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angulatum, Fusus, Pleurotoma, Rostellaria ampla, Voluta nodosa, Nautilus centralis, N. (Aturia) ziczac, N. imperialis, &c. The Annelide Ditrupa plana is common, and sometimes fossil wood with Teredo-borings is met with.
The London Clay is a marine formation, and Mr. Prestwich considers that its fauna indicates a moderate rather than a tropical climate, although the flora seems to be certainly tropical in its affinities. The lithological characters, he states, denote a tranquil and uniform deposit, of considerable duration, accompanied by a quiet and gradual subsidence of the bed of the sea. Prof. T. Rupert Jones remarks that the indication of sea-depth for the London Clay, afforded by the Foraminifera, is that the water was about 100 fathoms deep. The proximity of land is indicated by the remains of plants, mammals, and reptiles.
Amongst the reptiles were many turtles, also the seasnake Palæophis (probably about thirteen feet in length), and the Crocodile (C. toliapicus). The Odlontopteryx found at Sheppey is considered by Prof. Owen to have been a webfooted bird having jaws provided with bony teeth.
The Hyracotherium (allied to the living Hyrax), also the tapir-like Lophiollon and Coryphodon, are found in the London Clay.
Bojnor Beds.—On the shore near Bognor in Sussex are exposed beds of clay and calcareous sandstone, and so far as the series can be made out it comprises alternations of sands and clays with pebble-beds. Similar beds are developed at Portsmouth. They have generally been placed on the horizon of the lower part of the London Clay, but Mr. C. Evans has recently pointed out the difficulty of paralleling the organic
1 A deposit of yellow and white sand belonging to the basement-bed of the London Clay at Kyson near Woodbridge has vielded Mammalian remains of the genus Hyracotherium (the teeth of which were originally considered to belong to a Monkey) and also Didelphys.
remains in the deposits of Hants and the London Basin, while at the same time the variation in mineral character would seem to render it desirable to retain the distinctive term of Bognor Beds.
The Barns Rocks between Selsea and Bognor, the Round.. gate and Street rocks on the west, and Mixen rocks to the south of Selsea, are portions of the same bed : similar masses also appear at Stubbington.
In the Isle of Wight about 50 feet from the basementbed is a band of Ditrupa plana, called the Ditrupa-band. The junction with the Woolwich and Reading Beds is sharp and well-defined, and both in Alum and Whitecliff Bays the division is indicated by a band of Alint-pebbles—the basement-bed of Mr. Prestwich. At about thirty-five feet above the basement-bed there is a zone of Panopæa intermedia, and Pholadomya margaritacea; at fifty feet a band of Ditrupa plana; and at about eighty feet a band of Carlita occurs. (See fig. 20, p. 274.)
Fossil copal (Copaline) or Highgate resin was discovered during the excavations for the Highgate Archway.
The London Clay is everywhere very extensively used for brick- and tile-making.
Septaria or Cement-stones have been largely used in the manufacture of Roman cement. For this purpose they have been dredged in Chichester Harbour, at Harwich, and off the coast of Hampshire: they have also been collected near Southend.
* The septaria on the south of Walton on the coast of Essex are very imperfect; they are collected into heaps on the Nore, and shipped to Harwich, where they are manufactured by Government into a cement. Dale, in his History of Harwich (p. 101), speaking of the septaria so abundantly found in the cliffs of the neighbourhood, says, “ with these the walls of the town were for the most part built, and the streets generally pitched, they by ancient custom belonging to the town as their right.”
1 Cony beare and Phillips.
The long cliff of the London Clay extending along the northern side of Sheppey Isle furnishes abundance of Septaria, from which that excellent material for building under water and for stucco is made, and which is known by the name of Parker's Cement. Being separated fro:n the clay by the action of the sea, they are collected on the beach, and exported to various places where they are calcined and ground.
'In Ilampstead and Ilighgate Ilills in Middlesex, and in Bɔughton IIill in Kent, the layers of septaria occur about 50 feet below the summit. In Shouter's IIill they are very near the surface. At Epping, they were not found nearer than 100 feet beneath the grass, and continued to the depth of 300 feet.'1
The London Clay forms a stiff tenacious soil, making good pasture-land, and yielding by the application of marl good crops of corn.
Teazies are cultivated in Essex, and elin, oak, and ash timber in different places. The London Clay is impervious, and yields no water save in the basement beds.
LOWER MARINE (old authors).
The structure of the Bagshot Beds, so named from Bagshot Heath in Surrey, was first elucidated by Mr. Prestwich, who ascertained that they could be divided into three distinct and persistent divisions, severally characterized by peculiar groups of organic remains and by differences of lithological characters, thus:Upper Bagshot Beds.
( Barton Clay.
Cony beare and Phillips.
The series is perfectly conformable, and it is difficult to draw any hard lines between the divisions.
Lower Bagshot Beds. This deposit consists of pale yellow or buff-coloured siliceous sand and loam, with seams of pipe-clay, and occasional beds of flint-pebbles. Ironstone veins and nodules are sometimes met with. The thickness varies from 100 to 150 feet.
In the London Basin the beds locally show no inclination, but they are generally disposed with a slight dip to the southeast: in the Isle of Wight they are highly inclined. (See fig. 20, p. 274.)
Organic remains are exceedingly rare, only a few casts of mollusca having been found.
The Leaf-heds ( pipe-clay) of Alum Bay and Bournemouth have yielded many land-plants of sub-tropical genera, such as palms, maples, &c.
Mr. Prestwich considers that the Lower Bagshot Beds were derived by denudation from the older crystalline and granitic rocks, but Mr. G. Maw has suggested that some of the fine white clays may have been due to the destruction of the Chalk.
The pebble-beds in the Lower Bagshot series were first determined by Mr. S. V. Wood, jun. They occur at Brentwood, Stock, Billericay, and other localities in Essex. Their masimum thickness is 15 feet at Brentwood, where the section shows:
8. Pebble-beds .
2. Brickearth or loam
From the Bagshot Beds themselves varying so much in section, and from the passage upwards of the London Clay into them, it is impossible to be certain as to the horizon taken as the junction of the two formations in the many outliers of Essex. Where a purely sandy condition prevailed at one spot a loam may have been formed at another, and a clay at a third. Again the test of level avails but little when it is remembered to what changes the area has been subjected in later times, during and after the Glacial Period: nor is it likely that the beds were spread over a uniform level; so that taking these points into consideration, it seems that the boundary between the Bagshot Beds and the London Clay must be drawn mainly with reference to the features of each outlier.
Probably the best place for studying the Bagshot Beds in Essex is Brentwood, where the structure of both the sands and pebble-beds, and also their relation to the London Clay, are clearly shown. In the sections there the London Clay is seen to pass upwards into the Bayshot Sand. The brickyards well show the passage-beds, which consist of alternations of clays, sands, and loams, furnishing excellent brickearths. This passage makes the boundary-line between the two deposits very indefinite, and that line is liable to be taken at different horizons in different localities, even in the same outlier. There is no hard line anywhere, and it therefore becomes a matter of convenience, rather than of marked distinction, where to draw the boundary.
Outliers occur at Langdon Hill, Rayleigh, High Beech, Highgate, Hampstead, and Harrow, forming some of the highest hills near London, and commanding extensive views : that from Langdon Hill in particular being surpassed by few in England. The beds are exposed in Alum and Whitecliff Bays in
i Notes by H. B. W. in Mem. Gcol. Surv. vol. iv. part 1.