or horse-tail tribe; aquatic plants which, in a living state, are only two or three feet high in our climates, and even in tropical countries only attain, as in the case of Equisetum giganteum, discovered by Humboldt and Bonpland, in South America, a height of about five feet, the stem being an inch in diameter. The Calamites, however, of the Coal differed from these, principally in being furnished with a thin bark, which is represented in the stem of C. Suckowii (Fig. 261.), in which it will be seen.

that the striped external pattern does not agree with that left on the stone where the bark is stripped off, so that if the two impressions were seen separately, they might be mistaken for two distinct species.

Conifera.- The structure of the wood of certain coal plants displays so great an analogy to that of certain pines of the genus Araucaria, as to

U

lead to the opinion that some species of firs existed at this period. (See above, p. 82.)

Stigmaria. Fragments of a plant which has been called Stigmaria ficoides occur in great numbers in almost every coal-pit. It is supposed to have been a huge succulent water-plant of an extinct family; thin transparent sections of the stem exhibiting an anatomical structure quite different from the wood of any living tree.* According to

Fig. 262.

Stigmaria ficoides, Brong. One fourth of nat. size. (Foss. Flo. 32.)

Fig. 263.

the conjectures of some bot

anists, it approached most

nearly to the family Lycopodiacea; according to others same species, showing form of to Euphorbiacea. Mr. Hutton discovered one of these Stigmariæ forming a huge dome-shaped body, from which twelve branches spread horizontally in all directions, each, usually dividing into two arms, from twenty

* Lindley, Foss. Flora, p. 166.

to thirty feet long, to which leaves of great length were attached. Dr. Buckland imagines these plants to have grown in swamps, or to have floated in lakes like the modern Stratiotes.*

I shall postpone some general remarks on the climate of the Carboniferous period, arising out of the contemplation of its flora, until something has been said of the contemporaneous Mountain limestone and its marine fossils.

* Bridgew. Treat., p. 478.

436

CHAPTER XXI.

CARBONIFEROUS GROUP continued, AND OLD RED SANDSTONE.

Corals and shells of the Mountain limestone-Hot climate of the Carboniferous period inferred from the marine fossils of the Mountain limestone and the plants of the Coal Origin of the Coal-strata Contemporaneous freshwater and marine deposits Modern analogy of strata now in progress in and around New ZealandVertical and oblique position of fossil trees in the CoalHow enveloped - How far they prove a rapid rate of deposition Old Red sandstone its subdivisions its fossil shells and fish.

CARBONIFEROUS or Mountain limestone. We have already seen that this rock lies sometimes entirely beneath the Coal-measures, while, in other districts, it alternates with the shales and sandstone of the Coal. In both cases it is destitute of land plants, and usually charged with corals, which are often of large size; and several species belong to the lamelliferous class of Lamarck, which enter largely into the structure of coral reefs now growing. There are also a great number of Crinoidea and a few Echinida, associated with the zoophytes above mentioned. The Brachiopoda constitute a large proportion of the Mollusca, many species being referable to two extinct genera, Spirifer (or

Spirifera) (Fig. 264.) and Producta (Fig. 265.). There are also many univalve and bivalve shells

of existing genera in the Mountain limestone, such as Turritella, Buccinum, Patella, Isocardia, Nucula, and Pecten. But the Cephalopoda depart, in general, more widely from living forms, some being generically distinct from all those found in strata newer than the Coal. In this number may be mentioned Orthoceras, a siphuncled and chambered shell, like a Nautilus uncoiled and straightened. Some species of this genus are several feet long (Figs. 266, 267.). The GoniaFig. 266.

Fig. 267.

Portion of Orthoceras laterale, Phillips.
Mountain limestone.

0. giganteum, Sow. Section showing the siphuncle; reduced two thirds.

tite is another genus, nearly allied to the Ammonite, from which it differs in having the lobes of

* Phillips, Geol. of Yorksh. pl. 10. fig. 11.

Ibid., pl. 8. fig. 19.

‡ Ibid., vol. ii. p. 208.