Waihao Formation.

I have given this name to a series of beds of considerable thickness reposing upon the crystalline metamorphic schists or the gneiss granite formation, from which they are distinguished by having undergone only partial metamorphism; the line drawn, however, is arbitrary, principally along the direction of the Southern Alps, where these formations gradually blend with each other. The character of the rocks in the eastern division, as I shall show in the sequel, is however far more distinct and constant, and, in many respects, different from that of the rocks of the central chain; but the latter, in their turn, often assimilate in their upper portion to those of the next, or Mount Torlesse formation, so that it is very often impossible to find the boundary line between them. Captain Hutton has named the same beds, occurring in Otago, the Kakanui formation, but as I find that our boundaries, where the rocks cross the Waitaki, do not entirely agree, so that he might include beds which I consider to belong to the next, or Mount Torlesse formation, I have thought it more convenient to give to that formation, occurring in the Province of Canterbury, a local name, selecting it from the River Waihao, where the rocks are largely developed and show well their peculiar structure.

Extent.

Starting from the northern boundary of the former united Province of Canterbury, this zone begins below the junction of the Otira with the Taramakau, where it covers a rather narrow belt of country page 261situated entirely along the western watershed of the Southern Alps. Gradually it becomes broader, and, near Browning's Pass, crosses to the eastern side of the central chain, whence it continues to be largely developed as far as Whitcombe's Pass, the rocks on the western side of the Pass included. The summits of the Southern Alps continue to be generally formed of rocks belonging to this zone, till we reach Mount Cook, which consists of beds pertaining to the next, or Mount Torlesse formation. South of Mount Cook, in the Sealy range, the Waihao formation again becomes greatly developed, now increasing much in breadth, and being divided into two portions by beds of great thickness overlying them, which appear principally in the River Hunter, the eastern belt of the Waihao formation being the narrowest one. Another zone of the same formation enters the Province of Canterbury from the south, between the junction of the Hakataramea with the Waitaki and the mouth of that river, consisting of a series of [unclear: range] from 2,000 to 3,500 feet high, which are the apex of an anticlinal or saddle-back arrangement. They sometimes appear as high table-land, into which the rivers have cut deep gorges, and are bounded and overlaid on both sides by younger rocks. These younger rocks rise to higher mountain chains, on the eastern side as the Hunter, on the weatern as the Hakataramea ranges, situated on the right or western bank of the Hakataramea river. They continue as far as Fox Peak on the western side of the Opuha plains, getting gradually narrower where they disappear below beds belonging to the Mount Torlesse formation. Small outliers occur on both banks of the Pareora, Opihi, and Kakahu rivers, about their middle course. Judging from the lithological character of the altered beds occurring there, another outlier exists in Banks' Peninsula.

Position of Strata and Textue of Rocks.

Near the banks of the Taramakau, the rocks consist of fine light coloured silky clay-slates, nodular schists (Fruchtschiefer), and many other varieties belong to this group, alternating with quartzose schists, which dip to the south-east at an angle of 50 to 55 degrees. Near the sources of the river Styx, a tributary of the Hokitika, the same slate formation occurs in great abundance, but is sometimes more micaceous. There it also dips to the south-east, but at an angle of 70 degrees. Crossing into the head-waters of the Arahura, by the Wooded saddle, where the Waihao formation becomes more developed, the strata in Mount Sale are largely interlaminated with quartz, and page 262dip now to the west-north-west at an angle of 65 degrees, so that here the occurrence of an anticlinal is proved. Still more to the east, at Browning's Pass, the dip alters again to south-east, 70 to 80 degrees; but near the summit of the central axis, westerly dips were again observed. Rocks of the same character, and in similar stratigraphical positions, occur at the head of the more southern branches of the Rakaia, and near the glacier sources of the Rangitata; hut in those localities, the uppermost portion only of the formation under consideration appears, the interlaminations of quartz in the clay-slates (Phyllites), being either absent or appearing in a few instances only. Strata, rich in quartz, are either represented by felstones, or by a semi-crystalline sandstone, in which no particles of slates are enclosed.

On the western side of the Godley glacier altered sedimentary rocks, occur, and the western tributaries of the Great Tasman glacier bring down blocks of rock from the very summits of the Southern Alps, possessing a similar texture. In the Sealy range, south of Mount Cook, and on the western banks of the Tasman river, we meet with foliated altered quartzose schists, argillaceous schists with numerous quartz veins, green calcareous phyllites, true clay-slates or phyllites, some of them passing into gneissoid schists, generally having a westerly dip of 70 to 75 degrees. In the upper course of the two main branches of the Hopkins river, which falls into Lake Ohau, they form the bulk of the ranges where I have traced all the rocks hitherto described. Some of the phyllites are full of lenticular concretions of quartz; in others, the quartz is more regularly interlaminated in small layers, of a few lines in thickness. They vary much in strike and dip, but when all the readings are put together, they prove that at least two anticlinals and synclinals exist, disappearing at last at Mount Hooker, where they are overlaid by newer rocks. Another portion of the country where this formation can be well studied, is situated in the basin of the Makaroa river. Here, on the northern or left bank ot the Wilkin river, it appears to overlie conformably the gneiss granite zone, occuring round Lake Wanaka. The beds representing the Waihao formation, here consist of micaceous or fine grained, light coloured phyllites, often full of laminae of quartz. They are often much contorted, and generally have a dip of between 60 and 80 degrees, varying from north-east to south-west. In crossing Haast Pass, and following the course of the River Haast, we travel upon them for a considerable distance, and are able to observe how the easterly dip changes to a westerly one; and that, after another page 263synclinal has been formed, the easterly dip is again restored on the western slopes of the central chain, where we find them underlaid by the gneiss granite formation. I have spoken of the relation of the rocks in Jackson's Bay, coloured in my map as belonging to this division, when treating of the Westland formation. The rocks in the eastern zone, belonging to the Waihao formation, exhibit a somewhat different facies. There are some micaceous phyllites amongst them but the principal portion consists of peculiarly altered brecciated arenaceous or micaceous schists, alternating with chertoae beds, felstones and greenish schists. Interlaminations of quartz are seldom met with, but very often, parallel to the bedding of the rocks, a congregation of small veins of quartz, somewhat chalcedonic in its nature occurs at intervals, generally anastomosing and continuing its course over a long distance. In the upper course of the Waihao, there is a well defined anticlinal, the rocks dipping on the eastern side 45 to 55 degrees to the east, and on the western side, 70 to 78 degrees to the west. On the eastern banks of the Hakataramea river, all the rocks forming low ranges there, belong to this series. They are sometimes very micaceous, and dip about 60 degrees to the south-west. The outlier on both banks of the Pareora, above Mr. E. Elworthy's station consists of greyish felstones and dark phyllites, dipping 81 degrees to the east-north-east; above them, beds of brecciated micaceous schists are largely developed. The most instructive outlier is the one in the Kakahu river, where some of the schists are so full of interlaminations of quartz, from six lines to three inches in thickness, that the whole appears as one mass of quartz. Other strata contain a close network of small quartz veins. They repose upon beds of highly altered limestone, interstratified with greenish and brownish diabasic ashes and of beds of a quartzoze or chertose character. In some parts of the district, micaceous schists and felstones, intersected by a few well defined quartz reefs, in others, semicrystalline limestones, interbedded with micaceous phyllites, are predominant, apparently forming a number of small synclinals and anticlinals—a south-east and northwest dip, at angles often as high as 85 degrees, being the most frequent. Finally, the small zone in Banks' Peninsula, situated at the head of Lyttelton Harbour, and leading by Gebbie's Pass to Lake Ellesmere, and at the southern base of Castle hill, contains some of the same brecciated micaceous schists, alternating with chertose beds. The strata strike here generally from the north-west to the south-east, with a dip according to the localities, to south-west or north-east, and at a low angle.

Age and Thickness.

This combination of strata, which is of great thickness, resembles in many respects the rocks found in the Nelson Province, which form amongst other ranges, the Mount Arthur range. The latter has yielded fossils of old palæozoic, probably silurian, age. In some of the slates from the Waihao, traces of fossils are observable, but too faint forrecognition. In some sections where the strike and dip are constant, I have travelled nearly ten miles without finding any change, from which we might assume that this formation is at least 40,000 feet in thickness. However, it is very possible that a reduplication of the strata has taken place here and there, which has become effaced, or was not observed by me, in which case the thickness of the formation would be much less.

Igneous Rocks.

In the longitudinal zone running parallel to the main axis of the Southern Alps, first alluded to, I found no traces of igneous rocks, but, in the southern portion of the province, in the ranges forming the western banks of the Makaroa river, numerous dykes of igneous rocks, generally of small dimensions only, have been injected into the phyllites. Some of them are melaphyres, often amygdaloidal, which, on the banks of the River Young, near its junction with the Makaroa, can be observed in situ. On the eastern declivities of Castle Hill, near the head of the Makaroa, large blocks of phyllite crossed by dykes of diorite and dioriticporphyry, were lying on the mountain side, having doubtless been brought down from near the summit. In these dykes, angular pieces of phyllite are enclosed. Similar rocks were met with in the upper course of the Haast river, in nearly every affluent coming from the west, so that there is no doubt that the strata belonging to the formation under review have, in the eastern portion of the folds, been broken through by igneous rocks for a long distance.

Mineral Veins.

The interlaminations of quartz forming regular layers in the micaceous schists and phyllites, as well as the smaller aggregations, or strings of quartz, occurring in great variety and under different conditions, are to a certain degree auriferous, but they appear to be so very poor that only under a combination of most favourable circum-page 265stances, payable goldfields have been formed by their disintegration. In this province, no payable goldfield has been opened up amongst the rocks of this formation, and in Otago, according to Captain Hutton, only the Naseby Goldfields have exclusively been derived from it—(Geology of Otago, page 34). I only know of three reefs occurring in this formation on the eastern slopes of the Southern Alps, which might be termed regular lodes, but their unauriferous character has either been proved on closer examination, or they have not yet been tested. One of these reefs is situated in the small range between the two main Waihao branches. It consists of a yellowish, somewhat ferrugineous quartz, and appears to be several feet thick, but it is much covered up, so that it is impossible, without clearing it, to obtain further details. Another is situated on the southern banks of the Kakahu river; it is about three feet broad, strikes south-west and north-east, and consists of a flinty quartz. An assay, made of stone taken from this reef, did not give the least trace of gold, and it is therefore evident that the wash-gold found in small quantities in the banks of the Kakahu river, is derived from the interlaminated quartz; just as in the Upper Waihao, where regular quartz reefs are entirely absent. Another reef of considerable thickness, near McQueen's Pass in Banks' Peninsula, has also proved to be unauriferous. In the Makaroa valley, the "colour," to use a miner's term, can be obtained everywhere in the alluvial deposits, but nowhere has ground been discovered in that district, derived from the rocks belonging to the Waihao formation, sufficiently rich to pay working expenses. Of other ores, nothing of value has as yet been discovered in this formation. Some of the micaceous schists., as for instance near the head of the Makaroa, are full of iron pyrites. In others, the grains, or interlaminations of quartz, contain small nests or concretions of mispickel, as for instance in the River Hopkins.