41

a—9

Lower Carboniferous. Maitai Series. —These are the oldest rocks found or likely to be found on the Cape Colville Peninsula. Of them, Hochstetter says they form the nucleus of the mountain ranges of the Peninsula, and other succeeding writers have expressed the opinion that these rocks are to be or may be found from Cape Colville as far south as the Puriri River or Waihi Beach. During the investigations conducted for the purposes of this report the last traces of this formation were met with along a line drawn from the northern headland of Mercury Bay to Rocky Point near the Thames. The chief developments of this series are in the northern part, and along the western side of the Peninsula to the points stated. In the northern part, the slates and associated rocks form the headland of Cape Colville and the opposing headland on the west side of Port Jackson, they also rise into and form the mass of Moehau, the highest mountain in the northern part of the Peninsula. Thence they extend south along the west side to Cabbage Bay, and along the coast-line to the south of Cabbage Bay as far as Paparoa; are seen at Kennedy Bay, in the Tokatea Range and at Kuaotunu. Between the Tokatea Saddle and Castle Rock they form the lower western flanks of the main range. South of Coromandel Harbour they are largely developed a little inland of the coast, or on the coast-line, as far as Tapu Creek, and finally are seen at Rocky Point, a little north of Tararu Creek at the Thames. At Cape Colville, and thence to Stony Bay, the rocks of this series are mainly of a slaty character, dark-coloured and thin bedded. This also is their general character on the western headland of Port Jackson, although varied by bands of sandstone and grit beds. These rocks on the sea-coast are so rapidly denuded by the action of the tide that the effects of oxidation and decomposition are but little apparent, and thus they present a different aspect to what shows on ranges inland or some distance away from the coast-line, as in such latter positions they are prone to decomposition, and usually assume a buff- or pale stone-colour, except where recently and to some depth exposed by slips, or along the beds and banks of streams. Slates, mudstones, sandstones, &c, form the great mass of Moehau; but on the lower slopes of the mountain, towards the western head of Port Jackson, and on the east side of the Peninsula as far south as Sandy Bay and Port Charles, volcanic rocks form the outlying spurs, the slates descending to the shore-line of the Hauraki Gulf and to the sea, north of Port Charles. Owing to the presence of volcanic rocks on the flanks and lower slopes of the mountain, and of dykes cutting through the slates at various elevations, one large dyke forming the peak of the mountain itself, false ideas have been entertained regarding the real structure of Moehau. This uncertainty necessitated making an ascent of the mountain, but this through the pressure of other work was deferred till the end of the season, and then, owing to bad weather, had to be undertaken under very adverse circumstances. Meantime an ascent of the mountain from the Port Charles side was made by Mr. S. A. R. Mair. At my request he brought samples of rock from different heights on its slopes, and from the top of Moehau, and supplied me with the following notes respecting these and the ascent of the mountain. They are as follows : — "On Easter Sunday I made an excursion to the top of Moehau. For several days previous the peak had been cloud-clad; nevertheless, as the morning looked promising, we made a start at seven o'clock a.m. Nine o'clock saw us up the ridge to a height of 1,150 ft., where we left the andesite and entered on the decomposed slate. On top of the first shoulder, from where we coul d gaze on the coast on either side, and at a height of 2,050 ft. above the sea, I still found this yellow decomposed slate. Our course then led us along the ridge due north for about three miles. "At one spot along the ridge I came upon a ' shed' of small pieces of quartz mixed with slate, evidently being the outcrop of a leader. This was the only signs of reef matter encountered during the trip. " However, 2,350 ft. above the sea-level was the last place in which I was able to obtain slate of any description, but I would not say it did not go higher, as the great depth of peaty matter and thickness of undergrowth prevented me from making as complete observations as I should have wished to. At this stage of the journey huge basaltic boulders were frequently encountered, and nothing of geological interest was seen till the cone was reached. This is exactly what it appears to be, a basaltic deposit on the older formation." At a latter date my assistant, Mr. W. A. McKay, made the ascent, following upwards nearly the same route as that, taken by Mr. Mair. The results of the two expeditions are confirmatory of each other, and prove beyond all question that Moehau is essentially a mountain formed of sedimentary rocks belonging to the formation under description. The Assistant Geologist has supplied me with the following notes of the ascent made on the 17th May, 1897 :— " As directed, on the 11th May I left the Thames, Port Charles, for the purpose of making an ascent of Moehau from that side of the mountain. Owing to a variety of circumstances, mainly owing to bad weather, I found it impossible to make the attempt before the 17th of the month, but on that date, in spite of unfavourable weather, a start was made, and finally, after encountering many difficulties, the purpose of the expedition was accomplished. " The mountain which was the object of the examination occupies that portion of the Cape Colville or Coromandel Peninsula lying to the north and north-east of a line drawn from Port Charles to Cabbage Bay, and forms a considerable portion of the northern part of the Peninsula. " The mountain sends out long descending spurs, which have a moderately uniform slope to sealevel, and none of them rise into subsidiary peaks surrounding or flanking the main mountain mass. Lesser flanking ridges there are that on the east side lie between the mountain and the sea, but, despite of these, Moehau, as seen from north or south, or from each side of the Peninsula, stands alone and constitutes a mountain simply, and not the culminating and principal peak of a mountainrange. The northernmost spur or divide terminates at the western point of Port Jackson; while the 6—C. 9.