No abstract

Summary Various investigators (e.g. Vacquier, Holmes, Kintzinger & Lavergne 1957 , Ogilvy & Kuzmina 1972 ) have noted a connection between clay content in sandstones and induced polarisation (I.P.). A correlation between I.P. and permeability has also been briefly mentioned or inferred by some of these workers, though little systematic work has been done in this field. The investigations described below had two objectives, one of which was to find out if I.P. could be used to determine matrix conductivity ( Patnode & Wyllie 1950 , Worthington & Barker 1972 ) and the other to ascertain whether there was any simple relationship between I.P. amplitude and permeability in Triassic sandstones.

Detailed gravity and resistivity surveys have been made in the Vale south of Denbigh, and from the combined interpretations a Trias isopachyte map has been produced. The gravity interpretation indicates that the en echelon faults of the western side extend across to the Vale of Clwyd fault, and separate a complementary set of en echelon synclines. These structures are systematically arranged in a pattern that m a y be attributed to dextral wrenching. and are discussed against a range of literature on that subject. The wrenching may have been a prolonged activity that commenced during Carboniferous times.