- One of the large Sarsen Stones at Avebury Stone Circle, Oct 2012
What are Sarsen Stones?
Sarsen Stones are a prominent feature of the landscape in many areas around Hungerford, including Avebury, Fyfield and Lockeridge (all just west of Marlborough) and at Ashdown House near Lambourn. Some, especially those used in the Avebury Stone Circle, shown in the Photo Gallery from October 2012, are very large indeed, estimated to weigh over 60 tons.
To many people, they are a puzzle, but following a talk to the Hungerford Historical Association given in February 2013 by Dr Chris Carlon, BSc, PhD, FSEG, FGS, on "The Really Ancient History of Hungerford - Reading and Interpreting Rock Archives", he kindly gave the following explanation of Sarsen Stones:
"They are considered to be the cemented parts of formerly extensive Palaeogene sandstones which once lay over the top of the Chalk. These sandstones are usually very poorly cemented and therefore very friable and easily eroded. They can still be seen at Rushall Farm near Bradfield, which are the photos I showed, and around Great Bedwyn, Stype, the upper slopes of Kintbury and further east around Hampstead Marshall. They were deposited in a large river estuary draining south into a muddy shallow sea. The estuary had vegetation growing on it and the root systems of these plants are often preserved in the sands.
By inference the plant roots are also preserved in the sarsen stones - well seen a holes in the rocks at Weathercock Hill and around Ashdown House north of Lambourn.
They are here because:
- Around Hungerford is about the furthest west the Paleocene was deposited (although it can be found into east Wiltshire and on Salisbury Plain),
- They are simply the hard resistant remains of an otherwise soft and easily eroded rock unit.
The cementing agent was silica, slowly trickled into a porous sediment and infilling the pore spaces to make a uniformly very hard and resistant rock.
They are lying more of less where they were originally deposited, but you are correct - melt-water from the retreating glaciers to the north would have undoubtedly re-distributed them, and of course this melt-water was responsible for cutting many of the wide and obviously "too large" valleys in which very small streams now sit.
In short sarsens are the weathered relicts of formerly more extensive silicified Palaeogene (66-34 million year old) sandstones. Note that Palaeogene is made up of two time units - the Paleocene below (66-56my) and the Eocene (56-34my) above. We don't know exactly which of the sands form the sarsens and it may be several of different ages.
Incidentally the volcanic and igneous rocks of Arran, Skye, Ardnamurchan, Rhum and the Antrim plateau are the same age as the sarsens - but not connected in any way other than same age."