C—2b

11

The width of the syncline from the outcrop of the coal-measures to a point on the opposite limb where the coal-measures might be expected to appear is about eight miles. Consequently, a dip of, say, 25° decreases to zero in a distance of four miles — i.e., 6° 15' per mile. The inclination of the coal-seams, therefore, decreases 6° 15' in every horizontal mile. It is stated elsewhere that coal will probably not be profitably produced at a greater depth than 2,000 ft. At this depth the horizontal distance of the coal from the entrance to the mine is about 75 chains. Consequently the decrease in the dip amounts to, say, 5° 52' within what may be termed " mining distance." The calculations are based on the assumption that the syncline is symmetrical, but the change in average dip is so small in the area which could be worked that a slight degree of asymmetry will alter the results only slightly. It should be clearly understood that the inclinations mentioned are average dips, which can be found approximately by averaging a representative series of dips taken at regular intervals within, say, 5 chains of a given point along the line of dip. Some idea of the dip of the beds nearer the centre of the syncline can be obtained from observations on the Waitahu marine beds, which stretch out for some distance towards the axis, along the north bank of the Waitahu River. The inclination of the beds along these cliffs is slightly less than that of the underlying coal-measures into which they pass in depth, through a blended unconformity. The inclination of the beds deposited in a growing depression decreases from the lowest to the highest members of the series. (7) Quantity op Coal available. The figures are computed on the assumption that the conclusion reached in the discussion of the coal-seams beneath the alluvial flats is correct. Such factors as the regularity of the seam (as regards both thickness and quality) have been taken into account in arriving at the probable available tonnage of coal in the field, the extent of which has to be estimated on admittedly insufficient data. The assumed thickness is a safe minimum, used for the purpose of computation only ; it is not intended to represent the average thickness of the seam. It is fixed after consideration of the habits of the seam ; thus the thickness of a coal-seam which is very irregular has been reduced considerably from that of the outcrop. The figures for seams Nos. 1 and 3 should be accepted with reservation, as these seams are markedly irregular. If the field is bored, the conservative estimates given can be adjusted according to the proved thickness of coal. The tonnage computations are based on 100 tons per inch pe acre. The quantity thus obtained is the probable available tonnage of coal, which is less than the total tonnage in the field by an amount allowed for loss of coal along faults, coal left for support, coal lost in working, &c.

"Rise" Coal.

I Seam. I Locality. Area. Thickness. Tonnage. Acres. Feet. 4 Reefton to Reddale Valley .. .. 63 15 1,134,000 Reddale Valley to Burke's Creek .. .. .. 36 15 648,000 Burke's Creek to Stony Batter Creek .. .. 20 15 360,000 Stony Batter Creek to Madman's Creek .. .. 11 20 264,000 Madman's Creek to Painkiller Creek .. .. 40 20 960,000 Waitahu .. .. .. .. .. 12 15 216,000 Capleston Field .. .. .. .. .. 34 20 816,000 4,398,000 — 3 Reefton to Stony Batter Creek .. .. .. * Stony Batter Creek to Madman's Creek .. .. t Madman's Creek to Painkiller Creek .. .. 12 5 72,000 Waitahu .. .. .. .. .. 9 5 54,000 Capleston Field .. .. .. .. .. { 126,000 2 I Reefton to Reddale Valley .. .. .. 56 10 672,000 Reddale Valley to Burke's Creek .. .. . . § Burke's Creek to Stony Batter Creek .. .. t Stony Batter Creek to Madman's Creek .. . . f Madman's Creek to Painkiller Creek .. .. 21 10 252,000 Waitahu .. .. .. .. .. 10 6 72,000 Capleston Field .. .. .. .. .. 62 10 744,000 1,740,000 1 Reefton to Reddale Valley .. .. .. 19 4 91,000 Reddale Valley to Burke's Creek .. .. .. 6 5 36,000 Burke's Creek to Painkiller Creek .. .. .. * Waitahu .. .. .. .. .. 6 6 43,000 : Capleston Field .. .. .. .. .. 31 6 223,000 393,000 * Unworkable. f Worked out or almost worked out. J Probably unworkable. § Destroyed by fire.