Eype Fossil Hunting

1863 – John Day used the term Green Ammonite Beds for the fossil-rich Middle Lias clays of this coast
Day’s work on the Dorset coast established the Green Ammonite Beds as one of the classic fossil horizons of west Dorset. Although more often associated with Seatown and Golden Cap, the same fossil-rich succession continues through the Eype area and forms part of the scientific framework for the locality.

1933–1947 – Arkell’s classic work helped establish Eype as part of the great west Dorset Jurassic fossil coast
In his major studies and memoirs on the Dorset Jurassic, W. J. Arkell treated the Eype coast as part of the classic Lower and Middle Jurassic succession of west Dorset. This helped fix the locality’s reputation for ammonites, belemnites and fossiliferous limestone bands.

Late 20th century – the old Junction Bed terminology was revised and tied to Eype Mouth
Modern stratigraphic work replaced the old broad term “Junction Bed” with the Beacon Limestone Formation, and the Eype section became especially important because the former Junction Bed sensu stricto was formalised as the Eype Mouth Limestone. This gave the locality a direct role in the modern naming of the succession.

1999 – the Eype Mouth Limestone and Wattonensis Beds were formalised in the modern Dorset Jurassic framework
Modern revision of the Dorset coast succession formalised the Eype Mouth Limestone and recognised the Wattonensis Beds, with the Eype Mouth area and nearby Watton Cliff forming key reference exposures. This was one of the most important modern scientific milestones for the locality.

2003 – Eype Mouth and nearby sections were considered in discussion of the Toarcian and Oxfordian stratigraphic framework of the Dorset coast
Later work on Jurassic stage boundaries and coastal reference sections kept Eype and the surrounding cliffs within the discussion of the Dorset coast’s most important fossil and stratigraphic exposures.

Modern recognition – the Eype Starfish Bed became one of the locality’s most distinctive fossil horizons
The Eype Starfish Bed is now one of the best-known named horizons associated with the locality. It is famous for brittle stars preserved on the underside of sandstone blocks and is one of the most distinctive and unusual fossil beds on this part of the Jurassic Coast.

Modern collecting – Eype remains best known for ammonites from the Beacon Limestone Formation
Today Eype is still recognised as a productive fossil locality, particularly for ammonites weathering from the Beacon Limestone Formation in fallen blocks on the foreshore. Belemnites, bivalves and other Jurassic fossils also occur, but ammonites remain the main fossils most closely associated with the site.

EY numbers are editorial identifiers, not published bed numbers. The retained intervals are described with their named markers. Coastal reference values are explicitly labelled; visibility and completeness vary between exposures.

LIAS GROUP

Dyrham Formation (Lower Jurassic — Pliensbachian)

The Dyrham Formation is prominent on the coast from Eype Mouth westwards towards Thorncombe Beacon. Its Eype Clay, Down Cliff Sand and Thorncombe Sand members record mud-rich to increasingly sandy marine deposition. Faulting, folding and landslip interrupt the exposure; this description combines named coastal markers rather than claiming one uninterrupted visible section.

Eype Clay Member

Bed EY1 — Three Tiers Sandstone — Basal Marker Package

The Three Tiers marks the basal Eype Clay interval in the coastal reference succession. Three resistant, weakly laminated sandstone bands, each about 0.5–1 m in the published coastal account, alternate with sandy calcareous mudstone. The BGS memoir describes the complete package as up to 9 m; this is a coastal reference value, not a new measurement at this headland. Burrowing and bedding structures distinguish the sandstone bands. Lower parts may be obscured or outside the immediately visible cliff, so the full basal package is not promised at every point.

Bed EY2 — Lower Eype Clay

Pale grey to blue-grey, micaceous, variably silty mudstone with many small siderite nodules. This lower part of the member forms a soft, recessive cliff and is prone to slumping where it lies beneath more resistant sandy beds. Body fossils are generally scarce away from the concentrated Eype Nodule and Day’s Shell horizons; crushed Amaltheus and Tragophylloceras occur in the intervening clay. The member was formerly known as the Margaritatus Marls, reflecting its late Pliensbachian ammonite content.

Bed EY3 — Eype Nodule Bed

The Eype Nodule Bed is a useful marker within the silty mudstones. The BGS coastal account places it about 47 m above the member base, rather than simply halfway through the clay. It describes one or two levels of calcareous nodules, mostly less than 70 mm across, and records the bed at beach level at Eype Mouth. Some nodules were reworked into the succeeding shelly sandstone, with lateral changes associated with the Eypemouth Fault. Ammonites, bivalves and crinoid remains are recorded; weathering can leave the nodules projecting from softer mudstone.

Bed EY4 — Day’s Shell Bed

A fossil-rich shelly horizon close to the top of the Eype Clay Member, lying about 1 m below the Starfish Bed in the published coastal account. It contains concentrated juvenile bivalves and gastropods and is one of the most useful internal marker beds in the upper part of the member. The bed records a brief shelly concentration on the marine shelf immediately before the major sand influx that begins the Down Cliff Sand Member.

Bed EY5 — Upper Eype Clay

The uppermost Eype Clay consists of continued pale grey silty mudstone and sandy mudstone with abundant small siderite nodules. It becomes slightly more sandy upward and passes sharply into the basal Starfish Bed of the Down Cliff Sand Member. Fossil abundance is concentrated at particular marker horizons rather than uniformly rich throughout the clay. The overall lithology shows an increasing supply of fine clastic sediment toward the top.

Published conventions differ: the BGS memoir gives about 65 m for the coastal Eype Clay and includes the basal Three Tiers; the Lexicon gives about 60 m. Some field accounts describe roughly 60 m of clay above the Three Tiers. These descriptions are not silently combined, and no fixed complete local member thickness is assigned in the chart.

Eype Clay Thickness — Published Coastal Estimates

Down Cliff Sand Member

Bed EY6 — Eype Starfish Bed

The Starfish Bed marks the base of the Down Cliff Sand. It is a composite sandstone package with several sharp-based depositional units, laminated below and increasingly burrowed upwards. The ophiuroids occur on the lowest sole, not indiscriminately on every sandstone underside. GCR describes about 1 m, whereas the BGS memoir cites Woodward’s 1.4 m; these published measurements are not silently treated as one exact local thickness.

Siltstone Dykes In Fallen Starfish-Bed Blocks At Eype Mouth

The GCR records siltstone-filled cracks in fallen Starfish-Bed blocks near Eype Mouth. It specifically distinguishes this occurrence from Thorncombe Beacon farther west; the feature is not assumed at every coastal exposure.

Typical Fossils

Palaeocoma brittle stars, crinoid remains including Balanocrinus, other echinoderm debris and associated shelly marine fossils.

Bed EY7 — Lower Down Cliff Sands

Grey-brown muddy, very fine-grained sands and sandy mudstones, closely interbedded. These beds are more resistant than the Eype Clay below and form ledges and steeper cliff sections. They represent a low- to moderate-energy shallow-marine setting with persistent silt and fine sand influx, but still retain enough mud to weather into a softer, more friable cliff profile than the Thorncombe Sand above.

Crinoid-Ossicle Marl Above The Starfish Bed

The coastal reference account records a marl about 0.2 m thick a few metres above the Starfish Bed, rich in crinoid ossicles. It is a separate horizon from the brittlestar-bearing sandstone, and should not be merged with the Starfish Bed.

Bed EY8 — Upper Down Cliff Sands And Margaritatus Stone

The upper part of the Down Cliff Sand Member becomes sandier upward and culminates in the Margaritatus Stone, a bluish fossiliferous sandy limestone that marks the top of the member. This is the main upper boundary marker of the Down Cliff Sand at Eype and Thorncombe Beacon. The member as a whole thins eastward, from 30.5 m beneath Thorncombe Beacon to 21.3 m at Eype Mouth, reflecting local thickness variation within the Dorset basin.

Margaritatus Stone — Top Of The Down Cliff Sand

The coastal memoir records an approximately 0.3 m ironshot limestone, blue internally and yellow when weathered, with some conglomeratic texture. Its named ammonites include Amaltheus margaritatus and A. subnodosus. The Blue Band follows above.

Published Down Cliff Sand Thickness: 21.3 m At Eype Mouth

Thorncombe Sand Member

Bed EY9 — Blue Band (Basal Thorncombe Sand)

A blue-grey mudstone lying directly above the Margaritatus Stone and forming the formal base of the Thorncombe Sand Member. This bed provides a useful transition from the sandy mudstones of the Down Cliff Sand Member into the more yellow-weathering sands higher in the Thorncombe Sand succession.

The BGS coastal reference describes the Blue Band as approximately 2 m of blue-grey shelly mudstone. This is a published coastal value, not an exact newly measured thickness for every exposure.

Bed EY10 — Lower Thorncombe Sands

Yellow-weathering silty, very fine-grained sands and sandy silts, locally bioturbated and with hummocky cross-bedding. These beds form the more resistant upper cliffs beneath Thorncombe Beacon and are much yellower and sandier than the units below. They record a shallower, more energetic marine shelf environment with storm reworking and widespread burrowing.

Bed EY11 — Impersistent Mid-Member Limestone

A local limestone horizon about 0.3 m thick where present, developed within the Thorncombe Sand Member. Though not laterally persistent, it is a useful internal marker and indicates a short pause in sand influx with local carbonate cementation or accumulation.

Bed EY12 — Upper Thorncombe Sands And Top Grey Mudstone

Upper yellow-weathering silty sands and very fine-grained sandstones, passing up into a top interval of grey mudstone beneath the Beacon Limestone Formation. Following the BGS 2011 order, grey sandy mudstone lies above the Thorncombiensis Bed and varies laterally. The older GCR prose describes a different order around this marker, so the accounts are not assumed identical. BGS records 2.3–4.6 m in the coastal succession, thinning from Thorncombe Beacon towards Eype Mouth and removed east of there. It is not a uniform 2.3 m bed everywhere. These beds complete the sand-dominated late Pliensbachian succession at Eype before condensed limestone deposition begins above.

Thorncombiensis Bed

This distinct upper marker is described in the coastal memoir as about 0.35 m of brown calcareous mudstone and limestone, rich in the brachiopod Gibbirhynchia thorncombiensis. Amaltheus gibbosus supplies the associated ammonite-zone evidence. The variably preserved grey sandy mudstone lies above it and below the Beacon Limestone.

Thorncombe Sand Thickness — About 27 m In The BGS Coastal Reference Account

Beacon Limestone Formation (Upper Pliensbachian To Toarcian)

The Beacon Limestone Formation is the classic ‘Junction Bed’ facies at Eype and one of the most fossiliferous horizons on this part of the Dorset coast. It is thin but extremely condensed, highly fossiliferous and structurally interesting, especially around Eype Mouth where faulting and fissuring are conspicuous.

Marlstone Rock Member

The BGS memoir gives Marlstone Rock thicknesses of 0.3–0.45 m at Thorncombe Beacon. This local measurement is distinguished from more general coastal values and from nearby Watton, where this member is absent.

Bed EY13 — Lower Ferruginous Beacon Limestone

The lower part of the Beacon Limestone Formation is ferruginous and ooidal, commonly weathering pinkish, reddish-brown or brown. It records a highly condensed shallow-marine carbonate interval at the close of Dyrham deposition, with local conglomeratic textures and abundant iron staining. These ferruginous beds are the lower part of the classic Junction Bed complex at Eype.

Howarth’s Lettered Western-Cliffs Layers

Howarth (1992, pp.24–26) describes the condensed Junction Bed between Seatown and Eypesmouth separately from Watton Cliff east of the fault. The lettered layers below are from that western framework. They vary laterally, may be absent, and no single block contains them all. Published zero-to-maximum ranges express that variability; they are not summed into a continuous local total.

Layer R — Dark Ooidal Conglomeratic Limestone

The lowest named layer is hard dark-grey limestone containing coarse iron-rich ooids and sandstone pebbles. Howarth gives an absent-to-0.25 m range for the western cliffs and an Apyrenum Subzone fauna.

Layer Px — Grey-Pink Limestone

A harder grey-pink limestone with scattered ooids, assigned to the Hawskerense interval. Its western-cliffs range is absent to 0.25 m, with Pleuroceras recorded.

Layer P — Fine-Ooidal Brown And Grey Limestone

This ooidal limestone contains occasional sandstone pebbles and spans the later Spinatum and Tenuicostatum intervals in Howarth’s account. The reported western-cliffs range is absent to 0.30 m. The Pliensbachian–Toarcian time boundary does not coincide automatically with a new formation boundary.

Eype Mouth Limestone Member

Bed EY14 — Eype Mouth Limestone / Cephalopod Limestone

A condensed ammonite-rich cephalopod limestone forming the upper part of the Beacon Limestone Formation at Eype. This is the main fossil-bearing limestone horizon scattered across the foreshore as large hard fallen blocks and is the reason Eype is so well known to collectors. Between West Bay and Eype Mouth the Beacon Limestone locally thickens in a stepped fashion and is cut by fissures, some sub-parallel to bedding and others oblique, filled with pale calcilutite and younger marine faunas. These features are among the clearest indications of synsedimentary faulting on the west Dorset coast.

Typical Fossils

Abundant ammonites, belemnites, bivalves and other marine fossils in hard condensed limestone blocks, often requiring preparation to expose them fully.

Planar Hardground At The Marlstone–Eype Mouth Limestone Contact

The GCR describes a conspicuous planar hardground separating the members. It records an interruption and erosion of already firm sediment, rather than a continuously deposited contact.

Basal Stromatolitic Calcilutite

The basal Eype Mouth limestone is pink to buff and finely calcareous, with stromatolitic structures. The cited coastal account assigns its ammonites to the Serpentinum Zone; this is a source-specific local framework rather than an invented numbered bed.

Higher Pale Conglomeratic Limestone Layers

Paler conglomeratic beds above carry the younger Bifrons-to-Dispansum succession in the GCR scheme. Several planar erosion surfaces truncate ammonites and other fossils; pebble layers and worn skeletal material show reworking. Individual contacts and omitted intervals vary along the coast.

Layer N1 — Thorncombe White Nodular Limestone

Howarth gives 0.08–0.13 m for this white nodular limestone specifically at Thorncombe Beacon. It is the lower of the two named Thorncombe alternatives in the N/O interval, and belongs to the upper Exaratum Subzone.

Layer N — Thorncombe Ferruginous Seam

The overlying earthy iron-rich seam is 0.05–0.08 m in Howarth’s Thorncombe account. N and N1 are lateral equivalents of the three O layers at Ridge Cliff; those neighbouring O-layer thicknesses are not substituted into this locality. The source records Harpoceras serpentinum and other ammonites in the N/N1/O1 correlation interval.

Layer M — Massive Pink And Red-Patchy Limestone

A hard conglomeratic limestone, commonly massive rather than rubbly, with abundant large Harpoceras falciferum in the source collection. It belongs to the Falciferum Subzone and has an absent-to-0.23 m western-cliffs range.

Layer L — Pink-Yellow Rubbly Conglomeratic Limestone

This younger layer contains Hildoceras and other ammonites of the Commune and part of the Fibulatum intervals. Howarth records an absent-to-0.25 m range across the western cliffs.

Layer K — White Rubbly Conglomeratic Limestone

A thin white conglomeratic layer assigned to the Fibulatum and Crassum intervals, absent to 0.08 m in the western reference. Its characteristic ammonite record includes Hildoceras and Catacoeloceras.

Layer I — Pale Rubbly Limestone

The youngest layer in this particular lettered western log is pale and rubbly, absent to 0.08 m. Howarth assigns its Grammoceras fauna to the Striatulum Subzone. It is kept distinct from broader GCR/BGS summary age spans; the source does not show every younger biozone as a separate preserved lettered bed.

Lower Massive And Upper Pale Conglomeratic Eype Mouth Limestones

The broader BGS synthesis describes lower massive pink-red and higher pale conglomeratic limestones and gives a typical Eype Mouth Member thickness of 0.4–0.6 m at Thorncombe Beacon and adjoining western cliffs. Howarth’s lettered detail above supplies the finer framework without assuming every layer survives in one block. Its western-cliffs description and the structurally complex Watton succession are not merged.

Beacon Limestone Thickness — No Single Thickness Assigned Across Eype Mouth’s Faulted Exposures

Bridport Sand Formation (Lower Jurassic — Toarcian)

The Bridport Sand Formation is a separate unit above the Beacon Limestone. Its lower muddy beds and higher sands occur in the adjoining composite coastal succession, including beneath Thorncombe Beacon. It should not be used as the name for the older Dyrham sandstones that form much of the coast west of Eype Mouth. Hard beds and fallen blocks must be assigned by their position and lithology, not simply by their yellow weathering colour.

Down Cliff Clay Member

Bed EY15 — Down Cliff Clay At The Base Of The Bridport Sand

The basal Down Cliff Clay consists chiefly of grey, calcareous, bioturbated mudstone, locally micaceous and finely sandy. It rests sharply on Beacon Limestone and becomes more sandy upwards, with thin harder sandstone or sandy-limestone beds. This is the mud-rich basal member of the Bridport Sand, not the main cliff-forming sand facies.

Bridport Sand Formation — Undivided Sands Above The Down Cliff Clay

Bed EY16 — Main Bridport Sand Cliff-Forming Sequence

Grey sand and silt weather yellow-brown and contain harder calcite-cemented beds and lenses. This is the characteristic upper Bridport facies in the adjoining coastal succession. The BGS memoir distinguishes its well-known West Bay–Burton type cliffs from the separate, incomplete sections beneath Thorncombe Beacon. A regional thickness range is not treated as a measured Eype section.

Local Cliff Character

Dyrham sandstones, condensed Beacon Limestone and younger Bridport deposits need to be distinguished within the local faulted and landslipped coastline. Foreshore blocks may have moved from their original bed, and a fallen block does not by itself establish the unit forming the cliff immediately behind it.

Bridport Sand Thickness — Incomplete Composite Exposure; No Local Total Assigned

Depositional Environment

The Eype succession records a late Pliensbachian to early Toarcian marine shelf that became progressively sandier upward. The Eype Clay was deposited on a muddy shelf, with conspicuous fossil concentrations restricted mainly to particular horizons; the Down Cliff Sand records a more sand-influenced marine regime, including the famous storm-burial Starfish Bed; the Thorncombe Sand reflects still shallower, storm-worked and strongly bioturbated shelf sands; the Beacon Limestone marks a highly condensed cephalopod-rich interval with local synsedimentary faulting; and the Bridport Sand Formation records widespread Toarcian sand deposition in a shallow marine basin, with separate sandy exposures in the adjoining coast; West Bay lies east of Eype Mouth.

Composite Locality: No Summed Total Assigned To These Separate Exposures

References

Howarth, M.K. (1957). The Middle Lias of the Dorset coast.
Wilson, V., Welch, F.B.A., Robbie, J.A. & Green, G.W. (1958). Geology of the country around Bridport and Yeovil.
Hesselbo, S.P. & Jenkyns, H.C. (1995). A comparison of the Hettangian to Bajocian successions of Dorset and Yorkshire.
British Geological Survey Lexicon: Dyrham Formation, Eype Clay Member, Down Cliff Sand Member, Thorncombe Sand Member, Beacon Limestone Formation, Eype Mouth Limestone Member and Bridport Sand Formation.
British Geological Survey Special Memoir: Geology of South Dorset and South-East Devon and its World Heritage Coast.
Discovering Fossils and Wessex Coast Geology field guides for Seatown, Thorncombe Beacon and Eype Mouth.

BGS 2011 coastal memoir: Dyrham, Beacon Limestone and Bridport Sand. BGS Lexicon: Down Cliff Clay. The source-to-bed research record distinguishes exact locality evidence, nearby reference measurements and historical terminology.

Howarth (1992), The ammonite family Hildoceratidae in the Lower Jurassic of Britain: Western Cliffs and Watton sections, pp.24–26.