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The other fadt is very fimllar to this, and 

 may be explained in the fame manner. It 

 relates to the large pieces of flioerl which 

 are contained in this volcanic rock, and are 

 difcovered on its being broken into pieces, in 

 the fime manner as the quartz. Thefe are 

 compofed of a number of rhomboidal fho- 

 erlaceous prifms, fo confufedly heaped and 

 joined together, that it is impoffible to ob- 

 tain a fingle prifm entire. Excepting in 

 the largenefs of their fize, they perfectly 

 refemble thofe of the porous lava, with the 

 horn-ftone bafe, of Monte Doriati, of which 

 we have fpoken above. Thefe (hoerls, like 

 all the others of the Euganean mountains, 

 concur to prove the volcanization of the 

 latter, by the fame property which is found 

 in the black micas of this country ; I mean 

 their magnetifm. Baron Dietrich, defcrib- 

 ing the volcanos of Old-Brifach, fhews that 

 the adion on the magnet of the black cryf- 

 taliized Ihoerls, is the exelufive property of 

 thofe that are volcanic. Though, in the 

 courfe of this work, I believe, I have only 

 mentioned the fhoerls of Monte Roflb, at 



VOL. III. R Etna, 



