GLEN ROY, IN SCOTLAND. 
47 
glacier is thick enough to cover them com¬ 
pletely, and even to rise far above them. The 
roches moutonnSes about the Grimsel show that 
hills many hundred feet high have been passed 
over by the great glacier of the Aar, when it 
descended as far as Meyringen, without having 
seemingly influenced its onward progress. 
In enumerating the evidences of glacier ac¬ 
tion, we have to remember not only the effects 
produced upon the surface of the ground by 
the ice itself, but also the deposits it has left 
behind it. The loose materials scattered over 
the face of the earth may point as distinctly 
to the source of their distribution as does the 
character of the rocky surfaces on which they 
rest indicate the different causes of abrasion. 
In characteristic localities the loose materials 
deposited by glaciers may readily be recog¬ 
nized at first sight, and distinguished from 
water-worn pebbles ; nor is it difficult to dis¬ 
tinguish both from loose materiais resulting 
from the decomposition of rocks on the spot, 
— the latter always agreeing with the rocks on 
which they rest, while the decomposition to 
which they owe their separation from the solid 
rock is often still going on. Such debris are 
