The Hudson Bay crustal experiment of 1965 involved 41 shots placed on two lines, E–W and NW–SE, in the Bay. The first arrival data of eight land stations situated around the bay were utilized in the time–term analysis. The preferred crustal velocity was found to be 6.32 ± .06 km/s, and the velocity of the upper mantle to be 8.23 ± .03 km/s. Depth calculations from time–terms and employing Geological Survey of Canada near-surface data, show the Mohorovicic discontinuity to be undulatory in nature throughout the bay. An overall rise of this interface occurs from a depth at Churchill of approximately 41 km to a minimum depth of approximately 27 km towards Gilmour Island. Crustal thickening occurs again on the east side of the bay, with a depth of 41 km at Povungnituk. As well, the crust thins towards the NW from an approximate depth of 37 km in the center to a depth of 26 km near Chesterfield Inlet. The correlation between existing surface geology and the Mohorovicic discontinuity undulations is discussed.