SALSES. 213 



If we now cast a last glance at the kind of volcanic activ- 

 ity which manifests itself by the production of vapors and 

 gases, either with or without phenomena of combustion, we 

 lind sometimes a great affinity, and sometimes a remarkable 

 difference in the matters escaping from fissures of the earth, 

 according as the high temperature of the interior, modifying 

 the action of the affinities, has acted upon homogeneous or 

 very composite materials. The matters which are driven to 

 the surface by this low degree of volcanic activity are : aque- 

 ous vapor in great quantity, chloryd of sodium, sulphur, car- 

 bureted and sulphureted hydrogen, carbonic acid and nitro- 

 gen ; naphtha (colorless or yellowish, or in the form of brown 

 petroleum) ; boracic acid and alumina from the mud volca- 

 noes. The great diversity of these matters, of which, how- 

 ever, some (common salt, sulphureted hydrogen gas, and pe- 

 troleum) are almost always associated together, shows the 

 unsuitableness of the denomination salscs, which originated 

 in Italy, where Spallanzani.had the great merit of having 

 been the first to direct the attention of geognosists to this 

 phenomenon, which had been long regarded as so unimport- 

 ant, in the territory of Modena. The name vapor and gas 

 springs is a better expression of the general idea. If many 

 of them, such as the Fumaroles, undoubtedly stand in rela- 

 tion to extinct volcanoes, and are even, as sources of carbon- 

 ic acid, peculiarly characteristic of a last stage of such vol- 

 canoes, others, on the contrary, appear to be quite independ- 

 ent of the true fiery mountains which vomit forth fused 

 earths. Then, as Abich has already shown in the Cauca- 

 sus, they follow definite directions in large tracts of country, 

 breaking out of fissures in rocks, both in the plains, even in 

 the deep basin of the Caspian Sea, and in mountain eleva- 

 tions of nearly 8500 feet. Like the true volcanoes, they 

 sometimes suddenly augment their apparently dormant ac- 

 tivity by the eruption of columns of fire, which spread ter- 

 ror all around. In both continents, in regions widely sep- 

 arated, they exhibit the same conditions following one upon 



up scoriae), and that most of the very hot springs of South America 

 issue from granite (Las Trincheras, near Porto Cabello), gneiss, and 

 micaceous schist. More to the eastward of the meridian of Cu- 

 mana, in descending from the Sierra de Meapire, we first came to 

 the hollow ground (tierra huecct), which, dm*ing the great earthquakes 

 of 1766, threw np asphalt enveloped in viscous petroleum ; and aft- 

 erward, beyond this ground, to an infinity of hydrosulphurous hot 

 springs (Humboldt, Relation Ilistorique, t. i., p. 136, 34-i, 347, and 

 417). 



