Art. LVI.—The Waihao Greensands, and their Relation to the Ototara Limestone.

Transactions and Proceedings of the Royal Society of New Zealand, Volume 19, 1886, Page 434

Art. LVI.—The Waihao Greensands, and their Relation to the Ototara Limestone. By Alex. McKay, Assistant Geologist. [Read before the Wellington Philosophical Society, 20th October, 1886.] Differences of opinion possibly are never wanting in connection with material advances in such sciences as are dependent on accurate observation and sound judgment, and in this respect geology in New Zealand has nothing to complain of; for whether as regards Tertiary, Secondary, or Primary formations, differences of opinion exist, and have led to the necessity of supporting particular views at greater length than would otherwise have been needful. In the particular case I have to refer to on this occasion, the dispute concerns localities and beds rendered classical by the observations of the Hon. Mr. Mantell more than 40 years ago, differences of opinion even now existing with respect to the stratigraphical position of the Onekakara and Hampden beds, in the Moëraki District of Otago. These beds are placed by the Geological Survey as belonging to the Cretaceo-tertiary series; by Sir Julius von Haast as being of older Tertiary date; and by Professor Hutton they are referred to the Upper Miocene period. The Survey and v. Haast support their contentions with facts both stratigraphical and palæontological; Hutton's contentions are based almost wholly on palæontological grounds. South of the Kakanui River the beds in dispute are not overlaid by the Ototara limestones of Oamaru, these being denuded from the Moëraki District; but in the district north of the Kakanui, and in Southern Canterbury, the Survey and v. Haast agree in placing the equivalent beds under the Ototara limestone; and in the Waihao Valley it has been held that this position of the greensands can be demonstrated. Hutton admits that the Waihao limestone is the equivalent of the Ototara stone, or at all events belongs to the “Oamaru formation,” and also admits that the Waihao greensands are the equivalents of the Onekakara beds, but holds that the greensands are younger than the limestones, and, with the Onekakara beds, belong to the Pareora formation. North of Timaru the same greensands occur in the valley of the Kakahu River, and here also, by v. Haast and the officers of the Geological Survey, are said to underlie a representative of the Ototara limestone. Hutton believes that the greensand beds only appear to pass under the limestones in the Kakahu, and considers them as showing this apparent relationship in consequence of a fault, supposed to be present, but which has not yet been observed.

In 1865, the Director of the Survey placed the Hampden (Onekakara) beds below the calcareous rock of Oamaru, and the Caversham sandstone near Dunedin, referring both to the Eocene period; and in 1877 included them in the Cretaceotertiary series. In 1873, Hutton referred both the Hampden and the Kakahu beds to Upper Miocene; and in 1875, after having examined the stratigraphy, was confirmed in his opinions respecting the Miocene age of the Hampden beds. During 1867–68, v. Haast made collections from the Waihao green-sands, etc., which he forwarded to Otago Museum in 1875. These were examined by Hutton, who in the following year published a description of the new species the collection contained, and at the same time referred the Waihao greensands to the Pareora formation. In 1879, v. Haast took exception to the reference of the Waihao greensands to the Pareora formation, and, detailing the sequence, showed clearly that they underlaid the limestones belonging to the Oamaru formation. In 1880, I examined the geology of the Waihao Valley, and agreed with v. Haast that the greensands of the Waihao Forks underlaid the limestones in the near vicinity, and differed from him only in this, that I ascribed his Oamaru formation to the Cretaceo-tertiary period. In 1884, Lindop arrived at the same conclusion, as far as concerned the relative position of the greensands and the limestones. In 1873, Professor Hutton expressed the opinion that our young secondary and tertiary rocks are in many instances deposits accumulated in the narrow valleys of a submerged land;* “Geological Reports,” 1873–74. p. 37. and in 1875 he argues that, after the close of the Eocene period, these valleys were in some instances re-excavated and others formed, within areas covered by cretaceous and upper eocene deposits; and, in Upper Miocene times, were again filled with marine deposits. In this way he finds the stratigraphy of some districts of the east coast of the South Island very perplexing, and would have us believe that the so-called miocene beds appearing to pass under the upper eocene deposits in reality flanked them on the inland side, or filled valleys excavated in them.† “Geology of Otago,” 1875, p.—. This theory, though it obviated the necessity of grappling with a serious palæontological difficulty, led but to another, as it implied the existence in cretaceous times not merely of the principal outlines of the physical configuration of the country, but of many of the minuter details, and at the same time the existence of a profusion of fords and islands along the coasts of eastern Otago and South Canterbury during miocene times. Most other geologists holding that the phenomena thus to be explained were capable

of being accounted for in another way, this theory has not been generally accepted, and for a time seems to have been lost sight of even by its author. This theory was intended to explain how the Onekakara and Waihao greensands might appear as though they underlaid the Ototara limestone and yet be younger than the limestones. In 1885 Hutton appears to have altered his opinion respecting the position of the Waihao greensands, as he includes them with other beds in the Oamaru System, and as in position underlying the Ototara limestone. However, having in the meantime examined the Lower Waitaki Valley, the neighbourhood of Oamaru, Kakanui, and Hampden, and the Waihao Valley, where the greensands and limestones appear, he revives the fiord-island theory as the only one consistent with the palæontological evidence he brings forward. Selecting the Waihao Valley, as affording most convincing proofs of the correctness of his theory, on the 6th of May, 1886, he read before the Canterbury Philosophical Institute a paper, in which he discusses the relative age of the Waihao Forks green-sands and the limestones on the south side, opposite the Forks, and further down the river. In thus selecting the lower basin of the Waihao as the battle-ground within which the issues of the dispute are to be decided, he promised himself one or two advantages not afforded by other localities that might have been chosen. Here the stratigraphy was less decisively in favour of the opposing view than at the Kakahu, and the palæontological evidence as much in his favour as at Hampden. In the Waitaki Valley there was no disputing the position of the greensands in relation to the limestone members of the Oamaru formation; while at Mount Royal, and near Palmerston, the greensands had afforded him no palæontological evidences. Hampden and Onekakara, from the absence of the limestone there, failed to yield that measure of stratigraphical proof which was requisite to set off the superior claims of palæontology; while at the Waihao, if v. Haast did not support his views, at least he did not favour those of the Geological Survey. After examination, he decided that the stratigraphical evidence is obscure, but more in favour of his own theory than that of v. Haast, or of the Geological Survey. He discredits the evidence of sections he does not understand, and characterises as impossible others that he did not see.* The sections on the Waihao, at the south end of the Waimate Hills, and that at Elephant Hill, are here alluded to. With reference to the last, there is nothing in Professor Hutton's “Note on the Geology of the Waihao Valley” leading to the belief that the locality was visited by him. He totally ignores v. Haast's description of the sequence, and is equally silent as to the nature of the beds upon which the greensands rest. He proves in nothing the correspondence of the greensands with

any of the beds forming Mount Harris, and seems to think that most characteristic greensands may, through a vertical thickness of 200 feet, alter to beds of a totally diverse character in the horizontal distance of a few feet; and, amazed at the difficulties that beset his own explanation of the sequence, marvels that I could not discover the like from my point of view. Yet, regardless of what may follow, he decides that there is no proof of the greensands underlying the limestone; and, dismissing this part of his subject, is satisfied that the palæontological evidence is less unsatisfactory. This would indeed seem to be the case. According to Hutton's lists of fossils, the palæontological evidence is to all appearances decisive. Sixteen species of Mollusca are known; all of them said to have come from the Waihao greensands: the collections of 1867–68, named by him in 1876; and collections (of latter date?) now in the Canterbury Museum, 8 more, making 24 in all. Twenty-four, it would appear, then, are known to him, and in the Canterbury Museum; yet only 16 species are now cited by him—what of the remaining 8 species? They were sent by v. Haast to the Otago Museum and named by Prof. Hutton in 1876. They are cited as fossils of the “Waihao” in the “Geology of Canterbury and Westland,” and now they are not! What has become of them? Lost? No; for their record remains. But we have 16 left, the 16 that now constitute the fauna of the Waihao greensands. What of them? They have all been found in the Pareora formation: 9 of them have never been collected from beds of greater age, and 5 of them are actually living forms. Of the 16 species from the Waihao greensands, 9, or nearly 57 per cent, are unknown as coming from the Oamaru formation, and 60 per cent, are in like case, taking the Pareora formation as a whole; therefore the Waihao greensands are typical Pareora beds; and there is no need to inquire how their fossils stand related to those found in the neighbouring Mount Harris beds. The stratigraphy has been wrongly read hitherto, is difficult of decipherment, and at best obscure. If we admit all these premises, there can be no doubt, identifying myself with the stratigraphists, that ours is a desperate case; at least, it looks so on paper—hardly so bad along the banks of the Waihao. Last June I paid a short visit to the Waihao, and first examined the section at the Waihao Forks, south to the limestone scarp. I could not avoid the conclusion that the green-sands dipped south and passed under the limestone. I followed up the first creek below the junction, and in the west branch of that found it had cut through the limestone and exposed the greensands. I tried the middle branch with the like success, and that to the east with the same result. I examined the south bank of the river more to the east, and, opposite the

western end of the limestone, on its north bank, had further proof of the inferior position of the greensands. Here a small stream, coming from the northern slopes of Mount Harris, joins the Waihao. Part of its course is through a limestone gorge; nearer its junction with the river the limestone walls diverge, but again approach towards the infall of the creek. The basement beds of the limestone are 20 to 30 feet above the creek at its junction with the river on the east side, and higher on the west side. On the west side the limestone forms a high bluff overlooking the river, which sets as a deep pool at its foot. The lowest beds seen are dark, almost black, with greensand grains. The creeklet ripples over these into the pool. On the right hand (down the river) they form a flat ledge above ordinary flood-mark. Fossils were collected here, the same species as at Waikakahi Bridge farther down the river. The fossiliferous beds are overlaid by the “marl beds” under the limestone, and the dip of the conformable junction line can be traced from the side of the cliff facing the river round the corner, and up the little creek till it crosses and returns on the opposite bank. This carries us to the road-line, the creek being crossed by a bridge, above which greensands overlie the marly beds. The limestone frowns above, on the right bank of the stream; the greensands and other beds just described pass under the limestone. And again we are satisfied that the Waihao greensands cannot and do not overlie the limestone. The same beds are seen at Waikakahi Bridge; and if the passage of the greensands under the marl is less evident, on account of the junction being in low ground and obscured by the alluvial banks of the river, there is, at least, from what is seen, every probability that they do. A section on the north or left bank has been given by Professor Hutton (see ante, p. 433). That part of the same section from where the greensands (4) are made to rest on the east end of the limestone ridge (3), and thence across the valley marked “W.B.” on Hutton's section, I sketch below, but subdividing the strata as I read the section in 1880. There is certainly some difference in the rendering, which the reader must try to reconcile if he can.

North of Arno railway-station the reading of a similar sequence in the same relation of the beds to each other is unavoidable; and the same occurs in the west branch of the Waihao, above the road to Pudding Hill station; and evidence can scarcely have been looked for by those who say there is little evidence to be found, and that little not of a decisive character. No stratigraphy could be plainer than in some of the sections, and the evidence of those that are less clear supports, as far as it goes, that which the others exhibit. Beyond all question, the greensands underlie the Waihao limestone: and as explanations of the contrary view, islands and fiords without number, crush, faults, contortions, and, in short, all that might render the geology of a district complicated and obscure, are invoked in vain. Not merely do the sections specially examined show this; the general structure of this district, and that of all Southern Canterbury and North-Eastern Otago, points to the same conclusion; and it is rare, almost never, that the Pareora rocks rest on other beds than those of Upper Eocene or Cretaceo-tertiary age. Sir J. v. Haast, in “The Geology of Canterbury and Westland,” points out no instance of their doing so, but says: “The strata belonging to this series lie either conformably upon the Oamaru formation, or, what is still more usual, unconformably upon it.” I might here stop, and only ask the palæontologists to bend their pliant facts to conformity with the stratigraphical facts; and would have done so, but that I may be expected to say something respecting the nine species of Mollusca that, coming from the Waihao greensands, are said to occur only in Pareora or younger beds. The rest are acknowledged to be fossils of the Oamaru formation. The following is a list of the nine species referred to:— 1. Siphonalia nodosa, Martyn. 2. Ancillaria australis, Sowb. 3. Pleurotoma fusiformis, Hutton. 4. Pleurotoma buchanani, Hutton. 5. Pleurotoma awamoaensis, Hutton. 6. Clathurella hamiltoni, Hutton. 7. Voluta corrugata, Hutton. 8. Natica suturalis, Hutton. 9. Leda fastidiosa, Adams. 10. Siphonalia nodosa, or a form as like Martyn's species as that which from the Waihao receives the name, I collected from the Whaingaroa clay, Raglan, at the time Mr. Cox's first examination of these beds was made. This is, therefore, a fossil of the Oamaru formation of Hutton. 2. Ancillaria australis.—All the specimens from the Waihao greensand that could possibly be referred to this species, agree

badly with specimens now living, and closely resemble A. fusiformis from the Eocene deposits of Britain. 3. Pleurotoma fusiformis was described from Mount Harris. Von Haast does not mention it as coming from the Waihao greensands. I have collected it often, but not at the Waihao, and think it should be dropped from the list. 4. Pleurotoma buchanani.—This is mentioned by Dr. von Haast as a fossil of the Waihao greensands. A distinction of the Waihao specimens from those coming from younger formations might be shown, but I choose to admit it a fossil of the Waihao greensands. 5. Pleurotoma awamoaensis.—This, in the first lists, was given as a variety of P. awamoaensis. Why should it now be otherwise? 6. Clathurella hamiltoni.—I do not know this species, and accept it as coming from the Waihao. 7. Voluta corrugata.—That such a prominent fossil in all the beds in which it occurs should be absent from the collections made by v. Haast and myself, leads me to think that the specimen from the Waihao greensands must, in the first list, have been named V. elongata, Hutton. I have a species of this genus from the beds, but it is neither V. corrugata nor V. elongata; therefore, until its occurrence be verified, I cannot accept V. corrugata as a fossil of the Waihao greensands; though, at the same time, I suspect that it occurs in the Oamaru formation. 8. Natica suturalis comes from Mount Royal, near Palmerston, Otago, where the beds are most certainly the same as those elsewhere referred to the Oamaru formation of Hutton. 9. Leda fastidiosa comes from beds belonging to the Oamaru formation in the Trelissick Basin; that it is recent, concerns us not at the present time. Thus, of these nine species, there are only three that can be fairly claimed as being unknown in rocks of greater age than the Pareora beds. Pleurotoma fusiformis is very doubtfully a fossil of the Waihao greensands. Pleurotoma buchanani and Clathurella hamiltoni are, therefore, the only evidences that the Waihao greensands belong to the Pareora formation. Are the palæontological proofs, then, of such a character that we must disregard the clear stratigraphical evidence as above stated?