238 Eocene Series. 



brackish water, and others in the sea, and the con- 

 clusion to be drawn from this is, that they largely 

 consist of sediments that were thrown down at the 

 mouth of a great river. 



When we consider the original extension of these 

 Eocene river beds, it is also remarkable that they lie 

 within the same general limits as those of the older 

 fluviatile deposits of the Purbeck and Wealden strata, 

 as if, after a long interval, geological history were 

 repeating itself in the same area. In our own day, 

 occupying part of the same district, we have yet a 

 third estuary, that of the Thames, small, but in some 

 respects of more importance to the living world than 

 many an estuary of fifty times its size. 



The various subdivisions of the English Eocene 

 strata are given in the Table of British Formations 

 (p. 30), in which the classification of Professor Prest- 

 wich is used, which is also that adopted by Sir Charles 

 Lyell in his Manuals. As far, however, as England is 

 concerned, it is more philosophical, as it is certainly 

 more convenient, to divide them into three groups, as 



follows : 



rHempstead beds. 

 Upper Fresh- water J Bembridge 

 and Estuarine. 1 Osborne 

 v-Headon 

 r Upper Bagshot Sand. 

 Marine J Middle Bagstiot. f Barton Clay. 



" ] Lower Bagshot. 1 Bracklesham bed 5. 



L London Clay. 



Lower Fresh-water, r Woolwich ^ Readi bedg 

 Estuarine, and I Thanet gand> 

 Marine. L 



This classification has the merit of simplicity, being 

 founded on circumstances relating to variations in the 

 physical geography of the time in our area, while the 



