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Of the Calcareous Genus. 375 Marls alfo are much difguifed by bon; the foecimen, Lefke S. 453, is dark reddifh brown, and reddifh black; luftre, o ; tranfparency, o ; fraflure, partly even partly fplintery; trag- snents, oori, hardnefs, from 7 to 8 ; fp.gr. 8 . „ives ared ftreak-, effervefces with acids. Gyplumis frequently penetrated with mavl, cal careous fpar, fwineftone, fandftone, and perhaps with ftronthian, &c. thefe mixtures caufe a change both in its hardnefs and fpecific gravity; its co- iour is then either blackifh grey, or a mixture of whitifh and blackifh grey in layers or fpots and veins; luftre, either o or 1, from nrterfperfed ihining particles; fee the fpecimens in Lefce O. j c8o and S. 5 105 and this compound is itfelf often mixed with foliated gypfum whrch may eafily be taken for mica, as in the fpecimen, b. ^ 2, x • c “ All the varieties of gypfum are often met m veins in indurated clay. See Lefke S. 25°, &c. Sometimes this impure gypfum affumes a flaty form • and this often contains an excels of vimohc seid, 'as the fpecimen Lefke S. 2,59, wh, ch is in- ternally black, and externally dark bluifh grey ; its hardnefs, 7 j fp.gr. ^,473 J heated to rednefs it becomes reddifh white. . The fpecimen O. 15521s very remarkable, its colour, pure white; luftre, 2.3; tranfparency, 2; fraAure, partly granulär, partly fol.ated; hard- neft, 8 ; fp. gr. 1t fams mirture of granulär liinrftonc and foliated gyp Muriatic