GEOLOGY OF THE LAKE PLACID QUADRANGLE 39 



amounts of dark Grenville gneiss, it seems probable that the gran- 

 itic syenite magma took up the graphite from the Grenville. 



A fine big ledge, known as Pulpit rock, on the eastern shore 

 of Lake Placid contains some inclusions of Grenville. 



The hill just east of Connery pond is mostly a great barren ledge 

 of quite homogeneous granitic syenite. 



Granitic syenite as a transition rock between syenite and granite 

 is well exhibited on the southern side of Mt Whiteface, and also 

 on Catamount mountain ridge. 



Granite. As already stated, this rock is, so far as could be 

 determined, an acidic differentiation phase of the normal quartz 

 syenite. Rather arbitrarily, when a rock of the syenite-granite 

 series contains more than 25 per cent of quartz it is classed as 

 granite. In a few instances the transition from syenite to granite 

 takes place within too short a distance to permit mapping of the 

 intermediate gi^anitic syenite. Like the normal syenite, the granite 

 is more or less clearly gneissoid, medium grained, and often con- 

 siderably granulated. It is, however, nearly always pink or pinkish 

 gray instead of greenish gray like the syenite. The mineralogical 

 compositions of two typical granites are shown by nos. 47 and 

 48 of table 2. 



Ten areas of this granite appear on the accompanying geologic 

 map. Altogether they occupy only 8 or 9 square miles, and they 

 are confined to the western half of the quadrangle. 



The wide belt of granite on the southern side of Mt White- 

 face is very typical medium to moderately coarse grained, pink 

 to red, and distinctly gneissoid. Transition through granitic syenite 

 to syenite is well shown, but on the north it appears to come sharply 

 against the Whiteface anorthosite. A number of tongues of the 

 granite sharply cut the Whiteface anorthosite at the eastern end, 

 as already explained (see map). 



At High fall and in the gorge just below the granite is pinkish, 

 medium to moderately coarse grained, and very gneissoid. 



The granite of the southern end of Wilmington mountain grades 

 through granitic syenite into syenite. 



About Silver lake, and also just west of Still brook, the granite 

 clearly grades into the coarse granite porphyry. 



Several outcrops of granite south-southwest of Woodruff fall, 

 and also i mile southwest of Malcom pond, contain small, distinct 

 inclusions of Grenville hornblende gneiss as lenses or irregular 

 masses mostly parallel to the foliation of the granite. 



