Part 16

Chapter 163,318 wordsPublic domain

The convulsions and disturbances by which the surface of the earth was agitated did not extend, let it be noted, over the whole of its circumference; the effects were partial and local. It would, then, be wrong to affirm, as is asserted by many modern geologists, that the dislocations of the crust and the agitations of the surface of the globe extended to both hemispheres, resulting in the destruction of all living creatures. The Fauna and Flora of the Permian period did not differ essentially from the Fauna and Flora of the Coal-measures, which shows that no general revolution occurred to disturb the entire globe between these two epochs. Here, then, as in all analogous cases, it is unnecessary to recur to any general cataclysm to explain the passage from one epoch to another. Have we not, almost in our our own day, seen certain species of animals die out and disappear, without the least geological revolution? Without speaking of the Beaver, which abounded two centuries ago on the banks of the Rhône, and in the Cévennes, which still lived at Paris in the little river Bièvre in the middle ages, its existence being now unknown in these latitudes, although it is still found in America and other countries, we could cite many examples of animals which have become extinct in times by no means remote from our own. Such are the _Dinornis_ and the _Epyornis_, colossal birds of New Zealand and Madagascar, and the _Dodo_, which lived in the Isle of France in 1626. _Ursus spelæus_, _Cervus Megaceros_, _Bos primigenius_, are species of Bear, Deer, and Ox which were contemporary with man, but have now become extinct. In France we no longer know the gigantic wood-stag, figured by the Romans on their monuments, and which they had brought from England for the fine quality of its flesh. The Erymanthean boar, so widely dispersed during the ancient historical period, no longer exists among our living races, any more than the Crocodiles _lacunosus_ and _laciniatus_ found by Geoffroy St.-Hilaire in the catacombs of ancient Egypt. Many races of animals figured in the mosaics of Palestrina, engraved and painted along with species now actually existing, are no longer found living in our days any more than are the Lions with curly manes, which formerly existed in Syria, and perhaps even in Thessaly and the northern parts of Greece. From what happens in our own time, we may infer what has taken place in times antecedent to the appearance of man; and the idea of successive cataclysms of the globe, must be restrained within bounds. Must we imagine a series of geological revolutions to account for the disappearance of animals which have evidently become extinct in a natural way? What has come to pass in our days, it is reasonable to conclude, may have taken place in the times anterior to the appearance of man.

SECONDARY EPOCH.

During the _Primary Epoch_ our globe would appear to have been chiefly appropriated to beings which lived in the waters--above all, to the Crustaceans and Fishes; during the _Secondary Epoch_ Reptiles seem to have been its prevailing inhabitants. Animals of this class assumed astonishing dimensions, and would seem to have multiplied in a most singular manner; they were, apparently, the kings of the earth. At the same time, however, that the animal kingdom thus developed itself, the vegetation lost much of its importance.

Geologists have agreed among themselves to divide the Secondary epoch into three periods: 1, the _Cretaceous_; 2, the _Jurassic_; 3, the _Triassic_--a division which it is convenient to adopt.

THE TRIASSIC, OR NEW RED PERIOD.

This period has received the name of Triassic because the rocks of which it is composed, which are more fully developed in Germany than either in England or France, were called the Trias (or Triple Group), by German writers, from its division into three groups, as follows, in descending order:--

ENGLAND. FRANCE. GERMANY.

Saliferous and gypseous } Marnes irisées Keuper. 1,000 feet. shales and sandstone }

Wanting { Muschelkalk or Calcaire } Muschelkalk. 600 feet. { coquillier }

Sandstone and quartzose } Grès bigarré Bunter-Sandstein. conglomerate } 1,500 ft.

The following has been shown by Mr. Ed. Hull to be the general succession of the Triassic formation in the midland and north-western counties of England, where it attains its greatest vertical development, thinning away in the direction of the mouth of the Thames:--

NEW RED SANDSTONE.

In this new phase of the revolutions of the globe, the animated beings on its surface differ much from those which belonged to the Primary epoch. The curious Crustaceans which we have described under the name of _Trilobites_ have disappeared; the molluscous Cephalopods and Brachiopods are here few in number, as are the Ganoid and Placoid Fishes, whose existence also seems to have terminated during this period, and vegetation has undergone analogous changes. The cryptogamic plants, which reached their maximum in the Primary epoch, become now less numerous, while the Conifers experienced a certain extension. Some kinds of terrestrial animals have disappeared, but they are replaced by genera as numerous as new. For the first time the Turtle appears in the bosom of the sea, and on the borders of lakes. The Saurian reptiles acquire a great development; they prepare the way for those enormous Saurians, which appear in the following period, whose skeletons present such vast proportions, and such a strange aspect, as to strike with astonishment all who contemplate their gigantic, and, so to speak, awe-inspiring remains.

The _Variegated Sandstone_, or Bunter, contains many vegetable, but few animal, remains, although we constantly find imprints of the footsteps of the Labyrinthodon.

The lowest Bunter formation shows itself in France, in the Pyrenees, around the central plateau in the Var, and upon both flanks of the Vosges mountains. It is represented in south-western and central Germany, in Belgium, in Switzerland, in Sardinia, in Spain, in Poland, in the Tyrol, in Bohemia, in Moravia, and in Russia. M. D’Orbigny states, from his own observation, that it covers vast surfaces in the mountainous regions of Bolivia, in South America. It is recognised in the United States, in Columbia, in the Great Antilles, and in Mexico.

The Bunter in France is reduced to the variegated sandstone, except around the Vosges, in the Var, and the Black Forest, where it is accompanied by the Muschelkalk. In Germany it furnishes building-stone of excellent quality; many great edifices, in particular the cathedrals, so much admired on the Rhine--such, for example, as those of Strasbourg and Fribourg--are constructed of this stone, the sombre tints of which singularly relieve the grandeur and majesty of the Gothic architecture. Whole cities in Germany are built of the brownish-red stones drawn from its mottled sandstone quarries. In England, in Scotland, and in Ireland this formation extends from north to south through the whole length of the country. “This old land,” says Professor Ramsay,[54] “consisted in great part of what we now know as Wales, and the adjacent counties of Hereford, Monmouth, and Shropshire; of part of Devon and Cornwall, Cumberland, the Pennine chain, and all the mountainous parts of Scotland. Around old Wales, and part of Cumberland, and probably all round and over great part of Devon and Cornwall, the New Red Sandstone was deposited. Part, at least, of this oldest of the Secondary rocks was formed of the material of the older Palæozoic strata, that had then risen above the surface of the water. The New Red Sandstone series consists in its lower members of beds of red sandstone and conglomerate, more than 1,000 feet thick, and above them are placed red and green marls, chiefly red, which in Germany are called the Keuper strata, and in England the New Red Marl. These formations range from the mouth of the Mersey, round the borders of Wales, to the estuary of the Severn, eastwards into Warwickshire, and thence northwards into Yorkshire and Northumberland, along the eastern border of the Magnesian Limestone. They also form the bottom of the valley of the Eden, and skirt Cumberland on the west; in the centre of England the unequal hardness of its sub-divisions sometimes giving rise to minor escarpments, overlooking plains and undulating grounds of softer strata.”

[54] “The Physical Geography and Geology of Great Britain,” 2nd ed., p. 60.

“Different members of the group rest in England, in some region or other,” says Lyell, “on almost every principal member of the Palæozoic series, on Cambrian, Silurian, Devonian, Carboniferous, and Permian rocks; and there is evidence everywhere of disturbance, contortion, partial upheaval into land, and vast denudations which the older rocks underwent before and during the deposition of the successive strata of the New Red Sandstone group.” (“Elements of Geology,” p. 439.)

The _Muschelkalk_ consists of beds of compact limestone, often greyish, sometimes black, alternating with marl and clay, and commonly containing such numbers of shells that the name of shelly limestone (_Muschelkalk_) has been given to the formation by the Germans. The beds are sometimes magnesian, especially in the lower strata, which contain deposits of gypsum and rock-salt.

The seas of this sub-period, which is named after the innumerable masses of shells inclosed in the rocks which it represents, included, besides great numbers of Mollusca, Saurian Reptiles of twelve different genera, some Turtles, and six new genera of Fishes clothed with a cuirass. Let us pause at the Mollusca which peopled the Triassic seas.

Among the shells characteristic of the Muschelkalk period, we mention _Natica Gaillardoti_, _Rostellaria antiqua_, _Lima striata_, _Avicula socialis_, _Terebratula vulgaris_, _Turbonilla dubia_, _Myophoria vulgaris_, _Nautilus hexagonalis_, and _Ceratites nodosus_. The _Ceratites_, of which a species is here represented (Fig. 81), form a genus closely allied to the _Ammonites_, which seem to have played such an important part in the ancient seas, but which have no existence in those of our era, either in species or even in genus. This Ceratite is found in the Muschelkalk of Germany, a formation which has no equivalent in England, but which is a compact greyish limestone underlying the saliferous rocks in Germany, and including beds of dolomite with gypsum and rock-salt.

The _Mytilus_ or _Mussel_, which properly belonged to this age, are acephalous (or headless) Molluscs with elongated triangular shells, of which there are many species found in our existing seas. _Lima_, _Myophoria_, _Posidonia_, and _Avicula_, are acephalous Molluscs of the same period. The two genera _Natica_ and _Rostellaria_ belong to the Gasteropoda, and are abundant in the Muschelkalk in France, Germany, and Poland.

Among the Echinoderms belonging to this period may be mentioned _Encrinus moniliformis_ and _E. liliiformis_, or _lily encrinite_ (Fig. 82), whose remains, constituting in some localities whole beds of rock, show the slow progress with which this zoophyte formed beds of limestone in the clear seas of the period. To these may be added, among the Mollusca, _Avicula subcostata_ and _Myophoria vulgaris_.

In the Muschelkalk are found the skull and teeth of _Placodus gigas_, a reptile which was originally placed by Agassiz among the class of Fishes; but more perfect specimens have satisfied Professor Owen that it was a Saurian Reptile.

It may be added, that the presence of a few genera, peculiar to the Primary epoch, which entirely disappeared during the sub-period, and the appearance for the first time of some other animals peculiar to the Jurassic period, give to the Muschelkalk fauna the appearance of being one of passage from one period to the other.

The seas, then, contained a few Reptiles, probably inhabitants of the banks of rivers, as _Phytosaurus_, _Capitosaurus_, &c., and sundry Fishes, as _Sphœrodus_ and _Pycnodus_. In this sub-period we shall say nothing of the Land-Turtles, which for the first time now appear; but, we should note, that at the Bunter period a gigantic Reptile appears, on which the opinions of geologists were for a long while at variance. In the argillaceous rocks of the Muschelkalk period imprints of the foot of some animal were discovered in the sandstones of Storeton Hill, in Cheshire, and in the New Red Sandstone of parts of Warwickshire, as well as in Thuringia, and Hesseburg in Saxony, which very much resembled the impression that might be made in soft clay by the outstretched fingers and thumb of a human hand. These traces were made by a species of Reptile furnished with four feet, the two fore-feet being much broader than the hinder two. The head, pelvis, and scapula only of this strange-looking animal have been found, but these are considered to have belonged to a gigantic air-breathing reptile closely connected with the Batrachians. It is thought that the head was not naked, but protected by a bony cushion; that its jaws were armed with conical teeth, of great strength and of a complicated structure. This curious and uncouth-looking creature, of which the woodcut Fig. 83 is a restoration, has been named the _Cheirotherium_, or _Labyrinthodon_, from the complicated arrangement of the cementing layer of the teeth. (See also Fig. 1, p. 12.)

Another Reptile of great dimensions--which would seem to have been intended to prepare the way for the appearance of the enormous Saurians which present themselves in the Jurassic period--was the _Nothosaurus_, a species of marine Crocodile, of which a restoration has been attempted in PLATE XIII. opposite.

It has been supposed, from certain impressions which appear in the Keuper sandstones of the Connecticut river in North America, that Birds made their appearance in the period which now occupies us; the flags on which these occur by thousands show the tracks of an animal of great size (some 20 inches long and 4½ feet apart), presenting the impression of three toes, like some of the Struthionidæ or Ostriches, accompanied by raindrops. No remains of the skeletons of birds have been met with in rocks of this period, and the footprints in question are all that can be alleged in support of the hypothesis.

M. Ad. Brongniart places the commencement of dicotyledonous gymnosperm plants in this age. The characteristics of this Flora consist in numerous Ferns, constituting genera now extinct, such as _Anomopteris_ and _Crematopteris_. The true _Equiseta_ are rare in it. The Calamites, or, rather, the _Calamodendra_, abound. The gymnosperms are represented by the genera _Conifer_, _Voltzia_, and _Haidingera_, of which both species and individuals are very numerous in the formation of this period.

Among the species of plants which characterise this formation, we may mention _Neuropteris elegans_, _Calamites arenaceus_, _Voltzia heterophylla_, _Haidingera speciosa_. The _Haidingera_, belonging to the tribe of _Abietinæ_, were plants with large leaves, analogous to those of our _Damara_, growing close together, and nearly imbricated, as in the _Araucaria_. Their fruit, which are cones with rounded scales, are imbricated, and have only a single seed, thus bearing out the strong resemblance which has been traced between these fossil plants, and the Damara.

The _Voltzias_ (Fig. 84), which seem to have formed the greater part of the forests were a genus of Cupressinaceæ, now extinct, which are well characterised among the fossil Conifers of the period. The alternate spiral leaves, forming five to eight rows sessile, that is, sitting close to the branch and drooping, have much in them analogous to the _Cryptomerias_. Their fruit was an oblong cone with scales, loosely imbricated, cuneiform or wedge-shaped, and, commonly, composed of from three to five obtuse lobes. In Fig. 84 we have a part of the stem, a branch with leaves and cone. In his “Botanic Geography,” M. Lecoq thus describes the vegetation of the ancient world in the first period of the Triassic age: “While the variegated sandstone and mottled clays were being slowly deposited in regular beds by the waters, magnificent Ferns still exhibited their light and elegantly-carved leaves. Divers _Protopteris_ and majestic _Neuropteris_ associated themselves in extensive forests, where vegetated also the _Crematopteris typica_ of Schimper, the _Anomopteris Mongeotii_ of Brongniart, and the pretty _Trichomanites myriophyllum_ (Göppert). The Conifers of this epoch attain a very considerable development, and would form graceful forests of green trees. Elegant monocotyledons, representing the forms of tropical countries, seem to show themselves for the first time, the _Yuccites Vogesiacus_ of Schimper constituted groups at once thickly serried and of great extent.

“A family, hitherto doubtful, appears under the elegant form of _Nilssonia Hogardi_, Schimp.; _Ctenis Hogardi_, Brongn. It is still seen in the _Zamites Vogesiacus_, Schimp.; and the group of the Cycads sharing at once in the organisation of the Conifers and the elegance of the Palms, now decorate the earth, which reveals in these new forms its vast fecundity. (See Fig. 72, p. 168.)

“Of the herbaceous plants which formed the undergrowth of the forests, or which luxuriated in its cool marshes, the most remarkable is the _Ætheophyllum speciosum_, Schimp. Their organisation approximates to the Lycopodiaceæ and Thyphaceæ, the _Ætheophyllum stipulare_, Brongn., and the curious _Schizoneura paradoxa_, Schimp. Thus we can trace the commencement of the reign of the Dicotyledons with naked seeds, which afterwards become so widely disseminated, in a few Angiosperms, composed principally of two families, the Conifers and Cycadeaceæ, still represented in the existing vegetation. The former, very abundant at first, associated themselves with the cellular Cryptogams, which still abound, although they are decreasing, then with the Cycadeaceæ, which present themselves slowly, but will soon be observed to take a large part in the brilliant harmonies of the vegetable kingdom.”

The engraving at page 191 (PLATE XIII.) gives an idealised picture of the plants and animals of the period. The reader must imagine himself transported to the shores of the Muschelkalk sea at a moment when its waves are agitated by a violent but passing storm. The reflux of the tide exposes some of the aquatic animals of the period. Some fine Encrinites are seen, with their long flexible stems, and a few Mytili and Terebratulæ. The Reptile which occupies the rocks, and prepares to throw itself on its prey, is the _Nothosaurus_. Not far from it are other reptiles, its congeners, but of a smaller species. Upon the dune on the shore is a fine group of the trees of the period, that is, of _Haidingeras_, with large trunks, with drooping branches and foliage, of which the cedars of our own age give some idea. The elegant _Voltzias_ are seen in the second plane of this curtain of verdure. The Reptiles which lived in these primitive forests, and which would give to it so strange a character, are represented by the _Labyrinthodon_, which descends towards the sea on the right, leaving upon the sandy shore those curious tracks which have been so wonderfully preserved to our days.

The footprints of the reptilian animals of this period prove that they walked over moist surfaces; and, if these surfaces had been simply left by a retiring tide, they would generally have been obliterated by the returning flood, in the same manner that is seen every day on our own sandy shores. It seems more likely that the surfaces, on which fossil footprints are now found, were left bare by the summer evaporation of a lake; that these surfaces were afterwards dried by the sun, and the footprints hardened, so as to ensure their preservation, before the rising waters brought by flooded muddy rivers again submerged the low flat shores and deposited new layers of salt, just as they do at the present day round the Dead Sea and the Salt Lake of Utah.

KEUPER SUB-PERIOD.

The formation which characterises the Keuper, or saliferous period, is of moderate extent, and derives the latter name from the salt deposits it contains.