tions of sandstone, coals, shales, ironstones, clays, and impure limestones; and, like the carboniferous shales already noticed, are principally of lacustrine origin. The minerals of this formation, especially the coal and iron which it yields, form an inexhaustible source of wealth. Its fauna is not very peculiar, save that INSECTS, apparently allied to the cockroach, beetle, and grasshopper, together with carnivorous arachnidae (scorpions, &c.) and reptiles of the batrachian or lowest order, appear here for the first time. But its flora is the most abundant and gigantic that ever appeared on the earth's surface. The number of plants hitherto discovered in the entire carboniferous system amounts to fully 500, of which 250 species are ferns. In the British Coal-Measures alone there have been enumerated 300 species; and of these, 120 are ferns. Coniferous trees of gigantic stature, huge lepidodendra, calamites, sigillariæ, equiseta, club-mosses, and other allied forms, crowd every bed of shale, and form the materials of which every seam of coal consists.

5. The Permian System, so named from its enormous development in the Russian government of Perm, where its strata cover an area of twice the size of France, forms the lower half of what was formerly known as the Saliferous or New Red Sandstone System. It consists principally of two formations-viz. the Lower Red Sandstone below, and the Magnesian Limestone above, both of which yield excellent building-materials, the latter especially being noted for its durability. The organic remains are neither numerous nor remarkable, but approximate far more closely to those of the Carboniferous System below than to the overlying Triassic. Hence it forms the terminating link of the great PALEOZOIC SERIES, which extends downwards to the base of the Silurian System. In this entire group the fishes are distinguished by having the heterocercal or unequally-lobed tail, whereas in all the systems above the Permian the homocercal or equally-lobed tail predominates, a form which is all but universal in the 8000 species of fishes now existing.

6. The Triassic System embraces the upper portion of what was formerly called the Saliferous or New Red Sandstone System. It derives the name Trias from the fact that, in Germany and other places where the system is highly developed, it consists of three well-defined formations-viz. the Bunter Sandstein, the Muschelkalk, and the Keuper Marls. In England the middle formation is wanting; the lower corresponds to the Bunter Sandstein, and the upper to the Keuper Marls. The last-named formation contains rich deposits of rock-salt, which sometimes attain a thickness of several hundred feet, besides valuable beds of gypsum. The organisms are widely different from those of the Permian and other Palæozoic systems, having nearly all their affinities with the plants and animals of the Oolitic and Cretaceous systems. The flora of the Trias is extremely limited, both in the number of species and of individual forms, especially in the British Isles. A few calamites continue to represent former ages; but the Cycadea, which attain such a luxuriance in the Oolite, have not yet made their appearance. The fauna also is comparatively unimportant. Among chambered shells, ceratites nodosus, a species of ammonite, is very abundant, and posidonia

and avicula among the bivalves. Of sauroid fishes numerous species have been discovered; and of reptiles, the bones and footprints of a gigantic batrachian, known as the Labyrinthodon. Though the organic remains are not numerous, they are held as marking the dawn of a new geological era, named the Secondary or Mesozoic, which extends upwards to the base of the Tertiary.

7. The Oolitic System embraces all the formations that lie between the Triassic and Cretaceous systems. In England, where it is most complete, it consists of three well-marked groups, which, proceeding upwards, are named the Lias, Oolite, and Wealden.

The composition, lamination, and organic contents of the Lias clearly indicate that it was deposited in a tranquil, deep sea. In general it consists of dark-coloured argillaceous limestones, bluish clays, and bituminous shales, and is exceedingly rich in fossil plants and animals. Among the former, the cone-bearing genera receive great accessions to their numbers, and approximate more closely to existing forms. Cycadea-a family of plants allied to the ferns on the one hand, and to the conifers on the other make their earliest appearance. The fauna embraces no fewer than 170 species of Mollusca, the most characteristic forms being ammonites, belemnites, cuttle-fishes, and grypha incurva, all of which appear here for the first time. Fishes are numerous and very characteristic, and still comprise both placoids and ganoids. It is quite a store-house of fossil reptiles, of large size and singular formation (Ichthyosaurus, Plesiosaurus, &c.); and here, indeed, this class of the Vertebrata attains its highest development, though the Ophidia, or serpents, do not appear earlier than the London Clay, a Lower Eocene deposit. But the most remarkable fact in the paleontology of the Lias is that BIRDS here make their first appearance-viz. in the valley of the Connecticut, Massachusetts, formerly supposed to belong to the Permian era. The remains alluded to belong to the order Grallatores (Wading Birds), and are allied to the cranes and herons of the present day.

The Oolitic or Jurassic formation consists of three principal groups, or Lower, Middle, and Upper Oolite. It is more varied in its mineral composition than the Lias, but consists mainly of alternations of Oolitic limestone, calcareous grits, and shelly conglomerates, and, like the Lias, is a strictly marine deposit. Its flora is abundant, comprising cycadeæ, ferns, equisetacea, and pines; and here cypresses, yews, dammaras, and thujas, together with liliacea and screw-pines, make their earliest appearance. The Brora coal, one of the most considerable Oolitic coal-seams in Europe, seems to have been formed exclusively of Equisetum columnare. It is also extremely rich in animal remains, especially in its Radiata, Mollusca, Crustacea, Fishes, Tortoises, and Sauroid Reptiles. Insects greatly abound, and appear to have formed the almost exclusive food of the MAMMALIA, which make their earliest appearance in the Lower or Inferior Oolite. The most ancient representative of this class, so far as yet known, is named Dromatherium sylvestre, a marsupial animal, allied to the kangaroo. The Marsupialia (Pouched Animals)

are regarded as the lowest order of Mammalia, and as forming in some respects a connecting-link between Placental or true Mammals and Birds. Till very recently, no higher order of Mammals was known in strata lower down than the earliest Tertiaries; but in 1857 numerous bones of Placental animals were detected in the Middle Purbeck beds of the Upper Oolite, only a few feet below the Wealden.

The Wealden formation (so called from the "wealds" or "wolds" of Sussex and Kent, in which it so extensively occurs) consists of two principal series of strata-the Hastings Sands and the Weald Clay. It is chiefly remarkable as being the only fresh-water formation occurring within the limits of the Secondary or Mesozoic Series. In the counties above-named it appears to occupy the site of an ancient estuary, which received the clay and sand of a gigantic river. Accordingly its fossils are partly fluviatile, and partly terrestrial, the spoils of the river and the land, not of the sea. Marine species, however, not differing from those of the lower beds of the Cretaceous System, frequently occur in what is supposed to have been the mouth of the estuary. The remains of plants are numerous, resembling in general those of the Oolitic formation. Among the most characteristic forms may be reckoned Sphenopteris gracilis (a sort of fern), leaves of Coniferæ and Cycadaceae, together with silicified Coniferous trees, and fruits resembling those of palms. Altogether, about 70 species have been described as belonging to this formation, all of them belonging to Monocotyledonous orders-that is, plants having no separable bark, no distinct concentric circles, not increasing at their periphery, no medullary rays, and the solidity decreasing inwards.

Its fauna, on the other hand, more closely resembles that of the chalk. The most characteristic forms among its Mollusca belong to genera which at the present day occur in rivers, marshes, and lakes, such as Unio, Cyclas, Paludina, Neritina, and Cypris. The Articulata comprise numerous species of Insects and Crustacea. The Fishes are of a peculiar character, somewhat resembling the perch, and belong to the placoid and ganoid divisions: among them are several species of Hybodus and Lepidotus. Reptiles of many genera are found, including Tortoises, Crocodiles, and other Saurians, of which the most remarkable is the Iguanodon, a gigantic herbivorous animal, upwards of 70 feet in length, including the tail. Pterodac tyles also, or flying reptiles, form a striking characteristic of the fauna of the Wealden. Uniting the characters of the bird and reptile, and somewhat resembling the bats of the present day, they were capable of leading an aerial, as well as a terrestrial existence.

Morris and Tennant give 998 species as belonging to the entire Oolitic system as developed in the British Isles, including 3 species of Mammalia, 40 Reptiles, 160 Fishes, 205 Cephalopoda, 103 Gasteropoda, 54 Brachyopoda, 127 Monomyaria, 210 Dimyaria, 12 Insects, 4 Crustacea, 3 Cirrhipedia, 23 Annelida, 41 Echinodermata, 33 Zoophyta, 7 Amorphozoa, and 75 Plants. Since the recent disco

veries in the Middle Purbecks, however, the number of Mammals has been considerably increased.

8. The Cretaceous System, which derives its name from the chalk (creta) that forms the main ingredient in its composition, is the uppermost member of the Secondary or Mesozoic series. It is usually regarded as embracing two well-defined formations-the Greensand and the Chalk, each of which must have been a deep-sea deposit. The flora of the system is not very abundant, and appears to consist, for the most part, of drifted and imperfect fragments. Of its 181 known species of plants, no fewer than 159 are common to it with the underlying Oolitic, Triassic, and Permian systems. The Ferns, Equisetacea, and allied forms, so characteristic of lower strata, become here very unfrequent; but the Cycadeæ and Coniferæ are still pretty numerous. But by far the most interesting feature in the flora of the Chalk is the appearance, for the first time, of leaves and other indications of EXOGENOUS, or Dicotyledonous trees, i.e. trees having a separable bark, distinct concentric circles, composed of progressive indefinite vascular bundles, increasing at their periphery, the solidity diminishing from the centre towards the circumference, and the pith enclosed in a longitudinal canal or medullary sheath, with cellular prolongations in the form of medullary

rays.

The fauna is so rich and varied that no attempt can be made here to describe it in detail. Suffice it to say, that all the types of life are strictly Mesozoic; for, of the numerous and often peculiar species found in it, not one has been identified with any organism occurring in the Tertiary strata above. The fossils of the Greensand, or Lower Cretaceous formation, are also, in general, specifically different from those of the Upper, or Chalk. Notwithstanding, however, the great diversity of animal life, little onward progress appears to have been made in the grand march of being, during the deposition of the Cretaceous strata. No reliable evidence of the existence of land mammals in the Cretaceous era has hitherto been found. Bones of seals and cetacea, however, have been detected in the Cretaceous beds of New Jersey. A similar statement may be made respecting Birds; for, excepting some traces in the Oolite, and the occurrence in the Chalk of Maidstone of the bones of a supposed bird (which Owen has named Cimoliornis Diomedeus, but which Mr Bowerbank maintains is a pterodactyle), no undoubted vestiges of this class of Vertebrata appear in the wide gap that separates the Lias of Connecticut from the Eocene strata. Reptiles, though still the dominant class, have now passed their meridian, and are visibly reduced in their standing; but turtles, pterodactyles, and oviparous saurians are not unfrequent. Fishes comprise between 30 and 50 species of placoids, between 15 and 20 ganoids, 6 species of CTENOIDS, and 12 species of CYCLOIDS. The last two orders appear in this system for the first time, and are gradually developed in creation until the human period, when they greatly exceeded in number and importance all other fishes. Of the Ctenoid or comb-scaled order, several species of beryx-a genus closely allied to the perch-are the most numer

ous; and of the Cycloid order, composed of fishes whose scales, like those of the salmon, are defined all round by a simple continuous margin, the Saurocephalus and Osmeroides are those most frequently met with. The remains of Mollusca are extremely numerous, and in the highest state of preservation. The chambered shells-especially certain species of ammonites, scaphites, belemnites, baculites, and turrilites-present a great contrast to the testacea of the Tertiary and recent periods. The bivalves embrace Inoceramus (a genus now extinct), Pectens, Ostrea, and Plagiostoma. The most characteristic species of univalves are rostellaria, cerithium, natica, dentalium, and littorina. The Articulata comprise several star-fishes, as goniaster and oreaster; and numerous echinidæ, as Salenia personata, Echinus granulosus, Galerites subuculus, Galerites cylindricus, Nucleolites carinatus, Galerites castanea, and Micraster cor-anguinum.

9. The Tertiary System, or Cainozoic Series, embraces three formations, named respectively the Eocene, Miocene, and Pliocene; or Lower, Middle, and Upper Tertiaries. The Pleistocene, or boulder clay formation, is also generally reckoned as a member of the Tertiary system; but as it is not an ordinary sedimentary deposit, and is for the most part devoid of fossils, we may omit it from present consideration. The remainder consists of vast and varied deposits -fluviatile, lacustrine, marine, and volcanic-all of which are usually found deposited in hollows and depressions of the chalk, but occasionally in those of older rocks. It would appear that during the period of their deposition important changes took place in the relative level of land and sea-that volcanic agency was developed on a vast and magnificent scale that the portion of Europe now forming the British Isles was the site of enormous lakes, which at the present day have their best analogues in the vast fresh-water lakes of Canada-and that, during the same epoch, a gradual refrigeration of temperature took place in European countries, and such an approximation to their present climate as to admit of the existence of plants and animals similar to, or identical with, those now existing in that part of the world.

On entering the Tertiary strata, the paleontologist finds that organic nature has undergone a vast change; that every plant and animal with which he became acquainted when studying the secondary rocks has passed away, and that he has entered on a wholly different order of things. "With the chalk," says Ansted, "we close as it were one great volume of animated creation. Everything up to this point belongs to the past; everything on this side of it may be ranked among indications of the present.' Never before, during the præ-Adamic history of our earth, did so thorough and total a change take place in its fauna and flora; for though that change was very great at the commencement of the secondary era, certain organisms connect that era with the paleozoic; whereas at the commencement of the Tertiary era it is universal, and there are no species common to both series serving to bridge over the chasm which separates them. The flora is especially distinguished from that of the older epochs by the

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