The clay minerals in samples of Quaternary tills from two regions (Uppland and Södermanland) in east-central Sweden and from the sea bed of the Baltic near Gotland have been studied with regard to the effects of weathering. The intensity and distribution of the latter influences such factors as soil fertility and buffering capacity. Additional research on a regional basis is necessary to arrive at firm conclusions. The results of the present study suggest that height above sea level is one factor controlling the intensity of weathering.