Definition of marl slate in English:

marl slate

noun

Geology
  • 1A fissile calcareous rock; calcareous shale.

  • 2Specifically (usually Marl Slate) a stratigraphic division of the Upper Permian system of England, corresponding to the Kupferschiefer of continental Europe.

Origin

Early 19th century; earliest use found in Robert Jameson (1774–1854), geologist and natural historian. After German Mergelschiefer.