SECTION XII. 



ON THE APPLICATION OF THE TABLES 

 OF MODIFICATIONS. 



THE preceding- tables of modifications are adapted 

 principally to two purposes. The first is, by the re- 

 marks they contain upon the comparative characters 

 of the secondary forms belonging to the different 

 classes of the primary, to assist the mineralogist in 

 determining the primary form of any mineral from an 

 examination of its secondary forms. And the second 

 is to enable him to describe any secondary crystal, 

 whose primary form is known. An attempt is thus 

 made to supply a language, by means of which the 

 secondary forms of crystals may be described inde- 

 pendently of the theory of decrements, and without 

 the assistance of mathematical calculation. 



The remarks upon the comparative characters of 

 the secondary forms, may not however be sufficient 

 to lead the observer from the secondary to the pri- 

 mary form of a mineral, without the assistance of a 

 few general rules. 



And although I cannot flatter myself that the slight 

 outline I am about to trace of the method of reading 

 crystals, will enable a person at once to refer any 

 given secondary crystal to its primary form, it will 

 nevertheless afford him a useful clue to the discovery 

 of that form. 



The first step in the process of determining the 

 mineral species to which any given secondary crystal 



