226 THE EARTH'S INTERIOR. 



the enormous pressure of millions upon millions of 

 tons of solid rock, and square miles upon miles of 

 profound ocean, must aloiie suffice to account for 

 a gradual increase of temperature at every few 

 hundred yards we dig down into the eartli's inte- 

 rior. On these and many other similar grounds, 

 such as the evidence of the igneous origin of 

 granite and of many other extruded rocks, it was 

 fairly concluded among men of science that the 

 earth's core must be regarded as in a liigh state of 

 white heat. The rocks that most often underlie 

 all the others, or that liave been poured upward 

 and t :tward through all the otliers, came up at first 

 as molten masses, it was reasonable to conclude 

 that the other rocks which still form the solid 

 centre were even now in a like condition of melt- 

 ing heat — were, in fact, one vast and motionless 

 internal sea of liquid fire, a genuine volcanic Med- 

 iterranean. 



When first astronomy began to busy itself seri- 

 ously with the origin and history of our sun and 

 his family, this idea of the molten centre gained 

 ground still further every day, because of its ap- 

 parently strict accordance with all that was other- 

 wise known or conjectured of the solar system. 

 Every sun and every planet, according to the 

 luminous views of Kant and Laplace, started in 

 life as a condensing haze-cloud, a mere scattered 

 mass of very thin and perhaps gaseous material, 



