74 Dr. Nugent on the Pitch-lake 



Two specimens of the more compact and earthy sort, analysed by Mr. 

 Hatchett, yielded about 32 and 36 per cent, of pure bitumen : the 

 residuum in the crucible consisted of a spongy, friable and ochraceous 

 stone, and 100 parts of it afforded, as flir as could be determined by 

 a single trial, of silica 60, alumina 10, oxide of iron 10, carbona- 

 ceous matter by estimation 11 ; not the smallest traces of lime could 

 be discovered, so that the substance has no similarity to the bitumi- 

 nous limestones which have been noticed in different parts of the 

 world.* I have already remarked, that this mineral production 

 differs considerably in different places. The specimens examined 

 by Mr. Hatchett by no means correspond in character with the great 

 mass of the lake, which, in most cases, would doubtless be found to 

 be infinitely more free from combination with earthy substances ; 

 though from the mode of origin which I have assigned to it, this in- 

 termixture may be regarded as more or less unavoidable. The ana- 

 lysis of the stone after the separation of the bitumen, as Mr. Hatchett 

 very correctly observes, accords with the prevalent soil of the coun- 

 try ; and I may add, with the soil daily deposited by the gulph, and 

 with the composition of the porcelain jasper, in immediate contact 

 with the bituminous mass. 



All the country which I have visited in Trinidad is either decidedly 

 primitive or alluvial. The great northern range of mountains 

 which runs from east to west, and is connected with the Highlands 

 of Paria on the continent, by the Islands at the Bocas, consists of 

 gneiss, of mica slate containing great masses of quartz, and in 

 many places approaching so much to the nature of talc, as to render 

 the soil quite unctuous by its decomposition, and of compact bluish 

 grey limestone, with frequent veins of white crystallized carbo- 



* Vide Linnean Trans, vol. 8. 



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