110 The N.Z. Journal of Science and Technology. [Mar. 
point hard gently dipping sandstones overlain by soft argillaceous sand¬ 
stone occur. 
The individual pebbles of the conglomerate bands are always well 
rounded, and consist for the most part of hard siliceous greywacke, pro¬ 
bably derived from the rocks of the Spenser Mountains, which lie to the 
south-eastward. The matrix of the conglomerate is generally gritty or 
sandy, and in places increases in amount until the rock contains only a 
few rounded pebbles. 
The exact position of these conglomerate and associated beds in the 
Tertiary sequence was not determined, but they are probably of about 
the same age as the lowest beds of the Sphinx Rock section, the 
differences of the conditions of deposition accounting for the difference in 
character. 
The Pleistocene and Recent deposits of the district form the Four-river 
Plain and various smaller flats along the streams. The latter are for the 
most part the flood-plains of the rivers, which once flowed at a higher level 
than at present, and the deposits form the merest veneer over the under¬ 
lying rock. In the Four-river Plain and its southern extension along the 
valley of the Matakitaki the gravels are apparently much thicker, and, 
except at points where the stream-channels approach the hills, the under¬ 
lying older rocks nowhere outcrop. On the left bank of the Matiri near the 
bridge, and again at the road-crossing over Husband Creek, soft blue silts, 
evenly bedded and lying horizontally, appear from beneath the river-gravels. 
This material is known to the alluvial miners of the district as “ pug,” and, 
in addition to the two localities mentioned, is reported to form the bottom ” 
at several points along the Matakitaki Valley. The silt is probably of 
lacustrine origin, and therefore it appears that a lake or lakes once occupied 
portions of the Four-river Plain. 
Structure. 
The structure of the Murchison district is similar to that of the West 
Coast generally. Several great fault-zones cross from north to south and 
divide the area into a number of earthblocks which have been warped, 
tilted, and moved differentially. To the westward lies the northern exten¬ 
sion of the great horst that south of the Buller forms the Brunner and 
Victoria Mountains, while to the eastward there is another elevated 
earthblock, from which Mounts Hope and Murchison have been carved. 
Between lies an elongated depressed area, the northern end of which forms 
the Murchison district. 
The most westerly of the principal fault-zones that cross the Buller 
Valley in the area mapped is that at Eight-mile Creek, where several pug- 
filled fractures may be seen on the roadside. The zone appears to strike 
north-north-eastward, and has probably determined the course of the valleys 
of Eight-mile and Little Deepdale Creeks and that of the Buller in this 
locality. Another powerful fracture is marked by the occurrence, a little 
east of the Newton Stream, of a narrow belt of steeply dipping limestone. 
The main portions of the Newton and Deepdale Valleys follow this fracture, 
and to it is due also the horseshoe bend in the Buller a mile and a half above 
Newton Flat. Four miles farther eastward the edge of a fault-bound zone of 
highly inclined Tertiary rocks is reached. These continue along the northern 
bank of the Buller for about two miles, and are traversed by several sub¬ 
sidiary breaks. The fault along their western edge appears to have a general 
north - and - south course, and the valleys of the Matiri and Matakitaki 
