4 Of Simple Earths. C H A P. I. Of Simple Earths, their Number, and CbaraElers. Simple earths are thofe which are incapable of being converted or analyzed by any tneans hitherto known, either into eacli other, or into any other fubftance. Of thefe we have nine; the Calcareous, the Barytic, the Magneßan or Muriatic, the Argilla- ceous, the Siliceous, the Scottiß or Stronthian, the Jargonic, the Sydneian, and the Adamantine. Of thefe, the five firft are by far the moft general, moft of the earths and ftones hitherto examined being refolvable into them. Next to thefe the Scottifti is, I believe, moft common; though, from its refemblance to the calcareous, it has probably been often overlooked. The three laft have very rarely, and the Sydneian indeed has only once, been met with. White is the natural colour of all earths ; the other colours which are found in them proceed from inflammable or metallic fubftances. Of Calcareous Earth. Calcareous earth, in its commoneft ftate, is called limeftone, or fpar; but in this ftate it is combined with a peculiar acid, expellible by heat, and by moft; other acids in an aerial form, and i hence