H.—34.

the harder more shattered Raukumara sandstone. Above them in some places is the white mudstone of the Tertiary Weber formation ; in some places hard shattered sandstones indistinguishable from the Raukumara occur. The Tapuwaeroa Series is predominantly black mudstone that weathers white or rusty and sulphur-coloured. In many places it is interbedded with green sandstone, the beds of black mudstone being 1 ft. to 2 ft. thick and the sandstone 2 in. to 3 in. thick. Generally the beds are contorted and twisted. They slump easily and do not afford good outcrops. From a distance they can be recognized by their pinkish decomposed outcrops in contrast to the darker Raukumara and the light Mangatu and Tertiary rocks. Mangatu Series. —In last year's annual report the beds above the Tapuwaeroa rocks were described as the Mangatu Series, and on the map, because of the difficulties of strict correlation with the Mangatu series of Waiapu they were shown as Tinui Series. Notwithstanding these objections the name " Mangatu Series " is here again used. Last year, too, the Mangatu Series was classified as Lower Tertiary and Upper Cretaceous, and it was stated that no Tertiary fossils had been found in it. No Tertiary fossils have yet been found, and so far as the Dannevirke Subdivision is concerned no fossils at all. It is accordingly impossible to say definitely what age the beds are. There is an important break above them : below the break only Cretaceous fossils are known and above it only Tertiary. This break is taken as separating the Cretaceous and the Tertiary. Accordingly the Mangatu beds are here again classified as Cretaceous. Some of the beds of the Mangatu Series are not distinct from the Tapuwaeroa, and until more evidence is obtained the conclusions are tentative. The characteristic part of the Mangatu Series is a thick set of light-coloured fine mudstone beds. These are interbedded with beds of white sandstone, spotted green with glauconite, and occur with beds of dark mudstone, chocolate mudstone, and grey sandstone not distinguishable from the Tapuwaeroa. Accordingly, where the white mudstone is conspicuous the beds with it are classed as Mangatu. The beds at Kate's Quarry are taken as the characteristic outcrop of the Mangatu ; and from that point they were followed along the strike north-east for five miles. Similar rocks, a mile and a half wide, back the coast behind Porangahau Station and extend north-east across Blackhead Survey District into Pourere Survey District. A mile north-west of this ridge another parallel ridge, a quarter of a mile wide, formed of the same rocks, extends from Hunter's Road south-west across Old Hill Road to Porangahau River. Again, the Whangai Range, on the west of the Wilder Depression, is formed of similar rocks and is here included in the Mangatu Series. It is probable that the extensive Whangai Range has in it more than one series of beds, but so far no evidence of breaks and no fossils have been found there. Several small inliers of similar rocks have been mapped in the south-west part of Motuotaraia Survey District, and part of a big block extending north-east from the middle of Motuotaraia is formed of the same rocks. Wanstead, Weber, and Ihungia Series. —In last year's annual report the lowest definitely Tertiary formation described was the Weber Series, which was said to grade up into the Ihungia beds. The Soil Survey distinguished not only these two groups but recognized a third type of soil named by them the " Wanstead type." The formation on which the Wanstead soils occur was difficult to place stratigraphically, for' no section could be found showing the sequence. In fineness of grain and absence of fossils the Wanstead resembles the Cretaceous, in texture and absence of jointing and slickensiding it resembles the Tertiary. Several contacts of Wanstead and Mangatu show pieces of shelly pebbly limestone, indicating that the Wanstead is unconformable to the Mangatu ; and the absence of any definite boundary between the Wanstead and the Weber indicates that these formations grade. It appears that, after the Mangatu land was exposed, the first wash off its decomposed surface formed the Wanstead beds and the later disintegration of the deeper harder Mangatu formed the Weber. As mentioned in last year's report, the Weber beds grade up into the Ihungia. The Wanstead is a very fine, flaky white clay with irregular blotches ; the Weber is a coarser, firmer white clay with traces of greensand in many outcrops and some fine conglomerates ; the Ihungia is a dark massive arenaceous mudstone. Along the west side of the Porangahau Range the boundary of the Mangatu and the Weber was followed with care, south of Porangahau Road by Mr. Gage, and north of it by the writer, and the erosion break between the Mangatu and the Weber is satisfactorily established. Thick coarse conglomerates of the basal Weber containing pebbles of the Mangatu were found in many places and can be seen on the roadside east of Porangahau River, between Note Creek and Maclennan Creek, in Porangahau Gorge, and north of Hunter's Road. Tutamoe Series. —No work was done on the beds of the Wilder Depression occupying the Akitio syncline, but, as Weber and Ihungia beds crop out along the margin, the middle will be younger and probably consist of Tutamoe beds. No fossils were found to confirm this or no erosion breaks, for the rocks are not exposed in the parts examined. In Motuotaraia Survey District the ridges between Purimu Lake and Nicholls Road are coarse sandstone with the characteristic Tutamoe fauna. At Pukekura Quarry a basal conglomerate containing pebbles of the underlying mudstone separates these beds from the mudstone below. Economic Geology. Petroleum and Natural Gas. —Black carbonaceous mudstone, the so-called kerosene shale, forms thick beds in the Tapuwaeroa and Mangatu Series. It weathers with a striking yellow efflorescence often referred to as sulphur. It is widely distributed in the district and is best exposed along the coast three to four miles south of Porangahau, where a tidal bench 6 chains wide is cut on the black mudstone and is backed by the cliffs of black mudstone. If this black shale is broken the fresh part smells of petroleum, and samples of it have been shown to yield a little oil on distillation. It is not an oil-sand, and as a shale is of no value.

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