392 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. [June 18. 



series there are in England 30, in France 35, and in Belgium 32, 

 which range upwards. 



Mr. Prestwich mentioned that M. Graves had recognized several 

 well-known Barton species, such as the Valuta depauperata^ V.athleta, 

 Oliva Branderi^ Conus scabriusculus, &c., in the Sables moyens of 

 the Oise. The total known number of the Sables moyens species is 

 377, and of the Barton clay species 252. 



These series the author proposed to term the "Paris Tertiary 

 Group " (its lower part), as the several members of it were more 

 complete in France than in England, and contained a richer and better- 

 preserved fauna. This Paris group forms the great Nummulitic 

 zone. Hitherto none of these Foraminifera {Nummulina) have been 

 found in the London group. 



The author concluded with some general observations on the extent 

 of the ancient seas and the position of the dry land, and took occasion 

 to observe on the fact, that, although the several deposits in each 

 country were so rich in organic remains, yet so small a proportion of 

 them should have hitherto been identified as common to the several 

 areas. Nevertheless the same genera prevailed, and the relative 

 number of species of each genus was generally tolerably well main- 

 tained. He hoped, therefore, that Palaeontologists would, in cases 

 where there was now good reason to believe the strata to be synchro- 

 nous, inquire further into the extent of variation which the same 

 species might undergo in areas where the sea had presented such dif- 

 ferent conditions of depth, mineral composition of sea-bottom, &c. 

 A certain number of peculiar species must necessarily result from 

 such different conditions, but the author considered it probable that 

 the same causes would lead to the existence of such marked varieties 

 as might, viewing each area separately and independently, cause 

 some varieties to assume the permanence and importance of specific 

 differences. Until the exact synchronism of any deposit is esta- 

 blished, the Palaeontologist cannot always fully take these causes 

 into consideration, and many admirable monographs on Tertiary fos- 

 sils have necessarily been founded, in great measure, upon the dif- 

 ferences actually apparent and persistent in the several areas. 



Mr. Prestwich stated that it was his intention to continue this 

 inquiry at a future period, and to examine into the correlation of the 

 interesting freshwater and fluviatile series overlying the Barton clay 

 on the Hampshire coast and in the Isle of Wight. 



