a—2b.

7

No. 4 seam has been worked in several places in the Capleston field ; its southern extension on this field is limited by the northern side of the washout which runs roughly along the course of Boatman's River, though the seam is thin, and stony for 8 chains northwards from that river.

Analyses* of Air-dried Samples of No. 4 Seam.

(c) Formation of Coal-measures. In early Tertiary times a longitudinal depression or graben originated in the area now occupied by the lower Inangahua Valley. The growth of the depression continued slowly throughout the remainder of the Tertiary era. The last movements are described on page 8, where the structure of the coalfield is discussed. The gently undulating surface of the greywackes and granites was folded into a series of low ridges and depressions. Erosion immediately commenced to reduce the surface of the ridges and. deposit the detritus in the shallow depressions. The character of the sediment which accumulated was governed by geographic conditions from time to time. These conditions changed rapidly. Biver-capture would occasionally occur in the initial stages of the dissection of the elevated blocks — sometimes, no doubt, brought about by differential earth-movements in a region that was tectonically unstable. In a long narrow submerged depression a change in the drainage systems in the neighbouring land-masses would have a profound effect upon the nature of the detritus which was deposited. The character of the sediment would also be governed by local earth-movements, which would determine the depth of water at different points along the depression. The micaceous mudstone was formed in those areas which were more deeply submerged, or which were more remote from a supply of coarse sediment brought down by rivers. The rapidly changing geographic conditions, however, did not permit the accumulation of a great thickness of this sediment. Interlaminated sandstone-beds appeared when the area was brought, either by local movements or by change in drainage systems, into the region of deposition of such a deposit, the supply of which may at any time be cut off for the same reasons as it was formed. Occasionally, when the necessary combination of conditions occurred, vegetable matter, which later formed the coal-beds, was accumulated in the manner described in the Drift Hypothesis. A narrow strip of sediment formed in this manner along the depression, the deepening of which proceeded contemporaneously with the deposition of the sediments which crept up the gently shelving sides, which became covered by an overlapping series of sediments ; thus the beds which lie on the basement rocks in the centre of the trough are older than those which immediately overlie the greywacke on the sides of the depression. The formations which were deposited in the graben consequently form lenticular masses, the strata of which stretch for considerable distances longitudinally without marked change in facies, whilst in. a transverse direction the nature of the sediments varies rapidly, and overlap is commonly observed. These features can be used to solve the economically important question of the continuation of the coal-seams beneath the Inangahua Valley. (4) The Waitahu Marine Beds. The coal-measures are succeeded by marine beds which vary in character and from place to place along the depression. In the southern half of the area the only rock visible is a soft homogeneous bluish mudstone, with no bedding-planes or sandy bands on which dip observations can be taken. It splits characteristically along planes parallel to the contour of the surface. A band of concretionary mudstone of unknown but probably variable thickness appears near the base of this mudstone, and is of value in locating outcrops of No. 1 seam. A bore sunk about 1920 near the rifle butts at Reefton penetrated these beds for 500 ft. It passed through soft mudstones and fine argillaceous sandstones for the whole of this distance. Mr. James Gibson, who was in charge of the drill, informed me that a carbonaceous band, 3 ft. in thickness, was penetrated at a depth of 100 ft. As this band is at least 1,600 ft. above the highest coal-seam, it becomes apparent that carbonaceous matter may be expected throughout the Waitahu beds. In the northern portion of the district the Waitahu beds are lithologically different. Predominate mudstone gradually gives way to a predominance of sandstone. On the Waitahu River the two types are equally developed. Farther north the mudstone has been almost entirely replaced by sandstone, of which many thousand feet are visible before the covering of high-terrace gravels obscures them from view. Thin carbonaceous or coaly bands appear as in the mudstone farther south, but are not developed sufficiently to be of economic value.

v i Volatile | ; Sulphur Locality. Hydro- ! Water. 1 Ash. Per- I Colour of Ash. Coking Properties. Remarks, uaroon. c . lrboIls> | centage. I Waitahu River .. 41-64 36-21 11-10 11-05 3-46 Yellowish-white Pulverulent .. Not yet opened up. Burke's Creek .. 43-35 40-31 9-68 9-66 2-55 Light purple .. Dense, weak .. "Upper half of seam. ,, .. 43-05 40-06 12-65 4-24 1-16 Greyish-yellow Dense, weak .. Lower half of seam. Archer's Mine .. 47-35 43-15 8-29 1-21 2-25 Reddish-brown Dense, weak .. Upper half of seam. „ .. 49-51 41-44 8-39 0-66 1-27 Reddish-brown Dense, weak .. Lower half of seam. Morris's lease .. 47-51 39-95 11-21 1-28 1-53 Brick-red .. Pulverulent .. Upper half of seam. ,, .. 46-72 38-56 13-95 0-77 0-68 Light brown .. Pulverulent .. Lower half of seam. Honey's Mine .. 44-22 41-02 11-69 3-07 2-09 Pink .. Pulverulent .. * Analyses by Dominion Analyst.