The Blue Lias is a geologic formation in southern England, part of the Lias Group. The Blue Lias consists of a sequence of limestone and shale layers, laid down in latest Triassic and early Jurassic times, between 195 and 200 million years ago.
Blue Lias is famous for its fossils, especially ammonites.
It is a prevalent feature of the cliffs around Lyme Regis and Charmouth, Dorset, as well as Somerset, particularly around Glastonbury and the Polden Hills. It has a blue-grey colour provided by its iron content.
Blue Lias can be found in buildings, fagstones, cobbles, walling, paving, local churches and cemeteries (where it is used in tombstones). A prime example of a 'Blue Lias' town would be Street, near Glastonbury. Other local examples of Blue lias buildings can be found in the nearby towns of Somerton and Ilchester.
Blue Lias is used as a building stone and as a source of lime for making lime mortar. Blue Lias has also been widely used as a raw material in cement.