113
ESSEX FIELD CLUB.—REPORTS OF
MEETINGS.
EXCURSION TO THE CROYDON BOURNE
448TH MEETING.
SATURDAY, 10TH APRIL 1915.
This was the first of a series of extra-territorial excursions imposed
upon the Club by reason of the military occupation of our own County,
which prohibited freedom of movement in the occupied districts, and was
undertaken in conjunction with the Geologists' Association. Just over
30 members of the two societies attended, and several members of the
Croydon Natural History Society were also present by invitation.
Mr. W. Whitaker, B.A., F.R.S., F.G.S., acted as conductor and
favoured the party with several instructive lecturettes at various points en
route upon "bournes" in general, and the Croydon Bourne in particular.
On leaving Woldingham station, he remarked that the valley which
we were about to descend was normally a dry waterless chalk-valley,
with, however, a thin scattering of flint-gravel in the bottom; and the
question at once arose, How did the gravel come there ? The explanation
was that a stream of some amount of erosive power must have
occupied the valley, in times of greater rainfall than the present; and
that the Croydon Bourne was but a diminished and periodic
representative of this erstwhile larger and persistent stream. "Bourne"
is one of several local names applied by custom to intermittent streams
which appear occasionally in chalk or limestone districts in various coun-
ties, and convert, for the time being, a dry valley into a swampy water-
course. Bournes were known in Surrey, in Kent, in Hertfordshire, small
ones occur in Essex, while in Dorset, Hants, and Wiltshire they were
numerous, as well as in Yorkshire and elsewhere. Formerly regarded as
prognostics of evil, and hence called "woe-waters" by the superstitious,
their sudden appearance was now recognised as being due to a previous
period of exceptionally-heavy rainfall, which caused the "plane of satura-
tion" in the chalk or limestone rocks of the district to become raised to a
height sufficient to allow the water to break out on the side of a valley,
probably at some point where a looser texture of the rock, or a multi-
plicity of joints, allowed of easy exit for the pent-up water.
The earlier geologists believed that huge underground caverns acted
as reservoirs for the water, and that these became emptied periodically
by syphonic action; but Mr. Whitaker regarded this as an untenable
hypothesis, since it would require a separate reservoir for each one of the
hundreds of bournes known to exist.
At Bughill Farm, near Woldingham station, the highest point at which
the Croydon Bourne has been known to rise, the ground was now perfectly
dry, although the bourne had reached as far up the valley as this point a
month ago, when at its greatest flow. The dry stream-course was followed
down from here (the grass thickly coated with a white limy deposit),
becoming more and more swampy, until, at Wapses Lodge, a shallow pool,
some 50 feet across, marked approximately the present and more usual
extreme limit of the Bourne. On 3rd March last, 3,500,000 gallons a