AN EARLY GALLERY AT CHISLEHURST CAVES
In 2006 during groundwork prior to building development at
Woodclyffe Drive, Chislehurst, a number of boreholes were sunk
to ascertain ground condition and to check for any unidentified
caves or voids. This investigative action was necessary as the
area of the development lies above part of the south-east
portion of the ‘Inner Series’ of Chislehurst Caves.
One such bore entered an unsuspected cavity at
approximately 16m below ground level in an area of disturbed
ground indicative of extensive subterranean failure. A CCTV
camera was lowered down the borehole and the images obtained
were recorded for civil engineering analysis to determine
suitable remedial action. The writer was kindly given a copy of
the recorded video footage by Mark Lett, the Acquisitions
Manager of the developers, Urban Solution Ltd, in order to make
an archaeological assessment of the cave space discovered.
The bore entered the roof of a mined gallery and,
having passed through a cavity estimated at 1-1.5m deep,
continued down through chalk debris. As there is no
reference-scale dimensions could only be estimated. The roof of
the passage surrounding the site of the borehole entry showed
signs of very recent falls. This almost certainly occurred when
the drill broke through the horizontal bed of chalk (c.10-15cm
thick) that forms the roof of the gallery. The views obtained
from the camera showed a straight horizontal passage with
possibly one short 90deg offshoot. Both ends of the tunnel were
totally blocked by roof falls and the floor was covered with
chalk and glauconitic Thanet Sand debris which shows evidence of
flooding at some time in the distant past.
It is known that Chislehurst Caves suffered severe
flooding in the mid 1860s and again as recently as 1968. The
Inner Series had already suffered a number of falls in its
entrance galleries after mining had ceased which effectively
sealed off access. The nineteenth-century floods caused further
serious collapses in this region. The observed gallery is within
the area of this major collapse zone.
The Inner Series was the first of the three chalk
mines which make up Chislehurst Caves to be worked, with
documentary evidence suggesting a commencement date of 1706.
Recent archaeological surveys in the accessible parts of the
mine confirm its eighteenth-century origin. The newly recorded
gallery would have been one of the earliest to have been dug
with a probable date of 1707-10.