198 FLCETZ ROCKS. fames occur in this fand, and the clay is ufually more or lefs bituminous, and fometimes contains Jchaum-earth. 9• Sandftone. Befides the gravel* fand, and clay, beds of fand- ,ftone fometimes occur in this formation, and this fandftone is ufually that particular kind denomi nated Quartzy Sandftone, from the particles being conne&ed together by a bafe of quartz *. 10. Clay-Ironftone. In the Feroe Iflands, beds of clay-ironftone are faid to occur in this formation. 11. Limeftone. Limeftone occurs along with bafalt in Bohemia, and in the valley of Ronca in the Veronefe, 12. Iron-Clay f. 13. ' Coal. 1. But the raoft important of thefe rocks is the coal, which very often forms the loweft part of the formation, * This rock refembles certain varieties of quartz. t I ron -clay is defcribed at page 603. of the fecond volume of this work.