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Monday, 25 June 2012

A possible source for the Altar Stone?


Note from Phil Morgan, for which many thanks:

I've attached a photo of of Hay Bluff, the Senni Beds of which could, arguably, be a candidate for the source of the Altar Stone. The base of the Senni Beds is indicated by the thin yellow line, and the  bed thickness in this area is about 160m.
As you probably know, the boundary between England and Wales runs along the crest of the Bluff, so if this striking feature turns out to be the source of the AS, then I wonder which nation will claim possession rights?
As usual, you are welcome to use the photo if you wish.


Thanks to Phil for this.  We have had a number of posts on this blog about the Altar Stone, referring frequently to the rejection of the idea that it came from the Cosheston Sandstones of Milford Haven.  Rob Ixer is sure it has come from the Senni Beds, which are extensive in South Wales.  The preference at the moment, among the geologists, is to provenance the Altar Stone to the Towy Valley or somewhere else around the western fringes of the Brecon Beacons and the South Wales Coalfield.  That makes sense to me, since valley glaciers flowing broadly southwards could well have introduced this stone -- and maybe others -- into the path of the Irish Sea Glacier which later on flowed broadly eastwards towards the coasts of SW England.

Could the stone have come from the Senni Beds of the Welsh Borders?  Personally I doubt it, but it's quite possible that erratics from the Hay area could have been carried to the Stanton Drew area and even onto the flanks of the Mendips.  What I don't know is how much variation there may be within the Senni Beds, and how accurate the provenancing of the Altar Stone can be.

Perhaps Rob or another geologist can enlighten us?

6 comments:

Robert John Langdon said...

Have I missed something?

Why do the micaceous sandstones of Stonehenge have to come from Wales or the SW?

Micaceous sandstones are found all over Britain and it is a stone of choice for some stone tools - little to none of which come from the areas you indicate as far as I am aware.

In fact most micaceous sandstone tools currently on museum display come from Scotland or Northern England.

RJL

BRIAN JOHN said...

Robert -- you have, I fear, missed a great deal.

Anonymous said...

Brian
On another wet summer's day what joy you bring. (cut to Vlad "Ah the Children of the Night what wonderful music they make")
Masterful reply.

The Altar stone I fear will be the most difficult to provenance.
Were I to have another go I would concentrate on finding a cornstone with the correct bedding and joint measurements so carefully inspect the Altar Stone as far as one can but have been saying this for 5 years or so.
Not high on my list but is tied in with the Palaeozoic sst saga.

What micaceous sst tools? - not axes: certainly saddle and rotary querns although slightly gritty ssts are better than fg micaceous sst. Oh some (rather poor quality) hones but they need a calcareous cement-actually rather like the Altar Stone-there goes another hare.
Oh the Pennant Sst from S Wales-other side of the Severn good hone material many in Med contexts woops.
GCU In two minds.

Robert John Langdon said...

"(No 2) Perforated axe hammer of reddish-brown micaceous sandstone,
24.4cm long"

Found in Lancashire

http://www.pastscape.org.uk/hob.aspx?hob_id=42961

RJL

chris johnson said...

Overly gnomic, GCU.

Please spell out where we should look next.

Anonymous said...

Oh I think we are all looking in the correct places. Devonian sst, probably Senni Beds somewhere in South Wales, or The Marches. Cannot be easier than that.
Oh we all know that were I to know definitively the location my name would be all over it.
Of course I could know but am keeping it to myself or it is not high on my list so have not thought about it deeply.
GCU In two minds