THE VOLCANIC ROCKS OF THE ANDES. 



Through the excellent work of Dr. Richard Kiich, ^ who has 

 recently published the results of his investigation of the rocks 

 collected by Reiss and Stiibel in Colombia, we are put in 

 possession of some important conclusions regarding the character 

 of all the volcanic lavas of the South American Andes. Most of 

 these conclusions are pointed out by Dr. Kiich in the work cited; 

 to these the present writer wishes to add a few not heretofore 

 noted. 



In order to appreciate the value of Kiich's work, it should be 

 observed that it was carried on upon the very extensive material 

 collected by Reiss and Stiibel during a prolonged exploration of 

 the high mountainous regions of South America, in which they 

 visited Colombia, Ecuador, Bolivia, Peru and Chili and brought 

 away with them 1 8,000 specimens. In some places as many as 

 800 were collected, in others much fewer ; for, as Reiss observes 

 in the introduction to the volume upon Colombia, many of the 

 mountains are well nigh inaccessible, their bases being covered 

 with dense forest, and their summits hidden beneath snow and 

 glaciers, and shrouded with clouds the greater part of the year. 

 This is equally true of the Cordilleras farther south, so that the 

 exploration of the region is attended with great difficulties. And 

 while it is not claimed that the collections are complete, they must 

 certainly be taken as representatives of the whole of the Andes. 



The volcanoes of Colombia chiefly occur along the crest of the 

 central range, rising above crystalline schists, and eruptive masses 

 in the Cretaceous formation, whose upturned strata compose 

 the ranges east and west of the central Cordillera. Hereto- 

 fore, with few exceptions, the volcanic rocks examined have 



' W. Reiss and A. Stiibel: Reisen in Siid - Amerika. Geologisclie Studien in der 

 Republik Colombia, I. Petrographie. i. Die \^ulkanisclien Gesteine bearbeitet von 

 Riciiard Kiich. Berlin, 1892. 



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