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Report on the Geology & Gold Fields of Otago

Putataka Formation. — Mataura Series of Lindsay and Hector

Putataka Formation.
Mataura Series of Lindsay and Hector.

Distribution.—This formation is confined to the Hokanui Hills and to the country lying between the lower Mataura and Cannibal Bay, near the Nuggets. But it is also seen in the beds of some of the creeks on the Seaward Downs, below the gravels.

Rocks.—The rocks composing it are slates, green and brown sandstones, shales, conglomerates, and thin seams of coal. At Benmore, in the Hokanuis, the conglomerates contain pebbles of a pale purple porphyry, with crystals of white felspar, like the dyke north of the Nuggets; and of pink granite like that at Preservation Inlet, as well as pieces of green, red, and blue slates, and quartz. At the north end of False Islet, near the mouth of Catlin’s River, the conglomerates are formed of quartzite, sandstone, jas-peroid slate, [gap — reason: illegible]quartz, diorite, white granite, red porphyry with white crystals of felspar, and grey porphyry with white crystals of felspar.

Position of Strata.—Behind Benmore Station, at the west end of the Hokanuis, these rocks dip 20° E.S.E., and at Bastion Hill, where a splendid section is seen, 10° S.E. by E. In a south easterly direction from this the beds get more horizontal, dipping in the Otapiri Gorge very gently to the north east. At the eastern end of the Hokanuis the dip is 30° S.S.W., and at the Mataura Falls 3° N.N.E. On the left bank of the Mataura River, below Wyndham, the dip is 10° N.N.W., and at the Toi-Tois 6° N.N.E. At Otaraia the dip is 35° S.S.W., at a high angle. From the mouth of the Mataura to Waikawa the rocks are nearly horizontal (See Sec. v.), but dipping slightly to the north. East of Waikawa the beds begin gradually to dip very gently to the north east, and this continues through Chasland’s Mistake, to Tautaku and Hakkup Bays, from which the dip increases to Jack’s Bay. On the south side of Jack’s Bay the rocks again flatten, dipping here 8° N. On page 43the north side of the bay they are horizontal, rising again with a S.S.W. dip towards Catlin’s River. (Fig. 3).

Fig. 3.—Jack’s Bay to the Nuggets. Distance, 6 miles.

Fig. 3.—Jack’s Bay to the Nuggets. Distance, 6 miles.

Jack’s Bay therefore occupies a synclinal curve. The S.S.W. dip continues until close to the entrance to Catlin’s River, when it changes sharply to the N.N.E.; the anticlinal running under the Pilot Station and Flagstaff. This direction in the lay of the rock is continued to False Islet, at the south end of which the dip is 50° N.E. False Islet itself is formed by a synclinal curve, the northern side of which is so sharply thrown up that at the north side of the Islet the dip is 80° S.S.W.; while on the north side of Cannibal Bay the beds are vertical, and strike S.E. by E. This vertical position of the strata is maintained through Roaring or Shaw’s Bay to the Nuggets, where the strike is S.E. and N. W. The rocks of the Putataka formation extend, I consider, to a little beyond the north point of Cannibal Bay, where they are followed quite conformably by the rocks of the Maitai formation.

Relation to Underlying Formation.—I was formerly of opinion that an unconformity existed between this and the Maitai formation, but the evidence I adduced, viz., different strikes in neighbouring localities,* is not of much weight, and I have since examined the coast section betwen Catlin’s River and the Nuggets, and find that the two are quite conformable. The formations here can only be distinguished by their fossils.

Thickness.—I estimate that the thickness of these rocks in the Catlin River district is between 9,000 and 10,000 feet.

Fossils.—From Bastion Hill 1 obtained in 1872 a small compressed Pholadomya about an inch in length, and three-fifths of an inch in height, concentrically furrowed, and finely radiately striated; and from the tributary of the Otapiri in which coal has been found, I found a species of Astarte, apparently identical with A. wollumbillaensis Moore.* From Tautuku Ammonites and Astarte have been obtained, and at Jack’s Bay I saw Astarte (?), Ostrea, and a species of Mytilus with a curved beak, perhaps M problematicus Zitt; and many fragments of wood. Fossil ferns, among which are Polypodium hochstetteri, and species of Tæniopteris are found at the Otapiri Creek, Seaward Downs, Mataura Falls, Waikawa, Owaike

* Reports of Geological Explorations 1871-2, p. 104.

* † Quar. Jour. Geol. Soc, xxvi., p. 250, pl. xii., fig. 12.

page 44Creek near Catlin’s River, and the upper part of the Omaru Creek. These ferns have not yet been described, but many of them are no doubt identical with those found near Port Waikato.

Age.—In 1864 Professor von Hochstetter and Dr. Zittel referred the rocks at Port Waikato, which belong to this formation, to the jurassic period. In 1867, in my report on the Lower Waikato district, I called them Neocomian, and in the same year Professor von Hochstetter, in his "New Zealand," considered them as cretaceous. In his Progress Report of 1868-9, Dr. Hector considers that this formation "corresponds in age with the coal measures of New South Wales;" but in 1869 and 1870, he placed it in his "cretaceo-tertiary" formation, and in his report on the coal fields of New Zealand, in 1873, he calls it "upper secondary." In 1872, in my report on the geoiogy of Southland, 1 referred it Back again to the middle jurassic period, and I still think that it is either middle or lower jurassic.

Nomenclature.—These rocks have been called the "Mataura series" by Dr. Hector; but if, as I think, they are the equivalents of the Port Waikato beds, my name of Putataka formation, given in 1867, will take precedence.