PETROLOGY OF SOUTH CAROLINA GRANITES 737 
this mineral would not exceed 32 per cent., and an average would be 
-about 25.5 per cent. The total feldspar content of these granites, 
based on the analyses above, averages about 66.8 per cent. propor- 
tioned about as follows: 25.5 per cent. potash feldspar and 41.25 
per cent. soda-lime feldspar. 
Attention is further directed in the analyses to the constant presence 
of titanium in very appreciable amount, ranging in the form of TiO, 
from 0.24 to 0.48 per cent. The microscope indicates its principal 
sources to be in sphene and titaniferous iron oxides, and to some 
extent as rutile filaments in the quartz. Manganese and phosphorus 
are noted, usually in traces only. 
TYPES OF THE GRANITES 
All the granites are biotite granites, muscovite being frequently 
present in subordinate amount and hornblende failing entirely except 
in a single locality. They vary in structure from massive to schistose, 
and in texture from even-granular to porphyritic rocks, and may be 
grouped on this basis into (1) even-granular massive granites, (2) 
porphyritic granites, and (3) schistose or foliated granites—granite- 
gneisses. 
The even-granular and porphyritic granites are textural variations 
of the same rock-mass and are sometimes indicated in the same 
quarry, but, in such cases, the porphyritic texture is likely to be of a 
less emphasized or pronounced type than is observed in parts of 
Georgia and North Carolina. The granite-gneisses have closely 
similar chemical and mineral composition to the massive granites, 
from which they were derived and from which they differ principally, 
in pronounced schistose structure secondarily induced in them by 
dynamic metamorphism. 
PETROGRAPHY 
EVEN-GRANULAR GRANITES 
General characteristics.—The even-granular granites have wide 
but variable distribution throughout the crystalline area of the state. 
They vary from fine- to medium-grained rocks in texture, less often 
coarse-grained, and are usually some shade of gray in color—light, 
medium, and dark blue-gray shades being frequent. In many 
localities a part of the feldspathic constituent is either of slight or 
