404 THOMAS L. WATSON 



good cleavage development, and twinning on the Carlsbad law. 

 Feldspar is the most abundant constituent, composed of microcline 

 and orthoclase, with httle plagioclase; quartz frequently occurring in 

 very small amount. Muscovite has been observed occasionally; and 

 tourmaline, garnet, and the rarer minerals sometimes associated 

 with pegmatites, are strikingly absent. 



Fig. 6. — Granite dike west of Salisbury, North Carolina. 



In the Raleigh city quarries where the only true aplite has been 

 observed, the aplite and pegmatite are associated as banded aplite- 

 pegmatite, the aplite being in contact with the pegmatite on one side 

 and the inclosing granite on the other. They are very light-colored 

 rocks, containing but little biotite; are fine-grained; and are only a 

 few inches across. Orthoclase, microcline, very little plagioclase, 

 microperthite, quartz, biotite, muscovite, chlorite, rutile, .magnetite, 

 and kaolin appear in thin section. Microscopically they are potash 

 aplites. 



