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Tuesday, 11 October 2011

Did ice carry the whole "bluestone quarry" to Stonehenge?


Before and After?  Just think about it.....
Above:  the Big Rocks erratic cluster at Okotoks in Alberta.  Below:  Stonehenge from the air.


In my last post I suggested that glacier ice might have entrained extremely large masses of bedrock (maybe weighing thousands of tonnes) during its passage across North Pembrokeshire during the Ice Age.  If that happened -- and such a thing is quite possible -- we do not have to worry about where the "bluestone quarry / quarries" might have been, since it or they might have have been dumped at or near to Stonehenge itself.  In other words, if we are looking for traces of bluestone quarrying, we need look no further than Stonehenge itself.

I don't think I have descended into madness here -- and indeed the specialist literature is full of examples of truly enormous slabs of bedrock that are dragged along on glacier beds or even entrained into glaciers along shear planes.  FOR EXAMPLE:

1.  A slab of Cretaceous rock in Caithness, measuring 200m x 137m x 8m
2.  A raft of limestone in Northumberland 800m long
3.  At Great Potton, a raft of limestone over 300m long
4.  At Melton Mowbray, a raft of Lincolnshire Oolite 275 x 90m in extent
5.  On Anglesey more than one limestone block over 90m long
6.  Near Abergavenny a gritstone erratic 180m long
7.  The "schollen" of Germany -- made of Tertiary and Cretaceous clays and sands -- up to 4 km x 3 km x 120m
8.  SW Alberta -- one erratic measures 24m x 12m x9m, weighing more than 18,000 tonnes
9.  Malmo, Sweden, an erratic mass of chalk resting on till is 5 km x 300m x 50m.  Extensively fractured, but still coherent.
10.  Ohio -- a tabular erratic resting on till has an area of 1850m2 and a weight of c 13,700 tonnes, but a thickness of only 1.5m.

Some of these dimensions are amazing, and the entrainment of erratics on this scale can only be accounted for by "freezing on" conditions at the rock-ice interface creating a bond that is stronger than the bond contained within the unfrozen bedrock deeper down.  So the frictional drag in the coherent rock is overcome, and massive slabs are dragged away.  So this happens -- the fact of the matter is supported by observations in the field, and by glaciological theory.

What happens after the entrainment has occurred?  Well, it has to be said that except in rare cases (see above) these great entrained slabs are quickly broken up during glacier transport.  Some great slabs survive for 20 km from their places of origin, but seldom for much further.  So the more common scenario would be for slabs to move up into a glacier along shear-planes and to be subjected to sufficient stresses to break them up into smaller bits and pieces, while still being carried along together, in a cluster.  That, in my view, is a distinct possibility with respect to the Stonehenge bluestones.  Because of the preexisting tendency of spotted dolerite (for example) to break up into pillars because of the joint / fracture pattern in the native rock, elongated pillars and slabs would have been the natural features to have resulted from this process.  If some larger masses of bedrock did survive until they were dumped somewhere on Salisbury Plain, then relatively simple wedging and levering might well have allowed these masses to be "quarried" by the builders of Stonehenge to give a supply of further useable orthostats.  The builders used up whatever resources were available to them -- and when they were gone, they were gone -- the building work shuddered to a halt, and there never were enough bluestones to finish the job. 

My preferred scenario here would be for some pillars and slabs to have been entrained individually by overriding ice from a number of locations where "entrainment conditions" were met at the base of the glacier -- with further supplies of stones coming from great entrained masses which were then, to a greater or lesser degree, broken up during transport.

Yes, this is an "extreme" theory -- and everybody will say that there is no independent evidence in support of it.  But we are very arrogant indeed if we think we already know everything there is to know about the sediments present on Salisbury Plain, and I for one am not yet prepared to rule out a number of glacial possibilities, of which this is just one.......

33 comments:

Tony Hinchliffe said...

I have emailed this directly on to Professor Mike Parker Pearson at his Sheffield University address, and suggested he cogitate upon it.

The Stonehenge Enigma said...

Brian

Looking at the old picture you posted, you should add the ice not only delivered the stones en-bloc but also put the stones up - with a missing sector!

Consequently, this means that you have either been corresponding with Kosta too much or emptying the wine cellar this afternoon?

RJL

Geo Cur said...

Here is another find of a marked erratic from a couple of years ago .http://www.themodernantiquarian.com/site/11603/tullich_hill.html .They tend not to be particularly ornate but they were certainly given more than pssing attention at the same time of all the Stonehenge phases . If the glacial theory stops somewhere in Somerset then surely the same applies to erratics. An equivalent scenario from the "strong " human transport side would be along the lines of it was all done by eight teenagers as a punishment for throwing conkers at celebrants at a ceremony at Pentre Ifan .

BRIAN JOHN said...

OK guys -- so you all think this theory is mad. They say that Stonehenge turns everybody mad who thinks too much about it...... and I suppose that might be true! Just look at some of the stuff on this blog and on all the others that deal with Stonehenge!

This post may represent "premature publication prior to peer review" -- but I'm thinking out loud here, and have a hypothesis to test.

So let's test it. Not sure, geo, whether erratics with marking on them are relevant. Since many erratics are incorporated in megalithic structures up and down the land, I wouldn't be at all surprised to see cup marks and other markings on them. Neither would I be surprised if prominent boulders were accorded some sort of significance and marked by our ancient ancestors. That doesn't mean to say that they actually moved them.

Geo Cur said...

I wasn't suggesting that the markings had anything to do with moving them simply that they were accorded some attention . And of course it doesn't mean that they didn't move them either .

Constantinos Ragazas said...

So Brian,

We now have an ice cover over Salisbury Plain with erratics riding on the surface! All you need to complete my Explanation is an ice meltwater basin at Stonehenge and prehistoric teenagers pushing stones over the ice edge!

You're getting hotter! Soon you'll break through the ice that's separating you from the truth!

Trust me when I say I will make your site historic!

Kostas

BRIAN JOHN said...

Don't get too enthusiastic here, Kostas. This is not the first time I have speculated about glacier ice reaching Salisbury Plain -- the glaciological models suggest it too. And there is NO similarity between your theory and mine -- I am talking about a glacier that obeys the laws of physics and behaves in ways that can be shown by analogy to be reasonable and predictable.

Constantinos Ragazas said...

Brian,

Lets just celebrate our agreements. Our differences will be bridged in time. In time you will come closer and closer to what I have been saying for a long time. It's inevitable! That's the essence of truth!

Did I tell you? I am very patient, persistent and selfless!

Kostas

David St. Fagan Evans said...

Hello Geo,
You are either psychic or privy to inside information, for if it's a 4 ton bluestone that needs shifting from Preseli to Stonehenge, then your reference to it being done by eight teenagers is probably very close to the mark.

Would you know whether, or not, Flat Holme and Steep Holme are two giant erratics deposited in the Bristol Channel?

BRIAN JOHN said...

David -- don't forget we are talking about 82 stones here (or so we are informed by the archaeologists) from many different source areas. So maybe there was a major job creation programme,involving the use of many hundreds of miscreants who had yo be punished by doing something useless? (Rather like the social programme for building canals in the limestone areas of Ireland, rather later on.....)

Now there's a nice thought - Flatholm and Steepholm being giant erratics. I doubt it -- but we'd better ask the geologists.

BRIAN JOHN said...

Kostas -- I never cease to be amazed as your list of virtues increases. I am lost in admiration!

Constantinos Ragazas said...

Aah! Brian,

This is not about me! It shouldn't be about you either. It is about knowing the truth about Stonehenge.

What I listed are only road signs to that destination!

Kostas

Anonymous said...

Boys I did say no mention of the K word despite those islands being close to the Variscan/Hercynian Front.
You are just working yourselves up for it. Tears before...
GCU In two minds
For the slower amongst us
K is for klippe.

Mr R BREMNER said...

The newly-beknighted 83-year-old Bruce Forsyth is RUMOURED to be working on a new, geomorphologically-based catch- phrase with his handlers.

"ICE to see you, to see you...........................ICE!"

He is also RUMOURED to be working on a new Game Show, in which obese audience participants volunteer to act as human erratics, entrained WITHIN MOVING glaciers. He says, as his audiences each week have to be dragged in, they won't mind more of the same!

REITH said...

I have it on good authority that well-known practical archaeologist Julian Richards, of BBC's "Meet The Ancestors", is planning a new TV Series in which singer and Pembrokeshire lass, Cerys Matthews, motivates a load of loutish local unemployed lads to drag the WHOLE of the Carn Meini "mountain" (in Brian's parlance) along the A40 in return for promises of songs. Any suggestions for the Show's title would be appreciated, says Julian.

BRIAN JOHN said...

In case anybody doesn't know what a "klippe" is, it's the German word for a cliff or precipice. It's also used in geology for an outlier of older rock sitting on younger rock, usually as a result of thrusting on a large scale. So the mechanisms of glacier thrusting are basically the same -- carrying slabs or blocks from their places of origin and then eventually dumping them on rocks that are unrelated. (Mind you, in this case the rocks underlying the dumped materials may be older or younger, or approx the same age.)

What Anon is suggesting is that there isn't anything very strange about Flatholm and Steepholm, in spite of them being located near a major thrust plane and fault zone in the Severn Estuary.

BRIAN JOHN said...

Reith -- Oh dear, not another rock musical, surely? Even with Cerys on board, it can't possibly get the ratings the TV moguls want.....

M BOYCE said...

David St Fagan Evans/ Constantinos Ragazas

Your remarks on Teenage Job Creation Schemes are entirely appropriate on a day when U.K.Unemployment figures stand at a 17-year high, at 2,570,000.

What is English Heritage, etc, and the National Trust going to do about it?

BRIAN JOHN said...

Well, there was quite a campaign a few years ago for Wales to claim the bluestones back. That would be an excellent job creation project -- bring all the stones back to their places of origin, just to prove that it was possible to carry them in the other direction ...... it could be done several times, just to test out the GW and MPP theories of transport by sea and overland. Then everybody would be happy.

REITH said...

Agreed, Brian. Cerys is much better on her Radio shows, anyway, This morning she did one on MY old Home Service (Radio 4 to youngsters) about FISHING, called "Hook, Line and Singer", in which she caught a shark.Lovely speakin' voice, ey??

MAX said...

Thank you, Brian. Do you mind if I work that idea into my routine soon? I'm On Tour as we speak. By the way, has Kostas caught my show? He seems to have a great sense of humour! At least, I hope he has!

BRIAN JOHN said...

Max -- it's a free world! Got your new song ready for when Wales win the World Cup? I see you are in the Millennium Centre on Sat -- after the Wales-France semi-final. I hope you have quite a party!

MAX said...

Yes indeed,Brian!! Never mind about flint factories and non-existent Preseli bluestone quarries: it's good to see the Wales fly-half factories are in good production again!

Anonymous said...

..........and congratulations to EVERYONE for managing to stay ON TOPIC!!!........well, more or less, I suppose, well. we can't have it all............

(Sir) Brucie

Constantinos Ragazas said...

Geo,

Like to tap your knowledge of all thinks prehistoric.

Looking for references, photos and descriptions of various henges, causewayed enclosures, stone circles, etc. with clear alignments of one, two or four 'avenues'.

Like to see what the ditch with outer/inner embankment looks like. And the surrounding countryside where these are situated.

Your references in the past have been very helpful. It will save me a trip across the pond to see for myself!

Kostas

Alex Gee said...

All on topic Sir Brucie ,

"didn't they do well" Sorry!!.

Geo Cur said...

Kostas , Avenues are not too common and excluding stone rows and post alignments , apart from Stonehenge others that come to mind are Durrington Walls henge (short and only discovered in the past few years ) , Broomend of Crichie (henge in Aberdeenshire ), Forteviot (henge in Perthshire short avenue ), Callanish stone circle (Hebrides ) , Avebury (henge and stone circle , there is the possibility of another avenue to the west of Avebury at Beckhamption ) , Stanton Drew (two short avenues at stone circle and possible henge ) the destroyed stone circle at Shap also had an avenue which was destroyed too .

Henges with inner banks , as at Stonehenge ,are uncommon and tend to be early Llandeagi A is possibly the earliest with an inner bank . Other major henges are Marden , Durrington Walls ,Ring of Brodgar , Stenness , Balfarg , Mount Pleasant , Maumbury rings Thornborough x 3 ,Arminghall , Milfield, Bull Ring ,Woodhenge . Usually henges are low lying but there are some found a wee bit higher e.g. Wormy Hillock ,Cairnpapple ,Weston ,Arbor Low . Some like Maxey have been destroyed or ploughed out but many of the above will be found on sites like The Modern Antiquarian and Megalithic Portal with plenty pics . Not sure quite how many sites are considered to be henges these days but it must be well over a hundred . Hope that helps .

Tony H said...

Geo Cur/ Kostas

Avebury's western avenue towards Beckhampton was rediscovered, since Stukeley's day, through excavations led by Joshua Pollard and Mark Gillings in the last 10-15 years.

Kostas, I would recommend "Avebury: the biography of a landscape",2002, by Josh Pollard and Andrew Reynolds, published by Tempus. It has plenty of good illustrations and colour plates. Not only are the stone circles and avenues covered, but also the important causewayed camp on Windmill Hill. There are good opening chapters devoted to the Mesolithic; earlier and later Neolithic.I'm sure you will be able to see a copy via libraries or bookshops in the USA.

Constantinos Ragazas said...

Geo,

Thanks for the references.

I have surfed the internet on henges and this is what stands out in my mind. How does it comport with your understanding?

From Wikipedia: http://en.wikipedia.org/wiki/Henge

Henges may be classified as follows:
Class I henges have a single entrance created from a gap in the bank;
Class II henges have two entrances, diametrically opposite each other;
Class III henges have four entrances, facing each other in pairs.


From Ancient Wisdom site: http://www.ancient-wisdom.co.uk/henges.htm

There is a tendency for Henges with a single entrance to have that entrance set in the north or north-east while sites with two entrances are aligned SE-SSE to NW-NNW or ENE-E to WSW-W.


Avenues may not be the right feature to consider here. Entrances is better.

I am drawn to this puzzlement!

Kostas

Geo Cur said...

Kostas , the typology of henges is a nightmare with many sub groups but the Class 1 ,11 etc system is useful in terms of numbers of entrances although these entrances do cover more points of the compass than suggested , worth mentioning that Stonehenge has another entrance at the south .The suggestion may have been influenced by the data from Roundels , earlier European monuments and similar to henges in that they have a ditch with a bank with 1- 4 entrances which tend to be oriented close to cardinal points although there is little to substantiate this from the minimal excavation reports and it could be fair to say that it is anecdotal at best .

Constantinos Ragazas said...

Geo,

Thanks for the info. From my sparse and sporadic reading the view is that entrances at henges follow the same alignment as avenues at Stonehenge. Prominent is the solstice alignment. Significant is the compass position of entrances. This fits well with my theory.

Consider this. Why is it that no pair of entrances at a site align in the same direction? And why is it that no avenue at Stonehenge aligns with the top but always the bottom of the hill?

Newton thinks gravity!

Kostas

Geo Cur said...

Kostas , a few years ago I compared the entrances of the major British henges and it was apparent that there was no association with alignments to solstices ,if anything there were more oriented on the lunar major standstills . I can send you the excel files if you like . Try to find another henge entrance with a similar orientation to Stonehenge , Coneybury is often mentioned in the literature as being aligned on the solstice but it’s a fallacy . Some sites with more than one entrance do have their entrances diametrically opposed e.g. Durrington Walls ,Avebury ,Devils Quoits Milfield north ,,Thornborough etc .

BRIAN JOHN said...

Geo and Kostas -- your interesting conversation is seriously off topic! Not sure we are getting anywhere -- calling this one to an end now please.