marl slate
Geology
noun
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.