Each beach you visit as you travel around the coast of the Channel Island of Guernsey seems to reveal a different combination of rock types. On the southern part of the island these are predominantly metamorphic rocks. In Havelet Bay close to St Peter Port, just south of the main rock bathing pool, and before the aquarium, metasedimentary rocks and gneisses outcrop on the pebble beach where the waves have polished the rock surfaces to reveal the patterns and textures. The actual contact between the Perelle Gneiss and the metasediments cuts through the centre of the swimming pool. The metasediments are described as interbanded semi-pelitic schists with migmatites (Roach et al. 1991).
I particularly remember this site because I nearly got knocked off my feet by a freak wave. I did not realise until later when I came across this sign that the ferries and other large ships going into and out of the harbour at St. Peter Port can create a wash with great impact especially around high tide.
British Geological Survey Classical areas of British geology: Guernsey, Channel Islands Sheet, 1 (Solid and Drift) Scale 1:25,000. NERC, Crown Copyright 1986.
De Pomerai, M. and Robinson A. 1994 The Rocks and Scenery of Guernsey, illustrated by Nicola Tomlins, Guernsey: La Société Guernsaise, ISBN 0 9518075 2 8, 30-34.
Roach, R. A., Topley, C. G., Brown, M., Bland, A. M. and D’Lemos, R. S. 1991. Outline and Guide to the Geology of Guernsey, Itinerary 9 – Jerbourg Peninsula, 76. Guernsey Museum Monograph No. 3, Gloucestershire: Alan Sutton Publishing. ISBN 1 871560 02 0, p 91-94.