various important subjects in Mineralogy. %17 
dom, in order to enable us to study the productions of this king- 
dom in their purest state. There are minerals which occur in 
single individuals , others appear in connexion with several other 
individuals of the same description ; others, again, are connect- 
ed with such individuals as do not allow any agreement between 
them to be discovered in nature. In the first case, the indivi- 
duals are homogeneous ; they are not so in the last. These ex- 
pressions, however, can be made use of only after having previous- 
ly developed the idea of the natural-historical species. In con- 
formity with the differences here stated, minerals have been dis- 
tinguished into simple , compound, and mixed , minerals,- — a dis- 
tinction of the highest importance and utility, in rendering all 
the departments of Mineralogy mutually consistent. A very use- 
ful consequence of this distinction already is, that we may now fix 
upon those properties which the individuals or simple minerals 
possess, when occurring either alone, or in various compositions 
and mixtures, as those whose consideration should form the ob- 
ject of Natural History ; whereas we must exclude all those 
which depend upon, or are produced by, their composition, or 
intermixture with others ; in the same w r ay as, in Botany and 
Zoology, the systematic inquiries of naturalists are directed to- 
ward the properties of individuals. Hence, the Natural History 
of the mineral kingdom refers exclusively to simple minerals or 
individuals, and has nothing to do with compound or mixed va- 
rieties. Upon these considerations we must ground our ideas of 
what is called the Natural History of Hocks, in so far as these 
are compound or mixed minerals. It is only the consideration 
of the simple minerals contained in them that forms an object 
of Natural History, and it is on this account solely that rocks en- 
ter within the province of Mineralogy. Geology, therefore, and 
not this latter science, is that which considers the composition of 
minerals, and has to determine the classification of rocks, which, 
though logical, must not be conducted according to the princi- 
ples of Natural History, because whatever could be attained in 
this way, has already been elicited, or must be supposed to have 
been so. The idea of a Natural History of rocks different from 
Mineralogy, thus appears to be at variance with the meaning at- 
tached to the expression itself. 
In the same way in which the individual of the mineral king- 
