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during the recession, but rearranged and also greatly added to by 
the advance of the sea. The remarkable extent to which the 
flints are worn shows that the duration of these conditions was 
very considerable, whilst the change in the fauna seems also to 
indicate a great lapse of time between these events. In some 
places rolled pebbles of the mottled clay are included, so that 
this must at least have been hardened by this time. 
In the London Clay we see a further depression of the land, 
enabling the Northern Sea to encroach gradually from the north- 
east, and ultimately reach as far west as the present borders 
of Dorsetshire. It never attained more than a few fathoms 
depth in the western area, and little more than 100 fathoms in 
the deeper eastern parts. The marine fauna is far more torrid 
looking, owing to a warmer period having set in, produced 
probably by the rise of land between England and North America 
which, there is evidence to show, took place about this time, 
and shut off the cold arctic currents in a manner] to be ex- 
plained further on. The increased temperature of the sea 
acted upon the land, and enabled a most luxuriant and varied 
flora to migrate thither ; its fruits and seeds are found at 
Sheppey just as they were stranded and buried in the delta- 
mud of the great western river. 
The river, whose delta has been seen to have been hitherto in 
the eastern area of the London Basin, seems now to have shifted 
its course to the south. Its mouth at this period may have been 
on the since denuded Wealden area, or still further off out at sea. 
The Lower Bagshots such as we have them at Alum Bay, 
Studland, Corfe, &c., show no proximity to the sea, but rather 
the filling in by river action, of a wide valley and shallow lake. 
The complexity of the stratification renders it doubtful whether 
two rivers did not unite in this valley, and shows plainly that 
the waters must in any case have been rapid at times, and sub- 
ject to periodical fluctuations of volume. 
As there are no passage beds or signs of any delta having 
existed here between the London Clay and Lower Bagshots, we 
must conclude that the river did not immediately occupy this 
part of the land left dry by the retreat of the London-Clay sea, 
but flowed over it long subsequently, gradually shifting its outfall 
from east to south and west. The great deposits of rolled flints 
above the London Clay in the eastern parts of the London Basin 
show that the North-Sea littoral occupied that area for an im- 
mense lapse of time. We see by the composition of the western 
fresh-water beds, that a granite area was still being worn away, 
and the total absence of flint shows that the western chalk hills 
were not yet raised into position for denudation by the river, as 
had they been upraised the course of the river would necessarily 
have been through them. The absence of lignites in this part 
