170 PHYSIOGRAPHY, GEOLOGY AND MINERAL RESOURCES

chlorite and hydromica (sericite) schists, often full of ottrelite, rutile,
biotite and other new constituents. The limestones have become
compact, hard, fine-grained marbles. The geological position of these
rocks has only in part been positively proved by fossils, and they are
therefore designated on the geological map by different colors.

THE QUARTZITE. —Isolated areas of quartzitic sandstone of sup-
posed Cambrian age are found developed along the eastern side of the
Monocacy valley in Frederick county. A single outlier, already refer-
red to, is found in the eastern division in northern Harford county,
which is supposed to be of identical age, but this fact has not been as
yet fully established. The most extensive deposit of this material
occurs in Sugar Loaf Mountain, near the boundary of Montgomery
county. Here the sandstone is very homogeneous, fine-grained and
compact, and is very light, frequently white, in color. The massive
sandstone strata of Sugar Loaf Mountain form a series of antichines
overturned toward the west. The formation continues toward the
north in a few insignificant sandstone patches, while toward the south
it soon disappears beneath the phyllite series. The Sugar Loaf sand-
stones pass on their eastern side upward by a gradual transition into
the overlying deposits, which in their unaltered portion are somewhat
shaley.

THE PHYLLITE AND CRYSTALLINE LIMESTONE. —The shaley layers
just described pass over into sandy slates, and these again into the
succession of sericite and chlorite schists, which compose the mass of
the " semi-crystalline" area. Considerable deposits of limestone,
which are now highly crystalline fine-grained marbles, also occur, par-
ticularly throughout the northern portion of the district in the area to
the west and north of Westminster. As these rocks are followed
across their strike toward the east they are seen to become more and
more contorted, cleaved and faulted. Closely folded and puckered
layers are frequent, and the secondary cleavage approaches nearer and
nearer to the vertical. The succession of beds is well displayed along
the main stem of the Baltimore and Ohio Railway between Araby and
Hood's Mills. The alteration, or re-crystallization, of these rocks,
attendant upon the increasing disturbance to which they have been