Volcanos and Earthquakes. ¥1 



may gradually increase by the solidifying of the melted mat- 

 ters; nay, the rent may be entirely solidified and obstructed, 

 so that it can only now be re-opened by the force of steam pre- 

 vious to a new eruption taking place. If even immense quan- 

 tities of lava are ejected by the steam, yet the level of the melt- 

 ed matters in the interior may be but slightly changed, for 

 in the same manner, as all seas on the surface of the earth 

 communicate together, so the melted matter in the interior does 

 the same. However, more or less time may elapse, before the 

 melted matter which has sunk at one place in consequence of 

 ejection, can regain its former level by the afflux of other melt- 

 ed matters from a distance. Therefore the repose and ac- 

 tivity of a volcano, besides depending on the interruption 

 and renewal of the supply of water to the volcanic focus, may 

 also proceed from the alternate obstruction and re-opening of 

 the lava channel by the melted matters. In, the latter case, in 

 the state of rest, exhalations of steam will take place, inasmuch 

 as water penetrates continually to the volcanic focus. 



But if the afflux of water be interrupted by an obstruction 

 of the water-ducts, and if none of the above-mentioned causes 

 be capable of restoring the communication ; or if. during the 

 repose of the volcano, the lava-ducts become so obstructed by 

 consolidation, that the steam cannot force its way through 

 them, a volcano may reach a state of perpetual repose. Such 

 causes may have effected the extinction of the volcanic activity 

 of the numerous extinct volcanos distributed throughout the 

 globe. If this took place at a former period, when the thick- 

 ness of the crust of the earth was still increasing considerably, 

 in consequence of the gradually cooling of the earth, and as 

 this process is still going on, there is no probability that such 

 extinct volcanos will at any time become again active. 



If volcanos, for instance Etna, are considerably elevated 

 above the surface of the earth, it commonly happens that the 

 walls of the lava-channels cannot resist the pressure of the 

 melted matter in their interior. In this case rents are formed 

 from which the lava issues. Such rents are always seen in the 

 direction of the axis of the volcanic cone,* and their extent is 



* Von Buck's Beobachtungen, &c. t. ii. p. 137. 



