A relief map of the surface of the prequarternary sediments of northern and eastern Switzerland is presented. This compilation shows the importance of glacial and fluviatile erosion of alpine and prealpine valleys during the Quaternary, particularly during the "big glaciation" (Riss glaciation?). In the marginal alpine lakes (Lake Constance, Walensee, Lake of Zug and Vierwaldstättersee) the depth of the base of the quaternary sediments varies between 100 m below and 100 m above sea level. A basement to 200 m below sea level has been measured in a well southeast of Lake Constance. Some valleys (Rhine valley near Basel; Limmat valley near Baden) already existed with near actual depth before the "big glaciation".