importation of cheap potash
from Germany, with probable further offerings from Alsace and Spain,
makes it impossible for the United States potash production to continue;
except, perhaps, for the recovery of by-products which will go on in
connection with other industries. Demand for a protective tariff has
been the inevitable result (see Chapters XVII and XVIII).

GEOLOGIC FEATURES

Potassium is one of the eight most abundant elements in the earth. It
occurs as a primary constituent of most igneous rocks, some of which
carry percentages as high as those in commercial potash salts used for
fertilizers. It is present in some sediments and likewise occurs in many
schists and gneisses. Various potassium silicates--leucite, feldspar,
sericite, and glauconite--and the potassium sulphate, alunite, have
received attention and certain of them have been utilized to a small
extent, but none of them are normally able to compete on the market.
Potential supplies are thus practically unlimited in amount and
distribution. Deposits from which the potash can be extracted at a
reasonable cost, however, are known in only a few places, where they
have been formed as saline sediments.

In the decomposition of rocks the potash, like the soda, is readily
soluble, but in large part it is absorbed and held by clayey materials
and is not carried off. Potash is therefore more sparingly present in
river and ocean waters than is soda, and deposits of potash salts are
much rarer than those of rock salt and other sodium compounds. The large
deposits in the Permian beds of Stassfurt, as well as those in the
Tertiary of Alsace and Spain, have been formed by the evaporation of
very large quantities of salt water, presumably sea water. They consist
of potassium salts, principally the chloride, mixed and
intercrystallized with chlorides and sulphates of magnesium, sodium, and
calcium. In the Stassfurt deposits the potassium-magnesium salts occupy
a relatively thin horizon at the top of about 500 feet of rock salt
beds, the whole underlying an area about 200 miles long and 140 miles
wide. The principal minerals in the potash horizon are carnallite
(hydrous potassium-magnesium chloride), kieserite (hydrous magnesium
sulphate), sylvite (potassium chloride), kainite (a hydrous double salt
of potassium chloride and magnesium sulphate), and common salt (sodium
chloride). The potash beds represent the last stage in the evaporation
of the waters of a great c