44 cosmos. 



metrical observations, in the latitude 6° 43' S., and at an 

 elevation of 1857 toises, or 11,990 feet, at the base of Cerro 

 de Gualgayoc, celebrated for the richness of its silver mines. 

 The summit of this almost isolated fortress-like and pictur- 

 esquely situated mountain rises 240 toises, or 1504 feet, high- 

 er than the streets of Micuipampa ; the external air at a dis- 

 tance from the mouth of the pit of the Mina del Purgatorio 

 was 42° *2 6 F. ; but in the interior of the mine, which lies 

 more than 2057 toises, or 13,154 feet above the sea, I saw 

 that the thermometer every where indicated a temperature 

 of 67°*64 F., there being thus a difference of 25°-38 F. The 

 limestone rock was here perfectly dry, and very few men 

 were working in the mine. In the Mina de Guadalupe, 

 which lies at the same elevation, I found that the temper- 

 ature of the internal air was 57° # 9 F., showing, therefore, a 

 difference of 15°*64 F. when compared with the external 

 air. The water which flowed out from the very damp mine 

 stood at 52°*34 F. The mean annual temperature of Micui- 

 pampa is probably not more than 45° -8 F. In Mexico, in 

 the rich silver mines of Guanaxuato,* I found, in the Mina 

 de Yalenciana, the external temperature in the neighborhood 

 of the Tiro Nuevo (which is 7590 feet above the sea) 70°-16 F., 

 and the air in the deepest mines — for instance, in the Planes 

 de San Bernardo — 1630 feet below the opening of the shaft 

 of Tiro Nuevo, fully 80° *6 F., which is about the mean tem- 

 perature of the littoral region of the Gulf of Mexico. At a 

 point 147 feet higher than the mouth of the Planes de San 

 Bernardo, a spring of water issues from the transverse rock, 

 in which the temperature is 84°'74 F. I determined the 

 latitude of the mountain town of Guanaxuato to be 21° 0'N., 

 with a mean annual temperature varying between 60°-44 and 

 61°-26 F. The present is not a fitting place in which to 

 advance conjectures, which it might be difficult to establish 

 in relation to the causes of probably an entirely local rise of 

 the subterranean temperature at mountain elevations, varying 

 from G000 to more than 12,000 feet. 



A remarkable contrast is exhibited in the steppes of 

 Northern Asia, by the conditions of the frozen soil, whose 

 very existence was doubted, notwithstanding the early testi- 

 mony of Gmelin and Pallas. It is only in recent times that 

 correct views in relation to the distribution and thickness of 

 the stratum of subterranean ice have been established by 



* JEssai Polit. sur le Roy. de la Nouv. Exj>agnc (2ume cd., t. iii., 

 p. 201). 



