LONDON CLAY. 437 



tapir-like Lophiodon, and the Coryphodon, have been found in the 

 London Clay of Sheppey, etc. A deposit of yellow and white sand 

 belonging to the basement-bed of the London Clay at Kyson 

 (Kingston) near Woodbridge, has yielded remains oi Hyracotherium 

 cunicidus (the teeth of which were originally considered to belong 

 to a Monkey, Macacus Eocienus) ; and also Diddphys Cokhcstcii, 

 obtained by Mr. W. Colchester in 1839 and 1840.^ 



The London Clay is a marine formation, and Prof. Prestwich 

 considers that its fauna indicates a moderate rather than a tropical 

 climate, although the flora is tropical in its affinities. The litho- 

 logical characters denote a tranquil and uniform deposit, of con- 

 siderable duration, accompanied by a quiet and gradual subsidence 

 of the bed of the sea ; the sediment was for the most part brought 

 down by a large river. Prof. T. Rupert Jones remarks that the 

 indication of sea-depth for the London Clay, afforded by the 

 P'oraminifera, is that the water was about 100 fathoms deep. The 

 proximity of land is indicated by the remains of Plants, Mammals, 

 and Reptiles. 



The London Clay has been divided into four stages by Prof. Prestwich, which 

 contain assemblages of fossils, the species of which, although not restricted, are 

 more abundant at certain horizons. These divisions are but roughly marked out 

 according to localities from which collections have been made, and they have no 

 distmctive lithological characters : they are, in descending order, as follows -."^ — • 



4. Beds at Sheppey, Brentwood, Southend, Egham Hill, etc 70 to 150 feet. 



3. Beds at Highgate Archway, Nevvnham, etc 80 to loo feet. 



2. Beds at Chalk Farm (Primrose Hill), Islington (Copen- 

 hagen Fields, etc.), Kew, Brentford, etc 1 00 to 140 feet. 



I. Beds at Harwich, Erith, Bognor, etc 50 to 90 feet. 



Certain species of Nautilus occur more abundantly at some horizons, but their 

 range does not appear to be restricted to any particular zones. 



The chief development of Plant-remains, of Fishes, and Reptiles, is in the 

 upper beds, while the lower stages indicate deeper-sea conditions. These con- 

 ditions, however, varied, as in the western parts of the area the London Clay 

 (which is there reduced in thickness; yields a fauna exhibiting conditions of 

 shallower water than on the east. 



The London Clay extends over the northern parts of Kent and 

 Surrey, over a considerable part of Berkshire, INIiddlesex, Hertford- 

 shire, and Essex, and it occurs along the borders of Suffolk to 

 Yarmouth in Norfolk. (See p. 431.) 



Bognor Beds. — On the shore near Bognor in Sussex are exposed 

 beds of clay and calcareous sandstone (Barnes and Bognor Rocks), 

 which form part of a series of sands and clays with occasional 

 layers of pebbles. These beds are developed at Portsmouth, and 

 they are generally placed on the horizon of the London Clay. Mr. 

 C. Evans has pointed out the difficulty of paralleling the organic 

 remains in the deposits of Hants and the London Basin, while at 

 the same time the variation in mineral character would seem to 



1 Prestwich, Q. J. vi. 272 ; Whitaker, Geol. Ipswich (Geol. Survey), p. 26 ; 

 Owen, Brit. Foss. Mammals, pp. 3, 424. 



"^ Q. J. X. 408 ; see also N. T. Wetherell, Phil. Mag. 1836, ix. 465. 



