MARYLAND GEOLOGICAL SURVEY 213

Spring valley and are employed for foundations and as flagstones.
This rock originally was probably a sandstone, but has been highly
metamorphosed, so that its original clastic structure is no longer
apparent. It is a hard resistant rock divided by parallel layers of
mica into thin slabs.

The sandstone product in Maryland in 1896 aggregated $35, 969.

THE SERPENTINE. —Serpentine is employed both as a building
stone and, when polished, for interior decoration. The chief deposits
in Maryland are found in Harford and Cecil counties and are the
product of alteration of the peridotite, which has been already de-
scribed. The rock is very hard and is a rich emerald green in color,
semi-transparent and clouded with darker streaks of included mag-
netite. Maryland serpentine has been used for interior decoration in
several large buildings in New York, Philadelphia, Baltimore and
Washington, and has great possibilities as a decorative stone. The
attempts at developing the stone have been only partially successful
hitherto, because of the hardness of the material, the expense of
extracting and polishing it, and the manner of quarrying. Only
$1, 000 worth of serpentine was quarried in Maryland during 1896.

MISCELLANEOUS MATERIALS. —The black gabbro, which has been
described already as a common rock in the eastern division of the Pied-
mont Plateau, is available to some extent as a building stone. The
rock weathers to a deep red soil, in which rounded boulders of the
unaltered rock are found. These are locally known as " niggerhead, "
and as they have to be cleared from the fields, they are extensively
used in building stone fences, foundations, etc. They are rarely used
in the construction of whole buildings, although that is sometimes
done. The rock is so extremely hard and tough that it cannot be
economically quarried and dressed, and is therefore seldom used in
that form.

The chlorite schist found at Westminster, Carroll county, has been
quarried to some extent as a local building stone. It is of a grayish
green color, with even texture, and is easily worked. Several public
and private structures have been made from this material.