The ACT is positioned on the Australian continent, which was once a part of the supercontinent Gondwana. The ACT is in the Tasmanides, the deformed rocks of the orogen that make up the core of the old mountain range that makes up the Australian continent east of the Tasman Line. These rocks are an addition onto the Proterozoic core of the continent. The Tasmanides are the result of compression, horizontal shortening, and vertical thickening of various "terranes" such as small continental fragments and volcanic island arcs that were plastered against the original continental margin as a result of plate tectonic movements.