SINGULAR NATUKAL PHENOMENON. 119 



Without doubt such decompositions are con- 

 tinually taking place in the earth's crust. The 

 mineral called iron pyrites, which is a sulphuret 

 of iron, on exposure to moisture decomposes with 

 rapidity, and eliminates a large amount of heat. 

 It is well known that immense masses of this ore 

 exist in the earth ; and if we can imagine that a 

 current of water flowed upon or through them, 

 we may easily recognise a source of much heat 

 in the changes which would succeed. A French 

 chemist, M. F. Leblanc, examined the air of the 

 galleries of a mine of iron pyrites in a district 

 in Brittany, and found, strange to say, that 

 the air only contained from 17 to 18 per cent, 

 oxygen, and in some parts only 10 per cent., 

 without the deficiency being replaced by car- 

 bonic acid. This singular effect is attributable 

 to the pyrites walls of the mine absorbing this 

 gas from the air. This constant chemical pro- 

 cess could not go on without the evolution of a 

 large amount of heat. We may conceive, there- 

 fore, that a part of the earth's heat is derived 

 from this source also. Yet it seems impossible 

 to suppose that it is entirely due to this cause. 



Upon the third view, the earth's heat is due 

 to a great central body of fire. Probable 

 though this may be, when we remember the 

 phenomena of volcanoes emitting burning lava, 

 of hotsprings and earthquakes, it is only as yet 



