CHAPTER IX 



THE EAETH'S CRUST 



Changes in the Earth's Condition. Several theories 

 have been offered concerning the original conditions of the 



SPIRAL NEBULA 



The condition of one of the faint stars as revealed by the tele- 

 scope. It is millions of miles in extent. Most scientists 

 believe that the solar system was in such a nebular state as 

 this ages ago. 



earth, but as yet no one of them has been fully accepted. 

 Almost all scientists agree, however, that the matter of 

 the earth was once in a nebular, or gaseous, state. Uncounted 

 ages afterward it came into a molten, or exceedingly hot 

 liquid, condition ; and it has been gradually cooling ever since. 



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