TRANSACTIONS OF THE SECTIONS. I! 



viz. : — 1st. Have not all the deep-sea species of European MoUusca originated in the 

 north, and spread southwards in consequence of the great arctic current ? 2nd. 

 Inasmuch as the Pliocene division of the Tertiary formation is now ascertained to 

 contain scarcely any extinct species, and future explorations may reduce the per- 

 centage of such species to >«V, may not that artificial division hereafter merge in 

 the quaternary formation, and the Tertiaries be restricted to Eocene, Miocene, and 

 Oligocene ? 



On the Ar/e of the Wealden. 

 By John W. Jxtdd, F.G.S., of the Geological Survey of England and Wales. 



Unconformities between formations indicate, as Mr. Darwin, Prof. Ramsay, and 

 other geologists have argued, the lapse of enormous periods of time. Between the 

 Oolitic system, terminating with the Portlandian, and the true Cretaceous, com- 

 mencing with the Gault, there is not only an immense physical break, but a total 

 change in species. The researches of continental geologists have shown that, inter- 

 calated between these two systems, there exists two others, each in every way 

 worthy to rank with them, the Tithonian and the Neocomian ; these do not, how- 

 ever, entirely bridge over the_ interval, for the Cretaceous is almost everywhere 

 unconformable to the Neocomian. 



The English Wealden consists of a mass of freshwater strata, probably not less 

 than 2000 feet thick. Forming its lower and upper members, however, are certain 

 fluviomarine strata, which form passages into the marine beds below and above 

 the Wealden. The lowest of these fluviomarine or passage series is the well- 

 known Purbeck formation, the marine beds of which contain Oolitic fossils. In 

 the Isle of Purbeck, the Isle of Wight, and elsewhere is found another series of 

 strata, less known, but not less important, which indicates the gradual passage up- 

 ward of the Wealden into the Upper Neocomian (Lower Greensand). 



Of especial interest, from the large fauna which it yields, is the marine band of 

 Punfield, to which the attention of geologists was first directed by Mr. Godwin- 

 Austen in the year 1850. This bed is only 21 inches thick, and is situated 140 

 feet below the top of the Wealden ; the author has found that it contains a series 

 of fossils (including many species and one genus quite new to this country) iden- 

 tical with those of the coal-bearing strata of Middle Neocomian age in Eastern 

 Spain, which are more than 1600 feet thick. 



The Wealden presents every appearance of being a single continuoiis formation. 

 In its lower portion it contains marine beds with oolitic fossils, and gi-aduates into 

 the Portlandian ; in its upper part it contains other marine beds with Middle Neo- 

 comian fossils, and graduates into the Upper Neocomian. We are thus led to the 

 conclusion that the great epoch of the Wealden commenced towards the close of 

 the Oolitic period, that it continued through the whole of the Tithonian and the 

 Lower and Middle Neocomian, and only came to an end at the beginning of the 

 Upper Neocomian. 



In confirmation of these views as to the age of the Wealden, there exists much 

 palseontological evidence. Still further support is afforded to them by the manner 

 an which Wealden and Neocomian beds are found alternating with one another in 

 France, especially in the Pays de Bray and in the district of Champagne. 



Professor Huxley has indicated the necessity of establishing a distinct classifi- 

 cation for freshwater and ten-estrial fonnations, the breaks between which do not 

 correspond with those of the marine series. Of this necessity the Wealden, repre- 

 senting, like the " Poikilitic," several very distinct marine formations, is a very 

 striking illustration. 



The author has before sho-\vn that the deposition of the Wealden strata of 

 Northern Germany commenced at the close of the Oolitic period, and had termi- 

 nated before the end of the Lower Neocomian. He concludes therefore that the 

 English and German Wealdens are not strictly contemporaneous, and that, the 

 areas being quite disconnected, they are probably the products of two different 

 rivers. 



