58 
TRINIDAD. 
-acrid saltness. Over the entire extent the degree of 
hardness varies with the intensity of the solar rays. At 
early morn the whole surface, excepting the centre, is 
hard, whilst at mid-day it becomes so softened as, to 
retain the impression of the slightest impress. Wlien- 
ever any quantity of bitumen has been dug and taken up 
from the lake, the excavation soon fills up, and a perfect 
level is restored within 24 or 48 hours. The deeper the 
digging the quicker the restoration. In the centre entire 
trees are sometimes seen emerging to the surface, to be 
re-submerged soon afterwards by a slow rotator)^ move- 
ment. Casks placed near that spot to receive bitumen 
have also disappeared ; and it is reported that strayed 
animals, venturing too far, have likeAvise been swallowed 
up in this vortex. It is evident, from the above obser- 
vations, that the operation going on in the Pitch Lake 
may be compared to the ebullition of a thick substance 
in a large boiler. The asphaltum is thrown iqi by the 
active operation of a physical cause constantly at work, 
and its upward motion prompted by the laws of hydro- 
statics. Tliere is also a perceptible sort of regidating 
process. The semi-fluid asphaltum not being cast iq> by 
any Anolent agency, partly spreads around and partly 
returns to the mass. Any (quantity of it, however, which 
has been left exposed to the action of the sun, is soon 
deprived, by evaporation, of its moisture and petroleum, 
and then becomes hardened. The solidity increases 
gradually, and by loss from evaporation, the volume of 
the substance diminishes, tlie surface cracks, and crevices 
are formed by a regular retraction, as is the case with 
clay soils. It is highly probable that the superficies or 
superstratiun only is of this hardened consistency, and 
that at a less or greater depth the bitumen is still soft 
•or semi-liquid. Neither do I admit the supposition of a 
subterranean volcanic action, for bitumen or asphaltum 
belongs to the carboniferous formation; therefore, its 
production cannot be different from that of coal or 
lignite.” 
