A time-term analysis is made of the first arrival data from the 41 shots of the1965 Hudson Bay seismic experiment. An investigation of the water-wave data is made to determine which of three possible series of navigation is most consistent. A single-layered crust with a compressional wave velocity of 6.33 km/s and an upper mantle compressional wave velocity of 8.27 km/s are proposed for Hudson Bay. The Mohorovičić discontinuity is found to have considerable topography with depths ranging from 42.7 km to less than 26 km. The Churchill–Superior boundary is proposed to be a three-dimensional crustal feature and is extended offshore from Cape Smith and extended westward to the north of the Ottawa Islands through approximately 59° 40′ N and 82° 00′ W. The Mohorovičić discontinuity rises to depths of about 26 km beneath Chesterfield Inlet and Baker Lake. The mantle is about 40 km deep at Churchill, Manitoba and rises to about30 km some 130 km west of Gilmour Island, then drops to almost 42 km farther east. The sudden drop is related to the Churchill–Superior boundary.