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Wednesday, 10 September 2014

Carn Goedog -- have the archaeologists been misled?



In yesterday's post  (which is, I think, rather an important one) I made the point that interesting though the recent geological paper on Carn Goedog undoubtedly is, it has NOT established beyond reasonable doubt that any of the spotted dolerite bluestones at Stonehenge have actually come from the craggy tor known as Carn Goedog.   What the paper HAS done is establish that some of the stones probably came from the Carn Goedog dolerite sill, the outcrop of which appears to run across country for something like 2 km, both to east and west of the tor.  That is a very different matter, and the geologists should have made it clearer to all of us, including the archaeologists, who cannot really be expected to read a highly complex geological paper and pick up on all the nuances.......

And I do want to have a bit of a dig at the geologists too, for not expressing themselves more clearly.  I really do think that they have been lulled into a false sense of security because they have accepted (while not actually admitting it) that the bluestones at Stonehenge have been carried there by human beings, who are more likely to have collected them from a fine upstanding craggy tor (namely Carn Goedog) than from a boring hole in the ground.......  The title of their paper is a bit naughty too:  "Carn Goedog is the likely major source of Stonehenge doleritic bluestones: evidence based on compatible element geochemistry and Principal Component Analysis."  And as for those press releases, the less said the better -- except that naturally enough they hyped up the discovery to as high a level as possible, on the lines of "Bluestones source puzzle is finally solved" etc etc.  To hell with scientific accuracy -- all the writers of press releases want is saturation media coverage!

 This photo shows three of the outcrops of the Carn Goedog sill on the mountainside within 500 m of Carn Alw

 This photo shows two more outcrops of the same sill within 300m of Carn Goedog

 Ice-smoothed rock face in one of the areas of outcropping spotted dolerites within 200m of Carn Alw

So where might the spotted dolerites have come from?  Well, I was up on Preseli today, doing a bit of mapping, and it appears that the Carn Goedog sill outcrops on the hillside across quite a broad swathe of country between Carn Goedog and Carn Alw, just over one km away.  Some of the dolerite outcrops occur in places where there aren't supposed to be any dolerites, with Ordovician sediments being shown on the geological map.  So the map is wrong.  According to my reckoning, there are at least five other outcrops in this area from which the spotted dolerites at Stonehenge might have come.  All of these appear to be on the edge of the same sill.  None of these outcrops, as far as we know, have been sampled geologically -- certainly there is no mention of any geological alalyses in the paper by Bevins, Ixer and Pearce.  So more geology is needed before this interesting problem can be sorted out.

So the message for the archaeologists is simply this:  if you go hunting for an "orthostat quarry" at Carn Goedog, don't be too disappointed if you don't find it, because the spotted dolerite orthostats at Stonehenge might not have come from there after all.

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