The Naganoken-seibu Earthquake of M6.8 occurred at 8 : 48a.m. on the 14th of September, 1984. It centered at about 35.5°N, 37.5°E. The hypocenters of the first and aftershocks were rather shallow, and were distributed within a small area on the southern slope of Mt. Ontake, a solitary volcano, 3063 m high, of Quaternary age. Large and small land slides triggered by the earthquake and associated mud flows devastated the villages and forests, and killed tens of men and women. Several members of the present authors were just surveying the geology of the area, and they, together with other members, made an urgen survey of the land slides and mud flows. The Quaternary strata of the southern slope of Mt. Ontake are classified as shown in the following table. [table] Among the four Quaternary formations the Tarusawa Formation, composed of thick series of lava flows, beds of tuff-breccias, volcanic mud-flows and beds of pyroclastic falls, is the main constituent of the present mass of Ontake Volcano, while the overlying Ohtaki Formation is composed of lava flows, beds of agglomerates, beds of tuff-breccias, beds of sand and gravel and aeolian volcanic ash beds. Significant is the remarkable unconformity between the two formations. In other wards, the rocks of the Tarusawa Formation had been eroded deeply, so that many deep and steep valleys and slopes were existent before the deposition of the Ohtaki Formation. Many of the land-slides occurred in the rock sequence of the Ohtaki Formation under the following conditions. 1) Many of the land slides (or collapses) occurred where thick beds of pumices and scoria of the Ohtaki Formation, overlain by inclined beds of lavas and tuff-breccias, accumulated in the valleys or on the slopes that had been eroded out of the Middle Pleistocene Tarusawa Formation. The Ohtaki Formation in and on the steeply inclined valleys and slopes were unstable from the beginning. 2) Where the basal surfaces of the Upper Pleistocene Ohtaki Formation made valley forms the groundwater gathered into the valley bottoms, and it expedited weathering and argillization of pumices and scoria. It also made easy to slide the overlying load. 3) The precipitation of the preceding five days had attained about 150 mm, which seeped into the rocks of the Upper Pleistocene Ohtaki Formation. It raised probably the groundwater table, and also increased pore-water pressure near the base of the deposits.

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In this paper we describe the fine structure of erupted pharyngeal teeth in Latimeria chalumnae. Pharyngeal teeth, situated on the medial side of the left first branchial arch, were obtained from Latimeria chalumnae (B. L. 175cm, B. W. 85kg, Female) and were used in this study. Cross stripes consisting of longitudinal and transverse grooves which penetrated into the surface layer were observed. Filmy structures were observed in the longitudinal grooves. It is thought that these filmy structures consist of organic matter, because these structures seemed to continue the dentin and disappeared after removal treatment for organic matter. A number of stripes almost parallel to the surface were observed in the section of the surface layer. These stripes were considered to be incremental lines. The stripes obliquely ended at the boundary between the surface layer and the dentin. Because the stripes nearer the surface ended closer to the basal portion and the stripes nearer the dentin ended closer to the apical portion, the pattern formed by these stripes resembles the incremental lines of mammalian enamel. Though the intervals between the stripes were 0.2-0.7μm, in this specimen the tendency was that form the intervals of the surface side to be narrower than those of the dentin side. The crystal-like granules of the surface layer were columnar or spindle shaped, 60-80 A in width and 600-800 A in length. Their width and length were relatively uniform. However, the arrangement of the crystal-like granules was irregular under high magnification. The outline of the crystal-like granules was never straight, but irregular. A number of fine electron-lucent spot-like, oval-like and line-like structures were seen in the crystal-like granules. It is considered that organic matter was present around the crystals of the surface layer, because fine networks which made us think of a negative view of the undemineralized section were seen after phosphotungstic acid (PTA) stain for undemineralized section on the grid. The boundary between the surface layer and the dentin was clear in observation with scanning and transmisson electron microscopes under low magnification. On the other hand, the boundary between the surface layer and the dentin became unclear in observation with a transmission electron microscope under high magnification and a mixed layer between the two, 0.3-1 μm in width, which was recognized from the density and arrangement of the crystal-like granules, was seen. Concerning the organic matrix of the dentin, the outermost layer of the dentin, 1-1.2 μm in thickness, which consists of electron-dense amorphous substances and loose collagen fibers, was recognized in the specimen after chromium sulfate demineralization. From the results described above, it is considered that the surface layer of the pharyngeal teeth in Latimeria chalumnae corresponds to true enamel because of its optical property, resolvability to acid, mineralization, fine structure and feature of organic matrix. In particular, the feature of the surface layer resembled the thin aprismatic enamel in amphibia.

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The Pliocene molluscan fauna of the Annogawa Formation in the Sasagami hills, Niigata Prefecture, is described and analysed. 1. The Annogawa formation is mainly composed of massive sandy siltstone. At locality 1 this formation includes some conglomerate lenses in the middle horizon and molluscan fossils occur densly in them with some other invertebrate remains. It is assumed that all of them are allochthonous in occurrence, because shells are fragmental and most of bivalves are disarticulated. They can be divided into four types of assemblages based on the bathymetrical range, the bottom character and^the life form of living equivalent species as follows. Type i: Dwellers of gravelly or sandy bottom from the intertidal to the upper sublittoral zones. Type ii: Infaunal dwellers of muddy bottom from the intertidal to the lower sublittoral zones. Type iii: Infaunal dwellers of muddy bottom in the lower sublittoral zone. Type iv: Epifaunal dwellers of gravelly bottom from the intertidal to the lower sublittoral zones. They are sessile or adhering. One attempt was made whether the bottom character of each type was correspond to the sedimentary facies of the Dainichi Formation or not. This analysis leads to the following-conclusion : the assemblage is composed of a part of the "biocoenosis" of muddy bottom in the lower sublittoral zone (Types ii and iii) and transported elements from various biotopes in the intertidal and the upper sublittoral zones (Type i and a part of Type iv). 2. From the result of the analyses of the molluscan fauna, it is assumed that the Annogawa Formation was deposited in the lower sublittoral zone and that an intertidal zone near by shore was developed not so far from there in the same age. 3. This fauna characterized by the elements of open-sea muddy bottom (Nuculacea, Pandorella and so on) is older than the Plio-Pleistocene Haizume fauna (KOBAYASHI, 1983) which includes many endemic species of the Omma-Manganji fauna. 4. Occurrence and characteristic form of cylindrical trace fossils created by Pholadidae pelecypods are described in outline.

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The Ryoke Belt in the central part of the Awaji Island is composed mostly of granitic rocks with minor amounts of metabasites and metasediments. The Sennan Group is found at the southern border of the Ryoke Belt, and the granitic rocks and the Sennan Group are intruded by many dykes of two stages, the older and the younger. The granitic rocks can be divided into six rock-masses which are grouped as follows, based on their stages of intrusion; 1 st stage Shioo and Tsushigawa granites 2 nd stage Shizuki, Sumoto and Ei granodiorites 3 rd stage Senzan granite The first stage granites are intruded by dykes of the older stage and granitic rocks of the second to third stages. The second stage granodiorites intrude also into the older stage dykes and the Sennan Group which consists of acid pyroclastics. The Senzan granite of the third stage is massive and intrudes discordantly into the Sumoto granodiorite of the second stage as well as the Tsushigawa granite of the first stage. The first stage granites, the dyke rocks of the older stage and the Shizuki granodiorite of the second stage are more or less mylonitized and schistose. It is considered that the main mylonitization in the area took place under a condition of relatively low temperature before the intrusion of the Ei granodiorite.

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Fission-track dating was carried out on six volcanic materials (one tuff layer, two rhyolitic lavas and three pyroclastic flow deposits) in Southern Kyushu by GBGRE method (YOKOYAMA, 1983). They are as follows; [table] These radiometric ages do not contradict the stratigraphical evidence shown in Fig. 3 and 13.

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中国浙江省の龍門山(Longmenshan)および会稽山(Kuaijishan)付近から南南西へ延び,江西省の懐玉山(Huaiyushan),九嶺山(Jiulingshan),湖南省の雪蜂山(Xuefengshan)を経て,広西省の九万大山(Jiuwandashan)に至る地帯には,原生代の堆積岩類,変成岩類が分布している.この地域を原生代江南変動帯(Jiangnan Proterozoic mobile belt)と呼ぶ.この変動帯中の最古の地層群は四壁(Sibao)層群で,タービダイト,オフィオライト,カルクアルカリ火山岩類からなり,その時代は1400Ma.よりやや古い.ただし,花崗岩化された岩体に含まれる円磨されたジルコンの同位体年代は2830Ma.である.おそらく四堡層群中の砕屑物の供給源は,江南変説帯の北西方の揚子卓状地(Yangzi platform)にあったであろう.何故ならば,揚子大陸の南東方には四堡層群より古い大陸性地殻の存在は知られておらず,一方,四川省中部で掘られたボーリングによると,そこには先震旦系の花崗岩質片麻岩が分布しているからである.四堡層群は原生代前半の東安変動(Dong'anianorogeny)によって変形,変成作用を受けた.会稽山,九嶺山,九万大山に露出するオフィオライトの種類と分布はそれぞれの地域で特色がある.東安変動は,九万大山地域では華南古海洋プレートが揚子大陸プレートに対してオブダクションすることによって,九嶺山地域ではサブダクションすることによって,また会稽山地域ではサブダクションに伴ない,島弧-海溝系ができることによって,進行した.背弧盆地に形成された地層群の露出は,新しい地層が広くこの地域に発達しているため,きわめて限られているが,貴州省の梵浄山(Fanjingshan)地域では梵浄山層群として知られている.この背弧盆地あるいは縁海は,東安輪廻(Dong'anian cycle)につづく雪峰輪廻(Xuefengian cycle)の期間にも継続して存在していたらしい.安徽省の舗嶺(Puling)層群,張八嶺(Zhangbaling)層群がそれにあたる.梵浄山地域の縁海が閉じたのは,おそらく東安変動時にオブダクションがあったためであろう.雪蜂輪廻は,1400-800Ma.の間にあり,この期間に板渓(Banxi)層群が形成された,浙江省の龍門出地域では,凝灰岩や溶岩を挾む火山砕屑性堆積物が,東安変動時の島弧性火山岩類を不整合に覆って分布し,その下底には礫岩がある.砕屑物の大部分は,カルクアルカリ性火成岩の地域から供給されている.江西省の幕阜山(Mofushan)地域では,砕屑岩は古い地層を不整合で覆うが,その南の九嶺山地域では,この板渓層群とそれより古い地層との間には不整合はない.雪蜂山地域でも,層座関係は複雑で,一部では,板渓層群の下位に不整合が認められるが,この関係に側方へ移り変って整合となる.九嶺山地域や雪蜂山地域は,この時期には隆起した島弧地帯であったと考えられる.広西省の龍勝(Longsheng)地域では,板渓層群は砕屑岩とオフィオライトよりなるが,このオフィオライトには,海洋性地殻起源と考えられるものと島弧起源と考えられるものとがあって,それらは化学的特徴により識別できる.海洋性地殻起源のオフィオライトはプレートの説きによって当時の大陸縁辺部に形成され,ひき続く大成活動によって島弧型のオフィオライトができたと推定される.江西省の懐玉山地域にも板渓層群に相当する砕屑岩とオフィオライトが分布するが,その構造方向は徳興(Dexing)地域で急激に南北方向へ変わる.これはオブダクションが起ったからであろう.雪峰輪廻前期の落下肢変動(Laokedong orogeny)によって,江南変動帯の中部と東部が隆起した.後期に入ると安山岩-流紋岩を含む浙江省の上墅(Shangshu)層群や安徽省の井潭(Jingtan)層群が堆積した.これらは島弧型火山活動の特徴をもったものである.一方,その頃,海洋性ソレアイトを含む安徴省の舗嶺層群や張八嶺層群が背弧盆地に堆積している.このような岩相の性質とその分布は,落下崠変動の後に,再び海洋プレートのサブダクションのあったことを物語っている.原生代の江南変動帯は,800Ma.に最後の雪峰変動(Xuefengian orogeny)によって後背斜地帯となり,広域変成作用を受ける.こうして江南変動帯は東安,落下崠,雪峰と呼ばれる3回の変動を経て形成されたが,注目すべきことに,この期間には緑色片岩相から低度の角閃岩相程度の変成作用はあったものの,角閃岩相より高い変成作用は認められず,また,それに伴なう花崗岩化作用も知られていない.この地帯の花崗岩類は,江西省の九嶺出花崗岩が838Ma.,広西省の摩天嶺花崗岩は800Ma.の年代値をもっていて,この頃になり大陸性地殻を特徴づける花崗岩が広く形成されるようになった.

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