NOME IV. TT/FO. 379 



base of the mountain may consist of slate; and 

 the red puzzolana of the Italians may be merely 

 that substance affected by fire. 



It is well known that, during the grand erup- Volcanic 

 tions of volcanoes, the sun is often hid, for entire 

 days, with thick columns and clouds of com- 

 minuted substances, called ashes by modern 

 writers ; while the ancients, with their usual dis- 

 cernment, used the word powder*. On their 

 fall, these powders become coherent and in- 

 durated, by humidity and the lapse of ages, so 

 as often to assume the consistence of stone. 

 These are also among the most dangerous phe- 

 nomena; the city Pompeia having been over- 

 whelmed with a hail of pumice, while Hercu- 

 laneurn was buried under a shower of powders ; 

 and in the theatre, constructed without a roof as 

 usual among the ancients, a piece was found 

 impressed with the breasts of a woman, who had 

 perished; a circumstance which evinces the 

 tenuity of the substance. The hills of the isle 

 of Ponza often present a white argillaceous tufo, 

 extremely soft, being chiefly composed of com- 

 minuted pumicef . Breislak observed in Ischia, 

 hills of a fine white tufo, sometimes stratified ; 



* Involutus est dies pulvere, populosque sulita nox terruit. 

 Seneca Quest, nat. 1. 2. &c. &c. 

 f Dolomieu, Ponces, 118. 



