22 NEW YORK STATE MUSEUM 



anorthosite with a few labradorite phenocrysts ; then, a belt 40 feet 

 wide of less coarse-grained anorthosite with a few labradorite 

 phenocrysts and scarcely any f emic minerals ; next, a belt 35 feet 

 wide of very coarse-grained, gabbroid anorthosite with pyroxene 

 and labradorite crystals from 6 inches to i foot each in length. 

 None of these belts or zones is very sharply separated, though in 

 some cases the change from one into the other takes place within 

 a few inches. 



At the rapids of Boreas river, just before the stream enters the 

 Brace dam reservoir, a big ledge of typical Marcy anorthosite with 

 very few femic minerals contains a very irregular shaped mass of 

 highly femic and garnetiferous anorthosite some 30 feet long with 

 a maximum width of 10 feet. Except for the 20 to 30 per cent 

 of dark minerals, this femic anorthosite is much like the inclosing 

 anorthosite. Boundaries against the typical anorthosite are not 

 sharp, but the complete transition takes place within 5 or 6 inches. 

 The femic rock is nonfoliated, but the typical Marcy anorthosite 

 on one side of it has most of its labradorites (i to 2 inches long) 

 arranged parallel to the contact with the femic rock. This par- 

 allelism is most evident close to the contact and not at all notice- 

 able 6 or 8 feet out. 



By the road three-fourths of a mile east of where it crosses 

 Boreas river, a 50-foot exposure of typical Marcy anorthosite, with 

 less than 5 per cent femic constituents and with many labradorites 

 an inch long, exhibits very distinct foliation due to parallelism of 

 the labradorites. This rock grades into typical nonfoliated anor- 

 thosite of the adjacent exposure. 



By the same road above mentioned, but one-third of a mile far- 

 ther east, a 50-foot ledge of anorthosite with 10 or 15 per cent 

 femic minerals contains several distinctly foliated zones not sharply 

 separated from the rest of the rock. 



In a ledge of typical Marcy anorthosite on the middle-southern 

 slope of Saywood hill, a distinctly foliated zone occurs in contact 

 with nonfoliated anorthosite on either side. 



From Saywood hill to Clear Pond mountain there are large scale 

 variations represented chiefly by typical, nongabbroid, mostly non- 

 foliated, Marcy anorthosite with some labradorites up to 3 inches 

 long on Saywood hill ; very coarse, rather gabbroid, nonfoliated 

 anorthosite containing labradorites up to 6 or 7 inches long and lO 

 to 20 per cent femic minerals on Clear Pond mountain ; and many 

 fine exposures of more typical Marcy anorthosite with usually 10 

 to 15 per cent femic minerals and little foliation. 



