MEASUREMENTS of the Lower Palaeozoic magnetic field in the British Isles1 show that it changed from around D=355°, I=−50° to D=20°, I=−54° (corresponding to an apparent shift of the south palaeomagnetic pole from 0° W to 35 °W along the present Equator) between Ordovician and Devonian times. Following unpublished work by W. E. Tremlett and J. C. Briden, we report here conflicting evidence from the intrusive rocks between Conway and Pwllheli, North Wales. These rocks therefore seem to show either previously unrecognised tectonic rotations or hitherto unsuspected variation in the palaeomagnetic field.