Shale
SHALE, verb transitive To peel. [Not in use. See Shell.]
SHALE, noun
1. A shell or husk.
2. In natural history, a species of shist or shistous clay; slate clay; generall of a bluish or yellowish gray color, more rarely of a dark blackish or reddish gray, or grayish black, or greenish color. Its fracture is slaty, and in water it molders into powder. It is often found in strata in coal mines, and commonly bears vegetable impressions. It is generally the forerunner of coal.
Bituminous shale is is a subvariety of argillaceous slate, is impregnated with bitumen, and burns with flame.