﻿GEOLOGY OF THOUSAND ISLANDS REGION 1 75 



for paving blocks. It is fairly evenly and thinly bedded here, mostly 

 of red color, well indurated, and quite well adapted to the pur- 

 pose. The same would be true of much of the Potsdam of the 

 adjacent portion of the Alexandria sheet, were it as conveniently 

 situated as regards transportation. 



Limestone quarries 



There are many of these in the district, quarrying the Pamelia, 

 Lowville and Black River limestones, both for structural purposes, 

 and for burning for lime. The massive 7 foot tier of the Black 

 River is largely quarried, the large solid blocks obtainable render- 

 ing it an exceedingly serviceable material for heavy masonry con- 

 struction, much more so than the thinner bedded Lowville and 

 Pamelia limestones. Some of the beds of the upper Lowville are 

 also fairly thick, make very serviceable stone where construction is 

 less massive, and hence are quarried in many places. Most of the 

 Pamelia is much thinner bedded, and the thicker beds are mostly 

 separated from one another by much thin bedded material. Never- 

 theless the formation contains some good stone, and there are 

 numerous quarries in it all the way from Leraysville to west of 

 Clayton, which, however, chiefly serve a local use in the northern 

 part of the mapped area. It is not so largely quarried and used 

 as the upper Lowville. The dove limestones of the upper part of 

 the formation should, it would seem, make an excellent cement rock. 



A single quarry has been opened in the impure, thin beds of the 

 upper division, a few. miles south of Clayton, and the stone used 

 for flagging in Clayton. Owing to the joints only medium sized 

 slabs can be obtained, but otherwise the rock is fairly smooth sur- 

 faced and makes a very respectable flagstone. 



The quantity of limestone in the district available for these vari- 

 ous uses is enormous, and the nearness of water transportation 

 bespeaks a considerable future for the industry. 



PETROGRAPHY OF SOME PRECAMBRIC ROCKS* 



It is proposed here to treat, in somewhat more detail than seemed 

 suitable in the general account, of certain of the Precambric rocks 

 with discussion of chemical analyses. While some of the igneous 

 rocks of northern New York have already received detailed study, 

 more especially the syenites and certain gabbros, others have been 

 comparatively neglected, notably the granites. For the purpose of 



1 By H. P. Cushing. 



