In view of that continental shelves are essentially the erosional landform and also that the sea level fluctuation after Wurm glacial stage has played an important role i n the for mation of continental shelves, the author completed a model of continental shelf formation, which was based on a combination of coastal cliff recession and the postglacial transgression; the model is summarized in the following two equations:
_??_ (1)
and Z^*=-h_a+A(1-2e^-at+e^-2at), (2)
where X^* and Z^* are the coordinates showing the position of the point P (Fig. 9) and a continental shelf profile may be obtained by finding a locus of this point; c is the recession rate of the present coastal cliff, in meters per year; t is time in years, and t=0 and t=2×10⁴ show 2×10⁴ years B. P. and the present respectively; h_a is the critical water depth for submarine bedrock erosion, in meters and may be estimated approximately by
_??_
in which H₀ and L₀ are the deep water wave height and length in meters respectively and H and L are the wave height and length in meters, at the water depth h_a respectively, and a nomogram for this equation is shown in Fig. 1; W₀ is the width of abrasion platform in meters at t=0 and is written as
W₀=W_p-2×10⁴c,
in which W_p is the present platform width, defined as the horizontal distance from the present coastline to the place where water depth is h_a; A and a are constants appeared in the following equation expressing the curve of the postglacial sea level change:
Z=A(1-2e^-at+e^-2at)
which is shown in Fig. 8 and A=125 and a=1.98×10⁴ in this case.
The validity of this model was examined in three areas facing on the Pacific Ocean (Fig. 10). Physiographical and oceanographical conditions of these areas are listed in Table 2. Figure 15 shows comparisons between the continental shelf profiles in the fields and the ones calculated by using Eqs. (1) and (2); the actual profiles and the calculated ones are in fairly good agreement: this model can explain in full degree the first essentials of continental shelf formation.

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Kuenen and Margolis recognized frosting on the quartz sand grains as the result of mechanical and chemical process that were active in the eolian environment. On the contrary, Cailleux, Ottoman and Kosugi recognized it as the result of wind abrasion. On the basis of Cailleux, Ottoman and Kosugi's view, the writer reports the results of some measurements of the quartz sand grains and discusses them in this paper.
Approximately 82, 800 samples were collected from eight environments in Pleistocene and Holocene : offshore, foreshore, backshore, dunes I, II, III, inland dune, eolian sands beneath a black humus soils, and eolian sands of lower Pleistocene in western Japan and Antarctica. The length of quartz sand grains studied ranges from 0.35 to 0.71mm. Observations were made by the binocular microscope with canadabalsam on a green background. Magnification is x 60 for the 0.71mm grains, and x 75 for the 0.5 and 0.35mm grains. Among the quartz grains, four main types may be distinguished.
1) angular shiny grain (AS) 2) round shiny grain (RS)
3) semi dull grain (SD) 4) round dull grain (RD)
The results obtained may be summarized as follows:
1) Prevailing sand grains of RD type are observed in the eolian sand beds. In contrast to the eolian sands, the beach sands contain a high percentage of AS and RS type sand grains.
2) In the Holocene eolian sands, dune III sands contain relatively high percentage of sand grains of RD type (17 to 66 per cent). On the other hand, in the dune I sands, the percentage of sand grains of RD type is as low as 1 to 19. This is shown Figure 2.
3) Correlation of the thickness (t) and the percentage of sand grains of RD type (A) of dune III sands is shown to be A=0.878t+13, 188. This is shown in Figure 3.
4) In Wright valley, Antarctica, the migrating eolian sands contain higher percentage (76 per cent) of sand grains of RD type than in Japan.
5) In the pleistocene eolian sands, Tanegashima D3 sand and Hojyo eolian sand beds contain a high percentage of the RD type sand grains. Its properties differ greatly from Holocene eolian sands.

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In 1965, about 32 per cent of the cultivated land in Japan was the ordinary field, although the arable farming consisted chiefly of the paddy field cultivation.
The distribution of ordinary field was remarkably concentrated in four areas, namely Hokkaido, Northern Tôhoku, Kanto and Southern Kyushu, and the dominant type of farming practice in these areas was the ordinary field cultivation.
Examining the ordinary field cultivation, the dominant size of the small family farms. excluding those in Hokkaido, is less than two ha., and by 1955 the standard of farming methods was so backward that the level of productivity was very low.
On the other hand, one of the most striking features of economic changes in Japan during the period from 1955 to 1970 was on the increase in industrial productivity. At the same time the level of paddy rice productivity has also increased. On the contrary the production of ordinary field cultivation has shown a notable decline.
In order to clarify the mechanism of this trend, I made a case study analysing ordinary field cultivation in the northern part of Iwate Prefecture in Tohoku District. The results obtained by this investigation are as follows. Around 1955 the most important feature of ordinary field farming in this region was its backwardness. The typical size of production was covered by the small-scale farm management (see Table 3), and the old traditional farming practice still remained dominant. The basic crop rotation for two years consisted of burnyard millet, wheat and soybeans. Since 1955 this economic state of agriculture has began to change under the impact of rapidly expanding imports, particularly, of less expensive wheat and soybeans mainly from the United States.
As a result of the impact, the trend of prices in wheat and soybeans has been unfavorable, and the ordinary field cultivation has most severely been hit by this unstable situation. As shown in Table 5 the acreage of wheat and soybeans has begun to decrease remarkably. There were numerous efforts to improve such straitened circumstances. One of the attempts was to introduce intensive cash crops and livestock, especially dairy cattle. But this was nearly in vain except in the case of livestock raising due to three factors: the minute and fragmentary nature of farm enterprises, the predominance of backward farming methods and the instability of market prices with the low level of producer prices.
On the other hand, as shown in Table 6, there was an increase, to a certain extent, in dairy and beef cattle. The small size of herd prevailed in the region, so that a tendency towards stagnation and decline has become apparent in recent years.
The decline of ordinary field cultivation and the stagnation of livestock raising shows the fact that the majority of farmers have become increasingly dependent either on rice farming or on non-agricultural sources of income.
The guaranteed rice price of the Government for producers has been kept relatively higher. Thus the paddy rice cultivation was remarkably spread by the conversion of ordinary fields into paddy fields during the period of 1960 and 1970, especially after 1965. But the rice production in Japan has expanded rapidly since 1955, and they have had surplus production for the past several years.
Therefore, the Japanese Government has been obliged to restrain the rice farming areas since 1970, and the rice farming increase in this region has stopped with great difficulties.
In these circumstances the farmers in this region are almost hopeless to the agriculture itself, and the employment of non-agricultural labour for the farming population has intensely been going on in recent years.

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