The World Before the Deluge Part 10

The cla.s.s of Fishes seem to have held the first rank and importance in the Old Red Sandstone _fauna_; but their structure was very different from that of existing fishes: they were provided with a sort of cuira.s.s, and from the nature of the scales were called _Ganoid_ fishes. Numerous fragments of these curious fishes are now found in geological collections; they are of strange forms, some being completely covered with a cuira.s.s of many pieces, and others furnished with wing-like pectoral fins, as in _Pterichthys_.

Let any one picture to himself the surprise he would feel should he, on taking his first lesson in geology, and on first breaking a stone--a pebble, for instance, exhibiting every external sign of a water-worn surface--find, to appropriate Archdeacon Paley's ill.u.s.tration, a watch, or any other delicate piece of mechanism, in its centre. Now, this, thirty years ago, is exactly the kind of surprise that Hugh Miller experienced in the sandstone quarry opened in a lofty wall of cliff overhanging the northern sh.o.r.e of the Moray Frith. He had picked up a nodular ma.s.s of blue Lias-limestone, which he laid open by a stroke of the hammer, when, behold! an exquisitely shaped Ammonite was displayed before him. It is not surprising that henceforth the half-mason, half-sailor, and poet, became a geologist. He sought for information, and found it; he found that the rocks among which he laboured swarmed with the relics of a former age. He pursued his investigations, and found, while working in this zone of strata all around the coast, that a certain cla.s.s of fossils abounded; but that in a higher zone these familiar forms disappeared, and others made their appearance.

He read and learned that in other lands--lands of more recent formation--strange forms of animal life had been discovered; forms which in their turn had disappeared, to be succeeded by others, more in accordance with beings now living. He came to know that he was surrounded, in his native mountains, by the sedimentary deposits of other ages; he became alive to the fact that these grand mountain ranges had been built up grain by grain in the bed of the ocean, and the mountains had been subsequently raised to their present level by the upheaval of one part of its bed, or by the subsidence of another. The young geologist now ceased to wonder that each bed, or series of beds, should contain in its bosom records of its own epoch; it seemed to him as if it had been the object of the Creator to furnish the inquirer with records of His wisdom and power, which could not be misinterpreted.

[Ill.u.s.tration: Fig. 31.--Fishes of the Devonian Epoch. 1. Coccosteus, one-third natural size. 2. Pterichthys, one-fourth natural size. 3.

Cephalaspis, one-fourth natural size.]

Among the Fishes of Old Red Sandstone, the _Coccosteus_ (Fig. 31, No. 1) was only partially cased in a defensive armour; the upper part of the body down to the fins was defended by scales. _Pterichthys_ (No. 2), a strange form, with a very small head, furnished with two powerful paddles, or arms, like wings, and a mouth placed far behind the nose, was entirely covered with scales. The _Cephalaspis_ (No. 3), which has a considerable outward resemblance to some fishes of the present time, was nevertheless mail-clad, only on the anterior part of the body.

Other fishes were provided with no such cuira.s.s, properly so called, but were protected by strong resisting scales, enveloping the whole body.

Such were the _Acanthodes_ (1), the _Climatius_ (2), and the _Diplacanthus_ (3), represented in Fig. 32.

[Ill.u.s.tration: Fig. 32.--Fishes of the Devonian epoch. 1. Acanthodes. 2.

Climatius. 3. Diplacanthus.]

Among the organic beings of the Devonian rocks we find worm-like animals, such as the _Annelides_, protected by an external sh.e.l.l, and which at the present day are probably represented by the _Serpulae_.

Among Crustaceans the _Trilobites_ are still somewhat numerous, especially in the middle rocks of the period. We also find there many different groups of Mollusca, of which the _Brachiopoda_ form more than one-half. We may say of this period that it is the reign of Brachiopoda; in it they a.s.sumed extraordinary forms, and the number of their species was very great. Among the most curious we may instance the enormous _Stringocephalus Burtini_, _Davidsonia Verneuilli_, _Uncites gryphus_, and _Calceola Sandalina_, sh.e.l.ls of singular and fantastic shape, differing entirely from all known forms. Amongst the most characteristic of these Mollusca, _Atrypa reticularis_ (Fig. 33) holds the first rank, with _Spirifera concentrica_, _Leptaena Murchisoni_, and _Productus subaculeatus_. Among the Cephalopoda we have _Clymenia Sedgwickii_ (Fig. 34), including the _Goniat.i.tes_, ill.u.s.trating the Ammonites, which so distinctly characterise the Secondary epoch, but which were only foreshadowed in the Devonian period.

[Ill.u.s.tration: Fig. 33.--Atrypa reticularis.]

[Ill.u.s.tration: Fig. 34.--Clymenia Sedgwickii.]

Among the Radiata of this epoch, the order Crinoidea are abundantly represented. We give as an example _Cupressocrinus cra.s.sus_ (Fig. 35).

The Encrinites, under which name the whole of these animals are sometimes included, lived attached to rocky places and in deep water, as they now do in the Caribbean sea.

The Encrinites, as we have seen, were represented during the Silurian period in a simple genus, _Hemicosmites_, but they greatly increased in numbers in the seas of the Devonian period. They diminish in numbers, as we retire from that geological age; until those forms, which were so numerous and varied in the earliest seas, are now only represented by two genera.

[Ill.u.s.tration: Fig. 35.--Cupressocrinus cra.s.sus.]

The Old Red Sandstone rocks are composed of schists, sandstone, and limestones. The line of demarcation between the Silurian rocks and those which succeed them may be followed, in many places, by the eye; but, on a closer examination, the exact limits of the two systems become more difficult to fix. The beds of the one system pa.s.s into the other by a gradual pa.s.sage, for Nature rarely admits of violent contrasts, and shows few sudden transitions. By-and-by, however, the change becomes very decided, and the contrast between the dark grey ma.s.ses at the base and the superinc.u.mbent yellow and red rocks become sufficiently striking. In fact, the uppermost beds of the Silurian rocks are the pa.s.sage-beds of the overlying system, consisting of flagstones, occasionally reddish, and called in some districts "tile-stones." Over these lie the Old Red Sandstone conglomerate, the Caithness flags, and the great superinc.u.mbent ma.s.s which forms the upper portion of the system. Though less abrupt than the eruptive and Silurian mountains, the Old Red Sandstone scenery is, nevertheless, distinguished by its imposing outline, a.s.suming bold and lofty escarpments in the Vans of Brecon, in Grongar Hill, near Caermarthen, and in the Black Mountain of Monmouths.h.i.+re, in the centre of a landscape which, wood, rock, and river combine to render perfect. But it is in the north of Scotland where this rock a.s.sumes its grandest aspect, wrapping its mantle round the loftiest mountains, and rising out of the sea in rugged and fantastic ma.s.ses, as far north as the Orkneys. In Devon and Cornwall, where the rocks are of a calcareous, and sometimes schistose or slaty character, they are sufficiently extensive to have given a name to the series, which is recognised all over the world.

In Herefords.h.i.+re, Worcesters.h.i.+re, Shrops.h.i.+re, Gloucesters.h.i.+re, and South Wales, the Old Red Sandstone is largely developed, and sometimes attains the thickness of from 8,000 to 10,000 feet, divided into: 1.

Conglomerate; 2. Brown stone, with _Eurypterus_; 3. Marl and cornstones, with irregular courses of concrete limestone, in which are spines of Fishes and remains of _Cephalaspis_ and _Pteraspis_; 4. Thin olive-coloured shales and sandstone, intercalated with beds of red marl, containing _Cephalaspis_ 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 _Cephalaspis_, and the Arbroath paving-stone, containing what Aga.s.siz recognised as a huge Crustacean.

[Ill.u.s.tration: Fig. 36.--Trinucleus Lloydii. (Llandeilo Flags.)]

Some of the phenomena connected with the older rocks of Devons.h.i.+re 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 Devons.h.i.+re 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 Jukes, with some other geologists, was of opinion that the Devonian rocks of Devons.h.i.+re only represented 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 partly 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.[42] 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 _faunae_ were created and annihilated in the ma.s.s 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.

[42] For fuller details on this subject, see J. B. Jukes' "Manual of Geology," 3rd ed., p. 762. Also, R. Etheridge, _Quart. Journ.

Geol. Soc._, 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: 1.

The _Coal-measures_; and 2. The _Carboniferous 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 mult.i.tude 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 cl.u.s.ters 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 of the period. Conifers have been found of this period with concentric rings, but these rings are more slightly marked than in existing trees of the same family, from which it is reasonable to a.s.sume that the seasonal changes were less marked than they are with us.

[Ill.u.s.tration: Fig. 37.--Ferns restored. 1 and 2. Arborescent Ferns. 3 and 4. Herbaceous Ferns.]

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 acc.u.mulated 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 const.i.tuents, it has become transformed into a species of carbon, impregnated with those bituminous substances which are the ordinary products of the slow decomposition of vegetable 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 modern 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 lat.i.tudes 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 circ.u.mstance 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 lat.i.tudes. 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 everywhere. What we now call _climate_ was 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 enormous ma.s.s 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 the 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 number 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 a.s.sumption, totally deficient in proof. 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 a.s.sumed. 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 forming a sort of catkin composed of many rings of scales, carrying on their lower surface sacs full of _spores_ 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 been preserved to us: they bear the name of _Calamites_. The engraving (Fig. 38) represents one of these gigantic mare's-tails, or Calamites, of the Coal-period, restored under the directions of M. Eugene Deslongchamps.

It is represented with its fronds of leaves, and its organs of fructification. They seem to have grown by means of an underground stem, while new buds issued from the ground at intervals, as represented in the engraving.

The _Lycopods_ of our age are humble plants, scarcely a yard in height, and most commonly creepers; but the Lycopodiaceae of the ancient world were trees of eighty or ninety feet in height. It was the _Lepidodendrons_ which filled the forests. Their leaves were sometimes twenty inches long, and their trunks a yard in diameter. Such are the dimensions of some specimens of _Lepidodendron carinatum_ which have been found. Another Lycopod of this period, the _Lomatophloyos cra.s.sicaule_, attained dimensions still more colossal. The _Sigillarias_ sometimes exceeded 100 feet in height. Herbaceous Ferns were also exceedingly abundant, and grew beneath the shade of these gigantic trees. It was the combination of these lofty trees with such shrubs (if we may so call them), which formed the forests of the Carboniferous period. The trunks of two of the gigantic trees, which flourished in the forests of the Carboniferous period, are represented in Figs. 39 and 40, reduced respectively to one-fifth and one-tenth the natural size.

[Ill.u.s.tration: Fig. 38.--Calamite restored. Thirty to forty feet high.]

What could be more surprising than the aspect of this exuberant vegetation!--these immense Sigillarias, which reigned over the forest!

these Lepidodendrons, with flexible and slender stems! these Lomatophloyos, which present themselves as _herbaceous_ trees of gigantic height, furnished with verdant leaflets! these Calamites, forty feet high! these elegant arborescent Ferns, with airy foliage, as finely cut as the most delicate lace! Nothing at the present day can convey to us an idea of the prodigious and immense extent of never-changing verdure which clothed the earth, from pole to pole, under the high temperature which everywhere prevailed over the whole terrestrial globe. In the depths of these inextricable forests parasitic plants were suspended from the trunks of the great trees, in tufts or garlands, like the wild vines of our tropical forests. They were nearly all pretty, fern-like plants--_Sphenopteris_, _Hymenophyllites_, &c.; they attached themselves to the stems of the great trees, like the orchids and _Bromeliaceae_ of our times.

[Ill.u.s.tration: Fig. 39.--Trunk of Calamites. One-fifth natural size.]

[Ill.u.s.tration: Fig. 40.--Trunk of Sigillaria. One-tenth natural size.]

The margin of the waters would also be covered with various plants with light and whorled leaves, belonging, perhaps, to the Dicotyledons; _Annularia fertilis_, _Sphenophyllites_, and _Asterophyllites_.

How this vegetation, so imposing, both on account of the dimensions of the individual trees and the immense s.p.a.ce which they occupied, so splendid in its aspect, and yet so simple in its organisation, must have differed from that which now embellishes the earth and charms our eyes!

It certainly possessed the advantage of size and rapid growth; but how poor it was in species--how uniform in appearance! No flowers yet adorned the foliage or varied the tints of the forests. Eternal verdure clothed the branches of the Ferns, the Lycopods, and Equiseta, which composed to a great extent the vegetation of the age. The forests presented an innumerable collection of individuals, but very few species, and all belonging to the lower types of vegetation. No fruit appeared fit for nourishment; none would seem to have been on the branches. Suffice it to say that few terrestrial animals seem to have existed yet; animal life was apparently almost wholly confined to the sea, while the vegetable kingdom occupied the land, which at a later period was more thickly inhabited by air-breathing animals. Probably a few winged insects (some coleoptera, orthoptera, and neuroptera) gave animation to the air while exhibiting their variegated colours; and it was not impossible but that many pulmoniferous mollusca (such as land-snails) lived at the same time.

But, we might ask, for what eyes, for whose thoughts, for whose wants, did the solitary forests grow? For whom these majestic and extensive shades? For whom these sublime sights? What mysterious beings contemplated these marvels? A question which cannot be solved, and one before which we are overwhelmed, and our powerless reason is silent; its solution rests with Him who said, "Before the world was, I am!"

The vegetation which covered the numerous islands of the Carboniferous sea consisted, then, of Ferns, of Equisetaceae, of Lycopodiaceae, and dicotyledonous Gymnosperms. The Annularia and Sigillariae belong to families of the last-named cla.s.s, which are now completely extinct.

The _Annulariae_ were small plants which floated on the surface of fresh-water lakes and ponds; their leaves were verticillate, that is, arranged in a great number of whorls, at each articulation of the stem with the branches. The _Sigillariae_ were, on the contrary, great trees, consisting of a simple trunk, surmounted with a bunch or panicle of slender drooping leaves, with the bark often channelled, and displaying impressions or scars of the old leaves, which, from their resemblance to a seal, _sigillum_, gave origin to their name. Fig. 41 represents the bark of one of these Sigillariae, which is often met with in coal-mines.