90 volcanoes; earthquakes. 



Under the name of volcanic phenomena, we 

 include all those mighty exertions of underground 

 forces by which, — from openings torn in the earth's 

 crust, — streams of fire, smoke, and ashes (that is, 

 fine red-hot sand and dust) are thrown up often to 

 an incredible height, and glowing slags and stones, 

 and even great pieces of rock are hurled forth; 

 copious streams of lava, or melted mineral matter, 

 and in many cases enormous quantities of mud and 

 water are shot forth ; sometimes hills have been 

 lifted up in valleys and plains, and islands have been 

 thrown up in the sea. 



Numberless instances of such phenomena have 

 occurred within historical times, and are still re- 

 peated every year. 



In by far the greater number of cases, the out- 

 lets of this volcanic activity have served for only 

 one discharge. They become stopped up again, 

 when the force from below has exhausted itself for 

 the time. When the elastic powers within have 

 recovered themselves, they find vent by some other 

 way. Here and there, however, some lasting 

 channels have been established from the interior 

 up to the surface. These form, as it were, the 

 chimneys of the fire-places underground, and are 

 called especially Volcanoes, or Burning Moun- 

 tains. 



There are at present at least a hundred and sixty, 

 of great activity, scattered over the earth. Several 



