THE WORK OF SNOW AND ICE 



243 



moraines on one glacier, in which case some of them may be far 

 from the center. In valley glaciers, the surface terminal moraine 

 often connects two lateral moraines, making a loop roughly con- 

 centric with the end of the glacier. 



Besides the surface moraines, there may be scattered bowlders 

 and bits of rock of various sizes on the ice, and, in addition to the 



Fig. 199. Figure showing the union of glaciers and the development of 

 medial moraines by the union; also the position of lateral moraines. 

 (After Tyndall.) 



coarse material, there is often some dust which has been blown 

 upon the ice. 



Relief due to surface debris. The debris on the ice affects its 

 topography by influencing the melting of the ice beneath and about 

 it. The rock debris absorbs heat more readily than the ice. A 

 thin piece of stone lying on the ice is warmed through by the sun's 

 rays, and, melting the ice beneath, sinks, just as a piece of black 



