About the Long Past 



the Earth, on land and under the ocean ; but 

 numberless hot- water springs exist, some of them 

 a thousand miles away from any known volcano. 

 Then again, when deep mining or boring opera- 

 tions take place, it is noted that the degree of 

 warmth for a while corresponds to the state 

 of the weather above, but that beyond the 

 limits of seasonal change the temperature rises 

 with increase of depth. This looks like greater 

 heat below. 



Many scientists have held strongly that, as 

 above suggested, the whole inside of our Earth 

 is so far heated as to be in a molten condition, 

 contained within a cool hard crust, which may 

 be from twenty to fifty miles in thickness. 



Others have maintained that the said crust 

 cannot be less than two thousand miles thick, 

 with a small molten core. 



Others believe that the entire Earth is actually 

 solid throughout ; the outer parts from coolness ; 

 the inner parts from great pressure. 



Again, a theory has been started of a solid 

 centre and a solid crust, with an intervening 

 " fire-sea " of molten rocks ; and another of a 

 gaseous inner globe, surrounded first by molten 

 layers, then by a firm inclosing crust. 



All these different explanations rest upon one 

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