232 COSMOS. 



sible even during periods of eruption. It is impossible, with- 

 out an exact representation of the configuration — the normal 

 type, as it were, of fire-emitting mountains, to form a just idea 

 of those phenomena which, owing to fantastic descriptions and 

 an undefined phraseology, have long been comprised under the 

 head of craters, cones of eruption, and volcanoes. The mar- 

 ginal ledges of craters vary much less than one would be led 

 to suppose. A comparison of Saussure's measurements with 

 my own yields the remarkable result, for instance, that in the 

 course of forty-nine years (from 1773 to 1822), the elevation 

 of the northwestern margin of Mount Vesuvius [Rocca del 

 Palo) may be considered to have remained unchanged.* 



Volcanoes which, like the chain of the Andes, lift their sum 

 mits high above the boundaries of the region of perpetual snow, 

 present peculiar phenomena. The masses of snow, by their 

 sudden fusion during eruptions, occasion not only the most fear- 

 ful inundations and torrents of water, in which smoking scorias 

 are borne along on thick masses of ice, but they likewise ex- 

 ercise a constant action, while the volcano is in a state of per 

 feet repose, by infiltration into the fissures of the trachytic rock. 

 Cavities which are either on the declivity or at the foot of the 

 mountain are gradually converted into subterranean reservoirs 

 of water, which communicate by numerous narrow openings 

 with mountain streams, as we see exemplified in the highlands 

 of Quito. The fishes of these rivulets multiply, especially in 

 the obscurity of the hollows ; and when the shocks of earth- 

 quakes, which precede all eruptions in the Andes, have vio- 

 lently shaken the whole mass of the volcano, these subterra- 

 nean caverns are suddenly opened, and water, fishes, and tufa- 

 ceous mud are all ejected together. It is through this singular 

 phenoraenont that the inhabitants of the highlands of Quito 

 became acquainted with the existence of the little cyclopia 

 fishes, termed by them the prehadilla. On the night betwecD 

 the 19th and 20th of June, 1698, when the summit of Car* 

 guairazo, a mountain 19,720 feet in height, fell in, leaving 

 only two huge masses of rock remaining of the ledge of the 

 crater, a space of nearly thirty-two square miles was over- 

 flowed and devastated by streams of liquid tufa and argilla- 

 ceous mud (lodazales), containing large quantities of dead fish. 



* See the ground-work of my measurements compared with those of 

 Saussure and Lord Minto, in the Abhandlungen der Akademie der Wi*9. 

 zu Berlin for the years 1822 and 1823. 



t Pimelodes cyclopum. See Humboldt, Recueil d^Ohservatiovf ^t 

 Zoologie et d'' Anatomie Comparie, t. i., p. 21-25. 



