332 
Mohs' System of Crystallogreiphy 
in treating mineralogy ! W erner's natural historical genera (his 
Sippschaften ) are not, however, capable of being used; partly be- 
cause the species are not correctly fixed, and partly because the 
chemical genera have prevented the junction of congruous spe- 
cies. This latter circumstance is the reason of there being so 
few natural historical genera in the class of metallic fossils. 
46. Universal application of genus . genera compre- 
hend only one species ; but no genera are to be found, (as in 
Karsten’s Tables,) which do not comprehend any species. In- 
deed a consistent and regular system can comprehend no species 
without including it .under some genus ; though that genus 
should even be the only one of its order (51). The idea of 
genus must, therefore, be applied over the whole mineralogical 
system. 
47. Series of genera . — The reason why no series of species 
are to be found, in examining the productions of inorganic na- 
ture, lies in this circumstance, that, several of those species as- 
sume at once the same position, and form groups (40.) These 
groups are the natural historical genera. Hence the mineral Mng-^ 
dom consists of a series erf natural historical Genera., every one 
of which comprehends similar Species (41.), every species, in like 
manner, comprehending homogeneous Individuals (25.) The 
conception of the mineral kingdom is by this means made more 
distinct. 
48. Genus and Species are the essential steps of Classifica- 
tion . — From these considerations, it follows, that genus and 
species form the two essential steps of classification in the mine- 
ral kingdom : in other words, they are the only means neces- 
sary to be used for obtaining a distinct representation of that 
kingdom. But the mineralogical system, in order to be appli- 
cable to nature, (that is, to the distribution of minerals, as 
plants are usually distributed,) requires some more extensive 
groups to be presented ; and for this purpose, the degrees of 
similarity yet remaining may properly be used. 
49. Foundation of greater Groups or Collocations . — Select 
any genus from the mineral kingdom; say that to which pyrites be- 
longs. It has already been produced as an example (43.) So far 
as we yet know, it consists of three species. The first is common 
pyrites, tlie second includes radiated, hepatic and cristated pyrites, 
