Geology. 165 



the excavation of fiords and large lake basins, a power which is 

 questioned by many geologists and accepted by others equally, if 

 not more, numerous; the capacity of removing loose material 

 and of plucking away frost-loosened blocks, especially where 

 facilitated by vertical jointing, being, on the other hand, univer- 

 sally conceded. 



The arguments for deep erosion are discussed in detail and are 

 considered to be inconclusive. Following this, concrete illustra- 

 tions are given from- several glaciated mountain ranges, showing 

 a scouring and polishing action in valleys originating from pre- 

 glacial erosion rather than a topographic transformation of the 

 preglacial surface. 



Among the important consequences from such conclusions, 

 Fairchild considers that fiords and hanging valleys may and 

 ordinarily do occur as the result of preglacial erosion, masked, 

 however, by the glacial occupancy and signifying therefore cer- 

 tain preglacial changes in the altitude of the land. It is con- 

 ceded, however, that glacial action emphasizes and makes more 

 conspicuous hanging valleys of preglacial origin. 



Following the above is a discussion of the evidence from the 

 state of Xew York, with the conclusion that continental as well 

 as Alpine glaciation is ineffective as a powerful erosive agent. 



In many ways the quantitative value of ice erosion is an impor- 

 tant problem and the writer has certainly presented ably his views 

 upon the subject, but they would probably have met with a readier 

 acceptance among those holding different opinions if prefaced with 

 a less assertive and combative title. Many details of the argument, 

 such as the significance of cross striae as indicative of weak ero- 

 sive power, are still open to discussion in a manner similar to that 

 on the subject of hanging valleys; but coming down to the essen- 

 tial conclusions of the problem, Professor Fairchild and many of 

 his opponents upon this question are probably nearer together 

 than would at first appear, the problem turning on the quantita- 

 tive value of ice erosion : the one side holding that it is rapid and 

 important, the other that it is slow and very subordinate to the 

 aggregate effects of the previous fluvial and subaerial sculpture. 



J. B. 



16. Hanging Valleys; by I. C. Russell. Bull. Geol. Soc. 

 Amer., vol. xvi, pp. 75-90." Read Dec. 30th, 1904. Published 

 Feb., 1905. — A number of prominent physiographers have con- 

 sidered hanging valleys to result as a rule from the unequal 

 erosion of valleys by glaciers of unequal size and to represent 

 therefore the differential erosive power of the main and tributary 

 glaciers, the total erosive power being necessarily still greater. 



Dismissing the idea of glacial action as being the sole or neces- 

 sary cause, a hanging valley may be defined, as stated by Cham- 

 berlin and Salisbury, as " when the lower end of the tributary 

 valley is distinctly above the level of its main." On this basis 

 Russell divides hanging valleys into four species, namely, stream- 

 formed, ocean-formed, diastrophic, and glacier-formed. Even 



