. Elements of geology : a text-book for colleges and for the general reader. Geology. MOKAIXES. 55 its tributaries shows clearly the manner in which these moraines are formed. Both lateral and medial moraines are generally situated on a ridge of ice, sometimes fifty to eighty feet high, evidently formed by the protection of the ice, in this part, from the melting power of the sun. The fragments of rock brought down by glaciers are often of enormous size. One described by Forbes contained 244,000 cubic feet. The ground moraine is the mass of debris carried between the glacier and its bed. It is
. Elements of geology : a text-book for colleges and for the general reader. Geology. MOKAIXES. 55 its tributaries shows clearly the manner in which these moraines are formed. Both lateral and medial moraines are generally situated on a ridge of ice, sometimes fifty to eighty feet high, evidently formed by the protection of the ice, in this part, from the melting power of the sun. The fragments of rock brought down by glaciers are often of enormous size. One described by Forbes contained 244,000 cubic feet. The ground moraine is the mass of debris carried between the glacier and its bed. It is derived partly from erosion of the bed, and partly from top ma- terial (lateral and medial mo- raines) ingulfed and carried down to the bottom. Everything which falls upon the surface of the glacier is slow- ly and silently carried downward by this ice-stream, and finally dropped at its point. Much finely-triturated matter is also pushed along beneath the gla- cier, and finds its way to the same point. In the course of time an immense accumulation is formed, of somewhat cres- centic shape, as seen in Fig. 44. This accumulation is called the terminal moraine. It is the delta of this ice-river. The existence of moraines is a constant witness of the motion of the glaciers. Glaciers as a Geological Agent. Glaciers, like rivers, erode the surface over which they move, carry the materials gathered in their course often to great distances, and finally deposit them. In all these respects, however, the effects of their action are perfectly characteristic. Erosion.—When we consider the weight of glaciers and their un- yielding nature as compared with water, it is easy to see that their erosive power must be very great. This is increased immensely by fragments of stone of every conceivable size carried along between the glacier and its bed. These partly fall in at the sides and become. Fig. 44.—Mer de Please note that these images are extracted from scanned page images that m
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