4 PHYSIOGRAPHY. . 55. 



ties in the Mineral Kingdom, it is necessary to 

 construct a Collective or General Description. 



The problem to be resolved in constructing a General 

 Description is, to give a correct idea of all, or at least of 

 the known varieties of a species in their proper connexion ; 

 it must therefore contain at once all the descriptions of 

 these varieties, without its being itself in a strict sense a 

 description at all. It is evident that the only means of ar- 

 riving at this end, will be the employment of the series of 

 characters. 



The method of constructing a general description of a 

 species is as follows. First, any suitable variety of the 

 species is chosen, and described with all possible accuracy, 

 the single characters succeeding each other agreeably to 

 the order fixed upon, as above mentioned. The descrip- 

 tion will contain only single characters, consisting of a 

 certain form, a certain colour, a certain kind of lustre, a 

 certain degree of hardness or of specific gravity, &c., all of 

 these being members of their respective series. If in the 

 place of every one of these single characters, we substitute 

 the complete series to which it belongs, the Description cs 

 the Individual^ or of the variety, is transformed into the 

 Collective or General Description of the Species. 



The characters contained in the general description are 

 expressed in series, produced either by immediate observa- 

 tion and interpolation, or by derivation (. 79-)' The cha- 

 racters in the descriptions of determined varieties consist 

 of single members of these series. Evidently the collective 

 description not only produces a complete idea of the species 

 itself, but it also contains the individual description of every 

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

 arbitrarily any single member from every one of the men- 

 tioned series, and join these members in the adopted order 

 of succession, the result will be the description of a variety, 

 belonging to the species. 



The representation of the species as contained in the ge- 

 neral description, is far more complete, than it could be ob- 

 tained by immediate observation ; for it unites all the va- 



