C PROCEEDINGS OF THE GEOLOGICAL SOCIETY. 



In his former paper the author estabhshed the synchronism of the 

 lower member of this group in each country, namely, the unfossili- 

 ferous Lower Bagshot Sands of England ; the partially fossiliferous 

 Upper Ypresian System of Belgium ; and the Nummulitic Lits 

 Coquilliers and associated sands of France, or Glauconie Moyenne of 

 M. Graves ; — in the present it is his object to separate, as it were, 

 another layer, by placing the Bracklesham Sands and Barton Clay in 

 correlation also with synchronous formations of Belgium and France. 

 In this inquiry the author limits himself to the marine beds of the 

 Bracklesham and Barton periods, reserving the investigation of the 

 strata which subsequently exhibit freshwater conditions for a future 

 occasion, and uses the MoUusca principally as his elements in the 

 discussion. Now the Bracklesham Sands are 500 feet thick in the 

 Isle of Wight, whereas the Calcaire Grossier, with which they are to 

 be compared, does not exceed 140 or 150 feet; but, on the con- 

 trary, the Calcaire Grossier has supplied 824 species, and the Brac- 

 klesham Sands only 451, or of Mollusca alone 651 and 368 species 

 respectively ; — and thus the difference, both of physical characters 

 and of the relative richness of the faunae, naturally leads to the 

 judicious observation, that in such inquiries it is necessary to follow 

 out each bed laterally in space, in order to ascertain whether the 

 change in the fauna, as well as in the mineral condition, is also pro- 

 gressive laterally. Mr. Prestvrich gives a list of 171 Bracklesham 

 mollusca which also occur in the Paris Tertiaries, and exhibits their 

 distribution in the Paris beds thus : — 



Lits Coquilliers and Calcaire Grossier. 



Sables Inferieurs Glauconie Moyen. Two Lower Two Upper Sables 

 or London Group, Base of Paris Group, Divisions, Divisions, Moyens, 

 15. 75. 141. 43. 94. 



142 

 This table exhibits very strongly the much closer organic analogy 

 of the Bracklesham Sands with the Calcaire Grossier, taken as a 

 whole, than with even a lower or upper member of the Paris group, 

 whilst it separates them widely from the underlying London group ; 

 but it is curious to observe how little difference there is between the 

 organic proportions if compared with only the two lower members of 

 the Calcaire Grossier and with the Sables Moyens. The Belgian 

 equivalent is considered to be the Bruxellian system of sands, sili- 

 ceous and calcareous ; and, of the 113 fossils they have furnished, 

 the following is the distribution of those common to England and 

 France : — 



England. France. 



London Bracklesham Barton Lits Calcaire Sables 



Group, Sands, Clay, Coquilliers, Grossier, Moyens, 



15. 49. 32. 43. 73. 56. 



Mr. Prestwich has not compared these fossils with the Sables 

 Inferieurs in France as in the former case, but the table again marks 

 strongly the great difference of organic analogy between the Belgian 

 beds as compared with the London group and the Bracklesham beds, 

 thus indirectly confirming the propriety of separating the two latter. 



