MOVEMENTS AND DEFORMATIONS OF THE EARTH'S BODY. 569 



radical difference in the resulting movements, for, in the first case, the 

 movements are in a weak superficial shell that cannot accumulate great 

 stresses, and hence must yield practically as fast as the stresses arise, 

 while, in the second case, the stress-accumulating power of the thick seg- 

 ments may be great, and the stresses may gather for long periods and 

 give rise to great cumulative results at long intervals. In this respect 

 the last two views have much in common, though they differ in other 

 important particulars. 



With this general background of hypothesis, we may now turn to 

 the direct evidences of the distribution of internal temperature which 

 observations near the surface afford. Unfortunately they are limited 

 to a mere film, as it were, little more than t^q-q of the radius of the 

 earth. 



OBSERVED TEMPERATURES IN EXCAVATIONS. 



As the earth is penetrated below the zone of seasonal changes by 

 weUs, mines, tunnels, and other excavations, the temperature is almost 

 invariably found to rise. The rate of rise, however, is far from uniform. 

 If we set aside as exceptional the unusually rapid rise near volcanoes 

 and in other localities of obvious igneous infiuence, the highest rates 

 are still six times the lowest. A large number of records have been 

 collated by the Committee on Underground Temperatures, of the British 

 Association for the Advancement of Science. These range from 1° F. 

 in less than 20 feet to 1° F. in 130 feet, with an average of 1° F. in 50 to 

 60 feet, which has usually been taken as representative. The more 

 recent deep borings that have been carefully measured with due regard 

 to sources of error indicate a slower rate of rise. Some of the more 

 notable records are as follows:* 



Depth. Rate of rise. 



Sperenberg bore (Germany) 3492 feet. 1° F. In 51 . 5 feet. 



Schladeback bore (Germany) 5630 " 1°F. in67.1 " 



Cremome bore (X. S. Wales) 2929 " 1° F. in 80 " 



Paruschowitz bore (Upper Silesia) 6408 " 1° F. in 62 .2 " 



Wheeling well (W. Va.) 4462 " 1° F. in 74.1 " 



St. Gothard tunnel (Itah-Switzerland) 5578 " 1° F. in 82 " 



Mt. Cenis tunnel (France-Italy) 5280 " 1° F. in 79 " 



Tamarack mine (N. Mich.) . .\ 4450 " 1° F. in 100 "^ 



Calumet and Hecla mine (X. Mich.) 4939 " 1° F. in 103 "* 



Ditto, between 3324 feet and 4837 feet 1° F. in 93 . 4 " 



^ These are reckoned by assuming that the temperature of no variation at 50 feet 

 below the surface is 40° F. 



