The Journal of the Geological Society of Japan

Some pegmatites distributed in Mineyama granite region northwest of Kyoto are accompanied with allanite as an accessory mineral., By weathering, it was almost changed into limonitelike substance on the surface., Physical and chemical studies were made on the fresh interior portion as well as the weathered substance., By using Murble's method, the age of allanite was determined as 120x10⁶ years.,

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In 1948 and 1949 the writer and K., Kawai made the geological survey near Otaki-machi, Chiba-ken for exploitation of natural gas., First we made the complete geological columnar section, scale 1:100, by measuring all the stratum thicker than 0., 5cm., Finding out about 80 key beds (Tuffs), we traced them in the field, and knew lateral changes of rock-facies very accurately., Then the writer made foraminiferal samplings at the point of accurately determined geological horizon., Namely he sampled the mud-stone just beneath the keybed., Samples of the same horizon at several localities at distance were collected to clarify the lateral change of foraminiferal assemblages., At the beginning of July, 1950, the writer again made the geological survey and foraminiferal sampling of the upper part of Kokumoto Formation, Kakinokidai Formation and the lower part of Chonan Formation., 15 key beds (Tuffs) were found out and several of them were traced., The stratigraphical sequence in this district is as follows in descending order: Chonan Formation (sand-rich alternation and exceedingly mud-rich alternation), Kakinokidai Formation (mainly very thick massive siltstone, uppermost part of which contains two beds of sand, each about 5m thick), Kokumoto Formation (alternation of thick mudstone and thick sandstone), Umegase Formation (sand-rich alternation and thick sand), Otadai Formation (composite alternation of mud-rich alternation and sand-rich alternation), and Kiwada Formation (thick mudstone or exceedingly mud-rich alternation): all considered to be upper Pliocene., Results of this foraminiferal reserch along the standard section from Otaki-machi to Chonan-machi are shown in Fig., I., Comparing this section with another one which was chosen along the Pacific Coast, 13km east of Otaki-machi, the writer was convinced that the correlation by foraminiferal zonules is possible because the lateral change of foraminiferal assemblage is very scarce., The writer could distinguish about 120 species of foraminifera including 29 foraminiferal zonules belonging to two zones, namely Zone I Cassidulina subglobosa fauna and Zone II Bulimina aculeata-B., inflata-Uvigerina cf., bifurcata-Bolivina robusta fauna., Some of these zonules are subdivided into subzonules.,

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The Miyata formation in Miura-Peninsula overlies the basement rocks with distinct unconformity on all sides, forming a basin-structure., As a result of field work in 1948 and 49 the writer was led to the following conclusions on the mechanism of sedimentation of this formation: 1) This formation was not accumulated in the trough formed before its deposition., 2) The basin structure of this formation does not due to the folding after the deposition., 3) The basin structure of this formation has been formed during the deposition, accompanying to the successive depressions of basement rocks from north to south.,

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