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ilances, vvhcn the lava was In a ilate of 

 fufion, than to corrofions produced by the 

 influence of the atmofphere or any external 

 agent. It is certain that the air of the Tea 

 will greatly corrode many foffil fubftances 

 fituated in its vicinity J and I have witnelTed 

 extraordinary effects from its adion on 

 many low rocks, on the fhore of the Me- 

 diterranean, near Genoa, and efpecially at 

 Porto Venere, the Golfo della Spezia, and 

 at Lerici. I have alfo frequently obferved 

 the external part of many towers and 

 maritime buildings very much injured on 

 that fide which fronts the water. The 

 city of Commachio in the territory of Fer- 

 rara, perhaps, furnifhes fome of the moil 

 complete examples of fuch effedls. it is 

 lituated in the midft of fait lakes; and its 

 porticos and edifices are lo much corroded 

 and damaged by the air, that they are ob- 

 liged to undergo periodical repairs at the 

 end of no very long time, as I obferved with 

 furprife during a fhort ft ay which I made 

 there in Odober 1792. The fea air, how- 

 ever, does not ad thus on every foliil fubftance 



indif- 



