254 Natural History of Volcanos and Earthquakes. 



action, may, however, be thus imagined ; that the water which 

 descends to the volcanic focus is there converted into steam, 

 which, rising througli fissures into higher regions, meets with at- 

 mospheric waters which it warms, and with them returns to the 

 surface.* The course of hot springs produced in this manner 

 can, therefore, occur only at inconsiderable depths below the sur- 

 face. Lastly, it may happen that the lava last raised did not es- 

 cape from the crater or its lateral openings, but became solid on 

 its way onwards, and thus stopped up the channels. If, in this 

 case, water should descend through rents into this still extremely 

 hot lava, hot springs would also thus be produced, supposing a 

 communication between these and other rents which lead to the 

 surface at a lower level ; but these springs will decrease in tem- 

 perature by degrees as the lava gradually cools, till they reach 

 that degree which naturally belongs to the place where the lava 

 is situated. However, we have already proved by experiments 

 formerly mentioned, and calculations founded upon them, that, if 

 such masses of heated lava be of considerable extent, a very long 

 period may elapse before the decrease in the temperature of the 

 springs will be even perceptible.f On the other hand, there are 

 examples of a very rapid decrease in the temperature of hot 

 springs in the neighborhood of volcanos recently become extinct. 

 Thus, the temperature of the hot springs on JoruUo decreased 

 40^.5 F. in twenty four years, between the visits of Von Hum- 

 boldt and Burkart.| The temperature of the mixture of gases 

 which issues from the rents in the Pass of Quindiu, near the Mo- 

 ral, in the Quebrada del Azufral. decreased from 1801 to 1827, 

 according to the observations of Von Humboldt and Boussingault, 

 from 118° to 66°.4.*§> If, instead of this gas, a mineral spring had 

 flowed at this place, it would, doubtless, have suffered a similar 

 diminution of temperature. Boussingault mentions, on the other 

 hand, that, in a period of twenty-three years, the temperature of 



* Perhaps the numerous hot mineral springs which rise at the foot of the still 

 smoking mass of rocks on Pantellaria, as well as the numerous hot sulphureous 

 springs in the vicinity of Sciacca, in Sicily, have a similar origin. Hoffmann, 1. c. 



t Die vulkanischen Mineralquellen, &c. p. 150. — I have calculated, that, under 

 the circumstances there mentioned, a mass of melting basalt, equal in size to one- 

 third of the Donnersberg, near MiUeschau, in Bohemia, would be sufficient to have 

 heated all the water which has issued from the whole number of springs at Carls- 

 had since the time of Adam. 



t Burkart, loco cit. t. i, p. 226. § PoggendorfF's Annal. t. xviii, p. 353. 



