646 



existence even of trachyte has not yet been 

 verified in the Sierra Nevada de Merida, which 

 links the Andes with the chain of the shore of 

 Venezuela. It would seem as if the volcanic 

 fire, after the formation of primitive rocks, 

 could not pierce into eastern America (Vol. vi, 

 p. 583). Perhaps the little wealth, and the 

 little frequency of argentiferous veins observed 

 in those countries, arises from the absence of 

 more recent volcanic phenomena*. M. d'Esch- 

 wege saw at Brazil, some layers (veins?) of 

 diorite, but neither trachyte, basalt, dolerite, 

 nor amygdaloid e ; and he was therefore more 

 surprised to see, in the vicinity of Rio Janeiro, 

 an insulated mass of phonolithe, entirely similar 

 to that of Bohemia, pierce the gneiss soil-f-. I 

 am inclined to believe that America, on the 

 east of the Andes, would have burning volcanos 

 if, near the shore of Venezuela, Guyana, and 

 Brazil, the series of primitive rocks were inter- 

 rupted trachytes. The trachytes, by their fen- 

 dillation, and open crevices, seem to establish 

 that permanent communication between the 

 surface of the soil and the interior of the globe, 

 which is the indispensable condition of the 

 existence of a volcano. If we direct our course 

 from the coast of Paria, by the gneiss-granite 



* See my geogn. Essay, p. 118, 120. 



t Manuscript notes of Baron d'Eschwege. 



