VI INTRODUCTION. 



as it is found in very variable quantities, and is not considered as 

 essential. For what is known of the species added to the list of 

 organic compounds, see the 2d, 5th, 6th, and 7th Supplements to 

 Dana's Mineralogy. For changes in the systems of crystallization, 

 Des-Cloizeaux has generally been the authority. 



A table of the symbols used, with illustrations of the meaning 

 of the formulsB, are given on p. vii., and on p. ix. will be found a 

 table relating to the systems of crystallization. In the first column 

 are the simple forms from which all the others, of the same system, 

 are derived ; in the second the description of the axes of these 

 simple forms, and in the others the nomenclature that has been 

 adopted by the authors whose names stand at the head of the 

 column. The axes of a crystal are imaginary lines drawn through 

 its centre and about which it is symmetrical. It has been found 

 most convenient to refer to the systems of crystallization by the 

 numbers which have been placed on the left hand of the table. 



An asterisk following the name of a mineral, as Gold* p. 1, 

 denotes that it has been found in the United States. A dagger, 

 as Danbunte,1[ p. 14, denotes that it has been found in the United 

 States only. The other minerals have not, so far as is known, 

 been found in this country. 



T. EGLESTON. 



New Yoek, May, 1863. 



