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Monday 6 June 2022

More on "Newall's boulder"

Newall's boulder, now stored in Salisbury Museum

Thanks to Adrian Green of Salisbury Museum, we now know that the boulder (rather a small one) is in the Salisbury Museum collection, together with the lump that was cut off the side of it.  The thin section which was looked at by the IGS Chief Petrologist KK Harrison and described for Geoffrey Kellaway is apparently in the British Geological Survey collection at Keyworth.  I have never seen the thin section published, but we will no doubt see it eventually, since our old pals Ixer and Bevins are currently working on the Salisbury sample and maybe on their own thin sections in order to work out what the provenance may be.

The cut made on Newall's boulder when the sample was taken for geological analysis.

On checking back in the big 1991 paper by Olwen Williams-Thorpe and her colleagues, I see that they also analysed sample RSN18- ENQ2305 and gave it the number OU2.  The lump of rock that they examined weighed 244 grammes and measured 10 x 7 x 3.4 cms.  They refer to it as a grey weathered rhyolite, but they clearly had no information about the excavator or the sample find location.  They did not know about the connection withy either Newall or Hawley.

In table 14 (b) of that study, the OU team report on the chemical analysis of sample OU2, as below:

Thorpe et al noted that OU2 (ie the Newall boulder) was similar (but not identical) in chemical composition to many other rhyolite samples from Stonehenge (including samples from the Aubrey Holes), pointing to a similar source;  they said these samples could not have come from the rhyolites around Roch, but they were "consistent with a derivation from Carnalw."   They referred to OU2, and most other studied samples, as lavas but not as ignimbrites.

When Ixer and Bevins worked on the North Pembrokeshire rhyolites they initially defined five rhyolite types, numbered A-E, but in their 2011 on the rhyolites of Rhosyfelin they argued that types A-C were from a common source and that the bulk of the rhyolite debitage at Stonehenge could be traced to Rhosyfelin as the source. That is a speculation, and in my mind it is not adequately supported by the evidence.  They must have looked at sample RSN18 (OU2) in their studies, but I don't believe they have referred to it in previous papers.  Let's see what emerges...........

One thing we can say is that the hint about the rhyolites (including Newall's boulder) having come from the Carnalw area might not be all that reliable. In another paper (2013) Bevins and Ixer looked at the Carnalw connection and suggested that "not a single rhyolite fragment from the Stonehenge orthostats or debitage from anywhere in the Stonehenge Landscape can be attributed to Carn Alw."  That, as I have said before, is a pretty sweeping statement, since they still do not know where many of the rhyolite samples from Stonehenge have actually come from -- and they certainly do not know all about the whole of the Stonehenge Landscape.  But as we all know, the pet rock boys do love a bit of extravagance..........

So which rhyolite group does sample RSN18 actually belong to?  No doubt all will be revealed....... 

BEVINS, R.E., N.G. PEARCE & R.A. IXER. 2011. Stonehenge rhyolitic bluestone sources and the application of zircon chemistry as a new tool for provenancing rhyolitic lithics.   Journal of Archaeological Science 38: 605–22

50: 21–32.

I think at this stage we can probably assume that the "Newall boulder" is not from North Wales, but (on the basis of shared chemical characteristics) it is most likely to be from one of the rhyolite sources in North Pembrokeshire, as originally suggested by Thorpe et al in 1991. (I wouldn't mind betting that Ixer and Bevins will in due course declare that the Newall boulder has come from their famous and fantastical "quarry" at Rhosyfelin..............but we will need to see the colour of the evidence before we pass judgment on that one.)


PS.  Please note that this post contains information that has been overtaken by events!  The OU2 sample clearly had nothing to do with the Newall boulder RSN18 -- the correction is in this post, dated 19 June 2022:


Tony Hinchliffe said...

Now it would appear we have ANOTHER rhyolite sample from Stonehenge.......But this one, probably because of the outer APPEARANCE of the Newell boulder, will eventually be demonstrated by glacial geomorphologists who get the opportunity to actually HANDLE it, to turn out to have been GLACIALLY transported to its resting place within/ beneath the Stonehenge monument.QED.

BRIAN JOHN said...

Well, nothing is certain, but the fact that several experienced geologists have examined the boulder in the past, and have been rather convinced about the authenticity of the striations, is significant. And the weathering history picked up on by Harrison is also fascinating. Although Tim Daw is now suggesting the boulder is "questionably an artefact" we now know that it is not lost, and that is progress! If it looks like a small natural boulder, that is probably what it is...........

BRIAN JOHN said...

Having now had a chance to examine the Newall Boulder in the company of Tony, it’s now certain thet the OU sample OU2 did NOT come from the boulder. It had nothing to do with sample RSN18, so somewhere or other there has been a misidentification or mistake in labelling. Watch this space.