Page:Popular Science Monthly Volume 20.djvu/243

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231
NORTH AMERICA IN THE ICE PERIOD.

Scandinavia. The more eastern lines penetrate the edges of Russia and Prussia. Those passing into the Gulf of Bothnia and the Baltic Sea curve westerly so as to extend over the North Sea, English Channel, southern England, and the north of Scotland. England and Scotland are made to send off additional currents; and the limit of the ice sheet reaches to west longitude 14°, or where the shallow water begins to deepen. The chart is designed to show the probable path of the ice in Northwestern Europe during the period of maximum glaciation. This area is about seventeen hundred miles wide and fifteen hundred from north to south, and will hence compare favorably in size with that of Eastern America. The phenomena of dispersion are explicable upon the theory of the origin of the current from the central Scandinavian ridge, supplemented by radial streams from the Scotch and Welsh highlands; and there is no evidence, unless upon the outermost Hebrides, of any flow of polar ice into the European district. The ice masses have proceeded from higher to lower levels for the most part, rising somewhat to pass over Denmark and southern England; and there is no essential difference between the Alpine and Scandinavian areas save in size.

All the glaciated districts can now be referred to definite areas, separate from one another, and exhibiting grooves radiating from central points and lines. They are, first, the small Alpine district; second, the Scandinavian, with the British additions; third, the paleocrystic sea of the polar regions; fourth, Greenland; fifth, Eastern America, concerning which more will be said in the sequel; sixth, the Rocky Mountain areas, in which there were several groups of glaciers, confluent north of the Columbia River.

Maps will show how the several glaciated regions stand related to one another. They are isolated, disconnected, though all situated upon one hemisphere. Each was a center by itself. The ice moving from the central highlands made its way radially in all directions, carrying detritus and scouring the ledges. The larger ones do not vary greatly in their territorial dimensions. That of Eastern America exceeds the others, especially if we add to it the Arctic archipelago, where, owing to the high latitude, the mer de glace is nearly universal with no great amount of motion. But we do not discover from this delineation any confirmation of the notion of a general polar ice-cap, which has furnished the ice for both the European and American glacial sheets. The Scandinavian, Greenland, and American regions seem to have been entirely independent of each other—separated by deep ocean-water. All of them must have undergone their intense frigid conditions in post Tertiary times, because of some astronomical cause affecting the northern hemisphere equally throughout. We do not find distinct glaciated areas upon the Asiatic side of the pole, because the relations of land and water are unfavorable to the formation of ice-sheets, but the temperature is and has been low enough.