Thus coal may be said, speaking broadly, to be composed of two constituents:  firstly, mineral charcoal; and, secondly, coal proper.  The nature of the mineral charcoal has long since been determined.  Its structure shows it to consist of the remains of the stems and leaves of plants, reduced a little more than their carbon.  Again, some of the coal is made up of the crushed and flattened bark, or outer coat, of the stems of plants, the inner wood of which has completely decayed away.  But what I may term the “saccular matter” of the coal, which, either in its primary or in its degraded form constitutes by far the greater part of all the bituminous coals I have examined, is certainly not mineral charcoal; nor is its structure that of any stem or leaf.  Hence its real nature is at first by no means apparent, and has been the subject of much discussion.

The first person who threw any light upon the problem, as far as I have been able to discover, was the well-known geologist, Professor Morris.  It is now thirty-four years since he carefully described and figured the coin-shaped bodies, or larger sacs, as I have called them, in a note appended to the famous paper “On the Coalbrookdale Coal-Field,” published at that time, by the present President of the Geological Society, Mr. Prestwich.  With much sagacity, Professor Morris divined the real nature of these bodies, and boldly affirmed them to be the spore-cases of a plant allied to the living club-mosses.

But discovery sometimes makes a long halt; and it is only a few years since Mr. Carruthers determined the plant (or rather one of the plants) which produces these spore-cases, by finding the discoidal sacs still adherent to the leaves of the fossilized cone which produced them.  He gave the name of Flemingites gracilis to the plant of which the cones form a part.  The branches and stem of this plant are not yet certainly known, but there is no sort of doubt that it was closely allied to the Lepidodendron, the remains of which abound in the coal formation.  The Lepidodendra were shrubs and trees which put one more in mind of an Araucaria than of any other familiar plant; and the ends of the fruiting branches were terminated by cones, or catkins, somewhat like the bodies so named in a fir, or a willow.  These conical fruits, however, did not produce seeds; but the leaves of which they were composed bore upon their surfaces sacs full of spores or sporangia, such as those one sees on the under surface of a bracken leaf.  Now, it is these sporangia of the Lepidodendroid plant Flemingites which were identified by Mr. Carruthers with the free sporangia described by Professor Morris, which are the same as the large sacs of which I have spoken.  And, more than this, there is no doubt that the small sacs are the spores, which were originally contained in the sporangia.