252 



Mr W. J. Henwood on (he Temperature 



TABLE V. 



(1.) As the mining districts vary considerably in their geo- 

 logical characters, it might have been expected that the tem- 

 peratures at equal depths would not exactly coincide in all. 

 Of this inequality, which is very conspicuous in Table I., 

 it is not easy, and perhaps not possible, to give a satis- 

 factory explanation. As the situations of the mines differ 

 very much in their elevations, in very few instances do equal 

 depths below the surface hold the same positions with regard 

 to the sea-level. This is probably one cause of the observed 

 irregularities in temperature ; but it will presently be seen 

 that there are others, which depend on the geological charac- 

 ters of the rocks and veins. 



Table I. shews that the subterranean isothermal lines are 

 not exactly parallel to the configuration of the surface ;* al- 

 though, in many instances, there is a sort of distant resem- 

 blance in their outline. 



* " A chthonisothermal line of any temperature, ■which was under a small 

 district parallel to the surface, cannot continue its course under a neigh- 

 bouring mountain, either parallel to the external configuration of the moun- 

 tain, or in the continuation of its former direction, but must curve upwards," 

 Professor Bischof, Jameson's Edin. Nevj Phil, Journ,, xxiv. (1838), p. 146. 



