436 cosmos. 



character in regard to the composition and association of 

 their mineral aggregate. On the great transverse fissure 

 which, extending from sea to sea almost entirely in a direc- 

 tion from west to east, intersects a chain of mountains, or, 

 more properly speaking, an uninterrupted mountainous swell, 

 running from southeast to northwest, the volcanoes occur in 

 the following order: Colima (13,003 feet), Jorullo (4265 

 feet), Toluca (15,168 feet), Popocatepetl (17,726 feet), and 

 Orizaba (17,884 feet). Those situated nearest to each other 

 are dissimilar in the composition which characterizes them, 

 a similarity of trachyte occurring only alternately. Colima 

 and Popocatepetl consist of oligoclase, with augite, and con- 

 sequently have the trachyte of Chimborazo or Teneriffe; 

 Toluca and Orizaba consist of oligoclase with hornblende, 

 and consequently have the rock of ^Egina and Kozelnik. 

 The recently-formed volcano of Jorullo, which is scarcely 

 more than a large eruptive hill, consists almost alone of 

 scoriaceous lavas, resembling basalt and pitch-stone, and 

 seems more like the trachyte of Toluca than that of Colima. 

 In these considerations on the individual diversity of the 

 mineralogical constitution of neighboring volcanoes, we find 

 a condemnation of the mischievous attempt to introduce a 

 name for a species of trachyte, derived from a mountain 

 chain, chiefly volcanic, of more than 7200 geographical miles 

 in length. The name of Jura limestone, which I was the 

 first to introduce,* is unobjectionable, because it is taken 

 from a simple unmixed rock — from a chain of mountains 

 whose antiquity is characterized by its containing organic 



* In the course of a geological tour which I made, in 1705, through 

 the south of France, western Switzerland, and the north of Italy, I 

 had satisfied myself that the Jura limestone, which Werner reckoned 

 among his muschel-kalk, constituted a peculiar formation. In my 

 treatise on subterranean gases, published by my brother, Wilhelm von 

 Humboldt, in 1799, during my residence in South America, tbis 

 formation, which I provisionally designated as Jura limestone, was for 

 the first time mentioned (s. 39). This account of the new formation 

 was immediately transferred to the Oberbergrath Karsten's mineral- 

 ogical tables, at that time so generally read (1800, p. 64, and preface, 

 p. vii.). I named none of the petrifactions which characterize the 

 Jura formation, and in relation to which Leopold von Buch has ac- 

 quired so much credit (1839) ; I erred likewise in the age ascribed by 

 me to the Jura formation, supposing it to be older than muschel-kalk, 

 on account of its propinquity to the Alps, which were considered older 

 than Zechstein. In the earliest tables of Buckland, on the Superpo- 

 sition of Strata in the British Islands, the Jura limestone of Humboldt 

 is reckoned as belonging to the upper oolite. Compare my Essai 

 Gcoyn. sur le Gisement des Bodies, 1823, p. 281. 



