The author studied the river terraces and the gentle slopes along the Yoshida River which has its source in the Ou mountain range, and runs through the Yoshida Lowland situated in the northern part of Miyagi Prefecture. The following results are obtained.
1) Geomorphological surfaces along the river and in the hill-land to the north of the river are subdidived, from the upper to the lower, into Yoshioka I and Yoshikoka II Surfaces, Warimae, Yoshida and Omori Surfaces, and the Alluvial Plain.
2) Yoshioka Terrace by R. Tayama (1933) is subdivided into two, namely, Yoshioka I and Yoshioka II Surfaces. Yoshioka I Surface is an erosion surface and contemporaneous with the river terrace Yoshioka II Surface in its formation.
3) Yoshida Terrace by R. Tayama (1933) comprises the river terrace Yoshida Surface and a gentle erosion surface Warimae Surface along valley sides. At the time of the formation of the Warimae Surface, shallow valleys developed at the heads of the tributaries in the hill.
4) The characteristics of Omori Surface is similar to that of Warimae and is limited in a certain part of the hill in its distribution. Yoshida Surface does not exist in the part. From such a fact, concerning the nature of Alluvial Plain deposits and the characteristics of the morphology of the hill top, the author concludes that the tectonic line through the Niibori valley is efficient to the development of Surfaces. He calls the line the Omatsuzawa Tectonic Line.
5) Gentle slope Warimae Surface and shallow valleys are formed after the red weathering of the hill rocks, at the time of low sea level. Granted that the red weathering happened during a warmer stage, the surface must have been formed in a glacial stage.
The development of the surface is dependent on the direction of valley, so he thinks that tectonic as well as climatic effects were influential on its formation, though he can't differentiate the two.
Geological structure of the hill influenced the profile of the gentle slopes, namely, some profiles have knicks and others do not.
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