ORIGIN OP ERUPTIVE AND PRIMARY ROCKS. 331 



Kamschatka and the Aleutian Island, between a latitude of 50° 

 and 66° tbey exist as numerously as in the Sunda isles, Galapa- 

 gos and in Quito between 0° and 10° lat. But we find them 

 especially frequent on the coasts of continents or rising out of the 

 depth of the ocean, proving that there the conditions are especi- 

 ally present which are necessary to their development and activity. 

 From all this we may conclude that the material cause of Vulcan- 

 ism is present everywhere beneath the earth's crust, although it 

 may only have been able to break out along certain lines and at 

 certain points." By means of volcanoes and the subterranean 

 canals connected with them, a communication is established be- 

 tween the molten zone beneath the earth's crust and the atmos- 

 phere. This communication is liable to be interrupted by vari- 

 ous circumstances, and when this is permanently the case the 

 volcano is extinct. But even the active volcanoes are far from 

 being continually in a condition of violent eruption, their usual 

 activity is rather of a very temperate character, and F. Hoffmann 

 very correctly remarks that the energetic eruptions are more the 

 exception than the rule. Volcanoes in a state of rest exhale steam 

 and other gases and it is even the case, that a quiet effusion of 

 lava can take place unaccompanied by any extraordinary phe- 

 nomena. Generally however the ascent of the lava in the canal 

 and crater of the volcano is the immediate cause of all the sublime 

 effects and terrible devastations, which accompany and follow vol- 

 canic eruptions. It is still a matter of doubt among philosophers 

 as to what is the real cause of the ascent of the lava from its home 

 in the depths of the earth. The oldest hypothesis is that which 

 attributes the force, which expels the lava to highly compressed 

 steam, resulting from the access of water, and especially of sea 

 water, to the regions filled with igneous fluid beneath the earth's 

 crust. In later times this view has been adopted by very many 

 philosophers such as Gay Lussac, Von Buch, Angelot, Bischof, and 

 Petzholdt. On the other hand, Humboldt does not at all regard 

 the problem as completely solved,* and Naumann does not consid- 

 er it probable that the expansive force of the steam derived from 

 sea-water is the cause of the ascent of the lava, although he con- 

 siders it as quite certain, that sea and other water obtains access 

 through the eruptive canals of volcanoes to very great depths, 

 and on the ascent of the lava plays a very important part in the 

 phenomena of volcanic eruptions. Naumann's view so far as re- 



* Cosmus I, 243. 



