During the incalculable ages which the deposition of the various systems of sedimentary strata must have comprised, we find no evidence in the fossils hitherto observed, of the existence of Birds and Mammalia as the characteristic types of the faunas of the dry land. On the contrary, throughout the immense accumulations of the spoils of the ancient islands and continents, amidst innumerable relics of reptiles of various orders and genera, portions of six or seven lower jaws, and a few bones, of two genera of extremely small terrestrial quadrupeds, and the bones of a species of wading bird, are the only indications of the presence of the two grand classes, Mammalia and Aves, which constitute the chief features of the terrestrial zoology of almost all countries.

The earliest indications of air-breathing vertebrata in the ancient secondary formations, are the supposed footprints of a chelonian reptile on the Potsdam limestone (Lower Silurian) of North America,' and the bones of small saurian reptiles in the Carboniferous strata; a few vestiges occur in the succeeding group, the Permian. In the next epoch, the Triassic, colossal Batrachians (Labyrinthodons) appear; and on some of the strata of this formation are the footmarks of numerous bipeds, presumed to be those of birds, which have already engaged our attention; but at present the evidence required to establish the hypothesis is incomplete, for no bones of the animals that made those imprints have been discovered.

and

In the succeeding eras, the Liassic, Oolitic, Wealden, and Cretaceous, swarms of reptiles of numerous genera and species everywhere prevail; reptiles fitted to fly through the air, to roam over the land, to inhabit the lakes, rivers, and seas; yet not one identical with any existing forms! These beings gradually decline in numbers and species as we approach the close of the Secondary periods, and are immediately succeeded, in the Tertiary epochs, by as great a preponderance of warmblooded vertebrata-Birds and Mammalia-as exists at the present time, and an equal decadence in the Class of Reptiles. With the Cretaceous Formation the " Age of Reptiles" may therefore be said to terminate.

1 A discovery recently made by Mr. Logan is supposed to establish this fact. Casts of these very equivocal imprints may be seen in the highly instructive and beautifully arranged Museum of Practical Geology, in Jermyn Street, London.

FOSSIL BONES OF REPTILES.-The state of mineralisation of the fossils we have now to examine, differs considerably from that presented by the ornithic relics from New Zealand. The osseous carapaces and plastrons of the turtles, and the bones and teeth of the crocodiles and lizards, are almost without exception heavy, and of various shades of brown or umber, from the permeation of their structures by solutions of carbonates or oxides of iron.

In some instances, bones of a jet black are imbedded in white calciferous grit; the phosphoric acid in the original organism having combined with iron and produced a deep blue or black phosphate of that mineral, and left the surrounding stone uncoloured.

Infiltration of calcareous spar is a mode of fossilisation equally common; and the cancellous structure, and the medullary cavities of the long bones, are very often filled, more or less, with white calc-spar; brilliant pyrites also enters into the composition of these fossils, frosting over with a golden metallic deposit the linings of the cavities and fissures.

The petrifaction of the teeth by mineral matter, produces beautiful examples of the intimate tissues of those organs; the dentine is often stained throughout with a rich sienna tint, and sections viewed under the microscope by transmitted light, reveal the character and distribution of the calcigerous tubes more defined even than in recent specimens.

It is extremely rare that osseous structures are found silicified, or, in other words, petrified by flint; among the many thousands of bones which I have extricated from the rock, or have seen in collections, I know but of a solitary instance, a caudal vertebra of a Mosasaurus, which I obtained from a chalk-pit near Brighton. But notwithstanding the weight and apparent solidity imparted by these modes of mineralisation, the osseous substance is generally rendered extremely brittle, so that the development of the bones from the stone in which they are imbedded, and the removal of the hard ferrugino-calcareous crust investing them, is no easy task, but requires much tact and experience and patience to execute successfully.

The observer, therefore, must not suppose that specimens like the fossil Turtles and Reptiles in the first Cases, or the colossal bones from the Wealden, in Case B, or the

splendid skeletons of Plesiosauri spread out on slabs of grey limestone in Cases D and E, are to be found in the strata in a condition that would admit of their being even recognised as organic remains by the uninstructed eye. On the contrary, mere shapeless masses of rock, with here and there fragments of bone scarcely distinguishable from the surrounding stone, are in general the sole indications of these precious monuments of distant ages, that have been enshrined for an incalculable period, and which require the skill and labour of the practised explorer to develop and render intelligible to the comparative anatomist.

The degree of distortion which the strong and massive bones of the colossal reptiles of the Wealden have in many instances sustained, is truly remarkable. Leg and thighbones, and the bodies of vertebræ of enormous size, and which were originally of a sub-cylindrical form, are found twisted, contorted, and pressed almost flat, and yet with but slight indications of fracture. It is clear that the skeletons of the stupendous saurians must have been rendered plastic by long maceration in water before the mud and sand in which they were engulfed had consolidated around them, and ere their tissues were permeated by mineral matter.

The Maidstone Iguanodon, (Table-Case 23 of the plan, ante, p. 138,) is a striking example of this kind; in the entire series of bones exposed, there is scarcely one that is not more or less altered by compression. The humerus and thigh-bones especially, are completely distorted; the vertebræ pressed almost flat, or squeezed into abnormal shapes; one of the clavicles is twisted and thrown into the most fantastic position; and so great was the transformation the bones had sustained, that although Mr. Bensted had spent weeks in clearing out the most obvious masses of bone, and had marked the relative connexion of the principal pieces into which the specimen had been fractured by the explosion of the rock, it was several months, and with the aid of a mason, before I succeeded in cementing the pieces together, and restoring the fractured parts to their present state; nor could this have been successfully effected, had I not previously obtained perfect specimens of almost all the parts of the skeleton of the Iguanodon, which in this instructive fossil were found associated together for the first time, to guide

my chisel, and enable me to avoid the destruction of concealed portions of bone.1

With these prefatory remarks to prepare the uninstructed visitor for the general appearance of the fossilized osseous remains deposited in this apartment, we proceed to examine somewhat in detail, the various relics of petrified reptiles it contains.

FOSSIL TURTLES.-Wall-Cases A and B. [1, 2.]— The earliest indications of the presence of Reptiles on our planet, are those afforded by the foot-prints of Turtles or Chelonians, apparently of terrestrial species, on the surfaces of the layers of sandstone of the New Red formation, in Dumfriesshire in Scotland, at Storton, near Liverpool, and in several places in Germany. But no osseous remains of Chelonia have hitherto been found in strata antecedent to the Oolite.

2

The Solenhofen quarries have yielded the bones and carapaces of several species of marine Turtles: and scutes and bones of animals of this family have been found at Stonesfield, and in the Bath and Portland Oolite. In the Jura limestone at Soleure, two large species of Emydians (freshwater tortoises) have been discovered.

The Wealden formation contains Chelonian remains of fluviatile and marine genera; many specimens have been collected in the Isle of Purbeck; and my own researches in the strata of Tilgate Forest have brought to light several species, and in particular an interesting Chelonian related to the soft-skinned, fresh-water Tortoises (Trionyces).

In the Cretaceous formation of England the remains of these reptiles are not frequent. The Greensand of Cambridgeshire and of Kent has yielded marine species; and in the White Chalk a few beautiful examples have been obtained.

On the Continent, fossil turtles have been found in the slate of Glaris; and in the upper Cretaceous strata at Maestricht. At Melsbroeck, near Brussels, very fine specimens of fresh-water (Emydes), and marine (Chelonia) turtles have been discovered.3

'Consult "Medals of Creation, or First Lessons in Geology," for additional remarks on this subject.

2 See Dr. Buckland's Bridgewater Essay, vol. i. p. 259.

3 "Oss. Foss." Tome v. pp, 236, 239.

From the Eocene strata of England remains of several genera have been obtained. The Isles of Sheppey and Wight, and the coasts of Hants and Essex, have yielded fossil Chelonians in considerable numbers.

The Eocene Strata of France contain several fresh-water Tortoises, some of which belong to the family of Emydes, and others to Trionyces.

Testudinata, or Land-Tortoises, are exceedingly rare; no unquestionable remains of this kind are known in the British strata; but the Tertiary formations of India have furnished decided examples; and among the innumerable relics of vertebrata which the indefatigable labours of Dr. Falconer and Major Cautley have brought to light, and skilfully developed, are the remains of Land-Tortoises of prodigious magnitude, to which we have already adverted when pointing out the model of the Colossochelys Atlas, at the entrance of Room I. (ante p. 11). These remains are associated with the bones of gigantic extinct mammalia, allied to the Palæotheria and other pachydermata of the Paris basin; and with those of Gavials, and of small Land-Tortoises, of species that still inhabit India.

The fossil remains of Chelonian reptiles generally consist of the detached plates of the carapace and plastron, but considerable portions of the convex shell formed by the expanded and united costal plates, and of the plates of the sternum, are not uncommon. In a few instances, as in the Isle of Wight Eocene Turtles, collected and developed with consummate skill by the Marchioness of Hastings,—and some of the Sewalik Chelonians chiselled out of the rock by Mr. Dew, and placed in Room VI.—the entire carapace or buckler, and sternum or floor, are as perfect as in the recent skeleton. The cranium and bones of the pelvic and pectoral arches, and of the paddles, are often found detached, and occasionally in connexion with the carapace.

CHELONIANS.-Wall-cases A-B.-The fossil Turtles in this

1 At the head of British Chelonia (Brit. Rep. p. 190), Testudo Duncani (Owen), is placed; but the Report does not contain the description of any Chelonian remains that can be referred to this species. Equivocal imprints on stone are surely insufficient, in the absence of all corroborative evidence, to justify either generic or specific distinctions.