The United States produces almost its entire consumption of salt, which
is increasing at a very rapid rate. Salt is produced in fourteen states,
but over 85 per cent of the total output comes from Michigan, New York,
Ohio, and Kansas. Reserves are practically inexhaustible.

Exports and imports of salt form a very minor part of the United States
industry, each being equivalent to less than 5 per cent of the domestic
production. A large part of the imported material is coarse
solar-evaporated sea salt, which is believed by fish and pork packers to
be almost essential to their industry. Imports of this salt come from
Spain, Italy, Portugal, and the British and Dutch West Indies; during
the war, on account of ship shortage, they were confined chiefly to the
West Indies. A considerable tonnage of specially prepared kiln-dried
salt, desired by butter-makers, is imported from Liverpool, England.
There are also some small imports from Canada, probably because of
geographic location. Exports of domestic salt go chiefly to Canada,
Cuba, and New Zealand, with smaller amounts to practically all parts of
the world.

Salt is recovered from salt beds in two ways. About a fourth of the
salt produced in the United States is mined through shafts in the same
manner as coal, the lumps of salt being broken and sized just as coal is
prepared for the market. The larger part of the United States
production, however, is derived by pumping water down to the beds to
dissolve the salt, and pumping the resulting brine to the surface where
it is then evaporated. A considerable amount of salt, also, is recovered
from natural brines--which represent the solution of rock salt by
ground-waters--and from the waters of salt lakes and the ocean.

GEOLOGIC FEATURES

Common salt constitutes the mineral halite, the composition of which is
sodium chloride. It is rarely found perfectly pure in nature, but is
commonly mixed with other saline materials, such as gypsum and
anhydrite, and occasionally with salts of potassium and magnesium. The
general grade of rock-salt deposits, where not admixed with clay, is
perhaps 96 to 99 per cent of sodium chloride.

The ultimate source of salt deposits is the sodium and chlorine of
igneous rocks. In the weathering of these rocks the soda, being one of
the more soluble materials, is leached out and carried off by
ground-waters, and in the end a large part of it reaches the sea. The
chlorine follows a similar course