n. [ 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. ] (Geol.) 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 Oölite. See the Chart of Geology. [ 1913 Webster ]
a. (Geol.) Of the age of the Lias; pertaining to the Lias formation. --