抄録
There are broad Diluvial uplands on both sides of the lower course of the River Kuji, to the south of Abukuma plateau. Basing on the field observations and the analysis of terrace deposits, the author classified the uplands into three terraces, and explained the processes of their formation. The main subjects discussed in this paper are summerized as follows:
1. The Diluvial uplands are classified into three terraces with altitudes of 80-110m (Upper), 50m (Middle) and 20-30m (Lower). Among them the Middle is the most extensively distributed in this area, and continues to the terraces situated along the upper course of the River Kuji (fig. 1).
2. Three terraces are similarly composed of sand and gravel beds lying unconformably on Tertiary system and are covered by aeorian volcanic ash which contains a pumice band 10-20cm thick. Upper terraces are correlated with so-called Tame terraces. the Middle with Musashino, and the Lower with the Intermediate terrace between Musashino and Post-Loam terraces in the southern part of Kanto district.
3. The author investigated the thickness of gravel beds in the Middle and Lower terraces, and made the machanical and lithological analysis of gravels, from which she inferred the environment of deposition and the process of terrace formation (figs. 1, 3, 4 and tab. 1). The major part of the Middle terrace is an elevated coastal plain consisting of littoral deposits. The former shoreline has been elevated some 50 meters, which is determind by the presence of exotic gravels in the eastern part of the terrace. The deposits of the Middle terrace may be correlated with the upper part of Narita formation deposited in the Palaeo-Tokyo Bay in late Pleistocene. The area studied had occupied the northern limit of the bay. The Lower terrace is of fluviatile origin formed by the extended courses of the Rivers Kuji. Sato and Naka.
