44 H. L. FAIRCHILD — ICE EROSION THEORY A FALLACY 



and difficulties, and other questions might be raised. A few of these 

 points will be here mentioned. 



Gilbert agrees with Willis that the fiords of Puget Sound district are 

 chiefly river work. 



11 The system of troughs it (the ice sheet) left behind are regarded as pre-existent 

 stream valleys, only moderately scoured and straightened by the ice which over- 

 ran and occupied tliem." (Page 135.) 



". . . Regarded as stream valleys, the channels tell of a preglacial baselevel 

 at least 500 feet, and probably 1,000 feet or more, below the present sea surface." 

 (Page 136.) 



The question would naturally be asked why Alaska should not have 

 stood as high above ocean during Tertiary time as the district imme- 

 diately contiguous and possessing the same physiographic characters, 

 or what the rivers of Alaska were doing while those of Washington were 

 cutting the valleys that are now fiords ? The only argument which Doctor 

 Gilbert makes against such land elevation as would permit the stream 

 origin of the valleys now drowned is the following: 



" . . . Under present climatic conditions, such a change would carry a very 

 large area above snow-line, and would so promote the alimentation of glaciers as 

 to flood the whole district with ice and abolish stream erosion. Stream erosion 

 therefore could not have been carried, by lowering of baselevel, to the lowest 

 parts of the channel system without the aid of important climatic variation. 

 Without doubting the possibility of wide range in independent climatic factors, 

 it seems easier to assume that the lowering of baselevel was comparatively mod- 

 erate, and that a considerable part of the down-cutting of the channels was accom- 

 plished by Pleistocene glaciers." (Page 136.) 



The above argument seems to ignore the generally accepted fact of 

 warm climate over arctic lands during the early and middle Tertiary, 

 as shown by paleontologic evidence. Would it not seem easier to accept 

 the evidence of warm Tertiary climate over northern lands and the 

 stream origin of the Alaskan as well as the Washington fiord valleys, 

 which gives a harmony of facts, than to assume that the Pleistocene 

 glaciers could abrade the bottoms of their valleys 2,000 feet in crystal- 

 line rocks? 



If Alaska had been during the Tertiary 1,000 to 2,000 feet lower than 

 now, so that the fiords could not be the product of river work, there 

 ought to be found conspicuous and indisputable remnants of an uplifted 

 coastal plain, or at least lines of wave-work. 



The difficulty of accounting by ice erosion for the plexus or anasto- 

 mosing system of deep valleys which characterize the Alaskan and 

 Washington coast, or for even seriously deepening them, is recognized 

 but not discussed further than to offer a suggestion of differences in 

 rock structure. 



