Writhlington’s conserved colliery-spoil rock store preserves a remarkable late Carboniferous wetland community. Plant impressions and rare terrestrial arthropods have made it internationally important, but this finite scientific resource is visited through controlled arrangements: obtain permission and current joining instructions before travelling.
FIND FREQUENCY: ♦♦♦♦ – Plant impressions are the main interest; rare insects and other arthropods require careful examination and scientific recording.
CHILDREN: ♦♦ – Suitability depends on the authorised, supervised visit and the condition of the uneven spoil; do not plan an independent family collecting trip without agreement.
ACCESS: ♦♦ – Access to the rock store is controlled. Nearby paths and cycleways do not themselves grant entry or collecting permission.
TYPE – Preserved mining waste from Lower Writhlington Colliery, with mixed shale from distinct underground horizons; not an upright natural rock section.
DIRECTIONS
♦ The former Lower Writhlington colliery tip lies east of Radstock, near grid reference ST 703 553. The original guide’s locality reference is 51.29599°N, 2.42530°W; this is not a confirmed present-day parking or meeting point.
♦ Arrange permission and obtain the current meeting point and access route from the visit organiser or site manager before setting out. Published organised visits have used the railway/cycle-path approach from Waterloo Road, but arrangements for each visit should be followed.
♦ The older approach from the Radstock–Frome road via Manor Road and Church Road included a gate and a bridge described as damaged at that time. Do not climb gates, cross a suspect bridge or assume that this historical route remains an approved entrance.
♦ Park only in the place specified for the authorised visit. Keep roads, gates and private accesses clear, and stay within the designated conservation area.
DOWNLOAD THE UKF BOOKLET TO FOSSIL HUNTING AT WRITHLINGTON
FOSSIL HUNTING
Writhlington is best approached as a supervised search for evidence of an ancient ecosystem. The most familiar fossils are plant impressions and dark carbon films on fine grey shale. Examine naturally separated surfaces first, turning pieces towards the light so that shallow relief and contrasting films become visible. Work only in the material and manner permitted by the organiser. Keep the two halves of a split together: a faint impression on one may be much clearer on its counterpart.
Lycopsid remains include the bark patterns of Lepidodendron and Sigillaria. Diamond-shaped leaf cushions arranged in spirals characterise many Lepidodendron impressions, while the more rounded or hexagonal scars of Sigillaria often form vertical rows. Narrow ribbon-like leaves may be described as Cyperites, and Stigmaria records branching rooting structures with rootlet scars. These organ names can refer to different parts of the same kinds of plants rather than separate unrelated trees.
Ribbed, jointed stems and pith casts of Calamites represent tree-sized relatives of horsetails. Their foliage can occur as whorls called Annularia or Asterophyllites. Smaller scrambling sphenopsids include Sphenophyllum, with wedge-shaped leaves. Look for the junctions between stem segments, the arrangement of leaf whorls and repeated leaf-scar patterns rather than relying on the overall colour of the shale.
Fern-like fronds include both true ferns and seed ferns. Published Writhlington material includes Lobatopteris camertonensis, Alethopteris serlii, Neuropteris flexuosa and Macroneuropteris scheuchzeri, the last appearing under Neuropteris in older work. Fine vein patterns, how the leaflets attach and the branching of the frond matter for identification. A small or poorly preserved leaflet usually supports a less precise name than a complete, well-preserved frond.
Animal remains are much rarer than plants and may resemble inconspicuous scraps. Roach-like insects dominate the collected terrestrial animal fauna; wings can be recognised by their network of veins, which differs from the venation and outline of a leaf. Head shields, segmented bodies and isolated limbs also occur. Published arachnids include provisionally assigned Bornatarbus mayasii and the trigonotarbid Pleophrynus verrucosa. A trigonotarbid is not a true spider, although true spider remains have been recorded separately. Do not force an identification from a small, distorted impression.
The extraordinary records include plates and limbs of Arthropleura, horseshoe crabs such as Euproops danae, the eurypterid Adelophthalmus imhofi, clam shrimp, a possible shark egg capsule and trace fossils. The damselfly-like insect Bechlya ericrobinsoni was described from a rare wing. These discoveries show the site’s scientific value; they are not everyday collecting expectations. Photograph unusual material, keep its counterpart and show it to the leader before cleaning or removing surrounding shale.
A smaller component of the rock store comes from a higher coal-roof horizon rich in non-marine bivalves, including Anthraconauta tenuis. These freshwater or non-marine shells should not be called brachiopods. Most terrestrial animal material is associated instead with the dominant lower, lycopsid-rich shale. The spoil is mixed, so record the rock type and any source information provided at the visit rather than assigning a loose slab to a bed from its position on the heap.
Use a hand lens to inspect tracks, trails and possible feeding damage as well as body fossils. A trace records behaviour and can be valuable even when the animal itself is absent. The documented management scheme requires finds to be recorded and important specimens made available for study, and prohibits commercial collecting. Take only what is allowed, avoid unnecessary breakage and leave enough representative material for future research and visitors.
Significant discoveries, research and conservation milestones at Writhlington
1829–1973 – Colliery supplies the future rock store
Lower Writhlington worked Radstock coals from 1829 to 1894, both Radstock and Farrington coals from 1894 to about 1925, then Farrington coals until closure in 1973.
1983–1988 – Major plant collection assembled
Volunteers coordinated by Peter Austen and the West London Wildlife Group assembled a major Writhlington collection, much of it subsequently held by the National Museum of Wales as collection 90.8G.
1984–1986 – Rescue collecting during reclamation
Coal reclamation exposed fresh shale, and systematic rescue collecting revealed an exceptional terrestrial arthropod fauna.
1987 – Geological rock store conserved
About 3,000 tons of spoil were retained as a finite protected resource for research and controlled collecting.
1989 – Comprehensive reserve account published
E. A. Jarzembowski published a detailed account of Writhlington Geological Nature Reserve and its scientific importance.
1991 – Rock types, traces and arachnids studied
Todd examined lithological and floral associations, Pollard and Hardy documented trace fossils, and Beall investigated the phalangiotarbid arachnids.
1992 – SSSI designation
Writhlington was notified as a 0.5 ha SSSI for its Coal Measures flora and exceptional terrestrial arthropods.
1994 – Flora documented in detail
Thomas and Cleal described the diverse plant assemblage and its position in the Dicksonites plueckenetii Subzone.
1994 – Fauna and communities investigated
Specialist studies examined plant communities, non-marine bivalves, horseshoe crabs, arachnids and a possible early amniote footprint, keeping comparison material from other localities distinct.
1998 – Arthropleura material described
Proctor published plates and limbs, including material assigned to Arthropleura armata, from animals estimated at 46–66 cm long.
1999 – Eurypterid record published
Proctor documented Adelophthalmus imhofi, adding to the aquatic component of the fossil community.
2002 – Bechlya ericrobinsoni named
Jarzembowski and Nel described the extinct damselfly-like insect Bechlya ericrobinsoni from a unique wing in the No. 10 roof-shale material.
2003 – Decay experiments illuminate preservation
Duncan, Titchener and Briggs used cockroach decay and disarticulation experiments to interpret the fossil record at Writhlington.
2004 – Phalangiotarbids reassessed
Pollitt, Braddy and Dunlop explained some apparent arachnid diversity through tectonic distortion and provisionally assigned the material to Bornatarbus mayasii.
2004 – Illustrated animal atlas published
Jarzembowski brought the animal evidence together, relating it to principal plant assemblages and sedimentary settings.
2007 – Roach-like insects used in correlation
Jarzembowski and Schneider examined Writhlington material in a regional study extending Mylacris–Sooblatta insect zonation into southern Britain.
Late autumn 2017 – Rock store refreshed for conservation
The store was turned with Bristol Naturalists Society and Radstock Town Regeneration Fund support, landowner cooperation and Natural England involvement.
GEOLOGY
The main fossil-bearing material belongs to the Farrington Member of the Grovesend Formation, within the Warwickshire Group. It is late Carboniferous, or Pennsylvanian, in age, traditionally assigned to the Asturian or Westphalian D. Older literature uses Farrington Formation or Group, but these names should not be read as extra units above or below the modern member.
Fine mud and silt accumulated in a low-lying landscape of river channels, floodplains, wet forests and lakes. Peat formed coal seams, while floods and changing drainage buried plant debris and occasionally terrestrial animals. Some fossil-rich shale represents rapidly supplied sediment near lake margins or crevasse splays. Fine grain size, burial and limited decay helped preserve delicate impressions and carbon films, although later compaction and tectonic distortion altered some shapes.
The conserved store contains waste brought to the surface by mining, not beds exposed in their original order. Most of the studied shale came from above No. 10, or New Coal. A smaller shelly component came from above the higher Rock or Badger Coal, called No. 1 in the animal atlas. These source horizons differ in fossils and environment, but are mixed together on the heap. The height of a spoil mound is therefore neither a stratigraphic thickness nor a measure of geological time.
Plant associations offer another way to understand the rocks. Low-diversity lycopsid-rich material is associated with wet back-basin forest and relatively little transport; sphenopsid-rich material and more diverse fern-and-seed-fern associations reflect other settings and degrees of transport. The numbered ecological assemblages used by researchers are not numbered beds in a vertical section.
The original mine also worked other coal horizons during its history. Historical shaft sections, seam leaves and regional correlation charts explain this mining context, but cannot identify the source of every present loose block. The detailed section below keeps these records separate from the two main fossil-shale sources and avoids presenting regional seam thicknesses as a measured visitor log.
Detailed geology, fossil-shale sources and separate historical mine records at Writhlington
The preserved Lower Writhlington rock store is a mixture of mined material near ST 703 553. Its fossils and rock types can be related to underground sources, but the present heap has no continuous upright measured succession. Ecological assemblages, sedimentary facies and historical mine sections are therefore described as different kinds of evidence.
WARWICKSHIRE GROUP
Grovesend Formation
Farrington Member
The modern member consists principally of grey mudstone, with subordinate lithic sandstone, coal seams and substantial seatearths. The Writhlington fossil material is Asturian, traditionally Westphalian D, within the late Carboniferous Pennsylvanian. Historical Farrington Formation or Group terminology refers to the same broad coal-bearing interval under older classifications. The regional maximum member thickness of 425 m applies to the Radstock basin and is not the thickness of the retained spoil.
No. 10 or New Coal roof shale. This is the dominant source of the studied fossil-bearing material. Grey silty mudstone and clayey siltstone preserve plant impressions and most of the terrestrial animal remains. No thickness is assigned to the mixture remaining in the store, and its position on the present mound does not identify an original bed.
Rock or Badger Coal roof, called No. 1 in the atlas. A smaller component comes from a stratigraphically higher shelly mudstone, associated with lacustrine conditions and a different non-marine bivalve fauna. Records include Anthraconauta tenuis and Anthraconaia pringlei. Eagar’s study places this source about 200 m above the lower horizon; that is a stratigraphic source relationship, not a thickness measurable through the heap.
Dominant animal-bearing fine-grained facies. Medium-dark grey laminated silty mudstone, with subordinate clayey siltstone and abundant lycopsid debris, accounts for more than 90% of the animal finds in the GCR summary of Todd’s work. Flooding, crevasse-splay supply and prodelta or lake-margin deposition have been used to explain the rapid burial of this material.
Other fine-grained material. Todd’s original abstract distinguishes three sublithologies and four floral groups. More regularly laminated mud-and-silt material and paler, less laminated shelly material have been differentiated in accounts of the spoil, but they should not be arranged as successive measured beds. The separate, minor lacustrine source is supported by its bivalves; detailed facies assignments are less secure than the two principal coal-roof provenances.
Plant assemblage 4. Lycopsid-rich material includes a relatively low-diversity Lepidodendron aculeatum association interpreted as wet back-basin forest with limited transport. Most terrestrial animal remains are associated with this assemblage. The number identifies an ecological assemblage, not Bed 4.
Plant assemblage 5. Sphenopsid-dominated material represents a different plant association, with animal remains less frequent than in assemblage 4. It has no measured position above or below the other assemblages in the present spoil.
Plant assemblage 6. Fern-and-seed-fern-rich material represents a more diverse association interpreted as drier levee forest, with greater transport before burial. Animal remains are again less frequent. Environmental interpretation does not turn this association into a separate formation or member.
Aquatic and terrestrial animal records. The illustrated fauna includes Euproops danae, Adelophthalmus imhofi, the clam shrimp Anomalonema reumauxi and the egg capsule Palaeoxyris cf. carbonaria. The latter is compared with a shark egg capsule, rather than representing a shark skeleton. Terrestrial records include roach-like insects, arachnids, true spider remains and millipede-like arthropods. The individual palaeodictyopteran figured from Kilmersdon in the atlas is a different-locality specimen; other Writhlington palaeodictyopteran records are independently documented.
Arthropods and distortion. Writhlington Arthropleura plates and limb material include specimens attributed to A. armata; the studied animals were estimated at 46–66 cm long. Larger maximum sizes known from other coalfields do not measure these individuals. Reassessment of the phalangiotarbid arachnids provisionally referred distorted material to Bornatarbus mayasii, with tectonic flattening explaining some apparent differences. Pleophrynus verrucosa is a trigonotarbid, distinct from true spiders.
Rare wing and trace records. The unique wing of Bechlya ericrobinsoni, holotype Booth Museum BMB 018498–9 [W477a,b], came from the No. 10 roof-shale assemblage 4. It represents an extinct damselfly-like protozygopteran. Trace records include Kouphichnium aff. variabilis, Diplichnites cf. cuithensis, Cochlichnus, ostracod trails and plant-feeding damage. A possible early amniote footprint is compared with Pseudobradypus; it is not a vertebrate body fossil. The animal atlas reports no body fossils from the coal seams themselves, and animal bodies are rare in sandstone.
Historical underground records: separate from the visitor’s rock store. The following measurements describe mined seams, source relationships or wider correlation sections. They explain the colliery geology without assigning their complete fauna or thickness to the present spoil.
Tentative Rudge Vein. A hack roadway at ST 7051 5531 recorded 13 in of coal, with red measures 60 ft below. The Rudge identification is tentative, and neither figure describes a bed currently exposed in the rock store.
Probable No. 9 seam in Scott’s Branch. About 330 ft below No. 5, a historical section records a sandstone roof, 4 in of binching, 18 in of coal and a pan floor. The correlation with No. 9 remains probable rather than certain.
Coalescence of Nos. 8 and 9. The two seams in the generalised lower Farrington succession merge at Writhlington into No. 10 or New Coal. No unambiguous combined local thickness is supplied, so the separate regional seam values should not simply be summed to manufacture one.
Typical Rock or Badger Vein section. A regional section relevant to the extensively worked Lower Writhlington seam records a clift roof, 16 in of badger, a thin unmeasured black-mudstone parting, 18 in of coal and a pan floor. Roof fossils include Anthraconauta tenuis, A. phillipsii and Anthraconaia pringlei. This is the Survey’s typical seam description, not a measured section through the preserved heap.
Bull Vein in older Radstock workings. The local historical top-to-bottom record is 5 in of coal, an unmeasured parting, 6 in of coal, a 3 in band and 13 in of coal. It belongs to the Radstock Member workings, which are not the established source of the principal modern rock-store fossil assemblage.
Generalised Farrington comparison, youngest to oldest. Thomas and Cleal reproduced a regional table after Moore (1937). The values below belong to that comparison, not a measured Lower Writhlington tip section. Separate sediment intervals are kept distinct from coal thicknesses.
Rock Coal. The upper coal is listed as 0.89 m thick.
Sediment between Rock Coal and No. 5. The table gives 97.54 m of intervening sediment.
No. 5 Coal. The coal is listed as 0.56 m thick.
Sediment between Nos. 5 and 6. The intervening thickness is 10.67 m.
No. 6 Coal. The coal thickness is 0.56 m.
Sediment between Nos. 6 and 7. The intervening sediment is 34.14 m thick in the regional table.
No. 7 Coal. The table records 1.52 m of coal.
Sediment between Nos. 7 and 8. The intervening sediment thickness is 76.20 m.
No. 8 Coal. The coal is listed as 0.76 m thick.
Sediment between Nos. 8 and 9. The table records 13.72 m of sediment.
No. 9 Coal. The lowest listed coal is 0.56 m thick.
Regional table totals. The printed totals are 4.85 m of coal and 232.26 m of sediment, with a combined 237.1 m. The individually printed sediment values sum to 232.27 m, a small rounding discrepancy that does not change the table’s regional purpose. None of these totals is the thickness of the conserved material.
Regional correlation graphic. The historical diagram places Radstock above Barren Red, Farrington, Mangotsfield, Downend, New Rock, Vobster and Carboniferous Limestone intervals. Its enlarged Farrington portion shows Rock, Nos. 5–9, their relation to No. 10, and Rudge. These are historical classification and correlation labels; the drawing does not establish that all those units occur in the fossil store.
Lower Writhlington shaft structure. The Survey’s shaft section marks the Radstock Great, Middle and Slyving veins and Bull Vein, red measures, Rock, Nos. 5 and 6 and a probable No. 9, with deformation associated with the Radstock Slide. This faulted underground geometry cannot be read as an upright section visible on the visitor’s route, and no new thickness is measured from the drawing.
References.
Thomas and Cleal (1994), Writhlington plant fossils, including the regional comparison table.
Jarzembowski (2004), Writhlington animal atlas.
Geological Conservation Review: Writhlington.
Kellaway and Welch (1993), Bristol district Geological Survey memoir.
Waters and colleagues (2009), modern Carboniferous framework.
Todd (1991), rock types and plant associations.
SAFETY
Follow the organiser’s route and collecting instructions. Do not climb locked gates or fences, use a visibly unsafe bridge, enter mine workings or investigate shafts and disturbed ground. The older description of damaged fencing is a historical warning, not a verified report of today’s approved route.
Spoil can be steep, loose, overgrown and slippery. Keep away from unstable edges and trees, do not undermine slopes or roots, and leave paths clear. Children need close supervision and should attend only where the organiser considers the visit suitable.
If controlled splitting is permitted, wear eye protection and keep a safe distance from others. Do not swing tools near the public route or dig into its surface. Carry a charged phone and suitable footwear, and use the meeting and emergency arrangements for the visit.
EQUIPMENT
Bring a hand lens, camera, notebook, small scale, sturdy footwear, soft wrapping and rigid boxes. Support thin shale and keep counterpart halves labelled together.
Ask the organiser which tools are allowed before bringing a hammer or chisel. Spades and picks are not automatically permitted, and the preserved rock store should never be excavated simply because surface material has already been searched.
CLEANING AND TREATING
Fine shale impressions and carbon films can be destroyed by washing, scraping or adhesive applied too early. Photograph finds before treatment, support them flat and remove only loose dirt with a very soft brush if the surface is stable.
Keep part and counterpart together and retain any matrix that may preserve a wing tip, limb or trace. Do not varnish, coat or aggressively prepare a possible insect, arachnid or footprint. Show significant material to the organiser or a specialist so that identification, recording and conservation can be planned together.
IDENTIFY YOUR FINDS
Need help identifying a fossil? Share clear photos, where you found it and its size with the community.
FURTHER READING
Deposits: Writhlington revisited, part 1
Deposits: Writhlington revisited, part 2
Deposits: Writhlington revisited, part 3
Geological Conservation Review: Writhlington arthropods
Thomas and Cleal: plant fossils from Writhlington
Jarzembowski: illustrated atlas of Writhlington animals
Natural England: managing fossil collecting at Writhlington
Nature in Avon: conserving and promoting Lower Writhlington Tip
BGS Lexicon: Farrington Member
Natural England: Writhlington SSSI citation
ACCESS RIGHTS
Writhlington is a protected, finite geological rock store and SSSI. Natural England’s published management case study describes gated, permission-only access, supervised collecting, recording of finds, important material being available for study and a prohibition on commercial collecting.
Confirm the present permission and joining arrangements with the organiser or site manager before travelling. Organised visits have continued, but that does not establish unrestricted walk-in access or make an older named keyholder the current contact. Nearby public paths and cycleways do not confer entry or fossil-removal rights within the store.
It is important to follow our ‘Code of Conduct’ when collecting fossils or visiting any site. Please also read our ‘Terms and Conditions‘
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