Gravity and Magnetic Anomalies in North Wales

Summary Bouguer anomalies in North Wales have been calculated from a network of gravity stations in which the standard deviation of a gravity difference is about 0·2 mgl. Magnetic anomalies have been surveyed in part of the area. Rock densities have been measured in the laboratory and in the field. The depth to the Pre-Cambrian geosynclinal floor in North Wales is thought to influence the gravity anomalies in some areas, but may control the magnetic anomalies more directly. The regional gravity gradients are due to deeper density contrasts, possibly those involved in crustal warping. At the head of the Vale of Clwyd, 2500 feet of Upper Carboniferous is inferred; farther south, 2000 feet of Trias. The possibility of a Triassic basin under Cardigan Bay is discussed. Structures within the Flint Coalfield are reflected in the gravity anomalies.