Earths and Stones. 2 1 



precious {tones under the filiceous genus, 

 though the argillaceous be, in point of pro- 

 portion, predominant in their compofition. 



By fuper- compound Earths or Stones, I 

 mean aggregates of vifibfy different fimple 

 fpecies, in a notabls proportion, whether 

 thefe fpecies belong to the fame, or to different 

 genera. Thus I would call a compound of 

 gypfum and fluor fpar a fuper-compound, 

 though both belong to the calcareous genus * 

 and a fortiori granites and porphyries, which 

 forpi aggregates of fimple fpecies belonging 

 to different genera. Super- compounds, there- 

 fore, form compound fpecies, which may be 

 ranged under that genus which is found in 

 them in greater proportion. In general they 

 may be known by the eye, at leaft when 

 aided by a lens. 



In ftriclnefs, Earths of different genera, 

 each of which contain the aerial acid, fhould, 

 when mixed with each other, conftitute a 

 compound fpecies, yet, as this acid is eafily 

 expelled, and caufes no great difference in 

 the properties of the compound, and as in 

 facT: abforbent Earths, when combined with 

 no other faline principle, ' are feldom without 

 it, I {hall rank thofe compounds among the 

 fimple fpecies, and fo I {hall quartz and filex, 

 though feldom abfolutely pure, 



C 3 CHAP. 



