316 THE BEAUTIES OF NATURE CHAP, 
why it is so fine, soimpalpable. 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 
shght. ) 
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. 
