XII.] 



EARTHQUAKES AND VOLCANOES. 



195 



formation of a new cone seated within the old crateral 

 hollow. Great changes may indeed be effected in the 

 character of a volcano by successive eruptions, new cones 

 being thrown up at one time, and old ones obliterated at 

 another. Fig. 54, shows the summit of Vesuvius as it 

 appeared in 1756, when there were no fewer than three 

 separate cones, one within another, encircling as many 

 craters. But about ten years afterwards the summit pre- 

 sented the form shown in Fig. 55, where a single cone rises 



Fig. 54 — Summit of Vesuvius in 1756. 



from the floor of the great crater. The curious stages 

 through which a volcano may pass are well illustrated by the 

 story of Vesuvius. 



Rather less than two thousand years ago, that mountain 

 was as peaceful as Primrose Hill is at the present day. It 

 seems from all accounts to have had a very regular conical 

 shape, with a crater about a mile and a half broad. Yet its 

 shape led hardly any one to suspect that the mountain was a 

 slumbering volcano. Wild vines were growing over the 



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