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CLAY GENUS. Obfervations, 1. Alum earth is diftinguilhed from alum flate by its brownifh black colour, want of luftre, inferior c hardnefs and inflammability. 2. At Whitby in Yorldhire, there are very exten- five alum mines; but we are as yet ignorant, not only of the fpecies of the foflil from which the alum is obtained, but alfo of the formation to which it belongs.- I p^v'ENTEENTH