274 Transactions. 



The section in this river thus shows that there is a distinct series in which 

 gravels are the dominant beds lying unconformably on marine Tertiaries. 

 It should be noted that in the western branch there are no gravel beds 

 below the unconformity. Either they have never been deposited or they 

 have been removed by erosion. There is a strong suggestion from the 

 eastern branch that gravel beds are present among the higher members of 

 the underlying marine series, so that their presence cannot be taken as 

 decided evidence that beds containing gravels in this locality necessarily 

 lielong to the Kowai series. 



Ohuku River and Mairahi Downs. 



Similar gravels occur on the banks of the Okuku, especially on the 

 western side, where they form low hills fringing the base of Mount Thomas, 

 and stretching westward towards the Garry River and Glentui. Towards 

 the Ashley they are masked by more-recent gravels, but they reappear on 

 the south bank of the river, forming the Mairaki Downs. The strata here 

 consist of thick sandy gravels, sandy clays, and occasional la5'ers of carbon- 

 aceous shale. Opposite the mouth of the Garry they strike north-east 

 and dip north-west at an angle of 20°, forming the south-eastern wing 

 of a syncline which is developed farther west, while farther east, towards 

 Rangiora, the structure is anticlinal. The country directly between the 

 Mairaki and Mount Grey Downs is probably a syncline, but the surface is 

 completely masked by recent gravels and clays belonging to the Ashley 

 and Okuku Rivers and to the lower course of the Grey and Makerikeri 

 Rivers, the latter draining a considerable area on the south-western flank 

 of the Mount Grey Downs. 



Kowai River, North Branch. 



An excellent idea of the structure and general features of the northern 

 part of the downs area can be obtained by examination of the high banks 

 of the North Kow^ai, and especially of a tributary which rises in Mount Brown 

 itself and flows in a south-easterly direction across the strike of the beds, 

 thus exposing all the members of the series present in this locality. The 

 following is a general description of the beds encountered, starting with the 

 Mount Brown beds and following up to the highest members of the series : — 



At the contact with the upper members of the Mount Brown series the 

 latter consist of sands, and marine gravels with shells, striking north-east 

 and dipping south-east at an angle of 10°. The Mount Brown beds are here 

 capped unconformably with sandy gravels containing rounded and sub- 

 angular greywacke pebbles, and belonging in all probability to the high-level 

 terrace-gravels of the present Kowai River. Lower down sands, sandy clays, 

 and sandy gravels dipping south-east at very low angles are exposed on the 

 banks of the stream and in the deep gullies on the northern side. There is 

 certainly a disagreement in dip between these beds and the underlying Mount 

 Brown beds, suggesting an unconformity, but nowhere could I see an actual 

 contact in order to determine this point precisely. The slight escarpment 

 of the downs which faces Mount Brown at this point is determined by the 

 presence of the gravel beds which occur at this horizon. It is noteworthy 

 that there is an entire absence of the gravel beds with broken-shell layers 

 which cover the Mount Brown beds in the vicinity of Weka Pass, a point 

 which increases the probability that the beds forming the downs rest on the 

 Mount Brown beds unconformably. 



