60 J. W. Judd — On Volcanos. 



this conclusion are afforded by the great fissures filled with volcanic 

 materials, with which all geologists are familiar, as traversing older 

 rock-masses where exposed by denudation. 



Nor must we forget that the volcanic band, which has been indi- 

 cated as passing through the great central vent of the Liparis and 

 Stromboli, would, if produced, strike the great earthquake-shaken 

 tract of Calabria, and by a slight deflection pass through the volcanic 

 districts of Southern and Central Italy ; while the southern continua- 

 tion of the same, passing through Lipari, Vulcanello, and Vulcano, 

 points to Etna, the Val di Noto, and the volcanic islands lying south 

 of Sicily. These facts are interesting, as indicating that Von Buch's 

 classification of volcanos, according to their mode of arrangement, 

 in linear systems and groups, cannot be sustained. AIL volcanic 

 action appears to be developed along lines of fissure, though these 

 may present very varied relations and connexions with one another, 

 I shall take occasion, hereafter, to show that the principal of these 

 combinations assumed by volcanic lines of fissure may be classified 

 as radial and parallel series. 



The fissures of the Lipari group afford an interesting example 

 of the radial arrangement, with some illustration of the production 

 of lateral or branching fractures on either side of the principal ones. 

 The whole, however, being probably a subordinate part of a great 

 band of subterranean volcanic action. 



It is a most interesting circumstance, and one by no means devoid 

 of suggestiveness to the geologist, that the two active volcanic vents 

 of the Lipari Islands are situated at distant, almost indeed extreme, 

 points of the group ; and that while one of them, Stromboli, ejects 

 materials of the most highly basic character — dolerite and basalt — 

 the other produces roeks of extremely acid, composition, quartz- 

 trachyte (Liparite) and obsidian. The striking differences in the 

 specific gravities of these two classes of rocks has been commented 

 on by many geologists. As every great volcanic area may fairly be 

 supposed to have beneath it a reservoir of materials in either an 

 actually or potentially 1 liquefied state, we may, without adopting 

 Durocher's notions of universal acid and basic magmas, suggest a 

 possible explanation of the peculiarities of the existing volcanic 

 phenomena of the Lipari Islands. If we imagine the area to be 

 underlaid by a reservoir of liquefied materials which is of inter- 

 mediate composition, this might have supplied the products of all 

 the earlier eruptions of the district; and it is only necessary to 

 suppose that, by the action of gravity, the materials (magmas) of 

 different densities were in process of time separated from one 

 another, while distinct fissures were opened connecting the upper 

 and lower portions of the mass, respectively, with different parts of 

 the surface, — to see that just such phenomena as now take place 

 would be called into play. 



1 By a rock in a potentially liquefied state, I of course mean one which,, either from 

 its elevated temperature or its condition of internal tension from imprisoned volatile 

 constituents, would assume a liquid form on being relieved from the pressure -which 

 maintains it in a solid state. 



