PREFACE. IX 



cile pursuit by the discovery of even the occasional use of 

 unintelligible language in a professedly elementary treatise 

 of its principles. 



The natural-historical arrangement of the species is 

 principally that brought forward by MOHS. I have never- 

 theless ventured, though not without considerable hesita- 

 tion, to propose a number of alterations, which will be ob- 

 vious on a comparison of the two systems. In making 

 these changes, I have endeavored so to constitute the ge- 

 nera that the species of each should be bound together by 

 a similar amount of resemblance. If in the execution of 

 this difficult task, I have not violated the affinities of the 

 species, an important advantage will have been secured in 

 the simplification of the nomenclature by the great reduc- 

 tion of genera, especially in the orders, Ore, Pyrites, 

 Glance and Blende. 



The formation of the new order, Picrosmine, appeared 

 to be indispensable in providing a place for a number of spe- 

 cies, which MOHS had declined incorporating with his sys- 

 tem from their deficiency in regular forms. The produc- 

 tion of the genus Lusine-Ore was rendered necessary for 

 a similar reason, in order to receive such species of the re- 

 quisite structure and specific gravity, as are believed to 

 owe their formation to the decomposition of other species. 

 The above mentioned writer does not allow such minerals, 

 provided they are in a friable state, to constitute distinct 

 species; remarking of them, that "it is in direct opposition 

 to the principles of Natural History, to consider decompo- 

 sed varieties of one species as varieties of another." To 

 the correctness of this as a general rule I readily assent, 

 allowing it full force when the resulting mass is not homo- 



B* 



