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Report on the Geology & Gold Fields of Otago

Waipara Formation

Waipara Formation.

This formation is very feebly represented in Otago, as it occurs only in two localities.

House Range.—The first of these is situated at the mouth of the Shag River, and in the Horse Range, and extends in a northerly direction to the south branch of the Otepopo River, or Rookery. Here it is interrupted by the schist rocks, but further to the north an outlier crosses the north branch of the Otepopo River, and continues up to Island Creek.

Rocks.—The lower portion of this series is composed of shales and sandstones, with thin beds of inferior coal, and conglomerates which are formed chiefly of fragments of slate and sandstone. Above these, in the Horse Range, are thick beds of quartz conglomerates, which thin out seaward, and are covered by a series of conglomerates, sandstones and shales, with good seams of pitch coal. The uppermost beds of all are sandstones and sandy clays, with almost spherical ferruginous concretions, which have been commonly mistaken for septaria, and confused with the true septaria of Moeraki, which belong to a much younger formation.

Position of Strata.—The lower beds, where they abut against the slates of the Kaikoura formation, dip at about 25° N.E., at the highest point in the road from Palmerston to Moeraki; but as these beds wrap round the denuded edges of the palæozoic slates, the dip constantly changes. To the east, along the Shag Valley, the dip increases until it attains to 60° S.E. at Mount Ivitai, and then gradually increases again until it is about 20° S.E., at the mouth of the Shag River. Towards the north an anticlinal axis is passed, page 45and the beds dip more gently to the north-east, the angle of incli nation at Shag Point, where the coal mine is situated, being about 6° N.E., and it decreases still more further to the north, where the beds containing ferruginous concretions reach the sea, and the beach is strewed with these rounded stone balls of all sizes, known as "Katiki boulders." Boulders, however, is not a correct term to apply to them, as it means a stone rounded by the action of water, while the spherical outline of the "Katiki boulders" is their original shape, they having been formed in the rock in which they are found by a chemical concretionary action, and have never been worn until washed out of their bed.

Fossils are scarce in these rocks, but several casts of bivalve shells have been obtained from the upper beds. These have not yet been properly examined, but they appear to me to be quite distinct from any found in the tertiary rocks. There is also in the Museum a fragment of an Ammonite, which is said to have come from this locality. Plant remains, especially leaves of dicotyledons, are more abundant; and a Dammara, which is not uncommon, has been identified by Dr. von Haast with one found at the Waipara associated with the remains of saurians. Dr. Hector in his catalogue of the Colonial Museum had previously classed these rocks with the Waipara beds.

Thickness.—I estimate the thickness of the Shag Point series to be between 6000 and 7000 feet.

Fig. 4.—Mount Hamilton Coal Beds.

Fig. 4.—Mount Hamilton Coal Beds.

Mount Hamilton.—The second patch of rocks belonging to this formation is found near the summit of Mount Hamilton in Southland, at an elevation of 2,500 feet above the level of the alluvial plain of the Oreti, or about 3,700 feet above the sea.

Rocks.—The lowest bed of the series is a conglomerate, overlaid by shales with several seams of coal, which are again covered by yellow sandstone with thin seams of coal.

Position of Strata.—This series forms a synclinal curve (see fig, 4), the axis of which inclines downward to the S.W. by S., the western portion dipping 25° S.E., and the eastern 30° W N.W.

Fossils.—The sandstones above the coal contain numerous impressions of leaves of dicotyledonous plants, many of which Mr. J. Buchanan informs me are identical with those from Pakawau, in he Nelson Province.

page 46

Relation to underlying formation.—Nowhere in Otago can a juration be seen between the Waipara and Putataka formations, but in the Nelson and Canterbury Provinces they are quite uncomformable. In the Horse Ranges the Waipara formation rests unconformably on both the Kaikoura and Kakanui formations (see Sec. VI.), and at Mount Hamilton it rests unconformably on the Maitai formation.

Age.—Professor Owen, in 1861, was of opinion that the beds from which Plesiosaurus australis had been obtained, were probably of Jurassic age,* but Dr. von Haast in 1865, considered them as tertiary. Speaking of this formation in 1869, Dr. Hector says, "I believe [it] corresponds with the wealden group of Britain, No. 6, [ferruginous clays and sands, with concretionary nodules containing saurian bones,] being the equivalent of the green sand." In my report on the geology of Southland, in 1872, I said that I was inclined to think that the Mount Hamilton beds would prove to be of upper cretaceous age, and later in the same year, an examination of the fossils in the Colonial Museum, from the Waipara and Amuri, made me come to the same conclusion with regard to the Waipara formation.§ In the following year Dr. von Haast so far modified his opinion as to class them in Dr. Hector’s "cretaceotertiary" formation, and Dr. Hector, when describing the Saurian remains|| from Amuri and Waipara, refers them to the cretaceous period; to the upper part of which I think they undoubtedly belong. No recent mollusca are known from this formation.

Nomenclature.—The term Waipara beds was applied by Dr. Hector to this formation, in his catalogue of the Colonial Museum, 1870, and previously by Prof. von Hochstetter.

* British Association Report, 1861, p. 122.

Report of the Geological Explorations of the West Coast, Christchurch, 1865.

Reports of Geological Explotations 1871-2, p. 184.

§ Reports of Geological Explorations, 1871-2, p. 184.

|| Transactions N. Z. Institute, VI., p. 337.