1920 .] 
Speight.—Broken River Coal Area. 
155 
The volcanic rocks met with in situ in the neighbourhood of the creek 
are all of basaltic character. In section this appears as a somewhat fine¬ 
grained basalt, the groundmass being composed of feldspar laths and much 
augite in grains, and the phenocrysts being almost exclusively of augite and 
olivine, the latter showing signs of serpentinization. There is a consider¬ 
able amount of ilmenite, in short rough-edged needles, distributed through¬ 
out the rock. Feldspar phenocrysts are almost entirely absent. There is 
little difference in texture between the rocks which are certainly dykes and 
those considered flows. 
In the bed of Sloven’s Creek occur occasional well-rounded pebbles of 
a gabbro similar to that which is widely distributed in the gravels or rivers 
of the mid-Canterbury region, and whose origin is unknown at present. 
Although gabbro intrusions are known in the valley of the Acheron River, 
a tributary of the Rakaia, which may have yielded the pebbles found in 
the gravels of that river, yet they can hardly have supplied those of 
the Waimakariri basin. From their frequency in the bed of the Broken 
River it is possible that they may have been shed from a mass in position 
on the northern slopes of Mount Torlesse, but this has not yet been located. 
The rock is even-grained, coarsely crystalline, with the crystal elements 
of subequal dimensions. The feldspar is a labradorite ; the augite is 
diallagic and somewhat strongly pleochroic for that mineral; the olivine 
is sometimes fresh, and again it is altered on the margins and along cracks, 
and stained with iron-oxide ; apatite occurs in short stumpy crystals; 
and there is a little magnetite. 
Up-stream from the Avoca Station the floor of the valley, apart from 
its coating of moraine and gravel, consists of greywacke, but about a 
mile and a half from the station coal-measures are exposed in the sides 
of a small gully coming down from the north-east corner of No Man’s Land. 
Although the drainage is towards Sloven’s Creek, yet this outlier lies to 
the north-west of the general line of the beds occurring in the creek, and 
is separated from them by a barrier of greywacke. It is thus analogous 
in position to, and may be on the same line as, the small outlier to the 
west of the mouth of Sloven’s Creek extending across Broken River. 
In this last occurrence the coal-measures consist of clays and sands, 
striking north-east and dipping north-west 70° ; they lie right against the 
greywacke, and are practically parallel with its surface. Some of the 
sandstones are concretionary, and stand out like walls on the surface of 
less resistant beds. Two seams of coal were worked by the Public Works 
Department for local supplies while the Midland Railway was being con¬ 
structed. The coal was similar to Kaitangata, and very gassy. The 
workings were discontinued after a short period, and have now fallen in. 
* About 300 yards to the west, on the northern slopes of No Man’s 
Land, there is an occurrence of sands and greensands, with a thick layer 
of oysters (Ostrea nelsoniana) analogous to that seen in the bed of Broken 
River in the Trelissick Basin. These beds apparently form the end of a 
syncline which has been tilted against the greywackes of No Man’s Land. 
The eastern wing apparently overlies the coal-measures, but the connection 
between the two sets of beds is not clear. The oyster-bed strikes north¬ 
east and dips north-west, while farther west there are concretionary sand¬ 
stones and grits dipping to the south-east. Immediately to the north the 
whole country is covered with moraine, and it is likely that this masks a 
considerable area containing coal, especially as coal has been met with still 
higher up Sloven’s Creek, but whether or not it will pay to work is quite 
uncertain. The proximity of the greywacke floor is rather against an}' 
