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....
To order, click
HERE

Monday, 30 January 2012

Bluestone haulage for wimps



I came across this photo today, in connection with a review of a new book about the Preseli Hills called "Ancient Wisdom and Sacred Cows" edited by Hefin Wyn (£14.95).  No idea who the photographer was, but he was clearly dangling from a tree at the time.

The pic is of course an addition to our photographic history of the ill-fated Millennium Stone Pull in the year 2000.  Very much a matter of stone-pulling for wimps.  Note the great lengths of nylon rope, the compulsory gardening gloves for all pullers (to avoid chafing and blisters), the excellent asphalt road surface, the beautiful masonry bridge, and the extensive use of low-friction nylon netting to reduce the friction on the underside of the sledge.  We were wimps, the whole lot of us!  (Yes, I was one of them.........)

In the old days, our heroic ancestors needed none of this -- they just went ploughing straight across the sort of terrain we see in the top right of the photo.  My God, they were tough in those days.  And they were probably naked too, just for good measure......

Saturday, 28 January 2012

Where is Rhosyfelin?


I notice that some contributors to this blog are still uncertain where Craig Rhosyfelin (Pont Saeson) is located.  (That's the site identified by Rob Ixer and Richard Bevins as the source for much of the Stonehenge foliated rhyolite debitage.)

My thanks to Jonathan Lee of Aberystwyth University for this splendid computer-generated topographic image -- it shows the coastline and the main relief features of NE Pembrokeshire very well.  I have put onto the image the locations of Craig Rhosyfelin and Carn Meini.  As you can see, Craig Rhosyfelin is well to the north of the Preseli Hills -- a nasty place for Neolithic stone-collecting expeditions, but quite a handy place for entrainment by a glacier flowing across the landscape from NW towards SE.

Friday, 27 January 2012

Unfinished projects



I got a message from Tony about unfinished projects, which we have discussed at length before.  He says:  "...... Burl's "Stonehenge - a New History" (2006), page 107.  He makes some good, reflective points there about what are indexed as 'unfinished projects', and proceeds to name quite a few from elsewhere in Britain, beyond Stonehenge'.   That's one book I haven't got on my shelf, but in Burl's "Stonehenge" this is what he says on p 145 with respect to the early settings of posts:


Splendid fellow, Aubrey Burl.  A man after my own heart.  The image at the top of this post is another interesting example of an aborted project -- it's an image of an area just a km or so south of the town of Newport (Pembs) -- showing Carn Llwyd at the top (thought by the OU team in 1990 to be one of the sources of the Stonehenge bluestones), a very nice round house at the bottom (probably Bronze Age?) and a piece of a ridge and ditch (in the centre) that goes nowhere and does nothing.  It looks as if it is a piece of a circumference of a large planned enclosure around a broad hill summit -- we have to assume that it's either Bronze Age or Iron Age, but it might be Neolithic.  I've never heard anybody argue that this is what was planned, and that we are looking at a completed structure.  So all we can do for now is speculate as to what it might have been intended for, and why it was abandoned.

Thursday, 26 January 2012

OK -- I eat my words.....

I have often said in the past that I think the dolerites, spotted dolerites and gabbros which are found outcropping in North Pembrokeshire are too coarse-grained to respond well to glacial abrasion  processes and to reveal striations.  I have based that assumption on the fact that all of the rock outcrops and the tops of erratic boulders projecting above the ground surface are weathered -- some subjected to weathering for 23,000 years or so, and some for far longer than that.  These weathered surfaces are generally stained and pitted -- and although I have seen ice-moulded surfaces, none of these surfaces has carried striations.  Rhyolites are a different matter -- I have seen striations, for example, on the outcrops at Carn Alw.

Well now -- one of my neighbours has been doing some landscaping with some heavy machinery, and this has involved cutting into a morainic mound and hauling out masses of boulders up to 3m long -- some of them probably weighing over 10 tonnes.  Some of these boulders that have been thrown up into a great pile are shown in the top photo.  On looking at the dolerite and gabbro boulders which have been buried up to 3m beneath the ground surface, and which have now been washed by the rain, you can see how beautifully smooth some of them are -- classic abrasion by fine-grained sediments on a rather fluid glacier bed.  And there are striations!  Lots of them......  When one ignores the damage done by heavy machinery, you can see quite deep gouges and abrasions even on the surfaces of some coarse-grained boulders -- the lower photo shows a boulder with two sets of striae, one set running up and down, and the other running across the face of the boulder beneath that patch of muddy turf.

OK -- revised opinion.  There is in principle no reason why the spotted dolerites, dolerites, rhyolites and ashes used as orthostats at Stonehenge should not carry striations resulting from glacier transport.  That would happen only if the stones were carried on the glacier bed -- although as I have argued on this site before, I doubt that that was the case.  Again, if the surfaces of the stones have been exposed to the atmosphere for just a fraction of the 450,000 years that have elapsed since the Anglian Glaciation, the chances of striations surviving would be virtually zero. 

Oh, for some cosmogenic dating of those bluestone surfaces at Stonehenge........

The Bluestone Argonauts -- did they sail or paddle?




 Above: the reconstructed Ferriby Boat called "Oakleaf"
Below: the Dover Boat

 I have been quite intrigued recently, on going through some of the literature, to see that the experts seem to think that in the early Bronze Age there was no knowledge of sails or sailing techniques in Western Europe -- and that means the waters around the coasts of Britain.  If that was the case, then there would certainly have been no sailing boats around in the Neolithic, when our heroic ancestors are supposed to have transported 82 bluestones over land and sea from Pembrokeshire to Stonehenge. Apparently the technical challenge which these earlier boatbuilders had not overcome was that of bedding a mast foot into the bottom or keel of a boat, so as to cope with the enormous stresses involved in catching and using the wind, often in rough sea conditions.  So this famous illustration by Alan Sorrel is probably up the creek...


See my post dated 27 November 2011 on the "Bluestone Argonauts" and their sea-going vessels.
http://brian-mountainman.blogspot.com/2011/11/even-more-danger-marine-engineers-at.html

I recall that Herbert Thomas, the man who started this whole hare running, was no great believer in the marine transport of the stones, and many others have shared that view, on the basis that the technical challenge would have been far too great for the Neolithic tribesmen to cope with.  Aubrey Burl shared that view, and analysed the maritime transport idea in some detail in more than one of his books.  HHT thought that the stones must have been transported overland, all the way.  It was Atkinson -- ably assisted by Alan Sorrell -- who enthusiastically promoted the idea of sea-going rafts and naked heroes braving the elements on a stormy shore.....  By God, sir, they were a tough bunch in those days......

Not only do we have to cope with the technical challenge of making a seaworthy vessel large enough to take a stone weighing up to 8 tonnes (we have to assume that the Altar Stone travelled the same way as the others) -- but we also have the technical challenges associated with sails, ropes and paddles, and paddle fixings.  Then there are the problems -- flagged up by Aubrey Burl -- on navigation and mental maps;  and he quite rightly asks whether Neolithic tribesmen would have had the capacity to identify a source area in West Wales, to map out in their minds how to travel there and back on many different occasions, and to cope with all of the navigational hazards which we all know about around the Pembrokeshire Coast, in Carmarthen Bay, and in the Bristol Channel
-- areas of high seas, rapid tide races and currents, and very high tidal ranges.

I think that in this part of  "The Great Stonehenge Story", more than in any other part, we are guilty of seeing as our heroes modern men in fancy dress.

That multi-million project...... whatever happened?



I recall seeing (on one of the multitude of Stonehenge videos on YouTube) some interesting pictures of Mike Pitts with a tape-measure, earnestly measuring up Stonehenge and saying this was in preparation for some great project which would involve a full-scale reconstruction of the jolly old ruin, which would allow all sorts of people to study it properly, free (presumably) of all those nasty constraints placed on research by English Heritage.   Was it a National Geographic video?  Can't remember now......

 Anyway, I was reminded of this when I came across this on the Ferriby Boats site:

"With projects such as a planned multi-million reconstruction of Stonehenge seeking to use full-scale replicas of the boats used to transport the bluestones from Wales, the experiment needs to continue." said John Davis, the Trustee who, with the support of local shipping businesses, helped bring the replica to the Humber. "The assessments made after initial trials on The Solent need developing into a more detailed evaluation of the boats' handling and load carrying abilities."

http://www.ferribyboats.co.uk/

http://www.archaeology.co.uk/the-timeline-of-britain/the-dover-bronze-age-boat.htm

So not only did we have plans (in 2009?) for the great reconstruction job,  but also a reproduction of the great stone-collecting voyages (assumed to have involved all those nice Ferriby-type boats) back in the Neolithic.

Does anybody know more about this project, and what happened to it?

Tuesday, 24 January 2012

Preseli in the conflict zone


Preseli in the conflict zone again --  this time it's not a conflict between archaeologists and geomorphologists, but between the Irish Sea Glacier and the local Preseli Ice Cap. 

I published the top map some time ago, as my current best estimate of where the Irish Sea Glacier skidded to a halt in the Devensian Glaciation.  I did suggest at the time that because there are ice-smoothed rock surfaces on the summit ridge of Carningli, and because there is a lot of fresh till and an erratic spread over the ridge and down onto the south side, the glacier might have crept over the ridge and extended down towards the Gwaun Valley. 

Anyway, look at the cosy fit between my suggested southern ice limit and the northern edge of the Preseli Ice Cap, as modelled by Henry Patton and others.   My dotted area is not that different from the proposed ice-covered area.   I find that rather satisfying -- a nice convergence between desktop studies and fieldwork.

There are still a couple of big questions here.  First, what was the role of the proposed "Glacial Lake Brynberian" in the sequence of events here?  Second, was the maximum extent of the Irish Sea Glacier exactly in phase with the maximum extent of the Preseli Ice Cap?  We are talking about a period of maybe 1500 years -- a very short time, geologically.

Watch this space.  There will be developments.

Monday, 23 January 2012

Another Preseli Ice Cap Image


This is another image of the Preseli Ice Cap, from the modelling work reported by Henry Patton and colleagues in 2011.  This shows the picture as it MIGHT have been around 23,850 years ago, with cold-based (thin) ice over the main Preseli ridge and with a few small patches elsewhere as well.  One of these patches is on Carningli -- assumed to have done nothing to the landscape.  Danny McCarroll and colleagues have said:

“East of the proposed ice limit, the western Preseli Hills (Mynydd Carningli) show no evidence of glaciation” (McCarroll et al., 2010)

Oh yes they do, chaps.  There are ice-moulded slabs on Carningli (very near the summit) and also morainic debris on the flanks of the upland.  So the ice was maybe not so cold in the Devensian, and it was certainly capable of affecting the landscape in a number of different ways.  But the complicating factor here is that the Irish Sea ice was coming in from the NW, and extending some way beyond the red line marked on the map.  So there may have been some mixing of Irish Sea Glacier ice and local ice  -- exactly as we see in Greenland today, where big ice streams exist right next to upland ice caps.

The red point shows the sampling point for the cosmogenic dates given by Mc Carroll and others --  as I have previously argued, those dates are wrong.  I'm pretty sure they are INHERITED dates.  More work needed.  We'll get there in the end.

That's the nice thing about models -- they give you something to work on and argue about......

Devensian Sea Level


In the Powerpoint presentation by Patton et al (2011) there is an excellent illustration of the current consensus regarding the Devensian sea-level curve.  In the illustration (based on the famous Barbados sea-level curve) we see that global sea-level reaches its low point of about -120m around 26,000 years BP, assumed to be the global glacial maximum.  In the UK and Ireland, it looks as if the ice sheet reaches its greatest extent a bit later;  not everything is in phase, and here and there we see lags of a thousand years or more.

The map on the right shows the "dry land area" at the time of the Devensian "sea level low point" -- in green.  But remember that it will not have been quite this simple.  Isostatic effects associated with ice buildup will have depressed parts of the crust in western Europe, and so parts of this green area might have been flooded.  There were complex interactions between eustatic (sea level) and isostatic (loading and unloading) effects.

Ice over All

Some members of our faithful blogging community have difficulties with the fact that ice caps and ice sheets develop ice surface profiles that are sometimes quite independent of the shape of the ground underneath.  So we effectively have a submerged landscape beneath a largely featureless ice expanse such as we see today in the centre of Greenland.

This is beautifully illustrated in the latest reconstructions of the Devensian Welsh Ice Cap by Hubbard et al (2011).  Above there are two cross profiles -- the top one for North Wales and the lower one for Mid Wales.  Note that there were a few small nunataks in North Wales (including Snowdon and Glyder Fawr) and that the ice surface was at about 1000m  In Mid Wales the whole of the landscape was submerged, and the summit of the ice dome was at about 1200m.

In general, ice velocities are greatest where the ice is thickest -- and the ice flows in ice streams, often in deep river valleys or troughs.  Where the ice is very thin -- near the mountain summits -- the ice temperatures will be low, and the ice will be "cold based" -- with very little or no erosion and with even quite delicate features like tors effectively protected.

Don't assume that this reconstruction is correct in every detail -- discussions are ongoing.  But the evidence does seem to be converging, and with every year that passes, the models and the "ground truthing data" get closer together......

On Glacial Cycles


This looks a bit daunting (from Patton et al, 2011) but it's really not that difficult.  It shows the main glacial cycles -- known from work all over the world -- over the past million years or so.  The interglacial phases (highlighted by nice yellow sunshine) are labelled I 1-11 and the glacials (marked with blue ice!) are numbered G 1-10.

The Devensian Glaciation is the most recent glacial episode, lasting from c 73,000 years ago to 14,000 years ago.  The Anglian Glaciation -- which I have assumed to be the one responsible for the transport of the Stonehenge bluestones -- was around 450,000 years ago.  But notice that there are several other big glaciations -- and we have very little idea what effects these episodes might have had in western Britain (in Eastern Britain things are a bit clearer).  Phases G2 and G7 were particularly large glaciations, and the ice of the Irish Sea Glacier might well have been almost as extensive in those phases as it was during the Anglian.

One of the great implications of this pattern is that any erratics that we might find in the landscape have probably had multiple trips and zig-zag courses....

Source:
Modelling the dynamic instabilities of palaeo ice-sheets
Henry Patton, Alun Hubbard, Neil Glasser ,Tom Bradwell, Nicholas Golledge
IGES Presentation 2011

The Preseli Ice Cap


I have drawn attention to the excellent work being done in Aberystwyth and elsewhere on ice cap and ice sheet modelling.  I came across this interesting reconstruction for the extent of the Preseli Ice cap at the peak of the Devensian Glacation -- around 23,500 years ago.   The authors (see below) suggest that the ice cap made brief appearances (for example around 25,000 yrs BP) and then grew to this extent around 23,500 yrs BP.  Its life span might have been 2,000 years at the most.  Notice that the ice is assumed to have been permanently cold-based, which means that it will have done very little to affect the landscape -- its role will have been largely protective. The authors assume that the whole of the Preseli ridge -- including all of the tors around Carn Meini etc -- was submerged beneath the ice.   
If this model is correct, it means that Pont Saeson and Craig Rhosyfelin will have been very close to the northern edge of the little ice cap at the time of its maximum extent. This means that when the ice cap melted -- possibly catastrophically over a few centuries -- there will have been a very large volume of meltwater rushing along the gorge of the Afon Brynberian towards the confluence with the Nevern Valley. 

A indicated in earlier posts, I'm not entirely happy with this model and its portrayal of the Irish Sea ice edge, but this is after all a computer-generated MODEL -- so it will be interesting to see how far the model and the hard evidence on the ground happen to converge........

Source:
Henry Patton, Alun Hubbard, Neil Glasser, Tom Bradwell, Nick Golledge:  "Modelling the dynamic instabilities of the British-Irish Ice Sheet: The Welsh Ice Cap"
If you want to look at the animations created over the past few years, click on the links below and you should be able to download them.

26th July 2011 – INQUA – Bern, Switzerland. .pptx presentation [52mb] (Modelling the dynamic instabilities of the British-Irish Ice Sheet: The Welsh Ice Cap); animation .wmv file [2.4mb].
18th May 2011 – IGES departmental seminar – Aberystwyth University. .pptx presentation [99mb] (Modelling the dynamics of palaeo ice-sheets); model .mp4 file [13mb].

Sunday, 22 January 2012

Those periglacial stripes are probably not periglacial



I have devoted some space before to those strange features examined over the years by archaeologists and generally referred to as "periglacial stripes" -- and referred to, with delightful quaintness, as "geological stripes" or "natural Ice Age gullies" by EH.  I've done a bit more digging into the literature -- a poor substitute for digging into the ground -- and I am increasingly convinced that they are not periglacial in origin.

Here are the latest EH statements about them -- probably guided by MPP and his team, who have most recently examined them:

Recent excavations and geophysical surveys have suggested the possible importance of geological features called periglacial stripes. They run parallel to the banks of the avenue and across the site of Stonehenge and align in places on the solstice axis. It is possible that these geological stripes may have been visible on the ground in early prehistory and could have led prehistoric people to believe that this was a special place.

http://www.english-heritage.org.uk/daysout/properties/stonehenge/history-and-research/history/
Outline of the main differences between the 1st edition of the
English Heritage Stonehenge guidebook (2005, reprinted 2007)
and the 2nd Edition (2011) (download as PDF)

v) The possibility that Stonehenge's location was chosen as a result of the
coincidental alignment with the solstice axis of natural landscape features
(periglacial stripes underlying the Avenue) coupled with the occurrence of a natural
sarsen (the Heel Stone) at the end of that alignment. 

A new paragraph has been added discussing the discovery of the existence of
natural Ice Age gullies parallel to the Avenue, and the possibility that the Heel
Stone is a rare local sarsen found near where it now stands, both features
providing a coincidental alignment on the solstices. It is suggested that this may
have provided the impetus for the building work that followed.

Added mention of the natural "visible stripes" that are Ice Age landscape
features in the chalk parallel to the Avenue along the straight section leading up to
the monument. Changed emphasis in discussing the solstice axis from "this cannot
be a coincidence" to "this alignment is deliberate".



Beware of optical illusions on this LIDAR image --if you are not careful the low parts of the landscape can look high, and vice versa......




 Vertical satellite image of the Avenue, running from Stonehenge (bottom L corner) 
towards the NW

If the evidence is reliable that these stripes run parallel with the first part of the Avenue (shown in both of the illustrations above) and even run through or beneath the Stonehenge earthworks, then that clearly suggests a great age for the features.  But we don't really know how extensive they are -- maybe somebody who knows the evidence on the ground can enlighten us on that.  If you look very carefully at this illustration you can see a faint line outside the Avenue edge which is interpreted as one of the "periglacial stripes."





What we need here is a detailed topographic survey, but my impression is that these stripes (like the Avenue) point towards the midsummer solstice or sunrise position on the horizon (have I got that right?) but that they do NOT run down the maximum slope inclination towards Stonehenge Bottom.  If there is one thing we do know about periglacial stripes it is this:  they always run down the maximum inclination of the slope.  I have seen a lot of such stripes in my time, in Antarctica, Greenland and Iceland, and I do not recall a single one that was aligned diagonally down a slope. 

In the absence of a detailed survey all I can do is speculate about this -- and to say that if these stripes really are periglacial in origin, they should be running from Stonehenge down towards the road junction we can see on the LIDAR image.


Far be it from me to suggest that something perceived as "natural" in origin should now be re-classified as "probably man-made" -- but that is exactly what I am doing!!

EH updates on Stonehenge bluestones



EH has made a number of changes to the Stonehenge Guidebook (2011 edition)  -- nothing very exciting, but if anybody is interested, there is a PDF available which details all the changes, point by point.  On the bluestones, there are new mentions of the recent TD/GW and MPP work, with mandatory mentions of the worlds of the living and the dead, and of the healing powers of bluestones "as a reason for going to the effort of transporting them from Preseli."  It's strange how wacky theories, without a shred of evidence to support them, get turned into truth and orthodoxy.  EH needs to take some responsibility for that, and the organization should be ashamed of itself.  In spite of the ongoing debate about the mode of transport of the bluestones, EH has steadfastly set its face against any mention of the glacial transport hypothesis.  Well, as I have said before, with the Olympics coming up, and a need to pull in as many punters to Stonehenge as part of the national recovery plan, they clearly don't want to say anything that might cast doubt upon the Gospels as written by the Apostles.  Certainty above objectivity, any day.....

Location of Preseli Hills has been changed from "west Wales" to just "Wales". Caption to the
first map has been changed from "Map showing a likely route" to "Map showing one
possible route" from the Preseli Hills to Stonehenge.

Discussion of the bluestones "original setting" of "an incomplete circle of
paired stones", the dismantling of it prior to the inner sarsen structure's construction
and the later reintroduction of the bluestones, has all been removed. This has been
replaced by a paragraph noting that the sarsen structures do not appear to have
been moved once erected whereas the bluestones have been rearranged more
than once. It notes that the stone settings were built between about 2500 and 2000
BC.

........... two additional potential reasons for its construction are
also outlined. These are: its use as a cremation cemetery from the earliest
monument coupled with the idea that the stones represent long dead ancestors
compared to timber circles which represented the houses of the living; and, a
possible belief in the healing powers of bluestones as a reason for going to the
effort of transporting them from Preseli.


http://www.english-heritage.org.uk/daysout/properties/stonehenge/history-and-research/history/

Outline of the main differences between the 1st edition of the English Heritage Stonehenge guidebook (2005, reprinted 2007) and the 2nd Edition (2011)
(download as PDF)

Saturday, 21 January 2012

When did Craig Rhosyfelin come into existence?


This is an interesting question:  when the large chunk (or chunks) of rock was/were taken from Craig Rhosyfelin by one process or another, and transported towards Stonehenge, did the landscape look anything like the landscape of today?  The provenancing of some of the Stonehenge rhyolite debitage to "within a few metres" at Rhosyfelin seems to be based on the assumption that the landscape is unchanged, and that the pronounced spur sticking out into the valley of the Afon Brynberian was there at the time of rock extraction.  I have questioned that assumption, and have wondered how accurate any provenancing can be, given sampling bias and other factors -- but putting that question to one side, I'm increasingly convinced that the landscape in and around this valley has changed quite substantially during the past 500,000 years.

On the top photo above, the MPP dig site is shown with the circle, on the flank of the rocky spur of Craig Rhosyfelin.  On the lower photo, that site is in the bottom R corner, and we see the deep valleys of the Brynberian and Nevern rivers.  Both are flowing partly in deep gorges, and I think most geomorphologists would agree with me that these are Pleistocene features, created at a time of deglaciation, with great volumes of meltwater flowing either under the ice or beyond the wasting ice edge, and trying to find its way towards lower land.  This is at the same time as the creation of the huge meltwater channels of the Gwaun - Jordanston system mentioned in earlier posts.

So if these are meltwater channels created for the most part at the end of the Anglian Glaciation, it follows that they were not there (and neither was Craig Rhosyfelin) at the time when thick ice was flowing across the landscape and entraining large blocks of foliated rhyolite.  So what did the landscape look like prior to the arrival of the ice?  Probably there would have been a shallower valley here, and probably there was a substantial crag of rock -- rather like the tors of Carnedd Meibion Owen -- standing proud of an undulating land surface.  Subsequently, after the erosion of this high crag, meltwater got to work, creating the main valley and the subsidiary valley on the northern flank of the rock.

A Whin Sill erratic cluster in the Stevenage area?



In the middle of our recent discussions about erratic clusters, I was reminded of this rather interesting paper by Olwen Williams-Thorpe and others from 1999:

"Geochemical provenancing of igneous glacial erratics from Southern Britain, and implications for prehistoric stone implement distributions"  by Olwen Williams-Thorpe, Don Aldiss, Ian J. Rigby, Richard S. Thorpe,  22 FEB 1999, Geoarchaeology, Volume 14, Issue 3, pages 209–246, March 1999

http://onlinelibrary.wiley.com/doi/10.1002/%28SICI%291520-6548%28199903%2914:3%3C209::AID-GEA1%3E3.0.CO;2-7/abstract

The main point of the paper was the link between erratics and stone implement distributions, on the assumption that Neolithic and even later people would instinctively have made use of whatever handy erratic material they found lying around in their neighbourhoods.  Leaving that on one side, this is another excellent example of the increasingly accurate provenancing that can now be done -- this time using geochemical methods.  The "cluster" of four Whil Sill erratics found near Stevenage, about 360 km from their source area and close to the southern limit of glaciation, is intriguing.  (The box on the map shows the area examined by the authors -- and from which they collected 16 erratics for detailed examination.)

Of course, far-travelled erratics are not at all uncommon -- one of the most common and distinctive erratic types found on Pembrokeshire beaches is Ailsa Craig microgranite, which has come from the Firth of Clyde, near the original source area of the Irish Sea Glacier.

In the article, the authors discuss the possibility of "selective" erosion of the Whin Sill by overriding ice and the possibility of a zig-zag transport route over several glacial episodes.  It's an interesting discussion, which obviously has a bearing on our debate with respect to Craig Rhosyfelin and Stonehenge.


=================

Abstract

Sixteen basic and intermediate composition igneous glacial erratics from Anglian (pre-423,000 years) deposits in Hertfordshire and Buckinghamshire, southern Britain, were selected for chemical and petrographic analysis in order to determine their original source outcrops. Major and trace element compositions suggest that seven samples (plus two uncertain) originated in the Lower Carboniferous volcanics of the Scottish Midland Valley (SMV), four came from the Upper Carboniferous quartz dolerite association which crops out in Scotland, northern England (Whin Sill) and extends to Norway, and one came from the northern England Cleveland Dyke. One sample of altered dolerite is ambiguous but has some similarity to the Old Red Sandstone (Devonian) age lavas of the SMV, and one meta-basalt sample may be from southwest Scotland or Scandinavia. These results identify specific outcrops which provided glacial erratics within currently accepted ice trails in the United Kingdom, and provide the first supporting evidence based on geochemistry, rather than petrography, for these ice movements. The distribution and provenance of glacial erratics are of importance in archaeological studies, because erratics provided a potential source of raw material for stone implement production. There is a marked geographical correlation between the distribution of prehistoric stone implements of quartz dolerite in the United Kingdom, and directions of ice movements from quartz dolerite outcrops within Britain. This correlation lends support to the hypothesis that prehistoric man made extensive use of glacial erratics for implement manufacture, as an alternative to quarrying at outcrops and subsequent long-distance trade.

On Faceted Stones in Nature



The pic which I recently published -- with what Rocky refers to as "eight faceted faces" -- has raised some interesting issues -- the most interesting of which is the means by which we recognize rock surfaces as having been shaped in some way by human beings in prehistoric times -- before the advent of metal tools like wedges, chisels, hammers and crowbars.  As far as I am concerned, the photo showed a piece of rock which appears to have fractured along a number of intersecting joints or planes of weakness -- which suggested to me that there had been no human intervention of any sort.

If you look at the pic above -- from one of the dolerite pinnacles close to Carn Meini -- it is very common for elongated blocks to have 5 or 6 facets.  Look closely (click to enlarge) and you will see that there are lines of quartz crystals running across the blocks in places.  These are also weakness lines, and cause transverse breakages.  You can see that one big chunk or flake is about to break away from one of the pillars.......

If we contemplate the hypothesis of that other rock having been fashioned by Neolithic rock workers, how would they get surfaces as smooth as that by working just with stone axes and maybe wooden wedges?  And why would they want to lever out a slab with that particular shape anyway, when there are thousands of other flattish (and elongated) slabs littering the landscape?  I just don't see any logic in it........

Friday, 20 January 2012

The Age of the Landscape

Top map:  the area of North Pembrokeshire which has been most affected by glacial processes (thanks to Prof David Bowen)
Middle photo:  Part of the area of thick fluvuioglacial sands and gravels, between Newport and Cardigan (the two gravel pits are Trefigin and Pantmaenog)
Lower photo:  Part of the Gwaun-Jordanston meltwater channel system, at the western end of the Gwaun Valley.  The big channel at the bottom of the photo is the Nantybugail Channel -- it can also be picked out on the map.

There have been several comments recently on this blog about the age of the landscape and the age of land surfaces, with some contributors apparently rather keen on the idea that a few thousand years ago there are valleys where there were once hills, and that some low-lying areas have suddenly been uplifted.  Well, let's get one thing clear -- the landscape of Pembrokeshire (and this goes for most of the British landscape) is for the most part very old indeed.  I'm talking about a landscape which has not changed much over millions of years, apart from superficial vegetation change and the introduction of new features created by massive civil engineering projects (motorways, water supply reservoirs, ports and harbours, airports etc).

The only places where we have had dramatic changes are around the coast, where cliff falls, landslides etc triggered off by marine erosion (especially on high-energy coasts) can occur, and where high rates of sedimentation can change the outlines of embayments and estuaries.  In Pembrokeshire, for example, we can see how some Iron Age promontory forts have been largely whittled away by coastal erosion over the course of 2,000 years or less.  But right next door there may be a bit of coast that has incredible stability and longevity, where there is less exposure to wave attack.

We know from coastal  and valley sediment sequences that most of inland Pembrokeshire hasn't changed much for more than 2 million years.  In other words, the basic pattern of hills, valleys and plateau areas is the same now as it was then.  But in the north of the county (see map at top) glaciation has wrought major changes in both surface altitudes and in the arrangement of rivers and valleys.  The big meltwater channels to the south of Fishguard -- and including the Gwaun Valley -- appear to be NEW features created initially underneath the ice -- maybe during the Anglian Glaciation around 450,000 years ago.  The valleys (which are in places more than 100m deep)  have been modified during subsequent glaciations.  There have also been major changes in the drainage pattern in the Teifi and Nevern Valleys, and in the interfluves where meltwater channels have been created subglacially and by overflowing lakes.  Some old valleys have been abandoned, and filled with glacial deposits, and other new valleys have replaced them.  Glacial, fluvio-glacial and lake deposits are is some places hundreds of metres thick.  There are hummocky moraine deposits, kame terraces and eskers -- two of which are currently exploited for sands and gravels for the building industry.

How old are these landscapes of sedimentation?  For the most part, Late Devensian, which means c 20,000 years old.  So these are Pembrokeshire's "young" landscapes.  Further to the south, in South Pembrokeshire, we seem to be looking at landscapes which may be well over ten million years old.....

Thursday, 19 January 2012

Worked rocks -- what do they look like?


One of our contributors, who wishes to remain anonymous, has sent these fantastic images of a "worked rock" close to one of the lower crags of Carn Meini -- the supposed source of at least some of the spotted dolerite orthostats at Stonehenge.  The upper image shows the "end on" view, and the lower one the "side view."

Sorry folks, but I don't see any signs of working here -- these angular features are very common in the volcanic rock exposures throughout this area -- both on bedrock outcrops and on detached slabs and smaller stones.

So what criteria should we use in order to identify genuine human working and to distinguish it from features that are entirely natural?

Tuesday, 17 January 2012

100,000 hits

I've just noticed that we have gone through the 100,000 hits barrier!  Here is the site meter -- this includes only genuine external hits, and excludes my own visits for reviewing comments, putting up new posts, editing etc.  It's interesting that there are now well over 500 page view hits per day, coming from an average of 243 site visits per day.  Visitors spend an average of over 5 mins per visit, which is I suppose nothing short of miraculous, given the short attention span of the modern human being.  Obviously those who read and contribute to this blog are made of sterner stuff, and are serious in their pursuit of knowledge!

Viewing this blog


http://brian-mountainman.blogspot.com/view/magazine

There are now so many entries on this blog that it can get confusing, even if you are using the search facility on the site.  Even if you use the Blogger magazine format, it can take a very long time to load, with a lot of scrolling required.  However, if you have the patience to load the whole blog into the magazine format, you will have ALL entries on a single page which you can scroll up and down -- I recommend that you save this as a web page onto your desktop, and it should then always be there, intact.  You can see all the entries adjacent to a thumbnail of the key illustration.  Makes it much easier to use.  Enjoy!

This will not automatically be updated with new entries -- for that you need to use a web browser like Firefox or Safari, as usual.

I am reminded of this because some recent contributors and readers appear to be unfamiliar with quite long and detailed posts and discussion threads in 2008-2011.

In case you missed it......

 It occurs to me that there are so many new readers on this blog that some of you, at least, may have not penetrated as far back in the records as 2008.  This is the article which I produced with Lionel Jackson for "Earth" magazine -- minus the illustrations.

http://www.earthmagazine.org/earth/article/1a1-7d8-c-1f

As you will see, there is a speculation (a very reasonable one, we think) relating to the movement of two parallel ice streams.

Richard Bevins to talk at Aberystwyth

In case anybody in the Aberystwyth area is interested:

Talk: 'Geological evidence for the origins of the Stonehenge Bluestones'
The inaugural event for the West Wales Geological Society will be presented by Dr Richard Bevins, Keeper of Geology at the National Museum of Wales.

'Richard, in partnership with Dr Rob Ixer (University of Leicester) and Dr Nick Pearce (Aberystwyth University) have been working on the rhyolite component of the Bluestones which leads them to believe it is of Welsh origin'.

Event Details
•    Date: 9th February 2012
•    Time: 1900
•    Cost: Members - Free. Non-members - £1.00
•    Location: Room A6, Llandinam Building, Aberystwyth University.
•    Parking: Aberystwyth Arts Centre

Whilst it is not necessary to register for this event, it would be useful for the society to anticipate numbers. Therefore, to register, use this link and contact the WWGS at info@westwalesgeolsoc.org.uk.

Monday, 16 January 2012

Ice streams

Above:  two distinct ice streams in the ice sheet edge, NW Greenland.
Lower pic:  two ice streams separated by a zone of more sluggish ice in Wilkes Land, Antarctica.  The ice embayment coincides with the zone of sluggish ice -- on either side of it the ice is moving much faster, and has pushed out across the coast in distinct tongues.


A number of people have asked recently what an ice stream is.  I have put in various posts before on this topic -- I suggest you do a search via the search box.  An ice stream is simply a stream of ice within an ice cap or ice sheet which is moving more rapidly than the surrounding ice.  That may be because there is a rock trough below and a large input of ice from further up-glacier;  there may then be ice melting on the bed and a subsequent acceleration in ice velocity.

"Streamlines" are simply the recreated ice flow directions, conventionally shown by arrows.   Note that you can also recreate streamlines for ice flow in areas affected by an ice cover, even though you are not dealing with an area covered by an ice stream. 

An ice stream may be highly crevassed -- and there is often another crevassed zone on the flanks of the ice stream where sluggish flanking ice is literally ripped apart.

Within the ice stream ice movement directions (and hence directions of erratic transport) will be rather consistent.  In the intervening areas (which are sometimes "ice shed" areas) ice movement directions may be highly eccentric and variable.  High rates of ice evacuation in an ice stream will lower the ice surface there, and cause ice from the intervening areas to flow towards the ice stream.  If the ice stream slows down, or if accumulation patterns vary, ice movement directions may literally be reversed in these zones.  Erratic movements in these areas will be very erratic indeed.......

The Irish Sea Glacier must have been an ice stream, flanked by ice-covered terrain on either side.  There must also have been big ice streams in the Moray Firth region and in the Firth of Forth. This is the BRITICE recreation for 23,000 years ago -- in the Devensian Glaciation:

One of the areas we have been talking about recently -- Aberdeenshire -- was in effect squeezed between these ice streams.  No wonder that geomorphologists have difficulty in determining exactly how and when erratics have been moved.......

See also:
http://brian-mountainman.blogspot.com/2009/10/on-bristol-channel-ice-stream.html

Sunday, 15 January 2012

More geology on the way......



Spotted on Rob Ixer's academic blog site -- from December.  More on the rhyolites on the way........ not sure if the paper is fully published yet. It is available online for subscribers.

Provenancing the rhyolitic and dacitic components of the stonehenge landscape bluestone lithology: New petrographical and geochemical evidence. Bevins, Richard E. / Ixer, Rob A. / Webb, Peter C. / Watson, John S., Journal of Archaeological Science, In Press, Accepted Manuscript, Dec 2011 

Abstract

The source of the bluestone component found in the Stonehenge landscape has long been the subject of great interest and considerable debate. The bluestones are a mix of lithologies, the standing orthostats being predominantly dolerites, variably ‘spotted’, with only four of them being of dacitic and rhyolitic composition and the Altar Stone being sandstone. However in the 1920s the spotted dolerites were sourced to outcrops which comprise tors in the summit regions of the Mynydd Preseli in north Pembrokeshire, west Wales. There were also speculations about the possible sources of the dacitic and rhyolitic components, ideas which were elaborated on in the early 1990s when the original petrological provenancing was supplemented by whole-rock geochemical analysis. Most recently, new petrographical investigations have been combined with zircon geochemical data to determine the possible source of one type of rhyolite, the so-called ‘rhyolite with fabric’, found abundantly as débitage in the Stonehenge landscape (but not composing the four orthostats) to outcrops in the vicinity of Pont Saeson, especially a large craggy outcrop called Craig Rhos-y-felin, located in low ground to the north of the Mynydd Preseli. In order to test this provenance whole-rock geochemical analysis has been undertaken on samples of débitage from the Stonehenge landscape and from the Pont Saeson area, including Craig Rhos-y-felin. These data are then compared with other new and existing geochemical data for dacitic and rhyolitic lithologies recovered from the Stonehenge landscape, including the four orthostats, as well as geochemical data from outcrops of the same lithologies from the two main volcanic horizons exposed across north Pembrokeshire, namely the Fishguard Volcanic Group and the Sealyham Volcanic Formation, both of Ordovician age. This study concludes that previous, 20th century, attributions of provenance to a number of dacitic and rhyolitic outcrops in the north Pembrokeshire have been in error whilst the new data for the Pont Saeson rhyolite accords well with elemental contents recorded in the ‘rhyolite with fabric’ lithology from the Stonehenge landscape débitage. This study therefore endorses the proposal that the Pont Saeson area is indeed the source of the ‘rhyolite with fabric’ lithology recovered from numerous sites in the Stonehenge landscape, and is the only reliable provenance for any of the dacitic and rhyolitic bluestone material collected to date. It also serves to endorse the use of zircon chemistry as a provenancing tool in archaeopetrological investigations.

List of the recent articles:
"Provenancing the rhyolitic and dacitic components of the stonehenge landscape bluestone lithology: New petrographical and geochemical evidence". Bevins, Richard E. , Ixer, Rob A. , Webb, Peter C. , and Watson, John S., Journal of Archaeological Science, 2012, pp

“Craig Rhos-Y-Felin, Pont Saeson is the dominant source of the Stonehenge rhyolitic ‘debitage’”, by RA Ixer & RE Bevins, Archaeology in Wales 50 (2011), 21–31

“Stonehenge rhyolitic bluestone sources & the application of zircon chemistry as a new tool for provenancing rhyolitic lithics”, by RE Bevins, NJP Pearce, & RA Ixer, Journal of Archaeological Sciences 38 (2011), 605–22

“The petrography, affinity and provenance of lithics from the Cursus Field, Stonehenge”, by RA Ixer & RE Bevins, Wiltshire Archaeological & Natural History Magazine 103 (2010) 1–15

“The detailed petrography of six orthostats from the bluestone circle, Stonehenge”, by RA Ixer & RE Bevins, Wiltshire Archaeological & Natural History Magazine 104 (2010), 1–14

Saturday, 14 January 2012

On the nature of evidence

First photo::  direct evidence of erratic transport and displacement :  Conwaybreen, Svalbard
Second photo:  indirect evidence of erratic transport and displacement: Easter Aquhorthies (in the centre, a reddish granite block, probably from Bennachie, a few miles to the west of the site.)  The fact that the large recumbent stone might have been levered up or "adjusted" on the site, or even moved a short distance by the monument builders,  is immaterial to the argument.

Above:  The distribution of the key recumbent stone circles in NE Scotland.
There are reputed to be at least 99 of them.

Erratic transport directions and other glacial features, NE Scotland (BRITICE Project).  Note that erratic occurrences exist at the points of the arrowheads.


On this blog, we have been wasting a vast amount of time recently in trying to elucidate what certain people mean by "evidence".  Without getting too deeply into epistemology, philosophy and the scientific method, and without pondering too deeply as to the meaning of "truth", time to make a few simple points.

In glacial geomorphology, when we are trying to interpret the impact of glaciation on the UK landscape, we are dealing with "circumstantial evidence".  However,  interpretation is informed by direct knowledge of what glaciers do and how they work, in the field, in places like Greenland and Iceland.  I have been to both those places, and have observed glaciers at close hand -- I hope it can therefore be assumed that I know what I am talking about when I form opinions about what has happened in the UK.   If I am right, my evidence will be accepted by my peers.  If I am wrong, one of my peers will come along and falsify my hypothesis through the provision of more reliable circumstantial evidence, well founded in field observations elsewhere, where processes are observable and measurable.  
It is not enough for somebody from another discipline to come along and say "I don't believe you because I don't accept your evidence, or because you have not proved your case."  The burden of proof is then upon him to produce sufficient new evidence, acceptable to the peer group, which will move things to a new conclusion.  
Within the glaciated areas of Britain, the default position must be that large boulders and slabs of rock that might be labelled as "erratics"  -- if found in areas downglacier of source areas -- must be assumed to have been moved by ice, simply because direct observation and direct evidence shows that that is what happens when glaciers flow across a landscape.  There is nothing contentious in that.  (That is true even if such large erratics have been incorporated into man-made monuments, since it seems to be a general rule that the builders of such monuments preferentially used the large stones that were readily to hand, rather than fetching them from a long way off.)  This field evidence is simple, well-established, and not seriously liable to challenge -- and if anybody does wish to make a contentious claim (for example that the large erratic stones have been moved by human beings rather than ice) the burden of proof rests upon him to come up with powerful new evidence.  In the case of NE Scotland, this would mean that he would have to overturn the interpretations incorporated into the BRITICE map and the published field evidence on which those interpretations are founded.

So when I look at large glacial erratics in a landscape which has been repeatedly affected by glacial processes, and call them glacial erratics because that is what my accumulated experience tells me,  I will accept a challenge from another glacial geomorphologist who thinks he or she has better evidence than mine.  But I will not accept a challenge from an archaeologist who knows nothing of glacial geomorphology and who simply says "I do not accept your evidence."   Such a challenge is intellectually dishonest;  it fails to accord me the respect that I deserve as a specialist in this field;  and it is a waste of everybody's time.

By the same token, I am not an archaeologist, and if I wish to say something contentious or to challenge a well-founded hypothesis based on sound direct or indirect evidence, the burden of proof rests upon me to come up with something better, and to marshall my evidence in support of what I am saying.

---------------------------------------------------

From Wikipedia

Evidence in its broadest sense includes everything that is used to determine or demonstrate the truth of an assertion. Giving or procuring evidence is the process of using those things that are either (a) presumed to be true, or (b) were themselves proven via evidence, to demonstrate an assertion's truth.  Evidence is the currency by which one fulfills the burden of proof.

Many issues surround evidence, making it the subject of much discussion and disagreement. In addition to its subtlety, evidence plays an important role in many academic disciplines, including science and law, adding to the discourse surrounding it.

An important distinction in the field of evidence is that between circumstantial evidence and direct evidence, or evidence that suggests truth as opposed to evidence that directly proves truth. Many have seen this line to be less-than-clear and significant arguments have arisen over the difference.

Circumstantial evidence directly supports the truth of evidence, from which the truth of the assertion may be inferred. 


Evidence in science

Main article: Scientific evidence
In scientific research evidence is accumulated through observations of phenomena that occur in the natural world, or which are created as experiments in a laboratory or other controlled conditions. Scientific evidence usually goes towards supporting or rejecting a hypothesis.

One must always remember that the burden of proof is on the person making a contentious claim. Within science, this translates to the burden resting on presenters of a paper, in which the presenters argue for their specific findings. This paper is placed before a panel of judges where the presenter must defend the thesis against all challenges.

When evidence is contradictory to predicted expectations, the evidence and the ways of making it are often closely scrutinized (see experimenter's regress) and only at the end of this process is the hypothesis rejected: this can be referred to as 'refutation of the hypothesis'. The rules for evidence used by science are collected systematically in an attempt to avoid the bias inherent to anecdotal evidence.


Burden of proof

Main articles: Legal burden of proof and Philosophic burden of proof
The burden of proof is the burden of providing sufficient evidence to shift a conclusion from an oppositional opinion. Whoever does not carry the burden of proof carries the benefit of assumption. Whoever bears the burden of proof must present sufficient evidence to move the conclusion to their own position. The burden of proof must be fulfilled both by establishing positive evidence and negating oppositional evidence.

There are two primary burden-of-proof considerations:

    • The question of on whom the burden rests.
    • The question of the degree of certitude the proof must support. This depends on both the quantity and quality of evidence and the nature of the point under contention. Some common degrees of certitude include the most probable event, reasonable doubt, and beyond the shadow of a doubt.
Conclusions (from evidence) may be subject to criticism from a perceived failure to fulfill the burden of proof.


See also:
Epistemology

See also:
The Burden of Proof
http://brian-mountainman.blogspot.com/2011/12/on-burden-of-proof.html

Rob's Podcast



Thanks to Rob for providing a link to this interesting podcast.  It's good to hear things explained carefully and clearly, after all that hype.  There are just a couple of things on which Rob might have been more careful.  There are not 80 bluestones at Stonehenge -- there are around 43, including both standing stones and stumps.  And the natural rock at Rhosyfelin does not naturally break up into long columns or orthostats.  It breaks up for the most part into smallish angular fragments as seen in the pic above -- with occasional larger blocks.

www.cbc.ca/quirks 

Sourcing Stonehenge

It has long been known that many of the so called "bluestones" that are part of the prehistoric monument Stonehenge, come from Wales. The bluestones, which are either buried or just above ground, are found in a ring inside the iconic standing stones.  Now Dr. Robert Ixer, a geologist from The University of Leicester has been able to pinpoint the source of a subset of these bluestones. By analyzing rock flakes from these stones at Stonehenge and comparing them to samples from a large region of Wales, he's found a match to a specific outcrop in Pont Saeson in North Pembrokeshire, Wales. This means these bluestones traveled hundreds of kilometres from Wales to the Salisbury Plain, site of Stonehenge.  Just how this happened is one of the enduring mysteries of Stonehenge.      
     

Related Links
Dr. Ixer's paper is not available online.  It was published in Archaeology in Wales 50, by the Council for British Archeology
National Museum of Wales press release
BBC News story
National Geographic article

That 99% -- the National Museum Press release

 This is the original National Museum of Wales press release which was picked up, chewed over,  regurgitated,  and generally abused by the media.  On the whole it is pretty straightforward, but it's now clear that the nonsense about 99% of the rhyolite debitage at Stonehenge coming from Craig Rhosyfelin can be traced straight back to the press release: 

 "Their recent discovery confirms that the Stonehenge rhyolite debitage originates from a specific 70m long area namely Craig Rhos-y-felin near Pont Saeson. Using petrographical techniques, Ixer and Bevins found that 99% of these rhyolites could be matched to rocks found in this particular set of outcrops."

The authors should have insisted that this form of wording was not used -- because ultimately they are the only people whose reputations suffer  from slapdash phraseology.  They should have referred to "99% of the rhyolite fragments collected from the debitage at specified excavation sites."  That, my dear Doctor Watson, is a very different thing.

---------------------------------------

News  19 December 2011

New geological discovery paves the way for further insight into the transport of Stonehenge rocks

http://www.museumwales.ac.uk/en/5/?article_id=728


A new paper in Archaeology in Wales, produced by Dr Rob Ixer of Leicester University and Dr Richard Bevins of Amgueddfa Cymru – National Museum Wales confirms, for the first time, the exact origin of some the rhyolite debitage found at Stonehenge. This work could now lead to important conclusions about how stones were transported from Pembrokeshire to Stonehenge.
Over a period of nine months, Bevins and Ixer have been carefully collecting and identifying samples from rock outcrops in Pembrokeshire to try and locate the provenance of rocks that can be found at what is today, one of the world’s most iconic archaeological sites.
Their recent discovery confirms that the Stonehenge rhyolite debitage originates from a specific 70m long area namely Craig Rhos-y-felin near Pont Saeson. Using petrographical techniques, Ixer and Bevins found that 99% of these rhyolites could be matched to rocks found in this particular set of outcrops. Rhyolitic rocks at Rhos-y-felin are distinctly different from all others in South Wales, which gives almost all of Stonehenge rhyolites a provenance of just hundreds of square metres.   
Yet, the story progresses. Along the Rhos-y-felin crags, the rhyolites are distinctly different on a scale of metres or tens of metres. This has enabled Bevins and Ixer to match some Stonehenge debitage samples to an even more precise locality at the extreme northeastern end of the area.
What this means is that the area is now small enough for archaeologists to excavate to try and uncover evidence for associated human activity so providing another strand of the story of how the stones from Pembrokeshire reached Stonehenge.
Dr Richard Bevins of Amgueddfa Cymru said:
“Many have asked the question over the years, how the stones got from Pembrokeshire to Stonehenge. Was it human transport? Was it due to ice transport? Thanks to geological research, we now have a specific source for the rhyolite stones from which to work and an opportunity for archaeologists to answer the question that has been widely debated. It is important now that the research continues.”
In addition the level of work carried out at Rhos-y-felin confirms that the four remaining above surface rhyolite and dacite orthostats at Stonehenge do not come from Rhos-y-felin and work is in hand to determine if their source can be identified.
Dr Rob Ixer of Leicester University added:
“Being able to provenance any archaeologically significant rock so precisely is remarkable, to do it for Stonehenge was quite unexpected and exciting. However, given continued perseverance, we are determined that we shall uncover the origins of most, if not all of the Stonehenge bluestones so allowing archaeologists to continue their speculations well into a third century.”
Date: 19 December 2011

Rope technology


 Now here's a thought.  All of the human transport technologies are dependent upon the existence and plentiful supply of rope -- often in great lengths.  It appears that rope has been around for a long time -- in short lengths -- and maybe of questionable strength.  It could be made with vegetable fibres or animal products --  see below.  The technique is well known too -- slow, laborious and fun for an amateur experimental archaeologist or self-sufficiency freak, but adequate for production on a semi-industrial scale? 

SO what evidence is there that really strong ropes, in sufficient quantities for hauling large numbers of very large stones either over land or sea, actually did exist in the Neolithic?

-----------------------------
From Wikipedia:

The use of ropes for hunting, pulling, fastening, attaching, carrying, lifting, and climbing dates back to prehistoric times. It is likely that the earliest "ropes" were naturally occurring lengths of plant fibre, such as vines, followed soon by the first attempts at twisting and braiding these strands together to form the first proper ropes in the modern sense of the word. Impressions of cordage found on fired clay provide evidence of string and rope-making technology in Europe dating back 28,000 years.[3] Fossilized fragments of "probably two-ply laid rope of about 7 mm diameter" were found in one of the caves at Lascaux, dating to approximately 15,000 BC.[4]

The ancient Egyptians were probably the first civilization to develop special tools to make rope. Egyptian rope dates back to 4000 to 3500 B.C. and was generally made of water reed fibres[5]. Other rope in antiquity was made from the fibres of date palms, flax, grass, papyrus, leather, or animal hair. The use of such ropes pulled by thousands of workers allowed the Egyptians to move the heavy stones required to build their monuments. Starting from approximately 2800 B.C., rope made of hemp fibres was in use in China. Rope and the craft of rope making spread throughout Asia, India, and Europe over the next several thousand years.

In the Middle Ages (from the 13th to the 18th centuries), from the British Isles to Italy, ropes were constructed in so-called Ropewalks, very long buildings where strands the full length of the rope were spread out and then laid up or twisted together to form the rope. The cable length was thus set by the length of the available rope walk. This is related to the unit of length termed cable length. This allowed for long ropes of up to 300 yards long or longer to be made. These long ropes were necessary in shipping as short ropes would require splicing to make them long enough to use for sheets and halyards. The strongest form of splicing is the short splice, which doubles the diameter of the rope at the area of the splice, which would cause problems in running the line through pulleys. Any splices narrow enough to maintain smooth running would be less able to support the required weight.

Leonardo da Vinci drew sketches of a concept for a ropemaking machine, but it was never built. Nevertheless, remarkable feats of construction were accomplished without advanced technology: In 1586, Domenico Fontana erected the 327 ton obelisk on Rome's Saint Peter's Square with a concerted effort of 900 men, 75 horses, and countless pulleys and meters of rope. By the late 18th century several working machines had been built and patented.

Some rope continues to be made from natural fibres such as coir and sisal, despite the dominance of synthetic fibres such as nylon and polypropylene which have become popular since the 1950s.


See also:

http://www.instructables.com/id/Make-rope-out-of-dead-plants----with-no-tools/?ALLSTEPS

Thursday, 12 January 2012

The Bluestones of Stonehenge -- a glacial erratic assemblage


The Bluestones of Stonehenge -- a glacial erratic assemblage

 A well-placed spy, who is obviously a Times reader, informs me that this is in the paper today.  This is what was sent.  Not sure whether the published version was identical........... but fair play to the Editor for at least accepting that there is a bit of a debate going on here!

---------------------------------------------------
Letters to the Editor
The Times

10th January 2012

Re:  Back to the Bluestones of Stonehenge 7th January 2012

Sir

The geological points made by Dr Olwen Williams-Thorpe in Norman Hammond's latest article are supported by research in the fields of glaciology and geomorphology.  It has been known for many years that the ice of the Irish Sea Glacier flowed across Pembrokeshire, up the Bristol Channel and into Somerset.  When it crossed the English coast it was flowing broadly eastwards.  We do not know whether the ice reached Salisbury Plain, but glaciological modelling by the BRITICE project shows that this was quite possible.  It is entirely reasonable to assume that the 30 or so rock types represented in the "bluestone assemblage" at Stonehenge are glacial erratics, since they seem to have come almost exclusively from the west.

I concur with Dr Williams-Thorpe when she says that the recent work by Ixer and Bevins at Craig Rhosyfelin is an exciting development, showing that very accurate provenancing of some of the bluestones is now possible.  However, their research has no archaeological significance, and tells us nothing about the mode of transport by which certain stones (or broken rock fragments) found their way from Pembrokeshire to Stonehenge.

Thank you for giving space to this timely debate.

Dr Brian John
Past Lecturer in Geography, Durham University
Author, "The Bluestone Enigma"

Trefelin
Cilgwyn
Newport
Pembrokeshire
SA42 0QN
Tel 01239-820470

The Mythology of Old Keig

I have been following up the material on these recumbent stone circles in Scotland, which are, as Chris reminds us, reputed to be  "monuments placed with care and accuracy."   Well, they are either that, or else monuments created around conveniently located large glacial erratics.  The myth about Old Keig is especially interesting, as Geo has reminded us, since over and again in the literature it is flagged up as a prime example of a RSC in which the recumbent stone (weighing in this case 53 tonnes) has been moved from the Don Valley, about 10 km away, including one steep uphill section, by our heroic ancestors.  That would mean the stone has been moved from the SE towards the NW -- in precisely the opposite direction to the assumed movement of ice at the peak of the Devensian Glaciation.

So how sound is all of that scientifically?  I'm not at all sure.  For a start, the sourcing of the stone is not as certain as we might assume.  The stone is made of a "sillimanite gneiss" which Gordon Childe (1933), who did the original dig, assumed might have come from "the Don valley between Kemnay and Tillifourie."  All he said was that "similar rocks" were to be found there.  No stronger than that.  But as far as I can see, that has been taken to be a definitive piece of provenancing, and has been used ever since in every succeeding paper or article.  I need to check that out, and am trying to look at the relevant material........

But far from being a tidy piece of provenancing, Childe also added (and this is conveniently forgotten) that "there are also areas of gneisses shown on the 1-inch map both to the west and to the north."  So he was admitting that the stone might have come from the west or the north.  This is confirmed when you look into the geology of the region.  Sillimanite gneiss seems to pop up all over the place, in a number of different geological formations -- and I am not at all sure whether these various examples of the rock type have been identified and differentiated to high modern standards.

Two recent maps showing reconstructed ice directions across NE Scotland.  Old Keig is a short distance to the west of Iverurie, in an area affected by ice that has flowed from the west and the north-west.

 There is one other feature of the Childe field report from 1933 -- and that is a clear impression that the superficial deposits in and around the site are made up of thin glacial till and areas of fluvioglacial sands and gravels.  The descriptions are difficult to interpret -- especially since Childe, like many archaeologists before and since, leaned towards an assumption that everything in the area (including the deposits beneath and around the big stone) was created because of human interference.

I'm trying to obtain more info about the geology of that famous recumbent stone and the sediments of the neighbourhood -- all info (convenient or otherwise) gratefully received.  But for the time being it will be just as well to reserve judgment on how that 53 tonne monster might have been moved, and where it came from..........


SOME RELEVANT MATERIAL
 ----------------------------------------------
"At Old Keig a recumbent stone circle situated on a slight crest on a ridge, and within a narrow windbelt. A recumbent stone, 16ft long on top, 6ft thick, 6 3/4ft high, two flankers, the westerly 5 1/4ft above the turf, the easterly 9 1/2ft, and a third orthostat, 9 1/2ft high, to the east, survive. "

"The circle is located on a very slight crest on rising ground with distant, sometimes magical, views over the Howe of Alford. The site was probably levelled and the enormous recumbent, which weighs 53 tons and is the largest known (4.9m by 2.1m by 2.0m) dragged from somewhere in the Don valley about 10km away. The last 1km would have been uphill at a gradient of 1:14, requiring well over 100 people."


http://canmore.rcahms.gov.uk/en/site/17530/details/old+keig/

Grid Reference: 57° 15' 48.7" N, 2° 40' 5.51" W.

http://www.ancient-wisdom.co.uk/scotlandoldkeig.htm

PDF available:
TRIAL EXCAVATIONS AT THE OLD KEIG STONE CIRCLE, ABERDEENSHIRE.
BY PROFESSOR V. GORDON CHILDE, B.LITT., P.S.A.ScoT.

"The Recumbent Stone is not of local origin. Similar rocks occur in
the Don valley between Kemnay and Tillifourie, and there are also
areas of gneisses shown on the 1-inch map both to the west and to the
north."

Refs

Atkinson, R J C (1962) 'Fishermen and farmers', in Piggott, S The prehistoric peoples of Scotland, London
Page(s): 17, 181

Burl, H A W (1973a) 'The recumbent stone circles of North-East Scotland', Proc Soc Antiq Scot, vol.102
Page(s): 60, 61, 63, 66-70, 72, 76, 78

Burl, {H} A {W} (1976a) The stone circles of the British Isles, London and New Haven
Page(s): 172, 174, 179-183, 352 Held at RCAHMS E.7.BUR

Burl, {H} A {W} (1979a) Rings of stone: the prehistoric stone circles of Britain and Ireland, London
Page(s): 17, 22-4,_32, 138-9 Held at RCAHMS E.7.BUR

Burl, {H} A {W} (1995) A Guide to the Stone Circles of Britain, Ireland and Brittany
Page(s): 105

Childe, V G (1933a) 'Trial excavations at the Old Keig Stone Circle, Aberdeenshire', Proc Soc Antiq Scot, vol.67
Page(s): 37-53 illust, plans

Childe, V G (1934a) 'Final report on the excavation of the stone circle at Old Keig, Aberdeenshire', Proc Soc Antiq Scot, vol.68
Page(s): 372-93 illust, plans

Coles, F R (1901) 'Report on the stone circles of the North-East of Scotland, Inverurie District, obtained under the Gunning Fellowship, with measured plans and drawings', Proc Soc Antiq Scot, vol.35
Page(s): 211-14

Henshall, A S (1963a) The chambered tombs of Scotland,, vol.1 Edinburgh
Page(s): 37, 39, Held at RCAHMS E.7.1.HEN

Kilbride-Jones, H E (1935a) 'An account of the excavation of the stone circle at Loanhead of Daviot, and of the standing stones of Cullerlie, Echt, both in Aberdeenshire, on behalf of HM office of Works', Proc Soc Antiq Scot, vol.69
Page(s): 168-214

Logan, J (1829c) Archaeologia, vol.22
Page(s): 201

Ralston, I (2009) 'Gordon Childe and Scottish Archaeology: The Edinburgh Years 1927-1946', European J Archaeol, vol.12
Page(s): 74

Shepherd, I A G (1986a) Exploring Scotland's heritage: Grampian, Exploring Scotland's heritage series Edinburgh
Page(s): 156, no. 97 Held at RCAHMS A.1.4.HER

Welfare, A (2011) Great Crowns of Stone: The Recumbent Stones Circles of Scotland: Gazetteer and Appendices, in S Halliday Edinburgh
Page(s): 422-7