Geology of the Paekakariki Area of the Coastal Lowland of
Western Wellington

By G. L. Adkin

of its constituent sandstone (more particularly that at 530ft. situated 3 miles ENE. of Levin) that led Oliver to postulate a fault at that place (5, p. 11; Fig. 39, p. 31; and Map 2, at end). As shown by the foregoing no such upthrust is necessary to explain the discrepancy in altitude in adjacent exposures of sandstone.

Stream alluvium of the district, usually ranging in age from Mid Pleistocene to Recent, but at the southern end of the lowland apparently coeval with the basal major fans, covers considerable areas of both the Horowhenua coastal plain of Otaki Sandstone and the less generally exposed surface of the piedmont plain of Early Pleistocene gravels. The surface of the alluvium takes the form of distinct minor fans and of coalescent fan-form slopes adjacent to hill-ridges, or of terraces and floodplain strips along river and stream courses. Portion of the later gravel deposits are the product of the incision of the upstream continuation of the major fans—the intermont valley-fill—by the former fan-building rivers, and the deposition of the reworked material on the downstream surface of the fans or in the trench since incised in each of them. Farther downstream where the entrenching finally peters out, a low-gradient secondary fan or fan-like deposit has been built forward by each individual river. Where, as in the case of the Otaki River, the trench incised in the main fan terminates close to the present coast, the shingle and gravels of the secondary fan deposit reach the present shoreline and replace to some extent the normal sand beach of this coast. In a manner similar to this the occasional bands and lenses of gravel observed incorporated in the Otaki Sandstone at Shannon and northward of that place (see Oliver, 5, Figs. 19 and 20, and pp. 20, 21, 39), also at Paekakariki, were carried forward and deposited. Such incorporated gravels by no means necessarily indicate oscillations of the shoreline as suggested by Oliver (op. cit., p. 39).

A Shoreline of Early Human Occupation in Horowhenua.

General considerations indicate that the earlier coast of submergence (Adkin, 2, p. 501; Oliver, 5, p. 37) of Western Wellington commenced to rise and was abandoned by the sea in the Mid Pleistocene (Adkin) or late Early Pleistocene (Oliver)^* as the result of secular uplift, orogenic in character, and greatest inland and northward and diminishing seaward and to the south. The uplift produced the Horowhenua coastal plain, lithologically the Otaki Formation. The uplift was continuous and is believed to be in progress at the present day. The rate of uplift no doubt varied from time to time but not to the extent of causing physiographic breaks of sufficient duration to produce anything of the nature of successive distinct shorelines.^†

The present writer (7) has briefly recorded evidence of a former shoreline or, more correctly, a series of shorelines, now well

present beach, of a sand formation heavily charged with water-worn lumps of pumice of all sizes from small pebbles to boulders a foot or so in diameter. Pumice artifacts also occur, including disc-shaped net-floats and rubstones.

The significance of this pumice-deposit, confined as it is to a band parallel to and not far inland from the present shoreline, was brought to the writer's notice by C. A. Fleming, of N.Z. Geol. Survey (personal communication). His field work in the Wanganui area had disclosed a late pumice deposit ascribed to material derived from a Taupo Shower deposit of the central plateau of the North Island (8, p. 225 and map facing p. 224; 10, pp. 77–8 and map showing volcanic showers, at end). The transport of pumice debris in enormous quantities, far exceeding in amount material derived from the inland deposits by current stream erosion, seemed good evidence of the distribution of the material by the larger rivers draining from the interior during the progress of a late Taupo pumice eruption. The Wanganui River, for example, was at that time so choked with floating pumice that masses of it became stranded on the low ground on its lower course. Immense quantities reached the sea and were cast up on, or became waterlogged and were buried in, beaches washed by the southward-flowing littoral marine current. The recording of shore-bordering pumice debris in Horowhenua (7) post-dating shorelines of early human occupation was received with interest since circumstances seemed favourable for determining an approximate date for the Taupo pumice shower. A search for and detailed examination of “marker” deposits of near-shoreline pumice at other points along the coast of Western Wellington was required to throw further light on the problem.

The Paekakariki Area.

The connection of the Paekakariki area (Figs., 1, 5) with the foregoing was brought about by a casual observation made by Fleming in December, 1948, at the beach adjacent to the Centennial Inn (Fig. 1), where he noted “a deposit of decomposed pumice fragments overlying greywacke gravels” (personal communication). In undertaking the obtaining of data of the incidence of this pumice deposit the present writer observed formations underlying the extreme southern end of the coastal lowland that had previously escaped notice.

The Modern Beach.

Southward from Paekakariki the broad sand beach at and north of that place is backed by a high foredune, the toe of which had been undercut and slightly cliffed prior to the building of the modern beach. Cliffing appears to have been somewhat accelerated in recent years, during high tides and coincident stormy seas, as a series of beds of non-aeolian origin at the base of the dunes is now exposed on the seaward side in a number of places. Southward from Paekakariki the sand beach is replaced by a fully-developed shingle beach and the 'tween tides seaward slope steepens. The whole of the shingle beach material is local greywacke. Beach cusps, of characteristic development in coarse and in fine detritus, are present in both local varieties of beach.

Fig. 2 gives the principal features of profile and constituent materials of the shingle beach and its relation to the cliffed foredune. At the outer, lower portion, the slope of the beach for about eleven yards above low-tide line is of sand, and the impression is gained that the inner part—of shingle—is a separate superficial feature overlying the basal beach of sand. High-tide line is surmounted by a storm beach, also of shingle and gravel, which extends inward to and overlaps the base of the slightly cliffed foredune.

The Paekakariki beach terminates (as the coarsest part of the shingle beach) at a point 14 chains south of Centennial Inn (a useful datum point), where it abuts on a rock-platform of marine abrasion, now slightly raised in relation to present sea-level. The slightly raised bench in its nearly intact condition now ends at its junction with the lowland-fringing shingle beach, but it formerly extended (as its remnants do still) 27 chains or more farther north, overlapping the southern end of the lowland strip by that amount. This portion of the shore-platform has been more severely abraded during the period of present base-level as the result of the effects of the contiguous shingle beach.

The Coastal Section.

The apparently recent cutting back and cliffing of the fore-dune in a number of places at and south of Paekakariki has now revealed the local structure of the lowland strip. The section visible comprises an unexpected multiplicity of local geological formations. For reasons suggested below, none of these well-defined formations is of any great thickness, but all have distinctive characters and thus throw considerable light on varying past relations of sea and land.

The basal formation, showing a thickness up to 3 feet above the inner overlapping margin of the modern storm beach, consists of rather fine sea-worn pebbles and occasional cobbles of greywacke in a (usually) sparse matrix of coarse sand. Intercalated lenses and bands of the same coarse sand occur in the upper part, and the lower part is, to some extent, cemented by oxide of iron. This formation is interpreted as a beach deposit originally laid down at sea-level, and though now above, there is evidence that it had been, at one stage, depressed below sea-level.

The next formation, overlying the last, is a clean, water-laid sand, in places finely laminated, exhibiting delicate cross-bedding, and varying in thickness as the result of subsequent stream erosion from 1 ½ to about 25 feet; at the places of maximum thickness, however, the base is obscured by talus; the maximum thickness noted in exposures where both upper and lower surfaces are visible was 4 feet. On various grounds—lithology, structure, geographical position, etc.—this marine sand is identifiable as Otaki, and is an attenuated tongue of the extensive coastal plain of marine sandstone of the region northward.

Exposures of Otaki Sand occur in three slightly differing relationships in the coastal section south of Paekakariki. Where first examined by the writer at exposures at the base of the fore-dune between 9 chains and 11 chains north of the Inn, it

Interpretation, and Formation Names.

The lower beach-gravel formation is interpreted as being an early marine abrasion product, localized at the Te Paripari cliffs of the Paekakariki area, of the late Early Pleistocene to Mid Pleistocene shoreline of Western Wellington. The deposit accumulated as an incipient strand-plain during an interval of stillstand or of very slow uplift. For it the local formation name of “Lower Paripari” is suggested

Submergence interrupted the accumulation of the Lower Paripari Formation and by carrying it below sea-level, allowed the deposition on it of the overlying marine sand. On similarity of lithology and internal structure, as well as geographical position and relationship to the “old land,” this sand is correlated with the established Otaki Formation in Horowhenua and northward. The name “Otaki Formation” is therefore retained for the Paekakariki portion.

Overlying the Otaki Sand is another sand formation of similar marine sedimentary origin but of different lithology. The distinctive lithology connects it with, on the hypothesis of its derivation from, a Taupo pumice shower; it is a waterborne facies of the product of a Taupo pumice eruption. Despite its limited thickness and areal extent, the geographical range and distinctive lithology of this pumiceous sand stratum makes it an important horizon marker. As a formation name, “Taupo Outwash,” or, in full, “Taupo Outwash Pumice-pebble Sand” has been adopted.

The upper beach-gravel formation, derived from renewed abrasion of Te Paripari cliffs, was also built forward as an incipient strand-plain during another interval of stillstand. It rests directly on a degraded surface of the Otaki Formation. The pumiceous sand is absent here, and as the upper gravels are regarded as slightly

older than the pumiceous sand, the former is presumed to have been raised above sea-level by renewed uplift just prior to the deposition of the sand. The pumiceous sand was then deposited on a shoreline seaward of the gravels at this place, and later completely removed here by the final sea advance. “Upper Paripari Formation” has been selected as a suitable local formation name for these gravels.

Diastrophic Factors.

To interpret correctly the sequence of Quaternary events that have left their mark in the Paekakariki area, it seems necessary to recognize and correctly assess the interaction of diverse diastrophic processes that have affected the terrain as a whole and that vicinity in particular. The working hypothesis already advanced by the present writer (4, p. 111; 10, pp. 146–8) may here be restated and developed in more detail.

The general concept is the extended contemporaneity of both epeirogenic and orogenic movements, the latter comprising two linked but opposing stresses, a major and a lesser, in operation simultaneously. The land-surface affected by these movements was the “pre-Miocene peneplain” (so called) to which the land had been reduced. Large areas of this subdued surface were submerged by Tertiary seas, other portions were gently upwarped and remained emergent. Evidence from the Port Nicholson area indicates that the Kaukau erosion-surface was part of the initial surface of the axial highland belt from which, in the North Island, the Tararua-Rimutaka collinear ranges have been carved. The whole forms part of the emergent portion of the “pre-Miocene peneplain,” or, more correctly, subdued matureland.

The Kaikoura orogenic uplift and deformation progressed to its climax at the close of the Pliocene. The drainage consequent on the uplift developed as the orogeny proceeded, the axial belt reaching a state of deep dissection at, or even prior to, the beginning of the Pleistocene. At this stage epeirogenic uplift supervened and at its maximum the glacial episode occurred. During this uplift, extra-axial areas were likewise elevated, and during pauses, the benches of partial erosion-cycles—Table Hill, Mana, Tongue Point, etc—were successively developed, each at the expense of the graded surface of the preceding epicycle.

With dissection proceeding, the initial surface of the axial belt was uplifted, tilted, and flexured into a secondary anticlinorium, finally faulted and upthrust on its eastern flank (11). Separating this deformed belt from the more uniformly uplifted and relatively gently warped superficies of the Wellington Peninsula “block,” there intervenes a long, narrow, subsiding (or relatively lagging) tectonic strip. This is the Port Nicholson-Porirua-Pukerua “sunk-land” strip. Its lateral boundaries appear to be monoclinal flexures and, in part, normal faults facing inwards (Fig. 4).

The particular diastrophic movements outlined, other than the epeirogenic movement, are visualized as being varying manifestations of the crustal forces behind the Kaikoura orogeny. The general

movement was one of uplift. It was of greatest intensity along the axial belt: stresses of lesser intensity elevated the Wellington Peninsula “block”; the interaction of these two units with perhaps some rotation of the axial segment, apparently produced a down-drag along the hinge-line of the contact, and by slowing up the uplift along that zone, gave it the semblance of a relatively subsiding strip.

The most recent effects of crustal stress in this relatively subsiding sunkland strip are three normal faults that cross it obliquely. These are respectively known as: the Wellington Fault (Cotton), the Owhariu-Kaka Fault (Quennell and Ferrar), and the Mount Welcome Fault (Adkin); their trend is sub-parallel. The inbreak of the Wellington Fault accelerated the local subsiding tendency very considerably and produced the fault-angle and, in part, the more strongly downwarped area of Port Nicholson and the Hutt Valley (Fig. 4). The Owhariu-Kaka fault-trace exhibits features of very recent movement but in part it coincides with an older fault-scarp, especially on the eastern side of Colonial Knob. Northward, the recent trace of the Owhariu-Kaka Fault intersects the older Kakaho Fault (see Fig. 4) at an acute angle, and recent movement on the northern part of the Kakaho Fault was probably due to movement on the Owhariu-Kaka line. The Mount Welcome fault-trace (Fig. 4) is one of the most recent of the local crustal fractures and there is little, if any, evidence of earlier movement on this line. It is probable, however, that the most recent movements on the northern part of the Mount Wainui Fault (Fig. 4) were produced by the northward extension of movement on the Mount Welcome Fault. The latter intersects the former at an acute angle (cf. the Owhariu-Kaka-Kakaho intersection, Fig. 4), and rejuvenation of the northern part of the older Mount Wainui Fault is indicated by notched spurs and by the postulated disruption of the Otaki Sandstone towards its (this fault's) extreme northern end, as submitted on a later page of this paper. About the end of the Early Pleistocene a second epeirogenic movement—this time of subsidence took place. This probably involved the whole of the South Island and the southern part of the North, and may have been uniform over that area, or of the nature of a slight tilt, possibly from north to south.

With sea-level thereby brought to a relatively higher altitude in relation to the diminished New Zealand land-mass (thus reduced to separate islands as now), the effects of ensuing orogenic movements together with apparent eustatic changes in sea-level became obvious. Continued orogenic uplift of the Tararua-Rimutaka axial range caused the sea to leave its late Early Pleistocene to Mid Pleistocene shoreline along the Tararua foothills and lay bare the Horowhenua coastal plain. The lesser complementary but opposing orogenic movement—i.e., the down-drag or lag of the Port Nicholson-Pukerua tectonic strip—slowed up the general upward movement, enabling eustatic changes in sea-level to produce occasional submergence of the narrow southern end of the coastal lowland.

Notes on Local Geological History.

The piedmont alluvial plain of coalescing major fans of Horo-whenua in the Early Pleistocene^* extended southward as far as Waikanae. These fans were the product of the larger rivers draining from the Tararua Range during its second-cycle uplift and were deposited on an extended lowland surface reaching far to the west.

There is evidence for the belief that the smaller but conspicuous fans fringing the foothills between Te Horo and Waikanae and from south of Paraparaumu to Paekakariki, were coeval with the major fans and thus formed part of the piedmont apron of basal gravels. As the product of comparatively small streams, the lesser fans have gradients of values greatly in excess of those of the larger and flatter fans of the principal rivers, and the apexes and upper slopes of the former stand at higher levels, making them striking features of the landscape. Truncation of the toe of most of these steep southern fans by faulting took place (see Fig. 4), a derangement of equilibrium that caused them to be breached and trenched by their originating streams. Later, a renewal of fan deposition resulted in some complexity of structure and surface configuration. Over the whole lowland area, however, stability and a cessation of fan-building had been reached for a lengthy period prior to the peripheral submergence that followed that aggradation.

The period of greater elevation, marked by the episode of Early Pleistocene glaciation, was followed by this regional subsidence. In the Paekakariki area the Lower Paripari Formation is taken as being related to the new coast of submergence. The submergence gave rise, in Western Wellington, to the highest Otaki shoreline, which is assigned to times extending from late Early Pleistocene to Mid Pleistocene. A slightly qualified concept of the date of the Otaki shoreline is introduced here. In the Paekakariki area coastal abrasion and the building forward of an incipient strand-plain took place at a rather earlier date than the abandonment of the earliest Otaki shoreline at the inland hill-region of the “old land” northward in Horowhenua. A late Early Pleistocene date (Oliver, 5, p. 37) for the former and an early Mid Pleistocene one (Adkin, 2, p. 502) for the latter may well apply in the respective localities, and cover the evident time lag between the two.

The submergence of the Lower Paripari strand-plain apparently by a eustatic rise in sea-level allowed the deposition upon it of the overlying Otaki Sand. In the Paekakariki area this sand deposit was more limited in thickness and lateral extent than in the region to the north. Uplift, on a restricted scale, then laid bare the sandy sea-bed to form a narrow strip of coastal plain—the southern wing of the Horowhenua coastal plain—originally extending southward past the present lowland terminus.

The Hypocreales of New Zealand
II. The Genus Nectria.

By Joan M. Dingley, Plant Diseases Division, Department of
Scientific and Industrial Research, Auckland.

scabrid, ostiole minute, papillate, perithecial wall pseudoparenchymatous 40μ thick, outer cells 10–20μ, lightly pigmented and thickened, sub-hymenial cells small 4–5μ diameter, densely pigmented and thickened. Asci cylindrical or clavate 20–50 × 4–7μ ends truncate, 6–8 spored, biseriate, occasionally obliquely uniseriate; pseudoparaphyses filamentous forming a network within the perithecia. Spores elliptical, filiform, ends truncate 9–13 × 3–4μ smooth, hyaline.

Type Locality: Auckland, Waitakere Ra., Anawhata Rd.

Distribution: New Zealand.

Habitat:

Coprosma grandifolia Hook. f.

Auckland, Waitakere Rn., Huia, August 1947, J.M.D.; Anawhata Rd., August 1947, J.M.D. (type collection); September 1947, J.M.D.; Waitakere Ra., Rua-te-whenua August, 1949, J.M.D.

Perithecia were collected on bark damaged by insects. Spores are larger than those of N. tawa and the ends are truncated, pyriform and often irregularly divided by a septum.

31. Nectria westlandica sp. nov.

Plate 24, fig. 7.

Perithecia gregaria, globosa 0·5–0·8 mm., brunneo-vinosa, inaequale tuberculata; ostiolo papillato; pariete perithecii 50μ crasso; pseudoparenchymato sed structura occulta parietibus cellulorum densatis et solide tinctis. Asci elliptici 95–140 × 10–16μ, evanescentes. Sporae uniseptatae, ellipticae vel naviculatae 30–42 × 9–12μ, leves, hyalinae.

Perithecia gregarious, globose 0·5–0·8mm. dark red, brown, vinaceous irregularly tuberculate, ostiole papillate, perithecial wall 50μ thick, pseudoparenchymatous but structure masked by thickened densely pigmented walls; tubercles hyaline, pseudoparenchymatous, cells thin walled and hyaline 10–12μ diameter. Asci elliptical 95–140 × 10–16μ, 8 spored, spores biseriate or obliquely uniseriate, pseudoparaphyses evanescent. Spores one-septate, elliptical or naviculate, sometimes falcate 30–42 × 9–12μ, smooth, hyaline.

Type Locality: Westland, Waiho.

Distribution: New Zealand.

Habitat:

Olearia avicenniaefolia Hook. f.

Westland, Waiho, November 1946. Type collection.

A species easily identified by its large elliptical spores and dense perithecial wall with small scale-like tubercles. When immature perithecia are smaller and scarlet.

Literature Cited.

Cayley, D. M., 1921. Annals of Botany, Vol. 25, pp. 79–92.

Colenso, W., 1886. Trans. N.Z. Inst., Vol. 19, pp. 301–313.

Cooke, M. C., 1879. Grevillea, Vol. 8, pp. 54–60.

—— 1884. Grevillea, Vol. 12, pp. 77–83, pp. 101–103.

Cunningham, G. H., 1925a. N.Z.J. of Agric., Vol. 31, pp. 102–103.

—— 1925b. Fungous Diseases of Fruit Trees, 382 pp.

Curtis, K. M., 1946. Annual Report Cawthron Inst. 1945–46 p. 16.

The Taxonomy of the Moss Archephemeropsis trentepohlioides Renn.

By G. O. K. Sainsbury

The Occurrence of Acantholybas brunneus Breddin in New Zealand
(Heteroptera: Coreidae)

By T. E. Woodward, Department of Zoology, Auckland University College

A New Species of Gall Midge (Cecidomyidae) from Hebe salicifolia Forst. Leaf Galls

By K. P. Lamb, Plant Diseases Division, Department of Scientific and Industrial Research

The American Lake Char (Cristivomer namaycush)

By G. Stokell

In a single specimen of Salvelinus malma from North America examined by the writer the number is 26. The American representatives of the genus Salvelinus would therefore appear to conform to the specifications of the European species, and the number of caeca must be regarded as providing a useful distinction between this genus and Cristivomer. There appears no justification for uniting the two genera, although their distinctness is somewhat affected by the existence of a common feature indicative of close affinity. All chars of the genera Salvelinus and Cristivomer that have come under the writer's observation have considerably more cross-rows of scales on the body than scales in the lateral line. The lateral line scales are not composed of hard, transparent material as are those on other parts of the body, but are almost cutaneous in character. They carry no circuli and are flexibly connected. The arrangement differs greatly from that in Salmo and Oncorhynchus, in which the lateral line scales number approximately the same as the cross-rows and are similar to those on the remainder of the body except that each carries a mucus tube. Another feature common to Salvelinus and Cristivomer is the presence of well-developed mucus pits below the lower jaw, usually ten on each side in Cristivomer. Obsolete pits with occasionally some small functional ones occur in Salmo trutta and Salmo salar, but they are lacking in Salmo gairdnerii and in all observed species of Oncorhynchus. The group known as Salmo clarki has a more definite development of mucus pits than occurs in typical Salmo, and, in this feature, comes close to the chars, which it further resembles in usually having teeth on the hyoid, but it is to be noted that the scales in the lateral line, although irregularly placed in relation to the cross-rows, agree with those of typical Salmo.

A redescription of Cristivomer namaycush is given below and a photograph of a typical specimen in shown in Fig. 1.

Cristivomer namaycush Walbaum

B. 11–12. D iii–iv 8–9. A iii 9. Gill-rakers 20–21. Pyloric caeca 128–164. Vertebrae 62.

Body of vomer elevated above level of head, in section an inverted V, toothless. Head of vomer with a blade-shaped structure extending posteriorly and, in its latter part, free from the body of the vomer, the extent of the free portion variable. Teeth on head of vomer arranged in an irregular chevron, uniserial on blade. Hyoid with a long patch of small strong teeth.

Head 4·41–4·51 in standard length, maxillary extending well behind posterior of eye. Dorsal fin inserted at 0·5–0·505 of the standard length, its height 1·07–1·38 times its basal length. Pectoral extending 0·42–0·45 of the distance from its root to the ventral, ventral inserted at 0·56 of the standard length, height of ancillary 0·28–0·31 of the height of ventral. Height of anal 1·3–1·34 times its basal length, caudal peduncle 2·1–2·21 times as long as its least depth, caudal fin deeply forked. Scales small and irregularly placed, about 190 cross-rows immediately above lateral line, 128–130 scales in lateral line.

Colour greenish-grey with pale spots and short markings, belly and lower fins tending to golden. Maximum total length observed 25 inches.

New Zealand Existence

In 1906 fifty thousand eggs of this fish were imported by the New Zealand Government and hatched by the North Canterbury Acclimatisation Society at its hatchery in Christchurch. The Society's Annual Report for 1907 states that 4,000 young fish were liberated in Lake Pearson in Canterbury and a similar quantity was forwarded to Westland for disposal by Government officials. The late T. E. Donne (1927), Government Tourist Officer, at whose instigation the eggs were obtained, gives the Westland locality as Lake Ianthe and states that the Canterbury lot was divided between Lake Pearson and Lake Grasmere. A few of the young fish were retained in the acclimatisation ponds and apparently reared to maturity. The Society's Annual Report for 1910 states that 56 four-year-old fish were held at that time, and it is obvious that a second generation was bred from them, as the 1911 Report records the presence of two-year-olds. There is no account of what became of these fish, but they appear to have been disposed of by 1913, as the only salmonoids recorded as being held in ponds at that time were brown trout and rainbow trout.

The only New Zealand water from which this char has been recorded is Lake Pearson, which is situated about four miles south of Cass, on the West Coast road. This lake has an altitude of 1990 feet and appears to have been ponded partly by moraine and partly by shingle fans. It is about two miles in length and about half a mile in width except at the middle, where it narrows to a neck about 30 yards wide. The principal tributary is the Craigieburn Creek, which is so unstable in the lower part of its course that it may divide its waters between the lake and the outlet stream or flow wholly into one or the other. The Ribbonwood Creek is usually dry in the lower part of its course, but assists in feeding the lake by soakage and there are several small trickles which usually maintain a connected flow. The outlet known as Winding Creek is at the south end and flows into Broken River, a tributary of the Waimakariri, but is frequently dry for a considerable distance just below the lake.

No records of the number of char taken at Lake Pearson have been kept, but it would appear from information received from several anglers who regularly fish the water that twelve fish per year would be a reasonable estimate. The largest fish observed by the writer was 7 lb. in weight and the average for the eight specimens examined is 5 lb. These weights are much lower than those recorded in North America, where fish of 15 lb. and 20 lb. are not rare, and individuals of double these weights are taken occasionally. The small size of the New Zealand fish appears to be explainable on the grounds of unsuitability of habitat, and it is even matter for surprise that the species has established itself in a lake so different from its native waters. The great depths and extremely cold waters of the Canadian lakes, in which this fish abounds, are in sharp contrast to the conditions at Lake Pearson, which is comparatively shallow and warm. A series of soundings showed that a considerable area of the northern section is between 35 feet and 40 feet deep, with a maximum depth of 45 feet recorded about the middle transversely and somewhat south of the middle longitudinally. The neck is shallow and the greater part of the

Notes on the Geological Structure of New Zealand

By A. R. Lillie, Auckland University College

has recently been recognised in New Zealand by Wellman and Cotton, and the former has advanced in a paper as yet unpublished the hypothesis of great transcurrent movement along the Alpine Fault.

Introduction

It is probably true that the strata of New Zealand are more difficult to decipher than those of western Europe and many other classic regions. The Lower Palaeozoic strata have been examined only in part and are difficult of access. Professor Benson has recently found Cambrian strata, and, with co-workers, has described a good graptolitic Ordovician succession, but no Silurian has yet been positively identified. The Devonian rocks are fossiliferous, but the relations to over- and underlying rocks are quite obscure. The Upper Palaeozoic and Mesozoic strata of New Zealand include thousands of feet of argillites and especially arkoses, commonly of greywacke facies, and their subdivision has proved difficult. Of these, the Carboniferous (if any) and Permian strata have not yet been separated, and, indeed, in some places are difficult to separate from the Trias. The Triassic and Jurassic rocks form a comprehensive and thick group, in places at least 28,000 feet thick, and sometimes grouped as the Hokonui System. All these earlier strata are distinctly more indurated, sheared, and folded than later beds, so that it is commonly possible to map the older beds as “undermass” and the later beds as “cover.” Indeed, of recent years much of the country, where Late Cretaceous and Tertiary stratigraphy and structures have presented immediate problems, has been so mapped, with consequent dearth of information concerning the undermass. Certain rocks, attributed to the Aptian and containing poor faunas, would seem, in degree of induration and diastrophic position relative to major unconformities, also to belong to the same comprehensive basement, including Triassic and Jurassic strata, and they can rarely be clearly separated from the earlier Mesozoic strata.

In many places there is passage from the upper Cretaceous to Tertiary and these two systems, in places of very monotonous lithology, and reaching locally total thicknesses of 30,000 feet, show considerable facies variations and local discordances.

In New Zealand any geologist who attempted on purely local evidence a division of strata into Primary, Secondary and Tertiary would be inclined to define his Primary as extending from the Devonian downwards, his Secondary as including the Permian and perhaps the lower Cretaceous, and his new Tertiary system would perforce include some upper Cretaceous rocks and perhaps even some Pleistocene. Moreover, the stratigraphical limits between the groups belonging to each era would be occupied by question marks, representing the times of our major orogenies which might vary slightly in age from place to place. There are no known strata bridging these time gaps within the country.

Although the lower Palaeozoic strata and their relations to some of the metamorphic rocks remain obscure, two problems have engrossed the New Zealand stratigrapher because of the great thicknesses of the formations involved. These problems are the subdivision

this material is current knowledge among members of the Survey, other geologists find difficulty in placing the shorter papers of the last few years in a general structural framework. The Survey workers, engrossed in regional mapping, revealing more and more details, have hesitated to write general statements on structure likely to be soon out of date and thus would seem not to have done themselves full justice. The appearance of the new geological map represents a milestone (the useful black and white maps of Morgan [1922] had already become out of date), and the Outline of the Geology of New Zealand, which accompanies the new map, is the most useful existing synopsis of New Zealand stratigraphy. Professor Benson, in 1921, 1922, produced admirable summaries of New Zealand geology which will long remain the stand-by of all those unfamiliar with the detailed literature. Cotton's papers of 1916 and 1925 shed further light on structure, particularly as revealed by land forms. Henderson summarised the fault pattern of New Zealand and gave a useful synopsis of the late Cretaceous and Tertiary strata of New Zealand (before Finlay-and-Marwick stages). Benson's papers of 1923 and 1924 relate the stratigraphy and structure of New Zealand to those of Australasia as a whole. Apart from these few papers hardly a single general statement on New Zealand geology appeared between Benson's papers and Macpherson's last memoir, which is a lively discussion of the author's views based on wide field experience and data collected by himself and other geologists. Confined to the Cretaceous and Tertiary movements, his work presents a synthesis of structure and covers in brief outline the relations of Cretaceous and Tertiary sedimentation to structural plan. Indeed, it renders much of this paper redundant, except that Macpherson has been more concerned with synthesizing than with describing general knowledge already familiar to the New Zealand geologist. His memoir is quoted extensively in this paper because it serves as a convenient starting point on which to examine theories concerning the structure of the country.

The next few pages comprise a running commentary on the chief views concerning structure that have been recently advanced, and omit many important references already quoted by Benson and Macpherson. A later section gives some further details for parts of the country and introduces some of the writer's own views, which can claim little originality, but maintain that further theories on the nature of late Cretaceous and Tertiary fold patterns require a closer attention to the structure formed in older orogenies.

Acknowledgments and Note on Sections

These notes were first written as a statement on recent work on the structure of New Zealand intended to help students and visitors to the country. Most of the text was completed when the new coloured geological map of New Zealand appeared (late 1948). With the object of making the paper more useful to the New Zealand student the writer has added sections based on published and unpublished information and the new geological maps formed the basis of large parts of the sections. In devising these sections the author is grateful to the following students who assisted him as follows:—Section DE,

FG, JK—Mr. P. Vella; Section NO—Mr. T. Grant-Taylor; some of Section PQ—Mr. D. McBeath. The information of unpublished theses by R. A. Couper and P. Vella is contained in Section JK.

New Zealand stage names have been retained on these sections, since several do not correspond exactly to the European divisions. The approximate correspondence is given in the legend and text.

The help of colleagues in the Geological Survey who generously offered oral information on details is acknowledged in the text.

Parts of all the sections are likely to be wrong even at the time of publication, especially those portions which were entirely compiled from the small scale geological map without access to unpublished reports. Nevertheless, it seems desirable to present them with their imperfections, for detailed studies within New Zealand have advanced far ahead of simple general statements, leaving a difficult gap for the student or stranger to bridge. To aim at great precision on various points would involve much more inquiry with consequent delay. The inspiration for these sketches lies partly in the early sections of workers on the old Geological Survey, particularly Hector. The table of orogenies is an attempt to outline in sweeping fashion the stratigraphic evidence bearing on fold movements. Professors Cotton and Kuenen have read the text critically and the writer is indebted to them for useful suggestions. Generous help, with pertinent criticism, has been proffered by Professor Benson, to whom the writer is deeply grateful. A number of his suggested improvements and additions to the bibliography have been incorporated in the text.

Whilst the information of most writers quoted in the text has contributed to the cross-sections, the most useful papers are those including sections by the following authors: Bell, Benson, Couper, Cox, Ferrar, Grange, Hector. Henderson, Hutton, McKay, Marwick, Macpherson, Ongley, Park, Vella, Williams, Willett. (Some of these await publication.)

Structural Outline

The main structural outline of New Zealand shown on the early maps of Hector and Hutton has been little altered by subsequent work, and the two coloured geological maps now published by the Survey bring out even more forcibly the dominant trends established by the pioneers. The impression of a general north-east trend shown by the coast line and mountain chains is accentuated by the great axial range of Mesozoic strata, largely Triassic and Jurassic and including some Permian (the primary fold, p. 8, of Macpherson, 1946) that extends in the North Island from the Bay of Plenty to Cook Strait. In the South Island an axial chain which also consists of Jurassic, Triassic and probably late Palaeozoic rocks, continues from the south of Nelson Province to Mount Aspiring. This north-east trend is indeed further accentuated on the new map by the interpolation of the great Alpine Fault along the western slope of the Southern Alps, a fault which has long been known in part but whose full extent has been best demonstrated by Wellman and Willett. East of the Alpine Fault the ranges consist only of greywacke and crystalline schists, flanked farther east by Cretaceous and Tertiary sediments. West of the fault lie granitic batholiths, schists which have suffered contact as well as regional metamorphism (Benson, 1928), rocks of

age as early as Cambrian, as well as Mesozoic and Tertiary rocks—a much more varied and complicated group of rocks. This fault, then, is a radical line in the New Zealand structural plan which requires fuller discussion later. It recalls the Median Line of Japan in many respects (Yehara).

The structure shown by the strata within the axial chain, both in the South and North Islands, is little known, but the chain can be accepted as constituting a much-faulted complex anticline in the dominant late Tertiary structural pattern. An ancient erosion surface is carved on the greywacke at many localities, and at the Manawatu Gorge (North Island) this surface and its covering of Pliocene beds form a broad anticline, striking north-east and broken by a great fault on its eastern edge (Ongley, 1935). Elsewhere in the North Island the structure of this axial chain presumably showns complications based on a similar pattern. There is marked axial pitch at the Manawatu Gorge and evidence of similar axial pitch on all the erosion surfaces of the greywacke “highs” which appear below the Tertiary in the country flanking the axial range to the east. Macpherson's map shows for the North Island several anticlinal ridges with greywacke cores whose general structure can be considered as rather similar to that of the axial chain.

Late Cretaceous and Tertiary Fold-movements

movements. Locally the base of the upper Senonian (Mangatu formation) is marked by giant boulder beds. In other places it is difficult to separate upper and lower Senonian. The evidence is too complicated to be cited here.

The Importance of Faulting in Tertiary Earth-movements

Early workers in New Zealand were quick to recognise great faults, and Cotton has stressed their existence in elaborating his views on geomorphology, but he has also described folds accompanying the faults (p. 60, 1916b, p. 91, 1925). From the structural as well as the physiographic aspect, the faults are certainly remarkable, but the geologist new to the country may find the nomenclature of some local geological papers between the years, say, 1920 and 1940, a little misleading. The structure of a tract of country may be entirely described in terms of “blocks”, more or less “tilted”, but the stranger, perhaps with a bias to deciphering structure in terms of the growing anticline, comes back from the same field with a mental picture of anticlines more or less pitching or closing, broken by immense faults along one limb. Also, many of the mapped “faults” can, on closer examination, be replaced by flexures (e.g. Wellman, pages 193–194, 1946). The term “block” may be convenient, and may even be correct (although unhappy in its implications): the term “tilt”, however, is actually misleading since it cannot be construed to cover the observed swing in strike of Tertiary strata sympathetic with the swing in strike of the underlying fossil erosion plane near the extremities of a greywacke “high”. The Saxonian nature of the folding and, indeed, the general significance of folds in the New Zealand tectonic pattern was first stressed by Benson (1930) and is well illustrated in his maps of Eastern Otago (1941). To-day the field worker tends to see his faults in most places as part of a general fold pattern, and an elongated dome or anticline can be visualised as one of the dominant “ancestral” forms for many of the fault-bounded structural “highs”. The descriptions of to-day are more akin to those of the earlier geological surveyors in containing a liberal sprinkling of anticlines and synclines. The faults are usually arranged in an echelon pattern and some care is necessary in reading small-scale maps like the Geological Survey map of 1948 because the trends of faults are usually slightly oblique to the general trend of the great axial chain of greywackes shown on this map.

Relations of Tertiary to Older Trends

It is now generally agreed that the trend between north-east and north-north-east results from the late Tertiary Kaikoura Orogeny and its precursor movements, for it is the dominant strike in most Tertiary strata. Moreover, it many fields where this fold trend is dominant the belts of facies in Cretaceous and Tertiary strata are roughly parallel, suggesting sedimentation in a framework of similar trend. In certain fields the evidence even points to a parallel strike in the greywacke strata, so that hypotheses can be advanced postulating Mesozoic and Tertiary geosynclines geographically coincident and with facies aligned parallel to the succeeding Kaikoura folds. Such a concept underlies parts of Macpherson's maps. But it would be wrong to extend this picture involving continuity in strike to the whole country,

for in certain places the strikes of Triassic and Jurassic greywacke are different from those of the Cretaceous and Tertiary strata. In such places these more ancient rocks show strong isoclinal folds much broken by faults and thrusts. The strikes of the actual fold axes are difficult to determine, for pitch is often considerable, but it is clear that a regional north-west strike of axes is in many of these localities common in the Mesozoic and sometimes older greywacke, although nearby Tertiary beds may show a marked north-east strike. Thus, it has been observed occasionally that where Mesozoic greywacke abuts against faults bounding Tertiary strata, the highly sheared greywacke beds strike parallel to the fault lines, but median parts of the same masses of greywacke may show regular strikes with a roughly northwestern trend. Further data on strikes within the pre-Cretaceous rocks will be presented later.

At a first glance one is apt to cavil at Macpherson's map of late Cretaceous and Tertiary structures, because, while in some places the trend lines are based only on the Kaikoura folds and faults bounding the greywacke cores, in other places the strikes seem to be based on measurements within the more ancient strata. Such criticism is not entirely just, however, for in many places he has backed up his acceptance of the latter strikes by indicating similar trends in the neighbouring Tertiary or Cretaceous strata. Macpherson was fully aware of complications. He wrote (p. 9):

“They are late Cretaceous and Tertiary basement folds developed on a subdued mature-land (new term: Willis, 1928) of lower and middle Mesozoic rocks. Their axial trends may in some cases be inherited from an earlier diastrophic cycle, but we have so little knowledge of the internal structure of the basement folds that it is preferable to regard the surface cut on the basement rocks as a datum of reference when studying the late Cretaceous and Tertiary folds of the covering beds that envelop them. Observations show that the foldings of the diastrophic cycle concerned here arched the basement rocks along trends that diverged from the trends of an older diastrophic cycle.”

And yet, in the structure of the South Island, and particularly Southland (p. 10) the strikes in ancient rocks seem to form the most important part of his argument in favour of an arcuate structure.

The New Zealand Recurved Arc

Indeed, the main thesis of Macpherson's paper is that New Zealand constitutes a recurved arc formed in the course of the late Cretaceous and particularly late Tertiary diastrophism. He rejects the idea of Marshall (1911) that the axial chain continues on a north-east trend towards the Tonga and Kermadec Islands, and in doing so he renders unnecessary Suess's idea of a syntaxis. By means of this syntaxis Suess joined the north-east trending fold system and the north-west trending chain of the North Auckland Peninsula somewhere in the Rotorua volcanic region, whose origin could perhaps be regarded as due to this crucial junction. Macpherson swings the trend of the axial range to assume a northerly direction near the Bay of Plenty, and considers that this is coincidental with a gradual regional swing to a north-west trend. Such gradual swing in strike is well seen on the West Coast of the North Island between Mokau and the Waikato River, and the north-north-west trend of faults bounding the Hauraki graben also fits the same picture. Macpherson cites also a marked north-west

Earlier Orogenies

Tertiary Kaikoura Orogeny with north-east trend, and particularly by the Alpine Fault. This interpretation has little good evidence to support it, except that of all the older pre-Tertiary rocks west of the Alpine Fault only the Greenland Series shows a dominant north-west trend. Alternatively, the Greenland Series may have been folded at a different earlier period.

It may be well here to anticipate by giving a view developed further in the present paper. The likelihood of renewal of movement along old trends has been discussed by several New Zealand writers, particularly Benson (1941). Such renewed folding is here regarded as the key to the north-west striking portions of Macpherson's recurved arc ascribed largely to late Cretaceous and Tertiary diastrophism. These are likely to be resuscitated trends first stamped on the rocks in the post-Hokonui Orogeny or even earlier. Although not all the folds of one period of orogeny will show a particular trend exclusively, it is nevertheless likely that the trend will be dominant. It is probably significant that in those areas where the greywacke does not strike north-west, the regional strike in these older rocks is north or north-east and commonly parallel to that of the adjacent Cretaceous and/or Tertiary strata. The Nelson region and the west coast of the North Island require further discussion later in so far as the more ancient and Tertiary strikes are there parallel.

Pre-Hokonui Orogenies

An attempt to disentangle orogenies even earlier than the Hokonui was made by Hutton (1900, p. 166), who postulated a Mid-Devonian folding with a north-east trend. Park (1921) revived this conception in a list of orogenies of doubtful value.

There is a great gap in our knowledge between strata containing Devonian fossils (found at Baton River and Reefton) and the Permo-Carboniferous fossiliferous strata of Nelson. The Devonian age and the north-east strike inferred for the folding were probably based on McKay's observation (1879, pp. 125–126) that a north-east strike appears in the Baton River beds, since shown by Shirley to be of Lower Devonian age.^* It is possible that most of the north-east strikes recorded in these beds are due to Tertiary faults and folding. The position of these Devonian beds may be similar to the Lower Devonian beds at Reefton (Allan, 1935) described by Henderson (1917, pp. 74–77) as being intensely faulted and sheared with accompanying Miocene beds. Discarding strikes in the obscure Devonian outcrops, some more consistent results can be obtained in the north-west Nelson district from the Lower Palaeozoic strata, in places fossiliferous. In the Mount Arthur beds, in part Ordovician, and certainly all Lower Palaeozoic, a general northerly trend was recorded by McKay (1879, p. 125), and the Ordovician rocks of the original Aorere Series in Collingwood Subdivision, N.W. Nelson (Ongley and Macpherson, 1923) show a similar strike. In the so-called “Aorere” Series of Reefton, for which Macpherson and Gage suggest a Devonian age

Similarity between South-west and North-west Parts of the South Island

Whether or not the Clinton River complex is partly of Mesozoic age, all the country lying between Lake Te Anau and the south-west corner of the South Island recalls roughly in its structural and stratigraphical ensemble the north-west corner of the island. If the south-west corner represents a coign—a foreland—for Hobbs, so also must the mass of ancient rocks at the north-west extremity. Ignoring detail and theorising sweepingly, a similar pattern can be seen in the south-west and north-west parts of the island, thus:

The positions of the two thrusts do not fit into the pattern nicely.

The writer is aware that this parallelism is already envisaged in part or in whole by colleagues in the Geological Survey, notably Mr. H. Wellman, who first insisted in conversation on a close similarity between the stratigraphy and structure of the Hokonui and Nelson synclines. The position here assigned to the Alpine Fault in the Nelson district, namely as continuing along the Wairan Fault east of the Marlborough schists, is that drawn on the Survey map,^* and may be queried by those who know this field more intimately. One merit in the scheme is that folded Tertiary beds fit into part of the picture, so that we are certainly dealing to some extent with late Tertiary diastrophism. On such parallels are based Hobbs’ suggestion of Alpine analogies and Wellman's interesting but tentative and unpublished discussions of possible immense transcurrent displacements. Until more detailed supporting evidence is forthcoming, the suggested parallels must be treated with great reserve, for they are partly dependent on comparing metamorphic rocks on which the petrographic information is very incomplete.

Original Extent of Tertiary Strata Flanking the Alpine Fault: Movement on the Fault

Park believed the Clinton River complex to continue south-eastwards into the Longwood Mountains, east of the Waiau River, and reappear on the coast at Riverton and Bluff; Macpherson (p. 10 and map) believed the outcrop of the complex to swing in a northwesterly directed curve through these points, and he deleted for purposes of clarity the Tertiary strata known to be of some thickness at the mouth of the Waiau Valley. In this manner he partially obliterated the southern extremity of the Waiau syncline, which has a general northerly orientation. Presumably geophysical evidence obtained at Orepuki, at the mouth of the Waiau River, partly justifies this procedure, but one is still inclined to consider that the general orientation of the Waiau Valley is more significant of late Tertiary diastrophic trends than is the strike of the Clinton River complex. The rocks of the Clinton River complex cannot be younger than early Mesozoic (and may well be much older), and Macpherson's view seems to accept the strike within this formation besides the trend of its margins, as indicative of late Tertiary trend lines. It is likely that Macpherson is referring to the Waiau syncline when he writes (p. 11): “In a minor fold of the major syncline late Cretaceous and early Tertiary terrestrial sediments and post-Eocene marine beds are involved. However, the Tertiary syncline although it curves with the regional arcuate structure, does not generally follow the major syncline or axes in the Mesozoic sediment, except where the major syncline peters out to the north-west.”

Following the Waiau syncline to the north, the Tertiary strata are seen to be folded between the Permian beds prolonging the southern limb of the Hokonui syncline and the rocks of the Clinton River complex. Tertiary strata can also be followed, deeply involved in the older rocks, over the Homer Saddle and Lake Fergus, immediately north of Lake Te Anau (Wellman and Willett, p. 299; Benson, 1935, p. 9). We can tentatively regard these mid-Tertiary beds as formerly continuous with those mapped along the coast west of the Alpine Fault in South Westland.

If we are to accept Macpherson's view concerning the great “Otago thrust”, it would have to be regarded as tectonically a much more significant branch than the seaward prolongation of the Alpine Fault, although Wellman and Willett insist on the dominance of the latter in their field mapping. The writer, however, would prefer to see any southern prolongation of this fault as following the western side of the Waiau Valley; for the displacement would then be defined in terms of deformed Tertiary strata. There has been great movement on the Alpine Fault in late or post-Tertiary time, although it may have been initiated in earlier times, but the latest movement on Macpherson's Otago overthrust, if such really exists, cannot be ascribed to late-Tertiary diastrophism: a glance at the geological map indicates that near the Mataura River, some fifty miles north-north-east of Bluff, Oligocene strata spread over any possible trace of the Otago thrust.

Wellman and Willett in their instructive paper also discuss the Tertiary history of the Southern Alps, pointing out that little is known of the surface on which the Tertiary strata were deposited, and that land on the site of the Southern Alps may well have existed before the Tertiary period. The distribution of “mid-Tertiary beds and the absence of lower Tertiary beds suggests that in mid-Tertiary time the lower Tertiary sea transgressed both along the southern part of the West Coast and eastward over western Otago and parts of adjoining Southland. The sea may not have extended over what is now the higher part of the Southern Alps,… the Alps have nevertheless since been elevated along a pre-Tertiary and possibly Mesozoic trend line.” (The Alpine Fault was regarded by Morgan as chiefly early Cretaceous in origin.) “The schist belt which lies along this line may represent a positive unit which has been intermittently uplifted in a similar manner at other times in the past.” The same authors point out that the Tertiary beds are most intensely deformed along the line of the Southern Alps (p. 303), and they postulate an uplift of about 10,000 feet along the Alpine Fault in later Tertiary time (approximately mid-Pliocene, but believe like most writers, particularly Benson and Cotton, that after this uplift the surface was reduced to a late mature surface of low relief. The present physiography of the Alps is ascribed to erosion of this peneplain (Wellman and Willett, p. 304), but the throw of 10,000 feet need not be necessarily concentrated into later Tertiary time, for the estimate of Wellman and Willett is based on the deformation of a peneplain surface alone, there being no Tertiary outliers immediately east of the Alpine Fault. The same authors also point out that the Tertiary beds where deeply involved in faults, as at the outcrops intervening between the Waiau Valley and the Tertiary of Jackson Bay, are so indurated as to be easily confused with the rocks of the older undermass (p. 303).

Greenstones

Greenstones of various types, including serpentinite, peridotite, talc schist, tremolite schist, etc., are aligned parallel to but not along the trace of the Alpine Fault, and their occurrences have been summarised by Benson (1926, pp. 42–44). C. O. Hutton has also described serpentinites and gabbros in the Livingstone Range, in western Otago (1937); and Turner, peridotites and serpentinites in the Cascade Valley (1930), South Westland.

Many of the rocks occur as intrusions, generally of sill-like character, commonly in schists belonging to the Otago schists or Arahura Series, or sediments of Mesozoic age belonging to the comprehensive Hokonui System, so that they have been provisionally correlated with the post-Hokonui fold movements, probably early Cretaceous.

Occurrences of greenstone that must have been emplaced at other periods are also known. At Auckland, Turner and Bartrum (1928, pp. 871–873) describe serpentinites and other ultrabasics as intruded in an orogeny later than the Cretaceous beds and preceding the deposition of the first Tertiary, presumably an early Tertiary orogeny (Bartrum, 1934; Benson, 1924, p. 130). They also describe (1928) pillow lavas, serpentinites, etc., of early Tertiary emplacement in the North Cape area. Fleming (1947) describes a serpentinite in contact with Oligocene and Miocene sediments near the Mokau River and gives good evidence for regarding its present position as due to a diapir thrust.

There are many other occurrences which cannot be mentioned here, and a complete restatement concerning all the greenstones of New Zealand and their relations to structure is highly desirable, for the concept of diapirism has been insufficiently considered.

More Detailed Discussion of Selected Regions

more conveniently regarded as an early expression of the second folding along an approximately north-east trend.

Now, evidently in a pattern showing such a diversity of trends formed within a small area and in a comparatively short lapse of time it is difficult to aver that trends definitely curve, for one may be joining the fold trends formed at different periods in a pattern which is essentially criss-cross. It may be legitimate to group the dominant structural outlines produced by several fold movements within a certain lapse of time as constituting an arc, but the existence of such an arc by no means invalidates Suess's idea of the north-east trend continuing towards the western edge of the Tonga deep. A glance at the new Geological Survey map gives no indication of the major structural swing postulated by Macpherson: instead, a major anticline striking north-east appears to be abruptly broken by west-north-westerly faults. To quote Ongley and Macpherson again: “The structure of the Tertiary beds in the north-east of the subdivision is dominated” [the writer's italics] “by faults rather than folds”, but the faults actually chop abruptly across the folds and there is no clear evidence of a swing in strike. Furthermore, if we accept a dominant pattern of folds and faults developed in the course of several consecutive fold movements as constituting an arc, the term syntaxis must be equally valid for apparently branching folds formed during several similar movements. Moreover, Fleming (unpublished) has recently cited important evidence, based on submarine contours, for believing that the Taupo graben can be traced as a trench for hundreds of miles towards the Kermadec Islands. Following Healy's discovery of marine Pliocene strata at Matata and Ohiwa, on the Bay of Plenty, Fleming considers that the trench must, at least in part, have been formed very late in Pliocene or even in Pleistocene times.

The Taitai Nappe

Macpherson regarded the Taitai rocks (of Aptian age), apparently overlying younger Cretaceous rocks, as evidence for an eastern over-thrust of some forty miles, also noting that the klippe-like masses appear to be concentrated in or near the Tapuwaeroa syncline. The emplacement of this nappe is regarded by Macpherson, very tentatively, as immediately anterior to the later Senonian, and there is stratigraphic evidence for a regional orogeny at this time, although there is no very pronounced early-formed north-east or north-striking fold and fracture pattern in the Cretaceous rocks such as might be expected with Macpherson's postulated thrust. The school of Grenoble, and particularly Schneegans, have returned to the concept of immense gravity slides of rock-masses as an explanation of some nappe structures, a process which was originally suggested in Schardt's revolutionary papers on the Pre-Alps and which Lugeon and Schneegans describe. If the Taitai rocks really represent klippen, such a process^* can readily be imagined as causing their emplacement as a result of an east-south-easterly tilt suggested by the pitch of folds affecting only Cretaceous rocks. The concentration of the klippen in the Tapuwaeroa syncline is also readily explained. This process

seems more in keeping with the regional tectonics than one of tremendous compressive folding in late Cretaceous time.

The interpretation of the Taitai rocks in Waiapu as klippen may, however, be completely denied, for the evidence is doubtful, and if the rocks are truly Aptian a diapir remains a possible explanation.

The example of Waiapu serves as a warning not to be dogmatic regarding constancy of trend throughout the movements of Cretaceous and Tertiary times. It is important, nevertheless, that where the Cretaceous and Tertiary strata show a dominant north-east strike, a comparatively simple pattern results with little or no cross-folding or faulting. On the other hand, where a north-west strike is common in Cretaceous and Tertiary rocks the pattern is always more complex, with some evidence of movement producing two strikes, often at right angles to each other. The Waiapu district also introduces us to Tertiary structural patterns that, although dominated by north-east strike, show minor transverse faults and folds.

The North Auckland Peninsula and the Auckland Region

The North Auckland Peninsula has been covered in some detail by Geological Survey bulletins, but both the structure and stratigraphy remain obscure in many places. The strata include Mesozoic greywackes, Cretaceous argillites, and Tertiary sandstones and mudstones, with also many Tertiary lava flows, and the Tertiary strata show many overlaps and unconformities. The outcrops, moreover, are very deeply weathered.

At the time of mapping, correlation by Tertiary fossils was on uncertain grounds. To add to the difficulties, it is likely that in some places the Tertiary beds were deposited in earlier-formed fault-angle depressions, whereas in other places the faulting followed the deposition of the Tertiary strata; but it is difficult to separate everywhere the structures according to age.

The dominant faults, those bounding the main outcrops of Mesozoic greywacke and adjacent Tertiary beds, strike mostly north-west, but there are numerous important cross fractures, some striking northeast and many roughly east-north-east. Comparatively few strikes of strata are recorded on the map and those few have a bewildering diversity, suggesting folding along varying trends, but some of the strikes and dips recorded in the Tertiary strata may well be primary dips due to sedimentation or compaction. The relations of the lavas to underlying rocks are also obscure and the whole region calls for a synthetic statement by a worker knowing the field intimately; but at the moment it seems clear that the north-west fabric is very considerably complicated by a cross fabric. Ferrar's (p. 33, 1925) description of quartzite “coulisses”, nearly vertical beds in the Triassic-Jurassic rocks, implies that their north-west trend was imparted in an orogeny preceding the deposition of the late Cretaceous strata, presumably the post-Hokonui (early Cretaceous) orogeny.

The vicinity of Auckland city has been described by Professor Bartrum and his students over a period of years (Turner, Searle, Laws, Firth, Lyons, and the authors of several unpublished theses). Firth's description of the Papakura-Hunua region immediately south

of Auckland City exemplifies clearly the Tertiary structures typical of the whole region. He describes two sets of faults, forming on the map a set of rough parallelograms, but he recognises clearly that the movements on faults parallel to one direction are in some places earlier, in others later, than movements on faults belonging to the other set. For such a structural pattern the term “block-faulting” in its strict sense seems very apt, as indeed it does also for the Tertiary structures over most of the North Auckland Peninsula. Bartrum in a synopsis (1949) of the Tertiary history of Auckland City gives evidence for alternating submergence and emergence. The Pareora series is absent and the base of the Waitemata sandstones (of early Miocene age) consists of great boulder beds containing igneous material from the “lost” hinterland which lay west of New Zealand. The Waitemata beds near Auckland show in places conspicuous but irregular folds formed possibly by sub-aqueous slumping, as suggested by Kuenen and Shepard during a visit to the city.

The Hauraki graben is bounded by faults striking approximately north-south, and these are cited by Macpherson as evidence for the general swing in strike which appears clearly along the west coast, and whose existence we have queried on the east coast. East of the Hauraki graben lies the Coromandel Peninsula, largely formed of Tertiary volcanic rocks, and the Geological Survey Bulletins on this region have generally agreed that the volcanism is likely to have commenced along early-formed fractures on the lines of those which now bound the graben. (A convenient and elementary summary by Bartrum, 1930, is listed.)

No attempt is made here to describe the Tertiary and Recent volcanicity of the North Island other than to note that the general concensus of opinion dates the graben of Taupo as formed later than the earliest volcanic outbursts, with fault movement continuing till the present day (Grange, p. 55, 1937). On the other hand it is evident from Healy's description (cyclostyled itinerary for the Pacific Science Congress, 1949) that considerable faulting occurred in the early Pliocene, and that the late Pliocene volcanicity is likely to have originated along such fractures.

The West Coast of the North Island

The West Coast between the Waikato and Mokau rivers is remarkable for the strong meridional strike shown by the Mesozoie greywacke (including fosailiferous Triassic and Jurassic beds). The Tertiary strata, dipping much less steeply, also show the same strike. The latter form several fault-bounded folds clearly marked on Macpherson's map (1946), which distinguishes three principal anticlines, with also one prominent syncline of Tertiary strata as described in the recent Te Kuiti bulletin by Marwick (1946). This field has been covered in detail by several workers, including Ferrar, Grange, Henderson, Marwick, Ongley, Taylor, and Williamson. Their results from adjoining areas tally closely in stressing the great thickness of Mesozoic strata (approximately 28,000 feet), with a lesser thickness of Tertiary beds (approximately 4,000 feet in Te Kuiti region). Cretaceous strata, of considerable thickness on the eastern side of the island, are entirely absent to the west, and the Upper Oligocene (Pareora Series), absent to the east, outcrops on the western side.

It is worthy of note that the cross fractures throughout the southern part of the coastal belt covered by the Te Kuiti bulletin, some 30 miles wide and 30 miles long, are subordinate and of little throw, but increase in number and size north of Kawhia Harbour (i.e. approaching Auckland), where they appear as two sets of faults showing a strike either dominantly east-north-east or north-north-east.

The stretch of comparatively homogeneous fold pattern seen in the Te Kuiti district is the most convincing evidence for the swing of strike required by Macpherson in his postulated arc structure.

Macpherson prolongs the axis of the Tertiary folds southward and east of Mount Egmont and runs them out to sea with a slight curvature.

Wellman, in oral description, has stressed stratigraphical similarities between the Mesozoic rocks of this Waikato-Mokau stretch and the Mesozoic rocks near Nelson, in the South Island, and considers them to have formed part of one geosyncline existing in both Mesozoic and Tertiary times. The rocks of both groups show in general parallel strikes, although the Mesozoic beds are more highly folded than the Tertiary. Wellman's interpretation seems acceptable, and there appears to lie between the Te Kuiti region and Nelson a tract of country where the north-west element in the folds affecting the Mesozoic is entirely suppressed.

Marwick (1946, p. 11) points out that in Te Kuiti district the principal fold movements appear to have occurred in late Miocene post-Tongopurutan times: “The movements presumably represent the Kaikoura Orogeny (Cotton, 1916) and indications are that, here, they were completed relatively early, perhaps before the end of the Miocene and at the latest in the early Pliocene (Waitotaran). After the orogeny, there ensued a fairly long period of stability during which the soft Tertiary rocks were stripped from the high blocks and peneplained… Then came an uplift of several hundred feet… In the Upper Pliocene the vast quantities of ignimbrite that invaded the subdivision from the south-east filled the main valleys and submerged much of the low country…”

South of Mount Egmont, only Pliocene and later beds are visible and they show a general slight south-westerly down-tilt, to be correlated with some differential uprise in the axial range in the vicinity of the Taupo region (M. Te Punga, unpublished thesis). Fleming has redescribed the whole classic Wanganui area of Pliocene sediments in an unpublished bulletin, and has told the writer that although the Pliocene beds must be generally interpreted as smoothly dipping, there are traces of minor folds with axes likely to be coincident with those of folds mapped by Macpherson (1946) to the north. Fleming therefore deduces some very late, but minor, folding.

The Axial Chain in the North Island

The structure of the axial chain is most imperfectly known and the dominant trends on maps are obviously north-east, following enormous faults, many of them formed in very late Tertiary times (post-Castlecliffian, i.e. late Pliocene or even Pleistocene).

A few scattered observations made by the writer suggest that within the least disturbed greywackes and argillites of the axial range there are stretches showing a general north-west strike, which may vary from

west-north-west to north-north-west, although the more sheared grey-wackes on the margins of great late Tertiary faults appear to show a north-easterly strike. This slight evidence is too inconclusive as yet, however, to substantiate a theory of the existence of a general ancient north-west strike within the greywackes forming the axial chain of the North Island.

These greywackes are certainly in part Mesozoic in age, as indicated by the discovery of a single vertebra of an ichthyosaur at Wellington (Benson, 1921), but the stratigraphy is for the most part obscure. Forming a tectonic unit quite distinct from those on the west coast in the Mokau-Waikato area, these rocks may be partly older and perhaps include some Palaeozoic strata.

East Coast of the North Island, from Hawke Bay to Cook Strait

East of the axial chain, the north-east trend already seen in the Tertiary strata north of Poverty Bay continues markedly impressed on all the upper Cretaceous and Tertiary strata from Poverty Bay to Cook Strait. This part of the country is already covered by reconnaissance reports by McKay and more recently, in detail, by Henderson and Ongley in Gisborne and Eketahuna subdivisions, by several other officers of the Geological Survey, and by oil geologists.

In general, from Hawke Bay to Cook Strait, the facies of late Cretaceous and Tertiary sediments appear to be aligned in belts roughly parallel to the north-east strike of the late Tertiary folds, indicating that some folding or faulting along this trend had probably already occurred in early Cretaceous and/or earlier times.

The structure revealed by Cretaceous and Tertiary beds in many places consists essentially of very elongated domes which, although broken by great faults on their eastern limbs, show a truly anticlinal disposition of the erosion surface, which separates the greywacke cores of the folds from the Tertiary cover.

The region constituting the Dannevirke Subdivision, east of the Manawatu Gorge and the Ruahine Range, is of stratigraphic interest in containing localities which show a complete passage from the late Cretaceous through Paleocene to Eocene stages as demonstrated by the detailed examinations of foraminifera carried out by Finlay. The localities of complete passage are concentrated on the margins of a major anticline in the centre of Dannevirke subdivision, while anticlines east and west give good evidence of non-sequences, unconformities and clastic deposition in the late Cretaceous and early Tertiary. It appears likely that during pre-Pliocene time there was progressive overlap of Tertiary sediments towards the axial chain of the Ruahine Range, with the deepest sedimentation near the major central anticline.

The Upper Oligocene (Pareora Series) is completely absent south of Hawke Bay, and its presence further north is doubtful. In parts of Waiapu and Poverty Bay district, Henderson, Macpherson, and Ongley have found prominent conglomerates developed at the base of beds representing the lower Miocene (Southland Series). The Pareora Series is absent in many other parts of New Zealand and obviously about Late Oligocene time some fold movement occurred which, although subordinate to the post-Pliocene movements, must

yet have been considerable. Again the influx of coarse clastics in the late lower Miocene (Upper Southland) makes a second period of widespread precursor movement at that time very likely.

The concentration of the greatest thickness of Pliocene beds west of the major anticline, and in places the eastward overstep and truncation of early Pliocene members by later ones, suggest that the main trough of Tertiary deposition migrated markedly westwards, with movement at the beginning of the Pliocene, through the influence of early development of the major anticline in the centre of the Dannevirke subdivision. Such movement seems to have continued intermittently during the Pliocene. The principal trough of Pliocene deposition seems to have lain between the early-rising central anticline and the Ruahine Range already largely emergent. Here, then, is a tract of country where the concept of the persistent “high” appears to be invalid, although there is good evidence of an anticline persistent throughout late Cretaceous and Eocene times on the present coast east of the major anticline.

This widespread early Pliocene movement inferred by the writer in Dannevirke subdivision can be compared with the movements described by Marwick in Te Kuiti as “before the end of the Miocene and at the latest in the early Pliocene”. They can be accepted as approximately contemporaneous, and both areas flank the axial chain, although the Te Kuiti subdivision is more distant from it. Now, in all the region from Hawke Bay to Cook Strait, the Pliocene beds have been very considerably folded and faulted by very late Pliocene movement and the writer has in this field restricted the term Kaikoura to these late movements. It appears, therefore, that along the axial chain and near it, great post-Pliocene fold movements occurred, but that farther away, on the west coast, these movements had the effect only of imparting a westward down-tilt, with folding very subordinate.

The axial chain shows remnants of an old erosion surface to which Waghorn, Cotton, and Ongley (1935) have called attention, and this is dated by the fact that it is covered by very shallow water Pliocene sediments in a few places. At the Manawatu Gorge these Pliocene beds form an anticline on an axial depression on the range, and Fleming and the writer (1941) have considered this to be a strait in Pliocene time. In another paper (as yet unpublished) the writer calls attention to this transverse depression, which appears to be ancient and yet has continued as a region of maximum axial pitch until recent times. The local strike within the greywacke strata is roughly parallel to the course of the transverse river. The Dannevirke major syncline flanking the Ruahine Range appears to have been already an elongated basin at the end of Pliocene time and the writer interprets the course of the Manawatu in this syncline east of the Ruahine as directly consequent. In its early history it is inferred to have drained the shrinking mud-flats of the infilled Pliocene basin towards and westward through the strait.

Lower Cretaceous (Aptian) Strata and the Post-Hokonui Orogeny

Macpherson's conception of the Taitai overthrust has already been discussed, but the Aptian age ascribed to the rocks of the Taitai series is of more general importance as it may affect the dating of the great

post-Hokonui Orogeny. The genera Maccoyella and Aucellina, considered to be Aptian (Finlay and Marwick, p. 17, in “The Outline of the Geology of New Zealand,” 1948), have not been found at Taitai, but at Koranga, some thirty-five miles west-north-west of Poverty Bay, and Aucellina in rocks of similar lithology in southern Hawke Bay. Large tracts of unfossiliferous greywacke and argillite on the south-east side of the North Island have been provisionally assigned to the Taitai series owing to resemblances in lithology and degree of induration. An abundance of basic igneous pebbles is supposed tentatively to characterise the conglomerates among these strata, but in degree of induration and of deformation, and by general lithology the rocks ascribed to the Taitai series over large tracts are indistinguishable from those which in the axial range are ascribed to the comprehensive Trias-Jura group. If the Aptian age is valid, some of the post-Hokonui movements may well be of age as late as post-Aptian, judging from the deformed state of the Taitai rocks. But it may well be that two orogenies were concentrated into the period between late Jurassic and post-Aptian time.

Outliers of Tertiary near Wellington: Wellington: Cook Strait

Apart from the Pliocene beds at the Manawatu Gorge, two other occurrences of Tertiary beds are known in the axial ranges. One of these, described by Macpherson (1949), is near Paraparaumu on the west coast some 37 miles north-east of Wellington, where beds of Lower Oligocene age occur in an infaulted block bounded by greywacke on all sides. The other beds, at Makara, near Wellington, appear to be of Pliocene age (Gage, 1940) and may be infaulted in the greywacke. These outcrops give evidence of the former extent of Tertiary beds now almost completely removed and of the great Tertiary movements which have dislocated them.

Cotton has described many of the geomorphic features around Wellington. Both the peneplains and the faults there are likely to be largely of post-Pliocene date and give evidence of great differential movement. But little is known of the earlier geological history of the Wellington district, since the approach appears to lie only in a patient mapping of highly crumpled and sheared greywackes or in a geomorphic attack through the correlation of peneplain remnants which lack Tertiary cover.

A zone, or zones, of red rocks, some of which are variolites, appears at several points along the Rimutaka Ranges, but at the moment it is premature to link all the outcrops of red rocks as marking an approximate strike line. H. Fyfe (unpublished) has recently shown that some of these red rocks in the Rimutaka Ranges are pillow lavas, in occurrence similar to those at Wellington (Broadgate, 1916; Benson, 1921, p. 18; Wellman, 1949), but at other localities they are jaspillites and possibly radiolarites.

The recently published geological maps indicate that it is quite feasible to conceive of the axial ranges as continuing across Cook Strait, and the latter may mark either a region of marked axial pitch or some transverse fracture. Certainly, L. C. King's (1939) suggestion of a lateral displacement in the nature of continental drift is unnecessary and is based more on correlation by physiography than on correlation of structural features. Some more detailed pictures of the relations of

structural elements in the North and South Islands to each other is, nevertheless, desirable, and C. A. Fleming has developed views (as yet unpublished) based partly on submarine morphology of Cook Strait which will help to fill this need.

The South Island: Canterbury, Marlborough, and Westland

The whole of the north-east side of the South Island, including Marlborough and most of the Canterbury province, is dominated by north-east-striking folds and faults formed chiefly by the late Tertiary movements and broken by a few cross faults of almost east-west trend. Indeed, it was in this region that McKay first recognised the importance of the late Tertiary orogeny. Reconnaissance reports by Fyfe and Healy give further descriptions of stratigraphy and structure.

Cretaceous and Tertiary stratigraphy has been described in considerable detail, but is outside the scope of this note; and the structural implications of the stratigraphy must be left to some other worker more conversant with the region.

For the region west of the Alpine Fault, the writer is unable to add much to the outline given earlier. The Greymouth coalfield has been surveyed in detail by officers of the Geological Survey and a detailed bulletin by Gage awaits publication. H. W. Wellman's studies on rank in the West Coast coals are also unpublished. The Tertiary strata of the West Coast yield good evidence indicating considerable mid-Tertiary earth movements. Wellman (1945) describes at Ross, south of Hokitika, a section through the Tertiary beds in which Pliocene (Waitotaran) strata rest with marked unconformity on Lower Oligocene, these earlier sediments, according to Wellman's tentative section, being folded into a recumbent syncline formed by movements preceding the Pliocene (Waitotaran). Gage (1945) and Gage and Wellman (1944) discuss further Tertiary sequences in Westland which contain conglomerates indicating earth movement during Tertiary time, as does also Wellman's description of the Fox River headwaters (1946). It seems likely that this area suffered locally movements comparable to those cited for Late Oligocene (Pareora), for Miocene (Upper Southland), and for early Pliocene times in southern Hawke Bay. These writers alone are able to synthesise this great field adequately.

Otago and Southland

Macpherson's views on the Otago and Southland districts have already been briefly outlined, and it is interesting to consider his views on late Cretaceous and Tertiary diastrophism in relation to earlier fold trends in that region.

It has long been known that the north-west trend of the Otago schists and the Hokonui syncline is of ancient origin. Cotton (1917, pp. 429–430) early recognised pre-Cretaceous faulting at the Shag Valley. Benson (1941, p. 216) summarises the position as regards the early history of the Shag Valley fault-zone, which strikes north-west and reaches the east coast some thirty miles north of Dunedin, as follows: “The fact that it has brought into apposition the Palaeozoic (?) Otago or Maniototo schist on the south-west with the Early Mesozoic (?) greywackes, etc., on the north-east, which were reduced

Further Comments on the Relations of Newer to Older Trends

Macpherson, in postulating a swing in the strike of the late Cretaceous and Tertiary folds to assume a north-west trend throughout Otago and Southland, is obviously reasoning from the regional structural plan and partly from the evidence of tectonics, i.e. folds in growth during these periods. But it remains an open question to what extent the latter evidence supports the north-west swing of strike as being a dominant feature of the late Cretaceous and Tertiary diastrophism. The north-east strike of eastern Otago seems to be relegated to the category of minor cross fracture and folding accom-

immediately applicable to the New Zealand pattern. Indeed, assuming a wildly speculative attitude, one might suppose that New Zealand lies on the intersection of two of Lake's great circles, those on which he located the centres of his ares of small circles.

Geomorphology in Relation to Structural Studies

The field worker in New Zealand carries a considerable amount of geomorphological ideas in his mental baggage, although his object may be solely structural and stratigraphical description. Many of the faults are first recognised by studying the physiography, and only later are they proved to dislocate strata. The recognition of ancient peneplains and fossil erosion surfaces, both Tertiary and early Cretaceous, is found to be essential in structural analysis in New Zealand, and the dislocations suffered by these surfaces are in many places the only reliable evidence bearing on the late Tertiary movements.

Recent transcurrent movement on faults in New Zeland is best demonstrated by the curious drainage pattern adjacent to the Alpine Fault near Jackson Bay. Wellman and Willett describe the Recent river courses along this fault as showing a remarkable displacement to the north-east immediately west of the Alpine Fault, the displacement for twelve rivers giving an average figure of 0·8 miles. Such transcurrent displacement over a long period could have produced lateral displacement on a great scale (compare Kennedy, 1946). H. Wellman has recently advanced the suggestion that dextral movement of approximately 300 miles along this fault has displaced the rocks west of the fault to the north-east. Thus he would account for the great distance separating areas of similar structure and stratigraphy on each side of the fault. An assessment of Wellman's view must await publication of his detailed evidence. Cotton (1947), in discussing the Alpine Fault, points out that some of the transcurrent movement along this north-east-striking fault could be absorbed by buckling along axes at right angles to the fault, and he cites the gentle south-westerly dip of a freshly cut marine platform, and other geomorphic evidence of local drowning, in support of this theory. It is instructive to compare the fold sequence of Waiapu with Cotton's suggestion for the recent pattern of warping. Such a mechanism can explain much of the New Zealand fold and fault pattern. Cotton (1948) also describes very clear geomorphic evidence at the Hope Fault near Hanmer, which shows transcurrent displacement of at least 8 feet, and for the fault in the axis of the valley of the Silver Stream near Wellington City, which shows a horizontal displacement of 130 feet. Faulting has continued intermittently on this line to the present day, and earthquake traces have been formed in very recent times.

This note has discussed geomorphology only insofar as it bears directly on the larger structures affecting Pliocene and older rocks and where other methods of approach have also been employed. There remains a wide field of geomorphological description covered by a voluminous literature, mostly by Cotton, and all more or less influenced by his teachings. The writer finds it impossible to summarise this aspect of the work. Certain of these papers are fundamental to understanding the large-scale structures, particularly in districts where the other

geological evidence is obscure. The vicinity of Wellington City is a typical example of such a district, and Cotton has devoted a number of papers to describing the downwarped Port Nicholson depression with a great late Tertiary fault bounding its western edge and running from the coast of Wellington along the Hutt Valley. Other important geomorphological papers bearing directly on the geological structure are cited in the list of references given below.

These topics are covered at length in Cotton's books, and a short paper by that author divides New Zealand into Geomorphic Provinces (1945).

In general, most recent papers tend to see a closer connection between tectonics and physiography. Thus, Cotton interprets the Hutt River as a stream initially installed in a fault-angle depression and thinks many major streams may be installed in early formed wrinkles of the earth's crust. From such streams directly reflecting tectonic pattern, he distinguishes others which he would define as structurally controlled, streams which have “worked down to find structural weaknesses” and, therefore, not directly indicative of the first-formed terrestrial pattern (1947). He has recently recognised a number of warpings of recent surfaces, some of them taking the form of gentle anticlines and synclines, but most of these have not yet been described in the literature. Interesting evidence of such warpings is cited by Cotton in the itinerary for a geological excursion in the North Island (Pacific Science Congress, 1949). This warping, or buckling, takes the form of gentle undulations with axes roughly oriented north-west, and is well seen near the Mohaka River (Hawke Bay). These recall the buckling which Cotton describes in discussing the Alpine Fault; but they have not been correlated with active trans-current faulting.

By combining geomorphology with detailed structural studies, there is good reason to hope that some continuity will be established between the palaeogeography of the later Tertiary and the morphological features of Recent times, even in those places where, as in large parts of the New Zealand region, fault and fold movements have intervened.

Conclusions

The structural plan of New Zealand is dominated by great folds and faults formed in late Tertiary times and generally ascribed to the “Kaikoura Orogeny”. Increasing evidence indicates that in some places the most considerable movements were concentrated into late Pliocene, possibly even early Pleistocene time, but that important precursor movements also took place earlier in the Tertiary, In other places the principal folding seems to have ceased in early Pliocene or even Miocene time, with only minor tilt and warping movements in the late Pliocene.

The rocks most deformed by Tertiary movements appear to be those which show evidence of late Pliocene movement, particularly in regions flanking the axial chain where Mesozoic and Palaeozoic strata are exposed.

The dominant strike of the Tertiary folds, particularly where of late Pliocene age, is north-east to north-north-east, but locally the

bably for one particular age of folding one trend is markedly dominant, but the folding over several ages—say within the late Cretaceous and Tertiary—may show many fluctuations from one extreme to the other. It seems likely that the repetition of folding along old trends may, particularly when the trends are so commonly north-east and north-west, be associated with the influence of some deeper texture in the earth.

References Cited

Allan, R. S., 1935. The Fauna of the Reefton Beds (Devonian), New Zealand. N.Z. Geol. Surv. Palaeont. Bull. 14.

Bartrum, J. A., 1930. The Geological History of the Thames Valley, Extract from Te Aroha Jubilee Book. (A very convenient summary for the visitor.)

—— 1934. The Pillow-lavas and Associated Rocks of North Cape Area. N.Z. Jour. Sci. Tech., vol. 10, pp. 158–9.

—— 1939. Interesting Phases of the Serpentines at Silverdale, Auckland. N.Z. Jour. Sci. Tech., vol. 20, pp. 311B–318B.

—— 1949. Auckland, New Zealand. Handbook presented to members of the Seventh Pacific Science Congress by Auckland Local Bodies.

Bartrum, J. A., and Branch, W. J., 1936. Geology of Bombay-Happy Valley Area, Franklin County, Auckland. Trans. Roy. Soc. N.Z., vol. 65, pp. 386–404.

Bartrum, J. A., and Turner, F. J., 1928. Pillow-lavas, Peridotites and Associated Rocks of Northernmost New Zealand. Trans. Roy. Soc. N.Z., vol. 59, pp. 98–138.

Bell, J. M., with Webb, E. J. H., and Clarke, E. de C., 1907. Geology of the Parapara Subdivision. N.Z. Geol. Surv. Bull. 3.

Benson, W. N., 1921. Recent Advances in New Zealand Geology. Austr. Assoc. Adv. Sci., Rept. Fifteenth Meeting, Melbourne.

—— 1922. An Outline of the Geology of New Zealand. Jour. Geol., vol. 30, no. 1.

—— 1923. Palaeozoic and Mesozoic Seas in Australasia. Trans. Roy. Soc. N.Z., vol. 54, pp. 1–62.

—— 1924. The Structural Features of the Margin of Australasia. Trans. Roy. Soc. N.Z., vol. 55, pp. 99–137.

—— 1926. The Tectonic Conditions Accompanying the Intrusion of Basic and Ultrabasic Igneous Rocks. Mem. Nat. Acad. Sci., Washington, vol. 19, First Memoir.

—— 1928. Metamorphic Rocks of New Zealand. Rept. Nineteenth Meeting Austr. Assoc. Adv. Sci., vol. 19, pp. 108–137.

—— 1930. Review of Professor Kober's “Bau der Erde.” N.Z. Jour. Sci. Tech., vol. 12, pp. 63B–64B.

—— 1933. Geology of the Region about Preservation and Chalky Inlets, South Fiordland, New Zealand. Trans. Roy. Soc. N.Z., vol. 64.

—— 1935. Some Land Forms in Southern New Zealand. Austr. Geographer, 2.

—— 1941. The Basic Igneous Rocks of Eastern Otago and their Tectonic Environment, Part I. Trans. Roy. Soc. N.Z., vol. 71, pp. 208–222.

—— 1942. The Basic Igneous Rocks of Eastern Otago and their Tectonic Environment, Part 2. Trans. Roy. Soc. N.Z., vol. 72, pp. 85–110.

Benson, W. N., and Keble, R. A., 1936. The Ordovician Rocks of New Zealand. Geol. Mag., 73, pp. 241–251.

Broadgate, F. K., 1916. The “Red Rocks” and Associated Beds of Wellington Peninsula. Trans. Roy. Soc. N.Z., vol. 48, pp. 76–80.

Cotton, C. A., 1916. The Structure and later Geological History of New Zealand. Geol. Mag., N.S. Decade VI, vol. 3, pp. 243–9, 314–20.

—— 1916. Block Mountains and a “Fossil” Denudation Plain in Northern Nelson. Trans. Roy. Soc. N.Z., vol. 48, pp. 59–75.

—— 1917a. The Fossil Plains of North Otago. Trans. Roy. Soc. N.Z., vol. 49, pp. 429–432.

The Syenite and Associated Rocks of the Mandamus-Pahau Area, North Canterbury, New Zealand

By Brian Mason,

the Hurunui Peak ridge nearly to the Hurunui River (Fig. 1). It is well exposed at many places, particularly in the gorge of the Mandamus River. Around Hurunui Peak itself an interesting igneous breccia is associated with the syenite. It is not separated from the syenite on the map illustrating this paper. About a mile to the north-east of the last outcrops of syenite a small area of gabbro is exposed in the bed of Hut Creek, a tributary of the Dove River. Associated with these plutonic rocks are a number of sills extending outwards from the plutonic bodies to distances of up to three miles. They are particularly well exposed in the Dove River and its tributaries, where they have been mapped in detail, and many were noted along the ridges, especially between the Dove and Glencoe rivers, and around the headwaters of Hut Creek and Cascade and Awatui streams; on the ridges and hill slopes, however, many such small intrusions were noted only from “float”, and many more are doubtless concealed by the soil cover. For this reason the map does not give a true picture of the abundance of these sills, as only those whose outcrop could be located accurately are recorded thereon.

It should be mentioned here that a number of small sills and dykes intruding the greywacke crop out along the Pahau River east and north of this area. Although some of these may be connected with the intrusions described here, the majority appear to be distinct, and a cursory examination of their petrology and field relations suggests that some at least represent feeding channels of the basalts and agglomerates which form part of the Tertiary sequence.

Description of the Rocks

fine-grained selvages against the greywacke are never more than a few inches thick.

Under the microscope the feldspar is usually grey and turbid from beginning kaolinization. It is generally a fine-textured microperthite, although in some specimens the microperthite structure is scarcely detectible and the feldspar is best described as a cryptoperthite. The ferromagnesian minerals are aegirine, biotite and alkaline amphibole. Aegirine (X ∧ c = 8°) is the most abundant ferromagnesian mineral; sometimes the aegirine grains have a core of colourless or pale green augite. The biotite is very strongly pleochroic from yellow-brown to practically opaque. The alkaline amphibole is less common than the other ferromagnesian minerals and is absent from some thin sections; it often replaces pyroxene; it has extinction angle Z ∧ c = 20° and pleochroism × = greenish-brown, Y = reddish-brown, Z = dark brown, and is probably barkevikite. In some specimens a little riebeckite was seen replacing aegirine. Accessory minerals are apatite in very small amount; black opaque material, probably magnetite; and rare enhedral titanite. A little natrolite occurs in the interstices of the feldspar laths. A small amount of secondary calcite and a little opal is present in cavities. The mode of the analyzed specimen is given with the analysis (Table I).

Occasional variants of the syenite were found. One specimen collected from near the edge of the intrusion on the north side of Hurunui Peak was practically free from ferro-magnesian minerals and carried occasional grains (< 5%) of primary quartz. Within a few inches of the contact with the greywacke the syenite is fine-grained (average grain size of equigranular feldspar 0·15 mm.) and in hand specimen has the colour, texture, and jointing of fine-grained greywacke. A thin section of a specimen from this marginal facies at the contact in Coal Creek shows that it has a similar mineralogical composition to the main mass of the syenite except that the ferromagnesian mineral is entirely alkaline amphibole (Z ∧ c = 22°, × = pale yellow, Y = yellow, Z = bluish-green, γ–α = 0·012). This section also showed occasional grains of titanite, strongly pleochroic (yellow to reddish-brown).

The mineralogical and chemical composition of the rock shows that the rock is a typical syenite in the broad sense of the term. It is distinctly alkaline, as shown by the presence of aegirine and alkaline amphibole, and is comparable with the umptekites and nordmarkites. Indeed, the rock is a nordmarkite as this term is defined by Barth (1945, p. 85) “… Nordmarkite [is] a syenite or quartz-syenite containing alkali feldspar (perthite or anorthoclase) without determinable amounts of plagioclase.” It is very similar in composition to some of the type nordmarkites of the Oslo region.

The structural classification of this syenite intrusion is not clearcut. It is transgressive to the general strike (about N.–S.) of the country rock. It is possibly a stock, although the noncommittal term pluton is perhaps preferable.

B. The gabbro

The presence of the gabbro was first inferred from the finding of pebbles of this rock in the gravels of the Mandamus and Dove Rivers.

hand specimen shows plagioclase laths averaging about 3–5 mm. in length; it is completely without augite phenocrysts. In thin section the rock is seen to consist for the most part of feldspar, with accessory magnetite, ilmenite and apatite. It is practically free from ferro-magnesian minerals. Some secondary calcite is present. The outcrop of this rock is small and isolated, and its field relationship to the normal gabbro is not visible. It is either a variant of the gabbro or a dyke cutting the gabbro.

Both mineralogical and chemical composition indicate that the rock of this intrusion, although gabbroic in appearance and general features, cannot be strictly classed with the gabbros, the average composition of the feldspar being andesine rather than labradorite. To call it a diorite would be misleading; in effect it is an andesine gabbro, if such a name were not to some extent self-contradictory. Its closest relative among named rocks is kauaiite, described by Cross (1915, p. 16) from the island of Kauai in the Hawaii group. The rock name kauaiite has recently been more precisely defined on a mineralogical basis by Barth (1945, p. 31) and applied to some rocks of the Oslo region originally classed as essexites. The Hut Creek gabbro shows a close relationship both in chemical and mineralogical composition with the original kauaiite from Kauai and the Oslo “essexites”.

C. The hypabyssal rocks

The hypabyssal rocks of the area are mainly sills intruded along bedding planes in the greywackes and argillites. They are generally quite thin, the thickest measured being 16 feet; the average thickness is about four feet. They occur in an area surrounding the intrusions of syenite and gabbro and fall off rapidly in numbers on going outwards from these intrusions. The situation is complicated along the Pahau River by the presence of small intrusions for the full length of the river, far beyond the limits of this map. These are not dealt with in this paper, as they are probably not directly connected with the syenite and gabbro, and some are quite distinct, apparently being feeding channels through which Middle Tertiary basalts and agglomerates were extruded.

These hypabyssal intrusives are best exposed in the banks of the Dove and Mandamus rivers, and along the ridges in the area. They are particularly abundant along the Dove River, in Hut Creek, and in the vicinity of Charing Cross. Only those actually observed in place are recorded on the map, which is therefore not a true record of their abundance. Undoubtedly many are concealed by soil and vegetation, and some types were collected only as pebbles and as float.

The principal rock types are porphyries and porphyrites, although a variety of other types, mainly carrying porphyritic augite and/or olivine were collected. The porphyries are grouped around the syenite and are evidently directly connected with it (compare analyses of syenite and porphyritic trachyte), the porphyrites around the gabbro.

The sills associated with the syenite, which are well exposed in the lower course of the Dove River, are porphyritic trachytes very similar in chemical composition (Table 3) to the syenite itself. In hand specimen the rocks show feldspar phenocrysts up to 5 mm. long

An interesting rock type was collected on the Hurunui Peak ridge about 60 chains east of the trig, station. The outcrop was a small isolated one and its geological relations could not be observed, but it appears to be a sill or dyke cutting the syenite. In hand specimen the rock is dense and black, with a few very small crystals visible to the naked eye; its fracture is almost glassy. Thin sections show phenocrysts of sanidine, sodalite, brown hornblende, aegirine, and magnetite in an almost opaque groundmass; under high magnification the groundmass is seen to consist of colourless material thickly peppered with small dark equant crystals which are probably a ferromagnesian mineral. At first glance the colourless groundmass appears isotropic, but in parts it shows vague birefringence suggesting beginning crystallization of feldspar; it is probably a devitrified glass. Table 4 gives an analysis of this rock; it is interesting for the high content of nepheline shown in the norm, the highest that has been recorded for rocks from this area. Some of the nepheline in the norm is represented by sodalite phenocrysts, but a considerable proportion is occult in the groundmass. It is difficult to find a satisfactory name for the rock, but sodalite phonolite fits it best. This rock is similar in chemical composition (except for H₂O+) to heronite, an analcitic dyke rock from Heron Bay, Lake Superior (Coleman, 1899).

D. The igneous breccia

The igneous breccia occurs in association with the syenite and is not differentiated from it on the map, mainly because it covers a comparatively small area around Hurunui Peak, and the actual contact with the associated syenite was nowhere seen. It forms the crest of Hurunui Peak itself and is found on the spurs leading down from this point. It makes prominent outcrops, but its field relationship to the syenite is obscured by the mantle of waste. It appears to be a capping over the syenite intrusion and is interpreted as having been formed by the shattering of the roof of the magma chamber by gas pressure in the last stages of crystallization of the syenite.

This igneous breccia is a mass of angular fragments in a fine-grained groundmass. These fragments range in greatest dimension from a foot down to a fraction of an inch, and consist mainly of syenite and trachyte with subordinate greywacke and argillite. The groundmass weathers more rapidly than the fragments, so that they stand out in relief on weathered surfaces (Fig. 3).

Under the microscope the groundmass is seen to be almost entirely feldspar laths, generally very small (up to 0·01 mm. long) with minute grains (< 0·005 mm.) of what appear to be an alkaline amphibole peppered throughout. Flow structure is generally marked in the groundmass. Sometimes the breccia carries numerous equi-dimensional feldspar crystals about 1 mm. long.

Table 5 gives an analysis of material from the summit of Hurunui Peak (chosen to determine the composition of the groundmass and hence as free of fragments as possible), and shows that its composition is very close to that of the syenite and trachyte. The same magma from which the syenite and trachyte were formed evidently gave rise to the igneous breccia. The analysis shows somewhat higher alumina than the analyses of the syenite and the trachyte. This gives rise to

Nature and Origin of the Rocks

The chemical affinities of the rocks are perhaps most simply and clearly expressed by the alkali-lime index, as introduced by Peacock (1931). By plotting the analyses of the igneous rocks of this area the alkali-lime index is found to be 52·5, which would place these rocks in Peacock's alkali-calcic group, not far from the boundary with alkalic group, which is at an alkali-lime index of 51. This correlates well with the mineralogy of the rocks themselves. In general terms the alkalic group and the alkali-calcic group are distinguished mineralogically by the occurrence of feldspathoids in the former and their absence in the latter. The Mandamus-Pahau intrusive rocks are free from feldspathoids (except for the sodalite phonolite, which probably represents an extreme differentiate) but are distinctly alkaline in character, as evidenced by the biotite and the small amount of anorthoclase in the gabbro, and the alkaline pyroxenes and amphiboles in the syenite and trachytes.

The relationship of the Mandamus-Pahau intrusives—geological, mineralogical, and chemical—suggests that they have differentiated from a common parent magma. The visible amount of the syenite is very much greater than that of the gabbro (it is of course dangerous to draw conclusions regarding the absolute amounts of the different intrusives on the basis of surface exposure). With these circumstances in mind, the writer suggests that the parent magma of the intrusive rocks of the Mandamus-Pahau area was intermediate in composition between the syenite and the gabbro, and that the gabbro represents an accumulation of early-formed crystals from this magma. This accumulation of early-formed crystals was separated from the remaining liquid by pressure due to crustal movements, and this liquid was injected into higher levels in the crust and formed the syenites and trachytes.

This concept of the origin of the syenite and trachytes as the products of crystallization of a magmatic liquid from which the products of early crystallization had been removed is supported by certain criteria developed by Bowen (1937). He points out that the laboratory study of silicate systems indicates that the residual liquids from the fractional crystallization of complex silicate magmas must be enriched

in alkali-alumina silicate; the alkali-alumina silicate system (NaAlSiO₄–KAlSiO₄–SiO₂) may thus be referred to as petrogeny's “residual” system. The laboratory study of this system has shown that it has a well-defined valley in the fusion surface, which is, of course, the composition area of the liquids having the lowest temperature of crystallization in the system. Bowen showed that the composition of many igneous rocks rich in alkali-alumina silicates, when plotted in terms of the NaAlSiO₄–KAlSiO₄–SiO₂ system, fell within this valley in the fusion surface, thus indicating that crystal ⇄ liquid equilibrium had been the dominant control in the production of these rocks, i.e. they represented the residual liquids of crystallizing magmas. Benson (1941) applied Bowen's criteria to the salic rock types of the Tertiary igneous rocks of the North Island, Banks Peninsula, and the Dunedin district, and showed that the idea that these rocks represented the solidification products of residual magmatic liquids was thereby supported. Bowen's scheme of plotting has been applied to the Mandamus syenite, trachyte, and phonolite, and the result is shown in Fig. 4. This figure shows that the composition of the alkali-alumina silicate in these rocks falls in the low-melting region of the diagram; for the syenite and the trachyte the points fall near the minimum between albite and orthoclase, and the point for the phonolite practically coincides with the lowest temperature in the diagram. This strongly supports the belief that these rocks represent late fractions of a magma whose evolution has largely been that of differentiation by fractional crystallization.

Comparison with Other Areas

The intrusive rocks of the Mandamus-Pahau area show a marked resemblance to some of the classic types of the Oslo region. The syenite can be matched chemically and mineralogically with the nordmarkites of the Oslo region, and the gabbro is strictly comparable with the well-known Oslo essexites which Barth (1944, pp. 26–31) has shown not to be essexites at all, since they contain no nepheline; they are alkaline gabbros which may be classified as kauaiites, the original kauaiite being described from Kauai, in the Hawaiian Islands (Iddings, 1913, p. 173; Cross, 1915, p. 16). The Mandamus-Pahau intrusives are of course, small in comparison to those of the Oslo region and are very much less diversified, but in both regions the major types are similar, suggesting parent magmas of comparable composition.

Within New Zealand the Mandamus-Pahau rocks show chemical and mineralogical resemblances to those of the Dunedin district, although the rocks of the latter district are mainly extrusives. The rocks of the Dunedin district are somewhat alkaline (alkali-lime index 50·1), which is reflected in the presence of numerous feldspathoidal types which are absent in the Mandamus-Pahau area. However, if the feldspathoidal types are omitted, the alkali-lime index for the rocks of the Dunedin district is then practically identical with that for the Mandamus-Pahau rocks. The similarities are particularly marked in the trachytes which are common to both areas. The trachytes described by Marshall (1906, 1914) from North Head and Portobello are mineralogically and chemically comparable with those of the Mandamus-Pahau area.

Rocks related both in geological occurrence and in chemical and mineralogical composition probably occur in the mountains to the south of the Mandamus-Pahau area, around the headwaters of the Waipara River. Benson (1942), pp. 177–8) has briefly described pebbles of doleritic and teschenitic types collected from the gravels of the Waipara River. They resemble the gabbro of the Mandamus-Pahau area in the presence of biotite and of minor amounts of alkali feldspar. Syenitic and trachytic types have not been observed.

Thomson (1912, 1919) described briefly some intrusive rock types from the Inland Kaikoura mountains. The rocks he described were mainly dolerites with alkaline affinities, similar to the gabbro described in this paper. A visit to this area in 1946 showed that the intrusive rocks cover a large area, extending from the headwaters of the Swale to those of the Muzzle River, and are considerably diversified in type. The syenite and gabbro from the Mandamus area are petrographically similar to some of the rocks from the Inland Kaikouras. Too much should not be made of this similarity, however, since the igneous rocks of the Inland Kaikouras have yet to be studied in detail and their mutual relations deciphered.

The closest analogies with the Mandamus-Pahau rocks are afforded by the small area of intrusive rocks at Onawe, in Akaroa harbour. These rocks, which were described in detail by Speight (1923, 1940), consist of gabbro and syenite, and some of the trachyte dykes of the Akaroa area are probably co-magmatic. The alkali-lime index of the Onawe rocks is 50.5, indicating that they re slightly more alkaline in general character. However, thin sections of the Onawe syenite and gabbro are very similar to sections of the syenite and gabbro from the Mandamus-Pahau area.

Much of the resemblance between the Mandamus syenites and trachytes and similar rocks at Onawe and in the Dunedin district may be due to their being all “residual magmas” in Bowen's sense, i.e. a final differentiate from the fractional crystallization of a large body of magma. The marked resemblances, however, suggest that the original magma in all those localities was similar, and that the same processes of differentiation were active in each ease.

The Age and Correlations of the Intrusions

The intrusion of these rocks was probably associated in time with the Hokonui orogeny. They are injected into greywackes and argillites whose are has not been directly established by fossil evidence, but which are correlated on lithological and structural similarities with fossilifereous rocks of Triassic and Jurassic age in other parts of Canterbury (Mason. 1949). Pebbles of syenite and trachyte occur in the basal Tertiary conglomerates (Mangaorapan. i.e. Lower Eocene) in Coal Creek. On this evidence intrusion was post-Jurassic and pre-Eocene. It appears most probable that the intrusion accompanied or followed closely the orogenic movements that brought to a close the long period of Hokonui sedimentation. The fact that the syenite often shows strong jointing like that o the surrounding greywacke suggests that it has been subjected to similar forces, and that hence it was intruded before the orogenic movements were completely spent.

From this discussion the time of intrusion would be correlated with the Hokonui orogeny, and would thus be Lower Cretaceous. An alternate hypothesis, which would be difficult to prove but which cannot be ruled out on the available evidence, is that intrusion took place at the end of the Cretaceous period. A widespread break in the sedimentary sequence occurred in North Canterbury at the end of the Cretaceous. Over a considerable area, post-Hokonui sedimentation begins with Mangaorapan beds. This stratigraphic break, though not at all comparable with that due to the Hokonui orogeny, is nevertheless an important one, and it must be borne in mind when attempting to date this igneous activity.

As mentioned in the introduction, igneous rocks associated with the Hokonui orogeny are rare. The large areas of Triassic and Jurassic rocks, both in North and South Islands, are monotonously free of associated igneous rocks. Probably the most extensive occurrence of intrusions in these rocks is that of the Inland Kaikoura mountains, which has yet to be mapped and examined in detail. Thomson considered that the igneous rocks of the Inland Kaikoura mountains were intruded in Clarentian (Lower Cretaceous) times. If this dating is correct, and the Mandamus-Pahau rocks are the same age, this implies that the Mandamus-Pahau rocks were intruded after the end of the Hokonui orogeny, rather than during the later stages of the orogeny itself.

Unfortunately, little evidence is available for dating the Onawe syenite and gabbro, which show such marked resemblances to the Mandamus-Pahau rocks. What evidence there is, however, does not conflict with the postulate that the intrusives in both areas may be of the same age. Speight's opinion (1940) was that the Onawe rocks are part of an older and distinct substratum belonging to an earlier epoch than that of the main mass of the Akaroa volcano; however, he made no statement as to their probable age.

General History of the Intrusion

It is believed that the rocks described in this paper were all derived from a common magmatic source by a process of differentiation by crystallization. The nature of the source magma is a matter of conjecture, but it was presumably such that both the gabbro and the syenite rocks were derived from it, the gabbro representing an accumulation of the early formed crystals and the syenite the crystallization product of the remaining magmatic liquid. This concept of the syenitic rocks as being the products of crystallization of a residual magmatic liquid is supported by the way in which the composition of the salic material in the actual rocks when plotted on the NaAlSiO₄—KAlSiO₄–SiO₂ diagram of Bowen (1937) falls in the low-melting “residual liquid” section (Figure 4). The points representing the rocks from this district occupy an area on Bowen's diagram corresponding to that set out by Benson (1941, p. 542) for the salic portion of the residual magmas of the Dunedin petrographic province.

In view of the absence of rocks intermediate between those of gabbroic and syenitie composition it is believed that the residual liquid from which the syenitie rocks were formed was isolated by crustal stresses from the early formed crystals of augite and plagioclase which

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Acknowledgments

I should like to express my appreciation to the residents of the district for their many kindnesses to me during the field work, particularly Mr. and Mrs. A. G. Groome, of the State Forest Service. Balmoral, Mr. and Mrs. W. A. Lake, Cascade Station, and Mr. and Mrs. A. C. Shand, Island Hills Station. They generously placed both transportation and accommodation at my disposal. I am also grateful for the assistance and companionship of a number of my students who accompanied me in the field on different occasions. This paper owes much of its substance to the chemical analyses of the major rock types. Four of these analyses were made at the Dominion Laboratory by Mr. T. A. Rafter, thanks to the co-operation of the Director of the New Zealand Geological Survey and the Director of the Dominion Laboratory, and one by Mr. M. C. Coller, chemist to the Geology Department, Indiana University. I am very much indebted to Mr. Rafter and Mr. Coller for the care with which these analyses were carried out. I would also like to express my thanks to Professor R. S. Allan, for his advice on many aspects of the problems encountered; and to Professor F. J. Turner, for helpful discussion of the petrology of these rocks.

My thanks are also due to the Hutton Fund of the Royal Society of New Zealand for defraying part of the cost of the work by a grant.

Vegetative Anatomy of Carpodetus serratus Forst.

By P. J. Brook, Botany Department, University of Otago

Stem Anatomy

Primary Structure

The primary stem structure (Pl. 38, A) has few noteworthy features. The epidermis bears frequent unicellular cutinised hairs (Fig. 1a)

Text Fig. 1—(a) L.S. hair on young stem. (× 235.) (b) T.S. portion of outer part of young stem showing origin of phellogen beneath a hair base. (× 240.)

and at wide intervals stomata of the normal type described by Haberlandt (18) for Narcissus biflorus and Helleborus. As in woody Angiosperms generally (11), there is not a typical endodermis, but a more or less definite ring of cells about the stele is regarded as such, since

in very young seedlings Caspary's bands were seen in this layer. The bundles of primary vascular tissue vary in size, the median leaf trace bundles being the largest, and showing marked radial arrangement of the primary xylem—a condition attributed by Esau (13) to repeated periclinal division of the procambial cells. Wood elements comprise annular, spiral, scalariform and dotted types. The spiral, annular and some of the scalariform and dotted cells are tracheids, but others of the last two types have end walls and are thought to be vessel segments. This possession of tracheids in primary, but not in secondary wood, is not abnormal (14). The primary phloem, in addition to sieve tubes, companion cells and parenchyma, contains peripherally groups of 2–10 small angular cells comparable with those described by Artschwager (1) from the potato, though in the present case consisting only of what he terms “conducting parenchyma.” These conducting parenchyma groups also occur in the stele between the collateral primary bundles. When traced longitudinally they were found to branch and anastomose and ultimately to fuse with the collateral bundles. The pith is solid and lignifies early.

The leaves are alternate with one-half phyllotaxis. The node Pl. 38, A) is trilacunar with the lateral traces each about a quarter of the circumference of the stem away from the larger median trace. These features of leaf arrangement and vascular supply are regarded as primitive (10, 29, 30), but the leaf itself, since it is not compound and lacks stipules, is not of the most primitive form in Angiosperms (10, 19).

Secondary Structure

The phellogen arises in the cortical layer immediately beneath the epidermis; appearing first, as is usual (11), at points where lenticels will develop. These are initiated mainly under hairs (Fig. 1b), stomata having little guiding and no limiting influence on their formation. The lenticels (Fig. 2) are small and rather greater in

Text Fig. 2—T.S. lenticel in mature stem. (× 110.)

transverse than in longitudinal extent. This is considered to be a primitive orientation (32). The complementary tissue is compact, the structure corresponding with Devaux's second type (9). The original phellogen persists throughout life of the tree, dividing slowly and maintaining only a thin cork layer seldom more than ten cells thick (Pl. 38, B). However, a wide zone of phelloderm is formed which matures into irregular masses of radially arranged stone cells (Fig.

groups become lignified, whereas nearly all parenchyma accompanying the vertical phloem elements is ultimately converted to stone cells. Sieve-tubes do not lignify, but neither they nor any unlignified parenchyma are greatly crushed. Apparently the thin cork and the capacity of cortex and periderm cells for radial division prevent the usual pressure developing between secondary wood and bark. It is noteworthy that a good many of the old companion cells do lignify (Figs. 3b, 3c), a phenomenon that does not appear to have been observed previously, it being usual for these cells to die and collapse along with their sister sieve-tube element (12).

The secondary wood is almost white in colour, with obscure growth rings, but prominent rays along which it invariably splits as it dries. The wood is diffuse-porous (Pl. 39, A), annual ring boundaries being defined by the contrast between summer and spring wood vessel diameters. Ray cells broaden tangentially in the summer wood. No tracheids are present, the vertical conducting cells all being vessels (Figs. 4e, 4f). By Chattaway's (6) standards these vessels are very numerous, and their thin-walled, angular segments have a “small” tangential diameter and are “extremely long.” (For actual measurements see Table of Descriptions.) Segment end walls are very oblique, often with tails, and with numerous narrow, fully-bordered perforations (Fig. 4g) which are always scalariform. The vessel pitting is opposite. Except for this last feature, which is considered slightly more advanced than sclariform pitting, the vessel segment is primitive in every respect (14, 15, 16). Very oblique end walls are the rule in woods such as Carpodetus which are not storied (5). The bulk of the tissue between the vessels is comprised of fibres (Fig. 5), which by Chattaway's standards are “very long” and “thin” walled. Pitting is fairly evenly distributed, on all walls, the pit chambers easily visible, borders strongly developed, and the inner apertures narrow and included. Such fibres are classed as fibre-tracheids (26) and considered to be a somewhat primitive type (2). As Priestley (23) has established as generally true, pits are not formed between fibres and other elements (Fig. 5). Vertical parenchyma are diffuse (Fig. 5), the cells in similar vertical series to the phloem parenchyma. Ray structure conforms with Krib's (22) heterogeneous type I, which both he and Barghoorn (3, 4) consider the most primitive in Angiosperms. In this type the uniseriate rays are high and composed of vertically elongated cells. The multiseriate rays possess high uniseriate tips identical with the uniseriate rays, and are in their multiseriate parts parallel-sided with elongated lateral cells (Pl. 39, B). Primary multiseriate rays are, of course, of interfascicular origin. Secondary ones were observed to arise by two of the methods described by Barghoorn (3, 4)—i.e., by widening of a uniseriate ray or by coalescence of several such rays, and they are occasionally split apparently by changeover from ray to fusiform initials in the cambium. On Chattaway's standards these rays are “very broad” and “extremely high.”

Table of Description of Secondary Wood

A description of wood in C. serratus has been prepared following the plan suggested by Rendle and Clarke (27, 28). It is based on four trees between 30 and 50 years old growing in a variety of situa-

Root Anatomy

The root system is composed of laterals, there being no persistent tap-root. These roots vary from 4-arch to polyarch, and always contain some pith which eventually lignifies. The initial phellogen forms well out in the cortex. and as in the stem is persistent and forms much phelloderm. There is little lignification of the phelloderm, but an almost complete sclerenchyma ring is formed further in by lignification of the old phloem parenchyma, outer parts of many phloem rays and the inner layers of the cortex. (Pl. 38, C.)

Secondary wood in roots that are exposed above the ground appears to differ from stem wood only in having broader rays (Pl. 39, C) (Fig. 4h), but subterranean roots have much larger vessels and correspondingly narrower multiseriate rays, fewer and thinner-walled fibres and more abundant vertical wood parenchyma (Pl. 39, D). Vessel segments in buried roots are shorter, including some very short vessels (Fig. 4i), a form never found in stems, and growth rings are more obscure. The precise extent of histological differences between stem and root wood, and between exposed and buried root wood is the subject of a separate investigation, and no statistical data will be presented here

Text Fig. 6—T.S. part of an adult leaf. (× 250.)

Leaf Anatomy

The three leaf traces unite in the petiole to form the usual arc of vascular tissue. This has no sclerenchyma associated with it, but the midrib and main veins possess a sclerenchyma sheath. The principal features of the lamina are shown in Fig. 6. The uppermost layer of palisade mesophyll, which amounts in all to from 2–4 layers, is intermittently replaced by clear hypodermal cells, as has been noted by Solereder (31). This hypodermis is not responsible for the mottled appearance of the foliage. This is due to a higher chlorophyll content of the mesophyll adjacent to large veins. Hairs and stomata are of the type already described from the stem, the latter being without subsidiary cells and confined to the lower epidermis. C. serratus is one of the New Zealand trees which possesses smaller leaves in juvenile than in adult trees. Juvenile leaves do not possess hypodermis and have no more than two palisade layers. Unpublished work by Johnston (21) has established that they have a closer vein network and more stomata per unit area than adult leaves.

Discussion and Summary

The fullest account of wood structure in the Cunoniales is by Record (24), who states that the Escalloniaceae are the only family in the order which combine conspicuously large rays with scalariform vessel perforations and strongly bordered pits in the wood fibres. The existence of all these features in C. serratus confirms the classification of the genus in that family. The Cunoniales occupies an early place in Hutchinson's evolutionary tree for woody Dicotyledons. The vegetative anatomy of C. serratus confirms that position, since this species exhibits a primitive condition in almost every feature to which phylogenetic significance has been attached—viz.:

Features which show a slight evolutionary advance are absence of tracheids in secondary wood, and opposite pitting of vessels. It has been contended that diffuse-porous woods are primitive, but Gilbert (17) points out that it can hardly be claimed that there is a general advance towards ring-porosity since this feature is confined to trees of the N. Temperate zone.

The cortical system in both stem and root is characterised by a phellogen arising near the exterior and producing little cork but

much phelloderm. The phelloderm, though partially converted to stone cells in the stem, retains great tangential elasticity through radial division of its parenchyma. Old secondary phloem thus persists uncrushed, and certain companion cells therein undergo lignification along with the phloem parenchyma—a most unusual occurrence.

The leaf is of a normal mesophytic type. Adult leaves possess an intermittent colourless hypodermal layer. Attention is drawn to the fact that though there are substantial differences, mainly in size and frequency of component elements, between stem and buried root wood, these differences largely disappear if the root is uncovered.

Bibliography

1. Artschwager, E. F., 1918. Anatomy of the Potato Plant with special reference to the Ontogeny of the Vascular System. Jour. Agr. Res., 14: 6.

2. Bailey, I. W., 1936. The Problem of Differentiating and Classifying Tracheids, Fibre Tracheids, and Libriform Wood Fibres. Trop. Woods, 45.

3. Barghoorn, E. S., 1940. The Ontogenetic Development and Phylogenetic Specialisation of Rays in the Xylem of Dicotylcdons. I. The Primitive Ray Structure. Am. Jour. Bot., 27: 10.

4. —— 1941. The Ontogenetic Development and Phylogenetic Specialisation of Rays in the Xylem of Dicotyledons. II. Modification of the Multiseriate and Uniseriate Rays. Am. Jour. Bot., 28: 4.

5. Chalk, L., and Chattaway, M. M., 1935. Factors affecting Dimensional Variations of Vessel Members. Trop. Woods, 41.

6. Chattaway, M. M., 1932. Proposed Standards for Numerical Values in Deseribing Woods. Trop. Woods, 29.

7. Cheeseman, T. F., 1925. Manual of the New Zealand Flora, ed. 2. Govt. Printer, N.Z.

8. Desch, H. E., 1932. Anatomical Variations in the Wood of some Dicotyledonous Trees. New Phyt., 31.

9. Devaux, H., 1900. Recherches sur les Lenticelles. Ann. Sci. Nat. Bot., 8 sér., 12.

10. Dormer, K. J., 1945. An Investigation of the Taxonomic Value of Shoot Structure in Angiosperms with Especial Reference to Leguminosae. Ann. Bot., N.S., 9.

11. Eames, A. J., and MacDaniels, L. H., 1925. An Introduction to Plant Anatomy, ed. 1. McGraw-Hill.

12. Esau, K., 1930. The Development and Structure of the Phloem Tissue. Bot. Rev., 5: 7.

13. —— 1943. Origin and Development of Primary Vascular Tissues in Seed Plants. Bot. Rev., 9: 3.

14. Frost, F. H., 1930. Specialisation in Secondary Xylem of Dicotyledons. T. Origin of Vessel. Bot. Gaz., 89.

15. —— 1930. Specialisation in Secondary Xylem of Dicotyledons. II. Evolution of End Wall of Vessel Segment. Bot. Gaz., 90.

16. —— 1931. Specialisation in Secondary Xylem of Dicotyledons. III. Specialisation of Lateral Wall of Vessel Segment. Bot. Gaz., 91.

17. Gilbert, S. G., 1940. Evolutionary Significance of Ring Porosity in Woody Angiosperms. Bot. Gaz., 102.

18. Haberlandt, G., 1928. Physiological Plant Anatomy. Engl. trans. from 4th German ed. by M. Drummond. MacMillan & Co.

19. Hutchinson, J., 1926. The Families of Flowering Plants. I. Dicotyledons. MacMillan & Co.

20. Jeffrey, E. C., 1917. The Anatomy of Woody Plants. University of Chicago.

21. Johnston, J. G., 1948. A Comparison of Adult and Juvenile Foliage of Carpodetus serralus Forst. with Special Reference to Xeromorphic Characters. Unpublished Thesis.

New Zealand Ichneumonidae
Paper No. 1
The Genus Netelia Gray (Paniscus of Authors) (Tryphoninae: Phytodietini)

By Arthur W. Parrott,
Curator of Insects, Cawthron Institute, Nelson, N.Z.

or transversely striate on its basal half above and with a somewhat curved transverse carina on each side just above its middle; discocubital vein strongly curved basally; areolet triangular, usually higher than wide, subpetiolate or shortly petiolate, rarely absent; second intercubital with a bulla below; second recurrent strongly curved, interstitial or nearly interstitial with second intercubitus, a bulla at its top and another just below its middle; apex of front tibia evenly rounded, without a suggestion of a tooth; spurs of front tibia long and slender, the comb-bearing part occupying less than one half of its length; tibia and tarsi with many conspicuous bristles; tarsal claws densely pectinate, with eight to fifty long teeth; petiole straight, gradually enlarged towards the apex, its spiracles before the middle; glymma deep; abdomen more or less compressed beyond the third segment; epipleura well developed on all segments; ovipositor from about one-fifth as long, to as long as, the abdomen; the tip tapering, not notched; female subgenital plate not strongly developed; ovipositor sheath transversely ridged, densely clothed with rather long hair; penis compressed.

Townes (loc. cit., p. 174) gives the following key for the separation of the two genera included in this tribe:

Key to Genera.

Only two species are known from New Zealand, belonging to the genus Netelia. One is endemic while the other is a widespread Australian species.

Genus Netelia Gray, 1860

Key to New Zealand Species of Netelia

Netelia ephippiatus (Smith)

Paniscus ephippiatus Smith, Trans. Ent. Soc. Lond., 1876, p. 478, female; Smith, loc. cit., 1878, p. 3, female; Hutton, Cat. N.Z. Diptera, etc., 1881, p. 126; Cameron. Mem. Manch. Soc., 42, pt. I, 1898, p. 35; Cameron, Trans. N.Z. Inst., 33, 1901, p. 105; Dalla Tore, Cat. Hymen., III, pt. I, 1901, p. 78.

Paniscus productus Hutton, Index Faunae Nov. Zeal., 1904, p. 102; Miller, N.Z. Journ. Agric., 19, 1919, p. 203, fig.

Paniscus smithii Dalla Torre, Cat. Hymen., III, pt. I, 1901, p. 80.

This species was first described by Smith in 1876 from a female collected in Otago, and two years later another female collected from Canterbury was described under the same name by the same author. Hutton gives both descriptions in his 1881 catalogue, but erroneously gives the locality for the 1878 specimen as Dunedin. Hutton was of the opinion that both descriptions referred to the one and the same species. Cameron records it from Greymouth (1898) and from Wellington (1901). Morley (1912) examined a specimen from Auckland. Female

Head brownish-yellow or light brown; ocular area and tip of mandibles black; ocelli and eyes nigger-brown; antennae brown, the apical 24 joints of a darker greyish-brown; pronotum pale yellowish-brown; mesonotum with three wide longitudinal bands of black, separated by the notauli; mesostern black; legs yellowish-brown; spines brown to blackish-brown; claws nigger-brown; abdomen, first tergite basally light brown darkening to brown towards apex; second tergite and basal part of third tergite brown, remaining part of third tergite and the posterior tergite dark brown shading to black; ovipositor dark brown to black; wings hyaline, veins and stigma brown to dark brown.

Ocelli large, posterior ones sub-contiguous with eyes, anterior ocellus separated from eyes by its diameter, and the same distance from antennal scrobes; frons finely but distinctly striolated, bordered by a lateral carina, running parallel with the inner border of the eyes, nearly glabrous; face slightly wider than long, weakly convex in centre, clothed with fine whitish pubescence and finely punctate; clypeus more especially along anterior border; flagellum with 53 joints and all coarsely punctate and clothed sparsely with longish white bristles, entirely clothed with short and fine pubescence, the joints becoming gradually shorter, the apical joint is about a quarter the length of the third joint. Scutellum prominent, oblong, narrowed towards apex, lateral carinae present, the whole surface punctate; propodeum finely, transversely striolated, strong carinae along the lateral posterior borders terminating anteriorly in a prominent spine-like process; mesostern with median sulcus deep; pleural sclerites distinct; all tibiae spined, the spines short, sharply jointed, and are more numerous on posterior tibiae; claws with strong pectinations; abdomen, first tergite, long and straight, gradually widening towards apex, the spiracles placed about one-third from base; second tergite slightly more than one-half the length of the first and sub-equal to the third tergite in length; apical spurs of posterior tibiae long, the outer the larger of the two; gastroeoeli shallow and minutely punctate; wings with areolet triangular, with only a small gap at the base of the outer side (Fig. 9); nervellus index 2·40 to 2·92 (Figs. 6 and 5).

Affinities

This species is closely allied to N. productus; indeed, it is rather difficult to detect macroscopical structural details that will separate one from the other, except, of course, by colour, which is fairly constant in density and distribution.

Biology

Miller (1919, p. 203) records and figures this species under the name Paniscus productus as attacking the New Zealand flax grub (Xanthorhoe praefectata). There is no doubt that the species he refers to is N. ephippiatus, for in describing this insect he states: “On the back, behind the head, is a large blackish spot, and another beneath the thorax between the front and middle legs, while the abdomen darkens towards the apex, in some cases being almost black.” The accompanying figure is undoubtedly this species. Miller (1930, p. 282) again referring to this species as attacking Xanthorhoe praefectata states: “… the parasite does not destroy the caterpillar until after pupation so that the injury by the caterpillars to the flax is not hindered.” The same author also observed that P. productus does not confine its attacks to O. praefectata but infests other species of caterpillars as well.

Gourlay (1930, p. 5) does not record Miller's observations, and does not include N. ephippiatus in his list.

The females are far more abundant than males, which are extremely rare in collections. The females especially are attracted by artificial light.

Distribution

This species is probably generally distributed throughout both islands. Specimens have been examined from the following localities: Dunedin (type locality), Canterbury, Greymouth, Nelson, in the South Island, and Wellington, Paihia, and Auckland in the North Island and the Chatham Islands.

Seasonal Distribution

The relative seasonal abundance of adults of Netelia ephippiatus is shown in graphical form in Fig. 10. The data upon which this graph is based were obtained from information accompanying specimens in the various collections that have been made over the past thirty years. The total number of specimens from which data were obtained was 58.

Netelia productus (Brulle)

Paniscus productus Brulle, Hist. Nat. Ins. Hymen., IV, 1846, p. 156 (female from Tasmania); Dalla Torre, Cat. Hym., III, pt. I, 1901, p. 156; Hutton, Index Faunae Nov. Zeal., 1904, p. 102; Gourlay, Dept. Sci. and Industr. Res. Bull. 22, 1930, p. 5.

Paniscus foveatus Cameron, Mem. Manoch. Soc., 42, pt. I, 1898, p. 36; Hutton, Index Faunae Nov. Zeal., 1904, p. 102; Dalla Torre, Cat. Hymen., III, pt. I, 1901, p. 78.

Brulle originally described this species from Tasmania in 1846. Cameron in 1898 described it as new under the name Paniscus foveatus from Greymouth, New Zealand.

Female

Head yellowish-brown tinge, especially behind eyes and on frons and caput; face usually a pallid-yellow; ocular area light brownish-red

or orange-brown; ocelli and eyes red-brown, eyes shaded with black; tips of mandibles black; antennae uniformly brown, not normally appreciably darkening apically, mesonotum brown, in some specimens faintly infuscated with darker brown; metanotum dark brown; abdomen red-brown, usually not appreciably darker towards apex; mesosternum brown; legs red-brown clothed with golden pubescence; claws dark brown; wings hyaline, veins and costa dark brown, stigma light to reddish-brown.

Frons finely but distinctly striolated, bordered by lateral carinae; face slightly wider than long and convex in centre; clothed with fine pubescence; face more closely punctured than clypeus; flagellum is usually 57 segmented; notauli grooves well marked; scutellum prominent, much narrowed towards apex, with strong lateral carinae and with the surface minutely punctured; propodeum finely transversely striolated, carinae posteriorly strong, terminating anteriorly in a prominent spine-like process; pleurae sclerites distinct; spines on tibiae as in N. ephippiatus; claws strongly pectinate; areolet of anterior wing triangular, usually more widely open along outer side (Fig. 8).

Male similar to female.

This species, at least in the case of the females, is slightly larger than N. ephippiatus, and differs from that species by the absence of black on the vertex, mesonotum and mesosternum, accompanied by a darkening of the apical portions of the abdomen. In the majority of specimens examined the propodeum may be slightly more convex and their lateral keels more distinct, and more deeply impressed at base, this depression being almost bifurcate, through the centre being raised. The lower part of the mesopleura is not depressed as it is in N. ephippiatus, also the stigma of the fore-wings is usually a lighter brown.

Affinities

Very close to N. ephippiatus. A species described from Fiji (Netelia fijiensis) would appear to be also closely related to the forms described here.

Biology

Gourlay (1930, p. 5) records this species as parasitising Melanchra composita and Aletia unipuncta, the parasite attacking the host larvae, the parasitic larvae emerging from the host larvae to pupate. Given (1944) figures an egg of a Netelia species found on the larvae of the white butterfly (Pieris rapae) at Nelson. A female of this species taken at Nelson on March 27, 1950, when placed in a cage with a larva of Cirphis unipuncta, laid three eggs on the larva. One was placed about halfway up in the suture separating the head from the first thoracic segment, a second lower down in the suture between the meso- and metathoracic segments, and a third attached at the base of a mesothoracic leg. The eggs were of large size, black in colour with a relatively long pedicel, and were very firmly attached to the surface of the larva. Within twelve hours of being laid the eggs hatched, the young larvae remaining between the two halves of the egg case, the egg splitting longitudinally. Unfortunately the caterpillar died and further observations on the development of the parasite were not possible. Both the egg figured by Given and the present eggs show difference in size and shape compared with those of a Netelia figured by Vance (1927).

Seasonal Distribution

The relative seasonal abundance of adults of Netelia productus is shown in Fig. 11. As in the case of N. ephippiatus, collections made over the past thirty years were tabulated by months and the graph constructed from the resulting frequency distribution. The total number of specimens from which data were obtained was 47.

Distribution

Australia, Tasmania and New Zealand. It is generally distributed throughout both islands of New Zealand; adults have been recorded from the following localities: Canterbury, Westland, Nelson, and Marlborough in the South Island, and Paihia, Whangarei, Manguiti, and Taupo in the North Island.

Notes on the New Zealand Species of Netelia

The two species of Netelia occurring in New Zealand are easily distinguished by their colour; structurally they are very similar. Two characters that have been found to be fairly constant are the incompleteness of the outer border of the areolet (Figs. 8 and 9) and the relative lengths of the upper and lower portions of the nervellus in the hind-wing (Figs. 6 and 7). In respect to the second character, 32 specimens of ephippiatus and 39 specimens of productus collected from widely separated localities were measured and the results are presented graphically in Fig. 5; this character is easily observed and will serve in doubtful cases as a reliable criterion for the separation of the two species.

A species described by Brues (1922, p. 19) from Fiji, which is closely related to productus, shows sexual dimorphism in that the males have the aciculations of the propodeum more clearly indicated medially and by the white face and orbits as well as the larger ocelli, while the lower outer side of the areolet is more distinct. The size of the ocelli and the aciculations of the propodeum show slight variations in the New Zealand forms, but few constant differences can be detected between the sexes.

There are several specimens of Netelia that at present I am unable to place satisfactorily; in particular there is a large female collected at Manguiti, on March 8, 1916. This may be a distinct species, but I have refrained from naming it until further specimens are obtained. There are certain indications, from the material I have examined, that when more information on the biology and habits of the species of Netelia is available, the present species may possibly be conveniently separated into several well-marked sub-species, based on slight but more or less constant structural details associated with seasonal and host distribution within New Zealand.

In the case of N. productus it is of interest to record the manner in which the Nelson and Kaikohe material was collected. The Nelson specimens were collected from the windows of a house at night, the insects being attracted by the light. This material consisted of eleven females and two males. The Kaikohe specimens, comprised entirely of males, were collected by sweeping herbage and long grass during the evening just before dark. Dr. R. A. Cumber, who collected this material, observed these insects on or near the ground probably hunting for females.

The Geology of Whangarei Heads, Northland

By L. R. Allen, N.Z. Geological Survey

of fairly recent submergence followed by considerable infilling of embayments, amongst which Parua Bay is remarkable on account of the abnormal constriction of its entrance (Fig. 4). South of Urquharts Bay, near the entrance to Whangarei Harbour, bold bluffs fringe the shore and continue east for nearly four miles facing the open sea, unbroken but for two small, shallowly re-entrant bays, Smugglers Bay and Peach Cove, and at many places hundreds of feet high. At Bream Head they turn north-west for a little over one mile, to be replaced by the long sandspit of Ocean Beach, which continues north west for a little over four miles to where the slopes of Kauri Mount initiate a further stretch of steep sea-cliffs. Behind this sandspit there is a belt of sand-dunes about half a mile in maximum width and then a zone of variable width which earlier was swamp or lagoon, but now is largely drained and laid down in pasture. The intricate ramifications of the inland margin of this zone of “swamp” represent the initial shoreline of the sub-recent emergence.

Metalled roads of variable quality give access to the bases of most of the higher elevations. The various volcanic masses in particular are often crowned by scrub or native forest, this latter particularly extensive on Manaia and Bream Head Ranges.

The earlier work on the district, in particular from the time of Cox (1877) onwards to his own time, is dealt with by Ferrar (1925). Bartrum (1925, 1935, 1936, 1937, 1948) has subsequently written about various topics mentioned later in this paper.

Outline of Stratigraphy

The basement rocks are greatly disordered greywackes, with minor argillites, which have been referred by Ferrar (1925) to the Waipapa Series, established by Bell and Clarke (1909) at Whangaroa further north, and may tentatively be included in the Hokonui (Trias-Jura) System. Waipapa sedimentation was ended by vigorous folding and uplift in the early Cretaceous, which were followed by the extensive erosion that is well known to have reduced most of New Zealand to a mature land, if not a peneplain. Widely throughout North Auckland there was submergence after these events and, in our local area, blackish shales and concretionary greenish sandstones of the Upper Cretaceous Otamatea Series of Ferrar (1934) were deposited. Evidence is not conclusive, but it is reasonably certain that, near Whangarei, uplift quickly ended this period of sedimentation, for the next beds in succession are those of the Onerahi Series of Ferrar (1920), which include amongst less calcareous phases the well-known globigerinid “hydraulic” limestone of which upper horizons at least are Middle Bortonian (Middle Eocene) on foraminiferal evidence (Finlay and Marwick, 1947).

Ferrar (1925) has shown that Onerahi sediments were acutely folded and eroded before the next series of marine sediments was laid down, namely the Whangarei Series with varied sandstones and a strong limestone which usually is markedly echinodermal. This limestone has been accepted on foraminiferal evidence as Waitakian (Mid-Oligocene), but Mr. J. Healy, of the New Zealand Geological Survey, has kindly given information, not yet in print, that at Whangarei he has found beds beneath the limestone which are Whaingaroan (Lower Oligocene) or possibly even earlier.

No marine sediments, other than those of sub-Recent or Recent age, of later date than the Whangarei beds are yet known in the Whangarei Heads area.

This history of the main vulcanicity can be briefly given: small extrusions of limburgite separate the basement greywacke from the conglomeratic basal phase of the Whangarei limestone on the north shore of McLeods Bay and there are in addition extensive dacites (plagioclase-rich “rhyolites”) which also may be pre-Whangarei, though the evidence is not conclusive. Various dykes with the compositions of quartz andesites on the north shore of McLeods Bay are almost certainly pre-Whangarei, for they have not been seen to pass up into Whangarei beds in the adjacent sea-cliffs. The main mass of andesites presents no evidence suggestive of its age, though on lithology it has long been correlated with the andesitic fragmentals of Waitakere Hills, west of Auckland City, now known to be Altonian (Lower Miocene). Reasons are given later for doubting this correlation. A fairly large mass of granodiorite-porphyry at Big Point on the southern shores of Bream Head Range intrudes Onerahi beds and has been classed as pre-Whangarei by Bartrum (1925); and by Ferrar (1925), who regarded it as the intrusive equivalent of the dacites. Recent discoveries by the writer have shown, however, that near Peach Cove, east of Big Point, identical granodiorite-porphyry intrudes the fragmental andesites of Bream Head Range. In addition, the relations between dykes of highly acidic quartz andesites and normal andesites near the south end of Ocean Beach seem most reasonably to be interpreted as indicating that the acidic rocks pierce the others.

It is clear from these facts that the order of succession from acidic to basic of Whangarei igneous rocks given by Bartrum (1925) was not as uninterrupted as he had concluded from the evidence then available to him.

Detailed Stratigraphy

Middle Jurassic conglomerates at Kawhia (Bartrum, 1935) and from xenoliths in serpentinites near Silverdale and Wellsford, north of Auckland (Bartrum, 1948).

The schists from “Whangarei Heads agree in grade of metamorphism, according to Bartrum, with the higher grade schists of southernmost Westland and Fiordland, so that they may be regarded as coming from an early Palaeozoic mass of considerable extent.

2. Waipapa Series (? Trias-Jura)

As mentioned in an earlier section, these rocks may well be included provisionally in the Trias-Jura Hokonui System, which is so widespread farther south throughout New Zealand.

The typical local rock is a quartzo-feldspathic fine-grained greywacke with small included pellets of very fine-grained andesitic lava and crystals of more or less wholly chloritized ferromagnesian minerals. Professor Bartrum informed the writer that this phase of greywacke is that almost ubiquitous in his experience of Auckland and North Auckland. As mentioned by Ferrar (1925), small masses of manganese ore occasionally rest in pockets on the surface of the greywacke and were mined many years ago at Parua Bay.

On the north shore of McLeods Bay, the greywacke includes, in addition to the general characteristic stringers of quartz or rarer calcite, local enrichments in or veins of epidote and irregular lenses up to five inches deep of spherulitic red jasperoid quartz. In the same locality it also shows phases which, in thin-section, are seen to consist largely of chlorite, with grains of quartz and a little epidote, and appear to represent earlier, fairly basic, igneous tuff. Veins of epidote may reach as much as an inch across in some of these “greywackes” and are themselves transected by stringers of quartz. The host rock consists essentially of quartz and chlorite with very little epidote; in the veins this last mineral fills the median portions of the fissures with quartz on the margins, but in narrow veinlets these relative positions are reversed. The facts indicate that the beds suffered early fracturing which permitted, at all events at deeper levels, the formation of veins of epidote, probably largely at the expense of earlier plagioclase. Subsequently, there was again the formation of fissures which were infilled in the main by quartz.

Towards the eastern end of this same north shore of McLeods Bay, the greywacke includes a dislocated and much shattered dyke of dolerite, about ten feet in width, which so greatly exceeds any other igneous rock of the area—even including pre-Whangarei limburgite—in the degree of alteration of its minerals that it is thought likely substantially to pre-date other local igneous rocks. Bartrum (Ferrar, 1925) has recorded finding serpentine near the same locality when with the Geological Survey, but has informed the writer that he has been unable to re-locate it during many subsequent visits. Presumably, therefore, it has long been buried by the advance of bay-head filling.

3. Otamatea Series (Upper Cretaceous; Senonian)

In 1925 Ferrar did not separate from his comprehensive Onerahi Series, beds which later he placed in his Otamatea Series. This series included the Batley Beds in which Marshall (1926) found abundant ammonites, enabling him to fix the age as Senonian. Indeed, at

along the north shore of Taurikura Bay, where black shales appear, intermixed often with material resembling the Onerahi limestone, as the crushed borders of intrusions.

At the Parua Bay occurrence (No. 1) black mudstones are associated with greensandstones from which concretions up to 6 ft. in diameter have been eroded, while not far distant is limestone of Onerahi type which is shortly overlain by “crystalline” limestone referable on lithology to the Whangarei Series.

The best section of Otamatea beds is that on the south shore of Urquharts Bay (No. 8) where steeply dipping greensandstones containing concretions which may reach 6 ft. in diameter appear to be folded in an anticline. Black mudstones appear on the slopes of the saddle leading to Smugglers Bay, though Onerahi limestone outcrops near the saddle itself. An approximate estimate shows that the Otamatea beds at this locality are not less than 220 ft. thick.

Concretions in Rocks of Otamatea Series

Highly characteristic, round concretions occur in greensandstones and range up to 8 ft. in diameter (Fig. 7). They largely consist of grains of quartz cemented by calcite and silica. Some show a central nucleus 8 in. or so across, while calcite-filled radial septarian cracks are not infrequent, the calcite sometimes in perfect rhombohedra. Occasionally imperfect cone-in-cone structure occurs in irregular bands within a concretion. Small concretions of barite found loose on shores may be shed from the Otamatea beds and not infrequently show cone-in-cone which sometimes simulates rosettes.

At McGregors Bay, Taurikura (opposite High Is.) and near Whangarei Heads wharf (east of Darch Point) there are a few irregular carbonate concretions, not over 4 ft. in maximum dimension, with solution-pitted, reddish-yellow surfaces.

Mr. R. N. Seelye, Chemistry Department, Auckland University College, very kindly carried out a partial chemical analysis of a sample from one of the concretions at Taurikura with the following results:

Abundant CO₂ was given off during digestion in acid.

A thin section of the material shows that the various bases are combined to give the one mineral, which constitutes a fine-grained holocrystalline rock.

Relation of Otamatea Series to other Series

Although no contact with the Waipapa greywacke is visible in the Whangarei Heads area, the Otamatea beds followed the epi-Hokonuian orogeny and subsequent peneplanation in the earlier Cretaceous and thus rest highly unconformably upon the older rocks.

Ferrar (1934) in the Rodney-Dargaville Subdivision and Turner and Bartrum (1928) in the Takapuna-Silverdale area, found little evidence of physical unconformity between the Otamatea and succeeding Onerahi Series. Harrington (MS.) also failed to distinguish a break between beds equivalent in age to those of the Otamatea Series

and those of Onerahi facies in the South Hokianga district. Yet Finlay and Marwick (1947) have referred the “hydraulic limestone,” more particularly as developed in the Kaipara region, to the Mid-Bortonian stage (Mid-Eocene), so that, unless there are hydraulic limestones developed at two different horizons. Onerahi beds must be unconformable to the Otamatea ones.

Suggestion of such unconformity is, indeed, presented in the writer's area at a small headland ¾ mile north of the southern end of Ocean Beach, for a matrix of argillaceous limestone indistinguishable from that typical of the Onerahi beds includes well-rounded but unsorted pebbles and boulders up to 2 ft. 6 in. in diameter of a sandstone indistinguishable from the concretionary greensandstones of Otamatea Series. (Fig. 8.)

4. Onerahi Series (? Mid-Bortonian–Mid-Eocene)

The beds referred to this series by the present writer are mainly an argillaceous limestone (the “hydraulic limestone” of local usage) and occasional siliceous or argillaceous phases associated with the more calcareous rock. A greensand exposed in a small quarry at the end of Robinsons Road, which runs from Taurikura towards Ocean Beach, may also belong to this series instead of to the Otamatea Series to which it has provisionally been referred above.

The inclusion of these beds with the Onerahi beds of Ferrar (1934) is based purely on lithology; as already mentioned, Finlay and Marwick (1947) have placed them in the Mid-Bortonian, but this correlation is doubtful in view of recent discoveries of the Geological Survey.^*

Though invariably greatly disordered by acute compressive forces, the Onerahi beds fail to show any decipherable structure in the writer's area, for bedding lamination is not present.

A little north of Calliope wharf, near Urquharts Bay, and, to a less extent a few chains south of the outcrop of Whangarei beds towards the middle of McLeods Bay, the Onerahi beds include interesting sedimentary dykes which are dealt with in detail in a later section.

5. Whangarei Series. (Lower to Mid-Oligocene. ? Whaingaroan to Waitakian)

This series includes basal conglomerates, which generally are fine in texture, argillaceous or glauconitic sandstones and limestone of varied purity which is crystalline in appearance owing to the abundance of broken echinodermal remains that it contains. The beds outcrop at Whangarei Heads wharf at the south shore of McLeods Bay, near Darch Point south-west of this, at the middle and northern shores of McLeods Bay (Fig. 10) and at various localities on the shores of Parua Bay. In contrast with the preceding Onerahi beds, they are relatively little disturbed except by faults.

Ferrar (1925; 1934) has shown that folding and erosion followed the deposition of the beds of Onerahi Series, so that Whangarei strata rest unconformably either on these latter or on the Trias-Jura greywacke basement.

Towards the east end of the southern shore of Parua Bay, Otamatea beds are followed first by those of Onerahi Series and these latter by 8 feet of coarse basal conglomerate of Whangarei Series with greywacke pebbles between 1 in. and 2 in. in diameter set in a plentiful matrix of echinodermal limestone. This is followed upward by grey sandstone which dips at 20° to the south-west and, in thin section, shows, in addition to grains of quartz, a little glauconite and abundant broken tests of Foraminifera. About 100 yards to the west of this section, the series abuts on greywacke and shows a sinuous strike with a dip of 70° to a little east of north. In conjunction with the steep rise of the greywacke in adjacent sea-cliffs and hill slopes to a height of over 300 ft., this disposition of the Tertiary beds strongly suggests that the beds are involved in a fault which strikes approximately parallel to the contact between the two series.

Near Whangarei Heads wharf, the Whangarei beds rest on black shales which appear to belong to Otamatea Series, but on their eastern margin they are succeeded by “hydraulic” limestone of Onerahi Series. They comprise about 150 ft. of beds which are undisturbed but for minor folding and associated faulting and consist of sandstones which become increasingly calcareous from the base up until they include a fairly pure flaggy limestone. In thin section this latter shows a varied assortment of Foraminifera, broken echinodermal remains, Polyzoa and occasional fragments of corals, calcareous algae and lamellibranch shells, along with grains of quartz and a little glauconite. Occasional thin layers are greatly enriched in a species of Amphistegina.

In their exposure near the mid-east shore of McLeods Bay the Whangarei beds show an alternation of sandstone layers in a sea-cliff about 18 ft. in height; some of the bands are fairly richly calcareous and they show in thin section numerous broken tests of Foraminifera. The writer failed to find, however, any horizon that afforded a micro-fauna that was of any use for determining the age of the beds; occasional broken macrofossils were found, especially in conglomeratic calcareous phases on the north shore of McLeods Bay, where the beds have been downthrown to the south along an east-west fault. At this last locality the basal Whangarei beds overlie a flow of limburgite and include boulders as much as 2ft. 6 in. across of this latter rock.

6. ? Pliocene Conglomerates

Ferrar (1925) has recorded stream gravels in a terrace 40 ft. above sea-level at the eastern base of Mt. Manaia and has suggested that they may be Pliocene. They contain no internal evidence of age, so that they may well be of the age to which Ferrar has assigned them.

7. Pleistocene Beds

Amongst the beds included here are early stream fans which flank the steep slopes of Mt. Manaia Range at the southern part of the eastern shore of McLeods Bay. They have been cut back into low terraces by wave action in the past, but shallowing of embayments of the initial shore-line of submergence has led to reversal of type of wave activity and there has been recent substantial progradation in front of the terraces.

Amongst other Pleistocene deposits there are elevated beaches which will be described later, and somewhat consolidated dune sands which appear from beneath modern dune sands at Smugglers Bay and Ocean Beach, often showing an earlier soil with plant roots around which concretions of impure limonite may occur. These consolidated dune sands appear here and there over a very extensive area at Ocean Beach and, particularly towards the southern end of this latter, are locally surfaced by very numerous pebbles averaging about 1 ½ in. in diameter and often carved into ventifacts. These stones cover areas several acres in extent at heights reaching over 60 ft. above sea-level and include representatives of almost every local type of rock. They contrast in size and lack of sign of having been heated by fire with the firestones common around Maori middens of the locality and are believed by Professor Bartrum^* to represent stones originally cast up on the adjacent sand beach by waves and gradually blown up the slopes of modern sand-hills by the winds of powerful gales. Subsequent deflation has removed the loose sand from them and caused them to be aggregated on the surface of older consolidated sands which have resisted deflation.* It may be mentioned that some countenance is given to Professor Bartrum's views by the presence of sporadic well-rounded pebbles up to 2 in. in diameter, without any indication of sorting, in early partly-consolidated dune sands at Smugglers Bay. These sands show characteristic large-scale cross-bedding and in thin section are seen to be well-rounded. About 80 per cent. of the grains are of plagioclase along with augite, hornblende, magnetite, a little quartz and tiny pellets of fine-grained andesite.

Such consolidation as is shown by the sands of these Pleistocene dunes is generally due to the oxidation of grains of magnetite.

It is obvious that some changes of conditions must have occurred to permit first of all the fixation of these early dunes and development upon them of a substantial soil horizon, and then later their covering by readvance of sand in recent times. The cause of the early cessation of supply of sand may well have been slight submergence, which perhaps completed the movement of depression that gave rise to the embayed shore-lines of North Auckland. Sub-Recent elevation up to a maximum of 15 ft. is shown freely around the local area by uplifted beaches; this may have inaugurated the phase of sand-dune formation that is now more or less in progress.

8. Recent Deposits

Recent deposits include narrow beaches and other bay-head fillings in suitably sheltered bays and the modern dune sands of Smugglers Bay and Ocean Beach.

Some comparison was made by the writer between the modern beach sands of these localities and the sands of the modern dunes. The grains of the beach sands are often well rounded, though not to so high a degree as those of the dunes. Mechanical analyses showed, as was to be expected, that the sands from the western portions of the dunes at Ocean Beach contain a much higher proportion of smaller grains than the beach sands. Near an outcrop of Onerahi limestone the dune sands contain grains of this limestone to the extent of as much as

Igneous Rocks

and rare brownish hornblende, enwrapped by a small amount of colourless isotropic residuum which, judging by the norm from analysis, appears to be analcite. Bartrum (Ferrar, 1925) overestimated the proportion of plagioclase in this rock, for he classed it as a basalt, though recognizing its equivalent near Pukenamu as a limburgite.

Mr. M. Ongley, Director of the New Zealand Geological Survey, very courteously arranged for analyses of both rocks at the Dominion Laboratory. These were carried out by Mr. F. T. Seelye, who kindly also worked out norms and classification according to the C.I.P.W. system. They are appended below along with others for comparison.

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3. Dacites of Parahaki Series (Ferrar, 1925)

These rocks have fairly extensive outcrop on the eastern shore of McLeods Bay, whence they extend inland at least as far as the nearby

road. They next occur farther south between McKenzies and Urquharts Bay and then again on much of the ridge that runs north from Busby Point and east of there on the western and southern flanks of Busby Head. There is also a further occurrence of unknown extent on the south-east flank of Mount Stewart.

These dacites are acidic rocks and range in silica from 70·89% to 67·98%, in potash from 4·26% to 2·19%, and in soda, conversely to the potash, from 2·62% to 4·31% (Ferrar, 1925). The proportion of plagioclase to potassic feldspar increases with the percentage of soda. Bartrum (Ferrar, 1925) has adequately described the petrography of the rocks and has mentioned the remarkable fluxional banding shown by those at McLeods Bay. The only information that the writer would add is that the dacite of the wave-cut shore platforms at Smugglers Bay contain not infrequent xenoliths of an earlier more acidic dacite.

The dacites at McLeods Bay have weathered very deeply to a clay which is being used extensively in Auckland in the ceramic industry. Usually this clay is white, but locally it shows vivid pink tints. The ferromagnesian mineral of the parent rock is biotite, which has become bleached during late stages of weathering to a pearly product which closely resembles white mica and in thin section is seen often to be closely crowded by sagenitic clusters of needles of rutile. Yellowish grey to greenish nodules of a clay mineral which closely resembles halloysite in macroscopic properties are abundant in the clay. Mr. I. McDowall, of the New Zealand Pottery and Ceramic Research Association, Wellington, has made full investigation of this clay and very kindly furnished the writer with his unpublished results. The analyses that he forwarded are interesting in that they show that the final product of weathering contains decidedly more silica and less alumina than are present in the intermediate product in which “mica” persists. The alumina has perhaps been carried away in colloidal form by downward percolating waters.

Ferrar (1925) regarded the dacites of Whangarei-Bay of Islands Subdivision as Eocene, but later, in dealing with the Dargaville-Rodney Subdivision, he stated (Ferrar, 1935) that this is incorrect and that they probably are Pliocene, for he found (Ferrar, loc. cit., p. 58) that near Waipu they have been extruded by way of a fault plane which he believed was formed during the Pliocene Kaikoura orogeny.

Doubtless, certain of the North Auckland dacites may well be Pliocene, but others definitely are Lower Miocene or earlier, for they occur plentifully in Altonian (Lower Miocene) conglomerates near Auckland.^*

In a discussion later in this paper on clastic dykes (p. 26) it is shown that there is strong suggestion that certain, if not all, of the dacites at Whangarei Heads are post-Onerahi and pre-Whangarei. If this is correct, they were extruded between the Middle Eocene and the Lower Oligocene.

4. Wairakau Series (Ferrar, 1925) of Andesitic Intrusions, Agglomerates and Minor Flows

Analyses published by Bartrum (1925) and his descriptions in the Geological Survey Bulletin (Ferrar, 1925) have shown that the rocks included here range from varied, relatively acidic, quartz andesites to normal types. Small intrusions abound, radiating irregularly from the many centres of andesitic eruption and normally of rock indistinguishable from extrusive phases. In addition, there are coarsely porphyritic intrusive types which are best described as porphyrites. They are usually present in bodies of considerably greater size than those of normal andesitic appearance. The considerable mass of Mount Stewart consists of such porphyrite and it is very doubtful if it is truly an intrusion; it is not unlikely to be the core, uncovered by erosion, of an early large tholoid.

The porphyrites and the quartz andesites universally have characters that distinguish them, apart from texture, from the normal andesites, for they invariably contain garnet and also numerous xenoliths of the igneous and metamorphic rocks that have been described by Bartrum (1937). The quartz andesites in addition are usually characterised by biotite, which does not appear in the normal andesites. It appears from these facts that the latter must originate from different magmatic sources from the others; it is difficult to understand why almost without exception they lack the xenoliths which are so prominent in members of the other group, for obviously the magma that gave rise to them must have arisen through the same basement rocks as the others. It possibly is the case that, as the normal andesites are associated with eruptive centres of considerable size, the uprising magma had sufficient volume and heat to assimilate any fragments broken from basement rocks through which it passed.

The normal andesites form agglomerates varied by occasional flows in the elongated Manaia Range, in Mount Aubrey southwest of Mount Manaia, in Bream Head Range and in Lions Head on the southwest margin of Urquharts Bay. In Manaia Range the agglomerates show good bedding with an easterly dip of about 25°; this appears to indicate that the fissure from which issued the eruptions that built the range was located west of the present crest of this latter, and that the western half of the original volcanic edifice has been removed by erosion, the debris being deposited in an early substantial valley which is now represented by McLeods Bay. Such erosion would be facilitated owing to the fact that soft Onerahi sediments, which rise to over 200 feet above modern sea-level, outcrop almost to the base of the precipitous western slopes of the range.

Near where the road to Parua Bay from Whangarei Heads turns east away from the shore of McLeods Bay, there is a conical mound of andesitic lava isolated amid sediments which appear to be mainly those of the Onerahi Series. Its time-relation to the eruptions that built the nearby Manaia Range is obscure, for its rock is petrographically distinct from that of the range.

A distinctive feature of the various accumulations of andesitic agglomerate is the manner in which they frequently are cut by wide-spaced prominent joints which in turn have controlled the topographic

crystals of sphalerite.^* Similar but smaller spherulites appear occasionally in the same type of rock a little west of Whangarei Heads wharf in McLeods Bay.

Age of Wairakau Series

The age of the Wairakau andesites is uncertain and, further, it is probable, from considerations of magmatic history, as already stated, that the quartz andesites and porphyrites have a magmatic source distinct from that of the normal andesites and need not, therefore, have been contemporaneous with these latter.

All these intermediate intrusions penetrate both Otamatea and Onerahi beds. The normal andesites have not been found locally in association with Whangarei strata, so that their relation to these latter is not shown. They have long been correlated on lithology with the Manukau Breccia Series of Waitakere Hills, Auckland, which are now found by Dr. H. J. Finlay^† on foraminiferal evidence to belong to the Altonian (Lower Miocene) stage.

For certain of the quartz andesites the position, however, is different, for on the northern shores of McLeods Bay several very large intrusions of these rocks, intersecting greywacke on the shore, almost certainly fail to pass up into Whangarei beds which rise for 80 feet or more above the greywacke. Talus has obscured actual contacts, but it is reasonably certain that, had the dykes invaded the Whangarei strata, their passage would have been indicated by blocks of their rock in talus and other signs. Such indications, however, are absent, so that early members of these quartz andesites almost positively are pre-Whangarei. Yet other highly acidic quartz andesites have relations to the normal andesites of a small headland near the south end of Ocean Beach which are best interpreted as indicating that a series of these light-coloured acidic dvkes there penetrates the normal andesites.

If these latter are correctly assigned to the Altonian, it is clear that intrusions of quartz andesites have occurred over a very long period of time, namely from a time in advance of local Whangarei sedimentation, which at latest is Waitakian (Mid-Oligocene), to the Altonian (Lower Miocene).

An alternative to acceptance of this conclusion, and it would appear to be a preferable one, is to discard the previously accepted correlation of local fragmental andesites with the Manukau Breccia Series and instead to correlate them with similar “First Period” rocks of Coromandel Peninsula. These latter overlie sediments of the Torehine Series (? Lower Eocene) from which Dr. Brian Mason has recently collected Foraminifera regarded as Waitakian by Dr. H. J. Finlay.†.

5. Granodiorite-porphyry of Big Point and Peach Cove on the Southern Shores of Bream Head Range

A little west of Big Point there is a large intrusion of granodiorite-porphyry, shown by analysis to be the analogue of local dacites, which

Magmatic History and Relationship

In describing the igneous rocks of the Whangarei-Bay of Islands Subdivision, Bartrum (Ferrar, 1925) accepted Ferrar's belief, based on the field evidence then available, that, apart from the pre-Whangarei limburgite on the north shore of McLeods Bay, the dacites were the earliest of the igneous rocks of the subdivision, classing as contemporaneous with them the granodiorite-porphyry of Big Point. Variation diagrams based on an excellent series of analyses showed that the rocks dealt with were members of a differentiation series. These were believed to maintain a regular order of decreasing acidity from the acidic dacites to sub-Recent olivine basalts, omitting from the series, however, the pre-Whangarei limburgite.

It has been shown above that this regularity of succession does not in fact exist; granodiorite-porphyry and some highly acidic quartz andesites (at Ocean Beach) alike have been found to post-date normal andesites. There thus has been alternation in time of injection or extrusion of more acidic and less acidic rocks in the early stages of the magmatic cycle of the Whangarei region; this cycle has closed with the emission of widespread basalts.

From his work on Keweenawan lavas, Broderick (1935) concluded that the presence of oxidized minerals at the upper levels of the flows indicated that volatile transfer played an important part in the differentiation of these lavas. Plotting the percentages of alkalies against the silica, he found that the curve cut across similar curves for the classical Katmai and Lassen Peak Series at the lower silica end and that only later did it turn and parallel these latter for the higher silica ranges. He believed, therefore, that the differentiation of the Keweenawan rocks was not wholly by differentiation as Bowen (1928) believes was definitely the case for the Katmai and Lasaen Peak rocks.

The present writer plotted a corresponding curve for the Whangarei Heads rocks, using the analyses published by Bartrum (1925; Ferrar, 1925) and found that it parallels those for Lassen Peak and Katmai. There is thus no need to invoke any other agency for the origin of the local rocks than crystallisation-differentiation.

The alkali-lime index of the Whangarei Heads rocks on the method of Peacock (1931) is approximately 62. This means that, at a point on the variation diagram where the silica percentage is 62, the sum of the alkalies equals the percentage of lime. In this respect also there is correspondence with the Lassen Peak series, where the alkali-lime index is similarly 62.

If the analyses of the Whangarei Heads limburgite published herein are included with those of the other rocks of the region, the curves of the various oxides in the variation diagram depart from the relatively smooth curves obtained when these analyses are omitted. This applies particularly to the curves for alumina, magnesia and ferrous oxide and results from the high proportions of augite and olivine in these limburgites. Bowen (1928) has shown that, if we assume that basalt is the parent magma, the composition of rocks such as these limburgites must be determined by that of a mesh of accumulated down-sunken crystals. In the case of the local limburgites, however, it is clear from the texture, which is characterised by an abundant fine-grained mesostasis enwrapping phenocrysts of olivine and augite, that crystal-settling had only limited importance in the genesis of the rock. A far more probable explanation is that involved in the reaction upon early separated hornblende which has sunk into a hotter liquid (Bowen, 1928, p. 270), whereby olivine and pyroxene, with perhaps some calcic plagioclase, are precipitated together with nepheline and probably leucite. The magma must then have been extruded before these reactions could be reversed.

Clastic Dykes in Onerahi Limestones

branching and re-branching stringers. Excavations made by the writer suggest that all are practically vertical.

The rock fragments in the dykes average under 1 inch in maximum dimension and tend to have their long axes parallel to the dykes, though there is no sign of any assorting. They are tightly interlocked and cemented one to another and to their walls by calcium carbonate. There is no sign of the dykes having been affected by earth movements since they were formed.

Similar but shorter dykes also occur close to the south side of Hollingworth's boat-slip near the middle of McLeods Bay.

Origin of Constituent Materials of the Clastic Dykes

The hydraulic limestone and dacite of the dykes have their parent masses close at hand, as mentioned already, but the presence of rocks of the greywacke series cannot be so easily explained, for, although these latter rocks undoubtedly underlie the area concerned, they do not outcrop nearer than the north shore of McLeods Bay, 4 ½ miles to the north-west, where they appear in an earth-block which has been upfaulted with reference to the adjacent southern block not less than 200 feet.

It is clear from the marked angularity of the greywacke fragments in the dykes that they cannot have been transported by water from so far afield as these north-western outcrops of the parent rock. There are, however, three other possibilities:

Before discussing these possibilities, it is necessary to decide, if possible, whether the dykes were filled by injection from below or from above. Lahee (1931) lists as evidence of infilling from below such features as upturned strata in wall-rock; upward thinning and final upward termination of the dykes; flow structure parallel to the walls in the filling; inclusion of wall-rocks in the dykes; considerable size and continuity of some of the dykes and similarity of their material to underlying rocks. Admittedly, several of these criteria apply to the dykes in question, but they could equally well support the hypothesis of filling from above.

Objections to the theory of filling by injection from below in consequence of pressure include the absence of fine-grained interstitial matrix that would appear essential for mobility of the mass, and the omission, so far as could be determined, of fragments of Otamatea beds, which are stratigraphically below those of the Onerahi Series. Yet these objections are not insuperable, for earlier finegrained matrix may have been strained off from the mesh of coarser fragments by pressure, whilst it is known that an erosional interval separated Otamatea from Onerahi sedimentation. Otamatea strata may well have been removed from the area concerned prior to the emplacement of the Onerahi beds and, therefore, of the dykes.