Speight. — Occurrence of Petroleum in Xew Zealand. 359 



In summing up the position, Morgan says (p. 148), " It seems not unlikely 

 that the source of the Kotuku petroleum may be at considerable depth, in a 

 horizon corresponding to the Omotumotu beds, Kaiata mudstone, or Island 

 sandstone. There is also the possibility of the oil originating in the Brunner 

 or Paparoa coal horizons. The chief evidence, however, in favour of the 

 view that the oil occurs at depth is based on the logs of the Brunner Company's 

 Nos. 2 and 9 bores. These logs state that a little oil and gas occur all 

 through the conglomerates that lie below the limestone. Since the bores 

 were cased, a mistake as to the occurrence can hardly have been made, 

 and therefore a deeper source than the conglomerate for all or much of the 

 Kotuku oil must be regarded as the most probable. The small amount of 

 benzene in the oil hitherto obtained supports the hypothesis of a deeper 

 source than the argillaceous sandstone or the limestone." 



In the Gisborne district, according to Adams,* the oil which occurs 

 on the surface as well-marked seepages at Waitangi is derived primarily 

 from a bed of oil shale which lies at the base of the Whatatutu series of the 

 Survey. The author says (page 40), ' ; As a result of the examination that 

 has just been completed, it seems certain that the clay shales which form 

 the lowest members of the Whatatutu series are the upper portion of or form 

 the impervious cover for the oil zone of this area. Every sample of this 

 rock which was obtained gave, when finely pulverized and subjected to 

 strong heat, a decided smell of hydrocarbons. From its character the clav 

 shale is advisedly suited for a cover for a stratum containing oil." 



These beds of the Whatatutu series are classified by Adams as of, Miocene 

 age, but it seems reasonable that McKay's classification of them as Cretaceous 

 is more correct, since he found Inoceramus shells in them ; and the report 

 has been recently confirmed by the discovery of these fossils in boulders 

 in the bed of the Waipaoa River in a matrix similar to that of the lowest 

 beds of the series. This discovery apparently confirms McKay's classi- 

 fication, and we may therefore look on the shale, or the beds associated 

 with it — probably the sandy beds — as the place of origin of the oil, and the 

 fact that indications are to be found freely in the overlying clays which may 

 be of Miocene age is attributable to migrations from a lower to a higher 

 horizon. In this locality the only possible origin for the oil is an organic 

 one, and almost certainly the oil has been derived from the remains of 

 animal-life of a former sea-bottom. 



In the East Coast district of Wellington the Miocene marls and clays 

 are well developed, and under them lies, in all probability unconformably, 

 a Cretaceous series.f Surface indications, such as gas emanations, are 

 frequent in the overlying beds, but in all probability the major portion 

 of the oil is derived from the lower series, in which black slaty shales are 

 interbedded with clays and sandstones. These are well exposed near the 

 coast, and have a general inland clip. The overlying marls are very thick — 

 certainly over 3,000 ft,, and probably over 5,000 ft. — and since they are marine 

 in origin and contain traces of marine organisms it is quite possible that 

 a part of the hydrocarbon matter they contain, and in some cases the 

 whole of it, has been derived from the beds themselves and has not been 

 accumulated by migration from the petroliferous beds underneath. 



If we consider, therefore, that a deep-seated source of oil exists, then 

 its probable mode of origin should be briefly referred to. The only accept- 



* Bulletin No. 9 (new series), N.Z. Geol. Surv., Geology of the Whatatutu Subdivision. 

 t See Park, Geol. Surv. Report for the year 1887-88, p. 20. 



