The South Daito Island is a remote island 370 kilometers to the east of the main island of Okinawa, and its economy is dependent upon sugarcane monoculture. Since 1967, sea-sonal laborers from foreign countries have been employed to harvest sugarcane on the island. After World War II, seasonal laborers were recruited from Okinawa Island during the harvesting seasons. As it became difficult to recruit laborers from the main island due to the increase of employment opportunities in the main island, laborers were recruited from remote islands of low wages, especially the Miyako Islands. Since 1964, the low price of sugarcane and the increases of wages in other sectors of the economy in the Ryukyu islands and Japan proper negatively affected the sugarcane cultivation of South Daito Island (Fig. 4). As the island suffered a population decrease, the use of labor in the cultivation became less intensive. The increasing difficulty in the recruitment of laborers even from the Miyako Island aggravated the problem. Finally in 1967 low-wage laborers were introduced from Taiwan, and their number increased rapidly to the point that they became indispensable to the sugar industry of the island (Fig. 7). Thus the outflow of the islanders and the seasonal inflows of foreign laborers presented a strange paradox. The severance of diplomatic relation between Japan and Taiwan concomitant with the restoration of diplomatic relation between Japan and the People's Republic of China in 1972 prevented the recruitment of the Taiwanese. In the 1972-73 harvesting season, sugarcane had to be harvested without the help of foreigners, which was a great shock to the island community. In the 1973-74 season Koreans were recruited for the harvest, and since then they have come to South Daito Island every year. It may be safely said that the easy going resort to the low-wage laborers from Taiwan retarded the mechanization of sugarcane agriculture, and caused the shock in 1972. On the other hand, it is also true that the very shock led to the mechanization. In fact, South Daito Island is now one of the areas in Japan that have made good use of machines in agriculture. But hand-reaping of sugarcane is still widely practiced, and a large part of it is carried out by the Koreans. With the abrogation in 1977 of the Okinawa Prefecture Reversion Act of 1972, whereby the seasonal employment of the Koreans in the prefecture is permited, it is impossible to secure foreign laborers in the following seasons. Can the farmers introduce more machines on an economically sound basis? Response of the sugar industry of South Daito Island to this pressing problem remains to be seen.
It has been said that the feature of longitudinal profile of divides are dependent on different rates of erosion controlled by the difference of geological structures i.e.: density of faults and joint fractures, and lithological differences. In this paper, the author has tried to make clear the relationship between the structures and the feature of longitudinal profile of high-standing divides located in the Shirouma Range (2, 300_??_2, 933m), Central Honshu, Japan. He examined the influence of geological structures on the divide form, by measuring the joint density and by making detailed geological maps. The joint density is represented by the number of joints intersecting the circular line of 1m-long on unweathered bedrocks. The joint density was measured at about 300 locations. The relationships between the joint bensity and variations of longitudinal profiles of the divides for different areas are graphically shown in Fig. 2 and Fig. 3, and Table 1 lists them numerically along with sites and lithologies. The altitude of divides becomes lower with the increase of joint density when the intervals between neighbouring locations are 1m to 2m, as illustrated in Figs. 2-a_??_e. The same relationshipalso exists for measuring-interval of 4m to 20m as shown in Figs. 2-f_??_h. Such relationship cannot be recognized, however, when the intervals are increased to 30m to 112m, as shown Figs. 2-i_??_k, Figs. 3-I and II. From these examinations, it can be concluded that the small-scale undulation of the longitudinal divide form with horizontal distances of shorter than 20m are strengly controlled by the difference of the joint density, but the large-scale undulation with horizontal distances of longer than 20m seems to be dependent not on the joint density but on the other geological structures.