In Ostrobothnia, western Finland, buried fossil soils have been recognised in a number of places in the sandy sediments that occur between glaciofluvial deposits and overlying till. Samples from the soil horizons as well as below and above them were taken for optically stimulated luminescence (OSL) dating. The same sites were also sampled for thermoluminescence (TL) dating. Altogether five TL dates and seventeen OSL dates were obtained. The OSL dates can be grouped into two age classes, (i) 120-163 ka and (ii) 76-106 ka, whereas all TL dates are of the order 135-1 55 ka. A comparison between the results obtained from the two dating methods Journal of Quaternary Science shows that OSL dates are generally younger than the TL dates for the same sample. The discrepancy may arise partly from problems of setting a correct residual level in TL dating. If this is the case then the TL dates may indicate an upper limit for the true age. The results support the geological interpretation that the fossil soils were formed during the last interglacial, that the soil-forming processes possibly also continued during the first Early Weichselian stadia1 and interstadial (Brplrup sensu lato), and that in general the till-covered glaciofluvial sequences, interpreted as eskers in Ostrobothnia, were deposited during the Saalian or Early Weichselian deglaciation.

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A historical review is given of the stratigraphic and chronological research of the Weichselian glaciation in Finland. Submorainic interglacial organogenic deposits have been found in Finnish Lapland and Ostrobothnia. Radiocarbon analyses give ages of over 50,000 years B.P. and the microfissil assemblages indicate climatic conditions that are more fovourable than at present. Interstadial deposits with radiocarbon ages of 42,000 to over 50,000 years B.P. contain fossil assemblages in dicating a poorer climate than at present. A tentative correlation of the Weichselian stratigraphy by various authors is presented.

A till-covered layer of clay, fine sand and organic-bearing silt was found at Hietamäki near Haapajärvi, Ostrobothnia (Pohjanmaa), western Finland. The organic-bearing silt layer is an infill sediment in a dead ice hollow within a glaciofluvial formation interpreted as an esker. The esker is covered by till, at the base of which is a layer or lense of clay 1.5 m thick. On the basis of pollen content, the layers of clay and organic-bearing silt were deposited during the Eemian interglacial stage. Pinus-Picea-Larix forests mixed with Betula and Alnus possibly represent aregressive phase of the late Eemian vegetational development, when thermophile trees had already withdrawn from the area.