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



should have left obstructions and irregularities in their beds, as shown 

 in plates 12-15. 



The end of the Unter Grindelwald glacier (plate 12) lies wedgingly in 

 a chasm of rock cut by water — probably subglacial. It convincingly 

 shows the failure of the glacier to effectively erode its bed, and all the 

 rock forms at and below the end of the glacier give the same evidence 

 of the glacial impotence. The walls of the valley have been merely 

 sandpapered, and the same condition is practically true of all the glaci- 

 ated valleys of the Alps. The accompanying plates give a few illustra- 

 tions from several fields of the Alps. These facts are commonplace to 

 Alpine geologists. It is an easy reply for the physiographic erosionists 

 to say that the various conditions of erosion in the Alps were unlike 

 those of Norway or the Sierras; but the burden of proof is on them to 

 show the practical difference. 



The valleys of the Aare* and the Ticino f have recently been de-. 

 scribed, from a physiographic standpoint, as showing great glacial ero- 

 sion. The writer recently walked through the Aare valle}' above Meir- 

 ingen (the Haslethal valley) and over the Grimsel, and passed by rail 

 up the Ticino, and saw only evidences of the absence of great ice erosion. J 

 The Aare valley is described by Brigham as having a series of expan- 

 sions and constrictions, which fact alone would seem to positively rule 

 out great enlargement by a valley glacier. The cliffs at Grimsel are 

 only smoothed by abrasion. In old photographs the rocks at the narrow 

 gorge of the Aare, b}^ the Grimsel hospice, appear to show glacial scor- 

 ings passing up and over the cliffs. But this is deceptive, for on the 

 ground it is seen that the strise are nearly horizontal and the abrasion 

 was not sufficient to obliterate the irregularities and the surfaces due 

 to jointing (plate 14). The jointing approaches the vertical, and the 

 smoothed joint surfaces give at a distance the false appearance of nearly 

 vertical ice scorings. 



The discussion appended to Brigham 's brief paper referred to above 

 contains the gist of the whole contention, and the explanation and argu- 

 ment by Turner adverse to ice erosion has not been answered, and is 

 believed to be unanswerable. 



* A. P. Brigham : "Glacial erosion in the Aare valley." Bull. Geol. Soc. Am., vol. 11, 1899, pp. 

 589-592. 



t W. M. Davis : "Glacial erosion in the valley of the Ticino." Appalachia, vol. ix, 1900, pp. 136- 

 156; "Glacial erosion in France, Switzerland, and Norway." Proc. Bos. Soc. Nat. Hist., vol. 29, 

 1900, pp. 273-322. 



% When the writer visited the Alpine valleys the descriptions referred to were not in mind, and 

 the problem of glacial erosion was in mind only incidentally. The observations noted and the 

 photographs taken were without any intention of discussion as to the origin of the valleys. This 

 fact is given in justice to the argument of this paper, and at the same time it illustrates how 

 physiographic features are subject to very different and even opposite interpretations according 

 to the mental attitude of the observer. 



