PETROLOGY OF SOUTH CAROLINA GRANITES 751 
quartz. (4) Pegmatite of the fourth class is coarse grained and con- 
sists chiefly of quartz and muscovite, with feldspar absent or only 
sparingly present. Feldspar is locally abundant. Cassiterite is an 
important constituent in places, and spodumene, apatite, and probably 
lithiophilite are noted. 
JOINT SYSTEMS 
Two systems of joints intersect the granites in the South Carolina 
quarries, namely, a vertical set and a horizontal set. These do not 
in all cases have the same degree of development, nor are the two 
systems always developed in the same quarry. Vertical joints, the 
commonest type, may have inclinations of as much as 50° to 60° 
with variable intervals of spacing. In the northeast quadrant the 
joints which extend approximately north-northeast and east-northeast 
are of about equal development; in the northwest quadrant those 
which extend approximately west-northwest comprise the dominant 
system. Only a few of the joints measured extended E.-W. and 
N.-S. The system of horizontal joints, which in general follow the 
surface configuration of the rocks, is less often developed in the granite 
of the South Carolina quarries than in the granites of the other 
southern states. 
