THE FIRE-HARDENED ROCKS 



information with which such a boring would furnish 

 engineers, miners, and geologists ; but the point that we 

 wish to make is that even with this enormous expenditure 

 of time, industry, and money we should be as far as ever 

 from knowing anything about the core of the earth. We 

 should have only gone about a third of the way through 

 what geologists call the earth's crust. 



Here, again, we are in a condition of difficulty. How 

 thick is the earth's crust ? and what is there beneath it ? 

 Well, as we are still such a long way from exploring it 

 we can only give a rather doubtful answer ; and we must 

 therefore try to show not only what is thought about the 

 earth's interior but why we think it. From Mr. Charles 

 Parsons' table it will be seen that he calculates that as 

 the boring went deeper it would find a higher and higher 

 temperature among the rocks. At two miles down it 

 would be hotter than the hottest summer's day at the 

 earth's surface ; at eight miles down water would boil by 

 itself; at twelve miles down, unless the cooling arrange- 

 ments were extremely good, the workmen would die like 

 flies. How does Mr. Parsons know that there would be 

 these temperatures, seeing that the deepest boring hitherto 

 made is only a mile ? He bases his calculations on what 

 we know already of the ascending temperature at deepen- 

 ing levels. 



For ten years Professor Agassiz took observations con- 

 cerning a very deep mine in the United States called the 

 Calumet and Hecla Mine. He and Professor Chamberlin, 

 after examining all the observations very carefully, came 

 to the conclusion that in going down from the earth's 



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