380 KEPORT UNITED STATES GEOLOGICAL SURVEY. 



CHAPTER VI. 



TEMPERATURE. 



SOURCE OF HEAT. 



In a preceding chapter we have noted that the waters of thermal 

 springs, and in fact of all springs, are meteoric in their origin, and we 

 now inquire whence is their heat derived. In the Greek Anthology, in 

 a poem on the Pythian hot baths by Paulas Silentiarias, chief silence- 

 keeper to the Emperor Justinian, is the following speculation as to the 

 cause of the heat of springs : 



It is conceived by some that there are narrow fissures below the earth ; that oppos- 

 ing currents meeting from various quarters are compressed, and by that compression 

 acquire no ordinary heat. Others, on the contrary, say that in recesses of the earth 

 there are somewhere sulphurous ores ; that the neighboring stream, therefore, meeting 

 with a violent heat, from the inability to remain below, rushes Tij)ward in a mass. 

 Which opinion will my readers adopt? The former? I do not myself embrace this. 

 I agree with the latter, for there is a mephitic oifensive stench clearly proving it. 

 * * * 'Twas thus the hot, bubbling fluid issued for the benefit of mankind — an 

 inanimate Hippocrates, a Galen untaught by art. 



This was written, in all probability, some time about 550 A. D. 

 As long ago as the third century the question was answered by St. 

 Patricus, who was probably bishop of Pertusa, as follows : 



Fire is nourished in the clouds and in the interior of the earth, as Etna and other 

 mountains near Naples may teach you. The subterranean waters rise as if through 

 siphons. The cause of hot springs is this : waters which are more remote from the 

 subterranean fires are colder, while those which rise nearer the fire are heated by it, 

 and bring with them to the surface, which we inhabit, an insiipportable degree of heat.* 



These quotations i)resent three of the theories as to the heat of the 

 earth — viz, chemical, mechanical, and volcanic agency. The following 

 are the sources of the earth's heat: 1st. The sun; 2d. Chemical and me- 

 chanical action; 3d. Internal heat. As sources of heat for thermal 

 springs, only the second and third need to be mentioned here. 



2d. Gliemical and mechanical action. — The amount of heat received by 

 the earth through chemical action is inconsiderable, and the theory that 

 the heat of thermal springs is due to chemical action, although it once 

 had many advocacies, was demolished by Bischof. In limited areas a 

 part of the heat may be due to chemical action. Mechanical action, 

 however, as in the motion attending the plicating and uplifting of rocks, 

 has been demonstrated by Mallet, Hunt, Le Conte, and others, to be 

 a very ef&cient source of heat. Professor .Eogers, Mr. G. K. Gilbert t, 

 and others have pointed out the coincidence between the occurrence of 

 thermal springs and mountain corrugation in the United States. In the 

 east we have the Appalachian region, in which we find a system of ther- 

 mal springs, in which, however, the temperatures do not exceed 108°. 

 In Arkansas, the Ozark ridges account for the presence of the springs, 

 and in the West we have the Eocky Mountain corrugations. Along the 

 Atlantic coast, in the Mississsippi Valley, and in the Colorado Plateau 

 we have no hot springs. 



That the teraijeratures in the mountain regions are not due alone to 

 the regular downward increase in tcmi)erature is probable, because, in 

 the case of the artesian well at Louisville, Kentucky, the water from 

 the bottom of the well has a temperature of 86^, while at the surface 

 it is only 70^, and in the Virginia region the surface temperature reaches 



* Humboldt's Cosmos, Bohn's edition, vol. 1, p. 221. 



t Report upon Geological and Geographical Explorations and Surveys West of the 

 100th Meridian, &c., vol. iii, pages 145-149. 



