Part 23

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.