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Monday, 26 September 2011

Outcrops and sampling

Excuse the rather crude lines drawn on this map, but you get the message!  The grain of the country here, around Craig Rhosyfelin, is roughly SW-NE.  I think that somewhere on the blog an unnamed geologist said that much of the rhyolite debitage at Stonehenge could be fixed to within an accuracy of 2m -- to the NE tip of that rocky ridge of Craig Rhosyfelin.  That assumes that the very special rhyolite texture identified isn't found anywhere else.  I did ask whether the density of sampling points in the neighbourhood allows a statement like that to be made with any degree of certainty.

So here is my question to any geologists who might read this:  are you sure that rocks with precisely these special characteristics are not also found on the other side of the valley?  -- in other words -- in the top right-hand corner of this photo?  And might they also be found in other areas to the SW, ie off the bottom left edge of the photo?

Can we please see a geological map of the area?  This isn't just an awkward question -- this is fundamental for an understanding of the mechanics of glacial entrainment.

14 comments:

Anonymous said...

Dear Brian
A blog is not the correct place to discuss the detail of a data-rich scientific paper but the title is not a randomly ill-chosen one but can be defended. Once it is published and individual questions arising from the closely-argued text are made then that will be the time to respond in this, a more casual, arena.
However good science is predicated on reproducible facts.
Therefore if you feel the density of the sampling is insufficient please resample the whole area or just the northeastern end of Craig Rhos-y-felin and I am happy to look at the resulting polished thin sections (but not pay for their manufacture) and if the paper is incomplete or the results result in a change in the interpreted and mapped geology so be it, you will be the second to know.
“But, but, but” it is bitter lesson best learned early by neophyte geology students-not all geomorphological features relate to geological boundaries or indeed lithological units and the best lines on a geological map are rarely straight and continuous (pace strike lines). Otherwise everyone would be a geologist.
Rob Ixer.

BRIAN JOHN said...

Fair enough, Rob. Let's see how the data stand up, and let's see what the field mapping looks like, when the paper is published. But my question is a highly relevant one which dos need an answer.

I don't have any hang-ups about using unpublished data on this blog -- I have pasted up large amounts of unpublished field observations of my own, and am happy for all of them to be tested and verified / disproved!!

Tony H said...

Comments on Brian's Post, "The Dig Site", which was posted on 24/09/11 include some very relevant details submitted 26/09/11 on the soon-to-be-published paper.

Alex Gee said...

Do you know the name of this anonymous geologist? Unless you mis-quote him/her. If he can pin down a rock sample source to within 2 metres, he must be either a genius or a deluded idiot. I know where I'd place my money.

BRIAN JOHN said...

I could not possibly comment!! I leave it to him / her to defend the claim......

BRIAN JOHN said...

Here's the post from 17 Sept -- we now know that he is a he, since his name is Thomas the Rhymer!

Anonymous said...

There is no doubt, but, that rocks from within 2 metres of that dig reached Stonehenge and appear amongst the debitage.
The rest is fung shei
My experience of British BA mining sites tells me that mauls are found by the hundreds-even thousands.
Mauls are common at Stonehenge-off hand cannot remember what sort of numbers.
What we need is a bit of Corded Ware.
Thomas Rhymer.
17 September 2011 10:12

Anonymous said...

luck and the prepared mind?
Auntie Sallie

BRIAN JOHN said...

Always a bit of luck is needed in this sort of research -- and yes, preparation and anticipation of points that may be raised by others. In publications, that's why peer-reviewed papers are deemed to be "more reliable" than invited papers or chapters in books. Will the paper mentioned by Rob be peer-reviewed?

Anyway, Auntie Sallie, nobody on this blog is trying to knock you over. That's a stupid occupation which can only lead to trouble. What I hope we are doing (ie those of us who contribute to the discussions) is to uncover the facts about Stonehenge and the bluestones bit by bit, through a process of respectful debate. A bit more diplomacy please, Alex?

Alex Gee said...

Sorry Brian
Diplomacy: not my strong suit I'm afraid. I do try though.

I revise my post as follows
"I would suggest that the view that you can identify the exact source location of the debitage at Stonehenge to within 2 mtrs is untenable"

How's that :)

BRIAN JOHN said...

Splendid, Alex!! That sounds much more like the language of the ivory towers. Now Auntie Sallie, Thomas the Rhymer, and Uncle Tom Cobbley can all respond with equal politeness.....

Anonymous said...

As with all good magical events you are made to wait for the prestige!
The applause will follow swiftly on.

Read Rhymer's words they are chosen with care and then compare with what you have said he said.
Life may be brutish and short but it is of nothing if it is not subtle.

Scarlet O'Hara

alex gee said...

Perhaps instead of posting strange and ambiguous comments, Anonymous could find the courage to reveal their true identity and indulge in some straight talking?

Anonymous said...

the stones were wrapped in brush and timber, almost like a wicker basket so they could be
rolled and floated, which show us how it was achieved. too much work to load them on a
raft.they weren't that dumb.
The next step is to look for evidence of more details as to how the stones
were rolled and floated down the River Avon to their final destination by early Britons.

BRIAN JOHN said...

Anon-- so you think that it would have involved LESS work to weave a highly complex wicker basket, large enough to roll the stones and to provide buoyancy? Hmmm -- I remain to be convinced, even after Garry Lavin's experiments.