3^4 CLAY GENUS. 1 1 It is not always pure, but is frequently mixed with felfpar and mica. t Geognostic Situation. It occurs in more or lefs mighty beds in primitive rocks, particularly in clay date; aifo in gneifs and mica date.' Geographic Situation. - It is found in Norway, Sweden, Scotland*, at Port- foy, &c.; Saxony, at Hartmanfdorf, Chemnitz, &c. * Mineralogy of the Scottifh iflej. FOURTH