(c) Petrography of the Second Taheke Flow (Fig. 12). In baud-specimen the basalt of the Second Taheke Flow typically is a light-grey rock with conspicuous olivine phenocrysts. In thin section, plagioclase is seen to make up about 60% of the rock and ferromagnesian minerals about 30% with augite usually more abundant than olivine, though the relative proportions of the two vary considerably. The texture in most sections is ophitic and phenocrysts of olivine and less commonly plagioclase occur in addition to the large, irregular plates of augite that show ophitic relation to the feldspar. The groundmass consists of feldspar laths, granules of augite and olivine in varying proportions, and grains of iron ore. In the typical ophitic types, plagioclase (basic labradorite) occurs mainly as small laths enwrapped by augite but in one section ophitic texture is lacking and plagioclase forms abundant phenocrysts which are about basic labradorite in composition whilst the groundmass laths are acid labradorite. The olivine commonly forms rounded phenocrysts, and in the less ophitic types is sub-equal to augite in amount. In most sections there is a small amount of chlorite apparently derived from the augite. (d) Petrography of the First Taheke Flow. Macroscopically, the basalt of the First Taheke Flow is a dark, fine-grained rock which often contains vesicles occupied entirely or in part by ?sphaerosiderite. Microscopically, the rock is most markedly ophitic and rather altered, and in each slide there is approximately 20% of radiating and fibrous aggregates of chlorite derived from the augite. Plagioclase (medium labradorite) makes up about 30% of the rock, and occurs mainly as small laths enclosed by the augite, though in each section there are four or five phenocrysts. Augite is sub-equal to plagioclase in quantity, whilst olivine occurs only in minor amount, usually in small rounded phenocrysts. Scattered throughout the rock are small rods of ilmenite and rare needles of apatite. Physiography Harrington (1944) points out that the accordance of summit level of the divides of the lowlands that surround Hokianga Harbour is so striking “that the area may be regarded as a peneplain dissected in consequence of later uplift” (Fig. 6). On the eastern fringe of the area discussed in this account, this “peneplain” has been protected from dissection by the Horeke and Taheke Lava Flows, and is preserved as a western extension of the southern block of the “faulted tableland” of Whangaroa Subdivision, at a general height of 600 to 800 feet. Evidence of similar peneplanation and uplift has been found elsewhere in North Auckland (e.g., Bartrum and Turner, 1928; Turner and Bartrum, 1929). Cotton (1938, p. 7B) believes that this peneplanation postdates the Kaikoura orogeny “if, as is not quite certain, the deformation of North Auckland was contemporaneous with, and not earlier than, the Kaikoura orogeny in the south.” The modern drainage was initiated by uplift of this peneplain and in the vicinity of Hokianga Harbour, the peneplaned surface was dissected to a stage of maturity by the Hokianga River and its tributaries. The reason for the constriction of the channel of this river (now represented by The Narrows) is not obvious in adjacent exposures, for on both sides of the harbour the rocks consist of sandstones and conglomerates of the Upper Cretaceous sequence. However, in this area there is strong deflection of the compass needle from its true position, so that it is probable that at The Narrows the beds are underlain by basic igneous rock (? Whirinaki Formation) on to which the Hokianga River was superposed.