On the top of the “Kuiperberg”, a hill near the village of Ootmarsum (Netherlands, province of Overijssel) tertiairy and quaternary deposits have been exposed in the now abandoned clay-pits of a brick-works. This paper deals with the tertiairy deposits. By studying the profiles of the clay-pits and from six auger-drillings the tertiairy deposits appeared to be strongly dislocated by glacial action, therefore a oomplete stratigraphic profile could only be estimated. The tertiairy deposits prooved to be of Oligocene and Miocene ages. At the base of the sandy lower Rupelian several beds of rewashed Eocene phosphorites are found. In and between them fossils of Oligocene age are recognised, therefore these strata can be assumed to belong to the Oligocene. The upper Rupelian is represented by the “Septaria Clay” (= Klei van Boom), which is present in three different facies. Faunal lists are given of the Eocene and Oligocene fossils. The Miocene consists of a clayey glauconitio sand, near the base of which a bed of glauconitic concretions is found in situ. The fauna represented in the conoretions as casts and offprints has not yet been studied in detail. A provisional list of the Miocene fauna is given. A probable correlation with the “Laag van Ticheloven” (type-locality in the municipality of Eibergen, province of Guelders, Netherlands) is suggested. In the appendix descriptions are given of the six auger-drillings that were brought down to supply the information collected in the clay-pits. The stratigraphioal investigation resulted in a SW – NE profile, as given in textfigure 6.