xxxvi * ‘ INTRODUCTION. vailing opinion, that external characters alone were fufficient; the increafmg tafte for chemiftry introdu ced the chemical characters, and thefe in their turn have been adopted by feveral mineralogilts, to nearly the exclufron of all the others. Werner teaches, that all the different kinds of characters are to be em ployed, but of thefe, he conftders the external cha racters as by far the moft certain and generally ap plicable. Thefe characters are not only fufficient for the defcription, but alfo for the arrangement of mine rals. That they are fufficient for the difcrimination of minerals is certain, from the obfervation of Werner, who declares, that no mineral has ever been difcover- ed which could not be diftinguifhed by its external characters, and that they are fufficient for its arrange- j inent is equally evident from the greater number of fpe- cies in the mineral fyftem being arranged folely by a- greements and differences in the external characters. As a knowledge of thefe external characters is ab- folutely required of every one who {hall venture on the ftudy of oryCtognofie, I fhould now proceed to give an account of them, I mud, however, from • the great extent of the fubjeCt defer this for the pre- fent •, but fhall give a full explanation of them in the following volume, v ti. In writing the defcription of a mineral, accord ing to its external characters, Werner recommends Method of lt foouid contain all the external characters. defcribin» _ r . a mineral. q'h e externa’- characters are not ot equal importance ; hence ievcral mineralogifts have judged it neceffary, ;n their defcriptions, to employ only the more charac terise