LESSON XV.

THE WINTER OF THE WORLD.

“Hark to that mighty crash!The loosened ice-ridge breaks away—Seaward the glittering mountain rides,While down its green translucent sidesThe foaming torrents dash.”

“Hark to that mighty crash!

The loosened ice-ridge breaks away—

Seaward the glittering mountain rides,

While down its green translucent sides

The foaming torrents dash.”

—Bryant.

Once upon a time the North Polar region, where all is now snow and ice, intense cold and six months of night, was a land of warmth and sunshine. At that time, how long agoit was we cannot tell, the North Polar Circle was a green and luxuriant flower-garden. The beech, oak, poplar, maple, and walnut grew there. The fragrant lime tree and the beautiful magnolia were there. Before this flora appeared, plants of the carboniferous era had flourished there,—pines, club-mosses, tree-ferns, cycads; and these had so abounded that a bed of coal thirty feet thick was laid down. Over this buried coal-bed the spruce, pine, fir, birch, cypress, elm, hazel, and viburnum grew in the Arctic zone. These trees were not the only representatives of the plant world; on the plains the grasses grew, on the ponds the water-lilies rocked, and reeds and sedges fringed in dainty beauty the borders of the pools. Many families of plants then growing in northern Greenland had at the same time their representatives in Central Europe.

WHEN ICE WAS KING.

Evidently at that date the Arctic zone had a mild climate, and day and night of moderate length. That the above numerated plants and almost two hundred other species grew within nine degrees of the North Pole is proved by finding their remains in all stages of growth, from seed to matured plant, from root to fruit, scattered over an extensive area of country. How did this happen? What occasioned the change? How came Greenland then to be a warm and smiling land? These are questions to which no answer can at present be given. No one knows how this could have been.

Over against this marvel of a mild climate, luxuriant vegetation, and nearly equal days and nights within the Polar Circle, we may set that other wonder of the glacial or ice age—the time when the polar cold wandered beyond its bounds and came down into the temperate zone to stay, for how long we cannot tell; for very long indeed, no doubt, though not for as long as a world-building epoch. The Glacial age was only a portion of the age that came just before the human period. This Glacial period is also one of the problems which continue to puzzle the geologist. Why was the Northern hemisphere then so cold? What occasioned the change from tropic warmth to nipping frost? How suddenly did this change come on? How far did it extend, and how long did it last? All these queries cannot be answered, but some of the wonders of that strange, forbidding age we can unfold.

We know that the northern half of the world grew colder and colder, and that in this chilling climate the flora andfauna greatly changed. The plants could not accommodate themselves to the cold and most of them perished, and their places were taken by flowers and trees which belonged to colder climates. Instead of palms, figs, cinnamon trees, and magnolias, grew dwarf birch, the willow, and pines, while the less hardy vegetation left representatives only in the tropics. The animals also changed, but more slowly than the plants. Some migrated to the south, others lessened in size and put on thicker coats of fur or feathers; many species perished entirely.

Still the cold increased. Vast snow fields loaded the Alps and the Pyrenees, and all the plains and valleys of northern and middle Europe and North America began to be filled with glaciers.

Here let us pause to consider that three-fourths of the surface of our globe is water. As we have seen from the study of the moon, a waterless globe is also a lifeless globe, bereft of plant or animal, and we owe in a large part the habitable character of the earth to its abundant water. This water has many forms, as lakes, seas, ponds, springs, rivers. It is salt and fresh, and varies in temperature from the boiling springs or geysers, to the icy seas of the poles. Water has changes of state; from the liquid form it changes by loss of heat to solid ice; moisture, frozen as it falls through the air, becomes crystals of snow; water diffused in the air is mist and dew; partially condensed in the air it forms clouds; and dew in a frozen state is frost.

Let us now see what was the work of water in its forms of ice and snow in the Ice age. Here we do not wander inuncertainties; for what we see to be now the work and changes of ice and snow in the High Alps and the frozen oceans of the north, we may accurately account to have been the work of the same agents in the Ice period. Let us therefore reason from the present to the past. A vast region such as Greenland or Spitzbergen or the high Alpine country is covered deep with snow, which falls upon it nearly every month in the year. For a little time in the summer the sun partially melts the snow even on the heights, so that floods of snow-water begin to run into the valleys. But freezing generally takes place in the night, and the melting period is short, so that the higher plains and valleys become filled with beds of ice; yet from beneath some of these ice-beds water runs out and descends to the lower plains and valleys, becoming in their warmer temperature broad rivers to water the land. As you look from the distance upon the snow-covered Alps, you see broad spaces flashing and shining like silver. These are the glaciers or ice-rivers between the snowy peaks.

These glaciers seem as you observe them to be stationary, but when they are measured they are found to have a steady motion. Thus, you set a post in the glacier and a post in line with it upon the rocks on each side of the glacier. Even in a day or two you will see that instead of three posts in line, thus

they stand in this fashion

and in a few weeks the central post will seem to have travelled some distance down the glacier. But no; the glacier has been sliding along in its bed and carrying the post with it. As the glacier of the Alps moves down, down, down, it comes intowarmer levels, melts and crumbles away, and feeds rivers. But the glacier of the Polar circle when it reaches the limit of its bed has not found a warmer level; it breaks off by its own weight, with a tremendous crash, and falls into the Polar sea, among floes of moving ice. The fallen fragment of glacier settles into the water for about eight-ninths of its entire height, and now takes a new name,—it is an iceberg.

The iceberg is often of great height above water; some bergs weigh hundreds of millions of tons. The air, sun, and dashing water cut the berg into beautiful and fantastic shapes of domes, pinnacles, and towers, from which the sun flashes back as from molten metal. The iceberg floats about the Polar sea, and finally may be carried by the currents southward into warmer waters and a milder climate. Then the melting process goes on swiftly, and when the lower portion becomes so much lessened as to destroy the equilibrium of the floating mountain, it turns over, or portions of it break away and fall into the sea. Thus the history of the marvellous mountain of ice is: first snow falling upon high lands; then from the melting and freezing of the snow, glaciers or ice-rivers; then the glacier moving beyond its bed, breaks off into a berg, and the vagrant of the Polar seas drifts to its destruction in warmer climes.

Now let us go back to the snow mountains and the forming glaciers. As these rivers of ice grind and crowd down their ravines they tear and crush the sides of the mountains and the face of the valley, so that they have beneath them what we may call another stream, and that not of ice, but of broken stones of all sizes. These are frozen to the bottom ofthe glacier and are dragged along with it as it slides down the ravine. The bottom of the glacier moves a little more slowly[30]than the surface; finally it comes down upon the valleys in something of the shape of aV, or the share of a plow. Thus entering the valley it drives a vast amount of débris, as boulders and pebbles, before it, and carries a vast amount more clinging to its upper and lower surfaces.

Now it is evident that as the glacier melts rapidly in the warm valley it will drop the load of stone that it carried with it in its descent from the heights. Such a bed of glacier-driven stone is termed a moraine, and when people have once seen a moraine they will not fail to recognize one wherever they find it, even if it is thousands of miles away from any glaciers. They will say: “Here is a moraine; once there must have been a glacier slowly moving here.” However warm the climate may now be, when we see a moraine we may be assured that once it was cold enough for snow mountains and for glaciers. It is as certain as that every peach-stone we see must once have been in a peach.

Again in the present glacier-districts we find that when glaciers and icebergs slide over beds of rock or masses of stone, they cut and groove them, chisel them in a peculiar fashion; and when on any rock we find these chisel-marks of the ice, they are unmistakable, and we know that ice heavy and strong enough to cut the rock has been there. Whenwe see a name or initial cut in a tree we know that some person with a knife has been there and cut the letters. We recognize the glacier-work just as clearly on the rock as the human work on the tree.

Once more, to go back to our glaciers, we find that they tear from the rocks large masses or lumps of stone; and these fragments being ground and dragged in the ice-bed, lose the sharpness of their edges and become rounded and smooth. The icebergs, as they break from the glacier, carry away these stones frozen to their lower surface, and as the ice melts the stones are let fall. These peculiar stones are called boulders, and some name them “lost stones,” as they are found so far away from their original rocks. These boulders, or lost stones, are scattered over a large portion of the Northern hemisphere. On high hills,[31]in wide fields, and deep valleys, they lie as the ice left them. Some are lodged in the most singular places. When we see a boulder on the crest of some high hill it may be hard to believe that once an icy sea rolled over such an eminence and covered it so deep that icebergs with their enormous masses had rocked above it in the cold, dark waves; but so it truly was. Sometimes we see a wide field covered with boulders lying so closely together that very little vegetation can grow among them. In this field, long ago, some iceberg grounded in the shallow waters and, melting away there, left its load of stones.

There are some geologists who consider that a solid cap or sheet of ice covered nearly the whole of the Northern hemisphere at some distant time, and that the boulders and boulder-clay were the deposit of this ice-sheet, and were not dropped by floating bergs. It is very likely that there were not only floating bergs carrying boulders, but also an ice-sheet extending below the Polar circle. Altogether the drift, the moraines, the ice-scratched rocks, and the boulders lying solitary hundreds of miles from the rocks of which they once formed a part, point out clearly to us what were the general features of the Glacial age of the world.

FOOTNOTES:[30]The bottom of an ice-stream moves more slowly than the surface: this is the case with any stream; thus the surface projects at last beyond the bottom and breaks off in bergs; while at last the lower part enters the valley something like the share of a plow.[31]On the bluffs of the Missouri River, Howard County, Mo., are ice markings, and a lump of copper weighing 23½ pounds was found on these bluffs. This copper was a “lost” lump brought by ice from the coast of Lake Superior.—J. B. S.

[30]The bottom of an ice-stream moves more slowly than the surface: this is the case with any stream; thus the surface projects at last beyond the bottom and breaks off in bergs; while at last the lower part enters the valley something like the share of a plow.

[31]On the bluffs of the Missouri River, Howard County, Mo., are ice markings, and a lump of copper weighing 23½ pounds was found on these bluffs. This copper was a “lost” lump brought by ice from the coast of Lake Superior.—J. B. S.

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