After lunch at the Sablons d’Or a short walk brought us to the headland to the west of L’Ancresse Bay. What looked like splashes of paint across the rocks were sugary-textured aplite intrusions in the heavily jointed and fractured L’Ancresse Granodiorite. The headland was also cut by an east-west trending dolerite dyke
In the next bay to the west the granodiorite abutted onto a patchy-looking rock, the Inhomogenous Facies. This consisted of both fine and coarse-grained rock indicative of different phases of magma injection. It was interspersed with an amorphous fault breccia suggesting that the L’Ancresse Granodiorite to the north and the Bordeaux Diorite to the south had ground together along a fault plane. Some spectacular acircular zoned hornblende crystals were found and eagerly acquired.
A short drive down the west coast brought us to the Baie des Pecqueries where, on an apparently uninteresting boulder-strewn shore, black rocks proved to be a 95% hornblende, a Hornblendite. The rocks here are a marginal facies resulting from mixing between the Bordeaux Diorite to the north and Cobo Granite to the south.
At our final stop at Port Soif on the Bordeaux Granite we were looking south to the Cobo Granite. The geo-morphology of the bay results from faulting. East-west trending dykes of weathered dolerite cut through it and spectacularly displace aplite dykes in the fault zone.
Though the wind remained keen there was here a reassuring flock of sand martins and swallows giving promise of warmer weather to come.
Janet Griffiths and Tony Sheehan