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are uniformly small; but, as the resemblance in this case is simply one of general form, and the great majority of other trees seem to possess no living type to which they can be referred, it is by no means impossible that these also may be completely lost. One example of them is seen in a plant, fragments of which are extremely common in the coal-measures, and which has been called Calamite* (fig. 30).

The remains of calamites consist of jointed fragments, which were originally cylindrical, but are now Fig. 30 almost always crushed and flattened. They resemble very closely, in general appearance, the common jointed reed growing in marshes, and called Equisetum, or mare's tail; but, instead of being confined to a small size, they would seem to have formed trees having a stem sometimes more than a foot in diameter, and jointed branches and leaves of similar gigantic proportions. They were evidently soft and succulent, and very easily crushed. They They seem to have grown in great multitudes near the place where the coal is now accumulated; and, though often broken, they seldom bear marks of having been transported from a dis

tance.

CALAMITE.

The calamites, although common fossils in the coalmeasures in all places where those rocks appear, are by no means so abundantly present as the fronds or leaves of ferns; and these latter seem, as has been already observed, to have belonged to that tribe of ferns, species of which grow to a great height and on a lofty Kalapos (calamos), a reed.

*

trunk, forming what are called tree ferns, well known in the Australian islands and colonies, and met with also in other countries where the conditions of vegetation are equally favourable for these plants.

There is nothing in the appearance of such leaves or their structure which distinguishes them very especially from the ferns of a later period or of the present day. Their great preponderance over all other fossils in the shales, proves how large a proportion they occupied of the whole flora, or at least of that portion capable of preservation; and the presence, also, of stems and trunks, marked with scars like those observed on modern tree ferns, shows that, like these, they attained a very large size, and grew in a very similar manner.

Two well-marked genera of lofty forest trees are almost the only other plants which appear, from their great abundance, to have contributed in large proportion to the solid matter of the coal. Of these, one, called by Geologists Lepidodendron* (see frontispiece,) seems to have risen to a great height from the ground, and to have given off branches at a very acute angle. The whole stem was covered with scars, or marks of the places from which leaves had fallen, and the leaves or fronds themselves seem to have been borne in long rows, arranged in a different manner from that observed in existing trees. The most probable account of this tree is, that it bore a considerable resemblance in some respects to a particular group of pines, but that it exhibited in other matters, and those too of great importance in classification, analogies with the

Aɛπiç, gen. Xɛπidoç (lepidos), a scale; dɛvòpov (dendron), a tree: the trunk of this tree being marked along its whole length with scales or scars.

singular club-mosses (Lycopodiacea), so close as almost to justify the opinion of its having formed a connecting link between these two very different natural tribes of plants.

Another genus, the Sigillaria* (fig. 31), must, if recent observations are correct, be considered as the stem of the tree of which the so-called Stigmaria+ was only the root. It was even more abundant, and a still more important element in the formation of coal, than the Lepidodendron. The stems of Sigillariæ exhibit no internal woody structure, having been Fig. 31

SIGILLARIA.-Trunk and Roots.

for the most part either hollow or succulent, and easily crushed, but they were evidently provided with a central woody axis, and also with an outer coating of bark, the latter often turned into coal, and sometimes being nearly an inch in thickness. The whole of the trunk is elegantly fluted, and there is a single row of small scars, the remains of leaves, at regular distances

*

From the Latin sigillum, a seal, or the impression made by it; the trunk of the tree appearing to have been stamped with a pattern in regular rows along the direction of its length.

+ Eriyua (stigma), a mark. The fossil was called Stigmaria, from the regular and deep marks or brands impressed on the supposed stem or root.

on each fluting. It is pretty clear that the leaves attached at these scars were connected through the bark with the central woody axis.

The fossils that have received the name Stigmaria, and which have been supposed to be roots belonging to Sigillaria, are in some places so extremely abundant in the shales lying under coal seams, that in South Wales they seem almost invariably to form a kind of floor on which the coal rests. In this case the slender fibres proceeding from the large roots are completely matted together, and form an entangled mass, traversing the bed in every direction. Like the Sigillaria trunk, these roots appear to have consisted of a tough bark inclosing a woody centre, the interval being filled with succulent matter. The plants thus described probably belonged to an extinct family, intermediate in character between the cone-bearing plants or pines and the Cycadææ, and they probably resembled the Zamia, although expanded into a lofty forest tree, and giving off branches as well as leaves.

But while such is the nearest approach that we can make to a description of their appearance, it must not be imagined that we have arrived at any very certain conclusions with regard to these vegetables. They appear to depart so widely from those which are now common in any part of the world, that we can only suggest what may perhaps have been similar, and dare not assert positively the existence of analogies, except that there is little doubt that in endeavouring to picture to ourselves the condition of the land during the deposit of the coal, we must rather look to the southern antipodal islands, and especially to New Zealand, for these analogies, than to other parts of the

world where vegetation, although even more luxuriant, belongs to a different type.

And there is, after all, nothing improbable in the notion, that, at the period of the deposit of the coalmeasures, the northern hemisphere in our latitudes was for the most part occupied by a great ocean, studded over with numerous islands, some of larger, some of smaller size; open water reaching from this archipelago quite to the arctic circle. Innumerable islands and reefs may have been there planted and destroyed, while some few, undergoing depression at a slow rate, became before their final disappearance the receptacle of those sandy and muddy banks among which the vegetable matter was embedded. Numerous inlets may have indented the coast line of the larger islands, and have received into them rivers or mountain streams, loaded with the fragments of trees and other vegetables brought down during the rainy season.

The whole of the interior of the islands may have been clothed with thick forest, the dark verdure of which would only be interrupted by the bright green of the swamps in the hollows, or the brown tint of the fern covering some districts near the coasts. The forest would have been formed by a mixture of several different trees. We should see there, for instance, the lofty and widely-spreading Lepidodendron, its delicate, feathery, and moss-like fronds clothing in rich luxuriance branches and stems, which are built up, like the trunk of the tree-fern, by successive leafstalks that have one after another dropped away, giving by their decay additional height to the stem, which might at length be mistaken for that of a gigantic pine.

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