﻿42 NEW YORK STATE MUSEUM 



the Canadian islands to the mainland and thence west to Kings- 

 ton, but until this has been done some reserve must be felt in 

 making the correlation. The rock near Clayton differs in con- 

 taining no quartz, and in being somewhat more mashed than 

 the generality of the rock. It is in fact an acid syenite rather 

 than a granite. Otherwise the two are exceedingly alike, and 

 since the granite itself is low in silica for a granite, approaching 

 a syenite in that respect, but slight variation is needed to cause 

 the disappearance of the quartz. 



It must be borne in mind, in inspecting the maps, that the 

 boundaries drawn between the Picton granite and the Laurentian 

 are in the highest degree conventional. They are of the same 

 vague sort as those between the Laurentian and Grenville, but 

 even more vague than those because of the similarity of the two 

 rocks. The fine grained dikes of the Picton are exceedingly like 

 the acid dikes sent out from the Laurentian, and it is almost an 

 impossible matter to tell which rock is in excess. On the other 

 hand the maps do show the chief areas of the two rocks, bring 

 out the fact that the one is younger than the other, and show 

 their relative distribution and extent as accurately as possible 

 in rocks of this kind. 



That the rock is the youngest of the intrusives of the region 

 is indicated in several ways. It shows less sign of mashing than 

 do any of the others, that is its unmashed central core is rela- 

 tively much larger. Besides its abundant inclusions of various 

 Grenville rocks it contains also frequent masses of granite gneiss 

 of Laurentian type, and sends abundant dikes into similar rock 

 where bordered by it, as it is locally on both Wellesley and 

 Grindstone islands; and also it contains inclusions of an augen 

 gneiss which is absolutely identical in character with the rock 

 of the Alexandria syenite. Such age for the rock then seems to 

 us in the highest degree probable, though it falls somewhat short 

 of actual demonstration. 



Dikes of the granite are thought to range widely in the rocks 

 east and south, though no attempt to indicate this upon the 

 areal maps has been made. They are believed to be numerously 

 present in the green schist belts of the western part of the 

 Alexandria quadrangle, and also in the granite gneiss of that 

 quadrangle. Even as far east as Alexandria Bay broad dikes of 

 acid, usually fine grained, granite occur abundantly, cutting the 

 granite gneiss all to pieces, and often inclosing sharp inclusions 

 of it. We have never seen inclusions of this type held abun- 



