STONEHENGE: GIANT GLACIAL ERRATIC HAILED AS "MISSING PIECE” OF BLUESTONE PUZZLE
A giant bluestone erratic just found near Mumbles, on the south Gower coast, has been hailed as one of the most important "chance discoveries" of recent times. It proves beyond doubt that the Irish Sea Glacier was capable of carrying large monoliths of dolerite rock from Pembrokeshire up the Bristol Channel towards Stonehenge.
The huge boulder, measuring 2.2m x 1.3m x 1m and weighing at least 7 tonnes, was found on the rocky foreshore around the mid-tide mark, at a location yet to be revealed, by Mumbles photographer Phil Holden. It’s difficult to know why it had been missed by all previous geologists who have investigated this coast, but from a distance its colour is very similar to that of the native limestone rock, and it might also have been previously covered by sand and beach cobbles.
Phil says: "I must have walked over this boulder a dozen times; lodged in a crevasse, it wasn't until a falling tide revealed its true colours that I realised this was not just another large erratic for me to photograph for my photo-library but something more significant! “
Phil then contacted retired glacial geomorphologist Dr Brian John, who has been collecting evidence relating to the transport of the Stonehenge bluestones for many years. Phil thought that the rock might be dolerite, so he also made contact with igneous geologist Dr Katie Preece at Swansea University with a request for help with identification. She reported that the rock is indeed dolerite (micro-gabbro). There are no rocks of that type anywhere near Gower, and the source area could be North Pembrokeshire.
He says: “This discovery is of huge importance to Ice Age research in South Wales and also to the debate about the origins and transport of the Stonehenge bluestones. Archaeologists — and some geologists — have previously assumed that it would have been “impossible” for glacier ice to transport large boulders, pillars and slabs of dolerite from North Pembrokeshire, or anywhere else, up the Bristol Channel towards Somerset and Stonehenge. Many smaller dolerite erratics are known from Gower and other parts of South Wales, but there have been no discoveries to compare with the “giant erratics” that are known from the coasts of Devon and Cornwall. Phil’s very exciting discovery demonstrates that the glacier did indeed transport large blocks of rock south-eastwards from their source areas. There must be other erratics of this size awaiting discovery along the South Wales coast, but unfortunately most of them are likely to be located under the murky waters of the Bristol Channel.”
Dr John adds that this discovery should encourage archaeologists to abandon their long-held belief that the bluestones at Stonehenge were quarried in North Pembrokeshire and transported by Neolithic tribesmen by land or sea on a number of epic expeditions. “Theirs is a nice story,” he says. “But the evidence of quarrying is highly suspect, and there is no solid evidence in support of the human transport hypothesis either. Most of the Stonehenge bluestones look like ancient glacial erratic boulders, and that is undoubtedly what they are.”
Note 1: Research is ongoing, and it is hoped that once geological sampling is done, it will be possible to confirm a North Pembrokeshire origin for the boulder and to fix a precise provenance. Even if the rock proves to have come from further afield (from North Wales or Scotland, for example) it still demonstrates that glacier ice has carried giant monoliths over a great distance up the Bristol Channel.
Note 2: This giant erratic could not have been transported into this position by Neolithic seafarers or anybody else. It is far bigger than any of the Stonehenge bluestones.
Note 3: For the moment the precise location of the giant boulder is being kept secret, pending further research. It is in quite a dangerous location.
Note 4: Photos are copyright Phil Holden. Please contact Phil for usage rates and high resolution images.
Phil Holden Photography
Dr Brian John
Dr Katie Preece