improbably marks a time of rest, when the vegetation was allowed to flourish unchecked, or when at least the sinking was so imperceptible that the successive generations of plants, springing up on the remains of their predecessors, contrived to keep themselves above the level of the water.

In the present world there is no vegetable growth now in progress quite like that of the coal-seams of the Carboniferous period. Perhaps the nearest analogy is supplied by the mangroveswamps of tropical coasts (p. 83). In these tracts, the mangrove trees grow seaward, dropping their roots and radicles into the shallow waters, and gradually forming a belt of swampy jungle several miles broad. That the coal-jungles extended into the sea is shown by the occurrence of marine shells and other organisms in the coal itself. But there were probably also wide swamps wherein the water was fresh. A single coal-seam may sometimes be traced over an area of more than 1000 square miles, showing how widespread and uniform were the conditions in which it was formed.

During the subterranean movements that marked the Carboniferous period, the Devonian physical geography was entirely remodelled. The lake-basins of the Old Red Sandstone were effaced, and the sea of the Carboniferous limestone spread over their site. Much of the Devonian marine area was upridged into land, and the rocks eventually underwent that intense compression and plication which have given them their cleaved, crumpled, and metamorphic aspect, and in connection with which they were invaded by granite and intersected with mineral veins. It is deserving of remark that volcanic action, which played so notable a part in Devonian time, was continued, but with diminished vigour, in the Carboniferous period. During the earlier half of the period, volcanic outbursts were frequent in different parts of Britain, particularly in Derbyshire, the Isle of Man, central and southern Scotland, and the south-west of Ireland. The lava and ashes ejected in some of these areas during the time of the Carboniferous Limestone form conspicuous groups of hills.

Of the plant and animal life of the Carboniferous period much is now known from the abundant remains which have been preserved of the terrestrial surfaces and sea-floors of the time. Beginning with the flora, we have first to notice its general resemblance to that of the Devonian period. Many of the genera of the older time survived in the Carboniferous jungles; but other forms appear in vast profusion, which have not been met with in any Devonian or Old Red Sandstone strata. The Carboniferous flora, like that which preceded it, must have been singularly monotonous, consisting as it did almost entirely of flowerless plants. Not only so, but the very same species and genera appear to have then ranged over the whole world, for their remains are found in Carboniferous strata from the Equator to the Arctic Circle. Ferns, lycopods, and equisetaceæ, constituted the main mass of the vegetation. The ferns recall not a few of their modern allies, some of the more abundant kinds being Sphenopteris, Neuropteris, and Pecopteris (Fig. 141). Among the

FIG. 141. Carboniferous Ferns. (a) Neuropteris macrophylla (f); (b) Sphenopteris artemisiæfolia (1); (c) Alethopteris (Pecopteris) lonchitica (1).

lycopods the most common genus is Lepidodendron, so named from the scale-like leaf-scars that wind round its stem (Fig. 142). Its smaller branches, closely covered with small pointed leaves, and bearing at their ends little cones or spikes (Lepidostrobus), remind one of the club-mosses of our moors and mountains; but instead of being low-growing or creeping plants, like their modern representatives, they shot up into trees, sometimes 50 feet or more in height.. Equisetaceæ abounded in the Carboniferous swamps, the most frequent genus being Calamites, the jointed and finely-ribbed stems of which are frequent fossils in the sandstones and shales (Fig. 143, a). This plant probably grew in dense thickets in the sandy and muddy lagoons, and bore as its foliage slim branches, with whorls of pointed leaves set round the joints (Asterophyllites, Fig. 143, 6). The Sigillarioids were among the most abundant, and, at the same time, most puzzling members of the Carboniferous flora. They do not appear to have any close modern allies, and their place in the botanical scale has been a subject of much controversy. The stem of these trees, sometimes reaching a height of 50 feet or more, was fluted, each of the parallel ribs being marked by a row of leaf-scars, hence the name Sigillaria, from the seal-like impressions of the scars (Fig. 144). These surface-markings disappeared as the

tree grew, and in the lower part of the trunk
they passed down into the pitted and
tubercular surface characteristic of the roots
(Stigmaria), still SO abundant in their
position of growth in fire-clay, and also as
drifted broken specimens in sandstones and
shales. Another plant that took a prominent
part in the Carboniferous flora was that
named Cordaites (Fig. 145). Its true
botanical place is still matter of dispute ;
some writers placing it with the lycopods,
others with the cycads, or even among the
conifers. It bore parallel - veined leaves
somewhat like those of a yucca, which, when
they fell off, left prominent scars on the
stem, and it also carried spikes or buds
(Carpolithes, Fig. 145). All the plants now
enumerated probably grew on the lower
grounds and swamps. But on the higher FIG. 142.
and drier tracts of the interior there grew

Carboniferous

Lycopod (Lepidodendron

Sternbergii, 1).

araucarian pines (Dadoxylon, Araucarioxylon), the trunks of which, swept down by floods, were imbedded in some of the sands of the time and now appear petrified in the sandstones.

While the terrestrial vegetation of the Carboniferous period has been so abundantly entombed, the fauna of the land has been but scantily preserved. That air-breathers existed, however, has been made known by the finding of specimens of scorpions, myriapods, true insects, and amphibians. Within the last few years vast numbers of the remains of scorpions have been discovered in the Carboniferous rocks of Scotland. These ancient forms (Eoscorpius) presented a remarkably close resemblance to the living scorpion, and so well have they been preserved among the shales that even the minutest parts of their structure can be recognised. They possessed stings like their modern descendants, whence we may infer the presence of other forms of life which they killed The

T

Carboniferous woodlands had plant-eating millipedes, and their silence was broken by the hum of insect-life; for ancestral forms

FIG. 143. Carboniferous Equisetaceous Plants. (a) Calamites Lindleyi (=C. Mougeoti, Lindl., 1); (b) Asterophyllites densifolius ().

of dragon-flies (Libellula), May-flies (Ephemerida), stone-flies (Perlida), white-ants (Termida), cockroaches (Blattida), spectre

FIG, 144. Sigillaria with Stigmaria roots (much reduced).

insects (Phasmida), crickets (Gryllida), locusts (Acrydiida), and curious transitional forms between modern types that are quite distinct have been detected, chiefly among the shales and coals of the Coal-measures. Some of these insects attained a great size; a single wing of one of them (Megaptilus) must have measured between 7 and 8 inches in length. While detached wings and more or less complete bodies have been found as rare and precious discoveries in many coal-fields in Europe and America, it is at Commentry in France that remains of insects have been met with in largest numbers-no fewer than 1300 specimens having there been disinterred, most of them admirably preserved. In the interior of decaying trees early forms of land-snails lived, having a

FIG. 145. Cordaites alloidius (), with Carpolithes attached.

striking resemblance to some kinds that are still to be found in our present woodlands (Puра).

The lagoons in which the coal-growths flourished were tenanted by numerous forms of animal life. Among these were various mussel-like molluscs (Anthracomya, Fig. 154, Anthracosia), which were possibly restricted to fresh water. But wherever the seawater penetrated, it carried some of its characteristic life with it, particularly Lingula, Discina, Aviculopecten, Goniatites, and other marine shells. The fishes of the lagoons were chiefly ganoids (Megalichthys, Rhizodus, Fig. 158, Cheirodus, Strepsodus, etc.) But some of the rays and sharks from the sea made their way into these waters, for their spines are occasionally found among the coal-seams and shales (Gyracanthus, Pleuracanthus, Fig. 158). That the larger fishes lived upon the smaller ones is shown by a curious and interesting piece of evidence. Many of the shales are full of small oblong bodies which contain in their interior the