By analyzing the topography of the Mikawa Highland, which extends about 150 square kilometers in the east of Nagoya, central Japan, and the fluvial terraces of the adjacent area, the geomorphic develop-ment and the geological age of the highland erosional surfaces, the so-called “Mikawa peneplaln”, have been discussed. Pedological observations on the surface soils of some fluvial terraces have also been described additionally.
Along the down stream of the Yahagi River, the western margin of the Mikawa Highland, several stepped terraces are extending: The highest one, about 240 meters above the sea-level, can be correlated northwestward with the depositional surface of the Seto Group, which is the lacustrine and fluvial deposits accumulated at Seto and Nagoya region in the Pliocene Epoch. While the lower terraces are fluvial ones built by the Yahagi River during the Pleistocene Epoch.
The topography of the Mikawa Highland is composed of four series of low-relief erosional surfaces, i. e. from older to younger, surfaces of 1, 100-1, 000, 900-700, 600-400and 300-100 meters in altitude, respectively (figes. 1 and 2). The lowest one, named the lower Mikawa low-relief surface, seems to be continuous with the basal surface of the Seto Group, which also represents an erosional level of low-relief (fig. 3). The basal surface of the Seto Group is intersecting the structure of the middle Miocene Mizunami Group. It is, therefore, most probable that the lower Mikawa low-relief surface was formed in the early Pliocene.
In the catchment area of the Yahagi a basin-forming movement with an axis of NE-SW trend, accom-panying faults of NE-SW direction along its both sides, has been continuing since the pre-Pliocene. Accordingly, the low-relief surfacesin the Mikawa Highland may be said the “Piedmonttreppen” formed in connection with theupheaval of the surrounding mountains, which is a counterpart of the above-mentioned basin-forming movement.
