In Kinki and Tokai districts, the eastern part of southwest Japan, three basins are developed, separated by mountain ranges of N-S trend. They are Osaka Bay, Lake Biwa and Isé Bay from west to east. The foothill-lands (50-300m. high) surrouding those basins are composed of Plio-Pleistocene sediments, wich are called the Osaka, Kobiwako and Tokai Groups respectively. The mountains consist of Cretaceous granitic rocks and Paleozoic formations. It was difficult to correlate accurately three groups because of the isolated distribution. But they contain many volcanic ashes by which the interbasinal correlation is possible. This paper mainly treats with tephrochronology and correlation by detailed examination of volcanic ashes. In addition, some problems of paleontology, paleogeography and tectonic development are discussed. 1) The Agé, Tokoname and Seto groups, which are used locally, are synthesized into the Tokai Group, because these groups have been deposited a single sedimentary basin, the Tokai Lake. The Karayama Formation corresponds to the upper part of the Tokai Group. 2) Table 1 shows the thickness, occurrence, type locality, heavy mineral composition and glass-index of volcanic ashes. Pumice Volcanic Ash-Layer is found through all three groups. The ash-layers found in neighbouring two groups are Nuka, Ichiuno, Dacite, Sagami, Kaigake, Komazuki, and Sakura. The tephrochronology of the three groups are established by the stratigraphical relations of those volcanic ash-layers. (Fig. 2) 3) Stratigraphic horizons of main fossils of mammal, mollusc and plant are shown in Table 2, along with climatic oscilation curve obtained by pollen analysis. 4) The depression of the Plio-Pleistocene age in Kinki and Tokai districts had the NE-SW axis and moved toward west. (Fig. 4, 5)
The present distribution of Larix Gmelini ranges from Siberia to Saghalin and southernmost part of the Kuriles, but that species is not found in the present flora of Hokkaido. As to the remains, some were once reported from the Kushiro formation and the presence of that species in Pleistocene deposits in Hokkaido has been predicted by pollen identification. Recently, the remains of it, such as many leaves, twigs and cones, were obtained from the peat bed in the Ishikari Plain. In this area, the Quaternary sediments are extensively distributed and those sediments are divided ascendingly from the Nopporo formation, the Nishinosato formation, the Takadai clay formation to the Shikotsu volcanic deposits. Among them, the remains of Larix Gmelini were found from the peat bed in Late Pleistocene Takadai clay formation. This fact indicates that Larix Gmelini had been in Hokkaido at that time and may contribute to the Pleistocene paleobiogeography as one of the important data.