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



mainly based on analogy, observation showing that glaciers clear their 

 channels, abrade their rock beds, and sometimes modify the form of 

 their valleys. No limit to the amount of such erosion has been deter- 

 mined, and hence an indefinite amount, equal to any requirement, is 

 assumed. The burden of proof has thus been tacitly thrown on oppo- 

 nents of the assumption, and the latter have timidly admitted a doubt 

 or conceded the possibility. The mere admission of the possibility of 

 deep ice erosion gives the argument from analogy full opportunity and 

 places the objector on the defensive. The opponents of the conception 

 have weakly rested in the attitude of defense instead of challenging the 

 production of positive evidence. The phenomena of glaciation are so 

 abundant that the advocates of wholesale glacial erosion should be asked 

 to prove, first, the competency of the agent, and, second, the fact in the 

 particular case. 



Argument for erosion. — In the absence of a complete theoretical state- 

 ment of the positive argument for deep glacial erosion the writer will try 

 to supply one, as follows : 



(1) Glaciated rock surfaces are proof of abrasion by rock-armed ice. 

 With sufficient intensity of the factors involved and a large time element 

 great effects could be produced. 



(2) It has been observed that the ice can " pluck " or grasp and carry 

 away masses of bed-rock. 



(3) Glacier ice behaves in a capricious manner, scoring hard rock in 

 some places, overriding and leaving soft materials in other places. This 

 suggests that intensified effects may locally be very great. 



(4) The analogy between rivers and Alpine glaciers suggests that 

 glaciers may do excavating work comparable to that of rivers. 



(5) The conspicuous milky sediment of glacier waters not only is a 

 proof of mechanical abrasion by the ice, but gives a volumetric measure 

 of that abrasion, often of large amount. 



(6) The presence of a large constituent of calcium carbonate in the 

 drift is evidence of large mechanical destruction of the rocks. 



(7) The enormous quantity of drift spread over the glaciated areas 

 implies great erosion to supply the material. 



(8) The existence of numerous lakes only in glaciated areas proves 

 their relationship to glaciation. 



(9) The attitude, form, and structure of many lake basins which lie 

 in the path of former glaciers (for example, lakes Cayuga, Seneca, 

 Chelan) are more readily explained by and argue strongly for glacial 

 excavation. 



(10) As some lake basins of the class noted above, under (9), have not 

 been explained by the work of aqueous agencies, it is proper to appeal 

 to ice action. 



