5

C— 2c

The oldest rocks are the greywackes of the Rangiora and Kukunui ranges, belonging to the Waipapa formation, which is regarded as of Trias-Jura age. These ranges lie in Ruakaka Survey District, near the east coast, and the formation soon disappears westwards beneath the covering of Notocene claystones and sandstones, which overlie the greater part of the subdivision. The claystones and limestones of the Onerahi formation have yielded no further internal evidence as to their age. These beds are correlated with the Waiparan of other parts of New Zealand and tentatively regarded as Cretaceous. The formation, which covers comparatively large •areas in the eastern and western parts of the subdivision, is present in small amount in the central part. Usually the deposits of Onerahi age are claystones, which give rise to very poor land, but occasionally they pass into argillaceous limestones, in places hard enough to serve as roadmaking-material. The Whangarei formation is usually a somewhat barren sandstone, locally passing into crystalline limestone, the age of which has been determined as Miocene. The formation is correlated with the Oamaruian of the South Island. The sandstone, especially where it is calcareous, forms a soil which supports a good pasture. At two points seams of coal are present. The limestone-deposits form the most valuable mineral resources of the district. Gravels and consolidated wind-blown sands, in places containing lignite, are correlated with tlie Purua beds of the Whangarei - Bay of Islands Subdivision, and are considered to be of Pleistocene age. The gravels occur mainly in the Wairoa Valley ; the sand-dunes cover tho area between the Kaihu Valley and the west coast. Recent deposits arc represented by fertile alluvial tracts in all the valleys eastward of Dargaville, and in the area between Dargaville and the west coast by swamps containing kauri-resin. Two types of igneous rock occur in the district. The Tangihua and Maungartt ranges, near the middle of the subdivision, and the Angiangi peaks, in the Kaihu Survey District, consist of igneous intrusions and conglomerates of post-Onerabi but pre-Whangarei age. The Tangihua and Maungaru ranges are block mountains probably formed during the Pliocene orogcnic movements. The second type, of igneous rock includes the basaltic lava-flows and scoria cone of Maungakaramea. To these rocks the high productivity of the soil of this prosperous district is largely due. Economic Geology. Tine systematic survey of the, Dargaville Subdivision has shown that minerals of high commercial value are practically absent. In North Auckland the coal-measures have, a sporadic development; and in the area dealt with in this report small quantities of coal arc known to occur in two localities only- namely, near Waipu, and at Avoca, fifteen miles from Dargaville. The examination of those localities has shown that the coal - outcrops are of little economic value. That near Waipu is a remnant capping an isolated hill :itis of small extent, and is thin and impure. The Avoca outcrop is a small remnant of a once extensive, seam. The greater part of the accessible coal here has already been marketed, and only a few cartloads of shattered material remain in sight. Of first importance to settlers are, the deposits of high-grade limestone occurring in different parts of the district. These deposits have been mapped, and estimates of the quantities available have been made. Notable localities are Takahiwai, on Whangarei Harbour ; Waipu Oaves ;on the railway-line near Waikiekie ; and in the Avoca district. Large areas of hydraulic limestone suitable for cement-making have been traced inland from Wilson's (N.Z.) Portland Cement Works, and similar deposits in Hobson County have been partly delineated. In the country to the west of Dargaville the swamp lands containing kauri-resin (commonly called " kauri-gum ") have been differentiated from the consolidated dune-sands on which they rest. The resin-dc posits are recent surface accumulations : they are not found intercalated in the aeolian sandstone beds. The mapping of this district provides a means of estimating the areas of those lands which contain kauri-resin in payable quantity, and which, when drained, will become productive dairy lands, and also the areas of land that could, be made available for afforestation. Since the productivity of the various soils of the subdivision depends largely upon the underlying rock formations, the geological map is virtually a soil-map. Six types of soil, each of which requires different treatment, are recognized. Clays useful for brickmaking, and sands suitable for glassmaking and other industries, have been located during the course, of the survey. In some localities roadmaking - material is difficult to obtain ; the, nearest source of road-metal for any particular point may often be, determined by examination of the geological maps, which show the boundaries of the different rock formations. 2. THE WAIAPU SUBDIVISION. (By M. Ongley and E. 0. Macpherson.) Introduction. In the annual report for 1921 the survey districts of Arowhana, Tutamoe, and Hikurangi were reported on under tho name of the " Tokomaru Subdivision" ;to that area the districts of Tokomaru, Mata, Waipi.ro, Mangaoporo, and Waiapu have now been added, and for this larger area the name "Waiapu Subdivision" has been adopted. The following brief notes, based on evidence collected during the field season, may be added to the account given in last year's report. It may be as well to mention in the first place that the geologist does not pretend to any mysterious power of finding mineral wealth or of indicating oil-well sites with gushers guaranteed, but proceeds by studying the rocks and indications exposed at the surface and comparing them with old-established mines and productive fields to estimate the probability of payable deposits being