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This lava, befides the pumices, contains 

 elegant feltfpathofe cryftals, which, toge- 

 ther with it, completely vitrify in the fur- 

 nace. 



Monte d'Arqua was the laft which I 

 vifited. Its fummit is compofed of a grey 

 compa6l lava, which has a horn-ftone bafc, 

 affords fparks with fteel, and contains mi- 

 caceous and feltfpathofe cryftals. This lava 

 is found in fome places in ftrata nearly ho- 

 rizontal. 



To thefe lavas, which I found on the 

 fpot, while accompanied in my refearches 

 by the Marchefe Orologio, I fhall add a 

 few others from the Monte del Catajo, 

 which were afterwards noticed and exa- 

 mined by that iliuftrious nobleman and 

 naturalift, who vifited every part of that 

 mountain to which his villa is contiguous, 

 and coUeded fpecimens of the fpecies of 

 moft importance, obferving the places 

 where they were found. At my requeft 

 hs tranfmittcd them to me, with their fe- 



