Fig. 448: Pecopteris elliptica, Bunbury.[[2]] Frostburg.
Fig. 449: Caulopteris primæva, Lindley.

When collecting fossil specimens from the coal-measures of Frostburg, in Maryland, I found in the iron-shales several species with well-preserved rounded spots or marks of the sori (see Fig. 448). In the general absence of such characters they have been divided into genera distinguished chiefly by the branching of the fronds and the way in which the veins of the leaves are disposed. The larger portion are supposed to have been of the size of ordinary European ferns, but some were decidedly arborescent, especially the group called Caulopteris (see Fig. 449) by Lindley, and the Psaronius of the upper or newest coal-measures, before alluded to ([p. 393]). All the recent tree-ferns belong to one tribe (Polypodiaceæ), and to a small number only of genera in that tribe, in which the surface of the trunk is marked with scars, or cicatrices, left after the fall of the fronds. These scars resemble those of Caulopteris.

No less than 130 species of ferns are enumerated as having been obtained from the British coal-strata, and this number is more than doubled if we include the Continental and American species. Even if we make some reduction on the ground of varieties which have been mistaken, in the absence of their fructification, for species, still the result is singular, because the whole of Europe affords at present no more than sixty-seven indigenous species.

Lycopodiaceæ—Lepidodendron.—About forty species of fossil plants of the Coal have been referred to this genus, more than half of which are found in the British coal-measures. They consist of cylindrical stems or trunks, covered with leaf-scars. In their mode of branching, they are always dichotomous (see [Fig. 454]). They belong to the Lycopodiaceæ, bearing sporangia and spores similar to those of the living representatives of this family ([Fig. 457]); and although most of the Carboniferous species grew to the size of large trees, Mr. Carruthers has found by careful measurement that the volume of the fossil spores did not exceed that of the recent club-moss, a fact of some geological importance, as it may help to explain the facility with which these seeds may have been transported by the wind, causing the same wide distribution of the species of the fossil forests in Europe and America which we now observe in the geographical distribution of so many living families of cryptogamous plants.

The Figs. 453–455 represent a fossil Lepidodendron, 49 feet long, found in Jarrow Colliery, near Newcastle, lying in shale parallel to the planes of stratification. Fragments of others, found in the same shale, indicate, by the size of the rhomboidal scars which cover them, a still greater magnitude.

The living club-mosses, of which there are about 200 species, are most abundant in tropical climates. They usually creep on the ground, but some stand erect, as the Lycopodium densum from New Zealand (see Fig. 456), which attains a height of three feet.

In the Carboniferous strata of Coalbrook Dale, and in many other coal-fields, elongated cylindrical bodies, called fossil cones, named Lepidostrobus by M. Adolphe Brongniart, are met with. (See Fig. 457.) They often form the nucleus of concretionary balls of clay-ironstone, and are well preserved, exhibiting a conical axis, around which a great quantity of scales were compactly imbricated. The opinion of M. Brongniart that the Lepidostrobus is the fruit of Lepidodendron has been confirmed, for these strobili or fruits have been found terminating the tip of a branch of a well-characterised Lepidodendron in Coalbrook Dale and elsewhere.