. 255. PHYSIOGRAPHY. 5 



rieties which may be produced by all possible combinations 

 of the single properties (the members of different series). 

 It would contain all the varieties possible in a species, if the 

 series themselves were complete, which can be maintained 

 only of those produced by derivation. Thus the conside- 

 rations referring to the Mineral Kingdom become both fer- 

 tile and interesting ; because, by means of the general de- 

 scription, 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 new- 

 ly discovered property with every combination of the 

 members of the other series, which the general descrip- 

 tion contains. The same process of reasoning is fol- 

 lowed here, by which we obtain from a newly ascertained 

 co-efficient, or from a number of derivation not known be- 

 fore, not merely a single form, but whole series of such 

 forms. 



The pure, or properly so called, general description, re- 

 fers only to the individuals of the species, because it is only 

 from these that we are entitled to derive characteristic 

 marks, fit for being employed in Natural History (. 192.). 

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

 done without mixing them up with the simple ones. 



From the preceding observations, it appears that the ge- 

 neral description pre-supposes the correct idea of the natu- 

 ral-historical species ; but none besides of the general ideas 

 developed in the Theory of the System (. 17-). 



The collective description explained here has no doubt 

 been the fundamental idea of the descriptions introduced 

 in Oryctognosy by the celebrated WERNER. In these too 

 series are made use of; and supposing the determination 

 of the species to be correct, they might be employed in the 

 place of the general descriptions of this work, if those se- 

 ries, upon which their completeness and utility more particu- 

 larly depends, had been known at an earlier period, and the 

 compound varieties properly separated from the simple ones. 



The general description requires in particular, that the 



