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Tuesday, 1 March 2011

Open to interpretation....



Top:  hammerstone, found today while wandering on the common, at c 270m on the south flank of Carningli.  it is made of dolerite, and is about the size of a man's fist.

Bottom:  cupmarks on a dolerite surface, c 260m asl on the south flank of Carningli.

Nah -- only joking!  The top picture shows a typical sub-rounded cobble found in a thin veneer of till on the south side of the mountain.  The one below shows a typical scalloped surface on a glaciated slab of dolerite bedrock.  The "cupmarks", hollows and pits are almost certainly weathering phemomena, possibly created under a peaty layer where acidic moisture collects in hollows and enhances the breakdown of the rock matrix and the release of mineral crystals.

It just goes to show that you need a geologist or a geomorphologist with you at all times!!

2 comments:

Constantinos Ragazas said...

Brian, you write

“The one [picture] below shows a typical scalloped surface on a glaciated slab of dolerite bedrock. The "cupmarks", hollows and pits are almost certainly weathering phenomena … “

This bedrock surface texture reminds me of some Atkinson pictures you posted awhile back from the excavations of the Stonehenge Layer. Of course, the bedrock of the Layer is chalk rather than dolerite. And the pits were more than just 'cupmarks'. But otherwise the 'texture markings' seem similar.

Glacier moraines may not exist at Salisbury Plain. But we should use the evidence we have, rather than the evidence we like to have to prove our case!

Kostas

BRIAN JOHN said...

This post was a bit of fun -- poked at those of us who see just what we want to see..... maybe we all do that to some extent.

I wouldn't draw any comparision with the stone sockets at Stonehenge -- the scale of magnitude is quite different, and so are the processes involved.