ice, has weathered away, leaving the rock quite rough; its general outlines alone tell the tale of the battle with the ice. But on the east side a huge ma.s.s of rock, that had been planed and gouged by the glacier, was detached and toppled over, turning topsy-turvy before it had weathered, and it lies in such a position, upheld by two rock fragments, that its glaciated surface, though protected from the weather, is clearly visible. You step down two or three feet between the two upholding rocks and are at the entrance of a little cave, and there before you, standing at an angle of thirty or forty degrees, is this rocky page written over with the history of the pa.s.sing of the great ice plane. The surface exposed is ten or twelve feet long, and four or five feet wide, and it is as straight and smooth, and the scratches and grooves are as sharp and distinct as if made yesterday. I often take the college girls there who come to visit me, to show them, as I tell them, where the old ice G.o.ds left their signatures. The girls take turns in stooping down and looking along the under surface of the rock, and feeling it with their hands, and marveling. They have read or heard about these things, but the reading or hearing made little impression upon their minds. When they see a concrete example, and feel it with their hands, they are impressed. Then when I tell them that there is not a shadow of a doubt but that the ice was at one time two or three thousand feet thick above the place where they now stand, and that it bore down upon Julian's Rock with a weight of thousands of tons to the square foot, that it filled all the Hudson River Valley, and covered the landscape for thousands of miles around them, riding over the tops of the Catskills and of the Adirondacks, and wearing them down and carrying fragments of rock torn from them hundreds of miles to the south and southwest,--when I have told them all of this, I have usually given them a mouthful too big for them to masticate or swallow. As a sort of abstract proposition contained in books, or heard in the cla.s.sroom, they do not mind it, but as an actual fact, here in the light of common day on the hill above Slabsides, with the waters of the Hudson glistening below, and the trees rustling in the wind all about us, that is quite another matter. It sounds like a dream or a fable.

Many of the processes that have made our globe what we see it have been so slow and on such a scale that they are quite beyond our horizon--beyond the reach of our mental apprehension. The mind has to approach them slowly and tentatively, and become familiar with the idea of them, before it can give any sort of rational a.s.sent to them. It has taken the geologist a long time to work out and clear up and confirm this conception of the great continental glacier which in Pleistocene times covered so large a part of the northern hemisphere. It is now as well established as any event in the remote past well can be. In Alaska, and in the Swiss Alps, one may see the ice doing exactly what the Pleistocene ice-sheet did over this country.

II

The other day in pa.s.sing a farmer's house I saw where he had placed a huge, roundish boulder, nearly as high as a man's head, by the roadside and had cut upon it his own name and date, and that of his father before him, and that of the first settler upon the farm, in the latter part of the eighteenth century. It was an interesting monument. I learned that the rock had been found in the bed of a small creek near by, and that the farmer had given a hundred dollars to have it moved to its place in front of his house. Had I seen the old farmer I am sure I could have added to his interest and pride in his monument by telling him that it was Adiron-dack gneiss, and had been brought from that region on the back, or in the maw, of a glacier, many tens of thousands of years ago. But it is highly probable that, were he an uneducated man, he would have treated my statement with contempt or incredulity. Education does at least this for a man: it opens his mind and makes him less skeptical about things not dreamed of in his philosophy.

This boulder had been rolled and worn in its long, slow ride till it was nearly round. I have a much smaller boulder, probably from the same quarry, which I planted at the head of my garden for a seat when the hoe gets tired. When it was dropped here on the land that is now my field, the bed and valley of the Hudson were occupied by the old glacier which, during its decline and recession, built up the terraces opposite me (where now stands a multimillionaire's copy of an Italian palace), and which added to and uncovered the river slopes where now my own vineyards are planted.

The flowing or the creeping of this old ice-sheet, so that it could transport large boulders hundreds of miles, is one of the most remarkable things about it: as slow or slower than the hour-hand of the clock, yet an actual progression, carrying it, in the course of thousands of years, from its apex in Labrador well down into New Jersey, where its terminal moraine is still clearly traceable.

A river of ice, under the right conditions, flows as literally as a river of water, fastest in the middle, and slowest along its margins where the friction is greatest. The old ice-sheet, or ice sea, flowed around and over mountains as a river flows around and over rocks. Where a mountain rose above the glacier, the ice divided and flowed round it, and reunited again beyond it. One may see all this in Alaska at the present time. Water, of course, flows because of its own pressure; so does ice, only the pressure has to be vastly greater. A drop of water on the table does not flow, but, pile it high enough, and it will. The old ice sea flowed mainly south, not because it was downhill in that direction, but because the acc.u.mulation of ice and snow at the North was so great. If through any climatic changes, the snowfall were ever again to be so great that more snow should fall in winter than could melt in summer, after the lapse of thousands of years, we should have another ice age.

VII

THE FRIENDLY SOIL

I never tire of contemplating the soil itself, the mantle rock, as the geologist calls it. It clothes the rocky framework of the earth as the flesh clothes our bones. It is the seat of the vitality of the globe, the youngest part, the growing, changing part. Out of it we came, and to it we return. It is literally our mother, as the sun is our father.

The soil!--the residuum of the rocks, the ashes of the mountains. We know what a vast stretch of time has gone to the making of it; that it has been baked and boiled and frozen and thawed, acted upon by sun and star and wind and rain; mixed and remixed and kneaded and added to, as the housewife kneads and moulds her bread; that it has lain under the seas in the stratified rocks for incalculable ages; that chemical and mechanical and vital forces have all had a hand in its preparation; that the vast cycles of animal and vegetable life of the foreworld have contributed to its fertility; that the life of the sea, and the monsters of the earth, and the dragons of the air, have left their ashes here, so that when I stir it with my hoe, or turn it with my spade, I know I am stirring or turning the meal of a veritable grist of the G.o.ds.

From its primal source in the Archaean rock, up through all the vast series of sedimentary rocks to our own time, what vicissitudes and transformations it has pa.s.sed through; how many times it has died, so to speak, and been reborn from the rocks; how many times the winds and the rains have transported it, and infused invisible, life-giving gases into it; how many of the elements have throbbed with life, climbed and bloomed in trees, walked or flown or swam in animals, or slumbered for thousands upon thousands of years beneath the great ice-sheet of Pleistocene time! A handful of the soil by your door is probably the most composite thing you can find in a day's journey. It may be an epitome of a whole geological formation, or of two or more of them. If it happens to be made up of decomposed limestone, sandstone, slate, and basalt rock, think what a history would be condensed in it!

Our lawns are made up of ashes from the funeral pyre of mountains, of dust from the tombs of geologic ages. What ma.s.ses of rock does this sandbank represent! what an enormous grist in the great glacier mill do these layers of clay stand for! Two feet of soil probably represent a hundred feet or more of rock. Strictly speaking, the soil is the insoluble parts of the ground-up and decomposed rocks, after the rains and the winds have done their work and taken their toll of the grist they have ground. Sometimes these mills take the whole grist and leave the rocks bare; but usually they leave a residuum in which life strikes its roots. We do not see all that the waters take from the soil. They have invisible pockets in which they carry away all the more soluble parts, such as lime, soda, potash, silica, magnesia, and others, and leave for the land the more insoluble parts. These, too, in times of flood they carry away in suspension, in the shape of sand, silt, mud, gravel, and the like.

When the waters really digest the rocks, they hold the various minerals in solution, and run limpid and dancing to the sea; when they have an undigested burden, they run angry and turbid.

It is estimated that the Hudson River deposits in the sea each year four hundred and forty thousand tons of mineral matter in solution which it has taken from the land, and the Mississippi one hundred and twelve million tons. Each carries away about four times as much in suspension. The digestive or chemical power of water, then, is only about one fourth as great as its mechanical power. Between the two the land is made to pay heavy toll to the sea. But in time, in geologic time, it all comes back. The suspended particles are dropped and go to make up the sedimentary rocks, while the solutes help cement the material of these rocks together, and also nourish the sea life from which limestone and other organic rocks are made.

When these rocks are again lifted to the surface and disintegrated into soil, then the debt of the sea to the land is paid. This process, this cycle of soil loss and soil growth, has gone on through all time, and must continue as long as the rain continues to fall, or as long as the sea continues to send its tax-gatherers to the land. In this great cycle of give and take of the elements, the affairs of men cut but a momentary figure; how puny they are, how transient! How the great changes, which in time amount to revolutions, go on over our heads and under our feet, and we rarely heed them, and are powerless to stay them! A summer shower carries the soil of my side-hill, which is mainly disintegrated Silurian rock and shale, into the river, and some millions of years hence, when it has become stratified rock, and been lifted up into the light of day, some other, and, I trust, wiser husbandman, will be gathering his harvest from it, and be worried over the downpour that robs him of it. The farmer's worry is bound to come back with the soil, and be pa.s.sed along with it.

VIII

PRIMAL ENERGIES

How puny and meagre is the utmost power man can put forth, even by the aid of all his mechanical appliances, when compared with the primal earth forces! Think, or try to think, of the force of pressure that causes the rock-strata to buckle or crumple or bend--layers of rock, thousands of feet thick, made to fold and bend like the leaves of a book--vast mountain-chains flexed and foreshortened, or ruptured and faulted as the bending of one's body wrinkles or rips one's clothes. Think of the over-thrusts and the folding and shearing of the earth's crust. The shrinking of the earth squeezes the rocks to an extent quite beyond our power of conception. "So overpowering has been the horizontal movement in some cases," says Dana, "that ma.s.ses of rock thousands of feet in thickness have been buckled up and sheared, or, simply yielding to pressure, have sheared without folding, and been thrust forward for miles along a gently inclined plane. These great reversed faults are termed over-thrusts or thrust-planes. Sometimes such thrust-planes occur singly, at other times the rocks have yielded again and again, great sheets having been sliced off successively, and driven forward one upon the other." In northern Montana there is an over-thrust of the Cambrian rocks upon the late Cretaceous, of seven or eight miles, carrying with it what is now called "Chief Mountain," which has been carved out of the extreme end of the over-thrust. The contemplation of such things gives one a sense of power in Nature beyond anything else I know of. The shrinking of the globe as a whole makes its rocky garment too big for it, and this t.i.tanic wrinkling and folding results. When the strata snap asunder under the strain, we have earthquakes. During the recent San Francisco earthquake, Mount Tamalpais, across the bay, and all the neighboring heights, were permanently shifted eight or ten feet. The sides of the mountain, it is said, undulated like a curtain. And this shaking and twitching of the great rocky skin of the earth was vastly less, in proportion to the size of the globe, than the twitching and trembling of the skin of a horse when he would shake off the flies, in comparison with the animal's body.

We see another exhibition of the magnitude of the earth's forces in what the geologist calls a "laccolite"--a great cave or cistern deep beneath the surface of stratified rock filled with hardened lava.

The lava is forced up from an unknown depth under such pressure that, not finding an outlet at the surface, the rock strata, hundreds or thousands of feet thick, are lifted up and arched like so much paper, and in the cavity thus formed the pent-up molten lava finds relief. These lava cisterns or pockets are sometimes uncovered by the process of erosion. The Henry Mountains in Utah are all laccolites. One of them, Mount Hillers, has a volume of about ten cubic miles. Much of the overarching sedimentary strata still covers it. Geologists read the evidence of a similar formation called a "sill" on the west side of the Hudson in New Jersey, forming the Palisades. The lava worked like a giant mole up through and then beneath the Tria.s.sic sandstone, lifting the strata up and arching them over a large area. During the millions of years that have elapsed since that time, the layers of superinc.u.mbent sandstone have been worn away so that now one sees a wide, smooth, gentle slope of basaltic rock covered by a very thin coat of soil. As one goes by on the train, one sees where the workmen of a stone-crushing plant have cut into the slope and uncovered the junction of the two kinds of rock, one born of water, and one born of fire. The igneous rock sits squarely upon the level sandstone, like a row of upright books standing upon a shelf. I never pa.s.s the place but that I want to stop the train and get out and have a close look at the precise spot where this son of Vulcan sat down so heavily and so hot upon his brother of the sedimentary deposits.

Probably no two chapters of the earth's history differ more than those of the two sides of the Hudson at New York. There is a great break here--a leap from Archaean times on the east side to Mesozoic times on the west. The east side is millions of years the older.

Here is the original Plutonic or Azoic rock which apparently has never been under the sea since it was first thrust up out of the fiery depths. The west sh.o.r.e, including the Palisades, belongs to a much later geologic era. The original granite here is buried under vast deposits of sedimentary rock of the Tria.s.sic age--the age of the giant reptiles, the remains of one of which has recently been found embedded in this sandstone, near the river's edge. As the traveler's eye follows along the even, almost level line of this escarpment of the Palisades, let it re-create for him the strata of the old Tria.s.sic sandstone that were millions of years ago piled high upon it,--how high can only be conjectured,--but which have been removed grain by grain under the eroding power of the forces of air and water that now seem to caress the huge wall so gently. Ah!

geologic Time, what can it not do? what has it not done? The old sill of Vulcan now presents a nearly vertical front to the Hudson, forming the Palisades, showing that some leaves of the earth's history here are missing, buried probably beneath the waters of the river. There is evidently a line of fault here, and the west side has been lifted up out of the old Mesozoic seas, probably in the convulsions that poured out the lava of the trap rock.