The Catalogue of the Wessex Museum Stonehenge Rock Thin Sections

William Cunnington Stonehenge rock thin sections - Catalogue

Rob Ixer and Richard Bevins

https://www.academia.edu/144337293/Cunningtons_Stonehenge_rocks_an_archive_of_the_thin_section_data

Salisbury Museum Accession Number 1983.20.47 - Patricia Cane

This catalogue, compiled by Rob Ixer and Richard Bevins in February 2025, documents 33 Victorian-era thin sections of Stonehenge rock fragments collected by William Cunnington between 1878 and 1881. These samples, primarily surface finds from within the Stonehenge circle and nearby excavations, represent an unbiased assortment of 'foreign rocks' (bluestones), excluding sarsens, and include the last known surface fragments from the monument's interior. The authors pair the thin sections—housed at the Wiltshire Museum—with corresponding hand specimens at the Salisbury Museum, providing macroscopic and microscopic petrographic descriptions. Historical identifications from researchers like Thomas Davies in Cunnington (1884), J.J.H. Teall (1894), and John Judd (1903), alongside later work by A.C. Harrison et al. (1979), are reconciled with modern nomenclature from Ixer and Bevins' ongoing studies (2010–2024). This reveals strong consistency in lithological groupings, such as spotted dolerites, rhyolitic tuffs from Craig Rhos-y-felin, and carbonate-bearing andesites, while debunking outdated names that have exaggerated the diversity of bluestone types to support glacial erratic theories. The collection's representativeness allows direct comparison with other Stonehenge debitage assemblages, affirming a restricted suite of Welsh-sourced volcanics and sandstones and the Scottish Altar Stone.

The detailed analyses in the appendices cover eight dolerites (including first petrographic descriptions of orthostats SH32 and SH61a), seven Rhyolite Group C tuffs, five Andesite Group A samples (with SH32c as type material), six Dacite Group B tuffs (type from SH38), one each of Dacite Group D, Altar Stone sandstone, and Greensand, plus three Lower Palaeozoic Sandstones. No novel rock types emerge, but the work highlights challenges like slide thickness and discolouration, which complicate observations. Appendices provide exhaustive microscopic descriptions, noting alterations (e.g., epidotisation, chloritisation) and key minerals (e.g., clinopyroxene, plagioclase, titanite). The authors advocate re-preparing polished thin sections for rarer lithologies and undescribed orthostats to enable advanced techniques like automated mineralogy.

Key Takeaways

• Representativeness and Consistency: The Cunnington collection mirrors other bluestone debitage from the Stonehenge landscape, comprising a narrow range of lithologies (e.g., dolerites, rhyolites, andesites, sandstones), reinforcing human transport from Wales over glacial deposition models.
• Nomenclature Updates: Modern reclassifications eliminate obsolete terms, clarifying that the bluestone suite is far less diverse than previously suggested, with most of the rhyolites tracing to Craig Rhos-y-felin and dacites distinguishing clearly in thin section.
• New Insights on Orthostats: First-time petrographic data for stones SH32, SH32c (type for Andesite Group A), SH49, and SH61a, plus expanded recognition of Dacite Group B debitage from SH38, potentially indicating wider distribution.
• Validation of Rare Groups: Confirms Dacite Group D as a legitimate bluestone lithology, based on this and prior finds, challenging its prior dismissal as non-monumental.
• Recommendations for Future Work: Re-sectioning key samples for polished slides is urged to support geochemical and mineralogical provenance studies.