Earths and Stones a 1 9 



By Compound Earths, I underftand thofe 

 that are combined or mixed in a notable pro- 

 portion* either with each other, or with a 

 faline, inflammable, or metallic principle, 

 yet not in fufficient proportion to require 

 them to be arranged under fuch foreign prin- 

 ciples. Such compounds being permanent, 

 and being the foundation of a peculiar deno- 

 mination, I call Jpeeiesy and fimple fpecies, 

 in order to diftinguifh them from fuper com- 

 pounds, which will prefently be mentioned. 

 Thus gypfum is a compound Earth, confifting 

 of calcareous Earth, and a faline principle, 

 not accidentally, but permanently mixed with 

 it. So alfo tourmaline is a compound Earth, 

 confifting of the argillaceous, filiceous, and 

 calcareous, and iron, in proportions deter- 

 mined within certain limits, and forms a 

 fimple fpecies. I faid a notable proportion, 

 becaufe it is difficult to affign this proportion 

 with precifion ; for it relates to denomina- 

 tions of fubftancps, and thefe are founded on 

 the neceffity of diftindlion, arifing fometimes 

 from the ufefulnefs of fubftances to mankind, 

 and fometimes from caprice. Thus, a com- 

 pound Earth, which fhould confift of calca- 

 reous Earth, and only two per cent, of gold 

 or filver, would be denominated an ore, 

 whereas, if it contained only two per cent, 

 of iron, or of another Earth, it would ftill 

 retain the name of, and be reckoned among, 

 calcareous Earths. However, in general we 



C 2 may 



