A recent study of the southeastern extremity of the Andean Cordillera on Isla de los Estados in Argentina Tierra del Fuego confirmed that the island consists exclusively of Upper Jurassic-Lower Cretaceous volcanic and sedimentary deposits. A very thick sequence of silicic volcanic rocks consisting of homogeneous tuffs and subordinate ignimbrites and lavas crops out over most of the island. These rocks, of quartz-latite to rhyolite composition, were deposited in a dominantly shallow-marine area with sporadic volcanic islands. The overlying sedimentary rocks are black calcareous mudstones cropping out in the northwest of the island. The boundary between the two formations is a concordant, transitional sedimentary contact. Preliminary analysis of detailed structural data ind cates that the rocks are disposed in a single large syncline, asymmetric and overturned to the north at the east end of the island, and upright in the west. Continuity of lithology and structure through the island from the Andean Cordillera toward the North Scotia Ridge reemphasizes the persistence of these geologic features into the Scotia arc.