212 PHYSIOGRAPHY, GEOLOGY AND MINERAL RESOURCES

was used in the construction of two locks. on the old Potomac canal,
built around the Great Falls of the Potomac. The red sandstone has
always been highly regarded, not only on account of its great strength
and durability, but also on account of the ease with which it is
worked, and its beautiful colors. It is susceptible when first quarried
of very delicate carving, but hardens on exposure. The Maryland
rock is regarded as one of the best of the Triassic sandstones. It
has been used in the construction of many important buildings, includ-
ing that of the Smithsonian Institution in Washington.

The highly metamorphosed micaceous sandstone or quartzite of
Deer creek in Harford county has been used to some extent as a build-
ing stone, and in quite recent, years a company has been organized to
work it. This stone is a pure quartz sandstone, in places plainly con-
glomeratic and contains more or less muscovite, chlorite and other
minerals. The fire-proof qualities of this micaceous sandstone have
long been recognized, and it is frequently employed for hearthstones
and furnaces.

The Weverton sandstone of Cambrian age, which occurs in nearly
unaltered condition in the Catoctin and Blue Ridge mountains, has
been quarried for various building purposes and has been used by
the railroads, canals and private individuals.

In the western portion of Maryland, particularly in Allegany
county, considerable use has been made locally of the sandstones of
the Tuscarora (Medina) and Monterey (Oriskany) formations. The
white sandstone of the former has been extensively quarried in the
narrows above Cumberland from detached boulders and has been
much used for steps, curbs and architectural trimmings. The
Monterey (Oriskany) sandstone has also been quarried at Cumberland
and has been used to some extent both in public and private structures.
Although oftentimes soft and yielding, the harder and more compact
layers furnish a very good building stone, which is of yellowish color
and presents excellent resistance to atmospheric action.

The foliate 1 quartz-schists which occur along the edge of the marble
belts in the eastern or holocrystalline division of the Piedmont Plateau
are quarried to some extent along the southern margin of the Green