• MINERALOGY. tos 
principal ingredient in the making of crucibles, 
retorts, &c. - 
The boles' have alnioft loft their value as me- 
dicines, and are employed to make bricks, pot- 
ters-ware,^ and pig-iron. 
The tripoli is an indifpenfible 'article for the 
polifhing of metals, and fome forts of ftones •, it 
is likewife on certain occalions preferred for 
rnaking moulds to caft metals in. ^ 
The common clay is of the greateft benefit in 
agriculture, except however the white clay and 
the fermenting clay, both of'Se6l. xc. which 
varieties we know not yet how to apply to 
any ufe^ By virtue of its coherency, this clay 
retains humidity, on which perhaps its chief be*^ 
nefit to vegetables depends, its other effedls being 
occafional, owing either to nature or art ; unlefs 
the clay has formerly been a mould or humus 
ater^ in which cafe it is juft, that part of it fliould 
enter again into the formation of the new vegeta- 
bles. The clay tifed in the refining of fugar, 
wants no other quality than that it may not dry 
too foon. But that fpecies which is to be em- 
ployed in fulling, muft, if we were to judge a 
priori^ befides the finenefs of its particles, be of 
a dry nature, or fuch as attrafts oils ^ though this 
quality may perhaps not be found in all thofe 
clays v/hich are now employed in that bufi- 
nefs. 
SECT. XCilL 
The Fifth Order,' 
The Micaceous Kind, Micaceie. The Glimmer^ 
Daze, or Glift, 
H 4 
Thefe 
