UK I. IKK OF GLACIERS 



137 



notably, and the ice beneath, being protected from the sun, is 

 melted less rapidly than that around it. The result is that the 

 bowlder presently stands on a protuberance of ice (Fig. 139). When 

 its pedestal becomes high, the oblique rays of the sun and the 

 warm air surrounding 

 it cause it to waste 

 away, and the cap- 

 ping bowlder falls. 

 The same prin- 

 ciples apply to mo- 

 raines. A surface 

 moraine protects the 

 ire beneath from 

 melting, and causes 

 the development of 

 a ridge of ice beneath 

 itself. As the ice on 

 either side is lowered 

 by ablation, the mo- 

 raine matter tends to 

 slide down on either 

 hand. So far does this 

 spreading go, that in 

 some cases the lower 

 end of a glacier is 

 completely covered 

 with debris which 

 has spread from me- 

 dial and lateral mo- 



Fig. 139. A glacial table due to the protection of 

 the ice beneath the flat stone from the rays of the sun. 

 T;ilefre Glacier. 



raines. 



Debris below the 

 surface. Debris carried by a glacier is not restricted to its upper 

 surface. Debris near the bottom is in some cases so abundant, espe- 

 cially near the ends and edges of the ice, that it is difficult to locate 

 the bottom of the glacier; for between the moving ice which is full 

 of debris, and the stationary debris which is full of ice, there seems 

 to be complete gradation. The debris in the lower part of arctic 

 glaciers, and to some extent of others, is in many cases disposed in 

 thin sheets between layers of clean ice. Debris also occurs to some 

 extent in tin- ice far above its base, in some places in sheets and in 



