_Deep Wells_ (Vol. iv., p. 492.).--Besides streams and sunk wells, there
is of course another source of water arising from natural springs; and
there are some on both sides of the Banstead Down, which are very
considerable. The chief, probably, is the source of the River Wandle, at
Carshalton, pronounced (with the same omission of the _r_ which P. M. M.
notices) as if it was spelt _Case-_, or _Cays-horton_.
But there is a very strong one at Merstham. These are both at the foot
of the Chalk hills. P. M. M. does not mention the geological causes on
which the relations between wells or springs depend. About thirty-five
years ago the spring at Merstham, which feeds a considerable spring,
failed, and there was a great dispute whether it was owing to
excavations in the neighbourhood. An action was brought, which decided
that it was not attributable to them; upon which I believe Mr. Webster
and Mr. Phillips, eminent geological authorities, were examined, and
which led, perhaps, to their respective accounts, in the _Geological
Transactions_, of the structure of that valley. The story was, that,
after having gained the cause, the proprietor of the quarries said, "I
think we may let them have their water back again." Certain it is that
after some time the water did return.
The Galt clay almost everywhere underlies chalk: this at Merstham is 200
feet thick, and upon the pitch and situation of it many apparently
strange phenomena of wells would depend, as is noticed with regard to
another clay stratum at Norton St. Philips, near Bath, in Conybeare and
Phillips' _Geology_.
There are very deep wells throughout the London clay, and other beds
below it, perhaps, at Wimbledon and at Richmond Park. The deep well at
Carisbrook Castle is well known. That is in the chalk; and where, the
chalk being thrown into a vertical position, it may be still farther to
the bottom of it.