Hokkaido is divided to three soil regions, that is, the northern, cetnral and southern regions as shown in Fig. 1. But the brown forest soils with leached top horizon are widely distributed in the southern soil region where the occurrence of the podzolic soils could not be expected under the recent bio-climatic conditions. The sequence of the ultimate pH through the profiles of these soils is not only different from that of the podzol but also from the typical brown forest soils. But seeing that the values tend to rise towards the bottom horizons, it may be quite reasonable tosuppose that these soils passed through the podzolization. They might have been regenerated from the former podzolic soils which were formed in the Würm glacial stage, to the equivalent of the brown forest soils, under the warmer climate during post-glacial stage. On the other hand, there are red coloured soils on the coastal terraces and gentle slopes at mountain foot especially in northern Hokkaido. The profile characteristics of these soils are quite similar to those of the subtropical red soils. But they could hardly be expected to be formed under the present sub-boreal bio-climatic conditions in this region. According to the modes of occurrence of these soils with special references to the topography of the coastal terraces, they should be regarded as the relict red soils which were formed during a warmer stage in the Pleistocene, probably in the Riss-Würm interglacial stage. It is quite interesting from pedogenetical point of view that such discordant paleosols as them are well preserved in situ even in the present sub-boreal bio-climatic conditions.
Based on the study on the geomorphological surfaces in Northeast Japan, the author concluded that the red weathering crusts were formed in the following two stages. The older stage is represented by the hillocks with red weathering crusts. The sea level in this stage was 100m higher than the present level. This stage was followed by the stage which characterized by the deposition of debris or clayey materials (Figs. 4-7). The younger one was followed by the stage of the “cryopediment” (Wako, 1963a) formation which prevailed in the valleys of Northeast Japan about 25, 000 yr. B. P. The lowest coastal terrace with red weathering crust stands 25m. above the sea level. The genesis of such weathering crusts in Japan was attributed to the former humid subtropical climate by some pedologists (e. g., T. Matsui and Y. Kato, 1962). Granted that the assumption is true, it seems probable that there was a certain relationship between the subaerial process of the hill surface formation and the conditions for red weathering occurrence.
The term “Kuroboku” soils is a tentative name for black-colored, mellow soils of both volcanogenous and non-volcanogenous origin. Pedological studies of the soils, especially on their humus accumulation suggest their genesis under grass vegetation and monsoonal climate. Part of the discussion on these problems was already presented in this Bulletin (Vol. 3, pp. 40-50). It is revealed, based on field occurrence, that the “Kuroboku” soils have been formed since an age not so older than late Pleistocene. The possible genetic conditions deduced from pedological studies seem to correspond with the history of late Quaternary. The climate aquired its present monsoonal character probably since the end of the last glacial age. No extensive grass vegetation could be introduced without destruction of naturally stable forest cover under the monsoonal climate. The destruction might be accelerated under more advanced human culture starting at later stage of the pre-Jomon culture (latest Pleistocene).