» Home > In the News

Altar Stone

26 October 2023
Archaeology, Geology

At https://www.sciencedirect.com/science/article/pii/S2352409X23003905 … a research paper in the excellent Journal of Archaeological Science: Reports, volume 15 [October 2023], says the Altar Stone is the largest of the Stonehenge foreign bluestones. Not native to Salisbury Plain, unlike the sarsens. They are mainly igneous rocks. The Altar Stone has an anomalous lithology but is a sandstone. Previously, it was regarded as coming from the Old Red Sandstone Formation in Wales, close to Mynedd Preseli, whence most of the other blue stones have been traced back to. Not all of them of course as some may have an origin in Pembrokeshire. Mynedd Preseli is 225 km from Stonehenge so archaeologists assume humans transported the stones to Salisbury Plain. Geologists are not so sure, but generally happy not to rock the boat. The Old Red Sandstone formation, in the Anglo Welsh Basin, even occurs in south Wales and the border zone. A pretty big area that includes the West Midlands and South West England. Spilling over into those areas. However, after sampling rocks all over the basin scientists have been unable to get a match with the Altar Stone. They conclude it must have come from somewhere else. The problem is that it has an unusually high Ba content, reflecting high modal baryte. Of the 58 samples analysed to date from the Anglo Welsh basin only four show a similarity – but at the lower end range of the Altar Stone composition. In the Conclusion section at the end of the article we are also told it had a heavy mineral laminae that might indicate a fluvial depositional system. On the other hand, the lack of trace fossils in the stone may indicate a non-marine depositional setting. The authors of the research suggest the Altar Stone should be de-classified from the bluestone category. They are now wetting their lips in anticipation of a link with archaeology on Orkney. It seems it may have an origin in Caledonian sandstones in Scotland.

In contrast with the  archaeologists themselves, the altar stone is now looking as if it might be an erratic – shifted by ice during the Pleistocene. This may still stand for the bluestones in general – moved east and south by meltwaters from rapidly shrinking glaciers in mountainous regions such as Wales and Scotland. Left stranded on Salisbury Plain, or nearby. Just the sort of unusual rock to appeal to the human eye and therefore their fancy. Archaeologists prefer the idea of a stone circle erected on Mynedd Preseli, which was later dissembled and taken to Salisbury Plain. Why would one stone originate from up north and the other bluestones did not? However, wherever the stone originates it doesn’t take anything away from Stonehenge. It simply bursts a few bubbles. Mind you, a source in the Orkneys would  set a new ball rolling.

Skip to content