Systematic Asymmetry of Crest-Lines. 285 



stronger expression of the ice-work, in the comparatively 

 high grade of the nonglacial profiles, and in the fact that 

 those profiles, as seen in the photograph, conceal south- 

 facing cirques of some magnitude. 



The asymmetry of these lower ridges is more pro- 

 nounced than that of any others, because instead of con- 

 trasting two phases of glacial erosion they contrast 

 glacial with nonglacial. It is worthy of note also, though 

 not strictly germane to my subject, that the contrast in 

 sculpture of the two ridge slopes serves to compare the 

 efficiency of subaerial degradation with that of one phase 

 of glacial degradation. The glaciers of these low ridges, 

 being able to develop only on the slopes most favorable 

 for snow accumulation, marked the lower limit of neve 

 conditions and were the feeblest of all the Sierra glaciers. 



Fig. 2. — Diagrammatic cross-section of a ridge 

 glaciated on one side only, with hypothetic 

 profile (broken line) of preglacial surface. 



Their lives must have been short, for they could exist 

 only when glacial conditions were at or near a maximum ; 

 they began long after and ceased long before the glaciers 

 of the higher districts. The topographic features they 

 produced were subject to the dulling influence of atmos- 

 pheric and aqueous attack during both interglacial and 

 postglacial times. And yet the degradation they accom- 

 plished was far greater than that of nonglacial agents 

 working on the opposite sides of the same ridges — agents 

 working not only during the same time, but during all 



