PETROLOGY OF SOUTH CAROLINA GRANITES 743 
present in largest amount. Micropoikilitic and granophyric struc- 
tures are common to the feldspars. 
The Bowling Green—Clover light-gray granite.—The extensive 
granite area in the northern central part of York County in the 
vicinity of Bowling Green and Clover is a medium-textured light- 
gray biotite granite, closely similar in mineralogy, color, and texture to 
the Mount Airy granite in Surry County, N. C. It varies from even- 
granular to porphyritic in texture, but in the porphyritic facies of the 
rock the feldspar phenocrysts are not very abundant and though 
frequently of large size, and sometimes showing crystal boundaries, 
they are usually without crystal outline and grade into the similar 
ground-mass constituent. In common with the porphyritic granites 
of the southern states, the feldspar phenocrysts of the porphyritic 
facies of this type inclose shreds of biotite, equal in size to those of the 
ground-mass. 
This granite consists chiefly of orthoclase, microcline, plagioclase 
(oligoclase), quartz, biotite, occasional muscovite, together with 
accessory apatite, zircon, and iron oxide, and secondary chlorite, 
epidote, colorless mica, and kaolin. Both feldspar and biotite show 
some alteration in the surface portions of the granite, the former 
appearing white opaque and chalky from partial kaolinization, the 
latter showing irregular areas of reddish-brown staining from iron 
oxide immediately adjacent to the biotite from partial leaching. 
Intergrowths of orthoclase with plagioclase (albite) as microperthite, 
and of feldspar with quartz as micropegmatite are frequent. ‘The 
larger feldspar individuals carry frequent inclosures of feldspar 
chiefly, quartz, and felsdpar-quartz intergrowths (micropegmatite). 
Microcline exceeds orthoclase in some sections and is much less in 
others. 
A chemical analysis of this type of granite is given in Col. ITI of the 
table of analyses on p. 735. Its close similarity in composition to 
that of the Mount Airy granite, North Carolina, is indicated in the 
following analyses, p. 744. 
The most noteworthy feature in these analyses is the excess of 
Na,O over K,O. On the basis of the percentages of Na,O and K,O 
in the analyses, the York County, S. C., granite contains 53.41 per 
cent. of soda-lime feldspar corresponding to Ab,An,, and the Mount 
