t-like the surrounding country, men will
go to it if minerals of value are discovered; and there they will
perhaps spend the whole of their lives, mining these substances
which are of such importance to the industries of the world.

COAL AND PETROLEUM

People are beginning to ask where fuel will be obtained when the
coal-beds are exhausted and the petroleum is all pumped out of the
earth. The cold winters will not cease to come regularly, and we
shall continue to need fires for many purposes. This is a question
which need not trouble us. So long as the sun lasts in the sky
and the oceans cover so much of the earth, and so long as there
are mountains upon the land, there must be streams with rapids
and waterfalls. The power of these streams, which has for ages
gone to waste, is now being turned into electricity for purposes
of light and heat. We may be sure that long before the mines cease
to produce coal and the wells to supply petroleum, there will be
something better ready to take their places.

But coal and petroleum are still such important commodities that
everyone should know something about the way in which they were
made. This earth of ours has had a very long history, much of which
has been recorded in the rocks beneath our feet, and the record
is more accurate than are many human histories which have been
preserved in the printed books.

The story of the earth has been divided into different periods,
each marked by the predominance of certain kinds of living things.
The Carboniferous period has been so named because at that time
the climate and features of the earth in many places favored the
growth of dense and heavy vegetation. This vegetation accumulated
through the long years, so that it formed thick deposits which
gradually changed to beds of coal. It would be wrong, however, to
think that all the beds of coal were formed at about the same time.
Ever since there have been forests and marshes upon the earth there
have been opportunities for the forming of coal-beds. Materials
are accumulating even now which will in time be transformed to
beds of coal.

We must be equally careful to gain correct ideas of the making
of petroleum, for many wrong notions are current. While coal has
come from the accumulation of plant remains, petroleum has been
derived from sea organisms, chiefly animals. If coal and petroleum
are found near each other, the occurrence is accidental and does
not mean that the two