208 LIGHT SCIENCE FOR LEISURE HOURS. 



craters within the great one. But these have now 

 united, and pressure from beneath has formed a vast 

 cone where they had been. The cone has risen above 

 the rim of the crater, and as we write torrents of lava 

 are being poured forth. At first the lava formed a 

 lake of fire, but the seething mass found an outlet, and 

 poured in a wide stream toward Ottajano. Masses of 

 red-hot stone and rock are hurled forth, and a vast 

 canopy of white vapor hangs over Vesuvius, forming 

 at night, when illuminated by the raging mass below, 

 a glory of resplendent flame around the summit of the 

 mountain. 



It may seem strange that the neighborhood of so 

 dangerous a mountain should be inhabited by races 

 free to choose more peaceful districts. Yet, though 

 Herculaneum, Pompeii, and Stabise, lie buried beneath 

 the lava and ashes thrown forth by Yesuvius, Portici 

 and Resina, Torre del Greco and Torre dell' Annun- 

 ziata have taken their place ; and a large population, 

 cheerful and prosperous, flourish around the disturbed 

 mountain, and over the district of which it is the some- 

 what untrustworthy safety-valve. 



It has, indeed, been well pointed out by Sir Charles 

 Lyell that "the general tendency of subterranean 

 movements, when their effects are considered for a 

 sufficient lapse of ages, is eminently beneficial, and 

 that they constitute an essential part of that mechanism 

 by which the integrity of the habitable surface is pre- 



