42 COSMOS. 



the Mina del Purgatorio was 42.26 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 everywhere indi- 

 cated a temperature of 67.64 F., there being thus a differ- 

 ence 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 temperature of the internal .air was 57.9 F., 

 showing therefore a difference of 15. 6 4 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 Micuipampa is probably not more than 

 45. 8 F. Iii Mexico, in the rich silver mines of Guanaxuato,* 3 

 I found in the Mina de Valenciana the external temperature 

 in the neighbourhood 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 temperature 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' 1ST., with a mean annual tem- 

 perature 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 tempera- 

 ture at mountain elevations, varying from 6000 to more 

 than 12,000 feet. 



A remarkable contrast is exhibited in the steppes of Nor- 

 thern Asia, by the conditions of the frozen soil, whose very 

 existence was doubted, notwithstanding the early testimony 

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

 rect views in relation to the distribution and thickness of 

 the stratum of subterranean ice have been established by 

 means of the admirable investigations of Erman, Baer, and 

 Middendorff. In accordance with the descriptions given of 

 Greenland by Cranz, of Spitzbergen by Martens and Phipps, 



43 Essai Polit. sur k Roy. de la Nouv. Espagne (2&me ed., t. iii, 

 P. 201). 



