Bluestones and Ice

So, like so many people, since visiting Stonehenge “up close” I’ve been intrigued by the west Wales source of the so called Stonehenge “Blue Stones”.  The idea that they were brought part or most of the way by sea seems very unlikely to me.  Human transport over land only seems feasible if the more sthan 40 tones were brought to Stonehenge over a significant period of time.  But what if the bluestones were already on Salisbury Plain having been brought there by glaciers during one of the ice ages?  That is a much simpler explanation and is consistent with all other Neolithic monuments in Britain being built using locally available stones (John 2018).

A comprehensive summary of the evidence for ice transportation, at least for a good fraction of the distance from west Wales to Stonehenge, has been provided by Brian John (2018), someone who has studied glaciers and who advocates the role of ice .  Here I will just summarise my own thoughts having skimmed through a selection of the various papers¹.  The latter is not easy!  Compared to the marine meteorology/oceanography papers I read (and wrote!) in the past, many of the papers about Stonehenge are lengthier and less succinct.  They include large tables which could be consigned to appendices or to “supporting evidence”, and there is much conjecture. It is a different style.

Bluestones as glacial erratics:  With regard to the BBC programme “The Lost Circle Revealed” I commented that the bluestones at Stonehenge are more rounded than the stones in the supposed “quarry”.  I’ve since learnt that they are a variety of rock types from different sources, although almost all from the Preseli mountains area. Thomas (1923) in identifying the source area for the bluestones dismissed the possibility that the “Foreign Stones” were brought to Salisbury Plain by ice, but did suggest that “the stones may have been taken from the boulder-strewn slopes on the immediate south and south-east of the Prescellys (sic)…. where all the types have been collected together by glacial action.”  That the bluestones were a collection of glacial erratics brought to Stonehenge from the Preseli mountains has been suggested in other more recent papers (e.g. ref).  If they are a collection of glacial erratics, that to me suggests that it was more likely that the source was closer to Stonehenge.

The logistics of transporting the stones from Preseli to Stonehenge by sea seem too difficult but transporting them by land almost equally so.  So why go all that way to bring back a collection of rocks some of which were not the best type for constructing a monument.   The argument that the rocks might have been special if “they existed close to their source in the form of a sacred circle or other construction of undressed megaliths” (Thomas 1923)  only puts the question back in time.  Why use unsuitable rocks for your monument when better rocks littered the nearby hillside or could be “quarried” ?

Transport to Salisbury Plain by ice:  Authors who have suggested the bluestones were brought to Salisbury Plain by glacial action include Kellaway (1971), Thorpe et al. (1991), and Thorpe & Williams-Thorpe, (1991).  It would appear that stone circles are normally constructed from stones available nearby; indeed that the availability of stone determines the location of circle building.   But the suggestion has been rejected by others on the grounds that the bluestones came from a very limited area of west Wales, that similar stones or other glacial deposits are not found on Salisbury Plain, nor are similar rock types found in terrace gravels (e.g. Green 1997, Scourse, 1997).

These various arguments have been considered by John (2018) who suggests (as I would put it) that ice can do unexpected things, which I am willing to believe, and that a boulder train from the Preseli mountains could have been deposited near, or to the west of Stonehenge without other signs of ice having been there.  Numerical modelling studies of the ice sheet (e.g. Hubbard et al. 2009, Fig.4) have shown that the ice could have covered Salisbury Plain. However the boundary conditions for the various simulations are not stated and the particular experiment where ice reaches Salisbury Plain (“E109b3”) may have been the most extreme perturbation.

Just as human transport from west Wales would seem just about possible but very unlikely, my feeling is that transport of bluestones by ice all the way to Salisbury Plain similarly requires arguments (e.g. that the monument makers used up all the stones, or that other stones are buried in field clearances, etc.) which are quite possible but unlikely.

Likely extent of glaciations:

So what is believed to have been the maximum glacial extent reached during the various ice ages?  The map shown by Lee (2011) seems typical of what appears to be more generally accepted. The ice did not reach Salisbury Plain but extending as far as the southern edge of the Bristol Channel² and no further.

But why would it stop there without encroaching into the Somerset Levels and the low lying region between Weston-Super-Mare, Langford, Wrington, Nailsea and Clevedon?  These areas are so low and flat that very little extra ice height would be needed to maintain the slope needed to drive the ice further inland.  Indeed there are reports of glacial deposits at various places inland from the Bristol Channel (e.g. Green 1992, Donovan 1995).

Distance from Stonehenge:  If a train of glacial boulders were brought to the southern edge of the Bristol Channel by ice is it possible that the Stonehenge people would have gone there to collect the bluestones?

I recently learnt about the geophysical surveys at Stanton Drew which suggest a monument similar to Woodhenge (near Stonehenge) with successive rings of timber posts.  There does not appear to be a definitive date for Stanton Drew but it, and Woodhenge, are considered more recent (~2500BC) than the bluestones arriving at Stonehenge (~3000BC or earlier).  However it does suggest that at the time of the main Stonehenge construction there were similar social practices, and presumably social interaction, between the two sites. How likely would that have been in Neolithic times?

Using modern roads and footpaths, Apple Maps suggests the walking distance between Stonehenge and Stanton Drew is 43 miles and that it would take under 22 hours walking time.  For a fit person used to walking everywhere it is probably a 2 day hike.  Unlike the hike of around 3 weeks to walk from Stonehenge to the Preseli area, it would have been possible to walk from Stonehenge to Staton Drew and back again, all within a week if need be.

You could go there for a party!

Bluestone transport from Somerset:

Choosing to build your stone circle using a collection of glacial erratics found amongst all the stone outcrops of the Preseli mountains needs an explanation. However stones in a boulder train deposited away from Preseli, whether on Salisbury Plain or near the south coast of the Bristol Channel, would be recognised as out of the ordinary and possibly magical.  John (2018, p217) gives an example from the North American Blackfoot People of folk legends concerning erratic boulders.

So if a train of glacial erratics were found near Stanton Drew, how easy would it have been to move these “special stones”. Using 3 miles/day for bluestone transport (Pitts 2022) the 43 miles from Stanton Drew to Stonehenge would take 14 days. If the bluestones had been deposited at the coast, let’s say Clevedon, Apple Maps has the walking distance as 56 miles (or 28 hours walk). At 3 miles/day thats 19 days.  There is a possibility of using river valleys to achieve greater speeds as the topographic map shows.  There is the Bristol Avon as far as, maybe, Trowbridge, and the River Wylye from Warminster towards Salisbury.  I don’t know whether use of the water would have helped that much, today the rivers are mostly shallow and in Neolithic times I would imagine that the river banks were overgrown and boggy. A 2 ton boulder can be carried rather than dragged (e.g. Parker Pearson et al. 2015) and a more upland route might have been easier.  However even if we assume it was a 14 to 19 day journey carrying the stones, that is still significantly less than my estimate of 3 months for transporting a single stone from the Preseli mountains.  Also the topography and the drier climate suggests that stone transport need not be confined to summer as suggested by Pitts (2022) for the Preseli route. Transporting 40 plus stones within two or three years starts to sound feasible.

So even if the ice did not reach Salisbury Plain, but deposited rocks from the Preseli area somewhere just south of the Bristol Channel, the transport of the bluestones to Stonehenge would be logistically much simpler than human transport all the way from Preseli.  But there is still the objection that other stone circles were constructed where there were stones available.  That would favour the transport by ice all the way to Salisbury Plain.

Note on the source of the Sarsens: Recently it has been claimed that the sarsen stones came from West Woods, 15 miles north of Stonehenge. According to Parker Pearson (2020) “This settles over 300 years of debate on whether the stones came from around Stonehenge itself or from the Marlborough Downs.”  The argument has been made that if the much larger sarsens could be transported from West Woods, transporting the bluestones from Preseli would be quite within neolithic capabilities  (ref).

However looking at Figure 3 of Nash et al. (2020) the origin of the sarsens from West Woods is less obvious to me.  It appears to rely on the larger scatter if rock characteristics within the West Woods outcrop to provide a fit which is not that much better than other sarsen sources tested.   Indeed, the paper only states “we identify West Woods… as the most probable source area or the majority of sarsens at the monument “; not the certainty implied by Parker Pearson (2020).  And in any case, I don’t see how it rules out the source as being an area of stones much closer to, or at, Stonehenge which no longer exists except as stones used to build the monument.

Incidentally, if the sarsens did come from West Woods then I think that wood implies that Neolithic people did possess long ropes in order to dragged such large stones over the land.

References

Donovan D.T. 1995. High Level Drift Deposits East of Bath. Proc. Univ. Bristol Spelaeol. Soc. 20 (2) , 109-126

Green C.P. 1997. The Provenance of Rocks used in the Construction of Stonehenge. Proceedings of the British Academy 92 257-270.

Green G W. 1992. British regional geology: Bristol and Gloucester region (Third edition). (London: HMSO for the British Geological Survey.) – see https://earthwise.bgs.ac.uk/index.php/Glacial_deposits,_Quaternary,_Bristol_and_Gloucester_region

Hubbard A., Bradwell T., Golledge N., Hall A, Patton H., Sugden D., Cooper R., Stoker M 2009. Dynamic cycles, ice streams and their impact on the extent, chronology and deglaciation of the British–Irish ice sheet. Quaternary Science Reviews 28 758–776.

John B. 2018. The Stonehenge Bluestones, Greencroft Books, 256pp.

Kellaway G. 1971. Glaciation and the Stones of Stonehenge. Nature 233, 30-35

Lee J.R.2011. Cool Britannia – from Milankovich wobbles to Ice Ages. Mercian Geologist 17 (4), 274-279.

Nash D.J., Ciborowski T.J.R., Ullyott J.S., Parker Pearson M., Darvill T., Greaney S., Maniatis G., WhitakerK.A., Origins of the sarsen megaliths at Stonehenge. Sci. Adv. 6 (31) 8pp.

Parker Pearson, M. and 13 others, 2015. Craig Rhos-y-felin: a Welsh bluestone megalith quarry for Stonehenge. Antiquity 89 (348), 1331 – 1352.

Parker Pearson M. (2020) https://www.ucl.ac.uk/news/2020/jul/new-research-reveals-origin-stonehenges-great-sarsen-stones

Pitts, M., 2022. How to Build Stonehenge. Thames & Hudson, 240pp.

Scourse, J.D. 1997. Transport of the Stonehenge Bluestones: Testing the Glacial Hypothesis. Proceedings of the British Academy 92, 271-314.

Thomas H.H. 1923.  The Source of the Stones of Stonehenge, The Antiquaries Journal 3  (3) 239 – 260.

Thorpe R.S., Williams-Thorpe O., Jenkins D.G., Watson J.S., Ixer R.A. ,Thomas R.G. 1991.  The Geological Sources and Transport of the Bluestones of Stonehenge, Wiltshire, UK. Proceedings of the Prehistoric Society. 57 (2):103-157.

Thorpe R.S., Williams-Thorpe O. 1991 The myth of long-distance megalith transport. Antiquity. 65 (246) 64-73.

Footnotes

¹ Much of what I refer to here is already described in posts in Brian John’s Blog https://brian-mountainman.blogspot.com which searches on google kept referring me to. However I have (courtesy of Southampton University Library) tried to always refer back to the original scientific publications.

² Sea level around 3000 to 2000 BC was likely lower than today by one or 2 metres, not enough to significantly change the line of the coast. However the height of land in the levels may have been lower too, I have not checked factors like peat formation rates.