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Wednesday, 28 September 2016

Hell Bay Moraine, Bryher, Isles of Scilly

There is a bit of discussion about the nature of a ridge of large boulders that runs part of the way across a narrow peninsula of land leading to Shipman Head on the Isle of Bryher.   I need to revise my opinion!

This is what I said in my working paper:

The Hell Bay Moraine on the west side of the headland runs straight downslope, and is made of a jumble of erratic boulders and slabs mixed with angular blocks of local origin.  This feature is shown on topographic maps as "castle ramparts" -- or as an Iron Age or Bronze Age defensive feature.  However, initial examination suggests that it is natural.  The boulders and slabs are much larger than those normally used in defensive ramparts, and many of them are faceted and abraded. 

I have been scrutinizing the satellite imagery, and I have enlarged a section of it above.  What we can see in the centre of the photo is a ridge made up of a litter of very large blocks.  Some of these may have moved downslope from the granite outcrops at the top of the photo.  The cliffs are just off the edge of the image. But I am still convinced that most of this material is contained within a very large moraine.  But look carefully to the right of it and you can see two roughly parallel lines of smaller boulders, with a continuation southwards in the form of an accumulation of even smaller blocks -- just the sort of material that Iron Age people all over Britain used for building their fortified defensive banks.  This was completely invisible to me on the ground when I walked across it -- maybe the vegetation was more extensive and higher than when this image was taken.

So now I think that I'm correct, and so are the archaeologists.  Moraine AND a man-made defensive feature.

So there we are then.  Nice compromise.


PeteG said...

I thought you and your readers might like to see this

BRIAN JOHN said...

Nice video, Pete! But this is not the only post-glacial alluvial forest in western Europe -- the submerged forest is all over the place, and there are many exposures in the bays of Pembrokeshire. The best known is probably the one at Borth in Ceredigion. Sometimes you see them and sometimes you don't!

TonyH said...

Then there is Nrth Devon's submerged forest at Westward Ho! (exclamation mark part of the Victorian resort's name, which derives from Charles Kingsley's novel of the same name).

If any fellow - bloggers are in nearby Barnstaple, there is an excellent reconstruction of the at submerged forest in the Barnstaple Museum,by the river, entrance free. Recommended for that and other re - creations of the lands thereabouts. Just seen it.

BRIAN JOHN said...

The submerged forests are everywhere around the coasts of southern Britain -- especially where there was noy much isostatic uplift going on. Sea level was gradually recovering from a low point of -120m below OD.