Natural Caves
Although the geology Kent and Sussex is not particularly good for the formation
of natural caves, a number of recent discoveries have shown, contrary to the
opinion of many cavers and geologists, quite extensive cave systems can be found
in the chalk. Small caves also occur in other rock including sandstone and
'Kentish Rag' (a sandy limestone), and including several important sites of
archaeological or palaeontological interest. There are also numerous examples of
sea-worn caves scattered around the chalk cliffs of the Kent and Sussex
coastline. None of the latter are very extensive, only rarely going beyond the
limit of daylight penetration, but they can be quite roomy and make nonsense of
the widely-held belief that chalk is too unstable for cave development. One
example in the Seven Sisters cliff near Cuckmere measures 65ft in length and up
to 50ft wide.
The processes involved in the formation of inland caves in chalk or limestone
are extremely complex and are still not fully understood. Basically they are the
result of water dissolving and eroding the rock along crevices known as joints,
bedding planes and faults. Caves formed by free flowing streams with an air
space above are known as 'Vadose' systems, while for those which are completely
waterlogged the term 'phreatic' is used. Caves of both types which are now
drained of the streams that formed them are described as 'fossil' systems. Most
of the chalk caves so far discovered in Kent and Sussex fall into the 'fossil
phreatic' category.
Caves can also form when large masses of rock resting on unstable clay simply
move apart, leaving what is in effect a large crack. These are known as
'tectonic' or fissure caves and are often associated with landslips. A good
example in chalk is Beachy Head Fissure near the lighthouse situated on the
cliff top above a landslip. It consists of a 50ft shaft leading to a tall
natural passage, descending to a depth of about 70ft. Similar caves in sandstone
occur at Cowden and behind the fishing huts at Hastings. The well-known Ightham
Fissures in Kentish Ragstone were also probably formed in this way.
A number of streams in S.E. England sink underground in what are generally
referred to as sinkholes, swallets or swallow holes and these features have
often been used as evidence of cave development in chalk. The best-known example
is at North Mimms in Hertfordshire where the Mymmshall Brook sinks
into the chalk and has been traced by dye tests to springs up to 11 miles away.
Good examples also occur in Kent at Lower Ensden near Chartham where several
streams draining off the clay sink into large swallets, up to 60ft wide and 40ft
deep at the clay/chalk boundary. One of these holes has a cave mouth at the
bottom but it is blocked after a few yards. An interesting recent development
was the discovery of a natural chalk cave system in a previously unrecorded
swallet at Warren Row in Berkshire. The lower Ensden swallets are almost
identical to the Warren Row example and in some cases are considerably larger
and take a lot more water.
It is also encouraging to know that the French have been searching for caves in
the chalk region of the Paris Basin, which is actually the continuation of the
North and South Downs on the other side of the Channel. In spite of 'expert'
predictions that any such caves would be small and uninteresting, they have
explored numerous examples of up to 2 kilometres in length. Nearly all these
French caves were found in wells and this has led to speculation that the
underground streamways were located by water divining. On one occasion, the
Water Services of Paris are said to have asked a dowser to indicate the exact
point at which to dig a well. Their engineer was not convinced, however, and
decided to sink a 90ft shaft to one side of the point indicated. At a depth of
60ft there was no sign of water so they dug a tunnel in the direction shown by
the dowser - here they met the course of an underground river.
Early Geological Survey publications and natural history journals contain
several interesting references to similar caves in Kent. In 1879 workmen digging
a tunnel from a well at Strood Waterworks broke into a large natural cavern
containing running water, which was eventually explored for about 200ft. Another
reference in
1907 described a cave in a well at Knockholt which measured 30ft long, 18ft high
and 12ft wide with a stream flowing through it. A similar cave and watercourse
is said to have been entered at a well near Chatham and three separate caves
were discovered at Blackheath during the construction of a sewer tunnel.
Unfortunately, none of these early finds are accessible today.
More recently, the search for chalk caves has concentrated on the sea cliffs. In
addition to the sea caves, there are many cavities at various heights in the
cliffs which cannot have resulted from marine erosion. Some of these are
infilled with rubble or sediment but others are open cavities large enough to
enter. Most of these cavities are inaccessible but some examples near the base
of the cliffs have been explored. These include Canterbury Cave and
Beachy Head
Cave, the latter extending for well over 1,000ft.
Another rock which might conceivably contain caves is the sandy limestone known
as 'Kentish Rag', The River loose near Maidstone flows underground in this rock
for a distance of a quarter of a mile at Boughton Quarries and,
although the valley has been altered by artificial landscaping and quarrying at
its sides, the disappearance of the stream appears to result from natural
causes. There are also three very powerful springs emerging from the ragstone
near West Mailing and the volume of the water is such that it suggests streams
flowing in open cavities rather than seepage through porous rock.
Natural caves can also form in gypsum. This rock does not outcrop at the surface
but it is extensively mined at Brightling and Mountfield (see GYPSUM MINES).
Conversation with some of the miners seems to confirm that natural caves have
been encountered and the miners refer to these caves as 'washouts'.
The entrance to this cave lies on the south side
of St Margaret's Bay, just above the high water mark. The name 'Canterbury Cave'
first appears on a map of the South Foreland in 1960 and it is apparently a
local name for the cave. At that time it was presumed to be a sea cave and it
was not until 1975, when it was examined and surveyed by members of Chelsea
Speleological Society, that its true significance was realised. It soon became
obvious that the cave could not have resulted from marine erosion as it was
above the normal range of the tides and quite extensive. What had happened is
that the cliff had exposed a fossil cave system originally formed by an
underground stream.
The entrance is a large recess behind a pile of boulders which have fallen from
the cliff face. At the rear of this opening, a passage averaging 7ft wide x 4ft
high extends into the cliff in a N.W. direction. About 80ft from the entrance,
the passage bends to the right and opens into a small chamber 30ft long x 12ft
wide x 5ft high, before resuming its original direction after a sharp left turn.
The roof and wails of the chamber have a pitted, sponge-like appearance which is
characteristic of a cave originally formed under 'phreatic' conditions when the
passage was completely filled with water.
About 50ft beyond this chamber, the passage veers to the left and becomes a flat
out crawl for about 20ft. The crawl ends at a T-junction with a roomier passage
trending north and the obvious way on is to the right. After crawling over and
around boulders for a further 70ft, the cave appears to end in an impenetrable
fissure, but closer inspection reveals a low opening on the left hand side. This
leads to another stretch of roomier passage, the end of which is choked with
rubble and boulders just over 300ft from the entrance.
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Entrance to Canterbury Cave |
To the left of the T-junction, the passage continues southwards but rapidly
diminishes in size and is almost choked with sediment, apparently derived from
the Thanet Sand which overlies the chalk in some areas. The passage was
eventually explored in this direction for about 45ft by digging out the floor
and, during the excavation, a number of rat and rabbit bones were unearthed. At
the furthest point a small fissure branches off to the left but the way ahead is
completely blocked.
The total length of explored passages is 360ft. The passages are clearly
joint-orientated but there is another less obvious feature that may have had a
considerable influence on the development of the cave, i.e. the thin sheet of
tabular flint seen beneath the floor near the entrance. In the cliff face
nearby, the chalk above the upper surface of the flint is honeycombed with tiny
cavities only a few inches wide. It is interesting to note that the cross
sections of the cave discovered at Strood Waterworks also show a flint seam at
floor level. Further examples of caves floored with tabular flint can be seen in
the cliffs at Beachy Head. These flint layers probably form an effective water
barrier which results in a saturated (phreatic) zone above the normal level of
the water table. Water held up in this way must eventually drain away, following
any Incline in the strata or leaking into unsaturated rock below wherever the
continuity of the flint is interrupted by faulting, etc. This would result in
significant underground water movements, particularly along the joint structure
on the upper surface of the flint.
This is one of the several caves situated in the
spectacular chalk cliffs at Beachy Head near Eastbourne. The entrance lies in a
particularly inaccessible location near the base of a 300ft vertical cliff and
involves a difficult climb to a ledge 14ft above the beach. This ledge is an
exposed bend in a cave passage with two low, semi-circular openings leading off
into the cliff. The cave was eventually explored and surveyed by members of
Chelsea Speleological Society during 6 visits in 1980. Careful planning was
required to avoid being cut off by the tide!
To the right of the ledge, the passage extends for 585ft and ends at a 'sump'
where it continues full of water. The cave passages are very small and progress
is slow - mainly flat out crawling with only occasional sitting or standing
space. The floor is either covered with dried out mud or littered with flint
nodules, and the whole place is literally crawling with fauna - spiders, gnats,
moths, etc. The passage follow~ the joint network of the chalk with many sharp
bends but maintains an overall trend in a N.E. direction away from the cliff
face. There are several small tributary passages, including a tube-like opening
in the roof which can be climbed to a height of 25ft.
The only significant change in the character of the main passage is a curious
14ft drop down a perfectly circular tube inclined at 45 degrees. Beyond this,
the previously dry and dusty cave suddenly becomes very damp with slimy black
deposits on the walls and puddles spreading across the floor towards the end. It
is in this damp section that the only cave formations are seen - some small but
attractive crystals and a 'botryoidal' stalactite resembling a cauliflower.
Beachy Head Cave |
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The left hand passage is initially very similar to the right hand series. It
extends for 465ft and nearly touches the cliff again in three places where
daylight enters from tiny tube-like openings. The passage beyond the second
point of daylight penetration is noticeably different from the rest of the cave,
formed along a fault with a boulder strewn floor and plenty of standing space.
This is followed by two very tight crawls, beyond which the passage steadily
increases in size until it is 6ft wide x 5ft high before heading downhill
through a series of S-bends. At the bottom of this slope, another very tight
crawl leads to a mud-floored passage with the channel of a tiny dried up stream
down one side. The passage finally ends where the sediment comes to within a few
inches of the roof but it could probably be extended by digging.
As in the caves at Strood and St Margaret's Bay, the cave is formed above a thin
tabular flint layer and sudden changes in the level of the passages seem to
coincide with displacement of the flint by faulting.
The total length of explored passages is 1,160ft, which makes it the longest so
far discovered in the English chalk, and the depth below surface is 300-400ft.
It is now one of the 50 caves in Britain scheduled as Sites of Special
Scientific Interest. Since the cave was surveyed, some spectacular cliff fails
have created two new entrances in the left hand series. The original entrance
ledge has also collapsed, effectively splitting the cave into two.
The chalk cliffs of the Isle of Thanet
originally contained over 100 caves but most of these have now been destroyed by
the construction of sea defences. Some of the best remaining examples are
situated in the relatively unspoilt cliffs of the Kingsgate area where various
paths and steps provide easy access to the beach at low tide. The largest cave
in this area is 'Smugglers Cave’ situated in Kingsgate Bay behind the Captain
Digby pub. This is over 200ft long x 30ft high but has obviously been
artificially enlarged with a high level side passage and blocked shaft at the
end, which originally led to the surface. Nearby is the entrance to 'Tower Cave'
which is entirely natural and extends for about 100ft.
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Whiteness Point sea cave and manmade tunnels |
At the western end of the bay, the headland known as Whiteness Point is pierced
by a natural sea cave and a system of manmade tunnels. One of the tunnel
entrances is accessible at high tide and a hole in the floor provides a
spectacular view of the sea cave below, especially during rough seas. A sketch
of this area made by Mr R. Staniforth in 1960 shows these tunnels but not the
sea cave, so presumably it did not exist at that time. The rate of erosion is
certainly extremely rapid as it has taken less than 30 years for the sea cave to
penetrate the 70ft wide headland. Eventually it will collapse and form an
isolated stack, similar to those in the adjoining Botany Bay area. None of the
other caves in the area shows any significant changes since Staniforth made his
sketches but a natural arch in Botany Bay has collapsed to form a new offshore
stack.
Archaeology & Palaeontology
There are three locations in Kent which have provided interesting finds relating
to the late Pleistocene period some 50,000-100,000 years ago. The well-known
'rock shelters' at Ightham are small natural caves and overhangs which occur in
the sandstone crags along the eastern edge of Oldbury Hill. Many interesting
features, including at least one fairly substantial cave, have unfortunately
been destroyed by quarrying of the outcrops during the early 19th century. The
main group of rock shelters surviving today consists of 8 low openings beneath
overhanging rocks, some of which interconnect in the form of a small but quite
complex cave system with over 150ft of passages. The caves occur in a soft,
silty layer sandwiched between hard chert, which forms the roof, and harder
sandstone below. They appear to have resulted from differential weathering of
the rock outcrops and erosion by springs. It is interesting to note that a small
stream rises from a spring at a similar level on the northern side of the hill.
In 1890 a local archaeologist, Benjamin Harrison, directed an excavation which
resulted in the discovery of a large collection of Palaeolithic (early Stone
Age) flint implements. These were recognised as 'cave dwelling types' almost
identical to those found at Le Moustier in France. Unfortunately, there is
considerable confusion as to the location of these finds.
A more recent excavation by Desmond and Anne Collins (1965) failed to find any
evidence of occupation in the immediate vicinity of the surviving rock shelters
but, further down the hillside, more examples of the distinctive 'Mousterian'
implements were found. They concluded that, whilst there was no definite
evidence of occupation of the shelters in their present-day form, it was
possible that the implements were associated with a former rock shelter now
destroyed by natural erosion or quarrying. Further excavations could throw more
light on the subject but there would seem to be little doubt that it was the
shelter provided by the natural caves and overrhangs that attracted the
Palaeolithic tool makers to this area some 50,000 years ago.
Another interesting site near Ightham was the 'Ightham Fissures', discovered and
subsequently destroyed by quarrying in the years preceding 1894. A photograph of
the site in Bennet's book titled 'Ightham' shows three narrow openings in a
ragstone quarry, the largest about 3ft wide. What made these features
particularly interesting was the wealth of Pleistocene fossils found inside. The
remains comprised 27 land snails, 47 mammals, 3 reptiles, 2 amphibians and 20
birds. The mammals included mammoth, woolly rhinoceros, brown bear, reindeer,
red deer, roe deer, horse, wolf, hyena, wild boar, badger, common and arctic
fox, otter, weasel, polecat, pika, pouched marmot, mole, shrew, field mouse, 5
species of bat and several species of vole and lemming. It will be seen that
some of these animals are now extinct or no longer present in the British Isles,
whilst others are still common species today.
There are also references to a 'Boughton Cave' near Maidstone where the remains
of mammoth, woolly rhinoceros, reindeer and red deer were found.