xxxlv -INTRODUCTION. v this method we are enabled to place all the fpecies in a natural order, and obtain on the one hand a tranfition into the zircon genus, and on the other into the clay genus. In the metallic genera, thofe fpecies which are in the metallic date are placed firft, next the different oxyds and combinations Great attention muff, however, be paid to the tranfitions, and their ar rangements. /tranjrr- g. As the fubfpecies are few, their arrangement is fubfpecics. comparatively eafier: we muff here attend, chiefly, to the rules of tranfition, fo that the arrangement may be natural. fnXerai". 1 °' The charafters which are employed in the defcription of minerals are, by Werner, divided into five claffes, i. External. 2. Chemical. 3. Phyfical. 4. Geognoftic, and 5. Geographic. r. External Characters—are thofe which are dif- coverable by the external fenfes, without inducing any confiderable alteration m the aggregation of the mineral; thus colour, fhape, luftre, fra&ure, hard- nefs, weight, &c. are of this kind. 2. Chemical Characters—are thofe which are afford ed by the complete analyfis of the mineral ; by trials with acids, with the blow pipe, and Wedgewood’s pyrometer. 3. Phyfical Characters—are thofe phyfical proper ties of minerals which are difcovered by trials with the magnet, or by rubbing or heating. ' 4. Geognostic Characters—The determinate occur rence of one mineral with another affords, what Wer ner t