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



and jointed strata, trending at the very best angle for cutting, and the 

 ice bottom freshly armed with Medina sands, gathered on the plain im- 

 mediately northward, giving an abrasive much harder than the rock to 

 be attacked. 



Now, it is no sufficient answer to say that ice behaves capriciously? 

 and we should expect local variation in its work. We should expect 

 it to get in its work where it had the best chance. If it were the great 

 engine of erosion which plowed out the Finger Lakes valleys it should 

 have exhibited some of its power in this locality. It is both illogical 

 and unfair to claim that the ice was locally weak in those places where 

 there is proof that it did not cut, and then to assume that it cut hun- 

 dreds or thousands of feet in other places where there is no evidence of 

 any cutting, but only a topographic difficulty. 



On the Medina plain. — In the article already quoted Doctor Gilbert 

 suggests some fluting by ice erosion in the Medina shales which underlie 

 the glacial and lacustrine deposits along the smooth belt bordering lake 

 Ontario, which we will call the Niagara-Genesee prairie. The present 

 writer regards the low swells, lying in the direction of the ice movement, 

 or northeast by southwest, as essentially drumlins. Near the Genesee 

 river, in Monroe county, they are typical New York drumlins. West- 

 ward in Orleans county they become lower and flatter, being only gentle 

 swells, and they are finally almost imperceptible in Niagara count} 7 . 

 Most of the western half of the prairie is perfectly flat to casual obser- 

 vation. No rock exposures have been found by the writer on any ridge, 

 although Doctor Gilbert refers to such, but the rock is frequently seen 

 in the hollows or troughs in the stream beds. Along the lake shore the 

 waves of Ontario have dissected the plain, though not deeply, and the 

 ridges and swells show only till. 



The singular parallelism of the stream directions, chiefly northeast- 

 ward, was certainly determined by the surface form of the superficial 

 drift, even if the ridges might sometimes have a rock core. However, 

 the point is not worth any extended or detailed discussion here, for the 

 matter in question is quantitatively unimportant. Doctor Gilbert sug- 

 gests a furrowing of the underlying shales of only 40 or 50 feet, which is 

 very moderate if the geest be included, as it properly should be; but 

 even much more erosion than this in weathered Medina shales would be 

 poor basis for claims of enormous cutting in granitic rocks. 



This paper by Doctor Gilbert is very significant in a negative way. It 

 should be expected that in a paper discussing and favoring ice erosion 

 he would present the best evidence possible. He admits the absence 

 of erosion on the schists near Carthage. On the Niagara cliff he con- 

 cludes that the erosion was inconsiderable. The most he finds is some 



