PETROLOGY OF SOUTH CAROLINA GRANITES 731 
position and texture the gneisses indicate derivation from original 
granites. ‘They are usually of light color, fine- to medium-grained 
texture, and contain, in addition to quartz and mica (biotite with 
frequently some muscovite), much microcline and some acid plagio- 
clase (oligoclase). ‘The hornblende schists (amphibolites) are com- 
posed usually of hornblende and feldspar (albite and oligoclase), 
some quartz and titaniferous iron oré, with epidote, zoisite, and in 
places calcite. The quartz-sericite schists are derived from fine- 
grained bedded porphyry tuffs,t corresponding in composition to 
granite and quartz monzonite. ‘These altered tuffs have been noted 
chiefly in the immediate vicinity of the gold deposits of York, Lan- 
caster, and Chesterfield counties, and presumably have large areal 
extent. Where noted in the vicinity of the gold deposits, their altera- 
tion has been chiefly one of silicification and recrystallization.? 
Metamorphic rocks of sedimentary origin include chiefly quartz 
schist, quartz-sericite schist, quartz-biotite schist, sericite schist, and 
crystalline limestone. The limestones are usually associated \ ith 
the schists into which they may grade along their edges within a short 
distance. They have been noted chiefly in the northwestern part 
of the state in Cherokee, Laurens, Oconee, and Union counties, 
where variation is from ordinary blue limestones to white coarse- 
grained marbles. ‘True foliation is usually most apparent near the 
margins or edges of the beds. These limestones are usually magne- 
sian, ranging, according to Sloan,* from less than 1 per cent. up to 
39.72 per cent. of magnesium carbonate. Ordinarily the blue lime- 
stones are the more calcareous and the light-colored ones dolomitic. 
Other minerals than the carbonates, chiefly silicates (amphibole, 
pyroxene, and mica) and quartz, are contained in the limestones in 
places. 
Granite, pegmatite, and diabase are the principal unaltered 
igneous rocks. Their general character and field relations to the 
surrounding rocks indicate that they were intruded subsequent to the 
1L. C. Graton, Bull. No. 293, U. S. Geological Survey, 1906, pp. 15, 16, 78, 79; 
Geo. H. Williams, Journal of Geology, Vol. II (1894), pp. 28 f. 
2L. C. Graton, op. cit., p. 16. 
3 [bid., p. 19. 
4 Earle Sloan, South Carolina Geological Survey, 1908, Series IV, Bull. No. 2, 
pp. 256-61. 
