CONTENTS. Xlll 



Mineralogical composition of volcanic rocks ; generalisation of the 

 term "trachyte," p. 428 ; Classification of trachytes, in respect to 

 the association of their essential ingredients, into six groups or 

 divisions, according to the determinations of Gustav Rose ; and 

 geographical distribution of these groups, pp. 429-434 ; names 

 of andesite and andesine, pp. 428, 436, and Note 609. Besides the 

 characteristic ingredients of trachyte formations, there are also 

 non-essential ones, whose frequency or constant absence in 

 different but often neighbouring volcanoes deserve great atten- 

 tion, p. 437 ; mica, p. 438 ; glassy felspar, p. 439 ; hornblende 

 and augite, pp. 439, 440 ; kucite, pp. 440, 441 ; olivine, pp. 441, 

 442 ; obsidian (and debate respecting the formation of pumice), 

 pp. 443-448 ; Subterranean pumice-stone quarries, separate from 

 volcanoes, at Zumbalica, in the Cordilleras of Quito, at Huichapa, 

 in the Mexican highland, and at Tschegem, in the Caucasus, 

 pp. 319-323 ; Diversity of conditions under which the chemical 

 processes of volcanic action proceed in the formation of the 

 simple minerals, and their association in trachytes, pp. 437, 447, 

 448. 



RECTIFICATIONS AND ADDITIONS ... . . . pp. 449-452 



EDITOR'S NOTES 453-516 



AUTHOR'S NOTES . i-clxxiii 



INDEX , clxxv 



