e 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
here and there some that had more resemblance to our existing yews and
fir-trees. We must suppose that, as the seasons rolled by, the plants
grew and developed their spores and seeds; that they shed these in
enormous quantities, which accumulated on the ground beneath; and
that, every now and then, they added a dead frond or leaf; or, at
longer intervals, a rotten branch, or a dead trunk, to the mass.

A certain proportion of the spores and seeds no doubt fulfilled their
obvious function, and, carried by the wind to unoccupied regions,
extended the limits of the forest; many might be washed away by rain
into streams, and be lost; but a large portion must have remained, to
accumulate like beech-mast, or acorns, beneath the trees of a modern
forest.

But, in this case, it may be asked, why does not our English coal
consist of stems and leaves to a much greater extent than it does?
What is the reason of the predominance of the spores and spore-cases
in it?

A ready answer to this question is afforded by the study of a living
full-grown club-moss. Shake it upon a piece of paper, and it emits a
cloud of fine dust, which falls over the paper, and is the well-known
Lycopodium powder. Now this powder used to be, and I believe still
is, employed for two objects, which seem at first sight to have no
particular connection with one another. It is, or was, employed in
making lightning, and in making pills. The coats of the spores contain
so much resinous matter, that a pinch of Lycopodium powder, thrown
through the flame of a candle, burns with an instantaneous flash,
which has long done duty for lightning on the stage. And the same
character makes it a