eably for the same
purposes.

The principal uses of sand in order of commercial totals are for
building purposes--for mortar, concrete, sand-lime brick, etc.,--as
molding sand in foundries, as a constituent of glass, in grinding and
polishing, in paving, as engine sand, as fire or furnace sand, in the
manufacture of ferrosilicon (a steel alloy), and in filters. Reference
is made to sand as an abrasive and in the manufacture of steel in
Chapters XIII and IX. Almost every state produces some sand, but for
some of the more specialized uses, such as glass sand, molding sand, and
fire or furnace sand, the distribution is more or less limited. The
United States Geological Survey has collected information concerning the
distribution of various kinds of sand and gravel, and serves a very
useful function in furnishing data as to supplies of material for
particular purposes. Fine molding sands have been imported from France,
but during the war domestic sources in New York and Ohio were developed
sufficiently to meet any requirements.

The sandstone of commerce includes the quartzites of Minnesota, South
Dakota, and Wisconsin, and the fine-grained sandstones of New York,
Pennsylvania, and elsewhere, known to the trade as "bluestone." In
Kentucky most of the sandstone quarried is known locally as "freestone."
The principal uses of sandstone are for building stone, crushed stone,
and ganister (for silica brick and furnace-linings). Other uses are for
paving blocks, curbing, flagging, riprap, rubble, grindstones,
whetstones, and pulpstones (see also Chapter XIII). Sandstone is
sometimes crushed into sand and is used in the manufacture of glass and
as molding-sand. Most of the states of the union produce sandstone, the
principal producers being Pennsylvania, Ohio, and New York.

"SAND AND GRAVEL"

Where sand is coarse and impure and mixed with pebbles, it is Ordinarily
referred to as "sand and gravel." For sand and gravel the principal
uses are for railroad ballast, for road building, and for concrete. Sand
and gravel are produced in almost every state in the union, the largest
producers being Pennsylvania, Ohio, Illinois, New Jersey, and North
Carolina.

CLAY, SHALE, SLATE

Shale is consolidated clay, usually with a fine lamination due to
bedding. Slate is a more dense and crystalline rock, produced usually by
the anamorphism of clay or shale under pressure, and characterized by a
fine cleavage which is usually inclined t