LOWER FRESH WATER FORMATION- 303 



basin, and appears to be analogous to that found in a si- 

 milar situation in the Isle of Wight basin ; and the French 

 sands agree in characters with those found in the Isle of 

 Wight basin. 



In the English basins there occur but few rocks that 

 can be identified with the coarse marine limestone of the 

 Paris basin. The rocks of Bognor appear to be the most 

 easily referable to some of the beds of the coarse lime- 

 stone of France; yet, in the Paris formation, there is no 

 single rock possessing the same external characters as 

 those exhibited by the London clay. But the London 

 clay contains the same petrifactions as the coarse lime- 

 stone; and if we could suppose a blending or mixture 

 between the French plastic clay, which is blackish, and 

 contains organic bodies, and the lower beds of the coarse 

 limestone with its green earth and petrifactions, we should 

 have a compound agreeing sufficiently near with the 

 London clay under all its varieties; with this difference, 

 that that of the French basin would have a greater pro- 

 portion of the calcarious, and of ours of argillaceous 

 matter. But with respect to the upper beds of the coarse 

 limestone of France, no strata have as yet been disco- 

 vered in England that correspond to them.* 



2. Lower Fresh Water Formation. 

 It consists of a series of beds of sandy, calcarious, and 

 argillaceous marls. Some of them appear to consist al- 

 most wholly of the fragments of fresh water shells, viz. 

 lymenus, planorbis, cyclostoma, and others resembling 

 helices, and mytuli. In its lower part it alternates with 

 beds containing marine remains. This formation occurs 

 in the Isle of Wight, but not in the London basin. 



* Webster's Geological Transactions, vol. ii. p 209, 



