400 AMYGDALOID AND PHONOLT. 



this superiority in number, the organic fossil world furnishes, 

 in every latitude, a further analogy with the inter-tropical 

 shells that now live at the bottom of the ocean. In fact, 

 M. Defrance, in a work* full of new and ingenious ideas, not 

 only recognizes this preponderance of the univalves in the 

 number of the species, but also observes, that out of 5500 

 fossil univalve, bivalve, and multivalve shells, contained in 

 his rich collections, there are- 3066 univalve, 2108 bivalve, 

 and 326 multivalve ; the univalve fossils are therefore to 

 the bivalve as three to two. 



XIII. FORMATION OF PYROXENIO AMYGDALOID AND 

 PHONOLITE, BETWEEN ORTIZ AND CERRO DE FLORES. I 

 place pyroxenic amygdaloid and phonolite (porphyrschiefer) 

 at the end of the formations of Venezuela, not as being 

 the only rocks which I consider as pyrogenous, but as 

 those of which the volcanic origin is probably posterior 

 to the tertiary strata. This conclusion is not deduced 

 from the observations I made at the southern declivity 

 of the littoral Cordillera, between the Morros of San Juan, 

 Parapara, and the Llanos of Calabozo. In that region, 

 local circumstances would possibly lead us to regard the 

 amygdaloids of Ortiz as linked to a system of transition 

 rocks (amphibolic serpentine, diorite, and carburetted slate 

 of Malpasso); but the eruption of the trachytes across rocks 

 posterior to the chalk (in the Euganean Mountains, and 

 other parts of Europe), joined to the phenomenon of total 

 absence of fragments of pyroxenic porphyry, trachyte, basalt, 

 and phonolite,t in the conglomerates or fragmentary rocks 

 anterior to the recent tertiary strata, renders it probable 

 that the appearance of trap rocks at the surface of the 

 earth is the effect of one of the last revolutions of our 

 planet, even where the eruption has taken place by crevices 

 (veins) which cross gneiss-granite, or the transition rocks 

 not covered by secondary and tertiary formations. 



Table of Organized Fossil Bodies, 1824. 



t The fragments of these rocks appear only in tufas or conglomerates, 

 which belong essentially to basaltic formations, or surround the most recent 

 volcanos. Every volcanic formation is enveloped in breccia, which is the 

 effect of the eruption itself. 



