C—2c

5

The sedimentary rocks of the eastern highlands are quite distinct from those described above. With the exception of a narrow strip of Triassic strata along part of the western base of the mountains all arc of Paleozoic age. These older beds are divided into the Pelorus (E. de C. Clarke MS.) and Maitai series, the former outcropping cast of and the latter west of great masses of basic and ultrabasic intrusive rocks. The rocks of the Pelorus Series, which occur only in the south-eastern corner of the district, are greenish conglomerates and greywackes, and in the absence of fossils are provisionally referred to a Paleozoic age. They are placed by McKay in the Te Anau Series. The beds of the Maitai Series are grits, greywackes, green and red argillites with irregular bands of limestone near the base of the formation. The strata are disposed in close folds, which in the northern half of Gordon Survey District strike north-east and in the southern half north-north-east, thus roughly following the. trend of the Waimca fault. Fossils occur in the limestone near the base of the series in the Dun Mountain Subdivision immediately to the north-east, and have been referred to the Permo-Carboniferous period by C. T. Trechmann. A great fault trending east-north-east separates the Triassic sediments from rocks of Maitai age. The beds, which consist of argillites, greywackes, grits, and granitic conglomerates, are closely folded in an east-north-cast direction. Many fossils have been collected from the well-known fossiliferous horizon of Eighty-eight Valley. Tertiary rocks, upturned along the fault-zone separating the lowlands from the western uplands, form a narrow strip along the Sherry and upper Tadmor valleys. Tertiary rocks also outcrop at two or three points at the foot of the eastern highlands, and probably extend beneath the gravels that cover the Waimea Plain and adjoining lowlands. Patches of Tertiary strata also occur in several localities among the western mountains, where they have been depressed by fault-movements and so partly preserved from erosion. The distribution, of these patches suggests that a continuous sheet formerly extended over the whole area now occupied by the western highlands. The lower Tertiary beds consist for the most part of quartzose grits and sandstones, evidently derived from the denudation of granitic areas. Layers of carbonaceous sandy mudstone and micaceous shale arc intercalated at many places, as well as occasional thin seams and streaks of coal. The upper beds are chiefly greenish and bluish argillaceous sandstones, which are calcareous in many localities and in a few pass into limestones. In the uj3per Tadmor and Sherry valleys the blue sandstones arc succeeded by arkositic grits and sandstones with thin bands of carbonaceous mudstone and fragments of lignitized wood. The thick deposits of gravel covering the greater part of the depressed area between the mountains rest unconformably on the 'Tertiary rocks. Where seen they are horizontally bedded and have not been affected by deformative movements. They consist for the most part of well-rounded pebbles and cobbles of greywacke in an impervious clay-sand matrix. They are deeply weathered to a yellow-brown colour, their original pale-grey tint being visible at few points. These fluviatile gravels are much dissected by the streams, and in the southern part of the subdivision form hills rising to over 2,000 ft. above sea-level. Granite, in places porphyrinic, forms the eastern portion of the western highlands, extending north and south through Tadmor Survey District. Granite outcrops also over a small area in the south headwater branch of Wangapeka River. This exposure is probably connected with the large masses of acid igneous rock that cover such large areas in west and south-west Nelson. The granites intrude the Mount Arthur and Aorere rocks, and are therefore post-Ordovician in age ; and since granitic conglomerates occur in the Triassic beds, acid igneous rocks must have been exposed in early Mesozoic times. Great masses of basic and ultra-basic plutonic rocks intrude the younger Paleozoic sediments of the eastern portion of the district. Gabbros and dunites with various intermediate types, in places altered to serpentine, and traversed by dykes of diorite and " rodingite " (Bull. No. 12, pp. 31-35), occur. Small dykes of diabase intrude the ancient rocks of the western highlands at many points. These are probably genetically connected with the large basic and ultra-basic intrusions of the Mount Arthur district lying immediately to the north. Economic Geology. The Recent gravels of the Rolling and Sherry rivers and of other streams in the western highlands have been extensively worked for alluvial gold. The principal part of the gold was obtained during the fifteen years following 1865, but many miners were constantly employed until 1900 and later. At the present time mining for alluvial gold has all but ceased. The detrital gold of the Rolling River and its branches Blue, Nuggety, and Connor creeks was undoubtedly derived from the extensive system of auriferous-quartz lodes traversing the rocks of this locality. Similarly, the veins of Mount Luna have supplied gold to Kinzett and Taylor creeks, draining its northern as well as to several southward-flowing branches of the north branch of the Wangapeka. On the other hand, the gold obtained from the gravels of the numerous small streams entering the Sherry from the west had its immediate source in the quartz grits and conglomerates at the base of the Tertiary beds. Part of the gold of the upper Wangapeka no doubt has a similar origin. The Pleistocene gravels in places carry a little gold, and, in parts of the Tadmor Valley where their base is exposed, loose gravels rewashed from them were profitably worked. Since their discovery in 1870 the auriferous lodes of the Rolling River valley have been prospected on several occasions, but so far no payable ore-body has been found. Many of them contain sulphides of lead, zinc, and copper. Very little prospecting has been done on any of the numerous quartz veins traversing the rocks in the neighbourhood of Mount Luna. Several veins in both localities as well as the general conditions appear favourable. A coal-seam, between 3 ft. and 4 ft. thick, and dipping gently westward, outcrops near the saddle between the Karamea and Mokihinui rivers, and one about 2 ft. thick is reported to occur in a small tributary of the north branch of the Wangapeka. Most of the minerals usually associated with ultra-basic intrusions have been found. Chrysotileasbestos in veins not exceeding Jin. wide occurs in the serpentine of tin; Red Hills at several points.