In this area situated around the boundary among Fukuoka, Oita and Kumamoto prefectures, Cenozoic formations are widely distributed. Among them, the most interesting formation consists of early to middle Miocene Green tuff. However, studies on Green tuff of this area are very poor. In this paper, the author describes geology and petrography of Cenozoic formations of the area and especially discusses geological implication of Green tuff of the area. 1. Basement rocks of the Cenozoic formations are the Chikugo metamorphics which are composed of green schist, pelitic schist and psamitic schist. 2. Cenozoic formations of the area are divided into the following in asscending order; Taio group, Maetsue formation, Mazi black andesite, Shimozuru lavas, Shakadake volcanics (Hohi volcanics), Tokamidake volcanics, Oyama volcanics and Aso welded tuff. The Taio group and Maetsue formation belong to green tuff formation and Mazi volcanics is correlated to the Setouchi volcanics. Volcanic rocks from the Shakadake to Oyama volcanics are products of the Pleistocene volcanism. Cenozoic volcanic rocks of the area mostly belong to calc-alkalic series. 3. Nakatsue granite complex, which is intruded at the last stage of deposition of the Taio group, is composed of diorite, porphyrite, granite and pegmatitic rocks. 4. Geological structure of the area is characterized by EW or WNW-ESE trend, which is indicated by trends of elongation of sedimentary basins, fold axis, fault system, elongation of intrusive mass and alteration zones. Such trend, especially of green tufff formation, indicates that the area belong to the inner belt of the Southwest Japan arc. 5. In the area, five alteration zones are discriminated according to assemblages of alteration minerals. Four types of alterations are also recognized as follows; diagenetic alteration, contact alteration, by granitic rocks, alteration related to gold-silver mineralization and sulfataration related to younger volcanism. Gold-silver mineralization has finished before the eruption of the Mazi black andesite. 6. Geological development of the area, especially in early to middle Miocene, closely resembles those of the Green tuff regions of the San-in and inner belt of Northeast Japan. However it is a character of the area that the Miocene thick formations, which attain to 3000m, have deposited under nonmarine environment.

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Two diatomite beds are developed at the sampling station as illustrated in the columnar section. The lower bed belongs to the Uryuzaka formation of the early pleistocene Komoro group, and the upper bed was formed during the deposition of the middle pleistocene Yaehara formation. Diatom assemblages of eight samples from the two diatomite beds were examined and clarified to be composed of 72 species and 27 genera. A. Physico-chemical spectra analysis of the ecological condition indicates that these diatoms were deposited in a slightly alkaline fresh-water lake. 1. The dominant species of diatom assemblages from the lower bed are Melosira italica, Melosira granulata, Stephanodiscus niagarae. The most of them are planktonic forms. The scarcity of benthic diatoms suggests that the diatomite was deposited at depth greater than 15 meters (PRESCOTT, 1968). 2. The dominant species from the upper bed are Fragilaria construens with its form variation, and some genera of Cymbella, Epithemia, Gomphonema are included. Most of them are benthic or epiphytic forms. These diatoms were deposited at shallow part of a lake as near shore. B. On the basis of dominant and subdominant species, the fresh-water diatomites from Japan were classified into three groups (OkuNo 1952). Two diatomite beds of the lower and upper parts come under two different groups of three.

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In the present paper, authors describe stratigraphy, biostratigraphy and geologic structure of the Neogene Formations in the Hamaishidake area, in the southwestern margin of socalled "Fossa Magna". The formations consist of flysch-like alternations, coarse-grained sediments and pyroclastics ranging from Late Miocene to Pliocene in age. They are complicated with faulting and folding. Results of the studies are surmmarized as follows: 1) The investigated area is formed of two formations, the Kogouchi Formation and the Hamaishidake Formation in ascending order. 2) The Kogouchi Formation consists of alternation of mudstone and sandstone, and the Hamaishidake Formation consists mainly of conglomerate, sandstone and tuff breccia. 3) The Hamaishidake Formation unconformably overlaps the Kogouchi Formation. 4) The geological age of the Formations is inferred from planktonic foraminiferal assemblages and molluscan index species. The Kogouchi Formation is Late Miocene and the Hamaishidake Formation is Pliocene in age. 5) The Hamaishidake Formation is subdivided into four sub-formations which are named the Murono, the Sattatoge, the Utugino and the Shishihara in ascending order. 6) Each stratigraphical relationships in the four sub-formations are discontinuity. 7) The Formations consist of a series of N-S trending structure, and all axes of anticlines and synclines plunge north. 8) Many trace fossils are observed in the Kogouchi Formation. This trace fossil facies are suspected to be corresponded with Cruziana facies (SEILACHER, 1967).

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In this article, fossil sea-lion Eumetopias ojiyaensis sp. nov. is described, which was excavated by the Niigata plain Collaborative Research Group in 1971. The materials were found at the cliff along the Nobe river, Ojiya city, Niigata Prefecture, northern Central Japan (lat. 37°17′09″N, long. 138°48′34″E.). The excavated materials were composed of sixty-four bones, which were classified into canines, a incisor, a molar, manus bones, pes bones, patella, tibia, fibulla caudal vertebrae and nails. The sandstone bed which yielded those bones is included in the Lowermost Formation of the Uonuma Group (Plio-Pleistocene). According to the Research Group, the sandstone bed is assigned to the same horizon in which were found plant remains of fuglans megacineria, Metasequoia disticha, Glyptostrobus pensilis, Liquidambar formosa and Menyanthes trifoliata and is estimated to have the range between 2.5×10⁶ Y.B.P. and 2.9×10⁶ Y.B.P. by the fission-track method. The results of the diatom analysis indicate that the sandstone was deposited under the littoral environment, and the Contained molluscan and foraminiferal fossils suggest the presence of a cold current as supported by Clinocardium californiense, Patinopecten (Mizuhopecten) yessoensis, Buliminella elegantissima, Elphidium sp. (A≒E. echigoense), Bucella frigida (The Niigata plain Collaborative research group 1972, Shinanogawa Nojiriko Tomonokai, 1976 (MS)). The materials have common morphological characteristics of Otariidae by KING (1964) as a whole. Among them, the form of canine is quite similar to that of living female of Eumetopias jubata, and the size of root of upper incisor is as twice as that of female E. jubata. As for the molar, only one tooth was found, which may belong to any of lower second to fifth molar. Both the lingual and the buccal side of molar form imperfect ovol. A groove runs vertically along the middle of each surface, and the lingual one is deeper than the buccal one. Moreover, the grooves divide the root of tooth into two apical portions. The crown of molar consists of three cusps : medial accessory cusp, main cusp and distal accessory cusp. The medial accessory cusp is remarkably higher than that of living E. jubata (6mm in the present specimen; 4mm in the living female Eumetopias). One tibia, one fibulla and many bones of manus and pes were excavated. Most of them are nearly the same size as those of living male Callorhinus ursinus, but each has smaller size, 7/10 to 8/10, in comparison with living female of E. jubata The author made the morphological Comparison of the bones to those of living Otariidae, and he came to a conclusion that the present materials are similar to E. jubata and different from other genus of otariidae. It is well-known that the size of bones of Otariidae has a great difference between male and female. Taking this fact into consideration, it is possible to consider that the present materials belong to a female of Eumetopias. It is clear that the present materials belong not to the living species of sea-lion, Eumetopias jubata, and they must belong to another independent species, E. ojiyaensis. The materials are estimated to be more than seventeen years old. In comparison of E. ojiyaensis with Eumetopias sp. (KASENO) MITCHEL 1968 from the Pliocene of Toyama Prefecture, the molar of the present species has common characteristics in root form, grooves in the middle part of root, bifurcation of root apex, formation of accessary cusps, and development of cingulum. Eumetopias sp. (KASENO) has been considered as male animal, so it is difficult to compare E. sp with E. ojiyaensis but it is possible to assume that Eumetopias ojiyaensis is close or same to the Eumetopias sp.

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