There are now two places on the earth where vast glaciers, or ice sheets, cover immense areas of land, one in the Antarctic, a region very little known, the other in Greenland, where there is an ice sheet covering land having an area more than ten times that of the State of New York. Let us study this region to see what is being done there, in order to compare it with what has been done in New York.
Fig. 29. The edge of a part of the great Greenland ice sheet (on the left) resting on the land, over which are strewn many boulders brought by the ice and left there when it melted.
In the interior is a vast plateau of ice, in places over 10,000 feet high, a great icy desert ([Fig. 28]), where absolutely no life of any kind, either animal or plant, can exist, and where it never rains, but where the storms bring snow even in the middle of summer. Such must have been the condition in northeastern America during the glacial period.
Fig. 30. A scratched pebble taken from the ice of the Greenland glacier.
This vast ice sheet is slowly moving outward in all directions from the elevated center, much as a pile of wax may be made to flow outward by placing a heavy weight upon the middle. Moving toward the north, east, south and west, this glacier must of course come to an end somewhere. In places, usually at the heads of bays, the end is in the sea, as the end of our glacier must have been off the shores of New England. From these sea-ends, icebergs constantly break off; these floating away toward the south, often reach, before they melt, as far as the path followed by the steamers from the United States to Europe. Between bays where the glacier ends in the sea, the ice front rests on the land ([Fig. 29]), as it did over the greater part of New York and the states further west. There it melts in the summer, supplying streams with water and filling many small ponds and lakes. The front stands there year after year, sometimes moving a little ahead, again melting further back so as to reveal the rocks on which it formerly rested.
Fig. 31. A part of the edge of the Greenland glacier, with clean white ice above, and dark discolored bands below where laden with rock fragments. In the foreground is a boulder-strewn moraine.
The bed rock here is found to be polished, scratched and grooved just like the bed-rock in New York; and the scratches extend in the direction from which the ice moves. Resting on the rock are boulders and pebbles ([Fig. 22]), sometimes on the bare rock, sometimes imbedded in a clay as they are in the drift. As we found when studying the soil in our own region, so here the pebbles are often scratched, and many of them are quite different from the rock on which they rest.