Natural History of Volcanos and Earthquakes. 253 



stances are exhibited, which indicate that these rocks are of very 

 different ages.* 



If the activity of a volcano ceases, but the channels by which 

 the waters enter remain open, the volcanic action may be replaced 

 by hot springs-! I'^ this case it is easy to conceive that the me- 

 teoric waters, continually sinking into the hot interior, would 

 there assume the surrounding high temperature, and rise again to 

 the surface with a temperature, diminished proportionally to the 

 decrease of pressure, either through the former lava-channels, or 

 other fissures more recently opened.^ But if at that depth, the 

 hydrostatic pressure be greater than the elastic force, which the 

 water has there acquired, no steam will be generated in the whole 

 course of the spring ; but, in the contrary case, from the lowest 

 point up to the point where the elastic force becomes greater than 

 the hydrostatic pressure, the water will escape in the form of a 

 vapor. However high the temperature of the water may be at 

 the lowest point of its course, whether in the liquid or in the 

 gaseous state, yet, when it reaches the surface, it cannot exceed 

 the boiling point. The reason of springs but seldom attaining 

 even this maximum, may be either the loss of heat communicated 

 to the superior strata of the earth, or that they meet with streams 

 of gas, (carbonic acid, or sulphuretted hydrogen,) which, even if 

 possessed of very high temperature, will cause a depression of 

 their temperature, as is proved by experiments cited in Chap. II, 

 of Memoir on Springs, p. 336, vol. xx, Ed. Phil. Journ.'^. The 

 production of hot springs, according to the last species of volcanic 



* L. Horner, 1. c. p. 467. 



t Von Buch, loco cit. p. 65. A remark of some interest, in tracing the connec- 

 tion of hot springs with volcanic phenomena, is made by Burkart, loco cit. vol. i, 

 p. 316, viz. that the boiling hot springs in the valley o? Pate are situated on a line, 

 running from east to west, parallel to the general line, of volcanos in Mexico. 



X Von Humboldt is also of opinion, Reise, &c. t. i, p. 187 and 188, that the va- 

 por which rises from the " JVarices del Pico" as they are called, and from the rents 

 in the crater of Teneriffe, is nothing but atmospherical water which has penetrated 

 by infiltration. 



§ According to M. Arago, the hottest spring in Europe unconnected with mod- 

 ern volcanic action is that of Clumdesaigues in Auvergne, whose temperature he 

 quotes at 176° Fah. Annuaire du Bureau des Longitudes, 1836. The next hot- 

 test to this seems to be Tkuez, in the Pyrenees, whose temperature is, according to 

 Professor Forbes, 1710.5 Fah. Phil. Trans, t. ii, p. 6(J3, for 1826. Forbes believes, 

 p. 610, the baths of Nero, near ^''ajjles, the hottest spring on the continent o? Eu- 

 rope, which is connected with modern volcanic action, the temperature bein<^ 

 182°.2 F. 



