A method is described for making a three dimensional analysis of the curvature or irregularity of a fault. This analysis may be used to determine the position of the openings or zones of low compression that are formed when fault movement takes place. Use is made of two cooerdinate directions lying within the plane of the fault, one parallel to the direction of fault movement, the other perpendicular to it. The angular variations of fault irregularity parallel to each of these directions, and also perpendicular to them give an analysis that considers all three dimensions of space. These angular variations may be conveniently shown by contours.The principles are briefly illustrated with dip-slip faults, and very briefly with strike-slip faults. The line of dip and line of strike of these faults approximate the two significant cooerdinate directions. Extension of the principles is left to the reader.Two occurrences of ore deposits in dip-slip faults are briefly analyzed.