316 THE BEAUTIES OF NATURE chap. 



why it is so fine, so impalpable. That glaciers 

 do deepen their beds seems therefore unques- 

 tionable. 



Moreover, though the depth of some of 

 these lakes is great, the true slope is very 

 slight. 



Tyndall and Ramsay do not deny that the 

 original direction of valleys, and consequently 

 of lakes, is due to cosmical causes and geo- 

 logical structure, while even those who have 

 most strenuously opposed the theory which 

 attributes lakes to glacial erosion do not 

 altogether deny the action of glaciers. Favre 

 himself admits that " it is impossible to deny 

 that valleys, after their formation, have been 

 swept out and perhaps enlarged by rivers and 

 glaciers." 



Even Ruskin admits "that a glacier may 

 be considered as a vast instrument of friction, 

 a white sand-paper applied slowly but irresist- 

 ibly to all the roughness of the hill which it 

 covers." 



It is obvious that sand-paper applied 

 " irresistibly " and long enough, must 

 gradually wear away and lower the surface. 



