Volcanic agglomerates, breccias, tuffs, and basalt flows of probable Miocene age were responsible for building the island above sea level. An upper terrace, 100-350 ft elevation, was cut; additional emergence and concurrent development of a coral reef and beach deposits occurred during the Pliocene. Further minor emergence resulted in cutting of a terrace now submerged to a depth of 10-15 ft, followed by submergence and tilting of the sedimentary rocks. Next emergence of 13-30 ft was developed to present sea level; late Pleistocene faunas date this last sea-level fluctuation. A recent shoreline has been developed with prominent sea cliffs, local coves, sand beaches, and a modern coral reef.

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