GEOLOGY OF THE BLUE MOUNTAIN QUADRANGLE IJ 



the same kind of rock. Most of the quartzites are fine to medium 

 grained and thin bedded. In general there are two important 

 varieties — one with feldspar and the other without. 



The feldspathic quartzites carry from lo to 25 per cent of feld- 

 spar together with 5 to 15 per cent of either biotite, muscovite or 

 green pyroxene, or slight amounts of tiny red garnets or graphite 

 flakes. 



The nonfeldspathic varieties contain 90 or more per cent of 

 quartz together with either biotite or muscovite. 



Among the better quartzite exposures are the following: on 

 several islands in the northern part of Blue Mountain lake; in the 

 ridge just north of Pine lake; and along the road at the county 

 line 9 miles east of Long Lake village. 



Feldspar-quartz-hiotite-garnet gneisses. These gneisses are not 

 very abundant and vary greatly. Perhaps the most common variety 

 is a fine to medium-grained, crudely banded, light-gray rock made 

 up mostly of feldspar and quartz in addition to 10 or 15 per cent of 

 biotite and varying amounts of pale pink garnets. 



Good exposures may be seen respectively three-quarters of a mile 

 and 13^2 miles east of Blue Mountain Lake village on the road; on 

 the small island just southeast of next to the largest island in 

 Blue Mountain lake (no. 23, table i) ; and on the ridge just north 

 of Pine lake. 



Feldspar-quartz gneisses. These light-gray to white gneisses are 

 represented in considerable amount. 



The most common variety is medium grained and made up very 

 largely of feldspar and quartz with scattering red or pink garnets 

 and almost no dark minerals. In exceptional cases grains of 

 pyrrhotite or pyrite, or flakes of graphite, occur. Rocks of this 

 sort are extensively exposed from i to i^ miles northwest and 

 north of Indian Lake village. Other good outcrops occur on Cedar 

 river one-half to three-quarters of a mile southwest of Pine lake 

 (no. 20, table i) ; on Cedar river i^A miles northeast of Waterbarrel 

 mountain ; and on the road respectively 6 miles (no. 53, table i) and 

 9 miles (at the map edge) east of Long Lake village. 



Apparently these gneisses are the same as certain white gneisses 

 recently described by the writer as occurring within the Lake 

 Pleasant ^ and the North Creek ^ quadrangles. That these are not 

 eruptive rocks is quite certainly proved by their interstratification 

 with definitely known Grenville strata and by their content of 



IN. Y. State Mus. Bui. 182, p. 11. 1915. 

 2 N. Y. State Mus. Bui. 170, p. 13. 1914. 



