CHAPTER XLII 



THE ROCKS AND BUILDING STONES OF THE EARTH 



Granite. Lava does not all find an outlet to the earth's 

 surface through vol- 

 canic vents. Large 

 quantities of it 

 never reach the sur- 

 face, but harden 

 underground in 

 cracks and fissures 

 and form under- 

 ground rock. Some- 

 times lava in its 

 effort to escape up- 

 lifts the overlying 

 rock, and creates an 

 elevation beneath 

 which it slowly cools 

 and solidifies. Lava 

 upon solidifying be- 

 comes igneous rock. 

 The character of 

 this rock depends 

 upon the parent lava 

 and the conditions 

 under which it 

 solidified. 



Granite, an ig- 

 neous rock, is close FIG. 283. Obsidian cliff, Yellowstone Park. 



417 



