E. Desor on the Drift of Lake Superior. 101 
boulders aré as massive and as heavy as those of the surface. It 
ls evident, therefore, that no theory can be admissible which 
tocks are harder and less prone to disintegration. Thus in 
rurdistrict they are most distinct on the trap and compact slates ; 
Pected to be found on the sandstone. Again, in many places the 
tegration, and there remains nothing but the rounded outline of 
the tocks, which, from their resemblance to fleecy clouds, have 
been called, in the Al ps, fleecy rocks. 
“To many instances the polished and grooved surfaces are con- 
| strik bject | 
boii Consists in the fact that, while one side is smoothed 
