224 GROVE KARL GILBERT— DAVIS IMemo,rs [ vouxxi i ; 



The deep notch cut by the Lockport discharge, which for a time appears to have rivaled 

 Niagara proper, has been chosen as the best point at which the Erie Canal should pass by a 

 series of locks from the higher level of the Niagara upland, which it crosses eastward from 

 Buffalo, to the lower level of the Ontario lowland, which it follows thence to the "long level" 

 of the Rome outlet into the Mohawk Valley. It is manifest that an understanding of the 

 pattern to which the upland escarpment was reduced by glacial erosion, as stated in the preced- 

 ing paragraph, was essential before the notches in the escarpment could be identified as the 

 postglacial work of the several competing Niagaras, as stated in this paragraph; and it is also 

 manifest that there is a gratifying measure of definiteness and precision, highly characteristic 

 of GUbert's quantitative work, in the conclusion of both paragraphs; but most remarkable 

 is the skill in interpretation by which the enchainments of all these many and diverse items are 

 brought into a well-ordered sequence. 



GLACIAL EEOSION IN WESTERN NEW YORK 



In association with the sculpture of the Niagara escarpment, an important statement was 

 made concerning the general forms of the land surface in the district of the Finger lakes. It 

 was concluded that "the great body of Devonian shale underlying that district owes more to 

 ice work than to antecedent water work, and that the face of the country is essentially a mou- 

 tonnee surface, the bosses of which are measured horizontally by miles and vertically by hundreds 

 of feet." Several years later a brief abstract of one of his papers contains the significant 

 statement that the uplands of western New York, south of the drumlin belt which occupies the 

 adjoining part of the Ontario lowland, constitute "a zone of great glacial erosion in which the 

 aspect of the land was revolutionized by ice sculp ture." 4 At about the same time a personal let- 

 ter made reference to the same problem : 



It is undeniable that the erosion of the limestone ledges by the last ice [invasion] was small, but on the other 

 hand the general configuration of the Finger lake troughs is distinctly glacial, and I see no way of accounting 

 for them without invoking a large amount of glacial erosion. 



The line of thought here appears to have been concerned much more with the visible 

 forms of the land than with any hypotheses as to the behavior of an ice sheet. Gilbert saw 

 with his outer sight that the Finger lake troughs have remarkably smooth sides, in which the 

 cascading streams of to-day are cutting narrow little trenches, locally known as "glens"; and 

 he saw with his insight that, if the troughs were the work of normal river erosion, the contempo- 

 rary work of side streams ought to have produced lateral valleys by which the trough sides would 

 be repeatedly interrupted. Thereupon he concluded that the abnormally smooth trough sides 

 testify to the excavation of the troughs by some abnormal agency, during the action of which 

 the erosion of side valleys would be prevented; and he identified the abnormal agency with the 

 ice of the Glacial period, his reason for this probably being that if ice did erode it would erode 

 troughs of such form as the Finger lakes occupy. 



He evidently recalled some such train of thought when writing the following passage in a 

 letter to his proglacial-lake correspondent in December, 1910: 



To appreciate how dependent they [the Finger Lake valleys] are on glaciation for depth and contour, we 

 must compare them with the norm in topography. I never knew that the forms of my native New York needed 

 special explanation till I had made a study of normal forms outside the area of glaciation. 



In other words, Gilbert, like many others whose field of early observation lay in a glaciated 

 area, assumed without special inquiry that its forms were of normal, subaerial erosion; and not 

 until he had studied the forms of never-glaciated areas did he come to see how peculiar the 

 forms of his home district are, and how large a share of their erosion must be ascribed to ice 

 instead of to water and weather. His experience thus in some respects duplicates that of many 

 European geologists who, in trying to resolve the problem of glacial erosion in mountainous 

 districts, were retarded in their approach to its true solution by the unconscious acceptance of 

 the forms of formerly glaciated mountains, such as the Alps, the Scandinavian mountains, and 

 the highlands of Scotland, as of normal origin, and by their inattention to the forms of never- 



' rhysiographic belts in Western New York. Science, xvii, 1903, 221. 



