242 Native Bitumens and the Pitch Lake of Trinidad. (April, 
flattened by pressure, and though always: the result of gaseous 
expansion, are commonly filled with water; in fact the entire 
mass of the pitch is saturated with water, so that even where quite 
soft it will not soil the hands, because the water oozes out and 
prevents adhesion. The earthy impurities of the pitch also assist 
in rendering untrue, in this instance, the old proverb that one can- 
not touch pitch without being defiled. 
The pitch is mined or quarried by excavating areas thirty or 
forty feet square to a depth of two to four feet. As soon as the 
work ceases on one of these cellar-like excavations the surround- 
ing asphalt, seeking to restore the equilibrium, begins to obliter- 
ate it, the walls not closing in perceptibly but the bottom rising 
up, and in a few days no trace of the opening remains. This is 
only one of many indications of greater fluidity below the sur- 
face. The plasticity of the pitch is evidently due to the oily matter 
which it contains, and not in any sensible degree to the tempera- 
ture. Hardened bitumen, it is true, may be fused by the applica- 
tion of sufficient heat, but that which is naturally fluid remains 
so at all ordinary temperatures. As already explained, when the 
asphalt is exposed to the air it becomes solid through loss of its 
volatile ingredients. Towards the center of the lake are several 
detached areas, a rod or two in breadth, which are softer than the 
rest of the surface,and yield under the feet, “so that on standing 
a few minutes one feels that he is gradually settling down, and in 
the course of ten or fifteen minutes he may find himself ankle deep.” 
“ But,” as Mr. Manross! truly says, “in no place is it possible to 
form those bowl-like depressions round the observer described by 
former travelers.” Nor is it probable that Kingsley is right in 
saying, “ No doubt there are spots where, if a man stayed long 
enough, he would be slowly and horribly engulfed.” The inferior 
density of the human body would prevent its submergence even 
if the pitch were quite fluid. 
In the vicinity of these places many small streams of gas 
escape from the pitch. The evil smell and. the deposit of sul- 
phur left on the pitch tell us that the gas is chiefly sulphuretted 
hydrogen; but the sulphurous odor ceases to be perceptible at a 
distance of a few rods, and does not extend for ten or twelve 
miles, as some writers have asserted, 
The surface of the lake does not present a continuous sheet of 
_ asphalt, but is traversed by a net-work of channels in which the 
1 American Journal of Science, 1855. 
