Mr. A. Brongniart, however, has decided, with Lindley and other investigators, to remove the calamities, the sigillaria, stigmara and lepidodendrons from the monocotyledons, and group them with the dicotyledons.

The presence of bitumen, and the consequent swelling and partial fusion of the ordinary bituminous coal, in making these experiments, render it difficult to obtain, from that species of coal, the tissues in the perfection in which they may be found in anthracite.*

Carbonization of Wood.-Dr. Mantell has treated at length on this interesting subject in his "Wonders of Geology." In a more recent work he remarks,-"that the structure and composition of a plant affected its carbonization there can be no doubt; for in the same layer of stone, [in the calciferous grit of Tilgate forest,] the stems resembling palms, Endogenites, invariably possess a thick outer crust of coal; while the stems and roots of the Clathrariæ,-plants allied to the yucca, or dracena,-have not a particle of carbonaceous matter, but are surrounded by a reddish brown earthy crust.

The nature of the stratum in which the plants were imbedded, must, of course, have also influenced the bituminous fermentation. Vegetable remains, when interposed between beds of tenacious clay, by which the escape of the gaseous elements, set free by decomposition, was prevented, appear to have been most favourably situated for their conversion into lignite or coal. Experience has shown that although the true coal-measures are only found beneath the saliferous formation [of England], the production of good combustible coal is not necessarily restricted to any period or series of strata; but may occur wherever the local conditions were favourable to the complete bituminization of beds of vegetable matter. In fact, the productive coal-fields of Buckeburg, in Hanover, are situated in deposits of the Wealden epoch."†

Coniferous Fossil Wood in the newer coal formation of Nova Scotia. For a knowledge of these fossil trees we are indebted to Mr. Dawson. According to his relation, at a particular level, in the lower part of the newer coal strata, calcareous petrifactions of coniferous wood are very abundant, in some instances appearing to have belonged to extensive rafts of drift-wood. A bed of sandstone, containing one of these petrified rafts, is well exposed on the shore between Cape Malagash and Wallace Harbour, and is there associated with a bed of gypsum, and a thin layer of limestone containing a few marine shells of species found in the lower carboniferous rocks. In the bed of coniferous wood at Malagash, the structure of many of the trunks has been very perfectly preserved; and slices exhibit, very distinctly, polygonal discs on the walls of the cells, like those of the genus Araucaria. On comparing them with others from different parts of Nova Scotia, and New Brunswick, Mr. Dawson found that the species of coniferous trees most abundantly found in the coal

* Silliman's Journal, May, 1846.

† Mantell-Wonders of Geology, pp. 373, 688. Medals of Creation, 1844. Vol. I. pp. $9-90.

formation of Pictou and Cumberland counties have the structure of Araucarian pines. On the weathered ends of trunks of Araucaria, in the sandstones at Pictou and near Wallace, rings of growth are often very apparent. In some instances, the layers of yearly growth having separated in the progress of decay, as is often seen in recent wood, they have left vacant spaces, occupied, in the fossils, by calcareous spar. In a transverse slice the rings of growth can easily be seen by the naked eye. They do not exceed in width those of vigorous individuals of many recent coniferous species, but their limits are much less distinctly marked than in any coniferæ now growing in this climate.

It is perhaps worthy of notice, that the alteration effected from the original structure of these calcareous fossils, consists merely in the filling up of the cavities of the cells with carbonate of lime, and in the carbonization of their walls. When fragments are exposed to the action of diluted hydrochloric acid, the calcareous matter is removed, and a flexible carbonaceous substance, retaining the form of the fragment, remains. This residual woody matter burns like touchwood, and leaves a very little white ash.

Coniferous wood is not unfrequent in the nodules of iron-stone, included in the great coal-bed at the Albion mines. More rarely they afford fragments with the structure of stigmaria.

Stigmaria. At the extremity of Malagash Point, Mr. Dawson discovered in a bed of shale, a fossil stump of a tree, having connected with it, roots with regular scars like stigmaria. A portion of one of the main roots, ten inches in length, was seen to be attached to the stump, and other portions appeared in the surrounding clay. The trunk exhibited an external coaly envelope or bark irregularly corrugated: its stony cast showed, indistinctly, alternate smooth and rough vertical stripes, and internally it possessed an eccentric core, probably corresponding with that of the roots, and having large transverse prominences, which appear to have been connected with fibres or bundles of vessels, whose remains extend onward and downward through the outer part of the cast.

Artisia or Sternbergia. Fragments of plants of this genus are frequently found in the sandstones of the Pictou coal-field; usually in beds which also contain calamites. They are in the state of stony casts, always invested with a thin bark or coating of lignite, whose outer surface is smooth and without transverse wrinkles. Mr. Dawson saw none with any trace of roots, leaves, or fruit, or even of a conical termination: all were cylindrical fragments, and so similar in their markings, that they may have belonged to one species.

Transversely ridged stems, of a character very different from the above, are occasionally found in the carboniferous beds of this province. They are stony casts, having irregular and often large transverse markings, and enclosed in a thick coat of lignite or fossil wood. Transverse sections showed cellular tissue apparently with medullary rays, and much resembling the wood of coniferæ. These last are referred to casts of the pith of trees. Those previously mentioned

apparently belonged to a plant having a very large pith and a comparatively thin woody envelope-in short a gigantic rush-like plant, perhaps leafless and nearly cylindrical, like some modern species of iuncus.* In this view Mr. Bunbury fully concurs, and recommends an adherence to the name Artisia given to these bodies, rather than that of Sternbergia, which name belongs to a genus of recent plants very different from these fossils.†

Coal vegetation of Frostburg in Maryland. There are some details. of the fossil forms at the Frostburg mines, deserving note, in an article in the Quarterly Journal of the Geological Society of London, in May, 1846, by Mr. Bunbury. These beautiful plants are figured and named as

1. Pecopteris emarginata. [Diplazites emarginatus of Goppert?] 2. Pecopteris elliptica.

3. Danaites asplenioides.

(Goppert.)

With these fossil ferns Mr. Bunbury describes the following less rare plants, which are collected at Frostburgh by Mr. Lyell.

4. Neuropteris cordata-very abundant, and certainly identical with the English plant.

5. N- gigantea ?

6. Cyclopteris?

7. Pecopteris arborescens.

8. P

9. P

11. Z

abbreviata.

(?)

10. Lepidodendron tetragonum.

12. L

of Brongniart.

aculeatum.

(?) resembling in its markings the Sigillaria menardi

13. Sigillaria reniformis? 14. Stigmaria ficoides.

15. Asterophyllites foliosa. tuberculata ?

16. A

17. A

18. A

equisetiformis?

undescribed, but said to be found in the "middle

Mr. Bunbury remarks that the very striking similarity between the coal plants of North America and those of Europe makes it probable that a similar kind of climate also existed in both countries at that era; and whatever conclusions we may arrive at, in relation to the carboniferous period in the one continent seems equally applicable to the other. Nothing, he continues, that has yet been ascertained relative to the coal formations of either continent seems at all

* Dawson on Nova Scotia Coal plants. Quarterly Journ. Geol. Soc. London, May, 1846, p. 132. † Bunbury, Ibid., p. 138. Also Mr. Dawes, on Sternbergiæ, Ibid., p. 139.

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 vegeta

*Travels 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 classification.

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.