XX. 



THE EARTH'S INTERIOR. 



From a very early period, in all probability, 

 man's curiosity, ever awake to every form of 

 mystery, has been nmch exercised as to the solid 

 ground that lay beneath his feet, unexplored and 

 'inexplorable. What supported it, and how did 

 it get there ? In ancient Hindoo fable the world 

 is said to have been upheld on a gigantic elephant 

 and the elephant again to have been lifted on the 

 back of a huge tortoise. But what supported the 

 tortoise that supported the elephant that supported 

 the world, Hindoo mythology did not either deign 

 or venture to speculate. Probably that titanic 

 reptile was conceived of by his inventors as float- 

 ing on the waters with which popular imagination 

 hai.' at all times filled the interior of our planet. 

 So long indeed as the earth was regarded as a flat 

 phiiii — as it is still considered to be by a few un- 

 scientific and half-insane enthusiasts — there was 

 a certain show of evidence forthcoming for the 

 crude idea that its lower depths were composed 

 of water. Wherever men sank a well, if only 

 they dug deep enough, they were almost sure to 



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