THE IGNEOUS OR ERUPTIVE ROCKS 55 
the rocks and cooling there. These are intruded or 
plutonic rocks. 
In all cases, in the course of time, these must become 
Fic. 14. 
A piece of lava from surface of a flow, showing ropy surface, caused by flowing 
just before cooling. 
cold and hard. If they are buried deep within the 
crust, they may lie for ages hidden from view; but, as 
the surface of the land is destroyed and melts down, 
they may in time be reached, and we then have re- 
