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Petunfe Porphyry. 353 with that fmartnefs, that homftone of that finer grain does. It paffes into argillite and trap. Thebafis ofthe horn-porphyry, Lefke S. 1041, feems a middle thing, between filiceous fhiftus, and argillite; its colour bluifh grey, with fome reddifh and whitifh fpecks ; frafture, thin flaty; hardnefs, 10; furface fhews a whitifh brown cruft from decömpofition. Petunfe Porphyry. Porphyry that has felfpar for its bäfis is Called by this namc. 1 Its colour is generally yellowifh brown, or red- difh brown, or brownilh red, or reddilh grey, or flefh coloured, or yellowifh red. Luftre, o. Tranfparency o, or fcarcely 1. Fra&ure unequal, or earthy,. or fine fplintery, or prefenting final 1 folia or lamelke, often prefents' diftinft concretions. Hardnefs, 10. The rock, mentioned in 2 Saufl. §. 728, feems different, being much more fufible,. See Lelke S. j158. Of Argillaceous Porphyries. Thefe may have indurated clay, hornblende, tf ap, wacken, rnullen, kragg> or argillite, for their bafis. Clay Porphyty, LeJke S. 1094, 1096, Its colour is generally of fome Ihade of grey, °fgreenifh grey, or brown, or blackilh, or red* dilh brown, or lfabella yellow. A a L« ft re,