OF VOLCANOS. 387 



the crater, and pouring down the slope of the cone of ashes. The 

 learned and zealous observer of the volcano, Monticelli, soon dis- 

 covered that this erroneous rumor had arisen from an optical illusion. 

 The supposed torrent of water was in reality a flow of dry ashes, 

 which, being as loose and movable as shifting sands, issued in large 

 quantities from a crevice in the upper margin of the crater. The 

 cultivated fields had suffered much from a long-continued drought 

 which had preceded the eruption towards its close, the " volcanic 

 thunder-storm" which has been described produced an exceedingly 

 violent and abundant fall of rain. This phenomenon is associated 

 in all climates with the close of a volcanic eruption. As during the 

 eruption the cone of ashes is generally enveloped in a cloud, and as 

 it is in its immediate vicinity that the rain is most violent, torrents 

 of mud are seen to descend from it in all directions, which the ter- 

 rified husbandman imagines to consist of waters which have risen 

 from the interior of the volcano and overflowed the crater; while 

 geologists have erroneously thought they recognized in them either 

 sea-water or muddy products of the volcano, " Eruptions boueuses/' 

 or, in the language of some old French systematists, products of an 

 igneo-aqueous liquefaction. 



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

 volcano rises into the region of perpetual snow (even attaining, in 

 some cases, an elevation twice as great as that of Etna), the melting 

 of the snows renders such inundations as have been described far 

 more abundant and disastrous. The phenomena in question are 

 meteorologically connected with the eruptions of volcanos, and are 

 variously modified by the height of the mountain, the dimensions 

 of that part of it which is always covered with snow, and the extent 

 and degree to which the sides of the cone of cinders become heated ; 

 but they are not to be regarded as volcanic phenomena properly so 

 called. Vast cavities also often exist on the slope or at the foot of 

 volcanos which, communicating through many channels with the 

 mountain torrents, form large subterranean lakes or reservoirs of 

 water. When earthquake shocks, which, in the Andes, usually 

 precede all igneous eruptions, convulse the entire mass of the 

 volcano, these subterranean reservoirs are opened, and there issue 

 from them water, fishes, and tufaceous mud. There is the singular 



