no doubt that the small sacs are the spores, which were originally
contained in the sporangia.

The living club-mosses are, for the most part, insignificant and
creeping herbs, which, superficially, very closely resemble true
mosses, and none of them reach more than two or three feet in height.
But, in their essential structure, they very closely resemble the
earliest Lepidodendroid trees of the coal: their stems and leaves are
similar; so are their cones; and no less like are the sporangia and
spores; while even in their size, the spores of the _Lepidodendron_
and those of the existing _Lycopodium_, or club-moss, very closely
approach one another.

Thus, the singular conclusion is forced upon us, that the greater and
the smaller sacs of the "Better-Bed" and other coals, in which the
primitive structure is well preserved, are simply the sporangia and
spores of certain plants, many of which were closely allied to the
existing club-mosses. And if, as I believe, it can be demonstrated
that ordinary coal is nothing but "saccular" coal which has undergone
a certain amount of that alteration which, if continued, would convert
it into anthracite; then, the conclusion is obvious, that the great
mass of the coal we burn is the result of the accumulation of the
spores and spore-cases of plants, other parts of which have furnished
the carbonized stems and the mineral charcoal, or have left their
impressions on the surfaces of the layer.

Of the multitudinous speculations which, at various times, have been
entertained respecting the origin and mode of formation of coal,
several appear to be negatived, and put out of court, by the
structural facts the significance of which I have endeavoured to