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Page 104 



In Trinidad the northern range of mountains is composed 

 of rocks, belonging chiefly if not entirely to the "Caribean 

 Group." These rocks attain collectively a thickness of more 

 than 10,000 feet. The whole thickness of the group is 

 probably much greater than this ; for the evidence furnished 

 by dip and other circumstances leads to the inference that a 

 portion of the series, as developed in Venezuela, is inferior 

 in position to any of the rocks exposed in Trinidad. In the 

 diagram, Fig. 3, this older portion is represented as thrown 

 down to the north of Trinidad, beneath the waters of the 

 Caribean Sea (Fig. 3, a). Besides this downthrow we have 

 evidence of two or three other lines of dislocation which 

 traverse the range through its length from east to west. 

 These dislocations are marked with a star in Fig. 3, and are 

 indicated on the sketch map, Fig. 1. They have caused, in 

 conjunction with other movements, of which I shall presently 

 speak, some peculiar phenomena in the physical geography 

 of the valleys, which are much narrower, and in some cases 

 quite ditch-like, to the south of the line of the greatest dis- 

 location (between rand d, in Fig. 3), and widen out above 

 into large basins. 



The separation of Trinidad from Venezuela was probably 

 produced by a great downthrow, which I have attempted to 

 represent in Fig. 2. The line of that downthrow, passing 

 through the Boca Grande, is laid down in the sketch map, 

 Fig. 1. From the facts intended to be illustrated by these 

 diagrams, it would appear that the Gulf of Paria occupies an 

 area of depression, the lowest axis of which passes through 

 the Boca Grande, running approximately north and south. 

 The amount of subsidence diminishes gradually as we pass 

 eastward, until at the valley of Arouca its effects disappear 



