Portishead Fossil Hunting

1816–1817 – Magnesian conglomerate and an ancient erosion surface described
Gilby analysed magnesium-rich conglomerate from Portishead and traced its unconformable relationship with tilted older rocks along the coast. His observations were presented in 1816 and published the following year, providing an early scientific account of the contrasting rock successions.

1836 – An early geological map of Portishead
A detailed geological description and map of the parish were published, documenting the arrangement of its rocks long before the fish beds became widely known. The authorship remains uncertain.

1863 – The Woodhill Bay fish remains enter the published record
William Sanders reported Holoptychius from Portishead. The discovery was credited to the Reverend B. Blenkiron, who had found fish-bearing loose blocks on the foreshore. This is the earliest published description cited for the Woodhill Bay Fish Bed.

1864–1865 – Fish remains traced into the coastal succession
William Hellier Baily described fish scales and bones from the beach and recorded further remains in the exposed rocks, including a scale of Holoptychius nobilissimus from a conglomeratic bed. His observations were presented in 1864 and published in the following year’s meeting report.

1867 – The Martyn collection is assembled
A geological visit by the Bristol Naturalists’ Society produced the historic Martyn collection of Woodhill Bay fish remains. The specimens, subsequently held in Bristol’s museum collections, came from the horizon later numbered Bed 8.

1886 – Battery Point and Woodhill Bay mapped together
C. Lloyd Morgan published a detailed study of Portishead’s geology, describing crinoidal limestone at Battery Point, tightly folded beds beside Woodhill Bay and the fish-bearing Old Red Sandstone farther south. His maps and sections helped explain why these contrasting rocks occur so close together.

1892 – The known fish fauna expands
E. J. L. Gardiner described further fish remains from loose blocks near the southern end of Woodhill Bay, identified with the help of A. Smith Woodward. These included Glyptopomus scales, Bothriolepis armour and other teeth and scales, demonstrating that the assemblage was more varied than the early records suggested.

1923–1924 – Coastal sections and geological structure documented
S. H. Reynolds and E. Greenly recorded the local Old Red Sandstone and Carboniferous successions and examined their folding and faulting. Their work placed the Portishead exposures within the structure of the coastal ridge and documented the change from continental deposits to marine limestone.

1927–1928 – The fish-bearing succession measured in detail
F. S. Wallis divided the Woodhill Bay section into numbered beds and related historic collections to particular fossil-bearing horizons. His work established a framework for comparing specimens, sedimentary environments and the distribution of fish remains through the succession.

1948 – Eurypterid remains discovered
In August, F. S. Wallis and B. N. Temperley found a fragment of a eurypterid in fine sandstone associated with the Woodhill Bay fish-bearing succession. Subsequent collecting by Tom Fry produced much more material of this extinct aquatic arthropod.

1951 – Drepanopterus abonensis named
Scott Simpson described the Woodhill Bay eurypterid as the new species Drepanopterus abonensis. Portishead is its type locality, and the original specimens became the reference material against which later discoveries and reconstructions were compared.

1952 – The geological coast receives SSSI protection
The Portishead Pier to Black Nore site was first notified as a Site of Special Scientific Interest. Its protected geological features include the folded Carboniferous rocks at Portishead Point and the Devonian coastal succession containing the Woodhill Bay Fish Bed.

1955 – The Old Red Sandstone succession placed in a regional framework
G. A. Kellaway and F. B. A. Welch distinguished the older Black Nore Sandstone from the overlying Portishead Beds and compared the succession with those across the Severn. The coastal exposures became a key reference for interpreting the Bristol and Mendip Old Red Sandstone.

1964 – River deposits and ancient soils investigated
M. C. Pick published a detailed subdivision of the coastal Old Red Sandstone and interpreted its sedimentary structures, conglomerates and limestone-rich horizons. Recognition of the latter as calcretes, formed in ancient soils, helped establish the continental conditions under which the succession accumulated.

1972 – A temporary Woodhill exposure records the marine transition
M. Butler, B. P. J. Williams and R. Bradshaw described a road cutting created during building work at Woodhill. The section showed sandstone-dominated deposits giving way to limestone and siltstone, preserving evidence of the transition towards the Early Carboniferous sea.

1975 – The rare armoured fish Groenlandaspis recognised
Alexander Ritchie reported Groenlandaspis from the Woodhill Bay Fish Bed. This unusual placoderm record connected Portishead’s Late Devonian fauna with a much wider geographical distribution and became an important reason for the site’s scientific interest.

1977 – The position of the Devonian break reconsidered
B. P. J. Williams and P. L. Hancock reassessed the coastal succession, questioning whether the principal break lay beneath or above the Woodhill Bay Conglomerate. Their interpretation highlighted the need to distinguish local channel erosion and calcrete formation from a major gap in geological time.

1986 – Wind-blown sand proposed within the river succession
Chris Dodd interpreted part of the sandstone beneath the Woodhill Bay Fish Bed as ancient wind-blown dunes. This added a possible aeolian component to the predominantly river-laid succession; the interpretation has subsequently remained a subject for further investigation.

1986 – SSSI boundaries and protection renewed
The coast was re-notified under the Wildlife and Countryside Act, with its boundaries adjusted. The designation brought together the structural interest of Portishead Point and the stratigraphic and fossil importance of the Devonian exposures farther south.

1993 – Geological Survey synthesis refines the fish-bed interpretation
A comprehensive account of the Bristol district reassessed the Portishead succession and its regional relationships. The Woodhill Bay fish assemblage was used to support a middle Famennian age, strengthening its value for comparing otherwise sparsely fossiliferous continental deposits.

1999 – The fossil-fish site’s national significance reviewed
A national review of Britain’s fossil-fish localities documented the diverse Woodhill Bay assemblage and its unusual placoderms. It emphasised the importance of the site for understanding Late Devonian fish communities in southern Britain.

2004 – New eurypterid material collected
O. Erik Tetlie collected additional Drepanopterus abonensis specimens from the Woodhill Bay succession. These joined older collections and helped provide the anatomical evidence needed for a substantially improved reconstruction of the animal.

2005 – The Old Red Sandstone reference section reviewed
A national geological review assessed Portishead’s role as a reference locality for the older and younger Old Red Sandstone. It highlighted the Woodhill Bay Conglomerate, Fish Bed and unusual calcrete development, while identifying unresolved questions about the main unconformity.

2009 – The Portishead eurypterid reconstructed anew
James C. Lamsdell, Simon J. Braddy and O. Erik Tetlie redescribed Drepanopterus abonensis using historic and newly collected specimens. They revised its body proportions and identified specialised feeding structures, showing its relationship to later eurypterids that swept sediment for food.

2015 – Portishead becomes the name of a wider stratigraphic unit
A revised geological classification raised the Portishead Beds or Formation to Portishead Subgroup and retained Woodhill Bay as its partial type section. The revision also included the former Black Nore Sandstone within the Brownstones Formation, explaining the different names encountered in older and modern accounts.

The two fossil-hunting areas expose different parts of the succession. Battery Point, also called Portishead Point, and the northern end of Woodhill Bay expose Early Carboniferous marine rocks. The Devonian fish-bearing cliffs lie farther south-west, at the southern end of Woodhill Bay towards Kilkenny Bay. The name Woodhill Bay Fish Bed is a stratigraphic name and does not mean that every exposure around Woodhill Bay belongs to it.

DEVONIAN

DAUGLEDDAU GROUP: OLDER DEVONIAN ROCKS FARTHER SOUTH-WEST

COSHESTON SUBGROUP

Brownstones Formation

On the wider coastal section towards Black Nore Point, the older river-deposited sandstones were traditionally called the Black Nore Sandstone Formation. The modern BGS framework includes them in the Brownstones Formation, within the Cosheston Subgroup of the Daugleddau Group. They are assigned to the Early Devonian. These beds lie below the younger, fossil-fish-bearing Portishead succession and should not be confused with the Woodhill Bay Fish Bed.

BRECON BEACONS GROUP: UPPER OLD RED SANDSTONE

PORTISHEAD SUBGROUP

The red-bed succession traditionally described as the Portishead Beds or Portishead Formation is now the Portishead Subgroup. It comprises sandstone, siltstone, mudstone and local conglomerate. Around the fish-bearing section, changing grain size, channel-shaped sandstone bodies and finer sediment record rivers crossing a floodplain, with quieter-water deposition between channels. Some sandstone beneath the fish bed has also been interpreted as wind-deposited.

Woodhill Bay Conglomerate Member

The basal conglomerate contains rounded quartz and quartzite pebbles and cobbles in a sandy matrix. Farther south-west along the section it rests on an irregular erosion surface above the older sandstones. This junction is conventionally used to mark the major break between the Lower and Upper Old Red Sandstone successions. Carbonate concretions, traditionally called cornstones, occur around the contact. They are geological features rather than fossils.

Pipe-Like Calcrete Crossing The Contact

At ST 4579 7681, the GCR describes an unusual carbonate body about 2.5 m wide at its base and 2.5 m high, extending from the older sandstone into the Woodhill Bay Conglomerate. Part of its pipe-like shape appears to follow a joint in the conglomerate. It is not interpreted as soil carbonate formed contemporaneously on the top surface of the older sandstone. This cross-contact feature is an important distinction when considering the unconformity; its presence should not be used as a simple marker of an ancient soil at that boundary.

PORTISHEAD SUBGROUP — ABOVE THE BASAL CONGLOMERATE

Woodhill Bay Fish Bed

This named interval is about 10 m thick in the published local section. It contains reddish micaceous siltstone and sandy siltstone, with several harder sandstone beds. Fossil evidence places it in the Famennian, the later part of the Late Devonian. The recorded fish assemblage includes Holoptychius, Glyptopomus, Bothriolepis, Asterolepis and Groenlandaspis. Isolated scales, teeth and fragments of bone or armour characterise the material; complete fish are not a normal expectation.

Fish remains are rare, but regularly found. Carbonised plant fragments also occur. Rare eurypterid remains are documented in sandstone above the fish-bed interval; these records should not be taken to imply that eurypterids are routine finds.

Published Devonian Marker Intervals: Pick’s Historical Letters

The following local subdivisions are retained as historical descriptive units, not modern formal formations. They are listed from the basal conglomerate upwards. Their measurements describe the southern Woodhill–Kilkenny section and must not be applied to Battery Point. The Fish Bed and conglomerate are described in detail above; the intervening sandstones matter because those two units are not directly adjacent.

Unit I — Woodhill Bay Conglomerate

GCR31 describes approximately 4–4.5 m in the local section. Rounded quartz and quartzite pebbles and cobbles lie in a coarse sandy matrix above an irregular erosion surface. Different accounts give broader thickness ranges, so this figure is not a whole-subgroup total.

Unit H — Channelled And Pebbly Sandstones

About 13.5 m of sandstone and pebbly sandstone includes subordinate siltstone and thin conglomerate. Cross-bedding and channel-shaped erosion surfaces record river transport.

Unit G — Pale Green Sandstone

About 14 m of well-sorted sandstone separates the underlying channelled beds from the Fish Bed. Its upper cross-bedded part has been interpreted as wind-deposited; that is an interpretation of this unit, not every green sandstone on the coast.

Unit F — Woodhill Bay Fish Bed

The approximately 10 m interval includes micaceous siltstone and several harder sandstone beds. GCR 31 identifies the principal fish concentrations with horizons correlated to Wallis beds 7, 8 and 10. The unit thins and is eroded out northeastwards; fragmentary remains, rather than complete fish, are characteristic.

Unit E — Overlying Channel Sandstone

A locally 7.5–17 m sandstone package has trough cross-bedding, quartz pebbles and mudstone clasts near its base. Rare eurypterid material is documented in this overlying sandstone, rather than being a routine find from every Fish Bed exposure.

Unit D — Upper Sandy Siltstone And Sandstone

About 3 m of finer red and green sandy siltstone with harder sandstone completes a fining-upwards channel package above unit E. Local mudcracks, burrows and fish fragments are recorded.

Older J1–J3 Subdivisions Below The Unconformity

Pick subdivided the older Black Nore sandstones, now Brownstones Formation, into three descriptive packages. J2 is distinguished by abundant calcrete clasts. The full historical 292 m older-rock section extends towards Black Nore, and is not the thickness exposed at the Fish Bed collecting stop.

Individual Historical Fish Horizons

Wallis Bed 7 — Conglomeratic Sandstone

The historical GCR 16 bed list identifies a conglomeratic sandstone. Several fossil records are assigned jointly to beds 7–8, so an exclusive fauna for bed 7 is not inferred.

Wallis Bed 8 — Conglomeratic Sandstone

A separate conglomeratic sandstone carries documented fish material. Historical collections and combined bed 7–8 records are not used to invent a finer split in occurrence.

Wallis Bed 10 — Brecciated Siltstone

GCR 16 preserves Wallis’s lithological description as brecciated siltstone. GCR 31 discusses the main fish concentrations more generally in the thick sandstone horizons; those descriptions are not silently forced into exact equivalence.

Wallis Bed 18 — Cliff-Top Siltstone

Thin-bedded siltstone at the cliff top has yielded fish fragments in the historical account. This is a separate record above the main named Fish Bed interval.

Pick J1 And J3: Descriptive Limit

The checked GCR account distinguishes J2 by abundant calcrete clasts but does not provide separate lithological descriptions for J1 and J3. Their shared older sandstone context is retained without inventing bed-specific differences.

CARBONIFEROUS

AVON GROUP: EARLY CARBONIFEROUS

The Avon Group belongs to the Carboniferous Limestone Supergroup and includes rocks historically called the Lower Limestone Shale. Its alternation of mudstone and fossiliferous limestone records the establishment of marine conditions over the older continental landscape. The group is of Tournaisian age.

The upper part of this succession is exposed at the northern end of Woodhill Bay, immediately south of Battery Point. The limestone beds contain abundant crinoid debris, and the BGS records the coral Vaughania vetus in red crinoidal limestone here. Older accounts use the name Cleistopora and the historical Cleistopora Zone; Vaughania vetus is the appropriate name for the coral discussed in those accounts. The limestones and intervening finer beds are folded into small anticlines and synclines.

The basal Shirehampton Formation is the regional transition between the red beds and the more fully marine Avon Group. At Portishead this transitional interval is concealed beneath modern tidal-flat deposits, so the Devonian–Carboniferous passage cannot be followed continuously on the open foreshore.

PEMBROKE LIMESTONE GROUP: EARLY CARBONIFEROUS

BLACK ROCK LIMESTONE SUBGROUP

Black Rock Limestone and its dolomitised equivalents form Battery Point and the ridge extending eastwards. These are younger than the Avon Group limestones. The subgroup principally comprises dark, crinoid-rich marine limestone, locally altered to dolomite; alteration can obscure fossil detail. The older term Black Rock Dolomite describes these altered rocks, rather than a separate younger deposit. The headland contains strongly folded beds, including locally overturned strata.

TRIASSIC

MERCIA MUDSTONE GROUP: TRIASSIC MARGINAL DEPOSITS

Younger breccias and conglomerates, traditionally called Dolomitic Conglomerate, occur discontinuously along the coast. They rest unconformably on the much older Palaeozoic rocks. These deposits contain fragments eroded from the older bedrock and must be distinguished from both Devonian fish-bearing sandstone and Carboniferous marine limestone.

The Devonian section lies on the southern side of the Portishead–Clevedon anticline and generally dips south-east. Faulting, local folding, younger deposits and modern beach cover interrupt the exposures. Consequently, a walk around the bay is not a simple, continuously visible passage through every bed between the Devonian and Carboniferous.

References

Barclay, W.J., Davies, J.R., Hillier, R.D. & Waters, R.A. (2015). Lithostratigraphy of the Old Red Sandstone successions of the Anglo-Welsh Basin. British Geological Survey Research Report RR/14/02.

British Geological Survey. Lexicon of Named Rock Units: Brownstones Formation; Portishead Subgroup; Woodhill Bay Conglomerate Member; Avon Group; Shirehampton Formation; Black Rock Limestone Subgroup.

Dineley, D. & Metcalf, S. (1999). Portishead, in Fossil Fishes of Great Britain. Geological Conservation Review Series 16. JNCC.

Kellaway, G.A. & Welch, F.B.A. (1993). Geology of the Bristol district. Memoir of the British Geological Survey, Bristol special sheet; especially the Portishead Down–Portishead–Portishead Point section.

Mitchell, M. (1980). The distribution of Tournaisian and early Visean (Carboniferous) coral faunas from the Bristol and South Wales areas of Britain. Acta Palaeontologica Polonica, 25, 577–585.

Wilby, P.R. (2005). Portishead, North Somerset, in Barclay, W.J. and colleagues, The Old Red Sandstone of Great Britain. Geological Conservation Review Series 31. JNCC.