Spricut.—Hanging Valleys of the Upper Rangitata Valley. 95 
Cockayne Glacier with the Heim on the Lyell. The latter member of 
these pairs would no doubt leave hanging valleys were the ice to disappear, 
and yet they would not be dependent for this feature on differential 
erosi 
size. The erosion of the lip of the hollows does not appear to be at all 
The possibility that hanging valleys might be eroded along a belt of 
weak rocks was considered by Davis (1900, p. 283), but he decided against 
it even in the critical case of the Linth Valley, leading into the Wallen 
conditions of erosion above inferred for the trunk glacier." Davis thus 
contemplates that rock-structure may have an important effect on the 
formation of corries, but it is hard to see why the formation of an 
extended basin should be delayed till change of climate. Why should 
this process not go on at the time when the trunk valley is filled with ice ? 
Some such mode of formation of hanging valleys is described by 
Russell (1905, p. 79). He says, " It is evident from the inspection that 
typical mountain-side glaciers are engaged in excavating depressions for 
themselves, which at an early stage in the process have the essential 
ures of cirques, and at a later stage develop a valley of the typical 
U-shaped cross-profile, flat bottom, &c., with a cirque at its head. These 
glaciers. may be said to burrow into the mountain-side by headward 
extension, chiefly, as is judged, by ‘ quarrying.’ The lower limit to which 
they are able to excavate their beds, or the local base level, is determined 
by melting. A glacier of the type referred to deepens its bed to this 
