( 137 ) 



fcrlbed elfewhere *. Thefe, with refpe^ to 

 the frefhnefs of their appearance, are not 

 diftinguifhable from the lava of vi^hich I 

 now fpeak. Yet is the latter of an antiqui- 

 ty beyond our knowledge, for we have no 

 record of any conflagration in Alicuda fince 

 hiftory has been written. I have chofen to 

 fpeak more at length on this peculiar pro- 

 perty of the prefent lava, to prove, or rather 

 to confirm what I have already proved, 

 how uncertain are all conclufions relative 

 to the greater or lefs antiquity of lavas, de- 

 rived from the more or lefs fenfible degree 

 of decompofition which they manifefl. 

 Such conclufions may be well founded, 

 when the lavas are of the fame nature, and 

 affeded by the fame extrinfic circumftances ; 

 fince, then, thofe of a more ancient date 

 muft be moft changed by time : but where 

 their nature and qualities are different, one 

 lava may be confiderably altered in a few 

 years, and even reduced to an earth, while 

 another fhall remain for ages, perfe(Sly 



♦ See Chap. VIII. 



preferved, 



