Art. XLIII.—Qn the Relative Ages of the Waitemata Series and the Brown Coal Series of Drury and Waikato. (With. Illustrations.)
[Read before the Auckland Institute, August 8, 1870.]
The only geologist who has hitherto published any classification of the tertiary rocks of the central part of this province is, I believe, Professor Hochstetter. In his lecture delivered in Auckland, in June, 1859, he divides the strata into two formations:—
1st. A younger, probably Miocene, comprising the series of clays and sandstones upon which Auckland stands, and which he called the “Waitemata series,” and
2nd. An older one, probably Eocene, which is found principally on the west coast, and in the interior, on both sides of the primary ranges.
This older formation he again subdivides into—
Sandstones of the Upper Waipa and Mokau.
Limestones of the Upper Waipa and Mokau, of Raglan, Kawhia, Papakura, and south of Port Waikato.
Clays and green sandstones on the eastern branches of the Raglan, Aotea, and Kawhia harbours.
Brown coal series of Drury and Lower Waikato.
Subsequently, in 1865, in the Geology of the Voyage of the “Novara,” he appears to have altered his views as to the relative ages of the beds as follows:—
Limestones of the Upper Waipa and Mokau.
Shales and limestones of Raglan, Aotea, and Kawhia.
Sandstone of Port Waikato.
Limestone of Papakura.
Brown coal series of Drury and Lower Waikato,
And in the map accompanying that volume, the rocks are divided into two formations—the younger containing Nos. 1, 2, 3, and 4 of this table, and the older Nos. 5 and 6.
During the month of November, 1866, I was employed by the Provincial Government to ascertain the probable limits of the Brown coal series in the Lower Waikato, and while thus engaged I was led to form a different opinion of the relative ages of the tertiary rocks to either of those proposed by Professor Hochstetter; consequently, in the report I then sent in, I altered his arrangement to suit my views, but as I had no idea at the time it was written that it would be published, I gave no reasons for my alterations.
I therefore propose now to place on record the evidence in favour of the conclusions I then arrived at, and which I have since seen no reason to alter.
Commencing with the Waikato coal field, we find on the right bank of the river, just opposite to the present mine, the section given by Professor Hochstetter in his New Zealand, p. 302, of the Brown coal series resting unconformably on the old slate formation of the Taupiri Range. The left bank of the river shows a somewhat similar section, the slate rocks being seen in the bed of the river, below the mine. At the mine, the coal series consists of—
|1. Yellow sandy clay, with nodules of clay ironstone||230 +||feet.|
|2. Upper fire-clay, dark blue||12–14||"|
|3. Shale, with leaves of dicotyledons||4||"|
|4. Brown coal||12–18||"|
|5. Lower fire-clay, light blue||20||"|
|6. Light coloured clays, with ironstone||30–100 +||"|
The fossils found in the bed No. 3 are leaves of dicotyledonous plants only; they are probably abundant, but it is only when the roof of the coal is being worked that they can be obtained. None of them have as yet been described. About seven miles west of the river, the coal series ends abruptly, and beds of calcareous sandstone rest on its denuded slopes. (Section I.) This sandstone belongs to a series extensively developed on the west coast, which, in my report previously alluded to, I called the “Aotea series.” It consists of—
Crystalline and tabular limestone of Raglan and Kawhia.
Calcareous sandstone of Aotea and Port Waikato.
Sandy clay of Aotea and Raglan, passing into marl further north.
Limestone south of Port Waikato.
Its characteristic fossils are Schizaster rotundatus, Zitt.; Ostrea Wullerstorfi, Zitt.; Pecten athleta, Zitt.; P. Burnetti, Zitt.; P. Williamsoni, Zitt.; P. Hochstetteri, Zitt.; Cucullœa singularis, Zitt.; Scalaria lyrata, Zitt.; two species of Dentalium, and Cristellaria Haasti, Stache. The upper parts are recognized by Pecten Burnetti, Scalaria lyrata, and Ostrea Wullerstorfi; the lower by Cuculœa singularis and the two species of Dentalium. Foraminiferœ abound, especially in the lower part of the series, and these have been considered by Dr. Stache to indicate an age about equivalent to that of the Mayence Basin, which is classed as Lower Miocene by some geologists, and as Upper Eocene by others. Of twelve species of shells from this series, one only, Waldheimia lenticularis, Desh., is recent.
Lying unconformably on the top of the Aotea series is a mass of reddish yellow sandstone, interstratified here and there with seams of bluish clay, containing indistinct plant remains, e. g., between Kaha and Kara Points, and north of Waikorea. The sandstone itself appears to be devoid of fossils, with the exception of a few impressions of dicotyledonous leaves, which I found near Kaha. Further north, at Nga-tutura, it is seen to be broken through by
a volcano, and covered with tuffs and basaltic lava streams. This sandstone 1 suppose to be the equivalent of the Waitemata series, for reasons which will appear further on.
Passing now to the Drury coal field, we find at the abandoned works of the Waihoihoi Coal Mining Company (Section II.) the Brown coal series dipping slightly N.W., and resting upon an uneven floor of dark blue sub- metamorphosed sandstones, in all probability of the same age as the slates underlying the Waikato coal field. The series here consists of—
|1. Light grey cláy|
|2. Brown coal, more or less impure||5 feet.|
|3. Light grey clay||20 "|
The coal crops out on the western slope of the Hunua Range, facing the Manukau, and at the base of the slope there is a series of quarternary, red, yellow, and white clays (f.), about fifty feet thick, which are underlaid, in all the borings yet made, by boulders, or flows of vesicular basalt containing chalcedony in its cavities. Further west, at Slippery Creek, near Drury, a bed of dark blue or green volcanic ash, that weathers reddish brown, is seen to underlie these clays. This rock is similar in appearance to the bed of tufa in the Waitemata series seen in the cliffs below Parnell. Whatever may be its age, it is probable, from its position, that it is younger than the Brown coal series.
Passing on further north, to Papakura, we find the coal series to consist of—
|1. White sandstone, chocolate at the base, with nodules of clay ironstone||50 +||feet.|
|2. Brown coal||4||"|
|3. Clay, with ironstone||3||"|
|4. Shale, with leaves of dicotyledons, and Anodonta elliptica, Hoch., MSS.||30||"|
|5. Brown coal||6||"|
|6. Yellow clay||1||"|
It is here broken by faults and dips at various angles. (Section III.) Resting unconformably upon it, we see, at Campbell's old saw mill, a mass of soft green sandstone. Still further north, the coal series has been washed away, and on its slopes has been deposited the group of sandstones and limestones which I here call the Papakura series. (Section III. c.) This series is found at Cruickshank's quarry at a higher level than the coal, dipping 8° N.W., and a little east of Papakura it is seen at the level of the Manukau flats.
At Cruickshank's quarry it consists of—
|1. Fine-grained grey sandstone||50 +||feet.|
|2. Blue and yellow sandy clay, with fossils Waldheimia gravida, Turbinolia, etc.||3||"|
|3. Crystalline limestone||5||feet.|
|4. Blue or green soft sandstone, weathering grey, with marine shells, and, according to Hochstetter, leaves of dicotyledonous plants||?||"|
Behind Mr. William Hay's house, the series consists of—
|1. Grey sandstone.|
|2. Calcareous grit, with fossils||3–6||feet.|
|3. Limestone; thins out to S.W.||5||"|
|4. Soft green sandstone, with fossil wood and leaves, pieces of coal and worm-borings (Teredo Heaphi ?)||?||"|
The whole dipping 10° N.N.W.
There can, I think, be little doubt but that No. 4 in both these sections represents the same bed, and that the mass of green sandstone seen at Campbell's mill is also a portion of the same, and, therefore, that the Papakura series rests unconformably on the Drury coal series.
Section III. represents a diagrammatic section through the district, and gives a combined view of the sections at Campbell's mill, Cruickshank's quarry, and behind Mr. Hay's house. It is one of the most important sections in the province, as it is probably the only one that shows the relations between the Waikato and Drury coals on the one hand, and those of Whangarei and the Bay of Islands on the other.
Passing still further north, to the district between the Wairoa and Howick, we find horizontal dark-green soft sandstone, with thin seams of coal and traces of plants, together with Foraminiferœ (Globigerino bulloides, etc.), lying unconformably on the older sub-metamorphosed slates and sandstones of the hills west of the Wairoa. There can be no doubt but that this green sandstone (Section IV. c.) is the same as No. 4 of the Papakura series, as it is petrographically identical, and distant only a few miles. Travelling to the west, we find, at Turanga Creek, the water-worn surfaces of this green sandstone covered by a series of yellow clays and sandstones (Section IV. e.), which can be traced through Howick to Auckland, and which form part of the Waitemata series of Professor Hochstetter. These beds are generally devoid of organic remains, traces of plants and seams of lignite being the most common; but, at Orakei, three small Pectens and other marine shells have been found, together with large quantities of Bryozoa and Foraminiferœ. Professor Rupert Jones is of opinion that the Foraminiferœ indicate a late tertiary period (Quar. Jour. Geo. Soc., Vol. xvi., p. 251), and Herr Karrer thinks that they indicate an Upper Miocene age, while Dr. Stoliczka thinks that the Bryozoa indicate an Upper Miocene, or, perhaps, Older Pliocene age.
It thus appears that the Drury coal series is overlaid unconformably by
the Papakura series, which, in its turn, is also overlaid unconformably by the Waitemata series. Also, that the Waikato coal series is overlaid unconformably by the Aotea series, which, in its turn, is also overlaid unconformably by reddish yellow sandstone with beds of blue clay containing plant remains, and we have now to try to connect the two and see what is the parallelism between them.
The Waikato and Drury coal fields both lie on the same flank of the same range of old slate hills, the hills of Pokeno, Razor-back, etc., which divide the Waikato from the Manukau being of much more recent date, so that at the time when the coal was forming they were both on the same shore of probably a large lake or lagoon. Intermediate patches of coal occur between the two on the Maramarua, and near Paparata, and although that of the Waikato is the best and purest, because coming from the largest seam, the coal at all these places is of the same class, and does not differ more than different parts of a large coal field might be expected to do. The fossil leaves found both at Wai- kato and Drury are dicotyledons. Those from the former place have not yet been described, but Dr. Hector, I believe, is of opinion that there is no species common to both, but as only seven species have been found at Drury, and probably only four or five at Waikato, this evidence is not of very great weight, especially as at Drury four species were found on Mr. Pollock's land, and four on Mr. Fallwell's, and only one of these, Fagus Ninnisiana, Ung., was common to both. It is therefore probable that at one time the coal extended from the present mines in Waikato, over Waikari Lake, across the Valleys of the Whangamarino and Maungatawhiri to the Drury mines, and perhaps to the Wairoa River, but that by far the greater part of it has been washed away, patches only being left here and there, although it may still exist below the Razor-back and Pokeno hills.
With regard to the corelation of the Aotea and Papakura series, the palœontological evidence is scanty. Professor Hochstetter mentions Schizaster rotundatus, Pholadomya, sp., and Turbinolia, sp., as common to both formations, and to these I can add two others, viz., Pecten Fischeri, which I found at Port Waikato, and Pecten, sp., belonging to the group P. pleuronectes, which is common in the base of the Aotea series. These are, however, enough to show that the two series are either equivalents, or very nearly on the same horizon, and I am inclined to think that the Papakura series forms the base of the Aotea series. I have also found a Turbinolia in green sandstone, at Whangarei Heads, which, as far as I can judge, appears identical with one I found at Papakura, and Dr. Hector informs me that Pecten Hochstetteri has been found in the green sandstone overlying the coal at Whangarei, and Lamna teeth are found at Whangarei and Aotea; it is therefore probable that the coal at Whangarei and the Bay of Islands is of the same age as the Papakura series, and, if such should be the case, it would appear that while the Aotea
series increases in thickness from Port Waikato southwards, the Papakura series increases in thickness from Papakura northwards.
Professor Hochstetter, when assigning a position to the Papakura series, appears to have been too much influenced by the apparently intermediate character of its fossils, between those of the Aotea and Waitemata series, so that when, in his lecture, he placed the Waitemata series in its true position, he made the Papakura series younger than parts of the Aotea series, and when he subsequently classed the Waitemata series with the Brown coal, he placed the Papakura series in its probably true position below the Aotea series.
The connection between the Papakura and Waitemata series was supposed to consist in the occurrence of Pecten Fischeri, Pecten, sp., group pleuronectes, and casts of Vaginella, in both, but Dr. Zittel has expressed doubts as to the specific identity of the Orakei Pectens with those from Papakura, and I have since found both species in the Aotea series, so that the connection now rests solely on the supposed casts of the interior of Vaginella shells being found in both.
That the sandstone that overlies the Aotea series on the west coast between Port Waikato and Raglan, is to be referred to the Waitemata series, is not so certain, the only reasons being that both are nearly destitute of fossils, except traces of plants, and both lie unconformably on the closely-related Aotea and Papakura series, while they are also both anterior to the basaltic outbursts. The interval, however, between these dates is far too great to speak with confidence on the synchronism of the two; all that can be said at present is, that if the West Coast beds are not the equivalents of the Waitemata series, they are probably younger than them.
[The section below cannot be correctly rendered as it contains complex formatting. See the image of the page for a more accurate rendering.]
|1||4||1||Waitemata series||Upper Miocene|
|2||1||2||Limestone of Raglan and Kawhia Aoteaseries||Oligocene.|
|2||3||Sandstone of Pt. Waikato & Aotea Aoteaseries||Oligocene.|
|3||1||4||Clays of Kaglan, Aotea, &c. Aoteaseries||Oligocene.|
|4||5||6||Brown coal series||Eocena.|