230 COSMOS. 



head of craters, cones of eruption, and volcanoes. The marginal 

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

 suppose. A comparison of Saussure's measurements with my 

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

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

 of the north-western margin of Mount Vesuvius (Rocca del 

 Palo) may be considered to have remained unchanged.* 



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

 summits 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 fearful inundations and torrents of water in which 

 smoking scoriae are borne along on thick masses of ice, but 

 they likewise exercise a constant action whilst the volcano is 

 in a state of perfect repose, by infiltration into the fissuies 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 earthquakes which precede all erup- 

 tions in the Andes have violently shaken the whole mass of 

 the volcano, these subterranean caverns are suddenly opened, 

 and water, fishes, and tuffaceous mud are all ejected together. 

 It is through this singular phenomenonf that the inhabitants 

 of the highlands of Quito became acquainted \vith the existence 

 of the little cyclopic fishes, termed by them the prenadilla. 

 On the night between the 19th and 20th of June, 1698, when 

 the summit of Carguairazo, 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 overflowed and devastated by streams of liquid tuffa and 

 argillaceous mud, (lodazales,) containing large quantities of 

 dead fish. In like manner, the putrid fever, which raged 

 seven years previously in the mountain town of Ibarra, north 



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

 Saussure and Lord Minto, in the Abhandlungen der Akademie det 

 Wiss. zu Berlin, for the years 1822 and 1823. 



t Pimelodes cyclopum; see Humboldt, Recueil d? Observations d\ 

 Zoologif. et d'Anatwnie Comparte, t. i. p. 21-25. 



