The strata of red and green marl, which follow the bone-bed in the descending order at Axmouth and Aust, are destitute of organic remains; as is the case, for the most part, in the corresponding beds in almost every part of England. But fossils have lately been found at a few localities in sandstones of this formation, in Worcestershire and Warwickshire, and among them the bivalve shell called Posidonia minuta, Goldf., before mentioned (fig. 321. p. 288.).

The upper member of the English "New Red" containing this shell, in those parts of England, is, according to Messrs. Murchison and Strickland, 600 feet thick, and consists chiefly of red marl or slate, with a band of sandstone. Spines of Hybodus, called ichthyodorulites, teeth of fishes, and footprints of reptiles, with remains of a saurian called Rhyncosaurus, were observed by the same geologists in these strata.[290-A]

In Cheshire and Lancashire the gypseous and saliferous red shales and loams of the Trias are between 1000 and 1500 feet thick. In some places lenticular masses of rock-salt are interpolated between the argillaceous beds, the origin of which will be spoken of in the sequel.

The lower division or English representative of the "Bunter" attains a thickness of 600 feet in the counties last mentioned. Besides red and green shales and red sandstones, it comprises much soft white quartzose sandstone, in which the trunks of silicified trees have been met with at Allesley Hill, near Coventry. Several of them were a foot and a half in diameter, and some yards in length, decidedly of coniferous wood, and showing rings of annual growth.[290-B] Impressions, also, of the footsteps of animals have been detected in Lancashire and Cheshire in this formation. Some of the most remarkable occur a few miles from Liverpool, in the whitish quartzose sandstone of Storton Hill, on the west side of the Mersey. They bear a close resemblance to tracks first observed in a member of the Upper New Red Sandstone, at the village of Hesseberg, near Hildburghausen, in Saxony, to which I have already alluded. For many years these footprints have been referred to a large unknown quadruped, provisionally named Chirotherium by Professor Kaup, because the marks both of the fore and hind feet resembled impressions made by a human hand. (See fig. 327.) The footmarks at Hesseberg are partly concave and partly in relief; the former, or the depressions, are seen upon the upper surface of the sandstone slabs, but those in relief are only upon the lower surfaces, being in fact natural casts, formed in the subjacent footprints as in moulds. The larger impressions, which seem to be those of the hind foot, are generally 8 inches in length, and 5 in width, and one was 12 inches long. Near each large footstep, and at a regular distance (about an inch and a half), before it, a smaller print of a fore foot, 4 inches long and 3 inches wide, occurs. The footsteps follow each other in pairs, each pair in the same line, at intervals of 14 inches from pair to pair. The large as well as the small steps show the great toes alternately on the right and left side; each step makes the print of five toes, the first or great toe being bent inwards like a thumb. Though the fore and hind foot differ so much in size, they are nearly similar in form.

The similar footmarks afterwards observed in a rock of corresponding age at Storton Hill, were imprinted on five thin beds of clay, superimposed one upon the other in the same quarry, and separated by beds of sandstone. On the lower surface of the sandstone strata, the solid casts of each impression are salient, in high relief, and afford models of the feet, toes, and claws of the animals which trod on the clay.

As neither in Germany nor in England any bones or teeth had been met with in the same identical strata as the footsteps, anatomists indulged, for several years, in various conjectures respecting the mysterious animals from which they might have been derived. Professor Kaup suggested that the unknown quadruped might have been allied to the Marsupialia; for in the kangaroo the first toe of the fore foot is in a similar manner set obliquely to the others, like a thumb, and the disproportion between the fore and hind feet is also very great. But M. Link conceived that some of the four species of animals of which the tracks had been found in Saxony might have been gigantic Batrachians; and Dr. Buckland designated some of the footsteps as those of a small web-footed animal, probably crocodilean.

In the course of these discussions several naturalists of Liverpool, in their report on the Storton quarries, declared their opinion that each of the thin seams of clay in which the sandstone casts were moulded had formed successively a surface above water, over which the Chirotherium and other animals walked, leaving impressions of their footsteps, and that each layer had been afterwards submerged by a sinking down of the surface, so that a new beach was formed at low water above the former, on which other tracks were then made. The repeated occurrence of ripple-marks at various heights and depths in the red sandstone of Cheshire had been explained in the same manner. It was also remarked that impressions of such depth and clearness could only have been made by animals walking on the land, as their weight would have been insufficient to make them sink so deeply in yielding clay under water. They must therefore have been air-breathers.

When the inquiry had been brought to this point, the reptilian remains discovered in the Trias, both of Germany and England, were carefully examined by Mr. Owen. He found, after a microscopic investigation of the teeth from the German sandstone called Keuper, and from the sandstone of Warwick and Leamington, that neither of them could be referred to true saurians, although they had been named Mastodonsaurus and Phytosaurus by Jäger (fig. 329.). It appeared that they were of the Batrachian order, and attested the former existence of frogs of gigantic dimensions in comparison with any now living. Both the Continental and English fossil teeth exhibited a most complicated texture, differing from that previously observed in any reptile, whether recent or extinct, but most nearly analogous to the Ichthyosaurus. A section of one of these teeth exhibits a series of irregular folds, resembling the labyrinthic windings of the surface of the brain; and from this character Mr. Owen has proposed the name Labyrinthodon for the new genus. By his permission, the annexed representation (fig. 330.) of part of one is given from his "Odontography," plate 64. A. The entire length of this tooth is supposed to have been about three inches and a half, and the breadth at the base one inch and a half.

When Mr. Owen had satisfied himself, from an inspection of the cranium, jaws, and teeth, that a gigantic Batrachian had existed at the period of the Trias or Upper New Red Sandstone, he soon found, from the examination of various bones derived from the same formation, that he could define three species of Labyrinthodon, and that in this genus the hind extremities were much larger than the anterior ones. This circumstance, coupled with the fact of the Labyrinthodon having existed at the period when the Chirotherian footsteps were made, was the first step towards the identification of those tracks with the newly discovered Batrachian. It was at the same time observed that the footmarks of Chirotherium were more like those of toads than of any other living animal; and, lastly, that the size of the three species of Labyrinthodon corresponded with the size of three different kinds of footprints which had already been supposed to belong to three distinct Chirotheria. It was moreover inferred, with confidence, that the Labyrinthodon was an air-breathing reptile from the structure of the nasal cavity, in which the posterior outlets were at the back part of the mouth, instead of being directly under the anterior or external nostrils. It must have respired air after the manner of saurians, and may therefore have imprinted on the shore those footsteps, which, as we have seen, could not have originated from an animal walking under water.

It is true that the structure of the foot is still wanting, and that a more connected and complete skeleton is required for demonstration; but the circumstantial evidence above stated is strong enough to produce the conviction that the Chirotherium and Labyrinthodon are one and the same.

In order to show the manner in which one of these formidable Batrachians may have impressed the mark of its feet upon the shore, Mr. Owen has attempted a restoration, of which a reduced copy is annexed.

To account for deposits of red mud and red sand, we have simply to suppose the disintegration of ordinary crystalline or metamorphic schists. Thus, in the eastern Grampians of Scotland, as, for example, in the north of Forfarshire, the mountains of gneiss, mica-schist, and clay-slate, are overspread with alluvium, derived from the disintegration of those rocks; and the mass of detritus is stained by oxide of iron, of precisely the same colour as the Old Red Sandstone of the adjoining Lowlands. Now this alluvium merely requires to be swept down to the sea, or into a lake, to form strata of red sandstone and red marl, precisely like the mass of the "Old Red" or New Red systems of England, or those tertiary deposits of Auvergne (see p. 182.), before described, which are in lithological characters quite undistinguishable. The pebbles of gneiss in the Eocene red sandstone of Auvergne point clearly to the rocks from which it has been derived. The red colouring matter may, as in the Grampians, have been furnished by the decomposition of hornblende, or mica, which contain oxide of iron in large quantity.

It is a general fact, and one not yet accounted for, that scarcely any fossil remains are preserved in stratified rocks in which this oxide of iron abounds; and when we find fossils in the New or Old Red Sandstone in England, it is in the grey, and usually calcareous beds, that they occur.

The gypsum and saline matter, occasionally interstratified with such red clays and sandstones of various ages, primary, secondary, and tertiary, have been thought by some geologists to be of volcanic origin. Submarine and subaerial exhalations often occur in regions of earthquakes and volcanos far from points of actual eruption, and charged with sulphur, sulphuric salts, and with common salt or muriate of soda. In a word, they are vents by which all the products which issue in a state of sublimation from the craters of active volcanos, obtain a passage from the interior of the earth to the surface. That such gaseous emanations and mineral springs, impregnated with the ingredients before enumerated, and often intensely heated, continue to flow out unaltered in composition and temperature for ages, is well known. But before we can decide on their real instrumentality in producing in the course of ages beds of gypsum, salt, and dolomite, we require to know what are the chemical changes actually in progress in seas where this volcanic agency is at work.

Yet the origin of rock-salt is a problem of so much interest in theoretical geology as to demand a full discussion of another hypothesis advanced on the subject; namely, that which attributes the precipitation of the salt to evaporation, whether of inland lakes or of lagoons communicating with the ocean.

At Northwich, in Cheshire, two beds of salt, in great part unmixed with earthy matter, attain the extraordinary thickness of 90 and even 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 with veins of salt. The highest bed thins off towards the south-west, losing 15 feet in thickness in the course of a mile.[295-A] The horizontal extent of these particular masses in Cheshire and Lancashire is not exactly known; but the area, containing saliferous clays 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 more than 1700 feet. Ripple-marked sandstones, and the footprints of animals, before described, 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 Red Sandstone. The evidence of such a movement, wholly independent of the presence of salt itself, is very important in reference to the theory under consideration.

In the "Principles of Geology" (chap. 28.), I published a map, furnished to me by the late Sir Alexander Burnes, of that singular flat region called the Runn of Cutch, near the delta of the Indus, which is 7000 square miles in area, or equal in extent to about one-fourth of Ireland. It is neither land nor sea, but is dry during a part of every year, and again covered by salt water during the monsoons. Some parts of it are liable, after long intervals, to be overflowed by river-water. Its surface supports no grass, but is encrusted over, here and there, by a layer of salt, about an inch in depth, caused by the evaporation of sea-water. Certain tracts have been converted into dry land by upheaval during earthquakes since the commencement of the present century, and, in other directions, the boundaries of the Runn have been enlarged by subsidence. That successive layers of salt might be thrown down, one upon the other, over thousands of square miles, in such a region, is undeniable. The supply of brine from the ocean would be as inexhaustible as the supply of heat from the sun to cause evaporation. The only assumption required to enable us to explain a great thickness of salt in such as area is, the continuance, for an indefinite period, of a subsiding movement, the country preserving all the time a general approach to horizontality. Pure salt could only be formed in the central parts of basins, where no sand could be drifted by the wind, or sediment be brought by currents. Should the sinking of the ground be accelerated, so as to let in the sea freely, and deepen the water, a temporary suspension of the precipitation of salt would be the only result. On the other hand, if the area should dry up, ripple-marked sands and the footprints of animals might be formed, where salt had previously accumulated. According to this view the thickness of the salt, as well as of the accompanying beds of mud and sand, becomes a mere question of time, or requires simply a repetition of similar operations.

Mr. Hugh Miller, in an able discussion of this question, refers to Dr. Frederick Parrot's account, in his journey to Ararat (1836), of the salt lakes of Asia. In several of these lakes west of the river Manech, "the water, during the hottest season of the year, is covered on its surface with a crust of salt nearly an inch thick, which is collected with shovels into boats. The crystallization of the salt is effected by rapid evaporation from the sun's heat and the supersaturation of the water with muriate of soda; the lake being so shallow that the little boats trail on the bottom and leave a furrow behind them, so that the lake must be regarded as a wide pan of enormous superficial extent, in which the brine can easily reach the degree of concentration required."

Another traveller, Major Harris, in his "Highlands of Ethiopia," describes a salt lake, called the Bahr Assal, near the Abyssinian frontier, which once formed the prolongation of the Gulf of Tadjara, but was afterwards cut off from the gulf by a broad bar of lava or of land upraised by an earthquake. "Fed by no rivers, and exposed in a burning climate to the unmitigated rays of the sun, it has shrunk into an elliptical basin, seven miles in its transverse axis, half filled with smooth water of the deepest cærulian hue, and half with a solid sheet of glittering snow-white salt, the offspring of evaporation." "If," says Mr. Hugh Miller, "we suppose, instead of a barrier of lava, that 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 fresh brine when the first stock had been exhausted by evaporation.[296-A]

We may add that the permanent impregnation of the waters of a large shallow basin with salt, beyond the proportion which is usual in the ocean, would cause it to be uninhabitable by mollusca or fish, as is the case in the Dead Sea, and the muriate of soda might remain in excess, even though it were occasionally replenished by irruptions of the sea. Should the saline deposit be eventually submerged, it might, as we have seen from the example of the Runn of Cutch, be covered by a freshwater formation containing fluviatile organic remains; and in this way the apparent anomaly of beds of sea-salt and clays devoid of marine fossils, alternating with others of freshwater origin, may be explained.

Dr. G. Buist, in a recent communication to the Bombay Geographical Society (vol. ix.), has asked how it happens that the Red Sea should not exceed the open ocean in saltness, by more than 1/10th per cent. The Red Sea receives no supply of water from any quarter save through the Straits of Babelmandeb; and there is not a single river or rivulet flowing into it from a circuit of 4000 miles of shore. The countries around are all excessively sterile and arid, and composed, for the most part, of burning deserts. From the ascertained evaporation in the sea itself, Dr. Buist computes that nearly 8 feet of pure water must be carried off from the whole of its surface annually, this being probably equivalent to 1/100th part of its whole volume. The Red Sea, therefore, ought to have 1 per cent. added annually to its saline contents; and as these constitute 4 per cent. by weight, or 2¹/₂ per cent. in volume of its entire mass, it ought, assuming the average depth to be 800 feet, which is supposed to be far beyond the truth, to have been converted into one solid salt formation in less than 3000 years.[297-A] Does the Red Sea receive a supply of water from the ocean, through the narrow Straits of Babelmandeb, sufficient to balance the loss by evaporation? And is there an undercurrent of heavier saline water annually flowing outwards? If not, in what manner is the excess of salt disposed of? An investigation of this subject by our nautical surveyors may perhaps aid the geologist in framing a true theory of the origin of rock-salt.

On the New Red Sandstone of the valley of the Connecticut River in the United States.

In a depression of the granitic or hypogene rocks in the States of Massachusetts and Connecticut, strata of red sandstone, shale, and conglomerate are found occupying an area more than 150 miles in length from north to south, and about 5 to 10 miles in breadth, the beds dipping to the eastward at angles varying from 5 to 50 degrees. The extreme inclination of 50 degrees is rare, and only observed in the neighbourhood of masses of trap which have been intruded into the red sandstone while it was forming, or before the newer parts of the deposit had been completed. Having examined this series of rocks in many places, I feel satisfied that they were formed in shallow water, and for the most part near the shore, and that some of the beds were from time to time raised above the level of the water, and laid dry, while a newer series, composed of similar sediment, was forming. The red flags of thin-bedded sandstone are often ripple-marked, and exhibit on their under sides casts of cracks formed in the underlying red and green shales. These last must have shrunk by drying before the sand was spread over them. On some shales of the finest texture impressions of rain drops may be seen, and casts of them in the incumbent argillaceous sandstones. Having observed similar markings produced by showers, of which the precise date was known, on the recent red mud of the Bay of Fundy, and casts in relief of the same, on layers of dried mud thrown down by subsequent tides, I feel no doubt in regard to the origin of some of the ancient Connecticut impressions. I have also seen on the mud-flats of the Bay of Fundy the footmarks of birds (Tringa minuta), which daily run along the borders of that estuary at low water, and which I have described in my Travels.[297-B] Similar layers of red mud, now hardened and compressed into shale, are laid open on the banks of the Connecticut, and retain faithfully the impressions and casts of the feet of numerous birds and reptiles which walked over them at the time when they were deposited, probably in the Triassic Period.

According to Professor Hitchcock, the footprints of no less than thirty-two species of bipeds, and twelve of quadrupeds, have been already detected in these rocks. Thirty of these are believed to be those of birds, four of lizards, two of chelonians, and six of batrachians. The tracks have been found in more than twenty places, scattered through an extent of nearly 80 miles from north to south, and they are repeated through a succession of beds attaining at some points a thickness of more than 1000 feet, which may have been thousands of years in forming.[298-A]

As considerable scepticism is naturally entertained in regard to the nature of the evidence derived from footprints, it may be well to enumerate some facts respecting them on which the faith of the geologist may rest. When I visited the United States in 1842, more than 2000 impressions had been observed by Professor Hitchcock, in the district alluded to, and all of them were indented on the upper surface of the layers, while the corresponding casts, standing out in relief, were always on the lower surfaces or planes of the strata. If we follow a single line of marks we find them uniform in size, and nearly uniform in distance from each other, the toes of two successive footprints, turning alternately right and left (see fig. 332.). Such single lines indicate a biped; and there is generally such a deviation from a straight line, in any three successive prints, as we remark in the tracks left by birds. There is also a striking relation between the distance separating two footprints in one series and the size of the impressions; in other words, an obvious proportion between the length of the stride and the dimension of the creature which walked over the mud. If the marks are small, they may be half an inch asunder; if gigantic, as, for example, where the toes are 20 inches long, they are occasionally 4 feet and a half apart. The bipedal impressions are for the most part trifid, and show the same number of joints as exist in the feet of living tridactylous birds. Now such birds have three phalangeal bones for the inner toe, four for the middle and five for the outer one (see fig. 332.); but the impression of the terminal joint is that of the nail only. The fossil footprints exhibit regularly, where the joints are seen, the same number; and we see in each continuous line of tracks the three-jointed and five-jointed toes placed alternately outwards, first on the one side and then on the other. It is not often that the matrix has been fine enough to retain impressions of the integument or skin of the foot; but in one fine specimen found at Turner's Falls on the Connecticut, by Dr. Deane, these markings are well preserved, and have been recognized by Mr. Owen as resembling the skin of the ostrich, and not that of reptiles.[298-B] Much care is required to ascertain the precise layer of a laminated rock on which an animal has walked, because the impression usually extends downwards through several laminæ; and if the upper layer originally trodden upon is wanting, one or more joints, or even in some cases an entire toe, which sank less deep into the soft ground, may disappear, and yet the remainder of the footprint be well defined.

The size of several of the fossil impressions of the Connecticut red sandstone so far exceeds that of any living ostrich, that naturalists at first were extremely adverse to the opinion of their having been made by birds, until the bones and almost entire skeleton of the Dinornis and of other feathered giants of New Zealand were discovered. Their dimensions have at least destroyed the force of this particular objection. The magnitude of the impressions of the feet of a heavy animal, which has walked on soft mud, increases for some distance below the surface originally trodden upon. In order, therefore, to guard against exaggeration, the casts rather than the mould are relied on. These casts show that some of the fossil birds had feet four times as large as the ostrich, but not perhaps larger than the Dinornis.

Some of the quadrupedal footprints which accompany those of birds are analogous to European Chirotheria, and with a similar disproportion between the hind and fore feet. Others resemble that remarkable reptile, the Rhyncosaurus of the English Trias, a creature having some relation in its osteology both to chelonians and birds. Other imprints, again, are like those of turtles.

Among the supposed bipedal tracks, a single distinct example only has been observed of feet in which there are four toes directed forwards. In this case a series of four footprints is seen, each 22 inches long and 12 wide, with joints much resembling those in the toes of birds. Professor Agassiz has suggested that it might have belonged to a gigantic bipedal batrachian; but the evidence on this subject is too defective to warrant such a bold conjecture, and if we were to give the reins to our imagination, we might as well conceive a bird having four toes projecting forwards as a huge two-legged frog. Nor should we forget that some quadrupeds place the hind foot so precisely on the spot just quitted by the fore foot, as to produce a single line of imprints like a biped.

No bones have as yet been met with, whether of reptiles or birds, in the rocks of the Connecticut, but there are numerous coprolites; and an ingenious argument has been derived by Mr. Dana, from the analysis of these bodies, and the proportion they contain of uric acid, phosphate of lime, carbonate of lime, and organic matter, to show that, like guano, they are the droppings of birds, rather than of reptiles.[299-A]

Mr. Darwin, in his "Journal of a Voyage in the Beagle," informs us that the "South American ostriches, although they live on vegetable matter, such as roots and grass, are repeatedly seen at Bahia Blanca (lat. 39° S.), on the coast of Buenos Ayres, coming down at low water to the extensive mud-banks which are then dry, for the sake, as the Gauchos say, of feeding on small fish." They readily take to the water, and have been seen at the bay of San Blas, and at Port Valdez, in Patagonia, swimming from island to island.[300-A] It is therefore evident, that in our times a South American mud-bank might be trodden simultaneously by ostriches, alligators, tortoises, and frogs; and the impressions left, in the nineteenth century, by the feet of these various tribes of animals, would not differ from each other more entirely than do those attributed to birds, saurians, chelonians, and batrachians, in the rocks of the Connecticut.

To determine the exact age of the red sandstone and shale containing these ancient footprints in the United States, is not possible at present. No fossil shells have yet been found in the deposit, nor plants in a determinable state. The fossil fish are numerous and very perfect; but they are of a peculiar type, which was originally referred to the genus Palæoniscus, but has since, with propriety, been ascribed, by Sir Philip Egerton, to a new genus. To this he has given the name of Ischypterus, from the great size and strength of the fulcral rays of the dorsal fin (from ισχὺς; strength, and πτερὸν, a fin). They differ from Palæoniscus, as Mr. Redfield first pointed out, by having the vertebral column prolonged to a more limited extent into the upper lobe of the tail, or, in the language of M. Agassiz, they are less heterocercal. The teeth also, according to Sir P. Egerton, who, in 1844, examined for me a fine series of specimens which I procured at Durham, Connecticut, differ from those of Palæoniscus in being strong and conical.

That the sandstones containing these fish are of older date than the strata containing coal, before described (p. 284.) as occurring near Richmond in Virginia, is highly probable. These were shown to be as old at least as the oolite and lias. The higher antiquity of the Connecticut beds cannot be proved by direct superposition, but may be presumed from the general structure of the country. That structure proves them to be newer than the movements to which the Appalachian or Alleghany chain owes its flexures, and this chain includes the ancient coal formation among its contorted rocks. The unconformable position of this New Red with ornithichnites on the edges of the inclined primary or paleozoic rocks of the Appalachians is seen at 4. of the section, fig. 379. p. 327. The absence of fish with decidedly heterocercal tails may afford an argument against the Permian age of the formation; and the opinion that the red sandstone is triassic, seems, on the whole, the best that we can embrace in the present state of our knowledge.

CHAPTER XXIII.

PERMIAN OR MAGNESIAN LIMESTONE GROUP.

When the use of the term "Poikilitic" was explained in the last chapter, I stated, that in some parts of England it is scarcely possible to separate the red marls and sandstones so called (originally named "the New Red"), into two distinct geological systems. Nevertheless, the progress of investigation, and a careful comparison of English rocks between the lias and the coal with those occupying a similar geological position in Germany and Russia, has enabled geologists to divide the Poikilitic formation; and has even shown that the lowermost of the two divisions is more closely connected, by its fossil remains, with the carboniferous group than with the trias. If, therefore, we are to draw a line between the secondary and primary fossiliferous strata, as between the tertiary and secondary, it must run through the middle of what was once called the "New Red," or Poikilitic group. The inferior half of this group will rank as Primary or Paleozoic, while its upper member will form the base of the Secondary series. For the lower, or Magnesian Limestone division of English geologists, Sir R. Murchison has proposed the name of Permian, from Perm, a Russian government where these strata are more extensively developed than elsewhere, occupying an area twice the size of France, and containing an abundant and varied suite of fossils.

Mr. King, in his valuable monograph, recently published, of the Permian fossils of England, has given a table of the following six members of the Permian system of the north of England, with what he conceives to be the corresponding formations in Thuringia.[301-A]

I shall proceed, therefore, to treat briefly of these subdivisions, beginning with the highest, and referring the reader, for a fuller description of the lithological character of the whole group, as it occurs in the north of England, to a valuable memoir by Professor Sedgwick, published in 1835.[302-A]

Crystalline or concretionary limestone (No. 1.).—This formation is seen upon the coast of Durham and Yorkshire, between the Wear and the Tees. Among its characteristic fossils are Schizodus Schlotheimi (fig. 333.) and Mytilus septifer (fig. 335.).

The brecciated limestone (No. 2.) contains no fragments of foreign rocks, but seems composed of the breaking-up of the Permian limestone itself, about the time of its consolidation. Some of the angular masses in Tynemouth Cliff are 2 feet in diameter. This breccia is considered by Professor Sedgwick as one of the forms of the preceding limestone, No. 1., rather than as regularly underlying it. The fragments are angular and never water-worn, and appear to have been re-cemented on the spot where they were formed. It is, therefore, suggested that they may have been due to those internal movements of the mass which produced the concretionary structure; but the subject is very obscure, and after studying the phenomenon in the Marston Rocks, on the coast of Durham, I found it impossible to form any positive opinion on the subject. The well-known brecciated limestones of the Pyrenees appeared to me to present the nearest analogy, but on a much smaller scale.

The fossiliferous limestone (No. 3.) is regarded by Mr. King as a deep-water formation, from the numerous delicate corals which it includes. One of these, Fenestella retiformis (fig. 336.), is a very variable species, and has received many different names. It sometimes attains a large size, measuring 8 inches in width. The same zoophyte is also found abundantly in the Permian of Germany.

Shells of the genera Spirifer and Productus, which do not occur in strata newer than the Permian, are abundant in this division of the series in the ordinary yellow magnesian limestone. (See figs. 337, 338.)

The compact limestone (No. 4.) also contains organic remains, especially corallines, and is intimately connected with the preceding. Beneath it lies the marl-slate (No. 5.), which consists of hard, calcareous shales, marl-slate, and thin-bedded limestones. At East Thickley, in Durham, where it is thirty feet thick, this slate has yielded many fine specimens of fossil fish of the genera Palæoniscus, Pygopterus, Cœlacanthus, and Platysomus, genera which are all found in the coal-measures of the carboniferous epoch, and which therefore, says Mr. King, probably lived at no great distance from the shore. But the Permian species are peculiar, and, for the most part, identical with those found in the marl-slate or copper-slate of Thuringia.