Geomorphic development since the latest Pleistocene of the drainage area of the Obitsu and the Yoro rivers, Boso Peninsula, Japan.

Investigates the chronological relation between the developmental process of valley incision and that of the alluvium deposition, and discusses the effect of sea level change on the development of the river valley in the upper to middle courses. 1) In the upper to middle courses of both rivers, valley incision has continued at least since ca. 20 000 y.B.P., because no fill top terraces can be found along the courses. 2) In the lower course of each river, the sedimentation of the Alluvium had began at the end of the Pleistocene. A retreat of the depositional area of the Alluvium is thought to be caused by a small fall of sea level since ca. 6 000- 5 000 y.B.P..-from English summary Univ. of Tokyo, Japan.