179

0.—3

have tended to their destruction; but the rain-waters swept these debris into the marshes preceding the basins of deposit; and before they arrived in these they underwent, under the water, a maceration, which gave rise to the formation of ulmic products and of a vegetable pulp containing in suspension barks fragments of leaves and other vegetable debris, which are still discernible, because they have undergone a less material alteration. The preceding statement corresponds specially to the ideas expressed by M. 0. Grand-Eury in his publication of 1882. In those of 1887 and 1890 he only introduced a slight modification, by supposing the coal to be deposited at the bottom of great marshy lakes, without having recourse to the intermediary of special marshes between the coal-forests marshes themselves and the basins of deposits. We shall say no more concerning the formation of the coal-seams, properly so called, in this theory ; but it is proper, before speaking of the origin of the surrounding rocks, to remark that the presence of stumps and of upright trunks rooted in these strata at different levels betokens that the tout ensemble could not continue to grow in height except on a mobile ground subject to depressions. Let us add that, according to M. C. Grand-Eury, these depressions, to which the sinking of the coal in process of formation only contributed in a very slight measure, would be due to the flexibility of the earth on which the coal was deposited. This ground would give way without fracture, on the supposition that the terrestrial crust was not yet hardened, following more the central axis of the basin, which, moreover, was laterally displaced, except towards the periphery; at the same time it seems to M. C. Grand-Eury that this central depression would receive a counterpoise in the raising of the edges. Although a great admirer of M. Grand-Eury, and partisan for the most part of his ideas, yet his view which attributes so great a plasticity to the substratum of the coal-formation cannot be shared. The coal-basins are usually divided very improperly into lacustrine basins and marine basins, according as they are either of slight importance in surface and circumscribed or of great extent. When beds of marine limestone are met with in the wall or roof of a seam of coal, as in Pennsylvania, for example, the name of marine coal-basin cannot be objected to, although marine formations are far from forming the whole of it; but in certain basins, commonly called marine, as well as in the lacustrine basins, there are surrounding rocks which have, like the coal-seams, an essentially Continental origin, and for which the name of marine basin ought to be repudiated. In these two last instances, M. Grand-Eury attributes the formation of these rocks to the denudation of terrestrial portions more elevated than the Carboniferous forests, perhaps also without being precise to their being ravined during the periods when the abundant waters carried into the coal-lake rocky detritus, containing only a small quantity of vegetable debris. There would then be alternations in the nature of the materials transported into the basins of deposit. Sometimes these would consist principally of vegetable debris carried along by streams of sufficient force to displace the dams of vegetable matters accumulated on the ground of the coalforests, but incapable of making ravines in it; sometimes the supply of muddy waters, charged with mud, sand, or gravel would give rise to schist, psamite, sandstone, and pudding-stone. M. A. de Lapparent, in 1892, opposed to this conception criticisms which seem very exaggerated, for on the one hand the thin argillaceous layers which are met with in the laminae of coal and the schistous intercalations which exist in the seams, and on the other hand the fossil vegetables and the coaly matters which are found in the stampes, show that the materials transported by the waters in the two cases are not so very different as that, by means of certain variations in the orographical conditions of their place of origin, this place of origin might not have been the same. Theory of M. H. Fayol. M. A. de Lapparent, whose authority is certainly very great, is one of the foremost and warmest admirers of M. H. Fayol's theory, which will now be described. This theory also supposes the ideas of M. Grand-Eury with respect to the previous disaggregation of the vegetables which formed coal, and it will be useless to further mention them. The fact has already been mentioned that in 1881 M. H. Fayol advanced the theory that all the materials constituting the Commentry formation were carried by waters and deposited in a deep lake. At that time this distinguished engineer, who is now Director-General of the Societe de Commentry-Four-Chambault, had charge of the coal-mines of Commentry; and for more than twenty years he has been occupied with investigating and working the coal of this basin. The great open workings made at the outcrop of these coal-seams afforded him an admirable field of observation, and, at the same time, facilitated the discovery of fossils. When, in 1866, he decided to publish the result of his studies on the Commentry coal-basin, and his theory of the method of the formation of coal in general, he had gathered together a very important collection of fossils, &c. The stud}' of these, intrusted to scientific specialists, added to the stratigraphical and lithological labours of M. Fayol, allowed of the publication, from 1886 to 1890, in the " Bulletin de la Societe de l'lndustrie Minerale de Saint-Etienne," of a series of very important works, presenting a complete monograph of the Commentry coal-basin from the threefold point of view of stratigraphy, lithology, and palaeontology. The profound study of the Commentry basin led this engineer to look upon it as the result of the progressive filling-up of a lake of elongated form, measuring 559 miles in length by 1-86 miles in breadth, and having a maximum depth of 2,619 ft. At the first the waters of this lake, surrounded by escarped mountains, covered all the surface now occupied by the coal-formation. The rain-waters, gradually wearing away the ground, hollowed out valleys in the slopes which surrounded the lake, and carried into it pebbles, sand, mud, and vegetation. These sediments were heaped up at the mouth of the watercourses under the form of deltas, of which one on the north shore of the lake, and a second on the east, were largely developed, whilst two others of less importance started from the west shore. The