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.
FIG. 5.—Boghead from New South Wales, X500.
From what precedes it seems to result, then, that anthracite is in a much less appreciable state of preservation than cannel coal, and that it is only rarely, and according to locality, that we can discover vegetable organs in it. Soft coal comes nearer to amorphous carbon. Boghead appears to be of an entirely different character (Fig. 5, magnified X300). It is easily reduced to a thin transparent plate, and shows itself to be formed of a multitude of very small lenses, differing in size and shape, and much more transparent than the bands that separate them. In the interior of these lenses we distinguish very fine lines radiating from the center and afterward branching several times. The ramifications are lost in the periphery amid fine granulations that resemble spores. We might say that we here had to do with numerous mycelia moulded in a slightly colored resin. Preparations made from New South Wales and Autun boghead presented the same aspect.
If boghead was derived from the carbonization of parts that were soluble, or that became so through maceration, and were made insoluble at a given moment by carbonization, we can understand the very peculiar aspect that this combustible presents when it is seen under the microscope.
The following figures were made in order to show the details of anatomical structure that are still visible in coal, and to permit of estimating the shrinkage that the organic substance has undergone in becoming converted into coal.