Norman Hammond’s piece in Today’s Times (“Bluestones theory is now frozen out”) highlights the work by Richard Bevins and Rob Ixer on the precise origins of the Stonehenge bluestones. This is landmark stuff, and worth trying, briefly, to summarise.
There’s a lot of stone debris under the ground at Stonehenge, and more in the area around. For much of the 20th century the former was known as the “Stonehenge layer”. William Hawley associated it with the original dressing of megaliths (hence, any pits found below it were said to be older than the standing stones), while Richard Atkinson thought it derived from destruction of the stones, and was largely post-medieval or modern. As I found at my small excavation on the roadside in 1980, at least some of this debris almost certainly is prehistoric. At the time, I claimed it was contemporary with the carving of the stones. Mike Parker Pearson and Tim Darvill would now like to associate it with prehistoric stone destruction; on available evidence, I think it’s impossible to be certain either way. However, while the debris across the site is likely to have a variety of different origins, most of it, at least, probably does come from stones used for megaliths. So it’s an extremely important resource for understanding Stonehenge.
At last, we have some substantial modern studies of this material. Hammond quotes the most recently published, by Ixer and Bevins in Archaeology in Wales. Other articles include theirs in the Wiltshire Archaeological Magazine, and one they authored with Nick Pearce in the Journal of Archaeological Science (see references). They bring an important insight: the great bulk of the non sarsen stones at Stonehenge (but not all), come from a very restricted region in Pembrokeshire, south-west Wales. So restricted, that Ixer at least is confident in saying that this alone points to human transport as the only likely mechanism for the stones having got to Stonehenge.
The best known type of bluestone is the spotted dolerite, of which all the stones in the surviving inner arrangement at Stonehenge are composed. These are long known to have originated in the Preseli Hills. Ixer and Bevins have also examined specimens of the other main class, rhyolitic tuffs.
The work began principally with a study of the stone fragments picked up on the surface or excavated in test pits near the Cursus, just north of Stonehenge. Though several different types of rhyolitic rock were represented, they found that most “had a restricted and distinctive petrography both in terms of their mineralogy and textures”, and that “this petrography was unusual for south-west Wales, being only recognised from the Pont Saeson area”. In subsequent fieldwork, building on Bevins’s extensive knowledge of the area, they located outcrops at Pont Saeson, in a deep valley on the northern edge of the famous Preseli Hills. In the JAS article, they reported that some rhyolites from Stonehenge were the same as samples from Pont Saeson (on Craig Rhos-y-felin), and further detailed work confirming this is reported in the Archaeology in Wales article. The location is so precise, we have every reason to think that actual quarries should now be found, opening up exciting fieldwork possibilities.
“Craig Rhos-Y-Felin, Pont Saeson is the dominant source of the Stonehenge rhyolitic ‘debitage’”, by RA Ixer & RE Bevins, Archaeology in Wales 50 (2011), 21–31
“Stonehenge rhyolitic bluestone sources & the application of zircon chemistry as a new tool for provenancing rhyolitic lithics”, by RE Bevins, NJP Pearce, & RA Ixer, Journal of Archaeological Sciences 38 (2011), 605–22
“The petrography, affinity and provenance of lithics from the Cursus Field, Stonehenge”, by RA Ixer & RE Bevins, Wiltshire Archaeological & Natural History Magazine 103 (2010) 1–15
“The detailed petrography of six orthostats from the bluestone circle, Stonehenge”, by RA Ixer & RE Bevins, Wiltshire Archaeological & Natural History Magazine 104 (2010), 1–14