Avon Wildlife Trust

In the first of a new series, we catch up with local groups who are involved in geoconservation in the Avon region. First up, Avon Wildlife Trust.

From belemnites & brachiopods to bats & bullfinches...

Avon Wildlife Trust is committed to working for people and wildlife in the local area, and we manage 35 nature reserves, some of which are also sites with outstanding geological features. One reserve which has been at the centre of our recent 'Bats for Bath' project is Brown's Folly.

Brown's Folly, Bathford. Photo credit: Avon WT

Browns Folly Nature Reserve is a Special Area of Conservation (SAC) and Site of Special Scientific Interest (SSSI) that has rare calcareous grassland habitats, unique geology, ancient woodland and a cave system with fantastic bat populations, with 12 of Britain’s 18 Bat species having been recorded here.  The caves are the remnants from mining the local oolitic limestone which was extracted for building material, and which is known locally as 'Bath Stone'. Oolitic limestone gets its name from the spherical particles or 'ooids' it contains. This word comes  from the Greek word for 'egg' because ooids are thought to resemble fish eggs. You can see fossils  in the exposed stone - thick shelled bivalves such as Trigonia, found today in the Pacific, along with brachiopods, ammonites and belemnites which once swam in the sea which covered this area 170 million years ago.

Oolitic limestone hand specimen (left) and thin section (right). Photo credit: http://www.earthscienceeducation.com

The stone was used for building in Roman times, but intensive mining of the limestone beds in the valley was carried  out from the 17th to the early 20th century. The characteristic stone was used for the construction of most of Bath's famous buildings, as well as Buckingham Palace and many stately homes across the country. The different mines, which were driven in to the rock in the  area, stretched for many miles and contained stables, cart-roads and tramways. Stone was extracted by the 'room and pillar' method, by which chambers were mined, leaving pillars of stone to support the roof.  By the time the mines closed down in 1930 there were over 300 acres of interconnecting underground workings and tunnels, which were used for storing ammunition and government  records during the Second World War.

Bats are very fussy about their roosting sites - they need somewhere with stable temperature and ventilation levels, and the old mine tunnels under the woodland seem to suit them very well. The huge size of the mines means that areas deep down are less affected by outside variations in climate - a perfect spot to hibernate for the winter months. The Trust has installed bat grilles on the entrances of the mines in the woodland to make sure that the bats remain at peace within their hilly homes. Bats are protected by law, and the grilles also prevent access to the mines - protection for people as well as preserving peace for the bats. In spring and summer when the bats awake and come out to feed at dusk, the grassland glades of the reserve are rich with insects right on their doorstep.

Greater horseshoe bat - just one of the twelve species recorded in the caves at Brown's Folly. Photo credit: Avon WT

Brown's Folly in Bathford is one of our most popular reserves that receives around 5000 visitors each year with most people enjoying the fantastic views from the grassland plateau across to Bath and the surrounding area, and talking long walks through the ancient woodland full of rocky fissures, giant veteran trees, mosses and ferns, and open glades that all help support the bats roosting in the caves.

You can read more about Brown's Folly and other Trust nature reserves here.

Pat Ellingham
(Avon WT Director of Communications and Development)


Look out for more information on the geology of Brown's Folly - it is soon set  to feature on the blog as a RIGS of the Month.