158 On the Pitch Lake of Trinidad. 
Streams of gas issue from below, sometimes rising through the 
water but more frequently hissing and gurgling from small open- 
ings in the pitch above water level. It appears to be chiefly sul- 
' phuretted hydrogen, smelling strongly of that gas and instantly 
blackening a silver coin laid among the bubbles. When inflamed 
it burns with a pale yellowish flame. 
he surface of the pitch is whitened in places by a deposit of 
sulphur. 
The temperature of one of the streams of gas was 97° Fah., 
the highest heat which I observed upon the lake. 
The water in some of the crevices was 95°. In such cases it 
appeared to be rising at one end of the opening, flowing along, 
and descending at the other. 
I have no doubt that the mere surface of the pitch is sometimes 
heated by the sun to a higher degree than this. But the copious 
streams of gas would certainly indicate the fact if a much higher 
heat existed at a moderate depth below. 
The pitch where most fluid had a temperature of only 95°. 
It is evident that the bitumen does not owe its fluidity in 
any great degree to heat. It is true that the already hardened 
pitch may be melted by a sufficient heat, but that which 1s 
already fluid remains so at all ordinary temperatures. 
Wherever it oozes out in streams it flows down over the 
hardened surface into the nearest channel of .water (which may 
have a temperature not above 85°), where it creeps along the 
bottom in a stream that looks like a huge serpent. 
The fluidity of the pitch is evidently owing to the oily matter 
which it contains. 'The whole thing seems more like a vast 
fountain of coal tar than anything else. The gradual hardening 
which has evidently taken place is due to oxydation and evap0- 
ration of the less fixed ingredients,—a process which the revolv- 
ing motion heretofore described must greatly facilitate. 
In one of the star sbaped pools of water, some five feet deep, 
acolumn of pitch had been forced perpendicularly up from the 
bottom. On reaching the surface of the water it had expanded into 
a sort of center table about four feet in diameter but without touch- 
ing the sides of the pool. The stem was about a foot in diame- 
ter. [ leaped out upon this table and found that it not only sus- 
the water on the lake, An alligator shuffled off from one of the 
areas at my approach. In two instances I scared birds resembling 
