The granulometric composition of glacial deposits of the Russian Plain is frequently dominated by the coarse silt fraction. Assimilation of the residues of underlying aleuritic hard rocks has a secondary importance in this phenomenon, and it may be basically attributed to the hypergenic transformation of initial crystalline igneous rocks. Since their mineral constituents are mainly sand-size, it seems reasonable to assume that coarse silt results from their physical disintegration. The greatest contribution to the latter process in terms of scale and probability was supposed to be made by cryogenesis.
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