510 



WITHIN THE EARTH'S CRUST 



have an area of about 1000 square miles, and the soil is 

 very fertile. The islands are mountainous, one of the 

 mountains rising to between 7000 and 8000 feet above the 

 sea. Their formation is due entirely to volcanic forces. 

 Islands of this kind and coral islands are the only projec- 

 tions rising to the surface from the deep ocean floor. 



In the Cordilleran region of the United States, west of 

 the meridian of Denver, there are a score or more of lofty 



THE CITY OF ST. HELENA 



peaks which show conclusive evidence of volcanic origin. 

 Until the summer of 1914 when Mt. Lassen suddenly began 

 to erupt, none of these had been active since white men 

 became familiar with the region. In the Aleutian Islands 

 are numerous volcanoes which are still active, and in Hawaii 

 are some of the greatest volcanoes on the earth. 



Extinct cones are sometimes found far in the interior of 

 continents, as the Spanish Peaks of Colorado, which are 



