l6 NEW YORK STATE MUSEUM 



Grenville sediments have a somewhat greater prominence than any 

 or all of the other Precambrian rocks. This is probably true also 

 as regards the drift-covered part of the quadrangle, from Canton 

 eastward, that is, throughout the area colored as inferred Precam- 

 brian, where the scarcity of outcrops prevents anything more than a 

 rough estimate of the relative abundance of the formations. The 

 exposed igneous material is practically confined here to a few 

 isolated areas of granite gneiss near its southern margin and to three 

 smaller occurrences of similar material in the east-central ninth« 

 The remainder of this Precambrian area, with the exception of a 

 few scattered occurrences of amphibolite of uncertain origin, and 

 a group of gabbro outcrops near the east border of the sheet, is 

 probably occupied preponderantly by sedimentary material. Assum- 

 ing this to be true, the proportion of elastics in the drift-covered 

 area may be larger than in the southern part w^here the greater 

 abundance of ledges permits a more precise comparison to be made. 



