A Manual of Elementary Geology / or, The Ancient Changes of the Earth and its Inhabitants as Illustrated by Geological Monuments

by Sir Charles Lyell

Freshwater beds (2. a, Table, [p. 175.]).—In the northern part of the Isle of Wight, beds of marl, clay, and sand, and a friable limestone, containing freshwater shells, are seen, containing shells of the genera Lymnea (see [fig. 170.]), Planorbis, Melanopsis, Cyrena, &c., several of them of the same species as those occurring in the Eocene beds of the Paris basin. Gyrogonites, also, or seed-vessels of Chara, exhibiting a similar specific identity, occur. At Headon Hill, on the western side of the island, where these beds are seen in the sea-cliffs, some of the strata contain a few marine and estuary shells, such as Cytheræa, Corbula, &c., showing a temporary occupation of the area by brackish or salt water, after which the river or a lake seems again to have prevailed. A species of fan-palm, Flabellaria Lamanonis, Brong., like one which characterizes the Parisian Eocene beds, has been recently detected by Dr. Mantell in this formation, in Whitecliff Bay, at the eastern end of the island.

Several of the species of extinct quadrupeds already alluded to as characterizing the gypsum of Montmartre have been discovered by Messrs. Pratt and Fox, in the Isle of Wight, chiefly at Binstead, near Ryde, as Palæotherium magnum, P. medium, P. minus, P. minimum, P. curtum, P. crassum, also Anoplotherium commune, A. secundarium, Dichobune cervinum, and Chæropotamus Cuvieri. In Hordwell cliff, also on the Hampshire coast, several of these species, with other quadrupeds of new genera, such as Paloplotherium, Owen, have been met with; and remains of a remarkable carnivorous genus, Hyænodon. These fossils are accompanied by the bones of Trionyx, and other tortoises, and by two land snakes of the genus Paleryx, Owen, from 3 to 4 feet long, also a species of crocodile, and an alligator. Among other fossils collected by Lady Hastings, Sir Philip Egerton has recognized the well-known gar or bony pike of the American rivers, a ganoid fish of the genus Lepidotus, with its hard shining scales. The shells of Hordwell are similar to those of the freshwater beds of the Isle of Wight, and among them are a few specifically undistinguishable from recent testacea, as Paludina lenta and Helix labyrinthica, the latter discovered by Mr. S. Wood, and identified with an existing N. American helix.

The white and green marls of this freshwater series in Hampshire, and some of the accompanying limestones, often resemble those of France in mineral character and colour in so striking a manner, as to suggest the idea that the sediment was derived from the same region, or produced contemporaneously under very similar geographical circumstances.

Barton beds.—Both in the cliffs of Headon Hill and Hordwell, already mentioned, the freshwater series rests on a mass of pure white sand without fossils, and this is seen in Barton Cliff to overlie a marine deposit, in which 209 species of testacea have been found. More than half of these are peculiar; and, according to Mr. Prestwich, only 11 of them common to the London Clay proper, being in the proportion of only 5 per cent. On the other hand, 70 of them agree with the calcaire grossier shells. As this is the newest purely marine bed of the Eocene series known in England, we might have expected that some of its peculiar fossils would be found to agree with the upper Eocene strata described in the last chapter, and accordingly some identifications have been cited with testacea, both of the Berlin and Belgian strata. It is nearly a century since Brander published, in 1766, an account of the organic remains collected from these cliffs, and his excellent figures of the shells then deposited in the British Museum are justly admired by conchologists for their accuracy.

Bagshot Sands (2. c, Table, [p. 197.]).—These beds, consisting chiefly of siliceous sand, occupy extensive tracts round Bagshot, in Surrey, and in the New Forest, Hampshire. They succeed next in chronological order, and may be separated into three divisions, the upper and lower consisting of light yellow sands, and the central of dark green sands and brown clays, the whole reposing on the London clay proper.[199-A] Although the Bagshot beds are usually devoid of fossils, they contain marine shells in some places, among which Venericardia planicosta (see [fig. 171.]) is abundant, with Turritella sulcifera and Nummulites lævigatus. (See [fig. 174.] [p. 200.])

Fig. 171.

Venericardia planicosta, Lamck.

Cardita planicosta, Deshayes.