VOLCANOES. 231 



of Quito, wa> ascribed to the ejection of fish from the volcano 

 of Imbaburu.* 



Water and mud, which flow not from the crater itself, but 

 from the hollows in the trachytic mass of the mountain, can- 

 not, strictly speaking, be classed amongst volcanic phenomena. 

 They are only indirectly connected with the volcanic activity 

 of the mountain, resembling, in that respect, the singular me- 

 teorological process which I have designated in my earlier 

 writings by the term of volcanic storm. The hot stream 

 which rises from the crater during the eruption, and spreads 

 itself in the atmosphere, condenses into a cloud, and surrounds 

 the column of fire and cinders which rises to an altitude of 

 many thousand feet. The sudden condensation of the vapours, 

 and, as Gay Lussac has shown, the formation of a cloud of 

 enormous extent, increase the electric tension. Forked 

 lightning flashes from the column of cinders, and it is then 

 easy to distinguish (as at the close of the eruption of Mount 

 Vesuvius, in the latter end of October, 1822) the rolling 

 thunder of the volcanic storm from the detonations in the in- 

 terior of the mountain. The flashes of lightning that darted 

 from the volcanic cloud of steam, as we learn from Olafsen's 

 report, killed eleven horses and two men, on the eruption of 

 the volcano of Katlagia, in Iceland, on the 17th of October, 

 1755. 



Having thus delineated the structure and dynamic activity 

 of volcanoes, it now remains for us to throw a glance at the 

 differences existing in their material products. The subter- 

 ranean forces sever old combinations of matter in order to 

 produce new ones, and they also continue to act upon matter 

 as long as it is in a state of liquefaction from heat, and 

 capable of being displaced. The greater or less pressure 

 under which merely softened or wiiolly liquid fluids are soli- 

 dified, appears to constitute the main difference in the forma- 

 tion of plutonic and volcanic rocks. The mineral mass which 

 flows in narrow, elongated streams from a volcanic opening 

 (an earth-spring) is called lava. Where many such currents 

 meet and are arrested in their course, they expand in width, 



* [It would appear, as there is no doubt that these fishes proceed 

 from the mountain itself, that there must be large lakes in the interior, 

 nbvh in ordinary seasons are out of the immediate influence of th 

 volcanic action. See Daubeney, op. cit., op. 488, 497.] Tr. 



