Abstract A north-east trending Paleozoic glacial valley has been cut in Devonian Aztec Siltstone at Alligator Peak, southern Victoria Land. The valley, which is exposed in a north-west-south-east cross-section, has walls as steep as 50°, and is filled to a depth of 80 m with glacial and fluvial sediments of the Metschel Tillite (Permian — Carboniferous (?)). The oldest fill is complexly folded and comprises locally brecciated glacial and fluvioglacial sandstone, conglomerate, and claystone. This is overlain by fluvial sandstone, and the fill is completed by a lacustrine siltstone lens. Strikes of fold axes and other linear features in the valley trend north-east, subparallel to the strike of the valley wall, indicating that the oldest fill was deposited by slumping of the valley wall and not by “ice shove” along the length of the valley.