Description of technique and density of flight cover [of subject survey: initially, on 9/9/61, six reconnaisance lines were flown covering 650 miles at 2000 feet height above sea level; subsequently the main survey, which took place between 1 - 21/12/61, covered 5992 miles along a basic grid of lines spaced 20 miles apart, with extra infill lines then spaced 2, 6, 6 and 6 miles apart. A Shoran navigation system was employed.] A fairly uniform regional gradient exists over SE portion of the surey area. Anomalies attributed to basalt extend 20 miles NW from Portland along coast. Regional minimum between Cape Northumberland and Cape Banks, with its axis swinging from E-SE-NW away from coast. Basement deep but not specified. South of Kingston get broad NW striking features. Basement depth about 5,000 feet. West of Kingston get basement high trending NW along the coast (2,000 feet deep): a similar high occurs further west (irregular). The trough in between (between 139 and 139 30 E, south of 36 S) is over 6,000 feet deep. Trends strike N-S. In the area south and SW of Cape Jervis, trends are E-W. Basement here lies about 1,000 feet deep or less, but its depth increases at distances greater than 60 miles south of Cape Jervis.