Apparatus has been installed at the Dominion Observatory Research Station at Meanook, Alberta, for the continuous recording of earth potentials. The theory due to Cagniard (1953) and others, in which relative amplitudes of horizontal components of electric and magnetic fields are used to interpret the sub‐surface structure, is applied in a modified form, to data from the Meanook records. Values of electrical conductivity between depths of 10 km and 100 km are estimated, and found to vary roughly between [Formula: see text] and [Formula: see text] e.m.u.

S U M M A R YThe Kapuskasing Uplift has been interpreted as an oblique cross-section of up to 25km of crust and thus provides the opportunity to examine the properties of exposed mid-to lower-crustal material. A magnetotelluric (MT) survey mapped a remarkably uniform upper crust and provided no evidence for upper crustal conductive zones that could be related to the often observed increase in mid and lower crustal conductivity. The only shallow conductive anomaly is related to the Ivanhoe Lake Cataclastic Zone but its electrical signature does not appear to extend more than one kilometer in depth.A regional apparent resistivity curve was determined from MT data and confirmed by subsequent controlled source electromagnetic surveys. Regional curves are essential for proper structural interpretation but are often difficult to determine because of electric field distortions. The data show a decrease in resistivity at depths below 15 km which is typical of continental crust in many areas of the world.There is a clear difference in orthogonal apparent resistivity and phase curves at periods greater than 10s which is most pronounced in a N65"E and N25"W coordinate frame. Two different models are proposed to explain the data. The first consists of a conducting 2-D slab of approximately 50 km width in the lower crust and striking N65"E. The strike direction is consistent with a number of regional structural trends but there is no other direct supporting evidence for it. The second model invokes either micro or macro electrical anisotropy in the upper mantle. There is considerable evidence for seismic anisotropy in the region. The electrical anisotropy could be the result of preferential conduction along the c-axis of olivine crystals, hydrogen dissolved in the olivine lattice with preferential conduction along the a-axis, or possible alignment of dykes, joints and faults in the upper mantle. If the anisotropy is related to strain induced orientations of crystals or fabric, it will provide evidence for the motions of the mantle associated with plate tectonics.

Summary The temperature gradients have been measured in six bores in Nottinghamshire and in two in north Yorkshire. The heat flow at some of the Nottinghamshire bores is much larger than is usual. The largest is 2.87 × 10‐6 cal./cm.2 sec. It is shown that this very local anomaly cannot be due to an excess of radioactivity or to igneous activity. An explanation is given depending on the flow of water from west to east over the Eakring anticline. The mean heat flow at the bores in Nottinghamshire is 2.24 × 10‐6 cal./cm.2 sec. and of those in Yorkshire 1.16 ×‐6. These results do not confirm the theoretical expectation that low‐lying places will have a small heat flow.

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Canadian geomagnetic data collected during the International Magnetospheric Study are used to investigate the terrestrial electrical conductivity structure of north-eastern Manitoba and part of the North-west Territories. The computed transfer functions resolve a major conductor trending east-west between the communities of Gillam and Back in Manitoba. Regional trends in the surface geology suggest that this conductor may be linked with the North American Central Plains electrical conductor. Twodimensional modelling of the data suggests that the conductor dips to the north from a small depth beneath Gillam and may extend to the lowermost C N S t .