86 WALKS AND TALKS. 



the cone. This is the valley which separates the highest and 

 principal summit of the mountain from Monte Somma, a frag- 

 ment of an ancient crater of much larger size than the modern 

 one. The height of Vesuvius varies from 3,900 to 4,300 feet. 

 Monte Somma stands 3,642 feet. The slope of the mountain 

 near the base is 10, while the active cone has a gradient of 

 29 to 30. Monte Somma rises almost perpendicularly from 

 the Atrio del Cavallo, while on the opposite side, it slopes to 

 the plain at an angle of three degrees. 



The entire mountain, so far as can be seen, is a vast pile 



j of lava, lapilli (stones) sand and ashes (powder-like lava) 

 resulting from a long succession of eruptions. The molten 

 mineral matter thrown out is lava. It escapes from the regu- 

 lar crater or bursts out through some new fissure near the 

 summit, around which the erupted materials may accumulate 

 and form a subsidiary crater. The molten lava has a tem- 

 perature above 2000 Fah. Often vapor of water escapes with 



> the lava, and throws the molten mineral up with such violence 

 as to break it into fragments, the larger of which are known 

 as lapilli and scoriae, while the minuter fragments constitute 

 volcanic sand and ashes. The vapors rise to a height of about 

 ten thousand feet, and spread over the mountain like a vast 

 umbrella or Cedar of Lebanon. Indeed, the height sometimes 

 attained by this enormous canopy of vapor and ashes has been 

 shown by measurements to reach twenty-three thousand to 

 twenty-six thousand feet. Enormous quantities of ashes borne 

 upward with the vapor, give the cloud a dark and angry 

 appearance, and its frowning aspect is confirmed by the flashes 

 of lightnings which dart through it. By night the vivid re- 

 flection of the light thrown upward from the crater gives the 

 appearance of terrific flames roaring from the summit of a 

 burning mountain. But no proper combustion exists. Often 

 the condensation of the vapor results in rain which descends 

 in a torrent. The ashes mingled with water con vert the storm 

 into a deluge of mud. This rushes down the mountain with 

 destructive effects, and in several instances, whole villages and 

 even cities have been buried in mud. 



