f heavier material than the surface layer; and geologists
believe that iron is an important element in the central mass of the
globe.

One thing that makes this guess seem reasonable is the great abundance
of iron in the earth's crust. Another thing is that meteors which fall
on the earth out of the sky prove to be chiefly composed of iron. All of
their other elements are ones which are found in our own rocks. If we
believe that the earth itself is a fragment of the sun, thrown off in a
heated condition and cooling as it flew through space, we may consider
it a giant meteor, made of the substances we find in the chance meteor
that strikes the earth.

Iron is found, not only in the soil, but in all plant and animal bodies
that take their food from the soil. The red colour in fruits and
flowers, and in the blood of the higher animals, is a form in which iron
is familiar to us. It does more, perhaps, to make the world beautiful
than any other mineral element known.

But long before these benefits were understood, iron was the backbone of
civilization. It is so to-day. Iron, transformed by a simple process
into steel, sustains the commercial supremacy of the great civilized
nations of the world. The railroad train, the steel-armoured battleship,
the great bridge, the towering sky-scraper, the keen-edged tool, the
delicate mechanism of watches and a thousand other scientific
instruments--all these things are possible to-day because iron was
discovered and has been put to use.

It was probably one of the cave men, poking about in his fire among the
rocks, who discovered a lump of molten metal which the heat had
separated from the rest of the rocks. He examined this "clinker" after
it cooled, and it interested him. It was a new discovery. It may have
been he, or possibly his descendants, who learned that this metal could
be pounded into other shapes, and freed by pounding from the pebbles
and other impurities that clung to it when it cooled. The relics of
iron-tipped spears and arrows show the skill and ingenuity of our early
ancestors in making use of iron as a means of killing their prey. The
earliest remains of this kind have probably been lost because the iron
rusted away.

Man was pretty well along on the road to civilization before he learned
where iron could be found in beds, and how it could be purified for his
use. We now know that certain very minute plants, which live in quiet
water, cause iron brought into th