Mineralogy, according to the Principles of Professor MOHS. 309 



simple forms. With the same facility, we establish, from experi- 

 ence, a series of individuals, all of which appear under the form of 

 the hexahedron, but which present various colours, as honey-yellow 

 (Annaberg), wine-yellow (Freiberg), white (Alston), apple-green 

 (Beeralston), sky-blue (St Agnes), azure-blue (Alston). If now 

 we find an individual which possesses a dark violet-blue colour, 

 and whose form is the hexahedron, like some of those varieties 

 which have lately been found at Gourock, this individual may be 

 considered as a member of the first series, and also, at the same 

 time, as a member of the second series ; and all the individuals 

 constituting the one will thus be brought under the idea of iden- 

 tity with all the individuals of the other ; so that we are now en- 

 titled to consider as identical not only those combinations of 

 form and colour which we have really observed, but also those 

 which may be obtained by joining arbitrarily any form, or any 

 colour, of the two series with each other. The varieties thus 

 produced are in fact very frequently likewise observed in nature. 

 According to the same principle, we may extend our considera- 

 tions to all those properties of minerals whose gradations form 

 series, and include an assemblage of individuals, which, notwith- 

 standing their differences, may yet be brought under the idea of 

 identity. Those individuals to which the process is not appli- 

 cable, are, at the same time, distinctly and accurately excluded ; 

 and the assemblage produced does not only contain every 

 thing that can possibly be united with it, but, at the same time, 

 every thing is distinctly excluded, which must be considered to 

 be foreign to it, according to the principles of natural history, .-/u 

 These assemblages of individuals, connected by the gradations 

 of their properties, in the same series, are designated in minera- 

 logy by the name of Species. The individuals comprehend- 

 ed, are intimately connected, and, at the same time, distinct- 

 ly separated, by these series of characters from aU the others. 

 A species may therefore be defined to be the assemblage of indi- 



