﻿GEOLOGY OF THOUSAND ISLANDS REGION 167 



the Cape Vincent branch of the New York Central Railroad, a 

 hard, gray blue till appears that is very unlike the prevailing drift 

 of the northward area. The latter exposure is shown in plate 52. 

 The resemblance of this drumlin till to the " old " tills farther south 

 is as close as might be expected when the differences in latitude, 

 source of the material, etc. are considered. However, we must 

 recognize that the drumlin till was subglacial, deposited beneath the 

 ice and under tremendous grinding pressure; while the surficial 

 drift of the area was dropped in standing water, and is conse- 

 quently incoherent, sandy, inclined to yellow or gray colors, and 

 carry few striated or abraded stones. The production of masses of 

 subglacial drift or drumlins is a sort of work which the later ice 

 did not do north of Watertown, at least to noticeable extent, and 

 it is doubtful if it did such work at Watertown. However, the 

 drumlin till is inconclusive, until we know if the Watertown drum- 

 lins are the work of the latest ice or of some earlier invasion. 

 This Watertown till is not in valley bottoms or deeply buried, but 

 in hills above the levels of the plain. 



Limestone ribbing. Over the southern part of the Clayton 

 quadrangle the limestones frequently exhibit series of parallel ribs 

 or ftUtings, a sort of washboard structure on a vast scale [pi. 60-63]. 

 These ribs positively have no genetic relation to the joint structure 

 of the rock. They are pronounced convexities, often quite cylindri- 

 cal but commonly rather flat, with a breadth from crest to crest, 

 or across the base, from 2 to 10 feet; the usual breadth being 3 to 

 5 feet. The hollows between the ribs are usually filled with drift 

 or soil, but when cleared they show quite cylindrical troughs of 

 uniform width and fair curvature, and parallelism with the ribs. By 

 solution-weathering the sides of the flutings are rarely steepened 

 and the bottoms perforated by solution holes, as in plate 63". 



Within any single exposure these flutings are strikingly parallel 

 [pi. 61] and are approximately so over the whole region, having 

 a direction about s. 45 ° w. Scores of them have been measured with 

 that direction, over all the area between Dexter and St Lawrence 

 village. The extreme variation in direction is s. 40 w. for the 

 heavy ribbing east of Dexter, and s. 50 w., south of Dexter, shown 

 in plate 63. Two other localities toward St Lawrence gave the 

 latter compass direction. 



Speaking broadly the flutings have lost all their glacial surfaces, 

 retaining only the erosional form, for their origin by ice erosion of 

 the limestone seems certain. In a very few cases a suggestion of 

 the heavier scorings are preserved, and some minor flutings on the 



