Summary An array of 41 three‐component magnetometers recorded geomagnetic disturbances during August and September 1972, between latitudes 42° and 54deg;N and longitudes 98° and 109° W. The objective was a detailed study of the North American Central Plains (NACP) conductive body earlier discovered striking northward from the Black Hills roughly along longitude 104° W in the United States. Source fields were provided by polar magnetic substorms and by other events with incident fields more uniform over the array. Northward mapping of the conductor was carried to within 90 km of the exposed Canadian Shield of north central Saskatchewan. Between latitudes 43deg;N and 48deg;N maximum depth estimates place the conductor within the lithosphere; the currents probably flow at smaller depths, i. e. within the crust. At the Shield edge the axis of the conductor is parallel to the strike of fold belts and fault zones in metamorphic rocks, including mylonites, characteristic of intense grinding and crushing. Graphitic conductors are known in many fracture zones. The conductivity anomaly links these structural elements in the Churchill Province Shield to the metamorphic belt mapped by Lidiak in the South Dakota basement, and to the Black Hills. South of the Black Hills the conductor turns southwest to the northern end of the Southern Rockies. There is evidence which suggests, but does not demonstrate, a conductive link there between the mantle conductor under the Southern Rockies and the NACP crustal conductor. It is postulated that the linear crustal structure may be a major continental fracture zone now mapped over a total length of 1800 km, of which 300 km is exposed in the Shield. Two of three earthquakes located in southern Saskatchewan have epicentres close to the axis of the conductive body.

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The extensive tarsand deposits of Ondo and Ogun States of Nigeria have previously been investigated only by the use of geological methods. In a recently completed exploration programme covering a 17 km2 area north of Agbabu, in the Ifesowapo Local Government area of Ondo State, the electrical resistivity technique was used extensively along with other exploration methods. The electrical resistivity survey was made up of 32 Schlumberger vertical electrical soundings (VES). The resistivity curves were interpreted by curve matching and computer based automatic interpretation techniques. Apparent resistivity values obtained varied between less than 10 ohm-m to greater than 1000 ohm-m. The results permitted fair to excellent correlation between the geoelectrical and Stratigraphic data, particularly the delineation of lithological boundaries and zone of bitumen saturation. The lithological boundaries and zone of bitumen saturation. The geophysical results also confirmed the regional block faulting and the consistent, increase in overburden thickness southwards.

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An array of 33 three-component recording magnetometers was operated in June and July 1980 in Alberta and British Columbia south of the Edmonton – Prince Rupert highway. This very large array, with its stations dispersed through 550 000 km2 and on average 150 km apart, had limited resolution and was designed to confirm known conductive structures, discover new ones, and locate them sufficiently for suitable placement of further arrays with closer spaced stations and, therefore, higher resolution. Magnetograms and three sets of Fourier transform anomaly maps are presented. They show the general attenuation of the vertical component of variation fields west of the Rocky Mountain Belt known from previous work and generally attributed to a conductive layer in the lower crust or upper mantle. Two prominent local anomalies are shown by variation fields of periods 15–30 min. The first indicates induced currents near Tête Jaune Cache, west of Jasper. The highly conductive structure carrying the induced currents may include wet sediments in the Rocky Mountain Trench and possibly partial melt at depth associated with recent volcanics. The second local anomaly appears to be associated with a crustal conductive structure that strikes northeast–southwest across southern Alberta and crosses the southeast corner of British Columbia into eastern Washington State. This may be associated with a Precambrian rift in the lower crust discovered by Kanasewich and his colleagues using deep crustal seismic reflections some 15 years ago. Both of these anomalies are under further investigation by means of arrays operated in 1981 in locations indicated by the results of the array reported here. The regional westward attenuation of the vertical fields has been quantified by means of single-station transfer functions and artificial event analysis, as developed by Bailey and others, to show the Z response to unit southwest–northeast horizontal field at three periods, along a profile from Squamish, near Vancouver, to Edmonton. These response curves will be used in model studies of the regional conductive structure.