398 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. [May 26, 



from the same land, suspended in the same waters, and distributed 

 by the same currents. This is naturally modified as the sediment 

 from rivers flowing through different geological districts is swept 

 into these currents, but the characters thereby superadded may be 

 blended so gradually, that by the time they preponderate, and we lose 

 sight of our first guides, we shall recognise and receive these new 

 characters as representative forms, and be able to trust as fully to their 

 guidance in prolonging from distance to distance the synchronism of 

 widely ranging deposits. 



Conclusions. 



In conclusion, notwithstanding that the palseontological and stra- 

 tigraphical evidence afforded by the Bag shot sands is scanty, still we 

 must decide according to that eiddence ; and the deficiency in quan- 

 tity is in some measure compensated for by the strength of most of 

 the proofs and by a singular absence of conflicting testimony. 



It has been shown that, commencing with the lower division of 

 the Bag shot sands, we find them possessing a uniform and regular 

 character in the London district, and exhibiting with the Hampshire 

 presumed equivalent strata, a very close identity both of thickness, 

 lithological structure and organic remains ; and that they are both in 

 conformable superposition upon the London clay. 



The middle division of the Bag shot sands may, I think, be con- 

 sidered as the attenuated representative of the ^r«c/c?e5A«m ^«?/ beds, 

 formed as they both are, although in varying quantities, on the same 

 mineral type, and containing organic remains, not only of analogous 

 forms in the two districts, but also of the most distinctive species of 

 the period. 



The upper Bagshot sands we must place provisionally on a parallel 

 with the strata somewhere between the fossiliferous strata of Brackle- 

 sham and the Freshwater series. 



As a whole it results, that the interesting and varied succession of 

 strata composing the English tertiaries in Hampshire and to the 

 west"^ of London belong entirely to the Eocene period; that they 

 can be divided into three great groups, severally characterized by 

 peculiar mineral structure and organic remains. 



The first and lowest group is argillaceous, and consists of the 

 mottled clays and London clay, with a few subordinate beds of sand 

 chiefly confined to the first-named division, and is characterized by a 

 fauna of which a considerable proportion consists of forms confined 

 to it. 



Second, the central group, constituting the Bagshot ^Vi^ BracJde- 

 sham series, an arenaceous formation with subordinate green sands 

 and laminated clays, separable into three divisions, and exhibiting a 

 very distinctive fauna. 



Third, the upper group, of green marls, earthy limestones and 

 siliceous sands of freshwater or fluvio-marine origin, and which group 

 is also marked by fossils peculiar to it. 



* To the east of London other divisions are developed below the London clay : 

 of these we have not yet completed the investigation. 



