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total thickness is about 70 m (fig. 4 and 40). The key lithologic unit of the profile is a huge inter-till horizon of 6tratified fine-grained sands and the above-men-tioned grey varved clays which both commonly come to surface on the valley slopes in a thickness from a dozen or so twenty-odd metres. It was first distingu-ished by R. Galon (1934) as the so-called “fluvioglacial II”. Above that horizon there are two till strata, .separated by fluvioglacial deposits, which, according to former views (R. Galon 1961, J. E. Mojski 1969) represent the main stadial of the Baltic glaciation. Detailed stratigraphic subdivision and genetic-facial interpreta-tion of these deposits constitutes the main goal of investigations presented later on in the work.

AUXILIARY CRITERIA IN STRATIGRAPHIC AND FACIAL INTER PRĘT ATION

OF TILLS

To obtain additional criteria that would at the same time permit to comple-ment and check the methods of stratigraphic and structural investigation, statistical lithologic analyses of tills were applied. They comprise: petrographic composition of gravel fractions, fabric patterns and grain-size composition.

Analyses of the petrographic composition of gravels covered two fractions: 5—10 mm and 2—5 mm. The first to be examined were two strata of tills in the geological section of the valley slope at Morsk (east of Swiecie), where they occured in a considerable thickness, have typical facial developing and are in a clear-cut stratigraphic position. The analyses have shown that there are characteristic diffe-rences between the two strata as to the mutual relations between the petrographic composition of the 5—10 and 2—5 mm fractions. Whereas in the upper, first till strata the differences are manifested in the decreasing value of the O/K index in the 5—10 mm fraction and increasing index value in the 2—5 mm frac-tion vertically from top to bottom (fig. 5), in the second bipartite till strata the top layer, superglacial in character (phot. 3 — a), is characterized by a lower value of the O K index and by a higher value of the K/W index in the 2—5 mm fraction in relation to the 5—10 mm fraction; at the same time the bottom layer, being of lodgment-till type (phot. 3 — b), is characterized by an almost identical value of the K/W index in the 2—5 and 5—10 mm fractions and by a slight difference in the O/K index value between 2—5 and 5—10 mm fractions (fig. 6).

ANALYSIS OF DEPOSITS

Grudziądz Basin Slopes. In morę detail were analysed two selected sections located on the left slope of the Vistula valley near Sartowice (fig. 2). They expose deposits from the penultimate ice-sheet of the Baltic glaciation in the investigated area in their fuli vertical section. In the Górne Sartowice section (fig. 7) three genetic-facial types of tills were distinguished that formed in three different environments of glacial accumulation: in subglacial environment (a, b_u b₂), inglacial environment (b₃), and superglacial environment (Cj, c₂). The boundary between the subglacial and inglacial deposits is gradational in character, which is marked in gradual change of the grain-size composition and fabric patterns (fig. 8 and 9). The changes result from an up-strata growth of water participation in the glacial accumulation process. Superglacial deposits, whose presence speaks for areał decay of the ice-sheet, are styled in two varieties: as superglacial till