Rhosyfelin -- the story is changing

This is interesting.  After 15 years of maintaining the pretence that  the exposed rhyolites at Craig Rhosyfelin are unique, and characterised by a "Jovian fabric", Bevins and Ixer are at last admitting that things are a great deal more complicated than that.

On many occasions I have strongly criticized the use of the invented term "Jovian fabric," arguing that it is misleading and not a unique characteristic.  Similar foliated and lensoidal textures can be found in other heavily deformed rhyolites and volcanic tuffs across Pembrokeshire and other regions, as pointed out in my post:

https://brian-mountainman.blogspot.com/2024/02/the-special-rhosyfelin-rhyolite-triumph.html .

Using a non-standard and potentially common texture to claim a precise, small-scale provenance is scientifically unsound.  I also have serious reservations about the widespread use of the term "rhyolite with fabric" by Bevins, Ixer and Parker Pearson.  What on earth does that mean?  It appears to mean -- in the Ixer/Bevins lexicon  -- a particular type of secondary fabric arising from post-depositional deformation or stress.  They refer particularly to foliation and flattened lensoidal clasts, but fail to demonstrate that these features are absent from all the other related ourctops of rhyolite on the north flank of Mynydd Preseli.

In standard petrology, the textures of igneous rocks are classified using widely accepted terms like aphanitic, phaneritic, porphyritic, and vesicular, which describe grain size, crystal formation, and gas content.   Terms like "foliated" and "lensoidal" describe structural characteristics, often related to metamorphic processes that affect igneous rocks, and these are far from unique to one location.  A rock with a fabric resulting from intense tectonic stress is not an anomaly; it is a common feature in many geological settings where ancient volcanic rocks have been subjected to mountain-building events.
In summary, the "Jovian fabric" is a non-standard, invented term. Its perceived uniqueness has to be questioned, and its use as definitive proof for the human transport of the bluestones is frankly absurd.

Ten years ago Ixer referred to "sub Jovian" and "semi-Jovian" fabrics at Rhosyfelin, in recognition of the fact that there is considerable variation across the rock outcrop.  I think there was a reference to another three rhyolite types at Rhosyfelin -- and now, in the article on the Cunnington rock samples,  we see a reference to "Snowflake fabric" and "Zebra fabric".  These are not very technical terms, and they cover a multitude of sins........

I have made the point elsewhere that the Newall Boulder may share certain geochemical and petrographic characteristrics with some samples from Rhosyfelin, but it looks very different to anything I have seen at the "quarry" face, and it has NOT been demonstrated that it cannot have come from anywhere else.  Nor is it admitted that there are substantial variations within the Rhosyfelin collection of samples -- and again it has not been demonstrated that any or all of these cannot have come from anywhere else. I think that the extraordinary "spot provenancing"claims are in tatters. 

Can the "rhyolite with fabric" debitage all have come from the natural fracturing or human breakage of a a single boulder?   I think there is too much variation for that, and we still do not know what the full range of rhyolite characteristics may be across the Crosswell - Pont Saeson - Brynberian area.  I saw somewhere a claim that there have been over 200 samples now taken by Bevins across the area, mostly within the valleys of the Nevern and Brynberian streams.  Bevins and Ixer have told us that "Rhosyfelin foliated rhyolites with the same petrography and geochemistry" do not occur except at Rhosyfelin, but they have simply told us that, and we are expected to believe them.  Very dodgy.

This strange little map purports to show the sampling points in the valleys of the Nevern and Brynberian streams and in the Carnedd Meibion Owen area. How many oif these samples have actually been analysed?  And where are the results? 

To summarise, there is no "demonstrable" exclusivity.  Because a complete geological survey and analysis of every potential rhyolite source has not been conducted, it cannot be definitively proven that the Rhosyfelin rock type does not exist elsewhere. The possibility that a similar geological signature exists in an unsampled or poorly-sampled location remains, creating a "sampling bias" that undermines  the claim.

If the specific rock type exists elsewhere, as I suspect, it weakens the claim of an exceptionally precise match "within a few square metres" at Rhosyfelin.  The precision of the match is contingent on the uniqueness of the geological fingerprint, and if that uniqueness is not proven, the accuracy of the source identification is brought into question.

According to the Hitchens Razor, extraordinary claims require support from extraordinary evidence.  The jury is still out, and the evidence we need is still missing. 

As I have said many times before, the biggest mistake ever made by Bevins and Ixer was get sucked into the quarrying debate.  As soon as they started to refer to bluestone quarries in their papers, they opened themselves up to criticism on the grounds of sampling bias and circular reasoning.  They also chose to publish preferentially in archaeological journals rather than geological ones, in which the standard of peer review was inevitably much lower.  So we find them arguing (in their abundant articles) for the presence of a Neolithic quarry at Rhosyfelin on the grounds that rock samples from there were a reasonable match for some samples from Stonehenge.  And they argue that some of the stones that ended up at Stonehenge came from Rhosyfelin, because that is where the quarry was located.  Round and round.......

Where it all started:

Ixer, R.A and Bevins, E.R (2011) Craig Rhos-y-Felin, Pont Saeson is the dominant source of the Stonehange rhyolitic ‘debitage’; in Archaeology in Wales 50, 21-31

https://d1wqtxts1xzle7.cloudfront.net/31544116/rhos_AW-libre.pdf?1392324523=&response-content-disposition=inline%3B+filename%3DCraig_Rhos_y_felin_is_the_dominant_sourc.pdf&Expires=1761393598&Signature=Yj4RhTm3v7hNwk~odIMOfA1HpJ8yHo6T-D8XyR~75k8ov8gAkbYXPe54NEG9IYTq-0RnBBmK3HhPJ0qrLd8Jl-XHtD2EctMepawi5xsAGc9bdtFyoVSosA1OgWMokStJchCH47fdDcpmy9ZRDBlKyhp5FJOaIZqMNTiVOAFXJFMpiCMb5M7CK5GHmM2jom7vO4r65niW7ZQbz-2amM9mJTXHQiuifE9W9HUtfOmcvTOJDIvwOKHlZowb4f1WjiyiFccRisLymkOflRSyqnRxVJTgljCzIv-fd5DHNymBdlcAYtHPWGNzp1uOrM4EarJwXEgt4LS60OTATqQ55SqCFA__&Key-Pair-Id=APKAJLOHF5GGSLRBV4ZA

https://brian-mountainman.blogspot.com/2011/12/on-significance-or-otherwise-of-999.html

https://brian-mountainman.blogspot.com/2021/02/geology-sampling-progress.html