
Parr II. Scr. ii. § 5] GLACIER EROSION. 415 
rock having smooth undulating forms like dolphins’ backs are con- 
spicuous. These have received the name of roches moutonnées. The 
stones by which this scratching and polishing are effected suffer in 
exactly the same way. They are ground down and striated, and 
since they must move in the line of least resistance, or “end on,” 










































































































































Fic. 151.—V1EwW OF PART OF THE SIDE OF THE MER DE GuLace (J. D, ForBEs), 
their strize run in a general sense lengthwise (Fig. 154). It will be 
seen, when we come to notice the traces of former glaciers, how 
important is the evidence given by these striated stones. 
Besides its proper and characteristic rock-erosion, a glacier is 
aided in a singular way by the co-operation of running water. 
Among the Alps during day in summer much ice is melted and 
the water courses over the glaciers in brooks which, as they reach 
the crevasses, tumble down in rushing waterfalls, and are lost in the 
depths of the ice. Directed, however, by the form of the ice-passage 
against the rocky floor of the valley, the water descends at a par- 
ticular spot, carrying with it the sand, mud, and stones which it may 
have swept away from the surface of the glacier. By means of these 
materials it erodes deep pot-holes (moulins) in the solid rock, in 
which the rounded detritus is left as the crevasse closes up or moves 
down the valley. On the ice-worn surface of Norway singular cavities 
