INTRODUCTION. teriflic or effential ones. In fome inflances this may be done, but in the greater number of cafes, the omiffion of any of the charadters would lead to error. We mud, therefore, in our defcriptions, not only mention all the charadters, but every branch of them, a's far as they are charadterillic of the fpecies. b. That we jhould place all the characters together.— lhe older, and many of the modern writers in mine- ralogy, by endeavouring to follow the methods of the zoologift and botanift, have rendered their defcrip tions of minerals unintelligible. 'To obtain an ac quaintance with the external afpedt of a mineral from fuch a defcription, or rather feries of definitions, we muft combine the characters of the Clafs, order, ge nus and fpecies, and after this labour, what do we ob tain but a delufive and imperfedt pidture ? c. That thefe characters floauld not have any of the others intermixed ~—As the defcription of a mineral according to its external charafters is principally in tended to give us a diftindt pidture of its afpeft, and of certain phyfical properties it poflefles, we mull be Careful that it contains nothing foreign to that objedt; it mufl, therefore, contain no chemical, geognoftic, or geographic chandlers. d. That they Jhould be arranged in a determinate ci der W^hen the charadters are arranged in a deter minate order, we are not fo liable to omit any of them, and are enabled more eafily to recoiled! the pidture of the mineral. Werner arranges them in that order in which they naturally prefent themfelves to our f'enfes j thus beginning with colour, as that which