286 E. C. ANDREWS. 



examples of cirques will have steeper heads than the older 

 enveloping forms. This is from a consideration of the path 

 of a stream particle. 



It would thus appear that the bergschrund as we see it, 

 is an effect rather than a cause of the modern cirque. In 

 the conditions obtaining in the more vigorous ice cutting 

 period just departed, it is extremely improbable that a 

 crevasse situated vertically above the present bergschrund 

 could have penetrated to the glacial depths necessary to 

 have reached bedrock at the present change of slope between 

 cirque base and headward slope. The bergschrund and its 

 sympathetically curving schrunds appear to be a result of 

 tension in a crystalline solid which under earlier conditions 

 of greater volume has been a much more perfect stream mass 

 and which never excavated its channel base to depths 

 greater than those above which it could maintain its stream 

 characteristics. Under the present conditions a get-away is 

 of course found down the old thalweg, and the ice mass 

 yields partly by flow and partly by cracking, since it no 

 longer possesses volume enough to secure continuity of 

 surface. 



But even if this be so, it does not in the least discount 

 the value of Johnson's (pp. 573-576) report on cirques. 

 That report has been invaluable in glacial studies, inasmuch 

 as it has furnished us with the key to the formation of 

 cirques, namely, by headward recession; to the fact of 

 "steps" and "treads " occurring along a glacial valley floor; 

 and to the relatively heavy action at the bases of glaciers. 

 The point neglected in his note is apparently the variable 

 quantitative values (and their significance) of the corrasive 

 action of present and recent glaciers. 



Relation between Cirques and Valley "Steps." — The 

 cirque arises as a result of headward recession, but in this 

 process the channel base will doubtless be cut up into a 



