224 Baron Humboldt 07i the Stnicture and Action of 



into cliffs ; trachyte, rich in vitreous felspar, rises into domes. 

 In the most distant zones, large crystals separate similarly, 

 as by an internal development, from the compact texture of 

 the primitive mass, form themselves into groups, appear as 

 subordinate masses, and often announce the vicinity of indepen- 

 dent new formations. In this manner the whole inorganic world 

 is evidently pictured in every mountain chain of any extent. 

 To become perfectly acquainted, however, with the most im- 

 portant phenomena of the composition, relative age, and origin 

 of the formations, it is necessary to compare, with each other, 

 observations made in countries the most widely separated, pro- 

 blems which have long seemed enigmatical to geologists living in 

 the north, find their solution near the equator. If, as has been 

 observed, the distant zones do not furnish us with new forma- 

 tions, that is to say? unknown groups of simple substances, they 

 yet enable us to understand the uniform laws of nature, by 

 which the various strata support each other, penetrate into each 

 other'*s substance in the form of veins, or raise each other in 

 obedience to elastic powers. 



If it be true that our geognostical knowledge derives the 

 greatest advantage from researches made over vast expanses of 

 country, it ought not to excite surprise that the class of pheno- 

 mena which forms the principal object of this memoir should, 

 till lately, have been examined in a very imperfect manner, be- 

 cause the points of comparison are very difficult, and may even 

 be said laborious, to find. Until the end of the eighteenth 

 century, all that was known of the form of volcanoes, and of the 

 action of their subterranean powers, was derived from two moun- 

 tains in the south of Italy, Vesuvius and Etna. The former 

 being the most accessible, and, like all volcanoes of inferior ele- 

 vation, having more frequent eruptions, a small hill became, in 

 some measure, the type according to which a whole distant 

 world was represented, containing the great volcanoes of Mexi- 

 co, South America, and the Asiatic Isles. This mode of rea- 

 soning might naturally bring to our recollection Virgil's shep- 

 herd, who, in his humble cabin, imagined he saw the image of 

 the eternal city. 



An attentive examination of the whole Mediterranean, espe- 

 cially its islands and eastern shores, where the human race has 



