The Rhyolitic "debitage" around Stonehenge

 A thin section numbered SH80 -- acknowledgements to the authors of the paper cited below, and to Wilts Arch and Nat Hist magazine.  This rhyolite is very different from the Rhosyfelin ones -- so where does it come from?

There is a new paper by Ixer and Bevins, with a comment by Mike Pitts, in the latest edition of the Wilts Arch and Nat Hist magazine.   Thanks to Rob for passing it on.   It's very difficult to follow, since the authors spend most of the time  discussing very subtle differences between the 14 samples which they looked at, and deciding which category or sub-category to place them in.  The essential conclusion seems to be that the rhyolite fragments examined (which have still not been tied to any standing stones at Stonehenge) are mostly from the Rhosyfelin area -- the similarities with the samples taken from the crag are close enough for "micro-provenancing" in just one case, but in the others the authors have to admit to provenancing from the general area.  They do not speculate as to how wide this area might be -- so it could be covered by a grid 500m x 500m in extent, or it could be even larger.

One general problem that I have with the paper is that it tends to talk of the "Stonehenge rhyolitic debitage" as if it is homogenous or as if they have examined enough of it to be sure that any conclusions drawn are incontrovertible.  This is the problem that all scientists face -- when we have a sample of limited size, how wide are the conclusions we can draw?  It's not a bad idea to bear in mind that the parts of the Stonehenge "stone floor" or regolith or debris layer examined and sampled thus far is very small -- and as I have said before, there may be several "debitage" groups with quite different petrographic characteristics on other parts of the Stonehenge site or in other parts of the Stonehenge landscape. 

I wasn't entirely convinced by the attempt to push samples from SH 80 into the Rhosyfelin assemblage, and would like to know what the characteristics of rhyolites from other outcrops in the region might look like, and how they might compare with the samples examined.

Mike Pitts says:  "It is notable that all the samples matched in this study to Craig Rhos-y-felin come from debitage and not from megaliths (although Ixer and Bevins (201111a and b) have suggested that buried megalith SH32e may also come from Craig Rhos-y-felin). One of the distinctive features of the rhyolitic rocks is that they are flinty – they have a good conchoidal fracture. That makes them relatively easy to break up, if they are standing as monoliths at Stonehenge. But it also makes them suitable for making portable artefacts. There are flaked bluestone ‘tools’ from Stonehenge (including some from the stone floor). Which of these are made from debris created when stones were dressed on site? Which are made from broken up megaliths? And which were made in Wales and brought to Stonehenge by people visiting, perhaps on a pilgrimage of some kind? Clearly the distinction has important implications for how we understand Stonehenge."  Mike is seeking to open up the debate here and to avoid sticking to the standard story, but he is still seeing the world through the same tunnel as all the other archaeologists.  He fails to recognize that there is a further possibility, and he should also have asked this question:  "Which flaked bluestone tools -- and indeed which bits of debris -- might have come from smaller rhyolite stones found in the neighbourhood and which might be assumed to be small glacial erratics?"  I am referring here to stones which might have been too small to use as orthostats, or which might just have been the wrong shape, or which might have been too badly damaged during glacial transport and subsequent frost shattering.



Wilts Arch & Nat Hist Mag vol 106 (2013) pp 1-15

"A re-examination of rhyolitic bluestone ‘debitage’ from the Heelstone and other areas within the Stonehenge Landscape"
by Rob A. Ixer and Richard E. Bevins, with a contribution from Mike Pitts

ABSTRACT
Recently it has been proposed that the Stonehenge rhyolitic debitage can be distributed into five petrographical groups (A-E) (and that at least three of them (A-C) are from rocks cropping out at Craig Rhos-y-felin). This supersedes an earlier classification scheme of this important category of Stonehenge material. The earlier 1980s scheme, based on lithics found close to the Heelstone, divided the rhyolites into two groups (A and B) and sub-divided the larger into two further sub-groups (Bi and Bii). Re-examination of this earlier material together with other Stonehenge rhyolites has allowed the two schemes to be compared and integrated.
The original 1980s Group A lithics are identical to the present Group B, (both are small groups). This group is described in detail so completing the petrographical descriptions of the Stonehenge rhyolitic debitage. Despite bearing feldspar megacrysts this group shares sufficient petrographical characteristics with rocks from Craig Rhos-y-felin to support the view that that location is the geographical origin of the group.
Lithics belonging to the 1980’s groups Bi and Bii, however, are randomly distributed amongst the present A and C groups and there are no strict correspondences. The designation Bi and Bii should therefore be abandoned.
Using the new scheme it should now be possible to map more precisely the distribution of the rhyolitic debitage in the Stonehenge landscape to inform such questions as to the number of rhyolite orthostats originally present and their fate.