The present writer has tried to analyse the change in the agricultural structure in the Syunan region caused by the conversion of the farm land into other uses: factories, residence publicuses, etc・・・. The Syunan region, which is divided into the five administrative districts: Cities of Hofu, Tokuyama, Kudamatsu, Hikari and Town of Nanyo lie on the coastal plain along Seto inland Sea in Yamaguchi Prefecture. Most of the farm land in these districts was cleared up before the period of Meiji. The major income of farmers in the Syunan region comes from rice-products. In the past few years many factories and houses have been built up in the region and the cultivating land has gradually been converted into other uses in this area. The increase in urban uses of land has caused the dicrease in the management of agrculture. The present writer has tried to analyse this phenomenon as the decrease of agricultural land use and the decrease of the number of agricultural house holds and their family members. As a result, full-time farmers have increased in number. Farm land and the change in agricultural structure in the Syunan region may be classified into the following categories: 1. The farm land conversion has especially been conspicuous since 1961. This has corresponded to the very fast economic growth of Japanese capitalism. 2. From the viewpoint of the change in agricultural structure, the following three stages can be pointed out; the change in the urbanized area before 1960, the change of the surroundings of the factories from 1960 to 1963, the change in the area along the Road Rt. 2 and the foot of mountains since 1964. 3. Of large scale, the farm land conversions have been in the surroundings of the factories, of medium-scale along the road Rt. 2 and of small-scale at the foot of the mountains. 4. The farm land owners whose farm size is from 70a to 1ha have greatly been decreased. The bigger the farm land conversion has been, the more the decrease in the number of agricultural households and their family members have been. The part-time farmers have increased in the area of the big farm land conversion. 5. The categories of the relation between the farm land conversion and the change of agricultural households are shown in the figure 9. In the area of type 1 of the farm land conversion (Tokuyama, Kushigahama, Kami, Kudamatsu) most farmers have gotten side-businesses and farm management has greatly been declined. In the area of type II around the type I the part-time farmers had increased long before the farm land converted into other uses. In the area of type III, the farmers have mainly produced rice, but the part-time farmers has been increased. In the area of type IV , the farmers have brought commercial products such as mandarins, vegetables, livestock. It may not be adequate to consider this area is the leading area of commercial products.
The Tsuyama basin, situated between the Backbone Ridge of the Chugoku mountains and the Kibi Highland, is an erosional basin where the Tertiary bed is subjected to the selective erosion. In and around the basin, erosion surfaces having 6 to 7 stairs are distributed. The distribution and poperties of these surfaces may be summerized as follows: 1. "Upper erosion surface" in the Chugoku mountains is distributed around the peaks of the Backbone Ridge with the heights of 900-1300 meters, and confined to the northern part of the "Mimasaka thrust fault". 2. "Middle erosion surface" in the Chugoku mountains is chiefly found on the hills of the basin, the altitude of which 400-600 meters high. The border line between the above "Upper surface" and this "Middle surface" does not always accord with the Mimasaka thrust fault line, and runs in the northern part off the Mimasaka thrust excepting the foot of the Mt. Nagi. In addition, the shallow valleys which belong to "Middle surface" stretch into the Backbone Ridge. Consequently, the period of formation of "Middle surace" may be safely said to be considerably later than that of "Upper surface". 3 "Nihonbara surface" is the oldest surface among Tertiary beds in the Basin. It is protected by the outcrop of hard rocks which are older than the Tertiary bed. The surface of Nihon-genya is typical. 4. In the northern part of Nihon-genya, there are large-scale taluses. 5. Around and among "Nihonbara surface" there are erosional surfaces with 3 to 4 stairs, that is, upper terrace (terrace I ), middle terrace (terrace II ), lower terrace (terrace III), and flood plain. It may be fittingly said that these surfaces were formed through the degradation of Tertiary beds, caused by inter mittent upheaval of the area since the formation of "Nihorbara surface".