A total of 12 low‐level aeromagnetic profiles across the Labrador Sea were recorded with digitized rubidium‐vapor and fluxgate magnetometers. The resultant data are presented in the form of profiles with the regional gradient removed. There is good correlation between the anomalies on adjacent flight lines in a number of places, and the area may be divided into two zones having anomalous magnetic signatures. These zones can be followed through the central part of the Labrador Sea and are generally flanked by areas of lesser magnetic relief. The more westerly zone strikes toward Hudson Strait and appears to die out at about 59°N. The presence of the magnetic zones, marine seismic results, and the fact that five earthquakes are known to have occurred in the area between the zones are reasonably good evidence for the existence of an active buried median ridge in the Labrador Sea.

Six low‐level aeromagnetic profiles were obtained across the Reykjanes ridge southwest of Iceland during 1967. The 1300‐km long profiles spaced about 100 km apart were flown at right angles to the mid‐Atlantic ridge between the Greenland and European continental shelves. The magnetic anomalies have an excellent symmetry about the crest of the ridge, and the symmetry extends from the Greenland continental slope to about the 2000‐meter contour on the European side. A quantitative interpretaion of the results indicates that the intensity of magnetization (J) of the rock producing the axial anomaly is about 0.013 emu/cc. A plot of the average J over 20 km also shows excellent symmetry about the ridge axis, and the known geomagnetic polarity epochs have associated maxima and minima in the J plot. There appear to be twenty‐three polarity epochs in 480 km, so that the average length of an epoch is 2.1 m.y. if a constant spreading rate of 1 cm/yr is assumed. A power spectral analysis shows a major peak at 40 km, which is about the length of a complete reversal cycle. Digital filtering was, therefore, performed to separate the anomalies due to epochs and those due to events. There are sixty‐one reversals of the magnetic field in 500 km that are resolvable in the profiles. The magnetic anomaly pattern has a minimum amplitude and a maximum wavelength at points 260 km on either side of the ridge axes. The amplitude and wavelength are approximately symmetrical for distances of 160 km on either side of these 260‐km points. Two possible explanations of this symmetry are offered: (1) If it is assumed, as was suggested by Menard, that the thickness of the second layer is directly proportional to the spreading rate, both the change in anomaly wavelength and amplitude can be explained by a symmetrical 2:1 change in spreading rate. (2) The double axes of symmetry are the locus of two dormant ridges that were active in the middle Tertiary and migrated away from one another because the material between them could not itself migrate. Any continental crustal remnants would tend to be trapped between the double‐ridge system. When the two active ridges were approximately 320 km apart, they and possibly the Labrador Sea ridge became dormant. The present stage of single‐ridge ocean‐floor spreading began about 10 m.y. ago, and the unconformity between the two systems occurs at 100 km, where Ewing and Ewing have demonstrated that a discontinuity in the sediment thickness exists.

This paper describes an aeromagnetic profile from Prince Edward Island, through the Cabot Strait to the Tail of the Grand Banks of Newfoundland, and subsequently over the Flemish Cap. It is inferred that Burgeo Bank off the southwest coast of Newfoundland is possibly a granite intrusion of Devonian age. A distinct magnetic anomaly, approximately 400 gammas in amplitude, appears to be associated with the edge of the continental shelf at the Tail of the Bank. A series of sharp shallow-source magnetic anomalies was recorded over the Flemish Cap, and this feature appears to have a negatively polarized core whose long dimension is oriented in a NNW.-SSE. direction.

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