DOMAIN 'XII. VOLCANIC. 



very slow progressive movement into the sea 

 throughout the whole of the 16th, and the fol- 

 lowing night. It was conceived that the sudden 

 cooling of the lava in the sea would have pro- 

 duced a basaltic construction; but it became 

 firm without assuming any regular form, an 

 effect which possibly is to be ascribed to the 

 heap of drosses with which it abounded*. The 

 main stream, from the point where it issued from 

 the volcano to that at which it stopped in the 

 sea, measured 12,961 feet. Its breadth varied 

 greatly ; in some places it scarcely exceeded 

 322 feet, but in the plain it spread to 1111; and 

 at a medium, without risk of any great error, it 

 may be computed to have been 725 feet broad. 

 In thickness also it differed according to the 

 depth of the hollows it filled : in the plain it was 

 constantly from twenty-four to thirty-two feet 

 thick ; and if its mean thickness be reckoned at 

 the latter number of feet, it may possibly be 

 nearest the truth. According to these data the 

 mass of molten matter is 1,869,627 cubic fathoms. 

 Convulsions. During the eruption the convulsion of the moun- 

 tain was so great that even the houses in Naples 

 were shaken by it. Still it was not constantly 

 alike. At the beginning the trembling was con- 



* The explanations of Ferrara are better. P 



