Systematic Asymmetry of Crest-Lines. 281 



smaller fraction of the snowfall they received remained 

 to nourish glaciers. Thus the glaciers resting against 

 the southward slopes were comparatively ill-fed, and the 

 glaciers of the northward slopes were comparatively well- 

 fed. The north-south ridges may be assumed to have 

 been swept, then as now, by dominant westerly winds, 

 which carried much snow from the westward slopes over 

 the crests to the eastward slopes, where it accumulated; 

 and thus the glaciers resting against the eastward slopes 

 were better nourished than those of the westward. These 

 peculiarities of snow distribution may be readily observed 

 at the present time. If one stands, late in summer, upon 

 a peak in the midst of the glaciated district and looks 

 toward the east or north, he sees bare rock, with only 

 here and there a small remnant of snow ; but if he turns 

 toward the west or south, he looks upon a patchwork of 

 snow and rock in which the predominance of the rock 

 may not at once be apparent. Figure 2 of Plate XLII 

 illustrates the relations of surviving snow-banks in early 

 summer to northward and southward slopes. 



It can hardly be doubted that the distribution of 

 Pleistocene snow deposition stands in causal relation with 

 the distribution of asymmetry in the crest-lines of the 

 minor ridges. And it is in explanation of this relation 

 ■•ihat I avail myself of Johnson's hypothesis. Each glacier 

 which receives more snow on one side than on the other 

 adjusts its cross-profile to a condition of equilibrium by 

 moving away from the region of greater supply to the 

 region of lesser supply. This lateral motion is of course 

 combined with the general, and more rapid, forward mo- 

 tion of the glacier, but it is nevertheless competent to 

 produce at the side of the glacier phenomena quite similar 



