Reviews 



Glacial Erosion in France, Switzerland , and Norway. By William 

 Morris Davis. Proc. Bos. Soc. Nat. Hist., July 1900; 

 49 pp., 7 figures, 3 plates. 



In this admirable essay Professor Davis gives cogent reasons for 

 modifying his former views relative to the efficiency of glaciers as 

 erosive agents. A gradual change from a former conservative opinion 

 which had been in progress in recent years was greatly accelerated by 

 his studies in the Alps, Norway, and France during the past year. 

 These studies lay along those topographical lines which Professor 

 Davis had cultivated for the past two decades with such eminent suc- 

 cess. They centered on the great discordance which he observed 

 between the main and the tributary valleys when the former have been 

 occupied by ice streams and the latter have not, or at least have not 

 been effectively modified by glaciers. The tributaries in such cases 

 have been styled by Gilbert "hanging valleys" because, instead of 

 joining their primaries on well-adjusted normal gradients,, they enter 

 high up on the side walls. The tributary streams cascade down an 

 abrupt declivity in entering the main glaciated valley in a manner 

 quite out of harmony with their normal behavior within the tributary 

 valleys above or in the glacial valleys below. Associated with the 

 topographic break between the tributaries and the glacially worn pri- 

 maries there are contrasted physiographies that point, as it seems to 

 the author, and to the reviewer as well, unequivocally to the origin of 

 the phenomena. In the tributary valleys, although in Pleistocene 

 times they were involved in the general glaciation of the region, in 

 some measure at least, the characteristic configuration of weathering 

 and of water erosion clearly predominates, while in the main valleys, 

 which have been the chief channels of glacial movement, flat bottbms 

 and precipitous sides, bearing the peculiar aspects of glacially worn 

 troughs, prevail. No observant traveler in Switzerland has failed to 

 note the numerous small streams that cascade down the abrupt walls 

 of the glaciated valleys. The numerous falls of Aar Valley, especially 



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