C.—2c,

4

SPECIAL REPORTS. 1. MOTUEKA SUBDIVISION. (By J. Henderson and L. I. Grange.) Introduction. The third season's field-work in the Motueka Subdivision was begun on the 11th November, 1925, and ended on the 29th April, 1926. In all 530 square miles was examined, including the whole of Totaranui, Takaka, Kaiteriteri, and Moutere survey districts, together with parts of Waingaro, Harapaki, Flora, Mount Arthur, Motueka, and Wai-iti survey districts. The season was exceptionally favourable for field-work, and the rugged highlands drained by the Takaka River and its main branch were explored with unexpected despatch. In this part of the work Mr. S. J. H. Sylvester, of Canterbury College, gave able assistance. Physiography and Structure. A great fracture-zone, the Motueka fault of McKay, crosses the subdivision in a north-north-east direction, separating a western relatively elevated crust-block from an eastern depressed area, the northern portion of which is covered by the sea and the southern by gravels. Some of the component faults of this fracture-zone strike north-east, others nearly north. The faults of the uplifted area strike similarly —those of the northern part of the subdivision mostly north, and those farther south mostly north-east. The lower Takaka valley is a narrow trough extending north and south between the Pikikiruna Range on the east and an extensive group of extremely rugged mountains on the west. It is fifteen miles long and from two to four miles wide. The Pikikiruna Range, the broad highland lying between the Takaka trough and Tasman Bay, is an uplifted warped earth-block, the southern portion of which is tilted gently east-south-east and the northern portion east-north-east. The ranges west of the Takaka trough have been carved from a massive plateau tilted east. At its southern end the trough narrows, so that the lower edge of the western plateau approaches the Pikikiruna block and finally abuts against it. The Pikikiruna Range ends in this locality, but the highland continues south-west as the Mount Arthur Range. A prominent fault-angle extends south-west from the southern end of the trough for twenty miles or more along the north-west side of this range. The plateau is warped: the northern part slopes east and the southern part south-east. In several localities its ancient surface is well preserved over considerable areas near the fault, and above it the crests of the Mount Arthur Range rise in abrupt slopes 2,000 ft. to 3,000 ft. or more. Other faults, usually striking north or north-east, traverse the highlands. These, though important, are not so well marked physiographically as the great fracture above described (McKay's Karamea fault). The chief streams of the Pikikiruna Range flow eastward to Tasman Bay, but along the western edge, where calcareous rocks prevail, much water from this range reaches the Takaka trough by way of underground streams. The larger part of the area examined during the. season was in the basin of Takaka River, a stream of which the upper part is in or near the Karamea fault-angle and the lower in the Takaka trough. Its principal tributaries are the Cobb, Waingaro, and Anatoki rivers, flowing from the west. They are consequent streams, their direction having been determined by the initial tilt of the ancient plateau. The headwaters of all are strongly glaciated ; now, though snow-drifts persist at many points through summer and autumn, none of the peaks is above the line of permanent snow. General Geology. Three of the four great series of Palaeozoic sediments mentioned in last annual report as forming a large part of the western highlands occur in the northern part of the subdivision. They are strongly folded, distinctly metamorphosed, and intruded by large masses and dykes of acid and basic igneous rock. They form broad bands which in this part of the subdivision strike north and a little west of north. The beds as a whole dip steeply to the east. In the Pikikiruna Range, where only the rocks of the uppermost of the three series are seen, the structure is irregular. The oldest strata examined during the season outcrop at the heads of the Cobb, Waingaro, and Burgoo rivers, the last a branch of Aorere River. The rocks consist of dark and light-grey phyllites, quartzose greywackes, and quartzites, together with minor bands of dark carbonaceous phyllites, some of which contain graptolites, indicating a Lower Ordovician age. Marble is not present in the section examined, though it occurs in large lenses a little to the south, associated with the carbonaceous phyllites. The beds strike nearly north and south, and dip vertically or a few degrees from the vertical and then predominantly east. These rocks form the upper part of what in the two preceding annual reports was termed the Aorere Series, a name that cannot be consistently used if the view of the stratigraphical succession now held is correct, and must therefore be discarded. Lying to the east of the above-mentioned strata is a vast mass of sedimentary and igneous rocks that extends east for eight miles to the Cobb-Takaka junction. It consists chiefly of quartzites, green greywackes, fine and coarse breccias, breccia-conglomerates and conglomerates, light and dark phyllites containing marble lenses, and chloritic phyllites and schist, these last probably altered fragmental volcanic rocks. Of the numerous outcrops of basic igneous rocks some are intrusive, but many are probably contemporaneous flow rocks. The whole, which constitutes the Haupiri Series of Middle (?) Ordovician age, extends as a broad belt north and south through the western part of Flora and Takaka survey districts and the eastern part of Harapaki and Waingaro survey districts. The beds strike north, and dip in general steeply east. They are strongly folded and much metamorphosed. Their eastern boundary, where resistant schistose greywackes are in contact with the