﻿112 NEW YORK STATE MUSEUM 



The structure here is definitely anticlinal, though that is no indica- 

 tion of similar structure in the main fold, since minor folds on 

 its flanks must consist of both anticlines and synclines. It will 

 serve, however, as a sample of many similar exposures in the district 

 which show clearly that the series is folded, and that it is closely 

 folded. It also well illustrates the closely compressed conditions, 

 steep dips, and minor folds which prevail in the vicinity of the 

 axis of the supposed fold. 



The writer's opinion is that the structure here presented is syn- 

 clinal, similar to that depicted in figure 7. The discussion, how- 

 ever, serves to present the lack of certainty which prevails, and the 

 possibility that the structure is of precisely opposite character. 

 Either one indicates folding, but one precisely reverses the order 

 of rock succession of the other. 



It is also thought probable that the heavy quartzite along the 

 axis of the supposed fold is the same stratum as the even more 

 massive looking quartzite of Grindstone and Wellesley islands. If 

 the structure be synclinal, as supposed, this quartzite is the youngest 

 Grenville formation of the mapped district, but if anticlinal it is 

 the oldest. If these two quartzite belts do represent lines of out- 

 crop of the same quartzite formation, there should be an addi- 

 tional line of outcrop of the thick limestone somewhere between the 

 two, in the near vicinity of the river. This does not appear but 

 its absence is not a fatal objection to this interpretation of the 

 structure, since the Grenville rocks there have been completely cut 

 out by the granite of the Alexandria bathylith, and it is impossible 

 to say what may have originally been there. 



In summation it may be said that the Grenville rocks are greatly 

 tilted, suggesting strongly compressive folding, and frequent small 

 folds occur. Two belts of thick limestone and two of thick quart- 

 zite suggest a single formation of each in folded condition. Study 

 of the dips suggests that this folding is of a certain type, but it is 

 possible that, owing to very intense compression, the structure is 

 just the reverse of that suggested. It has not proved possible to 

 determine the order of succession of the various formations com- 

 posing the Grenville, and to use that succession as the key for un- 

 raveling the structure, as is the usual method in folded rocks. 

 Instead the attempt has been made to decipher the structure and 

 from that to determine the order of succession, but with only 

 indifferent success. 



Paleozoic folding. While the Paleozoic rocks of the district 

 show but a trifling amount of folding, it is of interesting nature 



