244 



GEOLOGY 



cloth on snow will sink because of the increased melting beneath 

 it. Though a good absorber of heat, rock is a poor conductor, and 

 so the lower surface of a thick mass of stone is not warmed notably, 

 and the ice beneath, being protected from the sun, is melted more 

 slowly than that around it. The result is that the bowlder present^ 



Fig. 200. A glacial table due to the protection of the ice beneath the H:it 

 stone from the rays of the sun. Talefre Glacier. 



stands on a protuberance of ice (Fig. 200). When its pedestal be- 

 comes high, the oblique rays of the sun and the warm air surround- 

 ing it cause it to waste away, and the capping bowlder falls 



The same principles apply to the moraines. A surface moral in* 

 usually protects the ice beneath from melting, and causes the de- 

 velopment of a ridge of ice beneath itself. As the ice on either 

 side is lowered by ablation, the moraine matter tends to slide down 



