48 cosmos. 



served in the mines of Mangan, Shilow, and Dawydow, which 

 are situated at about three or four miles from Irkutsk, in the 

 chain of hills on the left bank of the Lena, and which are 

 scarcely more than 60 feet in depth, that the normal stratum 

 of perpetual frost seems to be situated at 320 feet below the 

 surface.* Is this inequality only apparent in consequence 

 of the uncertainty which attaches to a numerical determina- 

 tion, based on so inconsiderable a depth, and does the in- 

 crease of temperature obey different laws at different times'? 

 Is it certain that if we were to make a horizontal section of 

 several hundred fathoms from the deepest part of Schergin's 

 shaft into the adjoining country, we should find in every di- 

 rection and at every distance from the mine frozen soil, in 

 which the thermometer would indicate a temperature of 4° # 5 

 below the freezing point ? 



Schrenk has examined the frozen soil in 67° 30' N. lat., in 

 the country of the Samojedes. In the neighborhood of 

 Pustojenskoy Gorodok, fire is employed to facilitate the 

 sinking of wells, and in the middle of summer ice was found 

 at only 5 feet below the surface. This stratum could be 

 traced for nearly 70 feet, when the works were suddenly 

 stopped. The inhabitants were able to sledge over the 

 neighboring lake of Usteje throughout the whole of the sum- 

 mer of 1813.| During my Siberian expedition with Ehren- 

 berg and Gustav Rose, we caused a boring to be made in a 

 piece of turfy ground near Bogoslowsk (59° 44' N. lat.), 

 among the Ural Mountains, on the road to the Turjin mines. | 

 We found pieces of ice at the depth of 5 feet, which were 

 imbedded, breccia-like, in the frozen ground, below which 

 began a stratum of thick ice, which we had not penetrated 

 at the depth of 10 feet. 



The geographical extension of the frozen ground, that is to 

 say, the limits within which ice and frozen earth are found 

 at a certain depth, even in the month of August, and conse- 



* Middendorff, bd. i., s. 160, 164, 179. In these numerical data and 

 conjectures regarding the thickness of the frozen soil, it is assumed 

 that the temperature increases in arithmetical progression with the 

 depth. Whether a retardation of this increase occurs in greater depths 

 is theoretically uncertain, and hence there is no use in entering upon 

 deceptive calculations regarding the temperature of the centre of the 

 earth in the fused heterogeneous rocky masses which give rise to cur- 

 rents. 



t Schrenk's Reise durch die Tundern der Samojeden, 1848, th. i., 

 s. 597. 



X Gustav Rose, Reise nach dem Ural, bd. i., s. 428. 



