U.S. GEOLOGICAL SURVEY 



MONOGRAPH XXXVl PL. XL 



^■y^m^f "*•"■ M 



M 



W^' 





N 



(^) 



(B) 



C-fl) MICA DIORITE PORPHYRITE. 



(B) MICA DIORITE PORPHYRITE SEEN BETWEEN CROSSED NICOLS. 



