6l8 THE JOURNAL OF GEOLOGY, 



its total volume, and this effect will be progressive with increas- 

 ing distance from the hill which was the occasion of the 

 whole phenomenon under consideration. 



In many cases there are bosses of rock in the path of a 

 glacier which the ice is able to override. They yield material 

 to the bottom of that part of the ice which passes over them, but 

 it is to be remembered that the bottom of the ice which passes 

 over them may be near the surface of the glacier. When the ice 

 has passed the prominence, the material which was borne from its 

 top may find itself in an englacial position, and may be far above 

 the bottom of the transporting ice. Subsequently, surface melting 

 may bring the surface of the glacier down to its level. Such 

 englacial material then becomes superglacial, and has the general 

 position of a medial moraine. It would be, in fact, a medial 

 moraine made up wholly of englacial-superglacial debris and 

 not produced by the union of lateral moraines. 



A lateral or medial moraine is likely to lose its distinctness 

 as the end of the glacier is approached. Where such a moraine 

 has sufficient body, it protects the ice beneath from melting. 

 The ice beneath therefore assumes the form of a ridge, which is 

 drift covered. Under these circumstances, the drift tends to 

 slide down the sides of this ice-ridge. In time the drift may 

 spread itself somewhat widely over a glacier sometimes even 

 covering its whole surface, near its lower end. 



The percentage of englacial material which will ultimately 

 become superglacial is believed to depend upon its position in 

 the ice, and upon the relative rates of surface and basal melting. 

 If surface and basal melting be equal, the material of the upper 

 half of the ice will ultimately come to be superglacial. If the 

 rate of melting at the upper surface of the ice be greater than 

 that at the lower, the englacial material carried by something 

 more than the upper half of the ice will ultimately become 

 superglacial, as the result of surface melting. 



It is a mooted question whether glacial motion is of such a 

 nature as to allow the transfer of material from the base of a 

 glacier to its surface. It is often urged that drift may be transferred 



