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Yistula valley between the outlets oj Dunajec and Breń

the sand-gravel deposits of the thickness less than 3 m. The age of the tree trunk stuck in these sands was 36 000 ± 1600 BP (Gd 1459). Although the trunk redeposition cannot be eliminated the whole complex of these sediments is located within the rangę of the erosional socle associated mainly with the middle terrace. Therefore, it seems possible that the deposits of the meadow terrace overtop the elder ones in some locations.

The grain size composition of the channel facies is diversified. Mean grain diameters are from —0.4 to 2.5 0 (1.4—0.18 mm) provided poor and medium sortings (Fig. 6).

The Carpathian sandstone materiał (Fig. 8, Wola Rogowska, Słupiec 20) with some flintstones, ąuartzites, hornstones and the northem materiał dominates in the petrographic composition of the gravel fraction. Quartz prevails in the fine fractions.

The madas occurring above the channel deposits are of a smaller thickness here which rarely exceeds 30 cm. Moreover, their occurrence is discontinuous and appears only above the fragments of bars and is-lands. With respect to the formation, these madas do not differ from those of the overflood terrace.

VISTULA VALLEY EVOLUTION

As it was already mentioned, the middle terrace in the studied section of the Vistula was under formation during the interglacial and younger pleniglacial of the Vistulian. It has been commonly accepted that the braided river had transported the large amounts of coarse unsorted materiał (Falkowski 1967; Szumański 1972, 1982). The coarse sediment load and lack of sorting of the Vistula deposits seem to be ąuestionable. The sandy layers which appear within this terrace in some spots do not sug-gest a definite dominance of coarse deposits (Fig. 9). Similarly, statistical indices of sorting do not indicate other sorting than in the case of younger alluvia of the meandering river (Fig. 6).

The traces of erosion in the Late Vistulian are not visible although the presence of the Late Glacial dunes is the case for erosion (Wojtanowicz 1968; Izmaiłow 1975). It has been not excluded that the Vistula flew at that time in a wide, fiat depression used actually by the Breń river. The analogical depression in the northem part of the valley drained by the Strumień Channel was possibly drained by the Nida river.

The stage of the river change from the braided into the meandering one cannot be reconstructed in the studied section. The ¹⁴C datings of the abandoned channel fills indicate their age just from the Atlantic. It seems likely that per analogy to the upper Vistula reaches (Kalicki, Starkel in press) próbably the elder abandoned channels lay lower and are buried by the overtopping younger ones.

The Atlantic and Sub-Boreal age of the paleochannel fills on the