Abstract
Abstract All the igneous rocks and breccia bodies described belong to the Manukau Breccia of the Waitemata Group (Otaian), and they form small bosses, dikes, and sills intruded along north-north-west and east-north-east trends; no surface flows were found. The rocks have been divided into the following eight types: olivine nephelinite, olivine basalt, pyroxene basalt, bronzite andesite, augite andesite, augite-hypersthene andesite, hornblende andesite, and dacite. The mineralogy and petrography of each rock type is described, illustrating a mineralogical gradation from olivine basalt to dacite through part of a differentiation series; an unusual feature of the series is the high calcium content of the plagioclase and pyroxene mineral groups.
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