Measurements of the magnetic properties, paleomagnetic field intensity, and the inferred paleomagnetic field polarity have been made using fine grained basalt and coarser grained rock samples dredged from the mid-Atlantic ridge near 45° N and supplied by the Geological Survey of Canada. The opaque mineralogy of the samples was studied by microscope, Curie point, and X-ray diffraction techniques. The natural remanent magnetization of the basalt is of the order of 5 to 10 × 10−3 e.m.u./cm3 with some values from the center of the median valley reaching 10−1 e.m.u./cm3. Magnetic anomalies over the ridge can be accounted for by the remanent magnetization of a few hundred meters of this basalt. The coarse grained rocks were relatively weakly magnetized, and while they contribute little to the magnetic anomalies, their diverse character suggests that the major portion of the oceanic crust, below a thin veneer of fine grained basalt, has differentiated into a complex structure.

Anorthositic rocks 20 to 30 km south of the Grenville Front in the Grenville Province of Ontario have a stable remanent magnetization which yields a paleomagnetic pole at 161 °E, 8 °N. This pole is close to other poles from the Precambrian of North America of 1050 m.y. age. Paleomagnetic results have also been obtained from two rock units in the southern part of the Grenville Province of Ontario. These are a pyroxenite exposed near Wilberforce and the Tudor Gabbro exposed near Madoc. The directions of remanent magnetization yield pole positions as follows: Wilberforce pyroxenite—148 °E, 14.5 °S; Tudor Gabbro—137 °E, 17 °N. These pole positions, together with others from the literature, which have been derived from rock units 200 km or more south of the Grenville Front, plot farther west in the Pacific than do poles of inferred similar age from other regions of North America. A possible interpretation of these results is that the southern part of the Grenville province was formed some 30° SE of its present position.

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The interpretation of both palaeomagnetic and geophysical prospecting data requires a better understanding of the magnetic properties of the iron oxide minerals found in rocks. The magnetic properties of ilmenite-haematite solid solutions have been investigated, the unusually large and pure haemo-ilmenite crystals from the Allard Lake region of Quebec being used. The magnetic component of these crystals is an ilmen-haematite phase, having a composition of about 10 mole % of ilmenite in haematite, and present in the form of exsolution lamellae that are roughly 5 µ long, 1 µ wide and 0.22 µ thick. The crystals have a very strong anisotropy causing magnetization in the basal plane and a weak anisotropy which produces an easy direction of magnetization within the basal plane. An improved ilmenite- haematite solvus curve has been produced by X-ray and Curie-point analysis of heat- treated crystals. Spontaneous reversal of magnetic polarity takes place with change in temperature in ilmen-haematite having between about 25 and 15% of ilmenite in haematite. This new reversing range of composition is quite different from that found to reverse by Uyeda. The reversal is due to a new antiparallel moment which grows as temperature falls. This has been interpreted as being due to an ordering of Fe 2+ ions on alternate cation layers b an electron transfer mechanism between trivalent and divalent iron atoms.

A study of the magnetization of 12 block samples of the Huntly and Insch masses of the Younger Gabbros of Aberdeenshire, Scotland, has shown that these bodies have a complex multicomponent magnetization. Combined AF and thermal treatment has isolated both polarities of two nearly horizontal axes directed NNW-SSE and NNE-SSW although only the first of these axes is obvious in the NRM directions. Microscope examination, electron probe analysis and Curie point studies indicate the magnetization to be due mainly to magnetite and haematite needles exsolved within pyroxene crystals and haematite formed by oxidation of a few primary magnetite grains. It is inferred that the Younger Gabbros were magnetized between their R b S r emplacement age of 189 f 17 Ma and their K-Ar cooling age of 468 f 4 Ma, by a combination of thermochemical and exsolution processes. The two axes of magnetization yield pole positions of 189.6" E. 27.8" N (dp = 4.7", dm = 9.4") and 151.6" E, 25.5" N (dp = 4.0", dm = 7.9"). In view of the unsatisfactory scatter in British Ordovician pole positions it is suggested that these be assessed giving consideration to possible unresolved multicomponent magnetizations as well as tectonic relationships, precise time of magnetization and evidence that the field was dipolar in nature.