104 Sir A. Crichlon on tite [Feb. 



America arise from the granitic and primary strata. As to the 

 hypothesis of their deriving their heat from the chemical decom- 

 position of sulphurets, &c. the limited and changeable operation 

 of such a cause, compared with the permanency and greatness 

 of the effect, are sufficiently strong reasons to make us abandon 

 this explanation. 



It is here that I must add a few facts which relate to the heat 

 of mines. The following are taken from a paper of Robert 

 Balds, Esq. in the Edinburgh Philosophical Journal, vol. vi. : — 



Whitehaven Colliery, Cumberland. 



Average temperature of a spring at the surface 49 Fahr. 



Ditto of water at the depth of 480 feet 60 



Air at the same depth 63 



Air at 600 feet 65 



Worki/igfoii Colliery, Cumberland. 



A spring at the surface 48 



Water at the depth of 180 feet 50 



Ditto at the depth of 504 feet below the level of ocean, 

 and unjler the Irish sea 60 



Teem Colliery, Durham. 

 Water at the depth of 444 feet 61 



Percy Mine Colliery, Northumberland. 



Average temperature of water at the surface 49 



Water 900 feet deeper than the level of the sea 68 



Difference 19 



Jarrow Colliery, Durham. 



Average temperature of water at the surface 49 



Water at 832 feet 68 



Killingivorth Colliery, Northumberland {being the deepest Coal 

 Mine in Great Britain). 



Water at the surface 49 



Air at 790 feet deep 51 



Ditto at 900 from the surface, after having traversed 



li mile from the downcast pit 70 



Water at the great depth of 1 200 feet 74 



Baron Humboldt, whose talents for observation, and whose 

 accuracy, cannot be doubted, informs us that the mine of Valen- 

 ciana is so warm, that the miners are constantly exposed to a 

 temperature of 91*4 of Fahrenheit, while the mean temperature 

 of the external air is 60*8. 



The springs which issue from veins of the same mine at the 

 depth of 1638 feet, have a temperature of 98*2, which is 5*4 



