THE FIRE-HARDENED ROCKS 



ness and weight and " rigidity " greater than that of 

 ordinary steel. 



We are still some way off an explanation of how the 

 many igneous rocks which were and are being " boiled 

 up " in some inner molten cauldron came to the surface ; 

 but the better to understand that we must ask our 

 readers to carry their imagination back to the very 

 beginning of the world when it was " without form and 

 void." 



89 



