12 NEW YORK STATE MUSEUM 



A hand specimen, from the prospect hole 2^ miles south of 

 Pottersville, is a very coarse-grained mass of calcite, brown horn- 

 blende, and graphite through which are scattered small flakes or 

 crystals of phlogopite, pyrite, and pyroxene (mostly serpentin- 

 ized). The hornblende and calcite crystals are as much as an inch 

 across. 



Quartzite. In the quartzite areas shown on the map south of 

 Sodom, south of Pottersville, and east of Chase mountain, the rock 

 consists almost wholly of distinctly bedded, pure quartzite (with 

 layers up to i^ feet thick) interstratified with thin layers of 

 biotite-quartz gneiss. 



The quartzite of the area southwest of Thurman contains many 

 closely involved tremolite and limestone beds. 



Thin layers of quartzite are occasionally present in the other 

 Grenville areas but these are usually rather impure containing 

 more or less feldspar, biotite, muscovite or graphite. 



H ornblende-garnet-feldspar gneisses. Of the two principal 

 facies of these gneisses, one is a gray, medium to fairly coarse- 

 grained hornblende-feldspar gneiss in which are embedded occa- 

 sional large brownish red garnets of the almandite type. The felds- 

 pars comprise both orthoclase and plagioclase and the hornblende 

 is very dark green to nearly black. Biotite, magnetite, and pyrite 

 generally occur in small amounts. The garnets never show crystal 

 form but are always more or less rounded and highly fractured. 

 These garnets commonly range in size from one to five inches and 

 are often surrounded by rims or envelops of pure hornblende 

 crystals. Fine specimens of such garnets, surrounded by rims of 

 hornblende and embedded in the gray matrix, may be obtained 

 at the old garnet mines near the top of Oven mountain and south 

 of Holcombville. 



Another facies is fine to medium-grained, darker gray (with 

 reddish tinge), less feldspathic, and more garnetiferous but with 

 the reddish brown garnets all very small and rather evenly scat- 

 tered through the rock. Small amounts of magnetite, quartz, and 

 pyrite are also usually present. 



These hornblende-garnet-feldspar gneisses are almost invariably 

 closely associated with the limestone beds, the two rocks often 

 appearing in a single outcrop. Numerous fine exposures may be 

 seen along the south and west sides of Crane mountain, i mile 

 west of Pine mountain, just northwest of No. 9 mountain, and 

 I mile east of Cherry ridge. 



