The upper part of the Pleistocene Atsumi group is called Toyohashi formation, which is composed of four members and superposed on the middle part of the group with local disconformity. The plant remains of this formation are separately occurred in two horizons, the lower of which indicates a cooler climatic condition, whereas the upper suggests warmer and drier one than that of recent date. Hence this formation is inferred to represent an interglacial deposit as a whole, although its lower part implies the influence of the glacial or subglacial climate immediately before the deposition of this formation. The Toyohashi formation may be referred to the late Pleistocene in age, judging from the predominance of Pinus Thunbergii, Aleurites cordata, Melia Azedarach and Mallotus japonicus, etc.
The extraordinary severe winters in which it was so cold that the river Yodo froze at Osaka (34°39'N, 135°32'E) and its vicinity had been successively occurred around A. D. 1820, where the eustatic curve established by Van Veen proves its minimum point during the recent 250 years. (Fig. 1) The great famines in the period of recorded history in Japan had been occurred in the epochs of Tenmei (A. D. 1782-A. D. 1787) and Tenpo (A. D. 1833-A. D. 1839), holding the severe period of winters between them. The secular rising trend of winter and summer temperatures in the recent instrumental age in Japan. (Fig. 2) is considered to be connected with the trend of warming from so called “Little Ice Age” in the beginning of the 19th century in Japan, in which the climate is generally characterized by the predominance of cold and snowy winters and of cooler and pluvial summers in Japan. It must be noticed that the amount of precipitations seems to have been changing with the opposite tendency in the Pacific side of Japan and in the northern part of Japan Island, that is to say, Hokkaido and Korea. (Fig. 3) By analogical reasonings and synthetic estimations, the following presumable conclusions are derived on the climatic conditions in the historical age of Japan. (i) The climate around A. D. 700 is concluded to be colder in winters and cooler and more rainy in summers than at present. (ii) “Little Climatic Optimum” is presumed centering around the 9th century, in which the climate was generally warmer and drier in the central and south-western part of Japan, but probably more rainy in Hokkaido districts than today. (iii) Corresponding to the PARIA Emergence of the eustatic curve of Fairbridge, the significant deterioration of the climate appears to have set in towards the 15th century, in which it was presumed to be severe in Japan and dry in summer in Korea.
The author surveyed the Quaternary system and topography, and compiled the chronology of topographic evolution around Lake Shinji and Nakaumi area. About the sub-surface conditions of alluvial plain in Japan, it is said that the upper bed consists of fan or deltaic deposits of the present time, the lower of the marine deposits of Post-glacial epoch and that at the base, fossil valley is buried under these deposits. The author recognized some details in addition to the above. They are considered to have occured as follows: 1. The sea level stayed on -10m--20m level in some period in the course of regression after the last Inter-glacial epoch. Consequently, the abrasion platforms were formed under that sea level. 2. The maximum fall of sea level in the last Glacial epoch is extimated to be at -80m depth in this area. 3. In the early period of Post-glacial transgression, valleys incised in the last Glacial epoch were buried under the basal fanglomerate, a part of which composes terraces on the land. 4. After that, the speed of the transgression was in excess of that of river sedimentation, and consequently, marine clay bed was deposited on the basal fanglomerate. 5. A fanglomerate bed lies between marine clay beds on the Level of -10m--30m. This suggests that the sea level stayed or regressed slightly on that level in the course of the Post-glacial transgression. 6. After that retardation, transgression began again and marine clay deposited on the fanglomerate. 7. Yumigahama sand bar began to be formed in some period about the maximum stage of Post-glacial transgression and the process still continues.
The Late Quaternary deposits of the Niigata lowland, recently drilled by authors, can be divided into four formations in ascending order: pre-gravel bed (G1) 1, gravel bed 1, the Nishikanbara Group and the Shirone Group, respectively. Of these, according to age determination by the Radio-Carbon method, the age of the gravel bed 1 is now estimated to be between 31, 000 and 26, 000 y. B. P. The Nishikanbara Group may have been deposited between 26, 000 to 25, 000 y. B. P., while the Shirone Group ranges in age from 20, 000 y. B. P, to the present. Possibly gravel bed 1 is a buried terrace deposit, produced during a glacial age when sea level was much lower than at present. It is perhaps correlatable to Hauptwürm 1. The Nishikanbara Group is thought to have been deposited during the inter-ice age that followed the preceeding stage of sea-level lowering, while the Shirone Group was deposited during a later stage when sea level again became higher following the Maximum Würm, begining about 20, 000 to 18, 000 years ago.