﻿GEOLOGY OF THOUSAND ISLANDS REGION IOO, 



show occasional small surface folds, or buckles, produced since the 

 ice sheet vanished from the region. 



Precambric folding. It has been shown that the Grenville beds 

 are now found for the most part in highly inclined condition, 

 dips of less than 45 ° being relatively rare, while those approach- 

 ing verticality are common. Averaging the dips of the entire 

 formation would give a result of at least a 55 ° to 6o° dip. It has 

 also been shown that the dip is not everywhere in the same direc- 

 tion but that, with the general direction of strike to the northeast- 

 southwest, the dip, while prevalently to the northwest, becomes at 

 times southeast. The southeast dips prevail over a belt of country 

 some 4 miles in breadth in the Butterfield lake district of the 

 Alexandria sheet. In the country lying south of this belt the dips 

 are all to the northwest. In the other direction the Grenville is 

 badly cut out by the syenite and granite of the Alexandria and 

 Picton bathyliths, but such as remains shows very steep to verti- 

 cal dips, chiefly to the northwest. The highly tilted condition of 

 the rock series, and these changing dips seem certainly indicative 

 of folding. Moreover many exposures exhibit small folds of ex- 

 ceedingly compressed type, often accompanied by extreme plica- 

 tion. It is reasonable to suppose that these are merely secondary, 

 or minor, folds superimposed upon folds of much larger scale. 



In order to demonstrate the presence of these larger folds it 

 is necessary that the order of superposition of the various Gren- 

 ville beds should be worked out, and in the early stages of the 

 field work it was hoped that this might be done. It is possible 

 that it might have been successfully accomplished had large scale 

 maps, say 4 inches to the mile, been available. But the structure is 

 so complicated, the dips so steep, the folds so compressed, the 

 series so greatly cut out by the igneous rocks, or so modified in 

 character by them, and so much of the territory is yet covered by 

 the Paleozoic rocks, that no certainty as to the Grenville succession 

 could be arrived at with the maps in hand. Certain suggestions 

 may however be made. 



Inspection of the maps will show that the Indian river, from 

 Theresa northward to the point where it passes off the Alexandria 

 sheet, follows a broad belt of Grenville limestone, averaging some- 

 what more than a mile in breadth. Except for being much cut up 

 by granite dikes and stocks, it is quite pure limestone. The dips 

 are steadily to the northwest, and flatter than the usual Grenville 

 dips, averaging about 45 °, and hence indicating a thickness of 

 about 4000 feet for the limestone. A few miles to the northward, 



