Dr. H. Brunsting, curator of the National Museum of Antiquities in Leiden, enabled the present writer, in April 1951, to study a layer of clay beneath a mound dating from the Roman period, situated at Hazerswoude, about 700 ms south of the Oude Rijn (co-ordinates on the Topographical Map: 99.2 and 459.6; see map no. 1 and no. 2). Dr. Brunsting hopes to give further information on the archaeological investigations later on. We only want to mention the date of the oldest (Roman) findings as about 50 years A.D. The palaeontological study was made in three places situated at some metres distance from each other. They will be indicated here as Haz. A, B and C. Of Haz. A and B the entire layer of clay was analysed, of Haz. C (situated between A and B), by way of trial, only a sample at 2.30 ms—O.D. (O.D. = N.A.P.). The strongly disturbed, entirely dug up clay with remainders of the settlement was not studied. The underlying 60 ems of the clay investigated could be sampled in profiles. About 30 ems of it originated from the layer raised by man. For the sampling of the clay below the ground waterlevel a Dachnowsky sampler was used. It was not possible to take out the humic clay deeper than 140 ems (3.10 ms—O.D.), since the sampler touched a hard layer of wood. Besides clay of the Rijn also two potsherds of the settlement from Roman times were examined for diatoms.