C.—3

174

My other specimen comes from a seam of excellent quality exploited in our basin. It presents on one of its surfaces, parallel to the small strata of the fragment, a beautiful imprint of Sigillaria, which belongs to the coal itself, for the schistous layer, which has allowed of its preservation, is so thin as to be hardly apparent. Moreover, the variety of coal that Haiiy has nominated daloid coal, and that MM. G. Grand-Bury, appropriately to its aspect, designates under the name of " fusain" (spindle-tree) is abundant in certain coal-seams, and its vegetable origin cannot fail to be recognised. More than this is not necessary for the vegetable origin of coal to be admitted without reserve, and we can betake ourselves to the examination of the theories which take this origin as a point of departure. Half a century after the publication of A. de Tussieu, Baron Holbach, in the article " Charbon Mineral," of the " Encyclopedia "of Diderot; and Valmont de Bomare in 1769, in his " Dictionaire Raisonne universel d'histoire Naturel," explains the formation of mineral coal, in which he comprises lignites, by the burying in the ground of forests of resinous trees. In 1778 the great naturalist, Buffon, in his "Epogues de la Nature," attributes the formation of coal to terrestrial vegetables transported by waters. According to him it was due to the first vegetables that the earth bore. The greater part of the earth's surface at that time, with the exception of certain isles, bearing an extremely abundant vegetation of trees and plants, would be covered with water, still lue warm. It would be the debris of this luxuriant vegetation, which, brought to the sea by rivers, would there produce the deposits of vegetable matter, which would be transformed into coal. Buffon instanced, in support of his opinion, the trees brought down by the Amazon to its mouth, and the great vegetable floats of the Mississippi, although the existence of such important rivers was not compatible with the insular constitution of the surface of the globe which he supposes. It has been objected to this theory that from such floats of wood and trees, containing, as they would do, in their interstices much sand and ooze, there would result only a very impure combustible. It has also been said that their total height, reasoning from that of the immersed portion, and the depth of the watercourses in which they circulated, if we take into account the considerable reduction brought about by the transformation of these floats into coal, would require for the formation of thick coal-seams to be enormous. Nevertheless, this last objection has not all the force that has been given to it, because thick seams are in general formed of successive layers of coal, each of which would have been formed from one particular float, of no exaggerated height. A very much more serious objection results from the regularity of the seams of the great coalbasins, such as that, for example, which extends, almost without interruption, from Westphalia to South Wales, passing through Belgium and the north of Erance, a regularity which cannot be conceived on the hypothesis of Buffon. Strongly combated, the theory of transport, such as it had been conceived at first, was not able long to subsist, and it suffered in the minds of men a complete reversal. Whilst Blumenbach and Schlotheim, at the commencement of the century, Sternberg and Adolphe Brongniart in 1820, gave, a remarkable impetus to the science of the ancient origin of coal, the theory of transport was completely abandoned in favour of that which saw only in coal the product of vegetables decomposed in the place where they had grown. Adoiphe Brongniart in 1837, in his " Considerations on the Nature of the Vegetables which have covered the Surface of the Earth at Different Epochs in its Formation," attributed the origin of coal to masses of accumulated vegetables, afterwards altered and modified, as beds of turf in our marshes would be if they were covered over afresh and compressed by beds of mineral substances. Since then, and although at the session of the British Association for the Advancement of Science, held in Manchester in June, 1842, Williamson read a paper, tending to prove that coal was formed by the drifting of vegetable matter into the sea, and not by the accumulation of these vegetables on the ground that the coal-deposits covered, although in the same session De la Bechee supported this view, whilst it is true that Sedgewick, Phillips, and Bonney admittted it in certain exceptional cases and within certain limits, yet the theory of the formation of coal on place reigned with undivided sway for nearly forty years. It was only when M. C. G-rand-Eury affirmed, in 1877, that the coal of the Loire basin contained vegetable remains placed flatly, and when M. H. Eayol advanced, in 1881, that all the materials constituting the coal-formation of Commentary had been brought by waters and deposited in a deep lake during a tranquil geological period, that this theory became once again a subject for discussion. Formation of Goal on Place. The formation of coal on place—that is, the theory which refers its origin to successive growths of forests in the positions and over the areas now occupied by the seams of coal themselves—has still its partisans, and, before speaking of the remarkable works of MM. C. Grand-Eury and H. Fayol, as well as of an ingenious hypothesis developed in 1885 by M. L. Breton, it would be well to point out the modern form in which, in M. Alph. Briart's disquisition, delivered on the 17th June, 1889, at the public seance of the science section of the Eoyal Academy of Belgium, this theory appears. First, let us remark, that the mode of formation supposed by M. Briart is often designated under the name of " tourbage " —peat, turf—because certain writers have believed that the plant-life analgous to that which now forms peat, and in which mosses of the genus Sphagnum (bogmoss) predominates, have played a part in the formation of coal; and that, for the other part, the name peat is to-day constantly extended to those vegetable accumulations formed of semi-aquatic plants of trunks and other debris of trees, although such accumulations, proper to woody marshes and boggy forests, cannot be assimilated with turf properly so called. In addition, M. Briart declares with reason that the tourbage, taken in an absolute sense, cannot be admitted to be coal. He says, " The peat bogs of the coal period ought to have an appearance quite different from ours of the present day. It is no longer a question of our analgous plants being changed into turf in proportion to their growth, but of a vegetation almost entirely arbores--