This British Geological Survey (BGS) geophysical survey took place in September to October 1973 in the SW Approaches and Lizard area on board the TSS Profiler and formed part of the British Geological Survey (BGS) regional mapping project. The main purpose was to compare methods of geophysical profiling and geotechnical testing. Geophysical lines run included Edo Western Echo Sounder & Bridge Echo Sounder, 1000 J sparker, with Geomecanique hydrophone and Huntec recorder, Transit Sonar MS 47, gravimeter and magnetometer. Equipment. Position fixing during the cruise was Decca Main Chain or AMI satellite navigation. These data are archived by BGS. Technical details of the survey are contained in BGS Technical Reports WB/MG/73/46.