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 and others, in which relative amplitudes of horizontal components of electric and magnetic fields are used to interpret the subsurface 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 10 (super -13) and 10 (super -14) e.m.u.