GLACIAL FEATURES 301 



me from solving the problem, but it offered sufficient evidence at 

 least to indicate the probable lines of approach to a solution. For 

 example it is noteworthy that in all the cases examined the 

 schrundline was better developed the further glacial erosion had 

 advanced. So constantly did this generalization check up, that if 

 at a distance a short valley was observed to end in a cirque, I 

 knew at once and long before I came to the valley head that a 

 shoulder below the schrundline did not exist. At the time this 

 observation was made its significance was a mystery, but it repre- 

 sents a condition so constant that it forms one of the striking 

 features of the glacial forms in the headwater region. 



The meaning of this feature is represented in Fig. 199, in 

 which three successive stages in cirque development are shown. 

 In A, as displayed in small val- 

 leys or mountainside alcoves 

 which were but temporarily oc- 

 cupied by snow and ice, or as in 

 all higher valleys during the 

 earlier stages of the advancing FlG i 99 _ Furtlier sta g e s in the de- 



hemicycle of glaciation, SnOW velopment of cirques. See p. 299 and Fig. 



collects, a short glacier forms, 



and a bergschrund develops. As a result of the concentrated frost 

 action at the base of the bergschrund a rapid deepening and steep- 

 ening takes place at a. As long as the depth of snow (or snow and 

 neve) is slight the bergschrund may remain open. But its existence 

 at this particular point is endangered as the cirque grows, since the 

 increasing steepness of the slope results in more rapid snow move- 

 ment. Greater depth of snow goes hand in hand with increasing 

 steepness and thus favors the formation of neve and even ice at 

 the bottom of the moving mass and a constantly accelerated rate 

 of motion. At the same time the bergschrund should appear 

 higher up for an independent reason, namely, that it tends to 

 form between a mass of slight movement and one of greater 

 movement, which change of function, as already pointed out, 

 would appear to be controlled by change from snow to neve or 

 ice on the part of the bottom material. 



