﻿12 NEW YORK STATE MUSEUM 



islands, and to a small extent on the mainland, and which is named 

 from Picton (Robbins) island, where the most extensive quarries 

 occur. This rock shows little or no signs of the crushing which 

 has affected the other Precambric intrusives in greater or less de- 

 gree ; though it becomes fine grained in certain situations, chiefly 

 marginal, and notably so in many of the dikes which it sends out 

 into the adjoining rocks. 



The rock holds a multitude of inclusions, of Grenville quartzites 

 and schists, of Laurentian granite gneiss, and of the augen 

 gneiss associated with the Alexandria syenite. Over much of 

 Wellesley island the abundant inclusions are but little disturbed. 

 in other words their dips and strikes are concordant and in accord 

 with those of the neighboring Grenville rocks, and with these un- 

 changed dips and strikes the inclusions occur in linear belts, now 

 of quartzite, now of schists and again of granite gneiss, so that 

 the original distribution of these rocks can be mapped as con- 

 fidently as though the granite invasion had never been. This in- 

 dicates that here we are near the very roof of the granite bathy- 

 lith, where cooling had rendered it so stiff and pasty as to be no 

 longer able to pluck away and engulf blocks from its roof, the 

 present inclusions being such as had been last broken away but 

 were unable to founder and retained their original orientation. 



The utter lack of signs of crushing in the rock leads to the rather 

 confident belief that it is the youngest of all these early Precam- 

 bric intrusives, though there is some question as to whether it is 

 actually younger than the syenite and the gabbro about Theresa, 

 and with no possibility of definitely settling the matter. 



The bathylith is also of large size, extending out of New York 

 into Canada among the islands and on the mainland. The granite 

 which outcrops about Kingston seems surely identical, and is dis- 

 tant 17 miles from the nearest outcrops of the rock on the west 

 end of Grindstone island. 



The molten mass of the granite was also richly charged with 

 mineralizing fluids and hence exhibits prominent contact effects on 

 the adjacent rocks, much more prominent than those shown by any 

 of the other intrusives of the immediate region. 



When compared with the Precambric rocks of the general Adiron- 

 dack region (the rocks hereabouts comprising the extreme western 

 edge of the Precambric of northern New York) the most obvious 

 difference to be noted is the comparative scarcity of igneous rocks 

 belonging to the syenites and gabbros in this western area. 



It seems, also to be the case that metamorphism is not so extreme 



