C.—3,

178

the barks are the parts best preserved, owing to their greater density and powers of resistance, yet most frequently their beds are disjointed, and deposited at a distance one from another. The spores only have hardly kept their cases. The trunks, filled with pith, or really ligneous, like those of the Cordaites, experienced habitually an internal disorganization almost complete, which reduced them to a thin cortical envelope, converted in the last place to coal. The products of this internal disorganization of the stems have united to form coal in two different ways : the one, mingled with those of the disaggregation of other tissues, produced a pulp—a kind of thick vegetable soup —which formed amorphous coal; the other, especially owing to the ligneous tissues, which a powerful desiccation before their burial in the ground would have broken to pieces, and rendered unfit to undergo the transformation into coal of the vegetable debris, have furnished fusain (spindle-tree) or daloid coal, which is met with in seams, and which also contributed to their formation. From the facts shown up to this point, M. Grand-Eury concludes that coal is a sedimentary formation, the result of a slow and tranquil deposit by waters of barks, leaves, and teguments, with the ulmic semi-liquid products of vegetable decomposition, these last being accompanied with particles of vegetable debris. Now and then there are found large portions of trunks furnished with roots in an upright position—that is to say, perpendicular to the strata. More frequently there are rooted stumps of trees, whose stem has been broken off more or less near to the bottom, but whose roots and radicles have remained complete. These rooted stumps form a mass, which broadens towards the base, and are now and again superposed to the coal-seams in exploitation, from which they are only separated by thin schistous layers. They have received from the miner the characteristic name of cZocte-bells, Somersetshire bell-mouth, and their accidental fall is well known to occasion accidents. Although M. H. Eayol considers that all the vegetables and vegetable debris of the coal-formation have been transported, M. Grand-Bury is of opinion, and we think with reason, that the upright trunks with roots, and also the rooted stumps, usually have lived in the place where they are found. He gives a strong proof-of this in the description of a remarkable ligneous trunk, presenting large roots in several stages, which are explained by a progressive widening of the plant during its development. It is rare that an upright trunk traverses a coal-seam ; M. Grand-Eury, in his memoire of 1882, declares that he only knows of one or two examples of trunks of Calamodendron traversing a small schistous coal-seam. Evidently this is not favourable to the theory of formation on place. As to the Stigmaria which, independently of their abundance at the wall of certain coal-seams, have played an important part in the constitution of the coal of Upper Silesia, M. Grand-Eury considers them to be aquatic plants, and incapable of living in the air. Whilst they are an important element in the formation of coal itself, they could have lived floating in the sufficiently deep waters, simply tracing by their extremities the mud of the bottom ; and they would have undergone ulterior displacements, not being the only plants that contributed to the formation of the coal-seam. On the other hand, he supposes that in the spots where the water was shallower the Stigmaria were able to root themselves more deeply, and were able to complete their growth by sending out stems of Sigillaria. Notwithstanding the quality of the functions of these two still enigmatical plants, the Stigmaria of the wall, as well as the stumps and the roots of other vegetables which are met with, are in general cut clean by the coal-seam, and the interior of one and the other been filled with argillaceous mud before the deposit of vegetable matters which constituted the seam. It is possible, then, to suppose that these matters were deposited in a basin, the bottom of which had been completely levelled before their deposition, apart from a few extremely rare trunks, which, as constituting exceptions, were only broken at a little distance above the wall of the seam of combustible material which was afterwards deposited. After these preliminaries, I am able to give a sketch of the geogonic theory of M. C. GrandEury, In the coal period there existed vast basins of deposit filled with fresh water of no great depth—at least, in certain places and at certain times—so that the vegetation with aerial stems might root themselves at the bottom. This vegetation was, moreover, adapted to humid situations, and could flourish even with its stems soaked in water several metres in depth. M. Grand-Eury thinks even that Calamites would go through their whole process of development under water. We find to-day, in place, trunks or fragments of trunks of trees upright, and of rooted stumps. The Stigmaria of the walls are also in place. The other organs of these vegetables in situ, as also the floating Stigmaria of certain regions, have only famished an insignificant portion of the vegetable matter which has produced coal. This vegetable matter was produced especially from marshy forests situated beyond the areas of deposit. Under the influence of a high temperature, comparable to that of the torrid zone, and nearly constant, under the action of excessive humidity and intense light, although tempered by an atmosphere permeated by steam, the growth of the coal-plants was extremely rapid, as is shown by the loose texture of the great majority of trunks and stems, whose whole force of resistance resides in the bark. Many of these plants were propagated by rhizomes, which also would spread themselves with prodigious rapidity. But if the coal-plants grew with vigour, of which real nature scarcely offers an example, the decrepitude and death of the vegetable arrived rapidly also, and the circumstances which helped its growth favoured also its decomposition. The appendicular organs of the trunks and the trunks themselves fell on to the ground more or less covered with water. With the exception of the ligneous of certain vegetable species, partially transformed into fusain (spindletree), as it has been called, the interior of the stems broken up underwent a profound alteration, which the barks and certain leaves resisted up to a certain point. If the emerged parts of these debris were exposed for a long time to the action of warm and humid air a slow oxidation would