Part 11 (1/2)

The _Stigmariae_ (Fig. 42), according to palaeontologists, were roots of Sigillariae, with a subterranean fructification; all that is known of them is the long roots which carry the reproductive organs, and in some cases are as much as sixteen feet long. These were suspected by Brongniart, on botanical grounds, to be the roots of Sigillaria, and recent discoveries have confirmed this impression. Sir Charles Lyell, in company with Dr. Dawson, examined several erect _Sigillariae_ in the sea-cliffs of the South Joggins in Nova Scotia, and found that from the lower extremities of the trunk they sent out _Stigmariae_ as roots, which divided into four parts, and these again threw out eight continuations, each of which again divided into pairs. Twenty-one specimens of Sigillaria have been described by Dr. Dawson from the Coal-measures of Nova Scotia; but the differences in the markings in different parts of the same tree are so great, that Dr. Dawson regards the greater part of the recognised species of _Sigillariae_ as merely provisional.[43]

[43] _Quart. Jour. Geol. Soc._, vol. xxii., p. 129.

[Ill.u.s.tration: Fig. 41.--Sigillaria laevigata. One-third natural size.]

[Ill.u.s.tration: Fig. 42.--Stigmaria. One-tenth natural size.]

Two other gigantic trees grew in the forests of this period: these were _Lepidodendron carinatum_ and _Lomatophloyos cra.s.sicaule_, both belonging to the family of Lycopodiaceae, which now includes only very small species. The trunk of the Lomatophloyos threw out numerous branches, which terminated in thick tufts of linear and fleshy leaves.

The _Lepidodendrons_, of which there are about forty known species, have cylindrical bifurcated branches; that is, the branches were evolved in pairs, or were _dichotomous_ to the top. The extremities of the branches were terminated by a fructification in the form of a cone, formed of linear scales, to which the name of _Lepidostrobus_ (Fig. 45) has been given. Nevertheless, many of these branches were sterile, and terminated simply in fronds (elongated leaves). In many of the coal-fields fossil cones have been found, to which this name has been given by earlier palaeontologists. They sometimes form the nucleus of nodular, concretionary b.a.l.l.s of clay-ironstone, and are well preserved, having a conical axis, surrounded by scales compactly imbricated. The opinion of Brongniart is now generally adopted, that they are the fruit of the Lepidodendron. At Coalbrookdale, and elsewhere, these have been found as terminal tips of a branch of a well-characterised Lepidodendron. Both Hooker and Brongniart place them with the Lycopods, having cones with similar spores and sporangia, like that family. Most of them were large trees. One tree of _L. Sternbergii_, nearly fifty feet long, was found in the Jarrow Colliery, near Newcastle, lying in the shale parallel to the plane of stratification. Fragments of others found in the same shale indicated, by the size of the rhomboidal scars which covered them, a still greater size. Lepidodendron Sternbergii (Fig. 43) is represented as it is found beneath the shales in the collieries of Swina, in Bohemia. Fig. 46 represents a portion of a branch of _L. elegans_ furnished with leaves. M. Eugene Deslongchamps has drawn the restoration of the Lepidodendron Sternbergii, represented in Fig. 47, which is shown entire in Fig. 44, with its stem, its branches, fronds, and organs of fructification. The Ferns composed a great part of the vegetation of the Coal-measure period.

[Ill.u.s.tration: Fig. 43.--Lepidodendron Sternbergii.]

[Ill.u.s.tration: Fig. 44.--Lepidodendron Sternbergii restored. Forty feet high.]

The Ferns differ chiefly in some of the details of the leaf.

_Pecopteris_, for instance (Fig. 48), have the leaves once, twice, or thrice pinnatifid with the leaflets adhering either by their whole base or by the centre only; the midrib running through to the point.

_Neuropteris_ (Fig. 49) has leaves divided like Pecopteris, but the midrib does not reach the apex of the leaflets, but divides right and left into veins. _Odontopteris_ (Fig. 51) has pinnatifid leaves, like the last, but its leaflets adhere by their whole base to the stalk.

_Lonchopteris_ (Fig. 50) has the leaves several times pinnatifid, the leaflets more or less united to one another, and the veins reticulated.

Among the most numerous species of forms of the Coal-measure period was _Sphenopteris artemisiaefolia_ (Fig. 52), of which a magnified leaf is represented. Sphenopteris has twice or thrice pinnatifid leaves, the leaflets narrow at the base, and the veins generally arranged as if they radiated from the base; the leaflets are frequently wedge-shaped.

[Ill.u.s.tration: Fig. 45.--Lepidostrobus variabilis.]

[Ill.u.s.tration: Fig. 46.--Lepidodendron elegans.]

CARBONIFEROUS LIMESTONE. (SUB-PERIOD.)

The seas of this epoch included an immense number of Zoophytes, nearly 400 species of Mollusca, and a few Crustaceans and Fishes. Among the Fishes, _Psammodus_ and _Coccosteus_, whose ma.s.sive teeth inserted in the palate were suitable for grinding; and the _Holoptychius_ and _Megalichthys_, are the most important. The Mollusca are chiefly Brachiopods of great size. The Productae attained here exceptional development, _Producta Martini_ (Fig. 53), _P. semi-reticulata_ and _P.

gigantea_, being the most remarkable. Spirifers, also, were equally abundant, as _Spirifera trigonalis_ and _S. glabra_. In _Terebratula hastata_ the coloured bands, which adorned the sh.e.l.l of the living animal, have been preserved to us. The _Bellerophon_, whose convoluted sh.e.l.l in some respects resembles the Nautilus of our present seas, but without its chambered sh.e.l.l, were then represented by many species, among others by _Bellerophon costatus_ (Fig. 54), and _B. hiulcus_ (Fig.

56). Again, among the Cephalopods, we find the _Orthoceras_ (Fig. 57), which resembled a straight Nautilus; and Goniat.i.tes (_Goniat.i.tes evolutus_, Fig. 55), a chambered sh.e.l.l allied to the Ammonite, which appeared in great numbers during the Secondary epoch.

[Ill.u.s.tration: Fig. 47.--Lepidodendron Sternbergii.]

Crustaceans are rare in the Carboniferous Limestone strata; the genus Phillipsia is the last of the Trilobites, all of which became extinct at the close of this period. As to the Zoophytes, they consist chiefly of Crinoids and Corals. The Crinoids were represented by the genera _Platycrinus_ and _Cyathocrinus_. We also have in these rocks many Polyzoa.

[Ill.u.s.tration: Fig. 48.--Pecopteris lonchitica, a little magnified.]

[Ill.u.s.tration: Fig. 49.--Neuropteris gigantea.]

[Ill.u.s.tration: Fig. 50.--Lonchopteris Bricii.]

[Ill.u.s.tration: Fig. 51.--Odontopteris Brardii.]

[Ill.u.s.tration: Fig. 52.--Sphenopteris artemisiaefolia, magnified.]

Among the corals of the period, we may include the genera _Lithostrotion_ and _Lonsdalea_, of which _Lithostrotion basaltiforme_ (Fig. 58), and _Lonsdalea floriformis_ (Fig. 59), are respectively the representatives, with _Amplexus corallodes_. Among the Polyzoa are the genera _Fenestrella_ and _Polypora_. Lastly, to these we may add a group of animals which will play a very important part and become abundantly represented in the beds of later geological periods, but which already abounded in the seas of the Carboniferous period. We speak of the _Foraminifera_ (Fig. 60), microscopic animals, which cl.u.s.tered either in one body, or divided into segments, and covered with a calcareous, many-chambered sh.e.l.l, as in Fig. 60, _Fusulina cylindrica_. These little creatures, which, during the Jura.s.sic and Cretaceous periods, formed enormous banks and entire ma.s.ses of rock, began to make their appearance in the period which now engages our attention.