The south part of the Musashino Diluvial Upland along the River Tama is a region where the Fluvial terrace topography formed by the River Tama dominates. In this region, four terraces from the older to the younger are distinguished, as follows : The Musashino terrace, Tachikawa terrace, Aoyagi terrace and Haijima terrace (Fig. 1). The Musashino terrace is divided into three terraces which constrict each relative height respectively toward the upper stream. In this paper, the third (the lowest) Musashino terrace is called the Nakadai terrace. To the west of Haijima, develops the Alluvial terrace under the Haijima terrace. It is divided into four terraces from the upper to the lower, as follows : The Amagase terrace, Chigase terrace, Kawahara terrace and Tabata terrace. The Tabata terrace develops to the west of Ome. In the east part of this region, The Den'en-chofu-dai, Ebara-dai and Yodobashi-dai, which are higher than the Musashino terrace, are recognized. They are the marine terraces, and are corresponded with the Shimosueyoshi terrace in the most eastern part of the Tama Hill. The geology of this region consists of two Groups, that is, the Miura Group (Pliocene) and the Narita Group (Pleistocene). The Miura Group dominates to the west of Okura-machi, Setagaya-ku, Tokyo-to, and to the east of it develops the Tokyo bed belonging to the Narita Group (Fig. 3). The Miura Group in this region can be divided into the following members in ascending order : The Kazumi gravel (150 m+ in thickness), Komiya sandstone (70 m±), Misawa mudstone (30 m±), Renkoji alternation (100 m+), Inaki sandstone (60 m±), Tsurukawa alternation (60 m+), Hirao sandstone (20 m+), Negata tuffaceous sandstone (30 m±), Ozenji alternation (40 m±), Detana sand and gravel (40 m±), Ikuta alternation (50 m±), Iimuro mudstone (50 m ±) and Takatsu alternation (70 m±). In the western half of this region, the Members of the Miura Group develop in ascending order from west to east in the gentle monoclinal structure. The Kazumi gravel is unconformably in contact with the old rocks of the Tamanouchi Palaeozoic zone in the Chichibu System-Middle Carboniferous system or Lower Permian system-and with the Futamatao sandstone and conglomerate zone in the Ohisano Group-Upper Triassic system at Ome in the Tama Valley mouth. These two systems develop extensively in the Kanto Mountain Land. The Komiya sandstone and the Misawa mudstone are in a disconformable relation with each other, but the time gap is short. In the eastern half of this region, the Miura Group forms a synclinal structure under the influence of the Mizonokuchi basin-like synclinal structure (Fig. 3). In this structure, our attention is attracted to the facts that the upper each member is, the farther east each synclinal axis shifts, and that the thickness of the Detana gravel, Ikuta alternation and Iimuro mudstone constrict to the east. The author thinks that these facts definitely show the following points : The formation of this structure was caused by both the gentle tilting to the east in the west of this region and the fairly rapid upwarping that formed the Kamihoshikawa dome-like anticlinal structure in the southeastern part of the Tama Hill, and these movements continued throughout the time of deposition of the Miura Group in the east. The Hachioji Fault-line along the eastern margin of the Kanto Mountain Land is a faultline formed before the deposition of the Miura Group, and it does not cut the Miura Group. According to my survey, it is not necessary either to conclude the existence of the Tamagawa Fault-line, which used to be presumed once along the north margin of Tama Hill (Fig. 7).
4) Fig. 5 is the extent of the Pleistocene and the present glaciation in China compiled by a Chinese geologist, which suggests general acceptance among Chinese geologists and geographers of the wide spread Pleistocene glaciation throughout the land, particularly in the central and the eastern part of China; the southern border of the past glaciation reached as far as the present subtropical China. Such a remarkable prevalence of glaciation was first remarked by Lee Szu-kuang in 1930's, when he claimed evidences of glaciation in the lower Yangtze valley, particularly around the hill of Lush an near the Poyang Lake in Kiangsi. His theory was widely disputed but was not generally approved by European scientists. However, it has had a great influence upon the thinking of Chinese scholars and the result is, after the war, a rapid increase in the number of Chinese geologists and geographers in favor of his theory and approval of evidences of glaciation over a wide area. In the discussion of the Lushan glaciation, Lee suggested three successive glaciations in Pleistocene; the Poyang, the Taku and the Lushan. In the present research of the Pleistocene Epoch in China some geologists added the last glaciation, the Tali; and the Poyang, the Taku, the Lushan and the Tali seems to be an authorized succession of glaciations in the central and the eastern part of China Mainland. The succession and the extent of the past glaciation, however, are not free from criticism even today among Chinese scientists. 5) Articles discussing glaciations in the central and the eastern part of China have been generally appeared in the scientific magazines and reports of geology, rather than of geography. Recently a special publication dealing with the problem was issued (1964), compiled by the Quaternary Era Research Committee in China, containing six articles approving remnants of glaciations in various parts of China. Among them is Lee's article claiming evidences of glaciation in the Western Hills. The Western Hills, Peking's nearest heights, form the western border of the Peking plain, which slopes gently towards the southeast. Lee's theory is based on the observations of topography and deposits which cannot be explained by other than glaciation, such as linearly arranged basin-like depressions cut into the floor rock of a valley, striated and polished surface produced on the bottom rock, uneven rock surface underlying the Peking plain (Fig. 7), glaciation remnants such as striated boulders, clay-and-boulder deposits which cover deeply the Peking plain. He attributed the la st one to the frequent floods occurred near the end of a glacial period. However, the exact period in Pleistocene during which glaciers flowed down to the foot of the Western Hills is not established. His discussion goes as far back as the climatic condition under which Peking Man lived. The analysis of pollen, plant and animal remains of the clay-and-boulder deposit; in the Choukoutien Cave by Chinese geologists revealed that the climate of Peking Man's period was rather warm or hot, while the upper and the lower layers of deposits were formed under cold climate. This exemplifies, according to Lee, the existence of at least one interglacial period and two glacial ones. Other articles contained in the special publication are dealing with glaciations of the Lungmen-Shan in Szechuan, the Great Khingan Mountains, the Tapieh-Shan, the Eastern Tsinling-Shan and the Taihan-Shan. However, a careful analysis and comparison of the evidences and conclusions of these articles reveal some inconsistencies from one another as to the occurrence of glacial periods, the altitude and the extent of glaciations (Table. 2), which suggest the glacial problems in the Pleistocene of China are not yet settled conclusively.
The occurrence of not only such natural disasters as ground subsidence due to the taking up groundwater, earthquake damage, flood losses, etc. but also such public nuisances as river pollution, air pollution, etc. have recently increased in the urban areas of Japan which are situated on recent alluvial lowlands along the coastal region, and accompany the rapid development of these regions, i. e. the rapid growth of industry and the rapid increase of population in these regions. Among the disasters, almost all of the natural disasters occurred in soft ground areas in connection with poor land and water utilization. Therefore, to examine and forecast the danger from disasters due to soft ground conditions is most important to allow reasonable plans for the regional development and the prevention of disasters to be made. The Shizuoka-Shimizu region, situated on the Pacific coast of Central Japan, is expected to be developed as a metropolitan area by the combination of two cities, Shizuoka and Shimizu (Fig. 1). The distribution and physical properties of soft ground, and problems of prevention of natural disasters caused by soft ground conditions, particularly earthquake damage, are described and discussed in this paper. (1) The recent alluvial lowlands in the region investigated, the Shizuoka-Shimizu Lowland, are limited by the Tertiary mountains to the north and Suruga Bay to the south (Fig. 2). The River Abe flowing down from the southern part of the Southern Japan Alps and having a great landslide area on its upper reaches, Ohya-kuzure, passes through in the western part of this region to enter the sea, and the eastern part of this region lies in the catchment area of the River Tomoe, which rises in the Tertiary mountains (Table 2). The Udo-san Hilllands composed mainly of Pleistocene gravel layers and having a plateau on the top, called Nihondaira, is located in the middle part of this region. Fig. 2 is a landform classification map compiled by aerial photographic interpretation. Micro-landform units shown in this map are classified systematically by origin and composition to inferred engineering soils, based on the methods and techniques of micro-geomorphological analysis for engineering soil surveys from aerial photographs (Kadomura 1965, 1966). From this map, the Shizuoka-Shimizu Lowland is divided into several “landform areas” as shown in Fig. 3 and Table 1, depending upon the distribution pattern of micro-landform units, the geomorphological agents, their topographic locations and other criteria. The “landform areas” consisting of gravelly layers are divided into two categories fluvial landforms such as alluvial fans and gravelly valley bottom lowlands, and marine landforms such as coastal shingle bars and sand banks. The areas of poorly-drained deltaic lowlands, which originated from former lagoons blocked by shingle bars and sand banks, are distributed along the both sides of the R. Abe Fan and in the downstream area of the R. Tomoe. These deltaic lowlands are formed of thick muddy deposits mentioned later. During the formation of these poorly-drained muddy lowlands as well as the formation of soft ground, coastal shingle bars and sand banks, which formed before the formation of the muddy lowlands, played a important role. (2) The ground in this region investigated and the surrounding mountain lands is divided into unit layers as in the other coastal lowlands of Japan shown in Table 3, for comparison of their relative foundation bearing strengths. Among these unit layers, the Upper Muddy Layer (Um), the Lower Muddy Layer (Lm), and a part of Upper Sand-and-Gravel Layer (Usg) composed mainly of sandy soils (Us), which are distributed along the margin of the Shirnizu Sand Bank and in abandoned low water channels, should be noted as soft ground layers.