The existence of a present day trough-like geomorphic depression between Cape Otway and King Island was recognized from bathymetric evidence by Lewis (1936) who termed it the Otway Trough, and by Jennings (1959) who proposed the term Otway Depression. In 1960 the Bureau of Mineral Resources loosely defined the Otway Basin as an east-west trough containing a thick sequence of Mesozoic and Cainozoic sedimentary and volcanic rocks, located between Lacepede Bay, South Australia and the eastern side of Port Phillip Bay in Victoria. Some difference of opinion exists among geologists contributing to the present study concerning the suitability of the term Otway Basin, but it was considered that its wide acceptance in the literature justified its retention. The B.M.R. (1966) has since defined the limits of the basin in greater detail. For the purposes of this study the northern edge of thick Lower Cretaceous Tertiary sedimentation, which is approximately delimited by a major steepening of the gravity gradient, has been adopted as the northern limit of the Otway Basin (Richards, 1965; Leslie, 1966; Fig. 1-1). Both the Lower Cretaceous and Tertiary sediments locally overlap this northern margin but are generally restricted to a thickness of less than 1,500 feet north of this line.