55

C— 9

The rocks in the Ohinemuri Gorge, from the Crown battery to a mile above the Township of Karangahake, stand out distinct from all those of the surrounding district. Between the pool opposite the Crown battery and the township is an outcrop of columnar andesite, forming darkcoloured —almost black —rocks on both banks of the river, which is remarkable on account of the small size of the prisms of which this rock is formed. This rock strikes south, and appears to be a dyke of very considerable width. Above the junction of the Waitawheta the rocks are characteristically those of the Thames Goldfield—grey tufaceous sandstone predominating, which on the whole appears more indurated than in the northern locality, but this appearance may be due to the rapidity with which the gorge has been cut down. In the Waitawheta Gorge and in the mountain between this and the Ohinemuri Gorge this indurated character of the tufaceous sandstones also is noticeable, and is a characteristic of Karangahake Mountain itself, as it is of the whole extent of this area of the Thames-Tokatea rocks. The rocks generally appear to be tilted so as to stand at high angles, and the strike is necessarily southward in the direction of Te Aroha. Quartz lodes are plentiful in these rocks, and a number of mines, important as dividend-paying ventures, are being worked in them. One very massive reef traverses the length of the area, and this is of such large proportions that properly it should be considered in dealing with the rocks of the group as developed in this part. On the north side of the Ohinemuri Gorge, and thence north to where the rocks of this group disappear under those of the Beeson's Island group, the central higher part of the range shows quartz in what appears to be mountain masses, and beyond the Rahau Saddle there are two isolated hills of quartz rock set in a cup-like depression under the slope of the higher range to the north-east. Towards the east these rocks suddenly disappear under andesic rocks of younger date, or at high levels on the south side of the gorge are overlain by rocks belonging to the Acidic group, rhyolites, &c. To the westward the dip of the contact line is not so high, but the junction is generally more obscure than on the eastern side of this development of the Thames-Tokatea rocks. Te Aroha Area. —This includes Mount Te Aroha and areas of the same rocks that, with a gradually lessening width of exposure, extend some distance both to the north and the south. To the north from Te Aroha Mountain they extend about four miles to the upper part of the Waitoki Stream, and in this direction form a line of lower hills flanking to the west the principal range. Beyond this the Beeson's Island rocks interpose between the rocks of this and the Karangahake area of the Thames-Tokatea group. South of Te Aroha and the Waiorongomai Stream in like manner the same rocks are continued as a range of flanking hills along the base of the higher mountains to within about a mile of where the county road from Te Aroha to Katikati begins to ascend the west side of the principal range. North-east of Te Aroha it would appear that, as a belt of some width, the same rocks extend into the upper part of the Waitawheta watershed, or that within that watershed there is a separate and distinct area of the same rocks containing lodes of quartz that were being prospected during the past summer. The rocks of this area differ considerably from those of the Ohinemuri Gorge and Mount Karangahake, and, on the whole, resemble more those of the Kapanga than the rocks of the Thames-Tokatea group generally ; in some respects they resemble the rocks of the Beeson's Island group. They consist cf coarse- or fine-grained breccias, grey or green in colour, with bands and floes of solid andesite, varying from dark-grey to greenish or light-grey. The breccias often present an appearance of stratification that is scarcely if at all seen within the Karangahake area. A large reef traverses these rocks from north to south, and this is perhaps the feature and circumstance that has mainly led to the correlation of these rocks with those of the Karangahake area and at the Thames. I follow here Mr. Cox and others in placing these rocks with the Thames-Tokatea group, but wish it to be understood that further examination will probably compel their being classified as belonging to the Waitekauri division of the Kapanga group, with which in their general aspect they better agree than with the rocks of the Ohinemuri Gorge and Karangahake. It will thus be seen that for the most part the Thames-Tokatea group of rocks is confined to the first or north-west of the series of subparallel ranges that trend across the peninsula from north-east to south-west, and that on this range alone do these rocks appear on the east slopes of any range in which they may be present. In the case of the Ohinemuri Gorge and in Mount Karangahake it may be contended that this peculiarity appears, but this is hardly the case, and the Thames-Tokatea group merely appears in the axis of the mountain-range, the lower flanks on each side being formed of much younger rocks. Hitherto this has proved the principal goldbearing formation on the peninsula, and there is every probability that it will maintain a prominent position, though it might be rash to say the first, among the different groups of rocks that carry gold-bearing reefs. Principal centres of mining are situated within its area on the Tokatea and Success Ranges, at the Tiki, Tapu Creek, Puru, and at the Thames, at Puriri, Karangahake, and at Te Aroha. During the past two years prospecting has been carried on at many other places, principally between the Thames and Tapu Creek and within Coromandel County, and finds that promise to be of great importance have been made on the west slope of the range between the Success Range and Castle Rock, and on the east side of the main divide within the Coromandel district many reefs are being prospected hopefully. The Kapanga Group. This has typical developments in three different districts of the Peninsula : First, in the northern part, in which it is present from Stony Bay, near Cape Colville, on both sides of the Peninsula, to a little south of Cabbage Bay, and thence along the west side through the Kapanga and Coromandel districts to the water-parting between the Waiau and Manaia Rivers. Second, from Table Mountain it forms the deeper-seated rocks along the mountain-range that forms the water-divide between the east and west drainage areas of that part as far to the south as the sources of the left-hand branch of the Puriri. This area includes Broken Hills on the east side of the Lower