Baron Humboldt on Volcanoes. 287 



formation of new islands, it raises up granvdar rocky masses 

 and conglomerates (layers of tufa full of marine plants) above 

 the level of the sea. Compressed gases escape through the 

 crater of elevation ; but a mass of such magnitude, thus u.p- 

 heaved, sinks doAvn again, and closes forthwith the openings, 

 which are only formed for such manifestations of force. No 

 volcano is produced." 



A proper volcano only arises where a permanent connection 

 is established between the interior of the earth and the atmo- 

 sphere. Here the reaction of the interior upon the exterior 

 proceed for lengthened periods. It may, as in the case of 

 Vesuvius (Fisove), be interrupted for centuries, and exhibit 

 itself anew with renovated vigour. In the time of Nero, 

 it was already customary, in Rome, to rank ^tna among 

 the number of the gradually expiring volcanic mountains ; 

 _^lian, indeed, at a later period, maintained that the seamen 

 began to see the sinking summit at a less distance on the 

 high seas than formerly. Where the evidence of the erup- 

 tion — I might say the old scaffolding — has been perfectly pre- 

 served, the volcano shews itself rising from a crater of ele- 

 vation ; there a high rocky wall, a rampart of greatly inclined 

 strata, surrounds the isolated cone in the manner of a circus. 

 Sometimes there is not a trace of this circus-like enclosure 

 visible ; and the volcano, not always conical in figure, then 

 arises as an elongated ridge immediately from the elevated 

 platform. This is the case with Pichincha, at the foot of 

 which stands the city of Quito. 



As the nature of mountain rocks, in other words, the 

 combination or grouping of simple minerals into granite, 

 gneiss, and mica-slate, into trachyte, basalt, and dolerite, in- 

 dependently of present climates, and under the most dissimilar 

 zones, is still the same ; so do we everywhere observe the 

 same laws of formation proclaiming themselves in the realm 

 of inorganic nature, laws according to which the strata of the 

 crust of the earth stand in a certain relationship to one ano- 

 ther, and under the influence of elastic forces, break through 

 one another as dikes. This recurrence of the same pheno- 

 mena is particularly striking in volainocs. When the naviga- 

 tor, among the islands of distant seas, finds himself surrounded 



