Ill 
1918.] The N.Z. Journal of Science and Technology. 
probably follow a parallel fracture forming the eastern edge of the block. 
A fault crosses the Mangles 20 chains above its junction with the Buller, 
and a fracture-zone of more importance occurs about a mile and a 
half farther east. The last-mentioned fault separates the steeply 
dipping conglomerate beds from the flat-lying sandstones that occur to 
the eastward. i 
Economic Geology. 
Sir Julius von Haast in 1860 washed colours of gold from the gravels 
of the Mangles and Buller Rivers; and, since the district is traversed by the 
most direct route between Nelson and the West Coast, the alluvial deposits 
were doubtless prospected in or soon after 1865. The population dependent 
upon mining was never large, but the gravels of several of the smaller streams 
yielded highly profitable returns, and the beaches and terraces of the Buller, 
Matakitaki, and lower Mangles were worked for many years. The most 
extensive workings are in the neighbourhood of Newton Flat, whence they 
extend up the valley of the Buller to beyond the junction of the Maruia 
River. Dredging began in the late “ nineties,” but was discontinued about 
ten years ago. Work, which on the whole was unprofitable, was confined 
to the lower valley of the Matakitaki and that portion of the Buller River 
within the Four-river Plain. 
The distribution of the gold shows that it was derived from the south¬ 
ward. Practically none occurs in the gravels cf the Matiri and Newton 
Rivers, and little in those of the Buller above the confluence of the Mangles. 
The bed of the last-mentioned stream up to the mouth of Blue Duck Creek 
yielded a considerable amount of coarse gold, although only a little fine 
gold was obtained from it above this point. Blue Duck Creek itself, a 
small stream entering the Mangles two miles above the Buller, was exten¬ 
sively and profitably worked, and probably furnished much of the gold 
obtained from the Mangles. The basin of Blue Duck Creek is entirely 
within conglomerates of Tertiary age, and that these rocks are the imme¬ 
diate source of the gold is practically certain. Other streams of which 
the gravels were found to be richly auriferous, such as Nugget, Taylor, 
and Doughboy Creeks, also drain areas of Tertiary rocks, as Cox* and 
McKayf long ago concluded. No doubt most of the alluvial gold of this 
district has been derived from the Tertiary conglomerates, but some must 
have been furnished by the auriferous-quartz veins known to occur near 
the head of Owen River and within the basin of Wheel Creek, a branch of 
Maruia River. 
A coal-seam about 4 ft. in thickness, striking a little south of east and 
dipping northward at about 40°, outcrops on the right bank of Maruia 
River about two miles and a half above its junction with the Buller. The 
enclosing rocks are grits that beneath the seam pass into a quartz con¬ 
glomerate. 
North of the Buller, rather more than a mile to the westward of the 
Mangles junction, a coal-seam 2 ft. in thickness was worked for several 
years while the dredges were in operation. The mouth of the adit, 10 chains 
north of the road, was overgrown at the time of the writer’s visit, and 
* S. Herbert Cox, On the District between the Maruia and Buller Rivers, Rep. 
Geol. Explor. during 1883-84, No. 16, 1884, p. 9. 
f A. McKay, Geology of the South-west Part of Nelson and the Northern Part of 
the Westland District, Mines Reports, 1895, C.-13, p. 26. 
