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Thursday 10 September 2015

Rhosyfelin and "spot provenancing"

 This is the "exact spot" from which a Stonehenge rhyolite bluestone orthostat is supposed 
to have been taken.......

Is it possible for geologists to provenance rock fragments found in one place to a locality a great distance away, with an accuracy of "a few square metres"?

As readers of this blog will know, Prof MPP claims to know exactly where at least one Stonehenge bluestone has come from, and he has pointed the spot out to many visitors to the Rhosyfelin dig site.  OK, you might say, he's just repeating what the geologists have told him.....

But hang on a minute.  If you read the papers by Ixer and Bevins rather carefully they are for the most part rather circumspect, and they are very cautious about making claims that might be difficult to sustain under close scrutiny.  So who's responsible for the hype here?  This is important, because the story of this "precise provenancing"  has been picked up by the media and by all sorts of august institutions like the Pembs Coast National Park and the Dyfed Archaeological Trust -- so the truth does become rather important.  So what are the facts?

Well, we have (according to a mysterious source) about 40-60 thin sections of rock samples from the Rhosyfelin - Pont Saeson area, and we can probably assume that there are an approx equal number of thin sections from the "foliated rhyolite" debitage in the Stonehenge area.  So do the matches match the hype?  Here we have a problem, because very few of these "Jovian fabric" slides have been published.  No problem with that, since no researchers ever publish ALL their data, and as Myris has reminded us, they try to publish slides that are "typical" or "representative" of the group as a whole.

The slides I have been able to find are reproduced below, with full acknowledgement to Richard Bevins and Rob Ixer and their colleagues.

 Rhosyfelin Location 8, near the tip of the rocky spur

 Point PS8 from Pont Saeson
 Point PS10 from Pont Saeson

OU18, from the Avenue at Stonehenge

Jovian fabric from Stonehenge samples -- sample STH08-738

Jovian texture -- sample from near the Heel Stone at Stonehenge

The top thin section -- actually representing the rocks at the tip of the spur at Rhosyfelin -- is the crucial one here, and what we need is something from Stonehenge that matches it almost exactly. 

The sample from the Heel Stone fragment is not all that good a match, because the black blobs look rather like tadpoles on that one  (excuse the scientific language.......).  The closest match is that of Sample STH08-738, but even that is not all that close, because the black blobs are less frequent and there is a sort of melted or fluidized look to the slide which is absent in the one from Rhosyfelin.  And the larger phenocrysts (right word?) are more prominent and texturally distinct at Rhosyfelin than they are in the Stonehenge sample.

Could the Heel Stone sample have come from another part of the Rhosyfelin crags, or is it matched to something further away?   Could OU18 have come from Pont Saeson PS10?  They do look rather similar.......

What we don't know at present is the extent of lateral variation in texture along a foliation plane, or the extent to which samples taken from the rock face at Rhosyfelin are representative of those rocks a metre or two "behind" the rock face, or higher up or lower down.  Maybe that info will be forthcoming in a future paper?

So on the evidence currently before us, M'Lud, I suggest that the case is not proven.  I do not see anything in the Stonehenge samples to convince me of an identical match.  Neither do we know how big a variation there is in the Stonehenge material.  Could the samples all have come from one or two stones that have been broken up, or could they have come from a much wider range of material in the Stonehenge landscape and transported by ice from the Rhosyfelin - Pont Saeson neighbourhood? Now there may well be other samples hidden away that we have not yet been shown.  But I suspect that if there had been "better" Stonehenge samples, we would have seen them by now.  On the principle of "Show, don't tell" may we have a look at any other thin sections that might help to convince us that there really is a match to "within a few square metres" between something at Stonehenge and something at Rhosyfelin?



TonyH said...

Spock and Captain Kirk peer out from the cockpit of the Starship Enterprise at the vast unforgiving landscape they have newly named 'Salisbury Plain (South)'.

SPOCK: Well, unprepossessing and unpromising though it looks, Captain, the Truth is out there somewhere, as I believe your mid - 20th Century Popular Group, the Moody Blues, sang.....

KIRK: Yes! However, our problem is, it clearly isn't SEXY enough for our Sponsors (who, after all, did GUARANTEE us safe passage Home again as Heroes after our vastly extravagant Flight of Fancy). Who was that Ancient Egyptian Egyptian we met in the Wormhole back in '69?

SPOCK: He called himself, rather grandly I thought, Myris of Alexandria, sir. Why? I don't follow your glacial drift.....

KIRK: Because Myris, or whatever he calls himself, rated this part of the Planet very high in its Rhyolite with Jovian/ Jupiter Fabric Ratings - and we could be "Quids In" as well as Heroes of Several Universes as far as the better - looking ladies are concerned back on Earth. They so love their dangly ear - rings made out of the highly - sought - after Rhyolite with Jovian Fabric! Read the Primary Literature!

SPOCK: I have sir, of course. My great - grandfather was Jupiter's most famed Geologist.

TonyH said...


......Vulcan's most famed Geologist.

The Myris of Alexandria said...

Not so grand were grandeur required then Triumphant John Kantakuzinos would serve.
Or even an ancient Greco-Syrian magician.
But merely Myris (of Alexandria).

I remember the meeting I thought them an emissary of the Gods.
They talked of a hard journey, of men carrying large stones and building a circular temple to Sublime Apollo. Their Truth was there to see, no icy blast of falsehood.
M aka JOHN K.

Or even

Evergreen said...

Has somebody put acid in my PG Tips this morning or are these exchanges part of the real world?

BRIAN JOHN said...

Yes, this blog does verge on the mystical and the metaphysical at times, with shades of Egyptian history and ancient folk and rock music. I admit to being totally confused for a lot of the time myself....... so no, it probably isn't down to laced PG Tips.

Myris of Alexandria said...

Mr wintergreen this blog is based upon the premise of unknown glaciers dropping 60 wonderfully tooled bluestone at Stonehenge whilst leaving not a shred of evidence from anywhere else on Salisbury Plain and you want the real world.
For that join mumsnet.

Read the primary literature or the poems of the great Alexandrian.

Do they still sell pg tips I thought we all drank redbush, no caffeine to interfere with our physcotropics.

Real life, here, get real


chris johnson said...

Firing lasers at volcanic rocks does strange things to the mind. I might even imagine a quarry.

BRIAN JOHN said...

Evergreen -- you have to forgive Myris. Only the great god Apollo knows what he has with his PG tops of a morning......

For "unknown glaciers" read "the Anglian Irish Sea Glacier".

For 60 read 43.

For "wonderfully tooled bluestones" read "a mottley collection of stones of all shapes, sizes and lithologies, some of which have signs of tooling."

For "whilst leaving not a shred of evidence from anywhere else on Salisbury Plain" read "in an assemblage of erratic stones and other debris that is best interpreted as a glacigenic deposit."

Reading the primary literature may help you on the matter of bluestone origins, but it will most certainly not help you in understanding how the stones got from here to there.

BRIAN JOHN said...

OOps -- PG Tips. I'm a Tetley man myself......

TonyH said...

Jean Luc Picard, alias Sir Patrick Stewart of Huddersfield (just up t'Road from my origins in deepest Mesolithic Deepcar)says his favourite tea is "Easy. Yorkshire Gold! Any other kind of tea needs two tea bags. By the way, did you know I am the man who introduced the CONCEPT of the double tea bag to the United States?"

Personally, I prefer Yorkshire Decaffinated. AND it's NOW on special offer for 160 bags at Tesco..... rush down! But it HAS to be Yorkshire. Leaves you with that decidedly SUPERIOR feeling. Ask Our Geoffrey (NOT Wainwright). Even MPP spent aeons as Professor at Sheffield University, no wonder he's so sure of hisself.

And, yes, "Myris of Alexandria" is, in fact, part of a modern poem by a Poet of Some Repute. Google it, folks. But I think even Star Trek's robot "Data" would have a job on figuring out some of Myris's ever - cryptic Comments on 'ere..... Still, it takes All Sorts to make a Galaxy, eh, Kostas?

Myris of Alexandria said...

And so are the others.
He was a hydrogeologist, well nearly, by profession.
Were he thirty years younger I think he would have had the Nobel prize for lit.
Now read the primary literature has real meaning here.
His best most ironic poem must be The Ides of March.
Still he did not write ......tears in the rain.

Brian I agree there is no convincing evidence for anthropogenic movement of the bluestones, so that finding/proving a quarry quarries is paramount. It has been said in those words since the 1990s.

Ms Doubter said...

I thought tea came from foreign climes not Yorkshire.
If envirommentalists drink green tea,do glaciologists drink iced tea?
So proving a quarry would be the ice-ing on the cake.
I don't know what a pun is so I don't know if it was intended.