Clastic intrusions of biogenic calcarenite occur as simple or branching dykes, sheets, sills, and as net-vein complexes. They are mainly intruded from below into volcaniclastic sediments and the lower part of a thick basanite lava flow. Where they penetrate the lava they are metamorphosed. The source of the limestone intrusions lies in shell sand layers which became mobilized as a slurry along joints. It is believed that rapid loading by the basanite flow was responsible for the upward injection.