12 NEW YORK STATE MUSEUM 



the mouth of the brook which drains Dunning pond. A similar 

 though smaller outcrop lies one-fourth of a mile still farther up the 

 same stream, while a third exposure occurs near the road one-half 

 of a mile southwest of the mouth of this stream. All this limestone 

 is coarse to medium-grained, pure calcitic except for a few tiny 

 flakes of phlogopite or graphite in some beds. A medium-grained, 

 greenish-gray limestone outcrops in the road nearly 2 miles north- 

 east of Wells (see map). This contains numerous small, greenish 

 pyroxene crystals and occasional quartz grains. 



In the Benson Center Grenville area the rocks are mostly medium- 

 grained, light to dark, distinctly banded, feldspar-quartz-biotite- 

 garnet gneisses, but these are frequently intimately shot through by 

 small amounts of granite or syenite, especially toward the north 

 where they pass into typical mixed gneisses. 



In the Grenville area lying from 1^/2 to 2 miles northeast of 

 Guideboard hill, the rock is largely Grenville dark, hornblende- 

 garnet gneiss with some wide bands or belts of quartzite.and a little 

 feldspar-quartz-biotite gneiss. 



Due north of Guideboard hill the Grenville along the main road 

 is a gray, feldspar-hornblende-garnet gneiss, while in the northern 

 portion of the same area the rocks are chiefly light, feldspar-quartz 

 gneisses associated with quartzitic and biotitic gneisses. 



The Grenville just west of Echo lake is but the southern end of 

 a considerable area of dark, hornblende-feldspar-garnet gneiss much 

 like that so commonly associated with limestone in the North Creek 

 quadrangle. Farther northward, limestone actually occurs with 

 this hornblende gneiss but none was seen within the map limits. A 

 few rods west of the road and near the map edge, a single ledge of 

 rusty looking graphitic gneiss was noted. 



The small Grenville inclusions mapped on the west shore of 

 Sacandaga lake; the top of Fish mountain; near Lake Pleasant 

 village ; and three-fourths of a mile east-southeast of Lookout 

 mountain are mostly of hornblende gneiss, usually garnetiferous. 



A fine exposure of Grenville limestone is shown in the old quarry 

 1% miles east-southeast of Lake Pleasant village. The rock is a 

 medium-grained, greenish-gray, calcitic marble, its greenish color 

 being due to the presence of many tiny, well-serpentinized crystals 

 of pyroxene. Occasionally large blotches or patches of deeper 

 green serpentinized material occur, causing the rock to have a sort 

 of " verde antique " appearance very, similar to that .of the marble 

 recently described by the writer from the quarries near Thurman 

 in the North Creek quadrangle. 



