ORDER VI. PARATOMOUS AUGITE-SPAE. 71 



Mr PHILLIPS, with the reflective goniometer, tte ang!e of 

 (Pr + cc) 3 is = 87 5'. It will be interesting to ascertain 

 how far the inclination of the axis extends to the forms of 



Pr - 

 the present species. The incidence of on Pr+ is stat- 



2 it 



ed in Augite by Mr PHILLIPS = 105 20', that of _ 



on Pr + cc = IOC 3 15'. But the inclination of the two faces 



p 

 of is given = 120 38', and the same inclination in 



also = 120 38'. ?? on (Pr + as) 3 = 100 10'. 



The present species unites a large number of varieties, 

 both simple and compound, among which there exist un- 

 interrupted transitions ; and for this in particular it be- 

 comes a most important subject in the study of Minera- 

 logy ; and, above all, for ascertaining the idea of the natu- 

 ral-historical species. But it is at the same time remark- 

 able for the high degree of resemblance which it bears to 

 the remaining species comprised within the same genus, 

 particularly those of which a great many different va- 

 rieties have been discovered ; and thus it likewise demon- 

 strates the existence of the natural-historical genus in 

 Mineralogy, which is formed by uniting those species, 

 which, notwithstanding their marked differences from 

 each other, are yet united by the highest degrees of 

 resemblance. Hence, on one hand, the difficulties be- 

 come evident which arise from dividing one species into 

 several ; on the other hand, the easiness with which they 

 may be confounded, if their characteristic properties be not 

 properly attended to, of which but too many examples 

 might be quoted from the writings and collections of che- 

 mists and mineralogists. A close examination, according 

 to the principles of Natural History, will prevent us from 

 falling into the same errors. The most ancient of those 

 species which have been distinguished within the species of 

 paratomous Augite-spar is Augite, which comprehends al- 

 most exclusively opake varieties, the colours of which are 

 black or blackish-green. One of its subdivisions; foliated 



