Pennsylvania Geology Final Report Volume 1 1981

THE JSTEWER GNEISS IN MARYLAND. 131
full of garnet, staurolite, cyanite, fibrolite, rutile, etc., and
cut with innumerable white quartzite veins.
c. Mica schist, without feldspar, but with garnets, etc.,
full of white quartz veins ; apparently a local variety of ^.
These are evidently the gneisses, mica schists, garnet
schists, and contorted and veined schists of Philadelphia.
There are other rocks which show little or no signs of any
such as :
original sedimentary disposition,
d. Setter's ridge quartz-schist, or quartzite, extensively
quarried north of Baltimore, and affording at many other
places a definite geological horizon ; always perfectly foliated
by parallel muscovite mica layers, at variable distances
from each other ; with plenty of stretched and broken tourmaline
crystals in the foliation planes.
e. Ort)icular quartzite, compact, fine-grained, with radi-
ating quartz crystals ; as at the Poor House quarry (along
the western edge of the Texas augengneiss area) and in the
Brooklandville marble.
/. Deer creek white conglomerate quartzite, in the center
of Hartford county, four miles long and less than half a mile
wide, marking a sharp, narrow 300-feet high ridge.
Under
the microscope it is seen to be completely re-crystallized,
but showing to some extent the original pebbles,
with a
secondary growth of wavy membranes of muscovite, large
radiating tufts of blue cyanite, chlorite, magnetite, tourmaline,
garnet, rutile. When better studied this may turn
out to be a basal conglomerate of the Peach Bottom i)hyl-
lite series, for its outcrop is just along the line which separates
the phyllite and gneissic areas.
g. Marble (highly crystallized magnesia-limestone, dolo-
mite) beds occur among these rocks, in irregular, sharplyfolded
patches at Cockeysville and Texas in Maryland, as
in Chester and Delaware counties on the Brandywine. Its
coarse-grained variety is called "Alum stone.'' It contains
crystals of phlogopite, tremolite, white pyroxene, tourma-
line, scapolite, rutile.
7i. The eruptive rocks are : (1) With a surplus of silica :
granite, granitite, hornblende granite, granite porphyry,,
augengranite gneiss, quartz porphyry (felsite), graphic