24 feet in thickness
interbedded with metamorphosed sandstones.

In general, graphite is primarily concentrated both by igneous processes
in dikes, and by sedimentary processes in beds. In the latter case
anamorphism is necessary to recrystallize the carbon into the form of
graphite.

GYPSUM

ECONOMIC FEATURES

The principal use of gypsum is in structural materials. About two-thirds
of the gypsum produced in the United States is used in the manufacture
of various plasters--wall plaster, plaster of Paris, and Keene's cement
(for statuary and decorative purposes),--and about a fifth is used as a
retarder in Portland cement. Another important structural use is in the
manufacture of plaster boards, blocks, and tile for interior
construction. Gypsum is used as a fertilizer under the name of "land
plaster," and with the growing recognition of the lack of sulphur in
various soils an extension of its application is not unlikely. Minor
uses are in the polishing of plate glass, in the manufacture of dental
plaster, in white pigments, in steampipe coverings, and as a filler in
cotton goods.

The world's gypsum deposits are widely distributed. Of foreign
countries, France, Canada, and the United Kingdom are the principal
producers. Germany, Algeria, and India produce comparatively meager
amounts. The United States is the largest producer of gypsum in the
world. In spite of its large production, the United States normally
imports quantities equivalent to between one-fifteenth and one-tenth of
the domestic production, mainly in the crude form from Nova Scotia and
New Brunswick for consumption by the mills in the vicinity of New York.
This material is of a better grade than the eastern domestic supply,
and is cheaper than the western supply for eastern consumption. During
the war this importation was practically stopped because of governmental
requisition of the carrying barges for the coal-carrying trade, but with
the return of normal conditions it was resumed. There is no prospect of
importation of any considerable amount from any other sources. The
domestic supply is ample for all demands.

Production of gypsum in the United States comes from eighteen states.
Four-fifths of the total comes from New York, Iowa, Michigan, Ohio,
Texas, and Oklahoma. There are extensive deposits in some of the western
states, the known reserves in Wyoming alone being sufficient for the
entire world demands for many decades.

The United St