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Rock seam in Birsay
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Rock seam in Birsay

Never noticed this before until a couple of weeks ago while at the beach before you cross to the Brough of Birsay.
Maybe a geologist could tell us more....
Picture added on 03 November 2007
I think the feature is called a dyke and there are several seen at the car park facing the Brough of Birsay running almost SW - NE.
Added by Lyndon on 06 November 2007
This feature is a basaltic dyke. It is formed when a fault in the rocks opens up and basalt wells up from below (the same stuff that makes up the Giants Causeway in Co. Antrim). It is then eroded so all you can see is a dark strip through the surrounding rocks. I noticed it on my last trip to Orkney and followed it from the shore at the Brough of Birsay to Skipi Geo.
Added by Rognvald on 20 December 2007
It carries on along the North Side through Tana Grana and Hesta Geo.
Added by Kevin Tullock on 03 August 2023
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