The Glan yr Afon erratics -- a change of hypothesis

 

As I have often said on this blog, although not in these precise words, if you get too fond of your hypotheses they are likely to turn on you and bite you in the bum.  You get my drift.....

Anyway, I have done two posts in the past on the rather splendid collection of erratics scattered about on common land not far from Crosswell and on the lane leading ultimately to Glan yr Afon Uchaf.  This is directly NNW of Carn Goedog, on the north flank of Mynydd Preseli.  The distance to the tor is about 2 km across open treeless moorland which is reasonably dry, in the Pembrokeshire sense of the word.

https://brian-mountainman.blogspot.com/2020/08/spotted-dolerite-erratics-at-glan-yr.html

https://brian-mountainman.blogspot.com/2017/10/the-spotted-dolerite-enigma.html

As we can see from this satellite image, Glan yr Afon is currently something of a building site -- the property is being developed, and it's taking a very long time.  I have put a red ring around the main concentration of boulders, but there are many others lying around too, on a landscape that is quite hummocky. 

In my discussions about this site I eventually suggested that this was an area of hummocky moraine formed at a short-lived ice edge during the LGM of last glacial episode, around 24,000 years ago. That's because the boulders in these stone concentrations were nearly all heavily weathered and rounded off or abraded -- but some appeared to be broken.  OK -- broken in glacial transport, I thought.  The boulders -- of many different sizes, were clearly not QUARRIED -- there were no signs of the sharp edges that quarrying would have produced. But the big problem was that the boulders were nearly all made of spotted dolerite, in an area where the nearest spotted dolerite is at Carn Goedog.  There are no recorded outcrops this far north of the upland ridge and its tors.  So had the boulders been carried northwards by ice from a Preseli Ice Cap?  I wasn't very convinced by the evidence, but thought it possible.

So on balance my working hypothesis was that this was indeed a morainic accumulation, with work still to be done in explaining how all those spotted dolerite boulders had accumulated in one spot.

Fast forward to these posts:

https://brian-mountainman.blogspot.com/2014/08/spotted-dolerite-ooh-theres-posh.html

https://brian-mountainman.blogspot.com/2014/09/did-carn-goedog-provide-stone-for-cana.html

https://brian-mountainman.blogspot.com/2020/08/cana-independent-chapel-facade-with.html

Aha!  Cana Chapel at Felindre Farchog -- about 4 km away from Glan yr Afon and c 6 km away from Carn Goedog.  There are written records of stones from Carn Meini being fetched to provide the facing materials for the chapel around 1857.  I thought once upon a time that the stones might have been collected from the top end of the tor and then carried along the old drovers road towards Carn Alw.  But on the quiet I wasn't all that happy about that, since I am not at all convinced that any large lumps of rock have been taken from the top end of the tor.  (This is of course where Prof MPP and his jolly quarrymen insist that there was a Neolithic bluestone quarry -- which I don't accept for a moment --but let that pass......)

So where is this taking us?  Well, in a flash of inspiration last night while I was in the bath, I saw Carn Goedog linked to the Glan yr Afon jumble of spotted dolerite "erratics" linked to Cana Chapel.  Suddenly it all makes sense.  The stone collection team made up of members of the Cana congregation collected spotted dolerite boulders from the easiest places possible, along the bottom edge of the tor near the group of medieval houses investigated by MPP and others.  They transported them across the dryish moorland, probably in the summer months, to Glan yr Afon, which is where a proper roadway started. They made a substantial stone depot there, where they undertook some stone dressing work, taking away the dressed blocks of stone and leaving behind great piles of broken debris -- these are still visible as grassy mounds on the common.  This was far more economical than carrying the boulders all the way to Felindre Farchog.  They actually had too much stone in the end -- and left a lot of it behind -- and we can see this residue today.  Actually, only the front facade of the chapel is made of dressed spotted dolerite -- the other three walls are made of cheap rubble.  Maybe the work of shaping and dressing the stones at the Glan yr Afon depot was too hard?  After all, spotted dolerite is incredibly difficult to work with -- I know, having stone faced my own house with spotted dolerite and rhyolite!  So maybe the intention of facing the whole of the chapel was simply abandoned on cost and labour grounds.  

Now I am much happier.  This makes much more sense.  Maybe a little strangely, I'm a glacial geomorphologist looking at a pile of stones and saying the pile is probably man-made and not natural.  Mind you, I have done that before, with respect to the Bronze Age quarries at Foel Drygarn.  We have to go where the evidence takes us.

So that is my new working hypothesis.  Hope you like it.......... 

The slide car (car llusg) was widely used in Wales for moving heavy loads across difficult terrain where wheels might have broken.  was something like this used as late as 1857 for moving bluestone boulders across the moor from Carn Goedog to Glan yr Afon?  At that point loads -- or shaped stones -- could have continued their journeys to Felindre Farchog on a wheeled vehicle such as a gambo or cart.