STRUCTURE AND ACTION OF VOLCANOS. 373 



the disengagement of caloric ensues. The celebrated and 

 talented chemist, who advanced this explanation of volcanic 

 phenomena, soon himself relinquished it. The experiments 

 which have been made in mines and caverns in all parts 

 of the earth, and which M. Arago and myself have col- 

 lected in a separate treatise, prove that even at an in- 

 considerable depth, the temperature of the earth is much 

 higher than the mean temperature of the atmosphere at 

 the same place. This remarkable, and almost universally 

 confirmed fact, is connected with what we learn from 

 volcanic phenomena. The depth at which we might re- 

 gard the earth as a fused mass, has been calculated. The 

 primitive cause of this subterranean heat is, as in all planets, 

 the formative process itself, the separation of the spherically 

 conglomerating mass from a cosmical aeriform fluid, and the 

 cooling of the terrestrial strata at different depths by the radia- 

 tion of heat. All volcanic phenomena are probably the result 

 of a permanent or transient connection between the interior 

 and the exterior of our planet. Elastic vapours press the 

 fused oxidizing substances upwards through deep fissures. 

 Volcanos therefore are intermittent earth-springs, from 

 which the fluid mixtures of metals, alkalies, and earths, which 

 become consolidated into lava currents, flow gently and 

 calmly, when being upheaved they find a vent. In a similar 

 manner, according to Plato's Phaedon, the ancients regarded 

 all volcanic streams of fire as effusions of the Pyriphlegethon. 

 I would fain be permitted to add one yet bolder observa- 

 tion to those I have already ventured to advance. May not 

 the cause of one of the most wonderful phenomena presented 

 by the study of petrifactions, be dependent on the condition of 

 the inner heat of our planet, which is indicated by thermometric 

 experiments on springs (3) rising from different depths, and 

 by observations on volcanos? We find tropical animals, 

 arborescent ferns, palms, and bamboos, buried in the cold 

 north, and everywhere the primitive world presents a distri- 



