MARYLAND GEOLOGICAL SURVEY 217

The flint is widely distributed throughout the rocks of the holo-
crystalline portion of the Piedmont Plateau and is especially abundant
in Cecil, Harford, Baltimore, Carroll and Montgomery counties. It
occurs as vein fillings in the form of pure granulated or vitreous
quartz. In Harford county, where the conditions are most favorable,
this quartz has been quarried in large amounts. It is finely ground
and bolted and then shipped in sacks to the potters. It is employed
largely in Baltimore, but has also been shipped extensively outside the
state. Flint has many uses, being employed in the manufacture of
crockery-ware, wall and sandpaper, soap, tiles and paints.

The best feldspar and kaolin produced in the United States is
obtained within a radius of 15 miles from the common corner of
Maryland, Delaware and Pennsylvania. It has been worked exten-
sively in all three of these states and shipped to potteries throughout
the country.

The total value of these materials produced in Maryland during
1896 was $25, 657.

THE MARLS.

The Eocene and Miocene formations of eastern and southern Mary-
land are rich in marl deposits, which have never been developed except
for local uses. Their importance to the agricultural communities
where they occur has not been up to the present time very generally
recognized, although they have been worked to some extent since the
early portion of the century.

The Eocene marls are glauconitic and are not unlike the famous
greensand marls of New Jersey, which have been so extensively em-
ployed as fertilizers throughout the eastern and southern portions of
that state. The Eocene marls of Maryland are found in Kent, Anne
Arundel, Prince George's and Charles counties and increase in thick-
ness southward. The greensand marls contain commonly a small per-
centage of phosphoric acid and some potash, while in some areas they
are also highly calcareous. When properly used they prove of much
value for certain crops. They are spread over the surface of the
land, or are applied in the form of a compost with barnyard manure.

The Miocene marls are mainly shell accumulations and are never