In Japan, most of the rice fields are submerged only for the greater portion of the rice-cropping period, in which oxidation-reduction potential of the cultivated surface soil is so low that ferrous iron and manganous manganese areformed, but the subsoil is usually kept in the oxidized state through the year. Such conditions result the deposits of iron and manganese compounds in the B horizon, and their characteristics depend upon oxidation-reduction potential of the surface soil (eluvial horizon) and of the subsoil (illuvial horizon), amount of the drainage water, and the nature of the soil material. The soil samples used in this work were taken from the rice fields situated near on the tops of the hills which were different in their composing materials and these soils had B-horizons having a great deal of the blackish brown mottling. The clay fractions(<2μ) were separated from the soil samples after treatment with H_2O_2 to remove organic matter, and were examined by the x-ray, thermal, chemical, electron microscopic, and glycol retention methods on the calcium or sodium clays. It is concluded that (a) the predominant minerals were montmorillonoid and illite in the Mera profile which was derived from the shales and sandstones of the Tertiary origin, (b) the Tani profile developed on the weathered andesite had hydrated halloysite, allophone, hallysite, and gibbsite, (c) vermiculite, illite, hydrated halloysite, halloysite, and quartz occurred in the Fukuma profile derived from diluvial deposits. The clay fractions of the A-horizons were found to be less in iron and manganese contents, and somewhat higher in the silica-alumina ratios than the clays from the B- or C horizons, respectively, but any definite tendency was not observed among the clays of the horizons in other characteristics. It is suggested that the kind of the clay minerals in the paddy soils examined was closely related to the parent materials and not to the paddy field state.
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