The Paleozoic rocks of south Pembrokeshire, southwest Wales, were folded and faulted during the Armorican orogeny following Carboniferous sedimentation. Superimposed on the Armorican structures are joint sets which were formed before the end of the Triassic. The relations of the folded, and faulted rocks and the joints in the area south of Milford Haven are elucidated. Several new terms are introduced. Kathetal joint is used for a joint surface normal to a bedding surface. Axial trace-fracture is a joint or fracture cleavage surface intersecting a bedding surface parallel to an adjacent fold axis. Lens-belt is applied to gaping en echelon tension fractures within a shear zone. The definitions are longer than given here and it is noted that axial trace- fractures will be enlarged on in a subsequent paper.

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