464 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. [May 16, 



strata*. The limestones are hard and compact, containing in cer- 

 tain localities vast quantities of fossil remains, the substance of which 

 is often replaced by crystalline spar, the form more or less obliterated, 

 and so intimately associated with the mass of the rock as rarely to 

 admit of separation. Occasionally limited to a few feet, the thickness 

 may attain 100 feet, and amounts to even 700 or 800 feet for the 

 great bed of Caripe, in which the grotto so minutely described by 

 Humboldt is situated. Shales are largely represented, generally 

 dark, containing a few flakes of white mica, and thin seams or layers 

 of the sandstone above-described. In the western division of the 

 mountains they experience a great development, and, assuming a 

 partial induration accompanied by a fissile structure, often closely 

 resemble clay-slates. A species of rock prevailing extensively in 

 some localities, especially at Caripe and in Trinidad, has been pro- 

 visionally termed ArgUlhie, since it contains 85 per cent, of clay, and 

 only about 3 of carbonate of lime : the colour is white or light-yellow, 

 and the specific gravity usually slight, on account of the porous 

 structure. It is sometimes jointed, producing a division into rhom- 

 boidal fragments, and presents a certain degree of induration. The 

 beds are often of considerable vertical extent, and contain thin layers 

 of the sandstone, or, more rarely, of the limestone. 



The term Chertine is applied to strata presenting a sufficient 

 resemblance to chert, but, in place of occupying lamina? in the lime- 

 stones, forming independent beds 70 to 80 feet in thickness and 

 divided into layers not exceeding 15 inches each : the texture is at 

 times quite vitreousf. They are especially prevalent in the more 

 shaly portions of the series (west of Barcelona). 



The sequence of the members of this great system would probably 

 be determined without difficulty by an observer possessing sufficient 

 leisure ; but the data on which these remarks are founded can only 

 furnish obscure indications on this subject. Thus, from Aragua, in 

 an ascending order (PL XXI. Sect. 2), we have the sandstones of the 

 adjacent Cerro ; alternations of limestone, sandstone, and argilline; 

 then powerful beds of the latter, and finally the Caripe limestone, — 

 representing on the whole certainly not less than 7000 or 8000 feet. 



Probably the sandstones of Aragua and Baranquin, on opposite 

 declivities of the Cordillera, are the same, as the thickness is about 

 1200 feet in either case, and they exhibit a similar succession of 



* According to M. Cordier and some of the French geologists, the siliceous 

 cement of sandstones is hydrated, soluble in acididated waters, and, when the 

 pores are entirely filled, may amount to one-third of the mass, then forming the 

 variety known as gres lustre. If this view is correct, it will conveniently explain 

 several facts observed in Venezuela. 



t Since the text was written, we find that this rock and the slaty shales have 

 already been mentioned as occurring in the Cretaceous formation of Northern 

 Venezuela (Senft, 'Die Felsarten,' pp. 155 & 1G0, who quotes Karsten), — the first 

 as siliceous schist (Kieselschiefer), and the second as clay-slate. We regard M. 

 Cordier's term of "phyllade " for argillaceous slate of whatever age, as a happy 

 invention and quite applicable in the case in question. The other substance 

 belongs to the series which he classes as " phthanite," consisting of extremely fine 

 siliceous with a little foreign matter. 



