Abstract
According to the analysis of the lake map (1:10, 000) issued by Geogr aphical Survey Institute (1964), there are seven developed sub-lake terraces in Lake Ogawara. The results of the present writer's geological survey of the lake's surrounding parts as well as of his analysis of the sub-lake deposits surveyed by Planning Bureau and GSI, Ministry of Construction (1971) are as follows:
1) The bed formation (H formation) is related to Akobo-surface of the 2nd surface of the upper terraces of the Oirase River.
2) The above is related to bed formation of the upper surface of Misawa Hill.
3) The G formation is comparable to the upper formation of the upper surface of Misawa Hill.
4) Judging from the results of an analysis of the sub-lake deposits, the H formation was developed at the first stage (R/W interglacial) of the higher sea-level of Misawa, the G formation at the maximum of Misawa (Shimosueyoshi), the E formation at one stage of the higher sea-level pre-Würm Glacial, and the C formation at the higher sea-level of Jomon Age, respectively.
5) The river terraces (since Akobo Surface) of the Oirase River and the sub-lake terraces (since H Formation) were formed at the same stage, and the development of these different terraces of the heights resulted from the different grade of the two rivers in the former shore line, and the sedimentation formed since Tertiary.
