Over the years, on this blog, I have tried, over and again, to reconstruct the ice streams of the Irish Sea Glacier during the Anglian Glaciation. I've also published many other reconstructions from glacial geomorphologists who have an interest in the matter.
Look at the two maps above. I am increasingly convinced that Geoffrey Kellaway, who was lampooned by a rather snooty archaeological establishment during his lifetime, was more sensible than the rest of them put together when it came to understanding erratic transport. The top map is a reconstruction of the Kellaway map, by Olwen Williams-Thorpe, and on it I have highlighted in pink the crucial streamline. Note some of the key locations on it -- Mynydd Preseli, the Llansteffan Peninsula, Pencoed, Flatholm, Boles Barrow, and Stonehenge...............
Lionel Jackson and myself, in our "Earth" paper in 2009, argued along similar lines that the bluestone erratics were carried along a contact zone between two converging ice streams -- Welsh ice to the north and Irish Sea ice to the south -- on essentially the same route.
https://www.researchgate.net/publication/270162075_Stonehenge's_mysterious_stones
So if the Altar Stone erratic did indeed come from Craig Ddu, as I am now suggesting, it is not an aberration at all, but an erratic picked up on exactly the right ice stream route. I have always argued that the Stonehenge bluestones look like an erratic assemblage (from the physical appearance of the stones) -- and the recent geological work by Rob Ixer, Richard Bevins and others suggests that the stones have come from a rather narrow band of countryside on the north flank of Preseli, with probable source locations including Carn Goedog, Cerrig Marchogion and Craig Rhosyfelin. Other igneous sources are still being looked for, as are sources for the Palaeozoic sandstones. I now think there is a very strong chance that these sandstones are Ordovician in age, and that they have come from the coastal zone between Fishguard and Ceibwr.
There's my hypothesis. Let's see how it works out as the geological work proceeds. Quarries? Who needs quarries?
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