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News from Rupert Soskin: stone pillar is blueschist
I don't know whether Rupert Soskin posts here any more (if he does come on to discuss this I will delete this entry). I've just read this on the Facebook "Standing with Stones" page and, having not long since visited Bryn Celli Ddu, found it Very Interesting indeed.
Below is Rupert's FB post:
"Hi folks, Rupert here.
I thought it important to share this as many of you have expressed an interest. I was contacted last night on Twitter by Ffion Reynolds who had been to Bryn Celli Ddu with a geologist who identified the 'tree' pillar as blueschist - i.e rock, not fossil.
Now, the interesting thing about blueschist is that it is a metamorphic rock which only forms in extremely particular circumstances, best explained by this quote from the United States Geological Survey's website:
For many years geologists have been able to relate individual facies to the pressure and temperature conditions of metamorphism.
But they had no satisfactory explanation for the geologic processes that form metamorphic rocks, that is, until the theory of plate tectonics emerged.
One good example is this relatively rare metamorphic rock called "blue schist."
Experimental work had shown that the minerals in blue schist form only under very unusual metamorphic conditions.
These conditions are a pressure range equivalent to a depth of 15 to 30 kilometers in the crust and a very cool temperature, only 200 to 400 degrees centigrade.
That's the approximate cooking temperature of a kitchen oven or toaster.
At a depth of 15 to 30 kilometers, however, the temperature is normally about twice as hot, 500 to 750 degrees centigrade.
So the only way that rocks can be metamorphosed to blue schist facies , is to be quickly shoved down to those extreme depths and then rapidly brought back up before the rocks have time to heat up completely.
And that's exactly what happens where two tectonic plates are colliding in a subduction zone.
In fact, blue schist bearing rocks normally occur in long linear zones that mark ancient plate subduction boundaries.
One of the principal reasons I clung to the fossil theory was the cylindrical tree-trunk shape which had clearly not been cut, despite all previous descriptions of it being 'carefully worked'.
The formation of blueschist could allow a seam of cooling rock to literally roll up between the tectonic plates rather like a piece of seaside rock.
This leaves us with two, rather lovely points:
One: The builders of Bryn Celli Ddu would know no difference, it was still a magical stone tree.
And Two: Metamorphic rock does not form in conveniently sized pieces. There must be more."
Exploring ancient life in the Vale of Pewsey
The Vale of Pewsey is not only rich in Neolithic archaeology. It is home to a variety of other fascinating historical monuments from various periods in history, including Roman settlements, a deserted medieval village and post-medieval water meadows. A suite of other investigations along the River Avon will explore the vital role of the Vale's environment throughout history.
Dr Leary continued: "One of the many wonderful opportunities this excavation presents is to reveal the secret of the Vale itself. Communities throughout time settled and thrived there - a key aim of the dig is to further our understanding of how the use of the landscape evolved - from prehistory to history."
Duncan Wilson, Historic England Chief Executive, added: "Bigger than Avebury, ten times the size of Stonehenge and half way between the Stonehenge and Avebury World Heritage Sites, comparatively little is known about this fascinating and ancient landscape. The work will help Historic England focus on identifying sites for protection and improved management, as well as adding a new dimension to our understanding of this important archaeological environment."
The Vale of Pewsey excavation also marks the start of the new University of Reading Archaeology Field School. Previously run at the world-famous Roman town site of Silchester, the Field School will see archaeology students and enthusiasts from Reading and across the globe join the excavation.
The six week dig runs from 15th June to 25th July. Visitors are welcome to see the excavation in progress every day, except Fridays, between 10:00am and 5pm. Groups must book in advance
Steve Marshall will be giving a talk on springs, rivers & the Avebury monuments in Swindon!
Friday 26th Sept, 7.30pm, Swindon Museum & Art Gallery, Bath Road.
Museum Friends £3.50, Non-members £4.50
Obama visits Stonehenge
"How cool is this" - BBC Points West publish a photo of President Obama strolling around Stonehenge this evening.
On Facebook under Points West.
Update on second year dig at Avebury WK Avenue
Archaeology students mostly from Southampton and Leicester universities have re-opened one trench from last year’s dig and opened another major area of investigation in West Kennet Avenue. This involves moving tons of turf and soil and getting down to a level of soil that has never been ploughed (“intact soil”) and so holds flints and other artefacts such as pottery shards, where they were dropped.
This part of the Avenue was chosen because it had been investigated by the marmalade millionaire Alexander Keiller in the 1930s and he had located a gap in Avenue’s stones. Such a gap must have been left for a reason – perhaps because there was a building or other special structure that had to be preserved.
Among these finds are several flint arrowheads – including one miniature barbed and tanged arrowhead (photo left) which the project's experts say is deliberately miniaturised. Whether it was made as a gift, a toy or for a ritual purpose is another matter altogether. Whatever the reason for making it, the workmanship is extraordinary.
This dig is part of the long term Between the Monuments programme which aims, as National Trust archaeologist Dr Nick Snashall puts it, “to put the people back into the Avebury site.” Finding out more about the routine lives and residence of the people who built and used Avebury’s henge and avenues should help understand why these monuments were made and why this site was chosen.
It is a collaborative research project between the University of Southampton (Dr Josh Pollard), University of Leicester (Dr Mark Gillings), Allen Environmental Archaeology (Dr Mike Allen) and the National Trust (Dr Ros Cleal & Dr Nick Snashall.)
On Tuesday (August 5), with only two full days to go before the dig had to finish and with some rain showers during the morning, people from the surrounding villages were shown over the site and heard about the project’s progress.
Despite the buckets, wheelbarrows and spades (there was even someone spotted wielding a pick axe – albeit on the upper layers of soil), archaeology makes use of all the latest technology. This year laser measuring equipment has been used on the site.
Dr Mark Gillings & soil samplesDr Mark Gillings & soil samplesAnd those plastic bags behind Dr Gillings (photo left) contain soil samples which will be analysed and may reveal tell-tale signs of plant life, what animals were about and so on. This is important as the soil is so acidic that snail shells and bones are not found – but pollen and chemical residues will be preserved and identified in the analysis.
Another recently available technique allows scientists to tell what different sizes and shapes of flint cutting tools were used for. This high-magnification process has shown one tool found last year was used to cut nettles – from which string and cords were made.
Another exciting find in one of last year’s trenches is what looks to the experts like the remains of a ‘possible hearth’. It was nearby in this trench that they discovered in 2013 twelve certain or probable stake-holes in a pattern that could justify the theory that they were part of a dwelling of some sort: it is very tempting to add two such finds together to make a dwelling.
And then, just when the students thought they had unearthed some really good and significant finds from many centuries BC, someone finds a mediaeval coin. Mind you, this coin far smaller than our five pence piece and paper thin, so spotting it amidst the soil and recognising that it was anything at all worth keeping from the spoil heap, is a testament to these students’ growing expertise and enthusiasm.
As ever, it is a matter of funding being available to allow a third year’s dig to reveal even more of the evidence of the human lives that flourished in between Avebury’s stones.
Extension To Salisbury Museum opens
A £2.4m extension to Salisbury Museum housing more than 2,500 rare artefacts has opened.
The Wessex Gallery of Archaeology, which was partly funded by a lottery grant, is home to to a large collection of Stonehenge-related pieces.
These include the skeleton of a wealthy and powerful Bronze Age man dubbed the "Amesbury Archer" discovered in 2003.
The gallery also includes the Wardour Hoard containing 4,000-year-old sword fragments, spearheads and chisels.
Bus service to be withdrawn
A friend in the Ramblers sent me this earlier today - am a bit gutted as have been known to use this service to walk up to Wayland's Smithy.
"Thamesdown Transport's route 47 between Swindon and Lambourn, via Bishopstone and Ashbury, is to be withdrawn. This will leave several villages without a bus service and make it more difficult to do linear walks along that part of the Ridgeway. At the time of writing it is unclear whether the Ridgeway Explorer bus X47, which runs only on Saturdays, will continue."
Bronze age mound at Ogbourne St Andrew being investigated
Small fry compared to the West Kennet Avenue dig but I found this quite at exciting.
Started a walk today from the church at Ogbourne St Andrew - a couple of archaeologists from Cranfield University were in the church-yard undertaking a geo-phys and mapping exercise of the Bronze Age mound which is in the churchyard. Apparently a small history group in the village had invited them in. I do hope the results will be published.
Archaeology walk with Dr Nick Snashall on 8th May
Was over at WK long barrow today when I bumped into a rather large but very well behaved group of people (inside the barrow). Dr Nick Snashall was leading a 'walking through the landscape' guided walk on behalf of the National Trust. The little bit of the talk I caught about WKLB sounded informative and, yes, I did learn something in a few short minutes.
Dr Snashall told me there is another such walk on 8th May (see her blog).
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Nature; stone circles and all ancient sites that involve walking through unspoilt countryside/being near the sea; islands around the the British Isles, especially those with ancient monuments.