During that period, the Peninsula of Crozon remains under shallow water. The sedimentation is characterized by sands and carbonated muds. The water was times clear enough to allow the growth of coral reefs which supported a profuse and varied fauna : Brachiopods, trilobites, mollusks, sea-lilies and fishes. 410 million years ago, the Armorican massif was in an tropical zone.

Drawing : Bernadette COLENO.