Blue Lias

The Blue Lias is a geological formation of alternating limestone and shale layers, laid down in the latest Triassic and earliest Jurassic between roughly 200 and 195 million years ago, spanning the Rhaetian through lower Sinemurian stages and fully encompassing the Hettangian; it is also known as the Lower Lias, the lowest of the three divisions of the Lower Jurassic. Its distinctive blue-grey color comes from iron content, much of it held in pyrite. The formation is exposed across southern, eastern and western England and parts of South Wales, with notable outcrops in the cliffs around Lyme Regis and Charmouth on Dorset's Jurassic Coast, in Somerset around the Polden Hills and Glastonbury, in the East Midlands, near Whitby in Yorkshire, and along the South Wales coast. It is famous for its fossils, especially ammonites, and also preserves abundant dinosaurs, pterosaurs, ichthyosaurs, plesiosaurs and fish, making it an unusually rich record of Early Jurassic marine life. This entity documents the Blue Lias specifically as a geological formation, an earliest Jurassic marine limestone and shale sequence.