Don’t believe everything you read: Beachcombing at Easington, County Durham
Stephen K. Donovan (UK)
One of the first volumes that I bought when I first took up palaeontology over 50 years ago was the very excellent Directory of British Fossiliferous Localities (Arkell et al., 1954; Donovan, 2025a), a tome full of meat. It was published in the same year as I was born, that is, it was already over 20 years old at that time. As I soon discovered, some localities had already been lost by being infilled or otherwise were no longer being accessible. I learnt to take every record in the Directory with a pinch of salt. Coastal localities were more reliably still open, but visiting a quarry inland was always a gamble.
This soon taught me that old accounts of potential collecting sites may no longer be accurate. Usually, sites, particularly inland localities, described many years ago have been destroyed or, at least, deteriorated. The coastal example I give below is just the opposite; it has improved. A field guide is commonly an excellent ‘taster’ for a locality, tempting you to investigate and informing you of what can be seen. For example, consider the words of the excellent book by Ellis (1968, p. 106):
Industry has brought to the Durham coast, not only the unsightliness which seems to be its inevitable accompaniment, but also two alien and unpleasing deposits … at Easington waste material from the collieries has been pitched over the cliffs, despoiling the beach below and blackening the beaches to the south …”
Oh, dear. But although this was true when Ellis’s volume was published, things have changed for the better now long after the collieries have ceased to be active. Yet a so-called new edition of Ellis’s fine book:
… showed very few revisions, failed to make the transition to a plate tectonic paradigm and erroneously repeated the above paragraph” (Donovan, 2025b, p. 142).
In fact:
… the colliery was closed by the Thatcher government in the 1980s and the beach is now a fabulous resource for [cobble and] pebble collecting” (Donovan, 2018, p. 798).
Ellis was correct in 1968, but the latest edition is mainly unaltered and, in this instance, just plain wrong.
In the absence of rock waste from coal mining, the coast at Easington has been ‘cleaned’ by the action of the sea. It has become a fine coast for someone like me, keen to collect lithoclasts with modern invertebrate borings and encrustations. Particularly, limestones and mudrocks can be further broken down by the action of boring organisms which weaken them, particularly at the outer rim. This part of a rock clast may be densely infested by borers settling from single spatfalls. In contrast, invertebrates that form gregarious, cemented accumulations on mobile rock substrates may act as an additional layer of armour, retarding the breakdown of the clast. It is these borers and encrusters that make Easington such an intriguing site. Come beachcombing with me.
Locality
Travel to Durham by rail and take a bus or taxi to Easington (OS Explorer Sheet 308 ‘Durham and Sunderland’). If driving, find the car park on the B1283, east of the railway and Fox Holes Dean (Fig. 1; NGR NZ 439 435). Cross the railway, and walk north between the railway and the cliff tops. Take the path down to beach level at Hawthorn Hive.
The beach north of Easington, County Durham (Fig. 1), retains many hundreds of rock clasts, including boulders, cobbles and pebbles.
Most are Permian Magnesian Limestone derived from the cliffs at the back of the beach and from further north (by longshore drift), and from offshore, submerged outcrop; other lithologies were most likely derived from a mixture of longshore drift, reworked glacial erratics (Trechmann, 1931a) and bricks. There is ample evidence that the rock clasts (and bricks) have been rolled most energetically in the sea, apparent by their common rounded shape; preservation on the beach would have been the work of storms in the North Sea. It is these rock clasts on the beach that are the subject of investigation, particularly those rich in invertebrate borings (Donovan et al., 2018, 2019).
Easington’s geology has a ‘Jekyll and Hyde’ relationship. The town is known for its colliery and the exploitation of coal from the Upper Carboniferous (Pennsylvanian). But this is hidden by the overlying marine Zechstein Group, Permian Magnesian Limestone, exposed particularly in the coastal cliffs of Co. Durham (Taylor et al., 1971, pp. 70-76; Ruffell et al., 2006, fig. 12.17 and supporting text). Beach clasts are common, and dominantly derived from Permian limestones and dolostones, making them attractive substrates for modern boring and encrusting organisms.
This beach is rich in limestone (and other) clasts; shells are rarer, but still occur and may be infested by other invertebrates. The specimens described below are a selection from samples seen between Hawthorn Hive south to below the Easington Raised Beach at Shippersea Bay (Fig. 1) and collected (Figs. 2-7). Every attempt was made to sample the full range of boring and encrusting invertebrate taxa, and clast lithologies, seen on the day they were collected. The variety of invertebrate encrusters on certain clasts is documented, providing a different pattern to that shown by borings. All collected specimens are deposited in the Naturalis Biodiversity Center, Leiden, the Netherlands (prefix RGM). This guide is based on Donovan et al. (2018) and Donovan (2025b, pp. 142-151).
Borings
Three invertebrate ichnogenera are common at Easington and elsewhere on the North Sea coast (Donovan et al., 2019). Caulostrepsis Clarke are “U-shaped borings that have a vane connecting the limbs of the U-boring” (Bromley, 2004, p. 460) and are the spoor of polychaete worms, in the North Sea most commonly generated by Polydora. They are typically shallow borings parallel to the surface of the clast and are soon lost by shallow corrasion of a mobile substrate. Where preserved, they are apparent in cross-section as slot or figure-of-eight shaped holes (Fig. 3E), but are more apparent in longitudinal section.
Straight specimens with a central vane, preserved in a cobble of Mississippian(?) limestone, are assigned here to the type ichnospecies, Caulostrepsis taeniola Clarke (Fig. 4A and 4B).
More teasing is a curved specimen, RGM 1332264, with an incomplete central vane and limbs that diverge more proximally (Fig. 2E). The curvature is reminiscent of Caulostrepsis sprialis Pickerill et al., previously only recorded from the Middle Miocene of Carriacou, Lesser Antilles, but that ichnospecies lacks a central vane. It is provisionally referred to Caulostrepsis isp. aff. C. spiralis. Sponge borings such as Entobia are:
“… generally an anastomosing network of canals that in most cases swell to form rounded chambers. Commonly the chambers dominate the boring and obscure the design of the network” (Bromley, 2004, p. 459).
The interplay of ontogeny and taphonomy commonly makes identification of Entobia to ichnospecies testing except where specimens are particularly well-preserved. Most specimens here are assigned to Entobia isp. for simplicity (Fig. 2A-D). The complexities involved are demonstrated by RGM 1332262 which exposes both the internal (Fig. 2D) and external morphology (Fig. 2C), with apertures, of what is presumed to be a single network. RGM 1332260 is at least superficially close to Entobia cateniformis Bromley and d’Alessandro (Fig. 2A).
Gastrochaenolites includes club-shaped borings in lithic substrates, including robust shells, like oysters, and wood. These are the most prominent borings in rocks on the beach at Easington, partly because of their comparatively large size, but also due to their high preservation potential. By boring vertical to sub-vertical to the surface of a clast, considerable corrasion is required to completely remove them (see, for example, Fig. 5), making Gastrochaenolites particularly persistent.
The easiest way to determine the ichnospecific identity of modern Gastrochaenolites borings is to take casts of the borehole using some suitable medium, in this case liquid latex. All of the casts taken from RGM 1332259, 1332263 and 1332266 were similar (Fig. 6), although none was complete. Comparison with Kelly and Bromley (1984, text-fig. 3) shows that they are closest to Gastrochaenolites turbinatus Kelly and Bromley, a junior synonym of Gastrochaenolites clavatus (Leymerie) (Donovan and Ewin, 2018).
Apart from those infested by Entobia isp., the bored limestone clasts illustrated here (Figs. 3, 4A, 4B and 5) include indeterminate small, round or rounded holes that appear to be more or less deeply perforate in the substrate. Without seeing the three-dimensional form of these borings, it is impossible to determine to which ichnotaxa they should be assigned. Nonetheless, it is suspected that at least some are referable to the simple, string-like, worm boring Trypanites isp. (Donovan and Harper, 2025).
Encrusters
Gregarious accumulations of balanid barnacles, most likely Balanus crenatus Bruguière, occur on substrates of coal (Fig. 4E) and sandstone (Fig. 4F). On both specimens the balanids are partially overgrown by serpulid worms, indicating a faunal succession. In turn, gregarious accumulations of small, presumed juvenile B. crenatus are found on some serpulids. On RGM 1332267 (Fig. 4F), the balanids and Lithothamnion show little evidence of interaction and may have been coeval.
Serpulid worms (Figs 4C-G, 7) are provisionally referred to Pomatoceros triqueter (Linné) (Campbell, 1982, pp. 134-135). They infest a range of substrates, sometimes densely, including gastropods, limestones (particularly within holes, such as vacant borings, particularly Gastrochaenolites), coal and sandstones, and have grown over Lithothamnion and Balanus, which in turn have encrusted Pomatoceros.
More than one specimen is encrusted by the white, chalky, warty calcareous alga referred to Lithothamnion sp. (Campbell, 1982, pp. 50- 51; Figs 4E, F, 7B here). It is possible that further calcareous algae are common at Easington, but not apparent because of their similarity to the surfaces of many pale limestone clasts that dominate the beach. RGM 1332267 preserves both encrusting Lithothamnion sp. and upright Lomentaria? sp. (Fig. 4F). RGM 1332274 is a sandstone pebble that is well-rounded, indicating considerable transport, and dense Lithothamnion sp. gives it the appearance of a limestone. It was encrusted by serpulid worms and their tubes were subsequently overgrown by Lithothamnion. Some of the serpulid tubes have broken through, giving a false impression of sinuous borings (Fig. 7B, just above centre). Some algae have also been lost by corrasion. Rare coiled spirorbid worm tubes and incomplete (corraded) encrusting bryozoan colonies also occur.
Discussion
The association of the boring ‘trinity’ of ichnogenera, Caulostrepsis, Entobia and Gastrochaenolites, is common on the coasts of the southern and western North Sea today (Donovan et al., 2019), and the Atlantic coast of Ireland (Donovan and Doyle, research in progress). These three ichnogenera can be easily separated by the novice ichnologist. The bored clasts are mobile and have been washed onshore, probably mainly during major storms, from the shallow shelf environment; they are all dwelling traces (= domichnia), taken together indicative of the shallow marine Trypanites Ichnofacies (MacEachern et al., 2007). Boring organisms only infest limestone substrates at this site; encrusters are recorded from various types of rock and shells, but not commonly on limestones.
It is relevant to compare the modern borings described here with trace fossils from the Easington 60-foot raised beach (Oxygen Isotope Stage 7 = late Middle Pleistocene, c. 38,000 years ago; Bridgland and Austin, 1999, p. 55; Davies et al., 2009). Bridgland and Austin (1999, p. 53) included Cliona sp. and Polydora sp. in a faunal list, and noted that “Pebbles bored by marine molluscs and annelid worms are also common (Woolacott, 1920, 1922; Trechmann, 1931b).” Cliona sp. is unlikely, but this probably refers to clionaid sponge borings, Entobia isp.
Similarly, the polychaete Polydora sp. would be a most unlikely fossil, but its borings, Caulostrepsis isp., are probable, particularly in Ostrea sp. which makes the same faunal list. Whether these are also the borings of “… marine … annelid worms” is possible. The marine molluscs boring pebbles were most likely boring bivalves producing Gastrochaenolites isp. Woolacott (1920, pp. 308-310; 1922, p. 66) and Trechmann (1931b, p. 295) noted rolled clasts of Magnesian Limestone with boreholes inhabited by Saxicava Fleuriau de Bellevue, a junior synonym of Hiatella Bosc, a nestling and boring bivalve (Tebble, 1976, p. 173). Thus, available evidence suggests that the ichnotaxa of Easington have changed little since the Middle Pleistocene.
References
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Bridgland, D.R. and Austin, W.E.N. 1999. Shippersea Bay to Hawthorn Dene. In: Bridgland, D.R., Horton, B.P. and Innes, J.B. (eds), The Quaternary of North-East England: Field Guide, pp. 51–56. Quaternary Research Association, London.
Bromley, R.G. 2004. A stratigraphy of marine bioerosion In: McIlroy, D. (ed.), The Application of Ichnology to Palaeoenvironmental and Stratigraphic Analysis. Geological Society, London, Special Publication, 228: 455–479.
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