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3 *»8 'Derivativei. proportions, and hence the variety of its colout and fpecific gravity offen arifes. The greener forts, if they have more luftre than ordinary, and if their denfity exceeds 2,8, may be fuppofed to contain a large proportion of horn blende flate; but, if deftitute of luftre, andif their denfity be below 2,78 and eafily fufible,they probably contais a proportion of wacken; if more iifficultly fulible, moft probably ferpentine. The light grey traps, when their denfity is un- «ler 2,78, may be fufpefted to contain mullen. The reddifi) brown moft probably are mixed with kragg. Mr. Karften fuppofes trap to be formed of an intimate mixture of hornblende, quartz, and ielfpar ; and in effeft if we fuppofe it formed 0,60 hornblende, 0,30 quartz, and 0,10 felfpar, we ihall have a ftone whofe fp. gr. (hall be 2,829; but this ftone will not contain the proportion of iron that Bergman found in trap, and which, by the various analyfes mentioned by Mr. Faujas in his Treatife on Traps, appears to be never lefs than 20 per ct.; for, hornblende, by my analyfis contains23 perct. ofiron, and by Mr. Wiegleb’s ilill lefs; confequently a ftone containing 60 parts cf.it can contain but 13,8 of iron at moft, nor can we obtain by this means a ftone whofe fp. gr* amounts to 2,98, as thatof trap often does. Siliciferous Trap. Lefke G. 173. This arifes from an intimate mixture of trap with Haare ftone of the filiceous genus. The Ipe- cimen