Abstract
The effect of secondary magnetization on the apparent position and polarity of a palaeomagnetic pole is examined and applied to measurements made by Momose on Pliocene rocks. It appears that in the Lower-Middle Pliocene the pole was near 70°N, 150°W, and that the polarity in the Lower Pliocene was normal and in the Middle Pliocene was reversed. A reversal of the earth's field appears to have occurred near the Lower-Middle Pliocene boundary.
