PHILOSOPHICAL SOCIETY OF WASHINGTON. 81 



lena, side by side with one of unmetallic lustre, as Blende," so 

 may an arrangement of this kind seem arbitrary and artificial, 

 but in a science like mineralogy, where we have no generic and 

 specific characters to guide us in the same way as in zoology, 

 and where a classification based upon exterior characters is utterly 

 impossible, we are forced to take the aid of chemistry, and 

 thereby regulate our systems, unless we wish to follow a so-called 

 "natural system," where the arrangement of groups and spe- 

 cies is based upon characters of less stability. By all mineral- 

 ogists of the present day, the importance of chemistry for their 

 studies is freely admitted, and however they may be opposed to 

 any chemical system, in case of a dispute regarding the validity 

 of some species, they are generally obliged to resort to analysis, 

 and in most cases such questions are ultimately decided by the 

 results of such analysis. 



As long as " natural systems" are allowed to expand and new 

 ones are created, there can be promised from them no satisfactory 

 classification of minerals giving at the same time due attention 

 to the physical and chemical characters. By adopting a system, 

 however, based upon our present knowledge of the composition 

 of minerals, we are enabled to look forward to some definite ar- 

 rangement by which all the features of a mineral will receive the 

 necessary attention, and only those that are unchangeable and 

 truly characteristic, will be employed in discriminating. 



Some systems profess to be arranged in such a manner as to 

 give the student more facilities in acquiring the knowledge he 

 seeks. These systems are mostly based upon an arrangement 

 of groups giving "natural" classes. But again to quote Dana: 

 " the distinction of ' useful' and ' useless,' or of ' ores' and ' stones,' 

 although bearing on 'economy,' is not science." 



Having given some of the reasons why a chemical system 

 would be preferable to any other, it may be well to propose 

 strict definitions of the various sections, etc., into which the 

 minerals would be divided. 



Dana's excellent system has been here adopted as a basis ; in 

 the application of the terms Section, Group, and Species, some 

 changes are proposed ; Subspecies, Variety, and Subvariety are 

 defined. 



A section, or divided subsection, will have a common general 

 formula. 



One or more species and subspecies having this same common 

 gfeneral formula and KO alike, will then form a group. 



Any metal or metalloid substance, occurring as such in the 

 mineral kingdom, or the representative of the simple general 

 formula denoting the nature and ratio of combination of any class 

 or subclass, will form a species. 



In most of the species a larger or smaller part of their basic 

 element is replaced by some other, often even by several, and 

 6 



