202 The American Geologist. ai^tw, 190i. 
Numerous smaller areas are widely distributed over the 
Piedmont region, but, in the cases studied, they naturally fall 
into one or the other of the types mentioned above, separate de- 
scriptions of which are unnecessary and beyond the scope of 
the present paper. 
The Oglesby-Lexington Blue-Gray Granite. The 
Oglesby-Lexington belt of dark-blue granite is continuous for 
thirty miles in a northeast-southwest course, with an average 
of four to six miles in width. Practically no variation in tex- 
ture is noted within these limits, but appreciable color variation 
is apparent in places, according to the quantitative variation in 
the biotite constituent. 
This variety consists of anhedra of an average size, 0.5-1.5 
millimeters. [Plate XVIII, figure i.] The texture is hypidio- 
morphic granular. Simple Carlsbad twins among some of the 
feldspars are readily recognizable in many of the hand speci- 
mens. The principal minerals are quartz, orthoclase, micro- 
cline, plagioclase near oligoclase, biotite, some muscovite, a 
little included apatite and zircon, and occasional grains of mag- 
netite and pyrite. Secondary chlorite, epidote, muscovite and 
kaolin are present to some extent. In addition, as an intersti- 
tial constituent, quartz is frequently present in drop-like in- 
clusions in the larger feldspar individuals ; and, at times, is in- 
tergrown with a part of the feldspar in the form of ovals or 
rounded discs of micropegmatitic intergrowths. The period 
of growth of the quartz and feldspar was in part simultaneous. 
Urthoclase is the predominating feldspar present, and frequent- 
ly exhibits microperthitic intergrowths with a second feldspar, 
probably albite. Microcline varies in quantity, but at times 
may equal the orthoclase. The habit of simple Carlsbad twins 
is common to the two potash feldspar varieties. The plagio- 
clase is always inferior in amount to the potash feldspars, and, 
as a rule, gives low extinction angles in basal sections. The 
percentage of lime in the analyses given below with the micro- 
scopic evidence indicates oligoclase as the triclinic feldspar 
present. The biotite is regularly distributed through the rock 
in irregular drawn-out single shreds and foils, deep brown in 
color and strongly pleochroic. It is intimately associated with 
foils of muscovite and is partially altered to chlorite. The re- 
maining accessories present no note-worthy features. 
