9 8 Calcareous Genus. are mentioned by Dr. Withering, Phil. Tranf. 1 773- 1. A brcwniß white marl, refembling a calca reous incruftation. It contains 53 per ct. aerated calx; the remainder fand. 2. A lead-coloured friable flaky marl, contained 48 per ct. aerated calx; remainder fand. ■ 3. A brownijh-grey marl, very hard, in irregu lär lumps, contained 53 per ct. aerated calx; the remainder fand. 4. A lead-coloured marl, in powder or fmall hard lumps ; it contained 66 per ct. aerated calx, with fand, and a fmall proportion of argill. 2d Clafs. Not readily difintegrabie by expofure to the »tmofphere. MarUtes. Light or dark grey, or bluilh or yellowifh grey, or browniih red, or flelh coloured, or grey- ilh black. Luftre o, tranfparency 0, when the limeftone is of the compatä kind; but, when it is of the granulär, fome luftre and tranfparency are per- ceived, as in the fpecimen, Lelke, 564. Frafture moftly earthy or conchoidal, feldom fplintery, frequently flaty, morerarely granularly foliated, fometimes mixed. Eardnefs from 4 to 8. Spec. grav. from 2,3 to 2,877. Effervefce