Natural History of Volcanos and Earthquakes. 263 



the great eruption of this volcano in 1822, at the beginning of 

 January, the springs at Resina, St. Jorio, and ]')articularly in the 

 places in the immediate vicinity of Vesuvius, diminished percep- 

 tibly.* Monticelli observed similar phenomena before the erup- 

 tion in 1813, and he thinks that, in general, they are a sure sign 

 of one. It is hardly to be doubted that rents were opened by 

 the earthquakes, through which the water descended to greater 

 depths, accumulating, perhaps, in great caverns, and from thence 

 found its way to the source of the volcanic action. 



We find considerable acciimulations of water in all mountains 

 traversed by numerous fissures. We will only now mention the 

 western dechvity of the Teutohurger Wald, in which such con- 

 siderable rivers have their source ; the Jiira mountains ; and the 

 Genwii.f The volcanic inundations, of which Von Humboldt 

 gives such extraordinary examples, J are an additional evidence of 

 the existence of such great subterranean accumulations of water, 

 in the vicinity of volcanos. Lastly, we have, further, examples 

 of volcanos coming into action after violent storms of rain; for 

 instance, the Mer-Api, in Java.'^ In the Andes of Quito, the 

 Indians imagine they have observed, that the quanity of percola- 

 ting snow-water increases the activity of volcanos. |j Can it, then, 

 any longer be doubted, that the proximity of the ocean is by no 



* The same was observed twenty three days before the earthquake in Calabria; 

 and also in the Peak of Tencriffe, in 17U6. Von Humboldt, Relat. Hist. t. i. p. 

 393. In Iceland, this phenomenon was observed before the terrible eruption of 

 Skaptar Jokul, in 1784. In general, in volcanic districts, the porous and much 

 fissured rocks swallow up the rain-water, and carry it down to very great depths. 

 Von Humboldt gives this as the cause of the extreme aridity which reigns in most 

 of the Canary Islands, notwithstanding the height of the mountains, and the mass 

 of clouds which travellers always see collected over this Archipelago. Reise, 

 t. i. p. 173. 



t Von Humboldt (Reise, t. iii, p. 229) mentions several rivers which lose them- 

 selves in the gneiss rocks. When these gneiss mountains were upraised, consid- 

 erable caverns may have been formed, which were afterwards filled with water. 



X Annal. de Chirri. et de Phys. t. xxvii, p. 128. This circumstance, however, 

 must be considered, that the strong heat over the active volcano dilates the atmos- 

 phere, and produces a rising stream of air. The consequence of that is an influx 

 of air from all sides. But lliis air is accompanied with moisture, which, rising 

 with it, is condensed in the higher regions of the atmosphere, and falls down in 

 showers. Therefore, an active volcano aifords not only water, which inmiediately 

 issues from its interior, but it also deprives all the environs of water. Du Carta sur 

 les inondat. Volcaniques. Journ. de Physique, t. xx, p. 103. 



§ Memoir of the Conquest of Java. London, 18] 5, p. 40 



II Von Humboldt's Reise, t. i, p. 263. 



