Beaucette Battery

We were next taken to a rather exclusive yacht marina, which was converted from a quarry in the 1960's when the Royal Engineers blasted a hole from the quarry to the sea.

The main rock here is the Bordeaux Diorite Complex. This is a particularly resilient, massive rock type, which could be cut to form lintels and curb stones of very high quality. Again, we were able to see the strange layering of the rocks only this time on a macro scale showing a prominent colour variation.

Diorite complex (10m) with clearly delineated colour banding. Horizontal pipes just visible in the darker layers. Could be a granite melt drawn through the diorite in similar high pressure conditions?

Of particular interest and cause of much debate was the strange pipe like structures containing a granite like rock deposit which cut through the diorite at a low angle these were oval to round with about 100 mm average diameter. They also showed metasomatic aureoles which, because they were harder than the diorite, also protruded from the rock face. Theories of the origin of the pipes are still being considered one being that they are blobs of low-density granite, which might have risen through the diorite whilst it was still plastically moving in an outward direction.

Weathered, horizontal pipe about 7cm in diameter with clear aureole standing proud. The pipe had been cut by a quartz vein.

From here we went on to have a much needed lunch at L'Ancresse Cafe; now hardened to the cold windy weather we were well adapted to eating our lunch out in the elements, el fresco.

Roger Nelson and Mary Herve