THE BOOK
Some of the ideas discussed in this blog are published in my book called "The Bluestone Enigma" -- available by post and through good bookshops everywhere. Bad bookshops might not have it....
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Thursday, 8 December 2016

The aurochs and snow sledge theory



Thanks to geologist Paul Sanday for reminding me of this article which he wrote about a year ago:
"To Stonehenge by snow sledge", Pembrokeshire Life magazine, Dec 2015, pp 4-8.

Paul said he won't be upset if I say it's nonsense, so here we go.  It's nonsense. (I suspect he wrote it with tongue firmly in cheek anyway.........)

He goes through the various theories of bluestone transport -- by boat, glacier ice, by land, aliens (ancient astronauts) and air (using magical powers).  He dismisses the boat or raft transport theory pretty quickly, and I agree with most of his points on that.  Then he comes to glacial transport, and goes seriously adrift -- a pity, but as we all know geologists do not necessarily do much homework on glaciology or geomorphology.

Paul's points re "problems" with the theory:

1.  Ice in the last glaciation didn't go further south than South Wales. He cites "Cambridge University" as his source.  Sadly, Cambridge University does not do research -- people do research, and some of them happen to be based at Cambridge. In any case, the assertion is incorrect.  Devensian ice extended as far south as the Isles of Scilly.  In any case, we are not talking about Devensian ice here, but Anglian ice.

2.  The ice was moving towards SW and not towards SE.  "Cambridge University" is again cited as the source.  Where on earth did this idea come from?  Of course the ice in the Bristol Channel was moving towards the E and SE -- that has been well known for over a century.

3.  Stonehenge is just one location -- erratics should be widely spread.  Maybe, and maybe not.  Lots on this blog on just this topic.  and we still do not know how far the Stonehenge builders needed to range across country during their efforts tomgather up stones.

4.  No other erratics found, such as Gower ORS or quartz conglomerate.  How many erratics do we want?  One might as well say that there "should" be erratics from Ailsa Craig at Haverfordwest or erratics from Anglesey at Milford Haven...... Glaciers tend to be rather unaccommodating for most of the time.

5.  The size and shape of the Stonehenge bluestones are "pretty consistent", rather than involving a range of sizes.  Not true.  The bluestones at Stonehenge are a pretty mottley collection of slabs, pillars, boulders and stumps.  The best collection of glacial erratics that you are likely to find anywhere in southern Britain.

6.  Bluestones at Stonehenge are either monoliths or flakes.  Not so.  There are stumps and lumps of bluestone too, and also all sorts of stones classified as "packing stones, hammer stones and mauls".

7.  Very specific rock types have been selected -- eg Preseli spotted dolerite.  Not so.  There are many rock types represented in the bluestone assemblage, including some that are not really very suitable for use as monoliths.

After all of this, Paul considers land transport according to MPP et al, and finds the theory wanting.  Similarly, he does not sound too impressed with aliens, space ships, giants, fairies and wizards.

And so he comes to his central hypothesis, partly based upon all sorts of things, including a new Cambridge University map of the Devensian glaciation.  I haven't got a clue what he's talking about there, or what its relevance is, so let's move on.  Paul starts off by saying that a lot of things happened earlier than previously thought.  We can live with that.  He then proposes that the bluestones were moved to Stonehenge "at the end of the last Ice Age"  around 12,000 -10,000 years ago, when the Severn Estuary would have been "non-tidal and frozen."  Well, we know that it wasn't frozen in the Younger Dryas, and it certainly wasn't non-tidal.  Sure, there was intermittent permafrost on land, but I have never seen any evidence of coastal ice action at this time.  Then he says that the Bristol Channel and Severn Estuary area beyond the glacier front was a permafrost plain, just right for hauling sledges with bluestones on them. So that assumes a much lower sea level.  The trouble is that the low sea level associated with the last glaciation was around 20,000 years ago, and that by Younger Dryas times it had risen to about -20m.  Quite low, but not low enough to leave the centre of the Bristol Channel as dry land. Sadly, Paul has got his glaciations, his sea levels and his permafrost episodes all screwed up........

Essentially, the thesis is that tame aurochs were used to haul bluestones from Pembrokeshire in the Palaeolithic or the Mesolithic, across a frozen landscape in the Bristol Channel, in nice snowy weather when sledges could be made to slide nicely.  How?  Why? When?    It's a very jolly image  -- why let lots of specifics get in the way of a delightful generalisation?  Why, indeed, let the truth get in the way of yet another jolly story?

Garn Fawr ring cairn


I found this wonderful photo the other day, showing Garn Fawr, a spectacular crag on Pen Caer, looking out over the coast at Pwll Deri towards St David's Head in the distance.  In this photo, Pwll Deri YHA is just off the photo to the left.

Normally the centre of attention is the Iron Age hillfort or fortified settlement site on the summit, but very prominent in this photo is a circular embanked feature on the hillslope below.  There are also traces of other curved or looped embankments below it.

In the Coflein and Archwilio records there are no mentions of this circular feature, which I suppose should be dated to the Bronze age.  Or could it be an Iron Age feature, connected to the fort?  On these RCAHM photos we can see the "ring cairn" quite clearly.  Does anybody know anything about it?




Monday, 5 December 2016

The Preseli Tors

This is a small glossary of the main tors on the Presely upland ridge -- extracted from the manuscript of a book that I never did get round to publishing........


I will enhance this post by adding photos as appropriate.

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Up Among the Presely Crags


Carn Afr (093302)

This is a very beautiful tor on the southern flank of the Presely ridge, only a couple of kilometres away from the hamlet of Rosebush and almost due south from Foelcwmcerwyn. Its name can be translated as "the cairn of the goat". It is a hillside tor (rather than a summit tor) at an altitude of 375m, and it looks down upon a shallow depression and then over the "step" of Mynydd Crwn. The main feature of the tor is a prominent pinnacle of rock which is visible from a great distance. Around it there are small vertical cliffs, grassy steps and clean slabs of rock, with a litter of massive boulders especially to the west. There are several perched boulders near the pinnacle. The rock is for the most part dolerite, but there are also foliated or layered volcanic rocks similar to those of Carn Alw. There is only a little scree, at the foot of the lowest of the cliffs. Just beneath the pinnacle there is a clean grassy bank which is perfect for a summer picnic or even an overnight camping stop. Beneath the tor there is a wonderful old sheepfold, and to the east a long-since abandoned rectangular enclosure with six small fields and a ruined cottage and garden. Nothing is known about its history. The tor is best approached across the common from the bridle path which runs along the south-eastern flank of Pantmaenog Forest.

Carn Alw (138338)

The largest and most spectacular tor in the whole of the Presely area, standing in glorious isolation above the sweeping grasslands on the northern flank of the main upland ridge. Translated, its name is "echoing rock" or "calling rock". Its summit is only about 240m above sea-level. It is most easily reached from the roadside south of Glynmaen Farm. Its northern and eastern faces are high, shadowy and forbidding, but the approach is easy from the west and south. It is made of light-coloured volcanic rocks including dolerite, rhyolite, felsite and various others with complicated names. Look at the glassy texture and "flow structures" in some of the rock outcrops, formed while the rock was cooling from the molten state. About 400 million years ago this was clearly a major centre of volcanic activity; perhaps it developed as a subsidiary eruption cone on the flank of the much larger Foeldrigarn volcano. Some pieces of rock from here were assumed by HH Thomas to have found their way to the "bluestone circle" at Stonehenge; probably they were eroded by ice moving along shear-planes in the Irish Sea Glacier as it crossed the upland ridge, and were later dumped when the ice melted not far from the famous and enigmatic monument. (Note: Thomas's work has been questioned by more recent geological research, reported on this blog.)  The most interesting feature of Carn Alw today is the small Iron Age fort located on its western flank and summit. Like some of the Norman castles of Pembrokeshire it has an "outer bailey" and an "inner bailey"; the former was the main settlement site, with traces of old hut circles still to be seen; and the latter, just beneath the summit, was the last defensive position that could be occupied if the outer defensive walls were breached by an attacking tribal army. The old defensive ramparts and portal are still visible, as is a wonderful "chevaux de frise" beyond them. This feature, very rare in Britain, was built to prevent cavalry attack and was made of pointed stones (and probably sharp wooden stakes) angled into the ground and set close together. Out on the moorland to the south-east there is a fine walled enclosure (now somewhat ruinous) probably used by the Carn Alw Iron Age community, and also other cairns, walls and man-made stream channels of similar age. There is a charming fairy story associated with this carn and a nearby farm (now lost) called Llech-y-deri. The hero of the story is a young man who was taken to fairyland after succumbing to the "enchanted music" of the fairies which he heard echoing around the rock; perhaps this is where the name "Carn Alw" comes from.




Carn Arthur (135323)

This tor is perched on the mountain side at 300m, looking down on the open depression of Cors Tewgyll and across to the crags of Carnmeini. The local rock here is coarse dolerite, and there are some outcrops which show the large while felspar crystals which are characteristic of spotted dolerite or bluestone. The rocky outcrop is easily approached from above, where there is a grassy platform close to a huge perched boulder. This massive block -- and possibly one or two others lower down on the outcrop -- were assumed by the locals to have been placed there by King Arthur or some other mighty hero. Less romantically, we now know these rocks to be nothing more than large glacial erratics left by retreating ice. The tor is in an advanced state of decay, with a great litter of broken blocks and scree banks on its lower part. Not far away is Bedd Arthur, reputed to be the burial place of the mysterious king.




Carn Bica (129326)

This little tor would be called "pointed carn" or "peaked carn" in English, in recognition of its conical shape. Its altitude is about 380m. It is not a very prominent feature, and has suffered from a great deal of frost shattering in the Ice Age, and also from comprehensive rearrangement by the Bronze Age folk who built a large burial mound on its flank. The mound of loose stones has since been further rearranged by various members of "Dad's Army" who manned a lookout post here during the Second World War; and by assorted boy scouts and cadets trying to make shelters from the wind and the rain in this bleak and exposed spot. Note that the rock here is classic spotted dolerite -- the rough surface texture of boulders is characteristic, and on broken fresh surfaces the large white feldspar crystals are very noticeable. This cairn is close to the route of the Bronze Age "Golden Road", and about 100m to the east you can see the strange stone arrangement referred to by the locals as Bedd Arthur or "the grave of King Arthur." The wooden posts close to the carn mark part of the route of Ras Beca, the tough fell trace which takes place in these hills in August each year.



Carn Breseb (137333)

This carn (translated as "manger rock") is a substantial outcrop of spotted dolerite on the northern flank of the upland ridge, at an altitude of about 300m. In reality there are several stepped outcrops here, all of them very much degraded because of frost shattering and the downslope movement of blocks and scree. The tor does not look much like a manger, but the name may indicate that the local farmers once used to feed their animals here. The most prominent feature of the carn to be seen from a distance is the flat slab which looks like a gigantic needle when seen end-on. There is a large area of broken rock (and some solid rock) here, and it is fascinating to explore the nooks, crannies and crevices and to discover the sheltered and nutrient-rich "micro-environments" which provide homes for lichens, liverworts, and higher plants in this otherwise hostile and open terrain. There are traces of very ancient stone walls on the north-eastern flank of the carn, suggesting that it may have been used by the Iron Age inhabitants of nearby Carn Alw.

Carn Ddafad-las (147330)

There is not much left of this little tor, which can be named "the cairn of the blue sheep" in English. Goodness knows where its name comes from; perhaps there was once a prehistoric sheep farmer here who marked his sheep with blue dye made from bilberries! It is one of a group of little tors at about 325m just to the north of the Golden Road track and close to Carn Gyfrwy. Frost shattering, and possibly the action of overriding glacier ice, have damaged the tor so badly that it now consists simply of a rickety pile of massive boulders. One feels that the whole thing could collapse at any moment, so if you explore this tor and climb on it, please employ great caution.

Carn Gaseg (160328)

This is a small tor south of Foeldrigarn and the Golden Road. It is on private land and like Carn Sarn is therefore difficult to visit; but there are similar small tors (Carn Goi, Carn Pant-teg, and Carn Bwdcyn being the only named ones) in the coniferous woodland to the west. They are made of dolerite and other volcanic rocks. Before the woodland was planted there were two smallholdings in the neighbourhood, now reduced (like many others around the flanks of the uplands) to tumbled cottage walls and a few traces of paddocks and kitchen gardens. When you approach Carn Gaseg from the north you may feel that it does not look very interesting; but you would be mistaken, for when you drop down over the brow of the hill you encounter several splendid rock bastions up to 6m high. When seen from downslope the tor is very spectacular, and very beautiful. Most of the dolerite rock faces overlook a grassy terrace of bedrock slabs with patches of gorse and heather. Some of the slabs appear to have been smoothed by the action of overriding ice. The dolerite here is fine-grained and in places flaky. There are a few elongated stones which have been broken from the solid rock by frost action, and the tor is still breaking down, with long deep cracks, gullies and perched blocks.

Carn Goedog (128333)

This is one of my favourite Presely tors, partly because of its impressive size and partly because it is a tranquil place, seldom visited by hill walkers. Located on the northern flank of the upland ridge, it is adjacent to the old drover's route used by many thousands of animals en route from Pembrokeshire farms to the meat markets of the Midlands and London in the 1700's and early 1800's. The up-slope flank of the tor (at about 300m) is not very prominent, but on the downslope side there is a wilderness of huge dolerite blocks, banks of scree, little grassy platforms, solid rock outcrops, crevices and caves. The rock is very coarse, with some spotted dolerite. One or two small trees have managed to survive here in places inaccessible to grazing animals; but the name ("woodland cairn" in English) indicates that there must once have been an extensive woodland here after most of the upland ridge had been cleared by burning, felling and grazing. Recently the tor has attracted attention following the suggestion by geologists Richard Bevins an Rob Ixer that many of the Stonehenge spotted dolerite monoliths have come from here.  Prof Mike Parker Pearson and colleagues claim that there is a Neolithic "bluestone quarry" here; but intensive investigations (reported on this blog) have revealed no unequivocal signs of quarrying in prehistoric times.




Carn Gwr (142330)

This name means "husband's cairn" or something similar. There are really five separate small tors here, scattered about on a broad saddle or col in the upland ridge at an altitude of c 315m. There are no steep slopes, and it is easy to stroll between one tor and another on the heather and bilberry moorland. Here you are right at the heart of "bluestone country", with tors all around you. Carn Bica, Carn Breseb, Carn Alw, Card Ddafad-las, Carn Gyfrwy, Carn Meini and Carn Arthur are all within easy walking range. As you walk around this area, with skylarks above and sheep and mountain ponies grazing on the moorland, you can feel the timeless serenity of Presely; and you can also see traces everywhere of human occupation of this landscape over 3,500 years or more. Slight ridges in the turf, pits, elongated hollows, fallen stone walls and small stone cairns may date back to Bronze Age or Iron Age times. An old cart track runs across the moorland here, linking the rock outcrops with the farming community to the north which used the area as a handy quarry for gateposts and other "special stones". The cart track, in places deeply entrenched, runs downslope between Carn Breseb and Carn Alw and then to the west of Carn Alw down towards Mirianog Ganol.

Carn Gyfrwy (147327)

One of the most prominent features on the Presely ridge, this cairn is more of a rock bastion than a tor. It is made of spotted dolerite or bluestone, and has a steep cliff face at its northern end, immediately overlooking the route of the ancient Golden Road. Its summit is about 365 m above sea-level. On the OS 1:25,000 Outdoor Leisure Map the place-name is incorrectly located; the name means "saddle cairn" in English, and there is no doubt which cairn has the saddle-like appearance. There is another error in the labelling of the so-called "sheep-fold" beneath the cliff face. This crude stone-walled enclosure has also been referred to in the literature as a "drover's hut." However, it is far too small to contain sheep, and it is some way from the old drover's route. It is more likely to be a simple shepherd's shelter used during bad weather. It is still used for this purpose by weary hill walkers caught out in the wind and rain.

Carn Meini (144325)

Carn Meini or Carn Menyn is the one Presely cairn whose name is known to people from all over the world, since it is reputed to be the source of some of the famous Stonehenge spotted dolerite bluestones. (Its reputation is largely undeserved, since recent geological work suggests that the said bluestones have probably come from other locations.) The single name is used to describe a cluster of seven or eight distinct tors arranged in an arc around a spur on the upland ridge. They are very spectacular indeed, and from a distance they give the skyline a jagged or "cock's comb" appearance. The name is interesting. In English the name Carn Menyn (used on recent OS maps) would be "butter cairn", but this is a nonsense name in this geographical setting, and it is much more likely that the alternative Carn Meini ("cairn of the stones") has the better historical claim. Also, the words "maen" (singular) and "meini" (plural) are used in the context of shaped or dressed stone, as in "maenhir" ("long stone") used by the old archaeologists as a word for a standing stone. We may speculate therefore that the name was first used to describe a place of special elongated stones; and indeed there are many elongated stones here as a result of columnar jointing in the spotted dolerite. The massive tumbled blocks which are characteristic of this area indicate that there has been large-scale frost shattering here during periods of prolonged cold climate; but there are also some wonderful ice-smoothed surfaces at the southernmost edge of the rocky spur, with deep gullies and cliffs which indicate that over-riding glacier ice has "plucked" or dragged away large quantities of broken rock. The rock fragments, some of them weighing several tonnes, were carried up into the body of the glacier along shear-planes as it flowed southwards and south-eastwards, to be dumped hundreds or even thousands of years later on the fringes of Salisbury Plain. There are a number of possible man-made features among the Carn Meini tors. For example the flat stone referred to as the "altar stone" may be a sub-Neolithic burial chamber or cromlech, and there are a number of traces of very old stone walls that may date back to the Iron Age. An ancient cart-track is cut into the hillside between two of the eastern tors; it runs down to the road near Glanrhyd, and was used by farmers who were collecting convenient elongated stones from the mountain for use as gate-posts, lintels, steps or sills.




Carn Sarn (159327)

Literally this means "causeway cairn", and indicates an alignment of rocks. This little tor is almost due south of Foeldrygarn and is on private land to the south of the Golden Road. The causeway or route remembered in the name may be the Golden Road itself, since it has been used by traders and local inhabitants over a period of at least 4,000 years. The tor is part of the same volcanic complex as Carn Meini and Carn Gyfrwy; and other small tors are now lost in the coniferous plantation of Llethyr-mawr. The tor is not very spectacular, consisting of little more than a few dolerite outcrops on the hillside and a few small pinnacles up to 3m high. There are broken boulders scattered across the slope, over an area of about 50m x 50m. There are grassy banks and patches of gorse and heather, and this is a pleasant sunny place sheltered from westerly and northerly winds.

Carn Sian (128322)

This little dolerite tor, almost in the centre of the Talfynydd upland spur, is named after someone called Sian or Jane. It is unremarkable as tors go, but well worth a visit since the walking is easy hereabouts, and there are fine views towards Carn Meini and Foeldrygarn. The land surface in the vicinity of the tor has been greatly modified by the hand of man. If you look carefully you will see the traces of old stone walls and enclosures which probably date back to the Bronze Age or Iron Age. There are many elongated hollows which show us the routes of ancient trackways. And the turf is pock-marked with long-abandoned peat cuttings, reminding us that large parts of the upland were used as turbaries by the commoners who owned the farms and smallholdings on the flanks of the mountain.

Cerrig Marchogion (112323)

Here, on the crest of the upland ridge at an altitude of about 400m, the strange craggy outcrops of Cerrig Marchogion make a lasting impression on all who pass by on the nearby Golden Road. They are really small tors and rock outcrops made of dolerite, surrounded by a litter of broken boulders affected by frost action and moverd about by glacier ice. There is a magical quality about this place, especially when it is raining, or when low cloud or mist is drifting across the mountain ridge. Literally, the name means "the stones of the knights". The explanation for the name can be found in the ancient book called "The Mabinogion", in the story of Culhwch and Olwen. This is adjacent to Cwm Cerwyn where, according to legend, King Arthur and his knights fought a pitched battle with the wicked black boar Twrch Trwyth and his cohorts. So bloody was the battle that eight of Arthur's knights were killed, and the rocks are supposed to be their petrified remains.




Craig Talfynydd (130314)

This is a series of rock outcrops with banks of scree and broken slabs on the eastern flank of the Talfynydd spur. Literally, the name means "crag on the end of the mountain". This is a beautiful sheltered spot when the wind is in the west or north-west, with many gullies, dolerite outcrops and grassy banks to explore. Some small trees have managed to survive in the rocky wilderness. Because the slope is quite steep in places, some of the rock slabs and scree banks are still moving periodically but inexorably downslope; they are therefore quite unstable, and great care is needed when you clamber across them. There is a very large rabbit warren here, and you are certain to see rabbits of all ages scuttling about among the rocks. The spring below the crags is used to supply water to the cottage of Dan-y-garn in the copse of trees.

Craig y Cwm (096313)

This rocky outcrop high above the hollow of Cwm Cerwyn is not really a tor, but a series of crags and cliffs created by a combination of glacial action and frost shattering. The name means "the rock of the valley". Located quite close to the Presely summit of Foelcwmcerwyn, the altitude here is about 490m. The crags are made of slates and other rocks metamorphosed close to the dolerite intrusion which outcrops on the mountain summit. Down below there is a small and very old slate quarry with pits, cuttings, a trial tunnel, spoil heaps and a cart track running southwards around the end of the spur. The quarry excavations have made Craig y Cwm quite dangerous, especially when the grassy slopes are wet or when visibility is bad; this is one of the few places on Presely where a serious accident can happen if you are lost in the mist. A few years ago there was a fatal air crash here when a light aircraft en route from Swansea to Dublin flew into the side of the mountain in poor visibility.  The cwm was probably the site of the last small glacier in Pembrokeshire;  morainic traces and exposures in stream cuttings suggest that there was a small glacier here around 10,500 years ago.


Foel Drygarn (158336 )

This prominent hill mass towards the eastern end of the Preseli upland ridge stands in glorious isolation, and the summit can only be reached via a stiff climb from the nearly "Golden Road" footpath.  The name means "the bare hill with three cairns" -- and the three massive Bronze Age burial mounds on the summit are the most spectacular features of this age in Pembrokeshire.  They lie within the confines of an Iron Age hillfort which contained both an animal enclosure and a substantial settlement site.  Scores of hut circles can still be made out in the turf.  The defensive ramparts are prominent.  A gorgeous location, with spectacular views in all directions.  Maybe we shouldn't classify this as a "Preseli tor" but on balance I have included it in this list because there are indeed spectacular crags here towards the western end of the summit.  The rocks are rhyolites rather than spotted dolerites, and as with the other high tors the dominant process which has shaped the crags in recent millennia is frost shattering and the downslope movement of detached blocks under the influence of gravity.  The jury is still out on whether the summit of Foel Drygarn was affected by glacier ice during the last glaciation.







Thursday, 1 December 2016

Rhosyfelin - More glacial misunderstandings



There is another post on Mike Pitts's blog, relating to the latest paper on the dating of the Fishguard Volcanic Group rocks.  As we have said before, this paper is not really of any relevance to the Rhosyfelin quarrying debate,  since it simply confirms that the FVG rocks are indeed in the right place in the Ordovician stratigraphic column.  Pure geology. 

https://mikepitts.wordpress.com/2016/10/20/another-chip-at-the-bluestone-problem/

Mike accepts that the new paper is "not dramatic",  but then he says: 

"But it confirms the direction of current work which suggests that many of the Welsh bluestones came from north of the Preseli hills, rather than the top or to the south as traditionally believed (HH Thomas identified Carn Alw as a source for these particular stones, see map). The significance of this, as argued earlier by Richard Bevins and Rob Ixer, is that while Carn Alw might allow for ice transport of stones at least part of the way to Wiltshire, the nearer the sources move downslope towards the coast, the less supportable that becomes. And Mike Parker Pearson may have another quarry to look for."

Where on earth does this strange and convoluted line of thinking come from?  Whoever said that a Carn Alw provenance for stones at Stonehenge might suggest glacial transport, but that provenances from the northern slopes of Preseli do not?  That is complete nonsense, as I have tried to explain many times on this blog.  Precisely the reverse is true.  Because ice crossing Preseli must have been compressing as it crossed the rising land between the north coast and the ridge of Mynydd Preseli, conditions for glacial entrainment would have been significantly enhanced.  Why do people keep on expressing these views when it is clear that they know nothing whatsoever about glaciology or glacier behaviour?

MPP also demonstrated his lack of understanding the other day by stating (so we are reliably informed) that glaciers never flow uphill......... that's almost as bad as his statement of a few years ago that there is no evidence of ice ever having travelled eastwards in the UK........ oh dear oh dear.......

Here, Mike Pitts gets more sensible, in referring to the newly dated rock samples:  "The other two, from the coast, are a little older, at around 464 and 465 million years old. Interestingly, the archaeological sample (which can be linked to stones 38, 40 and 46 at Stonehenge as well as 48) is also around 464 million years old. Not from Craig Rhos-y-felin, then, but, say the scientists, probably from Fishguard outcrops exposed across the low ground north of Mynydd Preseli. “This region”, they conclude, “provides an obvious target to search for further Neolithic quarry sites.”

Forget about the geologists' obsession with quarry sites -- if we want to put any interpretation on this work, it is to say that fragments from the FVG found at Stonehenge have come from several different localities in North Pembrokeshire -- and that that significantly increases the likelihood that they have been entrained and transported by glacier ice.  Nice and simple.






The weird obsession with periglacial stripes

 Image: Adam Stanford

There's a new post on Mike Pitts's blog called Digging Deeper.

https://mikepitts.wordpress.com/2016/11/

In it, he refers to the strange idea (emanating from MPP and his colleagues) that the undulations within the confines of the Stonehenge Avenue are "periglacial stripes" and that the orientation of these stripes coincident with the solstice axis is responsible for the placing of Stonehenge where it is.  I have always thought of that as a crazy idea, and Mike Pitts seems to think so too.  Mike has some nice illustrations in his piece, and displays a proper degree of scepticism, but he still seems to accept the periglacial origin for these features, and also for other small rills which are now visible at the new Larkhill excavation.

There is nothing at Larkhill either to suggest a "periglacial" role in the formation of these rills, and the perfectly obvious explanation for all of them, as we have said over and again on this blog, is that they are simply solutional rills created by water moving downslope, possibly assisted by permafrost (which has the effect of reducing the infiltration of water into the ground). 

It's very confusing to refer to patterned ground features like these as "periglacial" since there is no evidence at all of patterned ground processes at play, involving the lateral movement of particles into stripes of larger fragment sizes separated by stripes of fines.

Maybe some people just like the word "periglacial" because it sounds mysterious and scientific?

Wednesday, 30 November 2016

Oxford Gletscher, East Greenland









Something from the distant past! I was going through the official Greenland place-name gazetteer, looking for some photos, when I came across this: "Oxford Gletscher 71Ø-369 (71°32.8 ́N 25°16.7 ́W; Map 5). Glacier in the south Stauning Alper, draining south into the east end of Nordvestfjord. Named by the 1962 Oxford University expedition, which undertook survey work on the glacier. Oxford University is one of the world’s oldest and most prestigious universities, whose origins go back to the early 12th century. Uranus Glacier has also been used." 

 Dave Sugden and I named the glacier (and it was accepted by the authorities) after we did some rather difficult surveying and ice drilling work there in 1962. We were quite convinced that our ice temperature readings were rubbish, but actually we had discovered that the glacier was subject to surging behaviour. We were young and inexperienced, and did not know how to interpret the temperature anomalies.........  Hardly anything was known about surging glaciers at the time.

Talfynydd, Preseli -- unrecorded hut circle?


This apparent hut circle is located on the spur of Talfynydd, on the south side of the main Mynydd Presely upland ridge.  The grid reference is SN 127318.  Not far away to the NE is the tor called Carn Sian.  There is a gentle west-facing slope here, and the site looks out over Cwm Cerwyn.  This feature is 7-8m across, and as we can see there is a slight embankment littered with rather large boulders.  The feature is not perfectly circular, but slightly elongated downslope.  I have searches through all the Coflein and Archwilio records, and can find no trace of it.

Is it a Bronze Age hut circle?  There are certainly many others in the area -- but most of the interesting prehistoric remains on Talfynydd are on the eastern side of the ridge, whereas this one is on the west-facing (weather!) side.  There are of course similar features on Carningli as well.  Given its exposed location, I wonder whether this might have been an animal enclosure? But against that idea, there are no guiding walls anywhere near.........

Does anybody else know the site?  It's almost exactly 50m north of the site of the tragic Liberator crash of 19 September 1944, in which five airmen were killed.  The patch of bare ground (where the plane was burnt up deliberately after the crash, since it would have been very difficult to remove the debris from the mountain) can be seen on the image below, towards the bottom.  The "hut circle can also be seen quite clearly.