1869.] TATE GTJYA]S^A, IN YENEZTJELA. 349 



series skirting the Orinoco, and abutting against the northern escarp- 

 ment of the Itacama range of mountains is indubitably an extension 

 of the I^ewer Parian of Mr. Wall, which occupies the grassy plains to 

 the north of the river. In the neighbourhood of Bolivar its rocks rest 

 against the metamorphic boss on which the city stands, and consist 

 of a yellow sand-rock below, passing upwards into a red sandstone, 

 which in places is highly ferruginous ; surmounting the latter is a 

 quartose conglomerate in an iron-stone paste ; the pebbles are of the 

 size of marbles and are well water- worn. The whole of this series 

 stretches far away in every direction from Bolivar, and has a slight 

 dip to the north. The broad valley of San E-afael with its low 

 mural cliffs of from thirty to fifty feet in height is excavated 

 in the yellow sand-rock ; and the same series of strata forms 

 the banks of the Orinoco, l^o fossils were observed in the sandstone 

 beds ; but elongated cavities within the sand-rock appear to have 

 been occupied by fragments of the stems or roots of plants. 



That these arenaceous strata have originated from the wear and 

 tear of the metamorphic rocks is satisfactorily proved by sections 

 exhibiting the relation between the two series (see fig. 2). 



Resting on the granitoid gneiss is a loose ferruginous conglome- 

 rate containing large blocks of angular quartz, fragments of mica- 

 slate, &c., the constituents becoming finer and rounder as they are 

 traced from the insular mass around which they have been collected. 



Alluding to the probable origin of the Pitch lake, of Trinidad, Sir 

 Charles Lyell*, quoting Dr. Nugent, writes that *' the Orinoco has 

 for ages been rolling down great quantities of woody and vegetable 

 bodies into the surrounding sea, where, by the influence of currents 

 and eddies they may be arrested and accumulated in particular 

 places . . . . , and that these vegetable substances may have under- 

 gone those transformations and chemical changes which produce 

 petroleum." My observations do not confirm the speculation put 

 forth by this author as to the part played by the Orinoco. The 

 identity of the arenaceous strata of the Llanos of the Orinoco, which in 

 places are also lignitiferous and asphaltitic, with the similar strata of 

 the Moruga and Caroni series in Trinidad may be considered certain ; 

 and as the bed of the Orinoco, from Ciudad Bolivar (certainly so far 

 west) to the apex of the delta, is excavated in these same strata, it 

 is quite clear that the present river-valley is of more recent origin 

 than those beds to the accumulation of which, in the paragraph 

 quoted, it is implied the river has contributed. 



From the absence of fossils, other than vegetable remains, in the 

 Llanos-sandstones, and the presence of marine shells at Cumana and 

 in Trinidad, it appears highly probable that the arenaceous series of 

 the Llanos have been deposited in a shallow estuary, whilst the pre- 

 sent littoral areas of the same series have been accumulated under 

 marine conditions. 



YI. SuPEKFiciAL ACCTJMTJLATIONS OF LiMONiTE. — A striking feature 

 of the surface of much of the country passed under review, is the 

 presence of a hydrous oxide of iron — the moco de hierro of the 



* Principles of Geology, 9th edit. p. 250. 



2b2 



