134 Elements of Mineralogy. 



According to Mr. Bergman, 100 parts of 

 the bafaltes contain 52 of filiceous Earth, 15 

 of argill, 8 of calcareous, 2 of magnefia, 

 and 25 of iron. 3 Bergm. 213. And with 

 this Mr. Meyer very nearly agrees. 14^- 

 turfor/h. 5. 



SPECIES XIX. 



Siliceous Earth mixed 'with 0,69 of its weight 

 of Argill 9 and 0,41 of its weight of Iron in 

 a femiphlogifticatedjtate* 



Rowly Ragg. 



This ftone is alfo of a duiky or dark grey 

 colour, with numerous minute fhining cry- 

 ftals ; its texture granular ; by expofure to 

 the air it acquires an ochry cruft; its fpecific 

 gravity 2,748, 



Heated in an open fire it becomes mag- 

 netic. In a ftrong heat it melts perfe, but 

 more difficultly than bafaltes. 



According to Dr. Withering *s analyfis, 100 

 parts of it contain 47,5 of filiceous Earth, 

 32,5 of argill, and 20 of iron. 



XX. 



