( 231 ) 



colour, with few but large bubbles ; a fu- 

 finn takes place in the fhoerls, but not com- 

 pletely in the fcltfpars. 



From this defcriptlon we perceive that 

 this mal's of columns cannot properly be 

 called granitous ; the generality of natu- 

 raliRs, and the m.oft refpedable chemifts, 

 agreeing that by the term granite is under- 

 ftood a rock or ftone compofed of two or 

 more fubftances, frequently cryftallized and 

 united together without the appearance of 

 any connecting ground or cement. But 

 here the fhoerls, the m'ca, and the fe'tfpars 

 are enveloped in a petrofiliceous pafce ; 

 whence we ought rather to denominate 

 thefe columns porphyritic. The fame is 

 true of the remaining mafs of Monte RofTo, 

 which is almoft entirely formed of the fame 

 rock. 



Under this bafalriform group we find 



numerous globes of the fame rock, which I 



judge to be pieces of pnfms that have fallen 



down and become round by the erofion of 



Q^ 4 their 



