During the Permian, Britain lay on the supercontinent of Pangaea and experienced hot, dry conditions. Sandstones formed from desert sand dunes. Limestones and salts were deposited in a nearby inland sea (the Zechstein Sea). Many groups of animals became extinct at the end of the Permian.
During the Triassic, a hot and dry environment led to the deposition of sandstones, salts and mudstones in deserts, rivers and shallow lakes. Reptiles were common and the first dinosaurs evolved.
*Based on The Geologic Time Scale 2012 by F M Gradstein, J G Ogg, M Schmitz and G Ogg (2012), with additions.