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Thursday, 27 January 2022


Photo caption: Glacial geomorphologist Dr Brian John examining the Mumbles giant erratic boulder
on the rocky foreshore

Press Briefing



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.

Photo caption: The elongated 7-tonne dolerite giant erratic boulder nesting in a crevice in the limestone bedrock. At high tide it is completely submerged.

Brian John has now had a chance to examine the boulder on the beach. He says it is a typical large elongated but irregularly shaped glacial erratic, with heavily abraded flanks and facets indicating that slices have been sheared off its flanks during glacial transport. It looks remarkably fresh, indicating a very long history of abrasion by beach materials moved about by the waves. It may originally have been much larger, since there are a number of smaller dolerite boulders on the beach in the vicinity which might have been broken off during storm events. Its colour and texture are very similar to those of samples of unspotted dolerite from some western Preseli tors.

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.”

Caption: Erratic transport routes and iceflow directions calculated for the Anglian Glaciation, c 450,000 years ago. (Multiple sources)


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
Tel: 01792-367571

Dr Brian John
Tel: 01239-820470

Dr Katie Preece
Tel: 01792-602801


Grateful thanks to Phil for sharing the news of his discovery and for allowing the use of his photographs on this blog; thanks too to Katie for the initial geological analysis.

PS.  Phil's close-up photo of the sample taken from the erratic can be seen here:


Tony Hinchliffe said...

Splendid discovery by photographer Phil Holden, and my own thanks to Swansea University igneous geologist Dr Katie Preece for initial identification of the rock as dolerite.

Tom Flowers said...

It looks as if congratulations are in order, Brian. I do hope so, no one deserves it more.

BRIAN JOHN said...

The glory is all Phil's -- he spotted the boulder in what is admittedly a hell of a difficult and dangerous location, and realised that it was probably a dolerite. We are not being very specific about the location because we don't want people risking life and limb just to get a glimpse of it..........

Phil Morgan, Elf and Safety Inspector. said...

Excellent news, and it all goes towards solving the old problem.

BRIAN JOHN said...

There are some wonderful comments posted at the end of the Express article. I'm not going to get sucked into replying. I am constantly amazed at how FURIOUS some people get when their system of belief relating to Stonehenge is disturbed or challenged in any way. It is the sort of fanaticism normally associated with religious beliefs. Not much has changed, really, since the Middle Ages........

BRIAN JOHN said...

Phil, hope your Elf and Safety business is thriving. Be careful -- there are some goblins and gremlins stumping about right now, and they are not best pleased with this turn of events. But it is well known that they are easily irritated.....

Phil Morgan said...

Hello to Brian,
As you know I have carried out much work on the transport of heavy and awkward loads by people, and the method demonstrated at the National Museum Of Wales St Fagans site in 2011 has been vastly improved, however, I don't see any reason why the glacial transport theory and the human transport theory cannot run side by side; i.e. Glacial from Preseli to the terminus somewhere in the Wiltshire area, and then Human transport from there to the henge.
Always cautious of the Goblins but it does them good to be rattled now and again.

BRIAN JOHN said...

Yes, that's eminently sensible, Phil. We still don't know where the ice edge was, but one day we will. And yes, there must have been quite a lot of collecting and stone dragging from here, or there, or over by 'ere.........anding up at the building site. In the end there will have to be a compromise and a composite theory......

Dave Maynard said...

Does a certain TV presenter come along and make a programme with you, ending up with 'congratulations on proving your theory'?

Or do we look harder under the water for the remains of a Neolithic boat boat, wrecked trying to move this erratic up the channel?

I certainly liked the comment in the Express about the unique stone foot prints.

Congratulations to everyone involved in finding this erratic and good speed to those looking for more.


BRIAN JOHN said...

Thanks Dave! I'll give the weavers of fine tales a nice lead -- the Mixon bank is not far offshore. A perfect place for Neolithic seafarers to come a cropper! Once upon a time, on a dark and stormy night, there were some little hairy men on a mission, heading east with a secret cargo on their flimsy craft......... and so on.... and so on.......
Info here:
Mixon Bank: located right out side the Mumbles Head lighthouse. The Mixon dries out on low water spring and must be treated with respect, especially on an ebb tide, when the natural flow of the Bristol Channel is boosted by the waters of Swansea Bay emptying past the Mumbles Head. Marked by a buoy, the bank drops away to 100ft on the outside, and around 50ft on the inside.
Mixon Shoal 51 33 004N 003 58 002W. Mixon Bouy 51 33 N 003 58 008W

BRIAN JOHN said...

Have a look at this:

I love the bit about a game of cricket being played on the sands.....

Anonymous said...

I cant wait to see the peer reviewed science on this Brian :-)

BRIAN JOHN said...

Patience, dear boy. It will all be very interesting.

BRIAN JOHN said...

Somebody asked me if I would be terribly disappointed if the boulder turns out, on examination, not to be from Preseli at all. Not at all disappointed, as it happens. I'm quite prepared for a provenance to be declared as somewhere else to the north-west or west, up-glacier from where it has now ended up. That's why I have been quite careful in what I say in this press release and to the press. The chances are, I think, that it has come from Preseli -- but wherever it has come from, it shows the capacity of the Irish Sea Glacier to transport very large chunks of rock over very large distances, eastwards along the south Gower shoreline -- and this is something that MPP and his colleagues are going to have to accept, no matter how inconvenient that may be.

Tony Hinchliffe said...

May be too late for MPP now, sadly - he's getting on in years. As you have said elsewhere recently, folk are inclined to get set in their ways of thinking, whether to do with spirituality, religious beliefs, or Stonehenge.