GLACIERS. 



53 



the great transverse fissures are formed by the glacier passing over an 

 angle formed by a sudden change in the slope of the bed. Streams, 

 produced by the melting of ice, running on the surface of the glacier, 

 plunge into, these fissures with a thundering noise, and hollow out im- 

 mense wells, called moulins, and magnificent ice-caves. Although the 

 glacier moves, the great crevasses and the wells with their falls remain 

 stationary, precisely as the position of a rapid or breaker remains sta- 

 tionary, although the river runs onward ; and for the same reason, viz., 

 that it is reformed always on the same spot. 



From all these causes the surface of a glacier is often studded over 

 with conical masses and projecting points of every conceivable shape. 

 This is well shown in the accompanying figure (Fig. 42). These in- 



Fig. 42.— Inequalities of the Surface of a Glacier (after Agassiz). 



equalities are, of course, the result of differential melting. The whole 

 melting (ablation) is much greater, even as much as twenty-five feet 

 in the course of the summer.* 



Earth and Stones, etc. — The surface of a glacier is, moreover, largely 

 covered with earth and stones gathered in its course from the crumbling 

 cliffs on either side. These are often so abundant as almost to cover 

 the surface. More usually, however, they are distributed in two or more 

 rows, called moraines. Fig. 43 is a view of a glacier, with its moraines 

 and lateral crevasses. 



Such is a general description of the appearance of a glacier. There 

 are, however, several points which, by their importance and interest, 



* Prestwich, Geology, vol. i, p. 176. 



