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cliff and Alum Bays; they consist of mottled clays and sands, and have a thickness of 84 feet, according to measurements by Mr. Bristow. (See fig. 20, p. 274.)
In Dorsetshire the strata are exposed at Studland Bay, and there are some beds of plastic clay near Weymouth which have been referred to the Woolwich and Reading Series, as also the pebble-beds and sands of Bincombe Heath.
Fuller's Earth is said to have been found in the Reading Beds at Katesgrove Kiln, Reading.
The beds are largely used for brickmaking, also for coarse pottery; and sometimes pipe-clay is found in them.
Websterite (Hydrous sulphate of alumina) occurs at the junction of the Tertiary beds and Chalk at Newhaven and Brighton in Sussex, and to the south of Bromley in Kent.
This name was given by Mr. Whitaker in 1866 to the sands and pebble-beds that come between the London Clay and Woolwich Beds in Kent, which before that had been doubtfully classed by Mr. Prestwich with the basement-bed of the London Clay, and to a small extent with the Woolwich Beds. The true basement-bed of the London Clay may sometimes be seen overlying the Oldhaven Beds. The name is taken from Oldhaven Gap, on the coast of Kent, west of Reculvers, where the beds are well displayed.
The formation consists almost wholly of perfectly rolled flint-pebbles in a fine sandy base, or of fine sharp lightcoloured quartzose sand, and it occasionally contains limonite. Current-bedding is displayed in places. Sometimes the pebble-beds are cemented into a hard rock, or pudding-stone. The total thickness of the beds varies from 20 to 30 feet.
In the neighbourhood of Canterbury, at Shottenden Hill,
near Sittingbourne and Rochester, at Plumstead Common, Abbey Wood, Blackheath,' and Woolwich, the beds are well displayed. They thin out in the neighbourhood of Lewisham, and are not met with under London, nor in the western part of the London Basin.
The Oldhaven Beds are often fossiliferous. The fossils are partly estuarine and partly marine, being sometimes the same as those of the Woolwich Beds below, and sometimes more nearly approaching those of the London Clay above, seeming therefore to prove oscillations of surface or changes of current and nearness to land, conditions which might also be expected from the masses of pebbles. It would seem that these old pebble-beds were not formed as a beach along a chalk-shore, as in that case they should contain many flints but partly worn, and one is led therefore to infer that they must have been deposited some way off the shore, as a bank to which no flints could get until after having been long exposed to wearing action. (Whitaker.)
Sands of doubtful age. In certain localities on the Chalk in Kent and Surrey there have been found traces of sand and clay and iron-sandstone with casts of mollusc-shells, mostly bivalves; these deposits sometimes fill pipes in the Chalk, and have been met with at Headley, Chipsted, Paddlesworth, Lenham, &c. The examination of the beds by Mr. Prestwich, and a study by Mr. Wood of the fossils which have been found in two or three of the pipes (all of these, however, were very obscure), led to their being doubtfully referred to the Crag; but both Mr. Bristow and Mr. Whitaker incline to refer most of them to the Eocene period, regarding them as representatives of Woolwich or Oldhaven Beds. (See p. 280.)
1 Blackheath Beds.
This formation, so named by William Smith, consists of stiff brown and bluish or slate-coloured clay, containing layers of septaria or cement-stones. At its base it displays sandy and loamy beds containing flint pebbles, and sometimes 'cemented by carbonate of lime into semi-concretionary tabular masses;' this is called the 'Basement-bed' of the London Clay by Mr. Prestwich. The top strata are also sandy, passing up into the Lower Bagshot Beds above.
The surface of the London Clay frequently weathers into a loam. Mr. Whitaker observes that the brown colour at and near the surface is merely a colour of decomposition; the protosalt of iron that gives the bluish tint peroxidating by exposure to atmospheric action. The London Clay contains. much iron-pyrites and selenite. Its thickness varies from next to nothing in Wiltshire, and from 50 or 60 feet in Berkshire to nearly 500 feet in the south of Essex.
The London Clay yields a very extensive list of fossils, and, although specimens are abundant, it is not always easy to find them, as they occur in groups or zones conspicuous at one locality and not seen at all at the same horizon in another.
Among these organic remains are species of Mammals, Birds, Turtles, Crocodiles, Fishes, Mollusca, Crustacea, Entomostraca, Cirripedia, Annelida, Echinodermata, Actinozoa, Protozoa, and Plants.
Specimens have been obtained at Pebble Hill (near Hungerford), Newnham and Cuffell (near Basingstoke), Bognor, Highgate, Finchley, Holloway, Harwich, Sheppey, &c. At the last-named place were found in greatest abundance the fossil fruits described by Dr. Bowerbank; amongst these the palm Nipadites ellipticus is conspicuous. The Mollusca include Pectunculus brevirostrum, Punopea, Cryptodon
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 Odontopteryx 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 Lophiodon and Coryphodon, are found in the London Clay.1
Bognor 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 yielded 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 Roundgate 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.1
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 flint-pebbles-the basement-bed of Mr. Prestwich. At about thirty-five feet above the basement-bed there is a zone of Panopaa intermedia, and Pholadomya margaritacea; at fifty feet a band of Ditrupa plana; and at about eighty feet a band of Cardita 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 Conybeare and Phillips.