304 Transactions. 



alignment is very marked and can hardly be accidental ; but whether it is 

 a case of ordinary subsequent drainage conditioned by the existence of a 

 band of weak rocks, or of an old fault-zone, or is consequent on recent 

 faulting oblique to the general line of the Kaikoura faults cannot be deter- 

 mined on the evidence at present available. It is perhaps significant that 

 this line approximately connects the greatest develoj)ments of Clarentian 

 volcanics in the Clarence and Awatere Valleys, suggesting the existence of 

 a pre-Clarentian line of weakness in the same direction. 



In the period following the Kaikoura orogenic movements the Clarence 

 River became graded, and the lower slopes of the middle valley, consist- 

 ing largely of Notocene rocks, were reduced to mature erosion forms. This 

 mature topography has been partially obliterated, south-west of the Dee, 

 by smothering with gravel fans coalescing into a piedniont plain at the 

 base of the Kaikoura Range, and probably due, as explained above, to 

 a renewed uplift along the line of the great Clarence fault. Both the 

 mature erosion form^3 and these gravel plains have been jjartially dissected 

 by a revival of erosion caused by a late regional uplift, which elevated the 

 delta of the Clarence River 600 ft. (Cotton, 1914b), and gave rise, after 

 rejuvenation, to well-marked terraces of much less height between Quail 

 Plat and the Bluff Rivei'. 



In the strip of Notocene rocks involved along the line of the great 

 Clarence fault the hard strata of the Amuri limestone and Weka Pass 

 stone, lying between the softer Clarence mudstones and the " grey marls," 

 stand up as a monoclinal ridge cut through by the nximerous gorges of the 

 consequent tributaries of the Clarence River. The south-eastern slopes 

 present precipitous escarpments, passing below into great screes of dazzling 

 white limestone, which cover the outcrops of the highest Clarentian beds 

 and often those of the flint-beds. The north western dip-slopes where not 

 too steep are covered with a rich black soil, and afford the best pastures 

 of the valley. Since the ridge contains no air-gaps, and since the gorges 

 of the streams that cross it often fork within the limestone, Cotton con- 

 cludes that the drainage must have assumed its present form before 

 denudation had exposed the limestone monocline as a prominent ridge, 

 and that the streams now occupying the gorges may be described as 

 superposed consequents which flowed initially upon gieat screes from the 

 fault-scarp. 



Along the greater part of the great Clarence fault the great Marl- 

 borough conglomerate, which is also a resistant band, rests against the 

 pre -Notocene rocks, and does not form a marked feature in the topography ; 

 but to the north-east of the Swale Gorge, where it is surrounded on each 

 side by mudstones, it forms a series of hogbacks, the highest of which is 

 known as the Razorback Ridge. This is, nevertheless, much inferior in 

 height to the limestone monoclinal of the Chalk Range near by. 



The softer members of the Notocene series, and particularly the mud- 

 stones of the Clarentian and of the " grey marls," have been reduced to 

 lower relief with the development of subsequent streams along their lines 

 of strike. In the Clarentian the best-developed subsequents are those 

 of the Nidd, Cover, and Wharf, tributaries of the Swale Stream, which 

 separate low strike ridges, mainly of sandstone. Along the outcrop of 

 the " grey marls " there are a number of short subsequent streams form- 

 ing a single linear depression, which does not appear ever to have been 

 occupied by a single stream. The grade formerly established in the 

 insequent and subsequent tributaries of the consequents flowing into the 



