ing plants, while their earliest fossil representatives appear to have attained the dimensions of Forest Trees.*

Existing Lycopodiacea follow nearly the same law as ferns and Equisetaceae, in respect of geographical distribution; being largest and most abundant in hot and humid situations within the Tropics, especially in small islands. The belief that Lepidodendra were allied to the Lycopodiaceæ, and their size, and abundant occurrence among the fossils of the Coal Formation have led writers on fossil plants to infer that great heat, and moisture, and an insular Position were the conditions, under which the first forms of this family attained that gigantic stature, which they exhibit in deposites of the Transition period; thus corroborating the conclusion they had derived from the Calamites associated with them, as already mentioned.†

Lindley and Hutton state, that Lepidodendra are, after Calamites, the most abundant class of fossils in the Coal formation of the North of England; they are sometimes of enormous size, fragments of stems occurring from twenty to forty-five feet long; in the Jarrow colliery a compressed tree of this class measured four feet two inches in breadth.

* Prof. Lindley states that the affinities of existing Lycopodiacea are intermediate between Ferns and Conifere on the one hand, and Ferns and Mosses on the other; They are related to Ferns in the want of sexual apparatus, and in the abundance of annular ducts contained in their axis; to Coniferæ, in the aspect of the stems of some of the larger kinds; and to Mosses in their whole appearance.

†The leaves of existing Lycopodiaceæ are simple, and arranged in spiral lines around the stem, and impress on its surface scars of rhomboidal or lanceolate form, marked with prints of the insertions of vessels. In the fossil Lepidodendra, we find a large and beautiful variety of similar scars, arranged like scales in spiral order, over the entire surface of the stems. A large division of these are arborescent and dichotomous, and have their branches covered with simple lanceolate leaves. Our figure of Lepidodendron Sternbergii (Pl. 55, Figs. 1. 2. 3.) represents all these characters in a single Tree from the Coal mines of Swina in Bohemia.

The form of the scales varies at different parts of the same stem, those nearest the base are elongated in the vertical direction.

Thirty-four species of Lepidodendron are enumerated in M. Ad. Brongniart's Catalogue of fossil plants of the coal formation.

The internal structure of the Lepidodendron has been shown to be intermediate between Lycopodiaceae and Coniferæ,* and the conclusions which Prof. Lindley draws from the intermediate condition of this curious extinct genus of fossil plants, are in perfect accordance with the inferences. which we have had occasion to derive from analogous conditions in extinct genera of fossil animals. "To Botanists, this discovery is of very high interest, as it proves that those systematists are right, who contend for the possibility of certain chasms now existing between the gradations of organization, being caused by the extinction of genera, or even of whole orders; the existence of which was necessary to complete the harmony which it is believed originally existed in the structure of all parts of the Vegetable kingdom. By means of Lepidodendron, a better passage is established from Flowering to Flowerless Plants, than by either Equisetum or Cycas, or any other known genus." Lindley and Hutton's Fossil Flora, vol. ii. page 43.

Sigillaria.t

Besides the above plants of the Coal formation which are connected with existing Families or Genera, there occur many others which can be referred to no known type in the vegetable kingdom. We have seen that the Calamites take their place in the existing family of Equisetacea; that many fossil Ferns are referable to living genera of this extensive family; and that Lepidodendra approximate to living Lyco

* See annual report of the Yorkshire Phil. Society for 1832. Witham's Fossil Vegetables, 1833, Pl. 12. 13, and Lindley and Hutton's Fossil Flora. Pl. 98 and 99.

Pl. 56, Figs. 1, 2,

podiacea and Coniferæ. Together with these, there occur other groups of Plants unknown in modern vegetation, and of which the duration seems to have been limited to the Epochs of the Transition Period. Among the largest and tallest of these unknown forms of Plants, we find collossal Trunks of many species, which M. Ad. Brongniart has designated by the name of Sigillaria. These are dispersed throughout the sand-stones and shales that accompany the Coal, and can occasionally be detected in the Coal itself, to the substance of which they have largely contributed by their remains. They are sometimes seen in an erect position, where views of the strata are afforded by cliffs on the sea shore, or by inland sections of quarries, banks of rivers, &c.*

* On the coast of Northumberland, at Creswell hall, and Newbiggin, near Morpeth, many stems of Sigillaria may be seen, standing erect at right angles to the planes of alternating strata of shale and sand-stone; they very from ten to twenty feet in height, and from one to three feet in diameter, and are usually truncated at their upper end; many terminate downwards in a bulb-shaped enlargement, near the commencement of the roots, but no roots remain attached to any of them. Mr. W. C. Trevelyan counted twenty portions of such Trees, within the length of half a mile; all but four or five of these were upright; the bark, which was seen when they were first uncovered, but soon fell off, was about half an inch in thickness, and entirely converted into coal. Mr. Trevelyan observed four varieties of these stems, and engraved a sketch of one of them in 1816, which is copied in Count Sternberg's Table 7. Fig. 5.

In September, 1834, I saw in one of the Coal Mines of Earl Fitzwilliam, at Elsecar, near Rotherham, many large Trunks of Sigillaria, in the sides of a gallery by which you walk into the mine, from the outcrop of a bed of Coal about six feet thick. These stems were inclined in all directions, and some of them nearly vertical. The interior of those whose inclination exceeded 45° was filled with an indurated mixture of clay and sand; the lower extremity of several rested on the upper surface of the bed of Coal. None had any traces of Roots, nor could any one of them have grown in its present place.

M. Alex. Brongniart has engraved a section at St. Etienne, in which many similar stems are seen in an erect position, in sand-stone of the

The vertical position of these trunks, however, is only occasional and accidental; they lie inclined at all degrees throughout all the strata of the carboniferous series; but are most frequently prostrate, and parallel to the lines of stratification, and, in this position are usually compressed. When erect, or highly inclined, they retain their natural shape, and their interior is filled with sand or clay, often different from that of the stratum in which their lower parts are fixed, and mixed with small fragments of various other plants. As this foreign matter has thus entirely filled the interior of these trunks, it follows that they must have been without any transverse dissepiments, and hollow throughout, at the time when the sand, and mud, and fragments of other plants found admission to their interior. The bark, which alone remains, and has been converted into coal, probably surrounded an axis composed of soft and perishable pulpy matter, like the fleshy interior of stems of living Cactes; and the decay of this soft internal trunk, whilst the stems were floating in the water, probably made room for the introduction of the sand and clay.

These trunks usually vary from half a foot to three feet in, diameter. When perfect, the height of many of themi, must have been fifty or sixty feet, at least.*

Coal formation, and infers from this fact that they grew on the spot where they are now found. M. Constant Provost justly objects to this inference, that, had they grown on the spot, they would all have been rooted in the same stratum, and not have had their bases in different strata. When I visited these quarries in 1826, there were other trunks, more numerous. than the upright ones, inclined in various directions.

I have seen but one example, viz. that of Balgray quarry, three miles N. of Glasgow, of erect stumps of large trees fixed by their roots in sand-stone of the coal formation, in which, when soft, they appear to have grown, close to one another. See Lond. and Edin. Phil. Mag. Dec. 1835, p. 487.

* M. Ad. Brongniart found in a coal mine in Westphalia near Essen, the compressed stem of a Sigillaria laid horizontally, to the length of forty feet; it was about twelve inches in diameter at its lower, and six inches. at its upper extremity, where it divided into two parts, each four inches

Count Sternberg has applied the name Syringodendron to many species of Sigillaria, from the parallel pipe-shaped flutings that extend from the top to the bottom of their trunks. These trunks are without joints, and many of them attain the size of forest trees. The flutings on their surface bear dot-like, or linear impressions, of various figures, marking the points at which the leaves were inserted into the stem. This fluted portion of the Sigillariæ, formed their external covering, separable like true bark from the soft internal axis, or pulpy trunk; it varied in thickness from an inch to oneeighth of an inch, and is usually converted into pure coal. (See Pl. 56, Fig. 2. a, b, c.)

A fleshy trunk surrounded and strengthened only by such thin bark, must have been incapable of supporting large and heavy branches at its summit. It therefore probably terminated abruptly at the top, like many of the larger species of living Cactus, and the abundant disposition of small leaves around the entire extent of the trunk seems to favour this hypothesis.

The impressions, or scars, which formed the articulations of leaves on the longitudinal flutings of the trunks of Sigillariæ, are disposed in vertical rows on the centre of each fluting from the top to the bottom of the trunk. Each of these scars marks the place from which a leaf has fallen off, and exhibits usually two apertures, by which bundles of vessels passed through the bark to connect the leaves with the axis of the tree. No leaf has yet been found attached to any of these trunks; we are therefore left entirely to conjecture as to what their nature may have been. This. non-occurrence of a single leaf upon any one of the many thousand trunks that have come under observation, leads us to infer that every leaf was separated from its articulation, and that many of them perhaps, like the fleshy interior of

in diameter. The lower end was broken off abruptly. Lindley and Hutton's Foss, Flora, vol. i. p. 153.