( 2-9 ) 



lavas of the horn-ftone bafe, with the vitri- 

 ficatio'n of the fhoerls, feltfpars, and micas. 



From IMonte del Donati I proceeded to 

 Monte RoITo, celebrated for its mafs of 

 prifmatic columns. The iirfl: naturalift 

 Vvho pointed them out was Ferbcr ; they 

 afterwards were defcribed by Sir John 

 Strange*, who obferved that they are al- 

 moft perpendicular to the horizon, and 

 parallel to each other ; that they differ in 

 form and fize, and feem intimately con- 

 ne(Sled with the ftony body of the moun- 

 tain. On examining them, I found the 

 obfervations of the Englifh writer perfectly 

 accurate ; but I cannot refrain from mak- 

 ing a few remarks en the nature of this 

 columnar aggregate which he calls gra- 

 nitous. Both in the internal part and ou 

 the furface of thefe prifmatic columns, felt- 



* Opufc. Scelt. di Mllano, t. i. in 4ro. This de- 

 fcription was read to the Royal Society in 1774, and 

 is inferted in the Phllof. Tranfacf. vol. Ixv. part i. for 



