GLACIERS 



thus, in the first instance, rendered more irregular than before, 

 because the hollows formed by the varying depths to which 

 atmospheric disintegration descends (see p. 78) are cleared out 



and the rocks laid bare. 



Bare rocks, when exposed to 

 the action of the moving ice, 

 are ground down, scored, pol- 

 ished, and rounded in a way 

 that can be accomplished by 

 no other agent, and which is 

 the unmistakable autograph of 

 the glacier. Stones of all sizes, 

 pebbles, sand, and dust, make 

 their way from the surface to the 

 bottom of the glacier through 

 the crevasses, while others are 

 picked up from the bed. These 

 hard pieces are firmly held by 

 the great weight of the ice, 

 and are slowly pushed along 

 over the rocky bed with irre- 

 sistible power, cutting grooves 

 of a size corresponding to the 

 fragments which do the work. 

 Fine particles make hair-like 

 scratches, large boulders cut 

 deep troughs, such as the re- 

 markable ones found on Kelly's 

 Island in Lake Erie ; but all, 

 whether coarse or fine, are in 

 the direction of the glacial flow and keep parallel, often for 

 considerable distances. 



The smaller particles, earth and sand, and those which are made 

 by the abrasion of the bed, act as a polishing powder, and if the 

 rocks of the bed are sufficiently hard, they will be finely polished. 

 Hummocks of rock, over which the ice passes, are worn down 



