About the close of Pliocene time a positive movement of sea-level commenced and both north and south of Muriwai pumiceous muds and sands were deposited as the basal sediments of Kaihu Formation. The composition of the sands, fresh feldspar with quartz and pumice, points to a main source in the rhyolites of the central volcanic plateau of the North Island. South of Muriwai these sediments were gradually spread over an irregular basement of Manukau Breccia, but north of Pulpit Rock deeper water existed in the tectonically-formed Kaipara embayment and an embryo South Kaipara peninsula was soon built out. The rise of sea-level was not rapid, for locally, consolidated dune sands rest on top of the silts and muds at the base of the succession south of Muriwai. Silt layers at higher levels possibly represent lake beds which formed in interdune hollows, although the sea eventually reached and maintained for a considerable time a level at least 550ft. above its present level. This long still stand of sea-level allowed deposition of muds and silts that form the surface of the present 550ft. plateau between Bethell's Beach and Shelly Beach. South of Anawhata concurrent normal erosion of the Tertiary volcanic rocks carved at the same height a flat erosion surface, rarely more than one mile in width, which is preserved on stream interludes and rises gently inland. During this still stand also, local sand dunes added another 100ft. or more of cross-bedded sandstone to the surface of the plateau of deposition which rises to a maximum height of 690ft. south-east of Muriwai. Although the beginning of this important rise of the sea has been dated as late Pliocene (Fig. 5) it must be emphasised that no shelly beds have been found beneath the 550ft. surface and therefore no certain age can be assigned to Kaihu Formation. Nevertheless, the occurrence of Pliocene fossils 50ft. to 70ft. below sea-level near Otahuhu, 10 miles south of Auckland city, suggests that transgression commenced in the Opoitian and continued through to the early Pleistocene. Marwick (1948) pointed out that unfossiliferous sediments conformably overlying the shell beds at Otahuhu may be basal members of a younger formation.

Recession of ocean-level followed the development of the 550ft. plateau and was punctuated by periods of constant sea-level during which erosion surfaces were curved at 350ft. and 220ft. to 240ft. on both Kaihu Formation and Tertiary volca lies and sandstones. It was during this period of regression that subaerial sedimentation became important, but it was not until the sea had withdrawn beyond the 220ft. to 240ft. mark to a position well below modern sea-level that the dune mass of South Head Formation was formed. The dunes were added to the distal end of the spit that extended north from Pulpit Rock and was built mainly of subaqueous materials belonging to Kaihu Formation When the sea had withdrawn from the 550ft. level and cut terraces on the underlying sediments at 350ft. and 220ft. to 240ft., South Kaipara Peninsula was in existence in roughly its modern form. The abundance of rhyolitic debris in Kaihu Formation and the outlines of the fossil dunes of South Head Formation show that the peninsula was controlled in its growth by the same combination of south-west wind and long shore drift to the north that operates at present.

After the sea had retreated to a position well below modern sea-level and the dune sands of South Head Formation had accumulated, there was a change in the direct ion of movement of the strandline and the general theme of regression was interrupted by a minor transgression. This advance of the sea reached a maximum position 130ft. above its present level. The estuarine sediments of Shelly