The total thickness of the Wealden (inclusive of the Purbeck beds) is estimated at upwards of 1,500 feet, being equal to three times that of the delta of the Mississippi.*

WEALDEN STRATA OF THE ISLE OF WIGHT.-In the Isle of Wight but a small portion of the upper series of clays, sands, and sandstones is exposed to view. These deposits constitute the line of coast already noticed, in Sandown Bay, and the range of cliffs from near Atherfield Point to Compton Bay. The section exposed in the cliffs on the south-western coast, is shown in lign. 16. (p. 157), from Dr. Fitton's Memoir; to which reference must be made for details, which, though of great value in a scientific point of view, possess but little interest for the general observer.† The Wealden strata forming this line of coast consist of laminated clays, shales, and loosely coherent sands, full of freshwater shells and crustaceans, with lignite, and in some strata abundance of pyrites; layers, a few inches in thickness, of tough bluish argillaceous shelly limestones, some being composed chiefly of bivalves, and

with the leaves and stems of ferns, cycadeous plants, &c., in the strata of Tilgate Forest, of which there were not the slightest traces in the cretaceous deposits, corroborated the inferences suggested by my previous observations. In 1822 the Tilgate strata were first described, and their freshwater origin pointed out in "The Fossils of the South Downs." In June, 1822, I communicated to the Geological Society of London an account of the extension of these strata over Sussex, being the result of my own and Mr. Lyell's observations. In 1827, "The fossils of Tilgate Forest," containing nearly 200 figures of Wealden fossils, was published. See Dr. Fitton's charming little work-"A Geological Sketch of the Vicinity of Hastings." London, 1832. P. 13. * The delta of the Mississippi is computed by Mr. Lyell to be 528 feet, or about the tenth of a mile in depth; the area it covers, 13,600 square statute miles; the solid matter annually added, 3 billions 700 millions cubic feet; and the period required for its formation, many thousand years.

"Geol. Trans." vol. iv. second series, p. 197-220.

others of univalves; sands, with concretionary nodules of calcareous compact grit and sand-rock; and variegated clays, mottled with different shades of red, yellow, blue, green, and grey; waterworn bones of reptiles occur throughout. But the subdivisions of the Wealden are in a great measure arbitrary, for the same fossils and the same lithological characters pervade the entire series. Beds of sands, clays, and argillaceous limestones, and calciferous grits, almost identical in mineral composition, and containing similar organic remains, are found alike in the upper and lower part of the series; indicating a similar condition of the land and water throughout the Wealden epoch. In that part of Sussex over which my earliest researches extended, the univalve limestones (Sussex marble) and shales predominate in the upper series; sands and calciferous grits alternating with clays in the middle; and bivalve limestones and clays in the lower division. But in the Isle of Wight, the clays and limestones with bivalves are as abundant as those with univalves; and slabs from Sandown and Compton Bays could not be distinguished from the shelly limestones of Ashburnham and Battel, in Sussex.*

EXCURSION TO BROOK BAY.-The Wealden strata extend between six and seven miles along the coast; we have already noticed their emergence from beneath the greensand at Atherfield Point (ante, p. 163) and at Compton Bay (p. 156). From Compton Chine to Brook Chine, a distance of but little more than two miles and a half, the most interesting phenomena may be examined in a stroll

It may be worth inquiry whether the Wealden strata of the Isle of Wight really belong to the upper division-whether they may not be referable to a lower group, and the superior beds have been destroyed by the incursions of the sea, before the delta subsided, and the greensand was deposited upon the now uppermost bed of clay?

along the beach, which should be undertaken at the ebb of the tide, to allow of sufficient time for the collection of specimens. If a brief visit only be contemplated, the tourist should drive to Brook, and within a short distance of the chine,* and he may alight within a few hundred yards of the most interesting spot the fossil forest at Brook Point. The most favourable season for a geological examination of this part of the coast is the early springthe latter end of March or the beginning of April-for at low water a great extent of sand is laid bare, and reefs of Wealden sand-rock are seen stretching far out to sea; and the high tides often sweep away the shingle from the base of the cliffs, and the lowermost visible strata are exposed. The chance of obtaining fossil bones is also greater at this period of the year than at any other, owing to the inroads of the sea on the clay cliffs, and the consequent dislodgment of any bones they may contain; and as these relics are very heavy from an impregnation of pyrites, they fall on the shingle, and are left by the retiring waves.

We shall commence our ramble at the foot of Compton Chine, near which place fossils of the greensand and of the Wealden alike abound.

CLIFFS FROM COMPTON CHINE TO BROOK POINT.The description of the coast as seen from the foot of Afton Down, given on our previous visit to Compton Bay (p. 153, Pl. XI.), and a reference to the sections in lign. 16 and 17, p. 157, and to the map (Pl. XX.), will afford the necessary information as to the geological relations of the strata we are about to examine. As we descend to the sea-shore near Compton Chine, the top of the cliff, to the depth of ten or twelve feet, is seen to be composed of drifted gravel, clay, and loam; and this alluvial covering continues for several miles along the coast, forming, as shown in the

* There is no inn near the spot, but accommodation for horses may be obtained at a neighbouring farm-house or cottage.

M

annexed sketch (Pl. XIV.), a horizontal bed upon the edges of the inclined strata of which the lower part of the cliff consists. In this accumulation of drifted materials are numerous trunks of trees and quantities of hazel-nuts, in the usual condition of peat or bog-wood. The trunks are several feet in length, and a foot or more in diameter; the ligneous substance is very black and soft when first extracted, but hardens after exposure to the air; and some of the wood is so firm in texture as to be employed for various domestic purposes. I could not learn that any bones had been found in this subterranean forest, but I picked up, on a bank hard by, teeth of the horse and deer, which were deeply stained with phosphate of iron, and probably belonged to this alluvial deposit.

The Wealden strata, to the east of their junction with the greensand, principally consist of clays, with seams of shale and sand, and layers of shelly limestone. The appearance of the face of the cliff formed by these strata is shown in Pl. XIV. In this view the nearest headland is Bullface Ledge; that beyond, which extends far out to sea, is Brook Point, the western extremity of the bay; that in the far distance is the eastern boundary of the same. view of Brook Point from Afton Down (Pl. XI. p. 153,) shows the continuance of the cliffs from beyond Bullface Ledge and Brook Bay to Blackgang Chine.

The

Masses of the Wealden clay with freshwater shells, in connexion with the greensand containing marine shells, should be the first objects of research. Mr. Morris was so fortunate as to obtain from this spot a mass in which specimens of a very characteristic univalve (Potamides carbonarius, Pl. VI. fig. 5) were imbedded. Waterworn blocks of the shelly limestones (Pl. VI. figs. 2, 3, 4), and rolled fragments of bones washed out of the cliffs, will be found in abundance in the shingle. Slabs of the freshwater limestones may be observed in the cliffs at an accessible