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 the 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. [Illustration: _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. [Illustration: _Fig. 32. Hummocky surface of the boulder-strewn moraine of Greenland._] Going nearer to the ice we find the lower part loaded with pebbles, boulders and bits of clay very like those on the rocks near by. Fig. 30 shows one of these, scratched and grooved, which I once dug from the ice of this very glacier. The bottom of the ice is like a huge sandpaper, being dragged over the bed rock with tremendous force. It carries a load of rock fragments, and as it moves secures more by grinding or prying them from the rocks beneath. These all travel on toward the edge of the ice, being constantly ground finer and finer as wheat is ground when it goes through the mill. Indeed the resemblance is so close that the clay produced by this grinding action is often called _rock flour_.