Page:Popular Science Monthly Volume 35.djvu/705

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ARCTIC ICE AND ITS NAVIGATION.

on our coasts. There is but one narrow passage for the Bering floes, and the ice after passing through the strait scatters and becomes easier to avoid. The pack is not confined and caused to revolve between immense icebergs or many narrow passages, as in Greenland or eastern waters, so that the recent employment of steam whalers, instead of the old-time sailing vessels, has been dictated more by a desire for increased profits than by actual necessity.

But there is another and more dangerous ice than floe ice, as it takes many years for its formation. It is met with in isolated floes, but rarely if ever in pack below Smith's Sound, and the Scotch whalers seldom encounter it. Ships have been nipped hundreds of times in floe ice and escaped, but few if any have ever freed themselves from the fierce grasp of the ancient ice of the arctic, called by Nares floe-berg or paleocrystic ice. This bears evidence of great age, the part above water being from fifteen to forty-five feet in thickness, which would make its depth from one hundred and thirty-five to four hundred and five feet; the stoutest-built ship that ever put to sea would be crushed into matchsticks by the pressure of two such floes upon her sides. This ice forms the northern limit of the cruising-grounds of the American whalers north of Alaska. Some years it moves to the southward and closes up on them; again, it recedes, disclosing more of the mystery of the farther north. Scattered here and there through it are polynias, or lakes of ice, of one year's growth, inclosed by heavy floes arched and keyed together.

Paleocrystic ice is old pack ice built up by successive deposits of snow during a long period of time, thus giving it an appearance of stratification. There is an alternation of soft white and hard blue ice, representing, respectively, compressed snow and water formed during the sunshine by thaws, and frozen at night or when cloudy. (It is a remarkable fact that snow will melt and seep through floe ice in sunlight though the thermometer may record far below the freezing-point.) Eventually, during the long summer day, the floe is left bare and dry, but soft and porous, unless so far north that the snow-storms continue all the year round. Over some strata are layers of atmospheric dust, such as Nordenskiöld found on the Greenland glaciers; also the gradual decrease of the thickness of the layers—due to pressure and increase of blue ice—because of greater infiltration, as the lower part of the berg is approached, make certain the progressive nature of the formation.

Beyond the Melville Bay pack, averaging six feet in thickness, lies the "north water" of the whalers, corresponding to the open space usually found between the paleocrystic pack and Bering Strait. This is dotted with hummocks, rubble ice, or broken-up