Within the Auckland area, basalt used at Kauri Point pa, Birkenhead, has been sourced to pebbles within the Albany Conglomerates which are present on the shores of the Upper Waitemata Harbour and through to the Kaipara Harbour (Prickett 1989:195). This was undoubtedly a localised occurrence of stone with a very limited area of use.
Greywacke
The densely compacted sandstones and mudstones collectively known as greywacke, are present around the Firth of Thames and on the islands of the inner gulf. There is evidence it was worked on Motutapu and Rakino Islands. The so-called Motutapu greywacke is finer grained than the greywacke present on the lower Firth coastline and was worked by flaking techniques. In contrast the coarse grained greywacke was formed into items such as adzes and weapons by bruising and grinding.
On Motutapu Island, boulder outcrops of greywacke in two places near the coastline were worked before the eruption which formed Rangitoto Island. It continued to be used for several centuries but had a more localised distribution in the last 200-300 years before European contact, and the adzes tend to be of less formal shapes than in the early period of use of the stone. There was also a change over time in where people worked the stone. Evidence from R10/31 at Station Bay indicates boulders were being collected from the outcrops and taken back to the hamlets where they were worked into non-descript adzes.
Adzes made of Motutapu greywacke had a geographic distribution similar to Tahanga basalt, but the main concentration was in the Auckland-western Hauraki area. It was not as important a source of stone as Tahanga basalt.
Coarser greywacke was used for a number of artefacts including adzes, weapons, fishing sinkers, flax beaters, footrests for digging sticks, spinning tops, kokowai grinders and hammerstones. Unmodified stones were often used as anvil stones or for grinding kokowai to powder. Within the collection of artefacts from Oruarangi on the Waihou River, 43%of adzes were made of local Hauraki greywacke while 33%were of basalt (Furey 1996).
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