1. a type of sedimentary rock or clay, typically blue-gray in color, formed from marine deposits of the Jurassic period
Usage: geology; chiefly British

Examples

• The cliffs along the Dorset coast are composed largely of lias.
• Geologists identified lias deposits dating back to the Jurassic period.
• The blue lias formation is rich in fossils and marine remains.
• Quarries in the region extract lias for use in construction and road building.