VIII PREFACE. 



marks on crystallographic subjects, or on the his- 

 tory of the species. Here the species are also com- 

 pared with the determinations and divisions into 

 sub-species and kinds, as contained in the Werne- 

 rian system, which will enable the reader not only 

 to understand the principles of these divisions, but 

 also to form an idea of their contents in reference to 

 the varieties occurring in nature. These distinctions 

 are not susceptible of strictness and precision; the 

 only purpose, therefore, in treating of them, is to 

 convey the ideas with brevity and distinctness. 



Then follow some of the chemical properties of 

 the species, as exhibited before the blowpipe, or 

 when acted upon by acids, &c., and one or more 

 analyses, instituted by the most celebrated chemists, 

 in many cases accompanied by the formulae and cor- 

 responding proportions among the ingredients, as 

 proposed by BERZELIUS. To Professor MITSCHER- 

 LICH the translator is indebted for several interesting 

 facts regarding the circumstances under which cer- 

 tain species still continue to be formed or may be 

 produced at will, in laboratories and furnaces. 



In the third place, something of the geological 

 position of the species is mentioned ; it does not 

 contain every thing known in this respect, but only 

 so much as will suffice for giving a general idea of 

 the modes of occurrence in nature, peculiar to the 

 species. 



