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7extural dw er sity of JJuuial deposits

deepening. Headwater erosion commences, sometimes showing considerable ratcs (Froehlich 1982). In places, exploitation of the bed materiał is intensive in the Wisłoka valley (Klimek, Starkel 1974).

Beyond the Carpathian Foothills three well exposed sites: Brzeźnica, Grabiny and Podgrodzie have been examined in detail in the Wisłoka valley (Fig. 2).

In the upper Vistula valley materials have been collected at the Drogomyśl site including an exposure and borings madę across the floodplain (Fig. 3). Additional data were supplied by a boring at Kaniów and by a dug section at Chybie.

Studies of modern deposits gave data for comparison with the fossil sediments. The term “modern deposits” covers both sediments that are being accumulated in the river channel and on the floodplain during a concrete flood, as well as lateral gravel bar deposits which became exposed at Iow water levels.

METHODS OF STUDY

FIELD WORK

Samples have been obtained from each discernible stratum, at least 1 cm thick, in the exposures, whereas from the cores samples were taken, where lithological changes became evident.

Sampling was done on the bar surface. Gravels were collected from 1x1 m squares located in the central part of the form chosen. Gravels then were placed together in size classes each of 1 0 units by the direct measurement of the b diameter. Subseąuently, each gravel class was weighed out. Particles finer than 8.0 mm were collected into bags and shaken through a standard set of sieves in the laboratory.

LABORATORY ANALYSES

Samples were analysed by sieving and hydrometer techniąues to determine their grain size parameters (Stoch, Sikora 1979). Particles, 8.0 — 0.71 mm in diameter, were shaken through sieves with holes corresponding to divisions of the c. 0.5 0 scalę.

The abrasion of quartz grains was mechanically analysed using the automatic GW-02 graniformameter. Since very fine particles were abundant in the deposits examined, this analysis was madę in the finer fractions: 1.02 — 0.75 mm 0.75 — 0.5 mm and depending upon the highest freąuency of occurrence. Analyses were madę of 610 samples in the 0.75 — 0.5 mm fraction and of 415 samples in the 1.02 — 0.75 mm fraction. The abrasion of the 0.75 — 0.5 mm grains was interpreted in greater detail.

THE ELABORATION OF RESULTS

Corresponding percentile values of yarious grain size intervals were derived from graphs and the following grain size parameters using Folk's and Ward's formulae (1957):