HB M. Humboldt on SolJ'ataras and 



nomenon of the Salses*, ov air volcanos, wei*e very thick. 

 It is easily conceivable that, in the equinoctial zone, even very 

 low mountains may by a particular disposition of their sub- 

 terraneous cavities, and by the excessive abundance of the 

 tropical rains, be subject to cause frightful inundations each 

 ■time that they undergo shocks of earthquakes. Furthermore, 

 the phaenomena which we have been describing are repeated 

 from time to time far from the volcanos, in secondary moun- 

 tains, in the centre of Europe. Sad examples have proved 

 in our days that in the Alps of Switzerland, where no shocks 

 of earthquakes are felt, a simple hydrostatic pressure lifts up 

 and breaks with violence banks of rock, throwing them to a 

 great distance, as if they were projected by elastic forces. 



The trachytes of Purace contain sulphur like those of Mont- 

 Doi'e in Auvergne, of Budoshegy in Transylvania, of the 

 Isle of Montserrat in the Litde Antilles, and of the Anti- 

 sana in the Andes of Quito. It is still formed daily in the 

 clefts around the gulfs of Purace, either by a very slow subli- 

 roation, or by the contact of the sulphurous acid vapours 

 with the sulphuretted hydrogen of the lake. The volcano la- 

 bours in its interior like the solfataras; but it presents nothing 

 in its form that resembles the places which are designated by 

 that name, and which I have visited ; for example, the 50^- 

 taras of Puzzuoli, the Peak of Teneriffe, and the volcano 

 of Jorullo in Mexico. These last three are craters which 

 have vomited lava; they show that their first state was very 

 different to that in which we see them at present. With very 

 elevated temperatures, the chemical products of a volcano are 

 not the same as with a very low temperature. If the appella- 

 tion solfatara be given indefinitely to every place where sul- 

 phur is formed or deposited, this denomination may also be 

 applied to a district which I shall describe here, and which 

 contrasts singularly with the trachytes of volcanos. In cross- 

 ing the Cordilleras of the Andes of Quindiu, between the ba- 

 sins of the Cauca and of the Magdalena (lat. 4° 50'— 4° 45') 

 I saw an immense formation of gneiss and of micaceous schist 

 resting immediately on an ancient granite. The layers of 

 micaceous schist which alternate with strata of gneiss are free 

 from garnets, whilst the gneiss contains many. But, in these 

 same primitive micaceous schists, a little to the west of the 

 station of the Moral, at the height of 6800 feet above the 

 level of the sea, in the Qiiebrada del Azitfral, some decayed veins 



* There is only the muddy torrent {Jiume di fotngo) of Santa-Maria- 

 Nascemi (March 1 8, 1 790), in the Val di Noto, which seems to me to belong 

 to the action of the Salses. 



extremely 



