10 



THE ICE AGE IN NORTH AMERICA. 



the ice underneath it from melting; so that the moraine 

 will often appear to be much larger than it really is : what 

 seems to be a ridge of earthy material 

 being in reality a long ridge of ice, thinly 

 covered with earthy debris, sliding down 

 the slanting sides as the ice slowly wastes 

 away. Large blocks of stone in the same 

 manner protect the ice from melting un- 

 Modeoffoi^tion derneath, and are found standing on pe- 



FlG. 



of ice-pillars. 



destals of ice, where the general surface 

 has been lowered sometimes several feet. An interesting 

 feature of these blocks is that when the pedestal fails, the 

 block uniformly falls to- 

 ward the sun, since that 

 is the side on which the 

 melting has proceeded 

 most rapidly. 



All the material 

 brought down upon the 

 surface of the glacier in 

 the medial moraines is 

 deposited at the front, 

 forming a terminal mo- 

 raine, which will vary in 

 size according to the 

 abundance of material 

 transported by the ice, 

 and in proportion to the 

 length of time during 

 which the front rests at 

 a particular point. But, 

 ordinarily, for a consid- 

 erable distance this mo- 

 raine material near the 

 front will rest upon ex- 



tatigiVo Tnocaoa /vf \na FlG - 10 ~ Mer de Glace. The parallel lines in the 



itJilblve Uldbbtib Ul ice middle are medial moraines. The main ice- 



mVii/Vh f\W\xr clr*wh7 malf stream on the right pushes the others to the wall, 



wniCU Only SlOWiy melt and divides the terminal moraine above g. 



