Blue Lias Limestone
Stone supplied by Ashen Cross quarry, nr. Somerton, Somerset.
Laid down early in the Jurassic period, about 200 million years ago, the deposits which formed the rocks mainly consisted of clays, shell and shell debris, formed in warm tropical sea brimming with sea life.
From "Lower Jurassic Mudstones and Limestone's" By David Roche for Devon County Council.
Blue Lias is quarried in big slabs of up to 140mm in thickness and is mostly used for building and flooring. It outcrops extensively in Somerset, Gloucestershire, up into Worcestershire, Southern Wales, Devon and Dorset.
There are still a few working quarries in Somerset.