20 NEW YORK STATE MUSEUM 



mountain basic syenite was doubtless continuous with that across 

 the river before the gabbro intrusion. 



The area of basic syenite in the vicinity of The Gorge can not be 

 very satisfactorily delimited, but it appears to occupy less than i 

 square mile as shown on the map. Good exposures occur along the 

 river where the rock is greenish gray when fresh, medium grained, 

 distinctly gneissoid and granulated, and consists chiefly of plagio- 

 clase and diallage (see nos. ii and 53 of table on page 16). In 

 The Gorge this basic syenite does not seem to be sharply separated 

 from the gabbro (see below), and its relation to the other rocks, 

 except the diabase, is not apparent. 



In the small basic syenite area near Fiddler's lake, the rock has 

 a mineralogical composition (see no. 14 of table on page 16) very 

 similar to that of the Speculator-Lookout mountain area, while 

 megascopically it is practically indistinguishable from the typical 

 augite syenites represented by numbers 5, 6, and 10 of the table. 



A good example of the small masses (not mapped) of what look 

 like basic phases of the syenite is the single big ledge in the bed 

 of the river within the mixed gneiss area one-half of a mile south 

 of Meco lake. Its composition is rather gabbroi: and considerable 

 quartz content is noteworthy. The field relations clearly indicate 

 that this rock originated as an assimilation product. 



Number 15 of the table on page 16 represents another such rock 

 intermediate in character between the most basic and the normal 

 phases of the syenite. This rock, taken from the eastern border 

 of the small Grenville area or inclusion south of Elbow mountain, 

 has quite certainly been produced by the assimilation of some of the 

 basic Grenville by the syenite magma. At several places the various 

 stages in the process of assimilation of the borders of the Grenville 

 inclusion (see map) are represented by rocks of peculiar appear- 

 ance. 



Still another example certainly due to assimilation is represented 

 by number 24 of the table and described later in connection with the 

 granitic syenite. 



Granitic syenite. Under this heading are included all those rocks 

 which are transitional in character between the normal syenite and 

 the granite. Because of their intermediate features, accurate de- 

 limitation of these rocks, from the normal syenite on one side and 

 the granite on the other, is often not possible in the field. Suffi- 

 ciently detailed work has, however, been done to warrant a roughly 



