Craigielaw Point Fossil Hunting

1866 – Fossil-bearing shore succession described
Howell, Geikie and Young documented the limestone, shale, sandstone and coal succession on the Aberlady shore, including the igneous rocks of Craiglaw Point. Their account recorded corals, brachiopods, bryozoans and crinoids and established an early published framework for understanding the coastal exposures.

1910 – Four principal limestones mapped
A revised geological survey mapped the repeated outcrops between Kilspindie and Craigielaw and tabulated the Middle Long Craig, Upper Long Craig, Lower Skateraw and Middle Skateraw limestones with their intervening beds. The work related the visible shore pattern to folds and small faults, providing a much clearer basis for tracing the fossil-bearing layers.

1917 – Shore beds used in the Hurlet correlation debate
Peter Macnair compared the Kilspindie–Craigielaw succession with other Scottish limestone sections in his investigation of the Hurlet sequence and Abden fauna. His mapped and tabulated shore account was part of a wider effort to correlate marine horizons. The paper was issued separately on 25 June 1917, although the bound volume bears the date 1918; its historical correlations should be distinguished from today’s formal stratigraphy.

1949 – Dolomitised coastal limestones assessed
A national limestone-resource study described the Kilspindie shore succession and specifically included the Upper Long Craig outcrops at Craigielaw. It drew attention to the altered character of these limestones. The later analytical specimen associated with this wider-shore work came from east of Garlic Rock, rather than the exact point.

1978 – Coral layers investigated in detail
Alistair Sutherland published a mapped study of the Middle Longcraig coral fauna, based on field observations, sectioned specimens and comparison with museum material. Gridded records beside and north-east of Craigielaw distinguished lower solitary-coral layers from higher colonial-coral developments, documenting variation that a general description of coral limestone would miss.

1985 – Coastal mapping and detailed succession revised
McAdam and Tulloch’s work on the Haddington district presented a detailed Kilspindie coastal sequence, a local geological map and explicitly provenanced fossils. It clarified the repeated limestone outcrops and retained the sandstone, mudstone, rooted and coal-bearing intervals needed to interpret the shore as a changing marine and deltaic environment.

1993 – Measured sections and microscopic fossils studied
Ali Mohamed Karbub’s MPhil investigation measured and sampled the Aberlady section between Craigielaw and Aberlady Point. Thin sections documented fine subdivisions within the Middle and Upper Longcraig limestones, their alteration to dolomite and sparse microscopic fossil assemblages. The separately exposed Skateraw beds were also sampled; these measurements describe particular shore intervals rather than a single continuous section at the point.

2014–2015 – Geodiversity value assessed
A field assessment on 26 August 2014, published in 2015, documented the geological and educational value of the 2.2 km Kilspindie shore from Green Craig to Aberlady Point. Craigielaw’s limestones, structures and fossil-bearing surfaces formed part of this broader assessment, alongside the practical sensitivity of a tidal shore important for wildlife.

2020 – Regional age correlations reconsidered
Pedro Cózar and Ian Somerville reassessed East Lothian foraminiferal correlations and the limitations of the older Aberlady evidence. Their results provide a revised regional framework for the Longcraig and Skateraw horizons. The new samples came from other East Lothian coastal sections and a borehole, so this was a reinterpretation relevant to Craigielaw rather than a new fossil discovery at the point.

The account below separates three useful kinds of evidence: beds mapped beside Craigielaw Point; Karbub’s measured Aberlady shore section between NT 445 800 and NT 455 805; and the wider Kilspindie coastal composite published by McAdam and Tulloch. They describe overlapping ground, but their measurements are not interchangeable. Folds, faults and covered intervals prevent them being joined into a single uninterrupted log at the locality reference. Descriptions within each succession run upwards from older to younger beds.

STRATHCLYDE GROUP

Aberlady Formation

At Craigielaw, the Middle Longcraig Limestone, correlated with the Blackbyre horizon, and the beds above it up to the base of Hurlet belong to the Aberlady Formation. The formation spans a wider Asbian–Brigantian interval regionally; that range is not a precise age for every exposed bed. Modern regional correlation places Middle Longcraig near the end of the early Brigantian. No formal member subdivision is established here. The western Blackbyre type-area association with the Lawmuir Formation must not replace this local hierarchy.

Sandstone, seatearth and shale beneath Middle Longcraig. Karbub records approximately 1.2 m of fine-grained sandstone, followed by a thin seatearth whose thickness is not specified, then 0.3 m of dark-grey calcareous shale immediately below the limestone. The rooted soil and overlying calcareous mud record a change from a vegetated substrate towards marine conditions. These are three distinct intervals; the thin seatearth is described in the text even though the schematic log does not label it separately.

Middle Longcraig Limestone: the local Blackbyre horizon. This is the principal coral-bearing limestone north-east of Craigielaw. It has a grey basal part and commonly weathers brown or yellow where dolomitised. Karbub measured 3.7 m, McAdam and Tulloch described about 4 m on this shore, and Sutherland gave an average of 2.5 m in his mapped coral study. These are separate observations with differing scope, not a range obtained from one consistently measured bed. Corals, brachiopods and crinoid remains vary markedly within the limestone.

Karbub’s lower bioclastic interval, 0–1.8 m. The basal part of his measured Middle Longcraig is bioclastic wackestone, a limestone with skeletal grains in a muddy carbonate background. Brachiopod and crinoid fragments predominate. Dolomitisation has affected the foraminifers, leaving only a limited assemblage confidently recognisable in thin section.

Karbub’s crystalline interval, 1.8–2.8 m. The limestone changes to coarse crystalline dolomite with no fossils visible in the examined material. This records alteration and preservation, not proof that the original environment lacked organisms.

Karbub’s upper colonial-coral band, approximately 2.8–3.7 m. The uppermost 0.9 m contains colonies described as in situ and identified historically as Lithostrotion junceum and L. pauciradiale. The thin-section subdivisions are informal parts of this measured limestone, not newly named beds or members.

Sutherland’s basal solitary-coral horizon. His separate mapped study found the limestone base best exposed in the anticline at NT 4473 8022, farther north-east than the point itself. Grey, well-bedded limestone with brachiopods and bryozoans forms a horizon averaging 0.5 m. The solitary rugose corals lie parallel to bedding and generally point north-east–south-west. His historical identifications were Allotropiophyllum without a species name, Amplexizaphrentis curvilinea, A. enniskilleni, Claviphyllum eruca and Rotiphyllum granulare. The grid reference locates the basal exposure, not every collected specimen.

Sutherland’s papery shale parting. Above the basal limestone is a light-grey, fine papery shale, described as apparently unfossiliferous. Its thickness is not given. It is a meaningful internal parting and should not be absorbed into a single generic coral bed.

Sutherland’s lighter limestone above the parting. This contains a second solitary-coral association: Amplexizaphrentis curvilinea, Aulophyllum fungites, Caninia juddi, Clisiophyllum keyserlingi, Koninckophyllum magnificum and Zaphrentites sp. His brachiopods include Avonia, Productus, Spirifer and Rhynchonella; a bryozoan is printed as Fenestalla. These names retain the source’s identifications and spelling. No separate grid or measured thickness accompanies this faunal list, so it is not a new exact-point species inventory.

Sutherland’s broken-colony carbonate mud. The lighter limestone grades into light-grey carbonate mud containing broken Lithostrotion junceum. Sutherland tentatively attributed the muddy character to leaching soon after deposition; this remains an interpretation rather than a demonstrated timing of alteration.

Sutherland’s white crystalline colonial limestone. Hard white crystalline limestone overlies the muddy interval. Large colonies identified as Lithostrotion junceum are followed by the larger Diphyphyllum furcatum. A white crystalline exposure is separately located at NT 4475 8010. His high-water-mark description prints only one endpoint, NT 4485 8024, for a purported range, so a second endpoint cannot be supplied. The taxonomic placement of D. furcatum was already discussed as uncertain in the paper; the historical identification is retained without a modern redetermination.

Lateral coral observations and the yellow dolomitised top. Overturned Lithostrotion junceum colonies at NT 4460 8010 were tentatively interpreted as evidence of disturbance during deposition. Sutherland recorded Thysanophyllum orientale associated with and overlying L. junceum at NT 4468 8013 and NT 4487 8028; the latter specimen was left in place and lies beyond the core 200 m coral outcrop. The yellow dolomitised top at NT 4455 8008, close to Craigielaw, contains his L. junceum and D. furcatum. The paper also describes a yellow top at NT 4460 8010. These are distinct mapped observations, not a single continuous measured layer with an invented thickness.

Shale and rooted beds above the coral limestone. Sutherland records thin papery shale, seatearth and a poor coal beneath Upper Longcraig at Craigielaw, NT 4452 8008. His search of the topmost shale found Lithostrotion junceum and Diphyphyllum furcatum, but did not reconfirm an earlier report of Thysanophyllum orientale from that shale. His positive T. orientale records are from the limestone localities described above.

Figured fossils with broader-shore provenance. The Survey memoir’s Plate 6, figures 4, 5 and 7, identifies Pugilis pugilis, Composita cf. ambigua and Pleuropugnoides cf. pleurodon from Middle Longcraig at Kilspindie. These are specifically provenanced coastal records, but are not tied to the exact Craigielaw coordinate. Other specimens on the same plate come from elsewhere in the district and are not added to this locality’s fauna.

Karbub’s overlying silty shale, 1.8 m. Immediately above the coral band in his measured section lies silty shale with limestone nodules towards its top. This is followed by a separate 1.0 m grey sandstone that grades locally to siltstone and contains rootlets. The sandstone and rootlets record a return to a sandy, vegetated substrate between marine intervals.

Coal and marine shale below Hurlet. Above the rooted sandstone, Karbub measured 0.15 m of coal and then 0.27 m of grey calcareous shale. The shale contains bryozoan stems, crinoids, brachiopod spines and rare material recorded as Stacheoides, signalling a return to fully marine conditions. Duff separately reports coal locally reaching 0.25 m, while the later geodiversity audit describes 0.20 m at an exposure just before Craigielaw. These local values should not be treated as a uniform seam thickness. All of these beds, including the marine shale, remain within Aberlady Formation because its top is at the base of Hurlet Limestone.

CLACKMANNAN GROUP

Lower Limestone Formation

The base of Hurlet Limestone, called Upper Longcraig in the older East Lothian literature, starts this formation and group. The basal limestone succession here is Brigantian. The full formation’s regional Brigantian–Pendleian range does not imply that all those ages are exposed at Craigielaw. Karbub’s figure uses an older group bracket beginning above Middle Longcraig; it is not the modern formal boundary.

Hurlet Limestone, formerly Upper Longcraig. The Survey’s Kilspindie coastal composite gives 3.6–5.5 m. Its lower part is nodular, crinoidal and shelly, with colonial coral recorded as Lithostrotion junceum; the upper part is coarser and flaggy, with thin silty interbeds and a reddened upper surface. Duff describes pale-brown, partly dolomitic rock with a rubbly or nodular surface beneath flaggy limestone. His approximately 8.5 m scarp height is topographic relief, not the thickness of this bed. The soft shale and coal below have been undercut in places.

Karbub’s 4.5 m Hurlet section. His sampled limestone is strongly dolomitised and recrystallised. The petrographic list distinguishes dark-grey dolomitic wackestone with crinoids and rare foraminifers at 0–0.5 m, light-grey to buff crystalline dolomite at 0.5–2.5 m, further dolomitic wackestone at 2.5–4.0 m, and dark-grey dolomitic mudstone with crinoid and brachiopod fragments at 4.0–4.5 m. However, the introductory description puts the crystalline interval at 0.5–1.5 m, conflicting with the later list. The upper boundary of that interval is therefore unresolved within this source. Crinoid-dominated samples should not be taken to mean that Hurlet everywhere lacks corals: the Survey’s coastal table and the later audit also record colonial corals in this limestone.

Survey composite above Hurlet: basal silty mudstone, 0.5 m. The wider Kilspindie shore table starts the overlying interval with dark-grey calcareous silty mudstone containing sparse ironstone nodules.

Yellow sandstone, 1.8 m. Fine- to medium-grained sandstone follows, with cross-bedding, contorted bedding, ripple marks, worm tracks and pyritic patches. Its structures record movement and disturbance of sandy sediment and activity at the sediment surface.

Fissile mudstone, 0.9 m. Soft grey and black mudstone forms the next separately recorded bed.

Flaggy sandstone, 0.45 m. A pale-grey, flaggy sandstone overlies the fissile mudstone.

Thinly bedded silty interval, 3.5 m. Grey silty sandstone passes into silty mudstone, with ripple bedding and bioturbation. The alternation of sandier and muddier sediment and disruption by organisms distinguish it from the adjacent more massive sandstones.

Sharp-based sandstone, 2.1 m. Medium-grained sandstone with a sharp lower boundary weathers yellow and contains cross-bedding and ripple bedding.

Seatearth, 1.0 m. The overlying former soil marks a rooted surface beneath the next coal-bearing interval.

Coal and coaly mudstone, 0.08 m. This thin bed completes the Survey’s recorded clastic and rooted succession immediately below Lower Skateraw. The eight separate intervals above Hurlet total 10.33 m in this particular composite.

Centimetre-scale details on the Craigielaw approach. Duff’s Lower Skateraw exposure has only 2 cm of mudstone immediately beneath its limestone, above 3–5 cm of coal, followed downwards by seatearth, sandy shale and sandstone. These fine observations must remain distinct from the broader Survey table. Karbub describes a separate, incomplete 1.7 m clastic interval above his Hurlet, including 1 m of dark-grey shale, 0.4 m of silty argillaceous sandstone, a very thin sandy shale, seatearth, about 5 cm of coal and the same 2 cm mudstone. His sandstone is seen again about 27 m north-east of the separate Lower Skateraw exposure: 27 m is a shore distance, not a thickness. The 1.7 m account cannot replace the Survey’s 10.33 m composite or prove that its other beds are absent at Craigielaw.

Inchinnan Limestone, formerly Lower Skateraw. The Survey coastal table gives 0.6–1.2 m of hard grey, dolomitised, crinoidal limestone and records Gigantoproductus cf. giganteus. Duff describes a well-jointed bed about 1 m thick immediately south-west of Craigielaw; Karbub measured 0.7 m in a separate outcrop. Crinoid and brachiopod fragments occur in dolomitic wackestone. The very sparse foraminifers reported by Karbub include Endothyranopsis crassa and Palaeotextularia, supported by marked rows in his Lower Skateraw occurrence chart. This horizon is Inchinnan, not Blackhall.

Poorly exposed interval between Inchinnan and Blackhall, 6.1 m in the Survey composite. The table records a thin coal, seatearth, pyritic silty mudstone with iron-rich nodules and micaceous sandy siltstone within this interval. It supplies one aggregate thickness, without a measured thickness or secure internal order for each component. Karbub separately describes 0.6 m of dark-grey mudstone above Lower Skateraw, extensively bored by present-day molluscs. Duff also describes modern-bored mudstone beneath the Blackhall overhang. Those borings are recent bioerosion of Carboniferous rock, and the 0.6 m exposure is not the whole 6.1 m interval.

Blackhall Limestone, historically Middle Skateraw or Skateraw. The Survey exposes only its lower 3.6 m or more: hard grey, thickly bedded crinoidal limestone. On the western Craigielaw approach, Duff describes a massive dark-grey, well-jointed limestone with crinoid fragments and productid brachiopods, a gently undulating bedding surface and a local dip of about 15° south-south-west. Duff and the later audit estimate about 8 m there, whereas Karbub’s separately sampled exposure is 1.90 m. These are different exposure or bed estimates, not interchangeable complete measurements. Regional correlation combines the older Middle and Upper Skateraw with the Blackhall marine horizon; it does not create two separately exposed modern Blackhall beds here.

Microscopic fossils and age interpretation. Karbub’s actual distribution charts show a sparse Middle Longcraig assemblage, particularly low in his section, with marked records including Archaediscus, Tetrataxis, Earlandia, Endothyra, Endothyranopsis and several other foraminiferal genera. The numerous blank checklist rows are not occurrences. His Middle Skateraw prose and chart do not fully agree: the prose names Endothyra spira and Endothyranopsis crassa, while the chart mainly marks the algae Kamaena and Principia. Cózar and Somerville’s later assessment cautions against relying heavily on the older Aberlady microfauna. Their regional framework places Middle Longcraig in the uppermost early Brigantian, Hurlet and Lower Skateraw in the late Brigantian, and Middle–Upper Skateraw in a higher assemblage. Their new material came from Spilmersford and the Cove–Skateraw–Dunbar coast, not Craigielaw, and supplies no new exact-point species list.

Sutherland’s separate generalised column. His explicitly not-to-scale Aberlady column is another historical depiction, not a measurement to splice into either later log. Below Middle Longcraig it shows yellow sandstone and 0.5 m of seatearth. The limestone is divided descriptively into lower hard grey rock with small solitary corals, middle dark-grey rock with abundant corals and brachiopods, and upper hard white colonial limestone with Lithostrotion and Diphyphyllum. Above it he labels rootlet-bearing papery shale as 2 m, seatearth as 2.5 m and then a thin coal. Upper Longcraig is shown as 4.5 m of yellow-brown crinoidal limestone with a rubbly or nodular top.

Higher beds in Sutherland’s column. Above Upper Longcraig he shows 2 m of yellow sandstone, 1.5 m of ripple-marked sandy shale, a thin coal and Lower Skateraw up to 2 m thick, labelled with the historical fossils Productus giganteus and Fenestella. Another thin coal, sandy shale with plant remains and 20 cm of papery shale precede Middle Skateraw, shown as up to 8 m of hard grey thick-bedded crinoidal limestone with Productus giganteus. Dark shale and sandy bands above contain ferruginous nodules and ripple marks; the contact-altered exposure is labelled “Aberlady Point” in his diagram, beyond the core Craigielaw locality. His interval values and old group brackets are retained as a source-specific comparison, not adopted as the modern standard.

Earlier coastal sections: what changed. The 1866 account described three limestones within its broader Aberlady coastal section, with sandstone and shale between them, a 10-inch coal over fireclay, and 8 ft of shale above the lowest white limestone. The middle limestone was given as 10 ft; the highest was 6 ft in the list but about 5 ft in the prose. Its associated Craiglaw basalt and greenstone belong to the intrusive history, not the top of a sedimentary stack. Historical fossils in that account include Productus, Athyris ambigua, Rhynchonella pleurodon, Lithostrotion junceum and L. irregulare in the lowest described limestone, and crinoids, Rhynchonella pleurodon var. and Fenestella plebeia in the next. These are old section records, not revised identifications of present-day specimens.

The 1910 Survey table, kept in its own units. In ascending order, the mapped Kilspindie–Craigielaw section records 20 ft of yellow sandstone and grey papery shale with hard white oolitic rooted beds; 8 ft of Middle Long Craig coral limestone with white marly bands and shell-rich pockets; 6 ft of rooted papery shale and soft “daugh” bands; 10 inches of coal; 12–18 ft of nodular dolomitic Upper Long Craig limestone, more evenly bedded and shaly above; 8 ft of mixed sandy and calcareous shale with ripples, tracks, fragmentary marine fossils and rolled shale and wood; 4 ft of contorted yellow sandstone; 4–18 ft of ripple-marked sandy “fakes” and daugh with tracks; 3 inches of coal; 2–4 ft of Lower Skateraw; 20 ft of grey shale with calcareous and ferruginous oolitic nodules, plant-bearing daugh-like beds and a thin coal; and 12 ft of hard grey, thick-bedded Middle Skateraw. Dark shale, sandy bands and a thin limestone at Craigielaw, locally altered by the sill, complete the table without a thickness. These historical measurements should not be averaged with the metric sections above.

Macnair’s 1917 numbered section. His 14-row table is also a wider-shore account. Ascending from his bed 1, it gives: 20 ft of grey-green shale and yellow sandstone; 8 ft of white coral limestone; 6 ft of grey shale and fireclay with twisted rootlets; 10 inches of coal; 12 ft of nodular dolomitic crinoidal limestone; 8 ft of sandy black shale; 4 ft of cross-bedded sandstone; 8 ft of shale; a locally developed 3-inch coal; 2 ft of hard grey limestone with historical Productus giganteus; 7 ft of shale; unmeasured thin coal and fireclay; 12 ft of hard grey crinoidal limestone with Productus giganteus; and unmeasured dark shale with a thin Craigielaw limestone. His numbers and correlation letters are historical, not modern bed or formation definitions. The account’s fish-remain discussion does not establish a Craigielaw bone bed.

Folding, faults and sediment-filled fissures. Two small north-west-trending faults beside Craigielaw raise the intervening block and repeat Middle and Upper Longcraig outcrops. The Survey places the crest of a north-west–south-east anticline approximately 250 m north-east of Craigielaw; a complementary syncline 200 m south-west of Aberlady Point belongs to the wider shore. Dip changes around these structures. Duff’s 5° southward dip at Aberlady Point is not a uniform Craigielaw dip. Sandstone dykes, 5–7 cm wide, cut Middle Longcraig near the anticline; they are sediment-filled fissures, distinct from the igneous intrusion.

Historical limestone analysis. The analysed limestone specimen SL 64, later catalogued as S34553 in the 1956 petrographic supplement, came from the shore 100 yd east of Garlic Rock. Its dolomitised crinoid, bryozoan and shell remains describe that wider-shore sample, not an analysis of the exact Craigielaw point or of the igneous sill.

Gosford Bay Sill. The western approach exposes an analcime-bearing olivine dolerite or gabbro sill, described in the later audit as olivine-analcime-gabbro. Local white-trap alteration and baking of adjacent sediments are recorded. It is an intrusive body rather than another limestone bed or a large dyke, and the sources used here do not establish a local measured sill thickness.

Younger shore deposits. Beach sand, shingle, raised-beach material and blown sand must be kept separate from the Carboniferous bedrock. The memoir records stratified blown sand with broken beach shells south of Craigielaw at NT 4467 7980, of uncertain age. Its main text and locality-table thickness conflict, so no reliable thickness is assigned here. A raised-beach exposure at NT 4512 8028, farther north-east on Kilspindie shore, has 0.75 m of shelly sand and pebbles; an 8 m OD back-feature is an elevation, not deposit thickness.

The younger shell fauna. The original memoir fauna table’s Craigielaw column records abundant shells under the historical names Rissoa parva interrupta and Venus striatula, with common Hydrobia ulvae, Cerastoderma edule, Donax vittatus and Mytilus edulis, among a much broader molluscan assemblage. Those beach-derived shells in blown sand are not fossils of the coral limestone. Nor are the modern borings beneath Blackhall evidence of Carboniferous animals living within that rock.

References

Howell, H. H., Geikie, A. and Young, J. (1866). The Geology of East Lothian, pp. 54 and 76.
Clough, C. T. and colleagues (1910). The Geology of East Lothian, second edition, pp. 139–141 and Figure 7.
Macnair, P. (1917). The Hurlet Sequence in the East of Scotland and the Abden Fauna as an Index to the Position of the Hurlet Limestone. Proceedings of the Royal Society of Edinburgh 37, 173–209; issued 25 June 1917, bound volume dated 1918.
Robertson, T., Simpson, J. B. and Anderson, J. G. C. (1949). The Limestones of Scotland. Geological Survey mineral-resources memoir, volume 35, p. 93.
Muir, A., Hardie, H. G. M., Mitchell, R. L. and Phemister, J. (1956). Limestones of Scotland: Chemical analyses and petrography, specimen SL 64 / S34553.
Sutherland, A. (1978). The coral fauna of the Middle Longcraig Limestone at Aberlady Bay. The Edinburgh Geologist 3, 1–5.
McAdam, A. D. and Tulloch, W. (1985). Geology of the Haddington district. British Geological Survey memoir, coastal table, Figure 13 and locality-specific fossil records.
Karbub, A. M. (1993). Foraminiferal Biostratigraphy and Microfacies of the Lower Carboniferous rocks, Central Scotland. MPhil thesis, University of Edinburgh, pp. 30–36, Figure 2.2 and Section 2 occurrence charts.
Duff, P. McL. D. (1996). Gosford Bay–Aberlady Point, in Lothian Geology: An Excursion Guide, edited by A. D. McAdam and E. N. K. Clarkson, stops 4–8.
Browne, M. A. E. and colleagues (1999). A lithostratigraphical framework for the Carboniferous rocks in the Midland Valley of Scotland. BGS RR/99/07, Table 4; BGS Lexicon entries for Aberlady and Lower Limestone formations and the Blackbyre, Inchinnan and Blackhall horizons.
British Geological Survey (2015). East Lothian geodiversity audit: Kilspindie Shore, ELC 14, OR/14/063, pp. 91–97.
Cózar, P. and Somerville, I. D. (2020). Regional East Lothian foraminiferal reassessment, Earth and Environmental Science Transactions of the Royal Society of Edinburgh 111, 193–207, doi:10.1017/S1755691020000092.