234 STRUCTURE AND MODE OP ACTION 



his uncle's death, it may be clearly seen that the renewal of 

 volcanic outbursts, or what might be called the revival of 

 the slumbering volcano, began with an eruption of ashes. 

 The same thing was observed at Jorullo when, in September 

 1759, the new volcano, breaking through beds of syenite 

 and trachyte, rose suddenly in the plain. The country- 

 people took flight on finding their huts strewed with ashes 

 which had been emitted from the everywhere opening 

 ground. In the ordinary periodical manifestations of vol- 

 canic activity, on the contrary, the shower of ashes marks 

 the termination of each particular eruption. There is a 

 passage in the letter of the younger Pliny which shews 

 clearly that, at a very early stage of the eruption, the dry 

 ashes which had fallen had reached a thickness of four or 

 five feet, without accumulation from drift or other extraneous 

 cause. He writes, in the course of his narrative, " the 

 court which had to be crossed to reach the room in which 

 Pliny was taking his noon-day repose was so filled with 

 ashes and pumice, that, if he had longer delayed coming 

 forth, he would have found the passage stopped." In an 

 enclosed space like a -court, the action of wind in drifting 

 the ashes can scarcely have been very considerable. 



I have interrupted my general comparative view of vol- 

 canos by a notice of particular observations made on 

 Vesuvius, partly on account of the great interest excited 

 by the recent eruption, and partly on account of those 

 recollections of the catastrophes of Pompeii and Herculaneum, 

 which are almost involuntarily recalled to our minds by the 

 occurrence of any considerable shower of ashes. I have 



