The subducting Pacific plate was old, cold and dense, easily sinking into the mantle at a steep angle. The hinge zone of the plate also migrated oceanwards over time. So the trench retreated oceanwards, and the old trench and ocean floor become part of the continental plate. Volcanoes formed inwards from the trench. The part of the oceanic plate attached to the continent was compressed, the suboceanic crust was severely shortened and thickened as well, giving rise to a duplex structure. This happened at the end of the Ordovician period and in the Early Silurian. The sediments were heavily folded and overthrusted resulting in severe crustal shortening. In the Canberra area the sediments were raised above sea level and eroded. The land to the west (around Wagga Wagga) was raised higher.