i6o 



PHYSIOGRAPHY. 



[chap. 



moraines unite also, as in Fig. 41, where a B c d represent 

 the four lateral moraines of two glaciers. It is clear that, 

 after the union of the two branch-streams, the outer moraines, 

 A and D, will continue to occupy the sides of the trunk- 

 glacier ; while the two inner moraines will unite at the fork 

 E, and form only one ridge of detritus, which will be carried 

 along the middle of the main glacier. This middle line of 

 stones is therefore distinguished as a medial iiwraine. If a 



Fig. 41, — Laleral and medial moraines. 



glacier receives in its course many side-branches, each con- 

 tributing its moraines, the entire surface of the ice may 

 ultimately become strewn with rubbish. 



A glacier resembles a river, not only in its power of thus 

 transporting detritus from a higher to a lower level, but also 

 in acting as a direct agent of denudation. Just as a river 

 wears away its banks and its bed, so the ice acts on the sides 

 and bottom of the valley along which it travels. If the 



