| Summary: | The natural remanent magnetization of thirty-one early Tertiary lava flows from West Texas was measured. Stratigraphic controls and some potassium-argon dates were used to determine the relative age of the flows. Stability of magnetization was established by ac demagnetization. Because of large secondary magnetic components and chemical alteration it was not possible to obtain reliable remanent magnetic directions or pole positions for sixteen flows. Of the fifteen reliable flows, six are normally magnetized, seven are reversely magnetized, and two are intermediate. Seven of the reliable sites spanning a period of time from Eocene to Miocene yield remanent magnetic directions which are not significantly different. From these seven virtual geomagnetic pole positions an early Tertiary pole position for North America of 14°E and 75°N is deduced. The published European and North American pole positions have been examined on the basis of rigorous reliability criteria. No North American results were considered reliable, and a mean pole position of 145°E and 74°N was obtained from the reliable European early Tertiary results. The data is consistent with the hypotheses that the early Tertiary magnetic field was not aligned with the present spin axis, that North America has moved west relative to Europe a distance of 4° since early Tertiary time, and that the rate of sea floor spreading at present may be low relative to what it has been.
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