Refraction surveys were made in 1962 and 1963 in the islands north of the Canadian mainland as part of a program of exploration of the Polar continental shelf. The operation consisted of three stationary recording units and a shooting party that traversed the frozen sea in a tractor train. Three refraction profiles form a continuous section from the Canadian Shield through the Franklinian geosyncline and Sverdrup Basin to the Arctic Ocean. Post-Devonian sediments in the Sverdrup Basin are 10 km thick. The basaltic layer, with a velocity of 7.3 kmps, lies at a depth of 24 km, and the base of the crust is at 38 km.