Coastal terraces in the western-most part of Honshu can be divided into six series. The first, namely, oldest terrace is about 50m above sea level and is represented by the Oji terrace. Both the second and the third are widely distribused, and they are 20-30m high and 5-15m high, and are represented by the Furudono terrace and the Maruodara terrace, respectively. The fourth terrace is 6-14m below sea level and is called the Ubeoki terrace. These four series of terraces are the Pleistocene Epoch in age. The fifth terrace is about 15m high and is represented by the Kokuga terrace. The sixth, namely, younget terrace is the Chudo terrace, being 7-11m high. These two terraces are the Holocene Epoch in age. According to the stratigraphical data of the terrace-forming deposits, the first terrace may be correlated the Tama terrace, and the second to the Shimosueyoshi and the third to the Musashino, in the Kanto region, respectively. The fourth may be provably correlated to the Tachikawa terrace, with some questions. The fifth and the sixth may correspond to the Numa and the Yurakucho, respectively. The stone implements of the Ayaragi culture I indicating to the Paleolithic age, have been collected from the Upper-most horizon of the deposit forming the second terrace at Ayaragi, and the paleolithic implements of the Minogahama culture have been obtained from the uppe-mest horizon of the third terrace deposit at Minogahama. These are red soils formed during past warmer periods, on the first, second and third terraces, but the precise dating of the formation of these red soils is not fully established.
Caves are not infrequently found in the Paleozoic and Mesozoic limestones which are distributed near the Sakawa Basin. The age of formation of these caves are considered to be correlated with those of the middle and upper erosion surfaces and lower terrace surrounding this basin. In these caves yellowish or reddish brown clayer residuals intermingled with limestone gravels are deposited and some fossil bones of several kinds of animals are found frequently. Some artifacts are also excavated from the upper part of these deposits. However, the relation between the layer of the artifacts and the “Onji” which is deposited at the upper part of the terrace could not be traced. Some artifacts of the early Jomon period including tongued points were excavated from the Hijiritaki cave (Fudo-no-iwaya) (+150m) situated at Nishiyama, Sakawa-chô, on Feb. 1964. These artifacts are the oldest remains from Kochi Pref. and correlated to those of Kamikuroiwa in Ehime Pref. This fact suggests that cultural exchange might have occurred between the Seto Inland Sea region and Tosa, the Pacific coast of Shikoku, at that preiod.
Since the beginning of the Holocene age, the Mashu volcano, situated in east Hokkaido, had grown into strato-volcano. About 7, 000 years ago, a caldera depression occurred as a result of the out-flowing of a great deal of gray pumice. The pumice flow deposit (Ma-f) had widely formed a pyroclastic plateau around the volcano. Then, in some places the plateau was soon dissected by rivers and was covered by reworked pyroclastics. These processes are well known by recent researches of the volcanic geology and the tephrochronology including the 14C dating. Till present time, from the altitude of the plain, this plateau had been considered as a terrace plain formed in Pleistocene age. The authors emphasized that it will be sometimes unreliable to consider the terrace or terrace-like plains in volcanic areas, only by the view point of topography.
Ria coasts in the Japanese Islands have been considered to be submerged marginal zones of maturely dissected mountain lands. But poorly developed coastal terraces are distributed at various altitudes along shorelines of enbayments and margins of waste-filled drowned valleys in ria coasts. Among them terrace surfaces at levels of about 10 meters, 30 to 40 meters and 60 to 80 meters high above sea level rather commonly develop on most of ria coasts in the outer zone of Southwest Japan. From these facts the author concluded that ria coasts in the Japanese Islands had been drowned prior to the formation of the coastal terraces by marginal downwarping resulted from mountain-building crustal movement, presumably at the end of the Tertiary, and then have been mainly influenced by eustatic change of sea level caused by glacial fluctuation in the Pleistocone. Existing drowned valleys in ria coasts have been submerged by the post-Glacial eustatic rise of sea level.