Paper presents results of research on fillings of palaeochannels discovered in valley bottoms of Ner river near Lutomiersk and of Rawka river in Rawa Mazowiecka in central Poland (fig. 1). We have undertaken under study bedding and covering sediments of subfossil river channels as well. The analysis includes: lithology of series, geochemistry, archaeobotanic analysis. Some probes of organic sediments have been dated by radiocarbon method. Part of deposited layers have been dated by archaeological method. Both of registered subfossil channels have been discovered in the close vicinity of archaeological sites (fig. 2). In the case of Ner river, the settlement of Lusatian culture societies (Bechcice, site 1) was existing. It is dated on 4th and 5th Bronze Age Pariod and probably Halstat C Period. In Rawa Mazowiecka two prehistorie settlements (Rawa Mazowiecka sites 3 and 38) are known with main chronologic phase dated on Young Pre-Roman Period and on Old Roman Period. The beginning of filling of channel in Ner river we can correlate with the period about 1340-1150 BC and in the bottom of fillings deposits we have recognized fragments of pottery of Bronze Age Period and Hallstatt C Period (fig. 3). And the initiation of ox-bow accumulation in channel in Rawka river must be dated on before 530-380 BC (fig. 4, 5). In both of valleys are existing the thick cover of over bank deposits, represented by organic muddy and sands and accumulated in Medieval Period and Modern Period.
At the Koźmin Las site, in Central Poland, in the middle section of the Warta River valley, a series of well-preserved tree trunks and in situ stumps, as well as organic deposits, have been found. The tree remains are dated back to the period between 13,000–12,600 cal BP, i.e. to the Alleröd/Younger Dryas transition. The forest consisted predominantly of pines (Pinus sylvestris L.) of a maximum age of approx. 140 years and an average age of 68 years, and the river valley floor was overgrown. The forest was destroyed ca. 12,600 cal BP by deteriorating hydrological conditions or a sudden catastrophic event. The aim of the study was to assess the degree of degradation in terms of selected macroscopic, physical and chemical properties of a subfossil pine log. On this basis, a conservation process was developed,using aqueous solutions of polyethylene glycols (PEG) with varying concentrations of low- and high-molecular polymers. Treated and dried samples were comparedin terms of their tangential and radial dimensional stability, as well as their hygroscopic properties.