740 THOMAS LEONARD WATSON 
granite in Iredell County, N. C.;t and the Richmond-Fredericksburg 
dark blue-gray granite in Virginia. The granite of the Guilford 
and Waltersville Quarry near Guilford, Md., is somewhat similar, 
but is of lighter color and coarser crystallization. As would be 
expected, these granites may show minor variations in texture and 
color, but these are so slight that but little difference can be discerned 
between them in the hand specimens. Orthoclase, much microcline, 
oligoclase, quartz, biotite, apatite, zircon, and magnetite make up 
the principal primary minerals composing the Winnsboro blue-gray 
type of granite. 
An average of three analyses of the Winnsboro dark blue-gray type 
of biotite granite from South Carolina is given below in Col. I and 
is compared with analyses of the similar type from Georgia (Col. IT) 
and North Carolina (Col. ITI). 
I IT III 
SHOPS aineroae 69.79 69.59 66.01 
I Onan raone 66 16.08 16.84 17.44 
Hie; Oa nies eee 2.85 I.24 5-62 
Mig @ recency 0.53 0.76 ite itta 
CaO... 173 2.67 1.44 
INETAO bea aniah ae 4.07 Ana 5.00 
Ke Ove 4-45 4.93 3.16 
I. Average of 3 analyses of biotite granite from Anderson Quarry, Fairfield 
County, Excelsior Quarry, Lancaster County, and Leitzsey Quarry, Newberry County, 
S.C. South Carolina Geological Survey, 1908, Series IV, Bull. No. 2, pp. 252-54. 
II. Average of 2 analyses of biotite granite from Diamond Blue Granite Co.’s 
Quarry, Oglethorpe County, and Hill Quarry, Elbert County, Ga. Georgia Geological 
Survey, 1902, Bull. No. gA, pp. 191, 241. 
III. Biotite granite from Johnson Quarry, near Mooresville, Iredell County, N. C. 
North Carolina Geological Survey, 1906, Bull. No. 2, p. 84. 
It will be observed from the analyses that Na,O and K,O are 
essentially equal in the South Carolina and Georgia granites of this: 
type, and in the similar North Carolina type Na,O greatly exceeds 
K,O. Calculating CaO and Na,O in the analyses to anorthite and 
albite the following percentages of these minerals are obtained: South 
« Journal of Geology, Vol. XII (1904), pp. 392, 393; North Carolina Geological 
Survey, 1906, Bull. No. 2, pp. 81-85. 
2 Bull. Geol. Soc. Amer., Vol. XVII (1906), pp. 528, 520. 
