SALSES. 223 



cannot be far removed from the surface during their ordinary 

 condition. The reaction of the interior of the Earth on its 

 external surface is exhibited with totally different force in true 

 volcanoes or igneous mountains, at points of the Earth in 

 which a permanent, or at least continually renewed connexion 

 with the volcanic force is manifested. We must here carefully 

 distinguish between the more or less intensely developed 

 volcanic phenomena as, for instance, between earthquakes, 

 thermal, aqueous and gaseous springs, mud volcanoes, and the 

 appearance of bell-formed or dome-shaped trachytic rocks 

 without openings ; the opening of these rocks, or of the ele- 

 vated beds of basalt, as craters of elevation ; and lastly, the 

 elevation of a permanent volcano in the crater of elevation, 

 or amongst the debris of its earlier formation. At different 

 periods, and in different degrees of activity and force, the 

 permanent volcanoes emit steam, acids, luminous scoriae or, 

 when the resistance can be overcome, narrow band-like streams 

 of molten earths. Elastic vapours sometimes elevate either 

 separate portions of the Earth's crust into dome-shaped un- 

 opened masses of feldspathic trachyte and dolerite (as in 

 Puy de Dome and Chimborazo), in consequence of some great 

 or local manifestation of force in the interior of our planet, or 

 the upheaved strata are broken through and curved in such a 

 manner as to form a steep rocky ledge on the opposite inner 

 side, which then constitutes the enclosure of a crater of ele- 

 vation. If this rocky ledge has been uplifted from the bottom 

 of the sea, which is by no means always the case, it determines 

 the whole physiognomy and form of the island. In this manner 

 has arisen the circular form of Palma, which has been de- 

 scribed with such admirable accuracy by Leopold von Buch, 

 and that of Nisyros,* in the ^Egean sea. Sometimes half of 

 the annular ledge has been destroyed, and in the bay formed 

 by the encroachment of the sea corallines have built their 

 cellular habitations. Even on continents craters of elevation 

 are often filled with water, and embellish in a peculiar manner 

 the character of the landscape. Their origin is not connected 

 with any determined species of rock : they break out in 

 basalt, trachyte, leucitic porphyry (somma), or in doleritic 



* See the interesting little map of the island of Nisyros in Ross's 

 Reisen aufden griechischen Inseln, bd. ii., 1843, s. 69. 



