Abstract
Magnetic variation measurements made at 21 stations along the St. Lawrence River in eastern Canada have shown the existence of current concentrations, which appear to be coupled to oceanic currents and controlled by tectonic features. In particular, the line of Logan's fault, a thrust which marks the northern limit of the Appalachian region against the Precambrian Shield, is the locus of a current concentration for part of its length. However, in the region of present-day seismic activity on this fault, the current becomes much less defined. Possible explanations, for which models are being constructed, are that in this active region the current escapes vertically to the conducting mantle, or simply spreads out laterally. The active area is marked also by present-day decrease in elevation and by a positive gravity anomaly and may be a vestigial hot spot.
