Page:Popular Science Monthly Volume 4.djvu/666

646 the fine lines of striation. The soft sandstones and highly-jointed rocks are much less finely marked, and often show a broken and shattered surface.

—To understand the appearance of Northern Europe in the Ice period, we may consider the features presented by a similar ice-covered country in modern times, and no country will better illustrate this phase of geological condition than Greenland. This island is almost continental in its dimensions, containing not less than 750,000 square miles, and is all a bleak wilderness of ice and snow, save a little strip extending to 74° north latitude along the western shore.

The coasts are deeply indented with numerous bays and fiords or firths, which, when traced inland, are almost invariably found to terminate against glaciers. Thick ice frequently appears, too, crowning the exposed sea-cliffs, from the edges of which it droops in thick, tongue-like, and stalactitic projections, until its own weight forces it to break away and topple down the precipices into the sea. The whole interior seems to be buried beneath a great depth of snow and ice, which loads up the valleys and wraps over the hills. The scene opening to view in the interior is desolate in the extreme—nothing but one dead, dreary expanse of white, so far as the eye can reach no living creature frequents this wilderness—neither bird, beast, nor insect. The silence, deep as death, is broken only when the roaring storm arises to sweep before it the pitiless, blinding snow.

This represents perfectly the state of the northern part of our continent in the Ice age. We have a slight inkling of what it must have been universally, from the heroic messages sent down in the winter from the meteorological observatory stationed upon the summit of Mount Washington.

Some of the Greenland glaciers attain a vast size. Dr. Kane reports the great Humboldt glacier (see Fig. 1) as sixty miles wide at its termination. Its seaward face rises abruptly from the level of the crater to a height of 300 feet, but it is not known how deep it may extend under the sea. Another important ice-stream is the Glacier of Eisblink, on the northwest part of the island. It projects seaward so as to form a promontory thirteen miles in length. It comes from an unknown distance in the interior, and plunges deeply into the sea.

Since ice is lighter than water, whenever a glacier enters the sea the dense salt-water tends to buoy it up. The great tenacity of the frozen mass enables it to resist the pressure for a time. By-and-by, however, as the ice reaches deeper water, its cohesion is overcome, and large segments are forced from its terminal part, and floated up from the bed of the sea, to sail away as icebergs. The glacier evidently crops under the water to considerable depths, or, so long as the force of cohesion is able to resist the tendency of the salt-water to press it upward. The annexed diagram will show how the ice pushes down into the sea, carrying morainic materials at its base, which