PETROLOGY OF SOUTH CAROLINA GRANITES 745 
lar granites into which they grade, the porphyritic granites are biotite 
granites. The potash feldspar phenocrysts vary in size, form, and 
color. ‘They rarely exceed 30™™ in length, are both allotriomorphic 
and idiomorphic in outline, white or pink in color, often twinned on 
the Carlsbad law, contain inclusions of biotite, and are without 
marked orientation in any of the areas studied. 
Two rather unusual types of porphyritic granite in the southern 
states, the Clouds Creek blue-gray and the Heath Springs coarse 
gray granite, are described below. 
The Clouds Creek blue-gray granite.—This type of granite, occur- 
ring in an extensive belt in the southeastern part of Saluda County 
along Clouds and Moores creeks, does not resemble megascopically 
the granite of any known locality in the South. In hand specimens 
it is not unlike the coarse-textured augite-hornblende-biotite syenite 
found southwest of Concord in Cabarrus County, N. C., but differs 
from the latter in containing more quartz and in the absence of augite 
and hornblende. 
The rock is a massive porphyritic biotite granite (quartz mon- 
zonite) of blue-gray color, the ground-mass of which consists of 
anhedra averaging in size from 2 to 10™™ (quartz, 4 to 10™™, biotite, 
2to4™™, and feldspar 2 to 10+™™). Porphyritic texture is not very 
pronounced because of the regular gradation of the feldspar pheno- 
crysts into the similar ground-mass constituent without apparent 
difference in physical characters shown in the feldspar of the pheno- 
crysts and the ground-mass. ‘The quartz is of slight bluish opalescent 
color. Feldspar is prevailingly blue gray. In places much of it is 
nearly white, frequently showing a very faint greenish cast. Cleavage 
is well developed and Carlsbad twinning is common. ‘The feldspar 
phenocrysts grade into the ground-mass constituent, are of irregular 
outline (roughly rounded), from ro to 25™™ and more in diameter, 
usually blue gray in color though frequently nearly white, highly 
lustrous and cleavable, and contain inclosures of the ground-mass 
biotite. 
Thin sections show microcline, orthoclase (partly intergrown with 
albite as microperthite), plagioclase near oligoclase, quartz, and 
biotite, with secondary chlorite, iron oxide, and colorless mica. Carls- 
bad and albite twinning are frequent in the feldspars which show some 
