Hastings sands

Interval between the sand cliffs and the rise

of the Purbeck strata

3,500 paces.

200

The cliffs in Durlstone Bay are entirely composed of the Purbeck strata; those in the middle are much bent and undulated, but in the southern part, the arrangement of the beds is well displayed. The termination of this coast at Durlstone Head, consists of the marine strata called the Portland oolite, which are seen to emerge from beneath the Purbeck hills. (See lign. 28.)

In the coast section thus briefly described we have, therefore, the following series:

I. The Cretaceous System, comprising the upper and
lower white chalk, firestone, galt, and greensand.

II. The Wealden, including the Weald clays, the
Hastings beds, and the Purbeck.

III. The Oolite, of which the upper, or Portland group
is alone visible.

Of these, the Purbeck and Portland strata are for the first time brought under the observation of the reader, and will therefore require more particular notice.

THE PURBECK STRATA.-The uppermost Purbeck bed is a green, calcareous, and for the most part friable, deposit, containing shells of a small species of Unio; beneath this is a stratum of the well-known marble, composed of an aggregation of the small river snail-shells already described (Paludina elongata, Pl. VI. fig. 2); a polished slice of this marble is figured in lign. 29. Some of the layers contain interspersions of the large paludinæ (P. fluviorum, Pl. VI. fig. 3) of the Sussex marble, and also a few small river mussels. I have seen polished slabs of this kind in which sections of bivalves (Uniones) formed the principal markings; these shells were associated with cyprides and very small fragments of bones, and vegetable detritus. The white and

* "Geological Transactions,” vol. iv. p. 207.

cream-coloured slates and coarser limestones, or Purbeck stone, as they are termed, are also shelly conglomerates, the prevailing shells being small species of the genera Cyclas, Cyrena, &c.*

LIGN. 29.-POLISHED SLAB OF PURBECK MARBLE.

(Composed of petrified river snail-shells.)

The stone now quarried is in the upper part of the series of shales, clays, and limestones. Mr. Webster states, that in the thickness of 125 feet, there are more than fifty layers of useful stone; these include a remarkable deposit, twelve feet thick, termed "Cinder" by the workmen, and which consists of a regular oyster-bed. The lower 150 feet are made up of shales, clays, and shelly limestones, too friable to be of any value in an economical point of view. The total thickness, from the uppermost bed to the Portland marine limestone, is about 275 feet.† Fibrous carbonate of lime, in layers two inches thick, is often found adhering to the bands of marble, as in the instance observed in Sandown Bay (p. 97).

FOSSILS OF THE PURBECK STRATA.-From what has been stated, the reader will be aware that the fossils of the Purbeck strata are identical in their general character with those of the upper divisions of the Wealden, described in

* Some of the most ancient pavement in Ely Cathedral consists of slabs of the Purbeck bivalve limestone.

Mr. Webster, in "Geological Transactions," vol. ii., new series. Mr. Webster mentions having found some nodular concretions of chert, containing silicified freshwater shells in the state of chalcedony. I have not obtained any specimens of this kind.

the previous chapters. They consist of river shells, drifted land plants, bones of saurian and chelonian reptiles, with the remains of fishes, and crustaceans; the absence of ammonites, echinites, zoophytes, &c., being as complete as in the Sussex Wealden.

Many bones of reptiles have been procured from Swanage cliffs,* and from the quarries in the neighbourhood; but the most remarkable fossil of this kind hitherto discovered, I had the good fortune to obtain, through the intelligence and liberality of Robert Trotter, Esq., F.G.S., of Sussex.

THE SWANAGE FOSSIL CROCODILE.-In the summer of 1837, the workmen employed in one of the quarries near Swanage, had occasion to split asunder a large slab of the fawn-coloured limestone, when, to their great astonishment, they perceived many bones and teeth imbedded on each of the exposed surfaces. As this was no ordinary occurrence, -for though scales of fishes, shells, and fragments, of bones, were frequently met with, an assemblage of bones had. never been observed before, both slabs were preserved; and Mr. Trotter, who casually visited the place, purchased them, and presented them to me. These slabs measure 3 feet 10 inches by 3 feet, and are a few inches in thickness. Many of the bones were split asunder in separating the stone, others were deeply imbedded, and of a few, imprints alone remain. Much labour and care were required to unite the several parts of the bones, to develop the others, and bring the specimens into the state in which they now appear. On one slab, a considerable portion of the left side of the lower jaw, with two teeth, is preserved; and several teeth, and numerous dermal or skin-bones, of a very peculiar form, are dispersed about the stone.† The * A description of some bones of the Iguanodon found on the shore, half a mile north of Swanage, is given by Dr. Buckland in "Geological Transactions," vol. iii. p. 429, new series.

†These dermal bones are figured in "Medals of Creation," vol. ii. p. 702.

bones of the pelvis, and some of those belonging to the extremities, with many caudal and dorsal vertebræ, and chevron bones, are imbedded in the same slab. The corres

ponding piece of stone bears the impression of the portion of jaw, and contains numerous dermal bones, vertebræ, &c.* Teeth and dermal bones of this reptile were among my earliest discoveries in Tilgate Forest; several teeth are figured by Baron Cuvier, in Oss. Foss. tom. v., and in my "Fossils of Tilgate Forest." In the latter work portions of dermal bones, or scutes, are represented, and described as belonging to the freshwater turtles called Trionyces; and it was not until I discovered more perfect specimens that the true nature of these bones was apparent. The gigantic Gavial of the Ganges, has rows of osseous scutes, which are deeply pitted on the external surface. Those of

L

LIGN. 30.-TOOTH OF THE

SWANAGE CROCODILE.

(Goniopholis crassidens.)

the Swanage Crocodile are distinguished by a lateral conical projection, which fits into a corresponding depression on the under surface of the opposite angle of the adjoining plate. Numerous hexagonal and pentagonal scutes, articulated together by marginal sutures, also entered into the composition of the cuirass of this reptile, which therefore, must have constituted a flexible and impenetrable coat of armour, capable of resisting the attack of the most formidable assailant. The teeth of the Gonio

The slab first described is figured in the "Wonders of Geology," vol. i. pl. i. Both specimens are now placed in an upright glass case against the wall, near the doorway of the room containing the remains of the Iguanodon and other Saurians, in the Gallery of Organic Remains, in the British Museum.

there is a prominent ridge The successional teeth are perfect old teeth, as in the

pholis (lign. 30) resemble in form those of the crocodile, but he crown is strongly marked with numerous sharp, welldefined, longitudinal striæ, and down the middle of each side. often found in the base of the crocodile. Some specimens from Tilgate Forest are two inches long, and half an inch in diameter at the base.* The vertebræ are biconcave, and have an irregular medullary cavity in the centre of the bone: the chevron bones resemble those of the crocodile.

FOSSIL TURTLES.-Waterworn bones of turtles are very common in the Purbeck strata, and several almost perfect examples of the carapace, or buckler, and of the plastron, or sternal-plates, have been discovered; a remarkably fine specimen from Purbeck, was exhibited many years since in Mr. Bullock's museum, in Piccadilly.

FOSSIL FISHES.-Detached angular scales of the wellknown Wealden fish, the Lepidotus, are often met with in the clays and limestones: and many specimens of the entire fish, of a smaller species of the same genus (Lepidotus minor) have been obtained. The small hemispherical teeth, termed by the quarry-men fishes' eyes, are of very frequent occurrence in many of the beds. The slabs containing the Goniopholis, previously described, have numerous teeth and scales of the Lepidotus minor scattered among the bones.

THE PORTLAND OOLITE.t-The series of sedimentary deposits, termed the oolite formation by English geologists, and known as the Jura limestone on the Continent, from the mountain-range in which it is so largely developed,

* See "Fossils of Tilgate Forest,” Pl. V. figs. 1, 2, 9.

The term Oolite, or egg-stone, is derived from many of the limestones being composed of an aggregation of very small grains or spherules, which bear some resemblance to clusters of small eggs, or to the roe of a fish. This structure is merely concretional.