Measurements of the directions of natural remanent magnetism of rock samples from the dike swarm on Lundy island in the Bristol channel, about 15 miles off the north coast of Devonshire, southwestern England, and comparisons with Tertiary lavas of Scotland indicate that the dikes are Tertiary and pre-upper Oligocene in age and that reversal of the geomagnetic field occurred at the time of their intrusion.

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