214 PHYSIOGRAPHY, GEOLOGY AND MINERAL RESOURCES
THE LIME AND CEMENT PRODUCTS.

The limestone and marble deposits of Maryland have been exten-
sively burned for building and agricultural purposes. In the earlier
days the burning of lime was carried on largely over the state, but in
later times, since transportation facilities have become so good, the
old quarries and kilns scattered so widely over the country have been
for the most part abandoned. There are still several large industries
in the marble belt of the Piedmont area and in the semi-crystalline
portion of the Frederick valley, and there are also many small local
kilns for supplying lime for agricultural purposes, especially in the
Frederick valley. Many of the largest companies now located in
Maryland are deriving their supply from more favorably situated
deposits outside the state.

The limestone and marble are also used as flux for blast furnaces.
The coarse-grained marbles of Texas have furnished a large amount
for this purpose, and also the limestone quarries at Cavetown on the
Western Maryland Railroad. Hydraulic cement has been extensively
manufactured from the limestone of the Lewistown (Niagara—L.
Helderberg) formation of Silurian age at Cumberland and Hancock,
as well as from the older Shenandoah limestone of the Hagerstown
valley near Sharpsburg. The products from these industries have an
excellent reputation and have been largely employed both within and
without the state.

Another use to which the limestone of the state has been applied
in recent years has been in the manufacture of asphalt blocks for
street paving. These blocks are constructed of crushed and pulver-
ized limestone, Trinidad asphalt and a residuum of petroleum heated
separately and thoroughly mixed and then combined under heavy
pressure. These blocks have been used extensively in Washington
and Baltimore in recent years.

The total value of the lime and cement products of Maryland in
1896 was $472, 392.

THE CLAYS.

The clays of Maryland suitable for economic purposes are widely
extended, occurring in a great number of different formations. They