m THEORY OF THE SYSTEM. . 225. 



The genus is the resemblance of different species of bo- 

 dies. In Botany, this idea is commonly limited to the 

 similar formation of the organs of fructification. In Mi- 

 neralogy, such a restriction is impossible, because the pro- 

 ductions of the Mineral Kingdom do not present any parts, 

 different in the same manner from the rest, as is the case 

 in plants. But even supposing their existence, Minera- 

 logy will not admit of any such restriction, on account of 

 the necessity to preserve the idea of the species in its 

 original generality, which admits of no exceptions, devia- 

 tions, or ambiguities, necessarily connected with a restric- 

 tion to single characters. For the rest, the idea of the 

 species in Mineralogy is identical with that in Botany ; 

 and there is nothing more required, but to shew that it is 

 equally applicable. Thus we shall find ourselves enabled to 

 employ it with the same security in the Mineral Kingdom, 

 as in the Vegetable one. 



The species of hexahedral Iron-pyrites agrees so very 

 closely with that of prismatic Iron-pyrites in every charac- 

 ter, except the forms-, that but for this difference in their 

 systems of crystallisation, they would join into one and the 

 same species. They possess that degree of resemblance 

 which requires their union into the same genus ; a de- 

 gree of similarity expressed in the present instance by the 

 perfect agreement of all the natural-historical properties, 

 except the crystalline forms. The same degree of resem- 

 blance prevails among the two species of Emerald ; but 

 here, beside the difference in the systems of crystallisation, 

 there is also a difference in the specific gravity. In other 

 genera, as, for instance, in those of Garnet, of Kouphone- 

 spar, and others, we observe differences in many characters 

 at once ; and yet the resemblance is here as great as in the 

 above mentioned examples of Iron-pyrites and Emerald ; 

 a resemblance which becomes evident upon ocular in- 

 spection, the only method of ascertaining its existence. 

 The examples quoted prove, that there may exist differ- 

 ences sometimes only in a few, sometimes in many charac- 

 ters at a time, without having any influence upon the dc- 



