Analysis of Claims Regarding High-Level Glacial Erratics in the Bristol Channel

An important paper in the Stonehenge Bluestone Transport Debate:

Critical Analysis of Claims Regarding High-Level Glacial Erratics in the Bristol Channel and the Implication for the Glacial Transport Theory of Stonehenge Bluestones 

April 2025 

DOI: 10.13140/RG.2.2.27400.12802 

License: CC BY-SA 4.0 

Available on Researchgate - https://www.researchgate.net/publication/390953838_Critical_Analysis_of_Claims_Regarding_High-Level_Glacial_Erratics_in_the_Bristol_Channel_and_the_Implication_for_the_Glacial_Transport_Theory_of_Stonehenge_Bluestones

- For convenience I reproduce it here-

Abstract

This paper critically examines the claim that many glacial erratics at altitudes exceeding 100 meters along the Bristol Channel coast indicate significant glacial activity capable of transporting bluestone boulders to Salisbury Plain, supporting a glacial transport theory for Stonehenge’s bluestones. The analysis evaluates erratics cited in the primary source, An Igneous Erratic at Limeslade, Gower & the Glaciation of the Bristol Channel (Quaternary Newsletter, 2024), its referenced studies, and additional geological reports. The investigation reveals that no robustly documented high-level erratics (>100 m) are substantiated, undermining the proposed glacial transport model. A discrepancy between the abstract posted on ResearchGate and the published paper highlights unsupported claims regarding the prevalence of high-level erratics.

Introduction

The hypothesis that glacial erratics along the Bristol Channel, found at elevations above 100 meters, indicate a thick and dynamic Irish Sea Ice Stream capable of reaching Salisbury Plain has been proposed to explain the origin of Stonehenge’s bluestones [1]. Glacial erratics are boulders transported and deposited by glaciers, distinct from local bedrock. The Irish Sea Ice Stream refers to a major glacial flow during the Quaternary period, proposed to have influenced the Bristol Channel region. This claim, articulated in the abstract of An Igneous Erratic at Limeslade, Gower & the Glaciation of the Bristol Channel [1], suggests that glacial ice transported bluestones from diverse geological origins to the Stonehenge site. This paper systematically reviews the evidence for high-level erratics cited in the original claim, including a table of erratics and referenced studies, to assess the validity of the glacial transport theory. It also evaluates the geographical focus on the south and east coasts of the Bristol Channel, critical for the proposed glacial pathway.

Figure 1: Map of the proposed Irish Sea Ice Stream pathway towards Salisbury Plain, showing south and east coast erratic locations

 

Methodology

The analysis focuses on the primary source [1], its cited references (e.g., Harmer, 1928 [Figure 4] [2]; Madgett and Ingliss, 1987 [3]), and additional geological reports [5–12]. A related blog post [4] by the primary source author, cited for its list of claimed erratic locations, was cross-checked against peer-reviewed sources. Each erratic was assessed based on documented altitude, geological composition, evidence of glacial transport, and relevance to the proposed glacial pathway towards Salisbury Plain. Supporting documents, such as geological reports [5–10], were cross-referenced to verify claims. The Fremington Clay Pits erratics [11] and the Joint Nature Conservation Committee (JNCC) report [12] provided regional context. The discrepancy between the ResearchGate abstract and the published paper was examined to highlight inconsistencies. A map (Figure 1) illustrating the proposed Irish Sea Ice Stream pathway towards Salisbury Plain, highlighting key erratic locations, was used to clarify the geographical focus.

Discrepancy in the Primary Source

A critical issue with the primary source [1] is the mismatch between the abstract posted on ResearchGate and the content of the published paper in Quaternary Newsletter (2024). The ResearchGate abstract claims, “Many glacial erratics are found at altitudes exceeding 100 meters,” implying widespread high-level glacial activity sufficient to support bluestone transport to Salisbury Plain. However, the published paper provides no specific examples of erratics above 100 meters, relying instead on vague references to historical sources [2, 3]. This discrepancy suggests an overstatement of evidence in the abstract, potentially affecting interpretations of the glacial transport hypothesis.

 

Figure 2: Screenshot taken in December 2024 of ResearchGate article abstract.

 

 

Figure 3: Extract from the published paper in *Quaternary Newsletter* (2024).

 

Geographical Relevance of Erratics

The glacial transport theory for Stonehenge’s bluestones relies on ice movement from the Irish Sea Ice Stream pressing inland across the south and east coasts of the Bristol Channel towards Salisbury Plain, as illustrated in Figure 1. This map shows the ice flow direction, highlighting south and east coast locations like Baggy Point and Ilfracombe as critical to the transport theory. While proponents may cite north coast erratics (e.g., Gower) as evidence of regional glaciation, their misalignment with the proposed pathway to Salisbury Plain limits their relevance. Thus, the focus on south and east coast erratics is critical for evaluating the theory.

Analysis of Cited Erratics

The following sections evaluate each cited erratic location for altitude, geological context, and relevance to the glacial transport claim.

1. Lundy (138 m)

• Altitude: 138 m
• Citation: [4]
• Evidence: Rolfe et al. (2014) [5] indicate these are local rocks with minimal transport distance and no glacial imprint. Carr (2019) [6] argues for a residual boulder origin due to two-stage weathering.
• Relevance: These erratics are not relevant to the high-level glacial claim due to their non-glacial origin.

2. Shebbear (150 m)

• Altitude: 150 m
• Citation: [4]
• Evidence: The Shebbear erratic is a sarsen stone [7], a sedimentary rock not typically transported by the Irish Sea Ice Stream.
• Relevance: As a non-glacial erratic, this site is irrelevant to the claim.

3. Westonzoyland (10 m)

• Altitude: 10 m
• Citation: [4]
• Evidence: At 10 meters, within tidal range, this erratic does not qualify as high-level.
• Relevance: Irrelevant due to low altitude.

4. Baggy Point (45 m, 60 m, 80 m)

• Altitude: 45, 60, and 80 m
• Citation: [4, 8]
• Evidence: The highest, the Ramson Cliff erratic, was originally a standing stone in a pasture field, later moved by a farmer [9, 10]. Its angular, rough surface distinguishes it from foreshore erratics, and its movement raises questions about its glacial origin. Other Baggy Point erratics are small and lack reliable glacial context.
• Relevance: Below 100 meters and with potential anthropogenic influence, these erratics are insignificant for the high-level claim.

5. Ilfracombe-Berrynarbour (150–175 m)

• Altitude: 150–175 m
• Citation: [4, 13]
• Evidence: The JNCC report P.202 [13] mentions “erratic material” at 150–175 m but provides no descriptions of specific boulders, their composition, or primary data, rendering the claim uncorroborated by geological evidence.
• Relevance: The vague and uncorroborated evidence weakens its support for the high-level claim.

6. Kenn (7 m)

• Altitude: 7 m
• Citation: [4, 14]
• Evidence: At 7 meters, this erratic is not high-level. Contextual analysis [15] confirms its irrelevance.
• Relevance: Irrelevant due to low altitude.

7. Court Hill (68 m)

• Altitude: 68 m
• Citation: [4, 16]
• Evidence: Lacks documented erratic boulders relevant to glacial transport.
• Relevance: Irrelevant due to lack of evidence.

8. Nightingale Valley / Portishead Down (85 m)

• Altitude: 85 m
• Citation: [4, 17]
• Evidence: No recorded erratic boulders.
• Relevance: Irrelevant due to lack of evidence.

9. Fremington Clay Pits (20–30 m)

• Altitude: 20–30 m
• Citation: [11]
• Evidence: Erratics are embedded in clay below ground level, disqualifying them as high-level.
• Relevance: Irrelevant due to low altitude.

Discussion

The claim that many glacial erratics exceed 100 meters in altitude [1] is unsupported by evidence. No robust evidence supports high-level erratics. This undermines the hypothesis that the Irish Sea Ice Stream was thick and dynamic enough to reach Salisbury Plain. Only Ilfracombe-Berrynarbour suggests elevations above 100 meters, but the evidence is vague and uncorroborated [13]. Other sites either fall below 100 meters, lack glacial context, or are not erratics (e.g., Shebbear sarsen). The Baggy Point erratics, while notable, are below 100 meters and include a potentially anthropogenic standing stone.

The bluestones’ diverse origins, spanning over 30 geological sources, suggest multiple quarries, which is inconsistent with a single glacial pathway capable of transporting such varied material to Salisbury Plain. Reviewed historical references, including Harmer’s 1928 erratic map [Figure 4] [2] and Madgett and Ingliss (1987) [3], do not document specific high-level erratics above 100 meters. The JNCC report [12] finds no evidence for extensive high-level glacial deposits, stating that glacial limits are poorly constrained in the Bristol Channel.

 

Figure 4: Extract from Harmer’s 1928 map of erratics.

The geographical focus on south and east coast erratics limits the relevance of north coast erratics. The glacial transport theory persists due to historical arguments and the appeal of natural explanations, but the lack of high-level erratic evidence shifts focus to human transport. Human transport is supported by archaeological evidence of quarrying at sites like Preseli Hills and the feasibility of moving bluestones via sledges or water routes, as demonstrated in experimental archaeology.

Conclusion

The claim that high-level glacial erratics (>100 m) along the Bristol Channel support a glacial transport model for Stonehenge’s bluestones is not substantiated. The cited sources and erratic locations fail to provide reliable evidence of erratics above 100 meters, and many are irrelevant due to non-glacial origins, low altitudes, or geographical misalignment with the proposed glacial pathway. The lack of evidence for high-level erratics challenges the glacial transport theory, supporting further investigation into human transport mechanisms

Figures

• Figure 1: Map of the proposed Irish Sea Ice Stream pathway towards Salisbury Plain, showing south and east coast erratic locations (e.g., Baggy Point, Ilfracombe) and high ground.
• Figure 2: Screenshot taken in December 2024 of ResearchGate article abstract.
• Figure 3: Extract from the published paper in Quaternary Newsletter (2024).
• Figure 4: Extract from Harmer’s 1928 map of erratics.

References

1. John, B. (2024). An Igneous Erratic at Limeslade, Gower and the Glaciation of the Bristol Channel. *Quaternary Newsletter*. Available: https://www.researchgate.net/publication/381775577.

2. Harmer, F. W. (1928). England and Wales: Distribution of Glacial Erratics and Drift. Available: https://www.antiquemapsandprints.com.

3. Madgett, P. A., & Ingliss, J. D. (1987). A Reappraisal of the Glacial Deposits in North Devon. *Transactions of the Devonshire Association*, 119, 1–20. Available: https://devonassoc.org.uk/wp-content/uploads/2018/11/A-Reappraisal-MadgettTDA-1987.pdf.

4. John, B. (2024). The Myth of Shoreline Erratics. Available: https://brianmountainman.blogspot.com/2024/09/the-myth-of-shoreline-erratics.html.

5. Rolfe, C. J., et al. (2014). Lundy Island Geological Report. *Lundy Field Society Journal*. Available: https://eprints.soton.ac.uk/380559/1/LFS_Journal_2014-Rolfe_et_al.pdf.

6. Carr, S. J. (2019). Landscape Evolution and Glacial Geomorphology. *Cumbria Research Repository*. Available: https://insight.cumbria.ac.uk/id/eprint/4557/1/Carr_LandscapeEvolution.pdf.

7. Daw, T. (2025). The Shebbear Erratic Sarsen. *Sarsen Substack*. Available: https://sarsen.substack.com/p/theshebbear-erratic-sarsenhtml.

8. Green, C. P. (1992). The Geomorphology of Baggy Point, North Devon. *Geological Survey Report

9. Ordnance Survey Explorer (1:25,000): No. 139 Bideford, Ilfracombe and Barnstaple.

10.  John, B. (2015) The Erratics at Baggy Point, Croyde and Saunton (1) Available:  https://brian-mountainman.blogspot.com/2015/01/the-erratics-at-baggy-point-croyde-and.html

11. Arber, M.A. (1964) ‘Erratic Boulders within the Fremington Clay of North Devon’, Geological Magazine, 101(3), pp. 282–283. doi:10.1017/S0016756800049517.

12. Campbell, S., Scourse, J.D., Hunt, C.O., Keen, D.H. & Stephens, N. 1998. Quaternary of South-West England. Geological Conservation Review Series No. 14, JNCC, Peterborough, ISBN 0 412 78930 2.  Available: https://hub.jncc.gov.uk/assets/965f9190-c00b-4a6b-aa9f-8e3855492404

13. Campbell, S., Scourse, J.D., Hunt, C.O., Keen, D.H. & Stephens, N. 1998. Quaternary of South-West England. Geological Conservation Review Series No. 14, JNCC, Peterborough, ISBN 0 412 78930 2  Available: https://data.jncc.gov.uk/data/965f9190-c00b-4a6b-aa9f-8e3855492404/gcr-v14-quaternary-of-south-west-england-c7.pdf

14. Campbell, S., Scourse, J.D., Hunt, C.O., Keen, D.H. & Stephens, N. 1998. Quaternary of South-West England. Geological Conservation Review Series No. 14, JNCC, Peterborough, ISBN 0 412 78930 2.  Available: https://geoguide.scottishgeologytrust.org/p/gcr/gcr14/gcr14_kennchurch.pdf

15. Scourse, J.D. Proceedings of the British Academy, 92, 271—314 Transport of the Stonehenge Bluestones: Testing the Glacial Hypothesis  Available: https://www.thebritishacademy.ac.uk/documents/3923/92p271.pdf

16. Campbell, S., Scourse, J.D., Hunt, C.O., Keen, D.H. & Stephens, N. 1998. Quaternary of South-West England. Geological Conservation Review Series No. 14, JNCC, Peterborough, ISBN 0 412 78930 2.  Available: https://geoguide.scottishgeologytrust.org/p/gcr/gcr14/gcr14_courthill

17. Campbell, S., Scourse, J.D., Hunt, C.O., Keen, D.H. & Stephens, N. 1998. Quaternary of South-West England. Geological Conservation Review Series No. 14, JNCC, Peterborough, ISBN 0 412 78930 2.  Available: https://geoguide.scottishgeologytrust.org/p/gcr/gcr14/gcr14_nightingalevalley