The Fortress is a platform of Beacon Supergroup sandstone

Sandstone

Sandstone is a sedimentary rock composed mainly of sand-sized minerals or rock grains.Most sandstone is composed of quartz and/or feldspar because these are the most common minerals in the Earth's crust. Like sand, sandstone may be any colour, but the most common colours are tan, brown, yellow,...

 in Victoria Land

Victoria Land

Victoria Land is a region of Antarctica bounded on the east by the Ross Ice Shelf and the Ross Sea and on the west by Oates Land and Wilkes Land. It was discovered by Captain James Clark Ross in January 1841 and named after the UK's Queen Victoria...

, Antarctica, dissected to form four promontories bordered by cliffs over 300 m high. Situated on the shoulder to the northeast of Webb Glacier

Webb Glacier (Victoria Land)

Webb Glacier is a glacier just north of Mount Bastion and Gibson Spur, flowing south-east into the head of Barwick Valley in Victoria Land. It was named by the Victoria University's Antarctic Expeditions for P.N. Webb who, with B.C. McKelvey, did the first geological exploration in this area and...

, they form part of the divide between the Webb and Victoria Upper Glacier

Victoria Upper Glacier

Victoria Upper Glacier is a glacier occupying the upper northwest end of Victoria Valley. It was named by the Victoria University of the Wellington Antarctic Expedition for their Alma Mater which sponsored the expedition....

s. Named by the Victoria University of Wellington Antarctic Expedition (VUWAE), 1959–60, for its fortress-like appearance.