2l6 
The American Gcolozist. 
April, 1901. 
angles. Thin sections of several of these masses show micro- 
cline, orthoclase and plagioclase feldspars, with occasional 
microperthitic structures, a few shreds of biotite and some 
quartz. Hand specimens of others showed nearly equal pro- 
portions of feldspar and quartz with occasional biotite plates. 
2. CHEMICAL COMrOSITION. 
The following analyses give a good idea of the range in 
composition of the granitic rocks described above. These anal- 
yses present several points of interest, chief among which may 
A. TABLE OF CHEMICAL ANALYSES. 
Granites 
I 
lit 
III 
IVJ 
V 
VI§ 
Vim 
VIII 
Stone 
Lexing- 
Green- 
Oglesbv 1 
Campbell 
Elber- 
Coweta Meriw'r 
Mt. 
ton 
ville 
countv 
ton 
county 
countv 
Si02 
72.56 
69.95 
69.88 
69.86 
69.55 
69.17 
68.98 
63.27 
AI2O3' 
14.81 
16.08 
16.42 
16.98 
16.72 
16.54 
16.90 
19.93 
FesOa* 
0.94 
1.21 
1.96 
1.31 
0.99 
1.38 
1.25 
2.82 
CaO 
1.19 
2.38 
1.78 
1.99 
1.69 
1.99 
2.28 
2.89 
MgO 
0.20 
0.56 
0.36 
0.51 
0.27 
0.45 
0.90 
0.49 
K2O 
5.30 
5.07 
5.63 
5.04 
3.94 
4.66 
4.72 
4.85 
NasO 
4.94 
4.84 
4.45 
4.77 
5.88 
4.60 
4.98 
4.14 
Igni. 
0.70 
0.77 
0.39 
0.36 
0.27 
0.41 
0.62 
0.86 
Total 100.64 100.86 100.87 100.82 99.31 99.20 100.63 99.25 
Sp. Gr. 2.684 2.666 2.662 2.663 2.658 2.656 2.694 2.739 
PoRPHVRiTic Granites. 
IX 
X 
XI 
XII 
xiin 
XIV 
XV 
Fayette 
Pike 
Columbia 
Baldwin 
Sparta 
Fulton 
Greene 
County 
County 
Countv 
County 
Countv 
Countv 
Si02 
70.38 
70.24 
69.77 
69.37 
69.33 
69.17 
69.13 
AI2O3' 
15.86 
16.78 
17.05 
16.99 
16.26 
16.47 
17.14 
FeaOa' 
1.77 
1.46 
1.60 
1.99 
1.84 
1.23 
1.52 
CaO 
1.79 
2.00 
2.21 
2.03 
2.28 
2.02 
1.85 
MgO 
0.93 
0.76 
0.99 
0.84 
0.36 
0.61 
0.79 
K2O 
4.64 
5.03 
4.08 
4.54 
4.56 
4.41 
5.49 
NaoO 
3.94 
3.70 
3.97 
3.44 
5.07 
4.89 
4.06 
Igni. 
0.49 
0.50 
0.44 
0.55 
0.42 
1.06 
0.52 
Total 
99.80 
100.47 
100.11 
99.75 
100.12 
99.86 
100.50 
Sp. Gr. 
2.659 
2.674 
2.675 
* All iron estimated as Fe203. 
■}■ Average of 3 analyses representing different quarries. 
+ " "5 " 
§ •' "3 " 
II .. .. 3 .. 
f[ .. ..3 .. 
' Contains traces of P205.Ti02 and Zr02 when present. With sever- 
al exceptions, the usual qualitative test failed to indicate the presence 
of Ti02 in the Georgia acid rocks. F2O5 and Zr02 are invariably present 
in small microscopic proportions as prismatic inclusions of apatite and 
Zircon. 
