ilding operations, in tanning leather, and in a great variety of
chemical industries. The total quantity of limestone used for all
purposes in the United States nearly equals that of iron ore. Nearly
every state in the union produces limestone, but the more important
producers are Pennsylvania (where a large amount is used for fluxing),
Ohio, Indiana, New York, Michigan, and Illinois.

Closely associated with limestone in commercial uses, as well as in
chemical composition, is calcareous marl, which is used extensively in
the manufacture of Portland cement.

Chalk is a soft amorphous substance of the same composition as
limestone. The main uses of chalk are as a filler in rubber, and as a
component of paint and putty. It is also used for polishing. The
principal producers of this commodity are England, Denmark, and France,
and the chief consumer is the United States. The United States depends
upon imports for its supply of chalk for the manufacture of whiting.
Before the war two-thirds came from England and a third from France.
During the war importation was confined to England, with a small tonnage
from Denmark. No deposits of domestic chalk have been exploited
commercially. A somewhat inferior whiting, but one capable of being
substituted for chalk in most cases, is manufactured from the waste fine
material of limestone and marble quarries.

MARBLE

Marble is limestone which has been coarsely recrystallized by
metamorphism. The marble of commerce includes a small quantity of
serpentine as quarried and sold in Massachusetts, California, Maryland,
Pennsylvania, and Vermont, and also a small amount of so-called onyx
marble or travertine obtained from caves and other deposits in Kentucky
and other states. The principal uses of marble are for building and
monumental stones. Of the twenty-two states producing marble, the
leaders are Vermont, Georgia, and Tennessee.

A small amount of marble of special beauty, adapted to ornamental
purposes, is imported from European countries, especially from Italy.
Marble imports from Italy constitute about two-thirds, both in tonnage
and value, of all stone imported into the United States.

SAND, SANDSTONE, QUARTZITE (AND QUARTZ)

Sand is composed mainly of particles of quartz or silica, though
sometimes feldspar and other minerals are present. Sandstones are
partially cemented sands. Quartzites are completely cemented sands. To
some extent these substances are used interchang