In this treatise, six Palaeogeographic maps of Tertiary Japan are given, representing the different stages of the Tertiary Epoch. To facilitate comparison, those of the three stages of Cretaceous have been added. On each map is shown the distribution of Land and Sea when the sea transgression was the greatest. For this purpose, the classification and correlation of the Japanese Tertiary formation adopted here is that attempted by the writer in the “Geology and Mineral Resources of Japan (written in Japanese)” issued by the Imp. Geol. Survey, 1932, in which some parts of the classification are more or less different, because of the older investigations. In Japan, the early Tertiary time (Palaeocene) seems to have been a period of dominant land emergence. In Eocene and Oligocene epicontinental seas invaded Western Kyushu and probably at times the outer margin of Southwestern Japan. The Palaeogene coal-bearing formation extending from Western Saghalin to Central Hokkaido was probably an estuary deposit accumulated in a long, narrow, sinking trough extending north-south. The Early Miocene includes Aquitarian and Burdigalian substages, to which are attributed the marine sediments which contain the Asagai-Poronai fauna in North Japan, and those series yielding Vicarya callosa fauna in West Japan. The Middle Miocene (Vindobonian) transgression was most extensive, the sea having been spread over the greater parts of North Japan. At this time, the Japan Sea depression was first formed and as nearly wide as the present hasin whose existence in early Miocene is very uncertain. The Miocene crustal movement progressed and culminated toward its close, during which a severe orogeny accompanied by violent volcanic outburst affected the whole extent of Japanese islands. The Pliocene transgression of the sea seems to have been more restricted as compared with that of the Miocene, although some of former land areas have been ruptured and depressed under epeiric sea. After deposition of the Pliocene marine formations, the general area of North Japan seems to have been much elevated accompanying moderate foldings and faultings which resulted in many regions in the formations of inland basin depressions. In later Pliocene time, the emergence of land was pronounced, marine littoral deposits having being formed in limited areas.
The stratigraphy of the Shiodani Oil-Field, Niigata Prefecture, was fully investigated by Mr. I. Matsuzawa of the Imperial Geological Survey of Japan, according to whom the geological sequence of this area, enumerated from below, is as follows: Tertiary Lower Series……Alternation of Sandstone and Shale. (Tuff Sandstone.) Middle Series……Gray Shale and Sandy Shale. 450m. Upper Series……Shaly Sandstone and Sandstone. 300m. Uppermost Series……Sand, Gravel and Clay. Quaternary Terrace Deposits and Alluvium. Although fossil shells are rather rare in this field, we find many well preserved shells in the “Sandy Shale”, especially in the sand lenses of this horizon. The total faunal list is given in Table I. of the Japanese paper. A glance at the table is sufficient to show that this fauna is a mixed one, that is to say, a fauna of the sand facies is mixed with that of mud. The fauna, no doubt, is of cold current (Oyashio) type. The species that have been determined number only 32; the number of those that are not known to be living now amount to 14, which is 44 percent of the entire fauna. Needless to say, the number of fossils is too small to allow any determination of the geological age of this fauna. But we find some important fossil species, such as Clavatula cfr. dainichiensis (Yokoyama), Anadara trilineata amicula (Yokoyama), Mercenaria yolcoyamai Makiyama, Turritella (Haustator) fortilirata saishuensis Yokoyama, etc.-all essential components of the so-called Omma fauna of Kaga Province, which fauna is considered as a typical Pliocene fauna of the cold current type. Therefore, the fossil fauna of this field may be said to be of Pliocene (lower to middle) age.