Piedmont Plateau of Georgia. — Watson. 205 
blue-gray, and the Elberton-Echol's Mill light-gray types, and 
is intermediate in color and texture between the two latter va- 
rieties. The component minerals are quartz, orthoclase, mi- 
crocline, plagioclase near oligoclase, biotite, a little muscovite, 
apatite and zircon. Some secondary epidote and chlorite from 
the alteration of feldspar and biotite are usually present. Sev- 
eral small garnets have been noted in one or two places in the 
northern part of the belt. The orthoclase is microperthitic in 
structure and is the predominating feldspar, Microclinc 
nearly fails in places and is very abundant in others. Plagio- 
clase is of the usual kind noted above. Rounded disks of micro- 
pegmatitic intergrowths of quartz and feldspar are common. 
Biotite is present in variable amounts intimately associated 
with muscovite. Muscovite is always subordinate to biotite 
in amount. The biotite is deep brown in color with strong ab- 
sorption and variously altered to chlorite. Epidote, in the 
form of irregular grains and idiomorphic crystals, is somewhat 
abundant in thin sections of the Cole quarry granite near 
Newnan. The increased percentage of lime in the analysis 
of this rock corroborates the microscopic evidence (see analy- 
sis L) 
Chemical Axalyses of the Coweta County Medium Blue-Gray 
Granite. 
I. II. III. 
Si02 69.08 69.07 68.79 
AI2O3* 17.67 16.56 16.48 
FeaOat 1.41 1.37 0.98 
CaO 3.27 1.83 1.76 
MgO 0.64 0.76 1.30 
K2O 3.29 5 02 5.85 
NaaO 4.56 4.65 4.74 
Igni 0.56 0.92 0.38 
Total 100.48 100.18 100.28 
I. Biotite granite from the Cole quarry, near Newnan, Georgia. 
II. Biotite granite" from the Overby quarry, 10 miles northeast from 
Newnan, Georgia. 
III. Biotite granite from the Hill quarry, 3^4 miles southeast from 
Newnan, Georgia. 
The dark gray variety is more coarsely crystalline than the 
preceding and contains more biotite and perhaps more plagio- 
clase as a rule, with slightly less quartz. The specific gravity 
* Contains traces of PjOs, Zr02 and Ti02 when present. 
t All iron estim.ited as FcjOa. 
