truded into
Paleozoic slates and sandstones, and tin ores occur in fissures and
stockworks in the marginal zones. With the exhaustion of the more easily
mined placers, the lode deposits will doubtless be of increasing
importance.

Cassiterite is practically insoluble and is very resistant to
decomposition by weathering. Oxide zones of tin deposits are therefore
enriched by removal of the more soluble minerals. Stannite probably
alters to "wood tin," a fibrous variety of cassiterite. Secondary
enrichment of tin deposits by redeposition of tin minerals is
negligible.

URANIUM AND RADIUM ORES

ECONOMIC FEATURES

Radium salts are used in various medical treatments--especially for
cancer, internal tumors, lupus, and birth marks--and in luminous paints.
During the latter part of the war it is estimated that over nine-tenths
of the radium produced was used in luminous paints for the dials of
watches and other instruments. In addition part of the material owned by
physicians was devoted to this purpose, and it is probable that the
accumulated stocks held by the medical profession were in this way
reduced by one-half. The greatly extended use of radium, together with
the distinctly limited character of the world's known radium supplies,
has led to some concern; and considerable investigation has been made of
the possibilities of mesothorium as a substitute for radium in luminous
paints. Low-grade radium residues are used to some extent as
fertilizers.

Uranium has been used as a steel alloy, but has not as yet gained wide
favor. Uranium salts have a limited use as yellow coloring agents in
pottery and glass. The principal use of uranium, however, is as a source
of radium, with which it is always associated.

European countries first developed the processes of reduction of radium
salts from their ores. Most of the European ores are obtained from
Austria, where the mines are owned and operated by the Austrian
government, and small quantities are mined in Cornwall, England, and in
Germany. Production is decreasing. The European hospitals and
municipalities have acquired nearly all of the production.

The United States has the largest reserves of radium ore in the world,
and the American market has in recent years been supplied from domestic
plants. Before the war, radium ores were shipped to Europe for treatment
in Germany, France, and England, and radium salts were imported from
these countries. There are now radiu