PITCH LAKE IN TRINIDAD. 



203 



face of the water on both sides of the island, not where the 

 sea has encroached on and overwhelmed the ready-formed 

 land, but where it is obviously in a very rapid manner depo- 

 siting and forming a new soil. 



From a consideration of the great hardness, the specific Mr. HatchetO* 

 gravity, and the general external characters Srf the speci- supposition. 

 mens submitted a few years ago to the examination of Mr. 

 Hatchett, that gentleman was led to suppose, that a con- 

 siderable part of the aggregate mass at Trinidad was not 

 pure mineral pitch or asphaltum, but rather a porous stone 

 of the argillaceous genus much impregnated with bitumen. 

 Two specimens of the more compact and earthy sort, an- Specimens an* 

 alysed by Mr. Hatchett, yielded about 32 and 36 per alysed • y hinv 

 cent of pure bitumen : the residuum in the crucible con- 

 sisted of a spongy, friable, and ochraceous stone; and 100 

 parts of it afforded, as far as could be determined by a 

 single trial, of silica 60, alumine 10, oxide of iron 10, car- 

 bonaceous matter by estimation 11 ; not the smallest traces 

 of lime could be discovered, so that the substance has no 

 similarity to the bituminous 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 doubt- 

 less be found to be infinitely more free from combination 

 with earthy substances; though from the mode of origin 

 which J have assigned to it, this intermixture may be re- 

 garded as more or less unavoidable. The analysis of the 

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

 very correctly observes, accords 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 contact with the biruminous mass. 



AH the country which I have visited in Trinidad, is either Geology of the 

 decidedly primitive or alluvial. The great northern range is!anfl - 

 of mountains which runs from east to west, and is connected 

 with the highlands of Paria on the continent by the 



* Vide Linnean Trans, vol. 8. 



islands 



