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Monday 21 April 2014

Rhosyfelin-- the famous crack


There are lots of photos flying around which show clusters of earnest ladies and gentlemen gazing intently at this crack in the rock face at Rhosyfelin, having things explained to them by either Richard Bevins or Mike Parket Pearson.  I assume, therefore, that this is where the samples came from which have been matched up accurately with the debitage collection from Stonehenge.

However, to extend that geological work into an assumption that this is where at least one of the Stonehenge orthostats came from is taking things too far.  For a start, this crack is no more than 30 cms wide, and there is no way that a viable orthostat could have come out of that crack -- or "alcove" as it is described by some people.  Possibly small lumps of stone might have been taken for here, for the manufacture of tools.

But if an orthostat (or two) did travel from here to Stonehenge, by some means or other, it must have come from a slab of rock closer to the camera, which has now been entirely removed, or else from a slab of rock higher up, above the top of the current rock face.  The fractures here -- and the foliation -- run almost vertically.  So could the rock that found its way to Stonehenge have come from ten feet higher up?  Twenty feet higher?  Thirty feet higher?  It would be good to get a geological view on this -- leaving archaeology entirely to one side -- from either Rob or Richard.  Over to you, chaps.....





8 comments:

Myris of Alexandria said...

The crack is a joint plane, and runs at 90 degrees to the foliation.
It was unknown when the initial petrographical matching was achieved.
However I am pretty sure that Dr Ixer could find a number of samples in this photograph that show the Jovian texture.
The matching was done to the very small rock at the very end of the quarry face.
M

Myris of Alexandria said...

I find no significance to this joint plane.
A tear in the space-time condominium?
The bleat of an electric sheep?
M

BRIAN JOHN said...

Thanks Myris -- I too wonder why this crack has featured so prominently in lectures etc. I'm sure MPP said in one of his talks that the critical geological samples actually came from the location of the crack....

BRIAN JOHN said...

I still find it difficult to get the hang of Ancient Egyptian phraseology. What does this mean: "It was unknown when the initial petrographical matching was achieved." ??? Presumably that means it's not known when and how stone fragments got from Rhosyfelin to Stonehenge......

Myris of Alexandria said...

Do you not go to Delphi!
I see your error, I do so hate commas.
It (the joint plane) was unexcavated and therefore not in anyones knowledge, other than that of Sublime Apollo, when the Jovian texture was first recognised at SH and then at the small rock cropping out at the very end of the quarry face (site 6 8 or 9(the location is in the literature) Indeed a year had passed before that joint plane was recognised and given any significance. Its an owl and
you would have to be Batty not to recognise it as a tear in rain.
M
Although it is not known, for certain, how the stone fragments arrived at SH.

BRIAN JOHN said...

Thanks Myris -- a tear as in weeping, or a tear as in ripping?

Myris of Alexandria said...

In all cases as in weeping in the outer darkness.
I am not sure that anyone makes much of the joint plane anymore. Now had the joint spacing matched any orthostat, it does not, we would be hearing about it.
M

BRIAN JOHN said...

I stand corrected. Myris says I must not use the word "crack" when referring to this orifice (sort of) in the Rhosyfelin rock face. Point taken -- I shall endeavour to call it a "joint plane" in future. I think I understand the geology a little more now. Myris also tells me that the rock face (Myris -- please don't call it a "quarry face") is the foliation plane sampled by the geologists. So that is indeed at about 90 degrees to the joint planes (there are many of them) running into the rock face.

So this foliation plane presumably runs deep underground, and once ran high up into the air, into a lofty region from which all the rocks have been removed by the processes or erosion, including glacial processes......