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T. Sokołowski

terrace II A (6040 ±140, 4920 ±220, 3970 ±80 and 32701200 BP) together with their geometry suggest that these paleochannels have been formed by a river of a slowły migrating channel. Taking into account the fact that the younger abandoned channel deposits to the north of Szczucin appear in the peripheral parts of the valley (Fig. 1, 9) one can assume that the maximum widening of the contemporary flood plain bottom occurred also in the Sub-Boreal together with a generał tendency to aggradation which seems to last until the tum of the Vistulian.

The upper limit of the functioning of these abandoned channels is morę difficult to be determined. It cannot be eliminated that the single forms were still active in the first millenium AD. The presence of the earthwork located in the fork of the Vistula and Dunajec rivers, in the area of the point bar of the abandoned channel geometrically resambling the forms of the terrace II A, is behind the above statement. Based on the archeological finds Dąbrowska (1965) determines the earthwork for-mation for the 7th-8th century, or may be even for the 6th century. It seems that the natural conditions for defence were provided by the sur-rounding river channel.

The subseąuent terace II B is incised into the terrace II A. The accu-mulation of the cover of the former one was probably preceeded by a slight incision. The terrace in ąuestion was modelled by somewhat different river what is indicated by a smaller regularity of the abandoned channels occurring within its extent. It seems that it was the river of morę variable discharges. The traces of the point bar accretion suggest the river of a faster migrating channel. The timing of the terrace formation could be related to the 10th-15th centuries AD. The acceptance of such time limits is substantiated by the presence of the abandoned channels of another type on the terrace II A still in the first millenium AD. The upper time limit is determined by the presence of cutting the former ones which were undoubtedly still active in the 18th century. A certain additional datum can be the settlement development recon-structed by Mateszew (1974). According to that author’s summaries the villages in the vicinity of these channels were formed relatively late (16th—18th centuries), i.e. 200—400 years later than those located within the terrace II A. Finally, the changes in the river hydrology can be ex-pected in the morę regional change of the land management of the catch-ment which took place mainly in the 13th—14th centuries (Dembińska 1972).

Moreover, the aggradation of the river was possible during this terrace accumulation what is evidenced by the presence of tree trunks on the point bar of one of the abandoned channel to the east of Szczucin. (Fig. 1, 9). One of these trunks has been dated for 4900 ±100 BP. The young aggradation phenomenon is also known from the Vistula valley in the area of Cracow (Rutkowski in press; Kalicki, Starkę! in press).