246 A SYSTEM OF 



b. Blackifh grey, from Lerwik at Hclle- 

 fors in Weftmanland, and from Co* 

 logne in Germany. 



c. Light grey, from Hellefors in Weft- 

 man land. 



d. Black. The table flate, or that kind 

 u fed for large tables and for fchool- 

 flates. 



The naked eye, and the magnify- 

 ing glafs much better, difcovers the 

 micaceous particles in this kind to be 

 as it were twifted in one another ; fome 

 clay feems likewife to enter into the 

 compofition : However, it cannot yet 

 be certainly afferted that it is real 

 mica which has that appearance in 

 this kind. 

 Of very minute and clofely combined 

 particles, Cos pari i cults confians impalpa- 

 bilibus durus. The Turky ftone. 



This is of an olive colour, and feems 

 to be the fineft mixture of the firft fpe^ 

 cies of this genus It is found in loofe 

 (lones at EiorkfKoginas in the parifli of 

 Hellefors in Weilmanland, though not 

 perfectly free from crofs veins of quartz, 

 which always are in the furface of the 

 rock, and ipoil the whetflones. It is 

 alfo faid to be found in Tellemarken in 

 Norway. The bed of this fort come 

 from the Lev an r, and are pretty dear, 

 The whetftone kinds, when they fplit 

 eafily, and in this plates, are very fit to 

 cover houies with, though mod of them 

 are not fifed tor that purpofe. 



SECT. 



«* 

 O 



