386 Review of Dana's Mineralogy. 



tant variations from a strict chemical method. It has been shown that 

 owing to the isomorphism of bases, the old modes of chemical classifi- 

 cation are wholly unsatisfactory ; and the difficulties have of late be- 

 come so great that some authors have fallen into an alphabetical arrange- 

 ment, rather than be bound down to the usual chemical rules. More- 

 over, it has been remarked, that the union of the salts of metals into a 

 family is more correct on chemical principles than a distribution of them 

 under the several metals : and that as the salts of lime, magnesia, alu- 

 mina, are also salts of metals, the former fall naturally and chemically 

 into close associations with the latter, as in the system adopted. 



" Yet it is convenient to the chemist and to the metallurgist, to view 

 the ores of the several metals by themselves, and in general to be able to 

 survey at a glance the compounds of each element. For this purpose, the 

 following classification has been made out. Except in the metallic ores, 

 the mineral species have been kept together, as much as possible, in nat- 

 ural families, by taking into consideration the isomorphous relations of 

 the elements ; and it is believed that the classification here proposed 

 will be found to combine many of the more important advantages of 

 both systems. Chemists treat of the alums as a family, of the various 

 feldspars as another, and the varieties of hornblende and augite anoth- 

 er, and so on ; and instead of scattering them in the different parts of 

 a system, as was formerly done, arrange them together and treat of 

 them as distinct groups, although differing so much in chemical consti- 

 tution. These natural families are still retained in the method of ar- 

 rangement here brought forward." 



To this table are added the chemical formulas for composition, 

 derived from the most recent authorities.* The chemical sym- 

 bols, inasmuch as they speak more directly to the eye, have been 

 adopted in preference to the mineralogical, although printed with 

 more difficulty. 



The author has ingeniously substituted the black type (h, for 

 example) in place of the crossed letters used by Berzelius for 

 double atoms. 



An example of these new symbols for expressing a double 

 dose of base, is given in the formula for Haydenite in the present 

 article. It has the great advantage of being easily followed and 

 imitated, while the type introduced by Berzelius can only be had 

 at the expense of punches and matrices expressly made for the 



* Particularly from Rammelsberg's Handvvorterbuch der Chemischen Theils der 

 Mine.ralogie ; 2 vols. 8vo. pp. 442 and 326: Berlin, 1841 :— And, Erstes Supple- 

 ment, (first supplement to the same,) 8vo. pp.156: Berlin, 1843. This supple- 

 ment is to be continued biennially. 



