Review: Bluestone Fragments at Silbury Hill – Resolving Provenance and Prehistoric Significance

 

(Dolerite Chip in the Alexander Keiller Museum - Tim Daw)

The discovery of Stonehenge bluestone fragments from the top of Silbury Hill has provoked enduring debate, amid stratigraphic and petrological ambiguities. In the latest WANHM, Wiltshire Archaeological and Natural History Magazine, Ixer, Bevins, and Pollard (2025),  https://www.academia.edu/144003051/Slbury_Hill_lithics ,  provide a meticulous reappraisal, synthesising archival data with advanced microscopy to affirm these as deliberate human-transported debitage. A pivotal contribution lies in clarifying the corpus's fraught discovery history, particularly the discrepancy between Atkinson's published account—mentioning only a volcanic tuff—and the separate archival identification of a spotted dolerite via a museum label, a mismatch that has long muddled interpretations.

Five fragments comprise the corpus: four flaked spotted dolerites ('preselite') and one volcanic tuff (initially termed 'volcanic ash'). Atkinson's 1970 Antiquity note records just one find from an "undisturbed" summit context: the tuff fragment (Wilts 391), macroscopically identified as akin to Stonehenge's volcanic ash bluestone and recovered from clean chalk rubble ~0.7 m below the surface (Atkinson 1970, 314). Its pairing with a 'Windmill Hill ware' sherd—later deemed likely Anglo-Saxon—hinted at disturbance, undermining claims of Neolithic integrity. Unmentioned in Atkinson’s account but documented via a bag label in the Alexander Keiller Museum archive, is a second fragment from the 1969 topsoil: a spotted dolerite specimen. Three additional spotted dolerites surfaced from 2007 subsoil excavations, all lacking secure prehistoric associations (Ixer 2013). This selective reporting—overlooking the labelled dolerite—has sown confusion, with the tuff often conflated with the dolerite or dismissed as intrusive, as noted in subsequent syntheses (Field & Leary 2010, 60–61).

Post-excavation analyses amplified uncertainties. Wilts 391, the thin section derived from Atkinson's tuff fragment and prepared in the 1970s for the South West Implement Petrology Collection, was erroneously identified by R. V. Davis as Cornish hornblende schist, emphasising 'decomposed feldspar' (misread sparry calcite) while disregarding its clastic tuff fabric and Atkinson's macroscopic assessment (Clough & Cummins 1988, 162). The original rock specimen vanished, likely consumed in sectioning, prompting further conflations. Such lapses, compounded by incomplete documentation, invited speculation of post-Neolithic intrusion—via antiquarian activity or medieval remodelling (Field & Leary 2010, 60–61).

Ixer et al. (2025) disentangles this 'conundrum' through rigorous petrography, confirming all five as Stonehenge-sourced debitage and explicitly resolving the Atkinson-label disconnect by cross-referencing museum records with fieldwork archives. Wilts 391 exemplifies calcite-bearing Andesite Group A tuff, with limonite-stained 'rhyolite' clasts (fine-grained white mica-albite-chlorite-quartz intergrowths), vesicular lava inclusions, and tension gashes—hallmarks matching buried orthostat 32c from north Pembrokeshire's Fishguard Volcanic Group (Ixer et al. 2023). The dolerites, including the labelled 'Museum' piece, exhibit ophitic textures, epidotisation, and spinel spots diagnostic of 'preselite'. This validates Atkinson's intuition while exposing Davis's oversights, attributing the sherd to localised disturbance rather than wholesale rejection of Neolithic deposition.

Crucially, the authors dismiss glacial transport—once invoked for bluestone dissemination (e.g., Ixer 2009)—citing the flakes' knapped morphology, sub-centimetre scale, and orthostat-specific matches, which preclude Ice Age entrainment. Instead, they propose intentional Late Neolithic conveyance and deposition during Silbury's final phases (~late 24th/early 23rd century BC; Marshall et al. 2013), likely by Beaker-period groups effecting ritual fragmentation. This echoes Darvill and Wainwright's (2009) model for Stonehenge and parallels Cheviot granodiorite at West Kennet palisade (Ixer et al. 2022), suggesting token exotics as apotropaic or mnemonic elements in a networked monumental landscape (Richards et al. 2020).

As a review, Ixer et al. excels in transforming archival detritus into interpretive clarity, elevating these four small dolerite chips and single tuff flake to evidence of modest Wessex-wide mobility—chiefly by demystifying the Atkinson-dolerite enigma. Whether the fragments derive from a single larger piece or multiple orthostats remains unresolved, though their petrological affinities suggest the four dolerite chips are all off one block. Only Wilts 391 enjoys unambiguous Neolithic security, however, tempering conclusions.

My own speculative thought experiment based on the overland bluestone transport hypothesis positing an A40-aligned route from Preseli, with a River Severn crossing near Gloucester (Parker Pearson et al. 2015) the Avebury landscape lies on this natural route to Stonehenge.  Are the chips from Stonehenge or souvenirs of a passing monolith, maybe from initial shaping nearby?

References

Atkinson, R.J.C., 1970. Silbury Hill, 1969–70. Antiquity, 44, pp.313–314. Available at: https://doi.org/10.1017/S0003598X00104582 

Clough, T.H.McK. & Cummins, W.A. (eds.), 1988. Stone Axe Studies Volume 2: The petrology of prehistoric stone implements from the British Isles. Council for British Archaeology Research Report 67, London. ISBN: 0-906780-52-7. Available at: https://www.cambridge.org/core/journals/antiquity/article/reviews-t-h-mck-clough-w-a-cummins-ed-stone-axe-studies-2-the-petrology-of-prehistoric-stone-implements-from-the-british-isles-279-pages-42-figures-240-tables-3-maps-1988-london-council-for-british-archaeology-research-report-67-isbn-0906780527-paperback-35/4D955A236D2703A06740E01B2E4C44AE 

Darvill, T. & Wainwright, G., 2009. Stonehenge excavations 2008. The Antiquaries Journal, 89, pp.1–19. DOI: 10.1017/S000358150900002x. Available at: https://eprints.bournemouth.ac.uk/11797/ 

Field, D. & Leary, J., 2010. The Story of Silbury Hill. English Heritage, Swindon. ISBN: 9781848020467. Available at: https://books.google.nl/books/about/The_Story_of_Silbury_Hill.html

Ixer, R.A., 2013. The spotted dolerite fragments. In: Leary, J., Field, D., & Campbell, G. (eds.) Silbury Hill: the largest prehistoric mound in Europe, pp.60–61. English Heritage, Swindon.

Ixer, R.A., Bevins, R.E., Pirrie, D. & Power, M., 2023. Treasures in the Attic: Testing Cunnington's assertion that Stone 32c is the ‘type’ sample for Andesite Group A. Wiltshire Archaeological and Natural History Magazine, 116, pp.40–52. https://pure.southwales.ac.uk/en/publications/treasures-in-the-attic-testing-cunningtons-assertion-that-stone-3

Ixer, R, Bevins, R, Pearce, N, Pirrie, D, Pollard, J, Finlay, A, Power, M & Patience, I 2025, 'Exotic granodiorite lithics from Structure 5 at West Kennet, Avebury World Heritage Site, Wiltshire, UK', Wiltshire Archaeological and Natural History Magazine, vol. 118, pp. 1-18. Available at: https://www.academia.edu/125773662/West_Kennet_Granodiorites [

Ixer, R.A., Bevins, R.E. & Pollard, J., 2025. Bluestones from Silbury Hill. Wiltshire Archaeological & Natural History Magazine, 118, pp.269–278. Available at: https://www.academia.edu/144003051/Slbury_Hill_lithics

Marshall, P., Bayliss, A., Leary, J., Pollard, J., Vallender, J. & Young, G., 2013. The Silbury chronology. In: Leary, J., Field, D. & Campbell, G. (eds.), Silbury Hill: the largest prehistoric mound in Europe, pp.97–116. English Heritage, Swindon.

Parker Pearson, M. et al. (2015) ‘Craig Rhos-y-felin: a Welsh bluestone megalith quarry for Stonehenge’, Antiquity, 89(348), pp. 1331–1352. https://www.cambridge.org/core/journals/antiquity/article/craig-rhosyfelin-a-welsh-bluestone-megalith-quarry-for-stonehenge/D1E66A287D494205D22881CBF1F6DDE8 .

Richards, C., Bayliss, A., Beadsmoore, L., Bronk Ramsey, C., Card, N., Dunbar, E., et al., 2009. The date of the Greater Stonehenge Cursus. Antiquity, 83(319): pp.40–53. DOI: 10.1017/S0003598X00099363.  Available at: https://www.researchgate.net/publication/233882913_The_Date_of_the_Greater_Stonehenge_Cursus