400 
AMYGDALOID AKD PHOKOLT. 
this superiority in number, the organic fossil world furnishes, 
in every latitude, a further analogy with the intertropical 
shells that now live at the bottom of the ocean. In fact, 
M. Defiance, 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 nniltivalve shells, contained in 
his rich collections, there are 3060 univalve, 2108 bivalve, 
nnd 326 multivalve ; the univalve fossils are therefore to 
the bivalve as three to two. 
XIII. Formatios op Pyroxeyic Amygdaloid axd 
PlIONOLITE, BETWEEN OrTIZ AND CeRRO DE PlORES. — I 
place pyroxenic amygdaloid and phouolite (porphyrschiefer) 
at the end of the Ibrmatious 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 Juaii, 
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 w’here the eruption has taken place by crevices 
(veins) which cross gneiss-granite, or the transition rocks 
not covered by secondary and tertiary formati jns. 
• 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 ki breccia, which is the 
effect of the eruption itself. 
