The bleaching clays of commercial interest are the active clays of the Southeast and the activable bentonites of the Southwest and Southeast. No first-class clays of either type have yet been found in the Mid-Continent region. All the best active clays are substantially equal in bleaching power. The same is true of the activable clays. Each individual differs less from others in the same class than the variation with depth in one deposit. Practically unlimited quantities of the highest grade clays of both types are available and there are vast reserves of each only slightly inferior. Although other clays and minerals nearly as high in bleaching power as the active and activable clays of commercial interest have been found, none exceeds them in bleaching power or can compe e with them in price. Glauconite and Ordovician bentonite, properly prepared, may be of special service locally; they can not compete with the commercial clays for bleaching purposes at present. Special treatments of clays enhancing their bleaching power have been found to be not worth the added cost. Methods of testing and rating bleaching clays have been briefly outlined.