SUCCESSION AND RELATION OF LAVAS IN THE 

 GREAT BASIN REGION 1 



richthofen's studies 

 The Great Basin was early recognized as showing a variety 

 of Tertiary lavas which are identical over large areas, and 

 erupted in somewhat the same succession. The first deductive 

 studies from these facts were made by the Baron von Richt- 

 hofen, 2 and were published in 1867. Partly as a result of obser- 

 vations in the rocks of the Great Basin and of California, and 

 partly from studies in the volcanic regions of Europe, Richt- 

 hofen arrived at what he considered to be the natural law for 

 the sequence of massive eruptions, applicable to all centers of 

 volcanic activity. According to him the order of succession was : 



1. Propylite. 



2. Andesite. 



3. Trachyte. 



4. Rhyolite. 



5. Basalt. 



This law of succession was accepted without much question 

 for a long time by many European and American geologists. 



THEORIES OF THE ORIGIN OF IGNEOUS ROCK DIFFERENCES 

 PREVIOUS TO RICHTHOFEN 3 



By way of summarizing briefly the difference between 

 Richthofen's theories and those of his predecessors, it may be 

 remarked that Bunsen, who was one of the first to speculate 

 concerning rock differences, after visiting Iceland and studying 

 the volcanic phenomena, formed the hypothesis of two distinct 

 magmas or bodies of lavas, one acid, and the other basic ; 

 the normal " trachytic " and the normal "pyroxenic" magmas, 



'Published by permission of the Director of the United States Geological Survey. 

 2 "Natural System of Volcanic Rocks," Mem. California Acad. Sci., Vol. I, p. 36. 

 3 See Monograph XX, U. S. Geol. Surv., p. 273. 



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