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| Nigel was pleased that there were at least two people that didn't want their money back! |
We met in the Guernsey Pearl/Coppercraft car-park opposite Fort Grey on the west coast. After gentle persuasion and threats, we drove to Pleinmont car park, which was the starting point for our walk. Nigel decided that it would be more interesting to scrabble/walk/hop/skip
/jump along the shoreline rather than take the obvious, logical road route. After what seemed an eternity, we arrived at Fort Pezeries. We explored the fort, then listened the best we could in the lee of the fort while Nigel tried to explain the geological setting. We had been "walking" over L’Eree granite dated by Adams as 646Ma, late Precambrian, and we were now going to try to find the Pleinmont Metasediments exposed to the west of Fort Pezeries.
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| Nigel was pleased that there were at least two people that didn't want their money back! |
The granite here was almost gneiss like in appearance, being sheared and streaked out, even to the extent of having what looked remarkably like crossbedding. Alas we did not find the Metasediments as the tide was too high, so back to the path and through a narrow gap in the rock face to the south, which was once a dolerite dyke, which had been preferentially eroded away.
At the base of these rocks sedimentary structures could be seen. The rock was very fine grained, and was formed in a deep marine environment possibly following slumping from the continental shelf – they were probably turbidites. How old were they? It is thought that the metasediments dated from around 700-1000Ma, predating the granite. The contact was complex, with considerable evidence of lateral movement, which was consistent with the sheared and streaked out nature of the granite.
As we walked back, what appeared to be a stone circle was examined, La Table des Pions. Despite its appearance, it was relatively modern and was used as a meeting place by a local council.
Top soil under the grassy sward hereabouts is loess, similar to that seen in Jersey; the loess in turn overlies head deposits and is being eroded by the sea. The level of the grassy plateau corresponds to the 18m raised beach, and the whole section overlies the 8m raised beach.
Back to the cars, the majority using the tarmac road (no cars – the road is closed to motor vehicles due to the risk of subsidence), while Colin and Linda used the foreshore keeping up with us – oh the joy of being young and fit!!!
