CLASSIFICATION. 135 



Besides the natural and the artificial systems, there exists a va- 

 riety of classifications which cannot be included under these heads ; 

 such as the arrangement of the species in an alphabetical order, 

 which, being founded upon the name, possesses no real relation with 



The degrees of resemblance among the properties in different species 

 are not every where the same. We consider the species as varieties to 

 be classified, and compare them with each other in respect to their prop- 

 erties. We perceive that some of them are more, some of them less 

 allied to each other in resemblance. Common Iron Pyrites, for exam- 

 ple, is more similar to while Iron Pyrites than to Carbonate of Lime; 

 the latter species again is more similar to Arragonite than to Feldspar. 



An assemblage of species united by the highest degree of resemblance 

 in its properties is termed a GENUS. The species of Iron Pyrites 

 agrees so closely with that of white Iron Pyrites,, in every character 

 except that of forms, that but for this difference, the two species would 

 coalesce. Here is an example of that degree of resemblance which 

 forms a genus. The same degree of resemblance exists between Eu- 

 clase and Emerald. In the case of Idocrase, Garnet, and Stauro'.ide, we 

 observe differences in many characters at once, and yet the resemblance 

 is seen to be as great as in the examples of Iron Pyrites and Emerald. 

 These examples prove, that there may exist differences, sometimes only 

 in a few, sometimes in many characters at a time, without having any 

 influence upon the degree of resemblance itself. On this account, it 

 becomes impossible to express this resemblance by the agreement in one 

 or a certain number of characters. This, however, does not prevent 

 the application of the idea of the genus to these natural productions alto- 

 gether; for this application does not pre-suppose the idea to be limited 

 to single characters; but it allows, and even requires, to preserve it in 

 its full generality. 



The genera being thus founded upon the resemblance of the species 

 constitute a series, which it is clearly impossible should be the ca?e with 

 the species themselves. To convince ourselves of this, we have only to 

 attempt a series of species, in which those placed nearest, must (of 

 course,) resemble each other most, and where we may begin at any 

 chosen member. In forming such a series, we very soon me-et with spe- 

 cies, which render it doubtful whether the one or the other, or even a 

 third or fourth, &c. should follow the preceding species, and at last, we 

 must either entirely abandon the experiment, or we must suppose, that 

 two, three, or more species occupy the same place in the series. The 

 groupes of species thus formed, however, are the genera themselves in 

 a Natural system; in the real existence of which we discover the fact, 



