286 Baron Humboldt on Volcanoes. 



manent volcano within the crater of elevation itself, or amongst 

 the fragments of its previous constitution. At diiferent times, 

 along with different degi'ees of activity and force, permanent 

 volcanoes throw out jets of aqueous vapour, acids, glowing 

 ashes and scoriae, and, when the resistance can be overcome, 

 ribbon-shaped small fiery streams of melted earthy matter. 



As a consequence of a great but local manifestation of force 

 in the interior of our planet, elastic vapours raise either single 

 parts of the crust of the earth into dome-shaped, unopened 

 masses of felspathic trachyte and dolerite (Puy de Dome and 

 Chimborazo), or the upheaved strata are broken through, and 

 inclined outwards, in such wise, that upon the opposite inner 

 aspect a steep rocky edge is produced. This edge then be- 

 comes the boundary of a crater of elevation. When this 

 has risen from the bottom of the sea, Avhich does not, by any 

 means, happen in every case, it then determines the whole of 

 the characteristic physiognomy of the upheaved island. This 

 is the origin of the circular form of Palma, which Leopold 

 von Buch has described so carefully and so ably, as well as 

 of Xisyros, in the ^5ilgean Sea. Occasionally, one -half the 

 ring-like edge is destroyed ; and in the bay which the sea that 

 has flowed in then forms, the social coral polypi establish 

 themselves, and produce their cellular dwellings. Craters of 

 elevation on continents are also frequently found filled with 

 water, when they contribute to beautify the landscape in a 

 peculiar manner. 



Their origin is not connected with any particular moun- 

 tain rock ; they break out in basalt, trachyte, leucitic por- 

 phyry (Somma), or in doleritic aggregates of augite and Lab- 

 rador. Hence the very dissimilar natures and external forms 

 of this kind of crater edge. " No eruptive phenomena 

 take place from such boundaries. Through them there is no 

 permanent channel of communication established with the 

 interior ; and it is only very rarely that traces of still active 

 volcanic power are discovered in the precincts, or within the 

 cu-cuit of such craters. The force competent to bring about 

 such important eflfects, must long have accumulated, and 

 gained strength in the interior, before it could have over- 

 come the resistance of the superincumbent masses. On the 



