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Sunday 26 September 2021

Ceibwr-- a rather interesting pebble

 


This is one of the most interesting beach pebbles I have ever collected -- and I have picked up a fair number in my time.  Its maximum length is about 9 cms.  It's rough to the touch, but has a well-rounded shape and a rather spectacular colouring.  It was found on the beach at the head of Ceibwr Bay, and I know exactly where it has come from.  

It comes from the extraordinary deposit of cemented till at the entrance to the bay, which I suspect of being very old indeed -- maybe dating from the Anglian Glaciation.  This concreted till lies beneath the uncemented fresh till which I equate with the Irish Sea till as seen in Newport Bay and at Gwbert and Poppit in the Teifi Estuary. 

There are a few exposures of this old cemented till inside the bay itself, on its flanks, and here and there we can see that it roofs over gullies and small caves cut in the local shales and mudstones.  I assume that the roof of one such gully has collapsed, throwing this strange conglomerate material into the water, where waves and tides have done their work, washing fragments up onto the beach and rounding them in the process.

Very unusual and exciting! 

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