MINERALOGY. 419 



ing destroyed every thing in its way, and at length the 

 tumult ceases, and all is still. 



Third Period. After the volcano has become quiet, 

 and the smoke and flame has abated, new thunderings. like 

 the firing of heavy cannon, new explosions and tremblings 

 commence, amid which a majestic pillar of smoke ascends 

 from the crater to a great height, and spreads an ex- 

 tended broad, dark canopy over the whole mountain. 

 Spectators have likened this singular and striking phe- 

 nomenon to a gigantic pine. A steady rain or shower of 

 stones, fine volcanic dust, and pumice, or gray particles 

 of lava, now fall from the black, overhanging cloud which 

 canopies the mountain, extending to a considerable dis- 

 tance and obscuring % the light of the sun. This shower 

 of ashes often continues for many days, after which, ac- 

 companied by crashing thunder and vivid electric flashes, 

 a dark cloud settles upon the crown of the mountain. 

 Torrents of rain, the effect of condensed vapors, now 

 begin to fall, and from the inundations of mud which 

 they cause are dreaded as being more disastrous in their 

 consequences than the streams of burning lava, and close 

 the scene. After such fearful eruptions, various hurtful 

 gases are generated, and issuing from the crater, pollute 

 the air for miles around. The principal volcanic forma- 

 tions are, first, 



Lava, which, when cooled, exhibits no regular struc- 

 ture ; sometimes it is firm and compact above, at others 

 porous, cellular, or scoriaceous. There are also speci- 

 mens of lava which constitute regular rocklike masses ; 

 the colors are mostly brownish-yellow or greenish-gray 

 some, not seldom, contain mineral substances, as Obsidian 

 (volcanic glass), etc. 



Pumice Stine Bimstein is a light, porous scoria, 



