CLAY GENUS. SIXTH SUBSPECIES. Slate Clay. Schieferthon.—Werner. Slate clay, fhale, Kirw. t. i. p. 182.—L’Argile fchifleufe* Broch. t. i. p. 327. External CharaElers. Its colour is grey, of which it pref : nts the follow* ing varietes; fmoke grey, yellowilh grey, and alh grey, which latter fometimes approaches to blueilh grey. From afh grey it pafles into greyilh black. It is maffive. Internally it is dull, but when it contains inter mixed mica it is glimmering. Fra&ure more or lefs perfectly flaty, fometimes ap' proaching to earthy. Fragments indeterminately angular and tabular. It is opaque. Intermediate between foft and very foft. Mild. , Eafily frangible.
