230 STRUCTURE AND MODE OF ACTION 



slope of the cone of ashes. The learned and zealous ob- 

 server of the volcano, Monticelli, soon discovered that this 

 erroneous rumour had arisen from an optical illusion. The 

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

 which, being as loose and moveable 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 abun- 

 dant fail 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 

 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 terrified 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 recognised in them 

 either sea-water or muddy products of the volcano, te Erup- 

 tions 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 inunda- 

 tions as have beer described far more abundant and disastrous. 

 The phenomena in question are meteorologically connected 

 with the eruptions of volcanos, and are variously modified 



