Air-borne radio-echo sounding of valley, piedmont, and continental glaciers bordering the ice-free valleys of southern Victoria Land has provided profiles of ice thickness and subglacial topography. The Wilson Piedmont Glacier averages about 300m in thickness and buries the mouths of three deep east-west outlet glacier troughs. This high eastern threshold under the Victoria Valley helps explain why it has not been influenced by 600m marine submergence and multiple direct west- moving glacier invasions which have been important in the Wright Valley and Taylor Valley to the south. Profiles along the partly underfit Ferrar Taylor Glacier systems show clearly that ice sheet discharges through the valleys are controlled by subglacial bedrock thresholds. Topography of the Transantarctic Mountains may be the result of (?) block fautling and alpine glaciation.