748 THOMAS LEONARD WATSON 
eneiss of the Georgia localities. ‘The minerals are orthoclase, micro- 
cline, oligoclase, quartz, biotite, muscovite, sphene, zircon, apatite, 
iron oxide, and secondary chlorite, epidote, and colorless mica. 
Orthoclase is partly intergrown with a second feldspar as micro- 
perthite. Microcline shows evidence of having been derived in part 
from orthoclase. Micropegmatite intergrowths as small areas are 
indicated, and some of the larger feldspar individuals show micro- 
poikilitic structure (inclosures of rounded quartz chiefly). Granula- 
tion of the quartz and feldspar is pronounced and orientation of the 
biotite is usually well marked. 
The South Carolinat granite-gneiss (Col. 1) is compared chemi- 
cally with the Georgia? gneisses (Cols. 2 and 3) in the following 
analyses: 
Beverly Lithonia* Odessadale 
South Carolina Georgia Georgia 
SIO severance 68.15 75.09 76.37 
INO sacaninae 14.30 13.86 iegaeial 
Hey Osi ae aac 5.20 95 Dear 
IMR OES au aiyotece I.04 .16 0.10 
CAO Mer sce: 2.80 .98 ik ike) 
NasOr ence: 3.80 3.87 4.02 
LS OE pence 5 3.84 4.87 3.68 
* Average of 5 analyses. 
+ Total iron estimated as Fe.O3. 
Examination of these analyses shows at once the greater acidity of 
the Georgia gneisses over the gneiss from South Carolina, in the 
large excess of silica, and the smaller amounts of lime, magnesia, and 
iron oxide. In the percentages of alkalies, Na,O and K,O, the differ- 
ence is less apparent. Molecularly, Na,O exceeds KO in each case, 
but when CaO and Na,O are calculated to anorthite and albite the 
difference is more striking. For the South Carolina type total plagio- 
clase is 45.86 per cent., for Lithonia and Odessadale, Ga., 28.05 and 
39.10 per cent., respectively. Also, the plagioclase in the Georgia 
localities is more acid than that from the South Carolina locality. 
THE APLITES AND THE PEGMATITES 
A plites —Aplite dikes are only occasionally met with in the South 
Carolina granites. They were noted by me only at three localities, 
1 South Carolina Geological Survey, 1908, Series IV, Bull. No. 2, p. 250. 
2 Georgia Geological Survey, 1902, Bull. No. 9A, p. 243. 
