The objec tions an- fwered. Chemical arrange ment of minerals. sxlv INTRODUCTION. ferent In their Internal compofition; thus they re mark fapphire is placed in the flint genus, although it has been found to contain ninety-eight per cent, of alumina ; and opal in the clay genus, although ninety- eight parts of filiya. This objection, however, is founded on a mifconception of Werner’s opinion. He does not pretend that his arrangement Ihall always correfpond with the experiments of the chem.ift; for it is only when chemical refults agree with the natu ral alliances of the mineral that he gives them a place! in his fyftem. In inftances where the affinities of the mineral with thofe already in the fyftem have not been made out, and we are ftill uncertain as to its true nature, it is a matter of indifference where we place it. If it has been analyfed we may arrange it chemically, not however from a convi&ion that its place will thus be fixed, which cannot be done un til we have, by the examination of a complete fuite, combined with a knowledge of its geognoftic relations, difcovered whether or not its characters authorife the arrangement made by the chemift. If we were to allow the arrangement to be made according to the molt improved chemiftry of the prefent day, we fhould have very dilffmilar minerals grouped together, and thofe which are nearly allied feparated. In fuch a fyftem garnet and thumerftone would be confider- ed as the fame fpecies; chlorite would be arranged among the ores of iron, and we fhould have a tranfi- tion fuite beginning with pumice, and proceeding through pearlftone, pitchftone, clinkftone, felfpar, talc,