Introduction to the Study of Mineralogy . 399 



principle ? Where can we find differences more striking, 

 between the same substances, than those which depend upon 

 principles peculiar to each ? Now, when we classify the 

 substances of one and the same kingdom, we establish a 

 continued comparison between them, according to the re- 

 lations which connect and the differences which separate 

 them. This comparison will therefore be the most exact, 

 and at the same time the most natural possible, and the 

 least arbitrary, if the method chosen for establishing it is 

 that which unveils to us the intimate composition and foun- 

 dation of each substance, which teaches us what it is in it- 

 self, rather than that which only shows us the outlines, or 

 perhaps the external effects. 



We may remark, before going further, that there are in 

 the present case two problems to solve. The first consists in 

 dividing and subdividing the collection of substances which 

 a system should embrace, so that each may hold its true 

 place. This is called classifying. The second has for «its 

 object the furnishing of easy and convenient methods for 

 characterizing each substance in such a manner that we may 

 ascertain it, wherever it presents itself, and discover in the 

 system the place which has been assigned to it. The solution 

 of the first of these problems is the sole object at present. 



Let us now examine what are the resources presented to 

 us by the present state of science, in order to attain this ob- 

 ject. Among the minerals which in the common methods- 

 compose the class of stones, there are several in which ana- 

 lysis has demonstrated the presence of an acid combined 

 with an earth. Such are the calcareous carbonate of the 

 modern chemists, calcareous filiate, barytic sulphate, &c. 

 Other substances, such as the emerald, topaz, garnet, 8cc. r 

 have only presented earths combined with each other, and 

 sometimes with an alkali. We shall for a moment lav- 

 aside these last substances, in order to speak of those which 

 contain an acid in their composition. 



Here an important consideration presents itself relative to 

 the distribution of these compounds. The modern chemist?, 

 in 'forming the table of the results of that new.system whicri 



changed 



