Emily Dickinson Lexicon

LITH-O-MAR'GA, or LITH'O-MARGE, n. [Gr. λιθος, stone, and L. marga, marl.]

An earth of two species, friable and indurated, more silicious than aluminous, distinguished by its great fineness and its fusibility into a soft slag. – Dict. Nat. Hist. Kirwan. Ure.