called "iron ores" which have a sufficiently
high percentage of iron to be adapted to present processes for the
extraction of iron. When economic conditions demand it, it may be
assumed that iron-bearing rocks not now ordinarily regarded as ores may
be used to commercial advantage, and therefore will become ores.

Not only is an indefinitely long life assured for iron ore reserves as a
whole, but the same is true of many of the principal groups of deposits.

The question of practical concern to us, therefore, is not one of total
iron ore reserves, but one of degrees of _availability_ of different
ores to the markets which focus our requirements for iron.

The annual production of ore from a given district is roughly a measure
of that ore's ability to meet the competitive market, and therefore, of
its actual immediate or past availability. Annual production is the net
result of the interaction of all of the factors bearing on availability.
It may be argued that there are ores known and not yet mined which are
also immediately available. On the whole, they seem to be less available
than ores actually being produced; otherwise general economic pressure
would require their use and actual production.

In considering the future availability of iron ores, it is obvious that
tables of past production afford only a partial basis for prediction.
Presumably districts which have produced largely in the past may be
expected to continue as important factors. In these cases production has
demonstrated availability. Continued heavy production may thus be
expected from the ores of the Lake Superior region, from the Clinton
hematites of Alabama, from the ores of the Lorraine-Luxemburg-Briey
district, from the Cleveland ores of England, from the Bilbao ores of
Spain, from the high-grade magnetites of northern Sweden, and (assuming
political stability) from the ores of southern Russia.

Similarly, also, recent increases in production from certain districts
are probably significant of increased use of such ores in the future.
Among these developments are the increasing production of Swedish ores
and their importation into England and Germany, and the increasing use
of Clinton hematites and Adirondack magnetites in the United States.
Low-grade ores from the great reserves of Cuba are being mined and
brought to the east coast of the United States in increasing amounts,
and it is highly probable that they will take a larger share of the
ma