A thin section of a piece of Commentry cannel coal shows that this substance consists of a yellowish-brown amorphous mass holding here and there in suspension very different plant organs, such as fragments of Cordaites, leaves, ferns, microspores, macrospores, pollen grains, rootlets, etc., exactly as would have done a gelatinous mass that upon coagulating in a liquid had carried along with it all the solid bodies that had accidentally fallen into it and that were in suspension.
It is evident (as we have demonstrated) that other cannel coals may show different plant organs, or even contain none at all, their presence appearing to be accidental. The composition itself of cannel coal must be, in our theory, connected with the chemical nature of the materials from whence it is derived, and that were first dissolved and then became insoluble through carbonization. Several preparations made from Australian (New South Wales), Autun, etc., boghead have shown us merely a yellowish-brown amorphous mass holding in suspension lens-shaped or radiating floccose masses which it is scarcely possible to refer to any known vegetable organism.
Among the theories that we have cited in the beginning, the one that best agrees with the facts that we have pointed out is the third, which would admit, then, two things in the formation of coal. The first would include the different chemical reactions which cannot yet be determined, but which would have brought the vegetable matter now to the state of soft coal (with its different varieties), and now to the state of anthracite. The second would comprehend the preservation, through burial, of the organic matter in the stage of carbonization that it had reached, and as the result of compression and gradual desiccation, the development of the physical properties that we now find in the different carbonized substances.
We annex to this article a number of figures made from preparations of various coals. These preparations were obtained by making the fragments sufficiently thin without the aid of any chemical reagent, so as to avoid the reproach that things were made to appear that the coal did not contain. This slow and delicate method is not capable of revealing all the organisms That the carbonaceous substance contains, but, per contra, one is riot absolutely sure of the pre-existence of everything that resembles organs or fragments of such that he distinguishes therein by means of the microscope.
Our researches, as we have above stated, have been confined to different cannel coals, anthracite, boghead, and coal plants isolated either in coal pebbles, or in schists and sandstones.
FIG. 1. - Lancashire cannel coal; longitudinal section, X200.
FIG. 2. - Lancashire cannel coal; transverse section, X200.
Figs. 1 and 2 (magnified two hundred times) represent two sections, made in rectangular planes, of fragments of Lancashire cannel coal. In a certain measure, they remind one of Figs. 4 and 5, Pl 11, of Witham's "Internal Structure of Fossil Vegetables," and which were drawn from specimens of cannel coal derived likewise from Lancashire, but which are not so highly magnified. There is an interesting fact to note in this coincidence, and that is that this structure, which is so difficult to explain in its details, is not accidental, but a consequence of the nature of the materials that served to produce the coal of this region. In the midst of a mass of blackish debris, a, organic and inorganic, and immersed in an amorphous and transparent gangue, we find a few recognizable fragments, such as thick-walled macrospores, b, of various sizes, bits of flattened petioles, c, pollen grains, d, debris of bark, etc. In Fig. 2 all these different remains are cut either obliquely or longitudinally, and are not very recognizable.
It is not rare to meet with a sort of vacuity, e, filled with clearer matter of resinoid aspect, without organization.
FIG. 3. - Commentry cannel coal, X200.
In Fig. 3, which represents a section made from Commentry cannel coal, the number of recognizable organs in the midst of the mass of debris is much larger. Thus, at a we see a macrospore, at b a fragment of the coat of a macrospore, at c another macrospore having a silicified nucleus, such as has been found in no other case, at d we have a transverse section of a vascular bundle, at e a longitudinal section of a rootlet traversed by another one, at f we have a transverse section of another rootlet, at g an almost entire portion of the vascular bundle of a root, and at h we see large pollen grains recalling those that we meet with in the silicified seeds from Saint Etienne.
Cannel coal, then, shows that it is formed of a sort of dark brown gangue of resinoid aspect (when a thin section of it is examined) holding in suspension indeterminable black organic and inorganic debris, which are arranged in layers, and in the midst of which (according to the locality and the fragment studied) is found a varying number of easily recognized vegetable organs.
FIG. 4. - Pennsylvania anthracite, X200.
It is very rare that anthracite offers any discernible trace of organization. Preparations made from fragments of Sable and Lamore coal could not be made sufficiently thin to be transparent; the mass remained very opaque, and the clearest parts exhibited merely amorphous, irregular granulations. Still, fragments of anthracite from Pennsylvania furnished, amid a dominant mass of dark, yellow-brown, structureless substance, a few organized vegetable debris, such as a fragment of a vascular bundle with radiating elements (Fig. 4, a), a macrospore, b, and a few pollen grains or microspores, c.