226 JKOCEEDINGS OF THE GEOLOGICAI, SOCIETY. [Feb. 8, 



1. They present very distinct mineralogical characters, separating 

 them alike from the overlying Neocomian and the subjacent Wealden 

 proper. 



2. They are of considerable thickness, attaining a maximum of 

 230 feet. 



3. They present evidence of having been deposited under condi- 

 tions differing alike from those of the marine Neocomian above and 

 the purely freshwater Wealden below. 



4. They yield a considerable marine fauna (between 30 and 40 

 species being already known), which is remarkably distinct and well 

 characterized. 



5. They are the undoubted representatives of a formation which 

 in Spain attains to a vast thickness, and which, alike from its marked 

 palseontological characters and its great economic value, is of great 

 importance. 



6. Their relations to the Wealden and Neocomian are precisely 

 analogous to those of the Purbeck formation to the Oolite and 

 Wealden ; and they are therefore equally deserving with it of a di- 

 stinctive title. 



At the same time I have endeavoured to show that these beds 

 may be regarded indifferently either as the highest member of the 

 Wealden in our classification of the series of terrestrial strata, or as 

 a portion of the Neoeomian in our grouping of the marine series. 

 The application to them of a distinctive name is therefore, although 

 a necessary, perhaps only a provisional expedient ; but the same is 

 to a greater or less extent true of most of our geological terms. 



Discussion. 



The President remarked that the limited amount of freshwater 

 formations in this country was an obstacle to their correlation, and 

 stated that Constant Prevost had endeavoured to correlate the 

 Secondary freshwater and marine formations. 



Mr. Godwin-Attsten remarked upon the thinning out of the 

 Lower Greensand, especially in France, upon the imperfection of 

 our knowledge of the great Cretaceous formation, and upon the 

 probability of the intercalation of freshwater conditions in the 

 Lower Greensand. The formation at Punfield seemed to present an 

 intercalation of marine between purely freshwater conditions. He 

 indicated how a slight change of level might have intercalated ma- 

 rine conditions in the Wealden. The deposition of the White Chalk 

 and Oolite occupied enormous periods (in both cases purely marine), 

 during which the northern hemisphere was a great northern ocean ; 

 and as the distribution of land and water was due to the operation 

 of great cosmical laws, the duration of terrestrial and of the inter- 

 mediate freshwater conditions was probably of equal length. 



Mr. Etheeidge observed that out of sixty or seventy species 



employed the word in this paper, the term " system " being applied to the 

 greater groups of strata. 



