11

C—:2.B

4. KAIPARA DISTRICT, NORTH AUCKLAND. (By P. G. Morgan.) In September, .1.915, I spent two days at Kaipara Flats, and during that time visited the mouth of the Hoteo River. I then proceeded to Maungaturoto, and thence to Pahi, where two days were occupied in the examination of Pahi Peninsula and in a, launch trip to Komiti Bluff and Gibraltar Rock. Physiography . The greater part of the district examined is occupied by hills and ridges a few hundred feet in height, with some intervening river-flats and the " wide maturely sculptured depression known as the Kaipara Flats."* The most striking physiographic feature is presented by the numerous drowned valleys which allow the sea to penetrate far inland and form the intricate shore-line of Kaipara Harbour. The depression thus indicated has been offset to some extent by slight subsequent elevation, shown by an entrenching of the streams in their main valleyfloors and by a few probable wave-cut terraces about 20 ft. above high-water mark seen on the shores of Kaipara Harbour. General Geology. Owing to the briefness of my visit to the Kaipara district nothing of material importance can be added to the accounts given by Cox, Park, and other previous observers. Cox's sketchmap of 1881-)- appears to represent the geology of the district with a considerable degree of accuracy.. It may be stated, however, that numerous strong faults traverse the area, and render its geological structure decidedly complex. Many of these arc of post-Miocene age, but it is not improbable that some originated between the Cretaceous and the Miocene periods. Unconformity between Miocene and Cretaceous Rocks. According to the reports by Cox and Park, one or more angular unconformities may be detected in the rocks of the Kaipara district. Owing to faulting or to the obscurity of the stratigraphieal relations, some of their sections showing unconformity —for instance, that of Cox in the upper part of the Pahi Estuary near Captain Colbeck's old residence} —are unsatisfactory. A clear angular unconformity between Miocene and probable Cretaceous rocks may be seen at the south-east corner of Komiti Peninsula, at the point where Arapaoa Arm joins the Otamatea Estuary, three miles east-north-east of Komiti Bluff. This no doubt is the unconformable section mentioned by Hector,§ Cpx,|| arid Parkll as occurring at or near Komiti Point. Owing to adverse weather-conditions 1 was uuable closely to examine the section, which as viewed from the sea appears to consist of a yellowish sandstone resting with moderate angular unconformity upon concretionary greenish clays. At Kaipara Flats unconformity is indicated between Miocene and Early Tertiary or Cretaceous by the occurrence of conglomerate with pebbles of hydraulic limestone and of limestone of the Gibraltar Rock type.** E conomi o Geology . Goal. —ln the third gully south of Mr. Thomson's house, near Kaipara Flats Railway-station, the horizontally bedded marine sandstone contains tiny lenticular seams of plant-remains converted into coaly material. These cannot be regarded as indicative of workable coal-seams, but merely of the fact that while the sandstone was forming on the sea-bottom pieces of wood and other vegetable matter transported by streams to the sea were embedded in it. No. 1 of the following analysesft shows the composition of the coaly seams. No. 2, given for comparison, is the analysis of carbonized wood from the coal-measures in Miller Greek, State Coal Reserve, Greymouth : — (!•) (2.) Per Oent. Per Oent. Fixed carbon . . . . . . . . . . . . 34-42 43-61. Volatile hydrocarbons . . . . . . . . . . 38-16 30-22 Water .. .. .. .. .. .. 15-63 19-17 Ash .. .. .. .. .. .. .. 11-79 7-00 100-00 100-00 Total sulphur .. .. •. .. .. 1-43 0-34 Specific gravity .. . . .. . . . . 1-38

♦Henderson, J. : "Coal Possibilities of the Warkworth Flats." N.Z.G.S. Eighth Annual Repirt, published in 0.-2, 1914, p. 157. t Cox, S. H. : " Geology of the Rodney and Marsden Counties." Rep. Geo! Explor. during 1879-81), No. 13, 1881, map opposite p. 28. % Op. cit„ p. 19. § Hector, J. : "Progress Report " in Rep. Geol. Explor. during 1874-7(3, No. 9, 1877, p. v. ijCox, S. H. : Op. A, pp. 17, 33. 37 ; " North Auckland District." Rep. Gaol, Explor. during 1881, No. 14. 1882, p. 23. || Park, James : "Kaipara and Wade Districts, Auckland." Rep. Gjol. Explor. during 1888-87, No. 18, 1887, pp. 221, 228. ** la this connection see Henderson. J. : " Ooal Possibilities of the Warkworth District," N.Z G S. Eighth Annual Report, in C.-2, 1914, pp. 157-158. tt Taese a-id subsequent inalyses, unless otherwise stated, are the work of Dr. J. S. M lolaurln, Dominion A-ialyst, and his staff.