During palaeobotanical studies in the Antarctic Peninsula in February 1979, late Cretaceous or younger fossil angiosperm leaves were found within volcaniclastic rocks widely believed to be of late Jurassic age1. Although poorly preserved, these fossils are of great stratigraphical importance. They occur at Cape Alexandra, Adelaide Island (Fig. 1), in rocks correlated with the lowest part of the exposed succession (Sloman Glacier succession1). The fossils were found less than 10 km from the type locality for this succession at the head of Sloman Glacier (Fig. 1). However, towards the northern end of the island at Mount Bouvier (Fig. 1), ammonites and bivalves indicate that supposedly equivalent rocks1 are of Upper Jurassic age2. This intensive study of a very small part of the succession indicates that the volcanic history of Adelaide Island is much more complicated than was previously suggested by reconnaissance mapping.