When Humboldt visited them in 1801, they gave off hardly anything save nitrogen gas.

But in the year 1850, a 'bituminous odour' had begun to be diffused; asphaltic oil swam on the surface of the small openings; and the gas issuing from any of the cones could be ignited.

Dr.Daubeny found the mud-volcanoes of Macaluba giving out bitumen, and bubbles of carbonic acid and carburetted hydrogen.

The mud-volcano of Saman, in the Western Caucasus, gives off, with a continual stream of thick mud, ignited gases, accompanied with mimic earthquakes like those of the Trinidad Salses; and this out of a soil said to be full of bituminous springs, and where (as in Trinidad) the tertiary strata carry veins of asphalt, or are saturated with naphtha.

At the famous sacred Fire wells of Baku, in the Eastern Caucasus, the ejections of mud and inflammable gas are so mixed with asphaltic products that Eichwald says 'they should be rather called naphtha volcanoes than mud-volcanoes, as the eruptions always terminate in a large emission of naphtha.' It is reasonable enough, then, to suppose a similar connection in Trinidad.