Two new papers have kindly been brought to my notice -- each written by Bevins and Ixer together with assorted geological colleagues. They don't currently seem to be behind paywalls, but I have copies which I can supply as Email attachments on request.
Here are the details:(1) Treasures in the Attic: Testing Cunnington’s assertion that Stone 32c is the ‘type’ sample for Andesite Group A
by Rob A. Ixer, Richard E. Bevins, Duncan Pirrie and Matthew Power.
Wilts Archaeol & Nat Hist Magazine, vol. 116 (2023), pp. 1–15
In 1881 William Cunnington excavated and sampled buried Stone 32c from within the Stonehenge Circle and described it as a ‘calcareous chloritic tuff’. He suggested that it was the source (type material) for similar looking debitage within the Stonehenge Landscape. Last described fifty years ago his original thin sections have been rediscovered and their investigation has shown that it was a reasonable conclusion based on his limited sampling. However, twenty first century investigations of thousands of pieces of this debitage, now defined as Andesite Group A (formerly Volcanic Group A), show it to possibly comprise two sub-groups, one being calcite-rich and the other being calcite-poor. Thin sections from Stone 32c show many of the characteristics of the calcite-bearing sub-group, but fewer of the calcite-poor sub-group but, for the present, Stone 32c is assigned as the type material for all Andesite Group A. However, Stone 32c may be the sole parent to all Andesite Group A debitage or only its calcite-bearing sub-group or it may share parentage for some or all of Andesite Group A with at least four other, as yet unsampled, stones (33e, 33f, 40c and 41d) buried within the Stonehenge Circle. Further research will answer these questions.
(2) The Stonehenge Altar Stone was probably not sourced from the Old Red Sandstone of the Anglo-Welsh Basin: Time to broaden our geographic and stratigraphic horizons?by Richard E. Bevins, Nick J.G. Pearce, Rob A. Ixer, Duncan Pirrie, Sergio Ando, Stephen Hillier, Peter Turner, Matthew Power.
Journal of Archaeological Science: Reports 51 (2023) 104215
It has to be pointed out that that conclusion is wildly premature, since it is simply not well enough supported by the evidence base. Only 58 ORS samples from the map area have been analysed, and there has been hardly any new fieldwork. Altar Stone readings show Ba concentrations across a wide range, from below 1000 ppm to almost 6000 ppm, suggesting to me that BA may not be a very reliable indicator. Outcrops from across thousands of square kilometres of "candidate territory" have simply not been sampled at all, and the database shows that there are vast variations in lithology and geochemistry within the areas of outcropping sandstones. The problem is a common one -- too much speculation and not enough evidence.
This is of course all nonsense. First of all, the geologists define the term "bluestone" so narrowly that it excludes all the inconvenient foreign clasts at Stonehenge, and now they want to define it even more narrowly so that it excludes anything that does not demonstrably come from Mynydd Preseli. This is not the way to do science. It's bad enough that the authors of this article completely ignore the possibility of glacial transport or other transport mechanisms, but we are now into the theatre of the absurd.