Thursday 1 September 2022

The Newall Boulder - Not a Glacial Erratic

Current Archaeology has a fascinating article about the "rediscovery of a series of rock samples collected during the Victorian period has allowed new analysis of some of the stones of Stonehenge. By Rob Ixer, Richard Bevins, Nick Pearce, and David Dawson".

One of the more interesting parts is the final putting to bed of the theory that the so-called Newall Boulder is a glacial erratic. A theory that was first raised in 1991 by G A Kellaway in "The older Plio-Pleistocene glaciations of the region around Bath." - Hot Springs of Bath, pp 243-41 

The excavation of this rather small boulder was described in Col. Hawley's 6th Report Jan 1926 Vol V1 No.1 The Antiquaries Journal, and it may actually be pictured in the ground (middle extreme left).

Following its rediscovery in Salisbury Museum it has has be re-examined and the results are: "rhyolitic tuff (which) shows all the key characteristics needed to assign it to Rhyolite Group C from Craig Rhos-y-Felin in north Pembrokeshire, over 170 kilometres south of North Wales – the ‘glacial striae’ are in fact seen to be linear expressions of the internal fabric of the rock, or slickensiding, along one joint plane."

When the news of its rediscovery was first made public along with the thoughts that it might be a rhyolite with striae on it I was reminded of a very similar boulder pictured at Craig Rhos-y-Felin in John, Brian & Elis-Gruffydd, Dyfed & Downes, John. (2015). OBSERVATIONS ON THE SUPPOSED “NEOLITHIC BLUESTONE QUARRY” AT CRAIG RHOSYFELIN, PEMBROKESHIRE. Archaeology in Wales. 54. 139-148.  

Photo by Brian John

With a touch of photoshop the picture of the Newall Boulder can be superimposed on that photo and it can be seen that the shape of it is exactly as it might have been at the quarry where it originated. No glacial transport needed to explain its shape.

It was brought from Pembrokeshire along with the other bluestones. Nothing about it supports a glacial transport theory.

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