d, and it is
on a few regions that we must depend for all the future.

Before we can calculate how much iron we have we must understand that
it is not found in pure form, but mixed with various other substances:
clay, shale, slate, quartz, sulphur, phosphorus, etc. These must all be
removed, some by washing, but most of them by roasting, or "smelting,"
in blast furnaces, after which it is called pig iron. This of course
requires large quantities of fuel.

It is these things and also the position of the ore that must be taken
into consideration in estimating the amount of iron in the country. If
ore yields a large per cent. of iron in smelting, with a small amount of
waste, it is, of course, far more valuable than if the amount of iron in
every ton of material taken from the ground is small.

In all minerals, the relation of supply to price is marked. The cost of
labor and of power is exactly the same whether ore yields fifty-five
tons of pure iron to the hundred, or whether it yields only thirty tons,
but the price received is little more than half.

So if the price is low, it may cost more to mine and smelt the one
hundred tons of earth than will be paid for the thirty tons of iron that
the low-grade ore would yield. So the lands that produce only thirty
tons to the hundred will never be mined till the price of iron is so
high that it is above the cost of producing--that is, till it can be
worked at a profit.

The Lake Superior iron found in Minnesota is usually more than
fifty-five per cent. pure iron. That is, if a hundred tons of earth be
mined, more than fifty-five tons of pure iron would be obtained from it.
This is the highest grade of ore. Some ore is mined that yields only
forty tons or less. There are vast quantities, billions of tons, of iron
ore in the United States, that would yield less than thirty tons of iron
to the hundred. These low-grade ores and the ones known to lie so deep
in the earth that the cost of mining them is more than the finished
products of iron, are classed as "not available," that is, they can
never be profitably mined under present conditions. But we must remember
that as the higher grade ores are exhausted it will become necessary to
use the lower grades, and that prices will steadily advance as a result.

Iron is sometimes found almost directly under the ground, at other times
deep in the earth. That which is found just below the surface is, of
course, mined much more easily,