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Saturday 29 January 2011

Prudden on Holwell

I have had a look at Hugh Prudden's "Somerset Geology - a Good Rock Guide" (downloadable pdf) and found this:

23.  HOLWELL  ST 7245   5 km S W of Frome
Fissures with Triassic and Jurassic infills-tectonics

There are old quarry workings down a track to the right of the pub (ST 729 452).  A large multi-stage fissure runs the length of an old quarry wall at the eastern end of quarry used as a car park.  Part of the fill has collapsed enabling Triassic, Rhaetian and Jurassic sediments plus the mineralisation to be examined at close quarters.  The sediments appear to have entered the fissures in both a lithified and partly lithified state.  Deformation of the sediments seems to have been associated with the opening of the fissure and the intrusion of the sediments.  There are footpaths to the nearby village of Nunney which has a nice pub, castle ruins (Doulting and Bath Stone) and sarsen stones (Tertiary silcretes) on a wall and near castle at the bottom of the hill leading from Nunney Catch.

Park in lay-by to the east of the Bear Inn.  Please first contact Mr R Bullus of Valley Sawmills, Holwell, Nunney, Frome for permission to visit the site.

A viewing platform has been built overlooking Colemans large quarry on the north side of the workings. Park in lay-by at sharp corner on the road the Whatley at ST 7231 4529 and walk some 200 m NNW along footpath.  There is a fascinating view both of the quarry activity and the undulations of the same unconformity as seen at Tedbury Camp quarry.  In addition the view includes the overlying Jurassic and Cretaceous terrains to the east.  There are few better places where one can appreciate geological time and space.

I would imagine therefore that Hugh would interpret the Holwell deposits as being intruded sediments from the Jurassic, Triassic and Rhaetian which have entered fissures resulting from faulting.  Even more intriguing -- that explanation raises as many questions as it answers -- must definitely take a look.

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