X.] ICE AND ITS WORK. i6i 



ice has to turn a sharp corner, or make an abrupt descent, it 

 is forced to spHt, and in this way yawning chasms, perhaps 

 hundreds of feet in depth, are produced in the glacier. 

 Such rents are termed crevasses. Stones, sometimes of great 

 size, fall with a crash down these clefts, and reaching the 

 bottom of the glacier get frozen into its base. As the 

 glacier moves, these stones, pressed by the weight of ice 

 above, scratch and score the rocky bed in the direction of 

 the ice-flow; while the stones themselves, jammed in between 

 the ice and its floor, get bruised in turn, so that by the time 

 they are discharged at the terminal moraine they may be 

 covered with parallel scratches. 



At the same time, the smaller fragments worn off the rocks 

 by the passage of a glacier get ground down into fine 

 gravel, sand, and mud, which may be carried in suspension 

 by the stream of water which flows over the bed of the 

 glacier. For it should be noted that the bottom layer of 

 ice, pressed by the weight above, and grinding along the 

 floor, is generally in a state of thaw ; and, moreover, water 

 finds its way from the surface to the bottom through cre- 

 vasses. Hence, a little liquid stream separates the bottom ice 

 from the rocky bed; and at the end, or snout, of the glacier 

 this water issues forth, not indeed as a clear bright spring, but 

 as a thick stream laden with detritus. The Rhine, the Rhone, 

 the Po, the Ganges, and many other large rivers, may be traced 

 back to muddy streams springing from glaciers. The fine 

 detrital matter which the water thus carries along polishes 

 the surface of the rock over which it flows. The action of 

 a glacier is consequently twofold : the fine sandy matter 

 polishes the surface, while the large stones scratch furrows. 

 It is, in fact, as though some giant hand had rubbed the 

 surface of the rock with fine emery powder, and at the same 

 time rasped it with a huge file. 



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