322 CLAY GENUS. Chemical Charader. When expofed to heat it burns with a flame, and when left fome time expofed to a moift atmofphere it becomes warm, and at length takes fire.< Geognosiic Situation. Tt occurs frequently in beds of great magnitude, in alluvial land, and fometimes alfo in the floetz trap formation. Geographic Situation. It is found in Bohemia, Saxony, Auflria, Naples, Hungary, and in the Vivrais in France. Ufe. It is lixiviated to obtain the alum it contains; it is even fometimes ufed for fuel. Obfervations •