1 8 NEW YORK STATE MUSEUM 



graphite at some localities, for example, on Cedar river from one- 

 half to three-quarters of a mile southwest of Pine lake. This 

 matter is of considerable importance because these rocks so closely 

 resemble certain white gneisses recently described from the Sara- 

 toga quadrangle by Gushing and by him rather thought to be 

 ancient granites belonging with the so-called '' Laurentian granite." ^ 



Another variety of the feldspar-quartz gneisses is light gray, 

 medium grained, very homogeneous and rather syenitic looking. 

 This rock contains specks of pyrite and weathers brown. When 

 first encountered it was thought to be a special facies of the syenite, 

 but later the same sort of rock was found interbedded with true 

 Grenville gneiss. Good outcrops may be seen in the small Grenville 

 area i mile southwest of Long Lake village (no. 43, table i) ; in 

 the small Grenville area 2 miles northeast of Long Lake village ; and 

 on Gedar river respectively i^ (no. 7, table i) and 3^ miles north- 

 east of Waterbarrel mountain. 



Sillimanite gneisses. These are also light gray to white gneisses 

 but are rare, having been found at only two places. A big ledge, 

 100 feet across within the small Grenville area 2 miles northeast of 

 Long Lake village, consists of fine to medium-grained, banded, 

 feldspar-quartz gneiss with some layers very rich in glistening 

 needles of sillimanite. 



The top of the mountain ridge (mixed gneiss) just southwest of 

 Unknown pond shows sillimanite and garnet gneisses all shot 

 through by granite. The sihimanite gneiss is a mass of fine-grained 

 feldspar through which are scattered delicate, glistening needles of 

 sillimanite in great abundance. 



Tremolite gneiss. At the map edge on the Long Lake-Newcomb 

 road, tremolite gneiss is interstratified with thin-bedded quartz- 

 feldspar gneiss and dark pyroxene gneiss. The composition of this 

 rock is shown by no. 51, table i. 



Feldspar-graphite gneiss. On the largest of the three small 

 islands just southeast of the largest (Long) island in Blue Moun- 

 tain lake, there are good exposures of gray to brown, medium- 

 grained, thin-bedded, feldspar-graphite gneiss, the graphite being 

 disseminated through the rock as numerous tinv flakes Tno. 26. 

 table i). 



Anorthosite-gabbro 



Two small areas of anorthosite-gabbro are shown on the geologic 

 map respectively i^ miles northeast and i^ miles north of the 



1 N. Y. State Mus. Bill. 169, p. 21-26. 1914. 



