On many parts of the coast of England, what are commonly known as
"submarine forests" are to be seen at low water. They consist, for the
most part, of short stools of oak, beech, and fir trees, still fixed
by their long roots in the bed of blue clay in which they originally
grew. If one of these submarine forest beds should be gradually
depressed and covered up by new deposits, it would present just the
same characters as an under-clay of the coal, if the _Sigillaria_ and
_Lepidodendron_ of the ancient world were substituted for the oak, or
the beech, of our own times.

In a tropical forest, at the present day, the trunks of fallen trees,
and the stools of such trees as may have been broken by the violence
of storms, remain entire for but a short time. Contrary to what might
be expected, the dense wood of the tree decays, and suffers from the
ravages of insects, more swiftly than the bark. And the traveller,
setting his foot on a prostrate trunk, finds that it is a mere shell,
which breaks under his weight, and lands his foot amidst the insects,
or the reptiles, which have sought food or refuge within.

The trees of the coal forests present parallel conditions. When the
fallen trunks which have entered into the composition of the bed of
coal are identifiable, they are mere double shells of bark, flattened
together in consequence of the destruction of the woody core; and Sir
Charles Lyell and Principal Dawson discovered, in the hollow stools
of coal trees of Nova Scotia, the remains of snails, millipedes,
and salamander-like creatures, embedded in a deposit of a different
character from that which surrounded the exterior of the trees. Thus,
in endeavouring to comprehend the formation of a seam of coal, we must
try to picture to ourselves a thick forest, formed for the most part
of trees like gigantic club-mosses, mares-tails, and tree ferns, with