The lower sandy beds of the Paris basin are often called the sands of the Soissonais, from a district so named 50 miles N.E. of Paris. One of the shells of the formation is adduced by M. Deshayes as an example of the changes which certain species underwent in the successive stages of their existence. It seems that different varieties of the Cardium porulosum are characteristic of different formations. In the Lower Eocene of the Soissonais this shell acquires but a small volume, and has many peculiarities, which disappear in the lowest beds of the calcaire grossier. In these the shell attains its full size, and many distinctive characters, which are again modified in the uppermost beds of the calcaire grossier; and these last modifications of form are preserved throughout the whole of the "upper marine" (or Upper Eocene) series.[197-A]
ENGLISH EOCENE FORMATIONS.
The Eocene areas of Hampshire and London are delineated in the map ([fig. 153.] [p. 174.]).
The following table will show the succession of the principal deposits found in our island. The true place of the Bagshot sands, in this series, was never accurately ascertained till Mr. Prestwich published, in 1847, his classification of the English Eocene strata, dividing them into three principal formations, in which the Bagshot sands occupied the central place.[197-B]
| Localities. | ||||
| 1. Upper Eocene. | Wanting in Great Britain. | |||
| 2. Middle Eocene | { | a. Freshwater and fluvio-marine beds. | Headon Hill, Isle of Wight; and Hordwell Cliff, Hants. | |
| b. Barton beds. | Barton Cliff, Hants. | |||
| c. Bagshot and Bracklesham sands and clays. | Bagshot Heath, Surrey; Bracklesham Bay, Sussex. | |||
| 3. Lower Eocene | { | a. London Clay Proper, and Bognor beds. | Highgate Hill, Middlesex; I. of Sheppey; Bognor, Sussex. | |
| b. Mottled and Plastic clays and sands. | Newhaven, Sussex; Reading, Berks; Woolwich, Kent. | |||
Fig. 170.
Lymnea longiscata.
Freshwater Eocene strata, Isle of Wight.