The well indurated greywacke-argillite rocks of the Porirua district have been subjected to strong folding followed by more than one period of intense faulting and fracturing. The main axis of flexural folding trends NNE-NE and plunges 14° to 17° NE. Numerous small-scale fold; are described. They exhibit a wide range of forms: From open, symmetrical, and faulted fold; to isoclinal folds. A few localized folds, described as incongruous, have axes that cut across the NNE-NE trending regional fold axis. Faults are classified, on the basis of certain field criteria, into two broad age groups, early and late. The early faults include those associated with folding and those formed during subsequent episodes of faulting. Late faults comprise those that have been active during and possibly somewhat prior to the Quaternary.