The earliest epoch of the Jurassic period, lasting from about 208 to 178 million years ago.
- 1.1The system of rocks deposited during the Lias, consisting of shales and limestones rich in fossils.
- 1.2mass noun A blue-grey clayey limestone derived from marl deposited in the Lower Jurassic, found chiefly in south-western England.
Late Middle English (denoting blue lias): from Old French liais ‘hard limestone’, probably from lie (see lees).
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