An area of approximately 5500 square miles of the North Sea was investigated using bottom sampling and seismic techniques. It lies on the north-western edge of the East English Basin, where extensive exposures of Mesozoic sediments are proved. Detailed mapping of these strata is possible over large areas; the western and southern parts of the region are shown to be extensions of the onshore Cleveland Basin and East Midland Shelf areas, with which they have had a comparable geological history. In the east, the Mesozoic strata are strongly folded as a result of halokinesis within evaporites of the English Zechstein Basin, and the feather edge of the main North Sea Tertiary Basin cuts across earlier structures, apparently unaffected. The main periods of earth movement affecting the area are late Jurassic/early Cretaceous, and ‘mid’-Tertiary in age. Important structural lines are recognised as demarcating the Cleveland Basin, East Midland Shelf, and halokinetic areas.