XII. CLAY-SLATE FAMILY. This Family contains the following Species: Alum- Slate, Bituminous-Shale, Drawing-Slate, Whet-Slate, and Clay-Slate. 1. Alum-Slate. This species is divided into two subspecies, viz. Com mon Alum-Slate, and Glossy Alum-Slate. First Subspecies. * Common Alum-Slate. Gemeiner Alaunschiefer, Werner. Schirtusduminaris? Wall. t. ii. p-32._Var. of Alaunschiefer, Wid. s. 396. Id. Eslncr, b. ii. s. 651.—Gemeiner Alaun schiefer, Emm. b. i. s. 296.—Schisto aluminoso, Nnp. p. 264. —-Variete de l’Argile schisteusc, llamj.—Le Schiste alu- mineux commune, Brock, t. i. p. 386.—Gemeiner Alaun schiefer, lleuss, b. ii. s. 143.—Alaunschiefer, End. b. i. s. 110. Id. Suck, lr th. s. 529-—Sehiefrigcr Aluminit, Bert. s. 219- —Alaunschiefer, Moks, b. i. s. 454.—Gemeiner Alaunschiefer, Leonhard, Tabel. s. 22—Alaunschiefer, Ilaus. s. 86.—rGe- meincr Alaunschiefer, Karslen, Tabel. s. 36. Id. Sfcffeiu> b. i. s, 205. Id. Lenz, b. ii. s. 571. Id. Oken, b. i. s- 3(5 ~' External Characters. Its colour is intermediate between bluish and grejish black.