394 



EARTH FEATURES AND THEIR MEANING 



At the foot of the glacier the relatively angular rock debris, 

 which has been carried upon the surface, and the soled and polished 

 englacial material from near the bottom, are alike deposited in a 

 common marginal ridge known as the terminal or end moraine 

 (plate 21 B). 



Selective melting upon the glacier surface. The white sur- 

 face of the glacier generally reflects a large proportion of the sun's 



FIG. 421. Ideal cross-section of a mountain glacier to show the position of 

 moraines and other peculiarities characteristic of the surface of the bed. 



rays which reach it, and its more rapid melting is largely accom- 

 plished through the agency of rock fragments spread upon its 

 surface. Such fragments, however, promote or retard the melting 

 process in inverse proportion to their size up to a certain limit, 



FIG. 422. Fragments of rock of different sizes, to bring out their different 

 effects upon the melting of the glacier surface. 



