OF VOLCANOS. 389 



the accounts which have been current during the short interval 

 which has elapsed, it is nevertheless true that the eruption of ashes 

 from Vesuvius from the 24th to the 28th of last October (1822) is 

 the most memorable of any of which we possess an authentic account, 

 since that which occasioned the death of the elder Pliny. The 

 quantity of ashes, is, perhaps, three times as great as has ever been 

 seen to fall since volcanic phenomena have been attentively observed 

 in Italy. A stratum of ashes, from 16 to 19 inches thick, appears 

 at first sight insignificant compared with the mass which we find 

 covering Pompeii ; but, not to speak of the increase which that mass 

 has probably received by the effects of heavy rains and other causes 

 during the centuries which have, since elapsed, and without renew- 

 ing the animated debate respecting the causes of the destruction of 

 the Campanian towns, and which, on the other side of the Alps, has 

 been carried on with a considerable degree of skepticism, it should 

 here be recalled to recollection that the eruptions of a volcano, at 

 widely separated epochs, do not well admit of comparison, as respects 

 their intensity. All inferences derived from analogy are inadequate 

 where quantitative relations are concerned ; as the quantity of lava 

 and ashes, the height of the column of smoke, and the, loudness or 

 intensity of the detonations. 



From the geographical, description of Strabo, and from an opin- 

 ion given by Vitruvius respecting the volcanic origin of pumice, we 

 perceive that, up to the year of the death of Vespasian, i. e. pre- 

 vious to the eruption which overwhelmed Pompeii, Vesuvius had 

 more the appearance of an extinct volcano than of a Solfatara. 

 "When, after long repose, the subterranean forces suddenly opened 

 for themselves new channels, and again broke through the beds of 

 primitive and trachytic rocks, effects must have been produced for 

 which subsequent ones do not furnish a standard. From the well- 

 known letter in which the younger Pliny informs Tacitus of 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 



33* 



