Combe is a fine example of a typical Mendip gorge, and provides
a well exposed, easily accessible, section through the Carboniferous
Limestone sequence. The oldest rocks are exposed in the East and
West Twin valleys draining Blackdown, and show the transition from
the older Devonian sandstones of the Portishead Formation through
the limestone and mudstone of the Avon Group to the younger
marine Carboniferous Black Rock Limestone, which are very well
exposed in the upper part of Burrington Combe. The rest of the
Carboniferous Limestone sequence is exposed in the Combe.
Aerial view of Burrington Combe (click to enlarge view).
The overlying Burrington Oolite forms the prominent crag known as
the Rock of Ages. This is the site of the apocryphal story of the
Reverend Augustus Toplady who supposedly sought shelter during a
storm here, inspiring the hymn of the same name. The lower part of
the Combe cuts through the Clifton Down Limestone which can be seen
in the many small crags and quarries on the east side of the valley.
The Triassic Dolomitic Conglomerate can be seen in a series of small
roadside crags and old quarries on the hillside south of Blagdon.
North-east of Burrington is Blagdon Combe, a deep sinuous dry valley
cut into the Triassic Dolomitic Conglomerate. It was cut by the Congresbury
Yeo, which once flowed through here before abandoning its course
for an easier route through the softer rocks in the Vale of Wrington
to the north.
Several small streams drain the northern side of Blackdown and sink
on reaching the limestone, forming caves. The largest occur in
the East and West Twin valleys, including Goatchurch Cavern, an
abandoned former stream sink forming a complex three-dimensional
phreatic maze, Sidcot Swallet, a smaller cave about 250 m long,
and East Twin Swallet. Several other small phreatic caves also
Between Burrington Combe and Rowberrow Warren are a series of small
caves. The largest, Rods Pot, is popular with cavers and in one of
the neighbouring depressions Beaker age pottery (2500—600 BC)
and earlier Neolithic implements were found.
Geological map of the Burrington area with postulated drainage
routes (click to enlarge view)
The cave nearest Rowberrow Warren is Read's Cavern, once home to
early Iron Age occupants, and their remains were found during an
archaeological dig, buried under a rockfall.
In the Combe itself, just up the valley from the Rock of Ages is
Aveline's Hole. Discovered in 1797, it is a fine example of a phreatic
cave formed below the water table. It was once a spring, but was
abandoned by the river which now drains to two springs at Rickford
and Langford. The cave is an important archaeological site and contains
the earliest dated human cemetery in Britain; around 8400 years ago
during the Mesolithic period. It also contains one of the few known
examples of cave art in the UK.
The thin soils developed on the steep slopes of the Combe provide
a very species-rich limestone grassland habitat with many different
The warm, south-facing slopes of the valley are particularly important
for butterflies and other invertebrates, while many ferns, mosses
and liverworts flourish in the humid sheltered East and West Twin