Sunday, 29 December 2013

Provenancing bluestones popular account by Robert Ixer

New science pinpoints source of Bluestones

Richard Bevins,
Keeper of Natural Sciences,
National Museum of Wales
Rob Ixer,
Institute of Archaeology,
University College London

https://www.academia.edu/5541901/Provenancing_bluestones_popular_account

Click to enlarge

From Earth Heritage Summer 2013


Monday, 23 December 2013

The Solstitial Arrow at Stonehenge

English Heritage has installed a large Brass arrow on the old A344 to point out the Solstitial alignment of Stonehenge.

Here it is freshly installed and a photo from Simon Banton to show it works with the mid-winter sunset.

Saturday, 21 December 2013

Stukeley. Stonehenge, a temple restor'd to the British druids - online copy.

The ongoing mystery and obsession with Stonehenge, along with speculation on its supposed purpose, should be credited to William Stukeley (1687 –1765), a harbinger of modern archeological study and a pioneer in the restoration and preservation of ancient monuments and sites. Stukeley, a friend and biographer of Isaac Newton (acknowledged with creating the “apple falling” story), was a fascinating character in his own right. An English gentleman, scholar, historian, physician, freemason, and druid, Stukeley surveyed Stonehenge in the 1720s and published his principal work on the ancient monument in 1740. Although Stukeley incorrectly theorized that the monument was part of the druidic religion, he was the first to recognize and describe the alignment of Stonehenge with the solstice. His meticulous observations and thorough survey remain significant and valuable in the history of the monument.



“Stonehenge stands not upon the very summit of a hill, but pretty near it, and
for more than three quarters of the circuit you ascend to it very gently from
lower ground. At half a mile distance, the appearance of it is stately and awful,
really august. As you advance nearer, especially up the avenue, which is
to the north-east of it, (which side is now most perfect) the greatness of its con-
tour fills the eye in an astonishing manner… Nothing in nature could be of a more
simple idea than this vast circle of stones, and its crown-work or corona at top ;
and yet its effect is truly majestic and venerable, which is the main requisite
in sacred structures. A single stone is a thing worthy of admiration… ”
- William Stukeley



A complete copy of Stukely's book is available here:

Stukeley, William. Stonehenge, a temple restor'd to the British druids. London : Printed for W. Innys and R. Manby, at the West End of St. Paul's, 1740.

Friday, 20 December 2013

Best Book on Stonehenge for Christmas, and it is free!

262 pages of excellent Stonehenge Research, this is what Stonehenge is really about. Without out doubt the best book on Stonehenge for Christmas reading, and it is free!


Stonehenge World Heritage Site Synthesis Prehistoric Landscape, Environment and Economy


Report Number: 45/2013 English Heritage Research Department Reports

This report is a synthesis of the archaeological evidence for the environment and economy of the prehistoric period in the Stonehenge landscape. It draws together existing information and analyses from a variety of specialist areas of archaeology and science. The synthesis has been produced in order to inform the interpretation content of the new visitor centre at Stonehenge, feeding particularly into reconstructions and graphics depicting the area around Stonehenge in different time periods.

Edited by Matthew Canti, Gill Campbell and Susan Greaney

Download it here



CONTENTS
1. Summary and Introduction -Susan Greaney and Gill Campbell
2. Geology, Landscape and Soils - Matthew Canti
3. Vegetation History - Zoe Hazell and Mike Allen
4. Plant Resources - Gill Campbell and Ruth Pelling
5. Animal Resources - Fay Worley
6. People - Simon Mays
7. Diet - Gill Campbell, Simon Mays, Jonathan Last, Fay Worley and Ruth Pelling
8. Houses and Settlement - Susan Greaney and Jonathan Last
9. Depositional Practice - Jonathan Last
10. Design, Clothing and Personal Adornment - Alison Sheridan and Gill Campbell
11. Technology and Domestic Objects - Richard Brunning, Jonathan Last, Hugo Anderson-Whymark, Gill Campbell, Alison Sheridan, David Dungworth, Glyn Davies and Angela Middleton
12. Social Organisation and Gender - Jonathan Last
Bibliography


Click to enlarge






Thursday, 19 December 2013

Bluestone Chips, Paper by Ixer and Bevins And A New Discovery

A very interesting paper about the Bluestone chips or debitage at Stonehenge has just been released:

CHIPS OFF THE OLD BLOCK:

THE STONEHENGE DEBITAGE DILEMMA

Rob Ixer and Richard Bevins


Within this century there has been a renewed interest in
the lithology of the Stonehenge bluestones, both for the
standing orthostats and also for the vast numbers of broken
bluestone material, now referred to as debitage.
Increasingly it has been recognised that there are a number
of interesting problems associated with this debitage found
within the ‘Stonehenge Landscape’, most notably their
original geographical provenance, their internal Stonehenge
provenance (matching debitage to parent orthostat), the
reason for their presence and finally explanations for the
apparent mismatch between the lithologies of the (aboveground)
bluestone orthostats and the debitage both in terms
of type and numbers....

Full paper and download at https://www.academia.edu/5464937/Chips_off_the_old_block

This coincides with Rob Ixer kindly confirming that the bluestones chips pictured below (click to enlarge)look like Preseli Spotted Dolerite - a chemically altered igneous rock containing spots or clusters of plagioclase feldspar.


I discovered this surface scatter in the spoil from animal burrows, the black round object is from a rabbit, last summer.

Over two hundred chips have been seen so far on the surface. It is close to Stonehenge, in the landscape but not within the Stonehenge Triangle. I have of course informed the archaeologists at Stonehenge, and can't tell anyone else the location. Sorry.

UPDATE - They aren't "bluestones", Rob Ixer has done further analysis and provides this Press Release.

Lithics from within the Stonehenge landscape collected by Mr T. Daw.

A selection of small lithics were collected by Mr T. Daw from within the Stonehenge landscape, they were macroscopically identified using x20 magnification. Their uniform but very restricted size range is of note as this would be unusual for Stonehenge debitage.
They comprise a mixture of modern roadstones, mainly fine-grained basalt , altered basalt and felsite, plus a single Stonehenge saccharoidal sarsen. The majority of the lithics are fine-grained igneous and similar in appearance to the spotted dolerites comprising most of the bluestones. Although the lithics are too small to determine macroscopically they appear to include two different types. No non-dolerite bluestone (rhyolite, tuff/ashes, sandstone) was recognised.
Two representative samples were sectioned to determine if either main group of lithics was a Stonehenge bluestone but neither was.  A sample of the abundant white feldspar and one of the rare, white feldspar classes of possible preselite were sectioned and petrographically described in transmitted and reflected light.  Neither thin section showed Preseli Dolerite.
The abundant white feldspar is an altered feldspathic rock possibly a basalt and the rare white feldspar rock is an altered felsite and more acidic carrying primary quartz.
The two sections add to the large number of adventitious lithics-mainly 19th and 20th century roadstones found in the Stonehenge Landscape.
Archive
Saccharoidal sarsen                                                                                     1.3g
Purple fine-grained lava same as from Fargo Wood Test Pits             1.9; 0.4g
Black, non-epidote bearing fine-grained dolerite with ?bornite         1.4g
Basalt/micrite                                                                                                0.4g
Abundant white feldspar     basalt                                                             1.1; 0.9g
Few white feldspar                                                                                        1.6; 1.5; 1.0; 0.6g

Rare, white feldspar, some pale green colouration   felsite                  1.6; 1.4; 1.3; 1.2; 3x0.8; 2x0.7;       0.6; 0.4

Wednesday, 18 December 2013

Stonehenge: A Decade of Discovery (full version)




Published on 17 Dec 2013
Research funded by the AHRC over the last decade is directly feeding into the new multimillion pound visitors' centre to be launched at Stonehenge this week. The research has overturned previously held views on the origins and the history of the UK's foremost prehistoric monument and one of the most famous heritage sites in the world

To mark the opening of the new building and the central role these research findings will play in the visitor experience, the AHRC is launching a new film that examines a decade of research at Stonehenge, and how this research has transformed our knowledge of Stonehenge.

This AHRC film features Professor Mike Parker-Pearson whose research at the site has reached a global audience, Professor Parker Pearson's research at Stonehenge spans three major research projects that total a £1.75million investment by the AHRC. The Stonehenge Riverside Project in 2006 led to the discovery of a second, smaller stone circle. Dubbed 'Blue Stonehenge', the discovery made the front pages of newspapers around the world. The two subsequent projects, The Beaker People, and more recently, Feeding Stonehenge have furthered our understanding of the ancient monument, suggesting that Stonehenge was built to unite the tribes of stone age Britain with one another, and, crucially, with their ancestors, that periglacial formations which are coincidentally aligned with the winter solstice may have been the reason that the site was first chosen by the first builders and indeed that the main axis is the mid-winter sunset rather than midsummer sunrise. This last finding confirms the long-held belief that Stonehenge was built with an astronomical purpose.

North Barrow and The Missing Station Stone

The one thing we know about the North Barrow at Stonehenge is that it isn't a "barrow". This circular feature with a an outer bank, ditch and flat central section held a missing Station Stone originally. Where it fits into the chronology of Stonehenge is unclear. Atkinson's section of it is badly recorded and fails to answer one of the fundamental questions, is the circular structure older or younger, is it overlain or does it overlie the main henge bank. Even the age of it in relation to the Aubrey holes in it is unclear.

The best evidence seems to be from Sharpe's balloon photo which to my mind shows the barrow as a complete circle (partly destroyed by the track, with the henge bank overlying it, but others see the photograph as proving the opposite.

I also attach a detail from a photo Adam Stanford took this summer which shows the parch marks and a hint of the position of the Station Stone on the very edge of the path.





Click to embiggen

Tuesday, 17 December 2013

The Architects of the Stonehenge Visitor Centre Explain

Here's the full press release from Denton Corker Marshall:

New Stonehenge Visitor Centre Opens
Denton Corker Marshall’s new Stonehenge Visitor Centre opens its doors on 18th December, inviting more than one million visitors every year to experience the transformed ancient site.
Located 1.5 miles to the west of the stone circle at Airman’s Corner, just within the World Heritage Site but out of sight of the monument, the new visitor centre is designed with a light touch on the landscape - a low key building sensitive to its environment.
Stonehenge Visitor Centre by Denton Corker Marshall
Sited within the rolling landforms of Salisbury Plain, the design consists of a subtle group of simple enclosures resting on a limestone platform, all sheltered by a fine, perforated, undulating canopy.
Barrie Marshall, director at Denton Corker Marshall, said: "The design of the centre is based on the idea that it is a prelude to the stones, and its architectural form and character should in no way diminish their visual impact, sense of timeless strength and powerful sculptural composition. Where the stones are exposed, massive and purposefully positioned, the centre is sheltered, lightweight and informal. And where the stones seem embedded into the earth, the centre rests on its surface."
Stonehenge Visitor Centre by Denton Corker Marshall
Three pods, finished in different materials, provide the principal accommodation. The largest, clad in sweet chestnut timber, houses the museum displays and service facilities. The second largest, clad in glass, houses the educational base, a stylish café and retail facilities. Located between these is the third, by far the smallest and clad in zinc, which provides ticketing and guide facilities.
Oversailing them all, and resting on 211 irregularly placed sloping columns, is a steel canopy clad on the underside with zinc metal panels and shaped with a complex geometry reflecting the local landforms.
Stonehenge Visitor Centre by Denton Corker Marshall
Local, recyclable and renewable materials have been used wherever possible. The material palette includes locally grown sweet chestnut timber cladding and Salisbury limestone.
Stephen Quinlan, partner at Denton Corker Marshall, said: "Various strategies have been adopted in the design to ensure that the centre is environmentally sensitive and uses natural resources in a responsible way. These range from the natural sun shading qualities of the canopy which promotes natural ventilation and reduces the need for cooling in the pods, through to more technical solutions such as heat pumps and high efficiency insulation."
Stonehenge Visitor Centre by Denton Corker Marshall
The new building allows Stonehenge to have dedicated facilities on site for education and interpretation for the first time, with museum-quality exhibits that tell the story of the 5,000 year- old monument.
From the new centre, visitors can either walk to the monument or take a ten-minute shuttle ride. During the trip the henge emerges slowly over the horizon to the East.
Stonehenge Visitor Centre by Denton Corker Marshall
Dr Simon Thurley, chief executive of English Heritage, said: "For too long, people's appreciation of Stonehenge is this mysterious, impressive but anonymous monument. The Neolithic period itself is pretty much a murky expanse of time, shrouded by many outdated notions. We want people to come here and take away a fresh view."
Stonehenge Visitor Centre by Denton Corker Marshall
There will also be an outdoor gallery including the reconstruction of three early Neolithic houses, based on rare forensic evidence found near Stonehenge. These houses will be built by skilled volunteers and are due to be complete by Easter 2014.
Sustainable Design
The building is sensitively designed to sit lightly in the landscape. Reversibility – the ability to return the site to its current state - was a fundamental design concept. The building will last as long as it needs to but could, if necessary, be removed leaving little permanent impact on the landscape.
Stonehenge Visitor Centre Denton Corker Marshall
Site plan - click for larger image
This is achieved by constructing it on a concrete raft which in turn sits on an area of 'fill' with minimal cutting into the soil. The modern construction, using slender steel columns and lightweight framed walls, and semi-external spaces allow the depth of foundations to be minimised.
Stonehenge Visitor Centre Denton Corker Marshall
West elevation - click for larger image
Other green features include:
» An open loop ground source heating system that pumps underground water through a unit to extract/inject heat energy. This enables the building to be heated and provides some cooling without the need for fossil fuels.
» Fully insulated cavity walls - the timber pod is constructed of structurally insulated panels (SIPS), which enables efficiencies in construction whilst minimising material waste and ensuring the building is well insulated.
Stonehenge Visitor Centre Denton Corker Marshall
North elevation - click for larger image
» Mixed mode ventilation – the building will be naturally ventilated whenever external conditions allow, switching to an efficient mechanical ventilation system that enables the heat energy in the exhaust air to be 'recovered' and transferred to the supply air, thereby reducing the load on the heating plant and saving energy.
Stonehenge Visitor Centre Denton Corker Marshall
East elevation - click for larger image
» "Grey water", including rainwater collected from the roof of the building, will be used for the bulk of water required at the visitor centre, e.g. for flushing toilets. Other water – e.g. for drinking - will be drawn from the aquifer, a local and renewable resource.
» The facilities will use on-site water treatment for sustainability and to avoid intrusive trenching for connections to water and sewer mains.

Tuesday, 10 December 2013

Carrying The Bluestones To Stonehenge

Mike Parker Pearson  at the end of his recent excellent video lecture reveals the possibility that the Bluestones may have been carried from Wales to Stonehenge.  Gowland put forward some similar thoughts in 1901

From: Gowland, W, 1902, Recent excavations at Stonehenge.
Archaeologia, 58, 37–82



THE ERECTION OF STONEHENGE.
Transporting the Stones.—Our special concern will now be to see how the
stones could have been brought to Stonehenge, the manner in which they were
shaped, and the means adopted for setting them up. For these ends no elaborate
engineering appliances were required, neither was a knowledge of metals necessary.
All the operations could be efficiently carried out with tools of stone and deer’s
horn, trunks of trees, and ropes of hide.....
... as regards the transport of the blocks, they throw but
little light. For the solution of this problem we have, therefore, to turn to the
examples of similar work in countries where primitive methods for moving heavy
stones are still, or have been recently practised.
In Japan, where megalithic remains abound, and where the use of rude
massive stones was common almost up to our own times, and even now is
occasionally seen, enormous blocks were transported for considerable distances
without the aid of any appliances which were beyond the reach of the men of the
neolithic age.
In the walls of tue Castle of Osaka, built in the seventeenth century, there
are several enormous stones, the largest of which measures 40 feet by 10 feet by
at least 5 feet, and must weigh moro than 160 tons.
A picture printed in the eighteenth century, which I have seen, represents
the transport of one of these stones. In it the stone is represented resting on a
low frame of massive timbers fitted with rude solid wheels of wood. This is being
hauled by a vast number of men by means of huge cables to which numerous
small ropes are attached.
In other cases a number of rollers were substituted for the wheels, and this
method I have seen in operation.
The block is placed on the frame by first raising it to the required height
by the application of long wooden levers to either end alternately, and packing
it up with timber as it is being raised. The frame is then slipped, under it and
the packing removed.......
Another method which is illustrated in Plate V.b may be seen in use every-
where in Japan and in China for carrying about stones and timber of much
greater weight than the bluestones. In some of the hill districts in India stones
of 20 tons weight are thus carried. The huge block which is the pedestal of a
tomb stone is pierced with a central hole so that a strong beam of timber passed
through it is all that is required for the attachment of the bearing poles.


Generally, however, several horizontal beams are lashed to the stone, and to
these, at intervals of about two or three feet, transverse poles are fastened, of
sufficient length to accommodate the shoulders of from two to three or more men
at each side in the manner shown in the figure. The men keep time by shouting
simultaneously at each step, and in this they are guided by the man standing on
the stone waving his wand.
Any of the methods I have described were perfectly possible to the builders
of Stonehenge, and it is in the highest degree probable that the same or
similar methods were employed by them for the transport of the stones from
the places where they were found.




Click to embiggen




Monday, 9 December 2013

Airman's Cross and the site of the Stonehenge New Visitor Centre

I have been instructed not to blog about the new Visitor Centre at Stonehenge until it is all open and ready on the 18th Dec, so sorry for no updates on the exciting changes going on.

Google Streetview still shows Airman's Cross in its preconstruction pristiness, I thought it worthwhile capturing a few images and linking to the interactive view below.


View Larger Map





Click to embiggen

Tuesday, 3 December 2013

Tunnel Vision

A few snaps of the tunnel at Stonehenge as it faces its last couple of weeks of use.

Click any to embiggen






Cecil Chubb's Deed of Gift of Stonehenge

I couldn't easily find a copy of Cecil Chubb's Deed of Gift with which he gave Stonehenge to the Nation online. So I have combined several sources and think this is the most accurate version available now. 






This Indenture made the 26th day of October one thousand nine hundred and eighteen Between Mary Bell Alice Chubb of Bemerton Lodge Salisbury in the County of Wilts the wife of Herbert Edward Chubb of the same place Esquire Barrister at Law and the said Cecil Herbert Edward Chubb (hereinafter called “the Donors”) of the one part and The Commissioners of Works of the other part Witnesseth that the Donors being seized of the hereditaments hereinafter described as joint tenants for an estate in fee simple in possession free from encumbrances and being desirous of giving the same to the Commissioners of Works for the benefit of the Nation hereby in exercise of the power for that purpose conferred by the Ancient Monuments Consolidation and Amendment Act 1913 and by virtue of their estate convey unto the Commissioners of Works All and singular the hereditaments described in the Schedule hereto which hereditaments are delineated on the plan drawn hereon and are thereon coloured pink and are situate on Stonehenge Down in the County of Wilts and comprise the Ancient Monument known as Stonehenge and the site thereof and such part of the adjoining land as is required for the purpose of fencing and preserving the same from injury (together constituting an Ancient Monument within the meaning of the said Act) To Hold the same unto and to the use of The Commissioners of Works in fee simple And the Commissioners of Works hereby in exercise of the power for this purpose conferred on them by the said Act accept the gift hereby made to them and hereby covenant and agree with the Donors and each of them First that the public shall have free access to the premises hereby conveyed and Every part thereof on the payment of such reasonable sum per head not exceeding one shilling for each visit and subject to such conditions as the Commissioners of Works in the exercise and execution of their statutory powers and duties may from time to time impose Secondly that the premises shall so far as possible maintained in their present condition Thirdly that no building or erection other than a pay box similar to the Pay Box now standing on the premises shall be erected on any part of the premises within four hundred yards of The Milestone marked “Amesbury 2” on the northern frontage of the premises and Fourthly that the Commissioners of Works will at all times save harmless and keep indemnified the Donors and each of them their and each of their estates and effects from and against all proceedings costs claims and expenses on account of any breach or non observance of the covenants by the Donors to the like or similar effect contained in the Conveyance of the premises to the Donors Dated the thirty first day of December One thousand nine hundred and fifteen In witness whereof the Donors have hereunto set their hands and seals and the Commissioners of Works have caused their Common Seal to be affixed the day and year first above written

The Schedule above referred to
Number on 1/2500 Ordnance Map Description Acreage
Part 22 Stonehenge and Down 30.730

Signed Sealed and Delivered by the above named Mary Bella Alice Chubb and Cecil Herbert Edward Chubb in the presence of George Herbert Engleheart, Little Clarindon, Dinton Wilts, Fellow of the Society of Antiquaries of London

A pdf of the original is available - https://www.facebook.com/download/184442658409081/Deed%20of%20gift.pdf  



An early copy:



Click any to embiggen.

Monday, 25 November 2013

Mark Anstee Stonehenge Print

Mark Anstee – limited edition

Stonehenge Grand Tour Souvenir

Following his year long residency at Stonehenge, Mark
Anstee has made a souvenir for fellow grand tourists.

‘Stonehenge Portal’ – is a limited edition print from his
silverpoint drawing of an accidental trilithon. The drawing
was made at Stonehenge between March and July 2013
and took 132 hours to complete.




The edition comes ready mounted and wrapped in a
protective cardboard shell.

Title: Stonehenge Portal
Limited edition 150 (+15 artist proofs)
Print size 190mm x 190mm
Mount size 305mm x 305mm
Box size 335mm x 335mm
Digital print on 310gsm Hahnemühle German Etching
Paper with light-fast archival quality inks.

A certificate of authenticity issued by the printer is
included. The edition is strictly limited to just 150 prints.

The mount is a 2.6mm conservation mount board in
antique white.

Each print is signed and numbered by the artist, and the
artist’s personal monogram is stamped on the print and
its accompaniments.

Price - £115.00 (+ p&p)

Please get in touch at info@markanstee.com

Stonehenge Grand Tour is at www.markanstee.com/latest or
http://www.markanstee.com/category/stonehenge-the-grand-tour/

Sunday, 24 November 2013

Channel 4 - Walking through History - Stonehenge - The Route

Channel 4 - Walking through History - Stonehenge


Wiltshire is home to arguably the greatest concentration of prehistoric monuments in Europe, if not the world!


The 45 mile route begins at Windmill Hill before heading south to spend the first day walking amongst the stone circles of Avebury.




Download the walk; http://www.channel4.com/microsites/W/Walking-Through-History/Walking-Through-History2-Stonehenge.pdf


The download includes full day by day walking instructions with accompanying history guide.
Discover how the famous monuments of the area are connected and what they can tell us about life, and death, in Neolithic Britain. The walk takes us across some of the most beautiful landscape in the south west, as we uncover the actions of our ancestors here between 4000 and 2000BC.

Day 1

Avebury Stone Circle
Avebury Stone Circle
A gentle first day with plenty of time for admiring the monuments encountered along the route.
  • Windmill Hill to Avebury via Avebury Stone Circle and the Sanctuary

Distance: 6.5 miles


Day 2

West Kennet Long Barrow
We up the pace as we hunt for hard evidence of our elusive ancestors at Silbury Hill and the West Kennet Long Barrow. We skirt the Marlborough Downs and head up and over Milk Hill for some more modern mysteries, like crop circles.
  • Avebury to Honeystreet, via Silbury Hill, Swallowhead Springs, West Kennet Long Barrow, Field of Sarsen Stones, Milk Hill and the Alton Barnes White Horse, and Adam's Grave.

Distance: 15.5 miles


Day 3

The Avenue
The Avenue
We follow our ancestors down the River Avon to the greatest prehistoric monument of them all – Stonehenge.
  • Honeystreet to Stonehenge via: Durrington Walls, West Amesbury Henge and the Avenue

Distance: 23.5 miles


The Map

OS Explorer Maps 157, 130 (1:25k) or OS Landranger 173, 184 (1:50k)
All distances are approximate so allow plenty of time

Friday, 22 November 2013

Craig Rhos-y-felin is the likely major source of Stonehenge rhyolitic bluestones

Bluestone sources are very much in the news this weeks as Rob Ixer and Richard Bevins release news of their work. Confusion is reigning as journalists fail to point out there are many different types of "bluestone", Brian John has published a list: http://brian-mountainman.blogspot.co.uk/2011/12/bluestone-rock-types.html

A quote from Bevins: "I don't expect to get Christmas cards from the archaeologists who have been excavating at the wrong place all these years." has been taken as a put down of the work Mike Parker Pearson has being doing at Craig Rhos-y-felin. But as Bevins and Ixer's paper from earlier this year makes clear the "Bluestones" at Craig Rhos-y-felin are rhyolites and the new source discovery at Carn Goedog is of spotted Dolerite - see http://www.sarsen.org/2013/11/carn-goedog-is-likely-major-source-of.html and http://www.sarsen.org/2013/11/carn-goedog-and-craig-rhosyfelin-aerial.html for more detail:

Here's the abstract of their earlier paper; 

http://www.sciencedirect.com/science/article/pii/S0305440313001076

Carn Alw as a source of the rhyolitic component of the Stonehenge bluestones: a critical re-appraisal of the petrographical account of H.H. Thomas



(Click for larger)

Highlights

Stonehenge rhyolitic bluestones were sourced by Thomas (1923) to Carn Alw, Wales.
Recent geochemical investigations have questioned that west Wales source.
The original thin sections studied by Thomas have been re-investigated in this study.
Thomas's proposed provenance of the Stonehenge rhyolites to Carn Alw is disproven.




Abstract

The source of the Stonehenge bluestones was first determined in the early 1920s by H.H. Thomas who was an officer with the Geological Survey of England and Wales. He determined that the so-called ‘spotted dolerites’ could be petrographically matched to a small number of outcrops in the Mynydd Preseli district in south-west Wales. The bluestones, however, comprise a number of additional lithologies, including rhyolite and ‘calcareous ash’, as well as various sandstones. Thomas was convinced that the volcanic lithologies in the bluestone assemblage were all sourced from a small area at the eastern end of the Mynydd Preseli, with the rhyolites originating from the prominent outcrop known as Carn Alw. Recently, provenancing of these rhyolites to Carn Alw has been questioned on the evidence of whole-rock geochemistry. This raised concerns over the original petrographical attribution. Accordingly a re-investigation was undertaken of the rhyolite petrography by re-examining the original specimens used by Thomas. Three of the original four thin sections studied by Thomas were re-examined, along with a newly made thin section from the fourth of Thomas' rock samples as the original thin section could not be located. The new petrographical evidence demonstrates convincingly that the two pairs of thin sections from the Preseli and Stonehenge as examined by Thomas do not match despite his contention and argues strongly that Carn Alw is not the source of the Stonehenge rhyolites which Thomas described. This reinforces the geochemical evidence presented recently and supports the contention that Craig Rhos-y-felin, to the north of Mynydd Preseli, is an important source of rhyolitic debris in the Stonehenge Landscape. Nevertheless, there remain uncertainties over the provenance of other Stonehenge rhyolites (and dacites), including four of the orthostats themselves.

Wednesday, 20 November 2013

Carn Goedog and Craig Rhosyfelin Aerial View


Carn Goedog - White Circle - and Craig Rhosyfelin - Yellow Circle - Aerial View

Carn Goedog is the likely major source of Stonehenge doleritic bluestones

Journal of Archaeological Science

http://www.sciencedirect.com/science/article/pii/S0305440313003956

Carn Goedog is the likely major source of Stonehenge doleritic bluestones: evidence based on compatible element geochemistry and Principal Component Analysis

  • a Department of Geology, National Museum of Wales, Cathays Park, Cardiff, Wales CF10 3NP, UK
  • b Institute of Archaeology, University College London, London WC1H 0PY
  • c Institute of Geography and Earth Sciences, Aberystwyth University, Aberystwyth, Wales, SY23 3DB


Highlights

Stonehenge doleritic bluestones were first sourced to Carn Meini and Cerrigmarchogion in west Wales by Thomas in 1923.
Thorpe et al. in 1991 used incompatible element geochemistry to in part support Thomas’s attribution.
These attributions have been re-assessed using compatible element geochemistry.
Nearby Carn Goedog is now clearly identified as the major source of Stonehenge doleritic bluestones.

Abstract

The Stonehenge bluestones were first sourced to outcrops in the high parts of the eastern Mynydd Preseli in SW Wales by H.H. Thomas in the early 1920s. He recognised the distinctive ‘spotted dolerite’ from his fieldwork in that area and suggested that the tors of Carn Meini (also known as Carn Menyn) and Cerrigmarchogion were the most likely sources. In the early 1990s, in a major contribution to our understanding of the Stonehenge bluestones, the geochemistry of a set of samples from Stonehenge monoliths and debitage was determined and compared against the geochemistry of dolerites from the eastern Mynydd Preseli by a team from the Open University led by R.S. Thorpe. They argued that the majority of the Stonehenge dolerites could be sourced from outcrops in the Carn Meini-Carn Gyfrwy area, based on the concentrations of the so-called ‘immobile’ elements (elements which are not affected by rock alteration processes), in particular TiO2, Y, and Zr. However, these elements are incompatible during crystallization of mineral phases in basaltic systems (that is they do not enter into the mineral phases which are crystallizing but are concentrated in the residual liquid) which severely hampers their use in discriminating between different pulses of an evolving magma (as is the case of the doleritic sills emplaced high in the crust and now exposed in the Mynydd Preseli). An alternative strategy in this study re-examines the data set of Thorpe’s team but investigates the concentration of elements which are compatible in such basaltic systems (that is elements which do enter into the crystallizing mineral phases), namely MgO, Ni, Cr and Fe2O3. On the basis of the abundances of these elements on bivariate plots and also by using Principal Component Analysis on the dataset available and various sub-sets we identify three compositional groupings for the Stonehenge doleritic monolith and debitage samples and conclude that the majority of them (Group 1 of this paper) can be sourced to the prominent outcrop in the eastern Mynydd Preseli known as Carn Goedog. We also offer potential sources (with one exception) for those Stonehenge dolerites which appear not to relate to Carn Goedog.

Keywords

  • Stonehenge
  • Bluestones
  • Dolerite
  • Compatible element geochemistry
  • Principal Component Analysis;
  • Provenance
  • Mynydd Preseli
  • Wales

Figures and tables from this article:


Fig. 1.
Simplified geological map of the eastern Mynydd Preseli showing the locations of the main outcrops and the geographic locations of the analysed samples used in the geochemical plots in this paper. Geological detail based on British Geological Survey (2010).


Fig. 2.
Oblique aerial view of the eastern Mynydd Preseli looking approximately westsouthwest, showing the nature of the terrain and a number of the key geological outcrops. Photo courtesy of Sid Howells.

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