Discover Bath and Explore the Fossils and Geodiversity of Browns Folly
- Wayne Munday
- Jul 11, 2025
- 4 min read
Updated: Jan 3
Brown’s Folly Nature Reserve, perched above the River Avon near Bath, is a geological and ecological treasure. Spanning over 90 acres, this SSSI exposes Jurassic oolitic limestone from the Chalfield Oolite and Forest Marble formations, containing rare fossils such as ammonites, brachiopods, and crinoids. Above ground, a rich mosaic of ash woodland, grasslands, and scrub provides habitats for rare orchids, butterflies, and bats, including Greater Horseshoe Bats. Visitors can explore informal trails offering panoramic views of the Avon Valley, while safely observing the historical Brown’s Folly tower and subterranean Bath Stone quarries. Fossil collecting is permitted only on loose scree, preserving the scientific integrity of this site that also celebrates the legacy of William Smith, the “Father of English Geology.”
Brown’s Folly also holds a significant place in the history of geology. It was within the broader Bath area that William Smith often regarded as the “Father of English Geology,” first identified and named the Great Oolite. Brown’s Folly has an exceptionally well-preserved and accessible 30-metre-thick sequence that includes, at its uppermost, the Forest Marble Formation of interbedded limestones and clays deposited in stable, well-oxygenated and shallow marine shelf to lagoonal environments followed by the fossil-rich Bradford Clay a thin layer between 20–30 cm thick that preserves diverse marine fauna such as Digonella and Apiocrinus.
Both Digonella and Apiocrinus are extinct marine invertebrates. Digonella is an articulate brachiopods characterised by their hinged dorsal and ventral shells and their mode of life as benthic filter feeder anchored to the seafloor. By contrast, Apiocrinus is a stalked crinoid characterised by a long stem, cup-like body and feathery arms used to capture plankton in warm, shallow, low-sediment marine environments such as oolitic shoals.
An oolitic shoal is a shallow marine geological formation composed primarily of ooids or small, spherical grains with concentric mineral layers that form around a nucleus like a sand grain or shell fragment. These grains develop in warm moving water where mineral precipitation coats the sand nuclei and their accumulation and cementation produce oolite a distinctive limestone ooze. Oolitic shoals typically form on tidal flats and shallow banks and can range in size from a few meters to many kilometers.
Below the Bradford Clay lies the Corsham Limestone Formation a fine-grained limestone underlain by the Chalfield Oolite Formation. This basal unit includes three members: the Bath Oolite, the Twinhoe Member and Combe Down Oolite. Collectively, these rock units record repeated marine transgressions and regressions with an abundance of ooids laid down in a warm Bathonian sea.
Actually finding fossils in-situ is rare at Brown's Folly due to historical collecting and vegetation overgrowth. Fossil collecting is permissible only from loose scree or disturbed surfaces at the base of slopes. As an SSSI hammering or removing bedrock is not permissible and strongly discouraged to both preserve the scientific integrity of the exposures and to prevent erosion and personal injury.
Brown’s Folly calcareous soils supports an ancient Ash-dominated woodland, diverse grasslands and scrub land. The long-established woodland also features species like Oak, Wych Elm and Hazel.
The adjacent grasslands are among the UK's most biodiverse, home to a wide range of grasses, wildflowers like Wood Anemone, Yellow Archangel and notable orchids including the scarce musk orchid. Among the plants are rare butterflies like the Duke of Burgundy (Hamearis Lucina) and White-Letter Hairstreak (Satyrium w-album). This mosaic of habitats underscores the site's high biodiversity and the need for continued conservation efforts.
Brown’s Folly Mine is also part of the Bath and Bradford-on-Avon Bats Special Area of Conservation. The old mines and quarry workings are a crucial habitat, roost and winter hibernaculum for a range of bat species, particularly the Greater Horseshoe Bat (Rhinolophus ferrumequinum).
The reserve still contains a labyrinthine network of man-made tunnels and caves resulting from historical stone extraction. While these features have geological interest they pose a very real safety risks and are not suitable for unsupervised exploration. Visitors should avoid entering these underground spaces and refrain from climbing on quarry faces.
Brown’s Folly Nature Reserve is open to the public year-round and is best explored on foot via a network of informal trails. Visitors should be prepared for steep and uneven terrain making sturdy footwear an essential. Brown’s Folly will offer the visitor panoramic views over the Avon Valley.
A visit to Brown’s Folly is a journey through layers of natural and geological history, where stunning views over the Avon Valley meet the deep time of the Jurassic Period. From its landmark tower to its ancient underground stone mines, the reserve tells the story of Bath Stone, fossil-rich oolitic seas, and the legacy of William Smith, the “Father of English Geology.” Above ground, a rich mosaic of ash woodland, biodiverse grasslands, and scrubland supports rare orchids, butterflies, and bats, making Brown’s Folly both a geological treasure and an ecological haven. As you walk the reserves trails, tread lightly this Site of Special Scientific Interest depends on careful stewardship. Fossil hunting is allowed only from loose scree, and mine entrances should be admired from a safe distance. Whether you're here for the fossils, the wildlife, or the views, Brown’s Folly offers an unforgettable glimpse into Britain’s ancient past and living landscape.
