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



11 . . . The prominences are therefore abraded more rapidly than the adja- 

 cent hollows, and the profile is thus reduced to simple forms." (Page 203.) 



"Another factor on which rate of abrasion depends is pressure; the abrasion is 

 more rapid as the pressure of the glacier against the bed- rock is greater. . . . 

 Thus in a second way there is a tendency to reduce the profile of the bed to simple 

 forms." (Pages 203-204.) 



If plucking did occur in the beds of glaciers the scars should be found 

 there; but plucking and abrasion are mutually opposing factors and 

 can not long coexist. After abrasion has done its first work under the 

 pressure of thick ice, how is it conceivable for plucking to occur in live 

 rock? (See discussion, page 20 ) Plucking can be an effective process 

 only in superficial removal of loosened rocks. It is good evidence of 

 lack of deep erosion. 



Mention of the islets in the fiords is only made in saying that in num- 

 ber they are "uncounted," but the existence of numerous islets in the 

 fiords is not consistent with the origin or the great deepening of the latter 

 by glaciers. 



The body of facts relating to Alaskan geology seem to be thrown into 

 confusion by the hypothesis of ice erosion so intense as to deepen valleys 

 1,000 to 2,000 feet; but, under the view that the fiords are drowned 

 stream valleys of the Tertiary uplift, modified by ice occupation in the 

 Pleistocene, and with only proportionate glaciation over the general 

 and intervalley areas, the phenomena will be harmonious. But the 

 question may be asked, "What about the ' hanging' valleys? " The 

 reply is that they can probably be satisfactorily explained when the effort 

 is made in an inductive way. They exist in mountain regions where the 

 idea of deep ice-cutting will not hold and even in regions which are un- 

 glaciated.* Discordant drainage features have been found about the 

 Finger lakes, and the latter are positively not due to ice erosion. 



The most striking discordance of valleys which has so far been shown 

 occur in young mountains of crystalline rocks. Their relation to glacia- 

 tion is probably only incidental, except that they may have been made 



* Since this paper was written Professor I. C. Russell, in reviewing Doctor Gilbert's book, in 

 Science, vol. xix, May 20, 1904, page 785, questions the glacial origin of hanging valleys, andjwrites 

 as follows : 



"Again, in well glaciated mountains, like the Cascades and Sierra Nevada, the great differences 

 in level between a main valley and its tributary hanging valleys, amounting in some instances to 

 1,500 or 2,000 feet, and this where the main valley is short and has but a comparatively small 

 gathering ground for snow, must needs make the conservative glacialist pause before accepting 

 the conclusion that such discrepancies are solely due to differential ice erosion. Other consider- 

 ations in this connection might be mentioned, such as the fact that a deep glaciated valley with 

 hanging valleys along its sides not infrequently heads against a cliff, and its direct continuation 

 above the cliff also has the characteristics of a hanging valley. Then, too, hanging valleys may 

 be claimed to occur on the sides of steep mountains and on slopes overlooking the sea, where no 

 evidence of a controlling ice body at a lower level is obtainable." 



