INTRODUCTION. Vll 



as the eleventh ; while in fact they merely differ in colour. 

 In the magnesian division, what are bole, fullers' earth, &c. 

 but different modifications of the same mixtures ? Mr. Kir- 

 wan presents no exact arrangement, but uses Classes, Fami- 

 lies, and Branches, in such a manner as greatly to perplex the 

 reader : but all his species and families are mere modifications, 

 and the simple division into modes would convey a far 

 clearer idea*. 



The term Mode is therefore here adopted instead of what 

 are called Genera by some writers, and Species by others ; this 

 uncertainty, of itself, having demonstrated that there are 

 neither Genera nor Species in mineralogy. 



But as it is now universally allowed by all mineralogists, Chemical, 

 however different their systems, that the whole science rests 

 upon chemistry alone, and that no certainty can be found ex- 

 cept by chemical analysis, the word Mode, as finally admitted 

 into the present system, must be chiefly understood to refer 

 to the CHEMICAL MODE OF COMBINATION, upon which the 

 nature of the substances, as is now allowed by the greatest 

 chemists, is yet more dependent, than even upon the ingre- 

 dients combined. It is the MODE OF COMBINATION which 

 distinguishes a diamond from carbon, and a sapphire from 

 argil combined with a little iron : the essence of a mineral 

 consisting not only in the constituent earths, but in the pe- 

 "iliar way in which the mixture is modified ; and this modal 

 influence also prevails in many artificial mixtures and com- 

 pounds f. In short, the pretended species of former authors 

 are merely different MODES OF COMBINATION. 



* Dr. Thomson, in his valuable Chemistry, has preferred the families of 

 Werner, and discarded the old genera; iv. 247. Mr. Jameson tells us that 

 there is in fact only ONE species in mineralogy, namely the globe ; but even this 

 may be doubted till it shall have produced another at least, as round and as 

 wicked. 



j* Tliis may be exemplified from the Arragon spar, in which the ingre- 

 dients are the same as in calcareous spar, yet it differs in many properties, not 

 from composition but from modification, the gangart of red clay or gypsum pro- 

 bably imparting a tincture of iron. 



