It appears that a hydrothermal alteration and development of magnetite is largely responsible for a paleomagnetic resetting in a belt of mafic–intermediate rocks in eastern Massachusetts. The age of this thermal and metasomatic event is found to be about 370 m.y. by both geochronological and paleomagnetic evidence. This age does not coincide with the emplacement of plutons within the region (600 and 450 m.y.), nor with the 340 m.y. uplift and cooling shown by K–Ar ages on biotites.The age and tentative pole position obtained favour the hypothesis that an eastern region in New England and Maritime Canada comprised a single block in the Devonian that was separate from North America at that time, and fits the polar wanderpath of North Africa.