Glaciation of the Mendips

Somebody mentioned to me the other day that the thesis of glacial activity affecting the Mendips is coming back into fashion. I'm not sure what the new evidence may be, but am reminded that Geoff Kellaway and a few others have been convinced for many years that the deep gorges in the Mendips are not simply the result of karst processes including elongated cave collapse. If there really are glacial deposits in the vicinity of Bath, and not far from Glastonbury, then it is almost inevitable that glacier ice either pressed onto the flanks of the Mendips or overrode the hills entirely. Just found this extract:


From Geotimes May 2005
by Megan Sever

Ice sheets reached as far south as Cheddar, but the bigger factor in shaping the landscape was actually the meltwater once the glaciers receded during interglacial periods. After each ice age, glaciers released a torrent of meltwater through the Somerset rivers to the sea. Carrying boulders and gravel, the rivers scoured out gorges like Cheddar Gorge up to 400 feet deep and 3 miles long. Throughout time, as sea level has risen and fallen, Cheddar Gorge has gotten deeper and shallower. Along the climb to the ridge of the gorge, you can see various layers of limestone.

The Mendip Hills in Somerset, seen here on the drive to Cheddar Gorge, have been extensively shaped by glacial processes starting 1 million years ago. Today, sheep farms grace the rolling hillsides.

While the surface landscape was being carved by glacial meltwaters, underground rivers were similarly carving out vast caverns, such as Gough's Cave and Cox's Cave, the two caves in Cheddar Gorge. Floodwaters and underground rivers dissolved the limestone, slowly sinking lower and lower until they hit the harder sandstone layer and leaving caves above.

The Web Site

If any followers of this blog want to read about "The Bluestone Enigma" or follow my reasoned arguments relating the the glacial transport of the bluestones, you can click either on the heading of this post, or on the picture of the tumbledown ruin on the right.

The website is now somewhat dated, and one day I'll give it a comprehensive revamp......

Bluestone in Shrewton?

I'm often asked this question: "If there really are glacial deposits on or near Salisbury Plain, and if the bluestones at Stonehenge came from an assemblage of erratics, where are all the other erratics?" Well, I have to admit that there is nothing identified thus far which could be called with confidence "a glacial deposit" or even "a glacial landform." But there are erratics scattered all over the place, as i have described in my book. The most famous is of course the Boles Barrow bluestone boulder. One day I hope that somebody will do a systematic search on Salisbury Plain and in the villages around Stonehenge. But here is one stone that needs petrographic analysis. The shaped stone in the centre of this photo is built into the side of the little prison in the centre of Shrewton, not far from Stonehenge. It's called "The Blind House". To me the block (note the bluish-grey colour) looks like a well weathered block of dolerite, similar to those in some of the Stonehenge orthostats. The stones around it are quite different -- as indeed are all the other stones used in the building. I think these others are all blocks of sarsen.

So how did this bluish stone get to Shrewton? I would argue that it was probably picked up locally and shaped for the job in hand. Others would no doubt argue that if it really is a piece of Pembrokeshire dolerite, it must have been quarried from Stonehenge, thereby helping to account for the shortage of bluestones left behind on the site today..... That's the sort of thing the archaeologists always say! Look how convoluted the arguments got in trying to "explain away" the Boles Barrow bluestone.

To get a closer look at the stone, click on the image.

Carn Meini and the Battle of Preseli

It's not often realised that after the Second World War the War Office made a proposal to take in 58,000 acres of land -- encompassing virtually the whole of the Preseli upland area -- as a military training and bombing range. This caused an immediate and virtually unanimous reaction from all sections of the community in Pembrokeshire -- and the campaign to save the mountain was referred to as "The Battle of the Preselau" by author Hefin Wyn in a book published a couple of years ago. The campaign united the Welsh and English speaking parts of the community, and it was multi-faceted, with economic, political, social, religious and ethical arguments all thrown in the direction of the War Office by community leaders.

In situations like this, with a whole community feeling itself under threat, every possible argument is rehearsed and brought to bear on "the enemy." The politicians in Westminster must have been amazed by the vigour and the sophistication of the "Save Preseli" campaign. In this, a number of very prominent pacifists took a leading role, and many nonconformist religious leaders not only thundered from their pulpits but became involved in lobbying and protest activities. They stressed the importance of Preseli as a cultural and spiritual heartland of Wales, and demanded that the establishment of a firing or training range would be not only disrespectful to Welsh heritage but also sacrilege of the most abominable kind.

It was therefore not surprising that one of the arguments brought forward was connected with the supposed sanctity of the mountains as a whole but also Carn Meini in particular. The ideas of HH Thomas came in very handy indeed. a great quantity of purple prose landed on the desk of Prime Minister Attlee -- with frequent references to Carn Meini, the bluestones, and Stonehenge. The land was referred to over and again as "sacred" and words that crop up over and again in the correspondence include "heartland", "sanctity" and "sacrilege." The mountain around Carn Meini was a cradle of civilisation, a prehistoric cathedral, a treasure trove of antiquities, a place of mysticism and tranquillity, of spiritual regeneration and wonderment.

Wonderful stuff -- and it did the trick. The plans for the military range were abandoned, and the Army moved to Castlemartin and the Brecon Beacons instead, where there was much less opposition. So we must, I suppose, be grateful for the manner in which the ideas about the sanctity of Carn Meini played a part in saving the uplands for us to enjoy in perpetuity, as commons and as wild places.

But none of this should blind us to the fact that we are talking here about a full-blooded community campaign and about strategy and tactics. To a degree, the campaign was cynical in that it "pretended" a sort of reverence for eastern Preseli that I do not believe has ever been there in reality. In the years 1946-1948 the ideas of HH Thomas were given a massive boost, and the thesis that the Eastern Preseli Hills are "sacred" really dates from that time. All very handy indeed, when Profs Darvill and Wainwright came along looking for their bluestone quarry and for something to show that there was a spiritual or even religious reason for the carrying of lots of bluestones from here to there.

Pillars and columns

I took this photo the other day -- it's the best example I could find of pillars / columns in situ in the Carn Meini area. This outcrop is in one of the western tors of the group, some way away from the "enclosure" described by Darvill and Wainwright. The pillars look good at first sight -- ideal for plucking out of the bedrock and hauling off to Stonehenge, you might think......

But look again. The pillars of spotted dolerite are criss-crossed with weaknesses -- fractures and veins of quartz. When pillars like this are broken down by block collapse, or freeze-thaw, or even glacial action, the chances of the pillars surviving intact are very slim indeed. What you normally end up with is a collection of roughly rectangular blocks that are not much good for local gateposts, let alone heroic transport expeditions from here to Stonehenge.

Slabs, blocks and boulders

On the matter of predominant stone shapes at Carn Meini, I'm pretty convinced that slabs are more common than pillars or columns. This picture shows the famous "Altar Stone" or "Sacrifice Stone" at Carn Meini. It was probably neither an altar nor a place where virgins were sacrificed, although there seems to be a consensus that it MIGHT have been a small "sub-Neolithic" burial chamber. Slabs like this are very common in the area -- there are several others visible in the photo.

Of course, it is also a myth that most of the bluestones at Stonehenge are pillars. I have pointed out before that they are of all shapes and sizes, including small chips or flakes, small cobbles, rough boulders and slabs, and some pillars. I do not buy the idea that all of the small fragments have come from the working of the larger bluestones -- it would be absolutely typical of an erratic assemblage of bluestones that there would be a mixture of stone shapes and sizes, not to mention lithologies.

Carn Meini / Carn Menyn stone shapes

Above: the famous bluestone pillar at Carn Meini that was supposedly left behind. Below: the litter of stones of all shapes and sizes at Carn Meini. True pillars are not entirely absent, but they are extremely rare.

Yesterday I did a 17 km trek along the ridge of Mynydd Preseli (an absolutely wonderful day!) and spent a fair while pottering around Carn Meini, Carn Breseb, Carn Bica and other tors. I got to thinking about the myth (one of many!) that THE REASON WHY CARN MEINI WAS CHOSEN AS THE QUARRY SITE FOR BLUESTONES WAS THAT IT WAS LITTERED WITH PILLARS OR COLUMNS OF SPOTTED DOLERITE BEDROCK, BROKEN OFF FROM THE NATURAL ROCK OUTCROPS. In other words, the frequency of "ideal" stones was a key factor.

To quote from a 2005 Bournmouth University press release: "The enclosure is small (less than half a hectare) but according to Professor Darvill it provides a veritable 'Aladdin's Cave' of made-to-measure pillars for aspiring circle builders". (This refers to the small "enclosure" excavated some years ago.)

Made-to-measure pillars? Well, I hunted around over quite a large area, and in a sea of blocks and stones of all shapes and sizes, I found maybe 5 or 6 that might fit the bill as ideal Stonehenge bluestones. One of them is the famous bluestone shown above, described ad nauseam as "the bluestone that they left behind." Without doing a statistical analysis of Carn Meini stone shapes, I would argue that pillars or columns are incredibly rare at Carn Meini, and are just as frequent at other tors including Carn Breseb and Carn Goedog. The most common stone shape is roughly rectangular or box-shaped, with the long axis maybe up to twice the width or depth of the stone. (For a real pillar you need proportions of maybe 5x1x1.)

I also observed that where columns or pillars ARE present in the bedrock outcrops, when they are released and fall onto the scree they almost inevitably break across, because of transverse fractures or other weaknesses related to quartz veins etc.

So away with that particular piece of nonsense. I am quite convinced that there would have been NO reason for Neolithic tribesmen to "target" Carn Meini as an ideal quarry site. There was nothing special about the spotted dolerites (they outcrop over a very wide area), or about the stone shapes, or about the ease of access or stone extraction (other sites would have been easier).

For the best part of a century archaeologists have been indulging in special pleading with respect to Carn Meini. Once HH Thomas announced that that was where the spotted dolerites came from, one generation after another has sought to find justifications or reasons for the "choice" of the site. It's all there, in the literature......