Crystalline Metamorphic Formation East of the Central Chain.

Although in this zone the gneiss-granites and true gneiss schists-the lowest rocks visible on the West Coast—do not occur, the whole of page 254the rock approaches not only in character that of the upper beds of that series, but it is also overlaid in the same manner by the next or Waihao formation both east of the Central Chain, and on the West Coast. The rocks only fill a small corner in this Province, at the head of Lake Wanaka—the River Wilkin forming the northern and western boundary—but they are extensively developed in the Province of Otago, where they form a large belt about fifty miles broad, stretching in a north-north-east direction across that province to the Otago Peninsula. In this zone, named by Captain Hutton "the Wanaka formation," the richest and most extensive gold fields in New Zealand are situated.^*

The beds of which this formation is composed consist of gneissic, mica, and chlorite schists more or less crystalline. They generally possess less inclination to the horizon than the same beds on the opposite slopes of the Central Range, their dip on the eastern and northern sides of the River Wilkin being on an average about 55 degrees, ranging from south-east to north-east; and on the western side, about 45 degrees, ranging from south to south-west. They thus form an anticlinal, being surrounded on all three sides by the same series of beds, which I have named the Waihao formation.

Near Lake Wanaka and along the upper course of the River Wilkin, the rocks consist of mica and chlorite schists; more towards the centre of the anticlinal, of quartzose gneiss and of a very crystalline mica schist, full of laminae or lentil-shaped grains of quartz, often of considerable size, which cause the rock, when broken vertically to the foliation, to show a peculiar face. These laminæ of quartz are not uncommon throughout the beds, and always give to the-schists an uneven appearance. Some of these mica schists are often much contorted, so as to suggest that they were very much pressed together, when in a soft or pasty state, by the quartzose or gneissic beds of a harder nature, between which they are enclosed. Corrugations on a large scale are also observable, having all the appearance of ripple marks, but they might, as Captain Hutton suggests, be explained by considering them due to the effects of expansion by heat on soft rocks under great vertical pressure, the compression thus produced having been relieved by numerous small corrugations, instead of by fewer and larger contortions—(Hutton and Ulrich's page 255Geology of Otago, page 30). Captain Hutton states, in the same publication, that nowhere in Otago a junction can be found between this formation, which he names the Wanaka formation, and his Manipori formation, extending all along the west coast of Otago, and as far east as the Te Anau and Maniporo lakes, but I have no doubt that his Wanaka formation is simply the upper portion of his Manipori formation, and that both ought to be united.

My own researches have shown that similar rocks to those found in the Lake Wanaka zone occur abundantly in the upper portion of my gneiss granite formation in many localities along the western slopes of the Southern Alps. Moreover, the absence of eruptive rocks, of which I could not find any trace in the Wanaka district examined by me, and which, according to Captain Hutton, are also wanting throughout the whole zone in Otago, is a further argument in favour of my view, as such rocks are also wanting in the upper portion of the gneiss granite formation in Westland.

I have already alluded to the fact that the greatest quantity of gold, both at the West Coast and in Otago, is derived from this formation, and I have no doubt that in many localities large lodes containing gold and other precious metals will be found. Nephrite, the ponamu or greenstone of the Maoris, is also found in this formation on the West Coast in Greenstone Creek, the Arahura, and some other localities; however, I have never observed it in situ, and I am therefore unable to say with what portion of the rocks forming this formation it is associated. The Canterbury Museum possesses, however, a specimen of nephrite, to which a small portion of the bed-rock, chlorite schist, is still attached.