1980 年 33 巻 p. 14-21
The present writer aims at proposing a new classification of the erosion surfaces, in order to discuss more precisely geomorphic development of the Chugoku Mountains on which different disputes have long been made. In the central part of the Chugoku Mountains, erosion surfaces are clearly recogniz-ed at three levels. They are namely Dogo-yama, Takano and Hiwa surfaces in descending order. The Dogo-yama surface is seen distributed between 1000 and 1300m above the sea-level, mainly as summit fiats on the Backbone Ridges of the mountains. The surface had been formed before the transgression of Miocene sea and was isolated by dis-section and encroachment of lower erosion surfaces. The Takano surface is an erosion surface cutting the Miocene Bihoku group and extends between 550m and 900m, continuosly at the both sides of the Backbone Ridges. The Hiwa surface is distributed in small erosion basins in granitic rock areas and stands between 4001Tl and 600m. The Takano and Hiwa surfaces may be identified with the Kibi Highland surface to the south and are dif.ferentiated into two levels due to upwarping of the Chugoku Mountains. Relative altitude between the two surfaces increases towards the main devide. They are also dislocated by thrusting along the faults to the north of Miyoshi and Tsuyama basins.