Physical Geography. 255 



and in the genera of plants alone, it would be as allow- 

 able to refer the Cretaceou* flora of Aix-la-Chapelle 

 to the Miocene age, as it is to refer the Hempstead 

 beds to that epoch. The genera of mammalia, also of 

 the Hempstead strata, are truly Eocene, for Hyopotamus 

 is found in the Headon series, and Hyracotherium in 

 the London Clay. The Hempstead beds, in fact, merge 

 gradually into those below, and the uppermost stratum 

 of all is marine, containing Corbula pisum, which is 

 a well-known Eocene species, found in various sub- 

 formations as low as, and including, the Barton Clay. 

 The series may be said to be unfinished, and seems quite 

 naturally to belong to the Eocene epoch. In old times, 

 what kind of strata, if any, may have lain above the 

 Corbula bed, no one knows. 



In Hampshire, the same general series of fluvio-marine 

 strata occurs, with variations in lithological character, 

 but only as high as the Bembridge beds, the Hempstead 

 strata having been removed by denudation. 



If we now review the whole of the circumstances 

 relating to the English Eocene strata, we find that in 

 their lower and upper divisions they are decidedly of 

 fresh-water and estuarine character, the fresh- water 

 beds having been laid down in the broad mouth of a 

 great river, so near the sea, that the area was liable by 

 slight oscillations of level to intermittent influxes of the 

 salt water, which produced minor marine inter stratifi- 

 cations both in the Woolwich and Reading beds below, 

 and in the upper strata, from the Headon to the Hemp- 

 stead beds inclusive. But this is not all. Though, 

 technically, the London Clay and the Bracklesham 

 Barton and Bagshot beds are marine, as far as sea- 

 shells are concerned, yet no one is likely to believe that 

 these shell-fish lived and died in an open ocean. On the 



