TANE. 24, 1978

MOAS - NEW ZEALAND'S FIRST ROCKHOUNDS. EVIDENCE FROM KAWERUA

by Bruce W. Hayward

N . Z . Geological Survey, P.O. Box 30-368, Lower Hutt

SUMMARY

Highly-polished quartzose pebbles, found on the hills around Kawerua, are eroding out of two beds of wind-deposited Pleistocene sandstones (Kaihu Group). These pebbles consist predominantly of semi-precious gemstone lithologies (agate, chalcedony, chert, jasper, opal) that can only have come from source rocks 5-10 km away in the Waimamaku Valley.

Comparison with proven moa gizzard stones, and a process of elimination of all other modes of transport leads to the conclusion that these pebbles were brought to the Kawerua area in the gizzards of moas.

A study of records and available collections suggests that moas all over New Zealand roamed the countryside in search of semi-precious gemstones which they proceeded to collect and tumble polish in their gizzards. Moas were surely the fore-runners of our present-day rockhounds.

INTRODUCTION

Ever since the Auckland University Field Club established its Scientific-Station at Kawerua, on the west coast of Northland (Fig. 1), people have been finding small, highly polished, white pebbles (Figs 2,3) on the sandy hills surrounding the Station. Many have collected a handful and brought them back proclaiming, in jest, that they had found moa crop stones. Being rather sceptical of this conclusion, I decided to try and find out where these pebbles were coming from and their true origin.

PEBBLES IN PLEISTOCENE SANDS

The polished, white pebbles are generally found sitting loose on the ground in areas of active erosion (by wind or water), on bulldozed forestry roads or on hard, iron-pan deflation areas. In all these places, the hills are composed of Pleistocene sands of the Kaihu Group (Hayward 1972, MacFarlan 1974).

One of the richest localities for finding these pebbles is around the actively eroding Pukenuiorongo Bluffs, 1km east of Kawerua (Fig. 1). The Bluffs are 120m above sea level and consist of a series of large washouts exposing a 40m thick sequence of Pleistocene sands (figs 2,3 of MacFarlan 1974).

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Fig. 1. Right: Map of New Zealand showing location of Kawerua, on the west coast of Northland. Left: Map of Kawerua area showing Pukenuiorongo Bluffs immediately inland. The outcrop of Kaihu Group (Pleistocene sandstones) from which the polished pebbles are now eroding is stippled. The outcrops of three possible source rocks (Mangakahia Group, Tangihua Volcanics, Pukorukoru Formation) for the quartzose pebbles are shown around the Waimamaku Valley.

Pukenuiorongo Bluffs' Stratigraphy The sequence described as merely four units by MacFarlan (1974) was found

to be more complex at the top (Fig. 4). The lower two-thirds of the washouts consist of a massive iron-stained sandstone. This is overlain by two, fine, pumice sandstone horizons (tuffs) separated by a l-2m thick iron-stained sandstone and, in places, a thin soil horizon. The upper tuff is overlain by four layers consisting of (bottom to top) a silty sandstone, sometimes forming an iron-pan; a sandy carbonaceous layer; an extremely hard silicapan (silcrete); and a loose sandy topsoil (Fig. 4).

These four upper horizons are typical of deeply leached zonal podzols formed under mature kauri forest (Gibbs et al. 1968, p. 64), and probably developed from a single medium-grained sandstone unit, similar to that between the tuffs.

Environment of Accumulation This sequence probably accumulated on land as there is no evidence of water

deposition. This is supported by the presence of a soil horizon and of kauri cones and other plant matter in the sandstone between the tuffs. Although none of the sandstones of Pukenuiorongo Bluffs preserve any laminations or

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Fig. 2. Some of the well-rounded, polished white pebbles collected from Pukenuiorongo Bluffs, The grey mottled colour of many of these pebbles is caused by crustose lichens and fungi that have grown since the pebbles became exposed on the surface.

Fig. 3. A selection of the pebbles collected from Pukenuiorongo Bluffs to illustrate the range of size and shape present The one cent coin has a diameter of 18mm.

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crossbedding typical of dune deposits, they are probably wind-blown accumula­tions having advanced inland from the coast (much as similar sands are doing today in parts of this area). The tuffs are considered to be airfall deposits of wind-blown ash from eruptions in the Coromandel or Taupo regions.

Source of Pebbles

Most of the pebbles found around the Pukenuiorongo Bluffs occur loose on the surface of small outwash fans of sand that collect on steps in the upper half of the bluffs. A few occur loose on the exposed iron pan surface above the upper pumice sandstone. These pebbles must be eroding out of the upper layers of the sequence and because of their size and hardness are being concentrated on the surface by the removal and weathering of the sand grains.

On close examination of the bluffs several individual pebbles were located in situ in the medium sandstone between the tuffs, and also in the topsoil and silcrete layers above (Fig. 4). A dispersed cluster of up to ten pebbles was found cemented in the silcrete within an outcrop length of 0.8m and thickness of 0.2m. No pebbles were found in the thick basal sandstone, nor in the tuffs. The pebbles appear to be restricted therefore to the two original medium sandstones (presumably wind-blown sand deposits) between and above the tuffs.

0 3 m sandy topsoil with rootlets and gum 03 -0 5 m cemented quartz sandstone (silcrete) 01-02 m sandy carbonaceous horizon (humus layer)

0 5-13 m silty sandstone

3-5 m fine pumice sandstone

0- 01 m carbonaceous soil horizon

1- 2 m iron-stained medium sandstone with rare plant matter

1 m fine pumice sandstone

30 m * massive iron-stained medium sandstone

p pebbles in situ (moa gizzard stones)

Fig, 4. Stratigraphy of the upper parts of Pukenuiorongo Bluffs showing the units in which pebbles were found in situ.

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p

Age of Sequence

By comparison with the sequence of palynologically dated Pleistocene sandstones of the North Kaipara Barrier (Richardson 1975), it would appear that the sandstones of Pukenuiorongo Bluffs and the surrounding hills are of mid to late Pleistocene age (probably Castlecliffian).

PEBBLE LITHOLOGIES

All the pebbles were collected from within a sample area of 100 x 10m (1000m 2), running across the top of Pukenuiorongo Bluffs. The 358 pebbles collected from this area were grouped into a number of lithologic categories and counted (Table 1). The bulk of the pebbles (Fig. 2) consist of white, opaque chalcedony - a fine-grained quartz (68.7%), or mottled, veined, or slightly darker varieties of chalcedony (17.9%). 98.3% of the pebbles are composed of various types of quartz (agate, chalcedony, chert, opal, quartzite) with only five pebbles of local basalt and one of fine-grained dolerite (Fig. 5).

Source of Pebble Lithologies

All the pebbles are rocks of pre-Pleistocene lithology, such as underlie the extensive coastal strip of Pleistocene sandstones (Hayward 1972, MacFarlan 1974). The five basalt pebbles come from the Waipoua Basalt that directly underlies the sandstones and is intermittently exposed along the coast, in coastal stream valleys and further inland (MacFarlan 1974). Waipoua Basalt is the only pre-Pleistocene rock type exposed within 5km of Pukenuiorongo Bluffs but it has no associated quartz veins from which the majority of pebbles could have come.

The nearest source of quartz is from three groups of rocks, all of which occur in the Waimamaku Valley, 5- 10km north of Kawerua (Fig. 1). 1. Tangihua Volcanics forming the high country on the north side of the

Waimamaku Valley are cut by quartz veins and veinlets that are a possible source of the chalcedony, chert, jasper and quartzite. The single dolerite pebble most probably came from these rocks.

2. Cretaceous and Paleocene Mangakahia Group sediments outcrop throughout much of Waimamaku Valley (Fig. 1). Some of these are highly siliceous (Hay 1960) and are cut by quartz veins that are a likely source of many of the pebbles.

3. Pukorukoru Formation rocks occur within the basal part of the Waipoua Basalts around the mouth of the Waimamaku River (Hayward 1973). These sediments contain numerous pieces of wood, in places somewhat silicified, that could have been the source of the agatised wood, agate and possibly the jasper, opal and chert. The Pleistocene sandstones from which the pebbles are eroding, may have

accumulated during a glacial period when sea-levels were lower than the present. With lower sea-levels it is quite likely that Pukorukoru Formation rocks could

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Fig. 5. A selection of the pebbles collected from Pukenuiorongo Bluffs to illustrate some of the lithologies present, a = agate; aw = agatised wood; c = chalcedony; ch = chert; o = common opal; j = jasper; d = fine-grained dolerite.

have been exposed much closer to Pukenuiorongo Bluffs but unlikely that Mangakahia Group and Tangihua Volcanic rocks would have been.

PEBBLE SIZES AND SHAPES

The 358 pebbles collected from the sample area range in size from 9-74mm maximum diameter, with 80% within the range 17-40mm and a mean maximum diameter of 28mm (Fig. 6). Only nine pebbles are larger than 50mm.

All the pebbles are highly polished (except the basalts) and well rounded, but very few approach spherical in shape (Fig. 3). The majority are distinctly flattened and a few are moderately elongate. A small number of the pebbles are very slightly pitted or abraded, probably by wind-blown sand after they were eroded out of the Pleistocene sandstones. Several other pebbles, partly buried in the loose sand, had the exposed surface covered by the very slow-growing crustose lichen Lecidea (Fig. 2), indicating that they had been sitting there exposed to the elements for many years.

PEBBLE TRANSPORT

Since the majority of pebbles are quartz they must have been transported a distance in excess of 5km from their source rocks in the Waimamaku Valley to

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3 0 4 0

Max imum diameter (mm)

Fig. 6. Bar histogram showing size distribution of pebbles from Pukenuiorongo Bluffs.

their place of burial in the Pleistocene sandstones of Pukenuiorongo Bluffs. How were they transported?

The Waimamaku River could have carried the pebbles down to the sea and coastal currents could have transported them along the coast to the beach near

Fig. 7. Three polished pebbles from Pukenuiorongo Bluffs (left) compared to three pebble ventifacts (right) from a nearby deflation area to show the difference in surface textures.

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Table 1. Lithologic composition of polished pebbles collected from 1000m2 sample area, Pukenuiorongo Bluffs.

Lithology Number

of pebbles %

agatised wood 1 0.3 agate — banded 2 0.6

- purplish, transluscent 4 1.1 chalcedony - white, opaque 247 68.7

- mottled or banded white, opaque 16 4.5 - white with quartz veinlets 14 3.9 - blue-grey, sometimes mottled 33 9.2 - green-tinged with quartz veinlets 1 0.3

chert - yellow-brown 9 2.5 - brown with quartz veinlets 3 0.8 - dark rusty brown 1 0.3 - brown-black 2 0.6

common opal - semi-transluscent 7 2.0 jasper - red, opaque 2 0.6

- red with quartz veinlets 5 1.4 quartzite - crystalline, white 2 0.6

- spherulitic 1 0.3 - quartz vein 2 0.6

dolerite - fine-grained 1 0.3 Waipoua Basalt - coarse grained 2 0.6

- fine grained 3 0.8

T O T A L 358 100%

Kawerua. Since the Pleistocene sandstones in which the pebbles are preserved, are believed to be wind blown deposits, the pebbles washed up on the beach would have had to be moved inland by strong winds. This is a long process that would have exposed the pebbles to abrasion by wind-blown sands producing diagnostic surface pitting (Fig. 7) and ventifact shapes. Such a process is occurring today in the deflation area, 0.6km south of Kawerua (Hayward 1974). Here all the pebbles are deeply pitted and not at all polished or well rounded; the majority are of basalt (locally derived) and only a few are quartzose (probably derived by erosion of the Pleistocene sandstones).

Several lines of evidence argue strongly against this river — longshore drift — wind-blown transport explanation. 1. The required southward-moving longshore drift is contrary to the major

transport direction operating today. 2. Locally derived basalt pebbles, very rare in the Pleistocene sandstones, could

be expected to be dominant as in the modern situation. 3. The pebbles are highly polished and lack the pitted surface that could be

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expected for those exposed to long periods of wind-blown sand (Fig. 7). 4. The height above and distance from the probable coastline at the time of

accumulation make it very unlikely that the pebbles could have been transported as far from the beach by wind as implied by this explanation. What other modes of transport are available? No glacier existed as far north as

this, even during the glaciations. The only remaining possibility is transport by animals. No humans or terrestrial mammals were present in New Zealand at this time. Marine mammals such as sea-lions are known to carry pebbles (gastroliths) from place to place (Fleming 1951), but they generally prefer hard rocky coastlines to land upon and do not move far inland over hot dry areas of sand dune.

Most birds are known to carry grit or small pebbles in their gizzards but no living New Zealand bird is large enough to carry pebbles of the size found. The only possibility left is the group of large, extinct, flightless New Zealand birds, the moa (Order Dinornithiformes), which is known to have lived in large numbers throughout the country until a few hundred years ago. Could they have been responsible for transporting these pebbles from the Waimamaku Valley to this area?

MOA GIZZARD STONES

The gizzard of most graminivorous, herbivorous and some omnivorous birds contain small stones or grit (Farner et al. 1972, p. 377). These stones or grit are swallowed and held in the muscular, grinding gizzard to assist in the mechanical breakdown of the more fibrous or harder items eaten. The extinct New Zealand moas are well known to have had gizzard stones (commonly called "moa crop stones").

Like many other New Zealand birds, moas became extinct in the last few hundred years and when Europeans first arrived in this country there were many finds of moa bones, associated with neat heaps of gizzard stones, in caves, sand dunes or drained swamps (e.g. Chapman 1884, Hamilton 1892). More recently, excavations at Pyramid Valley, North Canterbury, uncovered three moa skeletons with gizzards still intact. "The three moa gizzards recovered during the 1965 excavations consisted of the usual "plum-pudding" of stones scattered through a matrix of seeds, leaves and other vegetable matter" (Gregg 1972, p. 155). These are thus the best authenticated moa gizzard stones recorded and data given by Gregg on their number, size and lithology is summarised in Table 2. The three Pyramid Valley gizzards are from three different moa species — one large and two medium-sized. The gizzard from Dinornis maximus, the largest known moa species (Oliver 1949, p. 175), contains 1800 stones ranging in size up to 68mm.

Gizzard stones could be transported about a district by a moa and deposited on the ground in several different ways. 1. The total stone contents of the gizzard could be deposited in one place on the

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Table 2. Comparison of documented moa gizzard stones with the pebbles collected from the sample area at Pukenuiorongo Bluffs, Kawerua. References: 1 Gregg (1972); 2Hamilton (1892); 3Chapman (1884); "National Museum Collection. Pyramid Valley gizzard stones are from three different moa species: a - Dinornis maximus; b -Euryapteryx gravis; c - Emeus crassus.

Number Size Locality of stones Total weight Range Composition

Pyramid Valley a 1 c. 1800 4380 g 2-68 mm greywacke

Pyramid Valley b 1 5 20 253 g 2-28 mm greywacke

Pyramid Valley c 1 180 35.5 g 2-22 mm greywacke

near Dunedin 5 9 2041 g; 2722 g 9 white quartz

Mackenzie Coun t ry 3 ? 1616 g; 1814 g; 2466 g 9 white quartz

Lake Manapouri 3 389 2013 g 9 white quartz

Lake Manapouri 3 342 2098 g J white quartz

Lake Manapouri 3 210 227 g 9 white quartz

Riverton 3 9 567 g ? mostly transparent quartz

Swampy H i l l , Dunedin 4 62 9-42 mm white quartz

Pukenuiorongo Bluff 358 4479 g 9-74 mm mostly white quartz

death and decay of an individual bird. 2. As the stones are ground down in the gizzard, smaller ones could pass through

the moa's digestive system and be deposited with the excreta. 3. A number of living birds are known to regurgitate or cough up the grit or

small stones from their gizzards. This was quite likely possible with moas also and would be a very effective method of depositing stones more or less at random.

COMPARISON OF PEBBLES WITH MOA GIZZARD STONES

Size Table 2 compares the collection of pebbles from Pukenuiorongo Bluffs with

collections of stones that definitely appear to be the total contents of individual moa gizzards. The Pyramid Valley and "near Dunedin" collections were separated from the fibrous contents of actual gizzard remains, whereas the remaining collections are the heaps of stones found in association with the bones of individual moas. These statistics show that pebble collection from Pukenui­orongo Bluffs have a size range comparable with stones from proven gizzards of larger moa species. The pebble collection, however, has a mean weight greater than any of the six gizzard stone collections with comparable statistics (Table 2). This is not considered to be significant for several reasons. 1. Many of the smaller pebbles may have been completely buried in the loose

sand of the sample area and would therefore be under-represented in the collection, whereas all the partly buried larger pebbles were collected.

2. The pebble collection obviously does not represent the total contents of any one moa gizzard. It is more likely a mixture of regurgitated gizzard stones from a number of individual moas. There are no moa bones associated with the pebbles of Pukenuiorongo Bluffs, a fact that might be used to rule out the possibility that they are derived from the gizzards of dead birds. However, conditions for the preservation of bones were probably not favourable in these Pleistocene sandstones as no bones have been recorded from the extensive areas of Kaihu Group sandstones anywhere in Northland or Auckland. (The large number of moa bones that have been found in northern New Zealand dune areas are from much younger Hawera Series and Holocene sands). Thus a comparison of the mean size of a mixture of probably regurgitated

pebbles with the mean size of the total stone contents of an individual gizzard is far less significant than the remarkable similarity of the total size ranges recorded.

Shape Authenticated moa gizzard stones (Table 2) possess a wide range of shapes

and surface textures, no doubt dependent upon the length of time each stone has been in the gizzard, grinding away and gradually becoming more and more rounded and polished. The greywacke gizzard stones from the Pyramid Valley

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moas range from subrounded to rounded but their surfaces are unpolished (Gregg 1972). I have examined quartzose gizzard stones found in association with moa bones in caves at Waitomo and Puketitiri, Hawkes Bay (P.R. Millener and National Museum collections). These ranged from subangular to well rounded and several had a highly polished surface. Most of the gizzard stones lacking a polished surface are subspherical while those that are highly polished are more variable in shape.

The pebbles collected from Pukenuiorongo Bluffs are generally flatter, more rounded and more polished than most of the authenticated moa gizzard stones, but are indistinguishable from the highly polished members of the gizzard stone suite. This would appear to support the contention that the pebble collection was not derived from the gizzards of dead moas, but more likely accumulated as gizzard stones coughed up by living moas. Rough, irregular stones could be expected to aid the mechanical break down of food in the gizzard far more than rounded, polished stones. Perhaps when the gizzard stones became worn down, highly polished and of lesser efficiency, the moa coughed them all up and replaced them with new stones. This rather speculative hypothesis would certainly explain the highly polished and somewhat flattened pebbles of Pukenuiorongo Bluff.

The Kawerua area is not the only place to have numerous polished and somewhat flattened quartzose pebbles scattered about in situations that seem best explained as stones transported there in moa gizzards (Archey 1941, p. 91). Examination of some of these scattered pebbles (National Museum Collections) showed them to be indistinguishable from those from Kawerua and possibly best explained as regurgitated gizzard stones.

Chapman (1884, p. 178) remarked "I had originally fancied that gizzard stones were worn somewhat flatter than water-worn stones, but abandoned this at the suggestion of a friendly critic. An examination of the beautiful set in the Colonial Museum at Wellington inclines me, however, to readopt this view." Most of the pebbles labelled "moa gizzard stones" in this institution are small scattered surface collections from a wide range of localities.

MOAS - NEW ZEALAND'S FIRST ROCKHOUNDS

The most acceptable explanation for the polished pebbles that are eroding out of the Pleistocene sandstones around Kawerua, is that they came from the Waimamaku Valley, 5-1 Okm to the north, having been picked up and swallowed by moas and carried around in their gizzards for some time before being coughed up in these sandy coastal areas and buried by the advance of dune sand.

One of the most striking features of these Kawerua pebbles (former moa gizzard stones) is their composition (Fig. 5). Almost all are rock types that the present-day rockhound would collect for tumbling, as they are fine-grained quartz varieties (semi-precious gemstones) that take a good polish. Several of these pebbles, such as the agate, agatised wood and opal, would be prized by

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many rockhounds. The fact that this district is not highly rated as a good rockhounding area today, is an indication of the relative scarcity of these rock types in the area. Basalt, andesite, sandstone, siltstone and other rock types far outnumber the minor quartz sources and it is therefore logical to conclude that the moas were not only very particular about the rock type they selected for their gizzard stones but they actually had to search for it. In a sense moas must have been New Zealand's first rockhounds.

Moas may have been attracted to the gleaming white colour of the majority of the quartzose pebbles, but the fact that a number of them are other colours (red, brown, black) leads me to suggest that it was the rock type and not the colour that they sought. Quartz is the most resistant rock type available in the district and therefore the most suitable as grinders in the moa gizzard.

Apparently moas did not restrict their rockhounding activities to Northland. The majority of collections of authenticated and assumed moa gizzard stones from around New Zealand are predominantly of quartz (Table 2). Hamilton (1892) for example, noted that all the stones from actual moa gizzards that he excavated from near Dunedin were of white quartz, the nearest source of which was 6km away. Other localities where gizzard stones have been recorded or observed to be almost entirely of quartz include Waitomo, Puketitiri (Hawkes Bay), Porangahau and Lyall Bay (Wellington) in the North Island and Nelson, Ashburton, Riverton, Mackenzie Country, Moorhouse Range, Manapouri and Swampy Hill (Dunedin) in the South Island.

In only two recorded localities the gizzard stones have not been predom­inantly quartz. At Pyramid Valley they are all greywacke (Gregg 1972). This valley passes through Tertiary limestones and soft sandstones with greywacke exposed in the headwaters. There appears to be no nearby source of quartz and the next most resistant rock type available is greywacke. A similar argument can be used to explain the dominance of greywacke over quartz in moa gizzard stones recorded from near Lake Tekapo (Chapman 1884, p. 175).

CONCLUSION

Thousands of years before the first human set foot in New Zealand, the now extinct, flightless bird the moa, was roaming the countryside searching for semi-precious gemstones (such as agate, opal, chalcedony, chert, jasper) which it proceeded to collect and tumble polish in its gizzard before coughing them up to admire, much in the same way as present-day rockhounds do.

A C K N O W L E D G E M E N T S

I am grateful to Phil Millener (University of Auckland), John Yaldwyn and Sandy Bartle (National Museum) for allowing me to examine their collections of moa gizzard stones and for helpful discussions. I would also like to thank Sir Charles Fleming (N.Z. Geological Survey) for reading the manuscript and suggesting improvements. Typing was undertaken by Mrs M . Ruthven.

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R E F E R E N C E S

Archey, G . 1941: The Moa, a study of the Dinornithiformes. Auckland Institute and Museum Bulletin No. I 135pp.

Chapman, F. 1884: Notes on moa remains in the Mackenzie Country and other localities. Transactions of the N.Z. Institute 1 7: 172-178.

Earner, D.S., King , j . R . & Parkes, K . C . 1972: "Avian Biology" vol. II. Academic Press, New York . 612pp.

Fleming, C . A . 1 951: Sea lions as geological agents. Journal of Sedimentary Petrology 21(1): 22-25.

Gibbs, H.S., Cowie, J .D. & Pullar, W.A . 1968: Soils of North Island in "Soils of New Zealand, Part 1". Soil Bureau Bulletin 26(1).

Gregg, D .R . 1972: Holocene stratigraphy and moas at Pyramid Valley, North Canterbury, New Zealand. Records of Canterbury Museum 9(2): 151-158.

Hamilton, A . 1892: Notes on moa gizzard stones. Transactions of the New Zealand Institute 24: 172-175.

Hay, R .R . 1960: Geology of the Mangakahia Subdivision. New Zealand Geological Survey Bulletin No. 61.

Hayward, B.W. 1972: Geology of the Kawerua coastline, North Auckland. Tane 18: 149-168.

Hayward, B.W. 1973: Miocene stratigraphy of the Hokianga - Waimamaku coastline, north of Kawerua, North Auckland. Tane 19: 119-125.

Hayward, B.W. 1974: Notes on orientation of ventifacts in a coastal reg, Kawerua. Tane 20: 152-155.

MacFarlan, D . A . B . 1974: Preliminary report on the inland geology of the Kawerua area. Tane 20: 111-114.

Oliver, W.R.B . 1949: The Moas of New Zealand and Australia. Dominion Museum Bulletin No. 15. 206pp.

Richardson, R . J . H . 1975: The Quaternary geology of the North Kaipara Barrier. Unpublished MSc thesis, University of Auckland.

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