a—2b

6

exposed at the surface in the Egmont Subdivision, and whether it has any development in the New Plymouth Subdivision west of Urenui seems doubtful. The Upper Onairo is well developed in the Ngatimaru Survey District and in the eastern part of Huiroa Survey District. To the westward it is unconformably overlain by an increasing thickness of volcanic debris belonging to the upper horizon of Clarke's Pouakai Series. At a distance of twelve or thirteen miles from the summit of Mount Egmont outcrops of Onairo rocks disappear, and to the westward only Pouakai and small patches of younger rocks are visible. The Onairo rocks are in general almost horizontally bedded. In some localities they show evidence of gentle but irregular folding, accompanied in one or two cases by slight faulting. The Lower Pouakai rocks consist of andesitic agglomerate and tuff, with contemporaneous andesitic lava-flows and dykes. In many places they show bedding to such an extent as to prove some measure of transportation and sorting of water, but water-worn material is nowhere present to any marked extent. To the Lower Pouakai are assigned the rocks of the Kaitake and Pouakai ranges (with the exception of surface material) and the agglomerates exposed in the valleys of the Oakura and Timaru streams and along the sea-coast from the boundary of the New Plymouth Subdivision to a point west of Oakura. Probably also the core of Mount Egmont belongs to the Lower Pouakai. On the coast-line near the mouth of the Tapuae Stream there is evidence of a distinct break between the lower and the upper portions of the Pouakai Series Here a thin inconstant conglomerate, followed upwards by a soft sandstone (probably partly marine and partly leolian) rests with clear unconformity upon agglomerate. The same unconformity appears on the coast at ISJew Plymouth, but has not been traced to the west of Oakura. In the main the Upper Pouakai rocks consist of fine tuff (generally horizontally bedded) and volcanic ash, but to them are also assigned the agglomerate and andesitic masses forming the conical hills previously mentioned, the lava-flows and fragmentary material that build up the visible portions of Mount Egmont, together with the sandstone and conglomerate mentioned above, and some contemporaneous fluviatile and marine debris. The tufaceous loam that forms the soil and subsoil of nearly all western Taranaki may be considered as part of the Upper Pouakai Series. Whilst the Upper Pouakai Series is necessarily unconformable to the Onairo rocks, as may be seen at various localities in the Huiroa Survey District, the relation of the Lower Pouakai Series to the Onairo Series is more doubtful. It is practically certain that the volcanic eruptions that built up the Kaitake Hills and the Pouakai Range began while the deposition of Onairo rocks was still proceeding in adjoining areas, and therefore complete unconformity cannot exist. No doubt in places there is some degree of local unconformity, and this seems also to be Clarke's view, though his remarks on the subject in the New Plymouth Bulletin* may perhaps be construed in a slightly different sense. Rocks younger than the Upper Pouakai Series have an extremely limited distribution. Their nature is sufficiently' indicated in the table of formations given above. Economic Geology. Soils. —Practically everywhere on the lower slopes of Mount Egmont and on the adjoining country, on the Pouakai. Range except on the highest points, and on the Kaitake Hills, one type of soil —a brown loam derived from decomposed volcanic tuff and ash —prevails. This is generally underlain by a deep subsoil of almost the same character except for the absence of vegetable mould, *-** but on the west side of Mount Egmont, and also near the so-called " radius line "f (boundary of Egmont National Reserve) on the east side, the subsoil is generally shallow, and in places not more than 1 ft. or 18 in. of loam is seen above the bed-rock —cemented grey tuff or agglomerate. The only other classes of soil found in the western part of the subdivision are the peaty soil of swamps bordering small watercourses or occupying small undrained areas (most of which are towards the coast), the gravelly soil of a few small stream-flats or terraces, and the sandy soil of dune-areas near the coast. Eastward from the, central portion of the subdivision the volcanic .soil gradually becomes mixed with more and more material derived from the Onairo rocks. The change is first apparent near the Manganui Stream, and in Ngatimaru Survey District the soils, except in swamp areas, are formed almost wholly of weathered sedimentary material. The volcanic constituents that seem to be present, in some of the river-flat soils are probably derived from the central part of the North Island, and not from the Mount Egmont area. Metallic Ores*. —The Kaitake or Patua Range has been prospected at intervals for gold, silver, and copper. Owing to the presence of quartz lodes and silicified pyritized belts of country which on assay are generally found to carry traces of gold, a litlte silver, and occasionally some copper, hopes of developing successful mines have been entertained, but no real justification for such expectations has been found. Manganese oxide occurs in small quantity at various places, for example, near Tipoka Road, in the neighbourhood of Cape Egmont. Near Puke-iti Hill, between the Kaitake and Pouakai ranges, is a deposit of low-grade rhodochrosite (carbonate of manganese). Very small deposits of magnetic oxide of iron (ironsand) occur on the coast of the subdivision. These have no commercial value. Limestone and Calcareous Sinter. —The bands of shelly limestone in the Onairo Series are too small and, as a rule, too impure to be of much value for agricultural purposes. Deposits of calcareous sinter occur (1) south of German Hill, a dome-like elevation five miles west-south-west of Inglewood; (2) three miles south-south-west of Inglewood, on a branch of the Waiongona-

* Clarke, E. de C. : Op. cit, pp. 14 (table of formations) and 25. t This term, locally applied to the boundary of the many-sided polygon that constitutes the Egmont National Reserve, is a complete misnomer.