marl·stone /ˈmɑr(ə)lˌston/
  泥灰土之一種
  Marl·stone n. Geol. A sandy calcareous straum, containing, or impregnated with, iron, and lying between the upper and lower Lias of England.
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  marlstone
       n : metamorphic rock with approximately the same composition as
           marl [syn: marlite]