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Report on the Geology & Gold Fields of Otago

Pareora Formation

Pareora Formation.

Distribution.—This formation is found in the Oamaru district, skirting the seaward side of the low hills between Oamaru and the Waitaki plains, and south of Oamaru to beyond the mouth of the Awamoa. Judging also from a few fossils that I received from the Waitaki, near Otakaik, I suspect that an outlier exists there also, but I have not seen it. South of the Kakanui River it extends to the Otepopo River, and runs north between the Oamaru and Kakanui formations to the Waireka. South of the Otepopo River it extends through Hampden to Moeraki and Kartiki Beach. Up the Shag River it is found as far as Coal Creek, and it forms the whole of the coast from the mouth of the Shag River to Waikouaiti Harbour. In the southern part of the Province it is found on the sea coast between the Tokomairiro and Clutha Rivers, at Wangaloa or Measly Beach (Sec VII., d.) It also occurs in the bed of the Pomahaka below Tapanui, and rises to an elevation of 1180 feet in the Conical Hills. Near Riverton it is again found in the bed of the Pourakino Stream, which flows out of the Longwood Range. In the interior it is extensively developed on the east side of Lake Te Anau from the Eglinton to the Whitestone River, and Mount Prospect, but the boundary between this and the younger lacrustine beds are here not easy to make out without a closer examination than I had time to give to the district. There are also in the museum two fragments of rock enclosing marine fossils belonging to this formation, which are labelled as coming from the Carrick Ranges, but I do not know whether they were obtained in situ or only from boulders.

Rocks.—This formation generally consists of blue sandy clay, often with calcareous concretions, which between Moeraki and Hampden assume the form of true septaria, and have sometimes on their exterior surface fine examples of that peculiar form of crystallation known as "cone-in-cone structure." Between the Shag page 58River and Waikouaiti bands of hard calcareous sandstone are interstratified with it, and at Wangaloa the rocks consists almost entirely of sandstones. In the Pomahaka district the upper beds, which form the Conical Hills, are composed of a white sharp quartz grit containing beautiful impressions of leaves of dicotyledonous plants, which have not yet been described. Inferior brown coal is also found in the Shag Valley and Pomahaka.

Position of Strata.—This formation is usually nearly horizontal in Otago, but on the south side of Oamaru Cape a blue clay belonging to it is seen lying on the Oamaru beds, and dipping conformably with them at an angle of 37° S.W. (Fig. 7, b.), but they soon get horizontal.

Relation to Underlying Formation.—As the Ahuriri formation, which should come in between this and the Oamaru formation, is absent in the Province,* the just mentioned conformity can be only apparent, and this is plainly seen in the Kakanui district, and also at the Shag River, where it warps round the bases of Mount Royal, Puketapu, and Janet Peak, all of which are composed of rocks belonging to the Oamaru formation, the beds of both series being horizontal. Up the valley the same thing can be observed, i.e., the newer beds lying at lower levels than the older ones, while both are horizontal. A good example can be seen at Coal Creek, across which the annexed section (Fig. 8) shows the Oamaru series,
Fig. 8.—Coal Creek, Shag Valley: a, River alluvium; b, older river gravels; c, sand with concretions; d, shale with lignite (Pareora formation); e, green sandstone; f, limestone (Oamaru formation); g, basalt; h, schist (Kakanui formation).

Fig. 8.—Coal Creek, Shag Valley: a, River alluvium; b, older river gravels; c, sand with concretions; d, shale with lignite (Pareora formation); e, green sandstone; f, limestone (Oamaru formation); g, basalt; h, schist (Kakanui formation).

(e, f, g), which once filled the Shag Valley, denuded away by Coal Creek, and beds of the Pareora formation (c, d,) deposited in the hollow.

Thickness.—I have not been able to estimate the thickness of these rocks.

Fossils.—I am acquainted with 154 species of mollusca from this formation, 58 of which, or 37½ per cent., I consider to be identical with still living forms. The following list gives the names

* Vide ante p. 25.

page 59of all the fossils belonging to this formation that have been found in Otago. The species of Mitra, Fasciolaria, and Conus are all small, while the scarcity of the large species of Cucullæa, so common in Otago during the Oamaru formation, and common in the northern parts of New Zealand during the Pareora formation, is remarkable, and points probably to a decrease in the temperature of the sea.
Awamoa. Waitaki. Hampden. Shag Valley. Mount Royal. Wangaloa. Pomahaka. Pourakino. Lake te Anau.
Mollusca
Dentalium mantelli, Zittel
Dentalium irregularis, Hutton
Dentalium conicum, Hutton
Dentalium lævis, Hutton
Fusus australis, Quoy
Fusus mandarinus, Duclos
Fusus plicatilis, Hutton
Fusus nodosus, Quoy
Fusus nodosus, var γ
Pleurotoma buchanani, Hutton
Pleurotoma trailli, Hutton
Pleurotoma awamoaensis, Hutton
Pleurotoma pagoda, Hutton
Bela striata, Hutton
Triton spengleri, Chemn
Triton minimus, Hutton
Cominella nassoides, Reeve
Cominella funereum, Gould
Cominella robinsoni, Zittel
Cominella sp.
Ancillaria hebera, Hutton ?
Ancillaria pomahaka, Hutton
Voluta pacifica, Lam var γ
Voluta subplicata, Hutton
Mitra apicalis, Hutton ?
Amycla, sp.
Marginella albescens, Hutton
Fasciolaria, sp.
Natica zealandica, Quoy
Natica ovata, Hutton
Neritella nitida, Hutton ?
Lunatia, sp.
Sigaretus subglobosus, Sow.
Conus ornatus, Hutton
Conus trailli, Hutton
Struthiolaria nodulosa, Lam.
Struthiolaria scutulata, Desh page 60
Mollusca
Struthiolaria cincta. Hutton, var γ
Struthiolaria tuberculata, Hutton
Struthiolaria sp.
Cerithium rugatum, Hutton
Cerithium cancellatum, Hutton
Rissoa vana, Hutton
Turritella rosea, Quoy
Turritella vittata, Hutton
Turritella gigantea, Hutton
Turritella tricincta, Hutton, var β
Turritella bicincta, Hutton
Turritella sp.
Turritella ornata, Hutton
Phorus conchyliophorus, Born
Calyptræa maculata, Quoy
Crypta incurva, Zittel
Crypta profunda, Hutton
Crypta contorta, Quay
Crypta ungiformis, Lam.
Trochus stoliczkai, Zittel
Emarginula striatula, Quoy
Cylichna striata, Hutton ?
Saxicava arctica, L.
Corbula dubia, Hutton
Zenatia acinaces, Quoy
Psammobia stangeri, Gray
Psammobia affinis, Reeve
Tellina alba, Quoy
Chione stuchburyi, Gray
Chione vellicata, Hutton ?
Chione accuminata, Hutton
Chione mesodesma, Quoy
Callista disrupta, Desh
Dosinea subrosea, Gray
Dosinea grayi, Zittel
Tapes intermedia, Quoy
Venericardia intermedia, Hutton
Lucina divaricata L
Mysia zealandica, Gray
Crassatella trailli, Hutton
Trigonia pectinata (?), Lam
Trigonia semiundulata, M‘Coy
Cucullæa, sp.
Pectunculus laticostatus, Quoy
Pectunculus globosus, Hutton page 61
Mollusca—
Limopsis insolita, Sow
Limopsis zealandica, Hutton
Nucula nitidula, Adams
Solenella australis, Zittel
Hinnites trailli, Hutton
Pecten hochstetteri, Zittel
Lima colorata, Hutton
Brachiopoda
Rhynchonella nigricans, Sow
Polyzoa
Pustulipora zealandica, Mantell
Echinodermata
Arachnoides placenta, L.
Arachnoides conica, Hutton
Schizaster rotundatus, Zittel
Actinozoa
Turbinolia, sp.
Diatomaceæ—
Coscinodiscus, sp.
Actinoclyclus, sp.

In addition to the above, beautiful casts in sandstone of dicotyledonous leaves are found at the Conical Hills near Tapanui.

Age.—The Moeraki, or Hampden clay was considered by Dr. Mantell and Professor Morris in 1850 to be pleistocene. In 1866 Dr. Hector called the Pomahaka series miocene, and the Moeraki clay eocene. In 1870, Mr. C. Traill stated his conviction that the Awamoa beds were not younger than miocene. In 1872, I referred the Awamoa beds to the upper miocene, and those at Te Anau Lake to the upper oligocene; and in 1873, I referred the rocks at Awamoa, Hampden, Pomahaka, and Waitaki to the upper miocene, and the Te Anau beds doubtfully to the lower miocene. I now consider them all to be the upper miocene.

Contemporaneous Eruptive Rocks.—The basaltic rocks at Moeraki are clearly seen to overlie the blue clay of Hampden, and must therefore be younger than it. Consequently, there have been two distinct periods of volcanic activity in tertiary times
Fig 9.—Moeraki roads; a, pleistocene silt; b, basalt; c, blue clay (Parcora formation).

Fig 9.—Moeraki roads; a, pleistocene silt; b, basalt; c, blue clay (Parcora formation).

page 62in Otago; and it is quite possible that some of the basalts that I have enumerated under the Oamaru formation may properly belong here, but the proof of their age in most cases will be difficult.

Nomenclature.—The name of Pareora series was first applied by Dr. von Haast to some rocks in the south of Canterbury. I have not been able to find where this name was first published, and I have never examined the rocks myself, but took the name from Dr. Hector’s catalogue of the Colonial Museum*

* Page 186.