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strata and łenses of very fine sands (sites: Brzeźnica B, Podgrodzie and Drogomyśl).

The second group indudes minerał channel fills due to the reactivadon of the river channel. For the most part, these are formed of sand and sandy du$u without organie mat ter (sites: Grabiny and Podgrodzie). Stratification is less well defined.

Modern deposits — the high discharge-formed sediments are characterisuc of the channel environment which corresponds to a concrete event with defined parameters. In the Wisłoka valley sam pies were collected aft er the peak flows recorded in 1980 and 1983. Water levels were in excess of 1 — 4 m above Iow level depending upon the channel widths. Locally, the floodplain was covered with water. After the 1985 flood samples also were collected in the upper Vistula valley. The water level was then by 2 — 4 m higher above Iow lcvel. Flood deposited sediments were observed to occur on the floodplain only at one site. On the contrary, lateral gravel bars are formed of the coarsest deposits being transported only at high stream discharges.

The high discharge-formed sediments in the channel consist of sand which sometimes includes an admixture of dust or clay (Mz — 2.2 0). Deposits which accumulate either far from the main current or in the higher part of the channel are finer (Mz = 3.0—4.1 0\ less well sorted, less well abraded and less homogeneous. On the contrary, deposits laid down on the floodplain are much finer (clayey dusts) (Mz — 6.6 —6.9 0) and poorly sorted.

On the fresh sandy-gravelly bar two minor zones may be distinguished: the proximal zonę is marked by coarse, gravelly-sandy deposits (Mz = 2.2 to -0.6 0), the properties of which correspond to those of the basal point bar deposits; the distal zonę shows finer, mainly sandy deposits (Mz — 0.8 —1.5 0) being similar to the top series of point bar deposits.

Gravelly lateral bar deposits are very coarse-grained (Mz = —6.0 to — 3.7 0). These are poorly sorted cobbles and pebbles. Quartz grains are less well abraded.

CHARACTERISTICS OF DIFFERENT TYPES OF DEPOSITS BASED ON GRAIN SIZE INDICES

The grain size indices describing the distribution make it possible to compare with each other dififerent grain sizes. On the scatter diagram of standard deviation versus mean grain diameter dififerent types of ancient deposits of differing age and of modern deposits are presented in order to define their properties, similarities and diflerences.

Older Pleniglacial channel deposits of the braided river show great yariations in Mz values, from ^-2.0 to +5.1 0, owing to the highly variable dynamics of water flow in the dififerent parts of the braided river channel. The sandy braided river dating from the Younger Pleniglacial is characterized by finer deposits (Mz = 1.3 — 7.0 0), the better sorting of which indicates moderate and less varied stream discharges (Fig. 14A). At the same time. ven fine materials showing properties of the non-current environment became deposited in the less active parts of the river channel.

Channel deposits of the lateglacial meandering river are marked by the