3 i8 HARRY FIELDING REID 



the bergschrund of one of the smaller Sierra glaciers, where he found 

 the rock impregnated with water melted from the ice, and the broken 

 nature of the rock led him to believe that much sapping was accom- 

 plished at this point by the frequent freezing and melting of the water. 

 This led to the belief that sapping of this kind explained the glacial 

 erosion. Mr. Johnson has since given up this idea, because the 

 bergschrund must be shallow in comparison with the depth of the 

 ice; but he thinks that the line of the ancient bergschrund can still 

 be recognized by a very steep cliff in the upper part of the walls of 

 the cirques of the Sierras. 



Mr. G. K. Gilbert 1 confirms the existence of a "schrundline," 

 and brings out the interesting fact that a distinct difference in slope 

 often exists on opposite sides of ridges in the high Sierras. The 

 steeper side is that on which the snow would naturally accumulate 

 as a result of the prevailing winds and of protection from the snow. 

 He therefore concludes that the glaciers formed from the snow have 

 by erosion steepened the slopes. In the volume of the Harriman 

 Alaska Expedition on Glaciers and Glaciation, briefly noticed in last 

 year's report, Mr. Gilbert presents a very strong argument in favor 

 of the great erosive action of glaciers. 2 



Dr. Albrecht Penck 3 discusses the action of glaciers in the Alps, 

 and shows how very difficult it is to explain all the physiographic 

 features of glacial valleys without assuming that these valleys have 

 been eroded by the glaciers. 



1 "Systematic Asymmetry of Crest Lines in the High Sierras of California," ibid., 

 pp. 579-88. 



2 Glaciers and Glaciation, Harriman Alaska Expedition, Vol. Ill (New York, 1904). 



3 "Glacial Features in the Surface of the Alps," Journal of Geology, Vol. XIII 

 (i9°5), PP- I-I9- 



