CLASS VIII.-VEGETABLE FOSSIL REMAINS.

Mr. Parkinson thus ably traces not only the geology but genealogy of these remains. When vegetable matter is accumulated in so large a quantity that the compactness of the mass may in a great degree exclude the atmospheric air from the internal parts of the mass, a considerable and peculiar change is effected the vegetable matter soon loses its green and acquires a brownish color; its flavor and odor are changed, and heat is to be produced, terminating, unless air is freely admitted, in combustion. The vegetable matter, thus changed into hay, acquires, among its other new properties, that of powerfully resisting any further change upon exposure to the atmosphere. But, should vegetable matter be thus accumulated in a situation in which moisture has almost constant access to it, a very different result ensues. Another process takes place, by which the vegetable matter, as the process goes on, loses its original forms, and becomes a soft magma, of a dark color and peculiar appearance; no traces of its former mode of existence being discoverable, except in the accidental presence of such vegetable matter as shall not have undergone a complete conversion. When dried, it forms a readily combustible substance, of a reddish-brown color, readily absorbing and tenaciously retaining water, and yielding, whilst burning, a strong bituminous odor. This is the substance termed peat, immense accumulations of which are formed in various parts, fa

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vorable to the collection of water and the growth of the sphagnum palustre, a plant by the conversion of which the supply of this substance is chiefly supported. In the peat-bogs or mosses, as the natural magazines of this substance are called, trunks of trees are often found imbedded, and partaking of the nature of the surrounding bituminous mass. This change is effected in different degrees; the deeper in the mass, and consequently the longer exposed to the process of bituminisation, the more perfect is the conversion. Some pieces are found to have nearly lost their ligneous appearance, their respective lines and markings having been molten down in different degrees during their bituminisation; whilst others, in which the nature of the substance is also entirely altered, are found still to retain almost all their characteristic markings. This substance has long been known by the designation of bituminous wood.

'Wood of a very different character, called moss fir, is also frequently found in the peat mosses or bogs. It much resembles, in its color and general external appearance, ordinary decayed fir-wood; but on examination it appears that the fibre of the wood is strongly imbued with resin, and that all its interstices are filled with resinous matter. It is so highly inflammable as to be employed, by the poor of the districts in which it is found, not only as fuel, but as torches As the real nature of this substance is not perhaps known, it would be very desirable that further enquiries might be made respecting it; it

might then be determined whether the opinion which is here offered be correct or not. From its retaining the color and appearance of decayed wood, it is conjectured to be wood which, by exposure to the atmosphere, had sustained the abstraction of all its constituent parts, except the resin and ligneous fibre impregnated therewith; and, from its having been thus rendered almost an entirely resinous mass, it has not been affected by the bituminisating process. Subterranean collections of bituminised wood and other vegetable matter are found at various depths in different parts of the world. The substance thus found is generally a compact, light, glossy, combustible substance; of a dark brown color, and frequently almost black; splitting longitudinally into plates of various thicknesses, breaking transversely with an imperfect conchoidal fracture, with a shining resinous lustre, and sometimes yielding the appearance of the markings of wood. This is the suturbrand of Iceland, the Bovey coal of this country, and the common brown coal of Thomson.

The fossil wood, now described, may be said to pass into jet, which is found, especially in the neighbourhood of Whitby in Yorkshire, in a state very nearly approximating to that of Bovey coal. It exists in plates, generally from half an inch to about an inch in thickness, between which a film of carbonate of lime, with pyrites, is disposed excepting that it more frequently shows marks of ligneous texture, its characters may be said to be those of jet; its color, velvet black; internal lustre, shining, resinous; fracture perfect, large, conchoidal; fragments, sharp edged, soft, rather brittle; easily frangible; very light. Jet is found in other situations, in a different form; resembling in its shape, and the markings of its surface, parts of the branches or trunks of trees, but rarely possessing, internally, any marks of vegetable origin; a circumstance easily accounted for, if its previous softening be admitted.'

Cannell coal is said to differ from jet chiefly in its holding a greater portion of earth in intimate mixture with it. It never manifests internally any traces of vegetable structure, but sometimes bears on its surface evident marks of impressions formed on it whilst in a soft state.

Common coal is composed of a similar bituminous matter, divided by films of calcareous spar mingled with pyrites, intersecting each other nearly at right angles: its fracture is thus rendered small grained, and uneven, and its fragments mostly cubical or trapezoidal. By this division and enclosure of the inflammable bituminous matter in combustible septa, the ascension and combustion of this substance are rendered more slow, and better adapted to the purposes for which it is destined. Traces of vegetable structure are very rarely discoverable in coal, except in the impressions of cactuses and of various dorsiferous and succulent plants.

But professor Jameson, speaking of the coal found in the neighbourhood of Edinburgh, says, the coal, which is black coal, occurs in beds, seldom more than a few inches in thickness, and is generally contained in the bituminous shale or slate clay, rarely in the sandstone. By the gra

dually increasing mixture of clayey matter, it passes into bituminous shale. The accompanying bituminous shale and slate clay contain impressions of ferns, a fact which has been adduced in support of the opinion which maintains the vegetable origin of black coal. We are inclined to call in question the supposed vegetable origin of this kind of coal, and are rather disposed to consider it as an original chemical formation; and that the occurrence of vegetable impressions in the adjacent rocks no more proves its vegetable origin, than the existence of fossil quadrupeds in the gypsum of Paris proves that rock to have been formed from the debris of animals of the class mammalia.

To these opinions it may be sufficient to oppose the following deductions of Dr. M'Culloch, from his experiments on certain products obtained from the distillation of wood, &c. The Dr. considers himself as authorised to state that,' examining the alteration produced by water on common turf, or submerged wood, we have all the evidence of demonstration that its action is sufficient to convert them into substances capable of yielding bitumen on distillation. That the same action having operated through a longer period has produced the change in the brown coal of Bovey is rendered extremely probable by the geognostic relations of that coal. From this to the harder lignites, suturbrand and jet, the transition is so gradual that there seems no reason to limit the power of water to produce the effect of bituminisation in all these varieties; nor is there aught in this change so dissonant from other chemical actions as to make us hesitate in adopting this cause.' Satisfied that jet, the bituminous lignite which approaches the nearest to coal in its chemical characters, is the result of the action of water on vegetable matter, Dr. M'Culloch was induced to try if this substance could, by heat under pressure, be converted into coal; the result of his experiment was, that the produce exhibited the true characters of coal, having not merely the color and inflammability, but the fracture of coal and its odor on burning. These experiments and observations, taken with those of Mr. Hatchett, appear to be sufficient to set the question, as to the vegetable origin of coal, at rest. The vegetable origin of naphtha, petroleum, aud asphaltum, is not yet positively ascertained.

Amber, from its being found generally in beds of fossil wood; the blue clay resin, found at Highgate and at Sheppey among the pyritified wood; and the retinasphaltum of Mr. Hatchett, discovered among the Bovey coal, may either owe their origin to the changes effected in vegetable matter during its subterraneous deposition, or may be vegetable resins, the original product of the trees which they accompany, and which, from their resinous nature, may have resisted the bituminizating process. The argillaceous ironstone nodules which accompany coal, contain, with the remains of many other unknown vegetables, parts of various cryptogamous plants, the recent analogues of a very few of which have been said to be found in some of the tropical regions. On these nodules being broken, the preserved remains are generally discovered on each

of the broken sides of the nodule; not, as might De expected, displaying different sides of the vegetable, but the same side of the leaf: for instance, on each broken surface; in one, in alto -in the other in basso relievo. The explanation of this curious circumstance, which long puzzled the oryctologists, is found in the vegetable matter, during its passing through the bituminous change, having become softened, and having filled its own mould with its melted and softened substance; the nodule, on being broken, showing on one side the surface of the adherent bituminous cast, and, on the other, the corresponding mould. In the argillaceous and bituminous slate forming the floors and roofs of coal mines are vast collections of the black bituminized remains of gramina, junci, cryptogami, and of numerous other plants, agreeing in their general characters with those of succulent plants, but differing from the recent ones known in Europe by their vast magnitude, and by the richness of the ornamental markings which appear on their trunks.

'Description,' says Mr. Parkinson, cannot succeed in an attempt to give an idea of the beauty and varieties of the figures which are displayed on the surface of many of those fossils, and which have been supposed to owe their markings to the bark of different trees of supposed antediluvian existence. Some are ornamented by regularly disposed straight plain ribs, disposed longitudinally or transversely over their whole surface; some by the decussation of nearly straight lines obliquely disposed; and many by the alternate contact and receding of gently waving lines, forming areas regularly, but most singularly varying in their forms, and having in their centres tubercles and depressions from which spines, or setæ, have in all probability proceeded. In others, lines obliquely disposed intersect each other at angles, varying in their acuteness in different specimens, in, it would seem, an almost endless variety; forming surfaces apparently covered with squamæ disposed in an imbricated manner, and frequently in quincunx order.'

Accounts have been given of the trunks of trees whose cortical markings were entirely unknown, having been found in the sandstones of Staffordshire, Derbyshire, Lancashire, and indeed in all those parts in which the coal formations have been explored. Having been favored, says Mr. Parkinson, with the opportunity of examining severals pecimens of this nature, through the kindness of Thomas Botfield, esq., of Bewdley in Worcestershire, I am enabled to say that these are not generally the remains of trees, but of succulent plants, the firm cortical parts of which, having been converted by the bituminisating process into jet, have formed that firm tube which is often found, in these instances, filled with sandstone, agreeing with that of the general matrix, and possessing the space left by the waste of the internal succulent part of the plant. The description of the last announced fossil of this kind, found in the neighbourhood of Glasgow, agrees exactly with the general account of these supposed fossil trees, and will, it is presumed, corroborate the opinion which has

been just advanced. In a quarry of sandstone belonging to the coal formation on which Glasgow is built, and in the neighbourhood of that city, it is stated that the quarrymen came upon the cast of a tree in situ just as it had been growing. The trunk is about twenty-six inches in diameter, not quite round but somewhat oval, so that the north and south diameter is several inches longer than the east and west diameter. The body of the tree itself is composed of sandstone precisely similar to the rest of the quarry; but the bark has been converted into perfect cherry coal, which adheres firmly to the tree, and renders it easy to remove the rock with which it is incrusted. About three feet of the bottom part of the tree has been uncovered; this portion is situated about forty feet below the surface of the earth in a solid quarry of sandstone. The upper part of the trunk and branches has not been discovered: indeed, it is some time since the upper portion of the quarry was removed. The roots may be seen dipping down into the earth precisely as the roots of living trees do. Four very large roots may be seen issuing from the trunks, and extending, some of them, about a foot before they are lost in the surrounding stone. There is nothing to indicate the species of tree of which the mould has been here preserved. From the appearance of the roots it is obvious that it was not a fir; it had more resemblance to a beech: the bark has been so completely bituminised, that its usual characters are effaced. The petrifaction, however, is not without its value; it demonstrates that the sandstone has been formed at a period posterior to the existence of large trees, and that the waterworn appearance of the quartz pebbles of which the sandstone is composed is not a deceitful indication.' Hence the ingenious observer is led to observe, that if the sandstone, which constitutes so great a proportion of the coal beds, be a formation posterior to the earth being covered with wood, we can entertain no doubt that this is the case also with the slate clay and the coal which alternate with this sandstone. Indeed, if the coal formation exists as a portion of the old red sandstone, we can entertain no reasonable doubt that the old red sandstone itself has been formed after the earth was covered with wood.' Annals of Philosophy, Nov. 1820.

"The size which these fossil plants have attained, compared with that of the cactuses known in Europe, must, as in the fossil last mentioned, lead to a doubt as to this opinion of their agreement with the recent cactus. But, to be enabled to form a correct judgment on this point, it is necessary to know the state in which these plants exist where the soil and climate are such as to allow them to develope themselves in their native luxuriance. The researches of the celebrated Humboldt, in the equinoctial regions, supply us on this head with the most appropriate and satisfactory information. The following detached observations of that philosopher will show not only the size to which these plants may arrive, but the vast tracts which, under favorable circumstances, they may overrun, as well as the great probability of their having been the first vegetable clothing of the earth. The hill of calcareous