GEOLOGY OF THE BLUE MOUNTAIN QUADRANGLE 1 5 



mine one-half of a mile east of Bullhead pond on the adjoining 

 Newcomb sheet. 



Hornblende-feldspar gneiss. These gneisses are also very com- 

 monly found in contact (or interbedded) with the limestone. They 

 are to be distinguished from the hornblende-feldspar-garnet gneisses 

 above described chiefly by the absence of garnet. One facies is 

 medium grained and nearly black with only lo to 20 per cent of 

 feldspar. Sometimes this gneiss, within an inch of a limestone 

 contact, is full of tiny red garnets, the lime for their development 

 apparently having been furnished by the adjacent limestone during 

 the process of metamorphism. 



Another variety is fine to medium grained and contains perhaps 

 30 to 40 per cent of feldspar together with a few per cent of biotite 



These hornblende-feldspar gneisses are nearly always found 

 where there are extensive exposures of limestone. 



Pyroxene gneisses. So far as could be determined, these gneisses 

 also mostly appear to be closely associated with the limestone either 

 clearly interbedded with them or distributed in irregular shaped 

 masses in them, having been broken up and forced into the relatively 

 plastic limestone under pressure (see plate 4). 



A common variety of the pyroxene gneisses is fine to medium 

 grained and greenish gray, consisting largely of bright green 

 pyroxene (coccolite), quartz and feldspar with numerous tiny red 

 garnets and some titanite through the mass. Sometimes a crude 

 banded appearance is due to a concentration of the pyroxene in 

 layers parallel to the foliation. Excellent exposures occur i mile 

 south-southwest of Indian Lake village in the mixed gneiss area 

 (nos. 6 and 11, table i). 



A rock very similar to this, but with numerous graphite flakes 

 instead of garnet, outcrops along the river just east of Waterbarrel 

 mountain. 



Another variety consisting mostly of green pyroxene (coccolite) 

 with some quartz and a little feldspar is very frequently closely 

 involved with the limestone. Excellent outcrops occur along the 

 road near the county line 9 miles east of Long Lake village, and 

 near the eastern end of the largest island in Blue Mountain lake 

 (no. 22, table i). 



Quart zites. As compared with the mapped areas of the southern 

 and southeastern Adirondacks, quartzites are not so prominently 

 developed in the Grenville of the Blue Mountain quadrangle. Also 

 they vary greatly in composition, scarcely any two localities showing 



