in Philadelphia have
no distinguishing mark; but coins minted in San Francisco are marked
with a tiny "S"; if minted in New Orleans, with an "O"; and if in
Denver, with a "D."

VII

IRON, THE EVERYDAY METAL

Did you ever realize that your food and clothes, your books, and the
house in which you live all depend upon iron? Vegetables, grains, and
fruits are cultivated with iron tools; fish are caught with iron
hooks, and many iron articles are used in the care and sale of meat.
Clothes are woven on iron looms, sewed with iron needles, and fastened
together with buttons containing iron. Books are printed and bound by
iron machines, and sometimes written with iron pens or on iron
typewriters. Houses are put together with nails; and indeed, there is
hardly an article in use that could be made as well or as easily if
iron was not plenty. If you were making a world and wanted to give the
people the most useful metal possible, the gift would have to be iron;
and the wisest thing you could do would be to put it everywhere, but
in such forms that the people would have to use their brains to make
it of service.

This is just the way with the iron in our world. Wherever you see a
bank of red sand or red clay or a little brook which leaves a red mark
on the ground as it flows, there is iron. Iron is in most soils, in
red bricks, in garnets, in ripening apples, and even in your own
blood. It forms one twentieth part of the crust of the earth. Iron
dissolves in water if you give it time enough. If you leave a steel
tool out of doors on a wet night, it will rust; that is, some of the
iron will unite with the oxygen of the water. This is rather
inconvenient, and yet in another way this dissolving is a great
benefit. Through the millions of years that are past, the oxygen of
the rain has dissolved the iron in the hills and has worked it down,
so that now it is in great beds of ore or in rich "pockets" that are
often of generous size. One of them, which is now being mined in
Minnesota, is more than two miles long, half a mile wide, and of great
thickness. The rains are still at work washing down iron from the
hills. They carry the tiny particles along as easily as possible until
they come upon limestone. Then, almost as if it was frightened, the
brook drops its iron and runs away as fast as it can. Sometimes it
flows into a pond or bog in which are certain minute plants or animals
that act as limestone does, and the particle