| Summary: | application/pdf For the purpose of determining the mode of variation and the stability of a geomagnetic field through the geologic past, the author undertook a palaeomagnetic study of volcanic rocks belonging to the Komoro, Shigarami and Enrei groups of formations (from the Upper Miocene to the Upper Pliocene). At the same time, the author examined the magnetic stability of rocks of which the magnetic directions were indicated to be much deflected from the present geomagnetic direction. From the results obtained, it was found that the geomagnetic field may have been reversed during Upper Pliocene time, and that during the time from the Upper Miocene to the Lower Pliocene it was normal. During the transitional stage from the normal to the reversed, the geomagnetic pole seems to have migrated through the equator; thus the change of polarity or the reversal might, through the transitional phase, have taken place with the pole settling at various positions. This conception regarding the manner of reversal of the geomagnetic field differs completely from the hypothesis hitherto propounded. The intensities of total geomagnetic force during this transitional phase were inferred from the ratios of Jn to JTc of the rocks: it was suggested that the geomagnetic intensity decreased through the time of reversal and then began to increase again as the change in the reversal proceeded to its finality. Plioceneにおける地球磁場の変動を究明する目的で小諸層群,柵(しがらみ)累層および塩嶺累層の古地磁気学的研究を行なつた,その結果次のことが明らかとなつた.(1)Upper Miocene-Lower Plioceneには地球双極子のS極は北極圏にあり,Later Pliocene departmental bulletin paper
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