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Tuesday, 30 September 2014

Flat Holm Erratic Hunt (2): the big erratics

These are the big erratics found on the island.  The pink granite erratic is of course well known, but the strange conglomerate found by Chris on the coast between Castle Rock and North-west Point is a very unusual one which had us all flummoxed.  More info will follow when we get it.  In the meantime, are there any opinions?

The famous pink granite erratic resting on a broken limestone surface at the north end of West Beach --directly to the west of the farmhouse.

Sid and Chris examining the mysterious conglomerate boulder.

The conglomerate found on the foreshore in the NW part of the island.  It does not look like the Cambrian Basal conglomerate or the Ridgeway Conglomerate of Devonian age -- one guess is that it might come from the Millstone Grit series.

And a false alarm!  I was quite excited when I saw this boulder on West Beach -- almost black in colour, very hard and heavy, and with a dense rectangular fracture pattern....  I thought it was basalt, but then realised that there was an outcrop not far away of incredibly hard (silicified) chert within the limestone series.  Great care is needed in erratic hunting......

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