14 NEW YORK STATE MUSEUM 



Feldspar-quartz light gneisses also occur three-quarters of a mile 

 south of Thurman ; at Starbuckville ; and one-quarter of a mile 

 north of Chestertown. 



Pyroxene gneisses. These gneisses are much less abundant than 

 those above described. The most common facies is a fine to me- 

 dium-grained intimate mixture of small grains or crystals of green 

 pyroxene and reddish brown garnet, with sometimes one and some- 

 times the other predominating. Such rocks are well exposed in the 

 Sanders Brothers mine near the mouth of Mill creek, and at the 

 old Parker mine just southwest of Daggett pond. 



Another facies is a greenish gray to greenish gneiss which con- 

 tains more or less feldspar in addition to the small garnets. Such 

 rock makes up the inclusion i mile west of The Glen, and also 

 occurs along the road one-quarter of a mile north of the north 

 end of Loon lake. Interbedded with the rock at this last named 

 locality is a schistose orthoclase, green pyroxene, phlogopite rock, 

 with occasional graphite flakes up to 3 or 4 millimeters across. 



Sillimanite- feldspar-garnet gneisses. Such rocks were observed 

 at but two localities, namely, three-quarters of a mile west-north- 

 west of Starbuckville and i mile south of South Horicon. A thin 

 section and specimen from the large outcrop at the latter place 

 shows the rock to be fairly coarse-grained, gray, moderately 

 gneissoid and made up of a matrix of orthoclase, microperthite, 

 and quartz in which are embedded many pale pink garnets, small 

 prisms of sillimanite, tiny graphite flakes, and some small magnetite 

 and colorless pyroxene crystals. At the first named locality the 

 rock is well banded and contains fibrous sillimanite in irregular 

 streaks and also some biotite. 



Graphite sehists or gneisses. As we have learned, graphite flakes 

 are common in the limestone and sometimes present in the quartz- 

 ites and various gneisses. True graphite schists or gneisses are, 

 however, rare, the only ones noted being at the old graphite mine 

 I mile southwest of Johnsburg where the rocks are light to dark 

 gray and thin to thick bedded. One specimen is almost a quartzite, 

 but with numerous small biotite and graphite flakes. Another 

 specimen is a feldspar-quartz schistose rock without biotite and 

 fairly filled with graphite flakes generally from i to 2 millimeters 

 across. Still another specimen is a feldspar-quartz-biotite gneiss 

 with few graphite flakes. 



Grenville stratigraphy. Any attempt to work out the strati- 

 graphy of the (irenville series must of necessity be much more 



