Above the Chalk we come first to a thick red clay called Plastic clay. It is much slipped, and the slip is overgrown. The only fossils found in the Island are fragments of plants; larger plant remains on the mainland show a temperate climate. This clay was formerly worked at Newport for pottery. The clay is probably a freshwater deposit formed in fairly deep water. On the mainland we find on the border shallow water deposits called the Woolwich and Reading beds. (The clay is 150 to 160 ft. thick at Whitecliff Bay, less than 90 ft. at the Alum Bay.) We come next to a considerable thickness of dark clay with sand, at the surface turned brown by weathering. This is the London clay, so called because it underlies the area on which London is built. At the base is a band of rounded flint pebbles, which extends at the base of the clay from here to Suffolk. In it, as well as in a hard sandstone 18 inches higher up, are tubular shells of a marine worm, Ditrupa plana. The sandstone runs out on the shore. About 35 ft. above the basement bed is a zone of Panopæa intermedia and Pholadomya margaritacea, at 50 ft. another band of Ditrupa, and at about 80 ft. a band with a small Cardita. In the higher part of the clay are large septaria,—rounded blocks of a calcareous clay-ironstone, with cracks running through them filled with spar. Pinna affinis is found in the septaria. The thickness of the clay in Whitecliff Bay is 322 feet. It can be seen on the shore, when the tide happens to have swept the sand away. Otherwise the lower beds are hardly visible, there being no cliff here, but a slope overgrown with vegetation.
In Alum Bay the London clay, about 400 ft. in thickness, consists of clays, chiefly dark blue, with sands, and lines of septaria. In the lower part is a dark clay with Pholadomya margaritacea, still preserving the pearly nacre. There are also Panopæa intermedia, and in septaria Pinna affinis. All these with their pearly lustre, are beautiful fossils. A little higher is a zone with Ditrupa, and further on a band of Cardita. Other shells also are found in the clay, especially in the lower part. They are all marine, and indicate a sub-tropical climate. Lines of pebbles show that we are near a beach. In other parts of the south of England remains from the land are found, borne down an ancient river in the way we found before in the Wealden deposits.
But times have changed since the Wealden days, and the life of the Tertiary times has a much more modern appearance. From leaves and fruits borne down from the forest we can learn clearly the nature of the early Eocene land and climate. Leaves are found at Newhaven, and numerous fossil fruits at Sheppey. The character of the vegetation most resembled that now to be seen in India, South Eastern Asia, and Australia. Palms grew luxuriantly, the most abundant fruit being that of one called Nipadites, from its resemblance to the Nipa palm, which grows on the banks of rivers in India and the Philippines. The forests also included plants allied to cypresses, banksia, maples, poplars, mimosa, custard apples, gourds, and melons. The rivers abounded in turtle—large numbers of remains of which are found in the London clay at the mouth of the Thames—crocodiles and alligators. With the exception of the south east of England, all the British Isles formed part of a continental mass of land covered with a tropical vegetation. The mountain chains of England, Scotland, and Wales rose as now, but higher. Long denudation has worn them down since. In the south-east of England the coast line fluctuated; and sea shells, and the remains of the plant and animal life of the neighbourhood of a great tropical river alternate in the deposits.
Fig. 4
| SECTION THROUGH HEADON HILL AND HIGH DOWN. SHOWING STRATA SEEN AT ALUM BAY. | |||||||||
| G | Gravel Cap. | LH | Lower Headon. | L | London Clay. | ||||
| Bm | Bembridge Limestone. | BS | Barton Sand. | R | Reading Beds. | ||||
| O | Osborne Beds. | B | Barton Clay. | Ch | Chalk. | ||||
| UH | Upper Headon. | Br | Bracklesham Beds. | ||||||
| MH | Middle " | Bg | Bagshot Sands. | ||||||
The London clay is succeeded by a great thickness of sands and clays which form the Bagshot series. These are divided in the London basin into Lower, Middle, and Upper Bagshot. In the Hampshire basin the strata are now classified as Bagshot Sands, Bracklesham Beds, Barton Beds, the last comprising the Barton Clay and the Barton Sand, formerly termed Headon Hill Sands. There is some uncertainty as to the manner in which these correspond to the beds of the Bagshot district, as the Tertiary strata have been divided by denudation into two groups, and differ in character in the two areas. It is possible that the Barton Sand represents a later deposit than any in the London area.
Almost the only fossil remains in the Bagshot Sands are those of plants, but these are of great interest. In Whitecliff Bay the beds consist for the most part of yellow sands, above which is a band of flint pebbles, which has been taken as the base of the Bracklesham series, for in the clay immediately above marine shells occur. The Bagshot Sands, in Whitecliff Bay, are about 138 feet thick, in Alum Bay, 76 feet, according to the latest classification. In Alum Bay the strata consist of sands, yellow, grey, white, and crimson, with clays, and bands of pipe clay. This is remarkably white and pure, as though derived from white felspar, like the China clay in Cornwall. The pipe clay contains leaves of trees, sometimes beautifully preserved. Specimens are not very easy to obtain, as only the edges of the leaves appear at the surface of the cliff. They have been found chiefly in a pocket, or thickening of the seam of pipe clay, which for forty years yielded specimens abundantly, afterwards thinning out, when the leaves became rare. The leaves lie flat, as they drifted and settled down in a pool. With them are the twigs of a conifer, occasionally a fruit or flower, or the wing case of a beetle. The leaves show a tropical climate. The flora is a local one, differing considerably from those of Eocene deposits elsewhere. The plants are nearly all dicotyledons. Of palms there are only a few fragments, while the London clay of Sheppey is rich in palm fruits, and many large palms are found in the Bournemouth leaf beds, corresponding in date to the Bracklesham. The differences may be largely due to conditions of locality and deposition. The Alum Bay flora is characterised by a wealth of leguminous plants, and large leaves of species of fig (Ficus); simple laurel and willow-like leaves are common, of which it is difficult to determine the species, and there is abundance of a species of Aralia. The character of the flora resembles most those of Central America and the Malay Archipelago.