666 WATSON AND STEIGER: SPINELLITE from VIRGINIA 



850 feet above sea level, and is characterized by the absence of 

 marked relief. 



The rocks are all crystalline and include a variety of metamor- 

 phic and igneous types that are prevailingly deeply weathered, 

 so that outcrops, especially of the metamorphic types, are few. 

 Schists and gneisses, chiefly the former, compose the rock com- 

 plex into which the igneous masses are intruded. They probably 

 form as much as five-eighths of the area mapped. Muscovite 

 schist with or without biotite and common red garnet is the pre- 

 vailing type, although other varieties of schists occur. The gneiss 

 is biotite-bearing, in places garnetiferous, and is of granitic com- 

 position. It was derived probably from an original granite, 

 while the schists were almost as certainly derived from 

 sediments. 



The strike of the foliation of the schist-gneiss complex is to 

 the northeast, ranging from N. 10°-85° E., with a probable av- 

 erage of N. 50° E. ; the dip varies from 40° S.E. to vertical, with 

 a probable averag-e of 65°. 



The igneous rocks, including granite of several kinds, olivine 

 norite, and olivine and olivine-free diabase, are intrusive into 

 the schist-gneiss complex. Olivine norite intrudes the granite 

 and is therefore younger, while the diabase is limited chiefly to 

 the schist-gneiss complex. With the exception of gneissoid 

 structure developed in the granite in places, the igneous rocks 

 are massive. Quartz veins and pegmatites of granitic composi- 

 tion are abundant. Black tourmaline and red garnet occur in 

 the pegmatites in several localities. 



Of the igneous rocks in the district granite, which probably 

 forms three-eighths of the area mapped, is the only one that 

 needs be considered, since the ore bodies are always closely as- 

 sociated with it and the two are undoubtedly genetically re- 

 lated. Two varieties of granite which are strongly contrasted 

 occur: (a) granitite, or biotite-granite, with or without musco- 

 vite, and (b) muscovite granite aplite-pegmatite. Both are 

 commonly massive although gneissoid structure may occur 

 locally. The two varieties appear to be intimately associated 

 in places and the muscovite aplite-pegmatite may carry minute 



