MARYLAND GEOLOGICAL SURVEY 215

are most widely distributed throughout the eastern and southern por-
tions of the state and oftentimes underlie broad areas of country.
Important clays also occur in the central and western portions of the
state. The clays of Maryland are suitable for brick-making, terra-
cotta work, fire-brick and pottery. Brick-making began in Maryland
in the colonial days, scattered references to the industry being found
in the earliest records. The clays most extensively used at the present
time are from the Columbia and Patapsco formations, and the centre
of the industry is at Baltimore. Residual clays in central and western
Maryland are also employed, while the fire clays of Allegany county
rank among the best in the United States.

The clays of the Columbia formation widely cover the surface at
the lower levels in the region about Baltimore, and in the country
to the south and east they generally consist of a yellowish or brownish
clay or loam which grades downwards into coarse sands and gravels.
They are highly regarded by the clay workers for certain classes of
products. Much of the Columbia clay has been removed in the im-
mediate vicinity of Baltimore, but is still capable of further develop-
ment in the southern and southwestern portions of the city about
Middle Branch, and in other sections of country in the adjacent
counties.

The clays of the Patapsco formation are developed along a belt
which extends from the northeast to the southwest across the state,
passing through Baltimore. In this locality, as well as in the region
adjacent to the city of Washington they have been extensively worked
and afford many high-grade varieties. The highly carbonaceous iron-
ore clays of the Arundel formation have also been used considerably
to the south and southwest of the city. The clays of both of these
formations have been employed for various purposes, but are capable
of much larger use than that to which they have already been put.

The manufacture of fire-brick has been one of the characteristic
industries of Maryland for 50 years, and the brick made from the
fire-clays of the Pottsville formation in Allegany county are regarded
as the best in this country. The oldest fire-brick concern in Allegany
county, that at Mount Savage, was organized in 1841 and was the
first of its kind in the United States. The main fire-clay deposit lies