Nearly 200 travel times of the phase ScS have been measured at World Wide Standardized Seismographic stations for 10 globally distributed deep-focus earthquakes. By comparing these times we have obtained estimates of the differences in one-way vertical shear wave travel times beneath various tectonic provinces of the earth. In particular, vertical shear wave travel times beneath normal ocean basins average about 5 s greater than times beneath continents, confirming the hypothesis advanced by Jordan and Anderson (1974) to explain the discrepancy between travel time base lines derived from free oscillation studies and those derived from body wave studies. The observed difference in vertical travel times, together with pure path surface wave dispersion data, implies that the differences between oceanic and continental structure extend to depths exceeding 400 km. ScS times for a station on the Galapagos Islands are smaller than those observed for normal ocean basins, suggesting that the velocities beneath these are higher than those beneath typical ocean basins. This observation is inconsistent with the existence of a simple thermal plume beneath the Galapagos.