228 PHYSIOGRAPHY, GEOLOGY AND MINERAL RESOURCES

of 40 tons valued at $1000; but the discovery of extensive deposits
in other regions has now entirely stopped any operations for this
mineral in Maryland.

MICA. —The coarse granite dikes which abound in many parts of
the eastern Piedmont region afford good-sized plates of light-colored
mica (muscovite), and attempts have been made to secure commercial
quantities of this in both Harford and Howard counties, but they
have not been successful.

GRAPHITE. —Traces of graphite have been found near Pylesville
in Howard county at the edge of the Peach Bottom slate belt. Sev-
eral deposits occur further northward in Pennsylvania, where they
have been mined to some extent.