Clay minerals from Tertiary samples of DSDP sites 280, 281, 282, and 283 were analyzed mainly by X-ray diffraction and cation exchange methods. Site 282, off the Tasmanian west coast, contains a persistent Australian clay mineral assemblage that reflects deep weathering conditions in Tasmania and basic volcanism increasing from Eocene into the Oligocene. Site 280, south of the South Tasman Rise, was probably situated close to Antarctica in the Eocene-Oligocene and shows a change from temperate source area condition in the Early(?) and Middle Eocene, to cold-glacial conditions in the Latest Eocene and Oligocene. This is supported by Oligocene-Miocene data from cores near Antarctica. It is unlikely that any deep oceanic connection existed between the basins on either side of the South Tasman Rise until probably the Late Oligocene when the circum-Antarctic current developed.