A thick lacustrine deposits with large amount of various volcanic products of the middle Pleistocene age are widely developed around Nobeyamahara, eastern foot of the Yatsukatake Volcanic Chain. These deposits have been called the Hirose Group (GOHARA, Y. et. al., 1978). The Hirose Group is divided into five stratigraphic units on the basis of the presence of disconformity: the Lowest, Lower, Middle, Upper and the Uppermost Unit. A close relation between volcanic activity and growth of the palaeo-lake basin is clearly recognized. Disconformities in the Hirose Group might have resulted from the fluctuations of the palaeolake basin. The results of the analysis of palaeo-lake water level changes in this region suggest that some regional tectonic movement occurred after the deposition of the Upper part of the Hirose Group. The palaeomagnetic study on the lacustrine sediments of the Hirose Group revealeded the following results. The remanent magnetization of the present samples demagnetized at 150oe or 200oe in 400Hz alternating field show the best grouping which estimated to be primary magnetizations. The palaeomagnetic polarity inferred from most of the Hirose Group was NORMAL, the results obtained from the three horizons belonging to the Lower and Upper part suggest the presence of INTERMEDIATE polarity. This INTERMEDIATE polarity suggests the presence of new geomagnetic excursion in the Brunhes normal epoch.

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Stratigraphy and geologic age of the Tamba Group in the northern hills of Kyoto City have been reexamined on the basis of conodonts and fusulinids. Firstly the relationship among e-shale formation, f-schalstein formation and g-shale and sandstone formation (Tamba Belt Research Group, 1969) has been clarified as follows. E-formation came in contact with f-formation by reverse fault and g-formation lay on f-formation concordantly. A lot of conodonts such as Metapolygnathus abneptis, Paragondolella polygnathiformis, Gladigondolella tethydis, etc., showing middle to late Triassic in age were discovered from bedded cherts of a few horizons in e-formation. Fusulinids such as Pseudofusulina sp. and Pseudoschwagerina sp. which were included in f-formation showed that the age of it was early to middle Permian. Valid fossils for age determination have not yet been discovered from g-formation at present. On the other hand, because middle to late Triassic conodonts have been discovered from b-chert formation, c-shale formation and/or d-chert and shale formation which lay under e-formation apparently by our preliminary survey, the stratigraphic reexamination of them will be also necessary in near future.

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The complete skeleton of Desmostylus is known only from Japan. It was found in Keton, Shisuka-machi, Shisuka-gun, South Sakhalin in 1933. The skull and post-cranial skeleton were described before (IJIRI and KAMEI, 1961 ; SHIKAMA, 1966) but the vertebrae, ribs, scapula and hip bone remain unexamined to date. In the present paper the atlas and nine thoracic vertebrae of the Keton specimen are described and the vertebral formula of the studied part is discussed. The characteristics of the thoracic vertebrae are as follows: Body compressed fore-andaft, low and transversely wide; size of vertebral foramen not so larger than the body, so that radices of vertebral arch projected due upward; cranial margin of vertebral arch slightly reduced; cranial articular processes not distinct; mammillary processes protruded forward dorso-laterally; caudal ones projected latero-posteriorly; cranial vertebral notches obscure, caudal ones deep and U-shaped; pedicles of vertebral arch not perforated; grooves for spinal nerves stretched slightly down-, out and backward; transverse processes short, projected more or less upward and due laterally; spinous process short, not inclined in the posterior thoracics; cross section triangular, cranial margin sharp, caudal one broad. Previous studies misregarded the left fifth metacarpus as the left first rib, and insisted that the thoracic vertebrae numbered 14 or 15 (NAGAO, 1941) or 14 (SHIKAMA, 1966), but it should be concluded that they number 13. The exact determination of the position and order nomination of thoracic vertebrae depends on the correctly recognized number of the lumbar vertebrae. Although earlier studies concluded that the lumbar vertebrae numbered 4 (NAGAO, 1941), or 6 (SHIKAMA, 1966), the Keton specimen proves impossible to distinguish the posterior thoracic vertebrae from the lumbar vertebrae by such characters as costal fovea or transverse process due to poor preservation. Fortunately, since a thoracic vertebra was found with its costal neck preserving the original position, the order nomination of thoracic vertebrae was able to be determined. Thus it can be concluded that Desmostylus has 13 thoracic and 4 lumbar vertebrae.

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Geology of the southern part of Sikhote-Alin is reviewed with reference to our field experience in the Kavalerovo region, where we visited as participants of the Scientific Tour II of the XIVth Pacific Science Congress (Khavarovsk) in September, 1979. Geology of the main anticlinorium zone, main synclinorium zone and coastal anticlinal zone, from west to east, of the Mesozoic Sikhote-Alin geosynclinal region, tin deposits of the main synclinorium and the fracture system of the Sikhote-Alin region are the main subject of this paper. Late Mesozoic-Cenozoic igneous activity in Primorie and Japan is summarized in Table 2. The tin ore deposits occur in folded sedimentary rocks associated with weakly magnetic magnetite-series granitoids and are subvolcanic reduced type veins characterized by much chlorite and sulfide minerals, an exact analogue of which is not known in the Japanese islands. Concerning the fracture system, a satellite image (ERTS) of the Central Sikhote-Alin fault (Plate II) and geologic lineaments on satellite images of the Sikhote-Alin region are given. In view of the major successive feature of the Jurassic eugeosynclinal facies, early Cretaceous flysch-like clastic facies and late Cretaceous-Paleogene acid magmatism combined with the ore genesis, it is emphasized that Sikhote-Alin was more closely allied to the inner side of Southwest Japan than to Northeast Japan during the Mesozoic-Paleogene time. However, the age and nature of the successive events are somewhat different between Southwest Japan and Sikhote-Alin. During that time, Sikhote-Alin and Southwest Japan formed two neighbouring but relatively distinct tectonic units within the major framework of the Late Mesozoic East Asian tectono-magmatic belt. With the opening of the Sea of Japan, the Japanese islands became the site of an active island arc during late Cenozoic, while Sikhote-Alin remained fixed to the continental side until the Recent and any Neogene marine volcanic basin, such as the Green Tuff region of Japan, is not developed in Sikhote-Alin.

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