Two types of terraces are alternatively developed along the Pacific coast of Japan, they are (1) Recent and ancient coastal plains and (2) ancient fluvial plains. The formation of type (1) contains a marine fauna and flora indicating relatively warm temperature, and type (2) contains a flora indicating cool temperature. From the sequence of these terraces, glacial eustasy can be recognized. The youngest terraces of type (2) may be dated to the cool and low sea-level time during the Würm Glacial Stage, though the lowest sea-level was after formation of these terraces.
The areas around Tokyo Bay offer the standard stratigraphic column of the Quaternary system in Japan. The writers have investigated the geomorphology and surface geology of the latest Quaternary in these areas. The results are summarized as follows: 1) The latest Quaternary marine and fluvial deposits (theso-called Alluvial deposits) in and around Tokyo Bay were accumulated during the regression and transgression that had occurred since the beginning of the Late Wisconsin (or WürmIII) glacial age or about 35, 000 B. P.. 2) Subsurface data from boring cores in the coastal areas is now sufficient for presenting the distribution of the depths of the base of the latest Quaternary deposits (fig. 2) and for presenting the section of sedimentary facies of the latest Quaternary deposits around Tokyo Bay from Hommoku Cape to Futtsu Cape (fig. 3). The deposits can be divided into two members, the Upper and the Lower, based on the cycle of sedimentation. 3) According to the mineral composition of the volcanic ash beds covering the terrace surfaces, the ashes on Aoyagi terrace (fig, 4, right) is correlated to the upper part of ones on Tachikawa terrace (fig4, left). 4) Fig. 5 shows the detailed isopach map (numericals in meters) of the latest Quaternary deposits along the lower part of the Tama River. 5) The longitudinal profiles of the terraces, the buried terraces and recent water course of the Tama River are projected in fig. 6. From the figs. 5 and 6, the gravel bed forming Haijima terrace can be correlated to the buried gravel bed of 60m below sea level at the mouth of the Tama, and the gravel bed forming Tachikawa terrace to the buried gravel bed of 20-40m below sea level. These two terraces have a steep gradient caused by the lowering of the sea level during the Late Wisconsin glacial age. 6) In conclusion, the writers have established the landform evolution of the areas during the latest Quaternary epoch. The sequence of the features is as follows: 1. Deposition of the gravel bed forming Tachikawa terrace and the buried gravel bed of 20-40m below sea level at the mouth of the Tama. 2. Deposition of the gravel bed forming Aoyagi terrace and Egota (or Ekoda) Conifer bed. 3. Deposition of Tachikawa volcanic ash beds during 1 and 2. 4. Deep entrenchment of rivers……deposition of the gravel bed forming Haijima terrace……forming of submarine terrace of 100m below sea level. 5. Rapid transgression……deposition of the Lower member of the latest Quaternary formation. 6. Retarded transgression (Alleröd)……forming of terrace now buried 20-30m in depth. 7. Re-transgression……deposition of the Upper member of the latest Quaternary formation. 8. Building of wave-cut terrace now buried less than 10m in depth and terrace of less than 4m in depth……forming of alluvial plain of Shitamachi. 7) The above evolution reflects world-wide events. The correlation between the development of landforms of Tokyo Bay and the eustatic changes of sea level is estimated as shown in fig. 7.
There have been hitherto supplied not a few discussions if the fluviatile terraces around the Japan Alps and other high mountains in Japan, could be of the origination during the glacial phase. It is true that the Pleistocene topographic landscapes are notably characterized by the well-developed fluviatile terraces standing along inland rivers. In basins and valleys around the Japan Alps is recognized a wide extension of the fill top terraces which seems to indicate the former existence of a time when a vast amount of detritus filled up these lowlands. Taking advantages of the modes of occurrence of the tephra-layers as the key beds of correlation, the author has reached a conclusion that the valley filling above-mentioned might perhaps have taken place during the 3rd Interglacial, as is shown in the suggested correlation put in Table 1. These facts seem to imply that the accumulation terracing in these basins and valleys around the Japan Alps have never been influenced seriously by the climatic deteriolation, accordingly that even during the glacial maximal phase, the territory the author has concerned with could by no means be assigned to the periglacial or the proglacial morphogenetic region.
The writer has studied the terraces and gentle slopes of erosional origin in the three valleys of the Northeastern Hokkaido, and classified them and correlated their date of development. The relations are shown in the following table. Some of the longitudinal profiles of river terraces of the Shokotsu as well as those of the other two rivers intersect one another (Fig. 3). Such relation may be attributed to the eustatic movements of sea level as well as to the tectonic movements (gradual upheaval of the upper course area). Nevertheless the latter element is not discussed here, and perhaps it is impossible to distinguish whether the influence was by former or the latter. Judging from the thickness of terrace deposits and deposits forming the coastal plain, the writer came to the conclusion that the teustatic movements here were more significant and universal than the tectonic ones. At the time of the formation of terraces when the sea level, namely the base-level of erosion had sunk there developed the gentle slopes of erosional origin. Judging from the structure of those gentle slopes, it is sure that there worked some erosion force from both sides of the valleys and that the erosion must have been different from such that forms the terraces. It may be presumed that in such a period cool climate prevailed, and vegettion was poor.
It has been suggested in a previous paper (1957) that, on the Pacific side of the Japanese islands, the subtropical region directly adjoins the temperate (s.s.) region without a warm temperate region between, but that warm temperate areas are found in isolated, more or less sheltered places, where the coastal water is predominant. The Inland Sea (Seto-naikai) is recognizable as a represen tative of these enclosed warm temperate areas. In contrast to the Pacific side, no such sharp boundary between the subtropical and temperate regions can be found on the Japan Sea side, where very strong ocean currents like the Kuroshio and Oyashio are lacking. The southern part of this coast is recognizable as a warm temperate region. The marine bio-geographies of the Pacific and Japan Sea sides of the Japanese islands are considered to be respectively comparable to those of the American and European coasts of the North Atlantic. The possibility is suggested that, on the American coast, the subtropical region comes into direct contact with the temperate (s.s.) region at Cape Hatteras, and that the warm temperate areas may be confined to sheltered, coastal-water areas on the coast between Cape Canaveral and Cape Cod, which has been recognized as the "Transatlantic" bio-geographical province.