﻿GEOLOGY OF THOUSAND ISLANDS REGION 2J 



and southwest of Alexandria Bay. But the bulk of the Grenville 

 of the district occurs as a great schist series, with rather rapid 

 alterations of varying types in bands of no great thickness, and 

 interbanded with these are thin limestones and quartzites. After 

 trial of various methods it was found that, on a map of this scale, 

 and with rocks of this rapidly varying character, no further 

 subdivision of the Grenville was possible than a separate map- 

 ping of the thicker limestone and quartzite beds, the entire 

 remainder being mapped singly as a schist formation. It is 

 feared that even this amount of subdivision has resulted in a 

 map too complicated for easy use. 



It was hoped that the careful, detailed mapping attempted 

 might solve the problem of the order of superposition of the rocks 

 and give some definite idea of the thickness of the whole. The 

 outcome was disappointing and neither hope distinctly fulfilled, 

 though some results were obtained. The mapping therefore is 

 purely lithological and not on a structural basis, as it was 

 endeavored to make it. 1 



The average trend, or strike, of the Grenville rocks is to the 

 northeast. The direction to be sure varies considerably, swinging 

 around to the north on the one hand, and to the east or even some- 

 what to the south of east on the other, yet these variations are not 

 sufficiently frequent to offset the general statement. The dips are 

 usually high, seldom less than 45 ° and frequently very steep or 

 even vertical [pi. 1, 2]. Over the greater part of the area north 

 dips prevail, but are replaced by south dips throughout a belt of 

 country from 2 to 3 miles broad across the Alexandria quadrangle. 

 This is certainly indicative of folding of large magnitude, and is 

 corroborated by the fact that in many localities minor folds are 

 clearly to be made out, and intricate minor puckering and corruga- 

 tion. Of the two broad limestone belts within the map limits, the 

 one along the Indian river north of Theresa, and the one about 

 Butterfield lake, the former has a north, and the latter a south dip, 

 and in each case the breadth of outcrop across the strike is about 

 a mile. With the steep dips a thickness of about 4000 feet is in- 

 dicated for this limestone in each case, and it is therefore conjec- 

 tured to be the same thick stratum, with the structure synclinal. If 

 this be the true interpretation then the complex of quartzite and 



1 Though the work was of vastly more detailed character than the earlier 

 work of Smyth on the same rocks, it will be seen by any one who will take 

 the trouble to compare the two maps that the basis for the subdivision^ of 

 the Grenville is substantially the same in each case. No more convincing 

 testimony could be given as to the high class character of Smyth's work. 



