STRUCTURE AND ACTION OF VOLCANOS. 367 



muddy products of the volcano, the so-called eruptions boueuses, 

 or, in the language of the old French systematisers, products 

 of an igneo-aqueous liquefaction. 



Where, as is generally the case in the chain of the Andes, 

 the summit of the volcano penetrates beyond the snow-line, 

 attaining sometimes an elevation twice as great as that of 

 Mount Etna, the inundations we have described are rendered 

 very frequent and destructive, owing to the melting and per- 

 meating snow. 



These are phenomena which have a meteorological connec- 

 tion with the eruptions of volcanos, and are variously modified 

 by the heights of the mountains, the circumference of the 

 summits which are perpetually covered with snow, and the 

 degree to which the walls of cinder cones become heated ; but 

 they cannot be regarded in the light of true volcanic phenomena. 

 Subterranean lakes, communicating by various channels with 

 the mountain streams, are frequently formed in deep and vast 

 cavities, either on the declivity or at the base of volcanos. 

 When the whole mass of the volcano is powerfully shaken 

 by those earthquakes which precede all eruptions of fire in 

 the Andes, the subterranean vaults open, and pour forth 

 streams of water, fishes, and tuffaceous mud. This singular 

 phenomenon brings to mind the Pimelodes Cyelojmm, or the 

 Silures of the Cyclops, which the inhabitants of the plateau 

 of Quito call Prcnadilla, and of which I gave a circumstantial 

 account soon after my return to Europe. When, on the 

 night between the 19th and 20th of June, 1698, the summit 

 of Mount Carguairazo, situated to the north of Chimborazo, 

 and having an elevation of more than 19,000 feet, fell in, all 

 the country for nearly 32 square miles was covered with 

 mud and fishes. A similar eruption of fish from the volcano 

 of Imbaburu was supposed to have caused the putrid fever, 

 which, seven years before this period, raged in the town of 

 Ibarra. 



I refer to these facts because they throw some light on the 



