Archaeologists cool on glacial theory

[Cross-posted to Revise and Dissent]

It’s that time of year again, but this year it’s not astronomy which has been the story around Stonehenge. It’s been the bluestones.

Foamhenge Sarsens and Bluestones

The bluestones are the peculiar stones in Stonehenge. They’re the smaller stones and currently at least 99% of archaeologists think they were shipped in from the Preseli Hills in Wales. Yet there is still some resistance to the idea and in February in the Oxford Journal of Archaeology another paper came out: Preseli Dolerite Bluestones: Axe-Heads, Stonehenge Monoliths, And Outcrop Sources. The good news is that this paper is part of an issue that’s currently open-access, so you can download the paper yourself. This is a particularly good idea as I don’t understand a lot of it. I have however checked the blogging rulebook and I see that blogging from ignorance is positively encouraged.

In principle provenancing the stones is easy. You sample the stone and then find a match from a known source and you have your stone source. Since the early twentieth century everyone’s been fairly happy that the stones of Stonehenge came from somewhere around Southwest Wales. The problem is that this information just gives us the source it doesn’t tell us how the stones got there.

People could carve them out of the rock in Wales and ship them to Salisbury Plain. A lot of work has gone into thinking about routes. You could follow the coast, but the favoured route is up the Bristol Channel and then overland and via rivers to Salisbury Plain, as this is the safer route. I’m not sure I follow the logic. It would be even safer not to bother shipping the stones and use something local instead. Safety may not have been the issue. Indeed if this is work for the gods then peril might give added value to the stones. Anyhow this is all possible, but it’s not very likely.

From what is currently though about Neolithic henges, if you dodn’t have the provenance of the stones, you’d assume they were local. No other stone circle uses stones from so far away, but then no other stone circle is quite like Stonehenge. Additionally the links between Salibury and West Wales seem quite tenuous apart from these stones. It’s not impossible people did it but, at least to me, it seems highly improbable. So what’s the alternative?

The other proposal is that the stones were moved by glaciers. In the Ice Age the stones were carved from the rock in Preseli and travelled with the ice to the Salibury Plain where they were dumped. This gives many archaeologists problems.

The usual first objection is a comment that it’s convenient that the glacier dumped exactly the right number of stones to make Stonehenge. It’s only really a good argument if you don’t think about it. To demonstrate get your self a roll of sweets, I prefer Fruit Pastilles, but any will do. Unwrap the sweets and arrange them into a circle. Now isn’t it amazing that there are exactly the right number of sweets to make a circle?

The glacial theorists counter-punch is that the Bluestones all have quite different properties. They can be more or less spotty or more or less friable*. The sort of mix you’d expect in fact if the stones were moved at random rather than specially selected. No-no-no reply the anti-glacialists, there were selected to be different to… umm… reflect the diversity of the Neolithic community. It should be apparent how the discussion can rapidly become quite snarky.

A better objection is to ask exactly which glacier dropped these bluestones. It’s currently thought that in the last Ice Age the glaciers didn’t get far enough south to cover Salibury Plain. Another line of argument is that even the glaciers which did get further south in the earlier Ice Ages weren’t moving in the right direction to carry the stones. To some extent the argument seems to have stalled, but the human agency theory is much more in favour than the glacial theory.

The interesting aspect of this OJA paper by Olwen Williams-Thorpe et al is that it tries to move the discussion on by looking beyond the bluestones of Stonehenge in trying to find a bluestone source. Instead Williams-Thorpe’s team analyses stone axes made from bluestone instead. They have found that the bluestone axes in England are of a different composition to the axes of Wales. Yet the English axes do have close affinity to the Stonehenge bluestones. If the axes are made from locally sourced rock then it would imply that the Stonehenge megaliths were also locally sourced rock. How likely that is is uncertain.

Stone axes were axes, but often they were also prestige objects. They do travel, presumably by local exchange, becoming more valuable as they reach distant lands. There is also current work in proress which indicates that people were also willing to travel long distances to find the right outcrops for themselves, so I’m not sure if the assumption that the English axes are local holds. It could be that bluestone was also transported for high status axes. It’s improbable, but not impossible.

Emotionally I’m on the side of the glacial theorists. Stonehenge would make a lot more sense if it was built from glacially moved stone. Realistically though Stonehenge will remain odd and, whatever the provenances of the axes, this paper does not yet provide evidence of the glacier which moved the stones. Without a suitable glacier the glacial theory remains impossible and as Conan-Doyle said, “Once you eliminate the impossible, whatever remains, no matter how improbable, must be the truth.”

You can read more about Stonehenge and glaciers at Wessex Archaeology, Archaeoblog and the Megalithic Portal.

The paper this entry discusses was, at the time of writing, available freely from the OJA.

*I was 3 days into a trip round Rome, listening to the guide saying how lots of buildings were made from friable stone blocks, before I found out friable meant crumbly rather than used in cookery.

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