INTERNAL CONDITION OF THE EARTH. 303 



surface, at least, was molten all over ; and it is 

 quite likely that the hypothesis more commonly 

 held namely, that it was molten throughout is 

 true. The most probable hypothesis that has been 

 given for the early history of the earth is, that it 

 was built up by the falling in of meteoric matter, 

 and that the matter falling in with great velocity, 

 acquired through gravitation, became heated by 

 collision. If this hypothesis is true, the heat caused 

 by the collisions, after the earth had grown to be 

 anything approaching to its present size, would be 

 far more than sufficient to melt the material 

 falling in. 



Let us now consider a red-hot liquid globe, and 

 suppose it to cool as does lava. The result of the 

 cooling is that as soon as any portion of the matter 

 reaches a temperature below the melting point, it 

 freezes and becomes solid. Instead of molten lava, 

 it becomes solid rock. And now comes the great 

 question will the solid rock thus formed sink or 

 float ? I wish this question could be answered. 

 We have at present very little information on the 

 subject -none of a definite kind, so far as I know, 



