Carbonate rock can frequently be found in the uplands and hilly regions of North Germany. In many places, this rock is covered by upper layers of limestone weathering debris and loess or loess derivatives. Soils arising from these parent materials often have a clay-poorer topsoil horizon over a considerably clay-richer subsoil horizon. The aim of this thesis is to clarify the genesis of clay-rich horizons by chemical, physical and mineralogical analyses. A total of nine forest soils from different slope positions were explored. It becomes apparent that the soils are composed of two parent materials: loess and solution residues of limestone weathering. Due to homogenisation processes, they are mixed with each other in the area of the former active layer of permafrost. All soils, except one, show clay illuviation in the subsoil, even in the horizon with the highest clay content.