in the Island of Trinidad. 259 
as the asphaltum, most probably occurs only in certain fissures 
and cavities; for, from the specimens noticed in the present pa- 
per, there is great reason to believe that a considerable part of 
that mass in Trinidad, which has been hitherto supposed to be 
pure mineral pitch or asphaltum, is in reality only a porous stone 
of the argillaceous genus, much impregnated with bitumen *. 
rents. This is constantly liquid, and smells stronger of tar than when indurated, and 
adheres strongly to any thing it touches; grease is the only thing that will divest the 
hands of it." Philosophical Transactions, 1789, p. 68. 
* Having acquainted Mr. Tobin with the result of my experiments, that gentleman 
in his answer. observes, “ I have indeed lately had reason to suppose that it could not 
be a perfect bitumen, from having been assured that it is made use of as a material 
Sor pavements, and that it Lears exposure to the heat of a tropical sun,” 
ET 
2712 3 | IV. Description. 
