This thesis is an account of the investigation into the physical nature of the proposed discontinuity in upper mantle conductivity in south eastern British Columbia responsible for the change in appearance of geomagnetic variations reported by Hyndman (1963). Variometer stations were established along two profiles, one east-west and one north-south, each several hundred kilometers in length. The geomagnetic records thus obtained are used to estimate the depth to a proposed highly conducting substratum. Parkinson diagrams are also derived for many stations on the profiles. The theoretical problem of magnetic induction in a 2-layer horizontally stratified half-space is solved. Theoretical expressions are derived for the attenuation of power in the vertical component of the earth's magnetic field relative to the two horizontal components as a function of frequency, conductivity, and thickness of the top layer. These theoretical curves are compared to data determined experimentally by power spectral analysis of geomagnetic records recorded at Crowsnest, Alberta, Lethbridge, Alberta; and Grand Forks, B.C. This analysis indicates Kootenay Lake to be near a region of anomalous induction in the earth. If the conductor is assumed to be two dimensional its strike appears to be magnetic east-west. The observed attenuation of the vertical component at stations west of Kootenay Lake relative to those of Kootenay Lake is accounted for in terms of the upheaval in the west of a highly conducting substratum. The analysis indicates a layer of conductivity 10⁻¹¹ e.m.u. rises to within 10 km. of the surface in the west while lying at a depth of 100 km. or more in the east. / Science, Faculty of / Earth, Ocean and Atmospheric Sciences, Department of / Graduate