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Today we know more about swallow holes, which occur only in
limestone rocks, of which chalk is a form. As Defoe explains,
they are holes or cracks in the river bed or river banks through
which river water passes into underground channels, so diminishing
the flow of the river. The average flow of the Mole above
Burford Bridge is 63 million gallons a day, while at Leatherhead,
down- stream, it is 55 million gallons: eight million gallons
have therefore disappeared some- where along the way, the
major part of which must go down the swallows. This leakage
from the river goes on all year round, but in the summer the
surface stream occasionally disappears completely. The bed
of the Mole is then dry, except for a few residual pools,
from Ham Bank near Norbury Park to a point near Leatherhead,
where water emerges again into the river bed from a series
of springs.
There are many subsidence holes, some old and some more recent,
at the foot of Box Hill and elsewhere in the valley. In 1940
a medium-sized oak tree dropped without warning into a chasm
behind a house in Mickleham. Apart from such odd happenings,
the river valley holds other secrets. The elusive kingfisher
may be seen at the foot of The Whites where the river is fordable
by means of stepping stones. The same area harbours grey and
pied wagtails, as well as moorhen, mallard and the gaudy semi-wild
mandarin duck. Wild mink have been reported and, even more
bizarrely, a small colony of the rose-winged parakeet has
become established near the river. Box Hill from Denbies Hill.
The River Mole winds between the trees at the base of the
escarpment The River'Mole is something of an enigma. According
to one school of thought, its name derives from its habit
of burrowing underground, like its animal namesake. Others
argue that in the Middle Ages the Mole was known as the Ernlyn
Stream and its present name stems from Molesey where the river
joins the Thames.Daniel Defoe, who lived in the neighbourhood
for a time in the early eighteenth century, recorded his detailed
observations of the River Mole in A Tour through the Whole
Island of Great Britain.
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