1968 年 77 巻 1 号 p. 37-55
The purpose of this paper is to classify low-altitude erosional surfaces in Japan and also to investigate the characteristic features of the granite mountains.
Mt. Suzugamine at the western part of Hiroshima city is consisting only of granite. The geomorphic surfaces of Mt. Suzugamine are classified roughly into two, Higher-Setouchi surfaces and Lower-Setouchi surfaces. Yamada surface of the Plio-Pleistocene in origin and Piedmonttreppen belong to the former and gentle slope remnants of early-middle Pleistocene and “Kannon surface” of middle-late Pleistocene belong to the latter. Neither marine terraces nor tephra are found in this area. As a result, it is difficult to correlate these with the geomorphological surfaces elsewhere which have already been well examined.
The gentle slopes were formed by the removal of deeply weathered granitic top soils about 50 m in thickness and the climatic change seemed to be less active.
Landforms were modified even in Würm glacial period as was seen in the “Kannon surface”. The agencies which formed the initial gentle slope is similar to one which formed “Kannon surface”.
Suzugamine mountains, which consists of granite, is characterized by gentle slope, box valley, earth fall, block stream, wide-opening valley and inward-opening valley. I should like to propose to term such geomorphology “granite topography”. It may be seemed that downwarping movement toward the Inland Sea (Setonaikai) has lasted down to the Pleistocene period, on the ground that the upper streams running down northward were captured by the ones running down southward.