54 NEW YORK STATE MUSEUM 



1 



In the small area one-half of a mile east of Keene, the Grenville 

 gneiss occurs as bands or inclusions in the anorthosite. 



The area 2 miles long on the southern end of AA'ilniington moun- 

 tain shows mostly Whiteface anorthosite, but nearly every outcrop 

 contains so man}^ inclusions of Grenville, chiefly green pyroxene 

 gneiss, that it has seemed advisable to map this as an area of mixed 

 rocks. Injection gneisses like those just described above were not 

 noted. The small area just to the north contains similar rock. 



Along the road just east of Franklin Falls there are some instruc- 

 tive ledges of Grenville and Whiteface anorthosite mixed gneisses. 

 One phase of this rock is white, medium-grained AA'hiteface anor- 

 thosite (practically all andesine to labradorite) containing approxi- 

 mately 20 per cent of irregular lenslike masses and bunches of dark 

 monoclinic pyroxene crystals, these masses ranging in size from 

 mere specks to an inch or two long and roughly parallel, causing 

 the rock to have a crude foliated structure. A thin section shows a 

 little ilmenite and apatite. Closely associated with this rock is a 

 true injection gneiss which is gray, medium grained and clearly 

 foliated. In thin section it reveals the following mineral percent- 

 ages : andesine to labradorite, 82 ; hornblende, 9 ; green and color- 

 less monoclinic pyroxene, 7^ ; biotite, i ; and ilmenite, ^. Still 

 another phase of the rock from the same ledge is very similar in 

 mineral composition to the last phase described, but it is finer 

 grained and contains several per cent of pale-red garnets in small, 

 scattering grains. It is very evident that this rock, with its several 

 facies, is a border phase of the considerable body of Grenville just 

 to the east (see map) where it has been penetrated more or less 

 intimately by the Whiteface anorthosite magma. 



The small area bordering the Grenville one-half ot a mile north 

 of Franklin Falls has a big ledge of gray, medium-grained, well- 

 foliated injection gneiss, similar to those above described, with 

 scattering light bluish gray labradorites up to nearly an inch long. 



By the road i^ miles north-northeast of Franklin Falls a 

 single outcrop exhibits streaks and narrow bands of Grenville rusty 

 biotite gneiss closely involved with Whiteface anorthosite parallel 

 to the foliation of both. 



At the edge of the quadrangle just east of Silver lake good 

 exposures show dark Grenville gneisses all shot through by White- 

 face anorthosite. 



Along the border between the Whiteface anorthosite and dark 

 Grenville gneiss east of the gabbro at the southern base of Cata- 

 mount mountain, the anorthosite contains streaks and bands of the 



