\Li"as\ (l[imac]"as), 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 O["o]lite. See the Chart of
{Geology}.