STRUCTURE AND ACTION OF VOLCANOS. 357 



trachyte, obsidian, and pearl-stone. These masses are deve- 

 loped from each other, and break through the lower chalk 

 formations and nummnlitic limestone, but have never been 

 emitted in narrow streams. Similar evidence of former 

 revolutions of our earth, is afforded in many parts of the 

 Greek Continent and in Western Asia, countries which will 

 undoubtedly some day yield the geologist ample materials for 

 investigation, when the light of knowledge shall again shine 

 on those lands whence it first dawned on our western world, 

 and when oppressed humanity shall cease to groan beneath 

 the weight of Turkish barbarism. 



I allude to the geographical proximity of such numerous and 

 various phenomena in order to show that the basin of the 

 Mediterranean, with its series of islands, might have enabled 

 the attentive observer to note all those phenomena which 

 have recently been discovered under various forms and struc- 

 tures in South America, Tcneriffe, and in the Aleutian 

 islands, near the Polar region. The materials for observation 

 were, no doubt, accumulated within a narrow compass ; but 

 it was yet necessary that travels in distant countries and 

 comparisons between extensive tracts of land, both in and out 

 of Europe, should be undertaken, in order to obtain a correct 

 idea of the resemblance between volcanic phenomena and of 

 their dependence on each other. 



Language, which so frequently imparts permanence and 

 authority to first, and often also erroneous views, but 

 which points, as it were, instinctively to the truth, has 

 applied the term volcanic to all eruptions of subter- 

 ranean fire and molten matter; to columns of smoke and 

 vapour which ascend sporadically from rocks, as at Colares, 

 after the great earthquake of Lisbon; to Salses, or argil- 

 laceous cones emitting moist mud, asphalt, and hydrogen, 

 as at Girgenti in Sicily, and at Turbaco in South America; 

 to hot Geyser springs, which rise under the pressure of elastic 

 vapours; and, in general, to all operations of impetuous 



