On the Pitch Lake of the Island of Trinidad. 1()9 



that gentleman was led to suppose that a considerable part 

 of the aggregate mass at Trinidad was not pure mineral 

 pitch or asphaltum, but rather a porous stone of the argil- 

 laceous genus, much impregnated with bitumen. Two spe- 

 cimens 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 spo)igy, 

 friable and ochraceous stone; and 100 parts of it afforded, 

 as far as could be determined by a single trial, of silica 60, 

 alumina 10, oxide of iron 10, carbonaceous matter by esti- 

 mation 11 ; not the smallest traces of lime could be dis- 

 coveVed ; so that the substance has no similarity to the bitu- 

 minous 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 e;rcat mass of the lake, 

 which, in most cases, would doubtfess be found to be in- 

 finitely more free from combination with earthy substances ; 

 though from the mode of origin which I have assigned to 

 it, this intermixture may be regarded as more or less una- 

 voidable. The analysis of the stone after the separation of 

 the bitumen, as Mr. Hatchett very correctly observes, ac- 

 cords with the prevalent soil of the country; and I may 

 add, with the soil daily deposited by the gulf, and with 

 the composition of the porcelain jasper in immediate con- 

 tact 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 con- 

 nected 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 ap- 

 proaching so much to the nature of talc as to render the 

 soil quite unctuous by its decomposition, and of compact 

 blueish gray limestone, with frequent veins of white crystal- 

 lized carbonate of lime. From the foot of these mountains, 

 for many leagues to the southward, there is little else than 

 a thick fertile argillaceous soil, without a stone or a single 

 pebble. This tract of land, which is low and perfectly 

 level, is evidently f.)rmed by the detritus of the mountains, 

 and by the copious tribute of the waters of the Orinoco, 

 which being deposited by the influence of currents, gra- 

 dually accumulates ; and in a climaie where vegetation is 

 astonishingly lapid, is speedily covered with the mangrove 



* Vi(l« LinoeaD Tiaui). vuLviii. 



and 



