The flooded brickpits at Yaxley, beside Hampton Vale, preserve a glimpse of the Middle Jurassic sea beneath modern Peterborough. Weathering of the fossil-rich Oxford Clay has yielded oysters, belemnites, ammonites and occasional marine-reptile remains along the lake embankment. The exposed shore changes with water level and vegetation, and access to lakeside paths does not automatically permit collecting on the banks. Check current signs and obtain permission before leaving the paths or removing material.
FIND FREQUENCY: ♦♦♦♦♦ Historically very productive where Oxford Clay and loose shoreline material are exposed. Water level, vegetation and permitted access determine what can be searched; finds cannot be guaranteed.
CHILDREN: ♦♦ The fossil-bearing bank is unsuitable for children because it borders deep water and can be slippery or unstable.
ACCESS: ♦♦♦ Approach through Hampton Vale and use the established lakeside paths. Bank access and collecting require separate permission; obey any fencing and local restrictions.
TYPE: Former clay pit and lake embankment. Search only permitted, loose weathered material on firm dry ground, without damaging the banks or wildlife habitats.
DIRECTIONS
♦ From the A1139 Peterborough bypass, take the A1260 towards Yaxley and the Hamptons. Follow signs for Hampton Vale, beyond Hampton Hargate; these are the corrected names of the estates in the original directions.
♦ The original approach was from the Hampton Vale estate to the lakeside path, then around the lake towards its south-eastern bank. Use the established paths and the map reference below to identify the locality; do not follow informal tracks through fenced land or reedbeds.
♦ Park only where current signs and road markings allow, without obstructing residents, access roads or pavements. The old estate-entrance parking advice is not a reserved or confirmed visitor parking place.
♦ Guide reference: 52.525517, -0.27292550. Grid reference: TL 17267 93362. These locate the historic collecting area, not a parking bay or an assurance of bank access.
♦ Nearest postcode in the original guide: PE7 3GB. Use it only for the general approach, with the grid reference for the lake; it is not a verified car-park postcode.
FOSSIL HUNTING
The most useful material is the weathered Oxford Clay and the small concentration of loose fossils and tougher fragments left where lake water has washed away fine mud. The original guide identifies the south-eastern embankment and the foot of the slopes as the productive area. Search only a dry, firm stretch that you are permitted to enter. A lowered water level may uncover more material, but a newly exposed muddy margin is not necessarily safe to walk on.
Oysters are an accessible starting point. The guide records Gryphaea dilobotes, with a thick curved lower valve and a much flatter opposing valve. Look for the shell’s growth lines and curved profile rather than expecting a complete paired shell. Weathered valves may be much more robust than the thin, flattened shells in the clay. Bivalve fragments can still show hinge or ornament details, so keep the collecting point with each specimen rather than giving every curved oyster an automatic species name.
Belemnite guards are another characteristic find. Their solid, elongated form distinguishes them from the coiled shell of an ammonite; broken ends may reveal a radiating calcite structure, and the broad end can retain part of the socket for the chambered shell. The legacy account names Hibolithes hastatus. Incomplete guards should be labelled as belemnites unless the diagnostic features are preserved, rather than treating that historical identification as a name for every specimen.
Ammonites include the ribbed and ornamented genus Kosmoceras. Many shells in the Peterborough Member have been flattened during burial, while small pyritised examples can retain a more three-dimensional shape. A 2012 Palaeontological Association field-trip report specifically records the search for tiny pyritised ammonites in the Yaxley embankment. Examine small loose fragments with a hand lens for coiling, ribs or chamber walls; a metallic-looking lump alone is not enough to identify an ammonite.
The original site account also records worm tubes and crinoid remains. These are usually less conspicuous than the larger shells: look for small calcareous tubes or disc-like stem pieces among the weathered debris, while recognising that worn fragments may not permit a close identification. Do not wash excavated clay through the lake or remove bulk samples. Permission to walk by the lake does not include permission to dig or to take sediment for sieving.
Marine-reptile material is documented in the guide’s photographs, including a pliosaur tooth, an ichthyosaur vertebra and a rib fragment. Such finds deserve a careful record rather than an expectation of a complete skeleton. Bone may show a dense outer surface and a porous or fibrous interior where broken; small dark pieces can also be mineral concretions. The legacy text mentions shark teeth and crocodile remains, but its misspelled crocodile name is not a secure identification. Record uncertain pieces at a broad level and seek specialist advice.
Photograph any substantial or associated bones in place, note their exact position and leave them undisturbed for the landowner and an appropriate museum or specialist to assess. Loose shells and small fossils can lose their relationship to the source clay through erosion, so keep a label distinguishing a loose shoreline find from material seen in undisturbed sediment. Wrap fragile specimens separately and retain any supporting matrix.
Image 1: The ammonite, kosmosceras is common here.
Image 2: Pliosaur tooth from Yaxley.
Image 3: Ichthyosaur vertebra
Image 4: Section of rib from a marine reptile
A chronological record of geological work at the former Yaxley clay pits and later study of the flooded collecting locality.
1968 – Historic clay-pit sections documented
Yaxley sections were included in the geological account of the Kellaways Beds and Oxford Clay. These older quarry exposures remain reference sections for the Kellaways Clay and Kellaways Sand members beneath the Oxford Clay; they are distinct from the lake bank described in this guide.
1986 – Quarry-floor fossil horizons recorded
Research on the working Yaxley brickpit documented Bed 10 concretions and the removal of the overlying shell bed during clay extraction. It also recorded the junction with the Middle Oxford Clay. These observations preserve geological information from quarry faces that cannot simply be reconstructed from today’s shore.
2012 – The flooded locality used for palaeontological field study
A university palaeontology field excursion visited Yaxley on 25 May. Its report describes searching the embankment for small pyritised ammonites, documenting continued collecting after the main pit had flooded.
2023 – Yaxley fossils sampled for Jurassic climate research
Belemnites and Gryphaea dilobotes from a former Yaxley clay pit contributed to a study of Jurassic environmental change. The sampled rocks were assigned to the Jason Zone of the Peterborough Member. The published locality account does not establish a numbered bed or precise sampling point on the modern bank.
GEOLOGY
Yaxley’s lakes are an industrial landscape cut into Jurassic marine mudstone. Extraction for brickmaking removed large volumes of Oxford Clay, leaving pits that later flooded and banks that weather into clay and scattered shell debris. The rocks are far older than the lakes. Their correct modern name here is the Peterborough Member of the Oxford Clay Formation, within the Ancholme Group. “Lower Oxford Clay” is the familiar older name for this member; it is not a separate Peterborough Formation.
The Peterborough Member is Callovian, within the Middle Jurassic. Its characteristic dark brownish-grey, fissile mudstone contains abundant organic matter, together with ammonites, bivalves and other marine fossils. These fine sediments accumulated on a marine shelf. Variations in oxygen at the seabed, sediment supply and biological activity helped produce contrasts between finely layered, organic-rich clay and less fissile, paler mudstone. The organic content also helped make the clay valuable to brickmakers, because it contributed fuel during firing.
The contrast between robust loose fossils and delicate specimens still in the clay reflects what happened during burial and after exposure. Many original aragonitic shells were crushed or dissolved, leaving flattened impressions or mineralised remains, whereas thick calcitic oysters and solid belemnite guards can survive weathering more readily. Pyrite formed in some fossils during early burial. It may preserve fine detail, but becomes vulnerable to oxidation after collection, which is why careful dry storage matters.
At the lake margin, rain and shallow wave action remove fine clay and can concentrate the more resistant fragments in a thin shoreline lag. This is a modern process, not a separate Jurassic shell bed. It also means a loose fossil does not necessarily mark the horizon directly beneath it. Former extraction and landscaping can further complicate the relationship between a present bank and the original succession.
The historic Yaxley brickpit is an important reference locality, but a measured section from that pit must not be treated as a measured log of the present collecting point. Published regional logs and the modern study of former-pit specimens provide valuable context for the member; they do not establish every bed at this particular lake bank. The detailed section below separates the directly supported modern exposure from historic Yaxley observations and wider Peterborough correlations.
The Oxford Clay at Hampton Vale, with the historical Yaxley quarry horizons distinguished from the present lake bank.
This guide concerns the lake bank near TL17267 93362 at Hampton Vale. Older geological papers describe Yaxley Brick Pit at TL178932, farther east. Those quarry records help explain the local rocks, but their working faces and pit-floor beds are not a measured section of the bank visited today.
ANCHOLME GROUP
The Oxford Clay belongs to the Ancholme Group, the predominantly marine mudstone succession recognised across this part of eastern England.
Oxford Clay Formation
The fossil-bearing clay is assigned to the lower part of the Oxford Clay Formation. Although the formation as a whole extends from the Callovian into the Oxfordian, the Peterborough Member is Callovian, within the Middle Jurassic.
Peterborough Member
Formerly called the Lower Oxford Clay, this member consists principally of brownish-grey, organic-rich mudstone that splits into thin layers. Paler, more blocky mudstones alternate with these fissile beds. Its regional succession contains crushed ammonites and bivalves, shell concentrations and bands of calcareous concretions. The lowest beds can be silty and rich in Gryphaea. These are characteristics of the member; they should not be read as a bed-by-bed log of this shore.
The present lake-bank exposure
Independent field-trip accounts identify the flooded Yaxley collecting locality with the Peterborough Member and describe fossils released by erosion of its banks. A 2012 visit specifically recorded small pyritised ammonites in the embankment. The bank is unmeasured here: no reliable published log was found that fixes its present exposures to individual numbered beds or establishes an exposed thickness.
Jason Zone: a former-pit record
A 2023 study sampled belemnites and Gryphaea dilobotes from a former Yaxley clay pit and assigned that material to the Jason Zone of the Peterborough Member. This supports a zoned record from Yaxley, but does not establish the zone of every part of the modern lakeshore.
Bed 10: the historical quarry-floor horizon
The former Yaxley workings exposed Bed 10 near the pit floor, and their large concretions were recorded as coming from this horizon. In the regional bed scheme, Bed 10 is an organic-rich, fissile shale containing calcareous septarian concretions and abundant flattened ammonites. It belongs to the Jason Subzone and forms part of the informal “Gryphaea and Reptile Beds”. Its importance for articulated vertebrates is established across the Peterborough brickpits; neither that regional yield nor measurements from other pits establish what is exposed on this bank.
Bed 11: the historical overlying shell bed
Bed 11 is a shell-rich horizon containing Gryphaea and ammonite remains in a greenish clay matrix. It overlies Bed 10, with sediment from the shell bed entering burrows in the underlying shale. At the working Yaxley pit, quarrying removed this bed and left Bed 10 as the floor. That account describes an industrial exposure, not a recognised horizon on the present shore.
Historical upper and lower limits
The old Yaxley quarry also exposed the junction with the Middle Oxford Clay, now the Stewartby Member. Beneath the Oxford Clay, Yaxley clay-pit sections are cited as reference exposures for the Kellaways Clay and Kellaways Sand members of the Kellaways Formation. None of these contacts has been verified at the guide’s present lake-bank exposure. The full regional succession, including numbered beds logged at King’s Dyke and other brickpits, must therefore remain separate from this locality’s unmeasured shore.
References
British Geological Survey, Ancholme Group, Oxford Clay Formation, Peterborough Member, Kellaways Clay Member and Kellaways Sand Member, BGS Lexicon of Named Rock Units.
Martill, D. M. (1986). The stratigraphic distribution and preservation of fossil vertebrates in the Oxford Clay of England. Mercian Geologist, 10(3), 161–186, especially pp. 162–171.
Hudson, J. D. and Martill, D. M. (1994). The Peterborough Member (Callovian, Middle Jurassic) of the Oxford Clay Formation at Peterborough, UK. Journal of the Geological Society, 151, 113–124.
Progressive Palaeontology Cambridge 2012 programme, pp. 2 and 7; Ortega-Hernández, J. and Crumpton, N. (2012), meeting report, The Palaeontology Newsletter, 81, pp. 48–50.
Price, G. D. and colleagues (2023). A climate perturbation at the Middle–Late Jurassic transition? Evaluating the isotopic evidence from south-central England. Palaeogeography, Palaeoclimatology, Palaeoecology, 628, 111755, section 2.3.
SAFETY
The former clay pits contain deep water close to the bank. Do not enter the lake, wade for fossils, reach out over the edge or assume a pale shallow-looking margin is firm. Keep back from undercut or crumbling edges and avoid lone collecting. The collecting bank is unsuitable for children, even where nearby paths are used by families.
Wet Oxford Clay can be extremely slippery and sticky, and apparently dry surfaces can conceal soft ground. Heavy rain may expose fossils while making footing worse. If the shore is wet, steep, unstable or cut off by water, stay on the established path and leave the visit for another time. Wear footwear with good grip; do not descend a bank unless you can return safely.
Respect fencing, development works, anglers and wildlife. Do not enter reedbeds, disturb nesting birds or move habitat piles. Bring a charged phone and tell someone where you are going; the old photographs and route description cannot show every current hazard.
EQUIPMENT
Sturdy boots, a hand lens, a camera or phone and small rigid containers are more useful here than heavy tools. Carry tissue or other soft packing so that shells, teeth and small pyritised ammonites cannot knock together. Label each container with Yaxley (Hampton Vale), the date and the precise collecting point.
Surface observation and photography are the appropriate default. Do not bring a pick, hammer or digging tool into use on the banks without explicit landowner permission and a safe, authorised purpose. Take a map and drinking water; keep hands free when walking near uneven ground.
CLEANING AND TREATING
Begin with minimal preparation. Allow damp clay specimens to dry gradually at room temperature, keeping fragile shells supported, then try a soft dry brush. Do not soak an unknown fossil or force matrix away from a thin shell. Photograph the specimen and its label before any cleaning; important bones or associated material should be assessed before preparation.
Pyritised fossils need particular care. Avoid routine washing, and never seal a damp specimen into a container. Once fully dry, keep susceptible material in a well-sealed conservation-quality box with a suitably maintained desiccant, away from humid rooms and large changes in temperature. Inspect it periodically. Powdering, cracking or pale surface deposits call for isolation and advice from a geological conservator.
The old recommendation to varnish every ammonite is not retained. A surface coating is not a dependable cure for pyrite oxidation and can hide detail or complicate future work. Use consolidation only where genuinely needed, choosing a reversible conservation material with specialist guidance. Avoid household acids, bleach and aggressive cleaning, especially on fossils containing carbonate shell or pyrite.
IDENTIFY YOUR FINDS
Need help identifying a fossil? Share clear photos, where you found it and its size with the community.
FURTHER READING
Denizens of the Oxford Clay (Deposits Magazine; regional background, including Fletton)
Progressive Palaeontology 2012 field guide, including Yaxley
Palaeontological Association Newsletter 81: the 2012 Yaxley field trip
British Middle Jurassic Stratigraphy: Peterborough Brickpits (regional and historic sections)
Natural History Museum: fossil preservation and pyrite decay
ACCESS RIGHTS
The lake paths, the fossil-bearing banks and the neighbouring protected reserve must be treated separately. This guide is a record of the Yaxley (Hampton Vale) collecting locality, not permission to enter private land, dig or remove fossils. Use the established paths, follow current notices and obtain the landowner’s permission before leaving them to collect. Public access for walking does not itself confer collecting rights.
The protected-site document linked by the old guide is for Orton Pit SSSI, designated for its great crested newts and standing-water habitats. The guide’s map reference lies outside the mapped Orton Pit boundary, but that point check says nothing about ownership or permission along the wider shore. It is therefore misleading either to call this exact collecting point an unrestricted SSSI fossil site or to infer that collecting is authorised because it is outside the designation.
Nearby Hampton Nature Reserve, also called Orton Pit, is a private reserve managed by Froglife and is closed to ordinary public access. Do not cross into it as part of a fossil visit; attendance at a specifically organised event is a separate arrangement. That reserve closure should not be described as proof that every Hampton Vale lakeside path is closed.
Where collecting permission is given, follow its limits and favour loose material without damaging the bank, vegetation or habitats. Leave any uncertain access point alone. Consult Froglife’s current Hampton Nature Reserve information and the Natural England Orton Pit site record for the neighbouring reserve, rather than treating the old collecting account as current consent.
Historical document retained from the original guide; it describes neighbouring Orton Pit and does not grant access or collecting rights at the guide point: SSSI Information – Yaxley
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