﻿13.2 NEW YORK STATE MUSEUM 



overlooking the Precambric areas to the northward. The drainage 

 is to the southwest and passes from the Precambric into the Paleo- 

 zoic limestone country, the streams deeply notching the cuesta front 

 as they pass into it. Of the lakes he says : " In most cases the 

 upper parts of these valleys, near where they pass through the 

 cuesta front, form the basins of long, narrow lakes. The water 

 seems in some cases to be held back by a drift dam, which partly 

 blocks the lower part of the valley. Certainly in some cases, in all 

 probability in most cases, the present lake basin is a rock basin 

 and the existence of the present lake is due either to warping or 

 possibly to differential erosion by ice. 1 " 



In this district of Wilson's the Potsdam and Theresa formations 

 are absent, the Pamelia, or Lowville, resting on the Precambric, 

 forming a single cuesta front that is more prominent than those in 

 our district. The lakes on the Alexandria sheet have their beds 

 either on Precambric or on Potsdam, and the limestone front is 

 more or less remote. They nestle in the extreme upper portions of 

 the valley heads on the north side of the divide which runs through 

 the region, and has just been described. They are in the extreme 

 upper portions of the valleys of north-flowing streams, instead of 

 occupying a special position in the valleys of southerly streams, as 

 in the case of the Ontarian lakes, and in this lies their chief dif- 

 ference from those. Hyde lake, in the northern portion of the 

 Theresa sheet, conforms more nearly to the Ontarian type, though 

 in Potsdam instead of Precambric, and Perch lake seems the shallow 

 remnant of another lake of similar type. The Alexandrian lakes, 

 however, differ as specified, and herein lies also the reason for their 

 localization. The old divide runs into higher ground passing east- 

 ward, and the relations of the rocks shift. The streams there rise 

 in the Precambric and run northward into the Paleozoic rocks of 

 tne St Lawrence valley, while our lake valleys here commence in 

 Potsdam and run north into Precambric. 



Most, of the lakes seem to be in rock basins, Crystal, Sixberry 

 and Millsite certainly are, and Butterfield probably is. Crystal lake 

 is entirely in Potsdam though its bed may be on the Precambric, 

 and is walled by high and continuous sandstone cliffs, with the 

 sharply cut valley head but a short distance back from the lake 

 margin [pi. 34]. Sixberry, Millsite and Butterfield are partly 

 walled by Potsdam, with characteristic cliffs, and with valley heads 

 cut in Potsdam, but with their beds in Precambric [pi. .54]. The 

 beds of the two latter are in large part in Grenville limestone. Six- 



1 Op. cit. p. 217. 



