GEOLOGY OF LAKE PLEASANT QUADRANGLE I9 



gested by the above-mentioned partially assimilated inclusion ; the 

 fact of the former presence of much Grenville hornblende gneiss 

 associated with more or less limestone in this northern portion of 

 the quadrangle as proved by the inclusions and the large area just 

 west of Speculator village ; the variable composition and appearance 

 of the so-called basic syenite which would be expected because of 

 the differences in amount and character of the rocks assimilated ; 

 the gradation of the basic syenite into the normal syenite ; and 

 the fact that these basic phases of the syenite so greatly resemble 

 similar rocks definitely known to have been formed by such a 

 process of magmatic assimilation in Warren county (see above). 



The second largest basic syenite area extends from Finch moun- 

 tain to near the mouth of Ninemile creek. Toward the west the 

 rock is much like the typical basic syenite from the Speculator- 

 Lookout mountain area just described. In a big ledge along the 

 river ij^ miles below the mouth of Ninemile creek, the rock is 

 light brown, moderately coarse grained, very gneissoid, and rich in 

 feldspar, with scattering hornblende crystals and occasional small to 

 large red garnets (see no. 3 of table on page 16). This rock is 

 distinctly different in appearance and composition from the normal 

 syenite, while it is in every way very similar to one of the transi- 

 tional phases betw^een basic Grenville and normal syenite in the 

 Rogers mine in Warren county.^ The clew to the origin of the 

 rock 1% rniles below the mouth of Ninemile creek appears to be 

 furnished by another ledge along the river one-third of a mile below 

 the mouth of the same creek, where part of the ledge, consisting of 

 good syenite without garnets and only moderately gneissoid, grades 

 rather rapidly into the very basic and gneissoid garnet-bearing rock. 

 It seems clear that this latter rock has been produced by nearly 

 complete assimilation of a very basic older rock still visible. One- 

 half of a mile below this ledge on the river, a mass of rather finer 

 grained syenitic rock is streaked with Grenville dark gneiss inclu- 

 sions or stringers where the assimilation has not been complete. 



Farther eastward, as in Finch mountain and also in the area lying 

 directly across the river from this mountain, the rock is rather fine 

 grained, more highly granulated, very gneissoid to schistose, more 

 biotitic, with hypersthene instead of hornblende, and without gar- 

 nets (see no. 9 of table on page 16). It appears to be a more highly 

 foliated or often sheared phase of the basic syenite with greatest 

 development of biotite along the narrow shear zones. The Finch 



1 N. Y. State Mus, Bui. 164, p. 101-2. 



