M I N E R A L O G^ Y..;.. 
SECT. ccxcv;> 
tf, Iceland agat^ Achates ifiandicusMgerl 
It is black, folid, and of a glafly textures 
but in thin pieces, it is greenifli and femi- 
tranfparent like glafs bottles, which con- 
tain much iron. The moft remarkable is» 
that fuch large folid mafles are found of it, 
that there is no pofTibility of producing the 
like in any glafshoufe^ > 
It is found in Iceland, and in the Ifland 
of Afcenfion : The jewellers employ it as 
an agat, though it is too foft to refift wean 
SECT. CCXCVL 
B. Rhenifh millftone, Lapis molaris Rhenamsl 
Is blackilh grey, porous, and perfectly re- 
fembles a fort of flag produced by Mount 
Vefuvius. If I am miflaken in this, I hope 
that fomebody elfe will deferibe the con- 
ftituent parts of this millflone. 
SECT. CCXCVII. 
C. Pumice-ftone, Pume;^, 
Is very porous and bliftered^ in confe- 
quence of which it is fpec^cally very light.. 
It rclernbies that froathy flag which is pro=* 
duced in our iron furnaces. 
1. White. 
2. Black. 
The colour of the ^rft h perhaps 
faded or bleached^ becaufe the fecond 
kind comes in that ftate from the labors-* 
tory itfel£ vis. the volcanos. 
S E C T* 
