Here we are, in the middle of August 2024, and over 100 years of received wisdom about the source of the Altar Stone at Stonehenge has apparently just been overturned.
Ever since H. H. Thomas suggested in 1923 that the bluestones came from South West Wales, the Altar Stone has been lumped in with them. But it's not a dolerite or a rhyolite or any of the other groups of rocks that have been traced to the Preseli Hills in Pembrokeshire.
Instead, it's a greyish-green sandstone of a type Thomas suggested possibly came from the Cosheston Beds of Old Red Sandstone near Milford Haven. His identification helped to cement the idea that the bluestones had been transported by sea and that the Altar Stone had been picked up en route just at the point of embarkation on the coastal journey.
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| The most obviously visible section of the Altar Stone seen between Stone 55b on the left and Stone 156 on the right |
The Altar Stone (Stone 80) isn't an easy one to find at Stonehenge - unless you know the site well. It lies, prone and mostly buried in the grass, in front of and overlain by the collapsed remains of the tallest trilithon, under the exact intersection point of the two solstice axes.
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| The Altar Stone lies along the secondary solstice axis (WSSR -> SSSS) and across the primary solstice axis (SSSR -> WSSS) |
It now seems ever more likely that the Altar Stone was not derived from the ORS of the Anglo-Welsh Basin, and therefore it is time to broaden our horizons, both geographically and stratigraphically into northern Britain and also to consider continental sandstones of a younger age. There is no doubt that considering the Altar Stone as a ‘bluestone’ has influenced thinking regarding the long-held view to a source in Wales. We therefore propose that the Altar Stone should be ‘de- classified’ as a bluestone, breaking a link to the essentially Mynydd Preseli-derived bluestones.
If ever a large hungry cat was ever set amongst some very sleepy pigeons, this was it.
Attention turned to the areas of Old Red Sandstone further north - around the West Midlands, the North of England and - most remarkably - Scotland.
Today, 14th August 2024, a paper in Nature was published entitled "A Scottish provenance for the Altar Stone of Stonehenge" (Clarke et al) with this astonishing map showing the most likely source for the Altar Stone.
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| The tan-coloured areas on this map are the closest match to the Altar Stone yet found |
The paper is replete with technical geological analysis, but the abstract is well worth quoting in full (my emphasis):
Understanding the provenance of megaliths used in the Neolithic stone circle at Stonehenge, southern England, gives insight into the culture and connectivity of prehistoric Britain. The source of the Altar Stone, the central recumbent sandstone megalith, has remained unknown, with recent work discounting an Anglo-Welsh Basin origin. Here we present the age and chemistry of detrital zircon, apatite and rutile grains from within fragments of the Altar Stone. The detrital zircon load largely comprises Mesoproterozoic and Archaean sources, whereas rutile and apatite are dominated by a mid-Ordovician source. The ages of these grains indicate derivation from an ultimate Laurentian crystalline source region that was overprinted by Grampian (around 460 million years ago) magmatism. Detrital age comparisons to sedimentary packages throughout Britain and Ireland reveal a remarkable similarity to the Old Red Sandstone of the Orcadian Basin in northeast Scotland. Such a provenance implies that the Altar Stone, a 6 tonne shaped block, was sourced at least 750 km from its current location. The difficulty of long-distance overland transport of such massive cargo from Scotland, navigating topographic barriers, suggests that it was transported by sea. Such routing demonstrates a high level of societal organization with intra-Britain transport during the Neolithic period.
If this is indeed true (I'm not a geologist so can't offer an informed opinion either way), then it is not an exaggeration to say that this is a discovery of truly monumental proportions whose implications are enormously far reaching.
1) The journey length is unprecedented for any large stone moving of the time
2) The societal organisation required is staggering
3) The communication network implied is astonishing
4) The motivation necessary to undertake the task had to be compelling
We now have to radically re-think our notions of how prehistoric Britain was structured - but we shouldn't be surprised by this, necessarily. There is a large body of evidence that long distance travel was not uncommon, including obvious links between Ireland, Brittany, the Scottish Isles, Denmark and Scandinavia shown by artistic styles that originated on one place before being taken up in another, embellished, modified and then passed on again.
The Ness of Brodgar in Orkney, together with the Stones of Stennes and the Ring of Brodgar indicate a highly sophisticated and organised society with a clear shared belief structure (something to do with pointing monuments at significant Solar and Lunar rising and setting events) and the ability to influence the wider mainland population.
Pottery styles emerging here made their way south and gradually supplanted local styles making "Grooved Ware" one of the most widespread and consistent fashions across much of Britain.
The very idea of "henging" (creating an encircling bank and ditch around a special space) first began on Orkney before extending south.
This also poses quite a problem for the "non-human" transport theory of how various stones made their way to Stonehenge. Where's the glacier that plucked the Altar Stone from Scotland and deposited it conveniently close to Salisbury Plain? Just the one stone please, from that location to this.
The position of the Altar Stone inside Stonehenge is clearly special (see the previous articles on this blog: The Secondary Solstice Axis and The Shadow of the Heelstone), and we've always known the stone was unique geologically.
Now we also know, at least for the moment, that it was so special it demanded an apparently superhuman effort to bring it to where it now lies.
One final question burns in my mind: just when was it brought to Stonehenge?
