To this head we refer all foſſils containing phlogiſton in ſuch great abundance, that under proper management they are inflammable. The Genera are obviouſly very few, and accurately ſpeaking there is only one Genus. But ſince phlogiſton is so very ſubtle as not by itſelf to become the object of our ſenſes, it will perhaps be adviſeable to conſider its more ſimple combinations as Genera: this has long been done ſo far as reſpects the metals, by univerſal conſent.