42 INTERNAL HEAT OF THE EARTH, 



the Mina de Guadalupe, which is at the same elevation, I 

 found the internal temperature 14'4 Cent. (57'9 Fahr.), 

 the difference from the external air being therefore 8*7, or 

 15* 8 Fahr. The waters which were streaming down in this 

 very wet mine showed 11'3 Cent. (52'3 Fahr.) The 

 mean annual temperature of the air at Micuipampa is 

 probably not above 1\ Cent., or 45^ Fahr. In Mexico, 

 in the rich silver mines of Guanaxuato, I found at the 

 Mina de Yalenciana( 43 ) the temperature of the external air 

 near Tiro Nuevo (7122 Paris, or 7590 English, feet above 

 the sea) 21'2 Cent., or 70'16 Fahr.j and the air in the 

 deepest part of the mine, in the Planes de San Bernardo 

 (1630 English feet below the opening of the shaft of Tiro 

 Nuevo), fully 27 Cent., or 80'5 Fahr., which is about 

 the mean temperature of the shore of the Gulf of Mexico. 

 In a part of the mine situated 147 feet higher than the floor 

 of the Planes de San Bernardo, there bursts out from the 

 rock a spring of water of the temperature of 29'3 Cent., 

 or S4'74 Fahr. The mountain town of Guanaxuato, 

 situated, according to my determination, in 21 N. lat., 

 has a mean temperature falling, approximately, somewhere 

 between 15-8 and 16'2 Cent., (60'44 and 61-16 Fahr.} 

 It would be unsuitable to enter here into conjectures, diffi- 

 cult to establish on any very certain grounds, as to the 

 causes, possibly of very local influence, which thus raise 

 the temperature of subterranean spaces, in ranges of moun- 

 tains from six to thirteen thousand feet high. 



A remarkable contrast to the above is presented by 

 the circumstances of the ground-ice in the steppes of 

 Northern Asia. Even the existence of this phenomenon 

 was formerly doubted, notwithstanding the testimony early 



