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Monday, 12 January 2015

Four crucial questions



Off the record, I've been chatting with a colleague about the key issues in the "bluestone transport debate" -- and he suggests that the following questions are all crucial.  He suggests that none of them have been answered, and I tend to agree with him.   Answers from archaeologists please.........

1.  If the bluestones at Stonehenge were revered or venerated to the extent that they were worth transporting at great cost across land and sea, why are there so many rock types, shapes and sizes represented in the bluestone assemblage, including many soft and flaky "rubbish" stones?

2.  If the bluestones were transported by human beings, why are there no stones in the orthostat group that have come from the north, east and south of Stonehenge?  Is it a pure coincidence that they have all come from the west, on a route known to have been followed by glacier ice?

3.  If the stones were carried by humans, how did the members of a Neolithic community centred on Salisbury Plain know of the existence of a supposedly “sacred mountain” in West Wales, and where is the evidence showing that they had the geological, geographical and navigational skills to locate it and exploit it?

4.  Why is it that other dolmens, standing stone settings and megalithic monuments dating from the British Neolithic are preferentially built with stones collected in the immediate vicinity?  Does this not suggest a “utilitarian” or pragmatic culture which had no interest in long-distance stone transport?

20 comments:

mountainsofmeaning.wordpress.com said...

I may be behind on the argument but is there not another question to be asked here: If the bluestones were carried to Wessex by glacial pathways where are all the other examples unused examples lying about in the locality? It would seem highly unlikely that the bluestones used at Stonehenge were the only ones that were carried here by the ice.
Pete

BRIAN JOHN said...

Of course this is a serious question, which we have addressed often. One answer is that "foreign" material is not restricted to Stonehenge, but is scattered throughout the landscape. Think of Cursus Field, Boles Barrow, other anomalous stones...... Another answer is that glaciers do not leave convenient and regular "spreads" of till and erratics on the landscape -- and this characteristic has been exercising the minds of geologists and geomorphologists for as long as I can remember. Another possible answer is that the builders of Stonehenge simply collected up whatever they could find in the way of convenient building stones -- bluestones and sarsens -- starting at the Stonehenge site and spreading further and further outwards until the costs became greater than the benefits -- at which point they simply gave up on the project and walked away from it.

Phil Morgan said...

I posted the following guestion under th Mount Hood Moraine thread but it must have become lost in the ether!!
It would seem that no satisfactory explanation is available for the fact that even though the Welsh Ice Cap removed vast amounts of Blue Pennant sandstone from the south Wales coalfield, there are NO Blue Pennant Sandstone erratics on Salisbury Plain!! These are the same Welsh glaciers that are reputed to have combined with the Irish Sea Ice that supposedly carried the bluestones to within carrying distance of Stonehenge.

TonyH said...

Apologies if I am strictly slightly off - topic here, but, beyond the Stonehenge orthostats, Brian pointed out in 'Bluestone Enigma' (2008), chapter on"The Science of the Stones" (page 108):

'Richard Thorpe & his colleagues assembled information in 1991 relating to other intriguing stone finds: .....a piece of rhyolite from a very early Neolithic pit fill on King Barrow Ridge (associated with pre - grooved pottery fragments and probably more than 4,500 years old)...'

I would comment that this find, dateable by its stratigraphic association with the pottery, makes its date of placement earlier than the earliest likely dates the human transport proponents suggest for erection of bluestone orthostats at Stonehenge itself.

This is quite similar, datewise, to the identification in 2008 of a "bluestone" from the fill of the Cursus pit as being identical to one of the sandstone stumps in the Stonehenge bluestone circle. Brian commented (pages 108 - 109) "That is potentially very significant, since it meand the lump of (Silurian?) sandstone was present before 3,200 B.C.* in this very early earthwork."

* I think the date of 3,200 B.C. has now been pushed back to an even earlier one.

Richard Thorpe also remarked on the finding of a piece of rhyolite near Avebury (Brian John, page 108), yet, as far as I am aware, none of the Avebury orthostats themselves are composed of rhyolite, leading to the suspicion that this piece may have arrived as a glacial erratic, perhaps this time on the side of Salisbury Plain closer to Avebury than Stonehenge.

TonyH said...

Your Question I:-

one answer to this could be, the so - called "bluestones" may have been revered or venerated, NOT because they were physically located in S.W.Wales, but because they were recognised as being EXOTIC to the Wessex region; that they had arrived SOMEWHERE IN "WESSEX" thanks to their movement by glacier. Prehistoric man may have "merely" recognised that these stones were different from anything they had laid eyes upon in their landscapes of Wessex. So they collected them all up, more or less, regardless of them being in 'rubbish' condition or not, and saw fit to lug them over towards the future site of Stonehenge (close to the area that Mesolithic man had thought important for thousands of years beforehand as we now know from Amesbury's Blick Mead O.U. digs). The distance of lugging may still have been 10 to 40 miles, for instance. People may well have decided that these exotic stones were, per se, worth incorporating into their megalithic monument, by virtue of their sheer uniqueness in their landscape.

BRIAN JOHN said...

That's a reasonable scenario, Tony. I could live with that -- but it still credits Neolithic man with some sort of geological expertise, which I have a problem with. This is because there is also a lot of variety in the sarsen collection, and as we discovered in our straw poll some time ago, sarsens are often bluer than the bluestones. So what characteristic might they have been looking for? texture? crystal arrangements? Friability or lack of it? There is such huge variation in the shapes, sizes and textural characteristics of the bluestones that I am not at all convinced they were originally targetted at all. I think I still prefer the scenario in which ALL the handy stones (including large and small sarsens) were gathered up, across a wider and wider circle, until at last the poor old fellows ran out of steam and went off to do something else instead.

Phil M. said...

And there are still no Blue Pennant Sandstone erratics on Salisbury Plain, and still no satisfactory explanation why.

BRIAN JOHN said...

Phil -- there aren't any gabbros from St David's head, or Carb Limestones from S Pembs, or ORS boulders either. You cannot just assume that because ice travelled from A to B, you should expect a representative sample of all the rocks passed over to end up in a tidy moraine at the glacier snout. or even a handy erratic trail. If only things were that simple......

Constantinos Ragazas said...

Brian,

I agree with Phil Morgan here. Advancing glaciers are not so selective to pick up some stones (size and kind) but leave other stones behind.

Whether a glacier is cold-based and frozen to the soil or not will not make its glacier debris (or this issue) go away.

But I also agree with Alex Gee. Neolithic quarries and long distant human transport does not explain the Alter Stone. Nor all the Stonehenge Layer debris that cannot be matched to any of the Stonehenge stones sampled.

Kostas

BRIAN JOHN said...

Kostas -- glaciers are VERY selective in which stones are entrained and which ones are not. It all depends on the glaciological conditions on the bed -- as I have frequently pointed out on this blog. If ice is frozen onto the bed, nothing much will be entrained -- and if ice is warm-based with compressive flow, there will be a lot of entrainment.

Myris of Alexandria said...

Kostas the Stonehenge Layer is an open context. This means that it has been added to since it first appeared in the Neolithic/BA. All the rubbish dumped at Stonehenge from the Beaker Folk onward including the New Age Folk are included that is why there are so many different rock types.
The use of trace numbers of random bits of siliceous rock in the Stonehenge landscape is fraught with danger. The rhyolite from West Kennet long barrow for example is not Stonehenge but group VIII of the mad axe group a well known polished stone axe group.
See Ixer in the Silbury Hill monograph.

Work on this is in progress. The Thorpe paper has very poor petrography apart from the two zinggy minor author's contributions.
M
Read Ixer's letter Stonehenge and the Inka for a different view.
FREE on his academia website.
Nice point about the tonnage of the Altar Stone. The suggestion that it is a large joint block has been around for some time.
M

BRIAN JOHN said...

Myris -- you are being rather hard on the OU team's work, which you were a part of. It was after all 25 years ago -- and it seems to me that they were broadly right on most things. Technology moves on. There have not been any massive readjustments from their broad conclusions re Carn Goedog etc etc

TonyH said...

I mentioned in a different Post a week or two back that, because those Good New Boys (as distinct from the primeval Good Ol' Boys) belonging to what they call English Heritage have decided to enlarge the brand new Stonehenge Visitor Centre car park at Airman's Cross, quite a distance from the monument, archaeological workers are busy trowelling the ground of the intended car park extension in case they end up disturbing something very significant.

I WISH, unfortunately without much HOPE, that these E.H. Boys and Girls may collect up ANY pieces of stone that appear in the slightest EXOTIC, and mail them to Myris, who we all know will welcome their arrival in the West Midlands with glee (or not!).

Constantinos Ragazas said...

Brian,

Of course if the glacier is frozen to the bedrock there will be no movement over the bedrock. And so no entrainment of debris from the bedrock. I agree. This is similar to the scenario in my BLOCKED post of an ice stream overriding a frozen glacier lake. There will not be much glacier debris left behind as evidence then either.

Were we to dig in the vicinity just outside the circular area that defines the Stonehenge Layer would we find similar selection of stones we find within the Layer? Discounting, of course, Myris's New Age stones!

This has been a burning question for me in several past posts. Answer please?

Kostas

Myris of Alexandria said...

No the main petrography of the Thorpe paper was poor. Richard was a tremendous geochemist, the idea and work revolutionary due to Richard and OWT working together but there was not a competent petrography between them and I don't think they cared much. Thomas and Ixer's work was added as a couple of appendices and nice of the main authors to do so.
The paper is essentially archaeology and geochemistry.
But it will stand for many decades to come, just not the petrography.
M

Phil M. said...

I’m a simple mining engineer with an interest in archaeology in general and the stones of Stonehenge in particular. From the maps and diagrams of the flowlines for the Irish Sea and Welsh Glacier provided in The Bluestone Enigma, it is fair for me to assume that the ice would have travelled over, and covered, many thousands of square miles. It is also fair to assume that the ice would have collected rock from many of the surfaces that it passed over.
A comparison of the area of the South Wales Coalfield with the area of the Preseli Hills shows that at approximately 190,000 hectares the coalfield is eleven times the size of the Preseli Hills at 17,000 hectares. It is also fair to say that the bedrock of the Preseli area is predominantly mudstone, with relatively small areas of bluestone-producing intrusive, and extrusive, igneous outcrops. This could account for the lack of bluestone erratics in the Salisbury Plain area, or even east of Bridgewater.
However, for nearly the whole of its area the South Wales Coalfield is overlain by the South Wales Upper Coal Measures Formation. These rock formations form a large plateau with deeply incised valleys. A simple calculation shows that the volume of rock removed from the plateau is approximately 270 cubic kilometres. It is agreed that not all of this rock has been removed by glacial action, so if we apply a large relaxation of 50% we still have about 135 cubic kilometres of rock missing from the plateau, and the majority of that rock would have been sandstone.
To give some idea of scale, 135 cubic kilometres of sandstone would allow a continuous wall to be constructed from the Preseli Hills to Stonehenge; however, the wall would measure half a kilometre wide, by a kilometre high, yet none of this missing sandstone appears on Salisbury Plain.
Surprisingly, we are now told that “there are no gabbros from St David's head, or Carb Limestones from S Pembs, or ORS boulders either”.
Damn, but these glaciers must of really fancied bluestones, or more likely it was through human endeavour that they reached Stonehenge.

BRIAN JOHN said...

Sorry Phil, bit this sort of numbers game is a total waste of time. Unless you know what the pre-Ice Age landscape of South Wales looked like, you can make no assumptions about the quantity of material moved by ice -- or when and how it was moved.

You might as well say that there should be vast piles of ORS boulders dumped at Stonehenge because there used to be ORS rocks covering most of N Pembs and because ice presumably played some part in stripping them away......

You might also want to argue that because the tunnel valleys of Cwm Gwaun etc have removed many cubic km of rock and transported it westwards, and because there are many dolerite sills exposed in the valleys, there ought to be piles of dolerite boulders piled up somewhere near Letterston. In the event, I don't know of a single Cwm Gwaun erratic in that area.

We are still in the very early stages in understanding the processes and sequence of entrainment events in South and West Wales. But we have made a start......

And don't pretend that bluestones are homogenous. They aren't -- as I keep on saying, they are very varied, and have come from at least 20 different locations. Which is why I keep on saying that they look to me like an assemblage of glacial erratics.

Constantinos Ragazas said...

Brian,

Repeating the same argument will not convince Phil or Myris or many others. They ask a legitimate question. If glaciers advanced to Salisbury Plain, cold-based or not, there should be more erratic stones and debris strewed in many various places in Salisbury Plain (unless the cold-based glaciation is local).

Pointing to a handful of erratic bluestones here and there is just not enough. Counter arguing the "numbers" is not convincing. Agreeing to disagree does not settle the matter.

In my view, the settling unsettling question is "how did the Rhosyfelin rhyolite debris got to be at Stonehenge from Wales"? . Clearly not carried there by Neolithic people!

Kostas

kostadinos@aol.com

BRIAN JOHN said...

Kostas -- you cannot go around saying "there SHOULD be more erratics here or there than there actually are..." That assumes you have a great understanding of the processes and timing of entrainment, transport and deposition events -- which you clearly do not have. Neither do I. I could just as well say "There should be more erratics in the Vale of Glamorgan than there are..." or "There should be more erratics in South Pembrokeshire than there are....."

The fact of the matter is that there is a strange group of stones, mostly from the eastern part of the Preseli Hills, on Salisbury Plain at a place called Stonehenge, where they happen to have been used to build an enigmatic monument."

Until we have a much better understanding of landscape history, we just have to say that the assemblage looks like an assemblage of glacial erratics, and that according to the good ol' Occam's Razor, it's best to assume that they were carried there by ice..." Unless, that is, some killer fact comes along to convince us that there is a better and more complex explanation.

Constantinos Ragazas said...

Brian,

Don't misunderstand me. I fully support your claim Neolithic people did not could not have carried stones to Stonehenge from Wales. Whether these be Preseli megaliths or Rhosyfelin rhyolite gravel! But your counter arguments to Phil and Myris on this issue of glacial erratics at Salisbury Plain need to be strengthened.

Along with the scatter of erratics in Salisbury Plain, why not include the many megaliths at the bottom of Bristol Channel and English Channel?

And what of all the boulders along the southern sea coast? How did these get there? Dropped by a flotilla of ice bergs? I don't think so! That does not explain the empty pits found in the bedrock along the coast!

I still believe the strongest argument based on current data are the thousands of erratic debris in the Stonehenge Layer that do not match with any of the Stonehenge stones sampled. But there are many other facts on the ground that can also make the case!

Kostas