HOW WERE THE EOCENES OF ENGLAND DEPOSITED? 287 
of the series may show the existence of lakeg such as that at 
Bovey Tracy which intercepted drifting timber ; its abundance 
in later beds marks the time when they had been filled in. 
In the age of the Bournemouth Beds we have the same 
deposits, but in a more open and level valley, and in close 
proximity to the sea. In all the lower or freshwater series we 
have no sign of the presence of sea-water. It is, therefore, not 
n case of river deposits encroaching on the sea, but of land 
sinking so gradually as to allow the sea to cover them. 
There are absolutely no indications, either in the Lower 
Bagshot or in the Bournemouth Beds, of the leaves having tra- 
velled from afar, and their preservation and local distribution 
indeed forbid the assumption that they have done so. 
In the Bournemouth Beds it is of extreme interest to trace 
the change from a comparatively upland flora to a valley, and 
then a swamp flora ; to watch the lowering of the land until it 
became sea; to trace the sea, first trickling in and forming 
lagoons, then boldly overwhelming their mud deposits with all 
the imbedded contents, and heaping over them shingle and 
sand ; to see the actual shore line, with land deposits full of 
plant remains on one side of it, and the bed of the sea with 
teeth of sharks and rays and shells on the other side. 
The elevation of the land towards the west which caused the 
Northern or London-Clay sea to recede was followed by a depres- 
sion towards the south-east, which not only diverted the embou- 
ehure of the river in that direction, but subsequently enabled the 
Southern sea, then occupying part of France, to encroach upon 
the land, and overlap to a small extent the older deposits. 
In those days the North Sea was completely separated from the 
Bay of Biscay, neither the English nor St. G-eorge’s Channels 
having been formed. Not only are the faunas of the two seas 
totally distinct, but the lithological characters of the deposits 
enable them everywhere to be identified. 
During the whole of the Eocene period until these beds are 
reached, we see that the now separate Tertiary Basins of London 
and Hampshire were continuous, and that identical series of 
strata were deposited over them without any discontinuity 
whatever. From this time, however, it is clear, from the total 
absence of any of the newer Eocene deposits in the former, that 
a separation had taken place, and that the London basin must in 
some manner have been severed from the latter. The London area, 
or at least the ridge which now separates it, must, therefore, 
have been upheaved at about this time, and perhaps again 
depressed when the elevation of the Weald took place. It has 
since been subjected to denudation on a large scale, and it is 
estimated* that the 66 vertical loss in the valley of the Thames 
* 11 Memoirs of Geological Survey,” iii. 55. 
