A Móra Ferenc Múzeum Évkönyve, 1970. 1. (Szeged, 1970)

referred to sea level (Fig. 4). Within this area, having a relative relief of 2.5 to 3.5 m, the ground-water table slopes markedly toward the lake. In springtime the groundwater may emerge from shaft-wells and boreholes and flow into the lake. The same phenomenon has been observed in the case of Lake Dongér, for example. In extremely dry seasons, in autumn, most of the lakes run dry. The most intensively alkalized areas lie close to the lake, where the greatest amount of water evaporates. Alkalization is brought about, beside the given hydrogeological characteristics, by concentration of the salts of ground- and meteoric waters. SUMMARY Genetically, three types of lakes have been explored hitherto in the southern Great Hungarian Plain, each having been closely linked with the geohistory of a landscape unit of characteristic geological setting: a) deflation lakes of the Danube-Tisza Interfluve, b) ox-bow lakes of the Trans-Tisza Region, and c) pre-flood-control lakes of the Tisza Valley. The paleostreams of the Trans-Tisza Region lakes can be traced back to the end of Pleistocene time. Since the beginning of the Holocene they have evolved as ox-bow lakes. The Danube-Tisza Interfluve lakes were formed early in Holocene time and after the Holocene hazel-nut stage. The Tisza Valley lakes appeared at the beginning of the Holocene. The large-scale alkalization of the deeper portions of lake vicinity has been produced by the strong evaporation of depression-bound meteoric and groundwaters and by their salt concentration. 70