VESUVIUS IN ERUPTION 63 



excessive nor violent. Then came a period of greatly 

 increased energy the steam-jet blew with such violence 

 that it shattered and dispersed the cone, lowering the 

 mountain to 3700 ft. in height, truncating it and leaving 

 a proportionately widened crater of a mile and a half 

 in diameter. And then the mountain reposed for long 

 centuries. We do not know how long this period of 

 extinction was, for we do not know when it began, but 

 we know that this was the state of the mountain when in 

 A.D. 79 it once more burst into life. In recent years that 

 is, since the seventeenth century A.D., a curious change 

 took place in the mountain : the vent or orifice of the 

 conducting channel by which eruptive matters were 

 brought to the surface ceased to be in the centre of 

 the wide broken-down crater of Pliny's time, and a vent 

 was formed a few hundred yards to the south of the 

 centre of the old crater, nearer to the south side of the 

 old crater's wall. From this ashes or cinders issued, and 

 were piled up to form a new cone, which soon added 

 600 ft. to the height of the mountain and covered in the 

 southern half of the old crater's lip, whilst leaving the 

 northern half or semicircle free. This latter uncovered 

 part was called by the Italians " Monte Somma," and 

 the new cone low down in the southern side of which 

 the rest of the old crater-lip could be traced, was hence- 

 forth spoken of as " the ash-cone " and sometimes mis- 

 leadingly as "the true" Vesuvius. Clearly it was not 

 u the true Vesuvius " since it was a new growth. The 

 original old Vesuvius was crowned by a crater formed by 

 the cliffs of Monte Somma and their continuation round 

 to the south side, now more or less completely concealed 

 by the new ash-cone. 



In the course of various eruptions during the last two 

 centuries the new ash-cone thus formed was blown away 

 more or less completely, and gradually grew up again. 



