Argillaceous Genus. 93 



II. VARIETY. 

 Greenifh Grey Horn-Jtone. 



This is of a granular texture, or ftriated ; 

 the fpecific gravity of the pureft fpecimen I 

 examined is 2,683 : it is not fo foft as the 

 fofteft of the former variety. 



I fufpect the common pale greenifh grey 

 whetftone to be of this fpecies : it is of a 

 clofe granular texture, exhales an earthy 

 fmell, affords a greenifh powder, does not 

 effervefce with acids, nor give fire with fteel; 

 its fpecific gravity is 2,664; ^ contains "65 

 per cent, of filex. 



III. VARIETY. 



Klllas. 



This ftone is chiefly found in Cornwall ^ 

 its colour is pale grey or greenifli grey ; its 

 texture either lamellar or coarfely granular : 

 the lamellar is fofter and lefs martial than the 

 roof fhiftus : its fpecific gravity from 2,63 to 

 2,666. 



I found too grains of the lamellar fort to 

 contain about 60 of filex., 25 of argill, 9 of 



magnefia, 



