CLAY GENUS, EIGHTEENTH SPECIES, i Drawing Slate, or black Chalk. Zeichenfchiefer.—Werner. Schiftus pi&orius nigrica, Wall. t. i. p. 358 Zeicheii' fchiefer, Wern. Cronjl. p. 206. — Black chalk, KirW- vol. t. p. 195 Schwartze kreide, EJiner, b. 2. f. —'Schiefer, Id. Emm. b. 1. f. 303.—Schifto pittorio* Nap. p. 269—Melantirite ou crayon noire, Lam. t. z ’ P• 1 r 2 —Argile fchifteufe gi aphique, Hauy t t. 4. p, 447' —Le fchiltc a ckffiuer, Broch. t. 1. p. 391. External Characters. Its colour is greyilh black, which fonietimes ap- proaches to blueilh black. Maffive. I.uftre of the principal fra&ure is glimmering> but the crols iratture dull. Principal fracture generally flaty, the crofs fra& urC fine earthy. Fragments