386 
The N.Z. Journal of Science and Technology. 
[Dec. 
DEPARTMENTAL REPORTS. 
The Splitting of the Mangatini-Matipo Coal-seam, Buller- 
Mokihinui Coalfield. 
By P. G. Morgan, New Zealand Geological Survey. 
In 1915 J. A. Bartrum and myself* described a remarkable split in the 
main seam of coal found in the central part of the Westport or Buller- 
Mokihinui Coalfield. Since an explanation of this split can be given which 
has a bearing on the more or less disputed question of the mode of forma¬ 
tion of coal it seems advisable to discuss it in a fuller manner than was 
done in Geological Survey Bulletin No. 17. 
General Description of District. 
The Westport coal-mines are situated on a bare and desolate, undu¬ 
lating upland, which extends northward from Mount Rochfort (3,382 ft.) 
almost to the Mokihinui Valley. This upland is the northern part of an 
uplifted, strongly distorted block, bounded east and west by great faults. 
The block as a whole is irregularly tilted to the east, and north of Mount 
Augustus (3,311 ft.) has a northerly pitch, so that it greatly lessens in height 
towards the Mokihinui River. Besides the two great faults already men¬ 
tioned many other faults, most of which trend to the north-north-east, are 
indicated on the geological maps of the district published with Bulletin 
No. 17. 
The basal rocks of the Buller-Mokihinui Coalfield are ancient greywackes 
and argillites, much intruded by gneiss, granite, and quartz-porphyry. On 
them rests a much-denuded, comparatively thin shell of partly eroded 
Eocene coal-measures, consisting of a basal conglomerate (absent in many 
places), followed by grits, sandstones, and shales containing one or more 
coal-seams. The principal localities where coal has been mined are (1) east 
of Denniston, (2) south-east of Millerton, and (3) south of Seddonville. 
The split to be described occurs in the Millerton district, which is shown 
on the sketch-map facing this page. The area in this district occupied 
by coal-measures varies in height from 3,300 ft. or more to 1,100 ft. or 
less. The dip of the strata, owing to the structure outlined above, is 
in general to the north-east at angles varying from 10° to 20°. In 
the watersheds of Granity and Mine Creeks are numerous outcrops of 
a large coal-seam, to which the name Mangatini has been applied. The 
maximum thickness of this seam is believed to be over 50 ft., but 
south-east of Mangatini Township it thins to 6 ft., then to 5 ft., to 
4 ft., and finally to less than 3 ft. Much coal, moreover, has been re¬ 
moved by erosion. Near a small stream known as T 31 Creek the 
Mangatini seam junctions with a thick underlying seam, the Matipo. 
In a small hill not far away (represented on the map by an oval 
outcrop) the Matipo seam (or, rather, the combined Mangatini-Matipo 
seam) is not less ( than 25 ft. thick. Westward from the point of junction 
the Matipo seam gradually thins, until at last it disappears, as shown in 
section below the map. 
* P. G. Morgan and J. A. Bartrum, The Geology and Mineral Resources of the 
Buller-Mokihinui Subdivision, N.Z. Geol. Surv. Bull. No. 17, 1915 (see pp. 142, 157 
et seq .). 
