The Lower Palaeozoic low-grade metamorphic rocks of the Brabant Massif are largely buried below a thick cover of post-Palaeozoic strata. Along the top of the subcrop, they comprise remnants of Cretaceous to Tertiary weathering pro®les that represent the lower part of thick saprolites. The alteration of the chlorite-and muscovite-dominated Palaeozoic rocks was characterized by the destruction of chlorite, accompanied by the formation of kaolinite and iron oxides and/or iron hydroxides. The ®rst product of chlorite weathering seems to have been regularly interstrati®ed chlorite-vermiculite or chlorite-smectite, which is now represented by interstrati®ed chlorite-muscovite with regular ordering. Outside the thin transitional zones in which this mineral occurs, the rube®ed intervals show only little variation in composition, which is due to the replacement of chlorite by kaolinite over short vertical distances and the stability of muscovite throughout the preserved parts of the saprolite. The rube®ed rocks do have a somewhat dierent composition along the top of some pro®les, which is related to an interaction with groundwater after burial, resulting in smectite formation, feldspar weathering and iron dissolution. Groundwater interaction is also responsible for the occurrence of weathering without rubefaction, outside the areas with saprolite remnants, which resulted in vermiculite, smectite and kaolinite formation.