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KiHas. 237 brown; and at laft, melts into an opake gloffy flagg. 1 he pale grey flates of Weftmoreland liave their fp. gr. 2,732, the purple 2,797, according to Dr. Watfon. Sorae of the former afforded him a ft roh g lime water after calcination. The filky glofs intimstes the prefence of magnefia. Aflj grey Slate of France. . According to Briflon its fp. gr. before it ab- forbs water is 2,6718, and after abforption 2,6905; it confequently abforbs T l T of its weight of water. Of other flates, ufed for roofs, he found the fp. gr. before abforption 2,8535, and after abforption 2,8592. The beft are thofe that abforb leaft. 3d Varicty, * * Killas. Pale bluifli grey, or red, or whittfh yellow. Luftre, filky, opake. Its furface undulated. Fra&urc, long fplintery, and imperfedly flaty. Flardnefs, froiü4to5; the whitifh yellow ftill fofter, but that of a dark grey, I am informed, is 9. The fp.gr. of the bluifh grey I- found in different fpecimens from 2,63 to 2,666; it con- tained by my analylis 0,60 filex, 0,25 argill, 0,09 magnelia, and 0,06 iron, and fome petrol or bi- tumen, as appeared by the greenifh hue which it gave to the nitrous acid. As it wants calx it can fcarce bedeemed a true argillite. 4th Variety.