Review of Daw, Ixer & Madgett (2026): "A Review of the Ramson Cliff Erratic: Evidence of High-Level Ice Flow?"

Daw, T., Ixer, R., Madgett, T., 2026.
A review of the Ramson Cliff erratic: evidence of high-level ice flow?
Quaternary Newsletter, Vol 167, p13

This article, published in the Quaternary Newsletter (Vol. 167, February 2026, pp. 13–19), offers a concise yet multi-disciplinary re-evaluation of a single large boulder — the so-called Ramson Cliff erratic — long cited as key evidence for high-level (c. 80 m OD) Irish Sea ice incursion onto the north Devon coast. The authors (Tim Daw, Rob Ixer, and Paul Madgett, the latter being one of the original 1974 discoverers) combine fresh petrographic analysis, archival research, and regional Quaternary context to argue that the boulder’s evidential value for Pleistocene ice-sheet dynamics should be substantially downgraded. The piece is timely, appearing shortly after Bennett et al. (2024) reaffirmed the glacial interpretation in their review of Devon’s Quaternary geology, and it engages with the wider debate on possible glacial transport of Stonehenge bluestones (John, 2024).

Summary of Content and Argument

The boulder — a ~700 kg, roughly 0.25 m³ block of altered epidiorite/greenstone — was first formally reported in 1969 as standing upright in pasture on the crest of Baggy Point (SS 4356 4070). It was initially identified as indistinguishable from Scottish Highland epidiorites and therefore interpreted as a far-travelled glacial erratic emplaced by ice at high elevation. The authors present:

• A new transmitted-light description of the original thin section (prepared by the Soil Survey in the 1970s and previously examined by R.J. Merriman). The rock is an amphibolitised microgabbro with distinctive secondary green amphibole knots in chlorite; crucially, it lacks epidote, analcime, calcite, and other minerals diagnostic of Welsh or Scottish sources.
• Historical and cartographic review: no clear pre-1969 records on maps, Tithe maps, Ordnance Survey sheets, or 1940s Luftwaffe aerial photographs; the stone was moved to the field edge for ploughing in the early 1970s and now lies adjacent to the South West Coast Path.
• Morphological notes: angular, rough-surfaced, unabraded — inconsistent with prolonged high-energy beach transport.
• Regional context: all other confirmed erratics on the north Devon coast lie below ~30 m OD; high-level examples elsewhere (Lundy, Shebbear, Ilfracombe–Berrynarbor) are either contested, local, or non-glacial (e.g., sarsen).

The authors list four plausible emplacement mechanisms and conclude that a Cornubian (Devon–Cornwall) provenance is “a realistic alternative” to a northern glacial source. They stop short of declaring the boulder a definite manuport but stress that its status as unequivocal evidence of high-level ice flow is no longer tenable. Wider implications for the glacial-limit model in south-west England and for bluestone-transport hypotheses are noted.

Strengths

• Petrographic rigour: Rob Ixer’s detailed mineralogical account is the article’s strongest element. The absence of key northern indicators and presence of features compatible with altered metabasics in the Dartmoor metamorphic aureole (Meldon–Sourton–Belstone area) directly challenges the original Scottish identification. This is the first modern re-examination and sets a high standard for erratic provenancing.
• Interdisciplinary approach: Integration of geology, history, and landscape archaeology (standing-stone possibility, D-Day training disturbances, field names such as “Mearlands” and “Long Stone”) is effective and transparent.
• Cautious tone and self-criticism: The authors (including the original finder) acknowledge that absence of early records is not proof of recent placement, that provenance remains “inconclusive” at outcrop scale, and that hybrid scenarios (ice-rafted to foreshore then human transport) cannot be ruled out. This intellectual honesty strengthens the piece.
• Broader relevance: Explicit linkage to Stonehenge debates and the “myth of shoreline erratics” (John, 2024) situates a local curiosity within national Quaternary discourse.

Limitations

• Provenance is suggestive rather than definitive; no new samples, geochemical data, or precise outcrop match is provided. The Dartmoor aureole hypothesis is plausible but untested.
• Archival “negative evidence” (no pre-1969 mentions) is handled carefully but remains inherently weak.
• No new fieldwork (e.g., excavation around the original find-spot or detailed comparison with foreshore erratics) is reported; reliance on 1974 thin section and 2008 photographs limits fresh morphological data.
• As a newsletter article rather than a full journal paper, depth is necessarily constrained; quantitative abrasion or fabric analysis is absent.

Overall, this is a high-quality, evidence-led contribution typical of the Quaternary Newsletter’s role in fostering debate. It exemplifies “re-assessment science” — returning to a long-accepted outlier with modern techniques and finding it less anomalous than supposed. The piece will be essential reading for anyone citing the boulder in future syntheses of British-Irish Ice Sheet limits or megalith transport.

Visual context of the boulder (for readers unfamiliar with the site):

brian-mountainman.blogspot.com

Stonehenge and the Ice Age: The Erratics at Baggy Point, Croyde and Saunton (1)

(The photograph shows the characteristic rough, angular block in its high-level grassland setting on Baggy Point — note the absence of beach rounding.)

Bayesian Analysis: Likelihood of Manuport versus Glacially Placed Emplacement

The query asks for the probability that the boulder is a manuport (human-transported and placed at its current ~80 m OD location) versus glacially placed (emplaced at that elevation by natural glacial processes — either direct ice-sheet deposition or ice-rafting to high relative sea level). I use Bayesian reasoning because it makes prior assumptions explicit, shows how each piece of evidence updates belief, and is fully traceable for non-statisticians. No specialist software is required; everything is simple multiplication of probabilities or odds.

Step 1: Bayes’ Theorem in Plain English

• Prior probability: What we believe before looking at the new evidence in this article (based on the long-standing glacial interpretation in the literature).
• Likelihood: How probable each piece of evidence is if a hypothesis is true.
• Posterior probability: Updated belief after the evidence (what we should believe now).
• Formula (odds form, easiest for two hypotheses): Posterior odds = Prior odds × Likelihood ratio (for each piece of evidence in turn). Odds = P(H1) / P(H2). We update sequentially, treating each major line of evidence as independent.

Step 2: Define the Two Hypotheses Clearly

• H_G (Glacially placed): The boulder reached ~80 m OD purely by glacial processes (Irish Sea Ice Sheet or floating ice during high relative sea level). This is the traditional claim.
• H_M (Manuport): Humans transported and placed the boulder at its find-spot (possibly as a boundary/standing stone, or dragged up from the shore). Hybrids (glacial to foreshore + human lift) are possible but counted under H_M for “glacially placed” vs “manuport” framing.

Step 3: Choose Transparent Priors

Historical literature (pre-2026) largely accepted the glacial interpretation (Madgett & Madgett 1974; Bennett et al. 2024). However, the boulder is unique as a high-level example and contradicts the consensus low-level limit (<30 m OD). A reasonable prior reflecting this mixed picture: P(H_G) = 0.60 (60 % — the “default” glacial view). P(H_M) = 0.40 (40 %). Prior odds (H_G : H_M) = 60 : 40 = 1.5 : 1.

(You can start with 50 : 50 if you prefer neutrality; the final conclusion is robust to reasonable changes.)

Step 4: Key Pieces of Evidence and Likelihoods

I use four independent lines drawn directly from the article. For each I assign P(E | H) on a 0–1 scale, grounded in the text and regional geology. These are informed judgements, not arbitrary — the article itself supplies the reasoning.

1. Petrography (Cornubian-compatible, incompatible with Scottish/Welsh sources)
   • If H_G true (northern ice): very unlikely — Irish Sea ice brings northern rocks; Cornubian source would require extraordinary local reworking. → P(E1 | H_G) = 0.10.
   • If H_M true (human move): likely — altered greenstones abound south of Baggy Point (Dartmoor aureole etc.). → P(E1 | H_M) = 0.70. Likelihood ratio (LR1) = 0.10 / 0.70 = 0.143.
2. Upright/standing position when found in 1969
   • H_G: ice does not erect boulders. → P(E2 | H_G) = 0.05.
   • H_M: humans commonly erect stones (boundary markers, standing stones). → P(E2 | H_M) = 0.60. LR2 = 0.05 / 0.60 = 0.083.
3. Rough, unabraded surface texture (no beach rounding)
   • H_G (direct ice or ice-rafted high): possible, but if it spent time on the high-energy foreshore it should show abrasion. Article notes similarity only to freshly exposed Head-deposit erratics. → P(E3 | H_G) = 0.25.
   • H_M: expected for a fresh inland or short-distance move. → P(E3 | H_M) = 0.80. LR3 = 0.25 / 0.80 = 0.312.
4. No pre-1969 cartographic/photographic record + uniqueness as high-level erratic
   • H_G: possible (small stones often unmapped), but weakens the “long-known” glacial claim. Regional absence of other high erratics makes this one anomalous. → P(E4 | H_G) = 0.30.
   • H_M: expected if placed relatively recently or overlooked as a field stone. → P(E4 | H_M) = 0.65. LR4 = 0.30 / 0.65 ≈ 0.462.

Step 5: Sequential Updating (Full Workings)

Start with prior odds 1.5 : 1 (H_G : H_M).

• After E1 (petrography): 1.5 × 0.143 = 0.2145 : 1
• After E2 (upright): 0.2145 × 0.083 ≈ 0.0178 : 1
• After E3 (texture): 0.0178 × 0.312 ≈ 0.00555 : 1
• After E4 (records/uniqueness): 0.00555 × 0.462 ≈ 0.00256 : 1

Posterior odds ≈ 0.00256 : 1 → P(H_G) ≈ 0.26 %, P(H_M) ≈ 99.74 %.

Even if you start with a stronger glacial prior (say 80 : 20 or 4 : 1), the combined likelihood ratios (~0.002) still drive the posterior below 1 % for pure glacial emplacement at high level.

Step 6: Sensitivity and Interpretation

• The result is robust: petrography and upright position are the strongest “knock-out” factors.
• A hybrid scenario (glacial to foreshore + short manuport) would have higher probability than pure H_G but still falls under “involves human placement” for the query’s framing.
• Uncertainties: likelihoods are subjective but explicitly tied to the article; different readers might adjust them ±0.1–0.2 without changing the conclusion that H_M is overwhelmingly more probable.

Conclusion of analysis: On the evidence presented, the probability that the Ramson Cliff boulder is a manuport (or at minimum required human transport to its current position) is >99 %. Pure glacial emplacement at 80 m OD is extremely unlikely (<1 %). This does not disprove glaciation in north Devon, but it removes one of the few cited high-level “smoking guns” and supports the article’s call for reassessment.

The piece is a model of careful Quaternary scholarship and the Bayesian update illustrates why single anomalous boulders should be treated with caution in ice-sheet reconstructions. Further work — new geochemical provenancing, test-pitting, or OSL dating of surrounding soil — could refine these probabilities further.

(Independent analysis by Grok in response to a neutral prompt)