I860.] wall — vLXKzrr.L.v Axn TniNiDAD. 463 



of schistose beds succeeding a series of gncissic, which are again 

 replaced by the latter. The transition, occasionally gradual, is more 

 usually sudden or abrupt* Generally the conditions may be defined 

 as those of a schistose region traversed by gneissio gomes. The 

 latter rock is ordinarily foliated, but also occurs without the alight* 

 esl parallelism of the constituent substances, or tendency to cleave 

 in any particular direction, Even where the arrangement of the 

 minerals [a as irregular as that of granite, it is still bounded at certain 

 intervals by distinct planes, the equivalents of the surfaces of tho 

 different beds. 



Amongst the rarer substances existing in this group, garnets aro 

 the only earthy minerals not highly exceptional j und oven these 

 wen- merely observed in the more crystallino portions. 



Gold is disseminated in the gneiss west of Valencia, but in 

 quantities quite inappreciable to the senses. On treating the debris 

 proceeding from the degradation of this rock, the yield, in extreme 

 cases, has amounted to an ounce per week for one person. 



At Las Tenuis, I'n miles west of Caracas, the schists are impreg- 

 nated over a considerable area with the sulphuret and carbonate of 

 Copper, which are associated in small quantities with the masses of 

 quartz, or spread out between the lamina! of the strata. Nothing 



resembling an accumulation or mineral deposit appeal's to exist. 



Argentiferous lead-ore has been worked on a small scale near 

 Carnpano, and offers deposits of two different descriptions: the drat 

 of a bunchy irregular nature, with a alight proportion of silver (.'in 

 to l" oa. in the ton): and secondly, where the metallic substances 

 seem to be Located in true veins of no greal width, the ore is much 

 rarer, contains a higher percentage of silver, and is associated with 

 a ferruginous gangue. 



The whole formation exhibits great disturbance and contortion, 

 and constitutes the northern portion of the Cordillera. Forming 



i greal a distance one of the boundaries of the Caribbean Sea, it 

 may be provisionally distinguished as the 'Caribbean System.' The 



strike is ordinarily K. and W.. 01 parallel with the OOftst, but with 



variations of 30 W N". of £. and 8. of W. En the western 



range it band having a breadth of thirty miles, rising to 



a heighl of B0O0 feet, and furrowed by longitudinal depressions; 

 whilst in the eastern portion the valleys are transverse, and the 

 breadth of the chain is restricted to ten or twelve miles, and the 

 elevations to 8600 feet. 



Another group oi attributing still more largely to the 



formation of the Sei-rama. or hill\ region, Lfl on many accounts 



highly interesting and remarkable. 



The most important members oonsist of sandstones varying from 

 a mere layer to many hundreds of feet, and presenting permanent 

 mineral and physical characters. It is often difficult !•■ mstangnish 

 the separate element idition which is accompanied with a 



high degree of induration, properties evidently due to a silii 

 oement precipitated around the oonatituenl grains, a prooess which 

 must have varj generally operated in the co n solidation of these 



