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 through 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 @ 
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.t On the other hand, there are 
examples of a very rapid decrease in the temperature of hot 
springs in the neighborhood of voleanos recently become extinct. 
Thus, the temperature of the hot springs on Jorullo decreased 
40°.5 F. in twenty four years, between the visits of Von Hum- 
boldt and Burkart.t| 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 ha 
: 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 
re 
* 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, |. & 
t Die vulkanischen Mineralquellen, &c. p. 150.—I have calculated, that, onde 
the circumstances there mentioned, a mass of melting basalt,.equal in 
third of the Donnersberg, near Milleschau, in Bohemia, would be s 
heated all the water which has issued from the whole number of sprin 
bad since the time of Adam. 5 ae 
t Burkart, loco cit. t. i, p. 226. § Poggendorff’s Annal. t. xvill; Pr" 
gs at Carls- 
Bk Nah A eee 
