40 NEW YORK STATE MUSEUM 



dikes of granite and syenite extending right out into Grenville are 

 well represented on the map north and northwest of Minerva, and 

 south-southwest of Irishtown. 



Description of syenite and granitic syenite. Practically all 

 the syenite of the quadrangle is more or less quartzose. As has 

 been the writer's custom for some years, when the rock contains 

 not over 20 per cent quartz it is classed as normal quartz syenite, 

 when the quartz content lies between 20 and 25 per cent it is called 

 granitic syenite, and when there is more than 25 per cent quartz 

 the rock is called granite. The syenite of the quadrangle is much 

 less extensively developed than usual in the Adirondack region, 

 and much of this is really granitic syenite, no attempt having been 

 made to separate the normal and granitic phases on the geologic 

 map because of the general unsatisfactoriness of exposures. 



The two facies of the syenite are typically medium grained, 

 though somewhat variable to finer and coarser grained. Distinctly 

 porphyritic facies were not observed. Granulation is very common, 

 in some cases being highly developed especially as regards the 

 feldspar, and less commonly the quartz. 



A dark greenish gray is the prevailing color of the fresh syenite 

 as usual in the Adirondacks, though the more granitic facies are 

 often pinkish gray. Reddish syenite, directly associated with 

 green syenite, is well exposed in and near the quarries one-half 

 of a mile east of South Schroon. All, except some ol the pinkish 

 facies relatively free from femic minerals, weather to light brown, 

 the weathered portion seldom extending more than a few inches 

 below the surface. 



Seldom does the syenite fail to exhibit a foliated structure. 

 It is, in most cases, moderately developed, but in some cases it 

 is faint and in others very pronounced. 



It should be noted that marked differences in granularity, granu- 

 lation, foliation and color not uncommonly occur locally, in some 

 cases in single outcrops, or even in hand specimens. 



Very typical, fresh, moderately gneissoid, greenish gray, normal 

 quartz syenite is finely exposed in the larger of the two quarries 

 by the road one-half of a mile east of South Schroon. No. 6 of 

 table 2 shows the mineral content of a thin section of this rock. 



