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of the problem in question. In one of these 

 solutions, the phonolite of the Cerro de Flores 

 is to be regarded as the sole volcanic production 

 of the tract ; and we are forced to unite the 

 pyroxenic amygdaloids with the rest of the 

 gruensteins in one single formation, that which 

 is so common in the transition mountains of 

 Europe, considered hitherto as not volcanic. In 

 the other solution of the problem, the masses of 

 phonolite, amygdaloid, and gruentfein, which 

 are found to the South of the ravine of Piedras 

 Azules, are separated from the gruensteins and 

 serpentine rocks, that cover the declivity of the 

 mountains North of the ravine. In the present 

 state of knowledge, I find difficulties almost 

 equally great, in adopting either of these suppo- 

 sitions : but I have no doubt, that, when the real 

 gruensteins (not the hornblende gruensteins) 

 contained in the gneiss and mica- slates, shall 

 have been more attentively examined in other 

 places ; when the basaltes (with pyroxene), 

 forming strata in primitive rocks % and the 

 diabases and amygdaloids in the transition 

 mountains, shall have been carefully studied ; 

 when the texture of the masses shall have been 

 subjected to a kind of mechanical analysis, and 



* For instance, at Krobsdorf in Silesia, a stratum of 

 basaltes has been recognized in the mica-slate by two 

 celebrated geognosts, Messrs. von Buch and Raumer. (Torn 

 Granit des Riesengtbirges, 1813, p. 70.) 

 VOL. IV. U 



