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.

[Ill.u.s.tration: Fig. 53.--Producta Martini. One-third nat. size.]

[Ill.u.s.tration: Fig. 54.--Bellerophon costatus. Half nat. size.]

[Ill.u.s.tration: Fig. 55.--Goniat.i.tes evolutus. Nat. size.]

[Ill.u.s.tration: Fig. 56.--Bellerophon hiulcus.]

[Ill.u.s.tration: Fig. 57.--Orthoceras laterale.]

[Ill.u.s.tration: Fig. 58.--Lithostrotion basaltiforme.]

[Ill.u.s.tration: Fig. 59.--Lonsdalea floriformis.]

The plate opposite (PLATE X.) is a representation of an ideal aquarium, in which some of the more prominent species, which inhabited the seas during the period of the Carboniferous Limestone, are represented. On the right is a tribe of corals, with reflections of dazzling white: the species represented are, nearest the edge, the _Lasmocyathus_, the _Chaetetes_, and the _Ptylopora_. The Mollusc which occupies the extremity of the elongated and conical tube in the shape of a sabre is an _Aploceras_. It seems to prepare the way for the Ammonite; for if this elongated sh.e.l.l were coiled round itself it would resemble the Ammonite and Nautilus. In the centre of the foreground we have _Bellerophon hiulcus_ (Fig. 56), the _Nautilus Koninckii_, and a _Producta_, with the numerous spines which surround the sh.e.l.l. (See Fig.

62.)

[Ill.u.s.tration: Fig. 60.--Foraminifera of the Mountain Limestone, forming the centre of an oolitic grain. Power 120.]

[Ill.u.s.tration: Fig. 61.--Foraminifera of the Chalk, obtained by brushing it in water. Power 120.]

On the left are other corals: the _Cyathophyllum_ with straight cylindrical stems; some Encrinites (_Cyathocrinus_ and _Platycrinus_) wound round the trunk of a tree, or with their flexible stem floating in the water. Some Fishes, _Amblypterus_, move about amongst these creatures, the greater number of which are immovably attached, like plants, to the rock on which they grow.

[Ill.u.s.tration: X.--Ideal view of marine life in the Carboniferous Period.]

In addition, this engraving shows us a series of islets, rising out of a tranquil sea. One of these is occupied by a forest, in which a distant view is presented of the general forms of the grand vegetation of the period.

It is of importance to know the rocks formed by marine deposits during the era of the Carboniferous Limestone, inasmuch as they include coal, though in much smaller quant.i.ties than in the succeeding sub-period of the true coal-deposit. They consist essentially of a compact limestone, of a greyish-blue, and even black colour. The blow of the hammer causes them to exhale a somewhat fetid odour, which is owing to decomposed organic matter--the modified substance of the molluscs and zoophytes--of which it is to so great an extent composed, and whose remains are still easily recognised.

[Ill.u.s.tration: Fig. 62.--Producta horrida. Half natural size.]

In the north of England, and many other parts of the British Islands, the Carboniferous Limestone forms, as we have seen, lofty mountain-ma.s.ses, to which the term _Mountain Limestone_ is sometimes applied.

In Derbyshire the formation const.i.tutes rugged, lofty, and fantastically-shaped mountains, whose summits mingle with the clouds, while its picturesque character appears here, as well as farther north, in the _dales_ or valleys, where rich meadows, through which the mountain streams force their way, seem to be closed abruptly by ma.s.ses of rock, rising above them like the grey ruins of some ancient tower; while the mountain bases are pierced with caverns, and their sides covered with mosses and ferns, for the growth of which the limestone is particularly favourable.

The formation is _metalliferous_, and yields rich veins of lead-ore in Derbyshire, c.u.mberland, and other counties of Great Britain. The rock is found in Russia, in the north of France, and in Belgium, where it furnishes the common marbles, known as Flanders marble (_Marbre de Flandres_ and _M. de pet.i.t granit_). These marbles are also quarried in other localities, such as Regneville (La Manche), either for the manufacture of lime or for ornamental stonework; one of the varieties quarried at Regneville, being black, with large yellow veins, is very pretty.

In France, the _Carboniferous Limestone_, with its sandstones and conglomerates, schists and limestones, is largely developed in the Vosges, in the Lyonnais, and in Languedoc, often in contact with syenites and porphyries, and other igneous rocks, by which it has been penetrated and disturbed, and even _metamorphosed_ in many ways, by reason of the various kinds of rocks of which it is composed. In the United States the Carboniferous Limestone formation occupies a somewhat grand position in the rear of the Alleghanies. It is also found forming considerable ranges in our Australian colonies.

In consequence of their age, as compared with the Secondary and Tertiary limestones, the Carboniferous rocks are generally more marked and varied in character. The valley of the Meuse, from Namur to Chockier, above Liege, is cut out of this formation; and many of our readers will remember with delight the picturesque character of the scenery, especially that of the left bank of the celebrated river in question.

COAL MEASURES. (SUB-PERIOD.)

This terrestrial period is characterised, in a remarkable manner, by the abundance and strangeness of the vegetation which then covered the islands and continents of the whole globe. Upon all points of the earth, as we have said, this flora presented a striking uniformity. In comparing it with the vegetation of the present day, the learned French botanist, M. Brongniart, who has given particular attention to the flora of the Coal-measures, has arrived at the conclusion that it presented considerable a.n.a.logy with that of the islands of the equatorial and torrid zone, in which a maritime climate and elevated temperature exist in the highest degree. It is believed that islands were very numerous at this period; that, in short, the dry land formed a sort of vast archipelago upon the general ocean, of no great depth, the islands being connected together and formed into continents as they gradually emerged from the ocean.

This flora, then, consists of great trees, and also of many smaller plants, which would form a close, thick turf, or sod, when partially buried in marshes of almost unlimited extent. M. Brongniart indicates, as characterising the period, 500 species of plants belonging to families which we have already seen making their first appearance in the Devonian period, but which now attain a prodigious development. The ordinary dicotyledons and monocotyledons--that is, plants having seeds with two lobes in germinating, and plants having one seed-lobe--are almost entirely absent; the cryptogamic, or flowerless plants, predominate; especially Ferns, Lycopodiaceae and Equisetaceae--but of forms insulated and actually extinct in these same families. A few dicotyledonous gymnosperms, or naked-seed plants forming genera of Conifers, have completely disappeared, not only from the present flora, but since the close of the period under consideration, there being no trace of them in the succeeding Permian flora. Such is a general view of the features most characteristic of the Coal period, and of the Primary epoch in general. It differs, altogether and absolutely, from that of the present day; the climatic condition of these remote ages of the globe, however, enables us to comprehend the characteristics which distinguish its vegetation. A damp atmosphere, of an equable rather than an intense heat like that of the tropics, a soft light veiled by permanent fogs, were favourable to the growth of this peculiar vegetation, of which we search in vain for anything strictly a.n.a.logous in our own days. The nearest approach to the climate and vegetation proper to the geological period which now occupies our attention, would probably be found in certain islands, or on the littoral of the Pacific Ocean--the island of Chloe, for example, where it rains during 300 days in the year, and where the light of the sun is shut out by perpetual fogs; where arborescent Ferns form forests, beneath whose shade grow herbaceous Ferns, which rise three feet and upwards above a marshy soil; which gives shelter also to a ma.s.s of cryptogamic plants, greatly resembling, in its main features, the flora of the Coal-measures. This flora was, as we have said, uniform and poor in its botanic genera, compared to the abundance and variety of the flora of the present time; but the few families of plants, which existed then, included many more species than are now produced in the same countries. The fossil Ferns of the coal-series in Europe, for instance, comprehend about 300 species, while all Europe now only produces fifty. The gymnosperms, which now muster only twenty-five species in Europe, then numbered more than 120.

It will simplify the cla.s.sification of the flora of the Carboniferous epoch if we give a tabular arrangement adopted by the best authorities:--