210 THOMAS C. CHAMBERLIN AND ROLLIN T. CHAMBERLIN 



at some point near the upper edge of the snow mass there should 

 come to be a line of strain between the thicker part below that 

 is forced to move and the thinner part above that lacks sufficient 

 stress to take on motion. A low temperature is essential to the 

 preservation of the elements that enter into the process. Through 

 this low temperature the snow-ice mass has become adherent to 

 the soil beneath it and more or less interlocked with the loose 

 rock that may be at or near the surface. The motion of the snow- 

 ice mass involves the motion of some part of this underlying 

 material. Under the snow-protected stationary part the loose 

 earth-surface remains behind. The line of division between the 

 stationary protective snow and the moving abrasive snow-ice 

 mass thus demarks a scar and this scar, if we interpret aright, is 

 the embryo of the future cirque. As the process goes on and the 

 excavation becomes deeper and by this deepening comes itself 

 to aid in the catchment process, the line of transition from the 

 ineffectively thin snow above to the effective deep snow below 

 becomes more sharply defined. Thus the delimitation of the 

 growing glacier-head and its product, the growing cirque, not 

 only becomes more pronounced but the line of parting between 

 the active and the inert becomes fixed by the process itself; and 

 so the declared cirque becomes established and its bergschrund 

 localized. With further progress the action graduates into the 

 still more declared forms of the cirque-generating process. 



In the exposition of Willard D. Johnson 1 as also in that of 

 G. K. Gilbert, 2 both of which we accept in the main, the berg- 

 schrund is made the dominant agency in the cirque formation. The 

 view just outlined carries the cirque-forming action back of even 

 the cirque itself and, potentially at least, back of any bergschrund 

 or any possible influence arising from the bergschrund. It makes 

 the bergschrund and the cirque-development sequent on conditions 

 and agencies that at an earlier stage controlled the snow-ice accumu- 



1 Willard D. Johnson, "The Profile of Maturity in Alpine Glacial Erosion," 

 Jour, of Geol., XII (1904), 569-78. Earlier papers are "An Unrecognized Process 

 in Glacial Erosion," Science (1899), p. 106; "The Work of Glaciers in High Moun- 

 tains," ibid., 1 1 2-13. 



2 G. K. Gilbert, "Systematic Asymmetry of Crest Lines in the High Sierra of 

 California," Jour, of Geol., XII, 579-88. 



