70 Mr. $Fohn Flower. 
except the Darent. This is left, but only as a weakly stream, 
deriving a small amount of water from the small valley 
which runs from Westerham towards Sevenoaks, but, with that 
exception, having altogether lost its connection with the 
Weald. It seems to stand, in fact, like one of those very 
ancient forms so well-known to physiologists, an isolated relic 
of a byegone age, left as a connecting link for our instruction. 
With the unimportant exception above mentioned, in the case 
of the Darent, the whole of the country to the south of the 
chalk hills between the Mole and the Medway is now drained 
by those rivers, the sole survivors in their struggle for 
existence, and their branches may now be seen in the fields 
below White Hill near Caterham, within a very short distance 
of one another. 
Another curious and interesting effect would seem to result 
from the state of things above described. The drainage down 
the gault valley would flow east and west into the rivers, and 
as these, following the natural dip of the strata, flow towards 
the north, the tendency of the flow of the water down the 
gault valley would be to cut off the corners, where the gault 
valley joins the river valley, and, taken with the gradual lower- 
ing of the gault valley, to form the trumpet-shaped mouths, 
with sloping sides, which are seen at the southern extremity 
of many of the river valleys on the north side of the Weald. 
With regard to the survival of the Mole, it seems probable, on 
reference to the map, that this has been due to the exceptional 
advantages which it has enjoyed over the other rivers in its im- 
mediate neighbourhood. In the first place the Lower Greensand 
formation is reduced to very small dimensions where the river 
passes into the chalk, and this has given it, without interrup- 
tion, the drainage of the large area of Weald Clay which lies 
immediately to the south of the Mole valley. Then again, 
in the way already pointed out, it has been enabled to secure 
for itself, and thus to monopolise, all the drainage of that part 
of the valley of the Gault which lies for 10 miles to the east 
and for some few miles to the west of it. And lastly the short 
distance which it has to pass over the Chalk before it reaches 
the London Clay, which here approaches very near to the Gault, 
has very materially assisted it. 
I have gone much into detail with regard to the struc- 
ture and history of the Weald because it is so closely 
connected with the districts which adjoin it that its past 
history is necessarily part and parcel of theirs: so much 
so indeed that until the manner in which it has been 
formed is properly understood, it will be impossible to under- 
stand the history of the valleys which run into it. If the above 
explanation be borne in mind it will not be difficult now to see 
