The remanent magnetizations of samples of sediments and lavas from Great Britain, representative of widely different geological epochs, have been studied. Evidence for the stability of these magnetizations from times soon after the formation of the rocks has been found. These results seem most easily interpreted in terms of a dipole field, the polarity of which frequently reverses. In Pre-Tertiary times the axis of this dipole field diverges considerably from the present geographical axis and this is tentatively interpreted as a slow change in the axis of rotation of the earth with respect to its surface.

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A series of abstracts is given of papers recently published by the author. The main conclusions reached are that the earth's magnetization has suffered repeated reversals, and that rock magnetism can be used for geological correlation and for studies of continental drift and polar wandering.

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From the present knowledge on the magnetism of rocks, palaeomagnetic study by means of the natural remanent magnetization of igneous rocks is reliable when and only when the natural remanent magnetization is ascertained to be the thermo-remanent magnetization acquired at the time of the rocks' formation. The authors propose, in this paper, several experimental methods for examining whether a given natural remanent magnetization can have definite palaeomagnetic significance or not, under the above mentioned criterion.
In short, the proposed set of testing methods comprises: thermo-magnetic, crystallographic and chemical analyses of the ferromagnetic minerals contained in the rock, and the comparison of the stabilities of the natural remanent magnetization and of the thermo-remanent magnetization, produced in laboratory, against the demagnetizing processes by heating in non-magnetic space and by applying an alternating magnetic field.
These proposed tests were actually carried out on several naturally adversely magnetized rocks found mainly in Japan. For three of them, including Dr. Hospers' Icelandic rock, it was concluded that their reverse natural remanence must have been brought about by the reversed earth's magnetic field at the times of their formation.
As to the Haruna type of the self-reversal of the thermoremanent magnetization, the two-constituent mechanism was investigated in detail with the aid of electron-microscopic observation on the intergrowth of the two constituents.

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In 1952 a study of the remanent magnetism of certain sedimentary rocks of the Triassic system in Britain was begun in the Physics Department of the University of Manchester. This work was transferred in 1953 to the Imperial College of Science, London, where it has been continued and extended. Measurements have now been made not only on Triassic rocks taken from a wide area of England, but also on certain older sediments of the Carboniferous and Devonian systems.
The results provide strong evidence for the hypothesis that the land mass which now constitutes Britain has rotated at some period in geological history relative to the geographic poles. This rotation, which amounts to between 30° and 35°, may have occurred during the late Triassic era, or at some subsequent time.
The measurements have already been described and discussed in detail elsewhere, (1) and the present communication will be confined to a brief summary of the findings and conclusions.

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Magnetizations observed in selected flat-laying sedimentary rocks in the eastern United States suggest that during Paleozoic time the earth's magnetic. field retained approximately its present day orientation. In contrast, the magnetizations of sediments in the folded Appalachian belt present a pattern of great complexity that in part, at least, can be explained on the basis of deformation. Pebbles embedded in conglomerates that field evidence indicates were once deeply buried and hence presumably raised in temperature, show uniformly the same direction of magnetization, one that departs significantly, though slightly, from the direction of the earth's field today. Conglomerates that were never deeply buried have polarizations that, though more scattered, are not completely at random. Pre-Cambrian acid and basic rocks —presumably akin to the source material of these sediments— show complex patterns of polarizations that are difficult to relate to uniform magnetizing field. A conservative appraisal of these observations is that the stability in time of magnetizations varied from sample to sample within unknown limits according to environment and constitution. The need still exists for developing combined laboratory and field procedures for identifying in rocks the magnetization which can be relied upon as valid indicators of past directions of the earth's magnetic field.

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