Aldwick and Bognor Rocks expose early Eocene London Clay when beach conditions permit. Shells, plant remains and fish-bearing nodules and pyritic debris make this an important fossil coast, also known for rare insects. The wider scientific section extends towards Pagham, with different reefs exposed in different places.
FIND FREQUENCY: ♦♦♦♦ – Scour controls exposure; finds are variable and rare insects are not routine.
CHILDREN: ♦♦♦♦♦ – Supervise children and keep them clear of soft clay and mud flats.
ACCESS: ♦♦♦♦ – Approach from western Bognor/Aldwick; check parking and beach conditions.
TYPE: London Clay foreshore, naturally loose concretions and washed debris.
DIRECTIONS
♦ Head to western Bognor Regis and Aldwick, west of the pier. The beach huts remain a useful landmark for the guide’s usual collecting area.
♦ Arun Council lists West Park car park on Silverston Avenue, PO21 2RB. Check posted charges and terms before parking.
♦ The broad scientific reference coast runs from Bognor towards Pagham; named reefs are not all beside the Aldwick beach huts.
♦ Original guide reference: 50.77960°N, 0.69369°W – SZ 934987 to SZ 889970
FOSSIL HUNTING
Start with the exposed London Clay and loose fossil-bearing blocks around Aldwick and Bognor Rocks. The most useful search ground changes as sand and shingle move: look for newly uncovered clay patches, weathered concretion surfaces and small accumulations washed out beside them. A sand-covered visit can be disappointing even at this rich locality. Some resistant blocks remain visible when the softer sediment is buried, but a projecting rock may still be part of the reef; visibility is not a reason to dig it out.
Shells and worm tubes make a more realistic starting point than the famous insects. The published Bognor succession records Astarte subrugata in the lower shell beds and Arctica planata in the historically named Cyprina Bed. Large molluscs associated with the Bognor Rock Bed include the bivalve Glycymeris brevirostris alongside gastropods and the coiled worm tube Rotularia bognoriensis. The sandy clay below also yielded the large pen shell recorded historically as Pinna affinis. These are locality records from different horizons, not a promise that every loose block will contain the same assemblage.
Examine a shell before trying to free it. The historical Pinna affinis has a wedge-shaped shell with lengthwise ribs, quite different from a compact rounded bivalve. Its thin shell may survive only in patches on the cast. Rotularia bognoriensis makes a ridged tube wound into a flat spiral: follow the tube around the coil rather than assuming that every spiral is a snail. Growth lines, shell margins and moulds can reveal less complete specimens. Weathered fragments can be useful for learning these distinctions, whereas forcing a large shell out of hard matrix may destroy both its outline and its fragile remaining surface. Photograph fossils in fixed blocks and concentrate any collecting on already detached material.
For smaller finds, inspect natural patches of heavy pyritic debris, traditionally called “pyrite pools”. Fish teeth, bones and otoliths occur in these concentrates, and tiny teeth and otoliths have also been recovered from beach sand. An otolith is a fish ear stone; its compact shape and surface grooves can be more informative than its colour. A hand lens helps separate possible fossils from glittering mineral grains. Such washed-out remains are usually isolated pieces, so label them as loose finds rather than assigning them to a named fish-tooth bed on appearance alone.
The Aldwick beds also contain phosphatic nodules with fish remains, sometimes retaining parts of an associated skeleton, as well as crustacean, reptile and nautiloid material. Do not smash an interesting nodule to see whether there is more inside. Keep a suspicious exposed patch and its surrounding matrix intact for examination. Plant debris adds another search target: woody texture, small fruits and seeds can be easily overlooked among the mineralised fragments.
Bognor’s pyritised beetles, including the illustrated Pissodites argillosus, are exceptional scientific finds rather than an ordinary visitor’s expected haul. The specialist account of Bognor’s fossil beetles explains their importance. Keep any possible insect, articulated fish or unusual plant specimen unprepared, record its finding place and seek expert advice. A few well-labelled representative finds are more valuable than an unrecorded bag of shells; do not excavate the clay or dismantle the fixed reefs.
A chronological record of fossil discoveries and geological research at Bognor Regis.
1850 – Early molluscan account
Sowerby’s account in Dixon documented 57 Bognor mollusc species, an early foundation for later faunal revisions.
1929 – Coastal stratigraphy documented
Venables published an early detailed stratigraphic account of the Bognor London Clay.
1960 – Fossil beetles described
Britton described the remarkable Bognor fossil beetle assemblage, establishing the locality’s importance for Eocene insects.
1963 – Fauna and succession expanded
Venables expanded the known Bognor molluscan assemblage to 128 species and supplied a more comprehensive coastal succession.
1972 – Brittle star described
Rasmussen described the brittle star Ophiura bognoriensis from the Starfish Bed.
1981 – London Clay framework revised
King revised the London Clay succession and its informal divisions, including the Bognor sandy unit.
1992 – Molluscan revision
Tracey’s revision listed 141 mollusc species: 75 gastropods, 65 bivalves and one scaphopod.
GEOLOGY
The London Clay here is early Eocene, Ypresian in age. The scientific coastal composite extends from Bognor through Aldwick towards Pagham, and includes several formal members and historical informal divisions. Those units are not all exposed together at the usual Aldwick entrance.
The London Clay is not uniformly clay-rich. Fine marine mud alternates with sandier intervals, and glauconitic sand is locally cemented into the resistant calcareous sandstone of Bognor Rock. This is the Bognor Sand Member, the sandy culmination of a lower coarsening-upward cycle. Hard beds and concretions survive as reefs or loose blocks while softer sediment is removed or concealed, so the foreshore appearance depends both on the original lithology and on changing beach cover.
The Aldwick succession includes fish-tooth and beetle-bearing horizons, with septarian and phosphatic nodules in the surrounding clay. Fish, crustacean, reptile and nautiloid remains occur in this marine sequence, while pyritised plants and insects record terrestrial material carried into it. Farther towards Pagham, the fine glauconitic sandstone of the Barn Rock Member caps the older division-B succession. Named Cainocrinus and Pholadomya horizons occur in the higher division-C context, but the historical accounts disagree over aspects of their ordering. These differing logs cannot be combined into one precise coastal column.
Barn Rock Member is a formal member, while older lettered divisions belong to historical schemes. The Reading contact is concealed, and the upper London Clay–Bracklesham contact is not exposed.
Published GCR accounts differ over some member assignments, bed ordering and represented thickness. The full historical 35-interval composite is retained separately in the detailed account without combining incompatible schemes into a falsely precise measured stack.
Detailed geology and stratigraphy of Bognor Regis.
The broad scientific section runs from Bognor westwards through Aldwick towards Pagham (SZ 934987–889970). The guide’s usual collecting focus is Aldwick/Bognor Rocks. Named higher reefs towards Pagham are contextual, not all present together beside the Aldwick beach huts.
THAMES GROUP
London Clay Formation
Early Eocene, Ypresian. Gently west-south-west dipping marine silty mud and sand is exposed intermittently by beach scour. GCR estimates almost 90 m across the broad composite: approximately 43 m of division A, 33 m of B and at least 12 m of C; measurement is difficult. These informal divisions are not members.
Astarte Bed. Low in the exposed succession west of the pier; calcareous molluscs include Astarte subrugata.
Septarian marker band. A concretionary layer separates the Astarte and Starfish beds in the published account.
Starfish Bed. Contains brittle-star remains identified as Ophiura bognoriensis, together with the molluscan assemblage.
Cyprina Bed. Characterized by fragments of Arctica planata, historically called Cyprina.
Sandy Clay. The upward-sandier interval contains the historically identified bivalves Ostrea tabulata, Pinna affinis and Panopea intermedia. These names follow the historical identifications in the cited account.
Walton Member
BGS recognizes this basal London Clay member. GCR identifies the lowest exposed division-A portion at Bognor as A2/Walton; division A1 is apparently absent. The member is not synonymous with the entire local A division.
Bognor Sand Member
The formal modern name replaces “Bognor Member” and “Bognor Rock Bed” in older descriptions. Bognor foreshore is the type section. Glauconitic sand is locally cemented into calcareous sandstone masses; the BGS Lexicon gives a regional thickness of 5–10 m.
Bognor Rock Bed. The sandy culmination of the first coarsening-upward cycle contains large molluscs including Glycymeris brevirostris and Athleta denudatus, with tubes of Rotularia bognoriensis.
London Clay Formation
These younger intervals are resumed here to avoid placing them inside Bognor Sand Member. The following named horizons are subordinate beds, not extra formations.
Basal division-B pebble horizon. Rolled dark flints occur in sandy mud, marking the next sedimentary cycle.
Lower Fish Tooth Bed. A named lower-B fossil horizon; the published planktonic-foraminiferal datum lies shortly above it.
Planktonic datum. A biostratigraphic marker, not an additional lithostratigraphic member or a measurable bed thickness.
Beetle Bed. Low division B near and west of Bognor Rocks is notable for pyritized insects and terrestrial plant material. Much material was recovered from loose foreshore concentrations, not directly in situ. Exposure is intermittent.
Upper Aldwick Beds. The published log recognizes this interval above the Beetle Bed. Division-B clay contains septaria and phosphatic nodules, with fish, crustacean, reptile and nautiloid remains; detailed individual-bed thicknesses are not supplied by the GCR summary.
Concentrate Bed. Named in Figure 6.21 above the Upper Aldwick Beds. The summary supplies its relative position but no defensible separate lithological description or thickness.
Craigweil Bed. A further named marker in the composite below Barn Rock. The summary provides its position but no separate lithological description.
Barn Rock Member
BGS recognizes the very fine glauconitic sandstone at the top of division B as a formal member, with a regional thickness of 2–3 m and an erosional contact beneath division C.
Barn Rock Bed. Partly cemented fine glauconitic sandstone caps division B farther west, near Pagham. Fossils may be sparse and poorly preserved; Cultellus affinis is reported.
London Clay Formation
Overlying informal division C, above the Barn Rock Member.
Cainocrinus Bed. One of two fossiliferous horizons occasionally exposed in division C, 9–12 m above its base. Keep it separate from the lower B2 occurrence of drifted Cainocrinus tintinnabulum debris against fossil logs.
Pholadomya Bed. The other named fossiliferous division-C horizon, shown above the Cainocrinus Bed. Its own thickness is not given; 9–12 m is position above the division base, not bed thickness.
The London Clay at Bognor is early Eocene, Ypresian.
Fish teeth, otoliths and pyritized plant and insect remains occur in loose foreshore concentrates. The rare fossil beetle Pissodites argillosus is illustrated in David Bone’s account.
The Reading contact is concealed by alluvium, and the upper London Clay/Bracklesham contact is unexposed. Older augering recorded a small basal “Oldhaven” interval eastwards; this is an augered record rather than a visible Aldwick layer.
Historical measured composite: separate source scheme
The following complete historical composite is reproduced as paraphrased factual bed data from GCR 16 pp 505–506, after Venables and King. It spans Bognor–Aldwick–Pagham and is not a single modern exposed section. GCR 15 and GCR 16 disagree over some member/division assignments, the Cainocrinus/Pholadomya ordering and represented upper thickness. The two accounts are therefore presented as separate schemes. In particular, GCR 16 groups the Lower Clay under A2/Walton whereas GCR 15 discusses the Astarte–Cyprina beds in A3.
Historical division C / Upper Clay — top down. These divisions and “groups” belong to the historical classification, rather than the modern formal hierarchy.
Undescribed upper deposits (6.1 m). No more detailed lithology supplied.
Plant-bearing grey clay (0.9 m). Plant remains reported.
Undescribed deposits (3.5 m). No lithological description is supplied for this interval.
Pagham Rock (0.6 m). A named upper marker towards Pagham, not an Aldwick cliff bed.
Sparsely fossiliferous clay (18.6 m). Only partly described in the source.
Cainocrinus Bed (1.2 m). Historical log places this above Pholadomya; GCR 15 Figure 6.21 reverses that plotted ordering. Unresolved correlation conflict.
Pholadomya Bed (0.6 m). Historical log places this below Cainocrinus; GCR 15 plots the opposite order.
Basal division-C clay (3.7 m). Partly described clay with a basal glauconitic pebble horizon.
Historical division B — top down. These divisions and “groups” belong to the historical classification, rather than the modern formal hierarchy.
Barn Rock Bed (2.4 m). The principal sandstone interval; modern BGS recognizes Barn Rock Member.
Base of Barn Rock (1.2 m). A separately listed interval in the historical composite, not automatically added to modern member thickness.
Undescribed deposits (1.2 m). No lithological details supplied.
Craigwell Bed (1.5 m). The same name is spelled Craigweil in GCR 15.
Undescribed deposits (3 m). Unspecified interval above Upper Aldwick.
Upper Aldwick plant-bearing clay (2.4 m). Pyritized plant remains.
Paired septarian bands (0.6 m). Two concretionary horizons.
Plant-bearing clay (1.2 m). Pyritized plants.
Septarian interval with Arctica (0.3 m). The source prints Artica; intended bivalve Arctica planata is supported independently by GCR 15.
Upper Fish-Tooth Bed (1.5 m). Named fossiliferous horizon.
Intervening unfossiliferous clay (3.7 m). Septarian band 1 m above its base.
Beetle Bed (1.2 m). Clay with a septarian band, in Lower Aldwick.
Lower Fish-Tooth Bed (0.6 m). Earthy clay with pellets and a basal dark-flint pebble bed.
Historical A3 / Bognor Rock Group — top down. These divisions and “groups” belong to the historical classification, rather than the modern formal hierarchy.
Bognor Rock Bed (6.7 m). Alternating loose grey sand and partially cemented fine glauconitic sandstone.
Sandy clay and soft sandstone (3 m). Underlying sandy transition; historical “group” boundaries are not necessarily the modern member boundaries.
Historical A2 / Lower Clay — top down. These divisions and “groups” belong to the historical classification, rather than the modern formal hierarchy.
Upper septarian band (0.6 m). White clay, iron-stained.
Cyprina Bed (5.5 m). Named shell horizon.
Starfish Bed (1.8 m). Named brittle-star-bearing horizon.
Clay (1.2 m). Intervening fine sediment.
Astarte Bed (2.4 m). Named molluscan horizon.
Friable clay (2.7 m). Unconsolidated fine sediment.
Clay with occasional pyritized plants (2.7 m). Terrestrial material in marine clay.
Sandy layer (0.3 m). Thin sandy interval.
Partly described clay (4.6 m). No further detail supplied.
Lower septarian band (0.3 m). White clay with iron staining.
Dark silty clay (0.6 m). Lowest described clay.
Alluvium-obscured interval (3 m). Cover/gap in exposure, not 3 m of a separately known London Clay bed.
References
Daley, B. and Balson, P. (1999). British Tertiary Stratigraphy. GCR 15, Bognor Regis, pp 201–205.
BGS Lexicon. Bognor Sand Member.
BGS Lexicon. Barn Rock Member.
Bone, D. (2017). Fossil beetles of Bognor Regis, West Sussex. Deposits.
SAFETY
Soft clay can trap feet, and the returning tide can isolate reefs. Plan a low-tide visit with time to return and avoid mud flats or uncertain ground.
Do not treat a cliff-free beach as hazard-free. Waves, slippery rock and concealed channels can make the shore difficult. Supervise children closely.
EQUIPMENT
Take a hand lens, small rigid boxes, soft wrapping, a camera and tide information. No hammer is needed for loose fossils on sand; do not excavate fixed reefs or in-situ beds.
CLEANING AND TREATING
Pack fragile shells separately and begin with gentle dry cleaning. Avoid routine soaking, acids, bleach or indiscriminate coatings; the stability of the shell and matrix determines what treatment is safe.
Pyritic material can deteriorate: keep it dry and seek specialist conservation advice if cracks, powder or other decay appear. Keep potentially important fish, insect and associated remains unprepared.
IDENTIFY YOUR FINDS
Need help identifying a fossil? Share clear photos, where you found it and its size with the community.
FURTHER READING
The fossil beetles of Bognor Regis, West Sussex
Daley and Balson, British Tertiary Stratigraphy: Bognor Regis, pp. 201–205 and figure 6.21
BGS Lexicon: Bognor Sand Member
BGS Lexicon: Walton Member
Dineley and Metcalf, Fossil Fishes of Great Britain: Bognor Regis, pp. 505–507
BGS Lexicon: Barn Rock Member
ACCESS RIGHTS
Respect protected geological exposures and current access signs. Limit collecting to genuinely loose material where permitted; seek site-manager permission for intrusive work, and do not extract fixed reef or in-situ clay.
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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