The Seven Sisters cliffs east of Cuckmere Haven expose flinty Late Cretaceous chalk, with echinoids, shells and other fossils in loose material. Distinctive flint bands trace the bedding through the high brows. This guide follows the east-bank coast; Seaford Head across the river is a separate locality.
FIND FREQUENCY: ♦♦♦♦ – Fossil exposure varies with scour and beach cover; productive visits are not guaranteed.
CHILDREN: ♦♦♦ – The long approach, shingle and tidal under-cliff shore require close supervision.
ACCESS: ♦♦ – The valley trail is about 2 km each way; it does not make the beach or foreshore wheelchair-accessible.
TYPE: Loose chalk fossils and blocks on the foreshore, away from cliffs and fall debris.
DIRECTIONS
♦ Approach Seven Sisters Country Park at Exceat on the A259. The North (Forest) and South (Riverside) car parks are paid and locked overnight; check posted times.
♦ Follow the signed valley trail, about 2 km each way, to the shingle beach. Toilets are beside the visitor centre, not on the beach.
♦ From the east-bank trail the Seven Sisters shore lies eastwards. Do not cross the Cuckmere river mouth at any tide; use the designated inland route when travelling between banks.
♦ Original guide reference: TV 52056 99489 – 50.775056, 0.155239
FOSSIL HUNTING
On the Seven Sisters shore east of the Cuckmere mouth, concentrate on the changing accumulations of loose chalk and flint. Sand, shingle and weed can conceal productive surfaces, while wave action moves and wears the material already on the foreshore. Inspect accessible weathered blocks and pebbles well away from the cliffs. There is no need to enter scree or freshly fallen debris, and walking farther beneath the cliffs is not automatically a better collecting strategy.
Echinoids are a good starting point. Local field accounts illustrate heart-shaped Micraster, rounded to conical Conulus and larger domed Echinocorys, in chalk or as flint moulds. Look for a repeated five-part pattern, paired pore rows or a convincing underside as well as the general shape. A worn flint pebble may preserve the internal form of an echinoid after its shell has disappeared, so it can be identifiable as an echinoid without retaining enough information for a species name. The local geological survey specifically records Micraster coranguinum and related forms, but that does not make every heart-shaped pebble that species.
Regular sea urchins are represented differently. Their separate plates and spines can survive after the rounded test has fallen apart. An illustrated Seven Sisters specimen of Temnocidaris sceptrifera sceptrifera is a primary spine with a swollen lower part, tapering shaft and strongly ornamented surface. Use this shape as a guide when examining the surface of a loose chalk fragment. Keep any associated plates and spines together; separating them can destroy information about whether they belonged to one animal.
Bivalves are also important. The site survey records Platyceramus and Volviceramus in the lower exposed succession, with Cladoceramus in fallen material from higher beds. Much of what a collector notices will be shell fragments or sections rather than complete paired valves. Look for curved, layered shell and repeated growth ornament, and photograph the piece in its matrix. The same survey records the crinoid Uintacrinus socialis in material fallen from above: this is evidence from the higher succession, not an indication that its source bed is exposed at the western entrance.
Sponges, brachiopods and bryozoans add variety to a careful search. Examine the surfaces of loose blocks as well as their obvious large fossils; small encrusting colonies and compact shells can be missed when attention is confined to echinoids. A knobbly or branching piece of flint is not automatically a sponge, since flint can also follow burrows. Towards the eastern Seven Sisters, the local survey documents opalised wood and ammonite aptychi in fallen Cuckmere Sponge Bed blocks. Aptychi are the paired hard plates of the ammonite’s lower jaw. Look for a plate with an organised outline and surface ornament, and keep matching pieces together. These unusual finds belong to the eastern part of the shore described here.
For useful records, distinguish a chalk fossil from a flint internal mould and record the actual stretch of beach where it was found. A block below a particular cliff need not have come from the rock exposed at beach level. Photograph unusual material before cleaning, preserve its associations, and keep potentially significant finds unprepared for advice. Follow current collecting guidance for the protected coast, take only permitted loose material, and leave fixed platform fossils for others to study. Often the most informative result is a well-recorded modest specimen rather than an unlabelled large fragment.
A chronological record of geological research, fossil evidence and conservation milestones associated with Seven Sisters.
1909 – The Cuckmere stratigraphic break investigated
J. V. Elsden considered a fault along the Cuckmere valley to explain the mismatch between Chalk levels on opposite sides of the estuary. This was an early recognition that the Seven Sisters cannot simply be joined bed for bed to Seaford Head across the gap in exposure.
1925 – A large fall at Baily’s Brow
A major collapse at Baily’s Brow produced a very large mass of chalk debris. It became a recorded example of the infrequent large falls that punctuate otherwise irregular cliff retreat along the Seven Sisters.
1939 – The cross-valley correlation reconsidered
C. T. A. Gaster also invoked faulting to account for the different Chalk levels across the Cuckmere valley. Later assessments retained uncertainty over how much reflects fault displacement and how much the orientation of dipping beds.
1986 – The Seaford Chalk divided into bed packages
Rory Mortimore’s work established the Belle Tout, Cuckmere and Haven Brow subdivisions and their flint markers. The Seven Sisters cliffs provide a key local section showing this framework.
1987 – Marker beds linked across the basin
Rory Mortimore and Bernard Pomerol demonstrated wider correlations of the White Chalk. The recognisable flint bands displayed at the Seven Sisters contributed to a framework extending across the Anglo-Paris Basin.
15 November 1999 – The current SSSI notification issued
The Seaford to Beachy Head notification recognised the Seven Sisters cliff–beach–platform system and the scientific importance of the coast’s Chalk landscape and geological processes.
2014 – A detailed annotated cliff section published
Rory Mortimore’s published section illustrated the Belle Tout, Cuckmere and Haven Brow packages together with individual flint markers and contrasting fracture patterns. This made the geological structure of the western Seven Sisters directly readable in the cliff face.
2026 – The coast joins the enlarged National Nature Reserve
The Seven Sisters became part of an enlarged reserve linking chalk downland, valley habitats and coastal reefs. The formal declaration was made on 18 February, followed by its public launch in March.
GEOLOGY
Seaford Chalk Formation makes up much of the Seven Sisters cliffs, with younger Newhaven Chalk on higher brows. These are White Chalk Subgroup rocks. The local succession is distinct from the measured Seaford Head section west of the river.
The chalk is a marine limestone largely built from the remains of microscopic calcareous plankton. Its flints form conspicuous nodular and sheet-like bands, while thin marl seams and concentrations of larger shells distinguish some of the otherwise similar beds. In the lower Belle Tout package, the local record includes the large inoceramid bivalves Platyceramus and Volviceramus. The overlying Cuckmere chalk is comparatively uniform and generally less conspicuously fossiliferous, so a white chalk block alone gives only limited information about its precise source.
Within the Cuckmere package, a sponge-bearing horizon is recorded towards the eastern part of the Seven Sisters, with opalised wood and ammonite aptychi documented in fallen material. Above the Seaford succession, the return of marl seams signals basal Newhaven Chalk on the higher brows; detached plates of Uintacrinus socialis are recorded from fallen higher beds. Younger flinty gravels, chalk-rich coombe rock and loessic material fill dry valleys cut into the Chalk. Frost-disturbed chalk and broken flint layers beneath those fills belong to later cold-climate processes, not to the original marine depositional setting.
Belle Tout, Cuckmere and Haven Brow are informal bed packages within Seaford Chalk. The Seven Sisters Flint Band separates the first two, while Michel Dean Flint marks the transition into Haven Brow. Further flint bands reveal the bedding through otherwise similar chalk.
The flint band’s height varies along the coast, and beach cover changes its visibility; it is not a continuous exposed sheet at every point on the foreshore. Cliff height also does not measure formation thickness.
Detailed geology and stratigraphy of Seven Sisters.
The Seven Sisters section begins on the east side of the Cuckmere mouth. The cliffs expose Seaford Chalk with younger Newhaven Chalk on the higher brows. Flint bands can be followed through the gently inclined beds, but cliff height is not a measure of formation thickness, and the measured Seaford Head succession across the river is a separate section.
CHALK GROUP
The Chalk is marine limestone, largely built from microscopic calcareous plankton. The modern subdivision used below separates the Grey Chalk from the overlying White Chalk; these are lithostratigraphic units, not simple colour labels.
WHITE CHALK SUBGROUP
The visible Cretaceous bedrock belongs to the White Chalk Subgroup. The Seaford Chalk here spans Coniacian to Santonian strata; the small amount of overlying Newhaven Chalk belongs to the higher Santonian part of the local cliff succession.
Seaford Chalk Formation
White chalk with conspicuous nodular and sheet flints forms most of the cliff and shore platform. The published Seven Sisters photograph identifies three informal bed packages: Belle Tout, Cuckmere and Haven Brow. These are informal groups of beds within the formation, rather than formal members.
Belle Tout Beds. The lowest of the three packages is present below the Seven Sisters Flint Band, particularly towards the western end. The local survey records Belle Tout marl markers near the cliff base. Inoceramids including Platyceramus and Volviceramus occur in this lower part of the section.
Belle Tout marls. These thin marl horizons interrupt the lower Seaford Chalk and help distinguish it from the less obviously marly chalk above. Three marls are used in the Sussex reference scheme, associated with shell-detrital horizons; local exposure varies and their Seaford Head measured spacings are not transferred here.
Seven Sisters Flint Band. A conspicuous dark sheet-to-semitabular flint marks the top of the Belle Tout package and the base of the Cuckmere Beds. It is visible in the western cliffs and descends eastwards towards Birling Gap. Its elevation changes with bedding and coastal topography; its occurrence on a platform is not a formation boundary.
Cuckmere Beds. The interval above the Seven Sisters Flint Band and below the Michel Dean Flint consists predominantly of relatively uniform white chalk. Compared with the shelly Belle Tout Beds it is generally less conspicuously fossiliferous. Near-vertical joints in this interval are clearly shown in the local annotated section.
Cuckmere Sponge Bed. An inaccessible sponge-bearing horizon occurs within the Cuckmere package. The local record specifically places opalised wood and ammonite aptychi in fallen material from this bed towards the eastern end of the Seven Sisters. Those eastern records do not establish a rich sponge bed at the western beach entrance.
Michel Dean Flint Band. The top surface of this conspicuous flint is the boundary into the Haven Brow Beds in the published Sussex scheme. It forms the lowest of the prominent flint markers shown above the Cuckmere Beds in the local section.
Haven Brow Beds. This higher Seaford package contains several prominent semitabular flints. Fallen blocks can include Cladoceramus; the local cliff survey records these from the higher succession without requiring them to be exposed at beach level.
Baily’s Hill Flint Band. This is a conspicuous double flint band above the Michel Dean marker. The paired character is shown in the Seven Sisters annotated photograph.
Flat Hill Flint Band. A further prominent flint lies above the double Baily’s Hill band. It helps subdivide the Haven Brow Beds rather than representing a separate formation.
Brasspoint Flint Band. This marker lies above the Flat Hill Flint and below the Rough Brow Flint. It is one of the continuous dark lines that reveal the bedding through the otherwise similar white chalk.
Rough Brow Flint Band. This upper Haven Brow marker succeeds the Brasspoint Flint and precedes the Short Brow Flint. Its local position is established by the labelled cliff section.
Short Brow Flint Band. Another high Seaford marker lies above the Rough Brow Flint and below the Exceat Flint, helping distinguish successive high-level beds in the western cliffs.
Exceat Flint Band. The highest named Seaford flint in the local annotated section lies near the top of the Haven Brow Beds, below the change into Newhaven Chalk.
Newhaven Chalk Formation
Basal Newhaven Chalk caps the higher brows. Compared with the underlying Seaford Chalk, the return of persistent marl seams marks a change in lithology. Fossil material from these upper beds reaches the beach in rockfalls; it is not all accessible in place.
Basal marl boundary and crinoid-bearing upper cliff. The Sussex formation boundary is defined at the base of Buckle Marl 1. The Seven Sisters section shows Newhaven Chalk above the Seaford flint succession, and the local fossil record includes detached plates of Uintacrinus socialis from fallen higher beds. No full sequence of Buckle or Friars Bay marls is claimed at the western shore.
Faults, joints and flint-guided fractures. The section dips gently eastwards towards the Birling Gap syncline. The annotated western cliff distinguishes vertical joint sets in the Cuckmere and Haven Brow Beds from polished, striated inclined shear surfaces in the Belle Tout Beds and near the base of Newhaven Chalk. These structures help control the shape and failure of cliff blocks.
Quaternary valley fills. The cliff cuts across dry valleys, exposing younger flinty gravels and coombe rock with a thin loessic cover. Deeply weathered Chalk and distorted or broken flint layers occur below the fills; cryoturbation lobes also affect the chalk surface away from valley bottoms. These cold-climate deposits are separate from the marine Chalk formations.
References
Hopson (2005), A stratigraphical framework for the Upper Cretaceous Chalk of England and Scotland, BGS RR/05/01
BGS Lexicon, SECK
BGS Lexicon, NCK
Sussex Geodiversity Partnership, Seven Sisters, 2011 field survey
Mortimore (2016), Why conserving South Downs geology is so important, Earth Heritage 46, pp.7–9; Seven Sisters annotated section from Mortimore (2014)
Mortimore, Wood and Gallois (2001), Cuckmere to Seaford account; Birling Gap comparison and regional marker definitions
May (2003), Beachy Head–Seaford Head, Coastal Geomorphology of Great Britain
SAFETY
Never cross the Cuckmere river mouth at any tide. The park and Coastguard direct walkers around the designated inland route.
Plan for tidal cut-off and a long return. Stay far from cliff bases and overhangs, avoid active fall debris and watch for slippery seaweed. The surfaced valley trail does not make the under-cliff shore a safe or accessible path.
EQUIPMENT
Take sturdy footwear with good grip, tide information, a hand lens, a camera, wrapping material and rigid specimen boxes. Keep the load manageable for the rocky shore.
Loose chalk fossils can be fragile. A soft brush and careful packing are more useful than levering specimens from the platform; do not hammer cliffs or in-situ features.
CLEANING AND TREATING
Allow wet specimens to dry slowly at room temperature, then begin with gentle dry brushing. Support thin shells and exposed echinoid tests rather than scrubbing them or trying to force away attached chalk.
Avoid acids, bleach and routine varnish. Hard chalk or flint preparation can damage the fossil as easily as the matrix; stop if the surface is flaking and seek specialist advice. Keep potentially important specimens unprepared.
IDENTIFY YOUR FINDS
Need help identifying a fossil? Share clear photos, where you found it and its size with the community.
FURTHER READING
Mortimore (2016), Why conserving South Downs geology is so important, Earth Heritage 46, pp. 7–9
Mortimore, Wood and Gallois (2001), Cuckmere to Seaford, British Upper Cretaceous Stratigraphy
May (2003), Beachy Head–Seaford Head, Coastal Geomorphology of Great Britain
Hopson (2005), A stratigraphical framework for the Upper Cretaceous Chalk of England and Scotland, BGS RR/05/01
Natural England: Seven Sisters National Nature Reserve public notice, 18 February 2026
National Trust (19 March 2026): Seven Sisters National Nature Reserve
Sussex Geodiversity Partnership, Seven Sisters, 2011 field survey
Seven Sisters Country Park: Plan your visit
ACCESS RIGHTS
Follow current country-park and protected-site guidance, including river-mouth restrictions. Keep collecting low-impact and limited to genuinely loose material where permitted; do not damage bedrock or recorded features, and seek permission for intrusive sampling.
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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