132 CLASSIFICATION. 



excluded with perfect distinctness and accuracy. An assemblage 

 of individuals, formed in this way, does not contain any thing for- 

 eign, nor does it want any thing capable of being united with it on 

 account of its natural properties. 



. 105. DIFFERENCE. 



Individuals which do not agree in all their properties are 

 not identical. 



If two individuals agree in every one of their properties, except 

 in their crystalline forms, or in color, or in hardness, or in specific 

 gravity, so as to differ only in one of these properties, nevertheless 

 they will not be identical. For the above properties are natural 

 properties, and upon them depends the identity or difference of in- 

 dividuals. 



The present proposition, being the reverse of . 104, like that, 

 requires some limitation. 



Accidental differences have no more effect upon the difference of 

 individuals than upon their identity. 



Difference between individuals is produced not by a difference in 

 the crystalline form, unless the forms belong to different series of 

 crystallization; nor in either or all of the remaining properties, if 

 individuals are known to exist capable of filling up the difference by 

 regular gradations. 



. 106. SPECIES. 



An assemblage of individuals, which fall under the idea 

 of identity, is termed a species, and the individuals belong- 

 ing to it are homogeneous individuals. 



This may be said to furnish an invariable idea of the species in 

 mineralogy; one which remains constant in all sciences which con- 

 cern the productions of the mineral kingdom. It is the foundation 

 of every system, whatever may be the principles followed in its 

 construction. Its correct determination is an object of the highest 

 consequence, since it is the fixed point from which every inquiry 

 has to start, whose object it is to procure some knowledge of the 

 mineral kingdom, of whatever kind this knowledge may be, 



