"In the Dalradian rocks of Knapdale in south-west Argyll two groups of minor folds have been developed which share the same axial plane; their fold axes lie at right angles to each other within the common axial plane. Field evidence indicates that the two fold groups are strictly contemporaneous. . . . Major structures parallel to both sets of minor folds are developed in the area. The fabric diagram of the fold groups shows tetragonal symmetry and this is taken to indicate that the stress field responsible for the deformation had itself tetragonal symmetry. The maximum compressive stress acted almost horizontally in a N.W.-S.E. direction while extension took place equally in all directions in a plane normal to the axis of maximum compression. The relations of contemporaneous fold structures to three basic strain patterns are briefly discussed."