12 NEW YORK STATE MUSEUM 



An important Grenville area, nearly 4 miles wide from north 

 to south across the valley at Indian Lake village, extends without 

 an interruption up the Cedar river valley for 11 miles with a width 

 usually from one-quarter to i mile. The most abundant rock of 

 this area appears to be coarse, crystalline, graphitic limestone with 

 closely associated hornblende and pyroxene gneisses. Exceptions 

 are i to i>^ miles north and northwest of Indian Lake village 

 where the rock is largely a white feldspar-quartz gneiss. 



Another prominent Grenville belt extends from Pine lake with- 

 out a break through the valley of Rock river to Thirty-four marsh 

 and thence into the basin of Blue ^Mountain lake. Its widest places 

 are in the vicinity of Rock lake (nearly 2 miles) and in the Blue 

 ^loimtain lake basin (nearly i^^ miles). The basin of Blue IMoun- 

 tain lake is largely occupied by Grenville limestone, many ledges 

 being visible both above and below the water level. \Mthin this 

 belt the only other limestone exposures were observed on Rock 

 river about a mile below the outlet of Rock lake. In the vicinity 

 of Thirty-four marsh, gray Grenville gneisses only were seen. 

 Ouartzite and gray gneisses are prominent in the ridge just north 

 of Pine lake, while on Cedar river, between one-half and i mile 

 above the mouth of Rock river, white feldspar-quartz gneiss 

 together wnth quartzite, hornblende gneiss and gray banded gneisses 

 are prominently developed. Northwest of Rock lake heavy drift 

 rather effectually conceals the Grenville. 



As shown on the geologic map, the two belts of Grenville just 

 described — one along Cedar river and the other along Rock river 

 — are certainly connected through the valley south of Rock lake, 

 but only a few exposures of hornblende and hornblende-garnet 

 gneisses and white gneisses could be found on account of the heav\' 

 drift in this valley. 



The small area extending northeastward from L'nknown pond 

 contains several exposures of Grenville limestone and it apparently 

 consists mostly of this rock and associated hornblende gneiss. 



The prominent depression crossing the line from the Blue IMoun- 

 tain to the Newcomb sheet and containing the Chain lakes (except 

 the first and second), ^lud, Beer, and Jackson ponds, is certainly 

 almost entirely occupied by Grenville limestone and its associated 

 hornblende gneiss. 



Where the road to Newcomb crosses the Essex county line, a- 

 small area of Grenville shows various quartzitic and pyroxenic 

 gneisses in comparatively thin layers. This is really only the west- 



