Stonehenge rhyolitic bluestones were sourced by Thomas (1923) to Carn Alw, Wales.
Recent geochemical investigations have questioned that west Wales source.
The original thin sections studied by Thomas have been re-investigated in this study.
Thomas's proposed provenance of the Stonehenge rhyolites to Carn Alw is disproven....
The new petrographical evidence demonstrates convincingly that the two pairs of thin sections from the Preseli and Stonehenge as examined by Thomas do not match despite his contention and argues strongly that Carn Alw is not the source of the Stonehenge rhyolites which Thomas described. This reinforces the geochemical evidence presented recently and supports the contention that Craig Rhos-y-felin, to the north of Mynydd Preseli, is an important source of rhyolitic debris in the Stonehenge Landscape. Nevertheless, there remain uncertainties over the provenance of other Stonehenge rhyolites (and dacites), including four of the orthostats themselves.