EOCENE STRATA IN ENGLAND, BELGIUM, AND FRANCE. 99 



occurrenco in the sandstones of imperfect vegetable impressions. 

 In Belgium the fluviatile conditions are more marked, Cyrena 

 cuneiformis and Melania mquinata having been found in wells at 

 Ghent and Ostend. Another connecting link is the abundance of 

 silicified wood and of silicified shells in these beds in East Kent and 

 in some parts of the north of the Paris Basin, 



These general features point to a common origin, — the mottled 

 and plastic clays in both areas having been, in all probability, de- 

 rived from the decomposition of plutonic and metamorphic rocks to 

 the southward, and the flint pebbles from neighbouring Chalk areas ; 

 while the quartzites, pudding-stones, and silicified shells result from 

 the cementation and fossilization effected by the soluble silica set 

 free simultaneously with the liberation of the kaolin which went 

 to form the mottled clays. 



This variability is characteristic of the whole of this series in the 

 Paris as well as in the Anglo-Belgian Basin, certain very distinct 

 mineral characters prevailing in adjacent areas, although on the same 

 horizon ; and while in some of these areas fossils abound, in others 

 they are rare or altogether absent. The fluviatile beds are merely 

 local lenticular intercalations. There is nothing, therefore, out of 

 line in the character of the Bracheux fauna, which, while having 

 many connecting links with the Woolwich fauna, yet has a local 

 type of its own. As the other beds to which this group belongs 

 range further eastward, they become more fully developed and 

 undergo considerable changes. They then constitute more especially 

 the series there better known as the " Sables Inferieurs," which, in 

 the Soissonnais and Champagne, is divided into several zones, the 

 lower one being the Sands of Chalons-sur- Vesles, and the upper ones 

 forming the zones of Aizy and Sainceny ; but it is not my object to 

 describe these beds, which become in this eastern area very fossili- 

 ferous, the total of the Mollusca amounting, according to the late 

 M. Watelet, to above 400 species. 



I would merely note that the French geologists coasider the Sands 

 of Chalons -sur-Yesles to be the equivalent of the Sands of Bracheux. 

 The former, I have reason to believe, pass, in the neighbourhood of 

 Bheims, under the freshwater concretionary marl of Hilly *, with 

 its peculiar species of Helix, Cyclostoma, PTiysa:, &c. Mr. Whitaker 

 has identified one species of Paludina (P. asperci) with a form 

 occurring in the Woolwich Beds at Dulwich. I therefore place, as 

 I did originally t, the Eilly Beds at the base of the "Lignites" 

 which immediately overlie them ; and it is probable that the beds 

 which directly underlie the Mottled Clays at Meudon belong to the 

 same zone. 



In the following list of the Woolwich shells, I have included those 

 of the Sundridge and Blackheath Beds, which Mr. Whitaker places 

 within the Oldhaven zone : — 



* This is not the opinion of my friend M. Hubert, who places the Eilly Beds 

 at the base of the Tertiary series. 



t Bull. Soc. Geol de France, 2« ser. vol. x. p. 330. 



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