432 REACTION OF THE INTERIOR OF THE EARTH 



Jurassic formation." The same mixtures of oligoclase 

 and hornblende which I have seen in the Aztec high- 

 lands (in Anahuac properly so called), but not in the 

 Cordilleras of South America, are also found far to the 

 westward of the Eocky Mountains and of Zurti, near 

 the Mohave Eiver, a tributary of the Eio Colorado. (See 

 Marcou, " Eesume of a Greological Eeconnaissance from 

 the Arkansas to California, July 1854," pp. 46 48 ; and 

 also two important French Memoirs entitled, " Eesume 

 explicatif d'une Carte Geologique des Etats-Unis, 1855," 

 pp. 113 and 116, and "Esquisse d'une Classification des 

 Chaines de Montagues de 1'Amerique du Nord, 1855;" 

 "Sierra de San Francisco et Mount Taylor," p. 23.) 

 Among specimens from Java, which I owe to the kind- 

 ness of Dr. Junghuhn, we have also recognised trachytes 

 belonging to the " third division," from three volcanic 

 districts; those of Burung-agung, Tjin-as, and Grunung 

 Parang (in Batugangi). 



Fourth Division.- "The ground-mass contains augite 

 with oligoclase. To this division belong the Peak of 

 Teneriffe ( 602 ), the Mexican volcanoes Popocatepetl ( 603 ), 

 and Colima ; the South-American volcanoes Tolima 

 (with the Paramo de Euiz), Purace near Popayan, Pasto 

 and Cumbal (according to the fragments collected by 

 Boussingault), Eucu-Pichincha, Antisana, Cotopaxi, 

 Chimborazo ( 604 ), Tungurahua, and the trachyte-rocks 

 which are covered with the ruins of old Eiobamba. In 

 Tungurahua we also find, with the augites, some blackish 

 green uralite crystals, from half a line to five lines long 

 (from about one twentieth of an inch to half an inch), 

 with perfect augite-shape and the planes of cleavage of 

 hornblende. (See Eose, Eeise nach dem Ural, Bd. ii. 



