Abstract
DR. J. A. CLEGG'S account1 of the discussion on “Rock Magnetism” at the British Association meeting makes reference to comparisons between the palæomagnetic measurements on rock series in Great Britain and the United States, and seeks to show that a comparison of the pole positions deduced for the Triassic of Great Britain by himself and colleagues2 and from Dr. J. W. Graham's measurements3 on the Permian sandstones of the United States “suggest that there may also have been a relative movement between Britain and North America …”. Although he qualifies this statement, it still appears to me to be misleading, because if one only had this comparison, one would not be led to any suggestion of the possibility of continental drift in the North Atlantic basin. The duration of the Permian and Triassic together is of the order of 70 million years4, and the geological time correlation of the red beds used in this palæomagnetic work can only be good to about half a geological period. Creer, Irving and Runcorn5 have shown that polar wandering takes place through geological time at about one-third of a degree per million years on the average, so that a motion of the pole of about 20° could possibly have occurred between the times represented by the rocks examined by Clegg et al. in England and those of Graham in the United States.
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RUNCORN, S. Rock Magnetism. Nature 179, 866 (1957). https://doi.org/10.1038/179866a0
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DOI: https://doi.org/10.1038/179866a0
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