Roots and Stumps _in situ_.]

If you examine carefully a piece of coal, you will find, more or less
clearly, markings like those which are seen in a piece of wood.
Sometimes they are very distinct indeed. Coal abounds in impressions
of leaves, ferns, and stems, and fossil remains of plants and
tree-trunks are found in numbers in coal-seams.

Coal is a vegetable substance. The wide coal-fields of Britain and
other lands are the _fossil_ remains of vast forests.

Long ages ago, as it seems, broad and luxuriant forests flourished
over the earth. In many parts generation after generation of trees
lived and died and decayed, leaving no trace of their existence,
beyond a little layer of black mould, soon to be carried away by wind
and water. Coal could only be formed where there were bogs and
quagmires.

But in bogs and quagmires, and in shallow lakes of low-lying lands,
there were great gatherings of slowly-decaying vegetable remains,
trees, plants, and ferns all mingling together. Then after a while the
low lands would sink and the ocean pouring in would cover them with
layers of protecting sand or mud; and sometimes the land would rise
again, and fresh forests would spring into life, only to be in their
turn overwhelmed anew, and covered by fresh sandy or earthy deposits.

These buried forests lay through the ages following, slowly hardening
into the black and shining coal, so useful now to man.

The coal is found thus in thin or thick seams, with other rock-layers