[CG] "Journal of the Geological Society," vol. xv.
[CI] See also "Acadian Geology," 2d ed., pp. 138, 461, 493.
1. The mineral charcoal or 'mother coal' is obviously woody tissue and fibres of bark, the structure of the varieties of which, and the plants to which it probably belongs, I have discussed in the paper above mentioned.
2. The coarser layers of coal show under the microscope a confused mass of fragments of vegetable matter belonging to various descriptions of plants, and including, but not usually in large quantities, sporangites.
3. The more brilliant layers of the coal are seen, when separated by thin laminæ of clay, to have on their surfaces the markings of _Sigillariæ_ and other trees, of which they evidently represent flattened specimens, or rather the bark of such specimens. Under the microscope, when their structures are preserved, these layers show cortical tissues more abundantly than any others.
4. Some thin layers of coal consist mainly of flattened layers of leaves of _Cordaites_ or _Pychnophyllum_.
5. The _Stigmaria_ under-clays and the stumps of _Sigillaria_ in the coal-roofs equally testify to the accumulation of coal by the growth of successive forests, more especially of _Sigillariæ_. There is, on the other hand, no necessary connection of sporangite-beds with Stigmarian soils. Such beds are more likely to be accumulated in water, and consequently to constitute bituminous shales and cannels.
6. _Lepidodendron_ and its allies, to which the spore-cases in question appear to belong, are evidently much less important to coal accumulation than _Sigillaria_, which cannot be affirmed to have produced spore-cases similar to those in question, even though the observation of Goldenberg as to their fruit can be relied on; the accuracy of which, however, I am inclined to doubt.
On the whole, then, while giving due credit to those who have advocated the spore-theory of coal, for directing attention to this curious and no doubt important constituent of mineral fuel, and admitting that I may possibly have given too little attention to it, I must maintain that sporangite-beds are exceptional among coals, and that cortical and woody matters are the most abundant ingredients in all the ordinary kinds; and to this I cannot think that the coals of England constitute an exception.