The geology of a very important upper Eocene fossil deposit is described, together with geology of the island not previously recorded. A dike complex indicates that the lavas were erupted chiefly through narrow dikes. Pillow lavas are scarce. Three series of tuffs or tuffaceous sediments and limestone of three distinctly different ages occur. The limestones are upper Eocene, Miocene, and Pliocene-Pleistocene in age. The island history has been one of volcanism, uplift, faulting, marine and stream erosion, and limestone deposition since the upper Eocene. A submergence of at least 560 ft occurred in the Pliocene(?), and coral reefs were built during the high stands of the sea during the interglacial epochs of the Pleistocene. No coral reefs predate the Pliocene, indicating that coral reefs are of fairly recent origin in this part of the Pacific.