Art. III—On Stage Names applicable to the Divisions of the Tertiary in New Zealand.
[Read before the Wellington Philosophical Society, 20th October, 1915.]
|II. Stage names derived from the Oamaru district||31|
|III. Stage names derived from the Wanganui district||35|
|IV. Stage names derived from the West Coast of the South Island||37|
|V. Summary and conclusions||39|
|VI. List of papers referred to||40|
[Note.—References are indicated by the date after the author's name, and will be found in the list of papers at the end of this article]
There are two objects to be aimed at in framing a classification of the younger rocks of New Zealand, and it is important to distinguish them. The first is to set up a standard of reference by which rocks from different parts of the country may be correlated with one another, the second is to correlate the various divisions of the classification thus established with their equivalents in the classifications of other parts of the world, and particularly in the accepted time-scale based on the rocks of Europe The need for attacking the problem of classification in this order is imposed by the differentiation of the world's fauna into geographical provinces, a differentiation that has been, on the whole, accentuated as the present day is approached It may be possible to correlate our Cretaceous rocks in individual districts directly with the European equivalents, but for the divisions of the Tertiary such a procedure is impossible in the present state of our knowledge
It is undesirable, therefore, to speak of Eocene or Miocene rocks of New Zealand if what is meant is really rocks of the age of the Ototara limestone, the age of which has not yet been firmly established For this reason the classification of the Upper Cretaceous and Tertiary rocks by Hector and McKay as Cretaceo-tertiary, Upper Eocene, Lower Miocene, Upper Miocene, and Pliocene must be abandoned, at least temporarily, so far as the names are concerned, whether or not one agrees with the distinctness of the groups of rocks on which it is based Instead we must adopt a classification on the lines followed by Hutton, Haast, Park, and Marshall, in which names for the various series recognized are derived from New
Zealand place-names. The subdivisions of Hector and McKay's classification followed the latter principle.
The difficulties in the way of framing a classification that shall receive general support are twofold. New Zealand geologists are not agreed as to the presence or absence of unconformities between certain rocks, and they are not agreed on the correlations that should be made between the rocks of different localities. As a matter of fact, neither of these difficulties need stand in the way of a classification by stages, provided that there is agreement as to the order of superposition in the localities on which they are based, and as to the order of preference of localities from which they are named.
It may be pointed out that the European time - scale (Cambrian, Ordovican, &c.) is now entirely independent of unconformities, although these were formerly used in drawing it up. There is no gap between Jurassic and Cretaceous time, although in many parts of England there are unconformities between Cretaceous and Jurassic, and again between different divisions of the Jurassic. In other parts of England the missing stages are represented What we should aim at in New Zealand, then, is a similar series of stage names corresponding to all the divisions of geological time represented in our rocks. If we can agree so far, a great advance will be made in several directions. In the first place, although the stages may be variously combined by different authors into geological systems, the subdivisions of their systems will remain the same, and the points at issue will be easily grasped by those who have not followed the whole perplexing controversies in New Zealand literature. In the second place, attention will be drawn to the lack of a satisfactory knowledge of the fauna of many of the stages, a lack which largely explains the divergent views hitherto held as to correlation. When this lack is supplied it will be possible to compare the rocks of other localities with those chosen as types for the various stages, and if important unconformities exist they will either be detected by the absence of known stages in the new localities or by the discovery of new stages unknown in the type localities. Such a palaeontological solution, of course, cannot be expected in cases like the Weka Pass, where one of the rocks—the Amuri limestone—is practically without fossils, unless the microscopic fauna can be brought into use. The subdivision of the Tertiary into stages, then, is not likely to advance greatly the solution of the Cretaceo-tertiary problem in areas where the Amuri limestone is developed, but should clear up our views on the stratigraphy of the Tertiary rocks.
In choosing localities and rocks to serve as types, and to give names to the various stages to be recognized, it would be desirable to adopt the principle of priority of mention in geological literature if this were practicable.* Names might thus be chosen from widely separated localities, and the order of the stages then determined by a comparison of the faunas. This method, adopted in Europe, South America, and Australia for the stages of the Tertiary, has frequently created controversies as to the equivalence or relative position of the various stages, and is undesirable
[Footnote] * The following is the rule adopted by the United States Geological Survey on this point (24th Ann. Rep., 1903, p. 24): “In the application of names to members, formations, and larger aggregates of strata, the law of priority shall generally be observed, but a name that has become well established in use shall not be displaced by a term not well known merely on account of priority. In general, a newly defined formation shall not receive & name that has been previously used in a different sense.”
in New Zealand, where so many localities exist in which numerous stages are in superposition, the younger on the older. It is, therefore, preferable to choose one or more such localities and base the stage names on these alone, applying priority of nomenclature wherever possible, but not insisting on its rigid application. As, however, I propose to use stage names with the termination “ian,” * on a strict reading of priority it is necessary to consider only previous uses of similar names, such as Park's use of “Oamaruian” and “Wanganuian” In the selection of the localities the abundance of fossils in the various stages represented must be a leading consideration, in order that correlations may prove possible Thus, although on the assumption of the conformity of the Amuri limestone and Weka Pass stone the Waipaia section offers the most complete sequence of Tertiary rocks known in New Zealand, the paucity of fossils in the Amuri limestone, Weka Pass stone, and grey marls is such that correlations on purely palaeontological grounds would be extremely difficult for stages based on these rocks
For the youngest Tertiary stages, apparently unrepresented in the South Island by marine rocks, unless in the Awatere Valley, we must choose between the rocks of Wanganui and of Hawke's Bay Both have been used already for names of series or systems, but Wanganui has come to be recognized as the type locality, and on grounds of priority may also be justified as such, since Mantell described the rocks of that district long before Hochstetter obtained younger Tertiary fossils collected by Triphook from the neighbourhood of Napier. For the middle and old Tertiary stages the Oamaru district is indicated alike from priority (Mantell's descriptions), general usage, and abundance of fossils For still older Tertiary stages, apparently not represented at Oamaru, we must go to the West Coast of the South Island
I propose further to consider these localities in the following order—Oamaru, Wanganui, West Coast—and to exhaust the possible stages of each in turn This is necessary, because probably all the stages found at Oamaru occur also in the West Coast, and some at least may underlie the younger beds at Wanganui as they do in the Awatere district, although in none of these cases are they so suitably developed as their correlatives at Oamaru to form the type occurrences of stages.
The geographical names at present applied to geological systems involve considerations not only of geographical occurrence, but of conformity and unconformity. Thus the term “Oamaru system” has been used in three distinct senses—
By Hutton for part only of the Tertiary sequence at Oamaru and its correlatives Hutton excluded the Awamoa beds because of a supposed unconformity and faunal difference between them and the uppermost member of his Oamaru system—viz., the Hutchinson Quarry beds.
By Park (1905) for the whole of the Tertiary sequence at Oamaru and its correlatives Park included the Awamoa beds in his Oamaru system.
[Footnote] * Abbreviated to “an” where the word from which it is derived ends in “i,” and to “n” where it ends in “a.” Hybrids between Maori words and anglicized Latin terminations are doubtless unfortunate, but they can hardly be avoided in view of the ictention of the Maori place-names throughout New Zealand They are less objectionable as technical geological terms than as words in the vernacular, and we find that such terms as “Tahitian,” “Fijian.” and “Samoan” have been easily enough assimilated into our everyday speech
By Marshall (1911) for the whole of the Tertiary sequence at Oamaru and its correlatives, and also for all other beds which in other parts of New Zealand are conformable with those correlatives. Marshall included the Cretaceous beds of the Waipara and Amuri Bluff districts in the Oamaru system because he considered that they lay conformably beneath Tertiary beds correlative with those at Oamaru
Since I am not here concerned with the validity or otherwise of an Oamaru system, these three usages need not be discussed in that light; but it may be suggested that for a system such as Marshall believes to exist the term “Waipara system” would be preferable on geographical grounds, for all the beds he places in it, including those at Oamara, have correlatives at Waipara. Park used such a geographical principle in 1910 when he replaced his Oamaru system of 1905 by a Karamea system, which included not only his former Oamaru system (now Oamaru series), but also lower beds without correlatives at Oamaru (Waimangaroa series). This is, I believe, a sound principle to follow wherever possible in the use of geological terms derived from place-names. To me, then, “Oamaruian” denotes the whole Tertiary succession as developed at Oamaru, and its correlatives elsewhere, but no other beds This use of the term fortunately coincides in extent with its former application by Park.
There is, however, a subtle but important difference between his usage and that which I now propose. In speaking, for instance, of the Weka Pass stone, the grey marls, and the Mount Brown beds of the Waipara section as Oamaruian we both mean that these beds are the correlatives of the beds at Oamaru; but Park means also that they are unconformable with the underlying and overlying beds, whereas I express by the term no opinion on the point In other words, Park's use of the term is systematic, while mine is geographical. I make the plea for such a geographical use of stage names terminating in “ian” as tending to bring about a greater uniformity of nomenclature.
II. Stage Names Derived From the Oamaru District.
The Oamaruian, as above defined, consists of a series of rocks to the members of which we may apply stage names with advantage. Thus the European Miocene, with which the Oamaruian is sometimes correlated, has been divided into six stages. It is not contended that the stages here proposed are of the same value as those of the European Miocene: that will be an interesting point to discuss when we are in a position to do so. All that is claimed is that these divisions can be recognized at Oamaru and the neighbouring districts, and probably will be capable of identification throughout New Zealand when our knowledge of the faunas is more complete. Incidentally, the recognition of distinct stages will throw into relief our lack of knowledge of some of these faunas.
The succession of rocks at Oamaru is somewhat varied in different localities within the district owing to the unequal development of volcanic rocks at different points, and some difference of opinion exists as to the actual order of succession. The difficulty is in reality palaeontological more than stratigraphical, and is explained by the fact that the fauna of the beds underlying the Ototara limestone and its correlative the Waihao limestone resembles that of the beds overlying the limestone more closely than that of the limestone itself. This is due, no doubt, to the similarity
of conditions in the formation of the two first-named sets of beds and the difference of conditions in the latter, combined with a relatively slow rate of evolution throughout the whole period of deposition Hutton (1887) thus placed certain beds near Enfield and Windsor in his Pareora system, correlating them on palaeontological grounds with the Awamoa beds, and supposing them to occupy a valley of erosion in the Oamaru system, whereas McKay (1884), from an examination of the field evidence, had placed them under the Ototara limestone. Park (1887) came to a similar conclusion to McKay, and my own observations leave me in no doubt that Hutton was mistaken in his account of the sequence
Park, in 1905, suggested an entirely new reading of the field evidence at Oamaru, designed to get over the problem, which he clearly recognized, of the “Pareora fauna” above and below the limestone. Thus he correlated, as Hutton did, the Waihao greensands, which he below the Waihao limestone, with the Awamoa beds, which he above the Ototara limestone. In consequence, he considered the Waihao limestone to represent a higher horizon than the Ototara limestone. My study of the brachiopods occur-ring above the limestone of Landon Creek and below the Ngapara and Maerewhenua limestones could be construed in the same way to support Park's explanation of two distinct limestones, but the stratigraphical facts do not seem to support it, and suggest rather that the similarity of the upper and lower faunas is due to the slow rate of evolution. In the Waihao district the existence of the Mount Harris beds with a “Pareora fauna” above the Waihao limestone is otherwise inexplicable Park found these beds resting on Lower Mesozoic beds, and, as they have a wide distribution, this may be locally the case through overlap. Between Mount Harris and the Waihao River, however, they rest on greensands resembling those of the Hutchinson Quarry beds, and these in turn rest on the limestone (Thomson, 1914). This suggests strongly that the Waihao limestone is the correlative of the Ototara limestone, and the Waihao greensands the correlatives of the Enfield-Windsor beds.
The only locality where Park described the two limestones developed in the same section is near Kakanui. I am in full accord with Uttley's interpretation of this section, contained in another paper in this volume (p 19)—viz, that there is only one limestone, which is sharply flexed from the beach to the top of the hill. It is easy, however, to see how any one starting oft with the view that there were two limestones could interpret it in the manner done by Park in a brief visit.
Park's interpretation of the Oamaru and Waihao districts was an ingenious attempt to meet a real difficulty which had long ago been stated by Haast (1879), and had never been boldly faced by other geologists. It had the merit of suppressing Hutton's ambiguous Pareora system, and thus initiated a real advance in the classification of the Tertiary rocks. I hope, therefore, that Professor Park will retire with honour from his insistence on the presence of two limestones at Oamaru, and clear the way for a complete accord as to the stages of the Oamaruian. Such a step will not at all affect his general position as to the relationship of the Tertiary and Cretaceous in New Zealand.
With these prefatory remarks, I may now give a short generalized account of the Oamaru district, based mainly on my own observations, but supplemented for the coastal district by information received from Mr G. H. Uttley.
There is a great escarpment of limestone, first described by W. Mantell (1850), and by him named the Ototara limestone, which runs from the neighbourhood of Kakanui for several miles in a northerly and then north-westerly direction towards the Awamoko River. The escarpment overlooks the Waiareka Valley opposite Alma and at Enfield, and the rock dips in an easterly direction towards Weston and Totara, where the Oamaru limestone quarries are situated. The Oamaru building-stone, the Oamaru limestone of Park (1905), is thus the Ototara stone, although Park in 1910 calls his supposed upper limestone the Ototara stone and the lower limestone the Oamaru stone. The dip of the beds does not remain long constant to the east, however, for the limestone reappears at numerous points in the triangle of country between the main escarpment, the sea-coast, and the Waitaki Valley. In all clear exposures the overlying beds are found to consist of calcareous greensand, often crowded with brachiopods, and generally known as the Hutchinson Quarry beds. The junction between the greensand and the limestone is not a simple one, for the upper surface of the limestone is often very irregular, and in many places covered with a brown varnish which has proved to be phosphatic (e.g., All Day Bay, Kakanui, Deborah, Devil's Bridge). In the upper layers of the limestone there are frequently rounded calcareous concretion-like masses, varying in size up to 3 in. or 4 in. in diameter, and containing tissue-like compartments within, suggesting an algal growth. The basal layers of the greensand are crowded with segments of Mopsea hamiltoni (Thomson), often in a phosphatized condition, while both unaltered and phosphatized brachiopods may be obtained. This peculiar junction has some analogies with that between the Weka Pass stone and the Amuri limestone, and seems to correspond to an abrupt change of conditions. It almost certainly denotes a non-sequence, though not in most places physical unconformity; but there is no reason at present for believing that the non-sequence is of any great extent. At Hutchinson's Quarry the greensands rest on a concretionary conglomerate consisting of rounded pieces of basalt and concretions similar to those described above, set in a calcareous cement; this bed, several feet thick, rests conformably on a thin band of hard white limestone, which has recently been determined by Morgan to be phosphatic, and this latter rests quite unconformably on a series of tuffs containing thin limestone bands. The formation of the limestone at this and other points seems to have been nearly prevented by the amount of volcanic material strewed into the sea, so that the limestone is represented by calcareous tuffs and thin bands of limestone.
Wherever the greensands of the Hutchinson Quarry horizon can be traced upwards they reveal less and less glauconite, and finally pass into shell-bearing sands and blue sandy mudstones—the Awamoa beds. No higher Tertiary rocks are seen in the Oamaru district.
In a few localities to the east of the main outcrop of the Ototara limestone, notably in the neighbourhood of Kakanui, Deborah, and Cape Wanbrow, exposures of older beds are seen. In all cases these are of volcanic origin, and it is evident at Kakanui, at any rate, that the uppermost of these must represent a replacement of the lower part of the Ototara limestone, since the Kakanui limestone is much thinner than the former and shows no characters which would lead one to suppose it formed at a slower rate, but rather the reverse.
To the west and north of the main outcrop of the Ototara limestone lies the broad low valley of the Waiareka River, on the far side of which*
[Footnote] * 2—Trans.
again rises the Ngapara tableland. The latter is a well-preserved part of an elevated plain of denudation which was formerly continuous to the coast-line, but has been more dissected in the neighbourhood of Oamaru, though it is still recognizable there. This old plain truncates the Tertiary rocks around Ngapara at a low angle, and it is probable that, under the loess deposits which cover it, remnants of the Hutchinson Quarry and Awamoa beds are preserved, though they have not so far been described. Near Ngapara itself the plateau is cut across the Ngapara limestone, which runs thence to the Awamoko River and the Waitaki Valley. There can be no doubt that the Ngapara limestone was formerly continuous across the Waiareka Valley with the Ototara limestone. The rocks underlying the two limestones are not, however, the same. The Ngapara limestone is underlain by greensands of considerable thickness, and these pass down into quartz sands without glauconite, interstratified with grits and conglomerates and a seam of brown coal. The succession thus exactly resembles that at Waihao. The Ototara limestone, on the other hand, is underlain opposite Alma by volcanic breccias of no great thickness, and these again by a deposit of diatomaceous earth, which in turn rests upon a considerable thickness of volcanic tuffs and lavas. The latter at Enfield rest on greensands, which can be traced thence at various points through Windsor to Ngapara. The volcanic series underlying the Ototara limestone in the Waiareka Valley has long been known as the Waiareka series, which, strictly speaking, must include the diatomaceous earth. The difference between the succession at Enfield and that at Ngapara is due mainly to the volcanic conditions existing during deposition at the former place, though a local subsidence, perhaps correlated with the volcanic activity, seems necessary to explain the formation of the diatomaceous earth, regarded by Hinde and Holmes as a deep-water deposit. The Ngapara succession represents more normal conditions of marine deposition, such as prevailed in the Waitaki Valley, Waihao, and other South Canterbury localities.
For the above-described succession at Oamaru the following stage names are suggested—
|Hutchinson Quarry beds and concretionary band||Hutchinsonian||Upper Oamaruian.|
|Ototara limestone||Ototaran||Middle Oamaruian|
|Waiareka tuffs and Enfield-Windsor greensands = Ngapara greensands||Waiarekan||Lower Oamaruian|
|Coal-measures, sands, conglomerates, and coal-seams||Ngaparan|
All ambiguity caused by the use of the terms “Pareora series,” “Pareora fauna,” &c, may be avoided by the adoption of “Awamoan” for the uppermost stage of the Oamaruian. On grounds of strict priority, the name for this stage should perhaps be founded on the Onekakara formation of Mantell (1850); but although the blue clay of All Day Bay, which Mantell included in that formation, and from which he described its fauna, is undoubtedly Awamoan, there is considerable doubt whether the Onekakara (Hampden) beds are not really Waiarekan, as McKay (1884) supposed, since their stratigraphical relationship to the Ototara limestone is not clear, and all that is known about them palaeontologically is that they contain the “Pareora fauna.”
No exception can be taken to “Hutchinsonian” on the grounds of priority, for no other earlier name has been used for this horizon in the Oamaru district. Park speaks of the Hutchinson Quarry beds as the Mount Brown beds; but the latter, in the Weka Pass district, include certainly the Awamoan as well as the Hutchinsonian stage, and possibly also the Ototaran. In the Hutchinsonian I would place all beds between the Ototara limestone and the shell-bed of Target Gully, described by Marshall and Uttley (1913), the latter bed forming the base of the Awamoan.
“Ototaran” is alike indicated by priority and subsequent usage as the most suitable name for the limestone member of the Oamaruian, and should be accorded general acceptance.
The Waiarekan stage has been studied in most detail as the Waihao greensands, but as the Waihao formation of Haast refers to much older rocks no stage name can be based on these greensands without ambiguity. The Waiareka tuffs are frequently included in older classifications, and a name based on them should find ready acceptance. Should this stage be too large in comparison with the others, the Waiarekan may be restricted to the tuffs themselves, and the underlying Windsor and Enfield beds may be made the type of a new stage.
The Ngaparan is the only one of the proposed stages that is not based on a well-established name for a geological series. Park, in 1905, called the coal-beds at the base of his Oamaru system the Awamoko beds. In 1910, however, he called them the Ngapara beds when speaking of the Oamaru district only, but for New Zealand generally he designated this horizon the Kaikorai coal-measures. For a subdivision of an Oamaru series a name derived from the Oamaru district is obviously most suitable. I select Ngapara as the type locality because it is nearer to the outcrop of the Ototara limestone than Awamoko, and the coal-beds there are demonstrably the basal member of the Tertiary series represented at Oamaru. The limits between the Ngaparan and Waiarekan cannot be exactly drawn without a more detailed investigation of the Ngapara district.
The Ngaparan in the North Otago and South Canterbury district does not contain a marine fauna, and cannot be correlated directly with marine beds of the same stage, such as probably occur in North Canterbury, and possibly on the West Coast. I suggest that “Ngaparan” should be restricted to coal-beds, and that a different stage name should be used for the normal marine beds of the same horizon. Applying the same principle throughout, we shall get a double set of stage names for the normal marine and for the littoral or terrestrial beds.
III. Stage Names Derived from the Wanganui District.
As in the Oamaru district, there has not been complete agreement amongst geologists regarding the order of succession of the rocks in the Wanganui district. The principal point in dispute relates to the beds of Kaimatera Cliff, considered by Hutton (1886) as an upper series of Pleistocene beds unconformable with the Pliocene beds of the district, and by Park (1887) as an integral part of the “Newer Pliocene.” As Hutton's view was founded on a brief inspection of the cliff without a full knowledge of the geological structure of the district, while Park's was based on an extensive reconnaissance survey, the latter may be accepted.
Park described a continuous section on the sea-coast between Wanganui and Patea, the beds of which are shown in the following table along with his later groupings :—
|Park, 1887||Park, 1905||Park, 1910|
|(1.) Wanganui beds||Newer Pliocene||Wanganui series||Petane series|
|Upper sandy beds|
|Lower blue clays|
|(2.) Kai-iwi blue clays|
|(3.) Okehu pumice beds|
|(4) Okehu sandy shell beds|
|(5.) Nukumaru Rotella beds|
|(6) Nukumaru limestone||Older Pliocene|
|(7) Waitotara Coralline series—||Upper Miocene||Te Aute or Wai-totara series||Waitotara series.|
|Brown micaceous sandstone|
|(8.) Patea blue clays and brown sands||Awatere series.|
Amongst the fossils of the Waitotara Coralline series given by Park in 1887 there are some extinct species not found in the higher beds, but known from the Oamaruian, some extinct species apparently not found either in the Oamaruian or in the higher beds—e g, Ostrea ingens; and some Recent species not known from the Oamaruian, but found in the higher beds—e g, Terebratella rubicunda. This shows, if Park's identifications are correct, that these beds occupy an intermediate position faunally between the Awamoan and the beds around Wanganui as seen at Shakespeare Cliff, Castlecliff, &c. There are, then, at least two stages represented in the above succession which are clearly superior to the Awamoan, and may be safely named. For the lower stage I propose “Waitotaran,” based on Park's “Waitotara Coralline series”. For the upper, “Wanganuian” is not available, as that name has been already used by Park to embrace the whole of the succession between Wanganui and Patea, and therefore includes the Waitotaran. The upper stage, to which Hutton's Wanganui system was confined, is best known by the often-described sections at Shakespeare Cliff and Languard's Bluff (Putiki), on the latter of which Hutton based his Putiki series. In neither of these localities, however, is the base of the upper stage represented, for it must include at least the Kai-iwi blue clays, which are inseparable from the blue clays of Park's Wanganui beds of 1887. I propose, therefore, to base its name on Castlecliff, from the point at which Park's section along the coast commences. The limits between the Castlecliffian and the Waitotaran must be left vague until the fauna of the beds between the Kai-iwi blue clays and the Waitotara Coralline series is better known. It is possible, but not probable, that a further stage may be found necessary between the Waitotaran and Castlecliffian.
It must also be left to further research to decide whether any further stages are necessary between the Waitotaran and the Awamoan. Park's Awatere series of 1910, which occupies such a position, is not founded on any definite set of beds in the Awatere district, and apparently presupposes that only one stage occurs there. As I pointed out in 1913, the
Awatere district contains a sequence of beds, and includes Oamaruian as well as Wanganuian stages. What is probably the uppermost stage, represented in the Starborough Creek beds described by Park in 1905, contains far fewer Oamaruian species than the Waitotaran list given by Park in 1887; so that, even allowing for some incorrect identifications in the latter, the former can hardly be earlier than Waitotaran. The same applies to the “Motunau beds” of the Waipara section, which rest directly, and apparently without unconformity, on the Awamoan. It does not appear probable, therefore, that any stage between the Waitotaran and the Awamoan will be necessary; but, as said before, further research, including a detailed investigation of the Waitotara beds, is necessary before the matter can be settled.
IV Stage Names Derived from the West Coast of The South Island.
It has been generally held that the rocks of the West Coast coalfields contain in their lower members horizons lower than those represented at Oamaru. At one time these horizons were considered Cretaceous, but as no definitely Cretaceous marine fossils have been described it is now generally agreed that the whole marine sequence is Tertiary. It is, therefore, necessary to examine the evidence available with a view to discovering whether infra-Oamaruian stages may be safely named.
The fullest sequence, showing not only all the upper horizons represented on the West Coast, but also lower horizons than exist in any other district, is contained in the Greymouth district, recently surveyed in detail by the Geological Survey (Morgan, 1911). So far as the development and the relationships of the rocks are concerned, this area is one of the best known in the Dominion, and Morgan's account, based on a detailed survey, must be accepted in preference to all earlier accounts. The Tertiary rocks are grouped by him as follows :—
|Pliocene beds||Soft sandstones, lignite, and somewhat consolidated gravels.|
|Greymouth series, Miocene||Blue Bottom formation.|
|Port Elizabeth beds.|
|Lower Kotuku conglomerate.|
|Coal-measures (Mawheranui series), Eocene||Kaiata mudstone.|
The so-called Pliocene beds are fluviatile, and contain no marine fossils. The whole of the Greymouth series and the Kaiata mudstone and Island sandstone of the Mawheranui series are marine, but the lower beds are sparingly fossiliferous. The Brunner and Paparoa beds consist of conglomerates, sandstones, grits, and shales, with coal-seams, and contain no marine fossils, but well-preserved leaf-impressions at several horizons.
Morgan correlated the middle and lower beds of the Greymouth series with the Oamaru formation of Hutton, suggesting the following individual correlations :—
Cobden limestone = Ototara stone.
Port Elizabeth beds = Middle Oamaru
Omotumotu beds = Possibly the coal horizon of the Oamaru formation.
This view of the correlation was influenced by Park's interpretation of the Oamaruian, in which the Ototara stone (i.e., the Waitaki stone) was considered as the closing member. In consequence, Morgan suggested that the Blue Bottom formation must, if Park's views were correct, be the equivalent of the Wanganui series. As a matter of fact, the Blue Bottom contains an Oamaruian fauna, and, if the Cobden limestone be really Ototaran, must represent the Hutchinsonian or the Awamoan, or both stages.
Morgan considered that the Kaiata mudstone and the Island sandstone represent a lower horizon than is developed at Oamaru; but the fossils he enumerates contain a large number of well-known Oamaruian forms, and only three—viz., Cardium brunneri, Kleinia conjuncta, and Schizaster exoletus—which are unknown from the Oamaruian. On the evidence of the marine fossils, then, it is unsafe to conclude that these beds are not Oamaruian; they may well be Waiarekan, so far as our present knowledge goes. The fact that an unconformity exists between these beds and the Greymouth series hardly affects the question, for there is no a priori reason why an unconformity should not be present between certain stages of the Oamaruian in some parts of New Zealand, although there is conformity in others. On the other hand, as we do not know what was the marine fauna of the times immediately preceding the Waiarekan, it is quite possible that it contained a large number of forms which survived into the Oamaruian, and that the Kaiata mudstone and Island sandstone do represent such an horizon. In the present state of our knowledge it is unsafe to base any stage names on these rocks.
The plant-fossils contained in the Brunner and Paparoa beds may yet yield important evidence as to the position of these horizons relative to the Oamaruian. Von Ettingshausen considered the flora of the Brunner beds Cretaceous and that of Shag Point Tertiary, while Morgan has shown that the flora of the Paparoa beds is more closely allied than that of the Brunner beds to the flora of Shag Point. The following explanation of this tangle may be suggested. Von Ettingshausen's correlation of the Shag Point beds as Tertiary, and of the Pakawau, Wangapeka, Grey, and Brunner beds as Cretaceous, was based on botanical comparisons with the floras of Europe, and cannot be held to have weight against the evidence yielded by the correlation of the overlying marine beds with those of other parts of New Zealand; but his correlation of the Pakawau, Wangapeka, Grey, and Brunner plant-beds with one another may be accepted. The marine beds overlying the Shag Point plant-beds must be correlated with the Cretaceous beds of the Waipara and Amuri Bluff district, and these plant-beds are therefore Upper Cretaceous. The marine beds overlying the various West Coast localities contain a marine fauna agreeing with or closely related to the Oamaruian, and certainly Tertiary. The West Coast plant-beds are therefore either Tertiary or Danian, and most probably Tertiary, but certainly higher in horizon than the Shag Point beds. The flora of the Paparoa beds as determined by Morgan shows them to be intermediate between the Brunner beds and the Shag Point beds, as might be expected from their position. They contain four species (viz., Podocarpus Parkeri, P. Hochstetteri, Dacrydium prae-cupressinum, and Aralia Tasmani) hitherto known only from Shag Point, and three others (viz, Quercus lonchitoides, Fagus ninnissiana, and Cinnamonum intermedium) which have been recorded both from Shag Point and from Tertiary localities, but only two
(Dacrydium cupressinum and Ulmophyllum latifolium) which are known from the Pakawau horizon.
Although relatively very little is known of the fossil floras of undoubtedly Oamaruian horizons, the absence of any common species in the few species known and in the relatively well-known. Pakawau-Brunner flora suggests that the latter is older than the Oamaruian; but until either the flora has been shown to be distinct from the Ngaparan flora or the fauna of the Kaiata mudstone and Island sandstone has been shown to be distinct from the Waiarekan fauna it would be unsafe to base a stage name on the Brunner series. It is certain, however, that even if the latter is Ngaparan the Paparoa series is older, and a stage may be safely based on it, and may be termed the Paparoan.
V. Summary And Conclusions.
Care has been taken in the above discussion to admit no stages that are likely to overlap on others. The following table gives the complete sequence of those proposed, and indicates the possible gaps :—
|(Other stages possible)|
|(Other stages possible.)|
Other stages for coal-beds are clearly necessary. Thus at Maharahara the coal-measures are immediately followed by marine beds with a Wanganuian and probably a Waitotaran fauna. The naming of these is best postponed until the correlation of the overlying marine beds with the named marine stages is rendered more definite.
The determination of the molluscan and brachiopodan fauna of the above marine stages has occupied the attention of Mr. Suter and myself for some considerable time, and it is hoped to publish the results before long. Fresh collections from any of the localities chosen as the types for stages will be gladly welcomed, for, although large collections have been examined, it is certain that much further collecting is still necessary before the complete range of the species can be stated, and until that is known correlations based on purely palaeontological grounds cannot have much value. The determinations so far made show that there a number of species which have a wide range in horizon and are also widespread in occurrence and abundant in the beds in which they occur. Such fossils are of little use as indications of horizon when taken singly. Fossils that are rare, and known from few localities, are obviously also of little use, for their rarity prevents their range being adequately known, while their absence in any given locality cannot be taken as evidence that they did not exist elsewhere at the time the beds of the said locality were being deposited. What must be sought are fossils which are at least moderately abundant and yet restricted in range. If such species can be found and the experience of other countries suggests that they can—correlation will be enormously
simplified, and it will be then possible to test the value of diastrophic considerations in correlation, and to apply these if they stand the test. Until the last few years the published lists of fossils and the analyses of the same were quite inadequate to support the classifications put forward. The three immediate needs of Tertiary geology in New Zealand may be stated as collecting, more collecting, still more collecting.
VI. List of Papers Referred to
Haast, J. von, 1879. “Geology of the Provinces of Canterbury and Westland,” Christchurch, p. 315
Hutton, F W, 1886 “The Wanganui System,” Trans NZ Inst, vol 18, pp. 336–67.
— 1887. “On the Geology of the Country between Oamaru and Moeraki,” ibid, vol. 19, pp 415–30
Mantell, G A, 1848 “Additional Remarks on the Geological Position of the Deposits in New Zealand which contain Bones of Birds,” Quart Journ. Geol. Soc., vol. 4, pp 238–41.
— 1850. “Notice of the Remains of the Dinorms and other Birds, and of Fossils and Rock-specimens, recently collected by Mr Walter Mantell in the Middle Island of New Zealand; with Additional Notes on the Northern Island,” ibid, vol 6, pp 319–42, pl. 28, 29.
Marshall, P, 1911 “New Zealand and Adjacent Islands,” Handbuch der regionalen Geologie, Bd vii, Abt. 1
— 1912. “Geology of New Zealand,” Wellington Marshall, P, and Uttley, G. H, 1913 “Some Localities for Fossils at Oamaru,” Trans. N Z Inst, vol. 45, pp. 297–307
McKay, A., 1884 “On the North-eastern District of Otago,” Rep Geol Explor., 1883–84, pp. 45–66.
Morgan, P. G., 1911. “The Geology of the Greymouth Subdivision, North Westland,” Bull No 13, N Z Geol Surv.
Park, J., 1887. “On the Geology of the Western Part of Wellington Provincial District, and Part of Taranaki,” Rep. Geol. Explor., 1886–87, pp. 24–73.
— 1887 “On the Age of the Waireka Tufas, Quartz-grits, and Coal at Teaneraki and Ngapara, Oamaru,” Rep Geol Explor, 1886–87, pp. 137–41.
— 1905. “On the Marine Tertiaries of Otago and Canterbury, with Special Reference to the Relations existing between the Pareora and Oamaru Series,” Trans. N Z Inst., vol. 37, pp. 489–551
— 1910 “The Geology of New Zealand,” Christchurch Thomson, J A, 1913. “The Tertiary Beds of the Lower Awatere Valley,” 7th Ann Rep. N Z Geol Surv, Mines Statement, 1913, p 123
— 1914. “Classification and Correlation of the Tertiary Rocks,” 8th Ann. Rep. N Z Geol Surv, Mines Statement, 1914, pp 123–24
— 1914. “Coal Prospects of the Waimate District, South Canterbury,” ibid., pp 158–62