272 TRAVELS THROUGH 



eben hardened in the before-mentioned veins. The 

 colour of the petra forte is either grey-yellow OJT 

 blveim. Sometimes both colours offer in the fame 

 bed (laft-ra); but generally each bed has but one 

 colour, whence arifes the different denomination of 

 pletra ligia and iurcbina, ; though, in fact, they be 

 of the lame kind, and, on account of their clayifh 

 mixture, equally affected by the acids. In fome 

 beds of the petra forte, as well as the Bardellonc, 

 offers a fine mixture of mica, which proves their 

 near relation with the macigno. The macigno is 

 not only fometimes Separated by fmali- Bardellone- 

 beds, but likewife of two. different "colours, blue 

 and yellow, fomething affected by acids, in the 

 fame proportion as being more or lefs pene- 

 trated by calcareous particles. Hence it appears, 

 that its difference from the petra forte is entirely 

 depending upon- its ftronger mixture with mica, 

 which has made it a fpecies of Ardefia. 



According to thefe facts, all the hills near Flor 

 rence are to be confidered as argillaceous, as really 

 in a greater depth they are a pure argillaceous 

 ilate-, which I have obfcrved in' the quarries in 

 monte Buoni> where the macigno dips under the 

 adjacent calcareous hills or branches of the Apen- 

 nines. 



In and upon the Rardelloni alk Campcra are often, 

 d bls,gk;-iron dendrkes j and Micheli has. 



found 



