General Geological Structure.

In the South Island the New-Zealand Alps, dividing Canterbury from Westland, form a narrow range, which rises in Mt. Cook or Aorangi to an altitude of 12,349 feet. To the north and to the page 195 south the mountains bulge out, somewhat in the shape of a dumbbell, the handle being bordered on the west by the plains of West-land, and on the east by the plains of Canterbury. The southern end of the dumbbell is also notched by the plains of Southland. The mountains are formed by a main anticlinal curve (fig. 1, a a) running from the neighbourhood of Lake Wánaka, in Otágo, in a north-easterly direction to Tasman's Bay, and forming the ge-anti-clinal of New Zealand. The greater part of the west side of this anticlinal has been removed by denudation in Westland, so that the

Fig. 1.—The South Island of New Zealand.

ridge of the Alps no longer coincides with the axis of the curve, but forms part of its south-easterly face. On the Canterbury side the rocks are thrown into three broad synclines (fig. 1, b, c, d), separated by two anticlines (fig. 1, e, f) running more or less at right angles to the main anticline. The most southerly of these synclines (b) goes from the neighbourhood of Palmerston, in Otágo, in a northerly direction to Lake Púkaki; the second (c) from the Gawler Downs, in South Canterbury, in a westerly direction to the junction of the Havelock and Clyde rivers, in the Upper Rangitata; the third (d) runs from Waiau in a northerly direction to the neighbourhood of the Wairau Gorge, in Nelson Province. The page 196 secondary anticline (e) runs from Hunters Hills, in South Canterbury, northerly to the Two Thumb range, dipping to the north. Mt. Cook is placed at the point where the synclines b and c and the anticline e meet (fig. 1, x). The anticline f runs from the gorge of the Ashley in a westerly direction. In Otágo the main anticline turns sharply to the south, dipping slightly in that direction, and on its westerly slope a syncline (fig. 1, g) runs from the Greenstone River, west of Lake Wakatipú, through the Hokanúi Mountains to Catlin's River, following with considerable exactness the direction of the Otágo anticline. In the northern part of the South Island the main anticline, turning more to the north, runs out at Tasman's Bay, and is flanked on the north-west by a syncline (h) passing through Snowdon and the Anatoki Mountains to Golden Bay; and on the south-east by another syncline (i) near Nelson, followed by an anticline (k) which runs from the neighbourhood of Top-house in a north-easterly direction through Picton and Queen Charlotte Sounds.

All the sedimentary rocks, up to the Hokanui System inclusive, partake in these flexures. The Waípara System is also, to some extent, involved in Otágo and Nelson; while the rocks of the Oamarú and younger systems either retain their original plane of deposition or are occasionally locally disturbed. These last occupy, for the most part, valleys, or wrap round spurs of the older rocks. A large fault (fig. 1, m) occurs in the west part of Otágo, running in a nearly north and south direction through Lake Te Anau, and throwing up the Manapoúri System to the west^*. No clear evidence of the age of this "Te Anau fault" has as yet been obtained, as the junction between the Manapoúri and Maítai Systems has not been closely studied; but it appears to have been formed before the deposition of the Maítai System.

The North Island is very different. A narrow ridge, rising in the Kaimánawa Range, east of Lake Taupo, to 5000 feet or more, runs from Wellington in a north-easterly direction, to near the East Cape, attaining here also, in Hikurangi, a height of 5500 feet. It is bordered on the south-east by hilly country, occasionally attaining nearly to the altitude of the main range, and on the northwest by country which is broken, but generally low, with the exception of three great volcanic cones—Mt. Egmont (8280), Ruapêhu (9195), and Tongaríro (6500)—near the central part of the island. The rocks also differ much from those of the South Island. The crystalline schists of the Tákaka System, which are so conspicuous on the south side of Cook's Straits, suddenly disappear and are quite unknown in the north. The main range is formed by rocks belonging to the Maítai and Hokanúi Systems, smothered on each side by Tertiary beds, through which rise, at intervals, throughout the Auckland Province, isolated ridges and peaks of the older Maítais and Hokanúis.

This sudden change at Cook's Straits strongly suggests the presence of a fault with the up throw to the south, although it is

^* 'Geology of Otago,' p. 23, Dunedin: 1875.

page 197 not possible to prove its existence. The rocks of the Oamarú and younger systems are found at nearly equal elevations on both islands; but are higher in the central part of the North Island than elsewhere. On the contrary, the rocks of the Waipara and older systems go to considerably greater heights in the South than in the North Island, consequently the "Cook's Strait fault," if it exists, was probably formed in the interval between the deposition of the "Waípara and Oamarú Systems, the downthrow being to the north.

Rocks belonging to the Hokanúi System are found on the eastern side of the Maítais in the Ruahine range in Wellington, and in the Eaukamara range near the East Cape. In the Kawhia and Raglan districts, in the Auckland Province, they lie on the western side of the Maítais. So probably the ge-anticlinal of the South Island runs through the centre of the North Island from Wanganúi to the Bay of Plenty.

All the rock systems, up to the Hokanúi inclusive, have much the same lithological characters throughout New Zealand, and can be broken up into series, which are chronologically distinct. They may be called "continental formations," that is, rocks formed on the shore of a continent with large rivers. All the rock systems above the Hokanúis are, on the contrary, very variable in lithological character in different localities, even when not far apart; the only exceptions being a few limestones, probably the relics of coral reefs. These may be considered as "insular formations," that is, as having been deposited round the margin of islands, from which ran no great rivers. It is impossible, at any rate at present, to divide these latter systems into series which are in all cases chronologically distinct. The series here are geographical, and overlap each other; but I have to some extent indicated their probable relations, in the table of formations.

Eruptive rocks cover but a small area in the South Island. Isolated exposures of granite occur along the ge-anticlinal axis from Paringa River in Westland to Lake Rotoiti in Nelson, and in a few other places west of the axis, the largest area being in the southwest of Otágo, at Preservation and Chalky Sounds. On the east there are a few patches of volcanic rocks of younger date. In the North Island, also, volcanic rocks are rare on the east side of the main range; but on the western side, from the centre of the island to Auckland, they cover more than half the country, and appear again in great force further north, between Hokianga and the Bay of Islands. There is no granite in the North Island.

Good roofing-slate is found in the Tákaka System in Otágo; statuary marble in the Manapoúri System at Caswell Sound; lithographic limestone, with rocks belonging either to the Waípara or Oamarú Systems, south of Bruce Bay, on the west coast of the South Island. Coal in thin beds is found in the Mataúra Series, but there are no workable seams older than the Matakéa Series at the base of the Waípara System. From the date of the Hokanúi System to the present day land has existed continuously in New Zealand, and no doubt decaying vegetable matter has constantly accumulated in favourable localities. But it was only when these accumulations were covered up by deposition that they have been preserved. This occurred in two ways:—(1) By marine deposits on subsidence of the land; and (2) by lacustrine and fluviatile deposits. Consequently we find coals or lignites at the base of the Waípara, Oamarú, Paroóra, and Wanganúi Systems covered by marine beds; and also we have coals and lignites of intermediate age covered by fresh-water beds. These latter, however, we may for convenience group in each case in the system to which the overlying series belongs, although there may be an unconformity between them. The New-Zealand coals, therefore, belong to what I have called insular formations. They do not form large basins, as in England, N. America, or Australia but occur wrapping round hills formed by older rocks, and are consequently almost always worked by day-levels and not by shafts.