120 Account of 'the Mountains of 'ancient Lai 'him. [Aug. 



from that of mount Gaurus. Thus it appears that Vesuvius, in 

 different eruptions, some from the summit and some from the sides, 

 produced exactly the same substance. 



It seems clear that the peperino extended as far towards that 

 quarter which is now occupied by mount Albanus and the others, 

 as it does towards the other quarters. 



That the eruptions of peperino took place at very different times, 

 is evident from the alternation of hard and soft beds of it, and 

 from that opposition of beds which I observed at the town of 

 Albano. 



There is no proof that the sea covering these regions occasioned 

 the conglutination of the peperino, and then retired to its present 

 bed. For no marine bodies can be found either in the peperino or 

 over it ; while the charcoal and wood found in it, seem to prove 

 that these regions, before the volcanic eruptions, were covered with 

 trees and shrubs like the Pontine marshes. 



The conglutination may have been effected by the rain-water 

 alone, which, passing through, filled up the intervals with powder, 

 and dissolving a portion of the carbonate of lime (assisted by the 

 carbonic acid of the atmosphere), deposited it again to serve the 

 purpose of a cement. I found that all the fragments of peperino, 

 even those in which no limestone could be perceived, effervesced 

 in acids, and that not merely in particular places, but through 

 their whole mass. In this respect peperino differs from volcanic 

 tuff, which seems rather cemented by a silicious matter, and may 

 be compared to the ashes above Herculaneum, which, being moist- 

 ened by water containing lime in solution, effervesce when mixed 

 with an acid. Yet calcareous matter must not be considered as the 

 only cement of peperino ; for some of its beds have rather an 

 earthy than a stony consistency; and as the composition of the 

 peperino itself differs, it is reasonable to infer the same difference 

 in its cement. 



Perhaps, after the emission of the powder which constitutes 

 peperino, the volcanic fire attacked other materials, which it lique- 

 fied and projected through various openings. Hence, probably, 

 the origin of all the mountains composed of sperone and basalt. 

 As no stratification is perceptible, we may conclude that the whole 

 was thrown out at once. 



It would be in vain to look for the craters from which this fluid 

 matter issued ; because as soon as the energy which throws out 

 these fluid matters ceases, the craters themselves being filled with 

 fluid matter, it solidifies, fills them up, and no depression can be 

 perceived in the place where the crater was situated. That the 

 fluid matter of which these mountains arc composed speedily be- 

 comes solid, is evident from their steepness; for fluid lava would 

 rather have spread wide than formed such precipices. 



When metallic matters arc in fusion we know that the heavy 

 metal sinks to the bottom, while the lighter scoriae float upon the 

 surface. In like manner the compact lava is almost every where 



