Controlled source magnetic induction experiments in the Adirondack Precambrian shield region of northern New York State indicate that the electrical conductivity in both the upper and lower crust are in conformity with laboratory studies of moist, igneous rock and in serious discord with such measurements on dehydrated rock. A two order of magnitude increase in the conductivity found at 20 km depth suggests a structural or phase change there. A single turn loop of wire 1.5 km in diameter was used to generate an oscillating magnetic dipole source field over the frequency range 0.4 to 390 Hertz. The amplitude and phase of the resulting fields were measured as a function of distance to 90 km from the source. Analysis of these measurements indicates approximate horizontal stratification of the electrical conductivity. The uppermost layer, which is no more than a few hundred meters thick, has a conductivity thickness product of 0.4 (ohms)-1. It is underlain by a conductivity of about 8¿10-5 (ohm meters)-1 to a depth of about 15 km. The conductivity between 15 and 20 km is approximately 10-3 (ohm meters)-1; the conductivity is greater than 10-2 (ohm meters)-1 below 20 km.