480 Plutonic Rocks of tlie Cordillera, paut el 



450 miles, I found it under most of the axes of elevation ; 

 in a collection of specimens from the Cordillera of Lima 

 in Peru, I immediately recognised it ; and Erman ■ 

 states that it occurs in eastern Kamtschatka. From 

 its wide range, and from the important part it has 

 played in the history of the Cordillera, I think this 

 rock has well deserved its distinct name of andesite. 



The few still active volcanos in Chile are confined 

 to the central and loftiest ranges of the Cordillera ; and 

 volcanic matter, such as appears to have been of sub- 

 aerial eruption, is everywhere rare. According to 

 Meyen, 2 there is a hill of pumice high up the valley 

 of the Maypu, and likewise a trachytic formation at 

 Colina. a village situated north of St. Jago. Close to 

 this latter city, there are two hills formed of a pale 

 feldspathic porphyry, remarkable from being doubly 

 columnar, great cylindrical columns being subdivided 

 into smaller four or five sided ones ; and a third hillock 

 (Cerro Blanco) is formed of a fragmentary mass of 

 rock, which I believe to be of volcanic origin, inter- 

 mediate in character between the above feldspathic 

 porphyry and common trachyte, and containing needles 

 of hornblende and granular oxide of iron. Xear the 

 Baths of Cauquenes, between two short parallel lines of 

 elevation, where they are intersected by the valley, there 

 is a small, though distinct volcanic district ; the rock 

 is a dark grey (andesitic) trachyte, which fuses into a 

 greenish-grey bead, and is formed of long crystals of 

 fractured glassy albite (judging from one measurement) 

 mingled with well-formed crystals, often twin, of augite. 

 The whole mass is vesicular, but the surface is darker 

 coloured and much more vesicular than any other part. 

 This trachyte forms a cliff-bounded, horizontal, narrow 



1 Geosraph. Journal,' vol ix. p. 510. 



2 Reise urn Erde,' Th. 1, SS. 338 und 362. 



