Powdered natural magnetite was compressed under one-directional high pressure, and after the removal of the pressure, it was examined magnetically by means of an astatic magnetometer.A remanent magnetic vector was found in a direction perpendicular to the axis of the applied pressure. The present authorproposed to call such a remanent magnetism caused by one-directional pressure Piezo-Remanent Magnetism (PRM) in order to distinguish it from TRM, DRM, CRM and other remanent magnetism.The effects of one-directional pressure on the remanent magnetism of rock have been examined with an artificial rock made of white cement in which fine ferromagnetic minerals were dispersed. It was found that both the intensity and the direction of remanent magnetization changed as the pressure increasedThe field evidence showing PRM was found from several canyons where some rock specimens were sampled from the side wall.The magnetization of dated rocks has been much used for the study of palaeogeomagnetism, using the natural remanent magnetism (NRM) of rocks as a kind of fossil of the geomagnetic field at the time they were formed in remote geological period. We must consider the possible change of remanent magnetization after its acquisition, that is to say, the magnetic after effect, the phenomena of self-reversal of magnetization and magnetostrictive or pressure effects etc. Especially, some investigators12)3)4)5)6)7)8) have recently discussed the effect of pressure and the role of magnetostriction in rock magnetism. The present author has also examined experimentally the effects of one-directional pressure upon the acquisition of magnetism of the ferromagnetic minerals.On the other hand, the effects of one-directional pressure acting for rather long period on the remanent magnetism of rocks have been examined with an artificial rock made of white cement in which fine ferromagnetic minerals were dispersed. The magnetism of some rocks collected from several places has also been examined to find the effect of pressure in the field.Powdered natural magnetite was packed into a cylindrical vessel made of copper and submitted to one-directional high pressure applied by a sturdy hydraulic press. All experiments were carried out in the present geomagnetic field which was at about * Present address;

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Samples of Quaternary basaltic rocks and Tertiary sediments of Yamaguchi Prefecture, West Japan, have been collected and their natural remanent magnetizations and other magnetic properties measured. The mean directions of the natural remanent magnetization of the Quaternary basalts is nearly parallel to the present geomagnetic field, and that of the Tertiary sediments of Miocene age also agrees with the present geomagnetic field, but the Paleogene sediments show very large deviations in the mean direction of their remanent magnetization from the present geomagnetic field. Some reversals of the remanent magnetization in situ were found among the samples of early Quaternary age. Virtual paleogeomagnetic dipole positions have been estimated from these data for Tertiary and Quaternary times in Yamaguchi Prefecture, West Japan.