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



have the power, which they use capriciously, of clearing valley, slope, or 

 plain of weathered or loose material. They change geest and alluvium 

 into drift. But these effects are not " erosion " in the full sense of the 

 word as commonly used. If the advocates of " glacial erosion " limited 

 the erosional work of ice to the operations mentioned above, there would 

 be little occasion for any disagreement. It is evident with a very little 

 thought that long and deep valleys and large lake basins are not pro- 

 duced by any of these operations, but that they would require vast and 

 deep excavation in solid or " live " rock by the ordinary flow of the gla- 

 cier in its open course. It must be admitted that the production of lake 

 basins like those of Chelan, or Cayuga, or valleys like the Norwegian 

 fiords imply an erosion not only vastly different in degree from the work 

 of glaciers conceded above, but essentially different in kind or quality. 

 The failure to make this discrimination and to recognize the limitations 

 of ice-work is the cause of much misconception in this matter. 



The term u erosion " will be used in this paper to signify the removal 

 by the ice of firm, hard, unweathered bed-rock. For the admitted and 

 competent work of ice other and self-explanatory terms will be used. 



Character of the argument for erosion. — The argument for extreme ice 

 erosion is founded in analogy and is almost wholly inferential. It is 

 mainly an assumption, resting on the argumentative method of exclu- 

 sion. Some topographic forms, the precise genesis of which is not clearly 

 explained, are assumed to be the product of ice erosion because ice was 

 the last occupant of the area. The strength of this claim on the thought 

 of students is due to their failure to discriminate the kinds of ice-work 

 and to recognize its limitations. Geological text-books and treatises 

 discuss the topic only in a general and indefinite way, and with more or 

 less qualification seem to approve the conception, or to at least admit the 

 possibility, of deep erosion by glaciers, while the leading text-books in 

 physical geography positively affirm deep ice erosion. 



Many American geologists who are compelled by the concrete evidence 

 to deny great erosional power to continental glaciers still have been will- 

 ing to admit that alpine glaciers might produce deep cutting. This is 

 partly a concession to the extravagant claims of the erosionists and partly 

 due to the teaching of the text-books. Probably most geologists of the 

 later decades began their work with an indefinite belief in the glacial 

 origin of some lake basins, valleys, or fiords, and if they have come to 

 new and different opinions it has been through outgrowth of the old 

 views. The writer belongs in this class. At the Minneapolis meeting 

 of the American Association for the Advancement of Science, in 1883, 

 there was a spirited colloquy on this topic between J. S. Newberry and 

 J. P. Lesley. The former held that even the basins of the Great lakes 



