58 THE OCEAN — A LECTURE. 



possessing the density of the earth, and having the same 

 velocity of rotation upon its axis, would, according to the 

 laws of gravity and motion, assume exactly the spheroidal 

 figure that the earth is known to possess — that is, an equa- 

 torial diameter greater than the polar by about twenty-six 

 miles. 



He said that facts in geology strongly corroborated this 

 position. The central nucleus of the crust of the earth is 

 composed of igneous, unstratified rock, the evident result of 

 the cooling of this molten mass of matter, of which the 

 granite rock is composed. 



The granite rock is of universal occurrence ; there is no 

 place on the surface of the globe where it could not be 

 found by penetrating to a sufficient depth. This was not 

 true of any other form of rock entering into the formation 

 of the crust of the earth. 



As a further evidence of the igneous character of the 

 granite, it was stated that a piece of granite rock might be 

 placed in a crucible and subjected to a degree of heat suf- 

 ficient to render it fluid, and then sufi'ered to cool under 

 pressure, that its texture and general appearance would in 

 no way be changed — it would still be granite, and possess 

 all the characteristics of that rock. This could not be said 

 of any of the stratified rocks — their whole structure and 

 appearance would be entirely changed. 



The legitimate inference to be drawn from this fact he 

 considered to be, that there was a time in the history of our 

 planet that no other rock existed but the granite, and that 

 this was in a state of fusion, or in a liquid state, from heat, 

 like melted iron. 



This position is further shown from the present condition 

 of our globe. 



By the most careful investigation b}^ Humboldt, and 

 other eminent men, it has been ascertained that there is a 

 line of equal and unvarying temperature, (49°F.,) in all 



