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C.—3

At the Commentry Mine the water issuing from the coal-wash cries forms a current of about 11 cubic feet per second, and holds in suspension from 5 to 6 per cent, of solid matter—mixture of coal, schist, pyrites, &c. The coarsest and heaviest grains are deposited in a channel 163-Jft. in length, and the dirty water entering at one extremity of the basin issues almost clear from the other, after successfully depositing the coarse grains, and afterwards the finer sorts, in small beds of still less and less inclination. The longitudinal and transverse sections in the deposits, obtained by numerous experiments of the kind, where the dimensions and the nature of the slimes are varied, as well as the rapidity and point of admission of the water, have shown numerous analogies between the arrangement of these artificial deposits and the lie of the strata at Commentry, which in other respects presents little regularity. They have also shown how the settling of such deposits is susceptible of modifying the aspect of beds composed of very fine materials, in producing either small local faults slips or nips and swells. With respect to the great coal-formations styled marine, such as that which extends from Westphalia to South Wales and even to Ireland, passing through Belgium and the north of Prance, the theory of M. Fayol, as it is interpreted by M. de Lapparent, supposes that the sea extended the whole of this length, and bordered a continent of luxuriant vegetation situated towards the south, whose slopes were denuded by abundant streams. The alluvial deposits, mingled with vegetable debris, classified themselves as they fell into the waters of the sea, and, in consequence of the fluctuation of the waves, spread themselves much further in the marine delta than they would in a lacustrine delta, and for the same reason the deposits were much more regular. Even for Commentry M. Fayol's theory does not seem to give a sufficient explanation of the degree of separation—rather imperfect, however—which exists between the materials constituting the different strata. Lastly, it does not seem possible to suppose that all the vegetable debris of this basin was transported, and that not one of the upright trunks and rooted stumps that are there met with are in the same place where they lived. And now, having made you acquainted with the recent theories on the formation of coal, as well as having briefly glanced at the more ancient ones, with the exception of that which deals with the transformation into coal of vegetable matters, or, to use the expression adopted by M. Grand-Eury, their " coalification," I have finished my self-imposed task. I cannot do more than mention the researches of Mr. W. Spring on the amount of carbon and hydrogen contained in the roof and the wall of coal-seams, which were made with the view of seeing whether the theory of transport, or that of the formation of coal on place, is to be preferred, and which, in this respect does not appear to me sufficiently conclusive. In my exposition of the various theories I have not concealed my preference for that of M. Grand-Eury, despite its vagueness, especially in that part of it which deals with the formation of the strata which separate the coal-seams. I entertain the hope that the continuance of his untiring efforts, the scope of which he is more and more enlarging, will yet conduct him to a solution approaching as near as possible the truth. The statements of facts which we owe to M. Fayol are, in addition, important elements which must not be overlooked in obtaining a fair solution of the problem. The theory of formation on place—recently restored to a place of honour by M. Briart, who, in consequence of the discoveries of M. Grand-Eury and others, has so far modified his theory as to admit of light interior transports in the middle of the turf-coal—does not appear to me sufficient to explain the parallel disposition of the small layers which form the seams of coal, and especially the levelling of their wall. Neither can I admit that the greater part of the deposits forming the rocks which separate the great Franco-Belgian basin are in great part marine deposits. Certainly in the ampelite and the phtanites, superposed on the Carboniferous limestone of marine origin, we find marine fossils, the presence of which is not in the least surprising, and these are met with again at some height above the base of the coal-formation; but above this the marine fossils are either rare or disputable. The fossil-shells that are met with are chiefly Unio or Anthracosia, which are fresh-water molluscs ; and there are also numerous vegetable fossils of terrestrial origin. If the strata of the exploited coal-seams, so often traversed by cross-cuts, were in great measure of marine origin it would be altogether astonishing if numerous marine fossils had not been met with. I am also of opinion that, with the exception of the lower portion of the coal-formation, the strata which separate the seams, as well as the seams themselves, are of an essentially Continental origin, and are chiefly the result of the denudation of pluvial waters of the terrestrial surface, without denying, nevertheless, the possibility of certain rapid incursions of marine waters, bearing in their course rare fossils and marine deposits. This is also one of the reasons which—taken with the presence in place of stumps and rooted trunks, with the clear separation of the coal and encasing rocks, and the regularity of the coal-seams of the Franco-Belgian basin, which, in spite of trifling variations in their slight thickness, is truly extraordinary, if compared with that of other strata—does not permit me to admit the application of M. Fayol's theory of coal deltas to a basin so poor in marine fossils, because, according to this theory, it would be formed under the waters of the sea. With respect to the objection made by M. de Lapparent to the theory of formation on place—which, up to a certain point, also applies to the theory of M. Grand-Eury, and which consists in this : that the enormous depressions supposed, by the first of these theories, would have necessitated the disappearance of the greater part of Europe—l shall present a few considerations which, in my opinion, allow of its being eliminated. The Franco-Belgian basin stretches towards the south, either directly or at greater or less distance. This latter fact is accounted for by one of the most important geological irregularities, called in the Province of Liege-Faille* Eifelienne, where it is well known, at least at l'Ouest d'Angleur, Faille dv Mideif in Hainaut, and most happily called by M. Gosselet, the Grande Faille.

* Fr., Fault. t Fr., South,