EECEXT DATE OF FORMER GLACIATIOX IX THE CORDILLERAS. 97 



the fact that the moraines remain in such a perfect state of preservation. In 

 many places they look as fresh and iniimpaired in the completeness of the 

 details of their forms as do those of the present Alpine glaciers. These 

 remarks apply especially to the glaciated regions of the Sierra Nevada ; but 

 the freshness of the glacial markings in the Rocky Mountains is not much 

 less strikina: than on the western edge of the Cordilleras. The writer did 

 not see any surfaces of rock in the mountains about South Park or at the 

 head of the Arkansas River Avhich retained their polish as perfectly as those 

 at the head of the Tuolumne and elsewhere in the Sierra ; but the moraines 

 descending the eastern flanks of the Sawatch Range seem entirely unim- 

 paired, perhaps quite as much so as those previously described as occurring in 

 the vicinity of Mono Lake. The contrast is very striking between the fresh- 

 ness of the indications of the former presence of ice in the Cordilleras, and of 

 those which display themselves in Northeastern North America ; to the char- 

 acter of these latter attention will be more specially directed further on in 

 the present volume. It may be added here, however, that there is strong 

 reason to believe, as the writer has become convinced by repeated examina- 

 tions of both regions, that the period of the former more extended glaciation 

 of the Alps dates back further than that of the similar geological events in 

 the Cordilleras. 



This simplicity of the phenomena of former glaciation in the Cordilleras 

 leads us also to infer that the time occupied by the Glacial epoch in that 

 jjortion of the continent must have been much shorter than that during 

 Avhicli the complicated series of events occurred which are referred to the 

 period of the Northern Drift in the Northeastern States and the region of 

 the Great Lakes. There are important general conclusions connected with 

 this aspect of the glacial question ; but their consideration may properly 

 be put oil" until a more advanced stage of the present discussion has been 

 reached. 



Some words may be added in this connection in reference to a subject dis- 

 cussed at some length in the Auriferous Gravels, namely, the forms of the 

 valleys or canons in the Cordilleras, the especial question here to be consid- 

 ered being whether the former pi'esence of ice reveals itself in any easily 

 recognized manner in the figure of the cross-section of tlie valleys through 

 which it has passed. Observers frequently speak of the characteristic U-shape 

 of glacial valleys, as contrasted with the V-fonn of caiions resulting from 

 aqueous erosion. This is an error partly of misapprehension and partly of 



