GLEN ROY, IN SCOTLAND. 
41 
deeply, but their edges are simply abraded on 
one line with the adjoining surfaces. What¬ 
ever be the inequality in the hardness of the 
materials of which the rock consists, even 
in the case of pudding-stone, the surface is 
abraded so evenly as to leave the impression 
that a rigid rasp has moved over all the undu¬ 
lations of the land, advancing in one and the 
same direction and levelling all before it. 
Among the inequalities of the glacier-worn 
surfaces which deserve especial notice are the 
so-called roches moutonnees. They are knolls 
of a peculiar appearance, frequent in the 
Alps, and first noticed by the illustrious De 
Saussure, who designated them by that name, 
because, where they are numerous and seen 
from a distance, they resemble the rounded 
backs of a flock of sheep resting on the ground. 
These knolls are the result of the prolonged 
abrasion of masses of rocks separated by deep 
indentations wide enough to be filled up by 
large glaciers, overtopping the summits of the 
intervening prominences, and passing over 
them like a river, or like tide-currents flowing 
over a submerged ledge of rock. It is evident 
that water rushing over such sunken hills or 
