Andesite from Trefgarn Gorge
16TH FEBRUARY 2022 NEWS
A rediscovery in our Museum stores featured in the February 2022 British Archaeology Magazine with an article by Mike Pitts.
Stonehenge must be as thoroughly researched as any ancient site in the world. Yet important evidence can still be found in museum archives.
The discovery identified in the Wiltshire Museum, Devizes by director David Dawson, consists of three wallets containing 34 geological thin sections, made for William Cunnington III from specimens collected “from under the turf within the area of the [Stonehenge] building” between 1876 and 1881. Though known to have been made, they were thought lost. They are of considerable interest to geologists, as few such early collections remain extant. They also hold important new clues about the nature of the bluestones, the small megaliths at Stonehenge mostly sourced in Wales.
The samples allow new descriptions of three stones. Numbers 32 and 61a are dolerite. Because thin sections cannot be analysed geochemically, the slides add to existing characterisations without changing them. Stone 32c, however, had not been scientifically studied before. It can now be allocated to “Andesite Group A”, say Rob Ixer and Richard Bevins, which they had previously defined using broken debris alone. It is the first megalith – and the slide is now the type specimen – to be scientifically assigned to this large group of material to which four other stones had been attributed by eye. Its source is thought to be somewhere in north Pembrokeshire. In addition, one of Cunnington’s samples proved to be an example of Ixer and Bevins’s “Dacite Group D”, one of only two known instances of this rock type from the Stonehenge monument.
Mike Pitts, British Archaeology magazine February 2022
The microscope and slides will be displayed at the Museum later in the Spring.
Stonehenge must be as thoroughly researched as any ancient site in the world. Yet important evidence can still be found in museum archives.
The discovery identified in the Wiltshire Museum, Devizes by director David Dawson, consists of three wallets containing 34 geological thin sections, made for William Cunnington III from specimens collected “from under the turf within the area of the [Stonehenge] building” between 1876 and 1881. Though known to have been made, they were thought lost. They are of considerable interest to geologists, as few such early collections remain extant. They also hold important new clues about the nature of the bluestones, the small megaliths at Stonehenge mostly sourced in Wales.
The samples allow new descriptions of three stones. Numbers 32 and 61a are dolerite. Because thin sections cannot be analysed geochemically, the slides add to existing characterisations without changing them. Stone 32c, however, had not been scientifically studied before. It can now be allocated to “Andesite Group A”, say Rob Ixer and Richard Bevins, which they had previously defined using broken debris alone. It is the first megalith – and the slide is now the type specimen – to be scientifically assigned to this large group of material to which four other stones had been attributed by eye. Its source is thought to be somewhere in north Pembrokeshire. In addition, one of Cunnington’s samples proved to be an example of Ixer and Bevins’s “Dacite Group D”, one of only two known instances of this rock type from the Stonehenge monument.
Mike Pitts, British Archaeology magazine February 2022
The microscope and slides will be displayed at the Museum later in the Spring.
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No doubt there will be another paper from Ixer and Bevins in due course, and while there are no earth-shattering revelations here, I'm interested to see the references to dacite and andesite. There's dacite on Carningli near Newport, and in other locations. There are many references to dacite fragments in the Stonehenge debitage, but andesite is rather more interesting. There isn't any andesite, to the best of my knowledge, in Mynydd Preseli, but there are outcrops which were quarried for many years in the Trefgarn Gorge. Has some of the debris at Stonehenge come from Trefgarn? All will be revealed....... but as the list of bluestone provenances inexorably builds up, for how much longer will MPP and his merry gang be able to maintain the fantasy of the bluestone quarries?
Ref:
A re-appraisal of the petrogenesis and tectonic setting of the Ordovician Fishguard Volcanic Group, SW Wales
Published online by Cambridge University Press: 28 July 2015
BETHAN A. PHILLIPS, ANDREW C. KERR and RICHARD BEVINS
(behind a paywall)
1 comment:
Hmmm..... I know Treffgarne Gorge, as it's closer to the area where my brother lives. And I'm also been, albeit briefly courtesy of our friendly Wiltshire coach driver, almost exactly to the spot where the Gower dolerite erratic has been identified. By the way, the coach driver had driven us a long distance along the A40, MPP's highly imaginative Pied Piper route for intrepid subservient Welsh treckers to VERY hypothetically hump their trophy 🏆 bluestones to Somewhere.
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