62 THE DENUDANTS OF 



r 

 J 



ran nearly parallel, tlie excavation would be long and 

 narrow. 



The work done by glaciers on their beds may appear 

 at first sight considerable, as the rivers always flow- 

 ing from them are ever turbid and white with the silt, 

 formed by the trituration of the blocks and fragments 

 of rock in the ice grinding against one another, 

 and the sides and bottoms of the valleys. 1 Moreover, 

 this work is never ending from year's end to year's 

 end, as long as the glacier lasts. On consideration, 

 however, it is apparent that the solid matter contained 

 in glacial rivers, is probably far from giving a true 

 indication of the real work done by a glacier in 

 abrading the rocks it passes over ; as the silt held 

 suspended in the waters of the glacial river is not 

 solely due to the abrasion of the rocks passed over, 

 since much, if not most of it, may have been formed 

 from the blocks in the glacier abrading one another. 

 Some of these blocks may have been lifted by the 

 ice and carried away by the glacier, but many of 

 them may have fallen from the adjoining hills on to 

 the glacier, having been dislodged by meteoric 

 action, to find their way afterwards into the body 

 of the glacier through crevasses. Also innumerable 

 particles of rock are carried on to the surface of a 



1 Hayes says, " The ice was perfectly pure and transparent " (of 

 "Tyndall glacier"), "and yet out of its very heart was pouring the 

 muddy stream of which I have made mention." " The Open Polar 

 Sea," p. 436. 



