Dorset Stones Query | Forum — The Modern Antiquarian

Squid Tempest Sep 14, 2006 10:18:35

On our recent visit to Dorset (thanks to all who suggested places to go and gave directions), we went to various sites: the Nine Stones of Winterbourne Abbas, The Grey Mare and her Colts, Kingston Russell and the Helstone Dolmen. One type of stone occurred at (I think) all of these places - the stone looked like a strange conglomerate - almost like flints set into concrete, but presumably is a natural form.

While out on a guided fossil hunt at Lyme Regis, I talked to a local geologist and asked what this conglomerate might be. He was not aware of it and couldn't give me an answer.

Does anyone know what this conglomerate is? Is it local to Dorset, or have these stones been imported from somewhere?

ocifant Sep 14, 2006 11:05:43

Replying to Squid Tempest

It wasn't puddingstone, by any chance?

Spaceship mark Sep 14, 2006 12:38:35

Replying to Squid Tempest

The stones are (i believe) a variety of Sarsen, certainly from the evidence at the Valley of the Stones, they seem to have been formed in the same way.
That would make them silcretes, these are unusual i that they are formed fairly close to the surface where the loose grains are cemented together by silica in the groundwater. They are generally formed in tropical conditions where there is a lot of movement up and down.
This process explains the presence of root holes in the Avebury stones and the silicified wood clearly visible in a couple of stones of Avebury's D-feature.
With the Dorset sarsen it would appear there were a lot of flint nodules in the loose chalk soil which was subsequently bound by the silica.
Incidentally this also explains why, although many of the sarsen stones at Avebury have clear solution features on some surfaces they do not appear to have suffered any further solution since there erection, i.e. the solution features were actually formed when the rock was not fully formed.
I think all that's right anyway...