258 Transactions. 



wide radius. The average direction of the base-line is N. 50° E. It makes 

 a decided angle with the strike of the rock strata. Where, road-cuttings 

 have been made parallel with the line of the scarp, rock outcrops run 

 up the face obliquely in one direction or the other, according to the dip 

 of the beds. Sloping down to the even base at an angle of 55° is a 

 flat and even face, separated into triangular facets by a number of 

 ravines. The mouths of some of these ravines overhang the shore, as 

 if a period or periods of standstill accompanied by erosion had sepa- 

 rated periods of movement the last of which took place at a very 

 recent date. There are, however, no traces of wave-cut shelves along 

 the scarp such as one would expect if the movement had been one of 

 elevation of the landward block. It would seem rather that the move- 

 ment was altogether a subsidence of the harbour block. Clay terraces 

 overhanging Tinakori Road, which were regarded by Bell* as beach de- 

 posits on a rising block, are clearly remnants of the floor of a mature 

 valley which was cut across obliquely by the fault. 



An alternative and perhaps the correct explanation of the hanging 

 ravines on the fault-scarp is that the ravines were developed when the 

 boundary of the Port Nicholson depression lay farther out, before the final 

 movement on the plane of the Wellington fault. By the final faulting 

 movement they would then be truncated. 



This hypothesis gains some support from the ^.jv^ ,^ > -~.,_ tw .^-— 



fact that tributaries of the larger streams. /' '-^X^^-I ^£S>2cr : ^\\ 

 the Kaiwarra and the Ngahauranga, which / <^*^^yy , -^ -— ^S,- 



cross the fault-scarp show evidence of recent 



/ 



\<W/>: 0- 



revival. | \ \^%{/ / . \\ \\ 



These two larger streams have been i i \ \\ .y/ / / \\ v \ 



sufficiently active to capture the drainage i ' \ '\ \l -I i J^w-i 



of a longitudinal valley at the back. The i X-^<^-^^f^^^^-' ^^ 

 changes in their courses are described in a 



later paragraph (p. 262). Both streams in FlGl 10 - -Truncated Valley 



,1 • i if i 4.1. 4.1 OVERHANGING THE NGAHAU- 



their lower reaches, where they cross the ranga Gorg] 



fault-scarp, flow in narrow, young gorges 



(see Plate XX, figs. 1 and 2).' The lme of the J"*" f f ce § ives 



tk m i l v x i-j.4.1 n a cross-profile of the upper 



Fig. 10, a sketch of a little valley part of the valley- 



truncated by the Ngahauranga, gives an 



indication of the depth to which the latter has incised its course below 



an older surface of moderate relief. 



The Kaiwarra, which is the larger stream of the two, has graded its 

 course, and for a distance of a mile from its mouth has worked out an 

 extremely narrow strip of flood-plain (Plate XX, fig. 1). The Ngahau- 

 ranga is not graded. A fall in its lower course is illustrated in Plate XX, 

 fig. 2. 



There is no doubt that both these streams are of extremely recent 

 origin. Their lower courses are consequent upon the slope of the fault- 

 scarp, or, at least, of the boundary of the Port Nicholson depression. 



Next to the extremely young character of the streams the most im- 

 portant piece of evidence in favour of faulting is the abrupt manner in which 

 the ridges separating them are terminated as a straight line of cliffs at 

 the harbour side. If the theory of faulting is not entertained these must 



* Loc. cit., p. 539. 



