 The formation laterally varies from east to west; the western lowland "coastal" sequence is over 2000 metres thick and primarily consists of deep water limestone and chalk, while the eastern "mountain" sequence is 500–700 metres thick and consists of shallow water limestone.Pterosaur fossils have been recovered from the formation, including those of "Mimodactylus" and "Microtuban".Insects are also known from compression fossils, including those of dragonflies.