The crust represents 18.5 m.y. of growth of Fe and Mn oxyhydroxides. The crust is composed of alternating botryoidal and laminated layers. The botryoidal layers formed during the same time intervals that widespread Neogene deep-sea hiatuses were forming in bottom sediments. The botryoidal layers represent growth during times of intensified deepwater flow, whereas the laminated intervals represent more quiescent conditions. The broader changes in composition occurred primarily at about 15, 11.5, 7.4, 6.4, 5.2 and 4.6 Ma, which may correlate with major changes in paleoceanographic circulation and development of ice caps at the poles. -Authors