FORMATION. 25 



Plastic Clay separate the London Clay from the chalk, and 

 are composed of sand, shingle, mottled clays and loam ; 

 marine shells sometimes occur in them, and along a portion 

 of the southern side of the London basin, a fluvio-marine 

 deposit (Woolwich, &c.), is intercalated in the beds imme- 

 diately overlying the chalk, proving the existence of streams 

 charged with their peculiar testacea, and emptying them- 

 selves into the ancient estuary. The London Clay forma- 

 tion is separated into two distinct basins, those of London 

 and Hampshire, which are bounded by the rising grounds 

 of the chalk, except on the seaward side ; the intervening 

 tract between the clay and chalk being usually occupied 

 by the sands, &c. of the Plastic Clay.* 



The Fauna and Flora of this period have decidedly a 

 tropical aspect. Among the testacea are many species of 

 Conus, Cancellaria, F'oluta, Nautilus ; besides numerous 

 species of fish and a great abundance of the fruit and 

 seeds belonging to tribes and genera indicative of the 

 warmer regions of the globe. 



* The deposits in the London and HampshiTC districts have hitherto generally been con- 

 sidered to be synchronous ; that is, the Clays of the London basin being equivalent to the 

 Barton and BracUesham beds, and the variegated sands of Alum Bay representing the 

 Plastic Clays, &c. 



Mr. Preatwich, hovrever, snggests that this view of their arrangement is somewhat erro- 

 neoos, and in a recent memoir commonicated to the Geological Society, (Geol. Proceedings 

 Feb. 3, 1S47,) he has explained by the aid of numerous and extensive sections over both dis- 

 tricts, by which the superposition of the beds is clearly exhibited, that the formation com- 

 prised within them, may be conveniently subdivided into certain groups, in the fidkmiikg 

 descending order, and to which their foreign equivalents are added. 



Engtuh Serin. Fmek Srria. 



Barton Clays. . . . . ^ Calcaire Grossier (in part.). 



BracUesham Sands. . . . / Glauconie Groasiere. 



London Clay and . . . . \ Lits Coquilliers et . . . 



Bognor Beds J Sables Inferieurs. . 



Mottled or Plastic Clays and Sands. Argile Plastique et Lignites. 



This view is also corroborated by the distribution of the organic remains, for, although 

 many species are common to all the divisions, still a large number of species are peculiar to 

 each of them, thus forming a somewhat distinctive and cliaracteristic Fauna. 



LOCALITIES FOE FOSSILS. 

 Of the London Clay. — Isle of Sheppy, Wliitstable,»Keiit ; Harwich, 

 Southend, Essex ; Highgate, Finchley, Middlesex ; Newnham, 

 s 



