Chapter VII: Part 7

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There is indisputable evidence that the Permian ocean covered an immense area of the globe. In the Permian period this ocean extended from Ireland to the Ural mountains, and probably to Spitzbergen, with its northern boundary defined by the Carboniferous, Devonian, Silurian, and Igneous regions of Scotland, Scandinavia, and Northern Russia; and its southern boundaries apparently stretching far into the south of Europe (King). The chain of the Vosges, stretching across Rhenish Bavaria, the Grand Duchy of Baden, as far as Saxony and Silesia, would be under water. They would communicate with the ocean, which covered all the midland and western counties of England and part of Russia. In other parts of Europe the continent has varied very little since the preceding Devonian and Carboniferous ages. In France the central plateaux would form a great island, which extended towards the south, probably as far as the foot of the Pyrenees; another island would consist of the mass of Brittany. In Russia the continent would have extended itself considerably towards the east; finally, it is probable that, at the end of the Carboniferous period, the Belgian continent would stretch from the Departments of the Pas-de-Calais and Du Nord, in France, and would extend up to and beyond the Rhine.

In England, the Silurian archipelago, now filled up and occupied by deposits of the Devonian and Carboniferous systems, would be covered with carboniferous vegetation; dry land would now extend, almost without interruption, from Cape Wrath to the Land’s End; but, on its eastern shore, the great mass of the region now lying less than three degrees west of Greenwich would, in a general sense, be under water, or form islands rising out of the sea. Alphonse Esquiros thus eloquently closes the chapter of his work in which he treats of this formation in England: “We have seen seas, vast watery deserts, become populated; we have seen the birth of the first land and its increase; ages succeeding each other, and Nature in its progress advancing among ruins; the ancient inhabitants of the sea, or at least their spoils, have been raised to the summit of lofty mountains. In the midst of these vast cemeteries of the primitive world we have met with the remains of millions of beings; entire species sacrificed to the development of life. Here terminates the first mass of facts constituting the infancy of the British Islands. But great changes are still to produce themselves on this portion of the earth’s surface.”

Having thus described the _Primary Epoch_, it may be useful, before entering on what is termed by geologists the _Secondary Epoch_, to glance backwards at the facts which we have had under consideration.

In this Primary period plants and animals appear for the first time upon the surface of the cooling globe. We have said that the seas of the epoch were then dominated by the fishes known as _Ganoids_ (from γανος, _glitter_), from the brilliant polish of the enamelled scales which covered their bodies, sometimes in a very complicated and fantastic manner; the _Trilobites_ are curious Crustaceans, which appear and altogether disappear in the Primary epoch; an immense quantity of Mollusca, Cephalopoda, and Brachiopoda; the _Encrinites_, animals of curious organisation, which form some of the most graceful ornaments of our Palæontological collections.

But, among all these beings, those which prevailed--those which were truly the kings of the organic world--were the Fishes, and, above all, the _Ganoids_, which have left no animated being behind them of similar organisation. Furnished with a sort of defensive armour, they seem to have received from Nature this means of protection to ensure their existence, and permit them to triumph over all the influences which threatened them with destruction in the seas of the ancient world.

In the Primary epoch the living creation was in its infancy. No Mammals then roamed the forests; no bird had yet displayed its wings. Without Mammals, therefore, there was no maternal instinct; none of the soft affections which are, with animals, as it were, the precursors of intelligence. Without birds, also, there could be no songs in the air. Fishes, Mollusca, and Crustacea silently ploughed their way in the depths of the sea, and the immovable Crinoid lived there. On the land we only find a few marsh-frequenting Reptiles, of small size--forerunners of those monstrous Saurians which make their appearance in the Secondary epoch.

The vegetation of the Primary epoch is chiefly of inferior organisation. With a few plants of a higher order, that is to say, Dicotyledons, Calamites, Sigillarias, it was the Cryptogamia (also several species of Ferns, the Lepidodendra, Lycopodiaceæ, and the Equisetaceæ, and some doubtfully allied forms, termed Nöggerathia), then at their maximum of development, which formed the great mass of the vegetation.

Let us also consider, in this short analysis, that during the epoch under consideration, what we call _climate_ may not have existed. The same animals and the same plants then lived in the polar regions as at the equator. Since we find, in the Primary formations of the icy regions of Spitzbergen and Melville Islands, nearly the same fossils which we meet with in these same rocks in the torrid zone, we must conclude that the temperature at this epoch was uniform all over the globe, and that the heat of the earth itself was sufficiently high to render inappreciable the calorific influence of the sun.

During this same period the progressive cooling of the earth occasioned frequent ruptures and dislocations of the ground; the terrestrial crust, in opening, afforded a passage for the rocks called _igneous_, such as granite, afterwards to the porphyries and syenites, which poured slowly through these immense fissures, and formed mountains of granite and porphyry, or simple clefts, which subsequently became filled with oxides and metallic sulphides, forming what are now designated metallic veins. The great mountain-range of Ben Nevis offers a striking example of the first of these phenomena; through the granite base a distinct natural section can be traced of porphyry ejected through the granite, and of syenite through the porphyry. These geological commotions (which occasioned, not over the whole extent of the earth, but only in certain places, great movements of the surface) would appear to have been more frequent at the close of the Primary epoch; during the interval which forms the passage between the Primary and Secondary epochs; that is to say, between the Permian and the Triassic periods. The phenomena of eruptions, and the character of the rocks called eruptive, are treated of in a former chapter.

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.

These rocks consist of a vast number of argillaceous and marly beds, variously coloured, but chiefly red, with tints of yellow and green. These are the colours which gave the name of _variegatea_ (Poikilitic) to the series. The beds of red marl often alternate with sandstones, which are also variegated in colour. As subordinate rocks, we find in this formation some deposits of a poor pyritic coal and of gypsum. But what especially characterises the formation are the important deposits of rock-salt which are included in it. The saliferous beds, often twenty-five to forty feet thick, alternate with beds of clay, the whole attaining a thickness of 160 yards. In Germany in Würtemberg, in France at Vic, at Dieuze, and at Château-Salins, the rock-salt of the saliferous formation has become an important branch of industry. In the Jura, salt is extracted from the water charged with chlorides, which issues from this formation.

Some of these deposits are situated at great depths, and cannot be reached without very considerable labour. The salt-mines of Wieliczka, in Poland, for example, can be procured on the surface, or by galleries of little depth, because the deposit belongs to the Tertiary period; but the deposits of salt, in the Triassic age, lie so much deeper, as to be only approachable by a regular process of mining by galleries, and the ordinary mode of reaching the salt is by digging pits, which are afterwards filled with water. This water, charged with the salt, is then pumped up into troughs, where it is evaporated, and the crystallised mineral obtained.

What is the origin of the great deposits of marine salt which occur in this formation, and which always alternate with thin beds of clay or marl? We can only attribute them to the evaporation of vast quantities of sea-water introduced into depressions, cavities, or gulfs, which the sandy dunes afterwards separated from the great open sea. In PLATE XIV. an attempt is made to represent the natural fact, which must have been of frequent recurrence during the saliferous period, to form the considerable masses of rock-salt which are now found in the rocks of the period. On the right is the sea, with a dune of considerable extent, separating it from a tranquil basin of smooth water. At intervals, and from various causes, the sea, clearing the dune, enters and fills the basin. We may even suppose that a gulf exists here which, at one time, communicated with the sea; the winds having raised this sandy dune, the gulf becomes transformed, by degrees, into a basin or back-water, closed on all sides. However that may be, it is pretty certain that if the waters of the sea were once shut up in this basin, with an argillaceous bottom and without any opening, evaporation from the effects of solar heat would take place, and a bed of salt would be the result of this evaporation, mixed with other mineral salts which accompany chloride of sodium in sea-water, such as sulphate of magnesia, chloride of potassium, &c. This bed of salt, left by the evaporation of the water, would soon receive an argillaceous covering from the clay and silt suspended in the muddy water of the basin, thus forming a first alternation of salt and of clay or marl. The sea making fresh breaches across the barriers, the same process took place with a similar result, until the basin was filled up. By the regular and tranquil repetition of this phenomenon, continued during a long succession of ages, this abundant deposit of rock-salt has been formed, which occupies so important a position in the Secondary rocks.

There is in the delta of the Indus a singular region, called the Runn of Cutch, which extends over an area of 7,000 square miles, which is neither land nor sea, but is under water during the monsoons, and in the dry season is incrusted, here and there, with salt about an inch thick, the result of evaporation. Dry land has been largely increased here, during the present century, by subsidence of the waters and upheavals by earthquakes. “That successive layers of salt may have been thrown down one upon the other on many thousand square miles, in such a region, is undeniable,” says Lyell. “The supply of brine from the ocean is as inexhaustible as the supply of heat from the sun. The only assumption required to enable us to explain the great thickness of salt in such an area, is the continuance for an indefinite period of a subsidence, the country preserving all the time a general approach to horizontally.” The observations of Mr. Darwin on the atolls of the Pacific, prove that such a continuous subsidence is probable. Hugh Miller, after ably discussing various spots of earth where, as in the Runn of Cutch, evaporation and deposit take place, adds: “If we suppose that, instead of a barrier of lava, sand-bars were raised by the surf on a flat arenaceous coast, during a slow and equable sinking of the surface, the waters of the outer gulf might occasionally topple over the bar and supply a fresh brine when the first stock had been exhausted by evaporation.”

Professor Ramsay has pointed out that both the sandstones and marls of the Triassic epoch were formed in lakes. In the latter part of this epoch, he is of opinion, that the Keuper marls of the British Isles were deposited in a large lake, or lakes, which were fresh or brackish at first, but afterwards salt and without outlets to the sea; and that the same was occasionally the case with regard to other portions of northern Europe and its adjoining seas.

By the silting up of such lakes with sediment, and the gradual evaporation of their waters under favourable conditions, such as increased heat and diminished rainfall--where the lakes might cease to have an outflow into the sea and the loss of water by evaporation would exceed the amount flowing into them--the salt or salts contained in solution would, by degrees, become concentrated and finally precipitated. In this way the great deposits of rock-salt and gypsum, common in the Keuper formation, may be accounted for.

Subsequently, by increase of rainfall or decrease of heat, and sinking of the district, the waters became comparatively less salt again; and a recurrence of such conditions lasted until the close of the Keuper period, when a partial influx of the sea took place, and the Rhætic beds of England were deposited.

The red colour of the New Red Sandstones and marls is caused by peroxide of iron, which may also have been carried into the lakes in solution, as a carbonate, and afterwards converted into peroxide by contact with air, and precipitated as a thin pellicle upon the sedimentary grains of sandy mud, of which the Triassic beds more or less consist. Professor Ramsay further considers that all the red-coloured strata of England, including the Permian, Old Red Sandstone, and even the Old Cambrian formation, were deposited in lakes or inland waters.[55]

[55] A. C. Ramsay, _Quart. Jour. Geol. Soc._, vol. 27, p. 191.

* * * * *

There is little to be said of the animals which belong to the Saliferous period. They are nearly the same as those of the Muschelkalk, &c.

Among the most abundant of the shells belonging to the upper Trias, in all the countries where it has been examined, are the _Avicula, Cardium_, and _Pecten_, one of which is given in Fig. 85. Foraminifera are numerous in the Keuper marls. The remains of land-plants, and the peculiarities of some of the reptiles of the Keuper period, tend to confirm the opinion of Professor Ramsay, that the strata were deposited in inland salt-lakes.

In the Keuper period the islands and continents presented few mountains; they were intersected here and there by large lakes, with flat and uniform banks. The vegetation on their shores was very abundant, and we possess its remains in great numbers. The Keuper Flora was very analogous to those of the Lias and Oolite, and consisted of Ferns, Equisetaceæ, Cycads, Conifers, and a few plants, which M. Ad. Brongniart classes among the dubious monocotyledons. Among the Ferns may be quoted many species of _Sphenopteris_ or _Pecopteris_. Among them, _Pecopteris Stuttgartiensis_, a tree with channelled trunk, which rises to a considerable height without throwing out branches, and terminates in a crown of leaves finely cut and with long petioles; the _Equisetites columnaris_, a great Equisetum analogous to the horse-tails of our age, but of infinitely larger dimensions, its long fluted trunk, surmounted by an elongated fructification, towering over all the other trees of the marshy soil.

The _Pterophyllum Jägeri_ and _P. Münsteri_ represented the Cycads, the _Taxodites Münsterianus_ represented the Conifers, and, finally, the trunk of the Calamites was covered with a creeping plant, having elliptical leaves, with a re-curving nervature borne upon its long petioles, and the fruit disposed in bunches; this is the _Preissleria antiqua_, a doubtful monocotyledon, according to Brongniart, but M. Unger places it in the family of _Smilax_, of which it will thus be the earliest representative. The same botanist classes with the canes a marsh-plant very common in this period, the _Palæoxyris Münsteri_, which Brongniart classes with the _Preissleria_ among his doubtful Monocotyledons.

The vegetation of the latter part of the Triassic period is thus characterised by Lecoq, in his “Botanical Geography”: “The cellular _Cryptogameæ_ predominate in this as they do in the Carboniferous epoch, but the species have changed, and many of the genera also are different; the _Cladephlebis_, the _Sphenopteris_, the _Coniopteris_, and _Pecopteris_ predominate over the others in the number of species. The Equisetaceæ are more developed than in any other formation. One of the finest species, the _Calamites arenaceus_ of Brongniart, must have formed great forests. The fluted trunks resemble immense columns, terminating at the summit in leafy branches, disposed in graceful verticillated tufts, foreshadowing the elegant forms of _Equisetum sylvaticum_. Growing alongside of these were a curious Equisetum and singular Equisetites, a species of which last, _E. columnaris_, raised its herbaceous stem, with its sterile articulations, to a great height.

“What a singular aspect these ancient rocks would present, if we add to them the forest-trees _Pterophyllum_ and the _Zamites_ of the fine family of Cycadeaceæ, and the Conifers, which seem to have made their appearance in the humid soil at the same time!

“It is during this epoch, while yet under the reign of the dicotyledonous angiosperms, that we discover the first true monocotyledons. The _Preissleria antiqua_, with its long petals, drooping and creeping round the old trunks, its bunches of bright-coloured berries like the _Smilax_ of our own age, to which family it appears to have belonged. Besides, the Triassic marshes gave birth to tufts of _Palæoxyris Münsteri_, a cane-like species of the Gramineæ, which, in all probability, cheered the otherwise gloomy shore.

“During this long period the earth preserved its primitive vegetation; new forms are slowly introduced, and they multiply slowly. But if our present types of vegetation are deficient in these distant epochs, we ought to recognise also that the plants which in our days represent the vegetation of the primitive world are often shorn of their grandeur. Our Equisetaceæ and Lycopodiaceæ are but poor representatives of the Lepidodendrons; the Calamites and Asterophyllites had already run their race before the epoch of which we write.”

The principal features of Triassic vegetation are represented in PLATE XIV., page 198. On the cliff, on the left of the ideal landscape, the graceful stems and lofty trees are groups of _Calamites arenaceus_; below are the great “horse-tails” of the epoch, _Equisetum columnare_, a slender tapering species, of soft and pulpy consistence, which, rising erect, would give a peculiar physiognomy to the solitary shore.

The Keuper formation presents itself in Europe at many points, and it is not difficult to trace its course. In France it appears in the department of the Indre, of the Cher, of the Allier, of the Nièvre, of the Saône-et-Loire; upon the western slopes of the Jura its outliers crop out near Poligny and Salins, upon the western slopes of the Vosges; in the Doubs it shows itself; then it skirts the Muschelkalk area in the Haute-Marne; in the Vosges it assumes large proportions in the Meurthe at Luneville and Dieuze; in the Moselle it extends northward to Bouzonville; and on the Rhine to the east of Luxembourg as far as Dockendorf. Some traces of it show themselves upon the eastern slopes of the Vosges, on the lower Rhine.

It appears again in Switzerland and in Germany, in the canton of Basle, in Argovia, in the Grand Duchy of Würtemberg, in the Tyrol, and in Austria, where it gives its name to the city of Salzburg.

In the British Islands the Keuper formation commences in the eastern parts of Devonshire, and a band, more or less regular, extends into Somersetshire, through Gloucestershire, Worcestershire, Warwick, Leicestershire, Nottinghamshire, to the banks of the Tees, in Yorkshire, with a bed, independent of all the others in Cheshire, which extends into Lancashire. “At Nantwich, in the upper Trias of Cheshire,” Sir Charles Lyell states, “two beds of salt, in great part unmixed with earthy matter, attain the thickness of 90 or 100 feet. The upper surface of the highest bed is very uneven, forming cones and irregular figures. Between the two masses there intervenes a bed of indurated clay traversed by veins of salt. The highest bed thins off towards the south-west, losing fifteen feet of its thickness in the course of a mile, according to Mr. Ormerod. The horizontal extent of these beds is not exactly known, but the area containing saliferous clay and sandstones is supposed to exceed 150 miles in diameter, while the total thickness of the Trias in the same region is estimated by Mr. Ormerod at 1,700 feet. Ripple-marked sandstones and the footprints of animals are observed at so many levels, that we may safely assume the whole area to have undergone a slow and gradual depression during the formation of the New Red Sandstone.”

Not to mention the importance of salt as a source of health, it is in Great Britain, and, indeed, all over the world where the saliferous rocks exist, a most important branch of industry. The quantity of the mineral produced in England, from all sources, is between 5,000 and 6,000 tons annually, and the population engaged in producing the mineral, from sources supposed to be inexhaustible, is upwards of 12,000.

The lower Keuper sandstones, which lie at the base of the series of red marls, frequently give rise to springs, and are in consequence called “water-stones,” in Lancashire and Cheshire.

(Living.)]

If the Keuper formation is poor in organic remains in France, it is by no means so on the other side of the Alps. In the Tyrol, and in the remarkable beds of Saint Cassian, Aussec, and Hallstadt, the rocks are made up of an immense number of marine fossils, among them Cephalopods, Ceratites, and Ammonites of peculiar form. The Orthoceras, which we have seen abounding in the Silurian period, and continued during the deposit of the Devonian and Carboniferous periods, appears here for the last time. We still find here a great number of Gasteropods and of Lamellibranchs of the most varied form. Sea Urchins--corals of elegant form--appear to have occupied, on the other side of the Alps, the same seas which in France and Germany seem to have been nearly destitute of animals. Some beds are literally formed of accumulated shells belonging to the genus _Avicula_; but these last-mentioned deposits are to be considered as more properly belonging to the Rhætic or Penarth strata, into which the New Red or Keuper Marl gradually passes upwards, and which are more fully described at page 207.

In following the grand mountainous slopes of the Alps and Carpathians we discover the saliferous rocks by this remarkable accumulation of Aviculæ. The same facies presents itself under identical conditions in Syria, in India, in New Caledonia, in New Zealand, and in Australia. It is not the least curious part of this period, that it presents, on one side of the site of the Alps, which were not yet raised, an immense accumulation of sediment, charged with gypsum, rock-salt, &c., without organic remains; while beyond, a region presents itself equally remarkable for the extraordinary accumulation of the remains of marine Mollusca. Among these were _Myophoria lineata_, which is often confounded with Trigonia, and _Stellispongia variabilis_.

France at this period was still the skeleton of what it has since become. A map of that country represents the metamorphic rocks occupying the site of the Alps, the Cévennes, and the Puy-de-Dôme, the country round Nantes, and the Islands of Brittany. The Primary rocks reach the foot of the Pyrenees, the Cotentin, the Vosges, and the Eifel Mountains. Some bands of coal stretch away from Valenciennes to the Rhine, and on the north of the Vosges, these mountains themselves being chiefly composed of Triassic rocks.

RHÆTIC, OR PENARTH SUB-PERIOD.

The attention of geologists has been directed within the last few years, more especially, to a series of deposits which intervene between the New Red Marl of the Trias, and the blue argillaceous limestones and shales of the Lower Lias. The first-mentioned beds, although they attain no great thickness in this country, nevertheless form a well-defined and persistent zone of strata between the unfossiliferous Triassic marls and the lower Liassic limestone with _Ostrea Liassica_ and _Ammonites planorbis_, _A. angulatus_ and _A. Bucklandi_; being everywhere characterised by the presence of the same groups of organic remains, and the same general lithological character of the beds. These last may be described as consisting of three sub-divisions, the lowermost composed of alternations of marls, clays, and marly limestones in the lower part, forming a gradual passage downwards into the New Red Marls upon which they repose. 2. A middle group of black, thinly laminated or paper-like shales, with thin layers of indurated limestone, and crowded in places with _Pecten Valoniensis_, _Cardium Rhæticum_, _Avicula contorta_, and other characteristic shells, as well as by the presence, nearly always, of a remarkable bed, which is commonly known as the “Bone-bed.” This thin band of stone, which is so well known at Aust, Axmouth, Westbury-on-Severn, and elsewhere, is a brecciated or conglomerated band of variable thickness which, sometimes a sandstone and sometimes a limestone, is always more or less composed of the teeth, scales, and bones of numerous genera of Fishes and Saurians, together with their fossilised excrement, which will be more fully and subsequently described under the name of Coprolites, under the Liassic period.

The molar tooth of a small predaceous fossil mammal of the Microlestes family (μικρος, _little_; ληστης, _beast_), whose nearest living representative appears to be some of the Hypsiprymnidæ or Kangaroo Rats, has been found by Mr. Dawkins in some grey marls underlying the bone-bed on the sea-shore at Watchett, in Somersetshire; affording the earliest known trace of a fossil mammal in the Secondary rocks. Several small teeth belonging to the genus Microlestes have also been discovered by Mr. Charles Moore in a breccia of Rhætic age, filling a fissure traversing Carboniferous Limestone near Frome; and in addition to the discovery of the remains of Microlestes, those of a mammal more closely allied to the Marsupials than any other order, have been met with at Diegerloch, south-east of Stuttgart, in a remarkable bone-breccia, which also yielded coprolites and numerous traces of fishes and reptiles.

The uppermost sub-division includes certain beds of white and cream-coloured limestone, resembling in appearance the smooth fracture and closeness of texture of the lithographic limestone of Solenhofen, and which, known to geologists and quarrymen under the name “white lias,” given to it by Dr. William Smith, was formerly always considered to belong to, and was included in, the Lias proper. The most remarkable bed in this zone is one of only a few inches in thickness, but it has long been known to collectors, and sought after under the name of Cotham Marble or Landscape Stone, the latter name having reference to the curious dendritic markings which make their appearance on breaking the stone at right angles to its bedding, bearing a singular resemblance to a landscape with trees, water, &c.; while the first name is that derived from its occurrence abundantly at Cotham, in the suburbs of Bristol, where the stone was originally found and noticed.

This band of stone is interesting in another respect, because it sometimes shows by its uneven, eroded, and water-worn upper surface, that an interval took place soon after it had been deposited, when the newly-formed stone became partially dissolved, eroded, or worn away by water, before the stratum next in succession was deposited upon it. The same phenomenon is displayed, in a more marked degree, in the uppermost limestone or “white lias” bed of the series, which not only shows an eroded surface, but the holes made by boring Molluscs, exactly as is produced at the present day by the same class of animals, which excavate holes in the rocks between high and low-water marks, to serve for their dwelling-places, and as a protection from the waves to their somewhat delicate shells.

The “White Lias” of Smith is the equivalent of the Koessen beds which immediately underlie the Lower Lias of the Swabian Jura, and have been traced for a hundred miles, from Geneva to the environs of Vienna; and, also, of the Upper St. Cassian beds, which are so called from their occurrence at St. Cassian in the Austrian Alps.

The general character of the series of strata just described, is that of a deposit formed in tolerably shallow water. In the Alps of Lombardy and the Tyrol, in Luxembourg, in France, and, in fact, throughout nearly the whole of Europe, they form a sort of fringe in the margin of the Triassic sea; and, although of comparatively inconsiderable thickness in England, they become highly developed in Lombardy, &c., to an enormous thickness, and constitute the great mass of the Rhætian Alps and a considerable part of the well-known beds of St. Cassian, and Hallstadt in the Austrian Alps. (See page 205.)

The Rhætic beds of Europe were, as a whole, formed under very different conditions in different areas. The thickness of the strata and the large and well-developed fauna (chiefly Mollusca) indicate that the Rhætic strata of Lombardy, and other parts of the south and east of Europe, were deposited in a broad open ocean. On the other hand, the comparatively thin beds of this age in England and north-western Europe, the fauna of which, besides being poor in genera and species, consists of small and dwarfed forms, point to the conclusion that they were in great part deposited in shallow seas and in estuaries, or in lagoons, or in occasional salt lakes, under conditions which lasted for a long period.[56]

[56] See A. C. Ramsay, “On the Physical Relations of the New Red Marl,
Rhætic Beds, and Lower Lias,” _Quart. Jour. Geol. Soc._, vol. 27,
p. 189.

In consequence of the importance they assume in Lombardy (the ancient Rhætia), the name “Rhætic Beds” has been given to these strata by Mr. Charles Moore; Dr. Thomas Wright has proposed the designation “Avicula Contorta Zone,” from the plentiful occurrence of that shell in the black shales forming the well-marked middle zone, and which is everywhere present where this group of beds is found; Jules Martin and others have proposed the term “Infra-lias,” or “Infra-liassic strata;” while the name “Penarth Beds” has been assigned to these deposits in this country by Mr. H. W. Bristow, at the suggestion of Sir Roderick Murchison, in consequence of their conspicuous appearance and well-exposed sections in the bold headlands and cliffs of that locality, in the British Channel, west of Cardiff.

A fuller description of these beds will be found in the Reports of the Bath Meeting of the British Association (1864), by Mr. Bristow; also in communications to the _Geological Magazine_, for 1864, by MM. Bristow and Dawkins;[57] in papers read before the Geological Society by Dr. Thomas Wright,[58] Mr. Charles Moore,[59] and Mr. Ralph Tate,[60] as printed in their _Quarterly Journal_; and by Mr. Etheridge, in the Transactions of the Cotteswold Natural History Club for 1865-66. The limits of the Penarth Beds have also been lately accurately laid down by Mr. Bristow in the map of the Geological Survey over the district comprised between Bath, Bristol, and the Severn; and elaborately detailed typical sections of most of the localities in England, where these beds occur, have been constructed by MM. Bristow, Etheridge, and Woodward, of the Geological Survey of Great Britain, which, when published, will greatly add to our knowledge of this remarkable and interesting series of deposits.

[57] _Quart. Jour. Geol. Soc._, vol. xx., p. 396.

[58] Ibid, vol. xvii., p. 483.

[59] Ibid, vol. xvi., p. 374.

[60] Ibid, vol. xx., p. 103.

JURASSIC PERIOD.

This period, one of the most important in the physical history of the globe, has received its name from the Jura mountains in France, the Jura range being composed of the rocks deposited in the seas of the period. In the term Jurassic, the formations designated as the “Oolite” and “Lias” are included, both being found in the Jura mountains. The Jurassic period presents a very striking assemblage of characteristics, both in its vegetation and in the animal remains which belong to it; many genera of animals existing in the preceding age have disappeared, new genera have replaced them, comprising a very specially organised group, containing not less than 4,000 species.

The Jurassic period is sub-divided into two sub-periods: those of the _Lias_ and the _Oolite_.

THE LIAS

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The World Before the DelugeChapter VII: Part 7

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