68 Mr. Fohn Flower. 
Sand. The Gault and Weald Clay have been worn away 
and removed, or, as it is technically termed, denuded, whilst 
the Chalk and Greensand, and the Hastings Sand, have 
been left standing as hills. The agency which has produced 
this denudation of the Gault and Weald Clay has been the 
subject of much controversy, and many theories have been put 
forward to account for it, but the theory now adopted by the 
members of the Geological Survey is very simple, almost 
provokingly so, and it is that the only agents which have 
produced this denudation are the action of the rain and the 
weather, and the streams. In this way the Weald has been 
formed into the shape in which we now see it. 
There is one more very important feature to be mentioned and 
explained, and that is the formation of the valleys of the rivers 
which now flow, or formerly did, flow out of the Weald. When 
the Weald district was first left by the sea and became dry 
land, numerous streams, with lateral branches, must have been 
formed at once upon its surface by the action of the weather. 
These would naturally flow down the slope, in all directions, 
from the central high ground of the Hastings Sand, following 
the natural dip of the strata, and would cut channels, more or 
less deep, through the Weald Clay, Lower Creensand, Gault, 
Upper Greensand, and Chalk. In this way it would seem that 
five rivers or streams were formed in our immediate neigh- 
bourhood, the Darent, the Ravensbourne, the Wandle, the 
Hog’s Mill River, and the Mole, which must have drained 
between them a considerable part of the country which lies to 
the south of the chalk hills.* As the denudation of the 
Weald progressed, the streams trom the Weald would 
necessarily experience between themselves a keen struggle for 
existence, which would end as all such struggles inevitably 
must end, in the destruction of the smaller streams, and the 
survival of the streams which were most favoured by the 
natural configuration of the ground or by other natural 
advantages. 
The first difficulty which the streams on the north side 
of the Weald would have to contend with would be created 
by the action of the weather on the Weald Clay. As 
this was worn down and denuded, the Lower Greensand 
formation would gradually be formed into a range of hills on 
its north side, and these would offer an impassable barrier to 
the passing of water northward from the Weald, except in 
places where the Lower Greensand was of small dimensions, 
* These names are here adopted because they are the nearest modern 
names which are available, but except, perhaps, in the case of the Darent 
and the Mole, the modern streams are very different to their ancient proto- 
types both in character and extent. 
