racter of the vegetation showed a
general unity of structure everywhere; but it was nevertheless broken up
into distinct botanical provinces by specific differences of the same
kind as those which now give such diversity of appearance to the
vegetation of the Temperate Zone in Europe as compared with that of
America, or to the forests of South America as compared with those of
Africa.

There can be no doubt as to the true nature of the Carboniferous
forests; for the structural character of the trees is as strongly marked
in their fossil remains as in any living plants of the same character.
We distinguish the Ferns not only by the peculiar form of their leaves,
often perfectly preserved, but also by the fructification on the lower
surface of the leaves, and by the distinct marks made on the stem at
their point of juncture with it. The leaf of the Fern, when falling,
leaves a scar on the stem varying in shape and size according to the
kind of Fern, so that the botanist readily distinguishes any particular
species of Fern by this means,--a birth-mark, as it were, by which he
detects the parentage of the individual. Another indication, equally
significant, is found in the tubular structure of the wood in Ferns. On
a vertical section of any well-preserved Fern-trunk from the old forests
the little tubes may be seen very distinctly running up its length; or,
if it be cut through transversely, they may be traced by the little
pores like dots on the surface. Trees of this description are found in
the Carboniferous marshes, standing erect and perfectly preserved, with
trunks a foot and a half in diameter, rising to a height of many feet.
Plants so strongly bituminous as the Ferns, when they equalled in size
many of our present forest-trees, naturally made coal deposits of the
most combustible quality. It is true that we find the anthracite coal of
the same period with comparatively little bituminous matter; but this is
where the bitumen has been destroyed by the action of the internal heat
of the earth.

Next to the Ferns, the Club-Mosses (_Lycopodiacae_) seem to have
contributed most largely to the marsh-forests. They were characterized,
then, as now, by the small size of the leaves growing close against the
stem, so that the stem itself, though covered with leaves, looks
almost naked, like the stem of the Cactus. Beside these, there are the
tree-like Equiseta, in which we find the articulations on the trunk
corresponding ex