Geological Society of London. 189 



The typical section of the beds is at Punfield Cove, in the Isle of 

 Purbeck, where they are about 160 feet thick, and include several 

 bands with marine shells. The lowest and most remarkable of these 

 yields about forty well-defined species, many of which, as well as 

 one of the genera, are quite new to this country. A section some- 

 what similar to that of Punfield is seen at Worborrow Bay. 



In the Isle of Wight, at Compton, Brixton, and Sandown Bays, 

 similar fluvio-marine beds are found at the top of the Wealden, and 

 attain to a thickness of 230 feet. The marine bands here, however, 

 yield but a very scanty fauna. Indications of the existence of beds 

 of the same character and in a similar position are found in the 

 district of the Weald. 



While the Purbeck formation exhibits the gradual passage of the 

 marine Portlandian into the freshwater Wealden, the Punfield 

 formation shows the transition of the latter into the marine Upper 

 Neocomian (Lower Greensand). Thus we are led to conclude that 

 the epoch of the English Wealden commenced before the close of the 

 Jurassic period, lasted through the whole of the Tithonian and of 

 the Lower and Middle Neocomian, and only came to a close at the 

 commencement of the Upper Neocomian. 



In tracing the Cretaceous strata proper from east to west, they 

 are found to undergo great modification; while the Neocomian 

 and Wealden, which they overlap through unconformity, besides 

 being greatly changed in character, thin out very rapidly. 



On stratigraphical and pateontological evidence, the Punfield 

 formation is clearly referable to the upper part of the Middle Neo- 

 comian. Its fauna has remarkably close analogies with that of the 

 great coal-bearing formation of Eastern Spain, which is of vast 

 thickness and great economic value. 



The claim of the Punfield beds, equally with the similarly situated 

 Purbeck series, to rank as a distinct formation, is founded on the 

 distinctness of their mineralogical characters, their great thickness, 

 the fact of their yielding a considerable and very well characterized 

 fauna, and of their being the equivalent of a highly important 

 foreign series. 



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-Austen 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 marine 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 intermediate freshwater conditions -was probably 

 of equal length. 



Mr. Etheridge observed that out of sixty or seventy species from the deposits in 

 Eastern Spain, we have thirty-nine or forty in Britain. The fauna was, indeed, pre- 

 cisely the same. He referred to several of the species, and intimated his intention of 



