of Mineral Species. 113 



extensive series of the minerals in question, they require the 

 joint efforts of mineralogical inquiry, for ascertaining the species 

 which have been destroyed, and those which have been formed ; 

 of chemical examination, for ascertaining the difference in the 

 ingredients of the two ; and of geological observation of the spe- 

 cimens in their natural repositories, in order to establish the 

 causes by which the chemical affinities, balanced by the forma- 

 tion of the original compounds, have again entered into action. 



From the preceding enumeration, it is but too evident, that 

 our knowledge of the facts, as well as of their causes, up to this 

 moment is scanty and imperfect. A wide field of research is 

 still open, promising a fair return for the labour^ naturalists may 

 bestow upon its cultivation. I have endeavoured to collect on- 

 ly some of the most remarkable and familiar instances of the 

 changes which may take place in the solid body of a crystal, the 

 ulterior study of which, while it illustrates the idea of species, 

 will throw some light also on the causes of such alterations as 

 do not appear conformable to the known laws of chemical affi- 

 nity, for which we cannot account at least in the present state of 

 our information. 



VOL. XI. PART I. 



