CERTAIN PHASES OF GLACIAL EROSION 21 1 



lation and brought on motion in the thicker part of the mass while 

 it left the thinner part stationary and protective. The berg- 

 schrund and the cirque cliff are themselves made, sequences of a 

 mobility and erosive competency more primitive than themselves. 

 This in turn is contrasted with adjacent inertness and erosive 

 inefficiency. 



All this, however, seems to us wholly compatible with a cordial 

 acceptance of the bergschrund and the cirque wall as auxiliary 

 sequential agencies which strikingly abet the more primitive 

 actions that brought them into being. Much as the bergschrund 

 may aid the backward sapping of the cirque wall, we think that the 

 more fundamental agencies are to be regarded as controlling the 

 process throughout its history. 



As already implied, a marked peculiarity of ice, shared in equal 

 degree by no other familiar body, is its tendency to grow under 

 tension and to form adhesions by such growth at the points where 

 tension has been developed. When forced to part, ice parts 

 suddenly by abrupt fracture attended by the elastic recoil of the 

 separated faces. In this its action is in marked contrast to the 

 separation of viscid bodies, which part by a gradual weakening and 

 stretching under continued strain. Within the bergschrund, as 

 also elsewhere and in general, the predisposition of the ice, when 

 at the critical temperature of congelation and below, is to freeze 

 to whatever falls in from the surface or is loosened from the walls. 

 This tendency to form adhesions is no doubt especially active at 

 the base of the schrund and at the foot of the cirque wall, where the 

 convergence of the walls wedges all such matter together and where 

 the conditions of temperature and moisture are likely to be favor- 

 able to glacial attachments in the active season. Whatever snow 

 falls in, slides in, or is blown into the gaping mouth of the schrund, 

 and whatever rock is detached from the cirque wall by the freezing 

 of such waters as may come down the bergschrund are subject to 

 such attachment to the head of the glacier and to removal by it 

 as it moves, as Johnson has indicated. In addition to this, such 

 waters as enter the mountain at any point above the cirque and 

 traverse internal joints and later come out to the face of the cirque 

 wall lower down are subject to freezing as they come near the 



