How the re-reading of the Shebbear stone and the Ramson Cliff boulder removes the high-level evidence for Irish Sea ice on the North Devon cliffs — and what is left standing once they are gone.
The Shebbear Sarsen
For the better part of two centuries the erratic boulders of the North Devon coast have been read as evidence that ice once reached, and in places rode over, this shore. Two stones carried more of that argument than the rest: the Devil’s Stone at Shebbear, and the block at Ramson Cliff on Baggy Point, sitting at about 80 m above Ordnance Datum. Both have now been looked at again. Neither survives the examination as a far-travelled glacial erratic. With them set aside, the North Devon record is a good deal more uniform than the textbooks allow, and the explanation that fits it best is not an overriding ice sheet but ice rafting onto a shore platform standing under a high relative sea level.
How we got here
The story begins in 1837, with the first report of a large non-local boulder at the foot of the Saunton cliffs. It belongs to a wider Victorian preoccupation. When the Boulder Committees were set up — the Scottish committee in 1871, the British Association committee reporting annually from 1873 to 1914 — the question they were chartered to settle was precisely ours: were the erratics of Britain and Ireland dropped from floating ice, or dragged by grounded glaciers? By the end of the century the answer for the country at large had gone to grounded ice, and that has remained the default reading of an erratic ever since.
The South West was always the awkward exception. The early catalogues — Prestwich (1892), Worth (1898), Ussher (1904), Reid and Scrivenor (1906), Reid (1907), and for North Devon’s igneous material Dewey (1910) — described foreign blocks strung along coasts and dredged from the sea floor, including the boulders Hunt recovered from the Salcombe fishing grounds well out in the Channel and the Giant’s Rock at Porthleven (Flett and Hill, 1912). A great many of these stones lie south and east of any limit a British or Irish ice sheet has ever been shown to reach. For those, grounded ice is not on the table; floating ice is the only carrier left. Rafting, in other words, is not a hypothesis in the South West but a demonstrated fact — the only open question has been how far its reach extends.
North Devon sat closer to the supposed ice, and so the older argument ran hotter there. Taylor (1956, 1958) catalogued the Saunton and Fremington erratics; the interpretation then split. Mitchell (1960, 1965) and Kidson (1971, 1977; Kidson et al., 1977) read the giant coastal blocks as the work of a regional ice sheet, generally placed in the Anglian or earlier. Stephens (1966, 1970, 1974) read them as rafted, and his positive argument is the one that has worn best: the largest erratics are confined to a narrow coastal band below about 9 m OD, within reach of present storm waves — a strange, selective distribution for an ice sheet that supposedly buried the ground, and exactly what one would expect of stones grounded out of floating ice at a former shoreline.
Into that argument came a wrinkle. Every North Devon erratic on record up to 1969 lay at the base of the cliffs. The block found afterwards on top of Baggy Point, at roughly 80 m OD, was first noted by Madgett & Madgett (1974) and formally described (as part of the full Saunton–Croyde erratic suite) by Madgett & Inglis (1987), did not fit. It became the high-level evidence: the one stone that seemed to require ice standing well above the present coast, riding over the headland rather than lapping its foot. The Devil’s Stone at Shebbear, higher still and inland, was pressed into the same service. Between them they propped up the reading that North Devon had been overrun, not merely fringed, by Irish Sea ice.
The standard synthesis, Campbell et al. (1998) in the Quaternary of South-West England volume of the Geological Conservation Review, left the ice-sheet-versus-rafting question formally open. The Fremington context was filled in by Croot et al. (1996), and the regional ceiling for independent ice was fixed by Evans et al. (2012), who identified the Dartmoor ice cap as the southernmost independent Pleistocene ice cap in the British Isles. Then the marine record tightened the limits hard. The BRITICE–CHRONO programme — Smedley et al. (2017), Scourse et al. (2021), Clark et al. (2022) — showed that the last Irish Sea Ice Stream pushed all the way to the Celtic Sea shelf break, but that its southernmost terrestrial ice stood on the Isles of Scilly at about 25 ka. Scilly is to the west; North Devon lies east of it, tucked into the inner Bristol Channel. And Scourse et al. (2024) supplied the missing mechanism for the low coastal erratics: early in the last cold stage a steep, ice-loaded crust held relative sea level high enough, while calving margins still existed, for ice to raft material onto southern shore platforms during Marine Isotope Stages 4 and 3. For the first time there was a dated, physical route by which the Saunton and Croyde blocks could have arrived where they sit, without an ice sheet ever touching them.
The two boulders, looked at again
The Shebbear stone is the simpler case. Read as a local silcrete — a sarsen, sitting on or close to its parent duricrust — it is not a travelled stone at all. It records the survival of a hard cap, not the passage of ice, and it never had any business in a discussion of transport mechanisms. A boulder that has gone nowhere tells you nothing about how far ice came.
Ramson Cliff is the consequential one, because it was the stone that seemed to demand grounded ice high above the coast. In A review of the Ramson Cliff erratic: evidence of high-level ice flow? (Quaternary Newsletter 167, 2026), Rob Ixer, Paul Madgett — one of those who recorded the block in the first place — and I went back to the original thin section and the archival record. The petrography is fully compatible with the altered greenstones of the Cornubian metamorphic aureole, and carries none of the diagnostic Scottish or Welsh minerals that a far-travelled provenance would require. The block has no documentary existence before 1969: no map, no photograph. It was first noticed standing upright in pasture. It shows none of the abrasion a marine or shore-platform history would leave. And it is the only claimed high-level erratic on the entire south Bristol Channel coast — a population of one, at an anomalous height, pointing nowhere distant.
An angular block of local greenstone, standing upright, unworn, undocumented before living memory, alone at its elevation. On the balance of the evidence that is a manuported stone, not a glacial one; and its value as proof of high-level ice should be reassessed accordingly.
What this changes
Take Shebbear and Ramson Cliff out of the account and a plain fact emerges: there is no longer any demonstrated far-travelled boulder above the coastal zone in North Devon. The genuinely foreign material — the Saunton “pink granite”, the granulite gneiss at Freshwater Gut, and the petrographically interesting coastal clasts such as Taylor’s No. 7 with its apparent Irish Sea affinities — is all low. All of it sits on or about the shore platform and the raised beach, in the narrow band below storm-wave reach.
That is, to the letter, the distribution Stephens flagged half a century ago, now stripped of the high-level counter-examples that always sat awkwardly beside it. It is also exactly what the glacio-isostatic, high-sea-level rafting model of Scourse et al. (2024) predicts. And it leaves nothing on the headlands to require a thick ice sheet riding over them.
The argument therefore reframes. The live alternative to rafting is no longer “grounded ice at 80 m” — that reading has lost the only stones that supported it — but the far more modest “low-level grounded ice reaching about the present coastline.” That remains geographically admissible for North Devon in a way it never was for the south coast, where the erratics lie wholly beyond any reconstructed ice limit and rafting is effectively compelled. A single boulder resting on a shore platform is genuinely hard to assign between a grounded margin standing at the coast and ice that floated there. But three things now tilt the balance toward rafting: the distribution is the wrong shape for an overriding sheet; there is a dated mechanism for rafting onto a high shore platform; and the absence of any surviving high-level erratic is itself an argument that no thick ice overrode these cliffs.
What it does not change
This is the better-supported position, not the agreed one. Bennett et al. (2024), in their recent review of Devon’s Quaternary, (published before the re-examination reported here), restated the glacial reading, and the matter is not closed. Nor does any of it disprove glaciation in North Devon; it removes two pieces of evidence that were doing more work than they could bear. If there is a moral, it is a dull methodological one that cuts in every direction: a single anomalous boulder is a poor foundation for an ice sheet. The Ramson Cliff block was carrying an ice margin on its back. It turns out to have been carried there by people.
The North Devon erratics are best read not as the wreckage of an ice sheet that climbed the cliffs, but as the marine signature of a high relative sea level with calving ice somewhere offshore. The two stones that seemed to say otherwise were, on inspection, saying something else entirely — one a local stone that never moved, the other a stone that moved, but not by ice.
References
Bennett, J.A., Cullingford, R.A., Gibbard, P.L., Hughes, P.D. & Murton, J.B. (2024). The Quaternary Geology of Devon. Proceedings of the Ussher Society 15, 84–130.
Campbell, S., et al. (1998). Quaternary of South-West England. Geological Conservation Review Series, No. 14. Joint Nature Conservation Committee, Peterborough.
Clark, C.D., et al. (2022). Growth and retreat of the last British–Irish Ice Sheet, 31 000 to 15 000 years ago: the BRITICE–CHRONO reconstruction. Boreas 51. https://doi.org/10.1111/bor.12594
Croot, D.G., Gilbert, A., Griffiths, J. & van der Meer, J.J. (1996). The character, age and depositional environments of the Fremington Clay Series, North Devon. Quaternary Newsletter 80: 1–15.
Daw, T., Ixer, R. & Madgett, P. (2026). A review of the Ramson Cliff erratic: evidence of high-level ice flow? Quaternary Newsletter 167: 13–19. https://doi.org/10.64926/qn.20517
Dewey, H. (1910). Notes on some igneous rocks from North Devon. Proceedings of the Geologists’ Association 21(4): 429–434.
Evans, D.J.A., Harrison, S., Vieli, A. & Anderson, E. (2012). The glaciation of Dartmoor: the southernmost independent Pleistocene ice cap in the British Isles. Quaternary Science Reviews 45.
Madgett, P. & Madgett, R. (1974). High level erratic on Baggy Point. Quaternary Newsletter 14: 1–2.
Madgett, P.A. & Inglis, A.E. (1987). A re-appraisal of the erratic suite of the Saunton and Croyde areas, North Devon. Transactions of the Devonshire Association 119: 135–144.
Scourse, J.D., et al. (2021). Maximum extent and readvance dynamics of the Irish Sea Ice Stream and Irish Sea Glacier since the Last Glacial Maximum. Journal of Quaternary Science 36. https://doi.org/10.1002/jqs.3313
Scourse, J.D., et al. (2024). The timing and magnitude of the British–Irish Ice Sheet between Marine Isotope Stages 5d and 2: implications for glacio-isostatic adjustment, high relative sea levels and ‘giant erratic’ emplacement. Journal of Quaternary Science. https://doi.org/10.1002/jqs.3611
Smedley, R.K., et al. (2017). New age constraints for the limit of the British–Irish Ice Sheet on the Isles of Scilly. Journal of Quaternary Science 32. https://doi.org/10.1002/jqs.2922
Veness, et al. (2025). Modelling erratic dispersal accounting for shifting ice flow geometries. Journal of Quaternary Science. https://doi.org/10.1002/jqs.3720
