Data from a 130 km long reversed seismic refraction profile on the Shatsky Rise are interpreted. P velocities in the upper crust beneath the rise are essentially the same as those found for the upper crust in ocean basins. No refractor with a P velocity appropriate for the mantle is observed, implying that if an M discontinuity exists, its depth is greater that 26 km. Gravity variations over the Shatsky Rise of 30 mGal can be accounted for by the surficial topography. If this large thickness of crustlike material composing the rise were overlying normal mantle material, the result would be a large negative free air anomaly, which is not observed. This suggests that an anomalously dense mantle underlies the central portion of Shatsky Rise.