In the East of Holland, in the Province of Overijssel, there is a region that, from the point of view of landscape, is one of the most beautiful and the most interesting we know in this country: Twente. Already in glancing through this publication it will be clear that this region played an important part in our research. Apart from the fact that our personal predilection for Twente undoubtedly was of some influence, this choice was equally directed by the geological wealth of that region coupled to the fact that here, as a consequence of numerous recent excavations, the deposits were excellently exposed. Of course, our research equally extended over other provinces but, whereas there a stress was laid on pollenanalytical research, geological research was less intensive than — for the reasons explained above — in Twente. Finally the research carried out near Usselo together with that carried out in S.W. Noord-Brabant, yielded together the solution for the dating of part of the coversands.