82 BULLETIN OP THE 



such a change in composition, if in certain and stable proportions, 

 not mei'ely an accidental admixture, will demonstrate a sub- 

 species. 



As a large number of minerals have the same chemical com- 

 position, but entirely different physical qualities, it .is necessary 

 to regard them as varieties. For the chemical mineralogist 

 these differing physical qualities cannot be of sufficient import- 

 ance to warrant his defining them as species or even subspecies. 



Suhvarieties will differ from the varieties and subspecies to 

 which they belong in presenting local alterations and replace- 

 ments of constituents by others in such a manner that they must 

 be regarded merely as accidental admixtures ; and subvarieties 

 will be further distinguished by some peculiar method of forma- 

 tion. 



In some cases these definitions may not seem to be quite suffi- 

 cient in determining the position of a mineral. Dolomite CaC + 

 Mg G might seemingly be placed under the species'Magnesite 

 almost as well as under Calcite, but in any case of this kind we 

 have the physical characters to resort to, and upon investigation 

 find that Dolomite in crystalline form, gravity, etc., more closely 

 resembles Calcite than Maguesite, therefore give it the position 

 as a subspecies of Calcite. 



The arrangement of species within a class or subclass ought 

 not to be arbitrary in a strict system, and enumerating them ac- 

 cording to their specific gravity of their K, beginning with the 

 lowest figure, might prove satisfactory. 



Within the groups the species and subspecies must be ar- 

 ranged according to their composition. As the representative 

 of the simple general formula of a class or subclass is defined as 

 species, and the subspecies have part of the K of the species re- 

 placed by other substances, they must follow in such order that 

 the one with most varied replacements will form the last member. 



The class of Carbonates among the minerals is one of the 

 most generally known, and I have selected the subclass anhy- 

 drous carbunafes for an arrangement based upon the principles 

 above elaborated. 



General Formula of Subclass: Anhydrous Carbonates ■= KG, 



