METAMOKPHIC EOCK8. 17 
fine grain and light color and exhibit by the position of the dark biotite flakes a derided 
foliation. When greatly weathered it is not always possible to distinguish them from 
granite. 
Mewed under the microscope quartz is seen to be fairly plentiful and shows crushing and 
strain shadows. Microcline is very abundant in many specimens, intergrown micropeg- 
matitically with the quartz. A little plagioclase is present and probably is albite. Small 
broken plates of brown biotite and of muscovite occur somewhat sparingly. Fragments of 
apatite crystals are sometimes seen and more rarely broken grains of zircon. Crushing seems 
to have taken place, especially along certain zones. 
The gneisses are most common along the Kings Mountain Range, but probably occur also 
at places in the eastern part of the area, as in the western part of Chesterfield County. 
As is showm on page 20, it is probable that these gneisses have a close genetic connection 
with the massive granites. 
SCHISTS OF SEDIMENTARY ORIGIN. 
QUARTZ SCHIST. 
Foliated or schistose rocks made up principally of quartz are common and conspicuous 
throughout the western part of the area. Original sandstones, arkescs. and quartz-pebble 
conglomerates have been changed into quartzitic rocks, which usually retain enough of their 
former structure to make their derivation a matter of certainty. 
The finer grained or sandstone members are made up of small polyhedral grains of quartz. 
in most cases combined with minute yellow . mica, muscovite, and a little biotite, 
but in some cases composed of quartz alone and then very friable or "sugary. " The mica- 
bearing varieties usually have a decided schistosity dependent en the parallel arrangement of 
the mica flakes. In some localities the scales of mica serve to bind the quartz grains together, 
and, being flexible, allow a slight movement of the quartz grains, producing the flexible sand- 
stone or itacolumite described at length by Lieber.a In these micaceous quartzites magnet- 
ite is commonly present and by its oxidation stains the rock pink, red, or brown. Under 
the microscope the polygonal outline of the quartz grains penetrated by foils of mica, usually 
muscovite, the numerous small octahedrons of magnetite, and the occasional crystals of 
garnet indicate that recrystallization has been considerable. 
Some varieties, perhaps different in original composition or possibly subjected to different 
conditions of metamorphism, have fresh microcline instead of muscovite and hold numerous 
small, irregular grains of garnet. 
The conglomerates are made up principa ly of quartz pebbles varying in diameter from a 
few millimeters to several centimeters, but most commonly 1 to H cm. These pebbles have 
been almost everywhere much flattened and drawn out by pressure, and in many places the 
resulting mass can be determined as a conglomerate only by observing the gradual change 
into more typical fades. The matrix of the pebbles is in some places a green, slaty, sericitic, 
and chloritic material, rather abundant as compared with the bulk of the pebbles which it 
contains and wrapped around the pebbles in a manner recalling the flow lines of a porphyry. 
In other places the pebbles, large and small, compose nearly the whole of the mass and the 
cementing material is mainly silica, probably derived from partial solution of the pebbles. 
Were it not for their flattening due to pressure, the pebbles would in most cases be well 
rounded. Surface specimens, however, fiequently show a peculiar faceting of the exterior 
pebbles and sometimes suggest a rude approach to crystalline form: but large exposures 
show that this faceting is due to solution. The surface of the conglomerates is covered with 
pits and depressions exactly similar to those produced by solution in many limestones. The 
very decided solution which is thus evidenced probably has some relation to the conditions 
existing in a region near base-level already referred to (p. 13). & 
a Survey of South Carolina, vol. 3 18-59. pp. 75-106. 
t> Campbell, M. R., erosion at base-level: Bull. Geol. Soc. America, vol. S, 1897, pp. 221-226. Cf. also 
Hayes, C. W., idem, pp. 213-220. 
Bull. 293—06 2 
