The past land connections are discussed in comparing with a number of closely related surviving species of animals in both the Continent and the Japanese Islands. The data used consist of animals whose species were precisely studied taxonomically with the development of their sudspecies. Their distribution areas, ecology and habits are also taken into account as far as possible. The taxonomic and zoogeographical material obtained by such a method may offer certain evidences to suggest the land connections, through which the surviving species of animals, or their ancestors, invaded the Japanese Islands from abroad.
In the Quaternary land stages of Japanese Islands, the land mammals largely migrated through the land bridges of Korea and Saghalien. When the sea level of Japan in glacial age was 140m lower than that of today, the Islands became a part of Chinese Continent and the Japan Sea an inland lake or lagoon. Its barren endemic species owes its origin to this geohistory. The Ryukyu land bridge was insufficient since the connection with Formosa in Villafranchian, and Tokara Strait between Amami- and Yaku-Tanega Islands had been open since Günz-Mindelian, causing strong separation between Holoearctic- and Oriental faunae. As shown in the Table, the writer mentions 6 land mammalian faunae respectively for the stages of I1-K of Japanese Quaternary. I2 fauna is much related to the Waiho faunae of Middle China. I1-I2 faunae migrated through the Korean land bridge from the Lower Yangtze area. J1 fauna is the most barren of all faunae. J2 fauna of Amur-alpine elements becomes the base of the succeeding funae. J3 fauna is much related with the Kushungrung fauna of Manchuria and seems to have migrated through the Saghalien land bridge. The abrupt appearance of exotic elements indicates a migration from continent, while specific-subspecific speciation reflects the stage of insulation. The Tsushima strait area in J3 stage had a kind of ecological control over the migration of land mammals. Rich endemic species of molluscan fauna of the Okhotsk Sea shows a sufficiently long history as sea and also the insufficient condition of the Kuril land bridge. It is a problem whether Japanese alpine flora and fauna are deduciable to the migration in Rissian or that in Würmian. The fauna of the Japan Sea is more closely related to that of the Okhotsk than to that of the warm Kuroshio. In Würmian the Kuroshio current could not intrude into the Japan Sea and its warm endemic types became almost extinct.
The fossil record and distribution of the Recent terrestrial fauna indicate that at some time during the Quaternary Japan had a land connection with Asiatic continent. The fossil mammals from the Nagahama Formation of the Boso Peninsula include Stegodon orientalis which is thought to be a warm temperature species from its distribution. This elephant must have migrated to Japan during a warm climate stage and probably of high sea-level. Land connection with the Asiatic continent is expected not only during the low sea-level stage but also during the high sea-level stage of the Early Pleistocene. The Middle and Late Quaternary eustatic oscillations of sea-level based on the terraces developed and distributed along the coast and off shore of Japan are shown in the text-figure, in which the idealized projected profiles of the terraces are in the left and the thickness of the conformable marine Pleistocene formations distributed and developed in the northern part of the Boso Peninsula whose top corresponds with the sea-level in the stage III in the right. The land connection is expected throughout the Middle and Late Quaternary except for stages of III and I, which are preceded by the low sea-levels. The land connection problem is geographical and biological in nature, and diastrophism may be concerned. The geological structure and topography of the Korean Strait and its vicinity suggest some probability of the isolation of Japan from the Asiatic continent due to diastrophism.
According to the recent studies of plant remains, pollen and glacial topography in Japan, it is indicated that the vertical vegetation zone of the main Würm age was about 1, 500m lower than that of the present. This 1, 500m drop of vegetation zone corresponds to about 7° southward shift of horizontal vegetation zone. Therefore, it is likely that polar front and typhoon tracks in the Würm age shifted southward from the present position, and thus intensive rain was less in the Würm age than in the present in Japan. On the other hand, some river terraces built in the Würm age have depositional character in mountains; and these Würm terraces have been entrenched by the postglacial rivers. These characteristics of Japanese river terraces may be explained on the above-mentioned difference of rain intensity between the Würm glacial and post glacial ages.
Both stratigraphical and pedological exmaminations reveal all of surveyed reddish soils found in Northeast Japan being Relict Red Soils formed during past warmer periods, probably, interglacial stages or substages, in the Pleistocene. Reddish soils in West Japan, which have hitherto been regarded as “zonal soils” by several pedologists, also have been made under the similar condition to them. Though the precise datings of their formations are not fully established, at least three warmer periods may be assigned to their datings, that is, pre-Shimosueyoshi, Shimosueyoshi and post-Shimosueyoshi stages, among which more cases examined indicate their datings to the Shimosueyoshi stage, possibly Riss/Würm interglacial. The upper parts of the Relict Red Soil profiles are subjected to modification toward other genetic soil types to be developed under recent bio-climatic environments. Soil geographical extension of recent zonal soil patterns in the world, especially of those in the coastal region of the Chinese continent (compiled by Ma and Ven, 1958) toward the circumference of Japan suggests that typical zonal Red Soils find their home distribution in the Amami Islands, the southern end of Japanese territory, and the southern regions. Most parts of West Japan except along the Pacific coast seem to be characterized by zonal soils akin to the Yellow Brown Forest Soils in China, and East Japan, by ones similar to the Brown Forest Soils, unsaturated subtype proposed by Fridland (1953). The genetical environments of the Relict Red Soils in Japan are probably not so far from those suggested above, that is, being represented by middle part of the subtropical humid climatic zone with mean annual temperature of 20°C or more, annual precipitation of 1, 500-3, 000mm., and annual cumulative temperature of more than 5, 000°C, on the one hand, and by evergreen broadleaved forests of Machilus Thunbergii, Distylium racemosum, Shiia Sieboldii, Cyclobalanopsis stenophylla etc., on the other hand. Paleontological evidences so far obtained seem to offer no positive proof to this assumed environments of the Relict Red Soils, being too warmer than shown by the formers. It is reserved for further studies whether the apparent discrepancy is caused by ill preservation of appropriate fossil indicators or by over-evaluation of the mean annual temperature effect as a soil forming factor. The cumulative temperature and precipitation factors might be worthy of appreciation in the latter possibility, if at all.
The degree of compression and deformation of the Menyanthes seed fossils in Japan has some intimate relations to their geologic ages. The relations can be fairly well represented when the morphometric values of the fossils are figured by the“Szaferowa's graphic method”. The younger the fossils are in their age, the nearer their Szaferowa's are graphs brought to the“unit line”. This tendency of the graphs seems to approve the results of correlation obtained by purely biostratigraphic method and, at the same time, gives some clues to establish Quaternary stratigraphy of the Menyanthes bearing beds in Japan, which are otherwise unable to be correlated at present.
Terraces and their deposits on the west coast of Ise Bay, Central Japan, are outlined to contribute to the Cenozoic geologic history. Topographic surfaces in this area are as follows: the highest erosion surface (stripped peneplain or fossil plain) on the summits of Suzuka Range and its equivalents, the lower erosion surfaces in Tertiary hilly lands, terrace surfaces, piedmont fans and Recent flood plains. Subdivision of the topographic surfaces and correlation of the deposits are shown in the table. Terrace deposits are mainly composed of fluviatile gravel and sand, while part of the middle terrace deposits such as the Takachaya, Mitachi etc. are marine origin. Its distribution, altitude and brackish fauna suggest glacio-eustatic movement in the Pleistocene in this area. It may be correlative to the deposits of the latest interglacial transgression.
Results of an attempt to clarify the paleo-climate of the Bibi fossil bed by means of pollen analysis are presented in this paper. The fossil bed situates in the southern part of the Ishikari depression, Hokkaido, and it has been estimated by carbon 14 dating that this bed was formed 20, 000 years ago. By our present pollen analytical study, it became clear that the bed contain pollens of such arborescent genera as Abies, Pinus, Picea, Larix, Betula, Quercus, Alnus, etc., and that the paleo-climate of the bed may be equivalent to the present climate of North Hokkaido or South Sakhalin.