(Vol. vii., pp. 238. 393.)
The bourne at Croydon is one of the most remarkable of those intermitting
springs which issue from the upper part of the chalk strata after
long-continued rains.
All porous earth-beds are reservoirs of water, and give out their supplies
more or less copiously according to their states of engorgement; and at
higher or lower levels, as they are more or less replenished by rain. Rain
percolates through the chalk rapidly at all times, it being greatly
fissured and cavernous, and finds vent at the bottom of the hills, in
ordinary seasons, in the perennial springs which issue there, at the top of
the chalk marl, or of the galt (the clay so called) which underlies the
chalk. But when long-continued rains have filled the fissures and caverns,
and the chinks and crannies of the ordinary vents below are unequal to the
drainage, the reservoir as it were overflows, and the superfluity exudes
from the valleys and gullies of the upper surface; and these occasional
sources continue to flow till the equilibrium is restored, and the
perennial vents suffice to carry off the annual supply. Some approach to
the full engorgement here spoken of takes place annually in many parts of
the chalk districts, where springs break out after the autumnal and winter
rains, and run themselves dry again in the course of a few months, or maybe
have intermissions of a year or two, when the average falls are short.
Thence it is we have so many "Winterbournes" in the counties of Wilts,
Hants, and Dorset; as Winterbourne-basset, Winterbourne-gunner,
Winterbourne-stoke, &c. (Vide Lewis's _Topog. Dict._) The highest sources
of the Test, Itchen, and some other of our southern rivers which take their
rise in the chalk, are often dry for months, and their channels void of
water for miles; failing altogether when the rains do not fill the
neighbouring strata to repletion.
In the case of long intermissions, such as occur to the Croydon bourne, it
is not wonderful that the sudden appearance of waters in considerable
force, where none are usually seen to flow, should give rise to
superstitious dread of coming evils. Indeed, the coincidence of the running
of the bourne, a wet summer, a worse sowing-season, and a wet cold spring,
may well inspire evil forebodings, and give a colourable pretext for such
apprehensions as are often entertained on the occurrence of any unusual
natural phenomenon. These intermittent rivulets have no affinity, as your
correspondent E. G. R. supposes, to subterraneous rivers. The nearest
approach to this kind of stream is to be found in the Mole, which sometimes
sinks away, and leaves its channel dry between Dorking and Leatherhead,
being absorbed into fissures in the chalk, and again discharged; these
fissures being insufficient to receive its waters in times of more copious
supply. The subterraneous rivers of more mountainous countries are also not
to be included in the same category. They have a history of their own, to
enlarge on which is not the business of this Note: but it may not be
irrelevant to turn the attention for a moment to the use of the word
_bourne_ or _burn_. The former mode of spelling and pronouncing it appears
to prevail in the south, and the latter in the north of England and in
Scotland; both alike from the same source as the _brun_ or _brunen_ of
Germany. The perennial bourne so often affords a convenient natural
geographical boundary, and a convenient line of territorial division, that
by an easy metonymy it has established itself in our language in either
sense, signifying streamlet or boundary-line,--as witness the well-known
lines:
"That undiscovered country, from whose bourne
No traveller returns."--_Shakspeare._
"I know each lane, and every alley green,
And every bosky bourn from side to side."--_Milton._