Source : Webster's Revised Unabridged Dictionary (1913)

Marlstone \Marl"stone`\, n. (Geol.)
   A sandy calcareous straum, containing, or impregnated with,
   iron, and lying between the upper and lower Lias of England.

Source : WordNet®

marlstone
     n : metamorphic rock with approximately the same composition as
         marl [syn: {marlite}]