RELATION OF STRATA TO SUCCESSION OF LIFE. 467 



ham fossil leaves in good preservation indicate nearness to land. This 

 estuarine condition is found as far south as Newhaven and Arundel, 

 and extends into France, indicating that an estuary occupied much of 

 the region which is now the Weald, and to this source we are disposed 

 to attribute the constant change in mineral character of the unfossili- 

 ferous sands and mottled clays which form the western part of the 

 deposit. Hence we should not regard the marine condition of the 

 beds as graduating into the estuarine, lacustrine, and fresh-water con- 

 dition of the deposit, but rather that sediments derived from different 

 sources, and bringing different materials, overlapped each other. The 

 succeeding Oldhaven beds are most instructive on this point, for in 

 East Kent they consist of sands with small flint pebbles ; and as the 

 beds are followed westward to Blackheath, the perfectly rounded flint 

 pebbles reach a thickness of 40 feet. There can be no doubt that the 

 chalk was denuded to form these pebbles, and that the rounding of 

 the pebbles furnished much flint sand, such as occurs irregularly in 

 the Woolwich beds at Reading. There is therefore reason to think 

 that the Oldhaven beds are an extension eastward of the upper part 

 of the strata termed Woolwich and Reading series in the Hampshire 

 basin, and that they were accumulated, as Mr. Whitaker suggests, as 

 a shoal at some distance from shore, but, as we believe, at the mouth 

 of an estuary, which came through France by way of Rheims. Next 

 succeeds the London clay. This brings us, as Professor Prestwich 

 first pointed out, a succession of new faunas, which are at least four 

 in number, in the eastern part of the London basin, but which are not 

 separated from each other in the same manner in the western part of 

 the Hampshire basin. The superposition of the London clay on the 

 Oldhaven beds indicates, first, a depression of land, which removed 

 from the British region the evidences of shallow-water deposits ; but 

 we find them persisting longest towards the south in the Bognor rock 

 and lower London clay sands, showing that it was from the French 

 direction that the underlying sands and pebble beds had been derived. 

 After the old land of Central Europe had thus become modified, and 

 sent down to the sea its mammals, birds, emydians, and crocodiles to 

 become mixed with the sea-serpents and chelonian reptiles of the 

 shore, the process of depression continued, bringing an ever-different 

 assemblage of species into the British area of the London clay sea ; 

 and then upheaval brought back again the crocodiles and fruits, until, 

 after a second depression and renewed upheaval, the old river, now 

 grown larger or brought nearer, swept a luxuriant flora into the clay 

 of what is now Sheppey and Belgium. The upheaval continuing, 

 brought back once more the condition of dry land to the south, super- 

 imposing sands upon the London clay, in which were fossilised the 

 leaves of such trees as yielded the fruits of Sheppey. These physical 

 conditions, here stated in brief abstract, not only govern the distribu- 

 tion of life, so as to explain why the fossils change with the successive 

 strata, but serve to demonstrate the relative differences of distribution 

 in depth of marine life preserved in the successive strata. The Thanet 

 sands yield a littoral fauna, but the fauna of the London clay is that of 



