K-Ar ages of 21 Quaternary basaltic rocks from the Kannabe Volcano Group and adjacent monogenetic volcanoes in the east San-in district were determined. In the Kannabe Volcano Group, the oldest ages, 0.7Ma, were gotten from the Nishiki Volcano. There was a long rest (about 0.5 Ma) of the volcanic activity after the eruption of the Nishiki Volcano. After that, from 0.22 Ma to recent, 6 volcanoes, if including adjacent volcanoes, 9 volcanoes, erupted intermittently. The east San-in district is the most active district of the basaltic volcanism in the San-in and Chugoku area, southwest Japan, in the present day.

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We clarified the relationship among the basal age of Kuroboku Soils, the humus properties of volcanic ash soils and the vegetation environment, according to the opal phytolith analysis and the humus analysis utilizing time marker tephras on the cumulative volcanic ash soils in Akasaka, Sannohe and in Kawamukai, Takko, the area of Towada volcanic ashes. Moreover, we examined the formation process of volcanic ash soils. 1. Kuroboku soils have been formed from Nb (Nanbu pumice) soil of Unit III in Kawamukai and from NA (Ninokura volcanic ash) soil of Unit IV in Akasaka. According to the ages of marker tephras, the basal age of Kuroboku soils is between 8,600 y. B. P. and 5,400 y. B.P. in Kawamukai and between 9,500 y. B. P. and 8,600 y. B. P. in Akasaka. Moreover, these ages corresponded with the time when the vegetation changed from forest to grassland. The basal ages of Kuroboku soils in Kawamukai and Akasaka are older than in Yunodai, Towadako (Hosono et al., 1992), where the relationship between the basal age of Kuroboku Soils and the change of vegetation was recognized also. We estimated that Kuroboku Soils formation following the formation of grassland had relation to human activities on forests and the older basal age of Kuroboku Soils in Kawamukai and Akasaka than in Yunodai accounted for earlier human activities on forests in the former than the latter, according to lower height and genialer climate of Kawamukai and Akasaka. Besides, the difference of the basal age between Kawamukai and Akasaka has relation to other factors, because both climate conditions are almost equal. 2. Both the Nb soil, Unit IK in Kawamukai and the NA soil, Unit TV in Akasaka had the sections of A/BC/C. The BC horizons of both soils were recognized the (A) horizons of Brown Forest Soils, according to vegetational career of broadleaved forest with Bambusoideae (Sasa). Therefore, both of soils cumulated (A) horizons of Brown Forest Soils and A horizons of Kuroboku Soils. We estimated that these cumulus were formed when atmospheric dust composed mainly from volcanic ash had been cumulating slowly under each other vegetation. We propose to call such soils as have cumulated plural soil units while soil forming factor changed on the process of soil formation and slow cumulus of parent material progressing side by side "Accumulatin Polygenic Soil".

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中国西南部,四川盆地の北西縁を限る龍門山系の中部地区には,形成機構の異なる二種類の異地性地塊群が存在する.一つは,thrusting-spreading nappeで,側方圧縮による衡上断層群によって形成されたナップ群であり,他の一つはgliding-spreading klippeで,重力滑動によって形成されたクリップ(飛来峰)群であって,龍門山構造帯はこの両者によって構成されている.またこの二種類の地塊群は成因的に密接な関係にあって,まずナップ群が"piggy-back thrust propagation"によって順次形成されてゆき,その重力に不安定な部分が,やがて山地本体と分離して滑動し,飛来峰群を形成したものと解釈される.さらに,重力滑動による飛来峰群は,内部構造の特徴によって二つの形式に区分される.一つは滑動褶曲型で,褶曲と断層とによる複雑な変形構造を示すが,他の一つは滑動岩盤型で,比較的単純な変形の水平に近い構造で下位の岩体を覆う.これらの飛来峰群を形成した重力滑動の時期は,インドシナ運動の最後の時相に当たるが,最終的にはヒマラヤ運動の時期に及んだものと思われる.

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The Ishikari-Teshio Belt is located in the western side along the Axial Zone of Hokkaido. The study area, located in the northern part of the Ishikari-Teshio Belt, is one of the areas where the Neogene formations are typically developed in Hokkaido. This area has two sedimentary basins, Tempoku and Haboro. In the Haboro Basin, nine diatom fossil zones are recognized from the Denticulopsis lauta Zone (14.85-15.70Ma) to the Neodenticula koizumii-Neodenticula kamtschatica Zone (2.50-3.70Ma), and can be fixed diatom biostratigraphy. They harmonize with reported radiometric ages. Comparing the lithofacies of the formations and the eustacy curve of Haq et al.(1987), sand-facies of the Kinkomanai Formation are well assigned to the sea-level fall around 10 Ma and mud-facies of the Embetsu Formation to the sea-level rise after 5.5 Ma. It is infered that the Sandstone Member of the Kinkomanai Formation around 10 Ma corresponds to the Bannosawa Formation and the sandstone members of the Wakkanai, Higashino and Mashike Formations. They are widely traceable from the northern to central part of the Ishikari-Teshio Belt.

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An accurate and rapid method for quantitative analyses of 10 trace elements (Nb, Zr, Y, Sr, Rb, Th, Pb, Zn, Cu, and Ni) in silicate rocks has been investigated by using a X-ray fluorescence spectrometer (Rigaku 3030) with Cr-tube, LIF (200) crystal and SC detector. Accelerating voltage and tube current are 50 kV and 50 mA, respectively. Pressed-powder pellets of standard rock samples of Geological Survey of Japan were used for the analyses. These were made by pressing 5g of the powdered rock mixed with 0.4g of 2% polyvinyl alcohol solution filled in an aluminum ring. An intensity of scattered radiation at 2θ=35.5° can be used to determine the mass absorption coefficient for the above 10 trace elements. Interference corrections must be made for the overlap of Sr-Kβ on Zr-Kα and of Rb-Kβ on Y-Kα. The correlation coefficients of calibration lines of the above elements exceed 0.993, except for that of Zr. The analytical results were well in agreement with recommended or proposed values (Ando et al., 1987). The values of calculated lower limit of detection are low enough to measure those elements in common silicate rocks.

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In this paper, I discussed about the fact that infant of anthropoid has alredy tendency to keep erect posture, and that human erect, too. So I wish to assert that characters of hominids and infant of hominoids are homology, and that hominids is neotenic species of infant of hominoids: This is a reason why human keeps erect posture and bipedal walk.

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