Tertiary, or Kainozoic Formations.
By far the greater part of the North Island of New Zealand is covered by rocks of Tertiary age.
The oldest of the Tertiary rocks would appear to be beds of brown coal, with accompanying shales. It is necessary to observe that there are beds of lignite found in the newer Tertiary sandstones, which may be defined as lignites, not brown coal.
These brown coal and shale strata are succeeded, in the Wellington province, by strata of blue clay and limestone, with Cucullœa singularis, of which beds this fossil is most characteristic. The blue clay is again covered by a succession of strata of sandstones, and arenaceous limestones, both being fossiliferous, and attaining in some parts a great thickness. Above these again a drift gravel is often found. In the Whanganui, Rangitikei, and other west coast rivers, some of these Tertiary strata are marked in a remarkable manner, with numerous horizontal bands, or lines, of boulders, or concretions surrounding boulders or some other substances, such as fossil shells. These boulders are generally either of Igneous or Palæozoic rocks. In the southern part of the Island, these Tertiary formations, or some of them at least, are found on both sides of the main range, lying generally horizontal or slightly inclined, and abutting on the Tararua and Ruahine ranges on both sides. They then stretch northward on the west side of the range, until they reach, and become mixed with, the volcanic products of the interior, continue to the N.W. probably all through the province of Taranaki (fringing Mount Egmont), into the province of Auckland—the Tertiaries of which will be hereafter described. From the western shores of Cook's Straits these Tertiaries have a gentle slope upwards until they reach to within half-a-mile of Tararua and Ruahine, where the inclination becomes greater, and the beds appear somewhat disturbed, as if the range had been thrust through them, or pressed against them from the eastward, and in support of this view there is a line of fault along the western, or Wairarapa, side of the ranges, in which the gravels of the plain, resting against the ranges are fissured, and that side of the fissure next the ranges is raised some four feet above the other.
In a similar way the nearly horizontal Tertiaries at the Whanganui part of the basin, are tilted at an angle of perhaps 20°, on approaching the volcanic chains.
We may, therefore describe the whole of the North Island, except the Palæozoic ranges, or, at all events, all that part of the country to the
westward of the main ranges, as the great Tertiary field of New Zealand; and the country sloping from the flanks of Tararua and Ruahine, from the Patea country and the end of Kaimanawa, and from the great volcanic chain, and also the slopes of Mount Egmont, and into, perhaps across, Cook's Straits, in fact, all the slopes towards Cook's Straits, as the great Tertiary basin of the country. On the eastern side of the main range, the usual Tertiaries are found, except the brown coal series, which has not yet been discovered, except in small quantity, but Cucullœa singularis is found on a tributary of the Pahaoa, and the usual Tertiary fossils abound in many places. The eastern rocks generally dip slightly to the westward, but, at about seven miles from the east coast, they are thrown up at a very high angle, where the edges of the upturned strata form a most striking series of peaks, called Taipo, and supposed by the aborigines to be the haunts of Taniwha, or other mysterious and mythical animals; and certain sandstones and limestones, of undetermined age, succeed them, which, as before stated, are probably of Mesozoic age.
The Tertiary rocks pass northward from the eastern side of the province of Wellington, through that of Hawke's Bay and appear to extend throughout along the east coast, to the East Cape, at which point they lie horizontal, and extend from that Cape to the nearest Palæozoic rocks in Hick's Bay, a distance of perhaps eight to ten miles.
It will be seen from the above, that the Tertiaries occupy a great breadth of country on the east coast, having an average width of about thirty miles, and as Hochstetter gives, perhaps somewhat undue prominence to the mountain chain extending N.N.E. from Cape Palliser, and inferentially to the older rocks along the east coast,1 I propose to amend his description of the main ranges, as follows, viz, which stretch along parallel to the east coast, and at an average distance of about thirty miles inland, from Cook's Straits to Hick's Bay, near the Bay of Plenty. This description will leave room for the Tertiaries, and probable Secondaries, which, although forming ridges of an average height of perhaps 1000 feet, or rather more, can barely be called mountainous, nor can they be considered as the continuation of the Southern Alps.
In the southern part of the Island the general character of the Tertiaries is as follows:—
On the eastern side, the upper beds are calcareous—the middle beds are arenaceous and argillaceous.
[Footnote] * Fischer's translation, p. 45.
On the western side, the upper Whanganui beds are arenaceous; the middle calcareous and argillaceous; and the lower argillaceous.
With regard to the Auckland Tertiaries, Hochstetter writes as follows:—“The various Tertiary strata are found for the most part in a horizontal position. A remarkable fact, from which we may conclude that even the numerous volcanic eruptions which took place during and after the period of their deposition had not power enough to dislocate the whole system, but merely to produce local disturbances.”
“The Tertiary period must be divided into two distinct formations, which may perhaps correspond to the European Eocene and Miocene. There is an older formation which is found principally on the west coast and in the interior on both sides of the primary ranges, and a newer one, which may be called the Auckland Tertiary formation.” After a description of the brown coal of the Auckland Province, the same writer goes on to state: “I now come to another series of the older Tertiary strata, examples of which are found occurring in great regularity on the west coast from Waikato to Kawhia. The lowest are argillaceous, the middle calcareous, and the upper arenaceous. The characteristics of the first clayey strata, are a light grey colour, very few fossils, small crystals of iron pyrites, and glauconitic grains, which give these clay marls a similarity to the gault and green sands of the cretaceous formation in Europe. They are found on the eastern branches of Whaingaroa, Aotea and Kawhia harbours.
Of greater interest and importance are the calcareous strata, consisting of tabular limestone, sometimes of conglomerate nature, sometimes more crystalline, the whole mass of which is formed of fragments of shells, corals, and foraminiferæ, interspersed with perfect specimens of terebratulæ, oysters, pectens, and other shells. The limestone when burnt makes excellent lime and may be wrought and polished for architectural purposes.” Beds of limestone in the Wairoa district, as well as rich fossiliferous strata from the Waikato Heads towards Kawhia harbour, also columnar blocks of the same adorning the entrance to Whaingaroa harbour, and the fine caves of the Rakaunui branch of Kawhia harbour, are then described.
“The limestone attains its greatest thickness (from 400 to 500 feet) in the Upper Waipa and Mokau district, between the Rangitoto range and the west coast.”
“The third and uppermost stratum of the older Tertiary strata consists of beds of fine fossiliferous sandstone, in which quarries of good building
stone may be found. There are whole ranges parallel to the Primary mountains which seem to consist of this sandstone. I will mention only the Tapui-wahine range, about 2000 feet above the level of the sea, in which is the pass from Mokau to the Whanganui country.”
“The horizontal beds of limestone and marls, which form the cliffs of the Waitemata, and extend in a northerly direction towards Kawau, belong to a newer Tertiary formation, and instead of coal, have only thin layers of lignite. A characteristic feature of this Auckland Tertiary formation is the existence of beds of volcanic ashes, which are here and there interstratified with the ordinary Tertiary layers.”
“Sandstone and Brown Coal have been found in places to the north of Auckland, in the districts from Cape Rodney to the North Cape.”
I have now, with Hochstetter's assistance, taken a glance at the Tertiary rocks, which occupy so much of the surface of the Island, but, as yet, little has been said of the brown coal, which is found in large quantities, and which, for inland navigation and other economical purposes, promises to prove of great value.
A description of the brown coals of the Auckland province, with several analyses, will be found in Hochstetter's work.1
Besides the localities in the Waikato valley, in which the brown coal is found, it has also been discovered in the direction of the Bay of Islands. In the Wellington province these coal measures are found cropping out in the upper part of the Whanganui river, and some of its tributaries, particularly in the Tangarakau, which takes its rise towards the head waters of the Waitera.
As the Tangarakau seams are found in, or near, the boundary of Taranaki, it is probable that that province also may contain much brown coal.
To the eastward of the main range, a thin seam, about nine inches thick, has been observed in the Hawke's Bay province, and it is not unlikely that good seams of brown coal may yet be discovered on that side of the island.
We may perhaps now consider the circumstances under which these Tertiaries have been deposited.
We find a flooring of Palæozoic rocks generally, perhaps invariably, inclined at high angles, and on this flooring we find the brown coal, with accompanying shales, deposited uncomformably. At the period of deposition of the coal, we must have had dry land for the growth of coal
[Footnote] * Fischer's Translation, commencing at page 18.
plants. After the deposition of the coal, the Island must have undergone depression, and as it sunk, the various Tertiaries must have been deposited above the coal. Not yet, perhaps, did the volcanic eruptions commence, but as the country gradually sunk, and reached its point of greatest depression, the crust of the earth was broken, and streams of basalt flowed over the surface; the depression probably reaching a depth of 1800 or 2000 feet. Nature having completed her work so far, the Island commenced to rise again slowly and steadily, but slightly disarranging the Tertiary rocks on either side of the Island, the volcanic eruptions doubtless still continuing. The Island appears to have rested in its rise at various points, at from 1000 feet to 1200, at 400, 150 to 200, at 15, and at 9 and 4 feet. Various comparatively slight oscillations of level appear to have taken place in recent times, for we find strata of trees, not yet converted into lignite, covered by marine deposits—as between Whanganui and Taranaki, on the Rangitikei river, in Palliser bay, and in places in the Auckland province.1
Thus, after a depression of 1800 or 2000 feet, and the deposition of successive beds of Tertiary strata, the Island rose again, and assumed somewhat of its present form, although probably at the time of emergence it was joined to the Middle Island.
I must not omit a most striking feature of the Tertiaries in the southern part of the Island, in the very broken character which they assume over large areas, notwithstanding their general horizontality. The great Tertiary basin in the interior of the west coast country appears to have formed a series of terraces, gradually rising to the volcanic plateau and chain, and to the Palæozoic ridges; but, whether from contraction, or from contraction, or from the shaking of earthquakes, or from unequal rising of the land, or simply from the wearing away of soft rocks by the action of rain and rivers, each, several, or all of these causes, have cut up the terraces into deep ravines of a very remarkable character.
To give a general idea of the character of the New Zealand landscape, as chiefly affected by its Geological formations, it will be desirable to travel round the coasts of the North Island.
On approaching New Zealand from the westward it is possible that the eye of the traveller will first light upon the magnificent cone of Mount Egmont, forming, with its bold outlying spur, the grand buttress
[Footnote] * Terebratulæ are found in gravel at Cape Palliser, 200 feet above the sea level, and a long rest of the sea level, at a lower elevation, may be inferred from the growth of Pohutukawa trees in certain inland districts of the Auckland province, a tree which only grows naturally on the sea shore.—Thomson, vol. p. 1, 10 and 19.
of Igneous rocks, which protects the great Tertiary basin of the North Island from the encroachments of the waves driven upon the shore by the westerly gales. Mount Egmont forms a regular cone of surpassing beauty, and may be regarded as the Vesuvius of New Zealand. Although hardly possessing the grand features of the great volcanic chain of the centre of the Island, Ruapehu and Tongariro, it has nevertheless a more graceful outline, and its beauty may perhaps be described as of a softer character, the more so, when we consider that the great central chain rises from a plateau of some 2000 feet above the sea, which is swept by cold blasts, and covered by the snows of winter, while the cone of Mount Egmont sweeps gracefully down to the sea level, into fertile plains and low plateaux, which enjoy a genial climate, and are clad in luxuriant vegetation.
The cone of Mount Egmont reaches an elevation of 8270 feet. Its rocks are composed of dolerites and trachytes. Its eruptions have probably ceased since the early Tertiary period; at all events, it does not appear that it has shown any activity since New Zealand has been inhabited.
There is a fanciful tale of the Maoris that Taranaki quarrelled with Tongariro, descended the Whanganui river, and established itself in its present position, but the most fertile imagination can hardly suppose this might refer to the rise of the cone of Mount Egmont, during the “recent” period.
In the neighbourhood of Taranaki are volcanic tuffs, forming cliffs of moderate elevation, and at their base on the sea beach, is found the well-known iron sand of Taranaki, released by degradation from some of the trachytes of the mountain, or its out-lying flows, or other Volcanic rocks along the coast, for the titaniferous iron sand appears to extend, more or less, as far north as Kaipara Heads, and as far south as Whanganui. Indeed small quantities are found still further south, at the Rangitikei and even at the Manawatu rivers, and there are few parts of the Island where its presence may not be detected; this, with siliceous sand, forms dunes on parts of this coast. The Tertiaries in the neighbourhood of Taranaki, are probably very recent. Coasting along to the northward, the Waitara river is passed and the country becomes higher and of a more broken character, the Tertiaries being much fractured and worn into narrow gullies, with an upper surface sometimes flat and sometimes forming sharp ridges. On a clear morning the central volcanic chain may be observed at this point from a short distance in the
offing. Passing onwards towards Mokau, a large area appears to be covered by a tabular limestone of a middle Tertiary age, composed of fragments of shells, corals, and foraminiferœ, interspersed with perfect specimens of terebratulœ, oysters, pectens, and other shells.1
The aspect of the west coast from Taranaki, we may say as far as the Kaipara Heads, or even to Cape Maria Van Diemen, is hilly and broken. The rocks principally consist of marine Tertiaries, viz:—sandstones and limestones, alternating with doleritic and trachytic lavas, conglomerates, and breccias of the same, an occasional volcanic cone (as at Karioi to the southward of Whaingaroa harbour), considerable formations of drift sand forming dunes which reach a height of 500 feet above the sea, and patches of Secondary rocks at the heads of the Kawhia and Whaingaroa harbours.
The coast ranges are hardly high enough to be called mountainous, but almost too high to be described as hilly.
The sand dunes appear to a great extent between the Waikato and Manukau Heads, and also at some points to the northward of the latter, but the country north of Auckland has never to my knowledge, been systematically described.
It appears, however, that this district shows in places a flooring of Palæozoic rocks, and a large proportion of marine Tertiaries. Secondary rocks are said to occur in the harbour of Hokianga to a limited extent. Limestones and calcareous sandstones are found profusely distributed in the Kaipara harbour, of which the age is undetermined, but they are probably Tertiary. Coal, of which the beds appear to be of considerable thickness, is found to the northward, and at the Bay of Islands appears to be of good quality, whatever its geological age may be.
The northern Peninsula is dotted over with numerous volcanic cones, and other remains of igneous action. The range which runs from Cape Rodney to the Kaipara harbour, on the ridge of which the escaped Waikato prisoners have built their “pa,” seems to be mostly composed of tufaceous materials, frequently arranged in spheroidal concretions. Similar rocks are found at Matakana and near Mahurangi, not far from which (at Waiwera) are hot springs.
At Wangarei North Head, are the remains of a magnificent crater, which formerly may have included the “Hen and Chickens” group of Islands, either as one gigantic crater, or as a series of cones forming a volcanic chain. Almost all of the old crater wall is now broken down
[Footnote] * See Hochstetter, Fischer's Translation, page 25.
and has disappeared, but, part of it I think may still be made out from inland of the Heads. Many first and second-class harbours indent the northern peninsula. The Palæozoic rocks of the “Barrier” on the left contrast with the more tame outline of the Tertiary landscape on the right.
Certainly the approach to the Waitemata harbour is very beautiful. The Hauraki gulf is dotted over with islands of all sizes; and being of various geological formations, they are in consequence of varied and picturesque outline. Those of tertiary formation, or of older rocks capped by Tertiaries, are of a low horizontal character. Those composed of Palæozoic rocks are bold and angular in outline, while the regular cone of Rangitoto guards with its hard volcanic rocks the entrance to the Auckland port.
There we find a great extent of the later Tertiaries, forming low cliffs along the coast, while the Isthmus of Auckland is found to be a crowded group of small volcanic cones. The decomposing rocks of this volcanic series form the richest soils of the north, and the slopes of these volcanoes are covered by fertile fields.
Passing round the Frith of the Thames, we find Palæozoic rocks on both sides, with low lands of alluvium and swamp in the interval. Thence passing between the mountainous country at Cape Colville, and the great Barrier Island, is found a tract of country of Palæozoic, flanked by basaltic rocks; and turning to the southward we pass along by the high Coromandel ranges, which attain a maximum elevation of 2700 feet, until we find ourselves trending to the eastward along the low shores of the Bay of Plenty, a large part of which presents to the sea a low swampy shore,1 with basaltic or trachytic rocks at various points, as at Okura and Matata. Approaching Whakatane, the long and lofty ridges of the Palæozoic rocks of the main ranges may be perceived coming up from the S.S.W., possibly invaded by some eruptive rocks, and amongst them, as Hick's Bay is approached, the high peaks of Mount Ikurangi, 5533 feet above the sea, show well out in the interior, and indicate an apparent volcanic or, to say the least, a trappean appearance for that mountain. About eight miles from the East Cape, at a place called Kawakawa, rocks, evidently of Tertiary age, and with cliffs much resembling those of the Whanganui river, appear abutting on the Palæozoic rocks. Their highestelevation is about 400 feet. Passing the East Cape, we find apparently the same Tertiaries, with possible Secondaries, all the way to Table Cape
[Footnote] * Hochstetter's Map.
and Portland Island; but this country has never been geologically examined. The interior, as seen from the sea, is much broken, and the long ridges of the Palæozoic ranges may generally be seen, some twenty or thirty miles inland. Between the Terakaka Peninsula and Napier, besides the marine Tertiaries, there is also said to be a good deal of drift pumice in places. Arriving at Napier, we find a Peninsula of new Tertiary limestone, rising to a height of several hundred feet, and forming a centre to long boulder banks on both sides. That on the northern side forms a protection to the inner harbour.
From the southern boulder bank the Ahuriri Plains sweep into the interior to join the plains of the Rua Taniwha, which are continued by the terraces of the Forty Mile bush to the Wairarapa Plain and to Palliser Bay.
Passing round the shores of Hawke's Bay we find the Tertiary limestones, sandstones, mudstones, and clays forming cliffs towards Cape Kidnapper; they dip slightly to the westward, and therefore it may be supposed that certain lines of trappean dykes, which are found further south, near Flat point, and elsewhere, here pass out diagonally seaward, and that their intrusion has caused the tilting action which will account for the westerly dip. At Cape Kidnapper there is some reason to suppose that the hydraulic limestones, of probably Mesozoic age, may be found lying uncomformably below the Tertiaries. From Cape Kidnapper, on a clear day, Ruapehu may be seen, but Tongariro and Ngauruhoe are hidden by the intervening ranges. Hence the Ruahine range shows out strongly and sharply, covered by snow for many months in the year. Passing to the southward from Cape Kidnapper, we skirt a range of calcareous and sandstone rocks, the probable Secondaries, rising to an average elevation of about 1000 feet, and preserving a monotonous sameness of character and outline. They hide the higher and more picturesque ranges in the background. At Castle Point, a small harbour is formed by a reef and peninsula of Tertiary limestone, with Pecten Burnettii, and here also certain sandstones and mudstones are found containing undefined impressions of plants and small seams of coal. Along this coast, and more particularly between Flat Point and Pahaoa, the hydraulic limestone series is met with, which may possibly be of Mesozoic age. At Waikekino, six miles south of Flat Point, reefs of Amphibolite are found on the shore and in the sea, penetrating the above-named calcareous rocks, and boulders of various trappean rocks are common in the Kaiwhata and other rivers. Passing to the south of the Pahaoa river, Palæozoic sandstones
and slates appear, with jasperoid rocks, and these continue round the bold buttress-like headland of Cape Palliser.
Proceeding round the abrupt and rugged country which lies behind Cape Palliser, we reach the level plain of the Wairarapa valley. An inland plain, of about ten miles broad, which passes up between the Rimutaka and Tararua ranges on the left and the lower slope of the Tertiary ranges on the right, continues with a similar width through the Forty Mile bush to the eastern Manawatu, thence to the Rua Taniwha plains and then turns seaward to Napier. An old Fjord, or possibly two separate arms of the sea, which formed gravel terraces, now offers an admirable line of communication between Wellington and Napier. In Palliser Bay the cliffs are from 50 to 150 feet high, composed of “drift” gravel on the western side, of gravel over blue clay on the eastern. Passing across Palliser Bay we arrive at the highly inclined rocks of the main range, cut off and scarped along this south coast, and at the Muka Muka are found trappean rocks, altering the slates into jasperoid rocks. At this point also was the greatest rise of land caused by the earthquake of 1855 (viz., 9 feet), and here the coast road which was before that time almost impassable, except at low tide, has now a broad stretch of rooky beach between it and the sea.
Proceeding to the westward along the south end of the Island, we continue to pass the vertical scarp of the rocks, caused by the great depression of Cook's Straits. The strata being highly inclined, and the mountains forming remarkably sharp ridges, rising to a height of from 2000 to 3000 feet, and running in a N.N.E. direction. Looking up the noble harbour of Port Nicholson, the alluvial valley of the Hutt may be perceived, forming the only great longitudinal valley of the mountain ranges. Proceding onwards, we may find the same evidence of the intrusion of Igneous rocks as at the Muka Muka, and may also perceive small patches of drift gravel, lying at various elevations from 400 feet downwards; from the position of these terraces we may, I think, conclude that they were formed previous to the depression which formed Cook's Straits. At Terawiti instead of passing along the great scarp at right angles to the strike of the rocks, we now proceed to the northward in their line of direction, and as we look into the harbor of Porirua we may think of the “plant beds” there, a further investigation of which may perhaps lead to a clear history of the age of these rocks. On the left we leave the flat topped island of Mana (Palæozoic), and pass on to the junction of the Tertiary and
and Palæozoic rocks, near Paekakariki, and here the great Tertiary basin commences. From this point the ranges of the old rocks pass away inland towards the N.N.E. while the Tertiaries, commencing the great western curve towards Cape Egmont, are as yet only represented by dunes of sand. Eight miles further on we reach Waikanae, opposite to which is the high Palæozoic island of Kapiti which forms a shelter from the prevailing westerly winds. In consequence of this protection the Waikanae river throws out a long point seaward. At Otaki, in addition to the sandy dunes, there is a considerble breadth of “drift” gravel formation, and also here and along this coast, there is much alluvium and swamp. At the Manawatu river, the sandhills which sometimes reach a height of from 40 to 50 feet, attain their greatest breadth, of about ten miles, and are intermixed with some rich tracts of swamp and alluvium. Inland of this, the “drift” gravel forms terraces, and what appears to be the blue clay shows itself a few feet above the river level, the mountains having receded to a distance of 25 or 30 miles from the coast. The coast now trends rapidly to the westward, fringed by sandhills, behind which may be seen the fertile country composed of Upper Tertiaries. Passing the low ground at Rangitikei the coast rises into cliffs towards Whanganui, of from 100 to 200 feet high. The bold outline of Ruapehu may now be seen overlooking the great Tertiary basin, and covered with snow, to the north of Whanganui. The ridges of Ruahine stretching to the N.N.E. are far in the distance, while to the westward the graceful cone of Mount Egmont also comes into the general view. Between Whanganui and Kai-iwi an “old forest” is found in the cliffs, and numerous remains of Moa in the sandhills above. Between this and Taranki the grand curve of the coast shows Tertiary cliffs to the sea, the upper beds of which appear to be very recent. This part of the coast has not yet been examined and it is more than probable that the basalts or other Igneous rocks may be exposed at different points on the coast and to the inland of the mountain. With this exception, the interior country here appears to be entirely composed of sedimentary Tertiaries, with the grand cone of Mount Egmont rising like an island from their midst.