inconsistent with the suggestion of Mr. Lyell,* touching the climate of the period in question.

This view is, that the climate was then characterized by excessive moisture; by a mild and steady temperature, and the entire absence of frost; but perhaps not by intense heat. It is admitted, indeed, that our materials for the foundation of this theory are perhaps somewhat scanty; being, chiefly, the general character of luxuriance of the carboniferous vegetation; the great abundance of ferns: and the presence of large leaved monocotyledonus plants of a tropical or sub-tropical aspect for with regard to the sigillariæ, stigmariæ, asterophyllites, calamites, &c., their real affinities are, he thinks, too doubtful to allow us to found any arguments on them.

That extreme heat is not necessary to the existence of a very luxuriant and quasi-tropical vegetation, is sufficiently clear from Mr. Darwin's interesting observations on Chiloe and other islands of the southern temperate zone.† Chiloe, situated in the 42d degree of south latitude, enjoying little summer heat, and subject to perpetual rains and mists, is covered, as he states, with forests of extraordinary density, and the luxuriance of the vegetation is such, that it reminded him of Brazil. Large and elegant ferns; parasitical monocotyledonous plants, and arborescent grasses, reaching to the height of thirty or forty feet, are abundant. Indeed, in the southern hemisphere generally, owing to the equable climate produced by the great proportional extent of sea, tropical forms, both of vegetable and animal life, range much farther from the equator than in our hemisphere. It appears very probable that the climate of the northern temperate zone, during the epoch in which the coal measures were formed may have been similar to that now existing in Chiloe and the adjoining parts of South America.

Still, considering that the principal coal-fields of England are situated from 13° to 15° farther north than that of Frostburg, the close resemblance of their vegetation is very striking. The absolute identity of some species is not perhaps so remarkable as the very great general similarity of the whole; for those among the Frostburg plants, which cannot be satisfactorily identified with the British species, are, in every instance, very closely allied to them. We should not find so great a degree of resemblance on comparing the recent floras of two regions separated by so many degrees of latitude, whether in Europe or North America. If we may reason at all as to climate, from the fossil vegetation of a country, we must suppose that the climate varied less rapidly with the latitude that it does at present.

In concluding this valuable paper, the writer suggests, that the plants, of which we now find the remains embedded in the carboniferous strata, may probably be but a very small proportion of those which, at that time, flourished on the earth. If, as seems to be now most generally believed, the coal beds are derived from the vegetaTravels in North America, vol. i. p. 148.

† Darwin's Journal, 2d edit., p. 242.

tion of ancient swamps or lakes, existing in the very localities now occupied by such beds of coal, we could not expect to find in them the remains of other plants than such as grew in those bogs, or lakes, or swampy forests, or immediately around them; together perhaps with some which might be washed into them by occasional inundations. May there not have existed at the same time, in other parts. of the world, [nay, perhaps at no very great distance from the carboniferous regions,] great tracts of country, indeed whole continents, in which the local circumstances were unfavourable to the preservation of vegetable remains, and of which, consequently, the flora is wholly lost to us?

I think, therefore, that we ought to proceed with great caution in theorizing with respect to the vegetation and climate of the carboniferous era. I believe that the preponderance of ferns in the flora of the coal measures, together with the other characteristic of the fossil vegetation of that period, affords, to a certain degree, good evidence respecting the climate of those particular regions in which the coal measures occur; but we should not be justified in extending our inferences farther. Those parts of Europe and North America, in which the coal-fields were accumulated, may have existed, at that time, in the state of islands, like those of the present Pacific ocean: but it would be rash to infer, as M. A. Brongniart seems disposed to do, that no extensive continents at that time existed in any part of the globe. If in all departments of geology, it is necessary to advance with caution, and to avoid dogmatism and rash generalizations, it is more especially necessary in the department of fossil botany, where so much of the evidence we possess is fragmentary and imperfect.*

MISCELLANEOUS NOTES AS TO COAL AND FOSSIL VEGETATION.

In continuation of this subject, we proceed to advert to the results of some observations which have been made of late years by individual naturalists. Were we to incorporate in this work the facts, theories, and speculations which have been discussed at different times on the coal subject, we should occupy at least an entire volume. There are many excellent treatises embracing these topics, which the reader, if seeking more information, may consult to advantage. The few notes we add here are inserted with little regard to classifi

cation.

The discovery, in 1839, during the progress of excavating a part of the route of the Manchester and Bolton Railway, within the limits of the Lancashire coal-field, of numerous fossil trees of the family sigillaria, standing in a vertical position, with their roots embedded in a thin coal seam, gave rise at the time to much discussion. Mr. Hawkshaw described these trees in two communications to the Geological Society. These trunks were wholly enveloped by a coating

* Bunbury on Fossil Ferns. Quarterly Jour. Geol. Soc. No. 6, p. 82. † Proceedings Geol. Soc. Lon., Vol. III. p. 139; and 269, 1840.

of friable coal, varying from one-quarter to three-quarters of an inch in thickness. Their internal casts consisted of shale, traversed beneath the place of the bark by irregular longitudinal flutings, less than one-quarter of an inch broad and about two inches apart.

Mr. Bowman communicated a paper on the same subject. He is opposed to the drift theory in accounting for coal beds, because they would have been intermixed with more earthy matter than is now proved to be the case in coal; and because they could not have maintained that singular uniformity of thickness and character throughout so many square miles, and such extensive areas that we find prevails in the coal measures; as an instance of which the author cites the thin seam below the Gannister or Rabbit coal, which extends in a linear direction thirty-five miles. It is much more rational to suppose, that the coal has been formed from plants which grew on the areas now occupied by the seams; that each successive race of vegetation was gradually submerged beneath the level of the water, and was covered up with sediment, which accumulated till it formed another dry surface for the growth of another series of trees and plants, and that these submergences and accumulations took place as many times as there are seams of coal within the confines of each basin.

Mr. Bowman proceeds to the examination of the phenomena presented by the fossil trees discovered in the railroad excavations above referred to by Mr. Hawkshaw. He describes, generally, the markings on the internal casts of the trees. The only indications of scars which he could find, his practised eye recognized to be those of a sigillaria.

From a careful consideration of the phenomena presented by the fossils, the author is convinced that they stand where they originally flourished; that they were not succulent, but dicotyledonous, hardwooded, forest trees; and that their gigantic roots were manifestly adapted for taking firm hold of the soil; and, in conjunction with the swollen base of the trunks, to support a solid tree of large dimensions, with a spreading top.

With reference to fossil trees in general, and especially to those near Manchester, Mr. Bowman proceeds to show; 1st, that they were solid, hard-wooded, timber trees, in opposition to the common opinion that they were soft or hollow; 2d, that they originally grew and died where they have been found, and consequently were not drifted from distant lands; and 3d, that they became hollow by the decay of their wood from natural causes, similar to those still in operation in tropical countries, and were afterwards filled with inorganic matter, precipitated from water.

The author states his reasons for believing that these were solid timber trees. In soft monocotyledonous trees, their stems never expand laterally, but are as thick when only a few years old, and a foot high, as when they attain the height of sixty or one hundred feet. Their roots, also, instead of being massive and forking, generally

present a dense assemblage of straight, succulent fibres, like those of an onion or a hyacinth.

Mr. Bowman then combats the view generally entertained, that fossil stems, with perpendicular furrows, as in the sigillariæ, were succulent or hollow plants. He showed by specimens of recent dicotyledonous wood from New Zealand, that, both upon the bark and on the naked wood, longitudinal ribs and furrows, as regular as those on sigillariæ, were displayed; proving, therefore, that these characters are not incompatible with a dicotyledonous structure. By sliced and polished specimens of the bark of one of these fossil trees, he showed evidence of coniferous structure, proving, also, further, their dicotyledonous character. We note this decision with the more particularity, since M. Brongniart at the same time had asserted that "no wood of dicotyledonous plants, properly speaking, have been found in the coal-fields,"* but has since materially changed his views on that point.

The roots of these trees are fixed in what is now a seam of coal nine inches thick. Mr. Bowman infers that one hundred years must be the minimum of time which would be required for the production of the vegetable matter out of which the nine inches of coal were produced; and he estimates that the thickness of the solid coal is equal to about one-third that of the vegetable matter out of which it was produced.†

An instance very similar to this was detailed by Mr. Witham, in a communication to the Philosophical Magazine, entitled, "On the vegetation of the first period of the world, during the deposit of the transition and coal series." The author illustrates by a diagram the fossil stems of sigillaria, which occur beneath the main seam in the great Newcastle coal-field, at one hundred and fifty yards beneath the surface.

The fossil plants stand erect in the sandstone, their roots being imbedded in the ten inch seam of coal below. "These stems, [as shown in the figure,] are truncated after passing through the sandstone, and are lost in the main coal seam; leaving room to believe that they may have formed part of this combustible mass or bed.” The saginariæ, the stigmariæ, and the calamites, he observes, do not appear to have been sufficiently strong to have resisted the force of a current of water, but are placed horizontally.‡

Position occupied by Sigillaria.-The trunks of these trees are found both in the floor and the roof of coal seams; their position commonly being the upper part of the coal and the lower part of its roof. The sigillariæ are arranged by M. A. Brongniart among the conifera; by Dr. Lindley under the name of caulopteris, and by Count Sternberg as syringodendrons. Some discussion and much new light have arisen, and it seems nearly settled that the numerous tribe of sigillariæ are to be removed altogether from the arborescent ferns to the

Histoire des Vegetaux Fossiles.

Proceedings Geol. Soc. London, Vol. III. p. 270.
Phil. Mag. January, 1830.

dicotyledon family. M. Brongniart has been able to take the measurement of one of these stems, which was horizontally extended to the distance of more than forty feet; but has rarely had opportunity to examine their height, their general form, and their mode of termination, on a large scale, in the mines.

In Pennsylvania we have had some favourable opportunities for observing and illustrating the position of enormous trunks in the anthracite mines. The Transactions of the American Philosophical Society contain a memoir on the fossil stems of large trees belonging to the family of sigillaria, which occur both in the roof and floor of a coal seam in Dauphin county.* They consist of several species of these trees, which are displayed in a very interesting manner upon the nearly vertical walls of the vein for several hundred feet in length.

The Floor.-As usual in Pennsylvania, the "bottom slate" consists of indurated clay and shale, more or less laminated. This lamination, it may be observed, is principally due to the flattened sheets of enormous sigillaria. Very few of these compressed trunks are of a less diameter than two feet; many of them are three feet; several are four and four feet and a-half wide, and one specimen is at least five feet broad in its flattened diameter. More than a hundred of these are exhibited in the drawing which illustrates the paper referred to. The coal seam had not at the time commenced to be worked; and as its position was approaching to vertical, the gallery of exploration was conducted longitudinally along it, having the floor on the right hand and the roof on the left. Consequently, although several hundred feet in length of walls were exposed on either side, the height denuded was comparatively limited, and afforded little chance for determining the length of the trunks. In no instance was the area of excavation sufficiently extensive to exhibit either extremity of these gigantic stems, notwithstanding that many of them are inclined in such a position as to be exposed for thirty, forty, and fifty feet of their length, without much apparent diminution or tapering upwards, and are perfectly straight.

The Roof. This is the north or hanging wall of the vein, and consists of coarse siliceous conglomerate of white quartz pebbles. Between it and the coal, and embossed, as it were, upon the surface of the pudding stone, is a very thin coating of clay slate, and an extraordinary assemblage of prostrated trunks of sigillariæ. In diameter they are much smaller than those of the species which form the floor. Instead of being straight like them, these are bent or curved, and some of them appear to be dichotomous, and to possess the charac ters of S. elegans. Such is the scale, as regards height, of these trees, that the extent of cleared space was, as in the floor, inadequate to elucidate their entire development at any point or in any in

stance.

* Memoir by Mr. Richard C. Taylor, in Trans. Amer. Phil. Soc., Vol. IX. part II., 1845.