Fig. 84.—Branch and cone of Voltzia restored. N2

to the Lycopodiaceae and Thyphaceae, the ^theophyllum 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 Cycadeacese, 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 Cycadeaceas, 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 Terebratulas. The Reptile which occupies the rocks, and prepares to thrown itself on its prey, is the Nothosatirus. 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 m these primitive forests, and which would give to it so strange a character, are represented by the LabyriniJiodoii, 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 oblite-rated 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.

XIV.—Ideal Landscape of the Keuper Sub-period.

Kejper 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 tv/enty-five to forty feet thick, alternate with beds of clay, the whole attaining a thickness of 160 yards. In Germany in Wiirtemberg, in France at Vic, at Dieuze, and at Chateau- 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 WieHczka, 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 \yy a regular process of mining by

galleries, and the ordinary mode of'^reaching the salt is by diggingpits, 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 sandydune, 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 ot 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 horizontality." 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 ot the Keuper period, when a partial influx of the sea took place, and the Rhgetic 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.'^ 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 Ainada, Cardiiun, and Fecten, 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

A, C. Ramsay, Quart. Jour. Geoi. Soc, vol. 27, p. 191.

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, Equisetacese, Cycads, Conifers, and a few plants, which M. Ad. Brongniart classes among the dubious monocotyledons. Among the Ferns may be quoted many species of SpJwiopteris or Pecopteris. Among them, Pecopteris Stutigartiensis, 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 Eqiusetites cohimnaris^ a great Equisetum analogous to the horse-tails of our age, but of infinitely larger dimen-

Fig. 85. — Pecten orbicularis.

sions, its long fluted trunk, surmounted by an elongated fructification, towering over all the other trees of the marshy soil.

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