580 REPORT OF NATIONAL MUSEUM, 1904. 



shape given to them by the debris piles which have accumulated against their 

 sides. The farther we descend the mountain slope the less the grade and conse- 

 quently the less the carrying power of the stream. Hence the valley which is 

 U-shaped in the upper part of its course acquires more and more of a V form as it 

 approaches the plain at the base of the range from which it heads. 



Whitney thought to be able to trace, not to go too much into detail, 

 a period of warmth and heavy precipitation followed by one of desic- 

 cation, but anticipated by one of cold and glaciation, the glaciers, how- 

 ever, being limited to the most elevated ranges of the Cordilleras. At 

 the outset he announced himself as opposed to the "wild and absurd 11 

 ideas that had prevailed regarding glaciation in the Sierras, and stated 

 it as his belief that here at least ice had played but an extremely sub- 

 ordinate part as a geological agent, though "there is no doubt that 

 the great California range was once covered with grand glaciers, but 

 little if at all inferior to those which now lend such a charm to the 

 Swiss Alps. 1 ' 



In the discussion of the question he called attention to the fact that 

 the Great Lakes of North America and most of those of other coun- 

 tries as well are included in areas underlain by Paleozoic rocks or 

 those partly Paleozoic and partly Archean, and are due not to glacial 

 erosion, but to orographic movements — Lake Superior, for instance, 

 occupying a s}mclinal depression in Paleozoic rocks just along the edge 

 of the Azoic series. 



The Lake region of the Great Basin while likewise orographic in 

 origin has become desiccated through climatic changes, he finding no 

 evidence that there has been any essential alteration in the configura- 

 tion or topography of the western side of the continent since the 

 Glacial epoch — that is, since the time when the crests of the highest 

 ranges were to some extent covered with snow and ice. Therefore, 

 no part of the desiccation which appears to have taken place since that 

 time can be due to orographic changes; the phenomenon must have 

 been a climatological one. 



The phenomenon of fiords he considered as due to aqueous erosion 

 along mountainous coasts which have since become depressed. 



It was Whitney's opinion, further, that the geological importance 

 of the ice sheet had been greatly exaggerated. It seemed to him 

 be}'ond question that the icebergs had played an important part in car- 

 rying and distributing the large angular bowlders which in man} 7 places 

 rest upon the surface in such a manner as to show that they could not 

 have been placed in their present position by running water or by a 

 general ice sheet. 



He regarded it as evident enough that the climate of northeastern 

 America during the Glacial epoch was a period of greater precipita- 

 tion than is now taking place, but that it was a period of intense cold 

 he would not admit. Glaciation or a Glacial period was due merely to 

 increased precipitation. In order that such precipitation should take 



