The sunklands of Port Phillip Bay and Bass Strait

The floors of Port Phillip Bay and Bass Strait were formerly portions of a continuous land surface joining Victoria with Tasmania.This land surface was drained by a river system of which the Riv-er Y arra was part, and was intersected by two orogenic ridges, the Bassian and King Island ridges, near its eastern and western margins respectively. progressive subsidence and eustatic adjustment, these ridges became land bridges and the main route for the migration of the flora and fauna.At present, their former trend is indicated by the chains of islands in Bass Strait and the shallower portions of the Strait.The history of the development of the River Yarra is largely that of the former land surface and the King Island land bridge, and is the main theme for this discussion.The Yarra River was developed, for the most part, during the Pleistocene or Ice Age.In Tasmania, there is direct evidence of the Ice Age in the form of U-shaped valleys, raised beaches, strandlines, and river terraces, but in Victoria the effects of glaciation are less apparent.A correlation of the Victorian with the Tasmanian deposits and land forms, and, incidentally, with the European and American, can only be obtained by ascertaining the conditions of sedimentation and accumulation of such deposits in Victoria, as can be seen at the surface 1 or as have been revealed by bores, particularly those on the N epean Peninsula; by observing the succession of river terraces along the Maribyrnong River; and by reconstructing the floor of Port Phillip Bay, King Bay, and Bass Strait, and interpreting the submerged land forms revealed by the bathymetrical contours.This contribution deals with the former courses of the Yarra River as a tributary stream to the trunk stream, the Tamar Major River, when the Yarra flowed over the land surfaces that are no,v 69