Long-lived polyphase tectonism in the Cambrian history of the Ross orogen is demonstrated by recent stratigraphic studies in both the central and Weddell Sea segments of the Transantarctic Mountains. We postulate that strong early Middle Cambrian deformation preceded a more widely recognized Late Cambrian-Early Ordovician period of contraction and magmatism. These Middle Cambrian movements were locally the principal phase of orogenic deformation. They profoundly altered sedimentation patterns along the Antarctic margin, so that in the Weddell Sea region, when carbonate platform sedimentation resumed, the platform margin was reestablished far oceanward of its Early Cambrian location. Intra-Cambrian tectonism along the paleo-Pacific margin of Gondwana was not confined to its Antarctic segment; comparable activity recently has been described from Australia and is known from South America. These movements may be related to amalgamation of East and West Gondwana.