H— 34.

Undifferentiated Triassic. —Hard greywackes and argillites classified as Triassio on lithologic grounds form the Rangitoto Range. Similar rocks outcrop over considerable areas in the eastern uplands and probably underlie all the younger rocks of that part of the subdivision. Herangi Series. —Rocks of Jurassic age, characterized by Pseudaucella marshalli, are well exposed on the coast section extending south from Te Maika, at the entrance to Kawhia Harbour. The series, for which the name Herangi is proposed, begins at the conglomerate band indicated in Bulletin No. 28 as the base of the Jurassic and is closed by the plant beds at Te Maika and Totara Point. It forms the great part of the Herangi Range, where Pseudaucella boulders are commonly found in the beds of the creeks on both the east and the west. Pseudaucella is found also in the east of Orahiri Survey District on the eastern limb of the syncline. The rocks of the series are fine-grained greywacke, argillite, and indurated claystone, overlain by 2,500 ft. of coarse-grained greenish sandstone, which weathers spheroidally. At Kawhia the beds have a total thickness of 5,000 ft. The Pseudaucella beds of the Herangi Series are correlative with the Bastion Series of the Hokonui Range, and the plant-beds at Te Maika probably correspond in part to the Flag Hill Series. Sufficient work has not yet been done in the Te Kuiti district to enable a subdivision of the Herangi Series and a closer correlation with the Hokonui beds. Kawhia Series. —Following the plant-beds which close the Herangi Series are softer argillites and sandstones with bands of igneous conglomerate and characterized by Inoceramus cf. galoi, I. haasti, Aucella boehmi, and Astarte. The section on which the series is based is exposed along the south side of Kawhia Harbour between Totara Point and Waiharakeke Inlet, where the overlying conglomerate is taken as the base of the next-succeeding series. The beds, where they outcrop on the harbour, dip regularly to the east, and show an apparent thickness of 10,000 ft. for the series. Examination of the beds of this formation exposed along the road between Kinohaku and Taharoa Lake reveals folding and faulting, and the actual thickness of the series may be less. The beds continue southward, and in Kawhia South and Maungamangero survey districts outcrop widely in the trough of the syncline and largely form the basement rock on which the overlying Tertiary beds rest. The series has a partial correspondence to the Putataka Series as defined by Hector in his classification of 1886. Puaroa Series. —Near Waiharakeke Inlet, on Kawhia Harbour, a conglomerate forms the ridge east of Kinohaku and continues southward to Te Anga, where it occurs at the falls in the Marakopa River, and thence disappears under Tertiary limestone. It passes up into coarse brown and grey sandstones and soft shale containing ammonites and carbonaceous fragments. The beds from the base of the conglomerate to the top of the Mesozoic sequence in this locality are the Puaroa Series of this report. They are flat-lying in the trough of the syncline, and southward were eroded prior to the deposition of the Tertiary beds, so that they are not now found south of Te Anga. The series is in the main the Mataura Series of McKay, who, however, included beds as far west as Te Waitere, now definitely shown by Trechmann to be of Bathonian-Oxfordian age. Pending an examination of the ammonites it is tentatively placed in the uppermost Jurassic. Te Kuiti Series. —Overlying the Mesozoic rocks with great unconformity are flat-lying Tertiary beds, containing thin coal-seams at the base. The lowest beds contain fossils which may be referable to the Whaingaroa Series ; but sufficient evidence to separate these beds from the overlying Te Kuiti series was not found. Therefore they have been shown on the accompanying map as part of the latter series. The Te Kuiti Series is in the main calcareous. In its lower portion the limestone is massive and decidedly arenaceous, but towards the top the rock consists of tabular layers of nearly pure calcareous material. The limestone is overlain by blue arenaceous mudstone containing shell-fragments and Foraminifera. In several localities the basal rock is separated from the limestone by thin deposits of fine conglomerate ; in others beds of blue mudstone intervene ; and in others grit, shale, and carbonaceous mudstone with seams of brown coal are to be found. Te Kuiti limestone forms the surface rock over a large area of the western uplands, and only in the southern part of Maungamangero Survey District is it overlain by younger rocks. In the Te Kuiti depression the limestone outcrops along the western edge, and also east of Te Kuiti ; but elsewhere it is overlain by younger beds. The dip of the beds is generally low, and over a large portion of the district the limestone is horizontal. Mahoenui Series. —The Mahoenui beds occur chiefly in the central depression, where they conformably overlie the Te Kuiti Series. For the most part they are calcareous argillaceous rocks, with thin sandstone bands. At Oparure, two miles and a half north-west of Te Kuiti, a limestone band 25 ft. thick occurs 200 ft. above the Te Kuiti limestone, and probably corresponds to the band of limestone occurring in the lower Awakino valley, which is there unconformable with a limestone of the Te Kuiti Series. West of Mahoenui are limestone and calcareous beds of Mahoenui a"ge, but limestone definitely referable to this series has not been observed elsewhere in the district. Index fossils are absent, and the subdivision has been made on lithologic comparison with the Mahoenui beds of the Tongaporutu district, where the series is well developed. Mokau Series. —In the southern part of the Te Kuiti depression a thick massive sandstone overlies the Mahoenui beds, and in part overlaps on to Te Kuiti limestone, and, in the east of the subdivision, on to Mesozoic rocks. In the latter locality there is a conglomerate bed at the base, consisting mostly of greywacke pebbles up to 1£ in. across ; above this are carbonaceous shales, containing some r coal. In the Mangapehi valley five miles east of Mangapehi Railway-station a seam of coal 10 ft. thick is reported to occur at this horizon.

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