The Wealden is a mass of petrified clay, sand, and sandstone, deposited from the fresh or brackish water of probably some great estuary, and extending over parts of the counties of Kent, Surrey, and Sussex. This fresh-water formation derives its name from the “Weald” or “Wold” of Kent, where it was first geologically studied, and where it is exposed by the removal of the chalk, which covers or overlies it, in other parts of the South of England.
The Wealden is divided into three groups of strata, which succeed each other in the following descending order:—
1st. Weald Clay, sometimes including thin beds of sand and shelly limestone, forming beds of from 140 to 280 feet in depth or vertical thickness.
2nd. Hastings Sand, in which occur some clays and calcareous grits, forming beds of from 400 to 500 feet in depth.
3rd. Purbeck Beds, so called from being exposed chiefly in the Isle of Purbeck, off the coast of Dorsetshire, where it forms the quarries of the limestone for which Purbeck is famous: the beds of limestones and marls are from 150 to 200 feet in depth.
One afternoon, in the spring of 1822, an accomplished lady, the wife of a medical practitioner, at Lewes, in Sussex, walking along the picturesque paths of Tilgate Forest, discovered some objects in the coarse conglomerate rock of the quarries of that locality, which, from their peculiar form and substance, she thought would be interesting to her husband, whose attention had been directed, during his professional drives, to the geology and fossils of his neighbourhood.
The lady was Mrs. Mantell: her husband, the subsequently distinguished geologist, Dr. Mantell,[2] perceived that the fossils discovered by his wife were teeth, and teeth of a large and unknown animal.
“As these teeth,” writes the doctor, “were distinct from any that had previously come under my notice, I felt anxious to submit them to the examination of persons whose knowledge and means of observation were more extensive than my own. I therefore transmitted specimens to some of the most eminent naturalists in this country and on the continent. But although my communications were acknowledged with that candour and liberality which constantly characterise the intercourse of scientific men, yet no light was thrown upon the subject, except by the illustrious Baron Cuvier, whose opinions will best appear by the following extract from the correspondence with which he honoured me:—
“‘These teeth are certainly unknown to me; they are not from a carnivorous animal, and yet I believe that they belong, from their slight degree of complexity, the notching of their margins, and the thin coat of enamel that covers them, to the order of reptiles.
“‘May we not here have a new animal!—a herbivorous reptile? And, just as at the present time with regard to mammals (land-quadrupeds with warm blood), it is amongst the herbivorous that we find the largest species, so also with the reptiles at the remote period when they were the sole terrestrial animals, might not the largest amongst them have been nourished by vegetables?
“‘Some of the great bones which you possess may belong to this animal, which, up to the present time, is unique in its kind. Time will confirm or confute this idea, since it is impossible but that one day a part of the skeleton, united to portions of jaws with the teeth, will be discovered.’”
“These remarks,” Dr. Mantell proceeds to say, “induced me to pursue my investigations with increased assiduity, but hitherto they have not been attended with the desired success, no connected portion of the skeleton having been discovered. Among the specimens lately connected, some, however, were so perfect, that I resolved to avail myself of the obliging offer of Mr. Clift (to whose kindness and liberality I hold myself particularly indebted), to assist me in comparing the fossil teeth with those of the recent LacertÆ in the Museum of the Royal College of Surgeons. The result of this examination proved highly satisfactory, for in an Iguana which Mr. Stutchbury had prepared to present to the College, we discovered teeth possessing the form and structure of the fossil specimens.” (Phil. Trans., 1825, p. 180.) And he afterwards adds:—“The name Iguanodon, derived from the form of the teeth, (and which I have adopted at the suggestion of the Rev. W. Conybeare,) will not, it is presumed, be deemed objectionable.” (Ib. p. 184.)
The further discovery which Baron Cuvier’s prophetic glance saw buried in the womb of time, and the birth of which verified his conjecture that some of the great bones collected by Dr. Mantell belonged to the same animal as the teeth, was made by Mr. W. H. Bensted, of Maidstone, the proprietor of a stone-quarry of the Shanklin-sand formation, in the close vicinity of that town. This gentleman had his attention one day, in May, 1834, called by his workmen to what they supposed to be petrified wood in some pieces of stone which they had been blasting. He perceived that what they supposed to be wood was fossil bone, and with a zeal and care which have always characterised his endeavours to secure for science any evidence of fossil remains in his quarry, he immediately resorted to the spot. He found that the bore or blast by which these remains were brought to light, had been inserted into the centre of the specimen, so that the mass of stone containing it had been shattered into many pieces, some of which were blown into the adjoining fields. All these pieces he had carefully collected, and proceeding with equal ardour and success to the removal of the matrix from the fossils, he succeeded after a month’s labour in exposing them to view, and in fitting the fragments to their proper places.
This specimen is now in the British Museum.
Many other specimens of detached bones, including vertebrÆ or parts of the back-bone, especially that part resting on the hind limbs, and called the “pelvis,” bones of the limbs, down to those that supported the claws, together with jaws and teeth, which have since been successively discovered, have enabled anatomists to reconstruct the extinct Iguanodon, and have proved it to have been a herbivorous reptile, of colossal dimensions, analogous to the diminutive Iguana in the form of its teeth, but belonging to a distinct and higher order of reptiles, more akin to the crocodiles. The same rich materials, selecting the largest of the bones as a standard, have served for the present restorations (Nos. 4 and 5) of the animal, as when alive: all the parts being kept in just proportion to the standard bones, and the whole being thus brought to the following dimensions:—
| Total length, from the nose or muzzle to the end of the tail | 34 | feet | 9 | inches. |
| Greatest girth of the trunk | 20 | ” | 5 | ” |
| Length of the head | 3 | ” | 6 | ” |
| Length of the tail | 15 | ” | 6 | ” |
The character of the scales is conjectural, and the horn more than doubtful, though attributed to the Iguanodon by Dr. Mantell and most geologists.
This animal probably lived near estuaries and rivers, and may have derived its food from the ClathrariÆ, ZamiÆ, Cycades, and other extinct trees, of which the fossil remains abound in the same formations as those yielding the bones and teeth of the Iguanodon.
These formations are the Wealden and the Neocomian or green-sand: the localities in which the remains of the Iguanodon have been principally found, are the Weald of Kent and Sussex: Horsham, in Sussex; Maidstone, in Kent; and the Isle of Wight.
Restorations of the Cycas and Zamia are placed, with the Iguanodon, on the Wealden division of the Secondary Island.
No. 6.—The HylÆosaurus. (HylÆosaurus Owenii.)
The animal, so called by its discoverer, Dr. Mantell, belongs to the same highly organised order of the class of reptiles as the Iguanodon, that, viz., which was characterised by a longer and stronger sacrum and pelvis, and by larger limbs than the reptiles of the present day possess; they were accordingly better fitted for progression on dry land, and probably carried their body higher and more freely above the surface of the ground.
Visiting, in the summer of 1832, a quarry in Tilgate Forest, Dr. Mantell had his attention attracted to some fragments of a large mass of stone, which had recently been broken up, and which exhibited traces of numerous pieces of bone. The portions of the rock, which admitted of being restored together, were cemented, and then the rock was chiselled from the fossil bones, which consisted of part of the back-bone or vertebral column, some ribs, the shoulder bones called scapula and coracoid, and numerous long angular bones or spines which seemed to have supported a lofty serrated or jagged crest, extended along the middle of the back, as in some of the small existing lizards, e.g., the Iguana: cut No. 6. Many small dermal bones were also found, which indicate the HylÆosaurus to have been covered by hard tuberculate scales, like those of some of the Australian lizards, called Cyclodus.
This character of the skin, and the serrated crest, are accurately given in the restoration, the major part of which, however, is necessarily at present conjectural, and carried out according to the general analogies of the saurian form. The size is indicated with more certainty according to the proportions of the known vertebrÆ and other bones.
No. 6. Diagram of the Slab containing the Bones of HylÆosaurus.
