32 NEW YORK STATE MUSEUM 



and quartz together with some calcite and tiny brown garnets and a 

 httle titanite (no. ii, table i). There are occasional nests, up to 

 8 inches in diameter, of pure bright-green pyroxene (coccohte). 

 Some of the layers of Grenville are pyroxene quartzite. The next 

 ledge on the road, a few yards to the south, contains Grenville 

 gneisses exactly like those just described, but which are all shot . 

 through by pinkish granite with more or less assimilation of the 

 Grenville by the granite. Sometimes Grenville streaks are fairly 

 distinct, and sometimes they clearly fade into the granite which 

 latter rock then contains a sprinkling of small crystals of green 

 pyroxene and has a composition really much more like granitic 

 syenite to normal quartz syenite, though quite different in outward 

 appearance. A thin section of this changed rock shows the follow- 

 ing mineral percentages : orthoclase i8; microcline 24; microperthite 

 25; oligoclase to andesine 5; quartz 21; pyroxene (coccolite) 6; 

 and less than i per cent each of magnetite, titanite, zircon and 

 muscovite. It is certain that the pyroxene of this granitic syenite 

 has somehow been derived from the Grenville gneiss, the evidence 

 rather clearly pointing to actual absorption or assimilation of some 

 of the Grenville by the granite. 



Area between Indian Lake village and Rock lake. In this area 

 of some 3 square miles, the most interesting exposures are on the 

 mountain lying southwest of Unknow^n pond. For about a mile the 

 top of the fire-swept mountain is an almost continuous, barren rock- 

 ledge in which a certain type of the mixed gneisses is beautifully 

 exhibited. Pink, medium-grained, biotite granite is all shot through 

 Grenville white gneiss and Grenville light-gray, feldspar-quartz- 

 garnet gneiss, these gneisses usually occurring in wavy, dis- 

 connected, thin layers throughout the granite. It is evident that 

 there has been no considerable assimilation, though usually the 

 gneiss boundaries are not sharply defined against the granite. 

 Farther down, on the south face of this mountain, fairly large 

 masses of dark, rusty-looking, Grenville gneisses occur in the 

 granite. 



Along the road directly west of the mountain just described, 

 there are closely associated gray granite and gray Grenville gneisses. 



The mountain directly south of Unknown pond consists mostly 

 of pink granite with numerous streaks or bands (sometimes 10 to 20 

 feet wide) of Grenville hornblende gneiss. 



Area south of Blue Mountain lake. This area of about 9 square 

 miles, extending from Blue Mountain lake southward to the base of 



