(Science: geology) The lowest of the three divisions of the jurassic period; a name given in England and Europe to a series of marine limestones underlying the Oolite.
Origin: cf. F. Lias, fr. Liais sort of limestone, OF. Also liois; perh. Of Celtic origin, cf. Armor. Liach, leach, a stone, gael. Leac, W. Llech. Cf. Cromlech.