58 NAPA RIM A. 



Ortoire, ^vLlicll is extinct, or at least quiescent ; but this, also, 

 I could not visit. It is about seventeen miles from the sea, 

 and about two hundred feet above it. As for the causes of 

 these Salses, I fear the reader must be content, for the present, 

 with a somewhat muddy explanation of the muddy mystery. 

 Messrs. Wall and Sawkins are inclined to connect it with 

 asphalt springs and pitch lakes. " There is," they say, 

 "easy gradation from the smaller Salses to the ordinary 

 naphtha or petroleum springs." It is certain that in the 

 .production of asphalt, carbonic acid, carburetted hydrogen, 

 and water are given off. " May not," they ask, " these 

 orifices be the vents by which such gases escape ? And in 

 forcing their way to the surface, is it not natural that the 

 liquid asphalt and slimy water should be drawn up and 

 expelled ? " They point out the fact, that wherever such 

 volcanos exist, asphalt or petroleum is found hard by. The 

 mud volcanos of Turbaco, in New Granada, famous from 

 Humboldt's description of them, lie in an asphaltic country. 

 They are much larger than those of Trinidad, the cones being, 

 some of them, twenty feet high. 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 volcanos of 



