OF VOLCANOS. 233 



ashes is, perhaps, three times as great as has ever been seen 

 to fall since volcanic phenomena have been attentively ob- 

 served 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 renewing the animated 

 debate respecting the causes of the destruction of the Cam- 

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

 been carried on with a considerable degree of scepticism, 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 de- 

 rived from analogy are inadequate where quantitative rela- 

 tions 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 

 opinion given by Yitruvius respecting the volcanic origin of 

 pumice, we perceive that, up to the year of the death of 

 Vespasian, i. e. previous 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. Prom the well- 

 known letter in which the younger Pliny informs Tacitus of 



