The purpose of this paper is to document the total area of kanna-nagashi sites (stopes) and the area occupied by rice fields lying within these stopes, and to estimate the quantity of earth moved by kanna-nagashi in the Takahashi and Tojo (a tributary) River basins in the Chugoku Mountains.
In Japan iron was produced only by the traditional iron sand smelting method, tatara, until western style smelting was introduced in 1853, and the tatara method continued to be used until the 1920s. The iron sand used as raw material is found in small quantities (about 0.35%) in weathering granitic rocks. It was collected by breaking up weathered rocks and sorting them in running water. This method of mining was known as kanna-nagashi. Mountains and hills in many parts of the Chugoku mountains have been much deformed by kanna-nagashi.
The main results may be summarized as follows:
1. Numerous kanna-nagashi stopes are distributed in the upper parts of the Tojo river basin (Fig. 1). Most of the stopes are geomorphologically located in the gentle piedmont slopes and mountain ridges, and geologically located in the regions consisting of granite or granito-diorite.
2. Most of the rice fields lying in the stopes are located on gentle piedmont slopes.
3. The total area of stopes, estimated by the interpretation of aerial photographs, is 2, 673 hectares in the Tojo River basin and 570 hectares in the main Takahashi Riever basin; the area in rice fields is 288 hectares in the Tojo River basin and 71 hectares in the main Takahashi River basin.
4. The quantity of earth moved by kanna-nagashi can be estimated by two methods, the documentary method and the geomorphological method. For the documentary method, the following data were used:
1) the ratio of the volume of iron sand collected to that of earth cut; 2) the volume of iron sand collected at one stope for one year; 3) the number of stopes; 4) the ratio of iron sand used for tatara to the tatara output; 5) the volume of iron sand used for one tatara for one year; 6) the output of one tatara for one year; 7) the number of tatara; and 8) the period, which was about 220 years, from the beginning of the 18th century to the 1920s.
Judging from the above calculations we concluded that the quantity of earth moved was 1.9×10⁸m³-2.3×10⁸m³ in the Tojo River basin and 4.1×10⁷m³-6.6×10⁷m³ in the main Takahashi River basin.
For the geomorphological method, the area of stopes and the heights of man -made cliffs and kanna-zankyu (mounds left in the stopes) were measured. From these calculations, the quantities of earth were 1.5×10⁸m³-2.2×10⁸m³ in the Tojo river basin and 3.3×10⁷m³-4.8×10⁷m³ in the main Takahashi river basin.
5. The reason for the great difference between the volumes calculated by the documentary method and those calculated by the geomorphological method for the main Takahashi River basin is the shortage of historical records. So we suppose that the figure calculated by the geomorphological method is closer to the actual volume of earth moved.

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