86 THE FORMS OF WATER IN 



§ 31. Sliding and Floiving. Hard Ice and Soft Ice. 



218. We have thus far confined ourselves to the 

 measurement and discussion of glacier motion ; but in 

 our excursions we have noticed many things besides. 

 Here and there, where the ice has retreated from the 

 mountain side, we have seen the rocks fluted, scored, 

 and polished ; thus proving that the ice had slidden over 

 them and ground them down. At the source of the 

 Arveiron we noticed the water rushing from beneath 

 the glacier charged with fine matter. All glacier 

 rivers are similarly charged. The Rhone carries its 

 load of matter into the Lake of Geneva ; the rush of 

 the river is here arrested, the matter subsides, and the 

 Rhone quits the lake clear and blue. The Lake of 

 Geneva, and many other Swiss lakes, are in part filled 

 up with this matter, and will, in all probability, finally 

 be obliterated by it. 



219. One portion of the motion of a glacier is due to 

 this bodily sliding of the mass over its bed. 



220. We have seen in our journeys over the glacier 

 streams formed by the melting of the ice, and escaping 

 through cracks and crevasses to the bed of the glacier. 

 The fine matter ground down is thus washed away; 

 the bed is kept lubricated, and the sliding of the ice 

 rendered more easy than it would otherwise be. 



221. As a skater also you know how much ice is 

 weakened by a thaw. Before it actually melts it becomes 



