384 THOMAS L. WATSON 



albite. Biotite is but sparingly present in the rock and is largely 

 altered to chloride. Occasional small grains of magnetite and 

 scattered inclusions of prismatic apatite, with some secondary musco- 

 vite, kaolin, and calcite, complete the list of accessories. 



The weathered surface of the granite is light in color. The feld- 

 spars are dull and opaque, and have lost much of their decided pinkish- 

 red color, so characteristic of the same constituent in the fresh rock. 



The Elm City area. — The Elm City granite is strongly contrasted 

 with the Wilson pink granite described above. It is much finer in 

 texture, of gray color, and contains more biotite and quartz than the 

 Wilson pink granite. Feldspar predominates and consists of the 

 potash varieties and much striated acid plagioclase. Extinction 

 angles measured on the plagioclase correspond to an albite of the 

 composition AbiaAuj. Areas showing alteration to kaolin and mus- 

 covite cloud some of the feldspars. Micropoikilitic structure is 

 strongly developed in some of the larger individuals of potash feld- 

 spar, the inclusions of which consist of large microscopic grains of 

 quartz and striated feldspar. Quartz is of the usual kind, forming 

 distinct areas of an interlocking finer mosaic. Biotite is distributed 

 through the sections as small plates of brown color and strong pleochro- 

 ism, bleached to green on alteration, and is further altered to chlorite 

 and some epidote. In one of the thin sections a few additional small 

 crystals of compact hornblende, showing the usual development of 

 the prismatic cleavages, occur. The principal accessories include 

 zircon, apatite, a little pyrite, titanite, and ilmenite. The granite 

 shows evidence both megascopically and microscopically of dynamic 

 metamorphism, manifested, in places, by a rather pronounced 

 schistose structure. 



The quarry opening indicated penetration of the granite by a dike 

 of very finely schistose amphibolite, closely jointed and containing 

 many disseminated small grains of pyrite. Additional quartz veins 

 penetrate the granite, wrapped, in cases, by films of thin layers of 

 hornblende. The surfaces of the joints are slickensided, coated with 

 a thin veneer of yellowish-green mineral substance, probably epidote 

 in part. Considerable epidotization characterizes the rock in places. 



The Rocky Mount area. — Westward from Rocky Mount the granite 

 is associated with an irregular but large body of crystalline schists 



