detritus into compact limestone may have resulted in part from pressure, but principally from the slow infiltration of crystalline carbonate of lime; a process which has so rapidly converted the mud of the Bermudas into a rock fit for building, that the imbedded shells, in many instances, retain their natural colour and polish.

It may, therefore, with great probability, be assumed, that at the period when the cretaceous strata were subjected to those elevatory movements which ultimately raised enormous mountain-masses of chalk, together with the Wealden deposits on which they rest, above the level of the sea, the last-formed, uppermost, and, of course, least coherent beds, would be the first exposed to the action of the waves; and if the elevation were gradual,* successive layers would be subjected to the same agency, until the fragments of the ancient ocean-bed, now the Downs, were lifted above the reach of further destruction. The drainings of the elevated portions of the soft calcareous rock would then commence, and give rise to streams and rills, by which the surface would be worn into furrows and channels. Funnel-like cavities, and deep and narrow cylindrical and tubular hollows, would be formed by the gyratory action of eddies or whirlpools, induced by opposing currents. Such effects may be observed on the muddy dunes of an estuary during the recession of the tide. The beds of loose and but slightly water-worn flints-the undulated and unbroken contour of the gently-swelling hills and the smooth basin-shaped coombes and valleys of chalk districts characters which are strikingly exemplified in the hills before us, would be the natural result of such operations.

FROM FRESHWATER GATE TO COMPTON BAY.-The road to Compton Bay sweeps round the southern slope of

* See Mr. Lyell, on the elevation and denudation of the Wealden districts. "Elements of Geology," vol. ii.

Afton Down. The pedestrian should take the path along the edge of the cliff to Compton Chine, where a narrow track leads to the sea-shore. As we approach this spot, a fine view is obtained of the line of coast from the bay to beyond Brook Point, as is shown in the slight sketch, Pl. XI. The foreground is part of the southern slope of Afton Down, consisting of flinty chalk; and the foot-track to the Chine is seen crossing it on the right. The cliffs in this view are composed of the clays, shales, and sands of the Wealden, which continue to near Atherfield Point. The nearest headland is Brook Point, the western boundary of Brook Bay; and the one immediately beyond is the eastern limit of the same. The ledges of rock, extending from the foot of Brook Point into the sea, are chiefly composed of petrified trees. The most distant cape is part of the greensand cliffs, near Blackgang Chine; and the lofty range on the horizon is St. Catherine's Hill.

Compton Chine is a deep chasm worn in the ferruginous sands by a stream that falls from the summit of the cliff. It is situated to the west of the Blockade-station.

The footpath to the shore slopes along the face of the crumbling cliffs of greensand strata, which rise from beneath the upper divisions of the cretaceous system, as is shown in lign. 16. The succession of the beds from Freshwater to Compton Bay, i. e., from west to east, is as follows:

1. Upper or flinty chalk.

2. Lower chalk.

3. Firestone, comprising the chalk marl.

4. Galt.

5. Greensand, consisting of beds of ferruginous sands, clays, sandstones, and layers of very compact ironstone grit.

6. Wealden clays, sands, shales, and limestones.

GEOLOGICAL SECTIONS OF THE SOUTHERN COAST.The strata incline to the west, as is shown in lign. 16, to beyond Brook Chine, where the eastern side of the anti

clinal axis begins, and the dip is to the east, as represented in the continuation of the coast in lign. 17.

This line of cliffs is, in fact, the counterpart of that of Sandown Bay (ante, p. 96, lign. 9); but the Wealden deposits are here more developed, and extend between six and seven miles along the shore. As these cliffs consist of clays, sandy marls, shales, and other materials that offer but feeble resistance to the action of the waves, the destruction effected by the sea during the winter and early spring, when the highest tides prevail, is very great; and the Wealden fossils washed out of the cliffs and strewn along these shores are so numerous, that the strand between Compton Bay and Atherfield has yielded a greater number of fossil bones of colossal reptiles than any other part of the Island. In short, these strata and their organic remains impart to this portion of the southern shore so much interest, that it is desirable to postpone a particular account of the Wealden deposits for a special excursion to Brook Bay. We will therefore continue our survey of the greensand by proceeding from Compton to Atherfield, and along the Undercliff to Sandown Bay, where our investigation of the south coast commenced.*

The chalk, firestone, and galt of Compton Bay are not very prolific in fossil remains; but the greensand yields ammonites, trigoniæ, pernæ, &c.; and numerous specimens of the large oyster-like gryphea sinuata (Pl. V. fig. 3) are generally scattered on the sands and shingle at the foot of the cliffs. At the point where the lowermost bed of the greensand is in contact with the Wealden clays, the distinctive characters of the marine and freshwater deposits may sometimes be observed in a mass of the stratum but a few inches thick; marine shells appearing

* The visitor who would find it more convenient to continue his observations along the cliff to Brook Chine, should refer to chapter ix.