A phrase used in the WRB Classification to mean either a doubling of the clay content within a vertical distance of 7.5 cm if the overlying horizon has less than 20% clay, or an absolute increase in clay of 20% within 7.5 cm if the overlying horizon has 20% or more clay. In this case some part of the lower horizon should have at least twice the clay content of the upper horizon (FAO, 2001, Annex 2).