THE

WONDERS OF GEOLOGY.

LECTURE V.

PART I. THE JURASSIC FORMATION OOLITE AND LIAS.

1. Zoology of the Chalk. 2. Zoology of the Wealden. 3. Site of the Country of the Iguanodon. 4. Lithological structure of the Country of the Iguanodon. 5. Lower Secondary Formations. 6. General view of the Oolite and Lias. 7. The Oolite or Roe-stone. 8. Geographical distribution of the Oolite. 9. Railway-sections. 10. Subdivisions of the Oolite: Portland Rock. 11. Kimmeridge Clay. 12. Oxford Oolite or Coral-rag. 13. Oxford Clay. 14. Kelloways-rock and Cornbrash. 15. The Cotteswold Hills. 16. The Stonesfield Slate. 17. Organic Remains of the Stonesfield slate. 18. Fossil Mammalia of Stonesfield. 19. Comparison of the Stonesfield and Wealden Fossils. 20. Lithographic stone of Germany. 21. Coal-bearing strata of the Oolite. 22. Collyweston Slates. 23. Coal-bearing Oolite of Brora. 24. Coal-bearing Oolite of Eastern Virginia. 25. The Lias. 26. Organic Remains of the Jurassic System. 27. Zoophytes and Radiaria. 28. Mollusca. 29. Crustaceans and Insects. 30. Fishes. 31. Reptiles of the Jurassic System.

1. ZOOLOGY OF THE CHALK.-The examination of the Cretaceous and Wealden formations has afforded an instructive exposition not only of the nature of oceanic and fluviatile deposits in general, but also of the condition of animated nature at the close of the geological cycle which comprises the secondary epochs. It will therefore be expedient in this stage of our inquiry to consider the general features of the animal kingdom during the periods embraced in this review.

In the ocean-ped of the cretaceous period, we find vestiges of all the principal groups of existing marine organisms; comprising many genera of the Shark-family-viz. species of Cestracion, Lamna, Corax, &c.; with fishes related to the Chimæra, Salmon, Mackerel, Basse, &c. ;-in fact, the leading types of the majority of the fishes that inhabit the present seas.* The Cephalopoda (Cuttle-fishes) and Echinodermata (Sea-urchins, Star-fishes, and Encrinites) were profusely developed; crustaceans allied to the Hermit-crab, Lobster, Water-flea, &c.; univalve and bivalve mollusca; and innumerable multitudes of Sponges, Bryozoa, and Foraminifera ;-all these forms of animal existence have left enduring memorials of their presence in the seas of those remote ages. And, although we have likewise proof that numerous extinct genera, together with others now of excessive rarity, swarmed in prodigious numbers in the cretaceous ocean, and negative evidence that the Cetacea (see above, p. 325), as the Whale, Porpoise, Seal, &c., were not among its inhabitants, yet the diversified types of animated beings whose relics are entombed in these strata show that the waters of the deep possessed the same general conditions, and maintained the same relations with the atmosphere and with light, as at the present time.

The most remarkable peculiarity in the zoological features of the Chalk relates to the abundance of marine Reptiles; for, with the single exception of a lizard belonging to the family of the Iguanide, which inhabits certain parts of the sea-coasts of South America,† the Chelonians or Turtles are the only known existing marine animals of this class. But the cretaceous sea was tenanted by several Saurians of con* See the chronological table in M. Agassiz's Recherches sur les Poissons Fossiles, tome i.; and Morris, Catal. Brit. Foss. p. 316, &c.

The Amblyrhynchus cristatus of the Galapagos Islands: see Mr. Darwin's Journal, in the Colonial Library, p. 385; and Lyell's Manual, p. 326.

siderable magnitude, - namely, the Mosasaurus (p. 319), Polyptychodon (p. 367), Ichthyosaurus, Plesiosaurus; and by others of smaller size, such as small Turtles and the eellike Dolichosaurus.

Of the terrestrial fauna and flora, the evidence to be derived from deep-sea deposits must of course be scanty. We have, however, proof that tne then dry land bore forests of pines; that ferns and plants of the cycadeous tribes formed the prevailing vegetation; and that the country was inhabited by Iguanodons, Pterodactyles, and other reptiles.

2. ZOOLOGY OF THE WEALDEN.-From data of a like nature, we learn that during the deposition of the Wealden there was an extensive region traversed by streams and rivers swarming with fishes, crustaceans, and mollusca, of extinct species, but belonging to the same principal types as those which inhabit the fresh waters of warm climates under similar conditions: and that then, as now, marshtortoises and crocodilian reptiles tenanted the swamps and lagoons.

Of the inhabitants of the land, we have more ample information from the relics ingulfed in the deltas and lacustrine sediments, than could be afforded by deposits accumulated in the depths of the ocean, and far from the regions whence they were derived.

Colossal herbivorous and carnivorous lizards, differing essentially in their organization from all existing reptiles, and of which no vestiges have been discovered in any strata newer than the Chalk, were the principal terrestrial vertebrata of the Wealden epoch. These, together with some small mammals, a few flying reptiles, and lizards of small size, and probably some wading birds, appear to have constituted the entire vertebrate fauna of the regions which furnished the materials of this formation. The flora consisted chiefly of ferns, coniferous trees, cycadeous plants, cypresses, and a few unknown, but apparently related forms.

In fact, the islands and continents of the late Oolitic and early Cretaceous epochs, during which time the Wealden deposits were being formed, appear to have possessed many similar zoological and botanical characters. Here then we have the first glimpse of extensive regions almost exclusively inhabited by enormous reptiles: for, though the leaves and fruits of delicate plants, the fragile bones of birds and flying reptiles, the wings of insects, and the brittle shells of molluscs with their ligaments and epidermis remaining, are abundantly found imbedded in the sediments of the rivers and seas, but few traces of mammiferous animals, and those of small size,* have been discovered in the Wealden deposits. We have now approached the Age of Reptiles ;-that geological epoch, in which the earth swarmed with enormous oviparous quadrupeds, and the air and the waters alike teemed with reptilian forms.

3. SITE OF THE COUNTRY OF THE IGUANODON.-Before we pass to the investigation of the older secondary formations, I would briefly reconsider the question as to the geographical position of the principal tracts of country during the deposition of the Wealden and Cretaceous strata; --whether England was then dry land, and enjoyed a tropical climate; and whether turtles, crocodiles, and gigantic lizards here flourished amid groves of tree-ferns, and other productions of intertropical climes; or, on the contrary, whether the country of the Iguanodon was situated far distant from the area now covered by its spoils ?

The unequivocal marks of transport which, as we have seen, the fossils of the Wealden so generally exhibit, seem to demonstrate that the reptiles and terrestrial plants could not have lived and died in the regions where their relics are imbedded: for, with the exception of the beds of river-shells and minute crustaceans, and the plants which indicate a

* The Spalacothere and Plagiaulax, and their allies, in the Purbeck series.

lacustrine condition, the organic remains frequently bear indisputable marks of having been transported from some remote country, by a river or powerful flood of fresh-water.*

The specimen of the Hylæosaurus (ante, p. 449) throws light on this question. Many of the vertebræ and ribs are broken and splintered, but the fragments remain near each other: and, though the bones are more or less displaced, yet they lie in situations bearing some relation to their natural positions. These facts demonstrate that the carcass of the animal must have been contused and mutilated, and that the dislocated and broken parts were held together by the muscles and integuments. In this state the headless trunk must have floated down the river, and at length have sunk into the mud of the delta, where is formed a nucleus, around which the stems and foliage of ferns and cycadeous plants accumulated, and river-shells became intermingled in the general mass. Here then we have evidence of the body of a terrestrial reptile having been transported from a considerable distance by a stream or current of fresh water; for not the slightest indication of marine detritus can be traced in the deposits in which it was imbedded. The country where this animal lived and died may therefore have been situated far from the spot where its fossil remains were entombed.

An eminent geologist + has the following remarks on this subject:

"If it be asked where the continent was placed from the ruins of which the Wealden strata were derived, and by the drainage of which a great river was fed, we are half tempted to speculate on the former existence of the Atlantis of Plato. The story of the submergence of an ancient continent, however fabulous in history, may be true as a geological event. Its disappearance may have been gradual; and we need

The upright trees of the Isle of Portland present an exception; but this forest may have grown on an island very remote from the mainland, inhabited by colossal reptiles.

Lyell; Elements of Geology, Second Edition, vol. i. p. 432.