VOLCANOES. 215 



trachytic conglomerates ; streams of obsidian ; quarried 

 blocks of pumice-stone, and not pumice-bowlders transported 

 and deposited by water) make their appearance, seeming to 

 be quite independent of the mountains, which only rise at a 

 considerable distance. Why should not the surface have 

 been split in many directions during the progressive refriger- 

 ation of the upper strata of tho earth by radiation of heat, 

 before the elevation of isolated mountains or mountain chains 

 had yet taken place ? Why should not these fissures have 

 emitted masses in a state of igneous fusion, which have hard- 

 ened into rocks and eruptive stones (trachyte, dolerite, mela- 

 phyre, margarite, obsidian, and pumice)? A portion of 

 these trachytic or doleritic strata which have broken out in 

 a viscid fluid state, as if from earth-springs,* and which 

 were originally deposited in a horizontal position, have, 

 during the subsequent elevation of volcanic cones and bell- 

 shaped mountains, been tilted into a position which by no 

 means belongs to the more recent lavas produced from ig- 

 neous mountains. Thus, to advert, in the first place, to a 

 very well known European example, in the Val del Bove on 

 jEtna (a depression which cuts deeply into the interior of 

 the mountain), the declination of the strata of lava, which 

 alternate very regularly with masses of bowlders, is 25° to 

 30°, while, according to Elie de Beaumont's exact determ- 

 inations, the lava streams which cover the surface of -ZEtna, 

 and which have only flowed from it since its elevation in the 

 form of a mountain, only exhibit a declination of 3° to 5° 

 on an average of 30 streams. These conditions indicate the 

 existence of -very ancient volcanic formations, which have 

 broken out from fissures, before the production of the vol- 

 cano as an igneous mountain. A remarkable phenomenon of 

 this kind is also presented to us by antiquity — a phenomenon 

 which manifested itself on Eubcea, the modern Negropont, 

 in an extended plain, situated at a distance from all active 

 and extinct volcanoes. " The violent earthquakes, which 

 partially shook the island, did not cease until an abyss, 

 which had opened on the plain of Lelantus, threw up a 

 stream of glowing mud (lava)."| 



* Cosmos, vol. L, p. 231. 



f Strabo, i., p. 58, ed. Casaub. The epithet 8ia7rvpog proves that 

 in this case mud volcanoes are not spoken of. Where Plato, in his 

 geognostic phantasies, alludes to these, mixing mythical matter with 

 observed facts, he says distinctly (in opposition to the phenomenon 

 described by Strabo) vypov ttt]\ov 7rora/<oi. Upon the denominations 

 7nj\oQ and pva£> as volcanic emissions, I have treated on a former oc- 



