Having been out to look at Rhosyfelin again yesterday, it's not a bad idea to look again at this statement:
Quote from Ixer and Bevins 2011
"This is the first time that any lithics from Stonehenge have been unequivocally assigned to an area of a few square metres, namely to within a very small single outcrop or couple of outcrops......"
Article: "CRAIG RHOS-Y-FELIN, PONT SAESON IS THE DOMINANT SOURCE OF THE STONEHENGE RHYOLITIC ‘DEBITAGE’
Rob Ixer and Richard Bevins, Archaeology in Wales 50, 2011, pp 21-31
This implies that Locality 8 on the air photo is actually the source of the "rhyolite with fabric" found in the Stonehenge debitage. It also explains why Mike Parker Pearson and his colleagues have become so obsessed with the idea of the "Rhosyfelin Quarry" -- in the conviction that the geologists have given them the "all clear."
However, the geology is not that simple, and I have previously questioned the reliability of that statement made by Rob Ixer and Richard Bevins.
I have argued that without a rather dense sampling grid, it would be a mistake to argue that the "foliated rhyolite with Jovian fabric" matched up with Stonehenge samples is restricted to the one site (locality 8) at the NE tip of the Rhosyfelin rocky ridge. The geologists don't know where else this particular rock type might outcrop -- or if they do know they haven't given the evidence to support the contention.
One problem I have with the evidence as presented is that we do not see (in the Archaeology in Wales paper) the thin section slides for the other localities, so we have nothing to compare with locality 8 or with the samples from Stonehenge. What we do have are these 3 illustrations:
Bear in mind that one of these illustrations is at a slighly different level of magnification than the other two. In the Heelstone sample, the black blobs look like little fishes or tadpoles -- and they do not look like this in the other slides. In the other Stonehenge sample there are fewer black blobs and they are less elongated, and the other components in the slide look almost liquid rather than crystalline. The locality 8 sample is different again, with a greater density of black blobs and with much more irregular shapes. To my untrained eye, these three fabrics do not look identical, but they are similar, suggesting that they are part of a continuum, and in my view it is quite possible that the Stonehenge samples have NOT come from the few square metres around locality number 8.
I would be more convinced if we had at our disposal the thin section slides showing us the fabric at all the other sampling points identified on the air photo. How different, or how similar, are they to the three slides shown above? At one point I recall Rob referring to locality 9 as the possible source of some of the Stonehenge debitage.......... was that a mistake, or was that at one time a working hypothesis, later changed when the slide from locality 8 had been examined?
So if the area of foliated rhyolite with Jovian fabric is more extensive, where might other outcrops be located? Here is a photo of the rock face:
Rob tells us that the crack featured in my last post is 90 degrees away from the direction of the foliations. We have to work in three dimensions here -- and this means that either the foliated band sampled at point 8 runs as a very thin band all the way along this face and might outcrop in other localities in the Rhosyfelin - Pont Saeson area, or else it runs more or less parallel with the rock face, either along the cliffline itself, or some distance outside it or some distance within it. Such a "sheet" (we cannot call it a bed) could run deep into the ground and could have been exposed much higher up than the current crest of the ridge. In other words, bits and pieces of it could have been carted away from this general area by overriding ice at a time when the landscape had a rather different appearance from the Rhosyfelin of today.
We need more geological info here, chaps........ is it in the publication pipeline?
I have just found this thin section slide from one of the other geology papers by Rob and Richard. It's from Point 10, quite a way to the south of the rock ridge where the archaeologists have been working and over 200m from Point 8. Is this also a part of the same "rhyolite with fabric" continuum? There are strong similarities with the slides shown above, except for the absence of the prominent black blobs.