645 



spathic rock, in which we find some crystals of 

 amphiboly but pyroxene very rarely, and never 

 any olivine. The Cerro of Flores is a hill co- 

 vered with tabulary blocks of greenish grey 

 phonolithe, inclosing long crystals (not fendi- 

 lated), of vitrous feldspar, altogether analogous 

 to the phonolithe of Mittelgebirge. It is sur- 

 rounded by pyroxenic amygdaloide ; it would 

 no doubt be seen in the depth, issuing imme- 

 diately from gneiss-granite, like the phonolithe 

 of BUiner Stein in Bohemia, which contains, 

 fragments of gneiss stu^k into the mass. 



Does there exist in South America another 

 group© of rocks, designated preferably by the 

 name of volcanic rocks, and which are as dis- 

 tinct from the chain of the Andes, and advance 

 as far towards the east, as the groupe that 

 bounds the steppes of Calabozo ? Of this I 

 doubt, at least in that part of the continent 

 situated to the northward of the Amazon, I 

 have often directed the attention of geognosts 

 to the absence of pyroxenic porphyry, trachyte, 

 basalt, and lavas (I range these formations 

 according to their relative age), in the whole 

 of America eastward of the Cordilleras. The 



generally above the basalts; and the extraordinary deve- 

 lopement of feldspar in that union, and the want of pyrox- 

 ene have always appeared to me very remarkable pheno- 

 mena. 



