GLACIAL FEATURES 299 



transformation into neve. In this view the schrund opens not at 

 the foot of the cirque wall but well above it as in Fig. 198, in 

 which C represents snow from top to bottom ; B, neve ; and A, ice. 

 The required conditions are then (1) that the steepening of the 

 cirque wall from x to y should be effected by sapping originated 

 at y through the agencies outlined by Johnson; (2) that the steep- 

 ening from x to y should be effected by sapping originated at x 

 through the change of the agent from neve to ice with a sudden 

 change of function; (3) and that the essential unity of the wall 

 x-y-z be maintained through the erosive power of the neve, which 

 would tend to offset the formation of a shelf along a horizontal 

 plane passed through y. The last-named process not only appears 

 entirely reasonable from the conditions of gradient and depth out- 

 lined on pp. 296 to 298, but also meets the actual field conditions in 

 all the cases examined in the Peruvian Andes. This brings up 

 the second and third of our main considerations, that the berg- 

 schrund does not always or even in many cases reach the foot of 

 the cirque wall, and that cirques exist in many cases where berg- 

 schrunds are totally absent. 



It is a striking fact that frost action at the bottom of the 

 bergschrund has been assumed to be the only effective sapping 

 force, in spite of the common observation that bergschrunds lie 

 in general well toward the upper limits of snowfields — so far, in 

 fact, that their bottoms in general occur several hundred feet 

 above the cirque floors. Is the cirque under these circumstances 

 a result of the schrund or is the schrund a result of the cirque? 

 In what class of cirques do schrunds develop? If cirque develop- 

 ment in its early stages is not marked by the development of 

 bergschrunds, then are bergschrunds an essential feature of 

 cirques in their later stages, however much the sapping process 

 may be hastened by schrund formation? 



Our questions are answered at once by the indisputable facts 

 that many schrunds occur well toward the upper limit of snow, 

 and that many cirques exist whose snowfields are not at all broken 

 by schrunds. It was with great surprise that I first noted the 

 bergschrunds of the Central Andes, especially after becoming 



