1920 .] 
Speight.—Broken River Coal Area. 
153 
8. Grit, with volcanic pebbles and ash, and frequent fragments of 
bryozoan limestone similar to that at Castle Hill. 
9. Calcareous volcanic tuff , with similar fragments of the same lime¬ 
stone. 
10. Volcanic tuff and lava-flow. 
11. Brownish-grey sands, slightly glauconitic, concretionary, and pass¬ 
ing up into— 
12. Greenish sands, distinctly glauconitic, weathering yellowish. These 
beds strike north and south and dip east 40°. 
Although this series certainly forms part of a conformable sequence and 
the lower beds are of similar lithological character to those of the main 
coal area farther west, which are considered equivalent to the beds under 
the limestones at Castle Hill, the presence of numerous fragments of bryozoan 
limestone certainly indicates that they are higher in the series than the 
limestone, and unconformable to it, and therefore by inference are uncon- 
formable to the beds underlying the limestone, and therefore to the coal- 
measures just referred to. While it may be urged that the pebbles occur 
in a volcanic tuff and its presence may imply an unconformity—although 
this is not a necessity—yet these limestone fragments occur in a grit which 
is apparently quite conformable to the underlying beds. Further, the 
pebbles form a considerable element in the beds in which they occur, are 
somewhat subangular in shape, and must have been derived from a bed 
in close proximity. There is now no such limestone exposed nearer than 
the junction of the Porter with the Broken River, a distance of seven 
miles in a straight line ; so the occurrence of these pebbles is remarkable 
not only as indicating an unconformity, but also as showing a former wide 
extension of the limestones in the Waimakariri basin, and their subsequent 
removal by erosive agents. There was in all probability a more or less 
continuous sheet connecting the limestones of the Trelissick area with 
those in the Esk River, in the north-east corner of the Waimakariri 
intermontane basin. The absence of fossils in the grit and tuff beds in 
contact with it is somewhat unfortunate, as they would enable a definite 
unconformity to be fixed in the Tertiary sequence as it exists in the mid- 
Canterbury area. 
It will be best now to consider the beds exposed in Sloven’s Creek itself. 
On the north side of Broken River, immediately opposite the farm buildings 
of the present Avoca homestead, the beds consist of concretionary green¬ 
sands, striking east and west and dipping north 40°, but near the mouth 
of Sloven’s Creek the strike changes slightly till it is south of east, and the 
dip becomes steeper. On the face of the bluff above Broken River are 
well-marked nearly horizontal shear-planes of small displacement. On 
the west of Sloven’s Creek and overlying the greensand is a marl which 
strikes south-east and dips north-east 40°. In its upper levels it is inter- 
stratified with volcanic ash, and is also overlain by ash with the same 
strike and dip. The marl continues along the ridge dividing the creek 
from Broken River for a few chains, when it is obscured by the terrace 
gravels and it is no more seen. In the bed of the creek a little distance 
above the bridge there is a small exposure of greensand apparently over¬ 
thrust by greywacke. The exposure is very limited, so that its precise 
relations cannot be well made out. Farther up-stream there is a great 
development of volcanic ash and agglomerate, and the disturbance caused 
by volcanic action has modified the regularity of the sedimentaries so 
that it is difficult to make out their relations with certainty. The 
ash-beds resemble very closely those occurring in the Whitewater and Cole¬ 
ridge Creeks of the Trelissick Basin ; they contain numerous small angular 
