252 PHYSIOGRAPHY. 



cies itself, but it also contains the individual description of every 

 one of its single varieties ; for as to the latter, if we choose arbi- 

 trarily any single member from every one of the mentioned series, 

 and join these members in the adopted order of succession, the re- 

 sult will be the description of a variety, belonging to the species. 



The representation of the species as contained in the general de- 

 scription, is far more complete, than it could be obtained by imme- 

 diate observation ; for it unites all the varieties which may be pro- 

 duced by all possible combinations of the single properties, (the 

 members of different series.) It would contain all the varieties pos- 

 sible in a species if the series themselves were complete, which 

 can be maintained only of those produced by derivation from given 

 forms. Thus the considerations referring to the mineral kingdom 

 become both fertile and interesting ; because, by means of the gen- 

 eral description, we obtain from every newly discovered variety, 

 though it should differ from those already known, only in a single 

 character, an almost endless number of new varieties, which may 

 be produced by uniting the newly discovered property with every 

 combination of the members of the other series which the general 

 description contains. 



The pure, or properly so called, general description, refers only 

 to the individuals of the species, because it is from these that we 

 derive the most perfect of the characteristic marks employed in 

 mineralogy. If the compound varieties are to be noticed, this must 

 be done without mixing them up with the simple ones. 



From the preceding remarks, it appears that the general descrip- 

 tion presupposes the correct idea of the species. 



. 126. ARRANGEMENT OF THE GENERAL DESCRIPTION. 



The general or collective descriptions require to be so 

 arranged, as to facilitate their use as much as possible, and 

 to produce, in fact, a complete general view of the species. 



In order to determine the series of crystallization of a species, it 

 becomes necessary to indicate the primary form, with its dimensions, 

 except in those cases where these are always the same as in the 

 regular Octahedron, Cube, &c. Accordingly, in the second part of 

 this treatise, this will first be given, along with the information 

 whether it be deduced from calculation, observed in the crystals 

 themselves, or obtained from cleavage. In forms of variable dimen- 

 sions, notice is also appended whether the value of their angles was 



