& 
-- 
S44 STRATIGRAPHICAL GEOLOGY.  [Boox VI. _ 
the Chalk, which, owing to denudation, have become detached into the ’ 
two well-defined basins of London and Hampshire. They have been 
arranged as in the subjoined table : 
Hampshire. London. 
- 
= Barton clay. Upper Bagshot sands. 
= 
re Bracklesham beds, and leaf beds Middle Bagshot beds, part of Lower 
=( of Bournemouth and Alum Bay. Bagshot sands. 
= 
5 Part of Lower Bagshot sands. 
rs London clay. 
= | London clay (Bognor beds). Oldharen baie 
3 Woolwich and Reading beds. Woolwich and Reading beds, 
Thanet beds. 
Lower.—The Thanet Beds! at the base of the London basin con- 
sist of pale yellow and greenish sand, sometimes clayey, and containing 
at their bottom a thin, but remarkably constant, layer of green-coated 
flints resting directly on the Chalk. According to Mr. Whitaker, it is 
doubtful if proof of actual erosion of the chalk can anywhere be seen 
under the Tertiary deposits in England, and he states that the Thanet 
Sands everywhere lie upon an even surface of chalk with no visible 
unconformability.” Professor Phillips, on the other hand, describes the 
chalk at Reading as having been “ literally ground down to a plane or 
undulated surface, as it is this day on some parts of the Yorkshire 
coast,” and having likewise been abundantly bored by lithodomous shells.? 
The Thanet Sands appear to have been formed only in the London basin ; 
at least they have not been recognized at the base of the Eocene series 
in Hampshire. Their fossils comprise about 70 known species (all 
marine except a few fragments of terrestrial vegetation). Among them 
are several foraminifera, numerous lamellibranchs (Astarte tenera, Cyprina 
planata, Ostrea bellovacina, Cucullea decussata (crassatina), Pholadomya 
cuneata, P. Konincki, Corbula regulbiensis, &c.), a few species of gastero- 
pods (Natica subdepressa, Aporrhais Sowerbii, &c.), a nautilus, and the 
teeth, scales, and bones of fishes (Lamna, Pisodus). 
The Woolwichand Reading Beds,‘ or “ Plastic Clay” of the 
older geologists, consist of lenticular sheets of plastic clay, loam, sand, 
and pebble-beds, so variable in character and thickness over the Ter- 
tiary districts that their homotaxial relations would not at first be 
suspected. One type, presenting unfossiliferous lenticular, mottled, 
bright-coloured clays, with sands, sometimes gravels, and even sand- 
stones and conglomerates, occurs throughout the Hampshire basin and 
in the northern and western part of the London basin. A second type, 
found in West Kent, Surrey, &c., consists of light-coloured sands and 
erey clays, crowded with estuarial shells. A third type, seen in East 
Kent, is composed only of sands containing marine fossils. These differ- 
Mem. Geol. Surv. yol. iy. (1872); Phillips, Geology of Oxford and the Thames Valley, 
1871. 
! Prestwich, Q. J. Geol. Soc. viii. (1852), p. 237. 
2 “ Geology of London,” Mem. Geol. Surv, iv. p. 57. 
% (feology of Oxford, p. 442. 
* Prestwich, Q. J. Geol, Soc. x, p. 75. Whitaker, Geol. Lond. p. 98, 

