80 BULLETIN OF THE 



species or group may be exactly defined and limited, while all 

 other systems are based upon more or less arbitrary divisions 

 and assumptions, except those based on crystalline forms; these, 

 however, cannot be properly carried out, as so very large a num- 

 ber of mineral substances show no crystalline structure what- 

 ever. In following a chemical system, which may seem the most 

 rational and satisfactory, we dare not lay undue weight upon 

 physical characters. A mineral species in any such system 

 must be a single, well-defined group of individuals, and must 

 contain all its subspecies, varieties, and subvarieties, arranged 

 according to rules by which a classification adapted to the nature 

 of minerals can be constructed. It cannot be denied that the 

 physical character of a mineral, even though it has the same 

 composition as some other one, will have some claim upon the 

 attention of a chemical mineralogist, but compared with the 

 composition, it can only be of subordinate value. 



Adopting Dana's classification of minerals based upon their 

 chemical constitution, we can divide into : 



Divisions, Subdivisions, 



Sections, Subsections, 



and in order to carry out a strict classification, adopt Dana's 



plan of Groups, and then give Species, Subspecies, Varieties^ 



and Subvarieties. For instance : 



Division : Oxygen Compounds, 



Subdivision: Ternary Oxygen Compounds, 



Section : Carbonates, 



Subsection: Anhydrous Carbonates, 



Group : Lime Carbonates, 



Species : Calcite, 



Subspecies : Calcite, 



Variety : Arragonite, 



Subvariety: Sprudelstein. 



The section " Carbonates" comes under the common general 

 formula, KO CO2 -f- (HO), and the anhydrous carbonates have 

 KO COj. The name of the Group will always be denoted by 

 the name of the basic element, with which for instance carbonic 

 acid is combined, and the simple combination of 1 KO with 

 1 CO2 would in this case constitute a species. The specific KO, 

 however, may be replaced in part by some other, and the compo- 

 sition of the mineral will to some extent be changed, whereby a 

 subspecies would be characterized. It is necessary to pay due 

 attention to the differences regarding physical characters within 

 the limits of a species, and as a chemical mineralogist cannot 

 recognize a species created upon physical distinctions alone, and 

 his subspecies denote chemical changes, the mineral thus differ- 

 ing will become a variety. 



As Dana says (Preface to 4th ed., 1854), "The mind unedu- 

 cated in science may revolt at seeing a metallic mineral, as Ga- 



