en it.

Peat is dug from bogs or marshes. We might say that a peat marsh is the
beginning of a coal bed. Peat is the partly decayed vegetation which has
slowly accumulated in wet places. In the colder countries it is formed
largely of moss and similar water-loving plants, but where the climate
is warm other kinds of marsh vegetation, and even trees, aid in forming
peat. Sometimes floods bring earth and deposit it in the marshes, in
which case the peat is less suitable for fuel, but forms a rich and
productive soil instead.

In many of the vast swamps of long ago, when there were no men nor even
the higher animals upon the earth, vegetation grew very rank. It is
believed that at that remote time the air contained more carbonic acid,
a substance which promotes the growth of plants. Thus the plants in the
warm, moist parts of the earth grew more densely and luxuriantly than
they usually do today.

In the decay of this vegetation deposits similar to the peat marshes
were formed, but they differed in being much thicker and more extensive.
If the story of these ancient peat marshes had stopped here, we should
never have had any coal. Fortunately it did not, for some of the swamps
sank beneath the water of a lake or ocean and thick beds of gravel,
sand, or clay were deposited over them. While buried deep in the earth,
the decaying vegetation was heated and pressed together by the great
weight of the earth above, and was finally changed to shining, black
coal.

After the coal was made, but before men came to the earth, parts of the
sea bottom with its buried treasures were raised to form hills and
mountains. Then the rainwater began its work upon the slopes, and after
a time washed away so much of the overlying material that the coal was
exposed at the surface. At last through some accident, such as lightning
perhaps, men learned that this black substance would burn. Coal was
little used, however, as long as there was an abundance of wood and the
needs of people were few.

As manufacturing and the use of the steam engine increased, coal grew in
value. The business of mining coal finally became one of the great
industries. The mining operations were carried on as carelessly as
though the supply in the interior of the earth were inexhaustible. In
the underground working it is customary to leave about one quarter of
the coal in the form of pillars for the purpose of supporting the roof.
At a little more expense other materia