C 133 ] 



they undergo by foktion^ whether by acids, or by 

 fire. 



It has been doubted by fome of the moft 

 refpedlable mineralogifts, whether we ought to 

 defcend below what are called generical diftindlions 

 in the folTil kingdom, fo infinitely do the fubjedls 

 thereof vaiy, and fo imperceptible in general is 

 that gradation by which they run into each other, 

 in the various combined forms, in which they 

 are found in the earth. In the mean time, fome 

 diftindlions of this kind feem quite necefTary in 

 fyftems eftablilhed principally on external cha- 

 raders. Thofe which have for their bafis the 

 elementary or conftituent principles of bodies^ as ana- 

 lyzed, may ftand with propriety in the form of 

 fynoptical tables, as exemplified in Cronftedfs mi- 

 neralogy. LiNN^us and Wallerius were among 

 the firft who attempted the arduous taflc of fixing 

 the fpecific charaders : whether future mineralo- 

 gifls will adhere to, and improve this part of the 

 fcheme, time only muft Hiew. 



In all fyftems of the foffil kingdom, writers 

 have been more particularly embarrafled by the 

 earths and ftones^ efpecially when thofe have been 

 more or lefs reduced to the flate of ores^ by the 

 admixture of metallic principles. Salts^ inflamma^ 

 bles, and melals, generally falling more eafily, and 

 almofl naturally, into their feveral claiTes, or or- 

 ders. The chemical fyftematics and metallur- 

 gifls, begin ufually with the earths^ confidering 

 them as the bafis of ftones : Linn^^ius begins 

 with the latter, profeffing to take a middle way 

 between the mere metalkrgijl., and thofe who 



K 3 ch^rafteri^c 



