GEOLOGY OF THE LAKE PLACID QUADRANGLE 1 3 



ville, not one of them more than a few square miles in extent, are 

 rather widely scattered over the quadrangle, but they make up only 

 a small percentage of its area. They are mere fragments of the 

 formerly continuous Grenville series which has been cut to pieces 

 by vast intrusions of plutonic igneous rocks, especially the anortho- 

 site and the syenite-granite series. 



The actual extent of Grenville strata is somewhat greater than 

 indicated directly as such on the geologic map. Thus, in the 

 vicinity of Newman, the bedrock, probably mostly Grenville, is 

 largely concealed under glacial deposits. Similar conditions prob- 

 ably also obtain in the areas of unknown bedrock west of the river 

 between Keene and Upper Jay, and between Franklin Falls and 

 West Kilns. Again, the areas of Grenville-anorthosite mixed 

 gneisses, and of syenite or granite and Grenville mixed gneisses, 

 contain much Grenville. Finally, there are occasional small 

 unmappable masses of Grenville which occur as inclusions in the 

 great intrusives. But, after making every reasonable allowance, 

 it is believed that Grenville rocks do not actually occupy more than 

 8 or 10 per cent of the area of the quadrangle. 



Compared with the Adirondacks in general, the Grenville rocks 

 of the Lake Placid quadrangle are mostly of quite the usual sorts, 

 namely, graphitic crystalline limestones, pyroxene gneisses, horn- 

 blende gneisses and quartzites. 



Areas in the vicinity of Lake Placid. In the extreme soiuth- 

 western corner of the quadrangle an area of about i square mile 

 shows some good outcrops of Grenville. Dark hornblende-feldspar 

 gneiss, hornblende-feldspar-garnet gneiss, together with some light- 

 gray garnetiferous feldspar gneisses and a little quartzite, make up 

 the main bulk of the rock. " At one locality (near the diabase dike) 

 the dark gneiss contains large red garnets with hornblende rims. 



The area which extends from Pulpit mountain to Connery pond 

 and southward several miles contains various Grenville rock types. 

 The eastern portion of Pulpit mountain consists mostly of dark 

 hornblende-feldspar-garnet gneiss with scattering red garnets up 

 to 4 inches in diameter enveloped in rims of black hornblende. 

 The hill south of Tom Peck pond contains mostly hornblende- 

 feldspar gneisses (often garnetiferous) interbedded with con- 

 siderable well-stratified pyroxene gneiss and a little biotite gneiss. 

 On the ridge for 2 miles south from Big Cherrypatch pond the 

 Grenville is mostly hornblende-feldspar gneiss, usually garnetifer- 

 ous and with a little interbedded pyroxene gneiss. The southern 



