The World Before the Deluge

OLD RED SANDSTONE AND DEVONIAN PERIOD. 12g

into: I. Conglomerate; 2. Brown stone, with Eurypierus; 3. Marl and cornstones, with irregular courses of concrete limestone, in which are spines of Fishes and remains of Ccphalaspis and Ptcraspis; 4. Thin olive-coloured shales and sandstone, intercalated with beds of red marl, containing Ccphalaspis and Auchenaspis. In Scotland, south of the Grampians, a yellow sandstone occupies the base of the system; conglomerate, red shales, sandstone and cornstones, containing Holoptychius and Ccphalaspis^ and the Arbroath paving-stone, c ontaining what Agassiz recognised as a huge Crustacean.

Some of the phenomena connected with the older rocks of Devonshire are difficult to unravel. The Devonian, it is now understood, is the equivalent, in another area, of the Old Red Sandstone, and in Cornwall and Devonshire lie directly on the Silurian strata, while elsewhere the fossils of the Upper Silurian are almost identical _ with those in the Devonian beds. The late Professor y^. 36.— Trinu- Jukes, with some other geologists, was of opinion that cieus Lioydu. the Devonian rocks of Devonshire only represented ^" ^^ ° ^s^-the Old Red Sandstone of Scotland and South Wales in part; the Upper Devonian rocks lying between the acknowledged Old Red Sandstone and the Culm-measures being the representatives of the lower carboniferous rocks of Ireland.

Mr. Etheridge, on the other hand, in an elaborate memoir upon the same subject, has endeavoured to prove that the Devonian and Old Red Sandstone, though contemporaneous in point of time, were deposited in different areas and under widely different conditions — the one strictly marine, the other altogether fresh-water — or, perhaps, partly fresh-water and parUy estuarine. This supposition is strongly supported by his researches into the mollusca of the Devonian system, and also by the fish-remains of the Devonian and Old Red Sandstone of Scotland and the West of England and Wales.* The difficulty of drawing a sharply-defined line of demarcation between different systems is sufficient to dispel the idea which has sometimes been entertained that special faiince were created and annihilated in the mass at the close of each epoch. There was no close: each epoch disappears or merges into that which succeeds it, and with it the animals belonging to it, much as we have seen them disappear from our own fauna almost within recent times.

• For fuller details on this subject, see J- B. Jukes' " Manual of Geology," 3rd ed., p. 762. Also, R. Etheridge, Quart. Journ. Geol. Soc.y vol. 23, p. 251.

CARBONIFEROUS PERIOD.

In the history of our globe the Carboniferous period succeeds to the Devonian. It is in the formations of this latter epoch that we find the fossil fuel which has done so much to enrich and civilise the world in our own age. This period divides itself into two great sub-periods: I. The Coal-measures; and 2. The Carhofiiferous Limestone. The first, a period which gave rise to the great deposits of coal; the second, to most important marine deposits, most frequently underlying the coal-fields in England, Belgium, France, and America.

The limestone-mountains which form the base of the whole system, attain in places, according to Professor Phillips, a thickness of 2,500 feet. They are of marine origin, as is apparent by the multitude of fossils they contain of Zoophytes, Radiata, Cephalopoda, and Fishes. But the chief characteristic of this epoch is its strictly terrestrial flora — remains of plants now become as common as they were rare in all previous formations, announcing a great increase of dry land. In older geological times the present site of our island was covered by a sea of unlimited extent; we now approach a time when it was a forest, or, ^rather, an innumerable group of islands, and marshes covered with forests, which spread over the surface of the clusters of islands which thickly studded the sea of the period.

The monuments of this era of profuse vegetation reveal themselves in the precious Coal-measures of England and Scotland. These give us some idea of the rich verdure which covered the surface of the earth, newly risen from the bosom of its parent waves. It was the paradise of terrestrial vegetation. The grand Sigillaria, the Stigmaria, and other fern-like plants, were especially typical of this age, and formed the woods, which were left to grow undisturbed; for as yet no living Mammals seem to have appeared; everything indicates a uniformly warm, humid temperature, the only climate in which the gigantic ferns of the Coal-measures could have attained their magnitude. In Fig. 37 the reader has a restoration of the arborescent and herbaceous Ferns

CARBONIFEROUS PERIOD.

f^'g- 37- — Fcnis rcbtorcd. i and 2. Arborescent Ferns. 3 and 4. Herbaceous Fems.

of the period. Conifers have been found of this period with concentric rings, but these rings are more slightly marked than in existing

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trees of the same family, from which it is reasonable to assume that the seasonal changes were less marked than they are with us.

Everything announces that the time occupied in the deposition of the Carboniferous Limestone was one of vast duration. Professor Phillips calculates that, at the ordinary rate of progress, it would require 122,400 years to produce only sixty feet of coal. Geologists believe, moreover, that the upper coal-measures, where bed has been deposited upon bed, for ages upon ages, were accumulated under conditions of comparative tranquillity, but that the end of this period was marked by violent convulsions — by ruptures of the terrestrial crust, when the carboniferous rocks were upturned, contorted, dislocated by faults, and subsequently partially denuded, and thus appear now in depressions or basin-shaped concavities; and that upon this deranged and disturbed foundation a fourth geological system, called Permian, was constructed. The fundamental character of the period we are about to study is the immense development of a vegetation which then covered much of the globe. The great thickness of the rocks which now represent the period in question, the variety of changes which are observed in these rocks wherever they are met with, lead to the conclusion that

this phase in the Earth's history involved a long succession of time.

Coal, as we shall find, is composed of the mineralised remains of the vegetation which flourished in remote ages of the world. Buried under an enormous thickness of rocks, it has been preserved to our days, after being modified in its inward nature and external aspect. Having lost a portion of its elementary constituents, it has become transformed into a species of carbon, impregnated with those bituminous substances which are the ordinary products of the slow decomposition ofvegetable matter.

Thus, coal, which supplies our manufactures and our furnaces,, which is the fundamental agent of our productive and economic industry — the coal which warms our houses and furnishes the gas which lights our streets and dwellings — is the substance of the plants which formed the forests, the vegetation, and the marshes of the ancient world, at a period too distant for human chronology to calculate with anything like precision. We shall not say — with some persons, who believe that all in Nature was made with reference to man, and who thus form a very imperfect idea of the vast immensity of creation — that the vegetables of the ancient world have lived and multiplied only, some day, to prepare for man the agents of his economic and industrial occupations. We shall rather direct the attention of our young readers to the powers of modem science, which can thus, after

such a prodigious interval of time, trace the precise origin, and state with the utmost exactness, the genera and species of plants, of which there are now no identical representatives existing on the face of the earth. Let us pause for a moment, and consider the general characters which belonged to our planet during the Carboniferous period. Heat — though not necessarily excessive heat — and extreme humidity-were then the attributes of its atmosphere. The modern allies of the species which formed its vegetation are now only found under the burning latitudes of the tropics; and the enormous dimensions in which we find them in the fossil state prove, on the other hand, that the atmosphere was saturated with moisture. Dr. Livingstone tells us that continual rains, added to intense heat, are the climatic characteristic of Equatorial Africa, where the vigorous and tufted vegetation flourishes which is so delightful to the eye.

It is a remarkable circumstance that conditions of equable and warm climate, combined with humidity, do not seem to have been limited to any one part of the globe, but the temperature of the whole globe seems to have been nearly the same in very different latitudes. From the Equatorial regions up to Melville Island, in the Arctic Ocean, where in our days eternal frost prevails — from Spitzbergen to the centre of Africa, the carboniferous flora is identically the same. When nearly the same plants are found in Greenland and Guinea; when the same species, now extinct, are met with of equal development at the equator as at the pole, we cannot but admit that at this epoch the temperature of the globe was nearly alike every^vhere. What we

now call climate woi'^ unknown in these geological times. There seems" to have been then only one climate over the whole globe. It was at a subsequent period, that is, in later Tertiary times, that the cold began to make itself felt at the terrestrial poles. Whence, then, proceeded this general superficial warmth, which we now regard with so much surprise? It was a consequence of the greater or nearer influence of the interior heat of the globe. The earth was still so hot in itself, that the heat which reached it from the sun may have been inappreciable. Another hypothesis, which has been advanced with much less certainty than the preceding, relates to the chemical composition of the air during the Carboniferous period. Seeing the enonnous mass of vegetation which then covered the globe, and extended from one pole to the other; considering, also, the great proportion of carbon and hydrogen which exists in the bituminous matter of coal, it has been thought, and not without reason, that tne atmosphere of the period

might be richer in carbonic acid than the atmosphere of the present day. It has even been thought that the small nmnber of (especially air-breathing) animals, which then lived, might be accounted for by the presence of a greater proportion of carbonic acid gas in the atmosphere than is the case in our own times. This, however, is pure assumption, totally deficient in proot. Nothing proves that the atmosphere of the period in question was richer in carbonic acid than is the case now. Since we are only able, then, to offer vague conjectures on this subject, we cannot profess with any confidence to entertain the opinion that the atmospheric air of the Carboniferous period contained more carbonic acid gas than that which we now breathe. What we can remark, with certainty, as a striking characteristic of the vegetation of the globe during this phase of its history, was the prodigious development which it assumed. The Ferns, which in our days and in our climate, are most commonly only small perennial plants, in the Carboniferous age sometimes presented themselves under lofty and even magnificent forms.

Every one knows those marsh-plants with hollow, channelled, and articulated cylindrical stems; whose joints are furnished with a membranous, denticulated sheath, and which bear the vulgar name of " mare's-tail; " their fructification fomiing a sort of catkin composed of many rings of scales, carrying on their lower surface sacs full of sp07'es or seeds. These humble Equiseta were represented during the Coal-period by herbaceous trees from twenty to thirty feet high and four to six inches in diameter. Their trunks, channelled ^longitudinally, and divided transversely by lines of articulation, have