dodendron are enumerated in M. Ad. Brongniart's Catalogue of fossil plants of the coal formation.

The internal structure of the Lepidodendron has been shewn to be intermediate between Lycopodiaceæ 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 53.

* 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.

Sigillaria.*

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 referrible to living genera of this extensive family; and that Lepidodendra approximate to living Lycopodiacea 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 colossal 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

*Pl. 56, Figs. 1. 2.

sea shore, or by inland sections of quarries, banks of rivers, &c.*

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

* On the coast of Northumberland, at Greswell 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 vary 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 our Pl. 56. fig. 1.

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

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 the stems of living Cacteæ; 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 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 sandstone of the Coal formation, and infers from this fact that they grew on the spot where they are now found. M. Constant Prevost 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.

of many of them must have been fifty or sixty feet, at least.*

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 one-eighth 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.

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